A method for multilayer coextrusion orientation of injection moldable thermally conductive plastics

Abstract

The application relates to a multilayer co-extrusion orientation processing method of injection-moldable heat-conducting plastic, and belongs to the technical field of polymer composite material processing. The method comprises the following steps: melt blending a first thermoplastic resin and heat-conducting fillers to obtain a first melt, and melt blending a second thermoplastic resin and reinforcing fillers to obtain a second melt; alternately stacking and co-extruding the first melt and the second melt through a co-extrusion die with a compression-expansion runner structure to form a layered sheet; mechanically crushing the layered sheet into granules; adding the granules into an injection molding machine, controlling the injection molding processing temperature to be between the melting point of the first thermoplastic resin and the melting point of the second thermoplastic resin, and rebuilding a heat-conducting network through mutual lapping of the sheet layers in the injection molding flow process to obtain a heat-conducting plastic product. The application solves the technical problems that the heat-conducting network is destroyed and the filler orientation is difficult to maintain due to multiple heat processes in the existing heat-conducting plastic processing process.

Description

Technical Field

[0001] This invention relates to the field of polymer composite material processing technology, and in particular to a multilayer co-extrusion orientation processing method for injection-molded thermally conductive plastics. Background Technology

[0002] Thermally conductive polymer composites are increasingly widely used in heat dissipation structural components in fields such as 5G communications, new energy vehicles, and consumer electronics due to their advantages such as lightweight, corrosion resistance, electrical insulation, and ease of processing and molding. By adding high thermal conductivity fillers such as boron nitride (BN), aluminum nitride (AlN), and aluminum oxide (Al2O3) to the polymer matrix, the thermal conductivity of the material can be significantly improved while maintaining the original properties of the polymer. Among these methods, injection molding has become one of the most important processing methods for thermally conductive plastics because it is suitable for producing products with complex shapes.

[0003] Currently, the conventional processing flow for thermally conductive plastics is "blending-granulation-injection molding": first, the polymer matrix and thermally conductive filler are melt-blended, then melt-granulated to obtain granules, and finally the granules are injection molded into products. To improve thermal conductivity, researchers are attempting to induce the orientation and alignment of sheet-like or fibrous fillers through specific flow fields to construct an ordered thermally conductive network. However, the above-mentioned conventional processing flow still has the following technical problems in practical applications: First, multiple thermal processes lead to the destruction of the thermally conductive network; the processing of thermally conductive plastics requires at least two thermal processes: raw material preparation (granulation) and product molding (injection molding). In each thermal process, the material is in a completely molten state. Even if the orientation network of the filler is initially constructed in the preceding steps (such as blending or co-extrusion), this network will be completely destroyed in the subsequent melt granulation and injection molding process due to the complete melting of the polymer matrix. In the final product, the filler is randomly distributed, making it difficult to form an effective thermally conductive path, which seriously restricts the improvement of the material's thermal conductivity. Second, the orientation structure is difficult to maintain; by aligning the sheet-like or fibrous filler through the flow field, the thermal conductivity of the material can be significantly improved. However, in existing technologies, to obtain granule morphology suitable for injection molding machines, a melt granulation step is necessary. In this step, the cylindrical granules undergo intense shearing and stretching during melt extrusion, completely destroying the pre-constructed orientation structure and resulting in low filler orientation in the final injection molded product. Thirdly, high thermal conductivity and processing performance are difficult to balance. To achieve high thermal conductivity, the filler content is usually increased (e.g., exceeding 30 wt%), but this leads to a sharp increase in melt viscosity and poor flowability. During injection molding, high-viscosity melts are difficult to fill complex mold cavities, easily resulting in defects such as material shortages and weld lines, leading to low product yield. Simultaneously, high-filler systems cause severe wear on equipment, significantly increasing production costs.

[0004] Therefore, how to effectively maintain and rebuild the ordered network structure of thermally conductive fillers during the processing of injection molded products without chemical modification, and achieve synergistic improvement in thermal conductivity and processing performance, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-layer co-extrusion orientation processing method for injection-molded thermally conductive plastics, aiming to solve the technical problems of multiple thermal processes damaging the thermally conductive network, difficulty in preserving the orientation structure of fillers, and difficulty in balancing high thermal conductivity and processing fluidity in existing processes. This method achieves efficient preservation and reconstruction of the three-dimensional orientation of thermally conductive fillers and the thermally conductive network, improves the thermal conductivity of products, and is suitable for continuous injection molding production.

[0006] This invention provides a multilayer co-extrusion orientation processing method for injection-moldable thermally conductive plastics, employing the following technical solution: A method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastics includes the following steps: S1. A first thermoplastic resin and a thermally conductive filler are melt-blended to obtain a first melt, and a second thermoplastic resin and a reinforcing filler are melt-blended to obtain a second melt; the melting point of the first thermoplastic resin is 10-50℃ higher than the melting point of the second thermoplastic resin. S2. The first melt and the second melt are alternately stacked and co-extruded through a co-extrusion die with a compression-expansion channel structure to form a layered sheet. S3. Mechanically crush the layered sheet into granules; S4. The granules are added to the injection molding machine, and the injection molding temperature is controlled between the melting point of the first thermoplastic resin and the melting point of the second thermoplastic resin. During the injection flow, the layers overlap and rebuild the heat-conducting network to obtain a heat-conducting plastic product.

[0007] Preferably, in step S1, the first thermoplastic resin is polycarbonate; The second thermoplastic resin is an acrylonitrile-butadiene-styrene copolymer.

[0008] Preferably, in step S1, the thermally conductive filler is at least one of boron nitride, aluminum nitride, and aluminum oxide, and the amount of the thermally conductive filler added to the first thermoplastic resin is 10-30 wt%.

[0009] Preferably, the reinforcing filler is at least one of silica microspheres and glass fiber, and the amount of the reinforcing filler added to the second thermoplastic resin is 5-15 wt%.

[0010] Preferably, in step S2, the compression-expansion channel structure includes an inlet area, a diversion area, a damping area, and a stacked area distributed along the material flow direction; The length a of the compression-expansion channel is 20-60mm, and the aspect ratio a / b is (3:1)-(6:1); the length c of the damping zone is 5-10mm.

[0011] Preferably, in step S2, the outlet expansion ratio of the first melt and the second melt at the co-extrusion die outlet is 1.29-3.13.

[0012] Preferably, in step S3, the granules are flat or flake-shaped; The length and width of the granules are both 1-10 mm, and the thickness is 1-3 mm.

[0013] Preferably, in step S4, the injection molding temperature is set to be 5-15°C lower than the melting point of the first thermoplastic resin and 20-40°C higher than the melting point of the second thermoplastic resin.

[0014] Preferably, the injection pressure is set to 80-120MPa, the holding pressure is 60-80MPa, and the holding time is 5-10s.

[0015] On the other hand, the present invention also provides a thermally conductive plastic granule prepared by the above method, which adopts the following technical solution: Thermally conductive plastic granules, wherein the granules retain a thermally conductive layer-reinforcing layer-thermally conductive layer structure or a thermally conductive layer-reinforcing layer-thermally conductive layer-reinforcing layer structure, wherein the thickness of the thermally conductive layer and the thickness of the reinforcing layer are both 0.3-1mm; the thermally conductive filler is oriented and arranged in the flow direction and perpendicular direction within the layer.

[0016] In summary, the present invention has the following beneficial technical effects: 1. This invention employs a four-step continuous processing flow of "blending-flow field orientation-crushing and granulation-injection molding," utilizing the melting point difference between the two resin systems to achieve a unique processing state where the low-melting-point resin is completely melted and the high-melting-point resin is softened and retains its shape during the injection molding step. Compared to the conventional "blending-granulation-injection molding" process, this invention avoids the complete destruction of the thermally conductive network during multiple thermal processes, ensuring that the orientation network constructed in the co-extrusion step is maintained and the interlayer overlap is reconstructed during the crushing and injection molding steps. The PC / ABS mobile phone casing prepared using this method achieves an in-plane thermal conductivity of 0.95 W / mK, a 46% improvement compared to the conventional blending and injection molding method (0.65 W / mK), and a 20% improvement in vertical thermal conductivity.

[0017] 2. This invention introduces a compression-expansion channel structure with an inlet zone (oriented compression), a diversion zone, a damping zone, and a stacked zone in the co-extrusion step. Systematic verification experiments determined the optimal channel parameter range (length-to-width ratio a / b of 4:1-5:1, damping zone length c of 7.5-10 mm, and outlet expansion rate of 2.86-3.13). Under these conditions, the sheet-like packing not only exhibits orientation in the flow direction but also a certain degree of orientation in the vertical direction, enabling the early construction of a three-dimensional thermally conductive network and laying the structural foundation for network reconstruction in subsequent injection molding steps.

[0018] 3. This invention utilizes a low-melting-point second thermoplastic resin that fully melts at the injection molding temperature, providing excellent flowability and avoiding injection molding defects caused by excessively high melt viscosity at high filler contents. Simultaneously, the first thermoplastic resin softens and retains its shape, supporting the main thermally conductive filler to form rigid sheets that overlap during flow. This invention, using a high filler system of 30wt% boron nitride in polycarbonate, can still successfully injection mold 5G base station shells, achieving an in-plane thermal conductivity of 1.52 W / mK and a vertical thermal conductivity of 0.61 W / mK, balancing high thermal conductivity with good injection molding performance.

[0019] 4. The co-extrusion step of this invention can continuously produce layered sheets, which are then mechanically crushed into flat granules, facilitating storage, transportation, and subsequent injection molding. Compared to layer multiplier technology, which can only produce sheet materials, the method of this invention can mold various irregularly shaped products (such as mobile phone casings, base station casings, optical modem casings, etc.), making it more feasible for industrialization and applicable to a wider range of scenarios. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a compression-expansion flow channel structure; Figure 2 In the diagram, 'a' represents the internal channel structure of the co-extrusion die. Figure 2 In the diagram, b is a schematic representation of the external structure of the co-extrusion die; Figure 3 This is a photograph of a layered sheet material with a thermally conductive layer-reinforcing layer-thermally conductive layer structure obtained by multi-layer co-extrusion orientation molding; Figure 4 In the middle, 'a' is a photograph of the flattened granules obtained after cutting. Figure 4 Photo b shows the flattened granules obtained after mechanical crushing. Figure 5 This is a diagram of the experimental setup for verifying the relationship between flow channel parameters and outlet expansion rate; Figure 6 This is a comparison chart of the thermal conductivity of the products in Example 1 and Comparative Example 1; Figure 7 This is a comparison chart of the thermal conductivity of the products in Example 2 and Comparative Example 2.

[0021] Explanation of reference numerals in the attached diagram: 1. Inlet area; 2. Diversion area; 21. Sub-channel; 3. Damping area; 4. Lamination area; 41. Dual inlet channel; 5. Channel area; 6. Sheet forming area. Detailed Implementation

[0022] The following examples, comparative examples, test cases, and appendices are presented in conjunction with embodiments, comparative examples, test cases, and appendices. Figure 1-7 The present invention will be described in further detail below.

[0023] Example Example 1 A method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastics includes the following steps: 1) Separate melt blending of two components A first thermoplastic resin is melt-blended with a thermally conductive filler to obtain a first melt, and a second thermoplastic resin is melt-blended with a reinforcing filler to obtain a second melt; the melting point of the first thermoplastic resin is 10-50℃ higher than that of the second thermoplastic resin. In this embodiment, the first thermoplastic resin is polycarbonate (PC) with a melting point of 220-250°C; the second thermoplastic resin is acrylonitrile-butadiene-styrene copolymer (ABS) with a melting point of 200-250°C; the thermally conductive filler is at least one of boron nitride (BN), aluminum nitride (AlN), and aluminum oxide (Al2O3), and its addition amount in the first thermoplastic resin is 10-30 wt%; the reinforcing filler is at least one of silica microspheres and glass fiber, and its addition amount in the second thermoplastic resin is 5-15 wt%. 2) Multi-layer co-extrusion orientation molding Reference Figure 1The first melt and the second melt obtained in step 1) are respectively conveyed to the compression-expansion channel structure. The compression-expansion channel structure is an integrated structure that extends continuously along the material flow direction, including an inlet area 1, a diversion area 2, a damping area 3, and a stacked area 4. The inlet area 1 is located at the feed end of the compression-expansion channel structure, and it gradually widens from the feed inlet to the discharge direction. The diversion area 2 has a Y-shaped bifurcation structure. Its inlet end is a rectangular channel with the same cross-section as the outlet of the inlet area 1. It gradually bifurcates symmetrically to the upper and lower sides along the material flow direction, forming two independent sub-channels 21. The bifurcation angles of the two sub-channels 21 are symmetrically set, and the outlet ends of the two sub-channels 21 are respectively connected to two sets of damping areas 3 to ensure that the cross-section and position of the two material flows after diversion are completely symmetrical when they enter the damping area 3. The two sets of damping areas 3 gradually narrow from the feed inlet to the discharge direction, and the size and cross-sectional shrinkage rate of the two sets of damping areas 3 are completely consistent, and they are related to the compression. - The expansion channel structure is symmetrical in the central plane; the stacked zone 4 is a symmetrical converging channel structure, with its inlet end being a double inlet channel 41 that connects to the outlets of the two damping zones 3 respectively. It gradually converges towards the center along the material flow direction, eventually forming a single flat rectangular outlet channel; the stacked zone 4 has a gradually expanding flat structure from double inlets to single outlet, with a cross-sectional width greater than its height. The overall structure is adapted to the material flow state at the outlet of the damping zone 3, ensuring that the two material flows are smoothly superimposed into a single layered flat material flow. That is, the first melt and the second melt first pass through the inlet zone 1 to generate high shear, causing the packing to be oriented and compressed along the flow direction, and then enter the diversion zone 2, the damping zone 3 and the stacked zone 4 in sequence to generate the outlet expansion effect; Among them, the length a of the compression-expansion channel structure is 20mm, and the length-to-width ratio a / b is (3:1)-(6:1); the length c of the damping zone 3 is 5-10mm, which is used to adjust the flow resistance of the first melt and the second melt; the outlet expansion ratio of the first melt and the second melt at the co-extrusion die outlet is 1.29-3.13. Under the condition of outlet expansion ratio of 2.3-3.1, the filler not only orients itself in the flow direction, but also generates a certain degree of orientation perpendicular to the flow direction, forming a three-dimensional heat-conducting network in advance structure.

[0024] Reference Figure 2 and Figure 3 , Figure 2 In the diagram, 'a' represents the internal channel structure of the co-extrusion die. Figure 2 Figure b shows a schematic diagram of the external structure of the co-extrusion die. The co-extrusion die is an existing type of die. In this embodiment, the co-extrusion die includes two sets of flow channels. Each flow channel includes a channel region 5, which connects to multiple sets of sheet forming regions 6. The sheet forming regions 6 of the two sets of flow channels are alternately distributed. That is, the two melt materials after being processed by the compression-expansion flow channels undergo the following process... Figure 2 The co-extrusion channels are alternately stacked to form a structure like... Figure 3The illustrated multi-layer composite sheet has a thermally conductive layer-reinforcement layer-thermally conductive layer structure or a thermally conductive layer-reinforcement layer-thermally conductive layer-reinforcement layer structure; 3) Crushing and granulation Reference Figure 4 The layered sheet obtained in step 2) is cut or mechanically crushed into granules for use as raw materials in the subsequent injection molding process; the length of the crushed granules is controlled to be 1-10mm, the thickness to be 1-3mm, and they are flat or sheet-like. The difference between the flat or sheet-like granules in this embodiment and conventional cylindrical granules is that the flat shape retains the layered structure and filler orientation of the co-extruded sheet, while the cylindrical granules will completely destroy the orientation structure during the melt granulation process. 4) Injection molding Add the granules obtained in step 3) to the injection molding machine, and control the injection processing temperature to be 5-15°C lower than the melting point of the first thermoplastic resin and 20-40°C higher than the melting point of the second thermoplastic resin. During the injection flow, the layers overlap and rebuild the heat conduction network to obtain a heat-conducting plastic product. In this embodiment, the injection temperature of the PC / ABS system is set to 220-240℃. At this temperature, the ABS melts completely into a continuous flowing phase, while the PC is in a softened state but not completely melted. During the injection process, the softened PC sheets are dispersed into several small pieces under the shearing action of the screw, but the sheet structure remains intact and the internal filler network is not destroyed. The molten ABS carries the softened PC pieces and flows into the mold cavity. During the flow, the PC pieces contact and overlap each other due to their rigidity, forming a continuous heat conduction path. The injection pressure is set to 80-120MPa, the holding pressure is 60-80MPa, and the holding time is 5-10s. After cooling and solidification, the mold is opened to obtain a thermally conductive plastic product with a filling network.

[0025] Examples 2-7 Reference Figure 5 To determine the optimal compression-expansion channel structure parameters, Examples 2-7 were established to study the influence of channel parameters on the outlet expansion rate. The specific steps of Examples 2-7 differ from those of Example 1 in that the length a, width b, and damping zone length c of the compression-expansion channel structure are the same; all other steps are identical to those of Example 1.

[0026] exist Figure 5 In the experimental setup for verifying the relationship between flow channel parameters and outlet expansion rate, a single-channel injection pump serves as the power source for melt delivery. It is used to precisely control the flow rates of the first and second melts in the co-extrusion die, in order to study the outlet expansion behavior under different flow channel parameters.

[0027] Test Principle: The single-channel syringe pump operates on the principle of precision volumetric delivery. A stepper motor drives a lead screw and nut assembly via a reduction gear, converting rotary motion into linear motion, which in turn pushes the syringe piston to precisely deliver the melt. By setting the motor's rotational speed, the injection speed can be precisely adjusted, thereby controlling the melt's volumetric flow rate and velocity. The pump body is equipped with a sensor monitoring system that automatically measures the syringe barrel diameter to determine the loading specifications. Combined with the operating parameters set by the input system, the control system automatically calculates the drive frequency to achieve stable delivery.

[0028] Testing Procedure: Before the experiment, a syringe containing either the first or second melt was installed into a single-channel injection pump. The sensor monitoring system automatically identified the syringe specifications and calibrated its initial position. The system was configured with the target flow rate and total delivery volume, and the control system calculated the corresponding motor drive frequency. Upon startup, the stepper motor drove the lead screw at the set frequency to advance the syringe piston, delivering the melt at a constant flow rate into the compression-expansion channel of the co-extrusion die. During the test, the sensor monitoring system monitored the syringe installation status and the operation of the micro-propulsion system in real time to ensure a stable, pulsation-free flow rate. By changing the channel parameters (aspect ratio a / b, damping zone length c) and coordinating with different injection pump flow rate settings, the outlet expansion rate data under various conditions was measured and recorded, ultimately determining the optimal combination of channel parameters.

[0029] The parameters for Examples 2-7 are shown in Table 1: Table 1 Experimental parameters and results

[0030] Table 1 shows that there is an optimal range for the aspect ratio a / b: when a / b increases from 3:1 to 4:1, the outlet expansion rate increases significantly from 1.40 to 2.86; however, when a / b continues to increase to 6:1, the expansion rate decreases to 1.33. Therefore, the optimal a / b range is 3:1-5:1, with 4:1-5:1 being preferred. The damping zone length c significantly affects the expansion effect: under the condition of a / b=5:1, when c increases from 5mm to 10mm, the outlet expansion rate increases significantly from 1.29 to 3.13; therefore, c=7.5-10mm is preferred. The optimal parameter combination is: a=20mm, a / b=4:1-5:1, c=10mm, which yields an outlet expansion rate of 2.86-3.13, at which point the packing exhibits significant orientation in both the flow direction and the vertical direction.

[0031] Experimental Example Experimental Example 1 A PC / ABS system mobile phone casing processing method is described below: 1) Separate melt blending of two components Thermal conductive layer (material A): 90wt% polycarbonate (PC), 10wt% boron nitride (BN); Reinforcing and toughening layer (B material): Acrylonitrile-butadiene-styrene copolymer (ABS) 85wt%, aluminum oxide (Al2O3) 10wt%, silica microspheres 5wt%; Material A and material B are melt-blended separately in a twin-screw extruder at 240°C and 150 rpm to obtain melt of material A and melt of material B. 2) Multi-layer co-extrusion orientation molding Using a two-layer co-extrusion die, the A material melt obtained in step 1) is conveyed to the inner flow channel, and the B material melt is conveyed to the outer flow channel; Flow channel parameters: a=20mm, b=5mm (a / b=4:1), c=7.5mm; Co-extrusion speed: 2m / min, resulting in a thermally conductive layer-reinforcing layer-thermally conductive layer structure sheet (ABA three-layer structure sheet) with a total thickness of 2mm (0.6mm for each layer A and 0.8mm for each layer B). The measured outlet expansion rate was 2.86. The BN packing was oriented along the flow direction in layer A and had a certain degree of vertical orientation. 3) Crushing and granulation The sheet material is crushed into injection-molded granules using a crusher. The size of the crushed particles is 8-12mm in length, 5-8mm in width, and 1.5-2mm in thickness, and they are irregularly flat.

[0032] 4) Injection molding Injection temperature: Barrel temperature 220-240℃ (nozzle temperature 240℃), mold temperature 60℃; At this temperature, ABS melts completely and PC softens (the temperature is about 10°C below the melting point). Injection pressure: 100MPa, holding pressure: 70MPa, holding time: 8s; Injection molded product: mobile phone casing, dimensions 150mm×70mm×1.5mm, weight 25g.

[0033] Experimental Example 2 A high thermal conductivity 5G base station shell is prepared using the following method: 1) Separate melt blending of two components Material A: PC 70wt%, BN 30wt%; Material B: ABS 75wt%, Al2O3 15wt%, silica microspheres 10wt%; The processing conditions are the same as in Example 1, but the screw speed for material A is reduced to 120 rpm to prevent excessive crushing of BN.

[0034] 2) Multi-layer co-extrusion orientation molding Flow channel parameters: a=20mm, b=4mm (a / b=5:1), c=10mm; The measured export inflation rate was 3.1. A sheet with a thermally conductive layer-reinforcing layer-thermally conductive layer-reinforcing layer structure (ABAB four-layer structure sheet) is obtained, with a total thickness of 2.5mm.

[0035] 3) Crushing and granulation The size of the crushed particles is 10-15mm in length and 2-2.5mm in thickness.

[0036] 4) Injection molding Injection temperature: 230-250℃ (higher than Example 1, as increased filler content requires improved flowability); Injection molded product: 5G base station shell, dimensions 200mm×150mm×2mm.

[0037] Comparative Example Comparative Example 1 Materials A and B were directly blended and granulated (to form cylindrical granules), and then molded under the same injection molding conditions. This Comparative Example 1 employed a traditional blending and granulation process. The main difference from Experimental Example 1 is the elimination of step S2 (multilayer co-extrusion orientation molding) and step S3 (layered sheet crushing and granulation) from Example 1, replaced by a traditional melt blending and granulation process. The specific preparation process is as follows: A traditional PC / ABS system mobile phone casing manufacturing process employs the following preparation method: 1) Separate melt blending of two components Thermal conductive layer composition (material A): Polycarbonate (PC) 90wt%, Boron nitride (BN) 10wt%; Reinforcing and toughening layer component (B material): Acrylonitrile-butadiene-styrene copolymer (ABS) 85wt%, aluminum oxide (Al2O3) 10wt%, silica microspheres 5wt%; Material A and material B are melt-blended separately in a twin-screw extruder at 240°C and 150 rpm to obtain melt of material A and melt of material B. 2) Direct melt blending granulation The A melt and B melt obtained in step 1) are added to a twin-screw extruder at the same ratio (A:B = 60:40, consistent with the layer thickness ratio in Experimental Example 1) for melt blending, extrusion and granulation; Processing temperature: 220-250℃ Screw speed: 100 rpm The melt is extruded, drawn into strips, and granulated to obtain cylindrical granules (granule length approximately 3-4 mm, diameter approximately 2-3 mm). 3) Injection Molding: The cylindrical granules obtained in step 2) are added to an injection molding machine and molded under the same injection molding conditions. Injection temperature: Barrel temperature 220-240℃ (nozzle temperature 240℃), mold temperature 60℃; Injection pressure: 100MPa, holding pressure: 70MPa, holding time: 8s; Injection molded product: mobile phone casing, dimensions 150mm×70mm×1.5mm, weight 25g.

[0038] Comparative Example 2 The processing procedure for a high thermal conductivity 5G base station casing differs from that in Comparative Example 1 in that... Material A: PC 70wt%, BN 30wt%; Material B: 75wt% ABS, 15wt% Al2O3, 10wt% silica microspheres; for Material A, the screw speed was reduced to 120rpm to prevent excessive crushing of BN, and the remaining steps were the same as those in Comparative Example 1.

[0039] Test case The thermal conductivity was determined using the transient plane heat source method (Hot Disk method) in accordance with the national standard GB / T42919.2-2023 "Determination of thermal conductivity and thermal diffusivity of plastics - Part 2: Transient plane heat source method", which is equivalent to the international standard ISO 22007-2:2022.

[0040] Test Principle: A planar probe with a double-helix structure is used as both a heat source and a temperature sensor, clamped between two identical test samples. During testing, a brief DC pulse is applied to heat the probe, causing heat to diffuse to both sides of the sample. The probe records the change in its resistance over time. By fitting the transient temperature response using a mathematical model, the thermal conductivity and thermal diffusivity of the material are directly calculated.

[0041] Specific testing procedure: First, prepare two sets of identical sheet samples. Each sample should have a diameter or side length of no less than 40 mm and a thickness of no less than 5 mm, with a smooth and flat surface. Before testing, place the samples in a standard laboratory environment (25℃, 50%RH) for 24 hours. Use a Hot Disk thermal constant analyzer, selecting a probe of appropriate diameter based on the sample's thermal conductivity. Measure the in-plane and perpendicular thermal conductivity using an anisotropic testing module. During testing, place the probe horizontally between the two samples, ensuring complete contact. Set the test power and time, start the test program, and the instrument automatically records the temperature response and calculates the thermal conductivity. Test the same set of samples at least three times and take the average value.

[0042] In view of the anisotropic characteristics of the product of this application, when the vertical thermal conductivity is tested, the probe plane is placed parallel to the surface of the sample layered structure, and the heat is conducted in the direction perpendicular to the layer; when the in-plane thermal conductivity is tested, an anisotropic module is used, and the thermal conductivity values ​​in the in-plane and vertical directions are measured simultaneously through a special algorithm.

[0043] Reference Figure 6 and Figure 7 The products prepared by Experimental Examples 1-2 and Comparative Examples 1-2 were subjected to performance tests, and the test results are as follows: The product obtained in Experiment Example 1 has the following thermal conductivity: in-plane thermal conductivity: 0.950 W / mK; vertical thermal conductivity: 0.356 W / mK. The product obtained in Experiment Example 2 has the following thermal conductivity: in-plane thermal conductivity: 1.52 W / mK; vertical thermal conductivity: 0.61 W / mK; meeting the heat dissipation and mechanical requirements of 5G base station shells.

[0044] The product obtained in Comparative Example 1 has the following thermal conductivity: in-plane thermal conductivity: 0.652 W / mK; vertical thermal conductivity: 0.296 W / mK.

[0045] The product obtained in Comparative Example 2 has the following thermal conductivity: in-plane thermal conductivity: 1.10 W / mK; vertical thermal conductivity: 0.45 W / mK.

[0046] Compared with traditional methods, the samples prepared using the method described in this patent have significantly improved thermal conductivity, with an in-plane thermal conductivity increase of 46% and a vertical thermal conductivity increase of 20%.

[0047] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastic, characterized in that, Includes the following steps: S1. A first thermoplastic resin and a thermally conductive filler are melt-blended to obtain a first melt, and a second thermoplastic resin and a reinforcing filler are melt-blended to obtain a second melt; the melting point of the first thermoplastic resin is 10-50℃ higher than the melting point of the second thermoplastic resin. S2. The first melt and the second melt are alternately stacked and co-extruded through a co-extrusion die with a compression-expansion channel structure to form a layered sheet. S3. Mechanically crush the layered sheet into granules; S4. The granules are added to the injection molding machine, and the injection molding temperature is controlled between the melting point of the first thermoplastic resin and the melting point of the second thermoplastic resin. During the injection flow, the layers overlap and rebuild the heat-conducting network to obtain a heat-conducting plastic product.

2. The method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastic according to claim 1, characterized in that, In step S1, the first thermoplastic resin is polycarbonate; The second thermoplastic resin is an acrylonitrile-butadiene-styrene copolymer.

3. The method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastic according to claim 1, characterized in that, In step S1, the thermally conductive filler is at least one of boron nitride, aluminum nitride, and aluminum oxide, and the amount of the thermally conductive filler added to the first thermoplastic resin is 10-30 wt%.

4. The method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastic according to claim 1, characterized in that, The reinforcing filler is at least one of silica microspheres and glass fiber, and the amount of the reinforcing filler added to the second thermoplastic resin is 5-15 wt%.

5. The method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastic according to claim 1, characterized in that, In step S2, the compression-expansion channel structure includes an inlet area (1), a diversion area (2), a damping area (3), and a stacked area (4) distributed along the material flow direction. The length a of the compression-expansion channel is 20-60mm, and the aspect ratio a / b is (3:1)-(6:1); the length c of the damping zone (3) is 5-10mm.

6. The method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastic according to claim 5, characterized in that, In step S2, the outlet expansion ratio of the first melt and the second melt at the co-extrusion die outlet is 1.29-3.

13.

7. The method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastic according to claim 1, characterized in that, In step S3, the granules are flat or flake-shaped; The length and width of the granules are both 1-10 mm, and the thickness is 1-3 mm.

8. The method for multilayer co-extrusion orientation processing of injection-moldable thermally conductive plastic according to claim 1, characterized in that, In step S4, the injection molding temperature is set to be 5-15°C lower than the melting point of the first thermoplastic resin and 20-40°C higher than the melting point of the second thermoplastic resin.

9. A multilayer co-extrusion orientation processing method for injection-moldable thermally conductive plastics according to claim 8, characterized in that, The injection pressure is set to 80-120MPa, the holding pressure is 60-80MPa, and the holding time is 5-10s.

10. A thermally conductive plastic granule prepared by the method according to any one of claims 1-9, characterized in that, The granules retain a thermally conductive layer-reinforcing layer-thermally conductive layer structure or a thermally conductive layer-reinforcing layer-thermally conductive layer-reinforcing layer structure, with the thickness of the thermally conductive layer and the thickness of the reinforcing layer both being 0.3-1 mm; the thermally conductive filler is oriented and arranged in the flow direction and perpendicular direction within the layer.

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