Patent Publication Number: US-9905330-B2

Title: Flexible cable

Description:
The present application is based on Japanese patent application No. 2015-254821 filed on Dec. 25, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to flexible cables handled manually by a human operator. 
     2. Description of the Related Art 
     In, for example, a health care site, health care professionals, such as doctors or nurses, are required to manually handle cables in some cases. For example, when providing an ultrasonic diagnosis, a health care professional has to manually handle a probe cable when applying a probe to an affected area. When providing endoscopy, a health care professional has to manually handle an endoscopic cable to insert an endoscope into the body. A flexible cable is thus used as a cable that requires manual handling, the flexible cable including an outer sheath made of a highly flexible material such as polyurethane resin, silicone rubber, a compound of styrene-based rubber and polypropylene resin, a compound of styrene-based rubber and polystyrene resin, or plasticized polyvinyl chloride (see, for example, Japanese Unexamined Patent Application Publication No. H5-205537). 
     SUMMARY OF THE INVENTION 
     However, a flexible cable including an outer sheath made of polyurethane resin, silicone rubber, a compound of styrene-based rubber and polypropylene resin, or a compound of styrene-based rubber and polystyrene resin is disadvantageous in that a human operator feels unsmoothness while manually handling the flexible cable because the outer sheath has a sticky surface. In the case of a flexible cable including an outer sheath made of plasticized polyvinyl chloride, the surface of the outer sheath is not sticky. However, the outer sheath made of plasticized polyvinyl chloride has lower thermal resistance than the outer sheet made of polyurethane resin, silicone rubber, a compound of styrene-based rubber and polypropylene resin, or a compound of styrene-based rubber and polystyrene resin. Thus, the outer sheath made of plasticized polyvinyl chloride is disadvantageous in that it may be damaged while being sterilized using an autoclave. 
     Accordingly, it is an object of the present invention to provide a flexible cable that is smoothly movable while being manually handled by a human operator and having an outer sheath that is less likely to be damaged while being sterilized using an autoclave. 
     The present invention is a flexible cable including an outer sheath at an outermost layer, the outer sheath including an inner layer made of an elastomer containing polypropylene resin and an outer layer surrounding the inner layer and made of polypropylene resin. 
     Desirably, the outer layer has a large number of cracks in a surface of the outer layer. 
     Desirably, the outer layer has a layer thickness of more than 0 μm and less than or equal to 100 μm. 
     Desirably, the outer layer is fusion-bonded with the inner layer. 
     The present invention is capable of providing a flexible capable that is smoothly movable while being manually handled by a human operator and having an outer sheath that is less likely to be damaged while being sterilized using an autoclave. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other exemplary purposes, aspects and advantages will be better understood from the following detailed description of the invention with reference to the drawings, in which: 
       FIGURE is a cross-sectional view of a flexible cable according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and more particularly to FIGURE, there is shown exemplary embodiments of the methods and structures according to the present invention. 
     An embodiment of the present invention is described below in accordance with the appended drawing. 
     As illustrated in FIGURE, a flexible cable  100  according to an embodiment of the present invention includes, for example, a strand  102  obtained by stranding multiple core wires  101  up, a first tape  103  wound around the strand  102 , a braid shield  104  disposed around the first tape  103 , a second tape  105  wound around the braid shield  104 , and an outer sheath  106  disposed around the second tape  105 . 
     The flexible cable  100  according to the embodiment of the present invention includes an outer sheath  106  at least at the outermost layer. The outer sheath  106  has a double layer structure including an inner layer  107 , made of an elastomer containing polypropylene resin, and an outer layer  108 , disposed around the inner layer  107  and made of polypropylene resin. 
     Examples of an elastomer containing polypropylene resin include Rabalon (registered trade mark), which is a compound of styrene-based rubber and polypropylene resin. Rabalon is a material having flexibility as high as the flexibility of a material such as polyurethane resin, silicone rubber, a compound of styrene-based rubber and polystyrene resin, or plasticized polyvinyl chloride. Moreover, Rabalon is a material having thermal resistance as high as the thermal resistance of silicone rubber, a compound of styrene-based rubber and polypropylene resin, or a compound of styrene-based rubber and polystyrene resin. Thus, using the inner layer  107  made of Rabalon can reliably provide the outer sheath  106  with flexibility and thermal resistance. 
     Rabalon, however, is a material having slidability as low as the slidability of a material such as polyurethane resin, silicone rubber, a compound of styrene-based rubber and polypropylene resin, or a compound of styrene-based rubber and polystyrene resin. Thus, when only the inner layer  107  made of Rabalon is used as an outer sheath, a human operator feels unsmoothness while manually handling the flexible cable because the outer sheath has a sticky surface. Thus, in the flexible cable  100  according to the embodiment of the present invention, a thin outer layer  108  made of polypropylene resin, which is a material having high thermal resistance and high slidability, is disposed around the inner layer  107  made of Rabalon to coat the inner layer  107 . 
     Desirably, the outer layer  108  has a large number of cracks  109  in its surface. If the outer layer  108  has a large number of cracks  109  in its surface, the outer sheath  106  can have a smaller friction coefficient since the area over which the outer sheath  106  is brought into contact with other object is reduced. Thus, a human operator is less likely to feel unsmoothness while manually handling the flexible cable  100 . 
     Desirably, the outer layer  108  has a layer thickness of more than 0 μm and less than or equal to 100 μm, more desirably, more than 0 μm and less than or equal to 50 μm. The reason why the layer thickness of the outer layer  108  of more than 0 μm and less than or equal to 100 μm is desirable is described as follows. If the layer thickness of the outer layer  108  exceeds 100 μm, the outer sheath  106  is more likely to have a protuberance (crease) as a result of the flexible cable  100  being bent. Thus, the outer sheath  106  is more likely to be easily foldable at a particular portion and may be broken at the portion. The reason why the layer thickness of the outer layer  108  of more than 0 μm and less than or equal to 50 μm is more desirable is because, a large number of cracks  109  are more likely to naturally occur in the surface of the outer layer  108  as the outer layer  108  has a smaller layer thickness. 
     Desirably, the outer layer  108  is fusion-bonded with the inner layer  107 . By concurrently performing tube extrusion of the outer layer  108  and the inner layer  107  to surround the second tape  105 , the outer layer  108  can be fusion-bonded with the inner layer  107  using the extrusion heat. When the outer layer  108  is fusion-bonded with the inner layer  107 , the outer layer  108  is brought into close contact with the inner layer  107 . Thus, the outer layer  108  is not separated from the inner layer  107  even when a large number of cracks  109  occur in the surface of the outer layer  108 . Thus, the outer layer  108  can reliably fulfill its function. 
     As described above, the flexible cable  100  according to an embodiment of the present invention includes the outer sheath  106  having an unsticky surface while having high flexibility and high thermal resistance as a whole. Thus, a human operator is less likely to feel unsmoothness while manually handling the flexible cable  100  and the outer sheath  106  is less likely to be damaged while being sterilized using an autoclave. 
     Although the invention has been described with respect to specific exemplary embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth. 
     Further, it is noted that Applicant&#39;s intent is to encompass equivalents of all claim elements, even if amended later during prosecution.