(19) & (11) EP 2 174 797 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.: 14.04.2010 Bulletin 2010/15 B42D 15/00 (2006.01) B42D 15/10 (2006.01) B41M 5/24 (2006.01) B41M 3/14 (2006.01) (21) Application number: 08017527.6 (22) Date of filing: 07.10.2008 (84) Designated Contracting States: • Klein, Sylke AT BE BG CH CY CZ DE DK EE ES FI FR GB GR 64380 Rossdorf (DE) HR HU IE IS IT LI LT LU LV MC MT NL NO PL PT • Montag, Heidemarie RO SE SI SK TR 64289 Darmstadt (DE) Designated Extension States: AL BA MK RS (74) Representative: Luderschmidt, Schüler & Partner Patentanwälte (71) Applicant: European Central Bank John-F.-Kennedy-Strasse 4 60311 Frankfurt am Main (DE) 65189 Wiesbaden (DE) (72) Inventors: • Arrieta, Antonio Jesús 60311 Frankfurt am Main (DE) (54) Laser-marked document showing a colour-shift effect (57) Document comprising a coating containing at the coated area with a pulsed laser beam at a rate of least one sort of effect pigments, wherein said document greater than 500 mm/s and a laser mark having a colour also comprises at least one laser mark having a high shift effect is obtained. contrast and a strong colour shift effect The authenticity of the document can be easily Said document is obtainable by a process, wherein, checked by visual inspection from different viewing an- a document comprising a coating containing at least one gles. sort of effectpigments which show differentcolours under different viewing angles is treated on at least a part of EP 2 174 797 A1 Printed by Jouve, 75001 PARIS (FR) EP 2 174 797 A1 Description BACKGROUND OF THE INVENTION 5 1. Field of the invention [0001] The present invention relates to a process for the manufacture of laser- marked documents, preferably security documents, such as banknotes, passports, chequebooks, etc, which show a colour-shift effect. 10 2. Description of the Related Art [0002] The use of self-authenticating security features for producing documents serves for protecting them against unauthorized reproduction by forgers. This is necessary, in particular, for securities such as banknotes, checks, traveller’s checks, stocks, etc. There is also a need for security papers which do not have a direct monetary value, such as 15 identification papers, passports etc., against unauthorized copying. [0003] In particular, in the case of securities, which are circulated daily, for example, banknotes, a forger may succeed in copying the optically recorded document contents, for example, the optical printed image of the banknotes, in a deceptively precise way. A protection against this is the authenticity feature contained in the security paper, used for producing the documents, as a result of the structure imparted to the security paper during manufacture which authenticity 20 feature supposedly practically cannot be copied by a forger with the means available to him. Moreover, the application of watermarks or the introduction of a security thread into the paper is known. These conventional measures, however, can no longer be considered totally satisfactory in view of the advances of the working means employed by forgers. [0004] One possible way to overcome this problem can be seen in the use of pearlescent coatings since the angle- dependent optical effects obtained from pearlescent pigments cannot be easily copied with photocopier machines or 25 photographic techniques making forging much more complicated and expensive. [0005] Furthermore the interactions between coated substrates (paper, board, film, laminate) and laser irradiation are also known. It is possible to mark a coated substrate by ablating the laser-sensitive coating from the substrate or to create marks within the coating layer by a suitable laser. The penetration of the laser beam in the coated substrate becomes higher with increasing the laser energy so that the substrate get certain tactility or become thinner until the 30 laser beam perforates finally the substrate. [0006] For security applications like applications on banknotes or other security documents special paper types are used in that context. These papers are often made from the natural raw material cotton or they contain cotton fibres. Depending on laser wavelength, pulse frequency and laser energy the laser beam could generate in these special coated or uncoated papers the following: 35 Marks by ablating the coating layers I Ablation of printing ink [Bank of England, DE 2836526] I Ablation of colour layer/polymer layer [ÖPS, US 4,740,269] 40 Marks by laser effects on the coating layers I Fine line marks in optically variable layers [G&D, DE 19544130] I Laser marks in laser-markable paper or paper coatings [Merck, DE 19704478, DE 19732860] 45 I Visible marks in laser-sensitive layer creating trough a laser-transparent optically variable layer [G&D, DE 10008851] I Dark or black marks in coated paper [G&D, DE 4243987] I Laser marks on paper or paper coating contains oxyanions of multivalent metals [ Sherwood, WO 02/074548] I Marks due to laser-markable composition for paper coating contains pigment (multivalent metal compound) 50 and conductive polymer [Sherwood, WO 2005/012442] Marks by laser treatment of the substrate I Changing of fibre structure of paper [ÖPS, US 4,740,269] 55 I Touchable marks in paper or paper coatings [G&D, DE 10232786, DE 10247591] I Tactility due to an embossed-like surface structure without removing of the surface layer J.A.[ Ramos de Campos, ECB, EP 1658992] I Reduction and bleaching of paper thickness by laser etching [Karel Schell, US 6,395,191]. 2 EP 2 174 797 A1 [0007] US 2006/0141391 A1 discloses a laser mark on a document of value, comprising at least one printing ink or printing-ink layer on a substrate, where the at least one printing ink or printing-ink layer comprises a laser-sensitive component, and wherein printing ink in at least one area of the at least one printing ink or printing ink layer is selectively removed by a laser, and optionally a microinscription/image is produced by the laser in a selectively removed area, and 5 in the case where otherwise there would be complete removal of the printing ink from the mark, said microinscription/ image is produced in the mark. [0008] According to this application, the laser- sensitive component used can be any material which absorbs the laser- light energy sufficiently in the stated wavelength range and converts it into heat energy. However, particularly preferred are pigments such as mica flakes coated with one or more metal oxides. The metal oxides used here are both colourless, 10 high-refractive-index metal oxides, such as, in particular, titanium dioxide, antimony (III) oxide, zinc oxide, tin oxide and/or zirconium dioxide, and also coloured metal oxides, such as, for example, chromium oxide, nickel oxide, copper oxide, cobalt oxide and in particular iron oxide (Fe2O3, Fe3O4). The laser-sensitive component used is particularly preferably antimony(III) oxide, alone or in combination with tin oxide. [0009] As to the preparation of the laser marks, the document does not specify the parameters to be used in detail, 15 but states that "the parameters of the laser used depend on the particular application and can readily be determined by the person skilled in the art in the individual case." The only example describes the use of a Nd vanadate laser (1064 nm), the power of which is varied from 30 to 80% in 10% steps at a rate of 500 mm/s and a frequency of 40 to 60 kHz in pulsed operation. However, the contrast and the colour-shift effect of the laser marks obtainable under such conditions is comparably low and difficult to identify. 20 SUMMARY OF THE INVENTION [0010] The main objective of the present invention is to provide a method for the production of a more flexible and reliable security means for documents, especially security documents which have improved forgery-proof properties. 25 Thereby it is desirable that the security means can be authenticated in an easy way. At the same time the security means shall be highly flexible regarding its design, comparable small in thickness and highly durable. [0011] In carrying out these and other objects of the present invention, there is provided a method for laser marking a document, preferably a security document, wherein a document comprising a coating containing at least one sort of effect pigments which show different colours under different viewing angles is treated on at least a part of the coated 30 area with a pulsed laser beam at a rate of greater than 500 mm/s and a laser mark having a high contrast and a high colour shift effect at the same time is obtained. [0012] Thereby a highly flexible and reliable overt security means for documents is made available that has improved forgery-proof properties and that can be identified in a very simple way. [0013] In particular, the security means of the document allows for simply checking its authenticity by visual inspection 35 from different viewing angles. However, in some cases, some of the special features of the present security means cannot be seen by the naked eye but require special tools such as a lens due to the small line thickness of the lasered mark. For example, slightly ablated marks may be viewed by microscope to see some single colour changing particles. [0014] In addition, the present invention overcomes the size, flexibility and durability limitations of conventional security means. The document of the present invention is extremely thin, preferably thinner than 100Pm. Furthermore, the 40 document of the present invention exhibits a very high flexibility, and a very high durability.