Magnetic tape cassette reel

A recessed portion (24) is formed on the upper surface of the lower flange (23). An annular positioning rib (25) is provided on the lower surface of the lower flange (23) so as to be coaxial with the revolving center of the reel main body (20) and so as to be integrated with the lower flange (23). A ventilating hole (26) is provided so as to penetrate the lower flange (23), running through the base end part of the annular positioning rib (25) and the recessed portion (24). The air between the layers of the wound tape can be exhausted via the ventilating hole (26) to the side of the base end part of the annular positioning rib (25) through the recess (24) along the direction of an arrow (B).

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic tape cassette reel for winding 
a magnetic tape therearound while the magnetic tape cassette reel is 
mounted inside a magnetic tape cassette, and specifically relates to a 
structure of the magnetic tape cassette reel for preventing sink marks 
from being left on a flange surface and for improving an appearance of the 
wound tape. 
Conventionally, a magnetic tape cassette reel, which winds a magnetic tape 
around the outer circumferential surface of the reel main body, is known. 
FIGS. 1 (a) through (c) show examples of the conventional magnetic tape 
cassette reel 40, in which reels for professional-use magnetic tape 
cassettes of different sizes, which are different from one another in the 
outer diameter of the reel main body 41 and the outer diameter of the 
flanges 42 and 43. 
The reel with the smallest outer diameters shown in FIG. 1(a) is utilized 
in a cassette known as the S-type cassette for professional-use; in the 
same way, the reel with the medium outer diameters shown in FIG. 1 (b) is 
utilized in a cassette known as the M-type cassette for professional-use 
and the reel with the largest outer diameters shown in FIG. 1 (c) is 
utilized in a cassette known as the L-type cassette for professional-use. 
These reels are driven at the bottom center in FIGS. 1(a)-1(c) by a drive 
unit (DU) so as to revolve to allow the winding of a magnetic tape (T). In 
FIG. 1(c), a cross section of the magnetic tape (T) wound on the reel main 
body and located on left side is schematically illustrated. 
Although not shown in FIGS. 1(a)-1(c), at least one recessed portion 
extending in a radial direction of the reel is provided on at least one 
side of the flange of the reel around which the tape is wound. 
The recessed portion is provided for removing an air, which is accompanied 
by the winding operation of the tape and hereinafter referred to as air 
film, in a thin space (TS) between layers of the wound tape. The air film 
will cause troubles such as unfavorable appearance of the wound tape. 
A pair of upper and lower flanges 42 and 43 are provided horizontally in 
parallel at the top and bottom of the reel main body 41 so as to face each 
other. The flanges 42 and 43 respectively regulate the widthwise movement 
(vertical movement in FIGS. 1(a)-1(c) of the magnetic tape when the 
magnetic tape is wound around the reel main body 41. On the bottom surface 
of the lower flange 43 in FIGS. 1(a)-1(c), an annular positioning rib 44 
and a reference ring 45 are provided. The annular positioning rib 44 and 
the reference ring 45 of the reels shown in FIGS. 1(a)-1(c) are the same 
in diameters (X and Y) one another. The annular positioning rib 44 is 
formed by injection molding to be integrated with the reel main body 44 
together with the lower flange 43. The annular positioning rib 44 
functions to position the reel main body 41 properly in a magnetic tape 
cassette (T). The reference ring 45 is utilized to provide a horizontal 
reference position. 
These conventional magnetic tape cassette reels are usually produced by 
injection molding and there has been a problem of sink marks occurred in 
the injection process for forming the annular positioning rib 44. 
The following describes the sink mark in detail. 
The annular rib 44 of the reel shown in FIG. 1(a) or (b) is formed by 
injection molding simultaneously on a surface of the lower flange 43 in 
the side on which no magnetic tape is wound, while nothing is formed on a 
surface of the lower flange 43 on the side on which the magnetic tape is 
wound. Therefore, unevenness in heat shrink occurs in the vicinity of 
where the annular rib 44 of the lower flange is formed, and thus irregular 
recesses or sink marks are generated and left in the vicinity of the 
position corresponding to the annular rib 44. 
The sink marks impair the flatness of the lower flange 43 and cause a wavy 
movement of the flange surface. The wavy movement causes unfavorable 
appearance of the wound tape and impairs stable tape feeding when the 
magnetic tape is wound. 
The reel shown in FIG. 1(c), however, as is evident from the figure, the 
sink marks will not be made and the problem will not occur. 
On the other hand, the annular rib is indispensable to positioning onto the 
cassette half, so that elimination of the annular rib and modification of 
the position and configuration thereof according to the reel size cannot 
be taken and thus the sink mark problem has remained unsolved. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to solve the above-described 
problem, and particularly to provide a magnetic tape cassette reel in 
which a favorable appearance of the wound tape and a stable tape feeding 
is realized by eliminating the air film between the layers of the magnetic 
tape being wound with high efficiency and by preventing the sink marks 
from being generated on the rear side of the annular positioning rib 
provided on the driving-side flange of the reel main body to thereby 
surely keep flatness of the flange surface and prevent the wavy movement 
of the flange surface from occurring. 
The object can be achieved by a magnetic tape cassette reel, according to 
the present invention, including a cylindrical hub around which a magnetic 
tape is wound, and a pair of flanges provided on both end of the 
cylindrical hub, wherein at least one of the flanges facing a drive unit 
(DU) side is made of plastic, the magnetic tape cassette reel comprising: 
an annular rib provided along the entire circumference on a drive unit side 
of the plastic flange so as to be coaxial with the cylindrical hub and to 
be fit into an opening provided on a cassette half; 
at least one recessed portion provided on one side opposite to the drive 
unit side of the plastic flange so as to extend in a radial direction; and 
a ventilating hole provided on the annular rib and communicated with the 
recessed portion for penetrating the plastic flange. 
With the construction of the magnetic tape cassette cartridge according to 
the present invention, the air film can be exhausted effectively to the 
outside immediately through the ventilating hole after passing the 
recessed portion. 
Since a thin wall structure is realized by provision of the ventilating 
hole in the annular rib, unevenness in heat shrink occurs little in the 
vicinity of where the annular rib of the plastic flange is formed by 
injection molding, and thus no irregular recesses or no sink marks are 
left in the vicinity of the position which corresponds to the annular rib 
on the surface of the plastic flange whereon the magnetic tape is wound.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A magnetic tape cassette reel of one embodiment according to the present 
invention is described below with references to drawings. 
FIG. 2 is a sectional drawing showing a part of the magnetic tape cassette 
reel as the embodiment of the present invention and FIG. 3 is a plane 
showing a part of the lower flange of the magnetic tape cassette reel in 
FIG. 2. FIG. 4 is a sectional drawing showing a part of the annular 
positioning rib of the magnetic tape cassette reel in FIG. 2 and the metal 
molds for the injection forming of the annular positioning rib. 
In FIGS. 2 and 3, a magnetic tape cassette reel 10 is mounted inside a 
magnetic tape cassette which is not shown in the figures and a magnetic 
tape (not shown in the figures) are wound around the reel main body 20. 
The reel main body 20 which is formed so that the magnetic tape can be 
wound around an outer circumferential surface 21 is driven to revolve by a 
drive unit which is not shown in the figures from one side in the 
widthwise direction of the magnetic tape being wound (i.e., from the lower 
side in FIG. 2). 
A pair of flanges 22 and 23, upper and lower, are provided on both the 
widthwise ends of the magnetic tape on the reel main body 20 (i.e., the 
top and bottom end parts in FIG. 2) so as to face each other along the 
widthwise direction (i.e., a vertical direction in FIG. 2) of the magnetic 
tape. The flanges 22 and 23 respectively control the widthwise movement of 
the magnetic tape being wound on the reel main body 20. 
At least one recessed portion 24 is formed on the upper surface of the 
lower flange 23 in FIG. 2, which faces the upper flange 22, along the 
revolving direction of the reel main body 20. The recessed portion 24 
function as a path of the air film caught between the layers of the 
magnetic tape wound around the reel main body 20. 
An annular positioning rib 25 is provided on the lower surface of the lower 
flange 23 in FIG. 2 so as to be coaxial with the revolving center of the 
reel main body 20 and so as to be integrated with the lower flange 23. The 
annular positioning rib 25 is formed by the injection molding of an 
integrated body of the reel main body 20 which incorporates the lower 
flange 23 through utilization of the metal mold 30 for injection forming 
shown in FIG. 4, without an "under-cut" and this is available with a 
simple molding system. The annular positioning rib 25 is fit to the 
cassette half (not shown in the figure) of the magnetic tape cassette so 
as to position the reel main body 20 onto the magnetic tape cassette. 
A ventilating hole 26 is provided at the base end part of the annular 
positioning rib 25. The ventilating hole 26 penetrates the lower flange 
23, running through the base end part of the annular positioning rib 25 
and the recessed portion 24. By the provision of the ventilating hole 26, 
the air film (i.e. an air generated and accompanied at a thin space 
between layers of the wound tape while the tape is being wound) is 
exhausted to the side of the base end part of the annular positioning rib 
25 through the recessed portion 24 along the direction indicated by an 
arrow B. 
FIG. 2 shows a reference ring 27 for providing the a horizontal reference 
position. The reference ring 27 is provided on the lower surface of the 
lower flange 23 and inside the annular positioning rib 25 (i.e. the left 
side in FIG. 2) so as to be incorporated with the lower flange 23. 
In addition, an arrow C in FIG. 4 indicates the direction to release the 
movable metal mold 30 after the annular positioning rib 25 and the 
ventilating hole 26 is molded. As shown in FIG. 4, the ventilating hole 26 
is formed into a trapezoid shape in a cross section, in such a manner that 
the lower flange 23 with the ventilating hole 26 can be formed by 
injection molding without the under-cut. 
Since the magnetic tape cassette cartridge according to the present 
invention comprises the cylindrical hub around which the magnetic tape is 
wound, a pair of flanges provided on both end of the hub, wherein at least 
one flange that faces the drive unit side is made of plastic, at least one 
recessed portion provided on at least one side of the plastic flange so as 
to extend in the radial direction, whereon the tape is wound, the annular 
rib provided along the entire circumference on the drive unit side of the 
plastic flange so as to be coaxial with the cylindrical hub and to fit to 
the opening provided on the cassette half, and the ventilating hole 
provided on such rib so as to run through the recessed portion, the air 
film can be exhausted effectively to the outside immediately through the 
ventilating hole after passing the recessed portion. 
Since the thin wall structure is realized by provision of the ventilating 
hole in the annular rib, unevenness in heat shrink occurs little in the 
vicinity of where the annular rib of the plastic flange is formed by 
injection molding, and thus no irregular recesses or no sink marks are 
left in the vicinity of the position which corresponds to the annular rib 
on the surface of the plastic flange whereon the magnetic tape is wound. 
Therefore, the problem of the sink marks that impair the flatness of the 
plastic flange and cause the wavy movement of the flange surface will not 
arise. 
Consequently, the problem of the unfavorable appearance of the wound tape 
and the impairment of the stable tape feeding when the magnetic tape is 
wound will not arise. 
Since the present invention provides a ventilating hole onto the annular 
rib which is an essential element of the magnetic tape cassette reel but 
involves a problem of sink marks causing such as unfavorable appearance of 
the wound tape, air film removal function and the sink mark preventive 
function can be simultaneously given to the magnetic tape cassette.