EP0488902A1 - Security document including a security element having photochromic properties - Google Patents

Abstract

Security document which is not woven, comprising integrally at least one security component comprising at least one photochromic compound reacting reversibly with an electromagnetic radiation reaching it and whose wavelength spectrum corresponds to that of the solar spectrum, over a period of time of less than 1 minute, for a number of cycles. The photochromic compound withstands temperatures ranging up to 120 DEG C and is chemically resistant to oxidising and/or reducing agents and/or bases and/or acids. Application to paper for bank notes and cheques in particular.

Description

The invention relates to a security document comprising at least one security element reacting to radiation. It relates more particularly to a security document comprising a security element having photochromic properties, that is to say that this element changes color reversibly as a function of the presence or absence of at least one electromagnetic radiation. This security element can for example be in the form of a fiber, a wire, a strip or boards.

Very often photochromic products are colorless or almost colorless in the absence of certain radiations, in particular ultraviolet rays or infrared rays, and become colored under the action of these radiations.

It is known that security documents, for example papers for banknotes or for checks or any other security of value, include chemical or physical means of authentication and / or indicators of falsification.

In general, it is known to use as chemical means, compounds which react to the falsifying agents commonly used by falsifiers. These falsification indicator means react for example to acids (hydrochloric, citric, acetic, sulfuric, etc.), bases (especially soda), oxidants (bleach), reducers and solvents.

• L'absence d'azurants optiques qui fluorescent en bleu, violet lorsqu'ils sont soumis à la lumière ultia-violette, et qui sont couramment utilisés dans la composition des papiers ordinaires afin d'augmenter leur blancheur.
• La présence de filigranes, c'est-à-dire une modification contrôlée de la densité des fibres de papier dans l'épaisseur de celui-ci, ce filigrane reproduisant un dessin donné qui n'est visible parfaitement qu'en lumière transmise, c'est-à-dire par transparence.
• La présence d'hologrammes, de moirages ou d'autres effets optiques obtenus avec des encres optiquement variables et déposées à la surface de la feuille.
• La présence ponctuelle d'éléments (par exemple des fils, fibres, planchettes, etc) qui peuvent être fluorescents et donner une fluorescence de couleurs diverses, colorés ou comporter des inscriptions ou posséder des propriétés physiques diverses telles que le magnétisme, la conductivité électrique, le thermomagnétisme, etc.

It is also known to use physical means of authentication which are most often the following:

• The absence of optical brighteners which fluoresce in blue, purple when subjected to ultraviolet light, and which are commonly used in the composition of ordinary papers in order to increase their whiteness.
• The presence of watermarks, that is to say a controlled change in the density of the paper fibers in the thickness thereof, this watermark reproducing a given design which is only perfectly visible in transmitted light, c that is to say by transparency.
• The presence of holograms, moiré or other optical effects obtained with optically variable inks and deposited on the surface of the sheet.
• The punctual presence of elements (for example wires, fibers, boards, etc.) which can be fluorescent and give fluorescence of various colors, colored or have inscriptions or have various physical properties such as magnetism, electrical conductivity, thermomagnetism, etc.

Furthermore, numerous mineral or organic photochromic compounds are known.

As inorganic compounds, mention may be made of silver halides, transition metal salts, tungsten and vanadium acids, optionally doped metal oxides, etc.

As organic compounds, mention may be made of fulgides (derivatives of succinic anhydride), fulgimides (derivatives of succinimide), stilbene derivatives, pyran derivatives, in particular spiropyranes, spirobenzo (or naphtho) pyranes, spiroxazines, hydrazones, oxazones, etc.

Such compounds are usually used for (mineral or organic) lenses of sunglasses, as described for example in documents FR-A-2 290 401, EP-A-246 114, FR-A-2 467 182, FR -A-2 450 469. These compounds give the glasses the property of darkening when exposed to full sunlight (containing UV rays) and of lightening in the shade.

These compounds have also been used to make documents non-photocopiable. They are incorporated into the document in bulk or locally to protect an inscription, and when the document is photocopied, the light from the photocopier transforms the colorless photochromes into their colored form and an illegible copy is obtained. Such an application is described for example in patent applications EP-A-302,774 and US-A-3,597,082.

Photochromic compounds are also used to manufacture security inks as described in documents EP-A-327,788, EP-A-248,631 or WO-A-88 01 288 and WO-A-83 00 568 The use of these inks can be used in particular to authenticate the document on which they are applied. However, it can be fairly easy to obtain these inks commercially and therefore it is quite easy to counterfeit documents by printing with these inks a sheet or card in which the other components of the document have been reproduced.

There has also been described in European patent application EP-A-328,320, a security device usable for marking articles, packaging or identification cards. The safety device is a woven material containing one or more threads made up of photochromic fibers. This woven material is used as a label which is placed on an authentic item, such as a garment, bag, fabric, etc. The authentication process consists in illuminating the label using a UV lamp to reveal the color of the photochrome.

It is understood that the recognition process will be carried out at the time of the sale or resale of a well-known brand object, and this to avoid counterfeiting of luxury objects. Thus, the authentication process will be carried out at most two to five times. To make such a label, it is sufficient for the photochrome to have a maximum number of transition cycles of 10.

Patent application JP-A-61 179 399 describes the manufacture of cellulose fibers dyed with photochromic compounds. These fibers are then used as basic fibers to make a document. Therefore, the entire document is photochromic. Such a document is very expensive, because the fibers require for their dyeing a particular compound and large quantities of photochromic compound.

An object of the invention is therefore to provide a security document which is not woven and which comprises at least one security element containing a photochromic compound, this compound being such that the transition from the non-activated form to the activated form is reversible and the number of transition cycles is very large.

Indeed, this security element is intended for the manufacture, for example, of banknotes, checks, restaurant vouchers, credit cards, identity cards, passport sheets, etc. It can therefore be used very often, for example several times a day and capable of being subjected to an authentication process at least once a week and even at least once a day.

Another object of the invention is to provide a security document which comprises at least one security element containing a photochromic compound which changes from its non-activated form to its activated form (photo) very quickly. Similarly, the reverse transition from its activated form to its non-activated form will be fairly rapid. Indeed, the security document according to the invention is intended to be authenticated more particularly by the man in the street or for example by a cashier in a payment center. If the number of documents to be authenticated is large, the user will want the color change to be rapid. In addition, the man in the street will immediately prefer the color change to be rapid when he uses the security document as a means of payment. Finally, the security document could constitute, for example, a passport or identity card sheet and here again, when verifying the identity of many people, the cycle of color change should be quick.

A third object of the invention is to provide a security document which comprises a security element containing a photochromic compound and which is introduced during the production of the document, the security element forming an integral part of the document. This is particularly important, because if the element is an integral part of the document it will be very difficult for counterfeiters to reproduce this document.

To achieve these goals, several problems arise for those skilled in the art.

• une transition rapide et réversible à un rayonnement électromagnétique,
• un nombre de cycles de transition élevé,
• une résistance aux conditions physiques de fabrication du support,
• une résistance aux agents de falsification couramment utilisés par les contrefacteurs,
• une résistance au vieillisement et plus particulièrement une résistance aux rayons de la lumière naturelle,
• une compatibilité avec les constituants du document de sécurité,
• une compatibilité avec les constituants de l'élément de sécurité.

Those skilled in the art will have to select from all the photochromic compounds existing on the market, photochromic compounds which simultaneously have the following properties:

• a rapid and reversible transition to electromagnetic radiation,
• a high number of transition cycles,
• resistance to the physical conditions of manufacture of the support,
• resistance to falsification agents commonly used by counterfeiters,
• resistance to aging and more particularly resistance to the rays of natural light,
• compatibility with the constituents of the safety document,
• compatibility with the components of the safety element.

The invention therefore aims to provide a security document which is not woven integrally comprising at least one security element comprising at least one photochromic compound, the security element having a long service life and being easy to authenticate. .

• réagissant réversiblement à un rayonnement électromagnétique lui parvenant et dont le spectre de longueur d'ondes correspond à celui du spectre solaire,
• réagissant en une période de temps totale de réversibilité inférieure à 5 minutes,
• présentant un nombre de cycles de transition élevé.

The invention provides a nonwoven security document integrally comprising at least one security element comprising at least one photochromic compound:

• reacting reversibly to electromagnetic radiation reaching it and whose wavelength spectrum corresponds to that of the solar spectrum,
• reacting in a total reversibility period of less than 5 minutes,
• with a high number of transition cycles.

Preferably, the total reversibility time period is less than one minute.

We know, for example, from KOSAR's book "Light-sensitive systems, page 384 (1965)" that photochromism is more pronounced if the photochromic is in a solvent medium. The speed of reversibility and the intensity of the coloration will therefore be favored if the photochrome is dissolved in at least one of its solvents. To achieve the aims of the invention, it is therefore advantageous to use the photochrome in dissolved form confined within a material at least partially transparent to electromagnetic radiation.

In particular the photochrome will be found on and / or in the security element in dissolved form in individual microdroplets within the material.

In addition, confinement has the advantage of protecting the photochrome from the chemical agents to which it could be subjected and also of isolating it from the compounds of the document with which it could interact in a harmful manner.

These microdroplets may be found individualized in microcapsules.

The microcapsules have walls at least partially transparent to active electromagnetic radiation. They must also have the highest possible resistance to pressure. To better protect the microcapsules against bursting under the effect of pressure, they can be used in admixture with protective elements such as glass microbeads.

As base material for the walls of the microcapsules, polyurethane, melamine-formaldehyde or urea-formaldehyde resins may be used.

Thus the invention more particularly provides a security document characterized in that the photochromic compound is present with at least one of its solvents in microcapsules with walls at least partially transparent to electromagnetic radiation.

The average size of the microcapsules is between 3 to 12 μm, preferably between 4 and 10 μm.

According to another embodiment of the invention, the photochromic compound can be present in the form of microdroplets dispersed within a varnish or a crosslinked binder and at least partially transparent to active electromagnetic radiation. The varnish or the binder can, for example, be crosslinked by UV radiation or by heat.

Preferably, the photochromic compound, optionally after confinement, is resistant to a temperature of up to 120 ° C. By resistant is meant that the photochromic compound does not lose its qualities of passage from the non-activated state to the photoactivated state and vice versa, when it is not subjected or subjected to electromagnetic radiation.

In addition, the photochromic compound, optionally after confinement, is chemically resistant to oxidizing agents and / or reducing agents such as hydrogen peroxide, sodium hypochlorite, or other hypohalides of alkali metals, to strong or weak acids, by example acetic, citric acid, with strong or weak bases.

According to a preferred embodiment of the invention, the security element is arranged at least partially between the two faces of the security document. It can be located completely on the surface of the document, or it can be placed in windows made in the document. Such windows are produced in a manner known from the prior art as described in document EP-A-059 056. The security element can also be completely included between the two faces of the security document, but then it must be located at a depth allowing electromagnetic radiation to reach it to induce coloring of the photochromic compound.

The security element may for example be a wire, a fiber, a board made of synthetic and / or natural material comprising a photochromic compound (possibly encapsulated) in mass or on the surface, uniformly or not.

Provision may be made for the security element to include the photochromic compound in the form of a bar code, for example it may be a wire printed using an ink comprising a photochromic compound, the printing being under form of bars perpendicular to the longitudinal axis of the wire. It can also be provided that the printing is done in the form of alphanumeric characters. When an electromagnetic radiation is made to act on such an initially colorless wire, legible impressions appear, then when it is withdrawn from this radiation, the impressions become invisible again.

An embodiment of the invention may consist in using mixtures of photochromic compounds, or different photochromic compounds for certain parts of the security element, these compounds giving different colors for a given radiation or reacting to radiation of lengths. different wave.

The photochromic compound (s) can be incorporated into the bulk security element or be deposited on the surface on at least one face of the element, for example by coating or printing. The photochromic compound can be deposited using a binder. As transparent binder, it is possible to use, for example, a polyvinyl alcohol (PVA), a polyvinyl acetate, an acrylic latex, especially when the photochromic is encapsulated.

The electromagnetic radiation to which the safety document according to the invention is subjected is preferably radiation whose wavelength spectrum corresponds to that of the solar spectrum.

The security document is preferably obtained by the wet method by producing an aqueous suspension of a mixture of natural and / or synthetic and / or mineral fibers, binders, flocculants and then by draining this suspension on a canvas, for example of a flat table of a fourdrinier machine or a canvas of a round shape and finally by pressing and drying the sheet obtained.

The following description with reference to the nonlimiting examples below will make it possible to understand how the invention can be put into practice.

EXAMPLES Example 1

A mixture of polycarbonate and of a photochromic compound of the spiro (or naphtho) pyran type is extruded comprising, as a substituent, an adamantane ring in position 2 of the spiropyran ring (as described in patent application EP-A-246,114). The film is biaxially stretched until a film with a thickness of 30 μm is obtained. A colorless film is obtained. This film is cut into strips 1 mm wide. The strip is incorporated into a sheet of paper according to the technique described in patent application EP-A-059 056. The sheet obtained is cut to make security documents.

If the security document obtained according to the invention is illuminated in full sunlight, the security document becomes very dark immediately. As soon as you put the security document in a dimly lit area, the security document clears up very quickly.

Example 2

A security document is produced as in Example 1, but a polymethacrylate is used in place of polycarbonate and as photochromic a stabilized fatigue-resistant spiroxazine is used, as described in patent application FR-A-2 523 593 .

Example 3

A 38 g / m² paper is printed with a photochromic gravure ink containing a spiroindolinonaphtoxazine. We cut this paper in the form of boards. These boards are introduced into a sheet of paper during its manufacture and so as to obtain a finished sheet comprising in large quantity of boards flush with the faces of the sheet. We transform this sheet into security documents.

By irradiating a document obtained at a wavelength of 366 nanometers, the security elements quickly color blue. They discolor very quickly if the document is placed in a non-irradiated place.

Example 4

A security document is produced by incorporating during its manufacture photochromic organic fibers, such as for example polyamide fibers (NYLON) described in US Pat. No. 3,578,389.

When the document obtained is exposed, in full sunlight, the photochromic fibers flush with one of the sides of the document change from orange to blue.

Example 5

A security document is produced as in Example 4, but glass mineral fibers having a high zirconia content and whose photochromic compound is a silver halide with copper oxide are used as photochromic fibers. Zirconia increases the speed of photochromic reversibility. The photochromic fibers can, for example, be obtained from mineral glass described in patent application FR-A-2 290 401.

Example 6

A photochromic compound with a solvent is encapsulated, according to a known encapsulation technique.

The walls of the capsules are for example made of melamine-formaldehyde; they are transparent.

The photochromic compound is a spirooxazine (VARIACROL sold by ENICHEM) dissolved at 1.2% in the solvent EXSOL D100 (sold by EXXON). Optionally, an additive can be added to facilitate its dissolution.

The capsules have an average diameter of 4 µm.

These capsules are deposited in mixture with a transparent binder, for example a polyvinyl alcohol (PVA) on a sheet of paper or on a plastic film (for example of polyester) using a MEYER bar.

The capsule / binder mixture is in a 50/50 ratio by dry weight.

The dry weight of deposited capsules is 10 g / m².

The sheet or film thus obtained are cut into threads or strips or boards which are then incorporated into a paper during its manufacture.

When the paper containing the photochromic capsules is exposed to solar radiation, it turns red in less than 10 seconds.

When this paper is removed from solar radiation, the red color disappears in less than 50 seconds.

Such paper is printable by conventional printing methods in the field of security papers.

To improve the protection of the capsules, glass microbeads (10 to 20% compared to the capsules) having an average size of 20 μm can be added to the binder-capsule mixture.

Claims (11)

1. Security document which is not woven integrally comprising at least one security element comprising at least one photochromic compound: - reacting reversibly to electromagnetic radiation reaching it and whose wavelength spectrum corresponds to that of the solar spectrum, - reacting in a total reversibility time period of less than 5 minutes, - with a high number of transition cycles. 2. Security document according to claim 1, characterized in that the total reversibility time period is less than 1 minute. 3. Security document according to one of claims 1 or 2, characterized in that the photochromic compound is present on and / or in the security element in dissolved form in individual microdroplets in at least one material partially transparent to active electromagnetic radiation. 4. Security document according to claim 3, characterized in that the photochromic compound is present with at least one of its solvents in microcapsules with walls at least partially transparent to active electromagnetic radiation. 5. Security document according to claim 4, characterized in that the average size of the microcapsules is between 3 and 12 µm, preferably between 4 and 10 µm. 6. Security document according to claims 4 or 5, characterized in that the microcapsules containing the photochromic compound are used in admixture with protective elements such as glass microbeads. 7. Security document according to claim 3, characterized by fact that the photochromic compound is in the form of microdroplets dispersed within a varnish or a crosslinked binder and at least partially transparent to active electromagnetic radiation. 8. Security document according to one of claims 1 to 7, characterized in that the photochromic compound, optionally after confinement, is resistant to a temperature up to 120 ° C. 8. Security document according to one of claims 1 to 7, characterized in that the photochromic compound, optionally after confinement, is chemically resistant to oxidizing and / or reducing agents and / or to bases and / or acids. 9. Security document according to one of claims 1 to 8, characterized in that the security element is arranged at least partially between its two faces. 10. Security document according to one of claims 1 to 9, characterized in that the security element is completely included between the two sides of the document, and located at a depth allowing the electromagnetic radiation to reach it .