U.S. patent application number 10/179875 was filed with the patent office on 2003-01-02 for method and apparatus for supplying resin material to injection molder, and foamed product.
This patent application is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Arai, Takashi.
Application Number | 20030001303 10/179875 |
Document ID | / |
Family ID | 19038243 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030001303 |
Kind Code |
A1 |
Arai, Takashi |
January 2, 2003 |
Method and apparatus for supplying resin material to injection
molder, and foamed product
Abstract
This invention has as its object to provide a method of
supplying a resin material to an injection molder with which cells
can be uniformly dispersed in a molded product. In order to achieve
this object, the method includes the absorbing step of placing a
resin material in a pressurized inert gas in a pressure vessel and
allowing the resin material to absorb the inert gas, and the
supplying step of supplying the resin material which has absorbed
the inert gas to an injection molder.
Inventors: |
Arai, Takashi; (Ibaraki,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
19038243 |
Appl. No.: |
10/179875 |
Filed: |
June 26, 2002 |
Current U.S.
Class: |
264/50 ; 264/101;
264/328.17; 425/4R; 425/542 |
Current CPC
Class: |
B29C 44/3453 20130101;
B29C 44/3442 20130101 |
Class at
Publication: |
264/50 ; 264/101;
425/4.00R; 425/542; 264/328.17 |
International
Class: |
B29C 044/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 2001 |
JP |
2001-201244 |
Claims
What is claimed is:
1. A method of supplying a resin material to an injection molder,
comprising: the absorbing step of placing a resin material in a
pressurized inert gas in a pressure vessel and allowing the resin
material to absorb the inert gas; and the supplying step of
supplying the resin material which has absorbed the inert gas to an
injection molder.
2. The method according to claim 1, comprising the steps of:
charging the resin material into the pressure vessel before the
absorbing step; reducing a pressure in the pressure vessel; and
introducing a predetermined amount of alcohol-based solvent into
the pressure vessel.
3. The method according to claim 1, further comprising the step of
controlling an interior of the pressure vessel to a predetermined
temperature before the absorbing step.
4. The method according to claim 1, wherein, in the absorbing step,
an interior of the pressure vessel is held to a predetermined
pressure to allow the resin material to absorb the inert gas.
5. An apparatus for supplying a resin material to an injection
molder, comprising: extracting means for extracting an inert gas
from an atmosphere; pressurizing means for pressurizing the inert
gas extracted by said extracting means; a pressure vessel for
storing a resin material and the pressurized inert gas; and
supplying means for supplying the resin material from the pressure
vessel to an injection molder.
6. The apparatus according to claim 5, wherein a pressure of the
inert gas in said pressure vessel falls within a range of 0.5 MPa
to 6 MPa.
7. The apparatus according to claim 5, further comprising
temperature controlling means for controlling a temperature of said
pressure vessel.
8. The apparatus according to claim 7, wherein the temperature in
said pressure vessel is less than a thermal deformation temperature
of the resin material, and the resin is maintained in a solid
state.
9. An apparatus for supplying a resin material to an injection
molder, comprising: extracting means for extracting an inert gas
from an atmosphere; pressurizing means for pressurizing the inert
gas extracted by said extracting means; a pressure vessel for
storing the resin material and the pressurized inert gas;
introducing means for introducing a liquid to said pressure vessel;
and supplying means for supplying the resin material from the
pressure vessel to an injection molder.
10. The apparatus according to claim 9, wherein a pressure of the
inert gas in said pressure vessel falls within a range of 0.5 MPa
to 6 MPa.
11. The apparatus according to claim 9, further comprising
temperature controlling means for controlling a temperature of said
pressure vessel.
12. The apparatus according to claim 11, wherein the temperature in
said pressure vessel is less than a thermal deformation temperature
of the resin material, and the resin is maintained in a solid
state.
13. The apparatus according to claim 9, wherein the liquid is a
predetermined solution.
14. The apparatus according to claim 9, wherein the liquid is an
alcohol-based liquid.
15. A foam molding product molded by using the method of supplying
a resin material to an injection molder according to claim 1.
16. A foam molding product molded by using the apparatus for
supplying a resin material to an injection molder according to
claim 5.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus
which are used in foam molding using an inert gas as a foaming
agent to supply a resin material to an injection molder, and a
foamed product.
BACKGROUND OF THE INVENTION
[0002] Foam molding has a long history. A technique for obtaining a
resin foamed product by injection molding is disclosed in, e.g.,
U.S. Pat. Nos. 3,268,639 and 3,384,691. In recent years, a foam
molding method using a chemical or physical foaming agent can be
learned from textbooks on synthetic resin molding.
[0003] Conventional foam molding has a very high foaming
magnification, as is known in foamed styrol, and is accordingly
excellent in weight reduction, but lacks mechanical strength. With
a chemical foaming agent, a master batch scheme with which a
thermally decomposable foaming material and a resin material are
mixed immediately before molding is often employed. This leads to
many problems such as harmfulness, mold corrosion, degradation in
molding environment, and handling difficulty.
[0004] Regarding this, U.S. Pat. No. 3,796,779 proposes a foam
which is obtained by blowing an inert gas such as carbon dioxide
gas into a molten resin material directly so the gas is penetrated
into the resin, and cooling the resultant resin. Since an inert gas
is used as the foaming agent, harmfulness, mold corrosion,
degradation in molding environment, handling difficulty, and the
like are solved.
[0005] In U.S. Pat. No. 3,796,779 as well, since the gas is
directly blown to the molten resin, the resin and the gas are not
uniformly mixed, and an island structure with various cell shapes
is formed. Then, the strength of the mixture becomes partially low.
In this manner, it is very difficult to control the foaming
state.
[0006] In order to solve these problems, a method of forming a very
small foam called a microcell was found at Massachusetts Institute
of Technology, USA early 1980. This method and an apparatus for it
are disclosed in U.S. Pat. Nos. 4,473,665, 5,158,986, 5,160,674,
5,334,356, 5,571,848, and 5,866,053. According to the method and
apparatus proposed by Massachusetts Institute of Technology, USA, a
supercritical inert gas is blown to that portion of the plasticizer
of an injection molder where a resin is to be fused. The
sufficiently molten resin and the gas are mixed by a static mixer.
The pressure and temperature are controlled. Consequently, a large
number of small cells with a size of 25 .mu.m or less are uniformly
dispersed in a resultant foamed product. As the cell size is small,
according to these references, a foamed product substantially free
from strength degradation can be obtained.
[0007] To improve the quality of the outer appearance of the foamed
product, the following method is known. That is, when a resin is to
be injected into a mold, the mold is filled with a gas in advance
so the interior of the mold is pressurized to be equal to or higher
than the atmospheric pressure. The resin is injected to fill the
mold completely. After that, the gas pressure applied to the
interior of the mold is released, so the gas in the resin allows
foaming upon pressure reduction.
[0008] According-to the conventional method, the gas is directly
blown into the molten resin material. When the gas is blown, that
portion of the molten resin which comes into contact with the gas
is quickly cooled. If the gas is blown continuously, a large part
of the molten resin is cooled. As a result, the viscosity
increases, and it takes time to restore a resin temperature and
viscosity suitable for molding.
[0009] When the gas is heated to near the melt temperature of the
resin in advance, as the temperature increases, the volume of the
gas increases. If the gas with the increased volume is blown into
the resin, as the gas pressure in the resin is low, the foaming
magnification after the resin is filled in the mold is very
low.
[0010] In order to compensate for these defects, a method is
available with which the temperature of the gas is increased and
simultaneously the pressure is increased. While the gas
concentration is maintained, the gas is blown into the molten
resin. In this case, the pressure of the gas is very high, and the
gas flows into the resin instantaneously when it is blown into the
resin. Hence, it is difficult to control the gas blow amount. Since
the gas is abruptly blown into the molten resin, the blown molten
resin forms two separate layers of the gas and resin. To uniformly
disperse the gas in the resin, kneading must be mechanically
repeated by a static mixer or the like again. As a result, the
apparatus becomes complicated, and the cycle is prolonged, so the
productivity is impaired.
[0011] Originally, a plasticizer in an injection molder or extruder
applies a certain degree of pressure to the molten resin in order
to remove air in the material or during metering. If a gas is blown
into the molten resin in the conventional manner and metering is
performed, the blown gas may be undesirably discharged to the
metering zone side of the plasticizer before it is dissolved in the
resin completely.
[0012] According to the method described above, when the resin is
to be injected into the mold, the mold is filled with the gas in
advance so the interior of the mold is pressurized to be equal to
or higher than the atmospheric pressure. After the resin is filled
in the mold, the gas pressure is released. With this method, when
the filling speed is high, the pressure of the gas filled in the
mold cannot be controlled, and accordingly the filled gas serves as
an obstacle to cause a short shot. When the filling speed of the
resin is decreased, the gas that fills the mold can be controlled,
so pressure control during and after resin filling can be
performed. However, as the filling speed is low, that surface of
the resin which is in contact with the mold is cooled by the mold
and solidified to form a large skin layer. For this reason, in the
foaming distribution of the foamed product, the foaming difference
becomes very large between the surface and the center in the
direction of thickness and between a portion in the vicinity of the
gate and the finally filled portion.
[0013] According to the so-called master batch scheme, pellets
containing a thermally decomposable chemical foaming material and
pellets not containing a foaming material are mixed immediately
before molding. With this scheme, it is very difficult to uniformly
disperse the chemical foaming material during plasticization.
Consequently, cells formed in the foamed product are dispersed
nonuniformly, and a sufficient strength and precision cannot be
obtained.
SUMMARY OF THE INVENTION
[0014] The present invention has been made in view of the problems
described above, and has as its object to provide a method and
apparatus for supplying a resin material to an injection molder
which can uniformly disperse cells in a foamed product, and to
provide a foamed product.
[0015] In order to solve the above problems and to achieve the
above object, a method of supplying a resin material to an
injection molder according the present invention is characterized
by the following process.
[0016] More specifically, the method comprises the absorbing step
of placing a resin material in a pressurized inert gas in a
pressure vessel and allowing the resin material to absorb the inert
gas, and the supplying step of supplying the resin material which
has absorbed the inert gas to an injection molder.
[0017] According to the first aspect of the present invention, an
apparatus for supplying a resin material to an injection molder is
characterized by the following arrangement.
[0018] More specifically, the apparatus comprises extracting means
for extracting an inert gas from an atmosphere, pressurizing means
for pressurizing the inert gas extracted by the extracting means, a
pressure vessel for storing a resin material and the pressurized
inert gas, and supplying means for supplying the resin material
from the pressure vessel to an injection molder.
[0019] According to the second aspect of the present invention, an
apparatus for supplying a resin material to an injection molder is
characterized by the following arrangement.
[0020] More specifically, the apparatus is characterized by
comprising extracting means for extracting an inert gas from an
atmosphere, pressurizing means for pressurizing the inert gas
extracted by the extracting means, a pressure vessel for storing
the resin material and the pressurized inert gas, introducing means
for introducing a liquid to the pressure vessel, and supplying
means for supplying the resin material from the pressure vessel to
an injection molder.
[0021] A foamed product according to the present invention is
characterized in that it is foamed by using the above method or
apparatus for supplying a resin material to an injection
molder.
[0022] Other objects and advantages besides those discussed above
shall be apparent to those skilled in the art from the description
of a preferred embodiment of the invention which follows. In the
description, reference is made to accompanying drawings, which form
a part hereof, and which illustrate an example of the invention.
Such example, however, is not exhaustive of the various embodiments
of the invention, and therefore reference is made to the claims
which follow the description for determining the scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a view showing an apparatus according to an
embodiment of the present invention;
[0024] FIG. 2 is a timing chart showing the operation of the
apparatus;
[0025] FIG. 3 is a detailed view of the interior of a pressure
vessel;
[0026] FIG. 4 is a detailed view of a pressure vessel portion;
[0027] FIG. 5 is a table showing processing conditions employed
when processing is performed with the apparatus shown in FIG. 1;
and
[0028] FIG. 6 is a photograph showing the state of cells of a
section of a molded product.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] A preferred embodiment of the present invention will be
described.
[0030] The first characteristic feature of this embodiment resides
in that it uses an inert gas as a foaming material. Preferably, the
foaming material is carbon dioxide gas, nitrogen, argon gas, or the
like. As the inert gas is used, harmfulness and undesired influence
on the environment are prevented while safety is maintained.
[0031] The second characteristic feature resides in that the
foaming material is penetrated into a solid-state resin material at
a temperature less than a thermal deformation temperature. This
solves the conventional problem described above which occurs when
the foaming material is mixed in the molten resin.
[0032] The third characteristic feature resides in that the inert
gas is penetrated into the resin by pressurization. When
pressurization is performed to a predetermined pressure, the
penetration speed of the inert gas into the resin material can be
increased, so the productivity can be improved.
[0033] The fourth characteristic feature resides in that a solution
is evaporated to come into contact with the resin material, and
after that the inert gas is penetrated into the resin material.
This can remarkably increase the penetration speed and penetration
depth of the inert gas into the resin material, so the productivity
and cell formation state (cell population and dispersion
properties) are improved.
[0034] The fifth characteristic feature resides in that the resin
material is held in an appropriate humidity, and after that the
inert gas is penetrated into the resin material. Since an
appropriate water content is adsorbed by the resin material, the
penetration speed of the inert gas into the resin material can be
increased. This is very effective for resins except a hydrolyzable
resin such as polycarbonate.
[0035] One embodiment of the present invention will be described in
detail.
[0036] FIG. 1 is a view showing the arrangement of a foam molding
apparatus according to an embodiment of the present invention.
Referring to FIG. 1, reference numeral 1 denotes a high-pressure
gas manufacturing unit; 2, pressure vessels; 3, a gas manufacturing
unit; 4, agitators; 5, a solenoid valve; 6, a solution supply unit;
7, a supply pump; 8, an injection molder; 9, a hopper; 10, a
material silo; and 11, a material feeder. The gas manufacturing
unit 3 has the function of extracting an inert gas from the
atmosphere.
[0037] The operation will be described with reference to FIG.
1.
[0038] Usually, a resin material is carried by a tank truck or in a
25-kg resin bag, and is stored in the material silo 10. The
material stored in the material silo 10 is fed by the material
feeder 11 to the pressure vessels 2 through material feed pipes and
solenoid valves. The pressure vessels 2 are connected to the
high-pressure gas manufacturing unit 1 by pipes through solenoid
valves. When a predetermined amount of material is supplied to the
pressure vessels 2, the solenoid valves of the pressure vessels 2
are closed, and the high-pressure gas manufacturing unit 1 supplies
an inert gas to the pressure vessels 2.
[0039] When the pressures of the inert gas in the pressure vessels
2 rise to predetermined values, the solenoid valves are closed.
This state is maintained for a predetermined period of time, so the
inert gas is penetrated into the resin material. The pressure
vessels 2 incorporate agitating plates connected to the agitators
4. The agitating plates are constantly rotated at a predetermined
rotational speed, thereby agitating the material. The temperature
in each pressure vessel 2 is controlled by a heater 25 and
temperature controller 26 (see FIG. 3) in accordance with the type
of the material. Usually, the temperature is managed between
25.degree. C. and 35.degree. C. The pressure is 4 MPa to 6 MPa, and
the process time is about 2 hrs.
[0040] As shown in FIG. 1, the apparatus according to this
embodiment has a plurality of pressure vessels. When a preset time
elapses, an appropriate amount of the resin material is transferred
to a pressure vessel 2C. The transfer amount is determined by the
capacity of the hopper 9 provided to the injection molder, the
weight of the foamed product per shot, and the molding cycle.
Usually, a resin amount corresponding in molding time to about 30
min is transferred. Although the capacity of the pressure vessel 2C
is smaller than those of pressure vessels 2A and 2B, its inner
pressure is managed and controlled in the same manner as those of
the pressure vessels 2A and 2B. When the material is to be
transferred from the pressure vessel 2A or 2B to the pressure
vessel 2C, the outlet solenoid valve of the pressure vessel 2C is
closed, to prevent the pressure in the pressure vessel 2A or 2B
from dropping to the atmospheric pressure.
[0041] When the resin material is to be transferred from the
pressure vessel 2C to the hopper 91 the solenoid valve 5 between
the pressure vessel 2A or 2B and the pressure vessel 2C is closed.
The high-pressure gas in the pressure vessel 2C is mostly recovered
once by the high-pressure gas manufacturing unit 1. Usually, the
resin material processed in the pressure vessel 2A or 2B at 6 MPa
for about 2 hrs is transferred to the pressure vessel 2C and then
sequentially to the hopper 9, plasticized by the injection molder
8, and injected into a mold to form a resin foamed product.
[0042] FIG. 2 is a timing chart showing the outline of the
operation of the apparatus according to this embodiment.
[0043] In FIG. 2, "pressure vessels A, B, and C" respectively
indicate changes of the pressures in the pressure vessels 2A, 2B,
and 2C over time, and "hopper" indicates the resin amount in the
hopper 9. Arrows in FIG. 2 show the transfer flow of the resin
material.
[0044] The material is transferred from the pressure vessel 2B to
the pressure vessel 2C once every 30 min, and then to the hopper 9.
The resin amount in the hopper 9 fluctuates between 20% and 100%.
When transfer is performed four times, that is, a total of 2 hrs
elapses, the pressure vessel 2B stops supply to the pressure vessel
2C, and the material is supplied from the pressure vessel 2A to the
pressure vessel 2C. A new resin material is supplied from the
material feeder 11 to the pressure vessel 2B, and is pressurized
again at 6 MPa for 2 hrs. In other words, supply of material to the
pressure vessel 2C is performed by the pressure vessels 2A and 2B
alternately at a certain period of interval time (2 hrs in this
case).
[0045] FIG. 3 shows the interior of the pressure vessel 2 of this
embodiment in detail.
[0046] Referring to FIG. 3, reference numeral 12 denotes an
agitating plate; 13, a pressure gauge; 14, a safety valve; 15, an
inert gas; 16, an exhaust solenoid valve; 17, a solution supply
port solenoid valve; 18, a pipe connected to the pressure vessel 2;
19, a pipe connected to the material feeder 11; 20, a pipe
connected to the high-pressure gas manufacturing unit; 21, a gas
inlet solenoid valve; 22, a pipe connected to the high-pressure gas
manufacturing unit 1; 23, a section showing the interior of the
pressure vessel 2; 24, a resin material; 25, the heaters and 26,
the temperature controller.
[0047] The operation will be described with reference to FIG.
3.
[0048] The resin material 24 is stored in the pressure vessels 2,
and is agitated by rotation of the agitator 4 and agitating plate
12. Hence, the entire surface of the resin material 24 comes into
contact with the inert gas 15, so the inert gas 15 is uniformly
penetrated into the resin material pellets. Usually, rotation with
a comparatively low rotational speed of 10 rpm to 30 rpm is
employed.
[0049] The solution supply unit 6 is attached to the pressure
vessel 2 through the solution supply port solenoid valve 17. The
solution supply unit 6 incorporates a solution tank, a metering
unit, and an injection unit, and can supply only a preset amount of
the solution into the pressure vessel 2. In the case of a PPE resin
material, 3 cc to 5 cc of isopropyl alcohol are supplied to a 200-L
pressure vessel.
[0050] The solution supplied from the solution supply unit 6
gasifies in the pressure vessel 2 by a pressure reducing unit
having a vacuum pump 27 shown in FIG. 4, to uniformly penetrate
into the resin material. The pressure in the pressure vessel 2
during pressurization is monitored by the pressure gauge 13. When
the pressure increases to a specified value or more, the safety
valve 14 operates to reduce the pressure to the specified
value.
[0051] As the penetration speed and amount of the inert gas into
the resin material change depending on the pressure, time, and
temperature, the temperature of the pressure vessel 2 is controlled
by the heater 25 and temperature controller 26 to a predetermined
value. This temperature is less than the thermal deformation
temperature of the resin material, and the resin material is
maintained in the solid state. Hence, the inert gas is uniformly
penetrated into the resin material.
[0052] FIG. 4 is a detailed view of the pressure vessel portion of
this embodiment, in which reference numeral 27 denotes the vacuum
pump; and 28, a vacuum pump solenoid vale.
[0053] The operation will be described with reference to FIG.
4.
[0054] As described above, after the resin material is charged into
the pressure vessel 2, the interior of the pressure vessel 2 is set
in a reduced pressure state by the vacuum pump 27. After that, the
solution supply port solenoid valve 17 is opened, and the solution
is supplied to the pressure vessel 2 and agitated for a
predetermined period of time. When the predetermined agitating time
has elapsed, the gas inlet solenoid valve 21 is opened to supply
the inert gas. During pressure increase, all the solenoid valves
are closed except for the one on the inert gas supply line. When
the pressure increases to a specified value, the gas inlet solenoid
valve 21 is also closed. When the process is performed for a
predetermined period of time, a solenoid valve 5b is opened, so the
resin material is fed to the pressure vessel 2C.
[0055] FIG. 5 shows processing conditions employed when processing
is performed with the apparatus shown in FIG. 1 of this embodiment,
and FIG. 6 shows the state of cells of a section of the resultant
foamed product.
[0056] As described above, according to the above embodiment, the
resin material is set in a high-pressure inert gas while it is
being agitated in the pressure vessel. This allows the inert gas to
penetrate uniformly into the resin material. The plurality of
pressure vessels are sequentially switched at a predetermined
interval, and the gas-penetrated material is fed to them.
Therefore, the foaming resin material can be supplied stably.
[0057] According to this embodiment, as described above, since the
inert gas is not injected into the molten resin material, the gas
and resin are mixed uniformly during plasticization of the resin
material. Since all the resin pellets uniformly contain the gas,
nonuniform dispersion of the foaming material (gas) for cell
formation, which poses an issue in the conventional master batch
scheme, is solved. Conventionally, the productivity is poor because
of the low dissolution rate of the inert gas into a solid resin
material. Regarding this, the dissolution rate increases remarkably
because of the use of an alcohol-based solution and humidity
management, which are the characteristic features of this
embodiment. Also, partly because of foaming resin interval supply,
which is described earlier, by the plurality of pressure vessels as
well, the productivity is improved remarkably.
[0058] In other words, according to this embodiment, the inert gas
as the foaming material can be uniformly dissolved and dispersed in
the resin material, and the productivity is improved remarkably.
According to the conventional method described above, a gas is
blown into a molten resin by attaching a gas injection unit to the
cylinder of the injection molder. When compared to this
conventional method, according to this embodiment, the conventional
(existing) injection molder need not be modified at all. This is
effective in capital investment as well.
[0059] As has been described above, according to the above
embodiment, cells can be uniformly dispersed in the foamed
product.
[0060] The present invention is not limited to the above
embodiments and various changes and modifications can be made
within the spirit and scope of the present invention. Therefore, to
apprise the public of the scope of the present invention the
following claims are made.
* * * * *