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Thermoplastische Vulkanisate von Vernetzung mittels Hydrosilylierung von acrylmodifiziertem Bromparamethylstyrol-Isobutylen Kautschuk
This invention relates to thermoplastic vulcanizate compositions
prepared using hydrosilylation crosslinking of the rubber component of the composition.
A thermoplastic vulcanizate is generally defined as a polymer or blend of polymers
that can be processed and recycled in the same way as a conventional thermoplastic
material, yet has properties and functional performance similar to that of vulcanized
rubber at service temperatures. Blends or alloys of plastic and rubber have become
increasingly important in the production of high performance thermoplastic vulcanizates,
particularly for the replacement of thermoset rubbers in various applications.
The acrylic modification of the butyl rubber results in faster, more efficient
crosslinking of butyl rubber with hydrosilylation crosslinking.
BACKGROUND OF THE INVENTION
Polymer blends which have a combination of both thermoplastic and
elastic properties are generally obtained by combining a thermoplastic resin with
an elastomeric composition in a way such that the elastomer component is intimately
and uniformly dispersed as a discrete particulate phase within a continuous phase
of the thermoplastic. Early work with vulcanized rubber components is found in
U.S. Pat. No. 3,037,954 which discloses both static vulcanization of the rubber,
as well as the technique of dynamic vulcanization wherein a vulcanizable elastomer
is dispersed into a molten resinous thermoplastic polymer and the elastomer is
cured while continuously mixing and shearing the blend. The resulting composition
is a micro-gel dispersion of cured elastomer in an uncured matrix of thermoplastic
In U.S. Pat. No. Re. 32,028 polymer blends comprising an olefin thermoplastic
resin and an olefin copolymer are described, wherein the rubber is dynamically
vulcanized to a state of partial cure. The resulting compositions are reprocessible.
U.S. Pat. Nos. 4,130,534 and 4,130,535 further disclose thermoplastic vulcanizates
comprising butyl rubber and polyolefin resin, and olefin rubber and polyolefin
resin, respectively. The compositions are prepared by dynamic vulcanization and
the rubber component is cured to the extent that it is essentially insoluble in
conventional solvents. A range of crosslinking, or curing, agents for the vulcanization
of the rubber are described in the early art, including peroxides, sulfurs, phenolic
resins, radiation, and the like.
U.S. Pat. No. 4,803,244 generally discusses the use of multifunctional
organosilicon compounds in conjunction with a catalyst as an agent for crosslinking
the rubber component of a thermoplastic elastomer by hydrosilylation. Hydrosilylation
involves the addition of a silicon hydride across a multiple bond, often with a
transition metal catalyst. This patent describes a rhodium catalyzed hydrosilylation
of EPDM rubber in a blend with polypropylene.
A further modification of hydrosilylation crosslinking of the rubber
in a thermoplastic elastomer composition is disclosed in European Patent Application
No. 651,009. A compatibilizing agent containing in the same molecule a component
having an affinity for the rubber and a component having an affinity for the thermoplastic
resin is incorporated into the composition, and is said to improve adhesion between
the rubber and resin in order to prevent agglomeration.
U.S. Patent 5,672,660 generally describes thermoplastic elastomers
prepared by hydrosilylation crosslinking of rubbers polymerized from monomers
including specific dienes. The use of lower amounts of platinum catalysts was also
SUMMARY OF THE INVENTION
The present invention is based on the discovery that the process for
hydrosilylation crosslinking of the rubber in a thermoplastic vulcanizate wherein
the rubber is a copolymer of at least isobutylene and paramethyltyrene which was
post polymerization functionalized with a carbon-carbon double bond from an acrylic
or alkacrylic group. This combination provides rapid crosslinking of the rubber
to a fully vulcanized state, yet requires an unexpectedly low concentration of
the catalyst in order to achieve the cure. In the instant invention no compatibilizer
is required in order to produce compositions with excellent mechanical properties,
no bubble formation and very good colorability, due to the extremely low levels
of catalyst concentration. Surprisingly, lower catalyst concentrations also produce
compositions with much improved heat aging characteristics, resistance to degradation
by ultraviolet light and having a non-hygroscopic character.
The compositions produced by the improved process have utility as
replacements for thermoset rubber compounds in a variety of applications, particularly
where molding or extrusion is involved and the combination of thermoplastic and
elastomeric properties provides an advantage. Typical uses include molded articles
for automobile underhood parts, engineering and construction materials, mechanical
rubber goods, industrial parts such as hose, tubing and gaskets, electrical applications
and household goods.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Thermoplastic vulcanizate compositions may generally be prepared by
blending a thermoplastic resin and a rubber, then melting the thermoplastic component
and mixing the melt until the blend is homogeneous. If a composition of vulcanized
rubber in a thermoplastic matrix is desired, crosslinking agents (also referred
to as curatives or vulcanizing agents) are added to the blend and crosslinking
occurs during the mixing. This latter process is described as dynamic vulcanization.
A wide range of thermoplastic resins and rubbers and/or their mixtures
have been used in the preparation of thermoplastic elastomers, including polypropylene,
HDPE, LDPE,VLDPE, LLDPE, cyclic olefin homopolymers or copolymes as well as olefinic
block copolymers, polystyrene, polyphenylene sulfide, polyphenylene oxide and ethylene
propylene copolymer (EP) thermoplastics, with ethylene propylene diene rubber
(EPDM), acrylonitrile butadiene rubber (NBR) and natural rubber (NR) as the elastomers.
When the elastomer component is crosslinked, agents such as sulfur, peroxide, phenolics
and ionic compounds are often used.
Hydrosilylation has also been disclosed as a crosslinking method.
In this method a silicon hydride having at least two SiH groups in the molecule
is reacted with the carbon-carbon multiple bonds of the unsaturated (i.e. containing
at least one carbon-carbon double bond) rubber component of the thermoplastic elastomer,
in the presence of the thermoplastic resin and a hydrosilylation catalyst. Silicon
hydride compounds useful in the process of the invention include methylhydrogen
polysiloxanes, methylhydrogen dimethyl-siloxane copolymers, alkyl methyl polysiloxanes,
bis(dimethylsilyl)alkanes and bis(dimethylsilyl)benzene.
Preferred silicon hydride compounds may be described by the formula
where each R is independently selected from the group consisting of alkyls comprising
1 to 20 carbon atoms, cycloalkyls comprising 4 to 12 carbon atoms and aryls. In
formula (1) it is preferred that each R be independently selected from a group
consisting of alkyls comprising 1 to 6 carbon atoms. Even more preferred is R =
methyl. R' represents a hydrogen atom, an alkyl or alkoxy group having from 1 to
about 24 carbon atoms. R'' represents R or a hydrogen atom.
D represents the group
D' represents the group
T represents the group
m is an integer having a value ranging from 1 to 50,
n is an integer having a value ranging from 1 to 50, and
p is an integer having a value ranging from 0 to 6.
Particularly preferred polyorganosiloxanes are those in which the
silicon atom of the silicon hydride functionality is bound by heteroatoms/atoms
having lone pairs of electrons. The preferred polyorganosiloxanes may also be substituted
with appropriate functionality permitting solubility in the reaction media. A type
of this functionalization is described in U.S. Pat. No. 4,046,930 which teaches
alkylation of polyorganosiloxanes. Weight percent of alkylation should not exceed
a level that does not permit adequate reaction rates due to steric constraints.
The amount of silicon hydride compound useful in the process of the
present invention can range from about 0.1 to about 10.0 mole equivalents of SiH
per carbon-carbon double bond in the rubber, and preferably is in the range of
about 0.5 to about 5.0 mole equivalents of SiH per carbon-carbon double bond in
the rubber component of the thermoplastic elastomer.
Thermoplastic resins useful in the compositions produced by the invention
include crystalline polyolefin homopolymers and copolymers. They are desirably
prepared from monoolefin monomers having 2 to 20 carbon atoms, such as ethylene,
propylene, 1-butene, 1-pentene and the like, as well as copolymers derived from
linear and cyclic olefins, with propylene being preferred. As used in the specification
and claims the term polypropylene includes homopolymers of propylene as well as
reactor copolymers of polypropylene which can contain about 1 to about 20 wt% of
ethylene or an - olefin comonomer of 4 to 20 carbon atoms, and mixtures thereof.
The polypropylene can be crystalline, isotactic or syndiotactic polypropylene.
Commercially available polyolefins may be used in the practice of the invention.
Other thermoplastic resins which are substantially inert to the rubber, the silicon
hydride and the hydrosilylation catalyst would also be suitable. Blends of thermoplastic
resins may also be used.
The amount of thermoplastic resin found to provide useful compositions
is generally from about 5 to about 90 weight percent, based on the weight of the
rubber and resin. Preferably, the thermoplastic resin content will range from about
20 to about 80 percent by weight of the total polymer. This can also be expressed
as a weight ratio of the thermoplastic resin to the rubber(s) of 5:95 to 90:10
more desirably 20:80 to 80:20.
Desirably the rubber is an acrylic or alkacrylic group functionalized
(modified by adding the functional group) copolymer of at least isobutylene and
paramethylstyrene. By the term acrylic or alkacrylic group, applicant means acrylic
or aklacrylic or combinations thereof. The term alkacrylic is intended to express
that the acrylic can have an alkyl or alkenyl substituent thereon of 1 to 5 carbon
atoms, preferably methyl or ethyl. The functionalization reaction involves halogenating
the copolymer of isobutylene and paramethyl styrene as set forth in EP publication
no. 0 344 021 (preferably by bromination) and then reacting the brominated polymer
where R1 and R2 are H or an alkyl of 1 to 5 carbon atoms and
R3 is H, an alkyl or an alkenyl of 1 to 5 carbon atoms. The amount of
acrylic or alkacrylic groups per polymer chain can vary depending on the properties
desired. Desirably, the number of moles of acrylic or alkacrylic or combinations
thereof, if both are present, is from about 0.1 to about 5 moles %, more desirably
from about 0.3 to about 1.5 moles % based upon the total moles of repeat units..
Desirably, the copolymer of isobutylene and paramethylstyrene comprises
repeat units from at least isobutylene and paramethyltyrene. Other copolymerizable
monomers can be present in small amounts. The amount of repeating units from isobutylene
is desirably from about 80 to about 99 weight percent, more desirably from about
90 to about 99 weight percent and the amount of repeat units from paramethylstyrene
is from about 1 to about 20 weight percent and more desirably from about 1 to about
10 weight percent.
While a preferred embodiment is using the acrylic or alkacrylic group,
or combinations thereof functionalized copolymer of isobutylene and paramethylstyrene
as the entire rubber component, it is possible to use a blend of said copolymer
with the rubbers listed below. Desirably in a blend of the copolymer with other
rubbers the copolymer is a majority by weight of the total rubbers in the thermoplastic
Unsaturated rubbers useful to prepare thermoplastic vulcanizates
include monoolefin copolymer rubbers comprising non-polar, rubbery copolymers of
two or more -monoolefins, preferably copolymerized with at least one polyene, usually
a diene. However, unsaturated monoolefin rubber such as EPDM rubber is more suitable.
EPDM is a polymer of ethylene, propylene and one or more non-conjugated diene or
non-conjugated dienes, and the monomer components may be polymerized using Ziegler-Natta
or metallocene catalyzed reactions, among others. Satisfactory non-conjugated
dienes include 5-ethylidene-2-norbornene (ENB); 1,4-hexadiene (HD); 5-methylene-2-norbornene
(MNB); 1,6-octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 1,3-cyclopentadiene;
1,4-cyclohexadiene; dicyclopentadiene (DCPD); 5-vinyl-2-norbornene (VNB) and the
like, or a combination thereof.
It has been found that rubber having a structure in which the diene
monomer has carbon-carbon multiple bonds which are predominately unencumbered,
i.e. bonds which are sterically unhindered such as terminal or pendant double bonds,
provide a greatly improved rate of cure in the hydrosilylation curing process of
the invention. Structures in which the bonds either normally are unencumbered or
are easily isomerized to form a sterically unencumbered double bond, are rapidly
hydrosilated, e.g. 1,4-hexadiene or ENB. This use of sterically unhindered carbon-carbon
multiple bonds is particularly beneficial where a fully cured rubber component
is desired. The use of an additional rubber in which the diene component is selected
from the group consisting of 5-ethylidene-2-norbornene, 5-methyl-1,4-hexadiene,
1,4-hexadiene and 5-vinyl-2-norbomene is preferred. 5-vinyl-2-norbomene is particularly
preferred as a diene component of such rubber.
Butyl rubbers are also useful as additional rubbers in the compositions
of the invention. As used in the specification and claims, the term "butyl rubber"
includes copolymers of an isoolefin and a conjugated monoolefin, terpolymers of
an isooolefin, a conjugated monoolefin and divinyl aromatic monomers, and the halogenated
derivatives of such copolymers and terpolymers. The useful butyl rubber copolymers
comprise a major portion of isoolefin and a minor amount, usually less than 30
wt%, of a conjugated multiolefin. The preferred copolymers comprise about 85-99.5
wt% of a C4-7
isoolefin such as isobutylene and about 15-0.5 wt% of a
multiolefin of 4-14 carbon atoms, such as isoprene, butadiene, dimethyl butadiene,
4-methyl-1,4-pentadiene and piperylene. Commercial butyl rubber, useful in the
invention, is a copolymer of isobutylene and minor amounts of isoprene. Other butyl
co-and terpolymer rubbers are illustrated by the description in U.S. Pat. No.
4,916,180. Isobutylene/divinylbenzene is particularly preferred as an elastomer
suitable for hydrosilylation crosslinking.
A further rubber suitable in the invention is natural rubber. The
main constituent of natural rubber is the linear polymer cis-1,4-polyisoprene.
It is normally commercially available in the form of smoked sheets and crepe.
Synthetic polyisoprene can also be used with the particularly preferred synthetic
polyisoprene elastomers being those that contain vinyl functionality pendant to
the main polymer chain, i.e. 1,2-enchainments.
Polybutadiene is also a suitable elastomer for hydrosilylation curing
with polybutadienes that contain vinyl functionality being the most preferred.
In preparing the compositions of the invention, the amount of rubber
generally ranges from about 95 to about 10 weight percent, based on the weight
of the rubber and thermoplastic resin. Preferably, the rubber content will be in
the range of from about 80 to about 20 weight percent of total polymer.
It has previously been understood that any catalyst, or catalyst
precursor capable of generating a catalyst in situ, which will catalyze the hydrosilylation
reaction with the carbon-carbon bonds of the rubber can be used. Such catalysts
have included transition metals of Group VIII such as palladium, rhodium, platinum
and the like, including complexes of these metals. Chloroplatinic acid has been
disclosed as a useful catalyst in U.S. Pat. No. 4,803,244 and European Application
No. 651,009, which further disclose that the catalyst may be used at concentrations
of 5 to 10,000 parts per million by weight and 100 to 200,000 parts per million
by weight based on the weight of rubber, respectively.
It has been found in the process of the present invention that significantly
lower concentrations of platinum-containing catalyst can be used, while obtaining
improvement in both the speed of the reaction and the efficiency of the crosslinking.
Concentrations of catalyst in the range of about 0.1 to about 10, 20, or 40 parts
per million by weight, expressed as platinum metal, are effective in rapidly and
completely curing the rubber in the process of dynamically vulcanizing blends of
thermoplastic resin and rubber. These low catalyst concentrations are particularly
effective in combination with acrylic or alkacrylic or combinations thereof functionalized
copolymer of isobutylene and paramethyl styrene having carbon-carbon multiple bonds
which are predominately sterically unhindered Catalyst concentrations of about
1 to about 25 parts per million by weight based on the weight of rubber, expressed
as platinum metal, are particularly preferred.
Platinum-containing catalysts which are useful in the process of the
invention are described, for example, in U.S. Pat. No. 4,578,497; U.S. Pat. No.
3,220,972; and U.S. Patent No. 2,823,218 all of which are incorporated herein
by this reference. These catalysts include chloroplatinic acid, chloroplatinic
acid hexahydrate, complexes of chloroplatinic acid with symdivinyltetramethyldisiloxane,
dichloro-bis(triphenylphosphine) platinum (II), cis-dichloro-bis(acetonitrile)
platinum (II), dicarbonyldichioroplatinum (II), platinum chloride and platinum
oxide. Zero valent platinum metal complexes such as Karstedt's catalyst are particularly
preferred, as described in U.S. Pat. No. 3,775,452; U.S. Pat. No. 3,814,730; and
U.S. Pat. No. 4,288,345 all of which are incorporated herein by this reference.
In order for the catalyst to function most efficiently in the dynamic
vulcanization environment, it is important that it is inherently thermally stable,
or that its activity is inhibited to prevent too rapid a reaction or catalyst
decomposition. Appropriate catalyst inhibitors that are suitable to stabilize the
platinum catalyst at high temperatures include 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane
and its higher analogs such as methylvinyl cyclic pentamer. However, other olefins
that provide stable, yet catalytically active platinum metal complexes include
maleates, fumarates, and substituted alkynes. It is also particularly preferred
in the invention to use a catalyst that remains soluble in the reaction medium.
The thermoplastic elastomer may contain conventional additives, which
can be introduced into the composition in the thermoplastic resin, the rubber,
or in the blend either before, during or after the hydrosilylation and curing.
Examples of such additives are antioxidants, processing aids, reinforcing and nonreinforcing
fillers, pigments, waxes, rubber processing oil, extender oils, antiblocking agents,
antistatic agents, ultraviolet stabilizers, plasticizers (including esters), foaming
agents, flame retardants and other processing aids known to the rubber compounding
art. Such additives may comprise from about 0.1 to about 300 percent by weight
based on the weight of the final thermoplastic elastomer product. Fillers and extenders
which can be utilized include conventional inorganics such as calcium carbonate,
clays, silica, talc, titanium dioxide, carbon black and the like. Additives, fillers
or other compounds which may interfere with the hydrosilylation should be added
after curing reaches the desired level.
In another embodiment, it has been found that the heat aging properties
of compositions prepared according to the invention can be greatly improved by
the addition of a metal chelating agent to the blend. This effect is believed to
be due to the fact that the hydrosilylation catalyst is in an active valence state.
This form of the platinum metal accelerates degradation of the thermoplastic elastomer,
particularly under conditions of elevated temperature over an extended time. Chelation
prevents the metal from causing degradation.
Typical chelating agents useful for this purpose include materials
such as 1,2-bis(3,5-di-ter-butyl-4-hydroxyhydrocinnamoyl)hydrazine and the like.
Surprisingly, these agents may be incorporated into the composition prior to or
after the hydrosilylation curing. Amounts of chelating agent ranging from about
0.025 parts per hundred parts of rubber (phr) to about 10 phr have been found to
be useful, and amounts in the range of about 0.1 phr to 2 phr are preferred.
In a further embodiment of the invention, it has been demonstrated
that reducing residual or unreacted silicon hydride functionality in the thermoplastic
elastomer products results in compositions which have improved heat stability.
Unreacted silicon hydride may be reduced or eliminated by reacting the silicon
hydride with compounds containing active hydrogen, carbon-carbon multiple bonds,
carbon-oxygen double bonds or carbon-nitrogen double bonds and the like. The residual
silicon hydride reacts with these compounds to eliminate silicon hydride functionality
and form silicon-oxygen or carbon-silicon bonds.
Typical compounds useful for this purpose are silica and water. These
agents are incorporated into the composition after the hydrosilylation cure is
complete. Water may be introduced as steam anytime after cure in a single or two
pass operation. Amounts of such compounds may be estimated by measuring residual
silicon hydride and adding a stoichiometric amount of the compound. One may also
desire to add a stoichiometric excess if necessary to eliminate a sufficient amount
of the residual silicon hydride in order to realize the desired improvement in
heat aging properties. Amounts of such compounds ranging from about one mole equivalent
to about 10 mole equivalents have been found to be useful, and amounts in the range
of about 1 to 3 mole equivalents are preferred.
The rubber processing or extender oils used in thermoplastic elastomers
generally are paraffinic, naphthenic or aromatic oils derived from petroleum fractions.
The type will be that ordinarily used in conjunction with the specific rubber or
rubbers present in the composition, and the quantity based on the total rubber
content of the thermoplastic elastomer may range from zero to several hundred pans
per hundred rubber. Important to the efficiency of the catalyst is that the oils
and other additives contain no or very low concentrations of compounds that are
catalyst inhibitors or that interfere with the activity of the catalyst. These
compounds include phosphines, amines, sulfides, thiols or other compounds that
may be classified as Lewis bases. Lewis bases, or other compounds that have a pair
of electrons available for donation, will react with the platinum catalyst, effectively
neutralizing its activity. It has been discovered that the presence of such compounds
has a surprisingly detrimental impact on hydrosilylation curing in the process
of dynamic vulcanization of the rubber component of the thermoplastic elastomer
compositions. If the concentration of compounds which have the chemical reactivity
of Lewis bases, such as compounds containing sulfur or nitrogen, is maintained
at or below a level which provides less than about 1000 ppm and 300 ppm of sulfur
and nitrogen respectively, then the amount of platinum catalyst required to promote
efficient hydrosilylation curing in dynamic vulcanization can be substantially
reduced, usually to the range of about 4 ppm or less, without impact on the cure
state of the rubber or the tensile properties of the thermoplastic elastomer product.
Concentrations of sulfur and nitrogen below about 500 and 200 ppm respectively
are, more preferred, and concentrations of less than about 30 ppm sulfur and less
than about 100 ppm nitrogen are most preferred. It has been discovered that, even
at catalyst concentrations as low as 0.25 ppm, full cure of the elastomer can be
achieved if the concentration of sulfur and nitrogen is within the most preferred
Most paraffinic petroleum oils for the rubber industry are derived
from a crude oil distillation stream. A typical refining history would include
some type of dewaxing to reduce the pour point, a solvent extraction to physically
remove aromatic compounds and a hydrotreating process to chemically modify aromatic
structures. Both extraction and hydrotreating result in a net increase in the total
concentration of saturated hydrocarbon structures and a net decrease in the total
aromatic, sulfur and nitrogen-containing compound concentration. The degree of
reduction in concentration of these compounds in the oil is dependent upon the
type and severity of the refining employed, and the nature of the crude oil. White
and paraffinic oils have been treated more extensively than aromatic and napthenic
oils and would contain a smaller concentration of aromatic, sulfur and/or nitrogen
compounds. It is difficult to elucidate the exact chemical structure of these compounds
due to their complexity. The tendency of an oil to interfere with platinum catalyzed
hydrosilylation is directly related to the concentration of sulfur and nitrogen
containing compounds, as well as compounds which contain phosphorus, tin, arsenic,
aluminum and iron.
The rubber component of the thermoplastic elastomer is generally
present as small, i.e. micro-size, particles within a continuous thermoplastic
resin matrix, although a co-continuous morphology or a phase inversion is also
possible depending upon the amount of rubber relative to plastic and the degree
of cure of the rubber. The rubber is desirably at least partially crosslinked,
and preferably is completely or fully crosslinked. It is preferred that the rubber
be crosslinked by the process of dynamic vulcanization. As used in the specification
and claims, the term "dynamic vulcanization" means a vulcanization or curing process
for a rubber blended with a thermoplastic resin, wherein the rubber is vulcanized
under conditions of shear at a temperature at which the mixture will flow. The
rubber is thus simultaneously crosslinked and dispersed as fine particles within
the thermoplastic resin matrix, although as noted above other morphologies may
exist. Dynamic vulcanization is effected by mixing the thermoplastic elastomer
components at elevated temperatures in conventional mixing equipment such as roll
mills, Banbury mixers, Brabender mixers, continuous mixers, mixing extruders and
the like. The unique characteristic of dynamically cured compositions is that,
notwithstanding the fact that the rubber component is partially or hilly cured,
the compositions can be processed and reprocessed by conventional plastic processing
techniques such as extrusion, injection molding and compression molding. Scrap
or flashing can be salvaged and reprocessed.
The terms "fully vulcanized" and "fully cured" or "fully crosslinked"
as used in the specification and claims means that the rubber component to be
vulcanized has been cured or crosslinked to a state in which the elastomeric properties
of the crosslinked rubber are similar to those of the rubber in its conventional
vulcanized state, apart from the thermoplastic elastomer composition. The degree
of cure can be described in terms of gel content, or conversely, extractable components.
Gel content reported as percent gel (based on the weight of crosslinkable rubber)
is determined by a procedure which comprises determining the amount of insoluble
polymer by soaking the specimen for 48 hours in organic solvent at room temperature,
weighing the dried residue and making suitable corrections based upon knowledge
of the composition. Thus, corrected initial and final weights are obtained by
subtracting from the initial weight the weight of soluble components, other than
rubber to be vulcanized, such as extender oils, plasticizers and components of
the composition soluble in organic solvent, as well as that rubber component of
the product which is not intended to be cured. Any insoluble polyolefins, pigments,
fillers, and the like are subtracted from both the initial and final weights. The
rubber component can be described as fully cured when less than about 5%, and preferably
less than 3%, of the rubber which is capable of being cured by hydrosilylation
is extractable from the thermoplastic elastomer product by a solvent for that rubber.
Alternatively the degree of cure may be expressed in terms of crosslink density.
All of these descriptions are well known in the art, for example in U.S. Pat. Nos.
4,593,062, 5,100,947 and 5,157,081, all of which are fully incorporated herein
by this reference.
The following general procedure was used in the preparation of thermoplastic
elastomers by the process of the invention, as set forth in the examples. The thermoplastic
resin, oil and rubber were placed in a heated internal mixer, with the hydrosilylation
agent and hydrosilylation catalyst. The hydrosilylation agent and catalyst can
be incorporated into the composition by any suitable technique, for example by
injection as solutions in oil or as neat components, although a dilute hydrosilylation
crosslinker and catalyst solutions are preferred. Additives such as antioxidants,
ultraviolet stabilizers and fillers may also be added as a slurry in oil. Masterbatches
of the components may also be prepared to facilitate the blending process. The
mixture was heated to a temperature sufficient to melt the thermoplastic component,
and the mixture was masticated, with added processing oil if desired, until a maximum
in the mixing torque indicated that vulcanization had occurred. Mixing was continued
until the desired degree of vulcanization was achieved.
The order of addition of the hydrosilylation agent and hydrosilylation
catalyst was found to be important. Maximum catalyst efficiency was obtained when
the hydrosilylation agent was added first to the blend, followed by the hydrosilylation
catalyst. The mechanical properties of the thermoplastic elastomer products, as
well as the degree of cure, were improved when this order of addition was followed.
The invention will be better understood by reference to the following
examples which serve to illustrate but not limit the present process. In the examples,
the following test methods were used to determine the properties of the thermoplastic
Hardness (Shore A)ASTM D 2240 Ultimate tensile strength (UTS - psi)ASTM D 412 Ultimate elongation (UE - %)ASTM D 412 Modulus at 100% elongation (M100 - psi)ASTM D 412 Tear Strength pliASTM D 412 Tension set (TS - %)ASTM D 412 Compression SetASTM D 395, Method B
The components used in the compositions prepared according to the
examples are further identified as follows.
Compositions Ia, Ib, Ic, and Id were prepared to compare the properties
of thermoplastic vulcanizates from methacrylate functionalized copolymers of isobutylene
and paramethyistyrene (Copolymer A) to the controls from thermoplastic vulcanizates
from conventional butyl rubber, Compositions IIc and IId (using Butyl rubber B,
a copolymer of isobutylene and a conventional diene for butyl rubber). Compositions
Ia through Id using the methacrylate functionalized copolymers had higher UE, M-100,
and Tear Strength and lower Tension Set and Compression Set than the control examples
IIc and IId. It was generally observed that the Butyl Rubber "B" did not cure under
the reaction conditions. Compositions Ia - Id vary. Composition Ia used 2.84 wt
% Si-H "A", 4.74 wt % Catalyst "A" and 23.7 wt % Oil "A" while Ib uses the same
amounts but substitutes Oil "B" (a polybutene oil) for an Oil "A" (a mineral oil).
Composition Ic varies from the first two compositions in that it uses only 1.48
wt % Si-H "A", 2.46 wt % Catalyst "A" and uses the Oil "B" (polybutene similar
to Composition Ib). Composition Id uses the lower amounts of Si-H and Catalyst
(similar to composition Ic) and then substitutes Oil "C" (a polybutene oil). The
properties of the thermoplastic vulcanizates did not change much going from Composition
Ia to Composition Ib indicating the oil type had little effect other than possibly
matching the refractive index of the rubber and plastic phases. The properties
only changed slightly going to Composition Ic and Composition Id indicating that
smaller amounts of hydrosilylation agent (Si-H) and catalyst are nearly as effective
as higher amounts of the same components. The physical properties of the two control
(Compositions IIc and IId) indicate that complete curing of the conventional butyl
rubber does not occur even when nearly twice as much hydrosilylation agent and
catalyst are used as compared to the lowest levels used to cure a methacrylate
functionalized copolymer of isobutylene and paramethylstyrene. The properties of
the two controls (especially the compression set and tension set) are generally
unsuitable for most thermoplastic vulcanizate applications.
The examples in Table 2 further illustrate the desirability of crosslinking
acrylic or methacrylic functionality on an isobutylene-p-methylstyrene copolymer.
None of the compositions of Table 2 include oil so they have higher Shore A hardness.
Composition IIIa is derived from a copolymer with a higher amount of methacrylic
functionality (0.51 mole %) than previous examples. Composition Ie is similar to
previous compositions but has no oil. Composition IVa is similar to earlier compositions
but uses a copolymer with 0.73 mole % methacrylic functionality. Composition Va
(control) is similar to IIIa but lacks silicon hydride crosslinker and catalyst.
Composition VIa (control) is similar to Ie but lacks silicon hydride crosslinker
and a catalyst.
While the best mode and preferred embodiment of the invention have
been set forth in accord with the Patent Statutes, the scope of the invention is
not limited thereto, but rather is defined by the attached claims.
A thermoplastic vulcanizate comprising:
a) a thermoplastic resin and
b) a butyl rubber copolymer of isobutylene and paramethylstyrene containing
acrylic and/or alkacrylic groups pendant on repeat units from paramethylstyrene
via a carboxyl linkage to the paramethyl group, said butyl rubber copolymer being
crosslinked via the reaction product of a hydrosilylation crosslinking agent and
a carbon-carbon double bond of said acrylic and/or alkacrylic groups.
A thermoplastic vulcanizate according to claim 1, wherein said butyl rubber
is the reaction product of acrylate modification of a brominated copolymer of at
least isobutylene and paramethylstyrene.
A thermoplastic vulcanizate according to claim 2, wherein said alkacrylic group
is derived from metal salt of acrylic or methacrylic acid.
A thermoplastic vulcanizate according to claim 2, wherein said butyl rubber
less said acrylic and/or alkacrylic group is a copolymer of from about 80 to about
99 weight percent isobutylene and from about 1 to about 20 weight percent paramethylstyrene.
A thermoplastic vulcanizate according to claim 2, wherein said copolymer includes
from about 0.1 to about 5 mole % acrylic or alkacrylic group or a combination thereof
if both of them are present.
A thermoplastic vulcanizate according to claim 2, wherein said thermoplastic
resin and said butyl rubber are present in ratios by weight of from about 20:80
to about 80:20.
A thermoplastic vulcanizate according to claim 6, wherein said butyl rubber
copolymer comprises from about 80 to about 99 weight percent repeat units from
isobutylene and from about 1 to about 20 weight percent repeat units from paramethylstyrene
and from about 0.1 to about 5 mole % acrylic or alkacrylic groups.
A thermoplastic vulcanizate according to claim 7, wherein said thermoplastic
resin comprises polyethylene or polypropylene.
A thermoplastic vulcanizate according to claim 8 further including residual
platinum from a platinum containing hydrosilylation catalyst.
A process for forming a thermoplastic vulcanizate, said process comprising:
1) a thermoplastic resin
2) a butyl rubber copolymer of isobutylene and paramethylstyrene having acrylic
or alkacrylic groups, or combinations thereof pendant from at least some of the
repeat units from paramethylstyrene via a carboxyl linkage from the acrylic or
3) a hydrosilylation crosslinking agent and,
4) a catalyst for hydrosilylation crosslinking,
b) crosslinking said butyl rubber copolymer with said hydrosilylation crosslinking
A process according to claim 10, wherein the weight ratio of thermoplastic
resin to butyl rubber copolymer is from about 20:80 to about 80:20 respectively.
A process according to claim 11, wherein said thermoplastic resin comprises
polyethylene or polypropylene.
A process according to claim 12, wherein said acrylic or alkacrylic, or combinations
thereof comprise acrylic, methacrylic, or ethacrylic or combinations thereof.
A process according to claim 12, wherein said catalyst comprises platinum containing
A process according to claim 12, wherein said copolymer of isobutylene and
paramethylstyrene comprises from about 80 to about 99 weight percent isobutylene,
and from 1 to about 20 weight percent paramethylstyrene.
A process according to claim 12, wherein said acrylic or alkacrylic groups
or combinations thereof, if both are present, are present in an amount from about
0.1 to about 5 mole %.