Flame retardant thermoplastic compositions

Flame retardant thermoplastic compositions are described which comprise 30-98% by weight thermoplastic, 1-40% by weight of a silicone fluid, 1-20% by weight of metal soap precursors and 1-20% by weight of a silicone resin. Such compositions offer simpler processing, improved impact resistance and other advantages over conventional flame retardant thermoplastic compositions.

FIELD OF THE INVENTION 
The present invention relates to flame retardant compositions and 
particularly flame retardant thermoplastics such as polyolefins. 
Specifically, the invention relates to blends of organic polymer, certain 
silicone polymers and silicone resins and precursors of metal soaps which 
form thermoplastic compositions exhibiting good flame retardancy. 
BACKGROUND OF THE INVENTION 
Many attempts have been made previously to provide flame retardant 
thermoplastics, however typically plastic materials have been heavily 
filled with additives until the desired degree of flame retardancy has 
been achieved, the loadings being large enough in many instances to 
detract from the physical properties of the plastic base material. Several 
patents, such as U.S. Pat. No. 4,265,801 (Moody et al.), U.S. Pat. No. 
4,235,978 (Luce et al.), U.S. Pat. No. 4,209,566 (Betts et al.) and U.S. 
Pat. No. 4,247,446 (Betts et al.), also describe compositions which make 
use of halogenated organic materials and/or heavy metal compounds (e.g., 
lead- or antimony-based) which produce acidic and perhaps toxic 
bi-products when burned. 
In U.S. Pat. No. 4,273,691 (MacLaury et al.) describes flame retardant 
compositions comprising a polyolefin, certain metal salts of carboxylic 
acids and a silicone, such as a silicone gum. In commonly assigned, 
copending application Ser. No. 344,167, filed Jan. 29, 1982, and U.S. Pat. 
No. 4,387,176 (Frye), thermoplastic compositions are described which 
derive flame retardancy from additive packages comprising low viscosity 
silicone fluids plus Group IIA metal carboxylic acid salts and a blend of 
Group IIA metal organic compound plus silicone plus silicone resin, 
respectively. 
All of the aforementioned patents and applications are incorporated herein 
by reference. It will be apparent that the present invention provides 
novel flame retardant compositions that represent a significant 
improvement over prior art compositions. 
The present invention is based on the discovery that efficient flame 
retardant thermoplastics can be prepared by combining during compounding 
in the correct proportions certain metal soap precursors, for example 
stearic acid and a reactive magnesium compound (e.g., magnesium hydroxide 
or magnesium ethoxide), which are precursors to magnesium stearate, with 
certain silicone fluids and silicone resins and adding them to a major 
proportion of a thermoplastic. Such flame retarding additives impart flame 
retardance at relatively low concentrations, cause less reduction in 
mechanical properties than conventional flame retardants, dramatically 
improve impact resistance, are believed to produce less toxic products 
when exposed to flame, and act to improve gloss and processability. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide novel 
thermoplastic compositions having a high degree of flame retardancy. 
It is a further object of the present invention to provide a combination of 
silicone fluid, silicone resin and metal soap precursors which is 
effective to render thermoplastics flame retardant. 
It is a further object of the present invention to provide flame retardant 
thermoplastics exhibiting improved electrical properties and 
processability. 
These and other objects will become apparent to those skilled in the art 
upon consideration of the disclosure herein of a flame retardant 
composition comprising: 
(A) 30% to 98% by weight of thermoplastic; 
(B) 1% to 40% by weight of a silicone fluid comprised of RR'SiO units, 
where R and R' represent, independently, a substituted or unsubstituted 
monovalent organic radical of 1 to 20 carbon atoms, and having a viscosity 
of about 600 to 300,000,000 centipoise at 25.degree. C.; 
(C) 1% to 20% by weight of metal soap precursors comprising: 
(i) 50% to 100% by weight of a carboxylic acid containing at least 6 carbon 
atoms, and 
(ii) 0% to 50% of a reactive Group IIA metal compound; and 
(D) 1% to 20% of a silicone resin. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is based on the discovery that the precursors of 
certain Group IIA metal carboxylates (metal soaps), for example stearic 
acid with a reactive magnesium compound, can be used in combination with 
certain silicone fluids and silicone resins to impart improved flame 
retardant properties to a variety of organic polymers, such as 
polyolefins, polyesters, polycarbonates, polystyrenes, etc. (hereinafter 
collectively referred to as "thermoplastics"). Furthermore the metal soap 
precursors can be added directly during melt compounding of the 
thermoplastic, no pre-mixing or pre-reacting is necessary. It has been 
found that the flame retardancy of such thermoplastics is substantially 
improved, as shown by verticle burn tests and horizontal burn tests, when 
the aforementioned soap precursors and silicone fluid and silicone resin 
additives are incorporated into such thermoplastics. 
It is contemplated that the organic polymers which can be used to make the 
flame retardant compositions of the present invention are, for example, 
low density polyethylene (LDPE) having a density of 0.91 g/cm.sup.3 to 
0.93 g/cm.sup.3 ; high density polyethylene (HDPE) having a density of 
0.94 g/cm.sup.3 to 0.97 g/cm.sup.3 ; polypropylene having a density of 
about 0.91 g/cm.sup.3, polystyrene, LEXAN.RTM. polycarbonate, and 
VALOX.RTM. polyester, both manufactured by General Electric Company, and 
other polymers such as, ionomers, polyurethanes, thermoplastic elastomers 
co- and ter-polymers of acrylontirile, butadiene and styrene; as well as 
acrylic, polybutylene, acetal resin, ethylene-vinyl acetate, 
polymethylpentene, polyvinylchloride, and polyphenylene oxide etc. The 
term "silicone fluids" includes essentially linear polydiorganosiloxanes 
consisting essentially of chemically combined units of the formula, 
##STR1## 
wherein R and R' are monovalent organic radicals. These organic radicals 
will preferably be selected from the class consisting of C.sub.(1-8) alkyl 
radicals, C.sub.(6-13) aryl radicals, C.sub.(6-20) alkenyl radicals 
halogen-substituted such radicals, cyanoalkyl radicals, etc. The 
aforementioned polydiorganosiloxanes are preferably in the form of silanol 
or trimethylsilyl chainstopped siloxane fluids having an approximate 
visocisty of 600 to 300,000,000 centipoise at 25.degree. C. 
The metal soap precursors contemplated by the present invention are, for 
example, the carboxylic acid or related carboxylic compound (e.g. 
anhydride, acid chloride, ester, etc.) and reactive metal compound 
components which can be used to form metal soaps such as magnesium 
stearate, calcium stearate, barium stearate, strontium stearate, and other 
carboxylates of Group IIA metals. Suitable carboxylic acids or related 
carboxylic compounds will contain at least 6 carbon atoms, as it is 
believed that approximately 6 carbon atoms or more are required to 
disperse Group IIA metals in the silicone fluids and, in turn, in the 
thermoplastic. It is believed that little advantage would be found in 
utilizing carboxylic acids containing more than about 20 carbon atoms, 
although they may be found useful for specific situations. Preferred 
carboxylic acids include stearic acid, isostearic acid, oleic acid, 
palmitic acid, myristic acid, undecylenic acid, 2-ethylhexanoic acid, 
hexanoic acid, and the like. Stearic acid is most preferred. 
Another possible component in the contemplated metal soap precursors is a 
reactive metal compound selected from periodic Group IIA elements, such as 
magnesium, calcium, strontium, barium, etc. It is believed that 
introduction of both the carboxylic acid and the reactive metal compound 
components into the thermoplastic composition during melt compounding may 
form in situ a metal soap or other compound effective to improve the flame 
retardancy of the thermoplastic. Carboxylic acid salts which may be formed 
in this manner include stearates (including isostearates), oleates, 
palmitates, myristates, laurates, undecylenates, 2-ethylhexanoates, 
hexanoates, etc. 
Presently the Group IIA metals are not believed to be effective flame 
retardants by themselves. However, it may be possible that Group IIA metal 
additives are effective when complexed with other organic moieties, and 
therefore, the metals are used effectively because of their ability to 
readily disperse throughout the silicone material. It is therefore 
contemplated that the Group IIA metal soaps described herein include other 
organic complexes of such metals as are effective for use as flame 
retardants. Salts of the following acids, for example, may be suitable: 
sulfinic, sulfonic, aromatic sulfenic, sulfamic, phosphinic and phosphoric 
acids. 
The remaining major ingredient of the flame retardant fomulation is a class 
of materials referred to as silicone resin. The present inventor has 
discovered that remarkably effective flame retardant thermoplastic 
compositions can be provided when one or more of such a silicone resin is 
combined with the previously described ingredients to provide a flame 
retardant composition. Silicone resins are well known materials coming in 
a variety of forms. Approximately 2 to 40 percent by weight of the total 
additive formulation will be silicone resin which is soluble in the above 
described silicone oil (i.e., fluid or gum) and which is effective for 
imparting improved flame retardancy to the compositions of the present 
invention. Among the preferred silicone resins are MQ silicone resins. The 
expression "MQ silicone resin" refers to the fact that such resins are 
typically comprised primarily of monofunctional M units of the formula 
R.sub.3 SiO.sub.0.5 and tetrafunctional Q units of the average formula 
SiO.sub.2 having a specified ratio of M to Q units. A notable effective 
silicone resin for use in the present invention is 
polytrimethylsilylsilicate which can have a ratio of, approximately, 0.3 
to 4.0M units per Q unit. A particularly effective masterbatch formulation 
might preferably contain from 6 to 30 percent by weight of such MQ resin 
and have a ratio of, approximately, 0.6 to 2M units per Q unit. An example 
of a commercially available MQ silicone resin in General Electric SR545 
(60% MQ resin solids in toluene). A preferred method of utilizing such an 
MQ resin solution is to mix it with the silicone oil component and 
thereafter remove the solvent. The solvent can be removed by well known 
methods, e.g., by distillation at moderate temperatures. 
It is contemplated that other silicone oil soluble forms of solid silicone 
resins may be effective for use in the flame retardant compositions of the 
present invention. Indeed, MT and TQ silicone resins (where T represents 
trifunctional RSiO.sub.1.5 units) may also be effective as well as 
mixtures and copolymers of each of the resins mentioned. These silicone 
resins are well known materials and are readily available. A criterion for 
suitability is that such effective silicone resinous materials be soluble 
or dispersible in the silicone oil base. 
Additionally it is to be noted that although the additive composition 
specifies the silicone oil (essentially D functional) and silicone resin 
(M,D,T, or Q functional) as discrete ingredients to be admixed, it is 
intended that the present invention encompass reaction products of such 
materials which may be equally effective as flame retardant additives. It 
is also foreseeable that a copolymer containing requisite M, D, T or Q 
functionality may be utilized in place of discrete silicone oil and 
silicone resin consituents. 
Surprisingly, it has been discovered that the carboxylic acid component of 
the metal soap precursor also provides some degree of flame retardancy in 
combination with the silicone fluid and resin. The carboxylic acids, 
therefore, may advantageously be used to replace a portion or all of the 
other metal soap precursors or other flame retardant additives employed in 
a given thermoplastic composition. For example, reducing the magnesium 
content by replacing a portion of the magnesium stearate (or magnesium 
stearate precursors) by a compound such as stearic acid could produce 
several advantages, such as improving the electrical properties of the 
plastic, and improving the shelf stability of a silicone premix (since 
magnesium stearate may catalyze silanol condensation). 
The relative proportions of carboxylic acid and reactive metal compound 
contemplated, where both precursor components are used, will vary 
according to the nature of the reactive metal compound, the type of acid, 
the type of metal soap thought to be formed in situ, and other factors 
that will be familar to persons skilled in this art. However, by way of 
illustration, where magnesium hydroxide or magnesium ethoxide is used in 
conjunction with stearic acid, amounts of 0 to 100 parts by weight of the 
magnesium base per 100 parts of the stearic acid have produced good flame 
retardancy where together they comprised approxmately 41/2 weight percent 
of a polypropylene formulation. Obviously, some experimentation to arrive 
at the optimal proportions for a given thermoplastic formulation is 
contemplated. 
In addition to the aforementioned ingredients, the flame retardant 
compositions of the present invention can contain additional ingredients, 
such as fillers, antioxidants, and additional additives. In particular 
instances, ingredients such as decabromodiphenylether, alumina trihydrate 
and talc also can be utilized. If desired, heat activated peroxides can be 
employed when utilizing polyolefins as the organic polymer. Suitable 
reactive peroxides are disclosed in U.S. Pat. Nos. 2,888,424, 3,079,370, 
3,086,966 and 3,214,422 (all incorporated herein by reference). Suitable 
peroxide crosslinking agents include organic tertiary peroxides which 
decompose at a temperature above about 146.degree. C. 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 
preferred peroxide is dicumyl peroxide, while other peroxides such as 
VulCupR.RTM. of Hercules, Inc., a mixture of para- and meta-, 
-bis(t-butylperoxy)-diisopropylbenzene, etc., can be used. Curing 
co-agents such as triallyl cyanurate can be employed in amounts of up to 
about 5 parts by weight of co-agent, per 100 parts of the polymer if 
desired. The polyolefins can be irradiated by high energy electrons, X-ray 
and like sources. 
The proportions of all 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 (by weight) of organic 
polymer from about 0.5 to 20 parts of the silicone fluid, 0.5 to 20 parts 
at the silicone resin and about 0.5 to 20 parts of the metal soap 
precursor. However, greater or smaller amounts may suffice in particular 
applications, and as previously indicated, other additives may be 
included. Alumina trihydrate, for example, can be utilized in a proportion 
of from 1 to 70 parts, and organic halogen compounds can be added at from 
about 5 to 30 parts, per 100 parts of the organic polymer. Reinforcing and 
non-reinforcing fillers are also contemplated. 
In the practice of the invention, the flame retardant compositions can be 
made by mixing together the organic polymer with the silicone fluid, the 
silicone resin, and the Group IIA metal soap precursors by means of any 
conventional melt compounding apparatus, such as a Banbury mixer, twin 
screw extruder, or two-roll rubber mill. However a twin screw extruder is 
expected to give the most reproducible product. Order of addition of the 
particular constituents does not appear to be critical, however, those 
skilled in the art will be able to optimize the flame retardant 
compositions contemplated herein without undue experimentation. 
Preferably, all the ingredients are formulated together except those which 
are sensitive to the temperatures in the range of from about 150.degree. 
C. to about 200.degree. C., such as heat decomposable peroxides. The 
ingredients are therefore at a temperature sufficient to soften and 
plasticize the particular organic polymer if feasible. An effective 
procedure, for example, would be to uniformly blend the aforementioned 
ingredients at a suitable temperature omitting the organic peroxide, then 
introduce the organic peroxide at a lower temperature to uniformly 
incorporate it into the mixture. 
It is envisioned that the flame retardant composition of the present 
invention can be extruded onto a conductor and in particular instances, 
crosslinked depending on whether a peroxide curing agent is present. Of 
course, there are numerous other applications where the flame retardant 
compositions of the present invention may be used to great advantage. Such 
materials may be successfully molded, extruded or compressed to form 
numerous useful products such as moldings, sheets, webbing, fibers and a 
multitude of other flame retardant plastic or polyolefin products. Thus, 
the flame retardant compositions of the present invention can be utilized 
in such applications as appliance housings, hairdriers, TV cabinets, smoke 
detectors, etc., automotive interiors, fans, motors, electrical 
components, coffee 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. 
Those skilled in the art will appreciate that there are several methods for 
testing and comparing relative flame retardancy of thermoplastics. Among 
the most well known are limiting oxygen index and horizontal and vertical 
burn tests. 
Underwriters' Labatories Bulletin UL-94 describes a "Burning Test for 
Classifying Materials", hreinafter referred to as "UL-94". In accordance 
with this test procedure, materials are rated V-O, V-I, or V-II based on 
the results of testing five specimens, which are evaluated according to 
the following criteria; 
V-O: Average flaming and/or glowing after removal of the igniting flame 
shall not exceed 5 seconds, and no individual specimen shall drip 
particles which ignite absorbant cotton or burn longer than 10 seconds. 
V-I: Average flaming and/or glowing after removal of the igniting flame 
shall not exceed 25 seconds, and no individual specimens shall drip 
particles which ignite absorbant cotton or burn longer than 30 seconds. 
V-II: Average flame and/or glowing after removal or igniting flame shall 
not exceed 25 seconds (with no individual burn greater than 30 seconds) 
and the specimens drip flaming particles which ignite absorbant cotton. 
The vertical burn tests conducted in connection with the following examples 
essentially follow the test procedures described in UL-94. However, the 
tests, since they were designed for screening purposes only and not for 
qualification of the products for specific applications, are not 
replicated to the extent set forth in the procedure. Accordingly, 
reference to UL-94 classifications V-O, V-I and V-II in the following 
examples represents the classification for the sample formulations which 
are believed will produce articles meeting the pertinent criteria of 
UL-94. 
In order that those skilled in the art may better understand the pratice of 
the present invention, the following examples are given by way of 
illustration and not by way of limitation.