EP3640040A1 - Safety film and method for manufacturing a safety film - Google Patents

Abstract

The present description relates to a security film (20) transferable onto a substrate (100) of a document to be secured, the security film comprising a support film (21) intended to be removed after transfer; a set of security layers (23) imparting a recognizable optical effect to the security film; a discontinuous controlled destruction layer (26) arranged between the support film and a first face of the set of security layers, said controlled destruction layer being intended to remain fixed to the set of security layers during transfer security film on the substrate.

Description

FIELD OF THE INVENTION

The present invention relates to the field of security marking. More particularly, it relates to a security film transferable to a document, a method of manufacturing such a security film and a method of securing a document by means of such a security film.

STATE OF THE ART

Numerous technologies are known for securing documents, and in particular for securing documents such as travel documents, for example passports or other temporary or final identification documents, official documents such as driving licenses, vehicle identification, certificates, or banknote-type value documents. These technologies aim to protect against attempts at falsification and counterfeiting through the use of optical security components, the optical effects of which depend on observation parameters (orientation relative to the observation axis, position and dimensions of light source, etc.) take on characteristic and verifiable configurations. The general purpose of these optical components is to provide easily identifiable and differentiating optical effects, for example optical effects visible to the naked eye, from physical configurations that are difficult to reproduce or imitate.

Among the optical safety components, the components of the OVD type for "Optical Variable Device" are known for example, and in particular the components of the DOVID type for "Diffractive Optical Variable Image Device", adapted to generate diffractive effects, in reflection or in transmission. , commonly known as "holograms". In addition to the optical security components configured to generate diffractive effects, there are known optical security components forming filters in wavelengths, for example interference filters for producing, for example, color change effects known under the English term " color shift ", bandpass filters using DID® type guided mode resonances (sold by SURYS®) or plasmon resonances, etc.

To secure documents using optical security components, it is known to include these components in multilayer films of “label” type, comprising a support film on which is arranged a set of layers including a set of active layers making it possible to give the optical component a recognizable optical effect and an adhesive layer. The average thickness of multilayer label type films is between 20 µm and 100 µm. Such multilayer films are intended to be bonded to a support of a document to be secured, for example by hot bonding, by means of the adhesive layer.

Patents and patent applications US5104471 and US20160200133 thus describe multilayer label type films.

For securing documents by means of optical security components, it is also known to include these components in films known as “multilayer transfer films” designed to be transferred locally to the document to be secured, in particular by hot pressing. After the transfer, the support film which was used to manufacture the component is removed. The component after transfer is therefore much thinner (typically of thickness less than ten micrometers) than a multilayer film of the label type. It generally covers a limited part of the surface to be protected, generally greater than 10 mm ² and typically a few cm ² ; it can be in one piece or consist of several contiguous or disjoint fragments.

The FIG. 1 thus illustrates a multilayer transfer film 10 configured to be transferred to a document. It generally comprises a support film 11, a release layer 12, a set of layers 13 called “optically active” or “security layers” making it possible to give the multilayer transfer film a recognizable optical effect, and an adhesive layer 14. When the transfer film is transferred onto a surface of a substrate 100 of a document to be secured by means of the adhesive layer 14, for example by hot pressing, the release layer 12 allows total separation of the part to be eliminated, namely the support film 11 and the release layer 12. In certain cases, after transfer and release of the support film and of the release layer, a protective film is applied to the entire substrate of the document coated locally with the set of optically active layers, in order to give the entire surface physical and chemical protection against natural or artificial attack.

Such multilayer transfer films are for example described in the published patent application. EP 1770670 or the published patent application FR 2 968 239 . Specifically, the document EP 1770670 describes a heat transferable multilayer transfer film, in the form of a continuous strip, and used for transferring one or more optical components to a valuable document, the shapes of which are determined by the form (s) of iron marking used for hot pressing.

Secured documents with multilayer transfer films known from the state of the art are in essence extremely difficult to replicate effectively, in particular because the technologies for producing the optically active layers are complex to implement. However, a counterfeiter could attempt to extract the optical security components transferred to a document in order to reuse them in counterfeit documents, even if it means using extreme extraction conditions (eg very high temperature, very low pressure). In practice, an ill-intentioned tear-off attempt of an optical component resulting from the transfer of a multilayer transfer film as illustrated on the FIG. 1 leads to destruction of the optically active layers according to an unpredictable pattern of destruction, and therefore unsatisfactory for preventing counterfeiting.

An object of the invention is to provide a security film transferable onto a substrate of a document, the optically active layers of which, ie forming the optical security component, have an ability to dissociate from the substrate according to a predetermined pattern of destruction. controlled in response to a subsequent attempt to tear off the component with fraudulent intent, in particular when it is covered with an additional protective film.

SUMMARY OF THE INVENTION

• un film support configuré pour être éliminé après transfert du film de sécurité sur le substrat;
• un ensemble de couches de sécurité conférant un effet optique reconnaissable au film de sécurité ;
• une couche de destruction contrôlée, discontinue selon un motif de destruction donné, agencée entre le film support et une première face de l'ensemble de couches de sécurité, ladite couche de destruction contrôlée étant configurée pour rester fixée à l'ensemble de couches de sécurité lors du transfert du film de sécurité sur le substrat.

According to a first aspect, the present description relates to a security film transferable onto a substrate of a document to be secured, the security film comprising:

• a support film configured to be removed after transfer of the security film to the substrate;
• a set of security layers providing a recognizable optical effect to the security film;
• a controlled destruction layer, discontinuous according to a given destruction pattern, arranged between the support film and a first face of the set of security layers, said controlled destruction layer being configured to remain fixed to the set of security layers during the transfer of the security film onto the substrate.

Such a security film allows, after transfer of the security film on the substrate of the document and during a subsequent and malicious attempt to tear off the set of security layers, a selective and controlled destruction of said set of layers according to the destruction pattern which reproduces the discontinuous pattern of the controlled destruction layer. It is therefore no longer possible for a counterfeiter to extract all or a substantial part an optical security component formed by said set of security layers.

According to one or more exemplary embodiments, the security film further comprises an adhesive layer for fixing the security film to the substrate. The adhesive layer is in contact with a second face of the set of security layers, opposite to said first face. For example, the adhesive layer comprises a material selected from the group comprising: a resin based on acrylic copolymer, and / or of a styrene-acrylate copolymer and / or of an ethylene vinyl acetate (EVA) copolymer, which may contain silica.

According to one or more exemplary embodiments, the thickness of the adhesive layer is between 1.0 μm and 6.0 μm.

According to one or more exemplary embodiments, the adhesive layer is continuous, in order to ensure a homogeneous adhesion of the security film on the substrate.

According to one or more exemplary embodiments, the security film further comprises a release layer, uniform, in contact with the support film, of a different nature from that of the controlled destruction layer. The release layer facilitates the release of the support film during transfer to the substrate. For example, the release layer comprises a material selected from the group comprising: a natural wax (eg candelilla, montan, carnauba or equivalent), a synthetic wax, a polyurethane resin, an acrylic resin, a cellulose resin, or a combination of these materials. During a hot transfer, for example, these materials can melt and allow total detachment by creep.

According to one or more exemplary embodiments, the thickness of the release layer is less than 0.5 μm.

In other embodiments of the present description, detachment of the support film during the transfer of the substrate can be facilitated by means, for example, of a pretreatment of the surface of the support film.

The release layer and / or the pretreatment of the support film allow total elimination of the support film after transfer of the security film to the substrate, without this total elimination causing degradation of the set of security layers.

According to one or more exemplary embodiments, the support film comprises a material selected from the group comprising: a polyethylene terephthalate (PET), a polypropylene (PP), a polystyrene (PS).

According to one or more embodiments, the controlled destruction layer comprises a material selected from the group comprising: a polyacrylate, a polyvinyl chloride, a polyvinyl acetate, a polyurethane, a polycarbonate, a polyester, an ethylene vinyl acetate copolymer, a hydrocarbon resin, a chlorinated polyolefin, a polyvinyl alcohol, a fluoropolymer, a melamine resin, a ketone / formaldehyde resin, an epoxy resin, a phenolic resin, a urea resin, a synthetic resin, a polystyrene, a polymeric cellulose compound, a polyamide, a liquid crystal polymer (LCPs), or a combination of the above materials.

In particular, security films according to the present description comprising controlled destruction layers comprising a fluoropolymer, for example a polyvinylidene fluoride (PVDF), for example a PVDF crystallizing in alpha form, have shown satisfactory selective destruction of an optical component security resulting from the transfer of the security film on a document to be secured. In particular, tests for measuring the peel force necessary for tearing off the optical safety component have shown a profile of the peel force characteristic of a pattern of controlled destruction.

According to one or more exemplary embodiments, the controlled destruction layer comprises at least one crosslinking agent in order to induce a bridging reaction with a layer in contact with said controlled destruction layer, and initially having little affinity with it. According to one or more exemplary embodiments, the controlled destruction layer comprises between 0.5% and 2% by weight of said crosslinking agent. According to one or more exemplary embodiments, said crosslinking agent is selected from the group comprising: a carbodiimide, a melamine resin, an aziridine, an isocyanate or a combination of the abovementioned materials. A bridging reaction can for example be triggered by a hot lamination process.

According to one or more exemplary embodiments, the thickness of the controlled destruction layer is between 100 nm and 2 μm, for example between 200 nm and 1 μm. The layer of controlled destruction being discontinuous, the thickness in question corresponds to a local thickness, that is to say to a thickness of the layer of controlled destruction corresponding to the case where the layer is continuous, that is to say say without empty parts. In other words, the thickness in question does not correspond to an average thickness taking into account the empty parts and the solid parts of the controlled destruction layer. Thus, the layer of controlled destruction is thin enough not to be detected on visual inspection.

According to one or more exemplary embodiments, the controlled destruction layer is transparent in the spectral band of visible light. By "transparent layer" is meant in the present description a layer having a transmission at least greater than or equal to 80%, for example greater than or equal to 90% in the observation spectral band. When the controlled destruction layer is transparent in the spectral band of light visible (400 nm to 800 nm), it is therefore invisible to the naked eye and can thus escape the attention of a potential counterfeiter.

According to one or more exemplary embodiments according to the present description, the controlled destruction layer comprises markers detectable only in a given spectral band. According to one or more exemplary embodiments, said spectral band is included in UVA, UVB, UVC, infrared, or a combination of these spectral bands. According to one or more exemplary embodiments, the markers are detectable under the action of light, thermal (e.g. thermochromic pigments), electromagnetic or piezoelectric stimulation. Such markers allow a first non-destructive control of the authenticity of the secure document. For example, the markers can include an ink of IRB900 type, defined in ISO1831 and detectable only in the near infrared (850 nm to 950 nm).

According to one or more exemplary embodiments, the set of security layers comprises a structured layer. Said structured layer can be produced for example by hot stamping of a thermoformable layer or by cold molding in a molding layer, followed by a crosslinking operation, according to a technology known by its English name of "casting" .

According to one or more exemplary embodiments, the set of security layers comprises a reflective layer, continuous or discontinuous. For example, the reflective layer is formed of a metallic coating, for example produced by vacuum deposition of one or more metallic films, comprising for example aluminum, chromium, copper or an alloy of these metals. The reflective layer can also be formed of a layer of dielectric material transparent in the visible and of an optical refractive index distinct from that of the surrounding layers, that is to say having a differential of refractive index greater than 0.2, advantageously greater than 0.5. The transparent dielectric material can for example comprise zinc sulfide (ZnS) or titanium dioxide (TiO ₂ ) or another material. The reflective layer may comprise an alternation of layers of metallic material and of layers of dielectric material, such as those mentioned above. It can also be carried out by applying a varnish containing metallic elements. Materials suitable for forming a reflective layer or multilayer in a set of security layers of the security film according to the present description are described for example in tables 1 to 6 of the published patent US4856857 , an interference filter as described for example in the published patent application CA2543790C .

According to one or more exemplary embodiments, the reflective layer is continuous. In other examples, it is discontinuous. The continuous or discontinuous nature of the reflective layer is provided according to the contrast or transparency needs of the set of security layers.

The set of security layers may further comprise an optional encapsulation layer.

A set of security layers in a security film according to the present description may be intended to form, without limitation, an optical security component of DOVID type, a reflective component at zero order as described for example in the published patent applications EP2567270 , EP3129238 , or EP2264491 , a component with plasmonic effect as described for example in the published patent application WO2013060817 .

According to one or more exemplary embodiments according to the present description, the thickness of the set of security layers is between 0.5 μm and 1.5 μm.

According to one or more exemplary embodiments according to the present description, the thickness of the security film once the support film has been removed is less than 10 μm.

According to a second aspect, the present description relates to a method of manufacturing a security film according to the first aspect.

• la provision d'un film support, ledit film support étant configuré pour être éliminé après transfert dudit film de sécurité sur ledit substrat ;
• optionnellement, le dépôt sur le film support d'une couche de détachement;
• l'impression sur la couche de détachement ou directement sur le film support en cas d'absence de couche de détachement, d'une couche de destruction contrôlée, discontinue selon un motif de destruction donné;
• le dépôt, après impression de ladite couche de destruction sur ladite couche de détachement ou sur ledit film support, d'un ensemble de couches de sécurité conférant un effet optique reconnaissable au film de sécurité, ladite couche de destruction contrôlée étant configurée pour rester fixée à l'ensemble de couches de sécurité lors du transfert du film de sécurité sur le substrat.

More specifically, the present description relates to a process for manufacturing a security film transferable onto a substrate of a document to be secured, comprising:

• providing a support film, said support film being configured to be removed after transfer of said security film on said substrate;
• optionally, the deposition on the support film of a release layer;
• printing on the release layer or directly on the support film in the absence of a release layer, of a controlled destruction layer, discontinuous according to a given destruction pattern;
• the deposition, after printing of said destruction layer on said release layer or on said support film, of a set of security layers conferring a recognizable optical effect on the security film, said controlled destruction layer being configured to remain fixed to the set of security layers during the transfer of the security film onto the substrate.

According to one or more exemplary embodiments, before or after the deposits of said layers, a surface treatment of one or more layers is carried out. Said surface treatment may for example include a corona treatment or else a plasma treatment. The plasma treatment can be carried out at ambient pressure (“atmospheric plasma”), or under high vacuum, at a pressure of the order of Pascal. The surface treatment of the layers can allow better adhesion between layers depending on the nature of the materials involved. Thus, in certain cases, a surface treatment can make it possible to moderate apparent incompatibilities related to the nature of the materials.

According to one or more exemplary embodiments, the controlled destruction layer is printed on the release layer or on the support film, over a limited area, between 30% and 70%, for example between 40% and 60%, of the total surface of the release layer or of the support film. Indeed, too small a printing surface of the controlled destruction layer will have the consequence of unfavoring the controlled destruction by tearing off the protective film, because the controlled destruction layer will be entrained in an exacerbated manner by the protective film. Likewise, too large a printing surface of the destruction layer may also disadvantage the controlled destruction, since the controlled destruction layer will be retained in an exacerbated manner on the substrate.

According to one or more exemplary embodiments according to the present description, the printing of the discontinuous controlled destruction layer comprises the printing of regular or irregular patterns. The patterns may include cells or other finished surfaces and / or straight lines and / or curved lines and / or broken lines and / or alphanumeric characters. Printing methods can include offset (indirect printing), rotogravure, screen printing, or flexography, for rapid printing, for example industrial printing in series. Inkjet type printing can also be used to allow variable printing, "à la carte", of the patterns of the controlled destruction layer.

• la fabrication d'un film de sécurité selon un procédé tel que décrit dans le deuxième aspect de la présente description ;
• le transfert dudit film de sécurité sur au moins une partie d'une première face d'un substrat dudit document sécurisé ;
• l'élimination du film support.

According to a third aspect, the present description relates to a method for protecting a secure document comprising:

• manufacturing a security film according to a method as described in the second aspect of this description;
• transferring said security film onto at least part of a first face of a substrate of said secure document;
• the elimination of the support film.

According to one or more exemplary embodiments, the transfer of said security film onto said substrate is obtained by hot pressing.

According to one or more exemplary embodiments, the method for protecting a secure document according to the third aspect further comprises depositing a protective film on said at least part of a first face of said substrate.

Thus secured, the document is not only safe from natural aggressions such as mechanical attacks (abrasion, friction) and physicochemical attacks (humidity, contact with a liquid) but also secure in the event of malicious misappropriation. Indeed, in a document thus secured, the applicant has shown that an attempt to tear off would result in a partial, predictable and controlled tearing of the set of security layers, resulting from the presence of the discontinuous controlled destruction layer.

A safety optical component thus transferred can cover a limited surface of the substrate. In addition, it can be in one piece or consist of several fragments, contiguous or disjoint. Thus, according to one or more exemplary embodiments according to the present description, the protective film is not only in contact with at least one optical security component but is also in contact with the substrate, and thus circumscribes one or more component blocks security optics.

The protective film must be able to adhere to the substrate in order to circumscribe the part or parts of the at least one face of the substrate coated with the at least one first optical safety component, while allowing controlled destruction of the at least one component. security optic during a malicious snatch attempt.

According to one or more exemplary embodiments, the protective film comprises a polymeric material. In certain exemplary embodiments of the present description, the protective film may comprise a layer of polyethylene PE and a layer of polyester PET, in which said layer of PE is the layer of the protective film in contact, in particular, with the layer of controlled destruction. According to one or more exemplary embodiments according to the present description, the layer of polyethylene PE can be coextruded on the layer of polyester PET.

In exemplary embodiments of the present description where the protective film is composed of a layer of PE coextruded on a layer of PET, when the protective film is deposited, it is the layer of PE which ensures the heat bonding on the substrate thanks to the hot-melt nature of PE linked to its softening temperature lower than PET.

According to one or more exemplary embodiments, the thickness of the protective film is between 75 μm and 300 μm, for example between 100 μm and 300 μm. For example, the thickness of the protective film is between 150 μm and 250 μm.

According to one or more exemplary embodiments, the controlled destruction layer comprises a fluoropolymer, for example a polyvinylidene fluoride (PVDF), for example a PVDF crystallizing in alpha form; such controlled destruction layers have shown satisfactory selective destruction of an optical security component resulting from the transfer of the security film onto a document to be secured, in particular after depositing a protective film. protection, and in particular a protective film comprising a layer of polyethylene PE and a layer of polyester PET in which said layer of PE is the layer of the protective film in contact, in particular, with the layer of controlled destruction.

According to one or more exemplary embodiments, the substrate is a physical support comprising a material which can be selected from the group comprising: paper, plastic, synthetic paper such as TESLIN® or else TYVEK®.

According to one or more exemplary embodiments, the substrate is opaque, i.e. of transmittance less than or equal to 20%, for example less than or equal to 10%. In certain exemplary embodiments, the substrate may comprise an opaque material present in sufficient quantity in the substrate to make said substrate opaque.

BRIEF DESCRIPTION OF THE FIGURES

• FIG. 1, déjà décrite, un exemple de film transfert selon l'art antérieur ;
• FIG. 2, un exemple de film de sécurité selon la présente description ;
• FIG. 3, un document sécurisé au moyen d'un exemple de procédé selon la présente description ;
• FIG. 4, un schéma illustrant un exemple d'effet recherché par un arrachement malintentionné du document de sécurité selon la présente description ;
• FIG. 5A et 5B, des motifs d'impression régulier et irrégulier, alvéolaires hexagonaux de la couche de destruction contrôlée sur le film support, selon un exemple de réalisation de la présente description ;
• FIG. 6A et 6B, deux graphes représentant des mesures de force de pelage effectuées conformément à la norme ISO/IEC 10373-1 :1998(E), et illustrant l'effet de destruction contrôlée d'un composant optique sécurité dans un document sécurisé selon un exemple de réalisation de la présente description.

Other characteristics and advantages of the invention will appear on reading the following description, illustrated by the following figures:

• FIG. 1 , already described, an example of transfer film according to the prior art;
• FIG. 2 , an example of security film according to the present description;
• FIG. 3 , a document secured by means of an example method according to the present description;
• FIG. 4 , a diagram illustrating an example of effect sought by a malicious tearing of the security document according to the present description;
• FIG. 5A and 5B , regular and irregular, hexagonal cellular printing patterns of the controlled destruction layer on the support film, according to an exemplary embodiment of the present description;
• FIG. 6A and 6B , two graphs representing peel force measurements carried out in accordance with ISO / IEC 10373-1: 1998 (E), and illustrating the effect of controlled destruction of a security optical component in a secure document according to an exemplary embodiment of this description.

DETAILED DESCRIPTION

A first example of a security film 20 according to the present description is shown in the FIG. 2 . The security film 20 as illustrated on the FIG. 2 comprises a support film 21 intended to be removed after transfer, and a set of security layers 23 imparting a recognizable optical effect to the security film 20. The security film 20 of the FIG.2 in this example includes an adhesive layer 24 (optional) for fixing the security film 20 on a substrate 100 of a secure document. The adhesive layer 24 is in contact with one face of the set of security layers.

The security film 20 further comprises a discontinuous controlled destruction layer 26, arranged between the support film 21 and a face of the set of security layers 23 opposite the face in contact with the adhesive layer 24. The layer of controlled destruction 26 is intended to remain fixed to the set of security layers 23 during the transfer of the security film onto the substrate 100.

In the example of the FIG. 2 , the set of security layers 23 comprises an at least partially structured layer 232, a reflective layer 231 and an optional encapsulation layer 233. The layer 232 comprises for example polymethyl methacrylate (PMMA). The layer 231 can be discontinuous. The structuring of the layer 232 makes it possible to form, by means known from the state of the art, an optical effect recognizable by an observer, in reflection or in transmission. The set of security layers forms, for example and without limitation, an optical component of the DOVID type, a reflective component at zero order using resonances of guided modes of the DID® type, a component with plasmonic effect.

The set of security layers may also be able to generate an interference filter, in which case structuring of the layer 232 is not always necessary. The set of security layers can thus comprise a stack of transparent dielectric layers and / or transparent semiconductor layers and / or semi-transparent metal layers.

More generally, the set of security layers can comprise any multilayer arrangement adapted to form in a known manner a recognizable otic effect, for example a static and / or dynamic colored effect, which varies according to the observation conditions.

In the example of the FIG. 2 , the security film further comprises a release layer 22. This layer 22 is optional. The release layer 22 is uniform, in contact with the support film 21, of a different nature from that of the controlled destruction layer 26, and configured to allow the release of the support film 21 during transfer to the substrate 100 for the protection of 'a secure document.

The support film 21 may also have a coating of a nature to facilitate its detachment, in particular in the case where the detachment layer 22 is absent.

The transfer of the security film according to the present description, such as that shown for example on the FIG. 2 , can be carried out hot or cold. The hot transfer can be carried out by pressing the security film on the substrate 100 of the document to be secured. Cold transfer, for example in the case of a cold stamping type transfer, can be carried out by UV crosslinking of the adhesive layer 24 of the security film on the substrate 100. In certain embodiments according to this description, the adhesive layer is not contained in the security film. In this case, an adhesive layer can be applied to the substrate 100 prior to the transfer of the security film.

The substrate 100 is for example a physical support comprising a material which can be selected from the group comprising: paper, plastic, synthetic paper such as TESLIN®, or even TYVEK®.

After transfer of the security film 20 onto the substrate 100, the support film 21 can be removed.

The FIG. 3 illustrates an example of a document secured by means of a method according to the present description, resulting for example from the transfer of a security film according to the example of the FIG. 2 , on a substrate 100 of a document.

The secure document 30 as shown in the FIG. 3 comprises the substrate 100 and at least a first optical security component resulting from the transfer of a security film according to the present description, on at least part of a first face of the substrate 100. The optical security component thus comprises the set of security layers 23 and the controlled destruction layer 26, the support film having been detached with the release layer, if applicable. The secure document 30 further comprises a protective film 31 deposited on the assembly of said at least one first face of said substrate 100 coated with said at least one first optical security component.

In practice, it is possible to transfer at least one first optical security component to at least one zone of a first face of the substrate 100. The component thus transferred can cover a limited part of the surface to be protected, typically a few cm ² , and it can be in one piece or consist of several fragments, the surface of each fragment being for example greater than 5 mm ² , for example greater than 2 mm ² , said fragments being contiguous or disjoint. The protective film 31 is then not only in contact with at least one optical security component but can also be in contact with at least part of the substrate 100 and thus circumscribe one or more optical security components.

When the protective film 31 covers the optical security component, it is in contact with the controlled destruction layer 26, but also with one face of the set of security layers 23, due to the discontinuous nature of the protective layer. controlled destruction 26.

The protective film 31 can for example comprise a layer of polyethylene PE coextruded on a layer of polyester PET, the layer of PE being intended to be in contact with the layer of controlled destruction 26 and the set of security layers 23.

The thickness of the protective film 31 can be between 75 μm and 300 μm.

The FIG. 4 illustrates a possible effect of an ill-intentioned tearing of the protective film 31 from the secure document 30. The attempt to tear off the protective film 31 from the secure document 30 causes selective, predictable and controlled destruction of the set of security layers 23 in the sense that the destruction pattern of the set of security layers 23 reproduces the discontinuous pattern of the controlled destruction layer over the entire tearing surface.

The selective and controlled destruction of the set of security layers 23 can also be reinforced by a vertical gradient of adhesion within the secure document 30. This vertical gradient of adhesion or differential of adhesion can result directly from the nature of the materials involved in the layers. Without wishing to be bound by any theory, the inventors believe that affinities between materials included in different layers, at the junction between layers, that is to say on the surface of the layers, generate as many differentiated weaknesses within of the secure document 30. For example, the difference in adhesion between the set of security layers 23 and the protective film 31 on the one hand and between the controlled destruction layer 26 and the set of security layers 23 d on the other hand can be guided by the nature of the materials forming these layers. The introduction of crosslinking agents into one or more layers can also influence these differentiated weaknesses by inducing the formation of bridges between layers. The adhesion differential can also result from the choice of the thicknesses of each layer, generating mechanical stresses during the tearing which, in combination with the nature of the materials included in the layers, will also influence the pattern of destruction of the whole. security layers 23.

From the moment when the selective tear-off pattern of the set of security layers 23 reproduces the discontinuous pattern of the destruction layer controlled during a tear-off, the technical effect is obtained. This does not exclude cases, not shown on the FIG. 4 , where the pattern of destruction of the adhesive layer 24 does not reproduce the discontinuous pattern of the adhesive layer. In the example of the FIG. 4 , the adhesive layer 24 is destroyed by reproducing the same destruction pattern as that of the set of security layers 23 and of the discontinuous pattern of the controlled destruction layer. However, one could imagine a different case from that of the FIG. 4 where after tearing, the rupture present at the level of the adhesive layer 24 is located within it (in the case of a cohesive rupture). Similarly, a rupture at the interface between the adhesive layer 24 and the set of safety layers 23, or a break between two layers of different natures included in the set of safety layers 23 (corresponding to a cohesive break in the within the set of security layers), can also be envisaged according to one or more exemplary embodiments according to the present description.

The FIG. 5A illustrates a regular pattern for printing a controlled destruction layer 26 of an example of security film according to the present description.

In this example of a printing pattern, the printing of the discontinuous controlled destruction layer 26 (see the black areas corresponding to the cells) is carried out directly on the support film 21 (see the white areas corresponding to the walls between the cells).

However, the opposite scenario, namely the negative of this printing pattern, where the white areas would correspond to the areas where the layer 26 is printed, not shown in the FIG. 5A , is however concerned by the invention.

The FIG. 5B shows an irregular pattern of printing of a controlled destruction layer 26 of another example of security film according to the present description. In this example, the hexagonal pattern shown on the FIG. 5A is made more complex by means of a curved line which is superimposed on the regular pattern.

In these two cases, the patterns can be obtained for example and according to certain printing techniques by a printing cylinder comprising an engraving pattern which is the negative of the printing pattern sought for the controlled destruction layer.

A demonstration of the technical effect of controlled destruction of an optical security component according to the present description is illustrated on the FIG. 6A and 6B , representing peel strength measurements carried out in accordance with the technique described in standard ISO / IEC 10373-1: 1998 (E). According to this standardized technique, peeling between layers of a card takes place in a displacement in a linear peeling direction, the direction of the applied peeling force being maintained at 90 ° from the plane of the card throughout the displacement.

The FIG. 6A illustrates the measurement of the peeling force applied, that is to say the force necessary to tear off the protective film from a substrate coated in places with an optical security component. The peeling force, expressed in arbitrary units and represented on the ordinate on the FIG. 6A , corresponds to the force required for peeling the protective film, as a function of a displacement in a linear direction of peeling, expressed in mm, represented on the abscissa on the graph.

In the case of FIG. 6A , the optical security component does not include a destruction layer controlled according to the present description. The substrate of the FIG. 6A is made of Teslin® and the protective film of PET / PE coextruded, the PE layer of the protective film being that in contact with the optical safety component and with the Teslin® in places where the latter is not covered with the component security optics. The lower part of the peeling force curve obtained, ie between approximately 40 mm and 60 mm, corresponds to the tearing forces at the level of the safety component, and illustrates the case of a tearing without effect of controlled destruction, the part bottom of the curve being smooth. In this case, the optical safety component remained attached to the Teslin®. Note that in the case of a rupture at an interface between two layers of the optical safety component, or else a cohesive rupture of the adhesive layer, a similar curve of the peel strength would have been obtained, ie a smooth plate with a different peel strength value.

The FIG. 6B illustrates the case where the same PET / PE protective film is torn off from a Teslin® substrate partially coated with an optical security component, in which, this time, a layer of controlled destruction is present, depending on the present description. In this case, the lower part of the peeling force curve, ie between approximately 40 mm and 60 mm, and corresponding to the tearing forces at the level of the safety component no longer takes the form of a smooth plate. The effect of controlled destruction is recognizable on the curve in the form of several undulations resulting from the discontinuity of the layer of controlled destruction.

Although described through a certain number of exemplary embodiments, the security film according to the invention and the method of manufacturing said film include different variants, modifications and improvements which will be obvious to those skilled in the art, it being understood that these different variants, modifications and improvements form part of the scope of the invention as defined by the claims which follow.

Claims (15)

Security film (20) transferable onto a substrate (100) of a document to be secured, the security film (20) comprising: - a support film (21) configured to be removed after transfer of said security film on the substrate; - a set of security layers (23) imparting a recognizable optical effect to the security film (20); - a controlled destruction layer (26), discontinuous according to a given destruction pattern, arranged between the support film (21) and a first face of the set of security layers (23), said controlled destruction layer being configured to remain attached to the set of security layers (23) during the transfer of the security film on the substrate (100). The security film (20) of claim 1, further comprising an adhesive layer (24) for fixing the security film (20) to said substrate (100), said adhesive layer (24) being in contact with a second face. of the set of security layers (23), opposite to said first face. Security film (20) according to any one of the preceding claims, in which the thickness of the controlled destruction layer (26) is between 100 nm and 2 µm. Security film (20) according to any one of the preceding claims, further comprising a release layer (22), uniform, in contact with the support film (21), of a different nature from that of the controlled destruction layer (26 ), and configured to allow detachment of the support film (21) during the transfer of the security film onto the substrate (100). Security film (20) according to any one of the preceding claims, in which the controlled destruction layer (26) comprises markers detectable only in a given spectral band. Method for manufacturing a security film transferable onto a substrate (100) of a document to be secured, comprising: - the provision of a support film (21), said support film being configured to be removed after transfer of said security film on said substrate; - Optionally, the deposition on the support film (21) of a release layer (22); - Printing on the release layer (22) or directly on the support film in the absence of a release layer, of a controlled destruction layer (26), discontinuous according to a given destruction pattern; - The deposition, after printing of said destruction layer on said release layer (22) or on said support film (21), of a set of security layers (23) imparting a recognizable optical effect to the security film (20 ), said controlled destruction layer being configured to remain fixed to the set of security layers (23) during the transfer of the security film onto the substrate (100). The method of claim 6, wherein the controlled destruction layer (26) is printed on the release layer (22) or the support film (21), on an area between 30% and 70% of the total area of the release layer (22) or support film (21). A method according to any of claims 6 or 7, wherein the printing of the discontinuous controlled destruction layer (26) comprises the printing of patterns comprising cells or other finished surfaces and / or straight lines and / or curved lines and / or broken lines and / or alphanumeric characters. The method of any of claims 6 to 8, further comprising depositing an adhesive layer (24) on said set of security layers. Method for protecting a document (30) comprising: - the manufacture of a security film (20) according to any one of claims 6 to 9; - the transfer of said security film (20) on at least part of a first face of a substrate (100) of said document (30) with a view to securing it; - elimination of the support film. The method of claim 10, wherein the transfer of the security film is done by hot pressing. A method according to any of claims 10 or 11, further comprising depositing a protective film (31) on said at least part of a first face of said substrate (100). Method according to claim 12, in which: - the protective film (31) comprises a layer of polyethylene PE and a layer of polyester PET; - Said layer of PE is in contact with the layer of controlled destruction (26). Method according to either of Claims 12 and 13, in which the thickness of the protective film (31) is between 75 µm and 200 µm. A method according to any of claims 12 to 14, wherein the controlled destruction layer comprises a fluoropolymer, for example a polyvinylidene fluoride (PVDF).

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