Printing – Stenciling – Processes
Reexamination Certificate
2000-12-28
2004-02-10
Eickholt, Eugene H. (Department: 2834)
Printing
Stenciling
Processes
C101S128400, C101S401100
Reexamination Certificate
active
06688221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for producing security foils for objects of value such as papers of value consisting of a transparent or translucent carrier foil and a cover layer applied thereto which is present in the form of characters or patterns and/or has coating-free areas in the form of characters, patterns or the like which are clearly recognizable in particular in transmitted light.
2. Related Art
Security foils in the form of threads or bands which are embedded in papers of value such as bank notes, checks, identity cards, credit cards and the like are known. To increase security and as protection from forgery such threads are frequently provided with so-called negative writing. Said writing is formed by metal-free areas in an otherwise all-over metallic coating of the transparent carrier material forming the threads. If one holds a paper of value containing such a thread against the light, the thread basically appears dark because of the opaque metallic coating. The metal-free areas stand out against this dark background as light and contrasting. This conspicuous incident/transmitted light effect provides very good protection from forgery. The protective effect of the negative writing lies in the elaborate and complicated production requiring great know-how, high equipment expense, special printing inks and a great number of operations. In contrast, usual printed information can be forged true to the original without great effort using copiers and printers available today.
Security foils are also known which have diffraction structures such as conventional holograms, cinegrams, pixelgrams, etc. The protection from forgery by said elements is based on the viewing angle-dependent interplay of colors which said elements show. Such security foils are frequently applied to the surface of objects of value in the form of strips or labels.
Mass production of the diffraction structures is usually effected by converting the diffraction structures into a relief structure which is subsequently used as an embossing die. Embossing is usually done in a thermoplastic layer or a lacquer or resin layer curable during the embossing process. Said layers can possibly be provided before the embossing process with a thin metal layer which on the finished product ensures that the diffraction structures are recognizable in reflected light. However, the metalization process is frequently effected only after embossing, in particular when embossing is done in liquid to viscous materials such as UV-curable lacquers which are only cured during the embossing process by corresponding treatment, e.g. irradiation with UV light.
Said production of such embossed lacquer layers can be effected directly on the object to be protected. According to an alternative, very common technology, transfer foils containing the embossed lacquer layer in their layer structure are produced in a separate operation. This layer structure is subsequently transferred to the object of value by means of suitable adhesive layers.
To increase the protection from forgery it has also been proposed to provide the reflecting layer of such a diffraction structure with negative writing, i.e. with gaps in the form of characters, patterns or the like (EP 0 330 733 A1). EP 0 330 733 A1 also states different methods for producing such gaps. Besides conventional etching methods, reference is also made to a production method by which an ink having thermoplastic properties and softening and becoming gluey at higher temperatures is printed on the metal-coated side of the foil. If a thus pretreated foil is laminated against a second untreated sheet of foil using heat and pressure, the two foils stick together in the area of the printed characters or patterns. When the two foils are separated the areas corresponding to the characters or patterns are then detached from the metal coating.
For producing packaging material it is known from DE-OS 36 10 379 to first print a printed image on the foils as is to appear later as a negative image in the metal coating, and only apply the metal coating in a second method step. The printing method can be intaglio or flexographic printing. For applying the printed image one uses inks or lacquers having low adhesion to the metal coating. The metal coating is then removed mechanically by the action of an air or liquid jet or by a mechanical squeegee.
All said known methods have in common that the information which is later to be present in the form of gaps must be printed with poorly adhesive or etching inks in a certain operation. Separate printing forms must be produced for this printing operation. Production of the forms is very elaborate. For an intaglio cylinder for example, a metallic cylinder must be prepared very elaborately, i.e. copperplated, polished, provided with the information to be printed and finally chromium-plated. The printing cylinder can in addition only be used for the particular printing job. In particular for mass articles such as holograms, negative characters can therefore only be provided if an accordingly high number of holograms is produced so that the additional costs are distributed over as many final products as possible. For small runs or productions which are to be provided with different negative characters, the production costs are hitherto prohibitive.
BRIEF SUMMARY OF THE INVENTION
The invention is accordingly based on the problem of proposing a method for producing security elements with negative writing that permits cost-effective production even for small runs or varying information.
The invention is based on the finding that the negative characters can be produced using simple and flexible printing processes based on highly modern digital technology which cannot be used in direct security printing. Said printing processes are readily accessible and frequently involve little equipment expense, so that information produced by such printing processes can be reproduced or forged just as easily and true to the original. For this reason one still uses in security printing complicated and elaborate techniques such as intaglio printing that cannot be imitated with customary printing processes used in computer technology.
With negative writing, however, the protective effect is not determined by the printing process used but by the plurality of working steps and their interaction. In most methods for producing negative writing, the direct printing result no longer appears on the final product. If the negative writing is produced by means of solvents for example, the print disposed in certain areas under the all-over opaque, preferably metallic layer and the opaque layer directly thereabove are removed by the action of the solvent. Since this production process is in addition effected in protected surroundings, it is not necessary to use a complicated and preferably forgery-proof printing process such as intaglio printing for the print.
According to the invention one therefore produces negative characters using printing processes permitting a simple and fast change of the information to be printed, regardless of the fact that the printing result might possibly be easily forged.
According to the inventive method one images the printing form already fastened in the printing machine, for example a printing cylinder. Imaging of the form is effected by means of digital data in computer-controlled fashion. This has the advantage that the information to be printed can be previously composed and processed on the monitor. Imaging of the form in the printing machine is preferably reversible, i.e. new imaging of the form can be effected very quickly, if necessary between two printing operations. One can thus vary the information to be printed quickly and easily without having to interrupt the continuity of the production process.
According to a preferred embodiment, the printing form used is an intaglio form provided with all-over screen engraving. For imaging in the printing machine the total screen is filled with a readily cura
Eickholt Eugene H.
Giesecke & Devrient GmbH
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