Abstract:
A method of producing an insert-molding product in which an insert product is covered with a synthetic resin by arranging the insert product in a cavity of a mold is provided. The method includes holding the insert product by a holding pin, pouring a molten synthetic resin into the cavity, and retracting the holding pin. At least one moving pin is provided adjacent the holding pin. After the cavity is filled with the synthetic resin, the holding pin is retracted and the at least one moving pin is moved to extrude and introduce the synthetic resin into a space where the holding pin used to be positioned prior to its retraction from the cavity.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an insert-molding method for obtaining resin-molded products in which insert products such as electronic parts are sealed with a resin to a sufficient degree without deviation in position, and to a molding device therefor. 
     2. Description of the Related Art 
     In order to maintain the water-proof properties of electronic parts, there have heretofore been employed a method by which the surfaces of the electronic parts are covered with a potting material, a method by which a resin sealing plug is attached thereto, and the like method. 
     In recent years, however, there has been widely employed a method by which the surfaces are sealed with a resin in order to decrease the cost of products and to enhance the ratio of recycling. The sealing with the resin is generally based on an insert-molding method which features excellent mass-productivity at a decreased cost. 
     As the device used for the insert molding, there has heretofore been known the one disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 55-91642. That is, as shown in FIG. 10, there has been proposed a molding device  9  comprising a mold  90  having a cavity  91  in which will be arranged an insert product  2 , and a holding pin  92  retractably provided in the mold  90  to hold the insert product  2  at a tip  921 . Reference numeral  95  denotes a port for pouring-in the synthetic resin. 
     Described below is an insert-molding method using the above-mentioned mold  9 . 
     First, the insert product  2  is arranged at a predetermined position in the cavity  91  being held by the holding pin  92 . Next, the cavity  91  is filled with a synthetic resin  3  and, then, the holding pin  92  is retracted from the cavity  91 . Thereafter, the cavity is further filled with the synthetic resin  3 . 
     Thus, there is obtained a resin-molded product in which the whole surface of the insertion product is sealed with the resin. 
     According to the above-mentioned insert-molding method and device, however, the quality of the molded product is affected by the timing of retracting the holding pin  92  from the cavity  91 . That is, when the holding pin  92  is retracted before the cavity  91  is completely filled with the synthetic resin  3 , there remains no melted portion caused by the holding pin  92 , and the sealing with resin is accomplished to a sufficient degree. Due to the synthetic resin  3  that is filled, however, the insert product  2  moves and its position is deviated. When the holding pin  92  is retracted after the cavity  91  is completely filled with the synthetic resin  3 , on the other hand, the space in which the holding pin  92  used to be positioned is not sufficiently filled with the synthetic resin  3 , and the insert product  2  is not sealed with the resin to a sufficient degree. 
     There has further been proposed a method according to which the synthetic resin  3  is forcibly extruded and introduced into space where the holding pin used to be positioned as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-163528 or Japanese Unexamined Patent Publication (Kokai) No. 8-306718. 
     That is, as shown in FIG. 11, a device  8  used for this method includes a mold  80  having a cavity  81 , a cylindrical holding pin  82  retractably provided in the mold  80 , and a pole-like moving pin  83  retractably provided in the holding pin  82 . 
     Briefly described below is the insert-molding method by using the above-mentioned molding device  8 . 
     That is, referring to FIG. 11, an insert product  20  is arranged in the cavity  81  and is held by the holding pin  82 . The cavity  81  is then filled with the synthetic resin  3 . 
     Then, as shown in FIG. 12, the moving pin  83  is moved in the direction of the cavity  81  while the holding pin  82  is retracted, and the synthetic resin  3  is forcibly extruded and introduced into space where the holding pin  82  used to be positioned. 
     The insert product  20  has a through hole  201  formed in the central portion thereof and an accessory  202  such as a reed frame on the end surfaces thereof, the accessory  202  extending beyond the cavity  81  so as to be held by the mold  80 . 
     However, the above-mentioned conventional insert-molding method and device have problems as described below. 
     That is, after the synthetic resin  3  is introduced, the surface of the synthetic resin  3  contacting to the holding pin  82  is cooled by the holding pin  82 , resulting in the formation of a skin layer (solidified layer on the surface of the resin)  31 . 
     The holding pin  82  has a cylindrical shape and, hence, the skin layer  31  assumes a cylindrical shape, too, as shown in FIG.  13 . 
     Therefore, the area of the skin layer  31  inevitably increases but is never concentrated to one point despite being extruded by the moving pin  83 . 
     Accordingly, the skin layer  31  does not melt again despite of the ambient heat or pressure, and the unmelted portion is very likely to remain. 
     When the holding pin  82  is retracted at a delayed timing, therefore, the unmelted portion remains and the insert product  20  is not sealed with the resin to a sufficient degree. 
     SUMMARY OF THE INVENTION 
     The present invention was accomplished in view of the above-mentioned problem inherent in the prior art, and its object is to provide an insert-molding method capable of sealing an insert product with a resin to a sufficient degree without permitting the position of the insert product to be deviated as a result of suppressing the residence of the unmelted portion caused by the holding pin, and a molding device therefor. 
     A first aspect of the present invention is concerned with an insert-molding method in which an insert product is arranged in a cavity of a mold and is held by a holding pin, a molten synthetic resin is poured into said cavity, and said holding pin is retracted to obtain an insert-molding product in which said insert product is covered with said synthetic resin, wherein a moving pin is provided adjacent to said holding pin, said moving pin is moved in the direction of the cavity while retracting said holding pin after said cavity is filled with said synthetic resin, and said synthetic resin is extruded and introduced into space where said holding pin used to be positioned. 
     In the present invention, what most draws attention is that the moving pin is moved in the direction of the cavity while retracting the holding pin after the cavity is filled with the synthetic resin, and the synthetic resin is extruded and introduced into space where the holding pin used to be positioned. 
     A second aspect of the present invention is concerned with a molding device for carrying out the above-mentioned molding method to produce an insert-molding product in which an insert product is covered with a synthetic resin, comprising a mold having a cavity for molding, and a holding pin retractably provided in said mold to hold the insert product, wherein said mold has a moving pin that retractably moves in the direction of the cavity adjacent to said holding pin. 
     In this molding device, what most draws attention is that the moving pin retractably moves in the direction of the cavity adjacent to the holding pin. 
     Therefore, the molding device of the invention makes it possible to produce an insert-molding product in which the insert product is sealed with the resin to a sufficient degree while suppressing the deviation in position of the insert product. 
    
    
     The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below together with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an insert-molding device according to an embodiment 1 of the present invention; 
     FIG. 2 is a view illustrating a state of just before a holding pin is retracted in an insert-molding method according to the embodiment 1 of the present invention; 
     FIG. 3 is a view illustrating a state of just after the holding pin is retracted in the insert-molding method according to the embodiment 1 of the present invention; 
     FIG. 4 is a view illustrating a state of after the moving pin is moved in the insert-molding method according to the embodiment 1 of the present invention; 
     FIG. 5 is a perspective view of an insert-molding product obtained by the insert-molding method according to the embodiment 1 of the present invention; 
     FIG. 6 is a sectional view of an insert-molding device according to an embodiment 2 of the present invention; 
     FIG. 7 is a sectional view of the insert-molding device according to an embodiment 3 of the present invention; 
     FIG. 8 is a sectional view illustrating the periphery of the holding pin in the insert-molding device according to an embodiment 4 of the present invention; 
     FIG. 9 is a diagram illustrating the measured results of changes in the temperature of the synthetic resin near the holding pin according to experiment of the present invention; 
     FIG. 10 is a sectional view of a conventional insert-molding device; 
     FIG. 11 is a sectional view of another conventional insert-molding device; 
     FIG. 12 is a sectional view illustrating a state of after the holding pin is retracted and the moving pin is moved in the another conventional insert-molding device; and 
     FIG. 13 is a sectional view along the line C—C in FIG.  12 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The insert-molding method and device according to an embodiment 1 of the present invention will now be described with reference to FIGS. 1 to  5 . 
     Referring to FIG. 1, an insert-molding device  1  of this embodiment possesses a mold  10  having a cavity  11  for molding, and a holding pin  12  retractably provided in the mold  10  to hold an insert product. 
     The insert-molding device  1  is the one for producing an insert-molding product  4  (FIG. 5) in which the insert product  2  is covered with a synthetic resin  3 . 
     The mold  10  has a moving pin  13  that retractably moves in the direction of the cavity  11  adjacent to the holding pin  12 . 
     The moving pin  13  is arranged to surround the holding pin  12  in concentric therewith. 
     The mold  10  has a guide hole  14  for guiding the moving pin  13  in the direction of the cavity  11 . 
     In this embodiment, the holding pin  12  has a diameter of 3.0 mm. 
     In FIG. 1, furthermore, reference numeral  15  denotes a port for pouring the synthetic resin  3 . 
     The insert product  2  is a speed sensor used for measuring the speed of an automobile or the like, and comprises a sensor terminal  21 , a coil  22 , a primary spool  23  and a magnet  24 . The insert product  2  further has a lead wire  25  which, during the insert-molding, extends out of the mold  10  through a cable tube  26  that covers the lead wire  25 . 
     A holding dent  28  with which an end of the holding pin  12  will come in contact is formed in the upper end of the insert product  2 . 
     The molding method using the above-mentioned insert-molding device  1  will now be described. 
     Referring to FIG. 1, first, the insert product  2  is arranged in the cavity  11  of the mold  10 , and the holding dent  28  at the upper end of the insert product  2  is held by an end  128  of the holding pin  12 . 
     Then, the synthetic resin  3  in a melted state is poured into the cavity  11 . At this moment, the end  138  of the moving pin  13  is positioned on the inside of an open end  141  of the guide hole  14 . 
     Referring next to FIG. 2, the cavity  11  is filled with the synthetic resin  3  and, then, the holding pin  12  is retracted (FIG. 3) and, at the same time, the moving pin  13  is moved in the direction of the cavity  11  until the end  138  thereof is located at the same position as the open end  141  (FIG.  4 ). Therefore, the synthetic resin  3  filled in the guide hole  14  is extruded into the cavity  11 . 
     Accordingly, the synthetic resin  3  is extruded and introduced into space  32  (see FIG. 2) in which the holding pin  12  used to be positioned. 
     Through the series of steps described above, there is produced an insert-molding product  4  (see FIG. 5) in which the insert product is covered with the synthetic resin  3 . 
     In FIG. 5, reference numeral  41  denotes a mark of the holding pin formed like a dent by the end  128  of the holding pin  12 . 
     Next, described below are the action and effect of this embodiment. 
     Referring to FIG. 2, when the holding pin  12  is retracted after the cavity  11  is filled with the synthetic resin  3 , space is once formed in a portion where the holding pin  12  used to be positioned. The space  32  is then filled with the surrounding synthetic resin  3  but not to a sufficient degree (FIG.  3 ). Upon moving the moving pin  13  adjacent to the holding pin  12  as shown in FIG. 4, however, the synthetic resin  3  surrounding the space  32  is extruded and introduced into the space  32 . Thus, the space disappears. 
     Furthermore, a skin layer (solidified layer on the surface of the resin) is formed on the surface of the synthetic resin  3  contacting the holding pin  12 . Due to the pressure of the surrounding synthetic resin  3 , however, the skin layer is concentrated to one point and melts again due to the pressure and heat of the synthetic resin  3 . 
     In this embodiment, in particular, since only one holding pin  12  is used, the skin layer is not formed at all. 
     Accordingly, the insert product can be sealed with the resin to a sufficient degree. 
     The holding pin  12  is retracted after the synthetic resin  3  has been introduced and, hence, the position of the insert product  2  is very little deviated. 
     According to this embodiment, therefore, it is possible to produce the insert-molding product in which the insert product is sealed with the resin to a sufficient degree without causing the position of the insert product to be deviated. 
     In the present invention, it is desired that one holding pin  12  is employed. In this case, the unmelted portion can be completely extinguished. 
     It is further desired that the holding pin  12  has a diameter of from 1.0 mm to 6.0 mm. When the diameter is smaller than 1.0 mm, it becomes difficult to hold the insert-molding product. When the diameter exceeds 6.0 mm, on the other hand, it is likely that the unmelted portion is formed to some extent. 
     It is desired that the moving pin  13  is arranged to surround the holding pin  12  in concentric therewith. 
     In this case, the synthetic resin can be extruded and introduced into the space where the holding pin  12  used to be positioned from the whole circumference thereof and uniformly. Therefore, the synthetic resin can be efficiently and reliably extruded and introduced into the space. 
     It is therefore allowed to more reliably produce the insert-molding product in which the insert product is sealed with the resin. 
     In embodiment 2, as shown in FIG. 6, the moving pin  13  is arranged separately from, and in parallel with, the holding pin  12 . 
     In other respects, embodiment 2 is the same as embodiment 1. 
     In this case, the insert-molding device  1  can be constructed relatively simply. In other respects, embodiment 2 exhibits the same action and effect as embodiment 1. 
     In embodiment 3, as shown in FIG. 7, the moving pin  13  is arranged at right angles with the holding pin  12 . In other respects, embodiment 3 is the same as embodiment 1. 
     In this case, a plunger for moving the moving pin  13  back and forth, and a cylinder for moving the holding pin  12  back and forth, can be arranged at separate places unlike that of embodiment 1. Therefore, their arrangement is facilitated. 
     In other respects, the action and effect are the same as those of embodiment 1. 
     In embodiment 4, as shown in FIG. 8, a cylindrical recessed portion is formed in the holding pin  12 , and a spiral heater  121  is contained therein. 
     In other respects, embodiment 4 is the same as embodiment 1. 
     When the cavity  11  is filled with the synthetic resin  3  in this case, no skin layer is formed on the surface of the synthetic resin  3  surrounding the holding pin  12  and contacting holding pin  12 . 
     This is because the synthetic resin  3  surrounding the holding pin  12  is maintained at a high temperature owing to the heater  121  contained in the holding pin  12 . Therefore, the synthetic resin  3  is not solidified. 
     Therefore, this embodiment makes it possible to produce an insert-molding product in which the insert product is sealed with the resin more reliably. 
     In the present invention, it is desired that the metal mold  10  has a guide hole  14  for guiding the moving pin  13  in the direction of the cavity, the end of the moving pin  13  is located on the inside of the open end of the guide hole  14  when the cavity is to be filled with the synthetic resin, the holding pin  12  is retracted after the cavity  11  is filled with the synthetic resin, and the moving pin  13  is moved in the direction of the cavity  11 . 
     When the cavity  11  is filled with the synthetic resin in this case, the guide hole  14 , too, is filled with the synthetic resin up to the end of the moving pin  13 . 
     Therefore, the moving pin  13  is moved in the direction of the cavity while the holding pin  12  is being retracted, and the synthetic resin filled in the guide hole  14  is extruded into the cavity  11 . Accordingly, the synthetic resin is extruded and introduced into the space where the holding pin  12  used to be positioned. 
     That is, according to the present invention, the synthetic resin to be introduced into the space in the guide hole  14  and can, hence, be extruded and introduced into the space to a sufficient degree. 
     It is therefore possible to produce the insert-molding product in which the insert product is sealed with the resin more reliably. 
     In an experimental example of the present invention as shown in FIG. 9, a change in the temperature of the synthetic resin near the holding pin  12  was measured when the holding pin  12  was retracted in conducting the insert-molding according to the present invention. 
     The measurement was taken while conducting the insert-molding shown in embodiment 1 by installing the temperature sensors at a point A and a point B shown in FIG.  3 . 
     The point A is near the open end  141  of the guide hole  14  of the mold  10 , and the point B is almost midway between the open end  141  and the holding dent  21  at the upper end of the insert product  2 . 
     During the insert-molding, the measurement was started from a moment when the holding pin  12  was retracted. Thereafter, changes in the temperature of the synthetic resin  3  were monitored at the points A and B. 
     The results of measurement are as shown in FIG.  9 . 
     As will be seen from FIG. 9, the temperature of the synthetic resin  3  at the point A sharply drops after the cavity  11  is filled with the synthetic resin, remains stable at about 100° C., and does not rise thereafter. At the point B, the temperature of the synthetic resin  3  once drops but rises again after the holding pin  12  is retracted. The temperature exceeds 230° C. which is the melting point of the synthetic resin for about one second from about 0.7 seconds after the retraction of the holding pin  12  until about 1.7 seconds after. 
     That is, during the above-mentioned period of one second, the skin layer melts and adheres again due to the pressure and heat of the surrounding synthetic resin  3 . 
     It will thus be understood that the insert product  2  is sealed with the resin to a sufficient degree upon moving the moving pin  13  within about 1.7 seconds after the holding pin  12  is retracted. 
     While the invention has been described with reference to specific embodiments selected for purposes of explanation, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.