System of switchable capsule-luminescent pigments

Abstract

The present invention relates to a system of at least two types of switchable capsule-luminescent pigments, wherein the capsule-luminescent pigments are polymer particles having a diameter of 0.1-1000 µm, each containing at least one luminescent substance and a photochemically switchable absorber, wherein a first type of capsule-luminescent pigment comprises a first luminescent substance emitting a first color in the VIS spectral range; a second type of capsule-luminescent pigment comprises the first luminescent substance and a second luminescent substance emitting a second color in the VIS spectral range, the first and the second colors being different from one another; and the two capsule-luminescent pigments each comprise the same photochemically switchable absorber, said photochemically switchable absorber having a first and a second switching state, wherein the absorption spectrum of said photochemically switchable absorber in the second switching state significantly overlaps the emission spectrum of the first luminescent substance. The present invention also relates to a switchable luminescent printing ink, comprising a system of at least two types of switchable capsule-luminescent pigments as described herein, and to a value document, preferably a banknote, having a switchable luminescent print that comprises a system of at least two types of switchable capsule-luminescent pigments as described herein.

Description

[0001] SYSTEM OF SWITCHABLE CAPSULE LUMINOUS PIGMENTS

[0002] Technical field

[0003] The present invention relates to a system of at least two types of switchable capsule luminescent pigments, wherein the capsule luminescent pigments are polymer particles with a diameter of 0.1-1000 pm, each containing at least one luminescent substance and a photochemically switchable absorber, wherein a first type of capsule luminescent pigment comprises a first luminescent substance emitting in a first color in the VIS spectral range; a second type of capsule luminescent pigment comprises the first luminescent substance and a second luminescent substance emitting in a second color in the VIS spectral range, wherein the first and the second color are different;and the two capsule luminescent pigments each comprise the same photochemically switchable absorber, wherein the photochemically switchable absorber has a first and a second switching state, and the absorption spectrum of the photochemically switchable absorber in the second switching state significantly overlaps with the emission spectrum of the first luminescent substance. The present invention further relates to a switchable luminescent printing ink comprising a system of at least two types of switchable capsule luminescent pigments as described herein, and to a security document, preferably a banknote, with a switchable luminescent print comprising a system of at least two types of switchable capsule luminescent pigments as described herein.

[0004] Technical background

[0005] Valuable documents and other valuables have long been protected against counterfeiting by being printed with inks that luminescent under UV light. Multicolored images created using several different luminescent inks, especially in the primary colors red, green, and blue, have a particularly high aesthetic and recognition value.

[0006] To further increase brand recognition, it is known to use luminescent printing inks with a dynamically changing luminescence effect, particularly by utilizing the following effects: - Combining a rapidly decaying luminescent material with a phosphor, especially with a different emission color. However, this requires switching the excitation light on and off.

[0007] - Combination of several separately excitable luminescent substances. However, this requires the use of multiple excitation wavelengths.

[0008] - Combination of a luminescent substance with a photochemically switchable absorber.

[0009] Photochemically switchable absorbers (hereinafter also referred to as "switches") are particularly well-known examples of diarylethenes, which can be repeatedly and reproducibly switched from a first to a second switching state under UV or visible light. The two switching states have different chemical structures and thus differ primarily in their absorption spectrum in the visible spectral range (VIS range). Such switchable absorbers are also called photochromic substances. Compared to other photochromic substances, diarylethenes are distinguished by their resistance to aging and their non-toxicity, and they also achieve a particularly high number of switching cycles.The switching effect is based on the fact that one of the two different absorption spectra of the two switching states does not overlap with the emission spectrum of an additionally present luminescent substance, and the other of the two different absorption spectra of the two switching states does overlap with the emission spectrum of an additionally present luminescent substance. In the case of overlap, a non-radiative energy transfer, such as a Förster resonant energy transfer (FRET), can occur between the luminescent substance and the switch, which causes the luminescence of the luminescent substance to be "switched off." Since a certain amount of radiative energy is required for the switch molecules to change from the first to the second switching state under appropriate illumination (e.g., by UV light), the luminescence of the additionally present luminescent substance only gradually fades for the human eye.For example, if a substrate printed with a printing ink containing the switch and the luminescent substance, such as a valuable document, was held under a UV lamp for a certain period of time.

[0010] To optimize printing properties and aging resistance, it is also known to incorporate luminescent substances into polymer capsules, as described, for example, in WO 2017 / 080 653 Al.

[0011] CN 1 13 174 004 A describes a switchable luminescent material based on

[0012] Tetraphenylporphyrin (TPP) and a diarylethene are combined, with the TPP and diarylethene encapsulated in nanoparticles. In the switched-on state, the diarylethene emits green light; in the switched-off state, it is dark, meaning a color change in the luminescence can be observed. In this case, the diarylethene itself emits differently in the two switching states but has no influence on the luminescence of the TPP. The TPP itself always emits a static red light. Thus, only emission colors are mixed.

[0013] WO 2017 / 080654 Al describes a system of differently colored encapsulated luminescent pigments with identical properties regarding excitation wavelength, aging and environmental resistance, lightfastness, and printing properties. In particular, several luminescent substances can be encapsulated together using energy transfer. The term "luminescent substances using energy transfer" means that a first luminescent substance is excited by radiation, for example, UV radiation, and the radiation emitted by the first luminescent substance excites a second luminescent substance. The second luminescent substance then emits radiation that determines the overall color impression of the encapsulated luminescent substances, since the luminescence of the first substance is essentially completely absorbed by the second luminescent substance and thus does not contribute to the overall color impression. However, WO 2017 / 080654 Al does not describe switchable luminescence of the encapsulated luminescent substances.

[0014] WO 2021 / 074 275 Al describes lanthanide complexes with photochromic ligands, in particular diarylethenes. Here, a chemical bond exists between the luminescent substance and the photochromic ligand to achieve and ensure the spatial proximity required for FRET energy transfer between the luminescent substance and the photochromic ligand. Emission colors are only mixed in this process.

[0015] CN 106978 164 A describes a mixture of an (organic or inorganic) perovskite and a diarylethene for switchable luminescence. However, the switch and the luminescent material are not encapsulated together, and the extinguishing of the luminescent material after switching the switch is insufficient. Furthermore, no luminescent materials are combined in this formulation.

[0016] A number of specific individual examples of switchable luminescent materials are known. However, for providing security features that are both easily verifiable in everyday use and aesthetically pleasing, a system of luminescent pigments would be desirable. In such a system, not only the excitation wavelength (for simple testing using only one wavelength, particularly 365 nm, as is common practice for security checks of banknotes at cash registers), aging and environmental resistance, lightfastness (also referred to here as "fatigue resistance"), and printing properties would be identical for all luminescent pigments, but also the wavelength and timescale for switching off, the conditions (temperature, illumination) and timescale for switching back on, as well as the aging properties of the switch. Ideally, the switching depth of the different pigments should also be comparable.

[0017] These requirements cannot be met with currently known switchable luminescent pigments (whether encapsulated or unencapsulated), because, firstly, different switchable absorbers must be used for luminescent substances with different emission wavelengths in order to achieve the necessary good overlap between the emission spectrum of the luminescent substance and the absorption spectrum of the (activated) switch. However, different switchable absorbers generally differ with regard to the aforementioned properties. Known systems with multiple luminescent pigments for producing luminescence-based security features with different color impressions are not switchable.

[0018] The present invention is therefore based on the objective of providing improved systems with multiple luminescent pigments compared to the prior art, which exhibit at least some, ideally all, of these advantageous properties. Furthermore, the present invention aims to provide improved luminescent printing inks that can be used to produce security features. Finally, the present invention aims to provide securities, preferably banknotes, that exhibit improved security features with the advantageous properties described above.

[0019] Summary

[0020] According to a first aspect, the present invention relates to a system of at least two types of switchable capsule luminescent pigments, wherein the capsule luminescent pigments are polymer particles with a diameter of 0.1-1000 pm, each containing at least one luminescent substance and a photochemically switchable absorber, wherein a first type of capsule luminescent pigment comprises a first luminescent substance emitting in a first color in the VIS spectral range; a second type of capsule luminescent pigment comprises the first luminescent substance and a second luminescent substance emitting in a second color in the VIS spectral range, wherein the first and the second color are different;and the two capsule luminescent pigments each comprise the same photochemically switchable absorber, wherein the photochemically switchable absorber has a first and a second switching state, and the absorption spectrum of the photochemically switchable absorber in the second switching state significantly overlaps with the emission spectrum of the first luminescent substance.

[0021] The present invention further relates, according to a second aspect, to a switchable luminescent printing ink comprising a system of at least two types of switchable capsule luminescent pigments, according to the first aspect of the present invention.

[0022] According to a third aspect, the present invention further relates to a security document, preferably a banknote, with a switchable luminescence print comprising a system of at least two types of switchable capsule luminescence pigments, according to the second aspect of the present invention.

[0023] Figures

[0024] Figure 1 shows the absorption spectra of a diarylethene switch (DAE 1) before and after switching (SZ1 and SZ2) and the emission spectrum of a luminescent substance (LS2) in the range of 245 to 700 nm.

[0025] Figure 2 shows the absorption spectra of a diarylethene switch (DAE 1) before and after switching (SZ1 and SZ2) and the emission spectrum of a luminescent substance (LS2) in the range of 390 to 690 nm.

[0026] Figure 3 shows in figures 3a-3d schemes to illustrate the switching effect of the at least two types of switchable capsule luminescence pigments of the system according to the invention when irradiated with UV radiation.

[0027] Figure 4A shows various monochrome printing patterns, comprising a switchable luminescent printing ink according to the invention and a non-switchable luminescent printing ink, before the switching of a photochemically switchable absorber.

[0028] Figure 4B shows various monochrome print patterns, comprising a switchable luminescent printing ink according to the invention and a non-switchable luminescent printing ink, after the switching of a photochemically switchable absorber. Figure 5A shows various print patterns, comprising a switchable luminescent printing ink according to the invention and a non-switchable luminescent printing ink, before the switching of a photochemically switchable absorber.

[0029] Figure 5B shows various printing patterns, comprising a switchable luminescent printing ink according to the invention and a non-switchable luminescent printing ink, after switching a photochemically switchable absorber.

[0030] Figure 6 shows a sample of a monochrome, switchable melange fiber comprising a print with a switchable luminescent printing ink according to the invention and a non-switchable luminescent printing ink.

[0031] Figure 7A shows a visually recognizable pattern for a switchable color-changing fiber prior to the switching of a photochemically switchable absorber.

[0032] Figure 7B shows a visually recognizable pattern for a switchable melier fiber with color change after switching a photochemically switchable absorber.

[0033] Detailed description of the invention

[0034] The present invention is based on the discovery of how one and the same switchable absorber can be used to switch different colored luminescence emissions. This allows for the provision of a system of switchable luminescent pigments emitting different colors, in particular red, green, and blue, such as red and green, or red and blue, or green and blue, which behave identically with respect to their switching properties. These switching properties include, in particular, the wavelength (for example, 365 nm) and intensity of the light for switching off the luminescence (i.e., the switching wavelength from the first to the second switching state), the switching speed during switching off, the wavelength for switching back from the second to the first switching state, especially in ambient light, and the switching speed during switching back.as well as the aging and environmental resistance of the switch. Further optimization of the amounts of material used also allows the switching depth of the various luminescent pigments to be matched. Thus, according to a first aspect, the present invention relates to a system of at least two types of switchable capsule luminescent pigments, wherein the capsule luminescent pigments are polymer particles with a diameter of 0.1–1000 pm, each containing at least one luminescent substance and a photochemically switchable absorber, wherein a first type of capsule luminescent pigment comprises a first luminescent substance emitting in a first color in the visible spectral range; a second type of capsule luminescent pigment comprises the first luminescent substance and a second luminescent substance emitting in a second color in the visible spectral range.wherein the first and second colors are different; and the two capsule luminescent pigments each comprise the same photochemically switchable absorber, wherein the photochemically switchable absorber has a first and a second switching state, and the absorption spectrum of the photochemically switchable absorber in the second switching state significantly overlaps with the emission spectrum of the first luminescent substance.

[0035] The system according to the invention comprises at least two types of switchable capsule luminescent pigments, wherein a first type of capsule luminescent pigment comprises a first luminescent substance emitting in a first color in the VIS spectral range; a second type of capsule luminescent pigment comprises the first luminescent substance and a second luminescent substance emitting in a second color in the VIS spectral range, wherein the first and the second color are different.The system can include any number of additional types of capsule luminescent pigments, for example, a third, fourth, and / or fifth type of capsule luminescent pigment, all of which comprise the first luminescent substance emitting in a first color in the visible spectral range, and additionally a further, for example, third, fourth, and / or fifth luminescent substance emitting in a third, fourth, or fifth color in the visible spectral range, wherein the colors of the first and the further, for example, third, fourth, and / or fifth luminescent substances are different. Each of the different types of capsule luminescent pigments thus has a different emission color, which can result from additive color mixing of the luminescence of the first luminescent substance and the second luminescent substance, or of the further, for example, third, fourth, and / or fifth luminescent substance.This can result from energy transfer between at least two luminescent materials. In this way, many types of switchable capsule luminescent pigments can be produced that emit in different colors, for example, green, yellow, red, orange, etc. For example, at least the second type of capsule luminescent pigment can comprise a further, third luminescent material emitting in a third color in the visible spectral range, wherein the third color is preferably different from the first and second colors. In one embodiment, the first type of capsule luminescent pigment can also additionally comprise a further, fourth luminescent material emitting in a fourth color in the visible spectral range, wherein the fourth color is preferably different from the first, second, and third colors.

[0036] It is also possible and preferred that, after excitation, an energy transfer, for example by FRET, can take place from the first or third to the second (or also from the second, third, or fourth to the first) luminescent substance or to each of the further, for example, third, fourth, and / or fifth, luminescent substances. This influences the respective overall color impression of a type of switchable capsule luminescent pigment, which in these cases then depends significantly on the luminescence of the second or the further, for example, third, fourth, and / or fifth, luminescent substance. Systems consisting of two or three types of switchable capsule luminescent pigments are preferred, and systems consisting of three types of switchable capsule luminescent pigments are particularly preferred. However, the system according to the invention can also consist of four, five, or more types of switchable capsule luminescent pigments.

[0037] It was surprisingly discovered that the luminescence of all types of switchable capsule luminescent pigments can be switched simultaneously, i.e., at the same wavelength and radiation intensity, by using the same switchable absorber in all types of switchable capsule luminescent pigments, whose absorption spectrum in the second switching state significantly overlaps with the emission spectrum of the luminescent substance emitting in a first color.

[0038] For example, the system of capsule luminescent pigments according to the invention can comprise two types of capsule luminescent pigments, for example, a first type of UV-excitable, green-emitting capsule luminescent pigment with a first luminescent substance and a second type of red-emitting capsule luminescent pigment comprising the first luminescent substance and a green-excitable, red-emitting second luminescent substance. Energy transfer can take place from the first luminescent substance to the second luminescent substance. Due to the presence of the same switchable absorber in both the first and second types of capsule luminescent pigments, switching the absorber from the first to the second switching state in the first, green capsule luminescent pigment can suppress or at least attenuate the luminescence of the first luminescent substance, so that the luminescence of this type of capsule luminescent pigment is (almost) completely extinguished.In the second, red capsule luminescent pigment, the luminescence of the first luminescent substance is also suppressed, so that without energy transfer, only the luminescence of the second luminescent substance remains visible. If energy transfer from the first to the second luminescent substance occurs, switching the absorber also suppresses or at least attenuates the luminescence of the second luminescent substance. This only happens if the energy transfer from the first luminescent substance to the absorber is more efficient than the energy transfer from the first luminescent substance to the second. It is preferred if such energy transfer occurs from the first to the second luminescent substance. In another embodiment, however, the second luminescent substance can be excited not only by the emission wavelength of the first luminescent substance, so that no energy transfer from the first to the second luminescent substance takes place.In this case, the luminescence of the second luminescent substance cannot be switched off by switching the absorber, but remains. This naturally presupposes that the second luminescent substance can then be excited by another suitable excitation wavelength.

[0039] In another preferred embodiment, the system of capsule luminescent pigments according to the invention comprises three types of capsule luminescent pigments, for example, a first type of capsule luminescent pigment comprising a first luminescent substance emitting in a first color in the VIS spectral range, and a second type of capsule luminescent pigment comprising the first luminescent substance emitting in a first color in the VIS spectral range and a second luminescent substance emitting in a second color in the VIS spectral range, wherein the first and second colors are different, and a third type of capsule luminescent pigment comprising a third luminescent substance emitting in a third color in the VIS spectral range and optionally the first luminescent substance emitting in a first color in the VIS spectral range and / or the second luminescent substance emitting in a second color in the VIS spectral range.wherein the first, second, and third colors are different; and the three different capsule luminescent pigments each comprise the same photochemically switchable absorber, wherein the photochemically switchable absorber has a first and a second switching state, and the absorption spectrum of the photochemically switchable absorber in the second switching state significantly overlaps with the emission spectrum of the first luminescent substance and the emission spectrum of the second and / or third luminescent substance. In order to ensure switching of the luminescence, the emission spectrum of the first luminescent substance must overlap with the absorption spectrum of the switchable absorber, but only in its second switching state, not in the first switching state. In the first switching state, the luminescence is then unaffected by the switchable absorber.In the second switching state, however, the luminescence is reabsorbed by the switchable absorber or the energy is transferred radiationlessly via FRET, thus significantly reducing the luminescence intensity.

[0040] To ensure significantly more intense luminescence of the first luminescent substance in the first switching state of the switchable absorber than in the second switching state, the absorption spectrum of the switchable absorber in the first switching state should not significantly overlap with the emission spectrum of the first luminescent substance, and the absorption spectrum of the switchable absorber in the second switching state should significantly overlap with the emission spectrum of the luminescent substance. This ensures the most efficient energy transfer possible.

[0041] A non-significant overlap of the first absorption spectrum of the switchable absorber (i.e., the switchable absorber before switching) with the emission spectrum of the first luminescent material means that the first absorption spectrum of the switchable absorber, normalized to 1 at the wavelength of highest absorption in the range of 245 to 700 nm, exhibits at most one absorption in the same wavelength range of an emission band in the emission spectrum of the first luminescent material, which (i.e., the absorption) at its highest point is less than 5%, preferably less than 3%, more preferably less than 2%, even more preferably less than 1%, and particularly preferably less than 0.5%, of the maximum emission of the first luminescent material in its emission spectrum normalized to 1 at the wavelength of highest emission in the range of 245 to 700 nm.

[0042] An emission band of the first luminescent material is defined as a wavelength range in which the emission corresponds to at least 10%, for example, at least 20%, of the maximum emission of the first luminescent material. The absorption maximum of the switchable absorber after switching, which arises in the second switching state, lies within this relevant emission band of the first luminescent material. The difference between the absorption curves of the first and second switching states of the switch in the region of the emission maximum of the first luminescent material is absolutely greater than 50%, preferably greater than 70%, more preferably greater than 80%, and particularly preferably greater than 90%, relative to the absorption maximum in the second switching state. For this purpose, the absorption in the second switching state of the switch is normalized to the value of the resulting absorption maximum (so that the absorption maximum corresponds to 100%) and used as a reference. The emission band is defined as above.

[0043] A significant overlap of the second absorption spectrum of the switchable absorber (i.e., the switchable absorber after switching) with the emission spectrum of the first luminescent material means that the second absorption spectrum (in the range of 245 to 700 nm) of the switchable absorber, normalized to 1 at the wavelength of highest absorption, exhibits absorption in the same wavelength range as an emission band in the emission spectrum of the first luminescent material, wherein the absorption in this emission band at its highest point is at least 5%, preferably at least 8%, more preferably at least 10%, even more preferably at least 12%, and particularly preferably at least 15%, of the maximum emission of the first luminescent material in its emission spectrum (in the range of 245 to 700 nm), normalized to 1 at the wavelength of highest emission.

[0044] It goes without saying that in the procedure described here for determining a non-significant or significant overlap of the first or second absorption spectrum of the diarylethene with the emission spectrum of the luminescent substance, the first and second absorption spectra are measured under the same conditions, for example under the same settings on the measuring instrument, at the same concentrations, etc.

[0045] Figure 1 illustrates this. The graph labeled "DAE SZ 1" (SZ = switching state) shows the first absorption spectrum of a diarylethene (DAE), i.e., a switchable absorber or photochromic, before switching. The absorption spectrum is normalized to 1 at the wavelength of highest absorption. From approximately 360 nm and above, the absorption spectrum shows no absorption by the unswitched diarylethene. The graph labeled "DAE SZ 2" is the second absorption spectrum of the diarylethene after switching. Here, too, the absorption spectrum is normalized to 1 at the wavelength of highest absorption. An absorption band is visible in the range of approximately 380 to 620 nm. The graph labeled "LY Em" is the emission spectrum of a first luminescent substance. The emission band is located in the range of approximately 450 to 640 nm.Figure 1 shows that the absorption spectrum of the unswitched diarylethene switch does not overlap with the emission spectrum of the luminescent material, since no absorption of the unswitched diarylethene switch is observed in the relevant range of 450 to 640 nm for the luminescence of the luminescent material. In contrast, the absorption spectrum of the switched diarylethene switch overlaps significantly with the emission spectrum of the first luminescent material due to the formation of an absorption band at approximately 380 to 620 nm. Figure 2 is a section of the wavelength range from 390 to 690 nm from Figure 1, in which the respective maxima have been normalized to 1 (100%), and illustrates that the maximum of the absorption band formed after switching the diarylethene switch lies in the region of the maximum emission of the luminescent material. This is desirable for efficient FRET energy transfer.Furthermore, Figure 2 shows that the absolute difference between the maxima of the absorption bands of the unswitched and switched diarylethene switch in the relevant range of 390 to 690 nm is at least 95%. This is desirable, among other things, for achieving a sufficient switching depth.

[0046] In particular, switching the switchable absorber results in a reduction of the luminescence intensity of the first luminescent substance by at least 10%, such as at least 20%, at least 30%, or at least 40%. Preferably, the reduction in luminescence intensity is at least 45%, such as at least 50%, at least 60%, or at least 70%. A reduction in luminescence intensity of at least 20% can be perceived, especially visually. The switching depth can be quantitatively determined by measurement using commercially available fluorescence spectrometers.

[0047] The wavelength at which the first luminescent substance can be excited is not inherently limited. However, for the use of the system according to the invention, comprising at least two types of switchable capsule luminescent pigments, in security applications such as for valuable documents, it is advantageous to select the excitation wavelength such that the luminescence of the luminescent substance is perceptible to the human eye. This will generally be the case with shorter excitation wavelengths. Excitation wavelengths in the UV range are preferred, for example, in the range of 310–400 nm, more preferably 350–380 nm. An excitation wavelength of 365 nm is particularly preferred, i.e., a wavelength commonly used in lamps for verifying the authenticity of banknotes at cash registers.

[0048] The wavelength at which the second luminescent substance can be excited is also not inherently limited. However, for the use of the system according to the invention in security applications, such as for valuable documents, it is advantageous to select the excitation wavelength such that the luminescence of the second luminescent substance is perceptible to the human eye. To enable simple verification of a security application comprising the system according to the invention, the excitation wavelength for the second luminescent substance should preferably correspond to the excitation wavelength for the first luminescent substance, preferably in the range of 310–400 nm, 350–380 nm, or 365 nm. In a more preferred embodiment, the second luminescent substance can be excited by the emission wavelength of the first luminescent substance, for example, in the range of 400–800 nm, 450–750 nm, or 500–700 nm.

[0049] Regarding the excitation wavelength for the optional additional, for example third, fourth and / or fifth, luminescent substances, the same considerations apply as for the second luminescent substance. In a preferred embodiment, the optional additional, for example third, fourth and / or fifth, luminescent substance can be excited by the emission wavelength of the first or second, preferably second, luminescent substance, for example in the range of 450 to 800 nm, in the range of 500 to 750 nm, or in the range of 550 to 700 nm.

[0050] The wavelength range in which the switching of the switchable absorber from the first to the second switching state can occur is not inherently limited, and in principle any suitable wavelength can be selected. However, as already explained above, it is advantageous and therefore preferred if the switching of the switchable absorber from the first to the second switching state can occur in the same wavelength range, or preferably even at the exact same wavelength, as the excitation of the first luminescent material. For example, the switching of the switchable absorber from the first to the second switching state and the excitation of the luminescent material can occur in the range of 310–400 nm, preferably in the range of 350–380 nm, and particularly preferably at an excitation wavelength of 365 nm.Simultaneous excitation of the luminescent substance and switching of the switch is advantageous because only one light / radiation source is then required, which significantly simplifies methods for verifying the authenticity of valuable documents based on the system according to the invention.

[0051] According to a further advantageous embodiment, it is therefore preferred that in the wavelength range of 310-400 nm the excitation spectrum of the first luminescent substance and the absorption spectrum of the switchable absorber overlap in the first switching state.

[0052] The light intensities required for switching are preferably comparable in the UV range to the excitation intensity of the first luminescent substance, so that both effects are triggered simultaneously with the UV lamps commonly used at checkout counters, and in the visible range at the level of typical room lighting. The intensity of the light source primarily influences the switching duration, but not the switching depth. The switching duration is defined as the time after which, with constant illumination from the excitation or switching light, the luminescence intensity no longer changes by more than 2%. The switching depth is the percentage difference between the initial luminescence intensity and the luminescence intensity reached after the switching duration. Another measure with which the luminescence properties of a luminescent substance can be described and quantified is the residual intensity (l). RThe residual intensity refers to the percentage of the intensity (or switching depth) of the luminescence measured after irradiation according to BWS3 in the unswitched state compared to the intensity measured before irradiation in the unswitched state.

[0053] Switching depth). The residual intensity can be measured, for example, by quantitatively measuring an indentation containing the respective luminescent substance(s) before irradiation using a commercially available fluorescence spectrometer. The obtained value is normalized to 100%, and the remaining residual intensity of the luminescence after reaching the Woll scale points is considered. For good optical perceptibility of a luminescence change with the human eye, a residual intensity of at least 50% is desirable. Accordingly, the capsule luminescent pigments used in the system according to the invention preferably have a residual intensity of at least 50%.Furthermore, for good optical perceptibility of a luminescence change of different capsule luminescence pigments relative to each other with the human eye, it is desirable if the difference in residual intensities and residual switching depths of the different capsule luminescence pigments is at most 20%. Accordingly, the difference in residual intensities and residual switching depths of the at least first and second capsule luminescence pigments used in the system according to the invention is preferably at most 20%, for example at most 15%, more preferably at most 10%, and particularly preferably at most 5%.

[0054] For example, a VL-6.LC UV lamp equipped with a 6W UV tube from Vilber can be used to switch from the first to the second state and / or to excite the luminescent material. Preferably, a visually detectable switching depth of at least 10%, such as at least 20%, at least 30%, or at least 40%, preferably at least 45%, such as at least 50%, at least 60%, or at least 70%, is achieved under UV light of the specified intensity and at a distance of approximately 20 cm within a period of less than 30 s, preferably less than 20 s, and particularly preferably less than 10 s.

[0055] Figure 3 illustrates an embodiment of the system according to the invention, comprising two types of switchable capsule luminescent pigments. Figure 3a shows a switchable capsule luminescent pigment containing a first luminescent substance emitting in a first color in the visible spectral range, and a switchable absorber. The first luminescent substance (here a mixture of luminescent substances) is excitable by UV light and is represented by the circles labeled "blue" and "green". After irradiation, the first luminescent substance emits green light (represented by the circle labeled "green"). The switchable absorber, represented by a switch symbol, is in the first switching state, so that no energy transfer from the emission of the first luminescent substance to the switch takes place. The green luminescence of the capsule luminescent pigment is thus possible (labeled "ON" in Figure 3a).Figure 3a shows the luminescence state of a first switchable capsule luminescent pigment at the beginning of irradiation. Figure 3b differs from Figure 3a in that the switchable absorber has now been switched to its second switching state by irradiation (for example, by the same UV irradiation used to excite the first luminescent substance). This allows the energy from the excited first luminescent substance to be transferred to the switchable absorber without radiation, for example, via FRET. The green luminescence of the first capsule luminescent pigment is therefore no longer possible (indicated by "OFF" in Figure 3b). Figure 3b shows the luminescence state of a switchable capsule luminescent pigment after a certain time and intensity of irradiation.Figure 3c shows a switchable capsule luminescent pigment containing a first luminescent substance emitting in a first color in the visible spectral range, a luminescent substance emitting in a second color, and a switchable absorber. The first luminescent substance is excitable by UV light and is represented by the circles labeled "blue" and "green." Upon irradiation, the first luminescent substance emits green light (represented by the circle labeled "green"). The green light emitted, in turn, excites the second luminescent substance, which then emits red light (represented by the circle labeled "red"). The switchable absorber, represented by a switch symbol, is in its first switching state, so no energy transfer from the emission of the first luminescent substance to the switch takes place.The red luminescence (the green emission of the first luminescent substance is absorbed by the red-emitting second luminescent substance) of the second capsule luminescent pigment is thus possible (indicated by "ON" in Figure 3c). Figure 3c corresponds to the luminescence situation of a second type of switchable capsule luminescent pigment at the beginning of irradiation. Figure 3d differs from Figure 3c in that the switchable absorber has now been switched to the second switching state by irradiation (for example, by the same UV irradiation used to excite the first luminescent substance). This allows the energy from the excited first luminescent substance to be transferred to the switchable absorber non-radiatively, for example, via FRET. This suppresses the green emission, so that the red-emitting second luminescent substance can no longer be excited.Therefore, red luminescence of the second capsule luminescent pigment is no longer possible (indicated by "OFF" in Figure 3d). Figure 3d represents the luminescence situation of a switchable capsule luminescent pigment after a certain time and intensity of irradiation.

[0056] The photochemically switchable absorber used as a molecular switch has a first absorption spectrum in a first switching state and a second absorption spectrum in a second switching state. Thus, the switchable absorber is limited in principle only in that it has two switching states, i.e., it is a photochromic substance, with the absorption spectra of the two switching states differing.

[0057] In principle, any suitable switchable absorber can be used that can be switched from a first switching state to a second switching state by radiation. A preferred class of suitable switchable absorbers are diarylethenes. In principle, any suitable diarylethene can be used in the capsule luminescent pigments of the system according to the invention. The selection of a suitable switchable absorber, in particular a diarylethene, for a specific application can be made by a person skilled in the art taking into account the desired switching wavelength of the switchable absorber, in particular a diarylethene switch, and / or the emission maximum of the first luminescent material (which, as described above, should overlap with the absorption spectrum of the second switching state of the switchable absorber) and / or the desired wavelength for the (re-)switching from the second to the first state.For example, the diarylethene can be a diheteroarylethene, preferably a dithienylethene, and most preferably a fluorinated dithienylethene. Suitable diarylethenes and their syntheses are described, for example, in JP 3 384 087 B2, JP 3 479 992 B2, JP 3 491 704 B2, JP Hll- 256 146 A, JP 2001- 254 074 A, JP 3 225 581 B2, and JP H09- 241 254 A, as well as in the articles by J. Mamiya, A. Kuriyama, N. Yokota, M. Yamada, T. Ikeda, Chem. Eur. J. 2015, 21, 3174, and by S. Kobatake, T. Yamada, K. Uchida, N. Kato, M. Irie, J. Am. Chem. Soc. 1999, 121, 2380. The following compounds have proven to be particularly suitable diarylethene switches: The switchable absorber, in particular a diarylethen switch, preferably switches back from the second to the first state when illuminated with visible light, for example in the wavelength range of 400–700 nm. It is further preferred that the switchable absorber, in particular a diarylethen switch, remains in its state in the dark at room temperature, i.e., neither switching from the first to the second state nor vice versa occurs. Preferably, the switchable absorber, in particular a diarylethen switch, can be switched from the second to the first state by the prescribed average illuminance of 500–750 lux at office workstations (DIN EN 12464-1).The switchable absorber, in particular a diarylethene switch, preferably switches automatically back from its second switching state to its initial state under daylight intensity of 500 lux within a period of less than 10 minutes, preferably less than 5 minutes, and most preferably less than 1 minute. This means that at least 95%, preferably at least 98%, of the initial intensity is achieved.

[0058] The first and second, as well as the optional third, fourth, and / or fifth luminescent substances, are not limited in principle, and any suitable luminescent substance can be used in the capsule luminescent pigments of the system according to the invention. For optimal applicability as a safety feature, the first luminescent substance is preferably selected such that it can be excited between 310 and 400 nm, preferably between 350 and 380 nm, and particularly preferably at 365 nm. The selection of the second and the optional third, fourth, and / or fifth luminescent substances is based, depending on the system, either on the excitation wavelength of the first luminescent substance, for example between 300 and 400 nm, between 350 and 380 nm, or at 365 nm, or is preferably selected such that it can be excited by the emission of the first luminescent substance.Furthermore, it is preferred that the luminescent substances emit visible light. The luminescent substance need not be a pure chemical substance, but can also be a mixture of several luminescent substances, for example, two, three, or four. In other words, the term "luminescent substance" as used herein also includes...

[0059] Luminescent mixtures, i.e., mixtures of two or more, for example, two, three, four, or five different luminescent substances. Suitable luminescent substances may be selected independently from the group consisting of diarylpolyenes, arylacetylenes, oxazoles, pyrazoles, benzazoles, anthrones, quinones, cyanines, rhodamines, oxazines, phenoxazines, thiazines, phenothiazines, perylenes, terylenes, coumarins, benzoxazinones or benzothiazinones, oxinates, aldazines, anthranilic acid derivatives, salicyclic acid derivatives, and mixtures thereof. Preferably, the luminescent substances are selected independently from the group consisting of perylenes, benzoxazinones, oxinates, benzthiazine, aldazines, anthranilic acid derivatives, salicyclic acid derivatives, oxazines, oxazoles, anthrones, and mixtures thereof. Suitable luminescent substances are described, for example, in WO 2006 / 014658 A2, US 2015 / 0132575Al, and EP 2195395Bl.

[0060] The luminescent substance and the switchable absorber, in particular the diarylethene switch, are preferably dissolved and / or dispersed as separate molecules in a polymer particle within the capsule luminescent pigments of the system according to the invention. Thus, there is no direct chemical bond between the luminescent substance and the switchable absorber, in particular the diarylethene, but rather they exist as separate molecules. The luminescent substance and the switchable absorber, in particular the diarylethene, can either be dissolved, for example, in a solvent enclosed within the capsule luminescent pigment, or dispersed, for example, in a polymer / polymeric matrix enclosed within the capsule luminescent pigment. It is understood that the term "separate molecules" in the context of the present invention also means that the diarylethene and the luminescent pigment are different from each other, i.e., they cannot be the same molecule.

[0061] Encapsulation means that the luminescent material and the switchable absorber, in particular the diarylethene, are together surrounded by a polymeric shell. The type of encapsulation is not restricted, as long as it is a polymer encapsulation. The polymer particle can be a core-shell particle, i.e., a polymer particle comprising a core of a first polymer and a shell of a second polymer, which may differ from the first polymer. In a preferred embodiment, the core consists of a first polymer and the shell of a second polymer that differs from the core polymer in at least one monomer. This core / shell structure additionally guarantees the chemical stability of the encapsulated components against external influences.External influences include, among other things: humidity, aqueous environment, sweat, fats, detergents, solvents and chemical compounds such as alkalis, acids, alcohols and acetone.

[0062] For example, the capsule luminescent pigments can be obtained by encapsulation as described in WO 2017 / 080653 Al (polymethyl methacrylate (PMMA) / melamine-formaldehyde resin (MF) coating) or WO 2017 / 080656 Al (polyurethane (PUR) / MF coating). The processes described therein for the production of core-shell particles containing a luminescent substance in the core can be modified for the production of the capsule luminescent pigments by adding the switchable absorber, in particular the diarylethene switch, in addition to the luminescent substance in the core material production step.

[0063] For example, the capsule luminescent pigments can contain as a core a polymer selected from polystyrene (PS), polyacrylates, polyethylene (PE), polypropylene (PP), polycarbonates (PC), polyamides (PA), polyurethanes (PU), polyureas (PH), polyethylene terephthalate (PET), other polyesters, or mixtures thereof, and / or as a shell a condensation polymer selected from aminoplasts, phenolplasts, melamine-formaldehyde resins (MF), melamine-phenol-formaldehyde resins (MPF), phenol-formaldehyde resins (PF), urea-formaldehyde resins (UF), melamine-guanidine-formaldehyde resins, phenol-resorcinol-formaldehyde resins, or mixtures thereof. Preferably, the capsule luminescent pigments contain as a core a thermoplastic polymer, in particular a thermoplastic polymer selected from polymethyl methacrylate or polystyrene, and / or as a shell a melamine-formaldehyde resin.Particularly preferably, the capsule luminescence pigments according to the invention contain as a core a thermoplastic polymer selected from polymethyl methacrylate or polystyrene and as a shell a melamine-formaldehyde resin.

[0064] The proportion of the luminescent material in the core of the capsule luminescent pigments can be independently 0.1 to 10 wt%, preferably 0.2 to 8 wt%, more preferably 0.3 to 7 wt%, such as 0.5 to 5 wt%, 0.7 to 4 wt%, or 0.8 to 3 wt%, and particularly preferably 1 to 2.5 wt%, in each case based on the total weight of the core material. If the luminescent material consists of several different luminescent materials, the proportions of the respective individual luminescent materials can be correspondingly lower, for example, 0.01 to 10 wt%, 0.02 to 8 wt%, 0.05 to 5 wt%, or 0.7 to 4 wt%, in each case based on the total weight of the core material.

[0065] The proportion of the photochemically switchable absorber in the core of the capsule luminescence pigments can be independently 1 to 20 wt%, preferably 1.5 to 18 wt%, more preferably 2 to 17 wt%, such as 2.5 to 15 wt%, 3 to 13 wt%, or 3.5 to 10 wt%, and particularly preferably 4 to 8 wt%, in each case based on the total weight of the core material.

[0066] The capsule luminescent pigments of the system according to the invention have a diameter of 0.1 to 1000 pm, for example, from 0.05 to 500 pm, from 1 to 200 pm, or from 1 to 100 pm, preferably from 1 to 50 pm, for example, from 1 to 30 pm or 1 to 20 pm or 1 to 10 pm, more preferably from 0.2 to 10 pm or from 1 to 5 pm, and particularly preferably from 1 to 3 pm. The diameter is generally specified as the D99 value, i.e., 99% of all capsule luminescent pigments have the specified diameter or are smaller. The determination of the diameter and the D99 value is well known to those skilled in the art. For example, the diameter and the D99 value can be determined using laser scattering, for example, using the Cilas 1090 Particle Size Analyzer from 3P Instruments.

[0067] According to a second aspect, the present invention relates to a switchable luminescent printing ink comprising a system of at least two types of switchable encapsulated luminescent pigments according to the first aspect of the present invention. The system of at least two types of switchable encapsulated luminescent pigments contained in the switchable luminescent printing ink according to the invention can thus be any system of at least two types of switchable encapsulated luminescent pigments described above.

[0068] In principle, any printing ink can be used as the basis for the switchable luminescent printing ink according to the invention, in particular any printing ink suitable for printing security documents, for example an offset ink or an intaglio ink, and a system of capsule luminescent pigments as described herein can be introduced to produce the switchable luminescent printing ink according to the invention. Suitable printing inks are known to those skilled in the art and are described, for example, in WO 2013 / 178 325 A2, EP 2 888 112 Bl, DE 10 2012 010 534 Al, WO 2018 / 197 039 Al and EP 3 660 110 Bl. The printing ink can preferably be oxidatively drying or curing or UV-curing, and particularly preferably UV-curing.For example, the ink may preferably be an oxidatively drying or UV-curing offset ink, an oxidatively drying or UV-curing intaglio ink, an oxidatively drying or UV-curing screen printing ink, or an oxidatively drying or UV-curing flexographic printing ink. Offset inks, especially UV-curing offset inks, are particularly preferred.

[0069] According to a third aspect, the present invention relates to a security document with a switchable luminescent print, comprising a system of at least two types of switchable capsule luminescent pigments according to the first aspect of the present invention, or a switchable luminescent printing ink according to the second aspect of the present invention. The security document can, in principle, be any type of security document, for example, a security document, a banknote, or an identity document, and is preferably a banknote or an identity document, and particularly preferably a banknote.

[0070] A security document typically comprises a substrate with optionally at least two opposing layers applied to it. Any substrate suitable for security documents can be used. These substrates are known to those skilled in the art and include, for example, paper substrates, substrates based on cotton fibers or mixed fibers, where mixed fibers may include, in particular, fibers from cotton, flax, linen, cellulose, and plastics, substrates based on plastic films, and impregnated and pre-coated substrates. Hybrid substrates can also be used, such as paper-plastic substrates or multilayer substrates, for example, film / paper / film substrates, as known from WO 2004 / 028 825 A2. The substrate can be impregnated with polymers of any kind and is preferably impregnated with polyvinyl alcohol.

[0071] The layers optionally applied opposite each other on the substrate are generally intended to protect the substrate, for example, by repelling dirt and / or moisture. However, they can also alternatively or additionally provide a substrate with improved adhesion for further layers, such as a printing layer. Accordingly, the layers applied opposite each other on the substrate can be, for example, sizing layers and / or primer layers. Potential sizing layers and primer layers, as well as methods for applying them, are known to those skilled in the art. A sizing layer and / or primer layer can, for example, be formed by a physically drying lacquer layer. "Physically drying" means that drying occurs through evaporation and / or dispersion of the solvents or dispersion agents into the substrate.The production of suitable coatings is described, for example, in EP 2 634 309 Al and WO 2004 / 072 378 Al. Water-based dispersion coatings are particularly preferred. For example, a sizing layer may contain polyvinyl alcohol and / or polyurethane. Examples of suitable primer compositions are those based on acrylates, polyester acrylates, urethane acrylates, polyester polyurethanes, and acrylonitrile styrene polyurethanes. Water-based dispersions, especially water-based dispersions of aliphatic components, are particularly preferred.

[0072] The security document according to the invention further comprises a print with a switchable

[0073] A luminescent print comprising a system of at least two types of switchable encapsulated luminescent pigments according to the second aspect of the invention. The print can be a full-surface or at least partially surface-surface printed layer, or a printed pattern, applied to the valuable document. This layer may consist of a first switchable luminescent printing ink according to the second aspect of the present invention, or a printing ink or ink mixture containing a system of at least two types of switchable encapsulated luminescent pigments according to the first aspect of the present invention. Parts or sections of a valuable document, such as a melange fiber, can also be printed with the switchable luminescent print.A printed design can, of course, also contain several printed patterns made from different printing inks, applied side by side or (partially) on top of each other, wherein at least one of the printing inks is a switchable luminescent printing ink according to the second aspect of the present invention, or a printing ink or printing ink mixture containing a system of at least two types of switchable encapsulated luminescent pigments according to the first aspect of the present invention. Likewise, in addition to at least one printed pattern made from a switchable luminescent printing ink, a further printed layer may also be applied to the entire surface or at least partially across the surface of the document. A printed design using more than one printing ink is preferred, wherein at least one of the printing inks is a switchable luminescent printing ink.The printing can be, for example, an intaglio print or a gravure print and can be applied directly to the substrate or to at least one, preferably both, of the two layers optionally applied opposite each other on the substrate or to any further layers of the security document.

[0074] Printing a security document with a switchable luminescent ink according to the second aspect of the present invention enables simple security verification of the document by visual inspection when the document is irradiated with a suitable wavelength, for example, 310 to 400 nm, preferably 350 to 380 nm, and particularly preferably 365 nm. The photochemically switchable absorber contained in the at least two types of switchable luminescent pigments from the system according to the invention switches from the first to the second switching state, as described above, when irradiated with a suitable wavelength. In the second switching state, the luminescence of the first luminescent substance, which is excited simultaneously, preferably at the same wavelength as the switch, is reduced by FRET in both the first and second types of switchable capsule luminescent pigments.For visual inspection, the luminescence of the luminescent dyes gradually diminishes when the radiation source is switched on. This is noticeable as a darkening or change in the printing ink during visual inspection. After the radiation source is switched off, the switch resets, preferably in daylight, so that further corresponding changes occur.

[0075] Security checks are possible.

[0076] In a preferred embodiment of the security document according to the invention with a luminescent imprint, the luminescence of the at least two types of capsule luminescent pigments can thus be switched off using light of the same wavelength, preferably between 310 and 400 nm, more preferably between 350 and 380 nm, and particularly preferably at 365 nm.

[0077] Preferably, the luminescent print of the security document according to the invention further comprises at least one additional luminescent color whose luminescence in the same wavelength range, preferably between 310 and 400 nm, more preferably between 350 and 380 nm, and particularly preferably at 365 nm, cannot be switched off and whose emission color in the VIS spectral range differs from that of the first and second switchable luminescent capsule pigments. In an alternative preferred embodiment, the luminescent print of the security document according to the invention further comprises at least one additional luminescent color whose luminescence in the same wavelength range, preferably between 310 and 400 nm, more preferably between 350 and 380 nm, and particularly preferably at 365 nm, cannot be switched off and whose emission color in the VIS spectral range corresponds to that of at least one of the first and second switchable luminescent capsule pigments.

[0078] The additional luminescent printing ink can contain the suitable luminescent substance or mixture of suitable luminescent substances as a simple component, i.e., as molecules freely incorporated into the additional luminescent printing ink, or alternatively and preferably encapsulated in the form of capsule luminescent pigments as described above, which, however, do not contain a switchable absorber. In this way, security features can be created in which some areas of the print darken upon irradiation with a suitable wavelength (i.e., the areas printed with the switchable luminescent printing ink according to the second aspect of the present invention) and some areas retain their luminescence unchanged (i.e., the areas printed with the additional, non-switchable luminescent printing ink). The security document according to the invention can, of course, also include prints with further printing inks.For example, printing with several, say, two, three, four, or five, switchable luminescent printing inks, as described in the second aspect of the present invention, which differ from one another, particularly with regard to their color appearance, is conceivable. Such printing with several, say, two, three, four, or five different switchable luminescent printing inks allows for the creation of complex patterns that only become visible under irradiation, for example, UV irradiation. Likewise, in complex color mixtures that produce luminescence in a specific color, the visually perceptible luminescence under irradiation, for example, UV irradiation, can be altered by selectively switching off individual components of the color mixture.The colors of the switchable luminescent printing inks according to the second aspect of the present invention, as well as the further non-switchable luminescent printing inks, can be adjusted by a person skilled in the art by mixing suitable luminescent colors by additive color mixing as required.

[0079] Part of the invention is thus a multi-colored, switchable luminescent print made from one or more luminescent printing inks with the inventive system of at least two switchable capsule luminescent pigments, as well as a security document with such a print. A system consisting of a switchable and a non-switchable luminescent printing ink is particularly advantageous, especially one with the same luminescent color tone with or without the photochemically switchable absorber. The luminescent color tone can be adjusted by combining the switchable luminescent pigments in the printing ink. This allows for the production of prints that initially exhibit a homogeneous color impression and a homogeneous luminescence intensity under UV illumination.With prolonged exposure to light, such as UV radiation, the luminescence of the switchable luminescent ink fades after a certain period, for example, after a few seconds (e.g., 5, 10, or 20 seconds), revealing a dark image against a light, luminescent background. Color-changing effects can also be achieved by combining switchable and non-switchable luminescent inks of different emission colors. In particular, combining one or more non-switchable (static) luminescent printing inks with one or more switchable luminescent printing inks of the same emission color can generate an image that changes shape or color under UV radiation.

[0080] Figures 4-7 show exemplary applications of the switchable luminescent printing ink according to the invention in printing patterns and melange fibers.

[0081] Figures 4A and 4B show monochrome printed patterns with shape changes using a switchable luminescent ink according to the second aspect of the present invention. Three pairs, each consisting of a conventional UV-luminescent ink and a switchable UV-luminescent ink, are applied to a substrate, for example, a security document, in separate areas. The colors within a pair have the same color impression, while different pairs have different color impressions. Figure 4A shows the first state immediately after the UV light is switched on, i.e., before the photochemically switchable absorber has switched to any significant extent. The vertically shaded, white, and horizontally hatched areas describe three different color impressions.After a certain switching time (after the photochemically switchable absorber has switched), the second state shown in Figure 4B is reached, in which the hatched areas retain their respective colors from the first state (i.e., the simple, non-switchable luminescent printing ink). The black-marked areas lose their luminescence and become dark (i.e., the switchable luminescent printing ink). The luminescent color effect is created, in particular, by a mixture of different colored switchable luminescent substances or luminescent pigments through additive color mixing.

[0082] For example, a print in its initial state, when exposed to UV light at a wavelength of 365 nm, shows a red, a green, and a yellow luminescent square. After irradiation with UV light, the print shows rotated rhombuses in the corresponding luminescent colors red, green, and yellow. The black areas no longer luminesce.

[0083] Figures 5A and 5B show color-changing printed patterns using a switchable luminescent ink according to the second aspect of the present invention. Three pairs of inks, each consisting of a conventional UV-luminescent ink and a switchable UV-luminescent ink, are applied to separate areas of a substrate, for example, a security document. In the initial state shown in Figure 5A, immediately after switching on the UV light, i.e., before the photochemically switchable absorber has switched to any significant extent, all colors exhibit the same color impression (in Figure 5A, the white areas describe a uniform color impression). After a certain switching time, the state shown in Figure 5B is reached, in which the white areas retain their respective colors from the initial state (i.e., the simple, non-switchable luminescent ink).The hatched areas change their color appearance (the different directions of the hatching represent different luminescent color impressions) because one or more of the luminescent pigments used (i.e., the switchable luminescent printing ink) are extinguished. The luminescent color impression arises primarily from a mixture of different colored switchable and non-switchable luminescent substances or luminescent pigments through additive color mixing. For example, three white luminescent squares in the hatched area will change color to red, blue, and orange, respectively, when exposed to sustained UV light. The white areas remain white.

[0084] Figure 6 shows a possible pattern of a monochrome, switchable luminescent fiber, comprising a print with a switchable luminescent ink according to the invention and a non-switchable luminescent ink. A first, switchable luminescent ink (black areas) and a second, non-switchable luminescent ink (white areas) are incorporated into a luminescent fiber. The first and second luminescent inks have the same luminescent color. The second, non-switchable luminescent ink does not change its intensity upon irradiation, for example, UV irradiation, while the first luminescent ink darkens. The two luminescent inks consist, for example, of any mixture of blue, green, and red luminescent substances. The corresponding luminescent color is obtained by additive color mixing.

[0085] Figures 7A and 7B show a possible visually recognizable pattern for a switchable luminescent fiber with color change before (Figure 7A) or after (Figure 7B) the activation of a photochemically switchable absorber. A first, non-switchable luminescent printing ink (white areas), a second switchable luminescent printing ink according to the present invention (hatched areas, inclined to the right), and a third switchable luminescent printing ink (hatched area, inclined to the left) are incorporated into a luminescent fiber. At the beginning of irradiation, the first, second, and third luminescent printing inks have the same luminescent color, which is produced by the additive mixing of different luminescent pigments (Figure 7A). For example, the first luminescent printing ink does not change its intensity or color under UV irradiation, while the second and third luminescent printing inks do change their color (Figure 7B).In particular, a color change occurs in the second and third luminescent printing inks, as one or more of the pigments in the respective luminescent dye mixtures darken, thus changing the color composition. This can result in a color change to different colors in the final state.

[0086] For example, a white luminescent melange fiber turns pink and blue in the hatched areas after irradiation with UV light. The white areas, however, continue to luminescent white. Examples:

[0087] Methods

[0088] To produce the printing inks, the pigments were incorporated into an offset printing ink (Sicpa Holding SA) using an Engelsmann JEL 25 / 53 ink rubbing machine (manufactured in 2013). The pigmentation level was 15% by weight. The printing inks were applied at a printing thickness of 1 g / m². 2Printed on security paper, the proofs were dried at 60 °C for 2 hours. Subsequently, the proofs were visually assessed for their switching time and depth. The switching depth was quantitatively determined using a commercially available fluorescence spectrometer. The proofs were then subjected to the lightfastness and fatigue resistance test described above and again assessed for switching time, switching depth, and residual intensity of the luminescent substance in its initial state.

[0089] Lightfastness and fatigue resistance were determined using the European Blue Wool Scale (BWS), commonly used for determining the lightfastness of absorption inks, e.g., analogous to standard EN ISO 105-B01:1999. However, instead of the (absorptive) color impression, the intensity of luminescence emission at the various points of the wool scale was determined. For this purpose, the respective luminescence intensity of the prints was quantitatively measured before irradiation using a commercially available fluorescence spectrometer and normalized to 100%. The remaining residual intensity of the luminescence after reaching the wool scale points was considered. To quantitatively assess lightfastness, fatigue resistance, and chemical resistance, a test procedure analogous to WO 2017 / 080 654 Al was used. Both the luminescent material and the photochemically switchable absorber were required to pass the BWS test.The luminescent material is measured, particularly in the first switching state of the photochemically switchable absorber, and exhibits a residual luminescence intensity of at least 50% of the original luminescence intensity at "BWS3". The photochemically switchable absorber should be stable with respect to its switching depth, i.e., the switching depth at "BWS3" should be at least 50% of the original switching depth.

[0090] Diarylethene syntheses 3,3'-(Perfluorocyclopent-l-ene-l,2-diyl)bis(2-methyl-6-nitrobenzo[b]thiophene) (DAE 2)

[0091] DAE 1 DAE 2 69%

[0092] AcjO (0.50 mL, 0.54 g, 5.29 mmol, 8.2 eq.) was dissolved in 6 mL AcOH (99.8%), cooled to 10°C, and 1,2-bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-l-cyclopentene (DAE 1, TCI Chemicals) (300 mg, 0.64 mmol, 1.0 eq.) was added. Subsequently, 0.3 mL of conc. HNO3 was added dropwise, the reaction mixture was heated to room temperature, and stirred overnight at room temperature. The reaction was stopped by the addition of 10 mL of NaHCOs faqj and taken up in 20 mL of EtOAc. The phases were separated, and the aqueous phase was extracted with EtOAc (3 x 10 mL). The combined organic phases were washed with NaCl(aq) (1 x 20 mL), dried over Na₂SO₄, filtered, and the solvent was removed under vacuum. The product was purified by column chromatography (SiO₂, H / EtOAc = 5 / 1 -> 4 / 1 -> 1 / 1, UV) and isolated as a colorless solid (247 mg, 0.44 mmol, 69%).

[0093] 3-Bromo-2,5-dimethylthiophene

[0094] 74%

[0095] 2,5-Dimethylthiophene (5.05 mL, 5.00 g, 44.6 mmol, 1.0 eq.) was dissolved in 500 mL of CH₂Cl₂, NBS (7.94 g, 44.6 mmol, 1.0 eq.) was added in one portion, and the reaction solution was stirred overnight at room temperature. After concentration under vacuum, the residue was reconstituted in 250 mL of Et₂Ü, with H₂O (3 x 50 mL) and NaCl( aq ) (1 x 100 mL) washed, dried over Na₂SO₄, filtered, and the solvent removed under vacuum. The product was purified by column chromatography (SiC>2, H, UV) and isolated as a colorless oil (6.29 g, 32.9 mmol, 74%). 2,5-Dimethyl-3-(perfluorocyclopent-l-en-l-yl)thiophene (lnt-1) lnt-1

[0096] 64%

[0097] 3-Bromo-2,5-dimethylthiophene (3.00 g, 15.7 mmol, 1.0 eq.) was dissolved in 30 mL of dry THF, cooled to -78°C, n-BuLi (2.5 M, 7.0 L, 17.5 mmol, 1.1 eq.) was added dropwise, and the reaction mixture was stirred for 1 hour at -78°C. This solution was added dropwise, while still cold, to a solution of octafluorocyclopentene (4.2 mL, 6.66 g, 31.4 mmol, 2.0 eq.) in 15 mL of dry THF, also cooled to -78°C. The reaction mixture was stirred for 1 hour at -78°C, warmed to room temperature, and stirred overnight at room temperature. The reaction was stopped by adding HCl (1 M, 40 mL), the phases were separated, and the aqueous phase was extracted with EtjO (3 x 40 mL). The combined organic phases were treated with NaCl( aq The sample (1 x 80 mL) was washed, dried over NajSCU, filtered, and the solvent was removed under vacuum. The product was purified by column chromatography (SiC₂, H₂, UV) and obtained as a pale yellow oil (3.07 g, 10.1 mmol, 64%).

[0098] 2-(2-(2,5-Dimethylthiophen-3-yl)-3,3,4,4,5,5-hexafluorocyclopent-l-en-l-yl)-3-methylbenzo[b]thiophene (DAE 3)

[0099] 3-Methylbenzo[b]thiophene (0.44 mL, 0.49 g, 3.29 mmol, 1.0 eq.) was dissolved in 10 mL of dry THF, cooled to 0°C, and n-BuLi (2.5 M, 1.5 mL, 3.75 mmol, 1.1 eq.) was added dropwise. The reaction solution was then stirred for 30 min, and a solution of Intermediate 1 (1.00 g, 3.29 mmol, 1.0 eq.) in 5 mL of dry THF was added dropwise. The reaction mixture was stirred at 0°C for 1 hour, warmed to room temperature, and stirred overnight at room temperature. The reaction was stopped by the addition of HCl (1 M, 10 mL), the phases were separated, and the aqueous phase was extracted with EtjO (3 x 10 mL). The combined organic phases were treated with NaCl( aqA sample of j (1 x 20 mL) was washed, dried over Na₂SO₄, filtered, and the solvent was removed under vacuum. The product was purified by column chromatography (SiO₂, H₂, UV) and obtained as a yellow solid (1.28 g, 2.95 mmol, 89%).

[0100] 5,5'-(Perfluorocyclopent-l-ene-l,2-diyl)bis(2,4-dimethylthiophene) (DAE4)

[0101] To a solution of 2,4-dimethylthiophene (2.40 mL, 2.52 g, 22.5 mmol, 1.0 eq.) in 50 mL of dry THF, n-BuLi (2.5 M in H, 9.80 mL, 24.5 mmol, 1.1 eq.) was added dropwise, and the reaction mixture was heated to 35°C for 1 hour. After cooling to -10°C, octafluorocyclopentene (1.50 mL, 2.36 g, 11.2 mmol, 0.5 eq.) was added dropwise, the reaction mixture was stirred for 1 hour at -10°C, heated to room temperature, and stirred overnight at room temperature. The reaction was stopped by adding 20 mL H₂O, 20 mL NaCl(aq), and 40 mL EtjO, the phases were separated, and the aqueous phase was extracted with EtjO (3 x 20 mL). The combined organic phases were treated with NaCl( aq (1 x 40 mL) was washed, dried over NazSCU, filtered, and the solvent was removed under vacuum. The product was purified by column chromatography (SiOz, H, UV) and isolated as a pale yellow solid (3.33 g, 8.41 mmol, 75%).

[0102] Example 1: Pigment system consisting of red and green luminescent pigments switchable in the UVC range (100-280 nm) with a polymethyl methacrylate core and a melamine-formaldehyde shell [a] green luminescence via energy transfer

[0103] The green switchable capsule luminescent pigment was prepared according to Example 2 of WO 2017 / 080 653 Al and contains, as the luminescent agent dissolved in the core, a mixture of diisobutyl 4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4) and 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S). 1,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-1-cyclopentene (DAE 1, C23H14F6S2) was used as the photochemically switchable absorber. Each of the individual luminescent agents is used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.The red switchable capsule luminescent pigment was produced according to Example 2 of WO 2017 / 080653 Al and contains as the luminescent substance dissolved in the core a mixture of diisobutyl-4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4), 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S) and 2,9-bis(2,6-diisopropylphenyl)-4,7,11,14-tetraphenoxyanthra[2,1,9-de / :6,5,10-c / 'e / ']diisoquinoline-1,3,8,10(2H,9H)-tetraone (LS3, C72H58N2O8). The photochemically switchable absorber used was 1,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-l-cyclopentene (DAE 1, C23H14F6S2). Each of the individual luminescent substances was used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0104] The resulting pigments luminesce green or red under illumination at 365 nm and UVC light (100-280 nm), depending on their composition, and switch under irradiation with light in the UVC wavelength range. LSI and LS2 correspond to a first luminescent substance, and LS3 corresponds to a second luminescent substance. The emission band of the first luminescent substance lies in the range of 452-636 nm. The absorption maximum of the diarylethene switch in the second state is located at 523 nm and thus lies within the defined emission band. Additionally, the difference between the absorption curves of the first and second switching states at the emission maximum of the first luminescent substance is more than 50%. The second luminescent substance, LS3, can be switched from the first to the second luminescent substance using the same diarylethene switch via prevented energy transfer.

[0105] Due to the significant overlap of the absorption and emission spectra of the diarylethene switch and the first luminescent substance, a good switching depth of 36% and 16%, respectively, is achieved for the green and red switchable luminescent pigments at BWS0 and 38% and 31% at BWS3. This switching depth is thus well above the threshold of 10%, and the difference in luminescence intensity is clearly visible. Furthermore, the difference between the respective switching depths is a maximum of 20 percentage points. No difference in switching behavior or color shift is discernible when switching mixed colors from the two pigments. In the first switching state at BWS3, the residual intensity of the luminescent substance is significantly above the desired residual intensity of 50% at 75% for green and 91% for red, and the deviation between the two values ​​is less than 20 percentage points.Thus, after exposure to the same light intensity, the printed colors lose approximately the same amount of luminescence intensity, and the relative ratio of the emission intensities of the two colors does not change for the eye. In particular, the pigments with full residual switching depth at BWS3 showed exceptional fatigue resistance. The entire security feature can be uniformly recognized, and the system of the aforementioned switchable luminescent pigments is therefore ideally suited for use as a security feature.

[0106] Table 1 summarizes the experimentally obtained data for example aa.

[0107] Table 1.

[0108] [1] Residual intensity of the luminescent substance at BWS3,

[0109] [2] in percentage points

[0110] An improved switching depth in BWS3 is related to the partial decomposition of the luminescent substance. Specifically, the amount of diarylethene switch increases relative to the luminescent substance, resulting in a greater switching depth, since the switching depth depends, among other things, on the ratio of the luminescent substance to the diarylethene switch. lb) Green luminescence without energy transfer

[0111] The green switchable capsule luminescent pigment was prepared according to Example 2 of WO 2017 / 080 653 Al and contains / V-(2-(4-oxo-4H-benzo[d][l,3]oxazin-2-yl)phenyl)naphthalene-2-sulfonamide (LS4, C24H16N2O4S) as the luminescent agent dissolved in the core. l,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-l-cyclopentene was used as the photochemically switchable absorber.

[0112] (DAE 1, C23H14F6S2) is used. This involves using 0.5 wt% of the luminescent material and 5 wt% of the diarylethene switch.

[0113] The red switchable capsule luminescent pigment was produced according to Example 2 of WO 2017 / 080 653 Al and contains as a luminescent substance dissolved in the core a mixture of / V-(2-(4-oxo-4H-benzo[d][l,3]oxazin-2-yl)phenyl)naphthalene-2-sulfonamide (LS4, C24H16N2O4S) and 2,9-bis(2,6-diisopropylphenyl)-4,7,ll,14-tetraphenoxyanthra[2,l,9-de / :6,5,10-c / 'e / ']diisoquinoline-

[0114] 1,3,8,10(2H,9H)-tetraones (LS3, C72H58N2O8). 1,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-l-cyclopentene (DAE 1, C23H14F6S2) was used as the photochemically switchable absorber. Each of the individual luminescent substances is used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%. The resulting pigments luminesce green or red under illumination at 365 nm and UVC light (100-280 nm), respectively, and switch under irradiation with light in the UVC wavelength range. LS4 corresponds to the first luminescent substance, and LS3 to the second. The emission band of the first luminescent substance lies in the range of 483–627 nm. The absorption maximum of the diarylethene switch in the second state is located at 523 nm and is therefore within the defined emission band.Additionally, the difference between the absorption curves of the first and second switching states at the emission maximum of the first luminescent substance is more than 50%. The second luminescent substance can be switched via prevented energy transfer from the first to the second luminescent substance using the same diarylethene switch.

[0115] Due to the significant overlap of the absorption and emission spectra of the diarylethene switch and the first luminescent substance, a good switching depth of 13% and 18% respectively is achieved for the green and red switchable luminescent pigments (BWSO) and 14% and 24% respectively for BWS3. This switching depth is thus above the threshold of 10%, and the difference in luminescence intensity is clearly visible. Furthermore, the difference between the respective switching depths is a maximum of 20 percentage points. No difference in switching behavior or color shift is discernible when switching mixed colors from the two pigments. In the first switching state, the residual intensity of the luminescent substance (BWS3) is significantly above the desired residual intensity of 50%, at 75% for green and 91% for red, and the deviation between the two values ​​is less than 20 percentage points.Thus, after exposure to the same light intensity, the printed colors lose approximately the same amount of luminescence intensity, and the relative ratio of the emission intensities of the two colors does not change for the eye. In particular, the pigments with full residual switching depth at BWS3 showed exceptional fatigue resistance. The entire security feature can be uniformly recognized, and the system of the aforementioned switchable luminescent pigments is therefore ideally suited for use as a security feature.

[0116] Table 2 summarizes the experimentally obtained data for example lb).

[0117] Table 2.

[0118] [1] Residual intensity of the luminescent substance at BWS3,

[0119] [2] in percentage points

[0120] An improved switching depth in BWS3 is related to the partial decomposition of the luminescent substance. In particular, the amount of diarylethene switch increases compared to the luminescent substance, resulting in a greater switching depth, since the switching depth depends, among other things, on the ratio of the luminescent substance to the diarylethene switch.

[0121] Example 2: Pigment system consisting of red and green luminescent pigments switchable at 365 nm with a polymethyl methacrylate core and a melamine-formaldehyde shell

[0122] The green switchable capsule luminescent pigment was prepared according to Example 2 of WO 2017080653 Al and contains, as the luminescent agent dissolved in the core, a mixture of diisobutyl 4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4) and 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S). 3,3'-(perfluorocyclopent-1-ene-1,2-diyl)bis(2-methyl-6-nitrobenzo[b]thiophene) (DAE 2, C23H12F6N2O4S2) was used as the photochemically switchable absorber. Each of the individual luminescent agents is used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0123] The red switchable capsule luminescent pigment was prepared according to Example 2 of WO 2017080653 Al and contains as a luminescent substance dissolved in the core a mixture of diisobutyl-4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4), 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S) and 2,9-bis(2,6-diisopropylphenyl)-4,7,11,14-tetraphenoxyanthra[2,1,9-de / :6,5,10-d'e / ']diisoquinoline-1,3,8,10(2H,9H)-tetraone (LS3, C72H58N2O8). The photochemically switchable absorber used was 3,3'-(Perfluorocyclopent-l-ene-l,2-diyl)bis(2-methyl-6-nitrobenzo[b]thiophene) (DAE 2, C23H12F6N2O4S2). Each of the individual luminescent substances was used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0124] The resulting pigments luminesce green or red under illumination at 365 nm, depending on their composition, and switch upon irradiation with light of the same wavelength. LSI and LS2 correspond to a first luminescent substance, and LS3 corresponds to a second luminescent substance. The emission band of the first luminescent substance lies in the range of 452–636 nm. The absorption maximum of the diarylethene switch in the second state is located at 559 nm and thus lies within the defined emission band. Furthermore, the difference between the absorption curves of the first and second switching states at the emission maximum of the first luminescent substance is more than 50%. The second luminescent substance can be switched via prevented energy transfer from the first to the second luminescent substance using the same diarylethene switch.

[0125] Due to the significant overlap of the absorption and emission spectra of the diarylethene switch and the first luminescent substance, a good switching depth of 70% and 86%, respectively, is achieved for the green and red switchable luminescent pigments (BWSO) and 50% and 70%, respectively, for BWS3. This switching depth is thus well above the threshold of 10%, and the difference in luminescence intensity is clearly visible. Furthermore, the difference between the respective switching depths is a maximum of 20 percentage points. No difference in switching behavior or color shift is discernible when switching mixed colors from the two pigments. In the first switching state, the residual intensity of the luminescent substance (BWS3) is significantly above the desired residual intensity of 50%, at 65% for green and 71% for red, and the deviation between the two values ​​is less than 20 percentage points.Thus, after exposure to the same light intensity, the printed colors lose approximately the same amount of luminescence intensity, and the relative ratio of the emission intensities of the two colors does not change for the eye. In particular, the pigments with 71% and 81% residual switching depth at BWS3 showed exceptional fatigue resistance. The entire security feature can be uniformly recognized, and the system of the aforementioned switchable luminescent pigments is therefore ideally suited for use as a security feature.

[0126] Table 3 summarizes the data obtained experimentally for Example 2.

[0127] Table 3.

[0128] [1] Residual intensity of the luminescent substance at BWS3,

[0129] [2]In percentage points, a printing ink Fl was produced from green and red luminescent pigments to create a yellow-orange color impression. For this purpose, the pigments were incorporated into an offset printing ink (Sicpa Holding SA) using an Engelsmann JEL 25 / 53 ink rubbing machine (manufactured in 2013). The pigmentation level was 7.5% by weight for each pigment. The printing ink Fl was applied at a printing weight of 2 g / m². 2Printed on security paper, the proofs were dried at 60 °C for 2 hours. Subsequently, the proofs were visually assessed for their switching time and depth. In particular, the proofs exhibited exceptional fatigue resistance, switching depth, and uniform extinction of the luminescence for BWSO and BWS3 without any color shift during the switching process. The system of the aforementioned pigments is therefore ideally suited for use as a security feature, enabling a wide range of switchable luminescent colors that can be achieved through additive color mixing.

[0130] Example 3: Pigment system consisting of red and yellow luminescent pigments switchable in the UVC range (100-280 nm) with a polymethyl methacrylate core and a melamine-formaldehyde shell

[0131] The yellow switchable capsule luminescent pigment was produced according to Example 2 of WO 2017 / 080 653 Al and contains as the luminescent substance dissolved in the core a mixture of 2,9-Bis(2,6-diisopropylphenyl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone (LS5, C48H42N2O4) and 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S). The photochemically switchable absorber used was 1,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-l-cyclopentene (DAE 1, C23H14F6S2). Each of the individual luminescent substances was used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0132] The red switchable capsule luminescent pigment was produced according to Example 2 of WO 2017 / 080 653 Al and contains as a luminescent substance dissolved in the core a mixture of 2,9-bis(2,6-diisopropylphenyl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone (LS5, C48H42N2O4), 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S) and 2,9-bis(2,6-diisopropylphenyl)-4,7,11,14-tetraphenoxyanthra[2,1,9-de / :6,5,10-c / 'e / ']diisoquinoline- 1,3,8,10(2H,9H)-tetraones (LS3, C72H58N2O8). 1,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-l-cyclopentene (DAE 1, C23H14F6S2) was used as a photochemically switchable absorber. Each of the individual luminescent substances was used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%. The resulting pigments luminesce yellow, or yellow, under illumination with 365 nm and UVC light (100-280 nm), according to their composition.The luminescent substances are red and switch upon irradiation with light in the UVC wavelength range. LS2 and LS5 correspond to a first luminescent substance, and LS3 corresponds to a second luminescent substance. The emission band of the first luminescent substance lies in the range of 521–652 nm. The absorption maximum of the diarylethene switch in the second state is located at 523 nm and thus lies within the defined emission band. Additionally, the difference between the absorption curves of the first and second switching states at the emission maximum of the first luminescent substance is more than 50%. The second luminescent substance can be switched via prevented energy transfer from the first to the second luminescent substance using the same diarylethene switch.

[0133] Due to the significant overlap of the absorption and emission spectra of the diarylethene switch and the first luminescent substance, a good switching depth of 33% and 26%, respectively, is achieved for the yellow and red switchable luminescent pigments (BWSO) and 52% and 32%, respectively, for BWS3. This switching depth is thus well above the threshold of 10%, and the difference in luminescence intensity is clearly visible. Furthermore, the difference between the respective switching depths is a maximum of 20 percentage points, which is within the scope of the invention. No difference in switching behavior or color shift is discernible when switching mixed colors from the two pigments. In the first switching state, the residual intensity of the luminescent substance (BWS3) is significantly above the desired residual intensity of 50%, at 81% for yellow and 78% for red, and the deviation between the two values ​​is less than 20 percentage points.Thus, after exposure to the same light intensity, the printed colors lose approximately the same amount of luminescence intensity, and the relative ratio of the emission intensities of the two colors does not change for the eye. In particular, the pigments with full residual switching depth at BWS3 showed exceptional fatigue resistance. The entire security feature can be uniformly recognized, and the system of the aforementioned switchable luminescent pigments is therefore ideally suited for use as a security feature.

[0134] Table 4 summarizes the data obtained experimentally for Example 3.

[0135] Table 4. [1] Residual intensity of the luminescent substance at BWS3, [2] in percentage points

[0136] An improved switching depth in BWS3 is related to the partial decomposition of the luminescent substance. In particular, the amount of diarylethene switch increases compared to the luminescent substance, resulting in a greater switching depth, since the switching depth depends, among other things, on the ratio of the luminescent substance to the diarylethene switch.

[0137] Reference example 1: Pigment system consisting of red and green luminescent pigments switchable at 365 nm with a polymethyl methacrylate and polyurea core and a melamine-formaldehyde shell without adapted switching behavior

[0138] The green switchable capsule luminescent pigment was prepared according to Example 2 of WO 2017 / 080 656 Al and contains, as the luminescent agent dissolved in the core, a mixture of diisobutyl 4,10-dicyanoperylene 3,9-dicarboxylate (LSI, C32H26N2O4) and 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S). The photochemically switchable absorber used was 2-(2-(2,5-dimethylthiophen-3-yl)-3,3,4,4,5,5-hexafluorocyclopent-1-en-1-yl)-3-methylbenzo[b]thiophene (DAE 3, C20H14F6S2). Each of the individual luminescent substances is used at a weight of 0.5% and the diarylethene switch at a weight of 5%.

[0139] The red switchable capsule luminescent pigment was produced according to Example 2 of WO 2017 / 080 653 Al and contains as a luminescent substance dissolved in the core a mixture of diisobutyl-4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4), 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S) and 2,9-bis(2,6-diisopropylphenyl)-4,7,11,14-tetraphenoxyanthra[2,1,9-de / :6,5,10-d'e / ']diisoquinoline-1,3,8,10(2H,9H)-tetraone (LS3, C72H58N2O8). The photochemically switchable absorber used was 3,3'-(Perfluorocyclopent-l-ene-l,2-diyl)bis(2-methyl-6-nitrobenzo[b]thiophene) (DAE 2, C23H12F6N2O4S2). Each of the individual luminescent substances was used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0140] The green switchable capsule luminescence pigment and the red switchable capsule luminescence pigment therefore contain different photochemically switchable absorbers.

[0141] The resulting pigments luminesce green or red under illumination at 365 nm, depending on their composition, and switch to luminescence upon irradiation with light of the same wavelength. LSI and LS2 correspond to a first luminescent substance, and LS3 corresponds to a second luminescent substance. The second luminescent substance can be switched to the second by preventing energy transfer from the first to the second luminescent substance.

[0142] The emission band of the first luminescent substance lies in the range of 452–636 nm. The absorption maximum of the diarylethene switch DAE3 for the green switchable luminescent pigment is located at 469 nm in the second state and thus lies within the defined emission band of the first luminescent substance. Additionally, the difference between the absorption curves of the first and second switching states at the emission maximum of the first luminescent substance is more than 50%.

[0143] The absorption maximum of the diarylethene switch DAE2 for the red switchable luminescent pigment is located at 559 nm in the second state and thus lies within the defined emission band of the first luminescent substance. Additionally, the difference between the absorption curves of the first and second switching states at the emission maximum of the first luminescent substance is more than 50%.

[0144] Due to the significant overlap of the absorption and emission spectra of the diarylethene switches and the first luminescent substance, a very good switching depth of 80% and 86%, respectively, is achieved for the green and red switchable luminescent pigments at BWS3. This switching depth is thus well above the threshold of 10%, and the difference in luminescence intensity is clearly visible. Furthermore, the difference in the respective switching depths is only 6 percentage points. However, for BWS3, a switching depth of only 4% is achieved for the green switchable luminescent pigment. Therefore, the switching depth for green at BWS3 is below the threshold of 10%, and the difference in luminescence intensity is no longer visually noticeable. The red switchable luminescent pigment still shows a very good switching depth of 70% at BWS3.The switching depth for red at BWS3 is therefore significantly above the threshold of 10%, and the difference in luminescence intensity is clearly visible. Furthermore, the difference between the respective switching depths, at 66, far exceeds the maximum required 20 percentage points and is thus no longer within the desired range for BWS3. In particular, a clear difference in switching behavior and a significant color shift are noticeable when switching mixed colors from the two pigments at BWS3. Consequently, the printed colors do not lose the same amount of switching depth after exposure to the same light intensity, and the relative ratio of the emission intensities of the two colors changes noticeably during the switching process.

[0145] In particular, the pigments with a large difference in residual switching depths at BWS3 showed significantly different fatigue resistance. The overall safety feature can no longer be uniformly recognized, and the system of the aforementioned switchable luminescent pigments is therefore unsuitable for use as a safety feature.

[0146] Table 5 summarizes the data obtained experimentally for reference example 1.

[0147] Table 5.

[0148] [1] Residual intensity of the luminescent substance at BWS3,

[0149] [2] in percentage points

[0150] Reference example 2: Pigment system consisting of red and green luminescent pigments switchable at 365nm with a polymethyl methacrylate core and a melamine-formaldehyde shell without adapted switching behavior

[0151] The green switchable capsule luminescent pigment was prepared according to Example 2 of WO 2017080653 Al and contains, as the luminescent agent dissolved in the core, a mixture of diisobutyl 4,10-dicyanoperylene 3,9-dicarboxylate (LSI, C32H26N2O4) and 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S). 5,5'-(perfluorocyclopent-1-ene-1,2-diyl)bis(2,4-dimethylthiophene) (DAE 4, C17H14F6S2) was used as the photochemically switchable absorber. Each of the individual luminescent agents is used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0152] The red switchable capsule luminescent pigment was produced according to Example 2 of WO 2017080653 Al and contains as the luminescent substance dissolved in the core a mixture of diisobutyl-4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4), 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S) and 2,9-bis(2,6-diisopropylphenyl)-4,7,11,14-tetraphenoxyanthra[2,1,9-de / :6,5,10-d'e / ']diisoquinoline-1,3,8,10(2H,9H)-tetraone (LS3, C72H58N2O8). The photochemically switchable absorber used was 3,3'-(perfluorocyclopent-l-ene-l,2-diyl)bis(2-methyl-6-nitrobenzo[b]thiophene) (DAE 2, C23H12F6N2O4S2). Each of the individual luminescent substances is used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%. Consequently, the green switchable capsule luminescent pigment and the red switchable capsule luminescent pigment contain different photochemically switchable absorbers.

[0153] The resulting pigments luminesce green or red under illumination at 365 nm, depending on their composition, and switch to luminescence upon irradiation with light of the same wavelength. LSI and LS2 correspond to a first luminescent substance, and LS3 corresponds to a second luminescent substance. The second luminescent substance can be switched to the second by preventing energy transfer from the first to the second luminescent substance.

[0154] The emission band of the first luminescent substance, as defined above, lies in the range of 452–636 nm. The absorption maximum of the diarylethene switch DAE4 for the green switchable luminescent pigment is located at 436 nm in the second state and is therefore outside the defined emission band. Furthermore, the difference between the absorption curves of the first and second switching states at the emission maximum of the first luminescent substance is only 13%.

[0155] The absorption maximum of the diarylethene switch DAE2 for the red switchable luminescent pigment is located at 559 nm in the second state and thus lies within the defined emission band of the first luminescent substance. Additionally, the difference between the absorption curves of the first and second switching states at the emission maximum of the first luminescent substance is more than 50%.

[0156] Due to the significant overlap of the absorption and emission spectra of the diarylethene switch DAE2 and the first luminescent substance, a very good switching depth of 86% BWSO and 70% for BWS3 is achieved for the red switchable luminescent pigment. The switching depth is thus significantly above the threshold of 10%, and the difference in luminescence intensity is clearly visible.

[0157] The switching depth for the green switchable luminescent pigment is significantly lower at 38% for BWSO and 27% for BWS3, which is due to the significantly weaker overlap of the absorption and emission spectra of the diarylethene switch and the first luminescent substance.

[0158] In particular, the difference in the respective switching depths is significantly more than 20 percentage points and is therefore not within a desirable range for either BWSO or BWS3. Consequently, a difference in switching behavior and a color shift are noticeable when switching mixed colors from the two pigments, regardless of the wool scale. The residual intensity of the luminescent material in the first switching state for BWS3 is 75% for green and 71% for red, above a residual intensity of 50%, and the deviation between the two values ​​is less than 20 percentage points.The residual switching depths of the pigments also show good values ​​of 71% for green and 81% for red; however, the system of the aforementioned switchable luminescent pigments is not suitable for use as a security feature, as the differences in switching depths between BWSO and BWS3 are too large and the entire security feature can no longer be uniformly recognized due to a color change during the switching process.

[0159] Table 6 summarizes the data obtained experimentally for reference example 2.

[0160] Table 6.

[0161] [1] Residual intensity of the luminescent substance at BWS3,

[0162] [2] in percentage points

[0163] A printing ink, F2, was produced from green and red luminescent pigments to create a yellow color impression. For this purpose, the pigments were incorporated into an offset printing ink (Sicpa Holding SA) using an Engelsmann JEL 25 / 53 ink leveling machine (manufactured in 2013). The pigmentation level was 7.5% by weight for each pigment. The F2 printing ink was applied at a printing weight of 2 g / m². 2Printed on security paper, the proofs were dried at 60 °C for 2 hours. They were then visually assessed for their switching time and depth. In particular, the proofs showed good fatigue resistance. However, the proofs did not exhibit a uniform extinction of the luminescence, but rather a color shift from yellow to green during the switching process, as the red switchable luminescent pigment used has a significantly greater switching depth than the green switchable luminescent pigment. Therefore, the system of these pigments is not suitable for use as a security feature, since a consistent luminescent color cannot be guaranteed in practice.

[0164] Reference Example 3: Pigment system consisting of red and green UVC-switchable (100-280 nm) luminescent pigments with a polymethyl methacrylate core and a melamine-formaldehyde shell without adapted switching behavior. The green switchable capsule luminescent pigment was prepared according to Example 2 of WO 2017 / 080 653 Al and contains CD343 (Honeywell, LS6) as the luminescent substance dissolved in the core. l,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-l-cyclopentene (DAE 1, C23H14F6S2) was used as the photochemically switchable absorber. 0.5 wt% of the luminescent substance and 5 wt% of the diarylethene switch are used.

[0165] The red switchable capsule luminescent pigment was produced according to Example 2 of WO 2017 / 080 653 Al and contains as a luminescent substance dissolved in the core a mixture of diisobutyl-4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4), 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S) and 2,9-bis(2,6-diisopropylphenyl)-4,7,11,14-tetraphenoxyanthra[2,1,9-de / :6,5,10-d'e / ']diisoquinoline-1,3,8,10(2H,9H)-tetraone (LS3, C72H58N2O8). The photochemically switchable absorber used was 1,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-l-cyclopentene (DAE 1, C23H14F6S2). Each of the individual luminescent substances was used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0166] The green switchable capsule luminescence pigment and the red switchable capsule luminescence pigment therefore contain different luminescent substances.

[0167] The resulting pigments luminesce green or red under illumination at 365 nm and UVC light (100-280 nm), depending on their composition, and switch on under irradiation with light in the UVC wavelength range. In the red pigment, LSI and LS2 correspond to a first luminescent substance, and LS3 corresponds to a second luminescent substance. In the green pigment, LS6 corresponds to a first luminescent substance.

[0168] The emission band of the first luminescent substance lies in the range of 452–636 nm for the red pigment and in the range of 494–626 nm for the green pigment. The absorption maximum of the diarylethene switch in the second state is located at 523 nm and thus lies within the defined emission bands. Additionally, the difference between the absorption curves of the first and second switching states at the emission maximum of the two first luminescent substances is more than 50%. The second luminescent substance can be switched via prevented energy transfer from the first to the second luminescent substance using the same diarylethene switch.

[0169] Due to the significant overlap of the absorption and emission spectra of the diarylethene switch and the first luminescent substances, a good switching depth of 24% and 16%, respectively, is achieved for the green and red switchable luminescent pigments at BWS0 and 14% and 31% at BWS3. This switching depth is thus well above the threshold of 10%, and the difference in luminescence intensity is clearly visible. Furthermore, the difference between the respective switching depths is a maximum of 20 percentage points. No difference in switching behavior or color shift is discernible when switching mixed colors from the two pigments. In contrast, however, the residual intensity of the luminescent substance in the first switching state at BWS3, at 51% for green, is only slightly above the desired residual intensity of 50%. The residual intensity of the luminescent substance for red is 91%. The deviation between the two values, at 40 percentage points, is significantly more than 20 percentage points.Thus, the printed colors do not lose the same amount of luminescence intensity after exposure to the same light intensity, and the relative ratio of the emission intensities of the two colors changes significantly for the eye. Despite good fatigue resistance of the switching depth, the entire security feature cannot be uniformly recognized throughout the application, and the system of the aforementioned switchable luminescent pigments is therefore unsuitable for use as a security feature.

[0170] Table 7 summarizes the experimentally obtained data for reference example 3.

[0171] Table 7.

[0172] [1] Residual intensity of the luminescent substance at BWS3,

[0173] [2] in percentage points

[0174] An improved switching depth in BWS3 is related to the partial decomposition of the luminescent substance. In particular, the amount of diarylethene switch increases compared to the luminescent substance, resulting in a greater switching depth, since the switching depth depends, among other things, on the ratio of the luminescent substance to the diarylethene switch.

[0175] Reference example 4: Pigment system consisting of red and green luminescent pigments switchable at different wavelengths with a polymethyl methacrylate core and a melamine-formaldehyde shell without adapted switching behavior

[0176] The green switchable capsule luminescent pigment was prepared according to Example 2 of WO 2017 / 080 653 Al and contains, as the luminescent agent dissolved in the core, a mixture of diisobutyl 4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4) and 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S). 1,2-Bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-1-cyclopentene (DAE 1, C23H14F6S2) was used as the photochemically switchable absorber. Each of the individual luminescent agents is used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0177] The red switchable capsule luminescent pigment was produced according to Example 2 of WO 2017 / 080653 Al and contains as a luminescent substance dissolved in the core a mixture of diisobutyl-4,10-dicyanoperylene-3,9-dicarboxylate (LSI, C32H26N2O4), 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole) (LS2, C26H26N2O2S) and 2,9-bis(2,6-diisopropylphenyl)-4,7,11,14-tetraphenoxyanthra[2,1,9-de / :6,5,10-c / 'e / ']diisoquinoline-1,3,8,10(2H,9H)-tetraone (LS3, C72H58N2O8). The photochemically switchable absorber used was 3,3'-(Perfluorocyclopent-l-ene-l,2-diyl)bis(2-methyl-6-nitrobenzo[b]thiophene) (DAE 2, C23H12F6N2O4S2). Each of the individual luminescent substances was used at a weight of 0.5 wt%, and the diarylethene switch at 5 wt%.

[0178] The green switchable capsule luminescence pigment and the red switchable capsule luminescence pigment therefore contain different photochemically switchable absorbers.

[0179] The resulting pigments luminesce green or red, respectively, under illumination at 365 nm and UVC wavelengths, depending on their composition; however, they do not switch under irradiation with light of the same wavelength. LSI and LS2 correspond to a first luminescent substance, and LS3 corresponds to a second luminescent substance. The second luminescent substance can be switched via an energy transfer from the first to the second. The red pigment switches under irradiation with 365 nm wavelength light, while the green pigment switches under UVC wavelength light. Therefore, a difference in switching behavior and a color shift are noticeable when switching mixed colors made from the two pigments, regardless of the wool scale. This is because only one of the two switchable luminescent pigments reacts for each wavelength, and the security feature cannot be uniformly detected.The system of the aforementioned switchable luminescent pigments is therefore particularly unsuitable for use as a security feature due to the different switching wavelengths, UVC for green and 365 nm for red.

[0180] Table 8 summarizes the experimentally obtained data for reference example 4. Table 8.

[0181] [1] in percentage points

Claims

1. REQUIREMENTS 1. A system of at least two types of switchable capsule luminescent pigments, wherein the capsule luminescent pigments are polymer particles with a diameter of 0.1–1000 pm, each containing at least one luminescent substance and one photochemically switchable absorber, wherein a first type of capsule luminescent pigment comprises a first luminescent substance emitting in a first color in the visible spectral range; a second type of capsule luminescent pigment comprises the first luminescent substance and a second luminescent substance emitting in a second color in the visible spectral range, the first and second colors being different; and the two capsule luminescent pigments each comprise the same switchable absorber, wherein the absorber has a first and a second switching state, and the absorption spectrum of the absorber in the second switching state significantly overlaps with the emission spectrum of the first luminescent substance.

2. System according to claim 1, wherein an energy transfer takes place from the first to the second luminescent substance.

3. System according to claim 1 or 2, wherein at least the second type of capsule luminescent pigment comprises a further, third luminescent substance emitting in a third color in the VIS spectral range, wherein the third color is different from the first and second colors.

4. System according to one of claims 1-3, wherein at least the first luminescent substance is excitable in the UV spectral range, preferably in the range of 300-380 nm, more preferably in the range of 365-380 nm, and particularly preferably at 365 nm.

5. System according to one of claims 1-4, wherein the photochemically switchable absorber is a diarylethene.

6. System according to any one of claims 1-5, wherein the diarylethene is a diheteroarylethene, preferably a dithienylethene, and particularly preferably a fluorinated dithienylethene.

7. System according to one of claims 1-6, wherein excitation of at least the first luminescent substance can take place in the same wavelength range as switching the photochemically switchable molecule from the first to the second switching state, preferably between 300 and 380 nm, more preferably between 350 and 380 nm, and particularly preferably at 365 nm.

8. System according to any one of claims 1-7, wherein the first, second and third luminescent agent is independently selected from the group consisting of diarylpolyenes, arylacetylenes, oxazoles, pyrazoles, benzazoles, anthrones, quinones, cyanines, rhodamines, oxazines, phenoxazines, thiazines, phenothiazines, perylenes, terylenes, coumarins, benzoxazinones or benzothiazinones, rare earth metal complexes, oxinates, aldazines, anthranilic acid derivatives, and salicyclic acid derivatives, and preferably is selected from the group consisting of perylenes, benzoxazinones, oxinates, benzthiazones, aldazines, anthranilic acid derivatives, salicyclic acid derivatives, oxazines, oxazoles, and anthrones, as well as mixtures thereof.

9. System according to any one of claims 1-8, wherein the polymer particle is a core-shell polymer particle, preferably comprising as its core a polymer selected from polystyrene (PS), polyacrylates, polyethylene (PE), polypropylene (PP), polycarbonates (PC), polyamides (PA), polyurethanes (PU), polyureas (PH), polyethylene terephthalate (PET), other polyesters, or mixtures thereof, and / or comprising as its shell a condensation polymer selected from aminoplasts, phenolplasts, melamine-formaldehyde resins (MF), melamine-phenol-formaldehyde resins (MPF), phenol-formaldehyde resins (PF), urea-formaldehyde resins (UF), melamine-guanidine-formaldehyde resins, phenol-resorcinol-formaldehyde resins, or mixtures thereof, wherein the polymer particle is particularly preferably a core-shell polymer particle comprising as its core a thermoplastic polymer selected from polymethylmetharylate or polystyrene and / or contains a melamine-formaldehyde resin as a coating.

10. System according to one of claims 1-9, wherein the proportion of the luminescent material in the core is 0.1 to 10 wt.% and / or the proportion of the photochemically switchable absorber is 1 to 20 wt.%.

11. Switchable luminescent printing ink comprising a system of at least two types of switchable capsule luminescent pigments according to any one of claims 1-10.

12. A security document, preferably a banknote, with a switchable luminescent print, comprising a system of at least two types of switchable capsule luminescent pigments according to any one of claims 1-10 or the switchable luminescent printing ink according to claim 11.

13. A security document, preferably a banknote, with a luminescent imprint according to claim 12, wherein the luminescence of the at least two types of capsule luminescent pigments can be switched off using light of the same wavelength, preferably between 300 and 380 nm, more preferably between 350 and 380 nm, and particularly preferably at 365 nm.

14. A security document, preferably a banknote, with a luminescent print according to claim 12 or 13, wherein the luminescent print comprises at least one further luminescent printing ink, the luminescence of which is not switchable off in the same wavelength range, preferably between 300 and 380 nm, more preferably between 350 and 380 nm, and particularly preferably at 365 nm, and which differs in emission color in the VIS spectral range from the first and second switchable luminescent capsule pigments.

15. A security document, preferably a banknote, with a luminescent print according to claim 12 or 13, wherein the luminescent print comprises at least one further luminescent printing ink, the luminescence of which is not switchable in the same wavelength range, preferably between 300 and 380 nm, more preferably between 350 and 380 nm, and particularly preferably at 365 nm, and the emission color in the VIS spectral range corresponds to at least one of the first and second switchable luminescent capsule pigments.

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