Registers – Records – Fluorescent – phosphorescent – radiation emitting
Reexamination Certificate
1999-11-16
2003-03-11
Frech, Karl D. (Department: 2876)
Registers
Records
Fluorescent, phosphorescent, radiation emitting
C235S487000, C235S494000
Reexamination Certificate
active
06530527
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention concerns security documents with safety features in graphical form, preferably using intaglio printing, that can be caused to illuminate as points, strips, and/or surfaces. The targeted wavelengths are in the invisible UV range up to the range visible to the human eye, typically from 360 to 780 nm, as well as within the infrared range.
2. Discussion of the Related Art
In German Patent 43 10 082, electroluminescent foils are presented that are manufactured of inorganic, electroluminescent pigments and thermoplastic synthetics by means of extrusion or co-extrusion. In principle, extrusion or co-extrusion of this type of system onto security paper is conceivable, but graphical design options seem to be limited by process logistics. Also, the overall manufacturing process to produce a security document and the associated authenticity testing arrangement required for it appear to be very expensive.
In German Patent 43 15 244, a process is described that produces an electroluminescent film using sputtering technology. This process would also be fundamentally conceivable for the production of security documents, but a production process of this type would be extremely expensive due to the vacuum chambers necessary for this technology. This process would also be very difficult to integrate into a possible manufacturing process and it produces film layers that would have to be equipped with special added layers to withstand the high mechanical requirements of security documents.
In German Patent 41 26 051, a security document is presented having an embedded surface security element (security fibers). This document is designed with multiple layers and exhibits electroluminescent properties. A disadvantage of this arrangement is that a relatively high surface buildup must be taken into account since the electrodes that are necessary to excite the EL substances lie one on top of the other.
U.S. Pat. No. 4,355,300 shows a testing device to mechanically test the authenticity of a security document. An alternating voltage is applied to an opposing electrode arrangement and produces an electric field between the two electrodes. By placing the security document, with its security features contained on it, between the electrodes, the dielectric constant is modified inside the field gap (the dielectric constant is material-dependent). This changes the capacitive resistance, which can be measured using a measuring instrument and can be evaluated in an evaluation unit. However, this printed document contains no electrically excitable substances that are excited within the field gap and consequently no electromagnetic radiation is measured in the form of emitted photons. The device parameters must therefore be selected according to a measured condenser voltage and not according to a measured electromagnetic radiation.
SUMMARY OF THE INVENTION
A primary purpose of the invention, based on German Patent 41 26 051, is to further develop a value/security instrument with EL-active security features that have a considerably thinner layer construction on the surface of the security document.
This objective is met by means of the technical methods described, which provides an essentially planar electrode arrangement located on the value/security instrument. The electrodes lie next to one another in approximately the same plane and form a field gap between them. The field lines of the alternating electromagnetic field produced in the field gap penetrate the EL substances.
In this arrangement, there is a series of different embodiments of the invention. Applying the EL substances using steel plate intaglio printing and other printing processes employ the method of the invention. In particular, dry offset printing, wet offset printing, screen-printing, non-impact printing techniques and novel digital printing processes are among the alternative embodiments.
Instead of layering electrodes one on top of the other—as the state of the technology is well-known for—these types of electrodes are applied to the value/security instrument and/or testing device in an adjacent surface arrangement, at least partially. An advantage of the invention is thus the elimination a multi-layered arrangement of surface EL systems on top of one another.
In the present state of the technology, the fear is that the known laminate construction, which is subject to extreme sustained stress requirements, may not be sufficiently wear resistant. Another disadvantage is that a security fiber is not an integral component of a value/security instrument and can be removed. This known arrangement requires electrical contacts to be applied to the value/security instrument. In contrast, some of the embodiments of the invention do not need a contact on the value/security instrument.
In contrast to common electroluminescent (referred to as EL) systems that are built between surface electrodes, one variation of this invention does away with this relatively thick construction by building the electric field laterally, or within the surface itself. For an EL plate-condenser type construction according to the invention (in which, according to the invention, the condenser “plates” lie next to one another in essentially the same plane and the field needed for excitation is produced in the field gap between them), a transparent, electrically conducting layer is needed. This layer is attained using ITO pastes (Indium-Tin-Oxide). It can also be attained using pre-layered transparent foils or glasses.
Typically, biaxially-oriented, thermally stabilized polyester foils are used that are layered with evaporated or sputtered, electrically conducting tin oxide, ITO or, generally speaking, transparent, electrically conducting metallized surfaces. These surfaces have surface resistance values in the range of typically 20 ohms/square up to 300 ohms/square and above, and less than this for glass substrates.
High quality EL systems need an even luminous density and maximum light efficiency. Because of their high thermal strength in layering processes, glass substrates offer a higher quality solution, in general, with higher optical transmittance in the visible wavelength range with simultaneously better surface conductivity. However, the important advantage of the ITO paste printing technique, which this invention uses, is its relatively simple application and the nearly limitless graphical design possibilities. This is especially advantageous in more complex systems involving electrical connections.
Since these types of ITO screen printing pastes seldom yield surface resistances of less than 300 to 400 ohm/square, bus bars (edge strips with good electrical conductivity) are used in this invention. This creates even electrical fields and thus an even luminous density. Furthermore, this technique allows the connection of the ITO electrode to be structured with good functionality. Last but not least, the ITO electrode layer thickness can be reduced. This leads to higher transparency through its volume. According to the invention, bus bars are printed by means of printing technology using pastes of silver, carbon, copper, among others, or a combination of these elements. In this way, surface resistances in the range of a few 10 mohms/square can be attained.
According to the invention, various designs are described as follows. In each of these designs, the EL substances are excited using an alternating electromagnetic field.
1. A lateral electrode arrangement on the value/security instrument,
2. An electrode arrangement in a lateral or opposing arrangement located external to the security document, that is, in a signal detector.
3. A lateral electrode arrangement located on a transparent covering substrate in the signal detector.
In a preferred design, the value/security instrument has security elements based on microencapsulated inorganic group II and group VI compounds as found in the periodic table (for example ZnS, CdS). They are doped or activated with metals such as Cu, Mn, Ag, and are suitable for printing
Ahlers Benedikt
Franz-Burgholz Arnim
Gutmann Roland
Kappe Frank
Schmidt Wolfgang
Bundesdruckerei
Frech Karl D.
Nowlin April
The Maxham Firm
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