High-resistance pressure-sensitive carbon paste for thin film type array pressure sensor and preparation method and application of high-resistance pressure-sensitive carbon paste

Abstract

The invention belongs to the technical field of pressure sensors, and relates to a high-resistance pressure-sensitive carbon paste for a thin film type array pressure sensor, and a preparation method and application of the high-resistance pressure-sensitive carbon paste. According to the high-resistance pressure-sensitive carbon paste disclosed by the invention, in the cured carbon paste layer, the carbon powder and the epoxy resin cooperatively construct a stable three-dimensional network structure through the polyurethane elastomer. Wherein the polyurethane endows the material with excellent rebound resilience, so that the material can be quickly recovered after being pressed; the hollow glass beads are uniformly dispersed in the network, so that not only is the supporting capacity of the structure enhanced, but also the effects of stress dispersion and elastic supporting are achieved in the compression process, and rapid separation of carbon powder contact points after pressure relief is promoted; the epoxy resin provides excellent structural stability and adhesive force, prevents aging, cracking or performance degradation of the coating in long-term use, and ensures the durability of the sensor.

Description

Technical Field

[0001] This invention belongs to the field of pressure sensor technology, and relates to a high-resistivity pressure-sensitive carbon paste for thin-film array pressure sensors, its preparation method, and its application. Background Technology

[0002] Traditional thin-film array pressure sensors face many performance bottlenecks in practical applications. The most prominent problems are their small measuring range and poor rebound performance, which severely limit their reliable use in complex and dynamic pressure environments.

[0003] As a key material for the conductive functional layer of sensors, the inherent defects of ordinary carbon paste further exacerbate these problems, becoming one of the core factors restricting the overall performance improvement of sensors. Firstly, ordinary carbon paste is typically composed of carbon black, resin matrix, and solvent. After curing, it forms a relatively dense and rigid conductive network structure, making it difficult to achieve rapid and sufficient deformation recovery during repeated pressure and release processes. This results in significant hysteresis and residual deformation in the sensor after pressure is released. This poor resilience directly affects the sensor's dynamic response capability, causing it to react slowly to rapidly changing pressure signals, significantly reducing its response speed and making it unable to accurately capture instantaneous pressure peaks or subtle pressure fluctuations, thus weakening the real-time performance and accuracy of data acquisition.

[0004] Secondly, because the carbon paste layer cannot fully recover its original shape after repeated compression, its internal conductive pathways undergo irreversible changes, causing resistance drift. This leads to instability and reduced repeatability of the sensor's output signal, severely affecting measurement accuracy and long-term reliability. Furthermore, the contradiction between the mechanical strength and flexibility of ordinary carbon paste is difficult to reconcile: increasing the resin content to enhance adhesion reduces conductivity and makes the material more rigid; conversely, insufficient resin content can cause coating cracking and peeling, further shortening the sensor's lifespan.

[0005] More importantly, due to the physical properties of carbon paste itself, the pressure range that traditional sensors can detect is generally narrow, usually only suitable for light or medium pressure scenarios. Once the design range is exceeded, the carbon paste layer is very prone to plastic deformation or even structural damage, leading to permanent sensor failure. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention aims to provide a high-resistivity pressure-sensitive carbon paste for thin-film array pressure sensors. This paste possesses excellent resilience, allowing the pressure-sensitive signal to disappear quickly after the pressure is released. This effectively solves the problem of poor resilience of ordinary carbon paste affecting sensor performance, significantly improving the sensor's response speed and accuracy, and optimizing pressure monitoring performance.

[0007] One objective of this invention can be achieved through the following technical solutions: A high-resistivity pressure-sensitive carbon paste for thin-film array pressure sensors, the carbon paste comprising the following raw materials in parts by weight: 10-30 parts epoxy resin, 6.5-19.5 parts curing agent, 0.15-0.45 parts accelerator, 2-7 parts toner, 2-7 parts hollow glass microspheres, 35-55 parts polyurethane slurry, 0.2-1 part toner stabilizer, and 15-25 parts solvent.

[0008] In the aforementioned high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor, the curing agent is an acid anhydride curing agent, including at least one of phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and hexahydroanhydride.

[0009] In the aforementioned high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor, the accelerator includes at least one of triphenylphosphine, 2-ethyl-4-methylimidazole, 1-methylimidazole, 2-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole.

[0010] Preferably, the median particle size of hollow glass microspheres is 40-75 μm.

[0011] Preferably, the polyurethane slurry is prepared from isophorone, polyurethane particles and methyl nylon in a mass ratio of 1:(1-2):(3-5).

[0012] This invention effectively enhances the rebound capability of the sensor by adding hollow glass microspheres, preventing a decrease in the sensor's mechanical stability and lifespan due to the loose structure of the carbon paste itself. However, excessive microspheres can crowd out the contact space of carbon particles, disrupting the continuity of the conductive network. Controlling the amount added ensures that the sensor maintains stable conductivity. Too much addition can also alter the viscosity and rheological properties of the carbon paste, making it unsuitable for screen printing. Controlling the amount ensures a smooth printing process, preventing screen clogging or missed prints. Furthermore, excessively large or unevenly distributed hollow glass microspheres can easily cause agglomeration in the carbon paste. Controlling the particle size allows for uniform dispersion of the microspheres, ensuring consistent performance across all areas of the sensor. The mesh count of the screen determines the aperture size; if the microsphere size exceeds the aperture size, it will cause screen clogging; if it is too small, it may excessively penetrate the paste. Controlling the particle size ensures clear printed patterns and meets accuracy standards. This invention, by controlling the microspheres to have a uniform particle size, allows the carbon paste to form a uniform microstructure after solidification, preventing deviations in the sensor's pressure response due to localized microsphere size differences and improving detection stability.

[0013] In the aforementioned high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor, the toner stabilizer is a mixture of polyvinylpyrrolidone (PVP) and polyoxyethylene alkyl ether (POE) at a mass ratio of (2.5-3.5):1. This invention's toner stabilizer is a compound of PPVP and POE in a specific mass ratio, and their synergistic effect significantly improves the dispersion stability and printability of the carbon paste. PPVP, as the core dispersing component, is strongly adsorbed onto the toner surface through π-π conjugation in its molecular structure, achieving long-term stable dispersion and preventing sedimentation or aggregation during storage or use. POE, on the other hand, primarily plays an auxiliary role, improving the leveling properties of the carbon paste, reducing viscosity fluctuations during screen printing, effectively alleviating process defects such as screen clogging and rough pattern edges, and enhancing the compatibility between organic resins and inorganic fillers in the carbon paste system, improving overall uniformity and film quality. This composite dispersant system not only ensures good dispersion of the toner under high solids content conditions but also lays a crucial foundation for subsequent high-precision, high-consistency printing manufacturing.

[0014] Preferably, the solvent is ethylene glycol butyl ether, ethylene glycol butyl ether acetate, dipropylene glycol methyl ether, diethylene glycol butyl ether and diethylene glycol butyl ether acetate in a mass ratio of 1:(0.5-1.5):(0.5-1.5):(0.5-1.5):(0.5-1.5).

[0015] The present invention also provides a method for preparing a high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor, the method comprising the following steps: S1. Prepare the above-mentioned raw materials; S2. First, stir the epoxy resin, curing agent and accelerator evenly. S3. Then add toner stabilizer and 55-65 wt% toner and stir evenly. Then add polyurethane slurry and stir evenly. Add the remaining toner and stir evenly. Add 40-60 wt% solvent and stir to obtain a mixed slurry. S4. The mixed slurry is ball-milled, and then the remaining solvent is added and ball-milled again. After filtration, a uniform slurry is obtained. S5. The uniform slurry is defoamed and ground with three rollers, then hollow glass microspheres are added and stirred. Finally, after defoaming, a high-resistance carbon slurry is obtained.

[0016] Traditional preparation methods directly mix toner with resin and curing agent. However, this often results in agglomeration of the toner due to localized curing agents or accelerators affecting its dispersion, as the resin system is not pre-homogenized. This invention first stirs the epoxy resin, curing agent, and accelerator, allowing them to form a homogeneous and stable resin matrix. This eliminates localized component concentration differences, and the homogenized resin matrix provides a more uniform dispersion environment. When toner is added subsequently, it integrates more smoothly into the system, reducing toner agglomeration caused by matrix inhomogeneity. Furthermore, the active groups on the toner surface, if in direct contact with curing agents or accelerators without homogeneous dispersion, are prone to localized adsorption or slight reactions. Mixing the resin matrix before adding toner reduces premature direct contact between toner and curing agents / accelerators, preventing the toner surface from being coated by curing agents and affecting its dispersibility in the resin. It also prevents premature localized curing reactions, ensuring a consistent curing rate for the entire carbon paste and avoiding uneven toner distribution due to localized curing, which ultimately affects the sensor's conductivity. This invention indirectly optimizes the subsequent processing performance and final product quality of carbon paste. The homogeneous resin matrix combined with uniformly dispersed toner allows the carbon paste to maintain more stable viscosity and rheological properties, making it more suitable for processes such as screen printing. This reduces problems like screen clogging and uneven patterning during printing. Improved toner dispersion uniformity results in a more continuous conductive network in the sensor, effectively reducing performance differences between batches and regions, and improving the sensor's detection stability and consistency. Furthermore, the batch-addition of toner in this invention reduces dispersion difficulty, minimizes toner agglomeration, and allows for precise control of carbon paste viscosity and rheological properties, further enhancing the continuity and stability of the carbon paste conductive network.

[0017] In the above-mentioned method for preparing a high-resistivity carbon paste for a thin-film array pressure sensor, step S4 ball milling includes: mixing the slurry with milling beads at a mass ratio of 1:(2-5) for 25-35 minutes at 4500-5500 r / min, then adding solvent and continuing ball milling for 5-15 minutes, and adjusting the viscosity of the mixed slurry to 25000-40000 cP.

[0018] This invention features precise "solid-solid" pre-dispersion: high rotation speed + specific ball-to-material ratio ensures dispersion efficiency and effectiveness. Then, segmented ball milling is performed, dispersing first and then adjusting viscosity, balancing dispersion quality and process adaptability. The ball milling is divided into two stages: "pre-dispersion" and "viscosity adjustment," solving the problem of uneven dispersion that may occur when adding solvent all at once. Furthermore, the viscosity is precisely locked, directly matching the requirements of screen printing processes.

[0019] In the above-mentioned method for preparing a high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor, the grinding balls are stainless steel grinding balls with a mass ratio of (2-3):(2-3):1 and a particle size distribution of 4-6 mm, 2.5-3.5 mm, and 0.5-1.5 mm.

[0020] In the above-mentioned method for preparing high-resistivity pressure-sensitive carbon paste for thin-film array pressure sensors, defoaming is carried out in a vacuum homogenizer and defoamer, with the vacuum level set to -(0.05-0.15) MPa, the rotation speed to 1200-1800 r / min, and the time to 5-15 min. This invention eliminates the potential for air bubbles through multiple defoaming processes, directly solving the chain reaction of negative effects of air bubbles on the printing quality of the carbon paste and the performance of the sensor.

[0021] In the above-mentioned method for preparing high-resistivity pressure-sensitive carbon paste for thin-film array pressure sensors, three-roll milling is carried out in a three-roll mill with a feed roller spacing of 30-80μm and a discharge roller spacing of 10-40μm, and the slurry feed rate is controlled at 3-8L / h.

[0022] The present invention also provides a method for preparing a piezoresistive functional layer with high resistance and elasticity. The method includes the following steps: screen printing the above-mentioned high-resistivity pressure-sensitive carbon paste onto the surface of the silver electrode of a thin-film array pressure sensor, then pre-baking at 55-65℃ for 5-15 min, then heating to 80-120℃ and holding for 5-15 min, and finally heating to 120-140℃ and curing for 25-35 min to obtain a piezoresistive functional layer with high resistance and elasticity. In the cured high-resistance pressure-sensitive carbon paste layer, the carbon powder forms a three-dimensional network structure with the polyurethane elastic matrix and epoxy resin, and hollow glass microspheres are uniformly distributed within it. The polyurethane provides excellent resilience, and the hollow glass microspheres enhance the structural support and resilience, together ensuring rapid separation of the carbon powder contact points after pressure is applied. The epoxy resin ensures structural stability and avoids performance degradation during long-term use. The carbon powder forms a discontinuous conductive path on the surface of the silver electrode. When pressure is applied, the contact area of ​​the carbon powder increases, resulting in a decrease in resistance. After the pressure is released, the elastic matrix and hollow glass microspheres work together to rapidly restore the resistance, further improving the sensitivity and response speed of pressure monitoring.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The high-resistance pressure-sensitive carbon paste of this invention effectively solves the key bottleneck of traditional carbon paste in the application of thin-film array pressure sensors. Compared with traditional carbon paste, this carbon paste can maintain a high initial resistance after curing on the surface of the silver electrode, successfully overcoming the problem of low resistance at the pressure-sensitive point caused by the strong conductivity of the silver layer, significantly widening the measurable pressure range of the sensor, and greatly improving the upper limit of the sensor's range.

[0024] 2. The high-resistivity pressure-sensitive carbon paste of this invention exhibits excellent resilience, ensuring that the electrical signal at the pressure-sensitive point can quickly decay and recover to the baseline level after the pressure is released, effectively avoiding signal lag and residual deformation, thereby significantly improving the sensor's response speed, repeatability and measurement accuracy.

[0025] 3. In the high-resistivity carbon paste of this invention, the carbon powder in the cured carbon paste layer is synergistically constructed into a stable three-dimensional network structure by polyurethane elastomer and epoxy resin. Polyurethane imparts excellent resilience to the material, ensuring rapid recovery of its original shape after pressure; hollow glass microspheres are uniformly dispersed in the network, not only enhancing the structural support capacity but also playing a role in stress dispersion and elastic support during compression, promoting rapid separation of the carbon powder contact points after pressure relief; epoxy resin provides excellent structural stability and adhesion, preventing coating aging, cracking, or performance degradation during long-term use, ensuring the durability of the sensor.

[0026] 4. The high-resistance pressure-sensitive carbon paste and carbon powder of this invention form a discontinuous conductive path on the surface of the silver electrode. When pressure is applied, the contact area of ​​the conductive particles increases and the resistance decreases. After the pressure is released, the conductive network is quickly disconnected under the synergistic rebound effect of polyurethane and hollow glass microspheres, and the resistance quickly returns to the initial state, thus realizing high-sensitivity and fast-response dynamic pressure monitoring.

[0027] 5. Through material innovation and structural optimization, the high-resistivity pressure-sensitive carbon paste of this invention comprehensively improves the overall performance of thin-film array pressure sensors in terms of range, response speed, rebound performance and long-term stability, significantly optimizes the monitoring accuracy of pressure magnitude and distribution, and provides key material support for high-performance flexible pressure sensing. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the array pressure sensor prepared by thin film in Example 1 and Comparative Examples 1-2.

[0029] Figure 2 The images show the resilience test results of the thin-film array pressure sensor in Example 1 and Comparative Examples 1-2. Detailed Implementation

[0030] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0031] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, or article that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, or article.

[0032] The terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., used in this invention refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms are not necessarily directed at the same embodiment or example. Furthermore, the technical features involved in the various embodiments of the invention can be combined with each other as long as they do not conflict with each other.

[0033] The carbon powder is selected from beaded carbon black, sheet graphene powder and carbon nanotubes in a mass ratio of 2:1:2; the median particle size of the beaded carbon black is 25 nm; the median particle size of the sheet graphene powder is 5 μm; and the average diameter of the carbon nanotubes is 10 nm and the length is 200 μm. The epoxy resin used is a thermosetting epoxy resin; The curing agent is hexahydrogen anhydride; The accelerator is 2-ethyl-4-methylimidazole; The hollow glass microspheres were purchased from Henan Borun New Materials Co., Ltd., and the median particle size of the hollow glass microspheres was 55 μm. The solvent is 51 solvent, which is a mixture of ethylene glycol butyl ether, ethylene glycol butyl ether acetate, dipropylene glycol methyl ether, diethylene glycol butyl ether and diethylene glycol butyl ether acetate in a mass ratio of 1:1:1:1:1.

[0034] The toner stabilizer is a mixture of polyvinylpyrrolidone and polyoxyethylene alkyl ether in a mass ratio of 2:1.

[0035] The polyurethane slurry is formulated from 15.6 wt% isophorone, 22 wt% 5836 type PU (PU granules purchased from Dongguan Jiurui Plastic Raw Materials Co., Ltd.), and 62.4 wt% methyl nylonate (DBE). The specific steps include: first, stirring isophorone and methyl nylonate at 500 r / min for 1 min, then heating to 47℃, adding 5836 type PU and performing gradient mechanical stirring, successively stirring at 550 r / min for 15 min, 820 r / min for 10 min, 1280 r / min for 25 min, and finally stirring at 1420 r / min for 35 min.

[0036] Example 1: S1. The following raw materials are prepared: 12.9 parts epoxy resin, 8.4 parts curing agent, 0.2 parts accelerator, 3.4 parts toner, 3.4 parts hollow glass microspheres, 51.7 parts polyurethane slurry, 19.4 parts solvent, and 0.6 parts toner stabilizer.

[0037] S2. Weigh the epoxy resin, curing agent and accelerator, place them in a stainless steel mixing container, start the mixing equipment, and stir at 900r / min for 30 minutes at room temperature of 25℃ until the materials are completely dissolved and a uniform and transparent resin system is formed. S3. Then, slowly add 60wt% toner and toner stabilizer to the resin system while stirring (stirring speed maintained at 600r / min). Control the addition time within 10 minutes to ensure uniform dispersion of toner and avoid agglomeration. After the toner is evenly dispersed, add polyurethane slurry to the system, adjust the stirring speed to 1200r / min, and continue stirring for 30 minutes to fully integrate the elastic matrix with the resin and toner. Add the remaining toner while stirring (speed 600r / min). Add 50wt% of 51 solvent, adjust the speed to 800r / min, and continue stirring for 1 hour to form a preliminary mixed slurry with a solid content of about 60%. S4. Transfer all the initially mixed slurry to a stainless steel ball mill jar. Add stainless steel ball milling beads with a particle size gradient of 5mm, 3mm, and 1mm (mass ratio 2:2:1) at a slurry-to-milling-beads mass ratio of 1:3. Set the rotation speed to 5000r / min and start the equipment for ball milling for 30 minutes. The carbon powder is then dispersed secondaryly through high-energy collision. After 30 minutes of ball milling, slowly add the remaining 51 solvent to the ball mill jar and continue ball milling at 5000r / min for 10 minutes. Adjust the slurry viscosity to 30000cP (25℃). After ball milling, filter the slurry through a 200-mesh nylon screen to remove the ball milling beads and large particle impurities. Collect the filtered uniform slurry.

[0038] S5. Transfer the filtered slurry to a vacuum homogenizer and defoamer. Set the vacuum level to -0.09 MPa and the rotation speed to 1500 r / min for homogenization and defoaming treatment for 10 minutes to remove air bubbles from the slurry. After homogenization and defoaming, send the slurry to a three-roll mill for two fine grinding processes. For the first grinding, set the feed roller spacing of the three-roll mill to 70 μm and the discharge roller spacing to 35 μm, and control the slurry feed rate to 5 L / h. For the second grinding, set the feed roller spacing of the three-roll mill to 40 μm and the discharge roller spacing to 20 μm, and control the slurry feed rate to 5 L / h.

[0039] S6. After the three-roll milling is completed, the slurry is collected and transferred to a mixing container. Hollow glass microspheres with a particle size of 55 micrometers are weighed and slowly added to the slurry while stirring. The stirring speed is controlled at 800 r / min and stirring is continued for 1 hour to make the hollow glass microspheres evenly dispersed in the slurry. After stirring, the slurry is transferred to a homogenizer and defoamer again and treated at 1500 r / min speed and -0.09 MPa vacuum for 10 minutes to finally obtain a screen printing high-resistance carbon paste that is evenly dispersed, bubble-free, has stable viscosity and contains hollow glass microspheres.

[0040] S7. The printing equipment adopts a high-precision fully automatic screen printing machine. The screen is a 150-mesh polyester screen (55μm wire diameter, 45% aperture ratio), the photosensitive emulsion thickness is 20μm, and the pattern is precisely aligned with the silver electrode array. Printing parameter settings: Squeegee material is polyurethane (hardness 70 Shore A), squeegee pressure is 0.35MPa, printing speed is 35mm / s, ink return speed is 50mm / s, screen distance is 5mm, to ensure that the carbon paste evenly covers the surface of the silver electrode, and the wet film thickness is controlled at 25μm. During the printing process, maintain an ambient temperature of 25℃ and a relative humidity of 50% to avoid viscosity fluctuations in the paste due to environmental changes.

[0041] S8. After printing, the substrate is placed in a hot air circulating oven for step curing: first, pre-bake at 60°C for 10 minutes to remove low-boiling-point solvents from the paste; then raise the temperature to 100°C and keep it at that temperature for 10 minutes to promote the initial cross-linking of the resin; finally, raise the temperature to 130°C and cure for 30 minutes to allow the epoxy resin and curing agent to react completely and form a piezoresistive functional layer with both high resistance and elasticity. During the curing process, the heating rate is controlled at 5℃ / min to avoid cracking or bubble formation in the carbon paste layer due to rapid heating. After curing, the carbon paste layer is allowed to cool naturally to room temperature, at which point a strong ohmic contact is formed between the carbon paste layer and the silver electrode. Example 2: S1. Prepare the following raw materials: 10 parts epoxy resin, 6.5 parts curing agent, 0.15 parts accelerator, 2 parts toner, 2 parts hollow glass microspheres, 35 parts polyurethane slurry, 15 parts solvent, and 0.2 parts toner stabilizer.

[0042] S2. Weigh the epoxy resin, curing agent and accelerator, place them in a stainless steel mixing container, start the mixing equipment, and stir at 900r / min for 30 minutes at room temperature of 25℃ until the materials are completely dissolved and a uniform and transparent resin system is formed. S3. Then, slowly add 60wt% toner and toner stabilizer to the resin system while stirring (stirring speed maintained at 600r / min). Control the addition time within 10 minutes to ensure uniform dispersion of toner and avoid agglomeration. After the toner is evenly dispersed, add polyurethane slurry to the system, adjust the stirring speed to 1200r / min, and continue stirring for 30 minutes to fully integrate the elastic matrix with the resin and toner. Add the remaining toner while stirring (speed 600r / min). Add 50wt% of 51 solvent, adjust the speed to 800r / min, and continue stirring for 1 hour to form a preliminary mixed slurry with a solid content of about 60%. S4. Transfer all the initially mixed slurry to a stainless steel ball mill jar. Add stainless steel ball milling beads with a particle size gradient of 5mm, 3mm, and 1mm (mass ratio 2:2:1) at a slurry-to-milling-beads mass ratio of 1:3. Set the rotation speed to 5000r / min and start the equipment for ball milling for 30 minutes. The carbon powder is then dispersed secondaryly through high-energy collision. After 30 minutes of ball milling, slowly add the remaining 51 solvent to the ball mill jar and continue ball milling at 5000r / min for 10 minutes. Adjust the slurry viscosity to 28000cP (25℃). After ball milling, filter the slurry through a 200-mesh nylon screen to remove the ball milling beads and large particle impurities. Collect the filtered, uniform slurry.

[0043] S5. Transfer the filtered slurry to a vacuum homogenizer and defoamer. Set the vacuum level to -0.09 MPa and the rotation speed to 1500 r / min for homogenization and defoaming treatment for 10 minutes to remove air bubbles from the slurry. After homogenization and defoaming, send the slurry to a three-roll mill for two fine grinding processes. For the first grinding, set the feed roller spacing of the three-roll mill to 70 μm and the discharge roller spacing to 35 μm, and control the slurry feed rate to 5 L / h. For the second grinding, set the feed roller spacing of the three-roll mill to 40 μm and the discharge roller spacing to 20 μm, and control the slurry feed rate to 5 L / h.

[0044] S6. After the three-roll milling is completed, the slurry is collected and transferred to a mixing container. Hollow glass microspheres with a particle size of 55 micrometers are weighed and slowly added to the slurry while stirring. The stirring speed is controlled at 800 r / min and stirring is continued for 1 hour to make the hollow glass microspheres evenly dispersed in the slurry. After stirring, the slurry is transferred to a homogenizer and defoamer again and treated at 1500 r / min speed and -0.09 MPa vacuum for 10 minutes to finally obtain a screen printing high-resistance carbon paste that is evenly dispersed, bubble-free, has stable viscosity and contains hollow glass microspheres.

[0045] S7. The printing equipment adopts a high-precision fully automatic screen printing machine. The screen is a 150-mesh polyester screen (55μm wire diameter, 45% aperture ratio), the photosensitive emulsion thickness is 20μm, and the pattern is precisely aligned with the silver electrode array. Printing parameter settings: Squeegee material is polyurethane (hardness 70 Shore A), squeegee pressure is 0.35MPa, printing speed is 35mm / s, ink return speed is 50mm / s, screen distance is 5mm, to ensure that the carbon paste evenly covers the surface of the silver electrode, and the wet film thickness is controlled at 25μm. During the printing process, maintain an ambient temperature of 25℃ and a relative humidity of 50% to avoid viscosity fluctuations in the paste due to environmental changes.

[0046] S8. After printing, the substrate is placed in a hot air circulating oven for step curing: first, pre-bake at 60°C for 10 minutes to remove low-boiling-point solvents from the paste; then raise the temperature to 100°C and keep it at that temperature for 10 minutes to promote the initial cross-linking of the resin; finally, raise the temperature to 130°C and cure for 30 minutes to allow the epoxy resin and curing agent to react completely and form a piezoresistive functional layer with both high resistance and elasticity. During the curing process, the heating rate is controlled at 5℃ / min to avoid cracking or bubble formation in the carbon paste layer due to rapid heating. After curing, the carbon paste layer is allowed to cool naturally to room temperature, at which point a strong ohmic contact is formed between the carbon paste layer and the silver electrode.

[0047] Example 3: S1. Prepare the following raw materials: 30 parts epoxy resin, 19.5 parts curing agent, 0.45 parts accelerator, 7 parts toner, 7 parts hollow glass microspheres, 55 parts polyurethane slurry, 25 parts solvent, and 1 part toner stabilizer.

[0048] S2. Weigh the epoxy resin, curing agent and accelerator, place them in a stainless steel mixing container, start the mixing equipment, and stir at 900r / min for 30 minutes at room temperature of 25℃ until the materials are completely dissolved and a uniform and transparent resin system is formed. S3. Then, slowly add 60wt% toner and toner stabilizer to the resin system while stirring (stirring speed maintained at 600r / min). Control the addition time within 10 minutes to ensure uniform dispersion of toner and avoid agglomeration. After the toner is evenly dispersed, add polyurethane slurry to the system, adjust the stirring speed to 1200r / min, and continue stirring for 30 minutes to fully integrate the elastic matrix with the resin and toner. Add the remaining toner while stirring (speed 600r / min). Add 50wt% of 51 solvent, adjust the speed to 800r / min, and continue stirring for 1 hour to form a preliminary mixed slurry with a solid content of about 60%. S4. Transfer all the initially mixed slurry to a stainless steel ball mill jar. Add stainless steel ball milling beads with a particle size gradient of 5mm, 3mm, and 1mm (mass ratio 2:2:1) at a slurry-to-milling-beads mass ratio of 1:3. Set the rotation speed to 5000r / min and start the equipment for ball milling for 30 minutes. The carbon powder is then dispersed secondaryly through high-energy collision. After 30 minutes of ball milling, slowly add the remaining 51 solvent to the ball mill jar and continue ball milling at 5000r / min for 10 minutes. Adjust the slurry viscosity to 40000cP (25℃). After ball milling, filter the slurry through a 200-mesh nylon screen to remove the ball milling beads and large particle impurities. Collect the filtered, uniform slurry.

[0049] S5. Transfer the filtered slurry to a vacuum homogenizer and defoamer. Set the vacuum level to -0.09 MPa and the rotation speed to 1500 r / min for homogenization and defoaming treatment for 10 minutes to remove air bubbles from the slurry. After homogenization and defoaming, send the slurry to a three-roll mill for two fine grinding processes. For the first grinding, set the feed roller spacing of the three-roll mill to 70 μm and the discharge roller spacing to 35 μm, and control the slurry feed rate to 5 L / h. For the second grinding, set the feed roller spacing of the three-roll mill to 40 μm and the discharge roller spacing to 20 μm, and control the slurry feed rate to 5 L / h.

[0050] S6. After the three-roll milling is completed, the slurry is collected and transferred to a mixing container. Hollow glass microspheres with a particle size of 55 micrometers are weighed and slowly added to the slurry while stirring. The stirring speed is controlled at 800 r / min and stirring is continued for 1 hour to make the hollow glass microspheres evenly dispersed in the slurry. After stirring, the slurry is transferred to a homogenizer and defoamer again and treated at 1500 r / min speed and -0.09 MPa vacuum for 10 minutes to finally obtain a screen printing high-resistance carbon paste that is evenly dispersed, bubble-free, has stable viscosity and contains hollow glass microspheres.

[0051] S7. The printing equipment adopts a high-precision fully automatic screen printing machine. The screen is a 150-mesh polyester screen (55μm wire diameter, 45% aperture ratio), the photosensitive emulsion thickness is 20μm, and the pattern is precisely aligned with the silver electrode array. Printing parameter settings: Squeegee material is polyurethane (hardness 70 Shore A), squeegee pressure is 0.35MPa, printing speed is 35mm / s, ink return speed is 50mm / s, screen distance is 5mm, to ensure that the carbon paste evenly covers the surface of the silver electrode, and the wet film thickness is controlled at 25μm. During the printing process, maintain an ambient temperature of 25℃ and a relative humidity of 50% to avoid viscosity fluctuations in the paste due to environmental changes.

[0052] S8. After printing, the substrate is placed in a hot air circulating oven for step curing: first, pre-bake at 60°C for 10 minutes to remove low-boiling-point solvents from the paste; then raise the temperature to 100°C and keep it at that temperature for 10 minutes to promote the initial cross-linking of the resin; finally, raise the temperature to 130°C and cure for 30 minutes to allow the epoxy resin and curing agent to react completely and form a piezoresistive functional layer with both high resistance and elasticity. During the curing process, the heating rate is controlled at 5℃ / min to avoid cracking or bubble formation in the carbon paste layer due to rapid heating. After curing, the carbon paste layer is allowed to cool naturally to room temperature, at which point a strong ohmic contact is formed between the carbon paste layer and the silver electrode.

[0053] Example 4: The difference from Example 1 is that the toner is directly mixed with toner stabilizer, epoxy resin, curing agent, accelerator, hollow glass microspheres, polyurethane slurry and solvent, and then steps S4-S8 are performed.

[0054] Example 5: The difference from Example 1 is that in step S3, 100wt% of toner and toner stabilizer are slowly added to the resin system while stirring (stirring speed is maintained at 600r / min), and the feeding time is controlled within 10 minutes. Pre-dissolved polyurethane slurry is added to the system, the stirring speed is adjusted to 1200r / min, and stirring is continued for 30 minutes to fully integrate the elastic matrix with the resin and toner. 100wt% of 51 solvent is added, the speed is adjusted to 800r / min, and stirring is continued for 1 hour to form a preliminary mixed slurry with a solid content of about 60%.

[0055] Comparative Example 1: The only difference from Example 1 is that hollow glass microspheres were not added.

[0056] Comparative Example 2: The only difference from Example 1 is that the amount of hollow glass microspheres added is 1 part.

[0057] Comparative Example 3: The only difference from Example 1 is that the amount of hollow glass microspheres added is 20 parts.

[0058] Comparative Example 4: The only difference from Example 1 is that no toner stabilizer was added.

[0059] Comparative Example 5: The only difference from Example 1 is that the toner stabilizer is only polyvinylpyrrolidone.

[0060] Comparative Example 6: The only difference from Example 1 is that the toner stabilizer is only a polyoxyethylene alkyl ether.

[0061] The performance of the high-resistivity carbon paste in Examples 1-5 and Comparative Examples 1-4 was tested respectively. Viscosity was measured using a viscometer at a temperature of 25 degrees Celsius and a rotation speed of 50 rpm. The viscometer was manufactured by Shanghai Fangrui Instrument Co., Ltd.

[0062] The flowability was assessed using a standard screen printing machine. Semi-automatic screen printing was performed on a standard flexible PET film. The machine observed whether the ink passed smoothly through the mesh, whether the edges of the pattern were clear, and whether there were any trailing, stringing, accumulation, or broken lines. It also observed whether there was any "flowing" or "shrinking" before drying.

[0063] Sheet resistance is measured according to GB / T 1552 and is tested using a handheld four-probe tester (manufactured by Suzhou Jingge Electronics Co., Ltd.). The unit is kΩ. -cm / □.

[0064] Adhesion is determined according to ASTM D3359, "Standard Test Method for Determining Adhesion by Tape Method". 5B: No peeling at the cut intersection (≥95% retention) → Excellent adhesion; 4B: Slight peeling along the cut edge, or small pieces peeling off at the intersection (5-15% peeling); 3B and below: Peeling area >15%, adhesion unqualified.

[0065] Table 1: Performance Test Results of High Pressure Sensitive Carbon Pastes Prepared in Examples 1-5 and Comparative Examples 1-4 like Figure 1 As shown, firstly, row silver electrode layers and column silver electrode layers are fabricated on the substrate using a screen printing process. Then, row carbon paste layers are screen printed on the surface of the prepared row silver electrode layers, and column carbon paste layers are screen printed on the surface of the column silver electrode layers, ensuring that the carbon paste layers completely cover the corresponding silver electrode layers. Afterward, the row silver electrode structure with row carbon layers and the column silver electrode structure with column carbon layers are assembled and attached. At the same time, spacers are added around the row and column structures so that the row and column carbon layers in the middle only contact each other when pressure is applied, and finally the thin film array pressure sensor device is obtained. Figure 2The figures show the resilience test curves of the array pressure sensors prepared from thin films in Examples 1 and 1-2. The figures show the resilience test curves of a single sampling point in the thin-film array pressure sensor. The test was conducted in three stages: pressure application, pressure holding, and no pressure. In the pressure application stage, the resistance dropped sharply from the initial value to 2500 kΩ. In the pressure holding stage (approximately 250 ms), the resistance stabilized at nearly 20 kΩ. In the no-pressure stage, the resistance gradually recovered to the initial value, thus verifying the sensor's resilience and electrical performance stability. The differences in the curves corresponding to the three carbon pastes reflect their impact on the device's resilience: in the pressure application and pressure holding stages, there was no significant difference in the pressure-resistance conductivity of the three carbon pastes; however, in the no-pressure rebound stage, the carbon paste corresponding to Example 1 caused the resistance to recover faster and closer to the initial value, while the carbon pastes of Comparative Examples 1 and 2 showed slightly stronger lag in resistance recovery. This indicates that the carbon paste of Example 1 can significantly improve the device's resilience, allowing the sensor to recover to its initial state more quickly and thoroughly after pressure is released.

[0066] Example 4: Adding toner to the resin system all at once resulted in excessively high local concentrations, making it difficult for the toner to be fully wetted and dispersed, forming irreversible agglomerates. Even subsequent ball milling could not completely deagglomerate them, resulting in uneven conductive networks, printing pattern defects, and poor signal stability. Example 5: Adding solvent and all toner simultaneously in the initial stage diluted the viscosity of the resin matrix, weakening its ability to encapsulate and anchor the toner, exacerbating particle collision and agglomeration, resulting in poor slurry storage stability, rough film layer, and large sheet resistance dispersion. Comparative Example 1, without the addition of hollow glass microspheres, exhibits a dense pressure-sensitive layer with a continuous conductive path. However, it suffers from a small resistance change rate under pressure, slow recovery after unloading, and poor resilience, making rapid response difficult. Comparative Example 2, with only one part of hollow glass microspheres, has insufficient microstructure density, resulting in limited improvement in sheet resistance and elasticity, and no significant performance advantage. Comparative Example 3, due to excessive hollow glass microspheres (20 parts), causes the slurry solid content to far exceed the critical value, leading to a sharp increase in viscosity (>100,000 cP), extremely poor fluidity, and ineffective dispersion and printing. Comparative Example 4, without the use of toner stabilizer, suffers from severe toner agglomeration in the system, causing not only an abnormally high and fluctuating sheet resistance but also the appearance of particles on the printed film surface, affecting the uniformity of contact with the electrodes and the consistency of the sensor array. The above results indicate that only by constructing an elastic microstructure with an appropriate amount of hollow glass microspheres, ensuring high dispersibility with toner stabilizers, and combining stepwise feeding with high-energy ball milling processes can a high-resistance pressure-sensitive toner paste with high sheet resistance, excellent resilience, good printability, and high reliability be obtained. Compared to Example 1, which used a blend of polyvinylpyrrolidone and polyoxyethylene alkyl ether (mass ratio 2:1) as a toner stabilizer, Comparative Examples 5 and 6 used only one stabilizer. This difference directly resulted in the comparative examples having significantly inferior performance compared to Example 1. The reason for this is that the two stabilizers have a synergistic and complementary effect: polyvinylpyrrolidone (PVP) can coat toner particles through polymer chains, improving system stability and adhesion; polyoxyethylene alkyl ether can reduce interparticle forces, optimizing dispersibility and flowability. In Comparative Example 5, using only PVP, the molecular entanglement of a single polymer significantly increases the viscosity of the toner paste, and the lack of dispersion assistance from small molecule surfactants makes the toner prone to agglomeration. In Comparative Example 6, using only polyoxyethylene alkyl ether, the small molecule surfactant cannot provide sufficient coating and adhesive support, resulting in excessively low viscosity and weakened stability and adhesion of the toner paste. Example 1, through the synergistic effect of the blended stabilizers, achieved a comprehensive performance of moderate viscosity, excellent flowability, strong adhesion, and good stability, which also confirms the necessity of blending two stabilizers.

[0067] In summary, the high-resistivity carbon paste of this invention, after curing, features a stable three-dimensional network structure in which carbon powder is synergistically constructed by polyurethane elastomer and epoxy resin. Polyurethane imparts excellent resilience to the material, ensuring rapid recovery to its original shape after pressure. Hollow glass microspheres are uniformly dispersed within the network, enhancing the structural support and providing stress dispersion and elastic support during compression, promoting rapid separation of carbon powder contact points after pressure relief. Epoxy resin provides excellent structural stability and adhesion, preventing coating aging, cracking, or performance degradation during long-term use, thus ensuring the sensor's durability.

[0068] The embodiments herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0069] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0070] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A high-resistivity pressure-sensitive carbon paste for use in thin-film array pressure sensors, characterized in that, The carbon paste comprises the following raw materials in parts by weight: 10-30 parts epoxy resin, 6.5-19.5 parts curing agent, 0.15-0.45 parts accelerator, 2-7 parts toner, 2-7 parts hollow glass microspheres, 35-55 parts polyurethane paste, 0.2-1 parts toner stabilizer, and 15-25 parts solvent.

2. The high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor according to claim 1, characterized in that, The curing agent is an acid anhydride curing agent, including at least one of phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and hexahydroanhydride.

3. The high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor according to claim 1, characterized in that, The accelerator includes at least one of triphenylphosphine, 2-ethyl-4-methylimidazole, 1-methylimidazole, 2-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole.

4. The high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor according to claim 1, characterized in that, The toner stabilizer is a mixture of polyvinylpyrrolidone and polyoxyethylene alkyl ether in a mass ratio of (1.5-2.5):

1.

5. The high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor according to claim 1, characterized in that, The solvent is ethylene glycol butyl ether, ethylene glycol butyl ether acetate, dipropylene glycol methyl ether, diethylene glycol butyl ether and diethylene glycol butyl ether acetate in a mass ratio of 1:(0.5-1.5):(0.5-1.5):(0.5-1.5):(0.5-1.5).

6. A method for preparing a high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor as described in claim 1, characterized in that, The method includes the following steps: S1. Prepare the raw materials as described in claim 1; S2. First, stir the epoxy resin, curing agent and accelerator evenly. S3. Then add toner stabilizer and 55-65 wt% toner and stir evenly. Then add polyurethane slurry and stir evenly. Add the remaining toner and stir evenly. Add 40-60 wt% solvent and stir to obtain a mixed slurry. S4. The mixed slurry is ball-milled, and then the remaining solvent is added and ball-milled again. After filtration, a uniform slurry is obtained. S5. The uniform slurry is defoamed and ground with three rollers, then hollow glass microspheres are added and stirred. Finally, after defoaming, a high-resistance carbon slurry is obtained.

7. The method for preparing a high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor according to claim 6, characterized in that, Step S4 ball milling includes: mixing the slurry with the ball milling beads at a mass ratio of 1:(2-5) for 25-35 minutes at 4500-5500 r / min, then adding solvent and continuing ball milling for 5-15 minutes, and adjusting the viscosity of the slurry to 25000-40000 cP.

8. The method for preparing a high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor according to claim 7, characterized in that, The grinding balls are stainless steel grinding balls with a mass ratio of (2-3):(2-3):1 and a particle size distribution of 4-6mm, 2.5-3.5mm, and 0.5-1.5mm.

9. The method for preparing a high-resistivity pressure-sensitive carbon paste for a thin-film array pressure sensor according to claim 6, characterized in that, Defoaming is carried out in a vacuum homogenizer and defoamer, with the vacuum level set to -(0.05-0.15) MPa, the rotation speed set to 1200-1800 r / min, and the time set to 5-15 min.

10. A method for preparing a piezoresistive functional layer with high resistance and elasticity, characterized in that, The method includes the following steps: screen printing the high-resistivity piezoresistive carbon paste of claim 1 onto the surface of the silver electrode of the thin-film array pressure sensor, then pre-baking at 55-65℃ for 5-15 min, then heating to 80-120℃ and holding for 5-15 min, and finally heating to 120-140℃ and curing for 25-35 min to obtain a piezoresistive functional layer with high resistance and elasticity.

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