Note: Descriptions are shown in the official language in which they were submitted.
~ 3 Z ~
_a~ round_of the Invention
1. Field of the Invention:~-This invention relates to the
manufacture of articles of expandable polystyrene and the
like, and in particular, it relates to a change in the
polymerization recipe by which there are formed beads of
expandable vinyl aromatic monomer, e.~., polystyrene, whi~h
contains on the order of 5 to 9~ of pentane or other blowing
agent, and still more particularly, the invention relates
to a process for making such beads in which the beads have
incorporated in them about 500 to 5,000 parts of a Fischer-
Tropsch wax of a congealing point between 86 to 110C
In other aspects, the invention relates to
expandable or expanded thermoplastic-composition products
having considerable advantages in respect to various matters,
as hereinbelow more fully explained.
2. Description of the Prior Art:--Those skilled in the
art are familiar with two main practices by which-styrene
may be polymerized, in a suspension-polymerization process,
thereby obtaining beads of polystyrené having a molecular
weight on the order of 150,000 to ~00,000 and containing
on the order of 4 to 8~ of pentane as a blowing agent. In
one of the known methods, styrene, water, a small proportion
of protective colloid, such as polyvinylpyrrolidone, and
small but effective proportion of one or more free-radical
.. ~
Z~SO
initiators, such as various pero~Yides and perbenzoates or
the like) singly or in mi~tures Lhereof, are stirred and
heated to cause polymerization to take place for beads of
desired size. According to another suspension-polymeriza-
tion procedure, water and styrene are charged to a polymeri-
zation kettle, along with an agent such as calcium phosphate,
and heated with agitation, an emulsifier being added at a
particular stage of the heating to influence the bead size.
In either case, pentane or the like is added before) during,
or after the polymerization.
The use of additives of various kinds has been
proposed, such as the addition of hexabromocyclododec-ane to
inhibit the flammability of the product and to influence its
cell structure.
In U. S. Patent No. 3,647,723, it is taught that
styrene should be polymerized in the presence of a wax having
a melting point of 70 to 123C, an acid number of 0 to 45, and
a saponification number of from 3 to 150. This is said to
reduce the tendency of the beads to stick or clump in the
pre-expansion stage in hot water. The process is said to
be applicable to suspension polymerization of the kind
conducted in the presence of salt, and the patent goes on to
teach a further decreasing of the stickiness of the beads by
treating the beads with a zinc, calcium, or aluminium salt
of a fatty acid~ such as zinc stearate.
In U. S. Patent No. 3,320,188, the addition of
an ester wax of high melting point, of at least aboutilOC
higher than tha~ of the solidification point of the polymer,
in an extrusion process of polystyrene or the like, to
provide a nucleation effect~ is taught.
U. S. Patent No. 2,979,476 teaches mixing poly
styrene with about 1~ of microcrystalline or Fischer-Tropsch
waxe~, to form bulk-polymerized materials which are useful
for the manufacture of phonograph records.
U. S. Patent No. 3,060,138 is limited to making
foamable polystyrene particles with the use of isopentane
as a blowing agent and the addition of 0.5 to ~ of a paraf-
finic hydrocarbon having 16 to 46 carbon atoms. According
to this patent, the use of isopentane is essential, if a
desirably fine-celled product is to be obtained.
U. S. Patent No. 3,224,98~ teaches the addition
oE 100 to 5,000 parts per milli~n of a polyolefln wax
"or similar organic resinous polymeric substance". It
teaches that the addition of such material gives a desirably
small cell size, such as 80 microns, or about 12 cells per
millimeter, implying that this result, which is desirable
because it shortens the length of time that it is necessary
to keep the articles of expanded polystyrene in the mold and
thus in the final molding operation, is brought about by the
1~3Z~
use of such orgallic resinous polymeric substance. The
preferred material used is a polyolefin, is unlike the
Fischer-Tropsch wax used with the present invention, and
comprises a mixture of homologous but different molecular
species wi~h various Cl to C4 side chains. The patent
contains no teaching to the effect that a stable cell structure
in expandable polystyrene can be obtained, independent from
the internal water content of the beads, the polymerization
conditions or recipe, or drying and storage conditions of the
expandable polystyrene.
It is well known in the industry that the cell
structure of beads, when expanded shortly after t~e polymeri-
zation is completed, may vary sharply from the one obtained
after flash drying or after storage at different temperatures
and/or humidities. Such variations are further enhanced by
using different modifiers, like bromine compounds which
influence the flammability properties and may lead to a
very heterogeneous, non-reproducible cell structure, even
after applying the usual techniques of conditioning the
product, i.e., subjecting the beads to the action of~dry air.
A reproducible, uniform cell structure, however, is a prime
prerequisite for obtaining products with consistent properties
in processing and application.
o
The subject of the invention is the p~oduction of
expandable polystyrene with ~ni~orm,-~eproduc~ble c~ll strUc-
ture independent rom the polymerizatlon recipe~ temperature
and processing condi.tions prior to its use in expansion and
molding plus the combination with improved expandability,
reduction of clumping, lmproved wet and dry bead flow, lmproved
fusion, reduced water adsorption7 increased hydrophobicity,
good mol~ release and excellent smooth surface, in particular
of hot-wire-cut boards made from blocks of expandable poly-
styrene. The combinatlon of such properties has hitherto notbeen achie~ed nor taught in the abo~e cited patents.
Thus, in general, it is fair to state that the
prior art of which the applicant is aware does not teach or
suggest overcoming the various problems indicated above,
by the addition of the indicated quantities of Fischer-Tropsch
wax.
In particular, the present invention provides beads
of expandable polystyrene having a diameter of about 0.1 to 5
millimeters and containing 500 to 10,000 parts per million by
20~ weight based upon styrene of a Fischer-Tropsch wax having a
congealing point of 86 to 110 degrees Centigrade and an amount
of a blowing agent effective to permit said beads to be
expanded in a first step to a density of 10 to 250 grams per
liter.
In accordance wit~ another aspect of the present
invention, there is provided in a method of making an expandable
polystyrene in bead form by suspension polymerization in which
"~styrene monomer is mixed with water and subjected to poly-
me~ization conditions and a blowing agent is lncorporated
in sa~ beads ln an amount effective to permit said beads
to be expanded in a first step to a density of 10 to 250
grams per liter,
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!D
the i~proveme~t which consists i~ i~coxPox~ting
within said beads a Fischer-Tropsch WaX ha~ing a congealing
point of 86 to 110 degrees Centigrade in an amount o~ 500 to
10,000 parts per million by weight, based upon the amount of
styrene initially present.
The present invention also provides a process for
making expanded particles of expandable polystyrene having
a density of 10 to 250 grams per liter, said process comprising ~ ~
the steps of : -
conducting a suspension polymerization in which
styrene monomer is mixed with water and subjected to poly-
merization conditions and a blowing agent is incorporated in
beads produced by such suspension polymerization, a Fischer-
Tropsch wax having a congealing point of 86 to 110 degrees
Centigrade being incorporated in said beads during said
polymerization in an amount of 1500 to 5000 parts per million
by weight based upon the weight of said styrene monomer,
to yield raw beads, and then
subjecting said raw beads to the action of steam
to cause them to expand to a density of 10 to 250 grams per
liter.
Description of the Preferred Embodiments
Styrene is polymerized in aqueous suspension in
accordance with one of the usual practices, i.e., using either
calcium phosphate or the like plus an emulsifier, or an organic
protective colloid such as polyvinylpyrrolidone, polyvinyl-
acetate or the like with the single exception that in the
reaction mixture, there is added an amount such as
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D
11 1 3 ~ ~ ~
about 2,000 par~s per million of Fischer-Tropsch wax having
a congealing point of about ~6 to 110C. In the particular
work which I have done, there was used a wax melting at 9,2C
and having an average molecu ar weight of 750.
The consequence of making this change are immense.
First, this makes it possible to use the beads
immediately as they come from the reactor in which they are
formed because they now possess a stable and uniform cell
structure, even when polymerized at widely dif~ering
temperatures, using different reaction times and recipes.
Second, this invention yie]ds beads having a
stable and uniform cell structure which eliminates the need
for a special conditioning or drying process that would
otherwise be required in order to obtain a product with
defined, reproducible properties.
Third, these beads do expand readily to a density
such as 1~ grams per liter or less, without any shrivelling
or subsequent density increase, and this makes such a bead
product eminently suitable for the molding of blocks designed
for thermal insulation purposes.
Fourth, it is noticeable that the beads have a
much lower tendency to form clumps during the pre-expansion
operation, to the extent that the customary pre-treatment
of beads to be expanded with zinc stearate or other surface
coatings may be omitted.
;,;~. :
Fifth~ the pre-expanded beads have, in their wet
or dry sta~e, good free-flowing characteristics, and despite
no~ having a treatmen~ with zinc stearate or the like, show
a markedly improved mold-filling ability. Even molds which
usually are difficult to fill, or include portions wi~h
thin walls, can readily be filled with beads made according
to the present invention.
Sixth, because of the extremely stable cell
structure which in turn produces a very stable pre-expanded
bead and its good filling properties, it becomes possible
to mold successfully such beads after ~ storage time which
is shorter than usual. This increases the output of given
facilities.
Seventh, the beads may also be stored over ex-
tended periods of time, like during weekends or during
plant shutdowns, without losing their ability to produce
very well-fused articles, since there are no substances
~ on the bead surface which may interfere with the fusion of
the pre-expanded bead during the final expansion step in a
closed mold, as practiced in industry.
Eighth, because of the excellent fusion and the
hydrophobic surface of the bead, there is a markedly reduced
absorption of water during the cooling process in the mold
in the final molding operation.
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3 Z ~ 0
~ th. Inolcled articles have excellent mold-release
properties~ even without the use of rnold- release agents,
which in turn m~y interfere with the flammability characteris-
tics of articles molded from special modified grades of
expandable polystyrene. This makes it possible to reduce
also the time required for cooling the mold, because no mold
sticking occurs at higher mold temperatures either, thus
reducing the need for cooling water and producing a still
drier article.
Tenth, the use of the invention makes it possible
-~- to produce final products, in particular blocks, having a
lower density, because the amount of pentane or other blowing
agent which is added to the beads before, during, or after
the polymerization reaction may be permitted to be somewhat
greater than before. This makes it possible to achieve
densities of 13 grams per liter at more economical expansion
rates than have hitherto been possible.
Eleventh, the invention increases the speed of
hot-wire cutting of blocks significantly and produces boards
with an extremely smooth surface.
Twelfth,the addition of the wax does not in any
way adversely affect the results of flammability tests of the
kind hitherto used in the industry, and it is very important
that this be the case.
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11 ~ 3 ~ ~
In sul~-ary, the inven~ion provides an answer to
practically all of the problems which have been faced by
users of expandable polys~yrene beads, whether for the making
of blocks of insulation or for the production of shaped
pieces.
The invention is considered applicable to poly-
styrene and other vinylaromatic polymers of similar nature,
such as poly-alphamethylstyrene, or to copolymers which
result from the free-radical copolymerization of such mono-
mers with relatively minor amounts of olefinic comonomers
such as acrylonitrile. The term "expandable polystyrene"
will be understood in a generic sense as covering all such
polymers. Those skilled in the art will perceive the possi-
bility that the teachings of the invention may also be
applicable to the manufacture of other expandable or
foamable thermoplastic polymers.
The invention has been tried with n-pentane as the
blowing agent used, but there is no reason to believe that it
would not, in a proper case, operate in substantially the
same way if a different blowing agent, such as petroleum
ether, isopentane, hexane, one of the lower fluorocarbons,
etc., or compatible mlxtures thereof were used instead.
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~ ~3 ~
The invention has been tried particularly with the
use of a Fisch~r-Tropsch wax having a congealing point of
92 clegrees Centigrade and an average molecular weight of
about 750. Such a wax is commercially available from Moore
and Munger, Inc., of Stanford, Connecticut, U. S. A., under
a~ the designation "Paraflint Hl-N~" and is further character-
ized as a polymethylene Fischer-Tropsch wax of the family of
paraffinic hydrocarbons of the formula Cn H2n~z , where
"n" has an average value of 52 to 56. It is in the form of
a micronized powder with a maximum particle size of 10
microns. It will be evident to those skilled in the art
that similar Fischer-Tropsch waxes can be expected to perform
in the same mannerJ i.e.~ once having a congealing point of
approxima~ely 86 to 110 degrees Centigrade.
The proportion o wax used may be varied, within
limits. At rates of less than 500 parts per million by
weight, based upon the quantity of styrene used~ there is
little or no effect, and within a range of the lower rates
of useJ up to about 1500 or 2000 parts per million, there
is an increasing effect, with a noticeable decrease in the
cell size as the amount of Fischer-Tropsch wax used is
increased. At about 2000 to 4000 or 5000 parts per million,
there is rather little difference, but the higher values do
yield a modest improvement. It is believed that at beyond
about 5000 parts per milLion, there is no additional benefit
~ rr~e~ k
- 1 1-
obtained, though the use of proportions as great as lO,000
parts per million may conceivably be practiced. The cost
of the addition of such relatively modest amounts is
relatively very low, and the advantages which are obtained,
as explained above, are certainly so great that the overall
costs of the process are considerably reduced when the present
invention is practiced.
It does not matter whether the Fischer-Tropsch
wax is incorporated by being put into the pentane or other
blowing agent, into the styrene ~in which it is not soluble
at room temperature but quite soluble enough at a moderately
increased temperature such as 55 degrees Centigrade), or in
the form of a suspension in the water, though introduction
with the pentane is probably the most convenient.
It does not matter too importantly when the
pentane is introduced into the system whereby the expandable "
polystyrene is made; practices for introducing pentane or
other blowing agent in which the pentane is added last are
known and used~ but these are usually to be avoided if the
beads of expandable polystyrene which are being made are
relatively large, such as 5 millimeters in diameter,
because of t~e added time required for the diffusion of the ~
pentane into the beads, if they h8ve already been formed. `
In other words, it is usually more advantageous to add the
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pentane or the like befo~e or during the polymerization.
As has been indicated above, it is possible with
the use of the present invention to use slightly greater pro-
porlion of pentane, _._., 5 to 9 weight percent, based upon
the styrene, in con~rast to the usual range of 5 to 8
percent. More pentane is used if a lower-density final
product is desired. Previously, the use of greater propor-
tions of pentane than 8 percent was avoided because of the
greater tendency of the beads to give off pentane during
storage between when the formation of the beads and the
pre-expansion step. Moreover, the use of such greater
amounts of pentane would necessarily be associated with
attempts to obtain low density such as 8 grams per liter,
~-~~ but such attempts were usually not successful, at least
when it was tried to perform a pre-expansion in a single
step, because of the relatively lower throughputs of the ~ -
pre-expansion equipment and process under the condition
known prior to the present invention.
Those skilled in the art already know the practices
and equipment and recipes used for making expandable poly-
styrene beads of a given size by suspension polymerization,
and to a great extent, these remain unchanged, with the
possible exception indicated above.
.- . ~ .
.. . .
3 ~D
It has heen customary in the industry to subject
the beads removed from the polymerization kettle to a
drying or conditioning step, by draining ~he beads and
subjecting them to the action of dry air. Usually, when
the beads have not been so conditioned, there have quite
often been obtained certain undesirable effects, such as
the development of an undesirably coarse cell structure
(2 or only 1 cell per millimeter) in at least a portion
of the bead as expanded. Such coarse cell structure is
associated with other difficulties later on in the processing,
such as a need to take more time for the pre-expansion and
the final molding steps, and until the present inventionJ it
occurred sporadically, even with the best of the known
practices for preventing it. An advance such as the
present invention, which permits the user to obtain reliably
a finer cell structure, such as 8 to 12 cells per milli-
meter, is important to the art.
It has also been usual, after the conditioning
_ step, to subject the expandable polystyrene beads to
coating with a material such as zinc stearate, calcium
stearate, or some other equivalent material, usually one
in the nature of a water-insoluble metal salt of fatty
acid, as a measure chiefly intended to prevent clumping v
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- ~
~ 2~
of the beads during the operation of the pre-expander. It
is usua]ly in this as-coated form that the expandable
polystyrene beads are shipped to the customer, who at his
plant site performs the necessary further steps required
to obtain a finished product. These include at least a
first pre-expansion, followed usually by either a molding
into a shaped article, or a final expansion into a large block
(which may then be cut into smaller slabs or pieces of
desired shape), or inclusion in a lightweight aggregate,
etc.
It is here appropriate to observe that the
invention may be considered, in an article-o~-manufacture
aspect, as comprising the expandable polystyrene beads
of the applicant, which are characterized by the features
of being 0~1 to 5 millimeters in diameter, containing an
effective amount of a blowing agent, and in particular,
in containing 500 to 10,000 parts by weight, based on the
weight of the styrene, of a Fischer-Tropsch wax having a
congealing point of 86 to 110 degrees Centigrade. Such a
product may be obtained by some other method, such as an
extrusion process, yet have for practical purposes all the
advantages in respect to the matters which are of importance
to a user of the beads, as those skilled in the art will
appreciate.
,
.
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.
1~3ZC~
Coming now to a discussion of the pre-expansion
operation, it is kno~m how such an operation can be con-
trolled to yield pre-expanded particles of desired size.
Relevant considerations, such as feed rate of unexpanded
beads, change in the size of the effective volume of the
pre-expander, and control of the temperature of the steam,
used, are discussed in, for example, U. S. Patent No.
3,973,884. It is evident that the invention operates to
improve the throughput, because of the finer-cell structure
within the beads. There is less clumping and better flow
of the moist beads as they Leave the steam-heated pre-
expander. The pre-expanded beads have good handling
characteristics and do not tend to lose their usefulness .
if they are stored for some time, such as over a weekend,
before being given a final expansion or molding.
The importance of the invention is further ; -
made clear by reference to the following Examples, which
are to be taken as illustrative and not in a limiting
sense. Unless otherwise indicated, parts are by weight,
and parts per million are based upon the amount of styrene
used.
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': '' ` :
3Z~O
Example 1
Expandable polystyrene was produced from a
solution of 0.12 parts benzoyl peroxide and 0.26 parts
tertiarybutyl perbenzoate, 8 parts pentane, 0.2 parts of
Fischer-Tropsch wax having a congealing point of 92 degrees
Centigrade in 100 parts styrene which had been suspended,
using vigorous stirring, in 100 parts of water to which
1 part of polyvinylpyrrolidone had been addedO Polymerization
was effected by heating such suspension to 80 degrees
Centigrade, raising the temperature over a five-hour period
to 120 degrees Centigrade and then reacting for five more
hours at that temperature.
Beads so made were given an expansion test by
being subjected to steam at 100 degrees Centigrade for 2
minutes. Expanded beads with a uniform cell structure, 8
to 10 cells per millimeter, were obtained. There were no
shrivelled beads.
Examples 2 and 3
Example 1 was repeated, with a maximum temperature
of 110 degrees Centigrade (Example 2)-and 130 degrees Centi-
grade (Example 3) used in the polymerization. The results
w~re the same.
Example 4
Example 1 was re~eated, except that up to 15
parts of polystyrene was dissolved in the styrene monomer.
The results were the same.
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., . . ............................... ,.
,, . ~ .
Comparison Test A
Example 1 was repeated, but without the Fischer~
Tropsch wax.
In the expansion test, the cell structure was
coarse (one to two cells per millimeter) and 50 percent of
the beads were shrivelled.
Example 5
Example 1 is repeated, except that the styrene
monomer also contained 6500 parts per million of hexabromo-
cyclododecane.
When expanded immediately after cooling of the
polymerization reactor, the beads give a uniform cell
structure of 8 to 12 cells per millimeter in the bead
center and a thin shell, about 30 to 100 microns in thick-
ness, of very fine cells (up to ~0 cells per millimeter),
and the expanded beads do not exhibit any shrivelling.
Exam~_e 6
Example 5 is repeated, except that instead of
being expanded immediateiy, the beads are subjected to an
extended drying in air at temperatures of up to 40 degrees
Centigrade and for a time of up to 6 hours.
In the expansion test, the results are that the
thickness of the fine-grained outer shell increases to as
much as 500 microns and the internal cell structure is
further homogenized, to about 10 to 12 cells per millimeter.
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Compar~son Test B
... ..
Example 5 is repeated, but without the addition
of the Fischer-Tropsch wax.
In the expansion test, very unsatisfactory results
are obtained. There is a very coarse and heterogeneous cell
structure (one to five cells per millimeter) and extreme
shrivelling.
Comparison Test C
Example 5 is repeated, but without the addition
of the Fischer-Tropsch wax, and with extended drying of
the beads in air at temperatures of up to 40 degrees Centi-
grade for up to six hours. This amounts to Test B, but with
the extended drying step added between the polymerization
and the expansion.
In the expansion test, t~e results are variable.
Though much of the time, there is little shrivelling and a
uniform cell structure is obtained, there are times that,
for no known reason, a uniform cell structure is not obtained
a~ all.
Water-Effect Test
Beads according to Example 1 and beads according
to Comparison Test A were stored in a desiccator over
phosphorus pentoxide until an internal water content of less
than 0.03 percent was obtained in each case, and expansion
tests were conducted upon the beads, both before and after
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13~
sllch desiccation. The beads of th~ invention (Example 1)
were the same in each case. The beads of the prior art
(Test A) performed quite differently, giving different
cell structure, depending on the internal moisture content.
Pre-Expander Tests
A conventional Rodman-type expander having a
capacity of 0.22 cubic meters was used to expand beads to
a density of 15 grams per liter. Beads according to the
invention ~Example 1) could be expanded at a rate of 120
kilograms per hour, whereas beads according to the prior
art (no Fischer-Tr~psch wax, extended drying before the
pre-expansion) could be expanded only at the rate o~ 70
kilograms per hour.
In further testing with such a Rodman-type
expander, beads were screened to produce a fraction having
particle sizes ranging from 1.0 to 0.4 millimeters, and
then expanded to 16 to 18 grams per liter density. Beads
according to the invention, containing the Fischer-Tropsch
wax, gave only one twentieth as much clumping in the
expansion as did beads made in accordance with the prior
art.
In further testing, beads of the invention that
were made according to Example 5 ~containing hexabromo-
cyclododecane and the wax) were expanded, and no additional
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2 ~
coating of tl.~c beads had been done be~ween the polymerization
and the pre-expansion. The pre-expansion proceeded smoothly.
This is in sharp contrast to the usual behavior of beads
containing the bromine compound, which are known in par-
ticular for their tendency to give poor bead flow, both
within and from the Rodman expander, unless special coating
techniques are also practiced.
Hot-Wire Cuttin~ Tests
A block made of expandable styrene produced
according to this ivention was compared with one made
according to the prior art. Though the prior-art block
required 90 to 100 seconds for the hot-w;re cut made through
it, the block made from material according to this invention
was able to have an equal cut made through it in 65 seconds
and when the surfaces produced by the cuts were compared,
that through the material of the invention was the better
one, being much smoother than the cut through the material
of the prior art.
Example 7
An aqueous suspension of calcium phosphate is
prepared by dissolving 10.9 parts of trisodium phosphate
and 0.7 parts of sodium acetate in 950 parts of water,
then adding a solution of 16.7 parts of calcium chloride in
50 parts of water. T this mixture, there is added a
solution of 1.11 parts benzoyl peroxide and 1.91 parts of
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' . . ' '. . ' ~ '
~L~1320~
t-butyl perben~oate and 1.21 parts of a micronized Fischer-
Tropsch wax having a congealing point of 92 degrees Centi-
gracle in 607 parts of styrene. The mixture is polymerized
with vigo-ous agitation for 6 hours at 80 degrees Centigrade
then 0.018 parts of Cl2 to Cla sodium alkylsulfonate are
added, and the temperature is increased to 90 degrees Centi-
grade and maintained ther`e for an additional 5 hours. Seven
hours after the start of the polymerization at 80 degrees
Centigrade, there are added 75 parts of n-pentane. After
a total of 11 hours of reaction time, the temperature is
raised for 5 hours to 100 degrees Centigrade~ and finally,
` for an additional 5 hours, to 120 degrees Centigrade. The
reaction vessel is then cooled to room temperature and the
beads are recovered.
In a subsequent expansion test, beads with a
uniform cell structure of 8 to 10 cells per millimeter
are obtained. The same results are obtained if the Fischer-
Tropsch wax is added to the reaction mixture by being
dispersed in the aqueous phase.
Comparison Test D
Example 7 is repeated, except that the wax is
omitted.
In the expansion test, beads having a coarse and
heterogeneous cell structure (about 2 to 5 cells per milli-
meter are obtained.
-22-
13Z~)~
Example 8
When a polystyrene containing 8 to 10 parts of
pentane or other suitable blowing agent is extruded into a
bath of cold water and a microniæed Fischer-Tropsch wax
having a congealing point of 92 degrees Centigrade is
continuously added at a rate of 2000 to 5000 parts per
million to the granules or beads used as feedstock for
such an extrusion operation, and the strands resulting
from such an extrusion are cut into cylindrical granules,,
and these granules are thereafter expanded, the resulting
foam exhibit a coarse~ heterogeneous cell structure of
1 to 3 cells per millimeter. Subsequent heating of such
granules in an aqueous suspension which contains a suitable
protective colloid made by reaction of styrene with poly-
vinylpyrrolidone (such as the protective colloid used in the
suspension polymerization described above in Example 3) in
a reactor pressurized with 10 atmospheres of nitrogen, wsing ;
a temperature of 100 degrees Centigrade for 3 hours and
followed by cooling to room temperature, yields essentially
spherical particles of identical size. This gives a product
which is substantially the equivalent of that of Example 1,
i._. J a bead of expandable polystyrene containing an e~fective
amount of a Fischer-Tropsch wax having a congealing point of
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86 to 110 degrees Centigrade and an effective amount of a
volatile blowing agent, such as pentane or the like. Such
a bead product may be fur~her processed in ways known to
those skilled in the art.
In an expansion test upon such a bead product~
a uniform cell structure of 8 to 10 cells per millimeter is
obtained.
Comparison Test E
Example 8 is repeated except that the Fischer-
Tropsch wax is omitted.
In the expansion test, a héterogeneous cellstructure with 2 to 5 cells per millimeter is obtained.
While I have shown and described herein certain
embodiments of my invention, I intend to cover as well any
change or modification therein which may be made without
departing from its spirit and scope.
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