Delible magnetic ink and process for making the same

Description

[0001] The present invention relates to a delible magnetic ink particularly for marking documents and the like, and its process of manufacture.

[0002] As is known, magnetic inks, i.e. inks which contain, inside them, particles of magnetic material which allow to magnetically read the document on which the ink has been printed or in any way applied, are already commercially available.

[0003] These types of magnetic ink are practically indelible, i.e. they do not modify their original arrangement even if the document on which they are applied is treated with chemical elements which delete print and the like or with erasure by means of an eraser or similar elements.

[0004] The result of the above is thus that indelible magnetic inks are a valid support for the magnetic reading of the document on which a code made with indelible magnetic ink is applied, for example, but they cannot constitute a safety element which clearly reveals the forgery of the document in the region where the magnetic ink is applied.

[0005] The aim of the invention is indeed to solve the above described problem by providing a delible magnetic ink particularly for marking documents and the like which allows to modify its initial characteristics if the region where said delible magnetic ink has been printed or in any way applied is treated with chemical deletion products or with mechanical means such as erasers or scratch knives.

[0006] Within the above described aim, a particular object of the invention is to provide a delible magnetic ink which can be printed or in any case applied by using conventional printing methods, thus allowing to provide, for example, a bar code which, besides allowing the magnetic reading of the document, constitutes a forgery-preventing safety element, since it clearly reveals the attempt at forgery, by modifying its arrangement on the document, and thus making the code no longer readable or being in any case removed from said document.

[0007] Another object of the present invention is to provide a delible magnetic ink which, by virtue of its peculiar characteristics of execution, is capable of giving the greatest assurances of reliability and safety in use.

[0008] Not least object of the present invention is to provide a delible magnetic ink which can have a very wide range of applications, especially in all those cases in which it is necessary to ensure, besides the authenticity of the document, also the fact that it has not been forged.

[0009] This aim, these objects and others which will become apparent hereinafter are achieved by a delible magnetic ink particularly for marking documents and the like, according to the invention, characterized in that it comprises a mixture of water, gum arabic, colored pigment and finely ground magnetic material mixed with an easily hydratable vehicle.

[0010] Further characteristics and advantages will become apparent from the description of two preferred but not exclusive embodiments of a delible magnetic ink, given with the aid of the following description.

[0011] The delible magnetic ink, according to the invention, to be used particularly for marking documents and the like, contains magnetic particles obtained by taking ferrite (iron oxide) of the gamma type with an initial needle-shaped particle measuring 0.001 by 0.006 mm, with a 1/6 ratio, grinding it with a hyperfast colloidal mill with zirconia spheres, in a microsphere agitator of the Fryma type with a kinetic chamber, until the particles are reduced to a size of 0.004 mm with a 1/4 ratio.

[0012] The iron oxide which constitutes the magnetic particles thus obtained is then mixed with easily hydratable vehicles, such as for example glycerol, sorbitol and the like, which have the function in practice of creating, upon a chemical attack of the ink, a displacement of the particles of magnetic material and consequently a modification of the initial conditions which clearly reveal the occurrence of an attempt at forgery.

[0013] The magnetic ink is obtained by mixing 10/15% magnetic material, as previously described, with 10/15% colored pigment together with 10/15% water, 10/15% glycerol, 30/35% gum arabic and 5/10% mineral filler.

[0014] With the ink thus produced it is possible to print on documents codes which are magnetically detectable and can, for example, be constituted by a bar code with bars 0.08 mm wide spaced from one another by 0.04 mm, with the possibility of decoding by means of a reading head and a controlled-speed machine in order to obtain a bit sequence the peaks whereof are spaced by 0.12 mm and the individual bit has a distance of 0.08 mm between the positive peak and the negative peak.

[0015] If the code thus produced is attacked chemically, for example with an oxidizing-reducing agent, the positive peaks and the negative peaks are reduced and no longer have a distance of 0.08 mm but will arrive at a distance of 0.10 mm, consequently modifying the width of the interspace and consequently varying the reading conditions.

[0016] By chemically attacking the code by means of a conventional chemical product used to delete print, such as a potassium permanganate and sodium hyposulphite solution, the printing obtained with the delible magnetic ink described above gets larger, and by virtue of the gum arabic, which acts as receptor, it modifies its structure, allowing a displacement of the particles of magnetic material and thus in practice a "disruption" of the code, which is no longer detectable and readable.

[0017] Similarly, the gum arabic allows an easy mechanical removal of the ink by acting either with a normal eraser or with scrapers or other similar elements.

[0018] Similar results are also obtained by using, for deletion, chemical products constituted by solutions of 50% sulphuric acid and 50% of sodium hypochlorite.

[0019] According to a further embodiment, which allows better printing definition, the delible magnetic ink according to the invention, to be used particularly for marking documents and the like, comprises, in a mixture, a non-polar solvent commonly termed high-boiling aliphatic solvent with a boiling interval comprised between 240 and 310^oC and with an aromatic compound content of less than 5% and with no polynuclear aromatic compounds.

[0020] The solvent is added to a grinding vehicle which is constituted by phenolic resins or cresolformaldehyde, or possibly by maleic resins with a melting point between 150 and 170^oC, which are mixed with cross-linking unsaturated polyesters commonly termed alkyd resins, with an oil content between 65 and 80%.

[0021] In order to obtain the grinding vehicle, 40% phenolic and/or maleic resin and 25% alkyd resin are loaded into an 18/10 stainless steel boiler fitted with an agitator, and the entire system is raised to a temperature of approximately 200^oC for 30 minutes, and is then cooled while adding 35% aliphatic solvents.

[0022] The alkyd resin has the power of solubilizing the phenolic or maleic resin, whereas the non-polar aliphatic solvents are used so as to decrease the viscosity of the vehicle, bringing it all to a viscosity of approximately 500 poises, which in practice constitutes the ink base.

[0023] The inks are substantially prepared according to a conventional method, by loading into a blade-fitted agitator the grinding vehicle obtained as described above, adding the organic pigments, derived from food-product dyes laked, i.e. coated, on barium salts, and the inorganic pigments, which constitute the magnetic material or finely ground ferrite.

[0024] The inorganic pigments which constitute the magnetic material are preferably constituted by ferrite (F₂O₃) of the gamma type with an initial needle-like particle measuring 0.001 x 0.006 mm, thus with a 1/6 ratio; during the preparation of the inks, the organic pigments and the magnetic material are mixed until a 500-poise viscosity paste is obtained; said paste is refined in a three-cylinder refining unit until a grinding degree of less than 5 microns is obtained.

[0025] During the preparation of the ink, one uses 70 to 63% grinding vehicle, 10 to 12% organic pigment, 15 to 20% magnetic material, to which 5% aliphatic solvent is added so as to bring the viscosity of the ink to approximately 200 poises, possibly varying the addition of aliphatic solvent.

[0026] Naturally, according to the organic pigment used, one obtains various colors, such as yellow, red, blue and green; the inks can furthermore be mixed perfectly with one another, so that it is possible to obtain all the further shades of color required.

[0027] The inks thus obtained can be lithographed so as to obtain safety backgrounds, by means of wet offset or dry offset plates, with an extremely high fineness and printing definition.

[0028] The inks as described above furthermore react to chemical agents, solvents or erasers, such as potassium permanganate ink-remover, ball-point pen ink-remover, ethyl alcohol CH₃CH₂OH, Cellosolve H₂H₅OCH₂CH₂OH, 10% sulphuric acid H₂SO₄, 15% hydrochloric acid HCl, 2% caustic soda NaOH, bleach (sodium hypochlorite) NaOCl, or possibly even to erasers, such as for example the erasers used to erase ball-point pens of the Replay type.

[0029] An ink is thus provided which clearly reveals the occurrence of an erasure or of a tampering attempt, since with the magnetic ink it is possible to print a code which, once the modification or erasure attempt has occurred, can no longer be detected by the magnetic reading head according to the types and characteristics described above.

[0030] From what has been described above it can thus be seen that the invention achieves the intended aim and objects, and in particular the fact is stressed that a magnetic ink is provided which allows a considerable printing fineness which is fully comparable with the best inks used for conventional printing.

[0031] The invention thus conceived is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept.

[0032] All the details may furthermore be replaced with other technically equivalent elements.

Claims

1. Delible magnetic ink, particularly for marking documents and the like, characterized in that it comprises a mixture of water, gum arabic, colored pigment and finely ground magnetic material mixed with an easily hydratable vehicle.

2. Delible magnetic ink, according to claim 1, characterized in that said finely ground magnetic material is constituted by ferrite particles with a size of 0.004 mm and a 1/4 ratio.

3. Delible magnetic ink, according to one or more of the preceding claims, characterized in that it further comprises a mineral filler.

4. Delible magnetic ink, according to one or more of the preceding claims, characterized in that it comprises 10/15% water, 30/35% gum arabic, 10/15% colored pigment, 10/15% magnetic material, 10/15% of an easily hydratable vehicle, and a 5/10% mineral filler.

5. Delible magnetic ink, according to one or more of the preceding claims, characterized in that said easily hydratable vehicle is constituted by glycerol.

6. Delible magnetic ink, according to one or more of the preceding claims, characterized in that said easily hydratable vehicle is constituted by sorbitol.

7. Process for producing a delible magnetic ink, as defined in claims 1-6, characterized in that it consists in grinding ferrite of the gamma type with an initial needle-like particle measuring 0.001 by 0.006 mm, with a 1/6 ratio, in a hyperfast colloidal mill with zirconium balls until the particles are reduced to a size of 0.004 mm, with a 1/4 ratio, in mixing the ferrite with an easily hydratable vehicle, in mixing together with colored pigment, gum arabic, water and a mineral filler.

8. Delible magnetic ink, particularly for marking documents and the like, characterized in that it comprises, in a mixture, a non-polar solvent, a grinding vehicle, organic pigments and finely ground magnetic material.

9. Magnetic ink, according to claim 8, characterized in that said non-polar solvent is constituted by high-boiling aliphatic solvents with a boiling interval comprised between 240 and 300^oC with an aromatic compound content of less than 5% and with no polynuclear aromatic compound content.

10. Magnetic ink according to claim 8 or 9, characterized in that said grinding vehicle comprises phenolic resins or cresolformaldehyde mixed in a 25/40 ratio with cross-linking unsaturated polyesters commonly termed alkyd resins, with an oil content comprised between 65 and 80%.

11. Magnetic ink according to one or more of claims 8-10, characterized in that said grinding vehicle is constituted by maleic resins with a melting point comprised between 150 and 170^oC mixed in a 25/40 ratio with cross-linking unsaturated polyesters commonly termed alkyd resins with an oil content comprised between 65 and 80%.

12. Magnetic ink, according to one or more of claims 8-11, characterized in that said organic pigments are constituted by organic pigments derived from dyes for food products laked on barium salts.

13. Magnetic ink, according to one or more of claims 8-12, characterized in that said finely ground magnetic material is constituted by needle-shaped ferrite particles.

14. Magnetic ink according to one or more of claims 8-13, characterized in that it comprises 70 to 63% grinding vehicle, 10 to 12% organic pigment, 15 to 20% finely ground magnetic material, and the remaining percentage of aliphatic solvent in the amount required to reach the viscosity of ink of approximately 200 poises.

15. Process for producing a magnetic ink as defined in claims 8-14, characterized in that it consists in introducing, in a stainless steel boiler equipped with an agitator, 40% phenolic and/or maleic resin and 25% alkyd resin, in raising to a temperature of 200^oC for 30 minutes, in cooling while adding 35% aliphatic solvents, so as to obtain a 500-poise paste, in adding to said paste organic and inorganic pigments until an approximately 500-poise paste is obtained, in grinding the paste in a three-cylinder refining unit so as to obtain a degree of grinding of less than 5 microns, in adding aliphatic solvent until an ink viscosity of 200 poises is obtained.