U.S. patent application number 11/266190 was filed with the patent office on 2006-03-09 for polypropylene resin hollow molded foam article and a process for the production thereof.
Invention is credited to Teruyuki Akiyama, Daisuke Imanari, Naochika Kogure, Masato Naito.
Application Number | 20060051543 11/266190 |
Document ID | / |
Family ID | 31973449 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060051543 |
Kind Code |
A1 |
Imanari; Daisuke ; et
al. |
March 9, 2006 |
Polypropylene resin hollow molded foam article and a process for
the production thereof
Abstract
The present invention relates to a hollow molded foam article in
which a plurality of polypropylene resins are used as the base
resin, and to a process for the production of this hollow molded
foam article. More particularly, the present invention relates to a
polypropylene resin hollow molded foam article having a foam layer,
in which the base resin comprises (a) a polypropylene resin with a
melt tension of at least 98 mN and a melt flow rate of 0.5 to 15
g/10 minutes, (b) a polypropylene resin with a melt tension of less
than 30 mN (excluding O) and a melt flow rate of 2 to 30 g/10
minutes, and (c) a polypropylene resin with a melt tension of at
least 30 mN and less than 98 mN and a melt flow rate of 2 to 15
g/10 minutes, formed by positioning in a mold a softened
cylindrical foam having a foam layer obtained by extruding from the
die of an extruder a foamable molten resin composition containing a
foaming agent, wherein the melt tension at 230.degree. C. of the
polypropylene resin that forms the foam layer is at least 10 mN and
less than 49 mN, and the apparent density of the foam layer is no
more than 0.3 g/cm.sup.3.
Inventors: |
Imanari; Daisuke;
(Kanuma-shi, JP) ; Akiyama; Teruyuki; (Kanuma-shi,
JP) ; Kogure; Naochika; (Kanuma-shi, JP) ;
Naito; Masato; (Kanuma-shi, JP) |
Correspondence
Address: |
Roger C. Hahn;Sherman & Shalloway
415 N. Alfred Street
Alexandria
VA
22314
US
|
Family ID: |
31973449 |
Appl. No.: |
11/266190 |
Filed: |
November 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10667362 |
Sep 23, 2003 |
|
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11266190 |
Nov 4, 2005 |
|
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Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
B29K 2995/0015 20130101;
B29L 2031/30 20130101; B29K 2105/04 20130101; B29K 2995/0096
20130101; B29K 2077/00 20130101; C08J 3/226 20130101; B29K
2105/0026 20130101; B29C 48/19 20190201; B29C 48/0017 20190201;
B29K 2105/0032 20130101; C08J 2323/06 20130101; B29K 2995/0069
20130101; B29K 2025/00 20130101; B29K 2023/12 20130101; B29C 49/04
20130101; B29L 2023/00 20130101; B29K 2023/06 20130101; B29K
2995/0002 20130101; Y10T 428/1352 20150115; B29L 2031/3005
20130101; B29C 49/22 20130101; B29C 48/09 20190201; B29K 2105/0041
20130101; B29C 48/13 20190201; B29C 48/0018 20190201; B29K 2105/046
20130101; B29C 44/06 20130101; B29L 2031/7158 20130101; B29C 49/041
20130101; Y10T 428/13 20150115; B29C 48/0012 20190201; C08J 2423/10
20130101; B29K 2995/0067 20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B32B 27/08 20060101
B32B027/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2002 |
JP |
287761/2002 |
Claims
1. A polypropylene resin hollow molded foam article comprising a
polypropylene resin foam layer, formed by placing a softened
cylindrical foam in a metal mold, wherein the melt tension at
230.degree. C. of the polypropylene resin that forms said foam
layer is at least 10 mN and less than 49 mN, and the apparent
density of said foam layer is no more than 0.3 g/cm.sup.3.
2. The polypropylene resin hollow molded foam article according to
claim 1, having a resin layer on the outside and/or the inside of
the foam layer.
3. The polypropylene resin hollow molded foam article according to
claim 1, wherein the hollow molded foam is molded by blowing a gas
into the interior of a cylindrical foam.
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. The polypropylene resin hollow molded foam article according to
claim 2, wherein the hollow molded foam is molded by blowing a gas
into the interior of a cylindrical foam.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a hollow molded foam
article in which a plurality of polypropylene resins are used as
the base resin, and to a process for the production of a hollow
molded polypropylene resin foam, and more particularly relates to
the use of a plurality of polypropylene resins having specific melt
tensions and melt flow rates.
[0003] 2. Description of the Related Art
[0004] Blow molding technology has been utilized in the past to
obtain blow-molded foams having a foam layer. Various methods have
been proposed in the past for obtaining blow-molded foams, but the
most common is a method in which a foaming agent and a base resin
are melt-kneaded in an extruder, this mixture is extruded from a
die, the cylindrical foam thus formed is placed in a metal mold,
and blow molding is performed by blowing a pressurized gas into the
interior of this cylindrical foam.
[0005] Blow-molded foams produced by this method can be used in
applications that require thermal insulation, sound-proofing,
flexibility, and other such properties, specific examples of which
include containers, ducts, thermal insulation panels, and
automotive parts. The expansion ratio used in these applications is
3 to 30 times. For instance, there is a known blow-molded foam in
which polystyrene or polyethylene is used for the base resin and
the expansion ratio of the foam layer is 4 to 12 times (see
Japanese Patent Publication H3-59819, for example).
[0006] When the heat resistance of the molded article is taken into
account, it is preferable to use a polypropylene resin as the base
resin, and there have been numerous proposals for foams made from
polypropylene resins because of the good heat resistance and
rigidity of these resins. However, nearly all blow-molded foams
made using a general purpose polypropylene resin as the base resin
had a low expansion ratio in which the apparent density was over
0.3 g/cm.sup.2 when foamed with a chemical foaming agent.
[0007] When a general purpose polypropylene resin is used as the
base resin and is foamed with a physical foaming agent, foaming
occurs when the foaming agent kneaded into the base resin expands,
but with a polypropylene resin, changes in the temperature of the
molten resin near the foaming temperature result in large changes
in the melt tension and viscosity of the molten resin, and if the
temperature of this resin is even just a little too high, the
viscosity and melt tension will decrease to the point that the
foaming agent cannot be held in the resin, the result being that
the foaming agent escapes from the polypropylene resin during
extrusion and foaming, the cells become continuous or rupture, and
a good cylindrical foam cannot be obtained. In a worst case
scenario, foaming itself is impossible. Conversely, if the melting
temperature of the polypropylene resin is lowered in order to keep
the viscosity and melt tension of the polypropylene resin high, the
polypropylene resin undergoes crystallization, which prevents
adequate and uniform foaming from being achieved.
[0008] There is only a narrow range of temperatures suited to the
foaming of polypropylene resins, and it has been difficult to
obtain a blow-molded foam with thick walls and a high expansion
ratio using a general purpose polypropylene resin, but the present
applicant has proposed a blow-molded foam with thick walls and a
high expansion ratio, and a process for the production of this
foam, that overcome this difficulty, in which a polypropylene resin
having a specific melt tension and a specific melt flow rate is
used as the base resin (for example, International Laid-Open Patent
Application WO/99/28111).
[0009] Using a specific polypropylene resin having a specific melt
tension and melt flow rate as above does produce a thick-walled
foam with a good appearance, having a high expansion ratio, and
having excellent heat resistance, thermal insulation properties,
and so forth. Nevertheless, the above-mentioned specific
polypropylene resins are expensive, which drives up the cost of the
molded foam finished product thus obtained, so this is extremely
disadvantageous from a cost standpoint except in special
applications. Also, a large amount of flash is produced in the
production of blow-molded foams, and the use of recycled material
also poses problems.
[0010] Therefore, in light of the above situation, it is an object
of the present invention to provide a thick-walled hollow molded
foam with a good appearance and a high expansion ratio by using a
plurality of polypropylene resins having specific melt tensions and
melt flow rates, rather than using just one specific polypropylene
resin having a specific melt tension and melt flow rate, as well as
a process for the production of this foam.
SUMMARY OF THE INVENTION
[0011] As a result of various investigations aimed at achieving the
stated object, the inventors discovered that conditions suitable
for foaming can be easily achieved by using a base resin comprising
a plurality of polypropylene resins having melt tensions and melt
flow rates within a specific range, such as resins containing
general purpose polypropylene resins or reused polypropylene
resins, and that the production cost will be reduced, so that a
thick-walled molded foam having a high expansion ratio and an
attractive appearance can be obtained at a low cost.
[0012] Specifically, the present invention is:
[0013] (1) A polypropylene resin hollow molded foam article
comprising a polypropylene resin foam layer, formed by placing a
softened cylindrical foam in a mold, wherein the melt tension at
230.degree. C. of the polypropylene resin that forms said foam
layer is at least 10 mN and less than 49 mN, and the apparent
density of said foam layer is no more than 0.3 g/cm.sup.3.
[0014] (2) The polypropylene resin hollow molded foam article
according to (1) above, having a resin layer on the outside and/or
the inside of the foam layer.
[0015] (3) The polypropylene resin hollow molded foam article
according to (1) or (2) above, wherein the hollow molded foam is
molded by blowing a gas into the interior of a cylindrical
foam.
[0016] (4) A process for the production of a polypropylene resin
hollow molded foam article, in which a cylindrical foam having a
foam layer is formed by extruding from a die a foamable molten
resin comprising a base resin containing a foaming agent, and then
placing said cylindrical foam in a mold while in a softened state,
wherein the base resin is one selected from among the following
(i), (ii), (iii), and (iv):
[0017] (i) a resin composed of at least 20 wt % and less than 70 wt
% (a) polypropylene resin with a melt tension of at least 98 mN and
a melt flow rate of 0.5 to 15 g/10 minutes and over 30 wt % and no
more than 80 wt % (b) polypropylene resin with a melt tension of
less than 30 mN (excluding 0) and a melt flow rate of 2 to 30 g/10
minutes (the combined amount of (a) and (b) being 100 wt %)
[0018] (ii) a resin composed of 30 to 70 wt % (c) polypropylene
resin with a melt tension of at least 30 mN and less than 98 mN and
a melt flow rate of 2 to 15 g/10 minutes and 30 to 70 wt % (b)
polypropylene resin with a melt tension of less than 30 mN
(excluding 0) and a melt flow rate of 2 to 30 g/10 minutes (the
combined amount of (c) and (b) being 100 wt %)
[0019] (iii) a resin composed of at least 20 wt % and less than 70
wt % (a) polypropylene resin with a melt tension of at least 98 mN
and a melt flow rate of 0.5 to 15 g/10 minutes and over 30 wt % and
no more than 80 wt % (c) polypropylene resin with a melt tension of
at least 30 mN and less than 98 mN and a melt flow rate of 2 to 15
g/10 minutes (the combined amount of (a) and (c) being 100 wt
%)
[0020] (iv) a resin composed of (a) a polypropylene resin with a
melt tension of at least 98 mN and a melt flow rate of 0.5 to 15
g/10 minutes, (b) a polypropylene resin with a melt tension of less
than 30 mN (excluding 0) and a melt flow rate of 2 to 30 g/10
minutes, and (c) a polypropylene resin with a melt tension of at
least 30 mN and less than 98 mN and a melt flow rate of 2 to 15
g/10 minutes, with (a) accounting for 5 to 65 wt %, (b) for 30 to
78 wt %, and (c) for 5 to 65 wt % (with the combined amount of (a),
(b), and (c) being 100 wt %), and said resin having a composition
within the bounds of a quadrangle ABCD (including on the lines of
the quadrangle) drawn by connecting with straight lines the four
points A (17, 78, 5), B (5, 72, 23), C (5, 30, 65), and D (65, 30,
5) which are component coordinates (x, y, z) where the
polypropylene resin (a) component is given as x wt %, the
polypropylene resin (b) component is given as y wt %, and the
polypropylene resin (c) component is given as z wt % in a
triangular component graph in which the upper vertex of a regular
triangle is marked as 100 wt % polypropylene resin (a), the lower
left vertex as 100 wt % polypropylene resin (b), and the lower
right vertex as 100 wt % polypropylene resin (c).
[0021] (5) The process for the production of a polypropylene resin
hollow molded foam article according to (4) above, wherein the
cylindrical foam is a multilayer cylindrical foam having a resin
layer on the outside and/or inside of the foam layer, obtained by
co-extruding a foamable molten resin containing a foaming agent,
and a non-foamable molten resin containing no foaming agent.
[0022] (6) The process for the production of a polypropylene resin
hollow molded foam article according to (4) or (5) above, wherein
the hollow molded foam is obtained by blowing a gas into the
interior of a cylindrical foam placed in a metal mold.
[0023] (7) The process for the production of a polypropylene resin
hollow molded foam article according to any of (4) to (6) above,
wherein the foaming agent is a physical foaming agent containing
carbon dioxide.
[0024] The hollow molded foam article of the present invention is a
molded foam article having a foam layer whose surface is in a
favorable state and which has excellent rigidity, adequate wall
thickness, and low density.
[0025] With the present invention, in the production of a
polypropylene resin hollow molded foam article using a foaming
agent, a plurality of polypropylene resins having specific melt
tensions and melt flow rates can be blended in a specific weight
ratio, rather than using just one polypropylene resin with a high
melt tension as the base resin. Therefore, a molded foam article
having a foam layer whose surface is in a favorable state and which
has adequate wall thickness and low density can be obtained stably.
Furthermore, examining the melt tensions and melt flow rates makes
it possible to use general purpose polypropylene resins or reused
polypropylene resins, for example, which lowers the cost of the
finished product thus obtained.
[0026] In the production process of the present invention, when the
cylindrical foam is a multilayer cylindrical foam having a resin
layer on the outside and/or inside of the foam layer, obtained by
co-extruding a foamable molten resin containing a foaming agent,
and a non-foamable molten resin containing no foaming agent, the
molded foam article thus obtained has better dimensional precision,
strength, and so on, and also has a better appearance.
[0027] In the process for producing a molded foam article of the
present invention, if the molded foam article is formed from a
cylindrical foam made with a physical foaming agent containing
carbon dioxide, cooling after foam molding will take much less time
and production efficiency will be boosted. Also, the obtained
molded foam article will be less prone to problems such as sinks
and blistering, and the physical strength such as compression
stress will also be excellent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a diagram showing an example of a method of
manufacture according to the present invention;
[0029] FIG. 2 is a partially cut away perspective view showing an
example of a cylindrical foam employed in a method of manufacture
according to the present invention;
[0030] FIG. 3 is a cross-sectional view of a hollow molded foam
article of bottle shape according to the present invention;
[0031] FIG. 4 is a graph showing the relationship between melt
tension and time in measurement of melt tension; and
[0032] FIG. 5 is a triangular component diagram showing the
component composition employing three components (a), (b), and (c)
as the base resin according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] A hollow molded foam article (hereinbelow simply termed a
"molded foam article") according to the present invention is formed
by positioning a cylindrical foam in a softened state in a mold,
this body having a polypropylene resin foam layer, the melt tension
at 230.degree. C. of the polypropylene resin forming this foam
layer being at least 10 mN and less than 49 mN, and the apparent
density of this foam layer being no more than 0.3 g/cm.sup.3.
[0034] If the melt tension of the resin forming the foam layer of
the hollow molded foam article according to the present invention
is within the aforesaid range, an excellent balance is achieved
between product cost and the requirement that the molded foam
article should have a foam layer of low density with sufficient
thickness and of excellent surface condition. From this point of
view, the melt tension is more preferably at least 12 mN and less
than 49 mN, or even more preferably at least 15 mN and less than 49
mN.
[0035] The apparent density of the foam layer 21 of the molded foam
article according to the present invention is no more than 0.3
g/cm.sup.3. If the apparent density exceeds 0.3 g/cm.sup.3, there
is a risk that the excessively large density will adversely affect
such properties as light weight, impact damping ability,
flexibility and thermal insulation that are characteristic of foam.
From this point of view, a density of no more than 0.25 g/cm.sup.3
is desirable. In particular, from the point of view that the molded
foam article should display little generation of wrinkles caused by
corrugation and should consequently have an excellent appearance,
with little variability of thickness and density, a density of 0.07
to 0.3 g/cm.sup.3 is more preferable and 0.1 to 0.3 g/cm.sup.3 is
even more preferable.
[0036] The average thickness of the foam layer 21 of the molded
foam article according to the present invention depends on the
shape of the target molded foam article but, usually, at least 1 mm
is preferable, at least 2 mm is more preferable and at least 4 mm
is particularly preferable. The upper limiting value is about 30
mm. Molded foam articles having such a thickness satisfy
requirements in terms of physical properties such as heat
insulation, sound installation, flexibility and heat resistance and
are desirable since they may be suitably employed in various
applications such as ducts, automobile components or containers.
The same applies to the foam layer of multilayer molded foam
articles.
[0037] The average thickness of the foam layer 21 is taken as the
average thickness obtained by measuring the thickness of the foam
layer at 10 equally spaced locations in the cross-section
perpendicular to the direction of extrusion of the molded foam
article and calculating the arithmetic mean of these measured
values. However, since, depending on the shape of the molded foam
article, some portions thereof may be crushed or stretched, in
measurement of the average thickness of the foam layer 21 such
portions should be avoided.
[0038] The average thickness of the resin layer in the case of a
molded foam article having a resin layer according to the present
invention should preferably be at least 0.3 mm and more preferably
at least 0.5 mm, from the point of view of improving the rigidity
of the molded foam article obtained. On the other hand, the upper
limit is preferably no more than 5 mm or more preferably no more
than 3 mm, from the point of view of achieving a balance of light
weight and impact damping ability.
[0039] For the average thickness of the resin layer, values are
adopted obtained by measuring the average thickness of the resin
layer in the same way as when measuring the average thickness of
the foam layer 21.
[0040] The average cell diameter of the foam layer 21 of the molded
foam article according to the present invention preferably has a
lower limit of at least 0.1 mm, or, more preferably, at least 0.3
mm and an upper limit of no more than 5.0 mm, more preferably no
more than 3.0 mm, no more than 1.0 mm being particularly
preferable.
[0041] If the average cell diameter is too small, wrinkles caused
by furrow-shaped corrugations produced in the cylindrical foam tend
to be generated in the molded foam article. On the other hand, if
the average cell diameter is too large, there is a risk of
impairing the appearance of the molded foam article and heat
insulation, with the result that it may become unsuitable for
certain applications.
[0042] The average cell diameter of the foam layer 21 is measured
by a method in accordance with ASTM D 3576-77. Specifically, the
cross-section of the foam layer is magnified and projected, a
straight line is drawn in the thickness direction on this projected
image, the number of cells intersecting this straight line is
counted, and the length of the straight line on the image is
divided by the number of cells, to obtain a value, which is then
further divided by 0.616. Of the three intersecting directions
(extrusion direction, width direction and thickness direction), the
average cell diameter of the foam layer cross-section in the
thickness direction is found in the cross-section in the extrusion
direction and in the cross-section in the width direction, and the
value found by obtaining the arithmetic mean of the average cell
diameters in these cross-sections is then taken as the average cell
diameter of the foam layer 21. The location of measurement is the
middle region of the molded foam article. However, depending on the
shape of the molded foam article, measurement should not be
conducted at portions where the cells are considerably deformed,
such as portions where the molded foam article is crushed or
stretched.
[0043] The aforementioned molded foam article may for example be
obtained by employing as the base resin a resin obtained by
blending a combination of a plurality of polypropylene resins
having melt tension and melt flow rate within a specified range.
Specifically, the molded foam article is manufactured by forming a
cylindrical foam having a foam layer by extrusion of foamable
molten resin in which a foaming agent is contained in the base
resin into a low-pressure zone from a die and then positioning this
cylindrical foam, in a softened state, in a mold.
[0044] The method of manufacturing a molded foam article according
to the present invention will be described with reference to an
example of a molded foam article according to the present
invention, with reference to the drawings.
[0045] For example, as shown in FIG. 1, foamable molten resin
obtained by kneading a base resin and foaming agent in an extruder
(not shown) is extruded from a die 3 into a low-pressure zone to
form a cylindrical foam 2 having a polypropylene resin foam layer
21 (hereinbelow simply referred to as "foam layer"); if necessary,
gas may be blown into the cylindrical foam. Next, this cylindrical
foam is arranged in a divided type mold (hereinbelow simply
referred to as a "mold") 4, 4 of the desired shape and the mold is
closed so that the cylindrical foam is clamped by this mold. A
molded foam article of a desired shape may be obtained by blowing
in gas into the cylindrical foam 2, if required, concurrently with
the closure of the mold. Preferably, obtaining a molded foam
article by blowing in gas into the cylindrical foam 2 results in a
molded foam article being obtained that accurately reflects the
mold shape. Preferably, in the method according to the present
invention, an accumulator is arranged between the extruder and the
die 3 or within the die. Also, as shown in FIG. 1, by employing a
mold provided with pressure reduction piping 41 for the mold 4, 4,
good adhesion between the outside surface 9 of the cylindrical foam
and the inside surface 10 of the mold 4 can be achieved by forming
while reducing pressure while the mold is closed; in this way, a
molded foam article that more accurately reflects the mold shape
can be obtained and a molded foam article of excellent appearance
can be obtained.
[0046] While the mode of the hollow molded foam article depends on
the method of molded foam article and on the shape of the molded
foam article that is obtained, as shown in FIG. 1, a mode in which
the molded article is open at the bottom and a balloon-shaped mode,
in which the top and bottom of the cylindrical foam are closed, can
be obtained.
[0047] According to the present invention, a multilayer cylindrical
foam may be formed having a resin layer on the outside and/or
inside of the foam layer by co-extrusion of foamable molten resin
and non-foamable molten resin and a multilayer molded foam article
may be obtained by molding this multilayer cylindrical foam using
the same method as described above.
[0048] For example, in forming a multilayer cylindrical foam 2, the
base resin forming each layer is melt-kneaded within respective
separate extruders (not shown) and is then extruded to a low
pressure zone from a die 3 while merging and laminating these
layers within the die 3, to obtain various types of cylindrical
foam 2, of which examples are shown in FIG. 2. FIG. 2 shows a
partially cut away perspective view of a multilayer cylindrical
foam. In FIG. 2, (b), (c) and (d) show multilayer cylindrical foam
having a resin layer on the outside and/or inside of a foam layer.
21 indicates the foam layer and 22 and 23 indicate resin layers,
respectively. Regarding the molded foam article obtained from the
multilayer cylindrical foam 2, a molded foam article of multilayer
construction having a resin layer on the outside and/or inside of a
foam layer may be obtained corresponding to the construction of the
multilayer cylindrical foam. Molded articles of excellent
resistance to surface damage can be obtained thanks to the improved
surface strength achieved by using a molded article having a resin
layer on the outside surface of a foam layer.
[0049] FIG. 3 shows an example of a molded foam article obtained
from a multilayer cylindrical foam 2 of the construction of FIG.
2(d). The molded foam article of bottle shape shown in FIG. 3 is a
molded foam article, i.e. a bottle-shaped molded foam article
having a resin layer on the inside face and outside face obtained
by so-called blow molding, obtained by arranging a cylindrical foam
2 in a softened state having resin layers 22, 23 as shown in FIG. 2
(d) in the cavity of a bottle-forming mold as shown in FIG. 1,
closing the mold and reducing the pressure between the outside face
of the cylindrical foam 2 and the inside faces of the mold (molding
faces) and/or blowing in air from an air supply nozzle (not shown)
into the interior of the cylindrical foam 2, so that the outside
face of the cylindrical foam 2 adheres to the inside faces (molding
faces) of the mold.
[0050] According to the present invention, as the base resin, a
resin is employed obtained selecting two or more from the
polypropylene resin (a), polypropylene resin (b) and polypropylene
resin (c) indicated below, respectively, and blending these in a
specified ratio. By adopting such a composition, a plurality of
polypropylene resins having specific melt tension and melt flow
rate can be blended in a specified weight ratio without needing to
employ only restricted specific polypropylene resins having a
specific melt tension and melt flow rate. A thick molded foam
article can thereby be obtained having an excellent appearance and
a high foaming factor. In addition, by examining the melt tension
and melt flow rate, for example reused polypropylene resin or
general purpose polypropylene resin and the like may be employed,
making it possible to obtain a thick molded foam article with low
production cost.
[0051] The polypropylene resin (a) employed in the present
invention have a melt tension (MT) of at least 98 mN and a melt
flow rate (MFR) of 0.5 to 15 g/10 minutes. The polypropylene resin
(b) that are employed have a melt tension (MT) of less than 30 mN
and a melt flow rate (MFR) of 2 to 30 g/10 minutes. Also, the
polypropylene resin (c) that are employed have a melt tension (MT)
of at least 30 mN but less than 98 mN and a melt flow rate (MFR) of
2 to 15 g/10 minutes.
[0052] As the aforementioned polypropylene resin (a), polypropylene
polymers are employed comprising propylene homopolymer, a copolymer
of propylene and another copolymerizable monomer having a propylene
content of at least 60 wt %. As the copolymerization component of
the copolymer, ethylene, butylene or other .alpha.-olefins may be
mentioned by way of example. Desirably the .alpha.-olefin is an
olefin of carbon number no more than 12, preferably no more than 8.
Also, preferably the polypropylene resin (a) has free terminal
long-chain branching in the molecular structure; specific examples
include the high melt tension polypropylene "PF 814"
(homopolypropylene) and the "SD632" (propylene-ethylene block
copolymer) manufactured by San Alomar Company Ltd.
[0053] As the aforementioned polypropylene resin (b), specifically,
there may be employed comprising propylene homopolymer, a copolymer
of propylene and another copolymerizable monomer having a propylene
content of at least 60 wt % of for example propylene homopolymer or
copolymer, which, in contrast to the polypropylene resin (a), which
is of excellent foaming ability, are general purpose polypropylene
resins that do not have free terminal long-chain branching. As the
copolymerization component of the copolymer, ethylene, butylene or
other .alpha.-olefins may be mentioned by way of example. Desirably
the .alpha.-olefin is an olefin of carbon number no more than 12,
preferably no more than 8.
[0054] Also, as the aforementioned polypropylene resin (c), there
may be employed comprising propylene homopolymer, a copolymer of
propylene and another copolymerizable monomer having a propylene
content of at least 60 wt %. As the copolymerization component of
the copolymer, ethylene, butylene or other .alpha.-olefins may be
mentioned by way of example. Desirably the .alpha.-olefin is an
olefin of carbon number no more than 12, preferably no more than 8.
As the polypropylene resin (c), there may be indicated by way of
example polypropylene resins in which a superpolymer polyolefin
component such as polypropylene or polyethylene is dispersed
without unevenness of distribution in polypropylene resin by a
catalytic technique or polypropylene resins having free terminal
long-chain branching or polypropylene obtained by improving
polypropylene resin using isoprene monomer or the like. As a
specific example of a polypropylene resin in which a superpolymer
polyolefin component such as polypropylene or polyethylene is
dispersed without unevenness of distribution in polypropylene resin
by a catalytic technique there may be mentioned "NEWFOAMER FH 3400"
(melt tension 54 mN, melt flow rate 4 g/10 minutes) manufactured by
Chisso corporation. Of the above, resins having free terminal
long-chain branching are preferable. Specific examples of resins
having free terminal long-chain branching include raw materials
whose melt tension and melt flow rate are in the aforementioned
ranges, consisting of reused resin of molded products using reused
resin or reused resin of molded foam articles or sheets using the
polypropylene resin (a) as chief raw material and molded articles
obtained by heat molding sheets in a mold. Materials using the
polypropylene resin (a) as chief raw material means materials
employing at least 50 wt % of polypropylene resin (a).
[0055] With the present invention, foaming conditions such as the
foaming suitability temperature or molten viscosity can easily be
adjusted over a wide range, thereby making it possible to obtain
stable foam moldability. Also, with the present invention,
manufacturing costs can be lowered since it is possible to select
inexpensive polypropylene resin (b) over a wide range or to employ
reused resin from molded articles.
[0056] In the method according to the present invention, the base
resin is selected from the following (i), (ii), (iii) or (iv). (i)
if a combination of the aforementioned specified polypropylene
resin (a) and polypropylene resin (b) is employed, the blending
ratio of these two in the base resin is: polypropylene resin (a) at
least 20 wt % but less than 70 wt %; polypropylene resin (b) more
than 30 wt % but no more than 80 wt %, the combined amount of (a)
and (b) being 100 wt %. If the blending ratio of the polypropylene
resin (b) is 30 wt % or less, the cylindrical foam extruded from
the die tends to expand in the circumferential direction; although,
in the case where the molded foam article is of linear shape, a
molded foam article of good appearance can be obtained by for
example performing adjustment by blowing in gas, in the case of
complex shapes, wave-shaped corrugation marks tend to be left in
the surface of the molded foam article obtained, so, as a result,
it becomes difficult to obtain a good molded foam article.
[0057] Also, if the blending ratio of the expensive polypropylene
resin (a) component becomes large, it is difficult to achieve
sufficient reduction in product costs. It is therefore more
preferable that the content of the polypropylene resin (b) should
be at least 40 wt % and even more preferably at least 50 wt %.
[0058] On the other hand, if the content of the polypropylene resin
(b) exceeds 80 wt %, it becomes difficult to maintain a good
foaming suitability condition, so it becomes difficult to obtain
thick, low-density molded foam articles. It is therefore preferable
that the content of the polypropylene resin (b) should be no more
than 75 wt % and even more preferably should be no more than 70 wt
%.
[0059] The polypropylene resin (a) employed in the present
invention has a melt tension and melt flow rate as described above.
If the melt tension of the polypropylene resin (a) is less than 98
mN, even though the blending amount is within the range described
above, thick, low-density molded foam articles are difficult to
obtain, so the melt tension is preferably at least 150 mN and more
preferably at least 200 mN. On the other hand, in the method
according to the present invention, if the melt tension exceeds 400
mN, extrusion moldability is lowered in that for example fluidity
is adversely affected, resulting in the load acting on the screw
during extrusion becoming extremely high. Consequently, taking into
account extrusion moldability, it is preferable that the melt
tension should be no more than 300 mN and more preferably no more
than 250 mN.
[0060] If the melt flow rate is lower than 0.5 g/10 minutes,
fluidity is adversely affected, with a risk of lowering of
extrusion moldability. On the other hand, if the melt flow rate
exceeds 15 g/10 minutes, the draw-down becomes large, tending to
produce unevenness of thickness in the molded foam article that is
finally obtained and risking impairing molding stability. The melt
flow rate is therefore preferably 1 to 10 g/10 minutes and more
preferably 2 to 5 g/10 minutes.
[0061] The polypropylene resin (b) employed in the present
invention has a melt tension and melt flow rate as described above.
From the point of view of making it possible to keep the load
applied to the screw during extrusion low and being able to obtain
a thick, low-density molded foam article efficiently, it is
preferable that the melt tension of the polypropylene resin (b)
should be no more than 15 mN and more preferably no more than 10
mN. The lower limit is about 1 mN. Usually, there are substantially
no general purpose polypropylene resins whose melt tension exceeds
30 mN and the melt tension of the polypropylene resin (b) in the
method of the present invention is less than 30 mN; in the case of
polypropylene resins whose melt tension exceeds 30 mN, a large load
acts on the screw during extrusion and, in addition, resins whose
melt tension exceeds 30 mN are more expensive than general purpose
resins, so even if their blending amount is within the range
specified above, the overall raw material cost becomes high and, as
a result, the product cost is increased; they are therefore
undesirable. Also, if the melt flow rate is lower than 2 g/10
minutes, extrusion moldability is lowered in that for example
fluidity is adversely affected and, due to evolution of heat during
extrusion, a cylindrical foam having a low-density foam layer is
not obtained.
[0062] On the other hand, if the melt flow rate exceeds 30 g/10
minutes, the draw-down of the cylindrical foam becomes large,
tending to produce unevenness of thickness in the molded foam
article that is finally obtained and risking impairing molding
stability with the result that a good molded foam article is not
obtained. The melt flow rate of the polypropylene resin (b) is
therefore preferably 5 to 20 g/10 minutes and more preferably 5 to
15 g/10 minutes.
[0063] In the method of manufacture according to the present
invention, if (ii), as the base resin, a combination of
polypropylene resin (c) and polypropylene resin (b) is employed,
the blending ratio of these two in the base resin is: polypropylene
resin (c) 30 to 70 wt %; polypropylene resin (b) 30 to 70 wt %. The
total amount of (c) and (b) is 100 wt %. If the blending ratio of
the resin (b) is less than 30 wt %, the cylindrical foam extruded
from the die tends to expand in the circumferential direction;
although, in the case where the molded foam article is of linear
shape, a molded article of good appearance can be obtained by for
example performing adjustment by blowing in gas, in the case of
complex shapes, wave-shaped corrugation marks tend to be left in
the surface of the molded foam article obtained, so, as a result,
it becomes difficult to obtain a good molded foam article.
Furthermore, since there is a risk that, otherwise, sufficient
reduction of product costs might not be achieved, more preferably
the content of the polypropylene resin (b) is at least 40 wt %. On
the other hand, if the content exceeds 70 wt %, there is a risk
that the foamability may be lowered, with the result that a thick,
low-density molded foam article is not obtained; more preferably,
therefore, the content of the polypropylene resin (b) is no more
than 60 wt %.
[0064] It should be noted that the reason why, in the combination
of polypropylene resin (c) and (b), the blending ratio of the
polypropylene resin (b) has a smaller upper limiting value of 70 wt
% than in the case of the blending ratio of (b) in the combination
consisting of the polypropylene resin (a) and (b) referred to above
is that the foamability of the polypropylene resin (c) is lower
than that of the polypropylene resin (a), so, unless the blending
amount of (b) is less, at 70 wt %, a good molded foam article
cannot be obtained.
[0065] The polypropylene resin (c) employed in the present
invention has a melt tension and melt flow rate as described above.
If the melt tension of the polypropylene resin (c) is less than 30
mN, with the blending amount of the resin (c) in the combination of
polypropylene resin (b) and polypropylene resin (c) referred to
above, thick, low-density molded foam articles would not be
obtained, so the melt tension is preferably at least 40 mN and more
preferably at least 50 mN. On the other hand, from the point of
view of stable extrusion moldability when extruding when obtaining
the cylindrical foam, and product cost, preferably the melt tension
is no more than 90 mN, more preferably no more than 80 mN. Also, if
the melt flow rate of the polypropylene resin (c) is lower than 2
g/10 minutes, extrusion moldability is lowered in that for example
fluidity is adversely affected and a cylindrical foam having a
low-density foam layer cannot be obtained, due to evolution of heat
when extruding.
[0066] On the other hand, if the melt flow rate exceeds 15 g/10
minutes, the draw-down of the cylindrical foam becomes large,
producing unevenness of thickness in the molded foam article that
is finally obtained and impairing molding stability so that a good
molded foam article is not obtained. The melt flow rate of the
polypropylene resin (c) is therefore preferably 5 to 10 g/10
minutes.
[0067] In the method of manufacture according to the present
invention, if (iii), as the base resin, a combination of
polypropylene resin (a) and polypropylene resin (c) is employed,
the blending ratio of these two in the base resin is: polypropylene
resin (a) at least 20 wt % and less than 70 wt %; resin (c) more
than 30 and no more than 80 wt % (the combined amount of (a) and
(c) being 100 wt %.).
[0068] If the blending ratio of the resin (c) is an amount of less
than 30 wt %, the cylindrical foam extruded from the die tends to
expand in the circumferential direction; although, in the case
where the molded foam article is of linear shape, a molded article
of good appearance can be obtained by for example performing
adjustment by blowing in gas, in the case of complex shapes,
wave-shaped corrugation marks tend to be left in the surface of the
molded foam article obtained, so, as a result, it becomes difficult
to obtain a good molded foam article. Furthermore, since there is a
risk that, otherwise, sufficient-reduction of product costs might
not be achieved, more preferably the content of the polypropylene
resin (c) is at least 40 wt %. On the other hand, if the content
exceeds 80 wt %, there is a risk that foamability may be lowered,
with the result that a thick, low-density molded foam article is
not obtained; more preferably, therefore, the content of the
polypropylene resin (c) is no more than 70 wt %.
[0069] Next, in the method of manufacture according to the present
invention, the case (iv) in which, as the base resin, a combination
of three polypropylene resin (a), polypropylene resin (b) and
polypropylene resin (c) is employed will be described. If
polypropylene resin (a), (b) and (c) are employed, a base resin is
employed consisting of a component composition in the range of the
quadrangle A, B, C, D (and including on the lines of the
quadrangle) defined by joining up with straight lines the four
points represented by point A (17, 78, 5), B (5, 72, 23), C (5, 30,
65) and D (65, 30, 5) represented by component co-ordinates
constituted by the points (x, y, z), as shown in FIG. 5, where the
content of this polypropylene resin (a) component is x wt %, the
content of this polypropylene resin (b) component is y wt % and the
content of this polypropylene resin (c) component is z wt %, on a
triangle component diagram in which this polypropylene resin (a)
100 wt % is marked at the upper vertex of the regular triangle,
this polypropylene resin (b) 100 wt % is marked at the lower left
vertex and this polypropylene resin (c) 100 wt % is marked at the
lower right vertex and in which the content of polypropylene resin
(a) is 5 to 65 wt %, the content of polypropylene resin (b) is 30
to 78 wt % and the content of polypropylene resin (c) is 5 to 65 wt
% (where the total content of (a), (b) and (c) is 100 wt %).
[0070] In blends of the above three resin components, blends in
which the sum of the blending ratios of polypropylene resin (a) and
polypropylene resin (c) is at least 30 wt % are preferable in that
thicker molded foam articles with low density are obtained. On the
other hand, in order to achieve an excellent appearance of the
molded foam article and to achieve a sufficient reduction in
product costs, it is desirable that (a) and (c) should be no more
than 65 wt %.
[0071] With a composition consisting of polypropylene resin (a),
(b) and (c), it was found that, by blending at least 5 wt % in each
case of the polypropylene resin (a) and (c), as the base resin, the
surface smoothness of the molded foam article tended to be improved
and the ratio of the closed cells in the molded foam article
obtained tended to be higher, compared with a composition
consisting of polypropylene resin (a) and (b) or a combination
consisting of polypropylene resin (b) and (c) as described above.
It is inferred from this that the polypropylene resin (c) in the
composition comprising polypropylene resin (a), (b) and (c) may
have the effect of rendering the condition of dispersion of the
polypropylene resin (a) and (b) more uniform.
[0072] In the above three types of combination, in the case where
the blended amount of resin (b), of the polypropylene resin (a),
(b) and (c), is less than 30 wt %, in the case of resin
compositions indicated by the quadrangular region defined by H (70,
30, 0), G (0, 30, 70), N (0, 0, 100), L (100, 0, 0) in the
component coordinates shown in FIG. 5, sufficient lowering of the
product costs is not achieved; furthermore, the cylindrical foam
extruded from the die tends to expand in the circumferential
direction; although, in the case where the molded foam article is
of linear shape, a molded article of good appearance can be
obtained by for example performing adjustment by blowing in gas, in
the case of complex shapes, wave-shaped corrugation marks tend to
be left in the surface of the molded foam article obtained, so, as
a result, there is a risk of it becoming difficult to obtain a good
molded foam article.
[0073] On the other hand, of the resin (a), resin (b) and resin
(c), if the blending amount of resin (b) exceeds 78 wt %, in the
component coordinates shown in FIG. 5, in the case of resin
compositions in the region indicated by the triangle defined by E
(20, 80, 0), M (0, 100, 0), F (0, 70, 30), foamability is lowered
with the result that a thick, low-density molded foam article is
not obtained.
[0074] Also, in the above three types of combination, of the resin
(a), resin (b) and resin (c), if the blending amount of resin (c)
is less than 5 wt %, in the component coordinates shown in FIG. 5,
in the case of resin compositions in the region indicated by the
quadrangle defined by E (20, 80, 0), A (17, 78, 5), D (65, 30, 5)
and H (70, 30, 0), a molded foam article with a high ratio of the
closed cells is not obtained and surface smoothness is lowered.
These phenomena are more marked as the blending amount of resin (b)
is increased.
[0075] In addition, in the above three types of combination, of the
resin (a), resin (b) and resin (c), if the blending amount of resin
(a) is less than 5 wt %, in the component co-ordinates shown in
FIG. 5, in the case of resin compositions indicated by the
quadrangular region defined by B (5, 72, 23), F (0, 70, 30). G (0,
30, 70) and C (5, 30, 65), a molded foam article with a high ratio
of the closed cells is not obtained and there is a risk of surface
smoothness being lowered. These phenomena are more marked as the
blending amount of resin (b) is increased.
[0076] In these three types of combination, the reason that an
upper limiting value of the blending ratio of resins of (b) of up
to 72 wt % or up to 78 wt %, on the straight line AB shown in FIG.
5 can be allowed is that excellent molded foam articles are
obtained even if the blending amount of resin (b) is large,
compared with a resin composition consisting of a combination of
two of resin (c) and resin (b), since a high upper limiting value
of the blending amount of resin (b) can be employed, because resin
(a) which is of particularly excellent foaming ability and resin
(c) which is of excellent foaming ability compared with resin (b)
is included in a resin composition consisting of a combination of
resin (c) and resin (b) according to the present invention. In a
resin composition consisting of a combination of resin (a) and
resin (b) according to the present invention, since resin (a) which
is of particularly excellent foaming ability are included,
excellent molded foam articles can be obtained even if the upper
limit of the blending amount of resin (b) is large, at 80 wt %.
[0077] In a method of manufacture according to the present
invention, a resin mixture produced by selecting and combining at
least two or more of polypropylene resin (a), (b), or (c) having
respectively a specific melt tension and melt flow rate is employed
as the base resin, as described above; however, it is desirable, in
that a thick molded foam article of low density and attractive
appearance can be obtained and product costs can be lowered, to
adjust the melt tension of this mixture so as to be less than 98
mN.
[0078] It should be noted that it is possible to add other resins
within a range such as not to interfere with the object and
beneficial effect of the present invention to the aforementioned
polypropylene resins constituting the base resin, in the
manufacture of a molded foam article according to the present
invention. If this is done, preferably the added amount of such
other resins is no more than 20 wt % and more preferably no more
than 30 wt %, or even more preferably no more than 10 wt %.
[0079] There is no particular restriction concerning such other
resins but there may be mentioned by way of example the use of
thermoplastic resins such as polyethylene resins or polystyrene
resins, as resins for constituting a resin layer of a cylindrical
foam, to be described.
[0080] According to the present invention, in the case of all of
the base resins of a combination according to the present
invention, a cylindrical foam 2 is formed by producing foamable
molten resin containing foaming agent by heating and kneading
foaming agent and the base resin in an extruder, followed by
extrusion of this molten resin from a die into a hollow shape with
an extrusion rate per unit area (hereinbelow simply termed
"extrusion rate") of at least 15 kg/hrcm.sup.2, preferably at least
35 kg/hrcm.sup.2 and even more preferably at least 50
kg/hrcm.sup.2. The upper limit of the extrusion rate is about 500
kg/hrcm.sup.2, though this depends on the capacity of the extruder.
The extrusion rate referred to in the presence specification is a
value obtained by dividing the extrusion amount (kg/hr) of foamable
molten resin extruded from the die mounted at the leading end of
the extrusion device by the area of the aperture of this die.
However, if the method is adopted of performing intermittent
extrusion of molten resin from a die typically used to perform blow
molding, when the cylindrical foam is formed, since the molten
resin is extruded intermittently by changing from a condition in
which the aperture of this die is close to a condition in which it
is open, the area of the aperture changes during extrusion of the
molten resin and in some cases the extrusion amount of molten resin
may also change. In such cases, in order to find the extrusion
rate, for the amount of extrusion when the area of the aperture has
become a maximum, which changes in terms of the extrusion amount of
molten resin, the maximum value of the area of the aperture, which
changes in terms of the area of the aperture of the die, is adopted
and calculated as described above. The extrusion rate described
above is also adopted in the case where, by the co-extrusion
method, molten resins are extruded from the aperture of the die
after merging with another non-foamable molten resin and/or
foamable molten resin within the die.
[0081] If the aforementioned extrusion rate is too small, even
though a base resin is employed of no matter what combination
according to the present invention, it is difficult to obtain a
cylindrical foam having a thick foam layer and having a foam layer
of small apparent density and the physical strength, heat
insulation and appearance of the molded foam article obtained by
molding this cylindrical foam with a desired mold are adversely
affected.
[0082] Contrariwise, if the extrusion rate is too large, a large
amount of heat is emitted on extrusion of this molten resin from
the die, with the risk that a molded foam article of low density
(i.e. of high expansion ratio) may not be obtained, due to
breakdown of the cells of the foam layer.
[0083] As the foaming agents employed in the method according to
the present invention, there may be listed by way of example
aliphatic hydrocarbons such as propane, normal butane, isobutane,
normal pentane, isopentane, normal hexane, isohexane or
cyclohexane; chlorinated hydrocarbons such as methyl chloride or
ethyl chloride; fluorinated hydrocarbons such as
1,1,1,2-tetrafluoroethane, or 1,1-difluoroethane; aliphatic ethers
such as dimethyl ether, diethyl ether, or methyl ethyl ether;
aliphatic alcohols such as methyl alcohol, or ethyl alcohol;
organic physical foaming agents such as dialkyl carbonates such as
dimethyl carbonate or diethyl carbonate; inorganic physical foaming
agents such as carbon dioxide, nitrogen, air or water; or
decomposable chemical foaming agents such as sodium hydrogen
carbonate, sodium citrate or azodicarbonamide. These foaming agents
may be employed in mixed form. In the method according to the
present invention, of the foaming agents listed above, physical
foaming agents, in particular physical foaming agents containing
carbon dioxide, are preferable. As physical foaming agents
containing carbon dioxide, there may be employed simply carbon
dioxide or a mixed physical foaming agent comprising carbon dioxide
and another physical foaming agent.
[0084] Since the solubility of the carbon dioxide that is employed
as the foaming agent with respect to polypropylene resins is
smaller than that of organic physical foaming agents such as
butane, although the carbon dioxide dissolves in the polypropylene
resins of the base resin and the high pressure in the extruder,
when released from the die to atmospheric pressure, the carbon
dioxide is suddenly gasified and separates from the polypropylene
resins. Consequently, if carbon dioxide or a physical foaming agent
containing carbon dioxide is employed to form the foam layer, since
this foaming agent is rapidly gasified so that cell formation is
quickly completed and since scarcely any or none at all of this
foaming agent is left in the resin, there is no possibility of the
resin being plasticized and a cylindrical foam can therefore be
obtained having a foam layer that is in a harder softened state
than that of a cylindrical foam obtained using an organic physical
foaming agent.
[0085] When a molded foam article of the shape of the hollow region
of the mold is obtained by molding and cooling such a cylindrical
foam in a separable mold, the desired shape can be satisfactorily
maintained even though the molded foam article is withdrawn from
the mold at rather a high temperature and a molded foam article of
excellent physical strength such as compression strength can be
obtained; there are therefore the benefits that the cooling time
after molding the molded foam article can be considerably shortened
and production efficiency raised by employing a physical foaming
agent containing carbon dioxide as the foaming agent.
[0086] Also, carbon dioxide is non-combustible, so the curing time
for preventing ignition of a molded foam article formed using a
physical foaming agent containing carbon dioxide is shortened.
Furthermore, since combustible gas such as butane is not employed,
safety during manufacture and flame retardance of the molded foam
article obtained are improved.
[0087] It should be noted that, even if a mixed physical foaming
agent containing carbon dioxide (mixed foaming agent of carbon
dioxide and another, organic physical foaming agent) is employed, a
similar beneficial effect can be obtained as in the case where a
foaming agent consisting of carbon dioxide is employed, since the
employed amount of organic physical foaming agent, such as butane
employed as physical foaming agent, is reduced, albeit there may be
some difference in the level of the effect.
[0088] Preferably 0.1 to 0.8 mol of the physical foaming agent (in
the case of use of a mixed physical foaming agent, the total amount
of physical foaming agents) per 1 kg of base resin constituting the
foaming layer of the cylindrical foam is added and more preferably
0.2 to 0.5 mol thereof is added.
[0089] Depending on the application, it is undesirable for the
amount of this physical foaming agent added to be less than 0.1 mol
per 1 kg of base resin constituting the foam layer of the
cylindrical foam, since the apparent density of the foam layer
becomes large, resulting in a molded article of inferior heat
insulation and lacking in lightweight characteristics. On the other
hand, if the amount of the physical foaming agent exceeds 0.8 mol,
this risks the molded foam article being of lowered apparent
density and the closed cell ratio, with poor appearance, due to the
cells collapsing due to the cell film being unable to withstand the
foaming force produced by abrupt gasification of the large content
of foaming agent.
[0090] In the method of the present invention, if a physical
foaming agent containing carbon dioxide is employed as the foaming
agent, preferably the content of carbon dioxide is 20 to 100 mol %
with respect to 100 mol % of the physical foaming agent. More
preferably the content of carbon dioxide is 50 to 100 mol % and
even more preferably 70 to 100 mol %. With a foaming agent with
such a blending ratio, the foam layer of the cylindrical foam is
abruptly cooled by the abrupt gasification, so a cylindrical foam
with fine cell size and a high ratio of the closed cells can be
obtained.
[0091] Also, if a physical foaming agent containing carbon dioxide
is employed, as described above, the extent to which the
polypropylene resin is plasticized by the foaming agent is small,
or no plasticization takes place, so a molded foam article of
excellent dimensional stability and strength can be obtained, in
particular a molded foam article of excellent dimensional stability
and strength can be obtained immediately after extraction from the
mold or a very short time after extraction therefrom. In
particular, if polypropylene resins of straight-chain form are
employed as the base resin, the crystallization speed of the
straight-chain polypropylene resins is faster than the
crystallization speed of polypropylene resins having free terminal
long-chain branching in the molecular structure, so there is a
synergetic effect with the physical foaming agent containing carbon
dioxide and the benefit in terms of shortening of cooling time is
considerable.
[0092] Various types of additives such as cell adjustment agents,
ultraviolet absorbing agents, infra-red absorbing agents, infra-red
reflecting agents, flame retardant agents, fluidity improvers,
weatherproofing agents, coloring agents, heat stabilizers,
antioxidants, or fillers may be added to the base resin
constituting the foam layer in the present invention, in accordance
with requirements.
[0093] The melt tension (MT) in this specification was measured
using a melt tension tester type II manufactured by Toyo Seiki
Seisaku-sho, Ltd., extruding the resin into cord form under the
extrusion conditions: molten resin temperature 230.degree. C.,
piston speed 10 mm/minutes, using a cylindrical orifice having a
straight passage of length 8 mm, passage diameter 2.095 mm,
engaging this cord with a tension detection pulley of diameter 45
mm and then coiling with a coiling roller of diameter 50 mm while
gradually increasing the speed of coiling, with a ratio of about 5
rpm/second (coiling acceleration of the cord: 1.3.times.10.sup.-2
m/second.sup.2).
[0094] In order to find the melt tension, the coiling speed is
increased until the cord hooked on the tension detection pulley
breaks, to find the coiling speed: R (rpm) when the cord breaks.
Next, winding of the cord is again performed at a fixed winding
speed of R.times.0.7 (rpm) and the change with time of the melt
tension of the cord detected by the detector linked with the
tension detection pulley is measured; this change is shown on a
graph taking the melt tension as the vertical axis and the time as
the horizontal axis, to obtain a graph having an amplitude as shown
in FIG. 4.
[0095] As the melt tension in this specification, the central value
(X) of the amplitude of the stable portion of the amplitude as
shown in FIG. 4 is taken. However, if the cord has not broken even
on reaching a coiling speed of 500 rpm, the melt tension of the
cord is found from the graph in which the coiling speed is found by
coiling the cord as 500 rpm.
[0096] It should be noted that, when the change of melt tension is
measured with time, occasionally, peculiar amplitude values are
detected, but such peculiar amplitude values may be neglected.
[0097] When measuring the melt tension of the polypropylene resin
forming the foam layer, the melt tension be found by the same
method as described above, using a sample that has been de-foamed
by heating and melting a sample piece cut from the foam layer for
about 15 minutes in a vacuum oven at 200.degree. C.
[0098] The melt flow rate (MFR) of the polypropylene resin in this
specification is measured using a test load of 21.18 N at a test
temperature of 230.degree. C. in accordance with JIS K 7210
(1976).
[0099] Preferably the cylindrical foam in the method of the present
invention is a multilayer cylindrical foam having a resin layer on
the outside and/or inside of a foam layer obtained by co-extrusion
of foamable molten resin and non-foamable molten resin.
[0100] For example, as shown in FIG. 2 (b), a multilayered
cylindrical foam 2 wherein a resin layer 22 is provided on the
outside surface of a foam layer 21 and, as shown in FIG. 2 (c) a
multilayer cylindrical foam 2 wherein a resin layer 23 is provided
on the inside surface of a foam layer 21, or, as shown in FIG. 2
(d), a multilayered cylindrical foam 2 wherein a resin layer 22 is
provided on the outside surface of a foam layer 21 and a resin
layer 23 is provided on the inside surface of the foam layer 21 may
be employed.
[0101] Forming a molded foam article using such a multilayer
cylindrical foam 2 wherein a resin layer 22 and/or resin layer 23
is provided is a desirable mode in view of the fact that attributes
such as dimensional accuracy and strength of the molded foam
article obtained are improved and that the molded foam article
obtained also has an excellent appearance. The beneficial effects
are also exhibited that the extrusion stability is improved, that
the resin layers 22, 23 prevent collapse of the cells of the foam
layer 21 and that a molded foam article of low apparent density is
obtained.
[0102] Also, there is no restriction to resin layers 22 or 23, and
a multilayer can be included besides a single layer in the resin
layers. There may be mentioned by way of example multilayer resin
layers having a resin layer with gas barrier characteristics, such
as a polyamide resin.
[0103] As the resin constituting the resin layer of the cylindrical
foam, there is no particular restriction, but, usually,
thermoplastic resins such as polyethylene resins, polypropylene
resins or polystyrene resins may be employed on account of their
excellent moldability and ease of procurement. Resins having good
adhesion with the polypropylene resins constituting the base resin
of the foam layer are preferred.
[0104] Where the resin constituting the resin layer is a
polystyrene base resin, there may be mentioned by way of example as
polystyrene resins homopolymers of styrene or styrene copolymers,
the styrene-based monomer component contained in such copolymers
being at least 25 wt %, preferably at least 50 wt % or more
preferably at least 70 wt %. Specific examples that may be given of
styrene copolymers include polystyrene, rubber modified
polystyrene, styrene-acrylonitrile copolymer,
styrene-butadiene-acrylonitrile copolymer, styrene-acrylate
copolymer, styrene-methacrylate copolymer, styrene-methyl
methacrylate copolymer, styrene-ethyl methacrylate copolymer,
styrene-methyl acrylate copolymer, styrene-ethyl acrylate
copolymer, styrene-malleic anhydride copolymer,
polystyrene-polyphenylene ether copolymer and mixtures of
polystyrene and polyphenylene ether.
[0105] In order to improve the adhesion of the foam layer with
respect to the polystyrene resin constituting the resin layer,
preferably one or two or more of a compatibility-promoting
component, resilient component or polypropylene resin is added in
an amount of not more than 30 wt %, and is preferably added in an
amount of not more than 20 wt %. The lower limiting value is about
5 wt %.
[0106] As additives acting as the aforementioned
compatibility-promoting component or resilient component, from the
point of view of for example recycling and costs, there are
preferably employed rubber modified polystyrene such as high-impact
polystyrene, styrene conjugated diene block copolymers such as
styrene-butadiene-styrene block copolymer or
styrene-isoprene-styrene block copolymer, or for example the
hydrogenated forms of the above styrene-based polymers.
[0107] As the polyethylene resin employed in the aforementioned
resin layer, there may be mentioned by way of example resins a
homopolymer of ethylene or a copolymer of ethylene and
.alpha.-olefin of carbon number 3 to 12 having a ethylene content
of at least 60 wt %; specifically, high-density polyethylene,
medium density polyethylene, low-density polyethylene,
straight-chain low-density polyethylene, ultra-low density
polyethylene or ethylene-vinyl acetate copolymer are preferred.
[0108] In order to improve adhesion of the polyethylene resin with
the foam layer, preferably no more than 30 wt % of polypropylene
resin is added and more preferably no more than 20 wt % thereof is
added. The lower limit is about 5 wt %.
[0109] As the polypropylene resin that is added to the polyethylene
resin, there may be mentioned by way of example resins which are
similar to the polypropylene resins constituting the foam
layer.
[0110] As the polypropylene resins employed in the foam layer,
there may be mentioned by way of example polypropylene resins for
example propylene homopolymer or a copolymer of propylene and
another copolymerizable monomer having a propylene content of at
least 60 wt %; as copolymerization components, there may be
mentioned by way of example ethylene, butylene or other
.alpha.-olefins, the carbon number of these .alpha.-olefins being
no more than 12 and preferably no more than 8. The polypropylene
resins preferably constitute at least 60 wt % with respect to the
entire weight constituting the resin layer, more preferably at
least 70 wt % and most preferably 100 wt %.
[0111] However, the resin layer in the molded foam article
according to the present invention is not restricted to these and
thermoplastic resins such as for example polycarbonate resins,
polyamide resins or polyester resins could be employed.
[0112] Various types of additives such as ultraviolet absorbing
agents, infra-red absorbing agents, infra-red reflecting agents,
flame retardant agents, fluidity improvers, weatherproof ing
agents, coloring agents, heat stabilizers, antioxidants, fillers or
electrostatic charging preventing agents may be added to the base
resin constituting the foam layer in the present invention, in
accordance with requirements.
[0113] Molded foam articles derived from cylindrical foam 2 of
construction in accordance with FIG. 2 (d) according to the present
invention have improved strength such as compression strength,
bending strength and tensile strength and high surface hardness and
are therefore preferably employed for example for ducts, tanks,
containers or pallets.
[0114] The invention is described in more detail below with
reference to examples. However, the present invention is not
restricted to these examples.
EXAMPLE 1
[0115] Foamable molten resin was obtained by mixing 3.1 weight
parts of foam adjustment agent "master batch" (base resin: 85 wt %
of low-density polyethylene, 5 wt % of sodium stearate and 10 wt %
of talc) with 100 weight parts of base resin obtained by mixing 65
wt % of polypropylene resin (a) PF814 (MT: 200 mN, MFR: 3 g/10
minutes) manufactured by Sun Allomer Company Ltd and 35 wt % of
polypropylene resin (b) J-700 GP (MT: 4 mN, MFR: 9 g/10 minutes)
manufactured by Idemitsu Petrochemical Co., Ltd, supplying to an
extruder of internal diameter 65 mm and heating, melting and
kneading, then introducing under pressure and kneading 0.34 mol of
isobutane with respect to 1 kg of base resin (100 mol % of
isobutane with respect to 100 mol % of foaming agent) as foaming
agent from a point midway in the extruder.
[0116] Next, the temperature (hereinbelow simply referred to as the
"melt temperature") of the foamable molten resin was adjusted to
167.degree. C. and the resin was introduced into accumulators.
Next, pressure was applied to the ram of each accumulator and
foamable molten resin was extruded at an extrusion rate of 64
kg/hrcm.sup.2 from this die by opening a gate arranged at the
leading end of a circular die, thereby forming a cylindrical foam.
The cylindrical foams obtained had exceptionally excellent foam
condition and appearance.
[0117] Next, a cylindrical foam obtained was arranged within a
cylindrical-shaped mold positioned directly below the circular die
and the mold was closed. Molding was then performed by blowing in
pressurized gas (air) into the interior of the cylindrical foam
from a gas introduction port arranged at the bottom of the mold
while simultaneously, the pressure between the outer surface of the
cylindrical foam and the inner surface of the mold was reduced;
after molding and cooling, a duct-shaped molded foam article
(hollow body of dimensions of opening mouth is 70 mm.times.150 mm
and dimensions of length is 600 mm) was separated from the mold.
Excellent appearance was obtained with no wrinkles caused by
furrow-shaped corrugations generated in the cylindrical foam
appearing in the surface of the foam obtained.
EXAMPLE 2
[0118] In Example 1, foamable molten resin was obtained by mixing
3.1 weight parts of foam adjustment agent "master batch" as in
Example 1 with 100 weight parts of base resin obtained by mixing 30
wt % of polypropylene resin (a) PF814 and 70 wt % of polypropylene
resin (b) J-700 GP, and introducing under pressure and kneading
0.34 mol of isobutane with respect to 1 kg of base resin (100 mol %
of isobutane with respect to 100 mol % of foaming agent) as in
Example 1 as foaming agent from a point midway in the extruder.
[0119] Next, a duct-shaped molded foam article was formed by
arranging the cylindrical foam within a mold in the same way as in
Example 1 and conducting molding with a melt temperature and
extrusion rate in accordance with the conditions indicated in Table
1. Excellent appearance was obtained with no wrinkles caused by
furrow-shaped corrugations generated in the cylindrical foam
appearing in the surface of the foam obtained.
EXAMPLE 3
[0120] In Example 1, foamable molten resin was obtained by mixing
3.1 weight parts of foam adjustment agent "master batch" as in
Example 1 with 100 weight parts of base resin obtained by mixing 65
wt % of polypropylene resin (a) PF814 and 35 wt % of polypropylene
resin (b) J-700 GP, and introducing under pressure and kneading
0.34 mol of liquefied carbon dioxide with respect to 1 kg of base
resin (100 mol % of carbon dioxide with respect to 100 mol % of
foaming agent) as in Example 1 as foaming agent from a point midway
in the extruder.
[0121] Next, a duct-shaped molded foam article was formed by
arranging the cylindrical foam within a mold in the same way as in
Example 1 and conducting molding with a melt temperature and
extrusion rate in accordance with the conditions indicated in Table
1. Excellent appearance was obtained with no wrinkles caused by
furrow-shaped corrugations generated in the cylindrical foam
appearing in the surface of the foam obtained.
[0122] By employing a physical foaming agent consisting of carbon
dioxide, the cooling time of the molded foam article was shortened
to about 1/3 compared with Example 11.
EXAMPLE 4
[0123] In Example 1, foamable molten resin was obtained by mixing
3.1 weight parts of foam adjustment agent "master batch" as in
Example 1 with 100 weight parts of base resin obtained by mixing 20
wt % of polypropylene resin (a) PF814 and 80 wt % of polypropylene
resin (b) J-700 GP, and introducing under pressure and kneading
0.31 mol of isobutane with respect to 1 kg of base resin (100 mol %
of isobutane with respect to 100 mol % of foaming agent) as in
Example 1 as foaming agent from a point midway in the extruder.
[0124] Next, a duct-shaped molded foam article was formed by
arranging the cylindrical foam within a mold in the same way as in
Example 1 and conducting molding with a melt temperature and
extrusion rate in accordance with the conditions indicated in Table
1. Excellent appearance was obtained with no wrinkles caused by
furrow-shaped corrugations generated in the cylindrical foam
appearing in the surface of the foam obtained.
EXAMPLE 5
[0125] Foamable molten resin was obtained in the same way as in the
case of Example 3, except that 0.31 mol of liquefied carbon dioxide
with respect to 1 kg of base resin (100 mol % of carbon dioxide
with respect to 100 mol % of foaming agent) was introduced under
pressure and kneaded, from a point midway in the extruder.
[0126] Non-foamable molten resin for use as an inside layer and
outside layer was obtained by blending a coloring agent with reused
resin (MT: 45 mN, MFR: 7 g/10 minutes) of molded foam articles
obtained by Example 1, by respectively separately supplying this
raw material to two extruders of internal diameter 40 mm and
heating, melting and kneading.
[0127] Next, the temperature of the foamable molten resin was
adjusted to 172.degree. C. and the temperature of the non-foamable
molten resin was adjusted to 185.degree. C. and these were then
introduced into separate accumulators connected with respective
extruders. Next, a multilayer cylindrical foam was formed by
co-extrusion at an extrusion rate of 80 kg/hrcm.sup.2 of this
molten material from the die by opening a gate arranged at the
leading end of a circular die and simultaneously applying pressure
to the rams of the accumulators. A multilayer foam was thus formed
comprising an inner layer/foam layer/outer layer as shown in FIG. 2
(d) discharged from the die in layer form by merging of the molten
material injected by the accumulators into the die in the vicinity
of the gate provided in the vicinity of the leading end of the die.
The inner layer and the outer layer were non-foamed resin
layers.
[0128] The multilayer cylindrical foam obtained was of particularly
attractive appearance, being of cylindrical shape with little
vertical fluctuation of diameter in the length direction of the
extruded cylindrical foam.
[0129] Next, a duct-shaped molded foam article was formed by
performing blow molding in the same way as in the case of Example 1
using the multilayer cylindrical foam obtained. Excellent
appearance was obtained with no wrinkles caused by furrow-shaped
corrugations generated in the cylindrical foam appearing in the
surface of the foam obtained. The thickness of both the outside
resin layer and inside resin layer in the molded foam article was
1.0 mm each.
[0130] By employing a physical foaming agent consisting of carbon
dioxide, the cooling time after foaming was shortened to about 1/3
compared with Example 1.
[0131] Also, when comparing the cooling times of Example 3 and 15.
Example 5, since the blending amount of polypropylene resin (b) in
the case of Example 3 was more than in the case of Example 5, the
cooling time was shorter than in the case of Example 5.
COMPARATIVE EXAMPLE 1
[0132] Foamable molten resin was obtained by mixing 3.1 weight
parts of foam adjustment agent "master batch" in the same way as in
the case of Example 1 with 100 weight parts of base resin obtained
by mixing 85 wt % of polypropylene resin (a) PF814 (MT: 200 mN,
MFR: 3 g/10 minutes) manufactured by Sun 25 Allomer Ltd and 15 wt %
of polypropylene resin (b) J-700 GP, supplying to an extruder of
internal diameter 65 mm and heating, melting and kneading, then
introducing under pressure and kneading 0.34 mol of isobutane with
respect to 1 kg of base resin (100 mol % of isobutane with respect
to 100 mol % of foaming agent) in the same way as in Example 1 from
a point midway in the extruder.
[0133] A molded foam article was obtained in the same way as in
Example 1 by molding a cylindrical foam by extrusion using a melt
temperature the same as in Example 1 and an extrusion rate that was
substantially the same. However, although the appearance and
moldability of the molded foam article obtained were excellent, the
product cost was high.
COMPARATIVE EXAMPLE 2
[0134] Foamable molten resin was obtained by mixing 3.1 weight
parts of foam adjustment agent "master batch" in the same way as in
the case of Example 1 with 100 weight parts of base resin obtained
by mixing 15 wt % of polypropylene resin (a) PF814 manufactured by
Sun Allomer Ltd and 85 wt % of polypropylene resin (b) J-700 GP,
and introducing under pressure and kneading 0.34 mol of isobutane
with respect to 1 kg of base resin (100 mol % of isobutane with
respect to 100 mol % of foaming agent) from a point midway in the
extruder.
[0135] A cylindrical foam was molded by extrusion using a melt
temperature and an extrusion rate that were substantially the same
as in as in Example 1. However, cell collapse of the cylindrical
foam obtained was exceptionally severe, so that molding of a molded
foam article of suitable appearance could not be achieved on
account of the poor condition of the foam.
[0136] Table 1 shows, for the Examples 1 to 5 and Comparative
Examples 1 and 2, the MT and MFR of the raw material used, the
shape of the molded foam article (indicated in the table by
"shape"), the type of foaming agent, the kind of foaming agent, the
melt temperature and the extrusion rate per unit area (shown in the
table as "extrusion rate") and also, as the physical properties of
the molded foam article obtained, the apparent density of the foam
layer (shown in the table as "density of the foam layer"), the
average thickness (shown in the table as "thickness"), average cell
diameter, ratio of the closed cells, melt tension and
appearance.
[0137] In the table, "i-B" is an abbreviation for isobutane and
"CO.sub.2" is an abbreviation for carbon dioxide.
[0138] As can be seen from Table 1, in the case of the molded foam
articles obtained in the Examples, thick molded foam articles were
obtained with an average thickness of at least 4.0 mm.
TABLE-US-00001 TABLE 1 Raw Properties of Molded Foam Article
Material Density and Extrusion of the Average Ratio of Blending
Foaming Melt Rate Foam Cell the Closed Melt Amount Agent
Temperature (kg/hr Layer Thickness Diameter Cells Tension Appear-
(wt %) Shape (mol/kg) (.degree. C.) cm.sup.2) (g/cm.sup.3) (mm)
(mm) (%) (mN) ance Example 1 (a)/(b) = Duct Single i-B 167 64 0.16
5.0 1.0 56 48 .largecircle. 65/35 Layer (0.34) Example 2 (a)/(b) =
i-B 172 72 0.18 5.0 0.9 32 32 .largecircle. 30/70 (0.34) Example 3
(a)/(b) = CO.sub.2 166 70 0.15 5.0 0.5 65 46 .largecircle. 65/35
(0.34) Example 4 (a)/(b) = i-B 172 75 0.22 5.0 0.9 18 30
.largecircle. 20/80 (0.31) Example 5 (a)/(b) = Multilayer CO.sub.2
172 80 0.20 4.0 0.4 36 29 .largecircle. 20/80 (0.31) Compara-
(a)/(b) = Duct Single i-B 167 62 0.16 5.0 1.0 68 60 .largecircle.
tive 85/15 Layer (0.34) Example 1 Compara- (a)/(b) = i-B 168 78 --
-- -- -- -- -- tive 15/85 (0.34) Example 2 (a)Resin; PF814 (MT =
200 mN, MFR = 3 g/10 min) (b)Resin; J-700GP (MT = 4 mN, MFR = 9
g/10 min)
EXAMPLE 6
[0139] Foamable molten resin was obtained by mixing 3.1 weight
parts of foam adjustment agent "master batch" in the same way as in
Example 1 with 100 weight parts of base resin obtained by mixing 70
wt % of reused resin (c) (MT: 45 mN, MFR: 7 g/10 minutes) of molded
foam articles obtained in Example 1 as polypropylene resins with 30
wt % of polypropylene resin (b) J-700 GP, and introducing under
pressure and kneading 0.31 mol of isobutane with respect to 1 kg of
base resin (100 mol % of isobutane with respect to 100 mol % of
foaming agent) as foaming agent from a point midway in an extruder
as in Example 1.
[0140] A duct-shaped molded foam article was then obtained by
arranging the cylindrical foam obtained in a mold in the same way
as in Example 1 and conducting extrusion with the melt temperature
and extrusion rate conditions shown in Table 2. Excellent
appearance was obtained with no wrinkles caused by furrow-shaped
corrugations generated in the cylindrical foam appearing in the
surface of the foam obtained.
EXAMPLE 7
[0141] Foamable molten resin was produced in the same way as in the
case of Example 6 apart from the use of the raw material blend
shown in Table 2. A duct-shaped molded foam article was then formed
by arranging the cylindrical foam obtained in a mold in the same
way as in Example 1 and conducting extrusion with the melt
temperature and extrusion rate conditions shown in Table 2.
Excellent appearance was obtained with no wrinkles caused by
furrow-shaped corrugations generated in the cylindrical foam
appearing in the surface of the foam obtained.
EXAMPLE 8
[0142] Foamable molten resin was produced in the same way as in the
case of Example 6 apart from the use of the raw material blend
shown in Table 2. A duct-shaped molded foam article was then formed
by arranging the cylindrical foam obtained in a mold in the same
way as in Example 1 and conducting extrusion with the melt
temperature and extrusion rate conditions shown in Table 2.
Excellent appearance was obtained with no wrinkles caused by
furrow-shaped corrugations generated in the cylindrical foam
appearing in the surface of the foam obtained.
[0143] In addition, polypropylene resin (b-2) K1014 (melt tension
14 mN, melt flow rate 4.7 g/10 minutes) manufactured by Chisso
corporation in Table 2.
COMPARATIVE EXAMPLE 3
[0144] Foamable molten resin was produced in the same way as in the
case of Example 6 apart from the use of the raw material blend
shown in Table 2. Extrusion was then conducted with the melt
temperature and extrusion rate conditions shown in Table 2.
However, cell collapse of the foam layer of the cylindrical foam
obtained as a result was exceptionally severe, so that molding of a
molded foam article of suitable appearance could not be achieved on
account of the poor condition of the foam.
[0145] Table 2 shows, for the Examples 6 to 8 and Comparative
Example 3, the MT and MFR of the raw material used, the shape of
the molded foam article (indicated in the table by "shape"), the
type of foaming agent, the kind of foaming agent, the melt
temperature and the extrusion rate per unit area (shown in the
table as "extrusion rate") and also, as the physical properties of
the molded foam article obtained, the apparent density of the foam
layer (shown in the table as "density of the foam layer"), the
average thickness (shown in the table as "thickness"), average cell
diameter, ratio of the closed cells, melt tension and
appearance.
[0146] In the table, "i-B" is an abbreviation for isobutane and
"CO.sub.2" is an abbreviation for carbon dioxide.
[0147] In the case of the molded foam articles obtained in the
Examples, thick molded foam articles were obtained with an average
thickness of at least 5.0 mm. TABLE-US-00002 TABLE 2 Properties of
Molded Foam Article Density Extrusion of the Average Ratio of Raw
Material Foaming Melt Rate Foam Cell the Closed Melt and Blending
Agent Temperature (kg/hr Layer Thickness Diameter Cells Tension
Appear- Amount (wt %) Shape (mol/kg) (.degree. C.) cm.sup.2)
(g/cm.sup.3) (mm) (mm) (%) (mN) ance Example 6 (c)/(b-1) = Duct
Single i-B 167 70 0.20 5.0 0.9 61 30 .largecircle. 70/30 Layer
(0.31) Example 7 (c)/(b-1) = i-B 168 72 0.24 5.0 1.0 30 17
.largecircle. 30/70 (0.31) Example 8 (c)/(b-2) = i-B 172 72 0.23
5.0 0.9 5 26 .largecircle. 30/70 (0.31) Compara- (c)/(b-1) = Duct
Single i-B 174 76 -- -- -- -- -- -- tive 20/80 Layer (0.31) Example
3 (c)Resin; Recovered Raw Material in Practical Example 1 (MT = 45
mN, MFR = 7 g/10 min) (b-1)Resin; J-700GP (MT = 4 mN, MFR = 9 g/10
min) (b-2)Resin; K1014 (MT = 14 mN, MFR = 4.7 g/10 min)
EXAMPLE 9
[0148] Foamable molten resin was obtained by mixing 3.1 weight
parts of foam adjustment agent. "master batch" in the same way as
in Example 1 with 100 weight parts of base resin obtained by mixing
30 wt % of polypropylene resin (a) PF814, 30 wt % of polypropylene
resin (b) J-700 GP and 40 weight parts of reused resin (MT: 45 mN,
MFR: 7 g/10 minutes) of molded foam articles obtained in Example 1
as polypropylene resin (c), and likewise introducing under pressure
and kneading 0.31 mol of isobutane with respect to 1 kg of base
resin (100 mol % of isobutane with respect to 100 mol % of foaming
agent) as foaming agent from a point midway in the extruder in the
same way as in Example 1.
[0149] Next, the temperature of the foamable molten resin was
adjusted to 171.degree. C. and the resin was introduced into
accumulators. Next, pressure was applied to the ram of each
accumulator and foamable molten resin was extruded at an extrusion
rate of 75 kg/hrcm.sup.2 from this die by opening a gate arranged
at the leading end of a circular die, thereby forming a cylindrical
foam. The cylindrical foam obtained had exceptionally excellent
foam condition and appearance.
[0150] Next, a cylindrical foam obtained was arranged within a
cylindrical-shaped metal mold in the same way as in Example 1 to
form a duct-shaped molded foam article. Excellent appearance was
obtained with no wrinkles caused by furrow-shaped corrugations
generated in the cylindrical foam appearing in the surface of the
foam obtained.
EXAMPLE 10
[0151] Foamable molten resin was produced in the same way as in the
case of Example 9 apart from the use of the raw material blend
shown in Table 3. Extrusion was then conducted with the melt
temperature and extrusion rate conditions shown in Table 3.
Excellent appearance was obtained with no wrinkles caused by
furrow-shaped corrugations generated in the cylindrical foam
appearing in the surface of the foam obtained.
EXAMPLE 11
[0152] Foamable molten resin was produced in the same way as in the
case of Example 9 by introducing under pressure and kneading from a
point midway in an extruder, apart from the use of the raw material
blend shown in Table 3. Extrusion was then conducted with the melt
temperature and extrusion rate conditions shown in Table 3.
Excellent appearance was obtained with no wrinkles caused by
furrow-shaped corrugations generated in the cylindrical foam
appearing in the surface of the foam obtained.
COMPARATIVE EXAMPLE 4
[0153] Foamable molten resin was produced in the same way as in the
case of Example 9 by introducing under pressure and kneading from a
point midway in an extruder, apart from the use of the raw material
blend shown in Table 3. Extrusion was then conducted with the melt
temperature and extrusion rate conditions shown in Table 3.
[0154] However, cell collapse of the foam layer of the cylindrical
foam obtained as a result was exceptionally severe, so that molding
of a molded article of suitable appearance could not be achieved on
account of the poor condition of the foam.
COMPARATIVE EXAMPLE 5
[0155] Foamable molten resin was produced in the same way as in the
case of Example 9 by introducing under pressure and kneading from a
point midway in an extruder, apart from the use of the raw material
blend shown in Table 3. Extrusion was then conducted with the melt
temperature and extrusion rate conditions shown in Table 3.
[0156] However, although the appearance and moldability of the
molded foam article obtained as a result were excellent, the
product cost was high.
[0157] Table 3 shows, for the Examples 9 to 11 and Comparative
Examples 4 and 5, the MT and MFR of the raw material used, the
shape of the molded foam article (indicated in the table by
"shape"), the type of foaming agent, the kind of foaming agent, the
melt temperature and the extrusion rate per unit area (shown in the
table as "extrusion rate") and also, as the physical properties of
the molded foam article obtained, the apparent density of the foam
layer (shown in the table as "density of the foam layer"), the
average thickness (shown in the table as "thickness"), average cell
diameter, ratio of the closed cells, melt tension and appearance.
In the table, "i-B" is an abbreviation for isobutane and "CO.sub.2"
is an abbreviation for carbon dioxide. In the case of the molded
foam articles obtained in the Examples, thick molded foam articles
were obtained with an average thickness of at least 5.0 mm.
TABLE-US-00003 TABLE 3 Properties of Molded Foam Article Density
Extrusion of the Average Ratio of Raw Material Foaming Melt Rate
Foam Cell the Closed Melt and Blending Agent Temperature (kg/hr
Layer Thickness Diameter Cells Tension Appear- Amount (wt %) Shape
(mol/kg) (.degree. C.) cm.sup.2) (g/cm.sup.3) (mm) (mm) (%) (mN)
ance Example 9 (a)(b)(c) = Duct Single i-B 171 75 0.20 5.0 0.8 80
42 .largecircle. 30/30/40 Layer (0.31) Example 10 (a)(b)(c) = i-B
172 78 0.21 5.0 0.9 50 29 .largecircle. 15/75/10 (0.31) Example 11
(a)(b)(c) = i-B 171 76 0.20 5.0 0.9 70 37 .largecircle. 10/30/60
(0.31) Compara- (a)(b)(c) = Duct Single i-B 174 80 -- -- -- -- --
-- tive 5/90/5 Layer (0.31) Example 4 Compara- (a)(b)(c) = i-B 170
72 0.19 5.0 0.9 55 55 .largecircle. tive 70/10/20 (0.31) Example 5
(a)Resin; PF814 (MT = 200 mN, MFR = 3 g/10 min) (b)Resin; J-700GP
(MT = 4 mN, MFR = 9 g/10 min) (c)Resin; Recovered Raw Material in
Practical Example 1 (MT = 45 mN, MFR = 7 g/10 min)
[0158] The closed cell ratio was determined by the following method
in the case of both the Examples and the Comparative Examples.
[0159] (Measurement of the Closed Cell Ratio of a Foam Layer)
[0160] Using a test piece from the foam layer of the molded foam
article obtained, Vx is found by the procedure C of ASTM D 2856-70
(re-authorized in 1976) by using Air Comparison Pycnometer 930
manufactured by Toshiba Beckmanke Co., Ltd. and calculated by the
following expression. Portions where the cells are crushed are
excluded. The closed cell ratio
(%)=(Vx-Va(.rho.f/.rho.s)).times.100/(Va-Va(.rho.f/.rho.s)) [0161]
where [0162] Vx is the actual volume of the test piece (sum of the
volume of the closed cells portion and volume of the resin portion)
(cm.sup.3); [0163] Va is the apparent volume (cm.sup.3) found from
the dimensions of the external shape of the test piece; [0164]
.rho.f is the apparent density of the test piece (g/cm.sup.3); and
[0165] .rho.s is the density of the base resin of the test piece
(g/cm.sup.3)
[0166] It should be noted that, of the physical properties in
Tables 1 to 3, the apparent density of the foam layer is measured
as follows and the average thickness and average cell diameter are
measured by the method described above.
[0167] (Apparent Density of the Foam Layer)
[0168] Using a test piece cut from a foam layer of the molded foam
article obtained, the test piece weight (g) is found by dividing by
the volume (cm.sup.3) found from the external dimensions of this
test piece.
[0169] Evaluation of the appearance shown in Tables 1 to 3 is
conducted as indicated below.
[0170] (Evaluation of the Appearance)
[0171] Evaluation of the appearance is conducted in accordance with
the following criteria in regard to the molded foam article
obtained.
[0172] O . . . the shape of the cells is uniform, with little
fluctuation of thickness and no local formation of recesses
(sinks).
[0173] X . . . there is local formation of giant cells, with
considerable fluctuation thickness and local formation of recesses
(sinks).
* * * * *