JP2010165637A - Method of manufacturing extrafine coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an extrafine coaxial cable capable of forming a shielding layer with a film thickness of ≤10 μm and a low volume resistivity. <P>SOLUTION: In the method of manufacturing the extrafine coaxial cable provided with an insulation coating layer 23, a shielding layer 24, and a jacket layer 25 around a center conductor 22, with the shielding layer 24 made of a sintered body of metal fine particles obtained by coating and baking metal fine particle dispersion paste on the insulation coating layer 23, metal fine particle dispersion paste is used capable of forming metal coating with a volume resistivity of ≤5μΩ cm after heating for ≥30 minutes at a baking temperature of ≤240°C, the paste is die-coated on the insulation coating layer 23, and then, is heated and baked in a tubular baking furnace 4 to form a shielding layer 24. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a micro coaxial cable in which a shield layer is formed by coating and firing a metal fine particle dispersed paste.

  In recent years, ultrafine coaxial cables have been widely used for medical devices and mobile phones. As shown in FIG. 3, a conventional micro coaxial cable 30 includes an insulating coating layer 32 formed by extruding a fluororesin, a shield layer 33 formed by lateral winding of a fine metal wire, a fluororesin on the outer periphery of a central conductor 31 formed by twisting metal wires. A jacket layer 34 is formed by extrusion.

  As an example of the use of the ultrafine coaxial cable 30, a probe for medical equipment can be cited. The probe for medical equipment has a structure in which several hundreds of micro coaxial cables 30 are bundled, and next-generation products are required to improve high-frequency transmission characteristics while maintaining the same probe outer diameter. . Although this requirement can be satisfied by increasing the density of the core wire (extra-coaxial cable 30), it is essential to reduce the diameter of the ultra-coaxial cable 30 and, in particular, to reduce the thickness of the shield layer 33.

  However, in the conventional micro coaxial cable 30, the shield layer 33 is formed by horizontally winding a thin metal wire, so that the thickness of the shield layer 33 is 10 μm or more even in the thinnest product. Thinning was difficult. In addition, as the diameter of the fine metal wire used for the shield layer 33 becomes thinner, the trouble in the horizontal winding operation increases, so that the production speed becomes slow and the production at low cost is difficult.

  Therefore, Patent Document 1 proposes a method for manufacturing an ultrafine coaxial cable in which a shield layer made of a sintered body of metal fine particles and having a layer thickness of less than 10 μm is formed on the surface of an insulating coating layer made of a fluororesin.

  Specifically, the metal fine particle dispersion paste is applied to the insulating coating layer through a mist of metal fine particle dispersion paste or a paste bath, and the sintering treatment is performed at a low temperature of 170 to 230 ° C., more preferably 170 to 200 ° C. By doing so, a shield layer is formed. Thus, by forming the shield layer with a sintered body of metal fine particles, the shield layer can be thinned, the diameter of the ultrafine coaxial cable can be reduced, and the manufacturing cost can be reduced.

  In Patent Document 1, a metal fine particle mixed paste of metal nanoparticles (for example, an average particle size of 5 nm) and metal powder (for example, an average particle size of 5 μm) is examined as a metal fine particle dispersed paste, and the formed shield layer The metal nanoparticle group sintered body is disposed at a position where the gap between the metal powder group sintered body is filled. In addition, any metal fine particle-dispersed paste that can be sintered at low temperature, such as a paste in which only metal nanoparticles are dispersed, can be applied.

JP 2006-294528 A

  By the way, when the temperature at the time of baking the metal fine particle dispersed paste is increased, as shown in FIG. 4, the fluorine-based resin of the insulating coating layer 41 is thermally expanded at the time of sintering, and the shield layer 42 is cleaved. There is a fear. Therefore, in patent document 1, the deformation | transformation of the fluororesin of the insulating coating layer 41 at the time of baking is suppressed by setting baking temperature (sintering process temperature) as very low as 170-230 degreeC.

  However, in the above-described conventional method, since the firing temperature is set very low, it is necessary to use a metal fine particle dispersion paste capable of forming a shield layer having a film thickness of several μm to 10 μm at a low temperature. In order to produce such a metal fine particle-dispersed paste, an advanced production process is required for the surface treatment of the metal fine particles, and the produced metal fine particles are likely to aggregate. Problems arise.

  In addition, since a normal metal fine particle dispersion paste is used for forming a wiring on an insulating substrate, the firing time is assumed to be 30 to 60 minutes. However, in the production of a micro coaxial cable, the production speed is increased. Therefore, sintering by heating for a short time of 1 minute or less is required. Therefore, it is necessary to use the metal fine particle dispersion paste suitable for forming the shield layer of the micro coaxial cable, after clarifying the characteristics that the metal fine particle dispersion paste that can be sintered in such a short time should have.

  Furthermore, the electrical resistance of the shield layer is desired to be as low as possible in order to improve the shielding characteristics of the micro coaxial cable, and a micro coaxial cable having a shield layer with a low volume resistivity is required.

  Accordingly, an object of the present invention is to provide a method for manufacturing an ultrafine coaxial cable capable of forming a shield layer having a film thickness of 10 μm or less and a low volume resistivity without deformation of an insulating coating layer made of a fluororesin. is there.

  The present invention was devised to achieve the above object, and has an insulating coating layer, a shielding layer, and a jacket layer around a central conductor, and the shielding layer covers the insulating coating layer with a metal fine particle dispersion paste. In the method for producing an ultrafine coaxial cable composed of sintered metal fine particles obtained by firing, the metal fine particle dispersion paste has a volume resistivity of 5 μΩ · cm when heated at a firing temperature of 240 ° C. or lower for 30 minutes or more. A method for producing an ultrafine coaxial cable using the following metal coating capable of forming a metal coating, and applying the metal fine particle dispersed paste to the insulating coating layer by a die, followed by heating and firing in a tubular firing furnace to form the shield layer It is.

  The insulating coating layer may be made of a fluorine-based resin, and the metal fine particle-dispersed paste applied to the insulating coating layer may be fired at a temperature lower by 20 ° C. or more than the melting point of the fluorine-based resin.

  The insulating coating layer is made of a fluororesin, and the metal fine particle dispersed paste applied to the insulating coating layer is fired at a temperature lower than the melting point of the fluororesin by 15 ° C. or more and less than 20 ° C., and the firing time. May be 60 seconds or less.

  The insulating coating layer is made of a fluorine-based resin, and the metal fine particle-dispersed paste applied to the insulating coating layer is fired at a temperature lower than the melting point of the fluorine-based resin by less than 15 ° C., and the firing time is 30 seconds. It is good also as follows.

  The insulating coating layer may be made of a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA).

  According to the present invention, a shield layer having a film thickness of 10 μm or less and a low volume resistivity can be formed without deformation of the insulating coating layer made of a fluororesin.

It is the schematic of the shield layer forming apparatus used for the manufacturing method of the micro coaxial cable of this invention. It is a cross-sectional view of the micro coaxial cable produced with the manufacturing method of the micro coaxial cable of this invention. It is a cross-sectional view of a conventional micro coaxial cable. It is a shield layer covering line transverse cross section when an insulating coating layer deform | transforms and it cleaves a shield layer.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  First, the ultra-fine coaxial cable manufactured by the manufacturing method of the ultra-fine coaxial cable according to the present embodiment will be described.

  As shown in FIG. 2, the micro coaxial cable 20 is formed by sequentially forming an insulating coating layer 23, a shield layer 24, and a jacket layer 25 on the outer periphery of the center conductor 22.

  The center conductor 22 is formed by twisting a plurality of fine metal wires 21 together. In the present embodiment, as the central conductor 22, one obtained by twisting seven metal thin wires 21 made of Ag-plated copper having an outer diameter of φ16 μm is used.

  The insulating coating layer 23 is formed by extruding a fluororesin on the outer periphery of the center conductor 22. In the present embodiment, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) is used as the fluorine-based resin used for the insulating coating layer 23. Hereinafter, the central conductor 22 and the insulation coating layer 23 are collectively referred to as an insulation coating wire 26. In the present embodiment, the outer diameter of the insulation-coated wire 26 is about 120 μm.

  The shield layer 24 is made of a sintered body of metal fine particles, and is formed by coating and baking the metal fine particle dispersed paste on the surface of the insulating coated wire 26. The thickness of the shield layer 24 is 10 μm or less, for example, 7 μm. Hereinafter, the insulating covered wire 26 on which the shield layer 24 is formed is referred to as a shield layer covered wire 27.

  The jacket layer 25 is formed by extruding a fluororesin on the outer periphery of the shield layer 24. The jacket layer 25 is made of, for example, PFA.

  Next, the shield layer forming apparatus used for the manufacturing method of the micro coaxial cable according to the present embodiment will be described.

  As shown in FIG. 1, the shield layer forming apparatus 1 includes a feeder 2 that sends out an insulation-coated wire 26 in which an insulation coating layer 23 is formed on the outer periphery of a center conductor 22, and a metal is applied to the insulation-coated wire 26 from the transmitter 2. Tubular firing that forms a shield layer 24 by forming a shield layer 24 by firing a die (metal particulate coating die) 3 for coating and coating a fine particle dispersion paste and a metal fine particle dispersion paste coated on an insulating coating wire 26 A furnace 4 and a winder 5 that winds up the shield layer coated wire 27 are provided.

  The dice 3 are filled with a metal fine particle dispersed paste and connected to a supply means (not shown) for supplying the metal fine particle dispersed paste. The inner diameter of the nozzle of the die 3 was about 200 μm.

  As the tubular firing furnace 4, a furnace having a plurality of heaters 7 in the longitudinal direction and capable of individually setting the temperature for each predetermined distance is used. In this embodiment, as the tubular firing furnace 4, the temperature at a length of 9 m can be set every 1 m, and the temperature at a position 1 cm away from the central axis of the tubular firing furnace 4 is 0.5 m to 8. A device equipped with a temperature measuring means (not shown) capable of measuring 9 locations per 1 m up to 5 m was used.

  A heat insulating plate 6 is provided between the die 3 and the tubular firing furnace 4. In the present embodiment, the distance between the die 3 and the tubular firing furnace 4 is 20 cm.

  Next, the manufacturing method of the micro coaxial cable which concerns on this embodiment is demonstrated.

  In the manufacturing method of the micro coaxial cable according to the present embodiment, first, an insulation-coated wire 26 is produced by extrusion coating a fluororesin (PFA) on the outer periphery of the center conductor 22, and this is set in the transmitter 2. .

  The insulation coated wire 26 is delivered from the delivery device 2, and the metal fine particle dispersion paste is applied to the outer periphery of the insulation coating layer 23 of the insulation coated wire 26 through the die 3.

  As the metal fine particle dispersion paste, a paste capable of forming a metal coating having a volume resistivity of 5 μΩ · cm or less when heated at a firing temperature of 240 ° C. or less for 30 minutes or more is used. In the present embodiment, a metal fine particle-dispersed paste that is applied to a glass substrate and heated at a firing temperature of 240 ° C. for 30 minutes and has a volume resistivity of 5 μΩ · cm or less in a 7 μm thick metal coating is used. As the metal fine particles, Ag nanoparticles having an average particle diameter of 5 nm were used, and diluted with 1-decanol to adjust the paste viscosity to 1 Pa · s.

  Thereafter, the insulation-coated wire 26 coated with the metal fine particle dispersion paste is introduced into the tubular firing furnace 4 and heated and fired in the tubular firing furnace 4. Thereby, the metal fine particles contained in the metal fine particle dispersed paste are sintered to form the shield layer 24.

  In the present embodiment, 1 m from the inlet side of the 9 m tubular firing furnace 4 is set to 200 ° C., and thereafter the temperature is increased stepwise up to 4 m, and 5 m on the outlet side is set as the maximum temperature region where the temperature is constant. The temperature in the maximum temperature region on the outlet side 5 m is referred to as a firing temperature, and the time for passing through this region is referred to as a firing time.

  As an example, when the firing temperature is 290 ° C. and the firing time is 15 seconds (line speed 20 m / min), the thickness of the shield layer 24 made of Ag is about 7 μm and the volume resistivity is 3.5 μΩ · cm.

  After carrying out the firing treatment in the tubular firing furnace 4, this is wound up on a winder 5. Thereafter, when the jacket layer 25 is formed by extrusion coating a fluorine-based resin such as PFA on the outer periphery of the shield layer 24, the micro coaxial cable 20 shown in FIG. 2 is obtained.

  Here, the firing conditions and the characteristics of the metal fine particle dispersed paste are examined.

  As a metal fine particle dispersion paste, three types of Ag nanoparticle dispersion pastes A to C having different sintering temperatures shown in Table 1 were used for trial production of a shield layer, deformation of the insulating coating layer 23 made of PFA, and shield layer 24 The electrical resistance of was evaluated.

  The deformation of the insulating coating layer 23 made of PFA occurs when the firing temperature of the metal fine particle-dispersed paste is near the melting point of 310 ° C. of PFA, and the mechanical strength and insulation characteristics of the micro coaxial cable 20 are reduced. In addition, it is desirable that the electrical resistance of the shield layer 24 be as low as possible in order to improve the shield characteristics of the micro coaxial cable 20. Here, the firing conditions under which the volume resistivity of the shield layer 24 made of Ag is less than 5 μΩ · cm were examined.

  As shown in Table 1, paste A uses decane as a dispersion solvent. When applied to a glass substrate and heated at a firing temperature of 200 ° C. for 30 minutes, the volume resistivity of the 7 μm thick Ag coating is 4. 4 μΩ · cm. On the other hand, paste B uses 1-decanol as a dispersion solvent, and when heated at 240 ° C. for 30 minutes, the volume resistivity of the 7 μm thick Ag coating becomes 4.2 μΩ · cm. Paste C uses 1-decanol as a dispersion solvent, but the desorption / decomposition temperature of the dispersant from the Ag nanoparticles is higher than that of paste B, and the film thickness is increased by heating at 260 ° C. for 30 minutes. The volume resistivity of the 7 μm Ag coating is 4.8 μΩ · cm.

  Using the above pastes A to C, the firing temperature was changed from 230 ° C. to 320 ° C., and the firing time was changed in the range of 75 seconds to 4.3 seconds (line speed 4 m / min to 70 m / min). Each went. The length of the tubular firing furnace 4 was 9 m, the first 4 m was set at a preset temperature of 250 ° C., and the final 5 m was constant at the set firing temperature. The deformation of the insulation coating layer 23 is evaluated by observing the cross section of the shield layer coating wire 27 (the presence or absence of deformation of the insulation coating layer 23), and the electrical resistance of the shield layer 24 is evaluated by measuring the volume resistivity of the shield layer 24. Was done.

  The experimental results when using paste A are shown in Table 2, the experimental results when using paste B are shown in Table 3, and the experimental results when using paste C are shown in Table 4, respectively.

  As shown in Tables 2 to 4, in any of the pastes A to C, the insulating coating layer 23 made of PFA was not deformed if the firing temperature was 290 ° C. or lower. However, deformation of the insulating coating layer 23 and cleavage of the shield layer 24 were confirmed when heated at 295 ° C. for 75 seconds, at 300 ° C. for 30 seconds or longer, and at 310 ° C. for 15 seconds or longer (see FIG. 4).

  This is presumably because PFA heated at high temperature was softened and expanded. Although the softening / expansion occurs even at a firing temperature of 290 ° C., the softening / expansion of PFA is small at this temperature, and since the Ag nanoparticle-dispersed paste has been sintered and hardened, the insulating coating layer 23 made of PFA It is thought that the deformation of was able to be suppressed.

  From the above results, it is desirable that the firing temperature of the metal fine particle dispersed paste be 20 ° C. lower than the melting point of PFA in order to prevent deformation of the insulating coating layer 23 in forming the shield layer 24 on the insulating coating wire 26. When the difference between the melting point of PFA and the firing temperature is 15 ° C. or more and less than 20 ° C., the firing time is 60 seconds or less. When the difference between the melting point of PFA and the firing temperature is less than 15 ° C., the firing time is 30 seconds or less. It is necessary to limit to.

  On the other hand, it is known that the volume resistivity of the shield layer 24 increases when the shield layer 24 is unsintered. Therefore, the volume resistivity of the shield layer 24 of the produced shield layer-covered wire 27 is measured, and if the volume resistivity is 5 μΩ · cm or less, it is judged that it is sufficiently sintered, and “ When the rate exceeded 5 μΩ · cm, it was determined as “unsintered”.

  As shown in Tables 2 to 4, when the firing temperature was low and the firing time was short, the volume resistivity of the shield layer 24 was an unsintered coating exceeding 5 μΩ · cm. Further, from Tables 2 to 4, the lower the firing temperature (sintering temperature) of the metal fine particle-dispersed paste, the lower the temperature resistivity and the sintered shield layer 24 that the volume resistivity becomes 5 μΩ · cm or less can be obtained in a short time. I understand.

  As shown in Tables 2 and 3, in pastes A and B, for example, by setting the firing temperature to 290 ° C. and the firing time to 30 seconds, the insulating coating layer 23 is not deformed, and the sintered shield layer 24 can be formed. However, as shown in Table 4, there is no applicable firing condition for paste C, which has a high desorption / decomposition temperature from the Ag nanoparticles of the dispersant. That is, when the paste C is used, it is either unsintered or the insulating coating layer 23 is deformed even if sintered, and the insulating coating layer 23 is not deformed and sintered. There are no firing conditions that allow the shield layer 24 to be formed.

  For this reason, as the metal fine particle dispersion paste used for forming the shield layer 24 on the insulating coating layer 23 made of PFA, a paste having a volume resistivity of 5 μΩ · cm or less when baked at 240 ° C. or less for 30 minutes is used. This is desirable.

  As described above, in the manufacturing method of the micro coaxial cable according to the present embodiment, when the metal fine particle dispersion paste is heated at a firing temperature of 240 ° C. or less for 30 minutes or more, the metal coating having a volume resistivity of 5 μΩ · cm or less is used. After the metal fine particle dispersion paste is applied to the insulating coating layer 23 by a die, this is heated and fired in the tubular firing furnace 4 to form the shield layer 24.

  As a result, it is possible to form a sintered shield layer 24 having a volume resistivity of 10 μm or less and having a low volume resistivity without deformation of the insulating coating layer 23 made of fluororesin (PFA).

  Further, unlike the conventional method, it is not necessary to perform a special surface treatment or the like on the metal fine particles of the metal fine particle dispersed paste, so that the manufacturing cost can be suppressed.

  In this embodiment, the firing condition of the metal fine particle dispersed paste is set to a firing temperature that is 20 ° C. or more lower than the melting point of the fluororesin, or the firing condition is 15 ° C. or more and less than 20 ° C. lower than the melting point of the fluororesin. The firing time is set to 60 seconds or less at the temperature, or the firing temperature is lower than the melting point of the fluororesin by less than 15 ° C., and the firing time is set to 30 seconds or less.

  Thereby, there is no possibility that the insulating coating layer 23 made of fluororesin (PFA) is thermally expanded and deformed and the shield layer 24 is cleaved.

  In the above-described embodiment, the case of using the horizontal shield layer forming apparatus 1 that forms the shield layer 24 by sending the insulation coated wire 26 in the horizontal direction has been described. However, the vertical type is used to send the insulation coated wire 26 in the vertical direction. A shield layer forming apparatus configured as described above may be used. In the horizontal type, if the line speed is low or the viscosity of the metal fine particle dispersed paste is low, dripping may occur before firing, and the film thickness of the shield layer 24 cross section may become non-uniform. This can improve this problem.

  In the above-described embodiment, the case where the shield layer 24 is formed by one firing has been described. However, the shield layer 24 may be divided into a plurality of times and covered in multiple layers. By reducing the coating thickness per layer, the firing temperature can be lowered and the firing time can be shortened. In the above embodiment, as described above, a metal fine particle dispersion paste that is baked at 240 ° C. or lower for 30 minutes and has a volume resistivity of 5 μΩ · cm or lower can be applied, but the shield layer 24 is divided into multiple layers. By coating, a metal fine particle dispersed paste that is sintered at a temperature exceeding 240 ° C. is also applicable.

  Further, in the above embodiment, Ag nanoparticles are used as the metal fine particles. However, the present invention is not limited to this, and a metal having high conductivity may be used. Metal fine particles made of an alloy including Au, Cu, or Ag are used. It may be used.

  Moreover, although the said embodiment demonstrated the case where the manufacturing line which forms the insulating coating layer 23, the manufacturing line which forms the shield layer 24, and the manufacturing line which forms the jacket layer 25 were each separated, the insulating coating layer 23, The shield layer 24 and the jacket layer 25 may all be manufactured on the same manufacturing line.

DESCRIPTION OF SYMBOLS 1 Shield layer formation apparatus 2 Sending machine 3 Dies 4 Tubular baking furnace 5 Winder 6 Heat insulation board 7 Heater 21 Metal thin wire 22 Central conductor 23 Insulation coating layer 24 Shield layer 25 Jacket layer 26 Insulation coating wire 27 Shield layer coating wire

Claims (5)

An ultrafine coaxial cable comprising an insulating coating layer, a shield layer, and a jacket layer around a central conductor, and the shield layer is made of a sintered body of metal fine particles obtained by coating and baking the metal fine particle dispersed paste on the insulating coating layer. In the manufacturing method of
As the metal fine particle dispersed paste, a paste capable of forming a metal coating having a volume resistivity of 5 μΩ · cm or less when heated at a firing temperature of 240 ° C. or lower for 30 minutes or more is used. A method for producing an ultrafine coaxial cable, comprising: applying a die to a metal, and then heating and firing the resultant in a tubular firing furnace to form the shield layer.   The micro coaxial cable according to claim 1, wherein the insulating coating layer is made of a fluorine-based resin, and the metal fine particle-dispersed paste applied to the insulating coating layer is fired at a temperature lower by 20 ° C or more than the melting point of the fluorine-based resin. Production method.   The insulating coating layer is made of a fluororesin, and the metal fine particle dispersed paste applied to the insulating coating layer is fired at a temperature lower than the melting point of the fluororesin by 15 ° C. or more and less than 20 ° C., and the firing time. The method for producing a micro coaxial cable according to claim 1, wherein the length is 60 seconds or less.   The insulating coating layer is made of a fluorine-based resin, and the metal fine particle-dispersed paste applied to the insulating coating layer is fired at a temperature lower than the melting point of the fluorine-based resin by less than 15 ° C., and the firing time is 30 seconds. The method for producing an ultrafine coaxial cable according to claim 1, wherein:   The method for producing an ultrafine coaxial cable according to any one of claims 1 to 4, wherein the insulating coating layer is made of a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA).

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