U.S. patent application number 11/544580 was filed with the patent office on 2007-02-08 for injection molding method and injection mold.
This patent application is currently assigned to FUJI PHOTO FILM CO., LTD.. Invention is credited to Naoyoshi Chino, Keiji Shigesada, Seiichi Watanabe.
Application Number | 20070031533 11/544580 |
Document ID | / |
Family ID | 12671935 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070031533 |
Kind Code |
A1 |
Shigesada; Keiji ; et
al. |
February 8, 2007 |
Injection molding method and injection mold
Abstract
An injection molding method and an injection mold used therefor
are provided, in which a molded product free from burrs, whitening
and gate marks can be obtained with a simple structure mold, and it
can adequately serve the needs for multicavity molding as well. The
injection molding method comprises the steps of: introducing and
charging a molten resin material into a resin reservoir and a
molding cavity of an injection mold, a depth of the resin reservoir
being larger than a thickness of a communicating portion; and
moving a cut punch, when a portion of the resin material in the
resin reservoir is still molten, to push the molten resin in the
resin reservoir back from a gate into a runner so that the cut
punch not only closes the communicating portion but also cuts a
resin solidified portion in the resin reservoir away from a resin
molded product in the molding cavity at the communicating
portion.
Inventors: |
Shigesada; Keiji; (Kanagawa,
JP) ; Watanabe; Seiichi; (Kanagawa, JP) ;
Chino; Naoyoshi; (Kanagawa, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
FUJI PHOTO FILM CO., LTD.
|
Family ID: |
12671935 |
Appl. No.: |
11/544580 |
Filed: |
October 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09622360 |
Aug 16, 2000 |
7147814 |
|
|
PCT/JP99/00522 |
Feb 8, 1999 |
|
|
|
11544580 |
Oct 10, 2006 |
|
|
|
Current U.S.
Class: |
425/556 ;
425/441 |
Current CPC
Class: |
B29C 45/38 20130101;
B29C 2045/386 20130101 |
Class at
Publication: |
425/556 ;
425/441 |
International
Class: |
B29C 45/44 20070101
B29C045/44; B29C 45/38 20070101 B29C045/38 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 1998 |
JP |
10-043731 |
Claims
1. An injection mold comprising: a fixed die and a movable die
which form a cavity into which a molten resin material is injected
to form a resin molded product; a runner through which the molten
resin material supplied to said fixed die flows, said runner being
provided in said fixed die and passing through inside of said fixed
die; a resin reservoir formed by recessing said fixed die toward a
opposite side of said movable die and communicating with said
runner and said cavity; a communicating portion formed on a
boundary between said resin reservoir and said cavity and allowing
said resin reservoir and said cavity to communicate with each other
so that the molten resin material is introduced into said cavity
via said resin reservoir; a gate formed on a boundary between said
runner and said resin reservoir and at an end portion of said
runner in said fixed die and injecting to said resin reservoir the
molten resin material supplied to said fixed die and flowed through
said runner in said fixed die to charge the molten resin material
into the cavity through said communicating portion from said resin
reservoir; a cut punch provided on a side of said movable die that
confronts said gate through said resin reservoir and having a
distal end, said cut punch being movable between a first position
to close said communicating portion, in which said distal end of
said cut punch is inserted into said resin reservoir so as to be in
slidable contact with said resin reservoir and a second position to
open said communicating portion, in which said distal end of said
cut punch is drawn out of and apart from said resin reservoir; an
undercut portion provided at a periphery of said distal end of said
cut punch, disposed closer to an edge portion of said distal end
than a center portion of said distal end, said undercut portion
serving to hold a resin solidified portion formed in said resin
reservoir at the time of mold opening; and means for driving said
cut punch between said first position and said second position in a
moving direction of said cut punch toward the resin reservoir,
wherein said driving means drives said cut punch to locate said
distal end at said second position between said resin reservoir and
said cavity to open said communicating portion in such a way that
when the molten resin material is being charged into said cavity,
said resin reservoir and said cavity are allowed to communicate
with each other so that the molten resin material is introduced
into said cavity via said resin reservoir, wherein said driving
means drives said cut punch to move said distal end of said cut
punch toward said first position after the molten resin material
has been charged into said cavity and said resin reservoir, and to
locate said distal end at said first position in said resin
reservoir to close said communicating portion in such a way that
when an inner portion of the resin material that is present in said
resin reservoir is still molten, a portion of the resin material
thereof that is in direct contact with said cooled dies is
gradually solidified and thereby the portion of the resin material
at said communicating portion between said cavity and said resin
reservoir is semi-solidified, said cut punch is inserted into said
resin reservoir, whereby said cut punch not only closes said
communicating portion while forcibly pushing the still molten resin
material present in said resin reservoir back through said gate
into said runner, but also cuts the resin material at said
communicating portion so that said resin molded product formed in
said cavity is separated from said resin solidified portion formed
in said resin reservoir, and wherein said undercut portion of said
distal end of said cut punch holds the resin solidified portion
formed in said resin reservoir.
2. The injection mold according to claim 1, further comprising: a
sprue bush provided on said fixed die and having an introducing
hole that introduces the molten resin material supplied to said
fixed die, wherein said runner communicates with said introducing
hole of said sprue bush and the molten resin material supplied to
said fixed die and introduced into said introducing hole of said
sprue bush flows through said runner in said fixed die.
3. The injection mold according to claim 2, wherein said sprue bush
introduces into said introducing hole thereof the molten resin
material supplied to said fixed die from an injection nozzle of an
injection molding machine.
4. The injection mold according to claim 1, comprising plural pairs
of the cavities, the resin reservoirs and the cut punches.
5. The injection mold according to claim 1, wherein said runner is
a cold runner and has a tapered portion on an end side of said
runner inside said fixed die, and said gate is formed at said end
portion of said tapered portion of said runner.
6. The injection mold according to claim 5, wherein said gate is
closed with a semi-solidified resin material or a solidified resin
material after said cut punch has moved to said first position.
7. The injection mold according to claim 1, wherein said runner is
a hot runner. (8)
8. The injection mold according to claim 7, wherein said hot runner
has a valve gate structure. (9)
9. The injection mold according to claim 8, wherein said gate is
closed by means of said valve gate structure after said cut punch
has moved to said first position.
10. The injection mold according to claim 1, wherein said injection
mold is used to mold the resin molded product having an opening and
has said resin reservoir and said cut punch inserted into said
resin reservoir, said resin reservoir and said cut punch being
provided so as to correspond to the opening of the resin molded
product. (10)
11. The injection mold according to claim 1, wherein a depth as
viewed in a moving direction of said cut punch in said resin
reservoir is 1.5 to 10 times an opening distance of said
communicating portion. (11)
12. The injection mold according to claim 1, further comprising a
pushing device for removing the resin solidified portion which is
attached to said distal end of said cut punch, said pushing device
being slidably mounted inside said cut punch, so as to be
independent of said cut punch. (17)
13. An injection mold comprising: a fixed die and a movable die
which form a cavity into which a molten resin material is injected
via both a runner and a gate provided in the fixed die, the gate
being connected to the cavity through a resin reservoir formed by
recessing the fixed die toward the gate; and a cut punch provided
on the side of the movable die that confronts the gate through the
resin reservoir, the cut punch being movable so that the cut punch
can be inserted into the resin reservoir so as to be in slidable
contact with the resin reservoir, wherein when the molten resin
material is being charged into the cavity, a distal end of the cut
punch which extends in a moving direction of the cut punch that is
toward the resin reservoir is located between the resin reservoir
and the cavity at such a position as to open a communicating
portion that allows the resin reservoir and the cavity to
communicate with each other so that the molten resin material is
introduced into the cavity via the resin reservoir; wherein when an
inner portion of the resin material that is present in the resin
reservoir is still molten and a portion of the resin material
thereof that is in direct contact with the cooled dies is gradually
solidified after the molten resin material has been charged into
the cavity and the resin reservoir, the cut punch moves toward the
gate so that the cut punch is inserted into the resin reservoir,
whereby the cut punch not only closes the communicating portion
while forcibly pushing the still molten resin material present in
the resin reservoir back into the gate, but also cuts the resin
material at the communicating portion so that a resin molded
product formed in the cavity is separated from a resin solidified
portion formed in the resin reservoir, wherein the runner contacts
the resin reservoir, and the gate is disposed at the point where
the runner contacts the resin reservoir, such that the gate does
not protrude into the resin reservoir, and wherein an undercut
portion is provided at a periphery of the distal end of the cut
punch, disposed closer to an edge portion of the distal end than a
center portion of the distal end, the undercut portion serving to
hold the resin solidified portion formed in the resin reservoir at
the time of mold opening.(6)
14. An injection mold comprising: a fixed die and a movable die
which form a cavity into which a molten resin material is injected
via both a runner and a gate provided in the fixed die, the gate
being connected to the cavity through a resin reservoir formed by
recessing the fixed die toward the gate; and a cut punch provided
on the side of the movable die that confronts the gate through the
resin reservoir, the cut punch being movable so that the cut punch
can be inserted into the resin reservoir so as to be in slidable
contact with the resin reservoir, wherein when the molten resin
material is being charged into the cavity, a distal end of the cut
punch which extends in a moving direction of the cut punch that is
toward the resin reservoir is located between the resin reservoir
and the cavity at such a position as to open a communicating
portion that allows the resin reservoir and the cavity to
communicate with each other so that the molten resin material is
introduced into the cavity via the resin reservoir; wherein when an
inner portion of the resin material that is present in the resin
reservoir is still molten and a portion of the resin material
thereof that is in direct contact with the cooled dies is gradually
solidified after the molten resin material has been charged into
the cavity and the resin reservoir, the cut punch moves toward the
gate so that the cut punch is inserted into the resin reservoir,
whereby the cut punch not only closes the communicating portion
while forcibly pushing the still molten resin material present in
the resin reservoir back into the gate, but also cuts the resin
material at the communicating portion so that a resin molded
product formed in the cavity is separated from a resin solidified
portion formed in the resin reservoir, wherein the runner contacts
the resin reservoir, and the gate is disposed at the point where
the runner contacts the resin reservoir, such that the gate does
not protrude into the resin reservoir, and wherein a depth as
viewed in a moving direction of the cut punch in the resin
reservoir is 1.5 to 10 times an opening distance of the
communicating portion. (11)
15. An injection mold comprising: a fixed die and a movable die
which form a cavity into which a molten resin material is injected
via both a runner and a gate provided in the fixed die, the gate
being connected to the cavity through a resin reservoir formed by
recessing the fixed die toward the gate; a cut punch provided on
the side of the movable die that confronts the gate through the
resin reservoir, the cut punch being movable so that the cut punch
is operative to be inserted into the resin reservoir so as to be in
slidable contact with the resin reservoir, and a communicating
portion, formed between the resin reservoir and the cavity when the
cut punch is not in slidable contact with the resin reservoir, the
communication portion allowing the resin reservoir and the cavity
to communicate with each other so that the molten resin material is
introduced into the cavity via the resin reservoir, wherein a
molded resin product is formed when the cut punch device moves
through the resin reservoir towards the gate to close the
communication portion, which cuts the resin material at the
communication portion so that the resin molded product formed in
the cavity is separated from a resin solidified portion formed in
the resin reservoir, wherein the cut punch moves at a time when an
inner portion of the resin material that is present in the resin
reservoir is still molten and a portion of the resin material
thereof that is in direct contact with cooled dies is gradually
solidified after the molten resin material has been charged into
the cavity and the resin reservoir and wherein an undercut portion
is provided at a periphery of the distal end of the cut punch,
disposed closer to an edge portion of the distal end than a center
portion of the distal end, the undercut portion serving to hold the
resin solidified portion formed in the resin reservoir at the time
of mold opening. (15)
16. The injection mold according to claim 15, further comprising a
pushing device for removing the resin solidified portion which is
attached to the distal ends of the cut punch, the pushing device
being slidably mounted inside the cut punch, so as to be
independent of the cut punch. (17)
17. An injection mold comprising: a fixed die and a movable die
which form a cavity into which a molten resin material is injected
via both a runner and a gate provided in the fixed die, the gate
being connected to the cavity through a resin reservoir formed by
recessing the fixed die toward the gate; and a cut punch provided
on the side of the movable die that confronts the gate through the
resin reservoir, the cut punch being movable so that the cut punch
can be inserted into the resin reservoir so as to be in slidable
contact with the resin reservoir and having a distal end which
extends in a moving direction of the cut punch that is toward the
resin reservoir, the distal end located between the resin reservoir
and the cavity at such a position as to open a communicating
portion that allows the resin reservoir and the cavity to
communicate with each other so that the molten resin material is
introduced into the cavity via the resin reservoir; and means for
driving the cut punch when an inner portion of the resin material
that is present in the resin reservoir is still molten and a
portion of the resin material thereof that is in direct contact
with the cooled dies is gradually solidified after the molten resin
material has been charged into the cavity and the resin reservoir,
wherein the cut punch is driven toward the gate so that the cut
punch is inserted into the resin reservoir, whereby the cut punch
not only closes the communicating portion while forcibly pushing
the still molten resin material present in the resin reservoir back
into the gate, but also cuts the resin material at the
communicating portion so that a resin molded product formed in the
cavity is separated from a resin solidified portion formed in the
resin reservoir, and wherein an undercut portion is provided at a
periphery of the distal end of the cut punch, disposed closer to an
edge portion of the distal end than a center portion of the distal
end, the undercut portion serving to hold the resin solidified
portion formed in the resin reservoir at the time of mold
opening.(18)
Description
[0001] This is a continuation of application Ser. No. 09/622,360
filed Aug. 16, 2000. The entire disclosure of the prior
application, application Ser. No. 09/622,360 is considered part of
the disclosure of the accompanying continuation application and is
hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to an injection molding method
and an injection mold.
BACKGROUND ART
[0003] Injection molding methods have heretofore been used as a
molding method for producing resin molded products. It is well
known that an injection molding method is a method involving the
steps of: forming a cavity between a fixed die and a movable die;
charging a molten thermoplastic resin material from a gate provided
on part of the cavity by injection; and solidifying the
thermoplastic resin material into a predetermined shape
corresponding to a space in the cavity to obtain a resin molded
product; and taking the resin molded product out.
[0004] Further, injection molds used in injection molding methods
come in two types; one having means for heating part of a runner
that introduces a molten resin material into a cavity from an
injection molding apparatus, and the other not having such means.
It is also well known that a method using the former type of mold
having the heating means is called a hot runner system and that a
method using the latter type of mold not having the heating means
is called a cold runner system.
[0005] By the way, immediately after the end of an injection
molding process based on the cold runner system, a resin molded
product formed in the cavity and a resin portion solidified in the
runner are in one piece. Therefore, the resin molded product and
the solidified resin portion in the runner must be cut into
separate pieces at a gate portion, and thus some kind of mechanical
cutting means is usually provided in the mold.
[0006] On the other hand, the injection molding method based on the
hot runner system has a mold structure so that the resin in the
runner can be kept molten. Therefore, the cutting means is not
generally required. However, to fabricate a molded product having
an opening in its part, it is preferred not to form weld lines
(lines formed in the cavity by the confluence of molten resin
portions flowing in different directions, and it is desirable to
minimize the formation of such lines from the viewpoints of
external appearance and mechanical strength). To prevent the
formation of weld lines, it is desired that molding be done using a
mold in which the gate is previously provided so as to correspond
to an opening forming portion and that the portion be thereafter
cut away to form the opening. In this case, even the hot runner
system must have mechanical cutting means similarly to the cold
runner system.
[0007] Thus, irrespective of the systems, whether it is the cold
runner system or the hot runner system, various types of methods
and molds that involve the cutting operation are proposed in
injection molding methods. For example, Japanese Patent Application
Laid-open No. Sho 55-15834 proposes a molding method for obtaining
a ring-like molded product. In this molding method, a molten resin
is charged into a cavity through a sprue bush, and then the sprue
bush is retracted as a cut pin for cutting a solidified resin
portion near a gate portion moves forward, so that the gate portion
is sheared to separate a subrunner from a resin molded product.
Further, Japanese Patent Application Laid-open No. Hei 6-278177
proposes a method that provides a second bush. In this method, a
cut bush for cutting a solidified resin portion near a gate portion
is moved forward, and in synchronism with such forward movement of
the cut bush, the second bush retracts from a cavity in such a
manner as to mechanically absorb an amount of resin pushed out by
the cut bush. Still further, Japanese Patent Application Laid-open
No. Hei 2-67115 proposes a mold that cuts a number of disk gates.
That is, not only a sprue bush is operated while interlocked with
the movement of a fixed die away from a fixed table, but also a
punch cutter provided on a movable die is projected, so that a
number of disk gates are cut.
[0008] Furthermore, Japanese Patent Application Laid-open No. Sho
58-158231 proposes a method for separating a molded product from a
disk gate formed in a cavity. That is, in a gate portion within the
cavity, a gate cutting blade provided on a movable die so as to
face the inner surface of a fixed die is operated to bring a front
end of the blade into contact with the fixed die, so that the gate
disk is cut away.
[0009] Furthermore, Japanese Patent Application Laid-open No. Hei
8-294944 proposes a method for obtaining a resin molded product
having an opening at a central portion. In this method, a specially
shaped core pin having an external shape corresponding to the
opening of the molded product is caused to shuttle between a first
position and a second position. The first position stops at a gate
a flow of molten resin injected into a hot runner. The second
position opens the gate to introduce the molten resin into a
cavity, and is located at the opening portion that is the center of
axis corresponding to a disk gate portion. Moreover, Japanese
Patent Application Laid-open No. Hei 7-276437 proposes a method for
obtaining a resin molded product having an opening at the center of
axis. In this method, a fixed pin is slidably provided in a hot
runner provided in a fixed die and serves also as a hot gate, and a
movable pin is provided on a movable die so as to be slidable in
correspondence with the fixed pin and has a distal end formed so
that the distal end engages with and abuts against a distal end of
the fixed pin so as to be connected to and disconnected from the
distal end of the fixed pin. The distal end of the fixed pin and
that of the movable pin are engaged with and abutted against each
other in the cavity so as to correspond to the opening portion of
the molded product, so that the resin molded product having the
opening at the center of axis is obtained.
[0010] Still further, Japanese Patent Application Laid-open No. Hei
1-99821 proposes a method for cutting a gate portion using a
sleeve-like cutter that is driven toward a fixed die from a movable
die after a resin material charged into a cavity has substantially
solidified and before a resin portion at the gate portion
completely solidifies.
[0011] However, the methods and mold disclosed in Japanese Patent
Application Laid-opens Nos. Sho 55-15834, Hei 6-278177 and Hei
2-67115 are based on the concept that complicates the mold
structure in order to achieve the above object, and thus elevates
the cost and is highly likely to impair mechanical reliability.
Further, if such methods and mold are applied to multicavity molds,
the structure becomes further complicated. Thus, one can easily
guess that the cost increases and the mechanical reliability
impairs significantly.
[0012] Still further, the method disclosed in Japanese Patent
Application Laid-open No. 58-158231 proposes the use of a simply
structured mold, but imposes not only a problem that the gate
cutting blade comes in contact with the mold when cutting the gate
portion, and thus has difficulty stably cutting a solidified film
layer of the resin material, but also a problem that the fixed die
could be damaged by the gate cutting blade abutting against the
mold strongly.
[0013] The methods disclosed in Japanese Patent Application
Laid-open Nos. Hei 8-294944 and Hei 7-276437 impose a problem that
the molds are expensive since both methods require an exclusive
valve gate system having specially shaped or structured pins. The
methods also impose, e.g., a problem that burrs are likely to be
produced at a punched portion since an opening is punched before
the gate portion solidifies.
[0014] Still further, the method disclosed in Japanese Patent
Application Laid-open No. 1-99821 proposes a simply structured
mold, but imposes a problem that the method is effective when there
is an amount of resin plenty enough to absorb the driving stroke of
the sleeve-like cutter at the disk gate portion, but if the volume
of the disk gate portion is relatively small, the cutter is hard to
drive and thus the method is not applicable.
DISCLOSURE OF THE INVENTION
[0015] Therefore, an object of the present invention is to provide
an injection molding method that can obtain a molded product free
from burrs, whitening and gate marks using a simply structured
mold, and that can adequately serve the needs for multicavity
molding.
[0016] Further, another object of the present invention is to
provide an injection mold beneficially applicable to the
aforementioned molding method.
[0017] To overcome the aforementioned problems, one aspect of the
present invention provides an injection molding method wherein a
molten resin material, which is injected into a cavity defined by a
fixed die and a movable die via a runner provided in the fixed die,
is introduced from a gate provided in the fixed die and is molded,
and the method is characterized in that:
[0018] when the molten resin material is being charged into the
cavity through the resin reservoir from the gate, a cut punch,
which is provided on the side of the movable die that confronts the
gate through a resin reservoir formed by recessing the fixed die
toward the gate and which is movably provided so that the cut punch
is inserted into the resin reservoir so as to be in slidable
contact with the resin reservoir, has a distal end thereof
extending in a moving direction thereof that is toward the resin
reservoir, and the distal end is located between the resin
reservoir and the cavity at such a position as to open a
communicating portion that allows the resin reservoir and the
cavity to communicate with each other so that the molten resin
material is introduced into the cavity via the resin reservoir;
and
[0019] when the resin material that is still molten is present in
the resin reservoir after the molten resin material has been
charged into the cavity and the resin reservoir, the cut punch
moves toward the gate so that the cut punch is inserted into the
resin reservoir, whereby the cut punch not only closes the
communicating portion while forcibly pushing the still molten resin
material present in the resin reservoir back into the gate, but
also cuts the resin material at the communicating portion so that a
resin molded product formed in the cavity is separated from a resin
solidified portion formed in the resin reservoir.
[0020] Further, another aspect of the present invention provides an
injection mold wherein a fixed die and a movable die form a cavity
into which a molten resin material injected via a runner provided
in the fixed die is introduced from a gate provided in the fixed
die, and the mold is characterized in that:
[0021] the gate is connected to the cavity through a resin
reservoir formed by recessing the fixed die toward the gate;
[0022] a cut punch is provided on the side of the movable die that
confronts the gate through the resin reservoir, the cut punch being
movable so that the cut punch can be inserted into the resin
reservoir so as to be in slidable contact with the resin
reservoir;
[0023] when the molten resin material is being charged into the
cavity, a distal end of the cut punch extending in a moving
direction of the cut punch that is toward the resin reservoir is
located between the resin reservoir and the cavity at such a
position as to open a communicating portion that allows the resin
reservoir and the cavity to communicate with each other so that the
molten resin material is introduced into the cavity via the resin
reservoir; and when the resin material that is still molten is
present in the resin reservoir after the molten resin material has
been charged into the cavity and the resin reservoir, the cut punch
moves toward the gate so that the cut punch is inserted into the
resin reservoir, whereby the cut punch not only closes the
communicating portion while forcibly pushing the still molten resin
material present in the resin reservoir back into the gate, but
also cuts the resin material at the communicating portion so that a
resin molded product formed in the cavity is separated from a resin
solidified portion formed in the resin reservoir.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a cutaway view of cold runner type injection mold
used in the first embodiment.
[0025] FIG. 2 is a cutaway sectional view of main portion in the
cold runner type injection mold used in the first embodiment.
[0026] FIG. 3 is a illustrative view of cavity and resin reservoir
in the cold runner type injection mold used in the first
embodiment.
[0027] FIG. 4 to 7 respectively show a process of the first
embodiment.
[0028] FIG. 8 is a illustrative view of hot runner type injection
mold used in the second embodiment.
[0029] FIG. 9 is a cutaway sectional view of main portion in the
hot runner type injection mold used in the second embodiment.
[0030] FIG. 10 to 13 respectively show a process of the second
embodiment.
[0031] FIG. 14a, FIG. 14b and FIG. 14c respectively show prefered
emobodeiment of a sectional form of the resin reservoir in the
injection mold of the present invention.
BEST MODES FOR CARRYING OUT THE INVENTION
[0032] An injection molding method of the present invention
(hereinafter referred to as the "method of the present invention")
and an injection mold of the present invention will be described
below in details.
[0033] In the method of the present invention, a molten resin
material injected by an injection molding machine is charged into a
cavity defined by a fixed die and a movable die from a gate
provided in the fixed die via a runner provided in the fixed die.
At this time, the molten resin material introduced from the gate is
charged into the cavity while flowing into a resin reservoir that
is formed on the side of the gate in the fixed die. When the molten
resin material is introduced into the cavity via the resin
reservoir, a communicating portion that allows the molten resin
material to pass through a space between the resin reservoir and
the cavity is formed. A cut punch is provided on the side of the
movable die that confronts the gate through the resin reservoir and
is movable so that the cut punch is inserted into the resin
reservoir so as to be in slidable contact with the resin reservoir
in order to form the communicating portion, and the distal end of
such cut punch is arranged on the side of the movable die. As shown
in, e.g., FIG. 2 to be referred to later, when a molten resin
material is charged into a cavity 10 via a resin reservoir 12 with
a cut punch 15 not yet in operation, a distal end 23 of the cut
punch 15 is held on the side of the movable die in such a position
as to open a communicating portion 11 through which the resin
passes from the resin reservoir 12 to the cavity 10. Then, as shown
in, e.g., FIG. 4 to be referred to later, after the molten resin
material has been charged into the cavity and the resin reservoir,
the resin material gradually solidifies from a portion that is in
direct contact with the cooled dies toward the inner portion. At
this time, when the resin material that is still molten is present
in the resin reservoir, the cut punch is operated so that the punch
moves toward the gate in such a manner as to be inserted into the
resin reservoir. Then, as shown in, e.g., FIG. 5, the cut punch
closes the communicating portion while forcibly pushing the still
molten resin material present in the resin reservoir back into the
gate. At the same time, the cut punch cuts the resin material at
the communicating portion, so that a resin molded product formed in
the cavity is separated from a resin solidified portion formed in
the resin reservoir.
[0034] In an injection mold used in the method of the present
invention, the depth as viewed in a moving direction of the cut
punch in the resin reservoir (i.e., a distance between the distal
end of the cut punch that is not yet in operation and held on the
side of the movable die and a surface on the side of the gate of
the fixed die forming the resin reservoir), e.g., a distance
L.sub.1 shown in FIG. 2 and an opening distance of the
communicating portion in the moving direction of the cut punch,
e.g., a distance L.sub.2 shown in FIG. 2 are arranged so that
L.sub.1>L.sub.2. As a result of such arrangement, the
solidifying speed of the resin material in the resin reservoir
becomes completely lower than that of the resin material in the
communicating portion. Hence, even if the resin material in the
communicating portion has solidified almost completely or
half-solidified, the resin material that is still molten is present
in the resin reservoir. If the cut punch is operated to move toward
the fixed die under such condition, the still molten resin material
is forcibly pushed back into the runner via the gate, and this
gives the cut punch a moving stroke. Therefore, the larger the
thickness of the resin reservoir is when compared with the opening
distance of the communicating portion, the larger the difference
between the solidifying time of the resin material in the resin
reservoir and that of the resin material in the communicating
portion becomes. As a result, such arrangement is advantageous in
increasing the range of timings at which the cut punch is stably
operated. On the other hand, the resin reservoir is scrapped every
time the molding process ends, and thus it is not economically
desirable to make it thicker than necessary. Thus, as a range in
which the molding process can be performed stably and economically
and in which burring and whitening do not occur at such a part of a
resin molded product as to correspond to the communicating portion,
the depth as viewed in the moving direction of the cut punch in the
resin reservoir is preferably set from 1.5 to 10 times the opening
distance of the communicating portion, or more preferably from 2 to
6 times.
[0035] Further, in the injection mold used in the method of the
present invention, as shown in FIG. 14a, such a cross section of
the resin reservoir that the depth as viewed in the moving
direction of the cut punch 15 in the resin reservoir 12 is
gradually increased toward the gate 14 is advantageous in
increasing the operating area of the cut punch. Further, as shown
in FIG. 14b, such a cross section that the depth of the outermost
peripheral portions 12a at both ends of the resin reservoir 12 is
increased is also advantageous in ensuring the operating stroke of
the cut punch. Still further, as shown in FIG. 14c, such a cross
section that the depth as viewed in the moving direction of the cut
punch 15 in the resin reservoir 12 is gradually increased toward
the gate 14 and the depth of the outermost peripheral portions 12a
at both ends of the resin reservoir 12 is increased may also be
acceptable and is advantageous in ensuring the operating stroke of
the cut punch.
[0036] Still further, it is so arranged that the diameter of the
shaft of a pusher pin for pushing the resin solidified portion in
the resin reservoir is increased so that the area of projection of
the distal end of the moving cut punch as viewed in the moving
direction of the cut punch is decreased, and that the cut punch is
operated independently of the pusher pin so that when the cut punch
operates, the pusher pin does not operate. Such an arrangement is
advantageous in ensuring the operating area and stroke of the cut
punch.
[0037] In the method of the present invention, when the resin
material in the communicating portion between the resin reservoir
and the cavity semi-solidifies and the resin material that is still
molten is present in the resin reservoir after the charging of the
molten resin material into the cavity has been completed, the cut
punch is operated to move toward the gate of the fixed die, so that
the cut punch closes the communicating portion. The operating
timing of the cut punch is selected appropriately in accordance
with the shape of the molding cavity, i.e., the shape of a resin
molded product, the solidifying speed of the resin material, the
shape of the resin reservoir, and the like. Generally, if the cut
punch is operated when the resin material in the communicating
portion is still molten, i.e., if the cut punch is operated at an
early timing, the resin material creeps into an operating clearance
provided between a side surface of the resin reservoir and a side
surface of the cut punch since the mold is designed to have a
slight clearance from manufacturing and structural considerations.
As a result, there is a danger that burrs are formed at the cut end
of the resin molded product.
[0038] Further, if the clearance is decreased to overcome the
burring problem, the side surface of the resin reservoir abuts
against the cut punch to cause scorings, and in the extreme case,
there may be an operation problem, e.g., that the communicating
portion of the fixed die is damaged. In addition, if the cut punch
is operated after the resin material in the communicating portion
has completely solidified, i.e., if the cut punch is operated at a
later timing, tiny cracks are present at the cut end of a resin
molded product obtained and whitening appears over the exterior of
the product. Therefore, it is important to determine while
confirming the operating timing of the cut punch for the method of
the present invention through tests and the like so that the timing
comes later than when the cut end burrs and earlier than when the
cut end whitens in the resin molded products obtained.
[0039] In the method of the present invention, the larger the
diameter of the opening of the gate through which the molten resin
material passes when the resin material that is still molten in the
resin reservoir is pushed back into the runner by the operation of
the cut punch, the easier the molten resin material is caused to
flow back into the runner, and thus the larger diameter of the
opening of the gate is advantageous in operating the cut punch as
desired. On the other hand, in the case where a cold runner type
injection mold is used, a larger diameter of the opening of the
gate is likely to make it hard to separate the resin solidified
portion formed in the resin reservoir from the runner. To overcome
this problem, in the case where a cold runner type injection mold
is used, it is preferred to previously fabricate the mold having an
ordinary pin gate diameter, examine the operating conditions of the
cut punch by checking the burring or whitening conditions of an
obtained molded product, and determine an appropriate opening
diameter by increasing the diameter as necessary. This applies
similarly to the diameter of the opening of the gate of the
injection mold of the hot runner structure. In the case where a hot
runner type injection mold having a valve gate is used, there is no
need to consider the problem of separating the resin solidified
portion in the resin reservoir from the runner at the gate since
the gate is mechanically closed by a needle pin. Therefore, it is
preferred to increase the diameter of the opening of the gate as
much as possible. For example, the diameter of the opening of the
gate preferably ranges from 1.0 to 2.5 mm.
Embodiments of the Invention
[0040] An injection molding method and an injection mold, which are
preferred embodiments 1 and 2 of the present invention will now be
described based on FIGS. 1 to 13. FIGS. 1 to 7 show a first
embodiment for fabricating a bent plate-like resin molded product
using a cold runner type mold that is a preferred embodiment of a
mold of the present invention. FIGS. 8 to 13 show a second
embodiment for fabricating a thin annular part using a hot runner
type mold.
[0041] Cold runner type injection mold 1 used in the first
embodiment whose main portion is shown in FIG. 1 in the form of a
cutaway section includes a fixed die 2 and a movable die 3. The
fixed die 2 includes a fixed mounting plate 2a and a fixed die
plate 2c mounted on the fixed mounting plate 2a through a fixed
back plate 2b. A sprue bush 6 in which an introducing hole 5 is
formed is provided on the fixed mounting plate 2a. The introducing
hole 5 introduces a molten resin material injected from an
injection nozzle 4 of an injection molding machine into the mold.
The introducing hole 5 of the sprue bush 6 is formed inside the
fixed back plate 2b and the fixed die plate 2c, and communicates
with a runner 7 through which the molten resin material flows.
[0042] The movable die 3 has a movable mounting plate 3a and a
movable die plate 3c that is mounted on the movable mounting plate
3a through a spacer block 3b.
[0043] A resin reservoir 12 is formed by recessing the fixed die
plate 2c of the fixed die. That is, at the time the fixed die 2 and
the movable die 3 of the injection mold 1 are matched, a stepped
molding surface 8 formed on the fixed die plate 2c of the fixed die
2 and a stepped molding surface 9 formed on the movable die plate
3c of the movable die 3 so as to correspond to the molding surface
8 forms the resin reservoir 12 that communicates to a cavity 10
that forms the resin molded products through the communicating
portion 11 as shown by a plan view of FIG. 3. In FIG. 3, reference
numeral 14 denotes a gate for introducing the molten resin material
into the cavity.
[0044] Further, as shown in FIG. 2, the resin reservoir 12 is
connected to the runner 7 via the gate 14 formed in a resin
reservoir surface 13 on the molding surface 8 of the fixed die
plate 2c of the fixed die. The runner 7 introduces the molten resin
material from the nozzle 4 of the injection molding machine.
[0045] Further, a cut punch 15 is provided on the side of the
movable die plate 3c of the movable die 3 that confronts the gate
14 through the resin reservoir 12. The cut punch 15 is so arranged
that when the molten resin material is being charged into the
cavity, a distal end 23 of the cut punch is located between the
resin reservoir 12 and the cavity 10 at such a position as to open
a communicating portion 11 that allows the resin reservoir 12 and
the cavity 10 to communicate with each other so that the molten
resin material is introduced into the cavity via the resin
reservoir 12, and that when the resin material that is still molten
is present in the resin reservoir 12 after the molten resin
material has been charged into the cavity, the cut punch is moved
from the movable die 3 to the fixed die 2 so that the resin
reservoir 12 is separated from the cavity 10 at the communicating
portion 11. The cut punch 15 is secured to a cut punch driving
hydraulic cylinder 17 together with cut punch pusher plates 16a and
16b, and is urged by a spring 18 in a direction opposite to a
driving direction.
[0046] Further, a resin reservoir pusher pin 19 for pushing out a
resin solidified portion formed in the resin reservoir 12 is
inserted into the cut punch 15 so as to be slidable independently
of the cut punch 15. Also, molded product pusher pins 20a and 20b
for pushing out a resin molded product formed in the cavity 10 are
slidably inserted into the movable die plate 3c. The resin
reservoir pusher pin 19 and the molded product pusher pins 20a and
20b pass through the cut punch pusher plates 16a and 16b and are
mounted on pusher plates 22a and 22b that are urged by a spring 21
in a direction opposite to a driving direction of the pusher pins.
The resin reservoir pusher pin 19 and the molded product pusher
pins 20a and 20b are driven forward (in the elevating direction as
viewed in FIG. 1) when a pushing rod (not shown) of the molding
machine pushes first a pusher rod receiver 22c and then the pusher
plate 22b that is integrally mounted on the pusher rod receiver
22c.
[0047] As shown in FIGS. 1 and 2, undercut portions 25a and 25b are
formed in the distal end 23 of the cut punch 15. The portions 25a
and 25b allow the cut punch to hold the resin solidified portion
formed in the resin reservoir 12 so that the resin solidified
portion does not remain on the side of the fixed die at the time of
mold opening.
[0048] In the injection mold 1, the communicating portion 11
provided between the resin reservoir 12 and the cavity is arranged
so that the depth as viewed in the moving direction of the cut
punch 15 in the resin reservoir becomes larger than the opening
distance of the communicating portion in the moving direction of
the cut punch as shown in FIG. 2. That is, a distance L.sub.1
between a molding surface 8a of the fixed die plate 2c on a side
surface 26 of the resin reservoir 12 and the distal end 23 of the
cut punch 15 is arranged to be larger than the opening distance of
the communicating portion 11 extending in the moving direction of
the cut punch, i.e., a distance L.sub.2 between a molding surface
8b of the fixed die plate 2c and the distal end 23 of the cut punch
15 (L.sub.1>L.sub.2). As a result of such arrangement, when the
cut punch 15 is driven in a direction indicated by an arrow A, not
only a side surface 15a of the cut punch 15 closes the
communicating portion 11, but also cuts the resin molded product
formed in the cavity 10 away from the resin solidified portion
formed in the resin reservoir 12 at the communicating portion
11.
[0049] In the injection molding method using the injection mold 1
that has the cold runner structure shown in FIG. 1, first, the
movable die 3 is driven to close the fixed die 2 and the movable
die 3, which in turn forms the cavity 10 and the resin reservoir 12
communicating with the cavity 10. Then, the molten resin material
is injected from the injection nozzle 4 of the injection molding
machine, the nozzle 4 being brought into contact with the
introducing hole 5 that is formed in the sprue bush 6 provided in
the fixed mounting plate 2a. The injected molten resin material is
introduced into the resin reservoir 12 from the gate 14 while
flowing through the runner 7, and is further charged into the
cavity 10 via the communicating portion 11. At this time, the cut
punch 15 does not operate and is held on the side of the movable
die 3.
[0050] The resin material charged into the resin reservoir 12, the
communicating portion 11 and the cavity 10 is cooled by cooling
water circulating through cooling means, e.g., cooling water
passages appropriately provided within the fixed die 2 and the
movable die 3, and thus solidified. After the charging of the resin
material has been completed, the charged resin material is cooled
to solidify, as shown in FIG. 4, from the outside portion that is
in contact with the molding surface 8 of the fixed die plate 2c and
the molding surface 9 of the movable die plate 3c, and the resin
material at the communicating portion 11 where the molding surface
8 neighbors the molding surface 9 solidifies or semi-solidifies
first. On the other hand, in the resin reservoir 12 that is thicker
than the communicating portion 11, i.e., in the resin reservoir 12
in which the distance between the molding surface 8 of the fixed
die plate 2c and the molding surface 9 of the movable die plate 3c
is large, the outside portion of the resin material that is in
contact with the molding surfaces 8 and 9 solidifies or
semi-solidifies, but a resin material portion 27 that is still
molten is present in the inside.
[0051] At this time, the cut punch 15 that is mounted on the cut
punch pusher plates 16a and 16b is operated by the cut punch
driving hydraulic cylinder 17 against the urging force of the
spring 18, so that the cut punch moves from the movable die 3 to
the fixed die 2. The still molten resin material 27 in the resin
reservoir is pushed back from the gate 14 to the runner 7 by the
pushing force of the moving cut punch 15. As a result, the volume
of the resin in the resin reservoir is reduced, which in turn
provides a stroke for allowing the cut punch 15 to move. Hence, as
shown in FIG. 5, the cut punch 15 advances toward the fixed die
plate 2c, so that the side surface 15a of the cut punch 15 closes
the communicating portion 11 and a resin molded product 28 in the
cavity 10 is cut away from a resin solidified portion 29 formed in
the resin reservoir 12 at the communicating portion 11. At this
time, the cut punch 15 is mounted with its base 30 held between the
cut punch pusher plates 16a and 16b shown in FIG. 1, so that the
moving distance of the cut punch 15 is regulated by the distance
between an outside surface 31 of the cut punch pusher plate 16a and
a rear surface 32 of the movable die plate 3c. The resin reservoir
pusher pin 19 inserted into the cut punch 15 so as to be slidable
independently of the cut punch 15 does not move together with the
cut punch 15 when the cut punch moves, and thus a top face 24 of
the pin 19 forms a recess 33.
[0052] The resin material in the cavity 10 and the resin reservoir
12 is cooled and solidifies, so that the resin molded product 28 is
formed in the cavity 10, and the resin solidified portion 29
including a resin material portion solidified at the recess 33 and
the undercut portions 25a and 25b is formed in the resin reservoir
12. Then, as shown in FIG. 6, the movable die 3 is driven to open
the injection mold 1. At this time, the resin solidified portion 29
formed in the resin reservoir is separated from the resin molded
product, and held on the distal end of the cut punch 15. Further,
the solidified portion formed in the undercut portions 25a and 25b
functions as a holding portion for holding the resin solidified
portion 29 on the distal end of the cut punch 15.
[0053] Next, as shown in FIG. 7, the pusher rod (not shown) of the
molding machine drives the resin reservoir pusher pin 19 and the
molded product pusher pins 20a and 20b mounted on the pusher plates
22a and 22b against the urging force of the spring 21, and the
resin molded product 28 and the resin solidified portion 29 are
pushed out independently of each other and obtained in the form of
cut pieces.
[0054] Further, FIGS. 8 to 13 show the second embodiment for
fabricating thin annular parts using a hot runner type four-cavity
mold based on a valve gate system. FIG. 8 shows only a half of the
four-cavity injection mold, omitting the other half on the back of
the sheet. The following description is based on the half of the
mold with two cavities shown in FIG. 8, and a description of the
other half on the back of the sheet is omitted.
[0055] A hot runner type injection mold 41 used in the second
embodiment whose main portion is shown in FIG. 8 in a cutaway form
includes a fixed die 42 and a movable die 43. The fixed die 42 has
a fixed mounting plate 42a and a fixed die plate 42c mounted on the
fixed mounting plate 42a through a spacer block 42b. A sprue bush
46 in which an introducing hole 45 is formed is provided on the
fixed mounting plate 42a. The introducing hole 45 introduces a
molten resin material injected from an injection nozzle 44 of an
injection molding machine into the mold. The introducing hole 45 of
the sprue bush 46 is connected to a runner 48 that is provided in a
manifold block 47 interposed between the fixed mounting plate 42a
and the fixed die plate 42c, and communicates with hot runners 50a
and 50b of hot runner nozzles 49a and 49b provided in the fixed die
plate 42c. Needle pins 53a and 53b are inserted into the hot
runners 50a and 50b of the hot runner nozzles 49a and 49b,
respectively. The pins 53a and 53b are driven by needle pin driving
cylinders 51a and 51b provided in the fixed mounting plate 42a and
control the introduction of the molten resin material into resin
reservoirs 58a and 58b, and cavities 56a and 56b which will be
described later.
[0056] The movable die 43 includes a movable mounting plate 43a and
a movable die plate 43e secured to movable back plates 43c and 43d
that are mounted on the movable mounting plate 43a through a spacer
block 43b.
[0057] The resin reservoirs 58a and 58b are formed by molding
surfaces 54a and 54b and molding surfaces 55a and 55b,
respectively. That is, as shown in FIGS. 8 and 9, when the fixed
die 42 and the movable die 43 of the injection mold 41 are closed,
the stepped molding surfaces 54a and 54b formed on the fixed die
plate 42c of the fixed die 42 and the stepped molding surfaces 55a
and 55b formed on the movable die plate 43e of the movable die 43
so as to correspond to the molding surfaces 54a and 54b form the
resin reservoirs 58a and 58b that communicate with annular cavities
56a and 56b for forming resin molded products through communicating
portions 57a and 57b. Further, gates 52a and 52b are formed in
resin reservoir surfaces 59a and 59b of the molding surfaces 54a
and 54b of the resin reservoirs 58a and 58b on the side of the
fixed die plate 42c, respectively.
[0058] The resin reservoirs 58a and 58b are connected to the hot
runners 50a and 50b via the gates 52a and 52b formed in the resin
reservoir surfaces 59a and 59b of the molding surfaces 54a and 54b
on the fixed die plate 42c of the fixed die 42. The hot runners
introduce the molten resin material.
[0059] Cut punches 60a and 60b are provided on the side of the
movable die plate 43e of the movable die 43 that confronts the
gates 52a and 52b through the resin reservoirs 58a and 58b. The cut
punches 60a and 60b are so arranged that when the molten resin
material is being charged into the cavities, distal ends 67a and
67b of the punches are located between the resin reservoirs and
cavities at such positions as to open the communicating portions
that allow the resin reservoirs 58a and 58b and the cavities 56a
and 56b to communicate with each other so that the molten resin
material is introduced into the cavities via the resin reservoirs
58a and 58b, and that when the resin material that is still molten
is present in the resin reservoirs 58a and 58b after the molten
resin material has been charged into the cavities, the cut punches
are moved from the movable die 43 to the fixed die 42 so that the
resin reservoirs 58a and 58b are separated from the cavities 56a
and 56b at the communicating portions 57a and 57b. The cut punches
60a and 60b are connected to cut punch driving hydraulic cylinders
61a and 61b provided in the movable back plate 43c together with
the movable back plates 43c and 43d, and are urged by springs 62a
and 62b in a direction opposite to a driving direction.
[0060] Further, resin reservoir pusher pins 63a and 63b for pushing
out resin solidified portions formed in the resin reservoirs 58a
and 58b are inserted into the cut punches 60a and 60b so as to be
slidable independently of the cut punches 60a and 60b. Also, molded
product pusher sleeves 64a and 64b for pushing out resin molded
products formed in the cavities 56a and 56b are slidably inserted
into the movable die plate 43e.
[0061] The resin reservoir pusher pins 63a and 63b and the molded
product pusher sleeves 64a and 64b pass through the movable back
plates 43c and 43d and are mounted on pusher plates 66a and 66b
urged by a spring 65 in a direction opposite to a moving direction
of the pusher pins and sleeves.
[0062] The resin reservoir pusher pins 63a and 63b and the molded
product pusher sleeves 64a and 64b are driven forward (in the
elevating direction as viewed in FIG. 8) when a pushing rod (not
shown) of the molding machine pushes first a pusher rod receiver
66c and then the pusher plates 66a and 66b that are integrally
mounted on the pusher rod receiver 66c.
[0063] As shown in FIGS. 8 and 9, undercut portions 69a and 69b are
formed in the distal ends 67a and 67b of the cut punches 60a and
60b. The portions 69a and 69b allow the cut punches 60a and 60b to
hold the resin solidified portions formed in the resin reservoirs
58a and 58b so that the resin solidified portions do not remain on
the side of the fixed die at the time of mold opening.
[0064] Further, in the injection mold 41, the communicating portion
57a provided between the resin reservoir 58a and the cavity 56a and
the communicating portion 57b provided between the resin reservoir
58b and the cavity 56b are arranged so that the depth of the resin
reservoirs become larger than the opening distance of the
communicating portions in the moving direction of the cut punches
60a and 60b. That is, when the cut punches 60a and 60b are not
operated and held on the side of the movable die plate 43e, a
distance L.sub.3 between the molding surface 54a or 54b of the
fixed die plate 42c on a side surface 101 of the resin reservoir
58a or 58b and the distal end 67a or 67b of the cut punch 60a or
60b is arranged to be larger than the opening distance of the
communicating portion 57a or 57b extending in the moving direction
of the cut punch, i.e., a distance L.sub.4 between the molding
surface 54a or 54b of the fixed die plate 43e and the distal end
67a or 67b of the cut punch 60a or 60b (L.sub.3>L.sub.4). As a
result of such arrangement, the cut punch 60a is operated to move
in a direction indicated by an arrow A, so that a side surface 102a
of the cut punch 60a not only closes the communicating portion 57a,
but also cuts the resin molded product formed in the cavity 56a
away from the resin solidified portion formed in the resin
reservoir 58a at the communicating portion 57a. Further, a similar
operation is performed at the resin reservoir 58b and the cavity
56b.
[0065] In the injection molding method using the injection mold 41
that has the hot runner structure shown in FIG. 8, first, the
movable die 43 is driven to close the fixed die 42 and the movable
die 43, which in turn forms the cavities 56a and 56b and the resin
reservoirs 58a and 58b that communicate with the cavities 56a and
56b through the communicating portions 57a and 57b. Then, the
injection nozzle 44 of the injection molding machine is brought
into contact with the introducing hole 45 formed in the sprue bush
46 provided in the fixed mounting plate 42a, and the molten resin
material is injected. The injected molten resin material is
introduced into the hot runners 50a and 50b while flowing through
the runner 48. At this time, the needle pins 53a and 53b are driven
upward as viewed in the drawing by the needle driving cylinders 51a
and 51b to open the gates 52a and 52b, so that the molten resin
material is introduced and charged into the cavities 56a and 56b
via the resin reservoirs 58a and 58b and the communicating portions
57a and 57b. At this time, the cut punches 60a and 60b are not
operated and held on the side of the movable die 43.
[0066] The resin material charged into the resin reservoirs 58a and
58b, the communicating portions 57a and 57b and the cavities 56a
and 56b is cooled by cooling water flowing through cooling means,
e.g., cooling water passages appropriately provided within the
fixed die 42 and the movable die 43, and thus solidified.
[0067] Next, an operation at the resin reservoir 58a, the
communicating portion 57a and the cavity 56a will be described as
an example. An operation at the resin reservoir 58b, the
communicating portion 57b and the cavity 56b is also similar.
[0068] After the charging of the molten resin material has been
completed, the charged resin material is cooled and solidifies, as
shown in FIG. 10, from the outside portion that is in contact with
the molding surface 54a of the fixed die plate 42c and the molding
surface 55a of the movable die plate 43e, and the resin material at
the communicating portion 57a where the molding surface 54a
neighbors the molding surface 55a solidifies or semi-solidifies
first. On the other hand, in the resin reservoir 58a that is deeper
than the communicating portion 57a, i.e., in the resin reservoir in
which the distance between the molding surface 54a of the fixed die
plate 42c and the molding surface 55a of the movable die plate 43e
is larger than the communicating portion 57a, the outside portion
of the resin material that is in contact with the molding surfaces
54a and 55a solidifies or semi-solidifies, but a resin material
portion 103a that is still molten is present in the inside.
[0069] At this time, the cut punch 60a mounted on the movable back
plates 43c and 43d is moved from the movable die 43 to the fixed
die 42 by the cut punch driving hydraulic cylinder 61a against the
urging force of the spring 62a. The still molten resin material
portion 103a in the resin reservoir is pushed back into the hot
runner 50a from the gate 52a by the pushing force of the driven cut
punch 60a. As a result, the volume of the resin in the resin
reservoir is reduced, which in turn provides a stroke for allowing
the cut punch 60a to move. Hence, as shown in FIG. 11, the cut
punch 60a moves toward the fixed die plate 42c, so that the side
surface 102a of the cut punch 60a not only closes the communicating
portion 57a, but also cuts a resin molded product 105a in the
cavity 56a away from a resin solidified portion 106a formed in the
resin reservoir 58a at the communicating portion 57a. At this time,
the resin reservoir pusher pin 63a that is inserted into the cut
punch 60a so as to be slidable independently of the cut punch 60a
is not driven together with the cut punch 60a when the cut punch
60a is driven, and thus a top face 68a of the pin 63a forms a
recess 107a.
[0070] Then, the needle pin 53a is driven to close the gate 52a,
and the resin material in the cavity 56a and the resin reservoir
58a is cooled and solidifies. Then, the resin molded product 105a
is formed in the cavity 56a, and the resin solidified portion 106a
including a resin material portion solidified at the recess 107a
and the undercut portions 69a and 70a is formed in the resin
reservoir 58a. As shown in FIG. 12, the movable die 43 is
thereafter driven to open the injection mold. At this time, the
resin solidified portion 106a formed in the resin reservoir is
separated from the resin molded product 105a, and held on the
distal end of the cut punch 60a. Further, the solidified portion
formed in the undercut portions 69a and 70a functions as a holding
portion for holding the resin solidified portion 106a on the distal
end of the cut punch 60a.
[0071] Then, as shown in FIG. 13, the pusher rod (not shown) of the
molding machine drives the resin reservoir pusher pin 63a and the
molded product pusher sleeve 64a mounted on the pusher plates 66a
and 66b against the urging force of the spring 62a, so that the
thin annular resin molded product 105a and the disk-like resin
solidified portion 106a are pushed out independently of each other
in cut pieces.
EXAMPLES
Test Example 1
[0072] Tests were carried out to fabricate bent plate-like resin
molded product using the cold runner type injection mold of the
present invention shown in FIG. 1 by changing the used resin, mold
temperature, clearance of the sliding portion between the inner
surface of the resin reservoir and the outer periphery of the cut
punch.
[0073] The thicknesses of the product forming portion, the
communicating portion and the resin reservoir (at the time of
injection) of the injection mold used for the tests were as
follows. TABLE-US-00001 Thickness of product forming portion
(cavity 10) 1.5 mm Thickness of communicating portion(11) 0.5 mm
Thickness of resin reservoir (12) at the time of 1.0 mm
injection
[0074] In the tests, the cutting quality given by the cut punch and
associated problems are evaluated based on the following criteria.
The results are shown in Table 1.
[0075] Cutting quality evaluation criteria: [0076] .smallcircle.
Satisfactory without cracks and burrs at cut end [0077] .DELTA.
Acceptable in terms of external appearance although with some
cracks and burrs at cut end [0078] X Defective with cracks and
burrs at cut end
[0079] Problems:
[0080] K Unsatisfactory in terms of mold durability because of
scorings at sliding portion
[0081] B Burring at cut end of molded product
[0082] H Whitening at cut end of molded product or cutting of
molded product impossible TABLE-US-00002 TABLE 1 Mold Cutting Used
resin temperature Clearance quality Problems GPPS 50.degree. C.
Less than 5 .mu.m .largecircle. K 5 to 20 .mu.m .largecircle. None
more than 20 .mu.m .DELTA. To X B PC 90.degree. C. Less than 5
.mu.m .largecircle. K 5 to 20 .mu.m .largecircle. None more than 20
.mu.m .largecircle. None PA 70.degree. C. Less than 5 .mu.m
.largecircle. K 5 to 20 .mu.m .largecircle. None more than 20 .mu.m
.DELTA. To X B Notes: GPPS: General-purpose polystyrene PC:
Polycarbonates PA: Polyamides
[0083] It can be said from the results shown in Table 1 that
narrower clearances of the sliding portion between the inner
surface of the resin reservoir and the outer periphery of the cut
punch provide a better cutting quality, but too narrow a clearance
makes it easy to bring the cut punch into contact with the resin
reservoir, and this is not desirable in terms of mold durability.
Particularly, if the clearance of the sliding portion is less than
5 .mu.m, a mold of high accuracy must be used to avoid the mold
durability problem, and this increases the cost for the mold and
hence is not desirable economically. Therefore, when economic
advantages are considered, it is desirable to optimize the
clearance in accordance with the resin properties used. It has been
verified from the results shown in Table 1 that clearances of 10 to
20 .mu.m are preferred for GPPS and PC, whereas clearances of 5 to
10 .mu.m are preferred for PA.
[0084] Further, tests were carried out to fabricate bent plate-like
resin molded products using the same mold by changing the used
resin, mold temperature and cut punch drive timing to evaluate the
cutting quality given by the cut punch and associated problems
under the same criteria. The results are summarized in Table 2.
"Drive timing" means a time interval (in seconds) from injection
completion (pressure holding start) to cut punch drive start.
TABLE-US-00003 TABLE 2 Driving Used Mold Timing Cutting resin
temperature Clearance (sec) quality Problems GPPS 50.degree. C. 10
.mu.m Less than 0.5 X B 0.5 to 1.5 .largecircle. None more than 1.5
X H PC 90.degree. C. 10 .mu.m Less than 0.8 X B 0.8 to 2.5
.largecircle. None more than 2.5 X H PA 70.degree. C. 10 .mu.m Less
than 1.5 X B 1.5 to 2.5 .largecircle. None more than 2.5 X H
[0085] It can be said from the results shown in Table 2 that the
cut punch drive timing differs depending on the resin properties.
What is common to the above three kinds of resins is that an early
cut punch drive timing produces burrs at the cut ends and a late
cut punch drive timing produces whitening and a further late timing
makes it impossible to cut the products.
Test Example 2
[0086] Tests were carried out to fabricate thin annular parts by
using the hot runner type injection mold of the present invention
shown in FIG. 8 and using PA as a resin at a mold temperature of
70.degree. C. and by changing the clearance of the sliding portion
between the inner surface of the resin reservoir and the outer
periphery of the cut punch to obtain cut punch driving timings that
can give satisfactory cutting quality. The results are shown in
Table 3.
[0087] The thicknesses of the product forming portion, the
communicating portion and the resin reservoir (at the time of
injection) of the injection mold used for the tests were as
follows. TABLE-US-00004 Thickness of product forming portion
(cavity 56a) 0.17 mm Thickness of communicating portion (57a) 0.17
mm Thickness of resin reservoir (58a) at the time of 0.5 mm
injection
[0088] TABLE-US-00005 TABLE 3 Drive timing Used resin Mold
temperature Clearance (sec) PA 70.degree. C. 5 .mu.m 0.2 to 1.4 10
.mu.m 0.4 to 1.5 15 .mu.m 1.5 to 1.6 more than 20 .mu.m No
range
[0089] It can be said from the results shown in table 3 that
narrower clearances of the sliding portion between the inner
surface of the resin reservoir and the outer periphery of the cut
punch provide a wider drive timing range for giving satisfactory
cutting quality, whereas wider clearances provide a narrower drive
timing range for giving satisfactory cutting quality. Further, too
narrow a clearance makes it easy to bring the cut punch into
contact with the resin reservoir similarly to Test Example 1, which
is not desirable in terms of mold durability. When PA is used as a
resin, a clearance of 15 .mu.m makes the cutting quality-optimizing
drive timing as short as 0.1 sec, and this is not desirable in
terms of stable production. Further, a clearance of 20 .mu.m
provides no drive timing range that can optimize the cutting
quality. Therefore, the optimal cut punch drive timing that can
give satisfactory clearance and cutting quality differs depending
on the resin properties.
[0090] Further, tests were carried out to fabricate thin annular
parts by using the same mold and using PA as a resin at mold
temperatures of 60 and 80.degree. C. by changing the thickness of
the resin reservoir to obtain cut punch drive timings for giving
satisfactory cutting quality. The results are shown in Tables 4 and
5. TABLE-US-00006 TABLE 4 Resin reservoir Driving Mold thickness
timing Used resin temperature Clearance (mm) (sec) PA 60.degree. C.
10 .mu.m 0.2 0.1 to 0.2 0.25 0.1 to 0.3 0.5 0.3 to 1.2 1.0 0.5 to
2.0 1.7 0.5 to 2.5
[0091] TABLE-US-00007 TABLE 5 Thickness Resin ratio resin reservoir
Drive reservoir to Used Mold thickness timing communicating resin
temperature Clearance (mm) (sec) portion PA 80.degree. C. 10 .mu.m
0.2 0.1 to 0.2 1.2 0.25 0.1 to 0.4 1.5 0.35 0.3 to 1.0 2.0 0.5 0.5
to 1.7 2.5 1.0 0.6 to 2.5 5.9 1.7 0.6 to 2.9 10
[0092] It is understood from the results shown in Tables 4 and 5
that thicker resin reservoirs provide a wider range of cut punch
drive timings for giving satisfactory cutting quality. Further,
thickness ratios between the resin reservoir and the communicating
portion of 1.5 or less cannot provide an adequately wide drive
timing range, which imposes problems in terms of stable production.
Still further, the resin in the resin reservoir is scrapped every
molding cycle, and thus is a waste. Therefore, there is no need to
have a drive timing range wider than necessary, and thus from the
viewpoint of cut punch driving controllability and effective use of
resources, it is understood that the thickness of the resin
reservoir should preferably range from 1.5 to 10 times the
thickness of the communicating portion, or more preferably from
about 2 to 6 times.
INDUSTRIAL APPLICABILITY
[0093] As described in the foregoing, the injection molding method
of the present invention can provide the following advantages.
[0094] (1) When the resin is injected and charged, the resin
material in the resin reservoir solidifies from its outside
surface, and at the time the resin material in the communicating
portion that communicates with the cavity has solidified, the
molten resin material remains in the resin reservoir since the
resin reservoir is deeper than the communicating portion. When the
cut punch is driven under such condition, the molten resin material
in the resin reservoir can flow backward into the runner via the
gate. As a result, the volume of the resin in the resin reservoir
can be reduced, so that the moving stroke of the cut punch can be
provided. Hence, the method of the present invention can eliminate
the use of a complicated structure of the conventional mold, e.g.,
a moving sprue bush employed in a mold for fabricating optical disk
substrates. That is, the method of the present invention can
simplify the mold structure.
[0095] (2) If the resin reservoir is considered as part of a
product, the gate in the mold of the present invention functions as
a gate in an ordinary mold. Therefore, by adding only a cut punch
drive system, the mold of the present invention can be designed to
have a structure as simple as that of the conventional mold. As a
result, the design of a multicavity mold can be similar to that of
the conventional example, and thus becomes easy. Still further,
even if a hot runner type is employed, the structure of the mold of
such type can be designed as simple as that of a conventional
example. Therefore, a commercially available hot runner system can
be directly used, and thus an inexpensive mold can be provided.
[0096] (3) The solidified (or semi-solidified) resin material in
the communicating portion is cut away. Therefore, the cut end has
no burrs into which the molten resin can creep, and thus a resin
molded product having no gate marks can be obtained. Further, since
the molten resin does not creep into the cut end, an adequate
clearance between the cut punch and the resin reservoir into which
the cut punch is inserted can be provided, and thus the user does
not have to worry about scorings at this portion. Hence, a durable
mold can be provided and mold parts can be fabricated
inexpensively.
* * * * *