U.S. patent application number 12/083157 was filed with the patent office on 2009-10-15 for securing the authenticity of value documents by means of characteristic substances.
Invention is credited to Gregor Grauvogl, Ulrich Scholz.
Application Number | 20090258200 12/083157 |
Document ID | / |
Family ID | 37591705 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090258200 |
Kind Code |
A1 |
Scholz; Ulrich ; et
al. |
October 15, 2009 |
Securing the Authenticity of Value Documents By Means of
Characteristic Substances
Abstract
The invention relates to a feature substance for securing the
authenticity of documents of value, having at least one luminescent
substance in particle form and nanoparticles enveloping the
surfaces of the luminescent substance particles at least partially,
wherein the properties of the feature substance result from the
interaction of the properties of the luminescent substance and of
the nanoparticles. The invention furthermore relates to a method
for producing the feature substance, a method for securing the
authenticity of a security element or document of value using a
feature substance, as well as security elements and documents of
value with authenticity features on the basis of the feature
substance.
Inventors: |
Scholz; Ulrich; (Buchbach,
DE) ; Grauvogl; Gregor; (Oberhaching, DE) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE, FOURTH FLOOR
ALEXANDRIA
VA
22314-1176
US
|
Family ID: |
37591705 |
Appl. No.: |
12/083157 |
Filed: |
October 4, 2006 |
PCT Filed: |
October 4, 2006 |
PCT NO: |
PCT/EP2006/009603 |
371 Date: |
June 19, 2008 |
Current U.S.
Class: |
428/199 ;
252/301.4R; 427/157; 427/213.3; 427/595; 427/598; 427/7; 428/323;
428/372; 428/403 |
Current CPC
Class: |
B42D 25/29 20141001;
Y10T 428/25 20150115; Y10T 428/2927 20150115; B42D 25/387 20141001;
Y10T 428/2991 20150115; B42D 25/369 20141001; Y10T 428/24835
20150115; D21H 21/48 20130101; B42D 25/382 20141001 |
Class at
Publication: |
428/199 ;
428/403; 427/157; 428/323; 427/213.3; 427/598; 427/595; 427/7;
428/372; 252/301.4R |
International
Class: |
D21H 21/40 20060101
D21H021/40; B41M 3/14 20060101 B41M003/14; C09K 11/00 20060101
C09K011/00; B42D 15/00 20060101 B42D015/00; D21H 21/30 20060101
D21H021/30; B32B 5/16 20060101 B32B005/16; C09K 11/08 20060101
C09K011/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2005 |
DE |
10 2005 047 609.0 |
Claims
1. A feature substance for securing the authenticity of documents
of value, comprising at least one luminescent substance in particle
form excitable by radiation in at least one of the infrared visible
and ultraviolet spectrum to emit luminescence, comprising
nanoparticles enveloping the surfaces of the luminescent substance
particles at least partially, wherein properties of the feature
substance result from the interaction of the luminescence emission
properties of the luminescent substance and properties of the
nanoparticles.
2. The feature substance according to claim 1, wherein the
luminescent substance emits in at least one of the infrared,
visible and ultraviolet spectrum.
3. The feature substance according to claim 1, wherein the
luminescent substance particles are enveloped substantially
completely by substantially a monolayer of nanoparticles.
4. A method according to claim 1, wherein the luminescent substance
is selected from luminescent substances on the basis of host
lattices doped with at least one rare earth metal.
5. The feature substance according to claim 1, wherein the
luminescent substance is selected from the mineral-phosphorus
compounds.
6. The feature substance according to claim 1, wherein the
luminescent substance is selected from organic luminescent
substances.
7. The feature substance according to claim 1, wherein the
luminescent substance is present in the form of particles with an
average particle size in the range of 1 to 100 .mu.m.
8. The feature substance according to claim 1, wherein the
nanoparticles are selected from the group consisting of magnetic
materials, magnetizable materials, electrically conductive
materials, semiconductor materials and mixtures thereof.
9. The feature substance according to claim 1, wherein the
nanoparticles are selected from the group consisting of carbon nano
tubes, nano .alpha.-iron, nano Fe.sub.3O.sub.4, nano
NiFe.sub.2O.sub.4 and mixtures thereof.
10. The feature substance according to claim 1, wherein the
nanoparticles have an average particle size in the range of 1 to
1000 nm.
11. The feature substance according to claim 1, wherein the weight
ratio of luminescent substance particles to nanoparticles is in the
range of 10:1 to 1:10.
12. The feature substance according to claim 1, including
luminescent substance particles that are not enveloped by either or
both nanoparticles, and free nanoparticles.
13. The feature substance according to claim 1, including either or
both at least two different luminescent substances and at least two
different types of nanoparticles.
14. A method for producing a feature substance as defined in claim
1, comprising adding at least one luminescent substance in particle
form and at least one substance in the form of a nano powder to a
dispersant and stirring the mixture for such a time until a
dispersion is obtained.
15. The method according to claim 14, wherein the dispersion is
filtered to separate the feature substance.
16. The method according to claim 15, wherein the separated feature
substance is dried.
17. The method according to claim 14, wherein as dispersant water
is used.
18. The method according to claim 14, wherein the feature substance
is mixed with either or both at least one further feature substance
and/or and at least one further type of nanoparticles.
19. A method for securing the authenticity of a security element or
document of value, comprising: applying a feature substance as
defined in claim 1, on at least partial areas of at least one
surface of the security element or document of value, or
integrating a feature substance as defined in claim 1, in at least
one partial area of the volume of the document of value or security
element.
20. The method according to claim 19, wherein the security element
or document of value is subjected to electrical or magnetic fields
during the application or integration of the feature substance in
such a fashion that an orientation and, if desired, a migration of
the feature substance particles within the electrical or magnetic
field takes place.
21. The method according to claim 20, the migration leads to a
defined distribution of the feature substance particles that is
machine-verifiable or visually verifiable.
22. The method according to claim 21, wherein the defined
distribution forms a code.
23. A document of value or security element comprising at least one
carrier material and, on or within the carrier material, at least
one authenticity feature based on a feature substance, wherein the
feature substance is a substance as defined in claim 1.
24. The document of value or security element according to claim
23, wherein the carrier material comprises paper or plastic.
25. The document of value or security element according to claim
23, wherein the feature substance is provided in the volume of the
carrier material.
26. The document of value or security element according to claim
23, wherein the feature substance is present in a layer applied on
at least partial areas of a surface of the carrier material.
27. The document of value or security element according to claim
23, wherein the feature substance is present in a printing ink
applied on a surface of the document of value or security
element.
28. The document of value or security element according to claim
23, wherein the feature substance shows a defined distribution
which is visually verifiable or machine-verifiable.
29. The document of value or security element according to claim
28, wherein the defined distribution forms a code.
30. The security element according to claim 23, having a
configuration of at least one of a security thread, mottling fiber,
planchet or label.
31. The document of value according to claim 23, including a
security element according to claim 23.
Description
[0001] The invention relates to feature substances for securing the
authenticity of documents of value, methods for their production,
security elements and documents of value containing the inventive
feature substance, as well as methods for securing the authenticity
of security elements and documents of value using the inventive
feature substance. The inventive feature substances contain both at
least one luminescent substance and at least one further substance,
which is preferably magnetic or electrically conductive.
[0002] Security elements in the sense of the present invention are
elements with authenticity features applied on or integrated in a
document of value for the purpose of securing authenticity.
Documents of value within the framework of the invention are
objects such as bank notes, checks, shares, tokens, identity cards,
passports, credit cards, certificates and other documents, labels,
seals, and objects to be secured, such as for example CDs, packages
and similar. The preferred field of application is bank notes.
[0003] Securing the authenticity of documents of value by means of
luminescent substances has been known for a long time. Preferably
host lattices doped with rare earth metals are used, wherein
through a suitable adjustment of rare earth metal and host lattice
the absorption spectrum and the emission spectrum can be varied
within a large range. Also the use of magnetic and electrically
conductive materials for securing authenticity is known per se.
Magnetism, electrical conductivity and luminescence emission are
machine-detectable by commercially available measuring devices,
luminescence in the case of emission in the visible spectrum is
also visually detectable, provided that the intensity is
sufficient.
[0004] The problem that the authenticity features of the documents
of value are counterfeited is practically as old as the securing of
authenticity of documents of value. The falsification security can
for example be enhanced by not only using one feature substance,
but several feature substances in combination, for example a
luminescent substance and a magnetic substance, or a luminescent
substance and a substance influencing the luminescent
properties.
[0005] If several feature substances are to be used in combination,
the only possibility so far was to either produce a physical
mixture of the substances and to apply the mixture on the surface
of the document of value or to integrate it in the volume of the
document of value, or to apply the feature substances separately.
The separate application of the feature substances in two or more
steps is time-consuming and cumbersome. Combinations of feature
substances are therefore used primarily as mixtures. For producing
the mixtures first the individual feature substances are produced
separately, then the finished feature substances are mixed
together, usually in a dry state. In the physical mixture thus
produced the particles of the individual feature substances are in
contact with each other, but usually do not enter into any specific
interactions with each other, i. e. the feature substances can be
separated from each other again intentionally or unintentionally.
The individual feature substances are not associated with each
other in such a fashion that a product is created which can no
longer be separated into its individual components.
[0006] These mixtures have the disadvantage that during their
manufacturing process and application process a more or less strong
segregation can occur, leading to security features with differing
properties, depending on whether they were produced at the start or
at the end of a batch. Frequently segregation also takes place
during the storage of a mixture of feature substances, in
particular if storage takes place in the form of a dispersion, such
as for example a printing ink. Consequently, it has to be verified
regularly through quality checks whether segregation or partial
segregation has unintentionally led to the inhomogeneity and
uselessness of the mixture.
[0007] If feature substances are provided in the shape of a certain
pattern, for example form a luminescent coding, so far the only
possibility has been to print the feature substance or the mixture
of feature substances on the surface of a security element or of a
document of value in the shape of the desired pattern, for example
of the coding. A direct integration into the volume of a document
of value or of a security element in the form of a defined
arrangement, or the creation of a defined arrangement of the
feature substances on the surface of a document of value or of a
security element by any methods other than printing has so far been
impossible. In the production of codings an inhomogeneity of
mixtures of feature substances caused by partial segregation
represents a particularly serious problem, since it can lead to an
incorrect or unreadable coding.
[0008] It is therefore the object of the present invention to
provide a combination of feature substances having at least two
different substances forming a non-segregating system.
[0009] The combination of feature substances is to be adapted to be
provided preferably also by methods other than printing in the
shape of a pattern on or in a document of value or security
element.
[0010] It is also the object of the present invention to provide a
method for producing such a combination of feature substances.
[0011] It is furthermore the object of the present invention to
provide a method for securing the authenticity of a document of
value or security element by means of such a combination of feature
substances.
[0012] It is in addition the object of the present invention to
provide a security element or a document of value having at least
one authenticity feature on the basis of such a combination of
feature substances.
[0013] The solutions of the above objects result from the features
of the independent claims. Embodiments of the invention are
specified in the respective dependent claims.
[0014] The inventive combination of feature substances has at least
one luminescent substance, which is excitable by radiation in the
infrared and/or visible and/or ultraviolet spectrum to emit
luminescence, preferably emit fluorescence. Furthermore, the
inventive combination of feature substances has nanoparticles which
are bound to the surfaces of the luminescent substance particles by
adhesive forces. The adhesion is sufficiently strong that during
storage and processing no segregation of the luminescent substance
and the nanoparticles takes place, at least not to an extent which
interferes with the production of security features. Also during
storage in the form of a dispersion no segregation has to be
feared.
[0015] The inventive combination of feature substances consequently
represents a "composite feature substance", which is formed by at
least two different substances, but behaves like one single feature
substance. The properties of the composite feature substance
represent a combination of the properties of the luminescent
substance and the nanoparticles. Therein a "combination" can be a
mere additive combination and/or an influencing of the
properties.
[0016] The invention makes use of a phenomenon which is used
similarly for stabilizing emulsions and in suspension
polymerization.
[0017] In 1907 Pickering discovered that oil-water emulsions can be
stabilized by colloids that aggregate spontaneously on the
interfaces of the droplets. In the so-called "Pickering emulsions"
tiny solid particles act as emulsifiers, i. e. surfactant-free
emulsion systems can be produced. The solid particles arrange at
the oil-water interface and form a dense package enveloping the
droplets of the emulsion. This solid-particle network represents a
mechanical barrier preventing the coalescence of the droplets and
thus stabilizes the emulsion.
[0018] The precondition for solid particles to act as "Pickering
emulsifiers" is that the particle size is smaller than the desired
droplet size by at least factor 10, and that the solid substance is
wetted by the oil phase and the aqueous phase, but has a different
affinity to the two phases. In chemical process engineering
Pickering emulsifiers are used in suspension polymerization as
stabilizers to prevent the sticking together of the growing
suspension particles. The Pickering emulsifiers arrange at the
interface between the suspension particles and liquid phase,
envelop the suspension particles and thus prevent their
coalescence. The first precondition for the operating principle as
a Pickering emulsifier is that the emulsifier is insoluble in the
liquid phase and is substantially smaller than the suspension
particle to be stabilized. The precondition for the accumulation
process in the interface between the phases is a suitable
interaction force, i. e. adhesion between the suspension particle
to be stabilized and the Pickering emulsifier, but simultaneously
also a sufficiently good wettability of the Pickering emulsifier by
the surrounding liquid.
[0019] Surprisingly, it was now found that substances of the type
of the Pickering emulsifiers can under certain circumstances be
used for producing feature substances for securing the authenticity
of documents of value, wherein it is possible to obtain feature
substances with properties that could so far not be achieved.
[0020] According to the invention luminescent substance particles
are enveloped by nanoparticles, wherein typically a nanoparticle
monolayer is formed, in which the nanoparticles form a dense
packing. However, also a partial, preferably extensive envelope can
be sufficient. The luminescent substance particles have an average
particle size of approximately 1 to 100 .mu.m. The volumes of the
nanoparticles are smaller than the volumes of the luminescent
substance particles by at least one order of magnitude, preferably
2 to 3 orders of magnitude.
[0021] By enveloping a core of a luminescent substance particle by
nanoparticles different feature substances become one single
feature substance, consisting of a core and of an envelope.
Consequently, the inventive feature substance is actually a system
of feature substances whose properties result from the combination
of the properties of the individual components.
[0022] The luminescent substances usable for producing the
inventive feature substances are not limited in any way. Generally,
all substances, in particular luminescent substances, are suitable,
which can be exited to emission, in particular luminescence
emission, by irradiation with light in the infrared and/or visible
and/or ultraviolet spectrum. The emission or luminescence emission
takes place preferably also in the infrared and/or visible and/or
ultraviolet spectrum. The luminescent substances are preferably
fluorescent substances.
[0023] As examples for suitable luminescent substances host
lattices doped with rare earth metals, for example with ytterbium,
praseodymium, neodymium, etc., doped garnets or perovskites can be
quoted, also mineral-phosphorus compounds such as sulfides, oxides,
selenides with traces of heavy metals such as silver, copper,
manganese or europium are suitable. However, these examples
represent mere indications and are not to be understood to be
limiting in any way. Furthermore also organic luminescent
substances can be used, for example rhodamines, perylenes,
isoindolinones, quinophthalones and oxazinones. Methods for
producing the luminescent substances are known to the person
skilled in the art. Production methods are for example described in
WO 81/03508 A1. Many luminescent substances are also commercially
available, for example Paliosecure Gelb by BASF, and Cartax by
Clariant.
[0024] For forming the envelope around the luminescent substance
particles in principle all solid substances are suitable which can
be reduced to sufficiently small particles, which attach to the
luminescent substance particles in the reduced state, i. e. as
nanoparticles, and which either have feature-substance properties
themselves or at least modify the luminescent properties of the
luminescent substance.
[0025] Substances which modify the luminescent properties of the
luminescent substance are for example such substances which absorb
in certain wavelength ranges in which the luminescent substance
emits, and thus change the luminescence spectrum. An example for
such a combination is the example 9 of the above-referenced WO
81/03508 A1 as luminescent substance, and nano-scale
Fe.sub.3O.sub.4 as nanoparticle substance.
[0026] Furthermore as nanoparticles also luminescent substances can
be used, thus in principle the same substances which are suitable
also for forming the core of the inventive feature substance. A
combination of different luminescent substances results in an
overlapping luminescence spectrum.
[0027] However, preferably for the envelope of nanoparticles such
substances are used which have a machine-detectable feature
differing from the detectable feature of the core material, for
example magnetic or magnetizable substances, electrically
conductive substances and semiconductors. These substances have to
be stable in the application medium; for example nano-scale iron is
instable in water, but after wetting with water turns into an not
strictly definable magnetic oxide (nano-scale metals are as a rule
pyrophoric). When selecting the materials it has to be kept in mind
that they must not absorb strongly in spectrums which are essential
for identifying the luminescence spectrum. The luminescence
spectrum must not be influenced by the nanoparticles to an
interfering extent. The question of how strong a change may be so
as not to be regarded as an interfering influence, essentially
depends on the intended use. In some cases a change or weakening of
the luminescence spectrum and/or the absorption spectrum can
actually be desirable to render an identification more
difficult.
[0028] An example for a nanoparticle material are carbon nano tubes
(CNTs). CNTs are microscopically small tube-shaped structures of
carbon. In the walls of the tubes the carbon is sp.sup.2 hybridized
and forms a honeycomb structure like in the layers of graphite. The
diameter of the tubes is mostly in a range of 1 to 50 .mu.m, but
also smaller tubes can be produced. The length of the individual
tubes can be up to several millimeters. Several single-walled
carbon nano tubes (SWCNT) can be disposed inside each other
concentrically, so that multi-walled carbon nano tubes are given.
Depending on the exact structure, the electrical conductivity
within one tube can be metallic or semi-conducting.
[0029] CNTs are commercially available (e. g. from MER Corporation
or NanoLab Inc.) and can be reduced to the necessary dimensions by
conventional reduction procedures such as milling.
[0030] Further examples for nanoparticle materials combinable with
luminescent materials to form inventive feature substances are nano
a-iron, nano Fe.sub.3O.sub.4 and nano NiFe.sub.2O.sub.4. The
feature substances with nano .alpha.-iron, nano Fe.sub.3O.sub.4 and
with nano NiFe.sub.2O.sub.4 are luminescent and magnetic.
[0031] In the following some non-restrictive examples of
two-component combinations of a luminescent substance with nano
powders are listed. Example 9 of the above-referenced WO 81/03508
A1 as a luminescent substance, with
[0032] MWCNT (particle size 20-50 nm),
[0033] MWCNT (particle size 20-30 nm),
[0034] MWCNT (particle size 40-70 nm),
[0035] nano .alpha.-iron (APS 25 nm),
[0036] nano Fe.sub.3O.sub.4 (APS 20-30 nm), or
[0037] nano NiFe.sub.2O.sub.4 (APS 20-30 nm).
[0038] APS refers to the tube diameter of the carbon tubes. The
materials are for example available from MER Corporation.
[0039] The average particle sizes of the nano powders can be in the
range of approximately 1 to 1000 nm, wherein the optimal particle
sizes also depend on the size of the luminescent substance
particles. The luminescent substance particles typically have an
average particle size in a range of approximately 1 to 100 .mu.m,
and the nanoparticles are smaller by 1, preferably 2 to 3 orders of
magnitude. Preferred average particle sizes for the nano powders
are in a range of 1 to 500 nm, particularly preferred 10 to 100
nm.
[0040] The weight ratios of luminescent substance and nano particle
material depend on the type and the particle size of the materials.
Furthermore they depend on the exact characteristics of the desired
feature substance, i. e. whether a feature substance is required
whose luminescent substance particles are preferably optimally
surrounded by a nanoparticle envelope, whether also a partial
envelope is regarded as sufficient, or whether, if required, also
free (non-enveloped) luminescent substance particles are to be
present. If a feature substance is desired that consists of
luminescent substance particles that are preferably completely
enveloped by nanoparticles, but does not contain any free
luminescent substance particles and no free nanoparticles, the
weight ratio of the luminescent substance to the nano powder
typically lies in the range of about 1:1.
[0041] However, the weight ratios can also vary within a much
larger range, approximately from 100:1 to 1:100; preferably
approximately 5:1 to 1:3, in particular if the inventive feature
substance contains additional free luminescent substances and/or
nanoparticles. If such additives are used it has to be checked in
prior tests, whether the resulting system is stable against
segregation.
[0042] The inventive feature substance is not limited to
combinations of a type of luminescent substance with a type of
nanoparticle. Rather, two or more different luminescent substances
and/or two or more different nanoparticles can be combined with
each other. In this way it is for example possible to obtain a
luminescent substance which is also magnetic and electrically
conductive.
[0043] The detection of the combined properties of the inventive
feature substance takes place in the same way as the conventional
detection of the luminescent properties, the magnetic properties
and the electrically conductive properties of the individual
feature substances. The required spectrometers, checking devices
for luminescence or magnetism and conductivity meters are
commercially available.
[0044] The production of an inventive feature substance takes place
in a very simple manner, by adding the luminescent substance or the
luminescent substances and a material in the form of a nano powder,
or, if required, several different nano-powder materials, to a
dispersant and mixing them for such a time until a dispersion is
obtained. The dispersion can be used as such, but preferably the
feature substance is separated from the dispersion, usually by
filtering, and dried.
[0045] As dispersant preferably water is used. The source
materials, in particular the nano powder, are dispersible therein
only with difficulty, but in the course of time a growing number of
nanoparticles are bound to the surfaces of the luminescent
substance particles through adhesion, and if no surplus of
nanoparticles is present, finally a dispersion of the feature
substance is obtained, in which no nanoparticle "clusters" are
contained any more. The association of the nanoparticles to the
luminescent substance particles takes several hours. The
association is preferably carried out at room temperature, but the
temperature can also be raised slightly, however wherein a warming
only rarely results in an acceleration of the association of the
nanoparticles to the luminescent substance particles. The drying of
the feature substance filtered out of the dispersion preferably
takes place at an elevated temperature, wherein the temperature
depends on the chosen dispersant. If water is used as dispersant,
the drying preferably takes place at approximately 110.degree.
C.
[0046] In the case of filtration the dispersed nanoparticles are
not held back by conventional standard filters. They can at best be
retained by special filters. Thus, if a feature substance is to be
produced that consists of luminescent substance particles whose
surfaces are preferably fully enveloped by nanoparticles, however
wherein no free nanoparticles are to be present any more,
production can take place in a simple manner by using a substantial
surplus amount of nano powder, stirring for a sufficient time
(approximately 10 hours) and subsequently filtering. Nanoparticles
not bound to the luminescent substance particles in the form of a
coating, pass the filter or, depending on the density, float on the
surface of the dispersion, whereas the feature substance sinks and
later remains on the filter. If any nanoparticle clusters are left
in the dispersion, which are also retained by the filter, remedy is
provided by careful comminuting and washing after with dispersant
or prior skimming (e. g. in the case of specifically lighter MWCNTs
or large-volume inclusions of air of the nano-scale oxides).
[0047] The inventive feature substances are hybrid products of the
source components both regarding their properties (luminescence,
magnetism, electrical conductivity), and their appearance, such as
e. g. their color. If for example a white or transparent
luminescent substance is coated with a black or a brown nano
powder, the result is a homogeneous feature substance power of a
grey or light brown color.
[0048] The inventive feature substance is used for securing the
authenticity of documents of value or security elements.
[0049] Documents of value and security elements respectively
consist of at least one layer of a carrier material and possibly
further layers. Furthermore they have at least one authenticity
feature formed by one or several feature substances. In contrast to
a document of value, a security element is not brought into
circulation as such, but in connection with a document of value, on
which it is applied or in which it is integrated.
[0050] The inventive security elements and documents of value have
at least one authenticity feature formed by an inventive feature
substance.
[0051] Regarding its possible application, the inventive feature
substance does not differ from conventional luminescent substances.
It can for example be integrated in the volume or in partial areas
of the volume of a security element or document of value; wherein
the carrier material can consist of paper or plastic.
Alternatively, the feature substance can be provided in the form of
a coating on at least one surface or on partial areas of at least
one surface of a security element or document of value.
[0052] As a further alternative the feature substance can be
contained in a printing ink, which is printed on a security element
or document of value. The inventive feature substance is used
respectively in such concentrations that are usual for luminescent
materials in the individual application field, i. e. approximately
0.05 to 1 weight-%, if the feature substance is contained in the
volume of a paper layer, and approximately 10 to 40 weight-%, if
the feature substance is contained in a printing ink.
[0053] Security elements with the inventive feature substance are
preferably security threads, mottling fibers, planchets or labels
which are integrated in the volume of a carrier material of a value
document, or are stuck to a surface of the carrier material or a
different layer of a document of value.
[0054] To produce a security element the inventive feature
substance can for example be rubbed into a lacquer, which is then
extended to form a lacquer film and cut to a size fitting a
security element. A suitable lacquer is a polyamide lacquer, and
suitable concentrations are in a range of approximately 0.1 to 1
weight-%.
[0055] A special advantage of the inventive feature substances
becomes obvious if an inventive feature substance is to be provided
in a defined distribution, if the feature substance is to form a
code for example. In such a code, areas with a high concentration
of the feature substance alternate in a predetermined manner with
areas with a lower concentration of the feature substance, or
completely without the feature substance. The arrangement of the
areas with a high concentration of the feature substance and with a
low concentration of the feature substance (or without the feature
substance) is machine-readable. So far such codes could be produced
only by printing luminescent substances in a certain pattern. They
could not be formed directly in the volume of a document of
value.
[0056] However, the inventive feature substances have the special
characteristic that they do not only have luminescent features, but
that they are preferably also magnetic or magnetizable or
electrically conductive. In an electrical or magnetic field the
nanoparticles of the envelope of the luminescent substance
particles align with the field, and the feature substance has the
tendency to migrate within this field. The precondition for such an
alignment and possibly migration is that the surrounding medium of
the feature substance is sufficiently liquid in order to allow a
movement of the feature substance. In practice this means that the
inventive feature substance can be oriented or moved in a desired
manner within a carrier material or a printing ink by applying a
suitable magnetic or electrical field, as long as the carrier
material is still sufficiently soft or wet, or the printing ink is
still sufficiently liquid. A pattern of areas with a high
concentration of the feature substance and areas with a low
concentration of the feature substance in a paper layer can for
example be produced in that an inventive feature substance with
luminescent and magnetic properties is integrated in the humid
paper in the paper machine, while an arrangement of magnets in the
desired code pattern is arranged at the paper. The magnetic
nanoparticles of the feature substance then orient themselves in
the humid paper mass, and the feature substance particles migrate
toward the magnets, whereby they reproduce the arrangement pattern
of the magnets, thus the code. The code can be read out e. g.
spectrometrically.
[0057] In the following a general production procedure for an
inventive feature substance is specified.
[0058] 2 g of the above-mentioned example 9 of WO 81/03508 A1, and
1.5 g MWCNT nano powder are weighed out into a beaker with
approximately 50 ml water and are stirred at room temperature for
one day. At the beginning of the mixing process the nano powder
floats on top and partly forms big clusters. Once the hardly
dispersible nano powder is finely dispersed in the dispersion thus
produced, the material is filtered. The nano material does not
penetrate the filter through the filter pores. The filtered
material is dried at 110.degree. C. for example over night.
[0059] Subsequently, the thus obtained material can for example be
integrated in the production of bank note paper, e. g. at a dosage
of 0.4 weight-%.
[0060] Likewise the material can be rubbed into a polyamide lacquer
and the lacquer can be extended to form a lacquer film, wherein the
concentration of the feature substance also amounts to 0.4 weight-%
for example. The lacquer film is suitable for sticking onto bank
notes.
[0061] The authenticity of the bank note can now be verified both
by measuring the infrared luminescence and by measuring the
electrical conductivity determined by the nano powder. Of course
the authenticity can also be established by measuring both
features.
[0062] Instead of the example specified, also the nano powders
mentioned above in connection with WO 81/03508 A1 can be used.
Likewise, other luminescent substances can be used.
* * * * *