Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/40—Manufacture
  • B42D25/405—Marking
  • B42D25/41—Marking using electromagnetic radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M3/00—Printing processes to produce particular kinds of printed work, e.g. patterns
  • B41M3/14—Security printing
  • B41M3/148—Transitory images, i.e. images only visible from certain viewing angles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/24—Ablative recording, e.g. by burning marks; Spark recording
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
  • B42D25/29—Securities; Bank notes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
• • B42D2033/20—
• • B42D2035/24—

Definitions

• 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 fixed colour in a surrounding with a colour shift effect.
• security documents such as banknotes, passports, chequebooks, etc
• 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 feature supposedly practically cannot be copied by a forger with the means available to him.
• the application of watermarks or the introduction of a security thread into the paper is known.
• coated substrates paper, board, film, laminate
• laser irradiation 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 laser beam perforates finally the substrate.
• 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 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.
• 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.
• pigments such as mica flakes coated with one or more metal oxides.
• the metal oxides used here are both colourless, 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 (Fe 2 O 3 , Fe 3 O 4 ).
• the laser-sensitive component used is particularly preferably antimony(III) oxide, alone or in combination with tin oxide.
• the document does not specify the parameters to be used in detail, 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.
• the contrast and the colour-shift effect of the laser marks obtainable under such conditions is comparably low and difficult to identify.
• 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.
• the security means can be authenticated in an easy way and exhibits optically striking characteristics.
• the security means shall be highly flexible regarding its design, comparable small in thickness and highly durable.
• a method for laser marking a document preferably a security document, characterized in that a document comprising a coating containing at least one sort of effect pigments which show different colours under different viewing angles and at least one sort of laser sensitive pigments is treated on at least a part of the coated area with a laser beam operated in a continuous wave mode (cw mode) at a rate within the range of 500 mm/s to 2000 mm/s using a power within the range of 60 % to 100 %, wherein a laser mark having one of the different colours which are shown under different viewing angles by the effect pigment is obtained.
• said laser mark is located in a surrounding with a colour shift effect which is due to the action of the effect pigment.
• the security means of the document allows for simply checking its authenticity by visual inspection from different viewing angles.
• 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 100 ⁇ m.
• the security document of the present invention exhibits a very high flexibility, and a very high durability.
• the following is a detailed description of the present invention. It provides a method for laser marking a document, preferably a security document.
• a document refers to a bounded physical representation of body of information designed with the capacity (and usually intent) to communicate.
• a document may manifest symbolic, diagrammatic or sensory-representational information and has to be understood as a paper artefact, containing information in the form of ink marks.
• security document refers to all kind of documents that contain at least one feature that can be used to prevent counterfeiting by providing authentication, identification or classification of the document. In particular, they include banknotes, passports, chequebooks, identity cards, credit cards and/or debit cards.
• said document may comprise various substrates, such as, for example, paper, cardboard, board, plastics, plastic films and laminates.
• Particularly suitable for security applications are papers containing fibres from annual plants, such as cotton (for example cotton vellum paper) or cotton fibre blends or cotton fibre mixtures with plastic fibres, which may have a single- or multilayered structure.
• effect pigment comprises all kind of pigments showing different colours under different viewing angles and includes pigments with a pearl luster effect, with an iridescent interference effect and with a colour-shift effect.
• Pearlescent or nacreous pigments are well known in the art and have become very popular in the creation of lustre effects in coatings.
• the pearlescent effect is produced by the specular reflection of light from several surfaces of the platelets with parallel orientation at various depths within the coating film. Light striking the platelets is partially reflected and partially transmitted through the platelets.
• a pearly lustre effect is produced by the dependence of reflection on viewing angle, and the sense of depth is created by reflection from many layers.
• the platelets must be extremely smooth to maximize reflected light and any surface roughness diminishes the lustrous effect. Non fine particles or pigments with rough edges can also negatively affect the lustrous appearance.
• Pearlescent pigments show iridescence, i. e. an optical phenomenon characterized as the property of surfaces in which hue changes according to the angle from which the surface is viewed may be seen as may be seen of soap bubbles and butterfly wings. Iridescence is caused by multiple reflections from multi-layered, semi-transparent or transparent surfaces in which phase shift and interference of the reflections modulates the incident light by amplifying or attenuating some frequencies more than others. This process is the functional analogue of selective wavelength attenuation as seen with the Fabry-Pérot interferometer.
• the special attraction of the pearlescent pigments is the soft and smooth colour shift effect, which is unique in the art. They are very useful for security applications, because the overt colour-shift feature could not be duplicated by a copy machine.
• the pearlescent pigments show optical effects such as directed reflection, multiple reflection, interference, and a soft colour travel (angle-dependent optical effects), which generate their optical attractiveness because of the ability of easy parallel orientation of a multitude of platelet-like particles.
• the first is the illusion of optical depth, which is created by the arrangement of a multiplicity of platelet-like particles of a pearlescent pigment.
• the achieved impression is the result of reflection of light at the different interfaces between pigment and binder and at the boundary layers of the effect pigment itself. Such an effect is especially strong when extended areas are profiled.
• Multilayered pigments exhibiting such a startling effect are also called optically variable pigments.
• optically variable pigments are used as said effect pigments.
• Optically variable pigments are pigments that have at least two and at most four optically clearly distinguishable discrete colours at at least two different illumination or viewing angles, but preferably have two optically clearly distinguishable discrete colours at two different illumination or viewing angles or three optically clearly distinguishable discrete colours at three different illumination or viewing angles.
• only the discrete hues and not intermediate hues are preferably present, i.e. a clear change from one colour to another colour is evident on tilting the security element (or the coated substrate in this case) which comprises the optically variable pigments.
• Effect pigments particularly suitable for the present invention comprise a platelet-shaped transparent or semi-transparent dielectric carrier material coated with at least one layer of a metal oxide, preferably selected from the group consisting of SiO 2 , Al 2 O 3 , TiO 2 , SnO 2 , Fe 2 O 3 , Fe 3 O 4 , chromium oxides, silicon hydroxide, aluminium hydroxide or magnesium fluoride.
• a metal oxide preferably selected from the group consisting of SiO 2 , Al 2 O 3 , TiO 2 , SnO 2 , Fe 2 O 3 , Fe 3 O 4 , chromium oxides, silicon hydroxide, aluminium hydroxide or magnesium fluoride.
• the dielectric carrier material is preferably selected from the group consisting of platelet-shaped silicates such as natural or synthetic mica, talc, kaolin, glass plates, alumina flakes and SiO 2 -platelets.
• effect pigments where the platelet-shaped carrier is coated with a multiple layer coating comprising layers of different metal oxides having different refractive indices.
• layer sequences comprising alternating low refractive layers and high refractive layers.
• the materials mentioned above are preferably used for the metal oxide layers.
• the outer layer having optical activity is a high refractive layer.
• Materials with high refractive indices are materials having refractive indices which are equal or higher than 1.8 at 25°C, whereas materials with low refractive indices exhibit refractive indices which are lower than 1.8 at 25°C.
• the former are represented by TiO 2 , SnO 2 , Fe 2 O 3 , Fe 3 O 4 and chromium oxides, the latter by SiO 2 , Al 2 O 3 , silicon hydroxide, aluminium hydroxide and magnesium fluoride, to name only a few. With these multilayered pigments striking angle-dependent colour effects may be achieved.
• the refractive index increment preferably is greater than 0.1.
• the coating of the security document also comprises at least one sort of laser sensitive pigments.
• laser sensitive pigments refers to all kind of pigments, which are able to absorb the laser energy and to cause reactions within the coating layers of the substrate.
• the laser sensitive pigments are able to absorb more laser energy than the effect pigments.
• laser-sensitive pigments examples include:
• Said laser sensitive pigments may be present together with the effect pigments in one single layer or in separate layers.
• at least one kind of laser sensitive pigments and at least one kind of the effect pigments mentioned above are present in one single layer.
• the weight ratio of the effect pigments to the laser-sensitive pigments is preferably between 4:1 and 1:2.
• the coating of the document can be achieved in an usual manner.
• the according inks containing the effect pigments and the laser sensitive pigments are preferably printed on suitable substrates by usual printing or coating techniques like relief printing, gravure printing, flexographic printing, direct offset printing, indirect offset printing, pad printing, intaglio printing, screen printing, paper coating, K-coating, or doctor blade application. Furthermore, application of the ink by means of partial or full-area in-line or off-line lacquering is possible.
• the concentration of the effect pigments in the ink is preferably between 5 % by weight and 33 % by weight, very preferably between 10 % by weight and 20 % by weight.
• the concentration of the laser-sensitive pigments in the ink is preferably between 5 % by weight and 33 % by weight, very preferably between 10 % by weight and 20 % by weight.
• Suitable binders for the inks are:
• the binder content is preferably 10-50 % by weight, based on the total weight of the liquid system.
• Suitable solvents and cosolvents for the inks are:
• the solvent content is preferably 30 % by weight to 70 % by weight, based on the liquid system.
• a laser is a device that emits light through a specific mechanism for which the term laser is an acronym: light amplification by stimulated emission of radiation.
• the laser creates a coherent and monochromatic light with a low divergence.
• a laser consists of a gain medium inside an optical cavity, with a means to supply energy to the gain medium.
• the gain medium is a material (gas, liquid, solid or free electrons) with appropriate optical properties.
• a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium.
• one of the two mirrors, the output coupler is partially transparent. The output laser beam is emitted through this mirror.
• Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium. Part of the light that is between the mirrors (i.e., is in the cavity) passes through the partially transparent mirror and appears as a beam of light.
• the process of supplying the energy required for the amplification is called pumping and the energy is typically supplied as an electrical current or as light at a different wavelength.
• the light source can be a flash lamp or another laser.
• Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.
• the laser used in the present invention preferably has a wavelength within the range of 157 nm to 10.6 ⁇ m, very preferably within the range of 355 nm to 10.6 ⁇ m.
• Particularly suitable lasers enclose diode lasers (808-980 nm), Nd:YAG lasers und Nd:YVO 4 - lasers (355, 534 und 1064 nm) und CO 2 -lasers (10.6 ⁇ m).
• the mean laser power is preferably within the range of 2 W to 300 W, very preferably within the range of 4 W to 30 W.
• the laser is operated in cw mode.
• the output of the laser is relatively consistent with respect to time.
• the population inversion required for lasing is continually maintained by a steady pump source.
• a rate within the range of 500 mm/s to 2000 mm/s, preferably within the range of 500 mm/s to 1500 mm/s, is used.
• the laser power is within the range of 60 % to 100 %, more preferably within the range of 80 % to 100 %.
• the rate is preferably in the range of 500 mm/s to 1500 mm/s. Particularly favourable results are achieved by using a rate in the range of 500 mm/s to 1000 mm/s and a laser power within the range of 80 % to 90 %.
• a rate in the range of 500 mm/s to 2000 mm/s is preferably used. Particularly favourable results are achieved by using a rate in the range of 500 mm/s to 1000 mm/s and a laser power within the range of 90 % to 100 % provided that the power is greater 90% if the rate is 1000 mm/s.
• the laser effect pigments interact with the laser beam.
• a laser mark is formed in which one colour of the effect pigments with colour shift effect is fixed under laser irradiation and the colour shift effect is no longer observed after the laser treatment.
• the fixation of one colour of the effect pigment at any place of the substrate, preferably in a surrounding with an unchanged colour shift effect, is an unique feature, which can not be realized by printing techniques.
• the effect pigments are only removed gradually from the laser mark, if at all.
• more than 50 % of the original amount of the effect pigments are remaining on the marking after laser treatment, more preferably more than 80%.
• the actual size of the laser mark is of minor importance in the present invention. It is possible to create both, fine lines and bigger areas, wherein the optical effect might be observed for all sizes of the marking, especially when the surrounding rests optically variable.
• the authenticity of the document of the present invention can be easily checked by visual inspection from different viewing angles.
• the laser experiments are carried out with solid state or diode lasers (wavelength range of 355 nm, 532 nm, 980 nm, 1064 nm) and a gas laser, e.g. CO 2 -laser (10.6 ⁇ m), preferably with a Nd:YAG laser und Nd:YVO 4 - laser.
• a gas laser e.g. CO 2 -laser (10.6 ⁇ m
• Marked areas for example a rectangle of 5x5 mm
• a high contrast and a fixed red colour are obtained with the following laser parameter of a Nd:YVO 4 laser (1064 nm, mean power of 12 W) in cw-mode. These parameters are exemplary, but not limited only on this laser system. For evaluation the following ranking was applied. 1: very intensive colour with high brilliance 2: weak or matt colour
• Marking lines with a high contrast and a fixed red colour are obtained with the following laser parameter of a Nd:YVO 4 laser (1064 nm) in cw-mode.
• Table 2 Marking lines Laser speed v [mm/s] Power P [ %] Evaluation 2000 100 2 1000 100 1 1000 90 2 500 90 - 100 1 500 80 2

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• Manufacturing & Machinery (AREA)
• Health & Medical Sciences (AREA)
• Electromagnetism (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Business, Economics & Management (AREA)
• Accounting & Taxation (AREA)
• Finance (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)
• Credit Cards Or The Like (AREA)
• Inks, Pencil-Leads, Or Crayons (AREA)

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Publications (2)

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Cited By (15)

Citations (19)

• 2008
  • 2008-10-07 ES ES08017526T patent/ES2390984T3/es active Active
  • 2008-10-07 EP EP08017526A patent/EP2174796B1/fr not_active Not-in-force

Patent Citations (19)

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