A dynamically vulcanized semiconductive shielding material for cables and its preparation method

Abstract

This invention relates to the field of cable material technology, and more particularly to a dynamically vulcanized semiconductive shielding material for cables and its preparation method, comprising: melt-blending polyethylene, functional additives, ethylene-vinyl acetate copolymer, and ethylene propylene diene monomer (EPDM) rubber to obtain an initial blend; determining whether the compatibility of the initial blend meets the standard based on the phase formation index; adding a crosslinking agent to the initial blend to obtain a vulcanized mixture; determining whether the dynamic vulcanization process of the vulcanized mixture is qualified based on the vulcanization curing index, and adjusting the vulcanization temperature of the extruder according to the difference; adding conductive filler to the vulcanized mixture to obtain an initial semiconductive shielding material; determining whether the conductive network construction of the initial semiconductive shielding material is qualified based on the network construction index; and obtaining a dynamically vulcanized semiconductive shielding material under the condition that the conductive network construction is qualified. This invention improves the stability of the preparation of dynamically vulcanized semiconductive shielding materials.

Description

Technical Field

[0001] This invention relates to the field of cable material technology, and in particular to a dynamic vulcanization type semiconductive shielding material for cables and its preparation method. Background Technology

[0002] In power cable systems, semiconductive shielding layers are crucial components, primarily functioning to uniformly distribute the electric field, prevent partial discharge, and improve the interfacial properties between the conductor and insulation. Dynamically vulcanized semiconductive shielding materials are widely used in conductor and insulation shielding layers of medium and high voltage cables due to their excellent mechanical properties, thermal stability, and conductivity. These materials typically use polyethylene as a matrix, adding elastomers such as EPDM rubber to improve flexibility, and utilizing conductive fillers to construct a conductive network. Traditional semiconductive shielding material preparation processes mainly rely on simple melt blending and vulcanization, which suffers from poor compatibility between polyethylene and non-polar rubbers and polar polymers, easily leading to phase separation and affecting the material's uniformity and mechanical properties. The dynamic vulcanization process is extremely sensitive to temperature and time; under-vulcanization results in insufficient crosslinking density, a loose material structure, and poor thermal stability, while over-vulcanization causes polymer degradation, making the material brittle and deteriorating its conductivity and mechanical properties. The dispersion state of the conductive filler affects the material's volume resistivity and stability, leading to problems such as uneven resistivity or localized conductive failure during cable extrusion and long-term operation.

[0003] Chinese Patent Application Publication No. CN119192708A discloses a semi-conductive shielding material based on dynamic vulcanization and its preparation method, comprising: a continuous phase, a dispersed phase, a crosslinking agent, a functional additive, and a conductive filler; the dispersed phase is ethylene propylene diene monomer (EPDM) rubber, dispersed in the continuous phase; the conductive filler is confined and dispersed in the continuous phase, overlapping to form a conductive network; the continuous phase is polyethylene.

[0004] However, the existing technology has the following problems: relying on preset process parameters, it lacks monitoring and control of the formation of a uniform and stable "sea-island" structure of polymers with poor compatibility, resulting in uneven phase state of the blend, which leads to the stability problem of the preparation of dynamic vulcanized semiconductive shielding materials. Summary of the Invention

[0005] Therefore, the present invention provides a dynamically vulcanized semiconductive shielding material for cables and its preparation method, in order to overcome the problem in the prior art that relies on preset process parameters and lacks monitoring and control of the formation of a uniform and stable "sea-island" structure of polymers with poor compatibility, resulting in uneven phase state of the blend and thus affecting the stability of the preparation of the dynamically vulcanized semiconductive shielding material.

[0006] To achieve the above objectives, the present invention provides a method for preparing a dynamically vulcanized semiconductive shielding material for cables, comprising:

[0007] The initial blend is obtained by melt blending polyethylene, functional additives, ethylene-vinyl acetate copolymer and ethylene propylene diene monomer rubber under preset blending conditions.

[0008] The rheological data of the initial blend is obtained, and the phase formation index is determined based on the rheological data to determine whether the compatibility of the initial blend meets the standard. The blending temperature or blending speed of the internal mixer is adjusted according to the ratio of the phase formation index to the preset phase formation index.

[0009] A crosslinking agent is added to the initial blend that meets the compatibility standard, and the mixture is dynamically vulcanized under preset vulcanization conditions to obtain a vulcanized mixture;

[0010] Obtain the vulcanization curve of the vulcanization mixture, determine the vulcanization curing index based on the vulcanization curve to determine whether the dynamic vulcanization process of the vulcanization mixture is qualified, and determine the vulcanization temperature of the extruder to be adjusted according to the difference between the preset vulcanization curing index and the vulcanization curing index.

[0011] Conductive filler is added to the qualified vulcanized mixture during the dynamic vulcanization process, and the mixture is blended under preset mixing conditions to obtain an initial semi-conductive shielding material.

[0012] The volume resistivity of the initial semiconductive shielding material is obtained, and the network construction index is determined based on the volume resistivity to determine whether the conductive network construction of the initial semiconductive shielding material is qualified. The mixing time of the internal mixer is adjusted according to the relative difference between the preset network construction index and the network construction index.

[0013] Dynamically vulcanized semiconductive shielding material was obtained under the condition that the conductive network was constructed satisfactorily.

[0014] Furthermore, the initial blend's failure to meet compatibility standards is determined based on a comparison of phase formation indices that are less than or equal to a preset phase formation index, wherein...

[0015] The phase formation index is determined based on the energy storage modulus and loss modulus.

[0016] Furthermore, the process of adjusting the blending temperature of the internal mixer includes:

[0017] Calculate the ratio of the phase formation index to the preset phase formation index under the condition that the initial blend does not meet the compatibility standard;

[0018] The blending temperature is increased based on the comparison results where the ratio is less than or equal to a preset ratio.

[0019] The increased blending temperature is determined based on the blending temperature and the preset blending temperature adjustment coefficient.

[0020] Furthermore, the process of adjusting the mixing speed of the internal mixer includes:

[0021] Calculate the ratio of the phase formation index to the preset phase formation index under the condition that the initial blend does not meet the compatibility standard;

[0022] Based on the comparison results where the ratio is greater than a preset ratio, the mixing speed is increased;

[0023] The increased blending temperature is determined based on the blending temperature phase formation index, the preset phase formation index, and the preset blending temperature adjustment coefficient.

[0024] Furthermore, the failure of the dynamic vulcanization process of the vulcanized mixture is determined based on a comparison of vulcanization curing indices being less than or equal to a preset vulcanization curing indices, wherein,

[0025] The curing index is determined based on the minimum torque, maximum torque, and real-time torque.

[0026] Furthermore, the process of adjusting the vulcanization temperature of the extruder includes:

[0027] Calculate the difference between the preset curing index and the curing index under unqualified conditions of dynamic curing process of vulcanized mixture;

[0028] Based on the comparison results where the difference is less than or equal to a preset difference, the vulcanization temperature is increased by a first preset vulcanization temperature adjustment coefficient.

[0029] Based on the comparison results where the difference is greater than a preset difference, the vulcanization temperature is increased by a second preset vulcanization temperature adjustment coefficient.

[0030] Furthermore, the determination that the conductive network construction of the initial semiconductive shielding material is unqualified is based on a comparison result where the network construction index is less than or equal to a preset network construction index, wherein,

[0031] The network construction index is determined based on the standard deviation of volume resistivity and the average volume resistivity.

[0032] Furthermore, the process of adjusting the mixing time of the internal mixer includes:

[0033] Calculate the relative difference between the preset network construction index and the network construction index under the condition that the initial semiconductive shielding material fails to meet the conductive network construction requirements;

[0034] Based on the comparison results where the relative difference is less than or equal to the preset relative difference, the vulcanization temperature is increased by the first preset vulcanization temperature adjustment coefficient.

[0035] Based on the comparison results where the relative difference is greater than the preset relative difference, the vulcanization temperature is increased by the second preset vulcanization temperature adjustment coefficient.

[0036] Furthermore, the conductive filler is conductive carbon black and carbon nanotubes.

[0037] The present invention also provides a dynamically vulcanized semiconductive shielding material for cables, comprising: polyethylene, EPDM rubber, crosslinking agent, functional additives, ethylene-vinyl acetate copolymer, and conductive filler.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention obtains an initial blend by melt blending polyethylene, functional additives, ethylene-vinyl acetate copolymer, and ethylene propylene diene monomer (EPDM) rubber; compatibility is evaluated and blending parameters are adjusted using rheological data; a crosslinking agent is added to the blend with acceptable compatibility for dynamic vulcanization; the vulcanization temperature is optimized using vulcanization curves; conductive fillers are introduced into the vulcanized products, and a conductive network is constructed based on volume resistivity; the phase formation index ensures the uniformity and stability of the basic polymer system; the vulcanization curing index establishes dynamic feedback between the vulcanization process and temperature parameters, preventing structural loosening caused by under-vulcanization and avoiding performance degradation caused by over-vulcanization, thereby improving the crosslinking density and thermal stability of the vulcanized products; the conductive network construction index allows the dispersion state of the conductive filler to be controlled, avoiding conductivity fluctuations caused by filler agglomeration or uneven distribution, ensuring the resistivity stability and uniformity of the semiconductive layer, reducing the impact of process fluctuations on the final material properties, and thus improving the stability of the preparation of dynamically vulcanized semiconductive shielding materials.

[0039] Furthermore, this invention uses the phase formation index to determine the compatibility of the initial blend. If the compatibility is not met, the blending temperature or blending speed is adjusted. If the loss factor deviates little from the ideal compatibility system, it indicates that the entanglement of polymer molecular chains and interfacial forces have reached a balance, and the compatibility meets the standard. Increasing the blending temperature can enhance the thermal motion capability of molecular chains and promote phase interface fusion. Increasing the speed refines the particle size by enhancing the shearing action, improves the interfacial bonding strength, improves the molecular chain fluidity, and improves the performance uniformity of the semiconductive shielding material in high-voltage cables and electronic packaging. At the same time, the uniform phase structure can reduce stress concentration points, improve the tensile strength and aging resistance of the material, and precise control of the dispersed phase particle size is conducive to the uniform distribution of conductive fillers.

[0040] Furthermore, this invention uses the vulcanization curing index to determine whether dynamic vulcanization is qualified. If it is not qualified, the vulcanization temperature of the extruder is adjusted. Crosslinking defects are local under-vulcanization, so the temperature is increased to gently promote the crosslinking reaction. Insufficient crosslinking is due to uneven dispersion of the crosslinking agent, so the temperature is increased rapidly to ensure complete crosslinking reaction, thereby improving the crosslinking reaction rate. A complete crosslinking network can reduce stress relaxation during the use of the material and improve aging resistance. Temperature control avoids the increase in brittleness caused by over-vulcanization, ensuring a balance between the mechanical strength and flexibility of the material, thereby improving the stability of the preparation of dynamically vulcanized semiconductive shielding materials.

[0041] Furthermore, this invention uses a network construction index to determine whether the conductive network is qualified. If the conductive network is unqualified, the mixing time of the internal mixer is adjusted to ensure that the conductive filler forms a uniform and continuous network. The network construction index quantifies the uniformity of the conductive filler dispersion. When the conductive network defects are minor, a slight extension of the mixing time can gently promote filler dispersion. However, if the filler agglomeration is severe, a significant extension of the mixing time ensures that the filler is fully sheared and uniformly dispersed, improving the filler dispersion effect and enhancing the electrical performance stability of the semiconductive shielding material in high-voltage cables, electronic packaging, and other fields. Uniform filler distribution can form a continuous conductive path, reducing resistivity and improving shielding effectiveness. Controlling the mixing time avoids network breakage caused by excessive filler dispersion, ensuring the durability of conductive performance, thereby improving the stability of the preparation of dynamically vulcanized semiconductive shielding materials. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating a method for preparing a dynamically vulcanized semiconductive shielding material for cables according to an embodiment of the present invention.

[0043] Figure 2 This is a flowchart illustrating how to determine whether the compatibility of the initial blend meets the requirements in an embodiment of the present invention.

[0044] Figure 3 A flowchart for determining whether the dynamic vulcanization process of the vulcanization mixture is qualified according to an embodiment of the present invention;

[0045] Figure 4 This is a flowchart for determining whether the conductive network construction of the initial semiconducting shielding material is qualified in an embodiment of the present invention. Detailed Implementation

[0046] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0047] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0048] It should be noted that the data in this embodiment are all derived from a comprehensive analysis and evaluation of historical test data and corresponding historical test results from the three months prior to this test. Those skilled in the art will understand that the determination of the above-mentioned parameters for any single item in this invention can be achieved by selecting the value with the highest percentage based on the data distribution as the preset standard parameter, using weighted summation to obtain the value as the preset standard parameter, substituting each historical data point into a specific formula and using the value obtained from that formula as the preset standard parameter, or other selection methods, as long as the invention can clearly define different specific situations in the single-item judgment process through the obtained values.

[0049] Please see Figure 1 As shown, it is a flowchart of a method for preparing a dynamic vulcanized semiconductive shielding material for cables according to an embodiment of the present invention.

[0050] The present invention provides a method for preparing a dynamically vulcanized semiconductive shielding material for cables, comprising:

[0051] Step S1: Polyethylene, functional additives, ethylene-vinyl acetate copolymer and ethylene propylene diene monomer (EPDM) rubber are melt-blended under preset blending conditions to obtain an initial blend.

[0052] Step S2: Obtain the rheological data of the initial blend, determine the phase formation index based on the rheological data to determine whether the compatibility of the initial blend meets the standard, and determine the blending temperature or blending speed of the internal mixer according to the ratio of the phase formation index to the preset phase formation index.

[0053] Step S3: Add a crosslinking agent to the initial blend that meets the compatibility standard, and dynamically vulcanize it under preset vulcanization conditions to obtain a vulcanized mixture;

[0054] Step S4: Obtain the vulcanization curve of the vulcanization mixture, determine the vulcanization curing index based on the vulcanization curve to determine whether the dynamic vulcanization process of the vulcanization mixture is qualified, and determine the vulcanization temperature of the extruder to be adjusted according to the difference between the preset vulcanization curing index and the vulcanization curing index.

[0055] Step S5: Add conductive filler to the qualified vulcanized mixture in the dynamic vulcanization process, and blend under preset mixing conditions to obtain the initial semi-conductive shielding material.

[0056] Step S6: Obtain the volume resistivity of the initial semiconductive shielding material, determine the network construction index based on the volume resistivity, determine whether the conductive network construction of the initial semiconductive shielding material is qualified, and determine the mixing time of the internal mixer according to the relative difference between the preset network construction index and the network construction index.

[0057] Step S7: Under the condition that the conductive network is constructed successfully, a dynamically vulcanized semiconductive shielding material is obtained.

[0058] Specifically, this invention obtains an initial blend by melt blending polyethylene, functional additives, ethylene-vinyl acetate copolymer, and ethylene propylene diene monomer (EPDM) rubber. Rheological data is used to assess compatibility and adjust blending parameters. A crosslinking agent is added to the compatibility-compliant blend for dynamic vulcanization, and the vulcanization temperature is optimized using vulcanization curves. Conductive fillers are introduced into the vulcanized product, and a conductive network is constructed based on volume resistivity. The phase formation index ensures the uniformity and stability of the basic polymer system, while the vulcanization curing index establishes dynamic feedback between the vulcanization process and temperature parameters. This prevents structural loosening caused by under-vulcanization and avoids performance degradation caused by over-vulcanization, improving the crosslinking density and thermal stability of the vulcanized product. The conductive network construction index allows for the controllability of the conductive filler's dispersion state, avoiding conductivity fluctuations caused by filler agglomeration or uneven distribution. This ensures the resistivity stability and uniformity of the semiconductive layer, reduces the impact of process fluctuations on the final material properties, and thus improves the stability of the preparation of dynamically vulcanized semiconductive shielding materials.

[0059] The present invention also provides a dynamically vulcanized semiconductive shielding material for cables, comprising:

[0060] Polyethylene, EPDM rubber, crosslinking agents, functional additives, ethylene-vinyl acetate copolymer and conductive fillers.

[0061] In this embodiment of the invention, the dynamically vulcanized semiconductive shielding material is composed of the following parts by weight: 40-60 parts of polyethylene, preferably 50 parts; 20-30 parts of EPDM rubber, preferably 25 parts; 10-20 parts of ethylene-vinyl acetate copolymer, preferably 15 parts; 25-35 parts of conductive filler, preferably 30 parts; 1.5-2.5 parts of crosslinking agent, preferably 2 parts; and 1-3 parts of functional additives, preferably 2 parts.

[0062] In this embodiment of the invention, the conductive filler is conductive carbon black and carbon nanotubes.

[0063] In this embodiment of the invention, the crosslinking agent is dicumyl peroxide.

[0064] In this embodiment of the invention, the functional additives include dispersants, lubricants, and antioxidants, wherein the dispersant is oleamide, the lubricant is zinc stearate, and the antioxidant is antioxidant 168.

[0065] Specifically, in step S1, the preset blending conditions include: a blending temperature of 160-180℃, preferably 170℃, a blending time of 10-15min, preferably 12min, and a blending speed of 80rpm-100rpm, preferably 90rpm, wherein the melt blending of polyethylene, functional additives, ethylene-vinyl acetate copolymer and EPDM rubber is completed by an internal mixer.

[0066] Specifically, in this embodiment of the invention, a portion of the initial blend is pressed into a circular sample with a diameter of 25 mm and a thickness of 2 mm. The circular sample is then scanned using a rotational rheometer to obtain the rheological data of the initial blend. The scanning frequency of the rotational rheometer is 0.1 rad / s to 100 rad / s.

[0067] Please see Figure 2 As shown, it is a flowchart for determining whether the compatibility of the initial blend meets the standard in an embodiment of the present invention.

[0068] Specifically, in this embodiment of the invention, the compatibility of the initial blend is determined by comparing the phase formation index determined by the rheological data of the initial blend with the preset phase formation index.

[0069] When the phase formation index is less than or equal to the preset phase formation index, the compatibility of the initial blend is determined to be substandard.

[0070] When the phase formation index is greater than the preset phase formation index, the compatibility of the initial blend is determined to be satisfactory.

[0071] In this embodiment of the invention, the preset phase formation index range is [0.85, 0.95], preferably 0.9, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0072] In the implementation process, the phase formation index is obtained by extracting the energy storage modulus and loss modulus variation curves of the rheological data with frequency; the ratio of the loss modulus to the loss modulus is recorded as the loss factor; the ratio of the standard deviation to the average value of the loss factor is recorded as the loss coefficient of variation; the phase formation index is 1 - (loss coefficient of variation / loss coefficient of variation threshold of completely incompatible system), wherein the loss coefficient of variation threshold is set to 0.85.

[0073] Specifically, in this embodiment of the invention, when it is determined that the compatibility of the initial blend is not up to standard, the blending temperature or blending speed of the internal mixer is adjusted based on the comparison result of the ratio of the phase formation index to the preset phase formation index and the preset ratio.

[0074] When the ratio is less than or equal to the preset ratio, it is determined that the blending temperature will be increased to the corresponding value by using the preset blending temperature adjustment coefficient;

[0075] When the ratio is greater than the preset ratio, it is determined that the blending speed will be increased to the corresponding value by a preset blending speed adjustment coefficient of 1.2;

[0076] The ratio is the ratio of the phase formation index to the preset phase formation index.

[0077] In this embodiment of the invention, the preset ratio range is [0.3, 0.4], preferably 0.35, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0078] In this embodiment of the invention, the increased blending temperature is the blending temperature plus the square of the preset blending temperature adjustment coefficient multiplied by (the ratio of the phase formation index to the preset phase formation index - 1). The preset blending temperature adjustment coefficient has a value range of [15℃, 30℃], preferably 20℃. The increased blending speed is the product of the blending speed and the preset blending speed adjustment coefficient. The preset blending speed adjustment coefficient has a value of 1.2. To ensure that the adjusted blending temperature or blending speed meets the actual requirements, the adjustment range should not be too large. Therefore, an adjustment coefficient is set to control the adjustment range.

[0079] Specifically, this invention uses the phase formation index to determine the compatibility of the initial blend. If the compatibility is not met, the blending temperature or blending speed is adjusted. If the loss factor deviates little from the ideal compatibility system, it indicates that the entanglement of polymer molecular chains and interfacial forces have reached a balance, and the compatibility meets the standard. Increasing the blending temperature can enhance the thermal motion capability of molecular chains and promote phase interface fusion. Increasing the speed refines the particle size by enhancing shear action, improves the interfacial bonding strength, and improves the flowability of molecular chains. This improves the performance uniformity of the semiconductive shielding material in high-voltage cables and electronic packaging. At the same time, the uniform phase structure can reduce stress concentration points and improve the tensile strength and aging resistance of the material. Precise control of the dispersed phase particle size is beneficial to the uniform distribution of conductive fillers.

[0080] Specifically, in step S3, the preset vulcanization conditions include: a vulcanization temperature of 175–190°C, preferably 180°C; a vulcanization time of 3–6 min, preferably 4 min; and an extruder speed of 60–90 rpm, preferably 85 rpm.

[0081] Specifically, in this embodiment of the invention, a circular sample with a diameter of 25 mm and a thickness of 2 mm is taken from the vulcanization mixture, the circular sample is placed in the mold cavity of the vulcanizer, the circular sample is subjected to oscillation shear strain, and the curve of the change of the torque value of the vulcanizer over time is recorded, i.e., the vulcanization curve.

[0082] Please see Figure 3 As shown, it is a flowchart for determining whether the dynamic vulcanization process of the vulcanization mixture is qualified according to an embodiment of the present invention.

[0083] Specifically, in this embodiment of the invention, the dynamic vulcanization process of the vulcanization mixture is determined to be qualified based on the comparison between the vulcanization curing index determined by the vulcanization curve of the vulcanization mixture and the preset vulcanization curing index.

[0084] When the vulcanization curing index is less than or equal to the preset vulcanization curing index, the dynamic vulcanization process of the vulcanization mixture is determined to be unqualified.

[0085] When the vulcanization curing index is greater than the preset vulcanization curing index, the dynamic vulcanization process of the vulcanization mixture is determined to be qualified.

[0086] In this embodiment of the invention, the preset range of the vulcanization curing index is [0.9, 0.95], preferably 0.93, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0087] During implementation, the vulcanization curing index is obtained as follows: the lowest torque when the vulcanization mixture has not yet cross-linked in the initial stage of vulcanization is recorded as the minimum torque; the stable torque when the vulcanization mixture is fully vulcanized is recorded as the maximum torque; the torque collected during the vulcanization process of the vulcanization mixture at a preset frequency is recorded as the real-time torque, wherein the preset frequency is 3s / time; the vulcanization curing index is the ratio of the absolute value of the difference between the real-time torque and the minimum torque to the absolute value of the difference between the maximum torque and the real-time torque.

[0088] Specifically, in this embodiment of the invention, when it is determined that the dynamic vulcanization process of the vulcanized mixture is unqualified, the vulcanization temperature of the extruder is adjusted based on the comparison result of the difference between the preset vulcanization curing index and the preset difference.

[0089] When the difference is less than or equal to the preset difference, it is determined that the vulcanization temperature will be increased to the corresponding value by the first preset vulcanization temperature adjustment coefficient of 1.1.

[0090] When the difference is greater than the preset difference, it is determined that the vulcanization temperature will be increased to the corresponding value by the second preset vulcanization temperature adjustment coefficient of 1.3.

[0091] The difference is the difference between the preset vulcanization curing index and the vulcanization curing index.

[0092] In this embodiment of the invention, the preset difference value range is [0.15, 0.25], preferably 0.2, but the above value is not limited to this, and those skilled in the art can also adjust the value according to actual needs.

[0093] In this embodiment of the invention, the increased vulcanization temperature is the product of the vulcanization temperature and the preset vulcanization temperature adjustment coefficient. The preset vulcanization temperature adjustment coefficient includes a first preset vulcanization temperature adjustment coefficient with a value of 1.1 and a second preset vulcanization temperature adjustment coefficient with a value of 1.3. In order to ensure that the adjusted vulcanization temperature meets the actual needs, the adjustment range should not be too large. Therefore, an adjustment coefficient is set to control the adjustment range.

[0094] Specifically, this invention determines whether dynamic vulcanization is qualified by using the vulcanization curing index. If it is not qualified, the vulcanization temperature of the extruder is adjusted. Crosslinking defects are local under-vulcanization, so the temperature is increased to gently promote the crosslinking reaction. Insufficient crosslinking is due to uneven dispersion of the crosslinking agent, so the temperature is increased rapidly to ensure complete crosslinking reaction and improve the crosslinking reaction rate. A complete crosslinking network can reduce stress relaxation during the use of the material and improve aging resistance. Temperature control avoids the increase in brittleness caused by over-vulcanization and ensures the balance between the mechanical strength and flexibility of the material, thereby improving the stability of the preparation of dynamic vulcanized semiconductive shielding materials.

[0095] Specifically, in step S5, the preset mixing conditions include: a mixing temperature of 160-175°C, preferably 165°C; a mixing time of 5-8 minutes, preferably 7 minutes; and a mixing speed of 40-60 rpm, preferably 50 rpm.

[0096] Specifically, in this embodiment of the invention, a circular sample with a diameter of 25 mm and a thickness of 2 mm is taken from the initial semiconductive shielding material. The circular sample is placed between two electrodes of a resistance tester, and a stepwise increasing pressure is applied to the two electrodes to measure the volume resistivity of the circular sample under each pressure.

[0097] In a preferred embodiment, the pressure is 0.5 MPa, 1.0 MPa, 1.5 MPa, and 2.0 MPa.

[0098] Please see Figure 4 As shown, it is a flowchart for determining whether the conductive network construction of the initial semiconducting shielding material is qualified according to an embodiment of the present invention.

[0099] Specifically, in this embodiment of the invention, the conductivity network construction of the initial semiconductive shielding material is determined to be qualified based on the comparison between the network construction index determined by the volume resistivity of the initial semiconductive shielding material and the preset network construction index.

[0100] When the network construction index is less than or equal to the preset network construction index, the conductive network construction of the initial semiconductive shielding material is determined to be unqualified.

[0101] When the network construction index is greater than the preset network construction index, the conductive network construction of the initial semiconductive shielding material is deemed qualified.

[0102] In this embodiment of the invention, the preset network construction index range is [0.87, 0.93], preferably 0.91, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0103] During implementation, the network construction index is the ratio of the standard deviation of volume resistivity to the average volume resistivity at several pressure points.

[0104] Specifically, in this embodiment of the invention, when it is determined that the conductive network construction of the initial semiconductive shielding material is unqualified, the mixing time of the internal mixer is adjusted based on the comparison result of the relative difference between the preset network construction index and the network construction index and the preset relative difference.

[0105] When the relative difference is less than or equal to the preset relative difference, it is determined that the mixing time will be increased to the corresponding value by adjusting the first preset mixing time adjustment coefficient of 1.5.

[0106] When the relative difference is greater than the preset relative difference, it is determined that the mixing time will be increased to the corresponding value by the second preset mixing time adjustment coefficient of 1.7;

[0107] The relative difference is the relative difference between the preset network construction index and the actual network construction index, that is, the ratio of the absolute value of the difference between the preset network construction index and the actual network construction index to the preset network construction index.

[0108] In this embodiment of the invention, the preset relative difference range is [0.55, 0.65], preferably 0.5, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0109] In this embodiment of the invention, the increased mixing time is the product of the mixing time and the preset mixing time adjustment coefficient. The preset mixing time adjustment coefficient includes a first preset mixing time adjustment coefficient with a value of 1.5 and a second preset mixing time adjustment coefficient with a value of 1.7. In order to ensure that the adjusted mixing time meets the actual needs, the adjustment range should not be too large. Therefore, an adjustment coefficient is set to control the adjustment range.

[0110] Specifically, this invention uses a network construction index to determine whether the conductive network is qualified. If the conductive network is unqualified, the mixing time of the internal mixer is adjusted to ensure that the conductive filler forms a uniform and continuous network. The network construction index quantifies the uniformity of the conductive filler dispersion. When the conductive network defects are minor, a slight extension of the mixing time can gently promote filler dispersion. However, if the filler agglomeration is severe, the mixing time is significantly extended to ensure that the filler is fully sheared and uniformly dispersed, thus improving the filler dispersion effect and enhancing the electrical performance stability of the semiconductive shielding material in high-voltage cables, electronic packaging, and other fields. Uniform filler distribution can form a continuous conductive path, reducing resistivity and improving shielding effectiveness. Controlling the mixing time avoids network breakage caused by excessive filler dispersion, ensuring the durability of conductive performance, thereby improving the stability of the preparation of dynamically vulcanized semiconductive shielding materials.

[0111] Specifically, in this embodiment of the invention, under the condition that the conductive network of the initial semiconducting shielding material is qualified, a dynamically vulcanized semiconducting shielding material is obtained.

[0112] Example 1:

[0113] Weigh out 50 parts of polyethylene, 25 parts of EPDM rubber, 15 parts of ethylene-vinyl acetate copolymer, 1.5 parts of antioxidant, and 0.5 parts of lubricant by mass. Melt-blend at a blending temperature of 170℃, a blending speed of 90 rpm, and a blending time of 12 min to obtain an initial blend. Add 2 parts of dicumyl peroxide to the initial blend and vulcanize at a vulcanizing temperature of 180℃ and a vulcanizing time of 4 min to obtain a vulcanized mixture. Add 30 parts of conductive filler to the vulcanized mixture and mix at a mixing temperature of 165℃, a mixing time of 7 min, and a mixing speed of 50 rpm to obtain a dynamically vulcanized semi-conductive shielding material.

[0114] Example 2:

[0115] In this embodiment, except for 60 parts of polyethylene, 20 parts of EPDM rubber, 10 parts of ethylene-vinyl acetate copolymer, 2.5 parts of crosslinking agent, 3 parts of functional additives, and 35 parts of conductive filler, the rest are the same as in Example 1.

[0116] Example 3:

[0117] In this embodiment, except for 40 parts of polyethylene, 30 parts of EPDM rubber, 20 parts of ethylene-vinyl acetate copolymer, 1.5 parts of crosslinking agent, 1 part of functional additive, and 25 parts of conductive filler, the rest are the same as in Example 1.

[0118] Example 4:

[0119] Except for the sulfidation temperature of 160°C, the rest is the same as in Example 1.

[0120] Example 5:

[0121] Except for the mixing time being 3 minutes, the rest is the same as in Example 1.

[0122] Comparative Example 1:

[0123] Except for the absence of ethylene-vinyl acetate copolymer, it is the same as in Example 1.

[0124] Comparative Example 2:

[0125] Except for the sulfidation temperature of 176°C, the rest is the same as in Example 4.

[0126] Comparative Example 3:

[0127] Except for the mixing time of 7.5 min, the rest is the same as in Example 5.

[0128] Tensile strength, elongation at break, and tear strength were tested for Examples 1-5 and Comparative Examples 1-3 in accordance with (GB / T 18890.2-2015).

[0129] Table 1, Test Results

[0130]

[0131] The data in the table shows that in Example 4, due to insufficient vulcanization temperature, the vulcanization curing index was only 0.80, reflecting inadequate crosslinking reaction leading to a loose molecular network. This resulted in a sharp drop in tensile strength, elongation at break, and tear strength. In Comparative Example 2, after increasing the vulcanization temperature, the vulcanization curing index rose to 0.92, indicating sufficient crosslinking and a significant recovery in mechanical properties. This proves that the strategy of improving product performance by adjusting the temperature to increase the vulcanization curing index is correct and effective. In Example 5, due to insufficient mixing time, the network construction index was as low as 0.72, indicating uneven dispersion of the conductive filler and failure to form a complete network. Although the mechanical properties were not significantly affected... However, the volume resistivity is inevitably very high, which does not meet the requirements of semiconductive materials. In Comparative Example 3, after increasing the mixing time, the network formation index rose to 0.90, indicating that the filler dispersion was effectively improved and the mechanical properties were also improved simultaneously. This shows that sufficient mixing time is not only conducive to the construction of conductive network, but also helps the filler to be uniformly dispersed, thus having a positive impact on mechanical properties. In Comparative Example 1, due to the lack of EVA compatibilizer, the phase formation index was 0.78, indicating that the polymer matrix compatibility was poor and phase separation occurred, resulting in the inability to effectively transfer stress and causing poor mechanical properties. This illustrates the importance of ethylene-vinyl acetate copolymer for creating a uniform and stable matrix.

[0132] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a dynamically vulcanized semiconductive shielding material for cables, characterized in that, include: The initial blend is obtained by melt blending polyethylene, functional additives, ethylene-vinyl acetate copolymer and ethylene propylene diene monomer rubber under preset blending conditions. The rheological data of the initial blend is obtained, and the phase formation index is determined based on the rheological data to determine whether the compatibility of the initial blend meets the standard. The blending temperature or blending speed of the internal mixer is adjusted according to the ratio of the phase formation index to the preset phase formation index. A crosslinking agent is added to the initial blend that meets the compatibility standard, and the mixture is dynamically vulcanized under preset vulcanization conditions to obtain a vulcanized mixture; Obtain the vulcanization curve of the vulcanization mixture, determine the vulcanization curing index based on the vulcanization curve to determine whether the dynamic vulcanization process of the vulcanization mixture is qualified, and determine the vulcanization temperature of the extruder to be adjusted according to the difference between the preset vulcanization curing index and the vulcanization curing index. The process of adjusting the vulcanization temperature of the extruder includes, Calculate the difference between the preset curing index and the curing index under unqualified conditions of dynamic curing process of vulcanized mixture; Based on the comparison results where the difference is less than or equal to a preset difference, the vulcanization temperature is increased by a first preset vulcanization temperature adjustment coefficient. Based on the comparison results where the difference is greater than the preset difference, the vulcanization temperature is increased by the second preset vulcanization temperature adjustment coefficient. Conductive filler is added to the qualified vulcanized mixture during the dynamic vulcanization process, and the mixture is blended under preset mixing conditions to obtain an initial semi-conductive shielding material. The volume resistivity of the initial semiconductive shielding material is obtained, and the network construction index is determined based on the volume resistivity to determine whether the conductive network construction of the initial semiconductive shielding material is qualified. The mixing time of the internal mixer is adjusted according to the relative difference between the preset network construction index and the network construction index. The process of adjusting the mixing time of the internal mixer includes, Calculate the relative difference between the preset network construction index and the network construction index under the condition that the initial semiconductive shielding material fails to meet the conductive network construction requirements; Based on the comparison results where the relative difference is less than or equal to the preset relative difference, the vulcanization temperature is increased by the first preset vulcanization temperature adjustment coefficient. Based on the comparison results where the relative difference is greater than the preset relative difference, the vulcanization temperature is increased by the second preset vulcanization temperature adjustment coefficient. Dynamically vulcanized semiconductive shielding material was obtained under the condition that the conductive network was constructed satisfactorily.

2. The method for preparing a dynamically vulcanized semiconductive shielding material for cables according to claim 1, characterized in that, The initial blend's failure to meet compatibility standards is determined based on a comparison of whether the phase formation index is less than or equal to a preset phase formation index, wherein... The phase formation index is determined based on the energy storage modulus and loss modulus.

3. The method for preparing a dynamically vulcanized semiconductive shielding material for cables according to claim 2, characterized in that, The process of adjusting the blending temperature of the internal mixer includes: Calculate the ratio of the phase formation index to the preset phase formation index under the condition that the initial blend does not meet the compatibility standard; The blending temperature is increased based on the comparison results where the ratio is less than or equal to a preset ratio. The increased blending temperature is determined based on the blending temperature phase formation index, the preset phase formation index, and the preset blending temperature adjustment coefficient.

4. The method for preparing a dynamically vulcanized semiconductive shielding material for cables according to claim 3, characterized in that, The process of adjusting the mixing speed of the internal mixer includes: Calculate the ratio of the phase formation index to the preset phase formation index under the condition that the initial blend does not meet the compatibility standard; Based on the comparison results where the ratio is greater than a preset ratio, the mixing speed is increased; The increased blending speed is determined based on the blending speed and the preset blending speed adjustment coefficient.

5. The method for preparing a dynamically vulcanized semiconductive shielding material for cables according to claim 4, characterized in that, The failure of the dynamic vulcanization process of the vulcanization mixture is determined based on a comparison result where the vulcanization curing index is less than or equal to a preset vulcanization curing index, wherein, The curing index is determined based on the minimum torque, maximum torque, and real-time torque.

6. The method for preparing a dynamically vulcanized semiconductive shielding material for cables according to claim 5, characterized in that, The initial semiconductive shielding material is deemed unqualified based on a comparison of whether its network construction index is less than or equal to a preset network construction index. The network construction index is determined based on the standard deviation of volume resistivity and the average volume resistivity.

7. The method for preparing a dynamically vulcanized semiconductive shielding material for cables according to claim 6, characterized in that, The conductive filler is conductive carbon black and carbon nanotubes.

8. A dynamically vulcanized semiconductive shielding material for cables, comprising the preparation method of the dynamically vulcanized semiconductive shielding material for cables according to any one of claims 1-7, characterized in that, include: Polyethylene, EPDM rubber, crosslinking agents, functional additives, ethylene-vinyl acetate copolymer and conductive fillers.

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