EP2303589B1 - Securing of a printed image using a laser beam - Google Patents

Description

The present invention relates to securing a printed image by means of a laser beam.

The invention lies in the field of identification documents chip or without chip, such as driving licenses, identity cards, membership cards, access badges, passports, bank cards, electronic purses, multi-application cards and other valuable papers. Because of the value and importance associated with each of these documents, they are often subject to unauthorized copies, alterations, modifications, and counterfeits.

The invention aims more particularly at securing personalization information registered on any type of medium, so as to avoid any subsequent fraudulent modification of this information.

On the Figures 1 and 2 a customizable support 1, for example an identity card, comprising a body 2 provided, on a top face 3, personalization information 4, 6, 7 official relating to the card holder. This personalization information is reported via a graphical personalization means, for example YAG laser type. The card 1 comprises a card body 2, made of an opaque plastic material, for example of the polycarbonate, PET and / or ABS or PVC type. A transparent protective layer 5, also called "overlay" in the jargon of the cards, is advantageously fixed on at least one face of the card body. The card body 2 is designed to be provided on its upper face 3 with personalization information 4. Generally and by way of example, the personalization information 4 shown on the card body 2 comprises, with reference to the figure 2 , the photographic representation 6 of the holder of the card and alphanumeric characters 7 relating to the identity of the holder. In the example of the figure 2 to better visualize the invention, it is simply a detail (in this case the eye) enlarged of the photo of the holder. The personalization data 7 and the photograph 6 are, for example, written on the surface 3 of the card body by means of a laser beam, by burning the surface of the card body. The local discoloration of the resulting surface depends on the available energy, the inscription time as well as the material of the card body used. In other embodiments, the customization may be made directly in the transparent protective layer 5. In this case, the material used for the transparent protective layer 5 is a material doped with carbon particles which blacken under the action of a laser beam. Anyway, such customization made on the surface of the card body or in the transparent protective layer, is called official personalization in the rest of this document, as opposed to unofficial or fraudulent personalization, made in view to falsify a document or create a false document.

These personalized media are being used more and more, as an identity card or as a passport for example. Because of their intensive use and the sensitive nature of identity checks, they must be designed so as to be protected against any attempt at tampering or tampering with as high a degree of security as possible.

To meet this requirement, it is known to add, on the personalization information, curved lines, also called "guilloches". However, even if the guilloches form more or less complex diagrams, they remain predictable and always transposable from one medium to another. It is therefore possible, with a pattern of conventional guilloches to analyze the network of guilloches of a support, and thus prepare a falsification of customization information that avoids printing on the guilloches in question.

There are other techniques of creating security elements by making micro perforations in the body of the support, said micro-perforations reproducing the personalization information, such as the photograph of the holder of the medium for example, so as to authenticate the photo of the owner. For this, a laser technology is used to create the micro-perforations through the thickness of the support body, the perforations being arranged to form an image that becomes clearly visible to the naked eye when the document is illuminated, thus allowing easy verification. This technology, however, requires an additional step of reproducing identically, and therefore very accurately, personalization information by laser perforation. Such a solution is therefore long and complex to implement, and therefore relatively expensive.

Finally, the patent application EP1 747 897 describes a method for securing an image by converting the data of the image to be secured into character data. The characters are then printed, respecting the dark and light areas and maintaining the shape of the image, by means of a laser, on the surface of the medium to be printed. This solution requires means of image processing and complicated calculations and consumers of time, and therefore expensive.

Other laser marking techniques are disclosed in the documents EP-A-1,876,028 , US Patent 5,767,483 and US-2003 / 063.390 .

Also, the technical problem of the present invention consists in proposing a simple and inexpensive alternative to existing solutions, to effectively secure a printed image by means of a laser beam, which would make it possible to overcome the use of complex calculations, expensive, and time consuming.

The solution to the technical problem raised is obtained, according to the present invention, by the fact that the security method comprises a step consisting in arranging a lens on the path of the laser beam, upstream or downstream of a focusing device, in such a way that altering the shape of the laser beam and imparting the resulting printed pixels with a specific shape.

Thus, the printed pixels are no longer of conventional round or oval shape, but they have a specific shape, related to the structure of the lens used to deform the laser beam. It is therefore impossible to reproduce the shape of the pixels without having the corresponding specific lens. Therefore, any addition or modification of an image printed and secured in this way is very easy and quick to detect, by means of a simple magnifying glass for example. Indeed, in this case all the added pixels have a shape different from the original pixels.

The invention also relates to the use of a lens for securing a printed image by means of a laser beam, said lens being placed upstream or downstream of a beam focusing device, so as to deform the beam and imparting the resulting printed pixels with a particular shape.

Through the use of such a lens, the printing of the image is very fast since it does not require the use of any means of calculation.

• la figure 1, déjà décrite, un schéma en coupe d'un support personnalisable, de type carte, comprenant des informations de personnalisation,
• la figure 2, déjà décrite, un schéma d'une vue de dessus du support personnalisable de la figure 1,
• la figure 3, un schéma d'une vue de dessus d'un support personnalisable comprenant des informations de personnalisation sécurisées selon la présente invention,
• la figure 4, une vue agrandie d'un détail de l'image imprimée et sécurisée du support de la figure 3,
• la figure 5, un schéma du dispositif utilisé pour l'impression d'une telle image sécurisée.

Other features and advantages of the invention will appear on reading the following description given by way of illustrative and non-limiting example, with reference to the appended figures which represent:

• the figure 1 , already described, a sectional diagram of a customizable support, of card type, including personalization information,
• the figure 2 , already described, a diagram of a top view of the customizable support of the figure 1 ,
• the figure 3 a diagram of a top view of a customizable medium including secure personalization information according to the present invention,
• the figure 4 , an enlarged view of a detail of the printed and secured image of the support of the figure 3 ,
• the figure 5 , a diagram of the device used for printing such a secure image.

The figure 3 illustrates a customizable support 1 ', provided on one side with information printed in a secure manner. In this figure, the medium is represented in card format, but it is not limited to this format and can be in any other form. In fact, the invention applies to any printable medium by means of a laser beam, it can therefore be a card-size medium, as well as a passport-type booklet medium or any other single-sheet type medium. paper, cardboard, plastic etc.

The support 1 'of the figure 3 includes the photographic representation 6 'of the card holder, and alphanumeric characters 7' relating to the identity of the holder. All these data relating to the identity of the holder of the support are printed, in a conventional manner, by means of a laser beam. In the example of the figure 3 , to better visualize the invention, the photographic representation 6 'shown is simply a detail (in this case the eye) enlarged photo holder. A detail of this even larger eye is represented on the figure 4 . This detail makes it possible to visualize the particular shape of the printed pixels. Conventionally, when an image is printed by means of a laser beam, the pixels of the image are round or oval in shape. The shape-specific pixels 61-64 as illustrated on the figure 4 are achieved by using a specific diffractive lens in the path of the laser beam, the structure of which makes it possible to modify the shape of the laser beam and to give a specific shape to the resulting printed pixels. Modifying the shape of the printed pixels makes it possible to secure the image, since any attempt to fraudulently modify the image is immediately visible. Indeed, without the use of the specific lens, it is impossible to create pixels of the same shape.

In the example of the figure 4 , pixels 61-64 are in the form of a square, each corner is truncated, and comprising a notch on one side. Of course, this form is only an illustrative example. Pixels can take any shape more or less complex and difficult to reproduce easily. Thus, they may be in the form of a logo, a drawing of any shape, or a sequence of alphanumeric characters, or a map of a country, with an anomaly to further increase the with denser areas or points representing cities or rivers for example etc ... The shape of the pixels depends in fact on the structure of the lens used to deform the laser beam.

The figure 5 illustrates, very schematically, the device used to print a secure image according to the invention. A laser cavity 51 is used to create a laser beam 52, of cylindrical shape 60. In the path of the laser beam 52, upstream of the focusing device 56, or downstream, there is a diffractive lens 55 of specific structure. This lens makes it possible to modify the shape of the laser beam 52 which, after focusing 57, makes it possible to print pixels of specific shape 61 on a printable medium 10.

The lens 55 may be arranged upstream or downstream of the focusing device 56. In a preferred embodiment, it is placed upstream of the focusing device because the lens has a natural tendency to cause diffraction of the laser beam, that it is necessary to concentrate then to be able to obtain a pixel.

Preferably, the laser system used has a short focal length and emits in a range of short wavelengths. This may for example be an excimer laser, emitting in the ultraviolet, typically between 200 and 400 nm, for example around 355 nm. This type of laser makes it possible to print an image of better quality, with less interference, than a type YAG laser, monomode for example. However, the use of a Yag laser does not preclude also being able to obtain good results with a longer wavelength.

According to an alternative embodiment, it is also possible to increase the degree of security of the printed image by driving the lens in rotation, in the context of a positioning of the latter upstream of the focusing device, during of laser printing. This rotation drive can be achieved by means of a slave motor for example, and controlled by the same control unit for controlling the printing. Rotating the lens makes it possible to print pixels of the same shape but oriented differently relative to each other. The result of such an impression is clearly visible on the figure 4 . Indeed, in this figure, the pixels are rotated at different angles. In the example of the figure 4 , there are thus four different positions 61-64 pixels. Of course this is just a simple example where the pixels are rotated at an angle of 90 ° to each other. This example is in no way limiting and the pixels can be rotated relative to each other by an angle between 0 and 360 °. These angles depend essentially on the speed of rotation of the lens.

The rotational speed of the lens is thus predefined so that the pixels are printed with a predefined angle.

With this variant, it is therefore possible to introduce a code inside the image and therefore, to make it even more difficult to falsify or subsequently fraudulent modification.

To further increase the degree of security of the printed image, it is possible to drive the rotating lens, during laser printing, with a predetermined speed and variable over time.

The code thus introduced into the image can then be decrypted by means of a reading device comprising suitable image processing means.

In the context of a positioning of the diffractive lens downstream of the focusing device, the quality of the image obtained will be somewhat reduced, because of the diffraction of the beam on a part of the lens and the need to focus the beam. customization element on the support. The size, shape and orientation of each pixel being defined by the part of the lens used in the area of the customization defined, it is then difficult to rotate the latter to generate a variable code.

Claims (4)

1. A method for securing an image printed by means of a laser beam (52), comprising a step consisting in placing a lens (55) on the path of the laser beam, before or after a focussing device (56), so as to modify the shape of the laser beam and give the resulting printed pixels (61-64) a specific shape, characterised in that it comprises an additional step, as part of the positioning of the lens (55) before the focussing device (56), consisting in making the lens rotate at a predetermined speed during the printing process, so as to print the pixels with a specific shape and turn them in relation to each other at a predefined angle.
2. A method according to claim 1, wherein the rotation speed of the lens varies over time.
3. A method according to any of claims 1 to 2, in which the laser used emits in the ultraviolet wavelength range.
4. Use of a diffractive lens (55) to secure an image printed with a laser beam (52), wherein said lens is placed before or after a beam focussing device (56) and is made to rotate, so as to deform the beam and give the resulting printed pixels (61- 64) a specific shape.

Images