Modified plastic for force sensor elastomer, and preparation and application methods thereof

Abstract

The invention relates to the technical field of modified plastics, in particular to a modified plastic for a force sensor elastomer and preparation and application methods of the modified plastic for the force sensor elastomer. 20-40% of reinforcing fibers; 3-10% of a functional auxiliary agent; the base resin is one or more of PPS (polyphenylene sulfite), PA66 (polyamide 66), ABS (acrylonitrile butadiene styrene) and PEEK (polyether ether ketone); the reinforced fibers are obtained by pretreating chopped carbon fibers or glass fibers; the functional additive is prepared by mixing a creep resistant agent, an anti-aging agent, a flexibilizer and a lubricant according to the mass ratio of (1-2): (0.5-1): (1-3): (0.5-1). The prepared force sensor elastic body can simultaneously meet the requirements of ultrahigh elastic modulus, ultralow creep deformation and ultralow thermal expansion coefficient, and has highly isotropic mechanical and thermal properties, so that the force sensor elastic body can replace metal to be used in a multi-dimensional force sensor, and the overall weight of the sensor is reduced by more than 30% compared with that of a metal-based multi-dimensional force sensor with the same measuring range.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of modified plastics, in particular to a modified plastic for an elastomer of a force sensor, a preparation method and an application method. BACKGROUND

[0002] High-precision multi-dimensional force sensors are key components in the fields of robots, aerospace, precision automation, etc., and the core element thereof is an elastomer. Traditional elastomers are mostly made of aluminum alloy or stainless steel, which have high rigidity, low creep and stable thermal expansion performance. However, there are obvious limitations. On the one hand, the density of metal materials is relatively large, resulting in a relatively high overall weight of the sensor, which is difficult to meet the needs of weight-sensitive scenarios such as robot end effectors, portable detection devices, and lightweight components in aerospace; on the other hand, the processing technology of metal elastomers is complex (such as precision milling, grinding, wire cutting, etc.), which has a long processing cycle and high cost, and in some special working conditions such as corrosive environments and electromagnetic interference environments, metal materials are prone to corrosion failure or electromagnetic interference problems, which affect the long-term stability and service life of the sensor. In recent years, with the improvement of the performance of plastic materials, some existing technologies have begun to try to apply ordinary plastics to the elastomer structure of simple force sensors (mainly single-dimensional or two-dimensional force sensors). The core structure of this scheme includes an ordinary plastic elastomer, a force sensing element, a signal processing module, etc. For example, the patent with the publication number CN212483539U: a micro force sensor made of plastic material, which uses ordinary polyamide plastic to make a parallel beam elastomer, and pastes strain gauges on the surface of the beam body to detect small single-dimensional pressure; the patent with the publication number CN111537192A: a two-dimensional force sensor based on a plastic elastomer, which uses ABS plastic to make a cross beam elastomer, and arranges a strain gauge array on the beam arm to realize two-dimensional force detection. The original intention of this design is to realize the lightweight of the sensor by using the low density characteristics of ordinary plastics, and to reduce the material cost and processing difficulty. However, due to the fact that the mechanical properties of ordinary plastics are much lower than those of metal materials, and they are prone to creep, aging and other problems under conditions such as temperature changes and long-term stress, the detection accuracy, range and stability of such sensors are low, and they can only be applied to civilian scenarios with extremely low precision requirements, and cannot meet the application requirements of industrial-grade multi-dimensional force sensors.

[0003] Modified plastics, by adding modifiers to base resins, can achieve precise control of key indicators such as mechanical properties, thermal stability, and environmental resistance, providing a new technical path to solve the problem of lightweighting traditional metal-based sensors. Against this background, applying modified plastics to the design of elastomer structures for multidimensional force sensors has become an important research direction for achieving sensor lightweighting, cost reduction, and expansion of application scenarios. However, the inherent characteristics of plastic materials themselves severely restrict their application in high-precision sensors, mainly due to three material-related technical problems: (1) Plastics, especially fiber-reinforced plastics, are prone to orientation during flow processing, resulting in significant differences in elastic modulus and thermal expansion coefficients in different directions. When one direction is subjected to force, strain output will be generated in other directions, causing measurement errors. (2) Polymer molecular chains will slip and rearrange under long-term loads, exhibiting creep phenomena, causing the sensor zero point to drift slowly over time, resulting in unstable output signals. (3) The thermal expansion coefficient of plastics is usually much higher than that of metal strain gauges. When the temperature changes, the material and strain gauge expand and contract inconsistently, generating huge thermal stress, which is mistakenly detected as an external force signal, causing a decrease in measurement accuracy. Therefore, developing a modified plastic that can overcome the above three major defects and has comprehensive performance comparable to metal has become a key technological bottleneck in realizing the replacement of metal with plastic elastomers.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a modified plastic for use in force sensor elastomers, its preparation, and its application method. This modified plastic simultaneously satisfies ultra-high elastic modulus, ultra-low creep, and ultra-low coefficient of thermal expansion, and possesses highly isotropic mechanical and thermal properties. Therefore, the modified plastic can replace metal in multidimensional force sensors, reducing the overall weight of the sensor by more than 30% compared to metal-based multidimensional force sensors of the same range.

[0006] To address the aforementioned technical problems, the first objective of this invention is to provide a modified plastic with ultra-high elastic modulus, ultra-low creep and ultra-low coefficient of thermal expansion, as well as corrosion resistance and insulation, for use as an elastomer in force sensors.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 50~65%; Reinforcing fiber 20-40%; Functional additives 3~10%; The base resin is any one of PPS, PA66, PEEK, or a mixture thereof; The reinforcing fibers are obtained from chopped carbon fibers or glass fibers through pretreatment; The functional additives are prepared by mixing anti-creep agents, anti-aging agents, toughening agents and lubricants in a mass ratio of 1~2:0.5~1:1~3:0.5~1.

[0008] This invention constructs a continuous phase using a base resin and a dispersed phase using reinforcing fibers to form a three-dimensional reinforcing network. Functional additives are compounded in a specific ratio to create a synergistic effect, achieving synergistic regulation of multiple properties. When external force is applied to the material, the matrix first undergoes elastic deformation and effectively transfers the stress to the reinforcing fibers. The elastic modulus of the reinforcing fibers is much higher than that of the matrix resin, making them the main load-bearing unit. By pretreating the reinforcing fibers, it is ensured that the stress is better transferred without excessive concentration.

[0009] The base resin of this invention is any one of PPS, PA66, and PEEK, or a mixture thereof. When two resins are blended, a reactive compatibilizer needs to be added, with an amount of 0.5-3% of the total mass. The addition of the compatibilizer can significantly reduce the interfacial tension between the two phases, allowing the dispersed phase to be sheared and broken into a finer and more stable structure during melt blending, and inhibiting its subsequent agglomeration. The reactive compatibilizer is preferably at least one of epoxy-functionalized polymer or maleic anhydride-grafted polymer. In a multi-component blend system, the two can be used in combination to strengthen all potentially incompatible interfaces.

[0010] In some alternative implementations, to further adjust melt rheology, the base resin may contain less than 3%, for example, 0.5%-2%, of ABS. The amorphous structure of ABS gives it good flowability in the molten state, and adding even a small amount may help reduce the melt viscosity of high-viscosity systems, especially highly filled PPS / PEEK, improve mold filling during injection molding, and reduce fiber orientation and internal stress. However, when ABS is introduced, a compatibilizer must be added to ensure uniform mixing with the base resin components and avoid creating stress defect points.

[0011] Preferably, the chopped carbon fibers are 3-5 mm in length, ensuring a sufficiently large aspect ratio. This allows the fibers to overlap and form a primary load-bearing network throughout the composite material, achieving high elastic modulus and high strength. The glass fibers are 1-2 mm in length; shorter glass fibers can be more evenly distributed in the gaps between the long carbon fiber skeletons, forming a secondary reinforcement network. This prevents the long carbon fibers from buckling during processing or under stress and transfers and disperses stress between the carbon fibers, improving the material's integrity and toughness.

[0012] As a further preferred embodiment, the reinforcing fiber is obtained by pretreatment of chopped carbon fibers and glass fibers, with a mass ratio of chopped carbon fibers to glass fibers of 1 to 3:1. This invention, by compounding carbon fibers and glass fibers, uses high-modulus chopped carbon fibers with a length of 3 to 5 mm as the main load-bearing skeleton, providing high stiffness and a negative thermal expansion effect; shorter glass fibers with a length of 1 to 2 mm serve as filler and support, allowing for more uniform distribution within the voids of the long carbon fiber skeleton. The 1 to 3:1 mass ratio ensures that the two fibers form a complementary reinforcing network. Under shear flow, this helps disrupt the directional alignment of individual fibers, making the network structure more uniform in the X, Y, and Z directions, and avoiding severe anisotropy caused by fiber orientation.

[0013] Preferably, the pretreatment of the reinforcing fiber involves forming a 100-500 nm thick thermoplastic polyester elastomer pre-coating on the fiber surface via atomized spraying; followed by atomized spraying of a silane coupling agent onto the pre-coating. This invention, through pretreatment, forms a three-dimensional cross-linked interface structure of fiber, silane, and thermoplastic polyester elastomer on the fiber surface, reinforced by covalent bonds, achieving efficient stress and strain transfer and simultaneously improving stiffness and creep resistance. Furthermore, by pretreating the fiber, leakage current caused by exposed carbon fibers is avoided, ensuring the insulation effect of the material.

[0014] The thermoplastic polyester elastomer pre-coating formed by atomized spraying is a non-dense coating layer attached by physical adsorption. The silane coupling agent used subsequently is a small molecule substance. Under the action of pretreatment temperature and stirring, the small molecule silane coupling agent penetrates and diffuses through the micropores and molecular chain gaps of the thermoplastic polyester elastomer pre-coating, and finally reaches the fiber surface. The silanol groups generated by its hydrolysis undergo a dehydration condensation reaction with the active sites on the fiber surface to form covalent bonds. Its molecular chains and the functional groups at the other end are integrated into the thermoplastic polyester elastomer pre-coating, constructing a functionally complete surface with excellent reactivity and compatibility with the matrix resin, which is integrated and reinforced by chemical bonds.

[0015] The thermoplastic polyester elastomer pre-coating has a melting point above 150℃. The thermoplastic polyester elastomer is TPEE. Selecting TPEE with a melting point above 150℃ ensures that the coating maintains its structural integrity during subsequent silane treatment and substrate processing at 80-100℃, preventing dissolution and flow. Specifically, TPEE is dissolved in THF or acetone to form a 3-8% (w / w) solution. This solution is then atomized and sprayed onto the fiber surface. The TPEE molecular chains are physically anchored to the fiber through van der Waals forces and mechanical interlocking effects. Rapid drying is then performed at 60-80℃ with an airflow rate of 0.5-2.0 m / s. By controlling the solution concentration, drying temperature, and airflow rate, the solvent evaporates rapidly, inducing nanoscale micropores or channels in the formed TPEE pre-coating.

[0016] The dosage of silane coupling agent is 0.5-1.0% of the total mass of the reinforcing fiber; the pretreatment time is 1-2 hours, and the pretreatment temperature is 80-100℃. The silane coupling agent is KH-550. The 1-2 hour treatment ensures complete monolayer coating, and the dosage of 0.5-1.0% ensures the interface modification effect while avoiding excessive residue.

[0017] Specifically, it is prepared into a pretreatment solution with a concentration of 1~2wt% by mixing it with a mixed solution of deionized water and ethanol (water:ethanol = 5:95). First, KH-550 is hydrolyzed in water for 30 minutes to generate active silanol, which is then diluted with ethanol. In a high-speed mixer, the pretreatment solution is atomized and sprayed into the mixer through a precision atomizing nozzle. At the same time, a heat medium at 80~100℃ is introduced into the jacket of the mixer. The heat accelerates the evaporation of ethanol and provides the driving force for molecular motion. The heating is carried out simultaneously during the stirring process, so that the contact angle between the pretreated fiber and water becomes a moderate hydrophobic value. The pretreatment liquid, with its low surface tension, rapidly spreads to form a continuous liquid film on the TPEE pre-coating surface. Driven by the kinetic energy provided by heating and stirring, it penetrates the nanopores of the pre-coating through capillary action and comes into contact with the fiber body. This allows the active silanol to react with the -Si-OH groups on the glass fiber surface or the oxygen-containing functional groups on the carbon fiber surface to form covalent bonds. Meanwhile, the organic functional groups at the other end of the silane molecule, driven by heating, react chemically with the ester bonds, terminal hydroxyl groups, or terminal carboxyl groups on the TPEE pre-coating molecular chain. The coating and reaction are carried out simultaneously during dynamic stirring, resulting in higher efficiency and a stronger effect. The pretreated fiber provides good chemical compatibility and reactivity for the subsequent resin matrix, maximizing the interfacial strength.

[0018] Preferably, the anti-creep agent is silicate, mica powder, or talc powder; these lamellar or granular inorganic rigid fillers are dispersed in the matrix resin and together with the crisscrossing fiber network, they construct a multi-dimensional anti-creep locking structure; their large specific surface area generates strong adsorption and mechanical interlocking with the polymer molecular chains, which greatly restricts the movement and slippage ability of the molecular chain segments; when the material is subjected to long-term stress, these rigid particles effectively disperse the stress, prevent the persistent and directional rearrangement of the molecular chains, and thus significantly inhibit macroscopic creep deformation.

[0019] Preferably, the toughening agent is a maleic anhydride-grafted polyolefin elastomer or a core-shell copolymer; when the material is subjected to impact or high stress, these elastic particles absorb energy by inducing crazes and shear bands, effectively preventing the propagation of microcracks; preventing irreversible micro-damage caused by accidental overload or fatigue, avoiding the deterioration of sensor hysteresis characteristics, decrease in linearity and zero drift caused by the accumulation of micro-damage, and ensuring the long-term accuracy of the measurement signal.

[0020] Preferably, the anti-aging agent is a hindered phenolic or phosphite antioxidant; it is used to protect the chemical interface on the surface of the reinforcing fiber that is sensitive to the heat and oxygen environment, and to prevent highly reactive free radicals generated by the material under heat and oxygen from attacking the chemical bonds of the interface; the hindered phenolic antioxidant rapidly terminates alkyl free radicals by providing hydrogen atoms; while the phosphite prevents the generation of new free radicals from the source by decomposing hydroperoxides and converting them into stable alcohols. The two work together to maintain the material's low creep and low hysteresis performance.

[0021] Preferably, the lubricant is ethylene bis-stearamide, calcium stearate, or polyethylene wax. Its molecular structure has one end compatible with the polar polymer matrix and the other end a non-polar long chain. This ensures processing fluidity while maximally protecting the length and interfacial structure of the pretreated fibers. The lubricant migrates to the interface to form a molecular layer, reducing shear damage to the fibers from the screw and flow channels during melt blending. Through interfacial isolation and shear slip mechanisms, it significantly reduces melt viscosity and the coefficient of friction.

[0022] The second objective of this invention is to provide a method for preparing a modified plastic for a force sensor elastomer, thereby achieving the preparation of the aforementioned modified plastic.

[0023] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a modified plastic for a force sensor elastomer includes the following steps: S1 places the fiber in a high-speed mixer and uses an atomized spraying method to uniformly coat its surface with a layer of thermoplastic polyester elastomer solution. Then it is dried at 60~80℃ to evaporate the solvent and form a nanoscale pre-coating. A process combining atomized spraying and low-temperature stepped drying was used to construct a structurally controllable nanoscale TPEE pre-coating on the fiber surface. Atomized spraying ensures that the elastomer coating uniformly and completely covers each fiber, effectively avoiding fiber adhesion and uneven coating problems caused by traditional liquid immersion methods. Subsequent drying at 60~80℃ induces the formation of appropriate nanoscale microporous channels within the coating, providing pathways for the efficient penetration and diffusion of silane coupling agent molecules. At the same time, this drying temperature range fully ensures the stability and integrity of the fiber itself and the coating structure during the pretreatment process.

[0024] S2. Add 0.5-1.0% of the total mass of silane coupling agent to the fiber that has been treated above in a mist, and pretreat it by stirring at 80-100°C for 1-2 hours. The atomized spraying method ensures that trace amounts of silane coupling agent can be uniformly distributed at the molecular level on the pre-coated fiber surface, avoiding agglomeration caused by local enrichment. Specifically, under a thermal field of 80~100℃ and mechanical stirring, the hydrolysis, diffusion, and chemical reaction of the silane coupling agent with the fiber surface and TPEE coating surface are accelerated. The thermal energy provides the energy required to overcome the activation energy of the reaction, while stirring ensures that each fiber can be fully contacted and reacted by silane molecules, significantly enhancing the chemical compatibility between the fiber and the resin matrix.

[0025] S3: Pour the base resin, pretreated reinforcing fibers, and functional additives into a mixer and mix at room temperature for 5-10 minutes to form a uniform premix. Specifically, first, put all the pretreated fibers into a high-speed mixer and stir at a low speed of 200~300 rpm for 30 seconds to initially break up the fiber clumps. Then, add half of the base resin powder and stir at a medium speed of 400~600 rpm for 60 seconds to allow the resin powder to penetrate between the fibers, playing a physical isolation role and preventing the fibers from re-agglomerating. Finally, add the remaining resin and all functional additives and mix at a high speed of 800~1000 rpm for 5~10 minutes to achieve uniform mixing.

[0026] S4 feeds the premixed material into a twin-screw extruder for melt blending and extrusion granulation.

[0027] Preferably, a stepped heating process is adopted from the feed port to the die head, specifically set as follows: Zone 1 270~280℃, Zone 2 285~295℃, Zone 3 295~305℃, Zone 4 295~305℃, and die head 290~300℃; screw speed: 250~350rpm; in the twin-screw extruder, the resin particles melt under high temperature and high shear, and mix with the pretreated reinforcing fibers and functional additives. The molten matrix resin impregnates the surface of each pretreated fiber under pressure, and the molecular chains diffuse and entangle with the outer layer of TPEE to complete granulation.

[0028] The third objective of this invention is to propose a method for applying modified plastics to the elastomer structure design of multidimensional force sensors, thereby achieving lightweight and low-cost sensors that meet the needs of weight-sensitive applications such as intelligent end effectors, portable detection devices, and lightweight aerospace components.

[0029] A force sensor elastomer is obtained by injection molding from the aforementioned modified plastic.

[0030] Preferably, the force sensor elastomer meets all of the following performance indicators: 1) The elastic modulus is 18~30 GPa; This invention utilizes a rigid-flexible-rigid gradient interface structure constructed on the fiber surface by a silane coupling agent and a TPEE pre-coating. This achieves near-lossless stress transfer from the resin matrix to the carbon fibers, avoiding the problem of low stress transfer efficiency caused by weak interfacial bonding and ensuring the reinforcing effect of the carbon fibers. High-modulus carbon fibers serve as the main load-bearing skeleton, and their extremely high modulus can improve the overall stiffness of the composite material. Glass fibers and sheet-like or granular anti-creep agents further fill and strengthen the matrix regions between the carbon fiber skeletons, forming a multi-scale reinforcing network that collectively improves the elastic modulus of the material.

[0031] 2) Under conditions of room temperature and a rated load of 50% of the tensile yield strength, the creep rate after 1000 hours should not exceed 0.5%; The physical cross-linked network formed by the pretreated reinforcing fibers restricts the slippage and rearrangement free path of polymer molecular chains, fundamentally inhibiting creep. The sheet-like or granular anti-creep agents dispersed in the matrix further lock the movement of surrounding polymer molecular chains. The selected resins, such as PPS, PA66, and PEEK, are themselves semi-crystalline polymers, and their crystalline regions serve as natural physical cross-linking points, endowing the material with inherent creep resistance. Simultaneously, the TPEE flexible interface layer can absorb and dissipate some of the energy causing microscopic plastic deformation through its own elastic deformation, allowing the interface region to maintain good elastic recovery under long-term loads, thus achieving a low creep rate.

[0032] 3) The linear thermal expansion coefficient is not greater than 50 ppm / ℃.

[0033] In this invention, the resin matrix has a high positive coefficient of thermal expansion, the glass fiber has a low positive coefficient of thermal expansion, and the carbon fiber has a negative coefficient of thermal expansion. The flexible interface constructed by the pretreatment ensures that when the temperature rises and the resin matrix attempts to expand, the negative thermal expansion effect of the carbon fiber can be efficiently transferred to the resin matrix, thereby providing strong constraint and compensation for the thermal expansion of the matrix. The high-modulus fiber network and rigid filler constitute a strong three-dimensional rigid constraint on the surrounding resin matrix, physically limiting the large thermal movement space of the polymer molecular chains when heated.

[0034] As a further preferred embodiment, the force sensor elastomer also satisfies the following: 4) Density is 1.1~1.6 g / cm³ 3 ; In this invention, the base resins such as PPS, PA66, and PEEK used as the resin matrix have a density much lower than that of aluminum alloys or steel. Although carbon fiber and glass fiber are added, the overall density of the composite material is successfully controlled within a very low range by optimizing the fiber volume fraction and introducing low-density functional fillers, thus achieving high specific stiffness. The interface structure formed by the core TPEE pre-coating and silane coupling agent treatment has a thickness of nanometers, introducing minimal additional mass. By improving interface efficiency, less reinforcing material can be used while ensuring performance. Furthermore, the micropores formed by the functional additives at the matrix interface further reduce the overall compaction of the material at the molecular scale. Through multi-level synergistic control, lightweight control of material density is achieved while ensuring mechanical properties.

[0035] 5) Tensile strength is 200~400MPa.

[0036] The introduction of PEEK resin, with its inherent superior tensile strength, provides a high-strength foundation for the composite material. Based on this, a high-proportion, high-strength chopped carbon fiber is selected as the main reinforcement, forming a load-bearing skeleton. The core of this invention, the two-step pretreatment process of TPEE pre-coating and silane coupling agent, ensures the formation of a robust interface between the carbon fiber and the resin matrix through covalent bonds. This ensures that the fibers can be fully broken rather than pulled out of the matrix before the material is subjected to stress and fails, thus fully activating the ultra-high strength potential of the carbon fiber and improving the overall strength of the composite material. Simultaneously, the introduction of glass fiber and toughening agent, by inducing crazes and deflecting crack paths, prevents the unstable propagation of cracks, enabling the material to withstand higher loads before failure.

[0037] Preferably, the elastic modulus and coefficient of thermal expansion of the force sensor elastomer deviate by less than 10% in the X, Y, and Z directions. The blending of long and short fibers and optimized processing techniques ensure a uniform distribution of fibers in three-dimensional space. The TPEE pre-coating increases friction and entanglement between fibers, while functional additives interfere with fiber flow orientation in the melt, resulting in a more random three-dimensional distribution of fibers in space, rather than a unidirectional arrangement. This achieves greater consistency in mechanical and thermal properties in the X, Y, and Z directions, eliminating the obvious orientation of traditional injection-molded products.

[0038] Preferably, the injection molding is precision injection molding, and after molding, a stepped annealing process is performed to eliminate internal stress.

[0039] Preferably, the precision injection molding machine has a clamping force ≥1000kN, a positioning accuracy of ±0.005mm, and the mold is made of P20 pre-hardened steel with the cavity surface polished to Ra≤0.8μm. Injection parameters are controlled as follows: barrel temperature 250~320℃, mold temperature 80~150℃, injection pressure 80~120MPa, holding pressure 50~80MPa, and cooling time 15~30s, ensuring that the dimensional tolerance of the elastomer after molding is controlled within ±0.02mm, and the thickness tolerance of key parts such as L-shaped beams is ±0.01mm. The mold gate is designed as a fan-shaped gate or a multi-point submarine gate to avoid... To avoid the single-flow direction caused by a single-point gate, a multi-stage injection speed curve is adopted: the first stage is slow filling, which allows the melt to enter the cavity smoothly and form a stable flow front; the second stage is rapid filling, which avoids cooling of the melt front and reduces fiber orientation; the third stage is slow holding pressure, which reduces internal stress. Injection molding will cause the fibers to exhibit a certain orientation distribution, which makes the coefficient of thermal expansion of the material different in different directions. This invention actively controls the thermal expansion behavior of the final elastomer in a specific direction by adjusting process parameters such as gate position and mold temperature, so as to ensure that it achieves the best match with the strain gauge in a specific direction.

[0040] Step-by-step annealing includes holding at 50℃ for 1 hour, at 80℃ for 2 hours, and at 100~120℃ for 4 hours, followed by natural cooling to room temperature. Specifically, the injection-molded elastomer is placed in a hot air oven and heated in a step-by-step manner, then naturally cooled to room temperature. This eliminates ≥80% of the internal stress generated during injection molding, preventing the elastomer from drifting in precision due to stress release during subsequent use. During the heating stage, when the temperature rises to near the glass transition temperature of the material, the mobility of polymer molecular chain segments is activated. Frozen, high-energy molecular chains begin to relax and rearrange, effectively releasing the internal stress generated during injection molding. Slow natural cooling allows the molecular chains and crystalline regions sufficient time to reach a more stable thermodynamic equilibrium, avoiding the generation of new internal stress due to excessively rapid cooling. After this treatment, the dimensions of the elastomer reach their most stable state, minimizing zero-point drift during long-term use and temperature cycling.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention optimizes the resin matrix and precisely controls the ratio of carbon fibers with negative thermal expansion coefficients to fillers with low thermal expansion coefficients to obtain a special engineering plastic with high rigidity, low creep, and low thermal expansion coefficient. By designing a two-step pretreatment process of fiber pre-coating and silane coupling agent, a flexible buffer interface layer with thermoplastic polyester elastomer as the core is successfully constructed on the surface of carbon fibers and glass fibers. This changes the rigid stress transmission mode of traditional fiber-reinforced plastic interfaces. Through its nanoscale elastic deformation capability, it can reversibly absorb and release micro-strain energy under cyclic loading, thereby effectively suppressing hysteresis and long-term zero-point drift. At the same time, by introducing fillers of different shapes and sizes, the directional arrangement of fibers during processing is significantly disrupted, so that the force sensor elastomer made of this material exhibits highly consistent mechanical and thermal properties in the X, Y, and Z directions, greatly reducing interdimensional coupling interference in multidimensional force measurement.

[0042] This invention leverages the ease of injection molding of modified plastics to achieve mass production of elastomers through the design of an integrated injection mold. This replaces the precision machining process of traditional metal elastomers, reducing the total cost of sensors by more than 20%, while shortening the production cycle and improving production efficiency. The injection molding process is precision injection molding, followed by stepped annealing to eliminate internal stress. By adjusting process parameters such as the gate position and mold temperature, the thermal expansion behavior of the final elastomer in a specific direction is actively controlled, ensuring optimal matching with the strain gauge in that direction. Stepped annealing eliminates ≥80% of the internal stress generated during injection molding, preventing accuracy drift due to stress release during subsequent use. This ensures the elastomer reaches its most stable dimensional state, minimizing zero-point drift during long-term use and temperature cycling. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a flowchart illustrating the steps of the method for preparing the modified plastic used in the force sensor elastomer of the present invention. Figure 2 This is a graph showing the tensile strain and tensile stress variation of the modified plastic obtained in Example 1 of the present invention. Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0047] Unless otherwise specified, all raw materials involved in this invention are available from commercially available sources. Components Commercial sources PPS New and PA66 God PEEK Victrex Carbon fiber / glass fiber Chongqing International TPEE DuPont KH-550 Shandong Hengyu New Material Mica powder / talc powder Lingshou County Erping Mineral Product Processing Factory POE-g-MAH Nengzhiguang GMA-g-POE Dow PEEK-g-MAH Victrex Antioxidant 1010 / 168 Tianjin Li'anlong EBS / calcium stearate Qingdao Jiabaiter New Material Example 1: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 55%; reinforcing fiber 40%; functional additives 5%; The base resin is PEEK; the reinforcing fiber is obtained by pretreatment of short-cut carbon fibers; the pretreatment is as follows: spraying a 5% TPEE solution onto the fiber surface, drying at 70℃ to form a pre-coating of about 300nm; then treating with 0.8% KH-550 at 95℃ for 1.5h; the functional additives are prepared by mixing an anti-creep agent, an anti-aging agent, a toughening agent, and a lubricant in a mass ratio of 1:1:1.5:1; the anti-creep agent is mica powder; the toughening agent is POE-g-MAH; the anti-aging agent is antioxidant 1010; and the lubricant is EBS.

[0048] like Figure 1 The method for preparing a modified plastic for a force sensor elastomer, as shown, includes the following steps: S1 places short-cut carbon fibers in a high-speed mixer and uniformly coats their surface with a layer of thermoplastic polyester elastomer solution using an atomized spraying method. Then, it is dried at 70°C to evaporate the solvent and form a nanoscale pre-coating. 0.8% of the total mass of silane coupling agent is added to the fibers treated above in a mist and pretreated by stirring at 95°C for 1.5 hours. S2 pours the base resin, pretreated reinforcing fiber, compatibilizer and functional additives into the mixer and mixes them at room temperature for 6 minutes to form a uniform premix. S3 feeds the premixed material into a twin-screw extruder for melt blending and extrusion granulation.

[0049] Example 2: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 65%; reinforcing fiber 30%; functional additives 5%; The base resin is PPS; the reinforcing fiber is obtained by pretreatment of short-cut carbon fiber and glass fiber in a mass ratio of 2:1; the pretreatment is as follows: spraying a 5% TPEE solution onto the fiber surface, drying at 70℃ to form a pre-coating of about 300nm; then treating with 0.8% KH-550 at 95℃ for 1.5h; the functional additives are a mixture of creep inhibitor, anti-aging agent, toughening agent and lubricant in a mass ratio of 1.5:1:1.5:1; the creep inhibitor is mica powder; the toughening agent is POE-g-MAH; the anti-aging agent is an antioxidant 1010 / 168 mixed in a mass ratio of 1:1; the lubricant is EBS.

[0050] A method for preparing a modified plastic for a force sensor elastomer includes the following steps: S1 places short-cut carbon fibers and glass fibers in a high-speed mixer, and uses an atomized spraying method to uniformly coat their surfaces with a layer of thermoplastic polyester elastomer solution. Then, it is dried at 70°C to evaporate the solvent and form a nanoscale pre-coating. 0.8% of the total mass of silane coupling agent is added to the fibers treated above in a mist, and the mixture is stirred at 95°C for 1.5 hours for pretreatment. S2 pours the base resin, pretreated reinforcing fibers, and functional additives into a mixer and mixes them at room temperature for 6 minutes to form a uniform premix. S3 feeds the premixed material into a twin-screw extruder for melt blending and extrusion granulation.

[0051] Example 3: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 60%; reinforcing fiber 35%; functional additives 5%; The base resin is 30% PPS and 30% PA66; 0.5% compatibilizer is also added, which is prepared by mixing POE-g-MAH and GMA-g-POE in a 1:1 mass ratio. The reinforcing fiber is obtained by pretreatment of short-cut carbon fibers and glass fibers in a mass ratio of 1.5:1. The pretreatment is as follows: a 5% TPEE solution is sprayed onto the fiber surface and dried at 70°C to form a pre-coating of about 300 nm; then 0.8% KH-550 is used for treatment at 95°C for 1.5 h. The functional additives are prepared by mixing an anti-creep agent, an anti-aging agent, a toughening agent, and a lubricant in a mass ratio of 1:1:1.5:1. The anti-creep agent is mica powder; the toughening agent is POE-g-MAH; the anti-aging agent is antioxidant 1010; and the lubricant is EBS.

[0052] A method for preparing a modified plastic for a force sensor elastomer includes the following steps: S1 places short-cut carbon fibers and glass fibers in a high-speed mixer, and uses an atomized spraying method to uniformly coat their surfaces with a layer of thermoplastic polyester elastomer solution. Then, it is dried at 70°C to evaporate the solvent and form a nanoscale pre-coating. 0.8% of the total mass of silane coupling agent is added to the fibers treated above in a mist, and the mixture is stirred at 95°C for 1.5 hours for pretreatment. S2 pours the base resin, pretreated reinforcing fibers, and functional additives into a mixer and mixes them at room temperature for 6 minutes to form a uniform premix. S3 feeds the premixed material into a twin-screw extruder for melt blending and extrusion granulation.

[0053] Example 4: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 57%; reinforcing fiber 35%; functional additives 8%; The base resin is PA66; the reinforcing fiber is obtained by pretreatment of short-cut carbon fiber and glass fiber in a mass ratio of 3:1; the pretreatment is as follows: spraying a 5% TPEE solution onto the fiber surface, drying at 70℃ to form a pre-coating of about 300nm; then treating with 0.8% KH-550 at 95℃ for 1.5h; the functional additives are prepared by mixing an anti-creep agent, an anti-aging agent, a toughening agent and a lubricant in a mass ratio of 2:1:2:1; the anti-creep agent is talc; the toughening agent is POE-g-MAH; the anti-aging agent is antioxidant 168; and the lubricant is calcium stearate.

[0054] A method for preparing a modified plastic for a force sensor elastomer includes the following steps: S1 places short-cut carbon fibers and glass fibers in a high-speed mixer, and uses an atomized spraying method to uniformly coat their surfaces with a layer of thermoplastic polyester elastomer solution. Then, it is dried at 70°C to evaporate the solvent and form a nanoscale pre-coating. 0.8% of the total mass of silane coupling agent is added to the fibers treated above in a mist, and the mixture is stirred at 95°C for 1.5 hours for pretreatment. S2 pours the base resin, pretreated reinforcing fibers, and functional additives into a mixer and mixes them at room temperature for 6 minutes to form a uniform premix. S3 feeds the premixed material into a twin-screw extruder for melt blending and extrusion granulation.

[0055] Example 5: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 65%; reinforcing fiber 30%; functional additives 5%; The base resin consists of 35% PPS, 15% PEEK, and 15% PA66; 2% compatibilizer is also added, which is prepared by mixing PEEK-g-MAH and POE-g-MAH in a 1:1 mass ratio. The reinforcing fiber is obtained by pretreatment of short-cut carbon fibers and glass fibers in a mass ratio of 3:1. The pretreatment is as follows: a 5% TPEE solution is sprayed onto the fiber surface and dried at 70°C to form a pre-coating of about 300 nm; then 0.8% KH-550 is used for treatment at 95°C for 1.5 h. The functional additives are prepared by mixing an anti-creep agent, an anti-aging agent, a toughening agent, and a lubricant in a mass ratio of 1:1:1.5:1. The anti-creep agent is mica powder; the toughening agent is POE-g-MAH; the anti-aging agent is antioxidant 1010; and the lubricant is EBS.

[0056] A method for preparing a modified plastic for a force sensor elastomer includes the following steps: S1 places short-cut carbon fibers and glass fibers in a high-speed mixer, and uses an atomized spraying method to uniformly coat their surfaces with a layer of thermoplastic polyester elastomer solution. Then, it is dried at 70°C to evaporate the solvent and form a nanoscale pre-coating. 0.8% of the total mass of silane coupling agent is added to the fibers treated above in a mist, and the mixture is stirred at 95°C for 1.5 hours for pretreatment. S2 pours the base resin, pretreated reinforcing fiber, compatibilizer and functional additives into the mixer and mixes them at room temperature for 6 minutes to form a uniform premix. S3 feeds the premixed material into a twin-screw extruder for melt blending and extrusion granulation.

[0057] Comparative Example 1: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 65%; reinforcing fiber 30%; functional additives 5%; The base resin is PPS; the reinforcing fiber consists of short-cut carbon fiber and glass fiber in a mass ratio of 2:1; the functional additives are an anti-creep agent, an anti-aging agent, a toughening agent, and a lubricant mixed in a mass ratio of 1.5:1:1.5:1; the anti-creep agent is mica powder; the toughening agent is POE-g-MAH; the anti-aging agent is antioxidant 1010 / 168 mixed in a mass ratio of 1:1; and the lubricant is EBS.

[0058] The preparation method of the modified plastic is the same as in Example 2, but the carbon fiber and glass fiber are mixed directly with the resin without any pretreatment, which will not be described again here.

[0059] Comparative Example 2: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 65%; reinforcing fiber 30%; functional additives 5%; The base resin is PPS; the reinforcing fiber is obtained by pretreatment of short-cut carbon fibers and glass fibers in a mass ratio of 2:1 with a silane coupling agent; the pretreatment is performed using 0.8% KH-550 at 95°C for 1.5 hours; the functional additives are a mixture of creep inhibitor, anti-aging agent, toughening agent and lubricant in a mass ratio of 1.5:1:1.5:1; the creep inhibitor is mica powder; the toughening agent is POE-g-MAH; the anti-aging agent is an antioxidant 1010 / 168 mixed in a mass ratio of 1:1; and the lubricant is EBS.

[0060] The preparation method of the modified plastic is the same as in Example 2, but the carbon fiber and glass fiber are only pretreated with silane coupling agent, which will not be described again here.

[0061] Comparative Example 3: A modified plastic for use in force sensor elastomers, comprising, by weight percentage: Base resin 65%; reinforcing fiber 30%; functional additives 5%; The base resin is PPS; the reinforcing fiber is obtained by pretreatment of short-cut carbon fiber and glass fiber in a mass ratio of 2:1; the pretreatment is as follows: spraying a 5% TPEE solution onto the fiber surface, drying at 70℃ to form a pre-coating of about 1000nm; then treating with 0.8% KH-550 at 95℃ for 1.5h; the functional additives are a mixture of creep inhibitor, anti-aging agent, toughening agent and lubricant in a mass ratio of 1.5:1:1.5:1; the creep inhibitor is mica powder; the toughening agent is POE-g-MAH; the anti-aging agent is an antioxidant 1010 / 168 mixed in a mass ratio of 1:1; the lubricant is EBS.

[0062] The preparation method of the modified plastic is the same as that in Example 2, and will not be repeated here.

[0063] Performance testing: The force sensor elastomer was prepared using the modified plastic described above, and then precision injection molded and subjected to stepped annealing to eliminate internal stress. Specifically, the clamping force of the precision injection molding machine was ≥1000kN, the positioning accuracy was ±0.005mm, the mold was made of P20 pre-hardened steel, and the cavity surface was polished to Ra≤0.8μm. The injection molding parameters were controlled as follows: barrel temperature: zone 1 280℃, zone 2 300℃, zone 3 310℃, nozzle 305℃; mold temperature 140℃; a three-stage... Injection speed control: the corresponding injection speeds are 25mm / s, 60mm / s, and 15mm / s; injection pressure is 100MPa; two-stage holding pressure is used: the first stage pressure is 65MPa for 5s, and the second stage pressure is 40MPa for 10s; cooling time is 25s. After molding, the product is subjected to stepped annealing to eliminate internal stress: specifically, holding at 50℃ for 1h, holding at 80℃ for 2h, and holding at 110℃ for 4h, and then naturally cooling to room temperature in the furnace.

[0064] The test metrics and standards include: Density: determined by immersion method according to ISO 1183-1-2019 standard; Elastic modulus / tensile strength: determined according to ISO 527-2-2012 standard, at room temperature, at a test speed of 1 mm / min; Creep rate: Measured after holding at room temperature and 50% of tensile yield strength load for 1000 hours; Coefficient of thermal expansion: The average linear coefficient of thermal expansion measured by a thermomechanical analyzer in the temperature range of -40℃ to 85℃; Isotropic: The maximum deviation between the elastic modulus in the X, Y, and Z directions and the average value.

[0065] The test results for each specific embodiment and comparative example are shown in the table below: Group Density (g / cm 3 )]]> Tensile strength (MPa) Elastic modulus (GPa) Creep rate (%) Thermal expansion coefficient (ppm / ℃) Isotropic deviation (%) Requirements 1.1~1.6 200~400 18~30 ≤0.5 ≤50 <10 Example 1 1.59 330 29 0.15 32 8 Example 2 1.38 215 26 0.35 41 5 Example 3 1.28 235 23 0.4 45 6 Example 4 1.42 205 22 0.42 37 7 Example 5 1.55 285 27 0.28 38 6 Comparative Example 1 1.35 125 16 1.5 70 28 Comparative Example 2 1.37 165 20 0.85 58 20 Comparative Example 3 1.4 185 22 0.7 52 15 As the data above shows, all embodiments fully meet all performance indicators, fully demonstrating the effectiveness and universality of the technical solution of the present invention. Specifically, as follows... Figure 2 The figure shows the tensile strain and tensile stress variation of the modified plastic prepared in Example 1. It can be seen that it fractures at room temperature at a tensile strain of 1.2%, at which point the maximum tensile stress is 330 MPa.

[0066] In Comparative Example 1, the creep rate, coefficient of thermal expansion, and isotropy were severely substandard due to the lack of a high-efficiency interface structure constructed by the two-step pretreatment. During injection molding, the untreated fibers strictly align along the melt flow direction, resulting in significant performance differences in different directions. Furthermore, the untreated fibers and the resin matrix are only bonded by weak physical adsorption and mechanical interlocking, forming a fragile and unstable interface. When the temperature changes, debonding or microcracks will occur first due to thermal deformation mismatch, thereby interrupting the stress transmission path. The shrinkage of the carbon fibers cannot effectively constrain the expansion of the resin matrix. Moreover, when the material is subjected to long-term stress, the polymer molecular chains will continuously slide and rearrange along the smooth fiber surface.

[0067] In Comparative Example 2, the fibers were only pretreated with silane. Although the performance was better than that of Comparative Example 1, the creep rate, coefficient of thermal expansion, and isotropy still did not meet the standards. This is because the lack of a TPEE flexible buffer layer resulted in a traditional rigid interface structure. Rigid interfaces have extremely weak load-bearing capacity in the direction perpendicular to the fiber. When stress is applied in the transverse direction, the brittle interface is prone to debonding, resulting in a very low modulus in that direction. This amplifies the anisotropy caused by the fiber orientation itself, and the stress is highly concentrated at the interface. This can easily lead to irreversible slippage and microplastic deformation of polymer molecular chains in the interface region. Furthermore, there is no place to buffer the thermal stress at the interface, which can easily lead to microcracks in the interface itself or the nearby matrix, thereby weakening the confinement effect of the carbon fiber.

[0068] In Comparative Example 3, the excessively thick TPEE pre-coating increases structural density and reduces porosity, hindering the diffusion of the silane coupling agent. Under long-term loads, the outer layer can slip relative to the fiber. In the direction perpendicular to the fiber, stress cannot be transferred from the matrix to the fiber through a robust interface. When the material is subjected to transverse forces, the fragile interface is prone to failure, resulting in limited modulus improvement in that direction, and thus the isotropic properties remain unsatisfactory.

[0069] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A modified plastic for use in force sensor elastomers, characterized in that, Calculated as a percentage by mass, including: Base resin 50~65%; Reinforcing fiber 20-40%; Functional additives 3~10%; The base resin is one or more of PPS, PA66, and PEEK; The reinforcing fiber is obtained from chopped carbon fiber or glass fiber through pretreatment; The functional additives are prepared by mixing anti-creep agents, anti-aging agents, toughening agents and lubricants in a mass ratio of 1~2:0.5~1:1~3:0.5~1.

2. The modified plastic for a force sensor elastomer according to claim 1, characterized in that, The length of the chopped carbon fiber is 3-5 mm, and the length of the glass fiber is 1-2 mm.

3. The modified plastic for a force sensor elastomer according to claim 1, characterized in that, The pretreatment of the reinforcing fiber is as follows: a thermoplastic polyester elastomer pre-coating layer with a thickness of 100~500nm is formed on the fiber surface; and then a silane coupling agent is used for pretreatment.

4. The modified plastic for a force sensor elastomer according to claim 3, characterized in that, The thermoplastic polyester elastomer pre-coating has a melting point higher than 150°C, and the amount of the silane coupling agent is 0.5-1.0% of the total mass of the reinforcing fiber; the pretreatment time is 1-2 hours, and the pretreatment temperature is 80-100°C.

5. The modified plastic for a force sensor elastomer according to claim 1, characterized in that, The creep-resistant agent is a silicate, mica powder, or talc powder; the toughening agent is a maleic anhydride-grafted polyolefin elastomer or a core-shell copolymer; the anti-aging agent is a hindered phenolic or phosphite antioxidant; and the lubricant is ethylene bis-stearamide, calcium stearate, or polyethylene wax.

6. A method for preparing a modified plastic for a force sensor elastomer, characterized in that, Includes the following steps: S1. The fiber is placed in a high-speed mixer and coated with a layer of thermoplastic polyester elastomer solution evenly using atomized spraying method. Then, it is dried at 60~80℃ to evaporate the solvent and form a nano-scale pre-coating. 0.5~1.0% of the total mass of silane coupling agent is added to the fiber after the above treatment in atomized form and pretreated by stirring at 80~100℃ for 1~2 hours. S2: Pour the base resin, pretreated reinforcing fibers, and functional additives into a mixer and mix at room temperature for 5-10 minutes to form a uniform premix. S3 feeds the premixed material into a twin-screw extruder for melt blending and extrusion granulation.

7. A force sensor elastomer, obtained by injection molding from the modified plastic according to any one of claims 1 to 5.

8. The force sensor elastomer according to claim 7, characterized in that, The force sensor elastomer meets all of the following performance indicators: 1) The elastic modulus is 18~30 GPa; 2) Under the conditions of room temperature and a rated load of 50% of the tensile yield strength, the creep rate after 1000 hours is ≤0.5%; 3) Coefficient of thermal expansion ≤ 50ppm / ℃.

9. The force sensor elastomer according to claim 7, characterized in that, The elastic modulus and coefficient of thermal expansion of the force sensor elastomer deviate by less than 10% in the X, Y, and Z directions.

10. The force sensor elastomer according to claim 7, characterized in that, The injection molding is precision injection molding, and after molding, it undergoes stepped annealing to eliminate internal stress.

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