EP3233514B1 - Method for treating a security element - Google Patents

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, in particular banknotes, checks, vouchers or vouchers, entrance tickets to cultural or sporting events, transport tickets. It may also be a secure document chosen from certificates of authenticity or warranty certificates, or secure packaging, in particular for medicines, electronic parts, spare parts, perfumes, a secure card or a secure label. Preferably, it is a bank note.

Such documents are conventionally provided with security elements integrated into a substrate, in particular paper or polymer, on the surface, in the window or in bulk.

Banknotes are exposed during their life to many manipulations and risks of soiling. In order to give them 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 ensure the barrier function without unduly impairing the printability of the paper during the manufacture of the banknotes.

Cotton-based papers for banknotes, to which one or more layers of a transparent water-based coating are applied to protect them, are usually marketed as "high-durability substrate" (HD substrate), or " very-high-durability substrate "(THD substrate), depending on the case.

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 resistance to the circulation of banknotes by impregnating the fibrous substrate, before printing, with a composition which contains one or more binders chosen for their mechanical characteristics.

Requirement US 2007/0017647 A1 discloses a paper for the manufacture of banknotes, having improved soil 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 the application of a liquid polyurethane composition to a fibrous substrate, to form a protective coating.

Requirement US 2004/0023008 A1 discloses a security paper for use in 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 process for imparting resistance to moisture and dirt to a fibrous substrate, comprising impregnating the substrate on two opposite sides with an aqueous composition comprising one or more thermoplastic resins.

The patent EP 815 321 B1 discloses a paper intended for the manufacture of banknotes, an aqueous dispersion of polyurethane having been deposited on the fibrous substrate, this dispersion of polyurethane being free of fillers and transparent.

EP 1 783 273 discloses a security paper of improved durability, a composition containing a fluororesin having been surface applied.

WO 2012/156904 A1 describes 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 arrays.

The Motion® security thread sold by the company Crane constitutes such an example of a security element with a micro-lens array, used in the field of banknotes. This wire generates an image that moves when the note is tilted.

In general, the application of transparent protective coatings on an optical structure composed of an array of microlenses degrades the sharpness and clarity of the image produced by the optical structure. A transparent material such as a varnish, with a refractive index higher than that of the ambient air, modifies the path of the light radiation between the exterior and the lenses. The image then appears blurry and ill-defined. The blurring of the Motion® security thread by a protective coating of the varnish type is thus a well-known phenomenon.

However, more and more substrates for secure documents such as banknotes, incorporating a security element of the lenticular array type, are covered with a transparent protective coating, before or after printing this substrate.

In particular, cotton-based papers for banknotes, not only more and more often include security threads with a lenticular optical structure introduced at the start of paper manufacture, but are also covered with one or more layers of clear protective anti-fouling coating at the end of manufacture, as mentioned above.

The security threads are for example unwound at the head of the machine 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 special precautions during the application of the coating, the visual effect provided by the security thread is degraded on such papers thus coated.

The simplest method to avoid this phenomenon of blurring consists in not applying the coating to the surface of the security element with a lenticular optical structure 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 consists in reducing as much as possible the amount of coating deposited on the paper substrate and security element assembly. The main drawback is a reduction in the protection of the paper, while the image produced by the lenticular structure nevertheless loses in sharpness.

As has been explained previously, the state of the art is therefore not entirely satisfactory, since it does not allow the sharpness and clarity of the images produced by the micro-array optical structures to be preserved as much as desired. lenses of security elements inserted into high- or very-high-durability paper substrates.

WO 2012/153114 A1 teaches the production of a metallic and / or diffractive security wire with first regions making it possible to improve the formation of bonds hydrogen with the paper substrate, and between these first regions to apply a hydrophobic varnish to prevent the deposition of the pulp.

The invention aims to reduce the blurring of an optical structure of a security element by a transparent coating in aqueous phase, such as a protective varnish, usually applied to paper substrates for banknotes.

The invention meets this objective by virtue of a method of processing a security element for a secure document, in particular a security element in the form of a security thread, according to claim 1, the security element comprising on one side at the bottom. at least one optical structure, this method comprising the step of continuously treating said element so as to increase the hydrophobic character of said face.

By “continuously” it should be understood that the safety element is not treated by sections which alternate with untreated sections. In the case of a window security thread, the treated area is thus located both in the windows and between the windows, and extends from one edge of the document to the opposite edge, all the way through the element. of security. In the invention, the material whose deposition is prevented or reduced is therefore a protective coating applied in aqueous phase on the substrate and the security element, and not paper pulp, unlike WO 2012/153114 A1 .

The optical structure is preferably transparent. The optical structure is preferably non-planar. The optical structure is preferably refractive, and for example comprises a lenticular array. Where appropriate, the optical structure can be reflective, diffractive and / or diffusing.

The invention is particularly suitable for on-line 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 comprises applying a hydrophobic composition to said face. The composition applied advantageously has a beading activity. In other words, the expected level of hydrophobicity of the composition applied to the treated face, or even the treated faces, of the security element is high enough to greatly reduce the wetting of said surface by water and / or the aqueous phase preparation of the protective coating. It is a question in particular of inducing 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 not or only slightly film-forming, more preferably not film-forming. The term “no or little film-forming” is understood to mean in particular the fact that the composition forms on the security element a discontinuous surface deposit, the composition forming, for example, a two-dimensional network comprising cells devoid of composition, and / or preferably islands. or isolated clusters, for example in the form of droplets or platelets of composition. This makes it possible not to unduly disturb the interface between the optical structure and the ambient air. The deposit of composition, after drying, thus covers less than 100% of said face, better less than 50%, even better less than 25%.

The amount of composition applied, by dry weight, preferably ranges from 0.05 to 0.5 g / m ² .

• les cires, contenant en particulier les composés chimiques suivants :
  • ∘ esters carboxyliques aliphatiques, notamment esters d'acides gras
  • ∘ alcanes, notamment paraffines
  • ∘ acides carboxyliques aliphatiques, notamment acides gras
  • ∘ alcools primaires aliphatiques, notamment alcools gras
• les polymères, ou les oligomères, notamment,
  • ∘ polyoléfiniques,
  • ∘ acryliques,
  • ∘ styréniques,
  • ∘ vinyliques,
  • ∘ fluorés,
  • ∘ siliconés,
  • ∘ fluorosiliconés.

The hydrophobic composition advantageously comprises one or more hydrophobic compounds. This or these hydrophobic compound (s) are preferably chosen from:

• waxes, containing in particular the following chemical compounds:
  • ∘ aliphatic carboxylic esters, in particular fatty acid esters
  • ∘ alkanes, especially paraffins
  • ∘ aliphatic carboxylic acids, especially fatty acids
  • ∘ primary aliphatic alcohols, in particular fatty alcohols
• polymers or oligomers, in particular,
  • ∘ polyolefins,
  • ∘ acrylics,
  • ∘ styrenic,
  • ∘ vinyls,
  • ∘ fluorinated,
  • ∘ silicone,
  • ∘ fluorosiliconates.

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, roll transfer, gravure, flexography, screen printing or dip-wipe process.

Although the application of a treatment composition constitutes a preferred solution for protecting said face from the coating subsequently deposited, due to the simplicity of its implementation, said face can be further treated by grafting, in particular physical, chemical or physico-chemical. The latter can be carried out by chemical vapor deposition, assisted by plasma. Preferably, fluorinated sites are then grafted onto said face.

The processing of the security element is preferably carried out before the latter is integrated into a substrate of the secure document. The invention is particularly suitable for processing a security element in the form of a security thread.

A further subject of the invention is a method of manufacturing a secure document, according to claim 13, in which a security element such as obtained by implementing the method is incorporated on or in a substrate of said document.

This method may include the application to an entire face of the substrate, on which said face of the optical structure of the security element is visible, of an aqueous protective coating, in particular transparent.

The security element may be, during the application of this coating, in the form of a security thread integrated into the window (s).

A further subject of the invention, according to claim 11, is a security element as such, processed according to the method defined above. This security element can be characterized, according to one aspect of the invention, by the fact that it presents a discontinuous deposit, on a non-planar face of an optical structure, of a residue of hydrophobic composition, preferably a wax. . We also speak in this case of little or no film-forming deposit. The amount of composition residue preferably being between 0.05 and 0.5 g / m ² . This residue can cover less than 50%, better still less than 25%, of the face of the optical structure.

• la figure 1 représente de façon schématique en coupe longitudinale, un élément de sécurité selon l'invention.

The invention may be better understood on reading the detailed description which follows, of non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

• the figure 1 schematically shows in longitudinal section, a security element according to the invention.

Security element

The security element according to the invention can be in the form of any element introduced into the substrate of the document 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, a patch, a lamination strip, a protective film.

The security element can be a security thread introduced into the round shape or onto the flat paper forming table, either directly in a wet jet (fibrous layer), or between two wet jets.

• ASTM D7490 Standard test method for measurement of the surface tension of solid coatings, substrates and pigments using contact angle measurements
• NF EN 828 Février 2013 Adhésifs - Mouillabilité - Détermination par mesurage de l'angle de contact et de l'énergie superficielle libre de la surface solide
• ISO/CD 19403-2 Peintures et vernis - Mouillabilité - Partie 2 : Détermination de l'énergie libre de surface des surfaces solides par la mesure de l'angle de contact (norme en projet)

The treatment of the security element can result, on its surface, by a hydrophobicity which can be quantified by measuring the contact angle of the 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
• NF EN 828 February 2013 Adhesives - Wettability - Determination by measurement of the contact angle and the 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 (standard in draft)

The contact angle on the visible face of the optical structure is thus preferably greater than or equal to 90 °.

The treatment can also result in the presence of a residue of treatment composition on the treated side of the security element. This residue is preferably arranged other than in the form of a continuous film.

Besides the optical structure and the presence of the treatment composition residue, the security element may include other first, second or third level security means.

• motifs apparaissant en lumière transmise et formés par métallisation et/ou démétallisation,
• colorants, pigments luminescents, pigments interférentiels et/ou pigments à cristaux liquides, notamment sous forme imprimée ou mélangée à au moins une couche constitutive de l'élément de sécurité,
• composés, colorants et/ou pigments photochromes ou thermochromes, notamment sous forme imprimée ou mélangée à au moins une couche constitutive de l'élément de sécurité,
• absorbeur ultraviolet (UV), notamment sous forme enduite ou mélangée à au moins une couche constitutive de l'élément de sécurité,
• structure multicouche interférentielle,
• une couche biréfringente ou polarisante,
• une structure de diffraction,
• des moyens produisant un "effet de moiré", un tel effet pouvant par exemple faire apparaître un motif produit par la superposition de deux moyens de sécurité, par exemple par le rapprochement de lignes de deux moyens de sécurité,
• un filtre coloré.
• une sécurité lisible automatiquement, ayant des caractéristiques spécifiques et mesurables de luminescence (par exemple fluorescence, phosphorescence), d'absorption de la lumière (par exemple ultraviolet, visible ou infrarouge), d'activité Raman, de magnétisme, d'interaction micro-ondes, d'interaction aux rayons X ou de conductivité électrique.

It can 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,
• photochromic or thermochromic compounds, dyes and / or pigments, in particular in printed form or mixed with at least one layer constituting the security element,
• ultraviolet (UV) absorber, in particular in coated form or mixed with at least one constituent layer of the security element,
• multilayer interference structure,
• a birefringent or polarizing layer,
• a diffraction structure,
• means producing a "moiré effect", such an effect being able for example to reveal a pattern produced by the superposition of two security means, for example by bringing together lines of two security means,
• a colored filter.
• an automatically readable security, having specific and measurable characteristics of luminescence (eg fluorescence, phosphorescence), light absorption (eg ultraviolet, visible or infrared), Raman activity, magnetism, micro interaction waves, X-ray interaction or electrical conductivity.

When the security element is in the form of a wire, its width is for example between 1 and 10 mm and its thickness between 10 and 100 μm.

The security element may comprise a support film of thermoplastic material, in particular of polyester or polyester terephthalate. The optical structure may cover one side only of this support film, or alternatively, be disposed 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 an array of microlenses and / or one or more Fresnel lenses.

The optical structure may include spherical or aspherical micro lenses, in the form of a bidirectional network.

The microlenses may have a hexagonal or other shaped base.

The figure 1 shows in longitudinal section an example of a security thread incorporating a non-planar optical structure 1, formed by an array of microlenses.

This wire is shown inserted with windows 3 in a paper substrate 2. The windows 3 are separated by bridges 8.

The microlenses 9 produce, through the windows 3, an enlarged image of the micropatterns 4, the latter being for example located at the focus of the microlenses.

The optical structure 1 then has a non-planar face which is defined by all of the convex faces of the microlenses.

The local variation in the thickness of the security element, linked 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 with a hydrophobic composition with beading activity.

Solid residues 6 of composition may thus be present on face 5.

The thickness of these residues is for example less than or equal to 1 μm.

Residues 6 are present not only in windows 3 but also under bridges 8 between windows 3.

The optical structure 1 may be of thermoplastic material or may have been crosslinked by UV radiation, for example.

The optical structure 1 can be formed by embossing a polymer layer, by molding, printing, machining or engraving.

Examples of optical structures are described in the publications US 8,284,492 B2 and WO 2003/061983 .

Security element processing method

The invention makes it possible to make the visible 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 the spreading of the aqueous protective coating, following the modification of the surface tension of said face of the optical structure.

When this treatment includes the application of a composition, the fact that the treatment composition applied is not, or only slightly, film-forming, prevents it itself from being the cause of a blurring phenomenon.

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.

After drying, the composition covers less than 100%, preferably less than 50% and more preferably less than 25%, of said face of the optical structure. Preferably, the composition forms, after drying, individualized clusters.

When the security element is a security thread embedded in window (s) in a wet-laid 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 level of the bridges between the windows to reinforce the adhesion of the fibers of the paper to the thread.

It is thus preferable that the hydrophobicity property and the beading activity induced by the treatment are not excessive so as not to significantly disturb the formation of the papermaking bridges.

It is also preferred that the treatment does not generate residues of significant thickness on 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, better still 1 μm, being in particular between 0.1 μm and 1 μm.

The security element may either be pretreated at the manufacturer of the security element or at the manufacturer of the substrate of the secure document, before its incorporation. In the latter case, the security element, for example the security thread, can be pretreated directly at the head of the paper machine, when the thread is unwound.

The security element, when constituted by a security thread, can be treated by continuous application by a process of spraying, transfer to the roller, gravure printing, flexography, screen printing or soaking-wiping of the composition, at least on the side concerned 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 of the composition, before its incorporation into the substrate.

Treatment composition (not forming part of the invention as claimed)

The treatment composition can be aqueous 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, in particular with a beading effect, can be applied to the structure, replacing a paraffin emulsion.

• polyoléfiniques, comme le PE ou le PE,
• acryliques, en particulier contenant des chaînons butyl ou hexyl,
• styréniques,
• vinyliques, à base de longues chaînes aliphatiques,
• fluorés, par exemple le PTFE ou le PVDF,
• de silicones,
• de fluorosilicones.

They are in particular polymers, or oligomers:

• polyolefins, such as PE or PE,
• acrylics, in particular containing butyl or hexyl links,
• styrenic,
• vinyl, based on long aliphatic chains,
• fluorinated, for example PTFE or PVDF,
• silicones,
• fluorosilicones.

These polymers are mainly delivered as an emulsion, suspension, or dispersion in an aqueous or organic solvent phase. They are used in formulations which may contain other polymer 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 heat-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, otherwise 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, exhibiting hydrophobic properties, in particular beading, by grafting.

An example of a grafting process is plasma-assisted chemical vapor deposition. We then speak of PECVD, for Plasma-Enhanced Chemical Vapor Deposition. This technique makes it possible, in particular, to generate very hydrophobic fluorine derivatives.

Examples

The compositions of the examples below are applied in the laboratory to the optical face of a security thread with a Motion® micro-lenticular structure from the company CRANE.

The compositions are produced with different degrees of dilution of the hydrophobic compound, in order to vary the quantity of dry active material deposited on the surface of the microlenses.

Two series of pretreatment compositions are tested.

1 ^st round Example 1 (the contents are expressed by weight relative to the total weight of the composition):

Aquacer 539 * 100.0%, Water 0.0% * Commercial emulsion of paraffin modified in aqueous phase manufactured by the company BYK, the melting point of which is equal to 90 ° C., at 35.0% dryness.

Example 2 :

Aquacer 539 ** 33.3%, Water 66.7% ** Commercial emulsion of Example 1 diluted to 200% by adding 200 g of water to 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 adding 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 security thread, itself fixed on blotting paper absorbing the excess of composition. Then the wire is dried in a ventilated oven at 130 ° C.

The contraction of drops of water deposited on the yarn after drying shows that a beading effect has been generated 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 itself generate a blurring phenomenon. 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 the treatment, the security threads are incorporated into PVA coated banknote paper, by lamination at 140 ° C.

Two different transparent protective coatings in aqueous phase were applied to the secure substrate using size press rolls (or "size-press"). In this first series of tests, one of the size press rollers has a stainless steel surface, while the other is covered with a rubber casing. The transparent protective coating in aqueous phase is dried at 130 ° C. in forced convection for 3 min.

Coating 1

Aqueous protective coating for THD paper from the Applicant, based on polyethylene (PE).

Coating 2

Aqueous protective coating based on polyurethane (PU) for HD paper from the Applicant.

The sharpness of the images of the security threads with a Motion® micro-lenticular structure 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. Visual performance of the yarn. Security thread Without treatment Treatment by composition 1 to 3 according to the invention - Composition 3 Composition 2 Composition 1 No protective coating - 5 4 5 3 Protective coating 1 Protective coating 1 deposited at 2.3 g / m ² / side Passage through the size press on the stainless steel roller side 3 4 5 3 Passage through a gluing press on the rubber roller side 3 4 4 3 Average passages in a size press 3 4 4.5 3 The scale of results is as follows:
5 excellent, 4 very good, 3 good, 2 fair, 1 poor, 0 bad. Visual performance of the yarn Security thread Without treatment Treatment by composition 1 to 3 Composition 3 Composition 2 Composition 1 No protective coating - 5 4 5 3 Protective coating 2 Protective coating 2 deposited at 4.0 g / m ² / side Passage through the size press on the stainless steel roller side 3 5 4 2 Passage through a gluing press on the rubber roller side 2 5 3 2 Average passages in a size press 2.5 5 3.5 2

Laboratory evaluation shows that the hydrophobization of the security thread greatly improves its optical performance in the two cases studied.

The image transmitted by the array of micro lenses appears much clearer and more defined. On a scale of 0 to 5, the rating quantifying the sharpness of the image thus passes on average from 3.0 to 4.5 in the case of coating 1 for THD paper and from 2.5 to 5.0 with the coating 2 for HD paper, respectively due to the hydrophobic compositions 2 and 3 at the surface of the Motion® security thread.

It is also noted that it is possible to determine an optimum composition (composition 2 for the protective coating 1 and composition 3 for the protective coating 2).

2 ^th series Example 4 (the contents are expressed by weight relative to the total weight of the composition):

Aquacer 539

20.0%, Water 80.0%

Commercial emulsion of Example 1 diluted to 400% by adding 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% dryness.

Example 6 :

Aquacer 539

4.0%, Water 96.0%

Commercial emulsion of Example 1 diluted to 2400% by adding 2400 g of water and 100 g of wax emulsion, ie 1.4% dry.

The composition of each of Examples 4 to 6 is applied using a roller of cellular foam to the non-planar upper face of the security thread, itself fixed to blotting paper absorbing the excess of composition. Then the wire is dried in a ventilated oven at 130 ° C.

The contraction of drops of water deposited on the yarn after drying shows that a beading effect has been generated on the surface of the yarn 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 itself generate a blurring phenomenon. 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 incorporated into PVA coated banknote paper by lamination at 100 ° C. The two different transparent water-based protective coatings were applied to the secure substrate in a size press using rollers. In this second series of tests, the two rollers of the size press are covered with a rubber casing. The transparent protective coating in aqueous phase is dried at 130 ° C. in forced convection for 3 min.

Coating 1

Aqueous protective coating based on polyethylene (PE) for THD paper from the Applicant.

Coating 2

Aqueous protective coating based on polyurethane (PU) for HD paper from the Applicant.

The sharpness of the images of Motion® micro-lenticular structure security threads covered by coatings 1 and 2 is evaluated as a function of the implementation, or not, of a pretreatment with the compositions of Examples 4 to 6. Visual performance of the yarn. Security thread Without treatment Treatment by composition 4 to 6 according to the invention - Composition 6 Composition 5 Composition 4 No protective coating - 5 5 4 3 Protective coating 1 Protective coating 1 deposited at 1.4 g / m ² / side Passage through a gluing press on the front rubber roller side 2 4 4 3 Passage through a gluing press on the rear rubber roller side 2 3 4 3 Average passages in a size press 2 3.5 4 3 The scale of results is as follows:
5 excellent, 4 very good, 3 good, 2 fair, 1 poor, 0 zero. Visual performance of the yarn Security thread Without treatment Treatment by composition 4 to 6 Composition 6 Composition 5 Composition 4 No protective coating - 5 5 5 3 Protective coating 2 Protective coating 2 deposited, at 3.2 g / m ² / side Passage through a gluing press on the front rubber roller side 2 3 3 3 Passage through a gluing press on the rear rubber roller side 1 2 4 3 Average passages in a size press 1.5 2.5 3.5 3.0

Laboratory evaluation shows that the hydrophobization of the security thread greatly improves its optical performance in the two cases studied.

Likewise, the image transmitted by the array of microlenses then appears distinctly clearer and more defined. On a scale of 0 to 5, the rating quantifying the sharpness of the image thus passes on average from 2.0 to 4.0 in the case of coating 1 for THD paper and from 1.5 to 3.5 with the coating 2 for HD paper, in both cases due to the hydrophobic composition 5 on the surface of the Motion® security thread.

It is also noted that it is possible to determine an optimal composition (composition 5 for protective coatings 1 and 2).

Authentication process

The fact that the security element undergoes in the invention a treatment to be made more hydrophobic can be taken advantage of to authenticate the element.

This involves, for example, measuring the contact angle of the water and / or the trace of a discontinuous deposit of hydrophobic composition on the element.

A further subject of the invention is thus a method for authenticating a security element according to claim 14, in which the contact angle of the water on the non-planar face of the optical structure and / or l is measured. '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.

Counterfeiting is for example detectable by combining the observation of the security element and the measurement of the physicochemical properties thereof.

Concretely, there may be a suspicion of counterfeiting provided, on the one hand, a discontinuous or very fine deposit of hydrophobic compound (s) is observed on the surface of the security element, and on the other hand 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 finds application to other refractive optical structures.

The expression “comprising a” should be understood as being synonymous with “comprising at least one”, and “between” is understood to be limits included.

Claims (14)

1. Process for treating a security-document security element, and especially a security element taking the form of a security thread, the security element comprising, on a face (5), at least one, preferably non-planar, optical structure (1), this process comprising a treatment of said security element comprising applying a composition to said face (5), the composition comprising one or more hydrophobic compounds, the process being characterized in that it comprises the step consisting in continuously treating said element, i.e. the security element is not treated in segments that alternate with untreated segments right the length of the security element, so as to increase the hydrophobic character of said face, and in that the hydrophobic composition forms, on the security element, a discontinuous superficial deposit, the deposit of composition, after drying, covering less than 100% of said face.
2. Process according to Claim 1, the optical structure being non-planar, the optical structure (1) especially being able to comprise a lenticular array.
3. Process according to Claim 1 or 2, the treatment causing the contact angle of water on said face to increase by at least 10°, and especially to a value higher than or equal to 90°.
4. Process according to any one of the preceding claims, the applied composition having a beading effect, the composition especially being not or slightly film-forming and preferably not film-forming, the total mass content of hydrophobic compound(s) in the composition possibly being comprised between 10 and 100%, the one or more hydrophobic compounds possibly being chosen from:

   - waxes, in particular waxes containing the following chemical compounds:

   ∘ aliphatic carboxylic acid esters, especially fatty acid esters

   ∘ alkanes, especially paraffins

   ∘ aliphatic carboxylic acids, especially fatty acids

   ∘ aliphatic primary alcohols, especially fatty alcohols

   - polymers or oligomers, especially

   ∘ polyolefins

   ∘ acrylics

   ∘ vinyl polymers or oligomers

   ∘ styrene polymers or oligomers

   ∘ fluoropolymers or fluoro-oligomers

   ∘ silicone polymers or oligomers

   ∘ fluorosilicone polymers or oligomers,

   the composition possibly in particular comprising at least one wax, and preferably a paraffin wax.
5. Process according to one of the preceding claims, the one or more hydrophobic compounds being present within the composition in a total amount comprised between 10 and 100.
6. Process according to any one of the preceding claims, the composition comprising an adhesive, especially a heat-activatable adhesive.
7. Process according to any one of the preceding claims, the thickness of the residue of composition on said surface, after drying, being smaller than or equal to 5.0 µm, better still than 1.0 µm, and especially being comprised between 0.1 µm and 1.0 µm, and the deposit of composition, after drying, possibly covering less than 100% of said face, better still less than 50%, and even better still less than 25%.
8. Process according to any one of the preceding claims, the composition being applied using a spraying process, roll coating, rotogravure printing, flexographic printing, screen printing, or dipping-wiping, said face possibly being treated via physical, chemical or especially physico-chemical grafting.
9. Process according to any one of the preceding claims, the treatment of the security element being performed before the latter is integrated into a substrate (2) of the security document.
10. Process according to any one of the preceding claims, the security element being a security thread.
11. Security element obtained by implementing the process according to any one of the preceding claims.
12. Security element according to the preceding claim, comprising a discontinuous deposit (6) on the non-planar face (5) of the optical structure (1) of a residue of hydrophobic composition, preferably a wax, the amount of residue of composition being comprised between 0.05 and 0.5 g/m².
13. Process for manufacturing a security document, wherein a security element obtained by implementing the process such as defined in any one of Claims 1 to 10 is incorporated onto or into a substrate of said document, the process possibly especially comprising applying to all of one face of the substrate, on which face said face of the optical structure of the security element may be seen, an aqueous, especially transparent, especially PU-based, protective coating, the security element possibly especially taking the form of a security thread integrated into one or more windows.
14. Method for authenticating a security element such as obtained by implementing the process defined in any one of Claims 1 to 10, wherein the contact angle of water on the face (5) of the non-planar optical structure is measured 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 on the basis of this measurement and/or detection.

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