WO2023060673A1 - 具有高发泡度的射频同轴电缆的制造方法 - Google Patents

具有高发泡度的射频同轴电缆的制造方法 Download PDF

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WO2023060673A1
WO2023060673A1 PCT/CN2021/128857 CN2021128857W WO2023060673A1 WO 2023060673 A1 WO2023060673 A1 WO 2023060673A1 CN 2021128857 W CN2021128857 W CN 2021128857W WO 2023060673 A1 WO2023060673 A1 WO 2023060673A1
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foaming
cable core
insulating layer
insulating
coaxial cable
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PCT/CN2021/128857
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English (en)
French (fr)
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代康
钱熙文
郭志宏
唐青
郭雪雅
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江苏俊知技术有限公司
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B11/00—Communication cables or conductors
    • H01B11/18—Coaxial cables; Analogous cables having more than one inner conductor within a common outer conductor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
    • H01B13/016—Apparatus or processes specially adapted for manufacturing conductors or cables for manufacturing co-axial cables
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
    • H01B13/06—Insulating conductors or cables
    • H01B13/14—Insulating conductors or cables by extrusion
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A30/00—Adapting or protecting infrastructure or their operation

Definitions

  • the invention relates to the technical field of coaxial cables, in particular to a method for manufacturing a radio frequency coaxial cable with high foaming degree.
  • the operating frequency and bandwidth of communication and electronic equipment are constantly increasing, and the coaxial cables used in the equipment are facing high-frequency requirements.
  • radio frequency coaxial cables with a working frequency of 65 GHz have been developed internationally, and technical reserves for coaxial cables with a working frequency of up to 110 GHz (or even higher-frequency terahertz coaxial cables) have begun.
  • the most important factor limiting the high-frequency application of cables is the attenuation of cables at high frequencies. Cable attenuation consists of two parts: resistive attenuation and dielectric loss attenuation. The latter is proportional to frequency, and as the frequency increases, the proportion of the latter in the total attenuation gradually increases. Therefore, it is of great significance to reduce the lossy attenuation of the coaxial cable dielectric.
  • the main structure of a coaxial cable is an inner conductor, an insulating layer, an outer conductor and a sheath.
  • the insulating layer covers the outer surface of the inner conductor
  • the outer conductor covers the outer surface of the insulating layer
  • the sheath covers the outer surface of the outer conductor.
  • An important way to reduce dielectric loss attenuation is to use physical or chemical foam extrusion technology to prepare the insulation layer of the cable (the inner conductor and the insulation layer are collectively referred to as the insulated cable core below).
  • chemical foaming is to blend the chemical foaming agent with the insulation layer material.
  • the exothermic foaming agent azodicarbonamide (abbreviated as AC or AZO) is used as the chemical foaming agent.
  • the chemical blowing agent When the temperature is higher than the decomposition temperature of the chemical blowing agent, the chemical blowing agent will release gas, making the insulation layer foam.
  • base resin such as polyethylene, polyperfluoroethylene propylene
  • physical foaming is usually used, using nitrogen and/or carbon dioxide as a foaming agent, and the foaming agent is injected into the extruder chamber in a supercritical state when extruding the insulating layer.
  • the base resin for preparing the insulation layer of the RF coaxial cable that is used the most and has the highest degree of foaming is polyethylene plastic, that is, a blend of low-density polyethylene (LDPE) and high-density polyethylene (HDPE). material as the material for the preparation of the insulating layer.
  • LDPE low-density polyethylene
  • HDPE high-density polyethylene
  • the advantage of this process is that the foaming degree of the insulating layer can reach 82%, and the foaming ratio (the ratio of the density of the insulating layer before foaming to the density after foaming) can reach a level close to 6.
  • the radio frequency coaxial cable (including leaky coaxial cable) produced with this polyethylene blend as the base resin is widely used in mobile communication base stations and tunnel communication systems.
  • one-step foaming the foaming gas comes from nitrogen and/or carbon dioxide injected into the machine chamber in a supercritical state, or from the gas released by the chemical blowing agent because the extrusion temperature is higher than the decomposition temperature of the chemical blowing agent, Due to the high pressure in the extruder chamber and machine head, the melt is suppressed and cannot expand; when the insulating layer is extruded out of the mold, due to the release of pressure, the melt containing gas expands immediately, and the insulating layer foams accordingly.
  • This method will restrict the further improvement of the foaming degree, and cannot further reduce the dielectric loss attenuation of the coaxial cable.
  • the technical problem to be solved by the present invention is: to solve the technical problem that the method for preparing the coaxial cable in the prior art cannot further reduce the dielectric loss attenuation.
  • the invention provides a method for manufacturing a radio frequency coaxial cable with a high degree of foaming. Extrusion and foaming are divided into two independent processes, and the degree of foaming of the polyolefin insulating layer of the obtained radio frequency coaxial cable can be further improved. The bubble ratio can reach more than 10, which can further effectively reduce the dielectric loss attenuation of the coaxial cable.
  • the technical solution adopted by the present invention to solve the technical problem is: a method for manufacturing a radio frequency coaxial cable with a high degree of foaming, characterized in that the radio frequency coaxial cable includes an insulating cable core, an outer conductor and a sheath, so The outer conductor is covered on the outer surface of the insulating cable core, the sheath is covered on the outer surface of the outer conductor, the insulating cable core includes an inner conductor and an insulating layer, and the insulating layer is covered on the outer surface of the outer conductor.
  • the manufacturing method includes the following steps: S1: adding a chemical foaming agent, a nucleating agent, an ultraviolet crosslinking photoinitiator and a crosslinking sensitizer to the base resin, and making the chemical foaming agent Foaming agent, nucleating agent, ultraviolet light cross-linking initiator, cross-linking sensitizer and base resin are mixed uniformly to obtain material A for preparing insulating layer; S2: using low-temperature forced extrusion process, extruding material A The extruder extrudes the insulating layer on the outer surface of the inner conductor to obtain an unfoamed insulating cable core; S3: After the unfoamed insulating cable core is extruded from the head of the extruder, immediately use ultraviolet The light source irradiates the unfoamed insulating cable core, so that the insulating layer realizes micro-crosslinking; S4: heat and foam the unfoamed insulating cable core treated in step S3,
  • the base resin is high-density polyethylene or polypropylene, and the amount of chemical foaming agent added is 2%-10% of the mass of the base resin.
  • the ultraviolet crosslinking photoinitiator is benzophenone or 4-hydroxybenzophenone laurate, and the addition amount of the ultraviolet crosslinking photoinitiator is 0.5%-2% of the mass of the base resin.
  • the cross-linking sensitizer is trimethylolpropane triacrylate, pentaerythritol triacrylate, hexanediol diacrylate, triallyl cyanurate, triallyl isocyanurate or Trimethylolpropane trimethacrylate, the addition amount of the crosslinking sensitizer is 0.2%-0.6% of the base resin.
  • the temperature of the extruder chamber and head is lower than 180°C.
  • the low-temperature forced extrusion process adopts a single-screw extruder, and the inner wall of the machine chamber or the inner wall of the machine chamber liner of the single-screw extruder is provided with a spiral groove, and the spiral groove of the spiral groove The angle is 40°-65°, and the helical direction of the spiral groove is opposite to that of the screw rod.
  • the low-temperature forced extrusion process adopts a single-screw extruder, and the screw of the single-screw extruder is a pin-type screw.
  • the low-temperature forced extrusion process adopts a twin-screw extruder
  • the twin-screw extruder includes a conical co-rotating twin-screw extruder, a conical counter-rotating twin-screw extruder or a parallel twin-screw extruder. plastic machine.
  • a gel will be formed in the insulating layer treated in step S3, and the content of the gel accounts for 18%-50% of the total amount of the insulating layer.
  • the ultraviolet light source includes an ultraviolet LED lamp and a high-pressure ultraviolet mercury lamp.
  • the ultraviolet LED lamp is used as the ultraviolet light source; when the unfoamed insulating cable core When the thickness of the insulating layer is 3mm-5mm, the high-pressure ultraviolet mercury lamp is used as the ultraviolet light source; when the thickness of the insulating layer of the unfoamed insulating cable core is greater than 5mm, the ultraviolet LED lamp and the high-pressure ultraviolet mercury lamp are used as the ultraviolet light source at the same time .
  • the heating and foaming treatment in step S4 specifically includes: passing the unfoamed insulating cable core treated in step S3 through a heating tube, the temperature inside the heating tube is 230°C-300°C, and the length of the heating tube is is 15m-30m, and the speed at which the unfoamed insulating cable core passes through the heating pipe is 2-15m/min.
  • the manufacturing method of the radio frequency coaxial cable with high foaming degree of the present invention divides extrusion molding and foaming into two independent steps, adopts low-temperature extrusion molding during extrusion molding, prevents the insulating layer from foaming in advance,
  • the combination of ultraviolet crosslinking and heating is adopted at the time, so that the foaming degree of the insulating layer can reach more than 90%, and the foaming ratio can reach more than 10, which is significantly improved compared with the one-step foaming method of the prior art, and can effectively reduce radio frequency
  • the attenuation of the coaxial cable improves the transmission speed ratio.
  • Fig. 1 is a structural schematic diagram of the radio frequency coaxial cable of the present invention.
  • Fig. 2 is a flow chart of the manufacturing method of the radio frequency coaxial cable with high foaming degree of the present invention.
  • connection should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection. Connected, or integrally connected; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediary, and it can be the internal communication of two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.
  • the radio frequency coaxial cable includes an insulating cable core 1, an outer conductor 2 and a sheath 3, the outer conductor 2 is coated on the outer surface of the insulating cable core 1, and the sheath 3 is coated on the outer surface of the outer conductor 2,
  • the insulating cable core 1 includes an inner conductor 11 and an insulating layer 12 , and the insulating layer 12 covers the outer surface of the inner conductor 11 .
  • the manufacturing method of the radio frequency coaxial cable with high foaming degree includes the following steps.
  • the base resin can be high-density polyethylene or polypropylene.
  • AC can be selected as the chemical foaming agent.
  • polypropylene is selected as the base resin, AC or AZO can be selected as the chemical blowing agent.
  • the amount of chemical blowing agent added is 2%-10% of the mass of the base resin, preferably 2.5%-5%.
  • the addition of the chemical blowing agent of the present embodiment is much higher than the addition of the chemical blowing agent in the prior art (0.2%-1%, generally no more than 2%), doing like this is for subsequent independent foaming process A higher degree of foaming can be obtained.
  • Nucleating agents refer to functional chemical additives that can change part of the crystallization behavior, improve product transparency, rigidity, surface gloss, impact toughness and heat distortion temperature, shorten product molding cycle, and improve product processing and application performance.
  • the nucleating agent may be polytetrafluoroethylene plastic, for example.
  • the ultraviolet crosslinking photoinitiator may be benzophenone or 4-hydroxybenzophenone laurate, and the amount of the ultraviolet crosslinking photoinitiator added is 0.5%-2% of the mass of the base resin.
  • Cross-linking sensitizers are trimethylolpropane triacrylate, pentaerythritol triacrylate, hexanediol diacrylate, triallyl cyanurate, triallyl isocyanurate or trimethylol
  • the amount of cross-linking sensitizer added is 0.2%-0.6% of the base resin.
  • the chemical blowing agent AC decomposes at 205°C-212°C.
  • the extruder chamber and head The temperature must be higher than 215°C, so that the melt can expand immediately when it is extruded from the machine head to achieve foaming.
  • present embodiment is to avoid insulating layer from foaming in extrusion process, so the temperature of extruder machine chamber and machine head needs to be lower than the decomposition temperature of chemical foaming agent, for example, the temperature of extruder machine chamber and machine head The temperature is set to be lower than 180°C, such as 170°C.
  • the first type can be a single-screw extruder, and the inner wall of the machine chamber or the inner wall of the machine chamber liner of the single-screw extruder is provided with a spiral groove, and the helix angle of the spiral groove is 40°-65°.
  • the helical direction of the spiral groove is opposite to the helical direction of the screw rod.
  • the depth of the spiral groove is smaller than the diameter (2-4mm) of the material A particle, and the width of the spiral groove is greater than the diameter of the material A particle.
  • the number of spiral grooves is, for example, 3-6 grooves.
  • the number of grooves is related to the diameter of the extruder chamber. The larger the diameter, the more grooves can be set, but the inner lining of the machine chamber needs to be considered The strength requirements of the set.
  • a single-screw extruder can be used, and the screw of the single-screw extruder is a pin-type screw.
  • a twin-screw extruder can be used, and the twin-screw extruder includes a conical co-rotating twin-screw extruder, a conical counter-rotating twin-screw extruder or a parallel twin-screw extruder.
  • These three methods can be used alone or in combination, so that the melt of material A can still achieve good plasticizing quality and high-efficiency extrusion under the condition of lower than the decomposition temperature of the chemical blowing agent.
  • the unfoamed insulating cable core when the unfoamed insulating cable core is extruded from the head of the extruder, it is still in a molten state. At this time, the unfoamed insulating cable core is immediately irradiated with an ultraviolet light source. , to achieve ultraviolet cross-linking.
  • Cross-linking refers to the process in which linear or branched polymer chains are covalently connected to form a network or body-shaped polymer. The degree of cross-linking can be characterized by the gel content after cross-linking. After UV crosslinking, some gels will be formed in the unfoamed insulating cable core, and the molecular chains of these gel polymers will change from a two-dimensional structure to a three-dimensional structure.
  • the degree of cross-linking should not be too high (that is, the gel content should not be too much), otherwise it will cause difficulty in foaming and the degree of foaming will be low.
  • the degree of cross-linking should not be too low (that is, the gel content should not be too small), otherwise, the viscoelasticity of the insulating layer will be low, and it will not be able to withstand the tension generated by the expansion of the foaming gas, resulting in the rupture of the cells, causing the gas to flow from the surface of the insulating layer. Therefore, in this embodiment, the content of the cross-linked gel is controlled between 18%-50%, such as 30%-45%, so that the foaming effect of the insulating layer can be better.
  • ultraviolet light sources can be used for irradiation. Since the insulating core does not add any pigments, it is very suitable for crosslinking by ultraviolet radiation.
  • ultraviolet LED lamps can be used for irradiation; when the thickness of the insulating layer is 3mm-5mm, high-voltage ultraviolet mercury lamps can be used for irradiation; when the thickness of the insulating layer is more than 5mm, you can Simultaneously use ultraviolet LED lamps and high-pressure ultraviolet mercury lamps for irradiation, for example, first use ultraviolet LED lamps for irradiation, and then use high-pressure ultraviolet mercury lamps for irradiation. It should be noted that when using ultraviolet light sources for irradiation, the light sources should be as close as possible to the head of the extruder to improve the irradiation efficiency.
  • step S4 subjecting the unfoamed insulated cable core treated in step S3 to heating and foaming to make the insulating layer foam, and then cooling and shaping the insulated cable core to obtain a foamed insulated cable core.
  • a heating tube can be used for heating, and the unfoamed insulated cable core treated in step S3 is passed through the heating tube.
  • the speed at which the insulating cable core of the bubble passes through the heating pipe is 2-15m/min. After being irradiated by ultraviolet light source, a part of gel was formed in the unfoamed insulating cable core, and it showed certain viscoelasticity.
  • the temperature of the insulating layer is higher than the decomposition temperature of the chemical foaming agent, and the chemical foaming agent will release gas, making the insulating layer in a viscoelastic state foam, and due to partial condensation
  • the foaming degree of the insulating layer is very high (for example, reaching more than 92%), the foamed cells will not be broken, and a large number of uniform and fine cells can be obtained.
  • the heating time for the insulating cable core to pass through the heating tube and the temperature setting in the heating tube can be set according to the thickness of the insulating layer and the degree of foaming that needs to be achieved.
  • the degree of foaming of the insulating layer prepared in this embodiment can be further improved, and the size of the cells is more uniform.
  • outer conductor may be, for example, an outer conductor of a corrugated copper tube.
  • the minimum foaming density of the obtained high-density polyethylene insulating layer can reach 0.08g/cm 3 , and the corresponding expansion ratio can reach 12; the minimum foaming density of the polypropylene insulating layer can reach 0.05g/cm 3 cm 3 , the corresponding expansion ratio reaches 18, which is much higher than that in the prior art (generally below 6).
  • Adopt high-density polyethylene (Dow Chemical Company, DGDA6944) as base resin, add the chemical blowing agent (AC) of 5 mass parts in the high-density polyethylene of 100 mass parts, the nucleating agent (PTFE micropowder) of 0.5 mass part ), the ultraviolet crosslinking photoinitiator (benzophenone) of 1 mass part and the crosslinking sensitizer (pentaerythritol triacrylate or trimethylolpropane triacrylate) of 0.3 mass part, these additives and high density
  • AC chemical blowing agent
  • PTFE micropowder 0.5 mass part
  • the ultraviolet crosslinking photoinitiator benzophenone
  • the crosslinking sensitizer penentaerythritol triacrylate or trimethylolpropane triacrylate
  • a conical co-rotating twin-screw extruder is used for forced extrusion at low temperature.
  • the selected inner conductor has a diameter of 3.55mm and a characteristic impedance of 50 ⁇ .
  • the material A is extruded into an insulating layer on the outer surface of the inner conductor through an extruder, and the insulating layer is not foamed during extrusion, and the diameter of the extruded insulating cable core is 4.4mm.
  • the temperature at the barrel and head of the extruder is in the range of 150°C-170°C.
  • the insulated cable core is extruded from the head of the extruder, it is irradiated with an ultraviolet LED lamp.
  • the ultraviolet LED lamp is installed on the extrusion production line, and multiple ultraviolet LED lamps are arranged side by side to form an array of irradiation light sources, with a total power of 2kw.
  • the gel content in the insulating cable core after ultraviolet crosslinking is 40%.
  • the temperature in the heating tube is 230°C-250°C.
  • the heating time of the insulating cable core in the heating tube is 4min-7min.
  • the foaming of the insulating layer is realized in the heating tube.
  • the insulated cable core leaving the heating pipe is cooled and shaped by air cooling and water cooling, and then the cable reel is taken up by the take-up device. Finally, the foamed insulating cable core is covered with an outer conductor, and a sheath is extruded on the outer surface of the outer conductor to obtain a radio frequency coaxial cable.
  • embodiment 2 The difference between embodiment 2 and embodiment 1 is that polypropylene (Dow Chemical Company, JQDB-2230) is used as the base resin, and the diameter of the unfoamed insulating cable core obtained by extrusion is 5.3mm. , The temperature at the barrel and head of the extruder is in the range of 155°C-175°C.
  • Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the base resin used is a mixture of low-density polyethylene and high-density polyethylene, and a one-step foaming process is adopted.
  • the foaming degree of the insulating layer prepared in Examples 1 and 2 is obviously higher than that of Comparative Example 1, and the foaming degree of Example 1 is increased by 11.6%, and the expansion ratio reaches 9.7; the expansion degree of embodiment 2 has improved 13.2%, and expansion ratio reaches 11.2.
  • the attenuation of the coaxial cables of Example 1 and Example 2 is also significantly lower than that of Comparative Example 1, and the higher the frequency of the cable, the greater the attenuation reduction.
  • the transmission speed ratios of the cables of Example 1 and Example 2 are significantly improved compared with Comparative Example 1.
  • the two processes of extrusion and foaming of the insulating layer are realized in two independent processes respectively, and an unfoamed insulating cable core is first obtained by a low-temperature forced extrusion process, and then The extruded unfoamed insulating cable core is micro-crosslinked to form a partial gel in the insulating layer containing the chemical foaming agent.
  • the polymer molecular chain of these gels changes from a two-dimensional structure to a three-dimensional structure.
  • the insulating layer will not completely melt during the subsequent heating process, but exhibits a certain degree of viscoelasticity.
  • the chemical foaming agent When heating the insulating cable core, when the temperature of the insulating layer is higher than the decomposition temperature of the chemical foaming agent, the chemical foaming agent releases gas, which makes the insulating layer in a viscoelastic state foam, and because the insulating layer contains part of the gel, Even if the degree of foaming is high (for example, up to 92%), the foamed cells will not be broken, and a large number of uniform and fine cells can be obtained.

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Abstract

本发明公开了一种具有高发泡度的射频同轴电缆的制造方法，包括步骤：S1：在基础树脂中加入化学发泡剂、成核剂、紫外交联光引发剂和交联敏化剂，并混合均匀，得到制备绝缘层的材料A；S2：采用低温强制挤塑工艺，将材料A通过挤塑机在内导体外表面挤出绝缘层，得到未发泡的绝缘缆芯；S3：当未发泡的绝缘缆芯被挤出挤塑机的机头后，立即采用紫外光源对未发泡的绝缘缆芯进行辐照处理；S4：将经过步骤S3处理的未发泡的绝缘缆芯进行加热发泡处理，使得绝缘层发泡；S5：在发泡的绝缘缆芯外表面包覆上外导体，然后再通过挤塑机在外导体外表面挤出护套，得到射频同轴电缆。利用本发明，能够得到具有高发泡度的射频同轴电缆，降低电缆的衰减。

Description

具有高发泡度的射频同轴电缆的制造方法 技术领域
本发明涉及同轴电缆技术领域，尤其涉及一种具有高发泡度的射频同轴电缆的制造方法。
背景技术
通信和电子设备的工作频率和带宽不断提高，设备所用同轴电缆面临高频化的要求。例如，国际上已开发了工作频率为65GHz的射频同轴电缆，并开始对工作频率高达110GHz的同轴电缆(甚至更高频率的太赫兹同轴电缆)进行技术储备。限制电缆高频应用的最重要的因素是电缆高频下的衰减。电缆衰减由阻抗性衰减和介质损耗性衰减两部分组成，后者与频率成正比，且随着频率升高，后者在总衰减中所占比例逐步增加。因此，降低同轴电缆介质损耗性衰减具有重要意义。
目前，同轴电缆的主要结构为内导体、绝缘层、外导体及护套，绝缘层包覆在内导体外表面，外导体包覆在绝缘层外表面，护套包覆在外导体外表面。降低介质损耗性衰减的一个重要途径，是采用物理或化学发泡挤塑技术制备电缆的绝缘层(下面将内导体和绝缘层合称为绝缘缆芯)。其中，化学发泡是将化学发泡剂与绝缘层材料共混，通常采用放热型发泡剂偶氮二甲酰胺(英文缩写为AC或AZO)作为化学发泡剂，当挤塑机内的温度高于化学发泡剂分解温度时，化学发泡剂会释放出气体，使得绝缘层发泡。但是，无论采用怎样的基础树脂(如聚乙烯、聚全氟乙丙烯)，化学发泡方法很难获得50％以上的发泡度。要获得更高的发泡度，通常采用物理发泡，用氮气和/或二氧化碳作为发泡剂，在挤塑绝缘层时发泡剂以超临界状态注入挤塑机机膛。
目前，使用最多、且可到达的发泡度最高的射频同轴电缆的制备绝缘层用 的基础树脂为聚乙烯塑料，即将低密度聚乙烯(LDPE)和高密度聚乙烯(HDPE)的共混料作为制备绝缘层的材料。这一工艺的优势是绝缘层发泡度可以达到82％，发泡倍率(绝缘层发泡前密度与发泡后密度的比值)可以达到接近6的水平。用这种聚乙烯共混物作为基础树脂生产的射频同轴电缆(含漏泄同轴电缆)在移动通信基站、隧道通信系统中获得广泛使用。但想要继续提高发泡度，例如84％以上，则很变得非常困难甚至不可能，原因是LDPE/HDPE共混物熔体强度有限，发泡度继续增加将导致含有发泡剂的绝缘层熔体在通过挤塑机头膨胀发泡时，熔体内大量泡孔壁破裂，气体逸出，并导致绝缘层塌陷变形，严重时甚至造成挤塑出胶量不稳定，由此生产出的同轴电缆的电气性能(如衰减、电压驻波比等指标)将无法满足要求。
一直以来，电缆绝缘层不论是采用化学发泡还是物理发泡，都是将挤塑和发泡在一道工序完成，以下称为一步法发泡。在一步法发泡中，发泡气体或来自以超临界状态注入机膛的氮气和/或二氧化碳，或来自因挤塑温度高于化学发泡剂分解温度而导致化学发泡剂释放的气体，由于挤塑机膛和机头内的压力高而压制住熔体不能膨胀；当绝缘层挤塑出模后，由于压力释放，含有气体的熔体立刻膨胀，绝缘层因此发泡。这种方法会制约发泡度的进一步提高，无法进一步降低同轴电缆的介质损耗性衰减。
发明内容
本发明要解决的技术问题是：为了解决现有技术中制备同轴电缆的方法无法进一步降低介质损耗性衰减的技术问题。本发明提供一种具有高发泡度的射频同轴电缆的制造方法，将挤塑和发泡分为两道独立的工序，得到的射频同轴电缆聚烯烃绝缘层发泡度可以进一步提高，发泡倍率可以达到10以上，能够进一步有效降低同轴电缆的介质损耗性衰减。
本发明解决其技术问题所采用的技术方案是：一种具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述射频同轴电缆包括绝缘缆芯、外导体及护套，所述外导体包覆在所述绝缘缆芯的外表面，所述护套包覆在所述外导体的外表面，所述绝缘缆芯包括内导体和绝缘层，所述绝缘层包覆在所述内导体的外表面；所述制造方法包括以下步骤：S1：在基础树脂中加入化学发泡剂、成核剂、紫外交联光引发剂和交联敏化剂，并将所述化学发泡剂、成核剂、紫外光交联引发剂、交联敏化剂和基础树脂混合均匀，得到制备绝缘层的材料A；S2：采用低温强制挤塑工艺，将所述材料A通过挤塑机在所述内导体外表面挤出所述绝缘层，得到未发泡的绝缘缆芯；S3：当所述未发泡的绝缘缆芯被挤出挤塑机的机头后，立即采用紫外光源对所述未发泡的绝缘缆芯进行辐照处理，使得所述绝缘层实现微交联；S4：将经过步骤S3处理的未发泡的绝缘缆芯进行加热发泡处理，使得绝缘层发泡，然后再将绝缘缆芯进行冷却定型，得到发泡的绝缘缆芯；S5：在所述发泡的绝缘缆芯外表面包覆上外导体，然后再通过挤塑机在外导体外表面挤出护套，得到射频同轴电缆。
进一步地，所述基础树脂为高密度聚乙烯或聚丙烯，化学发泡剂的添加量为所述基础树脂质量的2％-10％。
进一步地，所述紫外交联光引发剂为二苯甲酮或4-羟基二苯甲酮月桂酸酯，所述紫外交联光引发剂的添加量为所述基础树脂质量的0.5％-2％；所述交联敏化剂为三羟甲基丙烷三丙烯酸酯、季戊四醇三丙烯酸酯、己二醇二丙烯酸酯、三聚氰酸三烯丙醋、三烯丙基异氰脲酸酯或三羟甲基丙烷三甲基丙烯酸酯，所述交联敏化剂的添加量为所述基础树脂的0.2％-0.6％。
进一步地，所述挤塑机机膛和机头的温度均小于180℃。
进一步地，所述低温强制挤塑工艺为采用单螺杆挤塑机，所述单螺杆挤塑 机的机膛内壁或机膛衬套内壁上开设有螺旋沟槽，所述螺旋沟槽的螺旋升角为40°-65°，所述螺旋沟槽的螺纹旋向与螺杆的螺纹旋向相反。
进一步地，所述低温强制挤塑工艺为采用单螺杆挤塑机，所述单螺杆挤塑机的螺杆为销钉型螺杆。
进一步地，所述低温强制挤塑工艺为采用双螺杆挤塑机，所述双螺杆挤塑机包括锥形同向双螺杆挤塑机、锥形异向双螺杆挤塑机或平行双螺杆挤塑机。
进一步地，经过步骤S3处理的绝缘层内会形成凝胶，所述凝胶的含量占绝缘层总量的18％-50％。
进一步地，所述紫外光源包括紫外LED灯和高压紫外汞灯，当未发泡的绝缘缆芯的绝缘层的厚度小于3mm时，采用紫外LED灯作为紫外光源；当未发泡的绝缘缆芯的绝缘层的厚度为3mm-5mm时，采用高压紫外汞灯作为紫外光源；当未发泡的绝缘缆芯的绝缘层的厚度大于5mm时，将紫外LED灯和高压紫外汞灯同时作为紫外光源。
进一步地，步骤S4中的加热发泡处理具体为：将经过步骤S3处理的未发泡的绝缘缆芯通过加热管，所述加热管内的温度为230℃-300℃，所述加热管的长度为15m-30m，所述未发泡的绝缘缆芯穿过所述加热管的速度为2-15m/min。
本发明的有益效果如下：
本发明的具有高发泡度的射频同轴电缆的制造方法，通过将挤塑和发泡分为独立的两个步骤，在挤塑时采用低温挤塑，防止绝缘层提前发泡，在发泡时采用紫外交联与加热结合的方式，使得绝缘层的发泡度可以达到90％以上，发泡倍率达到10以上，相比现有技术的一步法发泡有了明显提升，能够有效降低射频同轴电缆的衰减，提高传输速比。
附图说明
下面结合附图和实施例对本发明进一步说明。
图1是本发明的射频同轴电缆的结构示意图。
图2是本发明的具有高发泡度的射频同轴电缆的制造方法的流程图。
具体实施方式
现在结合附图对本发明作进一步详细的说明。这些附图均为简化的示意图，仅以示意方式说明本发明的基本结构，因此其仅显示与本发明有关的构成。
在本发明的描述中，需要理解的是，术语“中心”、“纵向”、“横向”、“长度”、“宽度”、“厚度”、“上”、“下”、“前”、“后”、“左”、“右”、“竖直”、“水平”、“顶”、“底”“内”、“外”、“顺时针”、“逆时针”、“轴向”、“径向”、“周向”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本发明的限制。此外，限定有“第一”、“第二”的特征可以明示或者隐含地包括一个或者更多个该特征。在本发明的描述中，除非另有说明，“多个”的含义是两个或两个以上。
在本发明的描述中，需要说明的是，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通。对于本领域的普通技术人员而言，可以具体情况理解上述术语在本发明中的具体含义。
如图1所示，射频同轴电缆包括绝缘缆芯1、外导体2及护套3，外导体2包覆在绝缘缆芯1的外表面，护套3包覆在外导体2的外表面，绝缘缆芯1包括内导体11和绝缘层12，绝缘层12包覆在内导体11的外表面。
如图2所示，具有高发泡度的射频同轴电缆的制造方法包括以下步骤。
S1：在基础树脂中加入化学发泡剂、成核剂、紫外交联光引发剂和交联敏化剂，并将化学发泡剂、成核剂、紫外光交联引发剂、交联敏化剂和基础树脂混合均匀，得到制备绝缘层的材料A。
在本实施例中，基础树脂可以为高密度聚乙烯或聚丙烯，当基础树脂选择高密度聚乙烯时，可以选择AC作为化学发泡剂。当基础树脂选择聚丙烯时，可以选择AC或者AZO作为化学发泡剂。化学发泡剂的添加量为基础树脂质量的2％-10％，优选为2.5％-5％。本实施例的化学发泡剂的添加量远高于现有技术中化学发泡剂的添加量(0.2％-1％，一般不超过2％)，这样做是为了在后续独立的发泡工艺中能够获得更高的发泡度。
成核剂是指能够改变部分结晶行为，提高制品透明度、刚性、表面光泽、抗冲击韧性和热变形温度，缩短制品成型周期，提高制品加工和应用性能的功能型化学助剂。本实施例中成核剂例如可以是聚四氟乙烯塑料。
在本实施例中，紫外交联光引发剂可以为二苯甲酮或4-羟基二苯甲酮月桂酸酯，紫外交联光引发剂的添加量为基础树脂质量的0.5％-2％。交联敏化剂为三羟甲基丙烷三丙烯酸酯、季戊四醇三丙烯酸酯、己二醇二丙烯酸酯、三聚氰酸三烯丙醋、三烯丙基异氰脲酸酯或三羟甲基丙烷三甲基丙烯酸酯，交联敏化剂的添加量为基础树脂的0.2％-0.6％。
S2：采用低温强制挤塑工艺，将材料A通过挤塑机在内导体外表面挤出绝缘层，得到未发泡的绝缘缆芯。
在本实施例中，由于添加了含量较高的化学发泡剂，为了防止化学发泡剂在挤塑过程中发泡，采用低温强制挤塑工艺进行挤塑，保证挤塑过程中的温度低于化学发泡剂的分解温度，同时不会影响挤塑效率。
化学发泡剂AC的分解为205℃-212℃，采用现有技术中的一步法发泡绝缘 层时，为了让化学发泡剂AC在挤塑机内分解，挤塑机机膛和机头的温度均要高于215℃，这样熔体从机头挤出时才能立刻膨胀，实现发泡。而本实施例是要避免绝缘层在挤塑工序中发泡，所以挤塑机机膛和机头的温度需要低于化学发泡剂的分解温度，例如，挤塑机机膛和机头的温度设置为均低于180℃，例如是170℃。
但是，在较低温度下挤塑时，聚烯烃熔融黏度较高，塑化不均匀，会造成挤塑困难甚至难以挤塑。因此，本实施例为了能够在较低温度下顺利挤塑，采用低温强制挤塑工艺实现挤塑。实现低温强制挤塑可以采用三种方式。第一种，可以采用单螺杆挤塑机，所述单螺杆挤塑机的机膛内壁或机膛衬套内壁上开设有螺旋沟槽，所述螺旋沟槽的螺旋升角为40°-65°，所述螺旋沟槽的螺纹旋向与螺杆的螺纹旋向相反。螺旋沟槽的深度小于材料A粒子的直径(2-4mm)，螺旋沟槽的宽度要大于材料A粒子的直径。螺旋沟槽的数量例如是3-6条沟槽，沟槽的数量挤塑机机膛内的直径相关，直径越大，沟槽的数量可以设置更多，但是还需要考虑到机膛内衬套的强度要求。第二种，可以采用单螺杆挤塑机，所述单螺杆挤塑机的螺杆为销钉型螺杆。第三种，可以采用双螺杆挤塑机，所述双螺杆挤塑机包括锥形同向双螺杆挤塑机、锥形异向双螺杆挤塑机或平行双螺杆挤塑机。这三种方式可以单独使用也可以联合使用，从而实现在低于化学发泡剂分解温度的条件下，材料A的熔体仍然可以实现良好的塑化质量、高效挤塑的目的。
S3：当未发泡的绝缘缆芯被挤出挤塑机的机头后，立即采用紫外光源对未发泡的绝缘缆芯进行辐照处理，使得绝缘层实现微交联。
在本实施例中，当未发泡的绝缘缆芯被挤出挤塑机的机头后，仍然是处于熔融状态下，此时，立即采用紫外光源对未发泡的绝缘缆芯进行辐照，实现紫 外交联。交联是指线型或支型高分子链间以共价键连接成网状或体型高分子的过程，交联度可以通过交联后含有的凝胶含量来表征。进行紫外交联后，未发泡的绝缘缆芯内的会形成部分凝胶，这些凝胶聚合物的分子链从二维结构变成了三维结构。并且，未发泡的绝缘缆芯从挤塑机机头挤出后，并没有完全熔化，而是表现出具有一定的粘弹性。在本实施例中，交联度不能过高(即凝胶含量不能过多)，否则会导致发泡困难，发泡度偏低。交联度也不能过低(即凝胶含量不能过少)，否则，绝缘层的粘弹性较低，会承受不住发泡气体膨胀产生的张力而导致泡孔破裂，导致气体从绝缘层表面逃逸出去，因此，本实施例将交联后凝胶的含量控制在18％-50％之间，例如是30％-45％，使得绝缘层的发泡效果可以达到更优。
此外，针对不同的绝缘层厚度，可以采用不同的紫外光源进行辐照。由于绝缘缆芯没有添加任何颜料，所以非常适合紫外辐照进行交联。当绝缘层的厚度为3mm以下时，可以采用紫外LED灯进行辐照；当绝缘层的厚度为3mm-5mm时，可以采用高压紫外汞灯进行辐照；当绝缘层厚度为5mm以上时，可以同时采用紫外LED灯和高压紫外汞灯进行辐照，例如先使用紫外LED灯进行辐照，然后再用高压紫外汞灯进行辐照。需要注意的是，在采用紫外光源照射时，光源都应该尽可能地靠近挤塑机机头以提高辐照效率。
S4：将经过步骤S3处理的未发泡的绝缘缆芯进行加热发泡处理，使得绝缘层发泡，然后再将绝缘缆芯进行冷却定型，得到发泡的绝缘缆芯。
需要说明的是，加热可以采用加热管，将经过步骤S3处理的未发泡的绝缘缆芯通过加热管，加热管内的温度为230℃-300℃，加热管的长度为15m-30m，未发泡的绝缘缆芯穿过加热管的速度为2-15m/min。在经过紫外光源辐照后，未发泡的绝缘缆芯内形成了部分凝胶，且表现出一定的粘弹性。当未发泡的绝缘 缆芯被加热时，绝缘层的温度高于化学发泡剂的分解温度，化学发泡剂会释放出气体，使得处于粘弹状态的绝缘层发泡，而由于部分凝胶的存在，当绝缘层的发泡度很高(例如达到92％以上)时，发泡泡孔也不会破裂，可以得到大量均匀细密的泡孔。绝缘缆芯穿过加热管受到的加热时间和加热管内的温度设置可以根据绝缘层的厚度及需要实现的发泡度进行设置。绝缘层越厚及要实现的发泡度越高，则加热管内的温度要设置得越高或受热时间设置得越长。如果加热管内的温度提高，则可以减少受热时间，有利于提高生产效率；或者延长受热时间，那么可以适当地降低加热管内的温度，防止绝缘缆芯因悬垂时间过长而不圆整。本实施例制备得到的绝缘层发泡度可以进一步提升，并且泡孔大小更佳均匀。
S5：在发泡的绝缘缆芯外表面包覆上外导体，然后再通过挤塑机在外导体外表面挤出护套，得到射频同轴电缆。
需要说明的是，外导体例如可以是轧纹铜管外导体。
采用本发明的制造方法，得到的高密度聚乙烯绝缘层的发泡密度最低可以达到0.08g/cm 3，对应的发泡倍率达12；聚丙烯绝缘层的发泡密度最低可以达到0.05g/cm 3，对应的发泡倍率达18，远远高于现有技术中的发泡倍率(一般在6以下)。
实施例1
采用高密度聚乙烯(陶氏化学公司，DGDA6944)作为基础树脂，在100质量份的高密度聚乙烯中加入5质量份的化学发泡剂(AC)，0.5质量份的成核剂(PTFE微粉)，1质量份的紫外交联光引发剂(二苯甲酮)以及0.3质量份的交联敏化剂(季戊四醇三丙烯酸酯或三羟甲基丙烷三丙烯酸酯)，将这些添加剂和高密度聚乙烯粒子充分混合均匀，得到制备绝缘层的材料A。
采用锥形同向双螺杆挤塑机进行低温强制挤塑。选用的内导体直径为3.55mm，特性阻抗为50Ω。将材料A通过挤塑机在该内导体外表面挤出绝缘层，挤塑时绝缘层未发泡，挤出的绝缘缆芯的直径为4.4mm。挤塑时，挤塑机机膛和机头处的温度为150℃-170℃范围内。
绝缘缆芯从挤塑机机头挤出后立即用紫外LED灯进行辐照，紫外LED灯安装在挤塑生产线上，且多个紫外LED灯并排组成辐照光源阵列，总功率为2kw。紫外交联后的绝缘缆芯内的凝胶含量为40％。然后再将该绝缘缆芯穿过加热管内进行加热，加热管内的温度为230℃-250℃，绝缘缆芯在加热管内的受热时间为4min-7min，在加热管内实现绝缘层的发泡。离开加热管的绝缘缆芯经过风冷和水冷进行冷却定型，然后由收线装置收上电缆盘具。最后，将发泡后的绝缘缆芯包覆上外导体，以及在外导体外表面挤出护套，即得到了射频同轴电缆。
实施例2
实施例2与实施例1的区别之处在于，采用聚丙烯(陶氏化学公司，JQDB-2230)作为基础树脂，挤塑得到的未发泡的绝缘缆芯的直径为5.3mm，挤塑时，挤塑机机膛和机头处的温度为155℃-175℃范围内。
对比例1
对比例1与实施例1的区别之处在于，采用的基础树脂为低密度聚乙烯和高密度聚乙烯的混合物，并且采用一步法发泡工艺。
实施例1-2及对比例1的制备得到的射频同轴电缆的特性如表1所示。
表1
Figure PCTCN2021128857-appb-000001
Figure PCTCN2021128857-appb-000002
由表1可知，与对比例1相比，实施例1和2制备得到的绝缘层的发泡度要明显高于对比例1，实施例1的发泡度提高了11.6％，发泡倍率达到9.7；实施例2的发泡度提高了13.2％，发泡倍率达到11.2。并且，实施例1和实施例2的同轴电缆的衰减相比对比例1也有了明显地降低，且电缆频率越高，衰减降低的幅度越大。此外，实施例1和实施例2的电缆的传输速比相比对比例1有了明显提高。
综上所述，本发明的制造方法，将绝缘层的挤塑和发泡两个过程分别在两个独立的工序来实现，先用低温强制挤塑工艺获得未发泡的绝缘缆芯，然后对挤塑后的未发泡的绝缘缆芯进行微交联处理，使含有化学发泡剂的绝缘层内形成部分凝胶，这些凝胶的聚合物分子链从二维结构转为三维结构，绝缘层在后续受热过程中不会全部熔融，而是表现出一定的粘弹性。当加热绝缘缆芯时，绝缘层的温度高于化学发泡剂的分解温度时，化学发泡剂释放出气体，使得处于粘弹态的绝缘层发泡，而由于绝缘层含有部分凝胶，即使发泡度很高(例如 高达92％)，发泡泡孔也不会破裂，可以得到大量均匀细密的泡孔。
以上述依据本发明的理想实施例为启示，通过上述的说明内容，相关工作人员完全可以在不偏离本项发明技术思想的范围内，进行多样的变更以及修改。本项发明的技术性范围并不局限于说明书上的内容，必须要如权利要求范围来确定其技术性范围。

Claims (10)

  1. 一种具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述射频同轴电缆包括绝缘缆芯、外导体及护套，所述外导体包覆在所述绝缘缆芯的外表面，所述护套包覆在所述外导体的外表面，所述绝缘缆芯包括内导体和绝缘层，所述绝缘层包覆在所述内导体的外表面；
    所述制造方法包括以下步骤：
    S1：在基础树脂中加入化学发泡剂、成核剂、紫外交联光引发剂和交联敏化剂，并将所述化学发泡剂、成核剂、紫外光交联引发剂、交联敏化剂和基础树脂混合均匀，得到制备绝缘层的材料A；
    S2：采用低温强制挤塑工艺，将所述材料A通过挤塑机在所述内导体外表面挤出所述绝缘层，得到未发泡的绝缘缆芯；
    S3：当所述未发泡的绝缘缆芯被挤出挤塑机的机头后，立即采用紫外光源对所述未发泡的绝缘缆芯进行辐照处理，使得所述绝缘层实现微交联；
    S4：将经过步骤S3处理的未发泡的绝缘缆芯进行加热发泡处理，使得绝缘层发泡，然后再将绝缘缆芯进行冷却定型，得到发泡的绝缘缆芯；
    S5：在所述发泡的绝缘缆芯外表面包覆上外导体，然后再通过挤塑机在外导体外表面挤出护套，得到射频同轴电缆。
  2. 如权利要求1所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述基础树脂为高密度聚乙烯或聚丙烯，化学发泡剂的添加量为所述基础树脂质量的2％-10％。
  3. 如权利要求1所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述紫外交联光引发剂为二苯甲酮或4-羟基二苯甲酮月桂酸酯，所述紫外交联光引发剂的添加量为所述基础树脂质量的0.5％-2％；所述交联敏化剂为三羟甲基丙烷三丙烯酸酯、季戊四醇三丙烯酸酯、己二醇二丙烯酸酯、三聚氰酸 三烯丙醋、三烯丙基异氰脲酸酯或三羟甲基丙烷三甲基丙烯酸酯，所述交联敏化剂的添加量为所述基础树脂的0.2％-0.6％。
  4. 如权利要求2所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述挤塑机机膛和机头的温度均小于180℃。
  5. 如权利要求1所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述低温强制挤塑工艺为采用单螺杆挤塑机，所述单螺杆挤塑机的机膛内壁或机膛衬套内壁上开设有螺旋沟槽，所述螺旋沟槽的螺旋升角为40°-65°，所述螺旋沟槽的螺纹旋向与螺杆的螺纹旋向相反。
  6. 如权利要求1所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述低温强制挤塑工艺为采用单螺杆挤塑机，所述单螺杆挤塑机的螺杆为销钉型螺杆。
  7. 如权利要求1所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述低温强制挤塑工艺为采用双螺杆挤塑机，所述双螺杆挤塑机包括锥形同向双螺杆挤塑机、锥形异向双螺杆挤塑机或平行双螺杆挤塑机。
  8. 如权利要求1所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，经过步骤S3处理的绝缘层内会形成凝胶，所述凝胶的含量占绝缘层总量的18％-50％。
  9. 如权利要求1所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，所述紫外光源包括紫外LED灯和高压紫外汞灯，当未发泡的绝缘缆芯的绝缘层的厚度小于3mm时，采用紫外LED灯作为紫外光源；当未发泡的绝缘缆芯的绝缘层的厚度为3mm-5mm时，采用高压紫外汞灯作为紫外光源；当未发泡的绝缘缆芯的绝缘层的厚度大于5mm时，将紫外LED灯和高压紫外汞灯同时作为紫外光源。
  10. 如权利要求1所述的具有高发泡度的射频同轴电缆的制造方法，其特征在于，步骤S4中的加热发泡处理具体为：
    将经过步骤S3处理的未发泡的绝缘缆芯通过加热管，所述加热管内的温度为230℃-300℃，所述加热管的长度为15m-30m，所述未发泡的绝缘缆芯穿过所述加热管的速度为2-15m/min。
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JPH0520928A (ja) * 1991-07-11 1993-01-29 Junkosha Co Ltd 絶縁電線及びその製造方法
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