Large-breadth flexible damage sensing material and preparation method thereof

Abstract

The invention relates to a large-breadth flexible damage sensing material and a preparation method thereof, belongs to the field of intelligent material preparation, and solves the problem that large-scale preparation of the large-breadth flexible damage sensing material is difficult in the prior art. The invention discloses a large-breadth flexible damage sensing material and a preparation method thereof. The large-breadth flexible damage sensing material comprises a flexible substrate layer, a conductive layer and a packaging layer, wherein the conductive layer is superposed on the flexible substrate layer; the packaging layer covers the conductive layer; the conductive layer is made of a laser-engraved polyimide film, a functional laser-induced graphene structure and an auxiliary separation structure which are etched by a laser engraving machine are arranged on the conductive layer, and the auxiliary separation structure comprises a film through hole and an edge cutting line; the large-breadth flexible damage sensing material provided by the invention is high in fineness, stable in performance and capable of meeting large-breadth sensing application, the preparation method of the large-breadth flexible damage sensing material is simple in step and high in preparation efficiency, and the large-breadth flexible damage sensing material which is stable in performance and high in fineness can be prepared in batches.

Description

Technical Field

[0001] This invention relates to the field of structural design technology, and in particular to a large-format flexible damage sensing material and its preparation method. Background Technology

[0002] Laser-induced graphene (LIG) is a porous graphite material formed directly on the surface of carbon-based materials (such as polyimide, wood, and paper) by laser irradiation. In recent years, LIG ​​has shown broad application prospects in flexible wearable devices and sensors due to its advantages such as simple preparation, low cost, and controllable patterning.

[0003] The fabrication of flexible LIG sensors involves directly scanning the surface of a carbon-based precursor material (such as a polyimide film) with a laser, causing it to carbonize and transform into a porous graphene structure. Due to its simple fabrication process and the ability to directly write pre-defined patterns, this technology shows great application potential in flexible electronics, sensors, and other fields. A typical fabrication process for a flexible laser-induced graphene sensor includes: etching a laser-induced graphene pattern onto a carbon-based precursor, transferring the pattern to a flexible substrate, and finally encapsulating it.

[0004] However, the industrial application of this technology, especially in fields such as aerospace that require large-size, lightweight monitoring components, is limited by key transfer steps. Existing transfer methods mainly fall into two categories: chemical etching and mechanical exfoliation. Chemical etching typically uses highly corrosive chemicals (such as potassium hydroxide solution) to remove the carbon-based precursor, which is not only dangerous to operate but also generates waste liquid that poses a threat to the environment, making it unsuitable for large-scale production. Mechanical exfoliation, while simple and environmentally friendly, has a fatal flaw: during the exfoliation process, uneven stress distribution easily leads to tearing, detachment, or damage to large-size or fine laser-induced graphene patterns. This uncontrollable damage severely reduces the success rate of fabrication and the reliability of the sensor, limiting the size of existing flexible laser-induced graphene sensors to a relatively small range, failing to meet the needs of large-format structural health monitoring.

[0005] Therefore, there is a need to provide a large-format flexible damage sensing material and its preparation method to solve the problem of the difficulty in large-format flexible damage sensing material preparation in the existing technology. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a large-format flexible damage sensing material and its preparation method, thereby solving the problem of the difficulty in large-scale preparation of large-format flexible damage sensing materials in the prior art.

[0007] The objective of this invention is achieved primarily through the following technical solution: a large-format flexible damage sensing material, comprising a flexible substrate layer, a conductive layer superimposed on the flexible substrate layer, and an encapsulation layer covering the conductive layer; the conductive layer is made of a laser-engraved polyimide film, and has a functional laser-induced graphene structure and an auxiliary separation structure etched by a laser engraving machine on the conductive layer. The auxiliary separation structure includes film through-holes and edge cutting lines. The functional laser-induced graphene structure includes several conductive rows and several conductive columns, which are arranged to form multiple squares. Each square has a film through-hole. Several edge cutting lines are provided at the edge of the polyimide film, penetrating the film from the thickness direction and distributed radially. One end of the edge cutting line reaches the edge of the film, and the other end does not contact the functional laser-induced graphene structure.

[0008] Furthermore, the flexible substrate layer is made of silicone film, thermoplastic polyurethane film, or polyethylene-polyvinyl acetate copolymer.

[0009] Furthermore, the encapsulation layer is made of silicone film, thermoplastic polyurethane film, or polyethylene-polyvinyl acetate copolymer.

[0010] A method for preparing a large-format flexible damage sensing material, used to prepare the large-format flexible damage sensing material of claim 1, includes the following steps: Step S1: Prepare a functional laser-induced graphene structure by etching the functional laser-induced graphene structure on a polyimide film using a laser engraving machine, thereby making the polyimide film a conductive layer. Step S2: Prepare the auxiliary separation structure. After the functional laser-induced graphene structure is etched, the conductive layer is cut using a laser engraving machine to produce the auxiliary separation structure. Step S3: Hot-press the flexible substrate layer and the conductive layer together; Step S4: Mechanically peel off the conductive layer, removing all parts of the conductive layer except for the functional laser-induced graphene structure from the flexible substrate layer, so that the complete functional laser-induced graphene structure is retained on the flexible substrate layer.

[0011] Furthermore, step S1 includes the following steps: Step S11: Pretreatment of polyimide film. Cut polyimide film with a thickness of 0.025mm~0.10mm to the required size, clean polyimide film with ethanol and acetone solution, and then put polyimide film into an electric heating drying oven at 50℃ for 1 hour before taking it out. Step S12: Obtain a functional laser-induced graphene structure; After pretreatment, place the glass with the polyimide film on the laser engraving machine platform, and use the laser engraving machine to perform laser scanning on the polyimide film in step S11, so that a functional laser-induced graphene structure is generated on the polyimide film.

[0012] Furthermore, in step S12, when using a laser engraving machine to generate a functional laser-induced graphene structure, the functional laser-induced graphene structure and laser engraving parameters are imported into the laser control system, and the laser power is set to 10.5W~11.5W and the speed is 5mm / s~15mm / s.

[0013] Furthermore, in step S2, the laser engraving machine is switched to laser cutting mode, and the cutting path of the auxiliary separation structure is preset by computer-aided design software, with the laser power set to 20W~30W and the speed set to 30mm / s.

[0014] Furthermore, in step S3, a flexible substrate layer with the same size as the conductive layer in step S2 and a thickness of 0.15 mm is cut out, and the flexible substrate layer is precisely stacked on the conductive layer to form a laminated structure. Then, the laminated structure is moved into a flatbed hot press for lamination.

[0015] Furthermore, in step S3, the process parameters for the hot pressing process are: temperature of 80℃~100℃, pressure of 0.1MPa~0.2MPa, heat preservation and pressure holding for 5min~10min. After the heat preservation and pressure holding is completed, heating is stopped and pressure is released, allowing the sample to cool naturally to room temperature in the hot press before being taken out.

[0016] Furthermore, in step S4, the stacked structure from step S3 is removed from the hot press. Starting from one corner of the stacked structure, the operator gently peels off the conductive layer with tweezers and slowly and steadily peels off the part of the conductive layer, except for the laser-induced graphene structure, from the flexible substrate layer at a small angle, so that the laser-induced graphene structure is completely preserved on the flexible substrate layer.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) The large-format flexible damage sensing material of the present invention has a conductive layer made of laser-engraved polyimide film. The conductive layer has a functional laser-induced graphene structure and an auxiliary separation structure etched by a laser engraving machine. By setting the auxiliary separation structure, the mechanical peeling step in the preparation process of the large-format flexible damage sensing material sets the peeling path, so that the peeling force is effectively guided, avoiding damage to the functional laser-induced graphene structure. This solves the problem that the traditional mechanical peeling method is prone to damage to the fine conductive structure, and significantly improves the manufacturing success rate and reliability of the large-format laser-induced graphene structure.

[0018] (2) The preparation method of the large-format flexible damage sensing material of the present invention adopts purely physical methods such as laser engraving, hot pressing and mechanical peeling, which completely avoids the use of dangerous and environmentally unfriendly chemical corrosives. The process is simple and safe, with high repeatability, which provides the possibility for the mass production and low-cost production of large-format flexible laser-induced graphene damage sensing materials.

[0019] (3) The preparation method of the large-format flexible damage sensing material of the present invention has fewer process steps but can achieve high operational precision. The prepared flexible damage sensing material not only has excellent flexibility, light weight and high precision, but also realizes the batch preparation of large-format materials and has good application prospects.

[0020] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the specification or be learned by practicing the invention. The objectives and other advantages of this invention can be realized and obtained from the content specifically pointed out in the text and accompanying drawings. Attached Figure Description

[0021] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0022] Figure 1 This is a top view of the conductive layer of the large-format flexible damage sensing material in Example 1; Figure 2 This is a flowchart of the preparation method of the large-format flexible damage sensing material in Example 2; Figure 3 This is a schematic diagram of the cross-sectional structure of the large-format flexible damage sensing material in Example 1.

[0023] Figure label: 1-Functional laser-induced graphene structure; 11-Conductive row; 12-Conductive column; 2-Auxiliary separation structure; 21-Through-hole in thin film; 22-Edge cutting line. Detailed Implementation

[0024] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention. Example

[0025] This embodiment discloses a large-format flexible damage sensing material, including a flexible substrate layer, a conductive layer superimposed on the flexible substrate layer, and an encapsulation layer covering the conductive layer.

[0026] The flexible substrate layer is made of silicone film (PDMS film), thermoplastic polyurethane film (TPU film) or polyethylene-polyvinyl acetate copolymer (EVA film); the conductive layer is made of laser-engraved polyimide (PI) film; the encapsulation layer is made of silicone film (PDMS film), thermoplastic polyurethane film (TPU film) or polyethylene-polyvinyl acetate copolymer (EVA film).

[0027] See Figure 1 The conductive layer is a regularly shaped polyimide (PI) film. The film has a functional laser-induced graphene structure 1 and an auxiliary separation structure 2 etched by a laser engraving machine. The auxiliary separation structure 2 includes film through-holes 21 and edge cutting lines 22. The functional laser-induced graphene structure 1 includes several conductive rows 11 and several conductive columns 12. The conductive rows 11 and conductive columns 12 intersect and are arranged to form multiple squares. Each square contains a film through-hole 21, which is generally a regular shape, such as square or circular. Additionally, the edges of the polyimide film... A plurality of edge cutting lines 22 are uniformly provided, extending through the film from the thickness direction and distributed radially. One end of the edge cutting line 22 reaches the edge of the film, and the other end does not contact the functional laser-induced graphene structure 1. It should be noted that the auxiliary separation structure 2 on the film is designed to quickly remove the polyimide film from the flexible substrate layer during the preparation process and to completely retain the functional laser-induced graphene structure 1 on the flexible substrate layer, ensuring that the functional laser-induced graphene structure 1 is not damaged or torn, thereby realizing the preparation of a large-format flexible damage sensing material.

[0028] The functional laser-induced graphene region has an electrode connection area to fix the wire electrode. Example

[0029] This embodiment discloses the preparation method of the large-format flexible damage sensing material in Embodiment 1. See [link to previous section]. Figure 2 It mainly includes the following steps: Step S1: Prepare functional laser-induced graphene structure; The conductive layer is made of laser-engraved polyimide (PI) film. Commercially available polyimide film is selected as the carbon-based precursor film because of its excellent thermal and chemical stability, making it an excellent precursor material for preparing laser-induced graphene.

[0030] Step S11: Polyimide film pretreatment; To ensure the uniformity of the laser processing effect and the adhesion quality of subsequent transfer, the polyimide film needs to be pretreated before laser processing. The pretreatment process includes: cutting a polyimide (PI) film with a thickness of 0.025mm~0.10mm to the required size, cleaning the PI film with ethanol and acetone solution to remove surface impurities such as oil and dust; then placing the PI film in an electric heating drying oven at 50℃ for 1 hour to completely remove the surface-adsorbed moisture.

[0031] Step S12: Obtain the functional laser-induced graphene structure. After pretreatment, use high-temperature tape to smoothly adhere the extracted PI film to the glass to ensure that it does not shift or wrinkle during processing. Then, place the glass with the PI film on the laser engraving machine platform, position and calibrate the laser focal length, and set the laser scanning parameters according to the sensor grid pattern pre-drawn in the computer-aided design software. Import the functional laser-induced graphene structure 1 and the laser engraving parameters into the laser control system, set the laser power to 10.5W~11.5W, and the speed to 5mm / s~15mm / s. Select the laser scanning mode to engrave the required pattern on the PI film. The characteristic of the laser scanning mode is that the laser energy is relatively low, which is insufficient to completely vaporize or cut through the polyimide film. Instead, it induces high temperature in a local area on the surface of the film through photothermal effect, causing the polyimide molecular chains to break, carbonize, and reconstruct into graphene with a porous three-dimensional network structure. The area on the PI film other than the functional laser-induced graphene structure 1 is still polyimide material.

[0032] Under the control of a computer program, the laser head precisely scans the surface of the polyimide film according to a preset grid path. After the scan is completed, a black, conductive functional laser-induced graphene structure 1 can be observed on the surface of the polyimide film. The laser-induced graphene pattern area is a high-density sensing grid used to sense strain or damage in subsequent applications.

[0033] It should be noted that the laser engraving machine used in this embodiment can be the OL-4060 laser engraving machine provided by Shandong Oulei Laser Technology Co., Ltd., which has a laser power of 100W and an effective processing area of ​​400mm×600mm, which is beneficial for preparing large-format laser-induced graphene patterns.

[0034] Step S2: Preparation of auxiliary separation structure; After the functional laser-induced graphene structure 1 is etched, the same laser engraving machine is used again, but switched to laser cutting mode for cutting. This mode is characterized by high laser energy density, which completely ablates and vaporizes the polyimide film, thereby forming a cut that penetrates the thickness of the film. The laser power is set to 20W~30W and the speed is 30mm / s. The cutting path of the auxiliary separation structure 2 is preset by computer-aided design software. The auxiliary separation structure 2 is set around and inside the laser-induced graphene pattern, including the edge cutting line 22 surrounding the entire outer contour of the conductive layer and the film through-holes 21 within the grid of the functional laser-induced graphene structure 1.

[0035] It should be noted that the function of the auxiliary separation structure 2 is to artificially create a predetermined weak path with extremely low structural strength on the polyimide film, so as to guide the polyimide film to be precisely peeled from the flexible substrate layer along the path of the auxiliary separation structure 2 in the subsequent mechanical peeling step S4. This can effectively avoid the peeling force from stretching or tearing the fragile functional laser-induced graphene structure 1, thereby obtaining a complete functional laser-induced graphene structure 1 with high precision.

[0036] Step S3: Hot-press the flexible substrate layer and the conductive layer together. Cut a flexible substrate layer with the same dimensions as the conductive layer in Step S2 and a thickness of 0.15 mm. Precisely stack the flexible substrate layer on the conductive layer to form a laminated structure, ensuring that the flexible substrate layer completely covers the conductive layer. Subsequently, transfer the laminated structure into a flatbed hot press and laminate it using a hot pressing process. The process parameters are: temperature 80℃~100℃, pressure 0.1MPa~0.2MPa, and holding temperature and pressure for 5min~10min. Under these conditions, the surface of the flexible substrate layer softens and, under pressure, penetrates and fills into the loose and porous microstructure of the laser-induced graphene. This makes the adhesion between the functional laser-induced graphene structure 1 and the flexible substrate layer greater than the adhesion between other areas of the conductive layer and the flexible substrate layer. After the holding temperature and pressure are completed, stop heating and release the pressure, allowing the sample to cool naturally to room temperature (e.g., below 40℃) in the hot press before removing it. The cooling process solidifies the softened flexible substrate layer, thereby firmly "grabbing" and adhering the laser-induced graphene conductive layer to the surface of the flexible substrate layer. Through the above process, it can be ensured that the functional laser-induced graphene structure 1 can be completely retained on the flexible substrate layer when the conductive layer is peeled off from the flexible substrate layer in the subsequent step S4.

[0037] Step S4: Mechanically peel off the conductive layer; Remove the cooled sample from the hot press. At this point, the functional laser-induced graphene structure 1 is tightly bonded to the flexible substrate layer. Starting from one corner of the sample, the operator gently peels off the conductive layer film with tweezers and slowly and steadily peels the conductive layer off the flexible substrate layer at a small angle.

[0038] In the above process, since an auxiliary separation structure 2 that penetrates the film is pre-fabricated on the conductive polyimide film, when the peeling force is transmitted to the film, the film will not undergo large-area overall deformation under stress, but will be easily peeled off and removed along the path of the weakest auxiliary separation structure 2. As for the area bearing the functional laser-induced graphene structure 1, since the graphene on it has been firmly adhered to the flexible substrate layer, the interfacial bonding force between the functional laser-induced graphene structure 1 and the flexible substrate layer is much greater than the bonding force between the polyimide film and the flexible substrate layer. Therefore, the functional laser-induced graphene structure 1 will be completely retained on the surface of the flexible substrate layer, thereby realizing the non-destructive transfer of large-format, fine patterns.

[0039] After the exfoliation is completed, a clear and complete functional laser-induced graphene structure 1 is formed on the surface of the flexible substrate layer. Microscopic observation and multimeter testing confirm that there are no unpredictable breakpoints in the transferred conductive network structure, and the structural integrity is guaranteed.

[0040] Step S5: Encapsulate and acquire flexible damage-sensing material; see [link / reference] Figure 3 In step S4, an electrode connection area is preset on the functional laser-induced graphene structure 1 (usually at the end of the pattern), and a small amount of conductive silver paste is coated on the electrode connection area to ensure good ohmic contact. Then, a flexible copper wire with a diameter of 0.5 mm is pasted on the conductive silver paste as the end point of the wire electrode, and cured after being kept in an oven at 80°C for 30 minutes to form the electrode lead-out end.

[0041] To protect the fragile graphene pattern and prevent it from being worn, oxidized, or short-circuited during use, encapsulation is required. A film with the same size and material as the flexible substrate layer is used as the encapsulation layer and is placed on top of the functional laser-induced graphene structure 1 with conductive electrodes, thus forming a sandwich structure. The sandwich structure is then placed in a hot press for secondary hot pressing. The hot press parameters are set to a temperature of 80℃~100℃, a pressure of 0.1MPa~0.2MPa, and a holding time of 5min~10min. This hot pressing process fuses the encapsulation layer and the flexible substrate layer around the functional laser-induced pattern, thereby completely sealing the functional laser-induced graphene structure 1 inside. After natural cooling to below 40℃, the material is removed to obtain the large-format flexible damage sensing material.

[0042] The flexible damage-sensing material can be adhered to the surface of the structure to be monitored during use. When the structure deforms or cracks, it causes stretching or compression of the flexible damage-sensing material, which in turn alters the length, width, or microcrack state of the conductive path in the functional laser-induced graphene structure 1 within it. Macroscopically, this manifests as a change in the resistance value measured through the conductive electrode. By monitoring the change in resistance value, the strain state or damage condition of the structure can be sensed in real time. The large-format flexible damage-sensing material successfully prepared in this embodiment demonstrates the efficiency and reliability of the non-destructive transfer method in this embodiment, laying the foundation for the application of laser-induced graphene technology in fields such as large-scale structural health monitoring. Example

[0043] This embodiment is another implementation of Embodiment 2.

[0044] Step S1: Prepare a functional laser-induced graphene structure; the conductive layer is made of laser-engraved polyimide (PI) film.

[0045] Step S11: Pretreatment of polyimide film; cut the 0.10mm thick PI film into a size of 450mm×450mm, clean the PI film with ethanol and acetone solution to remove surface impurities such as oil and dust; then put the PI film into an electric heating drying oven at 50℃ and dry for 1 hour before taking it out.

[0046] Step S12: Obtain the functional laser-induced graphene structure 1. After pretreatment, use high-temperature tape to smoothly adhere the extracted PI film to the glass to ensure that it does not shift or wrinkle during processing. Then, place the glass with the PI film on the laser engraving machine platform, position and calibrate the laser focal length, set the laser scanning parameters according to the sensor grid pattern pre-drawn in the computer-aided design software, import the functional laser-induced graphene structure 1 and the laser engraving parameters into the laser control system, set the laser power to 11.5W, the speed to 15mm / s, select the laser scanning mode to engrave the required pattern on the PI film, and obtain the functional laser-induced graphene structure 1.

[0047] Step S2: Prepare auxiliary separation structure 2; switch the laser engraving machine to laser cutting mode and cut, set the laser power to 30W and the speed to 30mm / s, engrave the auxiliary separation structure 2 on the conductive layer, and obtain a conductive layer with a size of 400mm×400mm by edge cutting.

[0048] Step S3: Hot-press the flexible substrate layer and the conductive layer together; cut a 0.15mm thick thermoplastic polyurethane film into a 400mm×400mm size and use it as the flexible substrate layer on the conductive layer to form a laminated structure. Then, move the laminated structure into a flatbed hot press for lamination. The process parameters are: temperature 80℃, pressure 0.2MPa, heat preservation and pressure holding for 5min. After the heat preservation and pressure holding is completed, stop heating and release the pressure, and let the sample cool naturally to room temperature (e.g., below 40℃) in the hot press before taking it out.

[0049] Step S4: Mechanically peel off the conductive layer; Starting from one corner of the sample, the operator gently peels off the conductive layer film with tweezers and slowly and steadily peels the conductive layer off the flexible substrate layer at a small angle, so that a clear and complete functional laser-induced graphene structure 1 is formed on the surface of the flexible substrate layer.

[0050] Step S5: Encapsulate and obtain flexible damage sensing material; On the functional laser-induced graphene structure 1 in step S4, a pre-set electrode connection area (usually at the end of the pattern) is applied and a small amount of conductive silver paste is coated on the electrode connection area to ensure good ohmic contact. Then, a flexible copper wire with a diameter of 0.5 mm is pasted on the conductive silver paste as the end point of the wire electrode and cured after being kept in an oven at 80°C for 30 min to form the electrode lead-out end.

[0051] A thermoplastic polyurethane film was cut into 400mm × 400mm dimensions and used as an encapsulation layer to cover a functional laser-induced graphene structure 1 with conductive electrodes, thus forming a sandwich structure. The sandwich structure was then placed in a hot press for secondary hot pressing. The hot press parameters were set to a temperature of 80℃ and a pressure of 0.2MPa, with a holding time of 5 minutes. This hot pressing process completely sealed the functional laser-induced graphene structure 1 within the sandwich structure. After natural cooling to below 40℃, the structure was removed, yielding the large-format flexible damage sensing material. Example

[0052] This embodiment is another implementation of Embodiment 2.

[0053] Step S1: Prepare a functional laser-induced graphene structure; the conductive layer is made of laser-engraved polyimide (PI) film.

[0054] Step S11: Pretreatment of polyimide film; cut the 0.025mm thick PI film into a size of 450mm×450mm, clean the PI film with ethanol and acetone solution to remove surface impurities such as oil and dust; then put the PI film into an electric heating drying oven at 50℃ and dry for 1 hour before taking it out.

[0055] Step S12: Obtain the functional laser-induced graphene structure 1. After pretreatment, use high-temperature tape to smoothly adhere the extracted PI film to the glass to ensure that it does not shift or wrinkle during processing. Then, place the glass with the PI film on the laser engraving machine platform, position and calibrate the laser focal length, set the laser scanning parameters according to the sensor grid pattern pre-drawn in the computer-aided design software, import the functional laser-induced graphene structure 1 and the laser engraving parameters into the laser control system, set the laser power to 10.5W, the speed to 5mm / s, and select the laser scanning mode to engrave the required pattern on the PI film to obtain the functional laser-induced graphene structure 1.

[0056] Step S2: Prepare auxiliary separation structure 2; switch the laser engraving machine to laser cutting mode and cut, set the laser power to 20W and the speed to 30mm / s, engrave the auxiliary separation structure 2 on the conductive layer, and obtain a conductive layer with a size of 400mm×400mm by edge cutting.

[0057] Step S3: Hot-press the flexible substrate layer and the conductive layer together; cut a 0.15mm thick silicone film into a 400mm×400mm size and use it as the flexible substrate layer on the conductive layer to form a laminated structure. Then, move the laminated structure into a flatbed hot press for lamination. The process parameters are: temperature 100℃, pressure 0.2MPa, heat preservation and pressure holding for 10min. After the heat preservation and pressure holding is completed, stop heating and release the pressure, and let the sample cool naturally to room temperature (e.g., below 40℃) in the hot press before taking it out.

[0058] Step S4: Mechanically peel off the conductive layer; Starting from one corner of the sample, the operator gently peels off the conductive layer film with tweezers and slowly and steadily peels the conductive layer off the flexible substrate layer at a small angle, so that a clear and complete functional laser-induced graphene structure 1 is formed on the surface of the flexible substrate layer.

[0059] Step S5: Encapsulate and obtain flexible damage sensing material; On the functional laser-induced graphene structure 1 in step S4, a pre-set electrode connection area (usually at the end of the pattern) is applied and a small amount of conductive silver paste is coated on the electrode connection area to ensure good ohmic contact. Then, a flexible copper wire with a diameter of 0.5 mm is pasted on the conductive silver paste as the end point of the wire electrode and cured after being kept in an oven at 80°C for 30 min to form the electrode lead-out end.

[0060] An organosilicon film was cut to a size of 400mm × 400mm and used as an encapsulation layer to cover a functional laser-induced graphene structure 1 with conductive electrodes, thus forming a sandwich structure. The sandwich structure was then placed in a hot press for secondary hot pressing. The hot press parameters were set to a temperature of 100℃ and a pressure of 0.2MPa, and the temperature and pressure were maintained for 10 minutes. This hot pressing process completely sealed the functional laser-induced graphene structure 1 inside. After natural cooling to below 40℃, the material was removed to obtain the large-format flexible damage sensing material. Example

[0061] This embodiment is another implementation of Embodiment 2.

[0062] Step S1: Prepare a functional laser-induced graphene structure; the conductive layer is made of laser-engraved polyimide (PI) film.

[0063] Step S11: Pretreatment of polyimide film; cut the 0.1mm thick PI film into a size of 450mm×450mm, clean the PI film with ethanol and acetone solution to remove surface impurities such as oil and dust; then put the PI film into an electric heating drying oven at 50℃ and dry for 1 hour before taking it out.

[0064] Step S12: Obtain the functional laser-induced graphene structure 1. After pretreatment, use high-temperature tape to smoothly adhere the extracted PI film to the glass to ensure that it does not shift or wrinkle during processing. Then, place the glass with the PI film on the laser engraving machine platform, position and calibrate the laser focal length, set the laser scanning parameters according to the sensor grid pattern pre-drawn in the computer-aided design software, import the functional laser-induced graphene structure 1 and the laser engraving parameters into the laser control system, set the laser power to 11.5W, the speed to 15mm / s, select the laser scanning mode to engrave the required pattern on the PI film, and obtain the functional laser-induced graphene structure 1.

[0065] Step S2: Prepare auxiliary separation structure 2; switch the laser engraving machine to laser cutting mode and cut, set the laser power to 30W and the speed to 30mm / s, engrave the auxiliary separation structure 2 on the conductive layer, and obtain a conductive layer with a size of 400mm×400mm by edge cutting.

[0066] Step S3: Hot-press the flexible substrate layer and the conductive layer together; cut a 0.15mm thick polyethylene-polyvinyl acetate copolymer film into a 400mm×400mm size and place it on the conductive layer as the flexible substrate layer to form a laminated structure. Then, transfer the laminated structure into a flatbed hot press for lamination. The process parameters are: temperature 85℃, pressure 0.1MPa, heat preservation and pressure holding for 5min. After the heat preservation and pressure holding is completed, stop heating and release the pressure, and allow the sample to cool naturally to room temperature (e.g., below 40℃) in the hot press before taking it out.

[0067] Step S4: Mechanically peel off the conductive layer; Starting from one corner of the sample, the operator gently peels off the conductive layer film with tweezers and slowly and steadily peels the conductive layer off the flexible substrate layer at a small angle, so that a clear and complete functional laser-induced graphene structure 1 is formed on the surface of the flexible substrate layer.

[0068] Step S5: Encapsulate and obtain flexible damage sensing material; On the functional laser-induced graphene structure 1 in step S4, a pre-set electrode connection area (usually at the end of the pattern) is applied and a small amount of conductive silver paste is coated on the electrode connection area to ensure good ohmic contact. Then, a flexible copper wire with a diameter of 0.5 mm is attached to the conductive silver paste as the end point of the wire electrode and cured in an oven at 80°C for 30 minutes to form the electrode lead-out end.

[0069] A polyethylene-polyvinyl acetate copolymer film was cut into 400mm × 400mm dimensions and used as an encapsulation layer to cover a functional laser-induced graphene structure 1 with conductive electrodes, thus forming a sandwich structure. The sandwich structure was then placed in a hot press for secondary hot pressing. The hot press parameters were set to a temperature of 85℃ and a pressure of 0.1MPa, with a holding time of 5 minutes. This hot pressing process completely sealed the functional laser-induced graphene structure 1 within the press. After natural cooling to below 40℃, the material was removed, yielding the large-format flexible damage sensing material.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A large-format flexible damage sensing material, characterized in that, It includes a flexible substrate layer, a conductive layer superimposed on the flexible substrate layer, and an encapsulation layer covering the conductive layer; the conductive layer is made of a laser-engraved polyimide film, and the conductive layer has a functional laser-induced graphene structure (1) and an auxiliary separation structure (2) etched by a laser engraving machine. The auxiliary separation structure (2) includes a film through hole (21) and an edge cutting line (22). The functional laser-induced graphene structure (1) includes several conductive rows (11) and several conductive columns (12). The conductive rows (11) and conductive columns (12) are arranged to form multiple squares. Each square has a film through hole (21). The edge of the polyimide film has several edge cutting lines (22) that penetrate the film from the thickness direction and are distributed radially. One end of the edge cutting line (22) reaches the edge of the film, and the other end does not contact the functional laser-induced graphene structure (1).

2. The large-format flexible damage sensing material according to claim 1, characterized in that, The flexible substrate layer is made of silicone film, thermoplastic polyurethane film or polyethylene-polyvinyl acetate copolymer.

3. The large-format flexible damage sensing material according to claim 1, characterized in that, The encapsulation layer is made of silicone film, thermoplastic polyurethane film, or polyethylene-polyvinyl acetate copolymer.

4. A method for preparing a large-format flexible damage sensing material, used to prepare the large-format flexible damage sensing material according to claim 1, characterized in that, Includes the following steps: Step S1: Prepare a functional laser-induced graphene structure by etching the functional laser-induced graphene structure on a polyimide film using a laser engraving machine, thereby making the polyimide film a conductive layer. Step S2: Prepare auxiliary separation structure, functional laser-induced graphene structure (1) After etching, use a laser engraving machine to cut the conductive layer to produce auxiliary separation structure; Step S3: Hot-press the flexible substrate layer and the conductive layer together; Step S4: Mechanically peel off the conductive layer, peeling off the part of the conductive layer except for the functional laser-induced graphene structure (1) from the flexible substrate layer, so that the complete functional laser-induced graphene structure (1) is retained on the flexible substrate layer.

5. The method for preparing the large-format flexible damage sensing material according to claim 4, characterized in that, Step S1 includes the following steps: Step S11: Pretreatment of polyimide film. Cut polyimide film with a thickness of 0.025mm~0.10mm to the required size, clean polyimide film with ethanol and acetone solution, and then put polyimide film into an electric heating drying oven at 50℃ for 1 hour before taking it out. Step S12: Obtain a functional laser-induced graphene structure; After pretreatment, place the glass with the polyimide film on the laser engraving machine platform, and use the laser engraving machine to perform laser scanning on the polyimide film in step S11, so that a functional laser-induced graphene structure is generated on the polyimide film.

6. The method for preparing the large-format flexible damage sensing material according to claim 5, characterized in that, In step S12, when using a laser engraving machine to generate a functional laser-induced graphene structure, the functional laser-induced graphene structure (1) and laser engraving parameters are imported into the laser control system, and the laser power is set to 10.5W~11.5W and the speed is 5mm / s~15mm / s.

7. The method for preparing the large-format flexible damage sensing material according to claim 6, characterized in that, In step S2, the laser engraving machine is set to laser cutting mode, and the cutting path of the auxiliary separation structure (2) is preset by computer-aided design software. The laser power is set to 20W~30W and the speed is 30mm / s.

8. The method for preparing the large-format flexible damage sensing material according to claim 7, characterized in that, In step S3, a flexible substrate layer with the same size as the conductive layer in step S2 and a thickness of 0.15 mm is cut out. The flexible substrate layer is precisely stacked on the conductive layer to form a laminated structure. Then, the laminated structure is moved into a flatbed hot press for lamination.

9. The method for preparing the large-format flexible damage sensing material according to claim 8, characterized in that, In step S3, the process parameters of the hot pressing process are: temperature 80℃~100℃, pressure 0.1MPa~0.2MPa, heat preservation and pressure holding for 5min~10min. After the heat preservation and pressure holding is completed, heating is stopped and pressure is released, allowing the sample to cool naturally to room temperature in the hot press before being taken out.

10. The method for preparing the large-format flexible damage sensing material according to claim 9, characterized in that, In step S4, the stacked structure from step S3 is removed from the hot press. Starting from one corner of the stacked structure, the operator gently peels off the conductive layer with tweezers and slowly and steadily peels off the part of the conductive layer except for the laser-induced graphene structure (1) from the flexible substrate layer at a small angle, so that the laser-induced graphene structure (1) is completely preserved on the flexible substrate layer.

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