FR3030363A1 - METHOD OF PROCESSING A SECURITY ELEMENT COMPRISING AN OPTICAL STRUCTURE HAVING A NON-PLANAR FACE - Google Patents

Abstract

Method for processing a security element for a secure document, in particular a security element in the form of a security thread, the security element comprising on one face (5) at least one optical structure (1), preferably not flat this method comprising the step of continuously treating said element so as to increase the hydrophobicity of said face.

Description

The present invention relates to the field of secure documents. Secure documents include identity documents, in particular identity cards and passports, means of payment, especially banknotes, checks, vouchers or vouchers, admission tickets at cultural or sports events, transport tickets. It can also be a secure document chosen from certificates of authenticity or guarantee certificates, or a secure packaging, especially for drugs, electronic parts, spare parts, perfumes, a secured card or a secure label. Preferably, it is a banknote.

Such documents are conventionally provided with security elements integrated into a substrate, in particular paper or polymer, surface, window or mass. Bank notes are exposed during their life to many manipulations and risks of soiling. In order to give them a high durability, the fibrous substrate is protected by one or more layers of a transparent protective coating having a barrier effect against soiling. This protective coating must however provide the barrier function without unduly harming the printability of the paper during the manufacture of the notes. Cotton-based papers for banknotes, on which one or more layers of water-based transparent coating are applied to protect them, are usually marketed under the name of "high-durability substrate" (HD substrate), or " very high-durability substrate (THD substrate), as the case may be. Many protective coatings have already been disclosed in the prior art. These coatings are applied after integration of the security elements. The patent EP 514 455 B1 thus discloses improving the circulation resistance of bank notes by impregnating the fibrous substrate, before printing, with a composition which contains one or more binders chosen for their mechanical characteristics. US 2007/0017647 A1 discloses paper for making banknotes, having improved dirt resistance. According to the teaching of this application, the protective coating comprises at least two layers applied successively, including a base layer which is in contact with the fibrous substrate and closes its pores and an outer layer which protects the substrate from physical and chemical influences. WO 96/28610 discloses applying a liquid polyurethane composition to a fibrous substrate to form a protective coating.

The application US 2004/0023008 A1 discloses a security paper for the manufacture of banknotes. The paper comprises a fibrous substrate which is coated on at least one of its faces with a transparent or translucent protective layer comprising colloidal silica and at least one transparent or translucent elastomeric binder comprising, for example, polyurethane.

The publication WO 2008/054580 A1 discloses a method for imparting to a fibrous substrate a resistance to moisture and soiling, comprising impregnating the substrate on two opposite sides with an aqueous composition comprising one or more thermoplastic resins. EP 815 321 B1 discloses a paper for the production of banknotes, an aqueous dispersion of polyurethane having been deposited on the fibrous substrate, this polyurethane dispersion being free of charges and transparent. EP 1 783 273 discloses an improved durability security paper, a fluororesin-containing composition having been surface-applied. WO 2012/156904 A1 discloses a sheet coated with an external printability layer based on polyurethane. Furthermore, it has been proposed to use as security elements optical structures having a non-planar face, such as lenticular networks. The Motion® security thread marketed by Crane is one example of a microlens network security element used in the field of banknotes. This thread generates an image that moves when the note is tilted. In general, the application of transparent protective coatings on an optical structure composed of a microlens array degrades the sharpness and clarity of the image produced by the optical structure. A transparent material such as a varnish, with a refractive index greater than that of the ambient air, modifies the path of the light radiation between the outside and the lenses. The image appears blurred and poorly defined. The blurring of the Motion® safety thread with a varnish-type protective coating is thus a well-known phenomenon.

Now, more and more secure document substrates such as banknotes, incorporating a security element type lenticular network, are covered with a protective transparent coating, before or after printing of this substrate. In particular, cotton-based papers for banknotes not only increasingly include security threads with a lenticular optical structure introduced at the beginning of papermaking, but are also covered with one or more layers of paper. transparent anti-fouling protective coating at the end of manufacture, as mentioned above. The security threads are for example unwound at the machine head between two jets of cotton fibers, which constitute the paper substrate after their meeting in the wet phase. Security threads usually appear in windows. The coating is then applied in the aqueous phase at the end of the machine, on the almost dry paper. Without particular precautions when applying the coating, the visual effect brought by the security thread is degraded on such coated papers.

The simplest method to avoid this blurring phenomenon is to not apply the coating to the surface of the lenticular optical structure security element by creating reserves during the application, that is to say by delimiting "physically" uncovered areas. This method is however difficult to implement in industrial conditions. In addition, the paper at the edge of the security element is no longer effectively protected by the coating. Another method is to reduce as much as possible the amount of coating deposited on the entire paper substrate and security element. The main disadvantage is a decrease in the protection of the paper, while the image produced by the lenticular structure still loses sharpness. As has been previously explained, the state of the art is therefore not entirely satisfactory because it does not make it possible to preserve as much as desired the sharpness and clarity of the images produced by the microlens array optical structures. security elements inserted into the high- or very-high-durability paper substrates.

WO 2012/153114 A1 teaches making a metallic and / or diffractive security thread with first regions making it possible to improve the formation of hydrogen bonds with the papermaking substrate, and between these first regions to apply a hydrophobic varnish intended to prevent the deposit of pulp. The aim of the invention is to reduce the blurring of an optical structure of a security element by a transparent coating in an aqueous phase, such as a protective varnish, usually applied to the paperboard substrate for banknotes. The invention fulfills this objective by means of a method for processing a secure document security element, in particular a security element in the form of a security thread, the security element comprising on one side at least one optical structure, this method comprising the step of continuously treating said element so as to increase the hydrophobicity of said face. By "continuously" it is to be understood that the security element is not processed in sections that alternate with untreated sections. In the case of a security wire in windows, the treated area is thus both in the windows and between the windows, and extends from one edge of the document to the opposite edge, all along the element of security. In the invention, the material which prevents or reduces the deposit is therefore a protective coating applied in aqueous phase on the substrate and the security element, and not the paper pulp, contrary to WO 2012/153114 A1. The optical structure is preferably transparent. The optical structure is preferably non-planar. The optical structure is preferably refractive, and comprises for example a lenticular array. If necessary, the optical structure can be reflective, diffractive and / or diffusing. The invention is particularly suitable for online processing of the security element. The treatment can cause the contact angle of the water on said face to increase by at least 10 °. The treatment can in particular bring the contact angle of the water on said face to a value greater than or equal to 90 °. The treatment preferably comprises the application of a hydrophobic composition on said face. The applied composition advantageously has a pearling activity. In other words, the expected hydrophobicity level of the composition applied to the treated face, or even the treated faces, of the security element is sufficiently high to greatly reduce the wetting of said surface by water and / or the aqueous phase preparation of the protective coating. It is in particular to induce on the said surface the formation of water droplets and / or the aqueous phase preparation of the protective coating, the number and spread of which is, however, as small as possible. The composition is preferably non-or slightly film-forming, more preferably non-film-forming. This makes it possible not to unduly disturb the interface between the optical structure and the ambient air. The composition deposition, after drying, thus preferably covers less than 100% of said face, better less than 50%, and even more preferably less than 25%. The amount of composition applied, in dry weight, is preferably from 0.05 to 0.5 g / m 2. The hydrophobic composition advantageously comprises one or more hydrophobic compounds. This or these hydrophobic compounds are preferably chosen from: - waxes, - polymers, or oligomers, in particular, o polyolefinic, o acrylic, o vinyl, o fluorinated, o silicone, o fluorosilicones. The treatment composition preferably comprises at least one wax, and more preferably a paraffin wax, which may be in the form of an emulsion. The composition can be applied by spraying, roller transfer, gravure, flexography, screen printing or dip-wipe processes. Although the application of a treatment composition constitutes a preferred solution for protecting said face vis-à-vis the coating subsequently deposited, by the simplicity of its implementation, said face can be further treated by grafting including physical, chemical or physico-chemical. The latter can be performed by plasma-assisted chemical vapor deposition. Preferably, fluorinated sites are then grafted on said face.

The processing of the security element is preferably carried out before it is integrated with a substrate of the secure document. The invention is particularly suitable for processing a security element in the form of a security thread. The subject of the invention is also a composition for treating a safety element, for carrying out the process according to the invention, comprising at least one hydrophobic compound, and having a pearling activity. This composition may be water-based. The invention also relates to a method of manufacturing a secure document, wherein incorporating a security element as obtained by the implementation of the method on or in a substrate of said document. This method may comprise the application on an entire face of the substrate, on which said face of the optical structure of the security element is visible, an aqueous protective coating, in particular transparent. The security element can be, in the application of this coating, in the form of a security wire integrated window (s). The invention also relates to a security element as such, in particular treated according to the method defined above. This security element can be characterized, according to one aspect of the invention, in that it has a discontinuous deposit, on a non-planar face of an optical structure, of a residue of hydrophobic composition, preferably a wax . In this case, we also speak of a deposit that is not very or not film-forming. The amount of residue of composition being preferably between 0.05 and 0.5 g / m2. This residue can cover less than 50%, better than 25%, of the face of the optical structure. The invention will be better understood on reading the following detailed description, nonlimiting exemplary embodiments thereof, and on examining the appended drawing, in which: FIG. schematic in longitudinal section, a security element according to the invention. Security Element The security element according to the invention may be in the form of any element introduced into the document substrate or on its surface.

This is for example a security thread introduced in window (s) ("window thread"), a foil, that is to say a film applied by transfer to the surface of the paper, of a patch, a lamination tape, a protective film. The security element may be a security thread introduced in the round shape or on the flat table forming the paper, either directly in a jet (fibrous layer) wet, or between two wet jets. The treatment of the safety element can be reflected on the surface of the safety element by quantifiable hydrophobia by the measurement of the contact angle of water according to the standards - ASTM D7490 Standard test method for measurement of the surface tension of solid coatings, substrates and pigments using contact angle measurements - EN 828 February 2013 Adhesives - Wettability - Determination by measurement of contact angle and free surface energy of the solid surface - ISO / CD 19403-2 Paints and varnishes - Wettability - Part 2: Determination of the free surface energy of solid surfaces by measurement of the contact angle (proposed standard) The contact angle on the visible face of the optical structure is thus preferably greater than or equal to 90 °. The treatment may also result in the presence of a treatment composition residue on the treated side of the security element. This residue is preferably arranged other than in the form of a continuous film. In addition to the optical structure and the presence of the treatment composition residue, the security element may comprise other first, second or third level security means. It may be: - patterns appearing in transmitted light and formed by metallization and / or demetallization, - dyes, luminescent pigments, interference pigments and / or liquid crystal pigments, in particular in printed form or mixed with at least one constituent layer of the security element, - compounds, dyes and / or photochromic or thermochromic pigments, in particular in printed form or mixed with at least one constituent layer of the security element, - ultraviolet (UV) absorber, in particular in coated form or mixed with at least one constituent layer of the security element, an interferential multilayer structure, a birefringent or polarizing layer, a diffraction structure, means producing a "moiré effect", such an effect being able to example to show a pattern produced by the superposition of two security means, for example by the approximation of lines of two means s rity, 15 to 1 color filter. - an automatically readable security having specific and measurable luminescence characteristics (eg fluorescence, phosphorescence), light absorption (eg ultraviolet, visible or infrared), Raman activity, magnetism, micro interaction electrons, X-ray interaction or electrical conductivity. When the security element is in wire form, its width is for example between 1 and 10 mm and its thickness between 10 and 100 i.tm. The security element may comprise a thermoplastic support film, in particular polyester or polyester terephthalate. The optical structure 25 may cover only one side of this support film, or alternatively, be provided on both sides of the support film. Non-planar optical structure The optical structure of the security element is preferably a refractive optical structure, comprising one or more microlenses. It may be a network of 30 microlenses and / or one or more Fresnel lenses. The optical structure may comprise spherical or aspherical microlenses, in the form of a bidirectional network.

The microlenses may have a hexagonal base or other shape. FIG. 1 represents in longitudinal section an example of a security thread incorporating a nonplanar optical structure 1 formed by a microlens array. This wire is shown inserted with windows 3 in a papermaking substrate 2. The windows 3 are separated by bridges 8. The microlenses 9 produce through the windows 3 an enlarged image of micromotives 4, these being for example located at the focus microlenses. The optical structure 1 then has a non-planar face which is defined by the set of convex faces of the microlenses.

The local variation of the thickness of the security element, related to the relief provided by the non-planar optical structure, may be greater than or equal to 5 μm. The non-planar face 5 of the security thread, partially visible through the windows 3, is treated according to the invention, for example by a hydrophobic composition with beading activity.

Solid residues 6 of composition can thus be present on the face 5. The thickness of these residues is, for example, less than or equal to 1 μm. The residues 6 are present not only in the windows 3 but also under the bridges 8 between the windows 3. The optical structure 1 may be made of thermoplastic material or have been cross-linked by UV radiation, for example. The optical structure 1 may be formed by embossing a polymer layer, by molding, printing, machining or etching. Examples of optical structures are described in US 8,284,492 B2 and WO 2003/061983. Method of processing the security element The invention makes it possible to render the apparent face of the optical structure physicochemically incompatible with the protective coating in aqueous phase subsequently applied to the document substrate and the security element. This makes it possible to limit the deposition of the coating on said face, and to reduce the blurring by said coating of the images produced by the optical structure.

The result of the implementation of the treatment process disturbs the wetting and spreading of the aqueous protective coating, following the modification of the surface tension of said face of the optical structure. When this treatment involves the application of a composition, the fact that the treatment composition applied is not, or is little, film-forming, avoids that it is itself causing a phenomenon of blurring. By "no or little film-forming" it should be understood that the composition does not form a continuous layer on the surface of the security element. Preferably, the composition forms individualized clusters after drying, or covers less than 100%, preferably less than 50% and more preferably less than 25%, of said face of the optical structure. When the security element is a window-embedded safety wire in a wet fibrous substrate, this feature offers a compromise between pushing back the subsequent coating layer to avoid blurring of the optical structure and the advantage of allowing the deposition of the fibrous suspension at the bridges between the windows to strengthen the adhesion of the fibers of the paper on the wire. It is thus preferable that the property of hydrophobicity and the beading activity induced by the treatment are not excessive so as not to significantly disturb the formation of paper mill bridges. It is also preferred that the treatment does not generate residues of significant thickness at the surface of the security element. The thickness of the composition deposit on said face, after drying, is preferably less than or equal to 5 μm, more preferably 1 μm, being in particular between 0.1 μm and 1 μm. The security element may be either pretreated at the security element manufacturer or at the security document substrate manufacturer prior to incorporation. In the latter case, the security element, for example the security thread, can be pretreated directly at the head of the paper machine, at the time of uncoiling the wire. The security element, when constituted by a security thread, may be treated by continuous application by a spraying, roller-transfer, rotogravure, flexographic, screen-printing or dip-wiping process. of the composition, at least on the relevant face of the optical structure.

This application preferably takes place over the entire width of the security element. The security element can pass through a drying device, for example under an infrared irradiation ramp (IR) or in a tunnel traversed by a flow of hot air, to evaporate the water or the solvent from the composition, before incorporation into the substrate. Treatment Composition The treatment composition may be water-based. The treatment composition preferably comprises at least one hydrophobic compound. It may be a compound in emulsion, suspension, or dispersion, in a solvent such as water. Most preferably, an emulsion paraffin wax is used. Other hydrophobic chemical compounds, including pearling effect, can be applied to the structure, replacing an emulsion paraffin.

These include polymers, or oligomers: - polyolefins, such as PE or PE, - acrylic, in particular containing butyl or hexyl, - vinyl, based on long chains aliphatic, - fluorinated, for example PTFE or PVDF, silicones, fluorosilicones. These polymers are mainly delivered in emulsion, suspension, or dispersion in an aqueous phase or organic solvent. They are used in formulations which may contain other polymeric resins, rheology agents, fillers and / or surface additives. The total mass content of hydrophobic compound (s) in the composition is preferably between 10 and 100% of the total weight of dry matter. The composition may comprise an adhesive, in particular based on thermoplastic or thermo-activatable polymers, in order to help the adhesion of the fibrous bridges to the surface of the security element. The adhesive must be sufficiently hydrophobic in nature, if not too hydrophilic, so that the final composition retains sufficient hydrophobicity. It is also possible to deposit on the surface of the security element non-polymeric compounds having hydrophobic properties, in particular pearling properties, by grafting.

An example of a grafting method is plasma enhanced chemical vapor deposition. This is called PECVD for Plasma-Enhanced Chemical Vapor Deposition. This technique makes it possible, in particular, to generate highly hydrophobic fluorine derivatives. Examples The compositions of the examples below are applied to the laboratory on the optical side of a safety thread with micro-lenticular Motion® structure from the company CRANE. The compositions are made with different degrees of dilution of the hydrophobic compound to vary the amount of dry active material deposited on the surface of the microlenses. Two sets of pretreatment compositions are tested. Example 1 (contents are expressed by weight relative to the total weight of the composition): Aquacer 539 * 100.0%, Water 0.0% * Commercial water-modified paraffinic emulsion manufactured by BYK, with a melting point of 90 ° C. at 35.0% sec Example 2: Aquacer 539 ** 333% Water 66.7% ** Commercial emulsion of Example 1 diluted to 200% by addition of 200 g of water at 100 g of wax emulsion, ie 11.6% dry Example 3: Aquacer 539 *** 20.0%, water 80.0% *** Commercial emulsion of Example 1 diluted to 400% by addition of 400 g of water and 100 g of wax emulsion, ie 5.0% dry The composition of each of Examples 1 to 3 is applied to the smooth bar on the non-planar upper face of the yarn. safety, itself fixed on blotting paper absorbing excess composition, then the wire is dried in a ventilated oven at 130 ° C. The contraction of drops of water deposited on the wire after drying shows that a beading effect was ge born on the surface of the yarn thus pretreated. The amount of composition deposited on the upper face of the security thread is large enough to induce a strong beading effect, but not too excessive so as not to generate itself a phenomenon of blur. This amount of composition, which is determined so as to obtain an optimum compromise, is preferably between 0.05 g / m 2 and 0.5 g / m 2. After processing, the security threads are embedded in PVA coated note paper by rolling at 140 ° C.

Two different water-based transparent protective coatings were applied to the secure substrate using press rolls (or "sizepress"). In this first series of tests, one of the rolls of the gluing press has a surface of stainless steel, while the other is covered with a rubber envelope. Drying of the transparent protective coating in aqueous phase is carried out at 130 ° C. in forced convection for 3 min. Coating 1 Aqueous protective coating for THD paper of the Applicant, based on polyethylene (PE). Coating 2 Aqueous protective coating based on polyurethane (PU) for HD paper of the Applicant. The sharpness of the images of the Motion® micro-lenticular structure security threads covered by the coatings 1 and 2 is evaluated according to the implementation, or not, of a pretreatment with the compositions of Examples 1 to 3.30 Visual performance of the thread. Safety thread Without treatment Treatment with composition 1 to 3 according to the invention - Composition 3 Composition 2 Composition 1 No protective coating - 5 4 5 3 Coating Coating Press passage gluing roller side stainless steel 3 4 5 3 protector 1 protector 1 deposited at 2.3 g / m2 / face Passage in 3 4 4 3 gluing press roller rubber side Average of 3 4 4.5 3 gluing presses The scale of the results is as follows: 5excellent, 4 very good, 3 good, 2 passable, 1 mediocre, 0 none. Visual performance of the yarn Safety thread Without treatment Treatment by composition 1 to 3 Composition 3 Composition 2 Composition 1 No protective coating - 5 4 5 3 Coating Coating Press passage gluing roller side stainless steel 3 5 4 2 protector 2 protector 2 deposited at 4 , 0 g / m2 / face Passage in 2 5 3 2 gluing press roll roller side Average of 2.5 5 3.5 2 passes in gluing press Laboratory evaluation shows that the hydrophobisation of the safety thread greatly improves its performance in both cases studied. The image transmitted by the microlens array appears much clearer and more defined. On a scale of 0 to 5, the notation quantifying the sharpness of the image thus passes on average from 3.0 to 4.5 in the case of the coating 1 for paper THD and from 2.5 to 5.0 with the coating 2 for HD paper, respectively because of the hydrophobic compositions 2 and 3 at the surface of the Motion® safety thread. It is also noted that it is possible to determine an optimal composition (composition 2 for the protective coating 1 and composition 3 for the protective coating 2). 2nd series Example 4 (the contents are expressed by weight relative to the total weight of the composition): Aquacer 539e 20.0%, Water 80.0% * Commercial emulsion of Example 1 diluted to 400% by addition of 400 g of water to 100 g of wax emulsion, ie 7.0% dry. Example 5: Aquacer 539 "6.7%, Water 93.3% ** Commercial emulsion of Example 1 diluted to 1400% by adding 1400 g of water to 100 g of wax emulsion, ie 2.3 % sec Example 6: Aquacer 539 * "4.0%, Water 96.0% *** Commercial emulsion of Example 1 diluted to 2400% by addition of 2400 g of water and 100 g of wax emulsion or 1.4% sec. The composition of each of Examples 4 to 6 is applied by means of a foam-shaped foam roller to the non-planar upper face of the security thread, itself fixed on blotting paper absorbing the excess composition. Then the wire is dried in a ventilated oven at 130 ° C.

The contraction of drops of water deposited on the wire after drying shows that a beading effect has been generated on the surface of the wire thus pretreated. Again, the amount of composition deposited on the upper face of the security thread is large enough to induce a strong beading effect, but not too excessive so as not to generate itself a phenomenon of blur. This amount of composition, which is determined so as to obtain an optimum compromise, is preferably between 0.05 g / m 2 and 0.5 g / m 2. After processing, the security threads are embedded in PVA coated note paper by rolling at 100 ° C. The two different water-based transparent protective coatings were applied to the secure substrate in a glue press using rollers. In this second series of tests, the two rolls of the gluing press are covered with a rubber envelope. Drying of the transparent protective coating in aqueous phase is carried out at 130 ° C. in forced convection for 3 min.

Coating 1 Aqueous protective coating based on polyethylene (PE) for THD paper of the Applicant. Coating 2 Aqueous protective coating based on polyurethane (PU) for HD paper of the Applicant. The sharpness of the images of the Motion® micro-lenticular structure security threads covered by the coatings 1 and 2 is evaluated according to the implementation, or not, of a pretreatment with the compositions of Examples 4 to 6. Performance visual of the wire. Safety thread Without treatment Treatment with composition 4 to 6 according to the invention - Composition 6 Composition 5 Composition 4 No protective coating - 5 5 4 3 Coating Coating Press passage gluing roller side front rubber 2 4 4 3 protector 1 protector 1 deposited at 1.4 g / reface Passage in 2 3 4 3 gluing press roller side rubber back Average of 2 3.5 4 3 passes in gluing press The scale of the results is the following one: excellent, 4 very good, 3 good, 2 passable, 1 mediocre, 0 none. Visual performance of the yarn Safety thread Without treatment Treatment with composition 4 to 6 Composition 6 Composition 5 Composition 4 No protective coating _ 5 5 5 3 Coating Coating Press passage gluing roller side front rubber 2 3 3 3 protector 2, protector 2 removal at 3.2 g / reface Passage in 1 2 4 3 gluing press roller roll back rubber Average of 1.5 2.5 3.5 3.0 gluing press passes Laboratory evaluation shows that the hydrophobization of security strongly improves its optical performance in the two cases studied. Similarly, the image transmitted by the microlens array then appears much clearer and more defined. On a scale of 0 to 5, the notation quantifying the sharpness of the image thus passes on average from 2.0 to 4.0 in the case of the coating 1 for paper THD and from 1.5 to 3.5 with the coating 2 for HD paper, in both cases because of the hydrophobic composition 5 at the surface of the Motion® security thread. It is also noted that it is possible to determine an optimum composition (composition 5 for protective coatings 1 and 2).

Authentication method The fact that the security element undergoes in the invention a treatment to be made more hydrophobic can be used to authenticate the element. It is then for example to measure the contact angle of the water and / or the trace of a discontinuous deposition of hydrophobic composition on the element.

The invention thus also relates to a method for authenticating a security element according to the invention, in which the contact angle of the water is measured on the non-planar face of the optical structure and / or the the presence on said face of a discontinuous deposit formed by a residue of hydrophobic composition is detected, and the authenticity of the element is determined at least on the basis of this measurement and / or detection.

The counterfeiting is for example detectable by combining the observation of the security element and the measurement of physicochemical properties thereof. Specifically, there may be suspicion of counterfeiting provided, firstly, to observe a discontinuous or very thin deposit of hydrophobic compound (s) on the surface of the security element, and secondly to measure a low surface energy on the non-planar face of the security element. The invention is not limited to the examples which have just been described. In particular, the invention is applicable to other refractive optical structures. The expression "comprising one" must be understood as being synonymous with "comprising at least one", and "between" means included limits.

Claims (27)

REVENDICATIONS1. Method for processing a security element for a secure document, in particular a security element in the form of a security thread, the security element comprising on one face (5) at least one optical structure (1), preferably not flat this method comprising the step of continuously treating said element so as to increase the hydrophobicity of said face. 2. Method according to claim 1, the optical structure being non-planar. 3. The method of claim 1 or 2, the treatment causing the contact angle of the water on said face to increase by at least 10 °. 4. Method according to any one of claims 1 to 3, the treatment bringing the contact angle of the water on said face to a value greater than or equal to 90 °. 5. Method according to any one of the preceding claims, the optical structure (1) comprising a lenticular network. 6. Method according to any one of the preceding claims, the treatment comprising the application of a composition on said face (5). 7. The method of claim 6, the applied composition having a beading activity. 8. A method according to one of claims 6 and 7, the composition being non-filmogens, preferably non-film-forming. 9. Process according to any one of claims 6 to 8, the composition comprising one or more hydrophobic compounds. 10. The method of claim 9, the total mass content of hydrophobic compound (s) in the composition being between 10 and 100 ° A. 11. The method of claim 9 or 10, the hydrophobic compound or compounds being chosen from: waxes, polymers, or oligomers, in particular o polyolefinic, o acrylic, o vinyl, o fluorinated, o silicone, o fluorosilicones. 12. The method of claim 10 or 11, the composition comprising at least one wax, preferably a paraffin wax. 13. Method according to one of claims 11 and 12, the hydrophobic compound or compounds being present in the composition in a total amount of between 10 and 100. 14. Method according to any one of claims 6 to 13, the composition comprising an adhesive, in particular thermoactivatable. 15. Process according to any one of the preceding claims, the thickness of the composition residue on said surface, after drying, being less than or equal to 5.0 μm, better still at 1.0 μm, being in particular between 0. , i.tm and 1.0 1.1.m. 16. A method according to any one of claims 6 to 15, the composition deposition, after drying, covering less than 100% of said face, better less than 50%, more preferably less than 25%. 17. A method according to any one of claims 6 to 16, the composition being applied by spraying process, roller transfer, gravure printing, flexography, screen printing, or dipping-wiping. 18. A method according to any one of claims 1 to 17, said face being treated by physical, chemical or physico-chemical grafting. 19. A method according to any one of the preceding claims, the processing of the security element being performed before it is integrated with a substrate (2) of the secure document. 20. The method of any one of claims 1 to 19, the security element being a security thread. 21. Security element obtained by implementing the method according to any one of claims 1 to 20. 22. A security element, particularly according to claim 21, having a discontinuous deposit (6) on the non-planar face (5) of the optical structure (1) of a hydrophobic composition residue, preferably a wax, the quantity with a composition residue of between 0.05 and 0.5 g / m 2. 23. A composition for carrying out the method as defined in any one of claims 6 to 22, comprising at least one hydrophobic and beading compound, especially an emulsion paraffin wax. 24. A method of manufacturing a secure document, wherein incorporating a security element obtained by the implementation of the method as defined in any one of claims 1 to 22 on or in a substrate of said document. 25. The method of claim 24, comprising the application on an entire face of the substrate on which said face of the optical structure of the security element is visible, an aqueous protective coating, especially transparent, in particular based on COULD. 26. The method of claim 24 or 25, the security element being in the form of a security wire integrated window (s). 27. A method of authenticating a security element as obtained by carrying out the method defined in any one of claims 1 to 20, wherein the contact angle of the water on the face (5) of the non-planar optical structure and / or the presence on said face of a discontinuous deposit formed by a residue of hydrophobic composition is detected, and the authenticity of the element is determined at least based on this measurement and / or detection.