A resistive porous flexible pressure sensor and a manufacturing method thereof

Abstract

A kind of resistive porous flexible pressure sensor and its manufacturing method, sensor is sandwich structure as a whole, bottom layer is structural substrate, surface layer is contact layer, middle layer is composed of several discrete sensitive units, discrete sensitive unit is composed of porous structure and conductive fiber, conductive fiber is embedded in porous structure and has multiple cross-sectional crack structures, separating cutting groove is arranged between adjacent discrete sensitive units, separating groove corresponding to cutting groove is opened in contact layer.The manufacturing method is to use molding spin coating process to prepare support structure first, then the coupling integration of conductive fiber is carried out using 3D printing method, finally the integrated controllable and reliable manufacturing of pressure sensor is completed using high-temperature foaming stretching and laser cutting process;The resistive porous flexible pressure sensor of the application can significantly improve the detection sensitivity and detection range of the pressure sensor on the one hand, and can realize the sensing decoupling of the contact interface for the measurement of distributed pressure on the other hand.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sensors, and particularly relates to a resistive porous flexible pressure sensor and a manufacturing method thereof. BACKGROUND

[0002] Compared with traditional rigid sensors, flexible sensors have attracted extensive attention of researchers in recent years due to their flexible characteristics such as bendability, extensibility and conformal adhesion to complex surfaces, and have shown great potential application value in wearable devices, soft robots, electronic skin and human-computer interaction.

[0003] As an important part of flexible sensors, the resistive porous flexible pressure sensor has attracted attention due to its simple structure, convenient signal collection and good linearity. The working principle of the resistive porous flexible pressure sensor is to convert external pressure stimulation into resistance change of a porous sensitive material in the sensor, to control the numerical value of an output voltage or current signal, and to realize quantitative feedback of external pressure through linear calibration. At present, the preparation methods of the porous sensitive material can be divided into two categories: one is to process a conductive material which does not have a porous structure into a porous conductor by means of 3D printing, etching and the like; and the other is to form a porous conductor by attaching a layer of conductive material inside or on the surface of a porous structure material by means of dipping, screen printing, inkjet printing and the like. Although the first manufacturing method can significantly improve the stability and durability of the sensor, it has many shortcomings such as complex preparation process, high cost and difficulty in large-scale production. Although the second step-by-step manufacturing method is simple in preparation process, low in cost and easy to mass-produce, the attached conductive material is prone to fall off during use, which seriously limits the stability and durability of the sensor. How to complement the advantages and offset the disadvantages of the above two methods is a technical constraint for the leap-forward development of the resistive porous flexible pressure sensor. SUMMARY

[0004] In order to solve the above technical problems of the prior art, the present application aims to provide a resistive porous flexible pressure sensor which can be manufactured integrally, has a simple preparation process, is low in cost, has high sensitivity, a wide detection range and good stability and durability, and can decouple the sensing signal for distributed pressure measurement.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0006] A resistive porous flexible pressure sensor, which is a sandwich structure as a whole, has a structural substrate as a bottom layer, a contact layer as a surface layer, and a middle layer composed of a plurality of discrete sensing units; the discrete sensing unit is composed of a porous structure and a conductive fiber, the conductive fiber is embedded in the porous structure and has a plurality of cross-section crack structures; a separate cutting groove is arranged between adjacent discrete sensing units, and a separate groove corresponding to the cutting groove is arranged on the contact layer.

[0007] A manufacturing method of a resistive porous flexible pressure sensor, comprising the following steps:

[0008] In the first step, a support structure is prepared: a composite material in a flow state is molded in a machined millimeter-scale template, and the excess composite material on the surface of the machined millimeter-scale template is removed by a spin coating process; then a layer of polymer is continuously filled on the surface of the machined millimeter-scale template as a structural substrate, the composite material and the structural substrate are heated at 50℃ for 4 hours for curing treatment, and after demolding, a support structure with an array of units on the surface is obtained;

[0009] In the second step, the conductive fiber is coupled and integrated: the 3D printing process parameters are set, the conductive fiber and the lead circuit are printed on the surface of each unit of the support structure by using a 3D printer, the conductive fiber and the lead circuit are bonded to the surface of the unit and remain shaped; a layer of composite material is continuously filled on the conductive fiber and the lead circuit, then the support structure, the conductive fiber and the lead circuit, and the continuously filled composite material are subjected to pre-curing treatment to obtain a pre-cured structure; finally, a layer of polymer is spin-coated on the surface of the pre-cured structure as a contact layer, and the pre-cured structure and the contact layer are heated at 50℃ for 4 hours for curing to obtain a cured self-connected structure;

[0010] In the third step, the resistive porous flexible pressure sensor is integrally prepared: the cured self-connected structure obtained in the second step is subjected to high-temperature foaming, so that the composite material in the first step to the second step expands into a porous structure, and the conductive fiber is stretched to generate a plurality of cross-section crack structures; then the surface of the foamed cured self-connected structure is customized cut by using a laser to obtain the resistive porous flexible pressure sensor.

[0011] In the first step to the second step, the composite material is obtained by mixing a polymer and a foaming agent in a mass ratio of 100:5-10 and fully stirring for 10 hours by using a small mixer; the foaming agent is selected from sodium bicarbonate, ammonium bicarbonate, azobis isobutyronitrile, or phenyl sulfonyl hydrazine.

[0012] In the second step, the 3D printer is a fused deposition modeling or ink direct writing modeling printer; the material of the conductive fiber and the lead circuit is selected to be a conductive polymer and has a viscosity coefficient of 300-500 Pa·s.

[0013] The pre-cured process parameters in the second step are heating at 50 DEG C for 5 minutes.

[0014] The contact layer thickness in the second step is in the order of 100 microns.

[0015] The polymers involved in the first and second steps are both silicone rubber or polyurethane.

[0016] The high-temperature foaming process parameters in the third step are heating at 60-110 DEG C for 1-5 minutes.

[0017] The present application has the following advantages:

[0018] The present application provides a resistive porous flexible pressure sensor and a manufacturing method thereof. The resistive porous flexible pressure sensor can utilize the excellent pressure-induced deformability of the high-porosity porous structure to drive the opening and closing changes of the cross-sectional crack structure of the conductive fiber, so that the number of conductive paths changes suddenly, significantly improving the detection sensitivity and detection range of the pressure sensor to pressure. On the other hand, since the stress of each discrete sensing unit in the intermediate layer is independent and does not affect each other, the sensing decoupling of the contact interface can be realized for the measurement of distributed pressure. Secondly, the low-cost, high-efficiency multi-structure, multi-material foaming stretching manufacturing process can realize the integrated controllable and reliable manufacturing of the resistive porous flexible pressure sensor, significantly improving its stability and fatigue service life. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 FIG. 1 is a structural schematic diagram of the resistive porous flexible pressure sensor of the present application.

[0020] Figure 2 FIG. 4 is a schematic diagram of the resistance change of each discrete sensing unit when the resistive porous flexible pressure sensor of the present application is in contact with the target surface and bears distributed pressure.

[0021] Figure 3 FIG. 6 is a schematic diagram of the present application after molding and filling the composite material in the machined millimeter-scale template.

[0022] Figure 4 FIG. 8 is a structural schematic diagram of the support structure of the present application.

[0023] Figure 5 FIG. 10 is a schematic diagram of the present application for 3D printing of conductive fibers and lead circuits on the surface of the support structure.

[0024] Figure 6 FIG. 12 is a schematic diagram of the present application for continuing to fill the composite material to cover the conductive fibers and lead circuits on the surface of the support structure.

[0025] Figure 7 FIG. 14 is a structural schematic diagram of the solidified self-connected structure of the present application.

[0026] Figure 8 Schematic diagram for generating porous structure by high temperature foaming and introducing cross-sectional crack structure to conductive fiber of the present application.

[0027] Figure 9 Schematic diagram for laser cutting process of the present application.

[0028] In the figure: 1, structural substrate; 2, contact layer; 3, porous structure; 4, conductive fiber; 5, cross-sectional crack structure; 6, target surface; 7, machined millimeter scale template; 8, composite material; 9, 3D printer; 10, laser; 11, cutting groove. DETAILED DESCRIPTION

[0029] The present application will be described in detail below with reference to the accompanying drawings and examples.

[0030] Reference Figure 1 A resistive porous flexible pressure sensor, which is a sandwich structure as a whole, the bottom layer is a structural substrate 1, the surface layer is a contact layer 2, and the middle layer is composed of a plurality of discrete sensitive units; the discrete sensitive unit is composed of a porous structure 3 and a conductive fiber 4, the conductive fiber 4 is embedded in the interior of the porous structure 3 and has a plurality of cross-sectional crack structures 5; a separate cutting groove 11 is provided between adjacent discrete sensitive units, and a separate groove corresponding to the cutting groove 11 is provided on the contact layer 2.

[0031] In the specific implementation process, the high-porosity porous structure 3 has excellent pressure-induced deformability, which can drive the cross-sectional crack structure 5 in the conductive fiber 4 to open and close during compression (i.e. micro-crack mechanism), so that the number of conductive paths changes suddenly, significantly improving the detection sensitivity and detection range of the pressure sensor to pressure; secondly, since each discrete sensitive unit in the middle layer is stressed independently / independently, the sensing decoupling of the contact interface can be realized: when the pressure sensor is in contact with the target surface 6 (the target surface 6 is an inclined plane) and bears distributed pressure, the discrete sensitive unit bearing larger pressure deforms more and the resistance changes more obviously, referring to Figure 2 That is, |ΔR1|>|ΔR2|>|ΔR3|>|ΔR4|>|ΔR5|.

[0032] A manufacturing method of a resistive porous flexible pressure sensor, comprising the following steps:

[0033] First step, preparation of support structure: referring to Figure 3In the low surface energy treated machined millimeter scale template 7, the composite material 8 filled with flow state is molded, and the excess composite material 8 on the surface of the machined millimeter scale template 7 is removed by the spin coating process. The spin coating process parameters are low speed 1000 rpm for 10 seconds, and high speed 5000 rpm for 50 seconds. Then, a layer of polymer with millimeter level thickness is filled on the surface of the machined millimeter scale template 7 as a structural substrate 1. The composite material 8 and the structural substrate 1 are placed in a 50°C environment for 4 hours to realize curing, and after demolding, a support structure with array units on the surface is obtained, as shown in Figure 4 ;

[0034] Preferably, the composite material 8 is obtained by mixing the polymer and the foaming agent at a mass ratio of 100:5-10 and fully stirring for 10 hours by a small mixer. The foaming agent is selected from materials that are easy to obtain, have large gas generation capacity, and have a decomposition temperature greater than 50°C, such as sodium bicarbonate, ammonium bicarbonate, azoisobutyronitrile, or phenylsulfonyl hydrazine.

[0035] Second step, coupling and integration of conductive fibers: referring to Figure 5 , the 3D printing process parameters are set, and a fused deposition modeling or ink direct writing modeling type 3D printer 9 is used to print conductive fibers 4 and lead circuits on the surface of each unit of the support structure. Since the just-printed conductive fibers 4 and lead circuits have viscosity, they can adhere to the unit surface and remain shaped. Then, a layer of composite material 8 with millimeter level thickness is filled on the conductive fibers 4 and lead circuits to cover them, and the pre-cured structure is obtained, as shown in Figure 6 ; then the spin coating parameters are set, a layer of polymer is spin coated on the surface of the pre-cured structure as a contact layer 2, and the pre-cured structure and the contact layer 2 are cured and self-connected by being placed in a 50°C environment for 4 hours, to obtain a cured and self-connected structure, as shown in Figure 7 ;

[0036] Preferably, the thickness of the contact layer 2 is in the order of hundreds of microns to improve the pressure-induced deformability of the resistive porous flexible pressure sensor.

[0037] Preferably, the material of the conductive fibers 4 and lead circuits is selected from TangoBlackPlus FLX980 conductive polymer, Eel conductive TPU fiber, or PDMS / CNTs composite material, and the viscosity coefficient is 300-500 Pa·s.

[0038] Preferably, the polymers involved in the first and second steps are both silicon rubber or polyurethane of the same material.

[0039] Third step, integrated preparation of the resistive porous flexible pressure sensor: the cured self-connected structure obtained in the second step is heated at 60-110°C for 1-5 minutes for high-temperature foaming. In this process, the blowing agent decomposes into gas, causing the composite material 8 to expand into a porous structure 3 in the first step to the second step. Meanwhile, the tensile stress generated during foaming promotes the cross-sectional crack structure 5 of the conductive fiber 4 to introduce micro-crack sensing effect, as shown in Figure 8 ; then the laser cutting process parameters are set, and the laser 10 is used to perform customized cutting on the surface of the foamed cured self-connected structure to realize integrated controllable and reliable manufacturing of the resistive porous flexible pressure sensor, as shown in Figure 9 .

[0040] The resistive porous flexible pressure sensor can utilize the excellent pressure-induced deformability of the high-porosity porous structure to drive the opening and closing changes of the cross-sectional crack structure in the conductive fiber, so that the number of conductive paths changes suddenly, significantly improving the detection sensitivity and detection range of the pressure sensor to pressure. On the other hand, since the stress of each discrete sensitive unit in the intermediate layer is independent / does not affect each other, the sensing decoupling of the contact interface can be realized for the measurement of distributed pressure. Secondly, the low-cost and high-efficiency multi-structure and multi-material foaming and stretching manufacturing process can realize the integrated controllable and reliable manufacturing of the resistive porous flexible pressure sensor, significantly improving its stability and fatigue service life.

Claims

1. A method of manufacturing a resistive porous flexible pressure sensor, characterized by: The method is used for manufacturing a resistive porous flexible pressure sensor, which is a sandwich structure as a whole, the bottom layer is a structural substrate (1), the surface layer is a contact layer (2), and the middle layer is composed of a plurality of discrete sensitive units; the discrete sensitive unit is composed of a porous structure (3) and a conductive fiber (4), the conductive fiber (4) is embedded in the porous structure (3) and has a plurality of cross-section crack structures (5); a separate cutting groove (11) is arranged between adjacent discrete sensitive units, and a separate groove corresponding to the cutting groove (11) is arranged on the contact layer (2); The method comprises the following steps: In the first step, the preparation of the support structure: the composite material (8) in a flow state is molded in the machined millimeter-scale template (7), and the excess composite material (8) on the surface of the machined millimeter-scale template (7) is removed by using a spin coating process; then a layer of polymer is continuously filled on the surface of the machined millimeter-scale template (7) as a structural substrate (1), the composite material (8) and the structural substrate (1) are heated at 50 DEG C for 4 hours for curing treatment, and after demolding, a support structure with array units on the surface is obtained; In the second step, the coupling and integration of the conductive fiber: the 3D printing process parameters are set, the conductive fiber (4) and the lead circuit are printed on the surface of each unit of the support structure by using a 3D printer (9), the conductive fiber (4) and the lead circuit are bonded to the unit surface and remain shaped; a layer of composite material (8) is continuously filled on the conductive fiber (4) and the lead circuit, then the support structure, the conductive fiber (4) and the lead circuit and the continuously filled composite material (8) are subjected to pre-curing treatment to obtain a pre-cured structure; finally, a layer of polymer is spin-coated on the surface of the pre-cured structure as a contact layer (2), the pre-cured structure and the contact layer (2) are heated at 50 DEG C for 4 hours for curing to obtain a cured self-connected structure; In the third step, the integrated preparation of the resistive porous flexible pressure sensor: the cured self-connected structure obtained in the second step is subjected to high-temperature foaming, so that the composite material (8) in the first step to the second step is expanded into a porous structure (3), and the conductive fiber (4) is stretched to generate a plurality of cross-section crack structures (5); then the surface of the foamed cured self-connected structure is customized cut by using a laser (10) to obtain the resistive porous flexible pressure sensor.

2. The method of claim 1, wherein: In the first step to the second step, the composite material (8) is obtained by mixing a polymer and a foaming agent at a mass ratio of 100:5-10 and fully stirring for 10 hours by using a small mixer; the foaming agent is selected from sodium bicarbonate, ammonium bicarbonate, azobisisobutyronitrile or benzenesulfonyl hydrazide.

3. The method of claim 1, wherein: In the second step, the 3D printer (9) is a fused deposition modeling or ink direct writing modeling printer; the conductive fiber (4) and the lead circuit material are selected to be a conductive polymer and have a viscosity coefficient of 300-500 Pa·s.

4. The method of claim 1, wherein: In the second step, the pre-curing process parameters are heating at 50 DEG C for 5 minutes.

5. The method of claim 1, wherein: In the second step, the thickness of the contact layer (2) is in the order of hundreds of microns.

6. The method of claim 1, wherein: The polymers involved in the first step and the second step are all silicon rubber or polyurethane of the same material.

7. The method of claim 1, wherein: The third step is heated for 1-5 minutes at 60-110 ℃.

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