Patent Publication Number: US-11664138-B2

Title: Composite cable including collective braided shield

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present patent application claims the priority of Japanese patent application No. 2020-189320 filed on Nov. 13, 2020, and the entire contents of Japanese patent application No. 2020-189320 are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a composite cable. 
     BACKGROUND ART 
     Composite cables combining power supply lines and signal lines are widely used as conventional cables (see e.g., the patent literature 1). 
     CITATION LIST 
     Patent Literatures 
     
         
         Patent Literature 1: JP 2011-90866A 
       
    
     SUMMARY OF INVENTION 
     In recent years, the development of automated driving technologies has made significant progress in automotive industry or the like. The image quality of cameras used for automated driving has been greatly improved, so the composite cables for such cameras need very high signal transmission speed that allows transmission of a large capacity of image data. Additionally, the composite cables for cameras used for vehicles may be wired over for several meters, therefore, high frequency characteristics that allow transmission of high-speed signals for a long distance are required. To secure safety of automated driving, the composite cables that allow stable high-speed transmission are required. 
     However, the high frequency characteristics of conventional composite cables are easily deteriorated, especially when composite cables are bent, twisted or the like. Thus, further improvement of high frequency characteristics has been required. 
     For the above reason, the object of the present invention is to provide a composite cable with improved high frequency characteristics. 
     For solving the above problems, one aspect of the present invention provides a composite cable comprising:
         a signal transmission cable including a pair of signal lines being arranged parallel to each other in a cable longitudinal direction and contacting to each other and a shield layer covering the pair of signal lines together;   a pair of power supply lines being arranged contacting to each other and contacting to the shield layer;   a collective braided shield covering around a cable core comprising the signal transmission cable and the pair of power supply lines collectively; and   a sheath covering around the collective braided shield,   wherein the collective braided shield is configured closely contacting to the shield layer in accordance with an outer shape of the shield layer.       

     Effect of Invention 
     According to the present invention, it is possible to provide a composite cable with improved high frequency characteristics. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a cross-sectional view showing a cross-section perpendicular to a longitudinal direction of a composite cable in an embodiment of the present invention. 
         FIG.  2    is a perspective view for explaining terminal treatment of the composite cable in  FIG.  1   . 
         FIG.  3    is a cross-sectional view of a metal tape that is used for a shield layer. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 
     The embodiment of the present invention will be explained below in conjunction with appended drawings. 
       FIG.  1    is a cross-sectional view showing a cross-section perpendicular to a longitudinal direction of a composite cable in the present embodiment. The composite cable  1  in  FIG.  1    is used, e.g., to connect cameras (e.g., cameras for automated driving) that are installed in vehicles. 
     As shown in  FIG.  1   , the composite cable  1  is composed of a signal transmission cable  2  including a pair of signal lines (signal wires)  21 , a shield layer  22  that covers the pair of signal lines  21  collectively, a pair of power supply lines (power supply wires)  3 , a collective braided shield  5  that covers a cable core  4  in which the signal transmission cable  2  and the pair of power supply lines  3  are stranded, and a sheath  6  that covers the collective braided shield  5 . 
     (Power Supply Line  3 ) 
     The pair of power supply lines  3  are used to supply electric power to a camera, etc. Each of the pair of power supply lines  3  is respectively composed of a conductor  31  and an insulator  32  that covers the conductor  31 . The conductor  31  is a strand wire conductor made of multiple metal wires stranded together. As metal wires used for the conductor  31 , annealed copper wires and copper alloy wires can be used as well as plated wires. In the present embodiment, the conductor  31  is produced by concentrically stranding seven metal wires made of tin-plated annealed copper wires with an outer diameter of 0.16 mm. As the insulator  32 , e.g., an insulator made of polyvinyl chloride resin composition can be used. The outer diameter of the conductor  31  is, e.g., 0.40 mm or more and 0.50 mm or less. The two power supply lines  3  should be arranged parallel to each other in a cable longitudinal direction. 
     (Signal Transmission Cable  2 ) 
     The signal transmission cable  2  is used to transmit image signals from the camera. The signal transmission cable  2  is composed of the pair of signal lines  21  that are arranged parallel to each other in the cable longitudinal direction and contacting to each other, and the shield layer  22  that collectively covers the pair of signal lines  21 . 
     Each of the pair of signal lines  21  is composed of a signal conductor  211  and an insulator  212  that covers around the signal conductor  211 . The signal conductor  211  is a strand wire conductor made of multiple metal wires stranded together. As metal wires used for the signal conductor  211 , annealed copper wires and copper alloy wires can be used as well as plated wires such as tin-plated or silver-plated wires. In the present embodiment, the signal lines  21  are configured by using metal wires made of silver-plated annealed copper wires with high conductivity. Also, the signal conductor  211  can be a compressed strand wire conductor that has been lightly compressed in such a manner that the strand wire conductor has a circular cross-section. By configuring the signal conductor  211  with a compressed strand wire conductor, the resistance of the signal conductor  211  is largely suppressed by reducing a gap between the metal wires, and at the same time, the signal conductor  211  with high flex resistance can be realized. It is preferable that the conductor cross-sectional area of the signal conductor  211  is equal to or greater than the conductor cross-sectional area of the conductor  31  of the power supply line  3 . This facilitates high speed transmission of signals such as image signals from cameras. Also, the conductor cross-sectional area of the conductor  31  is, e.g., 0.12 mm 2  or more and 0.20 mm 2  or less. 
     As the insulator  212 , it is preferable to use an insulator with least electric permittivity to maintain high frequency characteristics in good conditions. Also, it is preferable to adjust a thickness of the insulator  212  to make the characteristic impedance of the signal lines  21  a desired value. In the present embodiment, the thickness of the insulator  212  was adjusted to set the characteristic impedance of the signal lines  21  to 50Ω (characteristic impedance of the entire signal transmission cable  2  to 100Ω). Additionally, it is preferable to make the characteristic impedance of the signal transmission cable  2  in 100±5Ω. The measurement of characteristic impedance can be, e.g., figured out by TDR (Time Domain Reflectometry) method. If the thickness of the insulator  212  is adjusted here in order to set the characteristic impedance of the signal lines  21  to 50Ω, the insulator  212  becomes thicker and the outer diameter of the signal lines  21  becomes greater, and therefore, the connection to the existing connectors could be difficult. For that reason, in the present embodiment, the insulator  212  is configured with an inner insulator  212   a  that covers around the signal conductor  211  and an outer insulator  212   b  that covers around the inner insulator  212   a.    
     Therefore, as shown in  FIG.  2   , the outer diameter of the signal lines  21  is reduced at a cable terminal by stripping and removing the outer insulator  212   b  from the inner insulator  212   a  in the terminal processing. This enables an exposed part of the inner insulator  212   a  to be connected to a connector, and thus, facilitates the connection to an existing connector with high versatility. In other words, it enables the following two things at the same time: increasing the characteristic impedance by increasing the thickness of the insulator  212  in the signal lines  21  (by increasing the outer diameter of the signal lines  21 ) to transmit signals from cameras in high speed, and connecting the cable terminal to a connector without changing a connector structure according to an increased diameter of the signal lines  21  (for example, without changing the position of a connector pin for connecting the signal conductor  211  according to an increased diameter of the signal lines  21 ). It is preferable that the outer diameter of the inner insulator  212   a  is equal to or greater than the outer diameter of the power supply line  3 . For example, it is preferable that the outer diameter of the inner insulator  212   a  is in the range of 1 to 1.5 times of the outer diameter of the power supply line  3 . 
     It is preferable that the inner insulator  212   a  is made by full extrusion or tube extrusion. Especially, the inner insulator  212   a  can be easily stripped and removed from the signal conductor  211  by making the inner insulator  212   a  by tube extrusion, and thus, workability is improved in the terminal processing to connect the cable terminal to a connector, etc. Additionally, by making the inner insulator  212   a  by tube extrusion, the signal conductor  211  can be easily moved inside the inner insulator  212   a  when the composite cable  1  is bent or twisted, thus, the resistance to bending and twisting is improved. 
     It is preferable to make the outer insulator  212   b  by tube extrusion. By doing this, an inner surface of the outer insulator  212   b  does not easily adhere to an outer surface of the inner insulator  212   a , so that the outer insulator  212   b  can be easily stripped and removed from the outer surface of the inner insulator  212   a  when processing the terminal to connect the cable terminal to a connector, etc. Therefore, the workability in the terminal processing is improved. 
     In making the outer insulator  212   b  (at extrusion molding), to avoid the outer insulator  212   b  from being welded to the inner insulator  212   a , it is preferable to use a resin with a lower melting point for the outer insulator  212   b  than that of the resin used for the inner insulator  212   a . The melting point of the resin used for the inner insulator  212   a  is, e.g., 250° C. or more and 330° C. or less. The melting point of the resin used for the outer insulator  212   b  is, e.g., 90° C. or more and 170° C. or less. Also, to maintain the high frequency characteristics, it is preferable that the inner insulator  212   a , which is closer to the signal conductor  211 , has lower permittivity than that of the outer insulator  212   b . The permittivity of the inner insulator  212   a  is, e.g., from 2.0 or more and 2.8 or less (more preferably, 2.1 or more and 2.6 or less). Also, to maintain the high frequency characteristics, it is preferable that the thickness of the inner insulator  212   a  is thicker than that of the outer insulator  212   b . The thickness of the inner insulator  212   a  is, e.g., from 1.5 to 2.0 times of the thickness of the outer insulator  212   b  (more preferably in the range from 1.6 to 1.7 times). In the present embodiment, as the inner insulator  212   a , fluorine resins with low permittivity such as FEP (tetrafluoroethylene hexafluoropropylene copolymer) or PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer) are used. Also, as the outer insulator  212   b , resins such as PE (polyethylene) and PP (polypropylene) are used, because they have relatively low permittivity and are not easily welded to the inner insulator  212   a  which is made of fluorine resin. 
     Additionally, it is preferable that both the inner insulator  212   a  and the outer insulator  212   b  have elongation of 150% or above. With the above elongation, even if two signal lines  21  are arranged parallel to each other in the cable longitudinal direction and contacting to each other so that the two signal lines  21  are not easily moved when twisted, the inner insulator  212   a  and the outer insulator  212   b  are not easily broken by bending or twisting. Therefore, the signal transmission cable  2  is able to perform stable signal transmission, even if it is bent or twisted in wiring. 
     As described above, to set the characteristic impedance of the signal lines  21  to a desired value, the outer diameter of the signal line  21  is relatively large in the present embodiment. Thus, the power supply line  3  has a smaller outer diameter than that of the signal lines  21 . To be more specific, the outer diameter of the power supply line  3  is at least 0.5 times but less than 1 time of the outer diameter of the signal lines  21 . In the present embodiment, the outer diameter of the signal lines  21  is 1.50 mm or more and 1.80 mm or less, and the outer diameter of the power supply line  3  is at least 1.00 mm but less than 1.50 mm. 
     The pair of signal lines  21  are arranged parallel to each other and contacting to each other. In other words, the signal transmission cable  2  is a two-core parallel cable. Also, a resin tape made of PET (polyethylene terephthalate) and the like is spirally wrapped around the pair of signal lines  21 . The shield layer  22  is configured by spirally wrapping a metal tape around the resin tape  23 . 
     As shown in  FIG.  3   , the metal tape that configures the shield layer  22  has a metal layer  222  on one side of a resin layer  221  and an adhesive layer  223  on the other side of the resin layer  221 . In the present embodiment, a metal tape composed of an Al/PET tape wherein the metal layer  222  made of Al (aluminum) is provided on one side of the resin layer  221  made of PET (polyethylene terephthalate), and the adhesive layer  223  made of thermosetting resin is provided on the other side of the resin layer  221 , is used. However, the present invention is not limited thereto, and a metal tape with the metal layer  222  made of copper can be used. Also, a metal tape with the resin layer  221  made of polyester resin other than PET can be used. 
     The shield layer  22  is configured by spirally wrapping a metal tape around the resin tape  23  in such a manner that the adhesive layer  223  is at the side of the resin tape  23  (so that the metal layer  222  is at the side of the collective braided shield  5 ). By applying heat after wrapping a metal tape around the resin tape  23 , a thermosetting resin that configures the adhesive layer  223  adheres the metal tape to the metal tape as well as the metal tape to the resin tape  23 . With this configuration, the pair of signal lines  21  can be maintained more securely. Also, it suppresses the shield layer  22  from separating from the signal lines  21 , so it can control the position change of the signal lines  21  due to the separation from the shield layer  22 , and the deterioration of high frequency characteristics by restraining the distance change between the signal lines  21  and the shield layer  22  when they are bent or twisted. Additionally, because the shield layer  22  does not adhere to the signal lines  21  directly in this configuration, the shield layer  22  can be removed from the signal lines  21  easily when processing the terminal. Thus, the workability in the terminal processing is improved. 
     It is preferable that a wrapping direction of the metal tape that configures the shield layer  22  is different from a wrapping direction of the resin tape  23  which is a base of the metal tape. By doing this, the metal tape that configures the shield layer  22  and the resin tape  23  can adhere to each other firmly and the position of the two signal lines  21  arranged in parallel to each other cannot be easily changed when they are bent or twisted. Also, the signal lines  21  are not easily twisted over each other, so the distance between the signal lines  21  can be stabilized, and thus the characteristic impedance can be stabilized in the cable longitudinal directions. Additionally, the wrapping direction of the metal tape or the resin tape  23  is the direction where the metal tape or the resin tape  23  is rotating from one end to the other end when being viewed from the one end of the signal transmission cable  2 . 
     The shield layer  22  is configured in a substantially ellipse shape (rounded rectangle) in the cross-sectional view perpendicular to the cable longitudinal direction, and has a pair of flat areas  22   a  extending straight along an arrangement direction of the pair of signal lines  21 , and a pair of round areas  22   b  connecting the ends of the pair of flat areas  22   a  in one piece. 
     (Cable Core  4 ) 
     The cable core  4  is composed of the signal transmission cable  2  and a pair of power supply lines  3  stranded collectively (rigid strand). In other words, the signal transmission cable  2  and the power supply lines  3  are stranded with the same pitch. It is preferable that the stranding direction of the cable core  4  is the same as the wrapping direction of the metal tape that configures the shield layer  22 . This prevents the metal tape that configures the shield layer  22  from being opened (unwrapped) by stranding of the cable core  4 , so high frequency characteristics can be stabilized. Additionally, the stranding direction of the cable core  4  is the direction where the signal transmission cable  2  and the power supply lines  3  are rotating from one direction to the other, seeing from one end of the cable core  4 . 
     The pair of power supply lines  3  are arranged parallel to each other, and contacting to each other, and at the same time, they are arranged respectively contacting to the outer surface of the shield layer  22  of the signal transmission cable  2 . In other words, one power supply line  3 , the other power supply line  3 , and the signal transmission cable  2  are arranged sequentially in a cable circumferential direction, and the two power supply lines  3  and the signal transmission cable  2  are contacting to each other. The pair of power supply lines  3  are arranged respectively contacting to one of the flat areas  22   a  of the shield layer  22 . Additionally, the two power supply lines  3  can be stranded, but considering the downsizing of the composite cable  1  in diameter, and fixing the position of the signal transmission cable  2  (make it difficult to move) inside the cable core  4 , it is preferable that the two power supply lines  3  are arranged parallel to each other in the cable longitudinal direction. Also, the two power supply lines  3  are arranged so that the insulator  32  is contacting to the collective braided shield  5 . 
     Also, the arrangement direction of the pair of power supply lines  3  is almost equal to that of the pair of signal lines  21 , centers of the pair of power supply lines  3  (the position where the power supply lines  3  are contacting to each other) and centers of the pair of signal lines  21  (the position where the signal lines  21  are contacting to each other) are aligned perpendicular to the arrangement direction of the power supply lines  3  and the signal lines  21 . Therefore, the cable core  4  is configured in such a manner that a virtual line V connecting the centers of the pair of signal lines  21  and the centers of the pair of power supply lines  3  makes a trapezoid in the cross-sectional view perpendicular to the cable longitudinal directions. 
     (Collective Braided Shield  5 ) 
     The collective braided shield  5  covers around the cable core  4  entirely. The collective braided shield  5  is configured by braiding metal wires. As metal wire used for the collective braided shield  5 , annealed copper wire, copper alloy wire, aluminum wire, aluminum alloy wire, and the like can be used. Also, as metal wire used for the collective braided shield  5 , copper foil yarn which is a thread spirally wrapped by copper foil, can be used as well. 
     In the composite cable  1  according to the present embodiment, the collective braided shield  5  is configured closely contacting to the shield layer  22  in accordance with the outer shape of the shield layer  22  of the signal transmission cable  2 . Strictly speaking, an inner surface of the collective braided shield  5  is closely contacting over an entire outer surface (surface of the metal layer  222 ) of the flat area  22   a  on the side where the pair of power supply lines  3  are not contacting to, and over a part of the outer surface of the pair of round areas  22   b  (surface of the metal layer  222 ) at the both sides of the flat area  22   a  of the shield layer  22 . It is preferable that the collective braided shield  5  is closely contacting to at least more than half of the outer surface of the round areas  22   b . Additionally, “closely contacting” here means not only a case where two surfaces are contacting without a gap, but also a case where a little gap exists between them in the scope where the effects of the present invention described below are satisfied. In other words, a little gap between the shield layer  22  and the collective braided shield  5  is allowed as long as the effects of the present invention are not interfered. 
     Also, the composite cable  1  does not have a drain wire between the shield layer  22  and the collective braided shield  5 . If there is a drain wire between the shield layer  22  and collective braided shield  5 , a gap is made between the shield layer  22  and the collective braided shield  5 . As a result, high frequency characteristics may become unstable, because an electric potential difference is caused between the shield layer  22  and the collective braided shield  5 , or because the gap size is changed when the cable is bent or twisted. By configuring the collective braided shield  5  contacting to the outer shape of the shield layer  22  as the present embodiment, high frequency characteristics can be stably maintained even when the cable is bent or twisted. 
     Also, the collective braided shield  5  covers the entire cable core  4 , while contacting the outer surface of the pair of power supply lines  3  (an outer surface of the insulator  32 ). The collective braided shield  5  is configured in a substantially trapezoid shape (round trapezoid) in the cross-sectional view perpendicular to the cable longitudinal direction. By configuring the collective braided shield  5  in a substantially trapezoid shape as the present embodiment, the worker can easily see where the signal transmission cable  2  and the power supply lines  3  are arranged inside the composite cable  1 . Therefore, the workability in the terminal processing can be improved. 
     (Sheath  6 ) 
     The sheath  6  covers around the collective braided shield  5 . The sheath  6  not only protects the cable core  4  and the collective braided shield  5  but also presses inward the collective braided shield  5  so that it is closely contacting to the shield layer  22 . 
     The sheath  6  covers around the collective braided shield  5 , and its inner surface is configured along an outer shape of the collective braided shield  5  in substantially trapezoid shape in the cross-sectional view perpendicular to the cable longitudinal direction. Also, an outer surface of the sheath  6  is configured in a substantially circle shape in the cross-sectional view perpendicular to the cable longitudinal direction. In other words, the outer shape of the sheath  6  (an outer shape of the composite cable  1 ) is in a substantially circle shape in the cross-sectional view perpendicular to the cable longitudinal direction. It is preferable to make the sheath  6  by insert extrusion. By making the sheath  6  by insert extrusion, the outer shape of the sheath  6  can be a circle with very little gap between the sheath  6  and the collective braided shield  5 . The thickness of the sheath  6  is non-uniform along the cable circumferential direction. In concrete terms, the thickness of the sheath  6  is large in a part where the sheath  6  is covering the sides (straight sides in  FIG.  1   ) of the collective braided shield  5  of substantially trapezoid shape in the cross-sectional view perpendicular to the cable longitudinal direction, while the thickness of the sheath  6  is small in a part where the sheath  6  is covering the corners of the collective braided shield  5  (four round corners in  FIG.  1   ). 
     By configuring the sheath  6  in this structure, the sheath  6  tightens the collective braided shield  5  toward the cable core  4 , and thus, a gap cannot be generated between the collective braided shield  5  and the shield layer  22  (the collective braided shield  5  and the shield layer  22  are always closely contacting), even when the composite cable  1  is bent or twisted. As a result, the composite cable  1  can maintain the high frequency characteristics with very little deterioration, even if it is bend or twisted when wiring. Also, with a substantially circle shape as in the present embodiment, the composite cable  1  easy to wire even in a narrow space can be realized. Additionally, the cross-section (cross-sectional view perpendicular to the cable longitudinal direction) of the sheath  6  configured by tube extrusion can be in a substantially cylindrical shape, as long as the effects of the present invention are not interfered. 
     (Function and Effects of the Embodiment) 
     As explained above, the composite cable  1  in the present embodiment is composed of the pair of signal lines  21  that are arranged parallel to each other in the cable longitudinal direction and contacting to each other, the signal transmission cable  2  having the shield layer  22  that covers the pair of signal lines  21  collectively, and the pair of power supply lines  3  that are arranged contacting to each other and contacting to the shield layer  22  respectively, and the collective braided shield  5  that collectively covers around the cable core  4  having the signal transmission cable  2  and the pair of power supply lines  3 , the sheath  6  that covers the collective braided shield  5 . The collective braided shield  5  is configured closely contacting to the outer shape of the shield layer  22 . 
     Closely contacting the collective braided shield  5  and the shield layer  22 , for example, improves a fault that a gap between the collective braided shield  5  and the shield layer  22  is changed when the cable is bent or twisted, as in the case where a drain wire is installed between the collective braided shield  5  and the shield layer  22 . This improvement can realize the composite cable  1  whose high frequency characteristics are not easily deteriorated even if the cable is wired bent or twisted. Also, using a two-core parallel cable as the signal transmission cable  2  controls a length difference between the signal lines  21  and controls the deterioration of the high frequency characteristics due to skew. 
     Also, by configuring the pair of power supply lines  3  contacting to each other and the pair of power supply lines  3  contacting to the signal transmission cable  2  respectively, for example, compared with a case where the signal transmission cable  2  is placed between the pair of power supply lines  3 , the composite cable  1  with a smaller diameter can be produced so that the composite cable  1  can be easily wired even in a narrow space. Moreover, by closely contacting the collective braided shield  5  and the shield layer  22 , the diameter of the composite cable  1  can be further downsized. 
     SUMMARY OF THE EMBODIMENT 
     Technical ideas understood from the embodiment will be described below citing the reference numerals, etc., used for the embodiment. However, each reference numeral described below is not intended to limit the constituent elements in the claims to the members, etc., specifically described in the embodiment. 
     [1] A composite cable ( 1 ) comprising: a signal transmission cable ( 2 ) including a pair of signal lines ( 21 ) being arranged parallel to each other in a cable longitudinal direction and contacting to each other and a shield layer ( 22 ) covering the pair of signal lines ( 21 ) together; a pair of power supply lines ( 3 ) being arranged contacting to each other and contacting to the shield layer ( 22 ); a collective braided shield ( 5 ) covering around a cable core ( 4 ) comprising the signal transmission cable ( 2 ) and the pair of power supply lines ( 3 ) collectively; and a sheath ( 6 ) covering around the collective braided shield ( 5 ), wherein the collective braided shield ( 5 ) is configured closely contacting to the shield layer ( 22 ) in accordance with an outer shape of the shield layer ( 22 ). 
     [2] The composite cable according to [1], wherein the cable core ( 4 ) is configured in such a manner that virtual lines (V) connecting centers of the pair of signal lines ( 21 ) and centers of the pair of power supply lines ( 3 ) make a trapezoid shape in the cross-sectional view perpendicular to the cable longitudinal direction. 
     [3] The composite cable according to [1] or [2], wherein the shield layer ( 22 ) includes as one piece a pair of flat areas ( 22   a ) extending straight along an arrangement direction of the pair of signal lines ( 21 ) and a pair of round areas ( 22   b ) connecting ends of the pair of flat areas ( 22   a ), wherein the pair of power supply lines ( 3 ) are arranged contacting to one of the flat areas ( 22   a ), wherein the collective braided shield ( 5 ) is closely contacting to an entire part of the flat area ( 22   a ) at a side where the pair of power supply lines ( 3 ) are not contacting to and to a part of the pair of round areas ( 22   b ) at both sides of the flat areas ( 22   a ). 
     [4] The composite cable  1  according to any one of [1] to [3], wherein each of the pair of signal lines ( 21 ) comprises a signal conductor ( 211 ) and an insulator ( 212 ) covering around the signal conductor ( 211 ), wherein the insulator ( 212 ) comprises an inner insulator ( 212   a ) covering around the signal conductor ( 211 ), and an outer insulator ( 212   b ) covering around the inner insulator ( 212   a ), wherein the outer insulator ( 212   b ) has a lower melting point than a melting point of the inner insulator ( 212   a ). 
     [5] The composite cable  1  according to [4], wherein the inner insulator ( 212   a ) has a lower permittivity than a permittivity of the outer insulator ( 212   b ). 
     [6] The composite cable  1  according to any one of [1] to [5], wherein the signal transmission cable ( 2 ) further comprises a resin tape ( 23 ) spirally wrapping around the pair of signal lines ( 21 ), wherein the shield layer ( 22 ) comprises a metal tape on which a metal layer ( 222 ) is provided on one side of a resin layer ( 221 ) and an adhesive layer ( 223 ) is provided on an other side of the resin layer ( 221 ), and configured by spirally wrapping the metal tape around the resin tape ( 23 ) in such a manner that the adhesive layer ( 223 ) is provided at a side of the resin tape ( 23 ). 
     Although the embodiment of the invention has been described, the invention according to claims is not to be limited to the embodiment described above. Further, please note that not all combinations of the features described in the embodiment are necessary to solve the problem of the invention. 
     The invention can be appropriately modified and implemented without departing from the gist thereof. For example, in the above embodiment, a case where the insulator  212  of the signal lines  21  is composed of two layers is explained, but the insulator  212  of the signal lines  21  can be composed of three or more layers.