CH634363A5 - Paper reacting to tampering using chemical agents - Google Patents

Description

The present invention relates to a paper which reacts to falsification by chemical agents.

This paper is of the type known as security paper, belonging to the category of papers for printing writing and reacting in a very visible way to any attempt of falsification or alteration by chemical agents of a handwriting.

This type of paper is intended more specifically, although in a non-exclusive manner, for the production of payment vouchers or official documents, not pre-printed or pre-printed, as handwriting medium, whether they are paper to letterhead, stamped papers, notarial deeds, checkbook papers (ordinary checks, traveller's checks), identity papers (passport, card), paper for account books and, in general , all other papers, fiduciary or other.

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An average overall composition of the paper is generally as follows (percentages expressed relative to the weight of the paper): 2; 85% cellulose fibers, 15% mineral fillers, ^ 0.2% sizing agents, 0.4% alumina sulfate (acid sizing), 0.1% dyes.

It also comprises a product reactive to the basic medium. Papers containing certain compounds reactive to the basic medium are already known. This is why dyes such as methanil yellow or bright yellow and certain colored indicators derived from phthalein have been used for this purpose.

The present invention relates to a paper reacting to falsification by chemical agents bonded on both sides and comprising a product reactive to the basic medium, this product being chosen from nitro derivatives of phenol, of formula I defined in claim 1 and being advantageously present in paper at a dose between 0.2 and 1% (percentage expressed relative to the weight of the paper).

This type of reagent was chosen because it gives this paper a marked coloration where an attempt is made to alter or falsify the writing, using an alkaline chemical agent. Thus, a falsifier wishing to erase by such an alkaline agent the inscriptions made by a user to replace them with others, so as to gain an illicit profit from it, triggers on paper a very visible colored reaction, highlighting the attempted alteration. The alkaline agents used by the falsifiers can be concentrated or even diluted solutions of alkalis such as soda, potash, ammonia, amines, etc., used as such, also and above all, strong and even erasers. of low basicity which it is possible to find on the market, these erasing pencils generally being of the felt pencils type impregnated with an aqueous solution of bisulfite made more or less alkaline by the addition of sodium amine or bicarbonate.

The coloring which these products give in basic medium can, of course, as is already known, be reinforced by the simultaneous presence of fluorescent products such as stilbene derivatives, fluorescein derivatives or pyrannic derivatives.

The incorporation into the paper of a reagent capable of giving such a colored reaction to the action of an alkaline agent does not, of course, exclude the possibility of also incorporating into the paper any other reagent capable of reacting with other ways to the action of other chemical agents, in order to visibly highlight new attempts at falsification or alteration of writing.

This paper is also glued, in a manner known per se, on its two faces; these two layers of bonding agent further reduce the possibilities of falsification by scraping, because they prevent the paper from absorbing the ink; after scraping, the paper drinks, which reveals the falsification.

One method of manufacturing this paper consists in incorporating the reactive product in the basic medium into the mass of the pulp, prepared for the production of paper. However, for obvious economic reasons, the reactive product can also be applied at the end of manufacture, during impregnation with a solution of sizing product conventionally consisting of starch, polyvinyl alcohol and collage. The pH of this solution is adjusted to the optimum value so that the nitro derivative of phenol leaves this colorless solution or colors it only slightly: the pH must be lower than the turning pH of the chosen derivative.

It is important to recall here the theoretical reasons why the simplest nitro derivatives of phenol take on an accentuated coloration at alkaline pHs.

Indeed, like any molecule capable of behaving like a dye, that is to say capable of absorbing certain wavelengths of the visible spectrum while leaving visible the complementary color, the molecule of a nitro derivative of phenol the simpler, such as p-nitrophenol, is a molecule with conjugated double bonds constituted by the benzene nucleus and the chromophore —N02. It is said, in this case, that the delocalization of the electrons in the molecule is greater than in the case of benzene alone, due to the conjugation with the unsaturated chromophore —N02.

It is more generally known that the more extensive the molecular systems with coplanar conjugate bonds, the greater the electronic delocalization and the greater the mesomeric stabilization of the molecule, in its excited state, (under the effect of radiation) is important. But, moreover, the more such a system is extended, the smaller is the difference between the energy levels of the molecule corresponding to its excited state and to its ground state and, consequently, the more the excitation wavelengths absorbed see their spectrum moving towards long wavelengths (bathochrome effect).

In the case of p-nitrophenol, it is known that the binding to benzene of the only chromophore - N02, an unsaturated electron-accepting group, is not sufficient to reveal a coloration, the nitrobenzene being colorless, although the conjugation is increased. : the difference in energy between the two states, fundamental and excited, of the molecule is still too large for absorption to occur in the visible spectrum (average excitation wavelength too low).

But the complementary fixation of auxochrome —OH, electron donor group, further strengthens the conjugation, which then results in the appearance of a yellow coloration (absorption on the side of the short wavelengths of the visible spectrum) .

This example shows the classic role of chromophores, unsaturated functional groups, and auxochromes in the appearance of coloring for an organic compound.

We know that we characterize in a more precise way the influence of the substituents on the electronic delocalization in a system conjugated by so-called inductive effects (+ or - I) coming from differences of electronegativity between atoms (case of auxochromes and d 'other unsaturated substituents) and so-called mesomeric effects (+ or - M).

The effects - I and - M on electronic delocalization correspond to the electron accepting substituents, and the effects + I and + M correspond to the donor substituents.

Thus, in the case of p-nitrophenol, the nitro chromophore group which usually has an effect - I has, here also, an effect essentially - M, while auxochrome OM has an effect essentially + M.

These considerations concerning the various effects of the substituent groups attached to a benzene nucleus make it possible to better explain the observed deepening of the color of p-nitrophenol when p-nitrophenol is dissolved in alkaline solution, that is to say when the molecule goes to the phenate anion state: to the effect - M of the group - N02 is added, in the case of the phenate, the effect of the group - O, more strongly electron donor than the group --OH phenol.

This results in greater stabilization of the phenate ion, for which the electronic delocalization is more advanced than in the case of nitrophenol.

Consequently, the action of a light radiation results in a lower energy absorption of the molecule, that is to say by an absorption shifted towards the longer wavelengths: we thus pass from coloring yellow for a dilute solution of nitrophenol with an orange-yellow color when the solution is basified.

This effect of color evolution during the transition from the phenol form to the phenate form is found in connection with many other nitro derivatives of phenol and can be considered as a general law.

Furthermore, it should also be emphasized that, when comparing colors, and in particular color intensities, both the wavelength of the absorbed light and the absorption coefficient (or extinction coefficient) come into play. . The color change observed when switching from p-nitrophenol to p-nitrophenate illustrates the effect of a change in structure both on the wavelength and on the extinction coefficient. But it is possible to see in

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in other cases, a wavelength displacement without variation of the extinction coefficient, and vice versa.

This second effect on the extinction coefficient can be taken into account in the choice of a nitro derivative of phenol, capable of being used according to the invention.

More generally, this more or less large stabilizing effect of a phenate anion, this time arbitrary, linked to its possibilities of mesomerism and inherent in the very structure of the molecule (benzene nucleus and its substituents) depends on the nature of the substituents (chromophores or auxochromes) and their position on the nucleus with respect to the - O - flag.

It results correlatively by a more or less basicity of the phenate in relation to the effective mobility of the hydrogen. A phenate more stabilized by mesomerism corresponds to a more acidic phenol. In other words, the turning pH, that is to say the color change between the phenol form and the phenate form, depends on the stability of the phenate, therefore on the chemical structure of the phenol considered.

Thus, as a general rule, both the color of a phenolic derivative, in its phenol form as well as in its phenate form (more in-depth color), as well as the pK (turning pH) of the acid / phenol / phenate base couple together depend closely of the chemical structure of the nitro derivative under consideration.

The present invention therefore relates to the incorporation into paper, as means of combating an attempt of falsification in basic medium, of all the nitro derivatives belonging to all the families of the nitro derivatives of phenol (taken individually or not) such as , by the very nature of the basic aromatic carbide, by the nature and the position of the substituent groups (—OH and —NO 2 included), on the same aromatic nucleus appearing in the formula of this aromatic carbide, the pH of their shift is compatible with the pH of papermaking.

The preceding considerations on the nature of the basic aromatic carbide and on the nature and the position of the substituents of the phenolic nucleus make it possible to orient, by the choice of the substituents, the choice of the nitro derivative (s) of the phenol capable of being used according to the 'invention.

Indeed, the various substituents on the phenolic nucleus can exert, in relation to each other, a reinforcing action, but they can also cancel or contradict each other. For example, in the case of one of the simplest derivatives, metanitrophenol, the position of - NOz on the phenolic nucleus is such that the conjugation between the radical —OH and the radical - NOa, by l 'intermediate of the nucleus, is not possible, the effect - M of the group N02 not being exerted in this case. This explains the weak coloration of the phenate form and the uninteresting turning pK of this compound vis-à-vis the action of erasers. This is the reason why this compound is not preferred in the paper according to the invention.

On the other hand, other nitro derivatives of phenol having on the phenolic nucleus a nitro group in meta of the phenolic OH are extremely interesting in this application, because of the modifying influence of other substituents.

An advantage presented by the use as reactive products in the basic medium of the nitro derivatives of phenol having the general formula I is that it makes it possible to choose the color of the colored trace caused on the paper by the basic or acidic falsifying chemical agents: colorings ranging from yellow to orange, red, and even purple can thus be obtained, depending on the nitro derivative of the phenol chosen, these colorings naturally also varying according to the nature of the alkaline agent used by the possible falsifier (solution or eraser pencil).

Due to the coloring of certain nitro derivatives of phenol having the general formula I, it will also be possible to produce, as desired, a paper reacting to white or colored adulteration.

According to a first embodiment of the invention, the nitro derivatives of phenol are chosen from the compounds of general formula I nitrated in at least one of the positions 2,4, 5 and 6 of the phenolic cycle, such as:

- Paranitrophenol, applied in hydroalcoholic solution at 0.9 g / 1, which turns from colorless to yellow at pH 6.9 and reacts with all erasers;

- 2,4-dinitrophenol applied in aqueous solution at 0.9 g / 1, which turns from light yellow to orange between pH 3 and pH 4.5;

- 2,5-dinitrophênol, applied in hydroalcoholic solution at 0.9 g / 1, which turns from light yellow to orange between pH 4.0 and pH 5.8 and reacts with all erasers;

- 2,6-dinitrophenol, applied in hydroalcoholic solution at 0.9 g / 1, which turns from colorless to yellow between pH 2.0 and pH 4.0.

According to one embodiment of the invention, the nitro derivatives of phenol have the general formula I, in which R2 can be —H, - CH3 or NO2, R3 can be - CH3 or —H, R4 can be —N02 or —H, R5 may be - CH3 or - H, and R6 may be —Hou —N02, each CH3 possibly being substituted, for example, by a halogen, and they are chosen from the following compounds:

- 4-nitro-m-cresoI, applied in alcoholic solution at a dose of 0.05 to 1 g / 1, which changes from colorless to lemon yellow at pH 8.0 and reacts with erasers;

- 4,6-dinitro-o-cresol, applied in an aqueous solution at 1 g / 1, which changes from colorless to golden yellow at pH 9.5 and reacts with diluted alkalis;

- 2,4-dinitro-3,5-xylenol, applied in an aqueous solution at 1 g / 1, which changes from colorless to yellow-green at a pH greater than 10;

- 2,6-dinitro-3,5-xylenol, applied in an aqueous solution at 1 g / 1, which changes from colorless to yellow at pH greater than 10;

- a-chloro-4-nitro-o-cresol in hydroalcoholic solution, which changes from colorless to lemon yellow at pH 5.5.

The derivatives may also have the general formula I, wherein R2 is - NH2, R3 is --H, R4 is --H or - NO2, Rs is --H or - NO2, and R6 is --H or --NO2. In this case, they are advantageously chosen from the following compounds:

- 2-amino-5-nitrophenol, applied in aqueous solution to

1 g / 1, which turns from colorless to pink at pH 7.5 and gives a red coloring with all the erasers;

- 2-amino-4-nitrophenol, applied in hydroalcoholic solution at 1 g / 1, which turns from yellowish to orange at pH 6.5 and slowly develops an orange coloring under the action of erasers;

- 2-amino-4,6-dinitrophenol, applied in aqueous solution to

1 g / 1, which turns at pH 5.6 from yellow to reddish brown; in the latter case, the paper is initially colored.

When in the derivatives of general formula IR2 is - NO2 or - Cl, R3 and Rs are a hydrogen atom, R4 is a chlorine atom, and R6 is --H or --NOz, the derivatives according to the invention are chosen from the following compounds:

- 4-chloro-2-nitrophenol, applied in hydroalcoholic solution at 1 g / 1, which turns from yellowish to orange at pH 6.5 and slowly develops an orange color under the action of erasers;

- 2,4-dichloro-6-nitrophenol, applied in hydroalcoholic solution at 1 g / 1, which turns from lemon yellow to orange at pH 8.5 and reacts under the action of erasers.

These two compounds therefore make it possible, as mentioned above, to obtain at the outset a colored paper reacting to falsification.

In the general formula I, R2 can be - NH2, R3 and R6 --H, R4 - Cl and R5 - NO2; the selected compound is then advantageously 2-amino-4-chloro-5-nitrophenol, applied in aqueous solution at 1 g / 1, which turns from yellowish to red-brown at a pH greater than 8.0.

According to another embodiment of the invention, R2 is - N02 or H, R3 is H, R4. is - COOH, - H or - NO2, Rs is - H or --COOH, and R6 is --H or --COOH. The derivatives are then chosen from the following compounds:

- 2-nitro-4-carboxyphenol or 4-hydroxy-3-nitro- acid

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benzoic, applied in aqueous solution at 1 g / 1, which, turning from very light yellow to orange at pH 6, reacts with erasers;

- 2-nitro-5-carboxyphenol or 3-hydroxy-4-nitro-benzoic acid, applied in hydroalcoholic solution at 1 g / 1, which turns from very light yellow to orange yellow at pH 7.0 and reacts with pencils 5 erasers;

- 4-nitro-6-carbç> xyphenol or 5-nitrosalicylic acid, applied in hydroalcoholic solution at 1 g / 1, which turns from colorless to yellow from pH 7.8 and reacts with erasers.

According to a particular embodiment of the invention, the compound can have the formula I, in which R2 is - NO2, R3, R5 and R6 are —H, and R4 is - AsO (OH) 2. It is then 2-nitrophenol-4-arsenic acid, applied in hydroalcoholic solution at 1 g / 1, which turns from very light yellow to orange from pH 8.0 and reacts with erasers. 15

The compounds of formula I can be chosen from those in which R2 is —OH or —N02, R3 is —N02 or H, R4 is -CH2-COOH, -N02 or -OH, R5 is -H or -CH2-COOH, and R6 is —H or —N02. Advantageously, these compounds are:

- 3-nitro-4-carboxymethylcatechol, applied in a hydroalcoholic solution at 1 g / 1, which turns from colorless to orange at pH greater than 10;

- 4-nitro-5-carboxymethylcatechol, applied in an aqueous solution at 1 g / 1, which turns from colorless to cherry red at pH greater than 10; 25

■ - 4-nitrocatechol, applied in an aqueous medium at 1 g / 1, which turns from colorless to purple red at a pH greater than 9.0;

- dinitroquinol, applied in an aqueous solution at 1 g / 1, which turns from yellow-green to purple at a pH greater than 5.0.

In the compounds of formula I used in the paper according to the invention, the substituents of the general formula may have the following formulation: R2 is - NO2 or - OCH3, R3 is —H or —N02, R4 is —COOH, R5 is —H, and R6 is —OCH3 or —H. It is then, more particularly:

- 2-nitro-4-carboxy-6-methoxyphenol, applied in hydroalcoholic solution at 1 g / 1, which turns from colorless to orange at pH greater than 5 (5-nitrovanillic acid), and

- 2-methoxy-3-nitro-4-carboxyphenol, applied in hydroalcoholic solution at 1 g / 1, which turns at pH 4.9 passing from yellow to orange (2-nitrovanillic acid). 40

According to a particular form of the invention, in the general formula IR2 is -NH2, R3 is -H, R4 is -N02, R5 is -H and Re is —COOH, and the compound is 2-amino-4-nitro -6-carboxy-phenol, applied in hydroalcoholic solution at 1 g / 1, which turns at a pH above 9 from light yellow to deep red.

The compounds used in the paper according to the invention can also have the general formula I, in which R2 is —H or —N02, R3 is —N02 or H, R4 and R5 are each —H, and Re is the remainder

HO NO,

NH, or the rest

O

and the compounds, which are derivatives of biphenyl, are:

- 3-nitro-6-p-aminophenylphenol, applied in hydroalcoholic solution at 1 g / 1, which turns from colorless to intense red at a pH greater than 10, and

- 2-nitro-6- (2'-hydroxy-3'-nitro) phenylphenol, applied in an alcoholic solution at 1 g / 1, which turns from pale yellow to red at a pH above 8.

The compound used in the paper according to the invention may have the general formula I, in which R2 is —H, R3 is —N02, R4 and R5 are each - H, and R6 is the remainder - NH — CO — NH2; it is then 2-hydroxy-4-nitrophenylurea, applied in an alcoholic medium, which turns from colorless to red at a pH greater than 10.

According to another embodiment of the invention, the compounds can have the general formula I, where two neighboring vertices are the vertices of another optionally substituted conjugated aromatic ring.

Thus the compound can be 4-hydroxy-3-nitro-naphthoic acid or 2-nitro-4-carboxy-1-naphthol, applied in aqueous solution at 1 g / 1, which turns from yellow to red at pH 8.5 and therefore makes it possible to obtain a colored paper which reacts to the action of erasers.

It can also be l-nitro-6-methyl-P-naphthol applied in aqueous solution at 1 g / 1 and which turns from colorless to blood red at pH greater than 9.

Finally, the compounds used in the paper according to the invention can have the general formula I, in which two neighboring vertices are the vertices of a conjugated heterocycle, optionally substituted, this heterocycle preferably comprising a sulfur atom, or a nitrogen atom.

R

Claims (24)

634363 1. Paper reacting to falsification by chemical agents bonded on both sides and comprising in its mass and / or on its surface a product reactive with basic medium, characterized in that the product reactive with basic medium is chosen from the nitro derivatives of phenol of general formula I: OH r4 in which R2, R3, R4, Rs and R6, similar or different, are, in addition to a nitro group, a hydrogen atom, a halogen atom, a carboxy group, a hydroxy or substituted hydroxy group, a methoxy group or substituted methoxy, a substituted alkyl or alkyl • group, an amino or substituted amino group, a formyl group, a phenyl or substituted phenyl group, an arsenic group, or in which two neighboring vertices are the vertices of another conjugated ring, at least one of the symbols R2 to Rs being a nitro group. 2. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from nitro derivatives in at least one of the positions 2,4, 5 or 6 of the phenolic cycle. 2 3. Paper according to claim 2, characterized in that the nitro derivative of phenol is chosen from paranitrophenol, dinitro-2,4-phenol, dinitro-2,5-phenol and dinitro-2,6-phenol. 4. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of formula I, in which R2 is —H, —CH3 or —N02, R3 is —CH3 or —H, R4 is - NO2 or —H, R5 is —CH3, each CH3 possibly being substituted for example by halogen, or —H, andR6 is —Hou —N02. 5. Paper according to claim 4, characterized in that the nitro derivative of phenol is chosen from 4-nitro-m-cresol, 4,6-dinitro-o-cresol, 2,4-dinitro-3,5 -xylenol, 2,6-dinitro-3,5-xylenol and α-chloro-4-nitro-o-cresol. 6. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of general formula I, in which R2 is —NH2, R3 is —H, R4 is —H or —N02, R5 is - H or —N02, and R6 is —H or —N02. 7. Paper according to claim 6, characterized in that the nitro derivative of phenol is chosen from the following compounds: 2-amino-5-nitrophenol, 2-amino-4-nitrophenol and 2-amino-4,6 -dinitro-phenol. 8. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of formula I, in which R2 is - NO2 or Cl, R3 and R5 are a hydrogen atom, R4 is an atom chlorine, and R6 is —H or - N02. 9. Paper according to claim 8, characterized in that the nitro derivative of phenol is chosen from the following compounds: 4-chloro-2-nitrophenol, and 2,4-dichloro-6-nitrophenol. 10. Paper according to claim 1, characterized in that the nitro derivative of phenol is 2-amino-4-chloro-5-nitrophenol, compound of formula I in which R2 is - NH2, R3 and R6 - H, R4 - Cl, Rs -no2. 11. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of formula I, in which R2 is —N02 or H, R3 is H, R4 is —COOH, —H or —N02, Rs is —H or —COOH, and R6 is —H or —COOH. 12. Paper according to claim 11, characterized in that the nitro derivative of phenol is chosen from the following compounds: 2-nitro-4-carboxyphenol, 2-nitro-5-carboxyphenol and 4-nitro-6-carboxyphenol . 13. Paper according to claim 1, characterized in that the nitro derivative of phenol is 2-nitro-phenol-4-arsenic acid, compound of formula I in which R2 is —N02, R3, R5 and R6 are H, and R4 is —AsO (OH) 2. 14. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of formula I, in which R2 is —OH or —N02, R3 is —N02 or —H, R4 is -CH2-COOH , -N02 or -OH, Rs is -H or -CH2-COOH, and R6 is —H or —N02. 15. Paper according to claim 14, characterized in that the nitro derivative of phenol is chosen from the following compounds: 3-nitro-4-carboxymethylcatechol, le4-nitro-5-carboxyméthylcatéchol, 4-nitrocatéchol and dinitroquinol. 16. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of formula I, in which R2 is —N02 or —OCH3, R3 is —H or —N02, R4 is —COOH, R5 is —H, and Rs is - OCH3 or —H. 17. Paper according to claim 16, characterized in that the nitro derivative of phenol is chosen from the following compounds: 2-nitro-4-carboxy-6-methoxyphenol, and 2-methoxy-3-nitro-4-carboxyphenol . 18. Paper according to claim 1, characterized in that the nitro derivative of phenol is 2-amino-4-nitro-6-carboxyphenol, compound of formula I in which R2 is —NH2, R3 is —H, R4 is - NO2, R5 is —H, and R6 is —COOH. 19. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of formula I, in which R2 is —H or —N02, R3 is —N02 or H, R4 and R5 are each —H , and R6 is the rest HO NO, NH2 or the rest 20. Paper according to claim 19, characterized in that the nitro derivative of phenol is chosen from the following compounds: 3-nitro-6- (p-aminophenyl) phenol and 2-nitro-6- (2'-hydroxy -3'-nitro) -phenylphenol. 21. Paper according to claim 1, characterized in that the nitro derivative of phenol is 2-hydroxy-4-nitrophenylurea, compound of formula I in which R2 is —H, R3 is —N02, R4 and R5 are each —H , and R6 is the remainder - NH — CO — NH2. 22. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of formula I, where two neighboring vertices are the vertices of another optionally substituted conjugated aromatic ring. 23. Paper according to claim 22, characterized in that the nitro derivative of phenol is chosen from the following compounds: 4-hydroxy-3-nitro-1-naphthoic acid and 1 -nitro-6-m6thyl-ß- naphthol. 24. Paper according to claim 1, characterized in that the nitro derivative of phenol is chosen from the compounds of formula I, in which two neighboring vertices are the vertices of a conjugated heterocycle, optionally substituted, this heterocycle preferably comprising: a sulfur atom or a nitrogen atom.