CH679411A5 - - Google Patents

Description

1

CH 679 411 A5

2

Description

The present invention relates to a support for writing printing, in particular paper, reacting to a possible falsification by chemical agent and authenticated by heat.

It mainly concerns the field of usable security papers, for the production of handwritten payment vouchers and official documents such as, in particular, checks, paper money, savings bank vouchers, account books, accounting ledgers, titles, stamped papers, notarial acts, transport tickets and, in general, all security papers and comparable security means such as credit cards, etc.

For all these security papers, it is necessary to guard against any attempt to falsify the writing or stamp carried on these so-called papers. The falsification can be mechanical (scrubbing or scraping) or chemical: using chemical agents making it possible to cleanly remove the colored inks currently used for handwriting or printing by ink pads.

Known security papers may, in addition to the watermark and other physical security elements, such as threads, fibers, etc. contain certain reagents that raise awareness of chemical agents that can be used to falsify scriptures by chemically bleaching inks. For example, papers containing chemical reagents to chemical falsification agents have already been proposed, such as acids, alkalis, chlorinated bleaching agents such as chlorine water and bleach, ink erasing pencils (documents ARJO-MARI FR-A 2 365 656, FR-A 2 399 505, FR-A 2 402 739, Papeteries de VOIRON and des Gorges documents FR-A 2 406 027) and reducing oxidizing agents used in “CO-RECTOR” type erasers R (document ARJOMARl EP-A174 885).

In addition, most security papers available on the market do not have a simple and reversible authentication process which can be combined with protection against falsification.

The use of thermochromy for the authentication of security papers has been described in document DE-A 1 228 972 and document AT-A 362 658. But these methods used unusual products which are expensive and difficult to use. in stationery. Document GB-A 1 565 243 describes an authentication by thermochromy using thermochromic and thermomagnetic substances. Furthermore, in the document Aussedat-Rey FR-A 2 597 897, a security paper authenticated by thermochromy containing a violet lactone and an organic acid has been described. But such paper tends to color over time.

In addition, the protection of the paper against counterfeiting must maintain the non-fluorescent nature of the paper. Indeed, fluorescence constitutes a limitation of the security of these papers, since non-fluorescence is a sign of recognition very often used, in particular at the level of banks and in the general public. It is known that papers, in particular for printing-writing, are almost always fluorescent, the fluorescence being due to additives improving the whiteness of the paper.

Since the supply of non-fluorescent writing print paper is very tight, counterfeiters, unless they can divert non-fluorescent paper, will have every chance of using fluorescent paper. Non-fluorescent paper therefore constitutes a very effective prevention of counterfeiting and, when working on such paper that we have managed to make non-fluorescent, it is obviously essential that the security agents incorporated in the paper do not do not bring by themselves the characteristic of fluorescence which one had managed to avoid.

Among all these falsifying agents, sodium bisulfite is an effective reducing agent in erasing: it is used in erasers of the CO-RECTOR R type and can be very effective in blurring or removing stains caused by paper falsifications. said to be "unfalsifiable".

We have described in the document Verpackungs-Rundschau 11/1985 p. 1250-1253, a method of controlling the humidity of the air. A blotting paper, therefore extremely absorbent, is used on which an anhydrous salt of blue cobalt chloride is deposited. When the paper absorbs moisture from the air, it turns pink. This paper should not be in contact with the sweat of the hands to avoid untimely humidification.

Furthermore, document US-A 2 005 105 describes a paper reacting to bleaching or oxidizing agents, this paper being treated with an ink containing cobait ferrocyanide. Document US-A 1 804 978 describes a paper which reacts to ink erasers, treated with a solution containing water, alcohol, iodine, cobalt nitrate and sodium thiosulfate. .

Document DE-A 42 260 describes a paper reacting to chlorine-based erasers, this paper being treated with an ink containing a sulfated manganese oxide or cobalt chloride.

Document FR-A 1 509 715 describes a paper intended to react to bisulfite containing manganese ferrocyanide and a metal salt insoluble in water and forming a colored ferrocyanide. It is this ferrocyanide which gives coloring to the paper by the action of bisulfite. The metal salt can be a transition metal salt.

Thus, according to these publications, the transition metal salts are always used in combination with other salts to obtain either a reaction with bleaching or oxidizing agents, or a reaction with bisulfite. Those skilled in the art were therefore led to associate the metal salts with other salts.

An object of the invention is therefore to obtain a support for printing-writing, of non-fluorescent security, which can be authenticated with heat in a reversible manner, by virtue of a chemical composition which does not appreciably modify the coloring of the paper and which is furthermore compatible with other reagents known for sensitizing to acids, bases, oxidants, erasers, organic solvents.

Another object of the invention is to obtain a security paper, reacting with bisulfite.

5

10

15

20

25

30

35

40

45

50

55

60

65

2

3

CH 679 411 A5

4

At the end of intensive and prolonged tests, it was finally retained that the aim of the invention could be achieved by incorporating in or on the printing-writing medium at least one metallic salt colored in the wet state and of a different color. in the dry state, the amount of salt relative to the support, by dry weight, being such that the coloring of the support is not substantially affected at room temperature, and the coloring of the support being changed reversibly when raised the temperature of the support.

The object of the present invention is a support for printing-writing reacting to sodium bisulphite which is characterized by a content of a cobalt salt at the oxidation state 2. The cobalt salts, of oxidation state 2 are metallic salts which can pass from a crystalline state of one color to a crystalline state of another color in paper. A hydrated cobalt salt is introduced into the print-write support. The latter being preferably paper based on cellulosic fibers or a plastic support coated with a layer giving it the property of being able to be printed or to receive writing, it always contains from 5 to 7% of water after going through drying. Since the quantity of cobalt salts relative to the support by dry weight is low, that is to say between 0.1 and 4%, the cobalt salt remains in the hydrated state, even after going through drying. of the sheet of paper or printing-writing medium. The cobalt chloride is then pink. But its quantity is small enough not to give color to the paper which remains white.

In fact, the cobalt salts of degree of oxidation 2 are generally colored, but their introduction into the paper has little effect on the original shade of the paper with normal dryness and does not bring any fluorescence. Around 100 ° C, such paper takes on a blue or purple coloration, which spontaneously and quickly fades when the paper is returned to the ambient atmosphere. This coloring phenomenon, brought about by the presence of cobalt salts of degree of oxidation 2 in the paper, is only visible at high temperatures; it is therefore not annoying in the daily conditions of use of security papers. On the contrary, this coloring when the paper is dehydrated can be used as an easy and non-destructive heat authentication system for this type of security paper.

The paper can be authenticated by a specific heating with heating jaws, a breath of hot air, a heating pen.

According to the invention, it is possible to add desiccant salts, in particular sodium chloride, to the paper, by lowering the amount of available water, which makes it possible to lower the temperature threshold for color change.

On the other hand, it has surprisingly been found that the addition of cobalt salts to the paper makes it possible to obtain a reaction (and therefore protection) with several falsifying agents such as hypochlorite, alkalis and bisulfite sodium. This reaction is obtained by introducing the cobalt salt alone. Thus, the invention makes it possible to obtain a print-writing medium, authentifiable by heat and unforgeable by chemical agent, by introducing a single compound into the paper.

According to the invention, the paper can have any fibrous composition, purely cellulosic, or synthetic part, from synthetic fibers or coated synthetic films, more briefly hereinafter "paper", to which the conventional stationery additives can be added. namely: mineral fillers, various resistance agents, binders, resins, shading dyes, neutral, acid or basic bonding products, alumina sulfate for acid bonding or pH adjustment, etc.

The cobalt salts being generally very soluble, the introduction of these products according to the invention can preferably be done by impregnation by means of a size press or by coating.

The reaction to heat is perceptible to the naked eye from 500 ppm of cobalt salt of oxidation state 2 in the paper, but, for a clearly visible and rapid reactivity, industrial doses of between 0.1% and 4% cobalt of oxidation state 2 are more suitable.

These papers may also contain in their mass, in the dispersed pigmentary state, dyes insoluble in water but organosoluble, so as to preserve the writings or mentions made on these papers vis-à-vis attempts at falsification with using organic solvents. In addition, these papers can be watermarked or contain various devices intended to ensure recognition.

Thus, the invention makes it possible to manufacture a white, non-fluorescent paper, authentically reversible by heat and which develops, in the presence of an attempt at chemical falsification, colors detectable with the naked eye on this paper.

The paper which is the subject of the present invention can be printed by any of the printing methods and can be used as handwriting medium when it is desired to have permanent mention and to discover possible attempts to falsification of these writings. It is particularly interesting to apply it to the production of non-fluorescent handwritten payment documents such as checks, cash vouchers, savings account books, official documents, banknotes, etc.

Although most of the security papers used are white, one can also consider incorporating this means of tampering into a security paper, no longer white, but colored.

The following examples illustrate the invention without, however, reducing its scope.

EXAMPLE 1

On an impression-writing paper support is deposited on the surface by a conventional papermaking technique (size press) the aqueous coating solution comprising per liter of liquid:

-100 g of starch,

-15 g of cobalt chloride hexahydrate.

5

10

15

20

25

30

35

40

45

50

55

60

65

5

CH 679 411 A5

6

The paper, if worn locally around 100 ° C, takes on a blue tint which disappears in a few minutes when the heating is stopped.

A white paper is obtained which reacts in orange to sodium bisulfite or to the subsequent addition of a solution of permanganate and sodium bisulfite.

EXAMPLE 2

On a paper support identical to Example 1, the aqueous coating solution is deposited on the surface by a conventional paper technique (sizing press), comprising per liter of liquid:

-100 g of starch,

-15 g of hydrated cobalt sulfate.

Results similar to Example 1 are obtained.

EXAMPLE 3

Same process and same results as in Example 1 with 18 g of hydrated cobalt nitrate in place of cobalt chloride.

EXAMPLE 4

Same process and same results as in Example 1 with 15 g of cobalt acetate tetrahydrate in place of cobalt chloride.

EXAMPLE 5

Same process and same results as in Example 1 with 15 g of cobalt acetyl acetonate in place of cobalt chloride.

EXAMPLE 6

On a banknote-type support is deposited on the surface by a conventional papermaking technique (size press) the coating solution comprising per liter of liquid:

-100 g of polyvinyl alcohol

- 30 g of cobalt chloride hexahydrate -10 g of sodium chloride.

We get a white paper. This paper takes on a blue color from 80 ° C. It is therefore easily authenticated by occasional heating of the paper. The reaction is spontaneously reversible in a few minutes. In addition, the paper reacts strongly to bisulfite in orange.

EXAMPLE 7

On a high density polyethylene plastic support is coated by a conventional papermaking technique (drag blade, air knife ...) the aqueous coating sauce comprising per liter of liquid:

- 400 g of dispersed fillers (kaolin, talc, carbonate)

- 200 g of latex

- 30 g of hydrated cobalt chloride.

The coated plastic is white. In the heat, a very clear blue coloration is visible.

Claims (7)

Claims 1. Support for printing-writing reacting to sodium bisulfite, characterized in that it contains a cobalt salt with oxidation state 2. 2. Support according to claim 1, characterized in that the cobalt salt is in hydrated cobalt salt. 3. Support according to claim 1 or 2, characterized in that the cobalt salt is chosen from the group comprising cobalt sulfate, cobalt chloride, cobalt acetate, cobalt nitrate, cobalt acetylacetonate . 4. Support according to one of claims 1 to 3, characterized in that it gives an orange coloring to sodium bisulfite. 5. Support according to one of claims 1 to 4, characterized in that it contains 0.1 to 4% of hydrated cobalt salt with oxidation state 2. 6. Method for the treatment of a support for printing-writing to protect it against chemical falsification and for obtaining a support according to one of claims 1 to 5, characterized in that this process consists in introducing, in or on the surface of the support, a cobalt salt hydrated at the oxidation state 2, so as to obtain an orange coloration in the presence of sodium bisulfite. 7. Method according to claim 6, characterized in that the cobalt salt is deposited on the surface of said support by a papermaking technique from an aqueous coating solution containing said salt. 5 10 15 20 25 30 35 40 45 50 55 60 65 4