EP0243285B1 - Security paper made tamper-proof and/or authenticatable by way of thermochromism, and process for its preparation - Google Patents

Description

The present invention relates to a security paper that cannot be forged and / or authenticated by thermochromy. It also relates to its preparation process.

The so-called "security" papers, which can be used in particular for the production of handwritten payment documents and official documents such as checks, traveller's checks, as well as identity documents such as passport, etc., must be both protected against any attempt to falsify the writings or seals carried on the papers, using any chemical reagent or modern process, such as an ink erasing pencil, and both authentifiable so that we can put in evidence the origin of the document.

Most security papers available on the market do not have a simple and reversible authentication process which can be combined with protection against forgery with ink erasers.

These ink erasing pencils often cause the appearance of a fluorescent yellow color, difficult to see with the naked eye and, moreover, which can be troublesome for certain uses (cf. French Patent No. 2,399,505 and its certificate of addition 2402739, and patent ^No. 2410702).

The use of thermochromy for the authentication of security papers has already been developed in the German patent 1 228 972 and the Austrian patent 362 658. However, these described methods used uncommon, expensive and used products delicate paper mill.

British patent 1,565,243 describes the use of thermochromy in security papers from thermochromic and thermomagnetic substances, as well as sophisticated test equipment. This process is not easy to use.

• - dans les brevets japonais 75 40 475 et 77 140 483, les coréactants assurant la réversibilité de la réaction sont différents de ceux développés dans la présente invention,
• - d'autres compositions associant le cristal violet lactone au Bisphénol A ont été déposées : brevet japonais 72 53 649 (brevet allemand : 2 327 723), 74 78 682, 80 167 134 (brevet allemand 3 147 146) et 57 123 283.

In addition, many thermochromic compositions containing violet lactone crystal have been patented:

• in Japanese patents 75 40 475 and 77 140 483, the co-reactants ensuring the reversibility of the reaction are different from those developed in the present invention,
• - other compositions associating the lactone violet crystal with Bisphenol A have been filed: Japanese patent 72 53 649 (German patent: 2 327 723), 74 78 682, 80 167 134 (German patent 3 147 146) and 57 123 283.

All these patents present reverse thermochromic systems (at high temperatures, the materials being colorless and colored at low temperatures).

The prior art also knows the teaching disclosed by patent GB-1 507 454 relating to a document authentication method, as well as a combination of a document to be authenticated and an authentication composition.

In this authentication method, the document is printed on a security paper consisting of a base paper coated with a leuco-dye precursor dye can be bastone violet crystal, an inert filler and a binder. This document is authenticated by marking with an authentication composition comprising a mixture of a dark pigmented ink and a solution of the acid material which reacts with the dye precursor leuco-dye.

This method has the drawback of giving rise to an irreversible coloring reaction and is carried out in a liquid medium, without the intervention of heat.

A verification process has also been proposed by patent FR-A-2 279 570. According to this publication, the security document is characterized in that it comprises a substrate, a first substance incorporated into the substrate or applied to it , this first substance being able to participate in a toning reaction, and a second substance applied to the substrate and capable of participating in a different toning reaction, so that, during document verification by application of at least one reagent, first and second substances change color as a result of the toning reactions.

The proposed technique involves the use, impractical, of a liquid reagent to be applied and leads to an irreversible coloring.

Note also the publication in JOURNAL OF IMAGING TECHNOLOGY, vol. 11, n ° 5, pages 224-228. This publication describes typical uses of leuco dye precursors, in particular for thermoreactive recording systems. In these systems, there is a reaction in the molten state, under the effect of heat, between separate particles of a colorless solid dye precursor and an activator, also solid. The two products are dispersed as separate particles in a layer. The coloring, thermally formed, is irreversible.

In the present application, an invention is described making it possible to overcome the various technical and economic difficulties encountered in the use of known systems for obtaining papers which can be authenticated by thermochromy and in the implementation of the systems already proposed for making the papers tamper-proof. . The implementation of the present invention is easily adaptable to the production techniques of the various types of paper and it makes it possible to obtain, at will, either authentifiable papers, or tamper-proof papers, or papers being simultaneously authentifiable and tamper-proof.

The objective of the invention is to provide a new authenticated security paper, by simple temperature rise developing a reversible coloring allowing the paper to be restored. in its original and / or unfalsifiable state, by irreversible colored reaction, by reaction with erasable felts, bases or reducing products.

According to the invention, a water-soluble combination of crystal violet lactone (i) and an aliphatic organic acid with a short hydrocarbon chain (II) is introduced into the paper.

In this definition of the invention, the various terms and expressions have the meanings mentioned below.

By "introduction into paper" is meant that the soluble mixture according to the invention is present either in or on the surface of the paper.

The choice between the introduction of said soluble mixture into the mass of the paper or onto the surface thereof (for example in a coating layer) may depend on the nature of the paper and the purpose sought.

il est couramment utilisé en papeterie, notamment dans les papiers autocopiants.The lactone violet crystal (compound I) is a known product of formula:

it is commonly used in stationery, especially in carbonless papers.

By "aliphatic organic acid with a short hydrocarbon chain" (11) is meant acids having up to 6 carbon atoms, saturated or unsaturated, comprising one or more acid functions and, optionally, other substituents which may be: hydroxyl group, halogen ketone function ...

• - acide tartrique :
  
• - acide citrique :
  
• - acide glycolique :
  
• - acide maléique :
  
• - acide malonique
  
• - acide acétylène dicarboxylique :
  

• - acide cétomalonique :
  

• - acide tartronique :
  

• - acide propiolique :
  

• - acide dihydroxymaléique :
  

• - acide pyruvique :
  

• - acide trichloroacétique :
  

Among these acids, the preferred is oxalic acid but mention may also be made of:

• - tartaric acid:
  
• - citric acid :
  
• - glycolic acid:
  
• - maleic acid:
  
• - malonic acid
  
• - acetylene dicarboxylic acid:
  

• - ketomalonic acid:
  

• - tartronic acid:
  

• - propiolic acid:
  

• - dihydroxymaleic acid:
  

• - pyruvic acid:
  

• - trichloroacetic acid:
  

The quantities of crystal violet (I) and of the acid (II) to be used can, as we will see later, vary within wide proportions, giving rise to different effects, generally, the quantity of crystal violet can be the order of 0.01 to 0.2 g / m ² of paper surface and the weight ratio of II to 1 can be between 3 and 20.

The papers obtained can have any fibrous composition, purely cellulosic or partly synthetic, to which can be added the conventional stationery additives, namely mineral fillers, various resistance agents, binders, resins, shading dyes, bonding products, alumina sulfate for acid bonding or pH adjustment, etc.

These papers may also contain, in their mass, in the dispersed pigmentary state, one or more dyes insoluble in water but organo-soluble, so as to preserve the writings or men tions brought on these papers vis-à-vis attempts of falsification using organic solvents. In addition, these papers can be watermarked or contain various devices intended to ensure recognition, such as fibers, pellets, colored and / or fluorescent particles.

To the aqueous solutions of violet crystal and of acid, it is possible to add sensitizing reagents analogous to those already used today in security papers, for example, products ensuring a modification of the appearance of the paper by contact of the latter with oxidizing reagents. These products are introduced either in aqueous solution, in which case it is necessary to ensure their retention on the fibers by direct bonding or by means of fixing agents, or in the microdispersed or pigmented precipitated state.

We will now describe the action, on paper, of associations of violet crystal and acid.

Aqueous solutions containing violet crystal (1) and an acid (II) are deposited on the surface of a paper in varying concentrations and proportions. Different effects are then obtained, according to said concentrations and proportions, which have been represented in FIGS. 1,2 and 3.

In fig. 1, the compound II / compound I ratio is plotted on the abscissa of the weights of Il and 1 deposited on the paper and expressed in g / m ² of paper, and the amount of compound I is plotted on the ordinate (in g / m ² ) deposited. We studied the properties of paper and we were led to divide the plane into four zones separated by curves 1, 2 and 3.

For papers in zone O, there is practically no detectable phenomenon compared to untreated papers.

For papers in zone A (located between curves 1 and 2), the paper obtained has a blue background which is all the more pronounced as the concentration coordinates place the point in the middle part between curves 1 and 2.

In this zone, the coloring of the paper can be accentuated by heating, that is to say that the paper is authentifiable, the return to the initial blue background takes place fairly quickly after stopping the heat source. Due to the background coloring, the paper is not sensitive to ink erasers, bases and reducers.

In zone B (between curves 2 and 3), the paper is white or very slightly bluish, authenticity by heat is preserved and the reaction to the ink erasing felts, bases and reducers, is clearly perceptible. The paper is authentifiable and forgery-proof.

In area C, the paper is white and less reactive to heat. Authentication requires a higher temperature. On the other hand, the reaction to the ink erasing felts, bases and reducers, is very intense.

• - On a déposé une même quantité de composé 1 (cristal violet) à savoir 0,096 g/m² mais des quantités variables du composé II. On a porté en abscisse le rapport pondéral du composé II sur le composé I (fig. 2).
• - On a utilisé un même rapport des composés Il et I, à savoir 6, et on a fait varier les quantités de composé I. On a porté en abscisse ces quantités de composé 1 en g/m² (fig. 3).

In fig. 2 and 3, there is shown, on the ordinate, the coloration (measured with a GAM densitometer with yellow filter) of the various papers at three temperatures (ordinary temperature (TO), at 100 ° C. (T.100) and at 150 ° C. ( T.150)) for papers in which:

• - The same amount of compound 1 (purple crystal) was deposited, namely 0.096 g / m ² but variable amounts of compound II. The weight ratio of compound II to compound I was plotted on the abscissa (fig. 2).
• - The same ratio of compounds II and I, namely 6, was used and the quantities of compound I were varied. These quantities of compound 1 are plotted on the abscissa in g / m ² (FIG. 3).

It will be noted in these figures that, due to a continuous variation in the coloring density with the concentration parameters, it is visible that the choices of the limits of the zones are arbitrary and depend on the visual appreciation of the blue of the paper background ( at room temperature).

• - soit des papiers authentifiables par thermochromie (papiers de zone A),
• - soit des papiers blancs authentifiables et infalsifiables (papiers de zone B),
• - soit des papiers qui présentent une possibilité d'authentification réduite mais un caractère infalsifiable renforcé (papiers de la zone C).

These results show that by using suitable quantities of compounds 1 and of compounds II it is possible to obtain:

• - either papers which can be authenticated by thermochromy (zone A papers),
• - either white papers which can be authenticated and forged (zone B papers),
• - either papers which have a reduced possibility of authentication but an enhanced tamper-proof nature (zone C papers).

• 1 - Que les courbes 1, 2 et 3 de la fig. 1 sont des limites arbitraires susceptibles d'être déplacées en fonction, soit de la nature du composé Il, soit des conditions de détection des phénomènes recherchés, soit de la composition des papiers ...
  • C'est pourquoi il est souhaitable, en vue d'obtenir un papier selon l'invention ayant les propriétés optimales recherchées, de déterminer, sur ledit papier, des courbes analogues à celles des fig. 1, 2 et 3 et, à partir de ces courbes, de déterminer la meilleure composition et le meilleur mode d'application des mélanges des composés I et II.
  • Ainsi, on déterminera les paramètres : quantité du composé 1 à déposer et rapport composé II/composé 1 de façon à situer le papier dans la partie médiane des courbes 1 et 2 pour l'authentifiabilité avec un fond bleu, et dans le voisinage de la courbe 3 pour l'authentifiabilité associée à l'infalsifiabilité avec un fond blanc.
• 2 - Que les fig. 1, 2 et 3 ont été établies avec un support collé en milieu acide, la variation due au support, et surtout au collage du papier, est notable : le sulfate d'alumine utilisé en papeterie pour améliorer le collage abaisse d'autant plus la réactivité du papier qu'il est en quantité plus importante (les autres caractéristiques sont inchangées).
  • Le support d'enduction préféré sera donc un papier collé en milieu neutre ou en milieu acide avec très peu de sulfate d'alumine.
• 3 - Qu'il est visible sur les fig. 2 et 3 que l'intensité de coloration obtenue dépend de la température et du temps d'application de la source de chaleur. La réversibilité de la coloration dépend des mêmes paramètres, ainsi, plus la température est élevée, plus la coloration est intense et le retour à la coloration initiale du papier long.
• 4 - Que la réactivité des papiers enduits est affectée par les conditions hygrométriques : lorsque l'humidité relative atmosphérique augmente, la réactivité à une température donnée et le fond du papier augmentent, tout se passe en fait comme s'il y avait une diminution du rapport composé II/composé I.

We will note :

• 1 - That curves 1, 2 and 3 in fig. 1 are arbitrary limits capable of being displaced as a function of either the nature of the compound II, or the conditions for detecting the phenomena sought, or the composition of the papers, etc.
  • This is why it is desirable, in order to obtain a paper according to the invention having the optimum properties sought, to determine, on said paper, curves similar to those of FIGS. 1, 2 and 3 and, from these curves, to determine the best composition and the best mode of application of the mixtures of compounds I and II.
  • Thus, the parameters will be determined: quantity of compound 1 to be deposited and compound II / compound 1 ratio so as to locate the paper in the middle part of curves 1 and 2 for authenticity with a blue background, and in the vicinity of the curve 3 for the authentifiability associated with the unfalsifiability with a white background.
• 2 - That fig. 1, 2 and 3 have been established with a support bonded in an acid medium, the variation due to the support, and especially to the bonding of the paper, is notable: the alumina sulfate used in stationery to improve the bonding further reduces the reactivity of the paper that it is in greater quantity (the other characteristics are unchanged).
  • The preferred coating medium will therefore be paper bonded in a neutral medium or in an acid medium with very little alumina sulfate.
• 3 - That it is visible in fig. 2 and 3 that the intensity of coloring obtained depends on the temperature and the time of application of the heat source. The reversibility of the coloring depends on the same parameters, thus, the higher the temperature, the more intense the coloring and the return to the initial coloring of the long paper.
• 4 - That the reactivity of coated papers is affected by hygrometric conditions: when the atmospheric relative humidity increases, the reactivity at a given temperature and the background of the paper increase, everything happens in fact as if there was a decrease in the compound II / compound I ratio

The evolution over time (at constant relative humidity) of papers stored at room temperature, the characteristics of which are in zones A and B, is the same. Those located in zone C show little change.

In addition to compounds and II, the formulation comprises a coating binder which may be, by way of indication, synthetic or natural polymers with compatible hydroxy terminations, such as starch, alcohol po-. lyvinyl and cellulose derivatives.

Optionally, activators (waxes, salts, surfactants, etc.) or various stabilizers can be added to this composition.

The authentication of the document can be carried out by thermochromy, that is to say by the appearance of a blue coloration when the paper is placed in the presence of any heating source making it possible to bring its temperature between 70 _° C. and 170 _° C in a short time (a few seconds maximum), then by the very rapid weakening (a few minutes) of the color formed when the document is brought to room temperature. The initial whiteness is then restored more slowly. This authentication therefore makes it possible not to alter the reading characteristics of the authenticated document.

This authentication by reversible thermochromy can be carried out manually by contact with a heating element or infrared radiation and visual recognition of the color obtained, or else using an automatic apparatus suitable for this authentication. The document whose authenticity is to be checked is introduced into a machine which causes, using an appropriate device, the thermochromy of the paper: contact heating (regulated heating plate) or non-contact (hot air, IR radiation). ..). the coloration obtained is read using an optical device (densitometer equipped with suitable filters), which makes it possible to reject documents which do not have the hue and the coloration density corresponding to an authentic document.

When attempting to falsify documents having this chemical composition (at a concentration such that tamper-proofing is obtained) with an ink eraser, reducer or base, a blue non-fluorescent coloring appears on the paper.

The various examples given below will clarify the invention a little better but are in no way limiting and those skilled in the art will be able to provide other modes and other embodiments, without for this is outside the scope of the invention.

EXAMPLE 1:

On a paper support containing one or more dispersed organosoluble dyes by mass, these products being intended to give the paper sensitivity to the solvents which can be used to falsify the paper, is deposited on the surface, by a conventional papermaking technique (sizing press, roller systems), the coating solution comprising per liter of water:

The white paper obtained is colored blue with the erasable felts, the reducers and the bases. When the temperature is high by contact, at 100 _° C for example, a clearly visible blue color forms, then quickly loses its intensity: in 10 minutes, 75% of the initial color has disappeared.

EXAMPLE 2:

On any paper support, it is possible to obtain an authenticated and partially tamper-proof document by applying the coating solution containing per liter of water:

By the action of erasable felts, bases or reducers, the blue coloration is irreversible. When the temperature rises, the blue color that appears is reversible.

EXAMPLE 3:

On a paper support, identical to that of Example 1, the coating solution containing per liter of water is deposited on the surface:

The instant coloring, obtained with ink erasers, reducers and bases, is cyan blue. The bleach leads to a brown coloring, the solvents to variable coloring depending on the solvent and the dye introduced into the mass.

The paper turns blue with the temperature, when it is above 80 _° C (contact time of at least 3 seconds). The preferred test apparatus consists of a fan pulsing hot air at a temperature of 100 to 140 ° C to reveal the color, then blowing cold air (or ambient air) to accelerate the return to the initial whiteness of the paper.

EXAMPLE 4:

On any paper support, it is possible to obtain an authenticated document by applying the coating solution containing per liter of water:

When the temperature rises, the blue color that appears is reversible.

EXAMPLE 5:

On a paper support containing by mass dispersed organosoluble dyes, the following coating solution is deposited on the surface per liter of water:

The colors obtained are, for the ink erasers, the reducers, the bases and the increase in temperature of the blue, and for the bleach of the beige-brown. The solvents give variable colors depending on the dyes introduced into the mass and the solvents used.

EXAMPLE 6

On a paper support stuck in a neutral medium, it is possible to obtain an authentic white paper and very weakly reactive to erasers, bases and reducers by applying the following coating solution, comprising per liter of water:

In all of the preceding examples, the paper is white and not fluorescent after facing.

All these examples are given only by way of illustration and those skilled in the art may modify or supplement them with technical solutions or known products, without thereby departing from the scope of the invention, as defined. in the claims.

Claims (5)

1. Security paper, tamperproof because of an irreversible colour reaction and/or authenticatable because of a reversible colour, containing a water-soluble combination of crystal violet lactone (I) of formula

and of an aliphatic organic acid containing a short hydrocarbon chain.

2. Paper according to Claim 1, characterized in that the said acid is chosen from the following acids:

- oxalic acid:

- tartaric acid:

- citric acid:

- glycolic acid:

- maleic acid:

- malonic acid:

- acetylenedicarboxylic acid:

- ketomalonic acid:

- tartronic acid:

- propiolic acid:

- dihydroxymaleic acid:

- pyruvic acid:

- trichloroacetic acid:

the preferred acid being oxalic acid.

3. Paper according to either of Claims 1 and 2, characterized in that crystal violet (I) is employed in a proportion of 0.01 to 0.2 g/m2 and that the weight ratio of the compound (II) to the said crystal (I) is between 3 and 20.

4. Paper according to one of Claims 1 to 3, characterized in that the compounds (I) and (II) are deposited as a coating onto the paper.

5. Process for the preparation of paper according to one of Claims 1 to 4, characterized in that variable quantities of the compound (I) and of one of the compounds (II) are deposited onto the surface of a paper substrate, that the paper obtained is tested and that the quantities of (I) and of (II) to be employed in order to obtain a paper which is desired, namely authenticatable, tamperproof or having both properties, are thus determined for the paper substrate in question.

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