NL9100419A - SUBSTRATE FOR PRINT OR WRITING, WHICH CAN BE WARRANTED BY HEAT AND CANNOT BE DISTORTED BY THE USE OF A CHEMICAL AGENT. - Google Patents

Description

EXTRACT

The invention relates to a substrate for printing or writing which reacts with sodium bisulfite.

This substrate is characterized in that it contains at least one cobalt salt of bivalent cobalt.

The invention makes it possible to prepare a substrate for printing or writing which is protected against adulteration using sodium bisulfite.

Short designation: Substrate for printing or writing, which can be certified by heat and cannot be falsified with the aid of a chemical agent.

The present invention relates to a substrate for printing or writing, in particular paper, which shows a reaction to a possible adulteration by means of a chemical agent and can be certified by heat.

The invention particularly relates to the field of security paper, which can be used for the production of handwritten payment documents and official documents, such as in particular checks, paper money, savings bank certificates, account books, receipt books, deeds, sealed papers, notarial deeds, deeds of transfer and generally all security paper and similar security such as credit cards etc.

All security papers must be secured against any attempt to forge the writing or stamp affixed to such paper. The counterfeiting can be mechanical (erasing or scratching) or chemical: using chemical means that make it possible to neatly remove the colored inks that are currently used for handwriting or for printing with ink rollers.

Known security papers may contain, in addition to the watermark and other physical security elements, such as threads, fibers, etc., certain reagents that sensitize the chemical agents that can be used to falsify writing by chemically decolorizing the ink.

Paper has already been proposed which contains chemical reagents for chemical adulterants such as acids, alkalis, chlorinated decolorizers such as chlorinated water and bleach, ink pencils for inks CFR-A-2 365 656, FR-A-2 399 505, FR-A -2 402 739, FR-A-2 406 027) and oxidizing / reducing agents used in "CORECTOR" R type renders (EP-A-174 885).

Furthermore, for most commercially available security papers, a simple and reversible certification method is not available, which can also serve to protect against counterfeiting.

DE-A-1 228 972 and AT-A-362 658 describe the use of thermochromics for security paper authentication. But these methods use expensive, not very common products, the application of which is difficult in papermaking. GB-A-1 565 243 describes a method for thermochromic authentication using thermochromic and thermomagnetic substances. FR-A-2 597 897, incidentally, describes a security paper which can be certified by thermochromia and which contains a purple lactone and an organic acid. But such a paper tends to discolour with time.

Furthermore, the non-fluorescent character of the paper should be preserved in the protection of paper against counterfeiting. Indeed, the fluorescence is a limitation for the safety of these papers, because non-florescence is a very common identification mark, especially at banks and the general public. It is known that paper, especially for print or writing, is practically always fluorescent with the fluorescence resulting from substances added to improve the whiteness of paper.

Given that the provision of non-fluorescent paper for printing or writing is tightly controlled, counterfeiters will be likely to use fluorescent paper unless they are able to steal non-fluorescent paper. Non-fluorescent paper is therefore a very efficient prevention against counterfeiting and when processing such paper that one has managed to make non-fluorescent, it is of course important that the safety agents used in the paper do not themselves have the fluorescent properties. that they have just managed to avoid.

Of all adulterants, sodium bisulfite is an efficient erasing agent: it is used in CORECTOR R type eradicators and can be very effective in obscuring or eliminating the stains, which are called "non-adulterable" in adulteration. paper are triggered.

Verpackungs-Rundschau 11/1985 pp. 1250-1253 describes a method for checking the humidity of air.

Blotter paper, i.e. particularly highly absorbent paper, is used, on which an anhydrous salt of blue cobalt chloride is applied. When the paper absorbs moisture from the air, it turns pink. This paper should not come into contact with the sweat of the hands to prevent it from getting damp prematurely.

Furthermore, US-A-2 005 105 discloses a paper which reacts to bleaching or oxidizing agents, which paper has been treated with an ink containing cobalt ferrocyanide. US-A-1 804 978 discloses a paper which reacts with ink-grading agents, which has been treated with a solution containing water, alcohol, iodine, cobalt nitrate and sodium thiosulfate.

DE-A-42 260 discloses a paper which reacts to chlorine-based reagents which has been treated with an ink containing an oxide of manganese sulfate or cobalt chloride.

FR-A-1 509 715 discloses a paper intended to react to bisulfite containing manganese ferrocyanide as well as a metal salt which is insoluble in water and forms a colored ferrocyanide. It is this ferrocyanide that causes the discoloration of the paper due to the action of bisulfite. The metal salt can be the salt of a transition metal.

Thus, according to these publications, transition metal salts are continuously used in combination with other salts to obtain either a reaction to bleaching or oxidizing agents or a reaction to bisulfite. Thus, those skilled in the art are led to combine metal salts with other salts.

An object of the invention is to obtain a printing or writing surface which is protected, non-fluorescent and can be reversibly authenticated by heat, thanks to a chemical composition that does not appreciably modify the color of the paper and is further compatible with the other known reagents used to sensitize the paper to acids, bases, oxidizing agents, marking pencils, organic solvents.

Another object of the invention is to provide a security paper which reacts to bisulfite.

On the basis of extensive and lengthy tests, it was ultimately found that the object of the invention can be achieved by incorporating in or on the substrate for printing or writing at least one metal salt, which is colored in the moist state and has a different color in the dry state wherein the amount of the salt relative to the substrate on dry matter is such that the color of the substrate is practically unaffected at ambient temperature and the color of the substrate is reversibly changed as the temperature of the substrate is increased.

Preferably, metal salts which can change from a crystalline state of a certain color to a crystalline state of a different color are incorporated in the paper, and in particular cobalt salts with the degree of oxidation 2 are used. A hydrated cobalt salt is introduced into the substrate. print or writing. The latter is preferably made of paper based on cellulose fibers or is a plastic substrate coated with a layer, which gives it the property of being printed or written and still contains 5 to 7% water after being dried. Given that the amount of cobalt salts relative to the substrate on dry matter is small, i.e. between 0.1 and 4%, the cobalt salt remains in a hydrated state even after the sheet of paper or substrate for printing or writing dried. The cobalt chloride is therefore pink. But its amount is small enough not to add color to the paper, which therefore remains white.

Indeed, the cobalt salts of divalent cobalt are generally colored, but incorporating them into paper has little effect on the original color of paper in a normal dry state and does not give fluorescence. Near 100 ° C, such a paper takes on a blue or purple color that disappears spontaneously and quickly when the paper is returned to a normal ambient atmosphere. This color phenomenon brought about by the presence of divalent cobalt salts in the paper is visible only at elevated temperatures; it is therefore not disturbing in the daily circumstances of using this security paper. On the contrary, this discoloration during the dehydration of the paper can be used for a security paper of this type as a heat-authentication method, which is convenient and non-destructive.

The paper can be certified by a precise heating, clamped between heated plates or with a warm airflow or with a heated pen.

According to the invention, one can add water-absorbing salts to the paper, in particular sodium chloride, which decreases the amount of available water, which can also lower the threshold for the temperature at which color change occurs.

In addition, it has surprisingly been found that the addition of cobalt salts to the paper makes it possible to obtain a reaction (hence a protection) with various adulterants, such as hypochlorite, alkalis and sodium bisulfite. This reaction is obtained by only incorporating the cobalt salt. The invention therefore makes it possible to obtain a substrate for printing or writing which can be certified by heat and cannot be falsified by a chemical agent by incorporating a single substance in the paper.

According to the invention, the paper may have an arbitrary fibrous composition, consisting exclusively of cellulose fibers or partly synthetic on the basis of synthetic fibers or consisting of a coated synthetic film, for the sake of brevity hereinafter referred to as "paper", to which the customary papermaking materials adjuvants can add namely: mineral fillers, various reinforcing agents, binders, resins, dyes for hue, neutral, acid or basic glues, aluminum sulfate for acid gluing or pH adjustment etc.

Since the cobalt salts are generally very soluble, the processing of these products according to the invention into the paper can preferably be carried out by impregnation using a glue press or by applying a layer of the substances to the paper.

The heating reaction is visible to the naked eye from 500 ppm salt of divalent cobalt in the paper, but industrial doses ranging from 0.1% to 4% divalent cobalt are more suitable for a highly visible and rapid reaction.

The paper mass according to the invention may also contain dyes or pigments which are insoluble in water but soluble in organic solvents, in finely divided state, so as to preserve what is written or stated on the paper against counterfeiting attempts using organic solvents. In addition, the paper according to the invention can be watermarked or contain various artificial handles which serve to ensure recognition.

The invention therefore makes it possible to produce a white, non-fluorescent paper, which can be reversibly heat-certified and which, when an attempt has been made to chemically falsify, shows discolouration with it. naked eye on this paper can be discovered.

The paper which is the subject of the present invention can be printed by any printing method and can be used as a background for manuscript if one wishes to make the data applied thereon durable and to discover any attempts to falsify this manuscript. The paper is of particular interest for use in the manufacture of hand-written, non-fluorescent payment items, such as checks, receipts, savings bank booklets, official deeds, banknotes, etc.

Although most of the security paper used is white, one can also imagine incorporating this anti-counterfeiting agent into security paper that is not white but colored.

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

Example 1

On a substrate of paper for printing or writing, on its surface is applied in a thin layer an aqueous solution known in the paper industry (with the glue press), which solution contains per liter of liquid: - 100 g starch, - 15 g cobalt chloride hexahydrate.

The paper takes on a blue color when brought locally to about 100 ° C, which color disappears within a few minutes when the heating is stopped.

A white paper is obtained, which turns orange when treated with sodium bisulfite or by successive use of a solution of. sodium permanganate and sodium bisulfite.

Example 2

On a paper substrate, identical to that of example 1, an aqueous solution is applied in a thin layer, known in the paper industry (with the glue press), an aqueous solution containing per liter of liquid: - 100 g of starch, - 15 g of hydrated cobalt sulfate.

Results similar to those of Example 1 are obtained.

Example 3

Using 18 g of hydrated cobalt nitrate instead of cobalt chloride, the same results as in Example 1 are obtained by the same method.

Example 4

Using 15 g of cobalt acetate tetrahydrate instead of cobalt chloride, the same results as in Example 1 are obtained by the same method.

Example 5

Using 15 g of cobalt acetylacetonate instead of cobalt chloride, the same results as in Example 1 are obtained by the same method.

Example 6

On a surface of the type used for banknotes, a solution in a thin layer is applied to its surface by a technique known in the paper industry (with the glue press), which solution contains per liter of liquid: - 100 g of polyvinyl alcohol - 30 g of cobalt chloride hexahydrate - 10 g of sodium chloride.

A white paper is obtained. This paper takes on a blue color from 80 ° C. So it can be easily certified by precise heating of the paper. The reaction is spontaneously reversible within a few minutes. The paper also discolours strongly to orange · with bisulfite.

Example 7

A layer of an aqueous mixture containing per liter of liquid: - 400 g of dispersed fillers (kaolin, talc, talc) is applied to a substrate of high-density polyethylene plastic using a technique known in the paper industry (entraining layer, thin air stream). , carbonate) - 200 g latex - 30 g hydrated cobalt chloride.

The coated plastic is white. When heated, a very sharp blue coloration becomes visible.

Claims (7)

Substrate for printing or writing which reacts with sodium bisulfite, characterized in that it contains a cobalt salt of divalent cobalt. Substrate according to claim 1, characterized in that the cobalt salt is a hydrated cobalt salt. Substrate according to claim 1 or 2, characterized in that the cobalt salt is selected from the group consisting of cobalt sulfate, cobalt chloride, cobalt acetate, cobalt nitrate, cobalt acetyl acetonate. Substrate according to any one of claims 1 to 3, characterized in that it gives an orange color with sodium bisulfite. Substrate according to any one of claims 1 to 4, characterized in that it contains 0.1-4% hydrated cobalt salt of divalent cobalt. Method for protecting a substrate for printing or writing against chemical adulteration, characterized in that this method consists of applying a hydrated cobalt salt of divalent cobalt in or on the surface of the substrate, so that an orange color is obtained in the presence of sodium bisulfite. A method according to claim 6, characterized in that the cobalt salt is applied in or on said substrate according to a well known technique in the paper industry, starting from an aqueous solution containing said salt and with which the substrate is coated.