GB633746A - Improvements in or relating to paper base planographic printing plates - Google Patents

Abstract

633,746. Printing-surfaces. WARREN CO., S. D. Aug. 14, 1947, Nos. 22614 and 22615. Convention dates, Aug. 19, 1946, and July 14, 1947. [Class 100 (ii)] Planographic printing-surfaces containing hydrophilic colloids are subjected to a rubbing, buffing, or brushing action to improve their printing properties. Itis stated that the rubbing action prolongs the life of the surface by increasing its resistance to penetration by ink or the wetting liquid, the action probably being due to reducing the porosity of the surface. The rubbing &c. action may be effected by hand or machine, and the rubbing &c. surface may be of cloth, felt, plush, bristles, horse or badger hair, nylon, rayon, tampico fibre, or fine wire. A smooth polished hard surface may be used. If the printing-surface has a base coat and a final or wash coat, either or both surfaces may be treated. A preferred application comprises a flexible support such as a base coating of a hydrophilic colloid such as casein and a pigment or filler such as clay rendered insoluble by formaldehyde, or other hardening agent, and a light wash coat of a hydrophilic colloid free of pigment. In one specific example of printing- surface, a web weighing 36 lbs. per 1000 square feet was prepared from fibres of coniferous and deciduous trees, rosin size, melamine formaldehyde condensate, and alum. The web was surface-sized with a solution of ammoniacal casein containing formaldehyde. A coating of a mixture containing 100 parts clay, 20 parts casein, and 1.5 parts dimethylplurea was applied and the web calendered..A wash-coat was applied containing 0.7 lbs. per 1000 square feet of a dilute solution (3 per cent) of gelatine in water containing ammonium di-chromate. The wash-coat may contain alginic acid dissolved in alkali and ammonium chromate. As a further example a wet-strength paper was coated with a mixture containing by weight 15 parts of casein, 10 parts gum arabic, 100 parts of clay, 20 parts of 40 per cent formaldehyde solution. The dried coating was swabbed with a 15 per cent solution of zinc acetate, and was rubbed after final drying. The invention may be applied to printing-surfaces as described in Specification 633,747, which are treated with di-valent metal salts, and the rubbing action serves to remove crystallized salt.