EP0072481A1 - Tamperproof paper - Google Patents

Abstract

Counterfeit-proof paper, which gives a clear color when treated with an oxidizing and possibly reducing agent, contains as reagent a compound of the formula <IMAGE> in which A for N or C, B for NR, O or S, R for hydrogen or alkyl, X and Y represent hydrogen or conventional substituents and n and m represent the numbers 1 or 2.

Description

For a range of specialty papers such as There is great interest in protecting money, securities, ID documents and documents from being counterfeited. In particular, such papers should be protected against the use of handwriting, e.g. inked away by erasing.

A larger number of possibilities have been described in the patent literature as to how erasing with acids, bases, oxidizing agents, reducing agents and organic solvents can be made more difficult by the fact that colored substances are formed during this treatment. Most of the proposed substances react to alkali, acid or chlorine (see e.g. US 4 037 007, US 3 437 555 or FR 2 365 656).

A common counterfeiting method uses both a strong oxidizing agent and a reducing agent, such as the potassium permanganate / sodium bisulfite system - preferably in the acidic range. Potassium permanganate quickly and completely discolors ink; the manganese dioxide that forms on the paper then made colorless with bisulfite. Erasers based on this are in shape. of ready-to-use solutions in spotted vials in stores (eg "Ink Eradicator Les Siamoises X 2", -I. Herbin SA, Paris).

Protection. This counterfeiting method is particularly difficult since a substance is required which is colorless and becomes clearly colored with permanganate, but which cannot be decolorized with bisulfite.

bzw. deren Salze enthält, worin

• A für N oder C,
• B für NR, O oder S,
• R für Wasserstoff oder Alkyl,
• X und Y für Wasserstoff oder in der Chemie der Papierfarbstoffe übliche Substituenten und
• n und m für die Zahlen 1 oder 2 stehen und wobei sich die Aminogruppe in m- oder p-Stellung zu A befindet.

It has now been found that this counterfeiting method also has no chance of remaining undetected when using a paper which is a colorless compound of the formula as a reagent

or their salts, in which

• A for N or C,
• B for NR, O or S,
• R represents hydrogen or alkyl,
• X and Y for hydrogen or common substituents in the chemistry of paper dyes and
• n and m represent the numbers 1 or 2 and the amino group is in the m or p position to A.

Suitable salts are in particular the alkali and alkaline earth salts, preferably the Na, K, Li, Mg, Ca or ammonium salts.

Suitable alkyl radicals R are those which have 1-4 C atoms and are optionally substituted, for example by OH, CN, phenyl or C ₁ -C ₄ alkoxy.

Suitable substituents X and Y are - apart from H - for example C ₁ -C ₄ alkyl, C ₁ -C ₄ alkoxy, Cl, CF ₃ or CN. H, CH _{3 '} Cl and OCH ₃ are preferred.

• A für C,
• B für NH, N-C₁-C₄-Alkyl oder S,
• X für H, Cl, CH3 oder OCH_3'
• Y für H oder CH₃ und
• n und m für 1 oder 2 stehen.

Preferred compounds are those of the formula I in which

• A for C,
• B for NH, NC ₁ -C ₄ alkyl or S,
• X for H, Cl, CH3 or OCH _{3 '}
• Y for H or CH ₃ and
• n and m stand for 1 or 2.

• 2-(4'-Aminophenyl)-6-methyl-benzothiazol-7-sulfonsäure
• (= "Dehydrothio-p-toluidinsulfonsäure"),
• 2-(4'-Amino-3'-sulfophenyl)-6-methyl-benzothiazol,
• 2-(4'-Amino-3'-sulfophenyl)-6-methyl-benzothiazol-7-sulfonsäure,
• 2-(4'-Amino-3'-tolyl)-4.6-dimethyl-benzothiazol-7-sulfonsäure, 5-Methyl-2-(4'-aminophenyl)-benzimidazol-6-sulfonsäure, 5-Methyl-2-(3'-aminophenyl)-benzimidazol-6-sulfonsäure, 2T(4'-Aminophenyl)-benztriazol-5-sulfon- . säure, 2-(3'-Sulfo-4-aminophenyl)-benztriazol.

Examples include:

• 2- (4'-aminophenyl) -6-methyl-benzothiazole-7-sulfonic acid
• (= "Dehydrothio-p-toluidine sulfonic acid"),
• 2- (4'-amino-3'-sulfophenyl) -6-methyl-benzothiazole,
• 2- (4'-amino-3'-sulfophenyl) -6-methyl-benzothiazole-7-sulfonic acid,
• 2- (4'-amino-3'-tolyl) -4.6-dimethyl-benzothiazole-7-sulfonic acid, 5-methyl-2- (4'-aminophenyl) benzimidazole-6-sulfonic acid, 5-methyl-2- ( 3'-aminophenyl) benzimidazole-6-sulfonic acid, 2T (4'-aminophenyl) benzotriazole-5-sulfone. acid, 2- (3'-sulfo-4-aminophenyl) benzotriazole.

These compounds are known (cf. e.g. DE 92 011, 270 861, 2 302 522, 2 329 126, 2 421 822 and 2 716 503) or are easily accessible by methods known per se.

The papers according to the invention are produced in such a way that the compounds of the formula (I) are applied during or after paper manufacture by adding them to the paper pulp or by application to the paper surface or by an appropriate surface treatment.

These compounds are generally used in the form of the aqueous solutions of their readily soluble salts, in particular alkali salts.

Although these solutions are pale yellow in concentrated form, they become practically colorless when diluted below approx. 1%. If, according to a preferred production variant, the diluted solutions are applied to white paper alone or in combination with a binder, the appearance of the paper practically does not change.

As binders come e.g. Solutions of starch or carboxymethyl cellulose or also anionic plastic dispersions, e.g. based on polymers of butadiene and styrene or acrylic acid esters, as well as polyvinyl alcohol solutions.

The paper is usually sized in the pulp, e.g. with wood glue. However, it is also possible to omit the paper pulp sizing in whole or in part and combine the anti-counterfeiting reagent with an anionic surface sizing agent, possibly also using starch at the same time. This allows the solution of the reagent to penetrate deeper into the paper and, at the same time as the equipment, the sizing required for writing on the paper is achieved. Commercially available products are suitable as surface sizing agents, e.g. aqueous solutions or dispersions based on copolymers of maleic anhydride or their ammonium salts.

The paper treated with the compounds of the formula (I) becomes distinctly yellow when spotted with a dilute potassium permanganate solution and also remains yellow when the dark brown manganese oxides formed on the paper are decolorized with a dilute solution of sodium bisulfite.

Depending on the absorption capacity of the paper, there is a surface to achieve a clearly visible yellow color treatment with a 0.01 to 0.5% solution of the anti-counterfeiting reagent is necessary.

In principle, the reagent can also be added to the paper pulp (i.e. the paper fiber suspension). However, it can be expected that some of the product will go into wastewater during paper production. However, by adding aluminum sulfate or cationic retention or fixing agents (e.g. based on polyacrylamide, polyamide amine or dicyandiamide formaldehyde) the yield in the paper can be improved. In general, 0.1 - 5% reagent (based on the paper pulp) is required for this production variant.

A paper made from bleached sulfate pulp, which had been sized with resin glue and aluminum sulfate, was treated in a laboratory size press (System Werner Mathis AG, Niederhasli / Switzerland) with a 0.25% aqueous solution of "dehydrothio-p-toluidinesulfonic acid". This solution was prepared by stirring 0.25 g of the product in 100 ml of water and dissolving it by adding dilute sodium hydroxide solution. Potassium hydroxide solution or lithium hydroxide solution can also be used instead of sodium hydroxide solution.

The paper was dried on a hot cylinder at 100 ° C. It did not differ in appearance from the untreated paper.

When a dilute solution of potassium permanganate was spotted and then a dilute sodium bisulfite solution was applied to the paper so prepared, a very clear, permanent yellowing occurred.

Example 2

An unsized paper made from bleached cellulose, in the manufacture of which 1% aluminum sulfate had been added to the pulp, was surface-treated in a laboratory size press (System Werner Mathis AG, Niederhasli / Switzerland) with a 5% starch solution, which was 1% of a commercially available anionic surfaces Sizing agent based on styrene-maleic anhydride copolymer contained. This size press liquor was added with 0.2% dehydrothio-p-toluenesulfonic acid in the form of a 1% solution in dilute sodium hydroxide solution

In this way, the paper was simultaneously glued to the surface and equipped with the anti-counterfeiting reagent.

When a dilute solution of potassium permanganate was spotted and then a dilute solution of sodium bisulfite was applied to the paper so prepared, a very clear, permanent yellow color resulted.

Example 3

A suspension of 1% bleached sulfate pulp (freeness approx. 35 ° SR) in water was added with 1% dehydrothio-p-toluenesulfonic acid (based on the weight of the dry fibers) in the form of a 1% solution in dilute sodium hydroxide solution with stirring. Then 2% resin glue and 3.% aluminum sulfate were added and the mixture was stirred for 10 minutes.

The fiber suspension was diluted to 0.3% with water, suctioned off on a laboratory sheet former and the paper sheets formed were dried at about 100.degree.

The paper had a slight yellow tinge, which was hardly disturbing in practice, and turned yellow when spotted with permanganate and then bisulfite solution.

Claims (5)

1. Counterfeit-proof paper which, when treated with an oxidizing and possibly reducing agent, gives a clear color, characterized in that it is a compound of the formula as a reagent.

or their salts, in which A for N or C, B for NR, 0 or S, R represents hydrogen or alkyl, X and Y for hydrogen or common substituents in the chemistry of paper dyes and n and m represent the numbers 1 or 2 and the amino group is in the m or p position to A. 2. Counterfeit-proof paper according to claim 1, characterized in that it is a compound as a reagent of the formula given, wherein A for C, B for NH, NC _i -C ₄ alkyl or S, X for H, Cl, CH ₃ or OCH ₃ , Y for H or CH ₃ and n and m stand for 1 or 2. 3. Counterfeit-proof paper according to claim 1, characterized in that it contains 2- (4'-aminophenyl) -6-methyl-benzothiazole-7-sulfonic acid as reagent. 4. Counterfeit-proof paper according to claims 1-3, characterized in that it contains the reagent in the form of the alkali salts. 5. A method for producing the counterfeit-proof papers according to any one of claims 1- 4, characterized in that the reagents are applied during or after paper manufacture by adding to the paper pulp or by application to the paper surface or by an appropriate surface treatment.