U.S. patent application number 10/641778 was filed with the patent office on 2004-02-19 for rubber compositions and method for increasing the mooney scorch value.
This patent application is currently assigned to UNIROYAL CHEMICAL COMPANY, INC.. Invention is credited to Greene, Peter K., Hannon, Martin J., Hong, Sung W..
Application Number | 20040034150 10/641778 |
Document ID | / |
Family ID | 25483331 |
Filed Date | 2004-02-19 |
United States Patent
Application |
20040034150 |
Kind Code |
A1 |
Hong, Sung W. ; et
al. |
February 19, 2004 |
Rubber compositions and method for increasing the mooney scorch
value
Abstract
A rubber composition is disclosed wherein the rubber composition
contains at least (a) a rubber component; (b) a silica filler; (c)
a coupling agent; (d) a cure-enhancing amount of at least one
polyalkylene oxide; and (e) at least one high molecular weight
thiuram disulfide. The compositions may also include suitable
amounts of other ingredients such as carbon black, antiozonants,
antioxidants, etc.
Inventors: |
Hong, Sung W.; (Cheshire,
CT) ; Hannon, Martin J.; (Bethany, CT) ;
Greene, Peter K.; (Goshen, CT) |
Correspondence
Address: |
Michael E. Carmen, Esq.
DILWORTH & BARRESE, LLP
333 Earle Ovington Boulevard
Uniondale
NY
11553
US
|
Assignee: |
UNIROYAL CHEMICAL COMPANY,
INC.
|
Family ID: |
25483331 |
Appl. No.: |
10/641778 |
Filed: |
August 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10641778 |
Aug 15, 2003 |
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09945606 |
Sep 4, 2001 |
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6620875 |
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Current U.S.
Class: |
524/492 ;
524/201; 524/377; 524/378; 524/392; 525/332.6; 525/333.1;
525/333.8 |
Current CPC
Class: |
C08K 5/40 20130101; C08K
5/06 20130101; C08K 5/06 20130101; C08L 21/00 20130101; C08K 5/40
20130101; C08L 21/00 20130101 |
Class at
Publication: |
524/492 ;
524/392; 524/201; 524/377; 524/378; 525/332.6; 525/333.1;
525/333.8 |
International
Class: |
C08L 001/00 |
Claims
What is claimed is:
1. A method for increasing the mooney scorch value of a rubber
composition which comprises the step of forming a rubber
composition comprising (a) a rubber component; (b) a silica filler;
(c) a coupling agent; (d) a polyalkylene oxide; and (e) a thiuram
disulfide having a molecular weight of at least about 400.
2. The method of claim 17 wherein the rubber component is selected
from the group consisting of natural rubber, homopolymers of
conjugated diolefins, copolymers of conjugated diolefins and
ethylenically unsaturated monomers and mixtures thereof.
3. The method of claim 17 wherein the silica filler is selected
from the group consisting of silica, precipitated silica, amorphous
silica, vitreous silica, fumed silica, fused silica, synthetic
silicate, alkaline earth metal silicate, highly dispersed silicate
and mixtures thereof.
4. The method of claim 17 wherein the coupling agent is a
sulfur-containing coupling agent of the general formula:
Z-R.sup.1-S.sub.n-R.sup.2-Z in which Z is selected from the group
consisting of 3wherein R.sup.3 is an alkyl group of from 1 to 4
carbon atoms, cyclohexyl or phenyl; and R.sup.4 is an alkoxy of
from 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms;
and R.sup.1 and R.sup.2 are independently a divalent hydrocarbon of
from 1 to 18 carbon atoms and n is an integer of from about 2 to
about 8.
5. The method of claim 20 wherein the sulfur-containing coupling
agent is selected from the group consisting of
3,3'-bis(trimethoxysilylpropyl) disulfide,
3,3'-bis(triethoxysilylpropyl) disulfide,
3,3-bis(triethoxysilylpropyl) tetrasulfide,
3,3'-bis(triethoxysilylpropyl- ) octasulfide,
3,3'-bis(trimethoxysilylpropyl) tetrasulfide,
2,2'-bis(triethoxysilylethyl) tetrasulfide,
3,3'-bis(trimethoxysilylpropy- l) triasulfide,
3,3'-bis(triethoxysilylpropyl) triasulfide,
3,3'-bis(tributoxysilylpropyl) disulfide,
3,3'-bis(trimethoxysilylpropyl) hexasufide,
3,3'-bis(trimethoxysilylpropyl) octasulfide,
3,3'-bis(trioctoxysilylpropyl) tetrasulfide,
3,3'-bis(trihexoxysilylpropy- l) disulfide,
3,3'-bis(tri-2"-ethylhexoxysilylpropyl) trisulfide,
3,3'-bis(triisooctoxysilylpropyl) tetrasulfide,
3,3'-bis(tri-t-butoxysily- lpropyl) disulfide,
2,2'-bis(methoxydiethoxysilylethyl) tetrasulfide,
2,2'-bis(tripropoxysilylethyl) pentasulfide,
3,3'-bis(tricyclohexoxysilyl- propyl) 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(dimethylmethoxysilyle- thyl) disulfide,
2,2'-bis(dimethylsec.butoxysilylethyl) trisulfide, 3,3'-bis(methyl
butylethoxysilylpropyl) tetrasulfide, 3,3'-bis(di
t-butylmethoxysilylpropyl) tetrasulfide,
2,2'-bis(phenylmethylmethoxysily- lethyl) trisulfide,
3,3'-bis(diphenyl isopropoxysilylpropyl) tetrasulfide,
3,3'-bis(diphenylcyclohexoxysilylpropyl) disulfide,
3,3'-bis(dimethylethylmercaptosilylpropyl) tetrasulfide,
2,2'-bis(methyl dimethoxysilylethyl) trisulfide,
2,2'-bis(methylethoxypropoxysilylethyl) tetrasulfide,
3,3'-bis(butyldimethoxysilylpropyl) trisulfide, 3,3'-bis(phenyl
dimethoxysilyipropyl) tetrasulfide, 3-phenyl ethoxybutoxysilyl
3'-trimethoxysilyipropyl tetrasulfide,
4,4'-bis(trimethoxysilylbutyl) tetrasulfide,
6,6'-bis(triethoxysilylhexyl- ) tetrasulfide,
12,12'-bis(triisopropoxysilyldodecyl) disulfide,
18,18'-bis(trimethoxysilyloctadecyl) tetrasulfide,
18,18'-bis(tripropoxysilyloctadecenyl) tetrasulfide,
4,4'-bis(trimethoxysilyl-butene-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-methylpropy- l) disulfide and
combinations thereof.
6. The method of claim 17 wherein the polyalkylene oxide is
selected from the group consisting of dimethylene glycol,
diethylene glycol, dipropylene glycol, trimethylene glycol,
triethylene glycol, tripropylene glycol, polyethylene oxide,
polypropylene oxide, polybutylene oxide and mixtures thereof.
7. The method of claim 17 wherein the thiuram disulfide is of the
general formula wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 each
are the same or different and are hydrocarbons containing from
about 4 to about 30 carbon atoms, optionally containing one or more
heterocyclic groups, or R.sup.1 and R.sup.2 and/or R.sup.3 and
R.sup.4 together with the nitrogen atom to which they are bonded
are joined together to form a heterocyclic group, optionally
containing one or more additional heterocyclic atoms.
8. The method of claim 23 wherein R.sup.1, R.sup.2, R.sup.3 and
R.sup.4 each are the same or different and are hydrocarbons
containing from about 8 to about 18 carbon atoms.
9. The method of claim 23 wherein R.sup.1, R.sup.2, R.sup.3 and
R.sup.4 each are hydrocarbons of between 12 and 14 carbon
atoms.
10. The method of claim 23 wherein the polyalkylene oxide is
diethylene glycol and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 each
are hydrocarbons of between 12 and 14 carbon atoms.
11. The method of claim 16 wherein the silica filler is present in
an amount of from about 5 to about 100 phr, the coupling agent is
present in an amount of from about 0.5 to about 10 phr, the
polyalkylene oxide is present in an amount of from about 0.5 to
about 10 phr and the thiuram disulfide is present in an amount of
from about 0.1 to about 1.0 phr.
12. The method of claim 22 wherein the silica filler is present in
an amount of from about 5 to about 100 phr, the sulfur-containing
coupling agent is present in an amount from about 0.5 to about 10
phr, diethylene glycol is present in an amount of from about 0.5 to
about 10 phr and the thiuram disulfide is present in an amount from
about 0.1 to about 1.0.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] This invention relates generally to rubber compositions and
a method for increasing the mooney scorch value of the rubber
compositions. The rubber compositions are particularly useful for
tire tread applications in vehicles, e.g., passenger automobiles,
and trucks.
[0003] 2. Description of the Related Art
[0004] The tire treads of modern tires must meet performance
standards which require a broad range of desirable properties.
Generally, three types of performance standards are important in
tread compounds. They include good wear resistance, good traction
and low rolling resistance. Major tire manufacturers have developed
tire tread compounds which provide lower rolling resistance for
improved fuel economy and better skid/traction for a safer ride.
Thus, rubber compositions suitable for, e.g., tire treads, should
exhibit not only desirable strength and elongation, particularly at
high temperatures, but also good cracking resistance, good abrasion
resistance, desirable skid resistance, low tangent delta values at
60.degree. C. and low frequencies for desirable rolling resistance
of the resulting treads. Additionally, a high complex dynamic
modulus is necessary for maneuverability and steering control. A
high mooney scorch value is further needed for processing
safety.
[0005] Presently, silica has been added to rubber compositions as a
filler to replace some or substantially all of the carbon black
filler to improve these properties, e.g., lower rolling resistance.
Although more costly than carbon black, the advantages of silica
include, for example, improved wet traction, low rolling
resistance, etc., with reduced fuel consumption. Indeed, as
compared to carbon black, there tends to be a lack of, or at least
an insufficient degree of, physical and/or chemical bonding between
the silica particles and the rubber to enable the silica to become
a reinforcing filler for the rubber thereby giving less strength to
the rubber. Therefore, a silica filler system requires the use of
coupling agents.
[0006] Coupling agents are typically used to enhance the rubber
reinforcement characteristics of silica by reacting with both the
silica surface and the rubber elastomer molecule. Such coupling
agents, for example, may be premixed or pre-reacted with the silica
particles or added to the rubber mix during the rubber/silica
processing, or mixing, stage. If the coupling agent and silica are
added separately to the rubber mix during the rubber/silica
processing, or mixing, stage, it is considered that the coupling
agent then combines in situ with the silica.
[0007] A coupling agent is a bi-functional molecule that will react
with the silica at one end thereof and cross-link with the rubber
at the other end. In this manner, the reinforcement and strength of
the rubber, e.g., the toughness, strength, modulus, tensile and
abrasion resistance, are particularly improved. The coupling agent
is believed to cover the surface of the silica particle which then
hinders the silica from agglomerating with other silica particles.
By interfering with the agglomeration process, the dispersion is
improved and therefore the wear and fuel consumption are
improved.
[0008] The use of silica in relatively large proportions for
improving various tire properties requires the presence of a
sufficient amount of a coupling agent. The coupling agent and
silica however retard the cure. Therefore, a silica/coupling agent
tread formulation has been found to undesirably slow the cure rate
of the rubber. Additionally, by employing high amounts of the
coupling agents results in the rubber compositions being more
costly since these materials are expensive.
[0009] In order to increase the cure rate, secondary accelerators
such as, for example, diphenyl guanidine (DPG), have been added to
the rubber compositions. However, the use of secondary
accelerators, and particularly DPG with polyalkylene oxides, result
in the rubber composition having a lower mooney scorch value during
its manufacture thereby resulting in decreased processing time.
Problems associated with a decreased processing time include, for
example, precured compounds and rough surfaces on extrided parts.
Additionally, diphenyl guanidine is typically employed in high
amounts which result in the rubber compositions being more
expensive to manufacture since more material must be used.
[0010] It would be desirable to provide a rubber composition which
has a decreased cure time and a higher mooney scorch value without
sacrificing other physical properties, e.g., tangent delta value.
This will allow for better processing of the rubber composition
during its manufacture.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a
decreased cure time when forming the rubber compositions
herein.
[0012] It is also an object of the present invention to provide
rubber composition possessing a high mooney scorch value.
[0013] In keeping with these and other objects of the present
invention, the rubber compositions herein comprise (a) a rubber
component; (b) a silica filler; (c) a coupling agent; (d) a
cure-enhancing amount of a polyalkylene oxide and (e) a thiuram
disulfide having a molecular weight of at least about 400.
[0014] By employing a cure-enhancing amount of a polyalkylene
oxide, lesser amounts of a coupling agent can be used in forming
the rubber compositions resulting in the compositions disclosed
herein advantageously possessing a higher cure rate. Accordingly,
the delay in cure/vulcanization of rubber observed with the use of
silica and coupling agent alone as noted above has been lessened,
if not substantively overcome, in many cases by the cure-enhancing
amount of the polyalkylene oxides of the present invention. Thus,
the polyalkylene oxides herein have been found to increase the cure
rate and, in some instances, to fully recapture any cure slow down
presumed to have resulted from the use of the silica with higher
amounts of a coupling agent relative to the present invention which
employs lower amounts of a coupling agent with a polyalkylene
oxide. In this manner, the polyalkylene oxides have enabled
achievement of the silica benefits in full without the prior art
disadvantage while also achieving a greater economical advantage by
using less materials of the more expensive coupling agent.
[0015] Additionally, by further employing a high molecular weight
thuiram disulfide, i.e., a thiuram disulfide having a weight
average molecular weight (M.sub.W) of at least 400, with the
polyalkylene oxides, the mooney scorch value of the rubber
compositions are increased thereby allowing for better processing
of the compositions without sacrificing other physical
properties.
[0016] The term "phr" is used herein as its art-recognized sense,
i.e., as referring to parts of a respective material per one
hundred (100) parts by weight of rubber.
[0017] The expression "cure-enhancing amount" as applied to the
polyalkylene oxide employed in the rubber compositions of this
invention shall be understood to mean an amount when employed with
the coupling agent provides a decreased cure time of the rubber
composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The rubber compositions of this invention contain at least
(a) a rubber component; (b) a silica filler; (c) a coupling agent;
and (d) a cure-enhancing amount of at least one polyalkylene oxide
and (d) a thiuram disulfide having a molecular weight of at least
about 400.
[0019] The rubber components for use herein are based on highly
unsaturated rubbers such as, for example, natural or synthetic
rubbers. Representative of the highly unsaturated polymers that can
be employed in the practice of this invention are diene rubbers.
Such rubbers will ordinarily possess an iodine number of between
about 20 to about 450, although highly unsaturated rubbers having a
higher or a lower (e.g., of 50-100) iodine number can also be
employed. Illustrative of the diene rubbers that can be utilized
are polymers based on conjugated dienes such as, for example,
1,3-butadiene; 2-methyl-1,3-butadiene; 1,3-pentadiene;
2,3-dimethyl-1,3-butadiene; and the like, as well as copolymers of
such conjugated dienes with monomers such as, for example, styrene,
alpha-methylstyrene, acetylene, e.g., vinyl acetylene,
acrylonitrile, methacrylonitrile, methyl acrylate, ethyl acrylate,
methyl methacrylate, ethyl methacrylate, vinyl acetate, and the
like. Preferred highly unsaturated rubbers include natural rubber,
cis-polyisoprene, polybutadiene, poly(styrene-butadiene),
styrene-isoprene copolymers, isoprene-butadiene copolymers,
styrene-isoprene-butadiene tripolymers, polychloroprene,
chloro-isobutene-isoprene, nitrile-chloroprene,
styrene-chloroprene, and poly (acrylonitrile-butadiene). Moreover,
mixtures of two or more highly unsaturated rubbers with elastomers
having lesser unsaturation such as EPDM, EPR, butyl or halogenated
butyl rubbers are also within the contemplation of the
invention.
[0020] The silica may be of any type that is known to be useful in
connection with the reinforcing of rubber compositions. Examples of
suitable silica fillers include, but are not limited to, silica,
precipitated silica, amorphous silica, vitreous silica, fumed
silica, fused silica, synthetic silicates such as aluminum
silicates, alkaline earth metal silicates such as magnesium
silicate and calcium silicate, natural silicates such as kaolin and
other naturally occurring silicas and the like. Also useful are
highly dispersed silicas having, e.g., BET surfaces of from about 5
to about 1000 m.sup.2/g and preferably from about 20 to about 400
m.sup.2/g and primary particle diameters of from about 5 to about
500 nm and preferably from about 10 to about 400 nm. These highly
dispersed silicas can be prepared by, for example, precipitation of
solutions of silicates or by flame hydrolysis of silicon halides.
The silicas can also be present in the form of mixed oxides with
other metal oxides such as, for example, Al, Mg, Ca, Ba, Zn, Zr, Ti
oxides and the like. Commercially available silica fillers known to
one skilled in the art include, e.g., those available from such
sources as Cabot Corporation under the Cab-O-Sil.RTM. tradename;
PPG Industries under the Hi-Sil and Ceptane tradenames; Rhodia
under the Zeosil tradename and Degussa AG under the Ultrasil and
Coupsil tradenames. Mixtures of two or more silica fillers can be
used in preparing the rubber composition of this invention. A
preferred silica for use herein is Zeosil 1165MP manufactured by
Rhodia.
[0021] The silica filler is incorporated into the rubber
composition in amounts that can vary widely. Generally, the amount
of silica filler can range from about 5 to about 150 phr,
preferably from about 15 to about 100 phr and more preferably from
about 30 to about 90 phr.
[0022] If desired, carbon black fillers can be employed with the
silica filler in forming the rubber compositions of this invention.
Suitable carbon black fillers include any of the commonly
available, commercially-produced carbon blacks known to one skilled
in the art. Generally, those having a surface area (EMSA) of at
least 20 m.sup.2/g and more preferably at least 35 m.sup.2/g up to
200 m.sup.2/g or higher are preferred. Surface area values used in
this application are those determined by ASTM test D-3765 using the
cetyltrimethyl-ammonium bromide (CTAB) technique. Among the useful
carbon blacks are furnace black, channel blacks and lamp blacks.
More specifically, examples of the carbon blacks include super
abrasion furnace (SAF) blacks, high abrasion furnace (HAF) blacks,
fast extrusion furnace (FEF) blacks, fine furnace (FF) blacks,
intermediate super abrasion furnace (ISAF) blacks, semi-reinforcing
furnace (SRF) blacks, medium processing channel blacks, hard
processing channel blacks and conducting channel blacks. Other
carbon blacks which may be utilized include acetylene blacks.
Mixtures of two or more of the above blacks can be used in
preparing the rubber compositions of the invention. Typical values
for surface areas of usable carbon blacks are summarized in the
following Table I.
1TABLE I Carbon Blacks ASTM Surface Area Designation (m.sup.2/g)
(D-1765-82a) (D-3765) N-110 126 N-234 120 N-220 111 N-339 95 N-330
83 N-550 42 N-660 35
[0023] The carbon blacks utilized in the invention may be in
pelletized form or an unpelletized flocculent mass. Preferably, for
ease of handling, pelletized carbon black is preferred. The carbon
blacks, if any, are ordinarily incorporated into the rubber
composition in amounts ranging from about 1 to about 80 phr and
preferably from about 5 to about 50 phr.
[0024] In compounding a silica filled rubber composition of the
present invention, it is advantageous to employ a coupling agent.
Such coupling agents, for example, may be premixed, or pre-reacted,
with the silica particles or added to the rubber mix during the
rubber/silica processing, or mixing, stage. If the coupling agent
and silica are added separately to the rubber mix during the
rubber/silica mixing, or processing stage, it is considered that
the coupling agent then combines in situ with the silica.
[0025] In particular, such coupling agents are generally composed
of a silane which has a constituent component, or moiety, (the
silane portion) capable of reacting with the silica surface and,
also, a constituent component, or moiety, capable of reacting with
the rubber, e.g., a sulfur vulcanizable rubber which contains
carbon-to-carbon double bonds, or unsaturation. In this manner,
then, the coupling agent acts as a connecting bridge between the
silica and the rubber thereby enhancing the rubber reinforcement
aspect of the silica.
[0026] The silane component of the coupling agent apparently forms
a bond to the silica surface, possibly through hydrolysis, and the
rubber reactive component of the coupling agent combines with the
rubber itself. Generally, the rubber reactive component of the
coupling agent is temperature sensitive and tends to combine with
the rubber during the final and higher temperature sulfur
vulcanization stage, i.e., subsequent to the rubber/silica/coupling
mixing stage and after the silane group of the coupling agent has
combined with the silica. However, partly because of typical
temperature sensitivity of the coupling agent, some degree of
combination, or bonding, may occur between the rubber-reactive
component of the coupling agent and the rubber during an initial
rubber/silica/coupling agent mixing stage and prior to a subsequent
vulcanization stage.
[0027] Suitable rubber-reactive group components of the coupling
agent include, but are not limited to, one or more of groups such
as mercapto, amino, vinyl, epoxy, and sulfur groups. Preferably the
rubber-reactive group components of the coupling agent is a sulfur
or mercapto moiety with a sulfur group being most preferable.
[0028] Examples of a coupling agent for use herein are
vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane,
vinyltris(.beta.methoxyethoxy) silane,
.beta.-(3,4-epoxycyclohexyl)ethylt- rimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane,
.gamma.-glycidoxypropylmethyldiethoxysilane,
.gamma.-glycidoxypropyltriet- hoxysilane,
.gamma.-methacryloxypropylmethyldimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-methacryloxypropylmet- hyldiethoxysilane,
.gamma.-methacryloxypropyltriethoxysilane,
-.beta.(aminoethyl)-.gamma.-aminopropylmethyldimethoxysilane,
N-.beta.(aminoethyl).gamma.-aminopropyltrimethoxysilane,
N-.beta.(aminoethyl).gamma.-aminopropyltriethoxysilane,
.gamma.-aminopropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane,
-phenyl-.gamma.-aminopropyltrimethoxysilane,
.gamma.-chloropropyltrimetho- xysilane,
.gamma.-mercaptopropyltrimethoxysilane and combinations
thereof.
[0029] Representative examples of the preferred sulfur-containing
coupling agents are sulfur-containing organosilicon compounds.
Specific examples of suitable sulfur-containing organosilicon
compounds are of the following general formula:
Z-R.sup.1-S.sub.n-R.sup.2-Z
[0030] in which Z is selected from the group consisting of 1
[0031] wherein R.sup.3 is an alkyl group of from 1 to 4 carbon
atoms, cyclohexyl or phenyl; and R.sup.4 is an alkoxy of from 1 to
8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; and R.sup.1
and R.sup.2 are independently a divalent hydrocarbon of from 1 to
18 carbon atoms and n is an integer of from about 2 to about 8.
[0032] Specific examples of sulfur-containing organosilicon
compounds which may be used herein include, but are not limited to,
3,3'-bis(trimethoxysilylpropyl) disulfide,
3,3'-bis(triethoxysilylpropyl) disulfide,
3,3-bis(triethoxysilylpropyl) tetrasulfide,
3,3'-bis(triethoxysilylpropyl) octasulfide,
3,3'-bis(trimethoxysilylpropy- l) tetrasulfide,
2,2'-bis(triethoxysilylethyl) tetrasulfide,
3,3'-bis(trimethoxysilylpropyl) triasulfide,
3,3'-bis(triethoxysilylpropy- l) triasulfide,
3,3'-bis(tributoxysilylpropyl) disulfide,
3,3'-bis(trimethoxysilylpropyl) hexasufide,
3,3'-bis(trimethoxysilylpropy- l) octasulfide,
3,3'-bis(trioctoxysilylpropyl) tetrasulfide,
3,3'-bis(trihexoxysilylpropyl) disulfide,
3,3'-bis(tri-2"-ethylhexoxysily- lpropyl) trisulfide,
3,3'-bis(triisooctoxysilyipropyl) tetrasulfide,
3,3'-bis(tri-t-butoxysilyl-propyl) disulfide,
2,2'-bis(methoxydiethoxysil- ylethyl) tetrasulfide,
2,2'-bis(tripropoxysilylethyl) pentasulfide,
3,3'-bis(tricyclohexoxysilylpropyl) tetrasulfide,
3,3'-bis(tricyclopentox- ysilylpropyl) trisulfide,
2,2'-bis(tri-2"-methyl-cyclohexoxysilylethyl) 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(methylbutylethoxysilylpropyl) tetrasulfide, 3,3'-bis(di
t-butylmethoxysilylpropyl) tetrasulfide,
2,2'-bis(phenylmethylmethoxysilylethyl) trisulfide,
3,3'-bis(diphenylisopropoxysilylpropyl) tetrasulfide,
3,3'-bis(diphenyl cyclohexoxysilylpropyl) disulfide,
3,3'-bis(dimethylethylmercaptosilylpro- pyl) tetrasulfide,
2,2'-bis(methyldimethoxysilylethyl) trisulfide, 2,2'-bis(methyl
ethoxypropoxysilylethyl) tetrasulfide,
3,3'-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3'-bis(ethyl
di-sec. butoxysilylpropyl) disulfide,
3,3'-bis(propyldiethoxysilylpropyl) disulfide, 3,3'-bis(butyl
dimethoxysilylpropyl) trisulfide, 3,3'-bis(phenyl
dimethoxysilylpropyl) tetrasulfide, 3-phenylethoxybutoxysilyl
3'-trimethoxysilyipropyl tetrasulfide,
4,4'-bis(trimethoxysilylbutyl) tetrasulfide,
6,6'-bis(triethoxysilylhexyl- ) tetrasulfide,
12,12'-bis(triisopropoxysilyldodecyl) disulfide,
18,18'-bis(trimethoxysilyloctadecyl) tetrasulfide,
18,18'-bis(tripropoxysilyl-octadecenyl) tetrasulfide,
4,4'-bis(trimethokysilyl-bufene-2-yl) tetrasulfide,
4,4'-bis(trimnethoxysilylcyclohexylene) tetrasulfide,
5,5'-bis(dimethoxymethyl-silylpentyl) trisulfide,
3,3'-bis(trimethoxysily- l-2-methylpropyl) tetrasulfide,
3,3'-bis(dimethoxyphenylsilyl-2-methylprop- yl) disulfide and the
like. Preferred coupling agents for use herein are
3,3'-bis(triethoxysilylpropyl) disulfide and
3,3'-bis(triethoxysilylpropy- l) tetrasulfide.
[0033] The polyalkylene oxides used herein advantageously decrease
the cure time of the rubber compositions of this invention when
added thereto in a cure-enhancing amount. Suitable polyalkylene
oxides for use herein can be a polyalkylene oxide which is a
polyether of the general formula X(R--O--).sub.nH where R may be
one or more of the following groups: methylene, ethylene, propylene
or tetramethylene group; n is an integer of from 1 to about 50,
preferably from about 2 to about 30 and most preferably from about
4 to about 20; and X is a non-aromatic starter molecule containing
1 to about 12 and preferably 2 to 6 functional groups.
Representative of the polyalkylene oxides include, but are not
limited to, dimethylene glycol, diethylene glycol, dipropylene
glycol, trimethylene glycol, triethylene glycol, tripropylene
glycol, polyethylene oxide, polypropylene oxide, polybutylene oxide
and the like and mixtures thereof. A preferred polyalkylene oxide
for use herein is diethlyene glycol.
[0034] By employing the foregoing polyalkylene oxides herein in a
cure-enhancing amount, the amount of coupling agent necessary to
compound a silica filled rubber composition is reduced thereby
providing an economical advantage. Accordingly, amounts of the
coupling agent range from about 0.5 to about 10 phr, preferably
from about 1 to about 8 phr and most preferably from about 1.5 to
about 7 phr while the cure-enhancing amount of the polyalkylene
oxide will ordinarily range from about 0.5 to about 10 preferably
from about 1 to about 8 and most preferably from about 1.1 to about
5 phr. The foregoing polyalkylene oxides can be, for example,
premixed, or blended, with the coupling agents or added to the
rubber mix during the rubber/silica/coupling agent processing, or
mixing, stage.
[0035] The high molecular weight thiuram disulfides for use in the
rubber composition of this invention as a secondary accelerator
advantageously provide a rubber composition possessing a greater
mooney scorch value than that of a similar rubber composition in
which a significant amount up to the entire amount of the thiuram
disulfide has been replaced with diphenyl guanidine as an
accelerator. The thiuram disulfides herein will have a weight
average molecular weight of at least 400, preferably from about 500
to about 1250 and most preferably from about 800 to about 1000.
Representative of these thiuram disulfides are those of the general
formula 2
[0036] wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 each are the
same or different and are hydrocarbons containing, for example,
from about 4 to about 30 carbon atoms, optionally containing one or
more heterocyclic groups, or R.sup.1 and R.sup.2 and/or R.sup.3 and
R.sup.4 together with the nitrogen atom to which they are bonded
are joined together to form a heterocyclic group, optionally
containing one or more additional heterocyclic atoms. Specific
thiuram disulfides include those in which R.sup.1, R.sup.2, R.sup.3
and R.sup.4 are independently selected to be t-butyl, pentyl,
hexyl, cyclohexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl,
undecyl, dodecyl, stearyl, oleyl, phenyl, benzyl, tridecyl,
tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl,
nonadecyl, eicosanyl, and the like. It is particularly advantageous
to employ a thiuram disulfide wherein R.sup.1, R.sup.2, R.sup.3 and
R.sup.4 each possess between 8 to 18 carbon atoms. A particularly
preferred thiuram disulfide for use herein is wherein R.sup.1,
R.sup.2, R.sup.3 and R.sup.4 each possess between 12 and 14 carbon
atoms.
[0037] Generally, the thiuram disulfide is present in the rubber
composition of this invention in an amount ranging from about 0.10
to about 1.0 phr, preferably from about 0.15 to about 0.75 phr and
most preferably from about 0.20 to about 0.50 phr.
[0038] The rubber compositions of this invention can be formulated
in any conventional manner. Additionally, at least one other common
additive can be added to the rubber compositions of this invention,
if desired or necessary, in a suitable amount. Suitable common
additives for use herein include vulcanizing agents, activators,
retarders, antioxidants, plasticizing oils and softeners, fillers
other than silica and carbon black, reinforcing pigments,
antiozonants, waxes, tackifier resins, and the like and
combinations thereof.
[0039] The rubber compositions of this invention are particularly
useful when manufactured into articles such as, for example, tires,
motor mounts, rubber bushings, power belts, printing rolls, rubber
shoe heels and soles, rubber floor tiles, caster wheels, elastomer
seals and gaskets, conveyor belt covers, hard rubber battery cases,
automobile floor mats, mud flap for trucks, ball mill liners,
windshield wiper blades and the like. Preferably, the rubber
compositions of this invention are advantageously used in a tire as
a component of any or all of the thermosetting rubber-containing
portions of the tire. These include the tread, sidewall, and
carcass portions intended for, but not exclusive to, a truck tire,
passenger tire, off-road vehicle tire, vehicle tire, high speed
tire, and motorcycle tire that also contain many different
reinforcing layers therein. Such rubber or tire tread compositions
in accordance with the invention may be used for the manufacture of
tires or for the re-capping of worn tires.
EXAMPLES
[0040] The following non-limiting examples are intended to further
illustrate the present invention and are not intended to limit the
scope of the invention in any manner.
COMPARATIVE EXAMPLES A-D AND EXAMPLES 1-3
[0041] Employing the ingredients indicated in Tables II and III
(which are listed in parts per hundred of rubber by weight),
several rubber compositions were compounded in the following
manner: the ingredients indicated in Table II were added to an
internal mixer and mixed until the materials are incorporated and
thoroughly dispersed and discharged from the mixer. Discharge
temperatures of about 160.degree. C. are typical. The batch is
cooled, and is reintroduced into the mixer along with the
ingredients indicated in Table III. The second pass is shorter and
discharge temperatures generally run between 93-105.degree. C.
2TABLE II PHASE I Comp. Ex./Ex. A B C D 1 2 3 SOLFLEX 1216.sup.1
75.00 75.00 75.00 75.00 75.00 75.00 75.00 BUDENE 1207.sup.2 25.00
25.00 25.00 25.00 25.00 25.00 25.00 ZEOSIL 1165.sup.3 44.00 44.00
44.00 44.00 44.00 44.00 44.00 N234.sup.4 32.00 32.00 32.00 32.00
32.00 32.00 32.00 SILQUEST A1289.sup.5 3.52 1.76 1.76 1.76 1.76
1.76 1.76 DEG (LIQUID) 0.00 1.76 0.00 0.00 1.76 0.00 0.00
DIPROPYLENE 0.00 0.00 1.76 0.00 0.00 1.76 0.00 GLYCOL TRIETHYLENE
0.00 0.00 0.00 1.76 0.00 0.00 1.76 GLYCOL STEARIC ACID 1.00 1.00
1.00 1.00 1.00 1.00 1.00 FLEXZONE 7P.sup.6 2.00 2.00 2.00 2.00 2.00
2.00 2.00 SUNPROOF 1.50 1.50 1.50 1.50 1.50 1.50 1.50 IMPROVED
SUNDEX 8125.sup.8 40.00 40.00 40.00 40.00 40.00 40.00 40.00 MB1:
TOTAL 224.02 224.02 224.02 224.02 224.02 224.02 224.02
.sup.1Solution styrene-butadiene rubber low styrene and medium
vinyl content available from Goodyear. .sup.2Polybutadiene rubber
available from Goodyear. .sup.3Highly dispersable silica available
from Rhodia. .sup.4High surface area carbon black available from
Cabot Corp. .sup.5Tetrasulfide coupling agent available from OSI
Specialty Chemicals. .sup.6Paraphenylene diamine available from
Uniroyal Chemical Company. .sup.7Blend of hydrocarbon waxes
available from Uniroyal Chemical Company. .sup.8Aromatic oil
available from Sun Oil.
[0042]
3TABLE III PHASE II Comp. Ex./Ex. A B C D 1 2 3 MB-1.sup.9 224.02
224.02 224.02 224.02 224.02 224.02 224.02 Zinc Oxide 2.50 2.50 2.50
2.50 2.50 2.50 2.50 Delac NS.sup.10 1.50 1.50 1.50 1.50 1.50 1.50
1.50 Diphenyl 1.00 1.00 1.00 1.00 0.00 0.00 0.00 Guanadine ROYALAC
150.sup.11 0.00 0.00 0.00 0.00 0.25 0.25 0.25 SULFUR 21-10.sup.12
2.00 2.00 2.00 2.00 2.00 2.00 2.00 TOTAL 231.02 231.02 231.02
231.02 230.27 230.27 230.27 .sup.9MB-1 is the batch provided as set
forth in Table II. .sup.10N-t-butyl-2-benzothiazole sulfenamide
available from Uniroyal Chemical Company. .sup.11Tetraalkyl
(C.sub.12-C.sub.14) thiuram disulfide available from Uniroyal
Chemical Company having an average molecular weight of 916.
.sup.12Sulfur available from C.P. Hall.
Results
[0043] The compounded stocks prepared above were then sheeted out
and cut for cure. The samples were cured for the times and at the
temperatures indicated in Table IV and their physical properties
evaluated. The results are summarized in Table IV below. Note that
in Table IV, cure characteristics were determined using a Monsanto
rheometer ODR 2000 (1.degree. ARC, 100 cpm): MH is the maximum
torque and ML is the minimum torque. Scorch safety (t.sub.s2) is
the time to 2 units above minimum torque (ML), cure time (t.sub.50)
is the tiime to 50% of delta torque above minimum and cure time
(t.sub.90) is the time to 90% of delta torque above minimum.
Tensile Strength, Elongation and Modulus were measured following
procedures in ASTM D-412. Examples 1-3 illustrate a rubber
composition within the scope of this invention. Comparative
Examples A-D represents a rubber composition outside the scope of
this invention.
CURED PHYSICAL PROPERTIES
[0044]
4TABLE IV Comparative Example or Example A B C D 1 2 3 Cured
Characteristics obtained at 160.degree. C. ML (lb-in.) 6.57 6.95
6.49 7.23 7.65 7.29 7.44 MH (lb-in.) 34.15 36.10 34.18 36.65 34.00
32.38 34.66 Scorch safety t.sub.52 (min) 3.07 2.82 3.35 2.65 5.42
5.97 5.24 Cure time t.sub.50 (min) 4.71 4.32 5.01 4.15 7.95 9.11
7.69 Cure time t.sub.90 (min) 10.23 8.52 9.25 8.43 11.71 13.88
11.41 Cured at 160.degree. C. Cure Time @ 160.degree. C.(min) 15.0
15.0 15.0 15.0 17.5 20.0 17.5 100% Modulus (Mpa) 2.6 2.3 2.1 2.6
2.3 2.2 2.4 300% Modulus (Mpa) 11.9 10.2 9.3 11.0 10.2 8.8 9.8
Tensile Strength (Mpa) 18.0 17.9 16.4 19.0 18.4 17.8 19.4
Elongation, % at Break 410.0 490.0 490.0 490.0 490.0 520.0 540.0
Hardness, Shore A. 56.0 59.0 57.0 59.0 59.0 57.0 59.0 Mooney Scorch
(MS at 135.degree. C.) 3 Pt. Rise Time (min) 10 9 10 8 23 27 22
Mooney Viscosity(ML.sub.1+4 at 100.degree. C.) ML.sub.1+4 71 62 61
64 66 63 64 Tangent Delta 60.degree. C. (10 Hz) [RPA-2000] % Strain
0.7 0.106 0.118 0.115 0.110 0.110 0.126 0.122 1.0 0.111 0.134 0.136
0.128 0.121 0.137 0.140 2.0 0.139 0.171 0.173 0.153 0.157 0.174
0.161 5.0 0.168 0.187 0.189 0.185 0.176 0.189 0.179 7.0 0.168 0.190
0.194 0.187 0.176 0.186 0.182 14.0 0.158 0.185 0.191 0.184 0.173
0.182 0.178 Dynamic Modulus (G', kPa) % Strain 0.7 3106 4200 4055
4376 3535 3596 3902 1.0 2902 3902 3727 4017 3295 3355 3601 2.0 2495
3090 3038 3358 2683 2670 2880 5.0 1874 2299 2242 2478 2092 2039
2248 7.0 1722 2066 2010 2222 1927 1869 2020 14.0 1427 1608 1560
1720 1519 1492 1597
[0045] It can be seen from the above data that the examples
containing a high molecular weight thuiram disulfide and a
polyalkylene oxide (Examples 1-3) provide equivalent to improved
performance when compared to the examples containing DPG with no
polyalkylene oxide present therein (Comparative Example A) and a
polyalkylene oxide with DPG (Comparative Examples B-D). The mooney
scorch values for Examples 1-3 were significantly higher than those
of Comparative Examples A-D.
[0046] Additionally, the 100% and 300% Modulus and % elongation for
Examples 1-3 are comparable to those of Examples A-D. Thus, by
replacing 1 phr of diphenyl guanidine with 0.25 phr of tetraalkyl
(C.sub.12-C.sub.14) thiuram disulfide, the scorch safety of the
rubber composition has been significantly improved without any
sacrifice in physical properties resulting in an economical cost
advantage being realized.
COMPARATIVE EXAMPLES E-H AND EXAMPLES 4-6
[0047] Employing the ingredients indicated in Tables V and VI
(which are listed in parts per hundred of rubber by weight),
several rubber compositions were compounded in the following
manner: the ingredients indicated in Table V were added to an
internal mixer and mixed until the materials are incorporated and
thoroughly dispersed and discharged from the mixer. Discharge
temperatures of about 160.degree. C. are typical. The batch is
cooled, and is reintroduced into the mixer along with the
ingredients indicated in Table VI. The second pass is shorter and
discharge temperatures generally run between 93-105.degree. C.
5TABLE V PHASE I Comp. Ex./Ex. E F G H 4 5 6 SOLFLEX 1216 75.00
75.00 75.00 75.00 75.00 75.00 75.00 BUDENE 1207 25.00 25.00 25.00
25.00 25.00 25.00 25.00 ZEOSIL 1165 85.00 85.00 85.00 85.00 85.00
85.00 85.00 N234 5.00 5.00 5.00 5.00 5.00 5.00 5.00 SILQUEST A1289
6.80 0.00 0.00 0.00 0.00 0.00 0.00 DEG/SILQUEST 0.00 6.80 0.00 0.00
6.80 0.00 0.00 A1289 BLEND.sup.13 DIPROPYLENE 0.00 0.00 0.00 6.80
0.00 0.00 6.80 GLYCOL/SILQUEST A1289 BLEND.sup.13 TRIETHYLENE 0.00
0.00 6.80 0.00 0.00 6.80 0.00 GLYCOL/SILQUEST A1289 BLEND.sup.13
STEARIC ACID 1.00 1.00 1.00 1.00 1.00 1.00 1.00 FLEXZONE 7P 1.00
1.00 1.00 1.00 1.00 1.00 1.00 SUNPROOF 0.50 0.50 0.50 0.50 0.50
0.50 0.50 IMPROVED AROMATIC OIL 44.00 44.00 44.00 44.00 44.00 44.00
44.00 NAUGARD Q.sup.14 1.00 1.00 1.00 1.00 1.00 1.00 1.00 MB2:
TOTAL 244.30 244.30 244.30 244.30 244.30 244.30 244.30
.sup.13Polyalkylene oxide/silquest blends are physical blends added
to the mix as a combination. .sup.14TMQ, an antioxidant available
from Uniroyal Chemical.
[0048] After the ingredients listed in Table V were mixed and
subjected to processing conditions to form the batch as described
above, 4.00 phr of zinc oxide was added to each of the batches to
bring the total of the MB-2 batch to 248.30 phr for each of the
examples. The ingredients listed below in Table VI were then added
to the MB-2 batches as set forth below.
6TABLE VI PHASED II Comp. Ex./Ex. E F G H 4 5 6 MB-2.sup.15 248.30
248.30 248.30 248.30 248.30 248.30 248.30 Delac NS.sup.16 1.50 1.50
1.50 1.50 1.50 1.50 1.50 Diphenyl 2.00 2.00 2.00 2.00 0.00 0.00
0.00 Guanadine ROYALAC 150 0.00 0.00 0.00 0.00 0.25 0.25 0.25
SULFUR 1.80 1.80 1.80 1.80 1.80 1.80 1.80 TOTAL 253.60 253.60
253.60 253.60 251.85 251.85 251.85 .sup.15MB-2 is the batch
provided as set forth in Table V together with 4.00 phr of zinc
oxide. .sup.16N-t-butyl-2-bezothiazole sulfenamide available from
Uniroyal Chemical Company.
Results
[0049] The compounded stocks prepared above were then sheeted out
and cut for cure. The samples were cured for the times and at the
temperatures indicated in Table VII and their physical properties
evaluated. The results are summarized in Table VII below. Note that
in Table VII, cure characteristics were determined using a Monsanto
rheometer ODR 2000 (1.degree. ARC, 100 cpm): MH is the maximum
torque and ML is the minimum torque: Scorch safety (t.sub.s2) is
the time to 2 units above minimum torque (ML), cure time (t.sub.50)
is the time to 50% of delta torque above minimum and cure time
(t.sub.90) is the time to 90% of delta torque above minimum.
Tensile Strength, Elongation and Modulus were measured following
procedures in ASTM D-412. Examples 4-6 illustrate a rubber
composition within the scope of this invention. Comparative
Examples E-H represents a rubber composition outside the scope of
this invention.
CURED PHYSICAL PROPERTIES
[0050]
7TABLE VII Comparative Example or Example E F G H 4 5 6 Cured
Characteristics obtained at 160.degree. C. ML (lb-in.) 3.9 5.0 4.6
4.8 6.3 9.2 5.5 MH (lb-in.) 28.4 35.7 34.8 36.7 37.2 35.7 38.0
Scorch safety t.sub.52 (min) 1.6 0.5 0.9 0.3 1.6 2.9 0.3 Cure time
t.sub.50 (min) 5.6 3.7 4.5 4.6 5.8 5.1 7.1 Cure time t.sub.90 (min)
22.0 14.5 16.2 13.7 16.8 11.9 17.7 Stress/Strain Unaged at
160.degree. C. Cure Time @ 160.degree. C. (min) 25.0 17.0 19.5 17.0
19.5 15.0 20.5 100% Modulus (Mpa) 3.2 2.7 2.7 2.2 2.3 2.1 2.2 300%
Modulus (Mpa) 14.4 11.2 11.0 8.5 9.7 8.5 9.3 Tensile Strength (Mpa)
18.3 17.9 18.5 19.2 19.2 18.8 18.4 Elongation, % at Break 350.0
430.0 440.0 560.0 500.0 520.0 490.0 Hardness, Shore A. 67.0 70.0
68.0 67.0 67.0 66.0 67.0 Mooney Scorch (MS at 135.degree. C.) 3 Pt.
Rise Time (min) 15.0 9.4 11.9 13.6 16.9 14.6 23.5 18 Pt. Rise Time
(min) 22.1 13.3 16.9 17.9 20.5 17.0 29.3 Mooney
Viscosity(ML.sub.1+4 at 100.degree. C.) ML.sub.1+4 84 83 86 83 80
87 81 Stress Relaxation (%) 70.6 71.6 67.2 76.1 84.4 73.5 81.1
Tangent Delta 60.degree. C. (10 Hz) [RPA-2000] % Strain 0.7 0.088
0.061 0.063 0.051 0.052 0.037 0.053 1.0 0.096 0.060 0.075 0.062
0.058 0.040 0.058 2.0 0.119 0.086 0.084 0.084 0.076 0.061 0.081 5.0
0.156 0.141 0.134 0.136 0.132 0.125 0.130 7.0 0.156 0.151 0.142
0.147 0.145 0.135 0.138 14.0 0.172 0.189 0.176 0.189 0.185 0.174
0.176 Dynamic Modulus (G', Kpa) % Strain 0.7 4800 6687 6694 7620
8002 7161 6832 1.0 4497 6443 6399 7186 7782 6967 6547 2.0 3866 5768
5746 6451 6959 6476 5902 5.0 3020 4303 4069 4681 4945 4635 4281 7.0
2750 3736 3522 4001 4246 3989 3792 14.0 2068 2309 2390 2517 2733
2639 2455 Din Abrasion Volume Loss (mm.sup.3) 84.3 93.5 92.4 103.2
99.9 102.7 92.0 Abrasion Index 147.2 132.8 134.2 120.1 124.2 120.8
134.8
[0051] It can be seen from the above data that the examples
containing a high molecular weight thiuram disulfide and a
polyalkylene oxide (Examples 4-6) provide superior performance when
compared to the examples containing DPG with no polyalkylene oxide
present therein (Comparative Example F) and a polyalkylene oxide
with DPG (Comparative Examples F-H).
[0052] When comparing Example 4 and Comparative Example F, the
mooney scorch value was significantly higher without any sacrifice
in other physical properties, e.g., tangent delta value, by
replacing DPG with a high molecular weight thiuram disulfide.
Additionally, the cure time for Example 4 was relatively equivalent
to that of Comparative Example F.
[0053] Examples 5 and 6 likewise possessed a significantly higher
mooney scorch value when compared to Comparative Examples G and H,
respectively, while also having relatively equivalent cure times.
The tangent delta value for Examples 5 and 6 was lower than that of
Comparative Examples G and H, which is desirable in rubber
compositions.
[0054] Additionally, the 100% and 300% Modulus and % elongation for
Examples 4-6 were either comparable or better than those of
Examples E-H. Thus, by replacing 2 phr of diphenyl guanadine with
0.25 phr of tetralkyl (C.sub.12-C.sub.14) thiuram disulfide, the
scorch safety of the rubber composition has been significantly
improved without any sacrifice in physical properties resulting in
an economical cost advantage being realized.
[0055] Although the invention has been described in its preferred
form with a certain degree of particularity, obviously many changes
and variations are possible therein and will be apparent to those
skilled in the art after reading the foregoing description. It is
therefore to be understood that the present invention may be
presented otherwise than as specifically described herein without
departing from the spirit and scope thereof.
* * * * *