Note: Descriptions are shown in the official language in which they were submitted.
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W LCANIZATE ACTIVATOR SYSTEM FOR RUBBER COMPOSITIONS
Field of the Invention
The present invention relates to the
vulcanization of a sulfur curable rubber composition.
More particularly, the present invention relates to a
method for increasing the rate of cure of a sulfur
w lcanizable rubber by the addition of a methyl
trialkyl ~mmon;um salt.
Background of the Invention
The "rate of cure" is defined as the rate at
which crosslinking and the development of the
stiffness (modulus) of a rubber compound occurs. As
the rubber compound is heated, the properties of the
rubber compound change from a soft plastic to a tough
elastic material. During the curing step, crosslinks
are introduced, which connect the long polymer chains
of the rubber. As more crosslinks are introduced, the
polymer chains become more firmly connected and the
stiffness or modulus of the compound increases. The
rate of cure is an important vulcanization parameter
since it in part determines the time the compound must
be cured, i.e., the "cure time". In the manufacture
of vulcanized rubber articles, significant cost
savings can be realized through a reduction of cure
time. Through enhanced rates of cure, the cure time
required to meet m;n;mllm states of cure can be
reduced. Given the above, extensive research has been
conducted in order to shorten the cure times of
rubbers. Therefore, there exists a need for improved
methods which enhance
134~497
the rate of cure in the absence of imparting
undesirable properties to the vulcanizate.
Summary of the Invention
The present invention relates to a method for
enhancing the rate of vulcanization of a rubber
composition comprising adding to a sulfur vulcanizable
rubber a methyl trialkyl ammonium salt of the formula:
R2 (3
R1 - N R3 M
CH3
wherein R1, R2, and R3 are independently alkyl radicals
having 8 to 10 carbon atoms and M is selected from the
group consisting of Cl, Br, CH3SO4 and HSO4. In
addition, there is disclosed a sulfur w lcanizable
rubber composition comprising an elastomer containing
olefinic unsaturation, a sulfur vulcanizing agent, an
accelerator and a methyl trialkyl am~monium salt
selected from the above formula.
Detailed Description of the Invention
The present invention relates to the use of a
methyl trialkyl ammonium salt as an activator for
sulfur curable rubber compositions. A particularly
preferred methyl trialkyl am.monium salt is methyl
trialkyl(C8-C10) ~mmo~;um chloride which is
commercially available under the trademark Adogen~ 464
from Sherex Chemical Company of Dublin, Ohio and from
Henkel Corporation, Minneapolis, Minnesota, under the
trademark Aliquot~ 336. Methyl trialkyl ammonium
salts are generally known as phase-transfer catalysts
and are described in U.S. Patent 3,992,432.
134~49 7
For ease in handling, the methyl trialkyl ammonium
salt may be deposited on suitable carriers. Examples
of carriers which may be used in the present invention
include silica, carbon black, alumina, kieselguhr,
silica gel and calcium silicate.
Use of a methyl trialkyl ammonium salt does not
appear to affect crosslink distribution when used in
combination with primary and optionally secondary
accelerators. However, along with increased cure rate,
there is usually seen an increased curative efficiency
in the form of increased state or degree of cure.
The present invention may be used to cure sulfur
vulcanizable rubbers or elastomers containing olefinic
unsaturation. The phrase "rubber or elastomer
containing olefinic unsaturation" is intended to
include both natural rubber and its various raw and
reclaim forms as well as various synthetic rubbers.
Representative synthetic polymers are the
homopolymerization products of butadiene and its
homologues and derivatives, for example,
methylbutadiene, dimethylbutadiene and pentadiene as
well as copolymers such as those formed from butadiene
or its homologues or derivatives with other unsaturated
monomers. Among the latter are acetylenes, for
example, vinyl acetylene; olefins, for example,
isobutylene, which copolymerizes with isoprene to form
butyl rubber; vinyl compounds, for example, acrylic
acid, acrylonitrile (which polymerize with butadiene to
form NBR), methacrylic acid and styrene, the latter
compound polymerizing with butadiene to form SBR, as
well as vinyl esters and various unsaturated aldehydes,
ketones and ethers, e.g., acrolein, methyl isopropenyl
ketone and vinylethyl ether. Specific examples of
synthetic rubbers include neoprene (polychloroprene),
'~h
1340497
polybutadiene (including cis-1,4-polybutadiene),
polyisoprene (including cis-1,4-polyisoprene), butyl
rubber, copolymers of 1,3-butadiene or isoprene with
monomers such as styrene, acrylonitrile and methyl
methacrylate, as well as ethylene/propylene
terpolymers, also known as ethylene/propylene/diene
monomer (EPDM), and in particular, ethylene/propylene/
dicyclopentadiene terpolymers.
The activator used in the present invention may be
added to the rubber by any conventional technique such
as on a mill or in a Banbury. The amount of methyl
trialkyl ammonium salt may vary widely depending on the
type of rubber and other compounds present in the
vulcanizable composition. Generally, the amount of
methyl trialkyl ammonium salt is used in a range of
from about .05 to about 5.0 phr with a range of .1 to
about 1.5 phr being preferred.
Vulcanization of the rubber is generally carried
out at temperatures of between about 100~C and 200~C.
Preferably, the vulcanization is conducted at
temperatures ranging from about 110~C to 180~C. Any of
the usual vulcanization processes may be used such as
heating in a press or mold, heating with superheated
steam or hot air or in a salt bath.
In addition to the methyl trialkyl ammonium salt,
other rubber additives may also be incorporated in the
sulfur vulcanizable material. The additives commonly
used in rubber vulcanizates are, for example, carbon
black, tackifier resins, processing aids, antioxidants,
antiozonants, stearic acid, activators, waxes, oils and
peptizing agents. As known to those skilled in the
art, depending on the intended use of the sulfur
vulcanizable material, certain additives mentioned
above are commonly used in conventional amounts.
134~497
Typical additions of carbon black comprise about 20 to
100 parts by weight of diene rubber (phr), preferably
50 to 70 phr. Typical amounts of tackifier resins
comprise about 5 to 10 phr. Typical amounts of
processing aids comprise about 1 to 5 phr. Typical
amounts of antioxidants comprise 1 to about 10 phr.
Typical amounts of antiozonants comprise 1 to about 10
phr. Typical amounts of stearic acid comprise 1 to
about 2 phr. Typical amounts of zinc oxide comprise 2
to 5 phr. Typical amounts of waxes comprise 1 to 5
phr. Typical amounts of oils comprise 5 to 30 phr.
Typical amounts of peptizers comprise .l to 1 phr. The
presence and relative amounts of the above additives
are not an aspect of the present invention.
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 about 0.5 to 8 phr with
a range of from 1.5 to 2.25 being preferred.
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, a primary accelerator is
used in amounts ranging from about .5 to 2.0 phr. In
another embodiment, combinations of two or more
accelerators may be used which may consist of a primary
accelerator which is generally used in the larger
amount (.5 to 1.0 phr), and a secondary accelerator
r~~S,
13~ 4'.~7
which is generally used in smaller amounts (.05-.50
phr) in order to activate and to improve the properties
of the w lcanizate. Combinations of these accelerators
have been known to produce a synergistic effect of 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 effected by normal processing temperatures but
produce satisfactory cures at ordinary vulcanization
temperatures. 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 secondary accelerator is used, the secondary
accelerator is preferably a guanidine, dithiocarbamate
or thiuram compound.
The following examples are presented in order to
illustrate but not limit the present invention.
Examples 1-11
These experiments contrast the effectiveness of
methyl trialkyl(C8-C10) ammonium chloride (MTAAC) at
varying levels versus using an equivalent amount of
tetraethyl ammonium bromide (TEABr) as a control. The
MTAAC and TEABr were used in a typical sidewall rubber
stock comprising 40 parts by weight of polyisoprene, 60
parts cis-1,4-polybutadiene, .5 phr of a primary
accelerator and conventional amounts of carbon black,
tackifier, processing aids, antidegradant, stearic
acid, zinc oxide and sulfur. The various additives
were compounded using conventional techniques. Cure
testing was performed at 150~C on a Monsanto Cure
Rheometer according to ASTM test method D-2084-87. The
'~
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scorch of the compound was measured according to ASTM
test method D1646-87. Table I shows the results for
Examples 1-11.
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1340497
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134~497
The data of Table I show that the control compound
(tetraethyl ammonium bromide) showed little or no
effect on cure time as evaluated by t25 and t90. Use
of methyl trialkyl(C8-C10) ammonium chloride (MTAAC),
however, resulted in significantly reduced cure times.
Examples 12-19
Experiments (Examples 12-19) were conducted to
demonstrate the enhanced cure rates by the addition of
a methyl trialkyl(C8-C10) ammonium salt to a sulfur
w lcanizable rubber. An experiment (Example 12,
Control) was conducted for comparative purposes.
Experiments (Examples 13 and 14) were conducted to
demonstrate the effectiveness of using 68% by weight of
methyl trialkyl(C8-C10) ammonium chloride deposited on
calcium silicate. Experiments (Examples 15 and 16)
were conducted to demonstrate the effectiveness of
using 72% by weight of methyl trialkyl(C8-C10) ammonium
chloride deposited on silica. Experiments (Examples
17-19) were conducted to demonstrate the effectiveness
of using methyl trialkyl(C8-C10) ammonium methyl
sulfate. The eight rubber compounds were prepared
using varied levels of methyl trialkyl ammonium salt
(phr) and a typical sidewall rubber stock comprising 40
parts polyisoprene, 60 parts cis-1,4-polybutadiene, .5
phr of a primary accelerator and conventional amounts
of carbon black, tackifier, process oil, antidegradant,
stearic acid, zinc oxide, and sulfur. The various
additives were compounded using conventional techniques
and the samples were evaluated using the curing
procedures of Examples 1-11. Table II below lists the
cure properties for the compounds of Examples 12-19
which resulted in similar states of cure with different
cure rates as seen by t25 and t90.
j,... .
Table II
Example No. 12 13 14 15 16 17 18 19
Amount of methyl trialkyl
~mmnnil~ salt (phr) 0 0.251 .501 o.252 o~502 0.173 0.343 0.503
Rheometer, 150~C
t2, min. 7.0 5.8 5.2 5.8 4.8 5.9 5.2 4.9
t25, min. 9.4 7.5 6.6 7.5 6.3 7.6 6.8 6.3
t90, min. 26.8 19.8 17.4 19.3 16.6 19.6 18.1 17.2
Delta torque, dNm 21.2 24.5 25.9 24.6 26.1 24.2 25.5 25.8
Mocney scorch, 121~C
t5, min. 33.5 28.4 24.6 27.7 24.3 28.5 25.7 23.6
1 68% by weight of methyl trialkyl(C8-C10) ammoni~m chloride deposited on calcium silicate.
2 72% by weight of methyl trialkyl(C8-C10) ~mmrni1~ chloride deposited on silica.
3 Methyl trialkyl(C8-C10) ~mmnni1~ methyl sulfate.
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Examples 13-19 demonstrate that methyl
trialkyl(C8-C10) ammonium salts are effective in
enhancing the rates of cure. The data for Examples
13-16 indicate that use of various carriers are not
detrimental to the effectiveness of methyl
trialkyl(C8-C10) ammonium chloride. Examples 17-19
suggest that methyl trialkyl(C8-C10) ammonium methyl
sulfate is as effective as the other methyl trialkyl
ammonium salts used in the present invention.
Examples 20-21
The following experiments were conducted to
demonstrate the cure activation of methyl trialkyl
ammonium chloride (MTAAC). The formulation for Example
20 (Control) did not contain MTAAC and the formulation
for Example 21 contained .30 phr of MTAAC. Both
formulations comprised a typical sidewall rubber stock
containing 20 parts by weight natural rubber, 20 parts
by weight of synthetic polyisoprene, 60 parts by weight
polybutadiene, .5 phr of a primary accelerator and
conventional amounts of carbon black, waxes, oils,
antidegradants, tackifier resin, stearic acid, zinc
oxide, and sulfur. The various additives were
compounded and the samples were vulcanized by
compression molding for 18 minutes at 150~C. The cure
properties were evaluated in the same manner as in
Examples 1-11. The stress-strain properties were
tested according to ASTM method No. D412-87. The data
appear in Table III.
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13~U497
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1340 1.97
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The above data show that addition of a methyl
trialkyl ammonium chloride reduces the cure time
required to reach optimum cure. The use of the methyl
trialkyl ammonium salt has little effect on crosslink
distribution and allows for better utilization of
sulfur as evidenced by an increase in crosslink densitv
(v x 104) and increased 300% modulus.
Examples 22-23
The following experiments were conducted to
demonstrate the effectiveness of MTAAC in another
sulfur vulcanizable composition. The formulation for
Example 22 (Control) did not contain MTAAC and the
formulation for Example 23 contained .50 phr of MTAAC.
Both formulations comprised a typical tread rubber
stock containing 30 parts by weight of polybutadiene,
70 parts by weight of SBR, 1 phr of a primary
accelerator, .15 phr of a secondary accelerator and
conventional amounts of carbon black, waxes, oil,
peptizer, stearic acid, antidegradant, zinc oxide, and
sulfur. The various additives were compounded and the
samples were vulcanized by compression molding for 18
minutes at 150~C. After curing, these samples were
evaluated using testing procedures of Examples 20-21.
The data are set forth in Table IV.
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Table IV
Physical Properties of Example 22 (Control) and 23
Example 22 (Control)Example 23
Monsanto Rheometer, 1~ Arc, 150~C
Delta torque, MHF ~ ML (dNm) 22.8 24.5
Cure time, t90, min. 20 12.6
Cure time, t25, min. 8.6 6.6
tl pt. rise, min. 6.6 5.4
t90 - tl pt, min. 13.4 7.2
Crosslink Type Analysis
% Sx, Polysulfide 63 66
% S2, Disulfide 22 24
% Sl, Monosulfide 15 10
13~0497
Examples 22 and 23 demonstrate the effectiveness of
MTAAC in a polybutadiene/SBR blend.
Examples 24 and 25
The following examples were conducted in order to
demonstrate the effectiveness of MTAAC in another
sulfur vulcanizable composition. The formulation for
Example 24 (Control) did not contain MTAAC and the
formulation for Example 25 contained 0.2 phr of MT M C.
Both formulations comprised a typical tread rubber
stock containing 70 parts by weight of medium vinyl
polybutadiene, 30 parts by weight of
cis-1,4-polybutadiene, l.l phr of a primary
accelerator, .16 phr of a secondary accelerator and
conventional amounts of carbon black, waxes, oil,
antidegradants, stearic acid, zinc oxide and sulfur.
The various additives were compounded using
conventional techniques.
These samples were evaluated by the cure testing
procedures used in Examples 20 and 21. The data are
set forth in Table V.
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Table V
Cure Properties of
Example 24 (Control) and 25
Example 24
(Control) Example 25
Monsanto Rheometer, 1~ Arc, 150~C
Delta torque, MHF ML (dNm) 30.7 31.5
Cure time, t90, min. 13.8 11.2
Cure time, t25, min. 7.4 5.8
tl pt rise, min. 5.6 4.6
t90 - tl pt, min. 8.2 6.6
Examples 26-29
These experiments contrast the effectiveness of
methyl trialkyl(C8-C10) ammonium chloride (MTAAC) in
the presence or absence of an accelerator. The
remaining component of the formulations for Examples
26-29 comprised a rubber stock containing 50 parts by
weight of SBR, 50 parts by weight of polyisoprene and
conventional amounts of oil (28.75 phr), carbon black
(50 phr), zinc oxide (3 phr), sulfur (2 phr) and
stearic acid (2 phr). In Example 26, no accelerator or
MTAAC was used. In Example 27 no accelerator was used
but .50 phr MTAAC (68~ by weight of Adogen 464 on
calcium silicate carrier) was used. In Example 28, 1.5
phr of accelerator was used but no MTAAC was used. In
Example 29 1.5 phr of accelerator was used and .50 phr
of MTAAC (same as Example 27) was used. The various
additives were compounded using conventional
techniques. Cure testing was performed at 150~C on a
Monsanto Cure Rheometer according to ASTM test method
No. D-2084. The cure properties are given in Table VI
below.
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Table VI
Example 26 Example 27 Example 28 Example 29
Rheometer, 150~C
t2, min. - - 13.20 8.90
t25, min. - - 16.50 11.20
t90, min. - - 24.70 16.60
Delta torque, dNm 4.10 1 8.50 29.10 29.40
1 taken at 60 minutes. ~
:3
134~ i~7
Example 26 shows the very poor cure which occurs
when no MTAAC or accelerator is used. The data from
Example 27 show that, in the absence of an accelerator,
use of MTAAC does not result in any substantial cure.
The data for Example 28 show a typical accelerator
effect. The data for Example 29 show a dramatic
reduction in cure time when both an accelerator and
MTAAC activator are used.
