Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
HOE 74~E_100
~0~i99
The quality of a foamed polystyrene substantially depends
on the cellular structure and the density of the foamed shaped
article. A homogeneous cellular structure in the whole foamed
bloc or shaped article is desired. In the case of foamed
plastics obtained from polystyrene beads containing a blowing
agent the total cellular structure depends on the indi~idual
cellular structure of the prefoamed polystyrene beads and on
their optimum welding in the final foaming process. The
thermal treatment of the unfoamed polystyrene beads containing
a blowing agent is substantial for the quality of their cellu-
lar structure, the blowing agent and the content of blowing
agent being the same.
At the convention date of this application no expandable
polystyrene containing a blowing agent and any known nucle-
ating agent was known, which may be foamed after haYingbeen exposed to a temp=rature of from 40 to 50 C for one or
several hours prior to the prefoaming or foaming process to
give products having a density of about 14 g/l and a homoge-
neous fine cellular structure . The observations made hith-
erto confirm that the cellular structure more and more coar-
sens during s*orage at varying elevated temperature depending
on the time and the temperature, i.e. there are formed less,
but larger cellules at the expense of the small ones. The
- influence of heat especially acts on styrene polymers con-
taining a blowing agent and halides for preparing self-ex-
tinguishing foamed plastics. Some improvement may be obtained
by substituting n-pentane by isopentane as blowing ~gent, but
the fine cellular structure is also destroyed by storage at
29 a temperature of 50C for one hour.
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It was known that 1-chloro-1,2,2,3$3,4,4-heptafluoro-
cyclobutane ~nd 1,2-dichloro-1,2,393,4,4-hexafluorocyclobutane
may be used as blowing agent for polystyrene in an amount of
>10% by weight, for example from German Auslegeschrift No.
1,241,976.
It has now been found that beads of a styrene polymer
containing a blowing agent, which comprise from 0.01 to 0.5
by weight, preferably of from Oo1 to 0.3~ by wei~ht of octa-
- fluorocyclobutane, show a high heat resistance at temperatures
of up to about 50 C and yield foams of a homogeneous fine
cellular structure when foaming them after exposure to heat.
A process has moreove~ been found for preparing beads of
a styrene polymer containing a blowing agent and ha~ing a
high heat resistance at temperatures of up to a~out 5V C by
- 15 homo- or copolymerization of monomeric styrene in aqueous
-- suspension in the presence of at leastone blowing agant or
by incorporating the blowing agent or a mixture of t~Jo or
se~eral blowing agents into the styrene polymer, which com-
prises adding to the blowing agent(s) from 0.01 to 0.5% by
. 20 weight, preferably from 0.1 to 0.3% by weight of octafluoro~
cyclobutane.
Among the styrene polymers suitable for ma~ing the beads
according to the invention there may be mentioned homopoly-
styrene or copolymers of styrene with ~methylstyrene, a
styrene alkylated in the nucleus, acrylonitrile or methacry- ~-
lonitrile
The polymerization of mIl~eriC styrene in aqueous suspe~-
sion initiated by free radicals ~xm ~ro~desis carried out ~cor-
29 ding to the Btate of the art, by using as suspending auxili-
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HOE ~4/F 100
~1)4~i99
aries for exampls polyvinylalcohol, tricalcium phosphate
or polyvinylpyrrolidone. Examples of peroxides used are-di-
benzoylperoxide, tertiary butylperoctanoate, tertiary butyl-
perben~oate. The polymerization reaction is carried out in
the presence of the blowing agent at temperatures of from
90 to 130C.
Octafluorocyclobutane is suitably added togetherwith the
blowing agent, ad~antageously by dissolving the former in
the latter.
The polymerization is followed by the usual working up
such as cooling, centrifuging, drying and sieving.
Octafluorocyclobutane may also be added advantageously
in the impregnation process of sieved beads of polystyrene
in admixture with the blowing agent.
The preferred impregnation process is carried out at
temperatures of from 100 to 120 C with beads of polystyrene
suspended in water by means of dispersing agents such as
polyvinyl alcohol etc.. ~he impregnation of polystyrene with
the blowing agent/octafluorocyclobutane mixture may also be
effected in a suitable extruder according to known process~
es.
The blowing agents to be used are the usual lower ali-
phatic and cycloaliphatic hydrocarbons having from 4 to 6
carbon atoms, preferably the isomeric pentanes, especially
isopentane, in an amount of from about 5 to about 7.5% by
weight.
The invention is of great technical importance, especi-
ally for manufacturing plants in southern countries, especi-
29 ally for equatorial regions, but also for Europe. In these
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1046699
regions a heating of the expandable polystyrene to tempera~
tures of up to 50 C, for example in the storage or during
transportation may quite naturally occur in periods of hot
weather.
The following examples illustrate the inve~tion.
E X A M P L E S-
.
The examples manifest the technical progress obtained by
the invention at an extreme product temperature of 50 C.
The polymerization of styrene suspended in water in a
weight ratio of 1:1 was carried out for 8 hours at 90 C with
0.3~ by weight of dibenzoylperoxide and 0.15% by weight of
tertiary butylperbenzoate, both calculated on the monorneric
styrene. The dispersion was either effected with 0.3% by
weight of polyvinylpyrrolidone (PVP) or with 0.4% by weight
f tricalcium phosphate (TCP), both calculated on the monomerio
styrene. Aft~r the addition of 7.5~ by weight of blowing agent,
calculated on styrene, in admixture with the quantity of oc~a~
fluorocyclobutane, calculated on styrene)which is indicated
in the table, the reaction mixture was polymerized for 3
hours at 120 C, oooled to room temperature and separated
from the liquor by centrifuging while washing. The dried pro
ducts hav~ng aparticle diameter of from 800 to 1,600/u were
all prefoamed in the same manner with steam at a pressure
of 0.2 atmosphere gauge, stored at room temperature for 12
hours and welded at a pressure of about 0.3 atmosphere gauge
with steam in a mold of 5 cm X 10 cm X 10 cm (final foaming).
The foamed blocs stored for 1 day were cut into strips
having a ~ickness of 1 mm with a rotating knife and compared
29 qualitatively with a series oI` 10 structural standards. ~he
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HOE 74/~ 100
10~99
values found are indicated in the following table in the co-
lumns he~ded "foam structure". Figures 1 to 6 show a sel.ection
of the structural standards in a 25-fold magnification:
figure l... standard 2
figure 2... standard 3
figure 3... st~ndard 5
~igure 4... stand~rd 6
figure 5... standard 7
figure 6... standard lO
The blowing agents used were n-C5=n-pentane having a maxi-
mum content of iso-pentane of about 25~7 and i-C5=iso-pen-
tane having a maximum content of n-pentane of 15~.
~n the examples 4, 5 and 8 to 15 an addi.tional flame-proo-
fing was performed by means of 0.8% by weight o~ pentabromo-
phenylallyl ether as flame retarding agent being added to the
polymerization mixture.
The reduced specific viscosity (RSV) of the polystyrene
was determined on solutions of 1 g of polystyrene in 100 ml
o~ toluene at 25C.
The results are given in the following table.
Example 3, 4 and 5 are comparative examples according to
the state of the art.
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HOE 74/F` (35~9
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