A method is disclosed for increasing the rate of vulcanization of a sulfur rubber composition comprising heating a sulfur vulcanizable rubber composition to a temperature ranging from 100.degree. C. to 200.degree. C., said rubber composition, containing a sulfur vulcanizable rubber, a sulfenamide compound and a hydrated thiosulfate. Addition of the hydrated thiosulfate to a sulfur vulcanizable rubber and a sulfenamide compound significantly increases the rate of vulcanization of the rubber.

FIELD OF THE INVENTION 
The present invention relates to increasing the rate of vulcanization of a 
sulfur curable rubber composition. 
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 minimum 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 the rate of cure in the absence of 
imparting undesirable properties to the vulcanizate. 
SUMMARY OF THE INVENTION 
The present invention relates to the use of a sulfenamide compound and a 
hydrated thiosulfate in a sulfur vulcanizable rubber.

DETAILED DESCRIPTION OF THE INVENTION 
There is disclosed a method for increasing the rate of vulcanization of a 
sulfur vulcanizable rubber composition by heating a sulfur vulcanizable 
composition to a temperature ranging from 100.degree. C. to 200.degree. 
C., said rubber composition comprising 
(a) a sulfur vulcanizable rubber 
(b) from 0.5 phr to 5 phr of a sulfenamide compound of the general formula: 
##STR1## 
wherein R.sup.1 is hydrogen, an acyclic aliphatic group having from about 
1 to 10 carbon atoms, or a cyclic aliphatic group having from about 5 to 
10 carbon atoms; and R.sup.2 is hydrogen, a cyclic aliphatic group having 
from 5 to 10 carbon atoms or a mercaptobenzothiazolyl group of the 
formula: 
##STR2## 
(c) from 0.05 to 10 phr of a hydrated thiosulfate. 
There is also disclosed a sulfur vulcanizable composition comprising a 
sulfur vulcanizable rubber composition comprising 
(a) a sulfur vulcanizable rubber 
(b) from 0.5 phr to 5 phr of a sulfenamide compound of the general formula: 
##STR3## 
wherein R.sup.1 is selected from the group consisting of hydrogen, acyclic 
aliphatic groups having from about 1 to 10 carbon atoms, and cyclic 
aliphatic groups having from about 5 to 10 carbon atoms; and R.sup.2 is 
selected from the group consisting of cyclic aliphatic groups having from 
about 5 to 10 carbon atoms or a mercaptobenzothiazolyl group of the 
formula: 
##STR4## 
(c) from 0.05 to 10 phr of a hydrated thiosulfate. 
The present invention may be used to vulcanize 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. In the description of this invention, the terms 
"rubber" and "elastomer" may be used interchangeably, unless otherwise 
prescribed. The terms "rubber composition", "compounded rubber" and 
"rubber compound" 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. 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), polybutadiene (including 
cis-1,4-polybutadiene), styrene-butadiene copolymers, polyisoprene 
(including cis-1,4-polyisoprene), butyl rubber, styrene-isoprene 
copolymers, styrene-isoprene-butadiene terpolymers, methyl 
methacrylate-butadiene copolymers, methyl methacrylate-isoprene 
copolymers, as well as ethylene/propylene terpolymers, also known as 
ethylene/propylene/diene monomer (EPDM), and in particular, 
ethylene/propylene/dicyclopentadiene terpolymers. Mixtures of the above 
rubber may be used. The preferred rubber or elastomers are 
styrene/butadiene copolymer, polybutadiene, natural rubber and 
polyisoprene. 
The term "phr" as used herein, and according to conventional practice, 
refers to "parts by weight of a respective material per 100 parts by 
weight of rubber, or elastomer". 
The first essential component of the present invention is the hydrated 
thiosulfate. The hydrated thiosulfate that is used may vary. 
Representative examples of such hydrated thiosulfates include BaS.sub.2 
O.sub.3.H.sub.2 O, K.sub.2 S.sub.2 O.sub.3.1.5 H.sub.2 O, CaS.sub.2 
O.sub.3.6H.sub.2 O, MgS.sub.2 O.sub.3.6H.sub.2 O, NiS.sub.2 
O.sub.3.6H.sub.2 O, CoS.sub.2 O.sub.3.6H.sub.2 O, SrS.sub.2 
O.sub.3.5H.sub.2 O, Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O, MnS.sub.2 
O.sub.3.5H.sub.2 O, Li.sub.2 S.sub.2 O.sub.3.3H.sub.2 O and CdS.sub.2 
O.sub.3.2H.sub.2 O. Preferably, the hydrated thiosulfate is Na.sub.2 
S.sub.2 O.sub.3.5H.sub.2 O. 
The hydrated thiosulfate 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 hydrated thiosulfate may vary widely depending on the type 
of rubber and other compounds present in the vulcanizable composition. 
Generally, the amount of hydrated thiosulfate is used in a range of from 
about 0.05 to about 10.0 phr with a range of 0.1 to about 5.0 phr being 
preferred. 
For ease in handling, the sodium thiosulfate pentahydrate salt may be used 
per se or 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. 
The above sulfenamide compound is the second essential component of the 
present invention. The sulfenamide is generally present in an amount of 
from about 0.5 to about 5 phr. Preferably, the sulfenamide is present in 
an amount ranging from about 0.70 to about 2.0 phr. 
Representative of the sulfenamide compounds which may be used in the 
present invention include N-cyclohexyl-2-benzothiazylsulfenamide, 
N-t-butyl-2-benzothiazylsulfenamide, 
N,N-dicyclohexyl-2-benzothiazylsulfenamide, 
N-isopropyl-2-benzothiazylsulfenamide and 
N-t-butylbis-(2-benzothiazylsulfen)amide. Preferably, the sulfenamide 
compound is N-cyclohexyl-2-benzothiazylsulfenamide. 
The processing of the sulfur vulcanizable rubber is conducted in the 
presence of a sulfur vulcanizing agent. Examples of suitable sulfur 
vulcanizing agents include elemental sulfur (free sulfur), an amine 
disulfide, polymeric polysulfide or sulfur olefin adducts. Preferably, the 
sulfur vulcanizing agent is elemental sulfur. The sulfur vulcanizing agent 
may be used in an amount ranging from 0.5 to 8 phr, with a range of from 
1.5 to 5.0 being preferred. 
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 activators and retarders and processing 
additives, such as oils, resins including tackifying resins and 
plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, 
antioxidants and antiozonants and peptizing agents. 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 reinforcing type carbon blacks(s), for this invention, 
if used, are hereinbefore set forth. Typical amounts of tackifier resins, 
if used, comprise about 0.5 to about 10 phr, usually about 1 to about 5 
phr. Typical amounts of processing aids comprise about 1 to about 50 phr. 
Such processing aids can include, for example, aromatic, napthenic, and/or 
paraffinic processing oils. Typical amounts of antioxidants comprise about 
1 to about 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 344-346. Typical 
amounts of antiozonants comprise about 1 to 5 phr. Typical amounts of 
fatty acids, if used, which can include stearic acid comprise about 0.5 to 
about 3 phr. Typical amounts of zinc oxide comprise about 2 to about 5 
phr. Typical amounts of waxes comprise about 1 to about 5 phr. Often 
microcrystalline waxes are used. Typical amounts of peptizers comprise 
about 0.1 to about 1 phr. Typical peptizers may be, for example, 
pentachlorothiophenol and dibenzamidodiphenyl disulfide. 
In one aspect of the present invention, the sulfur vulcanizable rubber 
composition is then sulfur-cured or vulcanized. 
Vulcanization of the rubber composition of the present invention is 
generally carried out at conventional temperatures ranging from about 
100.degree. C. to 200.degree. C. Preferably, the vulcanization is 
conducted at temperatures ranging from about 110.degree. C. to 180.degree. 
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 sulfenamide compounds, additional accelerators are used 
to control the time and/or temperature required for vulcanization and to 
improve the properties of the vulcanizate. In one embodiment, only the 
sulfenamide may be used, i.e., primary accelerator. In another embodiment, 
combinations of a sulfenamide and a secondary accelerator might be used 
with the secondary accelerator being used in smaller amounts (of about 
0.05 to about 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 other than the sulfenamides that may 
be used in the present invention are amines, disulfides, guanidines, 
thioureas, thiazoles, thiurams, dithiocarbamates and xanthates. If a 
second accelerator is used, the secondary accelerator is preferably a 
guanidine, dithiocarbamate or thiuram compound. 
The rubber compositions of the present invention may contain sulfur 
containing organosilicon compounds. 
Examples of suitable sulfur containing organosilicon compounds are of the 
formula: 
EQU Z--Alk--S.sub.n --Alk--Z 
in which Z is selected from the group consisting of 
##STR5## 
where R.sup.1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or 
phenyl; 
R.sup.2 is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon 
atoms; 
Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer 
of 2 to 8. 
Specific examples of sulfur containing organosilicon compounds which may be 
used in accordance with the present invention include: 
3,3'-bis(trimethoxysilylpropyl) disulfide, 3,3'-bis(triethoxysilylpropyl) 
tetrasulfide, 3,3'-bis(triethoxysilylpropyl) octasulfide, 
3,3'-bis(trimethoxysilylpropyl) tetrasulfide, 
2,2'-bis(triethoxysilylethyl) tetrasulfide, 
3,3'-bis(trimethoxysilylpropyl) trisulfide, 3,3'-bis(triethoxysilylpropyl) 
trisulfide, 3,3'-bis(tributoxysilylpropyl) disulfide, 
3,3'-bis(trimethoxysilylpropyl) hexasulfide, 
3,3'-bis(trimethoxysilylpropyl) octasulfide, 
3,3'-bis(trioctoxysilylpropyl) tetrasulfide, 
3,3'-bis(trihexoxysilylpropyl) disulfide, 
3,3'-bis(tri-2"-ethylhexoxysilylpropyl) trisulfide, 
3,3'-bis(triisooctoxysilylpropyl) tetrasulfide, 
3,3'-bis(tri-t-butoxysilylpropyl) disulfide, 2,2'-bis(methoxy diethoxy 
silyl ethyl) tetrasulfide, 2,2'-bis(tripropoxysilylethyl) pentasulfide, 
3,3'-bis(tricyclonexoxysilylpropyl) tetrasulfide, 
3,3'-bis(tricyclopentoxysilylpropyl) trisulfide, 
2,2'-bis(tri-2"-methylcyclohexoxysilylethyl) tetrasulfide, 
bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl 
3'-diethoxybutoxy-silylpropyltetrasulfide, 2,2'-bis(dimethyl 
methoxysilylethyl) disulfide, 2,2'-bis(dimethyl sec.butoxysilylethyl) 
trisulfide, 3,3'-bis(methyl butylethoxysilylpropyl) tetrasulfide, 
3,3'-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2'-bis(phenyl 
methyl methoxysilylethyl) trisulfide, 3,3'-bis(diphenyl 
isopropoxysilylpropyl) tetrasulfide, 3,3'-bis(diphenyl 
cyclohexoxysilylpropyl) disulfide, 3,3'-bis(dimethyl 
ethylmercaptosilylpropyl) tetrasulfide, 2,2'-bis(methyl 
dimethoxysilylethyl) trisulfide, 2,2'-bis(methyl ethoxypropoxysilylethyl) 
tetrasulfide, 3,3'-bis(diethyl methoxysilylpropyl) tetrasulfide, 
3,3'-bis(ethyl di-sec. butoxysilylpropyl) disulfide, 3,3'-bis(propyl 
diethoxysilylpropyl) disulfide, 3,3'-bis(butyl dimethoxysilylpropyl) 
trisulfide, 3,3'-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenyl 
ethoxybutoxysilyl 3'-trimethoxysilylpropyl tetrasulfide, 
4,4'-bis(trimethoxysilylbutyl) tetrasulfide, 6,6'-bis(triethoxysilylhexyl) 
tetrasulfide, 12,12'-bis(triisopropoxysilyl dodecyl) disulfide, 
18,18'-bis(trimethoxysilyloctadecyl) tetrasulfide, 
18,18'-bis(tripropoxysilyloctadecenyl) tetrasulfide, 
4,4'-bis(trimethoxysilyl-buten-2-yl) tetrasulfide, 
4,4'-bis(trimethoxysilylcyclohexylene) tetrasulfide, 
5,5'-bis(dimethoxymethylsilylpentyl) trisulfide, 
3,3'-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide, 
3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide. 
The preferred sulfur containing organosilicon compounds are the 
3,3'-bis(trimethoxy or triethoxy silylpropyl) sulfides. The most preferred 
compound is 3,3'-bis(triethoxysilylpropyl) tetrasulfide. Therefore as to 
formula I, preferably Z is 
##STR6## 
where R.sup.2 is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms 
being particularly preferred; Alk is a divalent hydrocarbon of 2 to 4 
carbon atoms with 3 carbon atoms being particularly preferred; and n is an 
integer of from 3 to 5 with 4 being particularly preferred. 
The amount of the sulfur containing organosilicon compound in a rubber 
composition will vary depending on the level of silica that is used. 
Generally speaking, the amount will range from 0.5 to 50 phr. Preferably, 
the amount will range from 1.5 to 8 phr. Depending on the desired 
properties, the weight ratio of the sulfur containing organosilicon 
compound to silica may vary. Generally speaking, the weight ratio will 
range from 1:100 to 1:5. Preferably, the weight ratio will range from 1:20 
to 1:10. 
When the sulfur containing organosilicon is present, the rubber composition 
should contain a sufficient amount of silica, and carbon black, if used, 
to contribute a reasonably high modulus and high resistance to tear. The 
silica filler may be added in amounts ranging from 10 to 250 phr. 
Preferably, the silica is present in an amount ranging from 15 to 80 phr. 
If carbon black is also present, the amount of carbon black, if used, may 
vary. Generally speaking, the amount of carbon black will vary from 0 to 
80 phr. Preferably, the amount of carbon black will range from 0 to 40 
phr. 
Where the rubber composition contains both silica and carbon black, the 
weight ratio of silica to carbon black may vary. For example, the weight 
ratio may be as low as 1:5 to a silica to carbon black weight ratio of 
30:1. Preferably, the weight ratio of silica to carbon black ranges from 
1:3 to 5:1. The combined weight of the silica and carbon black, as 
hereinbefore referenced, may be as low as about 30 phr, but is preferably 
from about 45 to about 90 phr. It is to be appreciated that the sulfur 
containing organosilicon may be used in conjunction with a carbon black, 
namely pre-mixed with a carbon black prior to addition to the rubber 
composition, and such carbon black is to be included in the aforesaid 
amount of carbon black for the rubber composition formulation. The 
commonly employed siliceous pigments used in rubber compounding 
applications can be used as the silica in this invention, including 
pyrogenic and precipitated siliceous pigments (silica), although 
precipitate silicas are preferred. The siliceous pigments 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 about 40 
to about 600, and more usually in a range of about 50 to about 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 about 100 to about 400, and more 
usually about 150 to about 300. 
The silica might be expected to have an average ultimate particle size, for 
example, in the range of 0.01 to 0.05 micron as determined by the electron 
microscope, although the silica particles may be even smaller, or possibly 
larger, in size. 
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 
Rhone-Poulenc, with, for example, designations of Z1165MP and Z165GR and 
silicas available from Degussa AG with, for example, designations VN2 and 
VN3, etc. The PPG Hi-Sil silicas are currently preferred. The rubber 
compositions of the present invention may contain a methylene donor and a 
methylene acceptor. The term "methylene donor" is intended to mean a 
compound capable of reacting with a methylene acceptor (such as resorcinol 
or its equivalent containing a present hydroxyl group) and generate the 
resin in-situ. Examples of methylene donors which are suitable for use in 
the present invention include hexamethylenetetramine, 
hexaethoxymethylmelamine, hexamethoxymethylmelamine, 
lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride, 
trioxan hexamethoxymethylmelamine, the hydroxy groups of which may be 
esterified or partly esterified, and polymers of formaldehyde such as 
paraformaldehyde. In addition, the methylene donors may be N-substituted 
oxymethylmelamines, of the general formula: 
##STR7## 
wherein X is an alkyl having from 1 to 8 carbon atoms, R.sup.3, R.sup.4, 
R.sup.5, R.sup.6 and R.sup.7 are individually selected from the group 
consisting of hydrogen, an alkyl having from 1 to 8 carbon atoms and the 
group --CH.sub.2 OX. Specific methylene donors include 
hexakis-(methoxymethyl)melamine, N,N',N"-trimethyl/N,N', - 
N"-trimethylolmelamine hexamethylolmelamine N,N', N"-dimethylolmelamine, 
N-methylolmelamine, N,N'-dimethylolmelamine, 
N,N',N"-tris(methoxymethyl)melamine and 
N,N'N"-tributyl-N,N',N"-trimethylol-melamine. The N-methylol derivatives 
of melamine are prepared by known methods. 
The amount of methylene donor and methylene acceptor that is present in the 
rubber stock may vary. Typically, the amount of methylene donor and 
methylene acceptor that each is present will range from about 0.1 phr to 
10.0 phr. Preferably, the amount of methylene donor and methylene acceptor 
that each is present ranges from about 2.0 phr to 5.0 phr. 
The weight ratio of methylene donor to the methylene acceptor may vary. 
Generally speaking, the weight ratio will range from about 1:10 to about 
10:1. Preferably, the weight ratio ranges from about 1:3 to 3:1. 
When the compound of the present invention is used as a wire coat or bead 
coat for use in a tire, the compound generally contains an organo-cobalt 
compound which serves as a wire adhesion promoter. Any of the 
organo-cobalt compounds known in the art to promote the adhesion of rubber 
to metal may be used. Thus, suitable organo-cobalt compounds which may be 
employed include cobalt salts of fatty acids such as stearic, palmitic, 
oleic, linoleic and the like; cobalt salts of aliphatic or alicyclic 
carboxylic acids having from 6 to 30 carbon atoms; cobalt chloride, cobalt 
naphthenate; cobalt carboxylate and an organo-cobalt-boron complex 
commercially available under the designation Manobond C from Wyrough and 
Loser, Inc, Trenton, N.J. Manobond C is believed to have the structure: 
##STR8## 
in which R.sup.12 is an alkyl group having from 9 to 12 carbon atoms. 
Amounts of organo-cobalt compound which may be employed depend upon the 
specific nature of the organo-cobalt compound selected, particularly the 
amount of cobalt metal present in the compound. Since the amount of cobalt 
metal varies considerably in organo-cobalt compounds which are suitable 
for use, it is most appropriate and convenient to base the amount of the 
organo-cobalt compound utilized on the amount of cobalt metal desired in 
the finished stock composition. Accordingly, it may in general be stated 
that the amount of organo-cobalt compound present in the stock composition 
should be sufficient to provide from about 0.01 percent to about 0.35 
percent by weight of cobalt metal based upon total weight of the rubber 
stock composition with the preferred amounts being from about 0.03 percent 
to about 0.2 percent by weight of cobalt metal based on total weight of 
skim stock composition. 
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 including sulfur vulcanizing agents 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, silica and sulfur containing 
organosilicon, and carbon black if used, may be 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. 
Upon vulcanization of the sulfur vulcanizable composition at a temperature 
ranging from 100.degree. C. to 200.degree. C., the rubber composition of 
this invention can be used for various purposes. For example, the sulfur 
vulcanized rubber composition may be in the form of a tire, belt, hose, 
motor mounts, gaskets and air springs. In the case of a tire, it can be 
used for various tire components. 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. Preferably, the rubber composition is 
used in the tread of a tire. As can be appreciated, the tire may be a 
passenger tire, aircraft tire, truck tire and the like. Preferably, the 
tire is a passenger tire. The tire may also be a radial or bias, with a 
radial tire being preferred. 
The invention may be better understood by reference to the following 
examples in which the parts and percentages are by weight unless otherwise 
indicated. 
The following examples are presented in order to illustrate but not limit 
the present invention. 
Cure properties were determined using a Monsanto oscillating disc rheometer 
which was operated at a temperature of 150.degree. C. and at a frequency 
of 11 hertz. A description of oscillating disc rheometers can be found in 
the Vanderbilt Rubber Handbook edited by Robert O. Ohm (Norwalk, Conn., R. 
T. Vanderbilt Company, Inc., 1990), pages 554-557. The use of this cure 
meter and standardized values read from the curve are specified in ASTM 
D-2084. A typical cure curve obtained on an oscillating disc rheometer is 
shown on page 555 of the 1990 edition of the Vanderbilt Rubber Handbook. 
In such an oscillating disc rheometer, compounded rubber samples are 
subjected to an oscillating shearing action of constant amplitude. The 
torque of the oscillating disc embedded in the stock that is being tested 
that is required to oscillate the rotor at the vulcanization temperature 
is measured. The values obtained using this cure test are very significant 
since changes in the rubber or the compounding recipe are very readily 
detected. It is obvious that it is normally advantageous to have a fast 
cure rate. 
The formulation set out in Table 1 was utilized for all the examples unless 
otherwise stated. The various additives were compounded using conventional 
rubber compounding techniques and the samples vulcanized by compression 
molding methods for 36 minutes at 150.degree. C. unless otherwise stated. 
TABLE 1 
______________________________________ 
Non-Productive 
Antioxidant.sup.1 1.00 
Polyisoprene 50.00 
SBR.sup.2 1712C 69.75 
Processing Oil 10.00 
Stearic acid 2.00 
Zinc Oxide 3.00 
Carbon Black.sup.3 
50.00 
Productive 
Sulfur 1.75 
Sulfenamide.sup.4 1.25 
Hydrated Thiosulfate 
variable 
______________________________________ 
.sup.1 diarylphenylenediamine 
.sup.2 emulsion polymerized styrenebutadiene rubber available from The 
Goodyear Tire & Rubber Co under the designation SBR 1712C 
.sup.3 N299 
.sup.4 Ncyclohexyl-2-benzothiazolesulfenamide 
EXAMPLE 1 
In this example, sodium thiosulfate pentahydrate is evaluated as a cure 
activator which can be used to beneficially reduce cure times without 
sacrificing cured physical properties of the resultant vulcanizate. The 
rubber compositions are identified herein as Samples A, B, C, D and E of 
Table 2 with Sample A acting as the control compound containing no sodium 
thiosulfate pentahydrate, and Samples B, C, D and E utilizing sodium 
thiosulfate pentahydrate varying amounts from 0.5 phr to 5.0 phr, 
respectively. The date illustrates that with the addition of sodium 
thiosulfate pentahydrate to control A cure times were substantially 
reduced (Sample B with 0.5 phr sodium thiosulfate pentahydrate gave a cure 
time reduction of 27.9 percent; Sample C, a 41.0 percent reduction with 
1.0 phr sodium thiosulfate pentahydrate; Sample D, a 55.7 percent 
reduction with 2.0 phr sodium thiosulfate pentahydrate; and Sample E, a 
60.7 percent reduction with 5.0 phr sodium thiosulfate pentahydrate) 
without significantly impacting the physical properties of the final 
vulcanizate. 
TABLE 2 
__________________________________________________________________________ 
Sample # A B C D E 
__________________________________________________________________________ 
Sodium Thiosulfate Pentahydrate 
none 
0.5 1.0 2.0 5.0 
Monsanto Rheometer 1.degree. Arc, 
150.degree. C. 
M.sub.HF Torque Units (dNm) 
33 32.5 
32.3 
32.5 
32 
M.sub.L Torque Units (dNm) 
8.0 8.5 8.0 8.0 7.5 
M.sub.HF --M.sub.L Torque Units (dNm) 
25.0 
24.3 
24.3 
24.5 
24.5 
Cure Time, t'c(25), min 
20.0 
12.2 
8.3 4.5 3.6 
Cure Time, t'c(90), min 
30.5 
22.0 
18 13.5 
12.0 
% Reduction in t'c(90) cure time 
27.9 
41.0 
55.7 
60.7 
Stress-Strain Data 
Modulus at 300% Elongation, MPa 
6.99 
7.19 
7.35 
7.45 
7.35 
Tensile Strength, MPa 
18.38 
18.56 
18.9 
17.27 
18.38 
Elongation at Break, % 
605 602 602 567 594 
Shore A Hardness at 100.degree. C. 
48.4 
48.6 
48.4 
49.6 
48.3 
Percent Rebound at 100.degree. C. 
59 60 59.4 
60.4 
59.8 
__________________________________________________________________________ 
EXAMPLE II 
In this example, sodium thiosulfate pentahydrate, which can be used to 
beneficially reduce cure times, is compared to anhydrous sodium 
thiosulfate as a cure activator. The rubber compositions are identified 
herein as Samples F, G and H of Table 3 with Sample H acting as the 
control compound containing no sodium thiosulfate pentahydrate, Sample F 
containing sodium thiosulfate pentahydrate, and Sample G containing an 
equal molar equivalent of anhydrous sodium thiosulfate for comparison 
versus Sample F. The data unexpectively shows that with anhydrous sodium 
thiosulfate (Sample G) cure times were not reduced when compared to the 
control (Sample H) whereas with sodium thiosulfate pentahydrate (Sample F) 
cure times were substantially reduced when compared to the control. This 
illustrates the unique and unobvious character of the hydrated salt of 
sodium thiosulfate. 
______________________________________ 
Sample F G H 
______________________________________ 
Sodium Thiosulfate Pentahydrate (4.0 mmols) 
1.0 0 0 
Sodium thiosulfate (anhydrous) (4.0 mmols) 
0 0.64 0 
Monsanto Rheometer 1.degree. Arc, 150.degree. C. 
M.sub.HF Torque Unite (dNm) 
32 32.5 31.5 
M.sub.L Torque Unites (dNm) 
8 7.5 7.3 
M.sub.HF --M.sub.L Torque Units (dNm) 
24 25 24.2 
Cure Time, t'c(25), min 8.5 21 19.7 
Cure Time, t'c(90), min, 
17.5 31.8 29.5 
% Reduction in t'c(90) cure time 
40.7 none 
______________________________________ 
EXAMPLE III 
In this example, sodium thiosulfate pentahydrate is evaluated as a cure 
activator for a variety of sulfenamide-type accelerators. The rubber 
compositions are identified herein as Samples I, J, K, L, M, N, O, P, Q 
and R of Table 4 with Sample I, K, M, O and Q acting as the control 
compounds containing no sodium thiosulfate pentahydrate, and Samples J, L, 
N, P and R contain sodium thiosulfate pentahydrate at 0.50 phr. Table 4 
illustrates the cure activating power of sodium thiosulfate pentahydrate 
when used in conjunction with sulfenamide-type accelerators. Cure time 
reductions of 29.5 percent, 33.3 percent, 14.2 percent and 27.5 percent 
were respectively obtained when 0.5 phr of sodium thiosulfate pentahydrate 
was added to the formulations containing CBS (Sample J versus Sample I), 
TBBS (Sample L versus Sample K), DCBS (Sample N versus Sample M) and TBSI 
(Sample P versus Sample O). The use of sodium thiosulfate pentahydrate 
with MBTS did not provide any reduction in t'c(90) cure time. This shows 
that to be useful in reducing cure times, a sulfenamide accelerator should 
be present as part of the cure system. 
TABLE 4 
__________________________________________________________________________ 
Control 
Sample I J K L M N O P Q R 
__________________________________________________________________________ 
Accelerator CBS 
CBS 
TBBS 
TBBS 
DCBS 
DCBS 
TBSI 
TBSI 
MBTS 
MBTS 
(1.25 phr) 
Sodium 0 0.50 
0 0.50 
0 0.50 
0 0.50 
0 0.50 
Thiosulfate 
Pentahydrate 
Monsanto Rheometer 1.degree. Arc, 150.degree. C. 
M.sub.HF Torque 30.0 
30.0 
31.0 
30.5 
27.0 
27.0 
31.0 
31.5 
27.0 
26.2 
Units (dNm) 
M.sub.L Torque 8.0 
7.5 
7.0 7.0 7.0 7.5 7.0 8.0 6.0 6.0 
Units (dNm) 
M.sub.HF --M.sub.L Torque 
22.0 
22.5 
24.0 
23.5 
20.0 
19.5 
24.0 
23.5 
21.0 
20.2 
Units (dNm) 
Cure Time, 14.0 
8.0 
17.0 
9.5 23.5 
19.0 
22.0 
13.0 
9.5 6.0 
t'c(25), min 
Cure Time, 22.0 
15.5 
25.5 
17.0 
42.0 
36.0 
34.5 
25.0 
34.0 
34.0 
t'c(90), min 
% Reduction in 29.5 33.3 14.2 27.5 none 
t'c(90) 
cure time 
Stress-Strain Data 
Modulus at 6.86 
6.77 
7.39 
7.3 4.84 
5.16 
6.75 
7.13 
5.46 
5.12 
300% 
Elongation, MPa 
Tensile Strength, 19.05 
18.99 
19.51 
19.07 
19.41 
19.66 
19.27 
20.4 
19.8 
19.37 
MPa 
Elongation at 614 
612 
600 593 744 727 622 629 708 721 
Break, % 
Shore A 47.7 
47.4 
49 48.7 
43.4 
43.9 
47.5 
48.2 
43.6 
42.6 
Hardness at 60.8 
61.3 
100.degree. C. 
Percent Rebound 60.4 
60.9 
61.3 
60.9 
56.8 
56.2 
60.8 
61.3 
58.1 
56 
at 100.degree. C. 
__________________________________________________________________________ 
CBS = Ncyclohexyl-2-benzothiazolesulfenamide 
TBBS = Ntert-butyl-2-benzothiazolesulfenamide 
DCBS = N,Ndicyclohexyl-2-benzothiazolesulfenamide 
TBSI = Ntert-butyl bis2(2-benzothiazolesulfen)amide, Santocure .RTM. TBSI 
MBTS = 2,2dithiobisbenzothiazole, (Altax) 
EXAMPLE IV 
In this example, the vulcanizing activity of sodium thiosulfate 
pentahydrate is evaluated. Sample V illustrates sodium thiosulfate 
pentahydrate's vulcanizing activity in the sulfur vulcanizable rubber of 
Table 1 when no sulfur or sulfenamide accelerator such as CBS is present. 
As can be seen by the data, no cure takes place in the absent of sulfur 
and sulfenamide accelerator. Likewise as Sample W illustrates, no useful 
vulcanizate can be obtained when sodium thiosulfate pentahydrate and a 
sulfenamide accelerator such as CBS is cured in the absence of sulfur. 
When sulfur is added to the sulfur vulcanizable rubber composition of 
Sample W to produce Sample Y, a useful cure time reduction of 17.5 minutes 
is noted. Also, useful mechanical properties for the vulcanizate are 
obtained when sulfur is added to the sulfur vulcanizable rubber 
composition of Sample W providing large improvements in modulus at 300 
percent elongation, tensile strength, elongation at break, hardness and 
percent rebound. 
TABLE 5 
______________________________________ 
Sample V W X Y 
______________________________________ 
CBS.sup.1 1.25 1.25 1.25 
sodium thiosulfate 
0.5 0.5 0.5 
pentahydrate 
Sulfur 1.75 1.75 
Monsanto Rheometer 1.degree. 
Arc, 150.degree. C. 
M.sub.HF Torque Units (dNm) 
No Cure 10 30 30 
M.sub.L Torque Units (dNm) 
No Cure 5 4.5 5 
M.sub.HF --M.sub.L Torque Units 
No Cure 5 25.5 25 
(dNm) 
Cure Time, t'c(25), min 
No Cure 12 15 8.2 
Cure Time, t'c(90), min 
No Cure 35 22 17.5 
Stress-Strain Data 
Modulus at 300% Elonga- 0.8 7.55 7.19 
tion, MPa 
Tensile Strength, MPa 
0.34 4.87 17.88 18.62 
Elongation at Break, % 
284 1062 561 589 
Shore A Hardness at 100.degree. C. 
5.8 16.8 48.4 47.4 
Percent Rebound at 100.degree. C. 
31.4 34.6 61.3 60.8 
______________________________________ 
.sup.1 Ncyclohexyl-2-benzothiazesulfenamide 
EXAMPLE V 
In this example, other hydrated salts of thiosulfate are evaluated for cure 
activating potential. The rubber compositions are identified herein as 
Samples Z, AB, AC and AD of Table 6 with Sample Z acting as the control 
compound containing no hydrated salt of thiosulfate, Sample AB containing 
4.0 mmoles of potassium thiosulfate hydrate (1.5 moles of water), Sample 
AC containing 4.0 mmols of magnesium thiosulfate hexahydrate and Sample AD 
containing 4.0 mmols of sodium thiosulfate pentahydrate. In each example, 
cure time reductions are observed when compared the control with sodium 
thiosulfate pentahydrate giving the greatest reduction in cure times. 
TABLE 6 
______________________________________ 
Samples Z AB AC AD 
______________________________________ 
potassium thiosulfate hydrate.sup.1 
0.88 
4.0 mmols (phr) 
magnesium thiosulfate hexa- 1 
hydrate 4.0 mmols (phr) 
sodium thiosulfate pentahydrate 1 
4.0 mmols (phr) 
Monsanto Rheometer 1.degree. Arc, 
150.degree. C. 
M.sub.HF Torque Units (dNm) 
30 31 28.5 29.5 
M.sub.L Torque Units (dNm) 
4.5 5 5 5 
M.sub.HF --M.sub.L Torque 
25.5 26 23.5 24.5 
Units (dNm) 
Cure Time, t'c(25), min 
15 9.5 5.2 4.5 
Cure Time, t'c(90), min 
22 17 15 12 
% Reduction in t'(90) cure 
22.7 31.9 45.5 
time 
Stress-Strain Data 
Modulus at 300% Elongation, 
7.55 7.51 6.51 7.26 
MPa 
Tensile Strength, MPa 
17.88 16.83 17.44 19.0 
Elongation at Break, % 
561 543 604 603 
______________________________________ 
.sup.1 K.sub.2 S.sub.2 O.sub.3.1.5 H.sub.2 O