Electroluminescent device and method for producing an electroluminescent device

Abstract

The invention relates to an electroluminescent device and a method for producing such an electroluminescent device. The device comprises the following layers: a stretchable, translucent substrate (10), a translucent and conductive front electrode (20), a light-emitting layer (30), a dielectric layer (40), and a conductive back electrode (50). At least the light-emitting layer (30) and / or the dielectric layer (40) comprise a binder (70) and a solid (32, 42), the proportion of the solid (32, 42) being in a range from 30 to 70 percent by weight, and the binder (70) comprising polyurethane, silicone, or natural rubber.

Description

[0001] The invention relates to an electroluminescent device and methods for producing an electroluminescent device.

[0002] From US2009 / 0212690 A1 a flexible electroluminescent device and a manufacturing method for such a device are known.

[0003] WO2005 / 122643 A1 discloses another structure of a flexible electroluminescent device in which the light is emitted through the carrier material.

[0004] Furthermore, from US2005 / 191520A1 a deformable electroluminescent arrangement is known in which a conductive electrode layer containing at least one conductive polymer is located on the counter electrode or between the dielectric layer and the counter electrode.

[0005] CN 114 096 029A discloses a flexible electroluminescent film which is manufactured using a flexible epoxy resin.

[0006] The object of the invention is therefore to provide a device and a method which overcome at least one disadvantage of the prior art and enable the production of a cost-effective, three-dimensionally stretchable or deformable electroluminescent device.

[0007] According to the invention, this object is achieved by a device according to claim 1 and a method according to claim 7.

[0008] The electroluminescent device comprises the following layers: a light-transmitting substrate, a light-transmitting and conductive front electrode, a light-emitting layer, a dielectric layer and a conductive back electrode.

[0009] The light-emitting layer and / or the dielectric layer each comprise a binder and a solid. The proportion of the respective solid is in the range of 30 to 70 percent by weight, in particular 50%.

[0010] Due to the solid-to-binder ratio according to the invention, a stretchable electroluminescent device is produced which does not lose its functionality even after several stretching processes.

[0011] The stretchable, translucent substrate here comprises a stretchable thermoplastic polyurethane (TPU) film. Stretchable TPU films based on aliphatic isocyanates are particularly suitable for this purpose, as they are stretchable and retain their stability during one or more printing processes and a thermal drying process.

[0012] The substrate can also be designed as a stretch film, i.e., an elastic film. These films are advantageously extremely stretchable without tearing and, when stretched below their elastic limit, exhibit a high resilience. A degree of stretch of 100%, i.e., an elongation of, for example, 1 mm to 2 mm, is also advantageous.

[0013] For example, Gerlinger Polyurethane films 4220 100my or Expafol TPU films 100, 100my can be used here.

[0014] The Expafol TPU film 100 is characterized by a breaking elongation with the parameters L: 425 Kg / cm 2 and T: 600 kg / cm 2 Further information about the film can be found in the product data sheet (https: / / expafol.com / de / produkte / tpu-100 / ), the contents of which are included here in full.

[0015] For the purposes of this application, translucent materials are defined as materials or bodies that allow electromagnetic waves, at least in the visible range, to pass through. Physically, a further distinction is made between opacity and light transmission. Materials through which light can pass almost unhindered are described as translucent. Objects behind a transparent material can be seen clearly. Light can also pass through translucent or translucent materials - even if not completely. Translucent materials are further distinguished between regular and diffuse transmission. Regular transmission means that the rays can change direction as they pass through the material, but only in a systematic manner. In diffusely translucent materials, such as frosted glass, the light is randomly directed in all possible directions.If you look through diffusely permeable material, you cannot see any sharp images behind it.

[0016] Several layers are applied to the substrate, forming an electrical layer structure: The front electrode, which is also stretchable, can be made of any type of electrically conductive polymer, such as PEDOT:PSS. Conductive polymers make it possible for the front electrode of a device according to the invention to still exhibit high electrical conductivity even at a stretching degree of 100%. Layer thicknesses in the range of 0.25 to 1 µm, and particularly preferably in the range of 0.5 to 0.7 µm, are suitable.

[0017] Electrical conductivity σ is the ability of a material to conduct electrical current. The electrical conductivity of electrically self-conducting polymers is in the range of 10 -13 up to 10 3 S / cm.

[0018] For the light-emitting layer, layer thicknesses in the range of 20 to 80 µm, particularly preferably in the range of 20 to 40 µm, are suitable.

[0019] The light-emitting layer is also stretchable and can comprise a solid luminescent pigment, preferably zinc sulfide (ZnS) doped with materials such as manganese and / or copper.

[0020] Furthermore, the luminous pigments can be encapsulated with aluminum oxide, for example.

[0021] The light-emitting layer can be designed so that the luminescent pigments lie next to each other rather than on top of each other. The luminescent pigments are thus arranged side by side in one plane.

[0022] For the dielectric layer, a layer thickness in the range of 5 to 50 µm, preferably in the range of 10 to 25 µm.

[0023] The dielectric layer can comprise a solid ceramic filler with a high dielectric constant, such as barium titanate (BaTiO3). The ceramic filler can, for example, have a powder size of 0.1 to 50 µm. The barium titanate is preferably metal-based and preferably has a purity of 99.9% and a maximum grain size of 44 µm (+325 mesh screen: <=0.1%; mesh is a unit of mesh fineness in many English-speaking countries and is mainly used for sieves. At the same time, the mesh also refers to the grain size of the correspondingly sieved material. A sieve with 325 meshes per inch (25.4 mm) has a value of 325 mesh. However, since the thickness of the mesh wires must also be taken into account, 325 mesh does not correspond to a grain size of 325ths of an inch, but rather to a grain size of 44 µm).Thermo Fisher Scientific, for example, supplies a barium titanium oxide with corresponding properties (catalog number 012348.A3).

[0024] The electrically conductive stretchable back electrode has a layer thickness in the range of 5 to 40 µm, preferably in the range of 10 to 15 µm.

[0025] The front electrode and the back electrode can each be electrically connected to an electrical terminal with a layer thickness in the range of 5 to 40 µm, preferably in the range of 10 to 15 µm.

[0026] The device requires a preferably sinusoidal alternating voltage. The operating voltage can be between 30 and 300 volts at a frequency between 50 Hz and 4 kHz.

[0027] Highly elastic polymers such as polyurethane, silicone, or natural rubber can be used as binders. Ideally, these have a similar modulus of elasticity to the substrate. The binder preferably has a high dielectric constant.

[0028] The solids content of the stretchable light-emitting and / or dielectric layers is adjusted so that the luminous function is maintained even when stretched just below the elastic limit of the carrier layer. Thus, functionality is still guaranteed even at a 100% expansion rate, i.e., an extension from, for example, 1 mm to 2 mm.

[0029] The substrate and the electrical layer structure can be stretched in length by 20 - 40% during electrical operation without disturbing the light-emitting function.

[0030] In this way, the solid content can be reduced while maintaining the same electrical and light-emitting function and at the same time achieving a good mechanical connection between the individual layers.

[0031] The back electrode of the device according to the invention can be manufactured, for example, with an electrically conductive screen printing paste specially developed for stretchable or expandable electronics, which contains electrically conductive components such as silver, copper, conductive polymers, graphite or graphene, silver nanowires, or the like. This ensures that the back electrode remains electrically conductive even at a stretching degree of 100%. Polyurethanes, silicones, or industrially manufactured elastomers, as well as natural rubber, can be used as binders and are dissolved in a solvent, such as alcohol.

[0032] The device according to the invention can also be back-coated with a stretchable TPU film, ensuring secure encapsulation against environmental influences.

[0033] Preferably, the layered structure has a similar modulus of elasticity across all layers. This ensures the device's functionality even under multiple stretching and, for example, prevents cohesive and / or adhesive fracture of the device's layers.

[0034] The device constructed in this way retains its light-emitting function even when stretched below its elastic limit and even at a stretching degree of 100%, e.g. from 1 to 2 mm.

[0035] The individual layers of the device are preferably applied using a screen printing process.

[0036] Due to the printing pastes used, especially their binder and filler content, a good mechanical connection between the individual layers of the device can be achieved.

[0037] Preferably, the solvent content of the printing pastes used is less than 5% by weight. For example, a solvent with a proportion of 95% by weight water (H2O) and 5% by weight alcohol (ethanol, C2H6O) can be used.

[0038] The layers are applied sequentially to the stretchable substrate. The translucent and conductive front electrode, the light-emitting layer, the dielectric layer, and the conductive back electrode are applied one after the other.

[0039] The substrate may be releasably bonded to a carrier material such as paper during the manufacturing process.

[0040] However, the layers can also be applied using pad printing or slot-die coating. Slot-die coating is offered, for example, by MMC RYOTEC CORPORATION (see https: / / www.mmtc.co.jp / en / products / slotdie.html).

[0041] Together with the back electrode, electrical connectors can be applied which serve to electrically connect the front or back electrode to a voltage supply.

[0042] The individual layers can be dried after application. Drying can be performed in a conventional laboratory hot-air convection oven. Standard conditions include drying times of 3 to 15 minutes at 120°C to 130°C. For the translucent and conductive front electrode, the drying time can be significantly shorter or longer, depending on the layer thickness and the type of conductive polymer. Drying begins at approximately 80°C. However, depending on the material, longer drying times may be required. Drying can also be performed in a convection oven or an infrared (IR) oven.

[0043] The electroluminescent device according to the invention can be used, for example, in clothing items such as shoes, jackets, and bags. It can also be used as a luminous sheath for live cables. The invention can also be laminated onto, and illuminated by, textiles, synthetic leather, genuine leather, and generally upholstered surfaces subject to constant stretching and expansion, such as door panels, armrests, and headrests in a vehicle.

[0044] The invention is explained in more detail below with reference to schematic figures. They show: Fig. 1 is a plan view of an embodiment of an electroluminescent device; Fig. 2a, Fig. 2b, Fig. 2c and Fig. 2d a plan view of the substrate after application of the individual layers; and Fig. 3 a section through an embodiment of an electroluminescent device.

[0045] Fig. 1 shows a plan view of an embodiment of an electroluminescent device.

[0046] In the exemplary embodiment described here, a thermoplastic polyurethane (TPU) with a thickness of, for example, 100 µm is used as the translucent substrate 10. Due to the nature of the pastes used for the layer structure and their filler content, no special surface treatment or adhesion promoter is necessary for the carrier layer.

[0047] The top view also shows a back electrode 50, described in more detail below, and a first and a second electrical connection 60 and 61, respectively. The first connection 60 is electrically connected to a front electrode 20, also described in more detail below. The second connection 61 is connected to the back electrode 50.

[0048] In order to reduce the manufacturing steps of the device, the terminals 60 and 61 can be printed in one step together with the back electrode 50.

[0049] Fig. Figure 2a shows the device after a first manufacturing step. In a first step, a translucent and conductive front electrode 20 is applied to the substrate 10. This has a layer thickness in the range of 0.25 to 1 µm, preferably in the range of 0.5 to 0.7 µm.

[0050] The front electrode 20 can be applied in the desired geometry using a screen printing process. Screen printing is a printing process in which the printing paste is printed with a rubber squeegee through a fine-mesh fabric onto the material to be printed—here, in the first step, directly onto the substrate 10. At those points on the fabric where no ink is to be printed according to the print image, the mesh openings of the fabric are made impermeable to ink using a stencil. In this way, the first and all subsequent layers 20, 30, 40, 50, 60, 61 can be printed in the desired geometry. This creates electroluminescent devices, e.g., in the form of a light panel, one or more letters, numbers, images, or logos.

[0051] The electrical conductivity of the front electrode is in the range of 10 -13 up to 10 3 S / cm.

[0052] In the example, a polymer coating offered by Heraeus, marketed under the trade name Clevios™, is used as the printing paste for the front electrode. This allows the production of very thin, conductive polymer layers. Clevios™ PEDOT:PSS is a complex of a substituted polythiophene and a polyanion with an electrical conductivity of approximately 1000 S / cm.

[0053] If a Clevios™ coating is used, it requires thorough thermal drying at temperatures up to 120°C. After the drying step, the Clevios™ coating is fully functional; no further tempering or post-treatment steps are required.

[0054] Fig. Figure 2b shows the device after the application of the light-emitting layer 30. In the exemplary embodiment, this layer has the same geometry as the front electrode 20 and was also applied using a screen printing process.

[0055] The light-emitting layer 30 comprises a binder 70 and a solid 32. In the exemplary embodiment, the proportion of the solid 32 is in a range of 30 to 70 percent by weight, in particular approximately 50%.

[0056] Highly elastic polymers, such as polyurethane, silicones, or industrially manufactured elastomers, as well as natural rubber, can be used as the binder 70. These ideally have a similar modulus of elasticity to the substrate 10. The binder 70 also has a high dielectric constant.

[0057] The light-emitting and / or dielectric layers 30 and 40 are printed with a screen printing paste specially produced for stretchable electronics. This paste is mixed from a binder 70, a solid 32 and 42, respectively, and a solvent, for example, an alcohol-based one. Polyurethanes, silicones, or industrially manufactured elastomers, as well as natural rubber, can be used as the binder 70. The solid fill level is adjusted so that the luminous function is ensured even with an expansion only slightly below the elastic limit of the substrate 10. Thus, the function of the device is still guaranteed even with a plug-in degree of 100%, i.e., an extension from, for example, 1 mm to 2 mm.

[0058] Binder 70 and solid 32 or 42 are mixed together prior to application to ensure even distribution and wetting of the solid particles. A solids content of approximately 50 percent by weight has proven effective. The ratio of solid 32 or 42 to binder 70 refers to the ratio after the respective layer has dried.

[0059] In this way, the solid content can be reduced while maintaining the same electrical and light-emitting function and at the same time achieving a good mechanical connection between the individual layers.

[0060] For the light-emitting layer 30, layer thicknesses in the range of 20 to 80 µm, particularly preferably in the range of 20 to 40 µm, are suitable.

[0061] In the exemplary embodiment, a luminescent pigment, preferably zinc sulfide (ZnS) doped with materials such as manganese and / or copper, is used as the solid 32 for the light-emitting layer 30. Furthermore, the luminescent pigments can be encapsulated with aluminum oxide.

[0062] The light-emitting layer 30 is designed such that the luminescent pigments lie next to each other in or on the same plane, i.e., not on top of each other. This achieves a uniform layer thickness, and the individual pigments do not shadow each other.

[0063] Fig. 2c shows the device after the application of the dielectric layer 40. In the exemplary embodiment, this layer has the same geometry as the front electrode 20 and the light-emitting layer 30 and was also applied using a screen printing process.

[0064] The dielectric layer 40 comprises a ceramic filler with a high dielectric constant, such as barium titanate (BaTiO3), as a solid 42. The ceramic filler has a powder size of 0.1 to 10 µm.

[0065] Fig. Figure 2d shows the device after application of the back electrode 50. This was also applied using a screen printing process.

[0066] To avoid short circuits, the conductive back electrode 50 is not printed all the way to the edge of the underlying layers 20, 30, and 40. A margin of 0.1 to 2 mm, preferably 1 mm, is left free. The size of the light-emitting layer 30 and / or the dielectric layer 40 is selected to prevent a short circuit between the back electrode 50 and the front electrode 20, thus preventing the front electrode from coming into direct contact with the back electrode.

[0067] The back electrode 50 and the electrical connections 60, 61 can be applied in a single printing process. The electrical connections 60, 61 serve to electrically connect the front and back electrodes 20 and 50, respectively, to a power supply (not shown).

[0068] Fig. 3 shows a section AA through the Fig. 1. It shows a section through the substrate 10 and the layers 20, 30, 40, and 50 applied thereto. These are the front electrode 20, the light-emitting layer 30, the dielectric layer 40, and the back electrode 50.

[0069] The translucent substrate 10, here a thermoplastic polyurethane film, has a thickness of 100 µm. The translucent and conductive front electrode 20 has a layer thickness preferably in the range of 0.5 to 0.7 µm. The light-emitting layer 30 has a layer thickness preferably in the range of 20 to 40 µm. The dielectric layer 40 has a layer thickness preferably in the range of 10 to 25 µm, and the conductive back electrode 50 has a layer thickness preferably in the range of 10 to 15 µm.

[0070] In the embodiment described here, this results in a total thickness of the device in a range of 140.5 to 180.7 µm.

[0071] Also shown is a cross-section through terminal 60 of front electrode 20. These serve to electrically connect front electrode 20 to a voltage source (not shown).

[0072] The electrical layer structure 80 comprises the layers 20, 30, 40 and 50 arranged on the substrate. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2009 / 0212690 A1

[0002] WO 2005 / 122643 A1

[0003] US 2005 / 191520A1

[0004] CN 114 096 029A

[0005] Cited non-patent literature

[0000] s.https: / / www.mmtc.co.jp / en / products / slotdie.html

[0040]

Claims

[1] Electroluminescent device comprising - a translucent substrate (10) comprising a stretchable film, in particular a thermoplastic polyurethane film, - an electrical layer structure (80) comprising - a light-transmitting and electrically conductive front electrode (20) with a layer thickness in the range of 0.1 to 1 µm, in particular in the range of 0.5 to 0.7 µm, - a light-emitting layer (30) with a layer thickness in the range of 20 to 80 µm, in particular in the range of 20 to 45 µm, - a dielectric layer (40) with a layer thickness in the range of 5 to 50 µm, in particular in the range of 30 to 40 µm, - an electrically conductive back electrode (50) with a layer thickness in the range from 5 to 40 µm, in particular in the range from 10 to 15 µm, wherein the light-emitting layer (30) and the dielectric layer (40) each comprise a binder (70) and a solid (32, 42), and the proportion of the solid (32, 42) is in a range from 30 to 70 percent by weight, and wherein the binder (70) comprises polyurethane, silicone, or natural rubber. [2] Electroluminescent device according to claim 1, characterized by that the light-emitting layer (30) comprises as a solid (32) a luminous pigment, in particular zinc sulfide (ZnS) doped with manganese and / or copper. [3] Electroluminescent device according to one of the preceding claims, characterized by that the solid (32) has particles with a grain size of less than 25-50µm, in particular less than 44µm or less than +325 mesh screen. [4] Electroluminescent device according to claim 3, characterized by that the particles of the solid (32) are arranged such that the light-emitting layer (30) has a thickness of less than 50µm. [5] Electroluminescent device according to one of the preceding claims, characterized by that the dielectric layer (40) has as solid (42) a ceramic filler with a high dielectric constant, in particular barium titanate (BaTiO3). [6] Electroluminescent device according to one of the preceding claims, characterized by that the front electrode (20) and the back electrode (50) are each electrically connected to an electrical connection (60, 61) with a layer thickness in the range of 5 to 40 µm, or in the range of 10 to 15 µm. [7] A method for producing an electroluminescent device, comprising the following steps: - Providing a light-transmitting substrate (10) comprising a stretchable film, in particular a thermoplastic polyurethane film; - applying a light-transmitting and electrically conductive front electrode (20) to the substrate (10); - applying a light-emitting layer (30) to the front electrode (20), - applying a dielectric layer (40) to the light-emitting layer (30), - applying an electrically conductive back electrode (50), wherein at least the light-emitting layer (30) and the dielectric layer (40) each comprise a binder (70) and a solid (32, 42), and the proportion of the solid (32, 42) after drying is in a range of 30 to 70 percent by weight, and the binder (70) comprises polyurethane, silicone, or natural rubber. [8] Method according to claim 7, characterized bythat the front electrode (20), the light-emitting layer (30), the dielectric layer (40) and the back electrode (50) are applied by means of a printing process, for example screen printing or pad printing, or by means of a gap coating. [9] Method according to one of claims 7 or 8, characterized by that the solid (32, 42) and the binder (70) are dissolved in a solvent containing water and alcohol. [10] Method according to claim 9, characterized by that the proportion of water and alcohol is in a range of 2 to 10, in particular at a value less than 5 percent by weight.

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