Note: Descriptions are shown in the official language in which they were submitted.
r B}~SF Illrt i ~nqc~91,Al 1 .9~hA ft 933482 0 . Z~ . 0050~4487 1
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Expandable styrene polymers
The present invention relates to expandable styrene polymers
which are suitable for the productlon of elastic foams.
Foams based on polystyrene have achieved considerable industrial
importance as thermal insulation and packaging materials. They
are produced on an industrial scale by first preparing expandable
10 styrene polymers by suspension polymerization of styrene in the
presence of a blowing agent, expanding these polymers by heating
to give foam particles, and subsequently welding the particles in
molds to give moldings.
Polystyrene foams are rigid. Their low elasticity is disadvanta--
geous for many applications, for example in the packaging sector,
since protection of the packaged goods against impact is only
possible to an lnadequate extent, and the foam moldings used as
packaging materials break even on only small deformation.
Attempts have therefore already been made in the past to increase
the elasticity of polystyrene foams.
EP-A--561 216 describes a proces3 for elastifying polystyrene
oams, in which foam slabs having a density from 3 to 12 kg/l are
compressed to about 1/3 of their size in one direction and then
released again. Boards cu~ fLom the slabs treated in this way
have increased elasticity and are used, for example, for solid-
borne sound insulation.
However, the terhn1~1ities of the process mean that this proce--
dure is very difficult to apply to moldings and is therefore not
carried out.
US-A-4,424,285 and US-A-4,409,338 describe foamable styrene poly-
mers which are prepared by polymerization of a solution of from
O . 5 to 4 . 0 96 by weight of styrene-butadiene or styrene-butadiene-
styrene block copolymers ln styrene and which have a short mold
cooling time.
However, this only increases the elasticity of the foams to an
insignificant extent due to the small amount of rubber added.
In US-A-4,307,134 and US-A-4,333,970, shells of styrene-butadiene
copolymers are polymerized onto polystyrene beads with partial
grafting, and the resultant beads are impregnated with blowing
agent and 3ubsequently expanded. However, the resultant foams
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have an irregular 9hell structure and unfiatisfactory 1 Anir~l
properties .
GB-A-1,220,611 describes a foamable polymer composition having
increased oil resistance which comprises a styrene-acrylonitrile
copolymer and a polybutadiene elastomer, where the styrene-acry-
lonitrile copolymer $8 dispersed in the elastomer and the blowing
agent is absorbed in the elastomer phase with swelling and
partial dissolution. However, such foams have unsatisfactory
10 mechanical properties.
In all the prior-art processes described, the blowing agent
diffuses out of the beads very rapidly. After only a few days,
the 108s of blowing agent can be 80 large that proper foaming of
the beads i5 no longer possible. In particular, thi~ effect bc-
comes undesirably evident on addition of elastomer in proportions
of greater than 5 % by weight, as necessary ~or achieving ade-
quate elastificatlon.
20 It 18 an object of the present lnventlon to provide ~Yr~nA~hl e
~tyrene polymers which are sultable for the production of elastic
foams, do not lose slgnificant amounts of blowing agent even
after extended storage, and are recyclable.
We have found that this object is achleved by ~Yr~n~hl ~ styrene
polymers for elastlc polys~yrene foams, comprislng
a) from 75 to 99 % by weight of polystyrene and/or a styrene
copolymer containing at least 50 ~ by weight of copolymerlzed
styrene,
b) from 0 to 24 % by weight of at least one styrene-soluble
elastomer,
c) from 1 to 25 ~ by weight oi at least one graft oopolymer
having a core/shell ~uuLule,
d) from 1 to 15 ~ by weight, based on the sum of a), b) and c),
of a low-boiling blowing agent, and, if desired,
e) conventional additives in effective amounts.
The present invention accordingly provide~ r~n~l~hl ~ styrene
polymers for ela-tic polystyrene foams, comprising
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a) from 75 to 99 % by weight of poly8tyrene and~or a styrene
copolymer containing at lea5t 50 % by weight of copolymerized
styrene,
b) from 0 to 24 % by weight of at least one r~yL~ oluble
e1astomer,
c) from 1 to 25 % by weight of at lea3t one graft copolymer
having a core/shell ~LLU~:~UL~,
d) from 1 to 15 9~ by weight, based on the sum of a), b) and c),
of a low-boiling blowing agent, and, lf desired,
e) conventional additLve3 in effective amounts.
The present invention furthermore provides elastic polystyrene
foams ' ~ i n~
a) from 75 to 99 % by weight of polystyrene and/or a styrene
copolymer containing at least 50 9~ by weight of copolymerized
styrene,
b) from 0 to 24 % by weight of at least one ~LYL~ 301Ub1e
elastomer,
c) from 1 to 25 % by weight of at least one graft copolymer
having a core/shell ~lLLul~:LuLe~ and, if desired,
d) conventional additives in effective amounts.
The present invention rUL ' ' ~ provides ~L~ 55L5 for the
preparation of the elastic styrene polymers and moldings produced
from the elastic polystyrene foams.
c ~ L a) in the oYr~n~l~hl e styrene polymers ' ~o~ from 75
to 98 % by weight, preferably from 85 to 93 k by weight, of poly-
styrene and/or a styrene copolymer containing at least 50 % by
weight, preferably at least 80 % by weight, of copolymerized
styrene. Examples of suitable ~ are c-methylstyrene,
40 ring-halogenated styrenes, ring-alkylated styrenes, acrylo-
nitrLle, esters o~ acrylic or methacrylic acid with alcohols hav-
ing 1 to 8 carbon atom3, N-vinylcarbazole, maleic acid and maleic
anhydride. Irhe polystyrene t~d~ L~Iy~u~lly contains a small amount
of a copolymerized cr~alink~n~ agent, ie. a compound containing
more than one, preferably 2, double bonds, such as divinyl-
benzene, butadlene or butanediol diacrylate. Ihe crn9~1;nk;n~
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agent is generally used in amounts of from 0.005 to O.OS mol%,
based on styrene.
In order to achieve particularly high f-Yr~nd~h; l; ty, it is exre-
dient for the styrene polymer to have a mean molecular weight Mw
(weight average), measured by the GPC method, of from 100,000 to
200,000, in particular from 130,000 to 180,000. The foam has
improved processing properties if the high-molecular-weight flank
of the molecular-weight distribution curve measured by the GPC
10 method i8 80 steep that the difference between the means (M2+1-Mz)
is less than 150,000. The GPC method is described in G. Glockler,
Polymercharakterisierung, Chromatographi5che Methoden, Volume 17,
Huthig-Verlag, l~ lh-rg~ 1982. These means are described in
.G. Elias, Makromolekule, ~uthig-Verlag, llc.~ g, 1971, pages
52-64 .
Styrene polymers which have the abovementioned mean 1 rrl-l Ar
weights can be obtained by carrying out the polymerization in the
presence of regulators. Tha regulators used are expediently from
20 0 . 01 to 1:5 ~ by weight, preferably from 0 . 01 to 0 . 5 % by weight,
of a bromine-free organLc compound having a chain--transfer
constant E~ of from 0.1 to 50. Addit~on o~ the regulator during
the polymerization is expediently delayed until a conversion of
from 20 to 90 9~ has been reached in order to achieve a steep
hiyll --1 er~ll Ar-weight flank of the molecular--weight distribution
curve .
An advantageously high ~Yr--n~ n capacity can also be achieved if
component a) contains from 0.1 to 10 ~ by weight, advantageously
30 from 0.5 to 10 % by weight, of a styrene polymer having a mean
r-l~c-llAr weight (weight average) of from 500 to 5000.
Further detalls on r -1 I-rl-l Ar-weight regulation in the preparation
of f~Yrnn~ hl e 8tyrene polymers are given in EP-B 106 129 .
Styrene polymers which contain from 0.1 to 2 % by weight, prefer-
ably from 0 .15 to 1. 5 % by weight, of copoly ^r1 7ed acrylonitrile
give foams which are distinguished by substantial absence of
shrinkage. A mixture of from 95 to 99 . 5 % by weight of polysty-
40 rene and from 0 . 5 to 5 9~ by weight of a styrene-soluble styrene-
~lcrylonitrile ccpolymer also exhibits these properties if the
total acrylonitrile content in the mixture is from 0.1 to 2 % by
weLght, preferably from 0.15 to 2 ~ by weight.
Styrene polymers containing from 3 to 20 % by weight, preferably
from 5 to 15 % by weight, of copolymerized acrylonitrile give
foams having high oil resistance. A mixture of from 50 to 85 t by
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weight of polystyrene and from 15 to 50 % by weight of a styrene-
soluble styrene-acrylonitrile copolymer also exhibits this advan-
tageous property if the total acrylonitrile content in the
mixture is from 3 to 20 % by weight, preferably from 5 to 15 ~ by
weight. Such mixtures are prepared in a simple manner by dissolv-
ing the proposed amount of styrene-acrylonitrile copolymer in
styrene before the polymerization.
Styrene polymers containing from 2 to 15 % by weight, in parti-
10 cular from 3 to 12 9~ by weight, of maleic acid or maleic
anhydride a8 r r give foams which are distinguished by high
heat distortion resistance. It i9 advantageous to use a mixture
of polystyrene and a commercially available gtyrenc - 1 "; r
anhydride copolymer having a maleic anhydride content of from 15
to 49 % by weight, which can easily be prepared by dissolving the
copolymer in styrene before the polymerization.
Component b) is, in particular, a styrene--soluble elastomer hav-
ing a glass transition temperature of below O~C, preferably below
20 -10C, in particular below -20~C.
The elastomer i~ generally essentially uncrosslinked, if desired
only crt~l i nkt cl to the extent that the solubility in styrene i8
not impaired.
Preference i3 given for the novel styrene polymers to polybuta-
diene rubbers, in particular those having a r-lt~rulAr weight (Mw)
of from 200,000 to 300,000 and containing < 50 '6 of 1,4-cis
structures and from 5 to 20 ~ of 1, 2-vinyl structures (medium-cis
30 structure) or from 50 to 99 % of 1, 4-cis structures and ~ 5 % of
1, 2-vinyl structures ( high-cis structure ) .
The elastomer phase is dispersed in the styrene phase in the form
of cell particles in the polystyrene phase.
These cell particle3 should have diameters of from 0.1 to 10 llm,
in particular from 0 . 5 to 5 llm.
The presence of component b) produces, in particular, better com-
40 patibility betwe~n components a) and c) and a further increase in
the elasticity of the foams.
However, it is al30 possible to omit component b) in the produc-
tion of the novel products.
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The core/3hell rubbers u8ed a8 component c) are preferably pre- =
pared by emul5ion polymerization with partial grafting.
In thi3 process, first olefinically unsaturated monomers are
polymerized, usually in emulsion, and a Nshell" is then polymer-
ized onto the resultant particles ( "coren ) by polymerization of
other ~ f;nir~lly unsaturated monomers, again usually in emul-
sion, with grafting taking place between core and shell.
10 For the preparation of the novel styrene polymers, component c )
is, in particular, a product having a core of a flexible polymer
and a shell of a more rigid polymer. For the purposes of the
present invention, the term "flexible polymer is taken to mean a
polymer having a glass transition temperature of from 20 to -60C,
preferably from 10 to -40C. The core material here usually com-
prises products of the polymerization of mixtures of Cl-C8-alkyl
acrylates and alkyl aromatic `, such as styrene, and ccn-
ventional cr~slinkin~ agents and graft crosslinkin~ agents.
Preference ia given to mixtures of from 40 to 90 S by weight of
20 alkyl acrylate and from 10 to 60 " by weight of alkyl aromatic
The shell material here preferably ccmprises product3 of the
polymerization of mixtures o~ alkyl methacrylates and styrene,
where the styrene content is preferably from 80 to 99 S by weight
and the alkyl methacrylate content is preferably from 1 to 20 9
by weight.
The proportion of the core is from 40 to 80 ~ by weight and that
30 of the shell is from 60 to 80 ~ by weight, in each case based on
tha total weight of the monomers.
The core/shell rubber is usually precipitated after the polymer-
ization by a method known to the person skilled in the art, for
example by adding magnesium salts to the emulsion, washed, dried
and comminuted.
~owever, it is also pos~iibl~ to convert the rubber into a readily
conveyable form by spray drying. It is less common, but just as
40 possible to meter the aqueous emulsion mixture directly into an
extruder together with the poly3tyrene.
A description of such polymers and their preparation is given,
for example, in EP-A-0 376 096.
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Component c) is in the polystyrene phase in the form of capsule
particles having diameters of from 50 to 300 nm, in particular
from 100 to 200 nm.
Information on the morphology of elastomer-modified 6tyrene poly-
mers is given in: Echte, Rubber-Toughened Styrene Polymers,
Advance~ in ChemiYtry Series l~o. 222, 1989.
A~ component d), the ~YrAn~Ahle styrene polymers contain, in
10 homogeneous distribution, from 2 to 15 t by weight, preferably
from 3 to 10 ~ by weight, of a low-boiling blowing agent. The
blowing agent should not disaolve the polystyrene, but should be
soluble in polystyrene. The boiling point ~hould b~ below the
softening point of the polystyrene. Examples of suitable blowing
agents are propane, butane, pentane, hexane, cyclopentane, cyclo-
hexane, octane, dich1orodifluoromethane, trifluorochloromethane
and l,l,l-difluorochloroethane. Pentane is preferred.
The ~YrAnr1Ahle styrene polymers may furthermore contain effective
20 amounts of conventional additives, such as dyes, fillers, stabi-
lizers, flameproofing agents, synergists, nucleating agenta,
lubricants, antistatics, substances which have a non-stlck action
during foaminq, and agents for shortenLng the t~ nq time on
n ~ n .
Other suitable additives are poly ~ 2, 6-dimethyl ) -1, 4-phenylene
ether and poly-1,4-phenylene sulfide. In amounts of from 1 to
20 9~ by weight, based on component a), these additives increase
the heat distortion resistance of the foam.
The novel styrene polymers are preferably prepared by mixing oom-
ponents a), b), c) and, if used, d) in the melt, usually in an
extruder, where, during addition of d), the extrudate must be
cooled ao rapidly after extruaion that foaming does not occur.
The resultant styrene polymer is subseguently comminuted, usually
by granulation.
If the blowing agent d) is not added to the styrene polymer
during extrusion, it must be added after granulation.
It is furthermore posaible to dissolve component b) in styrene
and to polymerize this solution, in which case the polymerization
is preferably carried out in bulk.
In this procesa, component b) is dissolved in styrene and this
solution is polymerized by processes known per se, usually with
addition of free-radical initiators or by the supply of heat.
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However, it i8 al80 po88ible to carry out the polymerization in
bulk to a conversion of about 30 ~, to su~pend the resultant pre-
polymer in a known manner and to comelete the polymerization in
suspension .
Particularly favorable results are achieved if the styrene
polymers are prepared by bulk polymerization of a solution of
component b) in ~tyrene in the above-described manner and mixing
the polymer with component c ) .
The mixing of the polymer of a) and b) with component c) is pre-
ferably carried out in the melt, in particular by extrusion.
E~owever, it i~ also possible to add the dried component c)
together with component b) to the styrene before tha polymeriza-
tion and then to polymerize the mixture as described above Ln
order to save additional extrusion and granulation steps. In this
f.mhr~ t, it ig algo possible to add the blowing agent during
the polymerization and thus to save an additional step for addi-
20 tion of blowing agent.
Usually, however, the blowing agent is added by the impregnation
method. To this end, the novel polymers must be converted into
particle form. This is expediently carried out by eYtrusion with
subsequent granulation.
The granules are then usually in the form of particles, ie. in
bead form or granule ~orm. Their mean diameter is preierably from
0.1 to 6 mm, in particular from 0.4 to 3 mm.
For the impregnation, the granules are suspended in a liquid,
usually water, in th2 presence of conventional auxiliaries and
additives in a pressure container, and the latter is rendered
inert and brought to a temperature which is above the softening
point, but below the melting point, of the polymer. The blowing
agent i8 in~ected at this temper~ture. After cooling And decom-
pression, the impregnated granules are separated off, purified
and dried, preferably at room temperature, for example in a
stream o~ ~ir.
Further details on conventional prep~ration proce~ses are given,
for example, in Kunststoffh~n-lh~ h, Volume 5, Polystyrol, edited
by ~. Vieweg and G. D~ 1 f.r~ ~4rl--E~anser-Verlag, Munich, 1969.
For the production of foams, the ~Yr~nfiilhle styrene polymers are
expanded in a known manner by heating to temperatures above their
softening point, for example by means of hot air or preferably by
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means of steam . The f oam particlea obtained can bo expanded
further by re-heating after cooling and, if desired, after inter-
im storage. They can sub5eqUently be welded to form moldings in a
known manner in molds which do not seal in a gas-tight manner.
The foams obtained have den5ities of from 10 to 60 g/l. They are
distinguished by high elasticity. Thus, they have a r^~ n~^ of
up to 90 9~ on quadruple compression. They are thus clearly
superior to conventional polystyrene particle foams.
The losses of blowing agent from the unfoamed beads are very low.
Even after storage for several wee3cs, foaming was still possible
without problems.
The prefoamed beads have a uniform cell I~LU. LULe and weld during
molding without formation of voids. The moldings produced in this
way have excellent heat distortion resistance.
In addition, the novel foams have a surprisingly good thermal
20 insulation capacity of up to 10 % better than conventional poly-
styrenes of the same density. The foams and moldings can be
recycled without problems.
The invention is illustrated in greater detail with reference to
the examples below:
Example 1
3500 g of ~ polystyrene having a viscosity number of 74 cm3/g and
30 a molecular weight (Mw) of 220,000, and 1500 g of a core/shell
rubber having the composition: core 65 parts by weight (75 % by
weight o~ n-butyl acrylate/25 ~ by weight of styrene), shell
35 parts by weight ( 95 ~ by weight of styrene/5 9~ by weight of
methyl methacrylate ), were extruded ln a Werner und P~leiderer
twin-screw extruder having a diameter of 30 mm at 190C and a
throuyhput of 10 kg/h, giving a ~ , ~ mixture. The mixture
was forced through a die assembly having a 1 mm bore, and the
extrudate was passed through A water bath and, after cooling, was
cut into pellets measuring 1 X 1 x 3 mm.
In this mixture, the rubber was in the form of capsule particles
having a mean diameter of 100 nm. 6000 g o~ this blend were
illLL~Jiu~ ed into a 50 1 stirred reactor together with 21,000 g of
demineralizQd water, 76 g of sodium ~yL~ hv~ ate, 155 g of mag-
nesium sulfate heptahydrate and 50 g o~ a 40 ~ strength by weight
solution of an alkyl~ lf~^nAte (Mersolat~ ~ 30, 3ayer AG).
The reactor was ~losed, flushed twice wit~ 1 atm of nitrogen and
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heated to 130C with stirring at 250 rpm. Nhen a temperature of
130C had been reached, 720 g of a mixture of 80 S by weight of
n-pentane and 20 % by weight of isopentane were injected into the
reactor over a period of 15 minutes, and the mixture was stirred
at 130C for a further lO hours.
After cooling and ~ ssion, the reactor contents were dis-
charged. The beads were collected, washed twice with demineral-
ized water and dried in a suction filter by sucking through
10 ambient air at 23C.
The beads had a blowing agent content of 6.1 % by weight and an
internal water content of 0.11 ~ by weight.
After open storage for one day, batch prefoaming for 10 minutes
at 100C gave a bulk density of 11.4 g/l.
After open storage for fourteen day5, a bulk density of 11.8 g/l
was achieved under the same prefoaming conditions.
~
In both cases, the foam had a b j ~~~lq~ fine--cell ~Lu~:LuL~.
Steam treatment of foam beads for 20 secondD at a Du~e~
pheric pressure of 0.7 bar in a mold measuring 20 X 20 X 4 cm
which did not seal fully gave a board having a density of 21 g/l.
After quadruple compression by 70 S, this had a recovery of
88.5 &; at a density of 35.5 g/l, the elastic recovery in the
same experiment was 84 . 5 S ( determined in accordance with
DIN 53 577) .
The Poensgen thermal conductivity (DIN 52 616) was 7 S below the
~LLe D~Ilding value, determined under the same conditions, for
the standard polystyrene 5~yLv~vL~D F 14 (BASF AG) of the same
density .
Example 2
85 parts by weight of a polymer prepared by free--radical polymer-
ization of a solution of 8 parts by weight of a polybutadiene
40 having a molecular weight (~Iw) of 250,000 and a medium--cis struc-
ture in 92 parts by weight of styrene, and 15 parts by weight of
the core/shell rubber of Example 1 were blended and granulated as
~-qrr; h-cl in Example 1, impregnated with the blowing agent mix-
ture ~_qrr1 h~-l in Example 1 and foamed.
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Af ter work-up, the granule9 had a blowing agent content of 5 . 8
by welght and an internal water content of 0 . 6 'c by weight.
After open storage for one day, batch prefoaming for 7 minutes at
100C gave a minimum bulk density of 10.6 g/l.
After open storage for three days, a minimum bulk density of
10 . 9 g/l was achieved under the same prefoaming conditions.
10 In both cases, the foam had a homogeneous, fine-cell structure.
A board having a density of 19.8 gi~l produced ~8 in Example 1 had
a recovery of 92 % (determined in accordance with DIN 53 577)
after quadruple compression by 50 9~.
The Poensgen thermal conductivity (DIN 52 616) was 7 ~ below the
corresponding value, determined under the same conditions, for
the standard polystyrene sLyLu~uL$ F 14 (BASF AG) of the same
density .
Example 3 (comparison)
The ~Lu~;eduLe was similar to that of Example 1, but the core/
shell rubber was not added to the polystyrene.
After work-up, the product had a blowing agent content of 8.2 9
by weight and a water content of 0 . 03 ~ by weight.
AftQr open storage for one day, batch prefoaming for 10 minutes
30 at 100C gave a bulk density of 12.1 g/l.
After open storng~ for fourteen days, a bulk density of 16.9 g/l
was achieved under the same prefoaming conditions~
In both cases, the foam had ~ conrse structure.
A board having a density of 20 . 0 g/l produced as in Example l had
a recovery of ~4.5 9~ after quadruple compressLon by 70 &; at a
density of 36.5 g/cm, the elastic recovery in the same experiment
40 was 76.2 9~ (determined in accord~nce with DIN 53 577).
