EP0514455B1 - Sheet for protected documents having high printability and high handling resistance - Google Patents

Abstract

A printable sheet having a high printing quality and a high handling resistance. At least one of the sides of the sheet is treated with a composition which comprises at least one filler and at least one elastomeric binder. The elastomeric binder is selected from the group consisting of aqueous dispersions of polyurethane, acrylate copolymers, optionally carboxylated styrene-butadiene copolymers, and polymers of which one of the monomers is acrylonitrile, isoprene, or neoprene, or mixtures thereof. The sheet can be used for manufacturing protected documents.

Description

The invention relates to a sheet or film which can be used for manufacturing security documents, which is printable and which has a high print rendering, as well as good resistance to circulation, especially after printing.

The invention relates more particularly to sheets of paper for banknotes or other valuable securities which can in particular be printed by offset printing and / or by intaglio printing. It further relates to a composition for surface treatment or impregnation of a sheet so as to simultaneously give it properties of good printability and resistance to circulation.

It is known that security documents, for example papers for banknotes or for checks or any other security of value include chemical or physical means of authentication and / or indicators of falsification.

In general, it is known to use as chemical means, compounds which react to the falsifying agents commonly used by falsifiers. These falsification indicator means react, for example, to acids (hydrochloric, citric, acetic, sulfuric, etc.), to bases (especially soda), to oxidants (bleach), to reducers and to solvents.

• L'absence d'azurants optiques fluorescents en bleu-violet lorsqu'ils sont soumis à la lumière ultra-violette, qui sont couramment utilisés dans la composition des papiers ordinaires afin d'augmenter leur blancheur.
• La présence ponctuelle d'éléments (par exemple des fils; fibres, planchettes, etc) qui peuvent être fluorescents et donner une fluorescence de couleurs diverses, colorés ou comporter des inscriptions ou posséder des propriétés physiques diverses telles que le magnétisme, la conductivité électrique, le thermomagnétisme, etc.
• La présence de filigrane, c'est-à-dire une modification contrôlée de la densité des fibres de papier dans l'épaisseur de celui-ci, ce filigrane reproduisant un dessin donné qui n'est visible parfaitement qu'en lumière transmise, c'est-à-dire par transparence.
• La présence d'hologrammes, de moirages ou d'autres effets optiques obtenus avec des encres optiquement variables et déposés à la surface de la feuille.
• Le claquant du papier, c'est-à-dire un bruit caractéristique obtenu lorsqu'on agite rapidement le papier.
• La présence d'impressions à la surface du papier sous forme de dessins ou d'inscriptions de couleurs et de formes complexes qui sont de ce fait difficiles à reproduire.
• Le relief de l'impression obtenue par le procédé d'impression taille-douce. Ce procédé consiste à graver une plaque, à étendre une encre sur cette plaque et à presser la feuille de papier sur la plaque.

It is also known to use physical means of authentication which are most often the following:

• The absence of blue-violet fluorescent optical brighteners when subjected to ultraviolet light, which are commonly used in the composition of ordinary papers in order to increase their whiteness.
• The occasional presence of elements (for example wires; fibers, boards, etc.) which can be fluorescent and give a fluorescence of various colors, colored or have inscriptions or have various physical properties such as magnetism, electrical conductivity, thermomagnetism, etc.
• The presence of a watermark, that is to say a controlled modification of the density of the paper fibers in the thickness thereof, this watermark reproducing a given design which is only perfectly visible in transmitted light, c that is to say by transparency.
• The presence of holograms, moiré or other optical effects obtained with optically variable inks and deposited on the surface of the sheet.
• The slamming of the paper, that is to say a characteristic noise obtained when the paper is agitated quickly.
• The presence of prints on the surface of the paper in the form of drawings or inscriptions of colors and complex shapes which are therefore difficult to reproduce.
• The relief of the impression obtained by the intaglio printing process. This process involves etching a plate, spreading ink over the plate and pressing the sheet of paper onto the plate.

A given security document does not generally contain all of these means, since the cost of manufacturing the document increases with the number of authentication means and with their sophistication. However, the security documents always include a superficial impression and this is why it is necessary to carry out a printing of superior quality, both with regard to the colors and the layout, so as to make it difficult for them to be imitated by counterfeiters. In general, the general public is not not very attentive to the quality of the drawings and / or prints brought to the surface of a security document, but knowledgeable people like bank staff or merchants are very sensitive to the details of a drawing, the finesse and in general when printed, and can therefore judge the authenticity of a document, with the naked eye or with a magnifying glass.

The print rendering is the fact that the line obtained by printing is perfectly clear, that is to say that it does not have any burrs or in term used by the skilled person in the "feathering". These burrs cause the lines to spread out more than is desired, or the difficulty of producing an impression comprising very close lines without the risk of blurring. Therefore, the central bank that prints the paper to obtain security documents is forced to make insufficiently fine prints. It is therefore difficult to produce micro-prints. However, micro-prints are very useful as security elements because they are difficult to reproduce by photocopiers who currently cannot reproduce very fine prints. Print rendering is also characterized by the color density of the print.

In addition, the human eye has sufficient resolution to distinguish between an impression having a good rendering and an impression comprising a "feathering".

However, according to the prior art, the printing rendering on the security documents is quite poor and it is therefore possible to easily forge them using color photocopiers which are capable of reproducing almost exactly the color tones of an authentic document. Counterfeiting will not be obvious to the eye, even to a knowledgeable person, since the print rendering of the authentic document is not sufficiently superior to that of the image reproduced by photocopying.

Therefore, for sheets usable for making security documents, it is necessary to have a high print rendering in order to obtain prints that are difficult to counterfeit.

In addition, the quality and beauty of the print also contributes to the brand image of the document sender. For example, in the case of banknotes, the quality of the printing contributes to the prestige of the country which puts them into circulation. This is another reason to be careful when printing these documents.

It is known, in the field of papers for printing and writing, to improve their printability by depositing on their surface a layer of a binder-pigment mixture. The purpose of this treatment is to level the surface of the paper, which is naturally very irregular. The pigment particles fill the interstices existing between the fibers constituting the sheet.

The choice of pigments and binders that can be used to make such a layer is very wide. Pigments are most often mineral fillers, sometimes plastic pigments. The binders can be chosen from starch, casein, animal glue, polyvinyl alcohol, natural or synthetic latex, etc.

For example, pigmented layers containing bentonites have been studied in the field of usual printing-writing papers (TAPPI, vol.59, n ° 12, December 1976, NEW YORK, pages 76-80; R.L. JANES et Al).

In French patent FR-A-999 579 filed by N.C.R. and published in 1952, there has been described a printing paper resistant to spreading inks obtained by coating a composition containing clay crystals and a binder. This binder can be starch, polyvinyl alcohol, animal glue, casein.

Similarly, in patent FR-A-999,625 also filed by NCR, we have describes a similar paper, the layer containing a zeolitic substance instead of clay. The binder can be starch alone or combined with casein and / or latex.

In patent application FR-A-2 288 186, there has been described a paper for printing-writing coated with a composition comprising a coating pigment, a binder and an amorphous mineral product obtained synthetically, this product improving the ability to printing of paper.

However, in the very particular case of sheets or films for security documents, it is quite unusual to surface them with a pigmented layer. Indeed, it is necessary that the printing carried on the security documents produced from the sheets withstands all the mechanical actions which could alter it. However, given their exchange value in particular, these security documents circulate between individuals and pass through various machines, for example false document detectors, automatic distributors, etc. During these frequent manipulations and circulations, the documents undergo treatments liable to deteriorate them, for example they are folded, crumpled, wet, scraped, subjected to various rubs and can even undergo a washing treatment by accidental introduction into a washing machine. . With regard to intaglio printing, a very high pressure (often greater than 50 MPa) is applied when printing the document on the engraved and inked printing plates, the ink therefore penetrates very deeply in the sheet and the print is thus protected. The paper must have very good compressibility. Those skilled in the art believe that a layer on the sheet will form a certain barrier against the ink and reduce the penetration of the ink and its adhesion and therefore its resistance to circulation.

Of course, we are looking for good print performance whatever the type of printing used, intaglio, offset or other. Those skilled in the art naturally think that having a layer pigmented on the surface of a sheet intended for the printing of security documents in order to improve its printability, will decrease the resistance and the resistance of the printing. Due to its composition, this layer will not be very resistant to undergo the traffic constraints undergone by the security documents.

In addition, during circulation, security documents are soiled. Resistance to traffic also includes resistance to soiling. The sheet must therefore also have surface barrier properties to water, grease and low porosity.

Usually, to improve the resistance to circulation, in particular of banknotes, the sheet of paper is impregnated, before printing, in a bath which essentially contains one or more binders chosen for their very high mechanical characteristics.

There has been described in the French patent application filed by POLYSAR FR-A-2 300 843, a coated sheet of paper which is prepared by a process consisting in spreading on the surface of the paper a composition containing a latex of a flexible polymer and non-gelatinized friend granules, the granules having an average diameter less than the average interstitial distance between the surface fibers of the paper, removing any excess from the coating composition and drying the coated paper. This sheet of paper can be used for banknotes or for valuable securities. The sheet is coated with such a composition in order to improve its surface condition and therefore its printability. The filler is therefore organic, since it is starch, and it has a particle diameter which is important. The description of this request, although mentioning the problem of the print performance during the circulation of documents, does not suggest a solution to solve it and does not give a test concerning this print performance.

US-A-3,281,267 describes a coated paper used for printing and / or writing. These papers are used for magazine covers, for advertising. They must be very shiny and very icy. In addition, they must be flexible. To glaze these papers, a calendering is carried out which requires that the paper be flexible. In addition, we want the paper to be opaque. In this document, it is mentioned that flexibility is given by the elastomeric nature of the layer compound, while the so-called "plastomeric" properties make the coating composition moldable. The elastomer is added to the thermoplastic resin to give it the desired flexibility. It is even possible not to add an elastomer if the "plastomer" is sufficiently flexible. After deposition of the layer and calendering, the sheet is subjected to a heated surface which polishes the surface to obtain the gloss.

A coating composition described comprises an elastomer content of between 15 and 20 parts per 100 parts of pigments.

Document FR-A-2 288 186 describes a process for manufacturing a paper coated with a composition containing a particular amorphous filler in order to improve the printability of the paper by gravure printing. A typical composition contains a maximum of 7 parts of latex binder for 100 parts of fillers.

The article TAPPI, volume 59, n ° 12, December 1976, pages 76-80, R.L. James et al, describes a study of a coating composition containing bentonites. The printability of papers coated with this composition is tested for offset type printing and for gravure printing. The intaglio print is not studied.

The maximum rate of latex binder used is 15 parts per 100 parts of fillers, which is a conventional rate of binder for printing / writing papers. The nature and characteristics of the latexes used are not specified. We do not study or envisage the use of a particular binder which is elastomeric and at particular rates greater than 25 parts per 100 parts of fillers.

The present invention therefore aims to improve the rendering printing of a sheet intended for the production of security documents, without degrading the resistance to circulation of the printed documents.

The invention also aims to improve the resistance to circulation of such documents.

• un rendu d'impression élevé et donc
  • . une surface lissée,
  • . une bonne microporosité de surface,
  • . un caractère oléophile de la surface,
  • . une bonne compressibilité,
• une résistance élevée à la circulation et donc
  • . des propriétés oléophobes et hydrophobes de la surface,
  • . une faible porosité de surface,
  • . une forte affinité de l'encre d'impression avec la feuille,
  • . une forte tenue mécanique de l'impression.

The invention therefore aims to provide a sheet intended for the production of security documents which simultaneously has the following properties:

• high print rendering and therefore
  • . a smoothed surface,
  • . good surface microporosity,
  • . an oleophilic character of the surface,
  • . good compressibility,
• high resistance to traffic and therefore
  • . oleophobic and hydrophobic properties of the surface,
  • . low surface porosity,
  • . a strong affinity of the printing ink with the sheet,
  • . strong mechanical strength of the print.

It is understood that these necessary characteristics can be contradictory.

The Applicant has overcome the prejudices of those skilled in the art, namely that it has subjected the sheet to a surface treatment, by means of a particular composition, this treatment possibly being, for example, a coating.

The Applicant, after having tried numerous compositions containing at least one binder and at least one filler, has managed, surprisingly, to solve the problems posed by using a composition containing at least one filler and at least one binder of elastomeric character.

It is particularly surprising that a composition containing a binder and a filler does not increase the receptivity of the sheet to soiling since it improves the receptivity of the sheet to inks.

Thus the invention provides a printable sheet, usable for manufacturing security documents, having a high print rendering and resistance to circulation, which is characterized by the fact that at least one of its faces is treated by a composition comprising one or more fillers chosen from mineral fillers and / or plastic coating pigments and at least one elastomeric binder, the binder being in an amount greater than 25 parts per 100 parts of fillers by dry weight.

The elastomeric binder can however be used in admixture with other binders usually used in stationery. Tests carried out by the Applicant have shown that binders such as starch or PVA, even insolubilized, do not allow the impression required for security documents to be maintained when these binders are used alone with a filler.

The elastomeric binder can be chosen from the group formed by aqueous dispersions of polyurethane, of acrylate copolymers, of optionally carboxylated styrene-butadiene copolymer, of polymers one of the monomers of which is acrylonitrile or isoprene or neoprene. , or their mixtures. Polyurethane is preferably used.

The composition can comprise other dispersing additives, viscosity modifying agents, plasticizers, bacteriostatic agents, fungicides for example. It is not excluded that it includes other authentication or tampering agents.

The filler is preferably mineral, in particular it is chosen from silicas or kaolins. It can however be optionally chosen from other coating pigments such as plastic pigments.

The charge can have any BET specific surface. It may as well have a specific surface area measured according to the BET method (standard DIN 66 131) which is low, of the order of 5 to 20 m² / g, as a specific surface area which is high, for example of the order from 200 to 300 m² / g (the BET method gives a measurement of the total specific surface).

It is obviously possible to use a mixture of fillers having different specific surfaces. It is in particular advantageous that a portion of the fillers has a fairly high BET specific surface.

To deposit the pigmented layer, coats of the "reverse-roll", "champion", "bill-blade", dragging blade or air knife type can be used. It is preferable to choose an air knife coater. Indeed, this type of coating respects the filigree, that is to say its relief.

The sheet to be treated according to the invention can be a sheet based on a cellulosic composition, partially or completely synthetic or a film of synthetic material. Preferably the sheet is bank note paper.

The invention also aims to provide a composition for the treatment of at least one face of a sheet, giving this sheet a high print rendering and resistance to circulation, which is characterized by the fact that it comprises at least one filler and at least one binder of an elastomeric nature, the binder being in an amount greater than 25 parts per 100 parts of filler by dry weight.

• 1 à 50 parties en poids sec d'une charge, en particulier minérale
• 2 à 40 parties en poids sec d'un liant élastomère,
• éventuellement un agent plastifiant,
• éventuellement d'autres additifs utilisés en papeterie, la composition étant réalisée en milieu aqueux et faisant au total 100 parties en poids.

Preferably, the composition intended for treating the surface of the sheet according to the invention comprises:

• 1 to 50 parts by dry weight of a filler, in particular mineral
• 2 to 40 parts by dry weight of an elastomeric binder,
• optionally a plasticizing agent,
• possibly other additives used in stationery, the composition being produced in an aqueous medium and making a total of 100 parts by weight.

• 1 à 50 parties en poids sec d'une charge minérale
• 2 à 40 parties en poids sec d'un liant polyuréthane,
• 0 à 5 parties en poids de glycérine,
• éventuellement d'autres additifs utilisés en papeterie, la composition étant réalisée en milieu aqueux et faisant au total 100 parties en poids.

The invention is carried out according to the following preferred embodiment:
A sheet is formed on a paper machine (with a flat table or with a round shape) possibly comprising a watermarking device, from a composition of cellulose fibers, for example cotton. This sheet is then coated on an air knife coater with an aqueous composition containing:

• 1 to 50 parts by dry weight of a mineral filler
• 2 to 40 parts by dry weight of a polyurethane binder,
• 0 to 5 parts by weight of glycerin,
• possibly other additives used in stationery, the composition being produced in an aqueous medium and making a total of 100 parts by weight.

The weight of the deposited layer is between 1 and 15 g / m² in dry, preferably of the order of 10 g / m² in dry.

• résistance aux froissements à sec,
• résistance aux froissements en milieu humide,
• résistance aux frottements (basique, acide, oxydant, etc.)
• résistance à la salissure.

The sheets manufactured according to the invention can be printed in intaglio and offset, their resistance to circulation is tested according to the following four criteria:

• resistance to dry creases,
• resistance to wrinkling in a humid environment,
• resistance to friction (basic, acid, oxidant, etc.)
• resistance to soiling.

The results are estimated visually (with the naked eye or with a magnifying device (magnifying glass, microscope) and by comparison.

A control sheet which has not been treated is compared with a sheet treated with the pigmented compositions according to the invention. It is observed that the print rendering is much better for the sheets produced according to the invention and that the resistance of the sheet to circulation, in particular after printing, is not less than that of the control. In some cases it has even been improved.

The following nonlimiting examples, with reference to the appended drawings, allow a better understanding of how the invention can be put into practice.

Figure 1 is a photograph enlarged 7 times of a print of the first three letters of ARJOMARI, this print being made on a paper for traditional bank note.

Figure 2 is a photograph of the print made on paper according to the invention.

Figure 3 is a 20-fold enlarged photograph of the letter A from the print of Figure 1.

Figure 4 is a 20-fold enlarged photograph of the letter R from the print of Figure 2.

The tests for resistance to circulation (wrinkling and friction) are described in the article: WARING QUALITY OF EXPERIMENTAL CURRENCY-TYPE PAPERS, Journal of Research of the National Bureau of Standards, Volume 36, pages 249 to 268, March 1946.

• A. Salissure à sec
  On fait subir un froissement à chaque billet dans un appareil à froissement IGT. Puis on le défroisse manuellement. On le met dans un flacon qui ferme hermétiquement en présence de billes de 20 mm de diamètre et de pièces de 10 centimes qui ont été préalablement salies avec une poudre contenant des colorants jaune, brun, du noir de carbone et de la vermicullite. Le flacon est placé dans un appareil TURBULA qui est mis en rotation pendant 15 min.
• B. Salissure humide
  On fait subir au billet un froissement préalable. Puis on le place dans un flacon, comme ci-dessus, mais on ajoute de la poudre contenant les colorants et une composition de sueur artificielle.

Resistance to soiling tests on printed banknotes is carried out as follows:

• A. Dry soiling
  Each ticket is crumpled in an IGT crumpling device. Then we iron it manually. It is placed in a bottle which hermetically closes in the presence of beads of 20 mm in diameter and of 10-cent pieces which have been previously soiled with a powder containing yellow, brown dyes, carbon black and vermicullite. The bottle is placed in a TURBULA device which is rotated for 15 min.
• B. Wet soiling
  The ticket is subjected to a prior crumpling. Then place it in a bottle, as above, but add powder containing the dyes and an artificial sweat composition.

The banknotes tested are compared with each other or with a control banknote tested under the same conditions. The degree of soiling is assessed visually or a measurement of the whiteness is carried out.

Comparative EXAMPLE

A sheet is made on a paper machine from an aqueous suspension of cellulose fibers, optionally in admixture with mineral or synthetic fibers and other additives used in stationery.

This sheet is coated using a MEYER bar, # 0.4 with an aqueous composition comprising, in dryness relative to the total composition: - a non-elastomeric binder Polyvinyl alcohol 5.7 games PVA KL 318, sold by SEPPIC - a mineral filler Bentonite COPISIL D4A10 sold by SOCIETE FRANCAISE DES BENTONITES ET DERIVES specific surface (BET, nitrogen): 270 m² / g particle size: 2.5 micrometers 11.5 games - a plasticizing agent glycerin 4.5 games

To adjust the viscosity, a rheology modifier is added, for example carboxymethylcellulose or an acrylate / (meth) acrylic acid dispersion. The final viscosity is 50 mPa.s, at room temperature, measured with a BROOKFIELD viscometer, mobile no.1, at 100 revolutions / min. The weight of the dry layer is 11 g / m².

This sheet is intaglio printed and subjected to the circulation resistance tests mentioned above.

This sheet is compared to a control sheet produced under the same conditions but not coated.

Compared to the witness, we note that the rendering of the print has been improved but that the resistance to traffic has deteriorated.

EXAMPLE 1

A sheet is made on a paper machine from an aqueous suspension of cellulose fibers, optionally in admixture with mineral or synthetic fibers and other additives used in stationery.

This sheet is coated using a MEYER bar, # 0.4 with an aqueous composition comprising, in dryness relative to the total composition: - an elastomeric binder aqueous polyurethane dispersion POLYURETHANE V sold by BAYER 5.7 games - a mineral filler Calcined Kaolin ALPHATEX sold by ECC International specific surface (BET, nitrogen): 11 m² / g 11.5 games - a plasticizing agent glycerin 4.5 games

To adjust the viscosity, a rheology modifier is added. The final viscosity is 50 mPa.s, at room temperature, measured with a BROOKFIELD viscometer, mobile no.1, at 100 revolutions / min. The weight of the dry layer is 11 g / m².

This sheet is intaglio printed and subjected to the circulation resistance tests mentioned above.

This sheet is compared to the control sheet used in the preceding comparative example.

Compared to the control sheet, it can be seen that the printing performance of the sheet produced according to the invention is improved and that its resistance to circulation has not been degraded.

EXAMPLE 2

A sheet is produced on a paper machine from the fiber composition of Example 1. This sheet is coated using a MEYER bar, n ° 0.4 with an aqueous composition comprising, in dry compared to the total composition: - an elastomeric binder aqueous polyurethane dispersion POLYURETHANE V sold by BAYER 5.7 games - a mineral filler Bentonite COPISIL D4A10 sold by SOCIETE FRANCAISE DES BENTONITES ET DERIVES specific surface (BET, nitrogen): 270 m² / g particle size: 2.5 micrometers 11.5 games - a plasticizing agent glycerin 4.5 games

To adjust the viscosity, a rheology modifier is added. The final viscosity is 50 mPa.s, at room temperature, measured with a BROOKFIELD viscometer, mobile no.1, at 100 revolutions / min. The weight of the dry layer is 5 g / m².

The sheet is printed and tests are carried out as in Example 1. This sheet is compared (Figures 2 and 4) to a control sheet (Figures 1 and 3). The print rendering is significantly improved and the resistance of the sheet to circulation is not degraded, it has even been improved.

EXAMPLE 3

A sheet is produced on a paper machine from the fiber composition of Example 1. This sheet is coated using a MEYER bar, n ° 0.4 with an aqueous composition comprising, in dry compared to the total composition: - an elastomeric binder anionic aqueous dispersion of an acrylate copolymer ACRONAL S 360 D sold by BASF 5.7 games - mineral fillers Calcined Kaolin ALPHATEX from Example 1 6.5 games Bentonite COPISIL D4A10 from Example 2 5 parts - a plasticizing agent glycerin 4.5 games

To adjust the viscosity, a rheology modifier is added. The final viscosity is 50 mPa.s, at room temperature, measured with a BROOKFlELD viscometer, mobile no.1, at 100 revolutions / min. The dry layer weight is 9 g / m².

The sheet is printed and tests are carried out as in Example 1.

Compared to the witness, it can be seen that the print rendering has been improved and that the traffic resistance has not been degraded.

Claims (4)

1. Printable sheet, usable for producing security documents, having a high printing reproduction and high handling resistance, characterized by the fact that at least one of its faces is treated with a composition comprising one or more fillers selected from the mineral fillers and/or coating plastic pigments and at least one elastomer binder, and that the binder is contained in a proportion higher than 25 parts for 100 parts of filler, by dry weight.
2. Sheet according to claim 1, characterized by the fact that the elastomer binder is selected from the group formed by the aqueous dispersions of polyurethane, acrylate copolymers, optionally carboxylated styrene-butadiene copolymers, polymers one of the monomers of which is acrylonitrile or isoprene or neoprene, or mixtures thereof.
3. Composition for the treatment of at least one face of a sheet, conferring to said sheet a printing reproduction as well as a high handling resistance, characterized by the fact that it comprises one or more fillers selected from the mineral fillers or the plastic coating pigments and at least one elastomer binder, and that the binder is contained in a proportion higher than 25 parts for 100 parts of fillers, by dry weight.
4. Use of a composition according to claim 3 for treating sheets of paper intended for the production of banknotes.

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