Coating processes – Fraud or tamper detecting
Reexamination Certificate
1998-10-02
2001-03-13
Padgett, Marianne (Department: 1762)
Coating processes
Fraud or tamper detecting
C427S008000, C427S205000, C427S201000, C427S197000
Reexamination Certificate
active
06200628
ABSTRACT:
This invention relates to the use of inorganic particles which comprise at least two chemical elements in a predefined and analytically identifiable ratio, a method for tagging a substrate and to a method of tagging and identifying a substrate and/or an article.
Encoded micro-particles whose code is represented by at least three visually distinguishable coloured layers of organic resins and their use as tag and/or security feature in order to prevent counterfeiting of articles have already been described in DE 26 51 528 and U.S. Pat. No. 4,329,393. Originally, these particles have been developed to allow tracing of explosives from production to detonation. These tags are sold under the trade name Microtaggant or Microtrace.
As the colour sequence of the layers is the only coding feature, particle size and material selection limits the application of these tags. Particle size below 30 &mgr;m is a necessary requirement for many applications, particularly printing inks and related products. Highly resolved lines and figures are difficult to produce with printing inks containing particles larger than the printed feature itself. Particles made of organic laminate can hardly be ground down to sizes in the desired range.
A further disadvantage of these organic particles is their lack of heat resistance. This results in the destruction of a tagging or security element when the article is exposed to fire or heat.
U.S. Pat. No. 5,670,239 discloses a composition for the delocalized marking of articles, which makes the forging or improper exploitation of these articles difficult. The composition contains non-ubiquitous chemical elements, i.e. more or less rare elements from the main- and sub-groups of the periodic system. In particular these are elements which have an x-ray K
&agr;
line in the range between 3.69 keV and 76.315 keV and which may be present either in elemental form or in the form of any desired compound.
The elemental compositions and their concentrations serve as delocalized stored information which cannot be discerned with the naked eye. An information item, e.g. an encrypted numerical code or a number/letter combination, can be represented by a set of specific elements or compounds, where each specific element or compound represents a digit of the code, and the concentration of the element or compound expresses the value of that digit, e.g. the figure or the letter. If a specific element or compound belonging to the set is absent from the composition, then the value of the corresponding digit is zero or blank.
U.S. Pat. No. 5,670,239 shows several shortcomings. This marking method requires in any case the retrieval of precise concentrations for the marking composition components in the marked bulk materials, coatings or printing inks. This depends on a homogenous distribution of the marking components which are provided generally as solution. Finding compounds of all desired elements which dissolve homogenously in a coating composition over the whole required concentration range without forming precipitates is rather difficult.
Also the use of mixtures of solid state materials is precluded due to their inherent tendency to segregate according to particle size, specific gravity, etc..
An additional disadvantage is the restricted range of coding possibilities, since each specific chemical element or compound can only represent a n-valued digit of the code. The total coding capacity for m specific elements is therefore given by n
m
. The restricted coding capacity is due to the fact that in a delocalized coding system only chemical information is evaluated. The code may thus be broken by any sufficiently sensitive analytical method which is able to yield quantitative results, i.e. classical elementary analysis, X-ray fluorescence, Laser-Ablations-ICP-MS etc.. That makes the decoding and reverse-engineering for any potential counterfeiter easy.
A further disadvantage of the teaching of U.S. Pat. No. 5,670,239 is the sensitivity of the encryption to perturbing elements. One or more of the elements used for the encryption may accidentally be present for another reason in or on the marked object. This will impede a proper readout of the encoded digit. Perturbation of other security systems can, vice versa, occur by the presence of this type of encoding, in particular if soluble compounds of rare-earth ions are employed, which are often luminescent in the visible or infrared domain of the spectrum. This kind of interferences are likely to occur with security documents, where a plurality of security systems has to be combined.
It is therefore an object of the present invention to provide marking means which do not show the drawbacks of the prior art and which are particularly suitable for application on security documents.
It is a further object of the invention to provide a reliable forensic tool for marking articles against counterfeiting or improper use.
Another object of the invention is to provide marking means which are compatible with the existing security systems, especially those which are in use on security documents and which serve for their automated machine recognition.
Another object of the invention is an increase of the coding capacity.
Another object of the invention is to provide an encryption which makes the reverse-engineering difficult and which can not be broken by most of the commonly available analytic tools.
Another object of the invention is to provide marking means which are insensitive to perturbing elements.
Another object of the present invention is to provide marking means which do not depend on the formation of homogeneous mixtures with the base material or materials of the article, or with the coating or printing ink to be marked.
These objects were solved by the features of the independent claims.
Particulary they were solved by the use of at least one type of inorganic particle comprising at least two chemical elements in a predefined and analytically identifiable ratio as a marking means.
These particles are introduced into or applied onto the article as a marking mean. The specific ratio of elements in that inorganic particle, which is characteristic for each type of particles, represents a code, or part of a code.
The information containing particles can be localized by scanning electron microscopy (SEM) using backscattered electron detection.
Thus the sites, i.e. the particles where information is contained, must be localized in a first step. Subsequent to the localizing of the information containing particle, the ratio of chemical elements being comprised in that particle can be determined by energy- or wavelength-dispersive x-ray analysis (EDX). Both steps, i.e. the localizing of a particle and its analysis are performed on the same SEM equipment. The proper decoding of the marking according to the present invention is tied to analytical methods combining both, microscopy for the localizing, and elemental analysis for the reading of the code. By concentrating the coded information to at least one localized particle, the information retrieval is not dependent on homogeneous mixing. For the reading of such markings SEM/EDX is the best practicable method today. For SEX/EDX, a particle volume in the order of 0.01 &mgr;m
3
is sufficient to be properly read.
A further beneficial property of the SEM/BDX analysis method is its dependency upon standards in order to get reliable quantitative results. The quantity of an element present in a particle is determined from the intensity of its characteristic X-ray emission. This latter, however, depends upon the precise excitation conditions i.e. the energy of the exciting electron beam. As the energy of the exciting beam is more or less attenuated in function of the density of the material, the analysis must be performed against standard materials of similar chemical nature. In the absence of such standards, the quantitative results can be quite wrong. In security applications, the standards and their exact compositions are known to the owner of the marking, but not to the counterfeiter. The counterfei
Muller Edgar
Rozumek Olivier
Padgett Marianne
Shoemaker & Mattare, Ltd.
SICPA Holding S.A.
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