EP3015279B1 - Method for producing a security element having a lenticular image - Google Patents

Description

The invention relates to a method for producing a security element with a lenticular image for displaying one or more target images visible only from predetermined viewing directions, wherein the motifs of the target images are formed in particular by visually recognizable, contrasting metallic and demetallized portions of a motif layer.

Data carriers, such as valuables or identity documents, but also other valuables, such as branded goods, are often provided with security elements for the purpose of security, which permit verification of the authenticity of the data carrier and at the same time serve as protection against unauthorized reproduction.

Security elements with viewing-angle-dependent effects play a special role in the authentication of authenticity since they can not be reproduced even with the most modern copiers. The security elements are thereby equipped with optically variable elements that give the viewer a different image impression under different viewing angles and, for example, show a different color or brightness impression and / or another graphic motif depending on the viewing angle.

For example, ID cards such as credit cards or identity cards have long been personalized by laser engraving. In personalization by laser engraving, the optical properties of the substrate material are irreversibly changed by suitable guidance of a laser beam in the form of a desired marking.

The publication EP 0 219 012 A1 describes a badge with a partial lenticular structure. This lens structure inscribes information into the card at different angles with a laser. This information can then be detected only at this angle, so that when tilting the map, the different information appear.

If a lenticular image contains a metallic motif layer, the motifs shown can be formed by local demetallization of the metallic motif layer. Various ways are known to bring a design into a metallization with a laser by demetallization. On the one hand, demetallization can be effected by direct inscription by guiding a laser beam over the metallic motif layer by means of a suitable scanning device. However, such scanning devices are expensive and usually do not reach the speeds required in an industrial production line.

Another possibility of demetallization is the laser application via a mask. The mask should move in a roll-to-roll process, preferably at the speed of the paper or film web. In addition, each design requires its own mask so that in practice the mask can not simply be printed on the moving web. Alternatively, a separate exposure step must be carried out for each design, with the exposure mask having to be removed from the corresponding direction after laser exposure. In addition, a part of the laser radiation is masked or absorbed by a mask so that only part of the laser intensity is available for the laser inscription itself

The document WO 2012/162057 A2 discloses a method according to the preamble of claim 1. Based on this, the present invention seeks to provide a method of the type mentioned above, which avoids the disadvantages of the prior art, and in particular allows a high production speed and a high efficiency of the Laserdemetallisierung.

This object is solved by the features of the independent claim. Further developments of the invention are the subject of the dependent claims.

• ein Linsenrasterbild mit einem Linsenraster aus einer Mehrzahl von Mikrolinsen und einer von dem Linsenraster beabstandet angeordneten metallischen Motivschicht bereitgestellt,
• wird eine Markierungs-Laserquelle zur Erzeugung von gepulster Laserstrahlung bereitgestellt,
• wird die gepulste Laserstrahlung im Strahlengang zwischen der Laserquelle und dem Linsenrasterbild durch einen Strahlformer oder eine schaltbare Maske mit einem motivförmigen Strahlquerschnitt versehen, und
• wird eine Mehrzahl von Mikrolinsen des Linsenrasters gleichzeitig mit dem Laserstrahl mit dem motivförmigen Strahlquerschnitt beaufschlagt, um gleichzeitig eine Mehrzahl teilmotivförmig demetallisierter Teilbereiche in der darunterliegenden metallischen Motivschicht zu erzeugen.

According to the invention, in a method of the type mentioned

• a lenticular image is provided with a lenticular array of a plurality of microlenses and a metallic motif layer spaced from the lenticular grid,
• a marking laser source is provided for generating pulsed laser radiation,
• the pulsed laser radiation is provided in the beam path between the laser source and the lenticular image by a beam former or a switchable mask with a motif-shaped beam cross section, and
• a plurality of microlenses of the lenticular grid is impinged simultaneously with the laser beam with the motif-shaped beam cross-section, in order to simultaneously generate a plurality of partially motive demetallized portions in the underlying metallic motif layer.

In an advantageous variant of the method, a diffractive optical element (DOE) or a refractive optical element (ROE) is provided as the beam former. According to a likewise advantageous variant of the method, a micro-mirror actuator (Digital Micromirror Device, DMD) or a surface light modulator (SLM) is provided as a switchable mask.

Both the beamformer and the switchable mask can work in transmission or reflection. It has been found to be particularly advantageous when the beam shaper in transmission or the switchable mask works in reflection.

In the context of this description, microlenses are lenses whose size lies below the resolution limit of the naked eye in at least one lateral direction. The microlenses may be formed, for example, spherical or aspherical. However, the use of cylindrical lenses is currently preferred, so that the method advantageously provides a lenticular image with a lenticular grid of a plurality of micro-cylindrical lenses.

The spherical or aspherical microlenses preferably have a diameter between 5 μm and 100 μm, in particular between 10 μm and 50 μm, particularly preferably between 15 μm and 20 μm. The micro-cylindrical lenses preferably have a width between 5 μm and 100 μm, in particular between 10 μm and 50 μm, particularly preferably between 15 μm and 20 μm. The length of the micro-cylindrical lenses is arbitrary, it may for example correspond to the use of security threads of the total width of the thread and be several millimeters.

Advantageously, in the method, at least 20, preferably at least 50, in particular at least 500 microlenses are acted on simultaneously with the laser beam with the motif-shaped beam cross section.

The microlenses are advantageously acted upon by a laser beam whose beam cross-section is extended over a wide area and which is not limited to a linear surface area. In this case, the beam cross-section in particular has the form of patterns, characters, in particular alphanumeric characters, or a coding.

Furthermore, the microlenses of the lenticular grid are advantageously applied to the laser radiation at an angle for each target image at an angle which corresponds to the predetermined viewing direction of this target image. The microlenses of the lenticular grid can also be exposed to two or more laser beams with a motive beam cross-section from different angles. Alternatively or additionally, the microlenses of the lenticular grid can be exposed to two or more laser beams with different motif-shaped beam cross sections. The two or more laser beams may originate from different marker lasers or from the same marker laser.

Advantageously, the microlenses of the lenticular grid are exposed to pulsed laser radiation having a pulse length between 5 ns and 130 ns. As laser source, an infrared laser in the wavelength range of 0.8 .mu.m to 3 .mu.m, in particular a Nd: YAG laser or Nd: YVO ₄ laser has been proven. In order to locally demetallise certain metals, such as gold or copper, by laser application, shorter wavelengths, in particular in the range from 480 nm to 580 nm, are much better suited. These can be generated, for example, by means of frequency-doubled solid-state lasers.

The laser parameters are advantageously chosen so that the metallic motif layer is locally demetallized by erosion or transparency in the laser application. The transparency can be effected, for example, by a transformation of the metal of the motif layer into metal oxide, or by a laser-induced melting of the metal layer, in which microscopic metal droplets that are no longer recognizable to the naked eye form.

As a material for the metallic motif layer, aluminum has proven particularly useful, but there are also other metals, such as copper, gold, iron, chromium, nickel, silver, platinum, palladium, titanium, or an alloy of these metals into consideration. In addition to metals and metal alloys, metallic layer-containing thin-film elements with a color shift effect are also suitable for the metallic motif layer. Such thin-film elements typically consist of an absorber layer, a dielectric spacer layer and a metallic reflector layer. The reflector layer is made thin enough so that it can be provided by the laser radiation with the desired partial motive demetallisierten portions.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a representation true to scale and proportion has been dispensed with in order to increase the clarity.

Fig. 1

eine schematische Darstellung einer Banknote mit einem erfindungsgemäßen Sicherheitselement in Form eines Fenstersicherheitsfadens, der ein Kippbild mit zwei unterschiedlichen Sollbildern enthält,

Fig. 2

schematisch den Aufbau des Fenstersicherheitsfadens der Fig. 1 im Querschnitt,

Fig. 3

schematisch eine Bearbeitungsvorrichtung zur Illustration des erfindungsgemäßen Verfahrens,

Fig. 4

in (a) bis (e) jeweils schematische Aufsichten auf einen Ausschnitt der Linsenrasterfolie der Fig. 3 bzw. der metallischen Motivschicht in verschiedenen Stadien der Laserbeschriftung, und

Fig. 5

schematisch eine weitere Bearbeitungsvorrichtung zur Illustration des erfindungsgemäßen Verfahrens.

Show it:

Fig. 1

a schematic representation of a banknote with a security element according to the invention in the form of a window security thread, which contains a tilting image with two different target images,

Fig. 2

schematically the structure of the window security thread of Fig. 1 in cross section,

Fig. 3

schematically a processing device for illustrating the method according to the invention,

Fig. 4

in (a) to (e) are schematic plan views of a section of the lenticular screen of the Fig. 3 or the metallic motif layer in various stages of laser marking, and

Fig. 5

schematically another processing device for illustrating the method according to the invention.

The invention will now be explained using the example of security elements for banknotes and other value documents. FIG. 1 shows a schematic representation of a banknote 10, which is provided with a security element according to the invention in the form of a window security thread 12. The window security thread 12 emerges in window areas 14 on the surface of the banknote 10, while it is embedded in the intermediate web areas 16 in the interior of the banknote 10.

In the window areas 14, the security thread 12 shows a tilting image which is provided to the viewer from two different viewing directions 30A, 30B each presents another target image 18A or 18B. The target images 18A, 18B each show a motif formed from visually recognizable and contrasting metallic motif parts 20 and demetallized motif parts 22A, 22B. Concretely, the windowed safety thread 12 in the exemplary embodiment when viewed perpendicularly 30A shows a sequence of crest motifs 22A in front of a metallic shiny background 20, while oblique viewing 30B shows a sequence of numerical motifs 22B in the form of the denomination "10" in front of the metallic shiny background 20 (FIG. "negative" motif representation). When the banknote is tilted, the appearance of the window security thread 12 in the window areas 14 alternates between the two target images 18A, 18B. In an embodiment which is not shown here, alternatively, the motif parts 20 can also be demetallised and the motif parts 22A, 22B can be made metallic ("positive" motif representation). In the exemplary embodiment, the window security thread 12 would then show a sequence of glossy metallic coat motifs 22A when viewed perpendicularly 30A, and a sequence of shiny metallic figure motifs 22B in each case in front of a contrasting background 20 when viewed obliquely 30B.

FIG. 2 schematically shows the structure of the window security thread 12 of Fig. 1 in cross section. The window security thread 12 has a carrier 32 in the form of a transparent plastic film, for example a PET film. The upper side of the carrier 32 is provided with a lenticular grid in the form of a plurality of parallel cylindrical lenses 34, whose width b in the exemplary embodiment is b = 20 μm. On the underside of the carrier 32, a UV lacquer layer 36 is arranged, on which a motif layer 40 is formed of aluminum, which in the grid of the cylindrical lenses 34 spaced, demetallisierte portions 42 A, 42 B has.

The carrier 32, the UV lacquer layer 36 and the cylindrical lenses 34 are matched to one another in the exemplary embodiment so that the motif layer 40 is located in the focal plane of the cylindrical lenses 34.

When viewing the window security thread 12 from the vertical viewing direction 30A, only the demetallized portions 42A and the surrounding metallic background of the metallic pattern layer 40 are visible due to the focusing effect of the cylindrical lenses 34, while only the demetallized portions 42B and 42B are viewed from the oblique viewing direction 30B the metallic background surrounding these subregions is visible. Since the demetallized portions 42A, 42B, as described in more detail below, were introduced into the motif layer 40 from the directions 30A, 30B by means of laser radiation with a motive beam cross section, these subregions with their metallic background reappear when viewed from the viewing directions 30A, 30B the desired sequence of motifs 18A, 18B together.

Due to the small dimensions of the cylindrical lenses 34, a large number of demetallized partial areas 42A, 42B cooperate in the reconstruction of the motifs 18A, 18B. For example, at a height of the demetallised motif parts 22A, 22B of about 2 mm and a width of the cylindrical lenses of b = 20 μm, the demetallized subregions 42A, 42B that are involved in the reconstruction of the motifs 22A / 20 (coats of arms) and 22B / 20 (respectively). Number sequence "10"), distributed over an area of the motif layer 40, which is covered by 2 mm / 20 μm = 100 cylindrical lenses.

As in Fig. 2 Also shown, the window security thread 12 typically includes additional layers, such as a full-color layer 44, However, these or other functional layers are not essential to the present invention and are therefore not described in detail.

Although laser demetallization of metallic layers is known per se, direct laser marking processes are very time-consuming and therefore generally unsuitable for larger-scale production. In order to achieve a high production speed, the laser radiation of a pulsed laser source is provided by a beam former or a switchable mask with a motif-shaped beam cross-section and a plurality of cylindrical lenses 34 of the lenticular is simultaneously applied to the motif-shaped laser beam, so that with a single Laser pulse a plurality of part-motif demetallisierter portions 42 A, 42 B is generated in the metallic motif layer 40.

FIG. 3 shows a processing apparatus 50 with a marking laser 52, for example, a pulsed Nd: YAG laser with a wavelength of 1.064 microns and a pulse duration between 5 ns and 130 ns to illustrate the method. The lenticular sheet 70 to be processed is arranged in a working plane 72 and moves in the running direction 74 at a high line speed of, for example, 80 m / min.

The lenticular screen 70 provides a still uncut and not yet demetallized preform in Figures 1 and 2 The lenticular screen 70 has a lenticular array of a plurality of cylindrical lenses 34 and a spaced apart metallic motif layer 40. The lenticular sheet contains a plurality of individual benefits, which are cut after the demetallization in a suitable manner to endless material or singulated for individual use.

The beam cross section of the laser beam 54 initially has a generally Gaussian or top hat-shaped output intensity distribution 56, as in FIG Fig. 3 shown schematically. Optionally, the laser beam 54 can be widened by at least two lenses 58 to the beam cross section required for later processing. The expanded laser beam then passes through a beam former 60 designed specifically for the demetallization region 22A or 22B to be generated, which is formed in the exemplary embodiment by a diffractive optical element (DOE). The diffractive optical element redistributes the laser energy in the beam cross section of the laser beam such that the target intensity distribution 62 of the beam cross section in the processing plane 72 just has the shape and size of the crest motif 22A to be written or the digit sequence "10" to be written in (reference 22B).

The redistributed in its cross-sectional intensity laser beam 54, optionally by other optical elements such as one or more deflecting mirror 64, scanner mirror (not shown) and lenses 66, directed to a desired portion of the lenticular screen 70 such that in the plane of the motif layer 40, which can lie in particular in the focal plane of the cylindrical lenses 34, the correct image of the motif to be written results.

The laser beam with its motif-shaped beam cross-section acts simultaneously on a plurality of cylindrical lenses 34, so that the desired motif (coat of arms or numerical sequence "10" in negative motif representation or background in positive motif representation) each with only one single laser pulse can be written in the metallic motif layer 40. Because of the short pulse duration, within which the lenticular screen film 70 only moves by a few tens of nanometers, no compensation for the web speed of the lenticular screen film 70 has to be made during the exposure.

The various motifs 22A, 22B are placed on the lenticular screen 70 in a grid pattern in a plurality of parallel rows, the positions of the individual subjects 22A, 22B on the lenticular sheet 70 and the angles at which the subjects 22A, 22B are introduced, in a manner known per se can be selected by means of the scanning device, not shown.

The shape of the beam cross section of the laser beam between the beam shaper 60 and the working plane 72 is not important to the present invention. The beam shaper 60 merely has to be designed in such a way that the desired target intensity distribution 62 results there in the machining plane 72, taking into account the beam path between the beam shaper 60 and the machining plane 72.

To that in the Figures 1 and 2 The crest motif 22A must be inscribed under vertical laser beam incidence with a first beam former 60 which generates a target intensity distribution 62 in the shape and size of the crest motif 22A to be written in the processing plane 72, and must encode the digit sequence 22B with oblique laser beam incidence second beamformer 60 which generates in the processing plane 72 a target intensity distribution 62 in the form and size of the digit sequence "10" ( Fig. 3 ). This can be done for example in two machine passes or with a processing device, which contains two laser modules or optical modules. It is also possible to divide the radiation of a laser source appropriately and to use it for the two inscription processes. It is understood that it is also possible to form the first or second beam shaper 60, for example, such that this instead of the crest motif 22A and the numeral "10" in the working plane 72, a target intensity distribution 62 in the form and size of the respective inscribed , the outline of the coat of arms motif 22A and the number of "10" forming background 20 generated, thereby to realize a "positive" motif representation.

For further explanation shows Fig. 4 in (a) to (e) are schematic plan views of a section of the lenticular screen 70 and the metallic motif layer 40 in different stages of laser marking. Referring first to the FIGS. 4 (a) and (b) in each case a section of the lenticular screen film 70 is shown with a plurality of cylindrical lenses 34 in plan view, wherein in addition the cross-section 62 of the laser beam 54 is located in the working plane 72, in Fig. 4 (a) in the form of the coat of arms (reference 22A in FIG Fig. 1 ) and in Fig. 4 (b) in the form of the number "10" (reference 22B in FIG Fig. 1 ). As shown in the figures, the surface of the beam cross section 62 covers a large number of cylindrical lenses 34. For example, the beam cross section 62 simultaneously captures 100 cylindrical lenses at a height of the motifs 22A, 22B of 2 mm and a width of the cylindrical lenses of b = 20 μm ,

Due to the focusing effect of the cylindrical lenses 34, the laser radiation is focused on the underlying under the lenticular aluminum motif layer 40 and leads there to a local demetallization. The term "demetallization" encompasses both a local ablation and a transparency of the aluminum layer. A transparency can for example, by a laser-induced conversion of aluminum into aluminum oxide, or by a laser-induced melting of the aluminum layer, in which form with the naked eye unrecognizable, microscopic droplets.

As a result, the laser application of a single laser pulse simultaneously generates a large number of demetallized partial areas 42A, 42B in the aluminum motif layer 40. FIGS. 4 (c) and (d) For illustration, each show a plan view only on the motif layer 40 after a laser application with a laser beam with a crest-shaped beam cross section (FIG. Fig. 4 (c) ) or after a laser application with a laser beam with a numerical beam cross section ( Fig. 4 (d) ). As can be seen directly from the figures, the beam shaping in the form of motifs simultaneously demetallizes many, also irregularly shaped partial regions 42A, 42B, and thus a considerable acceleration of the production process can be achieved. The partial areas 42A, 42B each have the shape of a part of the motifs 22A, 22B and are therefore designated in the context of this description as partial motif-shaped partial areas.

For the sake of completeness, it should be noted that one of the FIGS. 4 (c), 4 (d) For better visibility due to a fictitious intermediate step in the production of the window security thread 12 shows. If the lenticular raster film 70 is first subjected to the crest-shaped beam cross section 62, then the motif layer 40 already has the demetallised subregions 42A when it is subjected to the zifferiform beam cross section 62. Conversely, the motif layer 40 already has demetallized partial areas 42B if the lenticular raster film 70 is first subjected to the digit-shaped beam cross-section 62. Since the subregions 42A and 42B are introduced under different directions of application, they are offset in the plane of the motif layer 40 against each other, in particular in Fig. 2 shown. The partial regions 42A and 42B can also be designed to overlap. In the exemplary embodiment, the width of the demetalliserten partial areas 42 A, 42 B therefore ideally corresponds to half the width of the cylindrical lenses 34 or is slightly larger than this. Thus, it can be achieved that when tilting the window, a direct transition from one motif to another can take place.

Overall, the demetallized portions 42A and 42B are introduced into the motif layer 40 by the double laser application, so that the in Fig. 4 (e) schematically shown appearance arises. In cooperation with the grid of the cylindrical lenses 34, which are not shown in the figure above the motif layer 40, the partial areas 42A, when viewed vertically, reconstruct the demetallized coat of arms motif 22A against a metallic background. When viewed obliquely, the subregions 42B also reconstruct the demetallized digit sequence "10" against a metallic background (FIG. Fig. 1 ). The concrete appearance of the demetallised motifs 22A, 22B can be determined by a suitable choice of the color layer 44 (FIG. Fig. 2 ) can be set as desired.

It is understood that a Einbelichtung a subject under several loading angles is possible. For example, subjects that should be visible over a wide range of angles can be imprinted at several consecutive angles. Also, more than two target images may be provided, for example, to realize a motion or pumping image when tilting the security element.

Instead of a diffractive optical element (DOE), the beam shaper 60 may also be formed by a refractive optical element (ROE). The in Fig. 3 Beam shaper 60 shown by way of example works in transmission, but it is also possible to use a beam shaper operating in reflection, in particular in the form of a reflective diffractive optical element or a reflective refractive optical element.

In a modification of the processing device of Fig. 3 shows Fig. 5 a further processing device 80, in which instead of a beam former 60, a switchable mask 82 is used to generate the motif-shaped beam cross section. As in the embodiment of Fig. 3 For example, the laser beam 54 of the pulsed marker laser 52 first has a Gaussian or top hat-shaped output intensity distribution 56. After the laser beam has expanded through the lenses 58, the expanded laser beam falls onto the switchable mask 82, which in the exemplary embodiment is formed by a micromirror device (DMD). Such micro-mirror actuators consist of a plurality of individual mirrors arranged in the form of a matrix, each of which is formed by an electronically tiltable mirror surface with an edge length of a few or a few tens of micrometers. Depending on the local position of the mirror surfaces, the laser radiation is forwarded (beam portion 84) or deflected towards an absorber 88 (beam portion 86), which receives the laser energy that is not required.

The remaining, provided with a motif-shaped cross-sectional intensity beam portion 84 is then as in the embodiment of Fig. 3 is directed and imaged onto a desired area of the lenticular screen film 70 by further optical elements, such as deflection mirrors 64, scanner mirrors (not shown) and lenses 66, where the laser beam with the desired target intensity distribution 62 impinges the cylindrical lenses 34 and through them the metallic motif layer 40 ,

The use of a switchable mask 82 has the particular advantage that different beam cross sections 62 can be generated with the same mask 82. The mirror surfaces of a micromirror actuator can be brought to a new position within a few microseconds and therefore permit different target images of a lenticular image to be successively imprinted despite the fast-moving web. The disadvantage, however, is that the unneeded part of the laser radiation 86 must be deposited in the absorber 88, so that a stronger laser source than required for the actual exposure must be used.

Instead of micro-mirror actuators, Spatial Light Modulators (SLM) can also be used as a switchable mask, which can redistribute the laser intensity in the beam, and therefore the advantages of a switchable mask (flexibility, ability to create multiple designs with a mask) Advantages of a beam former (use of the total energy of the laser beam) connect. In this case, on the in Fig. 5 Absorbers are dispensed with and the laser energy supplied by the marking laser 52 can be used almost completely for demetallization. Surface light modulators can operate in reflection as well as in transmission, with modulators operating in reflection being presently preferred since they tolerate a higher energy density.

In principle, a switchable mask operating in transmission can also be formed by an LCD display in which the areas to be masked are switched to dark.

LIST OF REFERENCE NUMBERS

10

bill

12

Windowed security thread

14

panes

16

web regions

18A, 18B

target images

20

metallic motif parts

22A, 22B

demetallised motif parts

30A, 30B

viewing directions

32

carrier

34

cylindrical lenses

36

UV lacquer layer

40

motif layer

42A, 42B

demetallized subareas

50

processing device

52

laser marking

54

laser beam

56

Output intensity distribution

58

lenses

60

beamformer

62

Target intensity distribution

64

deflecting

66

lenses

70

Lenticular sheet

72

machining plane

80

processing device

82

switchable mask

84.86

beam components

88

absorber

Claims (14)

1. A method for producing a security element (12) having a lenticular image for depicting one or more target images, which are only visible from predetermined viewing directions and the motifs of which are formed by visually recognizable, contrasting metallic and demetallized sections of a motif layer (40), in which method

   - a lenticular image with a lenticulation consisting of a plurality of microlenses (34) and a metallic motif layer, which is spaced apart from the lenticulation, is provided and

   - a marking laser source (52) for generating laser radiation (54) is provided,

   characterized in that the laser radiation is pulsed, wherein

   - the pulsed laser radiation is provided with a motif-shaped beam cross section in the beam path between the laser source and the lenticular image by means of a beam shaper (60) or a switchable mask and

   - a plurality of microlenses of the lenticulation are simultaneously acted upon by the laser beam with the motif-shaped beam cross section in order to simultaneously produce a plurality of sections (42A, 42B), which are demetallized in the shape of partial motifs, in the metallic motif layer lying thereunder.
2. The method according to claim 1, characterized in that a beam shaper in the form of a diffractive optical element (DOE) or a refractive optical element (ROE) is provided.
3. The method according to claim 1, characterized in that a switchable mask in the form of a digital micromirror device (DMD) or a spatial light modulator (SLM) is provided.
4. The method according to at least one of claims 1 to 3, characterized in that the beam shaper operates in the transmission mode and the switchable mask operates in the reflection mode, respectively.
5. The method according to claim 1 or 3, characterized in that the pulsed laser radiation is provided with the motif-shaped beam cross section by a switchable mask, which acts as a beam shaper.
6. The method according to at least one of claims 1 to 5, characterized in that a lenticular image with a lenticulation consisting of a plurality of cylindrical microlenses is provided.
7. The method according to at least one of claims 1 to 6, characterized in that at least 20 microlenses, preferably at least 50 microlenses, particularly at least 500 microlenses, are simultaneously acted upon by the laser beam with the motif-shaped beam cross section.
8. The method according to at least one of claims 1 to 7, characterized in that the microlenses are acted upon by a laser beam, the beam cross section of which is extensively laminar and particularly has the shape of patterns, characters, especially alphanumeric characters, or a coding.
9. The method according to at least one of claims 1 to 8, characterized in that the microlenses of the lenticulation are for each target image acted upon with the laser radiation at an angle, which corresponds to the predetermined viewing direction of this target image.
10. The method according to at least one of claims 1 to 9, characterized in that the microlenses of the lenticulation are acted upon by two or more laser beams with motif-shaped beam cross section from different angles.
11. The method according to at least one of claims 1 to 10, characterized in that the microlenses of the lenticulation are acted upon by two or more laser beams with different motif-shaped beam cross sections.
12. The method according to at least one of claims 1 to 11, characterized in that the microlenses of the lenticulation are acted upon with pulsed laser radiation having a pulse length between 5 ns and 130 ns.
13. The method according to at least one of claims 1 to 12, characterized in that the microlenses of the lenticulation are acted upon by an infrared laser that operates in the wavelength range between 0.8 µm and 3 µm, particularly a Nd:YAG laser or a Nd:YVO₄ laser.
14. The method according to at least one of claims 1 to 13, characterized in that the laser parameters are chosen such that the metallic motif layer is locally demetallized by means of material removal or transparentizing while being acted upon by the laser.

Images