Injection mold for producing spool

Details Injection mold for producing spool Injection mold for producing spool

1999-03-04

2001-09-04

Nguyen, Nam (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Shaping surface including means to release or remove product...

By movable mold sections

C249S080000, C249S135000, C249S160000, C425S577000

Reexamination Certificate

active

06283745

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an injection mold for producing a spool. More particularly, the present invention relates to an injection mold for producing a spool used in a photographic film cartridge or cassette for containing photographic film.
As roll-film for photography, 120 and 220 format roll-films are publicly known, in which photographic film with opaque paper is wound on the shaft portion of a spool having flanges at both ends thereof. 120 format roll-film for photography is photographic film having opaque paper fixed to the base side thereof as backing paper. The photographic film, together with the backing paper, is wound on the shaft portion of a spool. In 220 format roll-film for photography, opaque paper as backing paper is omitted, but instead, opaque paper known as “leader paper” is fixed to the leading end of photographic film, and opaque paper known as “trailer” is fixed to the trailing end of the photographic film, thereby allowing the length of the photographic film to be longer and making the number of exposures larger than in the case of 120 format roll-film. In either of the 120 and 220 format roll-films, the width of the opaque paper is set equal to or slightly longer than the distance between the flanges of the spool in order to ensure light-tightness between each side edge of the opaque paper and the inner wall of the associated flange.
FIG. 4
shows the external appearance of 120 format roll-film
1
for photography. As shown in
FIG. 5
, 120 format photographic film
2
used in the roll-film
1
has opaque paper
3
fixed to the base side thereof as backing paper by using adhesive tape
4
. The leading end portion
3
a
and trailing end portion
3
b
of the opaque paper
3
each have an end with a narrowed width.
FIG. 6
is a perspective view of a spool
5
.
FIG. 7
is a sectional view of the spool
5
. As shown in these figures, the spool
5
has a shaft portion
6
. The shaft portion
6
has a pair of flanges
7
at both ends thereof to regulate two side edges of the opaque paper
3
. In addition, the shaft portion
6
has an axially elongate slit
8
in a central portion thereof.
To wind the roll-film
1
on the spool
5
, the trailing end portion
3
b
of the opaque paper
3
is inserted into the slit
8
of the shaft portion
6
, and the photographic film
2
, which is backed with the opaque paper
3
, is wound around the shaft portion
6
with the emulsion side inside. The leading end portion
3
a
of the opaque paper
3
is folded with a predetermined width and fixed by using adhesive tape
9
. It should be noted that each flange
7
has a chucking groove
10
in the center thereof. The chucking groove
10
is engageable with a key shaft of a camera.
There must not be a gap between each side edge of the opaque paper
3
and the inner wall surface
7
a
of the associated flange
7
. Therefore, the width D
1
of the opaque paper
3
is set equal to or slightly wider than the distance (spool inside dimension) D
2
between the inner wall surfaces
7
a
. When the width D
1
is wider than the spool inside dimension D
2
, or when there are variations in the width D
1
, the opaque paper
3
cannot be wound fast to the shaft portion
6
. As a result, the roll diameter of the roll-film
1
wound on the shaft portion
6
increases undesirably. To prevent this problem, the inner wall surface
7
a
of each flange
7
is provided with an annular groove
11
(see
FIG. 8
) with a depth h. The groove
11
is concentric with respect to the shaft portion
6
. The groove
11
has a flat trapezoid-shaped or arcuate cross-sectional configuration. Therefore, it is possible to prevent the occurrence of such a problem that the side edges of the opaque paper
3
, which are brought into contact with the respective inner wall surfaces
7
a
of the flanges
7
, are undesirably folded and tucked in. Thus, the opaque paper
3
is prevented from causing an undesired increase in the roll diameter. In addition, the side edges of the trailing end portion
3
b
of the wound opaque paper
3
are completely brought into close contact with the respective inner wall surfaces
7
a
of the flanges
7
. Therefore, the required light-tightness is maintained satisfactorily.
Spools for photographic film such as the above-described spool
5
are usually produced by injection molding process.
FIG. 9
is a sectional view of a conventional mold assembled for the injection molding process. A product part (mold cavity)
20
is formed essentially by four mold members
12
to
14
. That is, the mold has a stationary mold member
12
for molding the lower half of the outer periphery of the shaft portion
6
of the spool
5
and the lower half of the inner wall surface
7
a
of each flange
7
, and a movable mold member
13
for molding the upper half of the outer periphery of the shaft portion
6
and the upper half of the inner wall surface
7
a
of each flange
7
. The mold further has a pair of slide mold members
14
for molding the outer wall surfaces of the flanges
7
.
FIG. 10
is an enlarged view showing a part of the product part
20
in the mold shown in
FIG. 9
that corresponds to one flange
7
. A movable pin
15
is rigidly provided in the center of each of the slide mold members
14
to form a chucking groove
10
at each end of the shaft portion
6
of the spool
5
. In addition, each slide mold member
14
is provided with a cooling water channel
16
for the purpose of shortening the cooling time needed to cool the slide mold member
14
.
The conventional injection mold for producing a spool for photographic film is made of a material having high mechanical strength and low thermal conductivity, e.g. a stainless mold steel, exclusive of the movable pins
15
. The movable pins
15
are formed by using a material having high thermal conductivity, e.g. a beryllium-copper alloy, with a view to accelerating cooling to thereby facilitate removal.
If the inner wall surface
7
a
of each flange
7
of the spool
5
to be injection-molded has a groove
11
that is concentric with respect to the shaft portion
6
as shown in
FIG. 8
, that is, if an undercut
19
is present inside a portion of the product part
20
that corresponds to each flange
7
, when the molded spool
5
is removed from the mold, both end surfaces of each of the stationary and movable mold members
12
and
13
must be forcedly removed from the inner wall surfaces
7
a
of the flanges
7
. This may flaw the inner wall surfaces
7
a
of the flanges
7
of the molded spool
5
, causing the light-tightness to be degraded. Furthermore, regarding the shape of the molded spool
5
, the flanges
7
tend to bow inward. Therefore, the dimension between the flange inner wall surfaces varies according to the position in the circumferential direction, and thus the flange inner wall surfaces suffer distortion. Furthermore, in order to obtain the dimensional stability of the flanges
7
, sufficiently long cooling time is needed. Therefore, it has heretofore been difficult to shorten the molding cycle.
SUMMARY OF THE INVENTION
In view of the above-described problems of the prior art, an object of the present invention is to provide an injection mold for producing a spool, which is designed so that the inner wall surfaces of flanges at both ends of the spool are not flawed, and the dimension between the flange inner wall surfaces is uniform and thus the flange inner wall surfaces are free from distortion, and further the cooling time is short and hence the molding cycle can be shortened.
To attain the above-described object, the present invention provides an injection mold for molding a spool having flanges at both ends of a shaft. The injection mold includes two mold members for molding the outer periphery of the shaft of the spool and the inner wall surfaces of the flanges. The injection mold further includes a pair of mold members for molding the outer wall surfaces of the flanges. The two mold members for molding the outer periphery of the shaft of the spool and the inner wall surfaces of the

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