EP0317514B1 - Process for producing a document of which at least a part is not reproducible by means of photocopying - Google Patents

Description

The subject of the present invention is a method of manufacturing a document at least part of which is not reproducible by photocopying, comprising a support and alphanumeric or graphic information carried by this support, in which the surface of the support is formed in said non-reproducible part of the document, adjacent areas by depositing a continuous background layer of dark color, then a discontinuous layer forming said alphanumeric or graphic information.

A document comprising a medium, for example a film or a paper, bearing alphanumeric or graphic information, prepared by manual writing, typewriter, photocopying, printing, telex or facsimile, can be reproduced by a large number of photocopy without the knowledge of the information holder. Illegal copying of documents is becoming increasingly common in the economic, scientific, political or military fields and can result in irreparable financial or moral harm.

Efforts to protect against forgery and counterfeiting of payment documents and official documents such as paper money, checks, cash vouchers, identity cards and passports have led to technical solutions based on use of watermarks, threads, fibers and colored, metallized or magnetizable boards. A technique in this field is described in patent GB 1,127,043. The security papers prepared according to these methods prevent correct reproduction by color photocopying, because the aforementioned technical means are not reproducible in this way, but they protect little or no documents against ordinary black and white photocopying. For its part, publication FR-A-2 429 292 describes a security paper provided with a layer comprising an iridescent substance as a security agent, with the aim of protecting against the falsification and counterfeiting of payment documents and documents official by reproduction with color photocopiers. As the iridescent substance gives optical effects such as changes in reflections, tints or shades depending on the angle of observation and these color effects cannot be reproduced by any photocopying system, an imitation or counterfeiting of the document does not is not possible. On the other hand, by means of an ordinary photocopier one can obtain copies in black and white which are completely readable.

In order to prevent the obtaining of legible copies, various processes, products and devices for prohibiting the reproduction of documents have been patented and sometimes marketed, such as, for example, a cocoa-colored coated paper produced by Calspan and Ludlow. Paper Co., Needham Heigts, Mass., USA. US Patent 3,597,082 relates to photochromatic pigments to avoid photocopying. Patent FR 2 177 292 issued to IBM recommends the use of special inks printed on a masking background. The publication FR-A-2,565,268 describes a non-photocopiable printing medium having a base layer produced using ink containing bronze particles capable of reflecting light specularly. The photocopy of a black print on this support is illegible. However, this protection can easily be bypassed if such a document is placed in a translucent plastic folder: the light scattering effect of the translucent folder eliminates the specular nature of the surface of this document and makes it possible to obtain legible photocopies of the document. GB-A-2 143 774 relates to a self-adhesive film intended to be applied to documents to protect them against photocopying. This product is composed of a mass-colored film and a semi-transparent metal layer deposited by vacuum metallization. This self-adhesive film gives good protection against photocopying. On the other hand, the weak contrast between the dark color of the background and the text constitutes a serious obstacle to the readability of the document. In addition, the use of a semi-transparent metal layer makes it difficult and expensive to manufacture this protective film. The company Nocopi International Inc. presented a security paper that cannot be reproduced by photocopying, based on a composition of dyes of dark colors covering the sensitivity spectrum of modern photocopiers. Again, the readability of an original printed in black on such paper is quite poor because of the low contrast between the adjacent areas. Consequently, the known security papers are expensive to manufacture or of limited application, or of poor quality as regards the contrast making it possible to read the document.

The object of the present invention is to provide a simple and economical process for the production of documents which, while having good contrast for the human eye, cannot be reproduced in the form of legible photocopies, even by black photocopying. and white, in particular by means of office reproduction apparatus.

According to a first aspect, the present invention relates to a method of the type indicated in the preamble, in which the discontinuous layer is dark, for example a black print, the method being characterized in that a layer containing at least one iridescent substance is applied. on the dark colored base layer, before depositing said discontinuous layer.

According to a second aspect, the invention relates to a method of the type indicated in the preamble, characterized in that said discontinuous layer, deposited on the dark-colored base layer, contains at least one iridescent substance.

The present invention is based on the discovery, during the search for the solution to the problem posed by the production of a document of which it is not possible to make a legible photocopy, only by photocopying a layer containing one or more iridescent substances and deposited on a dark layer, a black copy is always obtained, whatever the level of brightness, although the surface containing the iridescent substance (s) is colored. Thus, by juxtaposing dark colored ranges and ranges containing such iridescent substances, images can be formed with good contrast for the human eye, but which, photocopied, give a continuous black surface, without image discernible to the human eye.

By iridescent substance is meant a substance which, according to the principle of light diffraction by thin layers, causes, depending on the angle of observation, reflections whose colors cover the rainbow spectrum of decomposed white light. As iridescent substances which are suitable, mention may be made of pearlescent pigments composed of thin platelets of mica coated with a thin layer of titanium dioxide. Interference colors are formed by refraction and reflection of light on the layer of titanium dioxide with a high refractive index. Each colored shade results from a defined thickness of the layer of titanium dioxide. The successive coating of the mica with titanium dioxide and an additional dye, such as iron oxide (III) or chromium oxide (III) leads to iridescent pigments with bright colored effects combining the action pearlescent pigment and coloring pigment. Such pigments allow metallic effects to be achieved without being exposed to the disadvantages of metals or their alloys. The particle size range determines the effect. Large particles give a glittery effect, while finer particles give a rather silky luster. Among the iridescent pigments we can cite, for example, the Irodins manufactured by E.Merck, D-6100 Darmstadt, and the Merlin Luster Pigments manufactured by The Mearl Corporation, New York, NY, USA .

Layers containing one or more iridescent substances can be prepared according to techniques known in the printing and coating field, for example, gravure printing, offset printing or coating with Mayerbar. in the form of a single layer over the entire surface of the non-reproducible part of the document, either in the form of alphanumeric or graphic information. It is also possible to deposit the layers containing at least one substance iridescent in the form of a frame or any other motif.

The dark colored layers can be deposited by known techniques, in most cases in the form of alpha-numeric or graphic information, for example by manual or mechanical writing, or even by printing, such as offset or Gravure printing. Dark layers can also be formed by non-mechanical printing, such as inkjet, laser printer, photocopying or thermal transfer. They can also be deposited by chemical reaction, such as whether found in silver photography, diazotic images or carbon-free chemical papers. More information on these chemical processes can be found in GB 1 298 194, US 4,137,084 and US 4,162,165.

Figures 1 and 2 schematically illustrate, by way of nonlimiting examples, two of the possible modes of implementing the method according to the present invention.

FIG. 1 represents, in section, a part of the part which cannot be reproduced by photocopying a document obtained by a first mode of implementation of the method. This mode consists in depositing on a support 1, white or colored, first a single layer 4, of dark color, on which a single layer 2 is then deposited containing at least one iridescent substance and, on it, layers 3 of dark color, in the form of desired alpha-numeric or graphic information. The presence of layer 4 enhances the effect of the iridescent substance or substances contained in layer 2, so that a photocopy of the document thus obtained will be entirely dark.

FIG. 2 represents, in section, a part of the part which cannot be reproduced by photocopying a document obtained by a second mode of implementation of the method. This mode consists in depositing on a support 1, white or colored, a single layer 4, dark in color, then deposit, on this layer 4, layers 3 containing at least one iridescent substance, in the form of desired alpha-numeric or graphic information. In this case, the layers 3 are formed by printing at using ink comprising at least one iridescent pigment. They can also be formed by xerography, each by means of a layer of powder toner onto which the layer containing at least one iridescent substance is thermally transferred, from a special film. transfer process is marketed by Omnicrom Systems Ltd., GB- Bolton. Photocopying a document obtained by this mode of implementation of the process gives a black surface without image trace. On the other hand, the information represented by the ranges 3 appear with the colors specific to iridescent pigments when they receive ambient light at an angle less than the critical angle and are therefore clearly legible on the dark background 4.

Claims (4)

1. A method of producing a document of which at least a portion is unreproducible by photocopying, comprising a carrier sheet (1) and alphanumeric or graphical information carried by said sheet, wherein on the surface of the carrier sheet (1), within said unreproducible portion of the document, adjacent areas are formed by depositing a continuous background layer (4) of a dark colour, then a dark discontinuous layer (3) forming said alphanumeric or graphical information, characterised in that a layer (2) comprising at least one iridescent substance is applied onto the background layer (4) of a dark colour before deposition of said discontinuous layer (3).

2. A method of producing a document of which at least a portion is unreproducible by photocopying, comprising a carrier sheet (1) and alphanumeric or graphical information carried by said sheet, wherein on the surface of the carrier sheet (1), within said unreproducible portion of the document, adjacent areas are formed by depositing a continuous background layer (4) of a dark colour, then a discontinuous layer (3) forming said alphanumeric or graphical information, characterised in that said discontinuous layer (3) which is deposited on the background layer (4) of a dark colour comprises at least one iridescent substance.

3. A method according to claim 2, characterised in that the continuous layer (4) is applied immediately onto the carrier sheet (1), then the discontinuous layer (3) is applied immediately onto the continuous layer (4) .

4. A document produced by a method according to any one of the preceding claims.

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