DE102012003601A1 - Printing process with Passer between print and watermark - Google Patents

Abstract

The invention relates to a printing method for producing a security element (1), wherein a substrate (2) is provided which has a front and a back side (3, 4), at least for certain radiation (10) is translucent and a watermark (5 ), which modulates the opacity of the substrate (2), on the front side (3) a printing ink (9) is applied, wherein on the front side (3) the ink (9) at least partially covers the watermark (5), the printing ink (9) is modifiable by means of the determined radiation (10), and the substrate (2) is irradiated by the rear side (4) with the determined radiation (10), the watermark (5) being modified with respect to the modification of the ink (9) Mask is used and the ink (9) in the register to the watermark (5) is modified.

Description

The invention relates to a printing method for producing a security element, wherein a substrate is provided, which has a front and a back, is translucent at least for certain radiation and has a watermark, which modulates the opacity of the substrate, and applied to the front of a printing ink becomes.

To increase the security against forgery of protected objects, for example banknotes, watermarks are known. They are usually introduced in the production of the substrate from which the security element is made, usually a paper. Watermarks are easily recognizable when the security element is viewed through transmitted light, since they modify the opacity of the substrate. As a rule, in the production of the paper, the thickness of the substrate is varied, so that a reduction in thickness leads to an opacity reduction. However, other approaches to generating a watermark are also known, for example using so-called watermark colors, which also locally modify the opacity of the substrate.

Since watermarks are usually formed in the substrate in the production of the starting material for the security element, for example in the production of a banknote paper, it is fundamentally difficult in later printing to arrange printed elements in an exact position relative to the watermark, that is to pass.

Due to variations in the cutting process of a paper substrate, paper sheets usually have variations in the position of the watermark, which are in the millimeter range. In a printing process, additional register variations are added due to variations in placement positions, transfer variations in printing presses, paper moisture swings and a swaging effect of the paper in stitching.

In order to apply a pressure in the register to the watermark, it would be conceivable to detect the position of the watermark in the substrate by means of a transmission sensor, and to adjust the subsequent printing method to the current position of the watermark, e.g. B. by a mechanical adjustment of a printing cylinder or correction of the printing data of a digital printing system. This results in effort by the detection of the watermark position, an image analysis to be performed in real time to determine the watermark position and a correction of the printing position to be performed in real time. The effort increases with the printing speed.

The invention is therefore an object of the invention to provide a printing method that can be printed in the register to a watermark without previously determined the location of the watermark precisely and the printing system must be adapted to the location of the watermark.

This object is achieved according to the invention with a printing method for producing a security element, wherein a substrate is provided which has a front and a back, at least for certain radiation is translucent and has a watermark which modulates the opacity of the substrate, and on the front Ink is applied, solved in which the ink on the front side at least partially covers the watermark, the ink is modifiable by means of the particular radiation, and the substrate is irradiated from the back with the particular radiation, the watermark regarding the modification of the ink as Mask is used and the ink in the register is modified to the watermark.

The invention is based on the recognition that the energy of radiation is attenuated by the substrate. The more opaque the substrate, the stronger the weakening. Therefore, advantage is taken of the property of the watermark to modulate the opacity of the substrate. The watermark is used as a mask for a modification of the ink using a printing ink modifiable by certain radiation for which the substrate is translucent and the particular radiation from the back of the substrate to the front on which the ink is printed Watermark is applied overlapping, is irradiated. This masked by the watermark is a modification of the ink, which automatically lies in the perfect register to the watermark.

As a modification of the printing ink, in particular an ablation comes into question when a printing ink is used which is ablatable. In principle, however, any suitable modification of a printing ink can be used.

This modification can be done directly, ie by direct action of the particular radiation on the printing ink, or indirectly. In the latter case, the particular radiation modifies an element which in turn is used to modify a color perceivable on the front. For example, by means of the particular radiation, a layer can be modified which influences the adhesion of the printing ink on the front side. After the modification of this adhesion-influencing layer, the ink is then removed in a further step in the areas in which the layer was modified (or not modified in the inverse case). The procedure is similar to the principle of the so-called wash color. A further possibility for indirect modification is the modification of a developer layer which, in interaction with a developer or fixing medium, modifies the ink at those points at which the developer layer has been suitably exposed. An indirect influence on the printing ink is also possible in a two-stage process if the printing ink has an adhesive layer which is applied to the front side and exposed from the rear side with the participation of the watermark as a mask. In a second step, a color layer of the printing ink can then be applied, which adheres only to those places where the exposure took place. Optionally, the exposed adhesive layer can also be acted upon here in an intermediate step so that it remains only in those areas in which a suitable exposure took place (positive effect) or remains in those areas in which no suitable exposure took place (negative effect). The term "printing ink" thus also means a multilayer system, wherein a part of the layer system is applied to the front surface before the exposure and then illuminated with the determined irradiation. Another part of the layer system is then applied only after the exposure. As far as is spoken in this specification and in particular in the claims so of "printing ink" and the application of this ink is mentioned on the front over the watermark, it is also included that applied by a printing ink layer system, only a part of the layer system and with the specific irradiation is exposed; the other part is then applied after these steps and interacts with the exposed portion of the layer system to create a printed image in the watermark to the watermark.

Especially for the use of banknotes watermarks are common, which modulates the opacity of the substrate by varying a thickness of the substrate at a constant density of the substrate, since such watermarks are usually very difficult to emulate. These watermarks are well suited for the printing method according to the invention, which then supplements the appearance of the watermark by further image information, which lies in the register to the watermark. This makes it possible, for example, to add color information provided by the watermark. Also, the image information of the watermark, which appears per se only in transmitted light, by means of the invention produced in Passer print image in incident light observation can be seen.

A watermark that modulates the opacity of a substrate can also be generated by a so-called watermark color, rather than by varying the thickness of the substrate. The watermark color causes a reduction of the scattering of light in the substrate core. Basically, scattering is due to a large number of interfaces of fibers, fillers, glue, etc. to the surrounding air. These boundary surfaces to the surrounding air are significantly reduced by suitable binder components in the watermark color, so that in these areas the opacity decreases. Such a binder component is, for example, glycerin, which penetrates into the substrate and remains in the pores of the substrate.

Watermarks generated by watermark color are also referred to as "spurious" watermarks. Watermarks generated by varying the thickness of the substrate while maintaining the substrate's density are also referred to as "true" watermarks.

The same applies analogously if the watermark is caused by a coloration which modulates the opacity of the substrate.

A watermark can binarise the opacity of a substrate, i. H. it produces a structure which can be seen in the transparency in that the substrate is less opaque or more translucent at individual points. However, there are also known watermarks in the sense of gray scale modulation, which modulate the opacity or the translucency between two maximum values. In the transmitted light view, one then recognizes a grayscale image. Both types of watermarks are equally suitable for the present printing process. In the case of a watermark which is designed in the manner of a gray-scale image, it is, of course, particularly advantageous to use an ink whose modifiability goes beyond a simple threshold modification, the modification of which thus knows more than two states. The multilevel modulation by the watermark is then converted into a corresponding multistage modification of the printing ink.

A particularly finely graded opacity modulation can be achieved by combining a paper thickness modulating "true" watermark with a watermark color generated "spurious" watermark.

Printing inks usually consist of binders, auxiliaries, driers or drying accelerators and coloring constituents, such as dyes or pigments. If one irradiates on such printing inks a radiation having a wavelength which is absorbed by the coloring constituents to a certain degree, one achieves that the particular Radiation ablated the ink for modification. In the case of ablation, therefore, ink and certain radiation are chosen to match each other so that the particular radiation is absorbed by the ink so that ablation is possible.

In order to avoid influences of the particular radiation on other components of the substrate or on the substrate applied coatings as possible, it is preferable to irradiate the particular radiation as narrow as possible in the range of an absorption band of the ink. This is particularly easy to realize with laser radiation.

If a printing ink per se has no constituent which makes it suitable for ablation, it is preferable to add a certain amount of additive, for example soot, which absorbs the particular radiation to ablate the printing ink. In particular, the use of an admixture makes it possible to select the particular radiation such that it lies in the non-visible spectral range, for example IR radiation, when the admixture increases the absorption coefficient of the ink in the corresponding spectral range.

Of course, instead of ablation, which usually leads to brightening when using dark colors, it is also possible to design the modification such that it leads to a color change, for example by thermal activation of a color. This is especially true when using effect inks based on inks that show a viewing angle-dependent color impression (so-called optical variable ink) and colors that are structurable before drying by a magnetic field.

It is therefore preferred for the printing ink to comprise one or more of the following substances: an optically variable color, a magnetically orientable color, a metallic color, a color which is effective in the non-visible spectral range.

As already mentioned, the principle according to the invention provides that printing ink and certain radiation are coordinated so that the particular radiation is able to modify the printing ink, wherein the watermark which modulates the opacity of the substrate is used as a mask. The term "certain radiation" as used in this specification therefore expresses that a printing ink is used which is modifiable by means of this radiation. The modification, for example in the form of an ablation, is achieved in printing ink when the particular radiation at the front has a suitable intensity. The opacity modulation caused by the watermark reduces the intensity of the radiation on the front surface on which the ink is located. The radiation intensity on the backside is therefore adjusted so that the opacity modulation caused by the watermark on the front side results in a radiation modulation which modulates the modification effect on the ink. In other words, the radiation intensity on the backside is chosen so that at the points where the watermark causes the lowest opacity in the substrate, a modification of the ink occurs at the points where the watermark causes the highest opacity of the substrate, however, no or only a very slight modification is achieved. Then, the watermark serves as a mask in the irradiation of the substrate with the specific radiation. Since the modification of the printing ink generally requires a comparatively high radiation intensity, it is advantageous to use a beam that is scanned over the back side of the substrate. The beam may be in the form of a laser beam, for example. It is then not only easy to provide the required radiation intensity, also the intensity adjustment can be done easily, since it is less effort to adjust a beam in its intensity, as to effect a homogeneous intensity adjustment of a fanned light beam.

The use of a rasterized beam further has the advantage that the intensity of the particular radiation can be varied in addition to the use of the watermark as a mask to effect additional patterning of the modification of the ink. This additional modification is of course not in the register for the watermark.

In addition, it is possible to apply additional masking on the backside which attenuates or absorbs the particular radiation. This achieves a further structuring of the ink modification.

Investigations by the inventors have shown that no visually visible marking is formed on the backside when, with the printing method according to the invention on the front side, the printing ink is masked exposed by the watermark and modified, for example ablated.

In principle, the ink to be modulated can contain substances which can be ablated by radiation as well as substances which can be developed by radiation (for example thermochromic substances which preferably have a non-reversible change in color or opacity) and, in addition, substances which can not be ablated or developed by radiation. Depending on the color formulation, the last-mentioned substances remain undisturbed on the substrate or are only partially removed. Furthermore, the printing ink may contain a substance mixture in which the individual components are modified in stages as a function of the incident energy. For example, a first component at very low opacity and a second component is already ablated at medium opacity.

According to a preferred embodiment, the printing ink contains one EP 1 826 728 A2 known laser markable feature substance with core-shell particles, wherein one of the materials of core and shell absorbs the radiation of a marking laser and the other of the materials of the core and shell does not absorb the radiation of the marking laser. According to another preferred embodiment, the core-shell particle contains one EP 1 826 730 A2 known UV-excitable organic luminescent substance, wherein the organic luminescent substance forms the core, which is coated with a shell, which increases the chemical and / or physical resistance of the luminescent substance.

According to a further preferred embodiment, the printing ink contains one EP 1 826 246 A2 known modified iron blue pigment, which is coated with an alkali and / or acid-resistant shell.

The term ink used here stands out for the printing effect achieved by the watermark-masked and radiation-based modification. Of course, the printing ink itself can also comprise structures which go beyond conventional color systems, for example a film coating or a metallization.

Items to be protected within the scope of this description may include, for example, security papers, identity and value documents (such as bank notes, chip cards, passports, identification cards, identity cards, stocks, bonds, certificates, vouchers, checks, tickets, credit cards, health cards, etc.). ) as well as product security elements, such. As labels, seals, packaging, be.

The term security paper is understood here in particular as the precursor that can not yet be processed to form a value document which, in addition to the pressure produced according to the invention, may also have further authenticity features (such as, for example, luminescent substances provided in the volume). Under value documents here on the one hand from security papers produced documents, eg. B. banknotes understood. On the other hand, value documents can also be other documents and articles which are processed with the printing method according to the invention, so that the value documents have non-copyable authenticity features, whereby an authenticity check is possible and at the same time unwanted copies are prevented.

The substrate is particularly preferably made of paper made of cotton fibers, as used for example for banknotes. Preferably, the substrate can also be made of paper of other natural fibers, also preferably of synthetic fibers, d. H. a mixture of natural and synthetic fibers. Further preferably, the substrate consists of a combination of at least two superimposed and interconnected different substrates, a so-called hybrid, for example a combination of plastic film-paper-plastic film, d. H. a substrate of paper is covered on either side by a plastic film, or paper plastic film paper, d. H. a substrate made of a plastic film is covered on each of its two sides by a paper substrate.

Preferably, the substrate consists of an at least partially transparent plastic film. The watermark is generated in this case by a color which is applied to one side of the substrate and whose hue is at least similar to the hue of the substrate. Such a watermark is for example off DE 10 2009 056 462 A1 known.

Under translucency or translucent in this description, the partial translucency of a body understood, so the property of transmitting light scattering. Translucency is u. a. in contrast to the transparency (= image or view permeability) to see. The reciprocal property of translucency is opacity. As far as there is talk here that a watermark modulates the opacity, it can equally be said that it inversely modulates the translucency.

It is understood 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 or alone, without departing from the scope of the present invention.

The invention will be explained in more detail by way of example with reference to the accompanying drawings, which also disclose features essential to the invention. Show it:

1a and 1b a schematic representation of a substrate in a sectional view ( 1a ) or in plan view ( 1b ) to illustrate the opacity modulation by the watermark,

2 a schematic representation of the substrate of 1 for generating a watermarked printed image,

3a and 3b a schema representation similar to the 1a and 1b relating to an embodiment in which the watermark is generated by a watermark color,

4 a representation similar to the 2 for the substrate of 3a and 3b .

5a a schema representation similar to the 2 for an embodiment in which a non-modifiable coating is provided on the front side of the substrate,

5b and 5c Views of the substrate of the 5a from the back or the front of a modification and

6 to 8th Plan views ( 6a . 6b . 7 . 8th ) and sectional views ( 6c , d) an embodiment having a window thread.

1a shows in a sectional view a security element 1 , wherein for simplicity only one substrate 2 is drawn. The substrate 2 has a front 3 on (which is arranged in the figures without further restriction below) and a back 4 , In the substrate 2 is a watermark 5 incorporated the thickness of the substrate 2 and thus modulates its opacity. This opacity modulation is in 1b shown, which is a plan view of the front 3 of the substrate 2 schematically shows. There are areas 6 with high opacity in places where the substrate 2 has the maximum (not diminished) thickness. In areas 7 in which the thickness is reduced by an average amount, the substrate has 2 a medium opacity. In one area 8th in which the thickness is greatly reduced, the substrate has 2 a low opacity or a high translucency.

To create a printed image that has been adapted to the watermark, it is printed on the front side 3 applied an ink which is ablatierbar by means of laser radiation. 2 shows the substrate 2 with on the front 3 applied printing ink 9 , The printing ink 9 is (still) not further structured, but at least partly covers the area in which the watermark 5 in the substrate 2 is available.

From the front 3 now becomes a laser beam 10 guided over the substrate. He radiates through the substrate 2 , The wavelength of the laser beam is such that the printing ink 9 absorbs the radiation. The laser beam 10 will depend on the opacity of the substrate 2 which by the watermark 5 modulated, attenuated. At a position 10a where the substrate has high opacity by the watermark becomes the laser beam 10 strongly weakened. At a position 10b where the substrate has the least opacity, the laser beam is least attenuated. In 2 this is schematically by the thickness of the laser beam 10 illustrated. In fact, of course, only the intensity of the laser beam 10 but not its radiation cross section when passing through the substrate 2 weakened.

The intensity of the laser beam 10 is adjusted to give a modulation of the ablation effect that the laser beam 10 on the front 3 applied printing ink 9 has: in the area 8th with low opacity, the ink becomes 9 ablated at maximum, in areas 7 with medium opacity, the ink is ablated to a lesser degree, and in areas 6 with maximum opacity, the least or possibly even no ablation occurs. Of course, this only applies as far as the printing ink 9 on the front side 3 the area covered in the watermark 5 in the substrate 2 is trained.

The described embodiment can be modified such that instead of a watermark which modulates the opacity by a thickness variation of the substrate, a so-called "false" or printed watermark occurs, that is to say a watermark which is deposited on the substrate 2 was generated by a so-called watermark color.

The 3a and 3b schematically show the provision of such a printed watermark. On the back 4 of the substrate 2 becomes a watermark color 11 printed. The watermark color 11 penetrates accordingly 3b in the substrate 2 and causes after drying or other suitable processing, a translucency increase 12 in the substrate 2 in the places where the watermark color 11 was printed.

Press now, as in 4 represented, the substrate 2 with the printed watermark 12 with the laser beam 10 , in turn, gives the effect that the laser beam 10 at positions 10a in which the watermark or the watermark color the translucency of the substrate 2 increased, less attenuated in intensity than at positions 10b where the watermark does not have this effect. Again, an ablation of the ink is obtained 9 in the exact register to the watermark, without the application of the ink 9 this passer had been set.

The 5a to 5c refer to a third embodiment, in addition to the front 3 one not by the laser radiation 10 Modifiable coating 13 was applied to the laser radiation 10 is transparent and thus does not weaken it.

5a shows a sectional view similar to the 2 , where now in some areas the non-modifiable by the laser radiation coating 13 is applied. 5b shows a plan view of the back 4 with the coating 13 ,

5c shows a plan view of the front 3 after irradiation with the laser radiation 10 , Due to the different opacity of the substrate in the area of the watermark 2 becomes the printing ink 9 different degrees of laser radiation 10 influenced, so that the different areas 14 . 15 and 16 result. In the area 16 is the printing ink 9 almost unaffected, because the energy of the laser beam due to the opacity of the substrate 2 is greatly attenuated. In the area 14 is the printing ink 9 due to average laser energy dissipation through the substrate due to the average opacity of the substrate 2 modified to an average extent, for example ablated. The laser beam had a strong effect on the printing ink 9 in the area 15 because there is substrate there 2 has a low opacity and weakened the laser beam only slightly.

That on the basis of 5a to 5c Of course, the described embodiment can also be realized with a watermark that was generated by a watermark color and not by a thickness modulation.

Of course, it is basically possible for all embodiments to use a combination of watermark color and thickness modulation. A watermark ink is available, for example, from Sun Chemical under the designation 669440 Vernes UVSP (art.No .: JV 40000009).

Of course, the approaches described herein can also be performed on both sides of a substrate, with the ink 9 then alternately applied to the front and back of the substrate so that it does not overlap.

In addition, two different printing inks can be used, which can be modified by radiation of different spectral ranges. This makes it possible to work with different intensity profiles for these two radiations or to print on the front and back the same area with radiation-modified inks in the register to the watermark. For this purpose, a first ink is applied to the front and a second ink on the back. Subsequently, these inks are exposed and modified by laser radiation from the back (for the ink on the front) or the back (for the ink on the front).

• • mindestens zwei verschiedenen Druckfarben, die unterschiedliche Strahlungsintensitäten für eine Modifikation benötigen, oder
• • mindestens einer Druckfarbe, die Stoffe enthält, die unterschiedliche Strahlungsintensitäten für eine Modifikation benötigen, oder
• • mindestens einer Druckfarbe, die ein Gemisch aus Stoffen enthält, die modifizierbar und die nicht modifizierbar sind.

Similarly, the use of possible

• • at least two different inks that require different radiation intensities for modification, or
• • at least one printing ink containing substances requiring different levels of radiation for modification, or
• • at least one printing ink containing a mixture of substances that are modifiable and non-modifiable.

Three examples are described below for the printing process according to the invention:

Example 1:

A black, soot-based offset color was printed over the area of a watermark. The paint was dried for several days and then ablated by an ND vanadate laser from the back of the color on the front. In areas of low paper thickness, i. H. maximum translucent watermark was 80% to 95% of the color removed. In areas of maximum paper thickness, i. H. minimal translucency of the watermark, only 10% to 30% of the color was ablated.

Example 2:

The area of a watermark on the front side was overprinted by means of an OVI screen printing ink WP from the manufacturer SICPA. The paint dried out for several days. Subsequently, the color on the front was ablated by means of a Nd: Yag laser from the back. In areas of low paper thickness, 80% to 95% of the paint was removed. In areas of maximum paper thickness, 10% to 30% of the paint was ablated.

Example 3

The area of a watermark on the front side was overprinted by means of a magnetic OVMI screen printing ink of the manufacturer SICPA. The paint dried out for several days. Subsequently, the color on the front was ablated by means of a Nd: Yag laser from the back. In areas of low paper thickness, 80% to 95% of the color except a yellow colorant was removed. In areas of maximum paper thickness, 10% to 30% of the paint was ablated.

In general, the specific radiation should be chosen so that there is no absorption in the substrate Radiation occurs that would lead to a change in the substrate. Both continuous wave lasers and pulsed lasers are possible for this purpose. An example of a suitable CW laser is the model Innoslab, IS8I-E manufactured by EdgeWave GmbH, which is a Nd: YVO ₄ -based laser at a wavelength of 1064 nm. It provides a power of 100 watts in continuous wave mode. At a scan speed of 2.5 m / s to 5 m / s, the ablation of a soot-based color can be performed.

If an IR-modifiable color is used as the printing ink, there is the advantage that the printed image and the verification of the register can be machine-based by means of infrared measurement. This color may be visually visible or not visible.

The printing method according to the invention is also applicable to a watermark which is provided in connection with a so-called window thread in a substrate of a security element. 6a shows a top view in transmitted light on a front side 3 of a substrate 2 that has a window thread 17 having. In the substrate 2 are a sequence of strip-shaped areas 18 and 19 provided that form the watermark: in the areas 18 For example, the thickness of the substrate is unchanged so that the watermark has high opacity, and in the areas 19 the thickness of the substrate is reduced, so that the watermark has a low opacity (in the embodiment of the 6 to 8th is in contrast to the embodiments of the 1 to 5 the watermark on the front 3 of the substrate). This has the effect in incident light that the window thread 17 visible sections 20 has, in which one side of the filament according to 6d not covered by the substrate, and not visible because according to 6c in the substrate 2 fully embedded sections 21 Has. The effect in reflected light can be seen in 6b : only the visible sections 20 lie at the front 3 free and are visible.

Transmitted light is for the purposes of this invention, when an illumination of the substrate from the side opposite to the viewer, d. H. the illumination through the substrate takes place. Incident light is in the sense of this invention, when a lighting of the substrate from the side of the viewer is made.

In the area of the watermark 5 that from the fields 18 and 19 is formed, is now turn ink 9 on the front side 3 applied.

The 6c and 6d show a section through the substrate 2 of the 6a , where the 6c showing a cut in one area 18 lies, the 6d a cut in one area 19 , In the 6c is the thread 17 below the surface of the front 3 , so here's one of the invisible sections 21 lies. In the area 19 however, it is according to 6d the window thread 17 on the surface of the front 3 , making a visible section 21 is formed.

7 shows the top view on the front 3 after irradiation of the laser radiation from the backside 4 out. In the fields of 18 with high opacity is the printing ink 9 not ablated, there is an area 16 as in 5c in front. In the fields of 19 is the printing ink 9 but ablated, there is an area 14 in the sense of the 2 in front.

8th shows a modification in which the laser radiation no ablation, but an inverse modification, for. B. by the development of thermochromic effect pigments causes. The areas 14 and 16 are exactly reversed here.

Basically, it is not essential for the printing process, whether the ink 9 is applied to the front or back of the substrate. The only thing that matters is that the substrate 2 from the side irradiated with the radiation, which is opposite to the side on which the ink 9 is arranged. Of course, in all embodiments, the ink can be provided on the back and the radiation can be coupled from the front.

LIST OF REFERENCE NUMBERS

1

security element

2

substratum

3

front

4

back

5

watermark

6, 7, 8

Area

9

printing ink

10

laser beam

10a, 10b

position

11

Watermark Color

12

Transluzenzerhöhung

13

coating

14, 15, 16

Area

17

window thread

18, 19

Area

20, 21

section

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1826728 A2 [0027]
• EP 1826730 A2 [0027]
• EP 1826246 A2 [0028]
• DE 102009056462 A1 [0033]

Claims (10)

Printing method for producing a security element ( 1 ), wherein - a substrate ( 2 ), which has a front and a back ( 3 . 4 ), at least for certain radiation ( 10 ) is translucent and a watermark ( 5 ), which reduces the opacity of the substrate ( 2 ), - on the front ( 3 ) an ink ( 9 ) is applied, characterized in that - on the front ( 3 ) the printing ink ( 9 ) the watermark ( 5 ) at least partially covered, - the printing ink ( 9 ) by means of the determined radiation ( 10 ), and - the substrate ( 2 ) from the back ( 4 ) with the particular radiation ( 10 ), whereby the watermark ( 5 ) with regard to the modification of the printing ink ( 9 ) is used as a mask and the printing ink ( 9 ) in the register to the watermark ( 5 ) is modified. Printing method according to claim 1, characterized in that the watermark ( 5 ) of the provided substrate ( 2 ) the opacity of the substrate ( 2 ) by modulation of a thickness of the substrate ( 2 ) modulated. Printing method according to claim 1 or 2, characterized in that the watermark ( 5 ) of the provided substrate ( 2 ) has a color which determines the opacity of the substrate ( 2 ) modulated. Printing method according to one of the above claims, characterized in that the particular radiation ( 10 ) the printing ink ( 9 ) ablated for modification. Printing method according to claim 4, characterized in that for ablation the printing ink ( 9 ) with a certain radiation ( 10 ) absorbing admixture, z. As soot is provided. Printing method according to one of the above claims, characterized in that the printing ink ( 9 ) has one or more of the following substances: an optically variable color, a magnetically orientable, optically variable color, a metallic color, a color which is effective in the non-visible spectral range. Printing method according to one of the above claims, characterized in that the printing ink ( 9 ) additionally contains substances which, by means of the specific radiation ( 10 ) are non-modifiable or ablatable and absorb the radiation in the visual, infrared and / or ultraviolet wavelength range. Printing method according to one of the preceding claims, characterized in that the specific radiation is applied in the form by a beam, in particular a laser beam ( 10 ), over the back ( 4 ) to be led. Printing method according to claim 8, characterized in that in addition to the use of the watermark ( 5 ) as a mask during marking also an intensity of the particular radiation ( 10 ) is varied in order to provide additional structuring of the modification of the printing ink ( 9 ) to effect. Printing method according to one of the above claims, characterized in that on the rear side ( 4 ) an additional masking is applied which determines the particular radiation ( 10 ) attenuates or absorbs.

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