[0001] The present invention relates to a security sheet, particularly of the type that
includes an electrically conducting element.
[0002] In particular, the present invention relates to a security sheet that includes an
electrically conducting element that can be detected by virtue of means for detecting
electrical conductivity. Said security sheet, by allowing precise detection and simple
monitoring, is particularly useful in the production of security documents such as
currency bills, checks, identification documents, and credit cards.
[0003] Among electrically conducting elements conducting polymers are known which can be
roughly classified into two different groups: filled conducting polymers in which
a polymer is made conductive by the addition of a conductive filler, such as for example
carbon black, graphite, carbon fiber, metal powder, etcetera, and intrinsically conducting
polymers that are made conductive through a chemical process.
[0004] Filled conducting polymers are known since a long time; they present however certain
problems derived from the presence of the powder itself in the polymer structure.
[0005] Intrinsically conductive polymers (ICPs) are a class of molecules that was created
when it was discovered that polyacetylene could be made to conduct electricity by
"doping" (H. Shirakawa, E.J. Louis, A.G. Mac Diarmid, C.K. Chiang, A.J. Heeger, J.
Chem. Soc., Chem. Commun., 1977).
[0006] ICPs are conjugated polymers that can be obtained from the respective monomers by
virtue of normal polymerization reactions combined with, or followed by, chemical
"doping" processes, and have particular properties that consist, in particular, in
electrical conductivity. Known ICPs include polyaniline, which has high conductivity
and high environmental stability. In accordance with procedures for doping polyaniline
bases described in the literature (Y. Cao, P. Smith and A.J. Heeger, Sinth. Met. 48,
1992), the mixtures of polyanilines with conventional polymers or with their respective
copolymers (R.W. Gumbs, Sinth. Met. 64, 1994) are soluble in the commonest organic
solvents and are sufficiently stable in the melted state; therefore, their workability
with techniques used for conventional plastic polymers is easy and does not entail
difficulties.
[0007] Another specific characteristic of polyaniline is that during the production process
it is possible to preset and control, by means of the oxidation and protonation state,
the electrical properties of the polymer that is produced (E.M. Geniès, A. Boyle,
M. Capkowski, C. Tsintavis, Sinth. Met. 36 (1990); A.G. MacDiarmid, A.J. Epstein,
Faraday Discuss. Chem. Soc. 88, 1989).
[0008] Furthermore, in blends of polyaniline with the most common polymer matrices, the
percolation threshold is reached for very low polyaniline contents, on the order of
1% or even less (C.Y. Yang, Y. Cao, P. Smith, A.J. Heeger, Sinth. Met. 53, 1993).
Conductivity increases continuously as the concentration of polyaniline in the polymer
matrix increases, starting from the percolation threshold, until it reaches values
that are higher by several orders of magnitude (C. O. Yoon, M. Reghn, D. Moses, A.J.
Heeger, Y. Cao, Sinth. Met. 63, 1994). The low percolation threshold and the continuous
increase in conductivity starting from the threshold are particularly important characteristics,
since they allow to produce, in a reproducible and controlled manner, conducting composites
having electrical properties whose values can vary and can be preset over a wide range,
and they also allow to obtain, for said blends, excellent mechanical properties that
are very similar to those of the polymer that acts as matrix.
[0009] Recent studies on the response of conducting polyanilines to microwaves have shown
their metallic nature (A.G. Mac Diarmid et al., Phys. Rev. B. Condens Matter, 49,
1994). The magnetic properties of some aniline copolymers have been described in applications
no. EP 0 545 819 and EP-A-0 680 989.
[0010] It is known that security devices based on the properties of metals have been used
in security documents and particularly in currency bills in various forms and manners.
For example, CH-PS 472 081 describes how to provide currency bills with metal security
threads. Anti-forgery systems for currency bills are also known which insert a surface-metallized
plastic strip or thread in the bill paper. Metallization has been restricted, in practice,
to aluminum, since in this case the process for the evaporation and deposition of
the metal on the plastics is easy and relatively inexpensive, whereas other metals
require the use of sophisticated and expensive techniques and facilities, since it
is necessary to work in high vacuum.
[0011] This limitation entails a severe drawback from the security point of view, since
plastic films coated with aluminum having a thickness that is fully similar to that
of the threads that are inserted in currency bills are commonly commercially available
and have a wide range of uses for everyday requirements. Therefore, the validity of
this type of security device is very low. Furthermore, due to the stretching that
the strip undergoes during the process for inserting it in the paper, and due to the
stresses to which the currency bill can be subjected during its life, the aluminum
layer that coats the strip may crack, interrupting electrical conduction and losing
detectability.
[0012] It is also known that the inclusion of metallic fibers in a sheet of paper composed
of cellulose fibers entails problems due to the difficulty in dispersing the metallic
fibers in the fibrous mix because of their high relative density. Another drawback
is that once the metallic fibers have been inserted in the paper, they tend, under
the effect of mechanical stresses and most of all of repeated folding, as in the case
of bill paper, to cause micro-cracks in the paper and are sometimes expelled from
the fibrous structure. Furthermore, the process for producing said fibers is not simple,
since their diameter cannot in practice be greater than approximately ten microns
and this of course entails the use of highly sophisticated, complicated, and expensive
techniques.
[0013] Metallic pigments of various kinds are also known which can be included in printing
ink varnishes. In particular, copperplate-printing inks containing metallic pigments
constituted by iron particles in the form of microspheres have been used to print
security documents and currency bills.
[0014] However, the use of these pigments in copperplate-printing inks entails drawbacks;
their considerable abrasiveness affects the life of the PVC rollers that remove from
the printing plate the excess ink that is present outside the engravings after the
inking step. Furthermore, since the copperplate printing unit requires a system for
treating the waste, which is constituted by a watery sludge of excess ink, the presence
of iron pigments causes early wear of the components of the facility, particularly
the pumps and the critical parts of the piping.
[0015] The iron pigment can react with the acid components of the varnish of the ink and,
in the presence of condensation water, can produce gaseous hydrogen inside the container.
[0016] A principal aim of the present invention is to avoid or substantially reduce the
above described drawbacks.
[0017] It is an object of the present invention to provide a security sheet whose properties
can be easily detected and monitored so as to make it particularly difficult to forge.
[0018] It is another object to provide a sheet made of cellulose fibers (paper) that includes
an anti-forgery system that has the form of a security thread and allows precise detection
and simple monitoring by using detector devices.
[0019] Another object is to provide an ink that is adapted for the copperplate printing
of valued paper and security documents, constitutes a sophisticated anti-forgery system
and is not abrasive for printing machine rollers.
[0020] It is still another object to provide an ink which, once printed, is easily detectable
with the use of conventional detector means and at the same time ensures a high level
of security for the sheets to which it is applied.
[0021] With the foregoing and other objects in view, which will become apparent hereinafter,
there is provided, in accordance with the present invention, a security sheet comprising
a supporting matrix and an intrinsically conductive polymer.
[0022] The expression "support matrix", or "substrate", refers to matrices that are conventionally
used as basic material in the production of security sheets and documents, i.e., of
documents that include an anti-forgery system.
[0023] The expression "security sheets" refers to sheets used as base to produce currency
bills, checks, shares, identification documents such as ID cards, passports, credit
cards, restricted-area passes, and all documents used in everyday life that require
an anti-forgery system.
[0024] According to an aspect of the present invention, said support matrix is a structure
made of natural or synthetic fibers preferably chosen from the group including cellulose
fibers and synthetic fibers, and is preferably constituted by synthetic polymers.
[0025] According to a preferred embodiment of the present invention, said support matrix
consists of paper based of cellulose fibers, for example of the type that is commonly
used in the production of currency bills.
[0026] The security sheet according to the present invention can also comprise additives,
such as for example fillers, impregnating agents, and other agents known in the art
of making paper and derived products.
[0027] According to another aspect of the invention, said support matrix is a thermoplastic
polymer, preferably chosen from the group comprising polyester, polyvinyl chloride,
polyvinyl acetate, polyethylene, ABS, polystyrene, polycarbonate, polymethyl methacrylate,
polyethylene glycol, and mixtures thereof, polyester being the most preferred one.
[0028] Preferably, said intrinsically conductive polymer is chosen from the group comprising
polyaniline, polypyrrole, polythiophene, polyphenylene vinylidene, polydiphenylamine,
in substituted and unsubstituted forms, polyaniline being the most preferred one.
[0029] More preferably, the intrinsically conductive polymers of the invention are polymers
or copolymers whose relative molecular mass is such that they can form films or fibers,
derived from the polymerization of substituted or unsubstituted anilines, in positions
and with radicals of a known type, as described for example for polyaniline in WO
92/22911.
[0030] The intrinsically conductive polymers used in the invention also advantageously have
a relative molecular mass of more than 10,000.
[0031] According to one embodiment, said intrinsically conductive polymers are present in
the form of a blend with a conventional thermoplastic polymer.
[0032] Intrinsically conductive polymers produce, together with thermoplastic polymers,
blends that have high conductivity even at low concentrations of the conducting polymer-dopant
species. The high conductivity of the polymer blend that comprises the intrinsically
conductive polymers according to the invention indicates that said conductive polymers
are advantageously present as a continuous phase rather than as a phase of disperse
particles.
[0033] Furthermore, the thermoplastic polymer/intrinsically conductive polymer blend has
good mechanical and workability properties that can be likened to those of the thermoplastic
polymer.
[0034] The amount of conductive polymer that is present is preferably between 0.1% and 40%
by weight, more preferably between 0.5% and 20% by weight, even more preferably between
1% and 5% by weight, with respect to the weight of the thermoplastic polymer.
[0035] The conductivity of said thermoplastic polymer/intrinsically conductive polymer blend
can be advantageously varied over a wide range and is advantageously between 10
-8 and 10 S.cm
-1, more preferably between 10
-5 S.cm
-1 and 10 S.cm
-1, and even more preferably between 10
-3 S.cm
-1 and 1 S.cm
-1, as a function of the amount of intrinsically conductive polymer which is present
in the blend.
[0036] According to the present invention, the use of intrinsically conductive polymers
allows to provide different conductivity values and therefore allows to provide unequivocal
information for detection of the document and selective recognition thereof according
to the specific conductivity value of the polymer included therein, by using conventional
detector device that are described hereinafter.
[0037] According to one embodiment, the sheet according to the present invention comprises
a support matrix made of cellulose fibers and a security thread which is constituted
by a intrinsically conductive polymer/thermoplastic polymer blend of the type described
above, included in said support matrix.
[0038] The security thread according to the present embodiment has conductive properties
and high resistance to mechanical traction, and can be detected, as regards electrical
conductivity, by virtue of conventional means used for detecting metallic threads
inserted in paper, as described for example in EP-0 057 972.
[0039] Generally, said thread has a thickness between 10 and 50 microns.
[0040] In this manner, one obtains a security thread or strip that does not have a metallic
appearance and therefore, differently from what occurs for metallized threads, does
not clearly indicate its conductive properties to the ordinary user.
[0041] Furthermore, when the intrinsically conductive polymer is constituted by polyaniline,
said security thread is transparent or semitransparent and allows, by applying printing
ink, to produce symbols, images and the like that can be perceived against the light.
[0042] The transparency of the thread varies according to the content of polyaniline and
of the thermoplastic polymer used as host-matrix. Higher transparency values are obtained
with polymethyl methacrylate and polystyrene.
[0043] In particular, the use of a blend with a polyaniline content between 0.1% and 40%
by weight with respect to the matrix of thermoplastic polymer advantageously allows
to obtain transparency values in the range between 25% and 95%, whereas by using polyaniline
values between 0.5% and 20% one obtains transparency values between 60% and 85%.
[0044] According to another embodiment, the security thread or strip comprises a support
matrix made of thermoplastic polymeric material, which advantageously consists of
polyester, on which a continuous or discontinuous layer of an intrinsically conductive
polymer of the above described type is deposited. Preferably, said intrinsically conductive
polymer is in the form of a dispersion in a compatible vehicle.
[0045] Said vehicle is constituted by a medium or binder in which the intrinsically conductive
polymer can be dissolved or dispersed and is advantageously a polymer, preferably
of the acrylic type; the concentration of said intrinsically conductive polymer being
preferably between 1% and 40% by weight with respect to the weight of the binder.
[0046] In particular, the non-conductive thermoplastic polymeric material has a continuous
or discontinuous covering layer that is constituted by an intrinsically conductive
polymer, preferably polyaniline dispersed on a binder, with a thickness between 1
and 10 µm, more preferably between 1.5 and 5 µm. At this covering layer, one advantageously
has transparency values between 25% and 95%, more preferably between 60% and 85%.
[0047] By way of an example, mention is made of the product Incoblend 991762/43 by Zipperling
Kessler & Co. of Ahrensburg, in which the intrinsically conductive polyaniline (Versicon™
- 40-45% concentration) is in dispersed form in an acrylic polymer (lacquer). This
product is used in various solvents at concentrations, with respect to the solids
content, between 5% and 7.5%, so as to obtain deposits that have a surface resistance
between 10
3 and 10
5 ohm and a specific conductivity between 5 and 30 S/cm. Furthermore, by applying a
layer of approximately 2 microns it is possible to obtain a transparency value close
to 80%.
[0048] The deposition of an intrinsically conductive polymer dispersed in an appropriate
vehicle on a support matrix can be achieved by spreading with conventional means,
for example by spraying, followed by evaporation of the solvent, or by means of a
printing process.
[0049] Advantageously, said security thread or strip can be produced with various controlled
conductivity values, so as to allow its selective recognition on the basis of the
specific conductivity value of the intrinsically conductive polymer deposited on said
strip.
[0050] The conductivity values vary generally over a wide range between 10
-8 and 10 S.cm
-1. By way of example, by using polyaniline the conductivity values are between 10
-5 S.cm
-1 and 5 S.cm
-1, preferably between 10
-3 S.cm
-1 and 1 S.cm
-1, as a function of the amount of intrinsically conductive polymer that is present.
[0051] When said conductive polymer is constituted by polyaniline, it has a green coloring
that can be modified by adding dyes or fluorescent substances without compromising
the transparency and conductivity of the film.
[0052] Furthermore, on said strip/thread it is advantageously possible to apply continuous
or discontinuous deposits of magnetic materials, such as iron oxide, or other material
that can be detected by means of a magnet-resistor unit, such as iron powder. An application
of this type is described for example in EP 0 310 707.
[0053] Advantageously, these materials are applied in such a manner as to leave continuous
regions exposed along the strip of thermoplastic polymer, so as to allow to detect
conductivity and a characteristic that is visible against the light. Furthermore,
said strip/thread can include regions that are covered by a printing ink so as to
form portions (symbols or images) that can be detected visually against the light.
[0054] Further characteristics and advantages will become apparent from the description
of three preferred but not exclusive embodiments of security threads or strips included
in the sheet according to the invention, illustrated only by way of non-limitative
example in the accompanying drawings, wherein:
figure 1 is a schematic top view of a thread provided to the security paper of the
present invention;
figure 2 is another schematic top view of a security thread according to the present
invention;
figure 3 is a further schematic top view of a thread provided to the security paper
of the invention.
[0055] With reference to the above decribed figures, figure 1 is a view of a security thread
constitued by a support matrix made of nonconductive transparent polymeric material
(polyester) 1, on the surface whereof there is a continuous layer of intrinsically
conductive polymer (polyaniline) 2 and a magnetic material 3 deposited thereon so
as to form transversal bands.
[0056] Figure 2 is a view of a security thread constitued by a support matrix made of nonconductive
transparent polymeric material (polyester) 10, on the surface whereof there is a continuous
layer of intrinsically conductive polymer (polyaniline or polypyrrole) 20, and a magnetic
material 30 deposited thereon so as to form two longitudinal bands.
[0057] In the two-digit numbering that is used, the first digit corresponds to the single-digit
numbering used in figure 1 in order to indicate corresponding components.
[0058] Figure 3 illustrates a security thread that is constitued by a support matrix made
of nonconductive transparent polymeric material (polyester) 100, on the surface of
which there is a coloured layer of intrinsically conductive polymer (polyaniline)
200, applied by a printing method, for example rotogravure, so as to form in the regions
not covered by the coloured layer images like symbols 100', or letters 100'', allowing
thus to detect a characteristic that is visible against the light. On said layer a
magnetic material 300 is applied so as to form two longitudinal bands.
[0059] In the three-digit numbering that is used, the first digit corresponds to the single-digit
numbering used in figure 1 and to the first digit of the two-digit numbering used
in figure 2 in order to indicate corresponding components.
[0060] According to another embodiment, said intrinsically conductive polymers or blends
thereof with thermoplastic polymers are present in the form of fibers dispersed in
the support matrix, which is advantageously constituted by paper.
[0061] Said fibers are preferably between 1 and 20 mm long and their diameter advantageously
varies between 3 and 30 µm.
[0062] Said intrinsically conductive polymers and their blends with thermoplastic polymers
have a relative density that is advantageously between 1.4 and 1.5 g/ml, which corresponds
to a fraction of the relative density of metals.
[0063] A significant advantage with respect to the use of metallic fibers is constituted
by the fact that these values are similar to those of the cellulose fibers used in
the production of paper, facilitating the uniform and easy dispersion of said conductive
fibers in the mix without having to provide particular technical refinements.
[0064] It has been observed that said fibers constituted by blends of intrinsically conductive
polymers and thermoplastic polymers have the main properties of metallic fibers, such
as electrical conductivity and the ability to absorb electromagnetic waves. Furthermore,
when polyaniline is used in a blend with thermoplastic polymers (for example polystyrene,
polycarbonate, methyl methacrylate...), other properties, such as coloring and transparency,
have been observed which make the fibers detectable by using commonly employed detection
methods.
[0065] In particular, it is possible to detect microwave absorption ability with a device
that is commonly used in detection technology (according to the ASTM D4935-89 standard
method) and comprises a source of electromagnetic waves, to which the sheet according
to the invention is exposed through a tube that acts as waveguide, and a detector
that measures the amount of radiation transmitted by the sheet, which is preferably
made of cellulose. Electrical conductivity can be measured by measuring surface resistivity
with a device that has two electrodes that rest, according to a specific geometrical
arrangement, on the surface of the sheet (according to the ASTM D4496-87 method).
[0066] Said intrinsically conductive polymer, which is advantageously in fiber form, can
be treated, with particular reference to polyaniline blended with at least one thermoplastic
polymer, so as to vary the optical properties, modifying its transparency, color,
and fluorescence. Furthermore, by varying the amount of doping of the conductive polymer
and therefore its electrical properties, it is possible to vary the response of the
microwave absorption signal that can be detected for document identification.
[0067] The sheet according to the invention therefore has a high security value, allowing
to assign an unequivocal identification for its recognition by means of an adapted
device, differently from techniques that entail the use of metallic fibers, which
produce a standard response for a given content of fibers in the paper.
[0068] Furthermore, the intrinsically conductive polymer can be advantageously deposited
in a controlled manner, i.e., in preset and limited regions of the sheet, with preset
concentrations.
[0069] According to an aspect of the present invention, said intrinsically conductive polymer
in fiber form is included on the surface of the support matrix, preferably so as to
form straight bands or stripes.
[0070] The inclusion of the conductive polymer fibers in regions of the surface of the sheet
is performed by means of methods that are known in the art, for example by depositing
said fibers from an aqueous disperse system on a portion of the sheet in the wet section
of conventional paper-making machine.
[0071] According to a particular embodiment of the invention, particles of a film of intrinsically
conductive polymer blended with a thermoplastic polymer are deposited on the surface
of the support matrix, for example in a circular or hexagonal shape (so-called "planchettes").
In order to facilitate the dispersion of said particles in the water and their subsequent
adhesion to the sheet, it is possible to apply a synthetic lacquer, preferably of
the vinyl type, to the film of conductive polymer from which said particles are obtained;
said lacquer increases the wettability of said particles and develops, during the
drying of the sheet, a sufficient heat-sealing property, as described for example
in EP-A-0 544 917. Since the particles have the properties of electrical conduction
and microwave absorption, detection is possible with conventional means of the previously
described type.
[0072] According to another aspect of the present invention, an intrinsically conductive
polymer in powder form is embedded in said support matrix, which is advantageously
constituted by cellulose fibers.
[0073] Advantageously, the intrinsically conductive polymeric component in powder form is
blended with fillers of the type used commonly in the paper-making process. Preferably,
the sheet of paper comprising the intrinsically conductive polymer is interposed,
by virtue of conventional methods, between two sheets of paper that do not contain
the conductive polymer.
[0074] According to another aspect of the present invention, said intrinsically conductive
polymer is included as powder in a printing ink for detection with conventional means.
For this purpose, one preferably uses polyaniline in powder form, dispersed in varnishes
of inks commonly used in printing processes, such as for example copperplate printing,
which is a technique of prevailing importance in the printing of security documents
and in particular of currency bills.
[0075] According to yet another embodiment, said intrinsically conductive polymer, which
is preferably constituted by polyaniline, is blended in solution or in the melted
state with conventional polymers and receives the addition of dyes that allow to give
the resulting conductive powder a wide range of colorings and fluorescence characteristics.
[0076] Said conductive polymer, which is advantageously constituted by polyaniline, preferably
blended with dyes, is dispersed in powder form in the varnishes of printing inks at
concentrations preferably between 1% and 30% by weight with respect to said ink. The
particle size of the powder of said conductive polymer is preferably in the range
between 0.5 and 10 µm, more preferably between 1 and 2.5 µm.
[0077] The following examples are provided as further illustration of the present invention
and must not be understood to limit the scope of the invention as defined in the accompanying
claims.
Example 1
[0078] Films of polymeric blends constituted by blends of conductive polyaniline and conventional
thermoplastic polymers (polystyrene, polyethylene, polyesters, nylon, and the like)
are prepared by using conventional extrusion techniques, starting from the dissolved
or melted polymeric composite. The polyaniline fraction in the composite varies between
1% and 40% and the composite correspondingly assumes values between 10
-8 and 10 S.cm
-1. A film with a thickness of 25 µm, obtained from a blend that contains a 2% fraction
of conductive polyaniline, has a surface resistivity of 5.10
2 ohm/square and has remarkable transparency (65%). The transparency and color of the
film vary according to the polyaniline content and as a function of the thermoplastic
polymer used as matrix. Higher transparency values (70-85%) are obtained with polymethyl
methacrylate and polystyrene. The film thus obtained is cut into a strip that is 1.2
mm wide and said strip is embedded in a paper sheet with conventional methods.
Example 2
[0079] A 20-µm film or thread of polyester is covered with layers of varying thickness of
conductive composite (example 1), according to the data listed in Tables 1, 2, and
3. The conductive composite was applied by spreading lacquers containing polyaniline
with a vehicle, followed by evaporation of the solvent.
[0080] Two types of disperse systems (lacquers) of Versicon™ polyaniline in an acrylic binder,
produced by the company Zipperling Kessler & Co under the trade names Incoblend Lacquer
910002 and 9100016/43, were used.
[0081] The application of layers of 2 and 3 microns of Incoblend Lacquer 910002 has yielded
highly encouraging results, obtaining significant surface resistance values on the
order of 10
4 ohm together with good transparency of the film and good adhesion; furthermore, no
interruptions were found after a 50% elongation of the support polyester film. The
polyester film covered by the layer of conductive polymer was cut into a strip 1.2
mm wide, which was included in a currency bill paper with conventional methods.
TABLE 1
TYPE |
910016/43 |
910002 |
Thickness |
2 microns |
< 1 micron |
Plasticity |
breakage < 10% |
50% elongation without fractures |
Adhesion |
insufficient |
OK |
Surface Resistance |
1100 kohm |
860 kohm |
Densitometric value |
180 |
125 |
TABLE 2
TYPE |
910016/43 |
910002 |
Thickness |
7 microns |
2 microns |
Plasticity |
breakage < 10% |
50% elongation without fractures |
Adhesion |
insufficient |
OK |
Surface Resistance |
290 kohm |
83 kohm |
Densitometric value |
420 |
490 |
TABLE 3
TYPE |
910016/43 |
910002 |
Thickness |
10 microns |
3 microns |
Plasticity |
breakage < 10% |
50% elongation without fractures |
Adhesion |
insufficient |
OK |
Surface Resistance |
260 kohm |
56 kohm |
Densitometric value |
600 |
670 |
Example 3
[0082] A wire with a diameter of 20 µm, having a conductivity of 1.10
-1 S.cm
-1, is obtained from a solution of a blend that contains 2% polyaniline in polymethyl
methacrylate. The wire is cut so as to obtain fibers that are approximately 5 mm long.
The fibers are then dispersed in a mix of cellulose fibers until a 5% concentration
by weight is obtained. A sheet of paper having an average surface resistivity on the
order of 10
8 ohm/square is formed from the mix thus obtained.
Example 4
[0083] A powder of a conductive polymer based on polyaniline is finely ground until an average
particle size of approximately 1 µm is obtained. The relative density of the powder
is 1.4 g/cu cm and the conductivity is 10 S.cm
-1. The powder is then dispersed, by using techniques that are commonly used in the
production of printing inks, in a varnish for copperplate-printing inks, in such amounts
as to constitute 20% by weight with respect to the produced ink. A typical varnish
for copperplate-printing inks in paste form contains: 20% to 40% of unsaturated oleo-resinous
compounds that can polymerize due to oxidation reactions; 10% to 40% extenders such
as calcium carbonate, barium sulfate, titanium oxide, aluminum silicates; 15% to 30%
organic solvents constituted by a mixture of hydrocarbon mineral oils with a boiling
range up to 300
oC, glycol ethers, and small amounts of specific additives.
Example 5
[0084] The conductive polymer powder of Example 4 is dispersed in varnishes used to produce
letterpress, lithography, screen-printing, and rotogravure inks so as to thus obtain
the respective inks.
[0085] Where technical features mentioned in any claim are followed by reference signs,
those reference signs have been included for the sole purpose of increasing the intelligibility
of the claims and accordingly, such reference signs do not have any limiting effect
on the interpretation of each element identified by way of example by such reference
signs.
1. Security sheet comprising a support matrix and an intrinsically conductive polymer.
2. Sheet according to claim 1, characterized in that said intrinsically conductive polymer
is chosen from the group comprising polyaniline, polypyrrole, polythiophene, polyphenylene
vinylidene, polydiphenylamine, in substituted and unsubstituted form, and mixtures
thereof.
3. Sheet according to claim 2, characterized in that said intrinsically conductive polymer
is polyaniline.
4. Sheet according to any one of claims 1 to 3, characterized in that said intrinsically
conductive polymer is blended with a thermoplastic polymer.
5. Sheet according to any one of claims 1 to 4, characterized in that said support matrix
is a fiber structure.
6. Sheet according to claim 5, characterized in that said fiber structure is chosen from
the group comprising cellulose fibers, synthetic polymer fibers, and mixtures thereof.
7. Sheet according to claim 6, characterized in that said support matrix is constituted
by cellulose fibers.
8. Sheet according to any one of claims 1 to 4, characterized in that said support matrix
is a thermoplastic polymer.
9. Sheet according to claim 8, characterized in that said thermoplastic polymer is chosen
from the group comprising polyester, polyethylene, polyvinyl acetate, polyvinyl chloride,
ABS, and mixtures thereof.
10. Sheet according to any one of claims 1 to 9, characterized in that said intrinsically
conductive polymer is shaped as a security thread.
11. Security sheet, comprising a support matrix made of cellulose fibers and a security
thread including a blend of a thermoplastic polymer with an intrinsically conductive
polymer.
12. Sheet according to claim 11, characterized in that said thermoplastic polymer consists
of polyester.
13. Sheet according to claim 11 or 12, characterized in that said intrinsically conductive
polymer is polyaniline.
14. Sheet according to claim 13, characterized in that said polyaniline is present, in
said blend, in an amount between 0.1% and 40% by weight with respect to the weight
of the thermoplastic polymer.
15. Sheet according to claim 11, characterized in that said blend has conductivity values
between 10-8 and 10 S.cm-1.
16. Sheet according to claim 11, characterized in that said blend has transparency values
between 25% and 95%.
17. Security sheet comprising a support matrix made of cellulose fibers and a security
thread including a polyester layer on which there is a layer of intrinsically conductive
polymer blended with a compatible binder.
18. Sheet according to claim 17, characterized in that said intrinsically conductive polymer
is polyaniline.
19. Sheet according to claim 17 or 18, characterized in that said binder is of the acrylic
type.
20. Sheet according to any one of claims 17 to 19, characterized in that said intrinsically
conductive polymer is present in a layer whose thickness is between 1 and 10 microns.
21. Sheet according to any one of claims 17 to 20, characterized in that said intrinsically
conductive polymer is present in an amount between 1% and 40% by weight with respect
to said binder.
22. Sheet according to any one of claims 17 to 21, characterized in that said security
thread has transparency values between 25% and 95%.
23. Sheet according to any one of claims 11 to 22, characterized in that said security
thread also comprises a magnetic material.
24. Sheet according to claim 23, characterized in that said magnetic material is applied
discontinuously.
25. Sheet according to any one of claims 11 to 24, characterized in that said thread comprises
regions that are covered with printing ink so as to form portions that can be perceived
visually against the light.
26. Sheet according to any one of claims 11 to 25, characterized in that said security
thread has a thickness between 10 and 50 µm.
27. Sheet according to any one of claims 1 to 9, characterized in that said intrinsically
conductive polymer is in the form of fibers dispersed in said support matrix.
28. Sheet according to claim 27, characterized in that said intrinsically conductive polymer
fibers are localized in limited regions of the surface of said support matrix.
29. Sheet according to claim 27, characterized in that said intrisically conductive polymer
fibers have a length between 1 and 20 mm and a diameter between 3 and 30 µm.
30. Sheet according to any one of claims 1 to 9, characterized in that said conductive
polymer is applied to the support as security ink by means of a printing method.
31. Sheet according to claim 30, characterized in that said intrinsically conductive polymer
included in a security ink is applied to the support by copperplate printing.
32. Sheet according to any one of claims 1 to 9, characterized in that said support matrix
is made of polyester and said electrically conductive polymer is applied by screen
printing.
33. Use of an intrinsically conductive polymer to produce a security sheet having conductive
properties that can be detected by virtue of electrical conductivity detection means.
34. Use according to claim 33, characterized in that said intrinsically conductive polymer
is chosen from the group that comprises polyaniline, polythiophene, polypyrrole, polyphenylene
vinylidene, polydiphenylamine, in substituted or unsubstituted form, and blends thereof.
35. Use according to claim 34, characterized in that said intrinsically conductive polymer
is polyaniline.