U.S. patent application number 11/430870 was filed with the patent office on 2006-08-31 for die-expanded molding apparatus and method for synthetic resin, and die-expanded molded foam obtained thereby.
This patent application is currently assigned to Daisen Industry Co., Ltd.. Invention is credited to Kiyotaka Ida, Yoshiyuki Kobayashi, Tomio Nakajima, Iwao Nohara, Masahiko Sameshima, Kenji Yamaguchi.
Application Number | 20060194035 11/430870 |
Document ID | / |
Family ID | 27313985 |
Filed Date | 2006-08-31 |
United States Patent
Application |
20060194035 |
Kind Code |
A1 |
Nohara; Iwao ; et
al. |
August 31, 2006 |
Die-expanded molding apparatus and method for synthetic resin, and
die-expanded molded foam obtained thereby
Abstract
A die-expanded molding apparatus comprising starting material
bead supply for supplying beads on a current of air from a tank
through a packer into a cavity formed by a core and cavity molds; a
plurality of air expulsion devices having air pressure-adjusting
components communicating with the cavity, a dual-system air
expulsion device being such that steam chambers on the back side of
the core mold and the cavity mold are used as the air
pressure-adjusting components, each communicating with the cavity
through through-holes formed in the core and cavity molds,
respectively; an air expulsion device having one or more air
pressure-adjusting components communicating with a clearance
between the core and cavity molds; and a control for controlling
the air pressure in each of the air pressure-adjusting components
to be pressurized less than the pressure in the tank.
Inventors: |
Nohara; Iwao;
(Nakatsugawa-shi, JP) ; Nakajima; Tomio;
(Nakatsugawa-shi, JP) ; Ida; Kiyotaka;
(Nakatsugawa-shi, JP) ; Sameshima; Masahiko;
(Osaka, JP) ; Kobayashi; Yoshiyuki;
(Kitakatsuragi-gun, JP) ; Yamaguchi; Kenji;
(Osaka, JP) |
Correspondence
Address: |
ARMSTRONG, KRATZ, QUINTOS, HANSON & BROOKS, LLP
1725 K STREET, NW
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
Daisen Industry Co., Ltd.,
Nakatsugawa-shi
JP
Kaneka Corporation
Osaka-shi
JP
|
Family ID: |
27313985 |
Appl. No.: |
11/430870 |
Filed: |
May 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10462700 |
Jun 17, 2003 |
7070720 |
|
|
11430870 |
May 10, 2006 |
|
|
|
09674343 |
Oct 30, 2000 |
|
|
|
PCT/JP99/02355 |
Apr 30, 1999 |
|
|
|
10462700 |
Jun 17, 2003 |
|
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Current U.S.
Class: |
428/304.4 ;
264/413; 264/415 |
Current CPC
Class: |
B29C 44/445 20130101;
Y10T 428/249953 20150401 |
Class at
Publication: |
428/304.4 ;
264/413; 264/415 |
International
Class: |
B32B 3/26 20060101
B32B003/26; B29C 67/20 20060101 B29C067/20; B29C 44/00 20060101
B29C044/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 1998 |
JP |
H10(1998)-120166 |
Jun 25, 1998 |
JP |
H10(1998)-178743 |
Jul 2, 1998 |
JP |
H10(1998)-187514 |
Claims
1. A die-expanded molded foam, comprising a density of within
.+-.5% of the mean density in various locations in the molded
foam.
2. A die-expanded molded foam as set forth in claim 1, wherein the
degree of shape complexity is defined as the numerical value
obtained by dividing the surface area of the molded foam by the
volume, and the degree of shape complexity is 1.1 or more.
3. A die-expanded molded foam as set forth in claim 2, wherein the
wall thickness of the thin-walled portions of the molded foam is 10
mm or 3 mm.
4. A die-expanded molded foam as set forth in claim 1, wherein the
wall thickness of the thin-walled portions of the molded foam is 10
mm or 3 mm.
5. A die-expanded molded foam as set forth in claim 4, wherein 3 or
less beads are disposed in the thicknesswise direction of the
thin-walled portions of the molded foam.
6. A die-expanded molded foam as set forth in claim 1, wherein 3 or
less beads are disposed in the thicknesswise direction of the
thin-walled portions of the molded foam.
7. A die-expanded molded foam as set forth in claim 2, wherein 3 or
less beads are disposed in the thicknesswise direction of the
thin-walled portions of the molded foam.
8. A die-expanded molded foam as set forth in claim 3, wherein 3 or
less beads are disposed in the thicknesswise direction of the
thin-walled portions of the molded foam.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a division of Ser. No. 10/462,700, filed
Jun. 17, 2003, which is a division of Ser. No. 09/674,343, filed
Oct. 30, 2000, which is a 371 application of PCT Appln. No.
PCT/JP99/02355, filed Apr. 30, 1999.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a die-expanded molding
apparatus and method for synthetic resins, as well as die-expanded
molded foam obtained thereby, and more particularly to a technique
for improving the packing density of starting material beads in
cavities to obtain molded products with more uniform packing
density.
[0004] 2. Description of the Related Art
[0005] As shown in FIG. 13, a die-expanded molding apparatus for
forming molded products using starting material beads consisting of
a thermoplastic synthetic resin comprises a pair of mutually
opposed forming molds 100 and 101, and a packer 111 for packing
starting material beads in a cavity 104 formed by the two forming
molds 100 and 101, where chambers 102 and 103 are formed on the
back side of the two forming molds 100 and 101, respectively,
several vent holes 105 and 106 communicating between the cavity 104
and the chambers 102 and 103 are formed in the two chambers 100 and
101, respectively, and a service fluid such as steam, air, or
cooling water needed for molding is fed to the chambers 102 and
103. In this case, upper service ports 107 and 108 are provided in
the tops of chambers 102 and 103, respectively, to supply heated
steam, and bottom service ports 109 and 110 connected to a vacuum
pump or drain pipe are provided in the bottoms to supply steam to
the cavity 104.
[0006] The several vent holes 105 and 106 penetrating through the
forming molds 100 and 101 are actually provided when core vents,
which consist of cylinders having lids with an outside diameter of
7 to 12 mm perforated by vent holes consisting of round holes of
about 0.5 mm o or slits of about 0.5 mm width, are fitted into core
vent attachment holes arranged at a pitch of 20 to 50 mm in the
forming molds 100 and 101.
[0007] When expanded foam is molded using such an expansion molding
apparatus, the forming molds are first closed to form the cavity
104, pre-expanded starting material beads of polystyrene or the
like are transported from a starting material tank (not shown)
through the packer 111 into the cavity 104 and packed there, the
starting material beads in the cavity 104 are then heated with hot
steam, they are expanded and fused and are then cooled to
solidification, and the forming molds 100 and 101 are opened to
allow the expanded molded foam to be taken out.
[0008] One problem in particular which needs to be remedied in such
a molding method, however, is the considerable difference between
the packing density of the starting material beads at specific
locations in the cavity 104 and the packing density at other
locations. These specific locations can be broadly divided into (1)
the interior of the cavity 104 where the detailed portions of
molded products having complex shapes are formed, (2) the outer
peripheral distal portion 104a of the cavity 104, and (3) the parts
facing the packer 111 in the cavity 104.
[0009] Causes of this variation in packing density are described in
detail in sections (1) through (3) below, but before that, the most
commonly used method for packing starting material beads will be
briefly described.
[0010] ((1)) Cracked packing, ((2)) pressure packing, ((3))
compression packing, and the like are widely used methods for
packing starting material beads.
[0011] (1) Cracked packing is employed when the air used during
packing cannot be adequately expelled from the core vents alone,
which are arranged in the core mold and cavity mold; during
packing, the core mold and cavity mold are not completely closed,
but are left open (are cracked) to an extent equal to about 10% of
the floor thickness of the molded product, for example, to let the
air used during packing to escape from the gap between the core
mold and cavity mold.
[0012] (2) In pressure packing, the interior of the starting
material tank holding the starting material beads is pressurized to
between about 0.2 and 1.5 kg/cm.sup.2, while the cavity is left
open to atmospheric pressure through the core vents and chambers,
in which state the starting material beads are delivered into the
cavity and packed there by means of the pressure differential
between the starting material tank and the cavity.
[0013] (3) In compression packing, the pressure p in the starting
material tank is pressurized to about 1.0 to 5.0 kg/cm.sup.2, which
is higher than that in pressure packing, the interior of one
chamber is pressurized, and the pressure differential (p-p1) of the
pressure p1 in the cavity communicating through the vent holes is
varied, so as to deliver and pack the starting material beads.
[0014] Causes of the variation in packing density are described
below.
[0015] (1) Interior of Cavity for Forming Detailed Portions of
Molded Products Having Complex Shapes
[0016] In the three aforementioned packing methods, suitable
pressure differential is ultimately applied between the starting
material tank and the cavity, and the starting material beads are
delivered by the current of air produced on the basis of this
pressure differential. In the cavity 104 having the relatively
simple shape illustrated as an example in FIG. 13, the starting
material beads are fully packed throughout, resulting in a shape
with few local packing irregularities, so that a final expanded
molded foam can be obtained with relatively uniform quality and few
packing irregularities.
[0017] However, the results are different in the case of shapes
with deep, narrow recesses 112 having a pouch-shaped cross section
in the center plane of the core mold 101 such as that shown in FIG.
14(a) (in two locations above and below in FIG. 14) and in the case
of shapes with deep, narrow recesses 112 having a pouch-shaped
cross section in the center plane of the cavity mold 100 such as
that shown in FIG. 14(a) (similarly in two locations above and
below in FIG. 14). In these two cases, the current of air acting as
the advancing force for packing the starting material beads settles
in these portions, which makes it difficult for the starting
material beads to be packed all the way into the interior of the
recesses 112 or 113 having a pouch-shaped cross section and results
in drawbacks such as extremely uneven packing or, in the worst
cases, unsuccessful molding due to packing defects.
[0018] Efforts have been made to arrange special packers for
recesses that are difficult to pack in order to remedy such
problems, but they have resulted in the inconvenience of increasing
the amount of air that is used, or in the need to reduce the number
of molded foam articles which can be formed per mold, with the
problem of considerably lowered productivity. That is because the
number of packers that can be attached per molding apparatus is
usually limited to a certain extent because of the volume of the
starting material tank, the supply capacity of the pressurized air,
and the like. 18 packers are attached in the most common apparatus,
for example, with 3 packers set up per cavity when the molded
product has a simple shape, whereas when 6 are needed for molded
products having a more complex shape, even though there is room for
6 molded foam articles, only 3 can be molded, cutting productivity
in half.
[0019] In addition, the increase in the amount of air supplied to
the cavity per unit time when the number of packers is increased
results in a sudden drop in the air pressure in the cavity
immediately after packing and the like, and slows down the
expulsion of air from the cavity, and the like, causing all the
more variation in packing density. The number of packers used and
the arrangement of the packers are thus a concern for designers of
molds, and a great many elements require trial and error, making
standardization extremely difficult to achieve in this field. The
packing density tends to be lower particularly in parts that are
some distance from the packer or in narrow, bottomed parts such as
the recesses described above and the like, and it is necessary to
increase the overall packing density in order to ensure a suitable
packing density in such parts which are difficult to pack,
resulting in a heavier molded foam than when the density is
uniform.
[0020] Additionally, in terms of molding, it is necessary to
further expand the starting material beads, and to increase the hot
steam pressure, so that the starting material beads are thoroughly
fused in parts with low packing density when the packed starting
material beads are heated with steam. However, when the hot steam
pressure is increased in parts with such low packing density, the
parts with a high packing density become overheated, resulting in
expansion pressure which is higher than that during normal molding.
Thus, when the molded product is cooled, a longer time is needed to
reduce the high expansion pressure to an expansion pressure
allowing the molded product to be removed from the mold, and the
longer molding cycle leads to a drop in productivity. Furthermore,
the uneven expansion pressure in the various parts of the molded
product during heating or cooling results in poor mold
releasability and poor packing properties, and thus in the problems
of lower productivity and yields.
[0021] (2) Outer Peripheral Distal End of Cavity
[0022] In pressure packing and compression packing, as shown in
FIG. 13, the outer peripheral distal end 104a of the cavity 104
forms a dead end because the starting material beads are packed
into the cavity 104 while the two molds 100 and 101 are completely
closed. The current of air produced by the pressure differential
between the starting material tank (not shown) and the cavity 104
thus settles in the outer peripheral distal end 104a, making it
difficult to pack the starting material beads and tending to result
in irregular density.
[0023] In cracked packing, on the other hand, the core mold and
cavity mold are not completely closed, and are left open to an
extent equal to about 10% of the floor thickness of the molded
product, for example, so the outer peripheral distal end of the
cavity does not form a dead end, but since the core mold and cavity
mold are closed after being packed, the density in the floor
portion of the molded product is higher than that in other portions
to an extent corresponding to the cracked gap, resulting in a
separate problem of irregular density.
[0024] Additionally, when the two molds are completely closed after
being packed with the starting material beads in cracked packing,
the outer peripheral distal end of the cavity forms a dead end,
resulting in the following problems when the starting material
beads are heated by steam and cooled by cooling water to remove the
molded product from the mold.
[0025] When the starting material beads are heated, hot steam is
supplied from one chamber to another, for example, allowing the hot
steam to pass through the starting material beads in the cavity,
but, as shown in FIG. 13, when the outer peripheral distal end 104a
of the cavity forms a dead end, it becomes difficult for the hot
steam to reach the outer peripheral distal ends 104a, and heat
flows into the outer peripheral parts 100a and 101a of the mold
where the heat volume is relatively high, making it difficult for
the temperature of the starting material beads in the outer
peripheral distal ends 104a to increase, with a correspondingly
slower increase in temperature than in other parts, so that the
heating process takes a longer time, resulting in the problem of a
longer overall molding time.
[0026] When the molded product is cooled, cooling water is sprayed
onto the molds 100 and 101 from nozzles (not shown) disposed in the
chambers 102 and 103, the pressure in the chambers 102 and 103 is
reduced to allow the water adhering to the molds or moisture in the
cavity 104 to evaporate, and the expanded molded foam is cooled off
along with the molds by the vaporization heat at that time, but
now, in contrast to the heating time of the starting material beads
described earlier, the outer peripheral distal end 104a of the
cavity 104 becomes difficult to cool as a result of heat conduction
from the outer peripheral portions 100a and 101a of the molds, and
the time needed to sufficiently cool the parts of the expanded
molded foam located at the outer peripheral distal end 104a of the
cavity 104 is a problem.
[0027] When the molded product is released from the mold, the
expanded molded foam is pushed out by an ejector pin (not shown)
from the back side of the cavity mold 100 while the molds 100 and
101 are open, allowing the expanded molded foam to be taken out of
the mold, but a problem that occurs when the core mold 101 is
opened is that water which has collected in the inter-mold cavity
116 along the seams of the molding apparatus around the frames 114
and 115 and the outer peripheral portions 100a and 101a of the
molds flows out, wetting the expanded molded foam which is the
final product.
[0028] (3) Parts of the Cavity Facing the Packer
[0029] Although the packing density of the starting material beads
in this part is high, conventional packing methods will be
discussed in further detail before the relevant mechanism is
discussed.
[0030] In the three packing methods noted above, the starting
material beads in the packer 111 are returned to the starting
material tank at the end of the packing operations, and a step
referred to as blow back takes place, where the distal end of the
packer 111 is closed.
[0031] Blow back is described with reference to FIG. 15. First, the
packer 111 is composed of a packing pipe component 120, through
which the starting material beads pass, and a flange 121. The tip
is connected through a tube 102 to a supply hole 122 in the cavity
mold 100. A packing tube 124 is connected between a starting
material tank 123 and the packer 111, allowing the starting
material beads to be delivered into the cavity 103 between the two
molds.
[0032] When the pressure in the cavity 103 is adjusted to a
negative pressure relative to the pressure in the starting material
tank 123 with this arrangement, the starting material beads are
delivered from the starting material tank 123 through the packing
pipe 124 and the packing pipe component 120 of the packer 111 into
the cavity 104 by the pressure differential, as shown in FIG.
15(a). In this case, pressurized packing air is introduced from the
packing air valve 125 and is sprayed out from a spraying hole 126
in the distal end of the packing pipe component 120 as indicated by
the arrows in FIG. 15(a) in order to urge the starting material
beads in such a way that the delivered starting material beads
smoothly enter the cavity 104 and are tightly packed there.
[0033] When the cavity 104 is thus filled with the delivered
starting material beads, for example, in the manner depicted in
FIG. 15(b), the packing air introduced from the packing air valve
125 is blocked by the tightly packed starting material beads and
turns around in a U-turn from the spraying hole 126, resulting in a
back flow through the packing pipe component 120. Due to this
current of air, the starting material beads in the packing pipe
component 120 are pushed back toward the packing pipe 124, leaving
the component empty. This step in the blow back process is normally
referred to as the natural blow back process.
[0034] The starting material beads in the packing pipe component
120 are ejected by the natural blow back, a plunger shaft 127
housed in the flange 121 is then pushed out, and the plunger tip
128 is pushed out, as shown in FIG. 15(c), so that the starting
material bead supply hole 122 of the cavity mold 100 is closed off.
The starting material beads are thus packed in a sealed state in
the cavity 104. The starting material beads remaining in the
packing pipe 124 are also blown back and are all returned to the
starting material tank 123, ending the packing process.
[0035] In any type of conventional packing method, however, the
parts of the expanded molded foam corresponding to the location of
the aforementioned starting material bead supply hole 122 are
subject to the phenomenon of over-packing, resulting in the
problems of molded products with defective shapes and defective
appearance.
[0036] The phenomenon of over-packing occurs because the starting
material beads which are sent through the packing pipe component
120 of the packer 111 into the cavity 104 during natural blow back
are believed to adhere to the cavity 104 side of the supply hole
122, as shown in FIG. 15(b), and the excess starting material beads
collect into a protruding shape on the packer 111 side, but lumps
of the excess starting material beads are pushed into the packed
starting material beads by the plunger tip 128, as shown in FIG.
15(c), when the supply hole 122 is sealed off, presumably causing
an abnormal increase in the density in that portion.
[0037] Although measures have been attempted to prevent the build
up of lumps of excess starting material beads by adjusting the
pressure, spraying angle, time, and the like of the packing air
sprayed from the spraying hole 126 in order to prevent such
over-packing, further problems that have resulted include a longer
blow back treatment time, greater consumption of packing air, and
the like, yet the effects on over-packing have still been
unsatisfactory, and the problem remains to be solved.
[0038] An object of the present invention is to provide a
die-expanded molding apparatus and method for synthetic resins
allowing the packing density of the starting material beads in the
aforementioned areas to be uniformly adjusted, as well as the
die-expanded molded foam obtained thereby.
SUMMARY OF THE INVENTION
[0039] 1. Die-Expanded Molding Apparatus
[0040] The die-expanded molding apparatus pertaining to the present
invention comprises starting material bead supply means for
supplying starting material beads consisting of a thermoplastic
synthetic resin on a current of air from a starting material tank
through a packer into a cavity formed by a core mold and cavity
mold; at least dual-system air expulsion means having
pressure-adjustable air pressure-adjusting components communicating
with the aforementioned cavity, for allowing the air used to supply
the starting material beads into the cavity to be expelled from the
cavity by means of the pressure differential between the cavity and
the air pressure-adjusting components, the at least dual-system air
expulsion means being such that a steam chamber on the back side of
the core mold and a steam chamber on the back side of the cavity
mold are used as the air pressure-adjusting components, each
communicating with the cavity through through-holes formed in the
core mold and cavity mold, respectively; and control means for
independently controlling the air pressure in each of the air
pressure-adjusting components of the at least dual-system air
expulsion means.
[0041] In this molding apparatus, while the starting material beads
are supplied on a current of air into the cavity by the starting
material bead supply means, the air supplied into the cavity is
expelled from the cavity by the air expulsion means, allowing the
starting material beads to be packed in the cavity, but since the
air expulsion means has at least two systems, which are
independently controlled, the starting material beads can be packed
in areas, for example, where the packing density tends to be lower,
allowing the packing density in various parts of the molded product
to be regularized, the starting material beads can be packed first
in areas where greater strength and rigidity are desired, allowing
the packing density to be locally increased in those areas, and the
packing density in various parts of the molded product can be
adjusted to suitable levels without increasing the number of
packers, even in molded products which have parts where the packing
density tends to be lower, such as thin-walled parts.
[0042] Air expulsion means having the following structure can also
be provided in addition to the aforementioned dual-system air
expulsion means, allowing the air pressure in the air
pressure-adjusting components in the plurality of air expulsion
means to be controlled, independently or in any combination, by the
control means.
[0043] (1) Air expulsion means having one or a plurality of air
pressure-components in communication with the clearance between the
core mold and cavity mold may be provided. In this case, the air
supplied into the cavity can be effectively expelled to the outside
from the clearance formed at the outer periphery of the cavity.
Thus, when making a container or the like with a deep bottom, for
example, clearance can be formed at a location corresponding to the
open edge of the container, allowing a suitable packing density to
be maintained without increasing the number of packers, and the
quality of the container to be improved.
[0044] (2) Air expulsion means having one or a plurality of air
pressure-components in communication with the interior of narrow,
bottomed parts that are difficult to pack with the starting
material beads may be provided, and the air pressure in the air
pressure-adjusting components in the plurality of air expulsion
means may be controlled, independently or in any combination, by
the control means in such a way that the starting material beads
are packed first in the parts that are difficult to pack. Such a
structure allows molded products of good quality to be produced
because the density of the starting material beads can be
maintained in parts that are difficult to pack, even in molded
products with a complex shape having parts that are difficult to
pack, which have been difficult to produce conventionally because
the packing density could not be sufficiently ensured.
[0045] (3) Air expulsion means having one or a plurality of air
pressure-adjusting components in communication with the interior of
remote parts at a distance from the starting material bead supply
means may be provided, and the air pressure in the air
pressure-adjusting components in the plurality of air expulsion
means may be controlled, independently or in any combination, by
the control means in such a way that the starting material beads
are packed first in the parts that are difficult to pack. Such a
structure allows molded products of good quality to be produced
because the density of the starting material beads can be
maintained in parts that are difficult to pack, even in molded
products with a complex shape having parts that are difficult to
pack, which has been difficult to achieve conventionally because of
the inability to ensure sufficient packing density.
[0046] The aforementioned molding apparatus may also be provided
with plural-system air expulsion means in which the chambers on the
back side of the core mold and/or the back side of the cavity mold
are used as air pressure-adjusting components. In this case, the
packing density in various parts of the molded product is
controlled more precisely to increase the packing density in the
necessary parts and ensure suitable packing density in the molded
product as a whole.
[0047] Preferably, atmospheric release, pressurization, reduced
pressure, and/or these are combined and the internal pressure of
the air pressure-adjusting components is controlled by the control
means so that the packing density of the starting material beads
can be suitable determined in various parts of the cavity.
[0048] 2. First Die-Expanded Molding Method: Improved Packing
Properties in Outer Periphery of Cavity
[0049] This first die-expanded molding method is a die-expanded
molding method for synthetic resins in which starting material
beads are packed into a cavity formed by a core mold and cavity
mold, the material is heated, expanded, and fused to form molded
products, and the product is cooled and released from the mold,
wherein various service fluids for the supply of steam to the
cavity, pressurization and depressurization, the supply of
compression air, and the like are manipulated by using the
inter-mold clearance, formed in such a way as to communicate with
external service piping, at the seam of the core mold and cavity
mold located at the circumference of the cavity when the two molds
are closed.
[0050] Specifically, the method should comprise at least one of the
following operations to make more effective use of the clearance
between the core mold and cavity mold.
[0051] 1) Expelling the packing air through the clearance when the
starting material beads are being packed: This operation allows the
air to be expelled from the outer peripheral distal end of the
cavity in conjunction with the expulsion of air from the core vents
of the two molds, so that the starting material beads can cross
sufficiently to the outer peripheral distal end of the cavity
without the molds being cracked, and irregular packing density can
be prevented. The advantage of improving the packing properties of
the starting material beads can also be obtained even when the
molded product is a deep container and when the distal end has a
complex shape.
[0052] 2) Adjusting the pressure in the cavity through the
clearance when the starting material beads are being packed: With
this structure, the back pressure can be adjusted to the desired
pressure relative to the pressure of the packing air for sending
the starting material beads from the starting material tank, so
that the optimal packing method can be used, such as pressure
packing, compression packing, and vacuum or suction packing in
which the back pressure is adjusted to atmospheric pressure or
lower.
[0053] 3) Introducing steam into the clearance to heat the portions
around the clearance and into the cavity to facilitate the heating
of the starting material beads in the portions around the cavity
when the packed starting material beads are being heated: This
affords the advantage of allowing a shorter molding time to be
designed because the starting material beads in the outer
peripheral distal end of the cavity can be more rapidly heated,
since the flanges constituting the outer periphery of the two
molds, which in the past required a relatively large volume of heat
and were difficult to heat, are directly heated. Since it is
possible to ensure that the air is purged from the outer peripheral
distal end by steam and to independently adjust the pressure
through the clearance, the steam pressure can be controlled to a
positive or negative setting or the like relative to the chamber
pressure so as to set the temperature balance in the molds to
optimum conditions, allowing dramatic reductions in the cycle time
and energy conservation to be anticipated.
[0054] 4) Reducing the pressure in the cavity through the clearance
to promote cooling by the vaporization of moisture during cooling:
In this case also, the cycle time can be dramatically reduced
because of the ability to promote decreases in temperatures in the
flanges of the molds, which require large volumes of heat and are
difficult to cool.
[0055] 5) Expelling drainage from the clearance during mold release
operations to remove the expanded molded foam: Because drainage
collecting in the clearance and in the inter-mold cavity as a
result of water injection during cooling can be eliminated in this
case, it is possible to remedy drawbacks such as wetting of the
working area, even when the molds are opened to release the
product.
[0056] 3. Second Die-Expanded Molding Method: Improved Packing
Properties in Parts That are Difficult to Pack
[0057] The second die-expanded molding method is a die-expanded
molding method for synthetic resins in which starting material
beads are packed into a cavity formed by a core mold and cavity
mold, the material is heated, expanded, and fused to form a molded
product, and the molded product is cooled and released from the
mold, wherein at least the chamber on the back side of the mold
side, where narrow, bottomed portions that are difficult to pack
with the starting material beads are formed, is held at a negative
pressure relative to the atmospheric pressure of the starting
material beads packed into the cavity by the packer, and part of
the predetermined packing amount of the starting material beads is
delivered and packed in a concentrated manner in the
difficult-to-pack portions, while the remainder of the
predetermined packing amount is then delivered to pack all of the
starting material beads in the cavity.
[0058] In the second die-expanded molding method, the starting
material beads can be packed in a concentrated manner in parts that
are difficult to pack, making it possible to prevent local drops in
the packing density of the starting material beads in such parts
that are difficult to pack.
[0059] Examples of parts that are difficult to pack include
pouch-shaped recesses formed in at least one of either the core
mold or cavity mold. The current of packing air tends to settle in
such pouch-shaped recesses, and the packing density of the starting
material beads decreases, so such drops in the packing density can
be prevented by packing the starting material beads in a
concentrated manner in such parts which are difficult to pack.
[0060] The starting material beads can also be repeatedly packed in
parts that are difficult to pack, so that the starting material
beads are packed in a concentrated manner in such parts that are
difficult to pack.
[0061] 4. Third Die-Expanded Molding Method: Improved Packing
Properties in Parts That are Difficult to Pack
[0062] The third die-expanded molding method is a die-expanded
molding method for synthetic resins in which the aforementioned
die-expanded molding apparatus is used to pack starting material
beads in a cavity formed by a core mold and a cavity mold, the
material is heated, expanded, and fused to form a molded product,
and the molded product is cooled and released from the mold,
wherein starting material beads consisting of a thermoplastic
synthetic resin are supplied on a current of air from a starting
material tank through a packer into the cavity formed by the core
mold and cavity mold by starting material bead supply means when
the starting material beads are packed into the cavity; and the
starting material beads are packed while the current of air in the
cavity is controlled by adjusting the air pressure, independently
or in any combination, in a plural-system air expulsion means by
automatic control by control means.
[0063] In this die-expanded molding method, the air expulsion means
having air pressure-adjusting components in communication with
parts that are difficult to pack, for example, among the
dual-system air expulsion means, is first controlled to first pack
the starting material beads in those parts, so as to ensure that a
suitable packing density is maintained in those parts.
[0064] The following are methods for controlling the air expulsion
means by the aforementioned control means.
[0065] (1) The air expulsion means is controlled in such a way that
the starting material beads are packed first in the narrow,
bottomed portions where the starting material beads are difficult
to pack. In this case, molded products of good quality can be
produced because the packing density of the starting material beads
in the parts that are difficult to pack can be maintained at a
suitable packing density, even in molded products having a complex
shape such as parts which are difficult to pack and which have been
considered difficult to manufacture.
[0066] (2) The air expulsion means is controlled such a way that
the starting material beads are packed first in remote portions at
a distance from the starting material bead supply means. In this
case, molded products of good quality can be produced be
maintaining a suitable packing density in remote parts where the
packing density of the starting material beads tends to be
lower.
[0067] A desirable method for improving the packing properties in
parts where the starting material beads are difficult to pack is to
pack the starting material beads in the cavity as the amount of
starting material beads packed per unit time in the cavity is
adjusted by the adjusting means.
[0068] When the starting material beads are supplied to the cavity
on a current of packing air as the amount in which they are
supplied per unit time is adjusted by the adjusting means, the
starting material beads can be more efficiently supplied to parts
that are difficult to pack, such as narrow, bottomed, thin wall
parts that are difficult to pack with starting material beads or
remote parts that are at a distance from the packer. In other
words, when the amount in which the starting material beads are
supplied per unit time is adjusted, there is less contact between
the starting material beads and fewer collisions during packing,
and the flow of air is not hampered by the starting material beads
themselves, so the starting material beads can be smoothly packed
in parts that are difficult to pack.
[0069] As such an adjusting means, a supply means such as a screw
conveyor may be provided to supply the starting material beads
while the amount in which they are supplied per unit time is
adjusted by this supply means, but since the starting material
beads might be damaged or the cost of the molding apparatus might
be higher, it is desirable to provide adjusting means for adjusting
the amount in which the starting material beads are supplied per
unit time on a current of air for packing the cavity by diluting
the starting material beads with adjusting air, allowing the
starting material beads to be supplied while diluted with adjusting
air.
[0070] In regard to the specific numerical value of the degree to
which the starting material beads are diluted by the aforementioned
adjusting means, the final degree of dilution is defined as the
numerical value obtained by dividing the volume of air supplied to
the cavity during packing by the volume of the starting material
beads, and the final degree of dilution is 5 or more, preferably
between 10 and 50. In other words, a final degree of starting
material bead dilution of less than 5 results in a lower starting
material bead packing density in parts that are difficult to pack,
so the value should be set to 5 or more.
[0071] 5. Blow Back: Improved Packing Properties in Locations
Facing the Packer
[0072] The following blow back operations should be carried out
immediately before the conclusion of starting material bead packing
in the cavity in the aforementioned die-expanded molding
methods.
[0073] (1) The pressure in the cavity is set to a negative pressure
relative to the internal pressure of the starting material tank
holding the starting material beads, so as to allow the starting
material beads from the starting material tank to be packed into
the cavity when the starting material beads are being packed, and
the pressure in the cavity is adjusted to a positive pressure as
the pressure in the starting material tank is maintained during
blow back operations immediately prior to the conclusion of the
packing. With this structure, a current of air from the cavity to
the starting material tank is produced during blow back, and the
surplus starting material beads in the packer are allowed to adhere
to the cavity side, thereby preventing defects in the return flow
of the starting material beads, and making it possible to prevent
local increases in the packing density caused by such defects in
the return flow.
[0074] (2) The pressure in the cavity is set to a negative pressure
relative to the internal pressure of the starting material tank
holding the starting material beads, so as to allow the starting
material beads from the starting material tank to be packed into
the cavity when the starting material beads are being packed, and
the pressure in the starting material tank is adjusted to a
pressure equivalent to or lower than the pressure in the cavity as
the pressure in the starting material tank is maintained during
blow back operations immediately prior to the conclusion of the
packing. This also makes it possible to prevent local increases in
the packing density caused by defects in the return flow in the
same manner as in section (1).
[0075] (3) Natural blow back is carried out at an adjusted pressure
as described in sections (1) and (2) during blow back operations
immediately prior to the conclusion of the packing, the starting
material supply holes are subsequently closed off by a plunger, and
the forced blow back is then carried out. This ensures that the
starting material beads in the packer flow back into the starting
material tank.
[0076] 6. Die-Expanded Molded Foam
[0077] The density in various parts of the die-expanded molded foam
pertaining to the present invention is adjusted to within +5% of
the mean density, preferably within .+-.4%, more preferably within
.+-.3%. Such a molded product was considered difficult to form in
the past, but can be produced according to the aforementioned
die-expanded molding methods. The time of the heating and cooling
cycles during molding can be shortened, and thin-walled parts and
the like with satisfactory strength and rigidity can be ensured,
while lighter molded products can be produced.
[0078] Examples of specific structures for molded products in which
it would be desirable to thus set the density in various parts of
molded products to within .+-.5% of the mean density include those
in which the degree of shape complexity is 1.1 or more, where the
degree of shape complexity is defined as the numerical value
obtained by dividing the surface area of the molded product by the
volume, which is measured by cm unit; those in which the wall
thickness of the thin-walled portions of the molded product is 10
mm to 3 mm; and those in which 3 or less beads are disposed in the
thicknesswise direction of the thin-walled portions of the molded
product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0079] FIG. 1 is a vertical cross sectional view of a die-expanded
molding apparatus;
[0080] FIG. 2 is a cross sectional view of line 11-11 in FIG.
1;
[0081] FIG. 3 is a vertical cross sectional view of the area around
the through-holes;
[0082] FIG. 4 is a front view of a core vent;
[0083] FIG. 5 corresponds to FIG. 2 of another die-expanded molding
apparatus;
[0084] FIG. 6 is a vertical cross sectional view of the
die-expanded molding apparatus used in the first packing
method;
[0085] FIG. 7 is a cross sectional view of line VII-VII in FIG.
6;
[0086] FIG. 8 is an oblique view of a molded product;
[0087] FIG. 9 is a vertical cross sectional view of a molded
product;
[0088] FIG. 10 is a vertical cross sectional view of the
die-expanded molding apparatus used in the second packing
method;
[0089] FIG. 11 is an illustration of the packing density;
[0090] FIG. 12 is an illustration of the starting material bead
packing system;
[0091] FIG. 13 through FIG. 15 relate to the prior art, where FIG.
13 is a vertical cross sectional view of a die-expanded molding
apparatus;
[0092] FIG. 14 is a vertical cross sectional view of a die-expanded
molding apparatus with another structure; and
[0093] FIG. 15 is an illustration of a starting material bead
packing system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0094] Preferred embodiments of the present invention are described
below with reference to the drawings.
[0095] Die-Expanded Molding Apparatus
[0096] As shown in FIGS. 1 and 2, the die-expanded molding
apparatus 1 comprises a mutually opposed core mold 2 and cavity
mold 3, bead packing means for packing starting material beads 5 in
a cavity 4 formed by the core mold 2 and cavity mold 3, steam
supply means for allowing the starting material beads 5 packed in
the cavity 4 to be heated, expanded, and fused by steam, and
cooling means for cooling the molded product.
[0097] The core mold 2 and cavity mold 3 are attached to a housing
12 with a frame 10 and back boards 11, and chambers 30 and 31 are
formed on the back side of the cavity mold 3 and core mold 2,
respectively.
[0098] As shown in FIGS. 1 and 3, through-holes 15 consisting of
core vents 13 and core vent holes 14 are formed in the core mold 2
and cavity mold 3, and the chambers 30 and 31 communicate with the
cavity 4 through the through-holes 15. As shown in FIGS. 3 and 4,
the core vents 13 are members fitted into attachment holes 16
formed in the core mold 2 and cavity mold 3, and are bottomed
cylinders in which a plurality of round through-holes 17a of
smaller diameter than that of the starting material beads 5 or
longitudinal holes 17b are formed in the bottom surface. As shown
in FIG. 3, the core vent holes 14 are formed in the core mold 2 and
cavity mold 3, and are through-holes of smaller diameter than that
of the starting material beads 5.
[0099] Flanges 2a and 3a are formed on the outer periphery of the
core mold 2 and cavity mold 3, and an inter-mold cavity 32
communicating with the cavity 4 through the clearance 18 between
the core mold 2 and cavity mold 3 while the mold is closed is
formed between the flanges 2a and 3a. The clearance 18 between the
core mold 2 and the cavity mold 3 is smaller than the diameter of
the starting material beads 5, to let only the air supplied to the
cavity 4 along with the starting material beads 5 to pass through
when the starting material beads 5 are packed, so that the starting
material beads 5 stays in the cavity 4. The clearance 18 may be
formed along the entire periphery of the core mold 2 and cavity
mold 3, or it may be formed locally in just the necessary portions.
As shown in FIG. 5, moreover, the clearance 18 may be plurally
divided (into two in the figure), and a plurality of inter-mold
cavities 32 may be provided corresponding to the plurality of
clearances 18.
[0100] The chambers 30 and 31 and the inter-mold cavity 32 are
connected through service valves SV1, SV2, and SV3 and service
switching valves SWV1 and SWV2 to a steam supply pipe 20 and air
supply pipe 21, respectively, and are also connected through drain
valves DV1, DV2, and DV3 and switching valves SWV3 and SWV4 to a
drain pipe 22 and a vacuum pipe 23 equipped with a vacuum pump P,
respectively. Service fluids such as steam or vacuum air can be
individually supplied to or expelled from the chambers 30 and 31
and the inter-mold cavity 32 by the operation of the utility valves
SV1 through SV3, the drain valves DV1 through DV3, and the
switching valves SWV1 and SWV2. Also, when the clearance 18 and
inter-mold cavities 32 are plurally divided as described above, the
service fluids may be individually supplied to and expelled from
the respective inter-mold cavities.
[0101] The bead packing means is described below. As shown in FIG.
1, a starting material tank 24 is provided for storing the starting
material beads 5. A suction pipe 25 is connected to the starting
material tank 24, and the suction pipe 25 is equipped with a
suction valve V1, this suction valve V1 being controlled to adjust
the internal pressure of the starting material tank 24.
[0102] A packer 26 which opens into the cavity 4 is attached to the
back plate 11 on the cavity mold 3 side, a shutter 27 is attached
to the starting material tank 24, the packer 26 is connected
through a packing pipe 28 to the starting material tank 24, and the
starting material beads 5 in the starting material tank 24 are
supplied on an air current from the packer 26 into the cavity 4. A
packing air supply pipe 29 is connected to the packer 26, and
packing air of suitable pressure is supplied by a packing air valve
V2 mounted in the packing air supply pipe 29. The internal pressure
of the starting material tank 24 may thus be set to atmospheric
pressure, reduced pressure, or increased pressure when it is set to
or above the internal pressure of the chambers 30 and 31 and the
inter-mold cavity 32.
[0103] A material with physical properties suited to the conditions
of use or the like of the molded product that is to be prepared
should be selected as the material for the starting material beads
5. Polystyrene-based synthetic resin materials, polyolefin-based
synthetic resin materials such as polyethylene or polypropylene, or
copolymers and the like of such synthetic resin materials can be
used.
[0104] The degree of expansion of the starting material beads 5
depends on the material of the starting material beads 5, but a
range of 3 to 150 times is preferred. Specifically, starting
material beads consisting of a polystyrene-based synthetic resin
material should be expanded 3 to 100-fold, and preferably 3 to
80-fold, while starting material beads consisting of a
polyolefin-based synthetic resin material should be expanded 3 to
90-fold, and preferably 3 to 60-fold. A particle diameter in the
range of between 1 and 10 mm can be used. Starting material beads
of a polyolefin-based synthetic resin material in particular are
inherently soft, flexible and highly gas-permeable, resulting in a
particle shape that is far more deformable than starting material
beads consisting of a polystyrene-based synthetic resin material
having the same degree of expansion, so that the packing properties
in the present invention can be improved in a particularly
effective manner. In general, starting material beads of a
polyolefin-based synthetic resin material has a large dispersion in
the form and a poor packing properties comparing with starting
material beads consisting of a polystyrene-based synthetic resin
material. Accordingly, when using starting material beads of a
polyolefin-based synthetic resin material, the improved packing
properties of the present invention can be shown more easily.
[0105] Die-Expanded Molding Method
[0106] The following die-expanded molding method can be employed
with a die-expanded molding apparatus 1 equipped with the clearance
18 described above.
[0107] This die-expanded molding method is an expanded molding
method in which starting material beads 5 are packed in the cavity
formed and surrounded by the aforementioned pair of molds 2 and 3,
the beads are heated and expanded to form a molded product, and the
molded product is cooled and released from the mold, wherein
various service fluids for the supply of steam to the cavity,
pressurization and depressurization, the supply of compression air,
and the like are manipulated by using the inter-mold cavity 32
communicating with the cavity 4 through the clearance 18 at the
seam in the outer peripheral part of the two molds 2 and 3 located
at the outer peripheral distal ends 4a of the cavity 4 when the two
molds are closed; that is, a method in which various service fluids
are supplied and the pressure is adjusted.
[0108] In this case, the manipulation of service fluids through the
clearance by the manipulation of fluids to the inter-mold cavity
32, and the manipulation of service fluids through the
through-holes 15 of the molds 2 and 3 by the manipulation of
service fluids to the chambers 30 and 31, can be carried out
independently or in common, a matter which can be suitably selected
according to the molding conditions, although the former
independent manipulation is preferred because high-precision
operations can be managed.
[0109] The aforementioned expanded molding method of the present
invention can be put into practice as an expanded molding method
containing at least one of the following operations using the
aforementioned inter-mold cavity 32.
[0110] 1) The packing air that is sent to deliver the starting
material beads 5 from the starting material tank 24 in the starting
material bead packing step is expelled through the clearance 18
formed at the seam of the molds 2 and 3. In this case, since the
air is expelled from the outer peripheral distal end 4a portion of
the cavity 4 in conjunction with the expulsion of air through the
through-holes 15 of the two molds 2 and 3, the starting material
beads 5 cross through sufficiently without the molds being cracked,
and irregular packing density can be prevented. The advantage of
better starting material bead 5 packing properties can also be
obtained even when the expanded molded foam is a deep container or
when the distal end has a complex shape.
[0111] 2) Not only is air expelled in the manner described above
during the process for packing the starting material beads 5, but
the pressure in the cavity 4 is also adjusted through the clearance
18. That is, the back pressure is adjusted to a desired pressure
relative to the pressure of the packing air for sending the
starting material beads 5 from the starting material tank 24, so
that the optimal packing method can be used, such as pressure
packing, compression packing, and vacuum or suction packing in
which the back pressure is adjusted to atmospheric pressure or
lower.
[0112] 3) Steam is introduced into the clearance 18 to heat the
portions around the clearance and into the cavity 4 to facilitate
the heating of the starting material beads 5 in the portions around
the cavity 4 during the step for heating the packed starting
material beads 5.
[0113] This affords the advantage of allowing a shorter molding
time to be designed because the starting material beads 5 in the
outer peripheral distal end 4a of the cavity 4 can be more rapidly
heated, since the flanges 2a and 3a constituting the outer
periphery of the two molds 2 and 3, which in the past required a
relatively large volume of heat and were difficult to heat, are
directly heated.
[0114] Since it is possible to ensure that the air is purged from
the outer peripheral distal end 4a by steam and to independently
adjust the pressure through the clearance 18, the steam pressure
can be controlled to a positive or negative setting or the like
relative to the chamber pressure so as to set the temperature
balance in the molds 2 and 3 to optimum conditions, allowing
dramatic reductions in the cycle time and energy conservation to be
anticipated.
[0115] 4) In addition to the injection of cooling water during the
cooling step, the pressure in the cavity 4 is reduced through the
clearance 18 to promote cooling by the vaporization of moisture
penetrating into the cavity 4 due to water injection, as well as to
expel drainage.
[0116] In this case also, the cycle time can be dramatically
reduced because of the ability to promote decreases in temperatures
in the flanges 2a and 3a of the molds, which require large volumes
of heat and are difficult to cool.
[0117] 5) Drainage which has collected in the clearance 18 and
inter-mold cavity 32 is expelled during the mold release step to
remove the expanded molded foam. As a result, the drainage
collecting in the clearance 18 and in the inter-mold cavity 32 as a
result of water injection during cooling can be eliminated, making
it possible to remedy drawbacks such as wetting of the working
area, even when the molds are opened to release the product.
[0118] First Alternative Embodiment of Packing Method
[0119] A first alternative embodiment of the packing method is
described below.
[0120] This packing method is suitable for a die-expanded molding
apparatus for molding foam 50 having a complex shape such as that
shown in FIGS. 8 and 9, for example.
[0121] The die-expanded molding apparatus is described first. Since
this die-expanded molding apparatus has essentially the same
structure as the aforementioned die-expanded molding apparatus 1,
only the differences will be described. Parts that are the same as
those in the aforementioned die-expanded molding apparatus are
designated by the same symbols, and therefore will not be described
in detail.
[0122] As shown in FIGS. 6 and 7, narrow, bottomed components 40
that are difficult to pack have been formed in the core mold 2 of a
die-expanded molding apparatus 1A, and partitioned walls 51 are
formed in the molded product 50 as shown in FIGS. 8 and 9 by these
difficult-to-pack components 40. A drain pipe 41 communicates with
the deep ends of the difficult-to-pack components 40, and the drain
pipe 41 is connected through a drain valve DV4 and switching valves
SWV3 and SWV4 to a drain pipe 22 and vacuum pipe 23, respectively.
The shape of these difficult-to-pack components 40 and their
molding position can be set as desired according to the shape of
the molded product. For example, pouch-shaped recessed components
formed in a mold to make molded products with protrusions or the
like, or remote components which are at a distance from the packer
26, such as around the clearance 18 shown in FIG. 6, can be handled
in the same manner as the difficult-to-pack components 40, when it
is difficult to pack such components with the starting material
beads 5. The present invention can similarly be applied to molds
which do not have components that are difficult to pack.
[0123] In this packing method, the aforementioned chambers 30 and
31, inter-mold cavity 32, and space 33 in the drain pipe 41
upstream of (on the cavity 4 side) the drain valve DV4 constitute
an air pressure-adjusting component for the expulsion of, and the
simultaneous adjustment of the pressure of, air supplied along with
the starting material beads 5 when the starting material beads 5
are packed into the cavity 4.
[0124] A quadruple-system air expulsion means is composed of air
expulsion means from the chamber 30 through the drain valve DV1 to
the drain pipe 22 or vacuum pipe 23, air expulsion means from the
chamber 31 through the drain valve DV2 to the drain pipe 22 or
vacuum pipe 23, air expulsion means from the inter-mold cavity 32
through the drain valve DV3 to the drain pipe 22 or vacuum pipe 23,
and air expulsion means from the space 33 in the pipe through the
drain valve DV4 to the drain pipe 22 or vacuum pipe 23. One of
either the air expulsion means with the inter-mold cavity 32 or the
air expulsion means with the pipe space 33 may be omitted. At least
one of chambers 30 and 31 and the inter-mold cavity 32 may be
divided into a plurality of spaces to provide plural-system air
expulsion means in which the plurality of spaces serve as air
pressure-adjusting components. When there are several
difficult-to-pack components 40, plural-system air expulsion means
in which an drain pipe is connected to each of the plurality of
difficult-to-pack components may furthermore be provided.
[0125] Control means not shown in the figure for independently
controlling each of the aforementioned drain valves DV1 through DV4
are provided, and these drain valves DV1 through DV4 are
automatically controlled by the control means when the starting
material beads 5 are being packed, so that the internal pressures
in the chambers 30 and 31, the inter-mold cavity 32, and the pipe
space 33 are each adjusted, independently or in any
combination.
[0126] An adjusting air supply pipe 42 is connected between the
packing pipe 28 and the shutter 27 mounted in the starting material
tank 24, and adjusting air having a suitable pressure is supplied
to the packing pipe 28 by means of the adjusting air valve V3
located in the adjusting air supply pipe 42. The adjusting means is
composed of this adjusting air supply pipe 42 and adjusting air
valve V3, and the starting material beads 5 is supplied from the
starting material tank 24 to the packing pipe 28 while diluted with
the adjusting air. The amount of adjusting air supplied is varied
so as to adjust the amount of starting material beads 5 supplied
per unit time to the packing pipe 28, that is, the final degree of
dilution described below. The starting material beads 5 can be
supplied from the starting material tank 24 to the packing pipe 28
by a supply means such as a screw conveyor, in which case the
adjusting air valve V3 and adjusting air supply pipe 42 can be
omitted, and the rate at which the screw conveyor rotates can be
varied to adjust the amount in which the starting material beads 5
are supplied per unit time to the cavity 4.
[0127] An example of a method for packing the starting material
beads 5 using the aforementioned die-expanded molding apparatus 1A
is described below.
[0128] First, the core mold 2 and cavity mold 3 are closed, the air
in the starting material tank 24 is pre-pressurized, and the air in
the chambers 30 and 31, inter-mold cavity 32, pipe space 33, and
cavity 4 is pre-pressurized. The pressure in the chambers 30 and
31, inter-mold cavity 32, pipe space 33, and cavity 4 should be
adjusted according to the degree of packing difficulty.
[0129] Next, the packer 26 filler, shutter, packing air valve V2,
and adjusting air valve V3 are opened to begin packing the starting
material beads 5. The packing air pressure in the packing air valve
V2 is at least 2 kg/cm.sup.2 or more higher than the internal
pressure of the starting material tank 24, and is adjusted to an
absolute value of 4 kg/cm.sup.2 or higher.
[0130] During packing, the starting material beads 5 flow into the
cavity 4 while diluted by the compressed air in the starting
material tank 24, the compressed air from the adjusting air valve
V3, and the compressed air from the packing air valve V2. In terms
of the volumetric ratio between the air and starting material beads
5 flowing into the cavity 4 at this time, the final degree of
dilution is set to 5 or more, and preferably between 10 and 50,
where the final degree of dilution is defined as the numerical
value obtained by dividing the volume of air supplied to the cavity
4 during packing by the volume of the starting material beads 5.
When the final degree of dilution of the starting material beads 5
is greater than 50, the amount of starting material beads 5 packed
per unit time decreases, resulting in the problems of a longer
packing time, a longer molding cycle time, and greater air
consumption. The range is preferably between 10 and 50, because
when the final degree of dilution is lower than 10, there is
greater contact and there are more collisions between the starting
material beads 5 in the packing pipe 28, packing pipe 26, or cavity
4, resulting in the problem of increases in the resistance
hampering the packing of the starting material beads 5, and the
starting material beads 5 interfere with the current of air,
resulting in the problem of poor packing. However, when the
starting material beads 5 are supplied by a supply means such as a
screw conveyor, the rotating speed of the screw conveyor is
adjusted to the desired final degree of dilution, so as to
establish the amount in which the starting material beads 5 are
supplied per unit time to the cavity 4.
[0131] The compressed air thus flowing into the cavity increases
the pressure of the chambers 30 and 31, the inter-mold cavity 32,
and the pipe space 33 through the through-holes 15 and the
clearance 18. At this time, the pressures in the chambers 30 and
31, the inter-mold cavity 32, and the pipe space 33 can be
adjusted, individually or in any combination, by using the drain
valves DV1 through DV4, so that the starting material beads 5 can
be first packed into parts which are difficult to pack with
starting material beads 5 in order to control irregular density in
the various parts of the molded product and to ensure a suitable
packing density.
[0132] For example, when the internal pressures in the chambers 30
and 31, inter-mold cavity 32, and pipe space 33 are at or beyond
the set pressure, the drain valves DV1 through DV4 are successively
opened, and when the set pressure is in the order chamber
30>chamber 31>inter-mold cavity 32>pipe space 33, the
drain valve DV4 is opened first to allow the parts 40 that are
difficult to pack to be packed with the starting material beads 5;
and when the internal pressure of the chambers 30 and 31 and the
inter-mold cavity 32 increases as the parts 40 that are difficult
to pack are nearly completely packed with the starting material
beads 5, the drain valve DV3 is opened to allow the outer periphery
of the cavity 4 to be packed with the starting material beads 5.
The drain valves are thus successively opened in the order of
ascending set pressure to allow the cavity 4 to be packed with the
starting material beads 5.
[0133] In another control method, the packing process is divided
into four parts, where the cavity 4 is successively packed as the
air pressure in the pipe space 33 is controlled using only the
drain valve DV4 in the first step, the air pressure in the
inter-mold cavity 32 and pipe space 33 using drain valves DV3 and
DV4 in step 2, the air pressure in the chamber 31, inter-mold
cavity 32, and pipe space 33 is controlled using drain valves DV2
through DV4, and the air pressure in chambers 30 and 31, inter-mold
cavity 32, and pipe space 33 is controlled using drain valves DV2
through DV4.
[0134] After the starting material beads 5 have thus been packed,
the filler of the packer 26 is closed, the adjusting air valve V3
is closed, the starting material beads 5 remaining in the packer 26
and packing pipe 28 are returned to the starting material tank 24
using filling air, the packing cycle is then completed by closing
the packing air valve V2 and shutter 27, and a series of common
molding steps comprising heating, cooling, and mold release is then
carried out to obtain the desired molded product.
[0135] Molded products formed in this manner, which include, for
example, those in which the degree of shape complexity is 1.1 or
more, preferably 1.2 or more, more preferably 1.3 or more, where
the degree of shape complexity is defined as the numerical value
obtained by dividing the surface area of the molded product by the
volume, which is measured by cm unit, those in which the wall
thickness of the thin-walled portions of the molded product is 10
mm to 3 mm, preferably 8 mm to 3 mm, more preferably 6 mm to 3 mm,
and those in which 3 or less beads are disposed in the
thicknesswise direction of the thin-walled portions of the molded
product, can have good quality with little irregularity in density,
wherein the density in various parts of molded product is within
.+-.5%, preferably within .+-.4%, and even more preferably within
.+-.3%, of the mean density, even in molded products which have
conventionally been regarded as being difficult to pack. The
present invention is effective and useful for molded products which
are larger and have more complex shapes than small molded products
with simple shapes such as containers for cups of noodles. It is
particularly advantageous for molded articles having both thin and
thick walls.
[0136] Tests for assessing the quality of molded products formed by
packing starting material beads 5 according to this packing method
are described below.
[0137] Four types of molded articles 50 were manufactured by
packing the starting material beads 5 by four packing methods (the
starting material beads 5 were packed by cracked packing, pressure
packing, and compression packing, and by the method of the present
invention) as methods for packing the starting material beads 5 to
manufacture a molded product 50 having the shape given in FIGS. 8
and 9. The density was measured at the tip 51, middle 52, and base
53 of the partition walls 51 of the molded product 50, as shown in
FIG. 9, with the results shown in Table 1. The molded product shown
in Table 1 is manufactured by using polypropylene beads having a
degree of expansion of 53 times. The molded product is a box-type
having an outer size of a depth of 40 cm, a width of 25 cm and a
height of 14 cm. It has 5 ribs having a thickness of 0.8 cm in a
longitudinal and one rib having a thickness of 0.8 cm in a
transverse direction. The weight is 160 g, the degree of expansion
is 45 times, and the degree of shape complexity is 2.46. The degree
of shape complexity of rectangular parallelepiped having a same
outer size is 0.27 and the degree of shape complexity of a box-type
molded product without ribs is 1.04. TABLE-US-00001 TABLE 1 (unit:
g/L) Conventional packing methods cracked pressure compression
Measured packing packing packing Packing Tip 15 16 17 21 Middle 18
19 19 20 Base 24 22 21 20
[0138] As shown in Table 1, the density decreased from the base 54
to the tip 52 of the partition walls 51 in the molded products
produced by packing the starting material beads 5 using
conventional methods, whereas the density was generally uniform in
the molded products produced by packing the starting material beads
5 in accordance with the packing method of the present invention.
In other words, it may be seen that molded products of good quality
and little irregularity in density could be produced by the method
of the present invention. It has been necessary to design
conventional molded products on the basis of the parts with low
density so as obtain sufficient strength in those parts with low
density, resulting in the problem of heavier molded products,
whereas the generally uniform density in the various parts of the
molded product in the present invention allows sufficient molded
strength to be ensured, lighter molded products to be created, and
lower amounts of starting material beads 5 to be used, thus
lowering the manufacturing costs of the molded products.
[0139] In this embodiment, the internal pressure in the chambers 30
and 31, inter-mold cavity 32, and pipe space 33 were controlled in
such a way that the density in the various parts of the molded
product was uniform, but it is also possible to locally increase
the packing density of the starting material beads 5 in portions
where greater strength is desired. The present invention can, of
course, also be applied to form molded products with various shapes
other than that of the molded product 50.
[0140] Second Alternative Embodiment of Packing Method
[0141] A second alternative embodiment of the packing method is
described below.
[0142] As shown in FIG. 10, the die-expanded molding apparatus 1B
used in this packing method differs from the aforementioned
die-expanded molding apparatus 1A in that no clearance 18 or
inter-mold cavity 32 is formed between the two molds 2 and 3, the
drain pipe 41 and drain valve DV4 are omitted, and the drain valve
D3 and service valve SV3 are omitted. The structure is otherwise
the same, and parts that are the same are therefore indicated by
the same symbols and will not be discussed in detail.
[0143] Characteristic features are, first, that at least the
pressure of the chamber 31 on the core mold 2 side, where the
aforementioned parts 40 that are difficult to pack have been
formed, is controlled so as to maintain a negative pressure
relative to the atmospheric pressure of the packed starting
material beads 5, and part of the predetermined packing amount for
the entire cavity 4, preferably an amount corresponding to the
aforementioned parts 40 that are difficult to pack, of the starting
material beads 5 is delivered and packed in a concentrated manner
in the aforementioned parts 40 that are difficult to pack. In this
case, as shown in Table 2 below, the concentrated packing should be
facilitated by the supply of air under pressure to the chamber 30
on the cavity mold 3 side.
[0144] A second feature is that the pressures in both chambers 30
and 31 are adjusted during the aforementioned concentrated packing
to a negative pressure relative to the atmospheric pressure of the
packed starting material beads 5, so as to deliver the rest of the
predetermined packing amount of the starting material beads 5 and
pack them in the entire cavity 4. In this case, the standard
pressure serving as the atmosphere of the packed starting material
beads 5 can be represented by the increased pressure of the
starting material tank 24.
[0145] These operations are described in further detail in the
steps in the following Table 2. TABLE-US-00002 TABLE 2 Shutter
Service Drain Drain Packing Step 27 valve valve valve air valve
Details Packing closed closed open open closed Increased 1st
packing open .uparw. closed .uparw. open Portion Concentrate closed
open .uparw. .uparw. .uparw. Con- centrate Adjusted .uparw. closed
open .uparw. .uparw. Packing 2nd packing open .uparw. .uparw.
.uparw. .uparw. Packing 1st blow .uparw. .uparw. .uparw. .uparw.
.uparw. Natural blow 2nd blow open .uparw. .uparw. .uparw. open
Forced blow Note: "closing" of drain valves DV1 and DV2 indicates
an atmospheric expulsion or adjusted expulsion state.
[0146] (1) In the packing standby process, the starting material
tank 24 is pressurized to about 1.2 kg/cm.sup.2, for example, the
two chambers 30 and 31 are adjusted to about 1.0 kg/cm.sup.2, for
example, and the packing operations are prepared at a pressure
differential of about 0.2 kg/cm.sup.2.
[0147] The pressure differential is preferably set within a range
of 0.01 to 0.5 kg/cm.sup.2 for the sake of the packing rate,
reliability, ease of control, and the like.
[0148] (2) In the first packing process, the drain valve DV1 is
closed, the shutter 27 is opened as the pressure differential
between the pressure in the starting material tank 24 and the
chamber 31 is maintained, starting material beads 5 are delivered,
in an amount corresponding to the volume of the aforementioned
parts 40 that are difficult to pack, into the cavity 4 for the next
concentrated packing step.
[0149] (3) In the concentrated packing step, the supply of the
starting material beads 5 is temporarily suspended, the service
valve SV1 is opened, and the chamber 30 is pressurized to about 2.0
kg/cm.sup.2, for example. In this case, the chamber 31 is adjusted
to a pressure of about 1.8 kg/cm.sup.2, for example, to maintain a
pressure differential of about 0.2 kg/cm.sup.2. In about four
seconds, a current of air from the chamber 30 to the chamber 31 is
produced by the pressure differential, so that the starting
material beads 5 delivered earlier for that purpose flow into the
difficult-to-pack parts 40 and are packed in a concentrated
manner.
[0150] In this case, the pressure in the chambers 30 and 31 should
be set higher than in the case of the earlier first packing process
as noted above. At this set pressure, the starting material beads 5
are pressurized more forcefully and are compressed to a lower
volume, resulting in the advantage of more efficient flow into the
parts 40 that are difficult to pack.
[0151] This pressurization should increase the pressure in the
starting material tank 24 to within a range of 0.01 and 5.0
kg/cm.sup.2 as the aforementioned pressure differential is
maintained.
[0152] (4) In the subsequent pressure adjusting step, the
pressurization of chamber 30 is stopped, and the pressure in the
chambers 30 and 31 and the internal pressure of the starting
material tank 24 are returned to where they were in the first
packing step to prepare for the second packing step which is the
next full-scale operation.
[0153] In the present invention, the aforementioned first packing
step, concentrated packing step, and pressure adjusting step should
be repeated as often as needed when the aforementioned parts 40
that are difficult to pack are particularly deep and narrow, or
when there are multiple parts 40 that are difficult to pack.
[0154] (5) In the second packing step, the pressure in the two
chambers 30 and 31 is adjusted, the same pressure differential as
in the first packing step earlier is maintained, and the remainder
of the predetermined packing amount of starting material beads 5 is
delivered and packed in the entire cavity 4.
[0155] (6) Among the next first blow back and second blow back
steps, in the first blow back, referred to as natural blow back,
that is carried out, the layers of packed starting material beads
form a barrier and cause the packing air to flow back in the packer
26 when the starting material beads 5 are packed in the cavity 4,
whereas the second blow back that is then carried out comprises
forced blow back in which the inlet of the packer 26 is closed off,
and all of the starting material beads 5 left in the pipes such as
the packer 26 and the packing pipe 28 flows back into the starting
material tank 24.
[0156] When the above starting material bead 5 packing steps are
completed, the following heating step is undertaken.
[0157] In the description thus far, the parts 40 that are difficult
to pack were located in the core mold 2, but a method in which the
chambers 30 and 31 in the description thus far are reversed can be
used to obtain exactly the same action and effects when parts 40
that are difficult to pack have been provided in the cavity mold
3.
[0158] In this packing method, the structure is the same as above,
allowing parts that are difficult to pack, such as recesses having
a difficult-to-pack pouch-shaped cross section, to be packed in the
same manner as the other parts.
[0159] FIG. 11 shows the density distribution according to location
in expanded molded foam which is a box having a different shape
from Table 1 and the degree of shape complexity is 2.44. Here, the
horizontal axis (A) represents the convex protruding tip formed in
parts that are difficult to pack, comprising the pouch-shaped
recesses and edges of the peripheral wall of expanded molded foam,
the axis (B) represents the wall section of the expanded molded
foam, and the axis (C) represents the bottom part.
[0160] The results show that expanded molded foam obtained by a
conventional method, as indicated by O, had extremely irregular
density, where parts A and B had extremely low density, and part C
had high density, whereas the packing method of the present
invention, as indicated by .DELTA., reduced such irregular density
by about 1/2. In this case, density of each part of the expanded
molded foam is between 16.4 and 18.2, which is in a range of
.sub.--}5% of the average density of 17.3.
[0161] The present invention also remedies irregular density caused
by cracking because there is no, or minimal, cracking width during
packing. There is no need for a greater number of packers, which
can be kept to a minimum, allowing the amounts of service fluids
such as packing air to be greatly reduced. The number of packers
arranged per molded product can also be reduced to make more
effective use of the entire mold surface area, resulting in
advantages such as the same higher productivity that is obtained
with conventional molds of simpler shape.
[0162] Blow Back Method
[0163] Another embodiment of the blow back method is described
below. The blow back step is a step in which the starting material
beads remaining in the packer 26 or packing pipe 28 are allowed to
blow back into the starting material tank 24 after the end of the
packing operations, and is managed for all types of packing
methods, including cracked packing, pressure packing, and
compression packing.
[0164] The structure of the starting material bead packing system
is discussed first.
[0165] As shown in FIG. 12, the packer 26 is composed of a packing
pipe 60, through which the starting material beads pass, and a
flange 61. The distal end of the packing pipe 60 is connected
through the chamber 30 to the through-hole 62 formed in the cavity
mold 3. A packing air channel 63 opening into the supply hole 62 in
the vicinity of the distal end of the packing pipe component 60 is
formed along the packing pipe 60 inside the packing pipe component
60, and is connected to the packing air supply pipe 29 in the base
of the packing air channel 63.
[0166] The method is the same as that described in the Related Art
in that the pressure in the chambers 30 and 31 is adjusted to
0.8/cm.sup.2, for example, in order to adjust the pressure in the
cavity 4 to a negative pressure relative to the pressure in the
starting material tank 24, that is, a pressure which has been
adjusted to 1.0 kg/cm.sup.2, for example, so as to deliver the
starting material beads 5 into the cavity 4, and packing air with a
pressure of about 6 kg/cm.sup.2 is discharged through the packing
air valve V2 through the packing air channel 63 from the distal end
of the packing pipe component 60, as indicated by the arrows in
FIG. 12(a).
[0167] A feature of the first embodiment is that natural blow back
begins when the cavity 4 is filled with the starting material beads
5 thus delivered, such as the state shown in FIG. 12(b), but that
blow back is carried out at this time by controlling the pressure
in the chamber 30 and 31 to between 0.8 and 1.5 kg/cm.sup.2, for
example, so that the pressure in the cavity 4 is maintained at a
positive pressure as the pressure in the starting material tank 24
is maintained, specifically, is maintained at 1.0 kg/cm.sup.2.
[0168] The second embodiment is characterized in that, when natural
blow black begins, blow back is carried out by controlling the
pressure in the starting material tank 24 to a pressure equivalent
to the pressure in the cavity 4, at 0.8 kg/cm.sup.2, for example,
or to a negative pressure, while maintaining the pressure in the
cavity 4, in other words, maintaining the pressure at 0.8
kg/cm.sup.2. In this case, the pressure in the starting material
tank 24 should be adjusted to between 0.8 and 0.3 kg/cm.sup.2.
[0169] The maximum pressure differential of the pressure in the
starting material tank 24 relative to the pressure in the cavity 4
must be 0.5 kg/cm.sup.2, as indicated in the first and second
embodiments.
[0170] In this packing step, natural blow back is carried out under
such pressure conditions, the plunger shaft 64 in the plunger 61 is
then pushed out in the same manner as in the past, and the starting
material bead supply hole 62 of the cavity 4 should be closed off
by the plunger tip 65. The expanded molded foam thus obtained is
not compromised by the overpacking in parts located near the
packing holes 62, as happens in conventional packing methods.
[0171] This action is attributed to the following phenomenon.
[0172] When blow back is carried out as in the embodiments, the
pressure in the aforementioned cavity 4 and starting material tank
24 is adjusted under the pressure conditions given in the
aforementioned first and second embodiments, so that the current of
air moving the starting material beads 5 from the packer 26 to the
cavity 4 is weakened or stopped, and the pressure causing the
starting material beads 5 around the supply holes 62 of the cavity
mold 3 to adhere to the inside of the cavity 4 is also weakened,
preventing the build-up of excess starting material beads 5, as
shown in FIG. 12(b).
[0173] Overpacking varies, depending on the weight ratio of the
starting material beads 5 and the wall thickness of the cavity 4
around the starting material supply hole 62, and the pressure
differential between the pressure in the starting material tank 24
and the pressure in the cavity 4 must be suitably set according to
the final product, while the use of the two natural blow back
methods in the aforementioned embodiments must be suitably
selected.
[0174] The maximum pressure differential is 0.5 kg/cm.sup.2 because
a pressure greater than 0.5 kg/cm.sup.2 causes the starting
material beads 5 to flow back and results in at least the partial
destruction of the packed state in the cavity 4.
[0175] The start of natural blow back can be detected because the
flow of the starting material beads 5 in the packing pipe 28 stops,
so the pressure in the starting material tank 24 and the pressure
in the cavity 4 should be adjusted in the manner described above.
In the present invention, the pressure in the cavity 4 may be
treated as being virtually equivalent to the pressure in the
chambers 30 and 31 surrounding the cavity 4, so the pressure in the
cavity 4 can be adjusted by the control of the supply and expulsion
of air to and from the chambers and manipulation based on their
pressures.
[0176] To adjust the pressure in the cavity 4 so as to keep the
prescribed pressure differential relative to the internal pressure
in the starting material tank 24, a preferred method in the present
invention is to individually adjust the pressures in the chambers
30 and 31 to set the pressure differential in the cavity 4.
[0177] For example, when the pressure in the chamber 30 on the
cavity mold 3 side where the packer 26 is mounted is set higher
than the pressure in the chamber 31 on the other side on the core
mold 2 side, the pressure around the supply hole 62 can be set to a
positive pressure relative to the pressure in the starting material
tank 24 during natural blow back, and the starting material beads 5
that have already been packed can be kept in a state adhering on
the cavity mold 3 side, resulting in the advantage of a lower
tendency for starting material bead 5 back flow.
INDUSTRIAL APPLICABILITY
[0178] 1. Die-Expanded Molding Apparatus
[0179] According to the die-expanded molding apparatus relating to
the present invention, the air supplied into the cavity is expelled
from the cavity by air expulsion means as starting material beads
are supplied on an air current into the cavity by starting material
bead supply means, and the starting material beads are packed in
the cavity, but since the air expulsion means comprises at least
two systems, which are independently controlled, the starting
material beads can be packed first in parts where the packing
density tends to be lower, for example, a more uniform packing
density can be set in the various parts of the molded product, the
starting material beads can be packed first in parts where greater
strength and rigidity are desired, and the packing density can be
locally increases in such parts. The packing density can be set to
optimum levels in the various parts of molded products without
increasing the number of packers, even in molded products having
parts where the packing density tends to be lower, such as
thin-walled parts.
[0180] The provision of air expulsion means having one or a
plurality of air pressure-adjusting components in communication
with the clearance between the core mold and cavity mold as the air
expulsion means allows the air supplied into the cavity to be
expelled more efficiently to the outside from the clearance formed
around the cavity. When, for example, a deep-bottomed container or
the like is produced, a clearance is formed in a location
corresponding to the rim of the container, allowing a suitable
packing density to be maintained and the container quality to be
improved without increasing the number of packers.
[0181] The provision of air expulsion means having one or a
plurality of air pressure-adjusting components in communication
with the interior of bottomed, narrow parts, which are difficult to
pack with the starting material beads, as the air expulsion means
allows molded products of good quality to be produced because the
packing density of the starting material beads in parts that are
difficult to pack can be maintained at suitable levels, even in
molded products having a complex shape such as parts that are
difficult to pack that have been regarded as being difficult to
manufacture because the packing density could not be satisfactorily
maintained in the past.
[0182] The provision of air expulsion means having one or a
plurality of air pressure-adjusting components in communication
with the interior of remote parts, which are at a distance from the
starting material bead supply means, as the air expulsion means
allows molded products of good quality to be produced because the
packing density can be maintained at suitable levels in remote
parts where the packing density of the starting material beads
tends to be lower.
[0183] The provision of plural-system air expulsion means
comprising air expulsion means in which the chambers on the back
side of the core mold and/or the back side of the cavity mold are
divided into plural parts and used as air pressure-adjusting
components allows the packing density in various parts of molded
products to be even more precisely controlled so as to improve the
packing density in necessary parts and ensure a suitable packing
density in the molded product as a whole.
[0184] The atmospheric release, pressurization, pressure reduction
and/or these should be combined and the internal pressure of the
air pressure-adjusting components should be controlled by the
control means in such a way that the degree to which the starting
material beads are packed can be set as desired in any part of the
cavity.
[0185] 2. First Die-Expanded Molding Method: Improved Packing
Properties in Outer Periphery of Cavity
[0186] In the first die-expanded molding method, packing air is
expelled through the clearance when the starting material beads are
being packed, so that air can be expelled from the outer peripheral
distal end of the cavity as air is expelled from the core vents of
the two molds, thereby allowing the starting material beads to
sufficiently cross to the outer peripheral distal end of the cavity
without cracking the molds, so as to prevent irregular packing
density. Another advantage is that the packing properties of the
starting material beads can be improved even when the expanded
molded foam is a deep container or has tips with complex
shapes.
[0187] The pressure in the cavity is also adjusted through the
clearance when the starting material beads are being packed, and
the back pressure is adjusted to the desired pressure relative to
the packing air pressure for sending the starting material beads
from the starting material tank, so that the optimal packing method
can be used, such as pressure packing, compression packing, and
vacuum or suction packing in which the back pressure is adjusted to
atmospheric pressure or lower.
[0188] The provision of clearance in this manner affords the
following effects in addition to those obtained during packing.
[0189] ((1)) The advantage of allowing a shorter molding time can
be designed because the plunger constituting the outer periphery of
the two molds can be directly heated through the clearance, whereas
in the past these parts required a considerable volume of heat and
were difficult to heat. Since it is possible to ensure that the air
is purged from the outer peripheral distal end by steam and to
independently adjust the pressure through the clearance, the steam
pressure can be controlled to a positive or negative setting or the
like relative to the chamber pressure so as to set the temperature
balance in the molds to optimum conditions, allowing dramatic
reductions in the cycle time and energy conservation to be
anticipated.
[0190] ((2)) The cycle time can be dramatically reduced because of
the ability to promote decreases in temperatures in the flanges of
the molds, which require large volumes of heat and are difficult to
cool, during the aforementioned cooling.
[0191] ((3)) Because drainage collecting in the clearance and in
the inter-mold cavity as a result of water injection during cooling
can be eliminated, it is possible to remedy drawbacks such as
wetting of the expanded molded foam product and wetting of the
working area, even when the molds are opened to release the
expanded molded foam.
[0192] 3. Second Die-Expanded Molding Method: Improved Packing
Properties in Parts That are Difficult to Pack
[0193] According to the second die-expanded molding method, the
starting material beads can be packed in a concentrated manner in
parts that are difficult to pack, making it possible to prevent
local drops in the packing density of the starting material beads
in parts that are difficult to pack such as pouch-shaped recesses.
Particularly when the starting material beads are repeatedly
delivered to parts that are difficult to pack, the starting
material beads can be packed in a concentrated manner in such parts
that are difficult to pack.
[0194] 4. Third Die-Expanded Molding Method: Improved Packing
Properties in Parts That are Difficult to Pack
[0195] According to the third die-expanded molding method, the air
expulsion means having air pressure-adjusting components in
communication with parts that are difficult to pack, for example,
among the dual-system air expulsion means, is first controlled to
first pack the starting material beads in those parts, so as to
ensure that a suitable packing density is maintained in those
parts.
[0196] When the air expulsion means is controlled by the
aforementioned control means in such a way that the starting
material beads are first packed in parts having a bottomed, narrow
shape that are difficult to pack with starting material beads, it
becomes possible to produce molded products of good quality because
the packing density of the starting material beads in parts that
are difficult to pack can be maintained at suitable levels, even in
molded products having a complex shape such as parts that are
difficult to pack that have been regarded as being difficult to
manufacture because the packing density could not be satisfactorily
maintained in the past.
[0197] When the air expulsion means is controlled by the
aforementioned control means in such a way that the starting
material beads are first packed in remote parts that are at a
distance from the starting material bead supply means, it becomes
possible to produce molded products of good quality because the
packing density of the starting material beads can be maintained at
suitable levels in parts that are difficult to pack.
[0198] When, as another method for improving the packing properties
of the starting material beads in parts that are difficult to pack,
the starting material beads are supplied on a current of packing
air into the cavity while the amount of starting material beads
supplied per unit time to the cavity is adjusted by the adjusting
means, the starting material beads can be supplied more
efficiently, even in narrow, bottomed, thin-walled parts that are
difficult to pack with starting material beads or in remote parts
that are at a distance from the packer.
[0199] When the starting material beads are diluted with adjusting
air and are delivered into the cavity on a current of packing air
as the aforementioned adjusting means, the manufacturing costs of
the adjusting means can be reduced, and the starting material beads
can be prevented from damage during packing.
[0200] When the final degree of dilution of the starting material
beads is set to 5 or more using the aforementioned adjusting means,
it becomes possible to ensure that the starting material beads have
sufficient packing density in parts that are difficult to pack.
[0201] 5. Blow Back: Improved Packing Properties in Locations
Facing the Packer
[0202] According to the aforementioned die-expanded molding method,
when the pressure in the cavity is set to a positive pressure as
the pressure in the starting material tank is maintained during
blow back operations immediately prior to the conclusion of the
packing, or when the pressure in the starting material tank is
adjusted to a pressure equivalent to or lower than the pressure in
the cavity as the pressure in the starting material tank is
maintained, a current of air from the cavity to the starting
material tank is produced, making it possible to prevent defects in
the return flow of the starting material beads caused by the
adhesion of surplus starting material beads on the cavity side in
the packer as well as local increases in the packing density caused
by defects in the return flow.
[0203] The starting material supply hole is closed off by the
plunger after natural blow back, and subsequent forced blow back
makes it possible to ensure that the starting material beads in the
packer flow back into the starting material tank.
[0204] 6. Die-Expanded Molded Foam
[0205] According to the die-expanded molded foam in the present
invention, the density in various parts of the molded foam is
adjusted to within +5% of the mean density, making it possible to
ensure suitable strength and rigidity in thin-walled parts and the
like while creating molded products of lighter weight.
[0206] Molded articles having thin-walled parts or complex shapes,
that include those in which the degree of shape complexity is 1.1
or more, where the degree of shape complexity is defined as the
numerical value obtained by dividing the surface area of the molded
product by the volume, which is measured by cm unit, those in which
the wall thickness of the thin-walled portions of the molded
product is 10 mm to 3 mm, and those in which 3 or less beads are
disposed in the thicknesswise direction of the thin-walled portions
of the molded product, have been considered difficult to form in
the past, but they can be produced by the methods described above
so as to ensure adequate strength and rigidity by setting the
density in various parts of the molded product to within .+-.5%
relative to the mean density.
* * * * *