EP3083263B1 - Process for treating the surface of a security document and security document - Google Patents

Description

GENERAL TECHNICAL FIELD

The present invention relates to the field of security documents, such as fiduciary documents or the like.

For the purposes of the invention, "fiduciary document" means all documents such as banknotes, checks, bank cards, used to transmit a sum of money. "Assimilated document" means any document issued by an administration of the State to prove the identity of a person, his rights to drive a vehicle, such as in particular the identity card, the passport, driving license, etc. By this expression is also meant any document used to authenticate an object of value such as for example a label affixed to a luxury garment. We also hear any document used to certify the payment of a tax such as tax stamps.

STATE OF THE ART

The figure 1 illustrates a fiduciary document 1, more particularly a bank note, on which no protective coating has been affixed.

The bank note 1 comprises a cotton support 2 having two opposite faces 20 and 21. The bank note 1 also has on one of its faces several security prints 3 of at least one pattern.

In general, security impressions 3 of different security levels are affixed to the banknote 1, in particular to deter attempts to reproduce.

These security prints 3 are made by a succession of printing and securing processes, such as for example and without being limiting, laser marking or microperforation, flexography, screen printing, hot stamping, dry or wet offset, or intaglio printing. It is these security impressions 3 that gives the banknote 1 its high added value.

The first-level security prints 3 are detectable with the naked eye, in the light of the day or artificial and do not require the use of a particular device. The presence of a watermark, colored fibers, visible elements in transvision, or tactile reliefs produced by intaglio printing on the banknote 1, are examples of first-level security printing 3 .

The second-level security prints 3 are detectable using technologically modest devices such as ultraviolet or infrared lamps, or polarizing filters. These security impressions 3 allow in particular the authentication of the bank note 1 in various organizations, such as businesses and banking centers. Patterns or texts printed in invisible ink in the light of the day but visible under ultraviolet or infrared radiation, fluorescent fibers, or magnetic threads are examples of second-level security impressions.

Finally, third-level security prints 3 require sophisticated devices and therefore represent a high cost. These security prints 3, for example tracers with a specific spectral signature, are mainly examined by the central banks.

It is therefore the security impressions 3 that allow the banknote 1 to be authenticated.

However, one of the conditions necessary to guarantee the authentication of the security impressions 3 over time is the good aging of the banknote 1 and its security impressions 3.

Thus, with a view to both cost reduction and sustainable development, central banks are showing increasing interest in developing bank notes with a longer life span.

Several studies have been carried out by central banks to characterize the various possible causes of withdrawal of bank notes. Such causes are for example tears, soiling, horny corners, graffiti, loss of rigidity, etc.

However, according to DE HEIJ Hans, Durable Banknotes: an overview, In: Presentation of the BPC / Paper Committee to the BPC, May 2002, Prague, fouling is responsible for 60 to 80% of withdrawals of banknotes 1. Soiling seems to be the main reason for the withdrawal of banknotes 1.

Soiling is notably due to fatty substances such as human sebum naturally present on the surface of the skin. These fatty substances, which accumulate on the surface of the bank note 1 by lodging in pores and / or by weak chemical bonds, will contribute to tarnishing the original colors of the banknote 1. In addition, the oxidation of the fat accumulated on the surface of the banknote 1 will contribute over time to the appearance of a yellowish color, then brown which will be at the origin of the withdrawal of the circulation of the banknote 1.

Several solutions have already been provided by the actors of the business and in particular the paper manufacturers, such as anti-fouling coatings based on polyurethane or latex on the support 2 of the banknote 1.

However, such coatings do not necessarily make it possible to maintain the printability of the support 2 at its optimum level, nor to guarantee the protection of the security prints 3, which are essential for the authentication of the banknote 1.

In the document WO02051638 is described a technique which consists in performing a flexo varnishing of the support 2 at the end of the method of manufacturing the banknote 1. This varnish affixed superimposed improves the resistance to soiling of the ticket 1 and thus protects the security printing 3 in their totality.

However, although the method described in the document WO02051638 generally improves the anti-fouling properties of the ticket of bank 1, these improvements remain more mitigated in terms of hydrophobicity and oleophobia.

In is known from the state of the art the document WO2013 / 178986 in which is presented a security document comprising a varnish based on cellulose microfibrils. The cellulose microfibrils used in this varnish have a length of between 1 and 100 μm, and a width and a thickness of between 5 and 10 nm.

It is also known from the state of the art the document WO2012 / 127110 in which iridescent films of crystalline nanocellulose are described for security documents. Such films are for example obtained from an aqueous-based solution comprising crystalline nanocellulose which is deposited on the security document before proceeding to evaporate so as to form a solid film on the security document. Such a method is for example described in the document WO2010 / 066029 .

PRESENTATION OF THE INVENTION

The present invention therefore aims to overcome the disadvantages described above by providing a method of surface treatment of a security document to improve the resistance to soiling of the security document, as well as its hydrophobic and oleophobic properties. , and in particular to guarantee the protection of the security impressions which are essential to the authentication of the banknote.

More specifically, the subject of the present invention is a method of surface treatment of a security document which comprises, on at least one of its opposite faces, at least one security impression consisting of at least one motif, this face and this at least one associated printing being covered with a transparent protective coating, in which the printing or coating technique is applied with a varnish comprising crystalline nanocellulose of 0.5 to 10. % by weight of varnish, on said at least one face, and in which one proceeds to drying said layer of varnish.

Preferably, use is made of a varnish which comprises about 1% of crystalline nanocellulose.

According to one embodiment of the invention, said varnish is dried under ultraviolet radiation. According to a variant, said varnish is dried by a stream of hot air.

Preferably, the varnish is an epoxy-based varnish or an acrylate-based varnish.

Preferably, a solution comprising cellulose microfibrils is applied to at least one face of the security document, the cellulose microfibril layer is then dried, and the process is then followed. the layer of varnish on the cellulose microfibrils layer.

Preferably, the steps of applying a solution comprising cellulose microfibrils to at least one face of the security and drying document of the cellulose microfibril layer are repeated at least once before proceeding with the setting up of the varnish layer, so as to form at least two layers of cellulose microfibrils.

The present invention also relates to a security document comprising, at least on one of its opposite faces, at least one security printing consisting of at least one pattern, this face and this at least one associated printing being covered with a transparent protective coating, characterized in that said coating comprises at least one layer of a varnish incorporating crystalline nanocellulose at a level of 0.5 to 10% by weight of the varnish.

Preferably, the varnish comprises about 1% of crystalline nanocellulose.

Preferably, the varnish is an epoxy-based varnish or an acrylate-based varnish.

Preferably, the transparent protective coating further comprises at least one layer of cellulose microfibrils, arranged between the at least one face of the document and the varnish layer.

PRESENTATION OF FIGURES

• la figure 1 (déjà décrite) est une vue de dessus, partielle et schématique, d'un billet de banque avant mise en oeuvre du procédé ;
• la figure 2 est une vue simplifiée, en coupe, selon le plan II-II de la figure 1, du billet de banque selon un mode de réalisation de l'invention ;
• la figure 3 est une vue simplifiée, en coupe, selon le plan II-II de la figure 1, du billet de banque selon un autre mode de réalisation de l'invention ;
• la figure 4 est un organigramme du procédé de traitement mis en oeuvre sur le billet de banque représenté à la figure 2 ;
• la figure 5 est un organigramme du procédé de traitement mis en oeuvre sur le billet de banque représenté à la figure 3.

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings, in which:

• the figure 1 (already described) is a top view, partial and schematic, of a bank note before implementation of the method;
• the figure 2 is a simplified view, in section, according to plan II-II of the figure 1 bank note according to one embodiment of the invention;
• the figure 3 is a simplified view, in section, according to plan II-II of the figure 1 bank note according to another embodiment of the invention;
• the figure 4 is a flowchart of the processing method implemented on the banknote shown in FIG. figure 2 ;
• the figure 5 is a flowchart of the processing method implemented on the banknote shown in FIG. figure 3 .

DETAILED DESCRIPTION

The security document 1 comprises a support 2, for example made of wove paper made from cotton.

According to a variant, the support 2 is made of vellum paper comprising a mixture of cotton and natural fibers, for example flax or abaca fibers.

According to another variant, the support 2 is made of vellum paper comprising a mixture of cotton and synthetic fibers of polymer, for example based on polyethylene, polypropylene, polyester, polyamide.

According to another variant, the support 2 consists exclusively of polymer such as a bi-oriented polypropylene.

According to another variant, the support 2 is composite that is to say that the support 2 comprises an assembly of layers of natural fiber materials and continuous polymer layers such as polyesters, polyamides, or bi-oriented polypropylene .

The security document 1 is for example a bank note.

The support 2 has two opposite faces 20 and 21. In the examples presented in FIG. figure 2 and at the figure 3 , the bank note 1 has on one of its faces 20 several security prints 3 of at least one pattern. According to a variant (not shown), the bank note 1 has one or more security prints 3 on both faces 20 and 21 of the support 2.

The bank note 1 further comprises an optically transparent protective coating R covering one or both faces 20 and 21 and associated security prints 3.

The protective coating R comprises at least one layer 4 of a varnish in which crystalline nanocellulose NCC is incorporated at a height of 0.5 to 10% of the weight of the varnish. The crystalline nanocellulose NCC is, for example, in the form of a powder.

The term "varnish" means a varnish configured to dry with infrared and / or hot air or ultraviolet. For example, acrylic lacquers comprising an aqueous base, lacquers comprising an epoxy base, or lacquers comprising an acrylate base are particularly suitable for forming the layer 4. Varnishes, for example based on monomers of the family of cycloaliphatic epoxides which polymerize to give a polyepoxide matrix by means of initiators such as ultraviolet-activated onium salts are also adapted to form the layer 4.

Nanocellulose is an organic material composed of cellulose fibers of very small size, in particular of the order of 5 to 20 nm. NCC crystalline nanocellulose and MFC cellulose microfibrils are distinguished.

The microfibrils of MFC cellulose are obtained from a mechanical treatment of peeling of previously bleached fibers, then by treatments homogenization, microfluidization and micromilling. The dimensions of the MFC cellulose microfibrill particles vary according to the cellulose sources from which they are extracted. The MFC cellulose microfibrils generally have a diameter of 50 to 100 nm, a length of 1000 to 2000 nm and a specific surface of 10 to 100 m ² / g.

The crystalline nanocellulose NCC is obtained from the microfibrils of MFC cellulose, by a chemical treatment of acid hydrolysis. This acid hydrolysis makes it possible to avoid the degradation of the crystalline domains of the cellulose, while destroying the amorphous parts at the periphery and within the microfibrils of cellulose. Cellulose nanocrystals, also known as whiskers, are thus obtained. The dimensions of the NCC crystalline nanocellulose particles vary according to the cellulose sources from which they are extracted. The crystalline nanocellulose NCC has, for example, a diameter of 5 to 10 nm, a length of 100 to 500 nm and a specific surface area of approximately 500 m ² / g. The crystalline nanocellulose NCC is thus distinguished from the microfibrils of MFC cellulose by its dimensions, in particular by a length well below the length of the cellulose microfibrils.

Preferably, the NCC crystalline nanocellulose and varnish layer comprises about 1% by weight of the NCC crystalline nanocellulose varnish.

In the example presented at figure 2 , the protective coating R comprises a layer 4 of varnish and crystalline nanocellulose NCC. According to a variant (not shown), the protective coating R comprises several layers 4 of varnish and crystalline nanocellulose NCC.

The use of crystalline nanocellulose NCC in the dopant state, that is to say in a small amount as an additive in a varnish, has the surprising effect of substantially improving the resistance to soiling of the greenback 1, as well as as hydrophobic and oleophobic properties, while ensuring good mechanical properties.

The use of nanocellulose is particularly advantageous insofar as it comes from a natural, renewable, recyclable and biodegradable material.

The protective coating R comprising a layer of lacquer and crystalline nanocellulose NCC also has the advantage of being itself printable, and to be compatible with an epidermal contact, that is to say not to be toxic or allergenic.

In the example presented at figure 3 , the protective coating R further comprises a layer 5 of MFC cellulose microfibrils arranged between the layer 4 of NCC crystalline nanocellulose and varnish and the face 20 of the banknote 1. The MFC cellulose microfibrils are for example in the form of a gel incorporated in a solvent, especially water or isopropanol. The MFC cellulose microfibrils gel comprises, for example, a solids content of 2% by weight of the gel, when the solvent used is water, and a solids content of 2.5% by weight of the gel, when the solvent used is isopropanol.

Preferably and as illustrated in figure 3 , the protective coating R comprises at least two layers 5 of MFC cellulose microfibrils arranged between the layer 4 of NCC crystalline nanocellulose and varnish and the face 20 of the banknote 1.

The use of layers 5 of MFC cellulose microfibrils makes it possible, in combination with the layer of lacquer 4 and crystalline nanocellulose NCC, to provide a banknote 1 with improved resistance to soiling and hydrophobicity and oleophobicity. compared to the case where a single layer 4 of varnish and crystalline NCC nanocellulose is used. In addition, the use of MFC cellulose microfibre layers 5 makes it possible to improve the mechanical properties of the bank note 1, in particular the tear strength.

In addition, as previously indicated, the use of nanocellulose is particularly advantageous insofar as it comes from a natural material, renewable, recyclable and biodegradable.

The protective coating R comprising at least one layer of MFC cellulose microfibrils and a layer of NCC crystalline nanocellulose and varnish has the further advantage of being achievable by known industrial processes such as coating and printing, and to be compatible with an epidermal contact, that is to say not to be toxic or allergenic.

The surface treatment of the banknote 1 illustrated in FIG. figure 2 proceeds as follows.

In a first step 30 illustrated in figure 4 , the varnish comprising the crystalline nanocellulose NCC is placed on one or both sides 20 and 21 of the banknote 11 by the printing or coating technique, so as to form the transparent protective coating R.

The coating layer 4 comprising NCC crystalline nanocellulose is for example applied by flexographic printing, gravure printing or screen printing methods, or even methods of coating with air knife, curtain coating or roller coating. The layer 4 of varnish is for example applied in flexography with anilox of 15 cm ³ / m ² depositing on average between 4 and 5 g / m ² .

During a second step 31, the layer 4 of varnish comprising the crystalline nanocellulose NCC is dried. According to one embodiment, the drying of the layer 4 of varnish comprising the crystalline nanocellulose NCC is carried out under ultraviolet radiation. This embodiment is particularly advantageous when the varnish is a varnish comprising an epoxy or acrylate base. According to one variant, the drying of the lacquer layer 4 comprising the crystalline nanocellulose NCC is carried out by a stream of hot air. This embodiment is particularly advantageous when the varnish is a varnish comprising an aqueous base.

According to one embodiment of the invention (not shown), the first and second steps 30 and 31 are repeated at least once so as to form two or more layers 4 of NCC crystalline nanocellulose and varnish.

The surface treatment of the banknote 1 illustrated in FIG. figure 3 proceeds as follows.

In a first step 40 illustrated in figure 5 , a solution of MFC cellulose microfibrils gel and solvent is applied on one or both sides 20 and 21 of the bank note 1. The bank note 1 can be printed beforehand or not.

The application of the solution for example made in the laboratory by means of a threaded rod on which the solution comprising the MFC cellulose microfibrils gel is deposited. The rod is then moved along the face 20 or 21 of the banknote 1 so as to distribute the solution homogeneously. The threaded rod deposits for example a layer 5 of 36 microns thick solution.

According to a variant, the solution is applied to one or both sides 20 and 21 of the banknote 1 by the coating or printing techniques mentioned below. This variant is particularly suitable in industrial production conditions.

In a second step 41, the MFC cellulose microfibril gel layer 5 is dried. The drying of the MFC cellulose microfibrils gel layer 5 is for example carried out by a hot air stream and / or in the open air in the laboratory. During drying, the solvent of the solution evaporates and the thickness of the layer 5 decreases.

Preferably and as illustrated in figure 5 the first and second steps 40 and 41 are repeated at least once so as to form two or more layers of cellulose microfibril gel.

According to one embodiment of the invention (not shown), the support 2 is then laminated, for example by a passage intaglio with or without ink, to restore a uniform and smooth surface state to the support 2.

During a third step 42, the varnish comprising the crystalline nanocellulose NCC is placed on the cellulose microfibrils gel layer 5 applied last, by the printing or coating technique.

The coating layer 4 comprising NCC crystalline nanocellulose is for example applied by flexographic printing, gravure printing or screen printing methods, or even methods of coating with air knife, curtain coating or roller coating.

During a fourth step 43, the layer 4 of varnish comprising the crystalline nanocellulose NCC is dried. According to one embodiment, the drying of the layer 4 of varnish comprising the crystalline nanocellulose NCC is carried out under ultraviolet radiation. This embodiment is particularly advantageous when the varnish is a varnish comprising an epoxy or acrylate base, respectively cationic and radical polymerization. According to one variant, the drying of the lacquer layer 4 comprising the crystalline nanocellulose NCC is carried out by a stream of hot air. This embodiment is particularly advantageous when the varnish is a varnish comprising an aqueous base.

According to one embodiment of the invention (not shown), the third and fourth steps 42 and 43 are repeated at least once so as to form two or more layers 4 of NCC crystalline nanocellulose and varnish.

The table below lists the results obtained in the Cobb bonding test, the Fritsch test, the "Test kit" and the Bendtsen permeability test carried out on safety documents to which different treatments have been applied. Cobb Collage (g / m ² ) Fritsch Test ΔL * "Test kit" Bendtsen permeability (mL / min) Single-sided paper, 1-sided ~90 35 ± 1.2 0 11.7 Calendered paper 1 standard lacquered side ~15 4.1 ± 0.7 2 0 Calendered paper 1 standard lacquered side + NCC powder ~5 4 ± 0.3 7 0 1-side calendered paper with 2 coats of laminated MFC and standard varnish + NCC powder ~9 2 ± 0.6 9 0

The term "calendered 1 face", the fact that the support is passed in size on one side.

The term "laminated MFC layers" means that the MFC cellulose microfibrilayer layers are passed in non-inked intaglio.

The term "standard varnish" means a varnish based on monomers of the family of cycloaliphatic epoxides which polymerize to give a polyepoxide matrix through initiators such as activated onium salts under ultraviolet.

In the table above, the different tests were carried out on the calendered face and the two faces of each of the supports was varnished.

The Cobb bonding test makes it possible to characterize the hydrophobicity, that is to say the resistance of the banknote medium to the penetration of water, such as for example the water of sweat. It is more precisely the amount of water absorbed by the support in g / m ² for a period of 60 seconds.

The Fritsch test is used to characterize the resistance to soiling. The Fritsch test is carried out by means of a vibrating apparatus where small glass beads are spread and incrust on the support a dirty composition based on sand, peat, activated carbon, flour, and a fatty substance present in the sebum, the mono-oleate of glycerin, for 15 minutes. The luminance L * of the support is measured on several areas before and after the support has been exposed to the messy composition. The difference ΔL * obtained between the measurements before and after the test makes it possible to characterize the adhesion of the soil to the support. Thus, the smaller the gap, the better the dirt resistance of the support.

The "Test Kit" makes it possible to characterize the oleophobia of the support. It is a test during which the support is exposed to fatty substances, in particular a mixture of castor oil and high-boiling solvents, toluene and n-heptane. By varying the proportions of the aforementioned products, a composition is obtained in which the viscosity and the surface tension vary inversely with its impregnation capacity. Thus, a composition rich in castor oil is at the bottom of the scale, while a composition rich in solvents is at the top of the scale. this same scale. Twelve different compositions are generally used. The evaluation is done visually. It is accepted that a score greater than or equal to 6 confers a satisfactory barrier to fats. The results of this test are highly dependent on the surface condition of the media and the security impressions that cover it.

The Bendtsen permeability test is used to characterize the air permeability of the support, ie the air flow through the support on a measurement surface of 10 cm ² .

The table presented above makes it possible to highlight the advantages conferred by the invention.

Indeed, it is clear from this table that the application on the support 2 of the varnish in which crystalline nanocellulose NCC has been incorporated in the dopant state that is to say in a small proportion can improve significantly the resistance to soiling, and hydrophobicity, oleophobicity and air permeability properties of the banknote 1.

It also emerges from this table that the combination of the MFC cellulose microfibril layers and the NCC crystalline nanocellulose varnish still makes it possible to improve the properties of the banknote 1 already obtained by affixing the layer 4 of varnish alone. and crystalline nanocellulose NCC, especially in terms of soil resistance and oleophobia.

Furthermore, similar tests carried out on a paper comprising a layer of varnish in which MFC cellulose microfibrils powder has been incorporated, have revealed that the mixture of varnish and MFC cellulose microfibrils powder is difficult to print. Moreover, these tests did not provide significant results, especially in terms of resistance to soiling, and properties of hydrophobicity, oleophobia and air permeability. Thus, if the combination of the varnish and the crystalline NCC nanocellulose provides particularly interesting results in particular in terms of resistance to soiling, hydrophobicity, oleophobicity, and air permeability, this is however not the case of the combination of this same MFC cellulose varnishes and microfibrils. The results of these tests have thus revealed a particular synergy between the varnish and the crystalline nanocellulose NCC, even at low dose, which does not exist between the varnish and the MFC cellulose microfibrils.

The invention therefore has the advantage of providing a bank note 1 with greatly improved antifouling properties. Bank note 1 according to the invention may therefore be in circulation longer before withdrawal by central banks. Furthermore, according to the invention, the improvement of these antifouling properties is not to the detriment of the economic aspect, and does not use complex physical processes significantly increasing the cost of manufacturing the banknote 1. Finally, the MFC cellulose microfibrils and the NCC crystalline nanocellulose which are natural products, have the undeniable advantage of not being able to be listed on the lists of substances subject to restriction under the REACH regulation defined by the European Agency. Chemicals (ECHA).

Claims (11)

1. Process for the surface treatment of a security document (1) which comprises, at least on one of its opposite faces (21, 22), at least one security print (3) consisting of at least one pattern, this face and this at least one associated print being covered with a transparent protective coating (R), characterized in that one proceeds (30, 42) to the disposing by the printing or coating technique of a varnish comprising crystalline nanocellulose (NCC) in a proportion of 0.5% to 10% by weight of the varnish, on said at least one face (21), and that one proceeds (31, 43) to the drying of said varnish layer (4).
2. Process according to claim 1, characterized in that a varnish which comprises about 1% crystalline nanocellulose (NCC) is used.
3. Process according to claim 1 or claim 2, characterized in that one proceeds (31, 43) to the drying of said varnish under ultraviolet radiation.
4. Process according to claim 1 or claim 2, characterized in that one proceeds (31, 43) to the drying of said varnish by a hot air stream.
5. Process according to one of the preceding claims, wherein the varnish is an epoxide-based varnish or an acrylate-based varnish.
6. Process according to one of claims 1 to 5, characterized in that one proceeds (40) to the application of a solution comprising cellulose microfibrils (MFC) on at least one face (21, 22) of the security document (1), in that one proceeds (41) to the drying of the layer (5) of cellulose microfibrils (MFC), and in that one then proceeds (42) to the disposing of the varnish layer (4) on the layer (5) of cellulose microfibrils (MFC).
7. Process according to claim 6, characterized in that one repeats at least once the steps (40, 41) of disposing by the coating technique cellulose microfibrils (MFC) on at least one face (21, 22) of the security document (1) and of drying the layer of cellulose microfibrils (MFC) before proceeding (42) to the disposing of the varnish layer (4), so as to form at least two layers (5) of cellulose microfibrils (MFC).
8. Security document (1) comprising, at least on one of its opposite faces (21, 22), at least one security print (3) consisting of at least one pattern, this face and this at least one associated print being covered with a transparent protective coating (R), characterized in that said coating comprises at least one layer (4) of a varnish incorporating crystalline nanocellulose (NCC) in a proportion of 0.5% to 10% by weight of the varnish.
9. Document (1) according to claim 8, characterized in that said varnish comprises about 1% crystalline nanocellulose (NCC).
10. Document (1) according to claim 8 or claim 9, wherein the varnish is an epoxide-based varnish or an acrylate-based varnish.
11. Document (1) according to one of claims 8 to 10, characterized in that the transparent protective coating (R) further comprises at least one layer (5) of cellulose microfibrils (MFC), arranged between the at least one face (21, 22) of the document and the varnish layer (4).

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