A flexible wet distance sensing film based on direct writing 3D printing and its preparation method

Abstract

Disclosed are 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 center lead, an insulating layer, and a spiral humidity sensitive layer. The preparation method comprises first designing the shape and size of a sensing element, preparing a flexible film substrate made of nanocellulose, and preparing a nano-conductive filler / nanocellulose conductive humidity sensitive composite material. After printing and preparing a center lead and an insulating layer on the substrate, the spiral humidity sensitive layer is continuously printed, and the flexible wet distance sensing film is obtained after drying at room temperature. The present invention uses direct writing 3D printing technology to spiral the conductive humidity sensitive composite material on the flexible film substrate and prepare an insulating layer to lead out the center lead. The obtained flexible wet distance sensing film is intrinsically flexible and thin, and can be applied to narrow curved surface environments. The sensing film can detect humidity under DC excitation and detect distance under AC excitation. The preparation efficiency and process consistency of the film are also 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 advancement of science and technology, facilities and equipment in industrial applications are becoming increasingly miniaturized and integrated, resulting in an increasing number of narrow curved structures, such as the ball-jointed hinges in industrial robots and the pipes, bearings, and turbine blades in aerospace facilities. To ensure industrial safety and engineering efficiency, and to prevent equipment aging from causing losses to human safety and industrial production, it is necessary to ensure that the temperature, humidity, and surface gaps in these narrow curved structures remain appropriate. Traditional sensors, due to their inherent rigidity and large size, are difficult to apply to the narrow curved environments that are prevalent in industrial applications. To overcome these shortcomings, it is necessary to develop a flexible, thin-film sensor element that can be applied to complex curved environments, enabling it to not only measure humidity in narrow environments but also monitor the distance between narrow curved surfaces. Summary of the Invention

[0003] (1) Problems to be solved

[0004] With the advancement of science and technology, facilities and equipment in industrial applications are becoming increasingly miniaturized and integrated, resulting in an increasing number of narrow curved structures, such as the ball-jointed hinges in industrial robots and the pipes, bearings, and turbine blades in aerospace facilities. To ensure industrial safety and engineering efficiency, and to prevent equipment aging from causing losses to human safety and industrial production, it is necessary to ensure that the temperature, humidity, and surface gaps in these narrow curved structures remain appropriate. Traditional sensors, due to their inherent rigidity and large size, are difficult to apply to the narrow curved environments that are prevalent in industrial applications. To overcome these shortcomings, it is necessary to develop a flexible, thin-film sensor element that can be applied to complex curved environments, enabling it to not only measure humidity in narrow environments but also monitor the distance between narrow curved surfaces.

[0005] (2) Technical solution

[0006] The present invention provides a technical solution to solve the above problems: 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 both macrocellulose and nanomaterials, and is renewable and degradable, with a high aspect ratio and specific surface area. The nanocellulose paper produced has a three-dimensional microporous network structure, high smoothness, good hydrophilicity and flexibility, and can meet the requirements of flexible wet distance sensing films.

[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 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 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;

[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 h, ultrasonically dispersing for 0.5 h, and continuing stirring for 1 h to prepare a nanoconductive filler / nanocellulose conductive humidity-sensitive composite material;

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

[0017] 5) Continue printing 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 wet distance sensing film.

[0019] (3) 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 used for measurements in narrow curved surface environments.

[0022] (2) The present invention spirals the nano-conductive filler / nano-cellulose conductive moisture-sensitive composite material and prepares an insulating layer to lead out the center 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 Schematic diagram of the 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 This is an electron micrograph of a conductive humidity-sensitive composite material containing 0.5wt% and 1wt% of multi-walled carbon nanotubes and nanocellulose;

[0029] Figure markings: 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. However, 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, namely 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 flexible film substrate 1 and the insulating layer 3 are both made of 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 both macrocellulose 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 nanocellulose is interwoven in the flexible film substrate 1 to form a three-dimensional microporous network structure, which has high smoothness, good hydrophilicity and flexibility, and can meet the requirements of flexible wet distance sensing film.

[0033] The center lead 2 and the spiral humidity-sensitive layer 4 are both made of a conductive filler / nanocellulose conductive humidity-sensitive composite material. The conductive filler can be a nano-conductive filler such as carbon nanotubes, carbon black, graphene, nanosilver particles, or nanosilver wires. Multi-walled carbon nanotubes (MWCNTs) are quasi-one-dimensional nanomaterials with excellent electrical and chemical properties, high aspect ratio, and large specific surface area. They are suitable for use as a conductive phase in preparing a multi-walled carbon nanotube / nanocellulose (MWCNT / CNF) conductive humidity-sensitive composite material. Figure 4 This is an electron microscope image of a conductive humidity-sensitive composite material with a mass fraction of multi-walled carbon nanotubes and nanocellulose 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 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, part of the conductive network formed by the interwoven carbon nanotubes is destroyed, causing the resistance of the sensing element to increase. When the ambient humidity decreases, water molecules are desorbed from the micropores and the resistance of the sensing element decreases. Therefore, humidity sensing can be achieved by detecting the change in the resistance of the sensing element with humidity.

[0036] During the distance sensing process, the sensing 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 sensing 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 sensing element to increase. Conversely, when the distance decreases, the equivalent impedance of the sensing element decreases. By detecting the change in the impedance of the sensing element with distance, the distance between the sensing element and the target object can be sensed.

[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 at 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 %. The nanocellulose aqueous solution was poured into a mold and dried 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 at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. 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 2In the device shown, a CAD drawing is first used to draw a trajectory diagram of the center lead 2, the insulating layer 3, and the spiral humidity-sensitive layer 4 based on the size and shape parameters of the sensor element. The trajectory file is then imported into a 3D printer 5. The printing table 7 of the 3D printer 5 is leveled, and the flexible film substrate 1 is placed on the printing table 7. The conductive humidity-sensitive composite material is then injected into an extruder 8, which is connected to an air inlet pipe 9 and fixed to the Z-axis motion mechanism 6 of the 3D printer 5. The 3D printer 5 is then started, the trajectory file corresponding to the center lead 2 is selected, and the input air pressure is adjusted to extrude the conductive humidity-sensitive composite material at an appropriate speed. The center lead 2 is printed on the flexible film substrate 1, and the product is dried at room temperature for 0.5 hours.

[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, and continuing to print the insulating layer 3 on the flexible film substrate 1, and drying at room temperature for 0.5 h;

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

[0044] The present invention uses nanocellulose as a substrate material and a matrix material to prepare a flexible wet distance sensing film, making it intrinsically flexible and very thin, and applicable to narrow curved surface environments; the conductive filler / nanocellulose conductive moisture-sensitive composite material is spiralized and an insulating layer is prepared to lead out a center lead, so that the obtained flexible wet distance sensing film can detect humidity through resistance under DC excitation and detect distance through impedance under AC excitation; at the same time, the center lead, insulating layer and 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 merely a description of the preferred embodiment of the present invention and is not to be construed as limiting the scope of the claims. The present invention is not limited to the above embodiment, and variations in the specific structure are permitted. Any variations within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

Claims

1. A flexible wet distance sensing film based on direct writing 3D printing, characterized by: 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 microns. It has the characteristics of both macrocellulose 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 films. 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 h, ultrasonically dispersing for 0.5 h, and continuing stirring for 1 h 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 printing the insulating layer (3) on the flexible film substrate (1) and dry it 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 wet distance sensing film.

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