An ultra-low attenuation radio frequency coaxial cable

Abstract

This application belongs to the field of wireless communication technologies. More specifically, it relates to an ultra-low attenuation radio frequency coaxial cable, which includes an inner conductor, an insulating layer, an outer conductor, and a sheath arranged in sequence from the inside to the outside. By optimizing the formula of the insulating layer foaming material, the uniformity of the pores in the foaming layer is improved, and the foaming degree can reach up to about 85%, thereby effectively improving the overall attenuation index of the radio frequency coaxial cable. Compared with a radio frequency 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 1-1 / 4-inch radio frequency coaxial cable can be reduced from 6.3 dB to about 5.64 dB.

Description

Technical Field

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

[0002] The insulating medium of a radio frequency coaxial cable is generally a lightweight and highly foamed insulating medium made by physically foaming a polyethylene polymer, which has a dielectric constant performance close to that of air (the ideal air is 1, and the dielectric constant of a highly foamed polyethylene insulation can reach 1.2). According to the theoretical formulas of the dielectric attenuation α G and the conductor attenuation α R the dielectric attenuation and the conductor attenuation are jointly determined by the dielectric constants of the dielectric and the conductor. Therefore, both the conductor attenuation and the dielectric attenuation are affected by the dielectric constant of the insulating layer.

[0003] Adjusting the foaming degree of the insulating layer can greatly improve the overall attenuation index of the cable. Currently, the maximum foaming degree of domestic manufacturers can basically reach 80%, and the limit can reach 82% (but there will be a small amount of uneven holes), which in turn leads to the inability to further improve the overall attenuation index of the cable. This is mainly because after the foaming degree is too large, the bubble holes in the foaming layer grow too fast, and the foaming gas escapes too violently, resulting in uneven foaming layers and uneven bubble holes. Even, some bubble holes break and merge to form large holes, seriously affecting the electrical transmission performance of the cable.

[0004] The prior art proposes to use a mixture of different foaming gases for foaming. Depending on the different supercritical states of different gases, the foaming rates at positions with small and large diameters of the foaming layer are relatively closer to each other than those of a single gas. Therefore, the bubble holes are more uniform. Since the mass of the gas accounts for a very small proportion in the insulating layer under normal temperature and pressure, and the foaming gas has an inactive chemical property and a relatively low dielectric constant of its own, the influence of the dielectric constant of the gas on the dielectric constant of the foaming layer can be ignored. However, in the case of an extremely large foaming degree, this single-layer foaming mixed gas still has a severe and uneven gas escape situation, and the improvement of the foaming degree is limited (generally close to 82%, and it is difficult to reach a higher level). Summary of the Invention

[0005] Aiming at the defects of the prior art, this application provides an ultra-low attenuation radio frequency 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 radio frequency coaxial cable.

[0006] According to one aspect of this application, an ultra-low attenuation radio frequency coaxial cable is provided, which includes an inner conductor, an insulating layer, an outer conductor, and a sheath arranged in sequence from the inside to the outside. The insulating layer includes an inner skin layer, a foaming layer with a preset number of layers prepared by a multi-layer foaming extrusion process, and an outer skin layer from the inside to the outside;

[0007] For 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. 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. Furthermore, the pore uniformity and foaming degree of the insulating layer are improved through the multi-layer foaming extrusion process.

[0008] Through the above technical solutions conceived in this application, compared with the prior art, this application uses the multi-layer foaming extrusion process to prepare the foaming layer, and optimizes the types of foaming materials and foaming gases for each foaming layer, which can ensure that the pore sizes of each foaming layer are uniform and the foaming degree can reach up to about 85%. Furthermore, the overall attenuation index of the RF coaxial cable is effectively improved. Compared with a cable with a foaming degree of 80% of the same specification, the attenuation can be improved by about 10%.

[0009] As a further preference, when using the multi-layer foaming extrusion process to prepare the foaming layer, among 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:

[0010]

[0011] In the formula, is the pressure difference between the injection pressure and the barrel pressure of the outer foaming layer, is the barrel pressure of the outer foaming layer, is the pressure difference between the injection pressure and the barrel pressure of the inner foaming layer, is the barrel pressure of the inner foaming layer, is the barrel temperature of the outer foaming layer, is the barrel temperature of the inner foaming layer, is the foaming volume of the outer foaming layer, is the foaming volume of the inner foaming layer.

[0012] As a further preference, among two adjacent foaming layers, the foaming volume ratio of the inner foaming layer to the outer foaming layer is 1:1 to 1:4.

[0013] As a further preference, the number of layers of the foaming layer is 2 to 4 layers.

[0014] As a further preference, the foaming material includes one or more of homopolypropylene, low-density polyethylene, high-density polyethylene, and random polypropylene, and the foaming gas includes one or more of nitrogen, argon, carbon dioxide, and octafluorocyclobutane.

[0015] As a further preference, when the number of layers of the foaming layer is 2, the foaming layer 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 and low-density polyethylene, and the foaming gas is carbon dioxide; the foaming material of the second foaming layer is a mixture of high-density polyethylene and low-density polyethylene, and the foaming gas is perfluorocyclobutane.

[0016] As a further preference, when the number of layers of the foaming layer is 3, the foaming layer 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 and low-density polyethylene with a density of 0.951 g / cm 3 ~0.965 g / cm 3 and the foaming gas is nitrogen; the foaming material of the third foaming layer is a mixture of high-density polyethylene and low-density polyethylene with a density of 0.941 g / cm 3 ~0.950 g / cm 3 and the foaming gas is perfluorocyclobutane.

[0017] As a further preference, when the number of layers of the foaming layer is 4, the foaming layer 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 atactic polypropylene 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 and low-density polyethylene with a density of 0.951 g / cm 3 ~0.965 g / cm 3 and the foaming gas is nitrogen; the foaming material of the fourth foaming layer is a mixture of high-density polyethylene and low-density polyethylene with a density of 0.941 g / cm 3 ~0.950 g / cm 3 and the foaming gas is perfluorocyclobutane.

[0018] 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.

[0019] Generally speaking, compared with the prior art by the above technical solutions conceived in this application, the following technical advantages are mainly possessed:

[0020] 1. This application uses a multi-layer foaming extrusion process to prepare the foaming layer, and optimizes the foaming materials and types of foaming gases for each foaming layer, which can ensure that the cell sizes of each foaming layer are uniform and the foaming degree can reach up to about 85%. Furthermore, it can effectively improve the overall attenuation index of the radio frequency coaxial cable. Compared with the radio frequency coaxial cable with a foaming degree of 80% of the same specification, the attenuation index can be improved by about 10%. For example, for a 1-1 / 4-inch radio frequency coaxial cable, the attenuation per 100 meters at 2700 MHz can be reduced from 6.3 dB to 5.64 dB.

[0021] 2. In particular, this application optimizes the gas injection pressure and 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 cell rupture and merger to form large holes.

[0022] 3. In addition, this application optimizes the foaming volume of the inner and outer foaming layers in adjacent foaming layers, which can ensure that when the outer foaming layer expands, the inner foaming layer expansion is basically completed, avoiding mutual restriction during the foaming of the inner and outer layers and affecting the cell size at the boundary. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a cross-sectional view of the ultra-low attenuation radio frequency coaxial cable provided by the embodiment of this application;

[0024] Figure 2 is a schematic structural diagram of the ultra-low attenuation radio frequency coaxial cable provided by the embodiment of this application;

[0025] Figure 3 is a schematic diagram of the foaming of the extruder provided by the embodiment of this application.

[0026] In all the drawings, the same reference numerals are used to represent the same elements or structures, where:

[0027] 1 - inner conductor, 2 - insulating layer, 21 - inner skin layer, 22 - foaming layer, 23 - outer skin layer, 3 - outer conductor, 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

[0028] In order to make the objectives, technical solutions and advantages of this application clearer, the following further describes this application in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0029] As Figure 1 , 2 shown, this application provides an ultra-low attenuation radio frequency 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.

[0030] The inner conductor 1 is usually made of high-purity copper or copper alloy, such as annealed copper wire, annealed copper tube, copper-clad aluminum wire, etc. Sometimes, in order to reduce losses, silver is plated on the copper surface. For some special applications, steel-clad copper wire, aluminum-clad copper wire, aluminum tube or corrugated copper tube is also used. As the carrier for signal transmission, it is responsible for transmitting the radio frequency signal from one end to the other end;

[0031] The insulating layer 2 includes an inner skin layer 21, a preset number (i.e., a preset number) of foam layers 22 prepared by a multi-layer foam extrusion process, and an outer skin layer 23. The inner skin layer 21 is coated on the outside of the inner conductor 1 to facilitate close bonding with the foam layer 22, and the outer skin layer 23 is coated on the outside of the foam layer 22;

[0032] The foaming material of the foaming layer 22 reaches the supercritical fluid state under high temperature and high pressure in the extrusion equipment. 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, which can better mix and blend with other fluids. In this way, the foaming gas is fully and evenly mixed into the melt of the foaming material under high temperature and high pressure. 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 is 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 22 to that of the outer foaming layer 22 is 1:1.2 to 1:3, so as to ensure that the viscosity of the foaming material of the inner foaming layer 22 is greater than that of the outer foaming layer 22 to a certain extent, avoiding the low viscosity caused by too low melt flow rate and being not easy to foam and form. At the same time, the critical pressure of the foaming gas of the inner foaming layer 22 in the adjacent foaming layers 22 is more than 10 bar greater than that of the outer foaming layer 22, so as to use the gas volume matching the foaming material of each foaming layer, ensuring that the foaming degree of each foaming layer 22 is relatively uniform and the pore size is 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 reaching up to 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 thus effectively improving the overall attenuation index of the radio frequency coaxial cable. Compared with the radio frequency coaxial cable with a foaming degree of 80% of the same specification, the attenuation index can be improved by about 10%.

[0033] The outer conductor 3 is made of metals such as copper and aluminum. For a radio frequency coaxial cable, its outer conductor 3 is complete and continuous, usually in the form of a metal tube, a braided mesh or an aluminum-plastic composite tape, etc., which can well confine the electromagnetic energy to be transmitted within the medium between the inner and outer conductors;

[0034] Commonly used sheaths 4 include polyvinyl chloride (PVC), polyethylene (PE), polyurethane (PU), etc. They are used to protect the cable from environmental factors such as mechanical damage, chemical corrosion, moisture intrusion, and ultraviolet radiation, improve the service life and reliability of the cable, and at the same time provide additional insulation performance to ensure the safety of the cable during use.

[0035] The foaming degree is the volume ratio of the pore void part in the insulation layer to the volume of the insulation layer. An increase of 1% on the basis of 80% foaming degree means that the material consumption of the solid part of the insulation layer is reduced by one-twentieth. This application uses a multi-layer foaming extrusion process to prepare the insulation layer, and optimizes the foaming materials and types of foaming gases for each foaming layer, which can ensure that the pore sizes of each foaming layer are uniform and the foaming degree can reach up to about 85%, achieving a huge improvement compared with the existing technology of cables with 80% foaming degree, and thus effectively improving the overall attenuation index of the radio frequency coaxial cable. Compared with 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 1-1 / 4-inch radio frequency coaxial cable can be reduced from 6.3 dB to 5.64 dB.

[0036] Adopt as Figure 3 shown, an extruder is used to prepare the insulation 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 insulation 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 constant speed, and the insulating material is wrapped on 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 insulation 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 inner foaming layer have higher viscosity, the foaming gases of the inner foaming layer 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 forming volume and foaming degree of the foaming layer.

[0037] 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. 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 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, among the two adjacent foaming layers 22, the injection pressure and chamber pressure of the inner foaming layer 22 and the outer foaming layer 22 satisfy the following relationship,

[0038]

[0039] In the formula, is the pressure difference between the 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 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.

[0040] Furthermore, in two adjacent foaming layers, the foaming volume ratio of the inner foaming layer 22 to the outer foaming layer 22 is 1:1 to 1:4, so as to ensure that the inner layer is quickly shaped during the foaming process. When the outer layer starts to expand, the rapid expansion process of the inner layer is basically over, and there will be no large mutual restrictions between the inner and outer layers during foaming, which affects the pore size at the boundary.

[0041] 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 difficulties in production and increased production costs caused by too many layers.

[0042] Furthermore, the foaming material includes one or more of 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), homopolypropylene HPP, and random polypropylene PP-R. The foaming gas includes one or more of nitrogen, argon, carbon dioxide, and octafluorocyclobutane.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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 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.

[0047] The following further describes the technical solutions provided by the present application according to specific embodiments.

[0048] Example 1

[0049] An ultra-low attenuation radio frequency coaxial cable, comprising an inner conductor 1, an insulating layer 2, an outer conductor 3 and a sheath 4 arranged in sequence from inside to 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 foaming degree of the insulating layer 2 in the ultra-low attenuation radio frequency coaxial cable provided in this embodiment is about 82.8%.

[0050] Example 2

[0051] An ultra-low attenuation radio frequency coaxial cable, comprising an inner conductor 1, an insulating layer 2, an outer conductor 3 and a sheath 4 arranged in sequence from inside to 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; the foaming material of the second foaming layer is a mixture of high-density polyethylene with a density of 0.955 g / cm 3 and low-density polyethylene, with a melt flow rate of about 7.2 g / 10 min, the foaming gas is argon, the gas injection pressure is 266 bar, the barrel pressure is 170 bar, and the barrel temperature is 170 °C; the foaming material of the third foaming layer is high-density polyethylene with a density of 0.945 g / cm 3A mixture of high-density polyethylene and low-density polyethylene with a melt flow rate of about 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 bubble degree of the insulating layer 2 in the ultra-low attenuation radio frequency coaxial cable provided in this embodiment is about 83.9%.

[0052] Example 3

[0053] An ultra-low attenuation radio frequency 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. 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 about 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 about 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 and a melt flow rate of about 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 and a melt flow rate of about 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 bubble degree of the insulating layer 2 in the ultra-low attenuation radio frequency coaxial cable provided in this embodiment is about 85.1%.

[0054] The ultra-low attenuation radio frequency coaxial cables obtained in Examples 1 to 3 of the present invention and the ultra-low attenuation radio frequency coaxial cable with a foaming degree of 80% obtained by single-layer foaming in the prior art were used as comparative examples for application. The change in the attenuation value is shown in Table 1. It can be seen that as the foaming degree increases, the attenuation level is significantly improved. The attenuation per 100 meters of the 1-1 / 4-inch radio frequency coaxial cable at 2700 MHz can be reduced from 6.3 dB to 5.64 dB.

[0055] Table 1 Attenuation values of cables with different foaming degrees

[0056]

[0057] 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 of" means two or more, unless otherwise specifically defined.

[0058] In addition, the reference throughout this specification to "one embodiment"; 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 similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0059] 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 radio frequency coaxial cable, characterized in that: It comprises an inner conductor (1), an insulating layer (2), an outer conductor (3) and a sheath (4) which are arranged in sequence from the inside to the outside, wherein the insulating layer (2) comprises, from the inside to the outside, an inner skin layer (21), a foaming layer (22) of preset layers prepared by a multi-layer foaming extrusion process, and an outer skin layer (23); For any two adjacent foaming layers (22), the ratio of the melt flow rate of the foaming material of the foaming layer (22) on the inner side to that of the foaming layer (22) on the outer side is 1:1.2 to 1:3, and the critical pressure of the foaming gas of the foaming layer (22) on the inner side is greater than that of the foaming layer (22) on the outer side by more than 10 bar, thereby improving the uniformity of the pores and the degree of foaming of the insulating layer (2) through the multi-layer foaming extrusion process.

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

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

4.

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

5. The ultra-low attenuation radio frequency 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.

6. The ultra-low attenuation radio frequency coaxial cable according to claim 5, characterized in that: When the number of layers of the foaming layer (22) is 2, the foaming layer (22) comprises 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 and low-density polyethylene, and the foaming gas is carbon dioxide; the foaming material of the second foaming layer is a mixture of high-density polyethylene and low-density polyethylene, and the foaming gas is octafluorocyclobutane.

7. The ultra-low attenuation radio frequency coaxial cable according to claim 5, characterized in that: When the number of layers of the foaming layer (22) is 3, the foaming layer (22) comprises a first foaming layer, a second foaming layer and a third 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 argon; the foaming material of the second 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 homopolymer polypropylene and low-density polyethylene, and the density is 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.

8. The ultra-low attenuation radio frequency coaxial cable according to claim 5, characterized in that: When the number of layers of the foaming layer (22) is 4, the foaming layer (22) comprises 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 and low-density polyethylene, and the foaming gas is argon; the foaming material of the third foaming layer is a mixture of atactic ... 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.

9. The ultra-low attenuation radio frequency 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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