U.S. patent application number 14/748343 was filed with the patent office on 2016-12-29 for tire with tread for combination of low temperature performance and for wet traction.
The applicant listed for this patent is The Goodyear Tire & Rubber Company. Invention is credited to Nihat Ali Isitman, Paul Harry Sandstrom, Pascal Patrick Steiner, Georges Marcel Victor Thielen.
Application Number | 20160376428 14/748343 |
Document ID | / |
Family ID | 56137147 |
Filed Date | 2016-12-29 |
United States Patent
Application |
20160376428 |
Kind Code |
A1 |
Sandstrom; Paul Harry ; et
al. |
December 29, 2016 |
TIRE WITH TREAD FOR COMBINATION OF LOW TEMPERATURE PERFORMANCE AND
FOR WET TRACTION
Abstract
This invention relates to a tire with tread for promoting a
combination of wet traction and service at low temperatures of a
rubber composition containing a styrene/butadiene elastomer, cis
1,4-polybutadiene rubber, liquid high Tg styrene/butadiene polymer,
resin and vegetable triglyceride oil.
Inventors: |
Sandstrom; Paul Harry;
(Cuyahoga Falls, OH) ; Thielen; Georges Marcel
Victor; (Schouweiler, LU) ; Steiner; Pascal
Patrick; (Vichten, FR) ; Isitman; Nihat Ali;
(Ettelbruck, LU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Goodyear Tire & Rubber Company |
Akron |
OH |
US |
|
|
Family ID: |
56137147 |
Appl. No.: |
14/748343 |
Filed: |
June 24, 2015 |
Current U.S.
Class: |
523/156 |
Current CPC
Class: |
C08L 9/06 20130101; C08L
9/06 20130101; C08L 57/02 20130101; C08L 2205/025 20130101; C08L
45/02 20130101; C08K 3/36 20130101; B60C 1/0016 20130101; C08L 9/00
20130101; C08L 2205/02 20130101; C08L 91/00 20130101; C08L 2203/00
20130101; C08L 2207/324 20130101; C08L 9/06 20130101; C08L 9/06
20130101; C08L 45/02 20130101; C08L 91/00 20130101; C08K 3/36
20130101; C08K 3/36 20130101; C08L 9/00 20130101; C08L 91/00
20130101; C08L 9/00 20130101; C08L 57/02 20130101; C08L 9/00
20130101; C08L 9/06 20130101; C08L 2205/035 20130101; C08L 2205/06
20130101; C08L 2205/03 20130101 |
International
Class: |
C08L 9/06 20060101
C08L009/06 |
Claims
1. A pneumatic tire having a circumferential rubber tread of a
sulfur cured rubber composition comprised of, based on parts by
weight per 100 parts by weight elastomer (phr): (A) 100 phr of at
least one diene-based elastomer comprised of; (1) about 25 to about
75 phr of a styrene/butadiene elastomer having a Tg in a range of
from about -35.degree. C. to about -5.degree. C., (2) about 25 to
about 75 phr of high cis 1,4-polybutadiene rubber having a Tg in a
range of from about -100.degree. C. to about -109.degree. C., (3)
about 3 to about 50 phr of low molecular weight liquid
styrene/butadiene polymer having a number average molecular weight
in a range of from about 3,000 to about 30,000 and a Tg in a range
of from -25.degree. C. to about -5.degree. C., (B) about 50 to
about 250 phr of rubber reinforcing filler comprised of a
combination of precipitated silica and rubber reinforcing carbon
black in a ratio of precipitated silica to rubber reinforcing
carbon black of at least 9/1, together with silica coupling agent
having a moiety reactive with hydroxyl groups on said precipitated
silica and another different moiety interactive with said
diene-based elastomers and polymer, (C) about 7.5 to about 25 phr
of traction resin consisting of styrene-alphamethylstyrene resin
having a softening point in a range of from about 60.degree. C. to
about 80.degree. C. and a styrene content of from about 10 to about
30 percent, and (D) about 10 to about 50 phr of vegetable
triglyceride oil comprised of soybean oil, wherein said
styrene/butadiene elastomer is a tin coupled functionalized
elastomer having functional groups comprised of at least one of
siloxy, amine and thiol groups reactive with hydroxyl groups on
said precipitated silica, wherein said precipitated silica and
silica coupling agent are provided as a pre-reacted composite
thereof, and wherein said silica coupling agent is comprised of at
least one of a bis(3-triethoxysilylpropyl) polysulfide containing
an average of from about 2 to about 4 sulfur atoms in its
connecting polysulfidic bridge and an
organoalkoxymercaptosilane.
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. The tire of claim 1 wherein said tread rubber composition
further contains up to 25 phr of at least one additional diene
based elastomer.
10. The tire of claim 9 wherein said additional elastomer is
comprised of at least one of cis 1,4-polyisoprene,
isoprene/butadiene, styrene/isoprene and 3,4-polyisoprene
rubber.
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. The tire of claim 1 wherein said silica coupling agent for said
pre-reacted composite of precipitated silica and coupling agent is
an alkoxyorganomercaptosilane.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a tire with tread for promoting a
combination of winter service at low temperatures and for promoting
wet traction comprised of a rubber composition containing a
styrene/butadiene elastomer, cis 1,4-polybutadiene rubber, liquid
high Tg styrene/butadiene polymer, resin and vegetable triglyceride
oil.
BACKGROUND OF THE INVENTION
[0002] Tires are sometimes desired with treads for promoting
traction on wet surfaces. Various rubber compositions may be
proposed for tire treads.
[0003] For example, tire tread rubber compositions which contain
high molecular weight, high Tg (high glass transition temperature)
diene based elastomer(s) might be desired for such purpose
particularly for wet traction (traction of tire treads on wet road
surfaces). Such tire tread may be desired where its reinforcing
filler is primarily precipitated silica which may therefore be
considered as being precipitated silica rich.
[0004] Such rubber compositions often contain a petroleum based
rubber processing oil to reduce the rubber composition's uncured
viscosity and to thereby promote more desirable processing
conditions for the uncured rubber composition. The petroleum based
rubber processing oil can be added to the elastomer prior to its
addition to an internal rubber mixer (e.g. Banbury rubber mixer) or
be added to the rubber mixer as a separate addition to reduce the
viscosity of the rubber composition both in the internal rubber
mixer and for subsequent rubber processing such as in a rubber
extruder.
[0005] Because of the high molecular weight of such high molecular
weight elastomers, the uncured tread rubber compositions typically
have a Mooney viscosity (ML1+4) which is generally too high (e.g.
in a range of from 50 to 150) to be easily processible with
ordinary rubber processing equipment unless very high shear
processing conditions are used. Therefore, such rubber compositions
often contain a petroleum based rubber processing oil to reduce the
rubber composition's uncured viscosity and to thereby promote more
desirable processing conditions for the uncured rubber composition.
The petroleum based rubber processing oil can be added to the
elastomer prior to its addition to an internal rubber mixer (e.g.
Banbury rubber mixer) or be added to the rubber mixer as a separate
addition to reduce the viscosity of the rubber composition both in
the internal rubber mixer and for subsequent rubber processing such
as in a rubber extruder.
[0006] However, it is also desired to reduce the stiffness of such
tread rubber compositions, as indicated by a storage modulus G',
intended to be used for low temperature winter conditions,
particularly for vehicular snow driving.
[0007] It is considered that significant challenges are presented
for providing such tire tread rubber compositions for maintaining
both their wet traction and also low temperature (e.g. winter)
performance.
[0008] To achieve such balance of tread rubber performances with
tread rubber compositions containing such high Tg diene-based
elastomer(s), it is recognized that concessions and adjustments
would be required.
[0009] To meet such challenge of providing a silica-rich tread
rubber composition containing high Tg elastomer(s) to promote wet
traction combined with promoting a reduction in its stiffness at
low temperatures, it is desired to evaluate:
[0010] (A) replacing the petroleum based rubber processing oil
(e.g. comprised of at least one of naphthenic and paraffinic oils)
with a vegetable triglyceride oil such as, for example, soybean oil
to reduce its uncured rubber processing viscosity and to reduce the
Tg of the rubber composition itself to thereby promote a lower
cured stiffness of the tread rubber composition at lower
temperatures which will positively impact the low temperature
winter performance of such rubber compositions,
[0011] (B) adding a high Tg uncured liquid diene-based polymer
(particularly a low viscosity, high Tg, styrene/butadiene polymer)
which both helps to promote wet traction performance for such a
tread rubber composition and also helps to maintain a lower cured
rubber stiffness value at the lower temperatures required for
winter traction performance,
[0012] (C) adding a traction promoting resin in the tread rubber
composition, particularly at a relatively high resin loading, to
promote wet traction of the sulfur cured tread rubber which
contains the vegetable triglyceride oil,
[0013] (D) maintaining its high precipitated silica-rich rubber
reinforcing filler content to promote its wet traction.
[0014] Exemplary of past soybean oil usage, and not intended to be
limiting, are U.S. Pat. Nos. 7,919,553, 8,100,157, 8,022,136 and
8,044,118.
[0015] However, while vegetable oils such as soybean oil have
previously been mentioned for use in various rubber compositions,
including rubber compositions for tire components, use of soybean
oil together with precipitated silica reinforced high Tg diene
based elastomer(s), liquid diene based polymers and traction
resin(s) for tire treads to aid in promoting a combination of both
wet traction and winter tread performance is considered to be a
significant departure from past practice.
[0016] In the description of this invention, the terms "compounded"
rubber compositions and "compounds" are used to refer to rubber
compositions which have been compounded, or blended, with
appropriate rubber compounding ingredients. The terms "rubber" and
"elastomer" may be used interchangeably unless otherwise indicated.
The amounts of materials are usually expressed in parts of material
per 100 parts of rubber by weight (phr).
[0017] The glass transition temperature (Tg) of the solid
elastomers and liquid polymer may be determined by DSC
(differential scanning calorimetry) measurements, as would be
understood and well known by one having skill in such art. The
number average molecular weight (Mn) of the solid elastomers and
liquid polymer may be determined by GPC (gel permeation
chromatography) measurements as would be understood and well known
by one having skill in such art. The softening point of a resin may
be determined by ASTM E28 which might sometimes be referred to as a
ring and ball softening point.
SUMMARY AND PRACTICE OF THE INVENTION
[0018] In accordance with this invention, a pneumatic tire is
provided having a circumferential rubber tread intended to be
ground-contacting, where said tread is a rubber composition
comprised of, based on parts by weight per 100 parts by weight
elastomer (phr):
[0019] (A) 100 phr of at least one diene-based elastomer comprised
of; [0020] (1) about 25 to about 75 phr of a styrene/butadiene
elastomer having a Tg in a range of from about -35.degree. C. to
about -5.degree. C. and an uncured Mooney viscosity (ML1+4) in a
range of from about 50 to about 150, [0021] (2) about 25 to about
75 phr of high cis 1,4-polybutadiene rubber having a Tg in a range
of from about -100.degree. C. to about -109.degree. C., [0022] (3)
about 3 to about 50 phr of low molecular weight liquid
styrene/butadiene polymer having a number average molecular weight
in a range of from about 3,000 to about 30,000, alternately about
4,000 to about 15,000 and a Tg in a range of from about -30.degree.
C. to about 0.degree. C., alternately from about -25.degree. C. to
about -5.degree. C.,
[0023] (B) about 50 to about 250, alternately from about 75 to
about 175, phr of rubber reinforcing filler comprised of a
combination of precipitated silica (amorphous synthetic
precipitated silica) and rubber reinforcing carbon black in a ratio
of precipitated silica to rubber reinforcing carbon black of at
least 9/1, together with silica coupling agent having a moiety
reactive with hydroxyl groups (e.g. silanol groups) on said
precipitated silica and another different moiety interactive with
said diene-based elastomers and polymer,
[0024] (C) about 5 to about 35, alternately from about 7.5 to about
25, phr of resin comprised of at least one of terpene, coumarone
indene and styrene-alphamethylstyrene resins where such resins
desirably have a softening point (ASTM E28) in a range of from
about 60.degree. C. to about 150.degree. C., and
[0025] (D) about 10 to about 50, alternately from about 20 to about
40 phr of vegetable triglyceride oil such as, for example, such oil
comprised of soybean oil.
[0026] In further accordance with this invention, said tire is
provided being sulfur cured.
[0027] In on embodiment, the high molecular weight
styrene/butadiene elastomer having a Tg in a range of from about
-35.degree. C. to about -5.degree. C. has an uncured Mooney
viscosity in a range of from about 60 to about 120.
[0028] In one embodiment, the high molecular weight of the
styrene/butadiene elastomer may be evidenced by a relatively high
Mooney viscosity (ML1+4) in its uncured state in a range of, for
example, about 65 to about 90.
[0029] In one embodiment, the high cis 1,4 polybutadiene rubber has
a cis 1,4- isomeric content of at least about 95 percent and an
uncured Mooney viscosity in a range of from about 50 to 100.
[0030] In one embodiment said tread rubber composition further
contains up to 25, alternately up to about 15, phr of at least one
additional diene based elastomer. Such additional elastomer may be
comprised of, for example, at least one of cis 1,4-polyisoprene,
isoprene/butadiene, styrene/isoprene and 3,4-polyisoprene
rubber.
[0031] In one embodiment, said styrene/butadiene elastomer may be a
functionalized elastomer containing at least one of siloxane, amine
and thiol groups reactive with hydroxyl groups on said precipitated
silica.
[0032] In one embodiment, said styrene/butadiene elastomer may be a
tin or silicon coupled elastomer.
[0033] In one embodiment, said functionalized styrene/butadiene
elastomer may be a tin or silicon coupled elastomer.
[0034] In one embodiment, said precipitated silica and silica
coupling agent may be pre-reacted to form a composite thereof prior
to their addition to the rubber composition.
[0035] In one embodiment, said precipitated silica and silica
coupling agent may be added to the rubber composition and reacted
together in situ within the rubber composition.
[0036] In one embodiment, said resin may be a terpene resin
comprised of polymers of at least one of limonene, alpha pinene and
beta pinene and having a softening point in a range of from about
60.degree. C. to about 140.degree. C.
[0037] In one embodiment, said resin may be a coumarone indene
resin having a softening point in a range of from about 60.degree.
C. to about 150.degree. C.
[0038] In one embodiment, said resin may be a
styrene-alphamethylstyrene resin having a softening point in a
range of from about 60.degree. C. to about 125.degree. C.,
alternately from about 80.degree. C. to 90.degree. C. (ASTM E28),
and, for example, a styrene content of from about 10 to about 30
percent.
[0039] The precipitated silica reinforcement may, for example, be
characterized by having a BET surface area, as measured using
nitrogen gas, in the range of, for example, 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 might be
described, for example, in the Journal of the American Chemical
Society, Volume 60, as well as ASTM D3037.
[0040] Such precipitated silicas may, for example, also be
characterized by having a dibutylphthalate (DBP) absorption value,
for example, in a range of about 100 to about 400, and more usually
about 150 to about 300 cc/100 g.
[0041] Various commercially available precipitated silicas may be
used, such as, and not intended to be limiting, silicas from PPG
Industries under the Hi-Sil trademark with designations 210, 243,
etc.; silicas from Solvay with, for example, designations of Zeosil
1165MP and Zeosil 165GR, silicas from Evonik with, for example,
designations VN2 and VN3 and chemically treated precipitated
silicas such as for example Agilon.TM. 400 from PPG.
[0042] Representative examples of rubber reinforcing carbon blacks
are, for example, and not intended to be limiting, are referenced
in The Vanderbilt Rubber Handbook, 13.sup.th edition, year 1990, on
Pages 417 and 418 with their ASTM designations. As indicated, such
rubber reinforcing carbon blacks may have iodine absorptions
ranging from, for example, 60 to 240 g/kg and DBP values ranging
from 34 to 150 cc/100 g.
[0043] If desired, the vulcanizable (and vulcanized) tread rubber
composition may contain an ultra high molecular weight polyethylene
(UHMWPE).
[0044] Representative of silica coupling agents for the
precipitated silica are comprised of, for example;
[0045] (A) bis(3-trialkoxysilylalkyl) polysulfide containing an
average in range of from about 2 to about 4, alternatively from
about 2 to about 2.6 or from about 3.2 to about 3.8, sulfur atoms
in its connecting bridge, or
[0046] (B) an organoalkoxymercaptosilane, or
[0047] (C) their combination.
[0048] Representative of such bis(3-trialkoxysilylalkyl)
polysulfide is comprised of bis(3-triethoxysilylpropyl)
polysulfide.
[0049] It is readily understood by those having skill in the art
that the vulcanizable rubber composition would be compounded by
methods generally known in the rubber compounding art. In addition
said compositions could also contain fatty acid, zinc oxide, waxes,
antioxidants, 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. Representative examples of sulfur donors
include elemental sulfur (free sulfur), an amine disulfide,
polymeric polysulfide and sulfur olefin adducts. Usually it is
desired that the sulfur-vulcanizing agent is elemental sulfur. The
sulfur-vulcanizing agent may be used in an amount ranging, for
example, from about 0.5 to 8 phr, with a range of from 1.5 to 6 phr
being often preferred. Typical amounts of processing aids comprise
about 1 to about 50 phr.
[0050] Additional rubber processing oils, (e.g. petroleum based
rubber processing oils) may be included in the rubber composition,
if desired, to aid in processing vulcanizable rubber composition in
addition to the vegetable oil such as soybean oil, wherein the
vegetable oil is the majority (greater than 50 weight percent) of
the vegetable oil and rubber processing oil.
[0051] Typical amounts of antioxidants may comprise, for example,
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 through 346. Typical amounts of antiozonants may
comprise, for example, 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 may comprise, for
example, 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, when used, may be used in amounts of,
for example, about 0.1 to about 1 phr. Typical peptizers may be,
for example, pentachlorothiophenol and dibenzamidodiphenyl
disulfide.
[0052] Sulfur vulcanization 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. The
primary accelerator(s) may be used in total amounts ranging, for
example, from about 0.5 to about 4, sometimes desirably about 0.8
to about 1.5, phr. In another embodiment, combinations of a primary
and a secondary accelerator might be used with the secondary
accelerator being used in smaller amounts, such as, for example,
from 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 that may be used in the
present invention are amines, disulfides, guanidines, thioureas,
thiazoles, sulfenamides, and xanthates. Often desirably the primary
accelerator is a sulfenamide. If a second accelerator is used, the
secondary accelerator is often desirably a guanidine such as for
example a diphenylguanidine.
[0053] The mixing of the vulcanizable 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) of the preceding
non-productive mix stage(s). The terms "non-productive" and
"productive" mix stages are well known to those having skill in the
rubber mixing art. The rubber composition may be subjected to a
thermomechanical mixing step. The thermomechanical mixing step
generally comprises a mechanical working in a mixer or extruder for
a period of time suitable in order to produce a rubber temperature
between 140.degree. C. and 190.degree. C. The appropriate duration
of the thermomechanical working varies as a function of the
operating conditions and the volume and nature of the components.
For example, the thermomechanical working may be from 1 to 20
minutes.
[0054] The pneumatic tire of the present invention may be a race
tire, passenger tire, aircraft tire, agricultural tire, earthmover
tire, off-the-road tire, truck tire and the like. Usually desirably
the tire is a passenger or truck tire. The tire may also be a
radial or bias ply tire, with a radial ply tire being usually
desired.
[0055] Vulcanization of the pneumatic tire containing the tire
tread of the present invention is generally carried out at
conventional temperatures in a range of, for example, from about
140.degree. C. to 200.degree. C. Often it is desired that the
vulcanization is conducted at temperatures ranging from about
150.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. 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.
[0056] The following examples are presented for the purposes of
illustrating and not limiting the present invention. The parts and
percentages are parts by weight, usually parts by weight per 100
parts by weight rubber (phr) unless otherwise indicated.
[0057] The liquid (low viscosity) diene-based polymers evaluated in
the following Examples are shown in Table A. The indicated polymers
are liquid cis 1,4-polyisoprene polymer and liquid
styrene/butadiene polymers (liquid SBR's) identified as
styrene/butadiene polymers A, B, C and D.
TABLE-US-00001 TABLE A Styrene Number Average Liquid Polymer
Content Tg Molecular Weight Product Cis 0 -63.degree. C. 28,000 LIR
.TM.-30.sup.1 1,4-polyisoprene Styrene/ 25 -22.degree. C. 4,500
Ricon .TM. 100.sup.2 butadiene A Styrene/ 25 -14.degree. C. 8,500
SBR-820 .TM..sup.3 butadiene B Styrene/ 25 -6.degree. C. 10,000 SBR
841 .TM..sup.4 butadiene C Styrene/ 28 -61.degree. C. 8,600 Ricon
.TM. 184.sup.5 butadiene D .sup.1liquid cis 1,4-polyisoprene
polymer from Kururay .sup.2liquid SBR from Cray Valley .sup.3liquid
SBR from Kuraray .sup.4liquid SBR from Kuraray .sup.5liquid SBR
from Cray Valley
EXAMPLE I
[0058] In this example, exemplary rubber compositions for a tire
tread were prepared for evaluation for use to promote wet traction
and cold weather (winter) performance.
[0059] A Control rubber composition was prepared as Sample A with a
precipitated silica reinforced rubber composition containing
styrene/butadiene rubber and cis 1,4-polybutadiene rubber together
with a silica coupler for the precipitated silica
reinforcement.
[0060] Experimental rubber compositions were prepared as Samples B
through D with one or more of soybean oil, liquid styrene/butadiene
polymer, liquid polyisoprene polymer and styrene-alphamethylstyrene
resin being added to the rubber composition containing elastomers
as styrene/butadiene rubber and cis 1,4-polybutadiene rubber.
[0061] The rubber compositions are illustrated in the following
Table 1.
TABLE-US-00002 TABLE 1 Parts by Weight (phr) Control Exp'l Exp'l
Exp'l Sample Sample Sample Sample Material A B C D
Styrene/butadiene rubber.sup.1 55 60 60 60 Cis 1,4-polybutadiene
rubber.sup.2 45 40 40 40 Rubber processing oil.sup.3 40 0 0 0
Soybean oil.sup.4 0 40 30 30 Liquid styrene/butadiene polymer 0 0 0
10 A.sup.5 Liquid cis 1,4-polyisoprene rubber.sup.6 0 0 10 0
Styrene-alphamethylstyrene resin.sup.7 10 20 20 20 Precipitated
silica.sup.8 125 125 125 125 Silica coupler.sup.9 7.5 7.5 7.5 7.5
Fatty acids.sup.10 5 5 5 5 Carbon black 1 1 1 1 (carrier for silica
coupler) Wax 1.5 1.5 1.5 1.5 Antioxidants 3 3 3 3 Zinc oxide 2.5
2.5 2.5 2.5 Sulfur 1.2 1.5 1.5 1.5 Sulfur cure accelerators.sup.11
5 5.25 5.25 5.25 .sup.1A functionalized, tin coupled,
styrene/butadiene rubber containing a combination of siloxy and
thiol groups having a Tg of about -30.degree. C. to -10.degree. C.
and Mooney viscosity (ML1 + 4) of about 70 as SLR4602 .TM. from
Styron. .sup.2High cis 1,4-polybutadiene rubber as BUD4001 .TM.
from The Goodyear Tire & Rubber Company having a Tg of about
-102.degree. C. .sup.3Rubber processing oil primarily comprised of
naphthenic oil .sup.4Soybean oil as Sterling Oil from Stratus Food
Company .sup.5Liquid, sulfur vulcanizable styrene/butadiene polymer
having a Tg of about -22.degree. C. .sup.6Liquid, sulfur
vulcanizable polyisoprene polymer having a Tg of about -63.degree.
C. .sup.7Resin as styrene-alphamethylstyrene copolymer having a
softening point in a range of about 80.degree. C. to 90.degree. C.
(ASTM E28) and a styrene content in a range of from about 10 to
about 30 percent as Resin 2336 .TM. from Eastman Chemical.
.sup.8Precipitated silica as Zeosil 1165MP .TM. from Solvay
.sup.9Silica coupler comprised of a bis(3-triethoxysilylpropyl)
polysulfide containing an average in a range of from about 2 to
about 2.6 connecting sulfur atoms in its polysulfidic bridge as
Si266 from Evonik. The coupler was a composite with carbon black as
a carrier, although the coupler and carbon black are reported
separately in the Table. .sup.10Fatty acids comprised of stearic,
palmitic and oleac acids .sup.11Sulfur cure accelerators as
sulfenamide primary accelerator and diphenylguanidine secondary
accelerator
[0062] The rubber Samples were prepared by identical mixing
procedures, wherein the elastomers and liquid polymer with 80 phr
of precipitated silica, together with silica coupler and
compounding ingredients together in a first non-productive mixing
stage (NP1) in an internal rubber mixer for about 4 minutes to a
temperature of about 160.degree. C. The resulting mixtures were was
subsequently mixed in a second sequential non-productive mixing
stage (NP2) in an internal rubber mixer to a temperature of about
160.degree. C. with an additional 45 phr of precipitated silica.
The rubber compositions were subsequently mixed in a productive
mixing stage (P) in an internal rubber mixer with a sulfur cure
package, namely sulfur and sulfur cure accelerator(s), for about 2
minutes to a temperature of about 115.degree. C. The rubber
compositions were each removed from its internal mixer after each
mixing step and cooled to below 40.degree. C. between each
individual non-productive mixing stage and before the final
productive mixing stage.
[0063] The following Table 2 illustrates cure behavior and various
physical properties of rubber compositions based upon the basic
formulation of Table 1 and reported herein as Control rubber Sample
A and Experimental rubber Samples B through D. Where cured rubber
samples are reported, such as for the stress-strain, hot rebound
and hardness values, the rubber samples were cured for about 14
minutes at a temperature of about 160.degree. C.
[0064] To establish the predictive wet traction, a tangent delta
(tan delta) test was run at 0.degree. C. To establish the
predictive low temperature (winter snow) performance, the rubber's
stiffness (storage modulus G') test was run at -20.degree. C.
TABLE-US-00003 TABLE 2 Parts by Weight (phr) Control A Exp. B Exp.
C Exp. D Materials Styrene/butadiene rubber 55 60 60 60 Cis
1,4-polybutadiene rubber 45 40 40 40 Rubber processing oil 40 0 0 0
Soybean oil 0 40 30 30 Liquid styrene/butadiene 0 0 0 10 polymer A
Liquid polyisoprene polymer 0 0 10 0 Resin 10 20 20 20 Properties
Wet Traction Laboratory Prediction Tan delta, 0.degree. C. 0.46
0.41 0.41 0.45 (higher is better) Cold Weather (Winter) Performance
(Stiffness) Laboratory Prediction Storage modulus 3.4 3.1 2.8 2.7
(G'), (Pa .times. 10.sup.6) at -20.degree. C., 10 Hertz, 3% strain
(lower stiffness values are better) Rolling Resistance (RR)
Laboratory Prediction Rebound at 100.degree. C. 48 46 48 49
Additional properties Tensile strength (MPa) 11.8 11.8 11.4 11.8
Elongation at break (%) 470 598 564 615 Modulus (ring) 300% (MPa)
6.7 4.9 5 4.8 Tear resistance.sup.1 (Newtons) 34 73 52 69
.sup.1Data obtained according to a tear strength (peal adhesion)
test to determine interfacial adhesion between two samples of a
rubber composition. In particular, such interfacial adhesion is
determined by pulling one rubber composition away from the other at
a right angle to the untorn test specimen with the two ends of the
rubber compositions being pulled apart at a 180.degree. angle to
each other using an Instron instrument at 95.degree. C. and
reported as Newtons force (N).
[0065] From Table 2 it is observed that:
[0066] (1) For Experimental rubber Sample B, conventional petroleum
based rubber processing oil of Control rubber Sample A was replaced
with soybean oil, the SBR rubber was increased to 60 phr from the
50 phr of Control rubber Sample A, the resin increased to 20 phr
from the 10 phr of Control rubber Sample A and the rubber Sample
cured. As a result, an improved predictive cold weather (winter)
performance was obtained based on a lower storage modulus G'
stiffness value of 3.1 as compared to a value of 3.4 for Control
rubber Sample A. However, a loss in predictive wet traction was
experienced based on a tangent delta value of 0.41 compared to 0.46
for Control rubber Sample A.
[0067] (2) For Experimental rubber Sample C, the composition of
Experimental rubber Sample B was changed by replacing 10 phr of the
soybean oil with 10 phr of liquid polyisoprene polymer and the
rubber Sample cured. A further improvement of predictive cold
weather (winter) performance was observed as indicated by a
beneficially even lower storage modulus G' stiffness at -20.degree.
C. of 2.8 as compared to the value of 3.4 for Control rubber Sample
A and value of 3.1 for Experimental rubber Sample B. However,
similar to Experimental rubber Sample B, a loss in predictive wet
traction was also experienced based on a tan delta value of 0.41
compared to 0.46 for Control rubber Sample A.
[0068] (3) Experimental rubber Sample D was similar to Experimental
rubber Sample C except that 10 phr of the soybean oil of
Experimental rubber Sample B was replaced with a high Tg liquid
styrene/butadiene polymer instead of the liquid polyisoprene
polymer of Experimental rubber Sample C. An even further
improvement of predictive cold weather (winter) performance was
observed as observed by a beneficially even lower storage modulus
G' stiffness at -20.degree. C. of 2.7 as compared to the value of
3.4 for Control rubber Sample A and 2.8 for Experimental rubber
Sample C. However, an improvement in predictive wet traction was
surprisingly discovered based on an observed tan delta value of
0.45 which compared favorably and beneficially to the value of 0.46
for Control rubber Sample A.
[0069] It is thereby concluded from Experimental rubber Sample D of
this evaluation that a unique discovery was obtained of a sulfur
cured rubber composition composed of high Tg styrene/butadiene
rubber and high cis 1,4-polybutadiene rubber (with its low Tg of
about minus 102.degree. C.) together with the combination of
soybean oil, high Tg liquid styrene/butadiene polymer (Tg of
-22.degree. C.) and resin as shown in Experimental rubber Sample D,
as compared to Control rubber Sample A. The desired target of
improved cold weather (winter) performance (stiffness in a sense of
storage modulus G' at low temperature) without a loss of predicted
wet traction (in a sense of higher tan delta values at 0.degree.
C.) for a tire tread performance was obtained from such a cured
rubber composition.
[0070] Further, a discovery is observed that Experimental rubber
Sample D yielded a beneficially and significantly improved tear
strength resistance value of 69 Newtons compared to a value of only
34 Newtons for Control rubber Sample A while maintaining a similar
hot rebound value of 49 which is predictive of maintaining a
beneficially similar rolling resistance for a tire tread of similar
rubber composition.
EXAMPLE II
[0071] Additional experiments were made with variations in liquid
styrene/butadiene polymers (low viscosity SBR polymers).
[0072] The rubber formulation recipes of Example I were used except
for the liquid polymers being variations of the liquid SBR
polymers.
[0073] The experiments were composed of Control rubber Sample E
with a formulation referenced in Example I, Table 1, as Control
rubber Sample B, and Experimental rubber Samples F through H which
contained additional liquid SBR polymers for comparison to the
liquid SBR A evaluated in Example I. The liquid styrene/butadiene
polymers used are reported in Table 1.
[0074] The rubber Samples were prepared and tested in the manner of
Example I. The following Table 3 illustrates cure behavior and
various physical properties of rubber compositions.
TABLE-US-00004 TABLE 3 Parts by Weight (phr) Control E Exp. F Exp.
G Exp. H Materials Liquid SBR polymer A, 10 0 0 0 Tg = -22.degree.
C. Liquid SBR polymer B, 0 10 0 0 Tg = -14.degree. C. Liquid SBR
polymer C, 0 0 10 0 1 Tg = -6.degree. C. Liquid SBR polymer D, 0 0
0 10 Tg = -61.degree. C. SBR, solid, number 4,500 8,500 10,000
8,600 average molecular weight (Mn) Wet Traction, Laboratory
Prediction Tan delta (higher is 0.52 0.53 0.55 0.49 better) Winter
Performance (Stiffness) Laboratory Prediction Storage modulus 10.8
12.4 11.9 12.1 (G') at -20.degree. C. (Pa .times. 10 6) 10 Hertz,
3% strain (lower stiffness values are better) Rolling Resistance
(RR) Laboratory Prediction Rebound at 100.degree. C. 51 49 50 48
Additional properties Tensile strength (MPa) 10.9 11 11.4 11.5
Elongation at break (%) 522 539 514 542 Modulus (ring) 300% 5.2 5
5.6 5.3 (MPa) Tear resistance 38 33 38 33 (Newtons)
[0075] From Table 3 it can be seen that all of the liquid SBR
polymers with their varied range of Tgs provided the rubber
compositions with similar low temperature predictive stiffness
properties (G' values) ranging from 10.8 to 12.4.
[0076] However, Experimental rubber Sample H, which contained the
liquid SBR with the lowest Tg of -61.degree. C. (SBR polymer D),
gave the worst predicted wet performance based on having the lowest
tan delta value at 0.degree. C. and therefore the liquid SBR
polymer would be considered as having too low of a Tg for use in
this rubber composition where a combination of wet traction and
cold weather performance is desired.
[0077] In contrast, Experimental rubber Sample G, having the
highest Tg liquid SBR polymer gave the best predicted wet traction
based on its tan delta value at 0.degree. C., while sill giving
similar predicted winter traction performance based on its G' value
at -20.degree. C.
[0078] Therefore it is concluded that to achieve a combination of
high predicted wet traction together with beneficially low
predicted stiffness (at low atmospheric temperature) for the tire
tread rubber composition, a liquid (low viscosity)
styrene/butadiene polymer with a high Tg would be desired to be
combined with a high Tg, high molecular weight (evidenced by having
a high uncured Mooney ML1+4 viscosity), styrene/butadiene rubber in
the tread rubber composition which also contains the vegetable oil
(soybean oil) to aid in reducing the overall Tg of the rubber
composition to promote low stiffness for cold weather winter
driving conditions, the cis 1,4-polybutadiene rubber having its low
Tg of about -102.degree. C. to aid in promoting low stiffness for
cold winter driving conditions and traction resin to aid on
promoting the tire tread's wet traction.
[0079] It is concluded from these two laboratory studies that a
liquid SBR polymer having a Tg in a range of about -30.degree. C.
to about 0.degree. C. together with a number average molecular
weight in a range of from about 3,000 to about 30,000 should be
used for the rubber composition together with a solid SBR with a Tg
in a range of from about -35.degree. C. to about -5.degree. C. and
an uncured Mooney viscosity in a range of from about 50 to about
150, alternatively from about 60 to about 100, to provide the
beneficial combination of both improved low temperature stiffness
(G') at -20.degree. C. for cold weather winter performance and
higher tan delta at 0.degree. C. for wet traction for the
silica-rich rubber composition comprised of a combination of high
uncured Mooney viscosity styrene/butadiene and cis
1,4-polybutadiene rubbers which contained both the aforesaid low
molecular weight, high Tg, liquid SBR polymers and soybean oil and
traction resin, when sulfur cured.
[0080] While certain representative embodiments and details have
been shown for the purpose of illustrating the invention, it will
be apparent to those skilled in this art that various changes and
modifications may be made therein without departing from the spirit
or scope of the invention.
* * * * *