Phosphorescent label, method for writing, erasing and rewriting the label

Abstract

A label (1) comprising a functional layer, wherein each point of the functional layer can be selectively converted locally from a non-phosphorescent state to a phosphorescent state and the functional layer can be converted from the phosphorescent state to the non-phosphorescent state, wherein each point of the functional layer can be converted from the non-phosphorescent state to the phosphorescent state without contact, characterized in that the functional layer comprises a first organic material (3) and a second organic material (4), wherein a phosphor for phosphorescence is admixed to the first organic material (3), and wherein the second organic material (4) is in an oxygen-impermeable state at room temperature.

Description

Background of the invention

[0001] The project leading to this application has received funding from the European Research Council (ERC) through the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 67913 “BILUM”).

[0002] The invention is based on optically human- or machine-readable labels.

[0003] Labels are used in countless ways in everyday life. They are usually used to provide information about objects, such as addresses on packages, contents on boxes or bottles, information about the owner or intended location of objects, or file numbers on files. These labels are either human-readable or symbolic, or machine-readable, such as barcodes or QR codes.

[0004] It's not always desirable for labels to be readable by anyone at any time. For example, information about the contents and recipient of a package might not be intended for public view. Furthermore, applying conventional labels to visually functional surfaces is usually undesirable. For example, a label affixed to a small glass bottle impairs the quick visual inspection of the bottle's fill level, or a conventional label affixed to a window at least partially obstructs the view through the window.

[0005] Another problem with optically readable labels is that once they are printed, they are almost impossible to change. Deleting the information from the label and rewriting the label is usually not possible. If the contents of a package described on a label change, a new label must be printed and applied, and the old label must be made illegible or removed from the packaging. Information such as the last user of a machine, the fill level of a container, or the date of the last inspection of a device must also be constantly updated. Creating new labels, replacing old ones, and disposing of old ones is, in the long run, very tedious, time-consuming, environmentally questionable, and expensive.

[0006] For example, US Pat. No. 6,211,526 B1 discloses objects marked for identification with a luminescent label containing an optically stimulable glass with capture centers and luminescence centers. The glass matrix, consisting of the capture centers and the luminescence centers, generates optically stimulated luminescence. Furthermore, US Pat. No. 2003 / 0 064 532 A1 discloses nanoparticles that exhibit luminescence and optical switching processes based on such properties. A PMMA material system with a dye (NPB) is disclosed in Redondo, CS, and Reineke, S.: "Simultaneous fluorescence and phosphorescence from organic molecules," SPIE Newsroom, September 11, 2015. Disclosure of the invention

[0007] It is an object of the present invention to avoid the disadvantages mentioned in connection with the prior art and to provide a label which is readable after activation, which is flexible in its shape, which can be made transparent in the non-activated state and which can be written with information, from which the information can be erased and which can be written with information again after erasure.

[0008] The object of the present invention is achieved by a label according to the features of claim 1.

[0009] This advantageously makes it possible to write on the label in such a way that parts of it are phosphorescent, while the phosphorescent parts carry information, such as a QR code, a logo, or similar. Writing on the label can be reversed by converting the phosphorescent parts from the phosphorescent state to a non-phosphorescent state, thus erasing the information from the label. The writing and erasing processes can be repeated multiple times. Furthermore, the substrate can be freely designed, especially transparent.

[0010] In the context of the present invention, phosphorescent means excitable to phosphorescence. Activated, in the context of the present invention, means excited to phosphorescence. Phosphorescence is the property of a substance to continue to glow for an extended period after being illuminated with light. It occurs when a substance is excited by incident light and its electrons transition from a low energy level, for example, the ground state, to a higher energy level. Transitions between energy levels follow certain selection rules. There are transitions with high transition probabilities that occur quickly, and there are transitions with low transition probabilities that occur slowly.In phosphorescence, the excitation of an electron via a high-probability transition through intercombination is followed by a transition of the electron into a long-lived excited state, from which de-excitation to the ground state is only possible via low-probability transitions or quantum-mechanically forbidden transitions. The radiative de-excitation of the electron from this long-lived excited state is called phosphorescence.

[0011] In the context of the present invention, a point refers to a spatially extended location in the functional layer. The sum of all points is the functional layer. Selectively locally transferable, in the context of the present invention, means that the points can be transferred individually and specifically. This means that one point can be transferred without transferring another point.

[0012] It is conceivable that the label has a substrate. It is also conceivable that the functional layer is arranged on the substrate. It is also conceivable that the substrate is arranged in a plane. However, it is also conceivable that the substrate is arranged on a non-planar surface. For this purpose, the substrate has a non-constant geometric profile. It is conceivable that the functional structure has the same geometric profile as the substrate. It is also conceivable that the substrate is impermeable to oxygen.

[0013] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0014] According to an embodiment of the present invention, the functional layer comprises a first organic material and a second organic material, wherein a phosphor for phosphorescence is admixed to the first organic material and wherein the second organic material is in an oxygen-impermeable state at room temperature.

[0015] Oxygen inhibits phosphorescence in organic materials. In organic compounds, the ground state is usually a singlet state in which all electrons are paired. An example of a phosphorescent transition in organic substances is the transition from an excited triplet state to the ground state. This transition is quantum-mechanically "forbidden" and therefore associated with a low transition probability and long residence times of the electrons in the excited triplet state. Oxygen, which is usually present in a triplet state, interacts with the electrons in the excited triplet state, rapidly depopulating it. Thus, no long-lasting afterglow occurs.

[0016] By sealing the first organic material with the phosphor for phosphorescence by the second organic material, the influence of oxygen from the environment of the functional layer can be eliminated. The phosphor can be a dopant, for example. In the context of the present invention, admixing can mean doping.

[0017] According to a preferred further embodiment of the present invention, it is provided that the first organic material is arranged in a lower layer and the second organic material is arranged in an upper layer, wherein the lower layer is arranged between a substrate and the upper layer.

[0018] Due to the layered arrangement of the first organic material and the second organic material, the first organic material is sealed off from the environment by the second organic material and the substrate in an oxygen-tight manner. It is conceivable that the first organic material is applied to the substrate by means of spin coating or line application or pipetting or printing or spray coating and / or that the second organic material is applied by means of spin coating or line application or pipetting or printing or spray coating. It is also conceivable that the first organic material is dissolved in an organic solvent for application. It is conceivable that for this purpose the first organic material is dissolved in anisole, chlorobenzene, ethyl lactate or water. It is conceivable that the second organic material is also dissolved in an organic solvent for application.It is conceivable that the second organic material is dissolved in anisole, chlorobenzene, ethyl lactate, or water. Preferably, the first organic material and / or the second organic material are dried after application. This allows for controlled evaporation of the solvent. This could conceivably occur in an oven or on a hot plate.

[0019] Preferably, the lower layer has a layer thickness of between 200 nm and 2000 nm, preferably between 500 nm and 1500 nm, in particular of approximately 900 nm and / or the upper layer has a layer thickness of between 500 nm and 50 µm.

[0020] It is conceivable that the substrate is made of the second organic material. This advantageously results in a layered structure consisting of two outer layers of the second organic material and a layer of the first organic material enclosed by the two outer layers.

[0021] Furthermore, it is also conceivable that the first organic material and the second organic material are a mixture.

[0022] According to a preferred further embodiment of the present invention, it is provided that the functional layer can be converted from the non-phosphorescent state into the phosphorescent state by the incidence of light of a first characteristic on the first organic material and / or can be converted from the phosphorescent state into the non-phosphorescent state by the incidence of light of a second characteristic on the functional layer and / or can be converted from the phosphorescent state into the non-phosphorescent state by the introduction of heat into the functional layer.

[0023] It is conceivable that the light of the first characteristic is also suitable for exciting phosphorescence. The light of the first characteristic has a wavelength of less than 700 nm, preferably less than 550 nm, particularly preferably less than 460 nm. The light of the second characteristic is preferably IR light.

[0024] Furthermore, it is advantageously possible to use the same light source for the light of the first characteristic and the light for exciting the phosphorescence if the light of the first characteristic and the light for exciting the phosphorescence do not differ in wavelength, but in intensity, i.e. the light for exciting the phosphorescence is the light of the first characteristic with a second intensity. The light of the first characteristic then has a first intensity. The first intensity is higher than the second intensity. It is conceivable that the first intensity is 10 to 100 times greater, preferably 20 to 90 times greater, particularly preferably 50 to 80 times greater, and in particular approximately 70 times greater than the second intensity. It is conceivable that the first intensity is between 1 mWcm -2 and 20 mWcm -2 , preferably between 3 mWcm -2 and 15 mWcm -2 , particularly preferably between 5 mWcm -2and 10 mWcm -2 and especially at about 7 mWcm -2 Furthermore, it is conceivable that the second intensity is between 0.01 mWcm -2 and 1 mWcm -2 , preferably between 0.05 mWcm -2 and 0.5 mWcm -2 and especially at approximately 0.1 mWcm -2 lies.

[0025] According to a preferred further embodiment of the present invention, the first organic material is configured to bind oxygen upon the incidence of light having the first characteristic. This enables the removal of oxygen from the functional layer and thus enables phosphorescence.

[0026] According to a preferred further embodiment of the present invention, the second organic material can be converted into an oxygen-permeable state by the incidence of light of the second characteristic and / or the introduction of heat. This advantageously makes it possible to suppress phosphorescence in the functional layer by introducing oxygen. It is conceivable that the functional layer is configured such that upon the incidence of light of the second characteristic, the first organic material is heated and the heat is transported to the second organic material. It is further conceivable that the second organic material can be converted into an oxygen-permeable state by this heating.

[0027] According to a further preferred embodiment of the present invention, the first organic material is polymethyl methacrylate and / or the second organic material contains ethylene-vinyl alcohol copolymers and / or the phosphor is N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine. These materials are widely used, easy to process, and inexpensive. Preferably, two weight percent of N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine is admixed to the first organic material.

[0028] According to a further preferred embodiment of the present invention, the substrate is a film, with the side of the substrate facing away from the functional layer preferably being self-adhesive or magnetic. This advantageously enables the label to be easily applied to objects to be labeled. A film is flexible. This allows the label to be applied even to uneven objects.

[0029] According to a further preferred embodiment of the present invention, the film is transparent. This allows for a completely unobtrusive appearance of the label. The label can thus be applied, for example, to windows or screens without affecting their function. This is particularly advantageous for objects to be labeled that offer little surface area that is not visually functional.

[0030] According to a further preferred embodiment of the present invention, the substrate is a plastic plate, preferably a transparent plastic plate, or a metal plate, wherein the side of the substrate facing away from the functional layer is preferably self-adhesive or magnetic. This advantageously enables mechanical protection of the functional layer.

[0031] Another object of the present invention is a method for writing, erasing and rewriting the label according to the features of claim 10.

[0032] This allows information to be written to a label, erased from the label, and rewritten. The process can be repeated almost indefinitely. Furthermore, the targeted partial activation of phosphorescence in the form of the phosphorescent area enables the creation of geometric phosphorescent patterns. This makes it possible, for example, to store information in the form of text, images, logos, codes, pictograms, machine-readable text, barcodes, QR codes, or similar on the structure.

[0033] According to a preferred embodiment of the present invention, it is provided that during the writing process the phosphorescent region is illuminated with light of the first characteristic, wherein preferably the functional layer is partially covered with a mask such that only the phosphorescent region is illuminated and / or the functional layer is illuminated with light of the first characteristic by a locally meandering or line-by-line scanning light beam only in the phosphorescent region and / or the functional layer is illuminated only in the phosphorescent region by illuminating the functional layer with a light beam with a steel profile, wherein the beam profile on the functional layer corresponds to the phosphorescent region.

[0034] In the context of the present invention, the beam profile of a light beam means that the intensity of the light beam incident on the surface of the structure varies locally so strongly that the intensity of the light beam is above a threshold value for executing a reaction at locations of high intensity and below this threshold value at locations of low intensity. The reaction can, for example, be the conversion of the phosphor from the singlet state to the excited singlet state of the phosphor or heating until the second organic material is converted from the oxygen-impermeable state to the oxygen-permeable state.

[0035] According to a preferred embodiment of the present invention, UV light is used as the light of the first characteristic, wherein preferably oxygen is bound to the first organic material in a binding step, wherein before the binding step the oxygen is preferably converted in a triplet-triplet interaction with the phosphor from a triplet ground state of the oxygen into an excited singlet state of the oxygen, wherein before the triplet-triplet interaction the phosphor is converted by the light of the first characteristic from a singlet state of the phosphor into an excited singlet state of the phosphor and then by intercombination from the excited singlet state of the phosphor into an excited triplet state of the phosphor.

[0036] The phosphor is preferably organic. The phosphor is typically present in an unexcited singlet state, preferably the singlet ground state of the phosphor. The light of the first characteristic converts the phosphor into an excited singlet state, from which it can transition through intercombination into an excited triplet state, which is then available for a triplet-triplet interaction with the oxygen.

[0037] The binding step advantageously enables the photochemical deactivation of the oxygen, thus enabling phosphorescence. The oxygen is typically present in a triplet ground state. The oxygen is preferably converted from the triplet ground state of the oxygen to an excited singlet state of the oxygen in the triplet-triplet interaction with the phosphor of the first organic material. This excited singlet state of the oxygen is highly reactive. Thus, the oxygen can be bound in the binding step by oxidation of the first organic material.

[0038] According to a preferred further embodiment of the present invention, it is provided that heat is introduced into the functional layer during the erasing process, wherein the second organic material is preferably converted from an oxygen-impermeable state to an oxygen-permeable state by the heat.

[0039] In the unheated state, the second organic material forms an oxygen barrier, which keeps oxygen away from the first organic material and thus enables the reduction of unbound oxygen through oxidation of the first organic material. The heat transforms the second organic material from an oxygen-impermeable state to an oxygen-permeable state. This allows oxygen to penetrate to the first organic material and inhibits phosphorescence. It is conceivable that the heating is carried out using a heating element.

[0040] When the introduction of heat into the functional layer is stopped, the second organic material is converted back into the oxygen-impermeable state.

[0041] It is also conceivable that oxygen is introduced into the functional layer by waiting during the extinguishing process. Due to imperfections in the functional layer, the oxygen barrier formed by the second organic material is not perfect, allowing oxygen to diffuse in over a longer period of time.

[0042] According to a preferred further embodiment of the present invention, it is provided that the heat is introduced by irradiating light of the second characteristic, wherein the light of the second characteristic is preferably IR light.

[0043] This enables contactless erasure of the information on the label. It is conceivable that the functional layer is partially covered with a mask so that the area to be erased is illuminated, and / or the functional layer is illuminated with light of the second characteristic by a locally meandering or line-by-line scanning light beam only in the area to be erased, and / or the functional layer is illuminated only in the area to be erased by illuminating the functional layer with a light beam with a steel profile, whereby the beam profile on the functional layer corresponds to the area to be erased.

[0044] All the above statements under “Disclosure of the Invention” apply equally to the label according to the invention and the method according to the invention.

[0045] Further details, features, and advantages of the invention will become apparent from the drawings and the following description of preferred embodiments with reference to the drawings. The drawings merely illustrate exemplary embodiments of the invention, which do not limit the essential inventive concept. Short description of the drawings Fig. 1 (a) - (b) show schematic views of the label and the writing on the label according to an exemplary embodiment of the present invention. Fig. 2 shows a scheme of writing the label according to an exemplary embodiment of the present invention. Fig. Figure 3 shows a schematic of the phosphorescence of the phosphorescent region of the label according to an exemplary embodiment of the present invention. Embodiments of the invention

[0046] In the various figures, identical parts are always provided with the same reference symbols and are therefore usually named or mentioned only once.

[0047] In Fig. 1 (a) shows a schematic view of the label 1 according to an exemplary embodiment of the present invention.

[0048] The label 1 comprises the substrate 2. The substrate 2 is a transparent film. The first organic material 3 is applied to the substrate 2 in a 900 nm thick lower layer. The first organic material 3 consists of polymethyl methacrylate (PMMA), to which approximately two percent by mass of N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine is added. The second organic material 4, which contains ethylene-vinyl alcohol copolymers, is applied in an upper layer above the layer of the first organic material 3. The second organic material 4 is impermeable to oxygen in a normal state at room temperature and serves as an oxygen barrier between the first organic material 3 and the environment of the label 1.

[0049] In Fig. Figure 1(b) schematically shows the writing of the label 1 according to an exemplary embodiment of the present invention.

[0050] The label 1 is partially illuminated by the light of the first characteristic 8. For this purpose, the label 1 is partially covered with a mask 7, opposite the light source of the light of the first characteristic 8. The light of the first characteristic 8 thus irradiates the phosphorescent area 5 of the label. The non-phosphorescent area 6 of the label 1 is not irradiated by the light of the first characteristic 8.

[0051] In Fig. 2 is shown a schematic of the description according to an exemplary embodiment of the present invention.

[0052] The light of the first characteristic 8 (not shown) with a wavelength of approximately 365 nm induces a transition of the phosphor of the first organic material 3 in the phosphorescent area 5 of the label 1 (see Fig. 1 (b)) from the singlet state of the phosphor S0 to an excited singlet state of the phosphor S1. From this excited singlet state of the phosphor S1, a portion of the phosphor transitions via intercombination 10 to an excited triplet state T1. The first organic material 3 contains oxygen 9, which prevents phosphorescence 30. The oxygen 9 is in a triplet ground state of the oxygen T0. In a triplet-triplet interaction 11, the phosphor transitions from the excited triplet state T1 of the phosphor to the singlet state of the phosphor S0, and the oxygen 9 transitions from the triplet ground state of the oxygen T0 to an excited singlet state of the oxygen S1'. The oxygen 9 is highly reactive in its singlet state S1', oxidizes the first organic material 3 and is bound in the process (not shown).Thus, the oxygen 9 present in the lower layer in the phosphorescent region is effectively deactivated. The second organic material 4 acts as an oxygen barrier, preventing additional oxygen from penetrating the layer of the first organic material 3.

[0053] The non-phosphorescent region 6 is not irradiated by the light of the first characteristic 8. Thus, the oxygen 9 is not bound to the first organic material 3 and is not deactivated.

[0054] In Fig. 3 shows a schematic of the phosphorescence 30 of the phosphorescent region 5 of the label 1 of an exemplary embodiment of the present invention.

[0055] For phosphorescence 30, the mask 7 is removed, and the light of the first characteristic 8 is still used for illumination with significantly reduced intensity (not shown here). In the phosphorescent region 5, a transition of the phosphor from the singlet state of the phosphor S0 to the excited singlet state of the phosphor S1 is then induced. From this excited singlet state of the phosphor S1, the phosphor can transition via intercombination 10 to the excited triplet state of the phosphor T1. The transition from the excited triplet state of the phosphor T1 to the singlet state of the phosphor T0 is quantum mechanically "forbidden," and thus the excited triplet state of the phosphor T1 has a long lifetime.Nevertheless, over a long period of time, even after switching off the source of light of the first characteristic 8, transitions occur from the excited triplet state of the phosphor T1 to the singlet state of the phosphor S0, resulting in phosphorescence 30.

[0056] Since the oxygen 9 is not deactivated in the non-phosphorescent region 6, it prevents the phosphorescence 30 here (see Fig. 1 (b)). Thus, label 1 phosphoresces only in the phosphorescent region 5. List of reference symbols 1 label 2 Substrat 3 First organic material 4 Second organic material 5 Phosphorescent area 6 Non-phosphorescent area 7 Mask 8 Light of the first characteristic 9 Oxygen 10 Intercombination 11 Triplet-triplet interaction S0 singlet state of the phosphor S1 Excited singlet state of the phosphor S1' Excited singlet state of oxygen T0 triplet ground state of oxygen T1 Excited triplet state of the phosphor

Claims

[1] Label (1) comprising a functional layer, wherein each point of the functional layer is selectively locally convertible from a non-phosphorescent state to a phosphorescent state and the functional layer is convertible from the phosphorescent state to the non-phosphorescent state, wherein each point of the functional layer is contactlessly convertible from the non-phosphorescent state to the phosphorescent state, characterized by in that the functional layer comprises a first organic material (3) and a second organic material (4), wherein a luminescent substance for phosphorescence is admixed to the first organic material (3) and wherein the second organic material (4) is in an oxygen-impermeable state at room temperature. [2] Label (1) according to claim 1, wherein the first organic material (3) is arranged in a lower layer and the second organic material (4) is arranged in an upper layer, the lower layer being arranged between a substrate (2) and the upper layer. [3] Label (1) according to one of claims 1 to 2, wherein the functional layer is convertible from the non-phosphorescent state to the phosphorescent state by the incidence of light of a first characteristic (8) on the first organic material (3) and / or is convertible from the phosphorescent state to the non-phosphorescent state by the incidence of light of a second characteristic on the functional layer and / or is convertible from the phosphorescent state to the non-phosphorescent state by the introduction of heat into the functional layer. [4] Label (1) according to claim 3, wherein the first organic material (3) is configured to bind oxygen (9) by the incidence of light of the first characteristic (8). [5] Label (1) according to claim 3 or 4, wherein the second organic material (4) can be converted into an oxygen-permeable state by the incidence of light of the second characteristic and / or the introduction of heat. [6] Label (1) according to one of claims 1 to 5, wherein the first organic material (3) is polymethyl methacrylate and / or the second organic material (4) contains ethylene-vinyl alcohol copolymers and / or the phosphor is N,N'-di(1-naphthyl)-N,N'diphenyl-(1,1'-biphenyl)-4,4'-diamine. [7] Label (1) according to one of the preceding claims, wherein the substrate (2) is a film, wherein preferably the side of the substrate (2) facing away from the functional layer is self-adhesive or magnetic. [8] Label (1) according to claim 7, wherein the film is transparent. [9] Label (1) according to one of the preceding claims, wherein the substrate (2) is a plastic plate, preferably a transparent plastic plate, or a metal plate, wherein preferably the side of the substrate (2) facing away from the functional layer is self-adhesive or magnetic. [10] Method for writing, erasing and rewriting the label (1) comprising a functional layer, wherein the functional layer comprises a first organic material (3) and a second organic material (4), wherein a phosphor for phosphorescence is admixed to the first organic material (3) and wherein the second organic material (4) is in an oxygen-impermeable state at room temperature according to one of claims 1 to 9, wherein - for writing on the label (1), points of the functional layer are selectively converted locally from the non-phosphorescent state to the phosphorescent state in a contactless writing process, whereby a phosphorescent region (5) is formed by the points, - for erasing the label (1), the functional layer is converted substantially completely into the non-phosphorescent state in an erasing process, wherein heat is introduced into the functional layer during the erasing process, wherein the second organic material (4) is preferably converted from an oxygen-impermeable state into an oxygen-permeable state by the heat, and - to rewrite the label (1) the writing process is carried out. [11] Method according to claim 10, wherein during the writing process the phosphorescent region (5) is illuminated with light of the first characteristic (8), wherein preferably the functional layer is partially covered with a mask (7) such that only the phosphorescent region (5) is illuminated and / or the functional layer is illuminated with light of the first characteristic (8) by a locally meandering or line-by-line scanning light beam only in the phosphorescent region (5) and / or the functional layer is illuminated only in the phosphorescent region (5) by illuminating the functional layer with a light beam with a steel profile, wherein the beam profile on the functional layer corresponds to the phosphorescent region (5). [12] Method according to claim 11, wherein UV light is used as the light of the first characteristic (8), wherein preferably oxygen (9) is bound to the first organic material (3) in a binding step, wherein before the binding step the oxygen (9) is preferably converted in a triplet-triplet interaction (11) with the phosphor from a triplet ground state of the oxygen (T0) to an excited singlet state of the oxygen (S1'), wherein the phosphor is converted by the light of the first characteristic (8) from a singlet state of the phosphor (S0) to an excited singlet state of the phosphor (S1) and then by intercombination (10) from the excited singlet state of the phosphor (S1) to an excited triplet state of the phosphor (T1). [13] Method according to one of the preceding claims, wherein the heat is introduced by irradiating light of the second characteristic, wherein the light of the second characteristic is preferably IR light.

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