Patent DE-19915440-A1 (DE)
Title: Security marking for document and banknote paper
Inventor: PUTTKAMMER FRANK
IPC: D21F1/44
Filed: 1999-03-27
Abstract: The security markings for special papers, as proof of validity, uses electrically conductive materials added to the paper pulp or applied to the surface of the paper web. The marking materials are taken from a supply container (26) for delivery through a tube (17) to the web surface, or the marking material is applied to a watermark embossing roller for transfer to the paper. The marking material is an electrically conductive and transparent polymer, or conductive pigments or a combination of both. The marking material is used as a dispersion, suspension, solution or as a monomer with a polymerization agent bonded to the paper. It is applied partially or homogeneously into or on the paper, and is pref. mixed with pulp in the paper making machine vat. The container (26) for the marking material is pumped (20) into the delivery tube (17), fitted with a valve (19) and a control (18). The delivery tube (17) is set to deliver the marking material in equidistant droplets on the moving paper surface, or as lines in a continuous flow. The marking material can also be applied to all or part of the embossing surface of a watermark embossing roller, to be transferred to the paper as part of the watermark. At the paper processing stage, monitors register that the marking material is correctly in place, with control links to the marking material feed system. An Independent claim is included for an electrically conductive marking material, as a conductive polymer which can be with a film in the paper web bonded to the security marking. Preferred Features: The electrically conductive polymer can be at least partially in a printed image to be applied to the paper. The film structure is composed of a carrier film layer with a metallized surface, with partial metal removal to the edge of the carrier film. It has a further layer of electrically conductive polymer. The film structure is integrated into the paper web. A further adhesive layer can be between the carrier and the metallized surface, which also gives adhesion to the film structure within the paper. The carrier film can be metallized on one side and carry the electrically conductive polymer film on the other side, or the polymer film can be over the metal layer. A second carrier film can be used in the film structure, to carry the conductive polymer film layer. The conductive polymer film has a greater stretch than the carrier film and the metal coating. The marking material has a specific surface resistance, which is set by the application method, the integration technique and/or its composition and/or specific formulation. The conductive polymer has a resistance of 20-40 kOhm/sq. The polymer has a conductive grid structure, or contains conductive additives with at least a pigment visible to the human eye, which can be activated and deactivated for scanning by an optical monitor. The polymer additives have magnetic characteristics which can be neutralized. The paper can be given an optical or magnetic coding in addition to the conductive marking material. The conductive polymer is applied to the carrier film by transfer printing, printing, spraying or immersion. The carrier is the paper web itself, or a film integrated into the paper. The carrier can be a primer or adhesive applied to the base. The carrier can be a packaging or a product, or a visible security marking. The conductive polymer is transparent or virtually transparent, or has a metallic appearance. The polymer can be opaque to light passing through. It does not become detached from its environment, and is at least a surface which is bonded to the carrier, and it can be intermittent on the carrier. The conductive polymer can be applied as continuous or intermittent lines, or as local points. Before the conductive polymer is bonded to the paper web, it can be fitted with a film, a hardening varnish layer, a reflection layer and a protective layer. A further Independent claim is included for a scanning system which detects the marking material according to the data for its electrical conductivity and/or other physical values and/or chemical characteristics to give a multiple test operation. Preferred features: The scanning sensor has optical, magnetic and/or mechanical sensors to detect the electrical conductivity from a number of channels which scan the conductivity. The conductivity is scanned across the whole paper width, by capacitive sensors. To reduce the scatter coupling, on the first scan even number channels are used, followed by the odd number channels on subsequent scanning, with a scanning frequency of preferably 200 kHz. The gap is adjusted between the transmitter and receiver electrodes, according to the test structure and plane. The conductive marking material has a characteristic used as a reference value, as a double test for the conductivity. A retaining roller or sliding rail is near the scanning sensor, for a good paper movement through the scanning zone. Functional sensor electrodes are on both sides of the paper, and across the whole paper width, to test that the required parameters are present throughout. The scanning sensors are linked to a control, to set the feed of the marking materials.