Note: Descriptions are shown in the official language in which they were submitted.
~ETHOD FO~ P~ODUCTION OF
THEP~OPLASTIC ~ESIN FOA~lS
FIELD OF THE INVENTION
The present invention relates to a method for
production of thermo lastic resin foams. .A.ore particu-
larly, the present invention relates to an improved
method of ~roducing thermoplastic resin foams which
comprises expanding an expandable resin hy extruding it
through a plurality of holes and fusing together the
thus-extruded expanded materials while they are still
soft.
BACXGROUND OF THE INVENTION
It is known that a foam is produced bv ex~rud-
ing an expandable resin through a ?lurality of holes
bored in a die to form expanded materials and fusing
together .he expanded materials while they are still
soft. r~Jith this m~thod only, hot7ever, i~ is not
possible to produce a foam having a skin layer of high
density. The surface of a foam not having such a skin
layer of high density is easily scratched.
Hence, a method has been proposed to provide a
skin layer of high density on the surface oE a foam.
The feature of this method resides in that a frame
surrounding extrusion holes is f~tted to the extrusion
end surface of a die, and extruded materials are passed
~ , .
.. ..
~z~
through the frame where they are expanded and fused
together. If such a frame is provided and extruded
materials are passed through the frame while passing a
cooling medium through the interior of the frame, a foam
which has a skin layer of high density on the entire
surface thereof can be produced.
The above-proposed method is described in, for
example, Japanese Patent Publication No. 35231/79. This
method utilizes a frame in which the inner surfaces facing
extruded materials are composed of planes extruding in
parallel with each other in the extrusion direction. In
more detail, the inner surfaces of the frame are formed
by straight lines vertical to the extrusion end surface
of a die. However, experiments have revealed that if a
frame as described above is used, a skin layer of high
density can be formed on the surface of a molded product,
but when a number of extruded materials are fused
together, big voids are formed in the interior of the
molded product and, thus, it is difficult to produce a
high quality foam. The reason is considered that when a
number of extruded materials are fused together to form a
molded product having a large cross-sectional area, gas
resulting from a foaming agent is prevented from passing
through the extruded materials and remains therebetween.
.
It has also been proposed to use a frame whose
cross-sectional axea is increased toward the outer end,
in a method of molding a foam as described above.
Japanese Patent Publication No. 33585/76, for example,
discloses a frame having such inner surfaces whose cross-
sectional area increases toward the outer end. In more
detail, the cross-section of the frame is circular. A
frame having such inner surfaces, however, fails to form
a skin layer of high density over the entire surface of
a foam. Hence, it has been desired to develop a conve-
nient method to provide a high density skin layer uniform-
ly over the entire surface of a foam.
Giving attention to the fact that conventional
frames are such that the inner surfaces are extended in
parallel with each other in the direction of extrusion,
or the cross-sectional area is merely increased toward the
outer end, studies have been made on the relation
between the inclination of inner surfaces of a frame
and the structure or properties of a foam as produced
using the frame. As a result, it has been found that in
order to provide a skin layer of high density on the
surface of a foam while preventing the formation of
voids in the interior of the foam, it is insufficient to
merely incline the inner surfaces of the frame so that
its cross-sectional area is increased toward the outer
.
~,f ~ ~'
end, and it is necessary to design the frame so that the
inclination angle of each inner surface to the extrusion
direction is within -the range of from 5 to 30. It has
further been confirmed that it is necessary to cool the
inner surfaces and to bring extruded materials in contact
with the thus-cooled inner surfaces.
SUMMARY OF TIIE INVENTION
The present invention relates to:
(1) a method of producing a thermoplastic
resin foam which comprises extrudiny an expandable resin
through a plurality of holes bored in a die provided
with a frame in an adjacent relation with the extxusion
end surface of the die, said frame being adapted 'co
surround the holes, and fusing together the extruded
materials from the holes while they are expanded and
still softened, w h e r e i n the inner surfaces
of the frame are inclined so that its cross-sectional
area is increased toward the outer end thereof, the
inclination angle of the inner surface to the line
vertical to the extrusion end surface is maintained
within-the range of from 5 to 30, the temperature of
the inner surface is maintained lower than the softening
- temperature of the expandable resin, and the extruded
materials are fused together while kept in contact with
the inner surfaces of the frame; and
. -- 4 --
~22~
(2) a method of producing a thermoplastic resin
foam which comprises extruding an expandable resin
through a plurality of holes bored in a die provided
with a frame in an adJacent relation with the extrusion
end surface of the die, said frame being adapted to
surround the holes, and fusing together the extruded
materials from the holes while they ~re expanded and
still softened, w h e r e i n the inner surfaces
of the frarne are inclined so that its cross-sectional
area is increased toward the outer end thereof, the
inclination angle of the inner surface to the line
vertical to the extrusion end surface is maintained
within a range of from 5 to 30, the temperature of the
inner surface is maintained lower than the softening
temperature of the expandable resin, the distance from
the holes existing in the peripheral portion of the
extrusion end surface to the inner surface of the frame
is made to differ from place to place, and the extruded
materials are fused together while kept in contact with
the inner surfaces of the frame.
BRIEF DESCRIPTION OF THE DR~WINGS
Figure 1 is a cross-sectional view illustrating
an embodiment of the method of the invention;
Figure 2 is a front view of a frame 4 of
Figure 1;
Figure 3 is a transverse-sectional view of a
foam as produced using the frame of Figure 2;
Figure 4 is a view of a model to explain the
hole distribution area;
S Figures 5, 7, 9, and ll are each a front view
of a frame as used in the present invention; and
Figures 6, 8, lO, and 12 are cross-sectional
views of foams as produced using the frames of Fiyures i,
7, 9, and ll, respectively.
DETAII,ED DESCRIPTION OF TrIE INVENTION
The present invention, in one embodiment,
relates to a method of producing a thermoplastic resin
foam which comprises extruding an expandable resin
through a plurality of holes bored in a die provided
with a frame in an adjacent relation wi-th the extrusion
end surface of the die, said frame being adapted to
surround the holes, and fusing together the extruded
materials from the holes wnile they are expanded and
still softened, w h e r e i n the inner surfaces
of the frame are inclined so that its cross-sectional
area is increased toward the outer end thereof, the
inclination angle of the inner surface to the line
vertica] to the extrusion end surface is maintained
within the range of from 5 to 30, the temperature of
the inner surface is maintained lower than the softening
z~ ~
temperature of the expandable resin, and the extruded
materials are fused to~ether while kept in contact with
the inner surfaces of the frame.
An investigation has been made on a location
at ~hich the frame is fitted to the extrusion end surface
of the die in an adjacent relation. That is, it has
been studied whether, in fitting the frame to the
extrusion end surface, the inner surfaces of the frame
should be placed at an equal distance from tne periphery
of the holes on the extrusion end surface, or they should
be placed in a nearer relation with part of the holes.
As a result, it has been confirmed that if the inner
surfaces of the frame are positioned in a nearer relation
~lith part of the holes existing on the periphery of the
extrusion end surface, tnere can be formed a thic~er
skin layer in the nearer areas. Hence, the thickness
of the skin layer can be controlled appropriately and
optionally l the distance from the holes on the
peripher~ of t~e extrusion end surface to the inner
surface of the frame is made to differ from place to
place; that is, the time taken for the extrudèd material
to reach the inner surface of the frame is made to
differ from place to place.
In another embodiment, therefore, the present
invention relates to a method of producing a thermoplas-
tic resin foam which comprises extruding an expandable
,. .
resin through a plurality of holes bored in a die
provided with a frame in an adjacent relation with the
extrusion end surface of the die, said frame ~eing
adapted to surround the holes, and fusing together the
extruded materials from the holes while tney are
expanded and still softened, w h e r e i n the
inner suraces of the frame are inclined so that its
cross-sectional area is increased toward the outer end
thereof, the inclination angle of the inner surface to
the line ~ertical. to the extrusion end surface is
maintained within the range of from 5 LO 30, the
temperature of the inner surface is maintained lower
than the softening temperature of the expandable resin,
the distance from the holes existing in the peripheral
portion of tne extrusion end surface is made to d.iffer
from place to place, and the extruded materials are
fused together while kept in contact with the inner
surface of the frame.
The term "softening temperature" as used
herein refers to a Vicat softening point as determined
in ASTM D1525.
The present invention will hereinafter be
explained in detail with reference to the accompanying
drawings wherein:
Figure 1 is a cross-sectional view illustrating
an embodiment of the method of the invention;
l2~
Figure 2 is a front view of a frame 4 of
Figure l;
- Figure 3 is a transverse~sectional view of a
foam as produced using the frame of Figure 2;
Figure 4 is a view of a model to explain the
hole distribution area;
Figures 5, 7, 9, and 11 are each a front view
of a frame as used in the p.resent invention; and
Figures 6, 8, 10, and 12 are cross-sectional
views of foams as produced using the frames of Figures
5, 7, 9, and 11, respectively.
In Figure 1, the reference numeral 1 indicates
an extruder; 2, a die; 3, a resin extrusion end plate of
the die 2; 4, a frame; 5, a sizing die; 6, a water bath;
7, a foam; 31, a hole through which a resin is extruded;
41, a cavity; 42, a medium path; and 71 to 73, extruded
materials.
In accordance with the method of the invention,
an expandable resin containing a foaming agent is
introduced under pressure into the die 2 from the
extruder 1 and extruded through the holes 31-31 of the
extrusion end plate 3 in the inside of the frame 4 as
the extruded materials 71 to 73. ~hen, the extruded
materials 71 to 73 undergo foaming and increase their.
volumes. Of the extruded materials 71 to 73, the outer-
most layers, extruded materials 71 and 73, come into
contact with -the inner surfaces of the frame 4 and are
pressed thereto. As a result, the extruded materials 71
to 73 are fused together.
The frame 4 has a front structure as shown in
Figure 2. A cooling medium is circulated througll the
medium path 42 and cools the inner surfaces of the frame
4. The frame 4 is opened at both ends; that is, it has
an opening 43 at the inlet side and an opening 44 ak the
outlet side, and is composed of an upper plate 4i, a
left side plate 46, a right side plate 47, and a lpwer
plate 48. These plates 45 to 48 constitute the inner
surfaces of the frame 4 and extend forward, and make
an angle of inclination of from 5 to 30 to the line
vertical to the extrusion end surface of the extrusion
end plate 3.
The frame 4 of Figure 2 is explained below in
greater detail.
The inlet side opening 43 and the o~tlet side
opening 44 are both regular squares and are vertical to
an axial line passing through the centers of the openings.
Hence, the ridge lines formed between the upper plate 45,
the left side plate 46, the right side plate 47 and the
l~/er plate 48 are such that, when extended bac~ward, they
intersect on the axial line~ The upper plate 45 and the
' 10
2:~
lower plate 43 are in a symmetrical relation and i.ncline
at an angle of 6 to the axial line. ~lso, the left
side plate 46 and the righ-t side plate 47 are in a
symmetrical relation, and they incline at an angle of
S 20 to the axial line. In general, when the opposite
plates are spaced apart a great distance, the angle of
inclin~tion is increased, whereas when the~ are spaced
apart a small distance, the angle of inclination is
decreased. In any case, the angle of inclination is
maintained within the range of from 5 to 30, and the
inner surfaces are disposed so that the area of the
outlet side opening 44 is greater than that of -the inlet
side opening 43; that is, the cross-sectional area of
the frame 4 is increased toward the outer end.
The frame 4 as shown in Figure 2 is fitted to
the extrusion end plate 3, which is then fitted to the
die 2. While circulating a cooling oil through the
medium path 42, an expanda~le resin is extruded from the
extruder 1. Then, the extruded materials 71 to 73
travel throu~h the frame 4. During this travel, the
extruded materials undergo foamin~; the ex-truded
material 71 ls cooled on coming into contact with the
upper plate 45 of the frame 4, and the extruded material
73 i5 cooled on coming into contact with the lower plate
48 of the frame 4. Hence, in the extruded materials 71
- 11 ~
and 73, foaming is depressed which results in the forma-
tion of a skin layer of high density, i.e., 10~7 degree
of expansion. On the other hand, since the extruded
material 72 existing in the inner portion is prevented
from coming into contact with the inner surfaces of the
frame 4, it does not form a s.~in layer of high density.
In the frame 4 as sho~m in Figure 2, as
described above, the inner surfaces of the frame 4 are
disposed so that its cross-sectional area is increased
toward the outer end. Hence, any of the extruded
materials 71 to 73 is allowed to undergo foamin~ and
expand. Hence, even if a skin layer of high density is
formed, it does not prevent the extruded materials 71 to
73 from travelling through the frame 4. This will lead
lS to a smooth molding operationO Further, since the angle
of inclination of each inner surface is maintained
within the range of from 5 to 30~ to the axial line, the
rate of foaming and expansion of the expandable resin is
in good harmony with the rate of extrusion of the expand-
able resin. Hence, the desired high density skin layercan be provided on tne surface of a foam. Further,
since the outermost layers, extruded materials 71 and 73,
are pressed by the inner surfaces of the frame 4, they
are well fused together with the ex~ruded material 72
existing in the inner portion and thus there can be
- 12 -
. ,~ c
l2~L~
formed the foam 7 which is strong as a whole. During
this process, no gas is trapped between the extruded
materials 71 to 73 and thus the fusion i5 not prevented.
The thus-Eormed foam 7 is shown in Figure 3.
In the foam 7 of ~igure 3, the extruded materials 71 to
73 are strongly fused together with no voids therebetweenO
Further, in the surface of the foam 7, a skin layer 7H
- of high density is formed. Hence, the surface of the
foam 7 is scratched onlv with difficulty. Further, in
the foam 7, a big void is not formed between the
extruded materials 71 to 73. Hence, the foam 7 is a
high quality one.
The relation between the holes 31~31 bored in
the extrusion end plate 3 and the cross-section of the
foam is such that the hole distribution area constitutes
not greater than 70%, preferably not greater than 50% oE
the cross-sectional area of the foam. The term "hole
distribution area" as used herein refers to an area of
a polygon as obtained by linking the centers of holes
31-31 positioned at the periphery. In case that the
holes 31-31 are regularily disposed as shown in Figure 4,
the hole distribution area refers to an area of the
hatched zone. The above limitation that the hole distri-
bution area constitutes not greater than 70% of the
cross-sectional area of the foam means that since the
- 13 -
expandable resin expands beyond the foaming fine line
space, the degree of foaming is great. In conventional
foaming methods, particularly those methods to provide
a skin layer of high density, since the proportion of
the hole distribution area to the cross-sectional area
of the foam is greater than 70%l voids are formed iIl the
interior of a molded product and wrinkles occur in the
surface thereof. In the method of the present invention,
the proportion is not greater than 70% and preferably
not greater than 50~. In general, as the density of a
molded product being produced is high, the proportion is
increased.
The lengtn of the frame 4 in a direction
vertical to the extrusion end surface is from 10 to
50 mm. If the length of the frame 4 in the above~
- defined direction is longer than 50 mm, the length of
the inner surface with which the extruded material is in
contact during its travel through the frame is increased
and hence a high take-off tension may be applied to pull
the extruded materiall producing problems such as
breakage or damage of the foam. On the other hand, if
the length is shorter than 10 mm, -the length of the
inner surface with which the extruded material is in
contact is insufficient and the effect of producing a
high density skin layer cannot be obtained.
.
- 14 -
~ arious thermoplastic resins can be used in
the method of the present invention. For example, po~y-
styrene, polymethyl methacrylate, pol~carbonates, poly-
propylene, polyethylene, polyvinyl chloride, and poly-
amides can be used. Particularly preferred are poly-
styrene and styrene copolymers. These resins are inter-
mingled with foaming agents. Various foaming agents can
be used, including solid compounds, such as azodicarbon-
amide, which when heated, decompose and produce gases,
and organic compounds capable of dissolving or swellin~
the resins and having a boillng point lower than the
softening temperature of the resins, such as propane,
butane, pentane and various fluorinated hydrocarbons.
In the case of styrene- or olefin-based resins, it is
preferred to use halogenated aliphatic hydrocarbons,
such as trichloromonofluoromethane and dichlorodifluoro-
methane, in combination with fine powdery talc.
Figure 5 is a front view of a frame 4 similar
to that of Figure 2. In the frame 4 of Figure 5, a
lower plate 48 is not in a symmetrical relation with an
upper plate 45; the angle of inclination o the lower
plate 48 is greater than that of the upper plate 45.
That is, the upper plate 45 is inclined at an angle of
6 to the line vertical to the extrusion end surface;
the left side plate 46 and the right side pla-te 47, at
-- 15 --
~3
an angle of 20; and the lower plate 48, at an angle of
11. Hence, when the frame 4 is viewed from the front
thereof, it looks as if the breadth of the upper plate
45 is the narrowest, that of the lower pla-te 48 is
secondarily narrow, and those of the left. side plaet 46
and the right side plate 47 are the broaclest.
When an expandable resin is extruded using the
frame 4 of Figure 5 in the same manner as described
above, there is produced a foam having a cross-sectional
structure as shown in Figure 6. In the foam 7 of Figure
6~ a high density skin layer 7H with the same thickness
as described above is uniformly formed in the surfaces
which have been in contact with the upper plate 45, the
left side plate 46, and the right side plate 47, and a
high density skin layer 7S thinner than the skin layer
7H is formed in the surface which has been in contact
with the lower plate 48.
Although Figures 2 to 6 illustrate an embodi-
ment in which a typical foam having a rectangular cross-
section is molded, the method of the present inventioncan be applied to the production of foams having
complicated cross-sections. Figure 7 illustra-tes an
embodiment in which a foam having a complicated cross-
section is produced.
.. .
- 16 -
In Fiyure 7, a number of holes 31-31 are bored
in an extrusion end plate 3 in a predetermined configura-
tion. The configuration is such that only one hole 31a
is bored at the right end, three hoLes 31c-31c are bored
at the left end, and two holes 31b-31b are bored in the
intermediate portion. An inlet side openLng 43 of the
frame 4 is designed so as to surround a number of holes
31-31. The inner surfaces of the frame 4 are constructed
by base lines inclining at any point with an angle of 6
relative to a straight line passing through the inlet
side opening 43 and vertical to the extrusion end
surface. Although the inner surfaces may be divided
into an upper surface 45, a left side surface 46, a
right side surface 47, and a lower surface 48, there is
no clear boundary therebetween. Since the angle of -
inclination is the same and the thickness of the frame 4
in an extrusion direction is also the same, the upper
surface 45, the left side surface 46, the right side
surface 47, and the lower surface 48 of Figure 7 are the
same in breadth. Hence, strictly speaking, the outlet
opening 44 is not similar in shape to the inlet opening
43.
A oam 7 as produced using the frame of Figure
7 has a shape as shown in Figure 8, and a skin layer 7H
o~ high density is formed on the entire surface thereof.
Figure 9 shows a frame 4 to be used ln another
embodiment of the invention. In Figure 9, the holes
31-31 bored in an ex-trusion end surface 4 are distributed
in a U-form. As in the case of the Erame of Figure 7,
the inlet opening 43 of the frame 4 is designed so as to
surround the holes 31-31. It is also the same as in the
case of the frame of Figure 7 that the inner surfaces 45
to 48 are constructed by ~ase lines having a given angle
of inclination, for example, an angle of 6, relative to
a straight line vertical to the extrusion end surface.
The frame 4 of Figure 9 is different from the
frame of Figure 7 in that the holes 31-31 are not
positioned at the center in the direction of breadth of
the inlet side opening 43, but are shifted to the inner
side. In more detail, the difference resides in that the
holes 31-31 are composed of inner side holes 311-311 and
outer side holes 31Z-312, in which the inner side holes
311-311 are provided in an adjacent relation with the
inner edge of the inlet side opening 43, whereas the~
outer holes 312-312 are provided with some distance apart
from the outer edge of the lnlet side opening 43. Hence,
the upper surface 45 connecting to the inner edge is
positioned adjacent to the holes 311-311, and all of the
left side surface 46, the riyht side surface 47, and the
lower surface 4~ are positioned apart from the holes
312-312.
.
~f~
The use of the frame 4 of Figure 9 provides a
foam as shown in Figure 10. The foam 7 shown in Figure
10 has a U-shaped cross-section, the inner surface of
the U-shaped foam being a skin layer 7H which is large
in thic~ness and is of high density, and the outer
surface being a skin layer 7S ~Jhich is of high density,
but is reduced in thickness. The reason for the forma-
tion of such a difference in thickness of the skin layer
is considered as follows:
Since the holes 311-311 are closer -to the
inner surface 45, extruded materials extruded from the
holes 311-311 come into contact with the inner surface
45 immediately after extrusion and are cooled, as a
result of w~ich foaming is controlled. On the other
hand, the holes 312-312 are provided wi~h some distance apart
from the left side surface 46, the right side surface 47,
and the lower surface 48. Hence, extruded materials
leaving the holes 312-312 come into contact with the
left side surface 46, the right side surface 47, and the
lower surface 48 some time after extrusion, and thus
they are cooled after foaming proceeds to a certain
extent. As a result, the foaming is less controlled.
The embodiment described above is effective to
produce foams having a solid skln layer only at one
surface. In the present invention, the formation of the
-- 19 --
.
.. ,.. " .. -:
desired high density slcin layer can also be facilitated
by changing the inclination angle of the inner surface
of the frame 4.
In accordance with the present invention, an
expandable resin is extruded through a plurality of holes
bored in a die and extruded materia~s thus produced are
fused together to form a foam. In this case, since a
frame is provided in an adjacent relation with the
extrusion end surface of the die in such a manner that
it surrounds the holes, and the extruded materials are
fused together in the frame, the desired high density
skin layer can be formed on the foam. This is remarkable
as compared with foams as produced by extruding an
expandable resin through a single big hole bored in a
die. In a case in which an expandable resin is extruded
through such a single big hole, an extruded material is
deformed by foaming after it leaves the die and, there-
fore, in forming a skin layer, it is not possible to
form the skin layer uniformly. On the other hand, in
the method of the present invention, an expandable resin
is extruded through a plurality of holes, and an exkruded
material can be placed at the desired location~ Hence,
the method of the invention permits the formation of the
desired skin layer. Furthermore, in the method of the
present invention, the inner surfaces of the frame are
- 20 -
....
: '
l2~
inclined and designed so that the cross-sectional area
of the frame is increased toward the outer end thereof,
and the angle of inclination of the inner surfaces is
controlled within the range of from 5 to 30. Hence,
foaming occurs sufficiently to the interior of extruded
material in the frame and prevents the formation of
voids between the extruded materials. Thus, a high
quality foam not having a void in the interior thereof
can be produced.
l~ Furthermore, in accordance with the met'nod of
the invention, high density skin layers having different
thicknesses can be provided at the desired places by
changing the angle of inclination of the inner surfaces
within the range of from 5 to 30.
The thickness of the skin layer can be
increased by changing from place to place the distance
from holes existing on the periphery to the inner
surfaces of the frame, in more detail, by decreasing
the distance from the holes to the inner surfaces.
Conversely, by increasing the distance from the holes to
the inner surfaces, the thickness of the skin layer can
be reduced. The method of the present invention
produced advantages as described above.
The present invention is described in greater
detail with reference to the following Examples. All
parts are by weight unless otherwise indicated.
- 21 -
EXAMPLE
In this example, polystyrene was used as amaterial~ and an apparatus and a frame as shown in
Figures 1 and 2, respectively, were used to produce a
foam as shown in Figure 3.
Polystyrene ~100 parts) was mixed with 1.5
parts of fine powdery talc as a bubble-controlling agent
and 0.1 part of brown pigment. The resulting mixture was
introduced in an extrusion system consisting of an
extruder of bore diameter 40 mm and an extruder of bore
diameter 50 mm connected to each other, and heated to
190-220C. A foaming agent was intxoduced under pressure
at a suitable point of the extruder of bore diameter
40 mm. The mixture was extruded in an amount of 15 kg
per hour. As the foaming agentj a 1:1 mixture of
trichloromonofluoromethane and dich]or~di-
fluoromethane was used, and it was added in
an amount of about 1.5 parts per 100 parts of the resin.
The die 2 was heated to 150-160C by a plate
heater. An oil maintained at 60C was circulated
through the medium path 42 of the frame 4O In order to
avoid the conduction of heat from the die 2, the cavity
41 was provided.
The structure of the extrusion end plate 3 was
as follows:
- 22 -
,
~2~
The diameter of each hol.e 31 was 1.6 mm, and
its length in a direction of mo.vement was 10 mm. These
holes 31-31 were bored in the extrusion end plate 3 at
regular intervals of 2 mm; the number of holes in the
vertical di.rection was 4 and that in the horizontal
direction was 17. The total number of the holes bored
in the extrusion end plate 3 was 68. The hole distribu-
tion area of the extrusion end plate was 1.92 cm .
The thickness of the frame 4 in a direction
vertical to the extrusion end surface was 20 mm, and
there was formed therein a rectangular inlet side open-
ing 43 measuring 8 mm long and 34 mm wide. In connection
with the in~ler surfaces of the frame 4, the upper surface
45 and the :Lower surface 48 were both inclined at an
angle of 6~ to a direction vertical to the extrusion end
surface, and the left side surface 46 and the right side
surface 47 were both inclined at an angle of 20 to the
direction as described above; the cross-sectional area
of the frame was increased toward the outer end. The
outer end was the outlet side opening 44. The inner
surfaces of the frame 4 were coated with poly-
tetrafluoroethylene resin.
Extruded materials from the holes 31-31 were
expanded, fused together by bringing them into contact
25 with the inner surfaces 45 to 48 of the frame 4, shaped
. - 23 -
. ,, . ' .
`' :
~,2~Z~J~
in the desired form by passing through the sizing dye 5,
and then cooled by immersing in the water bath 6 to
produce the foam 7.
The cross-section of the foam 7 was rectangular
as shown in Figure 3; the long side was 50 mm and the
short side was 12 mm. Thus, the cross-sectional area
was 6 cm , and the proportion of the hole distribution
area to the cross-sectional area of the foam was 32%.
That is, the hole distribution area constituted 32% of
the cross-sectional area of the roam.
On the surface of the foam 7, the fused
surfaces between the extruded materials appeared in a
reguLarly grained form, but the fused surfaces were not
depressed, and the high density skin layer 7H was formed
uniformly over the entire surface of the foam. The
surface of the foam was scratched only difficultly, and
its appearance was good. The average density of the
foam was 0.35 g/cm3, and the hardness was 50 60 as
determined by a Shore D hardness meter. Thus, the foam
was nard irrespective of the fact that it was an
expanded material.
EXAMPLE 2
,
In this example, the procedure of Example 1
was repeated except that the extrusion end plate 3 and
the frame 4 were replaced by the ones as shown in
Figure 5.
- 24 -
:,, ,
~ f~ ~
In the extrusion end plate 3, holes 31-31
having a diameter of 1.6 mm and a length in the direction
of extrusion of 10 mm were bored at regular intervals of
2 mm; the number of holes in the vertical direction was
3 and that in the horizontal direction was 17. Thus,
the total number of holes bored in the extrusion end
plate 3 was Sl. The hole distribution area of the plate
3 was 1.28 cm2.
The thickness of the frame 4 in the direction
of extrusion was 20 mm, and there was formed therein a
rectangular inlet side opening 43, the long and short
sides being 34 mm and 6 mm, respectively. In connection
with the inner surfaces of the frame, the upper surface
, 45 was inclined at an angle of 6, the left side surface
46 and the right side surface 47 were inclined at an
angle of 20, and the lower surface 48 was inclined at
an angle o-E 11, all being to a straight line vertical
to the extrusion end surface. Thus, the cross-sectional
area of the Erame was increased toward the outer end
thereof. The outlet side opening 44 was of the same
size as the outlet side opening of the frame 4 as used
in Example 1.
The same resin composition as used in Example 1
was introduced in the same extruder as used in Example 1
and extruded from the extrusion end plate 3 as described
- 25 -
Z~L~
above to the frame 4 as also described ahove to produce
a foam. This foam was similar to that of Example 1, and
its transverse-sectional area was 6 cm2. Thus, the
proportion of the hole distribution area to the cross-
sectional area of the mold was 21.3~.
The foam as produced in this example was
greatly different from the foam of Example 1 in the
following respect. In the foam 7 of this example, as
shown in Figure 6, a thin, high density skin layer 7S
was formed only on one surface, and the surface hardness
of the surface was not so great. In more detail, the
foam surface 7H as produced by contacting with the uppex
surface, the left side surface 46, and the right side
surface 47 had a Shore D hardness of 45-50, whereas the
foam surface 7S as produced by contacting with the lower
surface 48 had a Shore D hardness of 30~35. The average
density of the foam was 0.33 g/cm3. The foam of this
example was equivalent to that of Example 1 in other
respects and thus it was of high quality.
F.XAMPLE 3
In this example, the extrusion end plate 3 and
the frame 4 as shown in Figure 7 were used.
To a resin mixture of 90 parts of polystyrene
and 10 parts of high-impact polystyrene were added 1.0
part of fine powdery talc and 0.1 part of brown pigment.
- 26 -
Z~Z~ ~
The resulting mixture ~7as introduced into an extrusion
system consisting of an extruder of bore diameter 40 mm
and an extruder of bore diameter 50 mm connected to each
other. As a foaming agent, about 2.0 parts of Furon 12
was introduced under pressure into the extrusion system.
The mixture was extruded in an amount of 20 kg per hour.
The die 2 was maintained at 1~5-150C, and an oil main-
tained at 50C was circulated through the frame 4.
In the extrusion end plate 3, holes 31-31
having a diameter of 1.6 mm were bored at nearly equal
intervals in a configuration as shown in Figure 7, and
the total number of the holes was 60. In more detail,
the holes were arranged in 3 columns in both directions
at the left end of the plate; there was onLy a single
hole at the right end; and at the intermediate portion,
the holes were arranged in 3 or 2 columns. The length
in the vertical direction was reduced steadily from the
left side to the right side, and the left end was bent
somewhat upward.
The inlet side opening ~3 was positioned at
different distances from the holes 31-31 existing on the
periphery. In more detail, the left and right edges of
the opening 43 were positioned at some dis~nce from the
holes 31c and 31a, respectively, but the upper and lower
edges of the opening 43 were positioned close to the
, ~. .
- 27 -
:~z~
holes 31b. This was based on the anticipation that in
foaming of extruded material, it would greatly broaden
in the horizontal direction, but would not broaden so
much in the vertical direction.
Using the extrusion end plate 3 and the frame
4 as described above, the resin composition was extruded
to produce a foam as shown in Figure 8. The transverse-
sectional area of the foam was 5~5 cm . Thus, the
proportion of the cross-sectional area of the foam to
the hole distribution area was a~out 33%. The average
density of the foam was 0.30 g/cm3, and a high density
skin layer 7H was formed over the entire circumference.
The surface hardness was 45-50 as represented in terms
of a Shore D hardness.
EXP~lPLE 4
In this example, the extrusion end plate 3 and
the frame 4 as shown in Figure 11 were used.
Polypropylene was used as a resin, and 2.0
parts of fine powdery talc was mixed with 100 parts of
polypropylene. The resulting mixture was introduced
into an extruder of bore diameter 40 mm and also, as a
foaming agent, about 3 parts o~ butane was introduced
thereinto under pressure. The mixture was extruded in
an amount of 10 kg per hour. The die 2 was maintained
at 160-170C, and an oil maintained at 80C was
circulated through the frame 4.
- 28 -
,~
,lZ~
In the extrusion end plate 3, as shown in
Figure 11, holes 31-31 having a diameter of 1.8 mm were
bored at regular intervals of 2.5 mm; the number of
holes in the vertical direction was 2 and -that in the
horizontal direction was 48. Thus, the total number oE
holes 31-31 was 96, and the hole distribution area was
2.93 cm .
The thickness of the frame 4 in the direction
of extrusion was 30 mm, and the inlet side opening 43
was in a rectangular form measuring 6.5 mm long and
120 mm wide. In connection with the inner surfaces of
the rrame 4, the upper surface 45 and the lower surface
. 48 were inclined at an angle of 6 to a straight line
vertical to the extrusion end surface, and the leEt
surface 46 and the right surface 47 were inclined at an
angle of 20 to the same straight line as defined above;
the cross-sectional area of the frame 4 was increased
toward the outer end.
Using the apparatus as described above, the
resin composition was extruded to produce the foam 7 as
shown in Figure 12. The transverse-section of the foam
7 was rectangular; the long side was 140 mm and the short
side was 10 mm Thus, the cross-sectional area of the
foam was 14 cm , and the proportion of the hole distribu-
tion area to the cross-sectional area of the foam was
. ,
- 29 -
20 . 9~ . The average density of the foam 7 was 0.19 g/cm2.
A high density skin layer was formed on the entire
circumference, and there was no void in the interior of
the foam. Thus, the foam had a good appearance and was
of high quality.
EX~PLE 5
The procedure of Example 1 was repeated except
that the extrusion end plate 3, the frame 4, and the
sizing die 5 were changed, and that the proportion of
the hole distribution area of the plate 3 to the cross-
sectional area of the foam was made greater than in the
other examples.
In the extrusion end plate 3, holes 31-31, the
diameter being 1.6 mm and the length in the direction of
extrusion being 10 mm, were bored at equal intervals of
2 mm; the number of holes in the vertical direction was
5 and that in the horizontal direction was 25. Thus,
the total number of the holes was 125. The hole distri-
bution area of the plate 3 was 3.84 cm .
The thickness of the frame 4 in the direction
of extrusion was 20 mm, and the inlet opening 43 was in
a rectangular form, in which the long side was 5~ mm and
the short side was 12 mm. The upper surface 45, the
left side surface 46, the right side surface 47, and
the lower surface 48 were all inclined at an angle of 8,
- 30 -
"
and thus the cross-sectional area was increased toward
the outer end. There was the outlet slde opening 44 at
the outer end. The inner surfaces of the frame 4 were
subjected to nickel plating.
The same resin composition as used in Example 1
was introduced in the same extruder as used in Example 1,
extruded from the extrusion end plate 3 as described
above into the frame ~ as described above in an amount
of 7 kg per hour, and taken through the sizing die 5 to
produce the foam 7.
The foam 7 had a rectangular cross-section in
which the long side was 60 mm and the short side was
10 mm. Thus, the cross-sectional area of the foam was
6 cm , and the proportion of the hole distribution area
to the cross-sectional area of the foam was 64~.
The average density of the foam as produced
above was 0.4 g/cm , and as ln the case of Example 1,
the high density skin layer 7H was formed on the entire
surface of the foam.
However, if the amount of the material being
extruded was increased to at least 15 kg per hour, a
high density skin layer was not formed sufficiently on
the surface of the foam 7, and no high quality f~am was
produced.
~: - 31
:
While the invention has been described in .
detail and with reference to specific embodiments
thereof, it will be apparent to one skilled in the art
that various changes and rnodifications can be made
therein wi-thout departing frorn the spirit and scope
thereof.
v. - 32 -
