An ultra-low attenuation leaky coaxial cable

Abstract

This application belongs to the field of wireless communication technologies. More specifically, it relates to an ultra-low attenuation leaky coaxial cable, which includes an inner conductor, an insulating layer, an outer conductor with slots, and a sheath. The insulating layer includes an inner skin layer, a foaming layer, and an outer skin layer. Among them, the foaming layer is prepared by a multi-layer foaming extrusion process. By optimizing the foaming material formula of the insulating layer, the pore uniformity of the foaming layer is improved, and the foaming degree can reach up to about 85%, thereby effectively improving the overall attenuation index of the leaky coaxial cable. Compared with a leaky coaxial cable with a foaming degree of 80% of the same specification, the attenuation index can be improved by about 10%. For example, the attenuation per 100 meters at 2700 MHz of a 1-5 / 8 inch leaky coaxial cable can be reduced from 5.8 dB to about 5.2 dB. At the same time, to avoid the problem that the insulating layer becomes soft due to too high a foaming degree, resulting in deformation of the insulating layer under pressure during the production of the finished product and then uneven outer diameter, the outer skin layer is made of a composite material of polyethylene and a hardening agent.

Description

Technical Field

[0001] This application belongs to the field of wireless communication technologies, and more specifically, relates to an ultra-low attenuation leaky coaxial cable. Background Art

[0002] The attenuation indexes of a leaky coaxial cable mainly include conductor attenuation (determined by the inner and outer conductor metal layers), dielectric attenuation (determined by the insulating dielectric between the inner and outer conductors), and radiation attenuation (only for leaky coaxial cables. There are slots on the outer conductor of the leaky coaxial cable that can radiate electromagnetic waves into the far-field space, and the outward radiation of energy causes the existence of radiation attenuation, and the radiation attenuation is basically determined by the form of the slots). Since the structure of the leaky coaxial cable has been roughly determined according to industry standards and national standards, and the conductor is made of high-purity copper with high material performance, in order to achieve ultra-low attenuation, currently, optimization mainly starts from the insulating material.

[0003] By adjusting the foaming degree of the insulating layer, the overall attenuation index of the cable can be optimized to a large extent. Currently, the maximum foaming degree achieved by domestic manufacturers is usually 80%, and the limit value can reach 82%. However, when the foaming degree approaches the limit, a small number of uneven holes will appear in the insulating layer, which hinders the further optimization of the overall attenuation index of the cable. The reason is that when the foaming degree is too high, the pores in the foaming layer will grow rapidly, and at the same time, the foaming gas will escape too violently, resulting in an uneven state of the foaming layer and the pores, and even the situation where the pores break and merge to form large holes, which has a serious negative impact on the electrical transmission performance of the cable.

[0004] The prior art uses different foaming gases for mixed foaming. By utilizing the differences of different gases in the supercritical state, the positions with different diameters in the foaming layer are closer in foaming rate compared with single-gas foaming, so that the pore distribution is more uniform. Since the proportion of gas mass in the insulating layer is extremely small under normal temperature and pressure, and the foaming gas has stable chemical properties and a low dielectric constant, the influence of the dielectric constant of the gas on the dielectric constant of the foaming layer can be ignored. Nevertheless, in the case of ultra-large foaming degree, this single-layer foaming mixed gas still has the problem of violent and uneven gas escape, which limits the improvement of the foaming degree. Generally, it can only approach 82%, and it is difficult to achieve a breakthrough in a higher foaming degree. Summary of the Invention

[0005] Aiming at the defects of the prior art, this application provides an ultra-low attenuation leaky coaxial cable, aiming to solve the problem that the existing foaming degree of the insulating layer cannot be further improved, resulting in the inability to further improve the attenuation index of the leaky coaxial cable.

[0006] According to one aspect of this application, an ultra-low attenuation leaky coaxial cable is provided, including:

[0007] Inner conductor;

[0008] Insulation layer, including an inner skin layer, a preset number of foaming layers and an outer skin layer arranged from inside to outside, wherein the foaming layers are prepared by a multi-layer foaming extrusion process, and in any two adjacent foaming layers, the ratio of the melt flow rate of the foaming material of the inner foaming layer to that of the outer foaming layer is 1:1.2 to 1:3, and at the same time, the critical pressure of the foaming gas of the inner foaming layer is more than 10 bar greater than that of the outer foaming layer, thereby improving the pore uniformity and foaming degree of the insulation layer through the multi-layer foaming extrusion process; at the same time, the outer skin layer is made of a composite material of polyethylene and a hardening agent to improve the hardness of the insulation layer and avoid the problem that the insulation layer is deformed under pressure during the subsequent finished product production process due to the increase in the foaming degree of the insulation layer, resulting in uneven outer diameter;

[0009] Outer conductor, with a preset number of slots opened on the outer conductor; and

[0010] Sheath.

[0011] Through the above technical solution conceived by the present application, compared with the prior art, the present application prepares the foaming layer through a multi-layer foaming extrusion process, and at the same time optimizes the types of foaming materials and foaming gases used for each foaming layer, which can ensure that the pore sizes of each foaming layer are uniform and consistent, and the foaming degree can reach up to about 85%, effectively improving the overall attenuation index of the leaky coaxial cable. Compared with a cable of the same specification and a foaming degree of 80%, the cable attenuation of the ultra-low attenuation leaky coaxial cable provided by the present application can be optimized by about 10%. In addition, by optimizing the formula of the outer skin layer, the present application can also avoid the problem that the foaming layer becomes soft due to too high a foaming degree, resulting in uneven outer diameter caused by the deformation of the insulation layer under pressure during the subsequent finished product production process.

[0012] As a further preference, the addition ratio of the hardening agent in the outer skin layer is 4%wt. - 6%wt.

[0013] As a further preference, the hardening agent includes one or more of talcum powder, calcium carbonate, and wollastonite.

[0014] As a further preference, the polyethylene is low-density polyethylene.

[0015] As a further preference, when preparing the foaming layer by a multi-layer foaming extrusion process, in any two adjacent foaming layers, the injection pressure and the barrel pressure of the inner foaming layer and the outer foaming layer satisfy the following relationship:

[0016]

[0017] In the formula, is the pressure difference between the injection pressure and the barrel pressure of the outer foaming layer, is the chamber pressure of the outer foamed layer, is the pressure difference between the gas injection pressure of the inner foamed layer and the chamber pressure, is the chamber pressure of the inner foamed layer, is the chamber temperature of the outer foamed layer, is the chamber temperature of the inner foamed layer, is the foaming volume of the outer foamed layer, is the foaming volume of the inner foamed layer.

[0018] As a further preference, in two adjacent foamed layers, the foaming volume ratio of the inner foamed layer to the outer foamed layer is 1:1 to 1:4.

[0019] As a further preference, the number of layers of the foamed layer is 2 to 4 layers.

[0020] As a further preference, the foaming material includes one or more of homopolypropylene, low-density polyethylene, high-density polyethylene, random polypropylene, and high-density polyethylene with a density of 0.941 g / cm 3 ~0.950 g / cm 3 and the foaming gas includes one or more of nitrogen, argon, carbon dioxide, and octafluorocyclobutane.

[0021] As a further preference, the diameter of the inner conductor is 4.6 mm to 18.5 mm, the outer diameter of the insulating layer is 12 mm to 42 mm, the outer diameter of the outer conductor is 12.5 mm to 44.5 mm, and the outer diameter of the sheath is 15 mm to 51 mm.

[0022] Generally speaking, compared with the prior art by the above technical solutions conceived in this application, the following technical advantages are mainly available:

[0023] 1. This application uses a multi-layer foaming extrusion process to prepare the foamed layer, and optimizes the foaming material and the type of foaming gas for each foamed layer, which can ensure that the cell size of each foamed layer is uniform and the foaming degree can reach up to about 85%. Furthermore, it can effectively improve the overall attenuation index of the leaky coaxial cable. Compared with the leaky coaxial cable with a foaming degree of 80% of the same specification, the attenuation index can be improved by about 10%. For example, the attenuation per 100 meters at 2700 MHz of a 1-5 / 8-inch leaky coaxial cable can be reduced from 5.8 dB to about 5.2 dB. At the same time, considering that a significant increase in the foaming degree of the foamed layer will lead to a decrease in the rigidity of the insulating layer, resulting in an uneven outer diameter problem due to local stress on the insulating layer during the subsequent finished product production process, this application also optimizes the formula of the outer skin layer, and improves the outer surface rigidity of the insulating layer by adding a hardening agent to avoid the problem of obvious deterioration of electrical performance caused by the generation of small standing waves at uneven places of the cable;

[0024] 2. Meanwhile, the present application optimizes the addition ratio of the hardener in the outer cortex, which can ensure the rigidity of the insulating layer while avoiding the reduction of the toughness on the surface of the insulating layer and the easy cracking.

[0025] 3. In particular, the present application optimizes the gas injection pressure and the chamber pressure of the inner and outer foaming layers in adjacent foaming layers, which can ensure that the cell sizes of each foaming layer are uniform and avoid the problem of large holes formed by the rupture and merger of cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a sectional view of the ultra-low attenuation leaky coaxial cable provided by the embodiment of the present application;

[0027] Figure 2 is a schematic diagram of the extrusion machine foaming provided by the embodiment of the present application;

[0028] Figure 3 is a schematic structural diagram of the ultra-low attenuation leaky coaxial cable provided by the embodiment of the present application.

[0029] In all the drawings, the same reference numerals are used to represent the same elements or structures, where:

[0030] 1 - inner conductor, 2 - insulating layer, 21 - inner cortex, 22 - foaming layer, 23 - outer cortex, 3 - outer conductor, 31 - slot hole, 4 - sheath, 5 - inner skin material chamber, 6 - first foaming material chamber, 7 - Nth foaming material chamber, 8 - outer skin material chamber. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] As Figure 1 、 3 shown, the present application provides an ultra-low attenuation leaky coaxial cable, which all includes an inner conductor 1, an insulating layer 2, an outer conductor 3 and a sheath 4 arranged in sequence from the inside to the outside.

[0033] The inner conductor 1 usually adopts a metal with good conductivity such as copper or aluminum. Among them, the inner conductor 1 of a small cable is commonly a copper wire or a copper-clad aluminum wire, while the inner conductor 1 of a large cable mostly uses a copper tube to reduce the cable weight and cost while ensuring the conductivity. As the carrier of signal transmission, the signal current flows in it and undertakes the important task of transmitting the electrical signal at the transmitting end to the receiving end, playing a key role in the quality and efficiency of signal transmission;

[0034] The insulating layer 2 includes an inner cortex 21, a preset number of foaming layers 22 and an outer cortex 23 arranged from the inside to the outside, where:

[0035] The endothelia 21 is coated on the outer side of the inner conductor 1 to facilitate close combination with the foaming layer 22;

[0036] The foaming material of the foaming layer 22 is under high temperature and high pressure in an extrusion machine to make the foaming gas reach the supercritical fluid state. In this state, the foaming gas has the dissolution and diffusion ability of a gas and at the same time has the form of a liquid, and can better mix and blend with other fluids. In this way, the foaming gas is fully and evenly mixed into the high-temperature and high-pressure foaming material melt. In the die head, as the pressure and temperature are gradually released, the foaming gas gradually escapes from the inside to the outside. With the help of the nucleating component, the mixture of the foaming material forms fine pores. The pores capture the escaping foaming gas and cause it to expand, finally forming a lightweight and highly foamed insulation layer structure. The difficulty in this process lies in that when the foaming degree is high, the amount of gas is large and the escape becomes more uncontrollable. Especially for the insulation layer 2 of a larger-sized cable, the thickness is relatively thick, and the expansion speed of the foaming material becomes slower from the inside to the outside (the expansion rate is inversely proportional to the insulation radius. The larger the foaming diameter, the smaller the change rate of the foaming expansion diameter). When the gas escapes, it is easy to cause the pores to burst, resulting in uneven large holes, which may cause the cable to be out of shape or have poor electrical performance. Therefore, this application proposes to use a multi-layer foaming extrusion process to prepare the foaming layer. For any two adjacent foaming layers 22, the ratio of the melt flow rate (MFR) of the foaming material of the inner foaming layer to that of the outer foaming layer is 1:1.2 to 1:3, so as to ensure that the viscosity of the foaming material of the inner foaming layer is somewhat higher than that of the outer foaming layer, avoiding that the viscosity is too low due to too low melt flow rate and being not easy to foam and form. At the same time, in the adjacent foaming layers 22, the critical pressure of the foaming gas of the inner foaming layer is more than 10 bar higher than that of the outer foaming layer, so as to use the gas amount matching the foaming material of each foaming layer, ensuring that the foaming degrees of each foaming layer 22 are relatively unified and the pore sizes are uniform. By optimizing the foaming material and foaming gas of each foaming layer, the pore uniformity and foaming degree of the insulation layer can be effectively improved, making the foaming degree of each foaming layer in the insulation layer 2 as large as possible, breaking through the limit of 82% in the prior art, and being able to reach about 85% at most, and obtaining closer pore sizes inside and outside, improving the pore uniformity in the insulation layer 2, making the dielectric constant of the insulation layer 2 as small as possible, and further effectively improving the overall attenuation index of the leaky coaxial cable. Compared with a leaky coaxial cable with a foaming degree of 80% of the same specification, the attenuation index can be improved by about 10%;

[0037] The outer skin layer 23 is made of a composite material of polyethylene and a hardening agent. Considering that after the foaming degree of the foaming layer 22 is increased, such as from 80% to about 85%, the solid medium content in the insulating layer 2 is reduced by 25%, which will cause the insulating layer 2 to become softer and the rigidity to decrease. During the longitudinal wrapping process of the leaky coaxial cable, a relatively tight mold is required to tightly wrap the outer conductive metal around the insulating layer 2 to form the outer conductor 3. However, the soft insulating layer 2 lacks sufficient support, and being squeezed when passing through the sizing die will cause the outer diameter to be uneven. Therefore, in this application, a hardening agent is added to the outer skin layer 23 to increase the rigidity of the outer surface of the insulating layer 2 and make it smoother, making it easier to pass through the die. After actual measurement, the outer diameter change rate is less than five-thousandths, which can be basically ignored. Thus, it can avoid the generation of small standing waves at the uneven parts of the leaky coaxial cable due to uneven outer diameter, which may seriously deteriorate the electrical performance and further affect the final use performance;

[0038] The outer conductor 3 is generally composed of copper tape, aluminum foil, metal braided mesh, etc. These materials have good electrical conductivity and shielding performance. A series of slots or gaps are provided on the outer conductor, such as continuous or discontinuous longitudinal slots, periodic eight-shaped slots, one-shaped slots, elliptical slots, Z-shaped slots, etc. Parameters such as the shape, size, pitch of the slots and the thickness of the outer conductor can be precisely controlled according to needs to achieve the specific leakage performance and electrical indicators of the leaky coaxial cable; On the one hand, the outer conductor 3 serves as a loop conductor for signal transmission and together with the inner conductor 1 constitutes a complete signal transmission path; on the other hand, it plays a shielding role, reducing the influence of external electromagnetic interference on the signals inside the cable. At the same time, by controlling the design of the slots, a part of the electromagnetic energy transmitted inside the cable can leak from the slots into the space along the line, realizing the coverage of the electromagnetic field blind area or receiving external electromagnetic signals;

[0039] The material of the sheath 4 can be polyvinyl chloride (PVC), polyethylene (PE), black linear low-density polyethylene, etc. For special requirements, low-smoke, halogen-free flame-retardant materials, etc. are also used; The sheath 4 should tightly wrap the outside of the outer conductor 3, have a certain thickness and mechanical strength, the surface is smooth, without obvious defects, and can adapt to different laying environments and usage requirements. At the same time, as the outermost protection structure of the cable, the sheath 4 mainly plays the roles of waterproofing, moisture-proofing, insulation and protecting the internal components, preventing the cable from being physically damaged, chemically corroded and ultraviolet radiation from the outside world, slowing down the aging process of the cable and extending the service life of the cable. At the same time, in some special cases, such as places with high fire protection requirements, it can also play the roles of flame retardancy and preventing the spread of fire.

[0040] The foaming degree is the volume ratio of the void part of the pores in the insulating layer to the volume of the insulating layer. An increase of 1% on the basis of 80% foaming degree means that the material consumption of the solid part of the insulating layer is reduced by one-twentieth. This application uses a multi-layer foaming extrusion process to prepare the insulating layer 2, and optimizes the foaming materials and types of foaming gases for each foaming layer 22, which can ensure that the pore sizes of each foaming layer 22 are uniform and the foaming degree can reach up to about 85%. This represents a huge improvement compared to the cables with 80% foaming degree in the prior art. At the same time, in combination with the formulation optimization of the outer skin layer 23 in the insulating layer 2, the problem of uneven outer diameter is avoided, thereby effectively improving the overall attenuation index of the leaky coaxial cable. Compared with the cables with 80% foaming degree of the same specification, the attenuation index can be improved by about 10%. For example, the attenuation per 100 meters at 2700 MHz of a 1-5 / 8 inch leaky coaxial cable can be reduced from 5.8 dB to about 5.2 dB.

[0041] Adopt, such as Figure 2 shown, an extruder is used to prepare the insulating layer 2 on the outer side of the inner conductor 1. The head of the extruder is sequentially connected with an inner skin material chamber 5, a first foaming material chamber 6,..., an Nth foaming material chamber 7 and an outer skin material chamber 8 along the extrusion direction, and then the insulating layer 2 with an inner skin layer 21, N foaming layers 22 and an outer skin layer 23 is prepared through a multi-layer foaming extrusion process. The inner conductor 1 in the head advances at a uniform speed, and the insulating material is wrapped around the inner conductor 1 from the inner layer to the outer layer according to the injection sequence into the head; the inner skin layer 21 and the outer skin layer 23 are respectively located at the innermost and outermost layers of the insulating layer 2. In a preferred embodiment of this application, the inner skin layer 21 and the outer skin layer 23 are non-foaming thin layers made of polyethylene. The middle of the inner and outer skin layers is the foaming layer 22, which is formed by melting and mixing different foaming materials and gases for foaming. The characteristics of the foaming materials of each layer are that the foaming materials of the foaming layer closer to the inside have higher viscosity, the foaming gases of the foaming layer closer to the inside have higher critical pressure, and the critical temperature of each foaming gas should be less than the melt temperature of the foaming material, so that the inner layer gas volatilizes and vaporizes from the foaming material melt relatively earlier during the process of the pressure drop in the extrusion head; the temperature and screw speed of each chamber can control the final formed volume and foaming degree of the foaming layer.

[0042] Furthermore, the addition ratio of the hardening agent in the outer skin layer is 4%wt. - 6%wt. Adding too much hardening agent will cause the surface toughness of the insulating layer 2 to decrease and be prone to cracking, while adding too little hardening agent will not achieve a good hardening effect. At the same time, the hardening agent is preferably one or more of talcum powder, calcium carbonate, and wollastonite, and the polyethylene is preferably low-density polyethylene.

[0043] Furthermore, the gas injection pressure difference of the outer foaming layer should be greater than that of the inner foaming layer. The greater the gas injection pressure difference, the greater the gas injection volume, which is conducive to the outer foaming layer with a larger volume obtaining a foaming degree matching that of the inner foaming layer; while the inner foaming layer has a small volume, and a relatively small gas injection volume can obtain a high foaming degree, but relatively more pores are likely to appear. At the same time, considering that the gas injection pressure is related to the chamber pressure, chamber temperature and foaming volume, therefore, in order to ensure that the pores of each foaming layer are uniform and the foaming degree is high, when preparing the foaming layer by the multi-layer foaming extrusion process, for any two adjacent foaming layers 22, the gas injection pressure and chamber pressure of the inner foaming layer and the outer foaming layer satisfy the following relationship,

[0044]

[0045] In the formula, is the pressure difference between the gas injection pressure and the chamber pressure of the outer foaming layer, is the chamber pressure of the outer foaming layer, is the pressure difference between the gas injection pressure and the chamber pressure of the inner foaming layer, is the chamber pressure of the inner foaming layer, is the chamber temperature of the outer foaming layer, is the chamber temperature of the inner foaming layer, is the foaming volume of the outer foaming layer, is the foaming volume of the inner foaming layer.

[0046] Furthermore, for two adjacent foaming layers, the foaming volume ratio of the inner foaming layer to the outer foaming layer is 1:1 to 1:4, so as to ensure that the inner layer foaming process is quickly finalized. When the outer layer foaming starts to expand, the rapid expansion process of the inner layer is basically over, and the inner and outer layers will not generate too much restriction on each other during foaming, thus affecting the pore size at the boundary.

[0047] Furthermore, the number of layers of the foaming layer 22 is 2 to 4 layers, so as to ensure uniform foaming of the insulating layer and avoid production difficulties and increased production costs caused by too many layers.

[0048] Furthermore, the foaming material includes one or more of homopolypropylene HPP, low-density polyethylene LDPE (density range: 0.910 g / cm³ - 0.930 g / cm³), high-density polyethylene HDPE (density range: 0.941 g / cm³ - 0.965 g / cm³), and random polypropylene PP-R, and the foaming gas includes one or more of nitrogen, argon, carbon dioxide, and octafluorocyclobutane.

[0049] Further, when the number of layers of the foaming layer 22 is two, the foaming layer 22 includes a first foaming layer and a second foaming layer arranged in sequence from the inside to the outside. The foaming material of the first foaming layer is a mixture of homopolypropylene (PP-H) and low-density polyethylene (LDPE), and the foaming gas is carbon dioxide; the foaming material of the second foaming layer is a mixture of high-density polyethylene (HDPE) and low-density polyethylene, and the foaming gas is octafluorocyclobutane.

[0050] Further, when the number of layers of the foaming layer 22 is three, the foaming layer 22 includes a first foaming layer, a second foaming layer and a third foaming layer arranged in sequence from the inside to the outside. The foaming material of the first foaming layer is a mixture of homopolypropylene and low-density polyethylene, and the foaming gas is argon; the foaming material of the second foaming layer is a mixture of high-density polyethylene with a density of 0.951 g / cm 3 ~0.965 g / cm 3 and low-density polyethylene, and the foaming gas is nitrogen; the foaming material of the third foaming layer is a mixture of high-density polyethylene with a density of 0.941 g / cm 3 ~0.950 g / cm 3 and low-density polyethylene, and the foaming gas is octafluorocyclobutane.

[0051] Further, when the number of layers of the foaming layer 22 is four, the foaming layer 22 includes a first foaming layer, a second foaming layer, a third foaming layer and a fourth foaming layer arranged in sequence from the inside to the outside. The foaming material of the first foaming layer is a mixture of homopolypropylene and low-density polyethylene, and the foaming gas is carbon dioxide; the foaming material of the second foaming layer is a mixture of random polypropylene (PP-R) and low-density polyethylene, and the foaming gas is argon; the foaming material of the third foaming layer is a mixture of high-density polyethylene (HMWHDPE) with a density of 0.951 g / cm 3 ~0.965 g / cm 3 and low-density polyethylene, and the foaming gas is nitrogen; the foaming material of the fourth foaming layer is a mixture of high-density polyethylene with a density of 0.941 g / cm 3 ~0.950 g / cm 3 and low-density polyethylene, and the foaming gas is octafluorocyclobutane.

[0052] Further, the diameter of the inner conductor 1 is 4.6 mm to 18.5 mm, the outer diameter of the insulating layer 2 is 12 mm to 44 mm, the outer diameter of the outer conductor 3 is 12.5 mm to 44.5 mm, and the outer diameter of the sheath 4 is 15 mm to 51 mm.

[0053] The following further describes the technical solution provided by the present application according to specific embodiments.

[0054] Example 1

[0055] An ultra-low attenuation leaky coaxial cable, comprising an inner conductor 1, an insulating layer 2, an outer conductor 3 and a sheath 4 arranged in sequence from the inside to the outside, wherein the insulating layer 2 includes an inner skin layer 21, a first foaming layer, a second foaming layer and an outer skin layer 23 prepared by a multi-layer foaming extrusion process. The foaming volume ratio of the first foaming layer to the second foaming layer is 3:5. The foaming material of the first foaming layer is a mixture of polypropylene and low-density polyethylene, with a melt flow rate of about 2.6 g / 10 min. The foaming gas is carbon dioxide, the gas injection pressure is 200 bar, the barrel pressure is 150 bar, and the barrel temperature is 160 °C; the foaming material of the second foaming layer is a mixture of high-density polyethylene and low-density polyethylene, with a melt flow rate of about 7.8 g / 10 min. The foaming gas is perfluorocyclobutane, the gas injection pressure is 266 bar, the barrel pressure is 170 bar, and the barrel temperature is 170 °C. During the production process, when the carbon dioxide in the first foaming layer starts to drop from the critical pressure of 73.9 bar to atmospheric pressure, it starts to gasify and expand earlier than the perfluorocyclobutane in the outer layer. Since the material viscosity of the first foaming layer is large and the pores are not easily broken, the first foaming layer can form an inner layer with a large foaming degree relatively quickly; the critical pressure of perfluorocyclobutane in the second foaming layer is 27.8 bar, which is relatively low. The foaming process starts later than the first foaming layer, and the outer diameter of this layer is large. When the temperature and pressure change, the growth rate of the outer diameter is slower than that of the inner layer. Therefore, it is necessary to keep the melt of the second foaming layer at a higher temperature to make the outer layer foam fully, and the small viscosity increases the expansion rate to a certain extent; the outer skin layer is made of polyethylene and 5%wt. calcium silicate; slots 31 are provided on the outer conductor 3. The foaming degree of the insulating layer 2 in the ultra-low attenuation leaky coaxial cable provided in this embodiment is about 82.8%.

[0056] Example 2

[0057] An ultra-low attenuation leaky coaxial cable, comprising an inner conductor 1, an insulating layer 2, an outer conductor 3 and a sheath 4 arranged in sequence from the inside to the outside, wherein the insulating layer 2 includes an inner skin layer 21, a first foaming layer, a second foaming layer, a third foaming layer and an outer skin layer 23 prepared by a multi-layer foaming extrusion process. The foaming volume ratios of the first foaming layer, the second foaming layer and the third foaming layer are 2.1:3.5:5. The foaming material of the first foaming layer is homopolypropylene and low-density polyethylene, with a melt flow rate of about 2.6 g / 10 min. The foaming gas is carbon dioxide, the gas injection pressure is 200 bar, the barrel pressure is 150 bar, and the barrel temperature is 160 °C; 3 The foaming material of the second foaming layer is a mixture of high-density polyethylene with a density of 0.955 g / cm 3A mixture of high-density polyethylene and low-density polyethylene, with a melt flow rate of approximately 15 g / 10 min, the foaming gas is perfluorocyclobutane, the gas injection pressure is 346 bar, the chamber pressure is 190 bar, and the chamber temperature is 180 °C; the outer skin is made of low-density polyethylene and 4% wt. of talc; slots 31 are provided on the outer conductor 3. The bubble degree of the insulating layer 2 in the ultra-low attenuation leaky coaxial cable provided in this embodiment is about 83.9%.

[0058] Example 3

[0059] An ultra-low attenuation leaky coaxial cable, including an inner conductor 1, an insulating layer 2, an outer conductor 3, and a sheath 4 arranged in sequence from the inside to the outside, wherein the insulating layer 2 includes an inner skin layer 21, a first foaming layer, a second foaming layer, a third foaming layer, a fourth foaming layer, and an outer skin layer 23 prepared by a multi-layer foaming extrusion process. The foaming volume ratios of the first foaming layer, the second foaming layer, the third foaming layer, and the fourth foaming layer are 2.1:3.5:5:5. The foaming material of the first foaming layer is homopolypropylene and low-density polyethylene, with a melt flow rate of approximately 2.6 g / 10 min, the foaming gas is carbon dioxide, the gas injection pressure is 200 bar, the chamber pressure is 150 bar, and the chamber temperature is 160 °C; the foaming material of the second foaming layer is a mixture of random polypropylene and low-density polyethylene, with a melt flow rate of approximately 6.8 g / 10 min, the foaming gas is argon, the gas injection pressure is 266 bar, the chamber pressure is 170 bar, and the chamber temperature is 170 °C; the foaming material of the third foaming layer is high-density polyethylene and low-density polyethylene with a density of 0.955 g / cm 3 , with a melt flow rate of approximately 8.9 g / 10 min, the foaming gas is nitrogen, the gas injection pressure is 346 bar, the chamber pressure is 190 bar, and the chamber temperature is 180 °C; the foaming material of the fourth foaming layer is a mixture of high-density polyethylene and low-density polyethylene with a density of 0.945 g / cm 3 , with a melt flow rate of approximately 16.7 g / 10 min, the foaming gas is perfluorocyclobutane, the gas injection pressure is 371 bar, the chamber pressure is 200 bar, and the chamber temperature is 200 °C; the outer skin is made of low-density polyethylene and 6% wt. of wollastonite; slots 31 are provided on the outer conductor 3. The bubble degree of the insulating layer 2 in the ultra-low attenuation leaky coaxial cable provided in this embodiment is about 85.1%.

[0060] The ultra-low attenuation leaky coaxial cables obtained in Embodiments 1 to 3 of the present invention and the ultra-low attenuation leaky coaxial cable with a bubble degree of 80% obtained by single-layer foaming in the prior art are used as comparative examples for application. The change in the attenuation value is shown in Table 1. It can be seen that with the increase in the bubble degree, the attenuation level has been significantly improved. The attenuation per 100 meters at 2700 MHz of a 1-5 / 8-inch leaky coaxial cable can be reduced from 5.8 dB to about 5.2 dB.

[0061] Table 1 Cable attenuation values at different foaming degrees

[0062]

[0063] In the description of the present application, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more, unless otherwise specifically defined.

[0064] In addition, the reference to "one embodiment" throughout this specification; the language such as "one embodiment", "one example" or the like means that the specific features, structures or characteristics described in connection with that embodiment are included in at least one embodiment of the present application. Thus, the appearances of the phrase "in one embodiment;" and "in one embodiment" and similar language throughout this specification may or may not all refer to the same embodiment.

[0065] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. An ultra-low attenuation leaky coaxial cable, characterized in that: include: Inner conductor (1); An insulating layer (2), comprising an inner skin layer (21) arranged from the inside to the outside, a preset number of foaming layers (22), and an outer skin layer (23), wherein the foaming layer (22) is prepared by a multi-layer foaming extrusion process, and in any two adjacent foaming layers (22), the ratio of the melt flow rate of the foaming material of the inner foaming layer to that of the outer foaming layer is 1:1.2 to 1:3, and the critical pressure of the foaming gas of the inner foaming layer is greater than that of the outer foaming layer by more than 10 bar, thereby improving the uniformity of the pores and the foaming degree of the insulating layer (2) by the multi-layer foaming extrusion process; at the same time, the outer skin layer (23) is made of a composite material of polyethylene and a hardener to improve the hardness of the insulating layer (2), thereby avoiding the problem that the insulating layer (2) is compressed and deformed during the production of the finished product due to the increased foaming degree of the insulating layer (2), thereby causing an uneven outer diameter; An outer conductor (3), the outer conductor (3) being provided with a preset number of slots (31); and Sheath (4).

2. The ultra-low attenuation leaky coaxial cable according to claim 1, characterized in that: The added ratio of the hardener in the outer skin layer (23) is 4%wt. to 6%wt.

3. The ultra-low attenuation leaky coaxial cable according to claim 1, characterized in that: The hardener includes one or more of talc, calcium carbonate, and wollastonite.

4. The ultra-low attenuation leaky coaxial cable according to claim 1, characterized in that: The polyethylene is low-density polyethylene.

5. The ultra-low attenuation leaky coaxial cable according to claim 1, characterized in that: When the foaming layer (22) is prepared by a multi-layer foaming extrusion process, in any two adjacent foaming layers (22), the gas injection pressure and the chamber pressure of the inner foaming layer and the outer foaming layer satisfy the following relationship: In the formula, is the pressure difference between the injection pressure of the outer foam layer and the chamber pressure, is the chamber pressure of the outer foam layer, is the pressure difference between the injection pressure of the inner foam layer and the chamber pressure, is the chamber pressure of the inner foam layer, is the chamber temperature of the outer foaming layer, is the chamber temperature of the inner foam layer, is the foaming volume of the outer foaming layer, It is the foaming volume of the inner foaming layer.

6. The ultra-low attenuation leaky coaxial cable according to claim 1, characterized in that: In the two adjacent foam layers (22), the foaming volume ratio of the inner foam layer to the outer foam layer is 1:1 to 1:

4.

7. The ultra-low attenuation leaky coaxial cable according to claim 1, characterized in that: The number of layers of the foaming layer (22) is 2 to 4.

8. The ultra-low attenuation leaky coaxial cable according to claim 1, characterized in that: The foaming material includes one or more of homopolymer polypropylene, low-density polyethylene, high-density polyethylene, and random polypropylene, and the foaming gas includes one or more of nitrogen, argon, carbon dioxide, and octafluorocyclobutane.

9. The ultra-low attenuation leaky coaxial cable according to any one of claims 1 to 8, characterized in that: The diameter of the inner conductor (1) is 4.6 mm to 18.5 mm, the outer diameter of the insulating layer (2) is 12 mm to 42 mm, the outer diameter of the outer conductor (3) is 12.5 mm to 44.5 mm, and the outer diameter of the sheath (4) is 15 mm to 51 mm.

Images