Disk cartridge made by injecting molten synthetic resin into a mold so that flash lines, weld lines and burn marks do not occur

Molten resin is ejected from the gate provided in the wall of a mold, which corresponds to the face of the head insertion opening of a disk cartridge, so that the molded half of the disk cartridge has scarcely any defect in the surface thereof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a disk cartridge rotatably accommodating a 
disk-like recording medium, such as a floppy disk, and to an equipment for 
molding the half of a disk cartridge from synthetic resin. 
2. Description of the Prior Art 
As to inventions of a 31/2 inch floppy disk, several applications have been 
already granted to the applicant for this invention under U.S. Pat. Nos. 
4,445,155, 4,445,157, 4,510,546, 4,517,617, 4,544,977, and 4,589,105. The 
31/2 inch floppy disk disclosed in those applications is shown in FIGS. 3A 
and 3B. 
In the drawings, a pair of upper and lower halves 1 are made of synthetic 
resin through an injection molding, and engaged with or welded to each 
other to form a cartridge 2 in which a 31/2 inch floppy disk 3 made of 
magnetic sheet is rotatably accommodated. That is, each of the upper and 
lower halves 1 has a plate portion 1a and a rib portion 1b perpendicularly 
extending from the outer periphery of the plate portion 1a, and the free 
ends of the rib portions 1b of the upper and lower halves 1 are engaged 
with or welded to each other. 
A rectangular head insertion opening 4 is provided in the center of one end 
of each of the plate portions 1a, and opened and closed by a shutter 5 
which has a U-shaped section, and is slidably secured to the outer face of 
the cartridge 2. Provided in the center of the plate portion 1b of the 
lower half 1 is a circular opening 7 in which the core 6 of the floppy 
disk 3 is loosely fitted. 
When above half 1 is made through the injection molding, it is well-known 
that molten resin is ejected from, for example, four gates 11 of about 1 
mm in diameter which are disposed in the wall of a mold so as to 
correspond to the four corners of the plate portion 1a of the square half 
1 as shown in FIG. 4, and as shown in FIG. 5A, the molten resin 14 is 
injected into the cavity 13 of the mold 12 in a direction perpendicular to 
the plate portion 1a of the half. In FIG. 5A, reference numerals 15 and 16 
denote an injection head and a runner, respectively. 
However, the flows of the molten resin ejected in directions of respective 
arrows shown in FIG. 4 from the four gates 11 collide with one another, so 
that various defects, such as weld lines 17, burn marks, uneven gloss 18 
and the like are often found in the surface of the half 1 after molding. 
Further, as shown in FIG. 5B, traces 21, such as recess 19 formed by the 
injection head 15, and a small projection 20 formed due to tearing off the 
resin and the like are left in the surface of the half 1 after molding. 
In addition, as the thickness of the plate portion 1a of the half 1 is less 
than 1 mm, and the molten resin is not only ejected from the gate 11 of 
about 1 mm in diameter, but also injected in the direction perpendicular 
to the plate portion 1a of the half 1, the time required to fill the 
cavity 13 with the molten resin is protracted due to the pressure loss 
caused by the gate 11, and as the result, much time is required to mold 
the half 1. If the injection pressure of the molten resin is raised, many 
flashes are apt to be formed in the face of the mold. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a disk 
cartridge in which a plurality of flows of molten resin are injected into 
the cavity of a mold without collision with one another, while the half of 
a disk cartridge is molded, and thereby, the appearance of the molded half 
is much improved. 
Another object of the invention is to provide a disk cartridge in which 
molten resin is injected into the cavity of a mold in parallel with the 
faces of the cavity which correspond to the upper and lower faces of the 
plate portion of the half which is a part of a disk cartridge, while the 
half is molded, and thereby, time required to fill the cavity with the 
molten resin is shortened, and flashes are not found in the face of the 
mold due to the low pressure of the ejected molten resin. 
A further object of the invention is to provide an equipment for molding 
the half of a disk cartridge, in which a gate is arranged to eject molten 
resin through such a wall provided in a mold as to form the face of an 
head insertion opening which exists in the half of a disk cartridge, and 
such a wall of the cavity of the mold as to form the plate portion of the 
half, within which the head insertion opening exists, is in alignment with 
the directions of the flows of molten resin which are injected into the 
cavity, and thereby, any defect, such as weld line, burn mark, uneven 
gloss or the like is scarcely developed, and also the trace of the gate is 
not found. 
A still further object of the invention is to provide an equipment for 
molding the half of a disk cartridge, as aforesaid, in which the gate is 
provided in a slide core movable in a direction perpendicular to a wall of 
the cavity as to form the plate portion of the half, so as to have 
synthetic resin shear between the gate and the half molded in the cavity, 
and thereby, any trace of the gate is not left in the surface of the half. 
In accordance with an aspect of this invention, a disk cartridge has a 
substantially square case in which a disk is rotatably accommodated, and 
which comprises an upper half and a lower half; an even plate portion of 
the half which is made of synthetic resin; a head insertion opening 
provided in the plate portion of the half; and a face of the head 
insertion opening which connects the upper face to the lower face of the 
plate portion of the half; wherein when the half is molded from synthetic 
resin, a gate is provided in the wall of a mold, which corresponds to the 
face of the head insertion opening of the half, and molten resin is 
injected in parallel with the wall of the cavity of the mold, which 
corresponds to the upper and lower faces of the plate portion of the half. 
In an equipment for molding the half of a disk cartridge, the equipment 
comprises a mold for molding the half from synthetic resin, the half 
having a substantially even plate portion and a head insertion opening 
provided in the plate portion; a cavity provided within the mold and 
having even faces within the wall thereof, so as to mold the plate portion 
of the half; an injection head of the mold provided across the cavity of 
the mold so as to mold the head insertion opening of the half; and a gate 
provided in the outer periphery of the injection head to enable molten 
resin to be injected into the cavity in parallel with the even faces of 
the cavity. 
The above, and other objects, features and advantages of this invention, 
will be apparent in the following detailed description of an illustrative 
embodiment thereof which is to be read in connection with the accompanying 
drawings wherein like reference numerals identify the corresponding parts 
in the several views.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawings in detail, and initially to FIG. 1 thereof, it 
will be seen that the half 31 of a disk cartridge has an even plate 
portion 31a and an elongated, for example, rectangular head insertion 
opening 32 located in the center of one end of the plate portion 31a. When 
the half 31 is made, molten resin is ejected through the wall of a mold 
which corresponds to the face of the head insertion opening 32. 
That is, in an equipment 33 for molding the half 31 from synthetic resin 
shown in FIG. 2A, an injection head 35 of a mold 38, which is formed into 
a slide core 37, is arranged to make the head insertion opening 32, and a 
gate 34 of the injection head 35 is disposed at the end of a runner 36 
which is formed in the slide core 37. The gate 34 extends in a line 
substantially all over the periphery of the wall of the injection head 35 
which corresponds to the face 41 of the head insertion opening 32. The 
face 41 connects the upper face 31b of to the lower face 31c of the plate 
portion 31a of the half 31. 
The molten resin is radially ejected from the gate 34, and injected into 
the cavity 39 of the mold 38 in parallel with the walls of the cavity 39 
which correspond to the faces 31b and 31c of the plate portion 31a of the 
half 31, so as to fill the cavity 39 therewith. After cooling, the half 31 
is molded. 
Then, the side core 37 is moved in a direction perpendicular to the plate 
portion 31a of the half 31 as shown in FIG. 2B, so that there is no trace 
of the gate 34 left in the face 41 of the head insertion opening 32 as 
shown in FIG. 2c. 
As the molten resin 40 is ejected from the wall of the mold 38 which 
corresponds to the whole face of the head insertion opening 32, and 
divergently injected into the cavity 39 as indicated by arrows in FIG. 1, 
the flows of the molten resin do not collide with one another within the 
cavity 39, so that the defects, such as weld lines, burn marks, uneven 
gloss and the like are not easily formed in the face of the molded half 
31. 
Moreover, as the length of the gate 34 can be made large enough so as to 
correspond to that of the whole face 41 of the head insertion opening 32. 
As compared with the well-known gate 11 of small diameter shown in FIG. 4, 
the pressure loss of the molten resin 40 incurred at the gate 34 is small 
and as the result, the time required to fill the cavity 39 with molten 
resin is shortened. The half 31 can be made in a short time. In addition, 
as it becomes possible to inject the molten resin 40 into the cavity 39 
under a low pressure, flashes are not easily formed in the face of the 
mold 38. 
According to the result of a comparative test shown in Table 1, the time 
required to fill the cavity 39 with molten resin 40 was shortened to about 
one third of the conventionally required time, and also, the ejection 
pressure at the time of injecting molten resin 40 into the cavity 39 was 
decreased to about one half of the conventionally required pressure when 
the injection molding equipment 33 of this invention is used. 
Having described an illustrative embodiment of this invention with 
reference to the accompanying drawings, it is to be understood that the 
invention is not limited to that precise embodiment described, and that 
various changes and modifications may be effected therein by one skilled 
in the art without departing from the scope or spirit of the invention as 
defined in the appended claims. 
The invention is also applicable to such a half of disk cartridge as to 
accommodate various kinds of disk-like recording medium. 
TABLE 1 
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Time required to 
The maximum of pressure 
fill the cavity 
required to inject 
with molten resin 
molten resin into the 
(sec) cavity (kgf/cm.sup.2) 
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The half of 
0.1 150 to 300 
this invention 
A conventional 
0.35 450 
half 
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