Security coating of documents

Abstract: A coating process that when applied to non-impact print/markings will improve the wear (or rub) characteristics and the security of the markings against fraudulent alteration.

Description: This invention relates to the security coating of documents, so that tampering or alteration of the previously fused or dried computer generated data is deterred as tampering or alteration can be detected. When documents are printed by traditional techniques - such as typing or impression printing, the paper substrate is indented and/or partially penetrated by the marking medium, typically ink. As a result, even when the document is altered, by scraping off surface ink, or by using blanking material, traces of the original imprint can be found in compression of the paper substrate by type impact, or residual ink particles which have entered into the substrate. Increasingly however, printing techniques which involve no impact of type on the paper are used, for economic reasons , and are generally associated with computer generated digital images. Impact free printers using bubble-jet, ink-jet, laser, LED, Ion Deposition and similar imaging technologies are increasingly used, since computer generated impact printing methods cannot operate at the very high character per second speeds required or have the imaging flexibility. Consequently, it is relatively easy for laser-printed or other toner printed documents to be alerted by removing the fused toner deposit, and substituting fresh characters, leaving no trace of the original characters. It thus not so far been possible to use laser printing for the creation of secure documents which are proof against relatively simple fraudulent alteration. EP-A-500, 372 discloses a thermal transfer material wherein an image is covered with a transparent protective layer, which may be applied all over a substrate or limited to the image zone, covered with a settable overall protective layer. The protective layer is a hot melt, which may be applied by a transfer sheet. According to EP-A-, 081, 887 a toner image may be formed on a substrate and then covered by a transparent toner which is applied electrophotographiccally so that the first toner is electrostatically charged and attracts the transparent tone, whilst in DE-A- 3, 610, 204 a fusible transparent layer is applied over the markings or their immediate vicinity. US-A-5232812 discloses a process for forming images which comprises generating an electrostatic image on an imaging member, developing the electrostatic image with a toner, optionally transferring the developed toner image from the imaging member to a substrate, applying to the developed toner image a curable liquid in which the toner is at least partially soluble, and curing the liquid to a solid. An object of the invention is to provide a process for secure printing of documents in such a way that fraudulent alteration or attempted alteration can be detected, so that a printing method can be used for the creation and economic reproduction of secure documents. The process for secure coating of variable computer generated markings on documents according to the present invention comprises first printing the desired markings generated by computer onto a substrate and applying a coating, characterised in that said markings are fused or dried onto a paper substrate and that the coating is applied over at least the areas containing said markings after fusing or drying of said markings, and is characterised in that the coating is restricted to the areas of the substrate with such markings and is effected by a flexographic, gravure or silk screen printing process. Any further coatings, to achieve other effects are carried out by similar means. Using the process of the invention, it is possible to create security documents, e.g. with personalisation and/or encoding. The application of the coating may be further restricted to specific critical areas of a document - such as a financial sum, or a digitally created signature, making the technique cost effective, and allowing use of conventional security printing techniques. The method may for example be used in the creation of financial documents, cheques, payment warrants, identification documents or the like, where alteration to a figure or a name by fraudulent alteration would give financial or other gain. The coating may comprise any one or more of a monomer, polymer or copolymer of vinyls, acrylates, polyesters, and/or urethanes; and a catalytic initiator which activates cross-linking when irradiated by e.g. an electron beam, UV, IR radiation or other suitable energy source. The coating may also be a resin based system capable of polymerisation by an external energy source, such as an electron beam, IR, UV radiation or other suitable energy source. Generally speaking, no organic or inorganic solvent or extender is used. Further coatings may be applied over areas where the coating has been applied using the same or different compositions. This makes it possible to create opportunities to develop high gloss effects over the non-impact laser toner print. The primary or subsequent coatings may be further enhanced by the addition of optically variable effects, such as UV or IR fluorescent reactions, thermo and/or photosensitive reactions, iridescent and interference pattern effects including the simulation of holograms. The application of the coating is preferably performed by a printing process so that it is possible to create intricate registered patterns and interactions which are not feasible by other techniques. It is also possible to produce tactile effects on the surface over the critical areas. The coating is preferably applied at a film weight of over 4 g/m 2 . A number of examples of the process according to the invention will now be described by way of example, and with reference to the accompanying drawing, which is a diagrammatic view of an apparatus for use in the process according to the invention. Example 1 - Laser Printing In accordance with the invention, a process for the coating of documents printed by laser printing comprises the steps of first laser printing and fusing the desired image or characters onto a paper substrate, and then applying a coating over at least the laser printed area of the substrate. In the case of laser printing an electrostatic image is formed on a drum or belt or other suitable surface by the laser in a dense dot matrix pattern corresponding to the characters desired. The counter charged toner particles are attracted to these areas, any toner in the non image areas is removed and recycled. The toner in the image areas is then transferred to the substrate and then fused by heat and overall pressure (or other suitable method) to the substrate. The fused toner forming the printed characters is however essentially a superficial deposit on the surface of the paper substrate and no impression is made either by entry of pigment into the substrate, or by deforming of fibres by impact or pressure in the image areas. The application of the coating has the effect of causing part of the non-impact laser toner print to enter into the substrate. This is caused by the coating penetrating into the fused toner and substrate wetting them thus allowing some penetration of the toner into the substrate. Consequently, in an attack on the printed image, not only the toner is removed, but also toner covered fibres are pulled from the paper. The result of this tampering will either leave a trace image of toner in the paper fibres, or detectable disturbance of the paper fibres. Example 2 - Improving wear (or rub) resistance The invention can be used to increase the wear resistance of computer generated data e.g. bar codes, MICR, etc. In the case of bar-codes which are read many times during their life cycle the image can deteriorate due to the reading head being in contact with the image and rubbing off some of the image each time. The application of the coating over the previously fused image (in the case of laser printing) protects the image extending its life. MICR characters tend to be used on documents which are read only once (or a few times). In this case particles are removed from the image and deposited on the reading head. This deposit can build up to a degree that the reading head becomes ineffective. The application of the coating over the MICR prevents the particles being removed thus the deposit on the head is avoided. Example 3 - Application of the coating using the flexographic printing process An image such as an emblem or a group of characters is printed by non-impact printing onto a paper substrate and is fused or dried then coated by this preferred method. In the process, a substrate sheet 1, such as paper of a suitable grade and weight is fed between an impression roller 2, and a plate cylinder or print roller 3. A coating chemical is circulated in an ink duct 6 in contact with an anilox roller 4, (or other suitable transfer device). The chemical is transferred to raised image areas 5 on a flexographic plate on the print roller 3 which in turn transfers the chemical to the required areas on the substrate 1 by use of the impression roller 2. After the chemical is coated onto the substrate 1, it is then exposed to an energy source which initiates polymerisation.

Claims: A process for secure coating of variable computer generated markings on documents, comprising first printing the desired markings generated by computer onto a substrate and applying a coating, wherein said markings are fused or dried onto a paper substrate and that the coating is applied over at least the areas containing said markings after fusing or drying of said markings, characterised in that the coating is restricted to the areas of the substrate with such markings and is effected by a flexographic, gravure or silk screen printing process. A process according to claim 1, wherein said coating is a monomer, polymer or copolymer of any one or more of vinyls, acrylates, polyesters, urethanes and/or other similar substances. A process according to claim 2, wherein the coating is polymerised by application of an external energy source comprising an electron beam, or IR, UV radiation or other suitable energy source. A process according to claim 3, wherein said coating comprises a synthetic plastics material and 9 catalytic reaction material which activates crosslinking when irradiated by said external energy source. A process according to claim 4, wherein said coating is a resin based system capable of polymerisation by an external energy source. A process according to claim 1 or 2, wherein the coating cross links without exposure to an external energy source. A process according to any preceding claim, wherein application of the coating is restricted to specific critical areas of a document. A process according to any preceding claim, wherein the area or areas to which said coating has been applied are treated by application of one or more further coatings, using the same or different composition. A process according to any preceding, wherein said coating or coatings are applied by a flexographic printing process.

Inventors: MANN PAUL GRAHAM, WELLS IVAN, MANN, PAUL GRAHAM, WELLS, IVAN
Applicants: SECURITY PRINTING AND SYSTEMS, SECURITY PRINTING AND SYSTEMS LIMITED
Application year: 1997
Main classification: B41M7
IPC codes: B41M3, B41M7