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Title:
PLANT FOR THE PRODUCTION OF ARTICLES MADE OF PLASTIC MATERIAL, RELATIVE METHOD AND ARTICLES THUS OBTAINED
Document Type and Number:
WIPO Patent Application WO/2004/071739
Kind Code:
A1
Abstract:
Plant and method for the production of articles made of plastic material covered with a thermoplastic decorative film, comprising a plurality of molding apparatuses (50) operating in parallel. Each apparatus (50) has a laying and cutting assembly (36) that prepares a segment of film, a transport plane (15) that transfers the film inside the mold, and a press (11) that supports and positions mold elements (12, 13, 22). The plant also comprises a ring nut (22) movable from a position inside the mold, on which the transport plane (15) rests in order to transfer the segment of film , to a position outside the mold wherein it discharges the article (37) when molding is complete. The position for preparing the segment of film is in proximity with the position for discharging the article (37), but is physically separated therefrom.

Inventors:
DAMO MARIO (IT)
Application Number:
PCT/IB2004/000359
Publication Date:
August 26, 2004
Filing Date:
February 12, 2004
Export Citation:
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Assignee:
G M P SPA (IT)
DAMO MARIO (IT)
International Classes:
B29C31/00; B29C37/00; B29C45/00; B29C45/14; B29C51/26; B29C67/24; (IPC1-7): B29C45/00; B29C31/00; B29C45/14; B29C51/26; B29C67/24
Domestic Patent References:
WO2002020239A12002-03-14
WO2002060668A12002-08-08
Foreign References:
US5800771A1998-09-01
US6379606B12002-04-30
EP0668231A21995-08-23
EP1249329A22002-10-16
US5273597A1993-12-28
US5368793A1994-11-29
US5940953A1999-08-24
EP1078731A12001-02-28
US4514246A1985-04-30
Other References:
PATENT ABSTRACTS OF JAPAN vol. 012, no. 378 (M - 751) 11 October 1988 (1988-10-11)
"INTEGRATION DER REINRAUMTECHNIK IN SPRITZGIESS-FERTIGUNGSSYSTEME", PLASTVERARBEITER, ZECHNER UND HUETHIG VERLAG GMBH. SPEYER/RHEIN, DE, vol. 46, no. 8, 1 August 1995 (1995-08-01), pages 90 - 91,94,96,98, XP000524710, ISSN: 0032-1338
Attorney, Agent or Firm:
Petraz, Gilberto (Piazzale Cavedalis 6/2, UDINE, IT)
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Claims:
CLAIMS
1. Plant for the production of articles made of plastic material covered with a thermoplastic decorative film, comprising a plurality of molding apparatuses (50) operating in parallel, each of said apparatuses (50) including at least: a laying and cutting assembly (36) suitable to prepare a segment of decorative film (19) on a work plane (31) arranged in a first position, transport plane means (15) able to pick up said segment of film (19) from said work plane (31) located in the first position and transfer it to a second defined position inside the mold resting on a mold element (12,13, 22), heating means, integrated with, or external to, the transport plane means (15), able to heat said segment of film (19) during its transfer from said work plane (31) to said mold element (12,13, 22), press means (11) able to support and position said mold elements (12,13, 22) in order to arrange them at least in a first open position wherein they cooperate with said transport plane means (15) to receive therefrom said segment of film (19) and thermoform it, and in a second closed position wherein, when the thermoforming of the film (19) is complete, the plastic material is injected and polymerized, characterized in that it also comprises: ring nut means (22) movable from a position inside the mold, wherein they cooperate with a relative mold element (12,13) to define at least part of the perimeter profile of said article (37), and on which said transport plane means (15) rest in order to transfer thereon the segment of film (19), to a position outside the mold wherein they discharge the article (37) when molding is complete, wherein said first position for preparing the segment of film (19) is in proximity with said position for discharging the article (37), but is physically separated therefrom.
2. Plant as in claim 1, characterized in that said plastic material is of the type consisting of at least two components that react when they are mixed during the injection and/or molding step.
3. Plant as in claim 2, characterized in that said plastic material is polyurethane or other similar or comparable twocomponent material.
4. Plant as in any claim hereinbefore, characterized in that it comprises at least an assembly arranged on one side of said press means (11) and suitable to perform change operations of at least part of the mold elements (12,13, 22), said assembly comprising at least a carriage (21) able to be arranged in cooperation with the specific press means (11) involved in the replacement and a store (39) of replacement mold elements.
5. Plant as in any claim hereinbefore, characterized in that said transport plane means (15) include integrated heating means and integrated vacuum means to form said segment of film (19) while they are heating it.
6. Plant as in any claim hereinbefore, characterized in that said transport plane means (15) include integrated vacuum means to grip and selectively retain said segment of film (19).
7. Plant as in claim 6, characterized in that said vacuum means can be selectively released at least during the transfer step of the segment of film (19) from the transport plane means (15) to the relative mold element (12,13, 22).
8. Plant as in any claim hereinbefore, wherein reel means (20) cooperate with said work plane (31) to feed said film (19) to said laying and cutting assembly (36), characterized in that said reel means (20) and said work plane (31) are associated with cover means (49) able to create an at least partly closed environment (46) preserved from environmental contamination.
9. Plant as in claim 8, characterized in that said at least partly closed environment (46) cooperates at least with suction/ventilation means (42), filtration means (43) and delivery means (44) able to create a circulation of air inside it.
10. Plant as in any claim hereinbefore, characterized in that it comprises at least an ionizing bar (45) arranged along the path of the segment of film (19) between said reel means (20) and the inside of the mold element (12,13, 22) and able to exert on said film (19) an effect of neutralizing the electrostatic loads.
11. Method for the production of articles made of plastic material, covered with a thermoplastic decorative film, in a plant comprising a plurality of molding apparatuses (50) operating in parallel, which provides at least: a first step wherein a segment of film (19) is prepared and cut to size in a first preparation and cutting position located laterally to a relative press means (11) that supports and moves relative mold elements (12,13, 22), a second step wherein said segment of film (19) is picked up by transport plane means (15), heated and preformed while it is being transferred by said transport plane means (15) to a second position of cooperation with at least one of said mold elements (12,13, 22), characterized by a third step wherein ring nut means (22) move from a first position outside the relative press means (11) to a second position inside said press means (11) in order to rest on a relative mold element (12,13), a fourth step wherein said transport plane means (15) rest on said ring nut means (22) with said segment of film (19) that is retained at least on the perimeter between said transport plane means (15) and said ring nut means (22), a fifth step wherein said film (19) is thermoformed and made to adhere to the inner wall of the relative mold element (12,13), after which the film (19) is transferred from said transport plane means (15) to said ring nut means (22), said transport plane means (15) then being discharged from the mold, a sixth step wherein the mold closes, the injection of the plastic material is started by means of an injection head (117) associated with a mold element (12,13, 22) and polymerization and molding is started, a seventh step wherein a new segment of film (19) is prepared in the first preparation and cutting position and is picked up by said transport plane means (15) to be heated and preformed, an eighth step wherein the mold is opened and said ring nut means (22), with the article (37) resting on the perimeter thereof, are removed and translated outside the mold itself in order to cooperate with discharge means (35) in discharging the molded article (37), wherein the discharge of the article (37) occurs in proximity with the zone where the segment of film (19) is prepared and cut, but in a position physically separated from said preparation and cutting zone.
12. Method as in claim 11, characterized in that said second step of transferring said segment of film (19) by means of said transport plane means (15) is at least partly superimposed temporally with said third step of moving said ring nut means (22) from outside to inside the mold element (12,13, 22).
13. Method as in claims 11 or 12, characterized in that said sixth step of polymerizing and molding the plastic material inside the mold is at least partly superimposed temporally with said seventh step wherein a new segment of film (19) is prepared, picked up by the transport plane means (15) and heated and preformed.
14. Method as in any claim from 11 to 13 inclusive, characterized in that the temperature at which the film (19) is heated is independent from the ideal polymerization temperature of the material.
15. Articles made starting from plastic material consisting of at least two components of the type able to react when they are mixed, covered with a thermoplastic decorative film (19) made in the plant and using the method as in any one of the previous claims.
Description:
"PLANT FOR THE PRODUCTION OF ARTICLES MADE OF PLASTIC MATERIAL, RELATIVE METHOD AND ARTICLES THUS OBTAINED" * * * * * FIELD OF THE INVENTION The present invention concerns a plant for the production of articles made of plastic material of the type consisting of at least two components that react when mixed, for example during the injection and/or molding step using R. I. M. (Reaction Injection Molding) technology.

The following description refers to polyurethane as an example of such plastic materials, but it comes within the field of the invention to use any plastic material having such characteristics, for example dicyclopentadine or other similar or comparable material.

The articles of plastic material to which the invention refers are covered with at least a thermoplastic film, possibly pigmented, and having a decorative and/or protective function.

The articles obtained according to the invention are relatively large and consist, for example, of panels, doors, wings or similar, with high aesthetic characteristics and including, or not, undercuts, inlays or handles.

BACKGROUND OF THE INVENTION Known methods for the production of articles made of plastic material with at least two components using the R. I. M. technology differ from each other mainly according to the technique used for the surface finishing of the article obtained.

A first solution provides to make the article in a mold, remove it, and then subject it to a completion step that comprises at least trimming, surfacing, sanding and painting operations. This technique is very laborious, does

not give satisfactory and repeatable results with acceptable levels of standardization, and requires a high use of manpower and long execution times. Moreover, it limits the possibility of automating the production process and entails the need for purifiers and ventilators, particularly in the sanding and painting steps. Moreover, the process is in itself slow and discontinuous because it is impossible to exploit a great part of the equipment during the time required for the plastic material to polymerize inside the mold.

For all these reasons this technology has until now had a limited development, entails high costs and considerable problems both environmental and in operating difficulties for the operators, connected to the surface finishing of the pieces.

A second finishing technique provides to apply a covering and protective film in the mold, wherein the film is both heated and also thermoformed in the mold in succession.

This technique, however, has a disadvantage because it is necessary to wait a relatively long time until the decorative film can be taken to the temperature suitable for thermoforming. Moreover, it has considerable difficulties in ensuring a homogeneous heating over the surface of the film. Furthermore, the time needed to heat the film is added to the time needed for thermoforming, since it is not possible to even partly superimpose these two different operations performed by the same molding apparatus.

Since the heating of the film is achieved by the punch of the mold, low calorific yields of heat transmission are obtained, since the punch cannot exceed the ideal polymerization temperature of the material. This also puts

limits on the types of materials that can be used, both plastic for the article and thermoplastic for the film.

With both techniques there are also considerable problems with the quality of the products obtained.

US-B-6.379. 606 describes a thermoforming method wherein two pieces molded separately are fused and joined together, with a rotating table which moves the pieces between various working stations, in each of which one step of the cycle is carried out. This document does not refer to the production of polyurethane articles covered with a thermoplastic film which is heated before it is introduced into the elements of the mold, and therefore it deals not with the problems connected with transporting, retaining, pre-heating and pre-forming the film, with introducing the material inside the mold, with discharging the article, etc.

US-A-5.800. 771, which is the most pertinent state of the art, concerns a method to mold an article made of resin covered by a film that, before being introduced into the mold, is heated by a transport table. However, this document does not provide means inserted inside the mold which collaborate in the operations to position the film, and to mold and discharge the article.

Applicant has devised, tested and embodied the present invention to overcome these problems, which until now have limited the diffusion of these technologies, and to obtain other advantages as will be shown hereafter.

The purpose of the invention is to achieve a plant suitable to produce in repetitive manner, with limited costs and times, with high and standardized quality and with a great automation of a large part of the operating steps, articles made of plastic material covered on at least one side with at least a decorative film.

Another purpose is to achieve a compact plant, of limited size and complete with accessory elements to perform all the operations connected to the finishing and completion of the work processes on the article.

Another purpose is to achieve a plant wherein the production times are optimized, eliminating pauses and waiting times as much as possible, and allowing a great automation of the entire process. A further purpose is to make the operations to change both the form of the article, changing at least part of the elements of the mold, and also the color and format of the decorative film easy, quick and able to be automated, without requiring complex operations of dis-assembly and re-assembly of parts, nor particular use of manpower.

SUMMARY OF THE INVENTION The present invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the main solution.

The plant according to the present invention comprises a plurality of molding apparatuses, able to work in parallel, and each comprising at least: - a device suitable to prepare, in a first position, a segment of thermoplastic decorative film, and to transfer said segment of film, after it has been heated and possibly pre-formed, from said first position to a second position wherein it is arranged on a molding element; - a press element able to support and move the relative mold elements, having one or more impressions; and - at least an injection head connected to at least a skimmer, able to inject the at least two-component plastic material inside the molding cavity defined by the mold elements located in the closed position, according to the R. I. M. (Reaction Injection Molding) technology.

Each molding apparatus also comprises first automated transport means that pick up, and possibly heat and pre- form, the segment of film during its transfer from the laying and cutting zone until it is positioned in a relative mold element.

According to a first embodiment of the invention, the first automated transport means are of the type with a heating plane and include means to grip, retain and pre- form the segment of film to prevent it from deforming, due to the fact that it is very thin, during the heating step.

Said heating plane means are able to move, positioning themselves on each occasion, from the zone, wherein the segment of film is laid onto a work plane and cut to size, as far as inside the press element, and to rest on a relative mold element to transfer thereto the heated, and possibly pre-formed, segment of film.

In a preferential embodiment, the heating plane means cooperate with the relative mold element, during the thermoforming step performed in the mold, clamping the segment of film on the perimeter and exerting thereon a retaining function.

According to a variant, the heating of the film is obtained using heating means located outside the transport plane, for example heating lamps, such as infra-red, ultra- violet or other suitable type, with which the automated transport means are taken to temporarily cooperate. In this case, the transport plane is not heated, or is heated only partly.

The laying, cutting, heating and pre-forming of the segment of film performed outside the mold serve on the one hand to reduce the times necessary for the thermoforming of the segment of film inside the mold, and on the other hand allow to exploit the polymerization times of the plastic

material after it has been injected into the mold. In this way, in the subsequent cycle, the segment of film is introduced into the mold already hot without the required heating and polymerization times being added entirely together in the cycle time.

Moreover, the heating performed outside the mold allows to make the temperature at which the film is heated independent from the temperature of the mold elements, which corresponds to the ideal polymerization temperature of the plastic material. This allows to use materials for the film that cannot be used in traditional apparatuses that heat the film inside the mold. Furthermore, the heating of the film is not limited by the geometry of the punch and therefore can be optimized according to the type and format of the film used.

According to another characteristic, each production apparatus comprises ring nut means movable between, and able to be positioned in, a first position outside and a second position inside the press element and at least partly superimposed over a mold element in order to cooperate with the latter at least during the molding of the article.

According to the invention, when polymerization and molding are complete, the ring nut element is able to be taken outside the press element in order to discharge the article and transfer it to an autonomous unloading position. The unloading position to unload the article is located in proximity with the position where the segment of film is laid and cut, but is separated therefrom so as to preserve the segment of film from contamination of dust or other dirt that can cause a deterioration in quality and wasted production.

According to another variant, in the first position

where the segment of film is laid and cut there is an automated reel-change apparatus to replace an empty reel with a new reel and/or to change the color and/or format of the film.

According to the invention, the zone where the segment of film is laid and cut consists of a substantially closed environment in order to prevent infiltrations of dust and dirt, and inside there is at least a suction/ventilation system to keep the ambient air constantly clean. According to a variant, during the transit from the laying and cutting zone to the inside of the mold element the segment of film is subjected to the action of at least an ionizing bar that neutralizes any possible electrostatic charge that might have accumulated and prevents the film from attracting particles of dust and other dirt.

According to another variant, on one side of every molding apparatus there is at least an automated device suitable to make the mold-change operations when it is necessary to change the figure of the article to be made.

BRIEF DESCRIPTION OF THE DRAWINGS These characteristics and advantages will become apparent from the following description of a preferential embodiment of the invention, given as a non-restrictive example with reference to the attached drawings wherein: - fig. 1 shows a plane view of a plant for the production of articles according to the present invention comprising four molding apparatuses arranged in parallel; - fig. 2 shows a longitudinal section of a molding apparatus of the plant in fig. 1; - fig. 3a shows a transverse section of the plant in fig.

1; - fig. 3b shows an enlarged detail of fig. 3a;

- figs. 4a to 41 show the production cycle of articles in the plant in fig. 1.

DESCRIPTION OF THE DRAWINGS In the attached figures, the reference number 10 denotes generally a plant for the production of articles 37 made of plastic material, for example polyurethane material or suchlike, consisting of a plurality, in this case four, of molding apparatuses 50 operating in parallel. Each apparatus 50 comprises a press element 11 suitable to support and move relative mold elements consisting, in this case, of a female part 13, or matrix, and a male part 12, or punch. The press element 11 can be driven to open/close by means of a movement actuator 30, according to the specific steps of the operating cycle. It comes within the field of the invention that the mold elements can have two or more impressions, and that the punch 12 can be replaced by another matrix or other similar or comparable element.

The punch 12, in this case in a substantially central position, has an injection channel 17, associated with an injection head 117. Through the channel 17, after the mold has been closed, a mixture is injected of at least two components so that they react, in successive steps, inside a molding cavity 28 (fig. 4f) defined between the punch 12 and the matrix 13 until they are consolidated.

It is clear that, within the framework of the invention, the injection channel 17 could be located in a non-central position, or there could be two or more injection channels, possibly usable alternately.

In this case, each apparatus 50 comprises feed reel means 20 able to feed a thermoformable and decorative covering film 19, which is made to adhere through thermoforming, as explained in more detail hereafter, to the inner wall of the matrix 13.

The feed reel means 20 are arranged in a preparation zone, located laterally to a relative press element 11, and are able to cooperate with a laying and cutting assembly 36 comprising laying means 38a and cutting means 38b able to prepare a segment of film 19 on a work plane 31. The film 19 is made of thermoplastic material, advantageously has a pigmented surface and, normally, a thickness of between 0.2 and 1.4 mm, but it can also be as much as 3 mm and more.

Each apparatus 50 also comprises a transport plane 15, which can also be a heating plane, movable between a first position outside the press element 11 and a second position wherein it is taken to rest on the matrix 13, in order to locate and transfer thereon a segment of said film 19 that has been cut to size. The function of the transport plane 15 is also to perform a pre-forming, for example upwards, of the segment of film 19 outside the mold, and then to transport said segment of film 19 inside the mold, while it heats it, so that thermoforming can be completed on the matrix 13. According to a variant that is not shown here, the transport plane 15 does not have a heating function, and the film 19 is heated before it is introduced into the mold by external means, for example infra-red lamps or suchlike, with which the transport plane 15 is taken to temporarily cooperate.

As will be seen better hereafter, the transport plane 15 cooperates with a mold element during the thermoforming step too, in order to exert a retention function on the perimeter of the segment of film.

In the specific embodiment shown here, the apparatus 50 also comprises an annular ring nut 22, of the type movable between the zone where the film 19 is prepared and a relative molding apparatus 50.

The zone where the film 19 is prepared is located in

proximity with, in this case above, the zone where, once molding is complete, the article 37 is discharged and unloaded by means of the movable ring nut 22.

This brings advantages both in terms of reducing the cycle times, in terms of facilitating cleaning and maintenance operations on the equipment, and also in terms of managing and controlling operations by the staff in charge.

The zone where the film 19 is prepared and the zone where the article 37 is discharged are physically separated from each other, however, by means of the work plane 31.

This physical separation of the two zones brings the advantage that all the detritus, flashes, dust and other dirt generated during the removal of the article 37 from the ring nut 22 do not contaminate the area above the work plane 31, where the film 19 is laid and where there is the transport plane 15. As a consequence, we prevent this dirt from being attracted by the electrostatic loads of the film 19, creating wasted production in subsequent cycles, with obvious advantages both in economic terms and in the quality of the finished product.

The feed reel means 20 and the work plane 31 are arranged inside a substantially closed environment 46 defined by a cover 49 and including suction means 42, filtration means 43 and means 44 to deliver air. As a result, residual or environmental particles of dirt and detritus are prevented from contaminating the environment above the work plane 31 and depositing on the surface of the film 19, thus compromising the quality of the article 37 and causing wasted production.

In the embodiment shown here, along the path of the segment of film 19 as it unwinds and/or transfers, there are one or more ionizing bars 45 that act on the exposed

surface or surfaces of the film 19 to neutralize any accumulated electric loads, which can attract residues of dust or suchlike.

The annular ring nut 22 not only has a function of discharging the article 37 but also, when it is resting on the matrix 13, of providing a supporting surface for the transport plane 15 during the transfer and forming of the segment of film 19, and of collaborating with the matrix 13 during the molding step, for example to achieve specific undercuts and perimeter profiles in the article 37.

Thanks to the presence of the annular ring nut 22, the article 37 can be discharged from the mold in a substantially finished form that only needs the perimeter trimming of the excess film 19.

The annular ring nut 22 is moved, in coordination or not with the transport plane 15, to insert and form the film 19 in the mold and then, as explained, to discharge the article 37 from the mold.

The plant 10 also comprises discharge means 35 able to discharge the article 37 from the ring nut 22; said discharge means 35, as explained, are arranged substantially in the zone where the film is laid and cut, below the work plane 31.

The transport plane 15, which in the embodiment shown also functions as a heating plane, comprises a bearing structure 16 on which a replaceable frame 41 is mounted to grip and pre-form the film 19. As described in a previous application in the name of the same Applicant, a heating element is mounted on the structure 16, for example with a sheet-type electric resistance, and also an insulating element and means able to create a vacuum according to temporal modes that can be selected depending on the step of the cycle in progress.

The movement means that cause the movement of the transport plane 15 can also be of the robotized type and allow to transport and handle the transport plane 15, with the segment of film 19, to any position whatsoever and with any orientation in space whatsoever. The movement means displace the transport plane 15 from its first position outside the mold to its second position inside the mold and vice versa, as described hereafter.

The frame 41 is provided with anchoring means to anchor, at least temporarily, the film 19 to the frame 41; it also has vacuum means, specific or unified, with the following functions: - to temporarily retain thereon the segment of film 19 while it is gripped, heated and transferred from the laying and cutting zone to the thermoforming zone; - to pre-form the film 19 upwards during the transfer; - to retain the film 19 throughout the thermoforming step, making the frame 41 adhere closely to the ring nut 22; - to transfer the film 19 from the frame 41 to the ring nut 22 and to the matrix 13.

The plant 10 also comprises, on one side of the press elements 11, a mold-change carriage 21 cooperating with a store 39 where molds are deposited. The mold-change carriage 21 is driven to replace the mold elements, matrix 13 and/or punch 12 and/or ring nut 22, of each of the molding apparatuses 50, when the product is changed. The replacement mold elements are arranged on the store 39 and are picked up by the mold-change carriage 21 to be selectively located in a position adjacent to the molding apparatus 50 involved in the replacement.

The automatic functioning cycle relating to each molding apparatus 50 as described above is as follows.

In fig. 4a, the ring nut 22 and the transport plane 15

are in a position outside the mold and in proximity with the feed reel means 20 that feeds the film 19. The transport plane 15 is above the work plane 31, has already picked up a relative segment of film 19, previously unwound from the feed reel means 20 by the means 38a and cut by the means 38b, and is heating it; the ring nut 22 is below the work plane 31 and has just discharged a molded article 37.

The second step (fig. 4b) provides that the transport plane 15 and the ring nut 22 translate on a substantially horizontal plane and are positioned between the matrix 13 and the punch 12. Then (fig. 4c), the ring nut 22 is taken to rest on, and couple with, the perimeter of the matrix 13 and the transport plane 15, with the film 19, is taken to rest on the ring nut 22.

Subsequently the thermoforming of the film 19 is started, during which the transport plane 15, thanks to its vacuum means, exerts an action to retain the perimeter of the film between itself and the ring nut 22.

During the thermoforming step inside the mold, the laying and cutting assembly 36 can already prepare a new segment of film 19 on the work plane 31, thus reducing the cycle times.

When the thermoforming of the film 19 on the matrix 13 has been completed, the transport plane 15 is raised (fig.

4d) and then discharged from the mold; during this step the vacuum means of the transport plane 15 and the ring nut 22 are selectively, released and activated to perform the transfer of the film 19 while it is gripped on the ring nut 22 and the matrix 13.

In the laying and cutting zone, a new segment of film 19 has been cut and laid on the work plane 31; the cutting means 38b move to a position of non-encumbrance on the work plane 31.

The transport plane 15 returns to the laying and cutting zone (fig. 4e), above the work plane 31 where the new segment of film 19 is ready. The transport plane 15 can be lowered to pick up the new segment of film 19 in order to start heating and pre-forming it.

At this point (fig. 4f), the press element 11 closes, taking the punch 12 onto the matrix 13, and the injection of the plastic material into the molding cavity 28 is started, thanks to the injection head 117.

The mold remains closed for the time needed to complete the polymerization reaction. The heat and pressure generated during polymerization complete the thermoforming of the film 19, which is definitively and stably attached to the outer surface of the plastic material that is in consolidation phase.

The time required for polymerization is in any case used both for laying and cutting, on the work plane 31, a segment of film 19 to be used in the subsequent cycle, and also for heating said film by the transport plane 15; this leads to a considerable reduction of the overall times needed to complete the cycle.

When the molding is complete, the mold is opened and the annular ring nut 22 is first raised (fig. 4g), and then translated laterally to its initial position, below the work plane 31, taking with it the article 37 (fig. 4h) that remains resting on said ring nut 22 due to the presence of the perimeter edge of the excess film 19. In this position the molded article 37 can be extracted and removed, by means of the discharge means 35 (figs. 4i, 41).

The new cycle can restart automatically from this moment, substantially without a pause, given the proximity of the position of the ring nut 22 and the transport plane 15, while the operator, in safety, can pick up the article

37 to send it to a trimming station where the perimeter of the film 19 can be trimmed, in order to complete the process and obtain the finished piece.

When the mold has to be changed, the carriage 21 is driven and translates with respect to the store 39 in order to pick up the replacement element; then it moves in front of the molding apparatus 50 involved in the replacement.

Modifications and variants may be made to the plant and method as described heretofore, but these shall remain within the field and scope of the present invention.

For example, a single press element 11 can comprise not only two or more impressions, but also two or more simultaneously driven molds. An automatic reel-change apparatus 20 can be arranged in the preparation zone in order to replace empty reels and/or to change the color of the film. Ionizing bars 45 can be arranged also outside the environment 46 and as far as in proximity with the press element 11. The discharge means 35 can be of any type even though it is preferable to use suction cup means or suchlike.