GB966225A - Improvements in or relating to paper-coating compositions - Google Patents

Abstract

In preparing a composition for coating paper, a salt-peptised protein, i.e. a protein peptised by a salt dissolved in an aqueous medium at a pH value not exceeding 7, e.g. containing 20 to 35%, by weight, of protein and 4 to 10% of the salt, is mixed with an aqueous slurry of a filler to reduce the concentration of the salt and thus increase the viscosity of the slurry and make it stiff, and the resulting mixture is agitated to disperse the protein and form a thin, homogeneous, liquid coating composition, in which free protein functions as a binder. Proteins specified are casein and soyabean protein. Fillers specified are clay, calcium carbonate, blanc fixe, talc and titanium dioxide. Salts specified are alkali metal and ammonium salts of strong monobasic acids, particularly sodium or ammonium nitrate. A small amount of a water-soluble, tallow-based soap and, preferably, a viscosity reducing agent, such as dicyandiamide, may be present during peptisation, which may be effected at temperatures above 60 DEG C., e.g. between 80 and 90 DEG C., followed by cooling to below 60 DEG C. to augment the increase in viscosity. The composition may also contain latex.ALSO:Paper is coated with an aqueous composition containing a protein such as casein or soyabean protein, an alkali metal or ammonium salt of a strong monobasic acid such as sodium or ammonium nitrate, for peptizing the protein (see Division C3) and a filler such as clay, calcium carbonate, blanc fixe, talc or titanium dioxide. The composition may also contain a water-soluble tallow-based soap, dicyandiamide and latex. The coating may be smoothed by an air-knife and the coated paper may be calendered.