METHOD FOR MANUFACTURE OF SAFETY PAPER Russian patent published in 1999 - IPC

FIELD: manufacture of safety paper that has safeguard signs. SUBSTANCE: paper is moulded in a wet state, has paper comprises one or more safeguard signs. Adhesive agent is applied onto paper for sizing. Then, a coating containing polyurethane uncolored by pigment is applied onto one or both sides of sized paper. The coating may contain a functional additive on condition that presence of functional additive will not cause an increase of paper opacity by more than 1%. After application of polyurethane the paper is subjected to drying. The composition of the coating provides for obtaining of a film, having a Kenig hardness of 15 to 130 s, after it is cast on a glass plate, as well as for withstanding of a water resistance test determined by the following stages: (a) use is made of compound for coating, which when cast on a glass plate, provides for obtaining of a film with a dry weight of 80 g/sq. m; (b) first the film is dried at a temperature of 23 C. When the film becomes nonsticking, it is dried additionally for an hour at a temperature of 80 C; (c) the film is weighed before and after wetting and breaking strength test in a wet state, and Young's modulus test, and checked visually for any change of its transparence; (d) the film specimen is boiled in water containing 10 g/litre of Na₂CO₃ during 30 minutes; (e) then the film is washed in cold water, and stages (b) through (c) are repeated; after the film is dried and weighed once more, it should satisfy the following criteria: breaking strength in a wet state and Young's modulus test of boiled film make up at least 90% of the breaking strength in a wet state and of the Young's modulus of the original film; the film does not reveal an appreciable loss of its transparence; and the film weight in a dry state makes up at least 98% of its original weight. EFFECT: enhanced duration of use and resistance to soiling. 18 cl, 6 ex