Method for preparing high-voltage cable semi-conductive shielding material by adopting melt blending method

Abstract

The invention belongs to the technical field of preparation of high-voltage cable insulating materials, and discloses a method for preparing a high-voltage cable semi-conductive shielding material by adopting a melt blending method, which comprises the following steps: uniformly mixing an antioxidant and conductive carbon black to form a carbon black-antioxidant premix; adding 1 / 3 by weight of EBA into the carbon black-antioxidant premix, and uniformly mixing to obtain a carbon black-antioxidant-EBA premix; the method comprises the following steps: melting 1 / 3 parts by weight of EBA at 119-121 DEG C to obtain molten EBA; and continuously stirring the molten EBA, adding the carbon black-antioxidant-EBA premix into the molten EBA in 3-5 batches, adding the remaining EBA, uniformly mixing, adding the cross-linking agent, blending, and cooling after blending is finished, thereby obtaining the high-voltage cable semi-conductive shielding material. No solvent participates in the whole process, uniform dispersion of the carbon black is achieved through premixing and step-by-step feeding, the heat loss of the antioxidant is reduced, the temperature stability of the volume resistivity of the shielding material is good, and the performance requirement of a high-voltage cable shielding layer can be met.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage cable insulation material preparation technology, specifically relating to a method for preparing high-voltage cable semi-conductive shielding material by melt blending. Background Technology

[0002] Semiconducting shielding material for high-voltage cables is a key component of cable systems. Its core function is to eliminate air gaps between the conductor and insulation layer, and between the insulation layer and sheath, preventing insulation aging caused by localized electric field concentration, while simultaneously achieving a uniform electric field distribution. Currently, the mainstream preparation methods for high-voltage cable semiconducting shielding materials in the laboratory include impregnation and traditional melt blending methods. The impregnation method achieves component composite by immersing a matrix mixture containing carbon black and antioxidants in an ethanol solution containing a crosslinking agent. However, this method has significant drawbacks: on the one hand, the dispersion of the crosslinking agent in the ethanol solution is easily affected by uncontrollable factors such as solvent evaporation rate and immersion time, resulting in the inability to control the content of DCP (dicumyl peroxide) in the impregnation; on the other hand, solvent residue will form micro-defects inside the material, reducing the breakdown resistance and high-temperature stability of the shielding material, making it difficult to meet the long-term operation requirements of high-voltage cables.

[0003] Although traditional melt blending does not require solvents, it often adopts a "one-time feeding" method, that is, all components such as matrix, carbon black, and antioxidant are added to the blending equipment at the same time. This can easily lead to uneven carbon black dispersion due to the large difference in melt viscosity between carbon black and matrix and the mismatch in mixing rate. Furthermore, antioxidants are prone to premature decomposition at high temperatures, losing their inhibitory effect on the thermo-oxidative aging of materials.

[0004] To address the shortcomings of existing preparation methods, there is an urgent need to develop a method for preparing high-voltage cable semiconductive shielding materials that features controllable component dispersion, no solvent residue, and stable antioxidant performance. This would solve key technical problems such as large fluctuations in the volume resistivity of the shielding material and poor high-temperature stability, thereby meeting the stringent performance requirements of high-voltage cables for shielding layer materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of existing methods for preparing semiconductive shielding materials for high-voltage cables (such as impregnation method), such as uncontrollable component dispersion, solvent residue, and easy loss of antioxidant efficacy. This invention provides a method for preparing semiconductive shielding materials for high-voltage cables using melt blending. By optimizing the feeding sequence, blending temperature, and rotation speed parameters, this invention achieves uniform dispersion of carbon black and stable retention of antioxidants, ultimately obtaining a semiconductive shielding material with uniform composition, excellent volume resistivity temperature stability, and reliable high-temperature mechanical properties.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing semiconductive shielding material for high-voltage cables using melt blending includes the following steps: The antioxidant in the raw material of the semi-conductive shielding material for high-voltage cables is mixed with conductive carbon black so that the antioxidant is evenly attached to the surface of the carbon black particles, forming a carbon black-antioxidant premix. Add one-third by weight of EBA from the raw materials of high-voltage cable semiconducting shielding material to the carbon black-antioxidant premix, mix evenly, and obtain carbon black-antioxidant-EBA premix. One-third by weight of EBA in the raw material of high-voltage cable semiconductive shielding material is melted at 119-121℃ to obtain molten EBA. The EBA is continuously stirred and melted, and the carbon black-antioxidant-EBA premix is ​​added to the molten EBA in 3-5 batches. Then, the remaining EBA in the raw materials of the high-voltage cable semi-conductive shielding material is added and mixed. After mixing, the crosslinking agent in the raw materials of the high-voltage cable semi-conductive shielding material is added and blended. After blending, the material is cooled to obtain the high-voltage cable semi-conductive shielding material.

[0007] Preferably, when the antioxidant is mixed with the conductive carbon black, the stirring speed is 29-31 rpm and the stirring time is 5-8 min; When adding one-third by weight of EBA from the raw materials of high-voltage cable semiconductive shielding material to the carbon black-antioxidant premix, the stirring speed is 29-31 rpm and the stirring time is 3-5 min.

[0008] Preferably, when melting one-third by weight of EBA in the raw material of the high-voltage cable semiconducting shielding material at 119-121°C, the stirring rate is 9-11 rpm and the stirring time is 3-5 min.

[0009] Preferably, when continuously stirring the molten EBA and adding the carbon black-antioxidant-EBA premix in 3-5 batches to the molten EBA, the stirring speed is 39-41 rpm, and the interval between batches of molten EBA added is 1-2 min.

[0010] Preferably, the carbon black-antioxidant-EBA premix is ​​continuously stirred and melted, and then added to the melted EBA in 3-5 batches. After adding the remaining EBA from the raw materials of the high-voltage cable semiconducting shielding material, the mixture is continued to be mixed for 19.5-20.5 minutes.

[0011] Preferably, when adding the crosslinking agent for blending, the stirring speed is 39-41 rpm and the stirring time is 5.5-6.5 min.

[0012] Preferably, the steps of the method for preparing high-voltage cable semiconductive shielding material by melt blending described above are performed in a torque rheometer.

[0013] The present invention also provides a high-voltage cable semi-conductive shielding material, which is prepared by the method described above.

[0014] Preferably, the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the crosslinking agent is dicumyl peroxide.

[0015] Preferably, the mass ratio of EBA matrix, conductive carbon black, antioxidant and crosslinking agent is (24.5-25.5): (7-8): (0.20-0.22): (0.62-0.64) by mass percentage.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a melt blending method to prepare semiconductive shielding materials for high-voltage cables. The entire process is solvent-free, avoiding micro-defects and environmental pollution caused by solvent residue. Furthermore, the "premixing + step-by-step feeding" control overcomes the uncontrollable DCP content problem in the impregnation method and ensures more uniform carbon black dispersion in the shielding material. Simultaneously, premixing antioxidants with carbon black ensures uniform adhesion of the antioxidants to the carbon black surface, reducing thermal decomposition losses during melt blending. Therefore, this method is suitable for laboratory research on the preparation of high-performance high-voltage cable semiconductive shielding layers, effectively improving the compositional uniformity and overall performance stability of the shielding material. Attached Figure Description

[0017] Figure 1 Comparison of volume resistivity of high-voltage cable semiconductive shielding material prepared by Example 1 and Comparative Example 1 (impregnation method) at 30℃ and 50℃.

[0018] Figure 2 The figures show the high-temperature mechanical test results of the shielding materials prepared in Example 1 and Comparative Example 1 of this invention.

[0019] Figure 3 The change of volume resistivity of the shielding material prepared in Example 1 of the present invention at 70°C over time. Detailed Implementation

[0020] The present invention will be further described clearly and in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0021] This invention employs a melt blending method to prepare semiconductive shielding material for high-voltage cables, comprising the following steps: 1) Raw material premixing: According to the raw material formula of the high-voltage cable semi-conductive shielding material, weigh a certain amount of high-voltage cable semi-conductive shielding material EBA (i.e., ethylene-butyl acrylate copolymer) matrix, conductive carbon black, crosslinking agent and antioxidant. Among them, the antioxidant can be a phenolic antioxidant, more specifically, antioxidant 1010 (i.e., pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]), and the crosslinking agent can be dicumyl peroxide (DCP); pour all the weighed antioxidant into a container containing conductive carbon black. In a black beaker, stir evenly with a glass rod at 30±1 rpm for 5-8 minutes to ensure that the antioxidant is evenly attached to the surface of the carbon black particles, forming a "carbon black-antioxidant premix". Then add 1 / 3 part by weight of EBA matrix to the beaker and continue stirring at 30±1 rpm for 3-5 minutes to obtain "carbon black-antioxidant-EBA premix" for later use. Divide the remaining EBA matrix into two equal parts (i.e., each 1 / 3 part by weight), and label them "EBA Part 1" and "EBA Part 2" respectively, for later use.

[0022] 2) Torque rheometer preheating and initial matrix feeding: Start the torque rheometer and set the temperature of the front, middle, and rear sections of its mixing chamber to 120±1℃. Adjust the rotation speed to 10±1 rpm, close the feeding port, and preheat at a constant temperature for 15-20 minutes to ensure uniform and stable temperature within the mixing chamber (temperature difference between the front, middle, and rear sections ≤ 0.5℃). Open the torque rheometer feeding port and slowly pour the "first portion of EBA" (1 / 3 mass of EBA matrix) into the mixing chamber. Close the feeding port and maintain a rotation speed of 10±1 rpm for 3-5 minutes until the EBA matrix is ​​completely melted (judging from the torque rheometer temperature curve: the temperature stabilizes at 119.4℃ with no significant fluctuations). In this step, a low rotation speed of 10±1 rpm is used for slow melting of the EBA matrix to avoid excessively high local temperatures caused by rapid shearing.

[0023] 3) Step-by-step feeding and main blending: After the EBA matrix in the mixing chamber is completely melted, increase the speed of the torque rheometer to 40±1 rpm; use a stainless steel key to add the prepared "carbon black-antioxidant-EBA premix" in 3-5 batches (that is, divide the carbon black-antioxidant-EBA premix evenly into 3-5 parts, add 1 part each time) into the mixing chamber. After all the "carbon black-antioxidant-EBA premix" has been added, with an interval of 1-2 minutes between each batch, add the next batch only after the previous batch has been completely integrated into the molten matrix to avoid carbon black agglomeration; immediately pour the "second part of EBA" (the remaining 1 / 3 mass of EBA matrix) into the mixing chamber and continue blending at 40±1 rpm for 20min±30s. The purpose of this operation is to use a small amount of EBA matrix (i.e., the "second part of EBA") to achieve "capping" coverage and prevent carbon black particles from escaping from the feeding port during high-speed blending.

[0024] 4) Crosslinking agent addition and final mixing: After mixing for 20 min ± 30 s, open the feed port of the torque rheometer and quickly add the weighed crosslinking agent. Close the feed port and continue melting and mixing at 120℃ ± 1℃ and 40 ± 1 rpm for 6 min ± 30 s. After mixing, open the discharge port of the torque rheometer, quickly remove the uniformly mixed material, cut it into small particles, and allow it to cool naturally to room temperature. Then, seal it in a vacuum-sealed bag for storage to obtain the high-voltage cable semi-conductive composite shielding material. In this step, adding DCP after 20 min ± 30 s of main mixing and mixing for a short time of 6 min ± 30 s ensures that DCP is uniformly dispersed in the matrix and avoids ineffective decomposition due to prolonged molten state, thus ensuring the efficiency of subsequent crosslinking reactions.

[0025] In the above-described scheme of the present invention, the temperature of the three-section cavity is 120±1℃, which is higher than the melting point of the EBA matrix (90~105℃) and can avoid premature decomposition of DCP (the half-life of DCP at 120℃ is 4.55h). In steps 3) and 4), a high rotation speed of 40±1rpm is used to enhance the shear force, promote the dispersion of carbon black particles, and at the same time ensure the uniform compounding of antioxidant and matrix.

[0026] The raw materials of the high-voltage cable semiconductive shielding material provided by the present invention include EBA matrix, conductive carbon black, antioxidant and crosslinking agent, wherein the mass ratio of EBA matrix, conductive carbon black, antioxidant and crosslinking agent is (24.5-25.5): (7-8): (0.20-0.22): (0.62-0.64).

[0027] In the following embodiments of the present invention, the torque rheometer used has a capacity of 30~35g.

[0028] Example 1 This embodiment describes a method for preparing semiconductive shielding material for high-voltage cables using a melt blending method, specifically including the following steps: 1) Raw material weighing: Weigh 25g of EBA matrix, 7.5g of conductive carbon black, 0.21g of antioxidant 1010, and 0.63g of crosslinking agent DCP; 2) Premixing: The antioxidant and carbon black were stirred evenly with a glass rod at 30±1 rpm for 8 minutes. Then, 1 / 3 of the EBA matrix (8.3 g) was added and the mixture was stirred evenly with a glass rod at 30±1 rpm for 5 minutes to obtain the premix. 3) Torque rheometer preheating: Set the three mixing sections to 120℃ for 20 minutes, add 1 / 3 EBA (8.3g), and mix at 10 rpm for 5 minutes until melted; 4) Stepwise feeding: Increase the speed to 40 rpm, add the premix in 3 batches (2 min interval between each batch), and after adding all the premixed materials, add the remaining 1 / 3 of EBA (8.4 g) and mix for 20 min. 5) DCP addition: Add DCP during the main blending process for 20 minutes, mix at 40 rpm for 6 minutes, remove, cool and seal to obtain the high-voltage cable semi-conductive shielding material of this embodiment.

[0029] Comparative Example 1 This comparative example uses an impregnation method to prepare semiconductive shielding material for high-voltage cables, specifically including the following steps: 1) Raw material weighing: Weigh 25g of EBA matrix, 7.5g of conductive carbon black, 0.21g of antioxidant 1010, and 0.63g of crosslinking agent DCP; 2) Premixing: The antioxidant and carbon black are stirred evenly with a glass rod for 8 minutes, then 1 / 3 of the EBA matrix (8.3g) is added and stirring is continued for 5 minutes to obtain the premix. 3) Torque rheometer preheating: Set the three mixing sections to 120℃ for 20 minutes, add 1 / 3 EBA (8.3g), and mix at 10 rpm for 5 minutes until melted; 4) Step-by-step feeding: Increase the speed to 40 rpm, add the premix in 3 batches (2 min interval between each batch), and after adding all the premixed materials, add the remaining 1 / 3 EBA (8.4 g), mix for 20 min, then remove the material block and cut it into small granules; 5) Impregnated sample: First, pour 20ml of alcohol into a small beaker, then add 0.63g of DCP and stir until it is completely dissolved in the alcohol; then add the granules and impregnate until the alcohol has completely evaporated to obtain post-impregnated granules.

[0030] The volume resistivity of the high-voltage cable semiconductive shielding material obtained under different preparation processes in Example 1 and Comparative Example 1 of this invention varies with temperature as follows: Figure 1As shown in the figure, the PTC strength of the shielding material prepared by different mixing processes changes with temperature, further confirming that the shielding material prepared by melt blending has better temperature stability of volume resistivity. At different temperatures of 30℃, 50℃, 70℃, and 90℃, comparing the shielding materials prepared by impregnation and melt blending methods, the PTC strengths of the melt blending samples were 0.02, 0.03, 0.05, and 0.07, respectively, while the PTC strengths of the impregnation samples were 0.02, 0.04, 0.06, and 0.10, respectively. It can be seen that the PTC strength (reflecting the sensitivity of material resistivity to temperature changes) of the melt blending samples is consistently lower than that of the impregnation samples. The lower the PTC strength, the smaller the fluctuation of material resistivity with temperature changes, i.e., the better the temperature stability of volume resistivity. For example, at 90℃, the PTC strength of the impregnation method sample was significantly higher than that of the melt blending method sample, indicating that the resistivity change of the shielding material prepared by melt blending is more gradual at high temperatures. At 30℃, 50℃, and 70℃, the PTC strength of the melt blending method sample was also lower than that of the impregnation method sample at the corresponding temperatures. This fully demonstrates that the shielding material prepared by melt blending exhibits more stable volume resistivity changes under different temperature environments, possesses superior temperature stability, and can maintain consistent electrical performance in a wide temperature range of applications.

[0031] High-temperature mechanical test results at 200°C of high-voltage cable semiconductive shielding material samples obtained by different preparation methods of the composite shielding material obtained in Example 1 and Comparative Example 1 of this invention. Figure 2 As shown in the figure, it is clear that the elongation at load of the shielding material prepared by melt blending is 70%, while that prepared by impregnation is 102%. Under the same formulation, the shielding material prepared by melt blending exhibits superior high-temperature mechanical properties. This conclusion is fully confirmed by the difference in elongation at load. Elongation at load is a key indicator for evaluating the deformation capacity of a material under high-temperature stress; a higher value indicates stronger ductility and mechanical stability of the material under high-temperature loads. Figure 2 The results show that the elongation under load of the shielding material prepared by melt blending is significantly lower than that of the sample prepared by impregnation. In the evaluation of high-temperature mechanical properties, a lower elongation under load usually reflects that the material is less prone to excessive deformation at high temperatures, has better mechanical strength and rigidity, and can maintain more stable structural performance under high-temperature conditions. Therefore, melt blending is effective in improving the high-temperature mechanical properties of shielding materials, making the shielding materials prepared by this process more reliable and durable in applications requiring high-temperature mechanical loads.

[0032] The volume resistivity of the high-voltage cable semiconductive shielding material obtained by melt blending in Example 1 of this invention changes with time at 70°C as follows: Figure 3As shown in the curve, the volume resistivity of the shielding material sample exhibits high stability over a 50-hour test period at 70℃. From 0 to 20 hours, the volume resistivity increases slightly and then remains stable at 105.20 Ω·cm, indicating minimal changes in the internal structure or conductivity of the sample in the early stages. From 20 to 30 hours, although there is a slight decrease, it remains within a narrow range of 105.20 to 104.03 Ω·cm. From 30 to 50 hours, it tends to stabilize at 104 Ω·cm with almost no significant fluctuations. This demonstrates that the shielding material exhibits excellent stability in volume resistivity characteristics after a 50-hour test at 70℃, with minimal impact on electrical performance due to time factors. It demonstrates good thermal and temporal stability, maintaining relatively stable electrical performance in applications requiring high electrical performance stability over extended periods at 70℃, thus meeting the demands of applications with high electrical performance stability requirements.

[0033] As can be seen from the above examples, the present invention is solvent-free throughout the entire process. By premixing and step-by-step feeding, carbon black is uniformly dispersed and the heat loss of antioxidant is reduced. This results in good temperature stability of the volume resistivity of the shielding material, which can meet the performance requirements of high-voltage cable shielding layers.

[0034] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A process for the production of a high voltage cable semiconductive shielding compound by means of melt blending, characterized in that, The method comprises the following steps: The antioxidant in the raw material of the semi-conductive shielding material of the high-voltage cable is mixed with the conductive carbon black to make the antioxidant uniformly adhere to the surface of the carbon black particles, thereby forming a carbon black-antioxidant premix; One-third of the EBA in the raw material of the semi-conductive shielding material of the high-voltage cable is added to the carbon black-antioxidant premix to uniformly mix the EBA, thereby obtaining a carbon black-antioxidant-EBA premix; One-third of the EBA in the raw material of the semi-conductive shielding material of the high-voltage cable is melted at 119-121 ℃ to obtain molten EBA; The molten EBA is continuously stirred, and the carbon black-antioxidant-EBA premix is added to the molten EBA in 3-5 batches, and then the remaining EBA in the raw material of the semi-conductive shielding material of the high-voltage cable is added, and the mixture is uniformly mixed, and then a crosslinking agent in the raw material of the semi-conductive shielding material of the high-voltage cable is added for blending, and after the blending is completed, the semi-conductive shielding material of the high-voltage cable is obtained after cooling.

2. The method for preparing semiconductive shielding material for high-voltage cables using melt blending according to claim 1, characterized in that, When the antioxidant is mixed with the conductive carbon black, the stirring rate is 29-31 rpm, and the stirring time is 5-8 min. When one-third of the EBA in the raw material of the semi-conductive shielding material of the high-voltage cable is added to the carbon black-antioxidant premix for mixing, the stirring rate is 29-31 rpm, and the stirring time is 3-5 min.

3. The method for preparing semiconductive shielding material for high-voltage cables using melt blending according to claim 1, characterized in that, When one-third of the EBA in the raw material of the semi-conductive shielding material of the high-voltage cable is melted at 119-121 ℃, the stirring rate is 9-11 rpm, and the stirring time is 3-5 min.

4. The method of claim 1, wherein the semi-conductive shielding material for high voltage cables is prepared by a melt blending method. When the molten EBA is continuously stirred and the carbon black-antioxidant-EBA premix is added to the molten EBA in 3-5 batches, the stirring rate is 39-41 rpm, and the interval for adding the molten EBA in batches is 1-2 min.

5. A method for preparing semiconductive shielding material for high-voltage cables using melt blending according to claim 1, characterized in that, After the molten EBA is continuously stirred and the carbon black-antioxidant-EBA premix is added to the molten EBA in 3-5 batches, and then the remaining EBA in the raw material of the semi-conductive shielding material of the high-voltage cable is added, the blending is continued for 19.5-20.5 min.

6. The method of claim 1, wherein the semi-conductive shielding material for high voltage cables is prepared by a melt blending method. When the crosslinking agent is added for blending, the stirring rate is 39-41 rpm, and the stirring time is 5.5-6.5 min.

7. The method of claim 1, wherein the semi-conductive shielding material for high voltage cables is prepared by a melt blending method. The steps of the method are performed in a torque rheometer.

8. A high voltage cable semiconductive shielding compound characterized in that, The semi-conductive shielding material of the high-voltage cable is prepared by the method of any one of claims 1-7.

9. A semi-conductive shielding material for high voltage cables according to claim 8, characterised in that, The antioxidant is tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, and the crosslinking agent is dicumyl peroxide.

10. A semi-conductive shield compound for high voltage cables according to claim 8, characterized in that, The mass ratio of the EBA matrix, the conductive carbon black, the antioxidant, and the crosslinking agent is (24.5-25.5):(7-8):(0.20-0.22):(0.62-0.64) in percentage by mass.

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