Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR PRODUCING THER~OPLASTIC RESIN FO~
BACKGROUND OF THE INVENTION
This invention relates to an apparatus for
prod~lcing a thermoplastic resin foam.
It has been known that the thermoplastic resin
foam can be e~fectively produced, continuously~ by means
of an extrusion method. (Therefore, it has been usual
to use the extrusion method fox this purpose.) In this
case, in order to obtain a highly expanded foam, an
extrudate is usually introduced immediately into a vacuum
chamber connected to a die member of the extruder to
enhance the expansion of the foam under reduced pressure.
In such a case, the foam accomplished expansion is
produced continuously from the outlet of the vacuum
chamber. Therefore, it is necessary to prevent air from
being introduced into the reduced pressure device
through an annular gap possibly formed between an outer
surface of the foam and an inner wall of an outlet hole
of the vacuum chamber. In order to realize the preven-
tion of air immigration into the vacuum chamber, U.S.
Patent 3,822,331 discloses either a flexible flap on an
outer end wall of the chamber or a flexible ring packing
provided on an inner wall of the outlet hole of the
chamber which acts to prevent air from passing through
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an annular gap between -the inner wall of the hole and
the outer periphery of -the extruded resin foam.
The flexible packing is of natural or synthetic
rubber or sof-t resin and is provided so that it covers
the outlet hole of the chamber except a center portion
thereof through which the extruded resin passes against
a resilient force acting to minimize the open area of
the center portion. It has been found that such packing
provided in the outlet of the chamber is insufficient -to
provide a satisfactory air tightness thereof. That is,
during a run of foam expansion, the volume of the foam
increases at one variable rate and thus the cross-
sectional configuration and size of the foam are not
always constant. The packing itself cannot follow these
physical variations of the foam. ThereEore, it has been
desired to improve the air tightness of the outlet of
the vacuum chamber.
SUMMARY OF THE INVENTION
This invention was made in view of the above
mentioned state of the art.
In order to obtain a good air tightness of the
outlet and/or inlet of the vacuum chamber, the inventor
has developed a cylinder made from a flexible sheet
material which is disposed at the outlet and/or inlet of
the vacuum chamber such that the extruded resin foam
passes through the flexible cylinder.
3L.~234~
~ urther, an air chamber is provided around the
flexible cylinder so that, when pressurized air is
introduced into the air chamber, the flexible cylinder
is inflated radially inwardly to eliminate the annular
air gap between the outer surface of the extruded resin
foam and the in~er wall of the outlet and/or inlet hole
of the vacuum chamber.
It has been confirmed that the above air
shielding construction provides a good result. Therefore,
the present invention resides in an apparatus for
producing thermoplastic resin foam, comprising a series
connection of an extruder, a die and a vacuum chamber, the
~acuum chamber including a cylinder body and an air
shielding device provided at least one end of the
cylinder body, the air shielding device comprising an
annular tube having an inside wall formed of a flexible
sheet, the flexible sheet being capable of being inflated
radially inwardly by a pressurized fluid introduced into
the annular tube.
In the above construction of the apparatus, i~
is possible to maintain an interior of the vacuum chamber
at reduced pressure when the extruded resin foam is
slidingly moved over the surface of the flexible sheet.
However, the flexible sheet is abraded by the extruded
and foamed resin and easily worn out. Therefore, it is
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necessary to periodically replace the sheet with a new
one at short intervals of time. Since it is impossible
to use the vacuum chamber during the replacement of the
flexible sheet, the extrusion which operates inherently
continuously must be stopped. Thus, the fre~uent
replacement of the flexible sheet produces ne~J problems.
In order to resolve the problem, an improvement was made
on the basis of a fact that, by providing a protective
sheet such as a metal mesh which is durable against
abrasion on an outer surface of the flexible sheet which
is adapted to be in con-tact with the extruded resin foam
so that the protéctive sheet directly contacts with the
latter, it is possible to totally maintain the air tight-
ness with an improved abrasion durability of the sheet.
Therefore, the present invention resides also
in the apparatus as mentioned above, wherein a flexible
protective sheet is provided on the flexible sheet so
that the flexible sheet, together with the flexible
protective sheet, is inflated by a pressurized fluid
introduced into the air shielding device, with only the
protective sheet being in direct contact with the foamed
resin.
BRIEF DESCRIPTION OF THE DRAWINGS
The above mentioned apparatùs of the present
invention will be described with reference to the
accompanying drawings.
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Fig. 1 is a cross-sectional view showing an
embodiment of the present invention;
Fig. 2 is an enlarged cross-sectional view
taken along a line II-II in Fig. l;
Fig. 3 is a cross-sectional view of an air
shielding member and associated portion of another
embodiment of the present invention;
Fig. 4 is a cross-section taken along a line
IV-IV in Fig. 3; and
Figs. 5a, Sb, 6a, and 6b are cross-sections of
flexible sheets to be used in this invention, respec-
tively.
DETA LED DESCRIPTION OF THE PREFERRED E~BODIMENTS
In Figs. 1 and 2, a reference numeral 1 depicts
a die, 2 a si~ing die, 3 a connecting plate, 4 a vacuum
chamber, 5 a vacuum suction inlet, 6 a support for a
foamed resin, 7 a pressure regulator valve, 8 a connect-
ing plate, 9 an air-shielding device, and 10 an extruded
and foamed resin. The air-shielding device 9 comprises
a frame 91, a flexible sheet 92, and a pressurized fluid
inlet 93.
In the apparatus shown in Fig. 1, the sizing
die 2 is provided at an end of the die 1 which is fixedly
secured to any conventional extruder (not shown), to
which an outer end of the vacuum chamber 4 is connected.
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In the shown embodiment, there may be no need
of an air-shielding at an inlet side of the vacuum
chamber 4 since it is connected air-tightly through the
connecting plate 3 to the sizing die 2 However, there
may be a case where the extruded resin from the die l is
firstl~ exposed~under atmosphere and then introduced
into the vacuum chamber 4. In such a case it is neces-
sary to provide the air-shielding device even in the
inlet side of the vacuum chamber 4.
~n any case, however, the outlet side of the
vacuum chamber must be opened to derive an extruded and
foamed resin. Therefore, it is always necessar~ to
provide an air-shield at the outlet side thereof. In
order to do so, the air-shielding device 9 is provided
in the outlet side of the vacuum chamber 4.
The frame 91 takes an annular form so that the
extruded and foamed resin can pass through the center
portion thereof. An outer configuration of the frame 91
should be determined such that it can cover the outlet
and/or inlet hole of the vacuum chamber 4. Further, the
frame 91 has a U-shaped cross-section when taken along
an axis thereof, with the inside surface portion thereof
being open. The inside annular surface portion means a
surface which faces the surface of the extruded and
foamed resin passing through the annular frame. The
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fluid pressure inlet 93 is provided at a suitable portion
of an outer surface of the frame 91. The frame 91 may
be of any rigid material and, preferably, of a metal
material.
By fixedly securing the frame 91 at one side
thereof to the outlet of the cylinder body constituting
the vacuum chamber 4, the outlet of the cylinder body is
opened indirectly through the center hole defined by the
flexible sheet 92 to atmosphere. Further, by introducing
a pressurized fluid such as pressurized air through the
fluid inlet 93 into the frame 31, the flexible sheet 92
is inflated inwardly to reduce the cross-sectional area
of the center hole. Therefore, when the extruded and
foamed resin 10 is passing through the hole, the inner
surface of the flexible sheet 92 contacts the surface of
the extruded and foamed resin 10.
Fig. 2 shows the hole in cross-section under
the latter conditions. That is, the surface of the
flexible sheet 92 is in intimate contact with the
surface of the extruded and foamed resin 10 except
portions thereof corresponding to corners 94 of the
flexible sheet 92 where it is folded. However, the
folding thereof is made very tight and, therefore, there
is substantially no leakage of air therethrough.
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The ~lexible sheet 92 may be of natural or
synthetic rubber or soft synthetic resin, etc~ The
synthetic rubber may include chloroprene rubber,
ethylene-propylene rubber, styrene-bu-tadiene rubber/
urethane rubber, silicon rubber ano fluoro rubber, etc.
The soft synthetic resin may include soft vinyl chloride
resin.
The cross-sectional shape of the flexible
sheet is not limited to those shown in Figs. 1 and 2.
It may be possible to take a shape shown in either one
of Figs. 5a and 6a, which can be inflated by introducing
pressurized fluid as shown in Figs. 5b and 6b, respec-
tively.
The apparatus shown in Figs. 1 and 2 operates
as follows: A melted foamable thermoplastic resin
composition is extruded from the die 1 and is initially
foamed in the sizing die 2. The resin 10 thus ~oamed is
introduced into the vacuum chamber 4. The vacuum
chamber 4 is evacuated through the suction hole 5 and
simultaneously cooled by a suitable means (not shown).
Therefore, if the interior of the vacuum chamber 4 is
kept at a predetermined reduced pressure, the resin 10
is further expanded and cooled in the vacuum chamber 4
resulting in a highly expanded foam. Since the chamber
4 is provided at the outlet and/or inlet thereof with
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the air-shielding device 9, the maintenance of the pres-
sure is achieved after an end of the resin lO reaches
the air-shielding device 9.
That is, the air-shielding device 9 is provided
such that it closes the outlet hole of the vacuum chamber
4 except the center portion thereof defined by the
flexible sheet ~2. The resin lO is introduced through
the inlet hole into the vacuum chamber 4 and then leaves '
it out through the center hole of the air-shielding
device. At this time, since a pressurized fluid is
introduced through the fluid inlet 93 into the air-
shielding device 9, the flexible sheet 92 is inflated
thereby to reduce the area of the center hole. The
degree of inflation of the flexible sheet 92 is
regulatable arbitrarily by controlling an amount of the
pressurized fluid to be introduced thereinto. The frame
91 is formed with a fluid discharge port and/or provided
with a relief valve to control internal pressure of the
air-shielding device 9 and to prevent excessive pressure
increase therein. Therefore, the innermost portion of
the flexible sheet 92 can be always in resilient contact
with the surface of the extruded resin lO, so that air
cannot be introduced into the interior of the vacuum
chamber. Thus, the inside of the vacuum chamber 4 is
kept at the reduced pressure regardless of continuous
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passing of the resin lO having variable configuration
and size therethrough. Thus, the resin lO is further
foamed within the vacuum chamber 4 and cooled, resulting
in a favorably expanded resin foam.
In the apparatus shown in Figs. l and 2, the
flexible sheet 92 is in direct contact with the foamed
resin 10. Therefore, as mentioned previously, the
flexible sheet 92 is abraded thereby and the life
thereof is shortened, causing the necessity of stoppage
of the manufacture of the foamed resin due to the
replacement thereof by a new one. Another embodiment of
the present invention improves this point.
The second embodiment has the same construction
as the first embodiment shown in Fig. l, with the air-
snielding device being improved. Fig. 3 mainlv showsthe improved air-shielding device.
The air-shielding device 9 in Fig. 3 is differ-
ent from that in Fig. l only in that a protective sheet
ll is provided on and along the flexible sheet 92. In
detail, in Fig. 3, at the outlet of the vacuum chamber 4,
the protective sheet ll is provided, with one end
thereof being supported in between a flange of the
cylinder constituting the vacuum chamber 4 and the
connecting plate 8. The other end of the sheet ll
extends overlapping the surface of the flexible sheet
92.
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The protective sheet 11 may be more flexible
than the flexible sheet 92. Therefore, the protective
sheet 11 is capable of prot~cting the flexible sheet 92
against abrasion with the resin 10 and of easily follow-
ing a variation of the varying cross-sectional shape of
the resin 10.
A fine metal mesh is one example of a protec~
tive sheet 11 r which can be made by weaving fine metal
wires. Stainless steel wire is suitable for this
purpose, and a stainless steel mesh of 50 meshes or more
is preferable.
Another example of the protective sheet 11 is
a metal foil. Aluminum, lead or copper foil, etc., may
be used for this purpose. Such foil can be thin enough
to provide a desired flexibility.
A further example of the protective sheet 11
is a cloth of metal fibers. "Nasron" ~hich is a regis-
tered trademark of Nippon Seisen Co. for a commercially
available stainless steel cloth has a flexibility similar
to that of the usual cloth and a very high abrasion
durability.
A mesh of plastic filaments may be also used
as the protective sheet 11. The plastic material for
the mesh should have high abrasion durability and heat
resistivity. For example, a polyester resin mesh or
polyamide resin mesh may he used.
-- 11 --
~L2~3~15
It is further possible to use an abrasion
durable plastic film as the protective sheet 11. Such
film may be of ultra-high-molecular-weight polyethylene,
polypropylene, polyamide, polyethylene-terephthalate
or polytetrafluoroethylene. Such resin is relatively
stiff. However; since they may be provided as a very
thin film, it can provide a flexibility enough to follow
the physical variation of the flexible sheet 92.
The protective sheet 11 may be also of a
natural or synthetic fiber cloth. The cloth may or may
not be a woven one. The natural fiber may include
cellulose such as cotton or jute and the synthetic fiber
may include that of vinylon, polyamide, polyethylene-
terephthalate, etc. Particularly, a cloth of aromatic
polyamide is most preferable. The cloth should be as
thin as possible.
The protective sheet 11 is slit to form a
plurality of webs connected together at one end thereof.
For exa~ple, it may comprise four webs as shown in Fig.
4. In Fig. 4, the protective sheet 11 includes upper
and lower webs 111 and 113 which are in contact with
upper and lower surfaces of the extruded and foamed
resin, respectively, and left and right webs 112 and 114
which are in contact with left and right side surfaces
of the resin, respectively. The upper and lower webs
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111 and 113 are substantially flat in cross-section and
webs 112 and 114 are curved in cross-section so that
side edges thereof overlap with side edges of the webs
111 and 113, respectively.
The o~erlapping portions are relatively
movable and thege webs of the protective sheet always
cover the surface of the extruded resin even if the
cross-sectional shape and size of the extruded resin 10
varies.
The latter embodiment employs the protective
sheet between the flexible sheet and the extruded and
foamed resin and, therefore, has a merit of providing an
improved durability of the flexible sheet which makes an
effective and continuous manufacture of the foamed resin
possible, while the merits of the preceding embodiment
are maintained as they are.
That is, since the protective sheet is highly
flexible, it can easily follow the inflation of the
flexible sheet by the pressurized fluid to keep the
periphery of the extruded resin air-tight. Further,
since the resin contacts with not the flexible sheet but
the protective sheet, the abrasion of the flexible sheet
due to the rubbing between the latter and the extruded
resin does not occur. Therefore, according to this
embodiment, there is no need of frequent replacement of
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234~5
the Llexible sheet by a new one and thus a continuous
manufac-ture of foamed resin can ~e realized effectively.
This invention can be applied effectively to
the cases where a foaming agent is added to a thermo-
plastic resin and the mixture is extruded to produce afoamed resin. That is, various thermoplastic resins
such as polystyrene, polyethylene, polyvinylchloride
and polypropylene, etc., may be used for this purpose.
Further, any foaming agent can be used. For example,
the aliphatic hydrocarbons such as ethane, propane,
butane, pentane, etc., the halogenous hydrocarbons such
as methylchloride, methylenechloride, ethylchloride,
ethylfluoride, chlorodifluoromethane, dichlorodifluoro-
methane, etc~, or the inert gases, such as carbon
dioxide, nitrogen, etc., may be used as the foaming agent.
The melted, foamable thermoplastic resin composition
means any of these resins which con~ains any of these
foaming agents and is melted by heating.
In this invention, any flat die such as a T
die, etc., a circular die or a rod die, etc., may be
used as the die.
Although, in the embodiment shown in Fig. 1,
the sizing die 2 is disposed between the outlet die 1
and the vacuum chamber 4, the sizing die 2 may be omit-
ted by directly connecting the vacuum chamber 4 to the
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die 1. In such a case, the extruded resin 10 may be
more expanded.
According to the apparatus of this invention,
the extruded and foamed resin 10 is ~ept in contact with
the flexible sheet 92 or the protective sheet 11 thereon
of the air-shielding device 9 and thus it is possible to
keep the vacuum chamber air-tight at the inlet or outlet
thereof. Therefore, it is possible to sufficiently foam
the extruded resin within the vacuum chamber 4 and to
produce the foamed resin effectively continuously. In
the case of the embodiment in Fig. 3, the flexible sheet
92 does not directly contact with the extruded resin and
thus the abrasion of the flexible sheet is avoided.
Therefore, the life of the flexible sheet is elongated
and thus the extrusion may be performed continuously for
a long time without replacement of the flexible sheet by
a new one.
The present invention will be described in
more detail with reference to the following examples in
0 which the term "%" means "% by weight".
EXAMPLE
The apparatus shown in Fig. 1 together with a
tandem type extruder having a diameter of 65-90 mm was
used. Polystyrene composition containing 1% talc as a
cell size controlling agent was fed into the extruder.
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From an inlet port provided in the extruder, 8% butane
was added into as a blowing agent.
The foamable melt uniformly kneaded within
the extruder was extruded at 122C through a flat die 1
having a 2.0 mm x 100 mm orifice and a sizing die 2.
The outlet area of the sizing die 2 was 42 mm x 200 mm.
A rectangular cylinder 10 m long was used as the
vacuum chamber 4, whose inner cross-sectional area was
150 mm x 400 mm. An air-shielding device 9 such as
shown in FLg. 1 was attached to the outlet of the
vacuum chamber. The frame 91 of the air-shielding
device 9 was made of iron and the flexible sheet 92
thereof was made of translucent rubber whose thickness
was 1 mm. The center open area defined by the flexible
sheet 92 through which the extruded and foamed resin 10
passes was 80 mm x 280 mm with corner curvature being
lOR.
Firstly, a foamed resin was ohtained without
evacuation of the vacuum chamber and without introducing
pressurized air into the air-shielding device. The take-
off speed was 2.1 m/minute. The foamed resin was 50 mm
thick and 233 mm wide with density being about 0.038 g/om3.
Then, the pressurized air of 0.65 kg/cm2 was
introduced through the pressurized fluid inlet 93 to
inflate the flexible sheet 92 to thereby position the
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latter into intimate contact with the resin 10 while the
resin was continuously taken off at 2.4 m/minute and the
vacuum chamber is evacuated to 460 mmHg (absolute pres-
sure). Then, the air pressure was reduced to 0.5 kg/cm2.
The foamed resin obtained was 55 mm thick and 250 mm wide
with the density being about 0.026 g/cm3. Such foamed
resin was obtained continuously for 15 minutes.
EXAMPLE 2
Example 1 was repeated except that air-shieldLng
device shown in Fig. 3 was used.
A stainless steel mesh 11 of 300 meshes and
0.1 mm thick was provided between the sheet 92 and the
resin 10.
Firstly, a foamed resin was obtained without
evacuation of the vacuum chamber and without injecting
pressurized air into the air-shielding device. The take-
off speed wàs 2.5 m/minute and the foamed resin thus
obtained had a thickness of 48 mm and width of 245 mm,
with density being 0.034 g/cm3. Then, pressurized air
of 0.65 kg/cm2 was introduced through the pressurized
fluid inlet 93 to inflate the flexible sheet 92 to
thereby bring the metal mesh 11 into intimate contact
with the resin 10 while the resin was continuously taken
off at 3.4 m/minute and the vacuum cha~er was evacuated
to 260 mmHg (absolute pressure). Then, the air pressure
~2~:34~5
was reduced to 0.5 kg/cm2. The foamed resin obtained
was 57 mm thick and 275 mm wide, the density being about
0.021 g/cm3 and was continuously obtained for 3 hours~
Thereafter, the inner pressure of the vacuum
chamber was increased to 360 mmHg (absolute pressure)
and the take-off speed was reduced to 3.1 m/minute,
resulting in a foamed resin 55 mm thick and 270 mm wide
with the density being about 0.021 g/cm3.
In any of these examples, the foamed resin
obtained was stable and it was found that there was no
need of varying air pressure to be introduced into the
air-shielding device even if the inner pressure of the
vacuum chamb~r was changed from 260 mmHg
(absolute pressure) to 360 mmHg (absolute pressure).
There was no abrasion of the flexible sheet.
It is readily apparent that the above~described
apparatus for producing foamed thermoplastic resin meets
all of the objects mentioned above and also has the
advantage of wide commercial utility. It should be
understood that the specific form of the invention
hereinabove described is intended to be representative
only,as certain modifications within the scope of these
teachings will be apparent to those skilled in the art.
Accordingly, reference should be made to the
following claims in determining the full scope of the
invention.
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