Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By gas forming or expanding
Reexamination Certificate
2000-11-22
2004-10-05
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By gas forming or expanding
C264S126000
Reexamination Certificate
active
06800227
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for filling material beads, a method for die-expanded molded foaming of synthetic resin using the above method, and a die-expanded molded foam product obtained thereby, in a die-expanded molded foaming apparatus which molds molded foam products using material beads made of thermoplastic synthetic resin, such as polyolefine and polystyrene.
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. 11
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 a 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 is exhausted from the cavity
104
through the vent holes
105
and
106
. 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 lower utility ports
109
and
110
connected to a pressure reducing pump or 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 approximately 0.5 mm&phgr; round holes or approximately 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.
12
and FIG.
13
.
In order to mold a molded foam body using such a molded foaming apparatus, preexpanded material beads made of thermoplastic synthetic resin, such as polyolefine and polystyrene, are supplied from a material tank (not illustrated) and filled into the cavity
1
via a filling unit
113
, are heated with the heating steam for foaming and fusing, are cooled and solidified, and then are taken out as a molded foam body.
Widely used methods for filling the material beads are 1) a cracking method, 2) a pressure filling method, and 3) a compression filing method, and these methods will be briefly described first.
1) The cracking method is a method for filling material beads by mechanically supplying the mechanical beads using an injector in a state where the material tank and the cavity are opened to atmospheric pressure, and has a disadvantage that air remaining inside is apt to cause filling unevenness, and increase the dispersion of filling density.
2) The pressure filling method is a method for filling the material beads by pressurizing inside the material tank to 0.2~1.5 kg/cm
2
, and supplying and filling the material beads into the cavity, which is opened to atmospheric pressure, through the chamber using the differential pressure. In this case, filling unevenness is less than the above mentioned cracking method, since differential pressure in the carrier passage from the material tank to the cavity can be utilized.
3) The compression filling method is a method for supplying and filling material beads by pressurizing the pressure P inside the material tank to 1.0~5.0 kg/cm
2
, slightly higher than the pressure filling method, and pressurizing one chamber so as to change the differential pressure (P−P
1
) with the pressure P
1
inside the cavity connected thereto via vent holes, and the filling property is good since the material beads are supplied in a compressed state.
Now, a method for heating, expanding and fusing the material beads, which are filled in the cavity as mentioned above, will be examined. As a heating expansion method for the material beads, a method stated in the Japanese Patent Laid-Open No. 57-174223 has been generally used. In this publication, the process drawing shown in
FIG. 14
is included, wherein (a)~(d) depict the preheat exhausting process for substituting air in the dies and air among the material beads with steam, and the concrete content of each process will be explained below. In
FIG. 14
, a black valve symbol indicates that the valve is closed, and a white valve symbol indicates that the valve is open.
(a) is 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
.
(b) is 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.
(c) is 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 hole
106
of the die
101
, among the material beads in the cavity
104
, and the vent hole
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.
(d) is 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.
(e) is 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.
In the case of the above mentioned molding method, wherein such a utility fluid as air and steam is supplied to the cavity or is exhausted from the cavity, the vent holes are indispensable, but forming vent holes will cause the following problems.
(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 b
Ida Kiyotaka
Kobayashi Yoshiyuki
Nakajima Tomio
Nohara Iwao
Sameshima Masahiko
Daisen Industry Co., Ltd.
Kuhns Allan R.
Westerman Hattori Daniels & Adrian LLP
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