METHOD FOR FORMING SURFACE-ENGRAVED PANELS CLAD WITH A SHEET OF THERMODEFORMABLE MATERIAL AND APPARATUS FOR IMPLEMENTING THE METHOD

Abstract: The method for forming surface-engraved panels clad with a sheet of thermodeformable material, particularly PVC, comprises a preliminary stage of engraving the surface of a chipboard substrate to obtain cavities therein in accordance with a predetermined design and a subsequent stage in which an adhesive is spread over said surface followed by a sheet of thermodeformable material which covers said cavities, and is characterised in that the panel (6) prepared in this manner is passed through at least one pair of rollers (7,8), of which the roller (8) in contact with said surface is formed of elastically yieldable material which causes the sheet of thermodeformable material, previously heated until soft, to penetrate into said cavities.

Description: This invention relates to a method for forming surface-­ engraved panels clad with a sheet of thermodeformable material, and an apparatus for implementing the method. Methods are known for forming surface-engraved panels clad with a deformable material sheet. One of these methods comprises a first stage in which a surface of the panel, generally in the form of a chipboard substrate, is engraved in order to form personalised effects and designs on it accordance with the client's requirements. Over said surface a layer of glue is then spread, on which a sheet of PVC or other thermodeformable material is then applied. The assembly is then subjected to the action of a press, the punch of which has a shape complementary to that of the engraved panel. The press acts under hot conditions on the PVC sheet to thus cause it do adhere to the cavities in the chipboard substrate. However, this known method has certain drawbacks, and in particular: - the need to correctly position the panel relative to the punch, - the need for different punches corresponding to the different design to be formed, - a considerable time wastage due both to the need to replace the punch every time the decorative panel motif changes, and to the laboriousness of this replacement operation. In this respect, in order to replace the punch it first has to be cooled, and after being replaced it then has to be raised to the working temperature in order to be able to again use it. To obviate these drawbacks, another method has already been proposed in which the stages involving the engraving of the chipboard substrate and the application of the thermodeformable material remain unchanged, but in which the panel is subjected to the action of a hot press, the fixed plate of which is in the form of a chamber filled with a fluid and having that surface in contact with the panel formed from a deformable elastic membrane. By virtue of the pressure and temperature increase of the fluid contained in the chamber, the membrane deforms by expanding, to cause the thermodeformable material to penetrate into the cavities previously formed in the chipboard substrate. This known method, which enables the same punch to be used for all types of design, has however other drawbacks, and in particular: - if the membrane is of a thin type, it is impossible to attain high pressure and thus impossible to obtain sufficient deformation in the case of cavities of a certain depth; in any event, the membrane undergoes stretching and is therefore subject to frequent rupture, - if the membrane is of greater thickness it adheres poorly to the cavity walls, and consequently results in an unfaithful reproduction of the design, - its application is limited due to the maximum attainable pressure and temperature. In this respect, if the chamber fluid is water, it is obviously impossible to operate at a temperature exceeding 100xC. If however the fluid is a diathermic oil, not only does the membrane disintegrate at the high temperature but the oil reacts chemically with it. The object of the invention is to obviate all these drawbacks and to produce surface-engraved panels clad with thermodeformable material, in a rapid, reliable and versatile manner. This object is attained according to the invention by a method for forming surface-engraved panels clad with a sheet of thermodeformable material particularly PVC comprising a preliminary stage of engraving the surface of a chipboard substrate to obtain cavities therein in accordance with a predetermined design and a subsequent stage in which an adhesive is spread over said surface followed by a sheet of thermodeformable material which cover said cavities, characterised in that the panel prepared in this manner is passed through at least one pair of rollers, of which the roller in contact with said surface is formed of elastically yieldable material which causes the sheet of thermodeformable material, previously heated until soft, to penetrate into said cavities. The present invention is hereinafter further clarified in a preferred embodiment with reference to the accompanying drawings in which: Figure 1 is a partly sectional diagrammatic side view of a machine for implementing the method according to the invention; Figure 2 is a front view thereof on the inlet side in the direction II-II of Figure 1; Figure 3 is an enlarged detailed perspective view of two adjacent pairs of rollers and the corresponding heater elements; Figure 4 is a diagrammatic plan view of a pair of adjacent presser rollers; Figure 5 is a plan view from above of a modified embodiment of a pair of adjacent rollers; and Figure 6 is a plan view from above of a further modified embodiment of a pair of adjacent presser rollers. As can be seen from the figures, the machine for implementing the method according to the invention consists essentially of a continuos press 1 comprising a fixed lower bed 2 and a mobile upper structure 3. At both ends of the press 1 there are provided conventional roller tables 4 and 5 for feeding and discharging the panels 6 respectively. A plurality of synchronously operates steel rollers 7 are mounted on the bed 2. Six rollers 7 are shown in the illustrated machine. The mobile upper structure 3 consists of a support frame for a like number of rollers 8 disposed parallel to the rollers 7 and facing these latter. The height of the frame 3 above the bed 2 can be adjusted by pneumatic cylinder-piston units 10. The rollers 8 are constructed of rubber of differing hardness which increase from the inlet end roller to the outlet and roller of the press. In the illustrated example, the hardness of the inlet roller 8 is about 18x Shore, and the hardness of the outlet roller is about 40x Shore, although these values can vary according to the materials to be treated and the work to be carried out. Above the frame 3 and facing each roller 8 there are provided pairs of radiant heater elements 9 disposed transversely to the press and extending over the entire length of the corresponding rollers 8. Between each pair of rollers 7, 8 and the adjacent pair there are also provided other radiant heater elements 11 secured to the frame 3 and disposed parallel to the heater elements 9. Finally, other radiant heater elements 12 are provided above the feed roller table 4. All the heater elements 9, 11 and 12 are adjustable in height and are provided with known potentiometric devices which enable their intensity to be varied. The machine according to the invention operates in the following manner: the height of the upper mobile structure 3 above the bed 2 is adjusted so that the minimum distance between the rollers 7, 8 of each pair is slightly less than the minimum thickness of the panels 6 to be treated, as measured at their cavities or grooves. The height and/or intensity of the heater elements 9, 11 and 12 are then adjusted in such a manner as to obtain increasing temperature both along the roller table 4 and along the press 1. More specifically: - the intensity of the heater elements 12 is adjusted in such a manner that the temperature along the roller table 4 increases progressively from ambient to about 30-40xC at the pair of inlet rollers of the press 1; - the intensity of the heater elements 9 and 11 is adjusted in such a manner that the temperature at the surface of the rollers 8 and within the press 1 increases progressively from a value of 30-40°C at the inlet roller to a value of about 120°C at the outlet roller. The temperature conditions are obviously related to the nature of the cladding material, although in all cases the outlet temperature of the roller table 4 must substantially correspond to the inlet temperature of the press 1 to prevent the adhesive and cladding undergoing undesirable thermal shock. When the machine has been arranged in this manner, the panels 6 to be treated consisting of a chipboard support, to the engraved surface of which there has previously been bonded a sheet of PVC or other thermodeformable material, are disposed on the roller table 4 and fed to the press 1. During this stage the preheating of that panel surface facing the heater elements 12 results in partial softening of said cladding layer and the softening of the adhesive which binds the cladding layer to the chipboard substrate. As the panel 6 advance along the press 1, the combined effect of the temperature, which increases proressively during passage between the adjacent pairs of rollers 7, 8 and softens the PVC sheet together with the pressure exerted by the rollers 8, which press with their rubber surface against said softened cladding until they cause it to penetrate into the cavities in the underlying chipboard substrate, is such as to perfectly and faithfully clad the panel surface. This operation is also effected gradually because of the progressively increasing hardness of the rubber of the rollers 8 which enables the pressure on the cladding material to be increased while maintaining the pressure with which the upper structure 3 is pressed by the cylinder-piston units 10 against the bed constant. From the aforegoing it is appartent that the method for forming surface-engraved panels according to the invention and the machine for implementing the method enable numerous advantages to be obtained and in particular: - they obviate the need for presses with punches, together with all their related drawbacks, - they enable panels engraved with any design to be treated, - because of the hardness and elasticity of the rubber layer of the rollers 8, they enable this layer to completely penetrate into the cavities formed in the chipboard substrate, with consequent faithful design reproduction, - they allow continuous working. In a further embodiment the machine according to the invention has its upper rollers of rubber, and these instead of being constructed in one piece (see the rollers 8 in figure 4) are constructed as a plurality of segments, which allow greater penetration in the case of panels with very deep cavities. These segments can be arranged either side-by-­ side with each other (see the rollers 8′ in figure 5) or spaced apart, in which case they are offset from the segments of the adjacent roller (see the rollers 8″ in figure 6). As it is often necessary to limit the heating effect of the heater elements 11 to only the width of the chipboard substrate without heating that cladding portion which projects beyond this, according to the invention screens 13 of adjustable distance apart can be provided in corrspondence with the heater elements 11 in order to limit the heating of the panels 6 by said heater elements 11 to the effective width of the panel 6.

Claims: 1. A method for forming surface-engraved panels clad with a sheet of thermodeformable material, particularly PVC, comprising a preliminary stage of engraving the surface of a chipboard substrate to obtain cavities therein in accordance with a predetermined design and a subsequent stage in which an adhesive is spread over said surface followed by a sheet of thermodeformable material which covers said cavities, characterised in that the panel (6) prepared in this manner is passed through at least one pair of rollers (7,8), of which the roller (8) in contact with said surface is formed of elastically yieldable material which causes the sheet of thermodeformable material, previously heated until soft, to penetrate into said cavities. 2. A method as claim in claim 1, characterised by passing the panel (6) to be treated through a plurality of pairs of rollers (7,8), and heating it between one passage and the next. 3. A method as claimed in claim 1 and/or 2, characterised by passing the panel (6) between pairs of rollers (7,8) of which the roller (8) formed of elastically yieldable material is heated. 4. A method as claimed in claim 1, characterised by preheating the panel (6) before passing it through the first pair of rollers (7,8). 5. A method as claimed in claim 4, characterised in that the panel (6) to be treated is preheated at progressively increasing temperature. 6. A method as claimed in claim 2, characterised by subjecting the panel (6) to heating and/or to progressively increasing pressure during its passage through the pairs of rollers (7,8). 7. A method as claimed in claims 1 and 4, characterised in that the surface of the panel (6) to be treated is preheated and/or heated by heater elements (11,12) disposed along the path of the advancing panel. 8. A method as claimed in claim 7, characterised in that the heating effect of the panel (6) to be treated is limited to only the engraved surface, the lateral edges being excluded by screens (13) interposed between said heater elements (11) and said panel (6). 9. A machine for implementing the method claimed in claims 1 to 8 characterised by comprising essentially: - at least one pair of rollers (7,8) between wich the panel (6) to be treated is passed, the roller (8) of said pair in contact with the panel surface to be treated being formed of elastically yieldable material, and - means for heating the panel surface to be treated, before its passage between the pair of rollers. 10. A machine as claimed in claim 9, characterised by comprising a plurality of pairs of rollers (7,8) and a plurality of heater elements (11) interposed between each of said pairs of rollers. 11. A machine as claimed in claim 9, characterised by comprising heater elements (9) for that roller (8) of each pair which is formed of elastically yieldable material. 12. A machine as claimed in claim 11, characterised in that those rollers (8) of each pair which are formed of elastically yieldable material are provided with heater elements (8) which raise the temperature of each roller to a value which increases progressively from the inlet to the outlet of the machine. 13. A machine as claimed in claim 10, characterised by comprising a frame along which the panels (6) to be treated are continuously fed, said frame comprising a fixed part (2) on which those rollers (7) acting on the panel surface not comprising the engraved design are mounted, and a part (3) which is mobile relative to said fixed part (2) and on which those rollers (8) formed of elastically yieldable material are mounted. 14. A machine as claimed in claim 10, characterised in that those rollers (8) acting on the engraved surface of the panels (6) are formed of elastically material having a hardness which increases from the inlet to the outlet of the machine. 15. A machine as claimed in claim 9, characterised in that the roller (8′) of elastically yieldable material is formed of side-by-side segments. 16. A machine as claimed in claim 10, characterised in that the rollers (8″) of elastically yieldable material are formed of spaced-apart segments which are offset from the segments of the adjacent roller (8″). 17. A machine as claimed in claim 9, characterised in that the heater elements (9) for the rollers (8) and/or the heater elements (11) interposed between the pairs of rollers (7,8) consist of lamps disposed external to each pair of rollers. 18. A machine as claimed in claim 10, characterised by comprising heat shields (13) interposed between said heater elements (11) and the panel (6). 19. A machine as claimed in claim 12, characterised in that the rollers (8) are formed of rubber having a hardness which increases progressively from 10° Shore to 45° Shore, and preferably from 18° Shore to 40° Shore.

Inventors: BERGAMO, LUCIANO
Applicants: 3B S.P.A.
Application year: 1987
Main classification: B29C63
IPC codes: B29K27, B29C33, B29C43, B29C65, B29C63, B29L9