It is known to fashion the surfaces of fibreboards in such a manner that they no longer appear as flat surfaces but have a specific structure, the structure varying as required. Structured surfaces of this kind are needed particularly in the manufacture of furniture. For example, in the manufacture of kitchen cupboards, but also in carcases, use is made of fibreboards and other panels made of wood where a structured surface in relief is desired.
The present invention is concerned with producing a structure on the surface of a fibreboard which has already been hardened, i.e. which has already been subjected to the usual production processes.
According to one known method of the type described at the beginning hereof, paper coated with melamine resin is placed upon the fibreboard, chipboard or the like after it has been hardened and the board is pressed, as the initial material, with the melamine-coated resin, in a short-cycle press. A short-cycle press is to be understood to be a known type of press using pressures of up to about 27 kp/cm.sup.2 and temperatures of up to about 180.degree. C. A structured pressure-plate is placed upon the layer of paper and this results in the structure of the pressure-plate being moulded into the paper, i.e. into the surface of the fibreboard. If smooth pressure-plates are used, glossy flat surfaces are obtained. In practice, the structure assumes only the surfaces of melamine-coated paper applied to the initial material, and the actual surface of the fibreboard is scarcely, or only slightly moulded. This structure then appears on the surface of the fibreboard. The advantage of this known method is that the surface of the fibreboard is protected, to some extent, by the melamine paper, and the surface of the paper is sealed or closed by the curing of the melamine resin. The known method is comparatively inexpensive and can thus compete with a lacquer-coating. The disadvantage is that the structure thus obtained are not very decorative. The surface of the paper usually remains visible and it is impossible, or very difficult, to obtain a natural wood appealing structure in this way. For this reason, this method of treating fibreboard surfaces is reserved mainly for furniture carcases and is not used for decorative surfaces.
There are also methods which, like the method according to the application, are concerned with applying a structure directly to the surface of a fibreboard. Such fibreboards are initially produced by conventional methods. The boards are then treated in a moire-calender, the rolls of which are structured on one or both sides. The structure is burned into the surface of the fibreboard under the action of pressure and heat. The temperatures used may reach about 1100.degree. C. at the surface of the rolls. The colour of the burned-in structure may be varied by varying the pressure, heat and the time taken for the board to pass through the calender. One advantage is that it is possible, with this method, to obtain a structure in the surface and not only on the surface of a fibreboard. There is also no need to use the melamine-impregnated paper. The disadvantage of this method is that the tinting of the burning-in is not always uniform. Nor is the appearance satisfactory if a natural wood structure is to be imitated. Furthermore, the surface of the board is rough and unprotected after the burning-in and, during subsequent processing, there may be mechanical damage or damage caused by moisture. This cannot be eliminated by grinding because this alters the burned surface to such an extent that the damage becomes even more obvious. Another disadvantage is that this process requires special installations and calenders and, if the results are to be in any way constant, pressure and temperature control must be extremely accurate.
In the case of another known method, especially for the decorative surfaces of furniture, the initial material used is a cured chipboard which is made particularly soft. The surface of this cured chipboard is indented and crushed by the use of pressure and heat, whereby macro-structures, such as grooves, ridges, reliefs and the like may be produced in the surface. Temperatures of up to about 180.degree. C. are used. The depth of the embossed grooves may be as much as 8 mm. Foils and papers may also be melted onto the surface. Surfaces thus treated may also be lacquered subsequently. Fortunately, this known method eliminates the need of a milling operation in order to produce the relief, but the optical effect is quite similar. The disadvantage of this method is that it requires presses having very high operating pressures. Furthermore, it can be used only for particularly soft chipboard.