A METHOD FOR THE MANUFACTURE OF FIBREBOARDS

Abstract: The invention relates to a method for the manufacture of fibreboards from a paper material ground to a fleece, coated with a thermoplastic and where the thermoplastic constitutes the bonding agent in the fibreboard.

Description: The present invention relates to a method for the manufacture of fibreboards by distributing between two plates a paper material ground to a fleece and subsequently subjecting the same to pressure and heat. Different types of fibre or particle boards have a wide field of application within the building industry and the manufacture of furniture. These boards may be of different quality and nature depending on the field of application. More strongly compressed boards are used, for example, as a substitute for the more expensive timber in furniture framework and fittings. More loosely compressed fibreboards may be used as partly insulating layers in walls, floors and roofs. The method of manufacturing fibreboards or particles boards is generally known and for this purpose wood particles of different qualities and coarsenesses are used, and in this way boards of different properties are obtained. Common to all the boards which are known is that a bonding agent of some kind has to be blended into the fleece material. As this bonding agent usually is in the form of a powder or grain the mixing can bring about problems as the fleece material quite often has a different grain size. Moreover, when coarser particles are used these should not be subjected to the mechanical effects which a mixing process involves as the particles are brittle and break readily. Conventional manufacture of particle boards also means that a wood has to be used as a raw material which on the one hand is expensive and, on the other hand, can be used for different purposes. Particle boards in accordance with known manufacturing processes, once they are made into boards, cannot be converted, since the bonding agent cannot be reheated and act again as a bonding agent. A Method according to the first part of claim 1 is described in DE-A-2 258 169 and in DE-B-1 151 374. This known method includes the steps of grinding sheets of paper and plastic material and to press and heat the fibres and particles of the material ground. It is an object of the present invention to obtain a smooth surface of the fibreboard in a simple and unexpensive way. The invention is claimed in claim 1 and further embodiments are claimed in subclaims. The paper material ground to a fleece is spread out between layers of paper material coated by thermoplastic material which layers are disposed on a pressure plate each. Then the 3 layers are subjected to pressure and heat. The thermoplastic will be substantially uniformly distributed in the fleece mass after melting and pressing. A paper material of the above mentioned type is found to be obtainable at a low price in the packaging industry which manufactures non-returnable packages for liquids from paper coated with thermoplastics. In the said industry a certain wastage always exists on changing of the material rolls, edge shearing, faulty printing or the like. This wast material is of little use in other fields and commands therefore a considerably lower price than does wood as a raw material for the conventional manufacture of particle board. When the spread out fibre mass is heated to a temperature above the melting point of the thermoplastic, that is to say at least 105°C, the plastic which adheres firmly to the paper particles melts. In practice a temperature of at least 170°C is required as transfer losses occur. If at same time the spread out fibre mass is subjected to a compressive stress, a fibreboard is obtained where the paper fleece is held together by the molten thermoplastic. The pressure which is to be applied is adapted to the type of board which one wishes to manufacture. To obtain a strongly compressed fibreboard which is substantially homogeneous and where virtually all the air is pressed out, a pressure of approx. 0,7 MPa (700 kN/m²) should be appliesd for approx. 1 min per mm finished board. Such a fibreboard with a substantially smooth surface may be used to great advantage as a substitute for timber or particle boards in furniture making and in the manufacture of fittings. Through the addition of colour to the fibre mass it is also possible to obtain fibreboards for a more decorative use. If profiled press plates are used, boards of the homogeneous type described above may also be manufactured, which may be given a desired three-dimensional shape already during manufacture. It is also possible to reheat these fibreboards with thermoplastic as a bonding agent manufactured in accordance with the invention and afterwards under pressure and in moulds impart to them a desired three-dimensional shape. In the manufacture of porous fibreboards a homogeneous paper layer, coated at least on one side with thermoplastic, is introduced between each pressure plate and the fibre mass. This thermoplastic surface is located nearest the fibre mass. During heat treatment this surface layer also melts and bonds together the paper fleace with the outer homogenous paper layer. To obtain a more porous board a pressure treatment at an appreciably lower pressure is required than for a corresponding homogeneous board. A pressure of approx. 0,02 MPa (20 kN/m²) is required. The temperature is to be approx. 200° C. A higher temperature is required due to the fact that the air caught between the fibres causes a greater loss of temperature, when the fibre material is pressed. The time duration of pressure application is dependent of the thickness of the fibre material to be pressed and the grade of porousity wanted. The fibre mass then still contains a quantity of air, so that this type of board can have wide uses in the building industry as a partly insulating building material, especially in countries with a shortage of timber.

Claims: Method for the manufacture of fibreboards by distributing a paper material ground to a fleece between two plates, and subsequently subjecting the same to pressure and heat, wherein the paper material is coated at least on one side with a thermoplastic which on treatment with heat and pressure is made to melt and in that way bonds together the paper fleece, characterized in that between each press plate and the fibre fleece a layer of paper material, coated at least one one side with a thermoplastic material, is introduced. Method as claimed in claim 1, characterized in that the thermoplastic surface of said layer of paper material is located nearest the paper fleece. Method as claimed in claim 1 or 2, characterized in that a homogeneous layer of paper material is used and the heat and pressure treatment is adapted so that the paper fleece is baked together to a substantially homogeneous board. Method as claimed in claim 3, characterized in that the heat treatment takes place at a temperature of at least 170°C and that the pressure treatment takes place at a pressure of about 0,7 MPa (700 kN/m²). Method as claimed in one of the preceding claims, characterized in that with the help of profiled press plates a desired three-dimensional shape is imparted to the fibreboard. Method as claimed in claim 5, characterized in that said three-dimensional shape is imparted to the finished fibreboard on renewed heating and pressure treatment. Method as claimed in one of the preceding claims, characterized in that the heat and pressure treatment is interrupted before the fibreboard becomes homogeneous in order to obtain a porous material with air enclosed between paper fleece fibres particles.

Inventors: NILSSON,INGVAR
Applicants: TETRA ALFA HOLDINGS S.A.
Application year: 1989
Main classification: B27N3
IPC codes: E04C2, B27N3, B27N5