EP3688223A1

EP3688223A1 - Paper support, security document which comprises same and manufacturing process

Info

Publication number: EP3688223A1
Application number: EP18782358.8A
Authority: EP
Inventors: Xavier Borde; Marjory LE BERRE; Julien Gillot
Original assignee: Oberthur Fiduciaire SAS
Current assignee: Oberthur Fiduciaire SAS
Priority date: 2017-09-26
Filing date: 2018-09-25
Publication date: 2020-08-05
Anticipated expiration: 2038-09-25
Also published as: WO2019063560A1; FR3071518A1; EP3688223B1; FR3071518B1

Abstract

The present invention relates in particular to a high-durability paper support for printing a security document, in particular a banknote, comprising cellulose fibres, in a proportion of at least 50% by weight relative to the total weight of the paper support in the dry state, additives and adjuvants, at least one binder, and which further comprises at least one olephobic and hydrophobic agent based on an organic compound containing perfluoropolyethers (PFPE), in a concentration of greater than 0% and less than or equal to 5% by weight in the dry state relative to the total weight of the paper support in the dry state, characterized in that it furthermore comprises at least one non-fibrous structural reinforcing agent from the family of softening agents, i.e. agents that increase the flexibility of the cellulose fibres, in an amount of between 0.5% and 15% by weight relative to the total weight of the paper support in the dry state.

Description

PAPER HOLDER, SECURITY DOCUMENT INCLUDING IT AND METHOD OF

MANUFACTURING

FIELD OF THE INVENTION

The invention relates to a paper medium with high durability for printing a security document, including a banknote.

The invention also relates to a method of manufacturing this paper support and a security document made from such a paper support.

BACKGROUND OF THE INVENTION

Security documents, particularly banknotes, are subject to numerous solicitations during their circulation. These may be of a mechanical nature, for example folds, wrinkles and other manipulations that may lead to more or less marked deterioration of the fibers or even tears thereof.

To this must be added the environmental constraints to which the safety documents are subjected, and it is thus possible to indicate the exposures to ultraviolet radiation or the drought and especially the relative humidity, which can contribute to modify the behavior of the ticket. In fact, exposure to a humid environment can cause the paper to swell, that is to say an increase in its weight and thickness, accompanied by a decrease in the stiffness of the paper. Conversely, an environment that is too dry can lead to a decrease in the humidity of the paper and therefore a brittle behavior of its fibers.

It is therefore essential for a paper that it retains its original properties of rigidity but also of general mechanical resistance during its life in the field.

Finally, it should be noted that among the fouling generally present on the banknotes, there is a combination of fats generally derived from sebum and fats for culinary purposes carried by the man and transferred from the successive carriers to the ticket. The accumulation of these fats on the surface of the note and more penetration within the fibers if the surface of the paper is deteriorated, contributes to the stickiness of the note and the unpleasant feeling that results from it.

Thus, there is a need to protect the surface of the paper, to avoid the accumulation of dirt but also the heart of the paper (the fibers) in order to slow down its destructuring and therefore the progression of external aggressors if however the surface protection came to become fragile or even disappear.

This phenomenon is particularly visible at the locations of the folds in particular where the fibers are stressed in bending. In these areas, where the surface protection will break under the effect of the fold, there is a need to improve the strength of the fiber and more particularly its resistance to bending to prevent it from breaking. This slows the risk of tearing or tearing of the paper in these zones of weakness.

In order to remedy this problem, various techniques are already known in the state of the art for improving the resistance to soiling and tearing of banknotes.

Thus, for example, according to document FR 2 975 408, a high-durability paper sheet covered with a protective coating comprising an external printability layer based on polyurethane is known.

Also known from the state of the art, papers with improved strength, in which are added to the pulp of cellulose fiber, materials such as polyamides, polyesters or polypropylene. For example, document EP 1 432 576 describes the use of polyester reinforcing fibers.

Also known are plastic banknotes, for example those made on bi-oriented polypropylene (BOPP), presented as products ensuring a long life and other hybrid products including both paper parts and other plastics based on polyamides or polyesters.

The central banks responsible for the issuance, circulation and withdrawal of banknotes have budgetary constraints that compel them to seek an increase in the longevity of banknotes in order to reduce the cost of the banknote cycle. cash, which makes them legitimately turn to the aforementioned solutions.

However, the substrates obtained with the techniques identified above have various disadvantages: To be difficult to print by the very closed nature of the supports. The inks penetrate the support with difficulty and thus their drying and their adhesion on the substrate can be disturbed; this results in certain difficulties during the production of the banknotes and sometimes low ink in time. In addition, dull colors can result from these impressions.

- Be difficult to implement during the process of forming the sheet in the wet state. Indeed, the addition of synthetic fibers can disrupt or even prevent the creation of bonds between the fibers and thus completely destructure the paper sheet.

Finally, in some cases, the varnishing of the support is mandatory to guarantee a minimum hold over time.

As a state of the art, one can also cite the document FR 3025532 in the name of the present applicant. It describes a paper medium with high durability and biodegradability. It comprises an oleophobic and hydrophobic bonding agent, as well as a biodegradable structural reinforcing agent.

In practice, the reinforcing agent is constituted by additional fibers of a different nature, which are added to the cellulose fibers already usually present in the paper structure.

Moreover, and in a completely different technical field than that of the present invention, WO 2007/000177 describes a process for manufacturing two-ply toilet paper in which, before joining these two plies, at least a surface of the outer sheet a softening composition providing a pleasant contact for the epidermis.

In any case, there is to date a need for a paper support for the manufacture and printing of a security document, including a banknote, which has characteristics of "high durability ", namely high barrier properties as well as a high resistance to mechanical stress without modifying the paper process, more precisely without adding fibers other than the cellulose fibers usually used for the manufacture of such a paper, nor disturbing the printing of the final support. More precisely, it is sought on the one hand to increase the flexibility of the fibers, while maintaining a relative rigidity of the paper support, so as to increase its resistance to folding and on the other hand to increase its resistance to water and water. oil to prevent deterioration of the support by water and fatty substances that are likely to be deposited on its surface.

SUMMARY OF THE INVENTION

Thus, the present invention relates to a high durability paper medium for printing a security document, especially a banknote, comprising cellulose fibers, in a proportion of at least 50% by weight relative to to the total mass of the paper support in the dry state, additives and adjuvants, at least one binder, and which further comprises at least one oleophobic and hydrophobic agent based on an organic compound containing perfluoropolyether groups (PFPE), in a concentration greater than 0% and less than or equal to 5% by mass in the dry state relative to the total mass of the paper support in the dry state,

This support also comprises at least one non-fibrous structural reinforcing agent of the family of softening agents, that is to say agents that increase the flexibility of the cellulose fibers, in an amount of between 0.5% and 15% by weight. relative to the total mass of the paper support in the dry state.

Moreover, according to other non-limiting and advantageous features of this support:

the Young's modulus of said support, measured according to the ISO 1924 standard, is at least 30%, preferably 50% to 60%, less than that of a paper support devoid of said structural reinforcing agent; it has an average SM / ST value of double fold resistance greater than 100%, and preferably 200%, than that of a paper support without said structural reinforcing agent;

the concentration of cellulose fibers is greater than or equal to 85% and less than 100% by mass in the dry state relative to the total mass of said paper support in the dry state;

the additives and adjuvants and binder are present in a concentration greater than 0% and less than or equal to 15% by mass in the dry state relative to the total mass of said paper support in the dry state; the structural reinforcing agent is selected from surfactants;

said structural reinforcing agent is chosen from cationic surfactants, in particular from quaternary ammonium compounds and cationic polymers;

said structural reinforcing agent is chosen from nonionic surfactants, especially from the group consisting of polybutylene, long-chain fatty acids, ie having a chain length greater than or equal to 10 carbon atoms, and ethoxylated fatty amino acids;

said structural reinforcing agent is chosen from anionic surfactants; and

the perfluoropolyether groups have in their chemical formulas the base fragments - (CF 2 CFO 2) m - (CF 2 O) n - where m and n are integers.

The invention also relates to a security document which comprises a support according to one of the preceding characteristics.

Advantageously, said document is a bank note.

Finally, it relates to a method of manufacturing such a paper support which comprises the following steps:

a) suspending the cellulose fibers in water,

b) refining the mixture,

c) addition of additives, adjuvants and binder,

d) purification and filtration of the fibrous suspension, e) shaping of the paper support,

f) pressing,

g) pre-drying,

h) paper coating,

i) post drying,

and steps of adding agent (s) for structural reinforcement and addition of agent (s) oleophobic (s) and hydrophobic (s), alone or in mixture, namely that:

when they are added alone, ie individually: the structural reinforcing agent is added in step c) and the oleophobic and hydrophobic agent in step h), or vice versa; or both agents are applied one after the other in step h) in line on the paper machine, the first of which is dried by hot air or infrared radiation, before to apply the second, itself dried by hot air or infrared radiation,

when they are added as a mixture, this addition is carried out during step c) or during step h).

Advantageously, the structural reinforcing agents and the oleophobic and hydrophobic agents are applied offline, separately or as a mixture, by coating, dipping, impregnation, surfacing, spraying, air-blading, curtain coating, pencil coating, roller coating. engraved, attendants or by transfer, type "size press", "film press", without this enumeration being exhaustive

As is shown in the following description, the properties of high durability are obtained by a surface treatment that does not require modification of the fibrous composition of the substrate. In addition, the air permeability obtained is not zero, unlike the permeabilities of the majority of high durability media currently known on the market. In addition, the Cobb bonding value obtained, that is to say the water absorption capacity of the support is normal and comparable to that of a standard paper for banknote, which reinforces its printability. Its printing is thus facilitated.

Furthermore, the support as described by the invention retains its barrier properties after creasing, including permeability values and Cobb which remain relatively low, unlike untreated paper. These characteristics are important parameters that allow the support to better withstand mechanical stresses when it is in circulation in the field.

Finally, the support as described by the invention has increased flexural strength while maintaining a normal overall stiffness and comparable to a standard paper. DETAILED DESCRIPTION OF THE INVENTION

The fibers used in the composition of the paper support are mainly cellulose fibers.

Advantageously, these cellulose fibers are chosen from fibers made from hardwoods, softwoods, seasonal plants. such as cotton, hemp or flax, for example. These different fibers can be used alone or as a mixture.

Preferably, however, the cellulose fibers used are cotton fibers. This fiber is used for its good physical and mechanical characteristics. Indeed, the long cotton fibers can measure up to 40 mm long, which gives the paper obtained a very good resistance to folding.

The paper support according to the invention also comprises nonfibrous additives and adjuvants, preferably chosen from antifoaming compounds, mineral fillers, wet strength agents and bonding agents used alone or in combination with mixture of at least two of them.

The antifoam compounds are, for example, agents such as silicones, silicone emulsions, polyethylene glycols, polyethylene glycol derivatives, synthetic polyalcohols, polyalcohol derivatives, amide antifoams, ester base; surfactants such as oligomers, ethylene oxides (EtO), polypropylene oxides (PPOx); hydrophobic agents such as hydrocarbon waxes, polyethylene waxes, fatty alcohols, fatty acids, fatty esters, ethylenesbis (steramide) (EBS), hydrophobic silicas.

These antifoam compounds will be added during the preparation of the pulp as well as in the wet part of the paper machine, in order to avoid the formation of foam, or even to destroy it and thus to improve the formation of the sheet.

Preferably, the mineral fillers are chosen from colloidal silica, sodium silicates, sodium aluminosilicates, natural or precipitated calcium carbonates, talc, natural or calcined kaolin, alumina hydrate, titanium and barium sulphate, alone or as a mixture of at least two of them.

These mineral fillers are added to modify the optical properties of the paper obtained, such as its whiteness, gloss or opacity, but also its surface properties. Some of these fillers are less expensive than fibers and are therefore added to reduce manufacturing costs.

The wet strength agents are thermosetting polymers which are added when the paper is still in the wet state and which reticens in the paper during its passage in dryness. They play a role of barrier to water once the paper is made.

It is preferable to use polymers which bind the fibers together, such as urea-formaldehyde (UF) resins, melamine-formaldehyde (MF) resins, polyamidoamine-epichlorohydrin resins (PAA-E ), glyoxal resins, metal ion complexes alone or in admixture.

Bonding agents retard the penetration of liquids into the paper. They are implemented either when the paper is still in the wet state (sizing in the mass of the paper), or at the gluing press

(surface sizing).

Preferably, natural products, such as modified natural resins (resin-based adhesives), starch or modified starch or synthetic products, such as alkyl ketene dimer (AKD), are used. anhydrous succinic alkenyl (ASA) and other polymers (for example copolymers based on esters of acrylic acid and maleic acid, acrylonitrile and styrene). AKD is the most commonly used bonding chemical and should preferably be used when product specifications permit. It is also possible to use paraffin wax and polyethylene waxes. These different products can be used alone or mixed.

As will be described later, the fibers, additives and adjuvants are mixed and are bonded together by the use of at least one binder.

This binder makes it possible to improve the strength of the paper in the dry state. Advantageously, the binder is chosen from polyvinyl alcohols, starch, starches, latex, hemicelluloses, CMCs (carboxymethylcelluloses), galactomannans, gelatins or polyamide-epichlorohydrin resins, taken alone or as a mixture of at least two of them.

According to the invention, the paper support also comprises an oleophobic and hydrophobic agent.

This oleophobic and hydrophobic agent is introduced preferably in the form of an aqueous dispersion based on perfluoro-polyether (PFPE), possed antdans lues o rm u chimiqu es f ra ts gm Ba - (CF 2 CF ₂ 0 ) _m - (CF20) _n - where m and n are integers. This agent can for example be chosen in the range Fluorolink ^® PFPE marketed by Solvay. For example, the commercial product "Fluorolink P56" water-based.

According to the invention, at least one non-fibrous structural reinforcing agent of the family of softeners is added to the fibers, additives, adjuvants and binders mentioned above. As used throughout the present application, an agent is used which makes it possible to increase the flexibility of the cellulose fibers of the paper. In other words, the Young's modulus of these fibers is decreased and their elongation at break is increased.

Preferably, the structural reinforcing agent is chosen from surfactants such as cationic surfactants, in particular from quaternary ammonium compounds and cationic polymers.

But it can also be chosen from:

nonionic surfactants, especially in the group consisting of polybutylene, long chain fatty acids, that is to say having at least 10 carbon atoms, and ethoxylated fatty amino acids;

anionic surfactants.

The amount of structural reinforcing agent, which may be described as softening agent is preferably between 1 and 30% by weight relative to the total weight of the softening composition.

Preferably, the softening agent solution contains water - between 20 and 90%, preferably between 60 and 90%.

It may also contain low molecular weight organic solvents such as polyethylene glycol, ethanol, isopropanol, n-propanol, acetone, methyl ethyl ketone, ethylene glycol, propylene glycol, glycerin, used alone or in mixture. The amount of these solvents may be between 0 and 30%, preferably between 3 and 15%.

This softening agent may be chosen, for example, from the range FiberPlus ^® sold by Henkel. For example, the commercial product "Aquence FiberPlus Ultra" or "Aquence FiberPlus Natural".

According to the invention, the aforementioned products are introduced in the following concentrations:

- Cellulose fiber: greater than or equal to 85% and less than 100%, preferably between 88 to 92%;

- Additives, adjuvants and binders: greater than 0% and less than or equal to 15%, preferably between 8% and 12%;

- Structural reinforcement agent: greater than 0% and less than or equal to 15%, preferably between 0.5% and 3%;

- Oleophobic and hydrophobic agent: greater than 0% and less than or equal to 5%, preferably between 0.5 and 2%;

These percentages are given in dry mass of a given product, relative to the total mass in the dry state of the sample considered of said paper support. An exemplary embodiment of the papermaking process is described in more detail below.

The cellulose fibers are suspended in water. The mixture is then refined to generate small fibrous elements that will allow the fibers to interlace more easily and the sheet to have excellent mechanical strength.

In a second step, the various additives, adjuvants and binders are added to the fibrous suspension. The structural reinforcing agent may be added at this stage, alone or in admixture with the oleophobic and hydrophobic agent.

The fibrous suspension is finally purified by gravity to remove impurities, and by filtration to remove agglomerates of fibers that could affect the homogeneity of the sheet.

If they are not added to the fibrous suspension, the oleophobic and hydrophobic bonding agent (s) containing the perfluoropolyether groups and the structural reinforcing agent may be integrated into the paper support by coating, dipping, impregnation, surfacing, spraying, coating. with air knife, curtain coating, pencil coating, engraved roll coating, attendant or transfer type, "size press", "film press", online or offline, singly or in combination.

The formation of the sheet constituting the paper support can be done with a round machine, with or without the addition of a pre-layer under pressure (commonly called in the fiduciaire industry "short train"), or with a flat table single or double jet.

A watermark, a security thread, security fibers, hilites, boards, or markers can be integrated into the paper support during its formation. According to one variant, the structural reinforcing agents as well as the oleophobic and hydrophobic bonding agents can be applied online or offline and separately, namely that the first product is dried before applying the second product. The order of application can be reversed.

According to another variant, the structural reinforcing agents and the oleophobic and hydrophobic bonding agents can be added in admixture with either the various additives, adjuvants and binders in the fibrous suspension, or by the various coating techniques mentioned above, online or offline.

The paper support thus formed is printable and convertible by all known printing and processing methods and especially those commonly used in the fiduciary industry (offset, screen printing, intaglio printing, hot layering, flexography, typography, etc.). It is also possible to varnish before or after printing.

Work has been done to observe the durability properties of the paper thus obtained.

Hydrophobicity is characterized as resistance to water penetration and is measured using the Cobb test (60 s), according to ISO 535. This is the amount of water absorbed by the substrate in g / m ² thanks to a cylindrical impregnation template, for a period of 60 seconds. This is an otherwise common test in the paper industry to characterize paper absorption.

The results may give an indication of the printability of the media. Indeed, if the value of Cobb is very low, we can expect a refusal of ink from the support. On the other hand, with a value that is too high, it may be difficult to achieve the desired rendering in terms of color intensity. The standard values for a bank note are between 40 and 80 g / m ² .

This test was also performed after "dry crumpling x1" (that is to say after a crumpling of the dry support) to evaluate the evolution of the barrier properties of the support after creasing.

According to this test, the crumpling was carried out once, on the dry sample of dimensions 6.7 x 6.7 cm using a device allowing wrinkling developed by the "National Bureau of Standards" and marketed by IGT Testing Systems, a device commonly used in the fiduciary field. The sample is wrapped around a fork before being slid in a tube with a cap. This tube is then engaged in a vertical sleeve provided with a solid rod. The tube must then be depressed until a detachment of the counterweight of the IGT apparatus is obtained, thereby applying a force of 100N to the sample. The sample thus wrinkled is then removed by opening the cap. Finally the sample is gently unwrapped manually.

Oleophobia is measured by a fat exposure test. The method used, called "Test Kit", uses a mixture of castor oil (fats) and high-boiling solvents, namely toluene (aromatic solvent) and n-heptane (aliphatic solvent ).

Depending on the different proportions of the aforementioned products, a composition is obtained in which the viscosity and the surface tension vary inversely with its aggressiveness, that is to say, its impregnation capacity.

A composition rich in castor oil is at the bottom of the scale, while a composition rich in heavy solvents is at the top of the scale.

There are 12 compositions and it is admitted that a grade greater than or equal to 5 already gives a satisfactory barrier to fat. The evaluation is done visually. The results are strongly dependent on the surface condition of the support. In fact, generally, the lower the roughness, the better the result of the test kit. For example, it has been observed that after reduction of the roughness in particular following a soft printing, the results of the test kit tend to be improved.

The mechanical strength of the support was evaluated by several well-known tests of the paper industry in the directions "Marche" (longitudinal that is to say in the direction of the fibers) and "Travers" (transversal that is to say in the direction perpendicular to the fibers) of the paper indicated respectively SM and ST:

- Double-fold resistance with a Frank Prufgerate branded apparatus according to ISO 5626;

- Tear resistance initiated according to the ISO 1974 standard;

- Dry and wet tensile strength according to ISO 1924-2;

- Wet resistance according to ISO 3781.

The rigidity of the support was also evaluated by the Kodak rigidity measurement according to ISO 5629. Surface properties such as Bendsten roughness and Bendsten air permeability were also measured, according to ISO 8791-2 and ISO 5636-3 standards on the front and back sides respectively, giving an indication of printability of the support.

As with Cobb, air permeability after

"Crumpling" x8 was evaluated to check the barrier properties after creasing.

Example 1

The results obtained with a 100% cotton wove paper backing coated on each side with a layer of cationic surfactant (product A which thus constitutes the structural reinforcing agent) and with a layer consisting of oleophobic and hydrophobic agent at 3% in water (product B) (called "high performance solution") are given in Table 1 below. The coating was carried out in two stages (product A then product B), by threaded rod on each side of a dry paper already formed of grammage 90 g / m ² . The aqueous solution is deposited along the rod and then it is moved on the sheet to distribute the solution homogeneously. The threaded rod used deposits a wet layer 6 μιη thick. The actual thickness of material obtained is lower after evaporation of the water during drying. The dry weight thus deposited of oleophobic and hydrophobic agent is about 0.5 g / m ² per side. That of the fabric softener is about 4.5 g / m ² per side.

The results obtained with this high performance solution were compared to paper alone, paper only with product A, paper with only product B, and paper with high durability known in the field of fiduciary printing. The tests are carried out in triplicate and the indicated values are averages.

The analysis of Table 1 above shows that the air permeability after crumpling (x8) of the solution according to the invention is more than two times lower than the untreated paper, which unambiguously indicates a destructuring well. bottom of the support.

The solution according to the invention also increases by two to three times (depending on the face considered) the water resistance, even after crumpling (crumpling x1) relative to the untreated support.

The applied treatment therefore retains a significant barrier effect even after creasing of the support.

The surface roughness of the solution is higher, from 40 to 60% depending on the face considered, than the untreated substrate. This roughness value can be decreased by calendering if necessary.

The resistance to oil is significantly improved with a score of 8 in the Test Kit on both sides.

As regards the mechanical properties, the results of the double-fold test of the solution according to the invention are more than three times greater than untreated Vellum paper thanks to the structural reinforcing agent which provides flexibility to the fibers.

This improvement in fiber flexibility is confirmed by the decrease in Young's modulus of 58% in the running direction and 70% in the cross direction, as well as the increase in elongation at break compared to untreated paper. . The results of dynamic stiffness of the support remain close to the standard values with results little different from those of the untreated paper.

The wet strength is improved by 7% both in the direction of travel and in the cross direction. This feature is important to ensure holding of notes in circulation especially in humid regions. Indeed, in the presence of water, the hydrogen bonds which bind the paper fibers between them are easily broken and this has the effect of greatly reducing the strength of the paper sheet which will then begin to destructure.

The adhesion of the inks on the paper support according to the invention was evaluated for three types of printing characteristic of the manufacture of bank notes: offset, intaglio and typography. The resistance of these inks was evaluated by a series of chemical (soaking in various chemicals) and mechanical tests. Among the mechanical tests, there is the "crumpling or crumpling test" which evaluates the crease resistance of the paper medium and the inks printed on the latter in the dry and wet state.

For wet crumpling, the sample is placed in water for 15 minutes before wrinkling. The wrinkling is repeated 4, 8 and 40 times on the dry sample and on the wet sample, 4 and 8 times, using an IGT crumpling apparatus described earlier in the text.

After the tests, the paper and the different printings (offset, fluorescent offset, numbering and soft copy) are evaluated visually and the damage is noted from 0 to 4, with the following meanings: 0 = disappearance of the elements, 1 = more 50% change, 2 = less than 50% change, 3 = slight change, 4 = no change.

The expression "disappearance of the elements" means the total disappearance of the printing, so that it is no longer visible on the ticket.

The results obtained are shown in Table 2 below.

The behavior of the inks is good with results equivalent to those obtained on papers without treatment according to the invention. For example, for fluo offset, it is common to have 0 or 1 marks on hot water and laundry tests on untreated standard paper.

Resistance to crumpling is good, especially after the very aggressive test of 40 creases in the dry state (last line).

Overall, the results obtained in this example are satisfactory, the treatment does not have a negative impact on the behavior of the inks on the support and therefore does not require a post-vernissage mandatory to strengthen this outfit.

Example 2

In Example 2, the treatment as described by the invention is applied by a 1300 mm wide coil-to-coil coating machine (product A and then produced B in line), on wove paper 100 % cotton. The machine scroll speed during the coating was 60m / min.

The product A is dried with hot air ovens before applying the product B itself dried by hot air oven.

The results obtained in this configuration on 100% cotton wove paper are detailed in Table 3. The dry grammages deposited per face were as follows: product A = 1 .4 g / m ² , product B = 1.5 g / m ² . The results obtained with the solution according to the invention were compared with paper alone, untreated.

The wrinkled air permeability (x8) of Example 2 is more than four times lower than the untreated paper.

The water resistance after crumpling (crumpling x1) is also improved: the absorption of water is twice as low with the support according to the invention as with the untreated support.

As in Example 1, the applied treatment retains its barrier effect even after creasing of the support.

Oil resistance is improved by five points on the front and back of the untreated paper. This result is lower than that obtained in Example 1, which can be attributed on the one hand to the difference in application technique ("bar coating" in one case and air-layering in the other) and, on the other hand, the roughness values of the treated support which are higher than those obtained in Example 1.

Indeed, as previously described in the explanation of the test kit, the surface roughness of the support can have an impact on the oil resistance. Note that it is possible to reduce the roughness by calendering the support after coating and drying of the latter.

The double fold results of the solution according to the invention are three times higher than the untreated standard paper.

The wet strength is also improved: 7% on the front and 6% on the back.

In this example, it is shown that one can accentuate a property (here the double fold) to obtain very high resistances (average SM / ST> 10,000) by having a correct resistance to the oil.

By dosing the proportions of agent A and B, it is possible to modify the final properties of the paper as desired.

As for example 1, the adhesion of the inks was evaluated on the paper thus produced for three types of printing characteristics of the manufacture of banknotes: offset, intaglio and typography. The results obtained are detailed in Table 4 below:

TABLE 4

The conclusions of example 1 are confirmed with good crumpling even after 40 creases dry. The applied treatment does not interfere with the adhesion of the inks to the paper.

Example 3

The treatment according to the invention has been applied to several vellum papers from different suppliers to check the compatibility and the effectiveness of the treatment on different papers.

As shown in the table:

The treatment is compatible with different Vellum papers.

After paper processing, the results all show a clear and frank tendency towards the increase of this property of double folds which, with one exception, shows values 3 to 5 times higher in the running direction and nearly 2 times higher in average in the mean direction.

Regarding the air permeability, some values are low after treatment because the untreated paper already had a low air permeability.

Legend: SM = running direction and ST = cross direction

Claims

1. Highly durable paper medium for printing a security document, especially a banknote, comprising cellulose fibers, in a proportion of at least 50% by mass relative to the total mass of the paper medium at the time of printing. dry state, additives and adjuvants, at least one binder, and which further comprises at least one oleophobic and hydrophobic agent based on an organic compound containing perfluoropolyether groups (PFPE), in a concentration greater than 0% and lower or equal to 5% by mass in the dry state relative to the total mass of the paper support in the dry state,

characterized in that it furthermore comprises at least one non-fibrous structural reinforcing agent of the family of softening agents, that is to say agents increasing the flexibility of the cellulose fibers, in an amount of between 0.5% and 1 5% by weight relative to the total mass of the paper support in the dry state.

2. Paper support according to claim 1, characterized in that the Young's modulus of said support, measured according to ISO 1924 is at least 30%, preferably 50 to 60% lower than that of a paper support without said structural reinforcing agent.

3. Paper support according to claim 1 or 2, characterized in that it has an average value SM / ST of resistance to the double fold greater than 100%, and preferably 200%, than that of a paper support without said structural reinforcing agent.

4. Paper support according to one of claims 1 or 3, characterized in that the cellulose fiber concentration is greater than or equal to 85% and less than 100% by weight in the dry state relative to the total mass of said paper support in the dry state.

5. Paper support according to one of claims 1 to 4, characterized in that the additives and adjuvants and binder are present in a concentration greater than 0% and less than or equal to 1 5% by weight in the dry state relative to to the total mass of said paper support in the dry state.

6. Paper support according to one of the preceding claims, characterized in that the structural reinforcing agent is selected from surfactants.

7. Paper support according to one of claims 1 to 6, characterized in that said structural reinforcing agent is selected from cationic surfactants, especially from quaternary ammonium compounds and cationic polymers.

8. Paper support according to one of claims 1 to 5, characterized in that said structural reinforcing agent is selected from nonionic surfactants, especially in the group consisting of polybutylene, long chain fatty acids, it is that is, having a chain length of at least 10 carbon atoms, and ethoxylated fatty acids.

9. Paper support according to one of claims 1 to 5, characterized in that said structural reinforcing agent is selected from anionic surfactants.

10. Paper support according to one of the preceding claims, characterized in that the perfluoropolyether groups have in their chemical formulas the base fragments - (CF2CF20) m- (CF20) n- where m and n are integers.

1 1. Security document, characterized in that it comprises a paper support according to one of the preceding claims.

12. Security document according to the preceding claim, characterized in that said document is a bank note.

13. A method of manufacturing a paper support according to one of claims 1 to 10, characterized in that it comprises the following steps:

a) suspending the cellulose fibers in water,

b) refining the mixture,

c) addition of additives, adjuvants and binder,

d) purification and filtration of the fibrous suspension,

e) formatting of the paper medium,

f) pressing,

g) pre-drying,

h) paper coating,

i) post drying,

and in that it comprises the steps of adding a structural reinforcing agent (s) and adding an oleophobic (s) and hydrophobic agent (s), alone or as a mixture, namely that:

when added alone, ie individually:

- the structural reinforcing agent is added in step c) and the oleophobic and hydrophobic agent in step h), or vice versa; or

the two agents are applied one after the other in step h) in line on the paper machine, the first of them being dried by hot air or infrared radiation, before applying the second one, - even dried by hot air or infrared radiation. when they are added as a mixture, this addition is carried out during step c) or during step h).

The manufacturing method as claimed in claim 13, characterized in that the structural reinforcing agents and the oleophobic and hydrophobic agents are applied off-line, separately or as a mixture, by coating, dipping, impregnation, surfacing, spraying, coating with a blade. air, curtain coating, pencil coating, coating by engraved rollers, attendants or transfer, type "size press", "film press".