TH23585A - Safety paper - Google Patents

Abstract

This invention relates to a method that combines wet paper forming, in which the paper is imbued with safety features, the application of an adhesive, and the application of a coating onto the already glued paper. The coating consists of a colorless polyurethane (which may include play-forming additives). After drying the paper, the coating forms a film that, when poured onto a glass surface, achieves a conic hardness of 15 to 130 seconds and is tested for durability as follows: (a) The coating is poured onto a glass plate to form a film with a dry weight of 80 g/m². (b) The film is dried at 23°C, and after detachment, it is dried for one hour at 80°C. (c) The film is weighed and wetted. (d) Boil the film samples in water containing 10 g/L Na2CO3 for 30 minutes. (e) Rinse the samples in cold water and repeat steps (b) to (c). Once the film is dry, (i) the tensile strength and wet Young's molasses of the boiled film must be greater than 90% of the original values. (ii) The film must not show any loss of transparency. (iii) The dry weight of the film must be greater than 98% of the original weight.

Claims (17)

1. A method for the production of safety paper incorporating safety features, which includes: (1) feeding the paper fibers into a paper-making machine; (2) incorporating at least one safety feature during its production and producing the paper; (3) applying an adhesive to the resulting paper to ensure adhesion; (4) selecting a mixture of mostly transparent coatings, consisting of colorless polyurethane, which may include playful fillers if their presence does not increase the opacity of the paper by more than 1%, where such coating mixtures are characterized to form a film when poured onto a glass surface with a conic hardness of 15 to 130 seconds and pass the water resistance test as defined by the following procedure: (a) pouring the entire coating mixture onto a glass plate to produce a film with a dry weight of 80 g/m²; (b) first drying the film at 23°C, after which the film is released from adhesion and is then processed. (c) Weigh the film before wetting and perform tensile strength, Young's modulus tests and visually check for any changes in transparency. (d) Boil the film sample in water containing 10 g/L Na2CO3 for 30 minutes. (e) Rinse the film in cold water and repeat steps (b) to (c) where, when the film is dried and weighed again, it must meet the following indications: (i) The wet strength and Young's modulus of the boiled film must not be less than 90% of the wet strength and Young's modulus of the initial film; (ii) The film must show no visible loss of transparency; and (iii) The dry weight of the film must not be less than 98% of its original weight. (5) Apply the selected coating mixture to one or both sides of the glued paper. (6) Afterward, dry the paper to produce the aforementioned safety paper. 2. The method proposed under claim 1, where polyurethane is in an aqueous distribution. 3. The method as claimed under either claim 1 or 2, in which the coating incorporates an expanding agent. 4. The method as requested in claim 3, where the expanding agent is a polyacrylate. 5. The method as claimed under any of the preceding claims, where the weight of the coating of the polyurethane-containing surface is between 0.05 and 20 g/m². 6. The method as requested under claim 5, where the coating weight is between 0.5 and 5 grams per square meter. 7. A method as claimed under any of the preceding claims where a polyurethane-containing coating is applied to the paper immediately after the application of the adhesive while the paper is still wet. 8. Any one of the methods under claims 1 through 6 in which a polyurethane coating is applied to dry paper after the conventional papermaking process is completed. 9. By any means applicable to any of the preceding claims, where the fibers contained in the paper are natural or synthetic fibers, or a mixture of natural and synthetic fibers. 10. The method as proposed in a prior claim, where polyurethane is an aliphatic polyester and is used in dispersion with a polyurethane content ranging from 2% to 70% by weight. 11. The method as requested in claim 10, where the distribution contains polyurethane in the range of 5% to 30% by weight. 12. A method that supports one of the preceding claims where urethane is of a cross-bonding type and cross-bonding occurs during the paper drying process. 13. The method under claim 12 in which cross-bonding is achieved by using achiridine as a cross-bonding agent. 14. The method in which a claim is made under any prior claim where the security characteristic is a watermark or thread may include visible or hidden security elements. 15. Any of the methods claimed under claims 1 through 14 in which a polyurethane mixture contains additives that are fluorescent or have iridescent colors. 16. The method prescribed in the preceding Clause One in which a thin metal sheet, including a flat thin metal sheet, hologram, or kinorag, is attached to security paper before or after printing. 17. Method of producing security documents where security paper is produced using a method as claimed in one of the preceding claims, and the resulting security paper is then printed to create security documents such as banknotes.