GB608252A - Improvements in or relating to a process for the manufacturing of compound compressed plates made of layers of pieces of wood and binding materials and compound compressed plates made according to the said process - Google Patents

Abstract

608,252. Plywood. FAHRNI, F. Dec. 27, 1945, No. 34950. Drawings to Specification. [Class 145 (ii)] Plywood sheets are made by arranging a layer of small wood chips coated with a binder between two layers of shavings also coated with a binder, and compressing the whole under heat to consolidate it. The chips are preferably from 5 to 50 mm. in length, 3 to 10 mm. in width and 1 to 5 mm. in thickness, and the shavings from .5 to 5 sq. cm. in area. Water may be added to the materials of the layers, more water being added to the shavings than to the chips, and a greater proportion of binder may be added to the shavings than to the chips. The shavings may also be coloured. In preparing the sheets, a frame may be reciprocated beneath a hopper to receive a number of thin layers of the binder coated shavings, and then reciprocated beneath a shoot down which the chips fall. The frame is again reciprocated beneath a hopper to receive the final layers of shavings. The layers are then subjected to pressure of from 5 to 25 kgs. per sq. cm. at a temperature of 120‹ to 150<SP>0</SP> C. Alternatively, the layers may be cold pressed in the frame, and then removed from the frame and compressed under heat. In one example, the chips are dried to a water content of 5 per cent by weight, water-proofed by treatment with 2.5 per cent of paraffin and then mixed with 3.5 per cent of a powdered urea-formaldehyde resin, and with a liquid hardening agent such as nickle nitrate solution. The shavings of white soft wood are coated with 14 per cent of a binder and sprinkled with water to give a water content of 18 per cent. In a second example, 800 parts by weight of chips dried to 4 per cent humidity are mixed with 32 parts of a binder as in the first example. The shavings. are dried to 10 per cent humidity and 150 parts by weight are mixed with 50 parts of finer hardwood shavings and the mixture treated with 20 parts of a urea or melamine condensation product and 20 parts of water; 10 parts of a powdered hard wax are then added. The plywood prepared as in this example is suitable for flooring and quartz powder or plaster may be added to at least one outer layer to give it a non-slip property.