| 主权项 |
1. A continuous method for producing a lightweight sandwich panel having a reference thickness, comprising:
a lower cover layer, and an upper cover layer, both of which consist of densely packed, permanently bonded wood chips, and have a smooth outer surface respectively, and a rough, steam-permeable inner surface respectively, and an intermediate layer comprising a synthetic resin foam which is disposed between the lower and upper cover layers and bonded permanently thereto, the method comprising at least the following steps: 1) providing a layered ply having at least one scattered lower cover ply and an upper cover ply scattered above it, both made from glued wood chips, 2) compressing said layered ply between heated pressing surfaces with a pressure of up to about 30 bar and at a temperature of the pressing surfaces in the range from 130 to 250° C. to form a chipboard, 3) moving the pressing surfaces apart, and thereby releasing the pressure on the chipboard panel, thus causing the panel to split in the middle due to steam pressure built up in its core zone, and to divide into two equally wide cover layers, each having a smooth exterior and a rough interior surface, 4) guiding the cover layers apart, so that a polyurethane foam can be introduced therebetween, 5) spraying or otherwise inserting a foamable, curable hard polyurethane system containing at least the following components:
isocyanate and/or polyisocyanate(s),at least one polyol, andone or more volatile propellant(s) and/or water, wherein the water, if present, reacts with another component to form carbon dioxide, on the inner surface(s) of the lower cover layer or of both cover layers, 6) foaming and compacting the polyurethane system to form a viscous to plastically deformable, but still compressible, polyurethane foam layer, 7) guiding the upper and/or lower cover layer back such that their distance is (i) equal to the reference thickness if both cover layers of the lightweight sandwich panel have a smooth outer surface, or (ii) about 0.1 to 0.3 mm larger than the reference thickness if one or both cover layers of the lightweight sandwich panel has/have a matted outer surface due to fine sanding, 8) stabilising the lightweight sandwich panel calibrated according to 7) by passing it between pressing surfaces operating parallel to each other and at the distance defined in 7), until the polyurethane system has reacted fully to yield hard polyurethane foam, 9) cutting to length and trimming the edges of the lightweight sandwich panel in the form of a continuous strip to obtain panels with standard commercial dimensions, and 10) optionally matting the outer surface(s) of one or both cover layers by fine sanding to the reference thickness, wherein a) an intermediate layer is not scattered between the cover plies in step 1), b) the temperature of the pressing surfaces and the duration of the pressing process are selected such that a high steam pressure builds up in the region of inner surfaces of cover layers which pressure splits the woodchip panel produced in step 2) apart centrally through the release of pressure caused by divergent movement of the pressing surfaces in step 3) and divides said panel into two equally thick cover layers of densely packed, permanently bonded wood chips having smooth outer surfaces and rough inner surfaces, c) the cover layers are guided apart on leaving the press by means of rollers and/or conveyor belts so that the distance between their inner surfaces becomes large enough to allow a spraying or insertion apparatus for spraying or otherwise inserting the polyurethane system between the cover layers according to step 5, and d) the heat that was introduced into the cover layers during compression thereof is used to accelerate the reaction process of the polyurethane system. |
