Patent Publication Number: US-7211731-B2

Title: Cable with waterproof plug, connector cable with waterproof plug, manufacturing method of cable with waterproof plug, and connection structure between cable with waterproof plug and terminal

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a cable with a waterproof plug, a connector cable with a waterproof plug, a manufacturing method of a cable with a waterproof plug, and a connection structure between a cable with a waterproof plug and a terminal. 
   2. Description of Related Art 
   Connectors used in cars, portable devices, etc., are required to be waterproof for preventing water or the like from entering to cause a short circuit. 
   Cables used for connectors are generally classified into cables substantially circular in cross section and cables substantially rectangular in cross section such as flexible flat cables (FFCs) and flexible printed circuits (FPCs). The former and the latter differ in manner of being attached to connector housings. 
   In case of cables substantially circular in cross section, in general, a terminal is connected to one end of a cable and the terminal is inserted into a terminal receiving chamber formed in a connector housing. To give waterproofness to such a cable, for example, JP-A-7-245149 discloses a technique in which a waterproof plug is interposed between the cable and a terminal. In this technique, the waterproof plug has a crimp connection portion at its one end and a seal portion at its other end. After the waterproof plug is fitted on one end portion of the cable, one end of the terminal is wound on the outer circumferential surface of the connection portion of the waterproof plug and then the one end of the terminal is crimped. The connection portion of the waterproof plug is thereby also crimped with the one end of the terminal, so that three of the cable, waterproof plug, and terminal are fixed to one another. In this state, the terminal is inserted from its other end into a terminal receiving chamber of a connector housing. The outer circumferential surface of the seal portion of the waterproof plug is brought into close contact with the inner surface of the wall of the terminal receiving chamber so that water or the like can be prevented from entering the terminal receiving chamber. 
   In the above-described technique, however, the connection portion of the waterproof plug must have a sufficiently large thickness in order not to be broken when being crimped. Further, the seal portion of the waterproof plug has its outer diameter larger than that of the connection portion. In case of a connector provided with cables each having such a waterproof plug, therefore, the cables must be arranged at relatively wide intervals. This makes it difficult to attempt a decrease in size of such a connector. 
   Further, in the above-described technique, the cable and the waterproof plug are not fixed to each other before being crimped. They are fixed to each other by crimping. Thus, the waterproof plug may shift from its predetermined position when being crimped. This causes a problem of bad positional accuracy of such a waterproof plug. 
   Furthermore, in the above-described technique, one end of the terminal is made into a form that can be wound on the outer circumferential surface of the waterproof plug. However, if the cable has no need of waterproofness, that is, if no waterproof plug is used, a terminal must be used whose one end is made into another form, for example, that can be wound on the outer circumferential surface of the cable. Thus, terminals having different shapes must be prepared for cases of requiring waterproofness and not requiring waterproofness. This causes a problem of an increase in cost. 
   On the other hand, in case of cables substantially rectangular in cross section such as FFCs and FPCs, in general, a cable itself is inserted into a connector housing with using no terminal. To give waterproofness to such a connector structure, a technique is known in which a gelatinous sealing agent is interposed between the cable and the inner surface of the connector housing. However, such a gelatinous sealing agent can not be reused after the cable is detached from the connector housing. Thus, a fresh sealing agent must be used every time when the cable is attached to the connector housing. This causes an increase in cost. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a cable with a waterproof plug, a connector cable with a waterproof plug, a manufacturing method of a cable with a waterproof plug, and a connection structure between a cable with a waterproof plug and a terminal, capable of realizing a decrease in size of a connector, improvement of positional accuracy of the waterproof plug, and a decrease in cost. 
   According to an aspect of the present invention, a cable with a waterproof plug comprises a cable including a wire and an insulating coating covering an outer circumferential surface of the wire; and a waterproof plug made of an elastic material. The waterproof plug is formed integrally with the cable so as to cover an outer circumferential surface of the insulating coating in an annular region along the length of the cable. 
   According to the invention, the waterproof plug is not fixed to the cable by crimping but formed integrally with the cable. Thus, the thickness of the waterproof plug can be relatively small because the waterproof plug need not be endure such a crimping operation. As a result, when cables each provided with a waterproof plug are arranged to a connector, each interval between neighboring cables can be relatively narrow. Thus, a decrease in size of the connector can be realized. 
   In addition, because the waterproof plug has been already fixed to the cable before the terminal is connected to the cable, the waterproof plug scarcely shifts from its predetermined position when the terminal is connected to the cable. Thus, the positional accuracy of the waterproof plug is improved. 
   Further, when the terminal is connected to the cable with the waterproof plug, one end of the terminal need not be wound on the outer circumferential surface of the waterproof plug. This is because the waterproof plug has been already fixed to the cable before the terminal is connected to the cable, and thus the waterproof plug need not be fixed to the cable with the terminal. Therefore, in either of cases of requiring waterproofness and not requiring waterproofness, the same terminal can be used. This can bring about a decrease in cost. 
   Furthermore, in case of a cable substantially rectangular in cross section such as an FFC or FPC, because the waterproof plug made of an elastic material has been united to the cable without using any gelatinous sealing agent, an increase in cost due to repetitions of the inserting and drawing-out operations of the cable can be suppressed. This is because the waterproof plug made of the elastic material can be reused differently from such a gelatinous sealing agent, which can not be reused after the cable is once detached. 
   According to another aspect of the present invention, a connector cable with a waterproof plug comprises a cable including a wire and an insulating coating covering an outer circumferential surface of the wire; and a waterproof plug made of an elastic material. The waterproof plug is formed integrally with the cable so as to cover an outer circumferential surface of the insulating coating in an annular region along the length of the cable. The connector cable with the waterproof plug further comprises a terminal connected to the cable at a position nearer to one end of the cable than the portion where the waterproof plug is formed. 
   According to the invention, a decrease in size of a connector and improvement of positional accuracy of the waterproof plug can be realized for the same reasons as those described above. In addition, because the same terminal can be used in either of cases of requiring waterproofness and not requiring waterproofness, a decrease in cost can be realized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other and further objects, features and advantages of the invention will appear more fully from the following description taken in connection with the accompanying drawings in which: 
       FIG. 1  is a partial perspective view of a connector cable with a waterproof plug according to a first embodiment of the present invention; 
       FIG. 2A  is a partial vertical sectional view showing a state in which a terminal shown in  FIG. 1  has been inserted in a terminal receiving chamber of a connector; 
       FIG. 2B  is a sectional view taken along line B—B in  FIG. 2A ; 
       FIG. 3  is a partial plan view of the cable of  FIG. 1  on which the waterproof plug has not yet been formed; 
       FIG. 4A  is a partial plan view showing a state in which three cables of  FIG. 3  are being held with a jig; 
       FIG. 4B  is a partial sectional view taken along line B—B in  FIG. 4A ; 
       FIG. 5  is a partial sectional view showing a state in which a cable being held with the jig shown in  FIGS. 4A and 4B  has been set in a mold of an injection molding machine; 
       FIG. 6  is a partial side view showing a state in which a waterproof plug has been formed on the cable with the injection molding machine shown in  FIG. 5 ; 
       FIG. 7  is a partial side view showing a state in which a terminal has been connected to the cable with the waterproof plug shown in  FIG. 6 ; 
       FIG. 8  is a partial perspective view of a cable with a waterproof plug according to a second embodiment of the present invention, in which an FFC is used as the cable; 
       FIG. 9  is a partial perspective view of a cable with a waterproof plug according to a third embodiment of the present invention, in which an FPC is used as the cable; and 
       FIG. 10  is a table showing results of measurement of adhesive forces by various materials between cables and waterproof plugs according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, preferred embodiments of the present invention will be described. 
   First, a connector cable with a waterproof plug according to a first embodiment of the present invention will be described with reference to  FIGS. 1 ,  2 A, and  2 B, in which the whole of the connector cable and the waterproof plug is denoted by reference numeral  1 . As shown in  FIG. 1 , the connector cable of this embodiment includes a cable  11  and a terminal  2 . The cable  11  is provided near its one end with a waterproof plug  15  formed integrally with the cable  11 . The whole of the cable  11  and the waterproof plug  15  is denoted by reference numeral  10 . The terminal  2  is connected to the one end of the cable  11 . More specifically, the terminal  2  is connected to the cable  11  on the front side of the portion where the waterproof plug  15  is formed. 
   As shown in  FIG. 2B , the cable  11  includes therein seven wires  12  and an insulating coating  13  covering the wires  12 . The cable  11  is substantially circular in cross section. For example, it has an outer diameter of about 1.6 mm and a length of about 200 mm. The insulating coating  13  has also a function of electrically insulating the wires  12  from one another. 
   The material of the insulating coating  13  can be adequately selected in accordance with the material of the waterproof plug  15 , the adhesive component for bonding the insulating coating  13  and the waterproof plug  15  to each other, etc., as will be described later. In particular, from the viewpoint of the adhesive force to the waterproof plug  15 , the main component of the insulating coating  13  is preferably one of a polyethylene (PE) resin, a polyvinyl chloride (PVC) resin, a polyethylene terephthalate (PET) resin, a polyethylene naphthalate (PEN) resin, and a polyimide (PI) resin. Of them, a PET resin, a PEN resin, or a PI resin is more preferable. 
   As shown in  FIG. 1 , the waterproof plug  15  is disposed near one end of the cable  11 , more specifically, at a position somewhat distant from the one end toward the other end of the cable  11 . As shown in  FIGS. 2A and 2B , the waterproof plug  15  is cylindrical to cover the insulating coating  13 . 
   As shown in  FIG. 2A , an adhesive layer  20  is disposed between the outer circumferential surface of the cable  11  and the inner circumferential surface of the waterproof plug  15 , that is, at the interface between the cable  11  and the waterproof plug  15 . The waterproof plug  15  and the cable  11  are united with the adhesive component of the adhesive layer  20 . The adhesive layer  20  is made of, for example, a silane coupling agent having vinyl groups. 
   As shown in  FIG. 2A , the waterproof plug  15  has an expansion/contraction portion  18  and an annular portion  19  in this order from the one end toward the other end of the cable  11 . On the outer circumferential surface of the expansion/contraction portion  18 , peaks  18   a  and troughs  18   b  are alternately formed along the length of the cable  11 . The annular portion  19  has its outer circumferential surface even in height. The largest outer diameter of the expansion/contraction portion  18 , that is, the outer diameter at each peak  18   a , is the same as the outer diameter of the annular portion  19 . The largest outer diameter of the expansion/contraction portion  18  is somewhat larger than the diameter of a terminal receiving chamber  100  formed in a not-shown connector. 
   When the terminal  2  is being inserted in the terminal receiving chamber  100 , each peak  18   a  of the expansion/contraction portion  18  of the waterproof plug  15  is brought into contact with the wall  100   a  of the terminal receiving chamber  100  so that the vicinity of each peak  18   a  is radially pressed and contracted. Attendant upon this deformation of the vicinity of each peak  18   a , the expansion/contraction portion  18  is expanded as a whole along the length of the cable  11 . At this time, the annular portion  19  is also brought into contact with the wall  100   a  and thereby radially pressed and contracted. 
   As shown in  FIGS. 2A and 2B , in a state in which the terminal  2  has been inserted in the terminal receiving chamber  100 , the outer circumferential surface of the waterproof plug  15  is in close contact with the inner surface of the wall  100   a  of the terminal receiving chamber  100 . Thus, water or the like is prevented from entering the terminal receiving chamber  100 . 
   The waterproof plug  15  is made of an elastic material. In particular, the waterproof plug  15  is preferably made of a thermosetting elastomer or a thermoplastic elastomer. As the thermosetting elastomer, addition reaction type silicone rubber, the setting temperature of which can be relatively easily selected, is preferably used in order that the insulating coating  13  can not be expanded by heat when the waterproof plug  15  is formed with a mold  41  as described later. The main component of the addition reaction type silicone rubber is dimethyl polysiloxane. As the thermoplastic elastomer, one of styrene base, polyester base, polyamide base, and polyurethane base is preferably used from the view point of its adhesive force. 
   As shown in  FIG. 1 , the terminal  2  has a rectangular pipe-shaped terminal body  3 , an interconnecting portion  6  nearly U-shaped in cross section, extending horizontally from a lower portion of the terminal body  3 , a pair of left and right wire crimping portions  4  connected to the terminal body  3  by the interconnecting portion  6 , an interconnecting portion  7  extending horizontally from a lower portion of the wire crimping portions  4 , and a pair of cable crimping portions  5  connected to the wire crimping portions  4  by the interconnecting portion  7 . 
   Each of the wire crimping portions  4  is curved inward for crimping the wires  12  exposed from the one end of the cable  11 . The cable crimping portions  5  are for crimping the insulating coating  13  in the vicinity of the one end of the cable  11 . The cable crimping portions  5  are arranged along the length of the terminal  2  to be wound on the outer circumferential surface of the insulating coating  13  counterclockwise and clockwise from the lower portion of the insulating coating  13 , respectively. More specifically, as shown in  FIGS. 1 and 2A , the cable crimping portions  5  are disposed nearer to the one end of the cable  11  than the waterproof plug  15  to neighbor the waterproof plug  15 . 
   The cable crimping portions  5  provided at one end of the terminal  2  crimp the outer circumference of the cable  11  and thereby the terminal  2  is fixed to the one end portion of the cable  11 . That is, the one end portion of the terminal  2  is wound on not the outer circumferential surface of the waterproof plug  15  but the outer circumferential surface of the insulating coating  13  of the cable  11 . Thus, in a state in which the terminal  2  has been connected to the one end of the cable  11 , as shown in  FIGS. 2A and 2B , the largest outer diameter D of the cable crimping portion  5  is equal to the sum of the outer diameter of the cable  11  and the thickness of the cable crimping portion  5 . 
   As described above, in the cable with the waterproof plug of this embodiment, the waterproof plug  15  is not fixed to the cable  11  by crimping but formed integrally with the cable  11 . Thus, the thickness of the waterproof plug  15  can be relatively small because the waterproof plug  15  need not be endure such a crimping operation. As a result, when cables  11  each provided with a waterproof plug  15  are arranged to a connector, each interval between neighboring cables  11  can be relatively narrow. Thus, a decrease in size of the connector can be realized. 
   In addition, because the waterproof plug  15  has been already fixed to the cable  11  before the terminal  2  is connected to the cable  11 , the waterproof plug  15  scarcely shifts from its predetermined position when the terminal  2  is connected to the cable  11 . Thus, the positional accuracy of the waterproof plug  15  is improved. 
   Further, when the terminal  2  is connected to the cable  11 , one end of the terminal  2  need not be wound on the outer circumferential surface of the waterproof plug  15 . This is because the waterproof plug  15  has been already fixed to the cable  11  before the terminal  2  is connected to the cable  11 , and thus the waterproof plug  15  need not be fixed to the cable  11  with the terminal  2 . Therefore, in either of cases of requiring waterproofness and not requiring waterproofness, the same terminal  2  can be used. This can bring about a decrease in cost. 
   Furthermore, because the waterproof plug  15  is made of an elastic material, the cable  11  can be smoothly inserted in and drawn out from the terminal receiving chamber  100  of the connector with the waterproof plug  15  being elastically deformed as described above. At this time, because the outer circumferential surface of the waterproof plug  15  is brought into close contact with the inner surface of the wall  100   a  of the terminal receiving chamber  100 , the waterproofness can be ensured. Besides, even when the inserting and drawing-out operations are repeated, the waterproofness with the waterproof plug  15  is hard to be deteriorated. 
   Furthermore, the waterproof plug  15  is united to the cable  11  with the adhesive layer  20  provided at the interface between the cable  11  and the waterproof plug  15 . This realizes sure fixture between the waterproof plug  15  and the cable  11 . 
   Next, an example of a manufacturing method of the cable with the waterproof plug of this embodiment will be described with reference to  FIGS. 3 ,  4 A,  4 B,  5 , and  6 . 
   First, a cable  11  in which seven wires  12  are covered with an insulating coating  13 , though  FIG. 3  shows only some of the wires  12 , is cut into a predetermined length, for example, about 200 mm. The outer circumferential surface of the insulating coating  13  is then degreased with a degreaser such as isopropyl alcohol. 
   An adhesive, for example, a silane coupling agent having vinyl groups, is applied with a brush or the like even on the outer circumferential surface of the cable  11  at the portion where a waterproof plug will be formed. The adhesive is then dried to form an adhesive layer  20  as shown in  FIG. 2A . 
   Next, as shown in  FIGS. 4A and 4B , three such cables  11  are held with a jig  31 . 
   The jig  31  is made up of a pair of upper and lower substantially rectangular parallelepiped slender members  31   a  and  31   b  separable from each other. Through-holes are formed near both ends in the length of each of the slender members  31   a  and  31   b . A female screw is formed on the inner surface of each through-hole. Three recesses  33  are formed on the face of each of the slender members  31   a  and  31   b  to be opposed to each other. Each recess  33  extends in the width of the slender member  31   a  or  31   b . The recesses  33  are arranged at regular intervals along the length of the slender member  31   a  or  31   b . Each recess  33  is semicircular in cross section to form a circle of substantially the same diameter as the outer diameter of each cable  11  in cooperation with the corresponding recess  33  when the slender members  31   a  and  31   b  are united to each other. 
   To hold the cables  11  with the jig  31 , first, the vicinities of one ends of the three cables  11  are put in the respective recesses  33  formed on the lower slender member  31   b . At this time, each cable  11  is disposed so as to across the slender member  31   b . Afterward, the upper slender member  31   a  is put on the lower slender member  31   b  to sandwich the cables  11 . A wing bolt is then screwed into each through-hole of the slender members  31   a  and  31   b . The slender members  31   a  and  31   b  are thereby united to each other and the cables  11  are vertically pressed by the slender members  31   a  and  31   b . As a result, as shown in  FIG. 4A , the three cables  11  are held in a state of being arranged parallel to one another at regular intervals. 
   Next, as shown in  FIG. 5 , the cables  11  being held with the jig  31  are set in a mold  41  of an injection molding machine  40 . 
   The mold  41  is made up of a pair of upper and lower parts  41   a  and  41   b  separable from each other. On a face of each of the upper and lower parts  41   a  and  41   b  to be opposed, three cable receiving portions  48  are formed at the same intervals as the intervals between the three cables  11  being held with the jig  31 , though  FIG. 5  shows only one cable receiving portion  48 . Each cable receiving portion  48  is semicircular in cross section to form a circle of substantially the same diameter as the outer diameter of each cable  11  in cooperation with the corresponding cable receiving portion  48  when the upper and lower parts  41   a  and  41   b  are united to each other. 
   Substantially at the center of the length of each cable receiving portion  48 , to form a waterproof plug  15 , a cavity  42  having a shape corresponding to the waterproof plug  15  is formed. In other words, the cavity  42  is formed by recessing the wall of the cable receiving portion  48  substantially at the center of the length of the cable receiving portion  48 . 
   In the upper face of the mold  41 , a recess  43  is formed that can be fitted on the bottom of a material injection unit  45  of the injection molding machine  40 . The recess  43  is connected to the cavity  42  through an interconnecting hole  44 . Thus, the material of the waterproof plug  15  can be injected from the material injection unit  45  of the injection molding machine  40  to the cavity  42  through the interconnecting hole  44 . 
   To set the cables  11  in the mold  41  of the injection molding machine  40 , first, the three cables  11  are put in the respective cable receiving portions  48  formed in the lower part  41   b  of the mold  41 . At this time, the portion of each cable  11  where the adhesive layer  20  as shown in  FIG. 2A  has been formed is disposed in the corresponding cavity  42 . Afterward, the upper part  41   a  of the mold  41  is put on the lower part  41   b  to sandwich the cables  11 . Each cable  11  is thereby fixed at a predetermined position. 
   The material injection unit  45  of the injection molding machine  40  is then moved down so that the bottom of the material injection unit  45  is fitted in the recess  43 . Afterward, the material of the waterproof plugs  15  fed in the injection molding machine  40  is injected from material injection unit  45  to each cavity  42  of the mold  41  through the corresponding interconnecting hole  44 . The mold  41  in which the material has been injected is then heated to a temperature at which the insulating coating  13  of each cable  11  can not expand, for example, 120 degrees C. or less in case of the insulating coating  13  made of RVC. The material is thereby set. Afterward, the cables  11  are removed from the mold  41  of the injection molding machine  40 . In this manner, a cable with a waterproof plug of this embodiment is manufactured as shown in  FIG. 6 . 
   Afterward, as shown in  FIG. 6 , the insulating coating  13  of one end portion of the cable  11  is removed by a predetermined length to expose the wires  12 . The exposed wires  12  are crimped with the wire crimping portions  4  of a terminal  2  and the insulating coating  13  near the one end of the cable  11  is crimped with the cable crimping portions  5  of the terminal  2 . By thus connecting the terminal  2  to the one end of the cable  11 , a connector cable with a waterproof plug of this embodiment is manufactured as shown in  FIG. 7 . 
   In the cable with the waterproof plug of the above-described first embodiment, the waterproof plug  15  is fixed to the cable  11  with the adhesive layer  20  provided at the interface between the cable  11  and the waterproof plug  15 . However, the present invention is not limited to this structure. For example, a modification is thinkable in which the waterproof plug  15  is fixed to the cable  11  with an adhesive component existing not only the surface of the waterproof plug  15  but also the interior of the waterproof plug  15 . An example of a manufacturing method of a cable with a waterproof plug of this case will be described below. 
   First, the material of the waterproof plug  15  and an adhesive, for example, a silane coupling agent having vinyl groups, are fed in the injection molding machine  40 , and they are stirred and mixed. A cable  11  is cut into a predetermined length and the outer circumferential surface of the insulating coating  13  is degreased, like the above-described example. 
   Afterward, like the above-described example, cables  11  being held with the jig  31  are set in the mold  41  of the injection molding machine  40 . The stirred and mixed material is injected from the material injection unit  45  of the injection molding machine  40  into each cavity  42  of the mold  41 . The mold  41  in which the material has been injected is then heated to a temperature at which the insulating coating  13  of each cable  11  can not expand. The material is thereby set. Afterward, the cables  11  are removed from the mold  41  of the injection molding machine  40 . In this manner, a cable with a waterproof plug is manufactured in which an adhesive component exists substantially even on the surface and in the interior of the waterproof plug  15 . Afterward, like the above-described example, the wires  12  are exposed and a terminal  2  is connected to one end of the cable. In this manner, a connector cable with a waterproof plug is manufactured. 
   In case that an adhesive component exists substantially even on the surface and in the interior of the waterproof plug  15  as described above, the steps of applying an adhesive to the outer circumferential surface of the cable and drying the adhesive can be omitted and thus the manufacturing time can be shortened. More specifically, the step of mixing the material of the waterproof plug  15  and the adhesive with each other can be carried out, for example, while the cables  11  are set in the mold  41 . 
   Next, a cable with a waterproof plug according to a second embodiment of the present invention will be described with reference to  FIG. 8 . In this embodiment, an FFC  51  substantially rectangular in cross section is used as a cable, and a waterproof plug  55  made of an elastic material is formed near one end of the FFC  51  integrally with the FFC  51 . The whole of the FFC  51  and the waterproof plug  55  is denoted by reference numeral  50 . 
   The FFC  51  includes therein three wires  52  and includes an insulating coating  53  covering the wires  52 . Each wire  52  is substantially circular in cross section. The wires  52  are arranged substantially at regular intervals. 
   The waterproof plug  55  is cylindrical to cover the insulating coating  53  of the FFC  51  though the waterproof plug  55  differs in shape from the waterproof plug  15  of the first embodiment because the cables of both embodiments differ in structure. The waterproof plug  55  has an expansion/contraction portion  58  and an annular portion  59  like the expansion/contraction portion  18  and the annular portion  19  of the first embodiment. More specifically, peaks  58   a  and troughs  58   b  are alternately formed on the outer surface of the expansion/contraction portion  58  along the length of the cable  51 . The annular portion  59  has its outer surface even in height. The largest outer diameter of the expansion/contraction portion  58 , that is, the outer diameter at each peak  58   a , is the same as the outer diameter of the annular portion  59 . 
   Next, a cable with a waterproof plug according to a third embodiment of the present invention will be described with reference to  FIG. 9 . In this embodiment, an FPC  71  substantially rectangular in cross section is used as a cable, and a waterproof plug  75  made of an elastic material is formed integrally with the FPC  71  to cover the outer surface of the FPC  71 . The whole of the FPC  51  and the waterproof plug  75  is denoted by reference numeral  70 . 
   The FPC  71  includes therein three wires  72  and includes an insulating coating  73  covering the wires  72 . Each wire  72  is laterally oblong, substantially rectangular in cross section. The wires  72  are arranged substantially at regular intervals. 
   The waterproof plug  75  is cylindrical to cover the insulating coating  73  of the FPC  71 , like the waterproof plug  55  of the second embodiment. The waterproof plug  75  has an expansion/contraction portion  78  and an annular portion  79  like the expansion/contraction portion  58  and the annular portion  59  of the second embodiment. More specifically, peaks  78   a  and troughs  78   b  are alternately formed on the outer surface of the expansion/contraction portion  78  along the length of the cable  71 . The annular portion  79  has its outer surface even in height. The largest outer diameter of the expansion/contraction portion  78 , that is, the outer diameter at each peak  78   a , is the same as the outer diameter of the annular portion  79 . 
   In the second or third embodiment, a not-shown adhesive layer like the adhesive layer  20  of the first embodiment is formed at the interface between the cable  51  or  71  and the waterproof plug  55  or  75 . The waterproof plug  55  or  75  is united to the cable  51  or  71  with the adhesive component of the adhesive layer. 
   As for a manufacturing method of the cable with the waterproof plug of the second or third embodiment, if the shapes of each recess  33  of the jig  31 , each cavity  42  of the mold  41 , and so on, are changed so as to correspond to the shape of the cable  51  or  71 , the same manufacturing method as that in the above-described first embodiment can be adopted. 
   In case of the cable  51  or  71  substantially rectangular in cross section as in the above-described second or third embodiment, because the waterproof plug  55  or  75  made of an elastic material has been united to the cable  51  or  71  without using any gelatinous sealing agent, an increase in cost due to repetitions of the inserting and drawing-out operations of the cable can be suppressed. This is because the waterproof plug  55  or  75  made of the elastic material can be reused differently from such a gelatinous sealing agent, which can not be reused after the cable is once detached. 
   Next, specific examples of the present invention will be described. 
   EXAMPLE 1  
   A cable having a diameter of 1.6 mm phi and including an insulating coating made of a PVC resin was cut into a length of about 200 mm. The outer circumferential surface of the insulating coating was degreased with isopropyl alcohol. Afterward, an adhesive, DY39-067 manufactured by Dow Corning Toray Silicone Co., Ltd., was applied with a brush on the outer circumferential surface of the insulating coating and then dried in the air for 30 minutes. Such cables on each of which an adhesive layer had been thus formed were held with a jig  31  and set in a mold  41 . Using an injection molding machine, VS-15-7-L manufactured by Sanjo Seiki Co., Ltd., addition reaction type silicone rubber of a thermosetting elastomer, DY-35-405A/H manufactured by Dow Corning Toray Silicone Co., Ltd., as the material of waterproof plugs, was injected at a pressure into the mold  41 . The injection pressure was 1.02×10 −5  Pa; the molding temperature was 115 degrees C.; the molding time (crosslinking time) was two minutes; and the injection speed was 10%. The term “injection speed of 10%” means 10% of the set value of the injection molding machine. 
   After the material thus injected was set in the mold  41 , the cables were removed from the mold  41 . As a result, each cable was provided with a waterproof plug formed integrally with the cable. A cable with a waterproof plug according to the first embodiment of the present invention could be manufactured thus. 
   EXAMPLE 2  
   In place of the cable of Example 1, a heat-resisting FFC including an insulating coating made of a PE resin was used. The outer circumferential surface of the insulating coating was degreased with isopropyl alcohol, like Example 1. Afterward, another adhesive than that of Example 1, G-790 manufactured by Wacker Asahikasei Silicone Co., Ltd., was applied with a brush on the outer circumferential surface of the insulating coating and then dried in the air for 30 minutes. Such FFCs on each of which an adhesive layer had been thus formed were held with a jig and set in a mold. Using the same injection molding machine as that of Example 1, that is, VS-15-7-L manufactured by Sanjo Seiki Co., Ltd., the same material as that of Example 1 was injected at a pressure into the mold. The injection pressure, the molding temperature, the molding time, and the injection speed were the same as those of Example 1. 
   After the material thus injected was set in the mold, the FFCs were removed from the mold. As a result, each FFC was provided with a waterproof plug formed integrally with the FFC. A cable with a waterproof plug according to the second embodiment of the present invention could be manufactured thus. 
   EXAMPLE 3  
   Using the same cable as that of Example 1, the outer circumferential surface of the insulating coating was degreased with isopropyl alcohol, like Examples 1 and 2. Afterward, another adhesive than those of Examples 1 and 2, Chemlock 481 manufactured by Lord Chemical Products, was applied with a brush on the outer circumferential surface of the insulating coating and then dried with a batch drier at 80 degrees C. for 20 minutes. Such cables on each of which an adhesive layer had been thus formed were held with a jig  31  and set in a mold  41 . Using another injection molding machine than that of Examples 1 and 2, VSS-30-35-L manufactured by Sanjo Seiki Co., Ltd., a styrene-base thermoplastic elastomer, SEPTON CJ001 manufactured by Kuraray Co., Ltd., different from that of Examples 1 and 2, was injected at a pressure into the mold  41 . The injected material temperature was 240 degrees C.; the injection time was 0.5 seconds; the mold cooling time was 25 seconds; and the mold temperature was 85 degrees C. 
   After the material thus injected was set in the mold  41 , the cables were removed from the mold  41 . As a result, each cable was provided with a waterproof plug formed integrally with the cable. A cable with a waterproof plug according to the first embodiment of the present invention could be manufactured thus. 
   Next, the adhesive force between the cable and the waterproof plug will be described. 
     FIG. 10  shows results of evaluation-of adhesive force with “triangle”, “circle”, and “double circle” when the material of the insulating coating  13 ,  53 , or  73  of the cable  11 ,  51 , or  71  and the material of the waterproof plug  15 ,  55 , or  75  are varied. In  FIG. 10 , “triangle” represents a state in which the waterproof plug is bonded to the cable and can bring about waterproofness, “circle” represents a state in which the adhesive force is stronger than the state “triangle”, and “double circle” represents a state in which the adhesive force is stronger than the state “circle”. 
   As the material of the insulating coating  13 ,  53 , or  73  used were a PE resin, a PVC resin, a PET resin, a PEN resin, and a PI resin. As the material of the waterproof plug  15 ,  55 , or  75  used were setting type silicone rubber and addition reaction type silicone rubber as thermosetting elastomers, and styrene-base, polyester-base, polyamide-base, and polyurethane-base thermoplastic elastomers. Adhesives were adequately selected in accordance with the materials of the insulating coating and the waterproof plug. 
   From  FIG. 10 , it is understood that the waterproof plug can be formed integrally with the cable and good adhesive forces can be obtained in any combination of the above materials. Thus, a cable with a waterproof plug of the present invention can be manufactured in any combination of the above materials. 
   Particularly in case that the material of the insulating coating is the PET resin, the PEN resin, or the PI resin, very good adhesive forces could be obtained even when any of the above six kinds of materials was selected for the waterproof plug. On the other hand, in case that the material of the insulating coating is the PE resin, although the styrene-base and polyurethane-base thermoplastic elastomers as the material of the waterproof plug resulted in adhesive forces of “triangle”, the other materials brought about good adhesive forces. Further, in case that the material of the insulating coating is the PVC resin, although the polyurethane-base thermoplastic elastomer as the material of the waterproof plug resulted in an adhesive force of “triangle”, the other materials brought about good adhesive forces. In case that the material of the waterproof plug was the addition reaction type silicone rubber, any of the above five kinds of materials for the insulating coating brought about very good adhesive forces. 
   In general, a PE resin or a PVC resin is used as the material of the insulating coating. In such a case, it was found that a good adhesive force was obtained by using addition reaction type silicone rubber as the material of the waterproof plug and using a vinyl-base compound, for example, a silane coupling agent having vinyl groups, as the adhesive. 
   The same results as described above were obtained in any of the cases of applying the adhesive onto the outer circumferential surface of the insulating coating and mixing the adhesive in the material of the waterproof plug. 
   The waterproof plug suffices if it is made of an elastic material. The material of the waterproof plug is not limited to a thermosetting or thermoplastic elastomer. The material of the insulating coating is also not limited to the above-described materials, and various other materials can be used. 
   The adhesive is not limited to a vinyl-base compound such as a silane coupling agent having vinyl groups. Various adhesives can be used in accordance with the materials of the waterproof plug and the insulating coating of the cable. Further, the waterproof plug may not be united to the cable with an adhesive component. The waterproof plug may be united to the cable with a medium other than an adhesive component or without such a medium. 
   The cable may not be substantially circular or rectangular in cross section as in the above-described embodiments. Cables having various shapes can be used. 
   In the first embodiment, the terminal  2  has the cable crimping portion  5  and the cable crimping portion  5  crimps the insulating coating  14  of the cable  11  to fix the terminal  2  to the cable  11 . However, the present invention is not limited to this. That is, a terminal  2  may be fixed to a cable  11  with a structure other than such a crimping structure. 
   As for the manufacturing method, such a jig  31  as described above may not be used. Further, three cables in a lump may not be set in the mold. Only one cable may be set in each mold. Otherwise, two cables or four or more cables in a lump may be set in a mold. 
   The forming method of the waterproof plug is not limited to injection molding as described above. Compression molding, transfer molding, or calendering can be used. 
   While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the-art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.