Abstract:
A mold apparatus for forming a pair of mutually opposing guide walls respectively disposed and erected on an upper surface of a half-case of a magnetic tape cassette. The mold apparatus is divided into a third mold and a second mold, and the guide walls to be molded form the boundary between the third and second molds. After injecting resin into the mold apparatus in order to mold the guide walls, the second mold of the mold apparatus is firstly removed in the guide wall erected direction. Then, the third mold of the mold is removed in the same direction, while a distance between the formed guide walls is enlarged by elastic deformation resulting from contact between the guide walls and the third mold.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method for molding a magnetic tape cassette such as a video tape cassette and the like, and more particularly, for molding guide walls of a brake member, in the magnetic tape cassette, which prevents a magnetic tape from loosening. In addition, the present invention relates to an apparatus in which the above-mentioned molding method is operable.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventionally, there are known various types of magnetic tape cassettes that can be used in a video deck. As an example of the magnetic tape cassettes, there are relatively small-sized magnetic tape cassettes used in a digital video cassette (DVC).  
           [0005]    [0005]FIG. 4 is an exploded view of a general magnetic tape cassette  30  that is structured in the following manner. A pair of reels  32   a  and  32   b  is rotatably disposed on a lower half-case  31  (hereinafter referred to as “lower half”). Around the two reels  32   a  and  32   b , a magnetic tape T (shown in FIG. 2) is wound. The magnetic tape T is guided by two tape guides  33   a  and  33   b  located at the right and left sides of the front end of the cassette  30 . The two tape guides  33   a  and  33   b  allow the magnetic tape to pass through an opening  34  formed on the front end side of the lower half  31 . As shown in FIG. 4, teeth  35   a  and  35   b  are formed along the entire peripheral edges of the lower flanges  32 L a  and  32 L b  of the two reels  32   a  and  32   b.    
           [0006]    As also shown in FIG. 4, a brake member  38  is provided between the two reels  32   a  and  32   b  in a space  36  located on the rear side of the lower half  31 . The brake member  38  prevents the magnetic tape T from loosening when the magnetic tape cassette  30  is not loaded in a video deck (not shown), but is instead located in a storage place or is being carried.  
           [0007]    A pair of securing pawls  37   a  and  37   b  is provided near the front end of the brake member  38 . The securing pawls  37   a  and  37   b  form a lock member to lock the rotation of the reels  32   a  and  32   b  together with the brake member  38 . In addition, a compression spring (brake spring)  39  is provided at the rear end of the brake member  38  in the lower half-case  31 . The compression spring is used to urge the brake member  38  towards the front side of the lower half-case  31 .  
           [0008]    As shown in FIG. 4, an upper half-case  40  (hereinafter referred to as “upper half”) cooperates with the lower half  31  to form the magnetic tape cassette  30 . The upper half  40  includes a lid for covering the opening in the front end portion of the lower half  31 . The lid is composed of an outer lid  41 , an upper lid  42 , and an inner lid  43 . The opening can be freely opened and closed using these lids.  
           [0009]    The outer lid  41  of the upper half  40  includes a side plate  44  having a projecting lock pin  45 . Correspondingly, a lid lock  47 , which is rotatably mounted on one side plate  46  of the lower half  31 , locks the outer lid  41  of the upper half  40  by engaging with the lock pin  45 . A plate spring  48  urges the lid lock  47  toward the locking side thereof.  
           [0010]    As shown in FIG. 4, a rotary shaft  44   b  projects from an inner side of the side plate  44  of the outer lid  41 . A lid spring  49 , which is mounted on the rotary shaft  44   b , is used to open and close the outer lid  41 . In FIG. 4, reference numerals of components other than main components of the magnetic tape cassette  30  are omitted, since descriptions thereof are not believed to be essential for an understanding of the general cassette  30 .  
           [0011]    [0011]FIG. 5 shows a conventional lock device for locking the rotation of the reels  32   a  and  32   b  of the general magnetic tape cassette  30  described above with reference to FIG. 4. In the conventional lock device, the brake member  38  is urged in the forward direction, which is the direction in which the compression spring  39  (brake spring) is compressed. The compression spring  39  is supported along the floor surface  31   a  of the lower half  31  shown in FIG. 4, and has one end engaged with the floor surface  31   a  and the other end engaged with the rear end of the brake member  38 . The compression spring  39  urges the brake member  38  in the forward direction when the cassette  30  is not loaded in a video deck. An insertion hole  51  is formed substantially in the central portion of the bottom surface  38   a  of the brake member  38 . A lock release pin of the video deck (not shown) is inserted into the insertion hole  51  of the brake member  38  when the magnetic tape cassette  30  is loaded in a video deck, thereby allowing the reels  32   a  and  32   b  to rotate.  
           [0012]    A pair of guide walls  52   a  and  52   b  is provided on the left and right positions of the insertion hole  51 , and slidingly guides movement of the brake member  38 . Facing brake member removal-prevention projections  53   a  and  53   b  are provided on the upper ends of the two guide walls  52   a  and  52   b  so as to prevent the brake member  38  from being removed from the cassette  30 .  
           [0013]    As described above, the two guide walls  52   a  and  52   b  are conventionally provided on the left and right sides of the brake member  38 . The two guide walls  52   a  and  52   b  are located to the left and right of the insertion hole  51  because it is necessary to facilitate the removal of molds employed in a resin injection-molding method. FIG. 6 is a cross-sectional view of a metal mold  120  used for explaining the conventional molding method. The metal mold  120  is used to mold the lower half  31  of the cassette  30 , and is composed of an upper mold UM and a lower mold LM. The lower mold LM has a component mold CM for molding inner surfaces of the guide walls  52   a  and  52   b . As shown in FIGS. 5 and 6, if the two guide walls  52   a  and  52   b  are erected on the lower half  31  and are disposed adjacent to the insertion hole  51 , the component mold CM may be easily removed in the direction L 6  after completion of the injection-molding.  
           [0014]    However, the location of the pair of guide walls  52   a  and  52   b  has drawbacks in that the brake member removal-prevention projections  53   a  and  53   b , which are provided on the upper ends of the guide walls  52   a  and  52   b , do not sufficiently hold the brake member  38 . In other words, the pair of guide walls  52   a  and  52   b  holds only the substantially central portion of the brake member  38 . As a result, the brake member  38  can fly out or slip off from the two guide walls  52   a  and  52   b  due to the urging force of the compression spring  39  in the assembled magnetic tape cassette.  
           [0015]    In view of the above-described drawback, it is preferable to support the brake member  38  using two or more pairs of guide walls respectively with brake member removal-prevention projections that are the similar to those identified with reference numerals  53   a  and  53   b . For example, as shown in FIG. 2, if two pairs of guide walls have brake member removal-prevention projections, the brake member  38  can be supported in both the front and rear end portions. However, such an arrangement requires that the two pairs of guide walls should be located far from the insertion hole  51 .  
           [0016]    Moreover, the conventional apparatus and methods cannot be used to injection-mold such a two-pair structure because the component mold CM exists between the two guide walls  52   a  and  52   b . As described above, the component mold CM is conventionally removed from the insertion hole  51  in the direction L 6 , as shown in FIG. 6. Therefore, the component mold CM cannot be removed because the brake member removal-prevention projections  53   a  and  53   b  mutually overhang and prevent the component mold CM from being removed in the direction L 6 .  
         SUMMARY OF THE INVENTION  
         [0017]    It is an object of the present invention to overcome the above-mentioned drawbacks found in the conventional magnetic tape cassette molding method and apparatus. That is, it is an object of the present invention to provide a magnetic tape cassette molding method that more easily molds guide walls for holding a brake member.  
           [0018]    A further object of the present invention is to provide an apparatus for performing the above method.  
           [0019]    The above object can be attained by a mold apparatus for injection-molding a magnetic tape cassette having a pair of mutually opposing guide walls respectively erected on an upper surface of a half-case of the magnetic tape cassette.  
           [0020]    The opposing guide walls slidably support a brake member that locks rotations of a pair of tape winding reels disposed within the magnetic tape cassette. Each of the guide walls has a projection for preventing the brake member from being dislodged from between the guide walls. The mold apparatus comprises a first mold, a second mold and a third mold. The first mold, which is removable in a direction that is opposite the erected direction of the guide walls, forms a lower surface of the half-case. The second mold, which is removable in the erected direction of the guide walls, forms outer side surfaces of the guide walls. The third mold, which is removable in the erected direction of the guide walls, forms inner side surfaces of the guide walls that are brought into contact with the brake member. The third mold includes grooved portions respectively forming the projections of the guide walls. When assembled, the first, second and third molds form a molding cavity defined by the pair of mutually opposing guide walls.  
           [0021]    In the above-mentioned construction, it is preferable that the projections of the apparatus are respectively positioned at leading ends of the guide walls.  
           [0022]    Each of the projections of the apparatus, whether or not the projections of the apparatus are respectively positioned at leading ends of the guide walls, may have a surface that curved in cross section.  
           [0023]    At least two pairs of the guide walls of the apparatus, whether or not the projections of the apparatus are respectively positioned at leading ends of the guide walls, are arranged at a predetermined interval in a sliding direction of the brake member.  
           [0024]    Further, in accordance with the present invention, there is provided a method for injection-molding a magnetic tape cassette using a molding apparatus such as the one described immediately above. The method comprises the steps of forming a molding cavity using first, second and third molds such as the ones described above, molding molten resin into the molding cavity so as to form the mutually opposing guide walls, and then removing the second and third molds. The second mold is removed first, in the erected direction of the guide walls, so as to release the second mold from the molded guide walls. The third mold is then removed in the erected direction of the guide walls, while a distance between the projections formed on the guide walls is enlarged due to elastic deformation of the guide walls resulting from contact between the third mold and the projections formed on the guide walls.  
           [0025]    In addition, the method may further comprise the step of guiding the removal of the third mold using the projections, wherein each of the projections has a surface that is curved in cross section. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a plan view of the magnetic tape cassette molded by the magnetic tape cassette molding method according to the present invention;  
         [0027]    [0027]FIG. 2 is an enlarged perspective view of the main portions of the magnetic tape cassette shown in FIG. 1;  
         [0028]    FIGS.  3 (A) to (C) illustrate the mold apparatus and the magnetic tape cassette molding method according to the present invention, showing the order of the molding steps thereof;  
         [0029]    [0029]FIG. 4 is an exploded perspective view of a conventional magnetic tape cassette; and  
         [0030]    [0030]FIG. 5 is an enlarged perspective view of the main portions of the conventional magnetic tape cassette of FIG. 4; and  
         [0031]    [0031]FIG. 6 is a sectional view of a metal mold used for explaining the conventional magnetic tape cassette molding method. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    FIGS.  1  to  3 (A-C) show an embodiment of an apparatus for molding a magnetic tape cassette according to the present invention. Referring to FIG. 1, a magnetic tape cassette  1  includes an upper half (not shown in FIG. 1) and a lower half  2 . A pair of freely rotatable reels  3   a  and  3   b , having a magnetic tape T wound therearound, may be provided in the lower half  2 . Teeth  4   a  and  4   b  extend along the entire peripheral edge of each of the lower flanges of the two reels  3   a  and  3   b , respectively. The teeth  4   a  and  4   b  engage with securing pawls  8   a  and  8   b  (to be discussed further below).  
         [0033]    A lock device  6  is provided in a substantially triangle-shaped space  5 , which is located between and defined by the two reels  3   a  and  3   b . The lock device  6  locks the rotation of the two reels  3   a  and  3   b , and prevents the magnetic tape T from loosening when the magnetic tape cassette  1  is not loaded in a video deck (not shown). Elements or mechanisms, other than the lock device  6  of the present invention, are the same as those of the general magnetic tape cassette discussed above with reference to FIG. 4, and thus descriptions thereof are omitted here.  
         [0034]    The lock device  6 , as shown in FIG. 2, comprises a brake member  7 , two securing pawls  8   a  and  8   b  and a compression spring  9 . The brake member  7  is slidably interposed between the two reels  3   a  and  3   b  to lock the reels  3   a  and  3   b , while the two securing pawls  8   a  and  8   b  are respectively provided on the two sides of the leading end portion of the brake member  7 . The two securing pawls  8   a  and  8   b  engage with the teeth  4   a  and  4   b  that are formed on the reels  3   a  and  3   b , and lock the reels  3   a  and  3   b  in place. The compression spring  9  urges the brake member  7  toward the reels  3   a  and  3   b  when the cassette  1  is not loaded in the video deck.  
         [0035]    As mentioned above, movements of the brake member  7  result in the lock and release of the reels  3   a  and  3   b . This is accomplished by forming a releasing pin insertion hole  10  on the floor surface  31   a  of the lower half  2  (shown in FIG. 4), and a corresponding releasing pin insertion hole a in the lower surface  7   a  of the brake member  7 . When the magnetic tape cassette is loaded into the video deck, a releasing pin of the video deck (not shown) is inserted into the two releasing pin insertion holes  10  and  10   a . This insertion of the releasing pin causes the brake member  7  to return to its original position, and unlock the two reels  3   a  and  3   b.    
         [0036]    Two pairs of guide walls  11   a ,  11   b  and  12   a ,  12   b  are provided on the left and right sides of the brake member  7 , far from the releasing pin insertion hole  10 . In other words, the two pairs of guide walls  11   a ,  11   b  and  12   a ,  12   b  are located at the front and rear end portions of the sliding area of the brake member  7 , and are used for guiding the sliding movements of the brake member  7 . Brake member removal-prevention projections  111   a ,  111   b  and  112   a ,  112   b  are provided at the respective leading ends of the two pairs of guide walls  11   a ,  11   b  and  12   a ,  12   b . The brake member removal projections  111   a ,  111   b  and  112   a ,  112   b  project and overhang inwardly to support the brake member  7  at the top surface  10   b  of the brake member  7 , so as to prevent the sliding brake member  7  from dislodging from the guide walls  11   a ,  11   b  and  12   a ,  12   b.    
         [0037]    Therefore, the two pairs of guide walls  11   a ,  11   b  and  12   a ,  12   b  can smoothly guide the sliding brake member  7 . In addition, the brake member removal-prevention projections  111   a ,  111   b  and  112   a ,  112   b , which are additionally provided on the two pairs of guide walls  11   a ,  11   b  and  12   a ,  12   b , can prevent the brake member  7  from dislodging from the two pairs of guide walls  11   a ,  11   b  and  12   a ,  12   b.    
         [0038]    Each of the surfaces of the respective upper end portions of the brake member removal-prevention projections  111   a ,  111   b  and  112   a ,  112   b  is preferably curved in cross section. The curved surfaces facilitate the insertion, during assembly, of the brake member  7  from the uppermost portion of the guide walls  11   a ,  11   b  and  12   a ,  12   b . In order to insert the lock device  6  between the guide walls  11   a ,  11   b  and  12   a ,  12   b , pressure is applied to the brake member  7  in the downward direction. The pressure can cause the guide walls  11   a ,  11   b  and  12   a ,  12   b  to be elastically flexed in the transverse direction, thereby widening the space between the guide walls  11   a ,  11   b  and  12   a ,  12   b  and allowing the brake member  7  to pass. For this reason, it is preferable that each upper surface of the brake member removal-prevention projections  111   a ,  111   b  and  112   a ,  112   b  is curved in cross section.  
         [0039]    Further, in FIG. 1, when the magnetic tape cassette  1  is not loaded in the video deck, the compressing force of the spring  9  urges the brake member  7  toward the reels  3   a  and  3   b . This compression force thereby forces the securing pawls  8   a  and  8   b , which are provided on the leading end portion of the brake member  7 , into engagement with the teeth  4   a  and  4   b  formed on the peripheral edges of the lower flanges of the rotating reels  3   a  and  3   b . Under such a condition, the reels  3   a  and  3   b  are locked, and the magnetic tape can be prevented from slackening.  
         [0040]    On the other hand, when the magnetic tape cassette  1  is loaded into the video deck, the locking of the reels  3   a  and  3   b  can be released by a locking release pin (not shown) provided in the video deck. As shown in FIG. 1, a stopper  13 , located in the substantially triangle-shaped space  5  at a position near the center of the lower half  2 , is provided to restrict the moving range of the brake member  7 . Additionally, ribs  14  are placed to the left and right of the space  5  near the outer periphery of the lower half  2 , so as to reinforce the triangle-shaped space  5  of the magnetic tape cassette.  
         [0041]    FIGS.  3 (A) to (C) illustrate the method for molding the lower half  2  of the magnetic tape cassette, according to the present invention. A metal mold  20  used for performing this molding method is composed of an upper mold  21  and a lower mold  22 . The lower mold  22  can be composed of a single mold. On the other hand, the upper mold  21  is composed of both a guide wall inner mold  23  and a guide wall outer mold  24 . The guide wall inner mold  23  and the guide wall outer mold  24  define a cavity between the guide walls  11   a  and  11   b ,  12   a  and  12   b.    
         [0042]    The guide wall inner mold  23  forms the guide walls  11   a  and  11   b ,  12   a  and  12   b . The guide wall inner mold  23  has flat portions  25   a  and  25   b  that are preferably erected in the vertical direction on the lower half  2 . In addition, the guide wall inner mold  23  has curved-groove portions  26   a  and  26   b  that are grooved more inwardly than the flat portions  25   a  and  25   b , and are used for forming the brake member removal-prevention projections  111   a ,  111   b  and  112   a ,  112   b . The flat portions  25   a  and  25   b  and the curved-groove portions  26   a  and  26   b  are arranged in the substantially triangle-shaped space  5  shown in FIG. 2. The arrangement preferably corresponds to the front and back portions of the space  5  of the magnetic tape cassette  1  to be molded.  
         [0043]    As shown in FIGS.  3 (A) to (C), recessed grooves  27 , which are used to shape ribs  14 , are formed on the bottom surface of the guide wall inner mold  23 . In practical use, the one pair of guide walls  11   a  and  11   b  need not be arranged so as to form a row with the other pair of guide walls  12   a  and  12   b.    
         [0044]    As shown in FIGS.  3 (A) to (C), the guide wall outer mold  24  of the upper mold  21  is structured such that the inside portions thereof are formed as flat and vertical surfaces. Grooves  27  located on the bottom surface of the guide wall outer mold  24  are used to mold the ribs  14 . On the other hand, the lower mold  22  is structured so as to have a flat upper surface.  
         [0045]    As shown in FIG. 3(A), in order to injection-mold the lower half  2  of the magnetic tape cassette  1 , the metal mold  20  is first assembled. That is, the lower mold  22  and the upper mold  21 , which is composed of the guide wall inner mold  23  and the guide wall outer mold  24 , are assembled. Resin is then injected into the cavity defined by the metal mold  20 , and the lower half  2  (shown in FIGS.  3 (A) to (C)) is molded.  
         [0046]    After the lower half  2  is molded, the lower mold  22  is separated from the lower half  2  in the direction L 4 , as shown in FIG. 3(A). The guide wall outer mold  24  is then separated from the newly molded lower half  2  in the direction U 4 , as shown in FIG. 3(B). Because there are no recessed portions in the guide wall outer mold  24 , the guide wall outer mold  24  can be removed with ease. Alternatively, the lower mold  22  may be removed after the guide wall outer mold  24  and the guide wall inner mold  23  of the upper mold  21  are removed from the molded lower half  2 .  
         [0047]    Then, as shown in FIG. 3(C), the guide wall inner mold  23  of the upper mold  21  is removed from the lower half  2  in the direction U 4 . The guide wall outer mold  24  must be removed before the guide wall inner mold  23  so that the guide wall inner mold  23  can be removed smoothly. That is, after the guide wall outer mold  24  is removed, the molded guide walls  11   a ,  11   b ,  12   a  and  12   b , as shown in FIG. 3(C), may be elastically deformed in the widening direction Wa and Wb. This removal operation is termed “forcible removal”. Additionally, because each lower end of the brake member removal-prevention projections  111   a ,  111   b ,  112   a  and  112   b  has a surface that is curved in cross section, the guide walls  11   a ,  11   b ,  12   a  and  12   b  can be elastically deformed more smoothly while removing the guide wall inner mold  23 .  
         [0048]    With the conventional molding method described in the background section of this application, the structure of the apparatus determines the method of removal. Therefore, the guide walls having the brake member removal-prevention projections are unable to be molded at positions far from the releasing pin insertion hole  10 .  
         [0049]    On the other hand, according to the present invention, the lower half  2  of the magnetic tape cassette  1  can be injection-molded even though the magnetic tape cassette  1  has guide walls  11   a ,  11   b ,  12   a  and  12   b  including brake member removal-prevention projections  111   a ,  111   b ,  112   a  and  112   b . That is, the guide wall inner mold  23  can be removed easily even when the guide walls having the brake member removal-prevention projections are located at positions far from the releasing pin insertion hole  10 . This removal is easily accomplished because the upper mold  21  is divided into the guide wall inner mold  23  and the guide wall outer mold  24 , and the guide wall outer mold  24  is removed before the guide wall inner mold  23 .  
         [0050]    Since the brake member removal-prevention projections  111   a ,  111   b ,  112   a  and  112   b  of the guide walls  11   a ,  11   b ,  12   a  and  12   b  support the brake member  7  from above, the brake member  7  can be slid more smoothly than the conventional device. Furthermore, the additional support provided by the four projections virtually eliminates the possibility that the brake member  7  will become dislodged from the guide walls  11   a  and  11   b,    12   a  and  12   b.    
         [0051]    In the above-mentioned embodiment, the two pairs of guide walls  11   a ,  11   b  and  12   a ,  12   b  may be respectively provided in the front and rear portions of the brake member  7 . However, the invention is not limited to this structure. The invention may, for example, instead include a pair of long guide walls extending from the front to the rear portions of the brake member  7 . Such a structure also permits the components molds to be removed with ease, and can prevent the brake member  7  from being dislodged from the guide walls  11   a ,  11   b ,  12   a ,  12   b.    
         [0052]    As has been described hereinabove, according to the present invention, the upper mold is divided into a guide wall inner mold and a guide wall outer mold. First, the guide wall outer mold is removed in the upward and vertical direction. Next, the guide wall inner mold is removed in the same direction. Owing to this, it is possible to produce, by injection-molding resin using the metal mold  10 , a magnetic tape cassette that has guide walls located in a position far from the releasing pin insertion hole.  
         [0053]    Additionally, it is surely possible to prevent the brake member from becoming dislodged from the guide walls, even though the guide walls are located in positions far from the releasing pin insertion hole  10 .  
         [0054]    The present application is based on Japanese Patent Application No. Hei. 9-161441, which is incorporated herein by reference.  
         [0055]    While only certain embodiments of the invention have been specifically described herein, it will be apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention.