Note: Descriptions are shown in the official language in which they were submitted.
129981~
T 788 PCT
CROSS-LINKED FOAMED COMPOSITION AND PROCESS
FOR THE PREPARATION THEREOF
The invention relates to a cross-linked foamed composition and
to a process for the preparation thereof.
For cross-linked and foamed materials, natural rubber,
synthetic rubber, poly(l,2-butadiene) (1,2-PBD) and ethylene-vinyl
acetate copolymer (EVA) are known to be used. However, most of
these are prepared by a process in which the decomposition of the
blowing agent and the cross-linking reaction take place while the
starting compound is fully packed in the mould, after which foaming
is effected outside the mould.
The preparation of a foamed substance by cross-linking in hot
air without the use of a mould does not often occur, but it has
been tried with natural and synthetic rubber. However, the foamed
natural and synthetic rubber substances obtained by this cross-
linking method are unsatisfactory in that they have a low degree of
5 foam expansion and poor cushioning and gas permeability properties.
It is an object of the present invention to provide a
cross-linked foamed composition which has a high degree of foam
expansion, a light weight, good cushioning, gas permeability and
sound proofing properties.
Accordingly, the invention provides a cross-linked foamed
composition, characterized in that it is prepared by cross-linking
and foaming in a heat medium of a starting mixture comprising the
following components:-
(1) in the range of from 20-100~ by weight of a block copolymer of
an aromatic vinyl compound and a conjugated diene compound
and/or a selectively hydrogenated product thereof, and
(2) in the range of from O to 80% by weight of one or more rubbers
selected from natural rubber, diene type synthetic rubber and
non-diene type synthetic rubber
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the sum of said percentages being 100, and calculated on 100 parts
by weight of [(1) + (2)],
(3) in the range of from 0 to 300 parts by weight of a softener,
(4) in the range of from 0 to 600 parts by weight of an inorganic
filler,
(5) in the range of from 3 to 60 parts by weight of a blowing
agent, and
(6) in the range of from 0.1 to 10 parts by weight of a cross-
linking agent.
The invention further provides a process for the manufacture
of a cross-linked foamed composition which process comprises
blending the following eomponents:-
component (1) in the range of from 20 to 100~ by weight of a block
copolymer of an aromatic vinyl compound and/or a
seleetively hydrogenated product thereof and
component (2) in the range of from 0 to 80~ by weight of one or
more rubbers selected from natural rubber, diene
type synthetie rubber and non-diene type synthetic
rubber,
the sum of said pereentages being 100,
and, ealeulated on 100 parts by weight of [(1)+(2)],
component (3) in the range of from 0 to 300 parts by weight of a
softener,
component (4) in the range of from 0 to 600 parts by weight of an
inorganic filler,
component (5) in the range of from 3 to 60 parts by weight of a
blowing agent, and
component (6) in the range of from 0.1 to 10 parts by weight of a
eross-linking agent,
and eross-linking and foaming in a heat medium the blend thus
formed.
The aromatie vinyl-eonjugated diene block copolymer or
aromatie vinyl-hydrogenated conjugated diene block copolymer (1)
used in the present invention is thermoplastic and may be a block
copolymer represented by the following formula
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(A-B)nA, (A-B)n or ~(A-B)n)mC
wherein 4 2 n > 1, 8 > m 2 2,
A represents an aromatic vinyl compound polymer,
B represents a conjugated diene polymer or copolymer or a
hydrogenated polymer of a conjugated diene polymer or copolymer,
and
C represents a coupling agent residue.
In order that component (1) used in the present composition
has moderate hardness and cushioning, the aromatic vinyl compound
~A) is suitably present in a quantity in the range of from 7~ to
9o%~ preferably of from 10% to 70%, and its molecular weight lies
between 10,000 and 1,000,000, more preferably between 70,000 and
300,000, so that an even more excellent foamed composition
according to the present invention is obtained.
In the afore-mentioned component mixture [(1)+~2)], component
(1) is present in an amount in the range of from 20 to 100% by
weight, preferably 40-90% by weight, since with less than 20% by
weight it is difficult to obtain a foamed substance with a great
expansion rate.
Exemplary aromatic vinyl compounds are styrene, alpha-
methylstyrene, ortho-, meta- and para-methylstyrene, o-, m- and
p-ethylstyrene, o-, m- and p-methoxystyrene, dimethylaminostyrene,
o-, m- and p-isopropylstyrene, p-t-butylstyrene. Of these, styrene,
- para-methylstyrene and alpha-methylstyrene are preferred.
For the polymers, a polymer of only one, or a block or random
copolymer composed of two or more of these monomers may be used.
There are no limitations as to the content of the aromatic
vinyl compound present; it differs with the molecular weight and
the use envisaged, but s~itably it lies between 7~ and 90%,
preferably between 10% and 70~ and more preferably 10% and 50%.
For the conjugated diene polymer or copolymer or the hydro-
genated polymer of a con~ugated diene polymer or copolymer, a
single butadiene, isoprene, piperylene polymer, or a block or a
random copolymer composed of two or more thereof, or a copolymer in
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which the arrangement of the aromatic vinyl compound part is random
or tapered, and hydrogenated polymers of these conjugated diene
polymer may be used.
For obtaining the foamed substance aimed at in the present
invention it is preferred to use styrene as the aromatic vinyl
compound and butadiene and/or iosprene as the conjugated diene
compound.
In the present invention, natural rubber, diene-type synthetic
rubber, non-diene-type rubber are used in a range of 0 to 80~ by
weight, preferably of 10-60% by weight, mainly to control the
elasticity and the cross-linking speed of the foamed substance.
Exemplary are natural rubber (NR), diene-type rubbers, such as
polyisoprene rubber (IR), styrene-butadiene rubber (SBR),
polybutadiene rubber (BR), poly(l,2-butadiene) rubber (RB),
acrylonitrile rubber (NBR), chloroprene rubber (CR) and
non-diene-type rubbers, such as ethylene-propylene rubber (EPM),
ethylene-propylene-terpolymer (EPDM), ethylene-vinyl acetate
copolymer (EDA), acrylic rubber (ACM, ANM), fluorine rubbers.
Preferred are NR and diene-type rubbers, in particular IR and RB.
The softener used as component (3) in the present invention
may be an aromatic, naphthenic or paraffinic process oil,
petroleum-based asphalts, such as street asphalt, blown asphalt,
petroleum-based softeners, such as lubricating oil, solid
paraffins, l~quid paraffins, vaseline; coal tar softeners, such as
coal tar, coal tar pitch, resinous oil softeners, such as castor
oil, linseed oil, rape seed oil, coconut oi].; waxes, such as bees
wax, carnauba wax, lanolin; tolu oil and factice.
One or a combination of two or more of these may be used.
Suitable softeners are process oil, petroleum asphalt; preferably a
process oil and a petroleum asphalt are used simultaneously. When a
process oil and a petroleum asphalt are used simultaneously,
foaming during cross-linking is the same as when a process oil is
used alone, while the foamed composition will have a higher degree
of hardness.
~29~81~
The softener component (3) is present in a quantity in the
range of from 0 to 300 parts by weLght, preferably 50 to 150 parts
by weight on 100 parts by weight of components [(1)+(2)]. When more
than 300 parts by weight is present, there is a great risk of
softener bleed and handling becomes difficult.
The inorganic filler used as component (4) in the present
invention may be for instance light calcium carbonate, heavy
calcium carbonate, various kinds of surface treated calcium
carbonates, and talc, magnesium hydroxide, mica, clay, barium
sulphate, natural silicic acids, synthetic silicic acids (white
carbon), titania and various carbon blacks. Of these inorganic
fillers, heavy calcium carbonate is preferred for its economic
advantages.
The quantity of inorganic filler used is in the range of from
0 to 600 parts by weight, preferably 0 to 400 parts by weight,
calculated on 100 parts by weight of components [(1)+(2)]. When
more than 600 parts by weight is blended in, it will be hard to
obtain a high degree of foaming and the mechanical strength of the
foamed material obtained will be quite poor.
The blowing agent used in the present invention as component
(5) may be a well known inorganic or organic blowing agent. These
may also be used simultaneously. Exemplary blowing agents are
sodium bicarbonate, aluminium bicarbonate, sodium carbonate,
aluminium carbonate, azodicarbonamide (ADCA), dinitrosopenta-
methylenetetramine (DNPT), dinitrosoterephthalamide,
azobisisobutyro nitrile, azodicarboxylic acid barium, sulphonyl
hydrazide, toluenesulphonyl hydrazide. These blowing agents may
well be used together with such well-known blowing aids as urea and
urea derivatives.
The amount of blowing agent used is in the range of from 3 to
60 parts by weight, preferably 5 to 40 parts by weight on 100 parts
by weight of components [(1)+(2)]. When less than 3 parts by weight
of blowing agent is used, the foamed composition obtained will have
a low foam expansion rate and when more than 60 parts by weight is
present, the amount of gas formed by the decomposition of the
~Z99811
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blowing agent will become too large and the external appearance of
the foamed product will be poor.
In the preparation of the cross-linked foamed composition of
the present invention, a cross-linking agent is added in addition
to the afore-mentioned ingredienes to form the foam substance.
Moreover, energy such as electron rays, ultra violet rays may also
be used as cross-linking and blowing aids. As cross-linking agents,
sulphur and various kind of organic peroxides may be mentioned.
Exemplary organic peroxides are dicumyl peroxide, l,l-bis(t-butyl-
peroxy)-3,3,5-trimethylcyclohexane, t-butylperoxybenzoate,
2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, t-butyl peroxy-
isopropylcarbonate. The cross-linking agent is suitably present in
an amount in the range of from 0.5 to 5~ by weight, calculated on
lO0 parts by weight of the sum of components (1) and (2).
In the ease of sulphur vulcanization, various vuleanization
aceelerators may be added simultaneously to carry out the
eross-linking and blowing. Exemplary vulcanization accelerators are
dibenzothiazyldisulphide (MBTS), 2-mercaptobenzothiazole (MBT),
N-eyelohexyl-2-benzothiazyl-sulphenamide (CBS), N-oxyzoethylene-
2-benzothiazyl-sulphenamide (DBS), tetramethylthiurea disulphide
(TMTD), tetramethylthiurea monosulphide (TMTM).
Generally, in hot air eross-linking with an organic peroxide,
the surfaee is softened by deeomposition due to oxidation of the
surface of the cross-linked produet. In order to obviate this
softening, the surfaee of the blend (the area that is in contact
with the hot air) can be eovered with a thin polyester film, or a
thin sheet of a rubber eompound which does not blend with the
cross-linking agent, so that deeomposition by oxidation in hot air
cross-linking will be stopped and a good cross-linked foamed
substanee ean be obtained.
Further, from the point of view of cross-linking efficiency,
sulphur vulcanization is more desirable than cross-linking with an
organie peroxide.
Besides the afore-mentioned additives, other additives sueh as
cross-linking aids, anti-ageing agents, proeessing aids,
lX99811
- 7
plasticizers and tackifiers may suitably be added as required.
There are no specific restrictions as to the method of mixing
the afore-mentioned components (1)-(5) and further compounding
ingredients; the usual mixing methods for preparing rubber blends,
such as the Banbury mixer, pressure kneader, open roll may be
applied After the non-cross-linked product obtained is shaped as
required into, for instance, sheets, it is subjected to
cross-linking and foaming in a heat medium. Cross-linking and
foaming is carried out in hot air of a temperature in the range of
from 100 to 200 C, preferably 120 to 170 C, and as the
temperature rises above the decomposition temperature of the
blowing agent, the blend is cross-linked and the blowing agent
decomposes. During the process there is no particular need for
pressure, the cross-linking and foaming can be carried out at
atmospheric pressure.
The heat medium used in the present invention may be a gas,
such as air or nitrogen, hot fluids, hot solids, such as hot dust
and hot fine granules. Of these, a hot gas is preferred, and hot
air in particular. Furthermore, the cross-linking and foaming may
be carried out on top of a hot metal plate.
The cross-linking and foaming operations can be performed
batch-wise or continuously.
Even though the cross-linking in a heat medium is carried out
at atmospheric pressure and wlthout the use of a metal mould, the
cross-linked and foamed substance of the present invention has a
high degree of foam expansion, is light-weight and has very good
cushioning, gas permeability and sound proofing properties.
The cross-linked and foamed substance of the present invention
may be put to a wide range of uses, e.g. as material for foot wear,
industrial articles, as shock absorbing material, sealing material,
~~ lining material, such as sound proofing and sound absorbing
material, insulating material, carpeting and for metal plate
laminating.
The following Examp].es further illustrate the invention. The
comparative Experiments are not according to the invention. The
~ ~998~i
abbreviations "pbw" and "%wt" mean "parts by weight" and "per cent
hy weight", respectively.
In the Examples and Comparative Experiments, tensile strength
and tension pull were determined by the JIS K-6301 method, hardness
with the rubber test type C (sponge hardness meter, type Macro-
molecular Gauge), specific gravity with the floating method and the
foam expansion rate by comparing the thickness of samples taken
before and after foaming.
Example 1
100 pbw of a styrene-butadiene block copolymer (40% by weight
bonded styrene) ~ex Japan Synthetic Rubber, JSR TR 2000) and
further ingredients were mixed in a BR type Banbury mixer in
proportions as listed in Table 1 and rolled into 2 mm thick
sheeting with the aid of a 25.4 cm test roller to form a
non-cross-linked sheet, which was cross-linked and foamed for 25
minutes in hot air at a temperature of 145 C to obtain a foamed
substance. The resulting properties are listed in Table 1.
Examples 2-4
Foamed substances were prepared in the same way as in Example
1, except that 70 pbw of a styrene-butadiene block copolymer (40~
by weight bonded styrene) (ex Japan Synthetic Rubber, JSR TR 2000)
was used, and for the rubber components, 30 pbw of
1,2-polybutadiene (ex Japan Synthetic Rubber, JSR RB 820), 30 pbw
of polyisoprene rubber (ex Japan Synthetic Rubber, JSR IR 2200) and
30 pbw of natural rubber. The resulting properties are listed in
Table 1.
Examples 5-6
Foamed substances were prepared in the same way as in Example
1, except that 100 pbw of a styrene-butadiene block copolymer (60%
by weight bonded styrene) (ex Japan Synthetic Rubber, JSR TR 2400)
and 50 pbw of 8 styrene-butadiene block copolymer (60% by weight
bonded styrene) (JSR TR 2400) respectively, and 50 pbw of natural
rubber were used. The resulting properties are listed in Table 1.
~998~1
Examples 7-8
Foamed substances were prepared in the same way as in Example
1, except that 100 pbw of a styrene-isoprene block copolymer (15%
by weight bonded styrene) (ex Japan Synthetic Rubber, JSR SIS 5000)
and 70 pbw of a styrene-butadiene block copolymer (15% by weight
bonded styrene) (JSR SIS 5000), respectively, and 30 pbw
1,2-polybutadiene (JSR RB 820) were used. The resulting properties
are listed in Table 1.
Example 9
A foamed substance was prepared under the same conditions as
in Example 1, starting from 70 pbw of a styrene-butadiene block
copolymer (40% by weight bonded styrene) (ex Japan Synthetic
Rubber, JSR TR 2000) and 30 pbw of natural rubber and using the
blends listed in Table 1. The resulting properties are listed in
Table 1.
Comparative Experiments A and B
Foamed substances were prepared in the same way as in Example
1 but using the polymers in proportions outside the scope of the
present invention. 85 pbw of natural rubber was used with 15 pbw of
a styrene-butadiene block copolymer (40~ by weight bonded styrene)
(JSR TR 2000) and 15 pbw of a styrene-butadiene block copolymer
(60% by weight bonded styrene) (JSR TR 2400). The resulting
properties are listed in Table 2.
Comparstive Experiment C
A fosmed substance was prepared in the same way as in Example
1 but using 100 pbw styrene-butadiene rubber (ex Japan Synthetic
Rubber, JSR 1507 which is a random polymer) as the polymer The
results are shown in Table 2.
Comparative Experiment D
A foamed substance was prepared in the same way as in Example
1 but using 100 pbw natural rubber as the polymer. The resulting
properties are listed in Table 2.
From Tables 1 and 2 it will be seen that Examples 1-9, in
which the compositions used are in accordance with the present
invention, as compared with Comparative Experiments A-D, which are
outside the scope of the present invention, afford light weight
~.~998~1
- 10 -
products with a high degree of foam expansion.
The ingredients for the cross-linked and foamed substance
according to the present invention, viz. a block copolymer of an
aromatic vinyl compound and a conjugated diene compound and a
specified kind of rubber are blended in proportions lying within a
specified range and cross-linked and foamed in a heat medium such
as hot air to prepare a product of unprecedentedly good properties.
Since its foam expansion rate is high it is very light weight, and
therefore it can be expected to have very good cushioning, gas
permeability and sound proofing qualities, and it can be suitably
used as material for foot wear, industrial articles, as shock
absorbing material, sealine material, lining material, sound
proofing and sound absorbing material, insulating material and
carpeting.
1299811
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1299811
- 13 -
Table 2
Comparative Experiments
_ A B C D
JSR TR 2000 15 - - -
JSR TR 2400 - 15
JSR 1507 - - 100
NR RSS No. 3 85 85 - 100
*
Ultrasen 631
Zinc oxide No. 3 5 5 5 5
Stearic acid 3 3 3 3
Heavy calcium 200 200 200 200
carbonate
SRF carbon black 3 3 3 3
Naphtenic oil 35 35 35 35
Street asphalt 35 35 35 35
Vulcan. accelerator DM 1.5 1.5 2.5 1.5
" " M 0.5 0.5 0.5 0.3
" " TT 0.3 0.3 1.5 0.5
Sulphur 1.5 1.5 1.5 1.5
Percumyl D
Blowing agent *
Vinyol AK No. 2 25 25 25 25
Total 409.8_ 409.8412.0 409.8
Cross-linking
conditions
Temp. (~C) 145 145 145 145
Time ~min) 25 25 25 25
Properties
Foam expansion 2.6 2.4 1.9 2.1
Spec. gravity 0.58 0.63 0.79 0.71
Tensile strength 1.2 1.4 0.7 1.5
(Kgf/m2)
Tension pull (~) 90 90 50 90
Hardness (Type-c) 18 21 17 14
* Trade Mark
