Stock material or miscellaneous articles – Circular sheet or circular blank – Aperture containing
Reexamination Certificate
1999-08-06
2003-07-22
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Circular sheet or circular blank
Aperture containing
C428S064100, C428S066500, C428S068000, C428S131000, C428S134000, C301S108100, C301S108300
Reexamination Certificate
active
06596370
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a resin molded article having openings, which exhibits an excellent surface appearance and satisfactory strength and relates to a resin molded article.
2. Description of Related Art
A resin molded article, having a plurality of openings, produced by molding synthetic resin by using a mold, for example; a wheel cap
9
for an automobile, as shown in
FIG. 11
, is known.
The wheel cap
9
comprises a central portion
91
formed at a position in the inside portion of the wheel cap
9
, which is more adjacent to a resin-injection opening
2
than the position of the openings
95
, an outer peripheral portion
92
formed outside of the openings
95
and bridge portions
93
formed between the adjacent openings
95
.
The conventional mold for molding the wheel cap
9
comprises a plurality of projections for forming the openings
95
, a plurality of bridge-forming portions for forming the bridge portions
93
formed between the projections, a central-portion forming portion for forming the central portion
91
, and an outer-periphery forming portion for forming the outer peripheral portion
92
.
The synthetic resin, in which glass fiber has been blended, is injected into the cavity of the mold through the injection opening so that the wheel cap
9
is produced.
However, the foregoing conventional producing method sometimes causes a weld
99
beside the openings
95
at a position in the outer peripheral portion
92
of the wheel cap
9
(see FIG.
11
).
Formation of a weld
99
will specifically be described in relation to a wheel cap having draft holes for an automobile, for an example.
As shown in
FIG. 11
, the wheel cap
9
sometimes has a weld
99
having a width of 1 to 5 mm in the outer peripheral portion
92
located outside of the openings
95
.
This weld
99
is formed because of a number of reason.
As shown in
FIG. 12
, a mold
8
for molding the wheel cap
9
has a cavity
82
including projections
81
for forming the openings
95
. The synthetic resin
7
is injected through the resin-injection opening
2
positioned in the central portion
91
of the wheel cap
9
. Therefore, the synthetic resin
7
moves in the cavity
82
for molding the wheel cap toward the outer peripheral portion
89
, as shown in FIG.
12
.
Since the cavity
82
includes the projections
81
, the synthetic resin flow
7
branches to the right and left thereat (see
FIG. 12
) and then is joined in the rear of the projections
81
so that a conjunction portion
77
is formed (see
FIGS. 12
to
14
).
When the synthetic resin
7
moves forward in the cavity
82
, the leading end of the synthetic resin flow forms a fountain flow, as shown in FIG.
13
.
Accordingly, glass fiber
72
in the synthetic resin
7
is, in the vicinity of the conjunction portion
77
, oriented in the direction of the conjunction portion
77
, namely, in a direction substantially perpendicular to the surface of the wheel cap
9
, as shown in FIG.
14
.
At this time, the resin flow in the central portion of the cavity
82
also proceeds in a direction perpendicular to the direction of the thickness of the cavity
82
. Accordingly the leading end of the resin flow is formed into a shape having the central portion which slightly projects, as shown in FIG.
15
(B).
Since the thickness of the cavity
82
is substantially uniform, the amount of this projection is small. Thus, if the leading edges of the resin flow collide with each other at the projection portions, there is practically no space in which the flows can flow into the side portions. Therefore, the synthetic resin
7
substantially stands still on the collision.
The glass fiber
72
in the synthetic resin
7
on the collision is oriented in the direction substantially perpendicular to the surface
97
of the wheel cap
9
, that is, in the direction of the thickness of the cavity
82
.
Therefore, the synthetic resin flows
7
are joined to each other in this state. Accordingly, the glass fiber
72
is, in the conjunction portion
77
of the wheel cap
9
which is a produced article, oriented in a direction substantially perpendicular to the surface
97
of the wheel cap
9
, as shown in FIGS.
14
and
15
(A).
In a major portion of the wheel cap
9
, the glass fiber
72
is oriented in the direction of the flow of the glass fiber
72
, namely, along the surface
97
of the wheel cap
9
.
Then, the synthetic resin
7
injected into the mold
8
is cooled, thus allowing the synthetic resin
7
to be coagulated and contracted. The contracting direction of the synthetic resin
7
is mainly the direction perpendicular to the direction in which the glass fiber
72
is oriented. Therefore, substantially no contraction generates in the conjunction portion
77
in which the glass fiber
72
is oriented perpendicularly to the surface
97
. The surrounding portion in which the glass fiber
72
is oriented substantially in parallel with the surface
97
is contracted in the direction of the thickness.
As a result, the projecting weld
99
is formed on the surface
97
in the conjunction portion
77
, as shown in FIG.
14
.
Besides, since a surface solidified layer is inserted in the conjunction portion
77
, there arises another problem in that the strength of the foregoing portion is lower than that of the other portion.
Such problems are not limited to the wheel cap. Various resin molded articles, such as a bumper and garnish for an automobile, each having openings sometimes encounter the similar problems.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a method for producing a resin molded article having openings, which is free from having a weld in a conjunction portion of synthetic resin flows and which exhibits an excellent surface appearance and satisfactory strength, and for providing a resin molded article obtained thereby.
According to a first aspect of the present invention, a method for producing a resin molded article having openings includes the step of injection-molding synthetic resin by using a mold. The mold for molding the resin molded article includes a cavity which has projections for forming openings, projection-side peripheral portions surrounding the projections, and a flow-rate changing means for making the flow rate of the injected synthetic resin different at both sides of each projection and wherein the synthetic resin is injected into the cavity of the mold through a resin-injection opening so that molding is performed.
The key feature of the present invention is that the cavity of the projection-side peripheral portion surrounding projections comprises the flow-rate changing means for making the flow rate-of the injected synthetic resin different at the both sides of each projection.
Examples of the flow-rate changing means are a means for making the cross-sectional areas of the cavity different, a means for making the temperature of the cavity different, a means for providing obstacles, such as a dam with a part of the cavity, and a means for providing a groove formed along the synthetic resin flow at the bottom of the cavity.
The operation and effect of the present invention will now be described.
When the resin-molded article is produced, the synthetic resin is injected into the cavity of the mold through the resin-injection opening.
The synthetic resin is sequentially fed to the entire cavity.
The synthetic resin collides with the projections of the cavity and moves forward along projection-side peripheries of the both sides of the projections. Then, the resulting branch flows of the synthetic resin are again joined at the rear of the projections.
The “rear of the projections” means a position opposite the resin-injection opening.
The cavity of the projection-side peripheral portions surrounding the projections comprises the flow-rate changing means. Thus, the flow rates of the synthetic resin flows, which move forward around the projections along both sides thereof, are different from e
Hyuga Hiromi
Kawashima Daiichiro
Oba Tatsuya
Teramoto Yasunobu
Chevalier Alicia
Posz & Bethards, PLC
Pyon Harold
Toyoda Gosei Co,., Ltd.
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