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Description  |
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This invention relates to a resin composition comprising functionalized
polypropylene, a hydrogenated mono alkylarene-conjugated diene block
copolymer, oil, and a filler which can be blended to form a
self-extinguishing, low smoke and halogen free insulation composition
which exhibits high ultimate elongation and is relatively easy to process.
Background of the Invention
This application is related to U.S. Ser. No. 802,806, which is being filed
concurrently herewith.
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.
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 in 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.
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.
SUMMARY OF THE INVENTION
It has been found that functionalizing the polypropylene in an insulation
blend improves the physical properties, e.g., tensile strength and
elongation. It has been found that the brittleness problem can be
essentially eliminated by using functionalized polypropylene. The
functionalized polypropylene has reactive groups grafted to it which will
attach to a filler producing boning between the polypropylene and the
filler, thereby producing better physical properties.
According to the present invention there is provided a filled rubber
modified polypropylene composition having good physical properties, good
processability, good flame retardancy and low production of toxic and
corrosive gases when burned, said composition comprising
(1) between about 1 and about 40 weight percent of a functionalized
homopolypropylene,
(2) between 5 and 40 percent by weight of a hydrogenated monoalkyl
arene-conjugated diene block copolymer,
(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 hydrated inorganic
filler.
DETAILED DESCRIPTION OF THE INVENTION
The compositions of the present invention are prepared by combining the
required components in the correct porportions in conventional blending
equipment such as a rubber mill or mixer, for example, a Banbury mixer.
This is usually done above the melting temperature of the polymeric
materials.
FUNCTIONALIZED POLYPROPYLENE
Functionalized polypropylenes are well known in the art and may be
prepared, for example, according to the procedure described in U.S. Pat.
Nos. 3,480,580 or 3,481,910, which are hereby incorporated by reference.
The polymers may be prepared from homopolypropylene which preferably should
be isotactic and may be, for example, the types corresponding to Shell
PP-5944 S, PP-5520 and PP DX-5088, available from Shell Chemical Company,
Houston, Tex. Syndiotactic homopolymers also can be used. A preferred
functionalized polypropylene is maleic anhydride functionalized
polypropylene of the type corresponding to Plexar 2110, available from
Northern Petrochemical Company, Rolling Meadows, Ill.
FILLERS
The fillers used in the present invention are the hydrated inorganic
fillers, e.g. hydrated aluminum oxides (Al.sub.2 O.sub.3 3H.sub.2 O or
Al(OH).sub.3) hydrated magnesia, hydrated calcium silicate and zinc
borate. Of these compounds, the most preferred are hydrated aluminum oxide
and magnesium hydroxide.
Fillers may be surface treated with a coupling agent prior to blending to
enhance the bonding between the functionalized polypropylene and the
filler. Coupling agents may include fatty acid metal salts, e.g., oleates
or stearates; silanes, maleates, titanates, zircoaluminates, etc.
The filler particle size is relatively non-important and may be in
accordance with those sizes used by the prior art. Preferred particle
sizes are less than 5 microns.
BLOCK COPOLYMERS
The hydrogenated monoalkyl arene-conjugated diene block copolymers useful
in the present invention are well known in the art. This block copolymer,
as defined in U.S. Pat. No. 4,110,303, among other patents, has at least
two monoalkenyl arene polymer end blocks A and at least one polymer mid
block B selected from the group consisting of substantially completely
hydrogenated conjugated diene polymer blocks, ethylene-propylene polymer
blocks and ethylene-butene polymer blocks. The block copolymers employed
in the present invention may have a variety of geometrical structures,
since the invention does not depend on any specific geometrical structure,
but rather upon the chemical constitution of each of the polymer blocks.
Thus, the structures may be linear, radial or branched so long as each
copolymer has at least two polymer end blocks A and at least one polymer
mid block B as defined above. Methods for the preparation of such polymers
are known in the art. Particular reference will be made to the use of
lithium based catalysts and especially lithium alkyls for the preparation
of the precursor polymers (polymers before hydrogenation). U.S. Pat. No.
3,595,942 not only describes some of the polymers of the present invention
but also describes suitable methods for their hydrogenation. The structure
of the polymers is determined by their method of polymerization. For
example, linear polymers result by sequential introduction of the desired
monomers into the reaction vessel when using such initiators as
lithium-alkyls or dilithiostilbene and the like, or by coupling a two
segment block copolymer with a difunctional coupling agent. Branched
structures, on the other hand, may be obtained by the use of suitable
coupling agents having a functionality with respect to the precursor
polymers of three or more. Coupling may be effected with multifunctional
coupling agents such as dihaloalkanes or alkenes and divinyl benzene as
well as certain polar compounds such as silicon halides, siloxanes or
esters of monohydric alcohols with carboxylic acids. The presence of any
coupling residues in the polymer may be ignored for an adequate
description of the polymers forming a part of the compositions of this
invention. Likewise, in the generic sense, the specific structures also
may be ignored. The invention applies especially to the use of selectively
hyrogenated polymers having the configuration before hydrogenation of the
following typical species:
polystyrene-polybutadiene-polystyrene (SBS)
polystyrene-polyisoprene-polystyrene (SIS)
poly(alpha-methylstyrene)-polybutadiene-poly(alpha-methylstyrene) and
poly(alpha-methylstyrene)-polyisoprene-poly(alpha-methylstyrene).
It will be understood that both blocks A and B may be either homopolymer or
random copolymer blocks as long as each block predominates in at least one
class of the monomers characterizing the blocks and as long as the A
blocks individually predominate in monoalkenyl arenes and the B blocks
individually predominate in dienes. The term "monoalkenyl arene" will be
taken to include especially styrene and its analogs and homologs including
alpha-methylstyrene and ring-substituted styrenes, particularly
ring-methylated styrenes. The preferred monoalkenyl arenes are styrene and
alpha-methylstyrene, and styrene is particularly preferred. The blocks B
may comprise homopolymers of butadiene or isoprene and copolymers of one
of these two dienes with a monoalkenyl arene as long as the blocks B
predominate in conjugated diene units. When the monomer employed is
butadiene, it is preferred that between about 35 and about 55 mol percent
of the condensed butadiene units in the butadiene polymer block have 1,2
configuration. Thus, when such a block is hydrogenated, the resulting
product is, or resembles a regular copolymer block of ethylene and
butene-1 (EB). If the conjugated diene employed is isoprene, the resulting
hydrogenated produce is or resembles a regular copolymer block of ethylene
and propylene (EP). Ethylene-butene or ethylene-propylene blocks prepared
via direct polymerization and not by hydrogenation of conjugated diene
polymer blocks are also contemplated by the present invention.
Hydrogenation of the precursor block copolymers, if required, is preferably
effected by use of a catalyst comprising the reaction products of an
aluminum alkyl compound with nickel or cobalt carboxylates or alkoxides
under such conditions as to substantially completely hydrogenate at least
80% of the aliphatic double bonds while hydrogenating no more than about
25% of the alkenyl arene aromatic double bonds. Preferred block copolymers
are those where at least 99% of the aliphatic double bonds are
hydrogenated while less than 5% of the aromatic double bonds are
hydrogenated.
The average molecular weights of the individual blocks may vary within
certain limits. In most instances, the monoalkenyl arene blocks will have
number average molecular weights in the order of 5,000-125,000, preferably
7,000-60,000 while the conjugated diene blocks either before or after
hydrogenation will have average molecular weights in the order of
10,000-300,000, preferably 30,000-150,000. The total average molecular
weight of the block copolymer is typically in the order of 25,000 to about
250,000, preferably from about 35,000 to about 200,000. These molecular
weights are most accurately determined by tritium counting methods or
osmotic pressure measurements.
The proportion of the monoalkenyl arene blocks should be between about 8
and 55% by weight of the block copolymer, preferably between about 10 and
35% by weight.
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-methylenebis 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
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Typical Preferred
Most Preferred
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Block Copolymer
5-40 10-30 15-20
Plasticizer (oil)
1-20 2-15 4-8
Modified Polypropylene
1-40 2-20 4-8
Filler 10-85 40-75 6-75
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The particular amounts of each component may vary somewhat in the resultant
composition depending on the components employed and their relative
amounts.
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.
Block Copolymer 2 is a S-EB-S with GP block molecular weights of about
10,000-50,000-10,000.
Block Copolymer 3 is a S-EB-S with GPC block molecular weights of
7,000-35,000-7,000.
The oil was Penreco 4434 oil available from Penreco Company. The
polypropylene was homopolypropylene PP 5520 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 Thiocol Inc. with a secondary particle size of about 4 microns.
Surface treated Mg(OH).sub.2 was Kisuma 5B from Kyowa Chemical Industry
Ltd. which is oleate treated and has a secondary particle (aggregate) 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 18 AWG solid conductor 30 mils
samples. All insulation coatings were conducted at 190 deg. C. melt
temperature.
Control example LR 8506 contained conventional nonfunctionalized
homopolypropylene. The rest of the examples incorporate a maleic anhydride
functionalized polypropylene. The examples according to the present
invention showed at least a two fold and as high as a three fold increase
in the stress at break. The modified polypropylene is much more effective
in reinforcing these compositions.
TABLE II
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Block
Copolymer
LR 8506
IC 1104
IC 1157
IC 1158
IC 1162
IC 1163
IC 1187
IC 1188
IC 1189
IC
IC
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1193
Rubber 1
16.00%
14.70%
7.35%
18.37%
18.05%
21.40%
16.32%
17.67%
14.97%
-- --
Rubber 2
-- -- -- -- -- -- -- -- -- 16.32%
--
Rubber 3
-- -- -- -- -- -- -- -- -- -- 16.32%
Oil 8.00%
7.35%
7.35%
3.68%
4.00%
4.00%
5.68%
5.68%
5.68%
7.35%
7.35%
Polypropylene
5.00%
-- -- -- -- -- -- -- -- -- --
Modified
-- 7.35%
14.70%
7.35%
7.35%
4.00%
7.35%
6.00%
8.70%
7.35%
7.35%
Polypropylene
Surface Treated
70.40%
70.00%
70.00%
70.00%
70.00%
70.00%
70.00%
70.00%
70.00%
70.00%
70.00%
Mg(OH).sub.2
Irganox 1010
0.25%
0.10%
0.25%
0.25%
0.25%
0.25%
0.25%
0.25%
0.25%
0.25%
0.25%
Irganox 1024
0.10%
0.10%
0.10%
0.10%
0.10%
0.10%
0.15%
0.15%
0.15%
0.15%
0.15%
DLTDP 0.25%
0.40%
0.25%
0.25%
0.25%
0.25%
0.25%
0.25%
0.25%
0.25%
0.25%
Stress Break
400 960 970 1370 1350 1210 1260 980 1230 1090 950
(psi)
Elongation at
370 250 0 350 330 320 300 330 350 600 600
Break (%)
Line speed
250 -- 50 45 50 50 50 50 50 50 50
(FPM)
Screw speed
150 30 29 28 36 34 30 30 30 30 30
(RPM)
Power Input
10 17 13 23 24 23 16 19 20.5 17 14
(AMP)
Head Pressure
1340 4000 3100 5200 5500 5000 4000 4700 4800 4600 3500
(psi)
Limiting
31.0 29.5 28.5 30.0 -- -- -- 34.0 31.0 -- --
Oxygen
Index %
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