 |
Description  |
|
|
This invention relates to thermoplastic compositions and, more
particularly, to thermoplastic compositions comprising blends of polyester
and cross-linked rubber.
BACKGROUND OF THE INVENTION
Thermoplastics are compositions which can be molded or otherwise shaped and
reprocessed at temperatures above their melting or softening point.
Thermoplastic elastomers (elastoplastics) are materials which exhibit both
thermoplastic and elastomeric properties, i.e., the materials process as
thermoplastics but have physical properties like elastomers. Shaped
articles may be formed from thermoplastic elastomers by extrusion,
injection molding or compression molding without the time-consuming cure
step required with conventional vulcanizates. Elimination of the time
required to effect vulcanization provides significant manufacturing
advantages. Further, thermoplastic elastomers can be reprocessed without
the need for reclaiming and, in addition, many thermoplastics can be
thermally welded.
SUMMARY OF THE INVENTION
It has been discovered that compositions comprising blends of thermoplastic
linear crystalline polyesters and certain cross-linked rubbers exhibit
useful properties which properties vary depending on the proportion of
linear crystalline polyester and cross-linked rubber in the composition.
Compositions containing linear crystalline polyester and cross-linked
rubber are moldable thermoplastic compositions exhibiting improved
strength and greater toughness than similar compositions containing
substantially uncross-linked rubber. Compositions comprising less than 50
percent by weight of said linear crystalline polyester are elastoplastic,
i.e., they exhibit elastomeric properties yet are processable as a
thermoplastic. Compositions containing linear crystalline polyester and a
liquid plasticizer are also elastoplastic even though the weight of
polyester exceeds the weight of cross-linked rubber provided that the
linear crystalline polyester comprises no more than 50 weight percent of
the composition, the weight of plasticizer does not exceed the weight of
polyester and the total weight of the cross-linked rubber and plasticizer
does not exceed 85 weight percent of the composition.
A thermoplastic composition of the invention comprises a blend of
thermoplastic linear crystalline polyester and rubber cross-linked to the
extent that the gel content of the rubber is at least about 80 percent,
the rubber being a homopolymer of 1,3-butadiene, a copolymer of
1,3-butadiene copolymerized with styrene, vinyl pyridine, acrylonitrile,
or methacrylonitrile, a natural or synthetic polymer of isoprene, a
urethane polymer or a copolymer of two or more alpha monoolefins
optionally copolymerized with a minor quantity of diene or a mixture
thereof, said cross-linked rubber being in an amount not exceeding 85
weight percent of the composition. Generally, thermoplastic compositions
contain at least about 5 weight percent cross-linked rubber. Preferred
thermoplastic compositions contain no more than 75 weight percent of
polyester. More preferred thermoplastic compositions contain no more than
60 weight percent of polyester.
Elastoplastic compositions in accordance with this invention are
compositions comprising blends of (a) thermoplastic linear crystalline
polyester in an amount sufficient to impart thermoplasticity up to 50
weight percent of the composition, (b) rubber cross-linked to the extent
that the gel content of the rubber is at least about 80 percent, the
rubber being a homopolymer of 1,3-butadiene, a copolymer of 1,3-butadiene
copolymerized with styrene, vinyl pyridine, acrylonitrile, or
methacrylonitrile, a natural or synthetic polymer of isoprene, a urethane
polymer or a copolymer of two or more alpha monoolefins optionally
copolymerized with a minor quantity of diene or a mixture thereof, in an
amount sufficient to impart rubberlike elasticity up to 85 weight percent
of the composition and, (c) optionally, a plasticizer in an amount not
exceeding the weight of polyester, in which the total weight of the rubber
and plasticizer does not exceed 85 weight percent of the composition,
which compositions are processable as thermoplastics and are elastomeric.
Preferred elastoplastic compositions of the invention comprise blends in
which the amount of rubber exceeds the amount of polyester, particularly
blends of (a) about 20-50 parts by weight of thermoplastic polyester and
(b) about 80-50 parts by weight of rubber per 100 total parts weight of
polyester and rubber. More preferred compositions comprise blends of about
20-45 parts by weight of the polyester and about 80-55 parts by weight of
the rubber per 100 total parts by weight of polyester and rubber. The
elastoplastic compositions are elastomeric; yet they are processable as
thermoplastics even though the rubber is cross-linked to a point where it
is at least 80 percent insoluble in an organic solvent for the
unvulcanized rubber. Further, they retain thermoplasticity even when the
rubber is cross-linked to the extent that the rubber is essentially
completely insoluble. The indicated relative proportions of polyester and
rubber are necessary to provide sufficient rubber to give elastomeric
compositions and to provide sufficient polyester to give thermoplasticity.
When the amount of rubber exceeds about 85 parts by weight per 100 parts
total weight of polyester and rubber, there is insufficient polyester
present to provide a continuous phase and the composition is not
thermoplastic. When the quantity of rubber, in the absence of plasticizer
falls below about 50 parts by weight per 100 parts total weight of
polyester and rubber, or when the quantity of polyester exceeds 50 weight
percent of the composition, hard, rigid compositions having reduced
toughness are obtained. The blends of the invention are envisaged as
comprising microsized particles of cross-linked rubber dispersed
throughout a continuous polyester matrix. Especially preferred
compositions of the invention comprise cross-linked nitrile rubber.
Compositions characterized by improved toughness, as represented by
(TS).sup.2 /E, wherein TS is tensile strength and E is Young's modulus,
contain less than 50 weight percent polyester.
As indicated, the thermoplastic elastomers of the invention are rubbery
compositions in which the rubber portion of the blend is cross-linked to a
gel content of 80% or more or a cross-link density of 3 .times. 10.sup.-5
or more moles of effective cross-links per milliliter of rubber. The
procedure appropriate for evaluating the extent of cure depends upon the
particular ingredients present in the blends. The properties of the
compositions can be improved by further cross-linking the rubber until it
is essentially completely cured which state of cure is indicated by a gel
content of 96% or more. However, in this connection, essentially complete
gelation of say 96% or more is not always a necessary criterion of a fully
cured product because of differences in molecular weight, molecular weight
distribution and other variables among diene rubbers which influence the
gel determination. Determination of the cross-link density of the rubber
is an alternative means of determining state of cure of the vulcanizates
but must be determined indirectly because the presence of the polyester
interferes with the determination. Accordingly, the same rubber as present
in the blend is treated under conditions with respect to time,
temperature, and amount of curative which result in a fully cured product
as demonstrated by its cross-link density, and such cross-link density is
assigned to the blend similarly treated. In general, an effective
cross-link density of about 7 .times. 10.sup.-5 or more moles (number of
cross-links divided by Avogadro's number) per milliliter of rubber is
representative of the values for fully cured nitrile rubber, however, this
value may be as low as about 5 .times. 10.sup.-5 especially for
polybutadiene rubber or polybutadienestyrene rubber. An effect of curing
the composition is the very substantial improvement in mechanical
properties which improvement directly relates to its practical uses.
Surprisingly, the high strength elastomeric compositions are still
thermoplastic as contrasted to thermoset elastomers.
Vulcanizable rubbers, although thermoplastic in the unvulcanized state, are
normally classified as thermosets because they undergo the process of
thermosetting to an unprocessable state. The products of the instant
invention, although processable, are prepared from blends of rubber and
polyester which are treated under time and temperature conditions to
cross-link the rubber or are treated with curatives in amounts and under
time and temperature conditions known to give cured products from static
cures of the rubber in molds and, indeed, the rubber has undergone
gelation to the extent characteristic of rubber subjected to a similar
treatment alone. Thermosets are avoided in the compositions of the
invention by simultaneously masticating and curing the blends. Thus, the
thermoplastic compositions of the invention are preferably prepared by
blending a mixture of rubber, polyester, and curatives when required, then
masticating the blend at a temperature sufficient to effect cross-link
formation, using conventional masticating equipment, for example, Banbury
mixer, Brabender mixer, or certain mixing extruders. The polyester and
rubber are mixed at a temperature sufficient to soften the polyester or,
more commonly, at a temperature above its melting point. After the
polyester and rubber are intimately mixed, curative is added if needed.
Heating and masticating at vulcanization temperatures are generally
adequate to complete the cross-link formation in a few minutes or less,
but if shorter times are desired, higher temperatures may be used. A
suitable range of temperatures for cross-link formation is from about the
melting temperature of the polyester to the decomposition temperature of
the rubber which range commonly is from about 150.degree. C. to
270.degree. C. with the maximum temperature varying somewhat depending on
the type of rubber, the presence of antidegradants and the mixing time.
Typically, the range is from about 160.degree. C. to 250.degree. C. A
preferred range of temperatures is from about 180.degree. C. to about
230.degree. C. To obtain thermoplastic compositions, it is important that
mixing continues without interruption until cross-linking occurs. If
appreciable cross-linking is allowed after mixing has stopped, a thermoset
unprocessable composition may be obtained. A few simple experiments within
the skill of the art utilizing available rubbers and curative systems will
suffice to determine their applicability for the preparation of the
improved products of this invention. For additional information on dynamic
cross-linking processes, see Gessler and Haslett, U.S. Pat. No. 3,037,954.
Methods other than the dynamic vulcanization of rubber/polyester blends can
be utilized to prepare compositions of the invention. For example, the
rubber can be fully vulcanized in the absence of the polyester, either
dynamically or statically, powdered, and mixed with the polyester at a
temperature above the melting or softening point of the polyester.
Provided that the cross-linked rubber particles are small, well dispersed
and in an appropriate concentration, the compositions within the invention
are easily obtained by blending cross-linked rubber and polyester.
Accordingly, the term "blend" herein means a mixture comprising well
dispersed small particles of cross-linked rubber. A mixture which is
outside of the invention because it contains poorly dispersed or too large
rubber particles can be comminuted by cold milling (to reduce particle
size to below about 50.mu.) preferably below 20.mu. and more preferably to
below 5.mu.. After sufficient comminution or pulverization, a composition
of the invention is obtained. Frequently, the case of poor dispersion or
too large rubber particles is visibly obvious to the naked eye and
observable in a molded sheet. This is especially true in the absence of
pigments and fillers. In such a case, pulverization and remolding gives a
sheet in which aggregates of rubber particles or large particles are not
obvious or are far less obvious to the naked eye and mechanical properties
are greatly improved.
The compositions of the invention are all processable in an internal mixer,
to products which, upon transferring at temperatures above the softening
or crystallizing points of the polyester phase, to the rotating rolls of a
rubber mill, form continuous sheets. The sheets are reprocessable in the
internal mixer, after reaching temperatures above the softening or melting
points of the polyester phase. The material is again transformed to the
plastic state (molten state of the polyester phase) but upon passing the
molten product through the rolls of the rubber mill a continuous sheet
again forms. In addition, a sheet of thermoplastic composition of this
invention can be cut into pieces and compression molded to give a single
smooth sheet with complete knitting or fusion between the pieces. It is in
the foregoing sense that "thermoplastic" will be herein understood. In
addition, elastoplastic compositions of the invention are further
processable to the extent that articles may be formed therefrom by
extrusion or injection molding.
Where the determination of extractables is an appropriate measure of the
state of cure, an improved thermoplastic composition is produced by
cross-linking a blend to the extent that the composition contains no more
than about twenty percent by weight of the rubber extractable at room
temperature by a solvent which dissolves the uncured rubber, and
preferably to the extent that the composition contains less than four
percent by weight extractable and more preferably less than two percent by
weight extractable. In general, with non self-curing rubber, the less
extractables the better are the properties, whereas, with self-curing
rubber, respectable properties are obtained with extractables as high as
twenty percent, but with either non self-curing rubber or self-curing
rubber the more preferable compositions comprise low quantities of
extractable rubber. Gel content reported as percent gel is determined by
the procedure of U.S. Pat. No. 3,203,937 which comprises determining the
amount of insoluble polymer by soaking the specimen for 48 hours in a
solvent for the rubber at room temperature and 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 the
rubber, such as extender oils, plasticizers and components of the
polyester soluble in organic solvent. Any insoluble pigments, fillers,
etc., are subtracted from both the initial and final weights.
To employ cross-link density as the measure of the state of cure which
characterizes the improved thermoplastic compositions, the blends are
cross-linked to the extent which corresponds to cross-linking the same
rubber as in the blend statically cross-linked under pressure in a mold
with such amounts of the same curative if present as in the blend and
under such conditions of time and temperature to give an effective
cross-link density greater than about 3 .times. 10.sup.-5 moles per
milliliter of rubber and preferably greater than about 5 .times. 10.sup.-5
or even more preferably 1 .times. 10.sup.-4 moles per milliliter of
rubber. The blend is then dynamically cross-linked under similar
conditions (with the same amount of curative, when present, based on the
rubber content of the blend) as was required for the rubber alone. The
cross-link density so determined may be regarded as a measure of the
amount of vulcanization which gives the improved thermoplastics. However,
it should not be assumed, from the fact that the amount of curative is
based on the rubber content of the blend and is that amount which gives
with the rubber alone the aforesaid cross-link density that the curative
does not react with the polyester or that there is no reaction between the
polyester and rubber. There may be highly significant reactions involved
but of limited extent. However, the assumption that the cross-link density
determined as described provides a useful approximation of the cross-link
density of the elastoplastic compositions is consistent with the
thermoplastic properties and with the fact that a large proportion of the
polyester can be removed from the composition by extraction with a solvent
for the polyester such as a 60/40 mixture of phenol/tetrachloroethane as a
solvent for poly terephthalates.
The cross-link density of the rubber is determined by equilibrium solvent
swelling using the Flory-Rehner equation, J. Rubber Chem. and Tech., 30,
p. 929 (1957). The appropriate Huggins solubility parameters for
rubber-solvent pairs used in the calculation were obtained from the review
article by Sheehan and Bisio, J. Rubber Chem. & Tech., 39, 149 (1966). If
the extracted gel content of the vulcanized rubber is low, it is necessary
to use the correction of Bueche wherein the term v.sub.r.sup.1/3 is
multiplied by the gel fraction (% gel/100). The cross-link density is half
the effective network chain density .nu. determined in the absence of
polyester. The cross-link density of the vulcanized blends will,
therefore, be hereinafter understood to refer to the value determined on
the same rubber as in the blend in the manner described. Still more
preferred compositions meet both of the aforedescribed measures of state
of cure, namely, by estimation of cross-link density and percent of rubber
extractable.
Rubber satisfactory for the practice of the invention comprise essentially
random noncrystalline, rubbery polymer selected from the group consisting
of a homopolymer of 1,3-butadiene, a copolymer of 1,3-butadiene
polymerized with styrene, vinyl pyridine, acrylonitrile, or
methacrylonitrile, natural or synthetic polymers of isoprene, urethane
polymers and polymers of two or more alpha monoolefins optionally
polymerized with a minor quantity of diene or mixtures thereof.
Suitable monoolefin copolymer rubber comprises essentially noncrystalline,
rubber copolymer of two or more alpha monoolefins, preferably
copolymerized with at least one polyene, usually a diene. However,
saturated monoolefin copolymer rubber, commonly called "EPM" rubber, can
be used, for example copolymers of ethylene and propylene. Examples of
unsaturated monoolefins copolymer rubber, commonly called "EPDM" rubber,
which are satisfactory comprise the products from the polymerization of
monomers comprising two monoolefins, generally ethylene and propylene, and
a lesser quantity of nonconjugated diene. Suitable alpha monoolefins are
illustrated by the formula CH.sub.2 .dbd. CHR in which R is hydrogen or
alkyl of 1-12 carbon atoms, examples of which include ethylene, propylene,
1-butene, 1-pentene, 1-hexene, 2-methyl-1-propene, 3-methyl-1-pentene,
4-methyl-1-pentene, 3,3-dimethyl-1-butene, 2,4,4-trimethyl-1-pentene,
5-methyl-1-hexene, 1,4-ethyl-1-hexene and others. Satisfactory
nonconjugated dienes include straight chain dienes as 1,4-hexadiene,
cyclic dienes such as cyclooctadiene and bridged cyclic dienes such as
ethylidenenorborene. Commercially available rubbers suitable for the
practice of the invention are described in Rubber World Blue Book, 1975
Edition, Materials and Compounding Ingredients for Rubber as follows: EPM
and EPDM rubber, pages 403, 406-410, Nitrile Rubber, pages 416-430,
Polybutadiene Rubber, pages 431-432, Polyisoprene Rubber, pages 439-440,
Styrene Butadiene Rubber, pages 452-460, and Urethane Rubber, pages
463-466. Copolymers of 1,3-butadiene and about 15-60% acrylonitrile
commonly called nitrile rubber are preferred. Both self-curing and non
self-curing nitrile rubbers are suitable in the practice of the invention.
Non self-curing nitrile rubber as the name implies requires the presence
of curatives to cross-link the rubber under processing temperatures to the
extent that the gel content of the rubber is at least about 80 percent or
more. Self-curing nitrile rubber as the name indicates will cross-link
under processing temperatures in the absence of curatives (other than
curatives which may be inherently present) to the extent that the gel
content of the rubber is at least about 80 percent or more. Compositions
of the invention comprising blends in which the rubber component is
self-curing nitrile rubber generally exhibit superior tensile strengths
and consequently are preferred. Blends comprising self-curing nitrile
rubber may be cross-linked further by the use of conventional curatives as
hereinafter described which use generally results in a further increase in
the tensile strength of the resulting composition.
Whether a nitrile rubber is self-curing or non self-curing is not dependent
on acrylonitrile content or Mooney Viscosity but appears to be an inherent
property of certain rubbers. A convenient means for determining whether a
nitrile rubber is self-curing comprises masticating the rubber at
225.degree. C. in a Brabenber mixer and observing its tendency to scorch.
Self-curing nitrile rubbers generally scorch under the aforesaid
conditions within 2-8 minutes, whereas, non self-curing rubbers generally
may be subjected to the aforesaid treatment for twenty minutes or more
without scorching. Scorching as used above means the rubber loses its
ability to maintain a continuous mass in the mixer but instead crumbles
into discrete particles with some of the particulate crumbs discharging
from the throat of the mixer if the ram is lifted while mixing is
continued. The scorched rubber or the rubber having been masticated for
twenty minutes as described is dumped from mixer, compression molded at
230.degree. C. for five minutes and the gel content determined by
extraction in dichloromethane at room temperature. A self-curing rubber
will have a gel content of about 80 percent or more (weight extractable of
20 percent or less), whereas, a non self-curing rubber will have a gel
content of less than 80 percent.
Suitable thermoplastic polyesters comprise linear, crystalline, high
molecular weight solid polymers having recurring
##STR1##
groups including
##STR2##
groups within the polymer chain. The term "linear" as used herein in
respect to polyester means a polymer in which the recurring ester groups
are within the polymer backbone and not pendant therefrom. Linear
crytalline polyesters having a softening point above 50.degree. C. are
satisfactory with polyesters having a softening point or melting point
above 100.degree. being preferred with polyesters having a softening point
or melting point between 160.degree.-260.degree. C. being more preferred.
Saturated linear polyesters (free of olefinic unsaturation) are preferred,
however, unsaturated polyesters may be used provided that the rubber is
cross-linked prior to blending with the polyester or provided that the
rubber is dynamically cross-linked with a cross-linking agent that will
not significantly induce cross-link formation in the polyester.
Cross-linked polyesters are unsatisfactory for the practice of the
invention. If significant cross-link formation of the polyester is
permitted to occur, the resulting composition is not thermoplastic. Many
commercially available thermoplastic linear crystalline polyesters may be
advantageously employed in the practice of the invention or they may be
prepared by polymerization of one or more dicarboxylic acids, anhydrides
or esters and one or more diol. Examples of satisfactory polyester include
poly(trans-1,4-cyclohexylene C.sub.2-6 alkane dicarboxylates such as
poly(trans-1,4-cyclohexylene succinate) and poly(trans-1,4-cyclohexylene
adipate), poly(cis or trans-1,4-cyclohexanedimethylene) C.sub.0-2
alkanedicarboxylates such as poly(cis 1,4-cyclohexanedimethylene)oxalate
and poly(cis 1,4-cyclohexanedimethylene)succinate, poly(C.sub.2-4 alkylene
terephthalates) such as polyethyleneterephthalate and
polytetramethyleneterephthalate, poly(C.sub.2-4 alkylene isophthalates
such as polyethyleneisophthalate and polytetramethyleneisophthalate,
poly(p-phenylene C.sub.1-8 alkanedicarboxylates such as poly(p-phenylene
glutarate) and poly(p-phenylene adipate), poly(p-xylene oxalate),
poly(o-xylene oxalate), poly(p-phenylenedi-C.sub.1-5 alkylene
terephthalates) such as poly(p-phenylenedimethylene terephthalate) and
poly(p-phenylene-di-1,4-butylene terephthalate, poly(C.sub.2-10
alkylene-1,2-ethylenedioxy-4,4'-dibenzoates) such as
poly(ethylene-1,2-ethylenedioxy-4,4'-dibenzoates),
poly(tetramethylene-1,2-ethylenedioxy-4,4'-dibenzoate) and
poly(hexamethylene-1,2-ethylenedioxy-4,4'-dibenzoate), poly(C.sub.3-10
alkylene-4,4'-dibenzoates) such as poly(pentamethylene-4,4'-dibenzoate),
poly(hexamethylene-4,4'-dibenzoate and
poly(decamethylene-4,4'-dibenzoate), poly(C.sub.2-10
alkylene-2,6-naphthalene dicarboxylates) such as
poly(ethylene-2,6-naphthalene dicarboxylates),
poly(trimethylene-2,6-naphthalene dicarboxylates) and
poly(tetramethylene-2,6-naphthalene dicarboxylates), and poly(C.sub.2-10
alkylene sulfonyl-4,4'-dibenzoates) such as poly(octamethylene
sulfonyl-4,4'-dibenzoate) and poly-(decamethylene
sulfonyl-4,4'-dibenzoate. Additional examples of satisfactory linear
polyesters are described in Encyclopedia of Polymer Science and
Technology, Vol. 11, pages 68-73 and Korshak & Vinogradova Polyesters,
Pergamon Press, pages 31-64. The disclosures thereof are hereby
incorporated herein by reference. Suitable polycarbonates are also
commercially available. For suitable segmented poly(ether-co-phthalates)
see page 461, Rubber World Blue Book, supra. Polylactones such as
polycaprolactone are satisfactory in the practice of the invention.
Preferred polyesters of the invention are derived from aromatic
dicarboxylic acids such as naphthalenic or phthalic acids. More preferred
polyesters are poly(alkylene terephthalates) especially
poly(tetramethylene terephthalate), or mixed polyphthalates derived from
two or more glycols, two or more phthalic acids, or two or more glycols
and two or more phthalic acids such as poly(alkylene
tere-co-isophthalates).
Moreover, the particular results obtained by the aforedescribed dynamic
curing process are a function of the particular rubber curing system
selected. The curatives and the curative systems conventionally used to
vulcanize diene rubbers are utilizable for preparing the improved
thermoplastics of the invention. Any curative or curative system
applicable for vulcanization of diene rubbers may be used in the practice
of the invention, for example, peroxide, azide, quinoid or accelerated
sulfur vulcanization systems. The combination of a maleimide and a
peroxide or disulfide accelerator can be used. For satisfactory curatives
and curative systems, reference is made to columns 3-5 of Fisher U.S. Pat.
No. 3,806,558, which disclosure is incorporated herein by reference.
Sufficient quantities of curatives are used, when needed, to cross-link
the rubber to achieve a gel content of 80 percent or more. Excessive
quantities of curatives should be avoided because quantities well beyond
the amount necessary to fully cure the rubber can result in diminution of
properties, for example, a reduction in ultimate elongation. Peroxide
curatives are advantageously used in reducing quantities in conjunction
with other curatives such as sulfur or bismaleimide providing the total
amount of curatives is sufficient to vulcanize fully the rubber. High
energy radiation is also utilizable as the curative means.
Curative systems comprising phenylene bis-maleimide, optionally with a
peroxide activator, are especially recommended. Also, particularly
recommended are efficient or semi-efficient sulfur curative systems which
comprise high accelerator sulfur ratios as contrasted with conventional
sulfur curative systems wherein the amount of sulfur exceeds the amount of
the accelerator.
One aspect of the invention comprises adding a liquid plasticizer to the
blend which plasticizer extends the range of proportions of polyester to
rubber in the composition while still retaining elastoplasticity. For
example, without plasticizer the weight of polyester cannot exceed the
weight of rubber without losing rubberlike elasticity, whereas, with
plasticizer the weight of polyester may exceed the weight of rubber so
long as the amount of polyester does not comprise more than 50 weight
percent of the total composition and the weight of plasticizer does not
exceed the weight of polyester. Generally, the quantity of plasticizer
when present is between 10-30 weight percent of the total composition. Any
polyester plasticizer may be used. Suitable plasticizers include phthalate
esters such as dicyclohexyl phthalate, dimethyl phthalate, dioctyl
phthalate, butyl benzyl phthalate, benzyl phthalate, phosphates such as
tributoxyethyl phosphate, tributyl phosphate, tricresyl phosphate, cresyl
diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, isodecyl diphenyl
phosphate, and triphenyl phosphate, phthalyl glycolates such as butyl
phthalyl butyl glycolate and methyl ethyl glycolate, sulfonamides such as
N-cyclohexyl-p-toluenesulfonamide, N-ethyl-o,p-toluenesulfonamide,
o,p-toluenesulfonamide and o-toluene sulfonamide and extender oils for
hydrocarbon rubbers.
Another aspect of the invention comprises adding a rubber antidegradant to
the blend prior to dynamic vulcanization. The presence of a rubber
antidegradant protects the blend from thermal and/or oxidative degradation
resulting in compositions with superior properties. Preferably, the rubber
antidegradant is added early in the mixing cycle, and more preferably, for
greater effectiveness the antidegradant is masterbatched with the rubber
and a portion of the rubber-antidegradant masterbatch is mixed with the
polyester. The polyester then melts and after complete mixing, the
composition is dynamically cured as described above. For suitable rubber
antidegradants, refer to Rubber World Blue Book, supra, pages 107-140.
The properties of the thermoplastic compositions of this invention may be
modified, either before or after vulcanization, by addition of ingredients
which are conventional in the compounding of diene rubber, polyester and
blends thereof. Examples of such ingredients include carbon black, silica,
titanium dioxide, colored pigments, clay, zinc oxide, stearic acid,
accelerators, vulcanizing agents, sulfur, stabilizers, antidegradants,
processing aids, adhesives, tackifiers, rubber plasticizers, wax,
prevulcanization inhibitors, discontinuous fibers such as wood cellulose
fibers and extender oils. The addition of carbon black, rubber plasticizer
or both, preferably prior to dynamic vulcanization, are particularly
recommended. Preferably, the carbon black and/or rubber plasticizer is
masterbatched with the rubber and the masterbatch is mixed with the
polyester. Carbon black improves the tensile strength and rubber
plasticizer can improve the resistance to oil swell, heat stability,
hysteresis, cost and permanent set of the elastoplastic compositions.
Aromatic, naphthalenic and paraffinic extender oils are plasticizers for
polybutadiene and butadiene-vinylarene type rubbers. Plasticizers can also
improve processability. For suitable extender oils, refer to Rubber World
Blue Book, supra, pages 145-190. The quantity of extender oil added
depends upon the properties desired, with the upper limit depending upon
the compatibility of the particular oil and blend ingredients which limit
is exceeded when excessive exuding of extender oil occurs. Typically, 5-75
parts by weight extender oil are added per 100 parts by weight of rubber
and polyester. Commonly, about 10 to 60 parts by weight of extender oil
are added per 100 parts by weight of rubber in the blend with quantities
of about 20-50 parts by weight of extender oil per 100 p | | |
