High-temperature-resistant silicon dioxide insulated leaky coaxial cable and preparation process thereof

Abstract

The invention relates to a high-temperature-resistant silicon dioxide insulated leaky coaxial cable and a preparation process thereof. The cable comprises an inner conductor; the insulating layer is coated on the periphery of the inner conductor; the periphery of the insulating layer is coated with the outer conductor; the sheath layer is coated on the periphery of the outer conductor; wherein the insulating layer adopts a silicon dioxide insulating structure, and is formed by continuously coating the periphery of the inner conductor with silicon dioxide powder subjected to hydrophobic modification treatment through plastic forming. Surface hydrophobic modification treatment is carried out on high-purity silicon dioxide powder to prepare an insulating material with moisture-resistant and moisture-proof characteristics, and an industrial plastic forming production process is innovatively adopted to directly, continuously and uniformly coat an inner conductor with the modified silicon dioxide material to form a high-density insulating core wire. The cable prepared by the invention has the advantages of extremely low high-frequency transmission loss, excellent temperature stability, flame retardance and fire resistance and ultra-long service life.

Description

A high-temperature resistant silica-insulated leaky coaxial cable and its manufacturing process Technical Field

[0001] This invention relates to the field of communication cable manufacturing technology, and in particular to a high-temperature resistant silica-insulated leaky coaxial cable and its manufacturing process. Background Technology

[0002] As 5G and future 6G communication technologies evolve towards higher frequencies and larger bandwidths, and as application scenarios expand to extreme environments (high temperature, high humidity, and corrosive environments), more stringent requirements are placed on the performance of leaky coaxial cables.

[0003] Traditional leaky cables, insulated with polyethylene or polytetrafluoroethylene foam, experience a significant increase in dielectric loss at high frequencies, leading to exacerbated signal attenuation. These organic polymer insulation materials are hygroscopic, causing a deterioration in their dielectric constant and loss factor, affecting the cable's impedance stability and radiation performance. Furthermore, they soften and deform at high temperatures, become brittle at low temperatures, and release toxic fumes when burned, limiting their application in high-safety environments such as rail transportation, nuclear power plants, and chemical plants. Leaky cables are typically difficult to replace after installation, requiring a service life comparable to that of the building itself.

[0004] Therefore, there is an urgent need to provide a new generation of leaky coaxial cables that can simultaneously meet the requirements of high frequency and low loss, extreme environmental tolerance, ultra-long life and stable radiation performance, as well as an efficient and reliable industrial manufacturing method. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the technical problems of high high-frequency loss and poor environmental tolerance caused by the use of organic insulation materials in the prior art, as well as the inability to produce continuously and low product consistency caused by traditional ceramic preparation processes.

[0006] To solve the above-mentioned technical problems, the present invention provides a high-temperature resistant silica-insulated leaky coaxial cable, comprising: an inner conductor; an insulation layer covering the outer periphery of the inner conductor; an outer conductor covering the outer periphery of the insulation layer; and a sheath layer covering the outer periphery of the outer conductor; wherein the insulation layer adopts a silica insulation structure, which is formed by continuously coating the outer periphery of the inner conductor with hydrophobically modified silica powder through plastic molding.

[0007] In one embodiment of the present invention, the hydrophobic modification treatment uses hexamethyldisilazane to modify the surface of silica powder with a particle size range of 10μm-20μm, so that the insulating layer has moisture-proof and moisture-resistant properties and reduces the degradation of dielectric constant and loss factor caused by moisture absorption.

[0008] In one embodiment of the present invention, the inner conductor is made of oxygen-free copper tube, copper-clad aluminum, or copper-clad steel.

[0009] In one embodiment of the present invention, the outer conductor is formed by covering a thin copper strip and laser welding the seam to form a seamless sealing structure; the thin copper strip is provided with a slot structure for leakage radiation, and the slot structure is distributed at periodic intervals along the length of the cable.

[0010] In one embodiment of the present invention, the sheath layer is made of polyethylene.

[0011] This invention also provides a process for preparing a high-temperature resistant silica-insulated leaky coaxial cable, comprising: S1, silica powder is fed into an airflow drying tube via an automatic feeding and conveying system for instantaneous drying and dehydration, and then transported to a modification process through a closed pipeline; S2, the dried silica powder and the hydrophobic agent hexamethyldisilazane are fed together into a heated mixer in a predetermined ratio, and surface modification is performed under heating and shearing to obtain modified silica powder; S3, the modified silica powder is homogenized and then transported in a closed system to the main insulation material silo; S4, an aqueous solution is prepared by mixing silicone oil and sodium carboxymethyl cellulose in a predetermined mass ratio, the modified silica powder is metered from the main insulation material silo and mixed with the aqueous solution, and the modified silica powder and the aqueous solution are fed into a twin-screw compounding extruder in a predetermined mass ratio through a multi-group dispensing system; S5, the modified silica powder and the aqueous solution are mixed in a predetermined mass ratio. The liquid mixture is uniformly mixed and plasticized in the conveying section of a twin-screw compounding extruder, and after all gases are removed by a vacuum pumice machine, a uniform and dense silica slurry is obtained; S6, the silica slurry is placed in a pressing machine, and after pressure holding, a cylindrical insulating rod matching the mold size in the pressing equipment is formed. The cylindrical insulating rod is placed in the pressing equipment, the inner conductor is passed through the mold and the mold is pressed to continuously cover the outer periphery of the inner conductor to form an insulating layer, thus obtaining an insulated core wire; S7, the insulated core wire is placed into a segmented cooling water tank for shaping, and the outer diameter of the insulating layer is measured using a laser diameter gauge to check and correct to ensure that the dimensional deviation is within the range; S8, after periodic slots are processed on the surface of a thin copper strip using a grooving machine, the slots are covered on the outer periphery of the insulated core wire, and the joints of the thin copper strip are laser welded to achieve a seamless seal, thus forming an outer conductor; S9, polyethylene is extruded around the outer periphery of the outer conductor to form a sheath layer, thus obtaining the finished cable.

[0012] In one embodiment of the present invention, in step S1, the silica powder has a purity of 99% (or higher) and a particle size range of 10μm-20μm.

[0013] In one embodiment of the present invention, in step S2, the mass fraction of the hexamethyldisilazane is 5%, the mass ratio of silica powder to hydrophobic agent hexamethyldisilazane is 5:1, and the modification process is carried out under heating conditions of 180°C to 200°C.

[0014] In one embodiment of the present invention, in step S4, silicone oil and sodium carboxymethyl cellulose are fed into a twin-screw compounding extruder at a predetermined mass ratio of 10:1; modified silica powder and aqueous solution are fed into the extruder at a mass ratio of 3:2.

[0015] In one embodiment of the present invention, in step S5, the vacuum plow is set to 0.05 MPa; in step S6, the pressure is maintained at 60 MPa-80 MPa for 2 hours.

[0016] Compared with the prior art, the above-mentioned technical solution of the present invention has the following advantages: The high-temperature resistant silica-insulated leaky coaxial cable and its preparation process of the present invention, through surface hydrophobic modification treatment of high-purity silica powder, prepares an insulating material with moisture-proof and moisture-resistant properties, and innovatively adopts an industrial plastic molding production process to directly, continuously, and uniformly coat the modified silica material onto the inner conductor to form a highly dense insulated core wire. The cable prepared by the present invention has extremely low high-frequency transmission loss, excellent temperature stability, flame retardancy, and ultra-long service life; at the same time, the continuous and automated industrial production method of the entire process ensures the ultimate consistency of product performance and high-efficiency production capacity, making it particularly suitable for scenarios with stringent requirements for communication performance, security, and reliability, such as 5G / 6G high-frequency indoor deep coverage, rail transit, and energy and chemical industries.

[0017] This invention overcomes the shortcomings of existing cable insulation materials in terms of heat resistance and dielectric loss. It employs hydrophobic modifiers and related processes to modify silica powder with a particle size range of 10μm-20μm, effectively reducing the porosity of the dielectric layer and thus reducing signal attenuation. This is particularly beneficial for the long-term stable operation of leaky coaxial cables in complex environments (such as tunnels and subways). The beneficial effects of this invention are mainly reflected in the following aspects: This invention achieves improved electrical performance, especially suitable for high-frequency and harsh environments. Silica has a stable dielectric constant, and the hydrophobic modification and low-porosity structure greatly reduce dielectric loss caused by moisture absorption, resulting in lower signal loss, especially in humid environments. Compared to unmodified silica insulation layers, coaxial leaky cables with modified insulation layers have a lower standing wave ratio (VSWR). Simultaneously, the molding process ensures extremely high uniformity of the insulation, reducing signal reflection and distortion at high frequencies.

[0018] This invention achieves enhanced physical and environmental resistance, significantly improving reliability. Silica has an extremely high melting point and excellent temperature resistance and fire resistance, allowing it to operate stably at extreme temperatures, completely flame-retardant, and without releasing toxic fumes. Simultaneously, the silica insulation layer does not age, shrink, or deform; the rigid insulator can support the slotted structure and prevent deformation under pressure. High porosity usually means lower material density, leading to a decrease in mechanical strength and toughness. During cable manufacturing, installation, and use, the dielectric layer needs to withstand certain mechanical stress. Insufficient mechanical strength may cause cracks or structural damage to the dielectric layer; low porosity avoids this outcome. Performance degradation is minimal and lifespan is long in high-humidity environments such as tunnels and mines. Hydrophobic modification fundamentally prevents performance degradation caused by moisture intrusion.

[0019] This invention enables the quality and cost advantages of industrialized production. It boasts rapid production speed, controllable overall costs, and cost reduction. It has practical value in environments requiring high reliability and harsh conditions. It has applications in high-end markets with extreme requirements for performance, reliability, and lifespan, such as rail transportation, controlled nuclear fusion, and aerospace. Attached Figure Description

[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0021] Figure 1 is a schematic diagram of the axial cross-section of the coaxial leaky cable structure of the present invention.

[0022] Figure 2 is a schematic diagram of the longitudinal section of the coaxial leaky cable structure of the present invention.

[0023] Explanation of reference numerals in the accompanying drawings: 1. Inner conductor; 2. Insulation layer; 3. Outer conductor; 4. Sheath layer. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0025] In this invention, when directions (up, down, left, right, front, and back) are described, it is only for the convenience of describing the technical solution of this invention, and does not indicate or imply that the technical features referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0026] In this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc., are understood to exclude the stated number; "above," "below," "within," etc., are understood to include the stated number. In the description of this invention, the terms "first" and "second" are used only to distinguish technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0027] In this invention, unless otherwise explicitly defined, the terms "setting," "installing," and "connecting" should be interpreted broadly. For example, they can refer to a direct connection or an indirect connection through an intermediate medium; a fixed connection, a detachable connection, or an integrally formed connection; a mechanical connection, an electrical connection, or a connection capable of mutual communication; or the internal connection of two components or the interaction between two components. Those skilled in the art can reasonably determine the specific meaning of the above terms in this invention based on the specific content of the technical solution.

[0028] Referring to Figures 1 and 2, this embodiment provides a high-temperature resistant silica-insulated leaky coaxial cable, comprising: an inner conductor 1; an insulation layer 2 covering the outer periphery of the inner conductor 1; an outer conductor 3 covering the outer periphery of the insulation layer 2; and a sheath layer 4 covering the outer periphery of the outer conductor 3. The insulation layer 2 adopts a silica insulation structure, which is formed by continuously coating the outer periphery of the inner conductor 1 with hydrophobically modified silica powder through plastic molding.

[0029] Specifically, the hydrophobic modification treatment uses hexamethyldisilazane (HMDS) to modify the surface of silica powder with a particle size range of 10μm-20μm, giving the insulation layer 2 moisture-proof and moisture-resistant properties and reducing the degradation of dielectric constant and loss factor caused by moisture absorption. This targeted surface hydrophobic modification treatment of high-purity (over 99%) silica powder not only preserves the excellent dielectric and temperature resistance properties of silica, but also fundamentally endows it with the ability to resist environmental moisture corrosion, solving the problem of performance degradation of coaxial leaky cables in humid environments.

[0030] Specifically, the inner conductor 1 is made of oxygen-free copper tube, copper-clad aluminum, or copper-clad steel.

[0031] Specifically, the outer conductor 3 is formed by wrapping a thin copper strip and laser welding the seam to form a seamless sealing structure; the thin copper strip is provided with a slot structure for leakage radiation, and the slot structure is distributed at periodic intervals along the length of the cable.

[0032] Specifically, the sheath layer 4 is made of polyethylene.

[0033] This embodiment also provides a manufacturing process for the aforementioned high-temperature resistant silica-insulated leaky coaxial cable. The high-performance leaky coaxial cable uses hydrophobically modified silica as the insulating medium and is manufactured through a continuous plastic molding process. The manufacturing process includes the following steps: S1. Silica powder is fed into an airflow drying tube via an automatic feeding and conveying system for instantaneous drying and dehydration, and then transported to the modification process through a closed pipeline; S2. The dried silica powder and the hydrophobic agent hexamethyldisilazane are fed together into a heated mixer in a predetermined ratio, and surface modification is performed under heating and shearing to obtain modified silica powder; S3. The modified silica powder is homogenized and then transported in a closed system to the main insulation material silo; S4. Silicone oil and sodium carboxymethyl cellulose (CMC) are mixed in an aqueous solution according to a predetermined mass ratio. The modified silica powder is metered from the main insulation material silo and mixed with the aqueous solution. The modified silica powder and the aqueous solution are then fed into a twin-screw extruder in a predetermined mass ratio through a multi-group dispensing system. S5. The modified silica powder and the aqueous solution are mixed and plasticized uniformly in the conveying section of the twin-screw compounding extruder, and after all the gas is removed by the vacuum pumice machine, a uniform and dense silica slurry is obtained; S6. The silica slurry is placed in a rod press, and after being pressed, it is made into a cylindrical insulating rod that matches the size of the mold in the pressing equipment. The cylindrical insulating rod is placed in the pressing equipment, the inner conductor 1 is passed through the mold and the mold is pushed to continuously wrap around the outer circumference of the inner conductor 1. S7. An insulating layer 2 is formed to obtain an insulated core wire; S8. The insulated core wire is placed in a segmented cooling water tank for shaping, and the outer diameter of the insulating layer 2 is measured using a laser diameter gauge to check and correct for dimensional deviations within the range; S9. Periodic slots are machined on the surface of a thin copper strip using a slotting machine, and then wrapped around the outer periphery of the insulated core wire. Laser welding is used to achieve a seamless seal at the joints of the thin copper strip to form an outer conductor 3; S10. Polyethylene is extruded around the outer periphery of the outer conductor 3 to form a sheath layer 4, resulting in the finished cable. The sheath layer 4 not only provides mechanical and environmental protection, but its material and thickness design also need to be considered in conjunction with the slot structure to ensure that it can protect the slot structure from compression deformation or blockage by foreign objects, without excessively affecting signal leakage performance.

[0034] It's important to note that, firstly, porosity directly affects the dielectric constant of the dielectric layer. A lower dielectric constant means less electrical energy is stored in the dielectric layer during signal transmission, thus reducing energy loss. Therefore, the less air with a low dielectric constant, the better. Secondly, dielectric loss is directly related to signal attenuation rate. Although pure air and silica are good insulators, in practical applications, moisture or other impurities may be adsorbed inside the pores. The adsorption of water molecules significantly increases dielectric loss, leading to a sharp increase in signal attenuation rate. The application of hydrophobic modifiers is precisely to reduce the water absorption of the silica insulating layer 2. Furthermore, high porosity or uneven pore distribution leads to more structural defects and electric field concentration points inside the dielectric layer. These areas are prone to local breakdown under the influence of an electric field, forming conductive paths, increasing conductivity loss, and ultimately exacerbating signal attenuation. To address this issue, modifying silica powder with a particle size range of 10μm-20μm using hydrophobic modifiers and related processes can effectively control the pore structure of the dielectric layer, thereby reducing signal attenuation and maintaining its excellent performance in humid environments.

[0035] Example 2 This example provides a manufacturing process for a high-temperature resistant silica-insulated leaky coaxial cable. The inner conductor 1 of the leaky coaxial cable is an oxygen-free copper tube with a diameter of approximately 13.10 mm. An silica insulation layer 2 with an outer diameter of approximately 33.00 mm is set around the outer periphery of the inner conductor 1. An outer conductor 3 with a copper material and an outer diameter of 34.00 mm is set around the outer periphery of the silica insulation layer 2. A polyethylene sheath layer 4 with an outer diameter of 37.80 mm is set around the outer conductor 3.

[0036] The hydrophobic modifier used in the preparation of the insulating layer 2 of silica must possess sufficient hydrophobic properties at room temperature and reduce the dielectric constant of the composite material after high-temperature heat treatment. The preparation process includes the following steps: S1, silica powder with a purity of 99% and a particle size range of 10μm-20μm is fed into an airflow drying tube by an automatic feeding and conveying system for instantaneous drying and dehydration, and then transported to the modification process through a closed pipeline.

[0037] S2. The dried silica powder and 5% (by mass) hydrophobic agent HMDS are fed into a heated mixer at a ratio of 5:1. Under the action of heating and shearing at 180℃~200℃, the powder is crushed and ground to produce a rapid reaction.

[0038] S3. The modified powder enters the homogenization silo and is then transported by the air pump conveying system to the main insulation material silo for later use. This process is completely closed and there is no dust or solvent pollution.

[0039] S4. Modified silica powder is metered from the main feed silo and mixed with an aqueous solution of silicone oil and CMC at a ratio of 10:1. The mixture is then fed into a twin-screw compounding extruder at a powder to aqueous solution mass ratio of 3:2 through a multi-group distribution system.

[0040] S5. The materials configured above are uniformly mixed and plasticized in the shearing conveyor section of the twin screw, and all gases are removed in the vacuum slurry machine (set to about 0.05MPa), outputting uniform and dense silica slurry.

[0041] S6. Place the silica mud into the press and hold it under pressure at 60MPa-80MPa for 2 hours to make a cylindrical insulating rod that matches the size of the mold in the pressing equipment. Place the cylindrical insulating rod into the pressing equipment, pass the inner conductor 1 through the mold and press the mold to continuously cover the outer periphery of the inner conductor 1 to form an insulating layer 2, thus obtaining an insulated core wire.

[0042] S7. The extruded insulated core wire immediately enters a segmented cooling water tank for shaping. The outer diameter of insulation layer 2 is measured using a laser diameter gauge to inspect and correct for any deviations within the acceptable range.

[0043] S8. After using a grooving machine to process periodic slots on the surface of the thin copper strip, the strip is wrapped around the outer periphery of the insulated core wire, and laser welding is used to achieve a seamless seal at the joint of the thin copper strip to form the outer conductor 3.

[0044] S9. Polyethylene is extruded around the outer conductor 3 to form a sheath layer 4, thus obtaining the finished cable.

[0045] Finally, it should be noted that the above specific 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 examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-temperature resistant silica-insulated leaky coaxial cable, characterized in that, include: Inner conductor (1); insulation layer (2) covering the outer periphery of the inner conductor (1); outer conductor (3) covering the outer periphery of the insulation layer (2); sheath layer (4) covering the outer periphery of the outer conductor (3); wherein the insulation layer (2) adopts a silicon dioxide insulation structure, which is formed by continuously covering the outer periphery of the inner conductor (1) with hydrophobically modified silicon dioxide powder through plastic molding.

2. The high-temperature resistant silica-insulated leaky coaxial cable according to claim 1, characterized in that, The hydrophobic modification treatment uses hexamethyldisilazane to modify the surface of silica powder with a particle size range of 10μm-20μm, so that the insulating layer (2) has moisture-proof and moisture-resistant properties and reduces the degradation of dielectric constant and loss factor caused by moisture absorption.

3. The high-temperature resistant silica-insulated leaky coaxial cable according to claim 1, characterized in that, The inner conductor (1) is made of oxygen-free copper tube, copper-clad aluminum, or copper-clad steel.

4. The high-temperature resistant silica-insulated leaky coaxial cable according to claim 1, characterized in that, The outer conductor (3) is formed by wrapping a thin copper strip and laser welding the seam to form a seamless sealing structure; the thin copper strip is provided with a slot structure for leakage radiation, and the slot structure is distributed at periodic intervals along the length of the cable.

5. A high-temperature resistant silica-insulated leaky coaxial cable according to claim 1, characterized in that, The sheath layer (4) is made of polyethylene.

6. A manufacturing process for a high-temperature resistant silica-insulated leaky coaxial cable, characterized in that, include: S1. Silica powder is fed into an airflow drying tube by an automatic feeding and conveying system for instantaneous drying and dehydration, and then transported to the modification process through a closed pipeline. S2. The dried silica powder and the hydrophobic agent hexamethyldisilazane are fed together into a heated mixer in a predetermined ratio for surface modification under heating and shearing to obtain modified silica powder. S3. The modified silica powder is homogenized and then conveyed in a sealed manner to the main insulation material silo. S4. Silicone oil and sodium carboxymethyl cellulose are mixed into an aqueous solution in a predetermined mass ratio. The modified silica powder is metered from the main insulation material silo and mixed with the aqueous solution. The mixture is then fed into a twin-screw compounding extruder in a predetermined mass ratio via a multi-group feeding system. S5. The mixture of modified silica powder and aqueous solution is uniformly mixed and plasticized in the conveying section of the twin-screw compounding extruder. After all gases are removed by a vacuum pumice machine, a uniform and dense silica powder is obtained. S6. The silica slurry is placed in a press machine and pressed to form a cylindrical insulating rod that matches the size of the mold in the pressing equipment. The cylindrical insulating rod is placed in the pressing equipment, and the inner conductor (1) is passed through the mold and the mold is pressed to continuously cover the outer periphery of the inner conductor (1) to form an insulating layer (2) and obtain an insulated core wire. S7. The insulated core wire is placed in a segmented cooling water tank for shaping. The outer diameter of the insulating layer (2) is measured using a laser diameter gauge. The measurement and correction are performed to ensure that the dimensional deviation is within the range. S8. After periodic slots are processed on the surface of the thin copper strip using a grooving machine, the slots are covered on the outer periphery of the insulated core wire. Laser welding is used to achieve a seamless seal at the joint of the thin copper strip to form an outer conductor (3). S9. Polyethylene is extruded on the outer periphery of the outer conductor (3) to form a sheath layer (4) and obtain a finished cable.

7. The manufacturing process of a high-temperature resistant silica-insulated leaky coaxial cable according to claim 6, characterized in that, In step S1, the silica powder has a purity of 99% and a particle size range of 10μm-20μm.

8. The manufacturing process of a high-temperature resistant silica-insulated leaky coaxial cable according to claim 6, characterized in that, In step S2, the mass fraction of hexamethyldisilazane is 5%, the mass ratio of silica powder to hydrophobic agent hexamethyldisilazane is 5:1, and the modification process is carried out under heating conditions of 180℃~200℃.

9. The manufacturing process of a high-temperature resistant silica-insulated leaky coaxial cable according to claim 6, characterized in that, In step S4, silicone oil and sodium carboxymethyl cellulose are fed into a twin-screw compounding extruder at a predetermined mass ratio of 10:1; modified silica powder and aqueous solution are fed into the extruder at a mass ratio of 3:

2.

10. The manufacturing process of a high-temperature resistant silica-insulated leaky coaxial cable according to claim 6, characterized in that, In step S5, the vacuum plow is set to 0.05 MPa; in step S6, the pressure is maintained at 60 MPa-80 MPa for 2 hours.

Images