Method for producing a sensor material and / or a sensor using a 3D printer and sensor for detecting a measured quantity

Abstract

The invention relates to a method for producing a sensor material and / or a sensor using a 3D printer, comprising the following steps: - Fixing a substrate to a base plate of the 3D printer, - 3D printing a frame using a filament and the 3D printer onto the substrate, - Application of a liquid sensory layer material to the substrate within the frame, - Drying the liquid sensory layer material into a sensory layer and - Removing the frame from the substrate, resulting in a sensor material with a substantially homogeneous layer thickness and a free-standing outer edge of the sensor layer. Furthermore, the invention relates to a sensor for detecting a measured quantity.

Description

[0001] The invention relates to a method for producing a sensor material and / or a sensor using a 3D printer. Furthermore, the invention relates to a sensor for detecting a measured quantity, wherein the sensor comprises a substrate and two electrical contacts.

[0002] Manufacturing a sensor requires applying a sensor layer to a substrate. Commonly known methods for this include spin coating, inkjet printing, screen printing, soap coating, and drop casting. Paper is also known to be used as a substrate for ecological reasons. However, known substrate coating methods are only partially suitable for paper substrates and often do not result in a uniformly shaped and sufficiently thick layer of the applied sensor material, potentially leading to insufficient sensitivity in the finished sensor. For example, soak coating of a paper substrate results in a completely saturated paper surface, leading to an undefined sensor layer thickness. Furthermore, defining the external geometry of the applied sensor material requires additional effort.The use of screen printing results in defined structures on a paper substrate; however, a disadvantage of this method is the minimum required viscosity of the screen printing paste and a limitation regarding the maximum layer thickness. Classic drop casting as well as inkjet printing lead to irregular layers and ring-shaped deposits of the applied sensory material due to a coffee ring effect, which generally occurs when the solvent evaporates from drops of solutions or colloidal suspensions on solid surfaces.

[0003] US Patent 2023 / 0296548 A1 describes a method for manufacturing a system for measuring the temperature and humidity of air and soil, in which at least one capacitive humidity sensor and one resistance temperature sensor, as well as a bus system for data transmission, are printed on the surface of a body made of biodegradable, cellulose-based material, wherein the printing is carried out by a printing technique from the group of screen printing, stencil printing, flexographic printing, inkjet printing, micro-dispensing, micro-spraying and other methods.

[0004] A paper-based electrochemical sensor for the rapid on-site detection of antibiotics is known from CN 118050408 A. For its fabrication, a hydrophobic surface and a reaction surface are prepared on filter paper by applying wax using a wax printer and then heating it so that the wax melts and penetrates the filter paper to form a hydrophobic barrier. Subsequently, a working electrode, a counter electrode, and a reference electrode are applied to the reaction surface using screen printing.

[0005] IN 202311047380 A relates to a process for manufacturing a multifunctional electrochemical paper-based sensor. In this process, after spraying and drying a flame-retardant solution onto a paper matrix, a paraffin wax solution heated to 65 °C is applied in a targeted, uniform distribution to the surface of the flame-retardant paper matrix and cured at 110 °C for 10 minutes. Subsequently, a three-electrode pattern is laser-engraved into the hydrophobic paper matrix, and a surface of the reference electrode is coated with chlorinated silver paste and cured. The wax-modified surface retains its hydrophobicity, which is an important requirement for the finished sensor to perform measurements in liquid samples.

[0006] US 2022 / 0003682 A1 describes a sensor for detecting an analyte with a porous, planar substrate, such as paper, nitrocellulose, and / or nylon, and at least one photoluminescent nanostructure on or embedded within the porous planar substrate. The fabrication process can utilize a wax printing technique for structuring nanosensors onto nitrocellulose. In this technique, wax is printed onto the nitrocellulose using a wax printer and then thermally remelted to allow the wax to penetrate the pores of the nitrocellulose and form a hydrophobic barrier. A drop of sensor solution is then drop-cast into this hydrophobic wax barrier, resulting in a more uniform distribution and adjustable dimensions for the sensor area.

[0007] WO 2020 / 182830 A1 relates to a screen-printed, paper-based electrode for measuring free chlorine. The manufacturing process begins with printing a hydrophobic area onto a sheet of paper using a wax printer. Within this area lies a hydrophilic region. The waxed paper sheet is then treated in an oven at 100 °C. Subsequently, at least one electrode is printed onto the hydrophilic region using silver- or graphite-containing ink, and this electrode is then functionalized.

[0008] WO 2017 / 040947 A1 discloses a method for producing a sensory material, wherein a substrate with a cellulose matrix forming an interconnected porous structure is provided, and a hydrophobic barrier is distributed over the entire thickness of the substrate to define a porous channel within the cellulose volume. An electrically conductive material is arranged within the volume inside the porous channel to coat the cellulose matrix therein. The bulky, hydrophobic barrier can consist of a wax, a thermosetting resin, or a UV-cured resin. The electrically conductive material can be poly(3,4-ethylenedioxythiophene)polystyrenesulfonate (PEDOT:PSS), and the chemical reagent can be polyethyleneimine (PEI).

[0009] A disadvantage of known methods is that when wax is applied and subsequently heated, the wax penetrates the structure of the paper- and / or cellulose-based substrate, thus altering its properties. This hydrophobization of the substrate leads to poor adhesion, especially to hydrophilic materials in which the manufactured sensor is intended to be used. Because the wax is deliberately melted into the substrate, it not only changes the properties of the entire substrate but also reduces its environmental compatibility, thus preventing recycling at the end of the sensor's lifespan.

[0010] The purpose of the invention is to improve the state of the art.

[0011] The problem is solved by a method for producing a sensor material and / or a sensor using a 3D printer with the following steps: - Fixing a substrate to a base plate of the 3D printer, - 3D printing a frame using a filament and the 3D printer onto the substrate, - Application of a liquid sensory layer material to the substrate within the frame, - Drying the liquid sensory layer material into a sensory layer and - Removing the frame from the substrate so that a sensor material with a substantially homogeneous layer thickness and a free-standing outer edge of the sensor layer is present.

[0012] It is particularly advantageous that the process produces a sensor material which not only has a homogeneous layer thickness across its entire surface, especially at the outer edge, but also a free-standing outer edge with a defined geometry. This makes it easier and more effective to connect both the sensor material at the free-standing outer edge and the substrate to the material and / or sample being measured, both spatially and materially. Because the frame is applied to the substrate but removed again after the sensor layer has formed, the material properties of the substrate are advantageously not altered. Thus, the frame provides a spatial boundary for the liquid sensor layer material applied to the substrate within it, but does not change the material properties of either the liquid sensor layer material or the substrate.

[0013] The precise, well-defined spatial and material bonding of the sensor material and / or the sensor to the material being monitored, as well as the homogeneous layer thickness, improves the sensor's sensitivity and thus the representativeness and reproducibility of the measurement. Furthermore, the inventive method enables significantly larger, defined layer thicknesses with a uniform distribution of the sensor layer, even at the outer edge, free from a coffee-ring effect, compared to known prior art methods.

[0014] It is particularly advantageous that the sensor layer on the substrate can be manufactured to any desired shape, layer thickness and / or size.

[0015] Because the sensor layer is freestanding on the substrate and has a defined geometrically shaped outer edge, it is easy to flexibly manufacture it into a sensor, for example by contacting it with electrodes, and / or integrating it into a material being measured.

[0016] Thus, a sensor material and / or sensor is provided which, despite small dimensions of a few millimeters, offers high sensitivity, cost efficiency in manufacturing, and compatibility with the material being measured and optionally with additional material testing methods, such as structural monitoring using ultrasound, due to the homogeneous sensor layer.

[0017] A key aspect of the invention is to provide a limited space for receiving and drying the liquid sensor layer material during the production of a sensor material by means of a printed circumferential frame on the substrate. This limitation by means of the frame enables a homogeneous distribution of the liquid sensor layer material within the frame, thus ensuring a homogeneous thickness of the sensor layer and a defined shape of its outer edge. Because the frame is removed from the substrate and thus from the lateral outer walls of the sensor layer after drying, the sensor layer has a free-standing outer edge and free-standing side walls on the substrate.Due to the defined external geometry of the manufactured sensor layer, the sensor material can be easily bonded and further processed both spatially and materially.

[0018] The following terms will be explained:

[0019] A "sensor" (also called a "measuring device") is, in particular, a technical component used to qualitatively or quantitatively measure physical, chemical, and / or material properties. The sensor provides the measured quantity, especially as a processable electrical signal. In principle, a sensor can be any type of sensor. For example, a sensor can be active or passive. Examples of sensors include temperature sensors, humidity sensors, and / or strain gauges.

[0020] A "sensor layer" is, in particular, a solid layer of a material with a substantially homogeneous thickness, which changes its properties, especially its electrical properties, depending on a change in a measured quantity. In the case of a temperature sensor, a sensor layer is used whose resistance, as an electrical property, changes with temperature. The sensor layer has a thickness in the range of 0.5 to 20 µm, preferably 3 to 15 µm. The sensor layer is produced, in particular, by homogeneously applying a liquid sensor layer material to the interior of the frame on the substrate and by subsequent drying. The liquid sensor layer material is, in particular, a semiconductor. The liquid sensor layer material, in particular, comprises water and / or a solvent.The water and / or solvent base evaporates, particularly during the drying of the liquid sensory layer material, resulting in a solid sensory layer. The liquid sensory layer material can be any type of organic and / or inorganic conductor or semiconductor. The liquid sensory layer material is specifically compatible with the substrate and / or the frame and does not lead to significant changes in the respective material properties. For example, the liquid sensory layer material could be poly(3,4-ethylenedioxythiophene)polystyrenesulfonate (PEDOT:PSS). Similarly, a liquid sensory layer material could be, for example, a liquid semiconductor material from elemental groups II and VI, in which the corresponding nanoparticles are present in stable solution.Depending on the frame size, the liquid sensory layer material can be applied to the substrate in a volume ranging from 1.0 µl to 200 µl, particularly from 5.0 µl to 150 µl, preferably from 10 µl to 50 µl. The volume to be applied is scalable and depends in particular on the frame structure, and thus on the area within the frame, the desired layer thickness, and the frame height.

[0021] In principle, the liquid sensory layer material can be applied using any dosing device. Application can be carried out, for example, using a diaphragm and / or micro-dosing pump or a pipette. When pipetting for application, the pipette can be operated manually or automatically. Drying the liquid sensory layer material into a sensory layer can be done, for example, in an oven or on a hot plate. In the case of PEDOT:PSS as a liquid sensory layer material, drying takes place at 90 °C for 30 minutes. The drying temperature and duration are specifically chosen to ensure that the water-based and / or organic solvents are completely evaporated from the liquid sensory layer material.After drying, an additional liquid sensory layer material can optionally be applied to the manufactured sensory layer within the frame. This additional liquid sensory layer material can be the same material or a different one. For example, it can be applied by spraying, without the need for a dosing device or pipette. Similarly, an additional layer, especially if it is very thin and not present as a large volume of liquid, can also be sprayed, brushed, or otherwise applied to the solid sensory layer after the frame has been removed.

[0022] An "outer edge" refers in particular to the limiting edge and / or the circumferential border of the sensory layer, which points outwards. The outer edge is located, in particular, at the transition between the surface of the sensory layer and its respective side walls. The outer edge and / or the side walls are, in particular, freestanding. "Freestanding" means that, after removal of the frame from the substrate, the outer edge and / or the side walls of the sensory layer are not surrounded by any other solid material. The freestanding outer edge and / or the side walls are, immediately after removal of the frame, surrounded, in particular, by ambient air and / or cleanroom air.

[0023] A "substrate" is, in particular, a carrier for the liquid sensory layer material and the resulting solid sensory layer. The substrate can, in principle, be any material compatible with the liquid sensory layer material and the frame material. The substrate is, in particular, a planar material and / or a sheet-like material. The substrate can, in principle, be a natural material and / or a synthetically produced material. For example, the substrate can be paper, cardboard, wood, wood laminate, plastic, bio-based plastic, and / or a fibrous material. A smooth and / or coated glass plate can also, in principle, be used as a substrate. The substrate can, for example, have a layer thickness in the range of 0.5 to 500 µm, in particular from 3 µm to 300 µm, preferably from 50 µm to 250 µm.However, the layer thickness of the respective substrate also depends on the specific properties of the substrate, such as its stiffness and flexural strength.

[0024] In principle, two or more frames can be printed on the substrate simultaneously and / or sequentially, thus producing two or more layered materials and / or sensors. The two or more sensors produced in this way can then be used individually for different measurement tasks by cutting the substrate accordingly before use. Likewise, two or more sensors for the same or different measurement tasks can be used simultaneously on the substrate and / or be electrically and / or metrologically connected to each other.

[0025] The term "3D printer" refers specifically to a device used to deposit material layer by layer to create a three-dimensional structure and / or object. Printing with a 3D printer is, in particular, a generative and / or additive manufacturing process. A 3D printer typically includes a control unit, a print head (extruder), and a build plate. The filament used as the build material is melted within the 3D printer and deposited layer by layer onto the substrate by means of the print head, with the molten filament being extruded through the printer and / or extruder nozzle.

[0026] The term "extrusion" refers in particular to the pushing and / or pressing of the molten filament through the extruder nozzle.

[0027] Unlike conventional 3D printing, the molten filament is not applied to the build plate of the 3D printer, but directly to the substrate fixed to the build plate, layer by layer. For 3D printing and / or fused deposition, the 3D print head repeatedly moves along a work plane at a predetermined speed, line by line, to build the frame. The work plane is then moved upwards in a stacking fashion, creating the frame's shape layer by layer.

[0028] The term "filament" refers specifically to the material used to print and manufacture the frame. Before melting, the filament has a significantly larger length relative to its cross-sectional area. The filament is, in particular, a single fiber or multiple fibers of any length. The filament can also be a printing filament and / or a single strand. The filament can be made of a plastic and / or polymer, a metal, a metal alloy, glass, or a mixture of these and other materials. The filament is, in particular, a thermoplastic. The filament can be, in particular, modified polyethylene terephthalate. For example, the filament contains polyethylene terephthalate glycol (PET-G). The filament has, in particular, a diameter of 0.4 to 4.0 mm, preferably 1.5 to 2.0 mm.The filament is particularly materially compatible with the liquid sensory layer material and its contained solvents.

[0029] A "frame" is, in particular, an enclosure and / or a surrounding closed frame. The frame is connected to the top of the substrate, particularly by means of 3D printing, at its underside. The frame provides, in particular, an internal volume for the application and / or injection of the liquid sensory layer material. After the application and / or injection of the liquid sensory layer material, it rests, in particular, against the inner surfaces of the frame and on the substrate within the frame. The frame can, in principle, have any shape, such as square, rectangular, round, oval, triangular, and / or polygonal. The frame has, in particular, a height that is greater than the height of the applied liquid sensory layer material and / or any further applied layers. The frame has, in particular, a width in the range of 0.3 mm to 2.0 mm, preferably from 0.5 mm to 1.5 mm.The height of the manufactured 3D frame is adjusted, particularly during the preparation of a print file, to the volume of liquid sensory layer material to be applied and / or deposited, and thus to the thickness of the sensory layer. Preferably, however, the frame height is only slightly greater than the sensory layer material to be deposited, so that the depositing and / or drop-casting process is not impeded. The frame can have an internal length and / or width in the range of 0.5 mm to 20.0 mm, particularly from 5.0 mm to 15.0 mm. For example, the frame can have internal dimensions of 5.0 mm × 5.0 mm (L:W) or 1.0 mm × 1.0 mm, resulting in a slightly smaller sensory layer. Preferably, the frame has the same material width along its height. However, the frame can also be specifically shaped along its height and / or width.For example, the width of the frame can increase or decrease from the bottom to the top. Similarly, the frame, particularly in its upper area, can have specific structures, such as wave-like indentations, to, for example, support the distribution of the liquid sensory layer material and / or to imprint a specific shape on the sensory layer.

[0030] Additionally, a second frame, or further frames, can be 3D printed simultaneously or subsequently around the frame for holding the liquid sensor layer material, spaced apart. This allows multiple sensors to be manufactured on a single substrate. Similarly, one frame can surround another, and a further material can be introduced and / or dried between the two frames. Such a second material can selectively influence and / or improve the lateral bonding of the sensor layer if optimal bonding of the sensor layer material to the material being measured is not achieved.

[0031] "Removal" is understood to mean, in particular, that the frame is removed completely and without residue from the surface of the substrate and / or the side walls of the dried sensory layer. The frame is removed in one piece, as a whole. Preferably, the material properties of the frame, the substrate, and the sensory layer are selected such that the frame can be easily peeled off the top of the substrate and the side walls of the sensory layer, so that the inner sensory layer remains dimensionally stable and undamaged. However, a tool can also be used to lift and / or remove the frame from the substrate.For example, a spatula can be used to partially lift the frame from the substrate between its outer underside and the top surface, and then, ideally without further contact between the spatula and the sensor layer, the frame can be removed from the substrate. The frame is removed, in particular, after the sensor layer and / or sensor material has completely cooled.

[0032] In a further embodiment of the process, the surface tension of the liquid sensory layer material is broken during and / or after application, so that the liquid sensory layer material is distributed essentially homogeneously within the frame.

[0033] Breaking the surface and / or surface tension of the liquid sensory layer material is particularly useful when the volume and thus the layer thickness of the applied and / or introduced liquid sensory material is small relative to the height of the frame and therefore the internal volume enclosed by the frame, in order to distribute the liquid sensory layer material to the interior of the frame. Furthermore, breaking the surface tension can also prevent meniscus formation of the liquid sensory layer material on the inside of the frame.

[0034] The terms "breaking" and "broken" refer specifically to the mechanical action applied to the surface of the liquid sensory layer material. For example, the surface of the liquid sensory layer material is pierced and / or the liquid sensory layer material is stirred. This counteracts the surface tension and thus the tendency of the liquid sensory layer material to maintain a small surface area. To break the surface tension and / or surface of the liquid sensory layer material, a rod and / or the pipette previously used for application can be immersed in the liquid. Similarly, a stirrer can be inserted into the liquid sensory layer material, or the build plate of the 3D printer can be moved.

[0035] The term "essentially homogeneously distributed within the frame" means, in particular, that the liquid sensory layer material has an approximately uniform liquid level on the substrate within the frame. Therefore, certain deviations between the liquid level of the liquid sensory layer material and the thickness of the subsequently dried sensory layer are possible and tolerable.

[0036] To provide an electrically conductive sensor layer and to achieve easy handling, flexible shaping and good material compatibility during its production, an organic semiconductor, in particular poly(3,4-ethylenedioxythiophene)polystyrene sulfonate, can be used as the liquid sensor layer material.

[0037] The use of PEDOT:PSS is particularly advantageous because it is available as a ready-to-use aqueous suspension. Furthermore, the conductivity of the PEDOT:PSS liquid can be specifically increased by adding high-boiling solvents such as dimethyl sulfoxide or ethylene glycol.

[0038] In another design of the process, a substrate comprising a plant-based material and / or a fiber is used.

[0039] This ensures, on the one hand, good adhesion and / or a durable bond between the manufactured sensor layer and the top of the substrate, and on the other hand, that the frame can be easily removed from the surface of the substrate.

[0040] A “plant-based substance” can be any type of natural, plant-based substance and / or biopolymer, such as cellulose, lignin or a sugar molecule.

[0041] A "fiber" is a linear, elemental structure composed of a fibrous material. A fiber can be a natural fiber, meaning a naturally occurring, biogenic and / or mineral fiber. Likewise, a fiber can be a synthetic fiber, meaning an artificially created organic and / or inorganic fiber. A fiber can be a textile fiber, a polymer fiber, glass fiber, or a metal fiber. Naturally, the substrate can also contain two or more plant-based materials and / or two or more fiber types.

[0042] To achieve high ecological compatibility, good material compatibility of the sensor material and / or sensor and good adhesion to a measured object, a substrate containing paper, wood and / or bio-based plastic can be used.

[0043] In principle, any type of paper can be used. Preferably, the paper sheet should have a certain stiffness and flexural strength, as well as moderate absorbency. The paper could be, for example, standard printer paper or coated paper such as baking paper. The paper substrate could be, for example, printer paper, such as low-acid or acid-free printer paper. The paper could have a thickness of, for example, 71.0 µm. The paper could also be, for example, cardboard, card stock, or filter paper.

[0044] The term "bio-based plastic" refers specifically to all plastics produced from renewable raw materials. Bio-based plastic can be, in particular, a plastic made from a natural biopolymer such as starch or cellulose. It can also be made from polylactic acid and / or other renewable raw materials such as lignin, chitin, and similar natural polymers.

[0045] In a further embodiment of the method, two spaced-apart electrical contacts are attached and / or applied to and / or on the sensor layer, so that the sensor is present.

[0046] To apply the two spaced electrical contacts, for example, two electrodes can be printed onto the surface of the sensor layer using screen printing. Alternatively, the electrical contacts can be drawn onto the surface of the sensor layer using a guide pen. Another method is to first cut into the surface of the sensor layer, for example using a laser, and then insert and / or print an electrical contact and / or electrode into each of these cuts.

[0047] In another aspect of the invention, the problem is solved by a sensor for detecting a measured quantity, wherein the sensor has a substrate and two electrical contacts, and the sensor is manufactured according to a previously described method.

[0048] Thus, a sensor is provided which, due to the manufacturing process, has a substantially homogeneous layer thickness and a defined shaped and / or freestanding outer edge of the sensor layer.

[0049] In a further aspect of the invention, the problem is solved by a sensor for detecting a measured quantity, wherein the sensor has a substrate and two electrical contacts, wherein a solid sensory layer with a freestanding and / or spatially defined outer edge is arranged on the substrate.

[0050] In order to provide a defined spatially oriented contact surface of the sensory layer for bonding to a material being measured, a side wall of the sensory layer can have an angle to a perpendicular on the substrate between 0° and 60°, in particular between 0° and 45°, preferably between 0° and 20°, at the outer edge between a surface of the sensory layer and the substrate.

[0051] This provides a sensor with a high edge steepness of the sidewalls at the outer edge. Preferably, the sidewall(s) are perpendicular to the surface of the substrate. However, the sidewalls can also be deliberately inclined to the perpendicular to the substrate. For example, the surrounding sidewalls can widen conically from the surface of the substrate to the surface of the sensor layer. This conical shape of the sensor layer in cross-section advantageously anchors the sensor in the material being measured, especially when large mechanical forces act on the material and could otherwise lead to spatial displacement of the sensor.

[0052] In another embodiment of the sensor, the sensor layer has a deviation in its layer thickness of < 15%, in particular < 6%, preferably < 3%.

[0053] Thus, the thickness of the sensor layer is essentially homogeneous across its surface. The layer thickness may be slightly greater at the outer edge than in the center of the sensor layer. For example, with a layer thickness of approximately 11 µm in the center, the layer thickness at the outer edge is about 6% higher. With a thinner layer thickness of approximately 7 µm in the center of the sensor layer, the layer thickness at the outer edge can be 10 to 15% higher.

[0054] To provide optimal sensor properties and easy removal from the frame during manufacturing, the sensor layer features an organic semiconductor, in particular poly(3,4-ethylenedioxythiophene)polystyrene sulfonate.

[0055] In another embodiment of the sensor, the substrate comprises a plant-based material and / or a fiber.

[0056] To provide an environmentally friendly substrate, the substrate contains paper, wood and / or bio-based plastic.

[0057] In another aspect of the invention, the problem is solved by a fiber composite material, wherein the fiber composite material comprises fibers and a resin matrix, and the fiber composite material comprises at least one previously described sensor.

[0058] Thus, the sensor can be optimally integrated within a fiber-reinforced composite material, particularly within an uncured fiber-reinforced composite. It is especially advantageous that the substrate, particularly comprising a plant-based material, fiber, and / or paper, can be optimally arranged and / or bonded between the layers of a fiber-reinforced composite. Since the substrate and / or paper is not altered in its properties and / or not made hydrophobic during the manufacturing process, it can now absorb the resin matrix and thereby become metallurgically bonded to the fiber-reinforced composite. Consequently, the embedded and / or bonded sensor, for example, designed as a temperature sensor, can be used to monitor the curing process of the resin matrix inside the fiber-reinforced composite.In particular, the manufacturing parameters of prepregs (pre-impregnated) and thus of planar, fiber-reinforced semi-finished products pre-impregnated with special reactive resins can be monitored. Prepregs can contain all common reinforcing fibers, such as glass fibers, carbon fibers, and / or aramid fibers. An epoxy resin base is primarily used. The sensor can also be positioned between fiber laminates for moisture monitoring or be designed as a strain gauge.

[0059] In another aspect of the invention, the problem is solved by using a previously described sensor for manufacturing and / or product monitoring, in particular for monitoring the curing of a fiber composite material.

[0060] In principle, the sensor can be used in a wide variety of applications. Besides applications in production monitoring in the automotive, aerospace, shipbuilding, and wind turbine industries, further applications are possible in the area of ​​sustainable products, such as compostable single-use products. Product monitoring can also be carried out in the food sector, for example, to monitor the ripening process of fruit.

[0061] The invention will now be explained in more detail using exemplary embodiments. These will show... Fig. 1 A highly schematic cross-sectional representation of a sensory layer material on a paper substrate of a humidity sensor before removal of a frame. Fig. 2 a highly schematic representation of a top view of the manufactured humidity sensor, Fig. 3. A flow diagram of a manufacturing process, Fig. 4. Data on the course of relative humidity and temperature from conventional measuring instruments of a climate chamber, and Fig. 5 Data of the course of a resistance difference of two humidity sensors according to the invention with different sensor lengths measured in the climate chamber.

[0062] A humidity sensor 101 has a paper substrate 105 (acid-free printer paper). A sensor layer 103 is arranged on one top side of the paper substrate 105. In a top view, the sensor layer 103 has a square shape with four side walls 115 ( Fig. 2) The four side walls 115 are perpendicular to a top surface of the paper substrate 105, so that a free-standing outer edge 107 is present at the transition between a top surface of the sensory layer 103 and the respective side walls 115.

[0063] In the Fig. Figure 1 shows a state during the manufacture of the moisture sensor 101 in which the side walls 115 of the dried sensor layer 103 are still surrounded by a frame 117, which is removed during the manufacture (as shown below).

[0064] On the upper side of the sensor layer 103 of the humidity sensor 101, two spaced-apart silver electrodes 111 are arranged, so that a sensor measuring surface 109 is formed between them (see Fig. 2).

[0065] The humidity sensor 101 is manufactured using a manufacturing process 301 with the following steps:

[0066] The paper substrate 105 is fixed to a base plate of a 3D printer (step 303). Subsequently, a filament and a print head of the 3D printer are preheated (step 305) until the base plate reaches a temperature of 50 °C and the print head reaches a temperature of 225 °C. The filament is PET-G and has a diameter of 1.75 mm. It is applied to the paper substrate 105 by the print head at a printing speed of 75 mm / s, thereby 3D printing (step 307) a frame 117 layer by layer onto the paper substrate 105. The frame 117 is 3D printed such that its height is greater than one layer thickness of the manufactured sensor layer 103.

[0067] After the frame 117 is completed, liquid sensory layer material 113 PEDOT:PSS (CLEVIOS PH 1000, Heraeus GmbH) is applied to the top surface of the paper substrate 105 inside the frame using a pipette via drop casting. 40 µl of the liquid sensory layer material 113 is applied using the drop-casting process (step 309). The liquid sensory layer material 113 is then dried 311 in an oven until the solvent has evaporated and the dried, solid sensory layer 103 is obtained. Drying 311 is carried out at a temperature of 90 °C for a drying time of 30 minutes. Optionally, steps 309 and 311 can be repeated 313 to apply and dry another layer onto the sensory layer 103. After complete drying 311, the frame 117 is removed without residue from the paper substrate 105 (step 315).The following steps involve applying 317 of the two silver electrodes 111 to the top surface of the sensor layer 103. The silver electrodes 111 are applied by screen printing using flexible silver ink (901769, Sigma-Aldrich). After screen printing, the silver electrodes 111 are dried in an oven for 30 minutes at 130 °C. The result is a finished, functional humidity sensor 101.

[0068] The manufactured humidity sensor 101 has a layer thickness of 10.49 µm in its center and a slightly greater layer thickness of 11.16 µm at its outer edge 107 for the sensory layer 103, so that the layer thickness of the sensory layer 103 is essentially homogeneous. The sensory layer 103, with its side walls 115 and the free-standing outer edge 107, is arranged as a spatially clearly defined layer on the paper substrate 105 and is manufactured free of a coffee ring effect.

[0069] Measurements are carried out in a climate chamber (not shown) using the manufactured humidity sensor 101. Fig. Figure 4 shows the measured relative humidity (203%) in percent, with the scale on the left y-axis, and the temperature (205%) in °C, with the scale on the right y-axis, over a period of 201 hours. The measurements were taken using conventional measuring instruments in the climate chamber. The temperature remained approximately constant at around 70 °C throughout the entire period of 201 hours. The relative humidity (203%) decreased from approximately 80% to 20% in the first half hour and then gradually increased by 10% approximately every half hour until it reached 80%, before decreasing again to approximately 20% after 3.5 hours.

[0070] The humidity sensor 101 was used in the climate chamber in two different embodiments: sensor 209 with a 1 mm long sensor measuring area 109 between the two silver electrodes 111, and sensor 211 with a 3 mm long sensor measuring area 109 between the two silver electrodes 111. The respective resistance of sensors 209 and 211 was measured over time 201 in the climate chamber using a multimeter. The resistance difference 207 (ΔR) in Ω over time 201 is shown on the y-axis. As the Fig. 5 compared to the Fig.Figure 4 shows that the resistance differences 207 determined by sensors 209 and 211 correlate with the relative humidity 203 over time 201, with both sensors 209 and 211 exhibiting excellent sensitivity to the relative humidity 203 between 20 and 80% and reacting quickly to changes in the relative humidity 203. Sensor 211, with a length of 3 mm, has a higher sensitivity than sensor 209, which has a length of 1 mm.

[0071] In another embodiment not shown, the manufactured sensor is configured as a temperature sensor and is used to monitor the curing of a fiber-reinforced composite material with a two-component epoxy resin. Here, the resistance of the temperature sensor correlates with the changing curing temperature of the curing fiber-reinforced composite material. In this application, optimal adhesion of the temperature sensor is achieved due to the embedding of the paper substrate 105 in the layers of the fiber-reinforced composite material.

[0072] Thus, sensors 101, 209 and 211 are provided, which, due to their freestanding and / or spatially defined and very homogeneous sensory layer 103 with an outer edge 107, have optimal attachment to a measured material and high sensitivity. Reference symbol list 101 Humidity sensor 103 sensory layer 105 paper substrate 107 Outer edge of the sensory layer 109 Sensor measuring area 111 Silver electrode 113 sensory layer material 115 side wall 117 frames 201 Time, h 203 relative humidity, % 205 Temperature, °C 207 Resistance difference (ΔR), Ω 209 Sensor, 1 mm length 211 Sensor, 3 mm length 301 Manufacturing processes 303 Fixing a substrate to a base plate 305 Preheating the filament and printhead 307 3D printing a frame on the substrate 309 Application of a liquid sensory layer material to the substrate within the frame 311 Drying the liquid sensory layer material to form a sensory layer 313 (optional repeat) 315 Removing the frame from the substrate 317 Application of silver electrodes QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] US 2023 / 0296548 A1

[0003] CN 118050408 A

[0004] IN 202311047380 A

[0005] US 2022 / 0003682 A1

[0006] WO 2020 / 182830 A1

[0007] WO 2017 / 040947 A1

[0008]

Claims

[1] Method (301) for producing a sensor material (113) and / or a sensor (101) using a 3D printer comprising the following steps: - Fixing (303) a substrate (105) onto a base plate of the 3D printer, - 3D printing (307) of a frame using a filament and the 3D printer onto the substrate (105), - Application (309) of a liquid sensory layer material onto the substrate (105) within the frame, - Drying (311) of the liquid sensory layer material to form a sensory layer (103) and - Removal (315) of the frame from the substrate, so that a sensor material (113) with a substantially homogeneous layer thickness and a freestanding outer edge (107) of the sensor layer (103) is present. [2] Method (301) according to claim 1, characterized by, that during and / or after application (309) a surface tension of the liquid sensory layer material is broken, so that the liquid sensory layer material is distributed substantially homogeneously within the frame. [3] Method (301) according to one of the preceding claims 1 or 2, characterized by , that an organic semiconductor, in particular poly(3,4-ethylenedioxythiophene)polystyrenesulfonate, is used as the liquid sensory layer material. [4] Method (301) according to any of the preceding claims, characterized by , that as substrate (105) a substrate (105) comprising a plant-based material and / or a fiber is used. [5] Method (301) according to any of the preceding claims, characterized by , that the substrate (105) is paper, wood and / or bio-based plastic. [6] Method (301) according to any of the preceding claims, characterized by, that a connection and / or application (317) of two spaced-apart electrical contacts to and / or on the sensor layer (103), such that the sensor (101) is present. [7] Sensor (101) for detecting a measured quantity, wherein the sensor (101) has a substrate (105) and two electrical contacts (111), characterized by that the sensor is manufactured according to a method according to claim 6. [8] Sensor (101) for detecting a measured quantity, wherein the sensor (101) has a substrate (105) and two electrical contacts (111), characterized by , that a solid sensory layer (103) with a freestanding and / or spatially defined outer edge (107) is arranged on the substrate (105). [9] Sensor (101) according to claim 7 or 8, characterized by, that at the outer edge (107) a side wall (115) of the sensory layer (103) between a surface of the sensory layer (103) and the substrate (105) has an angle to a perpendicular on the substrate (105) between 0° to 60°, in particular between 0° and 45°, preferably between 0° and 20°. [10] Sensor (101) according to any one of claims 7 to 9, characterized by that the sensory layer (103) has a deviation in its layer thickness of less than 15%, in particular less than 6%, preferably less than 3%. [11] Sensor (101) according to any one of claims 7 to 10, characterized by , that the sensor layer (103) comprises an organic semiconductor, in particular poly(3,4-ethylenedioxythiophene)polystyrenesulfonate. [12] Sensor (101) according to any one of claims 7 to 11, characterized by that the substrate (105) contains a plant-based material and / or a fiber. [13] Sensor (101) according to any one of claims 7 to 12, characterized bythat the substrate (105) consists of paper, wood and / or bio-based plastic.

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