Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Reexamination Certificate
1998-05-08
2001-09-25
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
C428S141000, C428S156000, C428S457000, C428S913000, C428S915000, C428S916000, C428S042100, C428S041800, C428S213000, C283S086000, C283S901000, C283S902000, C430S001000, C430S002000
Reexamination Certificate
active
06294241
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
A security document and method of producing it The present invention relates to security documents such as bank notes, identity cards or the like, with multilayer security elements having a layer in which diffraction structures, in particular holographic structures, are embossed in the form of a relief structure and which are combined with a reflective layer, and to a method for producing the same.
2. Discussion of Related Technology
Optically variable elements such as holograms, diffraction grids or interference layer elements have been preferably used for some time as protection against forgery or copying due to their optical properties that vary with the viewing angle. For mass production of such elements it is customary to produce so-called master holograms which have the particular phase information in the form of a three-dimensional relief structure. Starting with the master hologram one produces by duplication so-called press dies for embossing the required holograms in large numbers of units.
The embossing can also be done directly on the document material as described in EP-A 0 338 378. In a continuous process bank note paper in a roll form is first printed on both sides and then provided in certain areas with a holographic structure. The lacquer to be embossed and the relief structure are simultaneously transferred to the paper by covering the surface structure of the press die with a radiation-curable lacquer. As soon as paper and press die are brought in contact the lacquer is cured. The lacquer now adheres to the paper surface and has the holographic relief structure. Then the embossed structure is given a thin vacuum metalized layer that permits the holographic information to be observed in reflection.
Since paper is virtually impermeable to UV radiation the curing of the lacquer can in this case only take place with the aid of electron radiation, a very elaborate and expensive method that furthermore damages the paper. For this reason the production of embossed holograms directly on the document material has not become accented in practice, although this procedure has great advantages with respect to resistance to forgery since the hologram is connected virtually undetachably with the substrate. Due to the much more cost-effective production and more versatile applicability embossed holograms are therefore usually prepared as multilayer elements on a separate carrier and transferred to the document by means of an adhesive layer. The layer structure is dimensioned, or prepared by additional measures, in such a way that the hologram can be removed from the carrier layer after being glued to the document.
The multilayer element applied to the carrier material can be produced e.g. by the method known from U.S. Pat. No. 4,758,296. A matrix in web form wound on rolls is provided with a liquid resin and brought in contact with a plastic carrier material. The liquid resin is simultaneously cured by UV or electron radiation. In a further step the relief structure is provided with a thin metal layer so that the hologram can be observed in reflection. To be transferred to a document the layer structure is finally provided with a hot-melt adhesive layer that is activated under the action of heat and pressure.
However this security element has the disadvantage that the hologram element might be detached from the document by reheating the hot-melt adhesive, and transferred to another.
In general, so-called transfer embossing foils have more than the layers described in U.S. Pat. No. 4,758,296. For example EP-A 0 170 832 describes a transfer embossing foil comprising a carrier material, a first layer of lacquer permitting subsequent detachment of the carrier material, a second layer of lacquer in which the diffraction structures are embossed, a metal layer and a layer of bonding agent. Such a foil can be glued to a document by the method known from EP-A 0 433 575. The embossing foil in which the hologram structure is embedded is applied to a document locally in the form of a marking. For this purpose the document is printed at a certain place with an adhesive which only becomes viscous and sticky through UV, gamma or electron radiation. This activation takes place either before or after the transfer foil and document are brought together.
Although this security element offers irreversible adhesion to the document since the cured adhesive is not reactivable, the embossed structure can be exposed if the layer bordering the relief structure or the metal layer has a different chemical base.
BRIEF SUMMARY OF THE INVENTION
Interestingly enough, the prior art also contains proposals for preventing embossed layers from being exposed by using chemically homogeneous materials or permeable metal layers (GB-A 2 093 404). But since these elements are applied with reversibly activable adhesives in all such proposals these elements are still detachable from the substrate and thus insufficiently protected from manipulation. The invention is therefore based on the problem of providing a security document with an embossed hologram, whereby the embossed hologram has a simple layer structure with a good laminar compound that is cost-effective and simple to produce, and the hologram is furthermore connected with the document irreversibly.
The invention offers many-sided advantages involving both the production of embossed holograms directly on the document material and the production and application of transferred embossed holograms.
For example it is possible to produce embossed holograms directly on the antifalsification Caper with the aid of light-curing substances in very uncomplicated fashion. Such substances are e.g. blue light-curing or delayed-curing lacquers.
These substances can of course be used just as advantageously for producing or applying transferred embossed holograms.
Along with this simple production or transfer, the inventive security documents also offer the crucial advantage that the security elements have a simple layer structure and an intensive laminar compound within the element or between element and document.
This is because the materials selected for plastic layers that are adjacent in the element layer structure are chemically homogeneous and therefore ensure a much more intensive compound in the boundary layers than chemically different substances. The firm compound with the document arises from the use of reaction lacquers or adhesives (i.e., lacquers and adhesives that polymerize or cross-link upon physical and/or chemical activation) which adhere irreversibly to the document.
To obtain a layer structure as simple as possible even in the case of the transferred embossed holograms, the metal layer disposed above the embossed layer is not covered with an additional foil layer which is then equipped with an adhesive layer but, according to the invention, is coated directly with the adhesive, the adhesive being selected so as to have a foil-like character in the cured state (on the substrate). These requirements are met by all reaction adhesives that polymerize by physical and/or chemical activation. To counteract manipulation of all kinds the embossed layer of the transfer element and the adhesive layer are formed according to the invention as chemically homogeneous layers. The metal layer located between these layers is designed so thin that it already has microcracks or pores with normal handling so that the embossed layer and adhesive layer are in contact through these randomly present openings and form a largely inseparable compound at these places. Exposure of the relief structure cr detachment of the security element therefore leads inevitably to destruction of the stated layer structure. Alternatively or additionally the metal layer can also be provided with openings systematically.
In a preferred embodiment the transfer element comprises a carrier material preferably bearing a UV-curable layer of lacquer in which the hologram structure is embossed, and a metal layer whose thickness is much smaller than 1 m
Grauvogl Gregor
Kaule Wittich
Bacon & Thomas
Giesecke & Devrient GmbH
Watkins III William P.
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