A conductive composite material prepared using a high shear field polymer incompatible system, its preparation method, and its applications.

Abstract

The application provides a conductive composite material prepared by using a high shear field polymer incompatible system and a preparation method and application thereof, and belongs to the field of advanced material technology.The polymer-based conductive composite material is prepared by micro-injection molding processing and is prepared from a conductive filler and an incompatible resin system.The composite material can realize a substantial improvement in the conductive performance by adding a small amount of the conductive filler, can be used as an electronic material, and will not affect the mechanical performance and processing performance of the composite material.Meanwhile, the micro-injection molding processing technology can obtain a conductive functional micro device with higher precision and smaller size, and meets more use requirements.The polymer-based conductive composite material can be widely used in the fields of micro devices, micro-electro-mechanical systems, electronic communication, automobiles, aerospace, etc., and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of advanced materials technology, specifically relating to a conductive composite material prepared using a high shear field polymer incompatible system, its preparation method, and its applications. Background Technology

[0002] Conductive composite materials are a new type of functional composite material. They consist of insulating polymers such as rubber and resin as the matrix, and highly conductive metal particles such as silver, copper, and nickel, as well as highly conductive carbon black, graphite powder, metal fibers, metallized inorganic fiber, and carbon fiber as conductive fillers. The polymers used in conductive composite materials include polypropylene (PP), polyethylene (PE), polyamide 6 (PA6), polystyrene (PS), and polymethyl methacrylate (PMMA). The resulting conductive composite materials possess advantages such as lightweight, easy processing, controllable conductivity, heat resistance, corrosion resistance, high mechanical strength, good wear resistance, and suitability for large-scale production. They are widely used in electronics, electrical engineering, petrochemicals, machinery, aerospace, and medical fields, and are used in the preparation of solar cells, structural components, antistatic materials, sensor materials, and integrated circuit materials.

[0003] Currently, the conventional method for preparing conductive composite materials is hot pressing. However, hot pressing requires alternating heating and cooling of the mold, resulting in a long molding cycle, low production efficiency, and potential mold damage. It also cannot produce products with high dimensional accuracy. With the development of science and technology, conductive composite materials are increasingly being applied to high-end fields such as aerospace. This is accompanied by the rapid development of microelectromechanical systems (MEMS), leading to a growing demand for conductive microdevices and micro-functional samples. Clearly, hot pressing can no longer meet these development needs. Therefore, the fabrication of microdevices with excellent conductivity and higher precision, and their applications, have attracted increasing attention.

[0004] Micro-injection molding (μIM) is an injection molding process commonly used to produce products with micron-sized dimensions and milligram-sized weights, and has therefore attracted much attention. Unlike traditional injection molding and thermoforming, μIM offers higher injection pressure, injection speed, and lower cycle time, making it suitable for the fabrication of highly precise micro-devices. However, the extremely high shear field and rapid cooling generated during sample preparation cause the conductive filler particles to be oriented to the maximum extent along the melt flow direction, which is detrimental to the construction of conductive channels within the micropolymer component and affects the conductivity of the micro-parts.

[0005] Furthermore, most polymers exhibit poor electrical conductivity, necessitating the addition of conductive fillers to enhance their properties. Carbon-based fillers are the most commonly used conductive fillers; however, when the filler content is low, the distance between the conductive filler particles is large, failing to form effective conductive pathways, resulting in limited improvement in the conductivity of the composite material. Conversely, when the filler content is excessively high, the agglomeration of filler particles is detrimental to the mechanical and processing properties of the composite material. Further research is needed to determine how to prepare composite materials with high conductivity using low filler content, while simultaneously considering the conductivity, mechanical properties, and processing performance of the conductive composite material.

[0006] Therefore, finding a conductive composite material that can improve the conductivity of the composite material, reduce the amount of conductive filler used, and be used in micro-injection molding to prepare conductive functional parts with good comprehensive performance and high precision is of great significance for the application of conductive composite materials, especially in high-end fields such as precision instruments, automotive electronics, and aerospace. Summary of the Invention

[0007] The purpose of this invention is to provide a conductive composite material prepared using a high shear field polymer incompatible system, its preparation method, and its applications.

[0008] This invention provides a composition for preparing conductive composite materials, which is composed of conductive fillers and incompatible resin systems as raw materials; the mass fraction of the conductive fillers in the composition is 0.1-40%, and the mass fraction of the incompatible resin system is 60-99.9%.

[0009] The incompatible resin system consists of two thermoplastic resins, A and B, with a mass ratio of 10–90:10–90 between thermoplastic resin A and thermoplastic resin B.

[0010] Furthermore, the composition contains 0.1-20% conductive filler and 80-99.9% incompatible resin system by mass.

[0011] And / or, the mass ratio of the thermoplastic resin A to the thermoplastic resin B is 30:70 to 70:30;

[0012] Preferably, the composition contains 5-15% conductive filler and 85-95% incompatible resin system by mass.

[0013] More preferably, the composition contains 7-10% by mass of conductive filler and 90-93% by mass of incompatible resin system.

[0014] Furthermore, the conductive filler is a carbon-based conductive filler or a metal-based conductive filler;

[0015] And / or, the thermoplastic resin A is polypropylene, polyethylene, polyphenylene sulfide, polycarbonate, polyetheretherketone, or polyethersulfone;

[0016] And / or, the thermoplastic resin B is nylon;

[0017] Preferably,

[0018] The conductive filler is a carbon-based conductive filler;

[0019] And / or, the nylon is nylon 6, nylon 6T, nylon 66 or nylon 12;

[0020] More preferably,

[0021] The conductive filler is a carbon nanotube;

[0022] And / or, the thermoplastic resin A is polypropylene;

[0023] And / or, the thermoplastic resin B is nylon 6.

[0024] The present invention also provides a method for preparing the aforementioned composition, comprising the following steps:

[0025] Conductive filler, thermoplastic resin A, and thermoplastic resin B are melt-blended or solution-blended.

[0026] Preferably, the blending time is 10 to 120 minutes;

[0027] And / or, the mixing speed is 10 to 500 rpm.

[0028] The present invention also provides the use of the aforementioned composition in the preparation of conductive composite materials.

[0029] The present invention also provides a conductive composite material, which is obtained by micro-injection molding from the aforementioned composition.

[0030] Furthermore, the injection speed of the micro-injection molding is 100–900 mm / s;

[0031] Preferably, the injection speed of the micro-injection molding is 100–700 mm / s;

[0032] More preferably, the injection speed of the micro-injection molding is 100-300 mm / s.

[0033] Furthermore, the melt temperature of the micro-injection molding is 100–300°C; and / or, the mold temperature of the micro-injection molding is 25–150°C; and / or, the mold closing pressure of the micro-injection molding is 50–300 MPa.

[0034] The present invention also provides a method for preparing the aforementioned conductive composite material, which includes the following steps:

[0035] (1) The conductive filler, thermoplastic resin A and thermoplastic resin B are melt-blended or solution-blended.

[0036] (2) The masterbatch obtained by blending is then subjected to micro-injection molding to obtain the final product;

[0037] Preferably,

[0038] In step (1), the blending time is 10 to 120 minutes;

[0039] And / or, in step (1), the rotational speed of the blending process is 10 to 500 rpm;

[0040] And / or, in step (2), the injection speed of the micro-injection molding is 100-900 mm / s;

[0041] And / or, in step (2), the melt temperature of the micro-injection molding is 100-300°C;

[0042] And / or, in step (2), the mold temperature for the micro-injection molding is 25 to 150°C;

[0043] And / or, in step (2), the clamping pressure of the micro-injection molding is 50-300 MPa;

[0044] More preferably,

[0045] In step (2), the injection speed of the micro-injection molding is 100-700 mm / s;

[0046] More preferably,

[0047] In step (2), the injection speed of the micro-injection molding is 100-300 mm / s.

[0048] The present invention also provides the use of the aforementioned conductive composite material in the preparation of conductive devices for micro-devices, microelectromechanical systems, electronic communications, automobiles, and aerospace.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] This invention uses an incompatible system as the matrix and a highly conductive filler as the filler. By controlling the enrichment of conductive filler particles in a certain polymer phase, the utilization efficiency of conductive functional particles is improved, enabling the composite material to achieve higher conductivity with low filler addition levels, thus preparing a highly conductive functional composite material. Furthermore, taking advantage of the extremely high shear field in micro-injection molding, the conductive filler-enriched phase is deformed and aggregated under the action of the high shear field, obtaining a continuous phase structure enriched with filler particles, thereby improving the conductivity of the micro-parts.

[0051] Compared to composite materials prepared using a single polymer matrix via micro-injection molding, the composite material of this invention exhibits significantly improved electrical conductivity, meeting the requirements for use as an electronic material. Furthermore, it can be used to fabricate conductive microdevices with higher precision and smaller dimensions, satisfying the needs of a wider range of applications. This invention achieves a substantial improvement in the conductivity of the composite material by adding only a small amount of conductive filler. While enhancing the conductivity, it does not affect the mechanical or processing properties of the composite material, thus expanding its application areas. This invention is expected to be widely used in fields such as micro-devices, microelectromechanical systems, electronic communications, automobiles, and aerospace, demonstrating promising application prospects.

[0052] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0053] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0054] Figure 1 The electrical conductivity results are shown for composite materials prepared with different PP and PA6 mass ratios.

[0055] Figure 2 These are scanning electron microscope (SEM) images of composite materials prepared with different PP and PA6 mass ratios under micro-injection molding. Images marked with the flow direction are microscopic morphology images along the injection direction, while unmarked images are microscopic morphology images perpendicular to the injection direction. ad represents PP. 70 / PA6 30 / CNT7; eh is PP 50 / PA6 50 / CNT7; il is PP 30 / PA6 70 / CNT7; mn is PP / CNT7; op is PA6 / CNT7; where PP 70 / PA6 30 The CNT content in CNT7 is 7wt%, and the mass ratio of PP phase to PA6 phase is 70:30.

[0056] Figure 3 The electrical conductivity results are shown for composite materials prepared from mixed masterbatches using different processing sequences.

[0057] Figure 4The images show SEM images of composite materials prepared from mixed masterbatches using different processing sequences. The images marked with flowdirection are microscopic morphology images along the injection direction, while those not marked are microscopic morphology images perpendicular to the injection direction: ab represents PP / PA6 / CNT7; cd represents PA6 / CNT7+PP; and ef represents PP / CNT7+PA6.

[0058] Figure 5 The electrical conductivity results are for composite materials with different CNT contents.

[0059] Figure 6 SEM images of composite materials prepared with different CNT mass fractions (1%, 5%, 10%), with flowdirection indicated by microstructure along the injection molding direction; ab represents PP. 70 / PA6 30 / CNT1; cd is PP 70 / PA6 30 / CNT5; ef is PP 70 / PA6 30 / CNT10; a, c, and e are the skin morphology of each composite material after the PA6 phase is etched with formic acid; b, d, and f are the core morphology of each composite material after the PA6 phase is etched with formic acid.

[0060] Figure 7 A schematic diagram of the micromorphological evolution of PA6 dispersed phase enriched with conductive filler CNT under a high shear field in micro-injection molding.

[0061] Figure 8 The rheological curves of composite materials with different CNT contents are shown below: a is the storage modulus curve; b is the Han curve; c is the complex viscosity curve.

[0062] Figure 9 Performance results of composite materials prepared at different injection speeds: a is tensile strength; b is electrical conductivity. Detailed Implementation

[0063] The raw materials and equipment used in the specific embodiments of the present invention are all known products, obtained by purchasing commercially available products.

[0064] Polypropylene granules (PP) (Product model: 1304E5, density 0.9 g / cm³) 3 Melt flow index of 11 g / 10 min (@275℃, 5 kg), melt temperature of 159℃, purchased from ExxonMobil, polyamide 6 granules (PA6) (product model: B3S, density 1.13 g / cm³ 3 The melt flow index is 160 cm⁻¹ 3 / 10min (@275℃, 5kg), melting temperature 220℃, purchased from BASF, industrial grade multi-walled carbon nanotube powder (CNT) (product model: TNIM2, density 2.1g / cm³). 3 (Length 30-50 micrometers, outer diameter 8-15 nanometers) purchased from Chengdu Organic Chemistry Co., Ltd., Chinese Academy of Sciences.

[0065] Example 1: Preparation of the conductive composite material of the present invention

[0066] CNT, PP, and PA6 were mixed evenly and then used to prepare a blend masterbatch using a torque rheometer (a one-step blending method where all three raw materials are blended together). The torque rheometer speed was 50 rpm, and the mixing time was 10 min. The mass fraction of CNT in the blend masterbatch was 7%, and the combined mass fraction of PP and PA6 was 93%. The mass ratios of PP to PA6 were 0:100, 30:70, 50:50, 70:30, and 100:0, respectively.

[0067] The blended masterbatch was micro-injection molded to obtain dumbbell-shaped samples. The melting temperature was 240℃, the mold temperature was 80℃, the injection speed was 300mm / s, and the mold closing pressure was 200MPa.

[0068] Composite materials (PP / PA6 / CNT) prepared with different PP and PA6 mass ratios were named PA6 / CNT7 and PP, respectively. 30 / PA6 70 / CNT7、PP 50 / PA6 50 / CNT7、PP 70 / PA6 30 / CNT7、PP / CNT7.

[0069] Example 2: Preparation of the conductive composite material of the present invention

[0070] CNT, PP and PA6 were mixed evenly and a blend masterbatch was prepared by torque rheometer. There are three sequences for preparing the blend masterbatch: (1) the one-step blending method as in Example 1, where the three raw materials are blended together (50 rpm, 10 min), denoted as PP / PA6 / CNT; (2) the two-step blending method, where PP and CNT are blended first (50 rpm, 5 min), and then PA6 is added and blended (50 rpm, 5 min), and the resulting blend masterbatch is denoted as PP / CNT+PA6; (3) the two-step blending method, where PA6 and CNT are blended first (50 rpm, 5 min), and then PP is added and blended (50 rpm, 5 min), and the resulting blend masterbatch is denoted as PA6 / CNT+PP. The mass fraction of CNT in the blended masterbatch is 7%, the sum of the mass fractions of PP and PA6 is 93%, and the mass ratio of PP to PA6 is 70:30.

[0071] The blended masterbatch was micro-injection molded to obtain dumbbell-shaped samples. The melting temperature was 240℃, the mold temperature was 80℃, the injection speed was 300mm / s, and the mold closing pressure was 200MPa.

[0072] The composite materials prepared by different blending sequences were named PP / PA6 / CNT7, PP / CNT7+PA6, and PA6 / CNT7+PP, respectively.

[0073] Example 3: Preparation of the conductive composite material of the present invention

[0074] CNT, PP, and PA6 were mixed uniformly and then used to prepare a blend masterbatch using a torque rheometer (a one-step blending method where all three raw materials are blended together). The torque rheometer was operated at 50 rpm for 10 minutes. The mass fractions of CNT in the blend masterbatch were 1%, 2%, 3%, 5%, 7%, 10%, and 15%, respectively, corresponding to the sum of the mass fractions of PP and PA6 of 99%, 98%, 97%, 95%, 93%, 90%, and 85%, respectively. The mass ratio of PP to PA6 was 70:30.

[0075] The blended masterbatch was micro-injection molded to obtain dumbbell-shaped samples. The melting temperature was 240℃, the mold temperature was 80℃, the injection speed was 300mm / s, and the mold closing pressure was 200MPa.

[0076] The conductive composite materials (PP / PA6 / CNT) prepared with different CNT mass fractions were named PP, PA6 ... 70 / PA6 30 / CNT1、PP 70 / PA6 30 / CNT2、PP 70 / PA630 / CNT3、PP 70 / PA6 30 / CNT5、PP 70 / PA6 30 / CNT7、PP 70 / PA6 30 / CNT10、PP 70 / PA6 30 / CNT15.

[0077] The following specific experimental examples demonstrate the beneficial effects of the present invention.

[0078] Experimental Example 1: Effect of PP / PA6 mass ratio on the conductivity of the conductive composite material of the present invention

[0079] 1. Experimental Methods

[0080] (1) Conductivity

[0081] The conductivity of conductive composite materials prepared according to the method described in Example 1 using different PP / PA6 mass ratios was tested. The specific method for detecting conductivity is as follows:

[0082] Conduct conductivity tests were performed in the flow direction (injection direction), and the resistance was greater than 10 ohms. 8 High-resistance samples within the Ω range were measured using the Shanghai Taiou ZC90F high insulation resistance meter; resistance below 10Ω was found. 8 Low resistance samples with Ω were obtained using Keysight 34401A6. 1 The / 2 digital multimeter (Agilent Technologies Inc., USA) uses the dual-probe method for testing. The resistance meter needs to be warmed up for at least 30 minutes before use.

[0083] The electrical conductivity of the composite material was calculated using the following formula:

[0084] σ = 1 / ρ = L / (RS)

[0085] In the above formula, σ is the electrical conductivity of the composite material, ρ is the volume resistivity of the composite material, R is the resistance value of the material being tested, L is the length of the test strip, and S is the cross-sectional area of ​​the material.

[0086] (2) SEM

[0087] Observe the SEM images of conductive composite materials prepared according to the method described in Example 1 using different PP / PA6 mass ratios.

[0088] Test method: The sample was fractured in liquid nitrogen, and then gold sputtering was performed on the fractured sample. The microstructure of the sample was observed using a Thermoscientific Apreo S scanning electron microscope.

[0089] 2. Experimental Results

[0090] (1) Conductivity

[0091] Figure 1 The conductivity of the composite material prepared when the CNT mass fraction is fixed at 7% and the PP to PA6 mass ratio is 0:100, 30:70, 50:50, 70:30, and 100:0. For example... Figure 1 As shown, the electrical conductivity of the composite material obtained by adding CNTs to pure PP or pure PA6 is less than 10. -8 The S / m indicates that the material remains in an insulating state, suggesting that a complete conductive channel network has not yet formed within it. Furthermore, the composite material obtained by adding CNTs to the PP / PA6 incompatible matrix exhibits significantly higher conductivity than that obtained by adding CNTs to pure PP or pure PA6, with the conductivity of the composite material exceeding 10. -8 The S / m ratio indicates that the material transitions from an insulating to a semiconductor state. This is due to the deformation and aggregation of the CNT-enriched PA6 phase under a high shear field, thus forming a complete conductive network even with a lower filler content. At this point, the CNT content is only 7%, having minimal impact on the mechanical and processing properties of the matrix material. Conductivity test results show that using the PP / PA6 incompatible system as the matrix can improve the conductivity of the composite material with a smaller amount of conductive filler, avoiding any impact on the mechanical and processing properties of the composite material.

[0092] (2) SEM image

[0093] Figure 2 These are microscopic morphology (SEM images) of PP / PA6 / CNT composite materials prepared under micro-injection molding with a CNT mass fraction of 7% using different PP to PA6 mass ratios (0:100, 30:70, 50:50, 70:30, 100:0). Images marked with blue arrows are SEM images observed along the injection direction, while images without blue arrows are SEM images observed perpendicular to the injection direction.

[0094] from Figure 2α-2p analysis reveals that, compared to the PP / CNT and PA6 / CNT systems, using a PP / PA6 incompatible matrix causes the CNT-enriched PA6 phase to deform under the high shear field of micro-injection molding, transforming from a spherical shape to an ellipsoidal or fibrous structure. This preferential enrichment of CNTs in the PA6 phase increases the "effective concentration" of conductive filler particles in the composite material, increasing the probability of contact between CNTs distributed within the PA6 phase. This facilitates the formation of continuous conductive pathways along the melt flow direction. Therefore, under micro-injection molding conditions, the conductivity of micro-parts prepared from PP / PA6 / CNT composites is significantly superior to that of the PP / CNT and PA6 / CNT systems.

[0095] Experimental Example 2: Effect of the order of addition of each component on the electrical conductivity of the composite material of the present invention

[0096] 1. Experimental Methods

[0097] (1) Conductivity

[0098] The conductivity of conductive composite materials prepared by blending masterbatches using different raw material addition sequences according to the method described in Example 2 was tested. The specific method for detecting conductivity was the same as in Experiment 1.

[0099] (2) SEM

[0100] Observe the SEM images of conductive composite materials prepared from blended masterbatches using different raw material addition sequences according to the method described in Example 2. The method is the same as in Experiment 1.

[0101] 2. Experimental Results

[0102] To investigate the effect of processing sequence on the construction of CNT conductive networks, this invention fixed the CNT mass fraction at 7% and the PP to PA6 mass ratio at 70 / 30. Blending masterbatch was prepared using a torque rheometer via a one-step or two-step blending method. Three processing sequences were designed for analysis: PP / PA6 / CNT was blended together for 10 minutes; PP and CNT were blended together for 5 minutes, followed by PA6 and blending for another 5 minutes; PA6 and CNT were blended together for 5 minutes, followed by PP and blending for another 5 minutes.

[0103] Figure 3 The conductivity of the conductive composite materials prepared under different blending orders is shown; Figure 4 SEM images of conductive composite materials with different blending sequences are shown. All image observation points are located in the shear layer (near the mold wall). Figure 3 and Figure 4It is known that the high shear force under micro-injection molding forces the two phases to deform under shear force. The high shear force causes the agglomerate size to become smaller, and the CNTs preferentially enriched in the PA6 phase are connected in the form of small agglomerates, creating a conductive path. The order of feeding materials has almost no effect on the conductivity of the final composite material, indicating that the order of feeding materials has almost no impact on the conductivity of the composite material.

[0104] Experimental Example 3: Effect of CNT content on the conductivity of the conductive composite material of the present invention

[0105] The results of Experiments 1 and 2 show that, regardless of the matrix component ratio, the electrical conductivity of the PP / PA6 incompatible composite material is higher than that of the single-component composite material. Furthermore, the order of feeding has almost no effect on the electrical conductivity of the incompatible composite material under high shear. Therefore, PA6 phase was designed as the dispersed phase and PP as the continuous phase. The mass ratio of PP / PA6 phases was fixed at 70:30. The composite material was prepared by one-step blending method to study the effect of different CNT contents on the structure and electrical conductivity of the composite material.

[0106] 1. Experimental Methods

[0107] (1) Conductivity

[0108] The conductivity of conductive composite materials prepared with different CNT mass fractions according to the method described in Example 3 was tested. The specific method for detecting conductivity was the same as in Experiment 1.

[0109] Meanwhile, following the method described in Example 3, conductive composite materials with different CNT contents were prepared as controls, using PP and PA6 mass ratios of 100:0 and 0:100.

[0110] (2) SEM

[0111] Observe the SEM images of the conductive composite materials prepared with different CNT mass fractions according to the method described in Example 3. The specific detection method is as follows:

[0112] The sample was first fractured in liquid nitrogen, then immersed in formic acid solution for 12 hours to etch the PA6 phase, rinsed several times with deionized water, dried, and then sputter-coated with gold. The microstructure of the sample was observed using a Thermoscientific Apreo S scanning electron microscope.

[0113] (3) Rheological properties

[0114] The rheological properties of conductive composite materials prepared with different CNT mass fractions according to the method described in Example 3 were tested. The specific testing method is as follows:

[0115] The processing rheological behavior of fillers in composite materials was tested using a modular intelligent advanced rotational rheometer. Circular samples, 25 mm in diameter and 1 mm thick, were prepared by hot pressing. The test temperature was kept constant at 240 °C, and the linear viscoelastic changes of the composite material were obtained using dynamic frequency scanning (0.01-100 Hz) under a constant strain of 1%.

[0116] 2. Experimental Results

[0117] (1) Conductivity

[0118] Figure 5 These are the conductivity results of PP / PA6 / CNT composites at different CNT mass fractions. Figure 5 It can be seen that the PP / PA6 / CNT composite material has the lowest conductivity percolation threshold and the highest conductivity; and in the PP / PA6 / CNT composite material, the conductivity increases the fastest when the CNT mass fraction increases from 5% to 7%, from 8.7*10 -10 Up to 1.2*10 -6 The amide and hydrogen bonds in PA6 give it higher polarity and surface energy, causing carbon nanotubes to preferentially accumulate in the PA6 phase. After thorough melt mixing, the CNT-rich PA6 phase is uniformly distributed within the continuous PP phase. Under the influence of the strong shear field commonly present in micro-injection molding, PA6 may deform into CNT-rich fibers, forming complete conductive channels along the melt flow direction, which contributes to a significant increase in conductivity. Therefore, the introduction of the incompatible PP / PA6 system is an effective means of reducing the conductivity percolation threshold under high-shear processing.

[0119] (2) SEM

[0120] Figure 6 These are SEM images of composite materials prepared with different CNT contents (1, 5, 10 wt%). In this invention, the composite materials were observed along the injection molding direction, and the PA6 phase was etched with formic acid. Figure 6 It can be observed that the orientation effect is more obvious in the skin layer, with the PA6 phase exhibiting a band-like shape along the injection direction; however, near the core layer region, the PA6 phase exhibits an ellipsoidal shape. Figure 7 This is a schematic diagram of the micromorphological evolution of the CNT-enriched PA6 phase under a high shear field. The high shear force of micro-injection effectively affects the phase morphology of the two incompatible phases. The strong shear field causes the spherical island phase to change into ellipsoidal, banded, and microfiber shapes, which is conducive to the interconnection of CNTs distributed in the PA6 phase, realizing the in-situ construction of a three-dimensional continuous conductive network.

[0121] (3) Rheological properties

[0122] To systematically understand how the dynamic flow behavior of the PP / PA6 incompatible system of this invention promotes the formation of conductive networks under high shear stress, this invention fixes the mass ratio of PP to PA6 at 70:30 and studies the dynamic rheological properties of composite materials prepared with different CNT mass fractions. 70 / PA6 30 This indicates that the mass fraction of CNTs is 0%. When a three-dimensional structure exists in a composite material, the material's solid-like properties are enhanced, and its resistance to deformation at low frequencies is improved. By analyzing the plateau region of the energy storage modulus, the construction of the three-dimensional CNT network structure can be obtained.

[0123] Figure 8 a Discover PP 70 / PA6 30 / CNT2 exhibits a clear plateau in its energy storage modulus in the low-frequency region, from Figure 8 As can be seen from b, when the CNT mass fraction is less than 2%, the Han curve basically conforms to a linear relationship, but the correlation between G' and G” deviates from a linear relationship at around 2wt%. This means that the PP / PA6 / CNT incompatible system undergoes a liquid-to-solid transition at a low CNT content, with a rheological percolation value of 2wt%, which provides a prerequisite for reducing the conductive percolation threshold under high shear.

[0124] Depend on Figure 8 As shown in c, the complex viscosity of the PP / PA6 incompatible system increases with the increase of CNT content, the shear thinning effect is more significant, and it is easier to reduce the viscosity by increasing the shear rate. This indicates that the PP / PA6 / CNT composite material has a greater response to high shear fields and produces a significant deformation effect, which helps to form conductive paths.

[0125] Experimental Example 4: The Influence of Injection Speed ​​in Micro-injection Molding on the Electrical Conductivity and Mechanical Properties of the Conductive Composite Material of the Present Invention

[0126] The conductive composite material of the present invention was prepared according to the method described in Example 1, with the mass ratio of PP to PA6 fixed at 70:30, and only the injection speed of micro-injection molding was changed (injection speeds of 300, 500 and 700 mm / s, respectively).

[0127] The mechanical and electrical properties of the composite materials prepared with different injection speeds were tested, and XRD and SEM were performed.

[0128] Mechanical property testing: The tensile properties of the composite material were tested using an Instron 5567 universal testing machine in accordance with GB / T 1040.2-2022 standard. The sample was a dumbbell-shaped specimen with a gauge length of 8 mm and a thickness of 0.3 mm. The tensile speed was 5 mm / min.

[0129] Conductivity test: Same as in Experiment 1.

[0130] SEM observation: Same as in Experiment 1.

[0131] Figure 9 At different injection speeds, PP 70 / PA6 30 Performance results of the / CNT7 composite material. During the process of increasing the injection rate from 300 to 700 mm / s, the shear rate increased from 10... 5 Increase to 10 6 s -1 . Figure 9 a indicates that as the injection rate increases from 300 to 700 mm / s, the tensile strength only increases slightly. From Figure 9 b found that the electrical conductivity of the composite material decreased with increasing injection speed, indicating that the increasing shear force dispersed the CNTs, reduced the aggregate size, and disrupted the effective connections between CNTs. Furthermore, under the influence of ultra-high shear and rapid cooling, the deformed polymer phase within the incompatible composite material was rapidly frozen before the oriented layered structure could relax, reducing the CNT contacts in the thickness direction, which is also one of the reasons for the decreased electrical conductivity.

[0132] It can be seen that the conductive composite material prepared has the best overall performance when the injection speed is 300 mm / s.

[0133] In summary, this invention uses an incompatible system (PP / PA6) as the matrix and highly conductive filler (CNT) as the filler to prepare a conductive composite material through micro-injection molding, a high-shear method. Compared with composite materials prepared using a single polymer as the matrix and micro-injection molding, the composite material of this invention exhibits significantly improved conductivity, meeting the requirements for use as a conductor material. Simultaneously, it can yield conductive microdevices with higher precision and smaller dimensions, satisfying a wider range of application needs. Furthermore, this invention requires only the addition of a small amount of conductive filler to achieve a significant improvement in the conductivity of the composite material. While improving the conductivity, it does not affect the mechanical and processing properties of the composite material, thus expanding its application areas. This invention is expected to be widely used in micro-devices, microelectromechanical systems, electronic communications, automotive, aerospace, and other fields, demonstrating promising application prospects.

Claims

1. A composition for making an electrically conductive composite material, characterized by: It is composed of conductive filler, incompatible resin system as raw material; the mass fraction of conductive filler in the composition is 7%, the mass fraction of incompatible resin system is 93%; The incompatible resin system is composed of two kinds of thermoplastic resin A and B, and the mass ratio of thermoplastic resin A and thermoplastic resin B is 30:70~70:30; The conductive filler is carbon nanotube; And / or, the thermoplastic resin A is polypropylene; And / or, the thermoplastic resin B is nylon 6.

2. Process for the preparation of the composition according to claim 1, characterized in that: It includes the following steps: The conductive filler, thermoplastic resin A and thermoplastic resin B are melt blended or solution blended.

3. The method of claim 2, wherein: The blending time is 10~120 minutes; And / or, the rotation speed of blending is 10~500 rpm.

4. The use of the composition of claim 1 in the preparation of conductive composite material.

5. An electrically conductive composite material, characterized by: It is obtained by micro injection molding of the composition of claim 1.

6. The conductive composite of claim 5, wherein: The injection speed of micro injection molding is 100~900 mm / s.

7. The conductive composite of claim 6, wherein: The injection speed of micro injection molding is 100~700 mm / s.

8. The conductive composite of claim 7, wherein: The injection speed of micro injection molding is 100~300 mm / s.

9. The conductive composite of claim 5, wherein: The melting temperature of micro injection molding is 100~300℃; and / or, the mold temperature of micro injection molding is 25~150℃; and / or, the clamping pressure of micro injection molding is 50~300 MPa.

10. A process for the preparation of the electrically conductive composite material according to any one of claims 5 to 9, characterized in that: It includes the following steps: (1) melt blending or solution blending of conductive filler, thermoplastic resin A and thermoplastic resin B; (2) the masterbatch obtained by blending is subjected to micro injection molding, namely.

11. The preparation method of claim 10, characterized in that: In step (1), the blending time is 10~120 minutes; And / or, in step (1), the rotation speed of blending processing is 10~500 rpm; And / or, in step (2), the injection speed of micro injection molding is 100~900 mm / s; And / or, in step (2), the melting temperature of micro injection molding is 100~300℃; And / or, in step (2), the mold temperature of micro injection molding is 25~150℃; And / or, in step (2), the clamping pressure of micro injection molding is 50~300 MPa.

12. The preparation method of claim 11, characterized in that: In step (2), the injection speed of micro injection molding is 100~700 mm / s.

13. The preparation method of claim 12, characterized in that: In step (2), the injection speed of micro injection molding is 100~300 mm / s.

14. The use of the conductive composite material of any one of claims 5~9 in the preparation of conductive devices for micro devices, micro-electro-mechanical systems, electronic communication, automobile, aerospace fields.

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