AU2014368503B2

AU2014368503B2 - Process for the surface treatment of a security document and associated security document

Info

Publication number: AU2014368503B2
Application number: AU2014368503A
Authority: AU
Inventors: Xavier Borde; Julien Gillot; Marjory LE BERRE
Original assignee: Oberthur Fiduciaire SAS
Current assignee: Oberthur Fiduciaire SAS
Priority date: 2013-12-20
Filing date: 2014-12-18
Publication date: 2019-10-17
Anticipated expiration: 2034-12-18
Also published as: CN106103126B; CN106103126A; EP3083263B1; WO2015091873A1; AU2014368503A1; RU2016129646A; KR102251250B1; FR3015356A1; EP3083263A1; PL3083263T3; RU2671098C1; KR20160118240A; CA2934631A1; CA2934631C; FR3015356B1

Abstract

The invention relates to a process for the surface treatment of a security document which comprises, 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, in which a varnish comprising crystalline nanocellulose in a portion of 0.5% to 10% by weight of the varnish is put in place via the printing or coating technique on said at least one face, and in which said varnish layer is dried.

Description

(57) Abstract : The invention relates to a process for the surface treatment of a security document which comprises, 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, in which a varnish comprising crystalline nanocellulose in a portion of 0.5% to 10% by weight of the varnish is put in place via the printing or coating technique on said at least one face, and in which said varnish layer is dried.

(57) Abrege : L'invention conceme un procede de traitement de surface d'un document de securite qui comporte, au moins sur 1'une de ses faces opposees, au moins une impression de securite consistant en au moins un motif, cette face et cette au moins une impression associee etant recouvertes d'un revetement de protection transparent, dans lequel on procede a la mise en place par la technique d'impression ou de couchage d'un vemis comprenant de la nanocellulose cristalline a hauteur de 0.5 a 10% en poids du vemis, sur ladite au moins une face, et dans lequel on procede au sechage de ladite couche de vemis.

PROCESS FOR THE SURFACE TREATMENT OF A SECURITY DOCUMENT AND ₄ ASSOCIATED SECURITY DOCUMENT

I

GENERAL TECHNICAL FIELD

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

By “fiduciary document” is meant in the context of the invention all documents such as banknotes, checks, bank cards, used to transmit a sum of money. By “similar

I document” is meant all documents issued by a State administration to attest to a 0 person’s identity, to his or her right to drive a vehicle, such as in particular a passport, identity card, 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 on a luxury garment. Also meant is any document used to attest to the payment of a tax, such tax disks or tags.

STATE OF THE ART

Figure 1 illustrates a fiduciary document 1, more particularly a banknote, on which no protective coating has been affixed.

The banknote 1 comprises a cotton substrate 2 having two opposite faces 20 0 and 21. The banknote 1 has in addition on one of its faces several security prints 3 of at least one pattern.

In general, the security prints 3 of various levels of security are affixed on the banknote 1, in particular to deter attempts to copy same.

These security prints 3 are prepared by a series of printing and security 25 processes, such as, for example, but not limited to, laser marking or microperforation, flexography, serigraphy, hot marking, dry or wet offset, or intaglio printing. It is these security prints 3 which give the banknote 1 its high added value.

The first-level security prints 3 are detectable with the naked eye, in daylight or artificial light, and do not require the use of a particular device. The presence of a 30 watermark, colored fibers, elements visible in transmitted light, or tactile reliefs produced by intaglio printing on the banknote 1 are examples of the first-level security prints 3.

The second-level security prints 3 are detectable using technologically ordinary devices such as ultraviolet or infrared lamps or polarizing filters. These security prints 3 enable in particular authentication of the banknote 1 within various organizations, such as shops and branch banks. Examples of the second-level 5 security prints 3 include patterns or text printed with ink invisible in daylight but visible under ultraviolet or infrared radiation, fluorescent fibers and magnetic wire.

Lastly, the third-level security prints 3 require sophisticated devices and represent, consequently, a high cost. These security prints 3, for example tracers having a specific spectral signature, are examined chiefly by central banks.

It is thus the security prints 3 which enable the banknote 1 to be authenticated.

However, one condition needed to guarantee authentication of the security prints 3 over time is the good aging of the banknote 1 and of the security prints 3 thereof.

Thus, from a point of view of both cost reduction and sustainable development, 5 central banks show increasing interest in developing banknotes having an extended lifespan.

Several studies have been carried out by central banks to characterize the various possible causes for the withdrawal of banknotes. Such causes are, for example, tearing, soiling, folded corners, graffiti, loss of stiffness, etc.

However, according to the document by DE HEIJ Hans, Durable banknotes:

an overview, In: Presentation of the BPC/Paper Committee to the BPC, May 2002, Prague, soiling is responsible for 60-80% of withdrawn banknotes 1. Soiling thus appears to be the leading cause for withdrawing banknotes 1.

Soiling is in particular caused by greasy substances such as human sebum naturally present on the skin surface. These greasy substances, which accumulate on the surface of the banknote 1 by lodging themselves within pores and/or by weak chemical bonds, will contribute to tarnishing of the original colors of the banknote 1. Moreover, oxidation of greasy substances accumulated on the surface of the banknote 1 will contribute over time to the appearance of a yellowish then brown 30 color which will lead to the banknote 1 being withdrawn from circulation.

Several solutions have already been provided by players in the field and in li particular paper manufacturers, such as for example polyurethane- or latex-based anti-soiling coatings on the substrate 2 of the banknote 1.

However, such coatings do not necessarily preserve the printing quality of the 5 substrate 2 at its optimum level, nor guarantee the protection of the security prints 3, which are essential to authentication of the banknote 1.

Document W002051638 discloses a technique which consists in flexographic varnishing of the substrate 2 at the end of the manufacturing process of the banknote

I

1. This overprint varnish improves the soiling resistance of the note 1 and thus 0 protects the security prints 3 in their totality.

However, although the process disclosed in document W002051638 generally improves the anti-soiling properties of the banknote 1, these improvements remain more mixed in terms of water repellency and oil repellency.

Also known from the state of the art is document WO2013/178986 which presents a security document comprising a cellulose microfibrils-based varnish. The cellulose microfibrils used in this varnish have a length of 1 to 100 pm and a width and a thickness of 5 to 10 nm.

Also known from the state of the art is document WO2012/127110 which discloses iridescent crystalline nanocellulose films for security documents. Such films 0 are, for example, obtained from an aqueous-based solution comprising crystalline nanocellulose which is deposited on the security document before proceeding to the evaporation thereof so as to form a solid film on the security document. Such a process is, for example, described in document WO2010/066029.

PRESENTATION OF THE INVENTION

The aim of the present invention is thus to overcome the above-mentioned disadvantages by proposing a process for the surface treatment of a security document for improving the soiling resistance of the security document, as well as the water-repellency and oil-repellency properties thereof, and in particular for 30 guaranteeing the protection of the security prints which are essential to authentication of the banknote.

More precisely, the present invention has as an object a process for the surface treatment of a security document which comprises, at least on one of its opposite faces, at least one security print consisting of at least one pattern, this face Li and this at least one associated print being covered with a transparent protective coating, in which a varnish comprising crystalline nanocellulose in a proportion of 0.5% to 10% by weight of the varnish is disposed via the printing or coating technique on said at least one face, and in which said varnish layer is dried.

Preferably, a varnish which comprises about 1% crystalline nanocellulose is used.

According to an embodiment of the invention, said varnish is dried under

I ultraviolet radiation. According to another variant, said varnish is dried by a hot air 0 stream.

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

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

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

The present invention also has provides a security document comprising, at least on one of its opposite faces, at least one security print consisting of at least one pattern, this face and this at least one associated print being covered with a transparent protective coating, characterized in that said coating comprises at least one layer of a varnish incorporating crystalline nanocellulose in a proportion of 0.5% 25 to 10% by weight of the varnish.

Preferably, the varnish comprises about 1% crystalline nanocellulose.

Preferably, the transparent protective coating further comprises at least one 30 layer of cellulose microfibrils, arranged between the at least one face of the document and the varnish layer.

PRESENTATION OF THE FIGURES

Other features, aims and advantages of the invention will become clearer from the description that follows, which is purely illustrative and non-limiting, and which should be read with reference to the appended drawings, in which:

- Figure 1 (already described) is a partial schematic top view of a banknote before implementation of the process;

- Figure 2 is a simplified cross-section view, along plane ll-ll of Figure 1, of the banknote according to an embodiment of the invention;

I

- Figure 3 is a simplified cross-section view, along plane ll-ll of Figure 1, of the banknote according to another embodiment of the invention;

- Figure 4 is a flowchart of the treatment process implemented on the banknote represented in Figure 2;

- Figure 5 is a flowchart of the treatment process implemented on the banknote represented in Figure 3.

DETAILED DESCRIPTION

The security document 1 comprises a substrate 2, for example made of cotton-based vellum paper.

According to a variant, the substrate 2 is made of vellum paper comprising a 0 mixture of cotton and natural fibers such as, for example, flax or abaca fibers.

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

According to another variant, the substrate 2 is made exclusively of polymer 25 such as, for example, a biaxially oriented polypropylene.

According to another variant, the substrate 2 is composite, i.e., the substrate 2 comprises an assembly of layers of natural-fiber materials and of continuous layers of polymer such as polyesters, polyamides, or biaxially oriented polypropylene.

The security document 1 is, for example, a banknote.

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

The banknote 1 further comprises an optically transparent protective coating C covering one or both of the faces 20 and 21 and the associated security prints 3.

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

I

By “varnish” is meant a varnish configured to dry under infrared radiation and/or hot air or ultraviolet radiation. For example, acrylic varnishes comprising an aqueous base, varnishes comprising an epoxide base, or varnishes comprising an acrylate base are particularly suited to form the layer 4. Varnishes containing monomers of the family of cycloaliphatic epoxides which polymerize giving a polyepoxide matrix via initiators such as ultraviolet-activated onium salts, for example, are also suited to form the layer 4.

Nanocellulose is an organic material made up of cellulose fibers of very small size, in particular about 5 to 20 nm. Crystalline nanocellulose CNC is distinguished from cellulose microfibrils CMF.

Cellulose microfibrils CMF are obtained by mechanical peeling of previously 0 bleached fibers, then by homogenization, microfluidization and microgrinding treatments. The dimensions of cellulose microfibril CMF particles vary according to the cellulose sources from which they are extracted. Cellulose microfibrils CMF generally have a diameter of 50 to 100 nm, a length of 1000 to 2000 nm and a specific surface area of 10 to 100 m²/g.

Crystalline nanocellulose CNC, in turn, is obtained from cellulose microfibrils CMF by a chemical treatment of acid hydrolysis. This acid hydrolysis prevents degradation of the crystalline domains of cellulose, while destroying the amorphous parts at the periphery of and within cellulose microfibrils. Cellulose nanocrystals, also called “whiskers”, are thus obtained. The dimensions of crystalline nanocellulose

CNC particles vary according to the cellulose sources from which they are extracted. Crystalline nanocellulose CNC has, for example, a diameter of 5 to 10 nm, a length of 100 to 500 nm and a specific surface area of about 500 m²/g. Crystalline nanocellulose CNC is thus clearly distinguished from cellulose microfibrils CMF by its dimensions, in particular by a length that is much shorter than the length of cellulose microfibrils.

Preferably, the layer of varnish and crystalline nanocellulose CNC comprises about 1% crystalline nanocellulose CNC in relation to the weight of the varnish.

In the example presented in Figure 2, the protective coating C comprises a layer 4 of varnish and crystalline nanocellulose CNC. According to a variant (not shown), the protective coating C comprises several layers 4 of varnish and crystalline

I nanocellulose CNC.

The use of crystalline nanocellulose CNC as dopant, i.e., in a small amount as additive in a varnish, has the surprising effect of substantially improving the soiling resistance of the banknote 1, as well as its water-repellency and oil-repellency properties, all while ensuring good mechanical properties.

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

The protective coating C comprising a layer of varnish and crystalline nanocellulose CNC also has the advantage of being printable itself and of being compatible with skin contact, i.e., not toxic or allergenic.

In the example presented in Figure 3, the protective coating C further comprises a layer 5 of cellulose microfibrils CMF arranged between the layer 4 of varnish and crystalline nanocellulose CNC and the face 20 of the banknote 1. The cellulose microfibrils CMF are, for example, in the form of gel incorporated in solvent, in particular water or isopropanol. The cellulose microfibril CMF gel comprises, for example, a solids content of 2% by weight of the gel when the solvent used is water, 25 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 C comprises at least two layers 5 of cellulose microfibrils CMF arranged between the layer 4 of varnish and crystalline nanocellulose CNC and the face 20 of the banknote 1.

The use of the layers 5 of cellulose microfibrils CMF makes it possible in combination with the layer 4 of varnish and crystalline nanocellulose CNC to provide a banknote 1 with soiling resistance and water-repellency and oil-repellency properties that are further improved relative to the use of a single layer 4 of varnish li and crystalline nanocellulose CNC. Moreover, the use of the layers 5 of cellulose microfibrils CMF improves the mechanical properties of the banknote 1, in particular tearing resistance.

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

The protective coating C comprising at least one layer of cellulose microfibrils

I

CMF and a layer of varnish and crystalline nanocellulose CNC also has the 0 advantage of being producible by known industrial processes such as coating and printing, and of being compatible with skin contact, i.e., not toxic or allergenic.

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

During a first step 30 illustrated in Figure 4, the varnish comprising crystalline 5 nanocellulose CNC is disposed on one or both of the faces 20 and 21 of the banknote 1 by the printing or coating technique, so as to form the transparent protective coating C.

The varnish layer 4 comprising crystalline nanocellulose CNC is, for example, applied by methods of flexographic printing, photogravure or serigraphy or indeed 0 even methods of air-knife coating, curtain coating or roll coating. The varnish layer 4 is, for example, applied by flexography with 15cm³/m² anilox rolls depositing on average between 4 and 5 g/m².

During a second step 31, the varnish layer 4 comprising crystalline nanocellulose CNC is dried. According to an embodiment, the varnish layer 4 25 comprising crystalline nanocellulose CNC is dried under ultraviolet radiation. This embodiment is particularly advantageous when the varnish is a varnish comprising an epoxide or acrylate base. According to a variant, the varnish layer 4 comprising crystalline nanocellulose CNC is dried by a hot air stream. This embodiment is particularly advantageous when the varnish is a varnish comprising an aqueous 30 base.

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

The surface treatment of the banknote 1 illustrated in Figure 3 proceeds as 5 follows.

During a first step 40 illustrated in Figure 5, a solution of cellulose microfibril CMF gel and solvent is applied on one or both of the faces 20 and 21 of the banknote 1. The banknote 1 may be printed beforehand or not.

I

The solution is applied, for example, in the laboratory by means of a threaded 0 rod on which the solution comprising the cellulose microfibril CMF 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 solution 36 pm in thickness.

According to a variant, the solution is applied on one or both of the faces 20 and 21 of the banknote 1 by the coating or printing techniques explained below. This variant is particularly suited to industrial production conditions.

During a second step 41, the layer 5 of cellulose microfibril CMF gel is dried. The layer 5 of cellulose microfibril CMF gel is, for example, dried by a hot air stream and/or in the open laboratory air. During drying, the solvent evaporates from the 0 solution 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 5 of cellulose microfibril gel.

According to an embodiment of the invention (not shown), the substrate 2 is 25 then laminated, for example by an intaglio process with or without ink, to return a homogeneous and smooth surface quality to the substrate 2.

During a third step 42, the varnish comprising crystalline nanocellulose CNC is disposed on the layer 5 of cellulose microfibril gel applied last, by the printing or coating technique.

The varnish layer 4 comprising crystalline nanocellulose CNC is, for example, applied by methods of flexographic printing, photogravure or serigraphy or indeed even methods of air-knife coating, curtain coating or roll coating.

During a fourth step 43, the varnish layer 4 comprising crystalline nanocellulose CNC is dried. According to an embodiment, the varnish layer 4 comprising crystalline nanocellulose CNC is dried under ultraviolet radiation. This embodiment is particularly advantageous when the varnish is a varnish comprising 5 an epoxide or acrylate base (cationically and radically polymerizable, respectively).

According to a variant, the varnish layer 4 comprising crystalline nanocellulose CNC is dried by a hot air stream. This embodiment is particularly advantageous when the varnish is a varnish comprising an aqueous base.

According to an embodiment of the invention (not shown), the third and fourth 0 steps 42 and 43 are repeated at least once so as to form two or more layers 4 of varnish and crystalline nanocellulose CNC.

The table below summarizes the results obtained with the Cobb sizing test, the Fritsch test, the Kit test and the Bendtsen permeability test carried out on security documents to which various treatments were applied.

	Cobb sizing (g/m²)	Fritsch test AL*	Kit test	Bendtsen permeability (ml/min)
Paper alone calendered 1 face	~90	35 ± 1.2	0	11.7
Paper calendered 1 face standard varnish	~15	4.1 ±0.7	2	0
Paper calendered 1 face standard varnish + CNC powder	~5	4 ±0.3	7	0
Paper calendered 1 face with 2 laminated CMF layers and standard varnish + CNC powder	~9	2 ±0.6	9	0

By “calendered 1 face” is meant that the substrate is intaglio printed on one face.

By “laminated CMF layers” is meant that the layers of cellulose microfibrils CMF are intaglio printed without ink.

By “standard varnish” is meant a varnish containing monomers of the family of cycloaliphatic epoxides which polymerize giving a polyepoxide matrix via initiators such as ultraviolet-activated onium salts.

In the table above, the various tests were carried out on the calendered face li and both faces of each substrate were varnished.

The Cobb sizing test characterizes the water repellency, i.e., the resistance of the banknote substrate to penetration of water, such as water in sweat, for example.

More precisely, it is the amount of water absorbed by the substrate in g/m² over a period of 60 seconds.

The Fritsch test characterizes soiling resistance. The Fritsch test is carried out by means of a vibrating device where small glass beads spread over and encrust on

I the substrate a soiling composition containing sand, peat, activated carbon, flour, and 0 a greasy substance present in sebum, glycerol monooleate, for 15 minutes. The luminance L* of the substrate is measured on several regions before and after the substrate has been exposed to the soiling composition. The difference AL* obtained between measurements before and after carrying out the test characterizes the attachment of the soiling on the substrate. Thus, the smaller the difference, the better 5 the soiling resistance of the substrate.

The Kit test characterizes the oil repellency of the substrate. It is a test during which the substrate is exposed to greasy substances, in particular a mixture of castor oil and high boiling-point solvents, toluene and n-heptane. By varying the proportions of the above-mentioned products, one obtains a composition the 0 viscosity and surface tension of which vary inversely with impregnation capacity.

Thus, a castor oil-rich composition is at the bottom of the scale, whereas a solventrich composition is at the top of this same scale. Twelve different compositions are generally used. The evaluation is performed visually. It is accepted that a score of 6 or higher imparts a satisfactory barrier to greasy substances. The results in this test 25 are highly dependent on the surface condition of the substrate and security prints covering said substrate.

The Bendtsen permeability test characterizes the air permeability of the substrate, i.e., the air flow passing through the substrate over a measurement surface area of 10 cm².

The table presented above highlights the advantages conferred by the invention.

2014368503 24 Sep 2019

Indeed, it is clear from this table that affixing on the substrate 2 varnish in which crystalline nanocellulose CNC has been incorporated as dopant, i.e., in a small proportion, significantly improves the soiling resistance and the water-repellency, oilrepellency and air-permeability properties of the banknote 1.

It is also clear from this table that the combination of layers of cellulose microfibrils CMF and of varnish comprising crystalline nanocellulose CNC further improves the properties of the banknote 1 already obtained by affixing the layer 4 of varnish and crystalline nanocellulose CNC alone, in particular in terms of soiling resistance and oil repellency.

Furthermore, similar tests carried out on paper comprising a varnish layer in which cellulose microfibril CMF powder was incorporated, revealed that the mixture of varnish and cellulose microfibril CMF powder was not easily printable. Moreover, these tests did not provide significant results, in particular in terms of soiling resistance and water-repellency, oil-repellency and air-permeability properties.

Thus, if the combination of varnish and crystalline nanocellulose CNC provides particularly advantageous results in particular in terms of soiling resistance, water repellency, oil repellency and air permeability, it is however not the case of the combination of this same varnish and cellulose microfibrils CMF. The results in these tests thus reveal a particular synergy between the varnish and crystalline nanocellulose CNC, even in a small amount, which does not exist between the varnish and cellulose microfibrils CMF.

The invention thus has the advantage of proposing a banknote 1 having greatly improved anti-soiling properties. The banknote 1 according to the invention could thus remain in circulation longer before being withdrawn by central banks.

Furthermore, according to the invention, the improvement of these anti-soiling properties does not come at the expense of economics, and does not use complex physical processes that greatly increase the manufacturing costs of the banknote 1. Finally, cellulose microfibrils CMF and crystalline nanocellulose CNC, which are natural substances, have the undeniable advantage of not appearing on the lists of substances subject to restrictions under the REACH regulation defined by the European Chemicals Agency (ECHA).

2014368503 24 Sep 2019

It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

2014368503 24 Sep 2019

Claims

1. A process for the surface treatment of a security document which comprises, at least on one of its opposite faces, at least one security print consisting of at least one pattern, this face and this at least one associated print being covered with a transparent protective coating, wherein one proceeds to the disposing by the printing or coating technique of a varnish comprising crystalline nanocellulose in a proportion of 0.5% to 10% by weight of the varnish, on said at least one face, and that one proceeds to the drying of said varnish layer.

2. A process according to claim 1, wherein the varnish comprises about 1% crystalline nanocellulose is used.

3. A process according to claim 1 or claim 2, wherein the varnish is dried under ultraviolet radiation.

4. A process according to claim 1 or claim 2, wherein the varnish is dried by a hot air stream.

5. A process according to any one of the preceding claims, wherein the varnish is an epoxide-based varnish or an acrylate-based varnish.

6. A process according to any one of claims 1 to 5, wherein one proceeds to an application of a solution comprising cellulose microfibrils on at least one face of the security document, the drying of the layer of cellulose microfibrils, and then the disposing of the varnish layer on the layer of cellulose microfibrils.

7. A process according to claim 6, wherein one repeats at least once the steps of disposing by the coating technique cellulose microfibrils on at least one face of the security document and of drying the layer of cellulose microfibrils before proceeding

2014368503 24 Sep 2019 to the disposing of the varnish layer, so as to form at least two layers of cellulose microfibrils.

8. A security document comprising, at least on one of its opposite faces, at least one security print consisting of at least one pattern, this face and this at least one associated print being covered with a transparent protective coating, characterized in that said coating comprises at least one layer of a varnish incorporating crystalline nanocellulose in a proportion of 0.5% to 10% by weight of the varnish.

9. A security document according to claim 8, wherein said varnish comprises about 1% crystalline nanocellulose (CNC).

10. A security document according to claim 8 or claim 9, wherein the varnish is an epoxide-based varnish or an acrylate-based varnish.

11. A security document according to any one of claims 8 to 10, wherein 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.