U.S. patent application number 11/990780 was filed with the patent office on 2009-05-14 for method for multilayer molding of thermoplastic resins and multilayer molding apparatus.
This patent application is currently assigned to UBE Machinery Corporation, Ltd.. Invention is credited to Kazuaki Miyamoto, Akio Okamoto.
Application Number | 20090121375 11/990780 |
Document ID | / |
Family ID | 37771603 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090121375 |
Kind Code |
A1 |
Okamoto; Akio ; et
al. |
May 14, 2009 |
Method for multilayer molding of thermoplastic resins and
multilayer molding apparatus
Abstract
A multilayer-molding method includes the steps of mixing at
least one thermoplastic resin selected from a plurality of types of
thermoplastic resins with a bubble-nucleating agent and a foaming
gas, injecting the plurality of types of thermoplastic resins into
a mold cavity such that the thermoplastic resins are layered in the
mold cavity, and then, after increasing the volume of the mold
cavity, foaming the at least one thermoplastic resin mixed with the
bubble-nucleating agent and the foaming gas. The multilayer-molding
method is characterized in that the foaming gas is supplied at a
pressure of 0.1 MPa or more but less than 1.0 MPa to at least one
injection-molding machine selected from a plurality of
injection-molding machines, and that the thermoplastic resin
plasticized in the injection-molding machine is mixed with the
foaming gas.
Inventors: |
Okamoto; Akio;
(Yamaguchi-prefecture, JP) ; Miyamoto; Kazuaki;
(Yamaguchi-prefecture, JP) |
Correspondence
Address: |
EDWARDS ANGELL PALMER & DODGE LLP
P.O. BOX 55874
BOSTON
MA
02205
US
|
Assignee: |
UBE Machinery Corporation,
Ltd.
Ube-shi
JP
|
Family ID: |
37771603 |
Appl. No.: |
11/990780 |
Filed: |
August 23, 2006 |
PCT Filed: |
August 23, 2006 |
PCT NO: |
PCT/JP2006/316508 |
371 Date: |
February 21, 2008 |
Current U.S.
Class: |
264/46.4 ;
425/4R |
Current CPC
Class: |
B29C 44/086 20130101;
B29C 44/0461 20130101 |
Class at
Publication: |
264/46.4 ;
425/4.R |
International
Class: |
B29C 67/20 20060101
B29C067/20 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2005 |
JP |
2005-244365 |
Claims
1. A multilayer-molding method of molding thermoplastic resins,
which includes the use of: a plurality of injection-molding
machines that plasticize and inject a plurality of types of
thermoplastic resins as molding materials; a mold that has a cavity
as a molding space to be filled with the thermoplastic resins
injected by the plurality of injection-molding machines; and a
clamping apparatus that can clamp the mold and open or close the
mold to increase or decrease the volume of the cavity, the method
comprising the steps of: mixing at least one thermoplastic resin
selected from the plurality of types of thermoplastic resins with a
foaming gas; injecting the plurality of types of thermoplastic
resins into the mold cavity such that the thermoplastic resins are
layered in the mold cavity; and then, after increasing the volume
of the mold cavity, foaming the at least one thermoplastic resin
mixed with the foaming gas, wherein the foaming gas is supplied at
a pressure of 0.1 MPa or more but less than 1.0 MPa to at least one
injection-molding machine selected from the plurality of
injection-molding machines, and the thermoplastic resin plasticized
in the injection-molding machine is mixed with the foaming gas.
2. The multilayer-molding method of molding thermoplastic resins
according to claim 1, wherein the pressure of the foaming gas
supplied to the injection-molding machine is in the range of 0.5
MPa or more but less than 1.0 MPa.
3. The multilayer-molding method of molding thermoplastic resins
according to claim 1, wherein a bubble-nucleating agent is premixed
with the foaming gas to be supplied into the injection-molding
machine, thereby allowing the thermoplastic resin injected into the
mold cavity to contain the bubble-nucleating agent.
4. The multilayer-molding method of molding thermoplastic resins
according to claim 1, wherein a bubble-nucleating agent is premixed
with a thermoplastic resin serving as a molding material, thereby
allowing the thermoplastic resin injected into the mold cavity to
contain the bubble-nucleating agent.
5. The multilayer-molding method of molding thermoplastic resins
according to claim 1, wherein the bubble-nucleating agent is one or
a mixture of at least two selected from the group consisting of
iron oxides, calcium silicate, zinc stearate, magnesium stearate,
organic acids, aluminum silicate, glass fiber, and talc.
6. The multilayer-molding method of molding thermoplastic resins
according to claim 1, wherein the foaming gas is supplied to the
injection-molding machine under controlled pressure.
7. The multilayer-molding method of molding thermoplastic resins
according to claim 1, wherein the foaming gas is supplied to a
hopper of the injection-molding machine, the hopper serving as a
charge port of a thermoplastic resin to be plasticized, or into a
plasticized thermoplastic resin in a plasticizing cylinder of the
injection-molding machine.
8. The multilayer-molding method of molding thermoplastic resins
according to claim 1, wherein the foaming gas is one inorganic gas
or a mixture of at least two inorganic gases selected from the
group consisting of air, carbon dioxide, and nitrogen.
9. An automotive interior multilayer-molded product manufactured by
the multilayer-molding method of molding thermoplastic resins
according to claim 1.
10. A multilayer-molding apparatus for manufacturing a
multilayer-molded product that contains a multilayer of a plurality
of types of thermoplastic resins, one layer of which is foamed and
composed of at least one thermoplastic resin selected from the
plurality of types of thermoplastic resins, the apparatus
comprising: a plurality of injection-molding machines that
plasticize and inject the plurality of types of thermoplastic
resins as molding materials; a mold that has a cavity as a molding
space to be filled with the thermoplastic resins injected by the
plurality of injection-molding machines; a clamping apparatus that
can clamp the mold and open or close the mold to increase or
decrease the volume of the cavity; and a unit for supplying a
foaming gas and a unit for supplying a bubble-nucleating agent each
for use in the foaming.
Description
TECHNICAL FIELD
[0001] The present invention relates to a multilayer-molding method
of molding thermoplastic resins and a multilayer-molding apparatus
for performing the multilayer-molding method.
BACKGROUND ART
[0002] Multilayer-molded products of thermoplastic resins that
contain a foam layer and a non-foamed layer have been used in
various fields for a long time. The foam layer in a
multilayer-molded product is light in weight and has excellent
heat-insulating properties, sound-absorbing properties, and
texture, because of bubbles inside the resin. The non-foamed layer
in a multilayer-molded product can provide rigidity and excellent
appearance. In recent years, in particular, resins used in products
have been foamed to reduce the amount of resin for the purpose of
weight reduction. Combined with the cost reduction resulting from
the weight reduction, multilayer-molded products that contain a
foam layer have found wider applications.
[0003] A foam layer in a multilayer-molded product is manufactured
by physical foaming or chemical foaming according to the type of a
foaming agent to be mixed with a resin. The physical foaming
utilizes an inert gas, such as nitrogen or carbon dioxide, or a
volatile substance, such as a hydrocarbon or a fluorocarbon, as a
physical foaming agent. The chemical foaming utilizes an organic
foaming agent, such as an azo compound or a nitroso compound, or an
inorganic foaming agent, such as sodium bicarbonate, as a chemical
foaming agent. A multilayer-molding method includes injecting a
molten resin that contains a foaming agent and a resin material
into a mold cavity, injecting a molten resin that contains a resin
material and no foaming agent into the mold cavity, and foaming a
resin mixed with the foaming agent. A multilayer-molded product
thus manufactured includes a foam layer that contains bubbles
having a diameter of about 80 to 300 .mu.m and a non-foamed
layer.
[0004] As a method for manufacturing a foam-molded product serving
as a foam layer in a multilayer-molded product, for example, Patent
Document 1 discloses a method for forming a foam-molded product
having bubbles therein, in which an olefin resin mixed with a
chemical foaming agent or a physical foaming agent is foamed by a
short-shot method. According to the method disclosed in Patent
Document 1, in a molding apparatus including an extruder, an
accumulator, and a mold, a molten resin that contains a resin
material mixed with an inert gas, such as a nitrogen gas, a
volatile substance, such as a hydrocarbon or a fluorocarbon, or a
chemical foaming agent is fed to the accumulator with an extruder.
The molten resin fed to the accumulator is injected into the mold
and is foamed, thus yielding a foam-molded product that contains
bubbles therein.
[0005] Furthermore, for example, Patent Document 2 discloses a
method for manufacturing a foam-molded product using a physical
foaming agent, in which air, another gas, or a volatile substance
is fed under pressure from an extruder hopper simultaneously with
resin-material feed. The melting of the resin material and the
inclusion and dispersion of bubbles are performed with a screw
extruder. According to the method disclosed in Patent Document 2, a
molded product of a sponge-like substance that contains closed
cells can be manufactured by using a polyethylene resin and air
having a pressure in the range of about 0.69 to 0.78 MPa.
Furthermore, for example, Patent Document 3 discloses a method for
remarkably increasing the bubble density (the number of bubbles per
unit volume) by using carbon dioxide, an inert gas, in a
supercritical state as a foaming gas, as compared with bubbles
formed in a molded product using a conventional chemical foaming
agent or a conventional physical foaming agent. According to the
method disclosed in Patent Document 3, a molding apparatus is
provided with a system composed of a booster and a feeder of a
supercritical fluid and a gas cylinder. Carbon dioxide in a
supercritical state is injected and dissolved into a molten resin
via a cylinder of the molding apparatus. The molten resin that
contains dissolved carbon dioxide is injected into a mold, and is
foamed, thus yielding a resin-molded product that contains
ultrafine pores, called microcells, having a size less than 1 .mu.m
therein.
[0006] [Patent Document 1] JP-B-44-6080
[0007] [Patent Document 2] JP-B-43-9913
[0008] [Patent Document 3] JP-K-6-506724
[0009] [Non-patent Document 1] SEIKEI KAKOU, 2001, No. 2, Vol.
13
DISCLOSURE OF INVENTION
[0010] However, the following problems become obvious when the
above-mentioned known methods for manufacturing a foam-molded
product are used to form a foam layer in a multilayer-molded
product.
[0011] In a case where means for supplying a resin and an organic
chemical foaming agent (such as an azo compound or a nitroso
compound) are employed (see Patent Document 1), pyrolysates,
including corrosive ammonia, gases, such as carbon monoxide and
water vapor, cyanic acid, and isocyanic acid, are released in the
air, and undesirably remain in a foam layer. Furthermore, when
sodium bicarbonate (inorganic foaming agent) is used as a foaming
agent, a minute amount of reaction residues, including alkaline
components, discolor a multilayer-molded product (final product),
and impair the weatherability of the multilayer-molded product. In
particular, the reaction residues corrode aluminum particles
contained in an aluminum coating.
[0012] On the other hand, in a case where means for supplying a
physical foaming agent, including volatile substances, such as
hydrocarbons and fluorocarbons, which does not produce
decomposition products, is employed, one should face to the problem
that its emission into the air is regulated as an environmental
pollution and a destruction substance.
[0013] By the means in which an inert gas, such as nitrogen, or air
supplied via an extruder hopper is kneaded with a resin material
under pressure using a screw (see Patent Document 2), the gas is
not finely dispersed in a molten resin. Thus, it is practically
difficult to produce a foam layer having a desired bubble density
or a desired bubble size.
[0014] In a case where means for dissolving carbon dioxide (foaming
gas) in a supercritical state in a molten resin is employed (see
Patent Document 3), the following problems occur. First, the means
requires a generator and a feeder of the supercritical fluid. Since
these apparatuses treat a high-pressure gas, the apparatuses are
under a legal restriction, which complicates the installation and
the operation of the apparatuses. Second, the means requires a
complicated mechanism for sealing a foaming gas injected into a
cylinder of an injection-molding machine. This increases the cost
of the injection-molding machine. Third, an increase in sealing
performance against a foaming gas reduces the plasticizing capacity
and therefore the productivity. Furthermore, a foaming gas is
generally injected at a controlled flow rate, which requires a
complicated controlling mechanism.
Means for Solving the Problems
[0015] In view of the situations described above, it is an object
of the present invention to provide an ecological
multilayer-molding means of thermoplastic resins, in which the
means generates no hazardous decomposition product, releases
neither environmental pollutants nor environmental destruction
substances in the air, does not require a generator or a feeder of
a supercritical fluid under a legal restriction, which complicates
the installation and the operation of the apparatuses, and can
produce a multilayer-molded product that contains a foam layer
having a desired bubble density or a desired bubble size. As a
result of repeated investigations, the present inventors found that
the above-mentioned object can be achieved with the means described
below.
[0016] Accordingly, first, the present invention provides a
multilayer-molding method of molding thermoplastic resins, which
includes the use of: a plurality of injection-molding machines that
plasticize and inject a plurality of types of thermoplastic resins
as a molding material; a mold that has a cavity as a molding space
to be filled with the thermoplastic resins injected by the
plurality of injection-molding machines; and a clamping apparatus
that can clamp the mold and open or close the mold to increase or
decrease the volume of the cavity, the method including the steps
of: mixing at least one thermoplastic resin selected from the
plurality of types of thermoplastic resins with a foaming gas;
injecting the plurality of types of thermoplastic resins into the
mold cavity such that the thermoplastic resins are layered in the
mold cavity; and then after increasing the volume of the mold
cavity, foaming the at least one thermoplastic resin mixed with the
foaming gas, wherein the foaming gas is supplied at a pressure of
0.1 MPa or more but less than 1.0 MPa to at least one
injection-molding machine selected from a plurality of
injection-molding machines, and the thermoplastic resin plasticized
in the injection-molding machine is mixed with the foaming gas
(also referred to as foaming gas mixing method).
[0017] In a multilayer-molding method of molding thermoplastic
resins according to the present invention, the pressure of the
foaming gas supplied to the injection-molding machine is more
preferably in the range of 0.5 MPa or more but less than 1.0
MPa.
[0018] The foaming gas for use in the formation of a foam layer is
generally supplied to a predetermined portion in the
injection-molding machine at a pressure in the range of 0.1 MPa or
more but less than 1.0 MPa. The pressure in this range allows for a
simple sealing mechanism in the injection-molding machine, thus
ensuring a plasticizing capacity of at least a desired level. For
example, in the case of a two-stage screw, the sealing performance
of the injection-molding machine is ensured by reducing a
screw-flight clearance at a boundary between a first stage and a
second stage. However, too narrow a screw-flight clearance prevents
a molten resin from passing through the clearance, resulting in a
decreased plasticizing capacity. However, the pressure range as
described above allows for a relatively large screw-flight
clearance, satisfying both the plasticizing capacity and the
sealing performance. Furthermore, in the pressure range as
described above, the emission of the foaming gas from the front-end
of a resin can be reduced to an appropriate level during filling
injection. Thus, a multilayer-molded product can have a desired
appearance. Furthermore, when the injection rate of the foaming gas
is regulated by pressure control, the saturating amount of
dissolved gas most suitable for a resin used can be obtained
independently of the molding conditions.
[0019] The gas-injection rate is determined by the difference in
pressure between the decompression zone (gas injection position) of
the two-stage screw and the injected gas. Furthermore, the amount
of nitrogen gas dissolved in polystyrene (200.degree. C.) is in the
range of 0.4 mol/kg (1 MPa) to 0.6 mol/kg (10 MPa) and does not
vary significantly with pressure (see Non-patent Document 1). Thus,
the amount of foaming gas required for foaming can be supplied
sufficiently at the pressure range of 0.1 MPa or more but less than
1.0 MPa described above. The injection of the foaming gas at the
above-mentioned pressure range can therefore achieve sufficient
foaming, without having a substantial influence on the product
characteristics.
[0020] When the pressure of the foaming gas supplied to the
injection-molding machine is less than 0.1 MPa, a foam layer having
a desired bubble density or a desired bubble size cannot be formed
in a desired multilayer-molded product. Furthermore, the pressure
of the foaming gas supplied to the injection-molding machine is set
to be less than 1.0 MPa for the following reasons. While a
multilayer-molded product having a desired bubble density or a
desired bubble size can sometimes be produced at 1.0 MPa,
occasionally, foaming cells become coarse, and the expansion ratio
varies greatly at different portions of the multilayer-molded
product. In addition, the multilayer-molded product may have a
defective appearance due to swirl marks. Furthermore, when the
pressure of the foaming gas is as high as 1.0 MPa or more, in the
molding of large multilayer-molded products, such as automobile
parts, a molding apparatus that can perform such molding requires
high sealing performance. However, it is difficult to achieve such
high sealing performance from the viewpoint of designing.
Furthermore, the facility must also be resistant to pressure. A
pressure-proof facility for housing large apparatuses requires huge
investments. Besides, even the present technology cannot completely
clear up uneasiness about high pressure.
[0021] While the foaming gas is supplied to the injection-molding
machine at a pressure of 0.1 MPa or more but less than 1.0 MPa, in
terms of the foaming status, the appearance, and the flexibility of
a multilayer-molded product, the pressure is more preferably in the
range of 0.2 MPa to 0.99 MPa and still more preferably in the range
of 0.5 MPa to 0.9 MPa. As described above, the foaming gas is
supplied to a hopper for feeding a thermoplastic resin or into a
molten resin in a plasticizing cylinder of the injection-molding
machine as described below. This ensures sufficient dispersion and
mixing of the foaming gas or the bubble-nucleating agent in a
molten resin. When the foaming gas is supplied with a two-stage
screw, which is employed as a screw in a plasticizing cylinder of
the injection-molding machine, the foaming gas and the
bubble-nucleating agent can be dispersed and mixed in a molten
resin. More preferably, the screw has a highly dispersive screw
head to improve the dispersibility of the foaming gas and the
bubble-nucleating agent in a molten resin.
[0022] In a multilayer-molding method of molding thermoplastic
resins according to the present invention, preferably, the
bubble-nucleating agent is premixed with the foaming gas to be
supplied into the injection-molding machine, thereby allowing the
thermoplastic resin injected into a mold cavity to contain the
bubble-nucleating agent.
[0023] In a multilayer-molding method of molding thermoplastic
resins according to the present invention, preferably, the
bubble-nucleating agent is premixed with the thermoplastic resin
serving as a molding material, thereby allowing the thermoplastic
resin injected into the mold cavity to contain the
bubble-nucleating agent.
[0024] In a multilayer-molding method of molding thermoplastic
resins according to the present invention, preferably, the
bubble-nucleating agent is one or a mixture of at least two
selected from the group consisting of iron oxides, calcium
silicate, zinc stearate, magnesium stearate, organic acids (citric
acid, tartaric acid, etc.), aluminum silicate, glass fiber, and
talc.
[0025] In a multilayer-molding method of molding thermoplastic
resins according to the present invention, preferably, the foaming
gas is supplied to the injection-molding machine under controlled
pressure.
[0026] In a multilayer-molding method of molding thermoplastic
resins according to the present invention, preferably, the foaming
gas is supplied to a hopper of the injection-molding machine, the
hopper serving as a charge port of a thermoplastic resin to be
plasticized, or into a plasticized thermoplastic resin in a
plasticizing cylinder of the injection-molding machine.
[0027] In a multilayer-molding method of molding thermoplastic
resins according to the present invention, preferably, the foaming
gas is one inorganic gas or a mixture of at least two inorganic
gases selected from the group consisting of air, carbon dioxide,
and nitrogen. Examples of the foaming gas for use in multilayer
molding involving a foam layer include carbon dioxide, a nitrogen
gas, and air, or mixtures thereof. Air or carbon dioxide is
preferred in terms of the characteristics of a multilayer-molded
product. The foaming gas must be selected in consideration of the
oxidation resistance of a resin. A gas other than air is preferably
used for resins having a group susceptible to oxidation. Air is
suitably used for resins having high resistance to oxidation, such
as polypropylene, also in terms of availability. Examples of the
bubble-nucleating agent include fine powders of inorganic
substances, such as iron oxides, calcium silicate, aluminum
silicate, glass fiber, talc, and sodium hydrogencarbonate (sodium
bicarbonate); metallic salts of organic acids, such as zinc
stearate and magnesium stearate; and organic acids, such as citric
acid and tartaric acid. As a matter of course, in consideration of
the function of the bubble-nucleating agent, for example, a
metallic salt and an organic acid may be used in combination.
[0028] Examples of the thermoplastic resin for use in a
multilayer-molding method of molding thermoplastic resins according
to the present invention include styrene-based resins, such as
polystyrene, AS resins, and ABS resins; olefin resins, such as
polyethylene and polypropylene; and so-called engineering resins,
including polyester resins, such as polyethylene terephthalate and
polybutylene terephthalate, polyamides, polyacetals,
polycarbonates, and modified polyphenylene ethers, and olefinic
thermoplastic elastomers. These resins may be used in combination
according to the application. Furthermore, if necessary, these
thermoplastic resins may be used in combination with additive
agents, such as a plasticizer, a mold-release agent, an antistatic
agent, and a flame retardant; various fillers for improving
physical properties, such as glass fiber and carbon fiber; and
coloring agents, dyes, and the like.
[0029] The present invention also provides an automotive interior
multilayer-molded product manufactured by any of the
above-mentioned multilayer-molding methods of thermoplastic
resins.
[0030] The present invention also provides a multilayer-molding
apparatus for manufacturing a multilayer-molded product that
contains a multilayer of a plurality of types of thermoplastic
resins, one layer of which is foamed and composed of at least one
thermoplastic resin selected from the plurality of types of
thermoplastic resins. The multilayer-molding apparatus includes a
plurality of injection-molding machines that plasticize and inject
the plurality of types of thermoplastic resins as a molding
material, a mold that has a cavity as a molding space to be filled
with the thermoplastic resins injected by the plurality of
injection-molding machines, a clamping apparatus that can clamp the
mold and open or close the mold to increase or decrease the volume
of the cavity, and a unit for supplying a foaming gas and a unit
for supplying a bubble-nucleating agent each for use in the
foaming.
[0031] A multilayer-molding method of molding thermoplastic resins
according to the present invention includes the steps of mixing at
least one thermoplastic resin selected from a plurality of types of
thermoplastic resins with a bubble-nucleating agent and a foaming
gas, and injecting the plurality of types of thermoplastic resins
into a mold cavity such that the thermoplastic resins are layered
in the mold cavity. The foaming gas is supplied at a pressure of
0.1 MPa or more but less than 1.0 MPa to at least one
injection-molding machine selected from a plurality of
injection-molding machines. Thus, a multilayer-molded product of
thermoplastic resins that contains a foam layer having a desired
bubble size and a bubble density and being free from hazardous
decomposition product residues can be manufactured without using an
environmentally hazardous foaming agent and a generator and a
feeder of a supercritical fluid.
[0032] Furthermore, the supply pressure of the foaming gas in the
range of 0.1 MPa or more but less than 1.0 MPa can simplify the
mechanism for sealing the foaming gas that is supplied to a
cylinder of the injection-molding machine. This prevents a
reduction in plasticizing capacity. In an injection-molding machine
having a two-stage screw, the sealing performance is ensured by
reducing a screw-flight clearance at a boundary between a first
stage and a second stage. The screw-flight clearance must be
reduced with an increase in pressure of the foaming gas. This
reduces the plasticizing capacity. A multilayer-molding method of
molding thermoplastic resins according to the present invention can
avoid such a problem. In addition, since the foaming gas is
supplied to the injection-molding machine at a pressure in the
range of 0.1 MPa or more but less than 1.0 MPa, unlike conventional
methods using a foaming gas in a supercritical state, a generator
and a feeder of a supercritical fluid are unnecessary. Furthermore,
since the supply pressure of the foaming gas is in the range of 0.1
MPa or more but less than 1.0 MPa, the emission of the foaming gas
from the front-end of a flowing molten resin during injection
filling is smaller than that at a pressure of 1.0 MPa or more.
Thus, a multilayer-molded product (final product) has better
appearance.
[0033] In a multilayer-molding method of molding thermoplastic
resins according to the present invention, the reason that the
supply pressure of the foaming gas is set to be 0.1 MPa or more is
that a desired bubble density or a desired bubble size cannot be
achieved at 0.1 MPa or less. The reason that the supply pressure of
the foaming gas is set to be less than 1.0 MPa is that the bubbles
become coarse at 1.0 MPa or more, the foam layer (molded product)
has a defective appearance due to swirl marks, and the
multilayer-molded product has different expansion ratios at
different portions, because the pressure applied to the front-end
of the flowing molten resin in the injection-molding machine is
greatly different from the pressure applied to the resin in the
mold during injection filling.
[0034] More preferably, the foaming gas is supplied to the
injection-molding machine at a pressure of 0.5 MPa or more but less
than 1.0 MPa under controlled pressure. This can provide a
multilayer-molded product that contains a foam layer having a
denser surface and a desired bubble density or a desired bubble
size.
[0035] In a preferred aspect of a multilayer-molding method of
molding thermoplastic resins according to the present invention,
the foaming gas is supplied to a hopper of the injection-molding
machine or into a molten thermoplastic resin in a cylinder. This
ensures sufficient dispersion and mixing of the foaming gas or the
bubble-nucleating agent in the molten resin, which forms a foam
layer. More preferably, the screw has a highly dispersive screw
head to improve the dispersibility of the foaming gas and the
bubble-nucleating agent in the molten resin.
[0036] In a preferred aspect of a multilayer-molding method of
molding thermoplastic resins according to the present invention,
the foaming gas is supplied under controlled pressure. Thus, the
saturating amount of dissolved foaming gas most suitable for a
thermoplastic resin used can consistently be obtained independently
of the molding conditions. For example, when a two-stage screw is
employed as a screw of the injection-molding machine, the amount of
supplied foaming gas is determined by the difference in pressure
between the decompression zone (injection position of the foaming
gas) and the supplied foaming gas. Furthermore, the amount of
nitrogen gas dissolved in a polystyrene resin is in the range of
0.4 mol/kg (1 MPa) to 0.6 mol/kg (10 MPa) at 200.degree. C. and
does not vary significantly with pressure (see Non-patent Document
1). Thus, the amount of foaming gas required for foaming can be
supplied sufficiently at a pressure in the range of 0.1 MPa or more
but less than 1.0 MPa. Furthermore, a pressure in the range of 0.1
MPa or more but less than 1.0 MPa should not have a significant on
the multilayer-molded product (final product).
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a general schematic view of a multilayer-molding
apparatus according to an embodiment of the present invention.
[0038] FIGS. 2(a) to (f) are process drawings of a
multilayer-molding method of molding thermoplastic resins according
to an embodiment of the present invention.
[0039] FIGS. 3(a) to (e) are process drawings of a
multilayer-molding method of molding thermoplastic resins according
to another embodiment of the present invention.
REFERENCE NUMERALS
[0040] 1 stationary platen [0041] 2 movable platen [0042] 3, 13
stationary mold [0043] 4 movable mold [0044] 10, 100 mold [0045] 20
clamping apparatus [0046] 30, 130 injection-molding machine [0047]
31, 131 cylinder [0048] 32, 132 screw [0049] 35, 135 hopper [0050]
40 means for supplying foaming gas [0051] 41 air source [0052] 42
carbon dioxide source [0053] 43 unit for supplying foaming gas
[0054] 61 unit for supplying bubble-nucleating agent [0055] 62 unit
for supplying bubble-nucleating agent [0056] 70 controller [0057]
80 (horizontal clamping) injection-molding machine [0058] 121, 221
non-foamed layer [0059] 122, 222 foam layer [0060] 124
(foaming-gas-free molten thermoplastic) resin [0061] 125
(foaming-gas-containing molten thermoplastic) resin
BEST MODE FOR CARRYING OUT THE INVENTION
[0062] The present invention will be described below by way of
embodiments thereof, if necessary, with reference to the drawings.
However, the present invention should not be construed as being
limited to these embodiments. Various changes, modifications,
improvements, and substitutions may be made by a person skilled in
the art without departing from the gist of the present invention.
For example, while the drawings indicate suitable embodiments of
the present invention, the present invention is not limited to the
aspects or the information shown in the drawings. While means
similar or equivalent to those described in the present
specification can be applied in the implement or the verification
of the present invention, suitable means are means described
below.
[0063] First, a multilayer-molding apparatus according to the
present invention will be described below. A multilayer-molding
apparatus according to the present invention is suitable to
implement a multilayer-molding method of molding thermoplastic
resins according to the present invention. FIG. 1 illustrates a
multilayer-molding apparatus according to an embodiment of the
present invention and is a general schematic view of a horizontal
clamping injection-molding machine. As illustrated in FIG. 1, an
injection-molding machine 80 is composed of a mold 10, a clamping
apparatus 20, two injection-molding machines 30 and 130, means 40
for supplying a foaming gas, and a controller 70.
[0064] The mold 10 is composed of a stationary mold 3, which is
attached to a stationary platen 1, and a movable mold 4, which is
attached to a movable platen 2. The stationary mold 3 and the
movable mold 4 have a semi-positive structure, and are fitted
together at a fitting part. In this fitted state, a face of the
stationary mold 3 that forms a cavity 11 (cavity-forming face) and
a face of the movable mold 4 that forms the cavity 11
(cavity-forming face) jointly form the cavity 11 of the mold 10.
The fitting part of the semi-positive structure is located all
around the cavity 11 of the mold 10. The fitting part has such a
structure that a resin in the cavity 11 of the mold 10 does not
leak out of the mold 10 even when the volume of the cavity 11 in
the mold 10 is increased after injection filling. The clamping
apparatus 20 includes a mold-clamping cylinder 22 that opens and
closes the mold 10, and is designed such that the movable mold 4
can move forward and backward along tie bars (not shown) relative
to the stationary mold 3.
[0065] Furthermore, the mold is not limited to the mold having the
semi-positive structure, in which a resin in the cavity does not
leak out during a predetermined stroke. Other molds, such as a
flash mold, may be used, provided that they are applicable to the
foam molding. Furthermore, an injection-molding machine equipped
with a toggle type mold-clamping system, an electric servomotor
type injection-molding machine, or a vertical clamping
injection-molding machine may be used in place of the horizontal
clamping injection-molding machine equipped with a straight
hydraulic mold-clamping system.
[0066] Two injection-molding machines 30 and 130 illustrated in
FIG. 1 include cylinders 31 and 131, screws 32 and 132, which are
disposed within the cylinders 31 and 131 and have flights, and
hoppers 35 and 135, through which molding materials are supplied to
the cylinders 31 and 131, and are provided with screw-traveling
means 33 and 133, which move the screws 32 and 132 forward and
backward, and screw-rotating means 34 and 134, which rotate the
screws 32 and 132. Heaters (not shown) are mounted on the periphery
of the cylinders 31 and 131. Furthermore, the injection-molding
machine 130 is designed such that a foaming gas is supplied from
the means 40 for supplying a foaming gas to the hopper 135 (opening
of the hopper) or into a molten resin in the cylinder 131.
[0067] The injection-molding machine 30 is designed such that the
screw-rotating means 34 rotates the screw 32 to feed molding
material pellets from the hopper 35 into the cylinder 31. The
molding material pellets fed are heated by the heater (not shown)
mounted on the cylinder 31, and are kneaded and compressed as the
screw 32 rotates. The resulting molten material is transferred in
front of the screw 32. The molten resin transferred in front of the
screw 32 is injected into the mold through a nozzle 36 disposed at
the tip of the cylinder 31 as the screw-traveling means 33 moves
the screw 32 forward.
[0068] Also in the injection-molding machine 130, the same action
and phenomena occur, except that the foaming gas is supplied into a
molten resin. While molding material pellets fed are kneaded and
compressed, the foaming gas and the bubble-nucleating agent are
mixed and dispersed in a molten material. The resulting molten
material is transferred in front of the screw 132. The molten resin
that contains the foaming gas and the bubble-nucleating agent
dispersed therein and is transferred in front of the screw 132 is
injected into the mold through a nozzle 136 disposed at the tip of
the cylinder 131 as the screw-traveling means 133 moves the screw
132 forward. The bubble-nucleating agent is supplied in an
appropriate amount from a unit for supplying a bubble-nucleating
agent described below, according to predetermined molding
conditions.
[0069] While the screw-traveling means 33 and 133 of the
injection-molding machines 30 and 130 are oil-hydraulic cylinders,
and the screw-rotating means 34 and 134 are oil-hydraulic motors in
this embodiment, the screw-traveling means or the screw-rotating
means may utilize an electric servomotor. Furthermore, in place of
an injection-molding machine including a single inline screw, which
performs both plasticization and injection, as in the
injection-molding machines 30 and 130, a screw-preplastication type
injection-molding machine, which performs plasticization and
injection separately, may be used. Furthermore, in place of a
two-stage screw in the injection-molding machines 30 and 130, a
single-stage screw may be used, for example, when the foaming gas
is supplied to the hopper.
[0070] The means 40 for supplying a foaming gas includes an air
source 41, a carbon dioxide source 42, and a unit 43 for supplying
a foaming gas. The air source 41 and the carbon dioxide source 42
are coupled through a supply passage. Furthermore, the means 40 for
supplying a foaming gas is provided with a foaming-gas-supply
passage connected to gas-supply ports disposed at the cylinder 131
and at the hopper 135 of the injection-molding machine 130. The
means 40 for supplying a foaming gas supplies a foaming gas to the
injection-molding machine 130 according to the instruction issued
by the controller 70. Furthermore, units 61 and 62 for supplying a
bubble-nucleating agent are disposed in the vicinity of ends of
supply passages that connect the unit 43 for supplying a foaming
gas with the injection-molding machine 130. The units 61 and 62
supply a bubble-nucleating agent to a foaming gas. The
bubble-nucleating agent may be added to a thermoplastic resin by
previously dry-blending a powdered bubble-nucleating agent with a
molding material, by the addition of a masterbatch of the
bubble-nucleating agent to a molding material, or by premixing the
bubble-nucleating agent with a molding material during the
production of the molding material.
[0071] The controller 70 illustrated in FIG. 1 is composed of a
first injection controller 171 and a second injection controller
71, which control the plasticization of a molding material, the
supply of a foaming gas and a bubble-nucleating agent, and the
injection of a molten resin into the mold, a clamping controller
72, which control the opening and closing of the mold 10 and the
mold-clamping force, and timers. The clamping controller 72
includes a unit for setting the position to which the movable
platen 2 travels and the speed of the traveling to provide a
desired volume of the cavity 11 at the beginning of a foaming
process for forming a foam layer of a multilayer-molded product.
The clamping controller 72 can maintain the position of the movable
platen 2 until the end of the foaming process. The foaming process
includes the steps of detecting the completion of filling of the
cavity 11 in the mold 10 with a resin to reduce the mold-clamping
force, and increasing the volume of the cavity 11 in the mold 10. A
skin layer and bubble nuclei are formed during the step of reducing
the mold-clamping force. A higher reduction rate of the
mold-clamping force results in a larger number of bubble nuclei.
The rate of increasing the volume of the cavity 11 in the mold 10
depends on the elongational viscosity of a molding resin, and is
desirably low for low elongational viscosity, and high for high
elongational viscosity.
[0072] Taking the use of the multilayer-molding apparatus
illustrated in FIG. 1 as an example and referring to FIGS. 2 and 3,
a multilayer-molding method of molding thermoplastic resins
according to the present invention will be described below. A
multilayer-molding method of molding thermoplastic resins according
to the present invention includes a step of injecting a molten
resin that contains a foaming agent into a mold cavity and then
increasing the volume of the mold cavity to foam the resin. The
multilayer-molding method is suitable to manufacture a
multilayer-molded product of thermoplastic resins that contains a
foam layer and a non-foamed layer.
[0073] FIG. 2, which includes (a) to (f), is a schematic process
drawing illustrating the mold 10 and two injection-molding machines
30 and 130 illustrated in FIG. 1, and illustrates a
multilayer-molding method of molding thermoplastic resins according
to an embodiment of the present invention. FIG. 3, which includes
(a) to (e), is a schematic process drawing only illustrating a mold
100 and two injection-molding machines 30 and 130, and illustrates
a multilayer-molding method of molding thermoplastic resins
according to another embodiment of the present invention. The mold
10 illustrated in FIGS. 1 and 2 is designed such that the cavity 11
is filled independently with a resin that contains a foaming gas
and a bubble-nucleating agent injected from the injection-molding
machine 130 and with a resin that contains no foaming gas and no
bubble-nucleating agent injected from the injection-molding machine
30. The mold 100 illustrated in FIG. 3 is the same as the mold 10
illustrated in FIGS. 1 and 2, except that, in a stationary mold 13,
there is provided a mixing portion 150 in which a resin containing
a foaming gas and a bubble-nucleating agent injected from the
injection-molding machine 130, before entering into the cavity 11,
flows into a resin that contains no foaming gas and no
bubble-nucleating agent injected from the injection-molding machine
30. Thus, a process based on FIG. 3 will be described below with
reference to FIG. 1, while the mold 100 (see FIG. 3) replaces the
mold 10 illustrated in FIG. 1.
[0074] First, referring to FIG. 2, a pressure oil is fed to a
piston head side of the mold-clamping cylinder 22 illustrated in
FIG. 1 to move a piston rod forward, thereby moving the movable
platen 2 toward the stationary platen 1 to close the mold 10. The
mold-clamping force is desirably the smallest force that can
prevent the mold 10 from opening owing to the filling pressure
during resin filling, in view of energy consumption and the life of
the molding apparatus. After the mold clamping is completed, a
resin that contains no foaming gas and no bubble-nucleating agent
(molding material) and then a resin that contains a foaming gas and
a bubble-nucleating agent (molding material) are injected into the
cavity 11 of the mold 10 according to predetermined values of the
injection volume, the injection pressure, and the injection
speed.
[0075] In the injection-molding machine 30, a pressure oil is fed
to the screw-rotating means 34 to rotate the screw 32. The molding
material fed from the hopper 35 is heated by the heater (not shown)
mounted on the cylinder 31, and is kneaded and compressed as the
screw 32 rotates. The resulting molten material is transferred in
front of the screw 32. A pressure oil is fed to the screw-traveling
means 33 to move the screw 32 forward, allowing a (molten) resin
124 (containing no foaming gas and no bubble-nucleating agent)
transferred in front of the screw to be injected into the cavity 11
of the mold 10 (see FIG. 2(a)). The volume of the cavity 11 in the
mold 10 is then maintained and cooled for a predetermined cooling
time to form (solidify) a non-foamed layer 121 (see FIG. 2(b)).
[0076] The pressure of a pressure oil applied to a piston head side
of the mold-clamping cylinder 22 is lowered to reduce the
mold-clamping force. At the same time, the pressure oil is fed to
the piston rod side to move the piston rod backward. This moves the
movable platen 2 away from the stationary platen and opens the mold
10, thus increasing the volume of the cavity 11 (see FIG. 2(c)).
The volume of the cavity 11 in the mold 10 is increased according
to the setpoints of a unit for setting the position to which the
movable platen 2 travels and the speed of the traveling, disposed
in the clamping controller 72. The movable platen 2 stops and stays
at a predetermined position.
[0077] In the injection-molding machine 130, a pressure oil is then
fed to the screw-rotating means 134 to rotate the screw 132. The
molding material fed from the hopper 135 is heated by the heater
(not shown) mounted on the cylinder 131, and is kneaded and
compressed as the screw 132 rotates. The foaming gas and the
bubble-nucleating agent are mixed and dispersed in a molten
material. The molten material is transferred in front of the screw
132. As a pressure oil is fed to the screw-traveling means 133 to
move the screw 132 forward, the (molten) resin 125 that contains
the foaming gas and the bubble-nucleating agent dispersed therein
and that is transferred in front of the screw is injected between
the non-foamed layer 121 previously formed and the movable platen 2
in the cavity 11 of the mold 10 (see FIG. 2(d)). After the resin
filling is completed (see FIG. 2(e)), the pressure of a pressure
oil applied to a piston head side of the mold-clamping cylinder 22
is lowered to reduce the mold-clamping force. The pressure oil is
then fed to the piston rod side of the mold-clamping cylinder 22 to
move the piston rod backward. This further moves the movable platen
2 away from the stationary platen and opens the mold 10, thus
further increasing the volume of the cavity 11. The volume of the
cavity 11 in the mold 10 is increased according to the setpoints of
a unit for setting the position to which the movable platen 2
travels and the speed of the traveling, disposed in the clamping
controller 72. The movable platen 2 stops at a predetermined
position, and maintains the position so as not to be forced back by
the resin-expansion pressure in the mold 10. When the volume of the
cavity 11 in the mold 10 is controlled to increase the volume of
the cavity 11 in the mold 10, the resin pressure in the cavity 11
of the mold 10 starts to decrease. At the same time, foaming starts
within the resin 125 that contains the foaming gas and the
bubble-nucleating agent. The volume of the cavity 11 in the mold 10
is then maintained and cooled for a predetermined cooling time to
form (solidify) a foam layer 122 (see FIG. 2(f)), thus producing a
multilayer-molded product.
[0078] Referring to FIG. 3, a pressure oil is fed to a piston head
side of the mold-clamping cylinder 22 illustrated in FIG. 1 to move
a piston rod forward, thereby moving the movable platen 2 toward
the stationary platen 1 to close the mold 100 (in place of the mold
10 in FIG. 1). The mold-clamping force is desirably the smallest
force that can prevent the mold 100 from opening owing to the
filling pressure during resin filling, in view of energy
consumption and the life of the molding apparatus. After the mold
clamping is completed, according to predetermined values of the
injection volume, the injection pressure, and the injection speed,
a resin that contains no foaming gas and no bubble-nucleating agent
is injected into the cavity 11 of the mold 100, during which a
resin containing a foaming gas and a bubble-nucleating agent is
also injected.
[0079] In the injection-molding machine 30, a pressure oil is fed
to the screw-rotating means 34 to rotate the screw 32. The molding
material fed from the hopper 35 is heated by the heater (not shown)
mounted on the cylinder 31, and is kneaded and compressed as the
screw 32 rotates. The resulting molten material is transferred in
front of the screw 32. A pressure oil is fed to the screw-traveling
means 33 to move the screw 32 forward, allowing a (molten) resin
124 (containing no foaming gas and no bubble-nucleating agent)
transferred in front of the screw to be injected into the cavity 11
of the mold 100 (see FIG. 3(a)). After a predetermined amount of
resin 124 that contains no foaming gas and no bubble-nucleating
agent is charged, the mixing portion 150 switches the flow pass. In
the injection-molding machine 130, a pressure oil is then fed to
the screw-rotating means 134 to rotate the screw 132. The molding
material fed from the hopper 135 is heated by the heater (not
shown) mounted on the cylinder 131, and is kneaded and compressed
as the screw 132 rotates. The foaming gas and the bubble-nucleating
agent are mixed and dispersed in a molten material. The molten
material is transferred in front of the screw 132. As a pressure
oil is fed to the screw-traveling means 133 to move the screw 132
forward, the (molten) resin 125 that contains the foaming gas and
the bubble-nucleating agent dispersed therein and that is
transferred in front of the screw is injected inside the previously
charged molten resin 124 that contains no foaming gas and no
bubble-nucleating agent (see FIG. 3(b)).
[0080] Slight opening of the mold in synchronization with the
charging of the molten resin 125 that contains the foaming gas and
the bubble-nucleating agent allows the resin 125 to be efficiently
charged inside the resin 124 (see FIG. 3(c)). Furthermore, the
resin 125 may be charged while the mold 100 is opened to have a
predetermined volume of the cavity 11.
[0081] When the cavity 11 is filled almost completely with the
resins 124 and 125, the mixing portion 150 changes the flow pass so
that the remaining resin 124 is charged (see FIG. 3(d)). This
prevents the resin 124 and the resin 125 to be mixed with each
other in the next molding. While the injection volumes of the
resins 124 and 125 are appropriately selected, it is important to
prevent the resin 125 from being exposed at the surface of the
resin 124. After the molten resins 124 and 125 are completely
charged, the pressure of a pressure oil applied to a piston head
side of the mold-clamping cylinder 22 is lowered to reduce the
mold-clamping force.
[0082] The pressure oil is then fed to the piston rod side of the
mold-clamping cylinder 22 to move the piston rod backward. This
further moves the movable platen 2 away from the stationary platen
and opens the mold 100, thus increasing the volume of the cavity
11. The volume of the cavity 11 in the mold 100 is increased
according to the setpoints of a unit for setting the position to
which the movable platen 2 travels and the speed of the traveling,
disposed in the clamping controller 72. The movable platen 2 stops
at a predetermined position, and maintains the position so as not
to be forced back by the resin-expansion pressure in the mold 100.
When the volume of the cavity 11 in the mold 100 is controlled to
increase the volume of the cavity 11 in the mold 100, the resin
pressure in the cavity 11 of the mold 100 starts to decrease. At
the same time, foaming starts within the resin 125 containing the
foaming gas and the bubble-nucleating agent, which is enclosed with
the resin 124 that contains no foaming gas and no bubble-nucleating
agent. The volume of the cavity 11 in the mold 100 is then
maintained and cooled for a predetermined cooling time to form
(solidify) a non-foamed layer 221 and a foam layer 222 (see FIG.
3(e)), thus producing a multilayer-molded product.
[0083] As illustrated in FIGS. 2 and 3, even when the mold 10 or
100 is slightly opened, the stationary mold 3 or 13 and the movable
mold 4 are fitted together at a fitting part. The molten resin in
the cavity 11 therefore dose not leak out of the mold 10 or
100.
EXAMPLES
[0084] The present invention will be further described below with
examples. However, the present invention is not limited to these
examples.
Example 1
[0085] A two-layer molded product (multilayer-molded product)
composed of one foam layer and one non-foamed layer was
manufactured by the multilayer-molding method (foaming gas mixing
method) illustrated in FIG. 2 using a horizontal toggle
injection-molding machine (Ube Machinery Corporation, Ltd.,
UBE-MD350 injection-molding machine) as an injection-molding
machine. To satisfy the rigidity and the surface texture of a
molded product (final product), a polypropylene resin (PP, Mitsui
Chemicals, Inc., automotive interior grade, MFR=35) was used as a
resin material (molding material) for the non-foamed layer, and an
olefin thermoplastic elastomer (TPO, JSR, injection-molding grade,
hardness HAS=40, MFR=10) was used as a resin material (molding
material) for the foam layer.
[0086] A mixture of sodium bicarbonate and citric acid was used as
a bubble-nucleating agent and was premixed with the resin
materials. Carbon dioxide was used as a foaming gas, and was
supplied into a molten resin in a cylinder at a pressure of 0.9
MPa. A two-stage screw having a mixing head at the tip was used as
a screw. A gas-seal portion was adjusted according to the pressure
of the foaming gas.
[0087] The two-layer molded product was a 350.times.220 mm
automotive interior component (glove compartment door). The foam
layer of the two layers had a thickness of 2.0 mm before foaming
and 4.2 mm after foaming (expansion ratio=2.1). Furthermore, the
molding conditions were a resin temperature of 200.degree. C. and a
mold temperature of 30.degree. C. The foaming status, the
appearance, and the flexibility of the molded product were
evaluated by visual inspection. Table 1 shows the results.
Examples 2 to 6 and Comparative Examples 1 and 2
[0088] A two-layer molded product was manufactured as in Example 1,
except that the foaming gas, the supply pressure of the foaming
gas, and the thicknesses of the foam layer before and after foaming
were changed. The foaming status, the appearance, and the
flexibility of the molded product were evaluated by visual
inspection. Table 1 shows the results, together with the foaming
gas, the supply pressure, and the thicknesses of the foam layer
before and after foaming.
Comparative Example 3
[0089] A two-layer molded product was manufactured as in Example 1,
except that no foaming gas was used, the foam layer was formed
using sodium bicarbonate (inorganic chemical foaming agent), and
the thicknesses of the foam layer before and after foaming were
changed. The foaming status, the appearance, and the flexibility of
the molded product were evaluated by visual inspection. Table 1
shows the results.
TABLE-US-00001 TABLE 1 Thickness of second Supply layer [mm]
Relative Foaming Foaming pressure After Before Expansion Foaming
plasticizing means agent [MPa] foaming foaming ratio status
Appearance Flexibility capacity Example 1 Foaming Carbon 0.9 4.2
2.0 2.1 A A A 0.8 gas dioxide (gas) mixing Example 2 Foaming Carbon
0.5 3.8 2.0 1.9 A A A 0.9 gas dioxide (gas) mixing Example 3
Foaming Carbon 0.2 3.0 2.0 1.5 B A B 0.9 gas dioxide (gas) mixing
Example 4 Foaming Nitrogen 0.5 4.0 2.0 2 A B A 0.9 gas (gas) mixing
Example 5 Foaming Carbon 0.7 4.2 2.0 2.1 A B A 0.8 gas dioxide +
mixing Nitrogen (gas) Example 6 Foaming Air (gas) 0.7 4.0 2.0 2 A A
A 0.8 gas mixing Comparative Foaming Carbon 10 6.2 2.0 3.1 B C A
0.4 Example 1 gas dioxide (gas) mixing Comparative Foaming Nitrogen
10 6.4 2.0 3.2 B D A 0.4 Example 2 gas (gas) mixing Comparative
Chemical Sodium -- 3.2 2.0 1.6 A B C 1.0 Example 3 foaming
bicarbonate
[0090] In the foaming status shown in Table 1, A denotes excellent
foaming with fine bubbles in aggregates, and B denotes the presence
of coarse bubbles. In the appearance, A denotes an excellent
appearance having a lesser number of swirl marks and silver
streaks, B denotes a slightly large number, C denotes a large
number, and D denotes a very large number of swirl marks and silver
streaks. In the flexibility, A denotes excellent, B denotes
slightly stiff, and C denotes stiff. The relative plasticizing
capacity in Table 1 is the plasticizing capacity (kg/h) relative to
that of the comparative example 3, which is taken as 1.0.
[0091] The results shown in Table 1 demonstrated that a molded
product having an excellent foaming status, an excellent
appearance, and high flexibility can be manufactured by a
multilayer-molding method of molding thermoplastic resins according
to the present invention, without a significant reduction in
plasticizing capacity.
INDUSTRIAL APPLICABILITY
[0092] A multilayer-molding method of molding thermoplastic resins
and a multilayer-molding apparatus according to the present
invention can be utilized as means for manufacturing any
multilayer-molded product. In particular, a multilayer-molding
method of molding thermoplastic resins and a multilayer-molding
apparatus according to the present invention can suitably be
utilized as means for manufacturing products that require both high
appearance quality and rigidity, for example, two-wheeled vehicle
parts, automobile parts, household electrical appliances, and home
equipment parts.
* * * * *