[0001] This invention relates to beads of expandable polystyrene which contain from 5 to
9% of pentane or other blowing agent and from 500 to 10,000 parts of a Fischer-Tropsch
wax of a melting point between 86 to 110°C.
[0002] The invention also relates to a method of making an expandable polystyrene in bead
form by suspension polymerization in which styrene monomer is mixed with water and
a wax and subjected to polymerization conditions and a blowing agent, preferably n-pentane
in an amount of 5 to 9 weight per cent, is incorporated in said beads, wherein there
is incorporated within said beads a Fischer-Tropsch wax having a melting point of
86 to 110 degrees Centigrade in an amount of 500 to 10,000, preferably of 1500 to
5000 parts per million by weight, based upon the amount of styrene initially present.
[0003] Finally, the invention relates to a process for making expanded particles by subjecting
the above defined expandable polystyrene beads to the action of steam to cause them
to expand to a density of 10 to 250 grams per liter.
[0004] Those skilled in tha art are familiar with two main practices by which styrene may
be polymerized, in a suspension-polymerization process, thereby obtaining beads of
polystyrene having a molecular weight on the order of 150,000 to 300,000 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 a small but effective proportion of one or more free-radical initiators, such
as various peroxides and perbenzoates, singly or in mixtures thereof, are stirred
and heated to cause polymerization to take place for beads of desired size. According
to another suspension-polymerization procedure, water and styrene are charged to a
polymerization 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 is added before, during, or after the polymerization.
[0005] The use of additives of various kinds has been proposed such as the addition of hexabromocyclododecane
to inhibit the flammability of the product and to influence its cell structure.
[0006] 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 123°C, 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.
[0007] In U.S. Patent No. 3,320,188, the addition of an ester wax of high melting point,
of at least about 10°C higher than that of the solidification point of the polymer,
in an extrusion process of polystyrene or the like, to provide a nucleation effect,
is taught.
[0008] U.S. Patent No. 2,979,476 teaches mixing polystyrene with about 1% of microcrystalline
or Fischer-Tropsch waxes, to form bulk- polymerized materials which are useful for
the manufacture of phonograph records.
[0009] 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 3% of a paraffinic
hydrocarbon having 16 to 46 carbon atoms. According to this patent, the use of isopentane
is essential, if a desirable fine-celled product is to be obtained.
[0010] In GB-PS 1 012 277 foamabie polystyrene particles are described which contain from
0.1 to 10% of a wax, preferably of polyethylene wax.
[0011] U.S. Patent No. 3,244,984 teaches the addition of 100 to 5,000 parts per million
of a polyolefin wax "or similar organic resinous polymeric substance". It teaches
that the addition of such material give 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 is is necessary to keep the articles of expanded
polystyrene in the mold and thus in the final molding operation, is brought about
by the use of such organic 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 with various
C, to C
4 side chains. The patent contains no teaching to the effect that a stable cell structure
in expandable polystyrene can be obtained, independept from the internal water content
of the beads, the polymerization conditions or recipe, or drying and storage conditions
of the expandable polystyrene.
[0012] It is well known in the industry that the cell structure of beads, when expanded
shortly after the polymerization 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.
[0013] The subject of the invention is the production of expandable polystyrene with uniform,
reproducible cell structure independent from the polymerization recipe, temperature
and processing conditions prior to its use in expansion and molding plus the combination
with improved expandability, reduction of clumping, improved wet and dry bead flow,
improved fusion, reduced water adsorption, increased hydrophobicity, good mold release
and excellent smooth surface, in particular of hot-wire-cut boards made from blocks
of expandable polystyrene. The combination of such properties has hitherto not been
achieved nor taught in the above cited patents.
[0014] 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.
[0015] Styrene is polymerized in aqueous suspension in accordance with one of the usual
practices, i.e., using either calcium phosphate plus an emulsifier, or an organic
protective colloid such as polyvinylpyrrolidone or polyvinylacetate with the single
exception that in the reaction mixture, there is added a Fischer-Tropsch wax having
a congealing point of 86 to 110°C.
[0016] The consequences of making this change are immense.
[0017] 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 differing temperatures, using different
reaction times and recipes.
[0018] Second, this invention yields 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.
[0019] Third, these beads do expand readily to a density such as 16 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.
[0020] 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.
[0021] Fifth, the pre-expanded beads have, in their wet or dry state, good free-flowing
characteristics, and despite not having a treatment with zinc stearate, show a markedly
improved mold-filling ability. Even molds which usually are difficult to fill, or
include portions with thin wails, can readily be filled with beads made according
to the present invention.
[0022] 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 a storage time which is shorter than usual. This increases
the output of given facilities.
[0023] Seventh, the beads may also be stored over extended 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.
[0024] 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.
[0025] Ninth, molded articles have excellent mold-release properties, even without the use
of mold-release agents, which in turn may interfere with the flammability characteristics
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.
[0026] 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.
[0027] Eleventh, the invention increases the speed of hot-wire cutting of blocks significantly
and produces boards with an extremely smooth surface.
[0028] 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.
[0029] In summary, the invention provides an answer to practically all of the problems which
have been faced by users of expandable polystyrene beads, whether for the making of
blocks of insulation or for the production of shaped pieces.
[0030] The invention is considered applicable to polystyrene and other vinylaromatic polymers
of similar nature, such as poly-alphamethylstyrene, or to copolymers which result
from the free-radical copolymerization of such monomers 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.
[0031] 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, or compatible mixtures thereof were used instead.
[0032] The invention has been tried particularly with the use of a Fischer-Tropsch wax having
a melting point of 92 degrees Centigrade and an average molecular weight of about
750. Such a wax is commercially available under the designation "Paraflint Hl-N3"
and is further characterized as a polymethylene Fischer-Tropsch wax of the family
of parafffinic hydrocarbons of the formula C
" H
2,
1+2, 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.
[0033] It will be evident to those skilled in the art that similar Fischer-Tropsch waxes
can be expected to perform in the same mannar, i.e., ones having a melting point of
86 to 110 degrees Centigrade.
[0034] The proportion of 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 use, 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 in increased. At about 2000 to
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 benefits obtained, though the use of proportions as great as
10,000 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.
[0035] 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.
[0036] It does not matter 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 the added time required for the diffusion
of the pentane into the beads, if they have already been formed. In other words, it
is usually more advantageous to add the pentane before or during the polymerization.
[0037] As has been indicated above, it is possible with the use of the present invention
to use slightly greater proportions of pentane, i.e., 5 to 9 weight percent, based
upon the styrene, in contrast to the usual range of 5 to 8 percent. More pentane is
used if lower-density final product is desired. Previously, the use of greater proportions
of pentane than 8 percent was avoided because of the greater tendency of the beads
to give off pentane during storage between 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.
[0038] Those skilled in the art already know the practices and equipment and recipes used
for making expandable polystyrene beads of a given size by suspension polymerization,
and to a great extent, these remain unchanged, with the possible exception indicated
above.
[0039] It has been customary in the industry to subject the beads removed from the polymerization
kettle to a drying or conditioning step, by draining the 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 undesirable 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 invention, 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 millimeter, is important to the art.
[0040] 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 of the beads during
the operation of the pre-expander. It is usually 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.
[0041] It is here appropriate to observe that the invention may be considered, in an article-of-
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 melting point of 86 to 110 degrees Centigrade. Such a product may be
obtained by some other method, such as an extrusion process, yet has 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.
[0042] Coming now to a discussion of the pre-expansion operation, it is known how such an
operation can be controlled 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.
[0043] 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.
Example 1
[0044] 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 melting 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 added. Polymerization was effected by heating such suspension
to 80 degrees Centrigrade, raising the temperature over a five- hour period to 120
degrees Centigrade and then reacting for five more hours at that temperature.
[0045] 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
[0046] Example 1 was repeated, with a maximum temperature of 110 degrees Centigrade (Example
2) and 130 degrees Centigrade (Example 3) used in the polymerization. The results
were the same.
Example 4
[0047] Example 1 was repeated, except that up to 15 parts of polystyrene was dissolved in
the styrene monomer. The results were the same.
Comparson Test A
[0048] Example 1 was repeated, but without the Fischer-Tropsch wax.
[0049] 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
[0050] Example 1 is repeated, except that the styrene monomer also contained 6500 parts
per million of hexabromocyclododecane.
[0051] 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 thickness, of very fine cells (up to 30 cells
per millimeter), and the expanded beads do not exhibit any shrivelling.
Example 6
[0052] Example 5 is repeated, except that instead of being expanded immediately, 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.
[0053] 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.
Comparison Test B
[0054] Example 5 is repeated, but without the addition of the Fischer-Tropsch wax.
[0055] 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
[0056] 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 Centigrade
for up to six hours. This amounts to Test B, but with the extended drying step added
between the polymerization and the expansion.
[0057] In the expansion test, the 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 at all.
Water-effect Test
[0058] 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 such desiccation. The beads of the invention (Examplel)
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 Test
[0059] 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-Tropsch wax, extended drying before the pre-expansion)
could be expanded only at the rate of 70 kilograms per hour.
[0060] 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.
[0061] In further testing, beads of the invention that were made according to Example 5
(containing hexabromocyclododecane and the wax) were expanded, and no additional coating
of the beads had been done between 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 particular for their tendency to give poor
bead flow, both within and from the Rodman expander, unless special coating techniques
are also practiced.
Hot-wire cutting Test
[0062] A block made of expandable styrene produced according to this invention was compared
with one made according to the prior art. Though the prior-art block required 90 to
100 seconds for the hot-wire 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
[0063] 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. To this mixture,
there is added a solution of 1.11 parts benzoyl peroxide and 1.91 parts of t-butyl
perbenzoate and 1.21 parts of a micronized Fischer-Tropsch wax having a melting point
of 92 degrees Centigrade in 607 parts of styrene. The mixture is polymerized with
vigorous agitation for 6 hours at 80 degrees Centigrade, then 0.018 parts of C
12 to C
18 sodium alkylsulfonate are added, and the temperature is increased to 90 degrees Centigrade
and maintained there for an additional 5 hours. Seven hours after the start of the
polymerisation 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 Centrigrade.
The reaction vessel is then cooled to room temperature and the beads are recovered.
[0064] 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
[0065] Example 7 is repeated, except that the wax is omitted.
[0066] In the expansion test, beads having a coarse and heterogeneous cell structure (about
2 to 5 cells per millimeter are obtained.
Example 8
[0067] 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 micronized Fischer-Tropsch wax having
a melting 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 exhibits
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 polyvinylpyrrolidone (such as the protective
colloid used in the suspension polymerization described above in Example 3) in a reactor
pressurized with 10 atmospheres of nitrogen, using a temperature of 100 degrees Centrigrade
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.e., a bead of expandable polystyrene containing an effective
amount of a Fischer-Tropsch wax having a melting point of 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 further processed in ways known to those skilled in the
art.
[0068] 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
[0069] Example 8 is repeated except that the Fischer-Tropsch wax is omitted.
[0070] In the expansion test, a heterogeneous cell structure with 2 to 5 cells per millimeter
is obtained.
1. Perles de polystyrène expansible, contenant de 5 à 9% en poids d'un agent porogène
et une cire et possédant un diamètre d'environ 0,1 à 5 mm, caractérisées en ce que
ces perles contiennent de 500 à 10,000 parties en poids d'une cire de Fischer-Tropsch
possédant un point de fusion de 86 à 110°C par million de parties en poids de polystyrène.
2. Perles suivant la revendication 1, caractérisées en ce que l'agent porogène est
le n-pentane.
3. Perles suivant la revendication 2, caractérisées en ce que le n-pentane est présent
en une proportion qui varie de plus de 8 et jusqu'a 9% en poids.
4. Procédé de fabrication d'un polystyrène expansible sous forme de perles par polymérisation
en suspension conformément à laquelle le styrène monomère est mélangé à de l'eau et
à une cire et est soumis à des conditions de polymérisation et un agent porogène est
incorporé auxdites perles, caractérisé en ce que l'on incorporé auxdites perles une
cire de Fischer-Tropsch possédant un point de fusion de 86 à 110°C en une quantité
de. 500 à 10,000 parties en poids par million de parties en poids de styrène initialement
présent.
5. Procédé suivant la revendication 4, caractérisé en ce que l'on utilise ladite cire
en une quantité qui varie d'environ 1,500 à 5,000 parties en poids par million de
parties en poids de la quantité de styrène initialement présente.
6. Procédé suivant la revendication 4, caractérisé en ce que l'incorporation s'effectue
en ajoutant ladite cire avec et dans l'agent porogène précité.
7. Procédé suivant la revendication 6, caractérisé en ce que l'agent porogène en question
est le n-pentane et qu'il est présent en une quantitié de 5 à 9% en poids.
8. Procédé suivant la revendication 4, caractérisé en ce que ladite incorporation
s'effectue en ajoutant la cire précitée sous la forme d'une suspension dans le styrène.
9. Procédé suivant la revendication 4, caractérisé en ce que l'incorporation s'effectue
en ajoutant ladite cire sous la forme d'une suspension dans ladite eau.
10. Procédé pour fabriquer des particules expansées de polystyrène expansible possédant
un poids spécifique de 10 à 250 gr par litre, caractérisé en ce que l'on effectue
une polymérisation en suspension au cours de laquelle du styrène monomère est mélangé
à de l'eau et à une cire et soumis à des conditions de polymérisation et on incorpore
un agent porogène dans les perles produites par cette polymérisation en suspension,
une cire de Fischer-Tropsch possédant un point de congélation de 86 à 110°C étant
incororée auxdites perles au cours de ladite polymmérisa- tion en une quantité de
1,500 à 5,000 parties en poids de cire par million de parties en poids dudit styrène
monomère, de manière à obtenir des perles brutes, et on soumet ensuite lesdites perles
brutes à l'action de vapeur d'eau de manière à provoquer leur expansion jusqu'à un
poids spécifique de 10 à 250 g par litre.
1. Perlen aus expandierbarem Polystyrol, die 5 bis 9 Gewichtsprozent Treibmittel und
Wachs enthalten und einen Durchmesser von etwa 0,1 bis 5 mm haben, dadurch gekennzeichnet,
daß die Perlen 500 bis 10,000 Gew.-ppm, bezogen auf das Gewicht des Polystyrols, eines
Fischer-Tropsch-Wachses mit einem Schmelzpunkt von 86 bis 110°C enthalten.
2. Perlen gemäß Anspruch 1, dadurch gekennzeichnet, daß als Treibmittel n-Pentan verwendet
wird.
3. Perlen gemäß Anspruch 2, dadurch gekennzeichnet, daß der Pentangehalt über 8 und
bis zu 9 Gewichtsprozent beträgt.
4. In einem Verfahren zurh Herstellung von expandierbarem Polystyrol in Perlenform
durch Suspensionspolymerisation, in dem monomeres Styrol mit Wasser und einem Wachs
gemischt und Polymerisationsbedingungen ausgesetzt wird und ein Treibmittel in die
Perlen eingearbeitet wird, die Verbesserung, die darin besteht, daß man in die Perlen
ein Fischer-Tropsch-Wachs mit einem Schmelzpunkt von 86 bis 110°C in einer Menge von
500 bis 10,000 Gew.-ppm, bezogen auf anfänglich vorhandenes Styrol, einarbeitet.
5. Verfahren gemäß Anspruch 4, dadurch gekennzeichnet, daß man das Wachs in einer
Menge von etwa 1500 bis 5000 Gew.-ppm, bezogen auf anfänglich vorhandenes Styrol,
verwendet.
6. Verfahren gemäß Anspruch 4, dadurch gekennzeichnet, daß die Einarbeitung durch
Zufügen des Wachses mit und in dem Treibmittel erfolgt.
7. Verfahren gemäß Anspruch 6, dadurch gekennzeichnet, daß man als Treibmittel n-Pentan
in einer Menge von 5 bis 9 Gewichtsprozent verwendet.
8. Verfahren gemäß Anspruch 4, dadurch gekennzeichnet, daß die Einarbeitung durch
Zufügen des Wachses in Form einer Suspension in Styrol erfolgt.
9. Verfahren gemäß Anspruch 4, dadurch gekennzeichnet, daß die Einarbeitung durch
Zufügen des Wachses in Form einer wäßrigen Suspension erfolgt.
10. Verfahren zur Herstellung expandierter Teilchen aus expandierbarem Polystyrol
mit einer Dichte von 10 bis 250 g/I, dadurch gekennzeichnet, daß man eine Suspensionspolymerisation
durchführt, bei der monomeres Styrol mit Wasser und einem Wachs gemischt und Polymerisationsbedingungen
ausgesetzt wird und ein Treibmittel in die bei der Suspensionspolymerisation gebildeten
Perlen eingearbeitet wird, wobei während der Polymerisation ein Fischer-Tropsch-Wachs
mit einem Erstarrungspunkt von 86 bis 110°C in einer Menge von 1500 bis 5000 Gew.-ppm,
bezogen auf das Gewicht des monomeren Styrols, in die Perlen eingearbeitet wird, wobei
man Rohperlen erhält, und daß man dann die Rohperlen mit Dampf behandelt, so daß sie
zu Teilchen mit einer Dichte von 10 bis 250 g/I expandieren.