Patent Publication Number: US-8123158-B2

Title: Reel and recording tape cartridge

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 12/509,502 filed Jul. 27, 2009, the disclosure of which is incorporated by reference herein. This application claims priority under 35 USC 119 from Japanese Patent Application Nos. 2008-193140 and 2009-174197, the disclosure of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a reel on which a recording tape, such as a magnetic tape or the like, is wound, and to a recording tape cartridge that accommodates, within a case, a reel on which a magnetic tape is wound. 
     2. Related Art 
     As described in Japanese Patent Application Laid-Open (JP-A) No. 2003-7030, a reel for a recording medium tape cartridge is known in which a circular disc-shaped flange is welded to an end portion of a tubular hub around whose outer peripheral surface a tape is wound, and the flange is formed of a resin material with an elastic modulus equal to or greater than a resin material of the hub. With this reel, deformation of the reel in response to a tape winding load may be suppressed. Further, as described in Japanese Utility Model Application Laid-Open (JP-U) No. 6-6355, a reel is known in which, in a tape reel formed of a hub and a flange, the flange is formed of a carbon fiber-reinforced plastic. This reel, with a structure that employs metal in the hub to withstand winding pressure of the tape, enables a reduction in weight of the reel as a whole. 
     However, it is desired not only that reel deformation due to winding pressure of a tape is suppressed, but also that a shape after deformation is an excellent shape. 
     SUMMARY OF THE INVENTION 
     In view of the aforementioned, the present invention relates to a reel in which the outer peripheral surface of a hub forms a proper shape in a state in which a recording tape is wound, and to a recording tape cartridge. 
     A reel of a first aspect of the present invention includes: a hub formed in the shape of a cylindrical tube with a base portion, on an outer peripheral surface of which a recording tape is wound; a base side flange portion that projects-out to a radial direction outer side of a base portion side of the hub; a flange member configured in a disc shape or an annular plate shape of a material with an elastic modulus at least equal to a material that constitutes the hub, the flange member being coaxially joined to an opening end portion of the hub; a metal plate formed in a circular plate shape or an annular plate shape, which is fixed coaxially to the base portion of the hub; and a groove wall that is formed integrally with the base portion of the hub and forms a groove portion which is continuous around the entire periphery between the groove wall and an outer peripheral surface of the metal plate. 
     In the above-described reel, because the flange member that is formed of the material whose elastic modulus is at least equal to the hub material is joined to the opening end portion of the hub, the opening end portion, at which stiffness of the hub body is lower than at the base portion side, is reinforced by the flange member. Therefore, deformation of the hub in association with winding of a tape onto the outer peripheral surface of the hub is suppressed. 
     Further, in the present reel, the groove portion which is continuous around the entire periphery is formed between the groove wall that is formed in the base portion of the hub and the outer peripheral surface of the metal plate. Therefore, for example, compared with a structure in which the metal plate is restrained in the radial direction, deformation the in radial direction is expedited at the base portion side of the hub, at which the stiffness is relatively high in the hub. Therefore, a difference in radii between the base portion side and the opening end portion side after deformation due to tape winding pressure is small. Moreover, in the present reel, there is not a portion which restrains the metal plate in the radial direction at the outer peripheral portion of the metal plate, the shape of the hub after tape being wound when viewed in the axial direction is a shape substantially equal to a perfect circle. Therefore, with the present reel, the hub shape after tape being wound is excellent. 
     Thus, with the reel of the first aspect, the outer peripheral surface of the hub forms a proper shape in the state in which the recording tape is wound thereon. 
     A reel of a second aspect of the present invention is the reel of the first aspect in which the material that constitutes the hub includes a thermoplastic resin, and the material that constitutes the flange member includes a thermoplastic resin, and a linear expansion coefficient of the material is equal to or less than a linear expansion coefficient of the material that constitutes the hub. 
     In the reel of the second aspect, because the linear expansion coefficient of the thermoplastic resin constituting the flange member is equal to or less than the linear expansion coefficient of the thermoplastic resin constituting the hub, deformation of the hub due to deformation of the flange member in accordance with temperature is suppressed. Moreover, under high-temperature conditions, deformation (inclining toward the axis) of the opening side end of the hub by the flange member is limited, and deformation of the hub opening end side is effectively suppressed. 
     A reel of a third aspect of the present invention is the reel of the first or second aspect in which the material that constitutes the hub includes reinforcing fibers in a thermoplastic resin, and the material that constitutes the flange member is a thermoplastic resin of the similar type as the thermoplastic resin that constitutes the hub, and the material includes reinforcing fibers in a proportion equal to or more than the material that constitutes the hub. 
     In the reel of the third aspect, the elastic modulus and linear expansion coefficient of the material constituting the flange member and the material constituting the hub may be specified (regulated) by inclusion ratios of the reinforcing fibers in the similar type of thermoplastic resin. Further, characteristics of joining of the flange member to the hub are excellent. 
     A reel of a fourth aspect of the present invention is a reel of the first to third aspects in which the flange member is formed by injection molding, and gate marks for injecting resin into a die are disposed at an inner edge side of the flange member and face in the axial direction. 
     In the reel of the fourth aspect, when the flange member is being formed by injection molding, the resin is injected into the die through gates oriented in the axial direction, which forms a substantial right angle with respect to a surface of the flange. Therefore, a cross-sectional area of the gates may be set larger, and flow characteristics of a material including a thermosetting resin that hardens to a high elastic modulus are excellent. Therefore, for example, a fiber-reinforced resin including reinforcing fibers in a thermoplastic resin can excellently flow into the die, and a flange member with a high elastic modulus may be obtained with ease. 
     A reel of a fifth aspect of the present invention is the reel of the third aspect in which the reinforcing fibers are included in the thermoplastic resin that constitutes the flange member in a proportion greater than the material that constitutes the hub. 
     In the reel of the fifth aspect, the elastic modulus and linear expansion coefficient of the flange member relative to the hub may be regulated by the inclusion proportion of the reinforcing fibers in the thermoplastic resin constituting the flange member more than in the similar type of thermoplastic resin constituting the hub. Therefore, deformation of the hub opening end side is effectively suppressed. 
     A recording tape cartridge of a sixth aspect of the present invention is a recording tape cartridge including: the reel of any of the first to fifth aspects; and a case that rotatably accommodates the reel. 
     In the recording tape cartridge of the sixth aspect of the present invention, because the hub around which the recording tape is wound forms a proper shape, curving of the recording tape in the transverse direction is suppressed. Traveling of the recording tape is thereby stable. 
     A reel of a seventh aspect of the present invention includes: a hub formed in the shape of a cylindrical tube with a base, on an outer peripheral surface of which a recording tape is wound; a base side flange portion that projects-out to a radial direction outer side of a base portion side of the hub; a flange member configured in a disc shape or an annular plate shape of a material with an elastic modulus at least equal to a material that constitutes the hub, the flange member being coaxially joined to an opening end portion of the hub; a metal plate formed in a circular plate shape or an annular plate shape, which is fixed coaxially to the base portion of the hub; and plate retention portions that are formed integrally with the base portion of the hub and touch an outer peripheral surface of the metal plate at at least four locations, which are at equal intervals in a circumferential direction of the hub 
     In the reel described above, because the flange member that is formed of the material whose elastic modulus is at least equal to the hub material is joined to the opening end portion of the hub, the opening end portion, at which stiffness of the hub body is lower than at the base portion side, is reinforced by the flange member. Therefore, deformation of the hub in association with winding of a tape onto the outer peripheral surface of the hub is suppressed. In addition, in the present reel, because the plate retention portions joined to the outer peripheral surface of the metal plate at the hub base portion are formed integrally with the hub base portion, strength of retention of the metal plate is higher. 
     Further, in the present reel, the aforementioned plate retention portions are provided at least four locations along the hub circumferential direction, that is, a shape is formed in which the peripheral surface of the metal plate is exposed (in incision shapes, recess shapes, groove shapes or the like) between the plate retention portions that are adjacent in the circumferential direction. Therefore, in comparison with a structure in which, for example, a plate retention portion is provided along the whole periphery of the metal plate, deformation in radial directions is expedited at the base portion side of the hub, at which the stiffness is relatively high. That is, incision shapes between the plate retention portions that are adjacent in the circumferential direction act as deformation expediting portions between the plate retention portions. Therefore, at the hub of the present reel, a difference between the base portion side and the opening portion side in radial direction deformation amounts due to tape winding pressure is small. Moreover, because the plate retention portions are provided at at least four locations in the hub circumferential direction, the shape of the hub after tape winding when viewed in the axial direction is a shape close to a perfect circle. Therefore, with the present reel, the hub shape after tape winding is excellent. 
     Thus, with the reel of the seventh aspect, the outer peripheral surface of the hub forms a proper shape in the state in which the recording tape is wound thereon. It is preferable, with regard to expediting deformation at the hub base portion side, if the circumferential direction lengths of the incision shapes (deformation expediting shapes) between the plate retention portions that neighbor in the hub circumferential direction are formed so as to be sufficiently long relative to the circumferential direction lengths of the plate retention portions themselves. 
     A reel of an eighth aspect of the present invention is the reel of the seventh aspect in which the material that constitutes the hub includes a thermoplastic resin, and the material that constitutes the flange member includes a thermoplastic resin, and a linear expansion coefficient of the material is equal to or less than a linear expansion coefficient of the material that constitutes the hub. 
     In the reel of the eighth aspect, because the linear expansion coefficient of the thermoplastic resin constituting the flange member is equal to or less than the linear expansion coefficient of the thermoplastic resin constituting the hub, deformation of the hub due to deformation of the flange member in accordance with temperature is suppressed. Moreover, under high-temperature conditions, deformation (inclining toward the axis) of the opening side end of the hub by the flange member is limited, and deformation of the hub opening end side is effectively suppressed. 
     A reel of a ninth aspect of the present invention is the reel of the seventh or eighth aspect in which the material that constitutes the hub includes reinforcing fibers in a thermoplastic resin, and the material that constitutes the flange member is a thermoplastic resin of the similar type as the thermoplastic resin that constitutes the hub, and the material includes reinforcing fibers in a proportion equal to or more than the material that constitutes the hub. 
     In the reel of the ninth aspect, the elastic modulus and linear expansion coefficient of the material constituting the flange member and the material constituting the hub may be specified (regulated) by inclusion ratios of the reinforcing fibers in the similar type of thermoplastic resin. Further, characteristics of joining of the flange member to the hub are excellent. 
     A reel of a tenth aspect of the present invention is a reel of the seventh to ninth aspects in which the flange member is formed by injection molding, and gate marks for injecting resin into a die are disposed at an inner edge side of the flange member and face in the axial direction. 
     In the reel of the tenth aspect, when the flange member is being formed by injection molding, the resin is injected into the die through gates oriented in the axial direction, which forms a substantial right angle with respect to a surface of the flange. Therefore, a cross-sectional area of the gates may be set larger, and flow characteristics of a material including a thermosetting resin that hardens to a high elastic modulus are excellent. Therefore, for example, a fiber-reinforced resin including reinforcing fibers in a thermoplastic resin can excellently flow into the die, and a flange member with a high elastic modulus may be obtained with ease. 
     A reel of a eleventh aspect of the present invention is the reel of the ninth aspect in which the reinforcing fibers are included in the thermoplastic resin that constitutes the flange member in a proportion greater than the material that constitutes the hub. 
     In the reel of the eleventh aspect, the elastic modulus and linear expansion coefficient of the flange member relative to the hub may be regulated by the inclusion proportion of the reinforcing fibers in the thermoplastic resin constituting the flange member more than in the similar type of thermoplastic resin constituting the hub. Therefore, deformation of the hub opening end side is effectively suppressed. 
     A recording tape cartridge of a twelfth aspect of the present invention is a recording tape cartridge including: the reel of any of the seventh to eleventh aspects; and a case that rotatably accommodates the reel. 
     In the recording tape cartridge of the twelfth aspect of the present invention, because the hub around which the recording tape is wound forms a proper shape, curving of the recording tape in the transverse direction is suppressed. Traveling of the recording tape is thereby stable. 
     As described above, the reel and recording tape cartridge relating to the present invention have the excellent effect that an outer peripheral surface of a hub forms a proper shape in a state in which a recording tape is wound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is an exploded perspective view of a reel relating to a first exemplary embodiment of the present invention. 
         FIG. 2  is a bottom view of the reel relating to the first exemplary embodiment of the present invention. 
         FIG. 3  is a perspective view showing, enlarged, a plate retention portion of the reel relating to the first exemplary embodiment of the present invention. 
         FIG. 4  is a sectional view showing a die structure for injection molding of a hub member with a lower flange that structures the reel relating to the first exemplary embodiment of the present invention. 
         FIG. 5  is a sectional view showing a die structure for injection molding of an upper flange member that structures the reel relating to the first exemplary embodiment of the present invention. 
         FIG. 6  is a graph illustrating shapes after tape winding of a reel hub outer peripheral surface structuring the reel relating to the first exemplary embodiment of the present invention. 
         FIG. 7  is a sectional view of a recording tape cartridge relating to the first exemplary embodiment of the present invention at a time of non-use. 
         FIG. 8  is a sectional view of a recording tape cartridge relating to the first exemplary embodiment of the present invention at a time of use. 
         FIG. 9A  is a view showing the recording tape cartridge relating to the first exemplary embodiment of the present invention, which is a perspective view viewed from above. 
         FIG. 9B  is a view showing the recording tape cartridge relating to the first exemplary embodiment of the present invention, which is a perspective view viewed from below. 
         FIG. 10  is an exploded perspective view of a reel-lock structure of the recording tape cartridge relating to the first exemplary embodiment of the present invention. 
         FIG. 11  is a perspective view of an upper flange member that structures a reel relating to a second exemplary embodiment of the present invention. 
         FIG. 12  is a sectional view showing a die structure for injection molding of the upper flange member that structures the reel relating to the second exemplary embodiment of the present invention. 
         FIG. 13  is a bottom view of the reel relating to a third exemplary embodiment of the present invention. 
         FIG. 14  is a perspective view showing, enlarged, a plate retention portion of the reel relating to the third exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A reel  10  relating to a first exemplary embodiment of the present invention, and a recording tape cartridge  11  that is configured so as to include the reel  10 , will be described on the basis of  FIG. 1  through  FIG. 10 . First, the schematic overall structure of the recording tape cartridge  11  including the reel  10  will be described, and then the characteristic structure of the reel  10  will be described. Note that, for convenience of explanation, the direction of loading the recording tape cartridge  11  into a drive device is denoted by arrow A, and this direction of arrow A is the front direction (front side) of the recording tape cartridge  11 . Further, the direction denoted by arrow U is the upward direction (upper side) of the recording tape cartridge  11 . 
     (Schematic Overall Structure of Recording Tape Cartridge) 
     As shown in  FIG. 7  through  FIG. 9B , the recording tape cartridge  11  relating to the present exemplary embodiment has a case  12 . The case  12  is configured by an upper case  14  and a lower case  16  being joined together. Specifically, the upper case  14  is configured such that a substantially frame-shaped peripheral wall  14 B stands erect along the outer edge of a ceiling plate  14 A which is substantially rectangular in plan view. The lower case  16  is configured such that a peripheral wall  16 B stands erect along the outer edge of a floor plate  16 A which has a configuration substantially corresponding to that of the ceiling plate  14 A. The case  12  is formed substantially in the shape of a box by the upper case  14  and the lower case  16  being joined together by ultrasonic welding or screws or the like in a state in which the open end of the peripheral wall  14 B and the open end of the peripheral wall  16 B abut one another. 
     At a corner portion of the case  12  at the leading side in the direction of loading the recording tape cartridge  11  into a drive device, the ceiling plate  14 A, the peripheral wall  14 B, the floor plate  16 A, and the peripheral wall  16 B are respectively cut-out such that an opening  18 , which is inclined with respect to the direction of loading, is formed. Further, a circular gear opening  20  which passes through the floor plate  16 A is provided in the substantially central portion of the floor plate  16 A, and is for exposing a reel gear  42  which will be described later. At the edge portion of the gear opening  20  at the floor plate  16 A, an annular rib  22  projects toward the interior of the case  12 , and is for positioning and dust-proofing the reel  10  which will be described later. 
     As shown in  FIG. 7 , only one of the reel  10  is rotatably accommodated within the case  12 . A magnetic tape T serving as a recording tape is wound on the reel  10 , and a leader block  30  serving as a leader member is attached to the distal end of the magnetic tape T. When the recording tape cartridge  11  is not in use, the leader block  30  is accommodated and held at the inner side of the opening  18  of the case  12 . Further, in this state, the leader block  30  closes-off the opening  18  and impedes entry of dust and the like into the case  12 . 
     When the magnetic tape T is pulled-out within a drive device, the leader block  30  is taken-out from the case  12  by a pull-out means of the drive device and is guided to a take-up reel (not shown) of the drive device. Note that, instead of a leader block, a leader pin shaped as a small shaft, or a tape-shaped leader tape may be employed as the leader member. In this case, for example, a door member for opening and closing the opening  18  is provided at the case  12 . Further, the opening  18  may be formed along the peripheral walls  14 B,  16 B (by cutting out only the peripheral walls  14 B,  16 B). 
     As shown in  FIG. 1  through  FIG. 3 , the reel  10  has a reel hub  32  that structures the axially central portion of the reel  10 . The reel hub  32  is substantially formed in the shape of a cylindrical tube having a base, and includes a cylindrical tube portion  34  on whose outer peripheral surface the magnetic tape T is wound, and a base portion  36  that closes-off the bottom portion of the cylindrical tube portion  34 . Further, a lower flange  38 , which projects-out toward the radial direction outer side of the reel hub  32 , is provided in a vicinity of the base portion  36  side end portion (the lower end portion) of the reel hub  32 . On the other hand, an upper flange  40 , which projects-out toward the radial direction outer side of the reel hub  32 , is provided from the upper end portion of the cylindrical tube portion  34 . The magnetic tape T is wound at the outer peripheral surface of the cylindrical tube portion  34  of the reel hub  32 , between the opposing surfaces of the lower flange  38  and the upper flange  40 . 
     The annular reel gear  42 , which is formed coaxially with the reel  10 , projects from a vicinity of the outer periphery at the bottom surface (outer surface) of the base portion  36  of the reel hub  32 . The reel gear  42  can mesh with a driving gear  102  that is provided at the distal end of a rotating shaft  100  of a drive device. On the other hand, as shown in  FIG. 1  through  FIG. 3 , an annular engaging gear  44  that is formed coaxially with the reel  10  is provided in a vicinity of the outer periphery at the top surface (inner surface) of the base portion  36  of the reel hub  32 . The engaging gear  44  is formed on an annular pedestal portion  46  that protrudes slightly from the inner surface of the base portion  36 . The engaging gear  44  can mesh with a braking gear portion  55 B of a braking member  55  that will be described later 
     A pass-through hole  50  is provided at the axially central portion of the base portion  36  of the reel hub  32 . A boss portion  52  for a clutch stands erect from the top surface of the base portion  36  along the edge portion of the pass-through hole  50 . This boss portion  52  for a clutch will be described together with a clutch member  60  that will be described later. 
     Although details thereof will be described later, the main portion of the reel  10  is formed by resin molding. The reel has an annular reel plate  54  that is fixed at the inner side of the reel gear  42  at the bottom surface (obverse) of the base portion  36  of the reel hub  32 . The reel plate  54  is formed in an annular shape of a magnetic material, and is fixed coaxially to the base portion  36  of the reel hub  32 . The annular reel plate  54  is fixed to the base portion  36  of the reel hub  32  by, for example, insert molding or welding. The reel plate  54  is for attraction and holding by a magnet  104  of the rotating shaft  100  of the drive device. 
     The above-described reel  10  is accommodated in the case  12 , and is disposed on the annular rib  22  when the reel  10  is not in use. Specifically, radial direction displacement of the reel  10  is restricted due to the outer side portion of a taper portion  43  that is continuous with the radial direction outer side of the reel gear  42  at the base portion  36  (i.e., a vicinity of the inner edge of the lower flange  38 ) abutting the top end surface of the annular rib  22 , and the inner edge portion of the top end of the annular rib  22  being a taper surface  22 A that corresponds to the taper portion  43 . 
     In this state, the reel  10  on the whole is positioned within the case  12 , and the reel gear  42  and the reel plate  54  are exposed from the gear opening  20  (see  FIG. 9B ). Namely, the reel gear  42  does not project-out from the outer surface (bottom surface) of the floor plate  16 A, and looks out on the exterior of the case  12  from the gear opening  20 . Further, the pass-through hole  50  looks out on the gear opening  20  through a through-hole  54 A that is formed in the axial center of the reel plate  54 . In this way, operation of the reel  10 , i.e., chucking (holding) and driving/rotating, are possible from the exterior of the case  12 . 
     Further, as shown in  FIG. 2 ,  FIG. 7  and  FIG. 10 , the recording tape cartridge  11  has the braking member  55  which is for impeding rotation of the reel  10  at times when the recording tape cartridge  11  is not in use. The braking member  55  is configured with a rotation restricting portion  55 A and the braking gear portion  55 B as the main portions thereof. The rotation restricting portion  55 A is inserted into a cross-shaped rib  56  that is formed to project from the ceiling plate  14 A of the case  12 , such that relative rotation with respect to the case  12  is restricted. The braking gear portion  55 B extends outwardly in the radial direction from the lower end of the rotation restricting portion  55 A, and can engage with the engaging gear  44  of the reel  10 . 
     The braking member  55  is configured so as to, by being displaced within the case  12  in the axial direction of the reel  10  when not in use, be able to selectively assume a braking position at which the braking gear portion  55 B meshes with the engaging gear  44 , and a rotation permitting position at which meshing of the braking gear portion  55 B and the engaging gear  44  is cancelled. A compression coil spring  58  is disposed in a compressed state between the braking member  55  and the ceiling plate  14 A of the case  12 . The braking member  55  is offset toward the braking position due to the urging force of the compression coil spring  58 . 
     Further, the recording tape cartridge  11  has a clutch member  60  that is operated from the exterior at the time of canceling the locked state of the reel  10  by the braking member  55 . When the driving gear  102  of the rotating shaft  100  of the drive device meshes with the reel gear  42 , the clutch member  60  is pushed by the rotating shaft  100  and displaces the braking member  55  upwardly, i.e., toward the rotation permitting position. 
     Specifically, the clutch member  60  is disposed between the braking member  55  and the base portion  36  of the reel  10 , and has a clutch main body  62  that passes-through the base portion  36 . Further, plural guide ribs  64  and plural stopper ribs  68  extend outwardly in the radial direction from the clutch main body  62 . Due to the guide ribs  64  being disposed in rotation restricting grooves  66  which are formed in the boss portion  52  for a clutch of the reel  10 , the guide ribs  64  exhibit the function of restricting relative rotation of the clutch member  60  with respect to the reel  10 , and the function of guiding the clutch member  60  in the axial direction of the reel  10 . Due to the stopper ribs  68  abutting stopper surfaces  70 A of stopper grooves  70  which are formed in the boss portion  52  for a clutch, the stopper ribs  68  exhibit the function of positioning the clutch member  60  with respect to the reel  10  in the axial direction (including a function of preventing the clutch member  60  from coming out). 
     As described above, the braking member  55  is configured such that, when the recording tape cartridge  11  is not in use, as shown in  FIG. 7 , the braking gear portion  55 B meshes with the reel gear  42  due to the urging force of the compression coil spring  58 , and rotation of the reel  10  with respect to the case  12  is prevented. On the other hand, as shown in  FIG. 8 , when the reel gear  42  of the reel  10  meshes with the driving gear  102  of the rotating shaft  100  of the drive device, rotation of the reel  10  with respect to the case  12  is permitted due to the clutch member  60 , which is pushed by the rotating shaft  100 , displacing the braking member  55  to the rotation permitting position. 
     (Detailed Structure of Reel) 
     As shown in  FIG. 1 , the reel  10  relating to this exemplary embodiment has a two-piece structure, of a hub member with lower flange  72 , in which the reel  32  and the lower flange  38  are integrally formed, and an upper flange member  74 , whose principal structural element is the upper flange  40 . The reel hub  32  and lower flange  38  of the hub member with lower flange  72  are integrally formed by injection molding of a resin. Further, this exemplary embodiment has a structure in which the reel plate  54  made of metal is insert-molded. 
     The upper flange member  74  is configured with an annular rib  76 , which fits into the inner periphery of the cylindrical tube portion  34  of the reel hub  32 , projecting-out from an inner edge portion of the upper flange  40 , which forms an annular shape. The upper flange member  74  is a structure of which, in a state in which the annular rib  76  is fitted into the cylindrical tube portion  34  of the reel hub  32 , an annular rib  76  radial direction outer side portion (a portion between the upper flange  40  and the annular rib  76 ) is fixed to an upper end surface  34 A of the cylindrical tube portion  34  by ultrasonic welding or the like. 
     As shown in  FIG. 2 , groove portions  78 , at which an outer peripheral surface  54 B (thick portion) of the reel plate  54  is exposed, are formed in the base portion  36  of the reel hub  32  (the hub member with lower flange  72 ) between the reel plate  54  and the reel gear  42 . The groove portions  78  are plurally formed (six in this exemplary embodiment) at equal intervals in the circumferential direction of the reel hub  32 . These groove portions  78  are formed as marks of portions of retention (positioning portions) of a die for the reel plate  54  when the reel plate  54  is being insert-molded into the hub member with lower flange  72 . 
     In the reel  10 , plate retention portions (grooveless portions)  80  are formed between the six groove portions  78 . As shown in  FIG. 3 , the plate retention portions  80  touch against the outer peripheral surface  54 B of the reel plate  54  while covering the outer peripheral surface  54 B from the radial direction outer side. Thus, as shown in  FIG. 2 , in this exemplary embodiment six of the plate retention portions  80  are disposed at equal intervals in the circumferential direction at the periphery of the reel plate  54 . 
     Now, in this exemplary embodiment, a groove width of the groove portions  78  (a radial direction gap between the reel plate  54  and the reel gear  42 ) is approximately 0.6 mm and the groove depth is approximately 0.8 mm. Further, in this exemplary embodiment, the diameter of the reel plate  54  is approximately 30 mm (the circumference of the reel plate  54  is approximately 94 mm) and the circumferential direction length of each plate retention portion  80  is approximately 2.5 mm. Thus, it is apparent that the circumferential direction lengths of the plate retention portions  80  are much shorter than the circumferential direction lengths of the groove portions  78  (approximately 13.2 mm). 
     The above-described hub member with lower flange  72  (the reel hub  32 ) is formed by injection molding of a fiber-reinforced plastic in which approximately 10% by weight of glass fibers, which serve as reinforcing fibers, is mixed into a polycarbonate which serves as a thermoplastic resin. The fiber-reinforced plastic with approximately 10% by weight of glass fibers mixed in has a bending elastic modulus of approximately 3400 MPa and a linear expansion coefficient of approximately 5 to 6 (10 −5 /K) (approximately 5 (10 −5 /K) in a direction substantially parallel to a fiber arrangement direction and approximately 6 (10 −5 /K) in a direction substantially orthogonal to the fiber arrangement direction). 
     The upper flange member  74  that structures the reel  10  is formed by injection molding of a material with a bending elastic modulus and linear expansion coefficient equal to the hub member with lower flange  72 . Specifically, the upper flange member  74  is constituted with a fiber-reinforced plastic in which approximately 10% by weight of glass fibers serving as reinforcing fibers is mixed into a polycarbonate which is a thermoplastic resin of the similar type as the resin material that constitutes the hub member with lower flange  72 , that is, basically the same material as the hub member with lower flange  72 . 
     When the above-described reel  10  is being fabricated, the hub member with lower flange  72  and the upper flange member  74  are formed respectively separately. The hub member with lower flange  72  is formed by injection molding using a die  200  as shown in  FIG. 4 . That is, the hub member with lower flange  72  is formed by the polycarbonate including glass fibers that is described above being charged into a cavity  206 , which is a space formed by a fixed side die plate  202  and a movable side die plate  204 . 
     In the reel  10  in which the pass-through hole  50  is formed at the axially central portion of the base portion  36  of the reel hub  32 , gates  205 , which are resin entry ports into the cavity  206 , are set at portions at which, of the annular region of the base portion  36  at which the reel gear  42  is formed, the reel gear  42  is not formed for a portion in the circumferential direction. As illustrated in  FIG. 2  as gate marks Gm 1 , which are marks of the gates  205 , in this exemplary embodiment three of the gates  205  are set at equal intervals in the circumferential direction. 
     When supplied for the injection molding, the resin material, which is injected from an unillustrated injector, passes along a flow path (what are known as a sprue  208  and runners  210 ) formed in the fixed side die plate  202 , passes through the three gates  205 , and flows into the cavity  206  in which the reel plate  54  has been set. The interior of the cavity  206  is charged with resin and cooled, and after hardening due to cooling of the resin material, the die  200  is opened and the hub member with lower flange  72  is separated from the die  200 . Thus, the hub member with lower flange  72  is formed, in which the reel hub  32  and the lower flange  38  are integrally formed and also the reel plate  54  is insert-molded. 
     Here, the reel plate  54  is positioned at the fixed side die plate  202  of the die  200  by an inner fitting portion  202 A and an outer fitting portion  202 B of the die  200 . The inner fitting portion  202 A fits into the through-hole  54 A, and the outer fitting portion  202 B touches the outer peripheral surface  54 B at six locations in the circumferential direction. The outer fitting portion  202 B of the fixed side die plate  202  is a structure that forms the groove portions  78 , and forms the plate retention portions  80  between the portions of contact with the outer peripheral surface  54 B of the reel plate  54  by the outer fitting portion  202 B.  FIG. 4  shows sectional views in which the two sides relative to a center line CL are different (with and without the outer fitting portion  202 B). At this reel plate  54 , plural step holes  54 C (four in the present exemplary embodiment) are provided at equal intervals in the circumferential direction. The step holes  54 C have a larger hole diameter at the lower side than at the upper side. The reel plate  54  is a structure that is retained at the hub member with lower flange  72  by resin that enters the step holes  54 C and by the plate retention portions  80 . 
     The upper flange member  74  is formed by injection molding using a die  300  as shown in  FIG. 5 . That is, the upper flange member  74  is formed by the aforementioned polycarbonate including glass fibers being charged into a cavity  306 , which is a space formed by a fixed side die plate  302  and a movable side die plate  304 . Gates  305 , which are resin entry ports into the cavity  306 , are submarine gates and are plurally set at an inner periphery portion of the annular rib  76 , at equal intervals in the circumferential direction. 
     Similarly to the case of the hub member with lower flange  72 , the resin material injected from an unillustrated injector passes along a sprue  308  and runners  310  that branch in accordance with the gates  305 , passes through the six gates  305 , and flows into the cavity  306 . The interior of the cavity  306  is charged with resin and cooled, and after hardening due to cooling of the resin material, the die  300  is opened and the upper flange member  74  is separated from the die  300 . Thus, the upper flange member  74  is formed. As shown in  FIG. 1 , at the upper flange member  74 , gate marks Gm 2  of the gates  305  are located at the inner peripheral surface of the annular rib  76 , facing to the radial direction inner side. 
     In a state in which the annular rib  76  is fitted into the cylindrical tube portion  34 , an annular rib  76  radial direction outer side portion of this upper flange member  74  is ultrasonically welded to the upper end surface  34 A of the cylindrical tube portion  34 , and thus fabrication of the reel  10  is completed. 
     Next, operation of the first exemplary embodiment is described. 
     At the recording tape cartridge  11  having the above-described structure, as shown in  FIG. 7 , when the recording tape cartridge  11  is not in use, the braking member  55  is positioned at the rotation locking position and the braking gear portion  55 B is meshed with the engaging gear  44 , due to the urging force of the compression coil spring  58 . Therefore, rotation of the reel  10  with respect to the case  12  is impeded. At this time, the reel gear  42  of the reel  10  is exposed from the gear opening  20 , and the clutch main body  62  of the clutch member  60  is inserted through the pass-through hole  50  and looks out on the gear opening  20 . 
     On the other hand, when the magnetic tape T is to be used, the recording tape cartridge  11  is loaded into the bucket (not shown) of a drive device along the direction of arrow A. Then, when the recording tape cartridge  11  is loaded to a predetermined depth in the bucket, the bucket is lowered, and the rotating shaft  100  of the drive device relatively approaches the gear opening  20  of the case  12  (moves upward) and holds the reel  10 . Specifically, the rotating shaft  100  causes the driving gear  102  thereof to mesh with the reel gear  42 , while attracting and holding the reel plate  54  by the magnet  104  in a non-contact state. 
     Accompanying the meshing-together of the reel gear  42  and the driving gear  102 , i.e., the relative movement of the rotating shaft  100  with respect to the case  12  in the direction of approaching the case  12  along the axial direction, the axially central portion of the rotating shaft  100  abuts the clutch main body  62  of the clutch member  60 , and pushes the clutch member  60  upward against the urging force of the compression coil spring  58 . In this way, the braking member  55 , which is abutting the clutch member  60 , also moves upward, and the meshing-together of the braking gear portion  55 B of the braking member  55  and the engaging gear  44  is cancelled. 
     Namely, the braking member  55  reaches the rotation permitting position relative to the reel  10 . When the rotating shaft  100  moves further upward, the reel  10  is brought upward together with the clutch member  60  and the braking member  55  (with their relative positions remaining unchanged) against the urging force of the compression coil spring  58 . At the recording tape cartridge  11 , the braking member  55  thereby reaches the relative rotation permitting position (with respect to the case  12 ), and the lower flange  38  separates from the annular rib  22 . In this way, as shown in  FIG. 8 , the reel  10  rises-up within the case  12 , and becomes able to rotate in a state of not contacting the inner surfaces of the case  12 . Further, although detailed description thereof is omitted, due to the bucket, i.e., the recording tape cartridge  11 , being lowered within the drive device, the recording tape cartridge  11  is positioned in the horizontal direction and in the vertical direction with respect to the drive device. 
     Thus, while a pull-out pin (not shown) of the pull-out means of the drive device engages with the leader block  30 , the pull-out means takes the leader block  30  out from the case  12  and guides the leader block  30  to the take-up reel of the drive device. Then, the leader block  30  is fit into the take-up reel and forms a portion of the take-up surface around which the magnetic tape T is taken-up. 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 the reel hub of the take-up reel. 
     At this time, the reel  10  of the recording tape cartridge  11  rotates synchronously with the take-up reel due to the rotational force of the rotating shaft  100  which is transmitted by the driving gear  102  which is meshed-together with the reel gear  42 . Then, recording of information onto the magnetic tape T, or playback of information recorded on the magnetic tape T, is carried out by a recording/playback head that is disposed along a predetermined tape path of the drive device. At this time, the braking member  55  which cannot rotate with respect to the case  12  slidingly-contacts the clutch member  60  which rotates together with the reel  10  with respect to the case  12 . 
     On the other hand, when the magnetic tape T is rewound onto the reel  10  and the leader block  30  is held in a vicinity of the opening  18  of the case  12 , the bucket in which the recording tape cartridge  11  is loaded rises. Thus, the meshing-together of the reel gear  42  and the driving gear  102  is cancelled, the abutment of the rotating shaft  100  and the clutch member  60  is cancelled, and the clutch member  60  moves downward together with the braking member  55  (with the state of abutment thereof maintained) due to the urging force of the compression coil spring  58 . 
     In this way, the respective stopper ribs  68  of the clutch member  60  abut the stopper surfaces  70 A, and the braking gear portion  55 B of the braking member  55  meshes with the engaging gear  44 . Namely, the braking member  55  returns to the rotation locking position at which it impedes rotation of the reel  10  with respect to the case  12 . Further, accompanying the operation of the braking member  55  and the clutch member  60  moving due to the urging force of the compression coil spring  58 , the reel  10  also moves downward. While the lower flange  38  of the reel  10  is made to abut the annular rib  22 , the reel gear  42  is returned to its initial state of being exposed from the gear opening  20 . In this state, the recording tape cartridge  11  is ejected from the bucket. 
     Now, in the reel  10  relating to the exemplary embodiment of the present invention, the upper flange member  74  including the upper flange  40  is constituted of a material with an elastic modulus equal to the hub member with lower flange  72  including the reel hub  32 . Therefore, the opening end of the reel hub  32  (the opposite side thereof from the base portion  36 ) is effectively reinforced by the upper flange member  74 . Thus, with the reel  10 , in the state in which the magnetic tape T is wound on the cylindrical tube portion  34  of the reel hub  32 , deformation of the reel hub  32  is suppressed, particularly deformation to the radial direction inner side of the opening end (upper end) portion of the reel hub  32  that has relatively low stiffness within the body of the hub member with lower flange  72 . 
     On the other hand, in the reel  10 , the groove portions  78  are formed in the base portion  36  of the reel hub  32  at the periphery of the reel plate  54 . Therefore, compared with a hub with a structure in which groove portions are not formed at the base portion, deformation of the base portion  36  side portion of the reel hub  32  toward the radial direction inner side in the state in which the magnetic tape T is wound on is expedited. 
     Thus, with the reel  10 , the opening end portion of the reel hub  32  with relatively low stiffness is reinforced by the upper flange member  74 , while the base portion  36  side portion with relatively high stiffness is expedited to deform (lowered in stiffness) by the groove portions  78 . Therefore, in the state in which the magnetic tape T is wound round, the reel  10  deforms with good balance between the top and bottom in the axial direction of the reel hub  32 . That is, with the present reel  10 , a shape of the reel hub  32  after winding of the tape T is excellent. 
     In this regard, a first Comparative Example, which uses an upper flange member formed of a transparent polycarbonate (a polycarbonate which does not include glass fibers, with a bending elastic modulus of approximately 2300 MPa) instead of the upper flange member  74 , for checking winding states of the magnetic tape T, and a second Comparative Example, which uses a hub member with a lower flange in which the groove portions  78  are not formed in the base portion  36  of the reel hub  32  and a upper flange member same as the upper flange member  74 , are supplied and compared. The plot of solid black triangles shown in  FIG. 6  represents hub shapes after tape winding (deformation amounts relative to radius, averaged over the circumferential direction) for the reel  10 , the plot of white circles represents the same for the first Comparative Example, and the plot of white triangles represents the same for the second Comparative Example. 
     From this graph, it is apparent that, in the first Comparative Example, because the elastic modulus of the upper flange member is low, a reinforcement effect of the opening end portion of the reel hub  32  by the upper flange member is slight, and deformation amounts at the other end of the reel hub  32  (positions around 15 mm) are large. In contrast, in the reel  10 , because of the reinforcement effect of the opening end portion of the reel hub  32  by the upper flange member  74  described above, deformation amounts at the upper end of the reel hub  32  are suppressed to be smaller by about 3 μm than in the first Comparative Example. 
     In the second Comparative Example, it is apparent that, because the upper flange member  74  is provided, deformation amounts of the upper end of the reel hub  32  are roughly equal to the same in the reel  10 . However, because there are no groove portions  78 , deformation amounts at the lower end side of the reel hub  32  are small, and a difference in deformation amounts between the upper and lower ends of the reel hub  32  is large. In contrast, in the reel  10 , because of the deformation expediting effect caused by the groove portions  78  described above, deformation amounts at the lower end of the reel hub  32  are larger by about 3 μm than in the second Comparative Example. 
     From the above, with the reel  10  relating to the present exemplary embodiment and the recording tape cartridge  11  equipped with the reel  10 , a difference between deformation amounts at the top and bottom of the reel hub  32  is small and, as described above, the shape of the reel hub  32  in the state in which the tape T has been wound on is excellent. 
     Further, in the reel  10 , because the plate retention portions  80  are provided between the groove portions  78 , the reel plate  54  is excellently retained at the base portion  36  of the reel hub  32 . That is, because the plate retention portions  80  are provided, the reel plate  54  is retained from the outer peripheral surface  54 B side thereof by contraction, inward in the radial direction, of the resin at the time of molding, and the reel plate  54  is unlikely to detach from the base portion  36  of the reel hub  32 . 
     In the reel  10 , because the six plate retention portions  80  (and groove portions  78 ), which is more than four, are provided in the circumferential direction, circularity is excellent in a plan view of the cylindrical tube portion  34  of the reel hub  32 . In a Comparative Example in which, for example, the plate retention portions  80  are provided at only three locations with equal intervals in the circumferential direction, because of imbalances in contraction at the time of injection molding of the hub member with lower flange  72 , the cylindrical tube portion  34  is likely to form a roughly triangular shape with corner portions at the positions of the plate retention portions  80 . Hence, with the reel hub  32  at which the cylindrical tube portion  34  is in an approximately triangular shape, winding pressure of the magnetic tape T tend to concentrate at the three corner portions, which is to say the portions at which the plate retention portions  80  are formed, and the deformation expediting effect at the lower end of the reel hub  32  by the aforementioned groove portions  78  would be smaller. In contrast, in the reel  10 , because at least four of the plate retention portions  80  are provided, circularity of the cylindrical tube portion  34  is improved relative to this Comparative Example, a winding pressure distribution of the magnetic tape T is made more uniform in the circumferential direction of the cylindrical tube portion  34 , and therefore the deformation expediting effect by the groove portions  78  as described above is obtained. 
     Further, with the reel  10 , because the linear expansion coefficient of the material structuring the upper flange member  74  is equal to the linear expansion coefficient of the material structuring the hub member with lower flange  72 , degrees of expansion and contraction due to temperature changes are the same for the hub member with lower flange  72  and the upper flange member  74 , and the reinforcement effect of the opening end portion of the reel hub  32  by the upper flange member  74  is obtained equally over a wide temperature range. That is, the reinforcement effect of the upper end surface  34 A side of the cylindrical tube portion  34  by the upper flange member  74  is obtained at respective temperatures without the opening end portion of the reel hub  32  being deformed by deformations of the upper flange member  74  in accordance with the temperature. 
     Second Exemplary Embodiment 
       FIG. 11  shows an upper flange member  86  structuring a reel  85  relating to a second exemplary embodiment of the present invention, in a perspective view. As shown in  FIG. 11 , this differs from the reel  10  relating to the first exemplary embodiment in that, on the upper flange member  86 , gate marks Gm 3  from injection molding of the upper flange member  86  are disposed at the inner edge side of an axial direction end portion of the annular rib  76 , facing in a direction substantially orthogonal to the flange surface of the upper flange  40 , that is, the axial direction lower side of the upper flange  40 . 
     This upper flange member  86  is formed by injection molding using a die  400  as illustrated in  FIG. 12 . That is, the upper flange member  86  is formed by the polycarbonate including glass fibers which is described above being charged into a cavity  406 , which is a space formed by a fixed side die plate  402  and a movable side die plate  404 . Gates  405 , which are resin entry ports into the cavity  406 , have pin gate structures, and are plurally set (three in this exemplary embodiment) at equal intervals in the circumferential direction, at the inner periphery side of an axial direction end portion of the annular rib  76  (the axial direction end portion at the opposite end thereof from the upper flange  40 ). 
     Similarly to the case of the hub member with lower flange  72 , the resin material injected from an unillustrated injector passes along a sprue  408  and runners  410  that branch in accordance with the gates  405 , passes through the three gates  405 , and flows into the cavity  406 . The interior of the cavity  406  is charged with resin and cooled, and after hardening due to cooling of the resin material, the die  400  is opened and the upper flange member  86  is separated from the die  400 . Thus, the upper flange member  86  is formed. 
     The material constituting the upper flange member  86  has a higher bending elastic modulus than the bending elastic modulus of the material constituting the hub member with lower flange  72 , while the linear expansion coefficient is smaller. Specifically, the upper flange member  86  is constituted of a material in which approximately 20 to 30% by weight of glass fibers is mixed into a polycarbonate of the similar type as the polycarbonate constituting the hub member with lower flange  72 . In this exemplary embodiment, the material constituting the upper flange member  86  has a bending elastic modulus of approximately 6600 MPa (when 30% by weight of glass fibers is included) and a linear expansion coefficient of approximately 3 to 6 (10 −5 /K) (approximately 3 (10 −5 /K) in a direction substantially parallel to a fiber arrangement direction and approximately 6 (10 −5 /K) in a direction substantially orthogonal to the fiber arrangement direction). 
     In the reel  85 , which is provided with a flange member  82  with the constitution described above, because the elastic modulus of the material constituting the upper flange member  86  is higher than the elastic modulus of the material constituting the hub member with lower flange  72 , the reinforcement effect at the opening end portion of the reel hub  32  due to the upper flange member  86  is higher. Therefore, at the plate retention portions  80 , the shape of the reel hub  32  after winding of the magnetic tape T is even more excellent than the reel  10 . Further, because the linear expansion coefficient of the material constituting the upper flange member  86  is lower than the linear expansion coefficient of the material constituting the hub member with lower flange  72 , deformation of the reel hub  32  in association with temperature changes is restrained by the upper flange member  86 . Therefore, deformation of the opening end portion of the reel hub  32  in association with temperature changes is effectively suppressed. 
     Further, at the plate retention portions  80 , because the gate marks Gm 3  of the upper flange member  86  face out in the axial direction of the upper flange  40 , during injection molding using the die  400 , resin may flow in through the gates  405  with a larger flow path cross-sectional area. Therefore, it is possible to assure flow characteristics when charging the polycarbonate including the 20 to 30 weight % glass fiber into the cavity  406 . Thus, molding the upper flange member  86  (the upper flange  40 ) with a material having higher elastic modulus and lower linear expansion coefficient than the material constituting the hub member with lower flange  72  is realized. 
     Third Exemplary Embodiment 
       FIG. 13  shows a hub member with lower flange  91  which configures a reel  90  relating to a third exemplary embodiment of the present invention, in a bottom view. As shown in  FIG. 13 , the hub member with lower flange  91  which configures the reel  90  differs from the hub member with lower flange  72  which configures the reel  10  relating to a first exemplary embodiment in the point that it does have the plate retention portions  80  which covers (holds or restrains) the outer peripheral surface  54 B of the reel plate  54  from the radial direction outer side. 
     In the third exemplary embodiment, a portion at the teeth bottom side of the reel gear  42  in the base portion  36  of the reel hub  32  is to be a groove wall  92  which faces the outer peripheral surface  54 B of the reel plate  54  around a whole periphery of the reel gear  42 . Therefore, in the reel  90 , an annular groove  94  as a groove portion is formed between the groove wall  92  of the reel hub  32  and the outer peripheral surface  54 B of the reel plate  54 , which is continuous around the entire periphery. Thus, as can be understood from the comparison between  FIG. 14  and  FIG. 3 , the reel  90  is configured so as not to have a portion which holds or restrains the reel plate  54  from the radial direction such as plate retention portions  80 . Other configurations of the reel  90  are the same as those which correspond to the reel  10 . 
     Next, operation of the third exemplary embodiment is described. It is noted that the operation and the effect of the recording tape cartridge  11  to which the reel  90  is applied are similar to those of the recording tape cartridge  11  to which the reel  10  is applied, therefore the description thereof is omitted. 
     In the reel  90  having the above-described configuration, the upper flange member  74  including the upper flange  40  is constituted of a material with an elastic modulus equal to the hub member with lower flange  91  including the reel hub  32 . Therefore, the opening end of the reel hub  32  (the opposite side thereof from the base portion  36 ) is effectively reinforced by the upper flange member  74 . Thus, with the reel  90 , in the state in which the magnetic tape T is wound on the cylindrical tube portion  34  of the reel hub  32 , deformation of the reel hub  32  is suppressed, particularly deformation to the radial direction inner side of the opening end (upper end) portion of the reel hub  32 , that has relatively low stiffness within the body of the hub member with lower flange  91 , is suppressed. 
     On the other hand, in the reel  90 , the annular groove  94  which is continuous around the whole periphery is formed around the periphery of the reel plate  54  in the base portion  36  of the reel hub  32 . Therefore, compared with a hub with a structure in which the groove portion is not formed in the base portion (a configuration in which the reel plate  54  is held or restrained in the radial direction), deformation of the base portion  36  side portion of the reel hub  32  toward the radial direction inner side in the state in which the magnetic tape T is wound on is expedited. 
     Thus, with the reel  90 , the opening end portion of the reel hub  32  with relatively low stiffness is reinforced by the upper flange member  74 , while the base portion  36  side portion with relatively high stiffness is expedited to deform (lowered in stiffness) by the annular groove  94 . Therefore, in the state in which the magnetic tape T is wound round, the reel  90  deforms with good balance between the top and the bottom in the axial direction of the reel hub  32 . That is, with the present reel  90 , a shape of the reel hub  32  after winding of the tape T is excellent. 
     From the above, with the reel  90  relating to the present exemplary embodiment and the recording tape cartridge  11  equipped with the reel  90 , a difference in radii at the top and the bottom after deformation (a difference between deformation amounts at the top and the bottom) of the reel hub  32  is small and, as described above, the shape of the reel hub  32  in the state in which the tape T has been wound on is excellent. 
     Further, with the reel  90 , because the linear expansion coefficient of the material structuring the upper flange member  74  is equal to the linear expansion coefficient of the material structuring the hub member with lower flange  91 , degrees of expansion and contraction due to temperature changes are the same for the hub member with lower flange  91  and the upper flange member  74 , and the reinforcement effect of the opening end portion of the reel hub  32  by the upper flange member  74  is obtained equally over a wide temperature range. That is, the reinforcement effect of the upper end surface  34 A side of the cylindrical tube portion  34  by the upper flange member  74  is obtained at respective temperatures without the reel hub  32  being deformed by deformations of the upper flange member  74  in accordance with the temperature. 
     The above exemplary embodiments illustrate an example in which the upper flange member  74  is joined to the hub member with lower flange  72  at which the lower flange  38  is formed integrally with the reel hub  32  (a “two-piece structure”), but the present invention is not limited to the same. For example, a structure in which the upper flange member  74  and (a member including) the lower flange  38  are joined to the reel hub  32  which has the form of a cylindrical tube with a base (a “three-piece structure”) will suffice. 
     Moreover, although the above-described exemplary embodiments are configured such that the magnetic tape T is used as the recording tape, the present invention is not limited to the same. It suffices for the recording tape to be interpreted as an elongated-tape-shaped information recording/playback medium onto which information can be recorded and from which recorded information can be played-back. Needless to say, the recording tape cartridge can be applied as well to recording tapes of any recording/playback systems. 
     Moreover yet, the above-described exemplary embodiments illustrate an example in which a polycarbonate including glass fibers is employed as the materials constituting the reel hub  32  and the upper flange  40  (the lower flange  38 ). However the present invention is not limited to the same and various materials may be employed. 
     Further, the above-described exemplary embodiments illustrate an example in which the reel  10  is applied to the recording tape cartridge  11 . However, the present invention is not limited to the same, and can be applied to recording tape cartridges that, for example, accommodate, within a case, two reels for drawing-out and taking-up. In this case, it suffices for the present invention to be applied to at least one of the reels. Further, the present invention can also be applied to the take-up reel of a drive device, or the like.