Abstract:
The present invention provides a stamper holding mechanism that is stable, cannot be loosened, that does not use frictional forces and is not affected by vibration and temperature variations. To that end, there is provided a die, for molding disc substrates, that forms a cavity  23  by providing a stamper  10  on either one or both of a stationary mirror plate  8  of a stationary die  1  and a movable mirror plate  16  of a movable die  11 , including: rotation mechanism for allowing a holding member, which holds the stamper  10  on the mirror plate and which can be removable, to advance or retreat; and engagement mechanism for abutting on the rotation mechanism to be engaged therewith in a direction to remove the holding member when the rotation mechanism is rotated in the direction.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a die, for molding disc substrates, having a function to change stampers and, in particular, it relates to a technique for preventing loosening of a stamper holding mechanism while a stamper is mounted and a molding operation is performed.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIG. 3 shows an example of a prior art die, for molding disc substrates, having a function to change stampers. In this example, an inner stamper holder  18  holds a center hole of a stamper  10  mounted on a surface of a movable mirror plate  16  to install the stamper  10  on the movable mirror plate  16 . The inner stamper holder  18  can advance or retreat in an axial direction perpendicular to a surface of the stamper  10  by rotation of a pinion rod  24   b  via a gear  25 . A flange portion  31  provided at the outward end of the pinion rod  24   b  is pinched between a holding plate  32  and an intermediate plate  13 , wherein the rotation of the pinion rod  24   b  is prevented by pressing the holding plate  32  against the intermediate plate  31  by a fixing screw  33 .  
           [0005]    Further, in another embodiment, as shown in Japanese Unexamined Patent Publication No. H07-214604, an attaching/detaching bush  20  that holds a center hole of a stamper plate  12  advances or retreats due to the rotation of an operating rod  22  meshing with a gear rack  21  provided on an outside surface of the attaching/detaching bush  20 . The rotation of the operating rod  22  is prevented by tightening a lock nut  26 , which is screwed on a male thread portion  24  provided on the outward part of the operating rod  22 , onto a die plate  27 .  
           [0006]    In either of the prior art techniques, a member for holding the stamper, or its equivalent, prevents the rotation of a rotating member such as the pinion rod or the operating rod with the help of a frictional force generated by clamping using the holding plate or the lock nut. Therefore, if the force to prevent the rotation of the rotating member is reduced as a result of vibrations and thermal expansion due to temperature variations during molding processes, the member for holding the stamper and the like may be loosened and projected in the removing direction. In this case, the melted resin may flow in the center hole area of the stamper to create burrs or, in the worst case, the member for holding the stamper and the like may be projected significantly to collide against the opposite surface to damage the dies.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    In view of the above problem, it is an object of the present invention to provide a stamper holding mechanism that is stable and cannot be loosened and that does not use frictional forces and is not affected by vibrations and temperature variations.  
           [0008]    Thus, according to the present invention, there is provided a die, for molding disc substrates, that forms a cavity by providing a stamper on either one or both of a stationary mirror plate of a stationary die and a movable mirror plate of a movable die, comprising: rotation means for allowing a holding member, which holds said stamper on the mirror plate and which can be attached or detached, to advance or retreat; and engagement means for abutting against the rotation means to be engaged therewith in a direction to remove said holding member when said rotation means is rotated in said direction. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    In the drawings elements designated by identical reference numerals have identical objects and functions throughout several views. In the drawings:  
         [0010]    [0010]FIG. 1 is a cross-sectional view showing an important part of a die implementing the present invention;  
         [0011]    [0011]FIG. 2 is an enlarged view on arrow A-A in FIG. 1; and  
         [0012]    [0012]FIG. 3 is a cross-sectional view showing an important part of a prior art die. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    A stationary die  1  is comprised of: a stationary die plate  2  that is attached to a stationary platen (not shown) of an injection molding machine via a thermal insulation plate  3 ; a stationary mirror plate  8  that is fastened to a surface of the stationary die plate  2 , which is opposite to that faced by the thermal insulation plate  3 , via a stationary back plate  7 ; a gate insert  6 , a sprue bush  5  and a positioning plate  4  that are inserted through center openings of the stationary die plate  2 , the stationary back plate  7  and the stationary mirror plate  8 ; and an stationary outer circumferential ring  9  that is inserted around end faces of the stationary back plate  7  and the stationary mirror plate  8  and fastened to the stationary die plate  2 .  
         [0014]    A movable die  11  is comprised of: a movable die plate  12 ; an intermediate plate  13  that is fastened to a surface of the movable die plate  12  facing the stationary die  1 ; a movable mirror plate  16  that is fastened to a surface of the intermediate plate  13  facing the stationary die  1  via a movable back plate  15 ; a stamper  10  that is disposed on a surface of the movable mirror plate  16  faced by the stationary mirror plate  8 ; an outer circumferential stamper holder  17  that pinches an outer circumferential end of the stamper  10  so that the stamper  10  is held on the movable mirror plate  16 ; an inner stamper holder  18  that acts as a holding member that is movably inserted through center openings of the intermediate plate  13 , the movable back plate  15  and the movable mirror plate  16  to pinch an inner circumferential end of the stamper  10  so that the stamper  10  is held on the movable mirror plate  16 ; a stationary sleeve  19  that guides an internal hole of the inner stamper holder  18  and is fastened to the movable die plate  12 ; an ejector  20  that is inserted through an internal hole of the stationary sleeve  19  slidably in the axial direction; a male cutter  21  that is inserted through an internal hole of the ejector  20  slidably in the axial direction; an ejector pin  22  that is inserted through an internal hole of the male cutter  21  slidably in the axial direction; a movable outer circumferential ring  14  that is inserted around outer circumferential end faces of the movable back plate  15  and the movable mirror plate  16  and fastened to the intermediate plate  13 ; and a rotation means  39  that drives the inner stamper holder  18  to advance or retreat in the axial direction. The movable die  11  is aligned with the stationary die  1  described above to constitute a die and form a cavity  23  therebetween.  
         [0015]    The inner stamper holder  18  acting as a holding member which can be attached or detached, is a cylindrical member that has an outside diameter to allow the inner stamper holder  18  to be inserted through an inner circumferential hole of the stamper  10  with a slight clearance and is equipped with a collar, on one end face thereof, for holding the stamper  10  by engaging with the end portion of the inner circumferential hole of the stamper  10 . An outer circumferential surface of the other end of the inner stamper holder  18  is provided with male threads, which are screwed with female threads provided on an inner circumference of a gear  25 . An outer circumferential end face of the gear  25  is guided into a hole provided in the axial direction of the intermediate plate  13  via a bush  29  and a surface perpendicular to the axis of the gear  25  is held by the intermediate plate  13  via a bearing  27  to receive a force in the axial direction. An outer circumferential side of the gear  25  is provided with teeth which mesh with a pinion provided at a tip portion of a pinion rod  24   a . The pinion rod  24   a  is rotatably held via a bearing  26  and a bush  28  in a vertical hole provided in the intermediate plate  13  in the direction normal to the axis of the die and also held in the axial direction by a bush  30 . Though the rotation means is constituted by the pinion rod  24   a  and the gear  25  in the above description, other rotation means such as, for example, that shown in Japanese Unexamined Patent Publication No. H07-214604, as mentioned above, may also be adopted.  
         [0016]    The other end of the pinion rod  24   a  opposite to the pinion is provided with a flange-like portion and an outer circumferential surface of the flange-like portion is provided with a ratchet  34 . The ratchet  34  has a sawtooth-like shape and is provided with a pawl  35  so as to permit clockwise rotation and prevent counterclockwise rotation from the viewpoint of A-A.  
         [0017]    The pawl  35  is a plate-like member, one end of which is rotatably attached to a rotation shaft  38  standing vertically on the movable die plate  12  and the other end of which is moved arcuately. A tip portion of the pawl  35  that is moved arcuately is shaped so that it abuts against sawtooth-shaped flanks of the ratchet  34  that are disposed substantially along radial lines from the central axis of the ratchet  34 . A spring  36  is provided between the intermediate plate  13  and a side of the pawl  35  that is opposite to that faced by the ratchet  34  and is perpendicular to the rotation shaft  38  so as to press the tip portion of the pawl  35  against the ratchet  34  continuously. A knob  37  is placed, vertically, on the outward surface in the neighborhood of the tip portion of the pawl  35  so that the top end of the knob  37  can be manipulated easily from the side of the movable die  11 . Though the engagement means is constituted by the ratchet  34  and the pawl in the above description, other engagement means of different configurations may also be adopted so long as the engagement means employ the engagement of members abutting against each other, such as those by a penetrating hole and a pin and the like.  
         [0018]    An operation for changing the stamper  10  will be described. In order to remove the stamper  10  that has been used in the preceding molding process, the movable die  11  is moved away from the stationary die  1  adequately and the outer circumferential stamper holder  17  is removed. First, the knob  37  is manipulated to rotate the pawl  35  so that the pawl  35  is moved away from the ratchet  34  against the elastic force of the spring  36  so as to disengage the pawl  35  from the ratchet  34 . Next, a handle (not shown) is attached to the end of the pinion rod  24   a  and rotated in a counterclockwise direction. As the pinion rod  24   a  rotates the gear  25 , the inner stamper holder  18 , which is screwed with the gear  25  and which is prevented from being rotated by a key (not shown) and permitted to be moved in the axial direction, is moved in the direction to unscrew it from the gear  25 . After the inner stamper holder  18  is moved till it is unscrewed from the gear  25 , the inner stamper holder  18  is removed to the outside of the movable die  11  along with the stamper  10 .  
         [0019]    Next, the newly prepared stamper  10 , with the inner stamper holder  18  inserted therethrough, is inserted into the movable die  11  and the handle is rotated in a clockwise direction. Meanwhile, the pawl  35  goes over the sawtooth-like ratchet  34  to permit the clockwise rotation of the pinion rod  24   a . The inner stamper holder  18  is screwed with the gear  25  and further advances till its end face abuts on the stationary sleeve  19 . At this time, the collar of the inner stamper holder  18  is engaged with the inner circumferential hole portion of the stamper  10  with an appropriate clearance so that the stamper  10  is attached properly. Then, the pawl  35  is engaged with the ratchet  34  to prevent a rotation of the pinion rod  24   a  in the counterclockwise direction, i.e., a detaching direction of the inner stamper holder  18 . Therefore, the stamper holding mechanism is stable without being affected by vibrations and temperature variations and the loosening of the inner stamper holder  18  that acts as a holding member for the stamper  10  is prevented.  
         [0020]    When disc substrates are molded in the die to which the stamper  10  is attached as described above, a die clamping device (not shown) allows the movable outer circumferential ring  14  of the movable die  11  to abut and be held to the stationary outer circumferential ring  9  of the stationary die  1  and an injection device (not shown) that abuts against the sprue bush  5  injects melted resin to fill the cavity  23 .  
         [0021]    Though an example in which the stamper  10  is provided on the movable die  11  is shown in this embodiment, the stamper  10  may be provided on the stationary die or on both the movable and stationary dies. Correspondingly, the holding member, the rotation means and the engagement means may be attached to the die to which the stamper  10  is attached.