EP3529416B1 - Security substrate - Google Patents

Description

The present invention relates to security substrates and their manufacturing methods.

A security substrate is a substrate used in the manufacture of secure documents, protected against counterfeiting by means that make it difficult for them to be reproduced or falsified by counterfeiters.

The invention applies to paper substrates, for example intended for the manufacture of banknotes, as well as to plastic substrates, used in particular in the manufacture of banknotes, of security elements such as security threads, films or foils.

The invention is more particularly interested in giving the substrate a specific signature in the infrared (IR), this signature making it possible to authenticate, or even identify, the substrate by comparison with a reference signature.

It is already well known to use security means exhibiting a specific response in the IR.

In particular, it has been proposed in the patent application EP 1790701 to use an intaglio printing ink that absorbs in the IR selectively at particular wavelengths. The detection can be carried out by reflection on the surface of the support printed with such an ink.

Requirement JP 2010084079 also discloses an IR-absorbent ink based on tin oxide doped with antimony and / or indium oxide doped with tin. The use of these substantially colorless materials allows better compatibility with the colored pigments used elsewhere to give the ink the desired color. Here again, the detection can be carried out by reflection.

Requirement KR10-1131145 discloses a security paper comprising an IR absorbent substance. This application aims to overcome the coloring problems encountered during the use of certain known substances which absorb in the IR, and proposes materials of white or opaline color based on alkali, alkaline earth or transition metals.

Requirement WO 2012/103578 discloses a security material comprising a transparent polymeric carrier medium having IR absorbing nanoparticles dispersed in the medium.

Requirement WO 2007/132214 discloses a composition comprising an ink and an IR absorbent material.

WO 00/32700 discloses a papermaking filler or coating derived from a hydrated clay having a metal oxide and / or a precursor of a metal oxide of a poor metal aggregated with the clay.

The invention aims to further improve the security of the substrates in order in particular to confer a signature, preferably unitary, in the IR detectable by machine in transmission, while preserving the optical properties of whiteness and opacity of the substrate when the latter is a paper maker, and intended for example for the manufacture of banknotes.

The term “unitary signature” should be understood to mean a signature associated in a one-to-one manner with a given substrate; for example the substrate used for the manufacture of all the banknotes corresponding to the same denomination has the same signature. In another example, all the banknotes issued by the same central bank have the same signature, regardless of the value of the denominations.

The invention achieves this objective by virtue of a paper security substrate according to claim 1.

The poor metal can be in the ionic (salt), molecular (oxide, in particular SnO ₂ ) doped or not, or atomic (dopant, in particular Al or Ga) form. The term “poor metal” denotes a metal chosen from the group consisting of aluminum, bismuth, tin, gallium, indium, lead, polonium and thallium, the latter two metals however not being. favorite.

Said oxide or metal oxide salt is preferably respectively an oxide or an oxide salt of a transition metal or of a metalloid.

Preferably, the feed comprises SiO ₂ or TiO ₂ as metal oxide and Sn as poor metal. The size of the particles of the filler is preferably between 0.2 and 5 μm, preferably being less than 1 μm and / or greater than 0.5 μm. The shape of the filler particles can be spherical, platelet or needle-like.

Preferably, the particles of the filler have a core made of TiO ₂ or SiO ₂ covered with tin oxide doped with antimony.

The invention makes it possible, depending on the particulate system used, to have a spectral signature in the unitary IR, readable in transmission over the entire substrate, due to the mass incorporation during its manufacture. By "IR" is meant the infrared in the spectral band 700nm - 1500nm. The invention also offers the advantage, through detection in transmission, of avoiding jamming the responses of other security elements detected in reflection. In addition, the detection can be carried out according to the invention in unprinted areas, which offers additional security compared to an ink absorbing in the IR and detected in reflection.

The invention also makes it possible, if desired, to dispense with the use of certain conventional paper fillers such as titanium dioxide, kaolin or calcium carbonate, or to reduce the content thereof, while at the same time achieving the optical properties of whiteness and opacity usually desired in the manufacture of paper for banknotes in particular. The substrate can thus comprise less than 4% by dry weight of TiO ₂ in the form of TiO ₂ particles, relative to the total dry weight of the substrate, better still being completely devoid of TiO ₂ in the form of TiO ₂ particles. The substrate may comprise less than 4% by dry weight of kaolin or of calcium carbonate relative to the total dry weight of the substrate.

Another advantage of the present invention is to provide electro-conductivity to the substrate, which can give it a specific electrical signature and help dissipate electrostatic charges in the event of the presence of large areas of plastic material, in particular during storage. 'joint use with a paper substrate of at least one plastic element such as a wide security thread, a lamination strip, a foil or a film, in particular in the case of a paper / plastic hybrid ticket.

Particulate system

The term “filler” should be understood to mean a compound introduced in the particulate state into the rest of the substrate, and which remains in the particulate state.

The particulate system can comprise or consist of a mixture of at least one filler consisting of at least one metal oxide or metal oxide salt, in particular a mica, and at least one lean metal in ionic, molecular form. , or atomic.

The particulate system can also comprise or be constituted by a filler consisting of at least one metal oxide or metal oxide salt, in particular a mica, and at least one lean metal in ionic, molecular or atomic form.

It is in particular a filler of the core-shell type comprising a core consisting of said metal oxide or metal oxide salt and a shell consisting of said poor metal in ionic, molecular or atomic form, preferably in molecular form.

According to one variant, it is a doped load, said metal oxide or metal oxide salt being doped with said lean metal in atomic form.

The metal oxide is chosen from TiO ₂ , ZnO, ZrO ₂ , CeO ₂ , SiO ₂ , Al ₂ O ₃ , mica, talc and their mixtures. The metal oxide may in particular have a refractive index greater than 1.8 (TiO ₂ , ZnO, etc.) or less than 1.8 (SiO ₂ , Al ₂ O ₃ , etc.) allowing for example to have a colorless filler which does not modify the optical properties of a papermaking substrate.

The doped poor metal metal oxide is doped with metalloids or poor metals, in particular with antimony, aluminum or germanium. Depending on the poor metals and metalloids chosen, the infrared absorption can be modified and thus obtain a different spectral response, to make it specific to each substrate if desired.

The poor metal can be in the form of tin oxide.

The doped poor metal metal oxide, on the one hand, and the metal oxide or the metal oxide salt, in particular a mica, on the other hand, can respectively constitute the shell and the core of a pigment to core bark structure. The heart can be hollow.

The particulate system may consist of particles with a maximum size less than or equal to 100 μm, preferably less than 60 μm.

The particulate system may consist of particles of number-average size D50 less than or equal to 10 μm, preferably 5 μm.

The particulate system may consist of particles of number-average size D50 less than or equal to 1 μm, preferably 0.5 μm.

The particulate system may consist of particles with a maximum size less than or equal to 5 μm, preferably less than 1 μm. The particulate system may consist of particles with a minimum size greater than or equal to 0.2 μm, preferably 0.5 μm.

The particulate system can comprise and / or be made up of spherical particles. As a variant, the particulate system can comprise and / or be made up of needle-like and / or platelet particles, which offers the advantage of increasing the specific surface.

The particulate system may comprise a single doped metal oxide or, alternatively, several doped metal oxides.

The particulate system can be substantially white and opaque to visible light, or alternatively be transparent.

The substrate preferably comprises between 0.1 and 20% by mass, relative to the total mass of the finished dry substrate, of said particulate system, better between 0.2 and 5, even better between 0.5 and 2.5% .

Preferably, the amount of said particulate system is adjusted so as not to darken the substrate unduly, giving it a grayish appearance.

Substrate

The substrate can be paper. The substrate may in particular be suitable for the manufacture of banknotes. The substrate can be watermarked. The substrate can also be non-fibrous. The substrate, when a papermaker, can comprise natural and / or synthetic fibers. In the case in particular of a substrate for banknotes, the latter may comprise flax fibers and / or cotton fibers, in particular cotton linters.

The substrate can be made of plastic, that is to say polymeric material, in particular of polyethylene terephthalate (PET), polycarbonate (PC), polypropylene (PP) or polyethylene (PE). The plastic can be extruded or co-extruded with the particulate system.

A further subject of the invention is a security document comprising a substrate according to the invention, in particular a bank note.

A subject of the invention is also a thread, a film, a lamination strip or a security foil comprising a substrate according to the invention.

Examples Samples made

Paper samples are made using a paper machine from a fiber composition 100% cotton linters.
The particulate system for samples according to the invention is introduced into the fiber dispersion 100% cotton linters before papermaking.

References :

_{TiO 2} pigment content (dry / dry fibers) Paper weight (g / m ² ) TO 5% 75 B 5% 115

Particulate systems tested (paper weight = 75g / m ² ).

Testing Oxide / Oxide salt Poor Metal Doping Size (µm) Pigment content (dry / dry fibers) Pigments shape 1 SiO ₂ Sn YES 3 2.5% Spherical 2 TiO ₂ Sn YES 0.3 2% Spherical 3 TiO ₂ Sn YES 0.3 2% Acicular 4 Mica - SiO ₂ Sn YES 10-15 2% Platelet / Spherical 5 Mica - TiO ₂ - ZrO ₂ Sn NO 10-60 5% Platelet 6 Mica - TiO ₂ - ZrO ₂ Sn NO 5-25 5% Platelet 7 SiO ₂ Sn YES 3 5% Spherical 8 Mica Sn YES 15 5% Platelet 9 Mica- Talc Sn YES 15 2.5% Platelet 10 ZnO Al YES 0.1 2.5 Spherical 11 ZnO Al YES 0.1 5 Spherical

Measures

IR absorption measurements (percentage absorption rate) are carried out in transmission between 400 nm and 1000 nm. The absorption spectra are then normalized (on the x-axis) at a wavelength of 500 nm to analyze the behavior of the pigment in IR.

Opacity and whiteness measurements were carried out according to ISO 2471-1 and ISO 2470-2 respectively

Results

On the graphs: on the ordinate we have the absorption percentage and on the abscissa the wavelength.

The tests show that the pigment used during test 1 exhibits a discriminating absorption from 2% by mass of the pigment. Pigments other than that of test 1, for example of different shape and size, such as those of tests 2, 3 and 4, also exhibit a discriminating response in the IR from a mass content of 2% . The pigments of tests 2 and 3 have a heart of titanium dioxide (TiO ₂ ), covered with tin oxide doped with antimony.

The pigments of tests 1 and 4 show a more intense response in the IR because they have a particle size greater than that of tests 2 and 3, which facilitates their retention within the structure of the paper during the manufacture of the paper. -this.

Measurements, the results of which are reported in the tables below, have shown that the pigments of tests 1,2,3 could be incorporated into the paper in substitution of a reference load of 5% titanium dioxide, without undue degradation of the whiteness, which remains acceptable, and retaining the opacity, or even improving it despite the fact that the load introduced now only presents 2.5% or 2% instead of 5%.

The pigment of Test 4 exhibits a particle size which influences optical properties such as whiteness and opacity much more.

Tests A and B demonstrate that the increase in weight does not significantly modify the IR absorption.

It can also be seen that the level of pigment used in test 7 makes it possible to have a very strong absorption in the IR but that this leads to marked modifications of the optical properties such as whiteness and opacity.

Furthermore, the IR response of the pigments of tests 5 and 6 has a different appearance from the other tests, which makes it possible to distinguish the IR signatures from one another. Finally, the two pigments reduce the optical properties such as whiteness and opacity, which can be compensated for by adding conventional paper fillers.

It can be seen that the pigments of tests 8 and 9 make it possible to have a very strong absorption in the IR but this causes marked modifications of the optical properties such as whiteness and opacity.

The pigments of tests 10 and 11 have a low contribution to IR absorption because their small particle size (<0.2 μm) does not allow optimal retention within the paper during its manufacture. TO 1 2 3 4 Whiteness % 88.5 81.1 80.61 85.03 77.03 Opacity % 86.30 88.68 89.32 87.29 87.94 TO B 5 6 7 Whiteness % 88.5 89.28 83.67 82.64 75.8 Opacity % 86.30 86.34 80.81 82.18 93.63 TO 1 8 9 10 11 Whiteness % 88.5 81.1 72.8 77.8 86 85.5 Opacity % 86.30 88.68 89.16 87.7 77.7 79.3

The invention is not limited to the examples which have just been given.

In particular, mixtures of fillers according to the invention can be used.

Claims (15)

1. Paper security substrate comprising, dispersed in the bulk thereof, preferably between 0.1% and 20% by weight, relative to the total weight of the substrate, better still between 0.2% and 5%, even better still between 0.5% and 2.5%, of an IR-absorbing particulate system, the particulate system comprising:

   - a mixture of at least one filler consisting of at least one metal oxide or metal oxide salt, in particular a mica, and of at least one filler consisting of at least one post-transition metal in ionic, molecular or atomic form, and/or

   - at least one filler consisting of at least one metal oxide or metal oxide salt, in particular a mica, and of at least one post-transition metal in ionic, molecular or atomic form,

   said particulate system giving said substrate a specific response in transmission in the IR, preferably with at least one absorption peak in the IR, in particular between 700 and 1000 nm, better still with several absorption peaks in the IR, in particular between 700 and 1000 nm,
   preferably, the particulate system comprising and/or consisting of spherical particles or the particulate system comprising and/or consisting of acicular and/or flakelike particles,
   the metal oxide being chosen from TiO₂, ZnO, ZrO₂, CeO₂, SiO₂, Al₂O₃, mica, talc, and mixtures thereof, the post-transition metal being in the form of metal oxide of post-transition metal doped with metalloids or post-transition metals.
2. Substrate according to Claim 1, the post-transition metal being in ionic (salt), doped or undoped molecular (oxide, in particular SnO₂), or atomic (dopant, in particular Al or Ga) form, preferably said metal oxide or metal oxide salt respectively being an oxide or an oxide salt of a transition metal or of a metalloid.
3. Substrate according to either one of the preceding claims, the metal oxide being chosen from TiO₂, SiO₂, ZnO, mica or talc, better still TiO₂ or SiO₂.
4. Substrate according to any one of the preceding claims, the metal oxide of post-transition metal that is doped being doped with antimony, or the metal oxide of post-transition metal that is doped being doped with aluminium or germanium.
5. Substrate according to any one of the preceding claims, the metal oxide of post-transition metal that is doped being an oxide of tin or of indium, preferably of tin.
6. Substrate according to any one of the preceding claims, the filler consisting of particles having an SiO₂ or TiO₂ core covered with antimony-doped tin oxide.
7. Substrate according to any one of the preceding claims, the post-transition metal on the one hand and the metal oxide or the metal oxide salt, in particular a mica, on the other hand respectively constituting the shell and the core of a pigment with core-shell structure, preferably the core being hollow.
8. Substrate according to any one of the preceding claims, comprising less than 4% by dry weight of TiO₂ in the form of TiO₂ particles, relative to the total dry weight of the substrate, better still being completely free of TiO₂ in the form of TiO₂ particles.
9. Substrate according to any one of the preceding claims, comprising less than 4% by dry weight of kaolin or of calcium carbonate relative to the total dry weight of the substrate.
10. Substrate according to any one of the preceding claims, the particulate system consisting of particles having a number-average size D50 of less than or equal to 10 µm, preferably less than 5 µm.
11. Substrate according to any one of Claims 1 to 8, the particulate system consisting of particles having a number-average size D50 of less than or equal to 1 µm, preferably less than 0.5 µm.
12. Substrate according to any one of the preceding claims, the particulate system comprising a single doped metal oxide or the particulate system comprising several doped metal oxides.
13. Substrate according to any one of the preceding claims, the particulate system being substantially white and opaque to visible light or the particulate system being transparent.
14. Security document comprising a substrate according to any one of the preceding claims, the substrate in particular being watermarked.
15. Security thread, film or foil comprising a substrate according to any one of Claims 1 to 13.

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