Patent Publication Number: US-2009224091-A1

Title: Reel and recording tape cartridge

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC 119 from Japanese Patent Application No. 2008-055042, the disclosure of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a reel for winding recording tape such as magnetic tape, for example, and to a recording tape cartridge disposed with this reel. 
     2. Description of the Related Art 
     There is known a technology where a circular cylinder-shaped metal insert portion is disposed in a hub that is made of resin and winds magnetic tape (e.g., see JP-A No. 2005-116163). 
     Incidentally, when the reel, into whose hub the metal insert portion is inserted, is formed by injection molding, there is the problem that it is easy for cracks running parallel to each other in the circumferential direction to form in the end surfaces of the hub because contraction in the circumferential direction of the hub is controlled by the metal insert portion, and this causes yield deterioration. 
     SUMMARY OF THE INVENTION 
     In view of these circumstances, it is an object of the present invention to obtain a reel and a recording tape cartridge that can control the occurrence of cracks in the end surfaces of a reel hub that is made of resin. 
     A reel pertaining to a first aspect of the invention is disposed with a reel hub made of resin whose outer peripheral surface is configured as a take-up surface of an object-to-be-taken-up and a reinforcement ring that is integrated with the reel hub by insert molding, with reinforcement fiber being mixed into the reel hub or a portion made of resin formed integrally with the reel hub, the reel comprising: marks of gates for injecting, into a die, a resin material that molds the reel hub; and at least one of thick portions that are positioned on the reinforcement ring side with respect to the marks of the gates and thin portions that are positioned on both sides, in a circumferential direction of the reel hub, with respect to the marks of the gates. 
     In the reel of the first aspect of the invention, resin that has been injected from the gates is solidified inside the die in which the reinforcement ring has been set, whereby the reel hub with which the reinforcement ring has been integrated is formed. In this reel, the marks of the gates are disposed on a radial direction inner side or outer side, with respect to the reinforcement ring, of the reel hub or the portion made of resin formed integrally with the reel hub. 
     Around the gates, there is formed at least one of thick portions that promote the flow of the resin along the radial direction of the reel hub from the gates and thin portions that control the flow of the resin in the circumferential direction of the reel hub from the gates, so the flow of the resin at the time of molding flows mainly from the gates toward the reinforcement ring along the radial direction of the reel hub and thereafter flows in the circumferential direction along the reinforcement ring and the take-up surface. Thus, in the present reel, the reinforcement fiber in the resin is oriented along the circumferential direction of the reinforcement ring and the take-up surface. For this reason, in the present reel, the occurrence of cracks along the radial direction in the end surfaces of the reel hub is effectively controlled. 
     In this manner, in the reel of the first aspect of the present invention, the occurrence of cracks in the end surfaces of a reel hub made of resin can be controlled. 
     A reel pertaining to a second aspect of the invention is disposed with a reel hub made of resin whose outer peripheral surface is configured as a take-up surface of an object-to-be-taken-up and a reinforcement ring that is integrated with the reel hub by insert molding, with reinforcement fiber being mixed into the reel hub or a portion made of resin formed integrally with the reel hub, the reel comprising: a mark of gates for injecting, into a die, a resin material that molds the reel hub; and marks of a guide structure that is disposed between the marks of the gates and the reinforcement ring and is for guiding the flow of the resin from the gates toward the reinforcement ring at the time of molding of the reel hub. 
     In the reel of the second aspect of the invention, resin that has been injected from the gates is solidified inside the die in which the reinforcement ring has been set, whereby the reel hub with which the reinforcement ring has been integrated is formed. In this reel, the marks of the gates are disposed on a radial direction inner side or outer side, with respect to the reinforcement ring, of the reel hub or the portion made of resin formed integrally with the reel hub. 
     Around the gates, there are formed the marks of the guide structure, so the flow of the resin at the time of molding is guided by the guide structure, whereby the flow of the resin at the time of molding flows mainly from the gates toward the reinforcement ring along the radial direction of the reel hub and thereafter flows in the circumferential direction along the reinforcement ring and the take-up surface. Thus, in the present reel, the reinforcement fiber in the resin is oriented along the circumferential direction of the reinforcement ring and the take-up surface. For this reason, in the present reel, the occurrence of cracks along the radial direction in the end surfaces of the reel hub is effectively controlled. 
     In this manner, in the reel of the second aspect of the present invention, the occurrence of cracks in the end surfaces of a reel hub made of resin can be controlled. 
     In the reel of the second aspect of the invention, the marks of the guide structure may include at least one of thick portions that are positioned on the reinforcement ring side with respect to the marks of the gates and thin portions that are positioned on both sides, in a circumferential direction of the reel hub, with respect to the marks of the gates. 
     In the reel of this configuration, the thick portions contribute to guiding the flow of the resin in the direction along the radial direction of the reel hub from the gates because of the relatively large flow path cross-sectional area of the thick portions, and the thin portions contribute to controlling the flow of the resin in the circumferential direction of the reel hub from the gates because of the relatively small flow path cross-sectional area of the thin portions. Because of at least one of these, at the time of molding of the present reel, the flow of the resin is guided in the direction along the radial direction of the reel hub from the gates. 
     Further, a recording tape cartridge is provided by comprising: a case; and the reel of the first aspect or the second aspect of the invention, with recording tape being wound around the take-up surface of the reel hub and the reel being housed in the case such that the recording tape is capable of being pulled out and taken up. 
     In the recording tape cartridge configured as described above, the recording tape that is wound around the reel hub of the reel is pulled out from the case, and reading and writing (or either one) of information are performed. The occurrence of cracks in the end surfaces of the reel hub is controlled because the recording tape cartridge employs the reel of the first or second aspect as this reel. 
     In this manner, in the recording tape cartridge of this configuration, the occurrence of cracks in the end surfaces of a reel hub made of resin can be controlled. 
     As described above, the reel pertaining to the present invention has the excellent effect that it can control the occurrence of cracks in the end surfaces of a reel hub made of resin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1A  and  FIG. 1B  are enlarged views showing relevant potions of a reel pertaining to an embodiment of the present invention, with  FIG. 1A  being a perspective view showing the reel as seen from above and  FIG. 1B  being a perspective view showing the reel as seen from below; 
         FIG. 2A  is a bottom view schematically showing resin flow directions at the time of molding of the reel pertaining to the embodiment of the present invention, and  FIG. 2B  is a bottom view schematically showing resin flow directions at the time of molding of a reel pertaining to a comparative example; 
         FIG. 3  is an exploded perspective view showing a partial cutaway of the reel pertaining to the embodiment of the present invention as seen from below; 
         FIG. 4  is an exploded perspective view showing the reel pertaining to the embodiment of the present invention as seen from above; 
         FIG. 5  is a cross-sectional view of a reel hub that configures the reel pertaining to the embodiment of the present invention; 
         FIG. 6A  and  FIG. 6B  are views showing the exterior of a recording tape cartridge to which the reel pertaining to the embodiment of the present invention is applied, with  FIG. 6A  being a perspective view showing the recording tape cartridge as seen from above and  FIG. 6B  being a perspective view showing the recording tape cartridge as seen from below; 
         FIG. 7  is a cross-sectional view, at a time when rotation of the reel is locked, of the recording tape cartridge to which the reel pertaining to the embodiment of the present invention is applied; 
         FIG. 8  is a cross-sectional view, at a time when rotation of the reel is unlocked, of the recording tape cartridge to which the reel pertaining to the embodiment of the present invention is applied; 
         FIG. 9  is a cross-sectional view showing a process of injection-molding the reel hub that configures the reel pertaining to the embodiment of the present invention; 
         FIG. 10  is a bottom view schematically showing resin flow directions at the time of molding of a reel pertaining to a modification of the embodiment of the present invention; and 
         FIG. 11A  and  FIG. 11B  are enlarged views showing relevant portions of the reel pertaining to the comparative example of the embodiment of the present invention, with  FIG. 11A  being a perspective view showing the reel as seen from above and  FIG. 11B  being a perspective view showing the reel as seen from below. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     A reel  28  pertaining to an embodiment of the present invention and a recording tape cartridge  10  to which the reel  28  is applied will be described on the basis of  FIG. 1A  to  FIG. 9 . First, the general overall configuration of the recording tape cartridge  10  will be described, next the configuration of the reel  28  will be described, and thereafter the configuration of gate mark portions, which are relevant portions of the present invention, will be described in detail. 
     In  FIG. 6A , there is shown a perspective view where the recording tape cartridge  10  is seen diagonally from above, and in  FIG. 6B , there is shown a perspective view where the recording tape cartridge  10  is seen diagonally from below. Further, in  FIG. 7 , there is shown a cross-sectional view along line  7 - 7  of  FIG. 6A . It will be noted that arrow A shown in  FIG. 6A  and  FIG. 6B  represents the direction in which the recording tape cartridge  10  is loaded into a drive device, and in the following description, the side represented by arrow A will be referred to as a front side for the sake of convenience. Further, the side represented by arrow U will be referred to as an upper side. 
     As shown in these drawings, the recording tape cartridge  10  is disposed with a case  12 . The case  12  is configured by joining together an upper case  14  and a lower case  16 . Specifically, the upper case  14  is configured as a result of a substantially frame-like peripheral wall  14 B being disposed upright along the outer edge of a top plate  14 A that has substantially rectangular shape when seen in a planar view, and the lower case  16  is configured as a result of a substantially frame-like peripheral wall  16 B being disposed upright along the outer edge of a bottom plate  16 A that has a shape substantially corresponding to that of the top plate  14 A. Additionally, the case  12  is formed in a substantially box-like shape when the upper case  14  and the lower case  16  are joined together by ultrasonic welding or with screws in a state where the open end of the peripheral wall  14 B and the open end of the peripheral wall  16 B have been brought into contact with each other. 
     An opening  18  that slants with respect to the loading direction is formed in the case  12  by cutting out corner portions of the top plate  14 A, the peripheral wall  14 B, the bottom plate  16 A and the peripheral wall  16 B on the leading side in the direction in which the recording tape cartridge  10  is loaded into the drive device. Further, a circular gear opening  20  that penetrates the bottom plate  16 A is disposed in the substantial center portion of the bottom plate  16 A and serves to expose a later-described reel gear  62 . An annular rib  22  is disposed on the edge portion of the gear opening  20  in the bottom plate  16 A so as to project inside the case  12  (see  FIG. 7 ) and serves to position the later-described reel  28 . 
     A pair of positioning holes  24  and  26  are formed in the outer surface of the bottom plate  16 A in the vicinity of the front end of the case  12 . The pair of positioning holes  24  and  26  are disposed sac-like inside projecting portions (not shown) disposed upright inside the case  12  from the bottom plate  16 A and are arranged apart from each other on a hypothetical line orthogonal to the loading direction. The positioning hole  24  near the opening  28  has a substantially square shape when seen in a bottom view that circumscribes a positioning pin of the drive device, and the positioning hole  26  is an elongate hole that is long along the hypothetical line and has a width corresponding to the diameter of a positioning pin. Thus, when the recording tape cartridge  10  is loaded into the drive device and the positioning pins are respectively inserted into the positioning holes  24  and  26 , the recording tape cartridge  10  is accurately positioned in the horizontal direction (left and right, front and back) inside the drive device. 
     Moreover, the portions of the bottom plate  16 A around the positioning holes  24  and  26  serve as positioning surfaces  24 A and  26 A that are finished more smoothly than the other portion (design surface) of the bottom plate  16 A. The positioning surfaces  24 A and  26 A are configured to contact positioning surfaces of the drive device disposed around the positioning pins when the positioning pins are inserted into the positioning holes  24  and  26 . Thus, the recording tape cartridge  10  is also positioned in the vertical direction inside the drive device. 
     As shown in  FIG. 7 , the reel  28 , which will be described in detail later, is rotatably housed inside the case  12  that has been described above. Just one reel  28  is disposed. Magnetic tape T that serves as recording tape is wound onto the reel  28 , and a leader block  30  that serves as a pullout member is attached to the leading end of the magnetic tape T. 
     The leader block  30  is configured to be housed and held inside the opening  28  in the case  12  when the recording tape cartridge  10  is not in use. In this state, the leader block  30  closes off the opening  18  and deters the ingression of dust or the like into the inside of case  12 . Further, an engagement concave portion  30 A is formed in the leading end of the leader block  30 , so that when the magnetic tape T is to be pulled out inside the drive device, the leader block  30  is pulled out from the case  12  by pullout means engaging with the engagement concave portion  30 A and is guided to a take-up reel of the drive device. Moreover, the end surface of the leader block  30  on the opposite side of the engagement concave portion  30 A serves as a circular arc surface  30 B and is fitted into the take-up reel to configure part of a take-up surface that takes up the magnetic tape T. 
     Further, the recording tape cartridge  10  is disposed with a brake member  32  for deterring rotation of the reel  28  when the recording tape cartridge  10  is not in use. The brake member  32  has, as its main portions, a disc portion  34  that is formed in a disc shape, a brake gear  36  that is formed face down on the peripheral edge portion of the disc portion  34 , a cross-shaped projection  38  that is disposed so as to project upward from the axial center portion of the disc portion  34 , and a slide-contact projecting portion  35  disposed so as to project downward from the axial center portion of the disc portion  34 . An insertion groove  38 A formed in a substantial cross shape when seen in a planar view is formed in the cross-shaped projection  38  in correspondence to the shape of the cross-shaped projection  38 , and a cross-shaped rib  40  disposed face down from the top plate  14 A is inserted into the insertion groove  38 A so as to be capable of relative movement (sliding motion) in the up and down direction. Thus, the brake member  32  is configured to be incapable of rotation with respect to the case  12  and capable of relative displacement in the up and down direction. 
     The brake gear  36  of the brake member  32  meshes with an engagement gear  52  disposed in a bottom plate  48  configuring the reel  28  (these will be described later) to thereby prevent rotation of the reel  28  with respect to the case  12 , and the brake member  32  moves in the up and down direction (axial line direction of the reel  28 ) with respect to the case  12  to thereby switch between a state where the brake gear  36  meshes with the engagement gear  52  and a state where the brake gear  36  disengages from the engagement gear  52 . A compression coil spring  42  that energizes the brake member  32  toward the bottom plate  48  is disposed in the recording tape cartridge  10 , and ordinarily the brake gear  36  of the brake member  32  is biased in a brake position where it is meshed with the engagement gear  52 . 
     Further, the recording tape cartridge  10  is disposed with a clutch member  44  that penetrates the axial center portion of the bottom plate  48  of the reel  28  and is supported so as to be capable of coaxial and integral rotation with the reel  28 , capable of relative displacement in the axial line direction with respect to the reel  28 , and incapable of falling out. The clutch member  44  is pressed by the slide-contact projecting portion  35  of the brake member  32  whose brake gear  36  is meshed with the engagement gear  52 , so that part of the clutch member  44  projects outside (below) the reel  28 . The brake member  32  is configured such that, when the slide-contact projecting portion  35  is pressed upward, the brake member  32  moves upward and reaches a release position where the meshing between the brake gear  36  and the engagement gear  52  is released. 
     In this embodiment, the clutch member  44  is configured to be pressed upward by a release surface  101  disposed in the axial center portion of a rotating shaft  100  of the drive device to thereby cause the brake member  32  to move from the brake position to the release position. 
     To add more in regard to the rotating shaft  100 , the rotating shaft  100  includes a rotating table  104  fixed to the upper end of a rotating axle  102 , and a drive gear  106  capable of meshing with the reel gear  62  (described later) of the reel  28  is formed facing upward on the peripheral edge portion of the rotating table  104 . Thus, the rotating shaft  100  is configured to move relatively upward with respect to the case  12  to thereby cause the drive gear  106  to mesh with the reel gear  62 . Further, a disc-shaped magnet  108  is disposed on the radial direction inner side of the drive gear  106  on the rotating table  104 , and the magnet  108  is fixed by a tap bolt  110  that penetrates the axial center portion of the magnet  108  and is screwed into the rotating axle  102 . The aforementioned release surface  101  is configured by a head portion  110 A of the tap bolt  110 . 
     The recording tape cartridge  10  that has been described above is configured such that, during rotation of the reel  28  (when the magnetic tape T is being pulled out or taken up), relative rotation occurs between the slide-contact projecting portion  35  (the brake member  32 ) that does not rotate with respect to the case  12  and the clutch member  44  that rotates together with the reel  28 , and the distal end (lower end) of the slide-contact projecting portion  35  and the upper surface of the clutch member  44  slide against each other because of this relative rotation. 
     (Configuration of Reel) 
     As shown in  FIG. 3  to  FIG. 5 , the reel  28  is disposed with a reel hub  45  that configures the axial center portion of the reel  28 . The reel hub  45  is formed in a substantially bottomed circular cylinder shape including a circular cylinder wall  46  whose outer peripheral surface serves as a tape take-up surface  46 A for winding the magnetic tape T and a bottom plate  48  that closes off the lower portion of the circular cylinder wall  46 . An upper flange  50  is disposed so as to extend coaxially and integrally outward in the radial direction from the upper end of the circular cylinder wall  46  of the reel hub  45 . 
     Further, the engagement gear  52  capable of meshing with the brake gear  36  of the brake member  32  is formed facing upward on the bottom plate  48  of the reel hub  45 . That is, as described above, the engagement gear  52  is configured to mesh with the brake gear  36  of the brake member  32  positioned in the brake position and, when the meshing between the engagement gear  52  and the brake gear  36  of the brake member  32  positioned in the release position is released, to allow rotation about the axis of the reel  28 . In this embodiment, the engagement gear  52  is formed such that its teeth are arranged annularly when seen in a planar view. 
     Moreover, a through hole  54  that penetrates the bottom plate  48  in its plate thickness direction is formed in the axial center portion of the bottom plate  48  of the reel hub  45  and is configured to be able to allow part of the clutch member  44  to project therefrom. A short circular cylinder portion  55  that serves as a cylindrical portion is disposed facing upward upright from the peripheral edge portion of the through hole  54  in the bottom plate  48 . The short circular cylinder portion  55  is formed integrally with the reel hub  45  and may be understood to have a turn-back shape with respect to the circular cylinder wall  46 . 
     Excluding a reinforcement ring  68  that will be described later, each portion of the reel hub  45  described above, whose main portions are the circular cylinder wall  46 , the bottom plate  48 , the engagement gear  52  and the short circular cylinder portion  55 , is formed integrally by resin molding as shown in  FIG. 5 . 
     Further still, as shown in  FIG. 3  to  FIG. 5 , the reel  28  includes a lower flange  56  that faces the upper flange  50 . The lower flange  56  is disposed so as to extend integrally outward in the radial direction from a center portion  58  that is joined together (this joined structure will be described later) with the bottom plate  48  of the reel hub  45 , and the lower flange  56  is fixedly held to the reel hub  45  via this center portion  58 . A lower flange member  60  that serves as a flange member is configured by the lower flange  56  and the center portion  58 . 
     The reel gear  62  capable of meshing with the drive gear  106  of the rotating shaft  100  of the drive device is formed facing downward on the center portion  58  of the lower flange member  60 . The reel gear  62  is configured overall such that its plural teeth are arrayed so as to form an annular shape that is coaxial with the lower flange member  60 , that is, the reel  28 . It will be noted that the reel gear  62  may also be configured to include regions where teeth are not formed in part of its circumferential direction. 
     Further, as shown in  FIG. 4  and  FIG. 5 , a clutch-use boss portion  64  for supporting the clutch member  44  is disposed facing upward upright from the axial center portion of the center portion  58 . The clutch-use boss portion  64  is formed in a circular cylinder shape, is configured such that slits  64 A that allow plural engagement pieces  44 A projecting radially from the upper portion of the clutch member  44  to enter are formed in its cylinder wall, and supports the clutch member  44  such that the clutch member  44  is capable of sliding in its axial line direction and is incapable of relative rotation and incapable of falling out at each slide position. The clutch-use boss portion  64  is configured such that its outer diameter substantially coincides with the inner diameter of the through hole  54 , that is, the short circular cylinder portion  55 , and to fit together with the short circular cylinder portion  55 . 
     Each portion of the lower flange member  60  described above, whose main portions are the lower flange  56 , the center portion  58 , the reel gear  62  and the clutch-use boss portion  64 , is formed integrally by resin molding. 
     Moreover, as shown in  FIG. 3  to  FIG. 5 , a reel plate  66  that serves as a metal plate comprising a magnetic body is fixedly disposed on the center portion  58 . The reel plate  66  is formed in a substantial disc shape having a clear hole  66 A in its axial center portion and is disposed coaxially on the radial direction inner side of the reel gear  62 . The reel plate  66  is configured to be attracted by magnetic force to, but without contacting, the rotating table  104  of the rotating shaft  100  of the drive device. 
     The reel plate  66  is fixed to the center portion  58 , that is, the lower flange member  60 , by insert molding. Specifically, plural (in the present embodiment, four) small holes  66 B disposed at equidistant intervals in the circumferential direction along a hypothetical circle coaxial with the clear hole  66 A are formed in the reel plate  66  so as to penetrate the reel plate  66  in its plate thickness direction, and the portions of the small holes  66 B on the underside of the reel plate  66  serve as an enlarged diameter portion to configure a so-called pillbox shape. The reel plate  66  is strongly fixed to the lower flange member  60  as a result of a resin material that has been injected into dies and has filled each of the small holes  66 B cooling and solidifying. It will be noted that the reel plate  66  may also have a structure where it is fixed to the lower flange member  60  by caulking or the like. 
     In the reel  28  that has been described above, the lower flange member  60  is, as described above, joined together with the bottom plate  48  of the reel hub  45  at the lower flange  56 . Specifically, in this embodiment, as shown in  FIG. 3 , welding-use projections (energy directors)  70  are disposed so as to project from the undersurface of the bottom plate  48 , and ultrasonic oscillation is applied in a state where the welding-use projections  70  have been brought into contact with the upper surface of the center portion  58 , whereby the reel hub  45  and the lower flange member  60  are ultrasonically welded together at the installation portions of the welding-use projections  70 . 
     From this drawing, it will be understood that the reel hub  45  and the lower flange member  60  are joined together inside the installation region of the reel plate  66 . More specifically, the welding-use projections  70 , that is, the welding sites, are, as shown in  FIG. 3 , disposed so as to project intermittently along a hypothetical circle that is coaxial with the reel  28 . This hypothetical circle is, as shown in  FIG. 5 , configured to have a smaller diameter than the inner edges of the engagement gear  52  and the reel gear  62  and a larger diameter than the diameter of a hypothetical circle that the outer diameter of the clutch-use boss portion  64  and the welding-use projections  70  inscribe. 
     Further, in this embodiment, the reel  28  is disposed with a reinforcement ring  68  that is integrated by insert molding with the circular cylinder wall  46  of the reel hub  45 . The reinforcement ring  68  is made of metal and is configured to have a structure that controls deformation of the circular cylinder wall  46 , whose upper end is open, in the direction in which the circular cylinder wall  46  collapses inward the radial direction by the winding pressure of the magnetic tape T. The reinforcement ring  68  is configured by a drawn material such as aluminium or an aluminium alloy, for example. In this embodiment, the reinforcement ring  48  comprises aluminium or an aluminium alloy and has a thickness along its radial direction of substantially 1.0 mm. More specifically, the reinforcement ring  68  is configured by an aluminium material that has a proof stress of 350 [N/mm 2 ]. This proof stress is set such that the deformation amount of the tape take-up surface  46 A with respect to the winding constriction (winding pressure) of the magnetic tape T that is wound around the tape take-up surface  46 A of the reel hub  45  becomes equal to or less than an allowable amount (such that settling does not arise). 
     The reel hub  45  is configured by polycarbonate (PC). The thickness of a portion  34 A on the radial direction outer side, with respect to the reinforcement ring  68 , of the circular cylinder wall  46  of the reel hub  45  is set to be in the range of 1.0 mm to 1.5 mm. In this embodiment, the thickness is set to be substantially 1.5 mm. In this embodiment, the reel hub  45  and the upper flange  50  are configured by polycarbonate into which glass fiber that serves as reinforcement fiber has been mixed at 10% by mass. 
     It will be noted that the reinforcement ring  68 , which is to be understood as a reinforcement (stiffening) member for improving the radial direction rigidity of the circular cylinder wall  46  of the reel  45 , is not limited to a dimension (thickness) and material (physical property) as long as it satisfies this function. Consequently, for example, a steel material, or a non-metal material such as resin or fiber-reinforced resin, can be used as the reinforcement ring  68 . It will be noted that, in this embodiment, a corrosion control treatment such as plating, for example, is administered to the surface of the reinforcement ring  68  because aluminium is corrosive. 
     (Configuration of Gate Mark Portions) 
     As shown in  FIG. 4  and  FIG. 5 , gate marks Gm, which are marks of gates Gt (injection openings) for injecting a resin material into dies when the reel hub  45  is injection-molded, are formed on the bottom plate  48  of the reel hub  45 . In this embodiment, the gate marks Gm are plurally (three) formed between the teeth of the engagement gear  52  on the bottom plate  48 . In other words, in the reel  28 , the engagement gear  52  is divided into three (three equal portions) in the circumferential direction by the three gate marks Gm. Consequently, the reel hub  45  is configured to be molded as a result of the resin material being injected from the upper surface side of the bottom plate  48  on the radial direction inner side with respect to the circular cylinder wall  46  and the reinforcement ring  68 . 
     As shown in the enlarged view of the gate marks Gm in  FIG. 1A , groove portions  72  that open upward are formed along the radial direction of the reel hub  45  on both circumferential direction sides of the gate marks Gm. The radial direction inner ends of the groove portions  72  are positioned further inward in the radial direction than a hypothetical circle that inscribes the three gate marks Gm, and the radial direction outer ends of the groove portions  72  are positioned close to the reinforcement ring  68  on the radial direction outer side of the hypothetical circle that inscribes the three gate marks Gm. The sites where these groove portions  72  are formed correspond to thin portions in the present invention. 
     Further, as shown in  FIG. 3  and  FIG. 5 , convex portions  74  are formed on the back surfaces of the gate marks Gm on the bottom plate  48 . The convex portions  74  are formed in a circular shape that is substantially concentric with the gate marks Gm when seen in a bottom view and are configured as marks of recesses of a die for ensuring the fluidity of the resin at the time of injection molding of the reel hub  45 . It will be noted that, in response to the dimensional shape of the reel hub  45  (the thickness of the bottom plate  48 , etc.), the reel  28  may also be given a configuration where the convex portions  74  are not disposed. 
     Additionally, as shown in  FIG. 1B , which shows the reel hub  45  as seen from its back surface (undersurface) side, in this embodiment, convex portions  76  are formed on the radial direction outer side of the convex portions  74 , that is, the gate marks Gm. The convex portions  76  are formed in substantially triangular shapes (each by itself has a substantially triangular cross section) when seen in a side view such that the convex portions  76  project downward and inward in the radial direction from a tapered portion  48 A whose diameter gradually becomes larger downward at the peripheral edge portion of the bottom plate  48 , and the convex portions  76  configure thick portions of the bottom plate  48 , that is, thick portions in the present invention. 
     As shown in  FIG. 3  and  FIG. 5 , the convex portions  76  are positioned between the reinforcement ring  68 , whose lower end  68 A is embedded between the circular cylinder wall  46  and the tapered portion  48 A of the bottom plate  48 , and the gate marks Gm, which are positioned close to the tapered portion  48 A, in the radial direction of the reel hub  45 . 
     Further, in the reel  28  pertaining to this embodiment, the convex portions  76  are configured to function as rotation stoppers when the reel hub  45  and the lower flange member  60  are joined together. That is, as shown in  FIG. 4 , three concave portions  78  are formed in the center portion  58  of the lower flange member  60  in correspondence to the three convex portions  76 , and the convex portions  76  are fitted inside the concave portions  78 , whereby the circumferential direction position of the lower flange member  60  is determined with respect to the reel hub  45  before ultrasonic welding. It will be noted that the concave portions  78  are configured so as to allow the corresponding convex portions  76  and the corresponding convex portions  74  to be fitted inside. 
     As described above, the reel hub  45 , where the groove portions  72  and the convex portions  76  are formed around the gate marks Gm, is configured such that, at the time of injection molding, the flow of the resin in the circumferential direction is controlled by the groove portions  72  that serve as thin portions and such that the flow of the resin outward in the radial direction (toward the reinforcement ring  68  and the circular cylinder wall  46 ) is promoted by the convex portions  76  that serve as thick portions. At least one of the groove portions  72  and the convex portions  76  corresponds to marks of a guide structure in the present invention. 
     Next, the action of the present embodiment will be described. 
     When the recording tape cartridge  10  of the above-described configuration is not in use, the brake member  32  is positioned in a rotation lock position and the brake gear  36  is caused to mesh with the engagement gear  52  by the energizing force of the compression coil spring  42 . For this reason, rotation of the reel  28  with respect to the case  12  is deterred. At this time, the reel gear  62  of the reel  28  is exposed from the gear opening  20 , and the lower portion of the clutch member  44  projects from the clutch-use boss portion  64  and is exposed at the gear opening  20 . 
     When the magnetic tape T is to be used, the recording tape cartridge  10  is loaded into a bucket (not shown) of the drive device along the direction of arrow A. Then, when the recording tape cartridge  10  is loaded a predetermined depth into the bucket, the bucket moves downward so that the rotating shaft  100  of the drive device relatively approaches (moves upward toward) the gear opening  20  in the case  12  and holds the reel  28 . Specifically, the rotating shaft  100  attracts and holds, but does not contact, the reel plate  66  with the magnet  108  and causes the drive gear  106  to mesh with the reel gear  62 . 
     In accompaniment with the drive gear  106  meshing with the reel gear  62 , that is, the relative movement of the rotating shaft  100  in its axial direction toward the case  12 , the rotating shaft  100  presses up the clutch member  44  that it is contacting at its release surface  101 . Then, because of this pressing force, the clutch member  44  is guided in the slits  64 A of the clutch-use boss portion  64  at its plural engagement pieces  44 A and moves upward in the axial line direction of the reel  28  counter to the energizing force of the compression coil spring  42 . 
     Thus, the brake member  32  contacting the upper surface of the clutch member  44  at its slide-contacting projection portion  35  also moves upward, and the meshing between the brake gear  36  of the brake member  32  and the engagement gear  52  is released. That is, the brake member  32  reaches a relative rotation allowance position with respect to the reel  28 . When the rotating shaft  100  further relatively moves upward, the reel  28  is lifted upward (without its relative position being caused to change) together with the clutch member  44  and the brake member  32  counter to the energizing force of the compression coil spring  42 , the brake member  32  reaches an absolute (with respect to the case  12 ) rotation allowance position, and the lower flange  52  separates from the annular rib  22 . Due to the above, the reel  28  rises inside the case  12  and becomes rotatable without contacting the inner surface of the case  12 . 
     Further, due to the lowering of the bucket, that is, the recording tape cartridge  10  inside the drive device, the positioning pins of the drive device respectively enter the positioning holes  24  and  26  in the case  12 , and the positioning surfaces of the drive device come into contact with the positioning surfaces  24 A and  26 A of the case  12 . Thus, the recording tape cartridge  10  is positioned in the horizontal direction and in the vertical direction with respect to the drive device. Then, the pullout means of the drive device causes its pullout pin (not shown) to engage with the engagement concave portion  30 A of the leader block  30 , pull out the leader block  30  from the case  12 , and guide the leader block  30  to the take-up reel of the drive device. Moreover, the leader block  30  is fitted into the take-up reel to configure part of the take-up surface that takes up the magnetic tape T. 
     In this state, when the leader block  30  rotates integrally with the take-up reel, the magnetic tape T is pulled out from the case  12  through the opening  18  while being taken up onto a reel hub of the take-up reel. At this time, the reel  28  of the recording tape cartridge  10  rotates synchronously with the take-up reel by the rotational force of the rotating shaft  100  that is transmitted by the drive gear  106  meshing with the reel gear  62 . Then, a recording and reproducing head disposed along a predetermined tape path of the drive device records information to the magnetic tape T or reproduces information that has been recorded on the magnetic tape T. At this time, the slide-contact projecting portion  35  of the brake member  32  that is incapable of rotation with respect to the case  12  slidingly contacts the upper surface of the clutch member  44  that rotates with respect to the case  12  together with the reel  28 . 
     When the magnetic tape T is to be rewound onto the reel  28  and the leader block  30  is to be held in the vicinity of the opening  18  in the case  12 , the bucket into which the recording tape cartridge  10  has been loaded is raised. Then, the meshing between the reel gear  62  and the drive gear  106  is released, the contact between the release surface  101  and the clutch member  44  is released, and the clutch member  44  moves downward together with the brake member  32  by the energizing force of the compression coil spring  42 . Thus, the brake member  32  returns to the brake position where the brake gear  36  meshes with the engagement gear  52 . Further, in accompaniment with operation where the brake member  32  and the clutch member  44  move by the energizing force of the compression coil spring  42 , the reel  28  also moves downward and returns to its initial state where the lower flange  56  is brought into contact with the annular rib  22  and the reel gear  62  is exposed from the gear opening  20 . In this state, the recording tape cartridge  10  is ejected from the bucket. 
     In manufacturing the reel  28  that configures this recording tape cartridge  10 , first, the reel hub  45  and the lower flange member  60  are separately formed by injection molding. The reinforcement ring  68  is integrated with the reel hub  45  by insert molding, and the reel plate  66  is integrated with the lower flange member  60  by insert molding. Next, the clutch-use boss portion  64  of the lower flange member  60  is fitted together with the short circular cylinder portion  55  of the reel hub  45 , the corresponding convex portions  76  and convex portions  74  are fitted inside the concave portions  78 , and the lower flange member  60  is centered (positioned) with respect to the reel hub  45 . 
     Then, ultrasonic vibration is generated from an ultrasonic horn in a state where the bottom plate  48 , the center portion  58  and the reel plate  66  are sandwiched between a receiver (not shown), which contacts the reel plate  66  in a region (between the reel gear  62  and the small holes  66 B) including the back surface portion of the site where the center portion  58  contacts the welding-use projections  70 , and the ultrasonic horn, which contacts the back surfaces (between the engagement gear  52  and the short circular cylinder portion  55  at the upper surface) of the welding-use projections  70  of the bottom plate  48 , and the reel hub  45  and the lower flange member  60  are ultrasonically welded together. Thus, the reel  28 , where the reel hub  45  and the lower flange member  60  are fixed and where the magnetic tape T that is wound around the tape take-up surface  46 A is protected by the upper flange  50  and the lower flange  56 , is configured. 
     To add more in regard to injection molding of the reel hub  45 , as shown in  FIG. 9 , the reinforcement ring  68  is set inside a space (cavity) formed by molding-use dies  80  and  82 , polycarbonate PC into which glass fiber has been mixed (below, sometimes simply called “the polycarbonate PC”) is injected from the gates Gt. This polycarbonate PC flows inside the cavity as indicated by the arrows in  FIG. 9  and fills the inside of the cavity (not shown). Thereafter, the polycarbonate PC is cooled and allowed to solidify, and the reel hub  45  that has been molded is removed from the molding-use dies  80  and  82 . 
     Incidentally, in the reel hub  45  where the reinforcement ring  68  made of metal has been insert-molded, contraction that accompanies the above-described cooling and solidification of the circular cylinder wall  46  that is a resin molded portion is controlled by the reinforcement ring  68 . In this embodiment, the coefficient of thermal expansion of the reinforcement ring  68  is 23 ppm with respect to 55 ppm, which is the coefficient of thermal expansion of the reel hub  45  (the glass fiber-including polycarbonate), so internal stress that accompanies tension in the circumferential direction occurs at the interface of the circular cylinder wall  46  with the reinforcement ring  68 . 
     Here, the reel  28  has a configuration where the convex portions  76  with respect to the gate marks Gm of the reel hub  45  are formed and where the groove portions  72  are formed on both circumferential direction sides of the gate marks Gm, so inside the cavity resulting from the molding-use dies  80  and  82 , the cross-sectional area of the flow path leading from the gates Gt outward in the radial direction is enlarged in the thickness direction by the convex portions  76 , and the cross-sectional area of the flow path leading from the gates Gt in the circumferential direction is narrowed in the thickness direction by the groove portions  72 . For this reason, in the present reel  28 , as indicated by arrows F in  FIG. 2A , at the time of injection molding of the reel hub  45 , the polycarbonate PC flows in the radial direction (both sides) from the gate marks Gm and thereafter flows in the circumferential direction beyond the installation range of the groove portions  72 . 
     Thus, in the reel hub  45 , the glass fiber that reinforces the polycarbonate PC that configures the circular cylinder wall  46  is oriented (so as to become long) along the circumferential direction of the circular cylinder wall  46 . That is, the circular cylinder wall  46  is effectively reinforced by the glass fiber with respect to tension in the circumferential direction. For this reason, in the circular cylinder wall  46  of the reel  28 , the occurrence of cracks resulting from control of contraction at the time of molding by the reinforcement ring  68  and running parallel to each other in the circumferential direction (along the radial direction) is effectively controlled. 
     For example, as shown in  FIG. 11A  and  FIG. 11B , in a reel hub  200  pertaining to a comparative example that does not include the convex portions  76  and the groove portions  72 , at the time of injection molding, the polycarbonate PC flows radially from the gates Gt of the resin material as shown in  FIG. 2B . For this reason, in the vicinities of the gate marks Gm, the effect of reinforcement in the circumferential direction resulting from the glass fiber is small because the glass fiber is oriented along the radial direction of the circular cylinder wall  46 . For this reason, in the reel hub  200  pertaining to the comparative example, internal stress that accompanies the above-described tension in the circumferential direction occurs and, as shown in  FIG. 11B , it is easy for cracks C running parallel to each other in the circumferential direction to form in the end surface of the circular cylinder wall  46  in the vicinity of the gate marks Gm. 
     In contrast, in the reel  28 , because of the structure where the convex portions  76  and the groove portions  72  are formed as described above, the resin that has flowed in the radial direction selectively in the bottom plate  48  flows in the circumferential direction in the circular cylinder wall  46 , whereby the glass fiber is oriented so as to resist the tension in the circumferential direction of the circular cylinder wall  46 , so the occurrence (development) of cracks C is controlled. Thus, in the reel  28 , dimensional deformation of the tape take-up surface  46 A that accompanies the occurrence and development of cracks C and insufficient strength of the circular cylinder wall  46  are controlled. In other words, yield improves. 
     It will be noted that, in the preceding embodiment, an example has been described where the three gate marks Gm were disposed equidistantly in the circumferential direction, but the present invention is not limited to this. For example, as shown in  FIG. 10 , the present invention may also be applied to a reel  90  where a gate mark Gm is disposed in the axial center portion of the bottom plate  48 . In a reel hub  92  of this reel  90 , the bottom plate  48  does not include the through hole  54 , and a rotation stop and release structure is applied. As this rotation stop and release structure, there can, for example, be employed a structure where a triangular release member, whose three leg portions pressed by the drive gear  106  that meshes with the reel gear  62  project from the site of the bottom plate  48  where the reel gear  62  is formed, is disposed on the bottom plate  48 . In this reel  90 , the groove portions  72  are formed along the radial direction from the gate mark Gm to the vicinity of the reinforcement ring  68 , and the convex portions  76  are formed on the radial direction outer side (the reinforcement ring  68  side) of the gate mark Gm, whereby flows of the polycarbonate PC as indicated by arrows F in  FIG. 10  can be generated at the time of injection molding. Consequently, according also to the reel hub  92  of the reel  90  pertaining to this modification, in the vicinity of the gate mark Gm in the circular cylinder wall  46 , the glass fiber is oriented in the circumferential direction of the circular cylinder wall  46  and the occurrence of cracks C is controlled. 
     Further, in the preceding embodiment, an example has been described where the reel  28  included both the groove portions  72  and the convex portions  76 , but the present invention is not limited to this, and it suffices for the reel  28  to include at least one of the groove portions  72  and the convex portions  76 . Further, the guide structure marks in the present invention are not limited to the groove portions  72  and the convex portions  76  and can employ any type of structure and shape. 
     Moreover, in the preceding embodiment, an example has been described where the gate marks Gm were disposed on the bottom plate  48  and where the upper flange  50  was disposed integrally with the circular cylinder wall  46 , but the present invention is not limited to this and can also be applied to various reels where the reinforcement ring  68  is insert-molded to the circular cylinder wall  46 . Consequently, for example, the reel may be given a configuration where the lower flange  56  is formed integrally with the circular cylinder wall  46  and where the upper flange  50  is formed separately from the circular cylinder wall  46  or a configuration where the gate marks Gm are formed on the lower flange  56 . Further, the gate marks Gm may also be disposed on the undersurface side of the bottom plate  48 . Moreover, for example, the present invention can also be applied to a reel with a so-called three-piece structure where the upper flange  50  and the lower flange  56  are separate from the reel hub  45 . 
     Further still, in the preceding embodiment, an example has been described where the reel hub  45  was formed by the polycarbonate PC into which glass fiber was mixed as reinforcement fiber, but the present invention is not limited to this. The reel hub  45  may also be configured by all types of resin material that are capable of being injection-molded instead of polycarbonate, and carbon fiber or mica may also be employed instead of glass fiber as the reinforcement fiber. Further, the circular cylinder wall  46  of the reel hub  45  may also be configured to have a dimension (thickness) different from what has been described in the preceding embodiment. 
     Further, in the preceding embodiment, an example has been described where the through hole  54 , the clutch-use boss portion  64  and the clear hole  66 A were formed in the axial center portion of the reel  28 , but the present invention is not limited to this, and the axial center portion of the reel  28  may also be closed, for example. Consequently, the rotation stop structure and the rotation stop and release structure of the reel  28  in the recording tape cartridge  10  to which the reel  28  is applied are not limited to the structures of the preceding embodiment. 
     Moreover, in the preceding embodiment, an example has been described where the thin portions and the thick portions in the present invention are set by the shape of the bottom plate  48 , but the present invention is not limited to this. For example, the thin portions and the thick portions may also be set by configuring by an insert body that sets part of the bottom plate  48  in the molding-use dies  80  and  82 . Further, holes and slits (portions of thickness  0 ) that penetrate the bottom plate  48  in its thickness direction on both circumferential direction sides of the gate marks Gm are also included in the marks of the guide structure in the present invention.