EP1447234A1 - Printing process on a security element and security element - Google Patents

Abstract

The process involves printing a semi-transparent security unit (2) with variable optical ink on a base (1) of a substrate. The security unit is printed to cover the base. The semi-transparent security unit is printed by a serigraphy process. A sifter utilized in the serigraphy process comprises 180 to 230 lines per inch according to X and Y directions of the sifter. An independent claim is also included for a value-paper.

Description

The present invention relates to a method of printing a security element for securities, such as bank notes, checks, credit cards, passports or identity documents and other similar documents.

The present invention also relates to a security element for securities, such as bank notes, passports, identity documents and Similar.

In the area of securities, in particular banknotes, there is a increasing need for security elements as protection against counterfeiting. In in recent years computers, scanners and photocopiers have suffered significant technical improvements and it is currently possible to buy devices very efficient at reasonable prices. As these devices have become very efficient, it has become necessary to develop new security elements, themselves also more efficient, for securities, such as banknotes bank, checks, credit cards, passports or identity documents and other similar documents in order to protect these documents against counterfeiting and prevent them from being copied by computers, scanners and photocopiers current.

Such security features use, for example, specific inks such as optically variable inks ("OVI" ®) and other inks with properties iridescent, these inks being used to print patterns or geometric shapes particular on the value paper substrate, optically variable elements ("OVD" ®) in the form of metallic patches (called "foils") or holograms, and also moire and other similar patterns, all of which are, on the one hand, very difficult even impossible to copy with current devices but, on the other hand, very easy to check visually or with the naked eye.

Other security features are formed by overlay combinations of lines and / or patterns with colors, which are only visible under certain conditions, for example UV light or transparency. Again, the interest of such security features is that they are easy to print or place on the document to be protected and they can be controlled by simple devices, even by eye naked, but they are impossible to reproduce with printers, scanners and current photocopiers.

For example, US Patent 6,050,606, incorporated by reference herein request, describes a security element for securities, for example for Bank notes. This security element is formed by a bottom having at least two juxtaposed regions, each region having its own geometric designs, said regions having a different color density. The security feature includes additionally a pattern corresponding to the region with the lowest color density which is printed superimposed on said region in a color chosen so as to compensate for the difference in color density between said two regions. So, the security element appears uniform and without pattern to the naked eye, but the pattern appears clearly when photocopying said item.

US Patent 5,443,579, incorporated by reference in the present application, describes a another method of printing a latent image on a substrate. According to this patent, combines the printing of raised lines with lines without relief. So, we create a latent color image that cannot be reproduced with a photocopier or other photomechanical processes.

US Patents 5,853,197 and US 5,487,567, incorporated by reference herein request, show security features that are not easily visible to the eye naked, but which, on the other hand, become clearly apparent during a reproduction of the item by photocopying or scanning.

Another specific technique uses watermarks in which the substrate, for example of paper, is marked with lines or a pattern that are only visible in transparency. A development of this technique concerns pseudo-watermarks formed by the creation of a window in the substrate, technique used in particular with paper substrates which themselves are not normally transparent, said window being transparent.

US Patent 6,082,778, the content of which is incorporated by reference herein request, describes an identity card protected against unauthorized copying by copiers. In this patent, the idea is to create a security element by combining the protective effect provided by a thin metal film with the physical properties, in particular optical, of an additional layer whose combination of effects prevents reproduction of the card. Under a transparent cover layer, there is a layer of metal over a layer having specific optical properties. In a first embodiment, the metal layer is demetallized locally thus exposing the layer with specific optical properties, i.e. making it visible in the demetallized zone. The difference in contrast between the layers makes them marks formed by demetallization easy to recognize with the naked eye. In a mode of particular execution, the layer having specific optical properties has a dark color, for example black. The combination of direct reflection of the area metallized and a layer with high absorption (black layer) prevents contrast difference detection so that the information formed by the demetallization disappears completely on a copy of this security element.

According to other techniques known in the state of the art, a laser is used either to mark the substrate directly, either to mark a layer applied to said substrate and thus create security elements impossible to reproduce by photocopying or scan.

An object of the invention is to define an improved printing method for an element security used in particular on securities.

Another object of the invention is to create a security element for securities improving the elements already known and requiring a simple and easy to put process in action.

Another object of the invention is to provide a very security element difficult to copy and counterfeit with modern standard scanners and photocopiers and other equivalent devices but which can be easily printed with the means current printing.

To this end, the method according to the invention is defined by the steps of claims 1 to 5 and the security element according to the invention is defined by the characteristics of the claims 6 to 9.

The description of several embodiments and the figures relating thereto will allow to better understand the invention.

Figure 1 shows a block diagram of the printing process forming an element of security according to the invention.

FIG. 2 shows a first embodiment of a security element according to the invention.

FIG. 3 shows a second embodiment of a security element according to the invention.

Figure 4 shows a security paper with a security element according to the invention.

In Figure 1, there is shown an embodiment of the method according to the invention under form of block diagram. In the first step, we first print a background on the substrate, for example using an offset process known in the state of the art. The background can be monochrome or polychrome, such printing can be performed by the methods known from the state of the art. According to this process, the pattern which will be printed is transferred from an offset plate cylinder inked by ink rollers on a blanket cylinder which in turn transfers the pattern to the substrate, by example of paper. The patent application FR 2 222 214 describes a process offset printing machine and an offset printing machine. The content of this request, in in particular the part concerning offset printing is incorporated by reference in the this request. As another example, US Patent 6,101,939, the content of which is incorporated by reference into the present application, describes another printing machine using the offset process. This background, can extend to the entire surface of the value paper or be limited to a particular area of it.

Over the printing of said background, a semi-transparent pattern is then printed on the using an appropriate printing process using optically variable ink. Such inks which have iridescent properties, contain metal particles and are generally applied in the form of an opaque pattern on securities, said pattern forming a security element. Indeed, due to the presence of particles of metal, these patterns formed from optically variable ink change color depending on the angle from which they are viewed, the colors depending on both the color ink itself and metal particles. Such inks are particularly efficient to form security elements because it is not possible to reproduce the iridescence effect with color photocopiers or scanners: when copying, the pattern formed from optically variable ink notably loses its iridescence properties so a copy is easy to identify with the naked eye.

Preferably, the semi-transparent pattern in optically variable ink is printed by a screen printing process. Such a printing process is known in itself in the state of technique. According to this process, the pattern to be printed is formed by a sieve through which ink is applied to the substrate, for example security paper. For a positive printing, the sieve holes are closed outside the pattern, so that the ink passes through the screen to form the pattern itself on the substrate, while for a negative print, the holes corresponding to the pattern are closed and the ink marks the outline of the pattern, the pattern itself being created by the absence of ink on the substrate. For example, US patents 6,109,172 and US 5,671,671, including the contents describing screen printing machines. are incorporated by reference to the this request.

In the context of the present invention, a determined printing process is combined, for example a screen printing process as described above and in the US patents mentioned, with optically variable ink but the fineness of the screen for screen printing, i.e. the size of the sieve holes, is chosen so that the pattern created in screen printing with optically variable ink is semi-transparent. So, on the one hand, we see the background printed on the substrate through the semi-transparent pattern in optically variable ink, however, on the other hand, said pattern being formed in optically variable ink, it retains iridescent properties due to optically variable ink. We therefore combine two very specific optical effects difficult to reproduce satisfactorily: on the one hand semi-transparency and on the other apart from the iridescence of the optically variable ink. In addition, we get a combination at least three superimposed colors (the background color and the two ink colors optically variable) which varies according to the angle of view of the pattern, the whole then forming a particularly effective security element.

In the case of a screen printing process, the fineness of the screen is of the order of 180 to 230 lines per inch, in each X and Y direction of the screen. Preferably, we chooses a fineness of the order of 230 lines per inch. Of course, we can adapt the fineness of the screen as a function of the optically variable ink used and in particular of the size of the metal particles contained in said ink, the aim being to obtain a semi-transparent printing with optically variable ink. Optimizing these parameters can of course be done by simple printing tests to adjust the size of the holes and consequently the quantity of ink deposited during the impression to achieve the desired effect.

Other printing methods allowing the deposit of a semi-transparent pattern in ink optically variable are of course possible, in particular a gravure process or a flexographic process, and the present invention is not limited to screen printing, the aim, as indicated above, being to obtain a semi-transparent pattern with optically variable ink. These methods are known in the state of the art. technique, for example from the publication DE 35 35 993 for flexography.

In the case of a gravure process, a printer form is preferably used having a fineness of weft of the order of 60 to 120 lines per centimeter whose angle of weft can vary from 0 ° to 75 ° and the depth of the engraved cells is between 10 microns and 50 microns. These parameters can of course be adapted according to the type of optically variable ink used and the degree of transparency desired get. The adjustment of these parameters can in particular be done by tests comparative.

In the case of a flexographic printing process an anylox cylinder is used having a linearity of the order of 100 to 120 lines per centimeter, the depth of which cells is between 30 microns and 50 microns. Parameters can be adapted depending on the type of optically variable ink used and the degree of transparency that is wants to get.

In the third step of the process which is optional, we then proceed to a step dry embossing of the security element. This step allows you to form a pattern additional and in relief in the security element created by the overlay of the bottom and semi-transparent printing, a relief motif which is of course also impossible to reproduce by photocopying or scanning. To carry out this embossing, a conventional intaglio process can be used in the printing field, omitting the use of ink to obtain a dry embossing. This pattern is also only visible according to a particular viewing angle of the security element, he who, in such an embodiment, combines effects of color, iridescence and a tactile effect by the relief motif.

A security element according to the invention is described with reference to Figures 2 to 4.

FIG. 2 shows a security element according to the invention with a bottom 1, printed by example in offset, and which includes the alphanumeric characters "2000" placed the next to each other. Over this background, we printed a pattern 2 in semi-transparency with optically variable ink. Although optically variable ink is used for pattern 2, which is normally opaque due to the ink optically variable, the process for printing pattern 2 is such that said pattern is semi-transparent, so that the background 1 is visible through the pattern 2. As shown above, a process that can be used to create the semi-transparent pattern with optically variable ink is a screen printing process in which the screen has a particular finesse, namely from 180 to 230 lines per inch.

A pattern is thus obtained having both the properties of a pattern printed with the optically variable ink and having in addition a semi-transparent effect allowing to see the background on which it is printed.

In Figure 3, we have highlighted the different elements making up the element of security according to the invention in a particular embodiment. There is always the bottom 1 with the characters "2000" repeated regularly, then we distinguish the motif 2 semi-transparent in optically variable ink through which we can see the background characters thanks to the semi-transparent effect. There is also a pattern in relief 3, in this case a face, which has been formed, for example, by embossing security element.

This adds a degree of security to the element, in that not only is it semi-transparent, it has the characteristics of an ink security element optically variable, but in addition we add a relief by dry embossing, all these various properties being very difficult, if not impossible, to reproduce with a modern photocopier or scanner.

In Figure 4, a value paper 4 is shown by way of example with an element of security according to the invention. This 4 value paper, in this case, a bank note schematic, has in its lower corner a security element with a bottom 1, a semi-transparent pattern 2 in optically variable ink and a dry embossing 3 such as shown with reference to Figure 3 of this application. It should be noted that the background 1 can extend over the entire surface of the security paper.

In addition, other printing techniques can be used to print the background 1 and motif 2, the important thing for motif 2 being to present both the characteristics an optically variable ink pattern and a semi-transparent effect.

Claims (10)

Method for printing a security element for securities, such as banknotes and other similar documents, on a substrate, characterized by the following steps: printing of a background on the substrate; semi-transparent printing of a pattern with optically variable ink, said pattern at least partially covering said background. Method according to claim 1, characterized in that the semi-transparent pattern is printed by a screen printing process, or a flexographic process or even by gravure printing. Method according to claim 2, characterized in that the screen used in the screen printing process comprises approximately 180 to 230 lines per inch in the X and Y directions of said screen. Method according to one of claims 1 to 3, characterized in that the background is printed by a monochrome or polychrome offset process. Method according to one of the preceding claims, characterized in that it comprises a step of dry embossing of the security element. Security element for securities, such as banknotes and other similar documents, placed on a substrate, said security element being characterized by a printed background (1) on the substrate, by a pattern (2) covering at least partially said background, said pattern being semi-transparent and formed by optically variable ink so as to leave visible said background (1). Security element according to claim 6, characterized in that the bottom (1) is offset printing. Security element according to claim 6 or 7, characterized in that the pattern (2) is in screen printing, or in flexographic printing or rotogravure. Security element according to one of claims 6 to 8, characterized in that it further comprises a dry embossing (3). Value paper (4), in particular bank note or other similar document, characterized in that it comprises a security element according to one of claims 6 to 9.

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