Note: Descriptions are shown in the official language in which they were submitted.
~7886
BACKGROUND OF THE INVENTION
The present invention relates to the thermoplastic
elastomer blends of l-olefin polymers such as polypropylene or
to copolymers such as polypropylene and polyethylene, and
styrene-butadiene rubber which require no curing or vulcaniza-
tion whatsoever to develop elastomeric properties. Addition-
ally, the invention relates to partially cured blends thereof.
Heretofore, a few specific types of thermoplastic
elastomers have been known. The term "thermoplastic elastomer"
has-generally been applied to elastomers which can be readily
processed and reprocessed, molded, or the like by common or
conventional thermoplastic methods and which do not require
vulcanization to develop the various physical properties.
Previous specific types of known thermoplastic
elastomers are the thermoplastic urethanes, the thermoplastic
polyesters such as the Hytrel* brand manufactured by DuPont,
and the styrene block copolymers sold under the brand names
of Kraton and Solprene manufactured, respectively, by Shell
Oil Company and Phillips Petroleum.
Another very recent thermoplastic elastomer is a
blend of polypropylene and EPDM (ethylene-propylene-non-
conjugated diene monomer) as described in U.S. Patent N~s.
3,758,743, 3,806,558, and 3,862,106 to Fischer of Uniroyal,
Inc. It is not surprising that blends of EPDM and polypropy-
lene form a material having good mechanical properties since,
due to the fact that EPDM contains a large number of monomer
units in its backbone identical to those in polypropylene,
there is good compatibility between these two polymers.
The blending of an incompatible rubber with a 1-
olefin polymer such as polypropylene can result in a material
with poor properties. Examples include polybutadiene or
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* Trade mark.
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~14'7886
nitrile rubber blended wi~h polyp~apYl~e. ~t is, thus, sur-
pris$ng that whe~ styrene~butad~ene rubber is blended wi~h a
l-olefin polymer such as polypropylene, a blend having good
physicai properties`results, since styrene-butadiene rubber is
so different from EPDM. That is, SBR contains an aromatic group
in cont~as-t to ~ almost completely al~phatic chain and, moreover,
it contains a great number of unsatur~ted groups in comparison
to the usual 2 to 4 percent unsaturation of the EPDM polymer.
Thus, the Fischer patents are not even suggestive of applicant's
present in~e~tion.
SUMMARY OF THE INVENTION
It would be advantageous to have thermoplastic
elastomer b~ends of l-olefin polymers or copolymer with styrene-
butadiene rubber.
It would also be advantageous to have thermo-
plastic elastomer blends, as above, whereln the blends may or may
not be partially cured, have good phYSical properties without any
fur~her vulcanization, and may be readily reprocessed and still
retaln their good physical properties.
It woul~ further be advantageous to have thermo-
plastic elastomer blends, as above, wherein the blends are mixed
at or aboYe the melting temperaturé of said l-olefin polymers or
copolymers.
It would additionally be advantageous to have
thermoplastic elastomer blends, as above, which may be partially
cured.
It would also be advantageous to have thermo-
plastic elastomer blends, as above, ln which both the l-olefin
polymers or copolymers and the styrene-butadiene rubber are in a
continuous phase.
Finally it would be adva~tageous to have thermo-
plastic elastomer blends, as above, which have exceedingly good
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1147886
ozone resistant and aging properties, good paint adhesion, a
low brittle point, good low temperature impact resistance,
minimum creep at high temperatures and good elongation.
Generally, the present invention provides a thermo-
plastic elastomer composition comprising a blend of a crys-
talline l-olefin polymer and styrene-butadiene rubber, said
l-olefin polymer selected from the class consisting of a homo-
polymer and a copolymer made from l-olefin monomers having
from 2 to 20 carbon atoms, said homopolymer or said copolymer
having a melting point of at least 90C, the amount of said
crystalline l-olefin polymer ranging from about 15 percent to
about 48 percent by weight based upon the total weight of said
blend, said blend including from about 2 to about 20 parts of
polyisobutylene by weight per 100 parts of said blend; and said
blend forming a thermoplastic elastomer.
In particular, the present invention provides a
thermoplastic elastomer composition, comprising, a blend of a
crystalline l-olefin polymer and styrene-butadiene rubber, said
l-olefin polymer selected from the class consisting of a poly-
propylene homopolymer and a copolymer made from a major amount
by weight of propylene monomers and a minor amount of ethylene
monomers, said propylene homopolymer containing up to about 15
percent by weight of an atactic polypropylene, said homopolymer
or said copolymer having a melting point of at least 90C,
the amoun~ of said crystalline l-olefin polymer
ranging from about 15 percent to about 48 percent by weight
based upon the total weight of said blend,
said blend lncluding from about 2 to about 20 parts
of polyisobutylene by weight per 100 parts of said blend; and
said blend forming a thermoplastic elastomer.
Additionally, the thermoplastic elastomer composition
can be partially cured to have a melt flow index of at least
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1Ø
Thus, the present invention provides a thermoplastic
elastomer composition, comprising;
a blend of a crystalline l-olefin polymer and
styrene-butadiene rubber, said l-olefin polymer selected from
. the class consistinq.of a polypropylene homopolymer and a t
copolymer made from a major amount by weight of propylene
monomers and a minor amount.of ethylene monomers, said pro-
pylene homopolymer containing up to about.l5 percent by weight
of an atactic polypropylene, said homopolymer or said copolymer
having a melting point of at least 90C,
the amount of said crystalline l-olefin polymer
ranging from about 15 percent to about 48 percent by weight
based upon the total weight of said blend,
said blend including from about 2 to about 20 parts
by weight of polyisobutylene per 100 parts of said blend,
said styrene-butadiene rubber being partially cured
and having a melt flow index of at least 1.0 to form a thermo-
plastic elastomer.
Generally, in accordance with another aspect the
present invention provides a process for making a thermoplastic
elastomer blend comprising the steps of, providing a blend of
a crystalline l-olefin polymer and styrene-butadiene rubber,
said 1-olefin polymer selected from the class consisting of a
homopolymer and a copolymer made from l-olefin monomérs having
from 2 to about 20 carbon atoms, sald homopolymer and said
copolymer having a melting point of at least 90C, the amount
of said crystalline l-olefin polymer ranging from about 15
percent to about 48 percent by weight based upon the total
weight of said blend, said blend including from about 2 to
; about 20 parts by weight of polyisobutylene per 100 parts of
said blend; and heating said blend at a temperature at or
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~147886
above the melting point of said crystalline l-olefin polymer
so that a reprocessable blend is formed.
The present invention also provides a process of
making a thermoplastic elastomer blend, comprising the steps
of;
providing a blend of a crystalline l-oLefin polymer
and styrene-butadiene rubber, said l-olefin polymer selected
from the class consisting of a polypropylene homopolymer and a
copolymer made from a major amount by weight of propylene
monomers and a minor amount of ethylene monomers,~said propyl-
ene homopolymer containing up to about 15 percent by weight of
an atactic polyprop~vlene, said homopolymer and said copolymer
having a melting point of at least 90C,
the amount of said crystalline 1-olefin polymer
ranging from about 15 percent to about 48 percent by weight
based upon the total weight of said blend,
.
said blend including from about 2 to about 20 parts
by weight of polyisobutylene per 100 parts of said blend; and
heating said blend at a temperature at or above the
melting point of said crystalline l-olefin polymer so that a
; reprocessable blend is formed.
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Add~tiona~ a p~oces~s. fo~ making ~he thermo-
plas~ic elastomer blend can include t~e ~dd~t~onal step o~ partial
curing said blend to have a ~el~ ~low ~ndex of at least 1.0
The present invent~on further provides a process
for making a thermoplastic elastomer blend, comprising the steps
of,
providin~ a blend of a ~rystalline l-olefin
polymer and styrene-butadie~e rubber, said l-olefin polyme~ selec-
ted from the class consisting of a polypropylene ho~opolymer and
a copolymer made from a major amount by weight of propylene mono-
mers and a mino~ amount of ethylene monomers, said propylene
homopolymer containing up to about 15 percent by weight of an
atactic polypropylene, sald homopolymer and said copolymer having
a melting point of at least 90C,
the amount of said crystalline l-olefin polymer
ranging from about 30 percent to about 42 percent by weight
based upon the total weight of said blend,
said blend including from about 1 to about 5
parts by weight per 100 parts of said blend of zinc oxide,
~0 said blend including from about 2 to about 20
parts by weight of polyisobutylene per 100 parts of said blend,
heating said blend at a temperature at or above
the melting point of said l-olefin polymer, and
partially curing said blend to have a melt flow
index greater than 1.0 so that a reprocessable blend is produced,
said partial cure being obtained by utilizing
a sulfur curatlve, the amount of said sulfur curative ranging
from about 0.1 parts to about 1.0 parts by weight per 100 parts
of said blend.
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~147~386
P~E~;RRl~;~ E~lBODI~IE~TS
The thermoplastic elastomers of the present
inventio~ relate to uncured or partlally cured blends of
l-olefin polymers wi~h styrene~butadiene rubber. The l~olefin
polymer can be a homopolymer or a copolymer of various l-olefin
monomers ~aving from 2 to 20 carbon atoms. Examples of suitable
- l-olefin monomers lnclude ethylene, propylene, l-butene, l-pentene,
l-hexene, l-octene, 4-methyl~l-hexene, 4-ethyl-1-hexene, 6-methyl-
~-heptene, and the like. A preferred monomer is ethylene with
a highly preferred monomer being propylene. In addition to the
homopolymers, the l-olefin polymer may be a copolymer made from
various l-olefin monomers, It is an important aspect of the
present invention that only l-olefin polymers or copolymers be
utilized which have a melting point of 90C or higher. Thus,
whenever Yarious l-olefin monomers are utilized in preparing
a copolymér, the amount o~ each must be such that a copolymer
is produced havlng a melting point of at least 90C. A preferred
copolymer is made from a major amount by weight of ethylene mono-
mers and a minor amount of propylene monomers. A highly preferred
; copolymer is made from a major amount by weight of monomers of
propylene and a minor amount by weight of ethylene monomers.
The amount by weight of a l-olefin polymer in
the total blend ranges from about 15 percent to about 48 percent
with from about 30 percent to about 42 percent being preferred.
Accordingly the remaining weight of the blend is the styrene-
butadiene rubber, that is, from 85 percent to about 52 percent
by weight with from 58 percent to about 70 percent by weight
being preferred.
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The butadiene-styrene rubber is a random copolymer
made from monomers of butadiene and styrene. The copolymer
can be prepared in any common or conventional manner well
known to the art such as through solution or emulsion polymer-
ization. Additionally, the specific type of styrene-butadiene
rubber may vary. For example, the butadiene portion may be
largely 1,2-polybutadiene, that is, as high as 90 or even
100 percentl or largely 1,4-poly-butadiene, that it, as high
as 90 or even 100 percent. The amount by weight of the
butadiene may vary greatly with a range of from about 60
percent to about 90 percent by weight based upon the total
copolymer being desirable, although larger or smaller amounts
can be used. The number average molecular weight of the
copolymer may range from about 50,000 to about 1,000,000.
Similarly, the l-olefin polymer such as the preferred
polyéthylene and the highly preferred polypropylene may be
prepared in any common or conventional manner so long as it is
largely crystalline such as an isotactic configuration.
Generally, the melt flow index of the isotactic l-olefin
polymer and especially isotactic polypropylene can range from
about 0.4 to about 30 with a preferred range being from about
2 to about 12 according to ASTM N. D1238. Thus, an isotactic
l-olefin polymer is primarily utilized, although an amount
such as from 0.1 up to about 15 percent by weight based upon
the total weight of the l-olefin polymer of a low crystalline
- atactic configuration may be utilized. Hence, in the highly
preferred embodiment, isotactic polypropylene is utilized
along with small amounts of atactic polypropylene. Small
amounts of the atactic configuration of a particular l-olefin
polymer are not only economical but also improve flow and does
not significantly reduce the various physical properties.
Generally, amounts in excess of a total of 15 percent of an
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~147886
atactic configuration of a specific l-olefin polymer are
undesirable since the physical properties are reduced; but,
in some applications, such a blend may be acceptable and even
desirable.
Regardless of the specific type of l-olefin polymer
utilized, the particle size is that produced by normal and
conventional polymerization techniques. Generally, the
; particle size is greater than 1.0 microns and desirably
larger than 5.0 microns, although any particle size may be
utilized. From a practical standpoint, large particles such
as up to 2 mm may be conveniently utilized, as well as even
larger particles. Of course, since the l-olefin polymer is
generally blended with the styrene-butadiene rubber on a mill,
large particles such as diced polypropylene may be utilized.
It has been found that the addition of from about
2 to about 20 parts of polyisobutylene per 100 parts of said
blend, surprisingly, improves the texture, smoothness, and
surface gloss of injection molded plaques and gives improved
tensile elongation when added to a blend of a l-olefin such
as polypropylene and styrene-butadiene rubber.
The blend of the l-olefin polymer and the styrene-
butadiene rubber, whether or not partially cured, results in
a thermoplastic elastomer. That is, the blend is considered a
thermoplastic elastomer in that it can be repeatedly reprocess-
ed and, if partially cured, does not require further
vulcanization to develop elastomer properties. In other
words, the blend can be readily and repeatedly molded, extruded,
or otherwise processed since it flows at temperatures at or
above the melting point of the l-olefin polymer. Generally,
a partial cure is preferred in that the properties exhibit
improved tensile set as well as a remarkable increase in
aging properties.
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1147886
By partial cure, it is meant that the styrene-
butadiene rubber portion of the blend is crosslinked to an
extent less than full cure or vulcanization. According to
the concepts of the present invention, a partial cure is
achieved when the melt flow index (ASTM N. D1238, condition
"L", but with the exception that the load is 100 pounds) is
at least 1.0 and preferably 10.0 or greater. Blends of the
l-olefin polymer and styrene-butadiene rubber which are cured
in excess of a partial cure and, thus, have a melt flow index
below 1.0 result in vulcanized blends or thermoset elastomers
which are clearly outside the scope of the present invention~
The partial cure may be obtained utilizing any conventional
curing agent compound or method as set forth below. Generally,
good blends of the present invention will have a melt flow
index of from about 90 to about 150 with a preferred melt
flow index of approximately 120.
It is a critical aspect of the present invention
that the l-olefin polymer and the styrene-butadiene rubber
be mixed together at a temperature equal to or greater than the
melting point of the 1-olefin polymer. Due to variations in
molecular weight and tacticity, the melting point will vary
over a small range for the particular 1-olefin polymer. The
typical polyethylene will have a melting point range of from
about 127C to about 140C with a typical melting point of
approximately 135C. The melting point range for the highly
preferred polypropylene is from about 150C to about 175C
with a practical or typical melting point temperature of about
160C. Thus, temperatures within this range, or desirably
above it, are necessary to the present invention. The actual
blending or mixing may be according to any common or conven-
tional mixing process and, thus, may conveniently take place
on a mill, a Banbury, a Brabender, a twin screw extruder, or
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~47886
the like. When a partial cure is utilized, preferably, the
two components are first blended and then partially cured,
although the styrene-butadiene rubber can be initially,
partially cured and then blended with the 1-olefin polymer.
Another method of preparation involves the addition
of all dry ingredients to a styrene-butadiene rubber latex.
When the SBR latex is coagulated by standard and well known
techniques, all ingredients are intimately mixed. This
mixture is then mixed in any manner, as on a mill, at tempera-
tures above the melting point of the polypropylene and the
thermoplastic elastomer blend is formed.
If a partial cure is utilized, the curing agent can
be conveniently added as well as other conventional processing
aids, compounding ingredients, and the like either before or
during the blending step. Moreover, the partial cure may be
achieved under either static conditions or under dynamic
co~ditione. Under static conditions, the partial cure can be
achieved by placing a mixed blend containing the curing agent
in an oven and heating to a desired temperature whereby partial
cure occurs such as at a temperature of from about 65C to
about 260C for approximately 5 to 30 minutes. The dynamic
partial cure is achieved by working or processing the blend
containing the curing agent on an open mill, in a Banbury,
in an extruder, or the like, at a temperature sufficient to
bring about a partial cure such as from about 65C to about
210C for approximately 5 to 20 minutes. Even if the dynamic
cure occurs below the melting point of the l-olefin polymer,
the dynamic blend temperature must be at a temperature above
the melting point of the l-olefin polymer.
As noted, the curing agent utilized, when a partial
cure is desired, may be any known or conventional-~rubber
curative or method known to those skilled in the art.
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Variations from standard procedures or compounds may, of
course, be utilized. Typical types of curing a~ents include
the sulfur curatives such as sulfur, itself, or sulfur donors,
the various peroxides. whether aromatic or aliphatic, and low
dosages of irradiation. If a sulfur curative is utilized,
generally from 0.01 to about 1.0 parts by weight per 100
parts of the blend is utilized with the preferred range being
from about 0.1 to about 0.2 parts. Some representative
examples of sulfur curatives include sulfur, tetramethyl
- 10 thiorea, 2-(hexamethyleniminothio)-benzothiazole, sulfur
dichloride, sulfur monochloride, alkyl phenol, disulfide,
and tetramethyl thiuram disulfide. A preferred curative is
sulfur, itself. Generally, it is desirable to use from about
1 to about 5 parts per 100 parts of blend of zinc oxide,
conventional amounts of stearic acid and an accelerator since
very good antioxidant properties are imparted to the blend.
In addition, this particular partial cure system in combina-
tion with carbon black, surprisingly, gives superior paint
adhesion. These unexpected results are especially noted with
regard to the highly preferred l-olefin polymer of polypropy-
lene.
The amount of the organic peroxides to effect a
partial cure generally varies from about 0.01 to about 0.5
parts by weight per 100 parts of the blend with a preferred
range being from about 0.1 to about 0.3. Once again, any
conventional peroxide compound may be utilized such as the
aromatic diacyl peroxides, the aliphatic diacyl peroxides,
dibasic acid peroxides, ketone peroxides, alkyl peroxyesters,
alkyl hydroperoxides, and the like. Specific examples include
dicumyl peroxide, dibenzoyl peroxide, diacetyl peroxide,
bis-2,4-dichlorobenzoyl peroxide, ditertiary-butyl peroxide,
tertiary-butylcumyl peroxide, and the like, Of course, the
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number of the various peroxides is enormous and any of them
can be utilized, with the above specific compounds merely
being representative examples. A preferred peroxide curative
is dicumyl peroxide and 2,5-bis(tertiary-butylperoxy)2,5-
dimethylhexane.
Of course, multiple peroxide curatives, multiple
sulfur curatives, as well as combinations of sulfur and
peroxide curatives may be utilized as well known to those
skilled in the art. Furthermore, the amount of the curative
range sét forth above, naturally, represents the amount of
the active compound. Thus, if a curative is utilized such as
dicumyl peroxide in a solvent system, only the weight of
dicumyl peroxide itself is considered. Additionally, the
exact amount of a specific curative utilized to obtain a
specific melt flow index will vary from one specific curative
to another, depending on the general activity or efficiency
of the specific curatives.
Another method of achieving the partial cure
involves subjecting the blend to ionizing irradiation.
Ionizing rays include alpha rays, beta rays, gamma rays,
electron beam, proton rays, neutron rays, and X-rays. In
most commercial applications, an accelerated electron beam is
utilized. The irradiation is desirably carried out by
subjecting pellets or a thin layer of the blend to the
irradiation. The irradiation may be admitted from one side
or from both sides of the blend composition. The amount of
irradiation, of course, will vary with the thickness of the
blend composition. In any event, a desirable amount of
irradiation is that which results in a partially cured blend
having a melt flow index above the index number set forth
above. Due to the inherent nature of the irradiation applica-
tion, the cross-link density of the styrene-butadiene
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copolymers will vary with the distance from the irradiated
surface. This aspect is acceptable as long as an overall,
partially cured system is produced~ However, too high of a
dose will result in a cross-linked system which cannot be
molded or extruded, that is, is not reprocessable. Generally,
when the irradiation is admitted to only one side of the blend
composition, the amount of irradiation may bary from about 0.1
to about 5.0 Megarads when an electron accelerator is utilized
~ and from about 0.1 to about 3.0 Megarads when the irradiation
is applied to each side of the blend composition~.
In addition to the curing agents, as noted above,
other rubber components, compounding agents, fillers, process-
ing aids, and the like may be added in conventional amounts.
Specific types of additives include in addition to accelerators,
activators, colorants, antioxidants, flame retardants, ozone
resistant compounds, and various processing aids such as oil,
stearic acid, and the like. Examples of fillers include
carbon black, such as from about 0.1 and preferably from about
0.6 parts to about 30 to 40 parts by weight per 100 parts of
the blend. Other fillers such as silica, the various clays,
calcium carbonate, talc, and the like can be utilized in
conventional amounts.
The blends of the present invention, whether or not
partially cured, generally have good physical properties and
generally consists of two continuous phases. A fe~ of the
properties were completely unexpected such as the low brittle
point. Other unexpected properties include minimum creep at
high temperatures, good low temperature impact resistance,
good elongation, good paint adhesion, and good ozone and aging
resistance. Generally, the unexpected properties as set forth
hereinbelow are generally achieved by the blends of the present
invention regardless of the exact amount of l-olefin polymer
D _ 13 _
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such as polypropylene and whether or not partially cured.
However, as previously noted, partially cured blends did give
improved tensile set as well as improved ageing properties.
Generally, the thermoplastic elastomer blends of the present
invention achieved an elongation of at least 50 percent at
break and, preferably at least 200 percent. The maximum
creep was less than 4 percent at 120C under a load of 0.08
MPa. The blends did not show any ozone cracking when tested
according to ASTM D518. The low temperature impact at minus
30C and paint scuff resistance were good as illustrated in
the examples. The brittle point of the blends is generally
- below minus 20C and, preferablyl below minus 45C. I
The aspect of the ozone resistance was completely
unexpected in that, as well known to those skilled in the art,
copolymers of styrene and butadiene exhibit poor ozone resis-
tance. Moreover, the blends also had very good flexibility
properties and exhibited very good heat aging properties upon
the addition of various heat resistant agents.
The exact combination of physical properties desired
will depend upon the intended applications. For example, in
automotive exterior applications, it is imperative that the
material be able to withstand impact at low temperature. When
the same material is used to make a kitchen spatula, low
temperature impact is irrelevant. The thermoplastic elastomer
blends of the present invention are very versatile and
flexible in that changes of the composition ratio of SBR to the
l-olefin polymer and especially to polypropylene and changes
of compounding additives, make it possible to generate a
wide range of desired physical properties. These changes will
be obvious to those skilled in the art of rubber or plastics
compounding.
The thermoplastic elastomer blends of the present
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~478~6
invention may be utilized to produce articles as by molding,
extruding, calendaring, vacuum-forming, and the like with
specific articles including tubing, gaskets, toys, and house-
hold articles. A desired area of use resides in various
automobile parts such as flexible bumpers, dash panels, bumper
filler panels, and the like.
The invention will be better understood by reference
to the various examples.
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7886
The following list identifies the various materials
used in the examples.
.~
Profax 6523 PM an isotactic polypropylene with a melt
flow index of 4.0, made by Hercules,
Inc.
FRS-2006 a Firestone "hot" emulsion polymeriæed
SBR copolymer with 23.5 percent bound
styrene, ML/4/212 = 50.
.~
FRS-1502 a Firestone ~cold" emulsion polymerized
SBR copolymer with 23.5 percent bound
styrene, ML/4/212 ~ 45.
Stereon 750 a Firestone solution polymerized BD/
styrene copolymer with 18 to 21 percent
bound styrene, ML/4/212 = 45 to 47
when oil extended with 37.5 pphr oil.
However, the examples used Stereon 750
with ho oil.
Stereon 700 a Firestone solution polymerized BD/
styrene copolymer with 18 to 21 per-
cent bound styrene, ML/4/212 = 50 to
60.
! Varox peroxide 2,5-bis(tert-butylperoxy)-2,5-dimethyl
¦ hexane - made by ~niroyal.
Santocure NS an accelerator, N-t-butyl-2-benzothia-
zolesulfenamide made by Monsanto
Chemical Co.
Afax 500 HL-l an atactic polypropylene wi~h a vis-
l cosity range of 2.5 to 5.5 Pa made by
20 ¦ Hercules, Incorporated.
¦ Vitanex L-120 polyisobutylene made by Exxon.
¦ Agerite Super- butylated bisphenol A, made by RT
¦ lite Solid Vanderbilt Company.
Irganox 565 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-
l di-tert-butylanilino)-1,3,5-triazine
¦ made by Ciba-Geigy Chemical Corporatio n.
I I
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EXAMPLE I
SBR/PP = 60/40 BY LATEX COAGULATION
Five hundred sixty grams of Profax 6523 PM poly-
propylene (PP) was stirred into 2 liters of water with 0.5 ml
Triton X-100 wetting agent. To this was added 3.03 liters of
FRS 2006 SBR latex with 27.7 percent solids to provide 840
grams of SBR rubber. While stirring vigorously, 4 liters of
methanol was added and then 10 ml H2S04 which had been
- diluted with water to 150 ml. The SBR coagulated rapidly
upon addition of the acid, trapping essentially all of the
polypropylene. The liquid was poured off and the coagulant
mass was washed several times before again being washed and
sheeted on a wash mill. The SBR with trapped polypropylene
powder was dried for 15 hours at 75C. The material was then
blended in a twin screw extruder on which all six heat zones
were held between 190C to 220C. The extrudate was chopped
into pellets to be injection molded. The following properties
were obtained:
Tensile at break 8.27 MPa
Elongation at break 2.88
(Tested at room temperature at 2,000 percent/minute
strain rate. No cracks due to ozone aging (60 pphm
ozone at 37C for 14 hours.)
EXAMPLE II
STEREON 750/PP 60/40
Profax 6523 PM in the amount of 1.2 kg. was stirred
into 7.2 kg hexane cement of Stereon 750 Duradene without oil
which had a 25 percent solids content to provide 1.8 kg of
Stereon 750 rubber. The mixture was dried on a drum dryer
which was steam heated to-about 150C. The polypropylene
powder was firmly held in the sheeted rubber until the
mixture was blended in a twin screw extruder on which all six
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heat zones were held at 190C to 220C. The extrudate was
chopped into pellets to be injection molded.
EXAMPLE III
STEREON 750/PP - 70/30
The procedure was identical to Example II, except
there were 2.1 kg Stereon 750 and 0.9 kg of Profax 6523 PM
utilized.
Examples II and III gave the following physical
properties:
TENSILE AT BREAK ELONGATION AT B~EAK
EXAMPLE II10.4 MPa 170
EXAMPLE III7.94 252
EXAMPLES IV THRO~GH XIII
DRY MIXING
The styrene-butadiene rubber was sheeted out on a
two roll mill at a temperature between 90-120C. The
remaining ingredients (set forth in Table I) were added, and
milling was continued until the additives were well dispersed
in the rubber. The blend was then cut into strips so that
20 it could easily be fed into a twin screw extruder. The
material was extruded at 200C into a quenching water bath
and subsequently chopped into small pellets, which were then
injection molded into plaques (15.2 x 10.2 x 0.2 cm). The
plaques were tested for physical properties.
Table I also lists several properties of the blends.
All tests are according to ASTM standards except the paint
adhesion and cold impact test which will, therefore, now be
described in more detail.
PAINT A~HESION TEST
-
Before painting, a test plaque was first washed
with a mild alkaline solution and water rinsed. After drying,
the plaque was then sprayed with Seibert Oxidermo primer and
B 18
~147886
flash dried for at least 2 minutes. A topcoat of Durethane
100 was then applied and cured for 40 minutes at 120C. The
paint scuff resistance was evaluated by scratching the
painted surface with the edge of a dime. For surfaces
showing excellent paint adhesion, the paint could not be
scraped cleanly from the surstrate. When adhesion was poor,
the paint could be easily stripped off with only mild pressure
exerted on the dime.
COLD IMPACT TEST
The cold impact test utilized was that General
Motors requires flexible thermoplastic elastomer parts to
. .
pass. For this test, the ends of a painted specimen (7.62 x
15.2 x 0.3 cm) were inserted into grooves that were cut into
a base plate 7.62 cm apart. The test sample was then allowed
to equilibrate at minus 30C for at least four hours. After
this, the dome-like test specimen was impacted at the apex
by a hemispherical dart (5 cm. diameter, 27 kg) dropped from
a height of 32.2 cm. In order to pass this test, the sample
must not break or crack.
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~147886
In addition to the properties given in Table I, it
is noted that all samples show no ozone cracking when tested
according to ASTM D518, and show less than 5 percent creep
when tested 30 minutes at 120C under a stress of 0.08 MPa.
To illustrate the ready reprocessability of the
blends, the blends of Example VIII were re-extruded three
times before in~ection molding. Essentially, identical
tensile properties were obtained when compared to the blend
which had been only extruded once and then molded.
While in accordance with the patent statutes,
various preferred embodiments have been illustrated and
described in detail, it is to be understood that the
invention is not limited thereto, the scope of the invention
being measured by the scope of the attached claims.
I
~ - 22 -
