GB696496A - Paper coating compositions - Google Patents

Abstract

An aqueous dispersion of barium sulphate for the preparation of photographic paper coating compositions contains as a peptizing agent between 1/300 and 1/100 part per part of barium sulphate of a product obtained by treating a synthetic resin containing carboxylic acid anhydride groups with ammonia or a primary or secondary aliphatic amine. The resin may be a copolymer of maleic, acrylic, methacrylic or aconitic anhydride with one or more CH2=C< compounds, e.g. vinyl acetate, vinyl chloride, methyl vinyl ether, styrene, acrylates and methacrylates. The reaction with ammonia or amine may be effected by sifting the comminuted resin into an aqueous solution thereof and allowing to stand when both the ammonium or amine salt and the amide are formed. Acyl groups which may be present are hydrolysed off. Suitable amines are those having alkyl groups of not more than 6 carbon atoms, such as monoethyl- and diethyl-amine, methylamine, propylamine, isopropylamine, n-butylamine, amylamine and di-isoamylamine. The treated resin may either be added to an aqueous dispersion of the barium sulphate or the barium sulphate may be dispersed initially in an aqueous solution of the peptizing resin. Other materials, such as gelatine, polyvinyl alcohol or rubber latex (natural or synthetic) may be added with the peptizer. The dispersions are preferably mixed with a binder before being used, suitable binders being gelatine, polyvinyl alcohol, rubber latex, water-soluble cellulose esters or a further amount of the synthetic resin used as the peptizer. Specifications 668,525, 669,187, 692,105 and U.S.A. Specification 2,047,398 and German Specification 540,101 are referred to.