EP3243669B1 - Production method of a security element - Google Patents

Description

The invention relates to a method for producing a security feature for a security element, a security paper or a data carrier.

Identification cards, such as credit cards or ID cards, are often provided with individual identification using laser engraving. The creation of continuous openings in documents of value, for example bank note papers, by laser cutting has also been known for a long time. For example, in the publication DE 4334848 C1 describes a security paper with a window-like opening closed by a transparent cover film, which can be produced by a laser cutting process.

the WO 2009/003587 A1 and the DE 10 2007 036622 A1 describe a manufacturing method and a corresponding security feature of the type mentioned at the beginning, which is generated by a laser cutting method in that laser radiation is radiated onto the carrier from an upper side. The carrier of the security feature is previously coated on the upper side with a marking substance that changes its color due to the action of laser beams. To produce the hole or holes, a cutting laser beam is used, the intensity of which is distributed non-uniformly, for example in a Gaussian shape, over the beam cross-section. Such radiation is referred to here as laser radiation, which is intensity-distributed over the beam cross-section, the radiation intensity falling towards the edge of the laser beam. As a result of this decrease in intensity, an edge is created on the upper side at which the carrier is no longer cut, but a modification of the marking substance with regard to its color effect takes place. In this way, the edge area of the hole generated by means of laser radiation appears colored on the upper side. This effect is from the WO 2011/154112 A1 and WO 2010/07232 A1 known. the DE 102008019092 A1 discloses the change in color in a substrate on which a foil element lies.

A colored border around the holes is also out of the WO 2009/003588 A1 known, but here several laser beams of different intensities are required in order to achieve a particularly large and thus easily recognizable color effect.

Marking substances sensitive to laser radiation 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 , US 8278244 and US 842028 .

From the EP 1641627 B1 a method for applying markings to both sides of a security paper is known, the processing taking place from one side. In order to provide the side of the paper opposite the side with a safety marking, laser radiation is radiated through the paper, the laser radiation ablating a photosensitive layer applied to the opposite side or changing its color.

the WO 98/36913 also deals with the production of security markings on both sides of a security paper, using a laser beam that ablates simultaneously on the front and back of the security paper, so that identical markings are created on both sides.

The use of laser radiation to modify security elements is also the subject of DE 10 2012 003601 A1 , DE 10 2008 019092 A2 , WO 02/03104 A2 , WO 2005/108109 A1 and the US 2011/240618 A1 .

the DE 102010053052 A2 discloses a data carrier which contains a marking generated by the action of laser radiation which, when viewed through, creates a different visual impression than when viewed from above.

Other examples of conventional methods of manufacturing a security feature are disclosed in US Pat DE10-2007-036622-A1 and DE10-2010-053052-A1 known.

The invention is therefore based on the object of providing a security element, security paper and data carrier of the type mentioned at the beginning to further improve the imitation security and to simplify the manufacturability.

The invention is defined in independent claim 1.

The invention effects a change in the thickness of the paper by irradiating the laser radiation from the front onto the carrier. This change in thickness is local. It can also be used as a reduction to zero thickness, i.e. H. be designed as a hole. On the rear side, which is opposite the front side from which the laser radiation is radiated, the laser radiation effects a color modification. This happens because the intensity of the laser radiation is no longer sufficient here to remove the carrier material, i.e. not enlarging the hole any further or making the depression even deeper, but is still able to modify the coating. In this way, a color marking is created on the opposite side in the exact register for thickness modification, which is incorporated from the front.

The terms "front side" and "rear side" are used in this description exclusively with reference to the irradiation of the laser radiation. The front side is the side on which the laser radiation is radiated, the rear side is the opposite side of the carrier. The carrier is flat. The terms front and back have nothing to do with a later use of the carrier. The choice of terms is not intended to imply that any of the pages must or may not have a special meaning for use.

The invention provides two variants: On the one hand, the paper is cut through. Then the local change in thickness is a hole. On the other hand a recess or score is made, i.e. the paper is thinned or scored from the front. In both variants, the local change in thickness is in register with the color modification on the back. So there is a hole or a depression / score that is in register with the color effect on the back.

The fact that a hole has been created by means of laser radiation can be seen from the security feature in that, during laser cutting, a flank to the direction of incidence of the laser beam is set that is not exactly parallel to the direction of incidence, since the abrasive effect of the laser beam decreases with increasing depth into the carrier. A security feature can be used to determine that a hole was created by means of a laser beam and was not punched.

The register accuracy is also used on the front side by also providing it with a coating that can be modified in terms of its color by the laser radiation. Then, for example, the WO 2010/072329 A1 Known effects on the fact that the edge around the reduction in thickness also has a color marking on the entry side. In the first variant, in which the change in thickness is a hole, this hole has a colored border on the front and on the back. The color effects can be designed differently if one uses coatings on the front and on the back that differ in terms of their color effect. Also, due to the mentioned fact that the edges of a laser cut are always at a certain angle to the direction of incidence of the laser radiation, the color markings on the front and back are in a characteristic register with one another, which is ultimately determined by the parameters of the laser beam (intensity distribution, total intensity and angle of incidence Surface of the Front and back) and the thickness of the carrier is determined. The same also applies to the second variant, in which the change in thickness is a depression. Here, in a preferred development, it can be ensured that the color marking on the rear side is bordered by the color marking on the front side in relation to the perpendicular to the surface of the front and rear side. When looking at transmitted light, you can see the color marking on the front as a circumferential edge or ring around the color marking on the back.

In a preferred development of the invention, it is provided to combine laser-markable coatings with different reaction enthalpies. For example, a substance that requires less energy input (and thus lower temperatures) for color modification can be used for the rear side coating. If the energy input on the upper side of the carrier is very high, a substance B, if it has a lower reaction enthalpy than a substance A, can be destroyed by the comparatively increased energy input, while substance A is retained. The laser energy is weakened as it passes through the carrier, which results in a color modification on the reverse side and not in the destruction of fabric B. It is possible to produce two colors on the back by varying the intensity of the laser radiation.

In the case of the second variant, in which the local change in thickness is a score or a depression on the upper side of the carrier, this has a colored edge if a coating is also applied to the upper side.

The security feature can be achieved through the use of an incorporated into a paper or on it, in particular spanning a window area, glued-on security thread in the case of banknote papers can be further improved in terms of its security against forgery if a hole is made in the security thread that extends as a recess in the carrier, the color modification also taking place under this recess on the back of the carrier. The color effect then interacts with the hole that is made in the security thread, so that the hole appears colored when viewed through it. This is particularly advantageous in the case of metallic security threads that have a reflective effect when viewed from above. When viewed from above, the security feature then shows the hole as a missing reflection, that is to say, for example, as a dark impression, and when viewed through the hole, the hole becomes colored.

A similar effect is obtained if the security thread is applied to the front side, but is not perforated with the laser radiation, but only provided with a recess. If a color-modifiable coating is applied between the security thread and the carrier on the front side at the same time, this is modified under the security thread. The color then also shines through in transmitted light because of the indentation which locally reduces the thickness of the metallic security thread. In both further developments using a security thread, perfect register accuracy is achieved due to the manufacturing process.

The security thread can also be used in addition to a change in thickness produced without it.

Furthermore, the two variants of the change in thickness can also be combined. This is done by setting the parameters of the laser radiation, for example the irradiation duration, the z. B. on the cutting speed A hole or a depression is then produced in the carrier, depending on the relevant parameters.

It should be pointed out that the depressions and / or holes can provide motifs or alphanumeric characters, as would be apparent to a person skilled in the art from the prior art cited at the beginning, for example in US Pat WO 2010/072329 A1 and WO 2011/154112 A1 or also the WO 2009/003588 A1 is known.

Insofar as the terms "above" and "below" are used in this description, this position specification relates to the direction of incidence of the laser radiation.

The term “color” is not limited to a colorful impression, but can also include white and black and the change between transparent and opaque.

The marking material does not have to be further structured or specially applied for the registration between the color and the hole / recess. It is even possible to provide the marking substance over the entire area in a much larger area than the area treated with laser radiation takes up.

Use is made of the fact that the laser beam energy in an outer region of the beam cross-section is sufficient to modify the marking substance in the zone around the edge of the hole or under the depression. In this way, a perfect registration of the opening and the laser-radiation-modified zone is automatically guaranteed.

Materials whose visible color is changed by the action of laser radiation are advantageous as marking materials. For example, thermoreactive color pigments, such as ultramarine blue, can be used for this purpose. It is also advantageous to use marking substances whose infrared-absorbing properties or whose magnetic, electrical or luminescent properties are changed by the action of the laser radiation. Security features with such laser-radiation-modified hole edges can be used in particular for the machine authenticity check. The use of a combination of different marking substances is also possible, for example in order to enable both a visual and a machine authenticity check of the security feature. If several marking substances are used, they can be placed next to one another or in different layers on top of one another. Alternatively, in one embodiment according to the invention, the modification of the carrier / marking substance can consist of removal or destruction. In this case, the marking substance is preferably a metallic coating.

According to an advantageous variant of the invention, laser-radiation-modifiable effect pigments are used as marking substance which can be modified by laser radiation. Such effect pigments are available to the person skilled in the art with different properties, in particular with regard to their body color, the color change under the action of laser radiation, the threshold energy and the required laser radiation wavelength. Effect pigments which, under laser radiation, not (only) change their visible color, but also their infrared-absorbing, magnetic, electrical or luminescent properties, are also known to the person skilled in the art. The modification of the effect pigments can be done with laser radiation in the ultraviolet, visible or infrared spectral range, for example with a CO ₂ laser with a wavelength of 10.6 microns.

In a further likewise advantageous variant of the invention, a pigment-free marking substance that can be modified by laser radiation is used. Pigment-free marking substances can also be applied to the carrier, for example as an engraving or printing ink. A coating of high transparency can be produced with pigment-free marking substances, into which a permanent and high-contrast marking can be made by laser action at high speed. Pigment-free marking substances can be modified by laser radiation in the ultraviolet, visible or infrared spectral range, for example with the 10.6 µm radiation of a CO _{2 laser.} Specific, non-limiting examples of pigment-free, laser-modifiable marking substances are given in the publications WO 02101462 A1 , US 4343885 and EP 0290750 B1 specified.

The invention also comprises a security element for security papers, documents of value and the like with a security feature produced according to the described method. The security feature has a carrier whose thickness is locally changed by the action of laser radiation and at the same time has a zone modified in terms of color by the laser radiation. The color-modified zone lies on the underside, which is opposite the front side from which the laser radiation is introduced. If the local change in thickness is a hole, the zone in which the color is modified is at the edge of the hole. If the thickness modification is a depression, the color zone is below the depression. Such a security element can, for example, in the form of a security thread, a label, a transfer element or a cover film for a window area or a hole in a value document, such as a bank note.

In addition, the invention also comprises a security paper for the production of documents of value or the like with a security feature produced according to the described method. The invention further includes a data carrier with a security feature produced by the method described, in particular a value document such as a bank note, identity card or the like, the data carrier having a carrier.

Further exemplary embodiments as well as advantages of the invention are explained below with reference to the figures, the representation of which is true to scale and proportions was dispensed with in order to increase the clarity.

Fig. 1

eine schematische Darstellung einer Banknote mit einem Sicherheitsmerkmal,

Fig. 2

eine Detailaufsicht auf eine mögliche Realisierung des Sicherheitsmerkmals der Fig. 1 von der Vorder- und Rückseite,

Fig. 3(a)-(b)

eine räumliche Energieverteilung eines Laserstrahls zur Erläuterung der Herstellung des Sicherheitsmerkmals,

Fig. 3c

eine Schnittdarstellung eines Teils des Sicherheitsmerkmals der Fig. 1 und 2 in einer ersten Ausführungsform, in welcher Löcher mit farbigem Rand erzeugt werden,

Fig. 4

eine Schnittdarstellung ähnlich der Fig. 3c, jedoch für eine zweite Ausführungsform, in welcher Vertiefungen auf einer Vorderseite des Sicherheitselementes und dazu in genauer Passerung farbige Bereiche auf der Rückseite des Sicherheitselementes erzeugt werden,

Fig. 5

eine Darstellung ähnlich der Fig. 2 für eine abgewandelte Variante des Sicherheitselementes und

Fig. 6-8

Darstellungen ähnlich den Fig. 3 und 4, wobei ein ein Fenster überspannender Sicherheitsfaden oder Patch vorgesehen ist, der ebenfalls mit Laserstrahlung strukturiert ist und einen in Passerung dazu liegenden Farbbereich hat.

Show it:

Fig. 1

a schematic representation of a banknote with a security feature,

Fig. 2

a detailed supervision of a possible implementation of the security feature of the Fig. 1 from the front and back,

Fig. 3 (a) - (b)

a spatial energy distribution of a laser beam to explain the production of the security feature,

Figure 3c

a sectional view of part of the security feature of FIG Figs. 1 and 2 in a first embodiment, in which holes with a colored border are created,

Fig. 4

a sectional view similar to that Figure 3c , but for a second embodiment, in which depressions are created on a front side of the security element and, for this purpose, colored areas on the rear side of the security element in precise registration,

Fig. 5

a representation similar to the Fig. 2 for a modified variant of the security element and

Fig. 6-8

Representations similar to the Fig. 3 and 4th wherein a security thread or patch is provided which spans a window and is also structured with laser radiation and has a color area in register therewith.

The invention is explained using the example of a bank note. the Fig. 1 shows a schematic representation of the bank note 10, which is an in Fig. 2 security feature 12 shown in more detail.

The security feature 12 is characterized, for example, by a motif in the form of an outline 18. Fig. 2 shows the security feature 12 in the left illustration from a front side 14, in the right illustration from an opposite rear side 16. Correspondingly, the outline 18 is mirrored in the illustration on the right compared to the illustration on the left. The outline 18 was created by placing a laser beam over the Front 14 was performed. Previously, the rear side 16 was provided with a laser-markable coating which, when exposed to laser radiation above a certain energy, shows a color effect, for example changes its color. In this regard, reference is made to the above general part of the description. The intensity of the laser radiation was varied when the contour line 18 was traced, so that the contour line 18 consists of different sections. In some sections, the intensity of the laser radiation was set in such a way that depressions 20 are worked into the carrier material of the security feature 12 from the front side 14. In other sections, the laser radiation is switched off or reduced in such a way that the carrier material is not processed. This results in gaps 22, which are shown in the illustration on the left in FIG Fig. 2 are symbolized by a narrow black line. The depressions 20 are symbolized by a line that is not filled. In other sections, on the other hand, the laser radiation intensity was set in such a way that a hole 24 is generated through the carrier. The holes 24 are symbolized by thicker, unfilled lines.

The effect of the laser radiation on the back is in Fig. 2 to recognize. In the sections in which there is a gap 22 on the front 14, there is also a gap 22 in the outline 18 on the rear 16 Laser radiation when exiting the rear side 16 was still sufficient to modify the laser-modifiable coating with regard to its color. At the locations of the holes 24 there is also a hole on the rear side 16, which however now has a colored edge 30 due to the coating.

As a result of this design of the outline 18, a motif 26 is produced overall from the front side 14, which is also recognizable on the rear side 16 as a mirror image and in a different color design than the motif 26 ′.

Of course, embodiments can also work only with holes or depressions and also without gaps. The motifs also do not have to be restricted to outlines 18. Large holes / depressions are equally possible, e.g. B. to produce two-dimensional motifs.

The principle of the simultaneous creation of the holes or depressions and the color design is in Fig. 3a illustrated. Fig. 3a shows an example of an essentially Gaussian spatial intensity distribution of a laser beam 34. The fluence thus decreases from the center to the edge.

In an inner area, a first working area A1, the laser beam intensity exceeds the minimum energy E1 required for cutting or ablating the carrier. With E2 is in Fig. 3a denotes a reaction energy of the marking substance which, when exceeded, causes the named color change. As can be seen directly from the figure, in an outer area of the laser beam profile, a second working area A2, the fluence lies between the reaction energy E2 required for the color change and the minimum energy E1 required for cutting, so that only one color change is induced in this area 34 , but the carrier is not cut.

The carrier is therefore discolored during laser cutting by the laser beam in a zone on the rear edge of each hole 24 in perfect register with the hole 24. The width of the colored border 30 corresponds to the width of the second working area A2 and depends on the intensity distribution the beam cross-section, the reaction energy of the effect pigments used and the material properties of the carrier, e.g. B. the banknote paper.

Outside the first working area A1 and the second working area A2, the laser beam intensity is below the reaction energy of the coating, so that the color of the carrier is not changed there.

For example, thermoreactive color pigments, such as ultramarine blue, can be used as a coating that changes its visible color as a result of the action of laser radiation.

It goes without saying that two or more coating substances with different threshold energies or a combination of visually and mechanically detectable substances can also be used in order to generate several matched edge effects.

Instead of the coating substance described by way of example, a pigment-free, laser-radiation-modifiable marking substance can also be used. Such marking substances can also be printed onto the carrier as a coating, for example as an engraving or printing ink. Non-pigmented, laser-radiation-modifiable coatings can have a very high level of transparency when they are not written on. By the action of laser radiation, for example a CO ₂ laser at 10.6 μm, permanent and high-contrast markings, for example black lettering, can be produced in the coating at high speed.

It is also possible that the heat generated during laser cutting causes the modification. In this way, the modified edge area of the opening can optionally even be larger than the beam extension.

Figure 3b FIG. 11 shows a beam profile of a laser beam 34 that has a lower maximum energy. The laser beam is thus able to make a recess in the material of the carrier, but does not create a hole. The recess is made as soon as the energy of the laser beam is above a threshold value E3. The maximum width of the depression is given by a width that is given from the first and the second working area A1 + A2. In a core area, the intensity of the laser beam when exiting the rear side of the carrier also exceeds the energy E2 which is required to change the color of the laser-modifiable coating applied to the rear side 16. In the first work area A1, the color marking 28 is thus produced on the rear side under the depression.

The explanations based on the Figures 3a and 3b assume an essentially Gaussian spatial distribution of the energy of the laser beam 34. As will be explained below, it is not absolutely essential that the intensity profile is Gaussian. Furthermore, the invention is not restricted to the production of circular holes. Rather, with the laser radiation 34, like the Fig. 2 shows a line to be cut.

the Figures 3a and 3b are based on a constant cutting speed. At constant cutting speed and high maximum power, the energy input of the laser radiation into the material of the carrier exceeds the energy required to create a hole in work area A1 or the energy required to create a recess in area A1 + A2.

The energy E1, which is necessary to create a hole, or the energy E3, which is necessary to create a recess but not a hole, is of course influenced by the cutting speed. In this way, with a constant cutting speed, the practically instantaneous variation of the laser power allows the hole size, for example the cutting width or the depth of the recess, to be varied as desired along the path along which the laser beam is guided.

The same applies if the laser radiation is kept constant by changing the cutting speed. At a high cutting speed, the laser radiation only acts on the material of the carrier for a relatively short time, so that the energy input is comparatively low. Accordingly, the energy E1 or E3 required to create a hole or create a depression is exceeded only in a small area. At a lower cutting speed, on the other hand, the laser radiation acts longer on the material of the carrier, so that a higher energy input into the carrier results. Correspondingly, a larger hole or a deeper and / or further depression results, since the area in which the energy E2 or E3 is exceeded is correspondingly larger. Accordingly, the structuring of the outline shown in Fig. 2 is shown, can also be generated in one operation in that the cutting speed at the transition from the sections 24 with a hole, 22 with a gap and 20 with a depression is varied accordingly. To create the hole 24, the cutting speed must be the lowest, and to create a gap, it must be the highest. The inverse applies to the energy at a constant cutting speed. To create the depressions 20, it lies in between.

For the sake of simplicity, the effects of changing the laser parameters energy and cutting speed have been explained separately. It goes without saying, however, that the two parameters can also be changed jointly and simultaneously in order to have a greater range of variation and / or a finer setting available. Optimization with a view to processing the carrier as quickly as possible is of course possible.

It is optionally also possible that the marking substance is removed or destroyed immediately next to the cut edge and is only modified from a certain small distance from the cut edge.

It is essential for generating the colored edge 30 that the laser beam 34 has an intensity distribution that is not constant, that is to say does not have a top-hat profile. Any intensity profile, in which the intensity of the laser beam 44 decreases towards the edge of the beam cross-section compared to the maximum value, can be used for generating the colored edge 30, the type of intensity profile naturally being related to the width of the edge 30 relative to the maximum hole diameter of each hole 24 affects. When creating a depression on the front side with a discoloration on the rear side in register therewith, on the other hand, an intensity distribution that has a top-hat profile is also possible. Such a profile is therefore an option for designs that only work with recesses and do not create any holes with a colored border on the back.

Figure 3c shows a schematic sectional illustration through the security feature 12 in the area of a hole 24. In the sectional illustration it can be seen that the carrier 38 on its front side 14 with a laser-modifiable Coating 40 is provided. The rear side 16 has a laser-modifiable coating 42. The coating 40 is optional. The laser radiation 34, for which the beam profile is plotted as an example, is radiated from the front side 14 from an incidence direction 36 which, in the example chosen, is perpendicular to the front side 14 and to the rear side 16. The laser beam 34 creates the hole 24, which has an upper edge 44 and a lower edge 46. Due to the usual removal of material for laser radiation, the hole has a flank 48 which is inclined to the direction of incidence 36. In other words, the width of the hole at the bottom 46 is less than the width at the top 44. The width at the bottom is B1 in Figure 3c registered.

The laser radiation modifies the coatings 40, 42 applied there on the upper edge 44 and on the lower edge 50, so that a colored edge 50 on the rear side 16 and a colored edge 52 on the front side 14 result for the hole 24. A color margin C1 at the lower colored edge 50 and a color margin C2 at the upper colored edge 52 are determined by the based on the Fig. 3a explained effect of the intensity distribution of the laser beam 34 is determined. An offset D1 between the lower and upper colored edges 50, 52 is also determined by the intensity distribution of the laser beam and thus its cutting effect and likewise by the thickness of the carrier 38.

This offset D1 can, as in Figure 3c registered, be positive. However, it can also be negative, ie the lower colored edge 50 and the upper colored edge 52 overlap when viewed along the direction of incidence 36. This offers a person skilled in the art design options with regard to the logo 26 in plan view or through view.

It is also possible to choose the coatings 40 and 42 differently, i. H. the colored edge 50 can have a different color than the colored edge 52. This opens up further design possibilities, in particular in combination with a negative offset D1. In the case of a negative offset D1, the hole is outlined in three colors when viewed through. In an inner area you can see the color of the lower edge 50. In an outer area the color of the upper colored edge 52. In the area of the negative offset D1 you can see the mixture of the two colors. As a result, the hole 24 is outlined in three colors when viewed through.

Fig. 4 shows a further embodiment in which the laser beam 34 does not produce a hole 24, but a recess 54. The laser beam exiting on the rear side 16 still has an energy above the minimum energy E2, at least in sections under the recess 54, which is required to produce the color effect in the coating 42. An ink zone 56 is thus established on the underside 16, which is in a precise position relative to the depression 54. As a score on the front side 14, the recess 54 can modify the optical impression of the carrier 38 from the front side 14. In Fig. 4 is like in Figure 3c also, the optional coating 40 is provided on the front face 14. A colored edge 52 of the depression 54 is thus established on the upper side, which is also in precise register with the color zone 56. The color zone 56 has an extent D2 which is predetermined by the intensity distribution of the laser beam 34 in combination with the thickness of the carrier 38 and, if applicable, the cutting speed (as explained above). The upper colored edge 56 has a width C2, again with an offset D1, which can also be positive or negative. Based on the above Figure 3c What has been explained applies here equally, with the color zone 56 now taking the place of the lower colored edge 50.

Fig. 4 shows that there are sections of the recess 54, underneath which there is no color zone 56. These are those sections at which the energy of the laser beam when exiting the rear side 16 was not sufficient to modify the coating 42 with regard to the color. This makes it possible to thin out the carrier 38 in areas, ie to reduce its thickness, without producing an ink zone 56 underneath.

It should be noted that generally, i. H. for all embodiments, the structuring of the color markings in the coatings 42 and, if present 40, does not depend on a structured application of the coatings, but is generated by the laser radiation. Of course, a combination with a structured application of the coatings is possible in order to achieve an additional structuring of motifs.

The embodiment of the Fig. 4 allows the front side 14 of the carrier 38 to be scored, which is in register with the ink zone 56 on the rear side 16 and, if provided, also to a colored edge 52 on the front side 14 of the carrier 38.

The coatings on the front and back can use different laser-sensitive marking substances. It is possible to provide a first fabric on the front and the back which shows a first color change. It is also possible to use a first fabric with a first color change on the front and a second fabric with a second color change on the back. This can also be combined with laser energies / cutting speeds, which ensure that the fabric is removed so that the original color of the fabric is no longer present. This can be seen as the third color change, which is ultimately an ablation of the substance.

It is also possible to combine laser-sensitive substances with different reaction enthalpies within each coating. Thus, in one embodiment, a substance can be used for the coating 42 on the rear side 16 which requires less energy to change the color. This substance is hereinafter referred to as the second substance. In one embodiment, it is combined with a first substance which has a higher enthalpy of reaction. These substances are contained in combination in the coatings on the front side 14 and the rear side 16. If the energy input on the front 14 is very high, the second substance, which has a lower reaction enthalpy than the first substance, is destroyed by the excessive energy input, while the first substance is retained. As a result, the recess 20 is then surrounded on the front side 14 by a colored border, the color of which is determined by the first material.

On the other hand, the first and the second substance are retained in sections with the application of lower laser radiation energy, which is not sufficient to create a depression or causes a shallow depression. The color impression in these sections of the outline 18, which are gaps 22 of shallower or absent depressions, results from the color modification of the combination of the first and the second substance. When it passes through the material of the carrier 38, however, the laser energy is weakened, as a result of which there is a color change when it exits the rear side 16 and does not result in the destruction of the second material. Sections then appear on the rear side in which a color marking 28 is effected, which results from a color change of the first and the second material.

If the first substance is not introduced into the coating 42 on the rear side 16, the color effect is brought about exclusively by the second substance. In Intermediate gaps 32, which correspond to the flatter or absent depressions in the gaps 22, which were exposed to laser radiation of lower intensity, the color effect is different. If only the second fabric has been used, its color effect may fail, for example. If the first and the second substance were used in the coating 42, the color effect of the first substance may be absent and that of the second substance may occur, for example. The result is a colored, structured contour line 18 on the rear side 16, which was structured exclusively by varying the intensity of the laser radiation when irradiated from the front side 14 with regard to its multicolor.

Fig. 5 shows a possible embodiment of the security feature from the front side 14 or the rear side 16, in which only two different markings are produced in an outline 18. The embodiment of the Fig. 5 is thus a simplification of the version according to Fig. 2 . On the front side 14, either a gap 22 is generated by the laser radiation, that is to say the embodiment according to the cross-section Figure 3c realized, or a recess 20, so the embodiment according to Fig. 4 . On the rear side 16 there is accordingly a gap 32 in the outline 18, which has a colored edge corresponding to the edge 50 of the Figure 3c has, or a color marking 28, which the color zone 56 of the Fig. 4 is equivalent to.

Fig. 5 shows on the front side 14 for the letter "P" a regular sequence of depressions 20 and gaps 22, for the letter "L" an at least partially irregular sequence to illustrate that both variants are possible.

The gaps 22 are generated with a laser beam energy which is higher than that for the generation of the depressions 20. In other words, the contour line 18 is formed with an energy of the laser radiation 34 that varies locally along the contour line. On the rear side 16, the sequence of gaps 32 with colored edges 50 and colored markings 28 corresponding to the color zones 56 is accordingly established.

Of course, the variation in intensity can also have the result that the color effect on the colored edge 50 of the gaps 32 differs in color from the color effect of the color zones 56 which form the color markings 28. Then the outline 18 on the rear side 16 is structured in color. The same can additionally or alternatively also take place on the front side 14. This is basically achieved in that a substance or a combination of substances shows a different color change depending on the intensity of the laser radiation. In other words, the change in color of the coating 40 and / or 42 depends on the intensity of the laser radiation.

Fig. 6 FIG. 4 shows an embodiment similar to that of FIG Fig. 4 . In addition to the creation of the color zone 56 and the colored edge 52 caused there by making the recess 54 in the carrier 38, a security thread 58 or patch or film element is also provided on the coating 40 next to the location where the recess 54 is made, into which a recess 60 is made by means of the laser radiation. This indentation ensures that a color zone 62 is formed in the coating 40 below the point at which the laser radiation is irradiated. Due to the different material composition of the security thread 58 compared to the carrier 38, the security thread 58 reacts differently to the laser radiation. In the example shown, the Fig. 6 are the circumstances so that the recess 54 and the recess 60 were produced with identical laser beam parameters and yet different depths result. This makes laser control easier.

Due to the weakening of the security thread 58 in the area of the recess 60, the color zone 62 is clearly visible from above. The same also applies to the underside of the carrier 38 if there is a corresponding transparency.

Fig. 7 shows a modification of the construction of the Figure 3c , with no coating 40 now being provided on the front side 14. In other words, the carrier 38 is provided with the coating 42 only on the rear side 16. Accordingly, the colored edge 40 results only in the area of the hole 24 and only on the rear side 16 of the carrier 38. This embodiment can, as in FIG Fig. 7 shown, can optionally be supplemented by again applying a security thread 58, patch or film element to the front side 14, into which a hole 64 is machined by means of the laser radiation, which extends as a recess 66 in the carrier 38. The laser radiation again results in a color zone 68 on the rear side 16 in precise registration with the hole 64 in the security thread 58.

Fig. 8 6 and 7 shows a combination of the features of the embodiments of FIGS. At the same time, a security thread 58, patch or film element is arranged on the front side 14 on the coating 40, into which the hole 64 was made with the laser radiation and extends as a recess 66 in the carrier 38. As a modification of the situation of the Fig. 7 this creates not only the color zone 68 on the rear side 16, but also a color edge 70, which the Hole 64 or the recess 66 surrounds. This colored edge 70 and the colored zone 68 are in exact register with the hole 64.

List of reference symbols

10

Banknote

12th

Security feature

14th

front

16

back

18th

outline

20th

deepening

22nd

gap

24

hole

26, 26 '

motive

28

Color marking

30th

colored border

32

gap

34

Laser radiation

36

Direction of incidence

38

carrier

40

Coating

42

Coating

44

edge

46

edge

48

Flank

50

colored border

52

colored border

54

deepening

56

Color zone

58

Security thread

60

Indentation

62

Color zone

64

hole

66

deepening

68

Color zone

70

Color rim

A1

Workspace

A2

Workspace

B1

Hole width

C1

Color margin

C2

Color margin

D1

Offset

D2

expansion

E1

Energy threshold

E2

Energy threshold

E3

Energy threshold

Claims (7)

1. Method for producing a security feature (12) for a security element, a security paper or a data carrier, wherein

   - a carrier (38), which has a front side (14) and a rear side (16), is provided,

   - the carrier (38) is provided with a coating (42), which can be modified in its colour by laser radiation (34), and

   - the carrier (38) is locally changed in its thickness by the action of laser radiation (34) of distributed intensity in the cross section of the beam,

   - wherein at the same time the coating (42) is modified in colour by the laser radiation (34),

   - the carrier (38) is provided on its rear side (16) with the coating (42),

   - the laser radiation (34) is radiated onto the carrier (38) from the front side (14), wherein

   -- either a hole (24) is produced in the carrier (38) as a local change in thickness and, as a result of the intensity distribution over the cross section of the beam, a zone (52), which surrounds a rim (46) of the hole (24) on the rear side (16) of the carrier (38), is modified in colour, or

   -- a depression (20) is produced on the front side (14) of the carrier as a local change in thickness and at the same time a zone (56), which lies underneath the depression (20) on the rear side (16) of the carrier (38), is thereby modified in colour,

   - the carrier (38) is also provided on its front side (14) with a coating (40), which can be modified by the laser radiation (34) in its colour, so that also a zone (50), which surrounds the rim (44) of the hole (24) or of the depression (20) on the front side (14) of the carrier (38), is modified in colour.
2. Method according to Claim 1, characterized in that the carrier (38) is a banknote paper and in that a security foil (58), in particular a security thread or patch, is applied to its front side (14) and an indentation (60) is introduced into it by means of the laser radiation (34), so that under this indentation (60) the coating (42) on the front side (14) of the carrier (38) is modified in colour.
3. Method according to either of Claims 1 and 2, characterized in that, in the modification, the coating (40) of the front side (14) undergoes a change of colour that differs from that of the coating (42) on the rear side (16).
4. Method according to Claim 1, characterized in that the carrier (38) is a banknote paper and in that a security thread (58) is applied to its front side (14) over the coating (40) and the depression (66) is introduced into it by means of the laser radiation (34), wherein also thereunder the coating (42) on the rear side (16) of the carrier (38) is modified in colour.
5. Security feature for a security element, a security paper or a data carrier, produced by a method according to one of Claims 1 to 4.
6. Security paper with a security feature (12) according to Claim 5.
7. Document of value or data carrier, in particular a banknote (10) or identity card, with a security paper according to Claim 6.

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