Note: Descriptions are shown in the official language in which they were submitted.
36Z~
This invention relates to a method for the extru-
sion foaming of synthetic resin, which enables economical
and continuous extrusion foamed ar-ticle of large and thick
cross section. Further, it relates to an economical
method for the manufacture o:E an extrusion foamed article
of synthetic resin excelling in flexibility, cushioning
property, resistance to heat and compression creep and
other properties.
Methods which effect desired foaming of a poly-
styrene resin, polyethylene resin, etc. by the steps of
mixing the resin with a blowing agent, heating and kneadin~
the mixture and extruding the resultant molten mixture into
a zone of decreased pressure enjoy a wiaespread acceptance.
With these techniques for the extrusion foaming of synthe-
tic resins, however, foamed article,having large and thick
cross section cannot easily be obtai.ned. If foamed article
of large thickness are to be produced at all under speci.al
conditions, such conventional techniques have inevitably
found it necessary to use a complicated processing system
.
' 20 and an extruder having a high extruding capacity and a
'' large screw diameter, inconveniencing the operation.
. If a cylinder-shaped extrusion foamed article
of about 150 mm in diameter is to ~e obtained by extrusion
foaming a low-denqity polyethylene resin, for example,
it is found necessary to use a large extruder of at least
' 60 mm in screw diameter. The difficulties experienced in
:~ the adjustment of extruding conditions ow.ing to the
, lar~eness of the size of extruder either result in impair
: uniformity of cell diameter or cell distribution or
necessitate use of complicate facillties or ski.iled
-- 2
,. bm.
.:
.
"~ fi20
manual manipulation for the adjus-tment of said conditions.
If the foamed article is used as a heat insulat-
ing material, cushioning material, etc., for example, it
is required to excel in various properties such as cell
porosity, recovery from compression, resistance to heat
and compression creep and thermal conductivity and to
have the numerical values of these properties invariably
exceed certain levels in concert. In this sense, all the
extrusion foamed articles obtainable by the existing
techniques are not satisfactory. For this reason, the
conventional techniques have su~fered from a disadvantage
that the particular resin subjected to a given extrusion
foaming should be selected very strictly so as to meet
finely defined use conditions. Foamed articles of a
polystyrene resin, for example, have the disadvantage that
they are deficient in flexibility and ability to absorb
repeated impacts, although they are excellent in compressive
~ .
strength and thermal insulating property. In the case of
the extrusion foamed article of a low-density polyethylene
resin, for example, there is a disadvantage that the
article is defici~nt in thermal-insulatin~ property and
in resistance to heat and compression creep despite its
excellency in flexibility and cushioning property. The
extrusion foamed article of an ionic copolymer (hereinafter
referred to as l'ionomer") resin is claimed to excel in
cushioning property and yet suffers from a disadvantage
that it shows notable deficiency in resistance to heat
and compression creep, compressive strength, etc. Besides
this drawback, it has a fault that the extrusion back
pressure at the time of extrusion foaming is abnormally
' '
~ 3 ~
bm.
,~
: '
~0736Z~
high so as not to enable the extrusion foaming to be
economically accomplished.
Numerous researches have been carried out with
a view to developing extrusion foamed articles of improved
properties by mixing two or more types of synthetic resins
and foaming the resultant resin blends. Unfortunately,
however, the techniques which have issued from such
researches cannot be called perfect since the plurality
of types of resins involved have no sufficient compati-
`' 10 bilityO
For example, the method disclosed by Japanese
Patent Laying-open Nos. 35471/1974 and 25675/1975, namely
a method which comprises the steps of preparinq a basal
resin by use of 60 to 90 parts by weight of a polyolefin
resin and 10 to 40 parts by weight of a polystyrene resin,
mixing this basal resin with a blowing agent (particularly
'l of trichlorofluoromethane) and extrusion foaming the
, mixture, has a disadvantage that the foaming effected
thereby suffers from heavy shrinkage, the method fails
to permit economic production of a foamed article having
large and thick cross section, and the cushioning property
exhibited by the article is of a level too 1QW for the
product to be rendered practicable.
The present ivention has originated in such
status of affairs. Its perfection has resulted from the
conception of the combination of resins which show notably
inferior compatibility to a combination of polyethylene
and polystyrene and which discoura~e everyone from givin~
due attention thereto, namely, the organic combination of
the three requirements indicated below:
`.'` .
,,,~,
- 4 -
bm.
~ .
3fi2~ ~
(1) A proper amount of an ionomer resin which shows inferior
compatibility with polyolefins, and
(2~ a proper amoun~ of a styrenic resin which shows inferior
compatibility with said polyolefins and said ionomer
(3) can be extrusion foamed in the presence of a volatile
blowing agent (of a type to be specified as occasion demands).
An object of the present invention is to provide an
economical method for extrusion foaming, which is capable of
easily extrusion foaming of high quality and large and ~hick
cross section by use of an extruder of a small screw diameter.
Another ob~ect of the present invention is to provide
a novel extrusion foamed article of synthetic resin, novel in
the sense that the numerical values of the properties a ~oamed
article is required to possess for use in thermal insulating
materlals, cushioning materials, etc. invariably exceed certain
fixed levels.
In one particular aspect the present invention provides
a process for producing a foamed article which comprlses
blending 10 to 90% by weight of an ionomer resin having a melt
index from 0.1 to 50 g/10 min. and 90 to 10% by weight of a
styrenic synthetic resin, and mixing 100 parts by weight oE the
resulting blend in the molten state with 5 to 60 parts by weight
of a volatile blowing agent, having a Kauri-butanol value up to
25, in an extruder at high temperature and pressure, and
extruding the resulting blended mixture into a ~one kept under
a pressure which is not higher than atmospheric pressure, thereby
allowing the extruda~e to expand.
In another particular aspect the present invention provides
a foamed article having a bulk density from 15 to 200 kg/m3
comprising a foamed resinous composition containing 10 to 90
weight percent of an ionomer resin having a melt index of from
0.1 to 50 g/10 min. and 90 to 10 weight percent of a styrenic
jr ~ ~ ~ 5-
:~73~
synthetic resin.
In the accompanying drawings, Figure 1 shows a schematic
drawing of the distribution of cells of the product of this
; invention;
Figure 2 an enlarged view of Figure 1;
Figure 3 a schematic drawing of the distribution of
cells in the product of prior art;
Figure 4 an enlarged view of Figure 3, respectively.
.; To accomplish the objects described above according to
the present invention, the present invention provides a process
for producing a foamed articl of synthetic resin, which
comprises blending 100 parts by
.. .
. ~
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.,
. ~ .
~'
. . . .
'.' .
.~ .
~. 30
., .
.' .
~ 5a-
... . . .
'.: ' . .. : ~ .
0~36Z~
weight of a molten resin mixture consisting of 10 to 90
weight percent of ionomer resin and 90 to 10 weight
; percent of a styrenic synthetic resin with 5 to 60 parts
by weight of a volatile blowing agent at an elevated
temperature under increased pressure, extruding the result-
ant mixture into a zone of a pressure not higher than
atmospheric pressure, thereby allowing the extrudate to
expand.
In the first place, the essential requirement
for the present invention resides in using as one component
of the basal resin an ionomer resin and as the other compo-
nent thereof a styrenic resin. This particular combination
of the components has been singled out on a very strict -
criterion from among a host of possible combinations of
synthetic resins. E~pec~al~y when the compatibility is
taken into account, it is a surprising and hardly imagin-
able thing even for a person of ordinary skill in the art
that the two components mix so thoroughly with each other
as to give rise to an extrusion foamed article of uniform
texture and, moreover, the resin blend resulting from said
mixture enjoys improved extrusion foaming property.
The ratio of the ionomer resin to the styrenic
resin which is advantageous for this invention is 10 to
90 percent, preferably 30 to 90 percent, of the ionomer resin
to 90 to 10 percent, preferably 70 to 10~ o~ the styrenic
resin. If the proportion of the ionomer resin exceeds
the upper limit 90 percent, the back pressure at the
time of extrusion abnormally increases to the extent of
. .
rendering the commercial production of extrusion foamed
article impracticable unless the volume of extrusion is
,,~
"
- 6 -
bm.
'.~J,
~''' ~ ' ' ' ' ,'.
., . . , ~ ' . .
~3620 ''
lowered or there is developed and employed a pressure proof
extruder of a special design. If the proportion of 'the
ionomer resin fails to exceed the lower limit of 10 percent,
the quality of the styrenic resin predominates over that of
the ionomer resin and the compatihility between the
components is adversely affected, with a disadvantageous
result that the extrusion foaming property of the resin
blend will be degraded.
As measured in terms of the crass section of
extrusion foamed article prepared under the optimum
conditions of a ~iven extruder, the moldability improved
by the blending of the two components mentioned above is
about five times as large as that obtained in the extrusion
of a low-density polyethylene resin and 'about two times as
large as that obkained in the extrusion of a styrenic resin.
Further, the back pressure involved in the extrusion by
the method of this invention is 40 to 60 percent less than
that involved in the extrusion of the ionomer res~in.
The term "ionomer resin" as used in the present
invention refers to a copolymer which is 'obtained when
represented by the following generic formula:
RI I ~ R" R ~ R~ R ~ R"
~CHCH2~a ~CH ~b ~ H-l~C -~CH f ~d
CO2 1O2M CO2H
wherein R denotes hydrogen atom or an alkyl group; each of
R~ and R" denotes hydrogen atom or a methyl group; R"
denotes a lower alkyl group such as methyl, ethyl or
propyl; M denotes a metal as is described below, and a, b,
c and d den~t~ mol percentages of the respective monomers
; 30 in the copolymer, and a is 50 mol % or more, b, c and d
.
- 7 -
; bm.
.
36~0
are determined from neutrality N which is 60 mol percent
or less and the saponification degree which is 50 mol percent
or more.
With respect to the ionomer resin of the foregoing
description, the neutrality N and the saponification de~ree
S will be as defined below.
7,,, N (mol percent) = c x 100
S (mol percent) = c + d x 100
b + c + d
In the present invention, the extrusion foamed
article produced thereby acquires discrete cells of a -
uniform size more readily when the neutrality N of the -~
copolymer in use does not exceed 60 percent. More prefer-
ably, N is in -the range from 10 to 40 percent. The saponifi-
cation degree S is only required to exceed 50 percent. For
the copolymer to enjoy uniform foaming more readily,
however, the saponification degree of the copolymer in use
is desired to be from 70 to 100 percent.
The sum of c ~ d is preferably in the range of
from 0.2 to 25 mol percent, most preferably in the range
: . .
of from 1 to 10 mol percent.
The ionomer resin, in its solid state, is ionically
;.,
. ,
crosslinked. When it is brought into a molten state, said
crosslinked will disappear or decrease in number. When it is
; bxought back into its solid state~, it is ionically cross-
~inked again.
' To be more specific about the metal ion component
, of said copolymer, it is the ion of any of the metals, 1 to
,~"~
~i~ 3 in valency, belonging to groups I, II, III, IV-a and VIII
.~
in the Periodic Table of Elements. Examples of the monovalent
?.~
,
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~'' bm.
,...................... .
.,.. ~. I ,
."," . ~ . ,
. ., , .. - , , . , , . ,; ,:
~~ l0~3~a
metal ions include Na , K , Li , Ag and CU ~ Examples of
the divalent metal ions include Be , Mg , Ca , Sr , Ba
Cu +, Cd++, Sn+ , Pb , Fe , Co , Ni and Zn . And
examples of the trivalent metal ions include Sc , Fe
++~
and Yt . For the purpose of the present invention, the
metal ion is desired to be Na , Zn , or Ca
- The processes disclosed in U.S~ Patents 3,264,272
and 3,789,035 can be applicable for preparation of the
ionomers as mentioned above.
The ionomer resin, in its solid state, retains
; an ionic crossed linkage, When it is brought into a molten
state, said crossed linkage ceases to exist or decreases~
When it is brought back into its solid state, it regains
said crossed linkage~
The value of the MI (as determined by the method,
Condition E, specified by ASTM-D-1238-70) of the ionomer
resin suffices in the range of from 0,1 to 50 g/10 minutes.
The copolymer produces uniform foaming more readily when
;; the MI thereof falls in the range of from 0,3 to 10 g/10
minutes, most preferably from 0.3 to 2.9 g/10 minutes~
; When the MI exceeds the upper limit 50 g/10 minutes,
the extrusion foamed article produced from the copolymer
fails to acquire discrete ce~ls of a uniform size and
consequently suffers from degradation oE both com~ressive
strength and cushioning property, The extrusion Eoamed
article likewise fails to acquire discrete cells of a
uniform size when the MI of the copolymer does not reach
the lower limit 0,1 g/10 minutes,
The term "styrenic resin" as used in the
specification and claims refers to a synthetic polymeric
. ~, .
. ~ ' .' .
~ 9 ~
bm:p'~
. ' '
~3~2~
resin containing at least 20 wt.% o~ styrene or styrene
derivative. The following groups of polymeric resins are
included:
(1) homopolymers of styrene or styrene derivative such as
2-methyl styr~ne, (o-, m-, p-) methyl styrene or aromatic
styrene;
(2) copolymers of styrene or styrene derivative with
other comonomers such as a vinyl monomer (e.g. methyl
methacrylate, acrylonitrile, etc.) or a conjugated diene
monomer (e.g. butadiene);
(3) rubber-reinforced styrene polymers or copolymers.
Typical examples of such polymers include poly-
styrene, styrene-acrylonitrile copolymer and styrene-malèic
anhydride copolymer, so called high-impact polystyrene and
high-impact acrylonitrile-butadiene-styrene copolymer (~BS
resin).
It has been confirmed that an extrusion foamed
article of thermoplastic resin containing uniform, discrete
cells and excelling in compressive strenqth, cushioning
property and foaming property is obtained when there is
used a styrenic resin containing 3 to 80 weight percent,
;~ preferably 5 to 50 weight percent, of a rubbery substance.
The rubber-reinforced resin used for the present
invention is a thermoplastic resin which contains either a
diene-type monomer or polymer. Examples o~ the resin are
resins such as styrene-butadiene block copolymers (e.g. so
called thermoplastic) and styrene-butadiene random copolymers
~- which are obtained by the chemical reaction of a styrene
monomer or polymer with a diene-type monomer or polymer,
mechanically mixed resins consisting of styrene homopolymers
'
-- 1 0 --
bm.
36~
or styrene-based copolymers and diene-type polymers having
a rubbery state at normal room temperature. The resins may
be used singly or in -the form of mixtures.
As to the melt flow property of the styrenic
resin used for the present invention, the MI of said resin
is desired to fall in the range of from 0.3 to 30 as deter
mined by the method, Condition G, specified by ASTM-D-1238-
70.
~ Selection of the blowing agent for use in t~e
- 10 present invention is also important. The selection can
advantageously be made by taking into account the K~B.
value which will be defined afterward. Generally, there
: is used a volatile blowing agen~ having a K.B. value of
not more than 25 and a boiling point of not more than 90~C
under normal pressure. The upper limit 25 of the K.B. value
is critical because the extrudability aimed at is not
' obtained when a volatile blowing agent having a K.B. value
: ,.
exceeding 26 i8 used alone. Concrete examples of such
volatile blowing agents are dichlorodifluoromethane (herein
~ 20 after referred to as F-12) (K.B. value 18, boiling point
; -29.8C under normal pressure), monochlorodifluoromethane
(hereinafter referred to as F-22) ~K.B. value 25, boiling
point ~40.8C), dichlorotetrafluoroethane (hereinafter
referred to as F-114) (K.B. value 12, boiling point 3.8C),
propane (K.B~ value 23, boiling point -42.1C) and butane
(~C.B. value 24, boiling point -0.5C). These volatile
blowing agents may be used either singly or in the form
of mixtures consisting of two or more members.
In order to ob-tain favorable properties of the
extrusion foamed article, it is preferred to use a mixture
'. ' `- '-'.
.~ ~
- 1 1 -
bm.
~ .
: . . . . ~ .... . . . .
,-'' lOq36Z~
which consists of 20 to 90 weight percen-t of at least one
member selected from the group of volatile blowing agents
possessed of K.B. values of not more than 25 (hereinafter
referred to as "group I") and 80 to 10 weight percent of
at least one member selected from the group of volatile
blowing agents possessed of K~B. values of not less than
26 and boiling points of not more than 90C under normal
pressure (hereinafter referred to as "group II"). Although
the mixing ratio of these groups I and II is variable with i .-
the properties of the particular agents to be actually
used, it constitutes an essential requirement for perfect
accomplishment of the object of the present invention.: .
Concrete examples of volatile blowing agents of
said group II include trichloromonofluoromethane (herein-
after referred to as F-ll) (K.B. value 60, boiling point
23.8C under normal pressure), dichloromonofluoromethane ..
(hereinafter referred ~o as F-21) (K~B. value 102, boiling
point 8.9~)~ trichlorotrifluoroethane (hereinafter referred
: to as F-113) (K.B. value 32, boiling point 47.6C), methyl
ch.loride (hereinafter referred to as "MeCQ") (K.B. value
80, boiling point -23.6C), methylene chloride (hereinafter
referred to as "MeCQ2") (K.B. value 136, boiling point 40C),
pentane (K.B. value 127, boiling point 36.1C) and hexane
(K.B. value 30, boiling point 68.~C).
The amount of the blowing agent to be used in
the present invention is generally in the range of from 5
to 60 parts by weight and, in case where the effectiveness
of the blowing agent demands due attentlon, in the range
; of from 5 to 35 parts by weight based on 100 parts by weight
: 30 of the basal resin. It may freely be selected within the
' ' .
- 12 - .
' '
. bm.
:
. .
``` 1~7362Q
~ range so as to satisfy the foaming ahility of the blowing
~ agent and the bulk density which the finally produced foamed
article is intended to possess.
If the amount of the volatile blowing agent does
not reach the lower limit 5 parts by weigh-t based on 100
--- parts by weight of the basal resin, then the foamed article
.. . .
- ~ - consequently obtained fails to acquire uniform cells. If
~ it exceeds the upper limit 60 parts by weight, then the
~- .- ~ -
-:-~ - cells being formed in the course of continuous foaming are
.L0 ruptured, making it impossible to provide continued produc-
~ tion of extrusion form having discrete cells of a uniform
:.: "' - '
size.
The basal resin of the present invention, as
occasion demands, may have incorporated in its component
resins or resin blend an effective amount of a stabilizer
;~ serving to repel the action of heat or light or prevent
, degradation, an additive useful for enhancing smoothness
and impact resistance or a coloriny agent. At the time
~ of extrusion foaming, a suitable amount of a substance
;~ 20 such as, for example, an inorganic carbDnate, organic
silicate, inorganic phosphate, metal salt of higher fatty
acid, or indigo which is generally used as the nucleic
agent, or stabilizing agent may be used additionally for
the purpose of adjusting and stabilizing the cell diameter,
cell distribution and foaminc~ conditibn. Furthermore,
other thermosplastic resins such as polyethylene or rubbery
substances can also be used as additives, if necessary.
Also for the purpose of adjusting the cell dia-
meter of the foam, an organic nucleic agent ~such as, for
example, calcium stearate or barium stearate) and/or
,
:.; .
- 13 -
bm.
, ~
362~
inorganic n~lcleic agent (such as, for example, talc) may be
used in the ordinarily accepted amount.
For practice of the invention, there can be used
conventional technique of extrusion foaming which enjoys
favorable acceptance for commercial application because of
its advantageous productivity. The operational procedure
usually comprises the steps of mixing a basal resin and a
volatile blowing agent in an extruder at elevated tempera-
tures under increased pressure, then cooling the resultant
0 blend for thereby lowering both pressure and temperature to
respective levels proper for foaming and subsequently
extruding the cooled blend through a die possessed of a
desired shape into the atmosphere for thereby causing
continuous ~oaming of the extruded blend.
For uniform dispersion of the volatile blowing
agent in the basal resin, it is an absolute ~lecessity that
said basal resin and volatile blowing agent be blended at
elevated temperatures under increased pressure w~thin the
extruder. Without uniform dispersion, it is hard to obtain
advantageous foaming. At low temperatures, there is a
possibility that sufficient blending of the resin and the
blo~in~ agent will no longer occur. Furthermore, thexe is
, also a possibility that the extrudability of the blend as
observed at the time of extrusion foaming will be spoiled.
In addition, the uniformity of distribution of cells in
the foamed article will be impaired. Accordingly, the
properties of the foamed article will be de~rade~.
Further, at low temperatures, since the viscosity of the
.;
. resin is heightened, it becomes necessary to adopt a
~1 30 complicate and expensive extruder of a special structure
;; :
bm.
.
.: ' ' '
-~ ~07~
capable of withstanding the added load and pressure exerted
for the actions of extrusion and blending, rendering the
commerical production disadvantageous. Under insuf-ficient
pressure, there tends to ensue a disadvantage that the blow-
ing agent is not uniformly distributed throughout the resin.
In the method of this invention, the temperature
and pressure conditions under which the blending is càrried
out within the extruder are desired to be such that, in the
metering zone or mixing zone of the leading-end portion of
~ 10 the extruder in which the resin and the blowinq a~ent are
; blended more thoroughly than elsewhere, the temperature
will fall in the range of from 120 to 300C and the
pressure in the range of from 50 to 250 kg~cm , respectively.
` To ensure advantageous foaming, the uniform blend
which has been formed under conditions of elevated tempera~
tures and increased pressure must be cooled so that its
; temperature and pressure will both be lowered to levels
proper for the desired foaming.
If the blend is extruded in its uncooled state
into the atmosphere, there is a fair possibility that the
blend will suffer from impaired extrudability which entails
disadvantages such as shrinkage of foamed article, loss of
surface smoothness and failure to keep a desired shape, for
example. There is also a possihility that the individual
cells will be heavily ruptured to greatly degrade ~arious
properties of the foamed articles. If the blend is suffered
to remain under said increased pressure, then it is ex- ;~
tremely difficult to provide desired foaming of the blend
and there tends to ensue a disadvantaqe that the individual
cells will be heavily ruptured. If the pressure exerted
. ' '
- 15 -
bm.
, .: .
'?~
, , . . , :: . . - :. .
~ iO~62~
: , .
on the blend is excessively lowered immediately before the
blend is extruded into the atmosphere, there readily ensues
a disadvantage that the individual cells will be ruptured
to a notable extent. To be more specific, if the extrusion
foaming is carried QUt under a pressure lower than the
pressure required for liquefying the blowing agent contained
; in the blend, foaming occurs within the foaming unit before
the blend is released into the atmosphere, making it
difficult to provide the operation and effect of improving
the extrudability of the blend and uniformizing the dis-
; tribution of discrete cells in the foamed ar-ticle through
advantageous utili~tion of the latent heat of evaporation
;~ involved when the blowing agent is vaporized and allowedi . .
~ to fulfill its intended function. Consequently, a dis~
7'-' advantage tends to ensue that the foamed article will have
ùnuniform distribution of cells and the individual cells
~; will readily be ruptured.
i j~ ,. . ..
For the purpose of the method of this invention~
the temperature of the blend which is about to be released
from the foaming unit into the atmosphere is desired to fall
,;;, .
in the range of from 70 to 110C, preferably from 85 to
100C. Desirably a rotary temperature regulator may be
disposed between the extruder and the die so as to enable
the temperature and pressure of the blend to be adjusted to
proper levels for extrusion foaming.
If, in the method of this invention, there is
used a chemical blowing agent (such as, for example, azo-
dicarbonamide) which libera-tes upon thermal decomposition
a foaming gas such as nitrogen or carbon dioxide which has
a very low boiling point and is difficultly miscible with
, . .
- 16 -
bm.
. ~
.'~ ' : . ,, ' . ' . . :
3~20
the basal resin, it becomes aifficult to maintain a pressure
proper for foaming at the temperature proper for the foamin$
of the basal resin, and the blowing agent itself tends to
vaporize within the foaming unit before the blend is r~leased
into the atmosphere~ Consequently t there is involved a
disadvantage that desirable foaming will no longer be obtained
and the distribution of cells in the foamed article will be
degraded. There~ore, such a chemical blowing agent is
excluded from the scope of the invention.
The method of this invention allows the tempera-
ture of the blend to fall in the range of from 70 to 110C
immediately before extrusion foaming. No other method so
far developed for the manufacture of a thermoplastic resin
foamed article tolerates such a broad temperature range.
This broad temperature range may well be called epochal in
the sense that it permits easy commercial production of the
, ,
foam.
For the purpose of the method of this invention,
it suffices to have the blend simply released into the
atmosphere. h7hen necessary, however, there may be adopted
a special device which is capable of keeping the released
blend under decreased pressure to the lower limit of 0~2
atm.
According to preferred embodiments, extrusion is
performed under conditions such that the extrudate has a
thickness ranging from 0.5 to 100 mm, more preferably from
2 to 50 mm and is allowed to an expansion ratîo of from 2
to 50 to produce a foamea article having a thickness of
from 1 to 1000 mm, more preferably from 20 to 1000 mm.
The foamed article obtained according to the
bm.
.
.
~736~o
process of the present invention is found to be ~pecific
in having well balanced properties and therefore can be
used for a great v~riety of uses, Typically, foa~ed articles
having thickness of 2Q mm to 1000 mm, preferably 30 to 500 mm,
and bulk density of Z0 to 5~ Kg/m3 produced from a resinous
mixture consisting of 40 to 70 wt.~, preferably 45 to 60 wt.%,
of an ionomer resin and 60 to 30 wt~, preferably 55 to 40
wt.~ of a styrenic resin containing at least 70 wt.% of
styrene or styrene derivative are unexpectedly found to be
endowed with all of the following properties: (as measured
by the methods as hereinafter described~
(a~ compxession strength ranging from 2 to 4 Kg/cm ;
(b) compression recovery ranging from 80 to 99%;
(c) maximum deceleration ranging from 100 to 50G;
and
;- (d) heat trans~er ratio ranging from 0,031 to 0,020
' Kcal/m.hour,C,
Furthermore, under most favorable conditions~ the product
can be provided with compression strength ranging from 3 to
4 Kg/cm , compression recovery ranging from 90 to 99%r
maximum deceleration ranging from 90 to 50G and heat transfer
ratio ranging from 0,03Q to 0,020,
Now, the terms to be used in the specification
' and claims will be defined. The method oE the present
invention will be descxibed in further detai:l with reference
to said ~referred embodiments and comparative examples,
a~ Bulk density (kg/m3)
This is expressed by the value resulting from the
division of the weight of the extrusion foamed article
by the volume thereof. This magnitude is of a nature
such that the degree of foaming obtained in the product
increases in reverse proportion to said value,
- 18 -
bm:p~
:. .
. .
~ 736~0
b) Mean cell diameter (mm)
This is expressed by the average value of the dia-
meters of all the cells contained within a 100-cm2
cross section of the foamed article.
c) Compression recovery (%)
This is expressed by the value calculated from the
., .
~ formula of QfQoX lOO ~ of which the variables Q0 and Q
- are to be found in an experiment comprising the steps
. of pressing a foamed article measuring 50 mm x 50 mm x
. -10 50 mm for an interual of 0.5 second under the
.
. ~ conditions of normal room temperature, 2 m per second
of deformation rate and 50 kg/cm of stress until 80%
~ . of the original wall thickness (Q0) of said foam is
.; - evenly shrunken, allowing the shrunken foam to stand . -
at normal room temperature for a total of 24 hours
. and measuring the wall th.ickness (Q) of the foam at
"~' the end of said standing.
'. d) Resistance to heat and compression creep (~) .
.~ . This is expressed by the value calculated from the
formula- Q0 Ql x 100, of which the variables Q0 and
. Ql are to be found respectively in the preceding
experiment on the compressive recovery and in a suh- ::
. sequent exper'ment comprising the steps of applying
. to the specim~n Eoamed article which has undergone ~.
said preceding experiment a static compressive load
of 0.1 kg/cm2 at a controlled temperature of 60C
evenly.in the same direction in which the foamed
article was pressed in the preceding experiment,
: allowing the foamed article to stand under the
applied load for a total of 24 hours and measuring
., . - .
` 19
.: bm.
' . :
~'
,, . . , ~
--` 10~736Z~
the thickness (~1) of the foamed article at the end
of the standing.
e) Compression strength (kg/cm )
This is expressed by the value of stress which is
exhibited when an extrusion foamed article measuring
50 mm x 50 mm x 50 mm is pressed at a deformation rate
of 12.5 mm per minute until 25~ of the original thick-
ness is evenly shrunken. Measurements are carried out
in the ~ertical, parallel and horizontal directions.
The largest value is determined as the compression
strength.
f) Maximum deceleration (G)
This is expressed by the value which is obtained by
dividing the maximum acceleration registered on the
accelerometer by the gravitational acceleration;
the maximum acceleration is to be obtained in an
experiment wherein a flat slab having 20 cm and
~! weighing 10 k~ and ~rovided with an accelerometer
is dropped onto a rectangular foamed article measuring
. 20 14 . 6 cm in area and 3 cm in thickness from the height
of an effective length of 60 cm in such way that the
slab will exert an even force on the surface of said
article in the direction of thickness.
g) Thermal conductivity (Kcal/m.hour.C)
This is the value to be obtained by the measure-
! ment carried out in accordance with the method specified
in ASTM-C-177~
h) Cell porosity (~)
A foamed article is kept under reduced pressure of
300 mmHg at normal room temperature for ten minutes.
,.`
, .
:: .
- 20 -
bm.
, .,
:, .. , . : ' -
; ' - . '.
7362~
The ar~icle, in its unaltered form, is submer~ed in
an aqueous 3~ polyethylene glycol (surface active
agent) solution and left to stand therein for ten
minutes. Then, the article is removed fr~m the
solution and wiped to dry the surface and weighed.
(Let Wl stand for the weight thus found.) Let (W0)
and (VF) stand for the weight and volume of the
article prior to exposure to said reduced pressure.
Then the cell porosity is expressed by the formula,
1 - 0 x 100. This value is of a nature such that
F
~ the proportion of dlscrete cells lncreases ln reverse
proportion to this value. This means that the suit-
ability of the article as a cushioning material or
heat-insuIating material increases in reverse
proportion to this value.
,.
i) Shrinkage (%)
This is expressed by the value to be calculated
.~ ,
from the formula, Bo _ 1 x 100, namely the value
corresponding to the difference between the volume
of the foamed articles (Bo) measured two minutes after
extrusion foaming and the volume (Bl) measured after
an interval of three days.
This value represents the de~ree of the dimensional
stability of the extrusion foamed article at the time
of extrusion foaming. This value is Oe a nature such
that the actual dimensions of the extrusion foamed
article approach the target dimensions and the work-
ability remarkably improves in proportion as the value
decreases.
j~ ~ross sectional area (cm2)
. , .
. .
. - 21 -
,~,; .
bm.
, . ~ .
~,oq36Z~ !
This is expressed by the area of the cross section
of the foamed article which is obtained when a foamable
resin gel is extrudea through a nozzle, 3.5 mm in
diameter, attached to the leading end of an extruder
30 mm in screw diameter with an extruding capacity of
3.8 kg/hour into a zone of atmospheric pressure. Said
foamable resin ~el is prepared by mixing 100 parts by
weight of basal polymer with 21 parts by weight of a
blowing agent with a view to uniformizing the bulk
density to the fullest possible extent.
k) Kauri-Butanol (K.B. ) value
This is measured hy the method of ASTM-D-1133-61.
. -The ionomer resins used in the preferred embodiments
of this invention and the comparative examples were
invariably trial products (A through L) by Asahi-Dow
Limited. In each product, A through J, the acid
component is methacrylic acid. The products K and
contain methacrylic acid as acid component and methyl.
; methacrylate as ester component. The typical numerical
values of their properties are shown in Table 1.
.~ '. .
, ' ' , "'
'` ' .~:
: ~
;.
'
,'
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- 22 -
bm.
,
,~ .
. ~
.: . . : ~ .
10~3
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. _ _ _ _ '.: '
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. _ . __ _ _ _ . , '' ''
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o~ r~ ~ o
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a) 1~ 1 ~ '
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E3 ~ i O r
.. 1~ / ~_1 la o ~1~ -1-) ~ ~1 ~ ~1 ...
u~ / ~1 ~ ~ s~ ~ ~ ~) ~z; ~
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- 23 -
bm .
- : , ' :' . , ' :''. : '.
3~2~
Example 1 and Comparative Example 1:
Six types of ionomer resins A, E, G, H, I and J
and three types of polystyrene resins [Styron (trade mark)
680 (MI 8.0), a product by Asahi~Dow Limited], [Styron
(trade mark) 666 (MI 7.0), a product by same company] and
[Styron (trade mark) 679 (MI 25.5j, a product by same
company] were mixed in the combinations and at -the percent
compositions indicated in Table 2 to prepare basal resins.
From each of the basal resins was prepared a mixed resin by
dry blending 100 parts by weight of the basal resin with
O.S part by weight each of talc and zinc stearate.
The mixed resin was fed through a resin inlet into
an extruder (30 mm in screw diameter) having the first zone
maintained at 125C and the second and third zones each at
, 190C, causing the resin to be melted and kneaded. Through
a blowing agent inlet disposed in the neighborhood of the
, starting point of the third zone of said extruder, a blowing
agent prepared separately (by mixing 80 parts by weight of
dichlorodifluoromethane with 20 parts by weight of methylene
chloride) was introduced under increased pressure at a rate
.,i . . ~
; of 21 parts by weight of said blowing agent per 100 parts
by weight of the basal resin, allowing the blowing àgent to .
be dispersed in said molten resin. The pressure under which
the introduction of blowing agent was effected in this case ~.
(corresponding to the back pressure of the extruder) was
found to fall in the range of from 105 to 115 kg/cm . The
` molten resin flowed through the cooling and kneading zones
and consequently had its temperature adjusted to about 100C.
Then, it was extruded through a nozzle 3.5 mm in diameter
~ 30 into an atmosphere zone at an extrusion capacity of 3.8
: - 2~ -
bm.
j`, ' ' .
. " .
" ~0~362~
kg/hour to produce an e~trusion foamed article.
The article thus produced was examined by way of
rating the extrudability of the corresponding basal resins.
The results of the rating were as shown in Table 2. In
Table 2, the basal resins (composed of ionomer and poly-
styrene resins) having polystyrene resin contents in the
range of from 10 to 70 percents are indicated as belonging
to Example 1 and those having polystyrene resin contents of
5 and 95 percents as belonging to Comparative Example 1
respectively.
,
,~ .
t
- ':
. :
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,"; .
' ' , ,.
- 25 -
bm.
.'' .
.. ... . ..
0~36~Z~
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t) ~ ~ o ~ ~ , :,
o ~ ~ o
o o U3
~ I ~ rd
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~ o o ~ ~ ~ ~ U~ .,, . .
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O t~ Q~. O O O O C5~ N ~ O .
d ~ ~ -- oo ~ r-l r-t ~I r-l r-l Ll~ d'
' ~___ ____ ___.__ _ _
,~ ~ . ' .'
_~ O O O O O O O O ' C~ O ~ O O
d~0~ 0
~r~ ~ . , , ~ . .
. r-lr~ O O ~ r-l O O~i~ ~ ~1 Ltl
U~ __ ___ _,
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. ~ ,.
.~ . ~
td r~ u~ U~U~ ~r ~) ~ L~ ~ r-J 00 ~ r-l
rd E~ O O O O O O o O ~I r; O r; ~1
J .___ _~ __ .,
:" ~ ~ . . ':''
~1 r t rt7
r-l ~ ~ ~ O ~ O d' u~ l ~1 1~ 1~ t9 If~ ~1
;~. ~ ) ~ ~ ~ ~ ,
.~ m rd .Y ~ ~ 0~ ~ ~ ~ ~ c~ 1~ co,~ ~ 1`
,., _ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ :;
., _ I
.,,
,4 r~ r~
u~ .a) ~ a~ ,1 o o o o o o o o o o o
~ 1r-l ~Ll'
r~ r~ h ~d
... , ~3 .... .~ .
~ (U r~
.,i~ ~ ~ ~1 o ~ a~ o o o oo o o
;.' ~ ~ ~ Ul ) ~ CO 00 CO 00
I, ~ ~ ~ =i ii i , ~ D ~
~0 ~ ~ r~ ~ ¢ ~ 1~ H~? 1~ l
H ~ D~
., /~ r-i ~ r
.~. / r-l-~l ~ h ~
. / X I~L
_. ____ ___ ._
-- 26 --
bm.
:
1~362~
Example 2 and Comparative Example 2:
Basal resins were prepared by following the :~
~ procedure of Example 1, except the ionomer resin E and a
styrene-butadiene copolymer (butadiene content 8 weight .
percent, MFI 7.0 g/10 minutes) were used in the amounts
inaicated in Table 3. :
~: Table 3 ~:~
~ . _ ~ . .
Amount
Item of Bulk Mban Shrink- Cross :-
10 ~ \ styrene den- cell age sec-
. ~ \ buta- sity poro- (%) tiona~ Foaming
\ diene (kcJ/ sity area
:: sifi \ polymer m3) (~m) (cm2)
cation .\ .(wt.%).
_ ~ ~ ., _ .
. 15 31.0 0.5 1.70 8.2 Gcod surface
smoothness and
; Exa~ple uni~orm foamin~ . .
. 2 40 - 34.. 2 0.6 0.30 11.9 ll
p. ~0 35.4 0.8 1.~0 ~0.1 ll ~
......... . .. . . .... . . .
'.' _ ., _ : :
5 . 32.1 1.1 3.10 5.2 Slightly poor
-~ Co~para- surfaoe smooth
tive ness and un-
Examp~e . . unifonm foamin : ..
. _ 95 36.0 ~.2 e.lo 5.l i _ " _ ..::, _ .
Example 3 and Comparative Example 3:
.The procedure of Example 1 was repeated,
. except that a mixed resin consisting of 50 weight percent
....
of ionomer resin E and 50 weight percent of polystyrene
resin ~Styron (trade mark) 680] was used as the basa]. resin
and dichlorodifluoromethane (F-12) alone, propane alonè, a
. 50/50 (by weight ratio; the same applicable hereinafter)
. 30 mixture of F-12/methyl chloride (MeCQ~, a 50/50 mixture of
.,' .
_ ~7 _
.
bm.
73~2~ :
propane/methyl chloride and a 75/25 mixture of F-l~/methylene
chloride (MeCQ2) (belonging to Example 3), methylene chloride
alone, -trichloromonofluoromethane (F-ll) alone and pentane
alone (belonging to Comparative Example 3) were used as the
blowing agent to be introduced into the basal resin. The
extrusion foamed articles thus obtained were examined to rate
the extrudability of the corresponding basal resins at the
time of extrusion. The results of the rating were as shown
; in Table 4.
The pressure under which the blowing agent was
introduced in this case invariably fell in the range of
from 105 to 115 kg/cm2.
~.
. . .
.l
',, . :
:,
;~
... .
',;
. .
- 28
bm.
J~6~
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rc) ~ d ~ ' ~ '~
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s~ 4~ ~ E~ ....
~a ~ ~ h
O ~ O ~: O ~
EL~ u~ ~ h u~ .~ ,~ 4~ -. .
~, rd ~ ~ ~ ~ 4~
O O-rl-rl O O-rl ~ O ~ t~
O ~ O ~ ~ ~ ~ ~ O
~ ~ s ~ ,':
~ . _ ___
o c~ o ~ ~ ~ o o~
~ o .. . . . . . .
C) U~ C~ D 1` O ~ ~ ~1
~_ :, :,
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.~ ô\o ~ O LO o a
h a~ -- ~i~ co co o . u~ ~i
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U~ ~ ~o o ~ ~ o~
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.. ~ ~`H h ~ .~ ~ ~ n o o ~. O ~ ~
u~ O~P u~ ~ ~1 u~ ~ ~ R a)
~1 0 ~ .. . . . d~l a) o R
r~ ~ a~N O ~ O ~ i a
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~ ~ . a
a) Q, O ~ E~
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r . ~ rl 3 o~
R u~ o o o u) U
a) o ~ ) o o u) u-) ~ o o o
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,: ~ al ~1o ,~ o~1 c) ~1 ~ .,~ .
,. o ~ I ~ Ia) I a) ~n
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.' _ , C~ '
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,., _ _
:` :
-- 29 --
.: .
~ bm.
. ~ , .
: i~
36Z~ :
Example 4 and Comparative ExampIe 4:
Extrusion foamed articles were produced by follow-
ing the procedure of Example 3 and Comparati~e Example 3,
except 80/20, 75/25, 50/50 and 40/60 mixtures respectively
of F-12/MeCQ2, 80/20 and 60/40 mixtures respectively of
propane/MeCQ, 50/50 mixture of propane/pentane and an
80/20 mixture of F-12/hexane (belonging to Example 4) were
used each as the blowing agent. They were examined by way
of rating the e,xtrudability of the corresponding basal ' '
resins and were tested for properties. The results were ,
as shown in Table 5. The pressure at which the blowing
agent was introduced invari,ably fell in the neighborhood
of 110 kg/cm2.
For referential purposes, molten resins to be
extruded were prepared in the percent composition indi-
cated herein below and they were extruded under the
optimum conditions to produce foamed axticles. I`he
~, articles were similarly examined and tested. The results
''~ were as shown in Table 5.
The principal conditions involved in the Compara-
, ,tive Example 4 and particular notes are shown below. In
each case, the extrusion temperature is kept at about 100C
~; (Sample 1)
Resin used: Ionomer resin lSamPle No. C (MI0.56)]
alone
Blowing agent: F-12 alone
, Specific conditions:
(1) When the blowing agent was used at a ratio of
, 21 parts by weight per 100 parts by weight of
,, 30 the resin, the foaming proceeded to the
.- .
'~ - 30 - -
bm.
.
.. , . ' '
extent of bringing about abnormal expansion.
Thus, the amount of the blowing agent was
reduced to 11 parts by weight.
(2) When an attempt was made to fix the extrusion
volume at 2 kg/hour (target 3.8 kg/hour), there
appeared indications of a possibility that the
pressure of introduction (corresponding to hack
pressure) would exceed the critical value of
press~re resistance. Thus, the extrusion was
performed at a decreased extrusion volume of
1.8 kg/hour. In this case, the pressure of
introduction rose to an abnormally high level
; of 210 kg/cm2.
(Sample 2) i~ Resin used: Polystyrene [Styron (trade maxk) 680, a
; product by Asahi-Dow Limited] alone
Blowing agent: A 40/60 mixture of F-12/MeC~
Specific conditions:
(1) When the blowing agent was used at a ratio
; 20 of 21 parts by weight per 100 parts by weight
: . .
of the resin, the foaming proceeded to -the
extent of bringing about abnormal expansion.
i Thus, the amount of the blowing agent was
decreased to 16 parts by weight. In this
case, the pressure for introduction of the
blowing agent was 120 kg/cm2.
~Sample 3)
Resin used: Low-density ~non-cross-linked) poly
`3 ethylene resin [M-2125 ~trade mark)
~ 30 produced by Asahi-Dow Limited, MI 2.5,
.,,,. .
~',~ ' '
- 31 -
bm.
',' ' . ' '
11)~3~;2~
.
density 0.921 g/cc] alone
slowing agent: Dichlorotetrafluoroethane (F-114
alone
Specific conditions: :
(1) When the blowlng agent was used at a ratio :~
of 21 parts by weight per 100 parts by weight ...
of the resin, the expansion ratio was not
. . sufficiently high. Thus, the amount of the ~ ;
blowing agent was increased to 24 parts by
weight. The pressure for introduction of the
; blowing agent in this case was 110 kg/cm2.
~Sample 4)
Resin used: A mixea resin consisting of 65 parts
by weight of low-density polyethylene
~ resin ~Yukalon (trade mark) HE-60 made
:; by Mitsubishi Petrochemical Co.] and
, .
35 parts by weight of polystyrene resin
! . [Styron (trade mark) 679 made by Asahi-
Dow Limited~
Blowing agent: F-ll alone
, Specific conditions:
100 parts (by welght) of the above resin, 0.5
. part of talcum, 0.005 part of polybutene and
.~
24 parts of freon were introduced at 210C
into an extruder. The pressure for intro-
~ duction of the blowing agent in this case.
`~ was 115 kg/cm2.
.. (Samples 5, 6 and 7)
The procedure for Sample 4 was repeated, except
a 50/50 (by weight ratio) mixture of F-ll and butane, a
. 50/50 (by weight ratio) mixture of F-ll and F-12 and
.. . .
. . .
- - 32 -
bm.
.
736Z~
a 50/50 (by weight ratio) mixture of F-11 and propane
were usea each as the blowing agent at a ratio a 25 parts
by weight based on 100 parts by weight of the basal resin.
In this case, the pressure of introduction was 105 to 110
kg/cm 2
. ' '~' ,' . . .
'. ''
. .
,
.
, ' '
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~ 33 -
.
bm.
...
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ta _ .
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~ .~ ~ .
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8~ ~ O~ æ ~ æ ~
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- 34
bm,
.: .
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,: . . ,
: . :
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hPl ~ ~ O
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u~ ~ ~a ~ 8 ~
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. ~ u~ ~ ~n ~ a~,
.__ _ _
o ~
o ~ :~ ~ o ~
No o ,~ O
,' Cl~ Ou~
. ~ O~ o o ~ ~, Ln '
o o o o o oo
o o o o o oo
c~ r O R oR o
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n O
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` o~w~WQ~ b~ b~ b~ b~ ba ~ ba~
...
3 5
~, . . .
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;. - I , - .
,"'; i ' ' ,
.. . .. .
.,,- . .
.,. 1 ~ . .
., ~
~' .. , . , ' ' ' '.
3~
As is clear from the comparison of Example 4 and
Samples 4, 5, 6 and 7 o~ Comparative Example 4, the foamed
articles obtained in Sa~ples 4, 5, 6 and 7 by extruding the
corresponding melts into the atmosphere at 23C ha~ small
cross sectional areas and large percents of shrinkage as
compared with those obtained in Example 4. These articles
had too inferior properties to be used effectively as the
cushioning material. These degraded properties may
possibly be ascribed to the shrinkage which the articles
underwent and to opened cells. These foamed articles
showed very high degrees of cell porosity possibly because
the basal resins contained no ionomer resin and, ther~fore,
the compatibility between polyethylene and polystyrene was
not sufficiently high desp~te the use of suitable blowing
~ agents. This trend toward degradation of properties became
`; conspicuous as the thickness of extrusion foamed article
exceeded 10 mm. The state of distribution af cells in the
product of Example 4 and its enlarged view are shown in
Figs. 1 and 2, respectively. For comparative purpose,
the state of cells in the product of Sample 5, 6, or 7 and
its enlarged view are shown in Figs. 3 and 4, respectively.
Example 5:
Foamed articles were produced by repeating the
procedure of Example 1, except basal resins were prepared
by mixing a total of 10 types of ionomer resins, A through
J, each with Styron (trade mark) 680 as the styrene resin,
at a ratio of 50/50 and an ~0/20 mixture of F-12/MeCQ was
used as the blowing agent. The extrusion foamed articles
were examined by way of rating the extrudability of the
corresponding basal resins and were tested for properties.
:
.,
- 36 -
bm.
~",1 , . . ..
36Z~ -
'l'he results were as shown in 'rable 6. For referential
purposes, the results obtained with respect to aforesaid
Samples 1 through 3 of Compartive Example 4 are also given
in the same table.
'~'
,~
;:
' '
- 37 -
bm.
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Example 6:
A basal resin was prepared by mixing 50 weight
percent of ionomer resin (Sample No. C, MI 0.56) and 50
weight percent of an impact-resistant polystyrene resin
containing 3 weight percent of polybutadiene (manufactured
product by Asahi-Dow Limited). A mixture consisting of
lO0 parts by weight of said basal resin and 0.5 part by
weight of talc and 0.4 part by weight of barium steara~e
was fed to an extruder having 30 mm in screw diameter and
having the first zone kept at 120C, the second zone at
210~C and the third zone at 240C. Through an inlet
disposed in the middle of the third zone of said extruder,
a mixed volatile blowing agent consisting of 30 wei~ht
percent of dichlorodifluoromethane and 70 weight percent
of dichloromonofluoromethane was introduced under
increased pressure at a ratio of 31 parts by weight per
lO0 parts by weight of said basal resin to be blended
! therewith. The blend was extruded through a die (3 mm in
diameter) attached to the forward tip of the temperature
adjusting member at a resin temperature of 105C into a
; low-pressure zone at the highest extruding capacity 3.3
kg/hour of the extruder, to undergo extrusion foaming.
At this time, the pressure for introduction of the blowin~
agent was 170 kg/cm~ and the resin pressure immediately in
ront o the die was 35 kg/cm2.
The bar-shaped foamed article thus obtained had
a bulk density of 25 kg/m3, contained uniform, discrete
cells and enjoyed good surface smoothness. The ratio of
voluminal decrease of the foamed article at the end of 48
; 30 hours' standing from the time of foaming was 2~,
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an exceptionally small value. The compressive strength
was 1.8 kg/cm2 and the maximurn deceleration was 65 G.
Example 7:
The procedure of Example 6 was repeated, except
a styrenebutadiene block copolymer containing 70 weight
percent of butadiene was used in place of the impact-
resistant polystyrene containing polybutadiene. In this
case, the pressure for introduction of the blowing agent
was 150 kg/cm2 and the pressure of the resin immediately
in front of the die was 31 kg/cm2.
The bar-like foame~ article thus produced showed
a bulk density of 3~ ky/m3, contained uniform, discrete
cells and had slightly coarse surface. The ratio of
voluminal decrease of the foamed article at the end of
48 hours' standlng from the time of foaming was 5%. The
article showed a compressive strength of 1.2 kg/cm2 and
a maximum deceleration of 51 G, indicating that it
excelled in cushioning property.
Examples 8 - 14 and comparative-Examples 5 - 6:
As the ionomer resin, there were used Sample No.
C (MI 0.56) and Sample No. D (MI 1.2) and Sample No. K
r
(Ca as metal, MI 0.7, S - 75%, N = 50~) and Sample No. L
,~ .
(Na as metal, MI 1.5, S = 58%, N = 45~). As the rubbery
substance-containing thermoplastic resin, there were used
` a polystyrene resin containing 3 weight percent of poly-
:, .
,~ butadiene (hereinafter abbreviated as "X"), a polystyrene
.~ .
resin containing 18 weight percent of polybutadiene
, (hereinafter abbreviated as "Y") and a mixed resin consist-
ing of 20 parts by weight of polystyrene resin, Styron
,~ 30 (trade mark) 680, produced by Asahi-Dow Limited and 80
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parts by weight o~ polybutadiene rubber, Diene (trade mark)
produced by Asahi Chemical Industry Co., Ltd. (hereinafter
abbreviated as "Z"). They were mixed at the ratios indi-
cated in Table 7 to prepare basal resins. Then, the
procedure of Example 6 was repeated, except the afore-
mentioned basal resins were used and the blowing agents
prepared by mixing F~12,'F-21, F-11, F-114 and ~eCQ2 at
the rat,ios indicated in Table 7 were used as the volatile
blowing agent.
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The present invention permits an extrusion foam-
ing of thermoplastic synthetic resin to be accomplished
with enhanced efficiency. For example, this invention is
effective in preventing the resin from being expanded or
shrunken at the t.ime of extrusion, improving the extxusion
foamed article in terms of cross section and keeping the
extrusion back pressure from abnormally increasing and,
consequently, brings about an effect of improving the
ec.on~my of the extruding and foaming steps. In addition,
this invention p.ermi.ts economically advantageous production
of a novel resin foamed article capable of satisfying the
various properties such as compression strength and
recovery, cushioning property, and thermal insulatin~
property all at once.
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