Patent Abstract:
A mold, for molding a cylindrical filter having a narrow-pitched mesh structure through resin injection molding, has a cavity divided into sections radially freely attachable/detachable. The sections of the cavity being formed as stacked assemblies bodies each having a number of thin plates, and with edge portions of alternating ones of the thin plates projecting further radially inward than edge portions of interposed alternating ones of the thin plates A core fits in the cavity a defines inside surface of the mesh structure. Air existing between the core and the cavity is externally released from gaps in the stacked thin plates during resin injection.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a mold for manufacturing a finely meshed plastic filter. 
   2. Description of the Related Art 
   To integrally mold a filter having a narrow-pitched mesh structure through injection molding, the gas or air must be completely removed from inside the mold. For the mold core and cavity to achieve this purpose, a porous sintered metal has been conventionally used in which gaps are formed between metal particles. The air inside the mold was externally released from between the metal particles. 
   On the other hand, the mold disclosed in Japanese Patent Application Laid-Open Publication No. 1998-193405 is formed with air bleeding guide paths communicating with the cavity. 
   The drawback to providing the core or cavity with a porous sintered metal is that the porous surface will gradually become blocked with resin, eventually resulting in failure to bleed the air. Moreover, the air bleeding guide paths of the aforementioned patent document are cumbersome to manufacture and likely permit entry of resin therein. And, in any case, the manufacture of the conventional molds has been cumbersome, resulting in a high mold cost. 
   SUMMARY OF THE INVENTION 
   In light of the foregoing, it is an object of the present invention to provide a mold for a fine-pitched cylindrical filter that is capable of externally releasing the air from inside the core and remains unblocked by solving the drawbacks. 
   In order to achieve the above object, according to an aspect of the present invention there is provided a mold for a plastic filter, the mold having a cylindrical space for molding a filter formed between the outer circumference of a core and the inner circumference of a cavity, wherein the cavity is made up of at least a pair of divisions that divide in such a manner as to be freely attachable/detachable in the direction away from a center line of the cylindrical space, wherein the divisions have each a stacked body formed by stacking a number of thin plates that have an inner circumference coinciding with each of horizontal cross-sections of the inner circumference of the cavity, the inner circumferential edge of one of the adjacent thin plates slightly projecting more toward the center line than that of the other thin plate to form horizontal ridges, with a number of groove portions formed between the adjacent horizontal ridges, wherein the inner end surface of each of the horizontal ridges is in contact with the outer circumference of the core, and wherein air existing between the core and the cavity is externally released from gaps in the stacked thin plates during resin injection. 
   The outer circumference of the core is formed with vertical ridges extending along the center line that are spaced apart from each other in the circumferential direction thereof, with a number of vertical groove portions being formed between the adjacent vertical ridges, and the vertical ridges are arranged such that the outer end surface of each of the vertical ridges is in contact with and intersects the inner end surface of each of the horizontal ridges of the cavity. 
   In order to attain the above object, according to another aspect of the present invention there is provided a mold for a plastic filter, the mold having a cylindrical space for molding a filter formed between the outer circumference of a core and the inner circumference of a cavity, wherein the cavity is made up of at least a pair of divisions that divide in such a manner as to be freely attachable/detachable in the direction away from the center line of the cylindrical space, wherein the core has a stacked body formed by stacking a number of thin plates of the same geometry in the direction of the center line, the outer circumference of the core being formed with a number of vertical ridges extending along the center line that are spaced from each other in the circumferential direction of the core, with vertical groove portions formed between the vertical ridges, wherein the outer surface of the vertical ridges is in contact with the inner surface of the cavity, and wherein air existing between the core and the cavity is externally released from gaps in the stacked thin plates during resin injection. 
   According to the mold for a plastic filter of the present invention, a cylindrical plastic filter can be manufactured in which slits (gaps), each measuring equal to the thickness of a thin plate  3   b , are formed in the direction of stacking thin plates  3   a  and  3   b . Therefore, a filter can be manufactured having a large number of slits that are thin to the extent possible by selecting the thickness of the thin plate  3   b.    
   On the other hand, the air inside groove portions  4  is externally released from gaps in the individual thin plates  3   a  and  3   b  during resin injection, allowing molten resin to be reliably guided into the groove portions  4  and providing a highly accurate mold for a plastic filter. 
   Further, divisions  2   a  and  2   b  of a cavity  2  can be divided in the direction away from a center line  25 , allowing for easy retrieval of the product after the injection molding. 
   A number of vertical ridges  5   a  are provided on the outer circumference of a core  1  and configured so as to be in contact and intersect horizontal ridges  4   a  of the cavity  2 , thus allowing providing a highly accurate meshed filter. That is, the filter has a number of vertical slits formed on the inner circumference and a number of horizontal slits formed on the outer circumference, with horizontal and vertical ribs on both sides of each of the slits connected at the individual intersection portions. 
   A filter can be provided that is easy to manufacture, that allows the air between the core  1  and the cavity  2  to be reliably released externally and that has fine slits. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic perspective view of a core  1  and a cavity  2  of the present invention; 
       FIGS. 2A ,  2 B and  2 C are enlarged fragmentary views of an A-A cross-section, a B-B cross-section and a C portion, respectively; 
       FIG. 3  is a vertical cross-sectional view showing the core  1  and the cavity  2  of the present invention as mounted; 
       FIGS. 4A and 4B  are a perspective view and an enlarged fragmentary view of a B portion, respectively, showing an example of a plastic filter  6  manufactured by the present mold; and 
       FIG. 5  is an enlarged cross-sectional view showing another example of the core  1  of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Description will be given below of an embodiment of the present invention with reference to the accompanying drawings. 
     FIG. 1  is a schematic view of the core  1  and the cavity  2  for manufacturing a cylindrical plastic filter, whereas  FIGS. 2A ,  2 B and  2 C are enlarged fragmentary views of an A-A cross-section, a B-B cross-section and a C portion, respectively. On the other hand,  FIG. 3  is a vertical cross-sectional view showing the core  1  and the cavity  2  as mounted.  FIG. 4A  is a schematic perspective view of an example of a plastic filter  6  manufactured by the mold, whereas  FIG. 4B  is an enlarged view of a portion B of the plastic filter. 
   This mold has the core  1  and the cavity  2  as shown in  FIG. 1 . The core  1  is formed in the shape of a column having a center hole on the outer circumference, with a number of the vertical ridges  5   a , spaced from each other in the circumferential direction, formed on the outer circumference of the core  1  in the direction of the center line. A number of vertical groove portions  5  are formed between the adjacent vertical ridges  5   a . These vertical groove portions  5  can be formed, for example, by cutting the outer circumference of the columnar body. It is to be noted that the vertical groove portions  5  are formed extremely small in width. And, the vertical groove portions  5  are formed between the adjacent vertical ridges  5   a  that are formed as shown in  FIG. 2C . 
   Next, the cavity  2  is made up of the divisions  2   a  and  2   b  divided into two parts on the diameter line passing through the center line  25  in the direction of the radius. The divisions  2   a  and  2   b  are respectively made of stacked bodies in which a number of thin plates  3   a  and  3   b  are stacked, with the inner circumferential edge of the thin plate  3   b —one of the two adjacent thin plates—slightly projecting more toward the side of the center line  25  than that of the thin plate  3   a , thus forming the horizontal ridges  4   a . The inner circumference of the cavity  2 , formed in cylindrical shape, is formed such that the radius from the center line  25  of the thin plate  3   a , one of the radiuses, is slightly larger than that from the thin plate  3   b.    
   Then, a number of the groove portions  4  are formed between the adjacent horizontal lines  4   a  as shown in  FIG. 2A . 
   It is to be noted that in this example, a plurality of vertical grooves  28  (six in this example) are arranged at constant intervals on the inner circumferential surface of the cavity  2  as shown in  FIG. 1 . These thin plates  3   a  and  3   b  are respectively easily formed by press forming. The thin plates  3   a  and  3   b  are each formed rectangular in outer circumference and semi-circular in inner circumference, with a pair of protruding portions for positioning  29  projected at one end of the outer circumference. As shown in  FIG. 2A , a semi-circle R 1  of the thin plate  3   a  is formed slightly larger than a semi-circle R 2  of the thin plate  3   b . The first and second thin plates  3   a  and  3   b  are in contact with each other at the surfaces, with a gap formed between the contact surfaces that passes air but does not permit penetration of resin and that is not visibly observable. 
   These divisions  2   a  and  2   b  are fitted into slide cores  22  having a rectangular hole that matches the divisions  2   a  and  2   b  as shown in  FIG. 1  and positioned by the protruding portions for positioning  29 . It is to be noted that the outer surfaces of the divisions  2   a  and  2   b  are closed and fixed by an appropriate block material after the fitting. On the other hand, air bleeding grooves  20  are preferably formed in the block material. It is to be noted that the air inside the cavity  2  may be externally guided from the gap between the divisions  2   a  and  2   b  of the cavity  2  and the slide cores  22  without providing the air bleeding grooves  20 . 
   Then, being supported by the slide cores  22  in the vertical cross-sectional view as shown in  FIG. 3 , the cavity  2  is positioned on top of a movable plate  13  and opens/closes in the direction of the radius relative to the center line  25 . That is, as the movable plate  13  moves vertically, the divisions  2   a  and  2   b  are moved in the direction of the radius by angular pins  14  projected on a fixed plate  12  via slanting holes  30  of the slide cores  22 . 
   Next, the core  1  is fixed, for example, at the edge portion of a main shaft pin  18  fixed on the movable plate  13  via a lock bolt  19  as shown in  FIG. 3 . In a closed mold condition as shown in  FIG. 3 , the outer surface of the vertical ridges  5   a  ( FIG. 2C ) is in contact and intersects the inner surface of the thin plate  3   b  of the divisions  2   a  and  2   b.    
   At this time, a filter space is formed in cylindrical shape between the core  1  and the cavity  2 , with a sprue  24  made to communicate with the space via a gate. 
   Then, pressurized molten resin is injected between the core  1  and the cavity  2  from the sprue  24 . At this time, the pressure applied to the resin externally releases the air—air inside a number of the vertical groove portions  5  of the outer circumference of the core  1  and air within a number of the groove portions  4  of the divisions  2   a  and  2   b —in the direction of the radius from the fine gaps in the individual thin plates  3   a  and  3   b , causing the air to flow out of the mold via the air bleeding grooves  20  and air discharge holes  21 . This allows resin to be filled completely into the groove portions  4  and the vertical groove portions  5 . After the hardening of the resin, as the movable plate  13  moves downward in  FIG. 3 , the pair of slide cores  22  opens externally in the direction of the radius. It is to be noted that the slide cores  22  are guided so as to be freely slidable on top of the movable plate  13 . 
   Then, the molded product is retrieved externally as an ejector  17  projects upward in the figure. 
   The molded product thus manufactured is formed as shown in  FIGS. 4A and 4B . In this example, the molded product is formed in cylindrical shape, with a plurality of reinforcement portions  9  arranged between upper and lower end portions  10  and  11  and spaced from each other in the circumferential direction. Filter portions  31  are formed between the reinforcement portions  9  and the upper and lower end portions  10  and  11 . The filter portions  31  have each a number of parallel horizontal ribs  8  and a number of vertical ribs  7  connecting between the horizontal ribs  8 . The vertical and horizontal ribs  7  and  8  are formed in one piece at the intersection portions. 
   Embodiment 
   According to the experiment conducted by the present inventors, the slits (gaps) formed between the horizontal ribs  8  in  FIG. 4B  were successfully made 0.1 mm in height. That is, in  FIGS. 2A and 2B , making the thin plate  3   a  0.1 mm in thickness allowed the air inside the groove portion  4 , formed in the thin plate  3   a , to be released externally. On the other hand, the gap between the vertical ribs  7  was successfully made 0.1 mm. This allowed the filter mesh to be 0.1 mm rectangular holes. 
   &lt;Modification&gt; 
   Next,  FIG. 5  shows another embodiment of the core  1  according to the present invention. This example has a number of disk-shaped thin plates  5   c  stacked in the direction of the center line, with the vertical ridges  5   a , spaced from each other in the circumferential direction, formed on the outer circumference of the core  1  in the direction of the center line. The vertical groove portions  5  are formed between the vertical ridges  5   a . Such the core  1  is manufactured by stacking plates with gear-shaped projections and depressions formed in advance on the outer circumference through press working or by cutting the vertical groove portions  5  with a number of disks stacked. 
   Such the core  1  can move the air inside the vertical groove portions  5  from the fine gaps in the individual thin plates  5   c  toward the center, externally releasing the air from the core  1 . 
   It is needless to say that the present invention is not limited to the aforementioned embodiments, and the plastic filter  6  may have a rectangular horizontal cross-section. 
   While illustrative and presently preferred embodiments of the present invention have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.

Technology Classification (CPC): 8