Security element comprising an interference pigment and a nanometric filler

Abstract

A security element, preferably a security wire, for a secure document, that may include a masking structure for reducing the visibility of a surface of the element when the latter is located inside the document or on the surface of the document, the masking structure comprising a nanometric filler and a multilayer interference pigment.

Claims

1. A security element for a secured document, comprising: a security structure comprising an opaque layer and at least one opening in this opaque layer; and a masking structure superposed at least partially on the security structure, for decreasing visibility of the security element in reflected light, the security element being present within the secured document or on a surface of the secured document, the masking structure comprising a nanoscale filler and a multilayer interferential pigment, the security element being visible under transmitted light through the masking structure.

2. The security element as claimed in claim 1, the security element forming a security thread, a foil, a patch, a flake or a fiber.

3. The security element as claimed in claim 1, the security element having two opposite major faces and the masking structure decreasing visibility of at least one of said faces.

4. The security element as claimed in claim 1, the multilayer interferential pigment comprising a mineral base coated with at least one layer of a refractive index different from that of the base.

5. The security element as claimed in claim 4, the base being a platelet base.

6. The security element as claimed in claim 1, an amount by weight of multilayer interferential pigment relative to a weight of the masking structure being comprised between 1 and 40%.

7. The security element as claimed in claim 1, a size of the multilayer interferential pigment being comprised between 2 and 150 microns.

8. The security element as claimed in claim 1, the nanoscale filler having a D50 size comprised between 30 and 1000 nm.

9. The security element as claimed in claim 1, the nanoscale filler comprising colloidal silica.

10. The security element as claimed in claim 9, said colloidal silica being present in an amount by weight comprised between 20 and 80%, relative to the weight of the masking structure.

11. The security element as claimed in claim 1, a thickness (t) of the masking structure being comprised between 2 and 30 microns.

12. The security element as claimed in claim 1, the pigment and the nanoscale filler being dispersed in a binder within a layer of the masking structure.

13. The security element as claimed in claim 1, the at least one opening taking a form of a negative script.

14. The security element as claimed in claim 1, comprising a carrier, made of a thermoplastic material.

15. The security element as claimed in claim 14, the security structure being located on one side of the carrier and the masking structure on the other side.

16. The security element as claimed in claim 14, the security structure and the masking structure being located on the same side of the carrier.

17. The security element as claimed in claim 1, comprising an additional nanoscale filler.

18. The security element as claimed in claim 17, said additional nanoscale filler being present in an amount by weight, relative to the weight of the masking structure, comprised between 1 and 40%.

19. The security element as claimed in claim 17 or 18, the nanoscale fillers having refractive indices that differ by at least 0.5.

20. The security element as claimed in claim 1 furthermore comprising a luminescent agent, mixed in a masking layer of the masking structure comprising the multilayer interferential pigment and the nanoscale filler.

21. The security element as claimed in claim 1, comprising a heat-sealing adhesive making contact with the masking structure.

22. The security element as claimed in claim 21, the adhesive comprising a luminescent agent.

23. The security element as claimed in claim 22, comprising a luminescent agent, within a layer distinct from the masking structure.

24. A document incorporating a security element as claimed in claim 1.

Description

(1) The invention will be better understood on reading the following detailed description of nonlimiting exemplary embodiments thereof, and on examining the appended drawings, in which:

(2) FIG. 1 schematically shows an exemplary secured document according to the invention;

(3) FIG. 2 shows in transverse cross section along II-II the secured document and the security element;

(4) FIGS. 3 and 4 show in transverse cross section along II-II variants of the security element;

(5) FIG. 5 shows in cross section a variant secured document according to the invention;

(6) FIG. 6 shows in isolation a variant security element; and

(7) FIG. 7 shows in isolation and from above the security element in FIG. 2.

(8) In the figures, the actual respective proportions of the various constituent elements have not always been respected, for the sake of the clarity of the drawings. In addition, certain layers may have been shown as monolayers in the figures whereas in fact they are made up of a plurality of sublayers. Adhesive layers may not have been shown between various constituent layers.

(9) FIG. 1 shows an exemplary secured document 1 according to an exemplary implementation of the invention.

(10) The document 1 comprises a substrate 2, preferably made of paper, formed from one or more plies.

(11) The document 1 integrates a security element 10 according to the invention, taking the form of a thread in the example in question.

(12) The security element 10 comprises a carrier 11 made of a thermoplastic material, which ensures the mechanical strength of the thread. This carrier 11 is for example made of a transparent thermoplastic material such as PET or polyester. The thickness e of the carrier 11 for example ranges from 6 to 30 m and the width w of the element 10 from 1 to 10 mm.

(13) The security element 10 comprises a security structure 12, for example formed by metallization/demetallization. The security structure 12 thus comprises, for example, an opaque metal layer 12a and openings 12b taking the form of letters or other recognizable patterns. These openings 12b are visible under light transmitted through a window 3 in the document 1. The security structure 12 may also form a recognizable half-tone image, the subject of which is for example moreover present on the document. Although the security structure preferably comprises a metallization/demetallization, it may also comprise printed patterns, for example printed with a metallic, magnetic or electrically conductive ink.

(14) The security element 10 comprises a masking structure 13, for example, as illustrated in FIG. 2, taking the form of a single layer located opposite the security structure 12 relative to the carrier 11.

(15) The security element 10 may also comprise a layer of a heat-sealing adhesive 14, preferably located, as illustrated, on an external face of the element 10, for example on the side opposite the security structure 12 relative to the carrier 11. The element 10 may comprise a heat-sealing adhesive layer on each of its external faces.

(16) The layer 14 may comprise a luminescent and especially fluorescent agent. The masking structure 13 makes it possible to decrease the visibility of the element in the substrate 2 while preserving the transparency of the patterns 12b in transmission, and the transparency to UV if required.

(17) The invention makes it possible to avoid a problem with excessive thickness within the substrate, because the masking structure 13 may be of relatively small thickness t.

(18) The invention, by virtue of the presence of the masking layer 13, allows a metal layer of relatively low optical density to be used to produce the security structure 12, without this in any way making the thread too visible in reflection.

(19) Preferably, the masking structure 13 comprises colloidal pyrogenated silica, the particle size of which is nanoscale, combined with an iridescent pigment, for example Iriodin from Merck.

(20) The pigment preferably has a transparent base that is for example made of mica, and optical properties that are complementary to those of the colloidal pyrogenated silica. When the substrate is white, the pigment is preferably blue or green or blue-green. The color of the pigment is that obtained in specular reflection at non-normal incidence.

(21) The colloidal pyrogenated silica consists of silica nanoparticles, the size of which is smaller than 120 nm for half of the particles.

(22) The size of the silica particles is preferably comprised between 30 nm and 1000 nm, again preferably between 30 and 500 nm and more preferably between 50 and 300 nm.

(23) The thickness t of the masking layer is preferably comprised between 2 and 30 m, again preferably between 5 and 20 m and better still between 8 and 13 m.

(24) The amount of multilayer interferential pigment relative to the weight of the masking structure is preferably comprised between 1 and 40%, better still between 2 and 30% and preferably between 3 and 15%.

(25) The size of the pigment is preferably comprised between 2 and 150 m, again preferably between 5 and 40 m and more preferably between 5 and 25 m.

EXAMPLE

(26) A masking layer 13 having the following composition is used: nanoscale filler Aerodisp W7330N from Evonik: 50% by dry weight; iridescent pigment of reference 221 from Merck: 10% by dry weight; and binder Cromelastic SE871 from Cromogenia-Units: 40% by dry weight.

(27) This layer may be applied by rotogravure (or roto-coating) in the form of a coating of uniform thickness of 10 microns.

(28) In this example, the security structure 12 is a layer of aluminum of 300 nm thickness, with a text in negative script, as illustrated in FIG. 4. The carrier 11 is made of PET.

(29) In one variant, above the metal layer of the security structure 12, at least one optically variable layer (called an OVI) may also be deposited. This additional layer (not shown) for example comprises liquid crystals, iridescent pigments and/or interferential layers or structures such as a hologram.

(30) The security element may also comprise a magnetic coating, for example in the form of a code.

(31) Generally, titanium dioxide may be added to the masking layer 13, in small amounts, in order to increase the scattering of light. It is preferably a question of Rutile PGG 121 titanium dioxide from Cristal the D50 particle size of which is smaller than 220 nm.

(32) In this case, the following composition may be substituted for the preceding one: nanoscale filler Aerodisp W7330N from Evonik: 50% by dry weight; iridescent pigment of reference 221 from Merck: 6% by dry weight; nanoscale filler Rutile PGG 121 from Cristal: 6% by dry weight; and binder Cromelastic SE871 from Cromogenia-Units: 38% by dry weight.

(33) Another variant consists in depositing the titanium dioxide in a separate layer between the carrier 11 and the masking layer 13.

(34) FIG. 3 illustrates the possibility for the security structure 12 and the masking structure 13 to be located on the same side of the carrier 11. The other face of the carrier may receive any additional security measure, for example a luminescent compound, an optically variable structure, a holographic structure or a structure based on a lenticular array.

(35) FIG. 4 shows a security element 10 in which the masking structure 13 is composed of two superposed layers 13a and 13b containing the nanoscale filler and the multilayer interferential pigment, respectively. These two layers may be applied one on the other.

(36) The security element may take the form of a security thread integrated entirely into the bulk of the substrate of the security document. In this case, the masking layer is advantageously applied to both faces of the thread in order to mask the latter in reflection and allow it to be observed under transmitted light.

(37) Although the invention is particularly advantageously applicable to a security thread, the security element 10 may also take the form of a foil or a patch applied to the surface of the substrate 2 of the document 1, as illustrated in FIG. 5.

(38) The masking structure according to the invention then makes it possible to make the interior face 19 of the element 10, i.e. that face which is turned toward the substrate 2, less visible when the masking structure is interposed between the substrate 2 and the one or more layers of the security element to be hidden.

(39) In the example in FIG. 6, the security element 10 takes the form of a flake. The masking structure may extend over both the major faces of the flake. The latter may comprise a luminescent and especially fluorescent compound.

(40) In another variant, the security element takes the form of an especially colored magnetic and/or metal fiber.

(41) Although the invention is preferably applied to a paper substrate that is white in color, the substrate may be slightly colored.

(42) In this case, the masking layer may be substantially white or have the same slight coloring. The color of the masking layer may be adjusted by adjusting the color of iridescence of the multilayer interferential pigment and, if need be, the color of the nanoscale filler.

(43) Nanoscale filler other than pyrogenated colloidal silica may be used, this filler preferably being a material that is transparent to UV and preferably also not opaque. Other nanoscale fillers such as calcium carbonate and barium sulfate may be used with and/or to replace silica.

(44) The expression comprising a must be understood as being synonymous with comprising at least one, unless otherwise specified.