Integrally-formed multidirectional carbon nanotube resin-based strain sensor and preparation method thereof

Abstract

The invention discloses an integrally-formed multidirectional carbon nanotube resin-based strain sensor and a preparation method thereof. The integrally-formed multidirectional carbon nanotube resin-based strain sensor comprises a carbon nanotube resin-based composite material, a polyimide film and an electrode, the carbon nanotube resin-based composite material comprises carbon nanotubes, a dispersing agent, epoxy resin and a curing agent, the carbon nanotube resin-based composite material is brushed on the polyimide film through the metal printing plate; the metal printing plate comprises a cross shape, an L shape and a separated L shape, so as to form a bidirectional strain sensor; or the metal printing plate is in a three-direction type to form a three-direction strain sensor; or the metal printing plate is circular to form a circular sensor. The sensor can accurately measure strain in different directions, so that wide application of the carbon nanotube composite material is promoted, and the sensor can be used for strain detection and long-term monitoring of stress structures in the fields of civil engineering, traffic, machinery, aerospace and the like.

Description

Technical Field

[0001] The present invention belongs to the field of strain measurement of load-bearing structures, and in particular relates to an integrally formed multi-directional strain sensor and a preparation method thereof. Background Art

[0002] Installing stable and reliable sensor elements on the surface or inside of the structure to detect or monitor the structural strain is a direct means to understand the stress state of the structure and can provide reliable data support for the early warning of the structure. Compared with metal strain gauges, carbon nanomaterial sensors, such as carbon nanotubes, graphene and carbon nanofiber sensors, have higher sensitivity. The unidirectional carbon nanotube resin-based sensors developed in the early stage have the advantages of high sensitivity and large measurement range (patent numbers CN117329962A, CN117347443A). Due to the complex stress of the actual structure, usually a measuring point needs to measure the strain in 2-3 directions to determine the principal stress of the point, so sensors need to be installed in multiple directions.

[0003] This patent develops high-performance carbon nanotube bidirectional and multidirectional sensors based on the selected carbon nanotube types and epoxy resin types in previous research. The sensor can measure strains in different directions at the same time, significantly improving installation efficiency and reducing detection costs, and is expected to further promote the development of carbon nanotube composite materials in the field of structural health monitoring and safety detection.

[0004] The difference between this patent and the unidirectional carbon nanotube resin-based strain sensor (patent number CN117329962A, CN117347443A) is that: 1) The sensor developed by this patent breaks through the limitations of unidirectional sensors and can monitor strains from multiple directions at the same time; 2) This patent optimizes the geometric shape of the multi-directional strain sensor; 3) The sensor developed by this patent is prepared by an automatic screen printing machine, which can be integrated into a multi-directional sensor with stable performance. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of low sensitivity of traditional metal sensors and low multi-directional measurement efficiency of carbon nano sensors. By rationally designing the geometric morphology of carbon nanotube resin-based sensors, performing sensor performance tests and microstructure characterization analysis, an integrated multi-directional carbon nanotube resin-based strain sensor with high performance and multi-directional sensing capabilities and a preparation method are developed, which can be used for strain detection and long-term monitoring of stress-bearing structures in the fields of civil engineering, transportation, machinery, aerospace, etc.

[0006] The technical solution adopted by the present invention is: an integrally formed multi-directional carbon nanotube resin-based strain sensor, including a carbon nanotube resin-based composite material, a polyimide film and an electrode;

[0007] The carbon nanotube resin-based composite material comprises carbon nanotubes, a dispersant, an epoxy resin and a curing agent; the carbon nanotube resin-based composite material is brushed onto the polyimide film through a metal printing plate;

[0008] The metal printed plates include cross-shaped, L-shaped and separated L-shaped plates, forming a bidirectional strain sensor;

[0009] Or the metal printed plate is a three-dimensional type, forming a three-dimensional strain sensor;

[0010] Alternatively, the metal printing plate is circular, forming a circular sensor.

[0011] Preferably, the carbon nanotube resin-based composite material contains 3.5% by mass of carbon nanotubes, 0.7% by mass of dispersant, 73.7% by mass of epoxy resin, and 22.1% by mass of curing agent. The sum of the mass percentages of the carbon nanotubes, dispersant, epoxy resin and curing agent is 100%.

[0012] Preferably, the bidirectional strain sensor is composed of two rectangular sensing elements with a size of 20 mm×5 mm combined along the 0° and 90° directions.

[0013] As a preference, considering that if the distance between the two sensor elements is too small, the responses to the same strain area will be close, which will produce repeated signals, and if the distance is too large, small strains cannot be captured, thereby reducing sensitivity, the most appropriate spacing for separating the L-shaped sensor elements is 10 mm.

[0014] Preferably, the three-axis strain sensor has a width and a height of 20 mm, the sensing elements are combined along the directions of 0°, 45°, and 90°, and the width of a single sensing element is 5 mm.

[0015] Preferably, the circular sensor can measure strain in any direction, and the designed diameters are 10 mm, 20 mm, and 30 mm respectively.

[0016] The method for preparing the above-mentioned integrally formed multi-directional carbon nanotube resin-based strain sensor comprises the following steps:

[0017] 1) Accurately weigh the required materials according to the mass ratio of carbon nanotubes to dispersant of 5:1, then fully mix the dispersant and N-methylpyrrolidone and transfer them to a sand mill; on this basis, add MWCNTs powder in batches for dispersion to prepare a carbon nanotube dispersion; during the entire dispersion process, a circulating water cooling system is used to ensure the temperature of the machine is stable;

[0018] 2) mixing the prepared carbon nanotube dispersion with epoxy resin; the mixture is firstly subjected to ultrasonic treatment to promote dispersion, and then stirred by a magnetic stirrer;

[0019] 3) After adding the curing agent, stir with a magnetic stirrer for 10 minutes, vacuum to remove bubbles in the material, and let it stand for 10 minutes;

[0020] 4) After the viscosity is appropriate, the uniformly mixed carbon nanotube resin-based composite material is brushed onto the cut polyimide film through a customized metal printing plate according to the designed geometric shape by screen printing technology. The metal printing plate includes a cross shape, an L shape, a separated L shape, a three-way shape and a circle;

[0021] 5) placing the composite material in a vacuum drying oven and curing at 100° C. for 5 h;

[0022] 6) After the composite material is completely cured, use conductive silver glue to stick the copper sheet as an electrode in the strain measurement direction of the sensor, and cure it again at 70°C for 3 hours (the curing temperature cannot exceed the glass transition temperature of the resin-based material) to enhance the adhesion and conductivity of the conductive silver glue; finally, use soldering technology to weld the copper wire to the copper electrode to complete the overall preparation of the one-piece multi-directional carbon nanotube resin-based strain sensor.

[0023] Preferably, in step 4), considering the need to adhere the copper sheet, the size of the polyimide film shall not be less than 200 mm×50 mm.

[0024] Preferably, in step 6), the thickness of the copper sheet is 0.05 mm.

[0025] The present invention provides an integrated multi-directional carbon nanotube strain sensor for the practical engineering field, which can accurately measure strains in different directions, thereby promoting the widespread application of carbon nanotube composite materials and promoting the development of structural safety detection and health monitoring fields.

[0026] Beneficial effects of the present invention:

[0027] (1) Simple sensor preparation: The sensor of the present invention is prepared by an automatic screen printing machine, which is easy to operate, has stable sensor element performance, and is convenient for large-scale industrial application.

[0028] (2) Strong designability: Strain sensors of various shapes can be formed in one piece to meet the needs of stress detection and long-term monitoring in the fields of civil engineering, transportation, machinery, and aerospace.

[0029] (3) Superior performance: The three types of multi-directional strain sensors developed by the present invention exhibit advantages such as high sensitivity, high stability, and large linear range in different directions, which promotes the development of multi-directional strain measurement technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a structural diagram of the carbon nanotube resin-based strain sensor S1 (cross-shaped) of the present invention;

[0031] Figure 2 This is a structural diagram of the carbon nanotube resin-based strain sensor S2 (L-type) of the present invention;

[0032] Figure 3 This is a structural diagram of the carbon nanotube resin-based strain sensor S3 (separated L-type) of the present invention;

[0033] Figure 4 This is a structural diagram of the carbon nanotube resin-based strain sensor S4 (three-dimensional type) of the present invention;

[0034] Figure 5 This is a structural diagram of a carbon nanotube resin-based strain sensor S5 (circle) of the present invention;

[0035] Figure 6 This is a structural diagram of the carbon nanotube resin-based strain sensor S6 (circle) of the present invention;

[0036] Figure 7 This is a structural diagram of a carbon nanotube resin-based strain sensor S7 (circle) of the present invention;

[0037] Figure 8 This is the resistance change rate-strain curve of the carbon nanotube resin-based strain sensor S1 of the present invention.

[0038] Fig. 9 This is the resistance change rate-strain curve of the carbon nanotube resin-based strain sensor S2 of the present invention.

[0039] Fig.10 This is the resistance change rate-strain curve of the carbon nanotube resin-based strain sensor S3 of the present invention.

[0040] Fig.11 This is the resistance change rate-strain curve of the carbon nanotube resin-based strain sensor S4 of the present invention.

[0041] Fig.12 This is the resistance change rate-strain curve of the carbon nanotube resin-based strain sensor S5 of the present invention.

[0042] Fig.13 This is the resistance change rate-strain curve of the carbon nanotube resin-based strain sensor S6 of the present invention.

[0043] Fig.14 This is the resistance change rate-strain curve of the carbon nanotube resin-based strain sensor S7 of the present invention. DETAILED DESCRIPTION

[0044] The specific implementation modes of the present invention are described in detail below with reference to the accompanying drawings.

[0045] Embodiment 1: An integrated multi-directional carbon nanotube resin-based strain sensor, comprising a carbon nanotube resin-based composite material, a polyimide film and an electrode; the carbon nanotube resin-based composite material comprises carbon nanotubes, a dispersant, an epoxy resin and a curing agent; the carbon nanotube resin-based composite material is brushed onto the polyimide film through a metal printing plate; the metal printing plate comprises a cross-shaped, an L-shaped and a separated L-shaped, forming a bidirectional strain sensor, such as Figure 1-3 shown.

[0046] The method for preparing the bidirectional strain sensor comprises the following steps:

[0047] 1) accurately weighing the required materials according to the mass ratio of carbon nanotubes to dispersant of 5:1, then fully mixing the dispersant and N-methylpyrrolidone and transferring them to a sand mill; on this basis, adding MWCNTs powder in batches for dispersion to prepare a carbon nanotube dispersion;

[0048] 2) Mixing the prepared carbon nanotube dispersion with epoxy resin in a predetermined ratio (the carbon nanotube content is 3.5 wt.%), ultrasonically dispersing for 30 min, and magnetically stirring for 30 min;

[0049] 3) After adding the curing agent, stir magnetically for 10 minutes, vacuum to remove bubbles in the composite material, and let it stand for 10 minutes;

[0050] 4) When the viscosity is moderate, use an automatic screen printer to brush the evenly mixed carbon nanotube resin-based composite material onto the cut polyimide film through a customized metal printing plate (cross-shaped, L-shaped, separated L-shaped);

[0051] 5) Place in a vacuum drying oven and cure at 100°C for 5 hours;

[0052] 6) Paste a copper sheet as an electrode in the strain measurement direction of the multi-directional sensor and place it in a vacuum drying oven at 70°C for curing for 3 hours; solder the copper wire to complete the preparation.

[0053] Embodiment 2: An integrated multi-directional carbon nanotube resin-based strain sensor, comprising a carbon nanotube resin-based composite material, a polyimide film and an electrode; the carbon nanotube resin-based composite material comprises carbon nanotubes, a dispersant, an epoxy resin and a curing agent; the carbon nanotube resin-based composite material is brushed onto the polyimide film through a metal printing plate; the metal printing plate is a three-dimensional type, forming a three-dimensional strain sensor, such as Figure 4 shown.

[0054] The method for preparing the above three-axis strain sensor comprises the following steps:

[0055] 1) accurately weighing the required materials according to the mass ratio of carbon nanotubes to dispersant of 5:1, then fully mixing the dispersant and N-methylpyrrolidone and transferring them to a sand mill; on this basis, adding MWCNTs powder in batches for dispersion to prepare a carbon nanotube dispersion;

[0056] 2) Mixing the prepared carbon nanotube dispersion with epoxy resin in a predetermined ratio (the carbon nanotube content is 3.5 wt.%), ultrasonically dispersing for 30 min, and magnetically stirring for 30 min;

[0057] 3) After adding the curing agent, stir magnetically for 10 minutes, vacuum to remove bubbles in the composite material, and let it stand for 10 minutes;

[0058] 4) When the viscosity is moderate, use an automatic screen printer to brush the evenly mixed carbon nanotube resin-based composite material onto the cut polyimide film through a customized metal printing plate (three-way type);

[0059] 5) Place in a vacuum drying oven and cure at 100°C for 5 hours;

[0060] 6) Paste a copper sheet as an electrode in the strain measurement direction of the multi-directional sensor and place it in a vacuum drying oven at 70°C for curing for 3 hours; solder the copper wire to complete the preparation.

[0061] Embodiment 3: An integrally formed multi-directional carbon nanotube resin-based strain sensor, comprising a carbon nanotube resin-based composite material, a polyimide film and an electrode; the carbon nanotube resin-based composite material comprises carbon nanotubes, a dispersant, an epoxy resin and a curing agent; the carbon nanotube resin-based composite material is brushed onto the polyimide film through a metal printing plate; the metal printing plate is circular, forming a circular sensor, such as Figure 5-7 shown.

[0062] The method for preparing the circular sensor comprises the following steps:

[0063] 1) accurately weighing the required materials according to the mass ratio of carbon nanotubes to dispersant of 5:1, then fully mixing the dispersant and N-methylpyrrolidone and transferring them to a sand mill; on this basis, adding MWCNTs powder in batches for dispersion to prepare a carbon nanotube dispersion;

[0064] 2) Mixing the prepared carbon nanotube dispersion with epoxy resin in a predetermined ratio (the carbon nanotube content is 3.5 wt.%), ultrasonically dispersing for 30 min, and magnetically stirring for 30 min;

[0065] 3) After adding the curing agent, stir magnetically for 10 minutes, vacuum to remove bubbles in the composite material, and let it stand for 10 minutes;

[0066] 4) When the viscosity is moderate, use an automatic screen printing machine to brush the evenly mixed carbon nanotube resin-based composite material onto the cut polyimide film through a customized metal printing plate (round);

[0067] 5) Place in a vacuum drying oven and cure at 100°C for 5 hours;

[0068] 6) Paste a copper sheet as an electrode in the strain measurement direction of the multi-directional sensor and place it in a vacuum drying oven at 70°C for curing for 3 hours; solder the copper wire to complete the preparation.

[0069] The key to the multi-directional carbon nanotube strain sensor of the present invention lies in the design of different forms of the multi-directional strain sensor, as shown in Table 1 below:

[0070] Table 1 Sensor shape parameters

[0071]

[0072] The results show that, as shown in Table 2, among the bidirectional sensors, the L-type S3 has the highest sensitivity (sensitivity GF = (ΔR / R 0 ) / ε, where △R is the resistance change, R 0 is the initial resistance, ε is the strain), compared with S1, it increases by 19.0% and 33.7% in the 0° and 90° directions respectively, and compared with S2, it increases by 13.3% and 18.0% in the 0° and 90° directions respectively. The linearity of S3 reaches 0.98. Among the multi-directional sensors, the circular sensor S7 has the highest sensitivity, which is 10.13, 16.10, and 22.15 in the 0°, 45°, and 90° directions respectively, and the linearity reaches 0.99. As the diameter-to-thickness ratio of the circular sensor increases, its sensitivity decreases further. In addition, the circular sensor has a smaller initial resistance and a more stable sensing performance, and the resistance difference in each direction does not exceed 10%. Figure 8-14 shown.

[0073] Table 2 Basic performance of multi-directional sensor

[0074]

[0075]

[0076] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and deformations of these embodiments within the scope of the principles and technical ideas of the present invention still fall within the protection scope of the present invention.

Claims

1. An integrated multi-directional carbon nanotube resin-based strain sensor, characterized in that: It includes carbon nanotube resin-based composite materials, polyimide films and electrodes; The carbon nanotube resin-based composite material comprises carbon nanotubes, a dispersant, an epoxy resin and a curing agent; the carbon nanotube resin-based composite material is brushed onto the polyimide film through a metal printing plate; The metal printed plates include cross-shaped, L-shaped and separated L-shaped plates, forming a bidirectional strain sensor; Or the metal printed plate is a three-dimensional type, forming a three-dimensional strain sensor; Alternatively, the metal printing plate is circular, forming a circular sensor.

2. The one-piece multi-directional carbon nanotube resin-based strain sensor according to claim 1, characterized in that: The carbon nanotube resin-based composite material has a carbon nanotube mass percentage of 3.5%, a dispersant mass percentage of 0.7%, an epoxy resin mass percentage of 73.7%, and a curing agent mass percentage of 22.1%. The sum of the carbon nanotube, dispersant, epoxy resin, and curing agent mass percentages is 100%.

3. The one-piece multi-directional carbon nanotube resin-based strain sensor according to claim 1, characterized in that: The bidirectional strain sensor is composed of two rectangular sensing elements with a size of 20 mm×5 mm, which are combined along the 0° and 90° directions.

4. The one-piece multi-directional carbon nanotube resin-based strain sensor according to claim 3, characterized in that: The spacing between the separated L-shaped sensing elements of the bidirectional strain sensor is selected to be 10 mm.

5. The one-piece multi-directional carbon nanotube resin-based strain sensor according to claim 1, characterized in that: The width and height of the three-axis strain sensor are both 20 mm, the sensing elements are combined along the directions of 0°, 45°, and 90°, and the width of a single sensing element is 5 mm.

6. The one-piece multi-directional carbon nanotube resin-based strain sensor according to claim 1, characterized in that: The diameters of the circular sensors are 10 mm, 20 mm, and 30 mm respectively.

7. The method for preparing the integrally formed multi-directional carbon nanotube resin-based strain sensor according to claim 1, 2, 3, 4, 5 or 6, characterized in that: The following steps are involved: 1) Accurately weigh the required materials according to the mass ratio of carbon nanotubes to dispersant of 5:1, then fully mix the dispersant and N-methylpyrrolidone and transfer them to a sand mill; on this basis, add MWCNTs powder in batches for dispersion to prepare a carbon nanotube dispersion; during the entire dispersion process, a circulating water cooling system is used to ensure the temperature of the machine is stable; 2) mixing the prepared carbon nanotube dispersion with epoxy resin; The mixture was first sonicated to facilitate dispersion and then stirred using a magnetic stirrer; 3) After adding the curing agent, stir with a magnetic stirrer for 10 minutes, vacuum to remove bubbles in the material, and let it stand for 10 minutes; 4) using a screen printing method to brush the uniformly mixed carbon nanotube resin-based composite material onto the cut polyimide film through a metal printing plate, wherein the metal printing plate includes a cross-shaped, L-shaped, separated L-shaped, three-way and circular type; 5) placing the carbon nanotube resin-based composite material in a vacuum drying oven and curing it at 100° C. for 5 h; 6) After the carbon nanotube resin-based composite material is completely cured, a copper sheet is pasted as an electrode in the strain measurement direction of the sensor using conductive silver glue and cured again at 70°C for 3 hours; finally, the copper wire is soldered to the copper electrode by soldering to complete the overall preparation of the one-piece multi-directional carbon nanotube resin-based strain sensor.

8. The method for preparing the integrally formed multi-directional carbon nanotube resin-based strain sensor according to claim 7, characterized in that: In the step 4), the size of the polyimide film shall not be less than 200 mm×50 mm.

9. The method for preparing the integrally formed multi-directional carbon nanotube resin-based strain sensor according to claim 7, characterized in that: In the step 6), the thickness of the copper sheet is 0.05 mm.

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