Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2000-07-10
2003-06-10
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
C264S328190, C425S557000, C425S560000
Reexamination Certificate
active
06576179
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an injection molding process and an apparatus therefor, and more particularly, related to a process for injection-molding a composite rein composition composed of particles and a binder resin, and an injection-molding machine used therefor.
Conventionally, as an injection-molding process and apparatus of such a type, there are known those described in Japanese Patent Application Laid-Open (KOKAI) No. 9-295329(1997).
As shown in
FIG. 11
, an injection-molding machine of the prior art is constituted by a kneader
1
for kneading a mixed starting material to be kneaded, an injection device
2
for injection-molding the kneaded material, a reservoir device
3
for temporarily storing the kneaded material to be fed to the injection device
2
, and a switching valve (directional control valve)
4
being switchable between one position where the kneaded material is fed to the reservoir device
3
and another position where the kneaded material is fed to the injection device
2
.
The kneader
1
is constituted by a heating barrel
5
, an extrusion screw
6
which is mounted in the barrel so as to be rotatably driven by, for example, an oil motor, and a hopper
7
for feeding a raw material to be kneaded, which is fitted onto an outside of the heating barrel.
The injection device
2
is constituted by a heating barrel
8
, an injection screw
9
which is mounted in the barrel so as to be rotatably driven by, for example, an oil motor and reciprocatively moved by a piston, and an injection nozzle
10
which is provided at a distal end thereof. Upon metering, a metering space
11
is formed on the front side of the injection screw
9
in the heating barrel
8
.
The reservoir device
3
is constituted by a reservoir chamber
12
in which an extrusion plunger
13
is accommodated so as to be reciprocatively driven by a piston in the vertical direction. When the extrusion plunger
13
is moved upward, a storage space
14
is formed in the reservoir chamber
12
underneath the extrusion plunger
13
.
The switching valve
4
is of a rotary type and has a valve body through which a straight passage for the kneaded material is formed.
An outlet (or inlet)
16
of the reservoir device
3
and an inlet
17
of the switching valve
4
are connected with each other through a passage
18
, and an outlet
19
of the switching valve
4
and an inlet
20
of the injection device
2
are connected with each other through a passage
21
. Further, a discharge end of the kneader
1
is opened into the mid-position of the passage
18
such that the kneader
1
is inclined downwardly toward the passage
18
.
When performing the injection molding process using the above injection molding machine, the switching valve
4
is held in the closed position as shown in
FIG. 11
(refer to a broken line in FIG.
11
), and the kneader
1
is operated, thereby introducing the kneaded material into the reservoir device
3
through the passage
18
. At this time, the extrusion plunger
13
is caused to move upward by the pressure of the kneaded material introduced, so that the kneaded material is temporarily stored in the storage space
14
formed underneath the extrusion plunger
13
.
Then, the switching valve
4
is opened, and after a predetermined period of time therefrom, the extrusion plunger
13
is moved downward, thereby forcing the kneaded material to discharge downward from the storage space
14
. The discharged kneaded material is merged (jointed) with a kneaded material freshly supplied from the kneader
1
. The jointed kneaded material is then fed to the injection screw
9
of the injection device
2
through the switching valve
4
, and the injection screw
9
is retarded, thereby transferring the kneaded material into the metering space
11
thus formed on the front side of the injection screw
9
to store the material therein.
Subsequently, as shown in
FIG. 12
, the switching valve
4
is closed, and the injection screw
9
is stopped to rotate and is allowed to move forward, whereby the kneaded material is injected through the injection nozzle
10
to obtain an aimed injection-molded product.
During the above injection molding step, the kneader
1
supplies a fresh kneaded material into the reservoir device
3
through the passage
18
. The extrusion plunger
13
is forced to move upward by the pressure of the kneaded material introduced, so that the kneaded material is temporarily stored in the storage space
14
formed underneath the extrusion plunger
13
.
Thus, the injection molding machine is returned to the initial condition as shown in
FIG. 11
, and subsequently the above operations are repeated.
However, in the conventional injection molding machine and injection molding process, when the kneaded material is discharged from the storage space
14
of the reservoir device
3
by the extrusion plunger
13
and introduced into the injection device
2
, the extrusion pressure exerted by the extrusion plunger
13
is transmitted through the passage
18
to the kneader
1
. For this reason, when the extrusion pressure acts on the kneader
1
, the torque of the extrusion screw
6
is temporarily increased, thereby failing to perform a stable kneading operation in the kneader
1
.
Further, the extrusion pressure tends to cause a reverse flow of the kneaded material from the reservoir device
3
through the passage
18
into the kneader
1
. In such a case, the kneaded materials having different heat histories are disadvantageously mixed together upon kneading.
Accordingly, in the conventional injection molding machines and processes, there arise problems such as non- uniform quality of obtained injection molded products due to such an unstable injection molding process.
As a result of the present inventors' earnest studies for solving the above problems, it has been found that using an injection molding machine having a pair of reservoir devices for temporarily storing a kneaded material, by (a) kneading particles and a binder resin using a kneader, (b) feeding the obtained kneaded material to one (A) of the two reservoir devices, (c) feeding the kneaded material stored in the reservoir device (A) to an injection device, and simultaneously feeding the kneaded material from the kneader to another reservoir device (B) to store the material therein, (d) feeding the kneaded material stored in the reservoir device (B) to the injection device, and simultaneously feeding the kneaded material from the kneader to the said one reservoir device (A) to store the material therein, and (e) repeating the steps (c) and (d), the obtained injection-molded product is free from uneven properties and can exhibit a good quality. The present invention has been attained on the basis of this finding.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved injection molding process and injection molding machine, wherein the kneading can be stably conducted without being adversely affected by the feed pressure from the reservoir devices.
It is an another object of the present invention to provide an improved injection molding process and injection molding machine, wherein it is possible to obtain an injection-molded product which is free from uneven properties and can exhibit a good quality.
To accomplish the aims, in a first aspect of the present invention, there is provided a process for injection-molding a composite resin composition, comprising:
(a) kneading particles and a binder resin using a kneader;
(b) feeding the obtained kneaded material to one (A) of two reservoir devices to store the material therein;
(c) feeding the kneaded material stored in the reservoir device (A) to an injection device wherein the kneaded material is then injection-molded, and simultaneously feeding the kneaded material from the kneader to another reservoir device (B) to store the material therein;
(d) feeding the kneaded material stored in the reservoir device (B) to the injection device wherein the kneaded material is then injection-molded, an
Abe Masaharu
Nakamura Kyoichi
Yamamoto Hiroshi
Fontaine Monica A
Heitbrink Jill L.
Nixon & Vanderhye P.C.
Toda Kogyo Corporation
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