GB1076516A - Coated paper and a method for its manufacture - Google Patents

Abstract

A coated paper has at least one side covered by at least one thin film with a microporous structure comprising a synthetic resin and having minute internal spaces in the coating film formed mainly by gas bubbles of substantially uniform microscopic size, anchored by adsorption to solid particles, likewise of microscopic size, consisting of at least one metal compound, such as an oxide or hydrate of a metal, which can be precipitated from a liquid phase with an evolution of gas in situ, the solid particles being distributed substantially uniformly throughout the entire volume of the film of synthetic resin. The metal compound may be selected from metal compounds which can be precipitated from a liquid phase by hydrolysis accompanied by the evolution of gas in situ, especially from carbides, nitrides or hydrides of metals, or organo-metallic compounds. The coating film may be formed by a plastic or plasticized resin and contains a small proportion, e.g. less than 6%, by weight of the metal compound. The coating film may be formed from a resin having little or no plasticity and contains a high proportion e.g. 20 to 40%, by weight of the metal compound. One side of the backing paper may be covered by a strongly adhering plastic coating containing a small proportion of metal compound and/or an adhesive substance, and the other side is covered by a poorly adhering and friable coating film, containing a higher proportion of metal compound. A poorly cohesive film of colouring matter e.g. a carbon black suspension, may be interposed between the backing paper and the friable coating film. The coating film may have a weight of the order of 5 g/sq.m. and a thickness of about 12 to 15 microns. The coated paper may be produced by depositing on the backing paper a coating which comprises a volatile liquid phase, a first dissolved or highly dispersed phase consisting essentially of a synthetic resin, and a second dissolved or highly dispersed phase consisting essentially of at least one metal compound, e.g. carbide, nitride or hydride of a metal or an organometallic compound, which can be precipitated e.g. by hydrolysis, in the liquid phase with the evolution of a gas in situ, as another compound of the metal such as the oxide or hydrate of the metal, then precipitating the metal compound contained in the coating deposited on the backing paper, and finally drying the coated paper. The hydrolysis of the metal compound may be produced (i) by drying the coated paper in air charged with moisture e.g. by a current of air having a temperature of approx 50 DEG C and a relative humidity of about 90%, or (ii) by the water formed in situ by a chemical reaction between two substances e.g. a hydroperoxide and a reducing agent, added to the coating, the reaction being initiated prior to the complete drying of the coated paper by the application of heat energy, direct or resulting from the conversion of energy of another kind. The liquid phase of the coating deposited on the backing paper may consist preferably of at least one volatile organic liquid, free from water and chemically inert to the paper and to the other constituents of the coating.