Patent GB-633747-A (GB)
Title: Improvements in or relating to paper base planographic printing plates
IPC: B41N3/03
Filed: 1947-08-25
Abstract: 633,747. Printing-surfaces. WARREN CO., S..D. Aug. 25, 1947, No. 23431. Convention date, May 9. [Class 100 (ii)] A planographic printing-surface comprising a paper base sheet having thereon a hydrophilic image-receptive surface is formed with a coating containing a water-soluble water-stable salt of a bivalent metal, which renders the printing- surface impenetrable to both grease and water while permitting the surface to take both grease and water. The paper base is made from beaten soda pulp and sulphate or bleached kraft, rosinsize, melamine formaldehyde resin, and alum, and is preferably surface-sized with ammoniacal casein and formaldehyde. The melamine formaldehyde may be replaced by urea formaldehyde or viscose. The paper is coated with a base coat composed of finely-divided pigment clay, 100 parts by weight, a hydrophilic adhesive base, e.g. casein in ammonia solution 17.5 parts, and dimethylolurea 1.75 parts. The proportions can be varied and the casein replaced by glue, gelatine, soya bean proteid, zein, gum arabic, insolubilized starch, or polyvinyl alcohol. The clay may be replaced by barium sulphate, calcined clay, talc, satinwhite, or titanium di-oxide. The material is now coated on one side with a hydrophilic colloid coating such as sodium alginate 1 part by weight, water 95 parts, and butanol 4 parts. In place of sodium alginate may be used gums such as arabic, mesquite, karaya, locust bean, guar, and ammonium alginate ; or proteins such as casein, soya bean protein, zein, glue, gelatin, albumin. Other substitutes are carboxy methyl cellulose, sodium polyacrylate, a carboxy derivative of polystyrene, starch, dextrine, and pectines and their derivatives such as sodium pectate. Compatible mixtures of-colloids may be used. The coated surface is then treated a. room temperatures with a solution of a salt such as an acetate of a bi-valent metal, to which is added butanol, or ethanol, propanol, or methanol. Example: zinc acetate 25 parts by weight, water 72 parts, butanol 3 parts. The treatment with the salt solution in some cases may precede the application of the hydrophilic colloid, or the two treatments may be combined by a single application of a mixture of the two solutions. In place of zinc acetate, salts of other acids such as chlorides, sulphates, nitrates, formates, may be used, and the choice of bi-valent metals covers metals of Groups 1, 2, 4, 7 and 8 of the periodic table, namely barium, cadmium, calcium, cobalt, copper, iron, lead, magnesium, manganese, mercury, nickel, strontium, and zinc. Mixtures of salts may be used which are compatible, and in some cases incompatibility can be removed by the addition of a solvent such as ammonia. Example of combined colloid and bi-valent metal salt (parts by weight): hydrophilic colloid (water solution of guar gum) 8.95; water solution of formaldehyde 1,75; silica aquasol 1.33; water solution of zinc acetate 33.40; butanol 1.50; dye (Victoria Green) 3.65. The hydrophilic material used in the combined solution may in addition to those mentioned above comprise hydroxy ethyl cellulose, polyvinyl alcohol, mannitol, sorbitol, sucrose, invert sugar, corn syrup, mannose. In making printing-surfaces for giving a small number of impressions a cheaper paper is used omitting the casein-formaldehyde size, and the melamineformaldehyde resin. The amount of casein in the base coating is increased. In making the surfaces for a long run (5000 or more copies) they are made to have additional resistance to water penetration, and may have a base coat composed of (1) 100 parts polyvinyl butyral; 40 parts butyl ricinoleate; 5 parts soap- 15 parts by weight of mixture; (2) clay 15 parts ; (3) water 25 parts. Other water barrier coatings include urea formaldehyde resin, polyvinyl chloride, polymerized vinylidene chloride, styrene polymers, acrylates, elastomer type resins, or mixtures of these. The printing- surfaces may be treated by the rubbing process described in Specification 633,746.