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Claims  |
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What is claimed is:
1. A method for producing a biodegradable resin foam comprising the steps
of:
arranging an air-permeable forming mold in front of a cylinder formed at a
front portion thereof with a narrowed opening
charging a biodegradable resin starting material containing biodegradable
resin and moisture in the cylinder;
raising a temperature of the biodegradable resin to fluidize the
biodegradable resin while forcibly transferring the biodegradable resin
starting material toward the narrowed opening in the cylinder;
extruding the fluidized biodegradable resin from the cylinder into the
air-permeable forming mold to rapidly release the biodegradable resin from
a heated and pressurized environment in the cylinder to foam the
biodegradable resin by an expansion force caused by vaporization of the
moisture resulting from rapidly releasing fluidized biodegradable resin
which is in a heated and pressurized environment and in which the moisture
is trapped; and
forming the foamed biodegradable resin into a shape depending on a
configuration of the forming mold.
2. A method as defined in claim 1, wherein an atmosphere in which the
forming mold is placed is kept decreased in pressure or ventilated since a
stage before starting of extrusion of the fluidized biodegradable resin
into the forming mold or since starting of the extrusion.
3. A method as defined in claim 1, wherein the step of extruding the
fluidized biodegradable resin into the forming mold is carried out while
placing a nozzle arranged with respect to said narrowed opening in the
depths of the forming mold at the time of starting of the nozzle and
retracting the nozzle relative to the forming mold during extrusion of the
biodegradable resin.
4. A method as defined in claim 2, wherein the step of extruding the
fluidized biodegradable resin into the forming mold is carried out while
placing a nozzle arranged with respect to said narrowed opening in the
depths of the forming mold at the time of starting of the nozzle and
retracting the nozzle relative to the forming mold during extrusion of the
biodegradable resin.
5. A method as defined in claim 1, wherein the step of extruding the
fluidized biodegradable resin into the forming mold is carried out while
keeping an atmosphere in the forming mold pressurized during the extrusion
and rapidly reducing a pressure in the atmosphere in the forming mold
after completion of the extrusion.
6. A method as defined in claim 3, wherein the step of extruding the
fluidized biodegradable resin into the forming mold is carried out while
keeping an atmosphere in the forming mold pressurized during the extrusion
and rapidly reducing a pressure in the atmosphere in the forming mold
after completion of the extrusion.
7. A method as defined in claim 1, wherein the step of extruding the
fluidized biodegradable resin into the forming mold is carried out by
injecting the biodegradable resin into the forming mold while keeping the
resin atomized.
8. A method as defined in claim 2, wherein the step of extruding the
fluidized biodegradable resin into the forming mold is carried out by
injecting the biodegradable resin into the forming mold while keeping the
resin atomized.
9. A method as defined in claim 3, wherein the step of extruding the
fluidized biodegradable resin into the forming mold is carried out by
injecting the biodegradable resin into the forming mold while keeping the
resin atomized.
10. A method as defined in claim 5, wherein the step of extruding the
fluidized biodegradable resin into the forming mold is carried out by
injecting the biodegradable resin into the forming mold while keeping the
resin atomized.
11. A method as defined in claim 1, wherein the biodegradable resin
starting material comprises said biodegradable resin and a hygroscopic
fine-particle material having moisture absorbed therein and added to said
biodegradable resin.
12. A method as defined in claim 2, wherein the biodegradable resin
starting material comprises said biodegradable resin and a hygroscopic
fine-particle material having moisture absorbed therein and added to said
biodegradable resin.
13. A method as defined in claim 3, wherein the biodegradable resin
starting material comprises said biodegradable resin and a hygroscopic
fine-particle material having moisture absorbed therein and added to said
biodegradable resin.
14. A method as defined in claim 5, wherein the biodegradable resin
starting material comprises said biodegradable resin and a hygroscopic
fine-particle material having moisture absorbed therein and added to said
biodegradable resin.
15. A method as defined in claim 7, wherein the biodegradable resin
starting material comprises said biodegradable resin and a hygroscopic
fine-particle material having moisture absorbed therein and added to said
biodegradable resin.
16. A method as defined in claim 1, wherein the biodegradable resin
starting material comprises moisture, said biodegradable resin and a water
repellent material.
17. A method as defined in claim 2, wherein the biodegradable resin
starting material comprises moisture, said biodegradable resin and a water
repellent material.
18. A method as defined in claim 3, wherein the biodegradable resin
starting material comprises moisture, said biodegradable resin and a water
repellent material.
19. A method as defined in claim 5, wherein the biodegradable resin
starting material comprises moisture, said biodegradable resin and a water
repellent material.
20. A method as defined in claim 7, wherein the biodegradable resin
starting material comprises moisture, said biodegradable resin and a water
repellent material.
21. A method as defined in claim 1, wherein the step of forming the foamed
biodegradable resin into a shape depending on a configuration of the
forming mold is carried out by forming the whole biodegradable resin into
an integrated configuration.
22. A method as defined in claim 2, wherein the step of forming the foamed
biodegradable resin into a shape depending on a configuration of the
forming mold is carried out by forming the whole biodegradable resin into
an integrated configuration.
23. A method as defined in claim 3, wherein the step of forming the foamed
biodegradable resin into a shape depending on a configuration of the
forming mold is carried out by forming the whole biodegradable resin into
an integrated configuration.
24. A method as defined in claim 5, wherein the step of forming the foamed
biodegradable resin into a shape depending on a configuration of the
forming mold is carried out by forming the whole biodegradable resin into
an integrated configuration.
25. A method as defined in claim 7, wherein the step of forming the foamed
biodegradable resin into a shape depending on a configuration of the
forming mold is carried out by forming the whole biodegradable resin into
an integrated configuration.
26. A method as defined in claim 1, wherein the biodegradable resin
comprises a first biodegradable resin ingredient having a melting point of
100.degree. C. or more and a second biodegradable resin ingredient having
a melting point of 100.degree. C. or less.
27. A method as defined in claim 2, wherein the biodegradable resin
comprises a first biodegradable resin ingredient having a melting point of
100.degree. C. or more and a second biodegradable resin ingredient having
a melting point of 100.degree. C. or less.
28. A method as defined in claim 3, wherein the biodegradable resin
comprises a first biodegradable resin ingredient having a melting point of
100.degree. C. or more and a second biodegradable resin ingredient having
a melting point of 100.degree. C. or less.
29. A method as defined in claim 5, wherein the biodegradable resin
comprises a first biodegradable resin ingredient having a melting point of
100.degree. C. or more and a second biodegradable resin ingredient having
a melting point of 100.degree. C. or less.
30. A method as defined in claim 7, wherein the biodegradable resin
comprises a first biodegradable resin ingredient having a melting point of
100.degree. C. or more and a second biodegradable resin ingredient having
a melting point of 100.degree. C. or less.
31. A method as defined in claim 26, wherein the second biodegradable resin
ingredient is selected from the group consisting of polycaprolactone and a
material containing it.
32. A method as defined in claim 27, wherein the second biodegradable resin
ingredient is selected from the group consisting of polycaprolactone and a
material containing it.
33. A method as defined in claim 28, wherein the second biodegradable resin
ingredient is selected from the group consisting of polycaprolactone and a
material containing it.
34. A method as defined in claim 29, wherein the second biodegradable resin
ingredient is selected from the group consisting of polycaprolactone and a
material containing it.
35. A method as defined in claim 30, wherein the second biodegradable resin
ingredient is selected from the group consisting of polycaprolactone and a
material containing it.
36. A method as defined in claim 1, wherein the biodegradable resin has a
substance selected from the group consisting of polyhydric alcohols and
derivatives thereof added thereto.
37. A method as defined in claim 2, wherein the biodegradable resin has a
substance selected from the group consisting of polyhydric alcohols and
derivatives thereof added thereto.
38. A method as defined in claim 3, wherein the biodegradable resin has a
substance selected from the group consisting of polyhydric alcohols and
derivatives thereof added thereto.
39. A method as defined in claim 5, wherein the biodegradable resin has a
substance selected from the group consisting of polyhydric alcohols and
derivatives thereof added thereto.
40. A method as defined in claim 7, wherein the biodegradable resin has a
substance selected from the group consisting of polyhydric alcohols and
derivatives thereof added thereto. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to biodegradable resin which has been recently
spotlighted in place of synthetic resin, and more particularly to a
biodegradable resin foam obtained by foaming the biodegradable resin and a
method and an apparatus for producing the same.
In general, synthetic resin has been applied to a variety of industrial
fields because of exhibiting satisfactory mass productivity, moldability
and durability. In particularly, a synthetic resin foam is light-weight
and exhibits increased cushioning properties, to thereby be widely used in
various forms such as a protective casing for a fragile article such as a
glass product, a cushioning material for packing, a tableware, a heat
insulation material, a sound insulation material and the like. However,
this causes the amount of disposal of such synthetic resin products to be
extensively increased, leading to various serious problems.
More particularly, incineration of synthetic resin causes a large amount of
harmful gas to be produced, leading to atmospheric pollution. Disposal of
synthetic resin other than the incineration causes environmental pollution
because it has resistance to oxidation and resistance to decomposition by
light and ozone. Also, synthetic resin is extensively increased in
intermolecular bond, so that the incineration causes generation of much
heat, leading to damage to an incineration furnace and therefore a
decrease in lifetime of the furnace.
In view of the foregoing, much attention has been recently directed to
biodegradable resin and a great effort has been made to develop
biodegradable resin.
As a result, processing of biodegradable resin into a film material is now
in the course of being put into practice. Also, development of foaming of
biodegradable resin would lead to spread of applications thereof, to
thereby permit advantages of biodegradable resin to be more widely
exhibited. Techniques of foaming synthetic resin which have been carried
out in the art include a method of producing foamed beads including the
steps of charging styrene beads in a forming mold and adding water vapor
thereto, followed by a decrease in pressure, a method of foaming synthetic
resin by charging an extruder with, for example, styrene resin together
with a foaming agent such as an organic solvent or the like to foam the
resin due to a pressure reducing action occurring when the resin is
extruded, and the like.
However, such conventional chemical foaming techniques for foaming
synthetic resin as described above fail to satisfactorily foam
biodegradable resin due to a relationship between a softening point or
melting point of the resin and a foaming temperature of a foaming agent
and the like. Thus, there are known many problems which are encountered
with techniques of foaming biodegradable resin to a high degree and
forming the foamed resin.
A first problem occurs when a biodegradable resin foam is to be produced by
means of, for example, an injection molding machine used for production of
a conventional synthetic resin foam. More particularly, when biodegradable
resin fluidized due to heating and pressurization in a cylinder is
extruded through a nozzle of the cylinder into a forming mold, to thereby
be decreased in pressure, moisture in the resin is vaporized, leading to
expansion. The moisture vaporized is then decreased in temperature,
resulting in suspending in the form of steam in the mold or being
condensed on an inner surface of the mold or an outer surface of a molded
product. Biodegradable resin generally exhibits increased hygroscopicity,
resulting in being readily softened and swollen when it is contacted wit
moisture. In particular, a film of each of foamed cells on an outer
portion of a molded or formed product is excessively decreased in
thickness, so that it is readily softened when it absorbs condensed water.
This results in the foamed cells being readily collapsed. Such collapse of
the cells is also caused due to re-adhesion of moisture evaporated from
the resin to the cells. The collapse causes portions of the formed product
at which the cells are collapsed to be shrunk, leading to deformation of
the formed product. When the formed product thus deformed is solidified,
it is caused to be in a solid form substantially free of any foamed cell.
Thus, the formed product thus obtained by injection molding fails to
exhibit desired cushioning performance.
A second problem is that the conventional chemical foaming techniques fail
to provide a foamed product having a desired configuration and exhibiting
a satisfactory cushioning function. More particularly, foaming of
biodegradable resin is started upon release from a pressurized state,
however, it is highly hard to reach the depths of a forming mold because
of exhibiting increased viscosity when it is fluidized by heating.
Therefore, foaming of biodegradable resin partially occurs before the
resin extruded from the cylinder reaches the depths of the forming mold,
resulting in a part of the resin which is to be foamed in the depths of
the mold carrying out foaming in the middle of the mold, so that any
cavity and/or void are formed in the foamed resin. Such a problem tends to
occur in a forming mold of a complicated configuration, Thus, the
so-formed biodegradable resin foam is pressedly forced by biodegradable
resin subsequently extruded, so that the portion of the resin which
carried out foaming on the way to the depths of the mold is crushed by the
subsequently extruded resin. Thus, the prior art fails to form the foamed
resin into a desired configuration. Also, the foamed resin fails to
exhibit a satisfactory cushioning performance.
A third problem occurs due to releasing of biodegradable resin fluidized by
heating and pressurizing from a heated and pressurized environment.
Releasing of the resin fluidized causes moisture contained in the resin to
be vaporized and expanded, resulting in foaming of the resin, to thereby
provide cells, during which the cells are decreased in temperature to a
level of about 100.degree. C. due to vaporization of the moisture. This
causes the cells to be somewhat shrunk and then solidified while being
kept shrunk. Also, the cells are somewhat shrunk by water vapor
surrounding the cells. Such cells are integrated together to form a foam.
Thus, cavities and/or voids occur in the foam solidified, so that
boundaries between the cells are discontinuous, to thereby cause the foam
to be unsuitable for use for a cushioning material.
A fourth problem encountered with the conventional chemical foaming
techniques is caused during formation of an pressure reduced atmosphere.
More particularly, when a heated and pressurized atmosphere in which
biodegradable resin is placed is to be changed into a pressure reduced
atmosphere, an evacuation or vacuum pump is generally used. Unfortunately,
formation of such a pressure reduced atmosphere requires a considerable
period of time, so that a pressure reducing action due to the change is
rendered slow or inactive. Also, this causes moisture to re-adhere to
cells while it is not fully exhausted, leading to softening of the cells,
followed by collapse of the cells, resulting in the resultant resin foam
being deteriorated in properties or quality. In order to prevent such
re-adhesion of moisture to the cells, it would be considered that
formation of the pressure reduced atmosphere is carried out using a
large-sized vacuum pump or the like, resulting in time required for
evacuation being reduced. However, this causes a significant increase in
manufacturing cost of the foam.
Further, injection of biodegradable resin from a nozzle of a cylinder of an
injection molding machine into a forming mold arranged in a closed
atmosphere causes injection resistance to be increased. In order to avoid
the problem, it is required to arrange a large-sized injection molding
machine. Unfortunately, this leads to an increase in cost of equipment and
therefore manufacturing cost. In particular, in order to form a foam with
high configuration accuracy, it is required to permit biodegradable resin
to be spread throughout the forming mold. This is advantageously
accomplished by keeping an atmosphere in the forming mold pressurized
during injection molding. However, this causes injection resistance to be
further increased, resulting in the above-described disadvantage being
rendered amplified.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing disadvantages
of the prior art.
Accordingly, it is an object of the present invention to provide a method
for producing a biodegradable resin foam which is capable of accomplishing
foaming of biodegradable resin while minimizing or substantially
preventing shrinkage of formed biodegradable resin due to re-adhesion of
moisture thereto, to thereby provide a uniform biodegradable resin foam.
It is another object of the present invention to provide a method for
producing a biodegradable resin foam which is capable of uniformly foaming
biodegradable resin.
It is a further object of the present invention to provide a method for
producing a biodegradable resin foam which is capable of minimizing or
substantially preventing collapse of cells of foamed biodegradable resin
to provide a biodegradable resin foam of a desired configuration and
uniform quality.
It is still another object of the present invention to provide a method for
producing a biodegradable resin foam which is capable of providing a
water-repellent biodegradable resin foam.
It is yet another object of the present invention to provide a method for
producing a biodegradable resin foam which is capable of providing a
biodegradable resin foam free of any discontinuous boundary between cells
even when any cavity and/or void occurs in biodegradable resin foamed.
It is even another object of the present invention to provide a
biodegradable resin foam which is substantially free of any discontinuous
boundary between cells even when any cavity and/or void occurs in
biodegradable resin foamed.
It is a still further object of the present invention to provide an
apparatus for producing a biodegradable resin foam which is capable of
preventing an increase in cost of equipment and accomplishing rapid
pressure reduction and evacuation of an atmosphere in a forming mold at an
appropriate timing, to thereby provide a biodegradable resin foam of
improved quality.
It is a yet further object of the present invention to provide an apparatus
for producing a biodegradable resin foam which is capable of preventing an
increase in cost of equipment and facilitating injection of biodegradable
resin into a forming mold while keeping injection resistance at a minimum
level, to thereby increase configuration accuracy of a biodegradable resin
foam.
In accordance with one aspect of the present invention, a biodegradable
resin foam is provided which is made of biodegradable resin by expansion
force due to vaporization of moisture caused by rapidly releasing
fluidized biodegradable resin which is in a heated and pressurized
environment and in which the moisture is trapped. The biodegradable resin
may comprise a combination of a first biodegradable resin ingredient
having a melting point of 100.degree. C. or more or a main biodegradable
resin ingredient and a second biodegradable resin ingredient having a
melting point of 100.degree. C. or less or a low-melting biodegradable
resin ingredient.
In a preferred embodiment of the present invention, the second
biodegradable resin ingredient may be selected from the group consisting
of polycaprolactone and a material containing polycaprolactone.
In a preferred embodiment of the present invention, the biodegradable resin
may have a substance selected from the group consisting of polyhydric
alcohols and derivatives thereof added thereto.
Thus, in the foam of the present invention, the second biodegradable resin
ingredient is kept from being immediately solidified, to thereby function
as an adhesive with respect to the first biodegradable resin ingredient.
Therefore, even when any cavity and/or void are unfortunately formed in
the foamed biodegradable resin, cells of the foamed resin are permitted to
adhere to each other through the second resin ingredient, resulting in the
foam being provided with satisfactory quality.
When the second biodegradable resin ingredient is selected from the group
consisting of polycaprolactone and a material containing polycaprolactone,
the function of the second biodegradable resin ingredient as an adhesive
is substantially enhanced. Also, when the biodegradable resin has
polyhydric alcohols and derivatives thereof added thereto, moisture in the
resin is increased in boiling point, resulting in functioning also as a
plasticizer, so that cells of the foamed biodegradable resin are rendered
dense and uniform.
In accordance with another aspect of the present invention, a method for
producing a biodegradable resin foam is provided. The method comprises the
steps of charging a biodegradable resin starting material containing
biodegradable resin in a cylinder formed at a front portion thereof with a
narrowed opening, raising a temperature of the biodegradable resin to
render the biodegradable resin fluidized while forcibly transferring the
biodegradable resin starting material toward the narrowed opening in the
cylinder, extruding the fluidized biodegradable resin from the cylinder
into an air-permeable forming mold arranged in front of the cylinder to
rapidly release the biodegradable resin from a heated and pressurized
environment in the cylinder to foam the biodegradable resin, and forming
the foamed biodegradable resin into a shape depending on a configuration
of the forming mold. Thus, moisture contained in the resin is increased in
boiling point under pressure, resulting in being in the form of liquid in
the cylinder, so that releasing of the resin from the heated and
pressurized environment in the cylinder causes the moisture to be
instantaneously vaporized, leading to foaming of the resin. The resultant
water vapor is outwardly discharged through the air-permeable forming
mold, to thereby be prevented from re-adhering to the formed foam.
In a preferred embodiment of the present invention, an atmosphere in which
the forming mold is placed is kept decreased in pressure or ventilated
since a stage before starting of extrusion of the fluidized biodegradable
resin into the forming mold or since starting of the extrusion. Such
construction prevents moisture from remaining in the form of steam in the
forming mold or being condensed on a surface of the resin foam due to a
decrease in temperature after vaporization and expansion of the moisture,
resulting in the form being provided with satisfactory uniformity.
In a preferred embodiment of the present invention, the step of extruding
the fluidized biodegradable resin into the mold is carried out while
placing a nozzle arranged with respect to the narrowed opening in the
depths of the forming mold at the time of starting of the nozzle and
retracting the nozzle relative to the forming mold during extrusion of the
biodegradable resin. This permits the biodegradable resin to be charged in
the forming mold in order from the side of the depths of the mold,
resulting in a difference between a timing at which the resin is spread
throughout the forming mold and a timing of foaming of the resin being
minimized or substantially eliminated, to thereby substantially prevent
cells of the foamed biodegradable resin from being collapsed.
In a preferred embodiment of the present invention, the step of extruding
the fluidized biodegradable resin into the forming mold is carried out
while keeping an atmosphere in the forming mold pressurized during the
extrusion and rapidly reducing a pressure of the atmosphere in the forming
mold after completion of the extrusion This permits the biodegradable
resin to be foamed while being spread throughout the forming mold, so that
the resin foam obtained is formed into a desired configuration.
In a preferred embodiment of the present invention, the step of extruding
the fluidized biodegradable resin into the forming mold is carried out by
injecting the biodegradable resin into the forming mold while keeping the
resin atomized. This permits not only the resin to be spread throughout
the forming mold but the atomized resin to be effectively foamed, followed
by integration of cells of the foamed resin without being collapsed, to
thereby provide the resin foam with increased uniformity.
In a preferred embodiment of the present invention, the biodegradable resin
starting material may comprise moisture and the biodegradable resin.
Alternatively, it may comprise the biodegradable resin and a hygroscopic
fine-particle material having moisture absorbed therein and added to the
biodegradable resin. Also, the biodegradable resin starting material may
comprise moisture, the biodegradable resin and a water repellent material.
The starting material of such composition ensures desired foaming of the
resin and permits it to be finely and uniformly foamed.
Also, the water repellent material may comprise a material which is not
fully evaporated when the resin fluidized is released from the heated and
pressurized environment. The material may include a natural fatty acid
polymer. Use of the polymer as the water repellent material permits it to
cover cells of the foamed resin to provide it with water repellent
properties, to thereby prevent the cells from being collapsed due to
contact with water.
In a preferred embodiment of the present invention, the step of forming the
foamed biodegradable resin into a shape depending on a configuration of
the forming mold may be carried out by forming the whole biodegradable
resin into an integrated configuration. This permits the resin foam to be
formed into a relative large volume or any desired configuration.
In a preferred embodiment of the present invention, the biodegradable resin
comprises a first biodegradable resin ingredient having a melting point of
100.degree. C. or more and a second biodegradable resin ingredient having
a melting point of 100.degree. C. or less.
In a preferred embodiment of the present invention, the second
biodegradable resin ingredient is selected from the group consisting of
polycaprolactone and a material containing it.
In a preferred embodiment of the present invention, the biodegradable resin
has a substance selected from the group consisting of polyhydric alcohols
and derivatives thereof added thereto.
In accordance with a further aspect of the present invention, an apparatus
for producing a biodegradable resin foam is provided. The apparatus
comprises a pressure adjusting chamber constructed in a manner to be
capable of being opened and closed hermetically, an air-permeable forming
mold arranged in the pressure adjusting chamber, a pressure reducing tank
connected to the pressure adjusting chamber to rapidly reduce a pressure
in the pressure adjusting chamber, and an injection machine for injecting,
into the forming mold, fluidized biodegradable resin placed in a heated
and pressurized environment and having moisture trapped therein. Thus, the
apparatus permits the pressure reducing tank to communicate with the
pressure adjusting chamber after injection of the resin into the forming
mold, so that water vapor produced in the forming mold may be effectively
outwardly discharged, to thereby eliminate retention of moisture in the
forming mold. Thus, the biodegradable resin foam product obtained is
provided with a desired configuration and uniform quality.
In a preferred embodiment of the present invention, the pressure adjusting
chamber has an evacuation valve connected thereto. Thus, when the pressure
adjusting chamber is rendered open to an ambient atmosphere in the course
of injection of the rein into the forming mold, resistance to the
injection is reduced because the forming mold is air-permeable, so that
the injection may be facilitated. Therefore, the injection machine is
prevented from being large-sized.
In a preferred embodiment of the present invention, the pressure adjusting
chamber has a compressor connected thereto. This permits injection of the
resin into the forming mold to be carried out while keeping moisture
positively trapped in the resin because actuation of the compressor
pressurizes the pressure adjusting chamber. Then, operation of the
evacuation valve results in the pressure adjusting chamber being released
from pressurization, leading to a decrease in injection resistance, so
that the resin may be spread throughout the forming mold.
In a preferred embodiment of the present invention, the pressure adjusting
chamber has a pressurizing tank connected thereto. This permits the
pressure adjusting chamber to be rapidly pressurized at an appropriate
timing when the resin is to be injected into the forming mold.
Also, in accordance with this aspect of the present invention, an apparatus
for producing a biodegradable resin foam is provided. The apparatus
comprises a pressure adjusting chamber constructed in a manner to be
capable of being opened and closed hermetically, an airpermeable forming
mold arraged in the pressure adjusting chamber, a pressure reducing tank
connected through a pressure reducing valve to the pressure adjusting
chamber to rapidly reduce a pressure in the pressure adjusting chamber, an
evacuation valve connected to the pressure adjusting chamber, a compressor
connected to the pressure adjusting chamber, a valve controller for
controlling operation of each of the valves, and an injection machine for
injecting, into the forming mold, fluidized biodegradable resin placed in
a heated and pressurized environment and having moisture trapped therein.
The valve controller functions to initiate actuation of the compressor
before or at the time when injection of the biodegradable resin into the
forming mold by the injection machine is started, carry out termination of
actuation of the compressor and opening of the evacuation valve in the
course of the injection, and carry out closing of the evacuation valve and
opening of the pressure reducing valve after the injection. Thus, the
pressure adjusting chamber may be controlled to pressurization, evacuation
or pressure reduction in association with a timing of injection of the
resin into the forming mold.
Further, in accordance with this aspect of the present invention, an
apparatus for producing a biodegradable resin foam is provided. The
apparatus comprises a pressure adjusting chamber constructed in a manner
to be capable of being opened and closed hermetically, an airpermeable
forming mold arranged in the pressure adjusting chamber, a pressure
reducing tank connected through a pressure reducing valve to the pressure
adjusting chamber to rapidly reduce a pressure in the pressure adjusting
chamber, an evacuation valve connected to the pressure adjusting chamber,
a pressurizing tank connected through a pressurizing valve to the pressure
adjusting chamber, a valve controller for controlling operation of each of
the valves, and an injection machine for injecting, into the forming mold,
fluidized biodegradable resin placed in a heated and pressurized
environment and having moisture trapped therein. The valve controller
functions to open the pressurizing valve before or at the time when
injection of the biodegradable resin into the forming mold by the
injection machine is started, carry out closing of the pressurizing valve
and opening of the evacuation valve in the course of the injection, and
carry out closing of the evacuation valve and opening of the pressure
reducing valve after the injection. Thus, the pressure adjusting chamber
is controlled to pressurization, evacuation or pressure reduction in
association with a timing of the injection.
In addition, in accordance with this aspect of the present invention, an
apparatus for producing a biodegradable resin foam is provided. The
apparatus comprises a pressure adjusting chamber constructed in a manner
to be capable of being opened and closed hermetically, an air-permeable
forming mold arranged in the pressure adjusting chamber, a pressure
reducing tank connected through a pressure reducing valve to the pressure
adjusting chamber to rapidly reduce a pressure in the pressure adjusting
chamber, an evacuation valve connected to the pressure adjusting chamber,
a valve controller for controlling operation of each of the valves, and an
injection machine for injecting, into the forming mold, fluidized
biodegradable resin placed in a heated and pressurized environment and
having moisture trapped therein. The valve controller functions to open
the evacuation valve in the course of injection of the biodegradable resin
into the forming mold by the injection machine and carry out closing of
the evacuation valve and opening of the pressure reducing valve after the
injection. Thus, the pressure adjusting chamber is controlled to
evacuation or pressure reduction in association with a timing of the
injection.
Furthermore, in accordance with this aspect of the present invention, an
apparatus for producing a biodegradable resin foam is provided. The
apparatus comprises a pressure adjusting chamber constructed in a manner
to be capable of being opened and closed hermetically, an air-permeable
forming mold arranged in the pressure adjusting chamber, a pressure
reducing tank connected through a pressure reducing valve to the pressure
adjusting chamber to rapidly reduce a pressure in the pressure adjusting
chamber, a pressurizing tank connected through a pressurizing valve to the
pressure adjusting chamber, a valve controller for controlling operation
of each of said valves, and an injection machine for injecting, into the
forming mold, fluidized biodegradable resin placed in a heated and
pressurized environment and having moisture trapped therein. The valve
controller functions to open the pressurizing valve before or at the time
when injection of the biodegradable resin into the forming mold by the
injection machine is started and carry out closing of the pressurizing
valve and opening of the evacuation valve after the injection. This
permits the pressure adjusting chamber to be controlled to pressurization
or pressure reduction in association with a timing of the injection.
In a preferred embodiment of the present invention, the injection machine
includes a cylinder having a narrowed opening formed at a front portion
thereof, a forcible transfer mechanism for forcibly transferring a
biodegradable resin starting material containing biodegradable resin and
charged in the cylinder and raising a temperature of the biodegradable
resin, to thereby fluidize it and extruding the fluidized biodegradable
resin through the narrowed opening into a forming mold, and an access
mechanism for reciprocating the narrowed opening and forming mold relative
to each other and retracting the narrowed opening relative to the forming
mold during injection of the fluidized biodegradable resin through the
narrowed opening into the forming mold.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and many of the attendant advantages of the present
invention will be readily appreciated as the same becomes better
understood by reference to the following detailed description when
considered in connection with the accompanying drawings; wherein:
FIG. 1 is a vertical sectional side elevation view generally showing an
example of an apparatus suitable for use for practicing an embodiment of a
method for producing a biodegradable resin foam according to the present
invention;
FIGS. 2(a) to 2(c) each are a schematic sectional view showing each of
steps of the method of FIG. 1;
FIG. 3 is a perspective view showing an embodiment of a biodegradable resin
foam according to the present invention;
FIG. 4 is a vertical sectional side elevation view showing an essential
part of another example of the apparatus suitable for use for practicing
the method of FIG. 1;
FIG. 5 is a vertical sectional side elevation view showing an essential
part of a further example of the apparatus suitable for use for practicing
the method of FIG. 1;
FIG. 6 is a vertical sectional side elevation view generally showing an
example of an apparatus suitable for use for practicing another embodiment
of a method for producing a biodegradable resin foam according to the
present invention;
FIGS. 7(a) to 7(c) each are a schematic sectional view showing each of
steps of the method of FIG. 6;
FIG. 8 is a vertical sectional side elevation view showing an essential
part of another example of the apparatus suitable for use for practicing
the method shown in FIG. 6;
FIG. 9 is a vertical sectional side elevation view generally showing an
example of an apparatus suitable for use for practicing a further
embodiment of a method for producing a biodegradable resin foam according
to the present invention;
FIGS. 10(a) to 10(c) each are a schematic sectional view showing each of
steps of the method of FIG. 9;
FIG. 11 is a vertical sectional side elevation view showing an essential
part of a further example of the apparatus suitable for use for practicing
the method shown in FIG. 9;
FIG. 12 is a vertical sectional side elevation view generally showing an
example of an apparatus suitable for use for practicing still another
embodiment of a method for producing a biodegradable resin foam according
to the present invention;
FIGS. 13(a) to 13(c) each are a schematic sectional view showing each of
steps of the method of FIG. 12;
FIG. 14 is a perspective view showing a modification of a nozzle arranged
with respect to a narrowed opening;
FIG. 15 is a perspective view showing a cylinder provided at a distal end
thereof with a shower;
FIG. 16 is a vertical sectional side elevation view showing an essential
part of another example of the apparatus suitable for use for practicing
the method of FIG. 12;
FIG. 17 is a vertical sectional side elevation view generally showing an
example of an apparatus suitable for use for practicing yet another
embodiment of a method for producing a biodegradable resin foam according
to the present invention;
FIGS. 18(a) and 18(b) each are a schematic sectional view showing each of
steps of the method of FIG. 17;
FIG. 19 is a perspective view showing another embodiment of a biodegradable
resin foam according to the present invention;
FIG. 20 is a vertical sectional side elevation view showing an essential
part of another example of the apparatus suitable for use for practicing
the method of FIG. 19;
FIG. 21 is a vertical sectional side elevation view generally showing an
embodiment of an apparatus for producing a biodegradable resin foam
according to the present in | | |
