Polyvinylidene fluoride composite master batch against magnetic field aging, preparation method and application thereof

Abstract

This invention discloses a polyvinylidene fluoride (PVDF) composite masterbatch resistant to magnetic field aging, its preparation method, and its application. The raw materials for preparing the PVDF composite masterbatch include PVDF resin and an antimagnetic material, wherein the antimagnetic material includes at least one of antimony, bismuth, gallium, and tin; the amount of the antimagnetic material added accounts for 0.01% to 1% of the total mass of the PVDF composite masterbatch. This invention adds an antimagnetic material to the PVDF resin matrix, which is uniformly dispersed within the PVDF resin matrix. This effectively shields or counteracts part of the effect of external strong magnetic fields on the PVDF molecular chains, effectively and significantly improving the magnetic field aging resistance of the PVDF composite masterbatch even at extremely low addition levels. Furthermore, the extremely low addition level of the antimagnetic material ensures that PVDF pipes prepared using this PVDF composite masterbatch still possess the original excellent chemical corrosion resistance, electrical insulation, mechanical strength, and processing performance of PVDF pipes.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polyvinylidene fluoride composite masterbatch resistant to magnetic field aging, its preparation method, and its application. Background Technology

[0002] During operation, high-voltage direct current (HVDC) converter valves generate significant heat loss due to the semiconductor switching devices and damping circuits in their core components. To ensure long-term safe and stable operation, a highly efficient and reliable cooling system is essential. Currently, large-capacity converter valves commonly employ forced water circulation cooling systems, which use circulating cooling water to remove heat from the valve body. The delivery pipeline, serving as the carrier of the cooling medium, runs through the entire converter valve tower and connects to external cooling equipment, making it one of the most complex, widely distributed, and demanding components of the converter valve cooling system. Simultaneously, the converter valve hall contains extremely strong power frequency and DC magnetic fields. The polyvinylidene fluoride (PVDF) pipelines, a critical component of the converter valve cooling system, are subjected to a harsh environment of combined strong magnetic fields, high water flow rates, and high temperatures. Existing research indicates that strong magnetic field environments accelerate the aging process of polymer materials such as PVDF. The mechanism may involve interference with the movement of polymer molecular chains, accelerated free radical generation, and long-term effects on the crystal structure, leading to molecular chain breakage, decreased degree of polymerization, and microstructural degradation. Ultimately, this manifests as decreased mechanical properties, increased brittleness, and increased susceptibility to cracking and leakage. PVDF pipelines directly affect the stability and effectiveness of the converter valve cooling system; failure of the converter valve cooling system will directly lead to the shutdown of the converter valve, causing significant economic losses.

[0003] Currently, solutions to this problem mostly focus on external magnetic shielding or optimizing pipe layout to reduce magnetic field strength, but these methods are costly, complex, and have limited effectiveness. Improving the inherent anti-magnetic aging capability of PVDF pipes from the material itself is a more fundamental and effective approach. However, there are no reports in the existing technology on material modification methods to improve the long-term stability of PVDF pipes under strong magnetic fields. Summary of the Invention This invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, an object of this invention is to provide a polyvinylidene fluoride composite masterbatch resistant to magnetic field aging. A second object of this invention is to provide a method for preparing such a polyvinylidene fluoride composite masterbatch resistant to magnetic field aging. A third object of this invention is to provide applications of such a polyvinylidene fluoride composite masterbatch resistant to magnetic field aging.

[0004] The inventive concept of this invention is as follows: Starting from the PVDF material itself, this invention introduces uniformly dispersed antimagnetic material powder of a specific type and content into the PVDF resin matrix to obtain a PVDF composite masterbatch resistant to magnetic field aging. PVDF pipes prepared by extruding this PVDF composite masterbatch can effectively resist the destructive effects of strong magnetic fields on the PVDF molecular structure (including chemical bonds and crystal structure), significantly slowing down its aging rate, thereby extending the safe service life of cooling pipes under harsh operating conditions in the converter valve hall.

[0005] To achieve the first objective mentioned above, the present invention provides the following technical solution: In a first aspect, the present invention provides a PVDF composite masterbatch resistant to magnetic field aging. The raw materials for preparing the PVDF composite masterbatch include PVDF resin and antimagnetic material. The antimagnetic material includes at least one of antimony (Sb), bismuth (Bi), gallium (Ga), and tin (Sn). The amount of antimagnetic material added accounts for 0.01% to 1% of the total mass of the PVDF composite masterbatch.

[0006] This invention starts with PVDF material itself, adding antimagnetic materials to the PVDF resin matrix to obtain a PVDF composite masterbatch that significantly enhances its antimagnetic properties. The antimagnetic materials specified in this invention are chemically stable and uniformly dispersed in the PVDF resin matrix. They can effectively shield or counteract some of the effects of external strong magnetic fields on the PVDF molecular chains, effectively and significantly improving the antimagnetic aging performance of the PVDF composite masterbatch even at extremely low addition levels. Furthermore, the extremely low addition level of the antimagnetic materials ensures that PVDF pipes prepared using this PVDF composite masterbatch retain the original excellent chemical corrosion resistance, electrical insulation, mechanical strength, and processing performance of PVDF pipes.

[0007] Preferably, the amount of the antimagnetic material added accounts for 0.01% to 0.95% of the total mass of the PVDF composite masterbatch; more preferably, the amount of the antimagnetic material added accounts for 0.01% to 0.9% of the total mass of the PVDF composite masterbatch; even more preferably, the amount of the antimagnetic material added accounts for 0.01% to 0.8% of the total mass of the PVDF composite masterbatch; and even more preferably, the amount of the antimagnetic material added accounts for 0.01% to 0.76% of the total mass of the PVDF composite masterbatch.

[0008] In some specific embodiments of the present invention, the amount of antimagnetic material added is any one of the following values ​​or a range formed by any two of the following: 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.24%, 0.28%, 0.3%, 0.4%, 0.45%, 0.49%, 0.53%, 0.57%, 0.60%, 0.66%, 0.71%, 0.73%, and 0.76% of the total mass of the PVDF composite masterbatch.

[0009] Preferably, the antimagnetic material includes at least two of antimony, bismuth, gallium, and tin.

[0010] Preferably, the antimagnetic material is a spherical powder. Spherical antimagnetic material is easier to disperse and uniformly distribute in the PVDF resin matrix.

[0011] Preferably, the average particle size of the antimagnetic material is 0.1~235μm; more preferably, the average particle size of the antimagnetic material is 0.3~200μm; even more preferably, the average particle size of the antimagnetic material is 0.7~180μm; and even more preferably, the average particle size of the antimagnetic material is 1~150μm. Within the average particle size range defined by this invention, the antimagnetic material can be uniformly distributed in the PVDF resin matrix, thereby significantly improving the anti-magnetic aging performance of the PVDF composite masterbatch.

[0012] In some specific embodiments of the present invention, the average particle size of the antimagnetic material is any value or a range formed by any two of the following: 1 μm, 8 μm, 15 μm, 20 μm, 23 μm, 28 μm, 31 μm, 37 μm, 40 μm, 42 μm, 46 μm, 50 μm, 60 μm, 63 μm, 69 μm, 78 μm, 89 μm, 94 μm, 98 μm, 100 μm, 102 μm, 106 μm, 110 μm, 120 μm, 128 μm, 135 μm, 147 μm, and 150 μm.

[0013] Preferably, the weight-average molecular weight of the PVDF resin is 300,000-450,000; more preferably, the weight-average molecular weight of the PVDF resin is 320,000-430,000; even more preferably, the weight-average molecular weight of the PVDF resin is 340,000-410,000; and even more preferably, the weight-average molecular weight of the PVDF resin is 350,000-400,000.

[0014] In some specific embodiments of the present invention, the weight-average molecular weight of the PVDF resin is any value of 350,000, 360,000, 370,000, 380,000, 390,000, 400,000, or a range formed by any two of them.

[0015] To achieve the second objective mentioned above, the present invention provides the following technical solution: In a second aspect, the present invention provides a method for preparing the PVDF composite masterbatch resistant to magnetic field aging as described in the first aspect, comprising the following steps: S1: Premixed material is obtained by mixing PVDF resin with antimagnetic material; S2: Extrude and granulate the premixed material described in step S1 to obtain the PVDF composite masterbatch.

[0016] Preferably, the mixing method in step S1 is mixing in a high-speed mixer or a three-dimensional motion mixer.

[0017] Preferably, the mixing time in step S1 is 10-20 min; more preferably, the mixing time in step S1 is 11-18 min; even more preferably, the mixing time in step S1 is 12-17 min; and even more preferably, the mixing time in step S1 is 14-16 min.

[0018] Preferably, the mixing speed is 800~2500 rpm; more preferably, the mixing speed is 1000~2300 rpm; even more preferably, the mixing speed is 1200~2000 rpm; and even more preferably, the mixing speed is 1500~1800 rpm. Preferably, the mixing time in step S1 is 3-15 min; more preferably, the mixing time in step S1 is 3-12 min; even more preferably, the mixing time in step S1 is 3-10 min; and even more preferably, the mixing time in step S1 is 3-8 min.

[0019] Preferably, the extrusion in step S2 is a twin-screw extrusion.

[0020] Preferably, the extrusion temperature in step S2 is 180~230℃; more preferably, the extrusion temperature in step S2 is 185~225℃; even more preferably, the extrusion temperature in step S2 is 190~220℃; and even more preferably, the extrusion temperature in step S2 is 195~210℃.

[0021] Preferably, the extrusion speed in step S2 is 200~300 rpm; more preferably, the extrusion speed in step S2 is 210~290 rpm; even more preferably, the extrusion speed in step S2 is 225~280 rpm; and even more preferably, the extrusion speed in step S2 is 240~260 rpm.

[0022] Preferably, the specific method of extrusion granulation in step S2 is to add the premixed material into a twin-screw extruder, and sequentially perform melt blending, extrusion, cooling and granulation to obtain the PVDF composite masterbatch.

[0023] To achieve the third objective mentioned above, the present invention provides the following technical solution: Thirdly, this invention provides a PVDF pipe resistant to magnetic field aging, wherein the PVDF pipe is obtained by extrusion molding of the PVDF composite masterbatch resistant to magnetic field aging described in the first aspect. Compared with the prior art that uses external magnetic shielding or optimizes pipeline layout to reduce the impact of magnetic field strength on PVDF pipes, this invention improves the service life of the pipe by modifying the PVDF material itself, with minimal cost increase, but significantly extends the maintenance cycle and reduces unplanned downtime, resulting in extremely high economic benefits.

[0024] In some specific embodiments of the present invention, after the PVDF tube is exposed to a magnetic field, Fourier transform infrared spectroscopy tests are performed on the PVDF tube at 976 cm⁻¹. - The intensity retention rate of the CH2 vibration peak (CH2 out-of-plane rocking vibration peak) at point ¹ is ≥93.2%; in some specific embodiments of the present invention, after the PVDF tube is exposed to a magnetic field, the Fourier transform infrared spectroscopy test of the PVDF tube at 976 cm⁻¹... - The intensity retention rate of the CH2 vibration peak at position ¹ was 93.2%–99.6%. The magnetic field frequency was 140–160 kHz, the magnetic field strength was 100–110 dB, and the exposure time was 8000–9000 h. 976 cm⁻¹ - The intensity retention rate of the CH2 vibration peak at ¹ is 976 cm⁻¹ after magnetic field exposure of the PVDF. - The intensity of the CH2 vibration peak at ¹ is similar to that of PVDF without magnetic field exposure at 976 cm⁻¹. - The ratio of the intensity of the CH2 vibration peak at position ¹.

[0025] In some specific embodiments of the present invention, after the PVDF tube resistant to magnetic field aging is exposed to a magnetic field, Fourier transform infrared spectroscopy tests are performed on the PVDF tube at 796 cm⁻¹. - The intensity retention rate of the CH2 vibration peak (CH2 in-plane rocking vibration peak) at ¹ is ≥93.8%; in some specific embodiments of the present invention, after the PVDF tube is exposed to a magnetic field, the Fourier transform infrared spectroscopy test of the PVDF tube at 796 cm⁻¹... - The intensity retention rate of the CH2 vibration peak at position ¹ was 93.8%–99.8%. The magnetic field frequency was 140–160 kHz, the magnetic field strength was 100–110 dB, and the exposure time was 8000–9000 h. 796 cm⁻¹ -The intensity retention rate of the CH2 vibration peak at ¹ is 796 cm⁻¹ after magnetic field exposure of the PVDF. - The intensity of the CH2 vibration peak at ¹ is similar to that of PVDF without magnetic field exposure at 796 cm⁻¹. - The ratio of the intensity of the CH2 vibration peak at position ¹.

[0026] This invention tests the "specific" characteristic peaks of α-crystalline PVDF (976 cm⁻¹, respectively). -1 and 796cm -1 The stability of PVDF chemical bonds after exposure to a magnetic field is determined by the intensity change of the characteristic peak (CH2 vibration peak), thereby determining the magnetic field aging resistance of PVDF pipes.

[0027] In some specific embodiments of the present invention, after exposure to a magnetic field, the characteristic peak intensity retention rate of the PVDF tube at 18.3° of the crystal plane, as measured by X-ray diffraction, is ≥92.8%; in some specific embodiments of the present invention, after exposure to a magnetic field, the characteristic peak intensity retention rate of the PVDF tube at 18.3° of the crystal plane, as measured by X-ray diffraction, is 92.8%~99.5%. The magnetic field frequency is 140~160kHz, the magnetic field strength is 100~110dB, and the exposure time is 8000h~9000h. The characteristic peak intensity retention rate at 18.3° of the crystal plane is the ratio of the characteristic peak intensity of the PVDF at 18.3° after magnetic field exposure to that of the PVDF without magnetic field exposure.

[0028] In some specific embodiments of the present invention, after exposure to a magnetic field, the characteristic peak intensity retention rate of the PVDF tube at 19.9° of the crystal plane, as measured by X-ray diffraction, is ≥91.9%. In some specific embodiments of the present invention, after exposure to a magnetic field, the characteristic peak intensity retention rate of the PVDF tube at 19.9° of the crystal plane, as measured by X-ray diffraction, is 91.9%~99.2%. The magnetic field frequency is 140~160kHz, the magnetic field strength is 100~110dB, and the exposure time is 8000h~9000h. The characteristic peak intensity retention rate at 19.9° of the crystal plane is the ratio of the characteristic peak intensity of the PVDF at 19.9° after magnetic field exposure to that of the PVDF without magnetic field exposure.

[0029] The present invention uses XRD to test the diffraction peaks of PVDF pipe at 18.3° (corresponding to the (020) crystal plane) and 19.9° (corresponding to the (110) crystal plane). The stability of the PVDF crystal structure after exposure to a magnetic field is judged based on the intensity change of the diffraction peaks at these two crystal planes, thereby judging the magnetic field aging resistance of PVDF pipe.

[0030] Preferably, the extrusion molding is a single-screw extrusion.

[0031] Preferably, the extrusion molding temperature is 190~230℃; more preferably, the extrusion molding temperature is 192~225℃; even more preferably, the extrusion molding temperature is 195~220℃; and even more preferably, the extrusion molding temperature is 200~215℃.

[0032] Preferably, the extrusion molding speed is 20~30 rpm; more preferably, the extrusion molding speed is 22~28 rpm; even more preferably, the extrusion molding speed is 23~27 rpm; and even more preferably, the extrusion molding speed is 24~26 rpm.

[0033] Preferably, after extrusion molding, the tube is sequentially cooled, drawn, and cut to a fixed length to obtain the PVDF pipe resistant to magnetic field aging.

[0034] Fourthly, the present invention provides a converter valve cooling system, the converter valve cooling system comprising the PVDF tube with magnetic field aging resistance described in the third aspect.

[0035] Preferably, the PVDF pipe resistant to magnetic field aging is used as a cooling medium delivery pipe in the converter valve cooling system.

[0036] Fifthly, the present invention provides the application of the PVDF tube with magnetic field aging resistance described in the third aspect or the converter valve cooling system described in the fourth aspect in the field of high voltage direct current transmission.

[0037] The beneficial effects of this invention are: (1) This invention starts from the PVDF material itself and adds antimagnetic materials to the PVDF resin matrix to obtain a PVDF composite masterbatch that can significantly enhance its antimagnetic properties. The antimagnetic materials specified in this invention are chemically stable and uniformly dispersed in the PVDF resin matrix. They can effectively shield or counteract part of the effect of external strong magnetic fields on the PVDF molecular chains. Even with extremely low addition amounts, they can effectively and significantly improve the antimagnetic aging performance of the PVDF composite masterbatch. In addition, the extremely low addition amount of antimagnetic materials also ensures that the PVDF pipes prepared using this PVDF composite masterbatch retain the original excellent chemical corrosion resistance, electrical insulation, mechanical strength, and processing performance.

[0038] (2) The preparation method of the present invention is simple and easy to implement, with low preparation cost. The method of PVDF modification is compatible with traditional plastic processing technology. Only the antimagnetic material powder needs to be added in the PVDF resin mixing stage. No complex process and equipment modification is required. Conventional preparation processes such as mixing and extrusion can be used to complete the process, which is suitable for large-scale industrial production.

[0039] (3) Compared with the existing technology of using external magnetic shielding or optimizing pipeline layout to reduce the influence of magnetic field strength on PVDF pipe, the present invention obtains PVDF composite masterbatch by modifying PVDF material itself, and then further extrudes it to obtain PVDF pipe resistant to magnetic field aging. The cost increase is minimal, but the maintenance cycle can be greatly extended and unplanned downtime can be reduced, which has extremely high economic benefits.

[0040] (4) After being subjected to accelerated aging in a simulated strong magnetic field, the PVDF tube of the present invention shows no significant attenuation in the intensity of the key chemical bond vibration peaks and the intensity of the crystallization characteristic peaks, demonstrating excellent structural stability. The superior anti-magnetic field aging performance of the PVDF tube of the present invention allows it to maintain excellent stability even under harsh conditions such as strong magnetic fields, high water flow rates, and high temperatures when used as a conveying pipe in a converter valve cooling system, thereby improving the stability and effectiveness of the converter valve cooling system. Attached Figure Description

[0041] Figure 1 The image shows the FTIR images of the PVDF tube resistant to magnetic field aging in Example 1 before and after magnetic field exposure. Figure 2 The XRD patterns of the PVDF tube resistant to magnetic field aging in Example 1 before and after magnetic field exposure are shown. Figure 3 The FTIR images of the PVDF tube in Comparative Example 1 before and after magnetic field exposure are shown. Figure 4 The image shows the XRD patterns of the PVDF tube in Comparative Example 1 before and after exposure to a magnetic field. Detailed Implementation

[0042] To enable those skilled in the art to more clearly understand this application, the present invention will be further described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. In the description of the present invention, it should be noted that unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments used that do not specify the manufacturer are all commercially available conventional products.

[0043] The PVDF resin and antimagnetic material used in the embodiments of this invention are all commercially available products, and this invention does not impose any particular limitations. Specifically, the weight-average molecular weight of the PVDF resin should be 300,000~450,000, and the melt flow rate should be 8~40 g / 10 min (tested according to ASTM D1238, test conditions: 230℃ / 5.0 kg). Furthermore, to better illustrate the present invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In some embodiments, materials, methods, and means well-known to those skilled in the art are not described in detail in order to highlight the spirit of the present invention.

[0044] Example 1 A PVDF pipe resistant to magnetic field aging is obtained by extrusion molding of PVDF composite masterbatch resistant to magnetic field aging. The raw materials for preparing the PVDF composite masterbatch resistant to magnetic field aging consist of PVDF resin and antimagnetic material; wherein the antimagnetic material is spherical bismuth powder with an average particle size of 50µm, and the mass of the spherical bismuth powder accounts for 0.2% of the mass of the PVDF composite masterbatch resistant to magnetic field aging.

[0045] The above-mentioned PVDF tubes resistant to magnetic field aging are prepared using the following method: S1: PVDF resin powder and spherical bismuth powder with an average particle size of 50µm are mixed in a high-speed mixer at 1600rpm for 15min to obtain a premix. S2: The premixed material from step S1 is fed into a twin-screw extruder, melt-mixed, extruded, water-cooled, and pelletized at a temperature range of 195-210℃ and a speed of 250 rpm to obtain PVDF composite masterbatch resistant to magnetic field aging. S3: The PVDF composite masterbatch with magnetic field aging resistance from step S2 is fed into a single-screw pipe extruder and extruded at 200-215℃ and 25rpm. Then, it is cooled, drawn, and cut to a fixed length to obtain the PVDF pipe with magnetic field aging resistance.

[0046] Example 2 This embodiment provides a PVDF pipe resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic material in this embodiment is spherical antimony powder with an average particle size of 10µm, and the mass of the spherical antimony powder accounts for 0.5% of the mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0047] Example 3 This embodiment provides a PVDF tube resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic material in this embodiment is spherical gallium powder with an average particle size of 150µm, and the mass of the spherical gallium powder accounts for 0.05% of the mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0048] Example 4 This embodiment provides a PVDF pipe resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic material in this embodiment is spherical tin powder with an average particle size of 5µm, and the mass of the spherical tin powder accounts for 0.6% of the mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0049] Example 5 This embodiment provides a PVDF pipe resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic material in this embodiment is spherical bismuth powder with an average particle size of 1µm, and the mass of the spherical bismuth powder accounts for 0.3% of the mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0050] In this embodiment, the average particle size of the spherical bismuth powder is only 1µm, which is an ultrafine powder, and it is more uniformly dispersed in the PVDF resin matrix.

[0051] Example 6 This embodiment provides a PVDF pipe resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic material in this embodiment is spherical antimony powder with an average particle size of 100µm, and the mass of the spherical antimony powder accounts for 0.76% of the mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0052] Example 7 This embodiment provides a PVDF tube resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic materials in this embodiment are spherical bismuth powder with an average particle size of 50µm and spherical tin powder with an average particle size of 10µm. The mass of the spherical bismuth powder accounts for 0.25% of the total mass of the PVDF tube resistant to magnetic field aging, and the mass of the spherical tin powder accounts for 0.1% of the total mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0053] Example 8 This embodiment provides a PVDF tube resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic materials are spherical antimony powder with an average particle size of 80µm and spherical bismuth powder with an average particle size of 30µm. The mass of the spherical antimony powder accounts for 0.3% of the total mass of the PVDF tube resistant to magnetic field aging, and the mass of the spherical bismuth powder accounts for 0.2% of the total mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0054] Example 9 This embodiment provides a PVDF pipe resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic material in this embodiment is spherical bismuth powder (70% of the powder has an average particle size of 5 μm, and 30% has an average particle size of 120 μm), and the mass of the spherical bismuth powder accounts for 0.4% of the mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0055] Example 10 This embodiment provides a PVDF pipe resistant to magnetic field aging. The difference between this embodiment and Embodiment 1 is that the antimagnetic material in this embodiment is spherical antimony powder with an average particle size of 20µm, and the mass of the spherical antimony powder accounts for 0.01% of the mass of the PVDF composite masterbatch resistant to magnetic field aging. All other aspects are the same as in Embodiment 1.

[0056] Comparative Example 1 This comparative example provides a PVDF pipe, which is prepared using the following method: S1: PVDF resin powder is fed into a twin-screw extruder, melt-mixed, extruded, water-cooled, and pelletized at a temperature range of 195~210℃ and a speed of 250 rpm to obtain PVDF masterbatch; S2: The PVDF masterbatch from step S1 is fed into a single-screw pipe extruder and extruded at 200~215℃ and 25rpm. Then, it is cooled, drawn, and cut to a fixed length to obtain the PVDF pipe.

[0057] Performance testing The PVDF pipe to be tested was processed into blocks (5mm in length, 5mm in width, and 5mm in thickness). Before testing, the samples were dried at 60℃ for 12 hours, and FTIR and XRD tests were performed on smooth surfaces.

[0058] Fourier Transform Infrared (FTIR) spectroscopy: Tests were performed using an IRTracer-100 Fourier Transform Infrared Spectrometer (SHIMADZU, Japan). The scanning range was 400–1600 cm⁻¹. 1 It employs total internal reflection (ATR) mode. 976cm -1 (Corresponding to the out-of-plane rocking vibration peak of CH2) and 796 cm⁻¹ -1 The CH2 in-plane rocking vibration peak is a unique characteristic peak of PVDF. The evolution of PVDF before and after exposure to a magnetic field can be judged based on the intensity change of the characteristic peak, and the stability of chemical bonds can be evaluated.

[0059] X-ray diffraction (XRD) analysis: A D8 Advance X-ray diffractometer (Bruker, Germany) was used, with an operating voltage of 40 kV and an operating current of 40 mA. A copper target was used, with λ = 0.1542 nm. The scanning speed was 10° / min, and the scanning range was 5°~90°. The diffraction peaks of PVDF at 18.3° (corresponding to the (020) crystal plane) and 19.9° (corresponding to the (110) crystal plane) are the strong characteristic peaks of the XRD curve. The changes in the intensity of the characteristic peaks at specific crystal planes of 18.3° and 19.9° before and after exposure to a magnetic field were measured to evaluate the stability of the crystal structure.

[0060] The PVDF tubes of Examples 1-10 (resistant to magnetic field aging) and Comparative Example 1 (PVDF tube) were analyzed using the FTIR and XRD tests described above to obtain the intensity of characteristic peaks. Then, the PVDF tubes of Examples 1-10 (resistant to magnetic field aging) and Comparative Example 1 (PVDF tube) were exposed to a magnetic field (with a frequency of 150 kHz and a strength of 105 dB, equivalent to the magnetic field strength in the converter valve hall environment) for 8760 hours, maintained at a constant temperature of 24.8–25.2 °C. The PVDF tubes after magnetic field exposure were then analyzed using FTIR and XRD tests to obtain the intensity of characteristic peaks. The ratio of the intensity of the characteristic peak of the PVDF after magnetic field exposure to the intensity of the characteristic peak of the PVDF without magnetic field exposure is the characteristic peak intensity retention rate.

[0061] The PVDF pipes of Examples 1-10 and Comparative Example 1 were used at 976 cm⁻¹ -1 and 796cm -1 The characteristic peak intensity retention rates, and the characteristic peak intensity retention rates at 18.3° and 19.9° are shown in Table 1. The FTIR spectra of the PVDF tube resistant to magnetic field aging in Example 1 before and after magnetic field exposure are shown in Table 1. Figure 1 As shown, the XRD patterns of the PVDF tube resistant to magnetic field aging in Example 1 before and after magnetic field exposure are as follows. Figure 2 As shown, the FTIR spectra of the PVDF tube in Comparative Example 1 before and after magnetic field exposure are as follows. Figure 3 As shown, the XRD patterns of the PVDF tube in Comparative Example 1 before and after magnetic field exposure are as follows. Figure 4 As shown.

[0062] Table 1. Characteristic peak intensity retention rate of different PVDF tubes

[0063] From Table 1 and Figures 1-4As can be seen, compared with Comparative Example 1, the PVDF pipes of Examples 1-10 exhibited higher retention rates of key chemical bond vibration peaks and crystallization characteristic peaks after accelerated aging in a strong magnetic field, demonstrating excellent structural stability. This indicates that adding antimagnetic materials to the PVDF resin in Examples 1-10 of the present invention can significantly enhance the antimagnetic aging performance of PVDF pipes.

[0064] In summary, this invention incorporates an antimagnetic material into the PVDF resin matrix. This material, uniformly dispersed within the PVDF resin matrix, effectively shields or counteracts some of the effects of external strong magnetic fields on the PVDF molecular chains, significantly enhancing the antimagnetic properties of the PVDF pipe itself. The antimagnetic material specified in this invention effectively and significantly improves the antimagnetic aging resistance of the PVDF pipe even with extremely low addition amounts. This extremely low addition amount also ensures that the PVDF pipe retains its original excellent chemical corrosion resistance, electrical insulation, mechanical strength, and processing performance. The superior antimagnetic aging resistance of the PVDF pipe of this invention allows it to maintain excellent stability even under harsh conditions such as strong magnetic fields, high water flow rates, and high temperatures when used as a conveying pipe in a converter valve cooling system. This improves the stability and effectiveness of the converter valve cooling system, reduces unplanned downtime, and offers significant economic benefits.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A polyvinylidene fluoride composite master batch against magnetic field aging, characterized by, The raw materials for preparing the polyvinylidene fluoride composite masterbatch include polyvinylidene fluoride resin and antimagnetic material, wherein the antimagnetic material includes at least one of antimony, bismuth, gallium and tin; the amount of antimagnetic material added accounts for 0.01% to 1% of the total mass of the polyvinylidene fluoride composite masterbatch.

2. The anti-magnetic aging composite master batch according to claim 1, characterized in that, The average particle size of the antimagnetic material is 0.1~235μm.

3. The anti-magnetic aging composite master batch according to claim 1, characterized in that, The weight-average molecular weight of the polyvinylidene fluoride resin is 300,000 to 450,000.

4. The process for the preparation of the polyvinylidene fluoride composite masterbatch against magnetic field aging according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Premixed material is obtained by mixing polyvinylidene fluoride resin with antimagnetic material; S2: The premixed material described in step S1 is extruded and granulated to obtain the resistant magnetic field aging polyvinylidene fluoride composite masterbatch.

5. The preparation method according to claim 4, characterized in that, The extrusion granulation in step S2 is a twin-screw extrusion, and the extrusion temperature of the extrusion granulation is 180~230℃.

6. A polyvinylidene fluoride pipe resistant to magnetic field aging, characterized by The magnetic field-resistant polyvinylidene fluoride tube is obtained by extrusion molding of the magnetic field-resistant polyvinylidene fluoride composite masterbatch as described in any one of claims 1 to 3.

7. The magnetically aged polyvinylidene fluoride tube according to claim 6, characterized in that The properties of the magnetic field-resistant polyvinylidene fluoride tube after magnetic field exposure include at least one of the following: (1) The intensity retention rate of CH2vibration peak at 976 cm - was ≥ 93.2% by Fourier transform infrared spectroscopy. (2) The intensity retention rate of CH2vibration peak at 796 cm - was ≥ 93.8% by Fourier transform infrared spectroscopy. (3) The intensity retention rate of the characteristic peak at 18.3° of the crystal plane of the polyvinylidene fluoride tube, as measured by X-ray diffraction, is ≥92.8%; (4) The intensity retention rate of the characteristic peak at 19.9° of the crystal plane of the polyvinylidene fluoride tube, as measured by X-ray diffraction, is ≥91.9%; The frequency of the magnetic field is 140~160kHz, the strength of the magnetic field is 100~110dB, and the exposure time is 8000h~9000h.

8. The polyvinylidene fluoride pipe resistant to magnetic field aging according to claim 6, wherein the extrusion molding is a single-screw extrusion and the extrusion temperature is 190~230℃.

9. A converter valve cooling system, characterized by The converter valve cooling system includes the polyvinylidene fluoride tube resistant to magnetic field aging as described in any one of claims 6 to 8.

10. The application of the anti-magnetic field aging polyvinylidene fluoride tube according to any one of claims 6 to 8 or the converter valve cooling system according to claim 9 in the field of high voltage direct current transmission.

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