Flexible wet distance sensing film based on direct writing 3D printing and preparation method thereof

Abstract

The invention discloses a flexible wet distance sensing film based on direct writing 3D printing and a preparation method thereof. The flexible wet distance sensing film comprises a flexible film substrate, a central lead, an insulating layer and a spiral humidity sensitive layer, the preparation method comprises the following steps: designing the shape and size of the sensing element, preparing a flexible film substrate made of nano cellulose, and preparing a nano conductive filler / nano cellulose conductive humidity-sensitive composite material; after a central lead and an insulating layer are printed and prepared on a substrate, a spiral humidity sensitive layer is continuously printed, and a flexible wet distance sensing film is obtained after room-temperature drying; the conductive humidity-sensitive composite material is spiralized on the flexible film substrate through the direct writing 3D printing technology, the insulating layer is prepared to lead out the center lead, and the obtained flexible wet distance sensing film has intrinsic flexibility, is light and thin and can be applied to a narrow curved surface environment; the sensing film can detect humidity under direct-current excitation and can detect distance under alternating-current excitation; and the preparation efficiency and the process consistency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible wet distance sensing films, and in particular to a flexible wet distance sensing film based on direct writing 3D printing and a preparation method thereof. Background Art

[0002] With the development of science and technology, facilities and devices in industrial applications tend to be miniaturized and integrated, and more and more narrow curved structures have appeared, such as ball joint hinge structures in industrial robots, pipes, bearings and turbine blades in aerospace facilities. In order to ensure industrial safety and engineering efficiency and prevent equipment aging from causing losses to personal safety and industrial production, it is necessary to ensure that the temperature, humidity and surface gaps in the above narrow curved structures are kept appropriate. Due to their own rigidity and large size, traditional sensors are difficult to apply to the narrow curved environment that is widely present in industrial applications. In order to overcome the above defects, it is necessary to develop a flexible thin-film sensor element that can be applied to complex curved environments, so that it can not only measure the humidity in a narrow environment, but also monitor the distance between narrow curved surfaces. Summary of the invention

[0003] 1. Problems to be solved

[0004] With the development of science and technology, facilities and devices in industrial applications tend to be miniaturized and integrated, and more and more narrow curved structures have appeared, such as ball joint hinge structures in industrial robots, pipes, bearings and turbine blades in aerospace facilities. In order to ensure industrial safety and engineering efficiency and prevent equipment aging from causing losses to personal safety and industrial production, it is necessary to ensure that the temperature, humidity and surface gaps in the above narrow curved structures are kept appropriate. Due to their own rigidity and large size, traditional sensors are difficult to apply to the narrow curved environment that is widely present in industrial applications. In order to overcome the above defects, it is necessary to develop a flexible thin-film sensor element that can be applied to complex curved environments, so that it can not only measure the humidity in a narrow environment, but also monitor the distance between narrow curved surfaces.

[0005] (II) Technical solution

[0006] The technical solution provided by the present invention to solve the above problems is: a flexible wet distance sensing film based on direct writing 3D printing, comprising a flexible film substrate, a center lead, an insulating layer, and a spiral humidity sensitive layer;

[0007] The flexible film substrate 1 and the insulating layer 3 are made of nanocellulose paper. Nanocellulose is a nanofiber material separated from natural cellulose, with a diameter of 1 to 100 nm and a length of several microns. It has the characteristics of macroscopic cellulose and nanomaterials, and is renewable, degradable, and has a high aspect ratio and specific surface area. The nanocellulose paper made of it has a three-dimensional microporous network structure, high smoothness, good hydrophilicity and flexibility, and can meet the needs of flexible wet distance sensing film;

[0008] One end of the central lead is connected to the center of the spiral humidity sensitive layer, and the other end is connected to the test circuit;

[0009] The insulating layer covers the center lead and is tightly connected to the flexible film substrate, and has electrical insulation properties;

[0010] The spiral humidity sensitive layer is a planar spiral structure, covering the insulating layer, and is tightly connected to the flexible film substrate. The center of the spiral is connected to the center lead, and the other end is connected to the test circuit.

[0011] The central lead and the spiral humidity sensitive layer are made of conductive humidity sensitive composite materials, which are composed of a mixture of nanocellulose and conductive fillers, wherein the conductive fillers are nano conductive fillers such as carbon nanotubes, carbon black, graphene, nano silver particles or nano silver wires;

[0012] The method for preparing a flexible wet distance sensing film based on direct writing 3D printing comprises the following steps:

[0013] 1) Design the size and shape parameters of the flexible wet distance sensing film;

[0014] 2) weighing and mixing nanocellulose and pure water, preparing a nanocellulose aqueous solution by mechanical stirring for 6 hours and ultrasonic dispersion for 0.5 hours, pouring the nanocellulose aqueous solution into a mold, and drying at room temperature for 12 hours to obtain a flexible film substrate;

[0015] 3) weighing and mixing nanocellulose, nanoconductive filler and pure water, mechanically stirring for 6 hours, ultrasonically dispersing for 0.5 hours, and continuing to stir for 1 hour to prepare a nanoconductive filler / nanocellulose conductive humidity-sensitive composite material;

[0016] 4) Printing a center lead on a flexible film substrate by direct writing 3D printing process and drying at room temperature for 0.5 h;

[0017] 5) Continue to print the insulating layer on the flexible film substrate and dry it at room temperature for 0.5 h;

[0018] 6) Continue to print the spiral humidity sensitive layer on the flexible film substrate, and dry it at room temperature for 0.5 h to obtain a flexible humidity distance sensing film.

[0019] (III) Beneficial effects

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] (1) The present invention uses nanocellulose as a substrate material and a base material to prepare a flexible wet distance sensing film, which has intrinsic flexibility and is very light and thin, and can be applied to measurements in narrow curved environments.

[0022] (2) The present invention spirals the nano-conductive filler / nano-cellulose conductive humidity-sensitive composite material and prepares an insulating layer to lead out a central lead, so that the resulting flexible wet distance sensing film can detect humidity through resistance under DC excitation and detect distance through impedance under AC excitation.

[0023] (3) The present invention realizes the patterning of the center lead, the insulating layer and the spiral humidity sensitive layer on the flexible film substrate through the direct writing 3D printing technology, which not only improves the preparation efficiency, but also improves the consistency of the preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 is a schematic diagram of the flexible wet distance sensing film of the present invention;

[0026] Figure 2 is a schematic diagram of a device used in the direct writing 3D printing process in the embodiment;

[0027] Figure 3 This is an electron microscope image of a flexible film substrate;

[0028] Figure 4 It is the electron microscope image of the conductive moisture-sensitive composite material with the mass fraction of multi-walled carbon nanotubes and nanocellulose being 0.5wt% and 1wt% respectively;

[0029] The accompanying drawings are marked with: 1. Flexible film substrate, 2. Center lead, 3. Insulation layer, 4. Spiral humidity sensitive layer, 5. 3D printer, 6. Z-axis motion mechanism, 7. Printing table, 8. Extrusion device, 9. Air inlet pipe. DETAILED DESCRIPTION

[0030] In order to further understand the present invention, the present invention is described below in conjunction with embodiments and drawings, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention rather than limiting the claims of the present invention.

[0031] like Figure 1As shown, a flexible wet distance sensing film includes a flexible film substrate 1, a center lead 2 printed on the flexible film substrate 1, an insulating layer 3 covering the center lead 2, and a spiral humidity sensitive layer 4 printed on the top layer. The size and structural parameters of the flexible wet distance sensing film, that is, the size of the center lead 2, the size of the insulating layer 3, and the number of turns, line width and line spacing of the spiral humidity sensitive layer 4 should be designed according to the specific application scenario.

[0032] The materials of the flexible film substrate 1 and the insulating layer 3 are both nanocellulose paper (CNF Paper) formed by the polymerization of nanocellulose (CNF). Nanocellulose is a nanofiber material separated from natural cellulose, with a diameter of 1 to 100 nm and a length of several microns. It has the characteristics of macro cellulose and nanomaterials, and is renewable, degradable, and has a high aspect ratio and specific surface area. At room temperature, nanocellulose is insoluble in water and other organic solvents, but can be effectively dispersed in water and some liquids. After the liquid evaporates, the nanocellulose will polymerize into transparent nanocellulose paper. The flexible film substrate 1 prepared therefrom has insulation, hydrophilicity, degradability, and high flexibility and smoothness. Figure 3 This is an electron microscope image of the flexible film substrate 1. It can be seen that in the flexible film substrate 1, nanocellulose is interwoven to form a three-dimensional microporous network structure, which has high smoothness, good hydrophilicity and flexibility, and can meet the needs of a flexible wet distance sensing film.

[0033] The materials of the central lead 2 and the spiral humidity sensitive layer 4 are both conductive filler / nanocellulose conductive humidity sensitive composite materials. The conductive filler can be a nano conductive filler such as carbon nanotubes, carbon black, graphene, nano silver particles or nano silver wires. Among them, multi-walled carbon nanotubes (MWCNT) as quasi-one-dimensional nanomaterials have excellent electrical properties, chemical properties, high aspect ratio and large specific surface area, and are suitable for preparing multi-walled carbon nanotube / nanocellulose (MWCNT / CNF) conductive humidity sensitive composite materials as a conductive phase. Figure 4 This is an electron microscope image of a conductive humidity-sensitive composite material with multi-walled carbon nanotubes and nanocellulose mass fractions of 0.5wt% and 1wt%, respectively. It can be seen that the multi-walled carbon nanotubes are evenly dispersed in the nanocellulose, forming an interwoven network structure and a conductive network inside. Therefore, the multi-walled carbon nanotube / nanocellulose conductive humidity-sensitive composite material has good conductivity, hydrophilicity and flexibility.

[0034] The humidity sensing process and distance sensing process of the above-mentioned flexible wet distance sensing film are as follows:

[0035] During the humidity sensing process, when the ambient humidity increases, water molecules are quickly captured by nanocellulose and adsorbed in the micropores of the composite material. After the composite material absorbs water and expands, a part of the conductive network formed by the interweaving of carbon nanotubes is destroyed, causing the resistance of the sensor element to increase. When the ambient humidity decreases, water molecules are desorbed from the micropores and the resistance of the sensor element decreases. Therefore, humidity sensing can be achieved by detecting the change in the resistance of the sensor element with humidity.

[0036] In the distance sensing process, the sensor element generates an alternating magnetic field under AC excitation, which stimulates eddy currents in the target object to resist the alternating magnetic field. When the distance between the sensor element and the target object increases, the resisting magnetic field generated by the eddy currents in the target object increases, causing the equivalent impedance of the sensor element to increase. Conversely, when the distance decreases, the equivalent impedance of the sensor element decreases. The distance between the sensor element and the target object can be sensed by detecting the change in the impedance of the sensor element with distance.

[0037] A method for preparing a flexible wet distance sensing film based on a direct writing (DIW) 3D process comprises the following steps:

[0038] 1) Design the size and shape parameters of the flexible wet distance sensing film according to the application scenario;

[0039] 2) adding 0.15 g of nanocellulose to 8.85 ml of pure water, mechanically stirring for 6 h, and then ultrasonically dispersing for 0.5 h, with an ultrasonic power of 200 w and an ultrasonic frequency of 40 kHz, to prepare a nanocellulose aqueous solution with a mass fraction of 1 wt%, pouring the nanocellulose aqueous solution into a mold, and drying at room temperature for 12 h to obtain a flexible film substrate 1;

[0040] 3) 0.1 g of nanocellulose and 0.05 g of multi-walled carbon nanotubes were added to 9.85 ml of pure water, mechanically stirred for 6 h and ultrasonically dispersed for 0.5 h, with an ultrasonic power of 200 w and an ultrasonic frequency of 40 kHz, and stirring was continued for 1 h to obtain a multi-walled carbon nanotube / nanocellulose conductive humidity-sensitive composite material with a mass fraction of multi-walled carbon nanotubes and nanocellulose of 0.5 wt% and 1 wt%, respectively;

[0041] 4) Figure 2 The apparatus used in the direct writing 3D printing process is schematically described, based on Figure 2The device shown in the figure first uses CAD to draw the trajectory diagram of the center lead 2, the insulating layer 3 and the spiral humidity sensitive layer 4 according to the size and shape parameters of the sensor element, imports the trajectory file into the 3D printer 5, levels the printing table 7 of the 3D printer 5, and places the flexible film substrate 1 on the printing table 7; then injects the conductive humidity sensitive composite material into the extrusion device 8, the extrusion device 8 is connected to the air inlet pipe 9, and is fixed to the Z-axis motion mechanism 6 of the 3D printer 5; then starts the 3D printer 5, selects the trajectory file corresponding to the center lead 2, adjusts the input air pressure, extrudes the conductive humidity sensitive composite material at a suitable speed, prints the center lead 2 on the flexible film substrate 1, and dries it at room temperature for 0.5h;

[0042] 5) injecting the nanocellulose aqueous solution into the extrusion device 8, selecting the trajectory file corresponding to the insulating layer 3, adjusting the input air pressure, continuing to print the insulating layer 3 on the flexible film substrate 1, and drying at room temperature for 0.5h;

[0043] 6) Inject the conductive humidity-sensitive composite material into the extrusion device 8, select the trajectory file corresponding to the spiral humidity-sensitive layer 4, adjust the input air pressure, continue to print the spiral humidity-sensitive layer 4 on the flexible film substrate 1, and obtain the flexible humidity distance sensing film after drying at room temperature for 0.5 hours.

[0044] The present invention uses nanocellulose as a substrate material and a base material to prepare a flexible wet distance sensing film, so that the film has intrinsic flexibility and is very light and thin, and can be applied to a narrow curved surface environment; the conductive filler / nanocellulose conductive moisture-sensitive composite material is spiralized and an insulating layer is prepared to lead out a central lead, so that the obtained flexible wet distance sensing film can detect humidity through resistance under direct current excitation and detect distance through impedance under alternating current excitation; at the same time, the central lead, the insulating layer and the spiral moisture-sensitive layer are patterned on the flexible film substrate through a direct writing 3D printing process, which not only improves the preparation efficiency of the flexible wet distance sensing film, but also improves the consistency of the preparation process.

[0045] The above description is only for the best embodiment of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. All changes made within the scope of protection of the independent claims of the present invention are within the scope of protection of the present invention.

Claims

1. A flexible wet distance sensing film based on direct writing 3D printing, characterized in that: It comprises a flexible film substrate (1), a central lead (2), an insulating layer (3), and a spiral humidity sensitive layer (4); The flexible film substrate (1) and the insulating layer (3) are made of nanocellulose paper. Nanocellulose is a nanofiber material separated from natural cellulose, with a diameter of 1 to 100 nm and a length of several micrometers. It has the characteristics of macroscopic cellulose and nanomaterials, and is renewable, degradable, and has a high aspect ratio and specific surface area. The nanocellulose paper produced has a three-dimensional microporous network structure, high smoothness, good flexibility and hydrophilicity, and can meet the requirements of flexible wet distance sensing film. One end of the central lead (2) is connected to the center of the spiral humidity sensitive layer (4), and the other end is connected to the test circuit; The insulating layer (3) covers the center lead (2), is tightly connected to the flexible film substrate, and has electrical insulation properties; The spiral humidity sensitive layer (4) is a planar spiral structure, covering the insulating layer (3), and tightly connected to the flexible film substrate (1). The center of the spiral is connected to the center lead (2), and the other end is connected to the test circuit. The central lead (2) and the spiral humidity sensitive layer (4) are made of a conductive humidity sensitive composite material, which is composed of a mixture of nanocellulose and a conductive filler, wherein the conductive filler is a nano conductive filler such as carbon nanotubes, carbon black, graphene, nano silver particles or nano silver wires; The method for preparing a flexible wet distance sensing film based on direct writing 3D printing comprises the following steps: 1) Design the size and shape parameters of the flexible wet distance sensing film; 2) weighing and mixing nanocellulose and pure water, preparing a nanocellulose aqueous solution by mechanical stirring for 6 hours and ultrasonic dispersion for 0.5 hours, pouring the nanocellulose aqueous solution into a mold, and drying at room temperature for 12 hours to obtain a flexible film substrate (1); 3) weighing and mixing nanocellulose, nanoconductive filler and pure water, mechanically stirring for 6 hours, ultrasonically dispersing for 0.5 hours, and continuing to stir for 1 hour to prepare a nanoconductive filler / nanocellulose conductive humidity-sensitive composite material; 4) printing a center lead (2) on the flexible film substrate (1) by a direct writing 3D printing process, and drying at room temperature for 0.5 h; 5) Continue to print the insulating layer (3) on the flexible film substrate (1), and dry at room temperature for 0.5 h; 6) Continue to print the spiral humidity sensitive layer (4) on the flexible film substrate (1), and dry it at room temperature for 0.5 hours to obtain a flexible humidity sensing film.

Images