Intelligent touch TPO synthetic leather and preparation method thereof

Abstract

The application discloses intelligent touch TPO synthetic leather and a preparation method thereof, and belongs to the technical field of functional synthetic leather. The method comprises the following steps: raw materials including polypropylene, ethylene-propylene-diene rubber, carbon nanotubes and flaky conductive graphite are prepared into a piezoresistive composite material, and then the piezoresistive composite material is formed into a TPO piezoresistive sheet through calendering and embossing; an electric heating setting temperature zone T1 of the sheet is determined in advance, and multiple resistance detection areas are divided after the sheet enters the T1, electric heating pulses with the same set voltage are applied to the areas, and the electric heating setting is controlled according to the discrete degree of the area resistance; then the sheet is cooled to a temperature conditioning temperature zone T2 lower than the T1, multiple loading and unloading are carried out, and the sheet is wound after cooling. The application can reduce the basic resistance difference of different areas of the sheet, reduce the zero-load resistance drift and piezoresistive hysteresis in the initial cycle, and improve the piezoresistive response consistency and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of functional synthetic leather technology, and more specifically, relates to a smart tactile TPO synthetic leather and its preparation method. Background Technology

[0002] Thermoplastic polyolefin elastomers (TPOs) combine the processing and molding properties of thermoplastic materials with the flexibility and resilience of elastomers. They are characterized by good weather resistance, recyclability, low odor, and strong processing adaptability, and have been increasingly applied in automotive interiors, smart homes, flexible surface materials, and electronic skin. With the development of intelligent interactive materials, introducing conductive fillers into the TPO matrix to form a piezoresistive conductive network allows the material to convert pressure, touch, or deformation into resistance signals. This further endows TPO synthetic leather with tactile sensing capabilities, thus enabling the synthetic leather surface to possess decorative, covering, and pressure-sensing functions.

[0003] Existing smart tactile TPO materials typically involve melt-blending carbon nanotubes, conductive carbon black, graphite, or other carbon-based conductive materials with a TPO matrix, followed by extrusion, calendering, embossing, and cooling to form sheets with a piezoresistive response. To balance flexibility and conductive stability, two or more conductive fillers can be used to construct a composite conductive network. This process creates continuous or near-percolation-like conductive pathways within the material, and changes in resistance occur through variations in the contact state and spacing between conductive particles under pressure.

[0004] However, in actual continuous production, piezoresistive performance depends not only on the total content of conductive filler but also on factors such as the local dispersion state of the filler, the two-phase structure of TPO, calendering orientation, embossing deformation, and subsequent cooling and crystallization processes. Even if the formulation, calendering roll gap, and process temperature remain basically consistent, the number of conductive filler contacts and the effective tunneling distance at different locations on the same sheet may still differ, leading to discrete variations in the basic resistance of different areas. For smart tactile TPO synthetic leather used for touch recognition and pressure sensing, these regional differences further manifest as inconsistent response starting points and signal amplitudes at different locations, thus increasing the difficulty of subsequent signal calibration and algorithm compensation.

[0005] Existing processes typically reduce these differences by improving mixing uniformity, enhancing conductive filler dispersion, minimizing calendering temperature and speed differences, and optimizing cooling conditions. However, once the conductive filler has entered the piezoresistive sensitive region at a lower filler content, further increasing the dispersion intensity or the amount of conductive filler may push the conductive network away from the more sensitive critical state, thereby reducing the magnitude of resistance change when the material is under pressure. At the same time, the localized differences in the conductive network formed after calendering and embossing are difficult to further correct by simply using uniform front-end processing parameters.

[0006] On the other hand, piezoresistive composite materials develop residual stress during calendering, embossing, and cooling processes, with some carbon-based conductive fillers in a critical overlapping or tunneling state. During the initial loading and unloading cycles, these unstable conductive contacts may re-engage, slip, or separate, causing changes in zero-load resistance, pressure response, and loading / unloading paths with the number of cycles, manifesting as initial signal drift and piezoresistive hysteresis. While simply increasing the conductive network density is beneficial for stabilizing the basic resistance, it may simultaneously reduce pressure sensitivity. Therefore, balancing regional resistance consistency and piezoresistive response stability remains a problem to be solved in the continuous manufacturing process of intelligent tactile TPO synthetic leather. Summary of the Invention

[0007] To address the issues of regional resistance differences and unstable initial piezoresistive response in existing smart tactile TPO synthetic leathers, this invention provides a smart tactile TPO synthetic leather and its preparation method, which can improve the resistance consistency and piezoresistive response stability of different regions.

[0008] To solve the above problems, the present invention adopts the following technical solution.

[0009] A method for preparing intelligent tactile TPO synthetic leather includes the following steps: A piezoresistive composite material is prepared by mixing raw materials containing polypropylene, ethylene propylene diene monomer (EPDM) rubber, carbon nanotubes and sheet conductive graphite, and then formed into TPO piezoresistive sheets through calendering and embossing. The electrothermal setting temperature range T1 of the TPO piezoresistive sheet is predetermined. The electrothermal setting temperature range T1 is the temperature range in which the stable resistance of the TPO piezoresistive sheet increases with the increase of the electrothermal input after being treated with different electrothermal inputs and cooled to the same reference temperature. The embossed TPO piezoresistive sheet is brought into the electrothermal setting temperature zone T1, the TPO piezoresistive sheet is divided into multiple resistance detection areas, and an electrothermal pulse with the same set voltage is applied to each resistance detection area. The electrothermal setting is controlled according to the resistance dispersion of each resistance detection area. After the electrothermal setting is completed, the TPO piezoresistive sheet is further cooled to a pre-conditioning temperature zone T2 that is lower than the electrothermal setting temperature zone T1. The TPO piezoresistive sheet is subjected to multiple loading and unloading cycles in the pre-conditioning temperature zone T2, followed by cooling and winding.

[0010] Preferably, carbon nanotubes are premixed with at least a portion of EPDM rubber to form a first predispersant, and sheet-like conductive graphite is premixed with at least a portion of polypropylene to form a second predispersant. The first predispersant, the second predispersant, and the remaining raw materials are then mixed a second time.

[0011] Preferably, the mass ratio of polypropylene to ethylene propylene diene monomer (EPDM) rubber is 55:45 to 70:30; based on 100 parts by mass of polypropylene and EPDM rubber, the amount of carbon nanotubes added is 0.6 to 1.4 parts by mass, and the amount of sheet-like conductive graphite added is 2.5 to 4.0 parts by mass; the temperature of the secondary mixing is 170 to 185°C, and the mixing time is 1 to 4 minutes.

[0012] Preferably, the cooling crystallization temperature range of the polypropylene phase is determined by differential scanning calorimetry, and the TPO piezoresistive sheet is subjected to different electrothermal input treatments within the cooling crystallization temperature range and its adjacent temperature range. The electrothermal setting temperature range T1 is determined based on the change in stable resistance after cooling with the electrothermal input.

[0013] Preferably, each resistance detection area is subjected to an electrothermal pulse with the same set voltage through the corresponding electrode. Each electrothermal pulse lasts for 0.3 to 2 seconds, the interval between adjacent electrothermal pulses is 1 to 5 seconds, the additional temperature rise generated by a single electrothermal pulse is 1.5 to 4°C, and the maximum additional temperature rise does not exceed 5°C.

[0014] Preferably, thermal equalization is performed after each round of electrothermal pulses, and the resistance of each resistance detection area is corrected to the same online evaluation temperature within the electrothermal setting temperature zone T1. Electrothermal setting is controlled based on the coefficient of variation of the corrected area resistance.

[0015] Preferably, the temperature preconditioning zone T2 is 50-90°C, and a periodic pressure of 20-80 kPa is applied to the TPO piezoresistive sheet in the temperature preconditioning zone T2, and 5-30 loading and unloading cycles are performed.

[0016] Preferably, the temperature preconditioning is completed based on the stability of the normalized resistance response of the TPO piezoresistive sheet during continuous loading and unloading. After the temperature preconditioning is completed, a constraint pressure of 2 to 10 kPa is applied to the TPO piezoresistive sheet and it is cooled to 45 to 55°C. After the constraint pressure is released, it is cooled to no higher than 35°C and then wound up.

[0017] A smart tactile TPO synthetic leather comprises a TPO matrix formed of polypropylene and EPDM rubber, and carbon nanotubes and sheet-like conductive graphite dispersed in the TPO matrix; under conditions of 23±1℃, the coefficient of variation of the stable resistance in different regions of the smart tactile TPO synthetic leather is no greater than 6%; during cyclic loading and unloading in the range of 0 to 60 kPa, the maximum zero-load resistance drift in the first 5 cycles is no greater than 3.0%, and the piezoresistive hysteresis rate is no greater than 8.0%; after 1000 loading and unloading cycles at 0 to 60 kPa and 0.5 Hz, the piezoresistive response retention rate under 60 kPa pressure is no less than 95%.

[0018] Preferably, the mass ratio of polypropylene to ethylene propylene diene monomer (EPDM) rubber is 55:45 to 70:30; based on 100 parts by mass of polypropylene and EPDM rubber, the content of carbon nanotubes is 0.6 to 1.4 parts by mass, and the content of sheet-like conductive graphite is 2.5 to 4.0 parts by mass; the absolute values ​​of the normalized resistance response at pressures of 20 kPa, 40 kPa, and 60 kPa are 10% to 15%, 20% to 28%, and 30% to 40%, respectively.

[0019] Compared with existing technologies, this invention sets an electrothermal setting temperature zone for the TPO piezoresistive sheet and applies an electrothermal pulse with the same set voltage to different resistance detection areas within this temperature zone. This allows different areas to receive different degrees of electrothermal effect according to their initial resistance state, thereby reducing the dispersion of basic resistance between different areas of the sheet and improving the spatial resistance consistency. Furthermore, by pre-dispersing carbon nanotubes with EPDM rubber and sheet-like conductive graphite with polypropylene before secondary mixing, it is beneficial to form a composite conductive network with different response tendencies, improving regional resistance consistency while reducing adverse effects on piezoresistive sensitivity. After completing the electrothermal setting, multiple loading and unloading cycles are performed in a lower temperature preconditioning zone, which allows some initially unstable conductive contacts and residual stress at the interface to be adjusted in advance, reducing zero-load resistance drift and piezoresistive hysteresis during the initial cycle process, and improving the stability of the piezoresistive response under repeated loading conditions. In addition, with the addition of light constraint cooling, it is beneficial to reduce the re-fluctuation of the conductive state caused by the free shrinkage of the sheet after conditioning, so that the resulting smart tactile TPO synthetic leather has good regional resistance consistency, piezoresistive response stability and cycle durability, and can be connected with the existing TPO calendering and embossing continuous production process. Attached Figure Description

[0020] Figure 1 This is a flow chart of the preparation process of the intelligent tactile TPO synthetic leather of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments and examples. The following content is used to illustrate the implementation process of the technical solution of the present invention and the coordination relationship between the various technical links. Those skilled in the art can make appropriate adjustments to the corresponding parameters according to the raw material grade, production equipment and product specifications without changing the basic technical concept of the present invention.

[0022] Based on the company's existing intelligent tactile TPO synthetic leather production system, this invention addresses the issues of discrete base resistance in different areas after continuous calendering and embossing, as well as the problems of piezoresistive response drift and loading / unloading lag in the initial use of the sheet material. It further controls the pre-dispersion method of conductive fillers and the post-conditioning process after embossing.

[0023] Specifically, such as Figure 1As shown, firstly, by utilizing the differences in thermal history response and mechanical deformation response between polypropylene and EPDM rubber, carbon nanotubes and sheet-like conductive graphite are formed in the TPO matrix through different pre-dispersion paths to create an interconnected composite conductive network with different distribution tendencies. Subsequently, during the cooling process after sheet calendering and embossing, an electrothermal conditioning temperature zone pre-calibrated with actual materials is used to perform isovoltage pulse conditioning on different regions, which is limited by temperature rise, to reduce the dispersion of the sheet's spatial fundamental resistance. Then, a limited number of loading and unloading cycles are performed at a lower temperature to adjust the initial unstable conductive contacts and residual stress in advance, thereby improving the cyclic stability of the piezoresistive response.

[0024] This embodiment uses polypropylene (PP) and ethylene propylene diene monomer (EPDM) rubber as the main material for TPO.

[0025] The mass ratio of PP to EPDM can be controlled between 55:45 and 70:30, preferably between 60:40 and 68:32. Increasing the PP ratio is beneficial for calendering dimensional stability, surface forming, and subsequent heat history conditioning, while increasing the EPDM ratio is beneficial for the sheet to maintain good softness, resilience, and compressive deformation capacity.

[0026] Based on 100 parts by weight of PP and EPDM, the amount of carbon nanotubes can be 0.6 to 1.4 parts by weight, the amount of sheet conductive graphite can be 2.5 to 4.0 parts by weight, and the total amount of carbon nanotubes and sheet conductive graphite is preferably 3.5 to 5.0 parts by weight.

[0027] Multi-walled carbon nanotubes are preferred for carbon nanotubes; micron-sized highly conductive graphite powder can be used for sheet-like conductive graphite. The term "sheet-like conductive graphite" as used in this article includes conductive graphite materials with sheet-like or flake-like microstructures that can form composite conductive pathways with carbon nanotubes.

[0028] Depending on the product's requirements for processability, weather resistance, and appearance, auxiliary materials such as ultrafine talc, polyethylene wax, calcium stearate, antioxidants, light stabilizers, matting components, and pigments can also be added.

[0029] Based on 100 parts by weight of PP and EPDM, the amount of ultrafine talc powder is 3 to 8 parts by weight, polyethylene wax is 0.5 to 1.5 parts by weight, calcium stearate is 0.1 to 0.4 parts by weight, composite antioxidant is 0.3 to 0.8 parts by weight, and light stabilizer is 0.3 to 0.8 parts by weight.

[0030] The amount of auxiliary components added should be sufficient to meet normal rolling and performance requirements, without causing significant failure of the piezoresistive conductive network.

[0031] In order to ensure that the two types of carbon-based conductive fillers retain different distribution tendencies in the final TPO matrix, it is preferable to pre-disperse them separately.

[0032] Carbon nanotubes are premixed with at least a portion of EPDM to disperse the carbon nanotubes in the EPDM, thus obtaining a first predispersed material.

[0033] The first pre-dispersed material can be prepared by internal mixing, open milling, or extrusion granulation. During the mixing process, the principle is to ensure that the carbon nanotubes are uniformly dispersed without being subjected to excessive high shear.

[0034] On the other hand, flake conductive graphite is mixed with at least a portion of PP. After the PP enters a stable plasticized state, the flake conductive graphite is added, allowing the graphite to be wetted and dispersed by the PP melt, forming a second pre-dispersion.

[0035] The first predispersant, the second predispersant, the remaining PP and EPDM, and other auxiliary components are then mixed a second time.

[0036] The preferred secondary mixing temperature is 170–185℃, and the preferred mixing time is 1–4 min.

[0037] The two types of pre-dispersed materials need to achieve macroscopic fusion and conductive bonding during the secondary mixing process, but the secondary mixing time should not be excessively prolonged. Excessive high-temperature shearing will increase the degree of re-migration and random distribution of the two types of conductive fillers, and may also further reduce the length of carbon nanotubes.

[0038] After the above treatment, carbon nanotubes have a relatively high distribution tendency in the EPDM enrichment region and the region adjacent to the PP / EPDM interface, while sheet-like conductive graphite has a relatively high distribution tendency in the PP enrichment region.

[0039] The above distribution is a statistically significant difference and does not require carbon nanotubes to be completely confined to the EPDM phase, nor does it require sheet-like conductive graphite to be completely confined to the PP phase.

[0040] Both types of conductive fillers can still form a composite conductive network that is connected across phases through direct contact, overlapping, and close-range tunneling.

[0041] Among them, the conductive branches enriched by carbon nanotubes contribute relatively highly to the mechanical deformation response of the EPDM phase and the PP / EPDM interface; the conductive branches enriched by sheet-like conductive graphite contribute relatively highly to the adjustment of the basic resistance formed during the cooling, crystallization, and thermal shrinkage processes of the PP phase. The two types of conductive branches jointly determine the final basic resistance and piezoresistive response of the sheet.

[0042] The pressure resistance composite material after secondary mixing is further plasticized and extruded and filtered.

[0043] The mixing and melting temperature can be controlled within the range of 170-185℃, with the discharge based on the completion of material plasticization and the stabilization of torque, thus reducing long-term high-temperature and high-shear treatment.

[0044] The extrusion process can employ a combined filtration structure of 80-150 mesh to remove significant agglomerates and impurities. The filtration precision should not be excessively increased to avoid a significant increase in melt pressure differential and shear force.

[0045] The filtered material enters a constant temperature feeding and multi-roll calendering equipment to form TPO piezoresistive sheets with a thickness of 0.7 to 1.4 mm. Commonly used products have a thickness of 0.9 to 1.2 mm.

[0046] Taking a five-roll calender as an example, the temperature of each roll can be set in segments between 160 and 180°C according to the plasticization state of the material, and the linear speed of each roll can be kept in small increments to avoid excessive unidirectional stretching of the sheet during the calendering process.

[0047] After calendering, surface embossing is performed.

[0048] The temperature of the embossing roller can be controlled at 150–160℃, and the pressure can be controlled at 0.45–0.60 MPa. Embossing conditions should ensure the formation of the texture while avoiding large-area permanent compaction of the conductive network inside the sheet.

[0049] Since the grade of PP, the ratio of PP / EPDM, the content of conductive filler and the processing history all affect the change of residual resistance after electrothermal treatment, this invention predetermines the electrothermal setting temperature zone T1 for the actual production formula.

[0050] First, differential scanning calorimetry was used to determine the cooling crystallization behavior of the actual formulation, and the cooling crystallization initiation temperature, crystallization peak temperature and crystallization termination temperature of the PP phase were obtained. The corresponding crystallization temperature range and adjacent temperatures were used as the initial screening range of T1.

[0051] Subsequently, electrothermal response tests were conducted using sheet samples with the same or essentially the same formula, calendering and embossing thermal history as those in the formal production.

[0052] Multiple candidate temperatures are set within the initial screening range, with at least three parallel samples used for each candidate temperature, and at least two different electrothermal input levels are set.

[0053] Different levels of electrical heating input can be achieved by adjusting the voltage, single pulse duration, number of pulses, or the resulting additional temperature rise.

[0054] After the electrothermal treatment, the sample was cooled at a rate and temperature similar to that of the actual production line when it was cooled from the corresponding temperature zone to room temperature, and then placed at 23±1℃ until the resistance stabilized.

[0055] Therefore, DSC testing is mainly used to identify possible crystallization-sensitive regions, while the actual T1 is determined based on the electrothermal response results after simulating the production thermal history.

[0056] Within a certain continuous temperature range, when the average value of the stable resistance after cooling corresponding to different electrothermal input levels increases in the same direction as the electrothermal input increases, and the difference in stable resistance between adjacent electrothermal input levels exceeds the repeatability fluctuation of the parallel sample itself, this temperature range is determined as the positive residual resistance response range and is used as the electrothermal setting temperature zone T1.

[0057] The above-mentioned positive residual resistance response is a process characteristic obtained through actual calibration based on specific formulations and corresponding thermal histories, and does not mean that all PP / EPDM conductive materials have the exact same response direction.

[0058] The embossed sheet is conveyed backward along the original cooling path.

[0059] When the sheet enters T1, it is detected and subsequently electrothermal conditioning is performed using corresponding segmented electrodes located on the upper and lower sides of the sheet.

[0060] Multiple independent electrodes are arranged along the width of the sheet, each electrode having an effective width of 30 to 100 mm, and a flexible conductive contact layer is provided.

[0061] In continuous production, the segmented electrodes in the width direction and the continuous movement of the sheet in the processing direction together form a continuous two-dimensional processing unit. That is, each width segment constitutes a resistance detection and conditioning area within a set conveying length.

[0062] The electrodes are kept at a light contact pressure of 3 to 15 kPa with the sheet to reduce the influence of slight changes in the embossed surface and thickness on the contact resistance.

[0063] Before the formal electrothermal treatment, the resistance of each area is measured using a small-signal detection voltage that will not cause significant self-heating. During the measurement process, the additional temperature rise of the sheet should preferably not exceed 0.2℃.

[0064] Abnormal regions are identified based on the median and discreteness of resistance in multiple regions.

[0065] When the resistance of a certain area deviates from the median resistance of the same batch of sheets by more than 20% to 30%, or when the continuous test results fluctuate significantly, the area can be marked as an abnormal area with filler agglomeration, impurities, local thickness abnormalities, or conductive breaks.

[0066] Such obvious manufacturing defects do not rely on subsequent electrothermal adjustment for forced repair. The first stage of treatment is mainly used to correct regional basic resistance dispersion within the normal manufacturing fluctuation range.

[0067] Multiple areas within the normal conditioning range are pulse-powered using essentially the same set voltage.

[0068] Each segment electrode preferably uses an independent power supply channel, and the actual terminal voltage deviation caused by differences in line resistance and contact conditions is reduced through terminal voltage feedback.

[0069] Under essentially the same voltage conditions, the region with lower initial resistance corresponds to a relatively higher electrothermal power, thus enabling a relatively larger electrothermal input.

[0070] Since the material is already in the pre-calibrated and confirmed positive residual resistance response temperature range T1, the initial resistance of the region with low resistance within the normal range will have a relatively large adjustment range after cooling after a moderately high electrothermal input, while the electrothermal input received by the region with high original resistance will be relatively small, thereby reducing the degree of dispersion of the final stable resistance between different regions.

[0071] The electrothermal treatment uses an intermittent pulse method.

[0072] The duration of a single pulse can be 0.3 to 2 seconds, and the interval between adjacent pulses can be 1 to 5 seconds.

[0073] The additional temperature rise caused by a single pulse is preferably 1.5 to 4°C, more preferably 2 to 3°C, and the maximum additional temperature rise in any region is controlled within 5°C.

[0074] The surface temperature of each area is detected using an infrared temperature array or other rapid non-contact temperature detection methods.

[0075] When the additional temperature rise in a certain area reaches the preset upper limit, the current pulse in that area can be terminated in advance to prevent continuous self-heating in the low-resistivity area.

[0076] After each round of electric heating pulses ends, the sheet enters a short-term thermal equilibrium phase.

[0077] After the temperature difference between each detection area decreases to no more than 2-3℃, the resistance of each area is measured again using the small signal method.

[0078] During the online control phase, the high-temperature resistor near T1 is not directly converted to the final stable resistor at 23℃.

[0079] Before formal production, a narrow-temperature-range online resistance-temperature calibration relationship was established for the actual formula near T1. This relationship was established using a thermal history and small-signal measurement method similar to that used in production, and was solely for correcting instantaneous resistance differences caused by temperature differences of several degrees Celsius between different regions.

[0080] Based on this correction relationship, the measured resistance of each region is corrected to the online evaluation temperature Te uniformly set within T1, thus obtaining the online evaluation resistance Re.

[0081] The online coefficient of variation (CVe) was calculated from Re values ​​in multiple regions.

[0082] During the initial process calibration, the company simultaneously establishes the correspondence between different CVE states and the final CVE region after the sheet is cooled to 23°C according to the standard cooling process.

[0083] During mass production, CVE is used to determine whether to continue with the next round of pulse conditioning; the spatial resistance uniformity of the final product is still evaluated by the room temperature resistance CV after the sheet has been completely cooled and stabilized under specified conditions.

[0084] When CVE reaches the target range determined by the previous calibration, the first stage of processing can be completed.

[0085] In addition, when the CVE decreases by no more than 0.5 to 1.0 percentage points after two consecutive rounds of electrothermal tuning, it can be determined that the current process has approached a stable plateau, and the electrothermal input should be stopped.

[0086] After completing the first stage, the sheet is cooled further by passing it through a cooling roller with a more stable temperature and then leaving T1 to reduce the possibility of prolonged stay in the crystallization-sensitive area, which could lead to uncontrolled changes in resistance later.

[0087] The first stage mainly involves adjusting the discreteness of the base resistance at different locations.

[0088] As the sheet continues to cool, residual stresses caused by calendering, embossing, and cooling may remain inside, while carbon nanotubes and some of their contact points with graphite are in a critical overlapping or critical tunneling state.

[0089] When the sheet continues to cool to the pre-conditioning temperature zone T2 of 50-90°C, a limited number of mechanical loading and unloading operations are performed, preferably T2 is 60-80°C.

[0090] The pre-conditioning peak pressure can be 20–80 kPa, preferably 30–60 kPa.

[0091] The number of cycles can be 5 to 30, preferably 8 to 20.

[0092] In continuous production, multiple sets of elastic pressure rollers can be arranged along the conveying direction. The sheet undergoes loading once as it passes through each set of pressure rollers, and is unloaded after leaving the roller gap. Multiple sets of pressure rollers work together to complete continuous pre-conditioning.

[0093] During the research and development and process finalization stages, the normalized resistance response can be detected at at least two pressure points that are no higher than the actual pre-conditioning peak pressure.

[0094] For example, when the preconditioning peak pressure is 45 kPa, 20 kPa and 40 kPa can be selected; when the peak pressure is 40 kPa, 20 kPa and 40 kPa can be selected; when the peak pressure is 55 kPa, 20 kPa and 40 kPa or 25 kPa and 50 kPa can be selected.

[0095] The normalized resistance response can be defined as follows: S = (Rp - R0) / R0 The calculation is performed, where R0 is the resistance under specified preload or zero load conditions, and Rp is the resistance under pressure P.

[0096] When different materials exhibit a reverse piezoresistive response, the absolute value of the normalized change can be used for evaluation.

[0097] When the rate of change of the normalized resistance response corresponding to the same detection pressure in three consecutive cycles is no greater than 5%, it can be considered that the temperature preconditioning has reached a stable state.

[0098] After the mass production process has been verified in the early stage, the number of pressure roller sets, peak pressure and production speed required to achieve the above stable standards can be solidified without having to calculate the complete piezoresistive loop meter by meter for the entire roll of material.

[0099] After temperature preconditioning, a certain degree of interfacial stress relaxation and conductive contact rearrangement has occurred inside the sheet.

[0100] To reduce the new thickness recovery difference caused by the immediate free shrinkage of the sheet, a light constraint pressure of 2 to 10 kPa can be applied and the sheet cooled.

[0101] It is preferable to release the light constraint after the sheet has cooled to 45-55°C, and then continue to cool it to no higher than 35°C and perform low-tension winding.

[0102] The light constraint pressure is much lower than the embossing pressure, and generally will not cause the surface texture to become significantly shallower.

[0103] The finished sheet was placed at 23±1℃ for 24 hours.

[0104] Select no fewer than nine equally sized testing areas within the same specified area, so that the testing locations cover different widths and different processing directions of the sheet.

[0105] Resistance in the thickness direction is measured using corresponding upper and lower electrodes of the same size.

[0106] For example, an effective electrode area of ​​25mm×25mm is used, the contact pressure is 5kPa, and a small signal test voltage that does not produce significant Joule self-heating is used.

[0107] After obtaining the stable resistance Ri of each region, calculate the average value Rave and the sample standard deviation s. The coefficient of variation of regional resistance is calculated according to: CV = s / Rave × 100% calculate.

[0108] The product manufactured using the complete process of this invention preferably has a regional resistance CV of no more than 6%.

[0109] The finished product was subjected to piezoresistive performance testing at 23±1℃.

[0110] A uniform loading range of 0–60 kPa is adopted, for example, according to: 0→20kPa→40kPa→60kPa→40kPa→20kPa→0 Loading and unloading are performed, with each pressure level held for 1–3 seconds.

[0111] The performance testing range of this finished product can be higher than the pre-conditioning peak pressure used in some embodiments during the production process, so as to compare the final piezoresistive performance of different products under uniform conditions.

[0112] Normalized resistance response is based on: S = (Rp - R0) / R0 The calculation is performed, where R0 is the stable resistance under zero load before loading, and Rp is the resistance under pressure P; when the material exhibits a reverse piezoresistive response, the absolute value of the normalized resistance response is used for comparison.

[0113] Piezoresistive sensitivity is evaluated by the ratio of the normalized resistance response change to the corresponding pressure change within a specified pressure range.

[0114] The initial cyclic zero-load drift was evaluated using five consecutive load-unload cycles from 0 to 60 kPa. Using the stable zero-load resistance R0 before the first loading cycle as a baseline, the zero-load resistance Ri was measured after each unloading to 0 kPa and stabilization, according to the following: Di = |Ri - R0| / R0 × 100% Calculate the zero-load resistance drift after the i-th cycle, and take the maximum value among the first 5 cycles as the maximum zero-load resistance drift for the first 5 cycles.

[0115] Piezoresistive hysteresis is evaluated based on the difference in normalized resistance response between the loading and unloading branches under the same pressure. The normalized resistance responses under loading and unloading are compared at the same pressure points within the range of 0–60 kPa. The maximum absolute difference ΔSmax between the two is taken, and the absolute value of the normalized resistance response S60 under a 60 kPa loading condition is used as the benchmark, according to: H = ΔSmax / |S60| × 100% Calculate the piezoresistive hysteresis rate.

[0116] The sample was subjected to 1000 cycles of testing under cycling conditions of 0–60 kPa and 0.5 Hz.

[0117] The response retention rate is calculated as the ratio between the normalized resistance response at 60 kPa after 1000 cycles and the stable response before cycling.

[0118] Some representative samples were further subjected to 10,000 cycle tests to observe the retention of the piezoresistive response after long-term repeated loading.

[0119] The static stability was determined by comparing the zero-load stable resistance of the finished product after 24 hours and 72 hours, and the resistance change ratio of 72 hours to 24 hours was calculated.

[0120] The first stage determines the positive residual resistance response region through actual material calibration, and utilizes the difference in the basic resistance of different regions to form different degrees of restricted electrothermal input under the same voltage conditions, mainly reducing the dispersion of stable basic resistance between different positions of the sheet.

[0121] Different pre-dispersion paths result in differences in the contribution of carbon nanotube-enriched conductive branches to mechanical deformation and thermal history responses compared to sheet-like conductive graphite-enriched conductive branches. Therefore, the first stage can reduce the extent to which the entire pressure-sensitive network is simultaneously and significantly altered while adjusting the basic resistance.

[0122] The second stage involves cyclic mechanical loading at a lower temperature, which allows some unstable contact points, critical tunneling locations, and residual stresses in the EPDM elastic phase, PP / EPDM interface, and sensitive branches related to carbon nanotubes to be adjusted in advance.

[0123] Therefore, the first stage mainly corresponds to the consistency of the basic resistance between spatial regions, and the second stage mainly corresponds to the cyclic consistency of the piezoresistive response during continuous loading.

[0124] Both stages can be arranged in the cooling path after the existing calendering and embossing processes of the enterprise, without changing the original main calendering manufacturing method of TPO synthetic leather.

[0125] The invention will be further illustrated below using specific production batches. Each batch uses the same batch of industrial raw materials and is completed on the same calendering and embossing production equipment. For batches requiring comparison of performance before and after treatment, a reference sample from the same batch is taken after embossing and directly cooled to room temperature following a cooling process essentially consistent with the main production line, without subsequent electrothermal setting or temperature-state mechanical pre-conditioning. This sample is used to determine the regional CV and piezoresistive sensitivity under the reference condition of the same batch.

[0126] Example 1: Based on a total mass of 100 parts PP and EPDM, the following components were used: 62 parts PP, 38 parts EPDM, 0.9 parts multi-walled carbon nanotubes, 3.2 parts sheet-like conductive graphite, 5.5 parts ultrafine activated talc, 0.9 parts PE wax, 0.2 parts calcium stearate, 0.5 parts composite antioxidant, 0.5 parts light stabilizer, 0.4 parts matting agent, and 0.4 parts rutile titanium dioxide.

[0127] 12 parts of EPDM were pre-dispersed with all carbon nanotubes; 20 parts of PP were pre-dispersed with all sheet-like conductive graphite. The two pre-dispersed materials were then mixed with the remaining PP, EPDM and auxiliary components at 178°C for 2.5 min.

[0128] The sheet was then subjected to twin-screw extrusion filtration, open mill feeding, and five-roll calendering, resulting in an average sheet thickness of 1.01 mm. The embossing roller temperature was 155℃, and the pressure was 0.52 MPa.

[0129] The DSC test of this batch of materials showed that the initial temperature of PP phase cooling crystallization was about 124.2℃, the peak temperature of crystallization was about 116.8℃, and the end temperature of crystallization was about 109.5℃.

[0130] The electrothermal response was calibrated at 104℃, 108℃, 112℃, 116℃, 120℃, 124℃ and 128℃, using a subsequent cooling process similar to that of the actual production line.

[0131] Table 1 shows the changes in the stable resistance of samples cooled to 23°C relative to the untreated samples of the same batch at different treatment temperatures, corresponding to additional temperature rises of approximately 1.5°C, 2.5°C, and 4.0°C.

[0132]

[0133] Within the range of 112 to 120°C, as the electric heating input increases, the stable resistance after cooling maintains a relatively clear positive change. Therefore, this range is determined as the electric heating set-temperature zone for this batch of materials, and the temperature of the production processing center is controlled at approximately 116°C.

[0134] During formal processing, nine sets of corresponding elastic electrodes are arranged along the width direction. The nominal pulse voltage of each independent channel is 60V, and the actual voltage of each region is kept basically consistent through terminal voltage feedback.

[0135] The duration of a single pulse is approximately 1.0 s, the interval between adjacent pulses is approximately 2.5 s, the additional temperature rise in each region is mainly 2.1 to 3.1 ℃, and the maximum additional temperature rise is controlled within 5 ℃.

[0136] The online evaluation temperature Te was set to 116℃. Based on the pre-established narrow temperature range correction relationship of 112~120℃, the measured resistance after thermal equalization of each region was corrected to 116℃ to obtain Re.

[0137] The initial online evaluation of this batch showed a CVE of 9.9%. After four rounds of electrothermal treatment, the CVE dropped to 5.2%. The improvement from further treatment had significantly decreased, so the first stage of conditioning was discontinued.

[0138] The area resistivity (CV) of the same batch of reference samples after cooling to 23°C and standing for 24 hours was 10.6%. The area resistivity of the sheet after the first stage of treatment was measured to be 4.6% to 4.8% after cooling according to the standard thermal history.

[0139] After the sheet was further cooled to 70°C, it underwent temperature preconditioning with a peak pressure of approximately 45 kPa, and experienced a total of 12 loading and unloading cycles. During the process finalization test, two pressure points, 20 kPa and 40 kPa, were used to evaluate the continuous cycle response.

[0140] It was then cooled to 50°C under a light constraint of approximately 6 kPa, the constraint was released, and it was cooled to 32°C before being wound up under low tension.

[0141] Example 2: This example uses 58 parts of PP, 42 parts of EPDM, 0.7 parts of multi-walled carbon nanotubes and 3.5 parts of sheet-like conductive graphite. The types and amounts of the remaining auxiliary components are the same as in Example 1.

[0142] Take 14 parts of EPDM to prepare the first predispersant and 18 parts of PP to prepare the second predispersant. Mix the two predispersants with the remaining materials at 174°C for about 2.0 min.

[0143] The average thickness of the resulting calendered sheet is 0.99 mm.

[0144] DSC testing revealed a PP phase crystallization peak temperature of approximately 114.3℃. Based on actual production cooling history and subsequent electrothermal response testing, the optimal electrothermal setting range for this batch was determined to be 111–117℃, with the production center temperature controlled at approximately 114℃.

[0145] The nominal voltage of the partition pulse is 54V, the single power-on time is about 0.8s, the interval is about 3.0s, and the additional temperature rise is mainly 1.8~2.7℃.

[0146] The online evaluation temperature Te was set at 114℃. The initial online CVE was 9.3%, which decreased to 4.9% after 5 rounds of treatment, and then the change slowed down.

[0147] The CV of the reference sample in the same batch was 9.8% in the room temperature region, while the CV of the finished product region after complete treatment was 4.4%.

[0148] After the sheet is cooled to 65°C, it is subjected to 15 loading and unloading cycles at a peak pressure of approximately 40 kPa. The process stability is evaluated using two pressure points: 20 kPa and 40 kPa.

[0149] It was then cooled to 48°C under a light constraint of about 5 kPa, and after the constraint was removed, it was cooled and wound up.

[0150] This batch has a relatively high EPDM content, resulting in sheet softness and relatively high piezoresistive response in low-pressure areas.

[0151] Example 3: This example uses 68 parts of PP, 32 parts of EPDM, 1.2 parts of multi-walled carbon nanotubes and 2.8 parts of sheet-like conductive graphite. The types and amounts of the remaining auxiliary components are the same as in Example 1.

[0152] Take 10 parts of EPDM to prepare the first predispersant and 22 parts of PP to prepare the second predispersant. Mix the two predispersants with the remaining materials at 182°C for about 3.0 min.

[0153] The average thickness of the resulting sheet is 1.02 mm.

[0154] DSC testing revealed a PP phase crystallization peak temperature of approximately 119.6℃. Based on electrothermal response calibration under actual production thermal history conditions, 115–123℃ was selected as the electrothermal setting range for this batch, with the production center temperature controlled at approximately 119℃.

[0155] The nominal voltage of the partition pulse is 62V, the single power-on time is about 1.2s, the pulse interval is about 2.0s, and the additional temperature rise is mainly 2.4~3.5℃.

[0156] The online evaluation temperature Te was set at 119℃, with an initial CVe of 9.6%. After four rounds of treatment, the CVe decreased to 5.4%, and further treatment showed little improvement.

[0157] The CV of the reference sample in the same batch was 10.1% in the room temperature region, while the CV of the finished product region after complete treatment was 5.0%.

[0158] After the first stage, the sheet was further cooled to 75°C and subjected to 10 loading and unloading cycles at a peak pressure of approximately 55 kPa. Cyclic stability was tested at two pressure points, 20 kPa and 40 kPa, during process finalization.

[0159] It was then cooled to 52°C under a light constraint of approximately 8 kPa, and after the constraint was removed, it continued to cool and was then wound up.

[0160] This batch has a relatively high PP content, and the deformation of the sheets under the same pressure is lower than that of Example 2, but the dimensional recovery and long-term response after cycling are still good.

[0161] Comparative Example 1: Prepared according to the company's original intelligent tactile TPO synthetic leather process.

[0162] The overall proportions of the main materials and carbon-based conductive fillers are the same as in Example 1. PP, EPDM, carbon nanotubes and sheet-like conductive graphite are added directly in the same mixing process without preparing pre-dispersed materials separately.

[0163] After the sheet is calendered and embossed, it is directly cooled and wound up according to the original gradient cooling conditions, without zonal electrothermal setting or temperature mechanical preconditioning.

[0164] Comparative Example 2: The formulation is the same as in Example 1. Carbon nanotubes and sheet-like conductive graphite are mixed together, and the first predispersant and the second predispersant are not prepared separately.

[0165] After the sheet was calendered and embossed, the batch of sheet was tested using the same electrothermal response calibration method as in Example 1. The obtained positive residual resistance response temperature range still covered around 116°C. Therefore, approximately 116°C was selected as the zoned electrothermal treatment temperature.

[0166] Subsequently, electrothermal conditioning was performed under the same partitioned isovoltage conditions as in Example 1, followed by temperature mechanical conditioning at approximately 70°C, with the remaining treatment conditions remaining essentially the same.

[0167] After electrothermal treatment, the regional resistance dispersion of this batch was reduced, and the resistance change per unit pressure was significantly lower than that of the untreated samples in the same batch.

[0168] Comparative Example 3: The same formulation and two types of pre-dispersion methods were used as in Example 1.

[0169] When the sheet enters the cooling stage at approximately 116°C, no separate heating pulses are set for each zone. Instead, the entire sheet is subjected to nearly uniform heat treatment by a hot roller, and the average additional heat input is at a similar level to that in Example 1.

[0170] Then continue to process under temperature-controlled mechanical conditioning conditions of approximately 70°C.

[0171] Comparative Example 4: The same formulation, pre-dispersion method and processing temperature as Example 1 were used.

[0172] The first phase of the zoned power supply was changed to constant current control, so that the set current of each zone was basically the same, and the maximum additional temperature rise limit of 5°C was still set.

[0173] The remaining cooling and temperature preconditioning processes are basically the same as in Example 1.

[0174] Comparative Example 5: The same formulation and pre-dispersion method as in Example 1 were used.

[0175] The embossed sheet continues to cool, and when the temperature drops to about 100°C, it undergoes a zoned isoelectric treatment.

[0176] The number of pulses and the additional temperature rise were kept close to those in Example 1, followed by a temperature-controlled mechanical preconditioning at approximately 70°C.

[0177] Comparative Example 6: The batching, double pre-dispersion, calendering, embossing and first-stage zoned electrothermal adjustment were completed according to Example 1.

[0178] After the first stage, normal cooling continues. No periodic pressure conditioning is performed at around 70°C. The sheet is directly cooled under light constraint and then wound up.

[0179] Each batch of finished products was placed at 23±1℃ for 24 hours before being tested.

[0180] The reference samples of the same batch were prepared according to the same calendering and embossing process as the corresponding embodiments. Before entering the post-conditioning process, the samples were taken and cooled according to the basic cooling conditions close to those of the main production line. This was used to obtain the regional CV and basic piezoresistive sensitivity of the batch of materials when they were not post-conditioned.

[0181] The spatial resistance detection uses nine equal-area regions, employing the same 25mm×25mm upper and lower electrodes, and a contact pressure of 5kPa.

[0182] The sensitivity retention rate is calculated as the ratio of the finished product's piezoresistive sensitivity to the corresponding reference sample's piezoresistive sensitivity in the same batch.

[0183] The initial cycle zero-load drift was evaluated by five consecutive cycles of loading and unloading at 0–60 kPa.

[0184] Piezoresistive hysteresis is calculated based on the maximum difference in the normalized resistance response of the loaded and unloaded branches under the same pressure.

[0185] The 1000-cycle test was conducted at 0–60 kPa and 0.5 Hz.

[0186] The main test results for each batch are shown in Table 2.

[0187]

[0188] As shown in Table 2, the CV of the regions after all treatments in Examples 1 to 3 was 4.4% to 5.0%, which was significantly lower than that of the corresponding reference samples in the same batch, while the piezoresistive sensitivity remained at 93.2% to 95.8% of the reference state.

[0189] Example 2 has a higher EPDM ratio and the lowest regional CV, but its cycle hysteresis and 1000-cycle retention rate are slightly lower than those of Examples 1 and 3. Example 3 has a higher PP ratio and a slightly higher final regional CV, but its hysteresis rate is lower and its 1000-cycle retention rate is higher.

[0190] Comparative Example 1 was prepared directly according to the original production route, and its finished product region CV was still about 10%, while the initial cycle zero-load drift and piezoresistive hysteresis were more obvious.

[0191] After undergoing post-conditioning similar to that of Example 1, Comparative Example 2 showed a reduction in regional CV to 6.1%, but a decrease in piezoresistive sensitivity retention to 83.6%. This batch indicates that when carbon nanotubes and sheet-like conductive graphite are co-mixed in the front end, subsequent thermal conditioning has a more significant impact on mechanically sensitive conductive contacts.

[0192] Comparative Example 3, after undergoing approximately uniform heat treatment across the entire area, showed a decrease in regional CV to 7.5%, which was less significant than the improvement observed in the example with partitioned isoelectric treatment.

[0193] After constant current treatment, the CV of the finished product in this batch increased from 9.7% in the same batch of reference samples to 11.1%. Under constant current conditions, the region with higher original resistance receives relatively higher electrothermal power, and the residual resistance increase on the high resistance side becomes more obvious in the positive residual resistance response temperature range. Therefore, the regional dispersion of this batch of materials is further expanded.

[0194] Although Comparative Example 5 uses partitioned isovoltage processing, the processing temperature is about 100°C, which is outside the positive residual resistance response region calibrated in Example 1. Therefore, the region CV is reduced to only 8.2%.

[0195] After the first stage of treatment, the final region CV of Comparative Example 6 reached 4.9%, which is close to that of Example 1; however, due to the lack of temperature mechanical preconditioning, the zero-load drift in the first 5 cycles was still 7.6%, the piezoresistive hysteresis rate reached 13.1%, and the retention rate after 1000 cycles was also lower than that of the complete process group.

[0196] It can be seen that the main impact of the first stage is concentrated on the dispersion of the basic resistance between different regions. The second stage has a smaller impact on the regional CV formed in the first stage. Its main role is to reduce the initial cycle zero-load drift, loading and unloading hysteresis, and improve long-term cycle stability.

[0197] After all the post-conditioning was completed, the finished product performance of Examples 1 to 3 was tested at 0 to 60 kPa under uniform room temperature conditions. The results are shown in Table 3.

[0198]

[0199] Example 2 has a higher EPDM ratio, resulting in greater elastic deformation under the same pressure, and therefore a relatively higher normalized resistance response. Example 3 has a higher PP ratio, resulting in a slightly lower response amplitude under unit pressure, but better cycle recovery and durability stability.

[0200] All embodiments showed a response amplitude that increased continuously with increasing pressure, indicating that after the first stage of reducing the spatial basis resistance dispersion, the sheet still retained a relatively obvious pressure-sensitive response.

[0201] Based on the 1000-cycle test, Example 1, Comparative Example 1 and Comparative Example 6 were selected for further 10000 cycles of 0-60 kPa test, and the results are shown in Table 4.

[0202]

[0203] Example 1 maintained a stable response of 92.8% after 10,000 load-unload cycles. Although Comparative Example 6 completed the first stage of resistance tuning, it lacked temperature-state mechanical pre-conditioning, and its long-term cycle retention rate was lower than that of Example 1. Comparative Example 1 showed significant fluctuations in spatial base resistance dispersion, initial cycle stability, and long-term cycle retention.

[0204] Based on the above results, the pre-dispersed composite conductive network, the electrothermal response temperature zone calibration, the zoned equal voltage electrothermal tuning, and the subsequent temperature-state mechanical preconditioning are interconnected in the continuous process.

[0205] The first stage can significantly reduce the basic resistance dispersion between different regions while maintaining a high level of piezoresistive sensitivity. The second stage further reduces zero-load drift and loading / unloading hysteresis caused by the initial mechanical cycle and improves the piezoresistive response retention capability after repeated loading.

Claims

1. A method for preparing intelligent tactile TPO synthetic leather, characterized in that, Includes the following steps: A piezoresistive composite material is prepared by mixing raw materials containing polypropylene, ethylene propylene diene monomer (EPDM) rubber, carbon nanotubes and sheet conductive graphite, and then formed into TPO piezoresistive sheets through calendering and embossing. The electrothermal setting temperature range T1 of the TPO piezoresistive sheet is predetermined. The electrothermal setting temperature range T1 is the temperature range in which the stable resistance of the TPO piezoresistive sheet increases with the increase of the electrothermal input after being treated with different electrothermal inputs and cooled to the same reference temperature. The embossed TPO piezoresistive sheet is brought into the electrothermal setting temperature zone T1, the TPO piezoresistive sheet is divided into multiple resistance detection areas, and an electrothermal pulse with the same set voltage is applied to each resistance detection area. The electrothermal setting is controlled according to the resistance dispersion of each resistance detection area. After the electrothermal setting is completed, the TPO piezoresistive sheet is further cooled to a pre-conditioning temperature zone T2 that is lower than the electrothermal setting temperature zone T1. The TPO piezoresistive sheet is subjected to multiple loading and unloading cycles in the pre-conditioning temperature zone T2, followed by cooling and winding.

2. The method for preparing intelligent tactile TPO synthetic leather according to claim 1, characterized in that, Carbon nanotubes are premixed with at least a portion of EPDM rubber to form a first predispersant, and sheet-like conductive graphite is premixed with at least a portion of polypropylene to form a second predispersant. The first predispersant, the second predispersant, and the remaining raw materials are then mixed a second time.

3. The method for preparing intelligent tactile TPO synthetic leather according to claim 2, characterized in that, The mass ratio of polypropylene to ethylene propylene diene monomer (EPDM) rubber is 55:45 to 70:30; based on 100 parts by mass of polypropylene and EPDM rubber, the amount of carbon nanotubes added is 0.6 to 1.4 parts by mass, and the amount of sheet-like conductive graphite added is 2.5 to 4.0 parts by mass; the temperature of the secondary mixing is 170 to 185°C, and the mixing time is 1 to 4 minutes.

4. The method for preparing intelligent tactile TPO synthetic leather according to claim 1, characterized in that, The cooling crystallization temperature range of the polypropylene phase was determined by differential scanning calorimetry, and the TPO piezoresistive sheet was subjected to different electrothermal input treatments within the cooling crystallization temperature range and its adjacent temperature range. The electrothermal setting temperature range T1 was determined based on the change in stable resistance after cooling with the electrothermal input.

5. The method for preparing intelligent tactile TPO synthetic leather according to claim 4, characterized in that, Each resistance detection area is subjected to an electrothermal pulse with the same set voltage through the corresponding electrode. Each electrothermal pulse lasts for 0.3 to 2 seconds, the interval between adjacent electrothermal pulses is 1 to 5 seconds, the additional temperature rise generated by a single electrothermal pulse is 1.5 to 4°C, and the maximum additional temperature rise does not exceed 5°C.

6. The method for preparing intelligent tactile TPO synthetic leather according to claim 5, characterized in that, After each round of electrothermal pulses, thermal equalization is performed, and the resistance of each resistance detection area is corrected to the same online evaluation temperature within the electrothermal setting temperature zone T1. Electrothermal setting is controlled based on the coefficient of variation of the resistance of the corrected area.

7. The method for preparing intelligent tactile TPO synthetic leather according to claim 1, characterized in that, The temperature preconditioning zone T2 is 50-90°C. In the temperature preconditioning zone T2, a periodic pressure of 20-80 kPa is applied to the TPO piezoresistive sheet, and 5-30 loading and unloading cycles are performed.

8. The method for preparing intelligent tactile TPO synthetic leather according to claim 7, characterized in that, The temperature preconditioning is completed based on the stability of the normalized resistance response of the TPO piezoresistive sheet during continuous loading and unloading. After the temperature preconditioning is completed, a constraint pressure of 2 to 10 kPa is applied to the TPO piezoresistive sheet and it is cooled to 45 to 55°C. After the constraint pressure is released, it is cooled to no higher than 35°C and then wound up.

9. A smart tactile TPO synthetic leather, characterized in that, The smart tactile TPO synthetic leather comprises a TPO matrix formed of polypropylene and EPDM rubber, and carbon nanotubes and sheet-like conductive graphite dispersed in the TPO matrix. Under conditions of 23±1℃, the coefficient of variation of the stable resistance in different regions of the smart tactile TPO synthetic leather is no greater than 6%. During cyclic loading and unloading in the range of 0 to 60 kPa, the maximum zero-load resistance drift in the first 5 cycles is no greater than 3.0%, and the piezoresistive hysteresis rate is no greater than 8.0%. After 1000 loading and unloading cycles at 0 to 60 kPa and 0.5 Hz, the piezoresistive response retention rate under 60 kPa pressure is no less than 95%.

10. The intelligent tactile TPO synthetic leather according to claim 9, characterized in that, The mass ratio of polypropylene to ethylene propylene diene monomer (EPDM) rubber is 55:45 to 70:30; based on 100 parts by mass of polypropylene and EPDM rubber, the content of carbon nanotubes is 0.6 to 1.4 parts by mass, and the content of sheet-like conductive graphite is 2.5 to 4.0 parts by mass; the absolute values ​​of the normalized resistance response at pressures of 20 kPa, 40 kPa, and 60 kPa are 10% to 15%, 20% to 28%, and 30% to 40%, respectively.

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