WO2023060674A1 - 同轴连接器的绝缘支撑体的制造方法 - Google Patents

同轴连接器的绝缘支撑体的制造方法 Download PDF

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WO2023060674A1
WO2023060674A1 PCT/CN2021/128858 CN2021128858W WO2023060674A1 WO 2023060674 A1 WO2023060674 A1 WO 2023060674A1 CN 2021128858 W CN2021128858 W CN 2021128858W WO 2023060674 A1 WO2023060674 A1 WO 2023060674A1
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insulating support
microporous
coaxial connector
support body
foaming
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PCT/CN2021/128858
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English (en)
French (fr)
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代康
钱利荣
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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Publication of WO2023060674A1 publication Critical patent/WO2023060674A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B19/00—Apparatus or processes specially adapted for manufacturing insulators or insulating bodies
    • 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

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  • the invention relates to the technical field of coaxial connectors, in particular to a method for manufacturing an insulating support body of a coaxial connector.
  • the frequency and frequency bandwidth of mobile communication continue to increase.
  • the fifth-generation mobile communication (5G) with a frequency below 6GHz has been commercialized, and the millimeter wave (frequency above 28GHz) 5G system will be launched in the future. Therefore, RF coaxial connectors for mobile communications should meet the requirements of high frequency of use, wide operating frequency band, low loss and small VSWR. To meet these requirements, the insulating support becomes the key.
  • radio frequency coaxial connectors usually use a solid insulating support made of polytetrafluoroethylene (PTFE).
  • PTFE polytetrafluoroethylene
  • PTFE has the lowest dielectric constant (2.01-2.03 below 1 GHz), extremely low dielectric loss, high dielectric strength and heat resistance. These characteristics of PTFE are conducive to reducing the loss of coaxial connectors and increasing the frequency of use of coaxial connectors.
  • the solid structure of the PTFE insulating support makes it a short board for improving the insertion loss and cut-off frequency performance of coaxial connectors.
  • the equivalent dielectric constant of the insulating support body of the coaxial connector should not be greater than 1.8, which requires the insulating support body to be a mixed insulating medium structure, that is, in the structure of the insulating support body Contains air.
  • the most commonly used method for the insulating support body to obtain a mixed insulating medium structure is the hollowing out method, in which annular grooves are opened on both ends of the insulating support body, and multiple air holes are opened on the cross-section of the insulating support body.
  • the circumference of the cross-section of the body is evenly distributed (as shown in FIG. 1 ), thereby forming a mixed insulating medium, which can reduce the dielectric constant of the insulating support body, and the dielectric loss will also be reduced.
  • the hollowing method is generally used for insulating supports of polyetheretherketone (PEEK) materials and polyetherimide (PEI) materials with high mechanical strength.
  • the hollow volume of the insulating support has to be increased, resulting in increased processing difficulty and reduced processing pass rate .
  • the dielectric loss of PEEK and PEI is significantly higher than that of PTFE.
  • the insulating support in addition to the above-mentioned hollowing out method, can also be provided with a microporous structure, that is, there are a large number of air micropores inside the insulating support.
  • PTFE is an infusible polymer, it cannot be melt-processed at high temperature, and it is difficult to obtain PTFE with a microporous structure by injection molding and extrusion.
  • tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers are usually used for foaming. microporous structure.
  • PFA meltable polytetrafluoroethylene
  • TFE tetrafluoroethylene monomer
  • PAVE perfluoroalkyl vinyl ether monomer
  • methods for preparing PFA insulating supports with microporous structures include chemical foaming and physical foaming.
  • Physical foaming refers to the injection of high-pressure nitrogen or carbon dioxide into the extruder chamber. In order to maintain the stability of the injected gas volume, the injected gas should be kept in a supercritical state. Physical foaming requires an additional gas injection system, which has high requirements on the extruder, and the nozzle for injecting gas is easily damaged during use, making it difficult to maintain the supercritical state of the gas.
  • the chemical foaming method is to add a chemical foaming agent to the plastic pellets to be extruded. The foaming process is simple and the foaming quality is stable.
  • the chemical blowing agents currently used include AC (azodicarbonamide), OBSH (4,4' (benzenesulfonyl hydrazide), etc.
  • the decomposition temperature of these chemical blowing agents is usually lower than 200 ° C, and fluoroplastics
  • the melting point is usually higher, for example, the melting point of PFA is about 310°C, and the melting point of polyperfluoroethylene propylene (copolymer of tetrafluoroethylene monomer TFE and hexafluoropropylene monomer HFP, abbreviated as FEP) is about 260°C.
  • the technical problem to be solved by the present invention is: to solve the technical problem that the preparation effect of the method for preparing the PFA insulating support with microporous structure in the prior art is unsatisfactory.
  • the invention provides a method for manufacturing an insulating support body of a coaxial connector, which can effectively reduce the effective dielectric constant of the insulating support body and increase the cut-off frequency of the coaxial connector.
  • the technical solution adopted by the present invention to solve the technical problem is: a method for manufacturing an insulating support body of a coaxial connector, the insulating support body has a microporous structure, and the cross section of the insulating support body is ring-shaped, the The manufacturing method includes the following steps: S1: mixing the PFA material and the FEP material to obtain a blended polymer A; S2: adding the MFA material to the blended polymer A to obtain a blended polymer B; S3: determining the insulation The inner diameter d1 and the outer diameter D1 of the support body; S4: adding the foaming material into the blended polymer B to obtain the raw material C for preparing the microporous insulating support body; S5: extruding the raw material C by using an extruder to obtain Microporous pipe, the inner diameter of the microporous pipe is consistent with the inner diameter d1 of the insulating support, and the outer diameter of the microporous pipe is consistent with the outer diameter D1 of the insulating support;
  • the mixing ratio of the PFA material and the FEP material is 2:1 ⁇ 4:1.
  • step S2 the mass of the MFA material added is 2%-5% of the mass of the polymer blend A.
  • the foaming material includes ammonium polyphosphate and a nucleating agent
  • the mass of ammonium polyphosphate is equal to that of the blend polymer B 0.2% to 2% of the mass
  • the mass of the nucleating agent is 0.05% to 0.8% of the mass of the blend polymer B.
  • the foaming material includes ammonium polyphosphate, nucleating agent and expanded microspheres
  • the quality of ammonium polyphosphate is the blending 0.2% to 2% of the mass of the polymer B
  • the mass of the nucleating agent is 0.05% to 0.8% of the mass of the blended polymer B
  • the mass of the expanded microspheres is 30% to 50% of the mass of the ammonium polyphosphate .
  • the method also includes: before adding the foaming material to the blend polymer B, adding the polyphosphoric acid FEP material is added to the mixture of ammonium and nucleating agent to obtain foaming additive masterbatch with FEP material as the carrier, the proportion of FEP material in the foaming additive masterbatch is 80% to 90%, and the rest is polyphosphoric acid ammonium and nucleating agent.
  • determining the inner diameter d1 and outer diameter D1 of the microporous insulating support in step S3 specifically includes:
  • the coaxial connector includes an inner conductor and an outer conductor, the outer conductor is covered outside the inner conductor, the microporous insulating support is embedded in the inner conductor and the outer conductor, and the inner conductor
  • the inner diameter is d
  • the outer diameter of the inner conductor is D
  • the outer diameter D1 is greater than the outer diameter D, so that a part of the microporous insulating support is embedded in the outer conductor, and the depth of the microporous insulating support embedded in the outer conductor is h;
  • d is the inner diameter of the inner conductor
  • D is the outer diameter of the inner conductor
  • ⁇ 0 is the relative effective permittivity of air
  • the outer diameter D and ⁇ 0 are known
  • the inner diameter d is determined according to formula (1);
  • d1 is the inner diameter of the microporous insulating support body
  • D1 is the outer diameter of the microporous insulating support body
  • ⁇ 1 is the relative effective dielectric constant of the microporous insulating support body
  • step S5 using an extruder to extrude the raw material C to obtain a microporous pipe specifically includes:
  • S51 Feeding section: Feed the raw material C into the machine chamber of the extruder, and the rotating screw in the extruder pushes the raw material C forward in the machine chamber, and set the temperature of the rear section of the feeding section to 200°C-270°C;
  • a gear pump is provided between the extruder chamber and the extruder head.
  • f c ' is the cut-off frequency at the microporous insulating support
  • c is the speed of light in vacuum
  • ⁇ 1 is the relative effective dielectric constant of the microporous insulating support
  • the thickness t of the microporous insulating support is less than or equal to a quarter of the wavelength ⁇ .
  • the manufacturing method of the insulating support body of the coaxial connector of the present invention can reduce the preparation cost and improve the processing efficiency by using PFA material and FEP material as the basic material; Foaming quality; in order to improve the degree of foaming, a combination of chemical foaming and physical foaming can be used.
  • the insulating support with a microporous structure obtained by the preparation method of the present invention has a high degree of foaming, good foaming quality, and fine and uniform cells, which can reduce the effective dielectric constant of the insulating support and further improve the performance of the coaxial connector. Cut-off frequency.
  • Fig. 1 is a cross section and a sectional view of a hollow structure of an insulating support body of a radio frequency coaxial connector in the prior art.
  • Fig. 2 is a flow chart of the method for manufacturing the insulating support body of the coaxial connector of the present invention.
  • Fig. 3 is a schematic diagram of the assembly of the insulating support of the present invention.
  • Fig. 4 is a flowchart of determining the inner diameter d1 and outer diameter D1 of the microporous insulating support in the present invention.
  • Fig. 5 is a flow chart of extruding raw material C to obtain a microporous pipe using an extruder according to 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 may be mechanically connected or electrically connected; it may be directly connected or indirectly connected through an intermediary, and it may 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.
  • a method for manufacturing an insulating support body of a coaxial connector includes the following steps.
  • PFA is the English abbreviation of fusible polytetrafluoroethylene
  • FEP is the English abbreviation of fluorinated ethylene propylene copolymer
  • FEP is a copolymer of tetrafluoroethylene and hexafluoropropylene
  • the crystal melting point of FEP is 304 °C. Due to the high cost of the PFA material, in order to reduce the preparation cost and improve the processing efficiency, this embodiment adds the PEP material to the PFA material, and the blended polymer A obtained by mixing the PFA material and the PEP material is used as the basic material for preparing the insulating support , PFA material and FEP material are plastic particles.
  • the mixing ratio of the PFA material and the FEP material is 2:1 ⁇ 4:1. Since the dielectric properties and high temperature resistance of PFA materials are significantly higher than those of FEP materials, the proportion of PFA materials in the blend polymer A is a little higher, but the cost of PFA materials is also higher than that of FEP materials. Therefore, the ratio of 2:1-4:1 selected in this embodiment achieves a balance between characteristics and cost, which can not only reduce the cost, but also retain the excellent performance of the coaxial connector with the PFA insulating support body.
  • adding MFA material to blend polymer A can improve the compatibility of PFA material and PEP material in the molten state and the uniformity of melt rheological properties, and ensure the subsequent foaming effect; at the same time, it can reduce During extrusion, the accumulation of coke at the die mouth of the extruder head.
  • the mass of the added MFA material is 2%-5% of the mass of the blend polymer A.
  • the main purpose of adding MFA material to the blend polymer A is to increase the compatibility of the contact interface between the FEP material and the PFA material. If too little MFA material is added, the desired effect cannot be achieved.
  • the relative permittivity of the PFA material, FEP material and MFA material are basically the same, for example, in the frequency range of 1 MHz-1 GHz, the permittivity is about 2.03.
  • the selected PFA material is DuPont's PFA420HP-J
  • the FEP material is DuPont's FEP9475
  • the MFA material is Solvay's Haflon MFA1041 or Solvay (Shanghai) Co., Ltd.'s F1540.
  • the fixing method of the insulating support is embedded in the inner conductor and the outer conductor.
  • Coaxial connectors have the least effect on VSWR.
  • the coaxial connector includes an inner conductor 1 and an outer conductor 2.
  • the outer conductor 2 covers the outside of the inner conductor 1.
  • the microporous insulating support 3 is embedded in the inner conductor 1 and the outer conductor 2.
  • the inner diameter of the inner conductor 1 is d
  • the outer diameter of the inner conductor 1 is D
  • the outer diameter D1 is greater than the outer diameter D, so that a part of the microporous insulating support 3 is embedded in the outer conductor 2, and the depth of the microporous insulating support 3 embedded in the outer conductor 2 is h.
  • d is the inner diameter of the inner conductor 1
  • D is the outer diameter of the inner conductor 1
  • ⁇ 0 is the relative effective permittivity of air
  • the outer diameter D and ⁇ 0 are known
  • the inner diameter d is determined according to formula (1).
  • the characteristic impedance is the inherent characteristic of the radio frequency transmission line affecting the amplitude and phase changes of the radio wave voltage and current.
  • the characteristic impedance of the coaxial connector is related to the inner and outer diameter of the conductor and the dielectric constant of the medium between the conductors. The same coaxial connector The characteristic impedance is constant.
  • the most typical characteristic impedances in coaxial connectors are 50 ⁇ and 75 ⁇ , and generally 50 ⁇ is the most commonly used.
  • 50 ⁇ is taken as an example to illustrate how to determine the inner diameter and outer diameter of the insulating support.
  • the cutoff frequency of the coaxial connector is related to the inner and outer diameters d, D of the inner conductor and the relative effective dielectric constant ⁇ 0 of the medium. The larger the cutoff frequency, the wider the frequency range of the coaxial connector.
  • the outer diameter D of the inner conductor can be determined according to the specifications of the coaxial connector, and the relative effective dielectric constant ⁇ 0 of air can be approximated as 1, so that the inner diameter of the inner conductor can be calculated according to formula (1) What is d.
  • d1 is the inner diameter of the microporous insulating support body 3
  • D1 is the outer diameter of the microporous insulating support body 3
  • ⁇ 1 is the relative effective dielectric constant of the microporous insulating support body 3.
  • f c ' is the cut-off frequency at the microporous insulating support
  • c is the speed of light in vacuum
  • ⁇ 1 is the relative effective permittivity of the microporous insulating support.
  • the thickness t of the microporous insulating support is less than or equal to a quarter of the wavelength ⁇ .
  • foam material can be divided into two cases.
  • the foaming material includes ammonium polyphosphate and a nucleating agent
  • the quality of ammonium polyphosphate is 0.2% to 0.2% of the mass of the blended polymer B.
  • the mass of the nucleating agent is 0.05% to 0.8% of the mass of the blend polymer B.
  • the foaming material includes ammonium polyphosphate, nucleating agent and expanded microspheres, and the quality of ammonium polyphosphate is 1% of the blend polymer B quality. 0.2% to 2%, the mass of the nucleating agent is 0.05% to 0.8% of the mass of the blended polymer B, and the mass of the expanded microspheres is 30% to 50% of the mass of the ammonium polyphosphate.
  • the FEP material Before adding the foaming material to the blended polymer B, the FEP material will be added to the mixture of ammonium polyphosphate and nucleating agent to obtain the foaming additive masterbatch with the FEP material as the carrier, and the FEP material in the foaming additive masterbatch The proportion is 80% to 90%, and the rest is ammonium polyphosphate and nucleating agent.
  • the foaming additive masterbatch will decompose and release gas when heated.
  • a twin-screw extruder can be used for granulation.
  • Expanded microspheres are a core-shell structure, the inner core is alkane with low boiling point, and the outer shell is thermoplastic polymer.
  • the diameter of expanded microspheres is generally 10-30 ⁇ m.
  • the inner core When heated, the inner core will gasify first, and then the outer shell will Soften, the gas inside makes the shell start to expand.
  • the volume of the expanded microspheres reaches the maximum, and the diameter of the expanded microspheres becomes several times that of the original. After cooling, the shell will harden again and expand.
  • the volume of the microspheres is fixed.
  • the expanded microspheres used in the present invention are high-temperature expanded microspheres produced by Xineng Chemical Technology Co., Ltd., and the highest foaming temperature can reach 280°C.
  • the melting points of the three materials in the polymer blend B are all relatively high, but most commercial chemical blowing agents will decompose before reaching the processing temperature of the polymer blend B, and cannot reach the foaming point. bubble effect.
  • AZ azodicarbonamide
  • the preferred chemical foaming agent in the communication cable industry it begins to decompose above 120°C, and its decomposition temperature in air is 195°C. Therefore, if AZ and the blended polymer B are compounded and granulated first, AZ has decomposed and released gas during the granulation process, and the obtained pellets have lost their gas when used in the next step of extrusion processing the microporous insulating support.
  • Foaming if the AZ masterbatch is added to the extruder when the microporous insulating support is extruded, then the blend polymer B begins to melt when AZ begins to decompose, and the gas released by AZ will escape from the feed port of the extruder.
  • the resulting insulating support will have a low degree of foaming. Therefore, it is necessary to find a foaming agent that decomposes and releases gas at a high temperature to realize the foaming of the insulating support in this embodiment.
  • ammonium polyphosphate is selected as the chemical foaming agent.
  • Ammonium polyphosphate will start to release ammonia gas at about 340°C, which is higher than the normal processing temperature of blend polymer B, and can be used as an endothermic chemical foaming agent. .
  • the proportion of the chemical blowing agent is too high, the residue after pyrolysis will increase, which will affect the dielectric properties of the insulating support and cause an increase in the insertion loss of the coaxial connector.
  • the ammonium polyphosphate addition ratio proposed by the present invention can take into account both the degree of foaming and the insertion loss performance of the final signal connection of the insulating support. If you want to continue to increase the degree of foaming, you can achieve it by adding expanded microspheres (physical foaming).
  • a nucleating agent may be added in order to cooperate with the chemical foaming agent for foaming.
  • the nucleating agent can be an inorganic nucleating agent or an organic nucleating agent, such as boron nitride, calcium tetraborate, silicon dioxide powder, etc., wherein the silicon dioxide powder can also absorb part of the chemical foaming The residue left after the decomposition of the agent.
  • the organic nucleating agent can be, for example, non-melting polytetrafluoroethylene (PFFE) powder, ultrafine polytetrafluoroethylene (PTFE) powder, and the like.
  • a composite nucleating agent is preferably used, and the inorganic nucleating agent and the organic nucleating agent are used in combination, which can reduce the dielectric loss of the polymer blend B.
  • the composite nucleating agent is mainly PTFE powder, and the mass ratio of inorganic nucleating agent to PTFE powder is 1:2 ⁇ 1:3.
  • the median particle size of the composite nucleating agent is controlled between 5 ⁇ m and 25 ⁇ m, preferably less than 10 ⁇ m.
  • Inorganic nucleating agents are stable at high temperatures, do not decompose, and are relatively low in cost, but have a negative impact on the insertion loss of coaxial connectors.
  • PTFE has a high cost, but its dielectric loss is low and will not affect the transmission performance of the coaxial connector. Therefore, in this embodiment, the inorganic nucleating agent and PTFE are combined as a composite nucleating agent, and the mass ratio of the inorganic nucleating agent to PTFE powder is 1:2 to 1:3, which can balance the cost and performance of the nucleating agent.
  • the addition ratio of the nucleating agent is related to the degree of foaming.
  • the mass of the nucleating agent added is 0.05%-0.8% of the mass of the blend polymer B.
  • Each micropore can be simply regarded as growing around a nucleating agent particle. The higher the degree of foaming, the more gas in the melt. In order to obtain fine micropores, the number of micropores needs to be increased, so it is necessary The addition ratio of the nucleating agent is increased, but too much nucleating agent will result in an increase in the material cost of the insulating support and a decrease in performance such as insertion loss.
  • Feeding section Feed the raw material C into the machine chamber of the extruder, and the rotating screw in the extruder pushes the raw material C forward in the machine chamber, and set the temperature of the rear section of the feeding section to 200°C-270°C. During the feeding section, raw material C has not yet melted and decomposed.
  • Melting section the temperature of the melting section is 300°C to 365°C, and raw material C will be melted after entering the melting section. in the melt.
  • the temperature of the melting section is preferably above 340°C, so that the blend polymer B can be fully melted, and at the same time, the foaming additive masterbatch can also decompose to generate gas, which can be dissolved in the melt to form bubbles. If expanded microspheres are also added to the foaming material, the expanded microspheres will also begin to expand at this time.
  • the foaming additive masterbatch has been decomposed into gas, due to the space limitation of the machine chamber, there are certain restrictions on the bubbles, so the melt will not foam in the machine chamber.
  • step S53 Metering section: the temperature of the metering section is 375°C to 390°C. After the gas-containing melt in step S52 enters the metering section, since the volume of the metering section is fixed, the rotating screw can transfer the fixed volume of the gas-containing melt into the metering section. The body is pushed into the head of the extruder. The function of the metering section is to control the amount of each push of the rotating screw. In the metering section, the melt will not foam.
  • the temperature of the die is 385°C to 390°C. After the gas-containing melt is pushed out of the die mouth of the die, it will expand and foam immediately to obtain a microporous pipe, and then cool the microporous pipe to shape it.
  • step S53 The melt in step S53 is pushed into the mold of the machine head, and then pushed out of the mold mouth.
  • the melt will foam when it exits the mold mouth form a microporous structure.
  • the pressure near the machine head will decrease, and the melt may foam in advance when passing through this place, resulting in an unsatisfactory final foaming effect. Therefore, in this embodiment, a gear pump is provided between the extruder chamber and the extruder head, and the gear pump can increase the pressure inside the head to prevent the melt from foaming in advance.
  • the extrusion temperature can be set according to the high-temperature melting characteristics of the PFA/FEP/MFA blend polymer B and the basic principle of extrusion processing.
  • the extrusion temperature should not only meet the requirement that the blend polymer B can be fully melted, but also allow the chemical foaming agent to decompose and dissolve in the melt as far as possible in the plastic melting section in the middle of the machine chamber. Therefore, in this embodiment, the temperatures of the feeding section, the melting section and the metering section of the extruder are set to gradually increase, and are respectively set to 200°C-270°C, 300°C-365°C and 385°C-395°C.
  • the temperature of the head is equal to or slightly lower than that of the metering section, for example, it is set to 375-390°C, which can take into account both extrusion processing efficiency (that is, reducing the residence time of the blend in the extruder bore) and the melting quality of the blend .
  • the length-to-diameter ratio of the screw of the extruder should not be lower than 25D (D is the diameter of the screw), and 30D is more suitable.
  • the microporous pipe can be cut into several microporous insulating supports with a thickness t by means of mechanical cutting.
  • the microporous insulating support can be divided into two parts along the diameter, which is convenient for installation into the inner conductor and the outer conductor.
  • the manufacturing method of the insulating support of the coaxial connector of the present invention by using the blended polymer B of PFA/FEP/MFA as the preparation material, not only can reduce the manufacturing cost, but also can improve the strength of the insulating support. Foaming effect, improve work efficiency.
  • the insulating support body with the microporous structure prepared by the invention has a lower effective dielectric constant and can increase the cut-off frequency of the coaxial connector.
  • the average diameter of micropores in the obtained insulating support body is 34 ⁇ m, and the foaming degree of the insulating support body is 42%.
  • micropores with an average diameter of 27 ⁇ m and a foaming degree of 69% are finally obtained.
  • the average cell diameter decreased, indicating that thermal expansion of the microspheres resulted in smaller cells than the chemical foaming method.
  • the surface of the finished product is smooth and fine, indicating that the foaming quality is good, and there is no cell collapse.

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Abstract

本发明公开了一种同轴连接器的绝缘支撑体的制造方法，绝缘支撑体具有微孔结构，且绝缘支撑体的截面为环形，制造方法包括以下步骤：S1：将PFA材料与FEP材料进行混合得到共混聚合物A；S2：将MFA材料加入到共混聚合物A中，得到共混聚合物B；S3：确定绝缘支撑体的内径d1和外径D1；S4：将发泡材料加入共混聚合物B中，得到制备微孔绝缘支撑体的原料C；S5：采用挤塑机将原料C挤出成型得到微孔管材，微孔管材的内径与绝缘支撑体的内径d1一致，微孔管材的外径与绝缘支撑体的外径D1一致；S6：将微孔管材切按照厚度t切割成若干个微孔绝缘支撑体。利用本发明，能够降低绝缘支撑体的有效介电常数，提高同轴连接器的截止频率。

Description

同轴连接器的绝缘支撑体的制造方法 技术领域
本发明涉及同轴连接器技术领域，尤其涉及一种同轴连接器的绝缘支撑体的制造方法。
背景技术
为了得到更大的通信容量和更高的传输速率，移动通信频率和频率带宽不断再增加。目前，频率在6GHz以下的第五代移动通信(5G)已商用化，未来还将开通毫米波(频率在28GHz以上)5G系统。因此，移动通信用的射频同轴连接器应满足使用频率高、工作频带宽、损耗低和电压驻波比小的要求。要满足这些要求，绝缘支撑体成为关键。
目前，射频同轴连接器通常采用由聚四氟乙烯(PTFE)材料制成的实心结构的绝缘支撑体。在众多聚合物中，PTFE具有最低的介电常数(在1GHz以下为2.01～2.03)，介电损耗极低，具有较高的介电强度和耐热性。PTFE的这些特点有利于降低同轴连接器的损耗，增加同轴连接器的使用频率。然而，PTFE绝缘支撑体的实心结构，使其成为改善同轴连接器插入损耗和截止频率性能的短板。当同轴连接器使用频率达到毫米波时，要求同轴连接器的绝缘支撑体的等效介电常数应不大于1.8，这就需要绝缘支撑体为混合绝缘介质结构，即绝缘支撑体结构中含有空气。
目前，绝缘支撑体获得混合绝缘介质结构的最常用的方法是镂空法，在绝缘支撑体两端面上开设环形槽，并在绝缘支撑体截面上开设多个空气孔，多个空气孔沿绝缘支撑体截面圆周均匀分布(如图1所示)，从而形成混合绝缘介质，能够降低绝缘支撑体的介电常数，介质损耗也会降低。
但是，由于PTFE材料机械强度不高，在绝缘支撑体上开槽和开孔很容易造 成绝缘支撑体损坏。另外，频率越高，绝缘支撑体的尺寸越小。例如，使用频率为110GHz的1mm规格的毫米波连接器，其外导体内径为1mm(装配好的连接器中的绝缘支撑体外径也为1mm)，这加大了镂空的难度，镂空工艺合格率大幅度降低。因此，镂空法一般用于机械强度较高的聚醚醚酮(PEEK)材料和聚醚酰亚胺(PEI)材料的绝缘支撑体。但是，由于PEEK和PEI的介电常数较高，要想使得绝缘支撑体的有效介电常数达到1.8及以下，绝缘支撑体镂空体积不得不加大，导致加工难度增加，加工合格率也会下降。并且，PEEK和PEI的介质损耗明显高于PTFE。
因此，为了降低绝缘支撑体的等效介电常数，除上述的镂空法外，还可以将绝缘支撑体设置成微孔结构，即在绝缘支撑体内部有大量的空气微孔。然而，由于PTFE为不熔性聚合物，不能进行高温熔融加工，很难用注塑和挤塑方法得到微孔结构的PTFE。
为了克服PTFE不能熔融发泡的缺点，通常采用四氟乙烯-全氟烷基乙烯基醚共聚物(一般称为可熔性全氟烷氧基共聚物，英文缩写为PFA)来发泡制得微孔结构。PFA俗称为可熔性聚四氟乙烯，是四氟乙烯单体(TFE)与少量全氟烷基乙烯基醚单体(PAVE)的共聚物，其介电性能、耐热性等性能十分接近PTFE，但高温机械强度是PTFE的两倍以上，且同样具备介电常数和介质损耗几乎不受温度变化影响的优点。
目前，制备微孔结构的PFA绝缘支撑体方法有化学发泡法和物理发泡法。物理发泡是指在挤塑机机膛内注入高压氮气或二氧化碳。为了保持注入气量的稳定，注入气体应保持超临界状态。物理发泡需要额外的气体注入系统，对挤塑机有较高的要求，且注入气体的喷嘴在使用中容易损坏，难以维持气体的超临界状态。化学发泡法是在待挤塑的塑料粒料中加入化学发泡剂，发泡工艺简 单，发泡质量稳定。目前使用的化学发泡剂有AC(偶氮二甲酰胺)、OBSH(4,4’(苯磺酰肼)等，然而这些化学发泡剂的分解温度通常都低于200℃，而氟塑料熔点通常更高，例如PFA熔点约310℃，聚全氟乙丙烯(四氟乙烯单体TFE与六氟丙烯单体HFP的共聚物，英文缩写为FEP)熔点约260℃。因此，在氟塑料挤塑发泡工艺中，这些化学发泡剂在挤塑机机膛加料段就会分解，气体从加料口逸出，无法在挤塑机机膛中段的塑料熔化段才分解并溶解在氟塑料熔体中，导致难以使熔体出模后再发泡。
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微孔结构的PFA绝缘支撑体的方法制备效果不理想的技术问题。本发明提供一种同轴连接器的绝缘支撑体的制造方法，能够有效降低绝缘支撑体的有效介电常数，提高同轴连接器的截止频率。
本发明解决其技术问题所采用的技术方案是：一种同轴连接器的绝缘支撑体的制造方法，所述绝缘支撑体具有微孔结构，且所述绝缘支撑体的截面为环形，所述制造方法包括以下步骤：S1：将PFA材料与FEP材料进行混合得到共混聚合物A；S2：将MFA材料加入到所述共混聚合物A中，得到共混聚合物B；S3：确定绝缘支撑体的内径d1和外径D1；S4：将发泡材料加入所述共混聚合物B中，得到制备微孔绝缘支撑体的原料C；S5：采用挤塑机将原料C挤出成型得到微孔管材，所述微孔管材的内径与绝缘支撑体的内径d1一致，微孔管材的外径与绝缘支撑体的外径D1一致；S6：将所述微孔管材切按照厚度t切割成若干个微孔绝缘支撑体。通过本发明的制造方法，能够获得发泡效果较好的绝缘支撑体，降低绝缘支撑体的有效介电常数，提高同轴连接器的截止频率，且能够降低制备成本。
进一步地，为了降低制备成本且提高加工效率，在步骤S1中，PFA材料与FEP材料进行混合的比例为2：1～4：1。
进一步地，为了保证发泡质量，在步骤S2中，加入的MFA材料的质量为所述共混聚合物A质量的2％～5％。
进一步地，当所需的微孔绝缘支撑体的发泡度小于或等于40％时，所述发泡材料包括聚磷酸铵和成核剂，聚磷酸铵的质量为所述共混聚合物B质量的0.2％～2％，成核剂的质量为所述共混聚合物B质量的0.05％～0.8％。
进一步地，当所需的微孔绝缘支撑体的发泡度高于40％时，所述发泡材料包括聚磷酸铵、成核剂以及膨胀微球，聚磷酸铵的质量为所述共混聚合物B质量的0.2％～2％，成核剂的质量为所述共混聚合物B质量的0.05％～0.8％，膨胀微球的质量为所述聚磷酸铵质量的30％～50％。
进一步地，为了使得化学发泡剂和成核剂能够均匀分布于共混聚合物B中，所述方法还包括：将所述发泡材料加入所述共混聚合物B之前，将在聚磷酸铵和成核剂的混合物中加入FEP材料，得到以FEP材料为载体的发泡添加剂母粒，所述发泡添加剂母粒中的FEP材料的占比为80％～90％，其余为聚磷酸铵和成核剂。
进一步地，步骤S3中确定微孔绝缘支撑体的内径d1和外径D1具体包括：
S31：同轴连接器包括内导体和外导体，所述外导体包覆在所述内导体外侧，所述微孔绝缘支撑体嵌设在所述内导体和外导体内，所述内导体的内径为d，内导体的外径为D，外径D1大于外径D，使得微孔绝缘支撑体的一部分嵌入所述外导体内，所述微孔绝缘支撑体嵌入所述外导体的深度为h；
S32：假设同轴连接器内的绝缘介质为空气，则同轴连接器截面的特性阻抗Z 0和截止频率f c为：
Figure PCTCN2021128858-appb-000001
Figure PCTCN2021128858-appb-000002
其中，d为内导体的内径，D为内导体的外径，ε 0为空气的相对有效介电常数，外径D和ε 0为已知，根据公式(1)确定内径d；
S33：所述同轴连接器在微孔绝缘支撑体处的特性阻抗Z 0和截止频率f c'为：
Figure PCTCN2021128858-appb-000003
Figure PCTCN2021128858-appb-000004
其中，d1为微孔绝缘支撑体的内径，D1为微孔绝缘支撑体的外径，ε 1为微孔绝缘支撑体的相对有效介电常数；
S34：深度h＝(D-d)×K，k为0.15～0.3，所述外径D1＝D+2h；ε 1为1.5～1.8，根据公式(3)确定内径d1。
进一步地，步骤S5中采用挤塑机将原料C挤出成型得到微孔管材具体包括：
S51：加料段：将原料C送入挤塑机的机膛内，挤塑机内的旋转螺杆将原料C在机膛内向前推进，将加料段的后段温度设置为200℃～270℃；S52：熔化段：熔化段的温度为300℃～365℃，原料C进入熔化段后会被熔化，此时，共混聚合物B熔化成熔体，发泡添加剂母粒分解成气体并溶解在所述熔体中；S53：计量段：计量段的温度为375℃～390℃，步骤S52中的含有气体的熔体进入计量段后，由于计量段的体积是固定的，旋转螺杆可以将固定体积的含有气体的熔体推入挤塑机机头；S54：机头的温度为385℃～390℃，所述含有气体的熔体被推出机头的模具口后，会立即膨胀发泡，得到微孔管材，再将微孔管材进行冷却降温定型。
进一步地，所述挤塑机机膛与挤塑机机头之间设有齿轮泵。
进一步地，设所述微孔绝缘支撑体处的截止频率f c'对应的波长λ为：
Figure PCTCN2021128858-appb-000005
其中，f c'为微孔绝缘支撑体处的截止频率，c为真空中的光速，ε 1为微孔绝缘支撑体的相对有效介电常数，所述微孔绝缘支撑体的厚度t小于或等于波长λ的四分之一。
本发明的有益效果如下：
本发明的同轴连接器的绝缘支撑体的制造方法，通过采用PFA材料和FEP材料作为基础材料，能够降低制备成本且能够提高加工效率；通过在共混聚合物A中添加MFA材料能够进一步提升发泡质量；为了提升发泡度可以采用化学发泡和物理发泡结合的方式。通过本发明制备方法得到的微孔结构的绝缘支撑体具有较高的发泡度，发泡质量良好，泡孔细腻均匀，能够降低绝缘支撑体的有效介电常数，进一步提高同轴连接器的截止频率。
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是现有技术的射频同轴连接器绝缘支撑体镂空结构的横截面和剖视图。
图2是本发明的同轴连接器的绝缘支撑体的制造方法的流程图。
图3是本发明的绝缘支撑体的装配示意图。
图4是本发明的确定微孔绝缘支撑体的内径d1和外径D1的流程图。
图5是本发明的采用挤塑机将原料C挤出成型得到微孔管材的流程图。
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2所示，一种同轴连接器的绝缘支撑体的制造方法，包括以下步骤。
S1：将PFA材料与FEP材料进行混合得到共混聚合物A。
需要说明的是，PFA是可熔性聚四氟乙烯的英文缩写，FEP是氟化乙烯丙烯共聚物的英文缩写，FEP是四氟乙烯和六氟丙烯共聚而成的，FEP结晶熔化点为304℃。由于PFA材料的成本较高，为了降低制备成本并提高加工效率，本实施例在PFA材料中添加PEP材料，将PFA材料和PEP材料混合得到的共混聚合物A作为制备绝缘支撑体的基础材料，PFA材料与FEP材料均为塑胶颗粒。在本实施例中，PFA材料与FEP材料进行混合的比例为2：1～4：1。由于PFA材料的的介电性能和耐高温特性显著高于FEP材料，因此，在共混聚合物A中，PFA材料的比例更高一点，但是，PFA材料的成本也比FEP材料更高。因此，本实施例选择的2：1～4：1的配比是在特性和成本上取得了平衡，既能够降低成本，又可以保留PFA绝缘支撑体同轴连接器的优良性能。
S2：将MFA材料加入到共混聚合物A中，得到共混聚合物B。
需要说明的是，在共混聚合物A中添加MFA材料，能够提高PFA材料和PEP材料在熔融状态下的相容性和熔体流变性质的均匀性，保证后续发泡效果；同时能够减少在挤塑时，挤塑机头模具口处的焦料堆积现象。在本实施例中，加入的MFA材料的质量为共混聚合物A质量的2％～5％。在共混聚合物A中添加MFA材料主要是为了增加FEP材料和PFA材料接触界面的相容性，如果添加的MFA 材料太少，则无法达到预期的效果。由于MFA材料的整体性能不如PFA材料，如果添加的MFA材料太多，则会降低同轴连接器传输性能。另外，PFA材料、FEP材料和MFA材料的相对介电常数基本相同，例如，在1MHz～1GHz频率范围内，介电常数在2.03左右。在本实施例中，选用的PFA材料为杜邦的PFA420HP-J，FEP材料为杜邦的FEP9475，MFA材料为索尔维(Solvay)的Haflon MFA1041或者苏威(上海)有限公司的F1540。
S3：确定微孔绝缘支撑体的内径d1和外径D1。
需要说明的是，在确定微孔绝缘支撑体的内径和外径时，绝缘支撑体的固定方式为嵌入内导体和外导体内部，这样，绝缘支撑体表面产生的不连续的电容最小，从而对同轴连接器的电压驻波比影响最小。
如图3和图4所示，具体的步骤为：
S31：同轴连接器包括内导体1和外导体2，外导体2包覆在内导体1外侧，微孔绝缘支撑体3嵌设在内导体1和外导体2内，内导体1的内径为d，内导体1的外径为D，外径D1大于外径D，使得微孔绝缘支撑体3的一部分嵌入外导体2内，微孔绝缘支撑体3嵌入外导体2的深度为h。
也就是说，微孔绝缘支撑体3的一部分是嵌入外导体2内侧的，绝缘支撑体3的外径D1＝D+2h。
S32：假设同轴连接器内的绝缘介质为空气，则同轴连接器截面的特性阻抗Z 0和截止频率f c为：
Figure PCTCN2021128858-appb-000006
Figure PCTCN2021128858-appb-000007
其中，d为内导体1的内径，D为内导体1的外径，ε 0为空气的相对有效介电常 数，外径D和ε 0为已知，根据公式(1)确定内径d。特性阻抗是射频传输线影响无线电波电压、电流的幅值和相位变化的固有特性，同轴连接器的特性阻抗和导体内、外直径大小及导体间介质的介电常数有关，同一同轴连接器的特性阻抗是不变的。同轴连接器中最典型的特性阻抗为50Ω和75Ω，一般50Ω是最常用的。本实施例以50Ω为例来说明如何确定绝缘支撑体的内径和外径。同轴连接器的截止频率与内导体的内外径d、D以及介质的相对有效介电常数ε 0相关，截止频率越大，同轴连接器的使用频率范围越广。一般来说，内导体的外径D可以根据同轴连接器的规格来确定，空气的相对有效介电常数ε 0可以近似为1，这样，根据公式(1)就可以计算出内导体的内径d是多少。
S33：同轴连接器在微孔绝缘支撑体处的特性阻抗Z 0和截止频率f c'为：
Figure PCTCN2021128858-appb-000008
Figure PCTCN2021128858-appb-000009
其中，d1为微孔绝缘支撑体3的内径，D1为微孔绝缘支撑体3的外径，ε 1为微孔绝缘支撑体3的相对有效介电常数。
S34：深度h＝(D-d)×K，k为0.15～0.3，外径D1＝D+2h；ε 1为1.5～1.8，根据公式(3)确定内径d1。
可以理解的是，深度h越大，微孔绝缘支撑体的外径D1就越大，同轴连接器在微孔绝缘支撑体处的截止频率f c'就越小，因此，在满足装配的前提下，应该尽可能减小微孔绝缘支撑体嵌入外导体的深度。比较公式(2)和(4)可知，相对有效介电常数与截止频率的大小密切相关，并且绝缘支撑体的相对有效介电常数ε 1大于空气的相对有效介电常数ε 0，因此，同轴连接器的截止频率会受到绝缘支撑体的影响，降低绝缘支撑体的相对有效介电常数ε 1能够提高同轴连接器 的截止频率，同时能够减少绝缘支撑体处的损耗。
设微孔绝缘支撑体处的截止频率f c'对应的波长λ为：
Figure PCTCN2021128858-appb-000010
其中，f c'为微孔绝缘支撑体处的截止频率，c为真空中的光速，ε 1为微孔绝缘支撑体的相对有效介电常数。为了防止同轴连接器出现横电磁模(TE11)，微孔绝缘支撑体的厚度t小于或等于波长λ的四分之一。
S4：将发泡材料加入共混聚合物B中，得到制备微孔绝缘支撑体的原料C。
需要说明的是，发泡材料可以分为两种情况。
例如，当所需的微孔绝缘支撑体的发泡度小于或等于40％时，发泡材料包括聚磷酸铵和成核剂，聚磷酸铵的质量为共混聚合物B质量的0.2％～2％，成核剂的质量为共混聚合物B质量的0.05％～0.8％。
例如，当所需的微孔绝缘支撑体的发泡度高于40％时，发泡材料包括聚磷酸铵、成核剂以及膨胀微球，聚磷酸铵的质量为共混聚合物B质量的0.2％～2％，成核剂的质量为共混聚合物B质量的0.05％～0.8％，膨胀微球的质量为聚磷酸铵质量的30％～50％。
将发泡材料加入共混聚合物B之前，将在聚磷酸铵和成核剂的混合物中加入FEP材料，得到以FEP材料为载体的发泡添加剂母粒，发泡添加剂母粒中的FEP材料的占比为80％～90％，其余为聚磷酸铵和成核剂。发泡添加剂母粒在受热时会分解释放出气体。例如，可以采用双螺杆挤塑机进行造粒。
膨胀微球是一种核壳结构，内部的核为低沸点的烷烃，外部的壳为热塑性聚合物，膨胀微球的直径一般为10～30μm，受热时，内核会先气化，然后外壳会变软，内部的气体使得外壳开始膨胀，当外壳内外的气压达到平衡时，膨胀微球的体积达到最大，膨胀微球的直径变成原来的几倍，冷却后，外壳会再次 变硬，膨胀微球的体积固定。本发明选用的膨胀微球为西能化工科技有限公司的高温膨胀微球，其最高发泡温度可以达280℃。
需要说明的是，共混聚合物B中三种材料的熔点均较高，但是大多数商业化的化学发泡剂还未达到共混聚合物B的加工温度就会分解殆尽，无法达到发泡效果。例如，以通信线缆行业首选的化学发泡剂偶氮二甲酰胺(AZ)为例，其在120℃以上即开始分解，在空气中的分解温度为195℃。因此，若先将AZ与共混聚合物B配混造粒，AZ在造粒工序中就已经分解释放出气体，得到的粒料在用于下一步挤塑加工微孔绝缘支撑体时已丧失发泡性；若在挤塑微孔绝缘支撑体时才将AZ母粒加入挤塑机，那么AZ开始分解时共混聚合物B才开始熔化，AZ释放的气体会从挤塑机加料口逃逸，得到的绝缘支撑体发泡度将很低。因此，需要找到高温下才分解释放出气体的发泡剂来实现本实施例的绝缘支撑体的发泡。本实施例选用聚磷酸铵作为化学发泡剂，聚磷酸铵在340℃左右会开始释放氨气，该温度高于共混聚合物B正常的加工温度，可以作为吸热型化学发泡剂使用。但是，如果化学发泡剂加入比例过高，高温分解后的残余物将会增多，从而影响绝缘支撑体的介电性能，造成同轴连接器插入损耗增加。本发明提出的聚磷酸铵添加比例，可以同时兼顾发泡度和绝缘支撑体最终信号连接的插损性能，如果想继续提高发泡度，则通过加入膨胀微球(物理发泡)来实现。
需要说明的是，为了配合化学发泡剂发泡，可以加入成核剂。成核剂可以是无机成核剂或者有机成核剂，无机成核剂例如是氮化硼、四硼酸钙、二氧化硅粉末等等，其中，二氧化硅粉末还可以吸收部分的化学发泡剂分解后留下的残渣。有机成核剂例如可以是不熔融的聚四氟乙烯(PFFE)粉末、超微细聚四氟乙烯(PTFE)粉末等等。在本实施例中，优选采用复合成核剂，将无机成核 剂和有机成核剂进行混合使用，可以降低共混聚合物B的介质损耗。复合成核剂以PTFE粉末为主，无机成核剂和PTFE粉末的质量之比为1：2～1：3。复合成核剂的粒径中间值控制在5μm～25μm之间，优选为小于10μm。
无机成核剂在高温下可以保持稳定，不会分解，且成本较低，但对同轴连接器插入损耗又有负影响。PTFE作为成核剂，其成本较高，但其介质损耗低，不会影响同轴连接器的传输性能。因此，本实施例将无机成核剂和PTFE结合作为复合成核剂，且无机成核剂和PTFE粉末的质量之比为1：2～1：3，能够均衡成核剂的成本和性能。成核剂的粒径越大，得到的微孔越粗糙，而粒径降低则会导致成核剂表面积降低，成核剂表面吸附、生长的气泡减少，进而影响发泡度。如果粒径过小，则成核剂的制造成本会急剧增加。例如，要得到细腻的无机成核剂，需要进行多次研磨。此外，粒径过小还会造成在后续与共混聚合物B的配混过程中，成核剂发生“团聚”的几率增加，表现出的粒径反而会增大。成核剂的加入比例与发泡度有关，本实施例中，加入的成核剂的质量为共混聚合物B质量的0.05％～0.8％。每个微孔可简单视为围绕一个成核剂颗粒而生长的，发泡度越高，说明熔体中的气体较多，为了得到细腻的微孔，生长的微孔数量需要增加，因此需要提高成核剂加入比例，但是成核剂过多则会造成绝缘支撑体的材料成本增加以及插入损耗等性能的降低。
S5：采用挤塑机将原料C挤出成型得到微孔管材，微孔管材的内径与绝缘支撑体的内径d1一致，微孔管材的外径与绝缘支撑体的外径D1一致。
需要说明的是，如图5所示，采用挤塑机将原料C挤出成型得到微孔管材具体步骤如下：
S51：加料段：将原料C送入挤塑机的机膛内，挤塑机内的旋转螺杆将原料C在机膛内向前推进，将加料段的后段温度设置为200℃～270℃。在加料段时， 原料C还未熔化和分解。
S52：熔化段：熔化段的温度为300℃～365℃，原料C进入熔化段后会被熔化，此时，共混聚合物B熔化成熔体，发泡添加剂母粒分解成气体并溶解在熔体中。熔化段的温度优选为340℃以上，使得共混聚合物B能够充分熔化，同时，发泡添加剂母粒也能够分解产生气体，气体可以溶解在熔体中形成气泡。如果发泡材料中还添加有膨胀微球，此时，膨胀微球也会开始膨胀。在熔化段中，虽然发泡添加剂母粒已经分解成气体，但是由于机膛的空间限制，对气泡有一定的制约，所以在机膛内，熔体并不会进行发泡。
S53：计量段：计量段的温度为375℃～390℃，步骤S52中的含有气体的熔体进入计量段后，由于计量段的体积是固定的，旋转螺杆可以将固定体积的含有气体的熔体推入挤塑机机头。计量段的作用是为了控制旋转螺杆每一次推的量，在计量段，熔体也不会进行发泡。
S54：机头的温度为385℃～390℃，含有气体的熔体被推出机头的模具口后，会立即膨胀发泡，得到微孔管材，再将微孔管材进行冷却降温定型。
步骤S53中的熔体被推进机头的模具中，进而再被推出模具口外，当熔体被推出模具口外时，由于外界的气压突然变小，熔体在出模具口的瞬间会进行发泡形成微孔结构。但是，由于本实施例采用的是挤管式模具，靠近机头的部分的压力会减小，熔体在经过此处时，有可能会提前发泡，导致最终发泡效果不理想。因此，本实施例在挤塑机机膛与挤塑机机头之间设有齿轮泵，齿轮泵能够增大机头内部的压力，防止熔体提前发泡。
在本实施例中，可以根据PFA/FEP/MFA的共混聚合物B的高温熔融特性和挤塑加工的基本原理来设定挤塑温度。挤塑温度既要满足共混聚合物B能够充分熔融，又要尽可能让化学发泡剂在机膛中段塑料熔化段才分解并溶解在熔体 中。因此，本实施例将挤塑机加料段、熔化段和计量段的温度设置成逐渐提高，分别设置为200℃～270℃、300℃～365℃和385℃～395℃。机头温度与计量段持平或略有降低，例如设置为375～390℃，这样能够同时兼顾挤塑加工效率(即减少共混物在挤塑机膛内的停留时间)和共混物熔化质量。挤塑机螺杆长径比应不低于25D(D为螺杆直径)，以30D较为适宜。
S6：将微孔管材切按照厚度t切割成若干个微孔绝缘支撑体。
本实施例可以采用机械切割的方式将微孔管材切割成若干个厚度为t的微孔绝缘支撑体。为了便于安装，可以将微孔绝缘支撑体沿直径剖分为两部分，方便安装到内导体和外导体内。
综上所述，本发明的同轴连接器的绝缘支撑体的制造方法，通过采用PFA/FEP/MFA的共混聚合物B作为制备材料，不仅能够降低制造成本，而且能够提高绝缘支撑体的发泡效果，提高工作效率。本发明制备得到的具有微孔结构的绝缘支撑体具有较低的有效介电常数，能够提高同轴连接器的截止频率。单独采用本发明的化学发泡法并配合发泡挤塑工艺，得到的绝缘支撑体内的微孔平均直径为34μm，绝缘支撑体的发泡度为42％。当采用本发明的化学发泡和加入热膨胀微球的方法，并配合上述发泡挤塑工艺，最终得到平均直径为27μm的微孔和69％的发泡度。泡孔平均直径减小，表明热膨胀微球可带来较化学发泡方法更小的泡孔。成品表面光滑细腻，表明发泡质量良好，没有出现泡孔塌陷等情况。
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. 一种同轴连接器的绝缘支撑体的制造方法，其特征在于，所述绝缘支撑体具有微孔结构，且所述绝缘支撑体的截面为环形，所述制造方法包括以下步骤：
    S1：将PFA材料与FEP材料进行混合得到共混聚合物A；
    S2：将MFA材料加入到所述共混聚合物A中，得到共混聚合物B；
    S3：确定绝缘支撑体的内径d1和外径D1；
    S4：将发泡材料加入所述共混聚合物B中，得到制备微孔绝缘支撑体的原料C；
    S5：采用挤塑机将原料C挤出成型得到微孔管材，所述微孔管材的内径与绝缘支撑体的内径d1一致，微孔管材的外径与绝缘支撑体的外径D1一致；
    S6：将所述微孔管材切按照厚度t切割成若干个微孔绝缘支撑体。
  2. 如权利要求1所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，在步骤S1中，PFA材料与FEP材料进行混合的比例为2：1～4：1。
  3. 如权利要求1所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，在步骤S2中，加入的MFA材料的质量为所述共混聚合物A质量的2％～5％。
  4. 如权利要求1所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，当所需的微孔绝缘支撑体的发泡度小于或等于40％时，所述发泡材料包括聚磷酸铵和成核剂，聚磷酸铵的质量为所述共混聚合物B质量的0.2％～2％，成核剂的质量为所述共混聚合物B质量的0.05％～0.8％。
  5. 如权利要求1所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，当所需的微孔绝缘支撑体的发泡度高于40％时，所述发泡材料包括聚磷酸铵、成核剂以及膨胀微球，聚磷酸铵的质量为所述共混聚合物B质量的0.2％～2％，成核剂的质量为所述共混聚合物B质量的0.05％～0.8％，膨胀微球的质量为所述聚磷 酸铵质量的30％～50％。
  6. 如权利要求4或5所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，所述方法还包括：
    将所述发泡材料加入所述共混聚合物B之前，将在聚磷酸铵和成核剂的混合物中加入FEP材料，得到以FEP材料为载体的发泡添加剂母粒，所述发泡添加剂母粒中的FEP材料的占比为80％～90％，其余为聚磷酸铵和成核剂。
  7. 如权利要求1所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，步骤S3中确定微孔绝缘支撑体的内径d1和外径D1具体包括：
    S31：同轴连接器包括内导体和外导体，所述外导体包覆在所述内导体外侧，所述微孔绝缘支撑体嵌设在所述内导体和外导体内，所述内导体的内径为d，内导体的外径为D，外径D1大于外径D，使得微孔绝缘支撑体的一部分嵌入所述外导体内，所述微孔绝缘支撑体嵌入所述外导体的深度为h；
    S32：假设同轴连接器内的绝缘介质为空气，则同轴连接器截面的特性阻抗Z 0和截止频率f c为：
    Figure PCTCN2021128858-appb-100001
    Figure PCTCN2021128858-appb-100002
    其中，d为内导体的内径，D为内导体的外径，ε 0为空气的相对有效介电常数，外径D和ε 0为已知，根据公式(1)确定内径d；
    S33：所述同轴连接器在微孔绝缘支撑体处的特性阻抗Z 0和截止频率f c'为：
    Figure PCTCN2021128858-appb-100003
    Figure PCTCN2021128858-appb-100004
    其中，d1为微孔绝缘支撑体的内径，D1为微孔绝缘支撑体的外径，ε 1为微孔绝缘支撑体的相对有效介电常数；
    S34：深度h＝(D-d)×K，k为0.15～0.3，所述外径D1＝D+2h；ε 1为1.5～1.8，根据公式(3)确定内径d1。
  8. 如权利要求6所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，步骤S5中采用挤塑机将原料C挤出成型得到微孔管材具体包括：
    S51：加料段：将原料C送入挤塑机的机膛内，挤塑机内的旋转螺杆将原料C在机膛内向前推进，将加料段的后段温度设置为200℃～270℃；
    S52：熔化段：熔化段的温度为300℃～365℃，原料C进入熔化段后会被熔化，此时，共混聚合物B熔化成熔体，发泡添加剂母粒分解成气体并溶解在所述熔体中；
    S53：计量段：计量段的温度为375℃～390℃，步骤S52中的含有气体的熔体进入计量段后，由于计量段的体积是固定的，旋转螺杆可以将固定体积的含有气体的熔体推入挤塑机机头；
    S54：机头的温度为385℃～390℃，所述含有气体的熔体被推出机头的模具口后，会立即膨胀发泡，得到微孔管材，再将微孔管材进行冷却降温定型。
  9. 如权利要求8所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，所述挤塑机机膛与挤塑机机头之间设有齿轮泵。
  10. 如权利要求7所述的同轴连接器的绝缘支撑体的制造方法，其特征在于，设所述微孔绝缘支撑体处的截止频率f c'对应的波长λ为：
    Figure PCTCN2021128858-appb-100005
    其中，f c'为微孔绝缘支撑体处的截止频率，c为真空中的光速，ε 1为微孔绝缘支撑体的相对有效介电常数，所述微孔绝缘支撑体的厚度t小于或等于波长λ的 四分之一。
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