WO2014097205A1

WO2014097205A1 - Method for producing a security and/or valuable film by penetrating a fibrous substrate with a thermo-activatable adhesive

Info

Publication number: WO2014097205A1
Application number: PCT/IB2013/061132
Authority: WO
Inventors: Vincent GODARD
Original assignee: Arjowiggins Security
Priority date: 2012-12-19
Filing date: 2013-12-19
Publication date: 2014-06-26
Also published as: FR2999618A1; FR2999618B1; EP2938785A1; EP2938785B1; EP2938785B2

Abstract

The invention relates to a method for producing a security and/or valuable film, comprising steps consisting in: a) penetrating a fibrous substrate (1) with a fluid composition (13) comprising a thermo-activatable adhesive that is dispersed, especially emulsified or suspended, or solubilised in a fluid medium (10) of the composition (13), the fibrous substrate (1) comprising a security element (5) or set to comprise a security element, and b) when the fibrous substrate is set to receive a security element, providing the fibrous substrate with said security element.

Description

Process for the preparation of a security and / or value sheet by penetration of a thermo-activatable adhesive within a fibrous substrate

The invention relates to fibrous substrates for applications in the field of secure documents, more particularly cotton-based papers for bank notes and their preparation methods.

Background

The two main methods of reinforcing security paper are to add synthetic reinforcing fibers to the cellulosic system or to impregnate or even flocculate non-reactive polymers in the fibrous batt as described in US Pat. EP 2 148 954.

Also known is US 2006/0198987 which describes processes for preparing papers by laminating a layer of thermoplastic polymer between two paper layers, the lamination producing a multilayer substrate in which the polymer penetrates the fibrous layers to a certain thickness. The products obtained using the techniques described in this document, however, have a penetration of the polymer within the relatively superficial paper layers.

Publication WO 02/20902 still discloses a coated security sheet which has good durability and print rendering properties and which makes it possible to observe the security elements that the sheet comprises.

Conventional methods of reinforcement may not give entirely satisfactory results, especially when they are intended to reinforce paper with a watermark.

Indeed, the addition of synthetic fibers of high rate reinforcement in the cellulosic system can, in this case, deteriorate the fineness and contrast of the watermark.

The impregnation or flocculation of nonreactive polymers in the fibrous mat can, for its part, strengthen only in a limited or partial way the mechanical properties. In addition, too much flocculated polymer in the fibrous mat may impair the quality of the watermark.

There is, therefore, a need to increase the mechanical strength of fibrous substrates used in security applications, including fibrous substrates having a watermark. There is still a need to improve the resistance to wear and soiling of such fibrous substrates.

The invention aims specifically to meet the aforementioned needs.

summary

According to a first aspect, the invention relates to a method for preparing a security and / or value sheet comprising the steps of:

a) to penetrate, within a fibrous substrate, preferably made of paper, a fluid composition comprising a dispersible thermo-activatable adhesive, in particular emulsified or in suspension, or solubilized within a fluid medium of the fluid composition, the fibrous substrate; having a security element or being adapted to receive one, and b) when the fibrous substrate is intended to receive a security element, providing the fibrous substrate with said security element.

The penetration of a dispersion or a solution of heat-activatable adhesive into the fibrous substrate advantageously makes it possible, after activation of said adhesive, to increase the mechanical strength of the fibrous substrate, in particular its resistance to double fold, its resistance to tearing , its resistance to wrinkling or its resistance to dry or wet elongation.

The invention also makes it possible to have fibrous substrates with improved resistance to wear and dirt.

For a bank note in particular, the ability to withstand a high number of folds is a property to which fiduciary printers and end users attach great importance.

The present invention makes it possible to reinforce the fibrous substrate of safety and / or value by penetration within it of the thermo-activatable adhesive. Such an adhesive may, in particular, replace the conventional bonding which involves, for example, polyvinyl alcohol (PVA). PVA bonding may not be entirely satisfactory because the amounts of PVA that can be deposited may be limited because above a certain level of solids PVA is too viscous.

The invention therefore advantageously allows the application of larger amounts of adhesive than in known PVA bonding processes. In addition, when seeking to achieve certain strength properties, the proportion of synthetic fibers within the fibrous substrate may need to be increased, which may not be feasible and / or may result in degradation of the watermark rendering.

The present invention achieves good strength properties by using a lower rate of synthetic fibers, and thus limits the degradation of the watermark rendering.

In an exemplary embodiment, the fibrous substrate is free of adhesion agent other than the heat-activatable adhesive. The fibrous substrate is, for example, devoid of a polyolefin, for example polyethylene or polypropylene, other than the thermo-activatable adhesive.

The impregnation of heat-activatable adhesives is known in the field of decorative papers, a field in which these adhesives are used for their adhesive functions during particleboard / decorative paper lamination. Unlike the field of decorative papers, the thermo-activatable adhesive is used, in the context of the present invention, to strengthen the fibrous base and not to bond the fibrous substrate to another element.

It may, in addition to the penetration of the heat-activatable adhesive and in the quantities used, have formed a layer comprising the heat-activatable adhesive on the surface of the fibrous substrate. However, it is necessary in this case that at least part of the heat-activatable adhesive has penetrated mass into the fibrous substrate.

Preferably, the fibrous substrate has, before step a), undergone any treatment capable of reducing the porosity of the zone of the fibrous substrate intended to be brought into contact with the fluid composition. Such treatments may be impregnating, coating, surfacing or spraying treatments, which may "plug" the pores of the fibrous substrate.

The fibrous substrate is preferably in the form of a sheet of paper. Thus, the fibrous substrate is preferably made of paper.

Alternatively, the fibrous substrate may be a nonwoven material.

The "fibrous substrate" within the meaning of the present invention covers the fibrous substrate of the sheet obtained after draining, pressing and drying a fibrous suspension but also, more generally, any fibrous mat formed during the manufacture of the sheet having sufficient cohesion to undergo step a). This fibrous mat may in some cases not be fully drained and / or dried.

In the present invention, step a) is performed after the formation of the fibrous substrate. Step a) is preferably carried out on a fibrous substrate of the sheet obtained after draining, pressing and drying a fibrous suspension.

The term "heat-activatable adhesive" is understood to mean any adhesive whose adherent properties increase very strongly as a result of a supply of thermal energy, this supply of energy causing a modification of the physical structure of the adhesive, and / or preferably of chemical reactions in-house , or even its interfaces.

Step a) does not involve the application of a hot melt adhesive (or

"Hot melt") without a fluid medium, for example in the molten state, the adhesive being, in this case in the pure state (i.e. not dispersed or solubilized in a fluid medium).

Thus, a heat-activatable adhesive can undergo a chemical reaction, for example a crosslinking, following a heat input in order to increase its adherent properties.

A heat-activatable adhesive may be further activated by simple melting due to heat input, said melting improving contact and, therefore, after cooling, adhesion of the adhesive to the fibers of the fibrous substrate.

The security element is preferably a watermark. The watermark can be clear, that is to say formed by a local decrease in thickness of the fibrous or dark substrate, that is to say formed by a local increase in thickness of the fibrous substrate. In an exemplary embodiment, the watermark is multi-tone.

In an exemplary embodiment, the fluid composition is, during step a), deposited on a surface of the fibrous substrate by impregnation, coating, surfacing and / or spraying. Preferably, the fluid composition is, during step a), deposited on a surface of the fibrous substrate by impregnation.

The fluid composition may be deposited on only one side of the fibrous substrate or, preferably, on two opposite sides. The fluid composition is preferably deposited over the entire surface of the fibrous substrate.

In a variant, the fluid composition is deposited in a pattern on the surface of the fibrous substrate. The fluid composition is preferably deposited over the entire surface of at least one face of the fibrous substrate. Step a) is preferably carried out by means of a device chosen from the following devices: impregnator, sizing press (also called "size press"), coater with air knife or doctor blade, curtain coater, coater Champion, gravure coater, film transfer coater (also called "film press"), for example "Twin-HSM" coater from BTG, or spray device, for example nozzle or gun. It is preferably implemented by a device selected from an impregnator, a size press (also called "size press") or a film transfer coater.

Step a) is preferably carried out on a paper machine before any other impregnation, coating, surfacing and / or spraying operation.

Performing this step before any other impregnation, coating, surfacing and / or spraying operation advantageously facilitates the impregnation of the fibrous substrate with the fluid composition and thus allows a relatively deep impregnation.

Preferably, the fluid composition penetrates the fibrous substrate obtained after implementation of step a) on at least 25%, preferably at least 50%, preferably at least 75%, preferably substantially all, of its thickness.

A large depth of penetration of the fluid composition, and therefore of the adhesive, into the fibrous substrate advantageously makes it possible to improve the mechanical strength of the latter and, in particular, its resistance to folding and creasing.

Preferably, the fibrous substrate undergoing step a) comprises synthetic reinforcing fibers, preferably at least 5%, and more preferably at least 15%, by dry weight of synthetic reinforcing fibers relative to the total weight of the substrate. fibrous.

The implementation, during step a), of a fibrous substrate comprising synthetic fibers advantageously makes it possible, after activation of the adhesive, to very greatly increase the mechanical strength of the fibrous substrate.

Indeed, on the one hand, the synthetic fibers increase the porosity of the fibrous substrate thus allowing a better impregnation / penetration of the adhesive, and, on the other hand, the adhesive has a better adhesion with the synthetic fibers.

(compared to adhesive / cellulosic fiber adhesion). In an exemplary embodiment, the method comprises a step c) of activation of the heat-activatable adhesive present within the fibrous substrate obtained after implementation of step a), the activation being carried out by heat treatment and being, preferably, carried out by heating the fibrous substrate obtained after carrying out step a), particularly preferably by positioning a heated surface in the vicinity of and / or in contact with the fibrous substrate and / or by blowing the substrate. heated air on the fibrous substrate. Activation of the heat-activatable adhesive can be achieved by:

- pressing preceded by infrared heating, hot air or microwaves,

- calendering preceded by infrared heating, hot air or microwaves,

- hot pressing, in particular by using a hot plate,

- calendering, in particular by using a heating cylinder, and / or

- Infrared heating, hot air or microwaves, without prior application of pressure.

In particular, the adhesive may be increased during the step c) activating a T activation temperature _is greater than or equal to the activation of T min minimum _temperature which can itself be higher than the temperature of implementation T _m of the fluid composition comprising the heat-activatable adhesive in step a).

Following the thermal activation, the adhesive power of the heat-activatable adhesive present within the fibrous substrate then increases considerably, for example due to chemical modification, in particular by chemical reaction or crosslinking, or physical, in particular by crystallization or growth. of the contact surface.

Is preferably considered as heat-activatable adhesive any adhesive whose adhesiveness to a temperature T after activation according to step c), is greater than the adhesiveness to the same temperature T before activation according to step c), the temperature T being less than the activation temperature T _a .

T _a min previously mentioned is the minimum activation temperature T _a for which the increase in adhesiveness following activation, as described in the previous paragraph, is verified.

In one exemplary embodiment, activation is effected by heating the fibrous substrate by contacting a heated surface with the fibrous substrate.

The heating of the fibrous substrate upon activation may be localized at one or more distinct areas of the substrate. For example, the heating substantially only at a central region of one or both opposite faces of the substrate.

In an exemplary embodiment, the heating of the fibrous substrate is spatially uniform, that is to say that each zone of the surface of the fibrous substrate receives substantially the same thermal energy.

Alternatively, the thermal energy imparted to the surface of the fibrous substrate has a nonzero spatial variation or gradient along the surface of the fibrous substrate.

In an exemplary embodiment, as mentioned above, the adhesive is heat-reactive and undergoes a chemical reaction, including crosslinking, in step c).

The crosslinking occurring in step c) is preferably limited so as not to obtain a thermosetting adhesive. In this case, the density of chemical bonds produced by the crosslinking reaction can be relatively low so that the heat-activated adhesive retains high flexibility and flexibility, and thus the substrate thus obtained also retains high flexibility and flexibility, particularly high folding resistance. The degree of crosslinking is preferably chosen so that the heat-activated adhesive has an elastomeric character.

Preferably, and in order to limit the crosslinking that takes place in step c), the substrate does not comprise any crosslinking agent.

By "heat-activated adhesive" is meant the product resulting from the activation of a heat-activatable adhesive. This product corresponds, for example, to the product obtained after crosslinking of the heat-activatable adhesive present within the fibrous substrate. Alternatively, this product corresponds to the product obtained after melting and cooling of the heat-activatable adhesive present within the fibrous substrate.

In an exemplary embodiment, the adhesive present within the fibrous substrate is, during step c), raised to a temperature greater than 40 ° C., preferably between 80 ° C. and 180 ° C., and / or pressure greater than or equal to 3 bars, preferably greater than or equal to 10 bars, is applied to the fibrous substrate during step c).

Step c) can last between 1 second and 15 minutes.

The adhesiveness of the adhesive can become maximal by raising its temperature between 80 ° C and 180 ° C for some or some tens of seconds, and preferably by maintaining the fibrous substrate under pressure. The temperature and the residence time can have a greater influence on the adhesion than the pressure.

The activation step c) is preferably carried out online.

An online activation advantageously simplifies and makes more efficient the methods according to the invention.

The fibrous substrate which has undergone or, preferably, undergoes step c) is preferably coated on all or part of its surface with a "non-adherent", that is to say non-adhesive, coating. for isolating the heat-activated adhesive from outside the fibrous substrate. The release coating may be applied before, during and / or after step c).

The release coating is preferably applied before the beginning of step c).

The non-stick coating is for example a film, in particular extruded or laminated, or a fluid composition.

Said fluid composition may be in the form of a dispersion, in particular an emulsion or suspension, or a solution in a fluid medium of the fluid composition. This dispersion, in particular emulsion or suspension, or solution may be in the aqueous phase.

The release coating is preferably applied by impregnating, coating, surfacing and / or spraying a fluid composition, or by extrusion or lamination of a film. It is more preferably applied by coating or surfacing a fluid composition.

According to one variant, the release coating is coated with an additional coating, in particular having printability and / or protection properties, for example against soiling.

According to a preferred variant, the release coating is a coating forming a protective layer in particular to improve the soil resistance of the substrate, and / or a coating for improving the printability of the substrate.

The non-stick coating advantageously prevents the fibrous substrate from sticking to various elements after activation. Thus, it can be avoided, that after activation, the fibrous substrate does not stick to elements of the paper machine or itself during winding or cutting for example. Preferably, all or part of the fluid medium present in the fibrous substrate obtained after implementation of step a) is evaporated before implementation of step c). The fluid medium is, in particular, liquid. The fluid medium may be a solvent when the heat-activatable adhesive is solubilized within the fluid composition.

Thus, all or part of the fluid medium can be evaporated without this resulting in an activation of the heat-activatable adhesive.

Alternatively, the fluid medium can be evaporated during step c), the heating of the fibrous substrate made in step c) being both able to activate the adhesive and evaporate the fluid medium.

It will be possible to control the temperatures used during the implementation of the methods according to the invention. In particular, the temperature for evaporation of the fluid medium from the fluid composition may be lower than the activation temperature of the heat-activatable adhesive.

Such a treatment advantageously allows the adhesive to temporarily retain a zero or low adhesiveness, which is advantageous in order to prevent the fibrous substrate from sticking to various elements if the substrate is not coated with an anti-adhesive coating. member.

The evaporation of the fluid medium is preferably carried out by positioning a heated surface, for example of one or more heated cylinders, in the vicinity and / or in contact with the fibrous substrate, and / or by blowing hot air on the fibrous substrate.

Such heating modes advantageously make it possible to obtain moderate heating and to avoid activating the adhesive, unlike infrared drying which may be too powerful.

According to another of its aspects, the invention relates to a security and / or value sheet, in particular prepared by a method as defined above, comprising:

a) a fibrous substrate, preferably made of paper, comprising a security element, and b) a set of islands of a heat-activatable adhesive present within the fibrous substrate. Such a sheet has the particular advantage, because of the non-activation of the adhesive, not to stick and not to disturb the manufacturing process (especially the impregnated fibrous substrate does not stick to the constituents of the machines used, especially to the webs, felts and rolls of the paper machine and the dispersion / solution does not clog the circuits).

a) a fibrous substrate comprising a security element, and b) a set of reinforcing adhesive islands of a thermoactivated adhesive present within the fibrous substrate, the islands being optionally reinforcing adhesive crosslinking islands. Such a sheet advantageously has a mechanical strength, including increased double-fold resistance.

The fibrous substrate may be coated on all or part of its surface with a non-stick coating.

In the sheets described above, the adhesive may be thermoreactive or may be the product resulting from the activation of a thermoreactive adhesive.

Preferably, in the sheets described above, the fibrous substrate comprises synthetic reinforcing fibers, preferably at least 5%, and more preferably at least 15%, by dry weight of synthetic reinforcing fibers relative to the total weight of the fibrous substrate.

As explained above, a sheet comprising synthetic fibers advantageously has a very greatly increased mechanical strength.

When moving along the thickness of the fibrous substrate starting from one face, the density of islands can decrease on a first portion of the thickness and then possibly increase on a second portion of the thickness up to at the second face, the first and second portions succeeding one another when moving in the same direction along the thickness of the fibrous substrate.

Preferably, the density of the islets is constant over the entire thickness of the fibrous substrate. The invention relates, in another of its aspects, a security document and / or value incorporating a security sheet and / or value as defined above.

The document is for example a means of payment, such as a bank note, a card, a check or a restaurant ticket, an identity document, such as an identity card, a visa, a passport or a passport. driver's license, a lottery ticket, a ticket or an entrance ticket to cultural or sporting events, a loyalty card, a service card, a subscription card, a playing card or collectible card , a voucher or a voucher or a bank note.

This is preferably a bank note.

In an exemplary embodiment, the sheet according to the invention can be laminated with at least one plastic layer.

According to another of its aspects, the invention relates to the use, within a fibrous substrate comprising a security element, of a dispersion or a solution of a thermo-activatable adhesive for the improvement of the mechanical properties, in particular the double-fold resistance of said fibrous substrate.

According to another of its aspects, the invention relates to the use, within a fibrous substrate comprising a security element, of a fluid composition comprising a thermo-activatable adhesive dispersed or solubilized within a fluid medium of the composition fluid for improving the mechanical properties, especially the double-fold resistance, of said fibrous substrate.

According to another of its aspects, the invention relates to the use, within a fibrous substrate comprising a security element, of a combination of a dispersion or a solution of a thermo-activatable adhesive and of synthetic fibers. reinforcement for improving the mechanical properties, especially the double-fold resistance, of said fibrous substrate.

According to yet another of its aspects, the invention relates to the use, within a fibrous substrate comprising a security element, of a fluid composition comprising a thermo-activatable adhesive dispersed or solubilized within a fluid medium of the fluid composition and reinforcing synthetic fibers for improving the mechanical properties, especially the double-fold resistance, of said fibrous substrate. Fibrous substrate

The fibrous substrate may comprise fibers conventionally used in the papermaking field, in particular cellulose fibers. The fibrous substrate may comprise a mixture of long and short cellulosic fibers. It is preferable to use fibers having good adhesion with respect to the heat-activated adhesive.

The fibrous substrate may comprise adjuvants conventionally used in the papermaking field, especially retention agents, bonding agents and / or wet strength agents. The fibrous substrate is for example based on cellulosic fibers (in particular cotton fibers) and / or natural organic fibers other than cellulosic and / or artificial fibers and / or synthetic fibers, for example such as polyester fibers. or polyamide, and / or optionally mineral fibers, for example such as glass fibers.

The fibrous substrate may comprise one or more fibrous layers (also called jets) assembled after formation, especially in the wet phase.

The fibrous substrate may comprise one or more safety structures obtained during manufacture, and the substrate may in particular comprise a fibrous layer carrying a watermark. The fibrous layer (s) of the substrate may be made on a flat-bed or round-shaped paper machine, and the watermark (s) may be made partly wet according to the conventional methods known to those skilled in the art.

The fibrous substrate obtained after activation may have a basis weight (according to ISO 536) of between 60 g / m ² and 140 g / m ² , preferably between 85 g / m ² and 115 g / m ²

The fibrous substrate obtained after activation may have a thickness of between 60 μπι and 250 μπι, preferably between 100 μπι and 140 μπι. In an exemplary implementation of the invention, at least one fibrous layer of the substrate comprises a recess, for example an opening in the form of a reserve without fibers, made for example on a paper machine or out of a paper machine. for example by reducing dewatering, by punching, by laser cutting or by water jet.

The recess or recesses present on at least one fibrous layer of the substrate may each have an area of between 0.1 and 10 cm ² . The recess or recesses may have any geometric shape, in particular rectangular or circular. The presence of the adhesive advantageously prevents the fibers from becoming detached, even if the fibrous substrate has a recess.

In an exemplary implementation of the invention, at least one security thread is introduced at least partially into the fibrous substrate. Such a security thread is particularly introduced in mass or window. The invention thus also makes it possible to improve the grip of said security thread in the fibrous substrate and thus contributes to improving the securing of the fibrous substrate.

Fluid and adhesive composition

Preferably, the adhesive comprises a thermoplastic polymer, the glass transition temperature (T _g ) of the thermoplastic polymer being preferably less than or equal to + 10 ° C. Tg is measured according to ISO 11357.

The use of thermoplastic polymers is advantageous because they can soften, possibly melt, then re-solidify repeatedly and without significantly losing their properties.

The use of thermoplastic polymers having a glass transition temperature of less than or equal to + 10 ° C. is advantageous because it makes it possible to impart sufficient flexibility and flexibility to the fibrous substrate obtained after activation.

The fluid composition may be in the form of a dispersion, in particular an emulsion or suspension, or a solution of the thermoplastic polymer within a fluid medium of the fluid composition. This dispersion, in particular emulsion or suspension, or solution may be in the aqueous phase.

Said thermoplastic polymer can be (a) hard (solid) or (b) soft (softened, liquid) at room temperature, that is to say at 20 ° C. It is a case of (a) a powder, for example a powder of a hot melt polymer (or "hot melt"). It is preferably a thermoplastic polymer according to the case (b).

In an exemplary embodiment, the thermoplastic polymer is chosen from the families of acrylic polymers, polyurethanes, polyolefins, in particular polyethylene, polypropylene, ethylene-vinyl acetate (EVA, "ethylene vinyl acetate"), ethylene acrylic acid (EAA, "ethylene acrylic acid"), ethylene methacrylate (EMA, "ethylene methacrylate"), methylethylene methacrylate (EMMA, "ethylene methyl methacrylate"), polyvinylidene chloride (PVDC "Polyvinylidene chloride"), thermoplastic resins of elastomer type, especially styrene-butadiene rubber latex (SBR, "styrene butadiene rubber"), or mixtures thereof or copolymers thereof.

When the thermoplastic resins are of elastomer type, the crosslinking may already have occurred during the manufacture of the resin.

The aforementioned polymer families are, in one exemplary embodiment, used in the context of the processes according to the invention in a fluid composition which is in the form of a dispersion, in particular an emulsion or suspension, or a solution of said polymer thermoplastic within a fluid medium.

Preferably, the fluid medium of the fluid composition is water, the fluid composition preferably being an aqueous dispersion, in particular of a polyurethane, an acrylic polymer, a polyethylene, a polypropylene or a copolymer of ethylene and propylene. It is more preferably an aqueous dispersion, especially a polyurethane.

Other fluid media such as organic solvents may be used in the context of the present invention.

To a certain extent, the thermoplastic polymer may, in addition, be thermosetting ("thermoset (ting) resins"). In this case, the thermosetting character is preferably limited as previously described so as not to unduly affect the thermoplastic properties of the polymer. In this case, the adhesive can crosslink under the effect of heat to form coval bonds irreversible by carrying out at least one chemical reaction.

The crosslinking is made possible, either directly if the resin is self-crosslinking, or by adding a resin or a crosslinking agent.

Moreover, the fluid composition may comprise other compounds, especially chosen from hot-melt agents, tackifiers, plasticizers, mineral fillers, taggants, antimicrobial agents, tracers or surfactants.

The adhesive may comprise at least one chemically or biochemical chemical tampering and / or authentication and / or identification reagent reacting in a colored manner with at least one falsification and / or authentication and / or 'identification.

The thermo-activatable adhesive used may be of plant or animal origin.

When the heat-activatable adhesive is of plant origin, the fibrous substrate preferably makes it possible to provide identification and / or authentication information by measuring the content of bio-sourced material by quantifying the isotope 14 of the carbon ( ¹⁴ C).

This content is evaluated according to ASTM D6866-11: Determining the Biobase of Solid, Liquid and Gaseous Samples Using Radiocarbon Analysis.

Safety elements that may be present within the fibrous substrate

Among the security elements that may be present in the fibrous substrate, some are detectable to the eye, daylight or artificial light, without the use of a particular device. These security elements comprise for example colored fibers or boards, fully or partially printed or metallized wires. These security elements are called first level.

Other types of additional security elements are detectable only with a relatively simple apparatus, such as a lamp emitting in the ultraviolet (UV) or infrared (IR). These security elements comprise, for example, fibers, boards, strips, wires or particles. These security elements may be visible to the naked eye or not, being for example luminescent under a lighting of a Wood lamp emitting in a wavelength of 365 nm. These security elements are said to be second level. Other types of security elements require for their detection a more sophisticated detection device. These security elements are for example capable of generating a specific signal when they are subjected, simultaneously or not, to one or more external excitation sources. The automatic detection of the signal makes it possible to authenticate, if necessary, the document. These security elements comprise, for example, tracers in the form of active materials, particles or fibers capable of generating a specific signal when these tracers are subjected to optronic, electrical, magnetic or electromagnetic excitation. These security elements are said to be third level.

Reagents may also be incorporated into the fibrous substrate, for example chemical or biochemical reagents for tampering and / or authentication and / or identification which may react with, respectively, at least one counterfeiting agent and / or or authentication and / or identification.

The additional security element (s) present within the fibrous substrate may have first, second or third level security features.

The fluid composition may have a second or third level security element function. For this purpose, it comprises for example a second or third level security element.

Reinforcing fibers

The fibrous substrate may comprise reinforcing fibers made from a synthetic or artificial polymer, preferably from a synthetic hydrocarbon polymer.

It is advantageous to use fibers having a good adhesion with respect to the heat-activated adhesive.

The reinforcing fibers may be chosen from polyester or polyamide fibers, and mixtures thereof.

According to one particular case of the invention, the reinforcing fibers are polyamide or polyethylene terephthalate (PET) fibers, and are present in an amount in dry weight greater than 3%, preferably between 3 and 35% relative to the total fibers of the substrate.

According to a particular case of the invention, the reinforcing fibers also have an authentication function. The reinforcing fibers may have luminescent properties, for example fluorescent.

It may be for example a polyester fiber, in particular polyethylene terephthalate (PET), which has a reactive compound (fluorescent for example) by grafting or by addition during the extrusion of the fiber. The length of the reinforcing fibers is preferably between 4 and 6 mm, being preferably about 4 mm.

The linear density of the fibers is preferably less than 3 dtex, preferably about 1.7 dtex.

The tenacity of the fibers is preferably greater than 4 cN / dtex. The rate of introduction into the fibrous substrate is for example between 3

% and 35% by dry weight relative to the total fibers of the substrate. It is for example about 10%.

Description of the drawings

The invention will be better understood on reading the following detailed description, non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

FIG. 1 represents a fibrous substrate on which a fluid composition has been applied in the context of an exemplary method according to the invention,

FIG. 2 represents the result obtained after implementation of a step a) according to the invention on the substrate of FIG. 1,

FIG. 3 represents the result obtained after evaporation of the fluid medium initially present within the substrate of FIG. 2, FIG. 4 represents the result obtained after applying an anti-adhesive coating to the substrate of FIG. 3,

FIG. 5 represents the result obtained after submitting the substrate of FIG. 4 to a step c) according to the invention, and FIG. 6 represents a banknote according to the invention.

One example of a method of manufacturing a security paper according to the invention will be described with reference to FIGS. 1 to 5.

FIG. 1 shows a fibrous substrate 1 which has just been formed and comprises a watermark 5, on which substrate has been deposited by impregnation by means of a gluing press a fluid composition 13 comprising a dispersion 14 of a heat-activatable adhesive 11 in a fluid medium 10.

The fibrous substrate 1 may be formed by any known means. The fibrous substrate 1 comprising the watermark 5 may be formed by a round machine. Alternatively, the fibrous substrate 1 may first be formed by a flat-bed machine (Fourdrinier) and then be provided with the watermark 5, for example by contact with a filigree roller, for example during the dewatering of said substrate fibrous 1.

The fibrous substrate 1 comprises synthetic reinforcing fibers. As illustrated, it is possible to deposit the fluid composition 13 over the entire surface of the fibrous substrate 1.

In non-illustrated variants, the fluid composition 13 is deposited on the two opposite faces 7 and 8 of the fibrous substrate, or even on only one side of the fibrous substrate.

The fluid composition 13 may also be deposited on only part of at least one face of the substrate.

The heat-activatable adhesive 11 may be a thermoplastic polymer, preferably belonging to the families described above.

The adhesive may be thermoreactive and crosslinked upon activation. The fluid medium 10 may be water and the fluid composition 13 for example be an aqueous dispersion of a polyurethane.

As mentioned above, the deposition of the fluid composition 13 can be carried out on the fibrous substrate 1 by impregnation, coating, surfacing and / or spraying. When the fibrous substrate is manufactured by a round machine, the fluid composition may be deposited after the fibrous substrate has been drained and, if the fibrous substrate is intended to include a watermark, after formation of the latter.

In the variant in which the fibrous substrate is produced by a flat-bed machine, the fluid composition may be deposited before or after the formation of the watermark, and preferably after the step of dewatering the fibrous substrate.

In step a), the amount of heat-activatable adhesive 11 deposited on the face 7 of the fibrous substrate 1 can be between 1 gram of thermo-activatable adhesive 1 1 per m ² and 30 grams of heat-activatable adhesive 11 per m ² preferably between 2 grams of heat-activatable adhesive 11 per m ² and 10 grams of heat-activatable adhesive 11 per m ² .

After the penetration of the fluid composition 13 into the fibrous substrate 1, the structure shown in FIG. 2 is obtained. As can be seen in this figure, the fluid composition 13 penetrates the fibrous substrate 1 obtained after implementation of the step a) over substantially its entire thickness e. It is not beyond the scope of the present invention if the penetration is only on a part of the thickness e of the fibrous substrate 1.

The substrate 1 shown in FIG. 2 then undergoes evaporation of the fluid medium in order to produce the structure 100 according to FIG. 3. This structure 100 constitutes a security paper in which a set of islands 15 of a thermo-activatable adhesive 11 is present in the fibrous substrate 1. In this structure 100, the adhesiveness produced by the heat-activatable adhesive 11 is relatively low due to the non-activation of the latter, the evaporation conditions being chosen so as not to activate the thermo-activatable adhesive 11.

On the substrate shown in Figure 3 is then applied a non-stick coating 40 which is intended to isolate the adhesive from the outside of the fibrous substrate 1 once the adhesive is activated. FIG. 4 shows the fibrous substrate 1 after application of the non-stick coating 40. As illustrated, the non-stick coating 40 may be applied at least on the face 7 on which the watermark 5 is present.

Applying the adhesive on the face on which the watermark is present advantageously makes it possible to reinforce the clear watermarks such as watermarks obtained by galvano (or electrotype) or the screened watermarks (for example as described in patent EP 1 122 360). The non-stick coating 40 may be applied to all or part of the face 7 on which the watermark 5 is present.

In a variant not shown, the release coating is applied to two faces of the fibrous substrate, for example on a face on which a watermark is present and on the opposite face.

All or part of the non-stick coating 40 is intended to be in contact with an element forming part of a paper machine, on which the fibrous substrate is intended to be placed.

FIG. 5 shows the product obtained after activation in which an assembly 16 of reinforcing adhesive islands 17 of a thermoactivated adhesive is present within the fibrous substrate 1.

The activation may be effected by exposing the fibrous substrate 1 to a temperature of between 80 ° C. and 180 ° C., for example by placing the fibrous substrate in an oven or in a press. The activation may allow the fibrous substrate to undergo a chemical reaction, for example crosslinking. In one variant, the activation comprises the melting of the heat-activatable adhesive and then its solidification, for example following a cooling, in order to form the adhesive reinforcing islands 17.

The activation is advantageously carried out in line, preferably on drying cylinders or on heated calenders.

FIG. 6 represents a banknote 200 incorporating a fibrous substrate

1 obtained after activation of the heat-activatable adhesive. This note 200 has an apparent mention 201 and has improved strength properties, including double-fold resistance.

Examples

Example 1

DISPERCOLL high molecular weight aqueous polyurethane dispersion

U 42 from Bayer is an example of a resin which can be used in the preparation of heat-activated adhesives effective for reinforcing paper for bank note, and, more generally, any fibrous substrate for security documents.

Its minimum activation temperature is between 80 ° C and 100 ° C. This dispersion generally finds textile applications because of the flexibility of the product obtained after thermal activation. In a first study, banknote composite paper was impregnated with, instead of the usual PVA bonding, the Dispercoll U 42 aqueous dispersion PU.

Composite paper with a high fiber content (30% polyamide fiber, length 6.0 mm, 87.0 g / m ² ) was used to increase the penetration of the product into the paper material.

The activation is carried out in press at 25 bar at 160 ° C. for 1 minute or in an oven at 130 ° C. for 10 minutes after application of an acrylic protective coating.

The use of a heat-activatable adhesive considerably improves the folding resistance of the composite paper. The gain can reach 300%. The best compromise is obtained with the diluted adhesive and activated by hot pressing. The bending strength and the tear strength increase respectively by at least + 92% and + 9% (see Table 1).

Unless otherwise indicated, the weights indicated in the following tables are expressed in dry weight.

Paper 1 Paper 2 Paper 3 Paper 4 Paper 5 Paper 6

(invention) (invention) (invention) (invention) (comparative) (comparative)

PVA composition repository

Composite paper comprising 30% Dispercoll U 42 such as Dispercoll U 42 diluted with ("PVA sizing") comprising commercially available polyamide fibers 200% water 6.25% solids

(comparative)

Press Oven Press Oven Press Oven 160 ° C 130 ° C 160 ° C 130 ° C 160 ° C 130 ° C

Total weight g / m ² - 126.1 125.8 118.3 118.7 111, 4 113.5

Mass of adhesive

or PVA

g / m ² / side 14.2 14.2 6.9 6.9 2.9 2.9 filed ("Sizing

weight ")

Mass of

coating anti / m ² / side 3.2 3.2 6.2 6.2 7.1 7.1 follower

Thickness pm - 168 195 175 194 175 197

Volume

specific ("cm ³ / g - 1.33 1, 55 1, 48 1.63 1.57 1.74 Bulk")

Resistance to MD 57.7 57.4 65.8 52.4 59.0 54.1 wet state% CD 78.4 79.5 84.7 77.3 73.1 66.4 ("Wet strength" ) Avg. 68.1 68.4 75.3 64.9 66.1 60.2

Dry elongation MD 7.3 7.1 7.4 7.5 5.8 5.9 ("Dry% CD 7.9 7.1 7.8 6.7 5.5 6.6 extension") Avg. 7.6 7.1 7.6 7.1 5.7 6.3

Elongation MD 10.8 10.2 11.6 10.1 9.4 8.9 wet ("Wet% CD 12.0 11.1 12.1 10.6 10.6 10.0 elongation") Avg. 11.4 10.7 11.9 10.4 10.0 9.5

Resistance to MD 15880 27289 14776 14024 5573 8087 double-fold Double CD 8537 29507 9081 12843 6889 5850 ("Schopper-fold

Avg. 12209 28398 11929 13434 6231 6969 folding ")

Resistance to MD 2080 2140 1760 2120 1760 1560 tearing mlM CD 2120 2260 1780 2200 1480 1720 (Tearing) Avg. 2100 2200 1770 2160 1620 1640

Table 1

The previously tested papers are taken again to evaluate their resistance to wrinkling.

Bendtsen porosity and Bekk smoothness are measured before and after wrinkling (Table 2). Before carrying out these measurements, the paper undergoes a calendering step under 15 bar on both sides. Compared to PVA bonding, the heat-activatable adhesive reduces the porosity of crumpled paper. The air flow through the crumpled paper decreases by at least 80%. Conversely, the leakage time of the Bekk smoothness test increases from + 50% to + 200%.

These results show that the use of heat-activatable adhesives significantly improves the wrinkle resistance of the paper for bank note.

Table 2

Example 2

In this example, pure cotton paper forms were respectively impregnated with a heat-activatable adhesive and the usual PVA bonding.

The adhesive tested is again the dispersible PU aqueous dispersion U 42 sold by the company Bayer. It is diluted by adding 200% water. The adhesive is Paper 7 Paper 8

(invention) (comparative)

PVA composition deposit ("PVA sizing")

Dispenoll U 42 cotton paper diluted with 200% water containing 6.25% solids

(comparative)

Oven 130 ° C Oven 130 ° C

Total weight g / m ² - 102.2 99.5

Mass of adhesive or

PVA filed ("Sizing g / m ² / 2.8 1.8 side

weight ")

Mass of coating

g / m ² / 3.7 side

non-stick 3.1

Thickness pm - 129 129

Specific volume ("

cm ³ / g

Bulk ") - 1, 26 1.29

Resistance to the state

wet% MD 50.0 45.0

("Wet strength")

Dry elongation% MD 7.99 7.47

Wet elongation% MD 12.04 11.32

Double resistance

Double fold MD 852 542

fold

("Schopper folding")

Resistance to

mlM MD 640 580

Tearing

Table 3 activated in an oven at 130 ° C for 10 minutes, after the application of a protective coating.

The heat-activatable adhesive improves the mechanical properties of pure cotton paper. The folding resistance and the tear strength increase by + 57% and + 10% respectively.

Example 3

In this example, billboard composite paper was impregnated with, instead of the usual PVA bonding, an aqueous PU dispersion of Dispercoll U 42.

Activation is carried out by hot calendering at a temperature of 180 ° C and 16 bar.

The use of a heat-activatable adhesive considerably improves the folding resistance of the composite paper. The bending strength and the tear strength increase respectively by at least + 32% and + 7% (Table 4). The tested papers are taken again to evaluate their resistance to crumpling.

Bendsten porosity is measured before and after creasing. Before carrying out these measurements, the paper undergoes a calendering step under a pressure of 15 bars on both sides.

Compared to PVA bonding, the heat-activatable adhesive reduces the porosity of crumpled paper. The air flow through the crumpled paper decreases by at least 80%.

The results in Table 4 show that the use of heat-activatable adhesives significantly improves the wrinkle resistance of banknote paper.

Table 4

When comparing the results of Table 3 with those of Table 1, the existence of a particularly advantageous effect in terms of increasing the mechanical strength resulting from the implementation of the combination within a single fibrous substrate of synthetic reinforcing fibers and a heat-activatable adhesive.

The following standards were used:

Measured weight according to ISO 536 "Paper and board - Determination of grammage",

- Thickness measured according to ISO 534 "Paper and board - Determination of thickness, density and specific volume", - Bendtsen porosity (before and after creasing) measured according to ISO 5636-3 "Paper and board; determination of air permeability (average value); Part 3: Bendtsen method ',

- Bekk smoothness (before and after creasing), similar to Bendtsen porosity but measured according to ISO 5627 "Paper and board - Determination of smoothness (Method

Bekk) ",

- Dry and wet elongation measured according to ISO 1924-2 "Paper and board - Determination of tensile properties - Part 2: Constant elongation gradient method (20 mm / min)", for "wet" value, samples are prepared in accordance with F03-056,

- Wet strength (%) = 100 x wet break length (ISO 3781) / dry break length (ISO 1924-2)

- Double-fold resistance (or Schopper folding) measured according to ISO 5626 "Paper; determination of the folding resistance »

- Tear resistance measured according to ISO 1974 "Paper -

Determination of tear strength - Elmendorf method »

Furthermore, some of the acrylic emulsions of LUBRIZOL are suitable starting resins for formulating heat-activatable adhesives for the impregnation of bank note papers within the scope of the present invention. The Hycar 26-0202 aqueous phase resin contains a thermoactivatable carboxylated styrene-acrylic copolymer. Its T _g is equal to -12 ° C. Carbobond 26373 is a self-curing dry extract acrylic resin that supports carboxylic chemical functions. Its T _g is + 5 ° C.

Another example of heat-activatable adhesive that can be used in the context of the present invention is the polyolefin dispersions sold by the company DOW, which also have reinforcing properties of the bank note papers following a heat activation. The Hypod 4501 carboxylated propylene dispersion has vitrification T _g and melting temperatures T _f of -26 ° C and 85 ° C, respectively. Similarly, the low carboxylated propylene dispersion Hypod XU 36534.00 has vitrification temperatures T _g and melting temperature T _f of -32 ° C and 85 ° C, respectively. The invention can be applied to multijet or monojet paper. In the case of the application to a multijet paper, one or a plurality of jets may be constituted by a paper according to the invention.

The expression "bearing (s)" must be understood as "containing at least one".

The expressions "between ... and ..." and "from ... to ..." must be understood as including the boundaries.

Claims

A method of preparing a security and / or value sheet (100; 110; 200) comprising the steps of:

a) penetrating, within a fibrous substrate (1), a fluid composition (13) comprising a dispersible thermo-activatable adhesive (11), in particular emulsified or in suspension, or solubilized in a fluid medium (10) of the composition (13), the fibrous substrate (1) comprising or being adapted to receive a security element (5), and b) when the fibrous substrate is intended to receive a security element, providing the fibrous substrate with said element of security.

2. Method according to claim 1, comprising a step c) of activation of the heat-activatable adhesive (11) present within the fibrous substrate (1) obtained after implementation of step a), the activation being carried out by heat treatment and preferably being effected by heating the fibrous substrate (1) obtained after carrying out step a), particularly preferably by positioning a heated surface in the vicinity and / or in contact with the substrate fibrous and / or blowing heated air on the fibrous substrate (1).

3. Method according to the preceding claim, the activation step c) being performed online.

4. Method according to any one of claims 2 and 3, the heat-activatable adhesive (1 1) undergoing during step c) a chemical modification, in particular by chemical reaction or crosslinking, or physical, in particular by crystallization or growth of the contact surface.

5. Method according to any one of claims 2 to 4, the fibrous substrate (1) having undergone or undergoing step c) being coated on all or part of its surface with a non-stick coating (40) allowing isolating the heat-activated adhesive (17) from the outside of the fibrous substrate, the release coating (40) being preferably applied before the beginning of step c).

6. A method according to any one of the preceding claims, the fibrous substrate (1) undergoing step a) comprising synthetic reinforcing fibers, preferably at least 5% by dry weight of synthetic reinforcing fibers relative to the total weight of the fibrous substrate (1).

7. Method according to any one of the preceding claims, the fluid composition (13) being, in step a), deposited on a surface (7) of the fibrous substrate (1) by impregnation, coating, surfacing and / or spray.

8. Method according to any one of claims 2 to 7, all or part of the fluid medium (10) present in the fibrous substrate (1) obtained after implementation of step a) being evaporated before implementation of step c).

9. A method according to any one of the preceding claims, the adhesive comprising a thermoplastic polymer, the glass transition temperature (Tg) of the thermoplastic polymer being preferably less than or equal to + 10 ° C.

10. Method according to the preceding claim, the thermoplastic polymer being chosen from the families of acrylic polymers, polyurethanes, polyolefins, especially polyethylene, polypropylene, ethylene-vinyl acetate (EVA), ethylene- acrylic acid (EAA), ethylene methacrylate (EMA), methylethylene methacrylate (EMMA), polyvinylidene chloride (PVDC), thermoplastic resins of the elastomer type, in particular styrene-butadiene rubber latex (SBR), or their mixtures or copolymers.

11. Process according to any one of the preceding claims, the fluid medium (10) of the fluid composition (13) being water, the fluid composition preferably being an aqueous dispersion, in particular of a polyurethane, an acrylic polymer, a polyethylene, a polypropylene or a copolymer of ethylene and propylene.

12. Method according to any one of claims 2 to 11, the adhesive present within the fibrous substrate (1) being, during step c), brought to a temperature above 40 ° C, preferably between 80 ° C and 180 ° C, and / or a pressure greater than or equal to 3 bar, preferably greater than or equal to 10 bar, being applied to the fibrous substrate (1) during step c).

Method according to one of the preceding claims, wherein the security element is a watermark (5).

14. Method according to any one of the preceding claims, the fluid composition (13) penetrating the fibrous substrate (1) obtained after implementation of step a) at least 25%, preferably at least 50%, preferably at least 75%, preferably substantially all, of its thickness (e).

15. A method according to any one of the preceding claims, the fibrous substrate being paper.

16. A method according to any one of the preceding claims, wherein step a) is carried out on a fibrous substrate obtained after draining, pressing and drying a fibrous suspension.

17. Security and / or value sheet (100), especially prepared by a method according to any one of the preceding claims, comprising:

i) a fibrous substrate (1), preferably made of paper, comprising a security element (5), and ii) a set (15) of islands of a thermo-activatable adhesive (11) present within the fibrous substrate (1). ).

18. Security and / or value sheet (110; 200), especially prepared by a process according to any one of the preceding claims, comprising:

i) a fibrous substrate (1) comprising a security element (5), and ii) an assembly (16) of reinforcing adhesive islands (17) of a thermoactivated adhesive present within the fibrous substrate (1).

19. Security and / or value sheet (100; 110; 200) according to any one of claims 17 and 18, the fibrous substrate being coated on all or part of its surface with a non-stick coating (40). ).

20. Sheet (100; 110; 200) according to one of claims 17 to 19, the fibrous substrate (1) comprising synthetic reinforcing fibers, preferably at least 5% by dry weight of synthetic reinforcing fibers with respect to total weight of the fibrous substrate (1).

21. Sheet (100; 110; 200) according to any one of claims 17 to

20, the adhesive being heat-reactive or being the product resulting from the activation of a thermoreactive adhesive.

22. Sheet (100; 110; 200) according to any one of claims 17 to

21, the adhesive comprising a thermoplastic polymer, especially chosen from families of acrylic polymers, polyurethanes, polyolefins, especially polyethylene, polypropylene, ethylene-vinyl acetate (EVA), ethylene-acrylic acid (EAA), ethylene methacrylate (EMA), methylethylene methacrylate (EMMA), polyvinylidene chloride (PVDC), thermoplastic resins of elastomer type, in particular styrene-butadiene rubber (SBR), or mixtures or copolymers thereof.

23. Safety and / or value document (200) comprising a sheet according to any one of claims 17 to 22.