Foaming cable and preparation method thereof

Abstract

The invention relates to a foaming cable and a preparation method thereof, and belongs to the technical field of communication cables. A foaming cable comprises a conductor, a foaming insulating layer, a shielding layer and a sheath. The foaming insulating layer comprises a first foaming insulating layer and a second foaming insulating layer; the first foamed insulating layer is formed from a first thermoplastic resin containing a tetrafluoroethylene-hexafluoropropylene random copolymer; the second foamed insulating layer is formed of a second thermoplastic resin containing an ethylene-styrene copolymer. According to the invention, the second foaming insulating layer of the wire is made of a material prepared by ethylene-styrene copolymerization; the material not only has a relatively low dielectric constant, but also has good heat resistance and flexibility, and meets the consistent requirements for manufacturing a foaming layer, and the ethylene-styrene copolymer has better heat resistance compared with polyethylene or polypropylene, and has lower cost compared with perfluororesin.

Description

Technical Field

[0001] The invention relates to a foamed cable and a preparation method thereof, belonging to the technical field of communication cables. Background Art

[0002] With the iteration of communication technology, more information needs to be transmitted at a higher speed. In communication cables, faster propagation speed and lower transmission loss are the common pursuits in this field. In order to increase the transmission speed and reduce the transmission loss, an effective way is to reduce the dielectric constant of the insulation layer. In order to achieve a low dielectric constant, one way is to find excellent materials to replace the traditional PE coating layer, and another way is to make the coating material into a foam.

[0003] For example, the invention patent with application number CN 201080022602.7 discloses a foamed wire and a transmission cable containing the foamed wire. The invention is obtained by mixing a base resin composed of a high-melting-point propylene resin with a melting point above 150°C and a masterbatch containing a thermally decomposable chemical foaming agent and a low-melting-point propylene resin with a melting point below 135°C, melting the low-melting-point resin, and then decomposing and foaming the thermally decomposable chemical foaming agent. The invention uses PP instead of PE to improve the heat resistance of the foamed insulation layer.

[0004] The invention patent with the authorization announcement number CN 105980426B discloses a foamed wire. The wire increases the propagation speed and has a small transmission loss. Specifically, the wire includes a conductor and a tetrafluoroethylene-hexafluoropropylene copolymer coating the conductor, the melt flow rate of the copolymer measured at 372°C is 35.0~45.0g / 10 minutes, the expansion rate is -8.0%~5.0%, and the total number of -CF2 groups and unstable terminal groups is less than 120 per 10^6 carbon atoms; the copolymer contains a polymerization unit from tetrafluoroethylene, a polymerization unit from hexafluoropropylene, and a polymerization unit from perfluoro(alkyl vinyl ether). The polymer is not easy to agglomerate when the wire is formed, and even if agglomerates are generated, it is not easy to produce large-sized agglomerates. However, the international market price of tetrafluoroethylene-hexafluoropropylene copolymers remains high, and the production of cables requires a large amount of perfluoro copolymers to make the coating layer, which leads to extremely high production costs of perfluoro foamed cables. Summary of the invention

[0005] The present invention aims to solve the above problems, and thus provides a foamed cable. The foamed cable first forms a first foamed insulation layer made of perfluororesin on the conductor, and then forms a second foamed insulation layer; the second foamed insulation layer has good insulation and is relatively low in price; the first and second foamed insulation layers are combined to form a foamed insulation layer, so the foamed insulation layer has a low relative dielectric constant and is even lower in price, thereby completing the creation of the present invention.

[0006] The technical solution of the present invention to solve the above problems is as follows: A foamed cable comprises a conductor, a foamed insulating layer, a shielding layer and a sheath; the foamed insulating layer comprises a first foamed insulating layer covering the conductor and a second foamed insulating layer covering the first foamed insulating layer; the first foamed insulating layer is formed of a first thermoplastic resin containing a tetrafluoroethylene-hexafluoropropylene copolymer; the second foamed insulating layer is formed of a second thermoplastic resin containing an ethylene-styrene copolymer.

[0007] The foamed cable in the above technical solution of the present invention achieves high propagation speed and low transmission loss, and optimizes the problem of high price of perfluororesin.

[0008] In the prior art, polyethylene and polypropylene have relatively low dielectric constants, but their heat resistance is average. Therefore, they are gradually abandoned in communication cables. Polystyrene has a relatively low dielectric constant and good heat resistance. However, it is highly rigid, hard and brittle, and is difficult to be applied to the insulation layer of the cable. It only has good physical parameters and relatively low cost. Therefore, the prior art basically focuses on perfluororesin, but the high cost of perfluororesin makes the price of communication cables high.

[0009] In the above technical solution of the present invention, polystyrene has a large number of benzene ring structures on the side chain relative to polyethylene, and the benzene ring is a rigid structure. The benzene ring also has a certain electron-withdrawing ability under the premise of its own stable properties, so it can significantly improve the stability of the polymer molecular chain. Therefore, ethylene-styrene copolymer has higher heat resistance than polyethylene, and the relative dielectric constants of the two are roughly equivalent; compared with polystyrene, the number of benzene rings is significantly reduced, and they are located on the side chain, and can be roughly evenly distributed on the molecular chain. Therefore, ethylene-styrene copolymer has higher flexibility, so it can be used as an insulating foaming material for wires. Therefore, after the wire is foamed and coated with ethylene-styrene copolymer, a high-quality insulating layer can be formed on the periphery of the wire. And the glass transition temperature of ethylene-styrene copolymer can be adjusted as needed, so as to adjust the rigidity and flexibility, heat resistance and other aspects as needed. Studies have shown that ethylene-styrene copolymer can significantly improve the flexibility of the material when the amount of styrene is not very high. This may be related to the fact that some of the copolymerized parts in the material are crystallized, while others are not crystallized, forming a state of physical crosslinking. This irregular arrangement of molecular chains results in a larger activity space between molecules, making it easy for them to move relative to each other under the action of external forces.

[0010] The above characteristics of ethylene-styrene copolymer enable it to replace perfluoropolymer to a certain extent. More importantly, the cost of ethylene-styrene copolymer is much lower than that of perfluoropolymer. Therefore, the manufacturing cost of the product can be significantly reduced by appropriately increasing the thickness of the foaming layer without reducing the product quality.

[0011] In the above technical solution of the present invention, the first foamed insulation layer is made of perfluororesin and the second foamed insulation layer is made of ethylene-styrene copolymer, mainly for the following two considerations. First, perfluororesin is expensive, so it is necessary to increase the thickness of the foamed layer as much as possible under the same dosage. The first foamed insulation layer is closer to the center of the wire than the second foamed insulation layer, so the total circumference of the first foamed insulation layer is smaller, so that the minimum dosage can be achieved under the same thickness; second, perfluororesin has better heat resistance and higher melting point / softening point. Using perfluororesin close to the wire can achieve better heat resistance, and during molding, because it is molded first, it will not affect the foamed layer formed by ethylene-styrene copolymer due to the higher melting point / softening point.

[0012] As a preferred embodiment of the above technical solution, in the ethylene-styrene copolymer, the molar content of styrene units is 50-60%.

[0013] As a preferred embodiment of the above technical solution, the thickness of the first foamed insulating layer is 100 μm to 200 μm; the thickness of the second foamed insulating layer is 100 to 200 μm.

[0014] As a preferred embodiment of the above technical solution, the thickness of the first foamed insulation layer accounts for more than 40% of the thickness of the entire foamed insulation layer.

[0015] In order to ensure the insulation effect, the thickness of the first foam insulation layer cannot be too low. Moreover, even if the thickness of the first foam insulation layer is the same as that of the second foam insulation layer, the material usage of the second foam insulation layer is much greater than that of the first foam insulation layer. Therefore, a proper increase in the usage of the first foam insulation layer will not significantly increase the overall cost of the cable, but it can significantly improve the performance, thereby achieving a better cost-effectiveness.

[0016] As a preferred embodiment of the above technical solution, the thickness of the first foamed insulation layer does not exceed 60% of the thickness of the entire foamed insulation layer.

[0017] As a preferred embodiment of the above technical solution, the relative dielectric constant of the first foamed insulation layer is less than 1.5; the relative dielectric constant of the second foamed insulation layer is less than 2.0.

[0018] As a preferred embodiment of the above technical solution, the relative dielectric constant of the first thermoplastic resin is between 2.0 and 2.3; the relative dielectric constant of the second thermoplastic resin is between 2.5 and 3.0.

[0019] As a preferred embodiment of the above technical solution, the second thermoplastic resin also includes polystyrene.

[0020] In the above technical solution of the present invention, polystyrene and ethylene-styrene copolymer have certain compatibility. Blending and modifying ethylene-styrene copolymer with polystyrene can improve the heat resistance of the material, but it will increase the rigidity of the material, which is not conducive to the formation and use of the foamed insulation layer. Therefore, the recommended usage of polystyrene is usually not more than 30% of the total mass of the blend.

[0021] As a preferred embodiment of the above technical solution, the first thermoplastic resin is composed of polystyrene and ethylene-styrene random copolymer, and the mass ratio of polystyrene to ethylene-styrene random copolymer is 100:(20~30).

[0022] As a preferred embodiment of the above technical solution, in the first thermoplastic resin, the molar content of hexafluoropropylene units is 15-20%.

[0023] As a preferred embodiment of the above technical solution, the first foamed insulating layer is prepared by nitrogen foaming.

[0024] Nitrogen foaming has the advantage of dense and uniform pore structure, and the foaming process is more mature and stable.

[0025] As a preferred embodiment of the above technical solution, the second foamed insulating layer is prepared by supercritical carbon dioxide foaming.

[0026] In the above technical solution of the present invention, due to the low polarity of CO2 molecules, large bond energy, strong interatomic force, small intermolecular force, and high molecular thermal stability. CO2 foaming can reduce the attenuation of the cable by reducing the equivalent dielectric constant of the insulating medium. Like N2 foaming, CO2 foaming also uses liquid canned gas, and the vaporization heat of liquid CO2 is very high. If liquid CO2 vaporizes freely, the surrounding temperature decreases due to the absorption of heat. At this time, part of CO2 becomes gas, and part of CO2 condenses into solid, which is a molecular crystal. Under normal pressure, dry ice directly sublimates and vaporizes without melting. This process requires a lot of heat absorption, so it is often used as a refrigerant. However, continuous gas injection is required during the foaming process, so solid CO2 is not easy to gasify, and the space of the gas injection pipe is relatively narrow. If the equipment does not take any measures, it is easy to cause pipeline blockage. In order to prevent solid CO2 from clogging the gas injection pipe, a heating device must be installed on the gas station gas storage tank, proportional valve and gas injection pipe. In addition, in order to obtain a more stable and uniform melt, an oil temperature controller is used at the foaming head to control the temperature, which better overcomes the disadvantage of uneven heating of the traditional electric heating ring. Since the solubility of CO2 in the polymer melt is 10 times higher than that of N2, the foaming degree obtained by using CO2 gas is significantly greater than that of N2. The foaming degree of N2 foaming can generally reach about 78%, and the pores are fine and dense, while the foaming degree of CO2 foaming is normally above 80%, and the maximum can reach 84%. The pores are slightly larger but very uniform, and are completely distributed in the form of uniform closed rings. The uniform pore structure has a positive effect on the electrical performance indicators of the cable, so the cable performance is better.

[0027] Another object of the present invention is to provide a method for preparing the foamed cable.

[0028] A method for preparing a foamed cable comprises the following steps: S1. Prepare conductor; S2, co-extrusion coating the first thermoplastic resin containing tetrafluoroethylene-hexafluoropropylene random copolymer with a relative dielectric constant between 2.0 and 2.3 on the conductor by nitrogen foaming to form a first foamed insulation layer with a relative dielectric constant below 1.5, to obtain a wire core; S3, making the two wire cores into double parallel wires; S4, foaming a second thermoplastic resin containing ethylene-styrene copolymer with a relative dielectric constant between 2.5 and 3.0 through supercritical carbon dioxide and co-extruding and coating on the two parallel lines to form a second foamed insulation layer with a relative dielectric constant of less than 2.0; S5, extruding a shielding layer on the second foamed insulating layer; S6. Extruding a sheath on the shielding layer.

[0029] In summary, the present invention has the following beneficial effects: 1. The second foamed insulating layer of the conductor is made of a material obtained by copolymerization of ethylene and styrene; the material not only has a relatively low dielectric constant, but also has good heat resistance and flexibility, which meets the consistent requirements for making a foamed layer. Ethylene-styrene copolymer has better heat resistance than polyethylene or polypropylene, and has lower cost than perfluororesin; 2. The present invention further improves the heat resistance of the material and adjusts the flexibility of the material by blending polystyrene and ethylene-styrene copolymer; 3. The present invention uses perfluororesin to foam and coat the conductor, and then uses ethylene-styrene copolymer to foam and coat it, so that the product has a better propagation rate and lower loss, and at the same time has a relatively lower manufacturing cost; 4. The present invention uses perfluororesin to make the first foamed insulation layer near the conductor, which can obtain a greater thickness with less usage and better play the role of perfluororesin; uses relatively cheap ethylene-styrene copolymer to make the second foamed insulation layer at a position far from the conductor, and reinforces the first foamed insulation layer in various aspects, thereby improving the cost performance of the product; 5. The second foamed insulation layer of the present invention is foamed with supercritical carbon dioxide. Compared with nitrogen foaming, the pores are slightly larger but very uniform, and are completely distributed in a uniform closed ring form. The uniform pore structure has a positive effect on the electrical performance indicators of the cable, so the cable performance is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic cross-sectional view of a foamed cable according to one configuration of the present invention; In the figure, 1-conductor, 3-shielding layer, 4-sheath, 21-first foamed insulating layer, 22-second foamed insulating layer. DETAILED DESCRIPTION

[0031] The present invention is further explained below in conjunction with the accompanying drawings.

[0032] This specific implementation is only an explanation of the present invention, not a limitation of the present invention. Any changes made by those skilled in the art after reading the specification of the present invention will be protected by the patent law as long as they are within the scope of the claims.

[0033] Example 1 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0034] Conductor 1 is a pair of copper wires, each with a diameter of 0.3 mm.

[0035] The first foamed insulating layer 21 is formed of a first thermoplastic resin tetrafluoroethylene-hexafluoropropylene random copolymer, has a thickness of 200 μm, and an average bubble diameter of the foamed insulating layer is less than 5 μm. The tetrafluoroethylene-hexafluoropropylene random copolymer has a molar content of hexafluoropropylene units of 15%.

[0036] The second foamed insulating layer 22 is formed of a second thermoplastic resin ethylene-styrene copolymer, has a thickness of 200 μm, and an average cell diameter of the foamed insulating layer is less than 5 μm. The molar content of styrene units in the ethylene-styrene copolymer is 50%.

[0037] The shielding layer 3 is a copper mesh braided layer.

[0038] The sheath 4 is made of olefin TPE material.

[0039] The method for preparing the foamed cable comprises the following steps: S1. Prepare conductor 1; S2, foaming a first thermoplastic resin with nitrogen and co-extruding and coating the conductor to form a first foamed insulating layer 21 with a relative dielectric constant of less than 1.5, to obtain a wire core; S3, making the two wire cores into double parallel wires; S4, foaming a second thermoplastic resin with supercritical carbon dioxide and co-extruding and coating the double-strand parallel wires to form a second foamed insulation layer with a relative dielectric constant of less than 2.0; S5, extruding a shielding layer on the second foamed insulating layer; S6. Extruding a sheath on the shielding layer.

[0040] Example 2 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0041] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0042] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 50%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:20.

[0043] The shielding layer 3 is a copper mesh braided layer.

[0044] The sheath 4 is made of olefin TPE material.

[0045] The manufacturing method of the cable and the parameters of each layer are the same as those in Example 1.

[0046] Example 3 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0047] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0048] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 50%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:25.

[0049] The shielding layer 3 is a copper mesh braided layer.

[0050] The sheath 4 is made of olefin TPE material.

[0051] The manufacturing method of the cable and the parameters of each layer are the same as those in Example 1.

[0052] Example 4 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0053] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0054] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 50%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:30.

[0055] The shielding layer 3 is a copper mesh braided layer.

[0056] The sheath 4 is made of olefin TPE material.

[0057] The manufacturing method of the cable and the parameters of each layer are the same as those in Example 1.

[0058] Example 5 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0059] Conductor 1 is a double copper wire.

[0060] The first foamed insulating layer 21 is formed of a first thermoplastic resin tetrafluoroethylene-hexafluoropropylene random copolymer, wherein the molar content of the hexafluoropropylene unit in the tetrafluoroethylene-hexafluoropropylene random copolymer is 15%.

[0061] The second foamed insulating layer 22 is formed of a second thermoplastic resin ethylene-styrene copolymer, wherein the molar content of styrene units in the ethylene-styrene copolymer is 60%.

[0062] The shielding layer 3 is a copper mesh braided layer.

[0063] The sheath 4 is made of olefin TPE material.

[0064] The method for preparing the foamed cable comprises the following steps: S1. Prepare conductor 1; S2, foaming a first thermoplastic resin with nitrogen and co-extruding and coating the conductor to form a first foamed insulating layer 21 with a relative dielectric constant of less than 1.5, to obtain a wire core; S3, making the two wire cores into double parallel wires; S4, foaming a second thermoplastic resin with supercritical carbon dioxide and co-extruding and coating the double-strand parallel wires to form a second foamed insulation layer with a relative dielectric constant of less than 2.0; S5, extruding a shielding layer on the second foamed insulating layer; S6. Extruding a sheath on the shielding layer.

[0065] Example 6 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0066] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0067] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 60%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:20.

[0068] The shielding layer 3 is a copper mesh braided layer.

[0069] The sheath 4 is made of olefin TPE material.

[0070] The manufacturing method of the cable and the parameters of each layer are the same as those in Example 1.

[0071] Example 7 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0072] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0073] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 60%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:25.

[0074] The shielding layer 3 is a copper mesh braided layer.

[0075] The sheath 4 is made of olefin TPE material.

[0076] The manufacturing method of the cable and the parameters of each layer are the same as those in Example 1.

[0077] Example 8 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0078] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0079] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 60%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:30.

[0080] The shielding layer 3 is a copper mesh braided layer.

[0081] The sheath 4 is made of olefin TPE material.

[0082] The manufacturing method of the cable and the parameters of each layer are the same as those in Example 1.

[0083] Example 9 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0084] Conductor 1 is a pair of copper wires with a diameter of 0.3 mm.

[0085] The first foamed insulating layer 21 is formed of a first thermoplastic resin tetrafluoroethylene-hexafluoropropylene random copolymer, wherein the molar content of the hexafluoropropylene unit in the tetrafluoroethylene-hexafluoropropylene random copolymer is 15%.

[0086] The second foamed insulating layer 22 is formed of a second thermoplastic resin ethylene-styrene copolymer, wherein the molar content of styrene units in the ethylene-styrene copolymer is 60%.

[0087] The first foamed insulating layer 21 has a thickness of 100 μm and an average pore size of 5 μm or less; the second foamed insulating layer 22 has a thickness of 200 μm and an average pore size of 5 μm or less.

[0088] The shielding layer 3 is a copper mesh braided layer.

[0089] The sheath 4 is made of olefin TPE material.

[0090] The manufacturing method of the cable is the same as that of Example 1.

[0091] Example 10 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0092] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0093] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 60%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:20.

[0094] The shielding layer 3 is a copper mesh braided layer.

[0095] The sheath 4 is made of olefin TPE material.

[0096] The manufacturing method of the cable is the same as that of Example 1, and the parameters of each layer are the same as those of Example 9.

[0097] Embodiment 11 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0098] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0099] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 60%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:25.

[0100] The shielding layer 3 is a copper mesh braided layer.

[0101] The sheath 4 is made of olefin TPE material.

[0102] The manufacturing method of the cable is the same as that of Example 1, and the parameters of each layer are the same as those of Example 9.

[0103] Example 12 like Figure 1 As shown, a foamed cable comprises a conductor 1, a foamed insulation layer, a shielding layer 3 and a sheath 4. The foamed insulation layer comprises a first foamed insulation layer 21 covering the conductor and a second foamed insulation layer 22 covering the first foamed insulation layer 21.

[0104] The first foamed insulating layer 21 is formed of a first thermoplastic resin, tetrafluoroethylene-hexafluoropropylene random copolymer.

[0105] The second foamed insulating layer 22 is formed of a second thermoplastic resin of polystyrene and ethylene-styrene copolymer. The molar content of styrene units in the ethylene-styrene copolymer is 60%. The mass ratio of the first thermoplastic resin, polystyrene and copolymer is 100:30.

[0106] The shielding layer 3 is a copper mesh braided layer.

[0107] The sheath 4 is made of olefin TPE material.

[0108] The manufacturing method of the cable is the same as that of Example 1, and the parameters of each layer are the same as those of Example 9.

[0109] Comparative Example 1 A foamed cable comprises a conductor, a foamed insulating layer, a shielding layer and a sheath.

[0110] Conductor 1 is a pair of copper wires, each with a diameter of 0.3 mm.

[0111] The foamed insulating layer is formed of tetrafluoroethylene-hexafluoropropylene random copolymer and has a thickness of 200 μm.

[0112] The shielding layer 3 is a copper mesh braided layer.

[0113] The sheath 4 is made of olefin TPE material.

[0114] Characteristics evaluation (1) Average pore size Take a section of the cable prepared in Examples 1 to 12 and Comparative Example 1 (excluding the shielding layer and the sheath), observe the cross section of the foamed insulation layer with a scanning electron microscope, and measure the pore diameters of 100 randomly selected foamed cells. The average value of the 100 foamed cells is calculated as the average foamed cell diameter.

[0115] (2) Heat resistance A section of the cable prepared in Examples 1 to 12 and Comparative Example 1 (excluding the shielding layer and the sheath) was taken and evaluated by a heating deformation test.

[0116] Place the foamed cable cut into 5 cm long on a cylindrical fixture, heat to 120°C, apply a load of 250 g for 1 hour, and measure the deformation rate. Perform 50 measurements.

[0117] Heating deformation rate = (length after heating - length before heating) / length before heating * 100%. Within 10% is considered qualified.

[0118] (3) Time delay difference A section (2 m) of the cables prepared in Examples 1 to 12 and Comparative Example 1 was taken, and the time delay differences of the 13 cables were measured using a Tektronix TDS8000 digital sampling oscilloscope.

[0119] The evaluation results are shown in Table 1.

[0120] Table 1 Performance parameters of various embodiments and comparative examples Average foam cell diameter (first insulating foam layer) Average foam cell diameter (second insulating foam layer) Heat resistance Time delay difference of two parallel core lines (ps / m) Example 1 37 26 qualified 8 Example 2 28 19 qualified 9 Example 3 34 23 qualified 7 Example 4 29 27 qualified 7 Example 5 26 21 qualified 8 Example 6 21 18 qualified 11 Example 7 17 28 qualified 6 Example 8 23 31 qualified 3 Example 9 22 35 qualified 12 Example 10 28 25 qualified 10 Embodiment 11 24 32 qualified 13 Example 12 36 18 qualified 9 Comparative Example 1 34 - qualified 12 The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A foamed cable, comprising a conductor (1), a foamed insulating layer, a shielding layer (3) and a sheath (4); characterized in that: The foamed insulation layer comprises a first foamed insulation layer (21) covering the conductor and a second foamed insulation layer (22) covering the first foamed insulation layer; the first foamed insulation layer (21) is formed of a first thermoplastic resin containing a tetrafluoroethylene-hexafluoropropylene copolymer, and the average bubble pore size of the foamed insulation layer is less than 5 μm; the second foamed insulation layer (22) is formed of a second thermoplastic resin containing an ethylene-styrene copolymer, and the average bubble pore size of the foamed insulation layer is less than 5 μm.

2. A foamed cable according to claim 1, characterized in that: The relative dielectric constant of the first foamed insulation layer (21) is less than 1.5; and the relative dielectric constant of the second foamed insulation layer (22) is less than 2.

0.

3. A foamed cable according to claim 2, characterized in that: The relative dielectric constant of the first thermoplastic resin is between 2.0 and 2.3; the relative dielectric constant of the second thermoplastic resin is between 2.5 and 3.

0.

4. A foamed cable according to claim 3, characterized in that: The thickness of the first foamed insulation layer (21) is 100 μm to 200 μm; the thickness of the second foamed insulation layer (22) is 100 to 200 μm.

5. A foamed cable according to claim 3, characterized in that: In the ethylene-styrene copolymer, the molar content of styrene units is 50-60%.

6. A foamed cable according to claim 3, characterized in that: The second thermoplastic resin also includes polystyrene.

7. A foamed cable according to claim 3, characterized in that: The second thermoplastic resin is composed of polystyrene and ethylene-styrene random copolymer, and the mass ratio of polystyrene to ethylene-styrene random copolymer is 100:(20-30).

8. The foamed cable according to claim 3, characterized in that: In the first thermoplastic resin, the molar content of hexafluoropropylene units is 15-20%.

9. The foamed cable according to claim 1, characterized in that: The second foamed insulating layer (22) is prepared by supercritical carbon dioxide foaming.

10. The method for preparing a foamed cable according to claim 1, comprising the following steps: S1. Prepare the conductor (1); S2, co-extruding and coating a first thermoplastic resin containing tetrafluoroethylene-hexafluoropropylene random copolymer having a relative dielectric constant between 2.0 and 2.3 on the conductor by nitrogen foaming to form a first foamed insulation layer (21) having a relative dielectric constant below 1.5, thereby obtaining a wire core; S3, making the two wire cores into double parallel wires; S4, foaming a second thermoplastic resin including an ethylene-styrene copolymer having a relative dielectric constant between 2.5 and 3.0 through supercritical carbon dioxide and co-extruding and coating the resin on the two parallel strands to form a second foamed insulating layer (22) having a relative dielectric constant below 2.0; S5, extruding a shielding layer (3) on the second foamed insulating layer (22); S6. Extruding a sheath (4) on the shielding layer (3).

Images