A conductive composite material for 3D printing, a preparation method thereof, a flexible strain sensor based thereon and a manufacturing process thereof

Abstract

This invention belongs to the field of sensor technology and provides a conductive composite material for 3D printing, a preparation method thereof, a flexible strain sensor based on the composite material, and a manufacturing process thereof. The invention proposes a method for preparing a carbon nanotube / silver nanoparticle / polydimethylsiloxane conductive composite material. By mixing a one-dimensional conductive material with silver nanoparticles, the localized agglomeration of the silver nanoparticles provides more conductive pathways for the MWCNTs, effectively improving the material's conductivity and sensing performance. The invention also utilizes electric field-driven jet micro-nano 3D printing or direct-write 3D printing technology to achieve 100% material utilization, allowing for customized printing of desired pattern shapes and sizes without generating waste liquid or gas, resulting in an environmentally friendly and simple manufacturing process. The method also enables large-scale, mass-produced, and low-cost production of flexible strain sensors.

Description

Technical Field

[0001] The present invention belongs to the field of sensor technology, and specifically relates to a conductive composite material for 3D printing, a preparation method thereof, a flexible strain sensor based thereon, and a manufacturing process thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the development of modern science and technology and the rapid rise of artificial intelligence, flexible devices are playing an increasingly important role in our daily lives. As one of the core elements of flexible devices, flexible strain sensors can convert mechanical signals into electrical signals and have a wide range of applications in wearable devices, electronic skin, soft robotics, biomedicine, and human-computer interaction.

[0004] Flexible strain sensors primarily consist of a flexible layer and a conductive layer. The flexible layer determines the sensor's maximum strain range and is typically made of materials such as polydimethylsiloxane (PDMS), polyurethane, and Ecoflex. PDMS is widely used in the fabrication of flexible strain sensors due to its excellent optical transparency, flexibility, breathability, and biocompatibility. Conductive materials, a crucial component in determining strain sensor performance, typically include metallic materials (silver nanoparticles: AgNPs, silver nanowires: AgNWs, and gold nanowires: AuNWs), carbon-based materials (carbon black, carbon nanotubes, and graphene), conductive polymers, and liquid metals. Carbon nanotubes (CNTs) are widely used in flexible strain sensors due to their excellent elongation at break and elastic modulus. Their excellent aspect ratio offers numerous potential applications in flexible strain sensors.

[0005] Currently, research on carbon nanotube flexible strain sensors primarily focuses on manufacturing processes and structural design, aiming to achieve high-performance flexible strain sensor fabrication through simplified processes and low-cost consumables. Currently, the main fabrication methods for carbon nanotube flexible strain sensors include coating, chemical vapor deposition (CVD), transfer printing, spinning, and 3D printing. Coating offers simplicity and high efficiency, but the sensor structure is simple and the cost is high. Chemical vapor deposition combined with transfer printing can achieve directional alignment, but the manufacturing process is complex and the material cost is high. Flexible strain sensors fabricated using spinning generally suffer from low sensitivity, while combining it with coating can effectively improve sensitivity, but the sensor fatigue life is low. 3D printing technology can effectively reduce material waste and enable structured and patterned fabrication of flexible strain sensors. However, due to limitations in printing materials and difficulties in large-scale fabrication, coating and CVD-based fabrication of flexible strain sensors remain the mainstream technologies. At the same time, although carbon nanotube-based strain sensors have been successfully applied in various fields, due to the mutual constraints of sensitivity and stretchability, the sensors usually exhibit high sensitivity and low strain sensing range, or low sensitivity and high strain sensing range. How to achieve high sensitivity while improving the strain sensing range remains a difficult problem that needs to be solved urgently.

[0006] Therefore, it is of great significance to develop a large-area, low-cost, high-efficiency, high-sensitivity, high-stretchability flexible strain sensor manufacturing process and its conductive composite material preparation method based on 3D printing technology. Summary of the Invention

[0007] In order to solve at least one technical problem existing in the above-mentioned background technology, the present invention provides a manufacturing process for directly preparing flexible strain sensors with both sensitivity and stretchability based on microscale 3D printing, and proposes a method for preparing carbon nanotube / silver nanoparticle / PDMS conductive composite materials. The present invention can realize large-area, batch, and low-cost manufacturing of flexible strain sensors.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides a method for preparing a conductive composite material for 3D printing. The materials used mainly include carbon nanotubes (MWCNTs), silver nanoparticles (AgNPs), polydimethylsiloxane (PDMS), a dispersant material, etc. The main preparation steps are as follows:

[0010] (1) Preparing a carbon nanotube dispersion: mixing carbon nanotube powder and a dispersant solution, and ultrasonically treating the mixture to uniformly disperse the carbon nanotubes in the dispersant solution;

[0011] (2) Preparing a silver nanoparticle suspension: Silver nanoparticles and 3-glycidyloxypropyltrimethoxysilane were added to an ethanol solution in proportion, and ultrasonic dispersion was performed to ensure that the surface of the silver nanoparticles was fully coated with 3-glycidyloxypropyltrimethoxysilane. Afterwards, the suspension was placed in a vacuum drying oven to fully evaporate the ethanol. The treated silver nanoparticles were dispersed in a dispersant solution, and a stable suspension was obtained after ultrasonic treatment.

[0012] (3) Preparation of MWCNT / AgNPs / PDMS conductive composite materials: CNT dispersion, AgNPs suspension and PDMS prepolymer were mixed and stirred thoroughly under ultrasonic conditions. Then, a preset amount of PDMS curing agent was added and stirring was continued at room temperature to complete the preparation.

[0013] Furthermore, MWCNT materials include but are not limited to multi-walled carbon nanotubes and single-walled carbon nanotubes. Multi-walled carbon nanotubes with a diameter of 3-15 nm and a length of 15-30 μm are preferred, and the MWCNT mass ratio is preferably 4.7 wt%;

[0014] Furthermore, silver nanoparticles with a diameter less than 150 nm are preferred;

[0015] Furthermore, the dispersant material includes but is not limited to n-hexane, tetrahydrofuran, dichloromethane, n-heptane, etc.

[0016] A second aspect of the present invention provides a conductive composite material for 3D printing, which is prepared according to the method for preparing a conductive composite material for 3D printing according to any one of the first aspects.

[0017] A third aspect of the present invention provides a process for manufacturing a flexible strain sensor based on a conductive composite material for 3D printing, comprising the following steps:

[0018] (1) Preparation of a hydrophilic substrate: The hard substrate is cleaned and pretreated, and then a layer of hydrophilic material is coated on the surface of the hard substrate. After heating and curing, the hydrophilic substrate is prepared;

[0019] (2) Preparation of flexible substrate layer: Spin-coat a layer of liquid PDMS on the surface of the hydrophilic substrate, and heat and cure to complete the preparation of the flexible substrate layer;

[0020] (3) Printing conductive structure: Using an electric field driven jet deposition 3D printer to print a conductive circuit pattern on the substrate surface according to a preset pattern shape. The printing material is a MWCNT / AgNPs / PDMS composite material. The printing method can be selected from electric field driven jet micro-nano 3D printing or direct writing 3D printing;

[0021] (4) Post-processing: The printed sample is sintered and cured to enhance the conductivity of the circuit pattern. Finally, the prepared sample is peeled off from the hydrophilic substrate using a peel-off demolding method to obtain a MWCNT / AgNPs / PDMS flexible strain sensor with high stretchability.

[0022] Furthermore, the hard substrate in step (1) includes but is not limited to a glass sheet, a silicon wafer, an acrylic plate, etc.

[0023] Furthermore, the typical steps of the substrate cleaning pretreatment in step (1) are: placing the substrate in an isopropyl alcohol solution for ultrasonic treatment, then placing it in deionized water for ultrasonic cleaning to remove the residual isopropyl alcohol solution, and finally blowing the substrate dry with nitrogen or other inert gas.

[0024] Furthermore, the hydrophilic material in step (1) includes but is not limited to polyvinyl alcohol (PVA), hydroxypropyl methylcellulose solution, etc.

[0025] The typical preparation process of hydroxypropyl methylcellulose solution is as follows: deionized water at 90°C and hydroxypropyl methylcellulose are mixed in a weight ratio of 20:1, stirred thoroughly until the solution becomes gel-like, and allowed to stand at room temperature for 8 hours until the bubbles are completely eliminated.

[0026] The typical preparation process for PVA solution is to mix 90°C deionized water and polyvinyl alcohol powder in a weight ratio of 10:1, stirring until the polyvinyl alcohol powder is completely dissolved. The solution is then placed in a vacuum drying oven to remove air bubbles. Coating methods include, but are not limited to, spin coating, pull-coating, and 3D printing.

[0027] Furthermore, in step (1), the curing temperature of the hydrophilic material is in the range of 30-150 degrees Celsius, and the curing time is in the range of 2-60 minutes.

[0028] Furthermore, the conductive circuit pattern in step (3) includes but is not limited to mesh, line grid, diamond and other designed circuit structures. The printing parameters (printing speed, back pressure, etc.) can be adjusted according to actual needs to adjust the wire width, period, shape and arrangement. Typical patterns are shown in the attached Figure 3 shown.

[0029] Furthermore, the sintering and curing temperature of the sample printed with the conductive circuit pattern in step (4) is in the range of 60-150 degrees Celsius, and the curing time is 15-120 minutes.

[0030] A fourth aspect of the present invention provides a flexible strain sensor based on a conductive composite material for 3D printing, and the flexible strain sensor is prepared according to the manufacturing process of a flexible strain sensor based on a conductive composite material for 3D printing described in any one of the third aspects.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The preparation method of the MWCNT / AgNPs / PDMS composite material provided by the present invention uses a one-dimensional conductive material mixed with silver nanoparticles. The local agglomeration of silver nanoparticles can provide more conductive pathways for MWCNT, effectively improving the electrical conductivity and sensing performance of the material.

[0033] Attachment Figure 1 Schematic diagram of the internal conductive network of MWCNT / AgNPs / PDMS. The interconnections between MWCNTs and AgNPs provide the composite's electrical conductivity. When stress is applied to the conductive composite, the internal conductive network is continuously broken down and rebuilt. As the PDMS matrix moves, the distances between adjacent nanoparticles (AgNPs-AgNPs, CNTs-CNTs, and AgNPs-CNTs) increase as the PDMS matrix stretches, increasing the tunnel resistance. Under stress, portions of the conductive network become disconnected, increasing the composite's resistance. Upon stress release, the MWCNTs and AgNPs reorient themselves within the PDMS matrix, reconnecting the partially disconnected networks. When carbon nanotube connections are damaged, AgNPs migrate into the gaps to repair and complete the conductive paths, ensuring effective connectivity within the MWCNT / AgNPs / PDMS material and restoring the conductive composite's resistance to its initial state.

[0034] (2) The MWCNT / AgNPs / PDMS composite flexible strain sensor provided by the present invention has the characteristics of high sensitivity and high stretchability. Using electric field-driven jet micro-nano 3D printing or direct write 3D printing technology, 100% material utilization can be achieved, and the pattern shape and size can be printed according to demand. No waste liquid or waste gas is generated, and it is environmentally friendly. The manufacturing process is simple, enabling large-scale, batch, and low-cost production of flexible strain sensors.

[0035] The flexible strain sensor of the present invention can be applied to fields such as wearable sensors for monitoring human movement. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding 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.

[0037] Figure 1 Schematic diagram of the microscopic conductive network constructed by MWCNTs and AgNPs in the PDMS matrix.

[0038] Figure 2 The process steps for microscale 3D printing of MWCNT / AgNPs / PDMS flexible strain sensors.

[0039] Figure 3 To print several different graphic images using MWCNT / AgNPs / PDMS conductive composite materials.

[0040] Figure 4 The performance of MWCNT / AgNPs / PDMS flexible strain sensor with a MWCNT / AgNPs ratio of 1:20 under different tensile strains was tested.

[0041] Figure 5 Characterization of the dynamic stability of MWCNT / AgNPs / PDMS flexible strain sensor.

[0042] Figure 6 Application of MWCNT / AgNPs / PDMS flexible strain sensor in human motion monitoring, including: (a) finger; (b) wrist; (c) elbow; (d) knee.

[0043] Figure 7 Application of MWCNT / AgNPs / PDMS flexible strain sensor in sound monitoring.

[0044] Figure 8 Schematic diagram of the multi-directional sensor structure and printed graphics, including: (a) schematic diagram of the multi-directional sensor structure; (b) printed graphics of the multi-directional sensor. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0046] Example 1

[0047] In this embodiment, tetrahydrofuran is selected as the dispersant material and a direct writing 3D printing method is used to manufacture a flexible strain sensor. The specific manufacturing process is shown in the attached Figure 2 The flexible strain sensor manufactured in this embodiment can be applied to human body motion status monitoring, etc.

[0048] 1. Preparation of MWCNT / AgNPs / PDMS composite conductive materials

[0049] Step 1: Prepare carbon nanotube (MWCNT) dispersion.

[0050] A preset amount of carbon nanotube powder and tetrahydrofuran solution were mixed and ultrasonically dispersed for 10 minutes to uniformly disperse the carbon nanotubes in the tetrahydrofuran solution.

[0051] Step 2: Preparation of silver nanoparticle (AgNPs) suspension

[0052] First, silver nanoparticles and 3-glycidoxypropyltrimethoxysilane were added to a pre-set amount of ethanol solution at a weight ratio of 10:1. Ultrasonic dispersion was performed for 20 minutes to ensure that the silver nanoparticles were fully coated with 3-glycidoxypropyltrimethoxysilane. The solution was then placed in a vacuum drying oven to evaporate the ethanol. The treated silver nanoparticles were then dispersed in the dispersant solution and ultrasonically treated for 20 minutes to obtain a stable suspension.

[0053] In this embodiment, the dispersant material includes but is not limited to n-hexane, tetrahydrofuran, dichloromethane, n-heptane, etc.

[0054] Step 3: Preparation of MWCNT / AgNPs / PDMS conductive composite materials.

[0055] The carbon nanotube dispersion, the prepared silver nanoparticle suspension, and the polydimethylsiloxane (PDMS) prepolymer were mixed and stirred at 200 rpm under ultrasonic conditions for 1 hour to ensure uniform mixing of the composite solution. The mixture was then stirred thoroughly for 140 minutes at 70°C using a heat-collecting magnetic stirrer to evaporate the bulk of the tetrahydrofuran solution. A predetermined amount of PDMS curing agent was then added and stirred at room temperature for another 30 minutes. A small amount of the tetrahydrofuran solution remained in the composite material to ensure that it had the desired rheological properties for 3D printing.

[0056] 2. MWCNT / AgNPs / PDMS composite flexible strain sensor manufacturing process steps:

[0057] Step 1: Prepare a hydrophilic substrate.

[0058] Mix 90°C deionized water and hydroxypropyl methylcellulose in a weight ratio of 20:1. Stir thoroughly until the solution becomes gel-like and let it stand at room temperature for 8 hours to completely eliminate bubbles. Pour the gel-like hydroxypropyl methylcellulose onto the surface of float glass. Set the spin coater speed to 2000 r / min and the spin coat time to 60 seconds. Spin coat a layer of gel-like hydroxypropyl methylcellulose on the float glass surface. Then, let it stand at 100°C for 20 minutes to allow the water to evaporate completely, resulting in a hydrophilic hydroxypropyl methylcellulose film.

[0059] Step 2: Prepare a flexible substrate layer.

[0060] PDMS prepolymer and curing agent were mixed at a weight ratio of 10:1 and vacuum-treated to remove excess bubbles. The treated liquid PDMS was poured onto the surface of a spin-coated hydrophilic substrate. A layer of liquid PDMS was spin-coated onto the hydrophilic substrate at a spin coater speed of 500 rpm for 30 seconds. The substrate was then placed in a vacuum drying oven at 100°C for 10 minutes to cure, yielding a flexible substrate layer.

[0061] Step 3: Print the conductive structure.

[0062] The designed conductive pattern structure is converted into motion code that can be recognized by the printing program using corresponding software. The code is then imported into the 3D printing device. The prepared MWCNT / AgNPs / PDMS conductive composite material is used as the printing material. The appropriate printing parameters (air pressure, printing height, printing speed, etc.) are adjusted to print the designed conductive pattern structure on the flexible substrate layer.

[0063] Conductive circuit patterns include but are not limited to mesh, line grid, diamond and other designed circuit structures. Printing parameters (printing speed, back pressure, etc.) can be adjusted according to actual needs to adjust the wire width, period, shape and arrangement. Typical patterns are shown in the attached Figure 3 shown.

[0064] In this embodiment, the printed pattern is a wire grid structure, the wire grid period is 1 mm, and the wire width is about 150 microns.

[0065] Step 4: Conductive post-treatment.

[0066] The printed conductive structure is cured at 100°C for 1 hour to ensure a complete bond between the conductive structure and the flexible substrate. A layer of stretchable conductive silver paste is then evenly applied to both ends of the conductive structure and cured at 100°C for another 1 hour to fully evaporate the organic solvent in the paste and improve conductivity. Conductive copper tape is then adhered to the silver paste, and the circuit is encapsulated with liquid PDMS to ensure a stable circuit connection. Finally, the encapsulated sensor is peeled off from the hydrophilic substrate using a peel-off demolding method, resulting in a highly stretchable MWCNT / AgNPs / PDMS flexible strain sensor.

[0067] The flexible strain sensor manufactured in Example 1 can be used to detect strain exceeding 100%. Figure 4 To test the performance of flexible strain sensors under different tensile strains, Figure 5To characterize the dynamic stability of the flexible strain sensor, the experimental results show that the flexible strain sensor manufactured in Example 1 can fully meet the various motion detection needs of the human body. In order to test the application of the sensor in wearable devices, the sensors are installed on the fingers, wrists, elbows and knees of the human body, and the relative resistance changes of the sensors under large and medium-sized strain are tested. The experimental results are shown in the attached figure. Figure 6 Flexible strain sensors are also suitable for small strain monitoring. To verify the feasibility of MWCNT / AgNPs / PDMS flexible strain sensors in a small strain range, the sensors were installed on the vocal cords to identify signal changes during vocalization. The experimental results are shown in the attached figure. Figure 7 shown.

[0068] Example 2

[0069] Tetrahydrofuran is selected as the dispersant material, polyvinyl alcohol (PVA) is selected as the hydrophilic material, and an electric field-driven jet micro-nano 3D printing method is adopted. The flexible strain sensor manufactured in this embodiment can be applied to multi-directional monitoring.

[0070] 1. Preparation of MWCNT / AgNPs / PDMS composite conductive materials

[0071] Step 1: Prepare carbon nanotube dispersion.

[0072] A preset amount of carbon nanotube powder and tetrahydrofuran solution were mixed and ultrasonically dispersed for 10 minutes to uniformly disperse the carbon nanotubes in the tetrahydrofuran solution.

[0073] Step 2: Preparation of AgNPs suspension.

[0074] First, silver nanoparticles and 3-glycidoxypropyltrimethoxysilane were added to a predetermined amount of ethanol solution at a ratio of 1:0.1. Ultrasonic dispersion was performed for 30 minutes to ensure that the silver nanoparticles were fully coated with 3-glycidoxypropyltrimethoxysilane. The solution was then placed in a vacuum drying oven to evaporate the ethanol. The treated silver nanoparticles were then dispersed in a tetrahydrofuran solution and ultrasonically treated for 20 minutes to obtain a stable suspension.

[0075] Step 3: Preparation of MWCNT / AgNPs / PDMS conductive composite materials.

[0076] The carbon nanotube dispersion, AgNPs suspension, and PDMS prepolymer were mixed and stirred at 300 rpm under ultrasonic conditions for 0.8 h to ensure uniform mixing of the composite solution. The mixture was then stirred thoroughly at 70°C for 140 min using a heat-collecting magnetic stirrer to evaporate the bulk of the tetrahydrofuran solution. A predetermined amount of PDMS curing agent was then added and stirred at room temperature for another 30 min. A small amount of the tetrahydrofuran solution remained in the composite to ensure the material had adequate rheological properties for 3D printing.

[0077] 2. MWCNT / AgNPs / PDMS composite flexible strain sensor manufacturing process steps:

[0078] Step 1: Prepare a hydrophilic substrate.

[0079] Mix 90°C deionized water and hydroxypropyl methylcellulose in a ratio of 20:1, stir thoroughly until the solution becomes gel-like, and let it stand at room temperature for 8 hours to completely eliminate bubbles. Pour the gel-like hydroxypropyl methylcellulose onto the surface of float glass. Set the spin coater speed to 2000 r / min and the spin coat time to 60 seconds. Spin coat a layer of gel-like hydroxypropyl methylcellulose on the float glass surface. Then, let it stand at 100°C for 20 minutes to allow the water to evaporate completely, resulting in a hydrophilic hydroxypropyl methylcellulose film.

[0080] Step 2: Prepare a flexible substrate layer.

[0081] PDMS prepolymer and curing agent were mixed in a ratio of 15:1 and vacuum-treated to remove excess bubbles. The treated liquid PDMS was poured onto the surface of a spin-coated hydrophilic substrate. A layer of liquid PDMS was spin-coated onto the hydrophilic substrate at a spin coater speed of 500 rpm for 30 seconds. The substrate was then placed in a vacuum drying oven at 100°C for 10 minutes to cure, yielding a flexible substrate layer.

[0082] Step 3: Print the conductive structure.

[0083] The designed multi-directional sensor structure is converted into motion code using the corresponding software, and the code is imported into the 3D printing device. The prepared MWCNT / AgNPs / PDMS conductive composite material is used as the printing material, and the appropriate printing parameters (voltage, air pressure, printing height, printing speed, etc.) are adjusted to print the designed conductive graphic structure on the flexible substrate layer. The printed structure of this embodiment is shown in the attached figure. Figure 8 shown.

[0084] Step 4: Conductive post-treatment.

[0085] The printed conductive structure is cured at 100°C for one hour to ensure a complete bond between the conductive structure and the flexible substrate. A layer of stretchable conductive silver paste is then applied to the conductive structure's terminals and cured at 100°C for another hour to fully evaporate the organic solvent and improve conductivity. Conductive copper tape is then applied to the silver paste, and the circuit is encapsulated with liquid PDMS to ensure a stable connection.

[0086] Attachment Figure 8 For the multi-directional sensor manufactured according to Example 2, in order to obtain better conductivity, the sensor adopts a parallel structure and leads out eight contact terminals from the center of the intersection. The circular design in the middle of the structure ensures stable connection of the sensor at all angles, which is conducive to signal monitoring at all angles.

[0087] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A manufacturing process for a flexible strain sensor based on a conductive composite material for 3D printing, characterized in that: Using a conductive composite material for 3D printing, including the following steps: (1) Preparing a hydrophilic substrate: cleaning and pre-treating a hard substrate, coating a layer of hydrophilic material on the surface of the hard substrate, and heating and curing to obtain a hydrophilic substrate; (2) preparing a flexible substrate layer: spin coating a layer of liquid polydimethylsiloxane on the surface of a hydrophilic substrate, and heating and curing to obtain a flexible substrate layer; (3) Printing a conductive structure: Using a 3D printer, the printed material is a conductive composite material, and the printing method is electric field driven jet micro-nano 3D printing or direct writing 3D printing. A conductive circuit pattern is printed on the surface of the flexible substrate layer to obtain a printed sample; (4) Post-processing: The printed sample is sintered and solidified. Finally, the prepared sample is peeled off from the hydrophilic base layer by a peel-off demoulding method to obtain a flexible strain sensor based on a conductive composite material; The method for preparing a conductive composite material for 3D printing comprises the following steps: (1) Preparing a carbon nanotube dispersion: mixing carbon nanotube powder and a dispersant solution, and then ultrasonically treating the mixture to uniformly disperse the carbon nanotubes in the dispersant solution; (2) preparing a silver nanoparticle suspension: adding silver nanoparticles and 3-glycidyloxypropyltrimethoxysilane in a certain proportion to an ethanol solution, performing ultrasonic dispersion treatment, and then placing the solution in a vacuum drying oven to disperse the treated silver nanoparticles in a dispersant solution, and obtaining a stable suspension after ultrasonic treatment; (3) Preparing a conductive composite material: mixing a carbon nanotube dispersion, a silver nanoparticle suspension, and a polydimethylsiloxane prepolymer, stirring the mixture under ultrasonic conditions, then adding a polydimethylsiloxane curing agent, and continuing to stir the mixture at room temperature to complete the preparation; The carbon nanotubes are multi-walled carbon nanotubes with a tube diameter of 3-15 nm and a tube length of 15-30 μm, with a mass ratio of 4.7 wt%; The dispersant material is tetrahydrofuran.

2. The manufacturing process of a flexible strain sensor based on a conductive composite material for 3D printing according to claim 1, characterized in that: The diameter of the silver nanoparticles is less than 150 nm.

3. The manufacturing process of a flexible strain sensor based on a conductive composite material for 3D printing according to claim 1, characterized in that: In the step (1), the step of cleaning and pre-treating the hard substrate is as follows: The substrate is placed in an isopropanol solution for ultrasonic treatment, and then placed in deionized water for ultrasonic cleaning to remove the residual isopropanol solution. Finally, the substrate is blown dry with nitrogen or other inert gas.

4. The manufacturing process of a flexible strain sensor based on a conductive composite material for 3D printing according to claim 1, characterized in that: In the step (1), the curing temperature of the hydrophilic material is in the range of 30-150 degrees Celsius, and the curing time is in the range of 2-60 minutes.

5. The manufacturing process of a flexible strain sensor based on a conductive composite material for 3D printing according to claim 1, characterized in that: In the step (1), the hydrophilic material includes polyvinyl alcohol or hydroxypropyl methylcellulose solution; The typical preparation process of the polyvinyl alcohol solution is as follows: deionized water at 90°C and polyvinyl alcohol powder are stirred and mixed uniformly in a weight ratio of 10:1 until the polyvinyl alcohol powder is completely dissolved, and then placed in a vacuum drying oven to remove air bubbles; The typical preparation process of hydroxypropyl methylcellulose solution is as follows: deionized water at 90°C and hydroxypropyl methylcellulose are mixed in a weight ratio of 20:1, stirred thoroughly until the solution becomes gel-like, and allowed to stand at room temperature for 8 hours until the bubbles are completely eliminated.

6. The manufacturing process of a flexible strain sensor based on a conductive composite material for 3D printing according to claim 1, characterized in that: When the printed sample is sintered and cured, the sintering and curing temperature range is 60-150 degrees Celsius, and the curing time is 15-120 minutes.

7. A flexible strain sensor based on a conductive composite material for 3D printing, characterized in that: A flexible strain sensor is prepared according to the manufacturing process of a flexible strain sensor based on a conductive composite material for 3D printing according to any one of claims 1 to 6.

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