Ultralow-attenuation radio frequency coaxial cable

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to an ultra-low attenuation radio frequency coaxial cable which comprises an inner conductor, an insulating layer, an outer conductor and a sheath which are sequentially arranged from inside to outside, by optimizing the foaming material formula of the insulating layer, the cell uniformity of the foaming layer is improved, the foaming degree can reach about 85% at most, and the service life of the cable is prolonged. Compared with the same specification of radio frequency coaxial cables with the foaming degree of 80%, the radio frequency coaxial cable has the advantages that the attenuation index can be improved by about 10%, for example, the 2700MHz attenuation of the radio frequency coaxial cables of 1-1 / 4 inches can be reduced from 6.3 dB to about 5.64 dB per hundred meters.

Description

Technical Field

[0001] The present 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 RF coaxial cable is generally a lightweight and highly foamed insulating medium formed by physical foaming of polyethylene polymer, which has a dielectric constant close to that of air (ideal air is 1, and the dielectric constant of highly foamed polyethylene insulation can reach 1.2). G and conductor attenuation α R According to the theoretical formula, dielectric attenuation and conductor attenuation are determined by the dielectric constants of the medium and conductor. Therefore, both conductor attenuation and dielectric attenuation are affected by the dielectric constant of the insulating layer.

[0003] Adjusting the foaming degree of the insulation layer can greatly improve the overall attenuation index of the cable. At present, the maximum foaming degree of domestic manufacturers can basically reach 80%, and the limit can reach 82% (but there will be a small number of uneven holes), which will lead to the inability to further improve the overall attenuation index of the cable. This is mainly because when the foaming degree is too large, the foaming layer cells grow too fast, the foaming gas escapes too violently, resulting in uneven foaming layer and cells, and even rupture and merge to form large holes, which seriously affects the electrical transmission performance of the cable.

[0004] The existing technology proposes to use different foaming gases for mixed foaming, relying on the different supercritical states of different gases to make the foaming rates of the small and large diameter positions of the foaming layer closer than that of a single gas, so that the bubbles are more uniform; because the gas mass accounts for a very small proportion of the insulating layer at normal temperature and pressure, and the foaming gas is chemically inactive and has a low dielectric constant, the influence of the dielectric constant of the gas on the dielectric constant of the foaming layer can be ignored, but this single-layer foaming mixed gas still has violent and uneven gas escape in the case of super-large foaming degree, 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] In view of the defects of the prior art, the present application provides an ultra-low attenuation RF coaxial cable, which aims 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 RF coaxial cable.

[0006] According to one aspect of the present application, an ultra-low attenuation radio frequency coaxial cable is provided, comprising an inner conductor, an insulating layer, an outer conductor and a sheath arranged in sequence from the inside to the outside, wherein the insulating layer comprises, from the inside to the outside, an inner skin layer, a foaming layer of preset layers prepared by a multi-layer foaming extrusion process, and an outer skin layer; For any two adjacent foaming layers, the ratio of the melt flow rate of the foaming material of the inner foaming layer and 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 more than 10 bar greater than that of the outer foaming layer, thereby improving the uniformity of the pores and the degree of foaming of the insulating layer through the multi-layer foaming extrusion process.

[0007] Through the above technical scheme conceived by the present application, compared with the prior art, the present application adopts a multi-layer foaming extrusion process to prepare the foaming layer, and optimizes the foaming material and the type of foaming gas of 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%, thereby effectively improving the overall attenuation index of the RF coaxial cable. Compared with the cable of the same specification with 80% foaming degree, the attenuation can be improved by about 10%.

[0008] As a further preferred embodiment, when the foaming layer is prepared by a multi-layer foaming extrusion process, in two adjacent foaming layers, the injection pressure and the chamber pressure of the inner foaming layer and the outer foaming layer satisfy the following relationship:

[0009] 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.

[0010] As further preferred, in two adjacent foam layers, the foaming volume ratio of the foaming layer located on the inner side to the foaming layer located on the outer side is 1:1 to 1:4.

[0011] As further preferred, the number of the foaming layer is 2 to 4 layers.

[0012] As further preferred, 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.

[0013] As a further preference, when the number of foaming layers is 2, the foaming layers include 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.

[0014] As further preferred, when the number of the foaming layers is 3, the foaming layers include 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.

[0015] As further preferred, 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 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 random polypropylene and low-density polyethylene with a density of 0.951g / cm 3 ~0.965g / cm 3 The foaming material of the fourth foaming layer has a density of 0.941 g / cm 3 ~0.950g / cm 3 It is a mixture of high-density polyethylene and low-density polyethylene, and the foaming gas is 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. This 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 can reach up to about 85%, thereby effectively improving the overall attenuation index of the RF coaxial cable. Compared with the RF coaxial cable of the same specification with 80% foaming degree, the attenuation index can be improved by about 10%, such as the attenuation of 1-1 / 4 inch RF coaxial cable at 2700MHz per 100 meters can be reduced from 6.3dB to 5.64dB; 2. 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 pores of each foaming layer are uniform in size and avoid the problem of pore rupture and merging to form large holes; 3. In addition, the present application optimizes the foaming volume of the inner and outer foaming layers in adjacent foaming layers, which can ensure that the expansion of the inner foaming layer is basically completed when the outer foaming layer expands, avoiding the restriction of the inner and outer layers when foaming and affecting the size of the pores at the boundary. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a cross-sectional view of an ultra-low attenuation radio frequency coaxial cable provided in an embodiment of the present application; Figure 2 It is a schematic diagram of the structure of the ultra-low attenuation radio frequency coaxial cable provided in an embodiment of the present application; Figure 3 It is a schematic diagram of foaming by an extruder 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, 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 , 2 As shown, the present application provides an ultra-low attenuation radio frequency 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 high-purity copper or copper alloy, such as annealed copper wire, annealed copper tube, copper-clad aluminum wire, etc. Sometimes, in order to reduce the loss, the copper surface is silver-plated. For some special applications, steel-clad copper wire, aluminum-clad copper wire, aluminum tube or corrugated copper tube is also used. It is used as a carrier for signal transmission and is responsible for transmitting the radio frequency signal from one end to the other end; The insulating layer 2 includes an inner skin layer 21, a foam layer 22 of a preset level (i.e., a preset number) prepared by a multi-layer foaming extrusion process, and an outer skin layer 23. The inner skin layer 21 is coated on the outer side of the inner conductor 1 to facilitate close bonding with the foam layer 22, and the outer skin layer 23 is coated on the outer side of the foam 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 dissolution 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, and finally form a lightweight and high-foaming insulation layer structure; 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 foam 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 diameter change rate of the foaming expansion). 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 22, the foaming layer 2 on the inner side 2 and the ratio of the melt flow rate (MFR) of the foaming material of the foaming layer 22 on the outside is 1:1.2 to 1:3, so as to ensure that the viscosity of the foaming material of the foaming layer 22 on the inside is greater than that of the foaming layer 22 on the outside to a certain extent, so as to 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 foaming layer 22 on the inside of the adjacent foaming layers 22 is greater than that of the foaming layer 22 on the outside by more than 10 bar, so as to use the gas amount matching the foaming material of each foaming layer, so as to ensure that the foaming degree of each foaming layer 22 is relatively uniform and The pore size is uniform. By optimizing the foaming materials and foaming gas of each foaming layer, the pore uniformity and foaming degree 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 82% limit in the prior art, and the maximum can reach about 85%, and the inner and outer pore sizes are closer, 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 RF coaxial cable. Compared with the RF coaxial cable of the same specification with a foaming degree of 80%, the attenuation index can be improved by about 10%; The outer conductor 3 is made of metal such as copper and aluminum. For radio frequency coaxial cables, the outer conductor 3 is complete and continuous, usually in the form of a metal tube, a braided mesh or an aluminum-plastic composite tape, which can well confine the electromagnetic energy to the medium between the inner and outer conductors for transmission; The sheath 4 is commonly made of polyvinyl chloride (PVC), polyethylene (PE), polyurethane (PU), etc., which is 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 provide additional insulation performance to ensure the safety of the cable during use.

[0022] The foaming degree is the volume of the voids in the pores of 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 amount of material used in the solid part of the insulating layer is reduced by one twentieth. This application adopts a multi-layer foaming extrusion process to prepare the insulating layer, and optimizes the foaming materials and foaming gas types 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%. Compared with the 80% foaming cable in the prior art, it has been greatly improved, thereby effectively improving the overall attenuation index of the RF coaxial cable. Compared with the cable of the same specification with 80% foaming degree, the attenuation index can be improved by about 10%, such as the attenuation of 1-1 / 4-inch RF coaxial cable at 2700MHz per 100 meters can be reduced from 6.3dB to 5.64dB.

[0023] Use Figure 3 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 injection pressure difference of the outer foaming layer is greater than that of the inner foaming layer. The greater the injection pressure difference, the greater the injection amount, and it is easier for the outer foaming layer with a larger volume to obtain a foaming degree matching the inner foaming layer; while the inner foaming layer has a small volume, and 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 foaming layer are uniform and the foaming degree is high, when the foaming layer is prepared by a multi-layer foaming extrusion process, in 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,

[0025] 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.

[0026] Furthermore, in the 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, thereby ensuring that the inner layer foaming process is quickly completed and finalized, so that when the outer layer foaming begins to expand, the inner layer rapid expansion process is basically completed, and the inner and outer layers will not significantly restrict each other during foaming and affect the size of the bubbles at the boundary.

[0027] 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.

[0028] Furthermore, the foaming material includes one or more of 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), homopolymer polypropylene HPP, and random polypropylene PP-R, and the foaming gas includes one or more of nitrogen, argon, carbon dioxide, and octafluorocyclobutane.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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 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.

[0033] The technical solution provided by this application is further described below based on specific embodiments.

[0034] Example 1 An ultra-low attenuation radio frequency 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 large, 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. 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 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 foaming degree of the insulating layer 2 in the ultra-low attenuation RF coaxial cable provided in this embodiment is about 82.8%.

[0035] Example 2 An ultra-low attenuation radio frequency 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 which are 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 foaming material with 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 has a melt flow rate of about 15g / 10min, the foaming gas is octafluorocyclobutane, the injection pressure is 346bar, the chamber pressure is 190bar, and the chamber temperature is 180°C. The foaming degree of the insulating layer 2 in the ultra-low attenuation RF coaxial cable provided in this embodiment is about 83.9%.

[0036] Example 3 An ultra-low attenuation radio frequency 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 16.7 g / 10 min, the foaming gas is octafluorocyclobutane, the injection pressure is 371 bar, the chamber pressure is 200 bar, and the chamber temperature is 200° C. The foaming degree of the insulating layer 2 in the ultra-low attenuation RF coaxial cable provided in this embodiment is about 85.1%.

[0037] The ultra-low attenuation RF coaxial cables obtained in Examples 1 to 3 of the present invention and the ultra-low attenuation RF 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 1-1 / 4 inch RF coaxial cable at 2700MHz can be reduced from 6.3dB to 5.64dB.

[0038] Table 1 Attenuation values ​​of cables with different foaming degrees

[0039] 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.

[0040] 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.

[0041] 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 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 material of the fourth foaming layer has a density of 0.941 g / 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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