Background art It is known that in the manufacture of anti-crash panels it is necessary to be able to arrange, inside the panel, synthetic or vegetable fibers which have a structural function and thus increase the mechanical strength of the panel.

For this purpose, it would be convenient to have relatively long fibers, which of course increase this kind of strength; with currently used solutions, which entail mixing the thermoplastic resin with the fillers and then performing extrusion, the fibers are inevitably broken and shredded, with a consequent significant decrease in mechanical strength.

The single step for mixing the thermoplastic resin and the vegetable or mineral filler can currently be performed with granular materials, such as wood flour or calcium carbonate or talc, thus obtaining a product which does not have the desired mechanical strength characteristics.

Disclosure of the Invention The aim of the invention is to solve the above-noted problem, by providing a method and an apparatus for obtaining essentially composite structures having a substantially uniform thickness and being substantially flat.

Such structures can be hot-molded again after manufacturing and can be used as panels to form sturdy, structural finished items, such as for example the internal paneling of cars, fruit crates, underbodies for trucks and containers and various items.

Within this aim, an object of the invention is to provide a method and an

apparatus which allow to include relatively long vegetable or mineral fibers, even of different sizes, without encountering problems in feeding the extruder.

Another object of the present invention is to provide a method which allows to avoid damaging the initial filamentous structure of the fibers, thus obtaining an end product particularly valid and having anti-crash properties, with greater mechanical strength due to the overlapping of the fibers.

Another object of the present invention is to provide a panel which can be obtained starting from commonly commercially available elements and materials and is also competitive from a merely economical point of view.

This aim and these and other objects which will become better apparent hereinafter are achieved by a method for manufacturing anti-crash panels, according to the invention, characterized in that it consists in conveying into an extruder assembly a metered amount of long fibers; in wetting said long fibers with a melted thermoplastic resin in a central portion of said extruder assembly in order to obtain a mixture of thermoplastic resin and long fibers without modifying the structure of the fibers; in extruding said mixture in the form of sheet-like pasty material, and in calendering the pasty material in order to obtain a sheet-like element having a constant thickness.

Brief description of the drawings Further characteristics and advantages will become better apparent from the following description of a preferred but not exclusive embodiment of an apparatus for manufacturing anti-crash panels according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a schematic partially sectional elevation view of the apparatus according to the invention ; Figure 2 is a schematic plan view of the single-screw extruder assembly; Figure 3 is a sectional view, taken along the line III-III of Figure 2; Figure 4 is a sectional view, taken along the line IV-IV of Figure 3;

Figure 5 is a plan view of a double-screw extruder assembly; Figure 6 is a sectional view, taken along the line VI-VI of Figure 5 ; Figure 7 is an elevation view of the apparatus for manufacturing a composite panel; Figure 8 is a schematic sectional view of a panel that can be obtained.

Ways of carrying out the Invention With reference to the figures, and particularly to Figure 1, the apparatus for manufacturing anti-crash panels comprises a reservoir 1 for containing long vegetable or synthetic fibers which preferably have a length between for example 10 and 150 mm.

The long filamentous vegetable fiber (coconut, jute, hemp, linen, cotton, kapok, sugar cane, and so forth) or synthetic mineral fiber (glass fiber, carbon fiber and the like) or natural mineral fiber, can be included in the mixture in a percentage by weight between 10 and 45%.

On the bottom of the reservoir 1 there is a rotating blade 2 for conveying the fibers toward a lateral opening 3, where there is a vertical transfer duct 4 in which a screw feeder 5 acts ; said feeder is adapted to perform a controlled feeding of the long fibers.

The duct 4 leads into an extruder assembly, generally designated by the reference numeral 10, inside which, with reference to Figure 1, there is a single-screw feeder 11 or optionally, with reference to Figure 5, there is a double-screw feeder 12 with contrarotating or corotating screws.

An inlet 15 is provided on the extruder assembly 10, upstream of the input region of the duct 4, for the introduction of waste and scrap from previously manufactured panels which can be fed by a corresponding hopper.

The fibers, together with any scrap, are subjected to heating by means of a heater 20, and there is also a degassing vent 21 which is adapted to allow any generated gases to vent outside.

Downstream of the free degassing vent 21 there is a region for wetting

the fiber with thermoplastic resin, designated by the reference numeral 30.

In this region, a mixture of thermoplastic resin, preferably a polyolefin resin, in practice wets the fibers and any scrap and includes the long vegetable or mineral fibers, possibly having uneven sizes and a relatively high moisture content.

In practice, the long vegetable or mineral fiber, fed by forced and controlled dosage, is completely wet and covered with thermoplastic material injected in the melted state under pressure over a long, controlled and balanced region with maximum wettability-surface, so as to leave practically intact the initial filamentous structure, which remains substantially unchanged, even after the wetting step, which in practice performs a mixing; during this step, the region affected by the extruder is not under pressure and therefore the gases are evacuated by way of the free degassing vent 21.

As shown in Figures 3 and 4, the wetting region 30 provides for the conveyance of the polyolefin thermoplastic material in the melted state, by means of an extruder 40 for the plastic material, which conveys said plastic material into an input channel 41 introducing it in a distribution channel 42, which in turn distributes the melted plastic by means of a plurality of annular channels 43 ending with openings 44, which fully surround the region for the passage of the fibers fed by the single-or double-screw extruder.

The wetting region has a certain length so that in practice it is possible to introduce the thermoplastic material on the fibers conveyed by the extruder and distributed in a metered amount.

An integral mixture is thus formed in which the fiber is wet and fully coated by the thermoplastic polymer, maintaining the length of the fiber intact.

Advantageously, the wetting process occurs in a relatively low-pressure environment, so that any formation of gas is forced to flow backward

toward the free degassing vent 21, without being embedded in the formed mixture.

The resulting mixture passes through a vacuum degassing region 50 which fully eliminates any residue of gases and monomers that might still be present.

The mixture, in the form of a pasty material, is then extruded by means of an extrusion nozzle 60 which places the material on a calender, generally designated by the reference numeral 70. The calender 70 is advantageously of the type with four rolls 71, receives the pasty and soft material that leaves the extrusion nozzle 60 and obtains a layer 51 having a uniform and regular thickness.

According to a different embodiment, it is possible to apply to the resulting panel a covering layer made of polyolefin material.

For this purpose, as shown in Figure 7, there is a calender 70'which has a first roll 80 and said second roll 81 for compressing the melted mass that forms the panel 51 and a third roll 82 for gauging the panel, obtaining the intended thickness.

A layer of polyolefin material 83 is applied on the third roll or cylinder 82 by means of an extrusion head 84 with subsequent gauging by means of the fourth cylinder 85, thus allowing to obtain a panel which has a soft, smooth or embossed outer surface.

The panel obtained as shown in Figure 8 is entirely recyclable, since both of the layers that compose it, i. e., the layer 51 obtained from the long fibers mixed with the thermoplastic resin and the covering layer 83, are both obtained from polyolefin resins.

From the above description it is thus evident that the invention achieves the intended aim and objects, and in particular the fact is stressed that a method and an apparatus are provided which allow to obtain anti-crash panels which can have high-level mechanical characteristics and further allowing full recycling.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

All the details may furthermore be replaced with other technically equivalent elements.

In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to requirements.

The disclosures in Italian Patent Application No. MI2000A000204 from which this application claims priority are incorporated herein by reference.