Field of the Invention
The present invention relates to a rubber composition comprised
of a functionalized elastomer which contains a dispersion of a starch/plasticizer
composite and coupling agent and to pneumatic tires having at least one component
comprised of such rubber composition. The rubber composition may also contain one
or more additional elastomers and may contain at least one particulate reinforcing
agent selected from, for example, precipitated silica aggregates, carbon black and
carbon black which contains silica domains on its surface. Such tire component can
be, for example, its circumferential tread or other component of the tire.
Background of the Invention
Starch, particularly starch/plasticizer composites, have
been suggested for use in elastomer formulations for various purposes, including
for various tire components. For example see 5,672,639.
Such starch/plasticizer compositions might be used alone
or in conjunction with silica and/or carbon black reinforcing fillers or also with
other fillers such as, for example, recycled, or ground, vulcanized rubber particles,
short fibers, kaolin clay, mica, talc, titanium oxide and limestone. Such short
fibers can be, for example, fibers of cellulose, aramid, nylon, polyester and carbon
US-A- 5,403,923, 5,258,430, and 4,900,361 further disclose
a preparation and use of various starch compositions.
Historically, various elastomer compositions have been
disclosed which contain one or more of starch/plasticizer composite, silica reinforcing
filler, silica coupling agent and functionalized elastomer such as, for example,
epoxidized natural rubber. For example, see patent publications such as US-B1-6,273,163,
WO 01/49785-A and EP-A-0644235.
The term "phr" if used herein, and according to conventional
practice, refers to "parts of a respective material per 100 parts by weight of rubber,
In the description of this invention, the terms "rubber"
and "elastomer" if used herein, may be used interchangeably, unless otherwise prescribed.
The terms "rubber composition", "compounded rubber" and "rubber compound", if used
herein, are used interchangeably to refer to "rubber which has been blended or mixed
with various ingredients and materials" and such terms are well known to those having
skill in the rubber mixing or rubber compounding art.
The term "carbon black" as used herein means "carbon blacks
having properties typically used in the reinforcement of elastomers, particularly
sulfur curable elastomers".
The term "silica" as used herein can relate to precipitated
or fumed silica and typically relates to precipitated silica aggregates, which is
well known to those having skill in such art.
A reference to an elastomer's Tg refers to its glass transition
temperature, which can conveniently be determined by a differential scanning calorimeter
at a heating rate of 10°C per minute (e.g. ASTM 3418).
Summary and Practice of the Invention
In accordance with one aspect of this invention, a rubber
composition is provided which comprises, based upon parts by weight per 100 parts
by weight elastomer (phr):
- (A) 100 parts by weight of at least one diene-based elastomer comprised of:
- (1) 20 to 50 phr of at least one elastomer selected from polymers of isoprene
and/or 1,3-butadiene and from copolymers of styrene with isoprene and/or 1,3-butadiene,
- (2) 50 to 80 phr of at least one functionalized diene-based elastomer selected
- (a) functionalized diene-based elastomer which contains one or more one or more
functional groups available for reaction with a coupling agent, wherein said functional
groups are selected from at least one of hydroxyl and carboxyl groups, and
- (b) functionalized diene-based elastomer which contains at least one functional
group selected from isocyanate groups, blocked isocyanate groups, epoxide groups,
amine groups (primary, secondary, tertiary amine groups), alkoxysilane groups, hydroxypropyl
methacrylate (HPMA) groups, acrylate groups and anhydride groups, and, correspondingly,
- (B) 30 to 180 phr of at least one elastomer reinforcing filler composed of:
- (1) one to 180 phr of at least one starch/synthetic plasticizer composite, and
- (2) from 29 to 179 phr of at least one of carbon black, precipitated silica
aggregates, and silica modified carbon black which contains silica domains on its
- (C) a coupling agent having a moiety reactive with hydroxyl groups contained
on the surface of said starch composite, with hydroxyl and/or carboxyl groups contained
on said functionalized diene-based elastomer, with hydroxyl groups contained on
the surface of said aggregates of precipitated silica and with hydroxyl groups contained
on the surface of silica domains on the surface of said silica-treated carbon black,
if said silica and/or silica-treated carbon black are used, wherein said coupling
agent has an additional moiety, moiety interactive with said elastomer which contains
said functional groups and with said additional diene-based elastomer if used.
In practice, preferably said starch is composed of amylose
units and amylopectin units in a ratio of 15/85 to 35/65, alternatively 20/80 to
30/70, and has a softening point according to ASTM No. D1228 in a range of 180°C
to 220°C; and the starch/plasticizer has a softening point in a range of 110°C
to 170°C according to ASTM No. D1228.
The moiety of the coupling agent reactive with the starch/plasticizer
composite, diene-based elastomer which contains said functional groups and hydroxyl
groups on said silica surfaces is generally considered herein as being capable of
reacting with at least one or more hydroxyl groups which may be contained on their
surfaces and possibly with other reactive groups thereon.
Representative of coupling agent is for example a coupling
agent of the representative Formula I:
- Si - R2 - Sn - R2 - (OR)3
wherein R is an alkyl radical selected from one or more of methyl and ethyl radicals,
preferably an ethyl radical, R2 is an alkyl radical containing from 2
through 6 carbon atoms, preferably a methyl or propyl and more preferably a propyl
radical, and n is a value of from 2 to 8 with an average of either from 2 to 2.6
of from 3.5 to 4.
Thus, such coupling agent may be, for example, a bis(3-alkoxysilylalkyl)
polysulfide having an average number of sulfur atoms in its polysulfidic bridge
in a range of from 2 to 2.6 or from 3.5 to 4.
Representative of such coupling agents is, for example,
bis(3-ethoxysilylpropyl) polysulfide having an average of from 2 to 2.6 or of from
3.5 to 4, sulfur atoms in its polysulfidic bridge.
For the purposes of this invention, it is intended that
the alkoxy groups, namely the (OR)3- groups, on the coupling agent are
primarily reactive with said hydroxyl and/or carboxyl groups of said diene-based
elastomer which contains one or more of such reactive functional groups.
It is to be appreciated that such alkoxy groups are also
reactive with hydroxyl groups of said starch/plasticizer composite, said precipitated
silica aggregates and said silica on said carbon black which contains silica domains
on its surface.
In this manner, then, it is contemplated that a complex
network of reinforcement of the rubber composition is obtained by combination of
reactions in situ within the elastomer host(s).
The diene-based elastomer which contains reactive hydroxyl
groups and/or carboxyl groups, is prepared by organic solvent polymerization of
isoprene and/or 1,3-butadiene or copolymerization of styrene or alpha methylstyrene
with isoprene and/or 1,3-butadiene.
The introduction of reactive hydroxyl and/or carboxyl groups
on said diene-based elastomer may be accomplished by, for example, radicalar grafting
one or more functional groups of interest onto the polymer backbone, copolymerization
of polymerizable materials which contain one or more functional groups of interest,
deprotection of protected copolymerized groups, addition of a fraction of unsaturations,
and for end terminated polymers a reaction of the living polymer chain with a molecule
containing the function of interest.
Exemplary of such diene-based elastomers which contain
hydroxyl and/or polar functional groups and multifunctional compatibilizers are,
for example hydroxyl terminated polybutadienes, hydroxyl terminated polyisoprenes,
anhydride-containing polybutadiene and/or polyisoprene elastomers, using, for example
anhydrides from the Sartomer Company as the Ricobond™ series of
anhydrides, urethane-containing polybutadiene and/or polyisoprene, using, for example,
urethane from the Sartomer Company as CN302™, diacrylate-containing
polybutadiene and/or polyisoprene using, for example diacrylate from the Sartomer
Company as CN303™, epoxide-containing elastomer such as, for example,
epoxidized natural rubber (epoxidized cis 1,4-polyisoprene), multifunctional additive-containing
polybutadiene and/or polyisoprene, using a material, for example, vinyl triethoxy
silane-methyl methacrylate copolymers, bis(triethoxy) ethane and bis[3-(triethoxysilyl)propyl]
In the practice of this invention, the starch/plasticizer
composite may be desired to be used, for example, as a free flowing, dry powder
or in a free flowing, dry pelletized form. In practice, it is desired that the synthetic
plasticizer itself is compatible with the starch, and has a softening point lower
than the softening point of the starch so that it causes the softening of the blend
of the plasticizer and the starch to be lower than that of the starch alone. This
phenomenon of blends of compatible polymers of differing softening points having
a softening point lower than the highest softening point of the individual polymer(s)
in the blend is well known to those having skill in such art.
For the purposes of this invention, the plasticizer effect
for the starch/plasticizer composite, (meaning a softening point of the composite
being lower than the softening point of the starch), can be obtained through use
of a polymeric plasticizer such as, for example, poly(ethylenevinyl alcohol) with
a softening point of less than 160°C. Other plasticizers, and their mixtures,
are contemplated for use in this invention, provided that they have softening points
of less than the softening point of the starch, and preferably less than 160°C,
which might be, for example, one or more copolymers and hydrolyzed copolymers thereof
selected from ethylene-vinyl acetate copolymers having a vinyl acetate molar content
of from 5 to 90, alternatively 20 to 70, percent, ethylene-glycidal acrylate copolymers
and ethylene-maleic anhydride copolymers. As hereinbefore stated hydrolysed forms
of copolymers are also contemplated. For example, the corresponding ethylene-vinyl
alcohol copolymers, and ethylene-acetate vinyl alcohol terpolymers may be contemplated
so long as they have a softening point lower than that of the starch and preferably
lower than 160°C.
In general, the blending of the starch and plasticizer
involves what are considered or believed herein to be relatively strong chemical
and/or physical interactions between the starch and the plasticizer.
In general, the starch/plasticizer composite has a desired
starch to plasticizer weight ratio in a range of 0.5/1 to 4/1, alternatively 1/1
to 2/1, so long as the starch/plasticizer composition has the required softening
point range, and preferably, is capable of being a free flowing, dry powder or extruded
pellets, before it is mixed with the elastomer(s).
While the synthetic plasticizer(s) may have a viscous nature
at room temperature, or at about 23°C and, thus, considered to be a liquid
for the purposes of this description, although the plasticizer may actually be a
viscous liquid at room temperature since it is to be appreciated that many plasticizers
are polymeric in nature.
Representative examples of synthetic plasticizers are,
for example, poly(ethylenevinyl alcohol), cellulose acetate and diesters of dibasic
organic acids, so long as they have a softening point sufficiently below the softening
point of the starch with which they are being combined so that the starch/plasticizer
composite has the required softening point range. Preferably, the synthetic plasticizer
is selected from at least one of poly(ethylenevinyl alcohol) and cellulose acetate.
For example, the aforesaid poly(ethylenevinyl alcohol)
might be prepared by polymerizing vinyl acetate to form a poly(vinylacetate) which
is then hydrolyzed (acid or base catalyzed) to form the poly(ethylenevinyl alcohol).
Such reaction of vinyl acetate and hydrolyzing of the resulting product is well
known those skilled in such art.
For example, vinylalcohol/ethylene (60/40 mole ratio) copolymers
can be obtained in powder forms at different molecular weights and crystallinities
such as, for example, a molecular weight of about 11700 with an average particle
size of about 11.5 microns or a molecular weight (weight average) of about 60,000
with an average particle diameter of less than 50 microns.
Various blends of starch and ethylenevinyl alcohol copolymers
can then be prepared according to mixing procedures well known to those having skill
in such art. For example, a procedure might be utilized according to a recitation
in the patent publication by Bastioli, Bellotti and Del Trediu entitled
A Polymer Composition Including Destructured Starch An Ethylene Copolymer,
Other plasticizers might be prepared, for example and so
long as they have the appropriate Tg and starch compatibility requirements, by reacting
one or more appropriate organic dibasic acids with aliphatic or aromatic diol(s)
in a reaction which might sometimes be referred to as an esterification condensation
reaction. Such esterification reactions are well known to those skilled in such
In the practice of this invention, additional inorganic
fillers for the rubber composition may be used such as, for example, one or more
of kaolin clay, talc, short discrete fibers, thermoplastic powders such as polyethylene
and polypropylene particles, or other reinforcing or non-reinforcing inorganic fillers.
Such additional inorganic fillers are intended to be exclusive
of, or to not include, pigments conventionally used in the compounding, or preparation
of, rubber compositions such as zinc oxide, titanium oxide and the like.
Such additional short fibers may be, for example, of organic
polymeric materials such as cellulose, aramid, nylon and polyester.
In practice, the said starch/synthetic plasticizer composite
has a moisture content in a range of zero to 30, alternatively one to six, weight
In practice, as hereinbefore pointed out, the elastomer
reinforcement may be
wherein a coupler is optionally used to couple the starch composite and the silica,
if silica is used, to the diene based elastomer(s).
- (A) the starch/plasticizer composite or
- (B) a combination of the starch/plasticizer composite and at least one of carbon
black and precipitated silica or
- (C) a combination of the starch/plasticizer, carbon black and/or precipitated
silica and at least one other inorganic filler,
It is considered herein that, where desired, the starch
composite can be used as
- (A) a partial or
- (B) complete replacement for carbon black and/or silica reinforcement for sulfur
vulcanizable elastomers, depending somewhat upon the properties desired for the
cured, or vulcanized, rubber composition.
In practice, it is generally preferred that the rubber
reinforcing carbon black is used in conjunction with the starch composite in an
amount of at least 5 and preferably at least 35 phr of carbon black, depending somewhat
upon the structure of the carbon black. Carbon black structure is often represented
by its DBP (dibutylphthalate) value. Reinforcing carbon blacks typically have a
DBP number in a range of 40 to 400 cc/100 gm, and more usually in a range of 80
to 300 (ASTM D 1265). If the carbon black content is used with a view to providing
an elastomer composition with a suitable electrical conductivity to retard or prevent
appreciable static electricity build up, a minimum amount of carbon black in the
elastomer composition might be, for example, about 10 phr if a highly electrically
conductive carbon black is used, otherwise usually at least about 25 and often at
least about 35 phr of carbon black is used.
If desired, and on a practical basis, it is usually preferred
that the coupling agent for the starch/plasticizer composite can be the same coupling
as could be used for the silica, if silica is used as well as for the diene-based
elastomer having the hydroxyl and/or carboxyl groups. Thus, it is considered herein
that the moiety of the coupling agent reactive with the surface of the starch/plasticizer
composite is also reactive with the hydroxyl (eg. silanol) groups, and/other reactive
groups typically on the surface of the silica.
It is important to appreciate that, preferably, the starch
composite is not used as a total replacement for carbon black and/or silica in an
elastomer composition. Thus, in one aspect, it is considered that the starch composite
is to be typically used as a partial replacement for carbon black and/or silica
reinforcement for sulfur vulcanizable elastomers.
It is important to appreciate that, while the starch may
be used in combination with the starch/plasticizer composite, they are not considered
herein as equal alternatives. Thus, while starch might sometimes be considered suitable
as a reinforcement for the elastomer composition together with the coupling agent,
the starch/plasticizer composite itself may be considered more desirable for some
applications, even when used without a coupler.
If silica is used as a reinforcement together with carbon
black, the weight ratio of silica to carbon black is desirably in a weight ratio
in a range of 0.1/1 to 10/1, thus at least 0.1/1, alternatively at least 0.9/1,
optionally at least 3/1 and sometimes at least 10/1.
The weight ratio of said coupling agent to the starch composite
and silica, if silica is used, may, for example, be in a range of 0.01/1 to 0.2/1
or even up to 0.4/1.
The starch is typically composed of amylose units and/or
amylopectin units. These are well known components of starch. Typically, the starch
is composed of a combination of the amylose and amylopectin units in a ratio of
about 25/75. A somewhat broader range of ratios of amylose to amylopectin units
is recited herein in order to provide a starch for the starch composite which interact
with the plasticizer somewhat differently. For example, it is considered herein
that suitable ratios may be from 20/80 up to 100/0, although a more suitable range
is considered to be 15/85 to 35/63.
The starch can typically be obtained from naturally occurring
plants, as hereinbefore referenced. The starch/plasticizer composition can be present
in various particulate forms such as, for example, fibrils, spheres or macromolecules,
which may, in one aspect, depend somewhat upon the ratio of amylose to amylopectin
in the starch as well as the plasticizer content in the composite.
The relative importance, if any, of such forms of the starch
is the difference in their reinforcing associated with the filler morphology. The
morphology of the filler primarily determines the final shape of the starch composite
within the elastomer composition, in addition, the severity of the mixing conditions
such as high shear and elevated temperature can allow to optimize the final filler
morphology. Thus, the starch composite, after mixing, may be in a shape of one or
more of hereinbefore described forms.
It is important to appreciate that the starch, by itself,
is hydrophilic in nature, meaning that it has a strong tendency to bind or absorb
water. Thus, the moisture content for the starch and/or starch composite has been
previously discussed herein. This is considered to be an important, or desirable,
feature in the practice of this invention because water can also act somewhat as
a plasticizer with the starch and which can sometimes associate with the plasticizer
itself for the starch composite such as polyvinyl alcohol and cellulose acetate,
or other plasticizer which contain similar functionalities such as esters of polyvinyl
alcohol and/or cellulose acetate or any plasticizer which can depress the melting
point of the starch.
Various grades of the starch/plasticizer composition can
be developed to be used with various elastomer compositions and processing conditions.
The starch typically has a softening point in a range of
180°C to 220°C, depending somewhat upon its ratio of amylose to amylopectin
units, as well as other factors and, thus, does not readily soften when the rubber
is conventionally mixed, for example, at a temperature in a range of 140°C
to 165°C. Accordingly, after the rubber is mixed, the starch remains in a solid
particulate form, although it may become somewhat elongated under the higher shear
forces generated while the rubber is being mixed with its compounding ingredients.
Thus, the starch remains largely incompatible with the rubber and is typically present
in the rubber composition in individual domains.
However, it is now considered herein that providing starch
in a form of a starch composite of starch and a plasticizer is particularly beneficial
in providing such a composition with a softening point in a range of 110°C
The plasticizers can typically be combined with the starch
such as, for example, by appropriate physical mixing processes, particularly mixing
processes that provide adequate shear force.
The combination of starch and, for example, polyvinyl alcohol
or cellulose acetate, is referred to herein as a "composite". Although the exact
mechanism may not be completely understood, it is believed that the combination
is not a simple mixture but is a result of chemical and/or physical interactions.
It is believed that the interactions lead to a configuration where the starch molecules
interact via the amylose with the vinyl alcohol, for example, of the plasticizer
molecule to form complexes, involving perhaps chain entanglements. The large individual
amylose molecules are believed to be interconnected at several points per molecule
with the individual amylopectine molecules as a result of hydrogen bonding (which
might otherwise also be in the nature of hydrophilic interactions).
This is considered herein to be beneficial because by varying
the content and/or ratios of natural and synthetic components of the starch composite
it is believed to be possible to alter the balance between hydrophobic and hydrophilic
interactions between the starch components and the plasticizer to allow, for example,
the starch composite filler to vary in form from spherical particles to fibrils.
In particular, it is considered herein that adding a polyvinyl
alcohol to the starch to form a composite thereof, particularly when the polyvinyl
alcohol has a softening point in a range of 90°C to 130°C, can be beneficial
to provide resulting starch/plasticizer composite having a softening point in a
range of 110°C to 160°C, and thereby provide a starch composite for blending
well with a rubber composition during its mixing stage at a temperature, for example,
in a range of 110°C to 165°C or 170°C.
In a further aspect of the invention, a tire is provided
having at least one component comprised of the said rubber composition of this invention.
Although not limited thereto, such tire components can be at least one of tread,
tread base or tread under tread, tire innerliner, sidewall apexes, wedges for the
tire shoulder, sidewall, carcass ply and breaker wire coating rubber compositions,
bead insulation rubber composition and cushion or gumstrips for addition to various
parts of the tire construction. As used herein, the tread and tread base may be
collectively referred to herein as the "tread", or "circumferential tread". Such
tire components are well known those skilled in such art.
As a feature of this invention, a tire is provided having
a circumferential tread comprised of the said rubber composition of this invention
with the aforesaid tire component, thus, being its tread. As is well known to those
skilled in such art, such tire tread is typically designed to be ground-contacting.
As a further aspect of this invention, a tire is provided
with sidewall apexes of the said rubber composition of this invention.
Historically, the more homogeneous the dispersion of rubber
compound components into the rubber, the better the resultant cured properties of
that rubber. It is considered herein that it is a particular feature of this invention
that the starch composite mixes with the rubber composition, which contains the
diene-based elastomer having the hydroxyl and/or carboxyl functionality, during
the rubber mixing under high shear conditions and at a temperature in a range of
140°C to 165°C, in a manner that very good dispersion in the rubber mixture
is obtained. This is considered herein to be important because upon mixing the elastomer
composition containing the starch/plasticizer composite to a temperature to reach
the melting point temperature of the composite, the starch composite will contribute
to the development of high shearing forces which is considered to be beneficial
to ingredient dispersion within the rubber composition. Above the melting point
of the starch composite, for example, around 150°C, it will melt and maximize
its reaction with the coupling agent.
In one aspect, such a rubber composition can be provided
as being sulfur cured. The sulfur curing is accomplished in a conventional manner,
namely, by curing under conditions of elevated temperature and pressure for a suitable
period of time.
In the practice of this invention, as hereinbefore pointed
out, the rubber composition is comprised of at least one diene-based elastomer which
contains hydroxyl and/or carboxyl functionality. Thus, it is considered that the
elastomer is a sulfur curable elastomer.
The diene based elastomer which does not contain hydroxyl
and/or carboxy functionality may be selected from at least one of homopolymers of
isoprene and 1,3-butadiene and copolymers of isoprene and/or 1,3-butadiene with
a aromatic vinyl compound selected from at least one of styrene and alphamethylstyrene.
Accordingly such elastomer, or rubber, may be selected, for example, from at least
one of cis 1,4-polyisoprene rubber (natural and/or synthetic, and preferably natural
rubber), 3,4-polyisoprene rubber, styrene/butadiene copolymer rubbers, isoprene/butadiene
copolymer rubbers, styrene/isoprene copolymer rubbers, styrene/isoprene/butadiene
terpolymer rubbers, cis 1,4-polybutadiene rubber and medium to high vinyl polybutadiene
rubber having a vinyl 1,2- content in a range of 15 to 85 percent and emulsion polymerization
prepared butadiene/acrylonitrile copolymers. Such medium to high vinyl polybutadiene
rubber may be more simply referred to herein as a high vinyl polybutadiene.
The rubber composition is preferably of at least two diene
based elastomers with one of the elastomers desired to contain the hydroxyl and/or
The silicas preferably employed in this invention are precipitated
silicas such as, for example, those obtained by the acidification of a soluble silicate,
e.g., sodium silicate.
Such silicas might be characterized, for example, by having
a BET surface area, as measured using nitrogen gas, preferably in the range of 40
to 600, and more usually in a range of 50 to 300 square meters per gram. The BET
method of measuring surface area is described in the Journal of the American
Chemical Society, Volume 60, Page 304 (1930).
The silica may also be typically characterized by having
a dibutylphthalate (DBP) absorption value in a range of 50 to 400, and more usually
100 to 300 cm3/100g.
Various commercially available silicas may be considered
for use in this invention such as, only for example herein, and without limitation,
silicas commercially available from PPG Industries under the Hi-Sil trademark with
designations 210, 243, etc; silicas available from Rhodia, as, for example, Zeosil
1165MP Zeosil 165GR and silicas available from Degussa AG with, for example, designations
VN2 and VN3, as well as other grades of silica, particularly precipitated silicas,
which can be used for elastomer reinforcement.
It is readily understood by those having skill in the art
that the rubber composition would be compounded by methods generally known in the
rubber compounding art, such as mixing the various sulfur-vulcanizable constituent
rubbers with various commonly used additive materials such as, for example, curing
aids, such as sulfur, activators, retarders and accelerators, processing additives,
such as oils, resins including tackifying resins, silicas, and plasticizers, fillers,
pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants, peptizing
agents and reinforcing materials such as, for example, carbon black. As known to
those skilled in the art, depending on the intended use of the sulfur vulcanizable
and sulfur vulcanized material (rubbers), the additives mentioned above are selected
and commonly used in conventional amounts.
Typical amounts of tackifier resins, if used, comprise
0.5 to 10 phr, usually 1 to 5 phr. Typical amounts of processing aids comprise 1
to 50 phr. Such processing aids can include, for example, aromatic, napthenic, and/or
paraffinic processing oils. Typical amounts of antioxidants comprise 1 to 5 phr.
Representative antioxidants may be, for example, diphenyl-p-phenylenediamine and
others, such as, for example, those disclosed in The Vanderbilt Rubber Handbook
(1978), Pages 344 through 346. Typical amounts of antiozonants comprise 1 to 5 phr.
Typical amounts of fatty acids, if used, which can include stearic acid comprise
0.5 to 3 phr. Typical amounts of zinc oxide comprise 1 to 10 phr. Typical amounts
of waxes comprise 1 to 5 phr. Often microcrystalline waxes are used. Typical amounts
of peptizers comprise 0.1 to 1 phr.
The vulcanization is conducted in the presence of a sulfur
vulcanizing agent. Examples of suitable sulfur vulcanizing agents include elemental
sulfur (free sulfur) or sulfur donating vulcanizing agents, for example, an amine
disulfide, polymeric polysulfide or sulfur olefin adducts. Preferably, the sulfur
vulcanizing agent is elemental sulfur. As known to those skilled in the art, sulfur
vulcanizing agents are used in an amount ranging from 0.5 to 4 phr, or even, in
some circumstances, up to 8 phr.
Accelerators are used to control the time and/or temperature
required for vulcanization and to improve the properties of the vulcanizate. In
one embodiment, a single accelerator system may be used, i.e., primary accelerator.
Conventionally and preferably, a primary accelerator(s) is used in total amounts
ranging from 0.5 to 4, preferably 0.8 to 1.5, phr. In another embodiment, combinations
of a primary and a secondary accelerator might be used with the secondary accelerator
being used in smaller amounts (of 0.05 to 3 phr) in order to activate and to improve
the properties of the vulcanizate. Combinations of these accelerators might be expected
to produce a synergistic effect on the final properties and are somewhat better
than those produced by use of either accelerator alone. In addition, delayed action
accelerators may be used which are not affected by normal processing temperatures
but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization
retarders might also be used. Suitable types of accelerators that may be used in
the present invention are amines, disulfides, guanidines, thioureas, thiazoles,
thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, the primary
accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator
is preferably a guanidine, dithiocarbamate or thiuram compound. The presence and
relative amounts of sulfur vulcanizing agent, or peroxide cure systems, and accelerator(s),
if used, are not considered to be an aspect of this invention which is more primarily
directed to the use of said starch composite as a reinforcing filler in combination
with a coupler and carbon black and/or silica.
The presence and relative amounts of the above additives
are not considered to be an aspect of the present invention which is more primarily
directed to the utilization of specified blends of rubbers, including elastomers
which contain hydroxyl and/or carboxyl functionality, in rubber compositions, in
combination with the said starch/plasticizer composite together with carbon black
and/or optionally precipitated silica and/or non-carbon black or non-silica filler,
and a coupling agent for the starch/plasticizer composite, elastomer which contains
one or more of said functional groups and precipitated silica, as the case may be,
for the reinforcement of the rubber.
The mixing of the rubber composition can be accomplished
by methods known to those having skill in the rubber mixing art. For example, the
ingredients are typically mixed in at least two stages, namely, at least one non-productive
stage followed by a productive mix stage. The final curatives are typically mixed
in the final stage which is conventionally called the "productive" mix stage in
which the mixing typically occurs at a temperature, or ultimate temperature, lower
than the mix temperature(s) than the preceding non-productive mix stage(s). The
rubber, starch composite, and fillers such as carbon black and optional silica and
coupler, and/or non-carbon black and non-silica fillers, are mixed in one or more
non-productive mix stages. The terms "non-productive" and "productive" mix stages
are well known to those having skill in the rubber mixing art.
The rubber compositions of this invention can be used for
various purposes. For example, they may be used for various tire compounds. Such
tires can be built, shaped, molded and cured by various methods which are known
and will be readily apparent to those having skill in such art.