Process and equipment for hot moulding of articles made of thermoplastic material

Abstract: A process for the hot moulding of articles (L) made of thermoplastic material, comprising the steps of: heating at least one plate of thermoplastic material (L) to a plasticizing temperature; compressing said heated plate (L) between two moulding surfaces (14, 16), set opposite one another, of a pair of half-moulds (10, 12); and forming, by injection moulding, at least one component (22) anchored to a surface of the plate (L), while the plate is being compressed between said moulding surfaces (14, 16).

Description: The present invention relates to a process and equipment for the hot moulding of articles made of thermoplastic material. The invention has been developed in particular for the moulding of panels for lining the interiors of motor vehicles. A conventional technology for the production of lining panels involves heating of at least one plate of thermoplastic material to a plasticizing temperature and setting the plate, together with a possible upholstery sheet, between two half-moulds of an apparatus for hot moulding, which are provided with respective moulding surfaces set opposite one another. Hot moulding involves the application of pressure on opposite surfaces of the plate in a plastic state, thus bestowing on the plate the desired shape. Normally, during moulding of the plate, also an upholstery sheet is applied on one surface of the plate itself. When panels are produced for internal lining of motor vehicles, it is often necessary to fix, on the rear surface of the panel, one or more inserts forming an anchoring seat for a fixing means, such as a screw, a snap-in pin, or the like. Normally, these inserts are produced by injection moulding separately from the hot moulding of the panel, and are subsequently fixed by welding on the rear surface of the moulded plate. Alternatively, the inserts produced by injection moulding may be fixed on the plate during hot moulding of the plate itself. In this case, the inserts are positioned in the hot-moulding equipment and are mechanically anchored to the plate during moulding. The latter approach requires injection-moulding equipment independent of the hot-moulding equipment and involves an operating step in which the inserts are fixed onto the moulded plates, or else a step in which the inserts are positioned on the moulding equipment. DE-A-19818881 discloses a process and equipment according to the preamble of claims 1 and 3. This document discloses an apparatus for forming an internal panel for a vehicle in which connectors and ribs are an integral part of the panel. This known apparatus comprises an upper mould and a lower mould for pressing a rigid substrate and an outer layer fabric. The lower mould has connector-forming and rib-forming recesses extending to an inlet tube via injection channels. Also disclosed is a panel moulding process in which the preheated substrate is placed on the lower tool, the fabric spread out on top and the tool closed to mould the panel. A polymer is then fed via the injection channels to fill the recesses and welds onto the rear surface of the panel substrate to form integral connectors and ribs. The object of the present invention is to provide a process and equipment for hot moulding of articles made of thermoplastic material, which will provide improved quality of the finished articles. According to the present invention, the above subject is achieved by a process and equipment having the characteristics specified in claims 1 and 3. The present invention will now be described in detail with reference to the attached drawings, which are provided purely to furnish a non-limiting example, and in which: Figure 1 is a schematic partial section of hot-moulding equipment according to the present invention; Figures 2 and 3 are schematic sections illustrating the equipment of Figure 1 in various steps of the operating cycle; Figure 4 is a schematic perspective view of the part indicated by the arrow IV in Figure 3; and Figure 5 is a detail at an enlarged scale of the part indicated by the arrow V in Figure 3. With reference to Figures 1-3, the numbers 10 and 12 respectively designate a top half-mould and a bottom half-mould of a hot-moulding apparatus. The half-moulds 10, 12 have respective moulding surfaces 14, 16, which are set opposite each other and are designed to apply a moulding pressure on a plate L of thermoplastic material, following upon movement from an open position to a closed position. Figure 1 illustrates the half-moulds in a closed position, at the end of hot moulding of the plate L. The plate L is first heated up to a plasticizing temperature and is set between the two half-moulds 10, 12 while these are in the open position. An upholstery sheet R may be set between the two half-moulds together with the plate L so that it will be applied on one surface of the plate L during moulding of the latter. The half-moulds 10, 12 are provided, in a conventional way, with a cooling system in order to ensure that, during the moulding operation, the plate L will be cooled down to a temperature substantially lower than the plasticizing temperature of the thermoplastic material. One of the two half-moulds (in the example illustrated, the bottom half-mould 12) is provided with at least one injection-moulding seat 18, which communicates with an injection channel 20. The seat 18 is designed to form an insert 22 having, for instance, the shape illustrated in Figure 4. The insert 22, illustrated to provide an example in Figure 4, comprises a portion 24 containing a hole 26 with its axis substantially orthogonal to the plate L. The portion 24 is connected to the plate L via three walls 28 fixed to the plate L , each along one of its edges 30. Figure 1 illustrates the configuration of the moulding equipment at the end of the hot-moulding step and before injection of plastic material into the injection-moulding seat 18. The seat 18 is defined between one portion of the mould 12 and a slider 32 which is mobile with respect to the half-mould 12 to enable extraction of the insert 22 that is formed in the seat 18. The slider 32 has a surface 34 which constitutes a portion of the hot-moulding surface of the half-mould 12. As may be seen in Figure 1, the moulding seat 18 communicates with the hot-moulding surface 16, 34 by means of a narrow section 36 which constitutes the joining edge 30 between the insert 22 and the plate L. The narrow section 36 has a surface substantially smaller than that of the transverse section of the remaining part of the cavity 18, so as to produce, at the narrow section 36, a marked reduction in the pressure of the plastic material injected into the moulding seat 18. With reference to Figure 2, after hot moulding of the plate L has been completed, and after partial cooling of the plate L by contact with the half-moulds 10, 12, plastic material compatible with the thermoplastic matrix of the plate L is injected into the injection-moulding seat 18. The injection of plastic material is performed according to a technology typical of injection moulding of plastic materials. For example, the plastic material may be propylene-based and may be injected at pressures in the region of 600-1000 bar and at a temperature in the region of 180°C. The narrow section 36 of contact between the moulding seat 18 and the plate L reduces the pressure against the plate L of the injected material and thus prevents the injected material from damaging the plate L and the upholstery sheet R. The dimensions of the narrow section 36 can be varied according to the parameters of the injection process so as to prevent damage to the plate and, at the same time, to obtain a surface for mutual fixing between the insert 22 and the plate L that is sufficiently large for providing firm anchorage. As illustrated in Figure 3, after the insert 22 has been obtained by injection moulding, the half-moulds 10, 12 are brought into the open position and, at the same time, the slider 32 is displaced with respect to the half-mould 12 in the direction indicated by the arrow A so as to enable extraction of the insert 22 from the seat 18. As illustrated in Figures 3 and 5, the insert 22 is anchored to the plate L along the edge 30 having a narrow section. The number of inserts 22 fixed to the plate L may vary according to the particular requirements. Also the shape and size of each insert 22 may vary widely with respect to what is described and illustrated herein purely for the purpose of providing an example.

Claims: A process for the hot moulding of articles (L) made of thermoplastic material, comprising the steps of: heating at least one plate of thermoplastic material (L) to a plasticizing temperature; compressing said heated plate (L) between two moulding surfaces (14, 16), set opposite one another, of a pair of half-moulds (10, 12); and forming at least one component (22) anchored to a surface of the plate (L) by injecting plastic material at high pressure into a seat (18) communicating with one of said moulding surfaces (14, 16) while the plate is being compressed between said moulding surfaces (14, 16), characterized by providing in said seat (18) a narrow section (36) designed to produce a reduction in the pressure of the plastic material injected in contact with the plate (L). A process according to Claim 1, characterized in that it comprises the step of displacing a slider (32) defining one part of said seat (18) for extracting the injection-moulded component (32) from the respective seat (18). Equipment for hot moulding of articles made of thermoplastic material, comprising a first half-mould (10) and a second half-mould (12) which are free to move with respect to one another between an open position and a closed position and are provided with respective moulding surfaces (14, 16) designed to carry out hot moulding of at least one plate (L) of thermoplastic material, wherein least one of said half-moulds (10, 12) comprises at least one injection-moulding seat (18) communicating with the respective hot-moulding surface (16, 34) and at least one injection channel (20) provided for injecting plastic material at high pressure inside said seat (18), characterized in that said injection-moulding seat (18) presents a narrow section (36) designed to reduce the pressure of the plastic material injected in contact with the plate (L). Equipment according to Claim 3, characterized in that the half-mould (12) provided with said injection-moulding seat (18) carries a slider (32) which is mobile with respect to the half-mould (12) between an operating position in which the slider (32) defines a part of said injection-moulding seat (18) and a non-operating position in which the injection-moulded component can be extracted from the seat (18).

Inventors: CESANO FRANCO, CESANO, FRANCO
Applicants: CRS SRL CT RICERCHE E SPERIMEN, CRS SRL CENTRO RICERCHE E SPERIMENTAZIONI
Application year: 2000
Main classification: B29C45
IPC codes: B29C43, B29C45