Ultralow-attenuation leaky coaxial cable

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to an ultralow-attenuation leaky coaxial cable, which comprises an inner conductor, an insulating layer, an outer conductor with a slotted hole and a sheath, the insulating layer comprises an inner skin layer, a foaming layer and an outer skin layer, the foaming layer is prepared by adopting a multi-layer foaming extrusion process, and by optimizing a foaming material formula of the insulating layer, the thickness of the outer skin layer is reduced. Compared with the leaky coaxial cable with the same specification and the foaming degree of 80%, the leaky coaxial cable has the advantages that the attenuation index of the leaky coaxial cable can be improved by about 10%, for example, the attenuation of 2700MHz per hundred meters of the leaky coaxial cable of 1-5 / 8 inches can be reduced from 5.8 dB to about 5.2 dB; meanwhile, in order to avoid the problem that the insulation layer is pressed and deformed in the production process of a finished product to cause non-uniform outer diameter due to the fact that the insulation layer becomes soft due to too high foaming degree, the outer skin layer is made of a composite material of polyethylene and a hardening agent.

Description

Technical Field

[0001] The present application belongs to the field of wireless communication technology, and more specifically, relates to an ultra-low attenuation leakage coaxial cable. Background Art

[0002] The attenuation index of leaky coaxial cable mainly includes conductor attenuation (determined by the metal layer of the inner and outer conductors), dielectric attenuation (determined by the insulating medium between the inner and outer conductors) and radiation attenuation (only for leaky coaxial cable, there are slots on the outer conductor of leaky coaxial cable that can radiate electromagnetic waves to the far field space. The outward radiation energy causes radiation attenuation, and the radiation attenuation is basically determined by the form of the slots). Since the structure of leaky coaxial cable has been roughly determined according to industry standards and national standards, and the conductor is made of high-purity copper, the material has a high cost performance. Therefore, in order to achieve ultra-low attenuation, the current optimization is mainly based on the insulation material.

[0003] By adjusting the foaming degree of the insulation layer, the overall attenuation index of the cable can be optimized to a large extent. At present, the maximum foaming degree achieved by domestic manufacturers is usually 80%, and the limit value can reach 82%. However, when the foaming degree is close to the limit, a small number of uneven holes will appear in the insulation layer. This phenomenon 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 the foaming gas will escape too violently, causing the foaming layer and the pores to be uneven, and even the pores will rupture and merge to form large holes, which has a serious negative impact on the electrical transmission performance of the cable.

[0004] The existing technology uses different foaming gases for mixed foaming, and uses the differences between different gases in the supercritical state to make the positions with different diameters in the foaming layer closer in foaming rate than when a single gas is foaming, so that the pore distribution is more uniform. Because at normal temperature and pressure, the gas mass accounts for a very small proportion of the insulating layer, and the gas used for foaming has stable chemical properties and a low dielectric constant, the effect of the gas dielectric constant on the dielectric constant of the foaming layer is negligible. Despite this, this single-layer foaming mixed gas will still have the problem of violent and uneven gas escape in the case of ultra-large foaming degree, which limits the increase in foaming degree, generally only close to 82%, and it is difficult to achieve a higher foaming degree breakthrough. Summary of the invention

[0005] In view of the defects of the prior art, the present application provides an ultra-low attenuation leaky coaxial cable, aiming to solve the problem that the foaming degree of the existing insulation 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 the present application, there is provided an ultra-low attenuation leaky coaxial cable, comprising: Inner conductor; An insulating layer, comprising an inner skin layer, a preset number of foaming layers and an outer skin layer arranged from the inside to the outside, wherein the foaming layer is 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 the critical pressure of the foaming gas of the inner foaming layer is greater than 10 bar than that of the outer foaming layer, thereby improving the uniformity of the pores and the foaming degree of the insulating 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 hardener to improve the hardness of the insulating layer, so as to avoid the problem of uneven outer diameter caused by compression deformation of the insulating layer during subsequent finished product production due to the increase in the foaming degree of the insulating layer; an outer conductor having a predetermined number of slots; and jacket.

[0007] Through the above technical scheme 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 foaming material and the type of foaming gas used in each foaming layer, which can ensure that the pore size of each foaming layer is uniform, and the foaming degree can reach up to about 85%, so that the overall attenuation index of the leaky coaxial cable can be effectively improved. Compared with the 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 foaming layer from becoming soft due to excessive foaming, resulting in the problem of uneven outer diameter caused by compression deformation of the insulating layer in the subsequent finished product production process.

[0008] As further preferred, the addition ratio of the hardener in the outer skin layer is 4%wt. to 6%wt.

[0009] As further preferred, the hardener includes one or more of talc, calcium carbonate, and wollastonite.

[0010] As further preferred, the polyethylene is low-density polyethylene.

[0011] As a further preferred embodiment, when the foaming layer is prepared by a multi-layer foaming extrusion process, in any two adjacent foaming layers, the gas injection pressure and the chamber pressure of the inner foaming layer and the outer foaming layer satisfy the following relationship:

[0012] 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.

[0013] As further preferred, in the two adjacent foam layers, the foaming volume ratio of the inner foam layer to the outer foam layer is 1:1 to 1:4.

[0014] As further preferred, the number of the foaming layer is 2 to 4 layers.

[0015] As a further preferred embodiment, the foaming material includes homopolymer polypropylene, low-density polyethylene, high-density polyethylene, random polypropylene, and a density of 0.941 g / cm 3 ~0.950g / cm 3 The foaming gas comprises one or more of nitrogen, argon, carbon dioxide, and octafluorocyclobutane.

[0016] As further preferred, 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.

[0017] In general, the above technical solutions conceived by this application have the following technical advantages compared with the prior art: 1. The present application adopts a multi-layer foaming extrusion process to prepare the foaming layer, and optimizes the foaming material and foaming gas type of each foaming layer, which can ensure that the pore size of each foaming layer is uniform and the foaming degree is up to about 85%, thereby effectively improving the overall attenuation index of the leaky coaxial cable. Compared with the leaky coaxial cable of the same specification with 80% foaming degree, the attenuation index can be improved by about 10%, such as the 2700MHz per 100 meters attenuation of the 1-5 / 8-inch leaky coaxial cable can be reduced from 5.8dB to about 5.2dB. At the same time, considering that the substantial increase in the foaming degree of the foaming layer will lead to a decrease in the rigidity of the insulating layer, resulting in the problem of uneven outer diameter due to the local stress of the insulating layer in the subsequent production of the finished product, the present application also optimizes the formula of the outer skin layer, by adding a hardener to improve the outer surface rigidity of the insulating layer, to avoid the problem of the cable generating tiny standing waves at uneven locations, thereby causing significant deterioration of electrical performance; 2. At the same time, the application optimizes the addition ratio of the hardener in the outer skin layer, which can ensure the rigidity of the insulation layer while avoiding the reduction of the toughness of the insulation layer surface and easy cracking; 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 pore sizes of each foaming layer are uniform and avoid the problem of pore rupture and merging to form large holes. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a cross-sectional view of an ultra-low attenuation leaky coaxial cable provided in an embodiment of the present application; Figure 2 It is a schematic diagram of foaming by an extruder provided in an embodiment of the present application; Figure 3 It is a schematic diagram of the structure of an ultra-low attenuation leaky coaxial cable provided in an embodiment of the present application.

[0019] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-inner conductor, 2-insulating layer, 21-inner skin layer, 22-foaming layer, 23-outer skin layer, 3-outer conductor, 31-slot, 4-sheath, 5-inner skin material chamber, 6-first foaming material chamber, 7-Nth foaming material chamber, 8-outer skin material chamber. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying 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.

[0021] like Figure 1 , 3 As shown, the present application provides an ultra-low attenuation leaky coaxial cable, each 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, The inner conductor 1 is usually made of a metal with good conductivity, such as copper or aluminum. The inner conductor 1 of a small cable is usually made of copper wire or copper-clad aluminum wire, while the inner conductor 1 of a large cable is usually made of copper tube, so as to reduce the weight and cost of the cable while ensuring the conductivity. As a carrier of signal transmission, the signal current flows in it, and it undertakes the important task of transmitting the electrical signal from the transmitting end to the receiving end, which plays a key role in the quality and efficiency of signal transmission; The insulating layer 2 includes an inner skin layer 21, a preset number of foaming layers 22 and an outer skin layer 23 arranged from the inside to the outside, wherein: The inner skin layer 21 is coated on the outer side of the inner conductor 1 to facilitate close bonding with the foaming layer 22; The foaming material of the foaming layer 22 is subjected to high temperature and high pressure in the extruder equipment so that the foaming gas reaches a supercritical fluid state. In this state, the foaming gas has the solubility and diffusion ability of gas, and at the same time has the form of liquid, which can be better mixed with other fluids. In this way, the foaming gas is fully and evenly mixed into the high-temperature and high-pressure foaming material melt, and the pressure and temperature are gradually released in the head. The foaming gas gradually escapes from the inside to the outside, and the mixture of the foaming material forms fine bubbles with the help of the nucleating component. The bubbles capture the escaped foaming gas and expand it, finally forming a lightweight The insulation layer structure with high foaming degree; the difficulty of this process is that when the foaming degree is high, the amount of gas is large, and the escape becomes more uncontrollable, especially when the insulation layer 2 of the cable with larger specifications is relatively thick, and the expansion speed of the foaming material becomes slower and slower from the inside to the outside (the expansion rate is inversely proportional to the insulation radius, and the larger the foaming diameter, the smaller the rate of change of the foaming expansion diameter). When the gas escapes, it is easy to cause the bubble cells to burst, resulting in uneven large holes, resulting in the cable being unformed or the electrical performance being poor. Therefore, the present application proposes to use a multi-layer foaming extrusion process to prepare the foaming layer. For any two adjacent foaming layers, The ratio of the melt flow rate (MFR) of the foaming material of the foam layer 22, the inner foam layer and the outer foam layer is 1:1.2 to 1:3, so as to ensure that the viscosity of the foaming material of the inner foam layer is greater than that of the outer foam layer to a certain extent, and avoid that the melt flow rate is too low, resulting in low viscosity and difficulty in foaming molding. At the same time, the critical pressure of the foaming gas of the inner foam layer in the adjacent foam layers 22 is greater than that of the outer foam layer by more than 10 bar, so as to use the gas amount matching the foaming material of each foam layer, so as to ensure that the foaming degree of each foam layer 22 is relatively uniform and the pore size is uniform. By optimizing the foaming materials and foaming gas of each foaming layer, the uniformity and foaming degree of the pores of the insulating layer can be effectively improved, so that the foaming degree of each foaming layer in the insulating layer 2 is as large as possible, breaking through the limit of 82% in the prior art, and the maximum can reach about 85%, and the inner and outer pores are closer in size, the uniformity of the pores in the insulating layer 2 is improved, and the dielectric constant of the insulating layer 2 is as small as possible, thereby effectively improving the overall attenuation index of the leaky coaxial cable. Compared with the leaky coaxial cable of the same specification with a foaming degree of 80%, the attenuation index can be improved by about 10%; The outer skin layer 23 is made of a composite material of polyethylene and a hardener. 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 conductor metal outside the insulating layer 2 to form the outer conductor 3. However, the soft insulating layer 2 lacks support and is squeezed when passing through the sizing mold, resulting in an uneven outer diameter. Therefore, the present application adds a hardener to the outer skin layer 23, so that the rigidity of the outer surface of the insulating layer 2 is improved, and it is smoother and easier to pass through the mold. The measured outer diameter change rate is less than 0.5%, which is basically negligible, thereby avoiding the uneven outer diameter causing the leaky coaxial cable to generate tiny standing waves at uneven locations, which may cause significant degradation of electrical performance in severe cases, thereby affecting the final use performance; The outer conductor 3 is generally made of copper strip, aluminum foil or metal braided mesh, etc. These materials have good electrical conductivity and shielding performance. A series of slots or gaps are opened on the outer conductor, such as continuous or discontinuous longitudinal slots, periodic eight-shaped slots, straight slots, elliptical slots, Z-shaped slots, etc. The shape, size, pitch of the slots and the thickness of the outer conductor and other parameters can be precisely controlled as needed 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, it constitutes a complete signal transmission path; on the other hand, it plays a shielding role to reduce the influence of external electromagnetic interference on the signal in 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 to the space along the line, thereby covering the blind area of ​​the electromagnetic field or receiving electromagnetic signals from the outside; The material of the sheath 4 can be polyvinyl chloride (PVC), polyethylene (PE), black linear low-density polyethylene, etc. For occasions with special requirements, low-smoke halogen-free flame retardant materials will also be used; the sheath 4 should be tightly wrapped around the outside of the outer conductor 3, have a certain thickness and mechanical strength, a smooth surface, no obvious defects, and be able to adapt to different laying environments and use requirements. At the same time, the sheath 4, as the outermost protective structure of the cable, mainly plays the role of waterproofing, moisture-proofing, insulation and protecting internal components, preventing the cable from external physical damage, chemical corrosion and ultraviolet radiation, etc., 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 a role in flame retardancy and preventing the spread of fire.

[0022] The foaming degree is the volume of the void part of the pores in the insulating layer divided by the volume of the upper insulating layer. An increase of 1% on the basis of 80% foaming degree means that the material usage of the solid part of the insulating layer is reduced by one twentieth. The present application adopts a multi-layer foaming extrusion process to prepare the insulating layer 2, and optimizes the foaming material and foaming gas type of each foaming layer 22, which can ensure that the pore size of each foaming layer 22 is uniform and the foaming degree is up to about 85%, which is a huge improvement compared with the 80% foaming cable in the prior art. At the same time, the formula of the outer skin layer 23 in the insulating layer 2 is optimized to avoid the problem of uneven outer diameter, thereby effectively improving the overall attenuation index of the leaky coaxial cable. Compared with the cable with the same specification and 80% foaming degree, the attenuation index can be improved by about 10%, such as the attenuation per 100 meters of the 1-5 / 8-inch leaky coaxial cable at 2700MHz can be reduced from 5.8dB to about 5.2dB.

[0023] Use Figure 2 The extruder shown prepares the insulating layer 2 on the outside of the inner conductor 1. The head of the extruder is connected with the inner skin material chamber 5, the first foaming material chamber 6, ..., the Nth foaming material chamber 7 and the outer skin material chamber 8 in sequence along the extrusion direction, and then the insulating layer 2 having the inner skin layer 21, the Nth foaming layer 22 and the outer skin layer 23 is prepared by a multi-layer foaming extrusion process. The inner conductor 1 in the head moves forward at a uniform speed, and the insulating material is wrapped on the inner conductor 1 from the inner layer to the outer layer according to the sequence of injection into the head; the inner skin layer 21 and the outer skin layer 23 are respectively the innermost layer and the outermost layer of the insulating layer 2. In a preferred embodiment of the present application, the inner skin layer 21 and the outer skin layer 23 are non-foamed thin layers made of polyethylene. The foaming layer 22 is between the inner and outer skin layers, which is formed by melting and mixing different foaming materials and gas. The characteristics of the foaming materials of each layer are that the foaming material of the inner foaming layer has a higher viscosity, the foaming gas of the inner foaming layer has a higher critical pressure, and the critical temperature of each foaming gas should be lower than the melt temperature of the foaming material, so that the inner layer gas evaporates from the foaming material melt relatively early during the process of pressure drop of the extruder head; the temperature of each machine chamber and the screw speed can control the final volume and foaming degree of the foaming layer.

[0024] Furthermore, the addition ratio of the hardener in the outer skin layer is 4%wt. to 6%wt., and adding too much hardener will reduce the surface toughness of the insulating layer 2 and make it easy to crack, while adding too little hardener will not achieve a good hardening effect. At the same time, the hardener is preferably one or more of talc, calcium carbonate, and wollastonite, and the polyethylene is preferably low-density polyethylene.

[0025] Furthermore, the injection pressure difference of the outer foam layer is greater than that of the inner foam layer. The greater the injection pressure difference, the greater the injection amount, and it is easier for the outer foam layer with a larger volume to obtain a foaming degree that matches the inner foam layer; while the inner foam layer has a small volume, a smaller injection amount can obtain a higher foaming degree, but it is relatively more likely to have bubbles. At the same time, considering that the injection pressure is related to the chamber pressure, chamber temperature and foaming volume, therefore, in order to ensure that the bubbles of each foam layer are uniform and the foaming degree is high, when the foam layer is prepared by a multi-layer foaming extrusion process, in any two adjacent foam layers 22, the injection pressure and chamber pressure of the inner foam layer and the outer foam layer satisfy the following relationship,

[0026] 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.

[0027] Furthermore, in the two adjacent foaming layers, the foaming volume ratio of the inner foaming layer to the outer foaming layer is 1:1 to 1:4, thereby ensuring that the inner layer foaming process is quickly completed and the inner layer rapid expansion process is basically completed when the outer layer foaming begins to expand. The inner and outer layers will not significantly restrict each other during foaming and affect the size of the bubbles at the boundary.

[0028] Furthermore, the number of the foaming layer 22 is 2 to 4, so as to ensure uniform foaming of the insulation layer and avoid production difficulties and increased production costs caused by too many layers.

[0029] Furthermore, the foaming material includes one or more of homopolymer polypropylene HPP, low-density polyethylene LDPE (density range is 0.910 g / cm³~0.930 g / cm³), high-density polyethylene HDPE (density range is 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.

[0030] Furthermore, when the number of foaming layers 22 is 2, 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 homopolymer polypropylene (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.

[0031] Further, when the number of the foaming layer 22 is 3, 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 homopolymer polypropylene and low-density polyethylene, and the foaming gas is argon; the foaming material of the second foaming layer is a mixture of polypropylene and low-density polyethylene with a density of 0.951 g / cm 3 ~0.965g / cm 3 The foaming gas is nitrogen; the foaming material of the third foaming layer has a density of 0.941g / cm 3 ~0.950g / cm 3 It is a mixture of high-density polyethylene and low-density polyethylene, and the foaming gas is octafluorocyclobutane.

[0032] Further, when the number of layers of the foaming layer 22 is 4, the foaming layer 22 includes a first foaming layer, a second foaming layer, a third foaming layer and a fourth foaming layer which are arranged in sequence from the inside to the outside. The foaming material of the first foaming layer is a mixture of homopolymer polypropylene 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 argon with a density of 0.951 g / cm 3 ~0.965g / cm 3 The foaming gas is nitrogen; the foaming material of the fourth foaming layer has a density of 0.941g / cm 3 ~0.950g / cm 3 It is a mixture of high-density polyethylene and low-density polyethylene, and the foaming gas is octafluorocyclobutane.

[0033] Furthermore, 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.

[0034] The technical solution provided by this application is further described below based on specific embodiments.

[0035] Example 1 An ultra-low attenuation leakage coaxial cable comprises an inner conductor 1, an insulating layer 2, an outer conductor 3 and a sheath 4 which are sequentially arranged from the inside to the outside, wherein the insulating layer 2 comprises an inner skin layer 21, a first foaming layer prepared by a multi-layer foaming extrusion process, a second foaming layer and an outer skin layer 23, 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, the melt flow rate is about 2.6g / 10min, the foaming gas is carbon dioxide, the injection pressure is 200bar, the chamber pressure is 150bar, and the chamber temperature is 160°C; the foaming material of the second foaming layer is a mixture of high-density polyethylene and low-density polyethylene, the melt flow rate is about 7.8g / 10min, the foaming gas is octafluorocyclobutane, the injection pressure is 266bar, the chamber pressure is 170bar, and the chamber 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 normal pressure, it starts to gasify and expand before the outer layer of octafluorocyclobutane. Since the material viscosity of the first foaming layer is high, the bubbles are not easy to break, so that the first foaming layer can quickly form an inner layer with a high foaming degree; the critical pressure of octafluorocyclobutane in the second foaming layer is 27.8 bar, which is lower, and the foaming process starts later than the first foaming layer. Moreover, the outer diameter of this layer is large, and when the temperature and pressure change, the outer diameter grows slower than the inner layer. Therefore, the melt of the second foaming layer needs to maintain a higher temperature to make the outer layer fully foamed, and the low viscosity increases the expansion rate to a certain extent; the outer skin layer is made of polyethylene and 5%wt. calcium silicate; and the outer conductor 3 is provided with slots 31. The foaming degree of the insulating layer 2 in the ultra-low attenuation leakage coaxial cable provided in this embodiment is about 82.8%.

[0036] Example 2 An ultra-low attenuation leaky coaxial cable comprises an inner conductor 1, an insulating layer 2, an outer conductor 3 and a sheath 4 which are sequentially arranged from the inside to the outside, wherein the insulating layer 2 comprises 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 ratio of the first foaming layer, the second foaming layer and the third foaming layer is 2.1:3.5:5, the foaming material of the first foaming layer is homopolymer polypropylene and low-density polyethylene, the melt flow rate is about 2.6g / 10min, the foaming gas is carbon dioxide, the gas injection pressure is 200bar, the chamber pressure is 150bar, and the chamber temperature is 160℃; the foaming material of the second foaming layer is a density of 0.955g / cm 3 The mixture of high-density polyethylene and low-density polyethylene has a melt flow rate of about 7.2g / 10min, the foaming gas is argon, the injection pressure is 266bar, the chamber pressure is 170bar, and the chamber temperature is 170℃; the foaming material of the third foaming layer is a density of 0.945g / cm 3The mixture of high-density polyethylene and low-density polyethylene, the melt flow rate is about 15g / 10min, the foaming gas is octafluorocyclobutane, the gas injection pressure is 346bar, the chamber pressure is 190bar, and the chamber temperature is 180℃; the outer skin layer is made of low-density polyethylene and 4%wt. talcum powder; the outer conductor 3 is provided with a slot 31. The foaming degree of the insulating layer 2 in the ultra-low attenuation leaky coaxial cable provided in this embodiment is about 83.9%.

[0037] Example 3 An ultra-low attenuation leaky coaxial cable comprises 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 comprises 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 ratio of the first foaming layer, the second foaming layer, the third foaming layer and the fourth foaming layer is 2.1:3.5:5:5, the foaming material of the first foaming layer is homopolymer polypropylene and low-density polyethylene, and the melt flow The rate is about 2.6g / 10min, the foaming gas is carbon dioxide, the injection pressure is 200bar, the chamber pressure is 150bar, and the chamber temperature is 160℃; the foaming material of the second foaming layer is a mixture of random polypropylene and low-density polyethylene, the melt flow rate is about 6.8g / 10min, the foaming gas is argon, the injection pressure is 266bar, the chamber pressure is 170bar, and the chamber temperature is 170℃; the foaming material of the third foaming layer is a density of 0.955g / cm 3 The high-density polyethylene and low-density polyethylene have a melt flow rate of about 8.9g / 10min, the foaming gas is nitrogen, the injection pressure is 346bar, the chamber pressure is 190bar, and the chamber temperature is 180℃; the foaming material of the fourth foaming layer is a density of 0.945g / cm 3 The mixture of high-density polyethylene and low-density polyethylene has a melt flow rate of about 16.7g / 10min, the foaming gas is octafluorocyclobutane, the gas injection pressure is 371bar, the chamber pressure is 200bar, and the chamber temperature is 200℃; the outer skin is made of low-density polyethylene and 6%wt. wollastonite; and the outer conductor 3 is provided with a slot 31. The foaming degree of the insulating layer 2 in the ultra-low attenuation leaky coaxial cable provided in this embodiment is about 85.1%.

[0038] The ultra-low attenuation leaky coaxial cables obtained in Examples 1 to 3 of the present invention and the ultra-low attenuation leaky coaxial cables with a foaming degree of 80% obtained by single-layer foaming in the prior art were used as comparative examples, and the changes in their attenuation values ​​are shown in Table 1. It can be seen that as the foaming degree is improved, the attenuation level is significantly improved, and the attenuation per 100 meters of the 1-5 / 8 inch leaky coaxial cable at 2700MHz can be reduced from 5.8dB to about 5.2dB.

[0039] Table 1 Attenuation values ​​of cables with different foaming degrees

[0040] In the description of the present application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the feature. In the description of the present application, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0041] In addition, references throughout this specification to "one embodiment"; "one embodiment", "an example" or similar language indicate that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present application. Thus, appearances of the phrase "in one embodiment"; "in one embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0042] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection 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.

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