JP5239304B2 - Coaxial cable and manufacturing method thereof - Google Patents

Description

  The present invention relates to a coaxial cable used for a transmission path of a high-frequency signal and a method for manufacturing the same, and in particular, an application in which space saving is regarded as important, such as an electronic device such as a mobile phone and a medical device such as an ultrasonic inspection apparatus. The present invention relates to a coaxial cable and a manufacturing method thereof.

  A general coaxial cable 41 shown in FIG. 4 includes an inner conductor 42, an inner insulator 43, an outer conductor 44, and an outer insulator 45. As the internal conductor 42, a metal single wire mainly composed of Cu or a stranded wire obtained by twisting single wires is used. As the internal insulator 43, a fluororesin having a low relative dielectric constant is generally used for the purpose of reducing a loss in transmission of a high-frequency signal. As the outer conductor 44, a structure in which a plurality of single wires are horizontally wound around the inner insulator 43 is widely used. Although various materials are used for the external insulator 45 depending on the application, a fluororesin excellent in insulation and heat resistance is often used.

  In recent years, electronic devices and medical devices have been reduced in size, weight, and functionality, and the coaxial cables used for them have been strongly demanded to have a smaller diameter. Therefore, technological development for reducing the diameter of each component of the coaxial cable has been advanced. For example, as for the outer conductor 44, a thin copper wire having a diameter of about 13 μm is mass-produced as a single wire used for horizontal winding.

  On the other hand, in terms of high-frequency signal transmission, it is possible to reduce the thickness of the outer conductor to several μm. Therefore, a technique for configuring the outer conductor with a thin metal layer has been studied and has already been published.

  For example, Patent Document 1 proposes a technique in which a metal thin film is formed around an internal insulator by a sputtering method and a metal layer is formed thereon by an electroplating method.

  Moreover, in patent document 2, after roughening the surface of an internal insulator with a metal sodium-naphthalene complex solution etc., a metal-plating catalyst is provided and the metal layer is formed by the electroless plating method and the electroplating method. Has been proposed.

  Furthermore, Patent Document 3 proposes a technique for forming an external conductor by attaching a paste containing metal nanoparticles and metal powder to the surface of a roughened internal insulator and firing at a temperature of 170 to 230 ° C. ing.

JP-A-5-342930 JP-A-6-187547 JP 2006-294528 A

  However, coaxial cables used in electronic devices and medical devices are required to have a long bending life in addition to a reduction in diameter.

  For example, in mobile phones, a folding type in which a display unit and an operation unit are separated has already become mainstream, and recently, a mobile phone that can rotate a display unit has become widespread. In particular, a thin coaxial cable is frequently used for the signal transmission path of the latter display unit and operation unit. Further, in a medical ultrasonic inspection apparatus, a coaxial cable is used as a probe cable connecting the sensor unit and the main body, and the bending operation of the probe cable is frequently repeated during the actual inspection.

  Therefore, it is very important that the coaxial cable used for the mobile phone or the ultrasonic inspection apparatus has a long bending life. Furthermore, with the widespread use of each device, there is a strong demand for lowering the cost of coaxial cables.

  When using a dry film-forming method such as sputtering as a method of forming the outer conductor, a large vacuum device is required, which increases the cost of the manufacturing equipment, and when forming a metal layer on the surface of a thin cable There is a problem that the manufacturing cost of the coaxial cable becomes extremely high due to the extremely low utilization efficiency of the raw materials.

  In the conventional technology for forming an outer conductor by a combination of electroless plating and electroplating, and the technology for forming an outer conductor using a paste containing metal nanoparticles and metal powder, the flex life of the produced coaxial cable is limited. There is a problem that it is extremely short compared to the coaxial cable 41 of the laterally wound outer conductor type of FIG.

  The bending life described here is not the life until the center conductor or the insulator breaks but the life until the outer conductor is cracked or broken.

  The first reason for the short flex life is low adhesion strength between the outer conductor and the inner insulator. In a coaxial cable having low adhesion strength between the outer conductor and the inner insulator, when the bending operation is repeated, the outer conductor partially peels from the inner insulator. If the bending operation is further repeated in this state, the peeled outer conductor is cracked or broken. A coaxial cable with an outer conductor cracked or broken significantly increases the transmission loss of high-frequency signals.

  Due to such a problem of the prior art, it has been difficult to apply a coaxial cable having an outer conductor made of a metal layer to an application requiring a bending life.

  Accordingly, an object of the present invention is to provide a highly reliable small-diameter coaxial cable having a long bending life at a low cost.

  Another object of the present invention is to make it possible to apply a coaxial cable having an outer conductor made of a metal layer to an electronic device such as a mobile phone or a medical device such as an ultrasonic inspection device, thereby reducing the size of the device. , Contributing to weight reduction and higher functionality.

The present invention has been devised to achieve the above object, and the invention of claim 1 includes a central conductor, an internal insulator made of a fluororesin formed on the outer periphery of the central conductor, and the periphery of the internal insulator. A coaxial cable having an outer conductor formed on the outer conductor and an outer insulator formed around the outer conductor;
Said outer conductor, see containing the metal nano-particle layer formed by fusing the following metal nano particles having an average particle size of 100nm from each other, the metal nanoparticle layer opening area from the surface toward the inside the inner surface thereof The coaxial cable has a concavo-convex structure with an average roughness of 1 μm or less including an increasing basal-shaped concave portion, and the resin of the internal insulator enters the concave portion of the concavo-convex structure .

The invention according to claim 2, wherein the metal nanoparticle is comprised of Ag nanoparticles and Cu nanoparticles, the was C u or the metal nanoparticle layer is in the range weight ratio of Ag is 0.1-10% claims The coaxial cable according to Item 1.

  A third aspect of the present invention is the coaxial cable according to the first or second aspect, wherein the metal nanoparticle layer has a thickness of 0.1 to 10 μm.

The invention of claim 4, wherein the outer conductor is a coaxial cable according to any one of claims 1 to 3 comprising electroplated Cu layer made form around the metallic nanoparticle layer.

The invention of claim 5, wherein the outer conductor, electroless plating Cu layer formed around the metal nanoparticle layer comprises an electroplated Cu layer made form around it, the metal nanoparticle layer consists Ag nanoparticles and Pd nanoparticles, the weight ratio of Pd in the metal nanoparticle layer are coaxial cable of claim 1, wherein in the range of 0.01 to 2%.

  A sixth aspect of the present invention is the coaxial cable according to the fifth aspect, wherein the metal nanoparticle layer has a thickness of 0.01 to 0.1 μm.

The invention of claim 7 includes a center conductor, an inner insulator made of PFA formed on the outer periphery of the center conductor, an outer conductor formed around the inner insulator, and an outer insulation formed around the outer conductor. In the method of manufacturing a coaxial cable having a body, a step for forming an outer conductor is to deposit a liquid material in which metal nanoparticles having an average particle size of 100 nm or less are dispersed in a dispersion liquid around the inner insulator. a step, in the liquid substance or 200 ° C. the deposition is cable, to form a metal nanoparticle layer by fusing the metal nanoparticles to each other 5 ° C. by heating at a lower temperature than the melting point of the PFA A first heating step, and a second heating step in which the metal nanoparticle layer is preferentially heated by induction heating in a range of 295 to 330 ° C. to allow the PFA to enter the recesses on the inner surface of the metal nanoparticle layer. Include It is a manufacturing method of a coaxial cable.

The invention according to claim 8 is a center conductor, an inner insulator made of PTFE formed on the outer periphery of the center conductor, an outer conductor formed around the inner insulator, and an outer insulation formed around the outer conductor. In the method of manufacturing a coaxial cable having a body, a step for forming an outer conductor is to deposit a liquid material in which metal nanoparticles having an average particle size of 100 nm or less are dispersed in a dispersion liquid around the inner insulator. a step, in the liquid substance or 200 ° C. the deposition is cable, the 5 ° C. than the melting point of PTFE is heated at a lower temperature to fuse the metal nanoparticles to each other to form a metal nanoparticle layer A first heating step, and a second heating step of preferentially heating the metal nanoparticle layer in a range of 320 to 349 ° C. by induction heating to allow the PTFE to enter the recesses on the inner surface of the metal nanoparticle layer; The manufacturing method of the coaxial cable containing this.

The invention according to claim 9 is a center conductor, an inner insulator made of ETFE formed on the outer periphery of the center conductor, an outer conductor formed around the inner insulator, and an outer insulation formed around the outer conductor. In the method of manufacturing a coaxial cable having a body, a step for forming an outer conductor is to deposit a liquid material in which metal nanoparticles having an average particle size of 100 nm or less are dispersed in a dispersion liquid around the inner insulator. a step, in the liquid substance or 200 ° C. the deposition is cable, to form a metal nanoparticle layer by fusing the metal nanoparticles to each other 5 ° C. by heating at a lower temperature than the melting point of the ETFE A first heating step, and a second heating step in which the metal nanoparticle layer is preferentially heated by induction heating in the range of 261 to 297 ° C. to allow the ETFE to enter the recesses on the inner surface of the metal nanoparticle layer; The manufacturing method of the coaxial cable containing this. In a tenth aspect of the present invention, the step for forming the outer conductor includes a step of applying at least one of an electroplated Cu layer and an electroless plated Cu layer around the metal nanoparticle layer. It is a manufacturing method of the coaxial cable in any one.

  According to the present invention, by optimizing the structure of the metal layer of the outer conductor and the method of forming the metal layer, it is possible to reduce the diameter of the coaxial cable and greatly improve the bending life.

  The present inventor mainly uses coaxial cables mainly used in electronic devices and medical devices, particularly when the outer conductor is composed of a metal layer, in order to achieve both a reduction in diameter and a longer bending life. The structure of the metal layer of the conductor and the formation method thereof were studied, and as a result of intensive studies, the present invention with an improved bending life of the coaxial cable was completed by optimizing these.

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

  FIG. 1 is a cross-sectional view showing an outline of the structure of a coaxial cable showing a preferred first embodiment of the present invention.

  As shown in FIG. 1, the coaxial cable 1 according to the first embodiment includes a central conductor 2, an internal insulator 3 made of a fluororesin formed on the outer periphery of the central conductor 2, and an internal insulator 3. The outer conductor 4 is formed around the outer conductor 4 and the outer insulator 5 is formed around the outer conductor 4.

  The center conductor 2 has a structure in which a plurality of single wires are twisted together. In the first embodiment, a single wire made of an alloy of Cu and Ag is used, and the number of single wires of the stranded wire is 7.

  As a material of the internal insulator 3, PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) is suitable from the viewpoint of uniformity of coating thickness when formed by an extrusion method, but is not limited thereto. In addition, fluorine resins such as PTFA (polytetrafluoroethylene) and ETFE (tetrafluoroethylene / ethylene copolymer) can also be applied.

  The outer conductor 4 includes an inner metal nanoparticle layer 4n and an electroplated metal layer 4p formed on the outer side by electroplating. The metal nanoparticle layer 4n is formed by fusing metal nanoparticles such as Ag nanoparticles and Cu nanoparticles having an average particle size of 100 nm or less, preferably 50 nm or less, more preferably 10 nm or less. In the first embodiment, the metal nanoparticle layer 4n is composed of Ag nanoparticles and Cu nanoparticles.

  The average particle diameter of the metal nanoparticles is a value measured by a particle size measuring apparatus using a dynamic light scattering method. As a particle size measuring device, for example, 9340UPA manufactured by Nikkiso Co., Ltd. is commercially available, and an average particle size of about 3 nm to μm order can be measured.

  The resistivity of the metal nanoparticle layer 4n can be suppressed to an extremely low level of about twice that of the bulk metal if the average particle size is 100 nm or less. However, when the average particle diameter exceeds 100 nm, the progress of fusion between the metal nanoparticles is inhibited, and the resistivity rapidly increases.

  The weight ratio of Cu in the metal nanoparticle layer 4n is in the range of 0.1 to 10 wt%, or the weight ratio of Ag is in the range of 0.1 to 10 wt%. This is because, within these alloy composition ranges, a value of 85% or more of pure Cu is obtained as the resistivity of the Ag—Cu alloy, and it becomes possible to form the outer conductor 4 having low resistance and excellent bending resistance. . Other than the above composition, the resistivity increases rapidly.

  The metal nanoparticle layer 4n has a thickness (film thickness) of 0.1 to 10 μm, preferably 0.1 to 7 μm, more preferably 0.1 to 1 μm. When the thickness is less than 0.1 μm, it is difficult to form the electroplated metal layer 4p due to an increase in electric resistance. When the thickness exceeds 10 μm, the bending life is significantly improved as compared with the above-described conventional coaxial cable, but the bending life is equivalent to the case where the outer conductor is formed only by the metal nanoparticle layer.

  The electroplated metal layer 4p is mainly for the purpose of improving solder resistance when the outer conductor 4 is soldered. For the electroplating metal layer 4p, it is preferable to use a metal having high adhesion to Cu or Ag. Furthermore, it is desirable that the metal has high corrosion resistance and high ductility.

  Ni is desirable as the material of the electroplating metal layer 4p, but is not limited to this material. For example, Sn, Sn—Zn alloy, and Sn—Bi alloy are also applicable. The average thickness of the electroplated metal layer 4p is preferably in the range of 0.1 to 0.3 μm. When the thickness is less than 0.1 μm, the solder resistance of the outer conductor 4 is lowered. On the other hand, if the thickness exceeds 0.3 μm, the transmission characteristics of the high-frequency signal deteriorate.

  In the first embodiment, Ni is used as the material of the electroplating metal layer 4p. The same material as that of the internal insulator 3 is used for the external insulator 5.

  In consideration of applications such as electronic devices such as mobile phones and medical devices such as ultrasonic inspection apparatuses, the outer diameter of the coaxial cable 1 is desirably φ0.6 mm or less.

  Next, a method for manufacturing the coaxial cable 1 will be described. Since the manufacturing method until the center conductor 2 is covered with the internal insulator 3 is the same as the conventional method, the description thereof is omitted.

  The fluororesin which is the material of the internal insulator 3 is chemically extremely stable, and when a metal layer is formed on the fluororesin, chemical bonding at the interface between the fluororesin and the metal layer cannot be expected. Therefore, the surface of the fluororesin is generally roughened in advance in order to increase the adhesion strength between the fluororesin and the metal layer. As a general roughening means, there are a wet processing method using a metal sodium-naphthalene complex solution and a dry processing method such as Ar reverse sputtering. However, in most cases, the concavo-convex structure formed by these methods has a substantially inverted pyramid shape when viewed from the surface of the fluororesin, and it has been difficult to obtain sufficient adhesion strength with the metal layer.

  Since metal nanoparticles are used for the outer conductor 4 of the coaxial cable 1, the present inventor has studied the formation conditions of the metal nanoparticle layer 4 n, particularly the heating conditions, by carefully examining the fluororesin and the metal nanoparticles. The manufacturing method according to the present embodiment, in which the adhesion strength of the layer 4n was improved, was completed.

  First, an organic protective agent such as octylamine that protects metal nanoparticles and suppresses fusion is deposited around the metal nanoparticles, and this is dispersed in a dispersion such as an organic solvent (eg, decanol). To produce a liquid substance.

  The organic protective agent is not limited to octylamine, which is an organic substance having 8 carbon atoms having an amino group, and other organic protective agents are also applicable. For example, an organic substance containing an alcohol group, a carboxyl group, a carbonyl group, an aldehyde group, or a sulfanyl group instead of an amino group can be used as the organic protective agent. By using these organic protective agents, it becomes possible to effectively suppress oxidation of the surface of the metal nanoparticles in the heat treatment step when obtaining the metal nanoparticle layer 4n from the liquid substance.

  As for carbon number of an organic protective agent, the range of 8-20 is desirable. When the number of carbon atoms is 7 or less, fusion between metal nanoparticles in the liquid material is observed even at room temperature. On the other hand, if the number of carbon atoms exceeds 20, the organic component remains in the metal nanoparticle layer 4n even after the heat treatment step is completed, and it becomes difficult to form the metal nanoparticle layer 4n having a low resistivity.

  A liquid material is deposited around the cable (first pre-cable) on which the internal insulator 3 is formed (deposition step). By heating the cable (heating step), the metal nanoparticle layer 4n having conductivity is formed around the inner insulator 3.

  More specifically, the heating process includes a first heating process (first heat treatment process) in which the deposited liquid substance is heated to form the metal nanoparticle layer 4n, and the external conductor 4 is formed by induction heating using high-frequency power. A second heating step (second heat treatment step) for heating.

  In the first heating step, a fine uneven structure having an average roughness (Ra) of 1 μm or less is formed on the surface of the metal nanoparticle layer 4n by appropriately controlling the heating conditions. In the concavo-convex structure, not only a simple inverted pyramid shape, but also a large number of tsubo-shaped shapes whose opening areas increase from the surface toward the inside are formed. Such an uneven structure is also formed on the surface of the metal nanoparticle layer 4n on the inner insulator 3 side.

  Here, the average roughness (Ra) is an arithmetic average roughness measured by a stylus type surface roughness measuring device. Since the cable surface is a curved surface and it is difficult to measure the average roughness, a metal nanoparticle layer is formed on the surface of a plate-like substrate formed using the same material as the internal insulator, and the average roughness is measured. The inventor further measures the shape of the surface and cross-section using a scanning electron microscope, thereby forming a metal nanoparticle layer having a substantially equivalent fine concavo-convex structure on the surface of the cable and the plate-like substrate. It was confirmed.

The upper limit of the heating temperature of the cable at the time of forming the metal nanoparticle layer 4n from liquid material containing metal nanoparticles, you about 5 ° C. lower than the melting point of the fluorine-based resin constituting the inner insulator 3. If the heating temperature of the cable is higher than that temperature, the internal insulator 3 is deformed, and the coaxial cable manufacturing yield is lowered. On the other hand, the lower limit temperature, you to 200 ° C. or higher. When it is lower than that temperature, the electrical resistivity of the metal nanoparticle layer 4n is significantly increased.

  In the second heating step subsequent to the first heating step, the metal nanoparticles are preferentially heated by an induction heating method using high-frequency power. The heating temperature at that time is preferably near the melting point of the fluororesin. When the temperature of the metal nanoparticle layer 4n rises to the vicinity of the melting point of the fluororesin, only the surface portion of the internal insulator 3 is softened, and the softened resin enters the concave portion of the surface uneven structure of the metal nanoparticles. In particular, when the resin enters and solidifies in the square-shaped recess, an anchor effect is obtained, and the adhesion strength between the internal insulator 3 and the metal nanoparticle layer 4n is greatly improved.

  For example, when PFA (nominal melting point 302 to 310 ° C.) is used for the internal insulator 3, good adhesion strength can be obtained by setting the heating temperature of the metal nanoparticle layer 4 n by the induction heating method to a range of 295 to 330 ° C. Is obtained. When the heating temperature is lower than 295 ° C., the adhesion strength is lowered, and the bending life of the coaxial cable is remarkably reduced. On the other hand, when the heating temperature is higher than 330 ° C., the internal insulator 3 is deformed, and the manufacturing yield of the coaxial cable is significantly reduced.

  When PTFE (nominal melting point 327 ° C.) is used for the internal insulator 3, good adhesion strength can be obtained by setting the heating temperature of the metal nanoparticle layer 4 n by the induction heating method in the range of 320 to 349 ° C. Similarly, when ETFE (nominal melting point 270 ° C.) is used, good adhesion strength is obtained in the range of 261 to 297 ° C.

  After forming the metal nanoparticle layer 4n, the electroplating metal layer 4p is formed around the metal nanoparticle layer 4 by electroplating, and the external insulator 5 is formed around the metal nanoparticle layer 4p in the same manner as the internal insulator 3, as shown in FIG. A coaxial cable 1 is obtained.

  The operation of the first embodiment will be described.

  In the coaxial cable 1, the outer conductor 4 includes a metal nanoparticle layer 4 n formed by fusing metal nanoparticles such as Ag nanoparticles and Cu nanoparticles having an average particle diameter of 100 nm or less.

  It is known that when the particle size of the metal particle is reduced to the nano order, the melting point is lowered and fusion occurs at a low temperature. The fusion proceeds even at room temperature. Therefore, when handling metal nanoparticles, it is convenient to protect the metal nanoparticles around them with an organic substance, disperse it in an organic solvent and make it liquid. When the liquid material in which the metal nanoparticles are dispersed is heated, the organic solvent and the protective organic material are evaporated and decomposed. At the same time, the metal nanoparticles are fused, and the metal nanoparticle layer 4n is obtained. The metal nanoparticle layer 4n does not include metal particles having an average particle size exceeding 100 nm.

  In the coaxial cable 1, by setting the average particle size of the metal nanoparticles to 100 nm or less, the fusion between the metal nanoparticles can be sufficiently advanced, and the metal nanoparticle layer 4 n having a low electrical resistance is formed as the outer conductor 4. It becomes possible to form.

  In particular, in the coaxial cable 1, the metal nanoparticle layer 4n which consists of an alloy of Ag and Cu can be obtained by using the material which mixed Ag nanoparticle and Cu nanoparticle as a metal nanoparticle material. In the coaxial cable 1 in which an Ag—Cu alloy is applied to the outer conductor 4, the outer conductor is composed of an Ag nanoparticle layer alone (Ag single material) or a Cu nanoparticle layer alone (Cu single material). The improvement of flex life is greatly improved. This is because the Ag—Cu alloy constituting the metal nanoparticle layer 4n improves mechanical properties such as tensile strength as compared with Ag and Cu.

  Further, since the coaxial cable 1 includes the metal nanoparticle layer 4n made of metal nanoparticles, the outer conductor 4 is formed when the outer conductor is formed by a combination of a conventional dry film forming method, electroless plating method, and electroplating method. In comparison, the manufacturing is simple and the manufacturing cost is low. In addition, the metal nanoparticle layer 4n has a dense structure as compared with the case where the external conductor is formed from a paste containing conventional metal nanoparticles and metal powder, so that the flex life of the cable can be greatly improved even if the cable diameter is reduced. .

  Therefore, according to the coaxial cable 1, by optimizing the structure of the metal layer of the outer conductor 4 and the forming method thereof, it is possible to reduce the diameter of the cable and greatly improve the bending life. Can be provided at low cost.

  Moreover, according to the coaxial cable 1, it is possible to apply the coaxial cable in which the outer conductor is formed of a metal layer to an electronic device such as a mobile phone or a medical device such as an ultrasonic inspection apparatus, and downsizing the device. It is also possible to reduce the weight and increase the functionality.

  The coaxial cable 1 constitutes the outer conductor 4 using an electroplated metal layer 4p in addition to the metal nanoparticle layer 4n. For this reason, in the coaxial cable 1, compared with the case where an external conductor is comprised only with the metal nanoparticle layer 4n, the bending life of a cable can be improved more. This is probably because the electroplating metal layer 4p has a denser structure than the metal nanoparticle layer 4n, and thus the flex life is improved.

  Further, since the coaxial cable 1 has the electroplated metal layer 4p formed around the metal nanoparticle layer 4n, the adhesion strength between the metal nanoparticle layer 4n and the electroplated metal layer 4p is high.

  The coaxial cable 1 is a metal made of an Ag—Cu alloy because the weight ratio of Cu in the metal nanoparticle layer 4n is in the range of 0.1 to 10 wt% or the weight ratio of Ag is in the range of 0.1 to 10 wt%. The electrical resistivity of the nanoparticle layer 4n can be lowered, and the outer conductor 4 having a low electrical resistance and a long bending life can be formed.

  Moreover, the manufacturing method of the coaxial cable 1 according to the present embodiment includes a step of depositing a liquid substance in which metal nanoparticles having an average particle size of 100 nm or less are dispersed in a dispersion liquid such as an organic solvent on an internal insulator, and thereafter Heating step. For this reason, according to the manufacturing method according to the present embodiment, the adhesion strength between the internal insulator 3 made of a fluororesin and the metal nanoparticle layer 4n can be greatly improved, and the bending life of the external conductor 4 is greatly improved. The coaxial cable 1 can be easily manufactured.

  A second embodiment will be described.

  As shown in FIG. 2, the coaxial cable 21 according to the second embodiment includes an outer conductor 24, an innermost metal nanoparticle layer 24n, and an electroplated Cu layer 24p formed by electroplating around the metal nanoparticle layer 24n. And an electroplating metal layer 4p formed by the electroplating method as the outermost layer.

  In the second embodiment, a part of the outside of the metal nanoparticle layer 4n in FIG. 1 is an electroplated Cu layer 24p thicker than the metal nanoparticle layer 24n. The thickness of the metal nanoparticle layer 4n and the total thickness of the metal nanoparticle layer 24n and the electroplating metal layer 4p are the same. Other configurations of the coaxial cable 21 are the same as those of the coaxial cable of FIG.

  In the coaxial cable 21, the main part of the outer conductor 24 is composed of the metal nanoparticle layer 24n and the electroplated Cu layer 24p, so that the electroplated Cu layer 24p, which is softer than the electroplated metal layer 4p, improves the flexibility of the cable. Therefore, the bending life is further improved as compared with the coaxial cable 1.

  A third embodiment will be described.

  As shown in FIG. 3, the coaxial cable 31 according to the third embodiment includes an outer conductor 34, an innermost metal nanoparticle layer 34n, and an electroless plating Cu formed around the metal nanoparticle layer 34n by an electroless plating method. The layer 34L has a four-layer structure including an electroplating Cu layer 24p formed by electroplating around the layer 34L and an electroplating metal layer 4p formed by electroplating which is the outermost layer.

  The metal nanoparticle layer 34n is formed in the same manner as each of the metal nanoparticle layers described above, and is composed of Ag nanoparticles and Pd nanoparticles, and the weight ratio of Pd in the metal nanoparticle layer 34n (Pd of Ag—Pd alloy). Weight ratio) is in the range of 0.01 to 2 wt%.

  This is because, in this composition range, the formation rate of the electroless plating Cu layer 34L by the electroless plating method is improved by 1.5 to 2 times as compared with the case where the metal nanoparticle layer is constituted only by the Ag nanoparticle layer. . When the composition is lower than 0.01 wt%, the formation rate of the electroplated Cu layer 24p is equivalent to the case where the metal nanoparticle layer is composed of only the Ag nanoparticle layer. Further, when the composition is higher than 2 wt%, the flex life of the coaxial cable is remarkably reduced.

  The average thickness of the metal nanoparticle layer 34n is appropriately in the range of 0.01 to 0.1 μm. When the thickness is less than 0.01 μm, the formation rate of the electroless plating Cu layer 34L by the electroless plating method is remarkably reduced. On the other hand, if the thickness exceeds 0.1 μm, the flex life of the coaxial cable becomes equivalent to the case where the outer conductor is constituted by the metal nanoparticle layer and the electrolytic plating Cu layer.

  In the coaxial cable 31, the main part of the outer conductor 34 is composed of the metal nanoparticle layer 34n, the electroless plating Cu layer 34L, and the electroplating Cu layer 24p, whereby the metal nanoparticle layer 34n and the electroplating Cu layer 24p are formed. The electroless plated Cu layer 34L with good adhesion becomes a buffer layer and improves the flexibility of the cable. For this reason, in the coaxial cable 31, compared with the coaxial cable 21 of FIG. 2 which comprises the main part of the outer conductor 24 by the metal nanoparticle layer 24n and the electroplating Cu layer 24p, the bending life is further improved.

  In the above embodiment, an example of an outer conductor including an electroplated Cu layer has been described. However, even when an outer conductor made of only a metal nanoparticle layer is used, the bending life of the coaxial cable can be significantly improved as compared with the conventional case.

  Further, the material of each metal nanoparticle layer for constituting the outer conductor may be Au, Pt, Ni, etc. in addition to the above-mentioned Ag, Cu, Pd, but the electrical characteristics such as resistivity, and the material price , Ag alone, Cu alone, or alloys thereof as described above are most desirable.

Example 1
The internal insulator 3 has a structure in which a single wire made of an alloy of Cu and Ag and having an outer diameter of 13 μm is twisted. The number of single wires of the stranded wire was 7, and the outer diameter of the stranded wire was about 40 μm. The internal insulator 3 is made of PFA as a material and has an average thickness of about 25 μm. The outer conductor 4 was composed of a metal nanoparticle layer 4n and an electroplated metal layer 4p. The metal nanoparticle layer 4n was formed by fusing Ag nanoparticles having an average particle diameter of about 8 nm, and the average thickness was about 6 μm. The electroplating metal layer 4p is made of Ni and has an average thickness of about 0.2 μm. The external insulator 5 is made of PFA as a material and has an average thickness of about 20 μm.

  In the manufacturing method of the coaxial cable 1, first, PFA is formed as an internal insulator 3 around the stranded wire constituting the central conductor 2 by an extrusion method, and then a liquid material in which Ag nanoparticles are dispersed is formed in the internal insulator 3. It was deposited around.

  The liquid material was composed of Ag nanoparticles having an average particle diameter of about 8 nm, an organic protective agent deposited around the Ag nanoparticles, and a solvent. Octylamine was used as the organic protective agent, and decanol was used as the solvent. The weight ratio of Ag nanoparticles in the liquid material was about 80%. Here, the weight ratio of Ag nanoparticles in a liquid substance is a ratio of the weight of Ag nanoparticles and the weight of a liquid substance containing Ag nanoparticles expressed in percentage. The first heat treatment step was performed by passing the cable coated with the liquid substance through the inside of the tubular heater.

  The tubular heater has a structure in which a resistance heating element is embedded in a tubular heat-resistant member, and the heating temperature of the cable (maximum) is optimized by optimizing the input power to the tubular heater, the length of the tubular heater, and the passing speed of the cable. Reached temperature). The first heat treatment step was performed in the air, and the heating temperature was about 280 ° C.

  Through the first heat treatment step, a conductive metal nanoparticle layer 4 n was formed around the inner insulator 3. After the first heat treatment step was completed, the second heat treatment step was performed by passing the cable through the induction coil.

  In the second heat treatment step, the heating temperature (maximum temperature reached) of the metal nanoparticle layer 4n was controlled mainly by optimizing the power and frequency input to the induction coil. The second heat treatment step was performed in the atmosphere, the heating temperature was about 320 ° C., and the frequency of the high frequency power was about 350 kHz.

  After the second heat treatment step was completed, an Ni layer having a thickness of about 0.2 μm was formed as an electroplating metal layer 4p around the metal nanoparticle layer 4n by electroplating. After the formation of the electroplated metal layer 4p was completed, PFA was formed as an external insulator 5 by an extrusion method.

  Through the above steps, the coaxial cable 1 shown in FIG. 1 having the main part of the outer conductor 4 composed of the metal nanoparticle layer 4n and the outer diameter of about 143 μm was produced.

  About the coaxial cable 1 of Example 1, the transmission characteristic of the high frequency signal was compared with the conventional coaxial cable 41 shown in FIG. As a result, equivalent characteristics were obtained with respect to characteristic impedance and signal attenuation at a frequency of 10 MHz. Here, in the conventional coaxial cable 41, the configuration of the outer conductor 44 is different from that of the first embodiment, and the outer conductor 44 is configured by horizontally winding a Cu wire having an outer diameter of about 16 μm.

  A left / right bending test was further performed on the coaxial cable 1 of Example 1. The test conditions were a bending angle of ± 90 ° left and right, a bending speed of 30 times per minute, a bending strain of about 3%, and a load of about 20% of the average breaking load of the coaxial cable.

  For comparison, a coaxial cable using an Ag layer formed by electroless plating and electroplating instead of the metal nanoparticle layer 4n in the coaxial cable 1 of Example 1 shown in FIG. 1, and the metal nanoparticle layer 4n. A left / right bending test was also carried out on a coaxial cable using a Cu layer formed by electroless plating and electroplating instead of. The coaxial cable produced for comparison is formed with an internal insulator, and then the surface is roughened with a metal sodium-naphthalene complex solution, etc., and then a plating catalyst is applied, and electroless plating and electroplating are used. A metal layer is formed. The total thickness of the plated metal layer was set to be substantially the same as that of the metal nanoparticle layer 4n.

  As a result of the left / right bending test, in the comparative coaxial cable using the plated metal layer instead of the metal nanoparticle layer, the number of times of bending is 50 times or less when the material of the metal layer is Ag or Cu. A break occurred in the conductor. On the other hand, in the coaxial cable 1 of Example 1, the outer conductor did not break until the number of bendings was 500.

  From the result of the left / right bending test, it was found that the bending life of the coaxial cable 1 of Example 1 was significantly improved.

  In the manufacturing method of the coaxial cable described in Example 1, it is desirable that the weight ratio of the metal nanoparticles in the liquid material is in the range of 50 to 90%. As described above, the metal nanoparticle layer 4n is formed by depositing a liquid substance containing metal nanoparticles around the inner insulator 3, and further through a heat treatment process. At this time, the thickness of the metal nanoparticle layer 4n can be controlled by the weight ratio of the metal nanoparticles in the liquid substance and the viscosity of the solvent constituting the liquid substance. is important.

  In Example 1, the metal nanoparticle layer 4n constitutes a main part of the outer conductor 4, and the thickness of the metal nanoparticle layer 4n is usually in the range of 2 to 10 μm from the functional aspect as the outer conductor. Designed. Further, when the weight ratio of the metal nanoparticles in the liquid material is 50% or less, it is difficult to form the metal nanoparticle layer 4n having a thickness of 2 μm or more. Further, when the weight ratio of the metal nanoparticles exceeds 90%, the fluidity of the liquid substance is remarkably lowered, and it is difficult to form the metal nanoparticle layer 4n having a uniform thickness.

(Example 2)
The coaxial cable 1 of Example 2 differs from Example 1 only in the material of the metal nanoparticle layer 4n, and the other structure is the same. In Example 2, as a material of the metal nanoparticle layer 4n, an Ag—Cu alloy having a Cu weight ratio of about 2 wt% was used. When producing a liquid material for forming the metal nanoparticle layer 4n, the metal nanoparticle layer 4n made of an Ag-Cu alloy was formed by mixing Ag nanoparticles and Cu nanoparticles at the above-mentioned weight ratio. . The average particle diameter of Cu nanoparticles was about 30 nm, and the same organic protective agent as Ag nanoparticles was used. The manufacturing method of the coaxial cable 1 of the second embodiment is the same as that of the first embodiment.

  As a result of evaluating the transmission characteristic of the high-frequency signal having a frequency of 10 MHz with respect to the coaxial cable 1 of Example 2, the outer conductor 4 was not broken up to 900 times. Therefore, the bending life was further improved by configuring the metal nanoparticle layer 4n with an Ag—Cu alloy (Cu weight ratio 2 wt%).

(Modification 1 of Example 2)
In Example 2, the metal nanoparticle layer 4n is composed of an Ag—Cu alloy having a high Ag weight ratio, but may be composed of an Ag—Cu alloy having a high Cu weight ratio. For example, even when the metal nanoparticle layer 4n is composed of an Ag—Cu alloy having a Ag weight ratio of 2 wt%, the same good effects as those of Example 2 were obtained in transmission characteristics and bending life.

  In the manufacturing method in that case, the second heat treatment step was performed in a reducing gas atmosphere. As the reducing gas, a mixed gas of nitrogen and hydrogen was used, and the volume ratio of hydrogen gas in the mixed gas was set to 2 vol%.

(Modification 2 of Example 2)
The difference between this modification and Example 2 is that Ag nanoparticles having an average particle diameter of about 80 nm and Cu nanoparticles having an average particle diameter of about 90 nm are used to form the metal nanoparticle layer 4n. It was a point. As a result of evaluating the transmission characteristics and the bending life of the coaxial cable 1 according to this modification, the same advantageous effects as those of Example 2 were obtained.

  In the trial production of the coaxial cable 1 according to this modification, in order to investigate the influence on the transmission characteristics and the bending life when the average particle size of the metal nanoparticles is further increased, Ag nanoparticles having an average particle size of about 120 nm and In the coaxial cable for the comparative test in which the metal nanoparticle layer is configured using Cu nanoparticles, the problem that the desired transmission characteristics cannot be obtained occurred and the flexing life was remarkably reduced to 50 times or less. The reason for the deterioration of the characteristics of the coaxial cable for the comparative test is that the metal nanoparticles were not sufficiently fused by increasing the average particle size of the metal nanoparticles to about 120 nm.

(Example 3)
Example 3 is the coaxial cable 21 shown in FIG. 2, in which the outer conductor 24 has a three-layer structure including a metal nanoparticle layer 24n, an electroplated Cu layer 24p, and an electroplated metal layer 4p. Hereinafter, the difference from the second embodiment will be mainly described.

  As a material of the metal nanoparticle layer 24n, an Ag—Cu alloy with a Cu weight ratio of about 2 wt% was used, and the average thickness was about 0.3 μm. The electroplating Cu layer 24p is a Cu layer formed by electroplating around the metal nanoparticle layer 24n, and has an average thickness of about 6 μm.

  In the manufacturing method, the weight ratio of metal nanoparticles in the liquid material for forming the metal nanoparticle layer 24n was about 30%.

  About the coaxial cable 21 of Example 3, as a result of evaluating the transmission characteristic of the high frequency signal of frequency 10MHz, the transmission characteristic substantially the same as Example 1 was obtained. Further, when the left / right bending test was performed, the outer conductor was not broken until the number of bendings was 1200 times. By configuring the main part of the outer conductor 24 with the metal nanoparticle layer 24n and the electroplated Cu layer 4p, the bending life was further improved as compared with the coaxial cable 1 of Example 2.

  In Example 3, the metal nanoparticle layer 24p constitutes a main part of the outer conductor 24, and also provides a plating seed layer for forming the electroplating Cu layer 24p, and adhesion strength between the inner insulator 3 and the outer conductor 24. It also functions as an adhesion layer for improvement.

As described above, the average thickness of the metal nanoparticle layer 4n is suitably in the range of 0.1 to 1 μm. When the thickness was less than 0.1 μm, it was difficult to form the electroplated Cu layer 24p due to an increase in electrical resistance. Further, when the film thickness exceeded 1 μm, the bending life was the same as that of Example 2 in which the main part of the outer conductor 4 was constituted only by the metal nanoparticle layer 4n.

  In controlling the thickness of the metal nanoparticle layer 24n, the weight ratio of the metal nanoparticles in the liquid material containing the metal nanoparticles is important. In the manufacturing method of Example 3, the metal nanoparticles in the liquid material are used. The weight ratio is preferably in the range of 10 to 50 wt%. By using a liquid substance containing metal nanoparticles with a weight ratio in that range, the thickness of the metal nanoparticle layer 24n can be controlled in the range of 0.1 to 1 μm.

Example 4
Example 4 is the coaxial cable 31 shown in FIG. 3, and the outer conductor 34 is composed of four layers including a metal nanoparticle layer 34n, an electroless plating Cu layer 34L, an electroplating Cu layer 24p, and an electroplating metal layer 4p. It is structured. Hereinafter, the difference from the third embodiment will be mainly described.

  As a material of the metal nanoparticle layer 34n, an Ag—Pd alloy having a Pd weight ratio of 0.2 wt% was used, and an average thickness was about 0.05 μm. The electroless plating Cu layer 34L is a Cu layer formed by an electroless plating method around the metal nanoparticle layer 34n, and has an average thickness of about 0.3 μm.

  In the manufacturing method, the weight ratio of the metal nanoparticles in the liquid material for forming the metal nanoparticle layer 34n was about 3%.

  About the coaxial cable 31 of Example 4, as a result of evaluating the transmission characteristic of the high frequency signal of frequency 10MHz, the transmission characteristic substantially the same as Example 1 was obtained. Further, when the left / right bending test was performed, the outer conductor was not broken up to 1600 times. By constituting the main part of the outer conductor 34 with the metal nanoparticle layer 34n, the electroless plating Cu layer 34L, and the electroplating Cu layer 24p, the bending life can be further improved as compared with the coaxial cable 21 of the third embodiment. I was able to.

  In Example 4, the metal nanoparticle layer 34n is mainly used as a plating catalyst layer for forming the electroless plating Cu layer 34L and an adhesion layer for improving the adhesion strength between the inner insulator 3 and the outer conductor 34. Also works. Further, the electroless plating Cu layer 34L constitutes a main part of the outer conductor 34 and also functions as a plating seed layer for forming the electroplating Cu layer 24p.

  Even if the electroless plating Cu layer 34L is formed to a thickness of about 6 μm instead of forming the electroplating Cu layer 24p, it is possible to obtain the same transmission characteristics and bending life as described above. Since the method has a slower Cu formation rate than the electroplating method, the combined use of the electroplating method can reduce the manufacturing cost of the coaxial cable.

  As described above, the weight ratio of Ag constituting the metal nanoparticle layer 34n and Pd of the Pd alloy is suitably in the range of 0.01 to 2 wt%. In this composition range, for example, the formation rate of the Cu layer by the electroless plating method is improved by 1.5 to 2 times compared to the case where the metal nanoparticle layer 34n is composed of Ag nanoparticles. With a composition lower than 0.01 wt%, the formation rate of the electroless plating Cu layer 34L by the electroless plating method was equivalent to that of the Ag nanoparticle layer. Further, when the composition is higher than 2 wt%, the flex life of the coaxial cable is remarkably reduced.

  As described above, the average thickness of the metal nanoparticle layer 34n is suitably in the range of 0.01 to 0.1 μm. When the thickness was less than 0.01 μm, the formation rate of the electroless plating Cu layer 34L by the electroless plating method was remarkably reduced. Further, when the film thickness exceeded 0.1 μm, the flexing life became equivalent to that of Example 3 in which the main part of the outer conductor was constituted by the metal nanoparticle layer 34n and the electroplated Cu layer 24p.

  In controlling the thickness of the metal nanoparticle layer 34n, the weight ratio of the metal nanoparticles in the liquid material containing the metal nanoparticles is important. In the manufacturing method of Example 4, the metal nanoparticles in the liquid material The weight ratio is desirably in the range of 0.1 to 10 wt%. By using a liquid substance containing metal nanoparticles with a weight ratio in the range, the thickness of the metal nanoparticle layer 34n can be controlled in the range of 0.01 to 0.1 μm.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional view which shows the outline | summary of the structure of the coaxial cable which is suitable 1st Embodiment of this invention. It is a cross-sectional view which shows the outline | summary of the structure of the coaxial cable which is suitable 2nd Embodiment of this invention. It is a cross-sectional view which shows the outline | summary of the structure of the coaxial cable which is suitable 3rd Embodiment of this invention. It is a cross-sectional view of a conventional coaxial cable.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coaxial cable 2 Center conductor 3 Inner insulator 4 Outer conductor 4n Metal nanoparticle layer 5 External insulator

Claims (10)

A coaxial cable having a central conductor, an internal insulator made of fluororesin formed on the outer periphery of the central conductor, an external conductor formed around the internal insulator, and an external insulator formed around the external conductor ,
The outer conductor includes a metal nanoparticle layer formed by fusing metal nanoparticles having an average particle size of 100 nm or less, and the metal nanoparticle layer has an opening area increasing from the surface toward the inside. A coaxial cable having a concavo-convex structure with an average roughness of 1 μm or less including a basal-shaped concave portion, and the resin of the internal insulator entering the concave portion of the concavo-convex structure.   The coaxial cable according to claim 1, wherein the metal nanoparticles are composed of Ag nanoparticles and Cu nanoparticles, and a weight ratio of Cu or Ag in the metal nanoparticle layer is in a range of 0.1 to 10 wt%.   The coaxial cable according to claim 1, wherein the metal nanoparticle layer has a thickness of 0.1 to 10 μm.   The coaxial cable according to claim 1, wherein the outer conductor includes an electroplated Cu layer formed around the metal nanoparticle layer.   The outer conductor includes an electroless plated Cu layer formed around the metal nanoparticle layer and an electroplated Cu layer formed around the outer layer, and the metal nanoparticle layer is made of Ag nanoparticles and Pd nanoparticles. The coaxial cable according to claim 1, wherein the weight ratio of Pd in the metal nanoparticle layer is in the range of 0.01 to 2 wt%.   The coaxial cable according to claim 5, wherein the metal nanoparticle layer has a thickness of 0.01 to 0.1 μm. Production of a coaxial cable having a central conductor, an internal insulator made of PFA formed on the outer periphery of the central conductor, an external conductor formed around the internal insulator, and an external insulator formed around the external conductor In the method, the step of forming an outer conductor includes a step of depositing a liquid material in which metal nanoparticles having an average particle size of 100 nm or less are dispersed in a dispersion liquid around the inner insulator; the deposited by cable at 200 ° C. or higher, a first heating step of forming a metal nanoparticle layer by fusing the metal nanoparticles to each other 5 ° C. by heating at a lower temperature than the melting point of the PFA, induction And a second heating step in which the metal nanoparticle layer is preferentially heated by heating in a range of 295 to 330 ° C. to allow the PFA to enter the recesses on the inner surface of the metal nanoparticle layer. A manufacturing method of a shaft cable. Production of a coaxial cable having a central conductor, an internal insulator made of PTFE formed on the outer periphery of the central conductor, an external conductor formed around the internal insulator, and an external insulator formed around the external conductor In the method, the step of forming an outer conductor includes a step of depositing a liquid material in which metal nanoparticles having an average particle size of 100 nm or less are dispersed in a dispersion liquid around the inner insulator; above 200 ° C. the deposition is cable, a first heating step of forming a metal nanoparticle layer by fusing the metal nanoparticles to each other 5 ° C. by heating at a lower temperature than the melting point of the PTFE, induction And a second heating step of preferentially heating the metal nanoparticle layer by heating within a range of 320 to 349 ° C. to allow the PTFE to enter the recesses on the inner surface of the metal nanoparticle layer. A method for manufacturing a coaxial cable. Manufacture of a coaxial cable having a center conductor, an inner insulator made of ETFE formed on the outer periphery of the center conductor, an outer conductor formed around the inner insulator, and an outer insulator formed around the outer conductor In the method, the step of forming an outer conductor includes a step of depositing a liquid material in which metal nanoparticles having an average particle size of 100 nm or less are dispersed in a dispersion liquid around the inner insulator; the deposited by cable at 200 ° C. or higher, a first heating step of forming a metal nanoparticle layer by fusing the metal nanoparticles to each other 5 ° C. by heating at a lower temperature than the melting point of the ETFE, induction And a second heating step in which the metal nanoparticle layer is preferentially heated by heating in the range of 261 to 297 ° C. to allow the ETFE to enter the recesses on the inner surface of the metal nanoparticle layer. A method for manufacturing a coaxial cable.   The coaxial cable according to any one of claims 7 to 9, wherein the step of forming the outer conductor includes a step of applying at least one of an electroplated Cu layer and an electroless plated Cu layer around the metal nanoparticle layer. Manufacturing method.

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