Note: Descriptions are shown in the official language in which they were submitted.
~3~
- 1 - 60SI-650
METAL SALT AND SILICONE FIRE RETARDANT FOR
THERMOPLASTIC POLYMERS
BACKGROUND OF THE INVENTION
The present invention relates to flame retardant
cornpositions which are blends of organic polymer, certain
effective low viscosity silicone polymers and a Group IIA
metal carboxylate salt containing 6 to 20 carbon atoms.
Prior to the present invention, as shown by
Betts et al. U.S. Patent No. ~,123,586, a mixture of
silicone gum and a dibasic lead salt, such as lead
phthalate, was effective as a flame retardant for
cross-linked polyolefins. However, -those skilled
in the art know that many lead compounds are known
to be toxic. It is therefore desirable to minimize
the use of lead in many applications, particularly
applications in the food industry where lead-containing
materials can create substantial food consumption
risks.
.
~i
3 3 S9 ~
60SI-650
It is to be noted that the present invention is al~o a specific
improvement over the inven~ion of ~acLaury and ~olub as disclosed
in ~.S. Patent ~o. ~,~73,691 which issued June 16, 1981.
In that patentO MacLaury et al. taught a range of
n~vel flame retardant compositions and articles which wese
generally comprised of a polyolefin, ce~tain metal salts ~
carboxylic acid as well as a broad range of silicone
compositions. Within the broad class of available silicone
compositions disclo~ed and claimed by MacLaury ~t al. they
preferred the use of silicone gums. Silicone gums are materials
of relatively high viscosity; indeed MacLaury et al. preferred
the gums to have a penetration value of 400 to 4,000 or more.
It was therefore quite surprising when the present applicants
discovered that improved flame retardance for thermoplastics
could be achieved with relatively low viscosity silanol or
trimethyl-silyl chain-stopped polydiorganosiloxane fluids, some
of which silicone fluid materials are somewhat less expensive
than the silicone gums preferred by MacLaury et al. Also the
silanol chain-stopped, low viscosity fluids tend to disperse with
greater ease thereby facilitating the preparation of flame
retardant compositions as compared to the use of high viscosity
gums.
It is well understood in the silicone art that altho~gh silicone
gums and fluids have similar chemical constit~ents, nonetheless
there are significant differences in physical properties among
.. , .. . . . _... _ _ _. . _ .. _ . _
1 2 3 3 ~ 9 ~ 60SI 6$0
these classe~ of silicones. Furthermore, prior to the present
invention, it would not have been obvious that such silicone
fluids as will be described herein would perform significantly
better, or even as well, in flame retardant application~ than
previo~ ly preferred silicone gums.
It is therefore an obje~t of the present invention to provide
thermoplastic compositions baving a relatively greater degree of
flame retardancy than heretofore available.
It is another object to provide a combination of low viscosity
silicone fluid and a Group IIA metal carboxylate salt which is
effective for rendering thermoplastics flame retardant.
It is another object to provide a process for rendering thermo-
plastics flame retardant.
These and other objects will become apparent to those skilled in
the art upon consideration of the present specification and
claims.
.. _ ... _ . . __ _ __... . . , _ _ _ .. _
~3359 60SI~65D
SUM~ARY OF T~E INVBNTION
There i~ provided a flame retardant composition comprising by
weight:
(A~ 60 to 98% of thermoplastic;
(B) 1 to 20~ of Group IIA metal carboxylic acid salt
containing fr~m 6 to 20 carbon atoms;
~C) 1 t~ 20% of a silicone fluid essentially of the average
formula
R I R R
X ~ -SiO - - 5iO Si - X
R R R
. n
wherein each R is independently a sl~bstituted or unsubstituted
organic radical and which preferably is a methyl radical, X is R
or a radical selected from hydroxyl or alkoxyl radicals and n is
an integer such that said silicone fluid has a viscosity of
approximately 2,000 to 600,000 centipoise at 25C.
.. . .. _ .. _ _ . . _ _ _ , . _ . . . _ . . ..
~335~
- 5 - 60SI 6~i0
DESCRIPTION OF THE IN~IENT:[ON
The present invention is based on the
diseovery that eertain earboxylic acid salts of
Group IIA elements, such as magnesium stearate,
can be used in eornbination with certain low
viscosity silieone fluids to impart improved
flame retardant pxoperties to a variety of
organic polymers including polyolefins, polyesters,
polyearbonates, polyamides, polystyrenes etc.
(hereinafter collectively referred to as "synthetie
organie polymer"). It has been found that the
flame retardant properties of a variety of
sueh organie polymers ean ~e substantially
improved as shDwn by oxygen index values and
horizontal burning tlmes (HBT) when the
aforementioned eombination of sueh Group IIA
carboxylic aeid salt and silicone ~luid is
ineorporated in sueh organie polymers.
It is eontemplated that the organic polymers
which can be used to ma]ce the flame retardant
compositions of the present invention are, for
example, low density polyethylene (LDPE)
having a density oE 0.91 g/em3 to 0.93 g/em3; high
density polyethylene (HDPE) having a density of
25 0.9~ g/em3 to 0.97 y/em3; polypropylene having a
densit~ oE about 0.91 g/cm3, polystyrene,
LEXAN ~ polycarbonate, and VAL,OX ~ polyester,
both manuEaetured by the ~eneral Eleetrie Company,
and other polymers sueh as polyamides, ionomers,
polyurethanes, eo- and ter-polymers of
aerylonitrile, butadiene and styrene; as well
as acrylic, polybutylene, ionomer, acetal resin,
ethylene-vinyl acetate, and polymethylpentene,
flexible polyvinylchloride (but not rigid PVC),
and polyphenylene oxide ete.
r 9 ~ 60SI-650
-6-
The term ~low viscosity silicone fluids" includes essentially
linear polydiorganosiloxanes consisting essentially of chemically
combined units of the formula,
-- SiO -- ,
where R i~ a monovalent organic radical. These organic radicals
will ordinarily be selected from the class consisting of C(l 8)
alkyl radicals, C(6 13~ aryl radicals, halogenated derivatives
- of such radicals, cyanoalkyl radicals, etc. In any case, the
aforementioned polydiorganosiloxanes are preferably
p~lydimethylsiloxanes which can contain from about 0.05 to 15
mole percent of methylvinylsiloxy units based upon the total
moles of chemically combined diorganos-loxy units. The
aforementioned polydiorganosiloxanes are preferably in the form
of silanol or ~rimethylsilyl chainstopped siloxane fluids having
an approximate viscosity of 2,000 to 600,000 centipoise at
25 & . Of the above mentioned materials, the aryl-containing
siloxanes are less preferred.
Included within the Group IIA metal carboxylic acid salts which
can be utilized in the practice of the present invention are, for
example, magnesium stearate, calcium stearate, barium stearate,
strontium stearate. Salts of other carboxylic acids include
isostearate, oleate~ palmitate, myristate, lactate, undecylenic,
2-ethylhexanoate, pivaleate, hexanoate, etc.
~'23~
60S~
In addition to the aforementioned ingredients, the ~lame retar-
dant composition~ of the present invention can contain additional
ingredients, s~lch a~ filler~, antioxidants, and additional
additives. In particular instances, ingredients such as
decabromodiphenylether, antimony oxide, processing aids and clay
~lso can be utilized. I~ desired, heat activated peroxide~ can
be employed when utilizing polyolefins as the organic polymer.
S~itable rea~tive peroxides are disclosed in U.S. Patent Nos.
2,888,424, ~,079,370, 3,086,966 and 3,214,422. Suitable peroxide
crosslinking agent~ include organic tertiary peroxides which
decompose at a temperature above about 295 F. and thereby
provide free-radicals. The organic peroxides can be used in
amounts of from about 2 to 8 parts by weight of peroxide per 100
parts of organic polymer~ A preierred peroxide is dicumyl
lS peroxide, while other peroxides such as VulCupR of Hercules,
Inc., a mixture of para and meta DL, d~ ,-bis(t-butylperoxy)-
diisopropylbenzene, etc., can be used. Curing coagents s~ch as
triallyl cyanurate can be employed in amounts of up to zbout 5
parts by weight of coagent, per 100 parts of the polymer if
desired. The polyolefins can be irradiated by high energy
electrons, x-ray and like sources.
In the practice of the invention, the flame retardant composi-
tions can be macl~ by mixing together the organic polymer with the
silicone fluid and the Group IIA carboxylic acid salt, herein-
after referred to as the "Group IIA salt" by means of any con-
ventional compounding or blending apparatus, such as a Banbury
mixer or on a two-roll rubber mill. Order of addition of the
particular constituents does not appear to be critical, however,
tho~e skilled in the art wlll be able to optimize the flame
retardant compositions contemplated herein without undue
experimentation.
. . .
123359~ 60SI-650
Preferably, all the ingredients are formulated together except
tho~e ~hich are ~ensitive to the temperature~ $n the range of
from about 3~0 F. to about 400F.~ such as heat decomposable
peroxides. The ingredients are therefore at a temperature
sufficient to soften and plasticize the particul~r organic
polymer if feasible. An effective procedure, for example, would
be to uniformly blend the aforementioned ingredients at a
suitable temperature with the absence of the organic peroxide,
then introduce the organic peroxide at a lower ~emperature to
uniformly incorporate it into the mixture.
The proportions of the various ingredients can vary widely
depending upon the particular application intended. For example,
for effective flame retardance there can be employed per 100
parts of organic polymer from about 0~5 to 20 parts of the
silicone fluid and 0.5 to 20 parts of the Group IIA salt.
However, greater or smaller amounts can suffice in particular
applications. As previously indicated, other additives may be
included. Antimony oxide can be utilized in a proportion from 1
to 10 parts, and organic haloyen compounds from 5 to 30 parts,
per 100 parts of the organic polymer. Reinforcing and
non-reinforcing fillers also can be employed.
The flame retardant composition of the present invention can be
extruded onto a conductor and in particular instances, cross-
linked depending on whether organic peroxide curiny agent is
present. Of course, there are numerous other applications where
the flame retardant compositions of the present invention may be
-
33S~
60SI-650
used to great advantage. Such materialz may be succes~f~lly
~old~d~ extruded or compressed etc. to form numerous useful
product~ such as moldinys, sheets, webbing, fibers and a
mul~itude o~ other flame retardant plastic or polyolefin
products. Thu , the flame retardant compositions of the present
invention al~o can be utilized in such applications as applicance
housings, ~hairdriers, TV cabinets, smoke detecto~6, etc., auto-
motive interiors, fans, motors, electrical componentsl cof~ee
makers, pump housings, power tools, etc. Such flame retardant
compositions might also be utilized in fabrics, textiles and
carpet as well as many other applications.
In order that those skilled in the art will be better able to
practice the invention~ the followiny examples are given by way
of illustration and not by way of limitation. All parts are by
weight.
ExamPle 1
A mixture oE 8g of a hydroxy terminated linear polydimethyl-
siloxane oil haviny a viscosity of approximately 100,000 cps at
25 C and 12g of magnesium stearate ~g Ster.) was compounded
with 180g of molten polypropylene ~Hercules Pro-Fax 6523) and
~ compression molded. I~Je resulting plastic had a higher limiting
; i oxygen index ~LOI=27) than the Pro-Fax 6523 alone (LOI=18). In
addition, 1/8 in. x 1/2 in. x 6 in. test strips of the compounded
plastic self-extinguished in ~ horizontal burning test. Other
silicone polymers of varying chain length and viscosity such as
:~3~
60SI-650
-10-
VISCASIL 100M also rai~ed the LOI o~ polypropylene and in s~me
ca~es caused the plastic to sel~ extingui~h in the horizontal
burning test.
~ able I compare the oxygen index values for various~ formula-
tions. In each case, the polypropylene was Hercules Pro-Fax
6523. Compoun~ing was performed on a Brabender mlxer at 400 F
and compression molded slabs were cut ~1/8 in. x 6 in. x 6 in.).
SE-33 is a high viscosity silicone gum available from General
Electric a~d used for comparison in the manner of ~acLaury et al.
TABLE I
Additives
(As Wt % of Pol~pro~Ylene) Oxyqen Index 2" Horizontal Burn
None approx. 18 Consumed in 150 sec.
6~ Magnesium Stearate approx. 18 Consumed in 258 sec.
15 44 Silicone Gum ~SE-33) 17.7 Consumed in 172 sec.
q~ S~-33 + 6% Mg Ster. 26 Self Extinguished 29 sec.
4% Silox~ne 1 ~ 6% Mg Ster. 26 Self Extinguished 56 sec.
8% Siloxane 1 + 12% ~g Ster. 27 Self Extinguished 32 sec.
4% Siloxane 2 + 6~ Mg Ster. 27.3 Self Extinguished 90 sec.
20 4~ Siloxane 3 ~ 6% Mg Ster. 26.5 Variable
44 Siloxane 4 + 6% ~y Ster. 25.2 Consumed in 90 sec.
J'~, ~ ~
4% VISCASIL 100~ + 6% Mg Ster. 24.1 Sel~ Extinguished 61 sec.
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3~
6aSI-650
--11 ~
NCIESo
The siloxane fluids ~1-4) listed in Table I are essentially linear
hydroxy chain-stopped polydimethylsiloxanes having varying
viscosities at 25C, as follows:
Siloxane 1 - approximately 100,000 cps.
Siloxane 2 - approximately 12,100 cps.
Siloxane 3 - approximately 2,800 cps.
Siloxane 4 - approxirnately ~50 cps.
The oxygen index test method employed herein is in accordance with
AST~ 2863-77. The horizontal burn test is essentially similar to
ASTM D635-81. ~igher oxygen index values indicated greater degrees
of flame retardancy.
Example 2
The following formulations were prepared by first milling together
15 the silicone and magnesium stearate to form a paste. This paste
was then cornpounded into molten polypropylene ~ercules Pro-Fax
. .. , , .. , . ... _ _ . _, _ . ., _ _ ............. . ...
.
' " ~ " ' ' ' ~ : '
' ~ ' ,' . '
.
1233S9~ 605I-650
-12-
6523) using ~ two-roll mill at 375 F. The relatively low
viscosity of the silicone fluids ga~e a paste that readily mixed
into the m~lten polyproylene. The compounded material was
compression molded at 375 F in a ~picture frame~ mold to form
1/8~ x 6~ x 6u ~labs. Strips ~1/8" x 1/2~ x 6a) cut from these
slabs were utilized in a hori~ontal burning test and for the
measurement of the limiting oxygen index.
FORMULATION
_
A Profax 6523
10 B 180g Pro-Fax 6523 and 89 silicone guml and 129
magnesium stearate
C 180g Pro-Fax 6523 and 89 silicone fluid and 12g
magnesiuM stearate
D 1809 Pro-Fax 6523 and 89 VISCASIL 100M and l2g
magnesium stearate
E 1809 Pro-Fax 6523 and 8y Gen~ral Electric SF-1147
and 12g magnesium stearate
. _ . ... _ _ ... . . _ .. . _ . _ . . , _ .. _ . . . _ .
33~
605I-650
-13-
NOTES
1 - a polydimethylsiloxane gum having 0.2 mole percent of
chemically combined methyl~vinylsiloxy units and a penetration
of between 1600 and 2500.
2 - a silanol stopped polydimethylsiloxane polymer haviny a
nominal viscosity of 90,000 - 150,000 centipoise ~90-150
Pa~cal second).
3 - 100,000 centistoke polydimethylsiloxane fluid, trimethylsilyl
stopped ~i.e. M-stopped) (available from General Electric).
4 - a methyl alkyl polysiloxane fluid of 50 centistokes ~General
~lect~ic~.
.
,
'
' '' "'
~Z33S9~ 60SI-650
-14-
F~RMULATION OXYGEN I NDEX 2 ~_ HORXZONTA~ BURN
A 18.~ Consumed in 150 sec, flaming drips
B 24.7 self e~tingulshed in 1~-41 sec, no
drips
C 26.5 self extinguished in 42-69 sec, no
dr ip
24.1 self extinguished in 59-63 sec, no
drips
E - consumed in 116-120 sec, flaming
d~ips
The limiting oxygen index test was conducted according to ASTM
2863-77. The hori20ntal burn was conducted by igniting a 1/8" x
1/2" x 6r strip of the material clamped at one end in a horizontal
position. If the material extinguished itself during the first
half inch, the time was recorded. If burning continued past the
first half inch, the burning rate was timed for the next two (2)
inches.
- These results demonstrate that the flame retarding property of the
i~ high molecular weight silicone gums preferred by MacLaury et al.
is also exhibited by relatively low viscosity silanol stopped
silicone polymers and M-stopped silicone fluids which are more
easily compounded into the plastic than high molecular weight gums.
. _ _ . . ... .. . ,. _ _
~33~9~ 60SI-650
--15--
~e~
~he following for~ulations were compounded and molded as ~n
Example 2.
PORMULATIONS
Pro-Fax 6523 etal Soa~ Silicone
A180g 129 Mg Stearate 89 90-150 Pascal sec. polyJner
B1809 18g Mg Stearate 8g 90-150 Pascal sec. polymer
C1809 12g Al Tristearate 8g 90-150 Pascal sec. polymer
D180g 12g Al Tristearate 8g 90-15- Pascal sec. pol~ner
E180g 12g Mg Stearate 8g 15-30 Pascal sec. polymer2
F180g 12g Mg Stearate 89 2.5~3.5 Pascal sec.
polymer3
G180g 12g Sn~II)Palmitate 8g 90-150 Pascal sec.
polymerl
H150g 10~9 ~g Stearate 6.8g gum4 ~ 8.6y
Sb2O~ ~ 24.29
Decabromodiphenyl oxide6
I2009 Pro-Fax PD-451 ~V-2 grade of flame retardant
polypropylene)
1233$9~ 60SI-650
-16
NOTES.
1 - silanol stopped polydimethyl~iloxane polymer, 90-150 Pascal sec
2 - silanol stopped p~lydimethyl~iloxane polymer, 15-30 P~scal ~ec
3 - silanol stopped polydimethylsiloxane polymer, 2.5-3.5 Pascal sec
4 - polydimethyl~iloxane gum having 0~2 mole percent of chemically
cc~bined methylvi~ylsiloxy units an~ a penetration between 1600
and 2500.
5 - Baker reagent
6 - available ~rom Great Lakes Chem. Corp., DE-83R
FORMULATION OXYGEN INDEX 2" HORI20NTAL BURN
A 27.0 extinguished in 11-85 sec with flaming
drips
B 24.4 extinguished in 18-44 sec, no drips
C 19.9 burned 2" in 84-93 sec, flaminy drips
D 19.9 burned 2n in 77-81 sec, flaming drips
E 24.4 extinguished in 10-22 sec, no drips
F 23.9 extinguished in 28-41 sec, no drips
G - burned 2" in 106-117 sec, flaming drips
27.5 extinguished in 6-13 sec, no drips
I 28.2 extinguished in 6-28 sec, occasional
flaming drips
. . ~
~3~
60SI-650
-17-
~hese flammability test results deJnonstrate that lower vi6coslty
~ilicones used in formulations E and P work as well as the highes
viscosity polymer used in A and the gum used in Example 1. The poor
performance of A in this par~icular experiment was an exception and
may have been due to heterogeneity from insufficient compounding.
Example 4
Several formula~ions were compounded and compression molded to
discover a possible syneryism between the silicone fluid/magnesium
stearate combination and the conventional organo halide/antimony
10 trioxide flame reta~dants.
Formulations
A) 180g Pro-Fax 6523 and 89 silicone fluid and 12g Mg stearate
B) 160g Pro-Fax 6523 and 16g silicone fluidl and 249 Mg stearate
C) 180g Pro-Fax 6523 and 4g Sb2O3 and 16g Decabromodiphenyl
Oxide
D) 160g Pro-Fax 6523 and 8g Sb2O3 and 329 Decabromodiphenyl
Oxide 2
E) 160g Pro-Fax 6523 and 8g silicone fl~idl and 129 ~9 stearate
and 49 Sb2o3 and 16g Decabromodiphenyl Oxide
F) 200g Pro-Fax 5523
The compression molded samples were subjected to the limiting oxygen
index test tASTM D2863-77), the Underwriters Laboratories UL-94
vertical burn test, and a horizontal burn test.
, , , , , _ _ . _ . _ . _ . . .. .. . .. . .
~;~3359~ 60sI-650
~18-
N~S:
1 - a silanol stopped polydimethylsiloxane having a nominal viscosity
Qf 90,000 - 150,000 centipoise t90-150 Pascal ~econds)
2 - available from Gre~t Lakes Chemical Co.
Formulation LOI ~orizontal Burn UL-94 Verti 1 Burn
A 25.2 extinguished in 7-10 sec, extinguished in 34-143
no drip sec, flaming drips
B ~4.2 extinguished in 8-11 sec, extinguished in 60-187
n~ drip sec, flaming drlps
lC C 21.0 consumed with flaming extinguished in 120
drips sec, ilaming drips
D 22.8 extinguished in 57-78 sec, extinguished in 6-231
flaming drips sec, flaming drips
E 20.5 extinguished in 3-18 secl extinguished in 34-71
flaming drips sec, flaming drips
F 18.0 consumed flaming drips consumed
These results show that only 10~ by weight of the silicone fluid and
stearate significantly raises the oxygen index of polypropylene ana
causes sel~-extinguishment in the hori~ontal burn test. However,
doublin~ the additives to 20~ of the polypropylene appears to cause no
further improvement. The organobromide/antimony additives are
ineffectual at these low concentrations. Combining 10~ levels of each
set of flame retardants (formulation E) is no improvement over A.
.
.. . . _ . ; .. . _ _ _ . .. . .
;3S9~ 60SI-6511
--19--
In the following table, Pro-Fax 6523, polypropylene was combined with
6 weight percent magnesium stearate and 4 wei~ht percent of the
specified ~ilicone. The various grades of silicones are currently
available from General Electric Company. Sample B in the table is
typical of the silicone ~lame retardants of the present invention and
was the only sample which self-extinguished in the hozizontal burn
test.
Sample Formulation Oxyqen Index Horizontal Burn
A Polypropylene control 18 Consumed
B Viscasil 100M Silicone Fluid 24 SE, 60 sec.
C SF~1147 Methyl Alkyl Fluid - Consumed
D DF-1040 Hydride Fluid - Consumed
E SF-1188 Surfactant - Consumed
F CF-1271 Phenyl Silicone Fluid - Consumed
G FF150-10M Fluorosilicone Fluid - Consumed
