Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By gas forming or expanding
Reexamination Certificate
2000-11-16
2003-05-06
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By gas forming or expanding
C425S00400R
Reexamination Certificate
active
06558592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a die-expanded molded foaming apparatus for forming molded foam products using material beads made of thermoplastic synthetic resin, such as polyolefine and polystyrene, and a method therefor.
2. Description of the Related Art
As a die-expanded molded foaming apparatus for manufacturing molded foam products using material beads made of thermoplastic synthetic resin, an apparatus shown in
FIG. 10
has been commercialized, wherein a set of dies
100
and
101
are disposed opposite each other, chambers
102
and
103
are disposed at the rear side of the dies
100
and
101
respectively, many vent holes
105
and
106
connecting the chambers
102
and
103
and the cavity
104
are formed in both of the dies
100
and
101
, and utility fluid, such as the later mentioned heating steam, is supplied to the cavity
104
or exhausted from the cavity
104
through the vent holes. In the structure of this case, upper utility ports
107
and
108
for supplying heating steam are disposed at the upper part of the respective chambers
102
and
103
, and the lower utility ports
109
and
110
connected to a pressure reducing pump and a drain pipe are disposed at the lower part of the respective chambers
102
and
103
so that steam is supplied to the cavity
104
.
For actually forming the many vent holes
105
and
106
opened in the dies
100
and
101
, a core vent
111
, which is a cylindrical body with a cap having an outer diameter of 7-12 mm where a plurality of vent holes
105
and
106
, which are approx. 0.5 mmø round holes or approx. 0.5 mm width slits, are opened, is embedded in the respective core vent attachment holes
112
, which are opened at a 20-50 mm pitch in the dies
100
and
101
, as illustrated in FIG.
11
and FIG.
12
.
Using such a die-expanded molded foaming apparatus, pre-expanded material beads are filled into the cavity
104
, are heated with the heating steam for foaming and fusing, are cooled and solidified, and then taken out as a molded foam body in a predetermined shape, and the role of the vent holes
105
and
106
in this molded foaming will now be further explained.
In the Japanese Patent Laid-Open No. 57-174223, the process drawing shown in
FIG. 13
is included, wherein FIGS.
13
(
a
)-
13
(
d
) depict the pre-heat exhausting process for substituting air in the dies and air among the material beads with steam, and the specific content of each process will be explained below. In
FIG. 13
, a black valve symbol indicates that the valve is closed, and a white valve symbol indicates that the valve is open.
FIG.
13
(
a
) shows an exhaust process, wherein after the material beads are filled in the cavity
104
, steam is supplied from the top utility ports
107
and
108
to the chambers
102
and
103
for a very short time, and at the same time, air in the dies, particularly in the chambers
102
and
103
, is exhausted from the bottom utility ports
109
and
110
by suction. In this case, pressure inside the chambers
102
and
103
is increased to be a plus pressure by steam so that steam enters among the material beads through the vent holes
105
and
106
.
FIG.
13
(
b
) shows a both-side exhaust process, wherein the top utility ports
107
and
108
are closed, and the vacuuming and pressure reducing operation is continued to reduce pressure inside the dies so that air existing in spaces among the material beads is sucked and exhausted through the vent holes
105
and
106
formed in the dies on both sides.
FIG.
13
(
c
) shows a one-side preheating process, wherein the bottom utility ports
109
and
110
are closed and steam is supplied from the top utility port
108
of one chamber
103
, which is in a pressure- reduced state, for a short time. In this case, the supplied steam passes sequentially through the vent holes
106
of the die
101
, among the material beads in the cavity
104
, and the vent holes
105
of the die
100
, and flows into the chamber
102
at the opposite side, by which all of the material beads and the dies
100
and
101
are preheated.
FIG.
13
(
d
) shows a one-side preheating process with an opposite flow of steam, wherein, a similar operation is carried out from the chamber
102
side so that air in the cavity
104
is completely exhausted, and at the same time, both dies
100
and
101
are preheated while decreasing the localized temperature difference as much as possible.
FIG.
13
(
e
) shows a heating process for fusion, wherein steam for heating for fusion is supplied to both of the chambers
102
and
103
for heating the dies
100
and
101
, and for heating the materials beads as well through the vent holes
105
and
106
of the respective dies
100
and
101
, so as to complete foaming, and to mutually fuse the material beads to form the molded foam body.
The vent holes formed in the dies in this manner play an important role as exhaust passages of the air among the material beads or as supply passages of heating steam for obtaining a homogeneous molded foam body, but on the other hand, the following problems have also been recognized.
(1) In order to compensate for strength which is decreased by opening many core vent attachment holes in the dies, the wall thickness of a die made of aluminum alloy material must be set thick, 8-12 mm for example, which increases heat capacity, causing such problems as poor heat efficiency for heating and cooling, or a slow speed of temperature rising and lowering, which drops control accuracy.
(2) Since 2000-4000 core vent attachment holes are opened in a general pair of dies, a complicated drilling operation increases processing cost, and since the core vents are attached manually, this operation is complicated, causing inevitable damage on the surface of the dies, where an extra operation for repair is necessary.
(3) Vent holes are clogged by e.g. scales, causing heat failure, mold releasing failure, and cooling failure, which makes a maintenance operation necessary, such as replacing core vents or periodic cleaning by high pressure cleaning water.
(4) Traces of core vents and vent holes remain on the surface of the molded foam product, which causes a drop in the beauty of the appearance of the molded foam product, and when the outer surface is printed, traces of core vents and vent holes become the cause of dropping printing quality.
(5) After molding, the molded foam product is cooled down by spraying cooling water into the chambers, and at this time moisture infiltrates into the cavity through the vent holes, resulting in the molded foam product containing 6-10% water inside, which makes a drying process necessary. Also the cooling water must be controlled to be a clean state to obtain a clean molded foam product, since the cooling water directly contacts the molded foam product.
(6) Since the material beads are heated for expanding and fusing under the same heating conditions by supplying steam from the chambers to the cavity, the surface property of the molded foam product obtained like this (hereafter equal heating molded foam product) changes depending on the fusion rate of the beads. Specifically, the surface property worsens as the fusion rate decreases, and surface property improves as the fusion rate increases. On the other hand, the at higher the fusion rate of the beads is set for an equal heating molded foam product, the better properties become, such as the mechanical strength of the molded foam product, but heating, expanding and fusing time, and cooling time become longer, which makes the general cycle time of molding longer, decreasing productivity.
For the above reasons, in the above mentioned molding technology, the fusion rate of beads of a molded foam product is set to e.g. 40-80% so as to improve surface property to insure beauty in appearance and to insure mechanical strength by setting a sufficiently high fusion rate, however the fusion rate must be set high enough to insure beauty in appearance even for a molded foam product which does not demand high
Ida Kiyotaka
Kobayashi Yoshiyuki
Nakajima Tomio
Nohara Iwao
Sameshima Masahiko
Armstrong Westerman & Hattori, LLP
Daisen Industry Co., Ltd.
Kuhns Allan R.
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