The invention relates to a composite multilayer panel, particularly suitable for formworks, especially in floors.

Such panels are known and one application thereof consists in building formworks for concrete placing.

Here, the panels form the walls for containing the poured concrete and are supported by metal frames or the like.

These panels are typically composed of a core consisting of a layer made of wooden parts, which is provided on its sides with a plastic protective coating glued to the wooden layer.

Although these panels can be excellent in fulfilling their purpose, they have a few considerable drawbacks: the attachment of the outer coating layers to the wooden core requires a gluing step; the panel is composed of materials such as plastic, wood and adhesives, which are generally incompatible for recycling; the outer plastic layers tend to come off the wood in time; the inner wooden core, also due to long periods of use in often unfavorable environmental conditions,

tends to degrade, for example due to moisture absorption which allows the growth of molds or else; these phenomena attack the wooden core of the panel whereby the latter can no longer meet the requirements for resistance to dynamic and static stresses.

In particular cases, such as the fabrication of formworks for floorslabs or of walkways of scaffolds or frameworks, said weakening can cause at best the panel to bend or bulge, and even break, which can affect the quality of building manufactures and be very dangerous for structure stability and/or personnel safety. On the other hand, it is impossible to inspect the inner part of each panel to verify its state of conservation without affecting the structure thereof. Also, the panel weight to load resistance ratio is often unsatisfactory, especially due to the weight of the wooden core.

The invention has the object to provide, by simple and inexpensive arrangements, a panel such as the one described hereinbefore, allowing to obviate the above drawbacks and particularly allowing to: reduce, with equal resistance, the weight of the panel as compared with known panels; provide a chemical and weathering resistant panel, with particular reference to the above mentioned effects of moisture absorption, so that the panel can maintain all its features in time, particularly static and dynamic resistance; make the panel from compatible materials, in view of the recycling steps, while also avoiding the use of

adhesives or the like; provide an effective penetration through the panel and a good hold or engagement of nails, screws, anchor screws or other similar fasteners, while maintaining or improving the so-called"nailability", i. e. the ductile fracture characteristics of the panel; provide a particularly safe panel, suitable, in particular, for use in making formworks for casting concrete floor slabs; provide that the panel has a pleasant aspect, even in terms of environmental impact, and that it has such chromatic characteristics as to represent a code for identifying particular areas, e. g. at the construction site; provide an panel which is very easy to fabricate while providing it with a great versatility both in terms of construction and in terms of application for use in a variety of fields.

The invention achieves the above purposes by providing a panel such as the one described hereinbefore, which has a core consisting of at least one layer made of a high density expanded or foamed material and/or by at least a honeycomb or grille like layer made also preferably of polyolefin-based material.

The above mentioned layers as taken singularly and alternatively one to the other or in any kind of combination one with the other are provided, at least on one side thereof, preferably on both sides, with a coating consisting of at least one outer plastic-based

layer (2) with a high resistance modulus.

The expanded or foamed material forming the core may be a polyolefin material, such as polypropylene or polyethylene, having a density of 100 to 300 g/m3, particularly of 130 to 200 g/m3.

The honeycomb or grilled layer may also be made of polyolefin resin based material which may be also provided mixed with and of one or more inert fillers, particularly cellulose fillers, such as a mixture of wood flour and polypropylene, particularly of a material known in the market as Wood-Stock@.

The outer coating layer may be made of a mixture of a polyolefin material fillers, particularly cellulose fillers, such as a mixture of wood flour and polypropylene, particularly of a material known in the market as Wood-Stock@.

This material forming the outer layer is of the type having a high resistance modulus, particularly of 2000 to 5000 megapascal.

Advantageously, the panel is closed, preferably in a water-tight manner, along its peripheral edges, by ribs which have, at least partly and at least for a part of their extension, a non-constant section, particularly receding towards the inner part of the panel, especially triangular. The particular conformation of said ribs provides the advantage of enlarging the adhesion surface between them and the panel core, while improving the moisture-tightness of the panel. These ribs also help to stiffen the peripheral edges of the panel.

The ribs may advantageously be made of a polyolefin material or of a filled polyolefin material, particularly filled with cellulose materials, preferably of a mixture of wood flour and polypropylene (Wood-Stock@).

More than one core layer of the same kind or of different kinds may be bond directly together or by interposed intermediate layers in order to form a composite multilayer core.

Also the outer coating layer may show a multilayer structure.

Thanks to the above features, a panel can be provided which has the following characteristics: A lower weight as compared with known panels, with equal resistance; The panel is substantially chemical and weathering resistant, with particular reference to moisture absorption; The panel maintains unaltered dynamic resistance characteristics in time, thus ensuring a longer life; Particularly thanks to the fact that the panel is made from materials belonging to the same family, particularly to the family of polyolefin materials, and that no adhesives of any type are required, since the attachment between layers is obtained by chemical and physical adhesion by heat and compression when the layers are joined together, the panel is made of compatible materials, in view of the recycling processes ; The expanded or foamed material forming the core

provides all the layers with a very good ductile fracture characteristic when nails or similar are inserted therein and effectiveness in engaging threaded parts, anchor screws or other fasteners, without chipping; Finally, the panel is very easy and inexpensive to make in various versions to suit different fields of application.

According to an advantageous improvement, the panel may be dynamically preloaded by arching it in one, two or more directions opposite to loading.

By this arrangement, the panel is particularly suitable for fabricating formworks for casting concrete floor slabs, since by being arched for preloading, it can endure deformations under load in a predetermined and controllable manner, thereby avoiding undesired bulging effects. Further, the panel, preloaded by arching may advantageously be thinner than the flat one.

In order to improve the resistance of the panel, while maintaining the same thickness, or to reduce thickness while maintaining the same resistance, the panel may have at least one inner, intermediate stiffening layer.

This stiffening layer may consist of a plastic plate, preferably made of a polyolefin material filled or not, in this case, with cellulose materials, e. g. of a mixture of polypropylene and wood flour (Wood- Stock@).

Alternatively, said layer may also consist of a

continuous or discontinuous sheet or plate made of plastic or metal, particularly of a net made of plastic, particularly polyolefin plastic, or metal.

As a further alternative, said layer can be made of natural or synthetic fibers or mixtures thereof, in the form of fabric, nonwoven fabric, like mat. The various types of stiffening layers as described above may be also provided in any combination.

The intermediate stiffening layer may be structured, i. e. also composed of several layers, or may have stiffening members, such as thicker parts, beads, ribs or the like, in different patterns to provide the required static or dynamic characteristics.

In this case, the adjacent layers made of the expanded or foamed material or other types of materials advantageously have complementary shapes.

According to another embodiment, the panel may have at least one honeycomb intermediate stiffening layer, preferably made of a filled or non-filled polyolefin material.

A further advantageous variant provides that at least one inner layer made of an expanded or foamed material has a plurality of grooves for housing stiffening bars, strips or the like. Advantageously, said grooves have a size corresponding to the section of the stiffening bars, strips or the like.

According to a preferred embodiment, the grooves are oriented in at least two transverse directions and form a grille pattern, while a complementary stiffening grille is provided.

The bars, strips, grilles or the like may be made of a filled or non-filled polyolefin material and/or of a material compatible with the layer made of the expanded or foamed material which is also a polyolefin material.

Further, said bars, strips, grilles or the like may advantageously be connected to the corresponding sides of the housing grooves of the layer made of the expanded or foamed material by chemical and physical adhesion, particularly by surface melting and/or welding of the mutually adhering faces, especially while joining together the layers of the panel under the action of heat and pressure.

According to a further advantageous improvement, the outer layers may be pigmented, i. e. colored, and each panel may have a single color, or partly one or more different colors either in the same panel or in different panels, and/or between sides and/or peripheral edges of the same panel.

The color or color combination of at least a part of at least one or both faces and/or of one or more peripheral edges of each panel may be a code for identifying at least major characteristics of fabrication, composition and/or designed use of the panel.

Particularly, the color or color combination of the panel may be a means to identify higher or lower risk areas, or particular areas of the structure built by using the panels.

Also, the color or color combination in each panel

and between panels may be a finishing element for the structure built by using the panels.

According to a further variant, at least one of the two outer layers may be further coated, on its outer face, with a finishing layer.

Finishing layers may be for example anti W layers or anti-scratch layers combined with further finishing layers or taken alone.

All the layers composing the panel may be directly bonded one to the adjacent other. Furthermore bonding may be achieved by means of adhesive layers or films, in particular based on polyolefin resins.

The outer layer, or at least one of the outer layers may be a composite one comprising at least one sheet made of plastic, preferably polyolefin resin based material and one wood sheet.

The wood sheet may be an intermediate sheet between two plastic layers.

Preferably the plastic sheet or sheets combined with the wood sheet are of polypropylene charged with inert charges and the wood sheet may be a multilayer wood or the like Thanks to these arrangements, the panel has a pleasant exterior aspect in terms of environmental impact, particularly in town environments, in which when buildings are built/redeveloped, huge structures formed by scaffolds or the like must often be erected.

Moreover, the above characteristics, both in terms of physics, i. e. mechanical and dynamical resistance and weight, and aspect, i. e. color, finishing coating,

etc. make the panel suitable to other applications, such as the fabrication of outside and inside walls or building works, caissons, prefabricated building manufactures or the like, containers, boxes, holders, packages, walls for modular and movable partitions, bulkheads and walls for ships and vessels or the like.

Further characteristics and possible improvements of the invention form the subject of the dependent claims.

The characteristics of the invention and the advantages derived therefrom will be more apparent from the following description of a few exemplary embodiments illustrated without limitation, in which: Fig. 1 is a cross sectional view of a first embodiment of the panel according to the invention.

Figs. 2 to 10 are views of certain different embodiments of the panel according to the invention.

Fig. 11 is a perspective exploded view of a detail of a further embodiment of the panel according to the invention.

Fig. 12 is a cross sectional view of a detail of the panel as shown in fig. 11.

Figs. 13 and 14 show, like figs. 11 and 12, a variant embodiment of the panel as shown thereby.

Referring to fig. 1, a first embodiment of the panel in accordance with the invention comprises a core consisting of a layer 1 made of a high-density expanded or foamed material. Said layer 1 may be made of any expanded or foamed material suitable for the purpose, though the use of a polyolefin expanded or foamed

material, such as polypropylene, polyethylene or other materials, is preferable. The density of the material forming the layer 1 is of 100 to 300 g/m3, particularly of 130 to 200 g/m3.

In the simples embodiment as shown in fig. 1, the core 1 made of an expanded material is externally coated on one side, preferably on both, with a layer 2.

The use of a single outer layer in the form of a plate shall be intended without limitation, since outer coating plates with a greater number of layers for each face can be provided. Said outer layer 2 is made of a mixture of a polyolefin material and fillers, particularly cellulose fillers, such as a mixture of wood flour or talc and polypropylene, particularly of a material known in the market as Wood-Stock@.

The outer layers 2 are made in such a way as to have a high resistance modulus, particularly a modulus of 2000 to 5000 megapascal.

The characteristics of the material forming the layer 1 provide the advantage of a considerable weight reduction, with equal resistance, as compared to the known wooden-cored panels. The polyolefin material forming the layer 1 also has the advantage of not being exposed to degradation phenomena due to molds or the like, caused by moisture absorption inside the panel.

Thereby, the panel according to the invention has the advantage of a longer life than known panels, and of considerable savings in fabrication costs and, as a consequence, in purchase costs for final users.

Moreover, the layer 1 made of the expanded or foamed

material provides the panel with ductile fracture properties for inserting for example nails, the so- called"nailability", while preventing chipping, which could affect the structure of the panel and shorten its life, as well as be a risk for the operator. Similar advantages are obtained as to the possibility to tighten screws or other threaded or self-tapping members, directly in the panel or as to the engagement and hold of anchor screws or other similar fasteners.

The outer panel/s 2 provide the panel with a considerable structural rigidity and a considerable resistance to stresses, particularly transverse stresses. Furthermore, their surface allows an easy removal of the panel from the material forming the concrete cast, thereby preventing the formation of irregular finished structures, or even having defects such as hollows or the like, caused by the adhesion of concrete fragments to the panel. This characteristic is particularly advantageous in making structures with architectural concrete surfaces. Further, Wood-StockX has the advantage of not chipping when it is cut, thereby allowing, for example, the panel to be adapted to particular sizes and/or shapes required by specific needs. The surface of Wood-Stock@ has excellent characteristics in terms of wear, chemical and weathering resistance, and can be easily cleaned to remove concrete residues or the like.

The embodiment of the panel as shown in fig. 1 is covered, along the peripheral edges, with ribs 3, having a triangular section, receding towards the inner

part of the panel. This particular conformation provides the advantage of enlarging the contact surface, and hence improving adhesion, between said ribs 3 and the material forming the internal layer 1 of the core and to ensure a better sealability of the edges of the panel, preventing, for example, moisture absorption. Said ribs 3 may have, at least partly, and at least for a part of their extension, any other section, particularly non constant and receding towards the inner part of the panel.

Advantageously, the ribs 3 are made of a polyolefin material or of a polyolefin material particularly filled with cellulose materials, preferably of a mixture of wood flour or talc and polypropylene(Wood-Stock@).

Therefore, the panel described herein is made of materials belonging to the same family, particularly that of polyolefin materials, thus providing considerable advantages in the recycling step. Also, all the panel parts described herein are joined together by chemical and physical adhesion, whereby the gluing step is avoided as well as the presence of any type of adhesives, which would be a foreign element in the panel composition and an obstacle to recycling.

Fig. 2 shows an embodiment of the panel according to the invention which has the same composition of layers and materials as the panel of fig. 1, but in this case, the panel is dynamically preloaded upon forming, by arching it in directions opposite to loading. Said arching operation may follow one, two or

more directions. This arrangement, which is particularly useful in making formworks for concrete floor slabs, provides the advantage of compensating the bulging effect caused by loading and ensure that, under load, the panel yields in a predetermined and controllable manner, taking the final desired flat shape. Thereby, panels can be provided, with the same thickness as the flat ones, which can be designed for higher loads, or need reduced support structures, while ensuring optimal results.

Analogous results are achieved when the layer 1 is made with a honeycomb or grille like structure such as the one disclosed with the reference numbers 8,8b, 10 in figures 6a, to 14. Regarding the layers 2 and the parts 3 each feature disclosed with reference to the embodiments according to figures 1 to 5 and 10 may be provided in combination with the said honeycomb or grille like intermediate layer.

According to an advantageous improvement, the panel as shown in fig. 3 has the same layer structure as the panels of figs. 1 and 2, with the addition of an intermediate stiffening layer 4, placed in a median position with respect to the two outer layers 2 of the panel. The stiffening layer may consist of a plate, preferably made of the same material (Wood-Stock@) as the outer layers 2.

This stiffening layer 4 may be positioned in any other desired intermediate position between the two outer layers 2. This solution provides the advantage of increasing the resistance of the panel while

maintaining the same thickness or of reducing the thickness while maintaining the same load.

The inner stiffening layers 4 may be also provided in a greater number. Particularly, in figs. 4 and 5, there are two of them, positioned in such a way as to divide the core 1 made of the expanded or foamed material into three layers 1,1', 1".

As shown in the figures, the intermediate stiffening layers 4 may be positioned in any manner, e. g. equally spaced from each other, symmetric to the median plane or asymmetric thereto and/or closer to said median plane (fig. 4) or closer to the outer layers 2 (fig. 5), having equal (fig. 4) or different thickness (fig. 5).

Any other location of these layers inside the thickness of the layer 1 of the panel, and in any number may be provided. Here again advantages are obtained from making said stiffening layer/s from a material compatible, in view of recycling operations, to the materials of the other panel parts. However, the stiffening layer/s may be made of materials differing from the one described herein, e. g. of a metal net, of a continuous or discontinuous plastic or metal film or plate, particularly of a net made of plastic, especially polyolefin plastic, or of metal, or in the form of layers made of natural or synthetic fibers, or mixtures thereof, in the form of fabric, nonwoven fabric, like mat. The above different stiffening layers may be also provided in any combination.

Referring to the variant as shown in figs. 6A and

6B, the panel has an inner honeycomb stiffening layer 8, preferably made of a polyolefin material, again in view of said recycling operations. The intermediate honeycomb layer 8 is interposed between two layers 1 made of a high density expanded or foamed material as defined above, and the panel is coated on each face with a layer 2 made of a filled plastic material.

The honeycomb stiffening layer 8 may be made from one piece or by joining together several layers 8a, 8b, 8c, as shown in fig. 6A.

In fig. 6B, the honeycomb layer 8 is thicker than the adjacent layers 1 made of the expanded or foamed material, whereas in fig. 7 these layers 1 have equal thickness. Obviously, different arrangements may be provided, with different positions of the three layers 8,1, possibly even in asymmetric positions to the outer coating layers 2.

Fig. 8 shows one more variant embodiment, wherein the core 1 of the panel is composed of a stiffening layer 4, consisting of a plate made of a filled polyolefin layer, e. g. Wood-Stock@, which is interposed first between two stiffening layers 8 made of a honeycomb material, and then between two layers 1 made of an expanded or foamed material.

Fig. 9 shows a further embodiment, wherein the core of the panel consists of a layer 1 made of an expanded or foamed material as defined above, interposed between two stiffening layers 8 made of a honeycomb material as defined above.

With reference to the variant as shown in figs. 11

and 12, a further construction arrangement for stiffening the core of the panel consists in this case in that a layer 1 made of an expanded or foamed material as defined above has a plurality of grooves oriented in two transverse directions which form a grille pattern. All these grooves 101 are designed to house a stiffening grille 11 composed of ribs 110 oriented transverse to the layer 1 made of the expanded or foamed material and shaped complementarily to the grooves 101. This grille 110 is advantageously made of a polyolefin material, in order to keep the above described advantages for the recycling step. The layer 1 provided with the grooves 101 may be inexpensively fabricated by injection. The grille 11 is connected to the corresponding adhering sides of the housing grooves 101 in the layer 1 made of the expanded or foamed material through chemical and physical adhesion, particularly melting and/or welding of the mutually adhering faces. This is advantageously performed while joining together the various layers of the panel under heat and pressure conditions.

Alternatively thereto or in combination therewith there may be provided stiffening bars, strips or the like. As a further alternative thereto or in combination therewith there may be provided that one or more intermediate stiffening layers 4 have possibly raised ribs, made of the same material or of another one, and having any conformation, in order to further stiffen said layer.

Figs. 13 and 14 show a variant embodiment of the

grille 10 as described in the previous embodiment.

Although the panel has been described mainly in its use for building formworks, the versatility of the materials in use make it suitable for different uses, such as building permanent and non permanent linings, movable or fixed walls, doors, roofs, floors, furniture, bulkheads for ships or vessels, caissons, packaging boxes or the like, with high weathering resistance, particularly to moisture, building manufactures or the like. The panels according to the invention may be used for building vans or caravans like campers or similar.

Particular applications may be the construction of prefabricated cabins for ships or prefabricated rooms for buildings. Furthermore the panels according to the invention may be used for fabricating suitcases or suitboxes, trunks, cases, sheats.

A further use of the panel according to the invention is the use in fabricating acoustic boxes for loudspeakers, or the like.

Relating to the use in furnitures, the panel according to the invention may be used for structural elements of furnitures, like for example structural elements for seats, chairs, settee, stools, tables, shelves, doors, or the like.

For some of the above purposes and also for other purposes, as shown in fig. 10, the outer layer 2 may be a composite layer. In an embodiment the panel has a finishing layer comprising a metal sheet 11, such as aluminum, tin foil or the like, and an outer

transparent, preferably glossy plastic laminating film 12, for example made of polypropylene. The result thereof is a panel with a mirror or metal surface.

Alternatively, other arrangements may be provided, such as a finishing coating consisting of fabric, imitation leather, nonwoven fabric, a film that may be glossy or matt, transparent, colored or else. The sheet 12 or a further outer sheet (not shown) may have protective characteristics such as anti W functions and/or anti scratch functions.

The layer 2 may have also a combined structure as being formed by an outer sheet 12 made of termoplastic material such as a polyolefin resin based sheet charged with inert charges like wood or similar. The sheet 11 may be a sheet of wood such as a multylayer wood plate or the like.

Obviously, the invention is not limited to the embodiments described and illustrated herein, but may be greatly varied, without departure from the guiding principle disclosed above and claimed below.