A radio frequency coaxial cable with phase change microcapsules

Abstract

The application relates to the technical field of radio frequency coaxial cables, in particular to a radio frequency coaxial cable with phase change microcapsules, which comprises a cable main body, the cable main body comprises an inner conductor and an outer conductor, the outer conductor is located at the outer circle of the inner conductor, a polyethylene insulation layer is arranged between the inner conductor and the outer conductor, the polyethylene insulation layer comprises a first foamed insulation layer and a second foamed insulation layer in sequence in the radial direction; the thermal conductivity coefficient of the first foamed insulation layer is greater than that of the second foamed insulation layer, and the second foamed insulation layer contains a phase change material; the thickness of the second foamed insulation layer is 50%-60% of the thickness of the first foamed insulation layer. In the case of keeping the foaming degree and electrical properties of the insulation layer, the thermal conductivity coefficient is improved, heat is controlled, and the whole cable works in an expected temperature range.

Description

Technical Field

[0001] This application relates to the field of radio frequency coaxial cable technology, and more particularly to a radio frequency coaxial cable with phase change microcapsules. Background Technology

[0002] Coaxial cables are widely used in communications, radar, broadcasting, and other fields, with low signal loss and stable temperature control being their core requirements. Currently, most coaxial cables use foamed materials as the insulation layer, which presents the following main problems:

[0003] 1. Although the dielectric loss under high foaming degree is significantly reduced compared to conductors with solid insulation layer, and the thermal coefficient is significantly reduced, even if the heat generated is very low, the heat cannot actually be quickly transferred to the surface of the cable because it is not a conductor of heat. The high foaming degree insulation material forms thermal resistance, which leads to heat accumulation.

[0004] Second, under high foaming degree, if the size of the foam formed is uneven, for example, at a foaming degree greater than 80%, the heat conduction in the length direction is not uniform. This further leads to the accumulation of heat and the formation of hot spots in local areas, which accelerates the aging of the medium at the corresponding location and may even cause breakdown.

[0005] In addition, high foaming degree leads to increased costs and requires the use of complex processes. Therefore, balancing the complexity of the process and the electrical performance of the product has become a problem that needs to be solved. Summary of the Invention

[0006] At least one aspect and advantage of this application will be set forth in part in the description which follows, or may be apparent from the description.

[0007] According to one aspect of this application, a radio frequency coaxial cable with phase change microcapsules is provided, comprising a cable body, the cable body including an inner conductor and an outer conductor, the outer conductor being located around the inner conductor, and a polyethylene insulation layer disposed between the inner conductor and the outer conductor, the polyethylene insulation layer comprising, in radial order, a first foamed insulation layer and a second foamed insulation layer; the thermal conductivity of the first foamed insulation layer is greater than that of the second foamed insulation layer, and the second foamed insulation layer contains a phase change material; the thickness of the second foamed insulation layer is 50%-60% of the thickness of the first foamed insulation layer.

[0008] According to one embodiment of this application, the first foamed insulation layer contains a first filler and a second filler, wherein the first filler is micro-nano boron nitride and the second filler is nano-sized boron nitride particles; the total addition ratio of the first filler and the second filler is 1%-2%.

[0009] According to one embodiment of this application, the ratio of the first packing material to the second packing material is from 10:1 to 50:1.

[0010] According to one embodiment of this application, the first filler comprises sheet-like boron nitride and spherical boron carbide.

[0011] According to one embodiment of this application, the second foamed insulating layer contains phase change microcapsules, the phase change microcapsules contain phase change material, and the phase change material is wrapped by a first polymer film and a second polymer film, the first polymer film and the second polymer film have the same composition; the phase change material is an inorganic salt with a melting point between 80 and 230 degrees Celsius.

[0012] According to one embodiment of this application, the phase change material is a molten salt with a melting point of 80-160°C.

[0013] According to one embodiment of this application, the first polymer film and the second polymer film are polyacrylate films.

[0014] According to one embodiment of this application, the diameter of the phase change microcapsules is 0.1-0.2 mm.

[0015] According to one embodiment of this application, the thickness of the first foamed insulation layer is 1-5 mm.

[0016] According to one embodiment of this application, the foaming degree of the first foamed insulation layer is greater than that of the second foamed insulation layer.

[0017] This application embodiment, while maintaining the foaming degree and electrical properties of the insulation layer, improves its thermal conductivity to achieve heat control, thereby enabling the entire cable to operate within a desired temperature range. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] Figure 1 A schematic diagram of the cross-sectional structure of a radio frequency coaxial cable with phase change microcapsules provided in one embodiment of this application;

[0020] Figure 2 This is a schematic cross-sectional view of a radio frequency coaxial cable with phase change microcapsules provided in one embodiment of this application. Detailed Implementation

[0021] The content of this application will now be discussed with reference to several exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and thus implement the content of this application, and are not intended to imply any limitation on the scope of this application.

[0022] As used herein, the term "comprising" and its variations are to be interpreted as open-ended terms meaning "including but not limited to". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment". The term "another embodiment" is to be interpreted as "at least one other embodiment". Those skilled in the art will understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, the terms "first", "second", etc., are primarily used to distinguish different components (the specific types and structures may be the same or different) and are not intended to indicate or imply the relative importance and quantity of the indicated components.

[0023] According to one embodiment of this application, a radio frequency coaxial cable with phase change microcapsules is provided, such as... Figure 1 and Figure 2 As shown, the radio frequency coaxial cable 100 with phase change microcapsules includes a cable body, which includes an inner conductor 1 and an outer conductor 3. The outer conductor 3 is located on the outer ring of the inner conductor 1. A polyethylene insulation layer 2 is disposed between the inner conductor 1 and the outer conductor 3. The polyethylene insulation layer includes a first foamed insulation layer 21 and a second foamed insulation layer 22 in radial order. The thermal conductivity of the first foamed insulation layer 21 is greater than that of the second foamed insulation layer 22, and the second foamed insulation layer 22 contains a phase change material. The thickness of the second foamed insulation layer 22 is 50%-60% of the thickness of the first foamed insulation layer 21.

[0024] Specifically, the inner conductor is typically made of a highly conductive metal such as copper or aluminum. Due to the skin effect, current flows on the surface of the conductor; therefore, the inner conductor can be made of commonly used copper wire or copper-clad aluminum wire. To reduce the weight of the cable, a copper tube can also be used as the inner conductor, thus reducing the cable's weight and cost while maintaining conductivity. The inner conductor serves as the carrier for signal transmission, and the signal current flows within it.

[0025] Specifically, the process of preparing the inner conductor may include: drawing a copper rod through a wire drawing machine step by step to achieve the radius required by the design; and then performing an annealing treatment to obtain the inner conductor used to prepare the coaxial cable.

[0026] Specifically, the outer conductor typically uses a seamless corrugated copper tube or longitudinally welded aluminum tube, which have excellent sealing properties, to prevent moisture, dust and other environmental media from entering the cable, thus avoiding moisture aging of the insulation layer and extending the cable's service life in outdoor, underground and other environments.

[0027] In some embodiments, the outer conductor can also be formed by winding a dense metal wire; or by seamlessly soldering a metal foil (e.g., copper foil) around the outside of the insulator. In most instances, the thickness of the outer conductor is not limited, as the current flows inside it and can be set as needed, for example, in the range of 0.1-0.5 mm.

[0028] The polyethylene insulation layer of this application includes a first foamed insulation layer and a second foamed insulation layer. The first foamed insulation layer is located between the inner conductor and the second foamed insulation layer, and the second foamed insulation layer is located between the first foamed insulation layer and the outer conductor. The thermal conductivity of the first foamed insulation layer is greater than that of the second foamed insulation layer. The first and second foamed insulation layers serve to reduce the dielectric constant, reduce signal loss, improve thermal insulation performance, optimize impedance characteristics, and improve flexibility and reduce weight. The thickness of the second foamed insulation layer is 50%-60% of the thickness of the first foamed insulation layer. When heat is transferred to the second foamed insulation layer, the phase change material within the microcapsules absorbs heat and undergoes a phase change, delaying the heat accumulation problem in the inner conductor and insulation layer, thus controlling the overall temperature of the cable and ensuring signal transmission stability. Although the overall thermal conductivity is relatively low due to the large foaming coefficient, and heat transfer is slower, the second foamed insulation layer can maintain the temperature of the outer conductor side within a relatively stable range to a certain extent and forms a temperature gradient, allowing heat from the inner conductor to be dissipated.

[0029] The first foamed insulation layer in this application uses a high foaming coefficient. A high foaming coefficient maintains the characteristic impedance stability of the coaxial cable, ensuring signal transmission quality. The high foaming degree reduces energy loss during signal transmission, which is crucial for the transmission of medium and high frequency signals, and also reduces dielectric loss. When used in conjunction with the foaming gas, it also maintains a stable dielectric constant.

[0030] The typical process for preparing the foamed layer is as follows:

[0031] The matrix material used to prepare the first foamed insulation layer and high-pressure gas (such as nitrogen or carbon dioxide) are injected into an extruder under high pressure. Then, by controlling the extrusion temperature and pressure, the molten plastic forms a uniform and dense closed-cell structure at high temperature, thereby achieving a high degree of foaming. This embodiment mainly involves the preparation process of the first and second foamed insulation layers. Low-temperature extrusion (e.g., 160-190℃) and nitrogen foaming processes can be used. Performance differences can be achieved by adjusting the foaming pressure (e.g., selecting 370 bar-200 bar and optimizing according to actual performance) and fillers. The process parameters are unified, facilitating industrial mass production.

[0032] In practice, the molten polyethylene formed under high temperature and high pressure in the extruder mixes and fuses with the injected foaming gas to form a uniform melt. The melt gradually releases pressure and temperature in the die head, and the foaming gas gradually dissipates from the inside to the outside. With the help of the nucleating components, the foaming material mixture forms fine pores and captures the foaming gas, ultimately forming a lightweight, high-foaming insulation layer structure.

[0033] If the amount of foaming gas is large during the above process, its dissipation becomes uncontrollable, which in turn affects the final performance.

[0034] To reduce the risk of cell rupture during the foaming process and ensure small, uniform, and closed-cell structures, the foaming degree was adjusted and controlled below 85%, preferably below 82%, and particularly within the range of 60-80%. Within this range, the drawback of increased unit product costs due to more stringent processing techniques is avoided.

[0035] In some embodiments, medium-density polyethylene or low-density polyethylene can be used to foam the first foamed insulation layer, and the first foamed insulation layer contains a small amount of boron nitride (BN) dispersion. Here, the BN dispersion is made by dispersing boron nitride into a hot melt adhesive such as ethylene acetate polymer (EVA) resin through mechanical mixing. During mixing, a larger BN addition ratio can be selected, such as forming an addition ratio of more than 20 wt% (e.g., 20-30%). Then, the BN dispersion is mixed with the polyethylene to be foamed in the required ratio and foamed.

[0036] In some embodiments, the radio frequency coaxial cable with phase change microcapsules further includes an inner sheath layer located between the inner conductor and the first foamed insulation layer.

[0037] Specifically, the first foamed insulation layer can be prepared directly on the surface of the inner conductor, or the insulation material can be foamed on the inner skin layer that is in direct contact with the inner conductor. This application embodiment uses the method of directly foaming the insulation material on the surface of the inner conductor to form the first foamed insulation layer. In the embodiment where the insulation material is foamed on the inner skin layer that is in direct contact with the inner conductor, the inner skin layer can be a polyethylene insulation layer. In application, this inner skin layer can be extruded at a high temperature (220°C); then the first foamed insulation layer can be prepared on the inner skin layer; or the inner skin layer can be a separate structure tightly wrapped around the inner skin layer. In application, a suitable material can be selected according to the required performance requirements of the inner skin layer. For example, low-density polyethylene and EVA adhesive can be mixed in a certain proportion, then heated to 120-195°C to make the material reach an extrudable molten state. Then, the heated and molten inner skin layer material is uniformly extruded onto the surface of the inner conductor through an extruder screw. Controlling extruder parameters, such as extrusion speed and temperature, ensures the inner skin layer has a uniform thickness that meets requirements. Generally, the inner skin layer thickness can be controlled between 0.05-0.1 mm. After extrusion, the inner skin layer is cooled using methods such as air cooling to rapidly solidify and shape it, forming a stable structure. At this point, the inner conductor with the inner skin layer is complete. Subsequently, it is processed according to the polyethylene insulation layer preparation process. Preparing the first foamed insulation layer on the inner skin layer avoids major modifications to existing processes and preserves the original performance to the greatest extent possible.

[0038] In this application, the phase change material generally uses molten salt-based inorganic materials. In practical applications, the phase change microcapsule preparation process includes: grinding and sieving a ternary molten salt (e.g., a molten salt with a melting point of 130 degrees Celsius, specifically a ternary eutectic system formed by sodium nitrate, potassium nitrate, and sodium nitrite) to obtain particles with a particle size no larger than 200 mesh; then granulating the particles by adding a solution of a non-ionic polymer (e.g., polyethylene, polystyrene); after granulation, removing the solvent, washing with deionized water, and drying; then performing a second granulation using the polymer solution. When preparing phase change microcapsules, the product particle size should not be too low, ideally controlled between 50-100 micrometers, otherwise the amount of molten salt encapsulated will be limited; if it is too large, it will affect the extrusion process. It should be noted that the temperature of the ternary molten salt in this application should be set according to actual needs, i.e., the actual thermal pulse peak should ensure that the temperature reached by the outer conductor is higher than the phase change point of the molten salt; otherwise, the molten salt cannot play a role in temperature equalization on the outer conductor side. Furthermore, since the extrusion temperature and the melting point of the molten salt are relatively close, in order to protect the basic stability of the molten salt structure and avoid the exposure of the molten salt leading to corrosion of the second foamed insulation layer at high temperatures, the phase change microcapsules should maintain a small particle size range to avoid damage during processing. After the melt is cooled as a whole, the molten salt is fixed in the system by both the encapsulated polymer medium and the foaming system, resulting in good stability.

[0039] In some embodiments of this application, the phase change microcapsules have a size of 100-150 micrometers, which balances the requirements for process difficulty and stability. If the upper limit is met, microcapsules with a size of 50-100 micrometers can be prepared, resulting in even better performance. Ternary and quaternary molten salts can be used as the molten salts in this application, with melting points varying between 120-150°C depending on the proportion. Binary molten salts with a melting point of 118°C can also be used in this application.

[0040] For better implementation, this application uses medium-pressure foaming and low-temperature extrusion. Under normal circumstances, heat is conducted to the second foamed insulation layer without causing a temperature change, and the molten salt does not act as a heat storage agent. However, in the event of instantaneous overheating, the heat causes a phase change in the molten salt, thus maintaining a constant temperature. After the heat peak disappears, the molten salt slowly releases heat. This allows the cable to maintain a relatively stable temperature, especially within the insulation layer where heat dissipation is difficult, even in extremely confined and poorly ventilated environments. With the aid of an external cold source, the cable temperature can be kept essentially stable.

[0041] According to one embodiment of this application, the first foamed insulating layer contains a first filler and a second filler. The first filler is micro / nano-sized boron nitride, and the second filler is nano-sized boron nitride particles. The total addition ratio of the first and second fillers is 1%-2%. Boron nitride itself is a high-insulation, low-dielectric-loss material. Using two types of boron nitride (BN) with complementary sizes can form complex pathways, which can radially conduct and spread out the dense heat (skin effect hotspots) on the inner surface of the outer conductor, and reduce local temperature peaks to a certain extent. Excessive addition ratio of the two types of boron nitride will affect the foaming process. Therefore, this application sets the ratio to 1%-2%, which neither changes the overall insulation characteristics of the first foamed insulating layer nor affects its electrical performance, ensuring the stability of the dielectric properties of the insulating layer and not increasing the transmission loss of radio frequency signals. In this embodiment, the total addition ratio of the first and second fillers is set to 2%, with a thermal conductivity exceeding 0.05 W / mK. Although this value is still low, it is an improvement over the original foamed layer's thermal conductivity and avoids affecting the foaming process.

[0042] According to one embodiment of this application, the ratio of the first filler to the second filler is 10:1 to 50:1. Since micro / nano-sized boron nitride is larger, it is easier to construct a core heat conduction path that runs through the first foamed insulation layer. However, nano-sized boron nitride particles are generally more expensive due to their finer manufacturing process and smaller particle size. Therefore, this ratio can significantly reduce the amount of the high-cost second filler, using the low-cost first filler as the main component to construct the heat conduction network. This minimizes the overall material cost of the first foamed insulation layer without sacrificing thermal conductivity.

[0043] When using boron nucleus (BN) as a filler, it can be mixed with EVA resin, and then mixed with polyethylene before foaming. Because BN contains small particles, no nucleating materials are needed in this process. Furthermore, during foam formation, the BN particles are distributed on the foam wall or adjacent sites of the foam. The overall foaming degree of the resulting product can reach 75-80%, with fewer irregular foams. However, the thermal conductivity of the foam obtained by using only spherical BN particles does not change significantly. For example, with a 75% foaming rate and 2% BN addition, the measured thermal conductivity is 0.012 W / mK, which does not meet our expectations. To improve… To improve thermal conductivity, we used a combination of various BN morphologies, covering BN particles ranging from flakes and spheres to micron- to nano-sized particles. We found that at low addition ratios, it can avoid affecting the foaming process and achieve a thermal conductivity exceeding 0.05 W / mK, specifically corresponding to an overall BN addition ratio of 2 wt%, where the ratio of the first filler to the second filler is 10:1 to 50:1. The first filler is used to form high thermal conductivity regions on the foam wall, while the nanoparticles are used for foaming and to form thermal conductivity pathways between high thermal conductivity regions, thereby achieving a thermal conductivity exceeding that of the foam material and thus achieving a balance between thermal conductivity and electrical performance.

[0044] According to one embodiment of this application, the first filler comprises sheet-like boron nitride and spherical boron carbide. Specifically, sheet-like boron nitride or spherical boron carbide can be used, or both can be used simultaneously. This embodiment uses both forms simultaneously, so that after the sheet-like filler forms a continuous macroscopic thermal conduction path in the insulating layer, the spherical boron carbide can be filled into the gaps formed by the stacked sheet-like boron nitride, making the sheet-like boron nitride more uniformly distributed in the substrate, thus avoiding the non-uniformity defects of using only sheet-like filler.

[0045] According to one embodiment of this application, the second foamed insulating layer contains phase change microcapsules, which contain a phase change material. The phase change material is encapsulated by a first polymer film and a second polymer film, the first and second polymer films having the same composition. The phase change material is an inorganic salt with a melting point between 80-230 degrees Celsius. Since the phase change material (inorganic salt) changes from a solid to a liquid state when it reaches its melting point (80-230°C), direct addition could easily lead to leakage. Therefore, by encapsulating it with the first and second polymer films, liquid microcapsules can be formed even at high temperatures, but because the outer shell prevents leakage, and the liquid state does not change the overall fluidity of the substrate, it avoids affecting the extrusion process.

[0046] According to one embodiment of this application, the phase change material is a molten salt with a melting point of 80-160°C. Most organic phase change materials are prone to crystallization at low temperatures due to decreased solubility, leading to uneven material distribution and decreased phase change performance. Molten salt, however, has a stable solid structure and good compatibility with the microencapsulated polymer film. It can maintain a uniform solid dispersion in low-temperature environments (e.g., ambient temperature < 80°C), ensuring long-term preservation and functional stability of the phase change material. Furthermore, the melting point range of 80-160°C matches the typical heating temperatures of applications such as cables and electronic components, ensuring that the molten salt melts and absorbs heat promptly when the temperature reaches the threshold, achieving heat regulation. On the other hand, the viscosity of liquid molten salt makes it more difficult to penetrate the capsule wall, preventing material leakage and contamination of the substrate, as well as affecting insulation or structural performance, even in a high-temperature phase change state.

[0047] According to one embodiment of this application, the first polymer film and the second polymer film are polyacrylate films. Since the processing temperature of cable insulation layers is typically 150-250°C, if the film's high-temperature resistance is insufficient during high-temperature extrusion, it is prone to softening, melting, or even cracking, leading to the exposure of the internal phase change material (or particles). Therefore, this application uses a chemically stable double-layer polyacrylate film, which can reduce the probability of encapsulation failure caused by high temperature and high pressure, prevent the phase change microcapsules from being destroyed, and ensure that the phase change material remains in a stable encapsulated state.

[0048] According to one embodiment of this application, the diameter of the phase change microcapsule is 0.1-0.2 mm. This setting simultaneously considers the amount of molten salt encapsulated and the extrusion process, avoiding the impact of the encapsulation amount of molten salt due to the microcapsule being too small, while preventing the extrusion process from being too large. Specifically, the diameter of the phase change microcapsule can be set according to the ratio of the thickness of the second foamed insulating layer to the thickness of the first foamed insulating layer. For example, in some embodiments, when the thickness of the second foamed insulating layer is 50% of the thickness of the first foamed insulating layer, the diameter of the phase change microcapsule is set to 0.1 mm; when the thickness of the second foamed insulating layer is 55% of the thickness of the first foamed insulating layer, the diameter of the phase change microcapsule is set to 0.15 mm; and when the thickness of the second foamed insulating layer is 60% of the thickness of the first foamed insulating layer, the diameter of the phase change microcapsule is set to 0.2 mm. Considering the increase in the thickness of the second foamed insulating layer, the diameter of the phase change microcapsule can be appropriately increased to increase the molten salt capacity without affecting the extrusion process. Experiments have shown that when the particle size of phase change microcapsules is below 0.1 mm, the processing does not damage the stability of their structure. Furthermore, when the particle size is between 0.01 and 0.05 mm, due to their more uniform dispersion, they have a better absorption effect on the heat peak of the outer conductor side and a lower possibility of breakage.

[0049] According to one embodiment of this application, the foaming degree of the first foamed insulation layer is greater than that of the second foamed insulation layer. The high foaming degree of the first foamed insulation layer effectively reduces losses, while the low foaming degree of the second foamed insulation layer prevents damage to the first foamed insulation layer caused by the high foaming degree of the second foamed insulation layer, thus avoiding impact on electrical performance. In some embodiments, the foaming degree of both the first and second foamed insulation layers is generally set to no more than 90%, for example, the foaming degree of the first foamed insulation layer is 85% and the foaming degree of the second foamed insulation layer is 75%. This reduces dielectric loss in signal transmission, improves withstand voltage performance, and prevents damage to the first foamed insulation layer due to pressure differences during the manufacturing process. It also improves cable flexibility and avoids the problem of excessive cable rigidity leading to deformation under external pressure, which can affect electrical performance.

[0050] The following is a specific embodiment to illustrate the fabrication process of the radio frequency coaxial cable with phase change microcapsules of this application.

[0051] Example 1:

[0052] 1. Preparation of the first melt: BN filler and EVA resin are mixed evenly at a mass ratio of 1:3 and then foamed with medium-density polyethylene, with the total addition ratio of BN filler being 1.5%. The foaming temperature is 180℃, the foaming pressure is 220 bar, the foaming gas is N2, and no nucleating agent is added. The BN filler includes the first filler, which is micro-nano BN particles or BN flakes with a particle size of 100 nanometers to 1.5 micrometers and a D50 of 300 nm; and the second filler, which is BN particles with a particle size of 50-100 nanometers.

[0053] 2. Preparation of the second melt:

[0054] The ternary molten salt with a melting point of 135℃ was ground to obtain a particle size of about 200 mesh, and then granulated once using a toluene solution of ethylene-vinyl acetate copolymer (EVA); the solvent was then removed, and the mixture was washed with deionized water and dried.

[0055] Subsequently, the product from the first granulation was subjected to a second granulation to obtain phase change microcapsules; the particle size of the final product was controlled to not exceed 150 micrometers during the granulation process.

[0056] Phase change microcapsules, EVA resin and low-density polyethylene are mixed by a planetary mill and then foamed at a foaming pressure of 200 bar and a foaming temperature of 165 degrees Celsius.

[0057] Then, a series extrusion process was used to first extrude 0.5 mm of high-density foamed polyethylene as the inner skin layer onto the inner conductor with a radius of 3 mm.

[0058] Then, the first foamed insulation layer is extruded onto the inner skin layer, with the extruder head temperature at 180℃;

[0059] Then, a second foamed insulation layer is extruded onto the first foamed insulation layer, with the extruder head temperature at 155℃.

[0060] Then, the wrapped inner conductor is inserted into the outer conductor, and then the outer conductor is stretched to make them bonded.

[0061] Then, an outer sheath is wrapped around the outer conductor to prepare a coaxial cable.

[0062] Testing of the cable revealed that when transmitting a 3.0 GHz signal, the temperature of the outer conductor was affected by factors such as dielectric loss and heat dissipation from the inner conductor. With existing cables, the outer conductor reached 135 degrees Celsius in 30 minutes; however, the cable of this application reached this temperature slightly later, with a delay of approximately 10 seconds. This demonstrates that the design of this application enables the cable to possess certain high-temperature operating performance. Furthermore, actual measurements showed that under low load, the temperature of the cable's outer sheath decreased more slowly, indicating that the ambient temperature remained essentially stable.

[0063] Example 2:

[0064] 1. Preparation of the first melt: BN filler and EVA resin are mixed evenly at a mass ratio of 1:3 and then foamed with medium-density polyethylene, with the total addition ratio of BN filler being 1.5%. The foaming temperature is 180℃, the foaming pressure is 220 bar, the foaming gas is N2, and no nucleating agent is added. The BN filler includes the first filler, BN particles or BN flakes with a particle size of 500 nanometers to 1.5 micrometers; and the second filler, BN particles with a particle size of 50-100 nanometers.

[0065] 2. Preparation of the second melt:

[0066] The ternary molten salt with a melting point of 135℃ was ground to obtain a particle size of about 200 mesh, and then granulated once using a toluene solution of ethylene-vinyl acetate copolymer (EVA); the solvent was then removed, and the mixture was washed with deionized water and dried.

[0067] Subsequently, the product from the first granulation was subjected to a second granulation to obtain phase change microcapsules; the particle size of the final product was controlled within the range of 100-150 micrometers during the granulation process.

[0068] Phase change microcapsules, EVA resin and low-density polyethylene are mixed by a planetary mill and then foamed at a foaming pressure of 200 bar and a foaming temperature of 160 degrees Celsius.

[0069] Then, a series extrusion process was used to first extrude 0.5 mm of high-density foamed polyethylene as the inner skin layer onto the inner conductor with a radius of 3 mm.

[0070] Then, the first foamed insulation layer is extruded onto the inner skin layer, with the extruder head temperature at 180℃;

[0071] Then, a second foamed insulation layer is extruded onto the first foamed insulation layer, with the extruder head temperature at 155℃.

[0072] Then, the wrapped inner conductor is inserted into the outer conductor, and then the outer conductor is stretched to make them bonded.

[0073] Then, an outer sheath is wrapped around the outer conductor to prepare a coaxial cable.

[0074] Testing of the cable revealed that when transmitting a 1.5GHz signal, the temperature of the outer conductor was affected by factors such as dielectric loss and heat dissipation from the inner conductor. With existing cables, the outer conductor reached 135 degrees Celsius in 3 minutes; however, the cable of this application reached this temperature slightly later, with a delay of approximately 5 seconds. This indicates that the design of this application enables the cable to possess certain high-temperature operating performance, and due to the increased particle size, the phase transition process inside the outer conductor and heat transfer within the insulation layer are slightly reduced. Furthermore, actual measurements showed that under low load, the temperature of the cable's outer sheath decreased more slowly, meaning the ambient temperature remained essentially stable.

[0075] Example 3:

[0076] 1. Preparation of the first melt: BN filler and EVA resin are mixed evenly at a mass ratio of 1:3 and then foamed with medium-density polyethylene, with the total addition ratio of BN filler being 1.5%. The foaming temperature is 180℃, the foaming pressure is 220 bar, the foaming gas is N2, and no nucleating agent is added.

[0077] 2. Preparation of the second melt: The BN filler includes a first filler, BN particles or BN flakes with a particle size of 100 nanometers to 1.5 micrometers; and a second filler, BN particles with a particle size of less than 100 nanometers;

[0078] The ternary molten salt with a melting point of 160℃ was ground to obtain a particle size of about 200 mesh, and then granulated once using a toluene solution of ethylene-vinyl acetate copolymer (EVA); the solvent was then removed, and the mixture was washed with deionized water and dried.

[0079] Subsequently, the product from the first granulation was subjected to a second granulation to obtain phase change microcapsules; the particle size of the final product was controlled to not exceed 150 micrometers during the granulation process.

[0080] Phase change microcapsules, EVA resin and low-density polyethylene are mixed by a planetary mill and then foamed at a foaming pressure of 200 bar and a foaming temperature of less than 150 degrees Celsius.

[0081] Then, a series extrusion process was used to first extrude 0.5 mm of high-density foamed polyethylene as the inner skin layer onto the inner conductor with a radius of 3 mm.

[0082] Then, the first foamed insulation layer is extruded onto the inner skin layer, with the extruder head temperature at 180℃;

[0083] Then, a second foamed insulation layer is extruded onto the first foamed insulation layer, with the extruder head temperature at 155℃.

[0084] Then, the wrapped inner conductor is inserted into the outer conductor, and then the outer conductor is stretched to make them bonded.

[0085] Then, an outer sheath is wrapped around the outer conductor to prepare a coaxial cable.

[0086] Testing of the cable revealed that when transmitting a 1.5GHz signal, the temperature of the outer conductor was affected by factors such as dielectric loss and heat dissipation from the inner conductor. With existing cables, the outer conductor reached 135 degrees Celsius in 3 minutes; however, the cable of this application reached this temperature slightly later, with a delay of approximately 15 seconds. This indicates that the design of this application enables the cable to possess certain high-temperature operating performance, and the reduced melting point of the molten salt causes the heat absorption process to begin earlier. Furthermore, actual measurements showed that under low load, the temperature of the cable's outer sheath decreased more slowly, meaning the ambient temperature remained essentially stable.

[0087] In the above embodiments, low-density polyethylene (LDPE) is the lightest variety of polyethylene resin, appearing as milky white, tasteless, odorless, non-toxic, and matte waxy granules. It possesses good flexibility, extensibility, electrical insulation, transparency, ease of processing, and a certain degree of air permeability. It exhibits good chemical stability, is resistant to alkalis and common organic solvents, and its density is generally 0.91-0.93 g / cm³.

[0088] In the above embodiments, high-density polyethylene (HDPE) is a white powder or granular product. It is non-toxic, odorless, has a crystallinity of 80%–90%, a softening point of 125–135°C, and a service temperature up to 100°C. Its hardness, tensile strength, and creep resistance are superior to low-density polyethylene, and its density is generally 0.941–0.960 g / cm³.

[0089] In the above embodiments, medium-density polyethylene (MDPE), abbreviated as MDPE, is a synthetic resin formed by copolymerization of ethylene and α-olefins (such as propylene, 1-butene, etc.), with a density range of 0.926-0.953 g / cm³.

[0090] In the above embodiments, the strength of the formed foamed insulation layer can be further increased by electron irradiation.

[0091] In the above embodiments, the inner conductor radius is 3mm, the outer conductor radius is 7.5mm, the inner skin layer on the surface of the inner conductor can be omitted, the overall thickness of the insulation layer can be between 4.4-4.5mm, the thickness of the first foamed insulation layer is 2.8mm, and the thickness of the second foamed insulation layer is 1.65-1.7mm; and the addition of EVA adhesive can be omitted during preparation in order to improve the foaming performance and the toughness of the foamed product. The addition of EVA can be omitted according to process requirements.

[0092] In the above embodiments, EVA is used to improve foaming performance and enhance the flexibility and foaming properties of polyethylene. The amount added can be reduced or omitted as needed. When omitted, BN can be directly dispersed in the high-temperature melt of polyethylene.

[0093] In the above process, since the first foamed insulation layer contains filler, its thermal conductivity is higher than that of the second foamed insulation layer. Furthermore, within a range of 50-60%, the thickness of the first and second foamed insulation layers can be adjusted, and retaining a larger proportion of the first foamed insulation layer can preserve the original electrical performance to the greatest extent.

[0094] During the above process, the parameters of the foaming process can be adjusted as needed to ensure that the degree of foaming meets the requirements.

[0095] It should be understood that the sequence numbers of the steps in the embodiments of this application do not absolutely imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The foregoing description of the implementation of this application has been given for illustrative and descriptive purposes. The foregoing description is not exhaustive and is not intended to limit this application to the exact form disclosed. Various modifications and variations may exist based on the above teachings, or various modifications and variations may be derived from the practice of this application. The above embodiments are specific examples of implementing this application, and in practical applications, various changes can be made in form and detail without departing from the spirit and scope of this application.

Claims

1. A radio frequency coaxial cable having phase change microcapsules, characterized by, The cable includes a cable body, which includes an inner conductor and an outer conductor. The outer conductor is located on the outer ring of the inner conductor. A polyethylene insulation layer is disposed between the inner conductor and the outer conductor. The polyethylene insulation layer includes a first foamed insulation layer and a second foamed insulation layer in radial order. The thermal conductivity of the first foamed insulation layer is greater than that of the second foamed insulation layer, and the second foamed insulation layer contains a phase change material. The thickness of the second foamed insulation layer is 50%-60% of the thickness of the first foamed insulation layer.

2. A radio frequency coaxial cable provided with phase change microcapsules according to claim 1, characterized in that, The first foamed insulation layer contains a first filler and a second filler, wherein the first filler is micro-nano boron nitride and the second filler is nano-sized boron nitride particles; The total mass ratio of the first packing and the second packing is 1%-2%.

3. A radio frequency coaxial cable provided with phase change microcapsules according to claim 2, characterized in that, The mass ratio of the first packing material to the second packing material is 10:1 to 50:

1.

4. A radio frequency coaxial cable provided with phase change microcapsules according to claim 3, characterized in that, The first filler comprises plate-shaped boron nitride and spherical boron nitride.

5. The RF coaxial cable having phase change microcapsules of claim 1, wherein, The second foamed insulating layer contains phase change microcapsules, which contain phase change materials, and the phase change materials are encapsulated by a first polymer film and a second polymer film, wherein the first polymer film and the second polymer film have the same composition. The phase change material is an inorganic salt with a melting point between 80 and 230 degrees Celsius.

6. A radio frequency coaxial cable provided with phase change microcapsules according to claim 5, characterized in that, The phase change material is an inorganic salt with a melting point of 80-160℃.

7. A radio frequency coaxial cable having phase change microspheres as claimed in claim 5, wherein, The first polymer film and the second polymer film are polyacrylate films.

8. A radio frequency coaxial cable having phase change microspheres as claimed in claim 5, wherein, The phase change microcapsules have a diameter of 0.1-0.2 mm.

9. The RF coaxial cable having phase change microspheres of claim 1 wherein, The thickness of the first foamed insulation layer is 1-5 mm.

10. The RF coaxial cable having phase change microspheres of claim 1 wherein, The foaming degree of the first foamed insulation layer is greater than that of the second foamed insulation layer.

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