Abstract:
The present invention relates to a method ( 100 ) for personalizing a document, said document comprising a support comprising printed patterns ( 201, 202 ), wherein said method ( 100 ) comprises generating at least a laser pulse on said support for carbonizing at least a printed pattern.

Description:
FIELD OF THE INVENTION 
     The present invention relates to official documents, such as an ID card, a passport or all laminated documents, and more particularly to methods for personalizing these documents. 
     BACKGROUND 
     Personalization of an official document is generally realized by a laser, which marks personalized elements, such as a name, a social security number, a validity date, etc, on the document body. Because of the value and importance associated with these data carriers, they are often subject of unauthorized copying and forgeries. As a consequence, security is one of the highest challenges for official documents. 
     To prevent counterfeiting activities, an official document must have sufficient observable security features to allow quick visual verification. Security elements such as guilloches are generally used to provide effective protection. Guilloches are precise and intricate repetitive patterns printed with ink on the document body or on specific layers laminated over said body, which prevent forged copies. Micro texts printed with ink all over an area of the document body or overlays can also be used as security elements. Many other security elements exist, such as Moiré patterns or Rainbow printing which is color variation on printed lines. 
     Pattern ink is either a standard ink, or a special ink such as an optical variable ink (OVI) which is an ink whose color changes with the observation angle, an infrared ink or an ultraviolet ink. 
     The printing process is inkjet process printing, offset process printing, flexographic printing, silkscreen printing or rainbow printing. 
     However, security is never optimal because counterfeiters always find how to copy and imitate or duplicate the security elements. Improving security features is a constant need for rendering counterfeiting more and more difficult. 
     SUMMARY 
     It is an object of the invention to describe a method for personalizing an official document, which reinforces the security elements. 
     To this end, the invention provides a method for personalizing a document, said document comprising a support comprising printed patterns, wherein said method comprises generating at least a laser pulse on said support for carbonizing at least a printed pattern. 
     Thus, printed patterns, which are security elements, are affected by the laser. As a consequence, the document is useless for another person: if a counterfeiter would like to erase a personalization element, he has to erase the security elements too, because some printed patterns have carbonized on the support and got a change of color. Thanks to this method, the visual aspect of the personalization of an official document is different: some printed patterns are impacted by the personalization, which is visible naked-eye. The laser dots allow personalizing at the same time the card support and carbonizing the ink which becomes darker than initially. Moreover, carbonization arrives as soon as the printed pattern is touched by the laser dot, which is really fast. The carbonization is then guided into the printed pattern. 
     According to not limited embodiments, the method can comprise one or more of the following additional characteristics:
         patterns are printed by an offset process or an inkjet process.   the patterns ink is an optical variable ink, an ultraviolet ink, or an infrared ink.   the laser is a green laser or an ultraviolet laser.   printed patterns comprise micro characters or micro shapes, and the method comprises a preliminary step of printing said micro characters or micro shapes such that the carbonization reveals a set of micro characters forming a control code.   the pulse power is comprised between 500 W and 50 kW, and the pulse lasts between some nanoseconds to some microseconds.       

     The invention also provides a support comprising printed patterns, wherein at least a printed pattern is carbonized. 
     According to not limited embodiments, the document can comprise one or more of the following additional characteristics:
         the patterns ink is an optical variable ink, an ultraviolet ink, or an infrared ink.   the printed patterns comprise micro characters or micro shapes.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments of apparatus and/or methods in accordance with embodiments of the present invention are now described, by way of example only, and with reference to the accompanying drawings, in which: 
         FIG. 1  shows a flowchart which illustrates a method for personalizing an official document, according to an embodiment of the invention; 
         FIG. 2  schematically illustrates a part of a document comprising printed patterns and a personalization element; 
         FIG. 3  schematically illustrates a part of a document comprising printed patterns and a personalization element; 
         FIG. 4  schematically illustrates an enlargement of the a part of  FIG. 3 ; 
         FIG. 5  schematically explicated the principle of printed pattern carbonization thanks to laser dots. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following description, well-known functions or constructions by the man skilled in the art are not described in detail since they would obscure the invention in unnecessary detail. 
       FIG. 1  is a flowchart illustrating a method  100  for personalizing an official document according to a non limited embodiment of the invention. 
     The method  100  applies to an official document comprising a support comprising printed patterns. Pattern ink is either a standard ink, or a special ink such as an optical variable ink (OVI) which is an ink whose color changes with the observation angle, an infrared ink or an ultraviolet ink. Besides, the printing process is inkjet process printing, offset process printing, flexographic printing, silkscreen printing or rainbow printing. 
     These printed patterns are for example guilloches or micro texts printed all over the support.  FIG. 2  shows an example wherein printed patterns are guilloches  201 , and  FIGS. 3 and 4  shows an example wherein printed patters are micro characters  202  forming a micro text. However, printed patterns can also be micro shapes, for example rectangles, squares or circles, Moiré pattern or changing patterns. 
     It is to be noted that the printed patterns are reproduced on an area of the support or on the whole surface of the support. The printed patterns are defined by their form, and possibly comprise information, for example an alphanumerical symbol. 
     The method  100  comprises:
         A first step  101  of selecting a high-powered laser, for example a green laser or an UV laser.   A second step  102  of selecting a pulse power for this laser, able to activate the auto-carbonization of the ink.   A third step  103  of marking a personalization element on the support by means of successive laser pulses, the laser selected in the first step working at the pulse power selected in the second step. It is to be noted that the marking is generally realized through a transparent overlay laminated over the support. The laser pulse is activated during a few nanoseconds, for example ten nanoseconds, to the peak power of several kilowatts, for example two kilowatts.       

     With this enough powerful laser pulse, if an area comprising ink is touched by at least a laser dot, the ink start to carbonize and the carbonization propagates in the pattern. The carbonization does not impact the areas of the support which do not carry any ink. As a consequence, some printed patterns become darker than initially. The carbonized printed patterns are kind of supplementary security elements for the official document: personalization elements are linked to printed patterns. 
       FIG. 2  shows four “8A” characters  203 , which are example of personalization elements. It is to be noted that the guilloches  201  are carbonized around the “8A” characters  203 . The carbonization is represented by widening the guilloche line more than reality for rendering them visible on a black and white drawing. Indeed, the ink of the guilloches  201  has reacted to the laser pulse, and has carbonized. The carbonization has spread around the laser personalization area. It is to be noted that the carbonization can spread differently into the guilloches  201  for the “8A” characters  203 , depending of the pulse power. Indeed, the pulse power necessary for causing carbonization is specific to ink reactivity. Reproducing the same laser power for causing carbonization is not so easy and that also constitute a security against modification of a document. 
       FIG. 3  shows a “CHRSET 16” inscription  204  which is an example of a personalization element, and  FIG. 4  is an enlargement of the “C” letter  205  of the “CHRSET 16” inscription  204 . It is to be noted that all micro characters  202  whose a part is located on the laser dots forming the “C” letter  205  are carbonized, as it is schematically explained in  FIG. 5 . The other micro characters  202  are not carbonized.  FIG. 5  shows three “A” micro letters  206 , one of which is carbonized because it has an intersection with a laser dot. 
     Indeed, the ink of this micro character  206  has crossed a laser dot, and has reacted to the laser pulse. As a consequence, the micro character  206  has carbonized completely. The carbonization has then spread in the micro character  206  fully. 
     Moreover, in a not limited embodiment, the method  100  can comprise a supplementary step of determining some micro characters to carbonize. The determination is realized through an algorithm, and letters are reached by the laser thanks to a camera and a set of mirrors. This allows hiding some messages in the micro text, carbonized micro characters appearing randomly burned for a person who does not know the algorithm.