CA1233592A - Metal salt and silicone fire retardant for thermoplastic polymers - Google Patents

Abstract

METAL SALT AND SILICONE FIRE RETARDANT FOR
THERMOPLASTIC POLYMERS

Abstract of the Disclosure 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 from 6 to 20 carbon atoms;
(C) 1 to 20% a silicone fluid of the average formula,

Description

~3~

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 ~

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 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~

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~

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.

.. ._ ._ . , . . _, _ . . _ _ .. _ . . _ . _ .. .. ... .

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 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~

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 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 ~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 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~

~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 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

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A flame retardant composition comprising by weight:
(A) 60 to 98% of a synthetic organic polymer;
(B) 1 to 20% of Group IIA metal carboxylic acid salt containing from 6 to 20 carbon atoms and selected from the group consisting of magnesium stearate, calcium stearate, barium stearate, strontium stearate, isosterate, oleate, palmitate, myristate, lactate, undecylenic, 2-ethylhexanoate, pivaleate, and hexanoate; and (C) 1 to 20% of silicone fluid of the average formula, wherein each R is independently a substituted or unsub-stituted organic 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 25°C.

2. A composition as in claim 1 wherein said organic polymer is high density polyethylene.

3. A composition in accordance with claim 1, where the organic polymer is low density polyethylene.

4. A composition in accordance with claim 1, where the organic polymer is polypropylene.

5. A composition in accordance with claim 1, where the organic polymer is polystyrene.

6. A composition in accordance with claim 1, where the silicone fluid is a polydimethylsiloxane fluid.

7. A composition in accordance with claim 1, containing an effective amount o-E an organic peroxide.

8. A flame retardant composition in accordance with claim 1, where the organic polymer is a acrylonitrile-butadiene-styrene terpolymer.

9. An article of manufacture comprised of a substrate and a coating of the composition of claim 1.

10. A composition as in claim 1 where the organic polymer is polymethylmethacrylate.

11. A composition as in claim 1 where the organic polymer is selected from polycarbonate and poly-phenylene oxide.

12. A flame retardant composition comprising by weight:
(A) 60 to 90% of a synthetic organic polymer selected from one of polystyrene, polycarbonate, polyphenylene oxide, polymethylmethacrylate and acrylonitrile-butadiene-styrene terpolymer;
(B) 1 to 20 parts by weight of a Group IIA metal carboxylic acid salt containing from 6 to 20 carbon atoms;
(C) 1 to 20 parts by weight of a silicone fluid of the formula, wherein each R is independently a substituted or unsubstituted organic 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 25°C.