Abstract:
A method and apparatus for vacuum assisted venting of an injection mold. The apparatus includes a main body structured to be mounted around an outer circumference of the injection mold and configured to facilitate application of a vacuum pressure therein. The method and apparatus are particularly directed towards preventing the accumulation of residual material inside an injection mold and reducing the frequency of disassembly and cleaning required for the injection mold.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This claims the benefit of copending United States Provisional Patent Application No. 60/199,718, filed Apr. 26, 2000, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a method and apparatus for improving the manufacturing process for injection-molded optical discs such as a CD, CD-R, and a DVD, for example. More particularly, the invention relates to a method and apparatus for vacuum assisted venting of an injection mold used to manufacture optical discs. 
     Since the introduction of optical disc technology, the industry is experiencing phenomenal growth as the number of optical discs including CDS, CD ROMs and DVDs manufactured world-wide continues to increase. Naturally, such rapid growth has come with an associated set of technical problems relating to the high-volume manufacturing process used in producing optical discs. The sheer number of optical discs produced at many manufacturing plants coupled with the high production quotas have put a premium on optimizing plant equipment. Of particular concern to optical disc manufacturers is minimizing equipment downtime due to maintenance and repair. 
     The leading manufacturing method for producing optical discs continues to be the standard stamper-injection molding process or some variation of it. During the injection-molding process, a moldable material such as a polycarbonate-based thermoplastic is used to form the disc substrate. The moldable material is liquified by heating to a temperature sufficient to permit uniform flow into the mold cavity. 
     A certain amount of residual material and vapors are released during this process and it therefore becomes necessary to address its collection and disposal. Typically, the injection mold includes a variety of specially configured gaps or vents to provide an area for the vapors and residual material to collect. To prevent the molding process from being adversely effected, however, it is necessary to regularly clean the injection mold and remove the unwanted residual materials from the injection mold. Cleaning the injection mold is a time consuming and cumbersome process that typically involves substantial disassembly of the mold. 
     There have been many improvements to the injection molding process directed generally towards reducing equipment downtime due to routine maintenance and repairs. While these solutions have helped the injection molding process become more streamlined and cost-effective, they have not been successful in substantially reducing the need for frequent disassembly and cleaning of the injection mold itself. 
     As such, there is a need for an innovation in injection molding technology that is oriented towards eliminating the burdensome and time-consuming task of clearing residual material out of the vents in an injection mold. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for vacuum assisted venting of an injection mold that is designed to satisfy all of the aforementioned needs. It is particularly directed towards preventing the accumulation of residual material inside an injection mold and eliminates the need for the time-consuming and difficult task of disassembling the injection mold and removing accumulated residual material. 
     It is an object of this invention to provide a method and apparatus structured to minimize downtime in optical disc manufacturing equipment by eliminating the need to periodically disassemble an injection mold for purposes of clearing and removing accumulated residual material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
     FIG. 1 is a partial cross-sectional view of an illustrative injection mold before the apparatus for vacuum assisted venting is secured (FIG. 1 shows a representative radial section of the mold, with the center of the mold on the left and the radially outer-most part on the right); 
     FIG. 2 is a partial cross-sectional view of the injection mold of FIG. 1 shown with illustrative apparatus for vacuum assisted venting in place; 
     FIG. 3 is a top view of an illustrative mounting bracket for use with the depicted apparatus for vacuum assisted venting; 
     FIG. 4 is a side view of the mounting bracket of FIG. 3; 
     FIG. 5 is a front view of the mounting bracket of FIGS. 3 and 4; 
     FIG. 6 is a side view of illustrative apparatus for vacuum assisted venting in accordance with the present invention taken along the line  6 — 6  in FIG. 7; 
     FIG. 7 is a plan view of the apparatus of FIG. 6; 
     FIG. 8 is a side view taken along the line  8 — 8  in FIG. 7; and 
     FIG. 9 is a cross-sectional view taken along the line  9 — 9  in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In order that the invention herein described may be fully understood, the following detailed description is set forth with reference to FIGS. 1-9. 
     The present invention is configured for use with typical manufacturing equipment for the production of optical discs such as used with the stamper injection molding process or variations of it. A typical injection mold, as shown in representative part in FIG. 1, includes a disc-shaped cavity  240  sandwiched between a stamper  220 , a top plate  260 , and a bottom plate  280 , generally configured as shown. A moldable material  250  such as a polycarbonate-based thermoplastic is commonly used to form the disc substrate. The moldable material  250  is liquified by heating to a temperature sufficient to permit uniform flow into the disc-shaped cavity  240  as shown. The liquified moldable material is forced into the center of the mold (on the left in FIG. 1) and flows radially out in all directions to completely fill cavity  240 . Unfortunately, a certain amount of residual material and vapors are released during the injection molding process. In order to release the residual material and prevent interference with the disc substrate, a variety of specially configured gaps or vents  202 ,  204 ,  206  are provided in the injection mold  200  as shown in FIG.  1 . For example, gaps or vents  202 ,  204 ,  206  preferably extend annularly all the way around the injection mold or are at least disposed at several spaced locations annularly around the mold. Gap or vent  206  is also the “parting line” of the mold (i.e., the line along which mold part  280  separates from the remainder of the mold to allow each successive disc produced in the mold to be removed from the mold). The apparatus for vacuum assisted venting of the present invention is configured to surround an outer circumference  210  of the injection mold  200 , as will be described in greater detail below, and prevent or at least reduce the accumulation of residual material within the vents  202 ,  204 , and  206 . 
     The method of vacuum assisted venting of an injection mold initially requires that vents in an injection mold are identified. Generally, as shown in FIG. 1, vents  202 ,  204  are disposed around an outer circumference  210  of an injection mold  200 . However, it will be appreciated by those skilled in the art that some injection mold configurations may have vent locations considerably different from those shown. The method of vacuum assisted venting of the present invention is designed for use with a variety of different injection mold configurations. In the preferred embodiment, after the vents are identified, at least some of them are surrounded in an enclosed area. Finally, a vacuum is applied to the enclosed area during the molding process in order to prevent or at least reduce the accumulation of residual material in or on the vents of the injection mold. The enclosed area may be configured in a wide variety of ways without departing from the method of the present invention. 
     Illustrative apparatus for vacuum assisted venting  10  in accordance with the present invention is generally shown in FIGS. 2, and  6 - 9 . As best shown in FIG. 7, apparatus  10  includes a main body  20  defining a circular opening  30  therein. As shown in FIGS. 6-9, apparatus  10  includes a top surface  22 , a bottom surface  24 , an inner surface  26 , and an outer surface  28 . Apparatus  10  is configured to be mounted around at least a substantial portion of an outer circumference  210  of an injection mold  200  as best shown in FIG.  2 . It will be understood by those skilled in the art that apparatus  10  can be manufactured from a wide variety of known materials (e.g., steel, structural plastic, or the like) without departing from the present invention. 
     In the preferred embodiment, the inside diameter of the main body  20  of apparatus  10  is adjustable to facilitate easier placement of apparatus  10  around the outer circumference  210  of injection mold  200 . This can be accomplished in a number of different ways. In the preferred embodiment, main body  20  includes an adjustable opening  21  as shown in FIG.  7 . By including an adjustable opening  21 , it is seen that the inside diameter of main body  20  may easily be adjusted by changing the width of adjustable opening  21 . The width of adjustable opening  21  may be changed in a number of ways. In one embodiment, first and second mounting brackets  51 ,  52  may be used similar to those shown in FIGS. 3-5. Preferably, mounting brackets  51 ,  52  are secured to main body  20  in a spaced-apart manner as shown in FIG.  7  and interconnected with a fastener  53 . As is apparent in FIG. 7, opening  21  in main body  20  may be adjusted by tightening or loosening fastener  53 . It will be appreciated by those skilled in the art that mounting brackets  51 ,  52  may be secured to main body  20  in a wide variety of ways. In one embodiment, main body  20  includes a recessed cavity  54 ,  55  to facilitate securing of mounting brackets  51 ,  52  by way of known fasteners. 
     As shown in FIG. 1, the typical injection mold  200  is designed with a variety of specially configured gaps or vents  202 ,  204 ,  206  to provide areas for vapors and residual material to escape during the injection molding process. In the preferred embodiment of the present invention, main body  20  is structured to abut the outer circumference  210  of injection mold  200  as best shown in FIG.  2 . As shown in FIG. 2, the inner surface  26  of main body  20  includes a recessed channel disposed circumferentially therein. Recessed channel  25  is configured to be aligned with vents  202 ,  204  in the injection mold  200  so as to facilitate the application of a vacuum pressure therein. Although apparatus  10  does not directly operate on gap  206 , it even helps keep gap  206  clear by increasing the amount, fraction, or proportion of the unwanted material that exits via gaps  202  and  204 . (Gap  206  should not be in any way obstructed by apparatus  10 , because gap  206  is the parting line of the mold which must open at the completion of each molding cycle to allow each successive disc to be removed from the mold.) 
     The main body  20  of the preferred embodiment includes at least one venting outlet  60  as shown in FIGS. 2,  6 , and  8 . It will be appreciated that a wide variety of configurations may be utilized for venting outlet  60  without departing from the present invention. It is important, however, that venting outlet  60  is structured to facilitate application of a vacuum pressure on vents  202  and  204 . In the preferred embodiment as shown in FIGS. 2,  6 , and  8 , venting outlet  60  is configured as a passageway extending from recessed channel  25  of the inner surface  26  of main body  20  to the outer surface  28  of main body  20 . It will be appreciated by those skilled in the art that a vacuum source may be matingly connected to venting outlet  60  to permit vacuum pressure to be exerted on vents  202  and  204  of injection mold  200 . As such, it is seen that the present invention prevents or at least reduces the accumulation of residual material in or on vents  202  and  204  of the injection mold and thereby substantially reduces the frequency at which the injection mold needs to be disassembled and cleaned. In this regard, it will be appreciated that a novel method and apparatus for vacuum assisted venting has been provided that fulfills the needs previously unmet by the prior art. One skilled in the art will appreciate that this invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation, and this invention is therefore limited only by the claims which follow.