Cassette half molding method therefor

Details Cassette half molding method therefor Cassette half molding method therefor

2000-12-13

2003-07-08

Heitbrink, Jill L. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

Shaping against forming surface

C264S328120

Reexamination Certificate

active

06589469

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technical field of a magnetic tape cassette and an injection molding method in case of molding a resin product for the magnetic tape cassette with molding dies, and more particularly, relates to a cassette half for forming a case of the magnetic tape cassette for accommodating a magnetic tape wound around a pair of take-up hubs and a molding method for molding the cassette half, a magnetic tape cassette provided with an improved friction sheet for preventing static charge of the magnetic tape and keeping slidability of the magnetic tape, and a magnetic tape cassette improved in detachability to a cassette automatic delivery apparatus.
2. Description of the Related Art
For example, a magnetic tape cassette used to an audio system or a computer may be exemplified as one example of the resin product. In general, the magnetic tape cassette has a structure in which a pair of hubs around which the magnetic tape is wound are rotatably incorporated and retained in a case body formed of upper and lower cassette halves coupled together in a lid-alignment manner. Such cassette halves are injection molded of thermoplastic resin such as PS (polystyrene), or ABS (acrylonitrile butadiene styrene resin) general. In order to observe and confirm the winding condition of the magnetic tape from the outside, the cassette halves as a whole are made of transparent material such as AS (acrylonitrile styrene) or PS, or a window portion that is transparent or semitransparent is formed in the opaque cassette half bodies.
Conventionally, this window portion is formed by adhesion with adhesive or supersonic welding of the window material molded separately from the cassette half bodies. However, in this case, since the molding step and adhesion step for the window portion are required, there is a restriction on a design and productivity is not so good. Accordingly, recently, the cassette half bodies and window portions are integrally molded through a color injection molding (or multi-color injection molding) method.
FIG. 8
is a plan view of an upper half of a conventional magnetic tape cassette.
A window portion
112
that is transparent or semitransparent is provided in the upper half
110
for observing and confirming the winding condition of the magnetic tape accommodated in the cassette halves from the outside. A pair of ribs
114
and
116
are provided for positioning and regulating the take-up hubs around which the magnetic tape is wound in this window portion
112
. These ribs
114
and
116
are divided into two portions, for example,
114
a
and
114
b
, and arranged in the circumferential direction in conformity with the shape of the take-up hubs.
A cross-sectional view taken along the line IX—IX of
FIG. 8
is shown in FIG.
9
.
As shown in
FIG. 9
, position regulating ribs
114
(
114
a
,
114
b
) of the take-up hubs are formed in the window portion
112
of the upper half
110
with a height in such an appropriate range that they can regulate the position of the take-up hubs and do not prevent the rotation of the take-up hubs.
A state that the window portion
112
is molded by means of, for example, the two-color injection molding method is shown in FIG.
10
.
Molten resin is injected into a space (cavity) surrounded by a front mold (cavity side part)
120
a
and a movable half (force side part)
120
b
of the molding dies and a slide core
122
to form the upper half body
110
. Thereafter, as shown in
FIG. 10
, the slide core
122
is slid by a thickness of the window portion
112
. Transparent or semitransparent resin is injected from a gate
126
into the space (cavity)
124
formed therein to form the window portion
112
.
At this time, recesses
128
(
128
a
,
128
b
) for take-up hub position regulating ribs
114
(
114
a
,
114
b
) to be formed in the window portion
112
are formed in the slide core
122
.
However, in the case where the window portion
112
of the upper half of the magnetic tape cassette is formed by the injection molding as shown in
FIGS. 8 and 9
like the above-described conventional case, there are the following defects. Namely, as shown in
FIG. 10
, the molten resin injected into the cavity
124
from the gate
126
flows as indicated by the arrows. In the flat portion, the resin flows horizontally without any deflection but in the recesses
128
a
,
128
b
corresponding to the portions of the take-up hub position regulating ribs
114
(see FIG.
8
), the resin enters the inside thereof once, and thereafter, again returns to move further forward. Also, at this time, the recesses
128
(
128
a
,
128
b
) are directed in a direction perpendicular to the advance direction of the resin and the flow is further obstructed. Furthermore, if a gas that is generated due to heat is contained in the resin, the flow of the resin is further obstructed.
Thus, since the molten resin is filled to ride the portion of the take-up hub position regulating ribs
114
(see FIG.
8
), the fludized layer of the resin is advanced while being subject to the resistance. As a result, the resin is spread and advanced more in the portion where no take-up hub position regulating ribs
114
are provided. As shown in a plan view of
FIG. 11
, the flows of the resin coming in the two directions are brought into contact with each other at the end portion of the window portion
112
(the final filling portion of the resin). As a result, an abnormal color portion having streaks that are called welds
130
is formed at the joint portion to cause a problem in that the outer appearance becomes worse. In particular, since the window portion
112
is transparent, there is a problem in that such a quality reduction is undesirable.
By the way, as well known, in the magnetic tape cassette, under the condition that the respective end portions of the longitudinal magnetic tape are fixed to the pair of take-up hubs, respectively, the pair of take-up hubs around which the magnetic tape is wound are accommodated in a cassette bodies (upper half and lower half). Only a part of the magnetic tape tensioned between the pair of take-up hubs is exposed to the outside of the cassette body such that the magnetic tape may be brought into contact with a magnetic head at least when the cassette is loaded on a recording/reproducing apparatus of the magnetic tape.
When the magnetic tape cassette is loaded on the recording/reproducing apparatus, the part of the magnetic tape tensioned between the take-up hubs and exposed from the cassette body is brought into contact with the magnetic head within the recording/reproducing apparatus, the take-up hubs are rotated, the magnetic tape travels and slidingly contacts with the magnetic head within the recording/reproducing apparatus, and the magnetic head records information onto the magnetic tape and reproduces the information from the magnetic tape.
In an audio magnetic tape cassette, when the magnetic tape cassette is loaded on the recording/reproducing apparatus, the part of the magnetic tape tensioned between the take-up hubs and exposed from the cassette body is brought into contact with the magnetic head within the recording/reproducing apparatus, the take-up hubs are rotated, the magnetic tape travels and slidingly contacts with the magnetic head within the recording/reproducing apparatus, and the magnetic head records information onto the magnetic tape and reproduces the information from the magnetic tape. In a cassette having a front cover for protecting the tape such as a video magnetic tape cassette, when the magnetic tape cassette is loaded on the recording/reproducing apparatus, the front cover is rotated and moved to a position where the magnetic tape is opened by a mechanism within the recording/reproducing apparatus in cooperation with the loading operation. The part of the magnetic tape tensioned between the take-up hubs is thus exposed from the cassette body. Then, the take-up hubs are rotated, and the magnetic tape travels and slides in contact with the magnetic head with

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