Thermally controlled reversible adhesive conductive composite for quick change of back-sticky flexible sensor

Abstract

The present application belongs to the field of adhesive, discloses a heat-controlled reversible adhesive conductive composite material for quick replacement of back-sticking type flexible sensor, which is prepared from bisphenol A diglycidyl ether, polyether amine, epoxy polyamide curing agent, succinic anhydride, PEDOT:PSS, fumed silica, 3-aminopropyl triethoxysilane, single-walled carbon nanotube and glycerol carbonate. In the composite material provided by the present application, PEDOT:PSS and single-walled carbon nanotube are introduced as conductive fillers, succinic anhydride is introduced to endow the material with thermal reversibility, epoxy polyamide curing agent is introduced to provide a rigid support skeleton, 3-aminopropyl triethoxysilane and glycerol carbonate are introduced to improve the performance of the material, the obtained composite material has excellent adhesive performance, can stably transmit electric signals, and can endow the back-sticking type flexible sensor with quick replaceability because the curing and debonding modes of the composite material are both temperature-controlled.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of adhesives, and specifically relates to a thermal control reversible bonding conductive composite material for quick replacement of back-sticker type flexible sensors. BACKGROUND

[0002] With the development of wearable electronic devices and artificial electronic skin, flexible sensors have attracted much attention due to their potential applications in human-computer interaction, biomedical monitoring and motion detection. Most flexible sensors adopt a sandwich structure of electrode layer-sensing layer-electrode layer, which can significantly improve sensitivity, response speed and multi-dimensional signal analysis capability through interlayer microstructure design (such as micro-dome array, porous network or interlocking topography). However, they usually face the problems of assembly difficulty and interface bonding performance trade-off during device assembly. In view of this problem, researchers have made explorations in multiple directions.

[0003] Patent CN116147796A provides a self-powered flexible sensor based on pressure and temperature, as well as its manufacturing method and application. The sensor adopts a flexible multilayer structure design, including a lower electrode layer, a thermoelectric self-powered layer, a thermal resistance sensing layer, an interlocking pressure-sensitive layer and an upper electrode layer stacked from bottom to top, to realize non-crosstalk detection and decoupling of pressure and temperature signals. Although the interlocking structure improves the stability of the device, other packaging layers are simply physically inserted and assembled, and the interface bonding performance is not improved by chemical methods, and the device faces the problems of poor repeatability and long-term signal transmission stability.

[0004] Patent CN119366927A provides a multi-modal physiological signal sensor, as well as its preparation method and application. The sensor adopts a flexible multilayer integrated design, including an upper packaging layer, a mechanical sensing layer, a lower packaging layer and an electrical physiological sensing layer from top to bottom, which can simultaneously and independently collect physical signals and electrical physiological signals to solve the problem of single sensor signal feature single and difficulty in accurately reflecting the complex state of the human body. Although the method of spin coating is used to assemble each layer, the interfacial bonding stability is improved, but when the flexible device is damaged, it faces the problems of difficulty in replacement and electrode layer reuse.

[0005] The paper "Efficient Fabrication of Bioinspired Flexible Pressure Sensors via Electrohydrodynamic Jet Printing Method" (Shiwei Shi, Zeshan Abbas, Xiaoguang Hu, et al. Macromol. Rapid Commun. 2024, 45:2400322.) describes a bio-inspired pressure sensor based on the structure of a gecko's foot. The core is to use EHD jet printing technology to manufacture micro-dome structures, and the surface is sprayed with carbon nanotubes (CNTs) to form a sandwich structure, which improves the sensitivity and stability of the device. However, the manufacturing process is complex, and the stability of the multi-interface combination is not considered.

[0006] The paper "A Hypersensitive, Fast-response Biomimetic Pressure Sensor Inspired by the Superior Sensing Structures of the Dragonfly's Neck" (Yuechun Ding, Rui Zhou, Changchao Zhang, et al. Journal of Bionic Engineering. 2025, 22:251-261.) achieves exponential growth of contact area through gradient interlocking design of horn-mushroom microstructure pairs. The sensitivity of this biomimetic interlocking mechanism is 75% higher than that of non-biomimetic structures, and the response time is less than 90 ms. However, the interlocking structure has two heterogeneous interfaces, and the alignment accuracy between the two layers needs to be sub-micron. The microstructure forming relies on magnetic field spatial positioning, and the PDMS / CIP composite slurry needs to be cured in two steps, which still has the problem of interface bonding difficulty and complex process forming.

[0007] The sensor with the same surface electrode gradually attracts the attention of researchers due to its advantages such as easy assembly between the electrode and the electrode, fewer functional layer structures, and simple manufacturing process. Among them, the back-pasted flexible sensor has the advantages of independent replaceability, electrode multiplexing, arrayability, and strong human-machine adaptability, and has become the most potential candidate for the combination of flexible sensor devices and electrodes.

[0008] Patent CN119931243A provides a photocuring composition, conductive flexible film layer and flexible pressure sensor and its preparation method and application, which uses a 3D printable material system of silane modified carbon nanotube composite photocuring resin, realizes the precise manufacturing of micrometer level pyramid / cone structure conductive flexible film layer through digital light processing (DLP) layering curing technology, and the sensor has high sensitivity and ultra-wide range. The 3D printed pressure sensitive layer is directly cut and attached to the interdigital electrode, when the pressure sensitive layer is damaged, only the old layer needs to be peeled off and a new printed unit is attached, and the electrode layer can be reused, but such physical combination can hardly ensure that the sensor can work stably without peeling when facing complex environment.

[0009] Patent CN113503992A provides a flexible pressure sensor based on a multilayer composite film and its preparation method and application, the sensitive layer is composed of two layers of porous reduced graphene oxide (rGO) sandwiching porous MXene film, the rGO layer pores and MXene layer pores form a gradient distribution, and wide range high sensitivity detection is realized by three layer superposition sensitive layer design. It directly prints the interdigital electrode structure on the metal double-sided conductive adhesive tape for bonding the substrate layer and the sensor device, although the interface bonding performance is improved, but when the sensor fails, there is no reasonable method to quickly peel off the sensor device.

[0010] The paper "High-Performance Flexible Pressure Sensor Based on Controllable Hierarchical Microstructures by Laser Scribing for Wearable Electronics" (Qifeng Du, Lanlan Liu, Ruitao Tang, et al. Adv. Mater. Technol. 2021, 6, 2100122.) by laser scribing for wearable electronics, by treating the PDMS stress sensing layer with oxygen plasma, treating the silver nanowire (AgNWs) solution with polyvinyl alcohol (PVA) modification, and finally heat curing to form AgNWs-PDMS interface, this process step strengthens the interface bonding between sensor devices, but only medical tape is used to package the flexible device and electrode, which greatly reduces the stability of the electrical signal transmission to the electrode interface.

[0011] The paper “High-Sensitivity Wearable Flexible Pressure Sensor Based on MXene and Polyaniline for Human Motion Detection” (Chunqing Yang, Weiwei Wang, Dongzhi Zhang, et al. ACS Appl. Polym. Mater. 2023, 5, 10386-10394) loads MXene and polyaniline (PANI) onto melamine sponge skeletons through a two-step immersion process, achieving high sensitivity and wide range synergy control under low-cost solution process. The encapsulation uses a simple mechanical encapsulation strategy, which improves the replaceability of the sensor when damaged, but the simple physical encapsulation cannot guarantee the stability of the electrical signal transmission.

[0012] Despite the significant progress in the interface combination of flexible sensor devices and electrode layers, there are still key problems in the application of rapid replacement, especially in the same surface electrode back-paste type sensor:

[0013] 1. Conflict between structure design and replacement demand: Traditional flexible sensor devices mainly include sensitive materials and electrode circuits, and their structure mainly adopts a sandwich structure. The design focuses on the stable combination of the two, but does not consider the possibility of failure of sensitive materials due to damage or aging in use. In practical applications, it is necessary to achieve the non-destructive peeling and replacement of sensitive materials from the electrode without damaging the integrity of the signal processing circuit. However, adhesives with strong bonding properties and controllable detachment characteristics are the core of the replaceability of back-paste type sensors, but current research is still relatively scarce.

[0014] 2. Main debonding techniques are difficult to balance the needs of “fast debonding” and “protecting flexible electrodes”: Solvent-assisted debonding (such as chelation reaction based on catechol groups) requires the addition of chelating agents, which can easily damage metal electrodes, and residual solvents may induce subsequent electrochemical corrosion; light debonding (such as based on azobenzene groups) is only suitable for thin layers or transparent materials on both sides of the adhesive, and has poor compatibility with non-transparent structures; laser debonding is highly concentrated in energy, and can easily ablate micro metal wires in the precision circuit.

[0015] 3、Temperature-controlled debonding Temperature-controlled debonding has strong penetration and theoretically meets the replacement requirements of back-mounted sensors, but the existing system has obvious shortcomings: thermoplastic adhesives (such as vinyl acetate and ethylene-vinyl acetate copolymer EVA) rely on linear molecular structure and achieve bonding through physical melting or solvent evaporation. Although they have reversible processability and flexibility, they have poor temperature resistance and weak creep resistance, and are prone to deformation or debonding under long-term load.

[0016] 4、Epoxy resin needs to be cured in a specific way to achieve strong adhesion, but the existing methods have limitations: light curing (such as ultraviolet curing) has limited curing depth and is only suitable for thin transparent systems, and has poor adaptability to shadow areas of complex substrates; solvent-based curing (such as polyaziridine) may erode flexible substrates (such as polyethylene terephthalate PET and PDMS), causing swelling or plasticization and affecting the stability of the sensor element; temperature curing can achieve deep and uniform curing (not limited by light), but flexible substrates (such as polyimide PI film and PDMS) and sensitive elements are not resistant to high temperatures, and high curing temperatures can easily cause substrate deformation, degradation or electronic component failure, so it is urgent to develop a milder curing strategy at a lower temperature.

[0017] 5、Defects of reversible processing of traditional epoxy glue: Traditional macromolecular epoxy resin relies on rigid covalent crosslinking network to form a three-dimensional structure, which gives it high adhesive strength and environmental stress resistance, but permanent crosslinking causes the material to lose reversible processing - debonding requires breaking high-energy covalent bonds, often relying on continuous high temperature or strong solvent, which not only consumes a lot of energy, but also easily causes substrate damage (such as metal oxidation and polymer thermal deformation), so dynamic modification is needed to reduce the debonding energy barrier and shorten the debonding time.

[0018] 6、Metallic conductive particles (such as silver powder) can improve the conductivity of epoxy glue, but their introduction can cause two problems: the rigid network formed significantly limits the movement of polymer molecular chains, making it difficult for the glue layer to completely peel off after interface failure and easily remaining on the substrate; aggregates (such as silver powder agglomerates) formed by uneven dispersion of particles become stress concentration sources under mechanical cyclic load, causing unstable electrical signal transmission in dynamic use.

[0019] 7、PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid) as a commonly used conductive material for flexible sensors can build a flexible conductive network, but has inherent defects: intrinsic conductivity is low and has a positive temperature coefficient characteristic (resistance decreases with temperature rise), resulting in poor glue conductivity and insufficient signal transmission stability in dynamic temperature environment, so fillers need to be added to regulate conductivity and balance the temperature drift effect.

[0020] 8、Interface bonding long-term reliability problem: although the epoxy resin has high bonding strength after curing, its rigid cross-linked network is difficult to effectively dissipate dynamic compression stress; and its combination with copper electrode mainly depends on physical adsorption (such as Van der Waals force) and mechanical anchoring, and the interface stress continues to accumulate under long-term use, which easily causes the expansion of micro-cracks between the glue layer and the copper electrode, and finally affects the reliability. Therefore, the interface of the glue layer or the copper electrode needs to be modified without reducing the debonding efficiency to enhance the long-term stable adhesion. SUMMARY

[0021] In order to solve the above technical problems, the present application provides a heat-controlled reversible bonding conductive composite material for back-pasted flexible sensor quick replacement, which aims to effectively improve the problems existing in the combination of traditional flexible sensor and electrode, such as complex packaging process, poor interface bonding stability, unstable signal transmission, and difficult quick replacement of device damage, so that the prepared heat-controlled reversible bonding conductive composite material can be widely used as an adhesive in back-pasted flexible electronic device packaging.

[0022] In order to solve the above problems, the present application adopts the following technical scheme:

[0023] The heat-controlled reversible bonding conductive composite material for back-pasted flexible sensor quick replacement is composed of the following components in mass percentage: polyether amine 28-32%, epoxy polyamide curing agent 7-11%, succinic anhydride (SA) 3-5%, PEDOT:PSS dispersion liquid with solid content of 2.8-3% 5-8%, single-walled carbon nanotube (SWCNT) 0.1-0.5%, fumed silica 1-2%, 3-aminopropyl triethoxysilane (APTES) 2-4%, glycerol carbonate (GC) 6-10%, and the balance is bisphenol A diglycidyl ether.

[0024] Most preferably, the heat-controlled reversible bonding conductive composite material is composed of the following components in mass percentage: bisphenol A diglycidyl ether 39.2%, polyether amine 29%, epoxy polyamide curing agent 9%, succinic anhydride 3.6%, PEDOT:PSS dispersion liquid with solid content of 2.8-3% 5.5%, single-walled carbon nanotube 0.4%, fumed silica 1.4%, 3-aminopropyl triethoxysilane 3.6%, and glycerol carbonate 8.3%.

[0025] The thermally controlled reversible adhesive conductive composite material provided by this invention uses bisphenol A diglycidyl ether as a matrix and achieves performance breakthroughs through precise component design: It employs the primary amine groups of succinic anhydride and polyetheramine as dynamic crosslinking agents, introducing a polysuccinamide (PSA) dynamic network as a reversible debonding functional unit. Simultaneously, the flexible segments of polyetheramine optimize the material's rigid-toughness balance and the stability of the conductive network. Specifically, the PSA dynamic network is formed by the reaction of succinic anhydride and amine. Under medium-temperature conditions (140-160℃), it triggers an intramolecular cyclization reaction, promoting the efficient conversion of amide bonds into five-membered succinimides. The released primary amine active sites significantly reduce interfacial adhesion energy, achieving non-destructive debonding of the sensor. Meanwhile, the amine groups and epoxy groups of the epoxy polyamide curing agent react to form a rigid covalent network framework, which both anchors the PSA dynamic network and ensures the integrity of the network framework during debonding. Through the synergistic effect of this material system, the problem of sensor structural damage caused by prolonged high-temperature melting of traditional hot melt adhesives is effectively solved.

[0026] Furthermore, the glycerol carbonate, due to the high ring strain of its five-membered ring, drives the primary amine groups of the polyether amine to preferentially undergo ring-opening reactions in the low-temperature range (25-80℃), generating a flexible urethane prepolymer network. This network can encapsulate the SWCNT-PEDOT conductive pathway to form a stress-buffered layer. Simultaneously, this prepolymer network provides skeletal support for bisphenol A diglycidyl ether and the epoxy polyamide curing agent at the high-temperature stage (120℃), promoting the crosslinking of epoxy groups and fixing the PSA dynamic network structure. This asynchronous crosslinking mechanism lowers the bulk curing temperature to 80℃, significantly improving the material's compatibility with flexible substrates.

[0027] Furthermore, the PEDOT:PSS / SWCNT composite conductive filler constructed through APTES interface modification can be protonated to -NH3 within the colloid by means of the amino group (-NH2) generated by the hydrolysis of the silane coupling agent APTES. + , with the sulfonate group (-SO3) of PSS - ) Forming ionic bonds, significantly enhancing charge carrier activity in PEDOT + The migration efficiency between the chain and SWCNT significantly improves the overall conductivity of the composite system; simultaneously, the negative conductivity temperature coefficient of SWCNT and PEDOT change with temperature. + The synergistic effect of the positive conductivity temperature coefficient caused by the thermal expansion of chain segments constructs a temperature drift self-compensation mechanism, making the resistance change rate of the material extremely low in the temperature range of 0-60℃, effectively suppressing the electrical signal drift problem caused by thermal stress in traditional conductive materials.

[0028] Further, the three-dimensional nanometer network formed by the fumed silica can fill the pores of the polymer matrix and form physical cross-linking points with the ether oxygen chain (-O-) of the polyetheramine by hydrogen bonding, limiting the molecular chain slip, thereby improving the elastic modulus and creep resistance of the composite material; at the same time, the fumed silica realizes confined dispersion on the PEDOT:PSS through the surface silicon hydroxyl (Si-OH), eliminates the anisotropy of the filler settlement, and further guarantees the stability of the electrical signal transmission of the adhesive layer.

[0029] Further, the silanol (≡Si-OH) generated by the hydrolysis of the silane coupling agent APTES can undergo condensation reaction with the oxide layer of the copper electrode to form high-strength Si-O-Cu covalent bond, and the interfacial bonding energy is jumped from the physical adsorption level to the chemical bonding energy level, thereby significantly enhancing the adhesion reliability of the colloid to the copper electrode.

[0030] The application further provides a preparation method of the heat-controlled reversible adhesive conductive composite material for quick replacement of the back-pasted flexible sensor, comprising the following steps:

[0031] Step 1: Bisphenol A diglycidyl ether and polyetheramine are added into a reaction kettle, and stirring is carried out at 60-70 DEG C and a rotating speed of 450-550 rpm for 25-35 minutes, so that the two are uniformly dispersed, then appropriate glycerol carbonate is added, and constant temperature stirring is continued until a homogeneous phase is obtained, thereby obtaining a resin matrix prepolymer solution;

[0032] Step 2: Epoxy polyamide curing agent and succinic anhydride are added into the resin matrix prepolymer solution, and stirring is carried out at 45-55 DEG C and a rotating speed of 450-550 rpm for 35-45 minutes, then fumed silica is continuously added, and stirring is carried out at a rotating speed of 1800-2300 rpm for 15-25 minutes, thereby obtaining solution A;

[0033] Step 3: Part of 3-aminopropyl triethoxysilane is uniformly mixed with appropriate glycerol carbonate at room temperature, single-walled carbon nanotubes are added, ultrasonic treatment is carried out at 55-65 DEG C for 1-2 hours, then drying is carried out at room temperature in a vacuum environment for 1 hour, thereby obtaining pretreated single-walled carbon nanotubes;

[0034] Step 4: PEDOT:PSS dispersion liquid is mixed with the remaining glycerol carbonate, ultrasonic treatment is carried out at room temperature for 15-25 minutes, the pretreated single-walled carbon nanotubes are added and ultrasonic treatment is continuously carried out for 35-45 minutes, the remaining 3-aminopropyl triethoxysilane is added and ultrasonic treatment is continuously carried out for 15-20 minutes, thereby obtaining solution B;

[0035] Step 5: Solution A is added into solution B, stirring is carried out at room temperature and a rotating speed of 450-550 rpm for 1-3 hours, vacuum defoaming is carried out, and a heat-controlled reversible adhesive conductive composite material for quick replacement of the back-pasted flexible sensor is obtained.

[0036] Further, the mass ratio of glycerol carbonate added in step 1, step 3 and step 4 is 1:1-1.5:0.5-1.

[0037] Further, the mass ratio of 3-aminopropyl triethoxysilane added in step 3 and step 4 is 1:0.1-0.2.

[0038] The application also discloses a use method of the heat-controllable reversible bonding conductive composite material, in particular to the following steps:

[0039] Step 1, first, the area to be pasted of the flexible printed circuit board (FPCB) is wiped with ethanol to oxidize the copper electrode surface of the area to be pasted, the heat-controllable reversible bonding conductive composite material is applied to the area to be pasted of the FPCB, then the back-sticking type flexible sensor is pasted, and the back-sticking type flexible sensor is pre-cured at 75-85 DEG C for 1.5-2.5 hours and then cured at 110-130 DEG C for 0.5-1.5 hours, so that the back-sticking type flexible sensor is pasted.

[0040] Step 2, when the back-sticking type flexible sensor is replaced, the heat-controllable reversible bonding conductive composite material loses adhesion by heating at 140-160 DEG C for 3-5 minutes, the back-sticking type flexible sensor to be replaced and the glue layer formed by the heat-controllable reversible bonding conductive composite material are removed, and the new back-sticking type flexible sensor is pasted according to the method of step 1.

[0041] Compared with the prior art, the application has the following beneficial effects:

[0042] 1. The epoxy resin-based heat-controllable reversible bonding conductive composite material provided by the application introduces a succinic anhydride-derived polysuccinamide dynamic bond in the main chain of the epoxy resin, so that the amide bond undergoes controllable cyclization-dissociation balance under heating conditions. This design replaces the traditional thermal melting debonding with selective chemical bond rupture, which not only combines the back-sticking type flexible sensor, solves the problem of complex device and electrode combination packaging process and difficult disassembly and replacement in the traditional sandwich structure, but also ensures that the back-sticking type flexible sensor is not scratched or damaged when it is quickly replaced.

[0043] 2. The heat-controllable reversible bonding conductive composite material provided by the application generates a dynamic amide bond network by means of the polysuccinamide dynamic bond and the polyether amine reaction, and triggers directional intramolecular cyclization reconstruction (forms a five-membered succinimide ring) to realize selective dissociation of the dynamic bond when heated. This heat-controllable debonding mechanism has the following advantages: it does not need to rely on the light transmittance of the substrate required for light debonding, and can be applied to non-transparent composite structures; it can avoid the corrosion of chelating agents to copper electrodes and the electrochemical corrosion caused by solvent residues in solvent debonding; and it realizes mild debonding through a uniform heat field, avoiding the risk of ablation of micro-wires caused by local energy focusing in laser debonding.

[0044] 3、The thermal control reversible bonding conductive composite material provided by the present application relies on the three-dimensional cross-linked network framework formed by curing bisphenol A diglycidyl ether, avoids the problems caused by linear molecular chain slippage of thermoplastic glue (such as EVA), and thus eliminates the risk of deformation and debonding under long-term load. At the same time, the epoxy skeleton is anchored by poly succinamide dynamic bonds and combined with the interpenetration of polyether amine flexible segments to form a rigid-tough interlocking structure, which gives the material high dimensional stability and anti-creep performance. In addition, the active epoxy group of the epoxy resin reacts with the primary amine group of the polyether amine to form a stable covalent bond layer, avoiding the problems of accidental debonding at low temperature and out-of-control side reactions caused by the low reverse reaction energy barrier of the typical dynamic covalent system (such as furan-maleimide).

[0045] 4、The thermal control reversible bonding conductive composite material provided by the present application introduces glycerol carbonate groups to trigger the primary amine ring-opening reaction driven by five-membered ring tension with polyether amine, generating a flexible urethane pre-network at the molecular level, providing support for the delayed crosslinking of the epoxy resin and the activation of the poly succinamide dynamic bond. This asynchronous crosslinking mechanism enables the entire epoxy material to achieve staged curing within a moderate temperature window of 80-120℃, ensuring that the reversible bonding conductive composite material is cured and assembled at a heating temperature much lower than the damage temperature of the flexible sensor and flexible copper electrode on both sides.

[0046] 5、The thermal control reversible bonding conductive composite material provided by the present application constructs poly succinamide dynamic bonds through succinic anhydride (SA), triggering the directional formation of five-membered succinimide rings at the molecular level. This mechanism reduces the debonding energy barrier of the overall adhesive, allowing the debonding process to be completed within 2 minutes of moderate heating at 140-160℃. The static covalent bond network formed after the epoxy polyamide curing agent is cured can anchor the PSA dynamic network, ensuring that the integrity of the glue layer after dissociation reaches 95%. Compared with traditional epoxy-based adhesive materials, the debonding temperature and time are significantly reduced, avoiding the risk of copper electrode oxidation and FPCB substrate thermal deformation caused by continuous high temperature.

[0047] 6、The thermal control reversible bonding conductive composite material provided by the present application constructs a flexible interpenetrating conductive network by introducing PEDOT:PSS intrinsic conductive polymer and fumed silica. The PEDOT:PSS conductive phase is dynamically anchored by the hydrogen bonds of polyether amine to form a stable and continuous conductive path, and the fumed silica nanoparticles limit the dispersion of PEDOT:PSS through the surface silicon hydroxyl groups (Si-OH), eliminating the anisotropy of filler sedimentation. The synergistic effect of the two materials not only ensures the formation of a stable conductive network in the glue layer, but also avoids the instability of electrical signal transmission caused by the aggregation of conductive fillers.

[0048] 7、 The heat control reversible adhesive conductive composite material disclosed by the application, by introducing pretreated single-walled carbon nanotubes into the epoxy resin matrix and the PEDOT:PSS conductive network, makes the amino group (-NH2) on the surface of the SWCNT bond with the sulfonate group (-SO3-) of the polystyrene sulfonate (PSS) in the PEDOT:PSS, and the reaction constructs a three-dimensional interpenetrating conductive network at the molecular level, so that the intrinsic conductivity of the composite material is improved. Meanwhile, the conductivity of the single-walled carbon nanotube has a negative temperature coefficient with temperature change, and the introduction of the single-walled carbon nanotube can balance the temperature drift problem caused by the positive temperature coefficient of the PEDOT:PSS.

[0049] 8、 The heat control reversible adhesive conductive composite material disclosed by the application, by wiping the copper electrode with ethanol to expose the oxide layer (Cu2O), the silanol (≡Si-OH) generated by the hydrolysis of APTES and the Cu2O are condensed to form a Si-O-Cu covalent bond, which greatly improves the interface bonding energy; meanwhile, the amino group (-NH2) of the APTES is protonated to -NH3 + in the colloid, and the sulfonate group (-SO3 - ) of the PSS forms an ionic bond, which not only enhances the stability of the conductive network, but also blocks the penetration of water and oxygen. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 The curing reaction and molecular structure formation mechanism of the heat control reversible adhesive conductive composite material prepared in the embodiment of the application.

[0051] Figure 2 The reversible reaction of the dynamic amide bond network of the heat control reversible adhesive conductive composite material prepared in the embodiment of the application with temperature change after curing.

[0052] Figure 3 The influence comparison of different curing temperature-time on the tensile shear strength of the heat control reversible adhesive conductive composite material.

[0053] Figure 4 The influence of APTES cooperated with copper electrode treatment on the tensile shear strength of the heat control reversible adhesive conductive composite material.

[0054] Figure 5 The influence of single-walled carbon nanotube cooperated with regulation on the conductivity and temperature drift characteristics of the heat control reversible adhesive conductive composite material.

[0055] Figure 6 The regulation of the mass ratio of epoxy polyamide curing agent / succinic anhydride on the optimal debonding temperature of the heat control reversible adhesive conductive composite material.

[0056] Figure 7 The influence of the mass ratio of epoxy polyamide curing agent / succinic anhydride on the fastest debonding time of the heat control reversible adhesive conductive composite material.

[0057] Figure 8 Influence of debonding temperature on debonding efficiency of the thermally controlled reversible adhesive conductive composite under the best ratio. DETAILED DESCRIPTION

[0058] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present application is not limited to the following embodiments.

[0059] Example 1

[0060] The thermally controlled reversible adhesive conductive composite for quick change of back-sticking type flexible sensor provided in the present embodiment has the following components in terms of mass percentage: bisphenol A diglycidyl ether (model DER332) 39.2%, polyetheramine (model D400) 29%, epoxy polyamide curing agent (model Ancamide 260A) 9%, succinic anhydride (SA) 3.6%, PEDOT:PSS dispersion liquid with solid content of 2.8-3% 5.5%, single-walled carbon nanotube (SWCNT) 0.4%, fumed silica (model Aerosil 200) 1.4%, APTES 3.6%, glycerol carbonate (GC) 8.3%. The specific preparation steps are as follows:

[0061] Step 1, 39.2g of bisphenol A diglycidyl ether and 29g of polyetheramine are added to a reaction kettle, stirred at 500rpm for 30 minutes at 65℃ to disperse the two, 2.8g of glycerol carbonate is added, and stirred for 20 minutes to obtain a homogeneous phase, to obtain a resin matrix prepolymer solution.

[0062] Step 2, 9g of epoxy polyamide curing agent and 3.6g of succinic anhydride are added to the resin matrix prepolymer solution, and stirred at 500rpm for 40 minutes at 50℃; 1.4g of fumed silica is further added, and stirred at 2000rpm for 20 minutes to obtain solution A.

[0063] Step 3, 3.2g of APTES is mixed with 3.0g of glycerol carbonate at room temperature, 0.4g of single-walled carbon nanotube is added, and ultrasonic treatment is performed at 60℃ for 1.5 hours, and then dried in a vacuum environment at room temperature for 1 hour to obtain pretreated single-walled carbon nanotube.

[0064] Step 4, 5.5g of PEDOT:PSS dispersion liquid with solid content of 3% is mixed with 2.5g of glycerol carbonate, ultrasonic treatment is performed at room temperature for 20 minutes, pretreated single-walled carbon nanotube is added and ultrasonic treatment is continued for 40 minutes, 0.4g of APTES is added and ultrasonic treatment is continued for 15 minutes to obtain solution B.

[0065] Step 5, add solution A to solution B, stir at room temperature at a speed of 500 rpm for 2 hours, and then deaerate at room temperature for 3 hours in a vacuum environment to obtain a thermally controlled reversible adhesive conductive composite material for quick replacement of a back-sticker type flexible sensor.

[0066] The use method of the thermally controlled reversible adhesive conductive composite material prepared in this embodiment is as follows:

[0067] Step 1, first wipe the area to be pasted of the FPCB with ethanol to oxidize the copper electrode surface of the area to be pasted, apply the thermally controlled reversible adhesive conductive composite material to the area to be pasted of the FPCB, then paste the back-sticker type flexible sensor, and place it at 80°C for 2 hours for pre-curing and then at 120°C for 1 hour for curing to complete the mounting of the back-sticker type flexible sensor.

[0068] Step 2, when replacing the back-sticker type flexible sensor, heat at 150°C for 4 minutes to make the thermally controlled reversible adhesive conductive composite material lose adhesion, remove the back-sticker type flexible sensor to be replaced and the glue layer formed by the thermally controlled reversible adhesive conductive composite material, and mount a new back-sticker type flexible sensor according to the method of step 1.

[0069] Figure 1 The reaction and molecular mechanism related to curing of the thermally controlled reversible adhesive conductive composite material prepared in this embodiment are presented. As can be seen from the figure, in the low-temperature curing stage, glycerol carbonate (GC) drives the primary amine of polyetheramine to preferentially open ring due to the high tension of the five-membered ring, generating a flexible urethane pre-polymer network at the molecular level; after warming up, the polyetheramine is opened ring with bisphenol A diglycidyl ether epoxy group and succinic anhydride (SA) to build a dynamic crosslinking network. In addition, the copper electrode is wiped with ethanol before curing to form an oxide layer, which reacts with the silane coupling agent APTES to build a Si-O-Cu covalent bonding layer, so that the interfacial bonding energy of the glue layer to the copper electrode is improved from physical adsorption to chemical bonding level, strengthening the long-term stable adhesion effect to the copper electrode.

[0070] Figure 2 The reversible reaction of the dynamic amide bond network of the thermally controlled reversible adhesive conductive composite material after curing with temperature change is shown. After curing, the SA forms a cyclic amide bond with the polyetheramine, which will start a dynamic reversible conversion as the temperature rises: through an intermediate state, a five-membered succinimide ring is gradually formed, and through this dynamic change at the molecular level, the glue layer is quickly debonded when heated; when cooled, the reaction is reversible, and the cyclic amide bond structure can be restored, so that the material has the characteristics of thermally controlled reversible adhesion, which meets the quick replacement requirement of the back-sticker type sensor.

[0071] Figure 3The tensile shear performance difference of the conductive composite material of the present embodiment at different curing temperatures and durations is presented. The conductive composite material is coated on the overlapping area of copper sheet A treated by ethanol wiping, and then a copper sheet B treated by ethanol wiping and having the same size is overlaid to form an overlapping joint. Then, the conductive composite material is cured by using different conditions. The tensile shear strength is tested by using a tensile press (strength value (MPa) = maximum load (N) / overlapping area (mm 2 ). It can be seen from the figure that within 2h at 80℃, the glycerol carbonate groups are largely consumed to generate a flexible urethane network to support the initial strength; after 2h, the comparison between the group cured at 80℃ all the time and the group switched to 120℃ is significant - high temperature accelerates the crosslinking of epoxy and amine, and the group of asynchronous curing (80℃ 2h + 120℃) has the optimal tensile shear strength of the adhesive layer due to the staged curing. For the group cured at 120℃ all the time, the epoxy needs an induction period to form crosslinking points, the initial strength grows slowly, and after 2h, the induction period ends and the crosslinking is rapid, so the final strength exceeds that of the group cured at 80℃ all the time, which reflects the regulation of curing temperature and duration on the mechanical properties of the material.

[0072] Figure 4 To verify the comparative test results of the conductive composite material of the present embodiment on the adhesion strength of copper electrodes, the effects of material formula, APTES addition and copper sheet treatment on the tensile shear strength are explored by comparing 5 groups of samples (A-E):

[0073] Group A: 39.2g of bisphenol A diglycidyl ether is mixed with 29g of polyether amine, stirred at 65℃ for 30 minutes at a speed of 500rpm, and then coated and cured;

[0074] Group B: 39.2g of bisphenol A diglycidyl ether is mixed with 29g of polyether amine, 3.6g of APTES is added, stirred at 65℃ for 30 minutes at a speed of 500rpm, and then coated and cured;

[0075] Group C: the conductive composite material is prepared according to the same raw materials and process of embodiment 1, except that the amount of APTES in steps 3 and 4 is 0, and then coated and cured after preparation;

[0076] Group D: the thermal control reversible bonding conductive composite material prepared by using embodiment 1 is coated and cured;

[0077] Group E: the thermal control reversible bonding conductive composite material prepared by using embodiment 1 is coated and cured.

[0078] All samples are prepared by using the process of “80℃ pre-curing for 2h + 120℃ curing for 1h”, and the copper sheet overlapping area of group E is additionally wiped by ethanol.

[0079] From the results of Figure 4 , it can be seen that:

[0080] Group A and Group C: The strength of Group C is significantly higher than that of Group A (traditional epoxy system), which shows that the adhesion performance of the material system of the application (even without APTES) to the copper electrode is much better than that of the traditional epoxy system, verifying the advantages of the formula design.

[0081] Group A / B and Group C / D: The strength of Group B is slightly higher than that of Group A, but the improvement is limited; the strength of Group D is much higher than that of Group C, which shows that APTES has a positive effect on the adhesion performance enhancement of the material of the application, but the enhancement effect of APTES alone on the basic epoxy system is not significant.

[0082] Group D and Group E: The strength of Group E is significantly higher than that of Group D, which shows that APTES alone cannot fully play a role and needs to be combined with "copper sheet ethanol wiping" to maximize the adhesion performance and achieve the best stability.

[0083] Therefore, the material system of the application needs to be synergized through "APTES chemical modification + copper electrode surface treatment" to fully play the role of interface strengthening and achieve the optimal adhesion effect.

[0084] Figure 5 A comparison chart of the conductive performance of the conductive composite material obtained in the present embodiment (labeled as the curve of PEDOT:PSS / SWCNT in the figure) and the conductive composite material without adding single-walled carbon nanotubes (labeled as the curve of PEDOT:PSS in the figure) is presented to verify the regulation effect of SWCNT on the conductive performance and temperature drift, wherein the conductive composite material without adding single-walled carbon nanotubes is prepared by the same method as in the present embodiment, and the difference is that steps 3 and 4 are replaced by: uniformly mixing 3.6 g of APTES and 5.5 g of glycerol carbonate at room temperature, ultrasonically treating at 60°C for 1.5 hours, adding 5.5 g of PEDOT:PSS dispersion liquid with a solid content of 3%, and ultrasonically treating at room temperature for 20 minutes to obtain solution B.

[0085] From the results of Figure 5 It can be known from the results that: the system containing only PEDOT:PSS has a continuously rising electrical conductivity with the increase of temperature (positive temperature coefficient characteristic), and the electrical conductivity changes significantly in the commonly used temperature range of the sensor, which has a serious temperature drift, which will lead to the decrease of the electrical signal transmission accuracy and affect the stability of the sensor. After the introduction of SWCNT, the electrical conductivity remains stable with the change of temperature, because: the negative temperature coefficient of SWCNT and the positive temperature coefficient of PEDOT:PSS form a "self-compensation mechanism" to offset the influence of temperature on the electrical conductivity; at the same time, the interpenetrating network constructed by SWCNT and PEDOT:PSS greatly improves the intrinsic electrical conductivity of the system. Therefore, SWCNT not only solves the temperature drift defect of PEDOT:PSS, but also significantly enhances the conductive performance, so that the composite material is more suitable for the demand of "high conductivity and low temperature drift" of the flexible sensor.

[0086] Figure 6 ,Figure 7 To explore the test results of the effect of the mass ratio of the epoxy polyamide curing agent (abbreviated as A260A in the figure) and succinic anhydride (SA) on the debonding performance of the reversible bonding conductive composite, in the experiment, the total mass of A260A and SA is fixed, the ratio of the two is adjusted (the horizontal coordinate is the mass ratio of A260A to SA, denoted as A260A (wt%): SA (wt%)), and two key parameters are determined through the “temperature gradient experiment”: the temperature point at which the debonding time significantly shortens as the temperature rises, and the debonding time changes slowly as the temperature continues to rise is the optimal debonding temperature; at the optimal debonding temperature, the time required for the shear strength to decrease to 5% of the initial value is the fastest debonding time.

[0087] As shown in Figure 6 , the relationship between the ratio and the optimal debonding temperature is: as the A260A / SA ratio increases (the horizontal coordinate increases), the optimal debonding temperature continues to rise. When the ratio is ≤2.5:1, the optimal debonding temperature grows relatively slowly; when the ratio is >2.5:1, the temperature needs to rise to nearly 200℃ to achieve efficient debonding, greatly increasing the process difficulty and the risk of substrate damage.

[0088] As shown in Figure 7 , the relationship between the ratio and the fastest debonding time is: when the ratio is ≤2.5:1, the fastest debonding time significantly shortens as the ratio increases (the curve rapidly decreases); when the ratio is ≥2.5:1, the debonding time decreases to about 2min and stabilizes, and further increasing the ratio has no obvious gain in debonding efficiency.

[0089] In summary, when the mass ratio of A260A to SA is 2.5:1, the material can achieve rapid debonding at a relatively mild temperature (to avoid damaging the substrate), which is the optimal ratio considering both “debonding efficiency” and “process compatibility”.

[0090] Figure 8 The present application embodiment presents the influence law of different debonding temperatures on debonding time after selecting the optimal mass ratio, sets 6 groups of debonding temperatures (80℃, 100℃, 120℃, 140℃, 160℃), tests the change of “shear tensile strength” with time at different temperatures, and takes the strength decreasing to 5% of the initial value as the debonding completion mark. From Figure 8It can be seen that: the lower the temperature (such as 80℃, 100℃), the slower the shear strength decreases, and it takes longer time to reach "5% strength retention rate" (even difficult to complete debonding within 10min); the higher the temperature (such as 140℃, 160℃), the faster the strength decreases, and the debonding efficiency is significantly improved. Within the temperature range of 140℃-160℃, the material can reduce the shear strength to 5% of the initial value within 3-5min, realizing efficient debonding; this temperature range neither damages the flexible substrate due to excessively high temperature, nor meets the actual needs of "fast sensor replacement"; it is the optimal interval considering both "debonding efficiency" and "substrate compatibility". Therefore, the best ratio material can balance efficiency and reliability when debonding at 140℃-160℃, and is suitable for the fast replacement scene of the back-sticking type flexible sensor.

[0091] The above embodiments are only part of the implementation ways of the present application, which are described in detail, but should not be understood as limiting the protection scope of the present application. It should be noted that those skilled in the art can make various forms of deformation and improvement without deviating from the core idea of the present application, and these adjustments all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the description of the appended claims.

Claims

1. A thermoreversible adhesive conductive composite for quick change of back-attached flexible sensor, characterized in that, The components in the heat control reversible bonding conductive composite are composed of polyether amine 28-32%, epoxy polyamide curing agent 7-11%, succinic anhydride 3-5%, PEDOT:PSS dispersion liquid with solid content of 2.8-3% 5-8%, single-walled carbon nanotube 0.1-0.5%, fumed silica 1-2%, 3-aminopropyl triethoxysilane 2-4%, glycerol carbonate 6-10%, and the balance of bisphenol A diglycidyl ether.

2. The thermally-reversible adhesive conductive composite for quick change of a back-sticker type flexible sensor according to claim 1, wherein The components in the heat control reversible bonding conductive composite are composed of bisphenol A diglycidyl ether 39.2%, polyether amine 29%, epoxy polyamide curing agent 9%, succinic anhydride 3.6%, PEDOT:PSS dispersion liquid with solid content of 2.8-3% 5.5%, single-walled carbon nanotube 0.4%, fumed silica 1.4%, 3-aminopropyl triethoxysilane 3.6%, glycerol carbonate 8.3%.

3. A method for producing the thermally controllable reversibly adhesive conductive composite material for quick change of a back-sticker type flexible sensor according to claim 1 or 2, characterized in that, It comprises the following steps: Step 1, add bisphenol A diglycidyl ether and polyether amine into a reaction kettle, stir at 60-70°C and a speed of 450-550 rpm for 25-35 minutes to disperse them uniformly, then add appropriate amount of glycerol carbonate, continue to stir at constant temperature until homogeneous phase to obtain a resin matrix prepolymer solution; Step 2, add epoxy polyamide curing agent and succinic anhydride into the resin matrix prepolymer solution, stir at 45-55°C and a speed of 450-550 rpm for 35-45 minutes, continue to add fumed silica, and stir at a speed of 1800-2300 rpm for 15-25 minutes to obtain solution A; Step 3, mix part of 3-aminopropyl triethoxysilane and appropriate amount of glycerol carbonate at room temperature to obtain a mixture, add single-walled carbon nanotube, ultrasonic treat at 55-65°C for 1-2 hours, then dry in a vacuum environment at room temperature for 1 hour to obtain pretreated single-walled carbon nanotube; Step 4, mix PEDOT:PSS dispersion liquid with the remaining glycerol carbonate, ultrasonic treat at room temperature for 15-25 minutes, add the pretreated single-walled carbon nanotube and continue to ultrasonic treat for 35-45 minutes, add the remaining 3-aminopropyl triethoxysilane and continue to ultrasonic treat for 15-20 minutes to obtain solution B; Step 5, add solution A into solution B, stir at room temperature and a speed of 450-550 rpm for 1-3 hours, and vacuum degassing to obtain a heat control reversible bonding conductive composite for quick change of back-stick type flexible sensor.

4. The method of claim 3, wherein: The mass ratio of glycerol carbonate added in step 1, step 3 and step 4 is 1:1-1.5:0.5-1.

5. The method of claim 3, wherein: The mass ratio of 3-aminopropyl triethoxysilane added in step 3 and step 4 is 1:0.1-0.

2.

6. A method for using the heat control reversible bonding conductive composite according to claim 1 or 2. Step 1, first wipe the area to be pasted of the flexible printed circuit board with ethanol to oxidize the copper electrode surface of the area to be pasted, apply the heat-controlled reversible adhesive conductive composite to the area to be pasted of the flexible printed circuit board, then paste the back-sticker type flexible sensor, pre-cure at 75-85℃ for 1.5-2.5 hours, and then cure at 110-130℃ for 0.5-1.5 hours, to complete the pasting of the back-sticker type flexible sensor; Step 2, when replacing the back-sticker type flexible sensor, heat at 140-160℃ for 3-5 minutes to make the heat-controlled reversible adhesive conductive composite lose adhesion, remove the back-sticker type flexible sensor to be replaced and the glue layer formed by the heat-controlled reversible adhesive conductive composite, and paste a new back-sticker type flexible sensor according to the method of Step 1.

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