GB1040629A - Fibreboard and method of making same - Google Patents

Abstract

Fibreboard is made by compressing a mixture of fibres and a " solution of the essentially unreacted ingredients of a thermosetting resin " between heated platens while applying a high-frequency electric field throughout the mixture to at least partially cure the resin-forming materials. The " solution of the essentially-unreacted ingredients of a thermosetting resin " may be a true solution, a suspension, a colloidal solution or any combination thereof. It may contain low-molecular-weight propolymers, an acidic catalyst for the resin-forming reaction (e.g. NH4Cl) and a suitable buffer (e.g. ammonia). It must have a viscosity of less than 100cP, at 68 DEG F. and a content of resin-forming materials equivalent to final solid resin amounting to 60% by weight of the original solution. In the examples, the resin-forming materials are urea and formaldehyde or urea, melamine and formaldehyde, and the solvent is water. The mixture may be formed into a mat which is precompressed before insertion between the platens. Two such precompressed mats may be superposed and pressed together to form a thicker board. The platens may be heated by steam or hot oil to a temperature high enough to prevent the condensation on them of steam driven out of the board during the curing. The fibres may be steamed or mechanically and/or chemically reduced wood, bagasse, straw, bamboo, sisal, cotton or asbestos. Sizes, fungicides, insecticides and drying oils may be included. The Specification also describes by way of comparison boards using as binders a partially reacted ureaformaldehyde solution having a viscosity of 200cP and a partially reacted phenol-formaldehyde solution having a viscosity of 100cP and a resin solids contents of 40%.ALSO:Fibreboard is made by compressing a mixture of fibres and a "solution of the essentially unreacted ingredients of a thermosetting resin" between heated platens while applying a high-frequency electric field throughout the mixture to at least partially cure the resin-forming materials. The "solution of the essentially-unreacted ingredients of a thermosetting resin" may be a true solution, a suspension, a colloidal solution or any combination thereof. It may contain low-molecular-weight propolymers, an acidic catalyst for the resin-forming reaction (e.g. NH4CC) and a suitable buffer (e.g. ammonia). It must have a viscosity of less than 100cP, at 68 DEG F and a content of resin-forming materials equivalent to final solid resin amounting to 60% by weight of the original solution. In the examples, the resin-forming materials are urea and formaldehyde or urea, melamine and formaldehyde, and the solvent is water. The mixture may be formed into a mat which is precompressed before insertion between the platens. Two such precompressed mats may be superposed and pressed together to form a thicker board. The platens may be heated by steam or hot oil to a temperature high enough to prevent the condensation on them of steam driven out of the board during the curing. The fibres may be steamed or mechanically and/or chemically reduced wood, bagasse, straw, bamboo, sisal, cotton or asbestos. Sizes, fungicides, insecticides and drying oils may be included. The Specification also describes by way of comparison boards using as binders a partially reacted urea-formaldehyde solution having a viscosity of 200cP and a partially reacted phenol-formaldehyde solution having a viscosity of 100 cP and a resin solids content of 40%.