Note: Descriptions are shown in the official language in which they were submitted.
~ COS-4~4/447
EXPANDABLE POLYMERIC STYRENE PARTICLES
Technical Field
This invention relates to expandable or foamable
polymeric styrene particles. More particularly, this
invention relates to such expandable particles having
increased utility in the manufacture of foamed articles by
reducing the final mold cooling cycle and in exhibiting
reduced flammability characteristics.
Background or the Invention
Expandable polymeric styrene particles and the
articles produced from such particles are well known in the
art. Such articles include insulated building panels,
decorative display objects, novelties, cushioning
materials, floatation devices, hot or cold beverage
containers, portable ice or cooling chests or boxes, etc.
The principal utilitarian characteristics of such foamed
articles are their light weight and good heat insulation
qualities.
Expandable polymeric particles are generally prepared
by impregnating the particles with from 1% to ~0~ by weight
of a suitable expanding or blowing agent such as pentane.
In producing the foamed articles, the impregnated
particles, or beads, are first subjected to a pre-expansion
step wherein the beads are heated with steam in an
unconEined space to produce a prepuff having a relatively
low density. Prepuffed beads are then placed into the
desired confined mold and final expansion accomplished with
the Eurther introduction of steam, follwed by cooling and
removal of the molded article.
In evaluating the utility of a particular expandable
polymeric styrene particle in producing the desired foamed
article, consideration must be given to the final mold
cooling cycle as it affects the rate, and consequently the
cost, of the production of the finished product.
In addition a prerequisite for the use of foamed
articles in certain applications is that such foamed
articles must exhibit reduced flammability. This would be
particularly true of foamed articles or panels employed in
building construction. While the prior art discloses a
number of additives that can be employed to reduce the
flammability characteristics of foamed articles, there
remains much room for further improvement.
Summary of the Invention
It is now been found that an expandable polymeric
styrene particle having incorprated therein a blowing agent
and a minor amount of ethylene-bis-stearamide and a minor
amount of dibromoethyldibromocyclohexane significantly
reduces the final mold cooling cycle in producing the
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finished molded article. It has been found that in
reducing the final mold cooling cycle in producing the
finished molded article, the combination of the two stated
additives exhibit a synergistic efEect; the reduction in
the Einal mold cooling cycle using the combination of the
two additives being greater than the theoretical expected
additive effects of the two.
It has also been Eound that finished foamed articles
having reduced Elammability characteristics are obtained
from expandable polymeric styrene particles having
incorporated therein a blowing agent, a minor amount of bis
(allyl ether) of tetrabromobisphenol A and a minor amount
of pentabromomonochlorocyclohexane. It has been Eound that
in reducing the flammability characteristics of the
finished foamed articles, the combination of the tWG stated
additives exhibit a synergistic effect; the reduction in
flammability characteristics using the combination of the
two additves being greater than the theoretical expected
additive effects of the two.
Description of a Preferred Embodiment
EX~MPLE 1
To a kettle equipped with an agitator was charged 100
parts by weight of water, 2 parts by weight of tricalcium
phosphate, .05 parts by weight of sodium dodecylbenzene
sulfonate, 10Q parts by weight of polystyrene beads having
a diameter of about 1 mm. and 8.0 parts by weight oE
n-pentane. In the examples which follow, ethylene-bis-
stearamide and dibromoethyldibromocyclohexane were also
charged at this point in the amounts indicated.
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The kettle was heated to a temperature of 215-230F
(102-110C) and maintained within this temperature range
for 7-10 hours with agitation. The kettle was then cooled
to room temperature, the contents acidiEied with nitric
acidl the beads separated from the aqueous medium, washed
with water and air dried at room temperature.
For pre-expansion, the beads were placed in a kettle
equipped with agitators and means for passing steam through
the beads. Prepuffs were formed by passlng steam at 5 psig
(34 kPa) through the beads for approximately ~ minutes.
The prepuff particles had a diameter of approximately 3/16
inch (5 mm.).
To test the qualities and characteristics of the
finished molded foamed article, a test mold 6"x12"x6" (15
cmO x 30 cm. x 15 cm.) was employed. The mold was jacke-ted
to permit steam injection into the contents of the mold.
The mold was partially filled with prepuffs, closed and
steam passed through the hold at 220F (104C) for
approximately 10-20 seconds. The molded article was then
allowed to cool until capable of removal from the mold.
Samples of the molded foamed articles were prepared
using the above procedure, with and without -the
incorporation of the ethylene-bis-stearamide and dibromo-
cyclohexane. The following examples illustrate the
comparative results.
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Example No. Additive Mold Cooling Cycle
1 None 33 minutes
2 0.3% ethylene-bis- 22 minutes
stearamide
3 1.0% dibromoethyl- 28 minutes
dibromocyclohexane
4 0.3% ethylene-bis-
stearamide
and 14 1/2 minutes
1.0% dibromoethyl-
dibromocyclohexane
The cooling cycle for the Einished molded foam article
was measured by the time required from steam shut off in
the final molding, using steam at 15 psig (103 kPa), to the
permissible removal of the article from the mold. The
dibromoethyldibromocyclohexane employed was a white
crystalline powder having a molecular weight of 428,
bromine content of 74% by weight, and a melting point of
65-80C.
Comparing the results of Examples 2 and 3 with the
results of Example 4, clearly illustrates the synergistic
effect of the additives of this invention.
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The improved characteristics of expandable polymeric
styrene particles discussed herein are realized by
incorporating only minor amounts of ethylene-bis-stearamide
into the polymeric styrene particles. Expandable polymeric
styrene particles containing from about 0.l~ to about 1.0%
of ethylene-bis-stearamide and from about 1.0~ to about
1.5~ of dibromoethyldibromocyclohexane, both by weight of
polymeric styrene, are particularly useful. In accordance
with the preferred embodiment of this invention, the
additives of this invention are preferably incorporated
into the polymeric styrene particle during the
incorporation of the blowing agent. ~owever, advantageous
results are also accomplished by external blending of the
additives with expandable polymeric styrene particles after
first incorporating the blowing agent. This can be carried
out by tumbling dried expandable polymeric styrene
particles with the desired quantity of the additives.
EXAMPLE 2
To a kettle equipped with an agitator was charged 100
parts by weight of water, 2 parts by weight of tricalcium
phosphate, .05 parts by weight of sodium dodecylbenzene
sulfonate, 100 parts by weight of polystyrene beads having
a bead diameter of about 1 mm. and 8.0 parts by weight of
n-pentane. In the examples which follow, the flammability
reducing additives of thi~ invention were also charged at
this point in the amounts indicated.
The kettle was heated to a temperature of 215-230F
(102-110C) and maintained within this temperature range
:~. L~t~
for 7-10 hours with agitation. The kettle was then cooled
to room temperature, the contents acidiEied with nitric
acid, the beads separated from the aqueous medium, washed
with water and air dried at room temperature.
For pre-expansion, the beads were placed in a kettle
equipped with agitators and means for passing steam through
the beads. Prepuffs were formed by passing steam at 5 psig
(34 kPa) through the beads Eor approximately 2 minutes~
The pre-puff particles had a diameter of approximatley 3/16
inch (5 mm.).
To test the qualities and characteristics of the
finished molded foamed article, a test mold 6"x12"~6" (15
cm. x 30 cm. x 15 cm.) was employed. The mold was jacketed
to permit steam injection into the contents of the mold.
The mold was partially filled with prepuffs, closed and
steam passed through the mold at 220F (104C) for
approximately 10-20 seconds. The molded article was then
allowed to cool until capable of removal from the mold.
Samples of molded foamed articles were prepared using
the above procedure, with and without the incorporation of
the flammability reduciny additives of this invention. The
following illustrates the comparative results obtained.
To measure the flammability characteristics of
finished molded foam articles, using a hot wire a test
strip was cut from the molded block prepared as described
above. The test strip measured 9"x4"x1/2" (23 cm. x 10 cm.
x 1.3 cm.). The test strip was suspended vertically, with
its longest dimension in the vertical position. A gas
flame approximately 1/2l' (1.3 cm.) long was directed
against the test strip approximately 1" (2.5 cm.) above its
base. The gas flame was directed against the test strip
until the material ignited, and the gas flame then removed. The
vertical (height) and horizontal (width) of the burn area were
measured and the combination of these two measurements used to
establish a burn rating in accordance with Table 1; rating 1 being
excellent and rating 4 failing.
Table 1
Rating ~ertical Burn Horizontal Burn
1 0 to 10 ~m. 3 to 4 om.
2 greater than 10 to 16 cm. greater than 4 to 6 c~.
3 greater than 16 to 20 cm. greater than 6 to 8 cm.
4 greater than 20 cm. greater than 8 cm.
The bis (allyl ether) of tetrabromobisphenol A employed
was an offwhite crystalline solid having a molecular weight
oE 623.9, bromine content of 51.2% by weight and a melting
point of 110-120C.
Table 2 sets forth the flammability characteristics
of molded foamed polystyrene articles containing the
flammability reducing additives of this invention compared
with molded foamed polystyrene articles containing no
additives. In each case the content of the additive is
expressed as percent by weight of polystyrene.
Table 2
Exampl_ Additive Test surn Rating
1 None 4
2 0.3% bis (allyl ether) of
tetrabromobisphenol A 4
3 0.6% pentabromomonochloro-
cyclohexane 3-4
4 0.3~ bis (allyl ether) of
tetrabromobisphenol A
and 1.4-1.6
0.6% pentabromomonochloro-
cyclohexane
Comparing the results of Examples 2 and 3 ~ith the
results of Example 4, clearly illustrates the synergistic
effect of the flammability reducing additives of this
invention.
The improved flammability characteristics of
expandable polymeric styrene particles discussed herein are
reali~ed by incorporating only minor amounts of bis (allyl
ether) of tetrabromobisphenol A and pentabromomonchloro-
cyclohexane into the polymeric styrene particles.
Expandable polymeric styrene particles containing -from
1 0
about 0.1~ to about 0.5~ of bis (allyl ether) of
tetrabromobisphenol A and from about 0.6% to about 1 5~ of
pentabromomonochlorocyclohexane, both by weight of
polymeric styrene are particularly useful. In accordance
with the preEerred embodiment of this inven-tion, the
additives are preferably incorporated into the polymeric
styrene particles during the incorporation of the blowing
agent. However, advantageous results are also accomplished
by external blending of the additives with expandable
polymeric styrene particles after first incorporating the
blowing agent. This can be carried out by tumbling dried
expandable polymeric styrene particles with the desired
~uanti-ty of the additives.
The invention has been described herein with
particular regard to expandable polystyrene particles
having incorporated therein a minor amount of the additives
of this invention. In its applicability, the invention is
not limited to polystyrene as other vinyl aromatic polymers
can be employed. These include polymers derived from such
vinyl aromatic monomers as vinyl toluene, isopropylstyrene,
alpha-methylstyrene, chlorostyrene, tertiarybutylstyrene as
well as to copolymers of vinyl aromatic monomers and
butadiene, alkyl acrylates, acrylonitrile~ etc. As used in
the specification and claims herein the expression
"polymeric styrene particles" is meant to include particles
of all such polymers and copolymers.
The invention has been described herein using pentane
as the blowing agent. The inveniton is not limited to the
use of pentane as other blowing agents can be employed.
Suitable blowing agents include butane, isopentane, cyclo-
~ 3
pentane, hexane, heptane, cyclohexane and the lower boilinghalogenated hydrocarbons. Mixtures of the various
mentioned blowing agents can also be employed. Expandable
polymeric styrene particles usually contain from 1 to 20
by weight of the blowing agent. Impregnation with the
blowing agent to produce expandable polymeric styrene
particles can be carried out over a wide temperature range,
namely, at temperatures ranging from about 140C (60C) to
about 302F (150 C).
