| 摘要 |
<p>Paper or board is made from a fibrous slurry by a process including the successive steps of adding to the slurry with agitation a soluble salt of a polyvalent metal, adding with agitation the ammonium or alkali salts of certain carboxylic acids, and introducing a polyethylene oxide of high molecular weight to control the size of the flocs of the precipitated salt of the polyvalent metal and the acid. The carboxylic acid is a resinous or fatty acid or a synthetic polymer containing carboxylic acid groups. Acids referred to are: wood rosin, tall oil fatty acids, extracted pinewood pitch, abietic, oleic, stearic and linoleic acids, and mixtures of these acids; shellac, alkali-soluble partial ester of a styrene-carboxylic acid copolymer or an alkalisoluble copolymer of vinyl acetate and crotonic acid. The polyethylene oxide is used at a concentration of 0.002 to 0.1% based on the total content of fibre and precipitate. The fibres may be of wood pulp, glass, asbestos or synthetic organic materials. The salts of polyvalent metals may be chlorides, nitrates, acetates or sulphates of calcium, barium, magnesium, strontium, aluminium, zinc, beryllium, cadmium, cobalt (bivalent), copper (bivalent), iron (bivalent), manganese (bivalent) mercury (bivalent), nickel, (bivalent) and tin (quadrivalent). There may also be added other substances such as melamine-formaldehyde resin, or polyethyleneimine. The pH may be controlled by the use of sulphuric acid or aluminium sulphate. The product may be formed or moulded under heat and pressure. Compound boards may be made in which the centre layers are of the invention and the surface layers are free of the precipitated salt, by applying appropriate pulp-stocks to a multi-cylinder machine. The specification also describes the purposes of comparison paper or board from which one or more of the ingredients has been omitted, or made from slurries to which they have been added in other orders.</p> |
