WO2000000343A1

WO2000000343A1 - Method and plant for continuously cladding panels using vacuum

Info

Publication number: WO2000000343A1
Application number: PCT/EP1999/004458
Authority: WO
Inventors: Disma Paro
Original assignee: 3B S.P.A.
Priority date: 1998-06-30
Filing date: 1999-06-28
Publication date: 2000-01-06
Also published as: IT1306473B1; ITVE980029A1; AU4778799A

Abstract

A method for continuously cladding panels, in particular of wood-based material, with a sheet of thermoplastic material, characterised by: positioning the panels (18), to one side of which a sheet of thermoplastic material has already been applied, on an endless conveyor (2) such that said side faces said endless conveyor and is maintained spaced therefrom at least at the panel edges; superposing on the surface of the panels (18) to be clad, the surface having been previously treated with heat-activated adhesive, a continuous sheet (10) of thermoplastic material; heating the panels (18) to activate the adhesive and soften the sheet of thermoplastic material (10); and applying vacuum to the panels (18) to cause the sheet of thermoplastic material (10) to intimately adhere to the surface and to the edges of the panels.

Description

METHOD AND PLANT FOR CONTINUOUSLY CLADDING PANELS USING VACCUM

This invention relates to a method for continuously cladding panels, in particular of wood-based material, with a sheet of thermoplastic material, and a plant for implementing the method.

Methods are known for cladding a surface and possibly the edges of a panel of wood-based material, for example MDF (medium density fibreboard) with a sheet of thermoplastic material, for example PVC. Generally, this method uses a press provided with a rigid plate and an elastically yieldable plate. A series of panels, already clad on one side with a sheet of PVC, melamine, paper or another material, are positioned in the press such that their clad side faces its rigid plate and is kept spaced therefrom, for example by a suitable spacer in the form of another panel of smaller dimensions than that being processed. The opposite side of the panel, ie the side facing the yieldable plate of the press, is treated with a layer of heat-activated adhesive and the plastic sheet is placed on it. On operating the press, the combined effect of temperature, pressure, any suction applied between the panel and plastic sheet, the yieldability of the elastically yieldable plate and the distance between the panel being processed and the rigid plate of the press, softens the thermoplastic material and by virtue of the heat-activation of the adhesive the thermoplastic sheet adheres completely and permanently to the possibly grooved surface of the panel and to its edges.

Presses without an elastically yieldable plate are also known. In these the thermoplastic sheet is softened and subjected to pressure to make it adhere permanently to the panel to be clad. As in ail cases the press dimensions are generally much greater than the panel dimensions, it is usual to position several panels on the press so that the press can operate simultaneously of them and accelerate the cladding operation. A drawback of these known methods is that the cladding method is always discontinuous, and between one press operation and the subsequent positioning of the spacers on its lower plate requires the panels for ciadding to be accurately positioned on them, followed by a waiting time while the press completes its action, then the removal of the processed panels and possibly the spacers from the press, these being operations which are laborious to carry out and involve lengthy waiting times.

To eliminate or at least reduce these drawbacks, methods and plants have already been proposed (EP-B1-0 593 427 and EP-B1-0 593 429) for simultaneously positioning several panels within a press in which the spacers are already present. These known solutions have proved effective, but still operate discontinuously, with its inevitable consequences.

This invention confronts and solves the problem of subjecting panels, particularly of wood-based material, which have already been clad on one side with a sheet of thermoplastic material, to continuous cladding with a separate sheet of thermoplastic material on their other side and their edges.

Such panels are continuously clad according to the invention through a method as claimed in claim 1.

According to the invention, to implement the method a plant is provided as claimed in claim 10. A preferred embodiment of the invention and some variants thereof are described in detail hereinafter with reference to the accompanying drawings, on which:

Figure 1 is a longitudinal schematic view of a plant for implementing the method of the invention,

Figure 2 is a plan view thereof on the line ll-ll of Figure 1 ,

Figure 3 is an enlarged partial longitudinal section therethrough on the line

Ill-Ill of Figure 2, Figure 4 is an enlarged cross-section therethrough on the line IV-IV of Figure 2,

Figure 5 is an enlarged cross-section therethrough on the line V-V of Figure

2, Figure 6 is an enlarged cross-section therethrough on the line VI-VI of Figure 2, and Figure 7 shows a variant in the same view as Figure 6.

As can be seen from the figures, the method of the invention is implemented by a plant which basically comprises an endless conveyor belt 2 extending from one end to the other of a bed 4 supported by legs 6 resting on the floor 8. On the bed 4 there is provided, in correspondence with the loading station (on the left observing Figures 1 and 2), a feed station for a continuous sheet 10 of thermoplastic material. This feed station is indicated overall by 12 and comprises a pair of uprights 14 applied to the bed 4 and supporting rollers 16 for different sheets 10. Downstream of the feed station 12, with reference to the direction of advancement of the conveyor belt 2, indicated by the arrow 13 in Figure 1 , there is provided a first oven 17, the purpose of which, as described hereinafter, is to heat the panels 18 continuously loaded onto the conveyor belt 2, and the continuous sheet 10. These panels, which are preferably of wood-based material, but could also be of other material, for example plastic or metal, are sprayed with a heat-activated adhesive, for example a polyurethane or vinyl adhesive.

Downstream of this first oven 17 there is provided a second oven 19, positioned within a sealed chamber maintained under vacuum by a suction system indicated overall by 20 and comprising a traditional vacuum pump. To ensure the necessary vacuum within said chamber there is provided in a position below the conveyor belt 2 a tank 22 with its upper surface perforated and facing the conveyor belt, which also comprises a plurality of apertures over its entire surface.

Within the sealed chamber there is provided to the sides of the oven 19 a pair of pressers consisting essentially of endless straps 24, maintained with a rectilinear portion adhering to the conveyor belt 2 by traditional systems, not shown on the drawings for simplicity of representation.

Downstream of the second oven 19 there is provided a ventilating chamber 28. This is also connected to a suction system similar to that connected to the oven 19, ie comprising a vacuum pump connected to a tank 28 having its upper surface perforated and facing the conveyor belt 2. However in contrast to the oven 19, the ventilating chamber 26 is also provided with a fan 29 able to feed a jet of cold air onto the upper surface of the underlying sheet of thermoplastic material 10. For reasons which will be apparent hereinafter, the conveyor belt 2 comprises a plurality of transverse projections 30 at intervals depending on the dimensions of the panels 18 to be processed.

The aforedescribed plant operates as follows: spacers 32 of dimensions slightly less than the dimensions of the panels 18 to be clad are placed on the conveyor belt 2 at its loading end, ie the left end with reference to Figure 1 , on each spacer there then being rested a panel 18 already clad on its lower surface with a sheet of thermoplastic material (for example PVC, melamine etc.) and previously sprayed on its upper surface, which may comprise ornamental grooves, and on its edges with a layer of heat-activated adhesive.

On the panels 18 arranged in this manner there is then laid the sheet 10 of thermoplastic material, which enters the first oven 17 together with them. The sheet 10 undergoes heat-softening therein and at the same time the adhesive previously sprayed onto the panels 18 becomes active. The speed of advancement of the conveyor belt 2 and the internal temperature of the oven 17 are correlated with the length of the oven sot that on leaving the oven it is ensured that the PVC sheed 10 will have softened and the adhesive become active. When the panels 18 enter the second oven 19, the combined effect of the heat and the vacuum causes the softened sheet 10 to adhere to the upper surface and edges of the panels 18, and also causes the sheet 10 retained between the conveyor belt 2 and the pressers 24 to wrap about the lower corners of the panels, so that they become completely clad. The lateral seal between the cladding sheet 10 and the conveyor belt

2 is provided by the contact between them and the effect of the pressers 24, whereas the frontal seal between the cladding sheet 10 and the conveyor belt 2 upstream and downstream of each panel 18, necessary to prevent vacuum loss, is ensured by contact between the sheet 10 and the transverse projections 30 provided on the conveyor belt 2. After the panels 18 have left the oven 19, they enter the ventilating chamber 26, through which an air stream is circulated to cool the panels while at the same time the suction system ensures that the sheet 10 remain adhering to the panels during cooling.

Consequently at their exit from the cooling chamber 26, paneis 18 are obtained completely clad with the continuous PVC sheet 10 and ready to be fed to the subsequent separation and finishing operations. At the same time the spacers can be removed one by one to be then repositioned on the conveyor belt 2 at the entry end of the plant.

From the aforegoing it is apparent that the method of the invention and the plant for implementing it are particularly advantageous in that they enable panels to be continuously clad on a surface and on the edges with a sheet of PVC or other thermoplastic material. in addition to the aforedescribed embodiment, a series of variants can be provided or suggested. For example instead of having the spacers 32 positioned on a conveyor belt 2, they can be formed directly on the belt, possibly using criteria which ensure their usability for panels of different dimensions, to hence dispense with the operations involved in applying each spacer to the loading end of the bed 4 and removing it from the discharge end. Moreover, as the only region of the conveyor belt 2 involved in the suction operation and hence in the passage of air through the belt is that relative to the oven 19 and the cooling chamber 26, the conveyor belt 2 could be formed in different sections, of which only that through the interior of said oven 19 and of said cooling chamber 26 is perforated.

Again, in order to provide the necessary seal in the case of imperfections irregularities or holes present in the continuous sheet 10 external to the zone of contact with the panels 18, which could totally or partially nullify the effect due to the suction system 20 within the oven 19, along the part of the line extending from the exit of the first oven to the exit of the second oven 19, the sheet 10 is covered with an endless membrane 34 extending between end rollers 36 and advancing at the same speed as the conveyor belt 2 and hence as the sheet 10. This variant is shown in Figure 7, which shows the membrane 34 extending transversely for the entire width of the continuous sheet 10 and then retained in correspondence with the longitudinal edges of the pressers 24. The same membrane 34 is also shown in Figure 3 for economy of representation. In another variant relative to the transverse sealing system between the continuous sheet and the conveyor belt 2, the membrane 34 is provided with inflatable transverse pockets, which are positioned between one panel and the next and inflated in synchronism with the advancement of these latter, in order to cause the underlying softened sheet 10 to forcibly adhere to the conveyor belt 2 and/or to the transverse projections 30.

The same result can also be obtained by providing in a position above the membrane 34 transverse pressers (not shown on the drawings) which are made to descend in synchronism with the advancement of the panels 18, to press the membrane and the underlying softened 10 against the conveyor belt 2 and/or against the transverse projections 30.

Claims

C L A I M S

1. A method for continuously cladding panels, in particular of wood-based material, with a sheet of thermoplastic material, characterised by:

- positioning the panels (18), to one side of which a sheet of thermoplastic material has already been applied, on an endless conveyor (2) such that said side faces said endless conveyor and is maintained spaced therefrom at least at the panel edges,

- superposing on the surface of the panels (18) to be clad, the surface having been previously treated with heat-activated adhesive, a continuous sheet (10) of thermoplastic material,

- heating the panels (18) to activate the adhesive and soften the sheet of thermoplastic material (10), and

- applying vacuum to the panels (18) to cause the sheet of thermoplastic material (10) to intimately adhere to the surface and to the edges of the panels.

2. A method as claimed in claim 1 , characterised by applying the heat- activated adhesive to the surface of the panels (18) before positioning the panels on the endless conveyor (2).

3. A method as claimed in claim 1 , characterised by spraying the heat- activated adhesive onto the surface of the panels (18) positioned on the endless conveyor (2), immediately before resting the sheet of thermoplastic material (10) on them.

4. A method as claimed in claim 1 , characterised by placing each panel (18) on at least one spacer (32) present on the endless conveyor (2).

5. A method as claimed in claim 1 , characterised by subjecting the panels to heating and vacuum simultaneously.

6. A method as claimed in claim 1 , characterised in that while the panels (18) are subjected to vacuum the sheet of thermoplastic material (10) is maintained forcibly adhering to the endless conveyor (2) external to the panels.

7. A method as claimed in claim 1 , characterised by subjecting the panels (18) to vacuum by means of a suction effect through the endless conveyor (2).

8. A method as claimed in claim 1 , characterised by subjecting the panels to simultaneous cooling and vacuum after the sheet of thermoplastic material (10) has been applied to them.

9. A method as claimed in claim 1 , characterised by causing the sheet of thermoplastic material (10) to adhere to the panels (18) by pressing it with a membrane (34) with advances at the same speed as that at which the panels are advanced by the endless conveyor (2).

10. A plant for implementing the method claimed in one or more of claims 1 to 9, characterised by comprising on a bed (4):

- for the panels (18) to be clad, an endless conveyor (2) provided with spacers (32) on which said panels rest,

- a feed station for a continuous sheet of thermoplastic material (10),

- an oven for heating the panels (18) which advance along said bed (2), - a zone in which vacuum acts on the heated panels (18) supporting said sheet of thermoplastic material.

11. A plant as claimed in claim 10, characterised in that the endless conveyor (2) comprises, at least in correspondence with the vacuum zone, apertures through which suction is applied to the space between said endless conveyor (2) and said sheet of thermoplastic material (10).

12. A plant as claimed in claim 10, characterised in that with the endless conveyor (2) there are associated presser elements (24) acting in the longitudinal direction on the sheet of thermoplastic material (10), laterally to the panels (18) to be clad.

13. A plant as claimed in claim 10, characterised by comprising a plurality of spacers (32) removably positionable on the endless conveyor (2).

14. A plant as claimed in claim 10, characterised in that the endless conveyor (2) is provided with a plurality of spacers (32) permanently applied to it.

15. A plant as claimed in ciaim 10, characterised in that the bed (4) is provided, downstream of the oven (17), with a further oven (19) and, in a position below the endless conveyor (2), a tank (22) connected to a vacuum pump (20).

16. A plant as claimed in claim 10, characterised in that the endless conveyor (2) is provided with a plurality of transverse projections (30) cooperating with the sheet of thermoplastic material (10) to provide a transverse seal between the two in correspondence with the vacuum zone.

17. A plant as claimed in claim 10, characterised by comprising, at least in correspondence with the vacuum zone, an endless deformable membrane (34) adhering to the sheet of thermoplastic material (10) and moving at the same speed as this latter.

18. A plant as claimed in claim 17, characterised in that the membrane (34) comprises a plurality of transverse pockets inflatable in synchronism with the advancement of the endless conveyor (2) to cause the sheet of thermoplastic material (10) to adhere to said endless conveyor within the interspaces between the panels (18).

19. A plant as claimed in claim 17, characterised by comprising in a position overlying the membrane (34), upstream and downstream of the vacuum zone, transverse pressers operated in synchronism with the advancement of the endless conveyor (2) to cause the sheet of thermoplastic material (10) to adhere to said endless conveyor within the interspaces between the panels (18).

20. A plant as claimed in claim 10, characterised by comprising a cooling station associated with the vacuum zone.

21. A plant as claimed in claim 20, characterised in that the cooling station comprises a chamber (26) overlying the endless conveyor (2) and provided with a fan (29), and a tank (28) underlying the endless conveyor (2) and associated with a vacuum pump.