Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE PREPARATION O~
EXPANDABLE STYRENE POLYMERS
Background f The Invention
l. Field of the Invention
The present invention relates to an improved process
for the preparation of expandable styrene polymers by
extrusion.
2. Description of Related Art
Federal Republic of Germany 21 54 754 discloses a
process for the preparation of expandable styrene polymers by
extrusion in which cylindrical extrudate is deformed by milling
and/or stretching into extrudate having an oval cross section
and then said extrudate is cut into slices in the direction of
the smaller axis of the oval cross section. The styrene
polymers can contain bromine compounds together with
synergistic additives as flame retardants.
In the commercial preparation of expandable styrene
polymers which contain organic bromine compounds as flame
retardants, one observes considerable corrosion in the extruder
screw when extruding" As a result of bubble formation, the
foam particles obtained by foaming have an inhomogeneous foam
structure and in turn they have an increased particle break
rate when used as loose fill packing materialO
U.S. Patent 3,441,524 discloses self-extinguishing
styrene polymers comprising organic bromine compounds and
Z003488
su~stituted dipherlyl ethanes. However, this patent offers no
solution for the extruder corrosion problem when extruding
expandable styrene polymers containing bromine compounds.
An object of the present invention is to overcome
these disadvantages. This object was surprisingly met by using
dicumyl as a synergistic additive.
Summary Of The Invention
A process for the preparation of expandable styrene
polymers, having an organic bromine compound as a fire
retardant and a synergistic additive in which a mixture of a
styrene polymer, blowing agent, flame retardant and additive
are extruded; the extrudate is quickly cooled so that it does
not foam and while the inside of said extrudate is still
plastic it is deformed by stretching and/or milling and then
reduced in size, wherein dicumyl is used as said synergistic
additive.
Detailed Description
Styrene polymers are understood to be polystyrene and
mixed polymers of styrene which contain polymerized in situ at
least 50 weight percent, more preferably at least 75 weight
percent of styrene. Typical mixed polymerization components
are ethylenically unsaturated copolymerizable compounds such
Z(~03 ~
as, for example, a-methylstyrene, ring halogenated styrenes,
ring alkylated styrenes having 1 to 4 carbon atoms in the alkyl
group, acrylonitrile, methacrylonitrile; esters of acrylic
acid, methacrylic acid or fumaric acid from alcohols having 1
to 10 carbon atoms; also butadiene or ~-vinyl compounds, such
as, for example, N-vinylcarbazole, N-vinylpyridine; or smaller
quantities, that i5 less than 0.5 weight percent, of divinyl
compounds, such as, for example, butanevinyl diacrylate or
divinylbenzene.
The expandable styrene polymers contain a blowing
agent. Conventional blowing agents are used, that is aliphatic
or cycloaliphatic hydrocarbons or halogenated hydrocarbons
having a maximum boiling point of about 90C which do not
dissolve the styrene polymers but can be homogeneously
distributed in them. Typical blowing agents used in quantities
of from about 2.5 to 3 weight percent are, for example, n-,
iso-, or neopentane, hexane, cyclohexane, n- or iso-butane,
propane, difluorodichloromethane or mixtures thereof.
The blowing agents can be added in any fashion and at
any time to the styrene polymers, for example, even when
polymerizing the monomers or ri~ht in the extruder which forms
the cylindrical extrudate.
Typical bromine compounds used as flame retardants
are used as the organic compounds. Moreover, they generally
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contain at least two bromine atoms and have a bromine content
of at least 40 weight percent. Typical bromine compounds are
1,2,3,4-tetrabromobutane, 1,2,~~tribromobutane,
tetrabromopentane; bromine substituted cycloalkanes, such as 1-
chloro-2,3,4,5,6-pentabromocyclohexane, 1,2,3,4,5,6-
hexabromocyclohexane, 1,2,5,6,9,10-hexabromocyclodecane,
octabromocyclohexadecane, dibromoethylbenzene,
pentabromodiphenylether, es~ers and acetals of dibromopropanol,
such as tris-(2,3-dibromopropyl) phosphate.
Hexabromocyclodecane is preferably used.
The organic bromine compound is used in conventional
effective quantities. The molding composition should have a
bromine content between 0.3 and 5 weight percent, more
preferably 0.5 and 4 weight percent and most preferably between
0.8 and 3 weight percent of brornine.
The styrene polymers contain dicumyl (2,3-diphenyl-
2,3-dimethylbutane) as the synergistic additive and typically
in an amount of from 0.05 to 1 weight percent, more preferably
0.1 to 0.5 weight percent, and most preferably 0.1 to 0.3
weight percent based on the styrene polymer.
In addition, the expandable styrene polymers can
contain other typical additives, such as, for example, dyes,
fillers, nucleating agents, stabilizers, etc. in effective
quantities.
2i~034~
When preparing the expandable styrene polymers the
styrene polymer, blowing agent, flame retardant and additives
are mixed in an extruder, melted and extruded. In addition,
nozzles having any cross section can be used depending on the
desired cross section of ~he extrudate. Preferably extrudate
having a cylindrical cross section is prepared which has a
diameter of from 3 to 15, more preferably 5 to 10 mm. The
material temperature when discharged from the nozzles generally
is ~0 to 150C, more preferably 110 to 130C. The extrudate is
cooled quickly in a cooling bath so that it does not, or p-
ractically does not foam. Cooling the extrudate is done on the
surface while the inside of the extrudate remains hot and
plastic. In this condition the ex~rudate can be further
stretched and~or deformed. To do this it is fed generally via
guide rollers from the cooling bath and through a pair of
rollers. A combination of one elastic and one non-elastic
roller, for example, rubber and steel has proven useful here.
The roller speed can be adjusted so that the extrudate can be
stretched more or less, or not stretched at all. The cross
section of the extrudate can be reduced by 5 to 60% by
stretchin~ or drawing. The roller pressure can be adjusted so
that the extrudate is deformed more or less, and so that it
assumes an oval and/or elliptical cross section, ~or example,
having an axis ratio of 1:1.3 to 1:2. ~or stretching and/or
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deforming the extrudate several roller pairs can be arranged in
sequence. The rollers are generally smooth but even profilated
are suitable. Conventional rollers can be used to feed
granulating units.
Efficaciously the extrudate is cut directly behind
the rollers, thus, practically at the same temperature and in a
state where the inside of the extrudate is still plastic. Said
extrudate is preferably cut by a sharp rotating knife in the
direction of the smaller axis of the oval cross section into
slices. The oval slices obtained generally have a thickness
whose ratio to the smaller axis of the extrudate cross section
is 1:1.5 to 1:10, more preferably 1:2 to 1:6.
The deformation and/or stretching by milling and
cutting the extrudate generally occurs at an average
temperature between 50 and 90C, more preferably 60 and 80C.
The temperature can easily be measured by measuring the
temperature of the granulate cut immediately after its
preparation.
By deforming and/or stretching and cutting the
extrudate while its interior is still plastic, the granulate
retains its inner tension. The net result is that the discs
curl easily before and especially after foaming. By foaming
oval discs of expandable material, one obtains convex-concave
or saddle-shaped foam discs which interlock with one another
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under pressure and accordingly are excellently suited as
flowable and shakable cushioning material and packaging
material.
Foaming is done in a conventional fashion in
commercially available equipment, for example, using steam at
from 100 to 150C. Generally the particles are foamed up to a
bulk density of from 4 to 15 grams per liter. When using
dicumyl as an additive according to the present invention,
unlike conventional synergists, such as dicumylperoxide, the
amount of organic bromine compounds required for good self
extinguishing p.operties can be drastically reduced. At the
same time usually prevented for the most part is extruder
corrosion. Surprisingly, when using dic~myl, bubble formation
is reduced which brings about a noticeable increase in the
density of the expandable particles and at the same time the
break rate of the foam particles prepared is reduced.
The parts in the examples refer to parts by weight.
201)348~
_amples 1 throuyh _
Polystyrene prepared by suspension polymerization
containing 6 weight percent oE pentane as a blowing agent was
plasticated in a heated twin sha~t extruder (Type ZSK 120)
while using the amounts of hexabromocyclododecane (HBCD) cited
in the table as the flame retardant additive; then extruded at
a mass temperature of 130~C through a breaker plate having
nozzle diameters of 8 mm into a water bath at 20C; and the
extrudate following a residency time of 15 seconds was fed via
guide rollers through a pair of rollers which contained one
steel and one rubber roller. By simultaneous stretching and
deformation of the cylindrical extrudate, it was shaped into
material having an oval cross section with a diameter of 5
mm/8.5 mm and subsequently cut into 2 mm thick pieces via a
rotating knife. Immediately after its preparation the
granulate had a temperature of 72C.
Oval foam particles were obtained by foaming with
flowing steam. The particles were slightly bent and had a bulk
density of about 8 grams per liter. The foam product was well
suited as loose shakable packaging material. The extinguish
times cited were measured by filling a wire mesh cage
(100x150x150 mm) with the foam particles after 72 hours of
intermediate storage and by igniting the foam with a natural
gas flame. The time to extinguish the flame was reported as a
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mean value of 20 individual measurements. The results of the
e~periments are compiled in table 1.
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