Shrinkage-resistant directional conductive supercritical foaming rubber and preparation method thereof

Abstract

The invention discloses anti-shrinkage directional conductive supercritical foaming rubber and a preparation method thereof, and relates to the technical field of conductive rubber foam, raw materials comprise a rubber matrix, a modified fiber forming polymer and an auxiliary agent system, and the modified fiber forming polymer is prepared from a fiber forming polymer and a conductive filler. The preparation method comprises the following steps: extruding and granulating the fiber-forming polymer and the conductive filler to obtain modified granules, blending the modified fiber-forming polymer granules and the rubber matrix, carrying out extrusion and traction processes to obtain an in-situ fiber-forming modified rubber material, carrying out directional open milling, adding an auxiliary agent system, carrying out vulcanization molding, and foaming in a supercritical fluid to obtain the rubber foam material. The directional conductive fiber is constructed in the rubber matrix in situ, the rubber foaming material with directional conductivity and shrinkage resistance is prepared, the conductive efficiency is high, the problem that a rubber supercritical foaming material is prone to shrinkage is solved, and the rubber foaming material has the characteristics of heat insulation, light weight, high strength and the like and can be used for buffering and damping, heat insulation, electromagnetic shielding, flexible sensing and other scenes.

Description

Technical Field

[0001] This invention relates to the field of functional rubber technology, and in particular to a shrinkage-resistant, directionally conductive supercritical foamed rubber and its preparation method. Background Technology

[0002] Conductive rubber foam has significant application value in fields such as cushioning and shock absorption, heat insulation, electromagnetic shielding, and flexible sensing. However, due to the viscoelastic cross-linked network characteristics of rubber, its supercritical foaming is more difficult than that of resin materials, and balancing conductive functionalization design with foaming performance and mechanical stability is even more challenging. For example, the polypropylene foam material with wave-absorbing function invented in CN202411993325.4 first involves nickel plating on molybdenum disulfide to obtain nickel-plated molybdenum disulfide; then, copper is in situ coated on the surface of the nickel-plated molybdenum disulfide to obtain wave-absorbing filler, which is then added to polypropylene for foaming to improve conductivity, permeability, and wave-absorbing ability. This method involves wastewater and solvent pollution in the nickel plating process during the early modification stage, and it does not have directional conductivity. CN202510086566.9 uses a co-extrusion process to prepare core-shell resin microparticles, selectively distributing polymer substrate and conductive filler in the skin and core, separating the conductive part from the insulating part, and then foaming the core-shell resin microparticles. This invention achieves the goal of material lightweighting and obtains molded parts with both insulation and electromagnetic shielding properties. However, this process is relatively complex and lacks directional conductivity. CN201911400099.3 discloses a directional conductive composite material and its preparation method and application. First, using polymer B as the matrix, and conductive filler, magnetic filler, compatibilizer, and polymer A as the dispersed phase, the dispersed phase is dispersed in the matrix in the form of fibers or microfibers to obtain the composite material. The melting point of polymer B is lower than that of polymer A. The composite material is placed in a thermo-directional magnetic field with a certain temperature and magnetic field strength for magnetic orientation to obtain the directional conductive composite material. The composite material designed in this invention has directional conductive properties and can achieve both insulation and electromagnetic shielding effects. However, the processing requires an external magnetic field, has high material selectivity requirements, and lacks universality. Furthermore, all of the above conductive foaming materials are resin-based. Supercritical carbon dioxide foamed rubber materials currently face the technical challenge of dimensional instability. CN202411635061.5 discloses a supercritical carbon dioxide foamed rubber material and its preparation method. By adjusting the formulation of vulcanizing agents, plasticizers, and reinforcing agents, it is possible to achieve basic dimensional stability after molding, enabling the production of shoe soles with relatively complex dimensions. However, this invention does not completely solve the problem of dimensional shrinkage in rubber foamed materials, nor does it address functional modification.

[0003] This invention adopts an in-situ fiber-forming approach, which is then modified to be applicable to rubber foaming to improve the shape stability and mechanical properties of foamed products. Furthermore, it innovatively prepares directional conductive functionalized rubber foam materials. The process is simple and feasible, with strong versatility and high conductivity. It can be used in scenarios requiring electromagnetic shielding and also has the characteristics of heat insulation, lightweight, and high strength. Summary of the Invention

[0004] To achieve the aforementioned objectives and address the aforementioned technical problems, this invention provides a method for preparing a rubber foam material with directional conductivity and shrinkage resistance by in-situ constructing conductive fibers within a rubber matrix. The specific solution is as follows: A shrinkage-resistant, directionally conductive supercritical foamed rubber comprises the following raw materials in parts by weight: 50-80 parts of rubber matrix, 20-50 parts of modified fiber-forming polymer, and the remainder is an additive system; The modified fiber-forming polymer comprises: 100 parts of fiber-forming polymer and 15-25 parts of conductive filler.

[0005] Preferably, the rubber matrix is ​​one of EPDM, natural rubber, VMQ, and fluororubber; When the rubber matrix is ​​EPDM or natural rubber, auxiliary agent system A is used, including 1-3 parts of crosslinking agent BIPB, 8-20 parts of plasticizer paraffin oil, 0.5-1.5 parts of SA, 0.5-1.5 parts of TAIC, 3-7 parts of ZnO, and 1-3 parts of antioxidant 1010; When the rubber matrix is ​​VMQ, the auxiliary agent system B is adopted, including 1-2 parts of crosslinking agent bis(2,5-dimethyl) vulcanizing agent, 0.5-1 part of accelerator TAIC, and 10-40 parts of fumed silica. When the rubber matrix is ​​fluororubber, the auxiliary agent system C is used, which includes 1.5-2.5 parts of crosslinking agent bisphenol AF, 0.4-0.8 parts of accelerator BPP, 3-6 parts of MgO, and 3-6 parts of Ca(OH)2.

[0006] Preferably, the fiber-forming polymer is one of PA, PP, PLA, and HDPE.

[0007] Preferably, the conductive filler is one or more of carbon nanotubes, conductive carbon black, metal fibers, and graphene.

[0008] The present invention also provides a method for preparing supercritical foamed rubber with anti-shrinkage and directional conductivity as described above, comprising the following steps: (1) The fiber-forming polymer and conductive filler are placed in a twin-screw extruder and extruded and granulated to prepare the modified fiber-forming polymer; (2) The rubber matrix and the modified fiber-forming polymer are placed in a twin-screw extruder, and after extrusion and traction, in-situ fiber-forming modified rubber material is produced; (3) Cut the in-situ fiber-modified rubber material, arrange it neatly, and put it into the open mill in the same direction. The open mill is oriented and the auxiliary agent system is added. After repeated oriented milling, the open rubber is cut and put into the mold for heating and pre-vulcanization to obtain rubber sheet. (4) Place the rubber sheet into a supercritical reactor, fill it with supercritical fluid for saturation reaction, take it out and put it into an oven for secondary vulcanization and shaping to obtain foamed rubber.

[0009] Preferably, the rubber material in step (2) can be in the form of filaments, strips, sheets, etc., depending on the shape of the die.

[0010] Preferably, in step (1), the extrusion temperature of the twin-screw extruder is 100-270℃ and the rotation speed is 80rpm.

[0011] Preferably, in step (2), the extrusion temperature of the twin-screw extruder is 80-255℃ and the rotation speed is 300rpm.

[0012] Preferably, the processing temperature of the open mill in step (3) is 100-135℃, and directional open milling refers to open milling only in the horizontal and vertical directions.

[0013] Preferably, the vulcanization temperature in step (3) is 140-190 ℃ and the time is 3-10 min.

[0014] Preferably, the supercritical fluid is a mixture of CO2 and N2 in a 1:1 ratio, with a total pressure of 15-20 MPa. The saturation temperature is 110-130°C, and the time is 1-2 hours.

[0015] Preferably, the secondary vulcanization setting temperature is 150-190℃ and the time is 0.5-2h.

[0016] The beneficial effects of the technical solution provided by this invention are as follows: 1. High expansion ratio and dimensionally stable foaming performance: The present invention can achieve a foaming ratio of 10-15 times under supercritical foaming conditions, and the volume shrinkage rate of each embodiment is stable at 8-15%, which is significantly better than the 60% shrinkage level in Comparative Example 1, thereby ensuring the dimensional stability and controllability of the foamed rubber under low density conditions.

[0017] 2. Anisotropic conductivity: Through in-situ fiber forming and directional open-milling processes, this invention forms a continuous conductive path in the longitudinal direction, achieving a longitudinal conductivity >10. -3 S / cm, transverse conductivity <10 -6 The significant difference in S / cm indicates that the conductivity is improved by 3-4 orders of magnitude compared to the unoriented material, demonstrating that the material possesses unique advantages in directional conductivity and efficient conduction.

[0018] 3. Excellent mechanical properties and structural skeleton effect: The crystalline fiber-forming polymer forms a microfibrillated "steel skeleton" in the rubber matrix, which significantly improves mechanical strength while ensuring lightweight foaming. For example, the longitudinal tensile strength of Example 3 reached 2.55 MPa, and that of Example 9 reached 9.77 MPa, which is much higher than the 1.16 and 1.21 MPa of Comparative Example 1 and Comparative Example 3, respectively, proving that the material can maintain high strength and high toughness while being lightweight.

[0019] 4. Thermal insulation and lightweight characteristics: Because the material can be foamed to a low density and has a stable structure, the foam body forms rich and uniform pores, giving it excellent thermal insulation and cushioning performance.

[0020] 5. Simple process and strong applicability: This invention adopts conventional processes such as twin-screw extrusion, directional milling and supercritical foaming. The process route is simple and the raw material system is flexible. It can be adapted to various fiber-forming polymers such as PA, PET, PP, HDPE and different rubber matrices, and has wide industrial applicability and promotion value.

[0021] 6. Due to its combination of dimensional stability, anisotropic conductivity, lightweight thermal insulation, and high strength and toughness, the foamed rubber material of the present invention can be widely used in fields such as cushioning and shock absorption, thermal insulation, electromagnetic shielding, and flexible sensors, and has significant advantages in the application of functionalized polymer materials. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation process of an embodiment of the present invention; Figure 2 This is a schematic diagram of the conductive fiber network of the foamed sample according to an embodiment of the present invention; Figure 3 This is a scanning electron microscope image of the unbubbled sample from Embodiment 5 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] Example 1 (1) 100 parts of PA and 15 parts of carbon nanotubes were placed in a twin-screw extruder. The twin-screw temperature was set as follows: Zone 1 170℃, Zone 2 220℃, Zone 3 245℃, Zone 4 245℃, Zone 5 240℃, Zone 6 240℃, Zone 7 230℃. The mixture was extruded and granulated at 80 rpm to prepare the modified fiber-forming polymer. (2) 80 parts of EPDM and 20 parts of modified fiber-forming polymer were placed in a twin-screw extruder. The twin-screw temperature was set as follows: Zone 1 100℃, Zone 2 200℃, Zone 3 230℃, Zone 4 230℃, Zone 5 220℃, Zone 6 190℃, Zone 7 170℃, and at 300 rpm, in-situ fiber-forming rubber modified material was prepared. (3) Cut the in-situ fiber-forming rubber modified material, arrange it neatly, and put it into the open mill in the same direction. Perform transverse and longitudinal directional open milling at a temperature of 125°C. Add 1.5 parts BIPB, 10 parts paraffin oil, 1 part SA, 1 part TAIC, 5 parts zinc oxide, and 1 part antioxidant 1010. After repeated directional open milling, cut the open mill rubber into a mold and heat it for vulcanization at a temperature of 160°C for 3 minutes to obtain rubber sheet. (4) The rubber sheet is placed in a supercritical reactor and filled with supercritical fluid for saturation reaction. The supercritical fluid is a mixture of CO2 and N2 with a mixing ratio of 1:1. The pressure of CO2 is 8 MPa, the pressure of N2 is 8 MPa, the saturation temperature is 120℃, and the saturation time is 2h to obtain foamed rubber.

[0025] (5) Place the foamed rubber in a 160℃ oven and heat for 1 hour for secondary vulcanization.

[0026] Example 2 Prepared using the same method as in Embodiment 1, except that: Add 65 parts EPDM, 35 parts modified fiber-forming polymer, and 8 parts paraffin oil; The initial melting temperature in step (3) is 130℃; Adjust the saturation temperature in step (4) to 130℃.

[0027] Example 3 Prepared using the same method as in Experiment 1, with the difference being: The fiber-forming polymer is HDPE; Add 50 parts EPDM, 50 parts modified fiber-forming polymer, and 8 parts paraffin oil; In step (1), the twin-screw temperature is set as follows: Zone 1 100℃, Zone 2 145℃, Zone 3 150℃, Zone 4 155℃, Zone 5 1500℃, Zone 6 150℃, Zone 7 145℃; In step (2), the twin-screw temperature is set as follows: Zone 1 80℃, Zone 2 100℃, Zone 3 135℃, Zone 4 155℃, Zone 5 155℃, Zone 6 130℃, Zone 7 125℃; Adjust the temperature of the open mill in step (3) to 130℃; Adjust the pressure of CO2 in step (4) to 9 MPa, the pressure of N2 to 9 MPa, and the saturation temperature to 130℃.

[0028] Example 4 Prepared using the same method as in Embodiment 1, except that: The fiber-forming polymer is PLA; 10 parts carbon nanotubes; Add 65 parts of natural rubber, 35 parts of modified fiber-forming polymer, and 15 parts of paraffin oil; In step (1), the twin-screw temperature is set as follows: Zone 1 120℃, Zone 2 150℃, Zone 3 150℃, Zone 4 170℃, Zone 5 170℃, Zone 6 160℃, Zone 7 160℃; In step (2), the twin-screw temperature is set as follows: Zone 1 80℃, Zone 2 100℃, Zone 3 140℃, Zone 4 165℃, Zone 5 165℃, Zone 6 130℃, Zone 7 125℃; Adjust the temperature of the open mill in step (3) to 110℃; Adjust the pressure of CO2 in step (4) to 10 MPa, the pressure of N2 to 10 MPa, and the saturation temperature to 110℃; Adjust the secondary vulcanization time in step (5) to 30 min.

[0029] Example 5 Prepared using the same method as in Embodiment 1, except that: Carbon nanotubes: 25 parts; Add 65 parts EPDM, 35 parts modified fiber-forming polymer, and 20 parts paraffin oil; Adjust the open mill temperature in step (3) to 130℃.

[0030] Example 6 Prepared using the same method as in Embodiment 1, except that: The conductive filler is 20 parts of conductive carbon black; Add 65 parts EPDM, 35 parts modified fiber-forming polymer, and 8 parts paraffin oil; Adjust the initial melting temperature in step (3) to 130℃; Adjust the saturation temperature in step (4) to 130℃.

[0031] Example 7 Prepared using the same method as in Embodiment 1, except that: The fiber-forming polymer is PP, and the conductive filler is 20 parts of metal fiber; Add 65 parts EPDM, 35 parts modified fiber-forming polymer, and 8 parts paraffin oil; In step (1), the twin-screw temperature is set as follows: Zone 1 130℃, Zone 2 160℃, Zone 3 180℃, Zone 4 190℃, Zone 5 185℃, Zone 6 180℃, Zone 7 175℃; In step (2), the twin-screw temperature is set as follows: Zone 1 100℃, Zone 2 140℃, Zone 3 170℃, Zone 4 185℃, Zone 5 180℃, Zone 6 160℃, Zone 7 150℃; Adjust the amount of BIPB used in step (3) to 2 servings; Adjust the saturation temperature in step (4) to 130℃.

[0032] Example 8 Prepared using the same method as in Embodiment 1, except that: The fiber-forming polymer is PP, and the conductive filler is 15 parts of carbon nanotubes; Add 65 parts VMQ and 35 parts modified fiber-forming polymer; The additive system consists of 1.5 parts of bis(2,5)-pentasulfide, 1 part of TAIC, and 10 parts of fumed silica. In step (1), the twin-screw temperature is set as follows: Zone 1 130℃, Zone 2 160℃, Zone 3 180℃, Zone 4 190℃, Zone 5 185℃, Zone 6 180℃, Zone 7 175℃; In step (2), the twin-screw temperature is set as follows: Zone 1 100℃, Zone 2 140℃, Zone 3 170℃, Zone 4 185℃, Zone 5 180℃, Zone 6 160℃, Zone 7 150℃; Adjust the temperature of the open mill in step (3) to 120°C; Adjust the saturation temperature in step (4) to 130℃.

[0033] Example 9 Prepared using the same method as in Embodiment 1, except that: The conductive filler is 15 parts graphene; Add 65 parts of fluororubber and 35 parts of modified fiber-forming polymer; The additive system consists of 2 parts bisphenol AF, 5 parts MgO, 0.5 parts BPP, and 3 parts Ca(OH)2. Adjust the initial melting temperature in step (3) to 130℃; In step (4), the pressure of CO2 is adjusted to 10 MPa, the pressure of N2 is adjusted to 10 MPa, and the saturation temperature is adjusted to 130℃. Adjust the secondary vulcanization temperature in step (5) to 170℃ and the time to 2h.

[0034] Comparative Example 1 100 parts of EPDM were mixed in a two-roll mill at 100°C, and 1.5 parts of BIPB, 8 parts of paraffin oil, 1 part of SA, 1 part of TAIC, 5 parts of zinc oxide, and 1 part of antioxidant 1010 were added. After mixing, the mixed rubber was cut and placed in a mold for curing at 160°C for 3 minutes to obtain rubber sheets. Rubber sheets were placed in a supercritical reactor and charged with a supercritical fluid for a saturation reaction. The supercritical fluid was a mixture of CO2 and N2 in a 1:1 ratio. The pressure of CO2 was 8 MPa, the pressure of N2 was 8 MPa, the saturation temperature was 120℃, and the saturation time was 2 hours, yielding a rubber foam material. The rubber foam material was then placed in a 160℃ oven and heated for 1 hour for secondary vulcanization.

[0035] Comparative Example 2 65 parts of EPDM and 35 parts of PA were placed in a twin-screw extruder. The twin-screw temperature was set as follows: Zone 1 100℃, Zone 2 200℃, Zone 3 230℃, Zone 4 230℃, Zone 5 220℃, Zone 6 190℃, Zone 7 170℃, and at 300 rpm, a modified rubber material was produced. The modified rubber material is cut, neatly arranged, and placed into a two-roll mill in the same direction. The two-roll mill is used for transverse and longitudinal directional mixing at a temperature of 130°C. 1.5 parts BIPB, 8 parts paraffin oil, 1 part SA, 1 part TAIC, 5 parts zinc oxide, and 1 part antioxidant 1010 are added. After repeated directional mixing, the two-roll rubber is cut and placed into a mold for heating and vulcanization at a temperature of 160°C for 3 minutes to obtain rubber sheets. Rubber sheets were placed in a supercritical reactor and filled with supercritical fluid for a saturated reaction. The supercritical fluid was a mixture of CO2 and N2 in a 1:1 ratio. The pressure of CO2 was 8 MPa, the pressure of N2 was 8 MPa, the saturation temperature was 130℃, and the reaction time was 2 hours to obtain a rubber foam material. The rubber foam material is placed in a 160℃ oven and heated for 1 hour for secondary vulcanization.

[0036] Comparative Example 3 100 parts of PA and 15 parts of carbon nanotubes were placed in a twin-screw extruder. The twin-screw temperature was set as follows: Zone 1 170℃, Zone 2 220℃, Zone 3 245℃, Zone 4 245℃, Zone 5 240℃, Zone 6 240℃, Zone 7 230℃. The mixture was extruded and granulated at 80 rpm to prepare modified fiber-forming polymer granules. 65 parts of EPDM and 35 parts of modified fiber-forming polymer were placed in a twin-screw extruder. The twin-screw temperature was set as follows: Zone 1 100℃, Zone 2 200℃, Zone 3 230℃, Zone 4 230℃, Zone 5 220℃, Zone 6 190℃, Zone 7 170℃, and at 300 rpm, in-situ fiber-forming modified rubber material was produced. The in-situ fiber-modified rubber material was cut and placed in a mixer at a temperature of 125°C. 1.5 parts BIPB, 8 parts paraffin oil, 1 part SA, 1 part TAIC, 5 parts zinc oxide, and 1 part antioxidant 1010 were added. The mixed rubber was then cut and placed in a mold for heating and vulcanization at a temperature of 160°C for 3 minutes to obtain rubber sheets. The rubber sheet was placed in a supercritical reactor and filled with supercritical fluid for a saturated reaction. The supercritical fluid was a mixture of CO2 and N2 in a 1:1 ratio. The pressure of CO2 was 8 MPa and the pressure of N2 was 8 MPa. The reaction temperature was 130℃ and the reaction time was 2 hours to obtain a rubber foam material.

[0037] The rubber foam material is placed in a 160℃ oven and heated for 1 hour for secondary vulcanization.

[0038] Experimental test: 1. Density test: The density of the foamed material is tested according to the ASTM D792 water displacement method.

[0039] Sample density ρ

[0040] In the formula, v1: the volume of the sample after blending or foaming, in cm³. 3 m1: Mass of the blended or foamed sample, g; m2: Mass of the sample to be tested in water, g; ρ0: Density of water, g / cm³ 3 .

[0041] 2. Tensile Strength Test: Tensile tests were performed at room temperature using a universal testing machine (AI-7000S) according to ASTM D3574. The speed of the test head was set to 500 mm / min, and five specimens of each type were tested.

[0042] 3. Conductivity Test: Each sample was tested using a DC resistance meter at room temperature. To minimize error, each sample was tested 10 times, then the maximum and minimum values ​​were discarded, and the average of the remaining data was taken. The formulas for calculating volume resistivity and conductivity are as follows: ρ=Rhd / L; σ=1 / ρ Where ρ is the volume resistivity of the material, Ω·cm; R is the measured resistance of the sample, Ω; h is the width of the sample cross-section, cm; d is the thickness of the sample cross-section, cm; L is the distance between the two electrodes, cm; and σ is the conductivity, S / cm.

[0043] Table 1 Test Data

[0044] The longitudinal conductivity of Examples 2, 4, 5, 8, and 9 reaches 10. -2 -10 -1 The S / cm is 3-4 orders of magnitude higher than that of the unoriented comparative example 3, while the lateral conductivity remains at 10. -6 The magnitude indicates that the present invention forms a continuous conductive path in the longitudinal direction through in-situ fiber formation and orientation processes, while no percolation network is formed in the transverse direction, demonstrating the highly anisotropic conductivity of the material.

[0045] Although Comparative Example 3 also contains PA and carbon nanotubes, it lacks the fiber-forming orientation step and only exhibits isotropic conductivity, with both longitudinal and transverse conductivity remaining at 10. -5 It is on the order of S / cm and cannot achieve direction-selective conductivity.

[0046] Comparative Example 1 is pure rubber foam, which has a severe shrinkage of up to 60%.

[0047] The shrinkage rate of each embodiment of the present invention is controlled at 8%-15%, which is significantly lower than the shrinkage rate of about 60% of ordinary rubber foam. The mechanism is that the crystalline fiber-forming polymer crystallizes rapidly during the foaming and cooling process, forming a rigid microfiber mesh structure similar to the steel reinforcement skeleton of concrete, which effectively inhibits shrinkage and improves dimensional stability.

[0048] Example 3 (with the addition of 50 parts of HDPE microfiber reinforcement system) showed an increase in longitudinal tensile strength to 2.55 MPa and transverse tensile strength to 1.42 MPa, which is much higher than that of Comparative Example 2 and Comparative Example 3 (both around 1.0-1.2 MPa).

[0049] Examples 8 and 9 further demonstrate the adjustability of mechanical properties. In particular, the longitudinal strength of the fluororubber + graphene system in Example 9 is as high as 9.77 MPa and the transverse strength is 5.56 MPa, proving that the technology can balance low-density foaming and high-strength structure.

[0050] The system of this invention generally achieves a concentration of 0.06-0.12 g / cm³. 3 Its ultra-low density can reach as low as 0.065 g / cm³. 3 (Example 1).

[0051] At this density level, the material still maintains excellent mechanical and electrical properties, indicating that it is lightweight, heat-insulating, and functional, and is superior to conventional rubber foam materials of the same density.

[0052] Figure 2 This is a schematic diagram of the conductive fiber network in a foamed sample according to an embodiment of the present invention. The hexagonal units in the diagram represent the cell structure after foaming, and the black curves represent oriented conductive fibers. The fibers are interconnected in the longitudinal direction to form stable conductive pathways, but there are fewer transverse connections, making it difficult to form a continuous network. Therefore, it exhibits anisotropic characteristics of high longitudinal conductivity and low transverse conductivity. Simultaneously, the fiber network acts as a skeletal support between the cells, effectively reducing the shrinkage of the foam.

[0053] Figure 3 This is a scanning electron microscope (SEM) image of the un-bubbled product from Embodiment 5 of the present invention. Figure 3 As can be seen, the modified fiber-forming polymer is uniformly distributed with the rubber matrix, exhibiting good interfacial bonding, and no obvious agglomeration or delamination is observed. The magnified partial image shows that the conductive filler is finely dispersed within the matrix, proving that the in-situ fiber-forming and compounding process of this invention effectively achieves uniform distribution of the conductive filler, laying the foundation for the subsequent formation of a stable conductive network and reduction of shrinkage.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A shrinkage-resistant, directionally conductive supercritical foamed rubber, characterized in that, The raw materials include the following parts by weight: 50-80 parts of rubber matrix, 20-50 parts of modified fiber-forming polymer, and the remainder is an additive system; The modified fiber-forming polymer comprises: 100 parts of fiber-forming polymer and 15-25 parts of conductive filler.

2. The anti-shrinkage, directionally conductive supercritical foamed rubber according to claim 1, characterized in that, The rubber matrix is ​​one of EPDM, natural rubber, VMQ, and fluororubber; When the rubber matrix is ​​EPDM or natural rubber, auxiliary agent system A is used, including 1-3 parts of crosslinking agent BIPB, 8-20 parts of plasticizer paraffin oil, 0.5-1.5 parts of SA, 0.5-1.5 parts of TAIC, 3-7 parts of ZnO, and 1-3 parts of antioxidant 1010; When the rubber matrix is ​​VMQ, the auxiliary agent system B is adopted, including 1-2 parts of crosslinking agent bis(2,5-dimethyl) vulcanizing agent, 0.5-1 part of accelerator TAIC, and 10-40 parts of fumed silica. When the rubber matrix is ​​fluororubber, the auxiliary agent system C is used, which includes 1.5-2.5 parts of crosslinking agent bisphenol AF, 0.4-0.8 parts of accelerator BPP, 3-6 parts of MgO, and 3-6 parts of Ca(OH)2.

3. The anti-shrinkage, directionally conductive supercritical foamed rubber according to claim 1, characterized in that, The fiber-forming polymer is one of PA, PP, PLA, and HDPE.

4. The anti-shrinkage, directionally conductive supercritical foamed rubber according to claim 1, characterized in that, The conductive filler is one or more of carbon nanotubes, conductive carbon black, metal fibers, and graphene.

5. A method for preparing supercritical foamed rubber with anti-shrinkage directional conductivity according to any one of claims 1-4, characterized in that, Includes the following steps: (1) The fiber-forming polymer and conductive filler are placed in a twin-screw extruder and extruded and granulated to prepare the modified fiber-forming polymer; (2) The rubber matrix and the modified fiber-forming polymer are placed in a twin-screw extruder, and after extrusion and traction, in-situ fiber-forming modified rubber material is produced. (3) Cut the in-situ fiber-modified rubber material, arrange it neatly, and put it into the open mill in the same direction. The open mill is oriented and the auxiliary agent system is added. After repeated oriented milling, the open rubber is cut and put into the mold for heating and pre-vulcanization to obtain rubber sheet. (4) Place the rubber sheet into a supercritical reactor, fill it with supercritical fluid for saturation reaction, take it out and put it into an oven for secondary vulcanization and shaping to obtain foamed rubber.

6. The method for preparing anti-shrinkage, directionally conductive supercritical foamed rubber according to claim 5, characterized in that, In step (1), the extrusion temperature of the twin-screw extruder is 100-270℃ and the rotation speed is 80rpm.

7. The method for preparing anti-shrinkage, directionally conductive supercritical foamed rubber according to claim 5, characterized in that, In step (2), the extrusion temperature of the twin-screw extruder is 80-255℃ and the rotation speed is 300rpm.

8. The method for preparing anti-shrinkage, directionally conductive supercritical foamed rubber according to claim 5, characterized in that, In step (3), the open mill processing temperature is 100-135℃, and directional open milling refers to open milling only in the horizontal and vertical directions.

9. The method for preparing anti-shrinkage, directionally conductive supercritical foamed rubber according to claim 5, characterized in that, In step (3), the vulcanization temperature is 140-190℃ and the time is 3-10min.

10. The method for preparing anti-shrinkage directional conductive supercritical foamed rubber according to claim 5, characterized in that, The supercritical fluid is a mixture of CO2 and N2 in a 1:1 ratio, with a total pressure of 15-20 MPa, a saturation temperature of 110-130℃, and a time of 1-2 h. The secondary vulcanization setting is carried out at a temperature of 150-190℃ for 0.5-2 h.

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