WO2018007768A1 - Rubber composition comprising a blend of natural rubbers having a molecular mass distribution, determined by sec-mals, that is respectively unimodal or bimodal, method for preparing same and tyre component - Google Patents

Abstract

The invention concerns a rubber composition made from at least: ─an elastomer matrix comprising natural rubber, ─a reinforcing filler, ─a crosslinking system, characterised in that said natural rubber is a blend (i) of a natural rubber having a molecular mass distribution, determined by SEC-MALS, that is bimodal and (ii) a natural rubber having a molecular mass distribution, determined by SEC-MALS, that is unimodal and having an initial plasticity index, P0, of less than 20, in weight proportions ranging from 90:10 to 20:80. The invention also concerns a method for preparing such a composition, a tyre component comprising same and a tyre comprising said component.

Description

 Rubber composition comprising a cut of natural rubbers having a molecular weight distribution, seen in SEC-MALS, respectively unimodal or bimodal, process for preparation and tire component The present invention relates to a rubber composition in which the natural rubbers are selected according to their molecular weight distribution.

 Natural rubber is an elastomer very widely used in the field of pneumatics because of its remarkable properties. For example, it is used in rubber compositions for the manufacture of semi-finished for vehicles carrying heavy loads, because of the compromise of performance that it can bring to the tire.

 The natural rubber used as elastomer in the rubber compositions comes from the rubbery dry material of the natural rubber latex, extracted from Hevea brasiliensis.

Molecular weight 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 weight distribution (MDD) of fresh natural rubber (NR) latex in SEC. The DMM of NR, seen through chromatography, is described as 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 at the height of the peak in the region of high molecular weights.

Type 2: distinct bimodal distribution with a peak in the region of low molecular weights whose height is at least two times smaller at the height of the peak in the high molecular weight region.

Type 3: unimodal distribution The study of the molecular weight distribution of natural rubber (Ribbed Smoked Sheet) of different varieties confirms a distinction of the molecular weight distribution.

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

 Natural polyisoprene, also called natural rubber, is obtained from rubber latex from the rubber groove. The coagulation of the latex may be a so-called "natural" coagulation (coagulation of the latex in the bleeding cup mainly due to the naturally occurring microbial activity) or so-called "artificial" coagulation, for example "chemical" by addition of acid or of salts.

In rubber, particularly for the preparation of tires, the natural rubber used is derived from a mixture of several coagulated latices, originating from several parcels of trees, without specifying their profile or their distribution of molecular masses.

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

 The strong raw recovery (increased stress at high elongations) may result in a higher potential for crystallization under tension and therefore an improvement in the performance of the composition in stations such as carcass plies (holding or maintaining distance of the wires 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 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 (i): (ii) ranging from 90 Å to 20:80.

 Advantageously, said natural rubber is a blend (i) of 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 initial plasticity index, PO, of less than 20, in mass proportions (i): (ii) ranging from 90: 10 to 30: 70, more preferably from 70:30 to 30:70, more preferably from 60:40 to 40:60, more preferably from 50:50.

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

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

 When containing a reinforcing inorganic filler, the rubber composition also comprises a coupling agent.

 In particular, the reinforcing inorganic filler is a silica.

 In particular, the reinforcing filler is carbon black.

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

The invention also relates to a method 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) selecting a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal and having an index of initial plasticity, PO, less than 20; incorporating into the elastomeric matrix, comprising a mixture of the natural rubbers selected in steps a) and b), in a rubber mass ratio of step a): rubber of step b) ranging from 90:10 to 20:80, during a so-called non-productive first step, the other ingredients of the composition, with the exception of the crosslinking system, thermomechanically kneading the whole until a maximum temperature of between 1 and 190 ° C is reached;

 cool the assembly to a temperature below 100 ° C;

 then incorporate, during a second so-called productive step, a crosslinking system;

 knead everything to a maximum temperature below 1 10 ° C

The invention also relates to a tire component comprising a composition according to the invention, advantageously further comprising wire 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.

The invention also relates to the use of natural rubber having a molecular weight distribution, seen in SEC-MALS, bimodal, and natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal and having a subscript of initial plasticity, P0, less than 20, in cutting to improve the processability, the green properties, the hysteresis of a rubber composition, without deterioration of rigidity. Such a rubber composition is then particularly suitable for use in a tire component comprising said rubber composition and wire reinforcing elements.

DESCRIPTION OF THE FIGURES

Figure 1): first derivative of the refractive index signal (broken line), obtained during SEC-MALS chromatography of RRIM600 natural rubber Figure 2): first derivative of the refractive index signal (broken line), obtained during SEC-MALS chromatography of 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 sieve of 1 μηι, was injected into columns of the SEC MALS (Steric Exclusion Chromatography + Multiangle Light Scanning Detector) according to the protocol described by Kim (2009) ³ (Kim, Chandy, Sainte-Beuve , Jerome, 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. 2249 -2259).

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

B) Mooney plasticity (before cooking):

An oscillating consistometer is used as described in the French standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the composition in the green state (ie, before firing) is molded in a cylindrical chamber heated to 100 ° C. After one minute of preheating, the rotor rotates within the test tube at 2 revolutions / minute and the useful torque is measured to maintain this movement after 4 minutes of rotation. Mooney plasticity (ML 1 +4) is expressed in "Mooney unit" (UM, with 1 UM = 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 vice versa, a result greater than 100, will indicate an increase in the value concerned. C) Curve force elongation (before cooking):

 The curve of strength green elongation is carried out on a specimen, of raw mixture, in dumbbell shape thanks to a traction machine. The test specimen has two ends connected together by a rod of thickness E of 2.5 mm, length L 26mm and width W 6mm. The test piece is subjected to a simple pull at a speed of 100 mm / min by moving a jaw of an "INSTRON 4501" commercial traction machine relative to a fixed jaw of said machine, said jaws enclosing said ends. with the same clamping pressure of 2 bar.

 For each specimen, the following parameters are calculated:

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

Apparent stress F / S ₀ (MPa) which represents the ratio of the force F (in N) measured by the sensor of the machine, to the initial section S ₀ of the specimen (S ₀ = WE in mm ² , W = 6 mm and E = 2.5 mm the thickness of the specimen before traction)

 The experiment is carried out at a temperature of 23 ° C. and at a humidity 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 vice versa, a result greater than 100, will indicate an increase in the value concerned.

D) Dynamic properties (after cooking)

 The dynamic properties G * and tan (5) max are measured on a viscoanalyzer

(Metravib V A4000), according to ASTM D 5992 - 96. The response of a sample of vulcanized composition (cylindrical specimen 4 mm in thickness and 400 mm ² in section) is recorded, subjected to a sinusoidal stress in alternating single shear, at the frequency of 10 Hz, under normal temperature conditions according to ASTM D 1349-99. A peak-to-peak deformation amplitude sweep of 0.1 to 50% (forward cycle) is performed, followed by 50% to 0.1% (return cycle). The result exploited is the loss factor, tan (5). For the return cycle, the maximum value of tan (5) observed (tan (δ) max) is indicated. The values of tan (5) max 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 vice versa, a result greater than 100, will indicate an increase in the value concerned.

E) Initial plasticity index (Wallace plasticity)

A disk-shaped test piece is compressed between the parallel plates of a plasma meter so as to reach a fixed thickness of 1 millimeter. The test piece is thus maintained for 15 seconds to reach a temperature of equilibrium close to that of the trays. It is then subjected to a constant compression force of 100 N for 15 seconds. The final thickness of the specimen (in hundredths of a millimeter) is considered as a measure of plasticity.

Preparation of test pieces:

 The spacing of the mixer rolls should be adjusted to a final thickness sheet of about 1.7 mm.

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

 Immediately fold the resulting sheet.

 Using the punch, cut three pellets into the folded sheet having 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.

He - 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 from more than a to less than b (i.e. terminals a and b excluded) while any range of values designated by the term "from a to b" means the range from a to b (i.e., including the strict limits a and b).

 By the term "composition based on" is meant 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 partly, during the different phases of manufacture of rubber compositions, belts and tires, in particular during their vulcanization.

 Moreover, the term "phr" 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, in the sense of the invention, a natural rubber having a molecular weight distribution, seen in SEC-MALS, bimodal. It may also be called "bimodal natural rubber".

 For the purposes of the invention, the term "natural rubber with unimodal molecular weight distribution" is intended to mean a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal. It may also be called "unimodal natural rubber".

 For the purposes of the invention, the term "initial plasticity" means the Wallace plasticity of the natural rubber, as measured by the protocol according to the invention.

 For the purposes of the invention, "cutting" is intended to mean the mixture of natural rubber with a bimodal molecular mass distribution and unimodal molecular weight distribution natural rubber which also has 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 natural rubbers selected according to their molecular weight distribution. This molecular weight distribution is observed by SEC-MALS chromatography. In order to discriminate more easily natural rubbers having a unimodal or bimodal molecular weight distribution, a first derivative has been applied at any point of the RI (refractive index) signal in a 24-point pitch. The derivative exacerbates the slope changes of the RI signal. Thus during a linear evolution, the derivative will be constant and during a slope break (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.

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

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

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

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

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

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

In the composition, the natural rubber is a blend comprising from 20% to 90% by weight, preferably from 30% to 90% by weight, more preferably from 30% to 70% by weight, more preferably from 40% to 60% by weight. weight, even more advantageously 50% by weight, based on the total weight of the cutting, 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, preferably from 10% to 70% by weight, more preferably from 30% to 70% by weight, more preferably from 40% to 60% by weight. weight, even more advantageously 50% by weight, with respect to the total weight of the cut, of natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal and having an index of initial plasticity of less than 20. The use of A bimodal natural rubber will make it possible to impart good green properties to a rubber composition comprising it. It appears that a bimodal natural rubber content of 20% by weight, based on the total weight of the blend, is sufficient for the final rubber composition to have improved raw rectification properties, compared to the control which is a gum plasticized composition comprising a natural rubber resulting from a mixture of several non-specifically selected latexes.

 The use of a unimodal natural rubber, which also has an initial plasticity index of less than 20, will make it possible to impart good processability properties, especially through the Mooney, to a rubber composition comprising it.

Surprisingly and strongly interesting, the cutting of these two selected rubbers will allow 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 gum, T0, comprising a natural rubber resulting from a mixture of several non-specifically selected latexes is used as a control. This natural rubber has previously undergone a plasticization step, the plasticization consisting of a mechanical work of the material allowing a decrease in its viscosity.

Depending on the compromise sought, the skilled person will then vary the respective proportions between the two natural rubbers selected. 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 the Mooney, of a composition comprising it. The initial plasticity index of unimodal natural rubber is advantageously less than 15. The initial plasticity index of the unimodal natural rubber is advantageously between 5 and 20, more advantageously between 5 and 15.

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

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

Other diene elastomer

 By elastomer or "diene" rubber, is generally meant an elastomer derived at least in part (i.e. a homopolymer or a copolymer) of monomers dienes (monomers bearing two carbon-carbon double bonds, conjugated or not).

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

 The diene elastomers, in known manner, can be classified into two categories: those said to be "essentially unsaturated" and those termed "essentially saturated". By "essentially unsaturated" diene elastomer is meant a diene elastomer derived at least in part from conjugated diene monomers having a level 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 may instead be described as essentially saturated diene elastomers. "(low or very low diene origin, always less than 15%). In the category of "essentially unsaturated" diene elastomers, the term "highly unsaturated" diene elastomer is particularly understood to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

 Given these definitions, the term "diene elastomer" can be understood more particularly to be used in the compositions according to the invention:

(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 conjugated dienes with each other or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

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

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

Although it applies to any type of diene elastomer, the person skilled in the tire art 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 various butadiene copolymers, the various isoprene copolymers, and mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), the latter being prepared by emulsion polymerization (ESBR) as in solution (SSBR), the isoprene-butadiene copolymers (BIR ), isoprene-styrene copolymers (SIR) and isoprene-butadiene-styrene copolymers (SBIR).

Among the polybutadienes, those having a content (mol%) in units -1, 2 of between 4% and 80% or those having a content (mol%) of cis-1,4 more than 80% are particularly suitable. Among the synthetic polyisoprenes, cis-1,4-polyisoprenes, preferably those having a content (mol%) of cis-1,4 bonds greater than 90%, are particularly suitable. Among the copolymers of butadiene or isoprene, is meant 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. Examples of suitable vinyl aromatic compounds are styrene, ortho-, meta-, paramethylstyrene, the commercial mixture "vinyl-toluene", para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinyinaphthalene. The copolymers may 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 a homopolymer or copolymer of isoprene, 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 copolymers of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene (SBIR). The synthetic polyisoprene is preferably of the cis-1,4 type. Among these synthetic polyisoprenes, polyisoprenes having a level (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used.

As non-isoprenic diene elastomers, mention may be made in particular of any unsaturated diene elastomer chosen in particular from the group consisting of polybutadienes (BR), in particular cis-1,4 or 1,2-syndiotactic polybutadienes, and those having a content (mol%) in units-1, 2 of between 4% and 80%, and butadiene copolymers, especially styrene-butadiene copolymers (SBR), and in particular those having a styrene content of between 5 and 50% by weight and more particularly between 20% and 40% by weight, a content (mol%) of -1,2 bonds of the butadiene part of between 4% and 65%, a content (mol%) 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 previously described as only diene elastomers, or

a mixture of natural rubbers as described above, and at least one other diene elastomer, the diene elastomer (s) that can be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers. 11.2. Reinforcing charge:

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

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

Suitable carbon blacks are all carbon blacks, especially blacks conventionally used in tires or their treads (so-called pneumatic grade blacks). Among these, the reinforcing carbon blacks of the series 100, 200, 300, or the series blacks 500, 600 or 700 (ASTM grades), for example the blacks N15, N134, N234, N326, will be mentioned more particularly. 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 carrier for some of the rubber additives used.

"Reinforcing inorganic filler" means any inorganic or mineral filler, irrespective of its color and 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 any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words able to replace, in its function reinforcement, a conventional carbon black of pneumatic grade; such a load is characterized generally, in a known manner, by the presence of hydroxyl groups (-OH) on its surface.

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferentially silica (SiO ₂ ). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and 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 (called "HDS"), mention may be made, for example, of the "Ultrasil" 7000 and "Ultrasil" 7005 silicas of Degussa, the "Zeosil" silicas 1 165MP, 1 135MP and 1 1 15MP of the Rhodia company, the "Hi-Sil" silica EZ150G from the company PPG, the "Zeopol" silicas 8715, 8745 and 8755 from the Huber Company, the high surface area silicas as described in the application WO 03/016387. As reinforcing inorganic filler, mention may also be made of mineral fillers of the aluminous type, in particular alumina (Al ₂ O ₃ ) or aluminum (oxide) hydroxides, or reinforcing titanium oxides, for example described in US 6,610,261 and US 6,747,087. The physical state in which the reinforcing inorganic filler is present is immaterial, whether in the form of powder, microbeads, granules or beads. Of course, reinforcing inorganic filler is also understood to mean mixtures of different reinforcing inorganic fillers, in particular of highly dispersible silicas as described above.

Those skilled in the art will understand that as an equivalent load of the reinforcing inorganic filler described in this paragraph, it would be possible to use a reinforcing filler of another nature, in particular an organic filler such as carbon black, since this filler reinforcing would be covered with an inorganic layer such as silica, or would comprise on its surface functional sites, including hydroxyl, requiring the use of a coupling agent to establish the connection between the filler and the elastomer. By way of example, mention may be made of carbon blacks for tires as described by example in the documents WO 96/37547,

WO 99/28380.

In the present disclosure, the BET surface area 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 the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: 1 hour at 160 ° C. - relative pressure range p / po: 0.05 to 0.17). The CTAB specific surface is the external surface determined according to the French standard NF T 45-007 of November 1987 (method B).

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

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

In order to couple the reinforcing inorganic filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner to ensure a sufficient chemical and / or physical connection between the inorganic filler (surface of its particles) and the diene elastomer. In particular, organosilanes or at least bifunctional polyorganosiloxanes are used. In particular, polysulfide silanes, called "symmetrical" or "asymmetrical" silanes according to their particular structure, are used, as described for example in the applications WO03 / 002648 (or US 2005/016651) and WO03 / 002649 (or US 2005/016650). As examples of silane polysulfides, more particularly of the polysulphides (especially disulphides, trisulphides or tetrasulphides) bis (alkoxyl (C ₁ -C ₄₎ alkyl (C ₁ -C ₄₎ alkyl silyl (-C C ₄ )), such as, for example, bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl) polysulfides. Among these compounds, bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT, of formula [(C ₂ H ₅ O) 3 Si (CH ₂ ) 3 S ₂ ] ₂ or bis (triethoxysilylpropyl) disulfide is especially used. , abbreviated TESPD, of formula [(C ₂ H ₅ O) ₃ Si (CH ₂ ) ₃ S] ₂ . Mention may also be made, by way of preferred examples, of polysulfides (in particular disulphides, trisulphides or tetrasulfides) of bis- (monoalkoxyl (C ₁ -C ₄ ) -dialkyl (C ₁ -C ₄ ) silylpropyl), more particularly tetrasulphide of 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, particular mention may be made of bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulfides (R ² = OH in formula I above) as described by US Pat. for example in patent applications WO 02/30939 (or US Pat. No. 6,774,255), WO 02/31041 (or US 2004/051210), and WO2007 / 061550, or else silanes or POS bearing functional azo-dicarbonyl groups, such as as described for example in patent applications WO 2006/125532, WO 2006/125533, WO 2006/125534.

As examples of other sulphurized silanes, mention may be made of silanes bearing at least one thiol function (-SH) (so-called mercaptosilanes) and / or of at least one blocked thiol group, as described, for example, in the patents or patent applications US 6,849,754, WO 99/09036, WO 2006/023815, WO 2007/098080, WO 2010/072685 and WO 2008/055986.

Of course, it would also be possible to use mixtures of the coupling agents described above, 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 is from 0.5% to 15% by weight relative to the amount of inorganic filler. Its level is preferably between 0.5 and 12 phr, more preferably in a range from 3 to 10 phr. This level is easily adjusted by those skilled in the art according to the level of inorganic filler used in the composition.

II.3. Various additives:

 The rubber compositions according to the invention may also contain coupling activators, inorganic charge-covering agents or, more generally, processing aids which can be used in a known manner, thanks to an improvement in the dispersion of the the charge in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to implement in the green 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 normally used in elastomer compositions intended for the manufacture of tires, for example pigments, protective agents such as anti-ozone waxes, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing or plasticizing resins, acceptors (for example phenolic novolac 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, plasticizing agents, preferably non-aromatic or very weakly aromatic selected from the group consisting of naphthenic oils, paraffinic oils, MES oils, TDAE oils, plasticizers ethers, ester plasticizers, 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 that can act as accelerator for vulcanizing diene elastomers in the presence of sulfur, in particular those selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated as "MBTS"), N-cyclohexyl-2-benzothiazylsulfenamide (abbreviated "CBS"), N N-dicyclohexyl-2-benzothiazylsulfenamide (abbreviated "DCBS"), N-tert-butyl-2-benzothiazylsulfenamide (abbreviated "TBBS"), N-tert-butyl-2-benzothiazylsulfenimide (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 production phase, the process described below, various known secondary accelerators or vulcanization activators such as zinc oxide. stearic acid, guanidine derivatives (in particular diphenylguanidine), etc. In the case of a use of the composition of the invention in tread tire, the sulfur content is for example between 0.5 and 3.0 phr, that of the primary accelerator between 0.5 and 5.0 pce.

11.4. Manufacture of the 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 weight distribution, seen in SEC-MALS, unimodal and an index of initial plasticity less than 20; Advantageously, the rubbers of steps a) and b) are intended to be subsequently used in cutting in mass proportions, rubber of step a): rubber of step b) ranging from 90:10 to 20:80, advantageously ranging from 90:10 to 30:70, more preferably from 70:30 to 30:70, still more preferably from 60:40 to 40:60, still more preferably from 50:50.

Advantageously, the rubbers of steps a) and b) do not undergo subsequent plastification; the plasticization consisting of a mechanical work of the matrix allowing a decrease 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 manufactured in suitable mixers, using two well-known successive preparation phases. of the person skilled in the art: a first phase of work or thermomechanical mixing (so-called "non-productive" phase) at high temperature, up to a maximum temperature of between 1 10 ° C. and 190 ° C., preferably between 130 ° C. C and 180 ° C, followed by a second phase of mechanical work (so-called "productive" phase) to a lower temperature, typically below 1 10 ° C, for example between 40 ° C and 100 ° C, phase in which the crosslinking system is incorporated.

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

 i. incorporating in the elastomeric matrix comprising the rubbers of steps a) and b), during a so-called non-productive first step, the reinforcing filler, as well as the other ingredients of the composition with the exception of the crosslinking system by thermomechanically kneading the whole until reaching a maximum temperature of between 1 10 and 190 ° C;

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

iii. then incorporate, during a second so-called productive step, a crosslinking system;

iv. knead to a maximum temperature below 1 10 ° C.

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

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

The invention relates to the rubber compositions described above both in the so-called "raw" state (i.e., before firing) 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, the natural rubber is obtained after coagulation of the latex (chemical or natural coagulation). The coagula are dried for 3 hours at about 120 ° C. Characterization of the gums:

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

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

The natural rubbers resulting from varieties PB217, PB235, CDC312 have a molecular weight distribution, seen in SEC-MALS, unimodal. The molecular weight distribution for the natural rubber from the variety PB217 is shown in FIG. The natural rubbers used in the examples did not undergo a prior plasticization step.

EXAMPLE 1

Preparation of the compositions:

A plasticized gum comprising a natural rubber resulting from a mixture of several non-specifically selected latexes is used as control T0.1. This natural rubber has previously undergone a plasticization step, the plasticization consisting of a mechanical work of the material allowing a decrease in its viscosity.

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

 Table 1

 NR1: natural rubber resulting from a mixture of several latexes. This NR has undergone a plasticization step by mechanical treatment.

NR2: Natural rubber from the variety PB235 having a molecular weight distribution, seen in SEC-MALS, unimodal, and an initial plasticity index, P0, of 37 (3) 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

 (4) NR4: Natural rubber from the variety RRIM600 having a molecular weight distribution, seen in SEC-MALS, bimodal

(5) Carbon black N234

 (6) 6PPD: N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine: antioxidant

(7) TMQ: 2,2,4-trimethyl-1,2-dihydroquinoline

 (8) ZnO: Zinc Oxide

 (9) SAD: Stearic acid

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

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

 At 115 ° C and 135 ° C, a pestle is performed in order to bring chaos into the mixture (improves the homogeneity of the mixture). The mixture thus obtained is recovered at a "fallen" temperature of 165 ° C after a total mixing time of about five minutes.

 This mixture is cooled on an external mixer at room temperature. The vulcanization system is incorporated into the mix with the roll 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 has also been made 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 1 12 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 of 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, P0, of 37 (T3) or for a composition comprising as natural rubber a natural rubber having a molecular weight 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 the processability seen through the Mooney.

B. properties of the compositions according to the invention

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 T0 containing a plasticized gum. The mixture of the composition C1 makes it possible to obtain a raw reinforcement level, seen through the fracture stress, which is very much improved compared to the plasticized gum without penalizing the elongation.

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

 A plasticized gum comprising a natural rubber resulting from a mixture of several non-selected latexes is used as a control T0.2. This natural rubber has previously undergone a plasticization step, the plasticization consisting in a mechanical work of the material making it possible to reduce of its viscosity.

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

Table 4 (1) NR1: natural rubber resulting from a mixture of several latexes. This NR has undergone a plasticization step by mechanical treatment.

 (2) NR2.2: Natural rubber from the variety CDC312 having a molecular weight distribution, seen in SEC-MALS, unimodal (3) NR2.3: Natural rubber from the variety CDC429 having a molecular weight distribution, view in SEC-MALS, bimodal

(4) Carbon black N234

 (5) 6PPD: N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine: antioxidant

(6) TMQ: 2,2,4-methylmethyl-1,2-dihydroquinoline

 (7) ZnO: Zinc Oxide

 (8) SAD: Stearic acid

 (9) N-cyclohexyl-2-benzothiazyl sulfenamide ("Santocure CBS" from the company Flexsys) In an internal mixer, whose initial tank temperature is about 80 ° C., elastomer matrices (natural rubbers) are introduced selected). After one minute of mixing, all the other compounds are introduced.

 At 115 ° C and 135 ° C, a pestle is performed in order to bring chaos into the mixture (improves the homogeneity of the mixture). The mixture thus obtained is recovered at a "fallen" temperature of 165 ° C after a total mixing time of about five minutes.

This mixture is cooled on an external mixer at room temperature. The vulcanization system is incorporated into the mix with the roll 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

 Table 5 By varying the respective proportions in each of the selected rubbers, preference is given to the processability or the straightening properties raw.

Bibliography

 (1) Subramaniam [1972] Gel Permeation Chromatography of Natural Rubber. Rubber 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, Thesis Kasetsart University & Montpellier Supagro, Montpellier - 206 p

Claims

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 a natural rubber having a molecular weight distribution, as seen in SECAMS, bimodal and (ii) a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal, and having an initial plasticity index of less than 20, in mass proportions (i): (ii) ranging from 90:10 to 20:80. Rubber composition according to claim 1, characterized in that the mass ratio (i): (ii) ranges from 70: 30 to 30: 70. Rubber composition according to claim 1 or 2, characterized in that it comprises between 30 and 100 phr of reinforcing filler. A rubber composition according to any one of the preceding claims, characterized in that the reinforcing filler comprises a carbon black or a reinforcing inorganic filler or a blend of these fillers. Rubber composition according to any one of the preceding claims, characterized in that the carbon black represents more than 50% by weight of the reinforcing filler 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) selecting a natural rubber having a molecular weight distribution, seen in SEC-MALS, unimodal and having an index of initial plasticity, PO, less than 20;  c) incorporating in the elastomeric matrix, comprising a mixture of the natural rubbers selected in steps a) and b), in a rubber mass ratio of step a): rubber of step b) ranging from 90: 10 to 20: 80, during a so-called non-productive first step, the other ingredients of the composition, with the exception of the crosslinking system by thermomechanically kneading the whole until a maximum temperature of between 1 and 190 ° C;  d) cooling the assembly to a temperature below 100 ° C;  e) then incorporate, during a second so-called productive step, a crosslinking system;  f) mix everything up to a maximum temperature below 1 10 ° C 1 1. A tire component comprising a composition according to any one of claims 1 to 9. The tire component according to claim 11, further comprising wire reinforcing elements. 13. Component according to claim 1 1 or 12, characterized in that said component is selected from the carcass ply and the crown plies. 14. A tire comprising a component according to any one of claims 11 to 13.