DE102021111065A1 - Security element for valuables with a one-way watermark - Google Patents

Abstract

The invention relates to a security element (100) for identifying the authenticity of valuables, having at least one element acting as a watermark (101). According to the invention, the element acting as a watermark (101) has at least one first layer (A, P) which has a part of the light (L) radiating onto the watermark (101) is absorbed by extinction, and has at least one second layer (B) which converts at least part of the light (L) radiating through the first layer, the first layer (A, P ) and the second layer (B) are arranged one on top of the other, and wherein the conversion is fluorescence and/or upconversion (photon upconversion), and at least a third layer (C, P) which has a further part of the watermark (101 ) Radiant light (L) absorbed by extinction, and the conversion of the light from a transmission area related to extinction of the first layer (A, P), into a transmiss ion region with respect to extinction of the third layer (C, P), and wherein at least one of these layers (A, P, C, P') absorbs either excitation light or emission light of the second layer (B) This arrangement results in the watermark only visible from one side.

Description

The invention relates to a security element for identifying the authenticity of objects of value, having at least one element acting as a watermark.

For easy identification of the authenticity of banknotes, securities, labels, it is known to equip them with hidden or open security features. Hidden security features generally require a technical device to check these security features for authenticity. Open characteristics, on the other hand, can usually be checked with the mere senses and without media disruption.

Customary security elements for authenticity detection generally include the measurement of special material properties or material combinations that are technically difficult and can only be produced with a great deal of specialist knowledge. The material combinations include windows in banknotes that are recognizable as such with the naked eye and without media discontinuity. It is also known to introduce watermarks and to place imprints corresponding to the watermark, with the relative alignment of the watermark and imprint requiring a particularly high level of skill during printing. Since counterfeiting products is a very lucrative business for counterfeiters, there is always a race for new authenticity features.

The object of the invention is therefore to provide a security feature for identifying the authenticity of valuables. The security feature should be objectively verifiable using readily available technologies.

The object according to the invention is achieved by a security feature with the features according to claim 1. Further advantageous configurations of the security feature are specified in the dependent claims of claim 1. Claim 11 claims the use and claim 12 claims a method for checking the authenticity of the security feature.

According to the invention, it is provided that a well-known watermark, which becomes visible when light shines through a sheet of paper or a foil, is only visible from one side. The watermark behaves similar to an optical diode. The general idea is that the element acting as a watermark has at least three layers, one on top of the other. A first layer and a third layer absorb light, preferentially in complementary regions of the spectrum that are not superimposed, and allow light to pass in different parts of the spectrum from UV-C to NIR or even IR. But at least the first layer and the third layer act as a cover layer. Together, the two outer layers block visible light, while the outer layers can still let light or residual light shine through, as is the case with paper, for example. So that the element acting as a watermark, ie the layer sequence consisting of at least three layers, can only be recognized from one side, a second layer, which is arranged between the first layer and the third layer, converts incident light. The conversion can be fluorescence or upconversion. The English term "upconversion" has also become common in German technical jargon to describe the effect of photon upconversion.

With fluorescence, light in a first part of the spectrum from UV-C to UV-B, UV-A, VIS to NIR and IR is converted into light with longer wavelengths, and therefore with less energy per single photon. With fluorescence, which occurs within visible light (VIS), the fluorescence changes the color of the light. Fluorescent dyes and fluorescent pigments in signal colors are known which convert light in the UV-A range to UV-B range into visible light by fluorescence. Because the intensity of the converted light is brighter than the environment and the brightness seems to come out of nowhere (from the non-visible UV range), signal colors appear as if they were shining themselves.

Exactly the opposite happens with upconversion. Light with a longer wavelength is converted by an upconversion dye or pigment into light with shorter wavelengths, and therefore with more energy per single photon. Upconversion does not violate the law of conservation of energy in physics because a dye is excited by a photon for upconversion and this excited state is stable for at least a short time. A further excitation with another photon finally leads to the emission of a photon with more energy than one of the exciting photons, but usually with less energy than the energy of the two exciting photons combined. This upconversion is a different effect than laser pumping, which produces light with shorter wavelengths due to non-linear effects in the excitation of optical materials such as harmonics. Upconversion is not very energy efficient and yields range from 1% to 2% for many known upconversion dyes. However, this yield is sufficient to produce effects that are visible to the naked eye or detectable with readily available technology.

In this first configuration, the security feature according to the invention with the watermark, which is only visible from one side, functions in that, for example, blue light enters the layer sequence through a red filter on a first side of the security feature. After the red filter, the first layer, the light hits the fluorescent or upconversion dye or the pigment that acts in this way in a second layer. There, the light is converted into red light, for example by fluorescence. Because of the red filter in the first layer, this red light can only emerge from the layer sequence on one side if the third layer has a blue filter, for example. In this layer sequence, the light cannot go backwards through the layer sequence because the blue light in the second layer that is used to excite the fluorescent dye is filtered out by the blue filter in the third layer. Even possibly incident UV light, which could also be converted by fluorescence, would not be able to emerge on the first side because there, in the first layer, there is a red filter.

• 1 ein erfindungsgemäßes Sicherheitsmerkmal in einer Ansicht auf eine erste und auf eine zweite Seite vor einer Lichtquelle,
• 2 eine Skizze mit Extinktionsspektren und Fluoreszenzspektren verschiedener Schichten in einem erfindungsgemäßen Sicherheitsmerkmal,
• 3 Schichten eines erfindungsgemäßen Sicherheitsmerkmals mit voneinander gelösten Schichten in einem ersten Ausführungsbeispiel,
• 4 Schichten eines erfindungsgemäßen Sicherheitsmerkmals mit voneinander gelösten Schichten in einem zweiten Ausführungsbeispiel,
• 5 Schichten eines erfindungsgemäßen Sicherheitsmerkmals mit voneinander gelösten Schichten in einem dritten Ausführungsbeispiel,
• 6 eine Skizze mit Extinktionsspektren und Fluoreszenzspektren der verschiedenen Schichten in dem dritten Ausführungsbeispiel aus 5,
• 7 Verwendung des Sicherheitsmerkmals auf einem beispielhaften Geldschein,
• 8 Verwendung des Sicherheitsmerkmals auf einem beispielhaften Konzertticket,
• 9 Verwendung des Sicherheitsmerkmals auf einer beispielhaften Medikamentendose,
• 10 Verwendung des Sicherheitsmerkmals auf einem beispielhaften Etikett für eine Ware.

The invention is explained in more detail with reference to the following figures. It shows:

• 1 a security feature according to the invention in a view of a first and a second side in front of a light source,
• 2 a sketch with extinction spectra and fluorescence spectra of different layers in a security feature according to the invention,
• 3 Layers of a security feature according to the invention with layers separated from one another in a first exemplary embodiment,
• 4 Layers of a security feature according to the invention with layers separated from one another in a second exemplary embodiment,
• 5 Layers of a security feature according to the invention with layers separated from one another in a third exemplary embodiment,
• 6 1 shows a sketch with extinction spectra and fluorescence spectra of the different layers in the third embodiment 5 ,
• 7 use of the security feature on a sample banknote,
• 8th use of the security feature on a sample concert ticket,
• 9 Use of the security feature on an exemplary medicine box,
• 10 Use of the security feature on a sample label for a product.

In 1 shows the external and visible effect of the watermark 101 that can only be seen on one side. A rear side 112 of the security feature 100 can be illuminated with light L using a corresponding light source. The watermark 101 is visible on the front side 111. However, if the security feature is turned over so that the back side 111 is illuminated, the watermark 101 on the back side 112 (in 1 right) not visible.

In 2 the principle of the invention is outlined using an example. This sketch with extinction spectra and fluorescence spectra (on the left in the figure) of various layers A, B and C in a security feature according to the invention shows that unfiltered light L penetrates the first layer A from below. A red/NIR/IR filter in the form of pigment 110 and/or dye 120 is present in or on layer A. This pigment 110 and/or dye 120 prevents red light, NIR light and IR light from passing through the following layers. The remaining light, which is blue for example depending on the position of the absorption edge, passes through the lower, first layer A. In the example shown here, UV-A light enters. A fluorescent dye and/or a fluorescent pigment and/or an upconversion dye and/or an upconversion pigment is arranged in or on the second layer B. This layer transforms or converts the UV-A light entering here, for example, into red light up to IR light in the NIR spectrum. This transformed or converted light cannot be reflected back due to the red filter / NIR filter / IR filter in the first layer A. However, it can pass through the following third layer C, because there a UV/blue filter in the form of pigment and/or dye is present in or on the third layer C. UV light/blue light cannot pass through the layers because it is absorbed by the UV/blue filter. Overall, it is only possible for UV light/blue light to enter the layer sequence from below, starting with layer A, and to exit the layer sequence upwards as red light/NIR light. Another light path is not possible. The three layers A, B and C can optionally be covered with top layers P. The cover layers P can be paper, polymer film, but also print layers with white pigment, printing inks, toner, varnish and/or ink.

The example described here lets UV light / blue light pass as converted red light / NIR light. Depending on the availability of dyes/pigments and the corresponding fluorescent or upconversion dyes, there are many combinations of input light and off step light possible. UV-C, UV-B or UV-A radiation can excite and leave the layer sequence as visual VIS light or as IR light. However, it is also possible for upconversion dyes and/or pigments to be excited with light having a longer wavelength and to leave the layer sequence as light having a shorter wavelength.

In 3 a sketch shows layers of a security feature 100 according to the invention with layers P, A, B, C, P′ separated from one another in a first exemplary embodiment. The security element 100 for authenticity detection of valuables 500, 600, 700, 800 shown in FIGS 7 , 8th , 9 and 10 , has at least one element acting as a watermark 101 . This element acting as a watermark 101 can be a print with fluorescent and/or upconverting pigments or dyes. It is also possible that the element acting as a watermark 101 is an imprint with classic printing inks on fluorescent and/or up-converting pigments. According to the idea of the invention, a multi-layer structure is provided. At least a first layer A absorbs part of the light L radiating onto the watermark 101 by extinction. The light L radiates through the optional cover layers P or P′ and the light composition is optionally changed by the filters in the layers, namely first layer A, second layer B and/or third layer C. At least one second layer B converts at least part of the light L radiating through the first layer A. For this purpose, the first layer A and the second layer B are arranged one above the other in the security feature. The conversion that takes place here is fluorescence and/or upconversion (photon upconversion). At least a third layer C absorbs another part of the light L radiating onto the watermark 101 by extinction. The positions of the absorption bands with respect to the extinction of the first layer A and the third layer C are different from one another. So that light L can shine through the security feature in one direction, it is provided that the conversion through the second layer B transfers the light L from the transmission area with regard to the absorbance of the first layer A to the transmission area with regard to the absorbance of the third layer C. In order for the effect of the watermark that is only visible or detectable on one side to occur, it is necessary for the first layer A and/or the third layer C to contain either the excitation light for the fluorescent dye/upconversion dye or fluorescent pigment/upconversion pigment in the second Layer B blocks or its emission light.

The different layers, namely the at least first layer A, the at least second layer B and the at least third layer C, have different properties depending on the design of the security element.

In one configuration, the at least one first layer A has a pigment 110 . The pigment makes the at least one first layer A opaque for most of the light L radiating onto the watermark 101 . So this part of the light does not pass through this layer. For a further part of the light L radiating onto the watermark 101, the first layer A is translucent. Because the layer contains pigments, it is not crystal clear or like colored glass, but the light shines through diffusely.

The fluorescent and/or upconverting (photon upconversion) pigments 110 or dyes 120 are located in or on the second layer B. Depending on the design, it is possible to select dyes and/or pigments. Depending on the further configuration, it is possible that the third layer C has a pigment and/or a dye, and that the third layer C is opaque for most of the light L radiating onto the watermark 101, and the third layer C for Light from the second layer B is translucent. If a top layer is present as the third layer, then it is possible for the top layer P to consist of paper or a polymer film, but also to be present as a printed layer with white pigment, printing ink, toner, varnish and/or ink.

In a further embodiment, it is also possible for the various layers to be transparent but colored. For this purpose, the at least one first layer can have a dye 120 in a clear matrix. For this purpose, the first layer A is opaque for most of the light L shining on the watermark 101, but the at least one first layer A is optically clear for the rest of the light L shining on the watermark 101.

The fluorescence range and/or the upconversion range can be freely selected, provided the appropriate dyes or pigments are available. The fluorescence can be excited by UV-C radiation with a wavelength of less than 280 nm, by UV-B radiation with a wavelength of 280 nm to 315 nm and/or by UV-A radiation with a wavelength of 315 nm to 380 nm. It is also possible to excite the conversion in the visual VIS region from 380 nm to 780 nm, with all excitations by fluorescence converting the wavelength of the light to longer wavelength light. Finally, upconversion dyes can also be excited from the NIR range in the wavelength range from 780 nm to 1,400 nm. Upconversion can also take place in the VIS range to shorter wavelengths, in the UV-A range to shorter wavelengths and in the UV-B range to shorter wavelengths. What the exemplary embodiments have in common is that the extinction ranges of the outer layers complement one another in such a way that light L cannot pass through the layer sequence through the at least one second layer B without being converted. Since the conversion only works in one direction, the path through the layers is only possible in one direction.

In 4 is one to 3 different embodiment of the security feature shown. Here the print of a watermark 101 is not arranged in the second layer B, but it lies here as layer D on the at least one, first layer A. It is also possible to place the imprint of the watermark 101 as layer D on the at least one third layer C (not shown here). Optionally, it is also possible to arrange the cover layers P and P' as the outermost layers, on one or both sides, in order to protect the inner layers from abrasion or to change the appearance so that the filter layers are not visible to the naked eye.

In 5 a sketch shows layers of a security feature 100 according to the invention with layers P, A, B, P′ separated from one another in a third exemplary embodiment. The security element 100 for authenticity detection of valuables 500, 600, 700, 800 shown in FIGS 7 , 8th , 9 and 10 , has at least one element acting as a watermark 101 . This element acting as a watermark 101 can be a print with fluorescent and/or upconverting pigments or dyes. It is also possible that the element acting as a watermark 101 is an imprint with classic printing inks on fluorescent and/or up-converting pigments. According to the idea of the invention, a multi-layer structure is provided. At least a first layer A absorbs part of the light L radiating onto the watermark 101 by extinction. The light L radiates through the optional cover layers P or P′ and the light composition is changed by the filter in the first layer A and the second layer B. The at least one second layer B converts at least part of the light L radiating through the first layer A. For this purpose, the first layer A and the second layer B are arranged one above the other in the security feature. The conversion that takes place here is fluorescence and/or upconversion (photon upconversion). So that light L can shine through the security feature in one direction, it is provided that the conversion through the second layer B takes the light L from a transmission area with regard to the extinction of the first layer A into a transmission area with regard to the extinction of the third layer P', here a top layer, transferred. The cover layer P' can be paper, polymer film, but also a printed layer with white pigment, printing inks, toner, lacquer and/or ink.

The different layers, namely the at least first layer A, the at least second layer B and the at least third layer P′, have different properties depending on the configuration of the security element.

In one configuration, the at least one first layer A has a pigment 110 . The pigment makes the at least one first layer A opaque for most of the light L radiating onto the watermark 101 . So this part of the light does not pass through this layer. For a further part of the light L radiating onto the watermark 101, the first layer A is translucent. Because the layer contains pigments, it is not crystal clear or like colored glass, but the light shines through diffusely.

The fluorescent and/or upconverting (photon upconversion) pigments 110 or dyes 120 are located in or on the second layer B. Depending on the design, it is possible to select dyes and/or pigments. Depending on the further configuration, it is possible for the third layer P′ to be translucent for light from the second layer B.

In a further embodiment, it is also possible for the various layers to be transparent but colored. For this purpose, the at least one first layer can have a dye 120 in a clear matrix. For this purpose, the first layer A is opaque for most of the light L shining on the watermark 101, but the at least one first layer A is optically clear for the rest of the light L shining on the watermark 101.

The fluorescence range and/or the upconversion range can be freely selected, provided the appropriate dyes or pigments are available. The fluorescence can be excited by UV-C radiation with a wavelength of less than 280 nm, by UV-B radiation with a wavelength of 280 nm to 315 nm and/or by UV-A radiation with a wavelength of 315 nm to 380 nm. It is also possible to excite the conversion in the visual VIS region from 380 nm to 780 nm, with all excitations by fluorescence converting the wavelength of the light to longer wavelength light. Finally, upconversion dyes can also be excited from the NIR range in the wavelength range from 780 nm to 1,400 nm. Upconversion can also take place in the VIS range to shorter wavelengths, in the UV-A range to shorter wavelengths and in the UV-B range to shorter wavelengths. What the exemplary embodiments have in common is that the extinction ranges of the outer layers complement one another in such a way that light L cannot pass through the layer sequence through the at least one second layer B without being converted. Since the conversion only works in one direction, the path through the layers is only possible in one direction.

In 6 is the principle of the invention as embodied in 5 sketched. This sketch with extinction spectra and fluorescence spectra (on the left in the figure) of different layers A and B in the security feature according to the invention according to the third embodiment in 5 shows that unfiltered light L penetrates the first layer A from below. In this example, UV-A light is chosen as the light entering the layer sequence from below. A red/NIR/IR filter in the form of pigment 110 or dye 120 is present in or on layer A. This pigment or dye prevents red light / IR light from passing through the following layers. The remaining UV-A light, for example, depending on the position of the absorption edge, passes through the lower, first layer A. A fluorescent dye, a fluorescent pigment, an upconversion dye or an upconversion pigment is arranged in or on the second layer B.

This layer converts or converts the UV-A light into IR light in the NIR spectrum. This transformed or converted light cannot be reflected back due to the red filter/NIR/IR filter in the first layer A. However, it can pass through the following third cover layer P'. Layer A can optionally be covered with a top layer P. The cover layers P, P' can be paper, polymer film, but also printing layers with white pigment, printing inks, toner, lacquer and/or ink.

The example described here allows UV-A light to pass as converted red/NIR light. Depending on the availability of dyes/pigments and the corresponding fluorescent or upconversion dyes, many combinations of input light and output light are possible. UV-C, UV-B or UV-A radiation can excite and leave the layer sequence as visual VIS light or as IR light. However, it is also possible for upconversion dyes or pigments to be excited with light having a longer wavelength and leave the layer sequence as light having a shorter wavelength.

In 7 A use of the security feature 100 on an example bill 500 is shown. The security feature 100 is arranged where a classic watermark is arranged on many banknotes 500, which is visible from both sides of the banknote 500 against the light.

In 8th A use of the security feature 100 on an exemplary concert ticket 600 is shown. The security feature 100 is arranged where, in the case of many concert tickets 600, a hologram is arranged as a security feature, which is visible from one side.

In 9 1 shows a use of the security feature 100 on an example medication container. Since many vials of medicine are colored but clear, the security feature 100 can be viewed either only from the front or only through the vial of medicine.

In 10 Finally, a use of the security feature 100 is shown on an exemplary label for a product, here a label for a modern shoe. Instead of shoes, high-priced goods such as jewelery or watches can also be considered. However, high-priced foods can also be marked with a security feature according to the invention on a label.

reference list

100

security element

101

watermark

110

pigment

111

first page

112

second page

120

dye

500

bank note

600

ticket

700

medicine box

800

shoe

A

layer

B

layer

C

layer

E

extinction

λ

wavelength

L

light

P

top layer

P'

top layer

Claims (12)

Security element (100) for authenticity detection of valuables (500, 600, 700, 800), having - at least one element acting as a watermark (101), characterized in that the element acting as a watermark (101) - has at least one first layer (A, P) which absorbs part of the light (L ) absorbed by extinction, and - has at least one second layer (B) which converts at least part of the light (L) radiating through the first layer, - the first layer (A, P) and the second layer (B) being arranged one above the other and - wherein the conversion is fluorescence and/or upconversion (photon upconversion), and - has at least one third layer (C, P') which transmits a further part of the light (L) radiating onto the watermark (101). absorbs absorbance, - the conversion converts the light - from a transmittance range in absorbance of the first layer (A, P), - into a transmittance range in absorbance of the third layer (C, P'), and where - m at least one of these layers (A, P, C, P') absorbs either excitation light or emission light of the second layer (B). security element after claim 1 , characterized in that the positions of the absorption bands with regard to the extinction of the first layer (A, P) and the third layer (C, P) are different from one another. Security element according to one of Claims 1 or 2 , characterized in that the first layer (A, P) has a pigment (110), and that - the first layer (A, P) is opaque for most of the light (L) radiating onto the watermark (101), and wherein - the first layer (A, P) is translucent for a further part of the light (L) radiating onto the watermark (101). Security element according to one of Claims 1 until 3 , characterized in that - the second layer (B) has fluorescent and/or upconverting (photon upconversion) pigments (110) or dyes (120). Security element according to one of Claims 1 until 4 , characterized in that the third layer (C, P) comprises a pigment, and that - the third layer (C, P) is opaque for most of the light (L) radiating onto the watermark (101), and wherein - the third layer (C, P) is translucent to light from the second layer (B). security element after claim 1 or 2 , characterized in that the first layer comprises a dye (120), and that - the first layer (A, P) is opaque to most of the light (L) radiating onto the watermark (101), and wherein - the first Layer (A, P) is optically clear for the rest of the light (L) radiating onto the watermark (101). Security feature according to one of Claims 1 until 6 , characterized in that - the first layer (A, P) has a pigment (110) and/or a dye (120) which is in a first range of light (L) in the spectrum from UB-C, through UV-B , UV-A, VIS, to NIR has an extinction of at least 50%, and that - the third layer (C, P) has a pigment (110) and/or a dye (120) which is in a second range of light (L) in the spectrum from UV-C, through UV-B, UV-A, VIS, to NIR has an extinction of at least 50%, and that - the second layer (B) between the first layer (A, P) and the third layer (C, P) is arranged, and a fluorescent and/or upconverting (photon upconversion) pigment (110) and/or a fluorescent and/or upconverting (photon upconversion) dye (120) which/which Light is transferred from a transmission area of the first layer (A, P) into a transmission area of the third layer (C, P). Security feature according to one of Claims 1 until 7 , characterized in that on the first layer (A, P) and/or on the second layer (B) there is a cover layer (P) made of paper or of a polymer film. Security feature according to one of Claims 1 until 8th , characterized in that the second layer (B) has a watermark imprint with fluorescent and/or upconverting pigments or dyes. Security feature according to one of Claims 1 until 9 , characterized in that a watermark is applied to the first layer (A, P), to the third layer (C, P) and/or to a further layer (D), the further layer (D) being on the first layer (A, P) or on the third layer (C, P). Use of a security feature according to the claims 1 until 10 , for a banknote (500), for a security, for a document (600), for a sticker on a bottle, such as a medicine jar (700) or for a label (800). Method for checking the authenticity of an object of value, having a security feature according to one of Claims 1 until 10 , characterized by - irradiating a first side (111) of the security feature (100) with light (L) in a predetermined wavelength range selected from the group consisting of: UV-C, UV-B, UV-A, VIS and/or NIR - detecting a predetermined pattern in the form of a watermark (101) on a second side (112) of the security feature in a predetermined wavelength range selected from the group consisting of: UV-C, UV-B, UV-A, VIS and/or NIR, - Irradiating the second side (112) of the security feature with light (L) in a predetermined wavelength range selected from the group consisting of: UV-C, UV-B, UV-A, VIS and/or NIR - detecting a predetermined pattern in the form of a watermark (101) on the first side (111) of the security feature (100) in a predetermined wavelength range selected from the group consisting of: UV-C, UV-B, UV-A, VIS and/or NIR, - outputting a signal, if the detection of the predetermined pattern (101) was positive on only one side (111, 112) of the security feature (100).

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