METHOD OF MAKING PANELS, APPARATUS FOR CARRYING OUT THE METHOD AND PANELS OBTAINED THEREBY

Abstract: The invention relates to a method for making panels which may or may not be used for subsequent molding, to the apparatus for providing this method and to the panels obtained thereby. The method comprises the steps of forming a mixture of thermoplastic resin and organic filler and the plastication of this mixture performed simultaneously with its formation. During the transfer of the organic filler to the subsequent mixing and plastication step, the same is desiccated and mixed. Moreover, during said mixing and plastication step to plasticated mixture is transferred to a subsequent extrusion step. The method is carried out in an apparatus including a single device (6) for the continuous production of a sheet (27) of extruded material.

Description: The present invention relates to a method for making panels, to the apparatus for providing this method and to the panels obtained thereby. The panels whereto the present invention relates consist of essentially stratified flat structures with uniform thickness. These can be successively heat-molded after the step which provides their formation and can be used, indeed as panels, to form finished items such as, for example, internal coverings of automotive vehicles. The starting material for the preparation of these panels substantially consists of a thermoplastic resin and an organic filler. Conventional methods and the related devices for producing these panels entail a separate mixing step, wherein a certain amount of a thermoplastic resin is placed in close contact with the organic filler. The latter substantially consists of wood powder of sawdust, desiccated in a step previous to the mixing step, stored and then transferred to the subsequent processing steps (with problems of protecting the desiccated product from external humidity). In known methods and devices of the type at issue, the particles or fragments of organic filler must be sifted and selected, since they must have (due to processing requirements) controlled and uniform dimensions. Furthermore, they must be added to the mix in amounts not exceeding 60% by weight, while it would be preferable to use greater amounts of this less expensive component. The aforementioned mixture is traditionally prepared in a turbo-mixer and the mixture thus obtained is subsequently transferred to a plastication and extrusion unit, provided separately from the previous units, and whereto corresponds a separate step of conventional methods. The material thus extruded is subsequently laminated. In traditional devices, lamination is performed in a device with rollers or cylinders which subjects the layer of material in output from the extruder to a traction force. This force can in turn lead to discontinuities and irregularities on the surface of the finished panel, or even lacerate the layer of extruded material. The panel laminated with known devices is furthermore "uncovered", that is, it does not have the coatings and reinforcements which may instead be required for particular final applications of the panels. The transfer of the desiccated organic filler to the mixing step and the transfer of the mixture to the plastication and extrusion unit is a problem of known devices and methods, as well as for the above described reasons, also due to the fact that they make the overall process longer and more troublesome, and increase the complexity of the apparatus by means of which this method is carried out. FR-A-2 200 112 shows a single screw for the mixing and plastication of plastic resins and organic filler, an extruding unit, and a subsequent lamination device. EP-A-165 092 discloses a double screw having an inlet for organic material, an inlet for thermoplastic resin arranged downstream thereof, and an outlet extruding end. The main aim of the present invention is to provide a method and the related apparatus allowing to obtain panels with a smaller number of steps with respect to known methods, in a simpler and more rapid manner, and starting from organic filler fragments with non-uniform shape and size and with an initial humidity content even higher than the values allowed by the prior art. A further object of the present invention is to provide an apparatus of the type mentioned, wherein the lamination unit does not cause breakages or discontinuities on the surface of the panels, and which furthermore performs, if required, their coating and reinforcement according to the requirements of the final use of these panels. Another object of the invention is to provide panels usable for molding, the composite material whereof is less expensive with respect to traditional materials and anyway still lightweight. Still another object of the invention is to provide a wood powder extrusion which, after leaving most of the original moisture content at the first processing region, is totally coated with plastic material injected in the melted state, leaving practically intact its initial filament-like structure, which remains essentially unaltered even after the mixing and compacting step, obtained at low pressure. This method also entails remarkable advantages for the final product, which has a greater mechanical resistance due to the overlapping of the wood powder fibers. Moreover, the panel has a reduced specific weight due to the low-pressure mixing and compacting, contrarily with respect to panels obtained with the prior art which cause a degradation and a disintegration of the wood powder, caused by the high pressure used to melt the plastic material mixed with the wood powder, obtaining panels with a specific weight of even 1.05 kg/dm³. These and other objects are achieved by the method according to the present invention for making panels as defined in the appended claims. In fact, according to the present invention it has been surprisingly discovered that, starting from a melted thermoplastic resin and performing its mixing with an organic filler simultaneously with the plastication step, it is possible to use more than 60% by weight of organic filler having even irregular starting size and dimensions. The organic filler mixing the desiccation step provided continuously in the same mixing, plastication and extrusion apparatus allows to start from a still-humid organic filler but without the use of desiccation, storage and transfer units which are instead normally required in traditional devices of this kind. The transfer of the material to the extrusion step, performed simultaneously with the mixing and plastication steps, also has the advantage of making the process according to the invention generally rapid and simple, and of making the apparatus according to the invention less expensive and complicated. The invention is now described with reference to the figures of the accompanying drawings, which illustrate a preferred embodiment of the apparatus for making panels usable for re-moulding, given only by way of non-limitative example of the invention, wherein: figure 1 is a longitudinal cross section view of the apparatus according to the invention; figures 2 and 3 are transverse cross section detail views of the apparatus of figure 1, respectively at its degassing region and at its resin feed region; and figure 4 is a perspective view in partial cross section of a panel usable for re-moulding obtained with the apparatus of figure 1. The apparatus according to the invention comprises a tank 1 provided at the bottom with a rotatable blade 2 and with a lateral opening 3. At the latter there is a vertical material transfer conduit 4 controlled by a screw or volute feeder 5. The conduit 4 substantially connects the inner chamber of the tank 1 with the chamber of a device 6 inside which is provided a double volute or worm screw 7 with counterposed rotation. For the sake of ease and clarity of description, the double volute 7, which in use has screws arranged side-by-side on a horizontal plane (see figures 2 and 3), is illustrated in figure 1 with screws or volutes arranged on a vertical plane. The form, the dimensions and the pitch of the screw of the volute 7 vary along its length so as to treat the material being processed in different manners according to its position inside the device 6. On the latter the resin feed sections 9 and 10 (figure 3) and the degassing sections 11 and 12 (figure 2) are also defined. These sections are in particular provided with small channels 32, 33 respectively for the ingress of resin into the device 6 and for the discharge of the vapors from the latter. At the end of the device 6 opposite to the end 15 connected to the tank 1 there is an extrusion head 13 downstream whereof is provided a lamination complex 14 which will be described in greater detail hereinafter. The organic filler is fed inside the tank 1. The filler is composed of wood fragments (shavings, wood powder sawdust) still humid and with irregular size and shape. It can be seen that neither the degree of humidity of the filler nor the dimensions of the possible aggregation between fragments are critical, so that it is possible to bulk feed the wood fragments to the tank 1 without having to perform a previous sifting or a verification of its degree of humidity. By virtue of its rotation, the blade 2 causes the advancement of the wood fragments towards the lateral opening 3, from which they fall along the conduit 4 towards the inner chamber of the device 6; the screw or volute feeder 5 substantially has the function of metering the amounts of organic filler discharged into the device 6. In the portion of the double volute 7 comprised between the section 15 for the inlet of the organic filler into the device 6 and the resin supply section 10, the wood fragments are subjected to the following treatments: they are heated by the heater plates 16 provided on the skirt of the device 6, they are mixed favoring thereby the formation of a uniform organic mass and facilitating the removal of humidity, and are finally conveyed towards the further processing steps. In this first portion of the device, there substantially occurs a desiccation of the wood shavings, their treatment, so as to make the mass formed thereby homogenous and uniform, and their movement along the device 6. This first portion also provides a section 9 for the inflow of a melted thermoplastic resin (polyethylene, polypropylene, polyvinylchloride) having substantially the function of lubricating the organic filler mass, thereby facilitating its transfer into the device 6. The resin, which is in any case not indispensable in this step, is fed in very small amounts. The release of the vapors through the degassing section 11 also occurs in this first portion of the device 6. The actual introduction of the thermoplastic resin into the device 6 occurs at the section 10. The thermoplastic resin is added in a melted state, and is substantially composed of polyethylene, polypropylene, polyvinylchloride alone or in mixture. In the portion of device 6 comprised between the resin inlet section 10 and the section 17 immediately upstream of the extrusion head 13, the following processes simultaneously occur: formation of a mixture of organic filler and thermoplastic resin; the amounts of the components fed to the device 6 being such that the mixture thus obtained contains from over 60% to 80% by weight of organic filler and from under 40% to 20% by weight of thermoplastic resin with respect to the overall weight of the mixture; plastication of the mixture as it forms; also in this portion of the device 6, heater plates 16 are in fact provided, which soften the mixture; transfer of the plasticated mixture to the subsequent extrusion step. A degassing section 12 is also provided in this portion of device 6 comprised between the above described sections 10 and 17. The plasticated mass, again under the thrust of the double volute 7, is extruded through the head 13 as a sheet-like paste material 18. The lamination device 14 comprises a calender, the rollers 19, 20 whereof are arranged below the extrusion head 13 so as to receive the material 18, paste-like and not very consistent, substantially by gravity feed. Indeed the material forms a small accumulation 21 on the calender which contributes to make the thickness of the layer of material more uniform and regular. Also, by acting on the distance and on the speed of the cylinders it is possible to achieve the accurate control of the dimensions of the sheet produced. The latter is covered on one side by a film of plastic material 29 of the same type as the material introduced into the device 6 at the film head 22, further laminated between the rollers 20 and 23, coated on the opposite side with another film of plastic material 24 (the same of different to the previous material) applied by means of the film head 25, further covered with a finishing material 31 (fabric, aluminum, etc.) and again laminated between the rollers 23 and 26. The stratified laminated material 27 at the output of the apparatus 14 is subsequently cooled and cut into panels 28 (figure 4). A reinforcement 34 (figure 1), consisting, for example, of a metal net embedded into the thickness of the material 18, can be included in the layer 18 of extruded material originating from the head 13. The panel 28 thus obtained can be further hot-molded to form items having different shapes, such as for example the dashboard and other inner parts of the passenger compartment of automotive vehicles, packaging material, such as continuously heat-formed fruit-boxes and the like. Naturally, the invention as described and illustrated above is susceptible to further modifications and variations without thereby abandoning the present scope of protection.

Claims: Method of making panels starting from a thermoplastic resin and an organic filler, of the type comprising the mixing of said resin with said organic filler, the plastication and the extrusion of the mixture thus obtained, said method providing in a single step, the formation of said mix of thermoplastic resin and organic filler, and the plastication of said mixture, the mixing and the desiccation of the starting organic filler being furthermore provided during the transfer of the latter to said single mixing and plastication step, in the starting organic filler mixing and desiccation step there being furthermore provided the heating of said organic filler and the removal of the vapors produced, the method characterized by the addition of an amount of thermoplastic resin in the starting organic filler mixing and desiccation step so as to lubricate the same to facilitate its transfer, the method further providing the lamination of the extruded material. Method according to claim 1, characterized in that said single mixing and plastication step is performed during the transfer of the mixture to the subsequent extrusion step. Method according to claim 1, characterized in that said mixture comprises from about 60% to 80% by weight of organic filler and from about 20% to 40% by weight of thermoplastic resin. Method according to claim 1, characterized in that said organic filler consists of fragments of wood processing, said mixture of thermoplastic resin being in the melted state. Method according to claim 1, characterized in that said thermoplastic material consists of polyethylene, polypropylene, and polyvinylchloride alone or in mixture. Method according to claim 1, characterized in that during said single mixing and plastication step the mixture is heated and the vapors thus formed are removed. Method according to claim 1, characterized in that the lamination of the extruded stratified material provides the application thereon of outer finishing and protective layers and the embedding into its thickness of reinforcement elements. Apparatus for carrying out a method of making panels starting from a thermoplastic resin and an organic filler, comprising a single device for the continuous production of a sheet of extruded material (18) obtained starting directly from fragments of organic filler and a thermoplastic resin in a melted state, said single device consisting of a double volute (7) with counterposed rotation comprising a first organic filler mixing and desiccation portion, a second portion for formation of a thermoplastic resin and organic filler mixture and for the plastication of said mixture, and finally an extrusion head (13), said double volute (7) simultaneously performing the transfer of the organic filler from the first to the second portion, and the transfer of the plasticated mixture to the extrusion head (13), said device being provided, at said first and second portion thereof, with degassing sections (11,12), and a section (10)for the feed of the melted thermoplastic resin into said second portion, the apparatus characterized in that said device is furthermore provided with a section (9) for feeding thermoplastic resin to said first organic filler mixing and desiccation portion. Apparatus according to claim 8, characterized in that the feed of organic filler to the device is controlled by a volute device (4,5), said device furthermore comprising, at the opposite end, an extrusion head (13). Apparatus according to claim 8, characterized in that a lamination device (14) is furthermore provided comprising a plurality of counterposed rollers (19,20,23,26) as well as film heads (22) to laminate the extruded layer (18) of material and to cover it with finishing materials (31). Apparatus according to claim 10, characterized in that said lamination device (14) is provided with means for dispensing a reinforcement material (34) adapted to be embedded in the thickness of the extruded sheet-like material (18) at the counterposed roller (19,20). Apparatus according to claim 10, characterized in that the rollers (19,20) of said lamination device (14) are arranged below said extrusion head (13) of the device so as to receive said layer of material (18) by gravity feed, thereby partially accumulating said material at the entry section of the device into the section of passage between the rollers (19,20).

Inventors: MIANI, MARIO
Applicants: MIANI, MARIO
Application year: 1987
Main classification: B27N3
IPC codes: B29C43, B29C47, B27N3, B27N1