U.S. patent application number 12/461241 was filed with the patent office on 2009-12-03 for radial-carcass tires formed by using specific cohesive, low-hysteresis compositions.
This patent application is currently assigned to MICHELIN RECHERCHE ET TECHNIQUE, S.A.. Invention is credited to Frederic Serre.
Application Number | 20090294012 12/461241 |
Document ID | / |
Family ID | 9541999 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090294012 |
Kind Code |
A1 |
Serre; Frederic |
December 3, 2009 |
Radial-carcass tires formed by using specific cohesive,
low-hysteresis compositions
Abstract
The subject of the present invention is the use of cohesive,
low-hysteresis compositions comprising small amounts of reinforcing
fillers to produce profiled filing members arranged in the bottom
zone of tires in order to improve the life thereof.
Inventors: |
Serre; Frederic;
(Veyre-Monton, FR) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
MICHELIN RECHERCHE ET TECHNIQUE,
S.A.
Granges-Paccot
CH
|
Family ID: |
9541999 |
Appl. No.: |
12/461241 |
Filed: |
August 5, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09501408 |
Feb 10, 2000 |
7588065 |
|
|
12461241 |
|
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|
|
Current U.S.
Class: |
152/547 |
Current CPC
Class: |
B60C 9/18 20130101; B60C
1/0025 20130101; Y10T 152/10855 20150115; B60C 15/06 20130101; C08L
21/00 20130101; B60C 1/00 20130101; Y10T 152/10846 20150115 |
Class at
Publication: |
152/547 |
International
Class: |
B60C 15/00 20060101
B60C015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 11, 1999 |
FR |
99/01766 |
Claims
1. A pneumatic tire comprising in its bottom zone comprising a
bead, an elastomeric internal filler mix in the form of a profiled
member which is located axially to the outside of the upturn of the
carcass reinforcement, or a reinforcement profile for the beads of
the tire which is located radially above the bead wire and adjacent
to said bead wire, said elastomeric internal filler mix comprising
a cohesive and low-hysteretic rubber composition comprising an
elastomeric matrix and a reinforcing filler, wherein the
elastomeric matrix comprises more than 70 phr of natural rubber or
synthetic polyisoprene having double bonds, the majority of which
are cis-1,4 bonds, wherein the reinforcing filler is precipitated
or pyrogenic silica having a specific surface area of between 30
and 260 m.sup.2/g, wherein said silica is present in an amount of
between 15 phr and 40 phr, and wherein the rubber composition does
not contain carbon black.
2. The tire of claim 1, wherein said silica is present in an amount
of 20 to 35 phr.
3. The tire of claim 1, wherein the composition further comprises
an additional diene elastomer, wherein the majority of elastomer in
the composition is the natural rubber or synthetic
polyisoprene.
4. The tire of claim 3, wherein the additional diene elastomer is
selected from the group consisting of a polybutadiene having double
bonds, the majority of which are cis-1,4 bonds, a butadiene/styrene
emulsion or solution copolymer having double bonds, the majority of
which are trans-1,4 bonds, a butadiene/isoprene copolymer, or a
styrene/butadiene/isoprene terpolymer.
5. The tire of claim 4, wherein the diene elastomer has active
groups on the elastomer chain or at the end of the elastomer chain,
said active groups being active with carbon black or with white
fillers, or is starred by a carbonyl, silicon or tin halide.
6. The tire of claim 4, wherein the diene elastomer has been
modified on the chain or at the end of the chain by a branching
agent comprising divinylbenzene.
7. The tire of claim 1, wherein the elastomeric matrix further
comprises a coupling agent and/or a covering agent.
8. The tire of claim 1, wherein the elastomeric matrix further
comprises a covering agent selected from the group consisting of
fatty alcohols, alkylalkoxy silanes, and diphenylguanidines,
polyethylene glycol and silicone oils.
9. The tire of claim 7, wherein the amount of said coupling agent
and/or covering agent is in a weight ratio relative to the silica
between 1/100 and 20/100.
10. The tire of claim 7, wherein the amount of said coupling agent
and/or covering agent is in a weight ratio relative to the silica
between 2/100 and 15/100.
11. The tire of claim 1, wherein said silica is present in an
amount of between 30 and 40 phr.
12. The tire of claim 2, wherein the composition further comprises
an additional diene elastomer, wherein the majority of elastomer in
the composition is the natural rubber or synthetic
polyisoprene.
13. The tire of claim 12, wherein the additional diene elastomer is
selected from the group consisting of a polybutadiene having double
bonds, the majority of which are cis-1,4 bonds, a butadiene/styrene
emulsion or solution copolymer having double bonds, the majority of
which are trans-1,4 bonds, a butadiene/isoprene copolymer, or a
styrene/butadiene/isoprene terpolymer.
14. The tire of claim 13, wherein the diene elastomer has active
groups on the elastomer chain or at the end of the elastomer chain,
said active groups being active with carbon black or with white
fillers, or is starred by a carbonyl, silicon or tin halide.
15. The tire of claim 13, wherein the diene elastomer has been
modified on the chain or at the end of the chain by a branching
agent comprising divinylbenzene.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of application Ser. No.
09/501,408, filed Feb. 10, 2000, which claims priority under 35
U.S.C. .sctn. 119 from French Patent Application, No. 99/01766,
filed Feb. 11, 1999, the disclosures of both of which are
incorporated by reference herein in their entirety.
SPECIFICATION
[0002] The present invention relates to the use of rubber
compositions intended for the manufacture of tires as elastomeric
internal filling compositions, also referred to as "cushion mixes",
in the bottom zone of a tire.
[0003] Radial-carcass tires for motor vehicles bearing heavy loads
at greater or lesser speeds, in particular those for heavy
vehicles, have a framework formed of reinforcements or plies of
metal wires coated with elastomers. Such tires comprise in the
bottom zone, one or more bead wires and a carcass reinforcement
extending from one bead wire to the other and, at the crown, a
crown reinforcement comprising two or more crown plies. This
framework is consolidated by elastomeric compositions.
Radial-carcass tires, intended to be fitted on vehicles bearing
heavy loads at greater or lesser speeds, in particular those for
heavy vehicles, are designed to be able to be recapped several
times when the tread that is in contact with the ground is worn.
This involves having available recappable carcasses which have not
been subject to serious damage after wear of one or more
treads.
[0004] The life of the tire is shortened due to the appearance of
damage within a rubber profiled filling member, for example a
break, which may then spread as far as the inner or outer surface
of the tire, with the result that the tire cover must be discarded
and replaced.
[0005] It is desirable for the cohesion of the rubber internal
filler mixes to be as great as possible to avoid or reduce these
incipient points for damage.
[0006] It is known to the person skilled in the art that
elastomeric internal filler compositions undergo deformation upon
each rotation of the wheel. Such deformation causes a great amount
of heating which is harmful to the life of said compositions
because, at operating temperatures which are frequently above
100.degree. C., the mechanical properties and the reinforcement
degrade over time by thermochemical and/or the thermo-oxidizing
aging, with the consequence that the compositions become less
resistant to mechanical stress.
[0007] In order to eliminate or at the very least minimize as far
as possible the risks of breaking of the elastomeric internal
filler mixes, i.e., those devoid of reinforcements, it is desirable
for these mixes to have high mechanical cohesion as well as
hysteresis loss characteristics which are as low as possible at the
operating temperature of the tire.
[0008] The person skilled in the art, confronted with the problem
of balancing minimal heating and high cohesion at high temperature,
has proposed a large number of solutions. Thus, it has been
proposed to use elastomeric internal filler compositions, i.e.,
cushion mixes, of relatively low hysteresis, in the form of: [0009]
(i) compositions based on natural rubber, pure or in a blend with
polybutadiene, the reinforcing filler being a carbon black having a
specific surface area preferably less than 110 m.sup.2/g and used
in an amount of about 25 phr (parts by weight per hundred parts of
elastomer), as described in U.S. Pat. No. 3,392,773; [0010] (ii)
compositions based on natural rubber, pure or in a blend with
polybutadiene, reinforced with a blend of carbon black and silica,
the usual amounts of carbon black being from 30 to 35 phr and those
of the silica from 10 to 15 phr; [0011] (iii) compositions based on
diene rubber and syndiotactic 1,2-polybutadiene as described in
Patent Application JP-A-94/092108; [0012] (iv) compositions based
on natural rubber, possibly in a blend with another diene
elastomer, comprising carbon black and thermoplastic polymer fibers
as described in Patent Application JP-A-95/330960.
SUMMARY OF THE INVENTION
[0013] The Applicant has discovered that it is possible to obtain a
balance between heating and improved cohesion and excellent
resistance to the mechanical stresses with high deformation by the
use of an elastomeric internal filler composition: [0014] (i) based
on natural rubber or synthetic polyisoprene having a majority of
cis-1,4 bonds, used pure or in a blend with another diene
elastomer, and [0015] (ii) reinforced with: [0016] a clear filler
selected from among precipitated or pyrogenic silicas comprising
SiOH functions at the surface, precipitated aluminas comprising
AIOH functions at the surface, a natural or precipitated
silicoaluminate comprising at the surface both SiOH and AIOH
groups, said clear filler being used in an amount from 15 phr to 40
phr and preferably from 20 phr to 35 phr, or [0017] a blend of
clear filler, as described above, and carbon black, the BET
specific surface area of which is between 30 and 160 m.sup.2/g,
preferably between 90 and 150 m.sup.2/g, and the DBP structure of
which is between 80 and 160 ml/100 g, wherein the total amount of
filler is between about 15 phr and 50 phr and the amount of clear
filler in phr is greater than or equal to that of the carbon black
in phr minus 5 phr.
[0018] The measurement of BET specific surface area is effected in
accordance with the method of BRUNAUER, EMMET and TELLER described
in "The Journal of the American Chemical Society", vol. 60, page
309, February 1938, corresponding to Standard NFT 45007 of November
1987.
DETAILED DESCRIPTION
[0019] In the case of using clear filler, it is necessary to use a
coupling and/or covering agent selected from among the agents known
to the person skilled in the art. Preferred coupling agents,
include, inter alia, sulphur-containing alkoxysilanes of the
bis-(3-trialkoxysilylpropyl) polysulphide type, and among these in
particular, bis-(3-triethoxysilylpropyl) tetrasulphide sold by
DEGUSSA under the names Si69 for the pure liquid product and X50S
for the solid product (blend 50/50 by weight with black N330).
Covering agents include a fatty alcohol, an alkylalkoxysilane, such
as a hexadecyltrimethoxy- or triethoxysilane sold by DEGUSSA under
the names Si116 and Si216 respectively, diphenylguanidine, a
polyethylene glycol, or a silicone oil possibly modified by means
of OH or alkoxy functions. The covering and/or coupling agent is
used in a ratio by weight relative to the filler of between 1/100
and 20/100, and preferably of between 2/100 and 15/100.
[0020] The elastomeric internal filler compositions or cushion
mixes according to the invention, that are arranged in the bottom
zone, are, for example, profiled members located axially to the
outside of the upturn of the carcass reinforcement, the
reinforcement profiles for the beads of the tire being located
between the upturn of the carcass reinforcement and the bead
reinforcement profiled member located radially above the bead wire
and adjacent to said bead wire and/or axially to the outside of the
upturn of the carcass reinforcement.
[0021] The diene elastomers which may be used in a blend with
natural rubber or a synthetic polyisoprene having a majority of
cis-1,4 bonds include a polybutadiene (BR) preferably having a
majority of cis-1,4 bonds, a solution or emulsion styrene-butadiene
copolymer (SBR), a butadiene-isoprene copolymer (BIR) or,
alternatively, a styrene-butadiene-isoprene terpolymer (SBIR).
These elastomers may be modified during polymerization or after
polymerization by means of branching agents, such as a
divinylbenzene, or starring agents, such as carbonates, tin halides
or silicon halides. Alternatively, the elastomers may be modified
by means of functionalizing agents resulting in grafting oxygenated
carbonyl or carboxyl functions or alternatively an amine function,
such as, for example, by the action of dimethyl- or
diethylamino-benzophenone on the chain or at the end of the chain.
In the case of blends of natural rubber or of synthetic
polyisoprene having a majority of cis-1,4 bonds with one or more of
the diene elastomers referred to above, the natural rubber or the
synthetic polyisoprene preferably comprises the majority of the
bond and, more preferably, comprises an amount greater than 70
phr.
[0022] When a clear filler is used as the sole reinforcing filler,
the hysteresis and cohesion properties are obtained using a
precipitated or pyrogenic silica, or a precipitated alumina, or
alternatively an alumosilicate of BET specific surface are of
between 30 and 260 m.sup.2/g. Preferably an amount of filler from
20 to 35 phr is used. Non-limiting examples of this type of fillers
include the silicas KS404 from Akzo, Ultrasil VN2 or VN3 and
BV3370GR from Degussa, Zeopol 8745 from Huber, Zeosil 175MP or
Zeosil 1165MP from Rhodia, HL-SIL 2000 from PPG, etc.
[0023] In the case of a blend of carbon black with a clear filler,
an amount of clear filler from 25 to 40 phr is preferably used.
[0024] Other examples of reinforcing fillers having the morphology
and the SiOH and/or AOH surface functions of the silica- and/or
alumina-type materials previously described, which can be used
according to the invention as partial or total replacement thereof,
include carbon blacks modified either during synthesis by adding to
the feed oil of the oven a compound of silicon and/or aluminum or
after the synthesis by adding an acid to an aqueous suspension of
carbon black in a solution of sodium silicate and/or aluminate so
as to cover the surface of the carbon black at least in part with
SiOH and/or AOH functions. As in the case of the above clear
fillers, the specific surface area of the filler lies between 30
and 260 m.sup.2/g, and the total amount of silica- and/or
alumina-type material filler is greater than or equal to 15 phr,
preferably greater than 25 phr, and less than or equal to 35 phr.
Non-limiting examples of this type of carbon-containing fillers
with SiOH and/or AOH functions at the surface include the CSDP-type
fillers described in Conference No. 24 of the ACS Meeting, Rubber
Division, Anaheim, Calif., 6-9 May 1997, and of those of Patent
Application EPA-0 799 854.
[0025] Additional fillers which may also be used to obtain the
diene internal filler compositions having the reinforcement and
hysteresis properties according to the invention include blends of
one or more carbon blacks with one or more of the other fillers
already mentioned having SiOH and/or AOH functions at the surface,
the overall amount of filler being between 15 and 50 phr,
preferably between 20 and 45 phr, and the amount of filler with the
SiOH and/or AOH surface functions being greater than or equal to
the amount of carbon black minus five.
[0026] Finally, with the aim of improving the working and/or the
cost of the compositions according to the invention, without the
hysteresis and cohesion characteristics being fundamentally
changed, the filler or the blends of reinforcing fillers described
above may be replaced in part by a less-reinforcing filler such as
a crushed or precipitated calcium carbonate, a kaolin, etc., on the
condition that x phr of reinforcing filler is replaced by x+5 parts
of less-reinforcing filler, x being less than 15 phr.
[0027] The compositions according to the invention may cross-link
under the action of sulphur, peroxides or bismaleimides with or
without sulphur. They may also contain the other constituents
usually used in rubber mixes, such as plasticizers, pigments,
antioxidants, and cross-linking accelerators, such as benzothiazole
derivatives, diphenylguanidine etc.
[0028] The compositions according to the invention may be prepared
using known thermomechanical working processes for the constituents
in one or more steps. For example, they may be obtained by
thermomechanical working in one stage in an internal mixer for 3 to
7 minutes at a speed of rotation of the blades of 50 rpm or in two
stages in an internal mixer for 3 to 5 minutes and 2 to 4 minutes
respectively, followed by a finishing stage effected at about
80.degree. C. during which the sulphur and the accelerator are
incorporated, in the case of a sulphur-cross-linked
composition.
[0029] The invention is illustrated by the following examples,
which in no way constitute a limitation to the scope of the
invention.
[0030] In all the examples, unless indicated otherwise, the
compositions are given in parts by weight. In these examples, which
may or may not be in accordance with the invention, the properties
of the compositions are evaluated as follows:
[0031] Mooney Viscosity
[0032] The Mooney viscosity ML (1+4) is measured in accordance with
Standard ASTM D1646.
[0033] Rheometry
[0034] The rheometry measurements are performed by measuring the
torque on a Monsanto Model 100S rheometer. They are intended to
monitor the vulcanization process by determining the time To in
minutes which corresponds to the vulcanization delay and the time
T99 in minutes which corresponds to 99% of the maximum torque
measured.
[0035] Moduli of Elongation
[0036] The moduli of elongation are measured at 100% (ME 100) and
at 300 (ME300) in accordance with Standard ISO 37-1977.
[0037] Scott Break Index
[0038] These indices are measured at 23.degree. C. or 100.degree.
C. The breaking stress (BS) is determined in MPa and the elongation
at break (EB) in %.
[0039] Tearability Index
[0040] These indices are measured at 100.degree. C. The force (TBS)
is determined in MPa and the elongation at break (TEB) in % on a
test piece of dimensions 10.times.105.times.2.5 mm notched at the
center of its length over a depth of 5 mm.
[0041] Hysteresis Losses (HL)
[0042] The hysteresis losses (HL), or hysteresis, are measured by
rebound at 60.degree. in accordance with Standard ISO R17667 and
are express in %.
Example 1
[0043] The object of this example is to compare natural rubber
compositions which are reinforced with silica, as a majority
filler, compared with control compositions based on a majority of
carbon black. These compositions are set forth in Table 1. They
comprise, in the case of test 1, a composition according to the
invention having a majority of silica and of carbon black, with the
covering agent for the silica being Si116
(hexadecyltrimethoxysilane, from Degussa) and, in the case of test
2, a composition of the invention having a majority of silica and
of carbon black, with polydimethylsiloxane of a molecular weight
close to 400 (PDMS) as covering agent for the silica. The
compositions used in tests 3 and 4 are controls representing the
known prior art. The composition of test 3 contains a majority of
carbon black and of silica bonded to the elastomer with the bonding
agent X50S from Degussa and that of test 4 is composition based on
N330. All these compositions are sulphur-vulcanizable. [0044] The
characteristics of the constituents are as follows: [0045] Peptized
natural rubber of Mooney ML (1+4) at 100.degree. equal to 60 [0046]
Antioxidant: N-(1,3-dimethyl butyl) N'-phenyl p-phenylene diamine
[0047] Soluble sulphur [0048] Vulcanization accelerating agents
[0049] The compositions of tests 1 to 4 are obtained by processing
all the ingredients, except for the sulphur and the accelerators,
by thermomechanical working in one stage in an internal mixer for
about 4 minutes at a speed of rotation of the blades of 50 rpm
until a dropping temperature of 170.degree. is reached, followed by
a finishing stage effected at 80.degree. C., during which the
sulphur and the vulcanization accelerators are incorporated.
TABLE-US-00001 TABLE 1 Test 1 Test 2 Test 3 Test 4 Composition
Invention Invention Control Control Natural rubber 100 100 100 100
UVN3 35 35 15 -- Black N330 5 5 -- 35 Black N347 -- -- 40 -- X50S
-- -- 3 -- Si116 5.00 -- -- -- PDMS -- 2.00 -- -- ZnO 7.00 7.00
7.00 2.10 Stearic acid 1.00 1.00 2.00 1.40 Antioxidant 1.50 1.50
1.50 0.70 Sulphur 1.75 1.75 1.80 1.75 Accelerators 1.50 1.51 1.25
1.00
[0050] The vulcanization is effected at 140.degree. for a time
sufficient to achieve 99% of the maximum torque at the
rheometer.
[0051] The properties of these four compositions are compared. The
results are set forth in Table 2.
TABLE-US-00002 TABLE 2 Test 1 Test 2 Test 3 Test 4 Composition
Example Example Control Control Natural rubber 100 100 100 100 UVN3
35 35 15 -- Black N330 5 5 -- 35 Black N347 -- -- 40 -- X50S -- --
3 -- Si116 5.00 -- -- -- PDMS -- 2.00 -- -- ME100 1.0 1.2 2.9 1.7
HL 60.degree. 13.5 15 18 12 Break index at 800 780 490 630
100.degree. C. EB % Tearability index 510 500 230 80 at 100.degree.
C. TEB %
[0052] It will be noted that the cohesion of compositions 1 and 2
according to the invention, which is evaluated by the elongation at
break at 100.degree. C. in the tearability test, is far greater
than that of control compositions 3 and 4, which are not in
accordance with the invention.
Example 2
[0053] The object of this example is to compare compositions
reinforced with silica as majority filler by varying the nature of
the bonding and covering agents. In this example, the vulcanization
system is adjusted so that the moduli of elongation at 100% are
sufficiently close to draw reliable conclusions as to the effects
of the parameters studied. The compositions according to the
invention are set forth in Table 3. They comprise, in the case of
tests 5, 6 and 7, compositions having silica as sole filler, in an
amount of 30 phr with, respectively, a coupling agent X50S (test
5), a polyethylene glycol covering agent of a molecular weight of
4000 (test 6) and another polydimethylsiloxane covering agent (test
7). In the case of tests 8 to 12, the reinforcing filler is formed
by a blend of silica and 5 phr of N330. The object of this example
is to compare compositions reinforced with silica as majority
filler by varying the nature of the bonding agents and covering
agents, the vulcanization system being adjusted so that the
rigidities of moduli of elongation at 100% are sufficiently close
to draw reliable conclusions as to the effects of the parameters
studied. The compositions according to the invention are set forth
in Table 3. They use, in the case of tests 5, 6 and 7, compositions
having as sole filler silica in an amount of 30 phr with,
respectively, a coupling agent X50S, a polyethylene glycol covering
agent of a molecular weight of 4000 and another
polydimethylsiloxane covering agent. In the cases of tests 8 to 12,
the reinforcing filler is formed by a blend of silica and 5 phr of
N330.
TABLE-US-00003 TABLE 3 Composition Test 5 Test 6 Test 7 Test 8 Test
9 Test 10 Test 11 Test 12 Natural rubber 100 100 100 100 100 100
100 100 UVN3 30 30 30 25 30 35 30 35 N330 -- -- -- 5 5 5 5 5 ZnO 7
7 7 7 7 7 7 7 Stearic acid 1 1 1 1 1 1 1 1 Antioxidant 1.5 1.5 1.5
1.5 1.5 1.5 1.5 1.5 X50S 7 -- -- -- -- -- -- -- PEG4000 -- 4.3 --
-- -- -- 4.3 5 PDMS -- -- 1.7 1.4 1.7 2.0 -- -- Sulphur 1.75 1.75
1.75 1.75 1.75 1.75 1.75 1.75 Accelerators 1.51 2.00 1.51 1.51 1.51
1.51 2.00 2.00
[0054] The compositions and vulcanizations of tests 5 to 12 are
obtained under the same conditions as in Example 1.
[0055] The properties of these eight compositions are compared. The
results are set forth in Table 4.
TABLE-US-00004 TABLE 4 Composition Test 5 Test 6 Test 7 Test 8 Test
9 Test 10 Test 11 Test 12 ME100 1.27 1.16 0.93 0.96 1.00 0.98 1.25
1.37 HL 60.degree. 9.4 9.6 11.7 11.4 12.7 15.6 11.3 13 EB
(100.degree. C.) 733 770 855 813 856 867 762 736 TEB (100.degree.
C.) 590 371 793 538 726 685 277 307 TBS (100.degree.) 84 38 60 51
67 62 38 38
[0056] For tests 5, 6 and 7, it will be noted that, with an amount
of silica filler which is constant and in accordance with the
invention, the coupling agent X50S surprisingly provides
tearability results encompassed by those obtained with the covering
agent PEG4000 and the covering agent PDMS.
[0057] For tests 8, 9 and 10, in the presence of the covering agent
PDMS, with an amount of black of 5 phr and an amount of silica
increasing from 25 to 35 phr, the best tearability results are
obtained for the intermediate amount of silica of 30 phr.
[0058] By comparing the results of tests 7 and 9, on one hand, and
6 and 11, on the other hand, it will be noted that 5 phr of carbon
black added to 30 phr of silica does not fundamentally change the
tearability results in the presence of the covering agents PDMS or
PEG4000.
[0059] Comparison of the results of tests 11 and 12 shows that
passing from 30 to 35 phr of silica in the presence of 5 phr of
carbon black slightly improves the results when the covering agent
PEG 4000 is used, whereas the reverse effect is observed with the
covering agent PDMS (tests 9 and 10).
Example 3
[0060] The object of this example is to compare compositions
reinforced with silica as sole or majority filler, where the
elastomeric matrix is based on natural rubber, either pure or in a
blend with another diene elastomer or based on synthetic
polyisoprene having a large number of cis-1,4 bonds. These
compositions are set forth in Table 5. They comprise, in the case
of tests 13, 14 and 15, natural rubber filled with increasing
amounts of filler. In the cases of tests 16 and 17, the natural
rubber of test 15 is replaced by a blend of natural rubber with
another minority diene elastomer or a cis-1,4 polybutadiene
(cis-1,4 BR), obtained with a titanium-based catalyst, and a
solution SBR of Mooney ML (1+4) of 54, of Tg -48.degree. C., having
a 1,2 bond content of 24% and a 16.5% styrene content. In the case
of test 19, the natural rubber with 30 parts of silica filler of
test 18 is replaced by a synthetic polyisoprene having a large
number of cis-1,4 bonds. In the case of test 20, which is not in
accordance with the invention, the blend of natural rubber and
cis-1,4 BR of test 16 is filled with 30 parts of N330.
TABLE-US-00005 TABLE 5 Composition Test 13 Test 14 Test 15 Test 16
Test 17 Test 18 Test 19 Test 20 Control Natural rubber 100 100 100
60 60 100 -- 60 Cis-polyisoprene -- -- -- -- -- -- 100 -- Solution
SBR -- -- -- -- 40 -- -- -- cis-1,4 BR -- -- -- 40 -- -- -- 40 UVN3
15 15 30 30 30 30 30 -- N330 -- 15 15 15 15 -- -- 30 Sil16 2 2 4 4
4 4 4 -- ZnO 5 5 5 5 5 5 5 5 Stearic acid 1 1 1 1 1 1 1 1
Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Diphenylguanidine 0.2
0.2 0.4 0.4 0.4 0.4 0.4 -- Sulphur 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6
Accelerators 1.0 0.55 0.55 0.55 0.55 1.0 1.0 0.55
[0061] The compositions and vulcanization of tests 13 to 20 are
obtained under the same conditions as in Example 1.
[0062] The properties of these eight compositions are compared. The
results are set forth in Table 6.
TABLE-US-00006 TABLE 6 Composition Test 13 Test 14 Test 15 Test 16
Test 17 Test 18 Test 19 Test 20 Control Natural rubber 100 100 100
60 60 100 -- 60 Polyisoprene -- -- -- -- -- -- 100 -- Solution SBR
-- -- -- -- 40 -- -- -- Cis-1,4 BR -- -- -- 40 -- -- -- 40 UVN3 15
15 30 30 30 30 30 -- N330 -- 15 15 15 15 -- -- 30 ME100 0.85 0.91
0.93 0.87 0.97 0.97 0.69 1.26 HL 5.4 11.0 16.5 24.4 25.2 8.2 11.5
12.8 EB(100.degree. C.) 834 809 845 864 830 820 857 564
TEB(100.degree. C.) 578 359 456 401 474 552 626 146 TBS(100.degree.
C.) 36 31 41 25 34 36 28 18
[0063] For the compositions according to the invention of tests 13
to 19, the characteristics of elongation at break in the
tearability test at 100.degree. C. are far higher than those
obtained with the composition not in accordance with the invention
containing 30 phr of carbon black. The natural rubber or a
synthetic cis-1,4 polyisoprene or a blend of natural rubber as
majority with another diene elastomer make it possible to obtain
high cohesion with the silica filler or blends of silica and carbon
black according to the invention.
[0064] In summary, the use of the compositions of the invention
either with the carbon black filler used in an amount close to 25
phr or with a white filler of the silica and/or alumina type used
alone or in a majority amount of about 35 phr independently of
whether a coupling or covering agent is used, makes it possible to
show that, compared with the known compositions based on carbon
black used alone or as majority filler, the effects of mechanical
stresses of the type of deformation imposed are less damaging and
make it possible to increase the life of the tire, even more so
since the compositions described are of low hysteresis, with the
consequences of lower internal heating during travel and reduced
thermal and/or thermo-oxidizing degradation of the carcass
reinforcement.
[0065] Of course, the invention is not limited to the examples of
embodiment described previously, from which other embodiments can
be conceived of.
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