Low smoke polypropylene insulation compositions

This invention relates to a resin composition comprising polypropylene, a functionalized hydrogenated mono alkylarene-conjugated diene block copolymer, oil, and a treated Mg(OH).sub.2 filler which can be blended to form a self-extinguishing, low smoke and halogen free insulation composition which exhibits high stress at break and is relatively easy to process.

This invention relates to a resin composition comprising polypropylene, a 
modified hydrogenated mono alkylarene-conjugated diene block copolymer, 
oil, and a treated Mg(OH).sub.2 filler which can be blended to form a 
self-extinguishing, low smoke and halogen free insulation composition 
which exhibits high stress at break and is relatively easy to process. 
BACKGROUND OF THE INVENTION 
The most common method for reducing the flammability of wire and cable 
insulation and jacketing materials is the use of an organic bromine or 
chlorine compound along with antimony oxide. This system is very effective 
as a flame retardant, but such materials produce a dense black smoke when 
burned, and also produce hydrogen chloride or hydrogen bromide, which are 
both corrosive and toxic. Because of this, there has been a great deal of 
interest in flame retarded systems that produce lower amounts of smoke and 
toxic and corrosive gases when they are burned. There appear to be two 
main approaches that are being followed to meet this goal. The first is to 
eliminate halogens from the system and use instead large loadings of 
alumina trihydrate, another common fire retardant, or the similar filler 
magnesium hydroxide. The second is to develop additives that reduce the 
smoke and acid gas production of the halogenated systems. In addition to 
low smoke low toxicity these compositions must also have attractive 
physical properties in order to be used for wire and cable applications. 
These properties include hardness, abrasion resistance, environmental 
stability, deformation resistance, low temperature flexibility, oil 
resistance and good electrical properties. At present there are no 
low-smoke, low-toxicity, flame-retardant materials which are readily 
available although some new materials including metal hydrate filled 
polyethylene are becoming available. 
Metal hydrates such as alumina trihydrate and magnesium hydroxide contain 
water bonded to a crystal structure with the metal atom. When heated to a 
sufficiently high temperature these compounds decompose and release water 
which subsequently vaporizes. This process of decomposition and 
vaporization absorbs heat, thus slowing down the initial heating of the 
insulation material and consequently slows down the subsequent burning of 
the material. After this cooling effect is overwhelmed however, the 
presence of the metal hydrates has little effect on the subsequent process 
of burning. Unlike the halogenated flame retardant composition, metal 
hydrate compositions with non-halogenated polyolefins break down quickly 
into monomer units and burn relatively cleanly without a great deal of 
smoke production. In addition, since metal hydrates only add water to the 
system, they should not increase the emission of toxic or corrosive gases 
beyond what already would be produced by the system. 
Polypropylene, which is readily available at a reasonable cost, has found 
many industrial uses because of its desirable physical properties, such as 
ease of fabrication by all conventional methods; high melting point of 
stereoregular, e.g., isotactic, polypropylene and compatibility with many 
other commercial resins, which permits a large number of blends having 
specific properties. Brittleness in these compositions can be reduced 
either by copolymerizing propylene with ethylene to form block copolymers 
or by blending homopolypropylene with rubbers. 
It is well known in the art that physical properties of these blends can be 
greatly enhanced by the incorporation of hydrogenated monoalkyl 
arene-conjugated diene block copolymers. 
It has been discovered that adding a modified (functionalized) block 
copolymer greatly enhances the physical properties of these blends. It is 
believed that the functionalized block copolymer provides for bonding 
between the polymer matrix and the filler. 
Magnesium hydroxide fillers along with alumina trihydrate fillers have been 
used in flame retardant polypropylene compositions. Alumina trihydrate is 
generally more effective as a flame retardant than is magnesium hydroxide 
due to the greater amount of water incorporated in that filler, however, 
magnesium hydroxide has specific advantages, for example, better 
processability when incorporated into a polyolefin composition and a 
higher decomposition temperature than alumina trihydrate (330.degree. C. 
versus 230.degree. C.). This increase decomposition temperature allows a 
flame retardant polymer composition containing magnesium hydroxide to be 
processed at a higher temperature than a compound with alumina trihydrate. 
The higher processing temperatures allow much faster processing due to 
lower viscosities. 
It has been found however that conventional magnesium hydroxide fillers 
cannot be successfully blended into rubber modified polypropylene 
compositions. These compositions when filled to a reasonable loading of 
magnesium hydroxide cannot be processed due to agglomeration of the filler 
particles. Accordingly, it would be desirable to provide a magnesium 
hydroxide filler which would not adversely affect the processability by 
agglomeration. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a blend containing 
polypropylene, functionalized hydrogenated monovinyl arene-conjugated 
block copolymer, oil and a filler having good physical properties, good 
processability, good flame retardancy and low production of toxic and 
corrosive gases when burned. More particularly, said composition comprises 
(1) between about 1 and about 40 weight percent of a homopolypropylene, 
(2) between 5 and 40 percent by weight of a functionalized hydrogenated 
monoalkyl arene-(A)-conjugated diene (B) block copolymer containing at 
least two A blocks and at least one B block, 
(3) between 1 and about 20 percent by weight of a hydrocarbon extending 
oil, and 
(4) between about 10 and about 85 percent by weight of a magnesium 
hydroxide filler which has been surface treated with a coupling agent.

FUNCTIONALIZED BLOCK COPOLYMERS 
Block copolymers of conjugated dienes and vinyl aromatic hydrocarbons which 
may be utilized include any of those which exhibit elastomeric properties 
and those which have 1,2-microstructure contents prior to hydrogenation of 
from about 7% to about 100%. These block copolymers need not be 
hydrogenated however the hydrogenated polymers are preferred. Such block 
copolymers may be multiblock copolymers of varying structures containing 
various ratios of conjugated dienes to vinyl aromatic hydrocarbons 
including those containing up to about 60 percent by weight of vinyl 
aromatic hydrocarbon. Thus, multiblock copolymers may be utilized which 
are linear or radial symetric or asymetric and which have structures 
represented by the formulae, A--B, A--B--A, A--B--A--B, B--A, B--A--B, 
(AB).sub.0-50 BA and the like wherein A is a polymer block of a vinyl 
aromatic hydrocarbon or a conjugated diene/vinyl aromatic hydrocarbon 
tapered copolymer block and B is a polymer block of a conjugated diene. 
The block copolymers may be produced by any well known block polymerization 
or copolymerization procedures including the well known sequential 
addition of monomer techniques, incremental addition of monomer technique 
or coupling technique as illustrated in, for example, U.S. Pat. Nos. 
3,251,905; 3,390,207; 3,598,887 and 4,219,627. As is well known in the 
block copolymer art, tapered copolymer blocks can be incorporated in the 
multiblock copolymer by copolymerizing a mixture of conjugated diene and 
vinyl aromatic hydrocarbon monomers utilizing the difference in their 
copolymerization reactivity rates. Various patents describe the 
preparation of multiblock copolymers containing tapered copolymer blocks 
including U.S. Pat. Nos. 3,251,095; 3,265,765; 3,639,521 and 4,208,356 the 
disclosures of which are incorporated herein by reference. 
Conjugated dienes which may be utilized to prepare the polymers and 
copolymers are those having from 4 to 8 carbon atoms and include 
1,3-butadiene, 2-methyl-1,3-butadiene(isoprene), 
2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and the like. 
Mixtures of such conjugated dienes may also be used. The preferred 
conjugated diene is 1,3-butadiene. 
Vinyl aromatic hydrocarbons which may be utilized to prepare copolymers 
include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 
1,3-dimethylstyrene, alpha-methylstyrene, vinylnaphthalene, 
vinylanthracene and the like. The preferred vinyl aromatic hydrocarbon is 
styrene. 
It should be observed that the above-described polymers and copolymers may, 
if desired, be readily prepared by the methods set forth above. However, 
since many of these polymers and copolymers are commercially avaiable, it 
is usually preferred to employ the commercially available polymer as this 
serves to reduce the number of processing steps involved in the overall 
process. The hydrogenation of these polymers and copolymers may be carried 
out by a variety of well established processes including hydrogenation in 
the presence of such catalysts as Raney Nickel, noble metals such as 
platinum, palladium and the like and soluble transition metal catalysts. 
Suitable hydrogenation processes which can be used are ones wherein the 
diene-containing polymer or copolymer is dissolved in an inert hydrocarbon 
diluent such as cyclohexane and hydrogenated by reaction with hydrogen in 
the presence of a soluble hydrogenation catalyst. Such processes are 
disclosed in U.S. Pat. Nos. 3,113,986 and 4,226,952, the disclosures of 
which are incorporated herein by reference. The polymers and copolymers 
are hydrogenated in such a manner as to produce hydrogenated polymers and 
copolymers having a residual unsaturation content in the polydiene block 
of from about 0.5 to about 20 percent of their original unsaturation 
content prior to hydrogenation. 
These block copolymers can be functionalized as described by Gergen in U.S. 
Pat. No. 4,578,429, which is hereby incorporated by reference, or by other 
methods which are well known in the prior art, e.g. Saito et al U.S. Pat. 
No. 4,292,414 and Hergenrother et al U.S. Pat. No. 4,427,828. The 
functionalized block copolymer is a thermally stable modified selectively 
hydrogenated high 1,2 content block copolymer wherein at least one acid 
compound is grafted to the block copolymer (base polymer). 
More preferably, the functionalized block copolymer is a functionalized 
selectively hydrogenated block copolymer selected from the group 
consisting of AB diblock copolymers and multiblock copolymers having at 
least two blocks A and at least one block B to which has been grafted an 
acid compound or its derivative wherein, 
(1) each A is predominantly a polymerized monoalkenyl aromatic hydrocarbon 
block having an average molecular weight of about 2,000 to 115,000; 
(2) each B is predominantly a polymerized conjugated diene hydrocarbon 
block having an average molecular weight of about 20,000 to 450,000; 
(3) the blocks A constituting 5-95 weight percent of the copolymer; 
(4) the unsturation of the block B is reduced to less than 10% of the 
original unsaturation; 
(5) the unsaturation of the A blocks is above 50% of the original 
unsaturation. 
The preferred modifying monomers for use in functionalization are those 
which are reactive with polyamides and may include unsaturated mono- and 
polycarboxylic-containing acids (C.sub.3 -C.sub.10) with preferably at 
least one olefinic unsaturation, and anhydrides, salts, esters, amides, 
thiols, thioacids, glycidyl, hydroxy, glycol, and other substituted 
derivatives from said acid. 
Examples of such acids, anhydrides and derivatives thereof include maleic 
acid, fumaric acid, itaconic acid, citraconic acid, acrylic acid, glycidyl 
acrylate, cyanoacrylates, hydroxy C.sub.1 -C.sub.20 alkyl methacrylates, 
acrylic polyethers, acrylic anhydride, methacrylic acid, crotonic acid, 
isocrotonic acid, mesaconic acid, angelic acid, maleic anhydride, itaconic 
anhydride, citraconic anhydride, sodium acrylate, calcium acrylate, and 
magnesium acrylate. 
Other monomers which can be used either by themselves or in combination 
with one or more of the carboxylic acids or derivatives thereof include 
C.sub.2 -C.sub.50 vinyl monomers such as acrylamide, and monovinyl 
aromatic compounds, i.e. styrene, chlorostyrenes, bromostyrenes, 
.alpha.-methyl styrene, vinyl pyridenes and the like. 
Other monomers which can be used are C.sub.4 to C.sub.50 vinyl esters, 
vinyl ethers and allyl ethers, such as vinyl butyrate, vinyl laurate, 
vinyl stearate, vinyl adipate and the like, the monomers having two or 
more vinyl groups, such as divinyl benzene, ethylene dimethacrylate, 
triallyl phosphite, dialkylcyanurate and triallyl cyanurate. 
The preferred monomers to be grafted to the block copolymers according to 
the present invention are maleic anhydride, maleic acid, fumaric acid and 
their derivatives. It is well known in the art that these monomers do not 
polymerize easily. 
Of course, mixtures of monomer can be also added so as to achieve graft 
copolymers in which the graft chains contain at least two different 
monomers (in addition to the base polymer monomers). The functionalized 
block copolymers can be added to the blend as described or cut back with 
up to 75% by weight of an unfunctionalized block copolymer. 
POLYPROPYLENE 
The homopolypropylene preferably should be isotactic and may be, for 
example, of the type corresponding to Shell PP-5944 S, PP-5520 and PP 
DX-5088, available from Shell Chemical Company, Houston, Tex. Most 
commercial isotactic polypropylenes are suitable in the compositions of 
this invention. Syndiotactic homopolymers also can be used. Modified 
polypropylenes, for example, maleic anhydride functionalized polypropylene 
of the type corresponding to Plexar 2110, available from Northern 
Petrochemical Company, Rolling Meadows, Ill., may also be used in the 
compositions of this invention. The functionalized polypropylenes are 
readily prepared according to procedures described in U.S. Pat. Nos. 
3,480,580 or 3,481,910, which are hereby incorporated by reference. 
FILLERS 
The magnesium hydroxide fillers useful in the compositions of the present 
invention are surface treated with a coupling agent to prevent 
agglomeration of the particles. When agglomeration occurs the effective 
particle size of the filler is increased dramatically and therefore the 
processability and the properties of the end product are degraded. 
Surfactants which are useful in the invention may include fatty acid 
salts, for example, oleates and stearates, also maleates, silanes, 
zirco-aluminates, titanates, etc. It has also been found that magnesium 
hydroxide fillers with a high aspect ratio crystallate shape and larger 
size are also less likely to agglomerate than those with a lower aspect 
ratio. Aspect ratios for the crystallites should be greater than 4 and 
mean secondary particle (agglomerate) size should be less than three 
microns. 
ADDITIONAL COMPONENTS 
In addition, the present composition may contain other components such as 
plasticizers, e.g., saturated hydrocarbon or mineral oils, hydrogenated or 
saturated hydrocarbon resins along with additives such as stabilizers and 
oxidation inhibitors. Aliphatic oils and resins are preferred to aromatic 
oils and resins since aromatics tend to cyclacize resulting in color 
bodies. Preferred oils are primarily aliphatic, saturated mineral oils. 
Preferred resins are saturated or hydrogenated hydrocarbon resins, such as 
hydrogenated polymers of dienes and olefins. These additional components 
must be compatible with the block copolymer component. The selection of 
the other components depends upon a number of factors--e.g., the method 
for coating a wire. 
As stated above, the compositions may be modified with supplementary 
materials such as stabilizers and oxidation inhibitors. Stabilizers and 
oxidation inhibitors are typically added to the compositions in order to 
protect the polymers against degradation during preparation and use of the 
composition. Combinations of stabilizers are often more effective, due to 
the different mechanisms of degradation to which various polymers are 
subject. Certain hindered phenols, organo-metallic compounds, aromatic 
amines and sulfur compounds are useful for this purpose. Especially 
effective types of these materials include the following: 
1. Benzothiazoles, such as 2-(dialkyl-hydroxybenzyl-thio)benzothiazoles. 
2. Esters of hydroxybenzyl alcohols, such as benzoates, phthalates, 
stearates, adipates or acrylates of 3,5-dialkyl-1-hydroxy-benzyl alcohols. 
3. Stannous phenyl catecholates. 
4. Zinc dialkyl dithiocarbamates. 
5. Alkyl phenols, e.g., 2,6-di-tert-butyl-4-methyl phenol. 
6. Dilaurylthio-dipropionate (DLTDP). Examples of commercially available 
antioxidants are "Ionox 220" 4,4-methylene-bis(2,6-di-t-butyl-phenol) and 
"Ionox 330" 
3,4,6-tris(3,5-di-t-butyl-p-hydroxybenzyl)-1,3,5-trimethylbenzene, "Dalpac 
4C" 2,6-di-(t-butyl)-p-cresol, "Naugawhite" alkylated bisphenol, "Butyl 
Zimate" zinc dibutyl dithiocarbamate, and "Agerite Geltrol" 
alkylated-arylated bisphenolic phosphite. From about 0.01 percent to about 
5.0 percent by weight of one or more antioxidants is generally added to 
the composition. 
TABLE I 
______________________________________ 
Typical 
Preferred 
Most Preferred 
______________________________________ 
Block Copolymer 
5-40 10-30 15-20 
(Modified + unmodified) 
Plasticizer (oil) 
1-20 2-15 4-8 
Polypropylene 1-40 2-20 4-8 
Filler 10-85 40-75 63-75 
______________________________________ 
The particular amounts of each component may vary somewhat in the resultant 
composition depending on the components employed and their relative 
amounts. 
The particular method of preparing the compositions and manufacturing the 
insulated or jacketed wire and/or cable which are the subject of the 
present invention is not critical and any of a number of commercially 
known techniques may be employed both for blending and extruding the 
modified block copolymer-polypropylene compositions and forming the 
jacketed and/or insulated wire and/or cable. 
The method used to form the blend is not critical provided the polymers are 
homogeneously dispersed. Incomplete mixing results in the formation of 
aggregates which impair the physical properties of the blend. 
Obviously, other modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that changes may be made in the particular embodiments of the invention 
described which are within the full intended scope of the invention as 
defined by the appended claims. 
EXAMPLES 
The following examples are given to illustrate the invention and are not to 
be construed as limiting. 
The components used were as follows: 
Block Copolymer 1 is a S--EB--S with GPC block molecular weights of about 
29,000-125,000-29,000. 
The modified block copolymer is S--EB--S which GPC block molecular weights 
of 7,000-35,000-7,000 which has been grafted with about 1.3 weight percent 
of maleic anhydride. 
The oil was Penreco 4434 oil available from Penreco Company. The 
polypropylene was homopolypropylene PP 5520 or PP 5944 from Shell Chemical 
Company. The modified polypropylene was a maleic anhydride functionalized 
polypropylene Plexar 2110 from Northern Petrochemical Company in Rolling 
Meadows, Ill. The ATH was alumina trihydrate, 1.0 micron precipitated 
Hydral 710B from Alcoa. The Mg(OH).sub.2 was from Ventron Division of 
Morton Thiokol Inc. with a secondary particle size of about 4 microns. The 
surface treated Mg(OH).sub.2 was Kisuma 5B from Kyowa Chemical Industry 
Ltd., which is oleate treated and has an average secondary (aggregate) 
particle size of about 0.8 microns. 
ANTIOXIDANTS 
Irganox 1010; tetra-bismethylene 3-(3,5-ditertbutyl-4 
hydroxyphenyl)-propionate methane from Ciba-Geigy. 
Irganox MD-1024; stabilizers from Ciba-Geigy. 
DLTDP; Plastanox DLTDP, American Cyanamid. 
Compositions are in percent by weight. 
Examples were extruded insulation coating on 18AWG solid conductor 30 mils 
samples. All insulation coatings were conducted at 190 deg. C. melt 
temperature. 
Example IC 1132 shows that a blend of block copolymer with polypropylene 
could not be blended or extruded because of the Mg(OH).sub.2 filler 
loading. Example LR8506 using a similar amount of an oleate treated 
Mg(OH).sub.2 was easily processed even though about 30% less polypropylene 
was incorporated. The blend however had an unacceptable stress at break. 
Examples IC 1046 and IC 1102 both showed acceptable properties however 
Examples IC 1102 with treated Mg(OH).sub.2 according to the present 
invention was much more easily processed than Example IC 1046 containing 
ATH as indicated by the 50% decrease in power input to the extruder. 
TABLE II 
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IC LR IC 
1132 8506 1046 IC-1102 
______________________________________ 
Block Copolymer 1 
14.7 16.00 11.40 4.7 
Modified Block -- -- 10.00 10.00 
Copolymer 
Oil 7.35 8.00 5.00 7.35 
Polypropylene 5944 
-- 5.00 -- -- 
Polypropylene 5520 
-- -- 5.00 7.35 
Modified Polypropylene 
7.35 -- -- -- 
ATH -- -- 68.0 -- 
Mg(OH).sub.2 70.00 -- -- -- 
Surface Treated Mg(OH).sub.2 
-- 70.40 -- 70.00 
Irganox 1010 0.10 0.25 0.10 0.10 
Irganox 1024 0.10 0.10 0.10 0.10 
DLTDP 0.40 0.25 0.40 0.40 
Stress Break (psi) 
* 400 2300 1450 
Elongation at Break (%) 
* 370 110 120 
Line speed (FPM) 
* 250 -- -- 
Screw speed (RPM) 
* 150 20 30 
Power Input (AMP) 
* 10 24.5 12.5 
Head Pressure (psi) 
* 1340 -- 2800 
Limiting Oxygen Index % 
* 31.0 32.0 28.5 
______________________________________ 
*Could not be coated.