EP0390638B1 - Base-sheet for security document, with a transparent coating - Google Patents

Description

The invention relates to a new sheet support with a layer capable of being made transparent. The invention also relates to a pigmented coating composition capable of coating a sheet support and such that the deposited layer which is opaque can be made transparent by application of a liquid. The invention also relates to the process for obtaining such a coated support.

Sheet supports are known which comprise an opaque microporous layer which can be made transparent permanently or temporarily, by local application of pressure, heat or a liquid.

Such a layer can be a lacquer or a varnish as described for example in patents US-A-3,031,328 and US-A-3,508,344.

This layer can also consist of pigments dispersed in a binder. The pigments can be inorganic as described in the patents US-A-2 854 350, US-A-3 247 006 or organic as described in the patent FR-A-2 373 120.

When local pressure or heat is applied to the microporous layer, the micropores are plugged, making the layer transparent. When a liquid is applied to the microporous layer, the micropores fill up and a transparency is obtained but provided that the refractive index of the liquid used and that of the lacquer or of the pigments and of the binder of the layer are not very different and the interfacial tension between the microporous layer and the liquid is lower than that between the microporous layer and its immediate gaseous environment (EP-A-0 040 242)

It may be advantageous if the microporous layer becomes transparent by pressure but resists heat (US-A-3 247 006), or it becomes transparent by heat and / or pressure but resists water (US -A-3 031 328), or else that it becomes transparent by application of a liquid but resists heat and pressure (EP-A-0 040 242). One of the advantages, in the latter case, is the possibility of reusing the coated support, the transparency being temporary and the support not being damaged during its handling.

In order to have a layer which is resistant to pressure and to heat, patent EP-A-0 040 242 describes the use of a composition in a solvent (non-aqueous) medium of thermosetting particles as pigment and of a thermosetting binder; the particles are kept in a pseudo-sintered juxtaposition and the binder is thermoset during a heat treatment (after coating the support) at 130 ° C for one and a half hours. The particles are preferably silicas and they are essentially free of internal pores. Such silicas are pyrogenic silicas, they therefore have the drawback of being manufactured in a particular and expensive manner. The fact of thermosetting the binder has the disadvantage of introducing an additional and costly step, during the production of the coated support.

The use of a non-aqueous solvent entails additional costs for manufacturing and safety risks during this manufacturing.

The invention aims to solve these problems by providing in a simple and inexpensive manner, in particular by the papermaking route, a coated support whose layer is microporous, which can become transparent by a liquid but resistant to pressure and to heat.

The applications of such media are varied (printing writing, revealing hidden clues, etc.). The invention also aims to provide a new application for these coated supports which can become transparent in the field of security documents.

Security documents, such as payment documents and official documents, including checks, paper money, credit cards, savings bank vouchers, account books, accounting ledgers, titles, stamped papers, notarial deeds , tickets, tickets to cultural or sporting events, include certain chemical reagents that raise awareness of the chemical agents that can be used to falsify these documents. Papers containing reagents with acids, alkalis, chlorinated bleaching agents have already been proposed (FR-A-2 365 656, FR- A-2 399 505, FR-A-2 402 739, FR-A- 2 406 027) and reducing oxidizing agents used in erasers of the CORECTOR ^R type (EP-A-174 885)

In addition, security documents also include physical recognition elements (threads, fibers, plates, watermarks) that allow documents to be authenticated.

The incorporation of thermochromic substances are other means of authentication of these documents (see patents DE-C-1228 972, AT-C-362 658, FR-A 2 597 897 and the French patent application FR-A- 2,620,146 filed by the plaintiff.

The use of such means of authentication sometimes requires sophisticated techniques and / or cannot always be combined with protection against falsification.

Another object of the invention is therefore to obtain a coated sheet support, in particular intended for printing and / or writing usable as a security document, which can be authenticated with water. reversibly thanks to a microporous pigmented layer which can become transparent, allowing the incorporation of reagents into the falsifying agents and possibly other means of authentication. The faking agent reagents can be in the support or in the microporous layer.

The Applicant has discovered, contrary to what the prior art might suggest, that the objects of the invention can. be achieved by producing a microporous layer, resistant to heat and pressure, from an aqueous coating composition characterized in that it contains non-thermoset particles provided with internal pores and at least one hydrophilic binder and at least one hydrophobic binder and optionally other additives. The resistance of the layer to heat and pressure is obtained without subjecting the product obtained after intensive and prolonged heat treatment after the layer has been deposited on the support.

• au moins une feuille flexible colorée cellulosique, synthétique ou mixte,
• au moins une couche déposée sous forme aqueuse sur la feuille flexible puis séchée, ladite couche étant microporeuse, opaque, et contenant au moins des particules minérales non thermodurcies pourvues de pores internes, ayant une granulométrie moyenne comprise entre 0,1 et 100 micromètres et ayant un indice de réfraction comprise entre 1,2 et 2,2, et au moins un liant hydrophobe et au moins un liant hydrophile.

The invention therefore relates to a sheet support comprising a layer capable of becoming, reversibly, transparent by water, resistant to marking by localized application of pressure and / or heat, characterized in that it comprises:

• at least one flexible colored cellulosic, synthetic or mixed sheet,
• at least one layer deposited in aqueous form on the flexible sheet and then dried, said layer being microporous, opaque, and containing at least non-thermoset mineral particles provided with internal pores, having an average particle size of between 0.1 and 100 micrometers and having a refractive index of between 1.2 and 2.2, and at least one hydrophobic binder and at least one hydrophilic binder.

The invention further relates to a security document, characterized in that it has a microporous and opaque layer on the surface and which does not interfere with the reactions to the falsifying agents and the authentication agents usually used for this type of document. . This security document is remarkable in that it is reversibly authenticated with water.

The hydrophilic binder is used to bind the layer well and retain the charge in order to avoid any dusting on printing. It also facilitates the penetration of the marking liquid into the layer and therefore improves transparency and contrast.

The hydrophobic binder allows writing in ink and also prevents the formation of halos which can appear after the transparency has disappeared. It also contributes to the good bonding of the layer on the support.

The hydrophilic binder can be, for example, polyvinyl alcohol (PVA), starch, a cellulose derivative such as carboxymethylcellulose, etc. PVA is preferably used.

The hydrophobic binder can be chosen from the bonding agents commonly used in stationery. Preferably, an acrylic polymer-styrene binder is used in aqueous emulsion.

The mixture of these two types of binders is therefore a compromise between hydrophilicity and hydrophobicity that a person skilled in the art will be able to adjust according to the applications of the invention envisaged. These two types of binder will be used in a ratio, by dry weight, preferably close to 1.

The particles used in the aqueous composition have a refractive index of between 1.2 and 2.2 and preferably between 1.3 and 1.6.

The particles used are mineral. Preferably, a silica provided with internal pores is used.

The particle size is between 0.1 and 100 micrometers, preferably between 1 and 10 micrometers. High whiteness may be desirable to improve contrast this is achieved by changing the relative amounts of particles and binders. The support can be cellulosic, synthetic or mixed (paper, mono or bi-stretched sheet (or a plate) of polyethylene, polypropylene, PVC, polyester for example).

The support may for example bear distinctive marks, contain specific compounds as indicated above in the particular case of security documents. The additives which may optionally be added to the composition are, for example, reagents to falsifying agents and certain agents for authenticating a document.

The aqueous composition is produced in the following general manner: the particles are dispersed in water, optionally using a dispersant. The hydrophilic binder, optionally previously baked, and the hydrophobic binder, already in the form of an aqueous emulsion, are added. The quantities are adjusted by a person skilled in the art according to the coating technique used and the application of the product envisaged.

The composition is then applied to the support according to a conventional coating technique used in stationery, such as for example coating by an air knife, "champion", using a "billblade", a trailing blade, of "reverse-roll" or by "size-press".

After having deposited the layer on the support, the support is passed through the drying station of a coater without subjecting it to any other intensive and prolonged heat treatment.

The marking liquid used must have a refractive index fairly close to that of the particles. If you want a quickly reversible transparency, use a liquid with a low boiling point. Water is perfectly suitable for the invention, but other liquids can be used.

The following examples will make it possible to better understand the interest of the invention and its implementation, without limiting its scope.

EXAMPLE 1

• n° 1 pour une viscosité maximale de 100 mPa.s
• n° 2 pour une viscosité maximale de 400 mPa.s
• n° 3 pour une viscosité maximale de 1000 mPa.s

The silica is dispersed in water. The PVA which has been previously cooked and the hydrophobic binder are added thereto. The viscosity of the aqueous composition obtained is 570 mPa.s. The viscosity measurement is carried out with a BOOKFIELD viscometer. The mobile turns at 100 revolutions / minute. The mobile number depends on the order of magnitude of the viscosity:

• n ° 1 for a maximum viscosity of 100 mPa.s
• n ° 2 for a maximum viscosity of 400 mPa.s
• n ° 3 for a maximum viscosity of 1000 mPa.s

The dry extract is 24.1%. In the laboratory, the composition is deposited using a MEYER bar on a support which is a sheet of paper weighing 120 g / m² and blue in color. This sheet is dried in an oven at 110 ° C for 5 minutes.

The weight of the deposited layer is by dry weight of 17.8 g / m². The layer is white and opaque.

The whiteness, measured by a PHOTOVOLT reflectrometer on a scale from 0 to 100 is 85. The layer resists ink No. 3808 in the classic IGT tear-off test, so the hold is good. This test is carried out according to test method No. 1 of "Test Methods for the Study and Control of the Printability of Paper and Cardboard" recommended by the Technical Center for the Paper, Cardboard and Cellulose Industry (France - Grenoble).

RESISTANCE TO PULLING UP (OR TO PUDDING) IGT

Test intended to measure the surface resistance of papers in order to predict their behavior during printing.

1 - CUT

The test pieces are cut in the crosswise direction of the paper (or in the running direction, depending on the printing process) into strips of 280 × 25 mm.

2 - MATERIAL

• IGT AIC 2-5 device
• graduated drawing ink from LORILLEUX.

3 - OPERATING CONDITIONS

• in conditioned room 20 ° C + 1 and 65% RH + 2
• ink volume 0.6 cm3
• roller inking time 30 min (the rollers are turned over every 2 min to allow better distribution of the ink).
• inking time of the aluminum wheel 2cm
  • . 1st dial 20 s
  • . 2nd wheel 25 s
  • . 3rd dial 30 s
  • . 4th dial 35 s
• spring tension 35 kgf / 2 cm
• rubber blanket covering
• pendulum movement (or possibly acceleration)
• number of ink intake per inking 4
• number of determinations per paper 4

4 - EXPLOITATION OF RESULTS

The surface resistance of the papers is determined by the number of the ink which causes the peeling and by the speed in cm / s from which the peeling occurs.

The test is carried out at increasing speed from 0 to 700 cm / s. The ink number given by the test result is the maximum number for which no removal is observed.

• bleu violacé   3802
• bleu   3803
• vert   3804
• jaune   3805
• orange   3806
• rouge   3807
• brun   3808

The graduated inks from LORILLEUX (France) are as follows:

• purplish blue 3802
• blue 3803
• green 3804
• yellow 3805
• orange 3806
• red 3807
• brown 3808

The aggressiveness of the ink increases with the number.

Part of the coated paper is wetted with water; the layer becomes transparent and reveals the support. The transparency quickly disappears by drying in air and at room temperature.

For a drop of water deposited, the drying time is 13 seconds.

The refractive index of water is 1.3.

If the coated paper is locally heated to 100 ° C, it does not become transparent. If we simulate writing on paper (writing with a ballpoint pen without ink), the layer does not become transparent. It therefore resists a pressure corresponding to that exerted during a writing. Similarly, if you fold the paper, the layer does not become transparent.

EXAMPLES 2 TO 5 (see table 1)

The invention is carried out according to Example 1 but the relative amounts of silica and binders vary.

In Example 3, another hydrophobic binder is used, an emulsion of acrylic-styrene polymer containing 45% of dry extract JONCRYL 8051 sold by SPECHEM (HOLLAND).

In Example 4, the aqueous composition is coated using a pilot coater, the coated paper is then dried in the drying station of the coater.

In Example 5, two kinds of PVA are used, KL 318 and MOWIOL 4/98 marketed by HOECHST in the report $$\frac{\text{KL 318}}{\text{M4 / 98}}\text{= 3}$$

COMPARATIVE EXAMPLES 6 AND 7

The invention is carried out according to Example 1, but the silica used has no internal pores. This silica is marketed by DEGUSSA (FRANCE) under the brand AEROSIL 200.

On the finished products, we observe that the layer does not mask the support well and that it does not become transparent.

These examples show the importance of using particles with internal pores.

COMPARATIVE EXAMPLE 8

The invention is carried out according to Example 1 but the average size of the silica particles is 100 micrometers. This silica is marketed by RHONE POULENC under the brand TIXOSIL 48A.

The particles are poorly bonded in the layer which is then abrasive. The layer does not mask the support well.

So practically, it is not interesting to use particles whose average particle size is greater than 100 micrometers.

EXAMPLE 9 TO 14: APPLICATION TO TRUST PAPERS

EXAMPLE 9 A watermarked paper comprising fluorescent fibers is coated according to the method and with the composition described in Example 1. The opaque layer does not affect the visibility of the watermark of the support in transparency. The fluorescent fibers remain perfectly visible under ultra-violet rays.

The layer becomes transparent when it is wetted with water, which is also a means of authenticating the document.

EXAMPLE 10 According to the process and with a composition described in Example 1, a paper support is coated containing additives reactive to attempts at falsification by acids, strong and weak bases, sodium hypochlorite, CORECTOR ^R , SLOAN'S ^R.

Reactions to erasing agents and solvents are still visible. The reagents "migrate" to the surface. The layer also becomes transparent when it is wetted with water, which is an additional means of authenticating the document.

EXAMPLE 11 To the aqueous composition described in Example 1, a falsification-preventing reagent (check dye sold by BAYER) is added at a rate of 0.01% on a dry basis relative to the bath. This composition is coated on a paper, and it is dried as in Example 1.

The paper obtained is tested with acids and bases. The same reactivities are obtained as on conventional fiduciary paper.

The surface of the paper obtained is wetted with water, the layer becomes transparent.

EXAMPLE 12 Example 10 is repeated, but the reagent is incorporated at a rate of 0.1%. The same effect is obtained as in Example 10.

EXAMPLE 13 0.2% of manganese sulphate is added to the aqueous composition of Example 1. A paper is coated and dried as in Example 1. The paper obtained is tested with chemical erasing agents. The same results are obtained as with conventional fiduciary paper.

EXAMPLE 14 0.2% of cobalt salt is added to the aqueous composition described in Example 1. The paper obtained is wetted with water, the layer becomes transparent and slightly pink. We heat the document locally, it turns blue.

This composition is a means of authenticating the document both with water and with heat (authentication with heat described in French application FR-A -2 620 146 in the name of the applicant)

Claims (8)

1. Base sheet comprising a layer capable of becoming, in reversible manner, transparent by contact with water, resistant to a marking by localized application of pressure and/or heat, characterized by the fact that it comprises:

   - at least one colored flexible sheet in synthetic or cellulosic material or a mixture thereof,

   - at least one layer applied in aqueous form on the flexible sheet and then dried, said sheet being microporous, opaque, and containing at least non-thermoset mineral particles provided with internal pores, of mean granulometry ranging between 0.1 and 100 µm, and having a refraction index ranging between 1.2 and 2.2, and at least one hydrophobic binder and at least one hydrophilic binder.
2. Base sheet according to claim 1, characterized by the fact that the mineral non-thermoset particles provided with internal pores are particles of silica.
3. Base sheet according to one of claims 1 and 2, characterized by the fact that the hydrophilic binder is selected among polyvinyl alcohol, starch, a cellulose derivative.
4. Base sheet according to one of claims 1 to 3, characterized by the fact that the hydrophobic binder is selected among the sizing agents.
5. Base sheet according to claims 1 to 4, characterized by the fact that the hydrophobic agent is an aqueous emulsion of acrylic/styrene polymer.
6. Base sheet according to one of claims 1 to 5, characterized by the fact that the layer contains additives which are agents preventing falsification.
7. Composition capable of forming a microporous and opaque layer which can become transparent by contact with a liquid and resistant to a marking by localized application of pressure and heat, characterized by the fact that it contains water, at least non-thermoset mineral particles provided with internal pores, of mean granulometry ranging between 0.1 and 100 µm and having a refraction index ranging between 1.2 and 2.2, and at least one hydrophilic binder and at least one hydrophobic binder.
8. Application of the base sheet according to one of claims 1 to 6, as security document .