EP0430810A1 - Security base-sheet comprising an element collecting radiation and conducting by reflection an induced radiation at one end of said element - Google Patents

Abstract

A security substrate, optionally printable. It comprises at least one security member arranged at least partially between the faces of the substrate and at least one end of which is flush with a section face of the substrate to permit the authentication of the substrate by exposure of at least one of its faces to a source of radiation and observation of the radiation at the said flush end. The security member consists of a flat strip, transparent to the radiation emitted by the source, the strip being such that it collects the radiation emitted by the source and conducts by reflection radiation induced within the strip, the said induced radiation being conveyed to the said flush end. The strip consists of at least one natural or synthetic substance in combination with an active material generating the radiation induced under the action of the collected radiation. The active material generating the induced radiation is chosen from luminescent, electroluminescent, thermoluminescent, bioluminescent, chemiluminescent and magnetoluminescent substances. Application, for example, to documents such as cheques and banknotes. <IMAGE>

Description

The invention relates to a new security support. This comprises a security element collecting radiation and conducting by internal reflection radiation induced at one end of the element which is flush with a section of the security support.

We already know from GB-A-2 148 486 of BRADBURY, the introduction of an optical fiber in a security document. Such an optical fiber would authenticate a document by illuminating one end of the optical fiber and observing the light transmitted at the opposite end of the fiber. A disadvantage of this fiber is that it is very fragile and can break inadvertently during the production or handling of the document. Broken fiber then transmits little light from one end to the other.

A security document comprising an optical fiber placed between the two faces of the document, one end of the fiber flush with a section of the document, has been described in US patent No. 4,710,614 of the applicant. The document is characterized in that the optical fiber has a transparent sheath and in that the thickness of the material (constituting the document) covering the optical fiber is less than the penetration depth of the electromagnetic radiation from the source. This allows the document to be authenticated by exposing one of its faces to a source of radiation and observing the radiation at the outcrop end of the fiber.

In the case of optical fibers, the radiation is conducted longitudinally with respect to the optical fiber due to the optical laws resulting from the differences in the refractive indices between the core and the cladding of the optical fiber. Thus, if n₁ is the refractive index of the core and n₂ the refractive index of the cladding, more the difference (n₁-n₂) between the index of the heart and the index of the cladding, the higher the transmission of the wave.

A disadvantage of optical fibers consisting of a core with index n₁ and a cladding with index n₂ is that the surface condition between the core and the cladding can be damaged during the traditional process of the introduction of a security feature in paper. During the production, processing or handling of the security document, the security element is subjected in particular to the action of heat, pressure, folds, etc. Consequently, the interface between the core and the sheath of the optical fiber becomes irregular, which results in losses of longitudinal transmission of the wave in the fiber.

In addition, the manufacture of optical fibers requires homothetic stretching processes. For example, starting from two concentric cylinders, if these cylinders are stretched longitudinally, we will obtain two concentric cylinders whose radius ratio is preserved. This drawing technique also requires working on unit fibers. Consequently, the process for manufacturing an optical fiber is long and expensive.

The invention aims to overcome these drawbacks.

An object of the invention is to provide a security document which makes it possible to observe at the end of a security element introduced into a document, induced radiation generated by radiation captured on the surface of the document, using a means different from optical fiber and having several advantages over it.

A first advantage of the invention is to provide a security element which is easy to manufacture. Thus, according to the invention, a security element is manufactured by mixing a synthetic or natural material with an appropriate active material, for example a luminescent material, by extruding and bi-stretching for form a film, then by cutting the film thus obtained into strips. It is therefore not necessary to manufacture the security element individually from the start. A bundle of strips is obtained which are introduced individually into the document. The invention is remarkable in that by judiciously choosing the synthetic and / or natural material and the active material, a security element is obtained in the form of a flat strip, capable of collecting on its longitudinal face, the radiation emitted by a source. and conduct by reflection an induced radiation inside the strip to bring it to one end of the strip.

A second advantage of the invention is that the radiation captured by the security element can be light radiation and the induced radiation can be electric, thermal, magnetic, light, depending on the nature of the active material.

A third advantage of the invention is that the security element is resistant to the heat and to the pressure to which it is subjected when it is introduced into the material constituting the security support, for example a paper or a sheet obtained by wet from natural and / or synthetic and / or mineral fibers. Thus, the conduction of the radiation induced in the security element is not degraded.

The invention therefore relates to a security support, possibly printable, comprising at least one security element, arranged at least partially between the faces of the support, and at least one end of which is flush with a section of the support to allow authentication of the support by exposing at least one of its faces to a radiation source and observing radiation at said outcrop end, characterized in that the security element consists of a flat strip, transparent to radiation emitted by the source, the strip being such that it collects the radiation emitted by the source and conducts by reflection an induced radiation inside the strip, said induced radiation being brought to said end of outcrop.

The invention is further such that the induced radiation is partially transmitted through the thickness of the strip.

The strip consists of at least one natural or synthetic material, associated with an active material generating the radiation induced under the action of the collected radiation. According to one embodiment of the invention, the active material generating the induced radiation is chosen from luminescent, electroluminescent, thermoluminescent, bioluminescent, chemiluminescent, magnetoluminescent materials.

Preferably, the luminescent material is chosen from rare earth derivatives, zinc and / or cadmium sulphide pigments, anthraquinic derivatives, rare earth chelates, coumarin derivatives.

More preferably, the active material generating the induced radiation is a coumarin derivative such as those described for example in patents EP 025,136, EP 047,881, EP 101,897 filed by BAYER.

The strip is preferably made of a synthetic material resistant to physical conditions, in particular temperatures and pressures, involved in the manufacture of the support. The synthetic material is also resistant to chemical agents used in the composition of the support. Thus in the case of a paper support, the synthetic material will be resistant to water and to the pH of the aqueous suspension of fibers used for the manufacture of paper. In addition, if the security support is intended to be handled often, for example if it is paper for banknotes, the synthetic material will be chosen so as to be, inter alia, resistant to solvents and to wrinkling. The synthetic material is preferably chosen from polycarbonates, polyesters.

Preferably, the strip has a thickness of between 10 and 100 micrometers.

It can be provided that the strip is covered, at least partially, on at most two of its faces, with a layer of a material promoting the internal reflection of the induced radiation. These are preferably the faces having the largest areas and which are opposite. The covering material has a thickness large enough to reflect the induced radiation and sufficiently small to allow penetration of the radiation emitted by the source. The covering material is a metal layer chosen from aluminum, gold, silver, metal oxides and the thickness of which is for example between 10 and 150 Å.

It is also possible to provide that the strip is covered at least partially on at most two of its faces with an external layer promoting the sliding ability of the strip, this layer being formed either of a material having a better coefficient of sliding than the base material constituting the strip, ie constituents giving a surface microroughness. Indeed, the manufacturing process of the film giving the safety strip described above is such that the faces of the film are very smooth and this has the effect that it is difficult to wind and unwind the film. Thanks to the good sliding coefficient or the surface microroughness of the outer layer (s), it becomes possible to easily wind the film.

The invention also relates to a method of manufacturing a security element as described above. This process consists in mixing a synthetic and / or natural material with an active material generating induced radiation, in extruding this mixture and in biaxial stretching to form a film with a thickness of between 10 and 100 micrometers, optionally cover at most the two sides of the film with a material favoring internal reflection and / or favoring the film's ability to wind, and cutting the film into strips.

The method according to the invention can consist in coextruding a mixture of a synthetic and / or natural material with a material generating an induced radiation and a material transparent to the radiation emitted by a source, with a refractive index lower than the refraction of said mixture, and preferably having a better coefficient of slip than that of said mixture, to stretch biaxially to form a film of thickness between 10 and 100 micrometers, and to cut the film into strips.

The material favoring reflection can be deposited, by evaporation under vacuum, by printing or by coating.

The outer layer improving the winding ability of the film can also be deposited by printing or by coating.

The following description, with reference to the appended drawings, will make it possible to understand how the invention can be put into practice.

Figure 1 is a view of an optical fiber according to the prior art.

FIG. 2 is a view in longitudinal section of the optical fiber of FIG. 1.

Figure 3 is a perspective view of a film before cutting into strips to provide security elements according to the invention.

FIG. 3 a is a perspective view of a film comprising on two of its faces, an external layer promoting the internal reflection of the induced radiation and / or the ability to wind the film.

Figure 4 is a longitudinal sectional view of the security element according to the invention.

Figure 5 is a perspective view of a security support comprising a security element according to the invention and its authentication mode.

Figure 6 is a cross-sectional view of the security element according to the invention.

The optical fiber 7 shown in Figure 1 consists of a core 8 and a sheath 9. The core 8 has a refractive index n₁. The sheath 9 is a polymer transparent to light with a refractive index n₂. The core 8 and the sheath 9 are cylindrical and coaxial. They have an interface 10.

When such an optical fiber 7 is introduced during the manufacture of the paper, for example by means known to a person skilled in the art, it is then necessary to dry the paper and to press it. This pressing and this drying then cause defects in the interface 10. Similarly when the document is printed, in particular by intaglio.

Thus, if a source S of radiation R₁, of wavelength L₁, laterally irradiates the optical fiber 7, this radiation penetrates into the sheath 9, then into the core 8. Because of the refractive indices of the materials used, this radiation is partially reflected along R₂ inside the core 8 and partially diffracted along R₃ outside the cladding 9. The final intensity of the radiation outside the fiber 7 is therefore much lower than the initial intensity of R₁ radiation. To be able to perceive an effect at the end of the optical fiber 7, a light source S of high intensity is therefore necessary. In addition, due to a deterioration of the interface 10, the radiation is not transmitted to the end of the optical fiber at an intensity sufficient to be perceived.

However, the security support 1 according to the invention comprises a security element 2, arranged at least partially between the faces F₁ and F₂ of the support 1 and at least one end 3 of the security element 2 is flush with a section 4 of the support 1 to allow authentication of the support by exposure of at least one face F₁ or F₂ to a source S 'of radiation R₄. The radiation R₈ is observed at the end 3 of outcrop.

If we consider Figures 4 to 6, the security element 2 consists of a flat strip. When the security element is subjected to radiation R₄ emitted by the source, the strip collects this radiation which reaches a particle of the active material 5. This particle gives a specific refracted ray R₆ of the active material and induced rays like R₇ which are completely reflected inside the strip and thus led to the end 3 where they are observed for example in R₈. Part of the incident ray R₄ leaves element 2 according to the transmitted ray R₅.

The invention is remarkable in the fact that if the radiation R₄ of the source at a wavelength or a range of wavelengths L₁-L₂, the radiation R₇ has a wavelength or range of lengths waves L₃-L₄ not strictly equal to that of the source S ′; it can be in another wavelength domain or be more restricted. Furthermore, if the intensity of the radiation R₄ is I₁, the intensity of the radiation R₈ has an intensity I₂ at least equal to I₁ and preferably greater. Thus, the safety support 1 according to the invention has an advantage over the elements known from the prior art, namely, when this element is irradiated using a source, it can be of low intensity . In addition, the invention is remarkable in that the transmitted radius R₆ which can be observed by transmission and therefore by transparency, has an intensity I₃ sufficient to allow an observer to see the element 2 by transparency. The observer can therefore see by transparency, through the document, the specific color transmitted from the active material and by reflection, on the edge of the document, a substantially distinct color.

According to a preferred embodiment of the invention, the source S ′ is a source of natural light, for example sunlight, or daylight coming through a window or a light usually used for lighting industrial or residential premises. It is therefore understandable that the invention has advantages when such a security element is introduced into a document such as for example paper for banknotes or for checks or for any other means of payment. It is enough for the person who wishes to know if the document is authentic, to look at a section of the document. A bright spot will appear on the edge. In addition, since the wavelengths that will be visible at the end of the document will be different or in a more limited range of the wavelengths of the source, authentication will be even easier. For example, if natural light is used as a source, the perceived wavelength L₃-L₄ will be different and thus the end of the security element flush with the edge will appear either orange, green, blue, etc. depending on the nature of the active material generating the induced radiation R₇.

The strip provides these effects both by its nature and by its geometry. The strip is composed of at least one natural or synthetic material associated with a material generating the induced radiation R₇. Natural or synthetic material must have several essential properties. It must be transparent to the radiation from the source S ′. For example, if this source is natural light, the strip must be optically transparent. It must therefore be made of a material which is amorphous at room temperature. In addition, the natural or synthetic material must be thermoplastic due to the process for manufacturing the security element. Finally it must be resistant chemically and physically.

In addition the geometry of the strip must be particular. Indeed, it is preferable that this strip is of rectangular section. This geometry has the advantage that the security element is manufactured using a simple and therefore inexpensive process. In addition, the thickness of the security element must be small in order to be able to be introduced into a thin planar support, for example paper. Finally, it is essential that the faces of this strip are perfectly flat so that the strip can sufficiently collect the radiation R suffisamment and conduct by internal reflection the radiation induced R₇.

• - des chélates de terres rares (par exemple un oxysulfure d'yttrium dopé à l'Europium) ou d'autres produits dopés (fluorures de métaux alcalins dopés, ferrites dopés), des sulfures de zinc, des sulfures de zinc et de cadmium (dopés par du cuivre);
• - des dérivés de la coumarine;
• - des dérivés du B-naphtol disulfoné;
• - des dérivés monoazoïques;
• - la fluorescéine. On peut ausssi utiliser des produits luminescents aux infra-rouges.

The active material generating the induced radiation can be selected from a whole range of materials. For example, luminescent materials will be chosen from the following group, given as an indication but not limiting:

• - rare earth chelates (for example a yttrium oxysulfide doped with Europium) or other doped products (doped alkali metal fluorides, doped ferrites), zinc sulfides, zinc and cadmium sulfides ( copper doped);
• - coumarin derivatives;
• - derivatives of disulfonated B-naphthol;
• - monoazo derivatives;
• - fluorescein. You can also use luminescent infrared products.

Pigments based on zinc sulfide emitting in various wavelengths have been described for example in patent applications EP-A-34059, EP-A-78538 and EP-A-91184 filed by KASEI OPTONIX.

In Figure 3, there is shown an intermediate sheet 11 for manufacturing a security element according to the invention. The sheet 11 is obtained by mixing between a synthetic or natural material which is transparent preferably in natural light and a luminescent material. Then the mixture is extruded and a biaxial stretching is carried out. Then the sheet 11 is cut along longitudinal lines C to form strips 12 which constitute security elements according to the invention. It should be noted that, unlike the optical fibers of the prior art, the security element according to the invention results from a cutting of a film and not from a longitudinal and unitary stretching.

It can be provided, as shown in FIG. 3 a , that before cutting the sheet 11 an external layer 6 is deposited on each of its faces. A film is therefore produced with an internal layer 11 a and one or two external layers 6. The outer layer 6 is for example laminated with a binder on the film 11. The outer layer 6 can also be deposited by evaporation under vacuum of a metal. This layer can also be deposited by printing. The main thing is that the external layer 6 is of sufficiently small thickness to allow the external radiation coming from the source to penetrate inside the security element. The outer layer (or layers) 6 can be a layer facilitating the winding of the film 11; this layer can be provided by coextrusion with the film 11, or by coating or by printing on the film 11. In the case of a layer facilitating the winding of the film, preferably a material or a mixture of transparent materials is chosen, l layer thickness can be a few micrometers.

EXAMPLES Example 1

A polyethylene terephthalate A02300, sold by the company AKZO, is mixed with a fluorescent yellow dye 10 GN sold by the company BAYER which is a derivative of coumarin. The mixture contains 0.05% by weight of dye relative to the polymer.

This mixture is extruded then a biaxial stretching (longitudinally and transversely) is carried out to obtain a film 32 micrometers thick. The manufacturing conditions are such that the amorphous structure of the mixture is kept at room temperature, so that the sheet obtained is transparent to radiation located in the visible range. This film is then cut into strips 1 mm wide and then these strips are introduced into paper during its manufacture, according to the technique usually used. The paper is then cut into portions which then constitute security supports.

By exposing one face of this security support to sunlight and observing the edge of the security element where the end of this security element is exposed, a light point of green color is seen.

Example 2

The polymer-dye mixture of Example 1 is coextruded, on one side, with a fluoropolymer such as for example PVDF (polyvinylidene fluoride), to obtain a film with a thickness of 35 micrometers after biaxial stretching.

The film obtained has better windability than the film of Example 1 due to the presence of the layer of fluoropolymer.

Example 3

The mixture of Example 1 is coextruded on two sides with the above fluoropolymer and then bi-stretched. The strip obtained machine well because of the existence of two layers which also play the role of protectors. The strips obtained resist well to the mechanical stresses to which they are subjected during the manufacture of paper.

Example 4

The film obtained in Example 1 is covered by vacuum evaporation, on its two faces, with a layer of aluminum which has a thickness of a few tens of Angstroms. The film is cut into strips. These strips are introduced into paper and then the paper is cut to form security supports. When illuminating one side of a security document with sunlight, there is a bright spot on the edge of the document.

Claims (18)

Security support, possibly printable, comprising at least one security element, arranged at least partially between the faces of the support, and at least one end of which is flush with a section of the support to allow authentication of the support by exposure of at least one of its faces to a radiation source and observation of the radiation at said outcrop end, characterized in that the security element consists of a flat strip, transparent to the radiation emitted by the source, the strip being such that it collects the radiation emitted by the source and conducts by reflection an induced radiation inside the strip, said induced radiation being brought to said end of outcrop. Support according to claim 1, characterized in that the induced radiation is partially transmitted through the thickness of the strip. Support according to claim 1 or 2, characterized in that the strip consists of at least one natural or synthetic material, associated with an active material generating the radiation induced under the action of the collected radiation. Support according to claim 3, characterized in that the active material generating the induced radiation is chosen from luminescent, electroluminescent, thermoluminescent, bioluminescent, chemiluminescent, magnetoluminescent materials. Support according to claim 4, characterized in that the active material is chosen from rare earth derivatives, zinc and / or cadmium sulphide pigments, anthraquinic derivatives, rare earth chelates, coumarin derivatives. Support according to one of the preceding claims, characterized in that the strip preferably consists of a synthetic material resistant to physical conditions, in particular temperatures and pressures, involved in the manufacture, processing or handling of the support . Support according to one of the preceding claims, characterized in that the synthetic material is also resistant to the chemical agents used in the composition of the support. Support according to one of the preceding claims, characterized in that the synthetic material is chosen from polycarbonates, polyesters. Support according to one of the preceding claims, characterized in that the strip has a thickness of between 10 and 100 micrometers. Support according to one of the preceding claims, characterized in that the strip is covered, at least partially, on at most two of its faces, with a layer of a covering material promoting the internal reflection of the induced radiation and / or favoring its winding. Support according to claim 10, characterized in that the covering material has a thickness large enough to reflect the induced radiation and sufficiently small to allow the penetration of the radiation emitted by the source. Support according to one of claims 10 or 11, characterized in that the covering material is a metallic layer chosen from aluminum, gold, silver, metallic oxides. Support according to claims 12, characterized in that the metal layer has a thickness of between approximately 10 and 150 Angstroms. Support according to one of claims 1 to 11, characterized in that the strip is covered at least partially on at most two of its faces with a material creating an external surface microroughness or having a coefficient of slip greater than that of the band. Method for manufacturing a security element for a support according to any one of the preceding claims, characterized in that a mixture of a synthetic material and a material generating the induced radiation is extruded, it is biaxially stretched to obtain a film with a thickness of between 10 and 100 micrometers, the film is cut into strips. Method according to claim 15, characterized in that a mixture of a synthetic material and a material generating the induced radiation and a transparent synthetic material are coextruded, with a refractive index lower than the refractive index of said mixture and preferably having a coefficient of slip greater than that of said mixture, it is biaxially stretched to obtain a film with a thickness of between 10 and 100 micrometers and the film is cut into strips. Method according to claim 15, characterized in that before cutting the film into strips, the material promoting reflection is deposited by evaporation under vacuum, or by printing or coating. A method according to claim 15, characterized in that before cutting the film into strips, the layer is deposited creating a surface microroughness by printing or coating.

Images