FR3053692A1 - RUBBER COMPOSITION COMPRISING NATURAL RUBBER CUTTING HAVING MOLECULAR MASS DISTRIBUTION, SECAMED VIEW, RESPECTIVELY UNIMODAL OR BIMODAL, PROCESS FOR PREPARATION AND PNEUMATIC COMPONENT - Google Patents

Abstract

Rubber composition comprising a cut of natural rubbers having a molecular weight distribution, seen in SEC-MALS, respectively unimodal or bimodal, method of preparation and tire component The subject of the invention is a rubber composition based on at least an elastomeric matrix comprising natural rubber, a reinforcing filler, a crosslinking system, characterized in that said natural rubber is a blend of (i) a natural rubber having a molecular weight distribution, seen in SEC- MALS, bimodal and (ii) a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal and having an index of initial plasticity, PO, less than 20, in mass proportions ranging from 90: 10 to 20: 80. It also relates to a method for preparing such a composition, a tire component comprising it and a tire comprising this component.

Description

Holder (s): COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN Limited partnership with shares, MICHELIN RECHERCHE ET TECHNIQUE S.A. Limited company.

Extension request (s)

Agent (s): REGIMBEAU.

FR 3 053 692 - A1 (54) RUBBER COMPOSITION COMPRISING A CUT OF NATURAL RUBBER HAVING A DISTRIBUTION OF MOLECULAR MASS, SEEN IN DRY-MALS, RESPECTIVELY UNIMODAL OR BIMODAL, PREPARATION METHOD AND TIRE COMPONENT.

©) Rubber composition comprising a blend of natural rubbers having a molecular weight distribution, seen in SEC-MALS, respectively unimodal or bimodal, preparation process and tire component

The subject of the invention is a rubber composition based on at least:

- an elastomeric matrix comprising natural rubber,

- a reinforcing filler,

- a crosslinking system, characterized in that said natural rubber is a blend (i) of natural rubber having a molecular weight distribution, seen in SEC-MALS, bimodal and (ii) of a natural rubber having a distribution of molecular mass, seen in SEC-MALS, unimodal and having an initial plasticity index, PO, less than 20, in mass proportions ranging from 90:10 to 20:80.

It also relates to a process for the preparation of such a composition, a tire component comprising it and a tire comprising this component.

i

Rubber composition comprising a blend of natural rubbers having a molecular weight distribution, seen in SEC-MALS, respectively unimodal or bimodal, preparation process and tire component

The present invention relates to a rubber composition in which natural rubbers are selected according to their molecular weight distribution.

Natural rubber is an elastomer which is very widely used in the tire sector due to its remarkable properties. For example, it is used in rubber compositions intended for the manufacture of semi-finished products for vehicles transporting heavy loads, because of the performance compromise which it can bring to the tire.

The natural rubber used as an elastomer in rubber compositions comes from the rubbery dry matter of natural rubber latex, extracted from YHevea brasiliensis.

Molecular mass and molecular weight distribution play an important role in the blending properties of polymers. Commonly known techniques such as GPC (gel permeation chromatography) or SEC (size exclusion chromatography) which allows the separation of polymer chains according to their size are used to study the macromolecular structure of polymers.

Subramaniam [1972] (1) was the first to study the molecular mass distribution (DMM) of fresh natural rubber latex (NR) in SEC. The MDM of NR, seen through chromatography is described as being either unimodal, presence of a population of macromolecular chains, or bimodal presence of 2 populations of macromolecular chains.

Subramaniam [1993] (2) distinguished three types of distribution:

Type 1: distinct bimodal distribution with a peak in the region of low molecular weights whose height is substantially equal to or slightly less than the height of the peak in the region of high molecular weights.

Type 2: distinct bimodal distribution with a peak in the low molecular weight region, the height of which is at least half the height of the peak in the high molecular weight region.

Type 3: unimodal distribution

The study of the molecular mass distribution of natural rubber from RSS (Ribbed Smoked Sheet) of different varieties confirms a distinction in the distribution of molecular masses.

Liengprayon (2008) (3) shows that the varieties RRIM600, GT1 and BPM24 have a bimodal molecular weight distribution while the variety PB235 shows a unimodal distribution.

Natural polyisoprene, also known as natural rubber, is obtained from latex from the rubber tree bleeding. The coagulation of the latex can be a so-called “natural” coagulation (coagulation of the latex in the bleeding cup mainly due to the microbial activity naturally present) or a so-called “artificial” coagulation, for example “chemical” by addition of acid or salts.

In rubber, in particular for the preparation of tires, the natural rubber used comes from a mixture of several coagulated latexes, coming from several plots of trees, without specifying their profile or their molecular weight distribution.

Surprisingly, it has been shown that the use of a mixture of specific natural rubbers, selected according to their molecular weight distribution seen in SEC-MALS (Steric Exclusion Chromatography - Multiangle Light Scatering Detector), and their initial plasticity index , then makes it possible to obtain a composition having a processability, a raw reinforcement (straightening of the Elongation Force Curve (CFA) raw) and an improved hysteresis level without penalization of the rigidity.

The strong raw recovery (increased stress at high elongations) can result in a higher crystallization potential under tension and therefore an improvement in the performance of the composition in stations such as carcass plies (holding or maintaining the 'wire gap for example).

The subject of the invention is a rubber composition based on at least:

- an elastomeric matrix comprising natural rubber,

- a reinforcing filler,

- a crosslinking system, characterized in that said natural rubber is a blend (i) of natural rubber having a distribution of molecular weights, seen in SEC-MALS, bimodal and (ii) of a natural rubber having a distribution molecular weights, seen in SEC-MALS, unimodal and having an initial plasticity index, PO, less than 20, in mass proportions (i): (ii) ranging from 90: 10 to 20: 80.

Advantageously, said natural rubber is a blend (i) of natural rubber having a distribution of molecular weights, seen in SEC-MALS, bimodal and (ii) of natural rubber having a distribution of molecular weights, seen in SEC- MALS, unimodal and having an initial plasticity index, PO, less than 20, in mass proportions (i): (ii) ranging from 90: 10 to 30: 70, more advantageously ranging from 70: 30 to 30: 70, more advantageously ranging from 60:40 to 40:60, more advantageously from 50:50.

The rubber composition advantageously comprises between 30 and 100 phr of reinforcing filler. The reinforcing filler is advantageously carbon black or an inorganic reinforcing filler or a blend of these charges.

Advantageously, the carbon black represents more than 50% by mass of the reinforcing filler.

When it contains a reinforcing inorganic filler, the rubber composition also includes a coupling agent.

In particular, the reinforcing inorganic filler is silica.

In particular, the reinforcing filler is carbon black.

The elastomeric matrix may include another diene elastomer. Advantageously, the elastomeric matrix comprises more than 50 phr of natural rubber, more advantageously 100 phr.

The subject of the invention is also a process for preparing a rubber composition according to the invention, characterized in that it comprises the following steps:

a) select a natural rubber having a molecular weight distribution, seen in SEC-MALS, bimodal;

b) select a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal and having an initial plasticity index, PO, less than 20;

c) incorporating into the elastomeric matrix, comprising a mixture of the natural rubbers selected in stages a) and b), in a rubber mass ratio of stage a): rubber of stage b) ranging from 90: 10 to 20: 80, during a first so-called non-productive step, the other ingredients of the composition, with the exception of the crosslinking system by thermomechanically kneading everything until a maximum temperature of between 110 and 190 ° C is reached;

d) cool the assembly to a temperature below 100 ° C;

e) then incorporate, during a second so-called productive stage, a crosslinking system;

f) knead everything up to a maximum temperature below 110 ° C.

The subject of the invention is also a tire component comprising a composition according to the invention, advantageously further comprising wired reinforcing elements. Said component is advantageously chosen from the carcass ply and the crown plies.

The invention also relates to a tire comprising a component according to the invention.

A subject of the invention is also the use of natural rubber having a distribution of molecular weights, seen in SEC-MALS, bimodal, and natural rubber having a distribution of molecular weights, seen in SEC-MALS, unimodal and having an index of initial plasticity, PO, less than 20, in cutting to improve the processability, the raw properties, the hysteresis of a rubber composition, without deterioration of the rigidity. Such a rubber composition is then particularly suitable for use in a tire component comprising said rubber composition and wired reinforcing elements.

DESCRIPTION OF THE FIGURES

Figure 1): first derivative of the refractive index signal (broken line), obtained during the SEC-MALS chromatography of RRIM600 natural rubber

Figure 2): first derivative of the refractive index signal (broken line), obtained during the SEC-MALS chromatography of the PB217 latex

I - MEASUREMENTS AND TESTS USED

A) SEC-MALS chromatography:

The natural rubber samples were dissolved in a solvent (THF) for 7 days at 30 ° C at a concentration of 2 mg / ml. The soluble part, after passing through a 1 μm sieve, was injected into SEC MALS (Steric Exclusion Chromatography + Multiangle Light Scatering Detector) columns according to the protocol described by Kim (2009) ³ (Kim, Chandy; Sainte-Beuve, Jérome; Guilbert, Stéphane; Bonfils, Frédéric. Study of chain branching in natural rubber using size-exclusion chromatography coupled with a multiangle light scattering detector (SEC-MALS. European Polymer Journal vol. 45 issue 8 August, 2009. p. 2249- 2259).

The detection system is twofold: a differential refractometric concentration detector and a MALS, a multi-angle light scattering detector sensitive to the variation of the scattered intensity depending on the size of the objects. The raw detector data is exported and is processed in the EXCEL spreadsheet for the calculation and graphic expression of the first derivative.

B) Mooney plasticity (before baking):

An oscillating consistometer is used as described in the French standard NF T 43-005 (1991). The Mooney plasticity measurement is made according to the following principle: the composition in the raw state (i.e., before baking) is molded in a cylindrical enclosure heated to 100 ° C. After one minute of preheating, the rotor turns within the test tube at 2 revolutions / minute and the torque useful for maintaining this movement is measured after 4 minutes of rotation. The Mooney plasticity (ML 1 + 4) is expressed in Mooney unit (MU, with 1 MU = 0.83 Newton.meter). For more readability the results will be indicated in base 100, the value 100 being attributed to the witness. A result less than 100 indicating a decrease in the value concerned, and conversely, a result greater than 100, will indicate an increase in the value concerned

C) Elongation force curve (before cooking):

The raw elongation force curve is produced on a test piece, of raw mixture, in the form of a dumbbell thanks to a traction machine. The test piece has two ends connected to each other by a rod of thickness E of 2.5 mm, of length L 26mm and width W 6mm. The test piece is subjected to a simple traction, at a speed of 100 mm / min by displacement of a jaw of a traction machine of the commercial name "INSTRON 4501" relative to a fixed jaw of said machine, said jaws enclosing said ends. with the same clamping pressure of 2 bars.

For each specimen, the following parameters are calculated:

Relative deformation a (%) = 100 x D / L (D being the displacement of said movable jaw in millimeters (mm) measured by the machine sensor during each test and L = 26 mm is the initial length of the test piece )

Apparent stress F / S _o (MPa) which represents the ratio of the force F (in N) measured by the sensor of the machine, on the initial section S _o of the test piece (S _o = WE in mm ² , W = 6 mm and E = 2.5 mm the thickness of the test piece before traction)

The experiment is carried out at a temperature of 23 ° C and a humidity rate of 50%.

For more readability the results will be indicated in base 100, the value 100 being attributed to the witness. A result less than 100 indicating a decrease in the value concerned, and conversely, a result greater than 100, will indicate an increase in the value concerned

D) Dynamic properties (after cooking)

The dynamic properties G * and tan (ô) max are measured on a viscoanalyzer (Metravib V A4000), according to standard ASTM D 5992 - 96. The response of a sample of vulcanized composition is recorded (cylindrical test tube of 4 mm thickness and 400 mm ² in cross section), subjected to a sinusoidal stress in alternating single shear, at the frequency of 10 Hz, under normal temperature conditions according to standard ASTM D 1349 - 99. A sweep is carried out in peak deformation amplitude at peak from 0.1 to 50% (outward cycle), then from 50% to 0.1% (return cycle). The exploited result is the loss factor, tan (ô). For the return cycle, the maximum observed tan (ô) value (tan (ô) max) is indicated. The tan (ô) max values given below are measured at 60 ° C.

For more readability the results will be indicated in base 100, the value 100 being attributed to the witness. A result less than 100 indicating a decrease in the value concerned, and conversely, a result greater than 100, will indicate an increase in the value concerned.

E) Initial plasticity index (Wallace plasticity)

A disc-shaped test piece is compressed between the parallel plates of a plastimeter, so as to reach a fixed thickness of 1 millimeter. The test piece is thus held for 15 seconds to reach an equilibrium temperature close to that of the plates. It is then subjected to a constant compressive force of 100 N for 15 seconds. The final thickness of the test piece (in hundredths of a mm) is considered a measure of plasticity.

Preparation of test pieces:

The spacing of the mixer cylinders should be adjusted so as to obtain a sheet with a final thickness of approximately 1.7 mm.

Take a test sample and pass it twice (by folding the sheet between passages) between the cylinders of a mixer

Immediately fold the sheet obtained.

Using the cookie cutter, cut three pellets from the folded sheet with a thickness between 3.0 mm and 3.8 mm.

After cooling the pellets for 30 minutes, the plasticity measurement must be carried out within a period not exceeding 4 hours.

The initial plasticity index (PO) is the median value of the measurements obtained with the three test pieces analyzed.

It - Detailed description

The rubber compositions according to the invention are based on at least:

- an elastomeric matrix comprising natural rubber,

- a reinforcing filler,

- a crosslinking system, as described in detail below.

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are percentages by mass.

On the other hand, any range of values designated by the expression between a and b represents the range of values going from more than a to less than b (i.e. limits a and b excluded) while any range of values designated by the expression from a to b signifies the range of values going from a to b (that is to say including the strict limits a and b).

The expression “composition based on” is intended to mean a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents being capable of, or intended to react with each other, at least in part , during the various stages of manufacturing rubber compositions, belts and tires, in particular during their vulcanization.

Furthermore, the term "pce" means within the meaning of the invention, part by weight per hundred parts of total elastomer.

By “natural rubber with bimodal molecular weight distribution” is meant, within the meaning of the invention, a natural rubber having a molecular weight distribution, seen in SEC-MALS, bimodal. It could also be called "bimodal natural rubber".

By “natural rubber with a unimodal molecular weight distribution” is meant, within the meaning of the invention, a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal. It can also be called "unimodal natural rubber".

By "initial plasticity" is meant, within the meaning of the invention, the Wallace plasticity of natural rubber, as measured by the protocol according to the invention.

By "cutting" is meant, within the meaning of the invention, the mixture of natural rubber with bimodal molecular weight distribution and natural rubber with unimodal molecular weight distribution having, in addition, an initial plasticity index of less than 20.

11-1. Diene elastomer

Natural rubber (NR: Natural Rubber)

The invention is characterized by the use in cutting of natural rubbers selected according to their molecular weight distribution. This distribution of molecular weights is observed by SEC-MALS chromatography.

In order to more easily discriminate natural rubbers having a unimodal or bimodal molecular mass distribution, a first derivative was applied at every point of the signal RI (refractive index) in a step of 24 points. The derivative exacerbates the slope changes of the RI signal. Thus during a linear evolution, the derivative will be constant and during a break in slope (change of population) the derivative is reversed.

The presence of several populations in the mass distribution is characterized by peaks on the graph of the first derivative.

Within the meaning of the present invention, a natural rubber has a bimodal molecular mass distribution when on the graph of the first derivative of the refractive index signal, obtained during SEC-MALS chromatography, two distinct peaks are observed. Each peak includes an ascending slope, a peak and a descending slope. In Figure 1, the space between the start of the upward slope and the end of the downward slope of each peak is indicated by a double arrow.

Natural rubber having a bimodal molecular weight distribution can be obtained from a latex obtained by natural coagulation or by chemical coagulation, in particular acid coagulation, for example with acetic acid.

The latex can be, in particular and without limitation, provided that the distribution is bimodal within the meaning of the invention, derived from harvests of the following varieties of Hevea brasiliensis: RRIM600, GT1, CDC429, PR107 ...

Within the meaning of the present invention, a natural rubber has a unimodal molecular mass distribution when, on the graph of the first derivative of the refractive index signal, obtained during SEC-MALS chromatography, a single distinct peak is observed.

Natural rubber having a unimodal molecular mass distribution can be obtained from a latex obtained by natural coagulation or by chemical coagulation, in particular acid coagulation, for example with acetic acid.

The latex can be, in particular and in a nonlimiting manner, provided that the distribution is unimodal within the meaning of the invention, resulting from the harvests of the following varieties of Hevea brasiliensis: PB217, CDC312, ...

In the composition, the natural rubber is a blend comprising from 20% to 90% by weight, advantageously from 30% to 90% by weight, more advantageously from 30% to 70% by weight, more advantageously from 40% to 60% by weight. weight, even more advantageously ίο

50% by weight, relative to the total weight of the blend, of natural rubber having a molecular weight distribution, seen in SEC-MALS, bimodal.

In the composition, the natural rubber is a blend comprising from 10% to 80% by weight, advantageously from 10% to 70% by weight, more advantageously from 30% to 70% by weight, more advantageously from 40% to 60% by weight. weight, even more advantageously 50% by weight, relative to the total weight of the cut, of natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal and having an initial plasticity index less than 20.

The use of a bimodal natural rubber will make it possible to confer good raw properties on a rubber composition comprising it. It seems that a bimodal natural rubber content of 20% by weight, relative to the total weight of the cut, is sufficient for the final rubber composition to have improved raw straightening properties, compared to the control which is a gum plasticized comprising a natural rubber resulting from a mixture of several latexes not specifically selected.

The use of a unimodal natural rubber, further having an initial plasticity index of less than 20, will make it possible to confer good processability properties, seen in particular through Mooney, on a rubber composition comprising it.

In a surprising and very interesting way, the cutting of these two selected rubbers will make it possible to combine the respective effects of each of these rubbers and thus to obtain a compromise between the processability and the raw properties. A plasticized rubber, T0, comprising a natural rubber resulting from a mixture of several latexes not specifically selected. This natural rubber has previously undergone a plasticization step, the plasticization consisting of mechanical work of the material allowing a reduction in its viscosity.

Depending on the compromise sought, the skilled person will then vary the respective proportions between the two selected natural rubbers.

It has been found that only a unimodal natural rubber having an initial plasticity index of less than 20 makes it possible to improve the processability, seen through Mooney, of a composition comprising it. The initial plasticity index of unimodal natural rubber is n

advantageously less than 15. The initial plasticity index of unimodal natural rubber is advantageously between 5 and 20, more advantageously between 5 and 15.

In addition to natural rubber, the compositions of the invention may contain diene elastomers, advantageously other than isoprenics, preferably in the minority by weight (i.e., for less than 50 phr). Natural rubber as described above more preferably represents 60 to 100% by weight of the total diene elastomers, ie 60 to 100 phr (phr = parts by weight per hundred parts of elastomer).

Natural rubber as described above is preferably used alone, that is to say without mixing with another diene or polymer elastomer.

Other diene elastomer

The term “elastomer or diene rubber” generally means an elastomer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

In the present context, this other elastomer is not a natural rubber.

Diene elastomers, in a known manner, can be classified into two categories: those called essentially unsaturated and those called essentially saturated. The term “essentially unsaturated diene elastomer” is understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of units or units of diene origin (conjugated dienes) which is greater than 15% (mol%). Thus, for example, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within this definition and can on the contrary be qualified as essentially saturated diene elastomers ( rate of motifs of diene origin low or very low, always less than 15%). In the category of essentially unsaturated diene elastomers, the term “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%.

These definitions being given, the term “diene elastomer capable of being used in the compositions in accordance with the invention” more particularly means:

(a) - any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b) - any copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

(c) - a ternary copolymer obtained by copolymerization of ethylene, of an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having of 6 to 12 carbon atoms, such as for example the elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene;

(d) - a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated, in particular chlorinated or brominated, versions of this type of copolymer.

Although it applies to any type of diene elastomer, a person skilled in the art of tires will understand that the present invention is preferably implemented with essentially unsaturated diene elastomers, in particular of the type (a) or (b ) above.

More preferably, the diene elastomer is chosen from the group consisting of polybutadienes (BR), synthetic polyisoprenes (IR), the different butadiene copolymers, the different isoprene copolymers, and the mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), whether the latter are prepared by emulsion polymerization (ESBR) as in solution (SSBR), isoprene butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprenebutadiene-styrene copolymers (SBIR).

Among the polybutadienes, particularly suitable are those having a content (molar%) in units -1,2 of between 4% and 80% or those having a content (molar%) of cis-1,4 greater than 80%. Among the synthetic polyisoprenes, the cis-1,4-polyisoprenes are particularly suitable, preferably those having a rate (molar%) of cis-1,4 bonds greater than 90%. Among the butadiene or isoprene copolymers, we mean in particular the copolymers obtained by copolymerization of at least one of these two monomers with one or more vinyl-aromatic compounds having from 8 to 20 carbon atoms. Suitable vinyl-aromatic compounds are, for example, styrene, ortho-, meta-, paramethylstyrene, the commercial vinyl-toluene mixture, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene, vinylnaphthalene. The copolymers can contain between 99% and 20% of diene units and between 1% and 80% of vinyl-aromatic units.

It is possible to use an isoprene elastomer other than natural rubber, that is to say an isoprene homopolymer or copolymer, in other words a diene elastomer chosen from the group consisting of synthetic polyisoprenes (IR), different isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will in particular be made of isobutene-isoprene (butyl rubber IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers ( SBIR). The synthetic polyisoprene is preferably of the cis-1,4 type. Among these synthetic polyisoprenes, polyisoprenes are preferably used having a rate (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%.

As diene elastomers other than isoprene, mention will be made in particular of any diene elastomer of the unsaturated type chosen in particular from the group consisting of polybutadienes (BR), in particular the cis-1,4 or 1,2-syndiotactic polybutadienes and those having a content (mol%) in units of 1.2 between 4% and 80%, and butadiene copolymers, in particular styrene-butadiene copolymers (SBR), and in particular those having a styrene content between 5 and 50% by weight and more particularly between 20% and 40% by weight, a content (molar%) of bonds -1,2 of the butadiene part of between 4% and 65%, a content (molar%) of bonds trans-1,4 between 30% and 80%, styrene-butadiene-isoprene copolymers (SBIR), and mixtures of these different elastomers (BR, SBR and SBIR).

The compositions of the invention may contain:

a mixture of natural rubbers as described above as sole diene elastomers, or a mixture of natural rubbers as described above, and at least one other diene elastomer, the diene elastomer (s) being able to be used in combination with any type synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.

11.2. Reinforcing filler:

The composition of the invention comprises any type of so-called reinforcing filler, known for its capacity to reinforce a rubber composition which can be used for the manufacture of tires, for example an organic filler such as carbon black, an inorganic reinforcing filler such as silica with which a coupling agent is associated in known manner, or else a mixture of these two types of filler.

Such a reinforcing filler typically consists of nanoparticles whose average size (by mass) is less than a micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

As carbon blacks, all carbon blacks are suitable, in particular the blacks conventionally used in tires or their treads (so-called pneumatic grade blacks). Among the latter, there may be mentioned more particularly the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM grades), such as, for example, the blacks N115, N134, N234, N326, N330. , N339, N347, N375, N550, N683, N772. These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a support for some of the rubber additives used.

By reinforcing inorganic filler, should be understood here any inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also called white filler, clear filler or even non-black filler as opposed to carbon black, capable of reinforcing on its own, without other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words capable of replacing, in its reinforcement function, a conventional carbon black pneumatic grade; such a charge is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) on its surface.

As reinforcing inorganic fillers, in particular mineral fillers of the siliceous type, preferably silica (SiO ₂ ), are suitable. The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface, both less than 450 m ² / g, preferably from 30 to 400 m ² / g, especially between 60 and

300 m ² / g. As highly dispersible precipitated silicas (known as HDS), mention may be made, for example, of “Ultrasil” 7000 and “Ultrasil” 7005 from Degussa, “Zeosil” 1165MP, 1135MP and 1115MP from Rhodia, and “ Hi-Sil ”EZ150G from the company PPG, the silicas“ Zeopol ”8715, 8745 and 8755 from the company Huber, the silicas with a high specific surface as described in application WO 03/016387.

By way of reinforcing inorganic filler, mention will also be made of mineral fillers of the aluminous type, in particular alumina (AI ₂ O ₃ ) or aluminum (oxide) hydroxides, or also reinforcing titanium oxides, for example described in US 6,610,261 and US 6,747,087.

The physical state under which the reinforcing inorganic filler is present is immaterial, whether in the form of powder, microbeads, granules, or even beads. Of course, the term reinforcing inorganic filler is also understood to mean mixtures of various reinforcing inorganic fillers, in particular highly dispersible silicas as described above.

Those skilled in the art will understand that, as an equivalent charge of the reinforcing inorganic charge described in this paragraph, a reinforcing charge of another nature, in particular organic such as carbon black, could be used, since this charge reinforcing would be covered with an inorganic layer such as silica, or would have on its surface functional sites, in particular hydroxylated, requiring the use of a coupling agent to establish the connection between the filler and the elastomer. By way of example, there may be mentioned carbon blacks for tires as described for example in patent documents WO 96/37547,

WO 99/28380.

In the present description, the BET specific surface is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in The Journal of the American Chemical Society Vol. 60, page 309, February 1938, more precisely according to French standard NF ISO 9277 of December 1996 (multi-point volumetric method (5 points) - gas: nitrogen - degassing: hour at 160 ° C - relative pressure range p / in: 0.05 at 0.17). The CTAB specific surface is the external surface determined according to French standard NF T 45-007 of November 1987 (method B).

Preferably, the rate of total reinforcing filler is between 30 and 100 phr. Below 30 phr, the reinforcement of the rubber composition is insufficient to provide an adequate level of cohesion or resistance to wear of the rubber component of the tire comprising this composition. Even more preferably, the rate of total reinforcing filler is at least 40 phr. Beyond 100 phr, there is a risk of an increase in hysteresis and therefore in the rolling resistance of the tires. For this reason, the rate of total reinforcing filler is preferably in a range from 40 to 80 phr, in particular for use in a carcass ply and a tire crown ply.

Carbon black advantageously represents more than 50% by mass of the reinforcing filler. In particular, the reinforcing filler is advantageously carbon black (100% by mass).

To couple the reinforcing inorganic filler to the diene elastomer, use is made in a well known manner of a coupling agent (or binding agent) at least bifunctional intended to ensure a sufficient connection, chemical and / or physical, between the inorganic filler (surface of its particles) and the diene elastomer. In particular organosilanes or polyorganosiloxanes which are at least bifunctional are used.

Use is made in particular of polysulphurized silanes, said to be symmetrical or asymmetrical according to their particular structure, as described for example in applications W003 / 002648 (or US 2005/016651) and W003 / 002649 (or US 2005/016650).

By way of examples of polysulphurized silanes, mention will be made more particularly of the polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis- ((C ₁ -C ₄ ) alkoxyl (C ₁ -C ₄ ) silylalky ^ CrC ^), such as for example the bis (3-trimethoxysilylpropyl) or bis (3triethoxysilylpropyl) polysulphides. Among these compounds, use is made in particular of bis (3triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, of formula [(C ₂ H ₅ O) ₃ Si (CH2) 3S2] 2 or bis- (triethoxysilylpropyl disulfide), abbreviated TESPD, of formula [(C ₂ H ₅ O) ₃ Si (CH ₂ ) 3S] 2. Mention will also be made, as preferred examples, of the polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis- (monoalkoxyl (C ₁ -C ₄ ) -dialkyl (C ₁ -C ₄ ) silylpropyl), more particularly bis- tetrasulphide monoethoxydimethylsilylpropyl as described in the aforementioned patent application WO 02/083782 (or US 7,217,751).

By way of example of coupling agents other than a polysulphurized alkoxysilane, mention may in particular be made of bifunctional POSs (polyorganosiloxanes) or also polysulphides of hydroxysilane (R ² = OH in formula I above) as described by example in patent applications WO 02/30939 (or US 6,774,255), WO 02/31041 (or US 2004/051210), and WO2007 / 061550, or also silanes or POS carrying azo-dicarbonyl functional groups, such as described for example in patent applications WO 2006/125532, WO 2006/125533, WO 2006/125534.

By way of examples of other sulphidic silanes, mention will be made of silanes carrying at least one thiol (-SH) function (called mercaptosilanes) and / or at least one blocked thiol function, as described for example in US Patents or Patent Applications 6,849,754, WO 99/09036, WO 2006/023815, WO 2007/098080, WO 2010/072685 and WO 2008/055986.

Of course, mixtures of the coupling agents previously described could also be used, as described in particular in the aforementioned application WO 2006/125534.

The content of coupling agent is advantageously less than 20 phr, it being understood that it is generally desirable to use as little as possible. Typically the level of coupling agent represents from 0.5% to 15% by weight relative to the amount of inorganic filler. Its rate is preferably between 0.5 and 12 phr, more preferably in a range ranging from 3 to 10 phr. This level is easily adjusted by a person skilled in the art according to the level of inorganic filler used in the composition.

II.3. Miscellaneous additives:

The rubber compositions in accordance with the invention may also contain coupling activators, agents for recovery of inorganic fillers or more generally agents for aid in use which are capable, in known manner, by virtue of an improvement in the dispersion of the load in the rubber matrix and a lowering of the viscosity of the compositions, of improving their ability to be used in the raw state, these agents being for example hydrolysable silanes such as alkylalkoxysilanes, polyols, polyethers , primary, secondary or tertiary amines, hydroxylated or hydrolyzable polyorganosiloxanes.

The rubber compositions in accordance with the invention may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tires, such as for example pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, reinforcing or plasticizing resins, acceptors (for example phenol novolak resin) or methylene donors (for example HMT or H3M) as described for example in the application WO 02/10269, adhesion promoters such as cobalt-based compounds, plasticizers, preferably non-aromatic or very weakly aromatic, chosen from the group consisting of naphthenic, paraffinic oils, MES oils, TDAE oils, plasticizers ethers, plasticizers esters, hydrocarbon resins having a high Tg, preferably greater than 30 ° C, as described for example in applications WO 2005/087859, WO 2006/061064 and WO 2007/017060, and mixtures of such compounds.

The crosslinking system is preferably a vulcanization system based on sulfur and an accelerator. Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used, in particular those chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated to MBTS), N-cyclohexyl-2-benzothiazyl sulfenamide ( abbreviated CBS), N, Ndicyclohexyl- 2-benzothiazyle sulfenamide (abbreviated DCBS), N-ter-butyl-2-benzothiazyle sulfenamide (abbreviated TBBS), N-ter-butyl-2-benzothiazyl sulfenimide (abbreviated TBSI) and mixtures of these compounds. Preferably, a primary accelerator of the sulfenamide type is used.

To this vulcanization system are added, incorporated during the first non-productive phase and / or during the productive phase, of the process described below, various secondary accelerators or known vulcanization activators such as zinc oxide , stearic acid, guanidic derivatives (in particular diphenylguanidine), etc. In the case of use of the composition of the invention as a tire tread, the sulfur level is for example between 0.5 and 3.0 phr, that of the primary accelerator between 0.5 and 5.0 pc.

11.4. Manufacture of rubber composition:

Natural rubbers are first selected. So, we select

a) a natural rubber having a molecular weight distribution, seen in SEC-MALS, bimodal;

b) a natural rubber having a molecular mass distribution, seen in SEC-MALS, unimodal and an initial plasticity index less than 20;

Advantageously, the rubbers of stages a) and b) are intended to be then used in cutting in mass proportions, rubber of stage a): rubber of stage b) going from 90:10 to 20:80, advantageously going from 90:10 to 30:70, more advantageously going from 70: 30 to 30: 70, even more advantageously going from 60: 40 to 40: 60, even more advantageously from 50: 50.

Advantageously, the rubbers of stages a) and b) do not undergo subsequent plasticization; plasticization consisting of mechanical work of the matrix allowing a reduction in its viscosity.

Then, the rubber composition according to the invention based on at least one elastomeric matrix comprising the rubbers of steps a) and b), a reinforcing filler is produced in suitable mixers, using two successive well-known preparation phases. skilled in the art: a first working phase or thermomechanical kneading (so-called "non-productive" phase) at high temperature, up to a maximum temperature between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, followed by a second mechanical working phase (so-called "productive" phase) to a lower temperature, typically below 110 ° C, for example between 40 ° C and 100 ° C, finishing phase during which the crosslinking system is incorporated.

The process for preparing the rubber composition according to the invention comprises the following steps:

i. incorporating into the elastomeric matrix comprising the rubbers of steps a) and b), during a first so-called non-productive step, the reinforcing filler, as well as the other ingredients of the composition with the exception of the crosslinking system by thermomechanically kneading all until reaching a maximum temperature of between 110 and 190 ° C;

ii. cool the assembly to a temperature below 100 ° C;

iii. then incorporate, in a second so-called productive stage, a crosslinking system;

iv. knead everything up to a maximum temperature below 110 ° C.

The final composition thus obtained can then be calendered, for example in the form of a sheet, a plate or even extruded, for example to form a rubber profile used for the manufacture of a semi-finished product for tire, such as treads, plies or other bands, under-layers, various rubber blocks, whether or not reinforced with textile or metallic reinforcements, intended to form part of the structure of the tire, in particular its tread.

The vulcanization (or baking) can then be carried out in a known manner at a temperature generally between 130 ° C and 200 ° C, preferably under pressure, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the baking temperature, the vulcanization system adopted and the vulcanization kinetics of the composition considered.

The invention relates to the rubber compositions previously described both in the so-called raw state (i.e. before curing) and in the so-called cooked or vulcanized state (i.e. after vulcanization).

The invention also relates to a rubber component comprising a reinforced rubber composition according to the invention.

The invention also relates to a tire of which at least one of its constituent elements is a rubber component comprising a reinforced rubber composition according to the invention.

EXAMPLES

In the examples which follow, natural rubber is obtained after coagulation of the latex (chemical or natural coagulation). The coagulums are dried for 3 hours at approximately 120 ° C.

Characterization of gums:

Natural rubbers have been characterized by SEC MALS. A first derivative was applied at every point of the signal RI (refractive index) on a step of 24 points in order to discriminate the distribution of molecular masses. This derivative exacerbates changes in slopes. Thus during a linear evolution, the derivative will be constant and during a break in slope (change of population) the derivative is reversed.

Natural rubbers from the varieties RRIM600, PR107, CDC429 have a molecular weight distribution, seen in SEC-MALS, bimodal. The molecular weight distribution for natural rubber from the RRIM600 variety is shown in Figure 1.

Natural rubbers from varieties PB217, PB235, CDC312 have a molecular weight distribution, seen in SEC-MALS, unimodal. The molecular mass distribution for natural rubber from the PB217 variety is shown in Figure 2.

The natural rubbers used in the examples have not undergone a prior plasticization step.

EXAMPLE 1:

Preparation of the compositions:

As control T0.1, a plasticized gum comprising a natural rubber resulting from a mixture of several latexes not specifically selected is used. This natural rubber has previously undergone a plasticization step, the plasticization consisting of mechanical work of the material allowing a reduction in its viscosity.

The compositions are given in the following table. The quantities are expressed in parts per 100 parts of elastomer (phr).

Composition T0.1 T3 T1.1 T1.2 C1 NR1 (1) 100 - - - - NR2 (2) - 100 - - - NR3 (3) - - 100 0 50 NR4 (4) - - 0 100 50 N234 (5) 48 48 48 48 48 6PPD (6) 2 2 2 2 2 Paraffin 1 1 1 1 1 TMQ (7) 1 1 1 1 1 ZnO (8) 2.7 2.7 2.7 2.7 2.7 SAD (9) 2.5 2.5 2.5 2.5 2.5 CBS (10) 1.1 1.1 1.1 1.1 1.1 Sulfur 1.1 1.1 1.1 1.1 1.1

Table 1 (1) NR1: natural rubber resulting from a mixture of several latexes. This NR underwent a stage of plasticization by mechanical treatment.

(2) NR2: Natural rubber from the variety PB235 having a molecular weight distribution, seen in SEC-MALS, unimodal, and an initial plasticity index, PO, of 37 (3) (4) (5) (6) (7) (8) (9) (10)

NR3: Natural rubber from the variety PB217 having a molecular weight distribution, seen in SEC-MALS, unimodal, and an initial plasticity index, PO, of 12

NR4: Natural rubber from the variety RRIM600 having a molecular weight distribution, seen in SEC-MALS, bimodal Carbon black N234

6PPD: N- (1,3-dimethylbutyl) -N’-phenyl-p-phenylenediamine: antioxidant TMQ: 2,2,4-trimethy 1-1,2-dihydroquinoline ZnO: Zinc Oxide

SAD: Stearic Acid

N-cyclohexyl-2-benzothiazyl-sulfenamide ("Santocure CBS" from the company Flexsys)

In an internal mixer, whose initial tank temperature is around 80 ° C, the elastomeric matrices (the selected natural rubbers) are introduced. After one minute of mixing, all of the other compounds are introduced.

At 115 ° C and 135 ° C, we use a pestle to bring chaos to the mixture (improves the homogeneity of the mixture). The mixture thus obtained is recovered at a "drop" temperature of 165 ° C. after a total mixing time of approximately five minutes.

This mixture is cooled on an external mixer to room temperature. The vulcanization system is incorporated into the mixture with the cylinder tool. These compositions are then calendered in the form of plates (thickness of 2 to 3 mm) for the measurement of their properties.

Characterization tests - Results

A. Mooney

The processability of the compositions comprising natural rubbers having a molecular weight distribution, seen in SEC-MALS, unimodal, and different initial plasticities was seen through the Mooney measurement. Such a measurement was also carried out for a composition comprising a blend of natural rubbers selected according to the invention. The results are reported in the following table:

Composition T0.1 T3 T1.1 T1.2 C1 Initial plasticity, PO - 37 12 30 - Mooney 100 112 76 113 95

Table 2

It is found that a composition comprising as natural rubber a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal, and a plasticity index less than 20 (T1.1) makes it possible to obtain a level of processability, seen through the Mooney, improved compared to the witness.

On the contrary, for a composition comprising as natural rubber a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal, and an initial plasticity index, PO, of 37 (T3) or for a composition comprising as natural rubber a natural rubber having a molecular mass distribution, seen in SEC-MALS, bimodal (T1.2), no improvement is observed, on the contrary a degradation is noted.

A composition comprising a blend according to the invention (C1) retains an improvement in processability, seen through the Mooney.

B. properties of the compositions according to the invention

Composition T0.1 T1.1 T1.2 C1 Mooney 100 76 113 95 Elongation Average break 100 105 93 96 Rupture stress 100 84 179 143 AG (G * 0.1% -G * 50%) MPa at 60 ° C 100 100 102 84 Tan (ô) max at 60 ° C 100 105 97 96 G * 50% at 60 ° C 100 96 102 95

Table 3

The mixture of the composition C1 makes it possible to obtain a level of processability, seen through the Mooney, almost identical to that observed with a mixture of the composition TO containing a plasticized gum.

The mixture of composition C1 makes it possible to obtain a bare reinforcement level, seen through the breaking stress very much improved compared to the plasticized rubber without penalizing the elongation.

The mixture of the composition C1 makes it possible to obtain a level of hysteresis, seen through 5 of AG * (G * 0.1% -G * 50%) and of tan (ô) a max, improved compared to the plasticized gum without marked penalty for stiffness seen through G * 50%.

EXAMPLE 2:

In this other example, the respective amounts of the selected natural rubbers were varied.

Preparation of the compositions:

As a control T0.2, a plasticized gum comprising a natural rubber resulting from a mixture of several unselected latexes is used specifically. This natural rubber has previously undergone a plasticization step, the plasticization consisting of mechanical work of the material allowing a reduction of its viscosity.

The compositions are given in the following table. The quantities are expressed in parts per 100 parts of elastomer (phr).

Composition T0.2 T2.1 T2.2 C2.1 C2.2 C2.3 NR1 (1) 100 - - - - - NR2.2 (2) - 100 0 75 50 25 NR2.3 (3) - 0 100 25 50 75 N234 (4) 48 48 48 48 48 48 6PPD (5) 2 2 2 2 2 2 Paraffin 1 1 1 1 1 1 TMQ (6) 1 1 1 1 1 1 ZnO (7) 2.7 2.7 2.7 2.7 2.7 2.7 SAD (8) 2.5 2.5 2.5 2.5 2.5 2.5 CBS (9) 1.1 1.1 1.1 1.1 1.1 1.1 Sulfur 1.1 1.1 1.1 1.1 1.1 1.1

Table 4 (1) (2) (3) (4) (5) (6) (7) (8) (9)

NR1: natural rubber resulting from a mixture of several latexes. This NR underwent a stage of plasticization by mechanical treatment.

NR2.2: Natural rubber from the variety CDC312 with a molecular weight distribution, seen in SEC-MALS, unimodal NR2.3: Natural rubber from the variety CDC429 with a molecular weight distribution, seen in SEC-MALS, bimodal Carbon black N234

6PPD: N- (1,3-dimethylbutyl) -N’-phenyl-p-phenylenediamine: antioxidant TMQ: 2,2,4-trimethy 1-1,2-dihydroquinoline ZnO: Zinc Oxide

SAD: Stearic Acid

N-cyclohexyl-2-benzothiazyl-sulfenamide ("Santocure CBS" from the company Flexsys)

In an internal mixer, whose initial tank temperature is around 80 ° C, the elastomeric matrices (the selected natural rubbers) are introduced. After one minute of mixing, all of the other compounds are introduced.

At 115 ° C and 135 ° C, we use a pestle to bring chaos to the mixture (improves the homogeneity of the mixture). The mixture thus obtained is recovered at a "drop" temperature of 165 ° C. after a total mixing time of approximately five minutes.

This mixture is cooled on an external mixer to room temperature. The vulcanization system is incorporated into the mixture with the cylinder tool. These compositions are then calendered in the form of plates (thickness of 2 to 3 mm) for the measurement of their properties.

Characterization tests - Results

Composition T0.2 T2.1 T2.2 C2.1 C2.2 C2.3 Raw properties (base 100 p / r Witness) Mooney 100 112 144 113 124 125 Curve Force Raw elongation at 23 ° C (based on 100 p / r Control) Elongation Break way 100 102 99 104 95 92 Rupture stress 100 107 237 124 161 184 Dynamic properties as a function of deformation (base 100 p / r Witness) Tan (ô) max at 60 ° C 100 99 86 93 95 89 G * 50% at 60 ° C 100 98 94 98 100 98 Tab water 5

By varying the respective proportions in each of the rubbers selected, priority is given to either the processability or the raw straightening properties.

Bibliography (1) Subramaniam [1972] Gel Perméation Chromatography of Natural Rubber. Rubber 10 Chemistry and Technology. 346-358 (2) Subramaniam, A. (1993). Characterization of natural rubber. in Int Rubb Technol Conf, pp. 18.

(3) Liengprayoon, S. (2008). Characterization of lipid composition of sheet rubber from Hevea brasiliensis and relations with its structure and properties, These Kasetsart university &

Montpellier Supagro, Montpellier - 206 p ² θ

Claims (14)

1. Rubber composition based on at least: a) an elastomeric matrix comprising natural rubber, b) a reinforcing filler, c) a crosslinking system, characterized in that said natural rubber is a blend (i) of natural rubber having a molecular weight distribution, seen in SECMALS, bimodal and (ii) of a natural rubber having a distribution of molecular masses, seen in SEC-MALS, unimodal, and having an initial plasticity index less than 20, in mass proportions (i): (ii) ranging from 90: 10 to 20: 80. 2. A rubber composition according to claim 1, characterized in that the mass ratio (i): (ii) ranges from 70: 30 to 30: 70. 3. A rubber composition according to claim 1 or 2, characterized in that it comprises between 30 and 100 phr of reinforcing filler. 4. A rubber composition according to any one of the preceding claims, characterized in that the reinforcing filler comprises a carbon black or an inorganic reinforcing filler or a blend of these fillers. 5. Rubber composition according to any one of the preceding claims, characterized in that the carbon black represents more than 50% by mass of the reinforcing filler 6. A rubber composition according to any one of the preceding claims, characterized in that the reinforcing filler comprises a reinforcing inorganic filler, in particular a silica, and in that the composition comprises a coupling agent. 7. A rubber composition according to any one of claims 1 to 4, characterized in that the reinforcing filler is carbon black. 8. Composition according to any one of the preceding claims, characterized in that the elastomeric matrix comprises another diene elastomer. 9. Composition according to any one of the preceding claims, characterized in that the elastomeric matrix comprises more than 50 phr of natural rubber, advantageously 100 phr. 10. Process for the preparation of a rubber composition according to any one of the preceding claims, characterized in that it comprises the following steps: a) select a natural rubber having a molecular weight distribution, seen in SEC-MALS, bimodal; b) select a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal and having an initial plasticity index, PO, less than 20; c) incorporate into the elastomeric matrix, comprising a mixture of the natural rubbers selected in stages a) and b), in a rubber mass ratio of stage a): rubber of stage b) ranging from 90: 10 to 20: 80, during a first so-called non-productive step, the other ingredients of the composition, with the exception of the crosslinking system by thermomechanically kneading everything until a maximum temperature of between 110 and 190 ° C is reached; d) cool the assembly to a temperature below 100 ° C; e) then incorporate, during a second so-called productive stage, a crosslinking system; f) knead everything up to a maximum temperature below 110 ° C. 11. Tire component comprising a composition according to any one of claims 1 to 9. 12. Tire component according to claim 11, further comprising wire reinforcement elements. 5 13. Component according to claim 11 or 12, characterized in that said component is chosen from the carcass ply and the crown plies. 14. A tire comprising a component according to any one of claims 11 to 13. 0.04 0.03 0.02 0.01 -0.01 1/1 2 well identified populations -0.02