U.S. patent application number 15/645697 was filed with the patent office on 2017-10-26 for elastomeric composition having a very good dispersion of the filler in the elastomeric matrix.
The applicant listed for this patent is COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN, MICHELIN RECHERCHE ET TECHNIQUE, S.A.. Invention is credited to Cecile BELIN, Marc SEVIGNON.
Application Number | 20170306109 15/645697 |
Document ID | / |
Family ID | 47351667 |
Filed Date | 2017-10-26 |
United States Patent
Application |
20170306109 |
Kind Code |
A1 |
SEVIGNON; Marc ; et
al. |
October 26, 2017 |
ELASTOMERIC COMPOSITION HAVING A VERY GOOD DISPERSION OF THE FILLER
IN THE ELASTOMERIC MATRIX
Abstract
The invention relates to a rubber composition based on at least
one diene elastomer, a reinforcing filler comprising at least
carbon black having a CTAB specific surface of greater than or
equal to 130 m.sup.2/g, a plasticizing oil and also a crosslinking
system, the dispersion of the filler in the elastomeric matrix
having a Z score of greater than or equal to 70.
Inventors: |
SEVIGNON; Marc;
(Clermont-Ferrand Cedex 9, FR) ; BELIN; Cecile;
(Clermont-Ferrand Cedex 9, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN
MICHELIN RECHERCHE ET TECHNIQUE, S.A. |
Clermont-Ferrand
Granges-Paccot |
|
FR
CH |
|
|
Family ID: |
47351667 |
Appl. No.: |
15/645697 |
Filed: |
July 10, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14364273 |
Jun 10, 2014 |
9751992 |
|
|
PCT/EP2012/075140 |
Dec 12, 2012 |
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15645697 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K 3/04 20130101; B60C
1/0016 20130101; C08J 3/22 20130101; C08J 2307/02 20130101; C08K
5/0016 20130101; C08J 2321/00 20130101; C08K 2201/006 20130101 |
International
Class: |
C08J 3/22 20060101
C08J003/22; B60C 1/00 20060101 B60C001/00; C08K 5/00 20060101
C08K005/00; C08K 3/04 20060101 C08K003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2011 |
FR |
1161463 |
Claims
1. A process for the preparation of a composition comprising at
least one diene elastomer, a reinforcing filler comprising at least
carbon black having a CTAB specific surface of greater than or
equal to 130 m.sup.2/g, a plasticizing oil and also a crosslinking
system, which comprises the following stages: preparing a first
masterbatch comprising the diene elastomer and the carbon black,
this first masterbatch exhibiting a dispersion of the filler in the
elastomeric matrix having a Z score of greater than or equal to 80,
incorporating the other constituents of the composition, with the
exception of the crosslinking system, in the first masterbatch in a
mixer, and kneading everything thermomechanically until a maximum
temperature of between 130.degree. C. and 200.degree. C. is
reached, cooling the combined mixture to a temperature of less than
100.degree. C., subsequently incorporating the crosslinking system,
kneading everything up to a maximum temperature of less than
120.degree. C.
2. The process according to claim 1, wherein the first masterbatch
is produced in the liquid phase from at least one elastomer latex
and a dispersion of carbon black.
3. The process according to claim 2, wherein the first masterbatch
is produced according to the following successive stages: feeding a
continuous stream of the diene elastomer in the form of a latex to
a mixing region of a coagulation reactor defining an elongated
coagulation region extending between the mixing region and an
outlet orifice, feeding a continuous stream of a fluid comprising
the filler under pressure to the mixing region of a coagulation
reactor in order to form a coagulated mixture, drying the coagulum
obtained above in order to recover the first masterbatch.
4. The process according to claim 1, wherein the plasticizing oil
is selected from the group consisting of a polyolefinic oil, a
paraffinic oil, a naphthenic oil, an aromatic oil, a mineral oil,
or mixtures thereof.
5. The process according to claim 4, wherein the plasticizing oil
includes a polyolefinic oil and/or a paraffinic oil.
6. The process according to claim 4, wherein the plasticizing oil
includes a naphthenic oil, an aromatic oil, a mineral oil, and/or
mixtures thereof.
7. The process according to claim 1, wherein the content of the
plasticizing oil varies from 2 to 50 parts per hundred parts by
weight of elastomer.
8. The process according to claim 1, wherein the diene elastomer is
selected from the group consisting of polybutadienes, natural
rubber, synthetic polyisoprenes, butadiene copolymers, isoprene
copolymers, and the mixtures of these elastomers.
9. The process according to claim 8, wherein the at least one diene
elastomer includes a natural rubber.
10. The process according to claim 4, wherein the plasticizing oil
includes a mineral oil or a mixture of mineral oils.
11. The process according to claim 8, wherein the diene elastomer
includes a blend of one or more natural rubber latexes with one or
more synthetic rubber latexes.
12. The process according to claim 1, wherein the content of the
carbon black varies from 20 to 80 phr.
13. The process according to claim 1 further comprising introducing
an inorganic filler, or a second elastomer, or both into the
composition simultaneously with the other constituents during the
kneading step.
14. The process according to claim 13, wherein the second elastomer
is identical to or different from the at least one diene
elastomer.
15. The process according to claim 13, wherein an inorganic filler
and a second elastomer are introduced into the composition in the
form of a second masterbatch.
16. The process according to claim 15, wherein the second
masterbatch is prepared prior to its incorporation into the
kneading step.
17. The process according to claim 13, wherein the content of the
inorganic filler varies from 5 to 50 phr.
18. The process according to claim 1, wherein an inorganic filler
and a second elastomer are introduced separately into the
composition, the inorganic filler being introduced before or after
the second elastomer.
19. The process according to claim 18, wherein the introduction of
the inorganic filler and of the second elastomer is offset in time
from a few tens of seconds to a few minutes with respect to the
introduction of the first masterbatch into the mixer.
20. The process according to claim 1, wherein the content of all of
the reinforcing filler varies from 20 to 200 phr.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This U.S. divisional patent application claims priority to
U.S. utility patent application Ser. No. 14/364,273 filed Jun. 10,
2014, which is a 371 national phase entry of PCT/EP2012/075140
filed Dec. 12, 2012, which claims priority to French Application
No. 1161463, filed Dec. 12, 2011, the entire content of which are
hereby incorporated by reference.
BACKGROUND
1. Field
[0002] The disclosure relates to a rubber composition in particular
for a tire tread and more particularly for a tire intended to equip
vehicles carrying heavy loads and running at sustained speed, such
as, for example, lorries, tractors, trailers or buses, aircraft,
and the like.
2. Description of Related Art
[0003] Some current tires, referred to as "road" tires, are
intended to run at high speed and over increasingly long journeys,
as a result of the improvement in the road network and of the
growth of the motorway network throughout the world. In point of
fact, since savings in fuel and the need to protect the environment
have become a priority, it is important for the tires to have a low
energy consumption. One of the sources of energy dissipation is the
heating of the tire.
[0004] In the same way, it is known that the treads of the tires
used in civil engineering are particularly sensitive to the
increase in temperature. In point of fact, there is a constant
search to improve the properties of tires and in particular their
wear resistance and, conventionally, the improvement in the wear
resistance is known to be reflected by an increase in energy
consumption.
[0005] In order to obtain such an improvement in terms of wear
resistance and energy consumption, attempts have been made to use
finer reinforcing fillers in the tread, in particular "fine" carbon
blacks, that is to say having a CTAB specific surface of greater
than or equal to 90 i m /g,indeed even "very fine" blacks, that is
to say carbon blacks having a CTAB specific surface of greater than
or equal to 130 m.sup.2/g. However, in order to obtain the optimum
reinforcement and hysteresis properties conferred by a filler in a
tire tread and thus a high wear resistance and a low rolling
resistance, it is known that it is generally advisable for this
filler to be present in the elastomeric matrix in a final form
which is both as finely divided as possible and as homogeneously
distributed as possible. Such conditions can only be achieved
insofar as this filler exhibits a very good ability, on the one
hand, to be incorporated in the matrix during the mixing with the
elastomer and to deagglomerate and, on the other hand, to disperse
homogeneously in this matrix.
[0006] In point of fact, very fine blacks are known to be extremely
difficult to correctly disperse in the elastomeric matrix and bring
about a deterioration in the processability (in comparison with the
use of the same content of coarser blacks). One solution for a
person skilled in the art would be to use plasticizing oil or resin
to improve the processability; however, it is known that the use of
such plasticizers with these very fine blacks has the consequence
of a very significant deterioration in the breaking energy
properties (elongation at break and breaking stress
properties).
SUMMARY
[0007] The Applicant has discovered, surprisingly, contrary to the
knowledge of a person skilled in the art, that the combination of
very fine carbon blacks in rubber compositions exhibiting a very
good dispersion of the filler in the elastomeric matrix and in the
presence of certain specific plasticizing oils makes it possible to
simultaneously obtain a good processability without damaging the
limiting properties at break.
[0008] A subject-matter of the invention, in an embodiment, is thus
a rubber composition based on at least one diene elastomer, a
reinforcing filler comprising at least carbon black having a CTAB
specific surface of greater than or equal to 130 m.sup.2/g, a
plasticizing oil and also a crosslinking system, the dispersion of
the filler in the elastomeric matrix having a Z score of greater
than or equal to 70.
[0009] Preferably, the content of plasticizing oil in the
composition varies from 2 to 50 parts per hundred parts by weight
of elastomer, preferably from 5 to 25 phr. According to a preferred
embodiment of the invention, the composition is obtained from a
first masterbatch comprising at least the diene elastomer and the
carbon black, and exhibiting a dispersion of the carbon black in
the elastomeric matrix having a Z score of greater than or equal to
80.
[0010] According to an alternative embodiment of the invention, the
first masterbatch is obtained by liquid-phase compounding starting
from a diene elastomer latex and an aqueous dispersion of carbon
black.
[0011] This is because there exist different methods for obtaining
a masterbatch of diene elastomer and reinforcing filler. In
particular, one type of solution consists, in order to improve the
dispersability of the filler in the elastomeric matrix, in mixing
the elastomer and the filler in the "liquid" phase. In order to do
this, recourse is had to an elastomer in the latex foi which is
provided in the form of elastomer particles dispersed in water and
to an aqueous dispersion of the filler, that is to say a filler
dispersed in water, commonly referred to as "slurry". Some
processes in particular, such as those described in the document
U.S. Pat. No. 6,048,923, make it possible to obtain a masterbatch
of elastomer and filler exhibiting a very good dispersion of the
filler in the elastomeric matrix, which is greatly improved with
respect to the dispersion of the filler in the elastomeric matrix
capable of being obtained during the solid-phase mixing of
elastomer and reinforcing filler. This process consists in
particular in incorporating a continuous stream of a first fluid
composed of an elastomer latex in the compounding region of a
coagulation reactor, in incorporating a second continuous stream of
a second fluid composed of an aqueous dispersion of filler under
pressure in the compounding region, in order to form a mixture with
the elastomer latex; the compounding of these two fluids being
sufficiently energetic to allow the elastomer latex to coagulate
virtually completely with the filler before the outlet orifice of
the coagulation reactor, and in then drying the coagulum
obtained.
[0012] Another subject-matter of the invention is a composition
based on at least one diene elastomer, a reinforcing filler
comprising at least carbon black having a CTAB specific surface of
greater than or equal to 130 m.sup.2/g, a plasticizing oil and also
a crosslinking system, obtained from a first masterbatch comprising
at least the diene elastomer and the carbon black, and exhibiting a
dispersion of the carbon black in the elastomeric matrix having a Z
score of greater than or equal to 80.
[0013] Preferably, the content of plasticizing oil in the
composition varies from 2 to 50 parts per hundred parts by weight
of elastomer, preferably from 5 to 25 phr.
[0014] According to a preferred embodiment of the invention, the
composition is obtained from a first masterbatch comprising at
least the diene elastomer and the carbon black, and exhibiting a
dispersion of the carbon black in the elastomeric matrix having a Z
score of greater than or equal to 80.
[0015] According to an alternative embodiment of the invention, the
first masterbatch is obtained by liquid-phase compounding starting
from a diene elastomer latex and an aqueous dispersion of carbon
black, preferably identical to the liquid-phase process described
in detail above.
[0016] The invention also relates, in an embodiment, to a process
for the preparation of a composition comprising at least one diene
elastomer, a reinforcing filler comprising at least carbon black
having a CTAB specific surface of greater than or equal to 130
m.sup.2/g, a plasticizing oil and also a crosslinking system, the
dispersion of the filler in the elastomeric matrix having a Z score
of greater than or equal to 70, which comprises the following
stages: [0017] incorporating all of the constituents of the
composition, with the exception of the crosslinking system, in a
mixer, everything being kneaded thermomechanically until a maximum
temperature of between 130.degree. C. and 200.degree. C. is
reached, cooling the combined mixture to a temperature of less than
100.degree. C., [0018] subsequently incorporating the crosslinking
system, [0019] kneading everything up to a maximum temperature of
less than 120.degree. C.
[0020] Preferably, a first masterbatch comprising at least the
diene elastomer and the carbon black, and exhibiting a dispersion
of the carbon black in the elastomeric matrix having a Z score of
greater than or equal to 80, is prepared prior to the incorporation
of all of the constituents of the composition in the mixer.
[0021] More preferably still, the masterbatch is produced in the
liquid phase starting from at least one elastomer latex and a
dispersion of carbon black, in particular according to the process
described in detail above.
[0022] The invention also relates, in an embodiment, to a process
for the preparation of a composition comprising at least one diene
elastomer, a reinforcing filler comprising at least carbon black
having a CTAB specific surface of greater than or equal to 130
m.sup.2/g, a plasticizing oil and also a crosslinking system, which
comprises the following stages: [0023] preparing a first
masterbatch comprising the diene elastomer and the carbon black,
this first masterbatch exhibiting a dispersion of the filler in the
elastomeric matrix having a Z score of greater than or equal to 80,
[0024] incorporating the other constituents of the composition,
with the exception of the crosslinking system, in the first
masterbatch in a mixer, everything being kneaded thermomechanically
until a maximum temperature of between 130.degree. C. and
200.degree. C. is reached, [0025] cooling the combined mixture to a
temperature of less than 100.degree. C., [0026] subsequently
incorporating the crosslinking system, [0027] kneading everything
up to a maximum temperature of less than 120.degree. C.
[0028] Preferably, the masterbatch is produced in the liquid phase
starting from at least one elastomer latex and a dispersion of
carbon black, in particular according to the process described in
detail above.
[0029] The invention also relates, in an embodiment, to a
masterbatch based on at least one diene elastomer, a reinforcing
filler comprising at least carbon black having a CTAB specific
surface of greater than or equal to 130 m.sup.2/g, and a
plasticizing oil, the dispersion of the filler in the elastomeric
matrix having a Z score of greater than or equal to 70.
[0030] Preferably, this masterbatch is obtained from a first
masterbatch comprising at least the diene elastomer and the carbon
black, and exhibiting a dispersion of the carbon black in the
elastomeric matrix having a Z score of greater than or equal to 80.
More preferably still, this first masterbatch is produced in the
liquid phase starting from at least one elastomer matrix and a
dispersion of carbon black, in particular according to the process
described in detail above.
[0031] The invention also relates, in an embodiment, to a
masterbatch based on at least one diene elastomer, a reinforcing
filler comprising at least carbon black having a CTAB specific
surface of greater than or equal to 130 m.sup.2/g, and a
plasticizing oil, obtained from a first masterbatch comprising at
least the diene elastomer and the carbon black, and exhibiting a
dispersion of the carbon black in the elastomeric matrix having a Z
score of greater than or equal to 80.
[0032] Preferably, this first masterbatch is produced in the liquid
phase starting from at least one elastomer latex and a dispersion
of carbon black, in particular according to the process described
in detail above.
[0033] A final subject-matter of the invention is a finished or
semi-finished article, a tire tread, a tire and a semi-finished
product comprising a composition as described above or a
masterbatch as described above.
[0034] The term "masterbatch" is understood to mean, in that which
follows: an elastomer-based composite into which a filler and
optionally other additives have been introduced.
Measurements and Tests
[0035] The rubber compositions are characterized, before and after
curing, as indicated below.
Mooney Plasticity
[0036] Use is made of an oscillating consistometer as described in
French Standard NF T 43-005 (1991). The Mooney plasticity
measurement is carried out according to the following principle:
the composition in the raw state (i.e., before curing) is moulded
in a cylindrical chamber heated to 100.degree. C. After preheating
for one minute, the (small-sized) rotor rotates within the test
specimen at 2 revolutions/minute and the working torque for
maintaining this movement is measured after rotating for 4 minutes.
The Mooney plasticity (MS 1+4) is expressed in "Mooney units" (MU,
with 1 MU=0.83 newton.metre).
Dispersion
[0037] In a known way, the dispersion of filler in an elastomeric
matrix can be represented by the Z score, which is measured, after
crosslinking, according to the method described by S. Otto et al.
in Kautschuk Gummi Kunststoffe, 58 Jahrgang, NR 7-8/2005, in
agreement with Standard ISO 11345.
[0038] The calculation of the 1 score is based on the percentage of
surface area in which the filler is not dispersed ("% undispersed
surface area"), as measured by the "disperGRADER+" device supplied,
with its procedure and its "disperDATA" operating software, by
Dynisco, according to the equation:
Z=100-(% undispersed surface area)/0.35
[0039] The percentage of undispersed surface area is, for its part,
measured by virtue of a camera which observes the surface of the
sample under incident light at 30.degree.. The light points are
associated with the filler and with agglomerates, while the dark
points are associated with the rubber matrix; digital processing
converts the image into a black and white image and makes possible
the determination of the percentage of undispersed surface area, as
described by S. Otto in the abovementioned document.
[0040] The higher the Z score, the better the dispersion of the
filler in the elastomeric matrix (a Z score of 100 corresponding to
a perfect dispersion and a Z score of 0 to a mediocre dispersion).
A Z score of greater than or equal to 80 will be regarded as
corresponding to a surface exhibiting a very good dispersion of the
filler in the elastomeric matrix.
Tensile Tests
[0041] These tensile tests make it possible to determine the
elasticity stresses and the properties at break. Unless otherwise
indicated, they are carried out in accordance with French Standard
NF T 46-002 of September 1988. The nominal secant modulus (or
apparent stress, in MPa) is measured in first elongation (i.e.
after an accommodation cycle at the extension rate provided for the
measurement itself) at 100% elongation (denoted M100). The tensile
measurements for determining tile secant accommodated moduli are
carried out at a temperature of 23.degree. C.+/-2.degree. C.) and
under standard hygrometry conditions (50+/-5% relative
humidity).
[0042] The breaking stresses (in MPa) and the elongations at break
(in %) are also measured. All these tensile measurements are
carried out at a temperature of 60.degree. C..+-.2.degree. C. and
under standard hygrometry conditions (50.+-.5% relative humidity),
according to French Standard NF T 40-101 (December 1979).
Dynamic Properties
[0043] The dynamic properties and in particular
tan(.delta.).sub.max, representative of the hysteresis, are
measured on a viscosity analyser (Metravib VA4000) according to
Standard ASTM D 5992-96. The response of a sample of vulcanized
composition (cylindrical test specimen with a thickness of 4 mm and
with a cross section of 400 mm.sup.2), subjected to a simple
alternating sinusoidal shear stress, at a frequency of 10 Hz, is
recorded under standard temperature conditions (23.degree. C.)
according to Standard ASTM D 1349-99 or, as the case may be, at a
different temperature; in particular, in the examples cited, the
measurement temperature is 60.degree. C. A peak-to-peak strain
amplitude sweep is carried out from 0.1% to 50% (outward cycle) and
then from 50% to 0.1% (return cycle). The results made use of are
the complex dynamic shear modulus (G*) and the loss factor
tan(.delta.). For the return cycle, the maximum value of
tan(.delta.) observed, denoted tan(.delta.).sub.max, is
indicated.
DETAILED DESCRIPTION OF THE INVENTION
[0044] The invention relates to a composition based on at least one
diene elastomer, a reinforcing filler comprising at least carbon
black having a CTAB specific surface of greater than or equal to
130 m.sup.2/g, a plasticizing oil and also a crosslinking system,
the dispersion of the filler in the elastomeric matrix having a Z
score of greater than or equal to 70.
[0045] According to one embodiment of the invention, this
composition is obtained from a first masterbatch comprising at
least the diene elastomer and the carbon black and exhibiting a
dispersion of the black of 80.
[0046] In the present description, unless expressly indicated
otherwise, all the percentages (%) shown are % by weight.
Furthermore, any interval of values denoted by the expression
"between a and b" represents the range of values extending from
more than a to less than b (that is to say, limits a and b
excluded), whereas any interval of values denoted by the expression
"from a to b" means the range of values extending from a up to b
(that is to say, including the strict limits a and b).
Diene Elastomer
[0047] As is customary, the terms "elastomer" and "rubber", which
are interchangeable, are used without distinction in the text.
[0048] The composition in accordance with the invention comprises
at least one first diene elastomer and optionally a second
elastomer identical to or different from the first, which can thus
be, or not, a diene elastomer.
[0049] A "diene" elastomer or rubber should be understood, in a
known way, as meaning an elastomer resulting at least in part
(i.e., a homopolymer or a copolymer) from diene monomers (monomers
carrying two conjugated or non-conjugated carbon-carbon double
bonds).
[0050] These diene elastomers can be classified into two
categories: "essentially unsaturated" or "essentially saturated".
Generally, "essentially unsaturated" is understood to mean a diene
elastomer resulting at least in part from conjugated diene monomers
having a content of units of diene origin (conjugated dienes) which
is greater than 15% (mol %); thus it is that diene elastomers such
as butyl rubbers or copolymers of dienes and a-olefins of EPDM type
do not come within the preceding definition and can in particular
be described as "essentially saturated" diene elastomers (low or
very low content, always less than 15%, of units of diene origin).
In the category of "essentially unsaturated" diene elastomers,
"highly unsaturated" diene elastomer is understood to mean in
particular a diene elastomer having a content of units of diene
origin (conjugated dienes) which is greater than 50%.
[0051] Among these diene elastomers, natural rubber and synthetic
elastomers are furthermore distinguished.
[0052] By synthetic diene elastomers capable of being used in
accordance with the invention, the expression "diene elastomer" is
understood more particularly to mean: [0053] (a) any homopolymer
obtained by polymerization of a conjugated diene monomer having
from 4 to 12 carbon atoms; [0054] (b) any copolymer obtained by
copolymerization of one or more conjugated dienes with one another
or with one or more vinylaromatic compounds having from 8 to 20
carbon atoms; [0055] (c) a ternary copolymer obtained by
copolymerization of ethylene and of an a-olefin having from 3 to 6
carbon atoms with a non-conjugated diene monomer having from 6 to
12 carbon atoms, such as, for example, the elastomers obtained from
ethylene and propylene with a non-conjugated diene monomer of the
abovementioned type, such as, in particular, 1,4-hexadiene,
ethylidenenorbornene or dicyclopentadiene; [0056] (d) a copolymer
of isobutene and of isoprene (butyl rubber) and also the
halogenated versions, in particular chlorinated or brominated
versions, of this type of copolymer.
[0057] The following are suitable in particular as conjugated
dienes: 1,3-butadiene, 2-methyl-1,3-butadiene,
2,3-di(C.sub.1-C.sub.5 alkyl)-1,3-butadienes, such as, for example,
2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene,
2-methyl-3-ethyl-1,3-butadiene or
2-methyl-3-isopropyl-1,3-butadiene, an aryl-1,3-butadiene,
1,3-pentadiene or 2,4-hexadiene. The following, for example, are
suitable as vinylaromatic compounds: styrene, ortho-, meta- or
para-methylstyrene, the "vinyltoluene" commercial mixture,
para-(tert-butyl)styrene, methoxystyrenes, chlorostyrenes,
vinylmesitylene, divinylbenzene or vinylnaphthalene.
[0058] The copolymers can comprise between 99% and 20% by weight of
diene units and between 1% and 80% by weight of vinylaromatic
units. The elastomers can have any microstructure, which depends on
the polymerization conditions used, in particular on the presence
or absence of a modifying and/or randomizing agent and on the
amounts of modifying and/or randomizing agent employed. The
elastomers can, for example, be block, statistical, sequential or
microsequential elastomers and can be prepared in dispersion or in
solution; they can be coupled and/or star-branched or else
functionalized with a coupling and/or star-branching or
functionalization agent. Mention may for example be made, for
coupling to carbon black, of functional groups comprising a C--Sn
bond or aminated functional groups, such as aminobenzophenone, for
example; mention may for example be made, for coupling to an
inorganic filler, such as silica, of silanol or polysiloxane
functional groups having a silanol end (such as described, for
example, in FR 2 740 778 or U.S. Pat. No. 6,013,718 and WO
2008/141702), alkoxysilane groups (such as described, for example,
in FR 2 765 882 or U.S. Pat. No. 5,977,238), carboxyl groups (such
as described, for example, in WO 01/92402 or U.S. Pat. No.
6,815,473, WO 2004/096865 or US 2006/0089445) or polyether groups
(such as described, for example, in EP 1 127 909 or U.S. Pat. No.
6,503,973, WO 2009/000750 and WO 2009/000752). Mention may also be
made, as other examples of functionalized elastomers, of elastomers
(such as SBR, BR, NR or IR) of the epoxidized type.
[0059] The following are suitable: polybutadienes and in particular
those having a content (mol %) of 1,2-units of between 4% and 80%
or those having a content (mol %) of cis-1,4-units of greater than
80%, polyisoprenes, butadiene/styrene copolymers and in particular
those having a Tg (glass transition temperature (Tg, measured
according to ASTM D3418) of between 0.degree. C. and -70.degree. C.
and more particularly between -10.degree. C. and -60.degree. C., a
styrene content of between 5% and 60% by weight and more
particularly between 20% and 50%, a content (mol %) of 1,2-bonds of
the butadiene part of between 4% and 75% and a content (mol %) of
trans-1,4-bonds of between 10% and 80%, butadiene/isoprene
copolymers and in particular those having an isoprene content of
between 5% and 90% by weight and a Tg of -40.degree. C. to
-80.degree. C., or isoprene/styrene copolymers and in particular
those having a styrene content of between 5% and 50% by weight and
a Tg of between -5.degree. C. and -50.degree. C. In the case of
butadiene/styrene/isoprene copolymers, those having a styrene
content of between 5% and 50% by weight and more particularly of
between 10% and 40%, an isoprene content of between 15% and 60% by
weight and more particularly of between 20% and 50%, a butadiene
content of between 5% and 50% by weight and more particularly of
between 20% and 40%, a content (mol %) of 1,2-units of the
butadiene part of between 4% and 85%, a content (mol %) of
trans-1,4-units of the butadiene part of between 6% and 80%, a
content (mol %) of 1,2-plus 3,4-units of the isoprene part of
between 5% and 70% and a content (mol %) of trans-1,4-units of the
isoprene part of between 10% and 50%, and more generally any
butadiene/styrene/isoprene copolymer having a Tg of between
-5.degree. C. and -70.degree. C., are suitable in particular.
[0060] To summarize, the synthetic diene elastomer or elastomers
according to the invention are preferably selected from the group
of highly unsaturated diene elastomers formed by polybutadienes
(abbreviated to BRs), synthetic polyisoprenes (IRs), butadiene
copolymers, isoprene copolymers and the mixtures of these
elastomers. Such copolymers are more preferably selected from the
group consisting of butadiene/styrene copolymers (SBRs),
isoprene/butadiene copolymers (BIRs), isoprene/styrene copolymers
(SIRs) and isoprene/butadiene/styrene copolymers (SBIRs).
[0061] As was specified above, liquid-phase compounding processes
are preferably used to make it possible to obtain masterbatches
based on diene elastomer and on carbon black exhibiting a very good
dispersion of the carbon black in the elastomer. Thus, in
particular for the preparation of the first masterbatch of diene
elastomer and carbon black, use will more particularly be made of a
diene elastomer latex, the elastomer latex being a particular form
of the elastomer which exists in the form of water-dispersed
elastomer particles.
[0062] The invention thus preferably relates to latexes of diene
elastomers, the diene elastomers being those defined above.
[0063] More particularly, for natural rubber (NR), which is
particularly suitable for the invention, this natural rubber exists
in various forms, as explained in detail in Chapter 3, "Latex
concentrates: properties and composition", by K. F. Gaseley, A. D.
T. Gordon and T. D. Pendle in "Natural Rubber Science and
Technology", A. D. Roberts, Oxford University Press-1988.
[0064] In particular, several forms of natural rubber latex are
sold: the natural rubber latexes referred to as "field latexes",
the natural rubber latexes referred to as "concentrated natural
rubber latexes", epoxidized latexes (ENRs), deproteinized latexes
or also prevulcanized latexes. The natural rubber field latex is a
latex to which ammonia has been added in order to prevent premature
coagulation and the concentrated natural rubber latex corresponds
to a field latex which has undergone a treatment corresponding to a
washing, followed by a further concentration. The various
categories of concentrated natural rubber latexes are listed in
particular according to Standard ASTM D 1076-06. Singled out in
particular among these concentrated natural rubber latexes are the
concentrated natural rubber latexes of the grade referred to as:
"HA" (high ammonia) and of the grade referred to as "LA"; for the
invention, use will advantageously be made of concentrated natural
rubber latexes of HA grade.
[0065] The NR latex can be physically or chemically modified
beforehand (centrifugation, enzymatic treatment, chemical modifier,
and the like). The latex can be used directly or be diluted
beforehand in water to facilitate the processing thereof.
[0066] Thus, as synthetic elastomer latex, the latex can in
particular consist of a synthetic diene elastomer already available
in the form of an emulsion (for example, a butadiene/styrene
copolymer, SBR, prepared in emulsion) or consist of a synthetic
diene elastomer initially in solution (for example, an SBR prepared
in solution) which is emulsified in a mixture of organic solvent
and water, generally by means of a surface-active agent.
[0067] An SBR latex, in particular an SBR prepared in emulsion
("ESBR") or an SBR prepared in solution ("SSBR"), and more
particularly an SBR prepared in emulsion, is particularly suitable
for the invention.
[0068] There exist two main types of processes for the emulsion
copolymerization of styrene and butadiene, one of them, or hot
process (carried out at a temperature close to 50.degree. C.),
being suitable for the preparation of highly branched SBRs, whereas
the other, or cold process (carried out at a temperature which can
range from 15.degree. C. to 40.degree. C.), makes it possible to
obtain more linear SBRs.
[0069] For a detailed description of the effectiveness of several
emulsifiers which can be used in the said hot process (as a
function of the contents of the said emulsifiers), reference may be
made, for example, to the two papers by C. W. Carr, I. M. Kolthoff
and E. J. Meehan, University of Minnesota, Minneapolis, Minn.,
which appeared in the Journal of Polymer Science of 1950, Vol. V,
No.2, pp. 201-206, and of 1951, Vol. VI, No. 1, pp. 73-81.
[0070] Regarding comparative examples of the implementation of the
said cold process, reference may be made, for example, to the paper
Industrial and Engineering Chemistry, 1948, Vol. 40, No. 5, pp.
932-937, E. J. Vandenberg and G. E. Hulse, Hercules Powder Company,
Wilmington, Del., and to the paper Industrial and Engineering
Chemistry, 1954, Vol. 46, No. 5, pp. 1065-1073, J. R. Miller and H.
E. Diem, B. F. Goodrich Chemical Co., Akron, Ohio.
[0071] In the case of an SBR (ESBR or SSBR) elastomer, use is made
in particular of an SBR having a moderate styrene content, for
example of between 20% and 35% by weight, or a high styrene
content, for example from 35% to 45%, a content of vinyl bonds of
the butadiene part of between 15% and 70%, a content (mol %) of
trans-1,4-bonds of between 15% and 75% and a Tg of between
-10.degree. C. and -55.degree. C.; such an SBR can advantageously
be used as a mixture with a BR preferably having more than 90% (mol
%) of cis-1,4-bonds.
[0072] It should be noted that it is possible to envisage using one
or more natural rubber latexes as a blend, one or more synthetic
rubber latexes as a blend, or a blend of one or more natural rubber
latexes with one or more synthetic rubber latexes.
[0073] The following are particularly suitable as the second
elastomer of the composition, if appropriate, when it is not a
diene elastomer: non-diene butyl elastomers, such as
poly(isobutylene) homopolymers or poly(isobutylene)-based
copolymers (of course, when it is a question of copolymers with
isoprene, the diene elastomers described above are re-encountered),
and also the halogenated derivatives, in particular generally
brominated or chlorinated derivatives, of these poly(isobutylene)
homopolymers and poly(isobutylene)-based copolymers.
[0074] The non-diene elastomers also suitably include copolymers of
isobutylene and of styrene derivatives, such as brominated
isobutylene/methylstyrene (BIMS) copolymers, among which is found
in particular the elastomer named Exxpro sold by Exxon. Mention may
also be made, as non-diene elastomer particularly suitable for the
invention, of non-diene thermoplastic elastomers (TPEs).
[0075] Advantageously, the fraction by weight of the first diene
elastomer in the elastomeric matrix is greater than or equal to 50%
and preferably greater than or equal to 60%.
Fillers
[0076] Use is made, as reinforcing filler, of an organic filler
composed of carbon black. All reinforcing carbon blacks having a
CTAB specific surface of greater than or equal to 130 m.sup.2/g and
more particularly still the carbon blacks having a CTAB specific
surface of greater than or equal to 160 m.sup.2/g are suitable as
carbon blacks.
[0077] It is specified that the CTAB specific surface is determined
according to French Standard NF T 45-007 of November 1987 (method
B).
[0078] This carbon black can be combined, in a blend, with one or
more other organic fillers, such as, for example, functionalized
polyvinylaromatic organic fillers, such as described in
Applications WO-A-2006/009792 and WO-A-2006/069793, and/or with one
or more reinforcing inorganic fillers, such as silica.
[0079] Thus, the term "inorganic filler" should be understood here
as meaning, in a known way, any inorganic or mineral filler,
whatever its colour and its origin (natural or synthetic), also
known as "white filler", "clear filler" or also "non-black filler",
in contrast to carbon black, this inorganic filler being capable of
reinforcing, by itself alone, without means other than an
intermediate coupling agent, a rubber composition intended for the
manufacture of a tread for tires, in other words capable of
replacing, in its reinforcing role, a conventional tire-grade
carbon black for a tread. Such a filler is generally characterized
by the presence of functional groups, in particular hydroxyl (OH)
functional groups, at its surface, requiring, in order to be used
as reinforcing filler, the use of a coupling agent or system
intended to provide a stable chemical bond between the isoprene
elastomer and the said filler.
[0080] Such an inorganic filler can thus be used with a coupling
agent in order to make possible the reinforcement of the rubber
composition in which it is included. It can also be used with a
covering agent (which does not provide a bond between the filler
and the elastomeric matrix), in addition to a coupling agent or not
(in this case, the inorganic filler does not act as
reinforcement).
[0081] The physical state under which the inorganic filler is
provided is not important, whether it is in the form of a powder,
microbeads, granules, beads or any other appropriate densified
form. Of course, the term "inorganic filler" is also understood to
mean mixtures of various inorganic fillers, in particular of highly
dispersible siliceous and/or aluminous fillers, as described
below.
[0082] Mineral fillers of the siliceous type, in particular silica
(SiO.sub.2), or of the aluminous type, in particular alumina
(Al.sub.2O.sub.3), are suitable in particular as inorganic fillers.
The silica used can be any silica known to a person skilled in the
art, in particular any precipitated or fumed silica exhibiting a
BET specific surface and a CTAB specific surface which are both
less than 450 m.sup.2/g, preferably from 30 to 400 m.sup.2/g.
Mention will be made, as highly dispersible precipitated silicas
("HDSs"), for example, of the Ultrasil 7000 and Ultrasil 7005
silicas from Evonik, the Zeosil 1165MP, 1135MP and 1115MP silicas
from Rhodia, the Hi-Sil EZ150G silica from PPG, the Zeopol 8715,
8745 and 8755 silicas from Huber or the silicas with a high
specific surface as described in Application WO 03/16837.
[0083] It is also possible to envisage the addition of filler to
the carbon black, such as carbon blacks partially or completely
covered with silica via a post-treatment or the carbon blacks
modified in situ by silica, such as, without implied limitation,
the fillers sold by Cabot Corporation under the name Ecoblack.TM.
CRX 2000 or CRX 4000.
[0084] Preferably, the content of total filler (carbon black and
inorganic filler, such as silica) is between 20 and 200 phr, more
preferably between 30 and 150 phr and more preferably still between
30 and 100 phr, the optimum being, in a known way, different
depending on the particular applications targeted: the level of
reinforcement expected with regard to a bicycle tire, for example,
is of course less than that required with regard to a tire capable
of running at high speed in a sustained manner, for example a
motorcycle tire, a tire for a passenger vehicle or a tire for a
utility vehicle, such as a heavy duty vehicle.
[0085] According to a preferred embodiment of the invention, use is
made of carbon black, the content of which varies from 20 to 80
phr, and it is possible to combine it preferably with an inorganic
filler, in particular silica, the content of which varies from 5 to
50 phr, more particularly the total filler of the composition
comprising carbon black, the content of which varies from 35 to 70
phr, and an inorganic filler, in particular silica, the content of
which varies from 5 to 35 phr, more preferably still the total
filler comprising carbon black, the content of which varies from 40
to 65 phr, and an inorganic filler, in particular silica, the
content of which varies from 10 to 30 phr.
Plasticizing Oil
[0086] The rubber compositions of the invention use an extending
oil (or plasticizing oil), the usual role of which is to facilitate
the processing, by a fall in the Mooney plasticity, and to improve
the endurance, by a decrease in the cured moduli of elongation.
[0087] At ambient temperature (23.degree. C.), these oils, which
are more or less viscous, are liquids (that is to say, as a
reminder, substances which have the ability to eventually assume
the shape of their container), in contrast in particular to resins
or rubbers, which are by nature solids.
[0088] Preferably, the extending oil is selected from the group
consisting of polyolefinic oils (that is to say, resulting from the
polymerization of monoolefinic or diolefinic olefins), paraffinic
oils, naphthenic oils (of low or high viscosity), aromatic oils,
mineral oils and the mixtures of these oils.
[0089] The number-average molecular weight (Mn) of the extending
oil is preferably between 200 and 25 000 g/mol, more preferably
still between 300 and 10 000 g/mol. For excessively low Mn weights,
there exists a risk of migration of the oil outside the
composition, whereas excessively high weights can result in
excessive stiffening of this composition. An Mn weight of between
350 and 4000 g/mol, in particular between 400 and 3000 g/mol, has
proved to constitute an excellent compromise for the targeted
applications, in particular for use in a tire.
[0090] The number-average molecular weight (Mn) of the extending
oil is determined by SEC, the sample being dissolved beforehand in
tetrahydrofuran at a concentration of approximately 1 g/l; the
solution is then filtered through a filter with a porosity of 0.45
.mu.m before injection. The apparatus is the Waters Alliance
chromatographic line. The elution solvent is tetrahydrofuran, the
flow rate is 1 ml/min, the temperature of the system is 35.degree.
C. and the analytical time is 30 min A set of two Waters columns
with the Styragel HT6E name is used. The injected volume of the
solution of the polymer sample is 100 .mu.l. The detector is a
Waters 2410 differential refractometer and its associated software,
for making use of the chromatographic data, is the Waters
Millennium system. The calculated average molar masses are relative
to a calibration curve produced with polystyrene standards.
[0091] A person skilled in the art will know, in the light of the
description and implementational examples which follow, how to
adjust the amount of plasticizer as a function in particular of the
pneumatic object in which it is intended to be used.
[0092] The content of plasticizing oil is preferably between 2 and
35 phr. Below the minimum indicated, the targeted technical effect
can prove to be insufficient while, above the maximum, the
tackiness of the compositions in the raw state, with regard to the
compounding devices, can in some cases become totally unacceptable
from the industrial viewpoint. The content of plasticizing oil is
more preferably still between 5 and 25 phr.
Masterbatches--Rubber Composition
[0093] Advantageously, the masterbatches and the compositions thus
produced are capable of being used in tire applications.
[0094] The rubber compositions for tires based on masterbatches and
on inorganic filler according to the invention can also comprise,
in a known way, a coupling agent and/or a covering agent and a
vulcanization system.
[0095] Use is made, in a known way, in order to couple the
reinforcing inorganic filler to the diene elastomer, of an at least
bifunctional coupling agent (or bonding agent) intended to provide
a satisfactory connection, of chemical and/or physical nature,
between the inorganic filler (surface of its particles) and the
diene elastomer, in particular bifunctional organosilanes or
polyorganosiloxanes.
[0096] Use is made in particular of silane polysulphides, referred
to as "symmetrical" or "unsymmetrical" depending on their specific
structure, such as described, for example, in Applications WO
03/002648 (or US 2005/016651) and WO 03/002649 (or US
2005/016650).
[0097] Suitable in particular, without the definition below being
limiting, are silane polysulphides referred to as "symmetrical",
corresponding to the following general formula (III):
(III) Z-A-S.sub.x-A-Z, in which: [0098] x is an integer from 2 to 8
(preferably from 2 to 5); [0099] A is a divalent hydrocarbon
radical (preferably C.sub.1-C.sub.18 alkylene groups or
C.sub.6-C.sub.12 arylene groups, more particularly
C.sub.1-C.sub.10, in particular C.sub.1-C.sub.4, alkylenes, in
particular propylene); [0100] Z corresponds to one of the formulae
below:
[0100] ##STR00001## [0101] in which: [0102] the R.sup.1 radicals,
which are substituted or unsubstituted and identical to or
different from one another, represent a C.sub.1-C.sub.18 alkyl
group, a C.sub.5-C .sub.18 cycloalkyl group or a C.sub.6-C .sub.18
aryl group (preferably C.sub.1-C.sub.6 alkyl, cyclohexyl or phenyl
groups, in particular C.sub.1-C.sub.4 alkyl groups, more
particularly methyl and/or ethyl), [0103] the R.sup.2 radicals,
which are substituted or unsubstituted and identical to or
different from one another, represent a C.sub.1-C.sub.18 alkoxyl or
C.sub.5-C.sub.18 cycloalkoxyl group (preferably a group chosen from
C.sub.1-C.sub.8 alkoxyls and C.sub.5-C.sub.8 cycloalkoxyls, more
preferably still a group chosen from C.sub.1-C.sub.4 alkoxyls, in
particular methoxyl and ethoxyl).
[0104] In the case of a mixture of alkoxysilane polysulphides
corresponding to the above formula (III), in particular normal
commercially available mixtures, the mean value of the "x" indices
is a fractional number preferably of between 2 and 5, more
preferably of approximately 4. However, the invention can also
advantageously be carried out, for example, with alkoxysilane
disulphides (x=2).
[0105] Mention will more particularly be made, as examples of
silane polysulphides, of
bis((C.sub.1-C.sub.4)alkoxyl(C.sub.1-C.sub.4)alkylsilyl(C.sub.1-C.sub.4)a-
lkyl) polysulphides (in particular disulphides, trisulphides or
tetrasulphides), such as, for example, bis(3-trimethoxysilylpropyl)
or bis(3-triethoxysilylpropyl) polysulphides. Use is made in
particular, among these compounds, of bis(3-triethoxysilylpropyl)
tetrasulphide, abbreviated to TESPT, of formula
[(C.sub.2H.sub.SO).sub.3Si(CH.sub.2).sub.3S.sub.2].sub.2, or
bis(triethoxysilylpropyl) disulphide, abbreviated to TESPD, of fon
iula [(C.sub.2H.sub.SO).sub.3Si(CH.sub.2).sub.3S].sub.2. Mention
will also be made, as preferred examples, of
bis(mono(C.sub.1-C.sub.4)alkoxyldi(C.sub.1-C.sub.4)alkylsilylpropyl)
polysulphides (in particular disulphides, trisulphides or
tetrasulphides), more particularly
bis(monoethoxydimethylsilylpropyl) tetrasulphide, such as described
in Patent Application WO 02/083782 (or US 2004/132880).
[0106] Mention will in particular be made, as coupling agent other
than an alkoxysilane polysulphide, of bifunctional POSs
(polyorganosiloxanes) or else of hydroxysilane polysulphides
(R.sup.2=OH in the above formula III), such as described in Patent
Applications WO 02/30939 (or U.S. Pat. No. 6,774,255) and WO
02/31041 (or US 2004/051210), or else of silanes or POSs bearing
azodicarbonyl functional groups, such as described, for example, in
Patent Applications WO 2006/125532, WO 2006/125533 and WO
2006/125534.
[0107] Processing aids capable, in a known way, by virtue of an
improvement in the dispersion of the inorganic filler in the rubber
matrix and of a lowering in the viscosity of the compositions, of
improving their ease of processing in the raw state will generally
be considered as covering agent, these processing aids being, for
example, hydrolysable silanes, such as alkylalkoxysilanes (in
particular alkyltriethoxysilanes), polyols, polyethers (for
example, polyethylene glycols), primary, secondary or tertiary
amines (for example, trialkanolamines), hydroxylated or
hydrolysable POSs, for example
.alpha.,.omega.-dihydroxypolyorganosiloxanes (in particular
.alpha.,.omega.-dihydroxypolydimethylsiloxanes), or fatty acids,
such as, for example, stearic acid.
[0108] In the rubber compositions in accordance with the invention,
the content of coupling agent is preferably between 0.1% and 12% by
weight of the inorganic filler for a CTAB specific surface of 160
m.sup.2/g, more preferably between 4% and 10% by weight of the
inorganic filler for a CTAB specific surface of 160 m.sup.2/g;
and/or the content of covering agent is preferably between 0.1% and
20% by weight of the inorganic filler for a CTAB specific surface
of 160 m.sup.2/g, more preferably between 5% and 20% by weight of
the inorganic filler for a CTAB specific surface of 160 m.sup.2/g,
it being possible for the content of coupling agent to be adjusted
to the level of specific surface of the filler.
[0109] A person skilled in the art will understand that a filler of
another nature, in particular organic nature, might be used as
filler equivalent to the inorganic filler described in the present
section, provided that this filler is covered with an inorganic
layer, such as silica, or else comprises, at its surface,
functional sites, in particular hydroxyls, requiring the use of a
coupling agent in order to form the connection between the filler
and the elastomer.
[0110] These rubber compositions in accordance with the invention
can also comprise all or a portion of the usual additives generally
used in elastomer compositions intended for the manufacture of
tires, in particular of treads, such as, for example, other
plasticizers, pigments, protective agents, such as antiozone waxes,
chemical antiozonants or antioxidants, antifatigue agents,
reinforcing resins, methylene acceptors (for example phenolic
novolak resin) or methylene donors (for example HMT or H3M), such
as described, for example, in Application WO 02/10269, a
crosslinking system based either on sulphur or on sulphur donors
and/or on peroxide and/or on bismaleimides, or vulcanization
accelerators.
[0111] It should be noted that it is also possible to envisage
producing the masterbatches in accordance with the invention by
incorporating therein, in particular before the drying phase of the
production of the masterbatch in the liquid phase, additives such
as described above, antioxidant, coupling agent, covering agent,
and the like.
Manufacture of the Rubber Compositions and Masterbatches
[0112] The rubber compositions of the invention are manufactured in
appropriate mixers, using two successive phases of preparation
according to a general procedure well known to those skilled in the
art: a first phase of thermomechanical working or kneading
(sometimes referred to as a "non-productive" phase) at high
temperature, up to a maximum temperature of between 130.degree. C.
and 200.degree. C., preferably between 145.degree. C. and
185.degree. C., followed by a second phase of mechanical working
(sometimes referred to as a "productive" phase) at lower
temperature, typically below 120.degree. C., for example between
60.degree. C. and 100.degree. C., during which finishing phase the
crosslinking or vulcanization system is incorporated.
[0113] According to a preferred embodiment of the invention, all
the base constituents of the compositions of the invention, with
the exception of the vulcanization system, are intimately
incorporated, by kneading, during the first "non-productive" phase,
that is to say that at least these various base constituents are
introduced into the mixer and are thermomechanically kneaded, in
one or more stages, until the maximum temperature of between
130.degree. C. and 200.degree. C., preferably of between
145.degree. C. and 185.degree. C., is reached.
[0114] According to a preferred embodiment of the invention, the
plasticizing oil and also the base constituents of the compositions
of the invention, with the exception of the vulcanization system,
in particular, if appropriate, the inorganic filler, such as the
silica, are incorporated in the diene elastomer and in the carbon
black, which have been prepared beforehand in the form of a first
masterbatch.
[0115] Preferably, this first masterbatch is produced in the
"liquid" phase. To do this, recourse has been had to the diene
elastomer in the form of a latex, which exists in the form of
water-dispersed elastomer particles, and to an aqueous dispersion
of the carbon black, that is to say a filler dispersed in water,
commonly known as "slurry". More preferably still, the stages of
the process described in the document U.S. Pat. No. 6,048,923 will
be followed, which process consists in particular in incorporating
a continuous stream of a first fluid composed of the elastomer
latex in the compounding region of a coagulation reactor, in
incorporating a second continuous stream of a second fluid composed
of an aqueous dispersion of carbon black under pressure in the
compounding region, in order to form a mixture with the elastomer
latex; the compounding of these two fluids being sufficiently
energetic to allow the elastomer latex to coagulate virtually
completely with the carbon black before the outlet orifice of the
coagulation reactor, and in then drying the coagulum obtained.
[0116] According to another preferred embodiment of the invention,
the inorganic filler and the second elastomer are incorporated in
the first masterbatch by also being provided in the form of a
second masterbatch which will have been prepared beforehand. This
second masterbatch can be prepared in particular in the solid form
by thermomechanically kneading the second elastomer and the
inorganic filler; it can also be prepared by any other process and
in particular it can also be prepared in the liquid phase.
[0117] It should in particular be noted that, in the case of the
incorporation of a second elastomer and/or of an inorganic filler,
this or these incorporations can be carried out simultaneously with
the introduction into the mixer of the other constituents (in
particular the first diene elastomer or first masterbatch) but also
advantageously that this or these incorporations can be offset in
time from a few tens of seconds to a few minutes. It should be
noted that, in the case of an addition of an inorganic filler and a
second elastomer, these can be introduced separately or in the form
of a second masterbatch comprising the second elastomer and the
inorganic filler. In the case of the introduction of the second
elastomer alone and the inorganic filler alone, offset in time from
a few tens of seconds to a few minutes, the inorganic filler can be
introduced before, after or simultaneously with the second
elastomer.
[0118] By way of example, the first (non-productive) phase is
carried out in a single thermomechanical stage during which all the
necessary constituents (if appropriate in the form of a masterbatch
as specified above), the optional additional covering agents or
processing aids and various other additives, with the exception of
the vulcanization system, are introduced into an appropriate mixer,
such as a standard internal mixer. The total duration of the
kneading, in this non-productive phase, is preferably between 1 and
15 min. After cooling the mixture thus obtained during the first
non-productive phase, the vulcanization system is then incorporated
at low temperature, generally in an external mixer, such as an open
mill; everything is then mixed (productive phase) for a few
minutes, for example between 2 and 15 min.
[0119] The crosslinking system is preferably a vulcanization
system, that is to say a system based on sulphur (or on a
sulphur-donating agent) and on a primary vulcanization accelerator.
Additional to this base vulcanization system are various known
secondary vulcanization accelerators or vulcanization activators,
such as zinc oxide, stearic acid or equivalent compounds, or
guanidine derivatives (in particular diphenylguanidine),
incorporated during the first non-productive phase and/or during
the productive phase, as described subsequently.
[0120] The sulphur is used at a preferred content of between 0.5
and 12 phr, in particular between 1 and 10 phr. The primary
vulcanization accelerator is used at a preferred content of between
0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr.
[0121] Use may be made, as (primary or secondary) accelerator, of
any compound capable of acting as accelerator for the vulcanization
of diene elastomers in the presence of sulphur, in particular
accelerators of the thiazole type, and also their derivatives, and
accelerators of thiuram and zinc dithiocarbamate types. These
accelerators are, for example, selected from the group consisting
of 2-mercaptobenzothiazyl disulphide (abbreviated to "MBTS"),
tetrabenzylthiuram disulphide ("TBZTD"),
N-cyclohexyl-2-benzothiazolesulphenamide ("DCBS"),
N,N-dicyclohexyl-2-benzothiazolesulphenamide ("DCBS"),
N-(tert-butyl)-2-benzothiazolesulphenamide ("TBBS"),
N-(tert-butyl)-2-benzothiazolesulphenimide ("TBSI"), zinc
dibenzyldithiocarbamate ("ZBEC") and the mixtures of these
compounds.
[0122] The final composition thus obtained is subsequently
calendered, for example in the form of a sheet or of a plaque, in
particular for laboratory characterization, or else extruded in the
form of a rubber profiled element which can be used, for example,
as a tire tread for a passenger vehicle, heavy duty vehicle, and
the like.
Exemplary Embodiments of the Invention
[0123] The examples illustrate the improvement in the properties in
terms of processability and of properties at break of rubber
compositions in accordance with the invention in comparison with
control rubber compositions which differ from the compositions of
the invention either in the CTAB specific surface of the carbon
black, or in the absence of plasticizing oil, or, finally, in the
poor dispersion (Z score) of the carbon black in the
composition.
[0124] The rubber compositions which follow were prepared, for
some, from a masterbatch produced in the liquid phase of natural
rubber and carbon black and, for others, by a solid-phase
compounding.
Preparation of Masterbatch of Natural Rubber and Carbon Black
[0125] The masterbatches of diene elastomer and carbon black used
in some of the compositions which follow are produced in the liquid
phase according to the process described in U.S. Pat. No.
6,048,923.
[0126] Thus, masterbatches are prepared, according to the protocol
described in detail in the abovementioned patent, respectively from
carbon black N234 and carbon black N134, sold by Cabot Corporation,
and natural rubber field latex originating from Malaysia and
exhibiting a rubber solids content of 28% and an ammonia content of
0.3%.
[0127] Masterbatches A of natural rubber and carbon black (with
carbon black N234 or carbon black N134) are thus obtained in which
the content of carbon black is 50 phr.
Preparation of the Rubber Compositions
[0128] The control compositions CC are produced according to a
conventional solid-form compounding process in which the elastomer,
thus natural rubber in these examples, and the reinforcing filler,
respectively, depending on the compositions: carbon black N234 and
carbon black N134, sold by Cabot Corporation.
[0129] The control rubber compositions CRC are produced from the
masterbatch A (including carbon black N234 or carbon black
N134).
[0130] The various compositions are produced in the following way:
The following tests are carried out in the following way: the
natural rubber in the solid form and the carbon black, for the CC
compositions, or the masterbatch A, for the CRC compositions, and
the various other ingredients, with the exception of the
vulcanization system, are introduced into an internal mixer which
is 70% filled and which has an initial vessel temperature of
approximately 90.degree. C. Thermomechanical working
(non-productive phase) is then carried out in one stage (total
duration of the kneading equal to approximately 5 min), until a
maximum "dropping" temperature of approximately 165.degree. C. is
reached.
[0131] The mixture thus obtained is recovered and cooled and then
the vulcanization system (sulphur and sulphenamide accelerator) is
added on an external mixer (homofinisher) at 70.degree. C.,
everything being mixed (productive phase) for approximately 5 to 6
min
[0132] The compositions thus obtained are subsequently calendered,
either in the form of plaques (thickness of 2 to 3 mm) or thin
sheets of rubber, for the measurement of their physical or
mechanical properties, or in the form of profiled elements which
can be used directly, after cutting and/or assembling to the
desired dimensions, for example as semi-finished products for
tires, in particular as tire treads.
Tests
[0133] The rubber composition CC1 is prepared "in bulk" from
natural rubber and carbon black in the solid form, as described in
detail in section 111-2; the compositions CRC1 and CRC2 not in
accordance with the invention and the compositions CRC3 and CRC4 in
accordance with the invention are prepared from masterbatches A
according to the process described in detail in section 111-2.
[0134] All of the compositions, whatever the manufacturing process,
have the following base formulation (in phr):
TABLE-US-00001 natural rubber 100 6PPD (a) 1.5 stearic acid 2 zinc
oxide (c) 3 accelerator (d) 1.4 sulphur 1.4 (a)
N-(1,3-dimethylbutyl-N-phenyl-para-phenylenediamine (Santoflex
6-PPD from Flexsys); (c) zinc oxide (industrial grade - Umicore)
(d) N-cyclohexyl-2-benzothiazolesulphenamide (Santocure CBS from
Flexsys)
[0135] In addition to these constituents, the CC and CRC
compositions differ from one another in their Z score, the nature
of the carbon black and the nature and the presence of plasticizing
oil, as described in detail in Table 1 below.
TABLE-US-00002 TABLE 1 Compositions CC1 CRC1 CRC2 CRC3 CRC4 Carbon
black (1) -- 50 -- -- -- Carbon black (2) 50 -- 50 50 50 Oil (3) 10
10 -- 10 -- Oil (4) -- -- -- -- 10 Z score 50 88 86 78 87 (1) N234,
sold by Cabot Corporation (CTAB 115 m.sup.2/g) (2) N134, sold by
Cabot Corporation (CTAB 135 m.sup.2/g) (3) Oil, Extensoil 1721,
sold by Repsol (4) Oil, MES-H, sold by Repsol
[0136] The properties measured before and after curing at
150.degree. C. for 40 minutes are given in Table 2 below.
TABLE-US-00003 TABLE 2 Compositions CCI CRC1 CRC2 CRC3 CRC4
Properties before curing Mooney 87 58 71 56 54 Properties after
curing Breaking stress 53 51 50 59 66 at 60.degree. C. (Mpa)
Elongation at 265 233 183 230 241 break at 60.degree. C. (%)
Breaking energy 140 118 91.5 136 160 tan(.delta.)max 0.12 0.11 0.12
0.10 0.10
[0137] It is found that the compositions in accordance with the
invention CRC3 and CRC4 exhibiting a high Z score (greater than or
equal to 70) and also having a CTAB of greater than or equal to 130
m.sup.2/g and a plasticizing oil in accordance with the invention
(with a different oil nature) make it possible, surprisingly, to
significantly improve the processability of the composition (lower
Mooney value) in comparison with a control composition CC1 without
damaging the properties at break (stress, elongation, energy),
indeed even while improving them (composition CRC4), in contrast to
the composition CRC1 (comprising a carbon black having a CTAB
specific surface of less than 130 m.sup.2/g), which improves the
processability but damages the properties at break, and in contrast
to the composition CRC2, which has damaged properties at break and
a poorer processability (equivalent to CC1).
[0138] Thus, it is observed that it is this specific compromise in
dispersion of the filler in the elastomeric matrix, in nature of
the filler and in presence of plasticizing oil which makes it
possible, surprisingly, to produce an improvement in the
processability of the composition without damaging the other
properties of the mixture.
* * * * *