Multi-point compression molding process

Details Multi-point compression molding process Multi-point compression molding process

1999-12-23

2002-10-29

Tentoni, Leo B. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

Plural sequential shaping or molding steps on same workpiece

C264S319000, C264S328700

Reexamination Certificate

active

06471902

ABSTRACT:

REFERENCE OF RELATED APPLICATION
This application claims the Paris Convention priority right of Japanese Patent Application No. Hei 10-371573 filed on Dec. 25, 1998, the entire disclosure of which is incorporated by reference.
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a multi-point thin portion compression molding method and a multi-point thin portion compression mold for use in this method, particularly to a multi-point thin portion compression molding method of filling a metal mold with molten resin and pressurizing and compressing a molded material by a movable telescopic member in a cavity to form a plurality of thin portions and a multi-point thin portion compression mold for use in this method.
(ii) Description of the Related Art
In a conventional art, a case formed by an injection molding technique is frequently used in the exterior member of an electronic apparatus. For this electronic apparatus case, in recent years, there has been a demand for reduction in size for carrying and other use purposes. Moreover, for the electronic apparatus case, there are demands for the integration of a circuit substrate and the thinning of the case in order that the increasing number of electronic components with various additional functions are efficiently contained inside. Particularly, for example, in mobile communication terminals such as a PHS phone and a cellular phone, the reduction in size for carrying and the thinning of the case for efficiently containing the increasing number of internal components with various additional functions are most important.
FIG. 11
is a sectional view showing a conventional injection mold for forming such case. Moreover,
FIG. 12
is a perspective view of a case
70
of a cellular phone formed by the injection mold shown in FIG.
11
. Furthermore,
FIG. 13
is a sectional view of a section taken along line I—I shown in FIG.
12
.
As shown in
FIG. 11
, the conventional injection mold is constituted of a pair of a fixed metal mold
60
and a movable metal mold
50
which are opened/closed, and attached to a predetermined mold opening/closing apparatus (not shown) and driven. Here, the movable metal mold
50
is movable in an arrow direction shown in
FIG. 11
, and attached to or detached from the fixed metal mold
60
. Moreover, a cavity space
61
having a molded material shape is formed between the fixed metal mold
60
and the movable metal mold
50
when the mold is closed. This cavity space
61
is connected to a gate
62
via which molten resin
1
is supplied from the outside of the fixed metal mold
60
, and this gate
62
is provided with a spool
62
a
and a runner
62
b
which are formed in the fixed metal mold
60
and the movable metal mold
50
, respectively. In the injection mold shown in
FIG. 11
, the gate
62
is formed in a submarine gate (tunnel gate) shape.
To form the molded material by the conventional injection mold formed as described above, the movable metal mold
50
is placed in contact with the fixed metal mold
60
to close the mold, the movable metal mold
50
is pressed onto the fixed metal mold
60
to clamp the mold, then the cavity space
61
is filled with the molten resin
1
, and the molten resin
1
is cooled to form the molded material. Subsequently, the movable metal mold
50
is detached from the fixed metal mold
60
to open the mold, and an ejector pin (not shown) is allowed to protrude from the movable metal mold
50
so that the molded material can be taken out.
The cellular phone case
70
formed by the above-described conventional injection mold will next be described in detail with reference to FIG.
12
. As shown in
FIG. 12
, the cellular phone case
70
formed by the conventional injection mold is provided with a circuit substrate
80
with a plurality of electronic components
82
mounted thereon to form a high frequency circuit section. In this case, when the circuit substrate
80
is attached inside the case
70
, the high frequency circuit section is requested to be shielded. Therefore, in the case
70
, a shield wall
76
for closing and shielding the high frequency circuit section is formed.
Here, the circuit substrate
80
with the electronic components
82
higher than the shield wall
76
mounted thereon is attached to the case
70
, and recessed thin portions
72
are formed so that the high electronic components
82
can be contained inside the shield wall
76
. The recessed thin portions
72
can be formed by disposing protrusions in the cavity space
61
of the movable metal mold
50
shown in FIG.
11
. Since the case
70
is provided with the thin portions
72
in this manner, an interval J between the surface of the circuit substrate
80
and the outer surface of the case
70
shown in
FIG. 13
can be formed to be thin, thereby thinning the entire cellular phone case.
However, in the conventional injection molding method, there are design restrictions determined by the resin property and metal mold. For example, with a large thickness, hardening requires much time and disadvantages such as sink marks are generated. On the other hand, with a small thickness the molten resin fails to flow in the terminal end of the injection molded material. The thickness of the generally used injection molded material is in a range of about 0.8 mm to 1.5 mm at standard. Moreover, in the design of the injection molded material, considerations are required so that the thickness of the injection molded material is as uniform as possible. Particularly, in the injection molding, when the cavity space is filled with the molten resin, the surface of the resin flowing along the wall surface of the cavity space is quickly cooled and hardened, and so-called skin layers
1
a
are formed as shown in FIG.
13
. The flow of the molten resin is further deteriorated by the skin layers
1
a
in the thin portions
72
shown in FIG.
13
.
Therefore, in the case
70
shown in
FIG. 12
, since the thickness of the thin portion
72
is not uniform, the flow of the molten resin supplied via the gate
62
is deteriorated. This causes the insufficient filling of the case
70
, and welds
70
a
by the resin flow in the thin portions
72
shown in FIG.
12
. Moreover, in the usual injection molding, since the injection molded material is cooled as it is without being pressurized during the cooling process, the sink marks are generated on the surface of the molded material because of a difference of shrinkage factor between the thin portion compressed during the cooling process and the usual thick portion.
There is a compression molding method as a method for solving the above-described disadvantages. This compression molding method, in which the resin in the cavity is pressurized during the cooling process, has been noted in recent years as a technique of filling the inside of the metal mold with the resin and subsequently moving a movable telescopic member to compress the resin so that the sink marks are locally controlled or the opening and thin portions can be formed without any welds. Such prior art is disclosed, for example, in Japanese Patent Application Laid-Open No. 230534/1998.
FIG. 14
is a sectional view showing such conventional compression mold. Moreover,
FIG. 15
is an operation explanatory view showing an operation of forming the molded material by the compression mold shown in
FIG. 14
,
FIG. 15A
shows the filled state with the molten resin,
FIG. 15B
shows that the molten resin is compressed by the movable telescopic member, and
FIG. 15C
shows that the inside of the cavity is filled by the movable telescopic member. Moreover,
FIG. 16
is a perspective view showing an IC card formed by the compression mold shown in FIG.
14
.
As shown in
FIG. 14
, the conventional compression mold is constituted of a pair of a fixed metal mold
100
and a movable metal mold
90
which are opened/closed, and attached to a predetermined mold opening/closing apparatus (not shown) and driven. Here, the movable metal mold
90
is movable in an arrow direction shown in
FIG.

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