EP3231625B1 - Laser treatment method of a coating comprising effect pigments - Google Patents

Description

The invention relates to a method for treating a coating, in particular for fiber substrates and foils, with laser radiation, the coating consisting of at least one binder, a laser-sensitive substance and an effect pigment.

the end DE 4334848 C1 , WO 2010/072329 A1 , WO 2011/154112 A1 ,

DE 10 2010 053 052 A1 , EP 1368 200 A2 , EP 2 528 742 A1 or DE 10 2008 046 513 A1 it is known that a substrate such as paper, for example, can be cut or perforated with a laser and that coatings applied to the substrate can be removed or discolored, whereby attractive and precisely registered effects can be produced.

the end EP 2 946 938 A1 a method for changing the optical properties of a coating is known in which a coating which contains at least one effect pigment and at least one component absorbing IR radiation is irradiated with an IR laser. As a result of the action of the laser radiation, the component absorbing IR radiation is partially or completely removed from the irradiated areas of the coating and the effect pigment is partially or completely exposed in the irradiated areas.

the end EP 2 174 796 A1 a method for laser marking a document is known, in which a document comprising a coating containing at least one type of an effect pigment that shows different colors at different viewing angles and at least one type of a laser-sensitive pigment on a part of the coated area is treated with a laser beam and a laser marking is obtained with a solid color, the solid color being one of the different colors shown by the effect pigment at different viewing angles.

The invention is based on the object of a generic security element to be further developed in such a way that the protection against counterfeiting is further increased.

This object is achieved by the features of independent claim 1. Developments of the invention are the subject of the dependent claims.

According to the invention, the laser-sensitive substance changes color when exposed to the laser radiation. The laser-sensitive substance is thus preferably converted or chemically reduced by the laser and is in particular not ablated or removed, (chemically) oxidized or displaced by the action of the laser radiation, so that the effect pigment is not partially or completely exposed in the irradiated areas .

An IR laser is preferably used as the laser, ie a laser with an emission wavelength in the infrared wavelength range, preferably from 0.05 μm to 50 μm. Such an IR laser is, for example, a carbon dioxide or CO ₂ laser with an emission wavelength in the range from 9 μm to 12 μm, particularly preferably 10.6 μm, a diode laser in the wavelength range from 50 nm to 1100 nm or a solid-state laser in the wavelength range from 1000 nm to 1100 nm, particularly preferably 1064 nm. In the coating according to the invention, the laser radiation of the IR laser causes molecular oscillations in the laser-sensitive substance, which in turn leads to kinetic energy and thus heat in the laser-sensitive substance and to a color change. The color change of the laser-sensitive substance takes place particularly well when the laser-sensitive substance has a high IR absorption for the emission wavelength of the laser radiation used, so that the majority of the incident laser energy can be converted into heat and thus the necessary temperature in the molecules of the laser-sensitive substance what is achieved is that these split up and colored connections are created.

Continuous, pulsed and quasi-pulsed lasers can be used. A quasi-pulsed laser is understood to be a laser that switches on the laser at full power for the specified switch-on time with a specified frequency and a specified switch-on time as a percentage of the resulting period duration. The laser used is preferably operated in the quasi-pulsed mode. With a CO ₂ laser with an emission wavelength of 10.6 µm and a maximum laser power of 30 W as well as an ammonium salt of molybdenum as a laser-sensitive substance, the pulse frequency is 25 kHz, with a switch-on time of 25%, a forward speed of 2500 mm / s . The focus diameter of the laser beam is approx. 160 µm. If a surface is to be created, experience has shown that a line spacing of 0.1 mm makes sense in this example.

A color change within the meaning of this invention is a change from one color to another color, for example from red to green, a change from a light shade to a dark shade, for example from light green to dark green, from a dark shade to a light shade or also a change from one contrast to another, for example from white or colorless to black.

Both solvent-based and water-based binders are suitable as binders. In particular, binders are preferred which have a high transmission for the wavelength of the laser radiation used, so that as much of the laser radiation as possible reaches the laser-sensitive substance and energy is available for the color change.

A metal salt is preferably used as the laser-sensitive substance, particularly preferably an ammonium salt of molybdenum. The color change in the case of ammonium salts of molybdenum is particularly good because they have a high Have IR absorption for the emission wavelength of a CO ₂ laser, so that the majority of the incident laser energy can be converted into heat and the temperature required in the molecules of the ammonium salts of molybdenum is reached so that they split and colored compounds are formed. Furthermore, copper (II) oxalate or iron (II, III) oxide Fe ₂ O 3 are preferably also possible.

Further possible laser-sensitive substances are known, for example, from the following publications: EP 1657072 B1 , EP 2332012 B1 , US 7270919 , US 7485403 , US 7998900 , US 8021820 , US 8048608 , US 8048605 , US 8083973 , US 8101544 , US 8101545 , US 8105506 , US 8173253 , US 8178277 , US 8278243 , EP 1 368 200 B2 , EP 2 528 742 B1 , US 8278244 and US 842028 .

The laser-sensitive substance is particularly preferably colorless or white, so that the non-lasered areas appear in the usual glossy effect, as is known from coatings with so-called pearlescent pigments (somewhat weakened by the laser-sensitive substance). If a color change is now induced in the laser-sensitive material (e.g. from white to black), for example through the necessary temperature input or by means of laser irradiation, a kind of "background color" is created, with the result that in these areas, in combination with the pearlescent pigments, a different color than the the non-lasered areas becomes visible. Depending on which laser-sensitive substance is used and which color change it shows (e.g. to red, green, blue, etc.), different background colors and thus also different colors in connection with the pearlescent pigments are created. A color change from white to black of the laser-sensitive substance used is preferably used.

According to the invention, the action of the laser radiation thus produces a background coloration which changes or intensifies the color and color saturation of the effect pigment used in each case, but without changing the effect pigment itself.

• Perlglanzpigmente, die beispielsweise aus WO 2004/087437 A1 bekannt sind, oder
• fluoreszierende Pigmente, d.h. Pigmente mit fluoreszierenden Eigenschaften, die unter Bestrahlung mit UV-Licht sichtbar werden, wie beispielsweise Lumilux Blau CD 710 oder das Pigment M396B von Pröll KG, oder
• OVI-Pigmente, die beispielsweise aus EP 0 227 423 B1 bekannt sind, oder
• Flüssigkristallpigmente, die beispielsweise aus WO 97/19818 A1 oder WO 2006/034780 A1 bekannt sind.

The effect pigments according to the invention are for example

• Pearlescent pigments, for example from WO 2004/087437 A1 are known, or
• fluorescent pigments, ie pigments with fluorescent properties which become visible when irradiated with UV light, such as Lumilux blue CD 710 or the pigment M396B from Pröll KG, or
• OVI pigments, which are made for example EP 0 227 423 B1 are known, or
• Liquid crystal pigments made, for example, from WO 97/19818 A1 or WO 2006/034780 A1 are known.

A preferred effect pigment or pearlescent pigment of this type is, for example, “Merck Colorstream® T10-03 Tropic Sunrise”, which, without a laser-sensitive dye, shows interference effects from light green to light red and pearlescent. A mixture of this pigment with a laser-sensitive dye, the color of which has already changed to black, shows dark green with a weak color shift to dark red. B. the CO ₂ laser radiation with an emission wavelength of 10.6 microns, a glittering surface. The glittering surface is created by the roughening of the surface by the longer-wave radiation, as will be explained in more detail below.

Another preferred pearlescent pigment “Merck Colorstream®T10―02 Arctic Fire” shows interference effects from light green to light purple and pearlescent without a laser-sensitive dye. A mixture of this pigment with a laser-sensitive dye, the color of which has already changed to black, shows green with a color change or color shift to purple. B. the CO ₂ laser radiation with an emission wavelength of 10.6 microns, a glittering surface.

Another preferred pearlescent pigment “Merck Iriodin® 225 Rutile Pearl Blue” shows a light pearlescent blue without a laser-sensitive dye. A mixture of this pigment with a laser-sensitive dye, the color of which has already changed to black, shows an intense blue with the use of longer-wave IR radiation, such as. B. the CO ₂ laser radiation with an emission wavelength of 10.6 microns, glittering surface.

Another preferred pearlescent pigment "Eckart Phoenix PX 1221 Gold" shows a light pearlescent gold without a laser-sensitive dye. A mixture of this pigment with a laser-sensitive dye, the color of which has already changed to black, shows an intense gold with the use of longer-wave IR radiation, such as, for. B. the CO ₂ laser radiation with an emission wavelength of 10.6 microns, strongly glittering surface.

The color of the effect pigment used in each case is intensified in the mixture with the laser-sensitive substance through the laser irradiation, i.e. a weak purple becomes an intensely glittering purple, a light green becomes a dark green, etc. The combination of these pigments with the laser-sensitive material enables different color changes and a wide range of different color changes due to laser irradiation.

If, on the other hand, a forger prints a black surface with a conventional printer and coats this surface with the respective pearlescent coating without laser-sensitive dye, another color is also visible in the surface. However, this color is significantly lighter than the color that is created with the laser-induced color effect, for example light green instead of dark green. Furthermore, clear interference effects and the strong pearlescent luster are still visible, which is not the case with the lasered black surface. Counterfeiting in this form does not lead to an optical effect that is comparable to that of the method according to the invention.

Especially when using longer-wave IR radiation, such as. B. the CO ₂ laser radiation with an emission wavelength of 10.6 µm, a glitter of the pearlescent coating can only be determined after the laser irradiation. This also gives you the option of marking the pure pearlescent coating with the laser without the need for a laser-sensitive material. The glittering areas then represent the marking.

In general, the glitter comes about when a high absorption of the corresponding laser wavelength is achieved in the coating and the laser energy is efficiently converted into heat. B. the CO ₂ laser radiation with an emission wavelength of 10.6 microns, is the case. As a result of the temperature, the surface of the coating is roughened and the flake-form effect pigments are exposed and set up. As a result, the light is refracted and reflected more strongly. If the laser-sensitive substance has a high absorption of the corresponding laser wavelength, more laser energy is converted into heat and the Surface roughened even more. This will further enhance the glitter.

For example, the surface of a coating that contains the pearlescent pigment "Merck Colorstream® T10-03" without a laser-sensitive substance is not as roughened as with the laser-sensitive substance, since the absorption of the laser wavelength used with such effect pigments and their coating is not as high as the absorption of the laser-sensitive substance for this wavelength. A glittering effect can still be observed, even if this is not as pronounced as with the coating with the addition of the laser-sensitive substance.

According to another possible interpretation, fine effect pigment particles with a diameter of less than about 10 μm generally produce a silky luster, while larger or coarser effect pigment particles with a diameter of about 10 μm to about 50 μm glitter with greater brilliance. The glittering effect of the lasered areas can then possibly also be attributed to the fact that the effect pigments melt due to the thermal effect of the laser and form larger agglomerates or pigment particles after cooling.

The combination of the laser-sensitive substance with effect pigments increases the security against forgery of the laser-induced color effects considerably, since such glitter effects and color changes in connection with the precisely registered combination with a laser cutting of the substrate, as it is for example from WO 2010/072329 A1 is known, a security thread or a security strip cannot be printed in the appropriate fineness and register.

According to a preferred embodiment, the mixture of the laser-sensitive substance and the effect pigments is colored with further color pigments. However, these coloring pigments must not absorb the wavelength of the laser used, so that they do not disintegrate into a differently colored substance and thereby cause unexpected color changes in the coating after the laser irradiation. The coloring of the mixture has the advantage that it is more difficult for counterfeiters to recognize a connection between the coating color and the color result after the laser irradiation. In addition, by using a suitable and IR-transparent color pigment (e.g. red), protection against UV radiation and thus a higher resistance to yellowing of the coating can be achieved.

According to a further embodiment, two or more surfaces are applied next to one another or in a pattern, at least one surface having a laser-sensitive coating without effect pigment and at least one adjacent surface having a laser-sensitive coating with effect pigment. In this way, different patterns, symbols or perforations can be lasered across areas, as shown, for example WO 2010/072329 A1 or WO 20111/54112 A1 are known, so that there are two different, but precisely registered color effects.

According to a further embodiment, two or more surfaces are applied next to one another or in a pattern, with at least one surface having a laser-sensitive coating with a color or an effect pigment that does not change color when the viewing angle is changed (so-called color fix), and at least an adjacent surface has a laser-sensitive coating with effect pigment, which changes its color when the viewing angle is changed (so-called color shift). If there is a change of the viewing angle, the area with Color-Fix does not change its color, whereas the area with Colorshift changes its color, whereby it is particularly preferred that both areas are exposed to laser radiation at least in partial areas in such a way that the colors of the partial areas of both areas match at a certain viewing angle. For example, the area with Color-Fix shows a green star after exposure to laser radiation, which does not change its color when the viewing angle is changed, and the area with Colorshift shows a blue stripe after exposure to laser radiation at a certain viewing angle, which when the viewing angle changes Changes its color to the green color of the star.

According to a further embodiment, two or more surfaces are applied next to one another or in a pattern, with at least one surface having a laser-sensitive coating with an effect pigment after exposure to laser radiation, which changes its color when the viewing angle is changed (first color shift), and at least one adjacent surface has a laser-sensitive coating with another effect pigment, which also changes its color when the viewing angle is changed, but differently (second color shift). When the viewing angle is changed, both surfaces change their color, but both surfaces show a different color-shifting effect. For example, when the viewing angle changes, one surface shows a color change from red to green and at the same time the other surface shows a color change from green to purple. It is particularly preferable for the colors of the two surfaces to match at a specific viewing angle. For example, after exposure to laser radiation, the area with the first color shift shows a blue star at one viewing angle and the area with the second color shift shows a blue stripe, both areas with another change their color to green at certain viewing angles. Alternatively, it is also possible that after exposure to laser radiation, the area with the first color shift shows a blue star at one viewing angle and the area with the second color shift shows a green stripe, with the star changing its color to green and the Stripe changes color to blue.

The color change and / or the non-changing color are possible both in the light of the visible wavelength range and in the non-visible wavelength range, for example in the ultraviolet wavelength range. For example, one area shows a color change or a non-changing color in the visible wavelength range and another area with fluorescent pigments shows a similar or different color change or a similar or different color in the ultraviolet wavelength range.

For the purposes of this invention, adjacent or adjacent is understood to mean both a "direct" abutment without a gap between the surfaces, possibly also with a slight overlap, and an adjoining with a gap.

According to a further embodiment, the lasering takes place in the form of a so-called negative pattern, with the entire surface being exposed to laser radiation and only a pattern, symbol, etc. to be generated is not exposed to laser radiation. Here, too, there is advantageously a high level of register accuracy.

Alternatively, a laser-ablatable ink or another laser-ablatable material (for example a film) can also be printed as an adjacent area or applied. The laser ablates this color or the respective substance and seamlessly changes over to the discoloration of the other surface.

According to a further embodiment, two areas of different color composition are printed on top of one another (also divided, in areas or in a pattern to one another), one area having the laser-sensitive coating without effect pigment and the other area having the laser-sensitive coating with effect pigment.

In this way, combinations of, for example, a laser hole with an edge effect (such as, for example, from WO 2009/003587 A1 or WO 2009/003588 A1 known), removal of the first layer and discoloration of the second layer, discoloration of the individual layers, removal up to the paper layer or color ablation by laser possible.

This results in numerous possibilities for the arrangement of the overprints in relation to the cut-out areas (that is, in the case of a combination of laser cutting or laser perforation, also with a color effect, for example from WO 2009/003587 A1 or WO 2009/003588 A1 known), depending on how the areas are printed (divided, in areas, patterns, symbols, letters, numbers, etc.) and in which areas are overlapped and over which areas are discolored, ablated, trimmed and cut through.

By adding effect pigments to the laser-sensitive paint, the present invention enables colored instead of just black laser markings, but the color of very thin lines that are colored by the laser is difficult to see with the naked eye.

the DE 10 2016 014 662 A1 describes a window lasered into the paper with, on the one hand, a see-through area and, on the other hand, a color shift or blue / gold metallization. In this way, surprisingly interrelated designs can be produced on the front and back of the bank note.

According to a further embodiment, building on the DE 10 2016 014 662 A1 The color of very thin lines is further improved by printing the laser-sensitive material combined with color pigments or effect pigments such as Iriodin, Liquid Crystals, STEP pigments, fluorescent pigments or pigments capable of Colorshift on the back of the banknotes behind the security film or where the window is should be placed. The window created with the laser can be supplemented inline in one laser step with a laser-induced color effect in 100% registration with the window.

A new combination option that improves the visibility of the thin colored lines is particularly advantageous. At the same time, new possibilities for upgrading the previously neglected and comparatively unattractive banknote reverse are given.

The window can be, for example, a laser hole, laser cut, filigram or a laser perforation.

The color and effect of the thin color effect lines come into their own when the back of the security film, which is visible through the window, has colors or effects that match the laser-sensitive material and color effect (e.g. color shift, fluo, gold-blue, LC etc.) .) shows. Color shift effects that also match (in terms of color) the color shift effects of the security film or correlate with them in a logical manner are also possible, as there are also color shift-capable effect pigments that have a color shift similar to that of the laser-sensitive material, but also of the laser-induced color effects enable.

Fluorescent pigments can also be mixed with the laser-sensitive substance and are very clearly visible in the ultraviolet spectral range. This results in further color combination possibilities, for example colors recognizable in the ultraviolet spectral range in combination with colors recognizable in the visible spectral range.

The lasered design on the back can be matched to or complement the design of security strips on the front of a banknote. This also creates a logical correlation in the design of two different security features. For example, a security strip shows corals on its front and the same corals are mirrored as a color effect lasered into the laser-sensitive material on the back of the banknote.

The surface of the laser-sensitive material can also be printed in the design of the bank note in order to generate an additional upgrade of the bank note design. For example, the laser-sensitive fabric is made in Iriodin blue, a blue shell is also visible through laser holes, a color effect matching the shell color is also visible and the laser-sensitive fabric can also be printed in a design. Further refinement in terms of variations in the color area size, color effect lines and window size is possible depending on productivity.

The general color of the design composition can particularly preferably be increased if a differently colored security film is visible through a window in the banknote substrate.

The laser-sensitive substance can particularly preferably function as a backside coating substitute.

The substrate particularly preferably consists of paper made of cotton fibers, as is used, for example, for banknotes, or of other natural fibers or of synthetic fibers or a mixture of natural and synthetic fibers, or of at least one plastic film. Furthermore, the substrate preferably consists of a combination of at least two different substrates arranged one above the other and connected to one another, a so-called hybrid. Here, the substrate consists, for example, of a combination of plastic film-paper-plastic film, i.e. a substrate made of paper is covered on each of its two sides by a plastic film, or a combination of paper-plastic film-paper, i.e. a substrate made of a plastic film is covered on each of its covered by paper on both sides. In the case of hybrid, the coating according to the invention is preferably located on the inner paper substrate and is particularly well protected against damage or counterfeit attacks by the plastic films.

Information on the weight of the substrate used is for example in the document DE 102 43 653 A9 specified. The font DE 102 43 653 A9 states in particular that the paper layer usually has a weight of 50 g / m ² to 100 g / m ² , preferably of 80 g / m ² to 90 g / m ² . Of course, any other suitable weight can be used depending on the application.

Documents of value for which such a substrate or security paper can be used are in particular banknotes, shares, bonds, certificates, vouchers, checks, high-quality admission tickets, but also other forgery-prone papers, such as passports and other identification documents, as well as cards, such as credit cards. or debit cards, the card body of which has at least one layer of security paper, and also product security elements such as labels, seals, packaging and the like. The simplified designation of value document includes all of the above materials, documents and product security means.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the specified combinations, but also in other combinations without departing from the scope of the present invention, insofar as this is covered by the scope of protection of the claims.

The advantages of the invention are explained on the basis of the following examples and supplementary figures. The examples represent preferred embodiments to which, however, the invention is in no way intended to be restricted. The proportions shown in the figures do not correspond to the conditions present in reality and serve exclusively to improve the clarity.

Fig. 1

eine erfindungsgemäße Beschichtung mit Perlglanzpigmenten "Merck Colorstream® T10-03" mit einem lasersensitiven Stoff, noch nicht gelasert,

Fig. 2

die erfindungsgemäße Beschichtung aus Fig. 1, gelasert,

Fig. 3

eine Beschichtung mit Perlglanzpigmenten "Merck Colorstream® T10-03" ohne einen lasersensitiven Stoff, noch nicht gelasert,

Fig. 4

die Beschichtung mit Perlglanzpigmenten aus Fig. 3, gelasert

Fig. 5

schematisch flächenübergreifendes Lasern über zwei unterschiedliche Flächen mit und ohne Perlglanzpigment,

Fig. 6

Negativ-Variante zu Abbildung 5 mit flächigem Lasern, wobei das Muster ungelasert bleibt,

Fig. 7

schematische Kombination für zwei übereinander gedruckte Schichten.

Show in detail:

Fig. 1

a coating according to the invention with pearlescent pigments "Merck Colorstream® T10-03" with a laser-sensitive substance, not yet lasered,

Fig. 2

the coating according to the invention Fig. 1 , lasered,

Fig. 3

a coating with pearlescent pigments "Merck Colorstream® T10-03" without a laser-sensitive substance, not yet lasered,

Fig. 4

the coating with pearlescent pigments Fig. 3 , lasered

Fig. 5

Schematic cross-surface lasering over two different surfaces with and without pearlescent pigment,

Fig. 6

Negative variant too Figure 5 with flat lasers, whereby the pattern remains unlasered,

Fig. 7

schematic combination for two layers printed on top of each other.

Fig. 1 shows a coating according to the invention, composed inter alia of pearlescent pigments “Merck Colorstream® T10-03” with a laser-sensitive substance that has not yet been exposed to the laser radiation of a CO ₂ laser, and Fig. 2 after exposure to laser radiation from a CO ₂ laser. The surface of the coating is heavily roughened as a result of the lasering. The CO ₂ laser with an emission wavelength of 10.6 µm and a maximum laser power of 30 W is operated in quasi-pulsed mode with a frequency of 25 kHz, with a switch-on time of 25%, an advance speed of 2500 mm / s and a line spacing (hatch) of 0.1 mm.

Fig. 3 shows a coating with pearlescent pigments “Merck Colorstream® T10-03” without a laser-sensitive substance, which has not yet been exposed to the laser radiation of a CO ₂ laser, and Fig. 4 after exposure to laser radiation from a CO ₂ laser with the above values. As a result of the lasering, the surface of the coating is also roughened, but much smaller than in Fig. 2 .

Fig. 5 shows cross-area lasing over two different areas 1 and 2 with and without pearlescent pigments. Area 1 has a laser-sensitive coating without pearlescent pigments (here color white) and area 2 has a laser-sensitive coating with pearlescent pigments (here color green). A laser beam hits the surfaces in the form of the three wave-like lines 3 and 4, so that in surface 1 there is a color change of the waves 3 from white to black and in surface 2 there is a color change of the waves 4 from pearlescent green to dark green. When using long-wave IR radiation, such as. B. the CO ₂ laser radiation with an emission wavelength of 10.6 µm, there is also a glitter effect in the lasered areas.

In contrast to Fig. 5 applied in Fig. 6 the laser covers the entire surface with the exception of the three wave-like lines, which therefore remain unlasered (so-called negative pattern). Overall, there is a color change 5 from white to black in area 1, with the exception of the three wave-like lines that remain white. In area 2, there is an overall color change 5 from pearlescent green to dark green with a glitter effect, with the exception of the three wave-like lines that remain green.

Fig. 7 shows a combination for areas printed one above the other, in which two layers of different color compositions are printed one above the other, with area 1 being the laser-sensitive coating without effect pigments and area 2 being the laser-sensitive coating with effect pigments. The laser beam generates as in Fig. 5 three wave-like lines, with the waves 3 in turn experiencing a color change from white to black and the waves 4 from pearlescent green to dark green. When using long-wave IR radiation, such as. B. the CO ₂ laser radiation with an emission wavelength of 10.6 µm, there is also a glitter effect in the lasered areas. In the case of the waves 7, the upper layer is removed, supplemented by a colored edge effect and a color effect on the lower layer. The edge effect is in Fig. 7 illustrated as black lines at the edge of the waves 7.

Claims (6)

1. Method for the treatment of a coating by laser radiation, in particular for fibrous substrates and for films, where the coating consists at least of a mixture of a binder, a laser-sensitive substance and a special-effect pigment, characterized in that the laser-sensitive substance undergoes a colour change on exposure to the laser radiation, where the exposure to the laser radiation produces a background colouring which changes or reinforces the perceived colour strength and the colour saturation of the respective special-effect pigment used, but does not change the special-effect pigment itself.
2. Method according to Claim 1, characterized in that a laser with an emission wavelength of 0.05 µm to 50 µm is used, preferably a carbon dioxide laser with an emission wavelength in the range of 9 µm to 12 µm or a diode laser with an emission wavelength in the range of 50 nm to 1100 nm or a solid-state laser with an emission wavelength in the range of 1000 nm to 1100 nm.
3. Method according to at least one of the preceding claims, characterized in that on exposure to the laser radiation the laser-sensitive substance undergoes conversion and, respectively, chemical reduction.
4. Method according to at least one of the preceding claims, characterized in that a metal salt, preferably copper(II) oxalate, an ammonium salt of molybdenum, or iron(II,III) oxide Fe₂O3 is used as laser-sensitive substance.
5. Method according to at least one of the preceding claims, characterized in that pearl-lustre pigments, fluorescent pigments, OVI pigments or liquid-crystal pigments are used as special-effect pigments.
6. Method according to at least one of the preceding claims, characterized in that the mixture of the laser-sensitive substance and the special-effect pigments is pigmented with further colour pigments, where the further colour pigments have the lowest possible absorption for the wavelength of the laser used.

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