WO1999028380A1

WO1999028380A1 - Rubber composition for tyres, reinforced with a carbon black coated with an aluminous layer

Info

Publication number: WO1999028380A1
Application number: PCT/EP1998/007679
Authority: WO
Inventors: Emmanuel Custodero; Laure Simonot; Jean-Claude Tardivat
Original assignee: Compagnie Generale Des Etablissements Michelin - Michelin & Cie
Priority date: 1997-11-28
Filing date: 1998-11-27
Publication date: 1999-06-10
Also published as: AU1876199A; KR20010032540A; BR9814910A; CN1284099A; JP2001525436A; EP1034215A1; CA2310131A1

Abstract

The invention concerns a sulphur-vulcanisable rubber composition, capable of being used for making tyres, comprising at least a diene elastomer, a reinforcing filler and a coupling agent ensuring the bond between the reinforcing filler and the elastomer. The invention is characterised in that said reinforcing filler consists wholly or partly of a modified carbon black having the following characteristics: (i) it is coated at least partly with an aluminium oxide and/or hydroxide layer; (ii) its specific BET surface ranges between 30 and 400 m2/g; (iii) its average particle size (in volume), marked d¿w?, ranges between 20 and 400 nm; (iv) its deagglomeration rate, marked α, measured by the so-called ultrasound-deagglomeration test, at 10 % of the power of an ultrasound probe of 600 watts, is greater than 1.10?-3 νm-1¿/s.

Description

RUBBER COMPOSITION FOR TIRES,

REINFORCED WITH A CARBON NODl COATED WITH AN ALUMINOUS LAYER

The present invention relates to diene rubber compositions which can be used for the manufacture of tires or semi-finished products for tires, in particular treads for these tires, as well as to reinforcing fillers capable of reinforcing such rubber compositions.

In order to reduce fuel consumption and the nuisance emitted by motor vehicles, significant efforts have been made by tire designers in order to obtain tires having both very low rolling resistance and improved grip both on dry ground than on wet or snowy ground and very good resistance to wear.

Many solutions have thus been proposed to lower the rolling resistance and improve the grip of the tires, but these generally result in a very significant decline in the wear resistance. It is well known in particular that the incorporation of conventional white fillers such as for example silica (SiO ₂ ), alumina (AI ₂ O ₃ ), titanium oxide (TiO ₂ ), chalk, talc, clays such as bentonite or kaolin for example, in rubber compositions used for the manufacture of tires and in particular treads, certainly results in a lowering of the rolling resistance and in an improvement of the grip on ground wet, snowy or icy, but also by an unacceptable decline in wear resistance linked to the fact that these conventional white fillers do not have sufficient reinforcement capacity with respect to such rubber compositions; these white charges are generally qualified, for this reason, non-reinforcing charges also called inert charges.

An effective solution to this problem has been described in patent application EP-A-0 501 227 which discloses a particular diene rubber composition reinforced with a highly dispersible precipitated silica. This composition makes it possible to manufacture a tire having a markedly improved rolling resistance, without affecting the other properties, in particular those of grip, endurance and above all resistance to wear.

Since the publication of this application EP-A-0 501 227, the interest in compositions reinforced with silica has been very largely revived. However, silicas are generally more difficult to disperse than carbon blacks. On the other hand, the compositions loaded with silica, compared with those loaded with carbon black, have in known manner the drawback of having on the one hand an implementation (ie an aptitude for transformation or "processabihty") in the more difficult raw state, on the other hand a very high electrical resistance.

Compositions having both improved hysteresis and adhesion properties, but also easy processing in the raw state, a high level of reinforcement, and therefore of wear resistance, as well as conductivity high electric power were therefore highly desirable for tire manufacturers. The Applicant discovered during its research a new composition which, thanks to a particular reinforcing filler, makes it possible, unexpectedly, to meet these different contradictory requirements.

Consequently, a first subject of the invention relates to a sulfur-vulcanizable rubber composition which can be used for the manufacture of tires, comprising at least one diene elastomer, a reinforcing filler and a coupling agent ensuring the connection between the reinforcing filler and the elastomer, this composition being characterized in that said reinforcing filler consists entirely or partly of a so-called "modified" carbon black having the following characteristics:

- (i) it is coated at least in part with a layer of aluminum oxide and / or hydroxide;

- (ii) its BET specific surface is between 30 and 400 m ² / g; - (iii) its average particle size (in mass), noted d _w , is between 20 and

400 nm;

- (iv) its deagglomeration speed, noted α, measured in the so-called ultrasonic deagglomeration test, at 10% of power of a 600 watt ultrasound probe, is greater than 1.10- ³ μm-Vs.

The compositions of the invention, thanks to this modified black and to its specific combination of characteristics, in particular its particular surface properties, have not only improved hysteresis and adhesion properties, but also a high electrical conductivity.

Rubber compositions comprising as reinforcing filler carbon blacks with modified surface, covered with a siliceous layer, have certainly been described in recent patent applications (see for example EP-A-0 711 805, EP-A -0 799 854, EP-A-0 799 867, WO96 / 037547); these new compositions and their potential for application in tires are still poorly understood by tire manufacturers. Compared with these compositions loaded with carbon blacks covered with a siliceous layer, the compositions of the invention have at least the notable advantage that the aluminous surface layer deposited on the surface of their reinforcing filler, made of oxides and / or aluminum hydroxides which, in known manner, are more stable and chemically more reactive than silicon oxides, will therefore be more adherent to black particles and more reactive than a siliceous layer can be. In addition, compared with compositions loaded with silica, even with highly dispersible silica, the compositions of the invention have the advantage of having an implementation in the raw state which is facilitated.

Patent application WO97 / 42256 describes diene rubber compositions which can incorporate, as reinforcing filler, carbon blacks treated directly in the reactor for synthesizing carbon black with various metal compounds, especially in the form of '' oxides, hydroxides or carbides of different metals (e.g. aluminum, zinc, magnesium, calcium, titanium, vanadium, cobalt, nickel, zirconium, tin, antimony, chromium, neodymium, lead, tellurium, barium, cesium, iron , molybdenum). The blacks thus treated at very high temperature in the synthesis reactor consist in fact of aggregates or hybrid particles in two phases, formed by an intimate mixture of carbon black and metallic compound, the metallic compound being located both inside and near the surface of the aggregates; it is specified in particular that the metal atom content can reach 50% or even 99% of the mass of the final aggregate (% by mass). It is well understood that such hybrid charges, if they were released by any means from their fraction of metallic compound, for example by an appropriate chemical treatment, would have neither the morphology nor the properties of a conventional carbon black, but those of carbonaceous residues with high porosity. In this, the treated carbon blacks described in WO97 / 42256 should not be confused with carbon blacks only coated with a layer of metallic compound which, after elimination of such a coating, would find their initial structure.

Nothing is said further in WO97 / 42256 on a rubber composition according to the invention, loaded with a modified carbon black having the specific BET surface characteristics. particle size d _w and disaggregation speed α above.

A subject of the invention is also the use of a rubber composition in accordance with the invention for the manufacture of rubber articles, in particular tires or semi-finished rubber products intended for these tires, these semi articles -finishes being chosen in particular from the group consisting of treads, underlayments intended for example to be placed under these treads, crown plies, sides, carcass plies, heels, protectors, chambers air or waterproof inner rubber for tubeless tires. The invention relates more particularly to the use of such a rubber composition for the manufacture of sidewalls or treads, due to its good hysteretic properties.

The subject of the invention is also these tires and these rubber articles themselves when they comprise a rubber composition in accordance with the invention.

The composition in accordance with the invention is particularly suitable for making tire treads intended to equip passenger vehicles, vans, two wheels and heavy goods vehicles, airplanes, civil engineering, agrarian or handling vehicles, these treads which can be used in the manufacture of new tires or for retreading used tires.

The invention as well as its advantages will be easily understood in the light of the description and of the exemplary embodiments which follow, as well as of FIGS. 1 to 3 relating to these examples which represent:

- a diagram of a device capable of measuring the ultrasonic disaggregation speed (α) of a charge in the form of agglomerates (fig. 1);

curves for the evolution of the size of the agglomerates during a sonification using the device of FIG. 1, for charges in accordance with the invention, curves from which the deagglomeration speeds α are determined ( Fig. 2 and Fig. 3). I. MEASUREMENTS AND TESTS USED

1-1. Characterization of reinforcing fillers

The reinforcing fillers used are characterized as indicated below.

a. "BET specific surface:

The BET specific surface is determined in a known manner, according to the method of Brunauer-Emmet-Teller described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938 and corresponding to standard AFNOR-NF-T45-007 (November 1987).

b) average particle size d _w :

The average size (by mass) of the particles, denoted d _w , is conventionally measured after dispersion, by ultrasonic deagglomeration, of the feed to be analyzed in an aqueous solution containing 15% ethanol and 0.05% of a nonionic surfactant (% by volume).

The term "particle" used in the present application must be understood in its usual generic sense of aggregate, and not in that of any elementary particle which may form part of this aggregate (by aggregate, we must understand in a known manner an indivisible whole of elementary particles, produced during the synthesis of the charge).

The determination takes place using a "DCP" type centrifugal photosedimentometer ("Disk Centrifuge Photosedimentometer" sold by the company Brookhaven Instruments). A suspension of 10 mg of carbon black is previously produced in 40 ml of an aqueous solution containing 15% ethanol and 0.05% of a nonionic surfactant (% by volume), per action for 10 minutes at 60% power (ie 60% of the maximum position of the "tip amplitude") of a 600 watt ultrasonic probe (1/2 inch Vibracell sonicator sold by the company Bioblock). During the sonication, a gradient composed of 15 ml of water (0.05% of a nonionic surfactant) and 1 ml of ethanol is injected into the disc of the sedimentometer in rotation at 8000 rpm in order to constitute a "step gradient". Then 0.3 ml of the carbon black suspension is injected at the surface of the gradient; after sedimentation for 120 min, the mass distribution of particle sizes and the average mass size d _w (d _w = ∑ (nj dj ⁵ ) / ∑ (nj d; ⁴ ) with number of objects of the size class d,) are calculated by the sedimentometer software.

c) deagglomeration speed α:

The deagglomeration speed noted α is measured in the test called "ultrasonic deagglomeration test", at 10% power of a 600 watt probe. This test makes it possible to continuously measure the change in the size of the particle agglomerates during a sonification, according to the indications below. The assembly used consists of a laser granulometer (type "Mastersizer S", sold by Malvern Instruments - He-Ne laser source emitting in the red, wavelength 632.8 nm) and its preparer ("Malvern Small Sample Unit MSX1 "), between which was inserted a continuous flow treatment cell (Bioblock M72410) fitted with an ultrasound probe (1/2 inch sonicator type Vibracell of 600 watts sold by the company Bioblock).

A small amount (15 mg) of filler to be analyzed is introduced into the preparer with 160 ml of an aqueous solution containing 20% by mass of ethanol, the circulation speed being fixed at its maximum. At least three consecutive measurements are made to determine according to the known Fraunhofer calculation method (Malvern calculation matrix 3 $$ D) the initial mean diameter (by volume) of the agglomerates, denoted d _v [0]. The sonication is then established at a power of 10% (ie 10% of the maximum position of the "tip amplitude") and the evolution of the mean diameter in volume d _v [t] as a function of time is followed for approximately 8 minutes " t "at a rate of approximately every 10 seconds. After an induction period of approximately 3 minutes, it is observed that the inverse of the mean diameter in volume l / d _v [t] varies linearly with time "t" (stable deagglomeration regime). The deagglomeration speed α is calculated by linear regression of the evolution curve of l / d _v [t] as a function of time "t", in the zone of stable deagglomeration regime. It is expressed in μπrVs.

By way of example and reference, the above ultrasound deagglomeration test, applied to a control silica well known to those skilled in the art for its very high dispersibility (silica sold by the company Rhône-Poulenc under the reference Zeosil 1165MP), leads to a disaggregation speed, denoted α ₀ , of approximately 1.5.10 ^-3 μπrVs.

Figure 1 shows schematically an example of mounting of the measuring device usable for carrying out this ultrasonic disaggregation test. This device consists of a closed circuit 1 in which a flow 2 of agglomerates of particles in suspension in a liquid can circulate. This device essentially comprises a sample preparer 10, a laser granulometer 20 and a processing cell 30. A put at atmospheric pressure (13, 33), at the level of the sample preparer 10 and of the treatment cell 30 itself, allows the continuous elimination of the air bubbles which form during the sonication (ie the action of the ultrasound probe).

The sample processor 10 ("Malvern Small Sample Unit MSX1") is intended to receive the charge sample to be tested (as it is or already in suspension in the liquid 3) and to send it through the circuit 1 to a speed set (potentiometer 17), in the form of a flow 2 of liquid suspension. This preparer 10 simply consists of a receiving tank which contains, and through which circulates, the suspension to be analyzed. It is equipped with a stirring motor 15, at adjustable speed, in order to avoid sedimentation of the agglomerates of particles of the suspension; a centrifugal mini-pump 16 is intended to ensure the circulation of the suspension 2 in the circuit 1; the inlet 11 of the preparer 10 is connected to the open air via an opening 13 intended to receive the load sample to be tested and / or the liquid 3 used for the suspension. The preparer 10 is connected to a laser granulometer 20 ("Mastersizer S") whose function is to continuously measure, at regular time intervals, the average size "d _v " of the agglomerates, as flow 2 passes, using a cell 23 to which are coupled the automatic recording and calculation means of the particle size analyzer 20. It will be recalled here briefly that laser particle size analyzers exploit, in known manner, the principle of light diffraction by solid objects suspended in a medium whose refractive index is different from that of the solid. According to Fraunhofer's theory, there is a relationship between the size of the object and the angle of diffraction of light (the smaller the object, the larger the angle of diffraction). In practice, it suffices to measure the quantity of diffracted light for different diffraction angles to be able to determine the size distribution (in volume) of the sample, d _v corresponding to the mean of this distribution (d _v = ∑ (n; dj ) / ∑ (n _j d _j ³ ) with n _s number of objects of the size class dj).

Interposed between the preparer 10 and the laser granulometer 20 is finally a treatment cell 30 equipped with an ultrasonic probe 35 (converter 34 and probe head 36) intended to continuously break up the agglomerates of particles as flow 2 passes.

It is preferred that the treatment cell 30 is placed between the outlet 22 of the particle sizer 20 and the inlet 11 of the preparer 10, in such a way that, in operation, the flow 2 of particles leaving the preparer 10 first passes through the laser granulometer 20 before entering the treatment cell 30. This arrangement has two major advantages for the measurements: on the one hand, the air bubbles due to the action of the ultrasonic probe are eliminated on passing through the preparer 10 ( which is in the open air), that is to say before entering the granulometer 20; they therefore do not disturb the measurement of laser diffraction; on the other hand, the homogeneity of the suspension is improved by prior passage through the preparer 10.

The treatment cell 30 is preferably arranged in such a way that the flow 2 of particles which enters it, via an inlet 31, passes first in front of the head 36 of the ultrasonic probe 35; this unconventional arrangement (flow 2 enters from the bottom 31 of the cell, and not from the top 32) has the following advantages: on the one hand, all of the circulating suspension 2 is forced to pass in front of the end 36 of the ultrasound probe 35, the most active area in terms of deagglomeration; on the other hand, this arrangement allows a first degassing after sonification in the body of the treatment cell 30 itself, the surface of the suspension 2 then being in contact with the atmosphere by means of a pipe 33 of small diameter .

The flow 2 is preferably thermostatically controlled by means of a cooling circuit 40 disposed, at the level of the cell 30, in a double envelope surrounding the probe 35, the temperature being controlled for example by a temperature probe 14 immersed in the liquid 3 at the level of the preparer 10. The arrangement of the various elements of the measuring device is optimized so as to limit as much as possible the circulating volume, that is to say the length of the connection pipes (for example flexible pipes ). 1-2. Characterization of rubber compositions

The rubber compositions are characterized, before and after curing, as indicated below. a) Mooney plasticity:

An oscillating consistometer is used as described in standard AFNOR-NF-T43-005 (November 1980). The Mooney plasticity measurement is carried out according to the following principle: the composition in the raw state 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. Mooney plasticity (ML 1 + 4) is expressed in "Mooney units" (MU).

b) tensile tests:

These tests make it possible to determine the elasticity stresses and the breaking properties. Unless otherwise indicated, they are carried out in accordance with standard AFNOR-NF-T46-002 of September 1988.

The secant modules at 10% elongation (M 10), 100% elongation (M 100) and 300% elongation (M300) are measured in second elongation (ie after an accommodation cycle). back to the actual section of the test piece. All these traction measurements are carried out under normal temperature and hygrometry conditions according to standard AFNOR-NF-T40-101 (December 1979). c) hysteretic losses:

Hysteretic losses (PH) are measured by rebound at 60 ° C on the 6th shock, and expressed in% according to the following relationship:

PH (%) = 100 [(W ₀ -Wt) / W ₀ ], with W ₀ : energy supplied; Wt: energy returned.

d) dynamic properties:

The dynamic properties, noted ΔG ^* and tan (δ) _max , measured as a function of the deformation, are carried out at 10 Hertz with a peak-peak deformation ranging from 0.15% to 50%. The non-linearity ΔG ^* is the difference in shear modulus between 0.15% and 50% of deformation, expressed in MPa. The hysteresis is expressed by the measurement of tan (δ) _max which corresponds to the maximum of tan (δ). II. CONDITIONS FOR CARRYING OUT THE INVENTION

In addition to the usual additives or those capable of being used in a sulfur-vulcanizable rubber composition which can be used for the manufacture of tires, the compositions according to the invention comprise as basic constituents at least one diene elastomer, a reinforcing filler and an agent. coupling between the reinforcing filler and the elastomer, said reinforcing filler being made up wholly or partly of a modified carbon black as described in detail below.

II- 1. Diene elastomer

By "diene" elastomer or rubber is meant in known manner 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 general, the term “essentially unsaturated” diene elastomer is understood here to mean a diene elastomer derived at least in part from conjugated diene monomers, having a rate of units or units of diene origin (conjugated dienes) which is greater than 15% (% in moles).

Thus, for example, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not enter into the preceding definition and can be qualified in particular 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 expression “highly unsaturated” diene elastomer is understood in particular to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

These definitions being given, the expression “diene elastomer capable of being used in the compositions according to the invention” is understood in particular to be:

(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) - any 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) - any 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 primarily implemented with essentially unsaturated diene elastomers, in particular of the type (a) or ( b) above.

As conjugated dienes, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C1-C5 alkyl) -1,3-butadienes such as, for example, are suitable. , 3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1, 3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene.

Suitable vinyl-aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene. , vinylnaphthalene.

The copolymers can contain between 99% and 20% by weight of diene units and from 1% to 80% by weight of vinyl aromatic units. The elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used. The elastomers can be, for example, block, statistics, sequences, microsequences, be prepared in dispersion or in solution.

Preferably, polybutadienes are suitable and in particular those having a content of -1,2 units between 4% and 80% or those having a cis-1.4 content greater than 80%, polyisoprenes, butadiene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of -1,2 bonds in the butadiene part of between 4% and 65%, a content of trans-1,4 bonds between 20% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content between 5% and 90% by weight and a glass transition temperature (Tg) between -40 ° C and -80 ° C, isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg of between -25 ° C and -50 ° C.

In the case of butadiene-styrene-isoprene copolymers, especially those having a styrene content of between 5% and 50% by weight and more particularly between 10% and 40%, an isoprene content of between 15% and 60% are suitable. by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of -1.2 units of the butadiene part of between 4% and 85%, a content in trans units -1.4 of the butadiene part between 6% and 80%, a content in units -1.2 plus -3.4 of the isoprene part between 5% and 70 % and a content of trans units -1.4 of the isoprenic part of between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg of between -20 ° C and -70 ° C.

Of course, the elastomer can be coupled and / or star or functionalized with a coupling agent and / or star or functionalization. The elastomer can also be natural rubber or a blend based on natural rubber with any elastomer, especially diene, synthetic.

In a particularly preferred manner, the diene elastomer of the composition in accordance with the invention is chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes, polyisoprenes or natural rubber, butadiene-styrene copolymers, butadiene copolymers -isoprene, isoprene-styrene copolymers, butadiene-styrene-isoprene copolymers, or a mixture of two or more of these compounds.

When the composition according to the invention is intended for a tread for a tire, the diene elastomer is preferably a butadiene-styrene copolymer prepared in solution having a styrene content of between 20% and 30% by weight, a content of vinyl bonds in the butadiene part of between 15% and 65%, a content of trans-1,4 bonds between 20% and 75% and a glass transition temperature between -20 ° C and -55 ° C, this butadiene-styrene copolymer being optionally used in admixture with a polybutadiene preferably having more than 90% of cis-1,4 bonds.

II-2. Reinforcing filler

The composition according to the invention is reinforced, at least in part, with a carbon black with modified surface, called "modified carbon black" or "modified black", having the following characteristics:

- (ii) its BET specific surface is between 30 and 400 m ² / g;

- (iii) its mean particle size (in mass), noted d _w , is between 20 and 400 nm;

- (iv) its deagglomeration speed, noted α, measured in the so-called ultrasonic deagglomeration test, at 10% of power of a 600 watt ultrasonic probe, is greater than 1.10- ³ μm " ¹ / s.

By aluminum oxide and / or hydroxide is meant any aluminum compound corresponding, apart from impurities and water of hydration, to the general formula (I) which follows (a and b real numbers):

(I) Al (OH) _a O _b , with: 0 <a ≤ 3 and b = (3-a) / 2.

Such a formula includes pure aluminum oxides or aluminas AI2O3 (a = 0), aluminum tri-hydroxides Al (OH) ₃ (a = 3), intermediate oxide-hydroxides (0 <a <3), as well as their possible hydrated forms, or a mixture of tri-hydroxides and / or oxide-hydroxides of aluminum. This formula is given with the exception of impurities, it being understood that the aluminum oxides and / or hydroxides present on the surface of the modified carbon black may contain a certain proportion of impurities linked to the process used for the manufacture of the filler. It is generally known that in order to obtain the optimal reinforcing properties imparted by a filler, it is especially advisable for the latter to be present in the rubber matrix in a final form which is both as finely divided as possible and distributed in the same manner. as homogeneous as possible. However, such conditions can only be achieved insofar as the filler has a very good ability, on the one hand to be incorporated into the matrix during mixing with the elastomer and on the other hand to disaggregate so to disperse homogeneously in the elastomer.

The intrinsic dispersibility of a charge can be evaluated using the so-called ultrasonic disagglomeration test described in chapter I above, by measuring its disagglomeration speed α.

It has been observed that for a speed α greater than 1.10 " ³ μmOs, the modified black has good dispersibility. That is to say that few micron agglomerates are observed by reflection under optical microscopy on a section of prepared rubber composition. according to the rules of art.

For an even better dispersion of the modified black in the diene rubber matrix, and therefore for optimal reinforcement, it is preferable for the deagglomeration speed α to be greater than 1.5 × 10 ⁻³ μnrVs. This is particularly advantageous in particular when the invention is used for the manufacture of treads having low rolling resistance.

For a BET surface area of less than 30 m ² / g, the compositions certainly exhibit easier processing and reduced hysteresis, but there is a decline in the breaking properties and resistance to wear in tires; for BET surfaces greater than 400 m ² / g, processing in the raw state becomes more difficult (higher Mooney plasticity) and the dispersion of the charge is degraded. For excessively large sizes d _w , greater than 400 nm, the particles behave like defects which localize the stresses and are detrimental to wear; sizes d _{w that are} too small, less than 20 nm, on the other hand, will penalize the implementation in the raw state and the dispersion of the charge during this implementation.

For all the reasons explained above, the BET surface is preferably within a range from 50 to 300 m ² / g and the particle size d _w is preferably within a range from 30 to 200 nm.

The modified carbon black, thanks to its aluminous surface layer, also exhibits a high surface reactivity, ie a high rate of reactive surface functions (Al-OH), vis-à-vis the coupling agent, which is particularly favorable to the mechanical properties of the rubber compositions of the invention, that is to say to the reinforcement function fulfilled by the filler.

Preferably, the aluminum content (of element Al) present on the surface of the modified carbon black is greater than 0.25%, more preferably greater than 0.5%, even more preferably adjusted in a range between 0.5% and 5% (% by mass of modified black, determined by chemical analysis).

Below the minimums indicated, the effect of lowering the hysteresis may be insufficient, depending on the nature of the compositions used, in particular that of the elastomer, while beyond the maximum recommended rate, it is generally observed more improvement of the hysteresis whereas one is exposed to the risk of leading on the one hand to a too low dispersibility of the modified black, known drawback of white charges compared to carbon black, on the other hand a decrease in adhesion of the aluminous layer to the surface of the carbon black. A rate greater than 5% would also require larger quantities of precursor product (aluminum alkoxide) or even longer impregnation times during manufacture, which is economically less advantageous.

To optimize the adhesion of the aluminous layer to the surface of the black as well as the dispersibility of the filler in the rubber composition, in particular when this composition is intended for a tire tread with low rolling resistance, it is prefer that the aluminum content be adjusted between 0.5% and 3%.

The black modified above can be used alone or combined with another reinforcing filler, for example with a reinforcing silica; in such a case, a highly dispersible precipitated silica is preferably used, in particular when the invention is implemented for the manufacture of tires having a low rolling resistance. As non-limiting examples of such preferred highly dispersible silicas, mention may be made of Perkasil KS 430 silica from Akzo, BV3380 silica from Degussa, Zeosil 1165MP and 1115MP silica from Rhône-Poulenc, Hi-Silica 2000 from PPG, Zeopol 8741 or 8745 from Huber.

The modified black, alone or possibly combined with silica, can also be used in cutting, i.e. in admixture, with conventional carbon black.

Preferably, in the compositions in accordance with the invention, the modified black constitutes the majority, i.e. more than 50% by weight, of the total reinforcing filler; it can advantageously constitute the entire reinforcing filler.

Preferably, the rate of total reinforcing filler in the compositions of the invention is within a range ranging from 20 to 300 phr, more preferably from 30 to 150 phr. the optimum being different depending on the intended applications: in known manner, the level of reinforcement expected on a bicycle tire, for example, is much lower than that required on a tire for a passenger vehicle or for a utility vehicle such as a heavy vehicle.

Synthesis of the modified black

The modified carbon black can be obtained according to the following process:

a) - we start with a pneumatic grade carbon black; b) - the starting carbon black is impregnated with a colloidal suspension formed by hydrolysis of a solution of aluminum alkoxide in an alcoholic solvent; c) - the alcoholic solvent is removed by evaporation; d) - the black thus impregnated is heat treated so as to transform the aluminous layer present on its surface into an adherent layer of aluminum oxide and / or hydroxide.

As the starting carbon black, all the reinforcing carbon blacks conventionally used in tires are suitable, particularly in the treads of these tires, in particular blacks of the HAF ("High Abrasion Furnace"), ISAF ("Intermediate Super Abrasion Furnace") type. "), SAF (" Super Abrasion Furnace "). Among the latter, there may be mentioned more particularly the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades).

Preferably, these starting carbon blacks have the following characteristics:

- a BET surface area between 20 and 200 m ² / g, more preferably between 50 and 170 m ² / g;

an average size (by mass) of particles d _w of between 20 and 400 nm, more preferably between 30 and 200 nm.

By way of nonlimiting examples of such preferred starting blacks, mention may be made of NI 15 blacks,

N134, N234, N339, N347, N375.

By colloidal suspension is meant in known manner a suspension of solid phase in a liquid whose size of solid objects is less than one micrometer. For the formation of the colloidal impregnation suspension, the aluminum alkoxide is dissolved, with stirring and at temperature, in the selected alcohol, for example methanol, ethanol, (iso) propanol, the various isomers of butanol. , then the whole is hydrolyzed by adding water. The aluminum alkoxide used is preferably an aluminum alkoxide having from 1 to 6 carbon atoms, for example a methoxide, an ethoxide, an (iso) propoxide or aluminum butoxides, or a mixture of two or more of these compounds.

The impregnation step can be carried out at room temperature (20 ° C) or at a higher temperature, for example between 30 ° C and 65 ° C depending on the nature of the alcohol or alcohols used, of course below the boiling point of the suspension, it being understood that the chosen temperature may be close to this boiling point. The duration of impregnation is chosen to be sufficiently long, from a few minutes to a few hours depending on the case, in order to create sufficient physicochemical interactions between the surface of the carbon black and the aluminum-based compound.

Preferably, the colloidal impregnation suspension comprises nitric acid used both as a catalyst for hydrolysis of the alkoxide solution and as a peptizing agent for the colloidal suspension. After reaction, the nitric acid will be removed by washing the impregnated black with water. The elimination of the alcoholic solvent, after impregnation of the carbon black, can be carried out by any suitable means, for example by evacuation under vacuum, with stirring.

The heat treatment step is preferably carried out under inert gas, for example under argon, the treatment temperature preferably being between 100 ° C. and 900 ° C., more preferably between 150 ° C. and 850 ° C. In general, the higher this treatment temperature, the more the formula (I) defined above "moves" from the hydroxide to the oxide (decrease in a and increase in b); treatment at a temperature of 800-850 ° C, for example, will lead to an aluminous layer essentially consisting of alumina (Al ₂ O ₃ ).

II-3. Coupling agent

It is well known to those skilled in the art that it is necessary to use, for a reinforcing silica, a coupling agent (silica / elastomer), also called bonding agent, which has the function of ensuring the bond between the white filler and the elastomer, while facilitating the dispersion of this white filler within the elastomeric matrix.

Modified black, because of its aluminous surface layer, also requires the use of such a coupling agent to fully ensure its function of reinforcing filler in the rubber composition according to the invention.

By “coupling” agent (filler / elastomer) is meant more precisely an agent capable of establishing a sufficient connection, of chemical and / or physical nature, between the filler considered and the elastomer, while facilitating the dispersion of this filler within the elastomeric matrix; such a coupling agent, at least bifunctional, has for example as simplified general formula "Y-T-X", in which:

Y represents a functional group ("Y" function) which is capable of physically and / or chemically binding to the white charge, such a bond being able to be established, for example, between a silicon atom of the coupling agent and the hydroxyl (OH) groups on the surface of the filler (for example surface silanols when it is silica);

X represents a functional group ("X" function) capable of binding physically and / or chemically to the elastomer, for example via a sulfur atom;

T represents a hydrocarbon group making it possible to link Y and X.

Coupling agents should in particular not be confused with simple agents for recovering the charge considered which, of known mother, comprise the active Y function with respect to the charge but are devoid of the active X function vis- against the elastomer.

Such coupling agents, of variable effectiveness, have been described in a very large number of documents; see for example US-A-3,842,111, US-A-3,873,489, US-

A-3 978 103, US-A-3 997 581, US-A-4 002 594 or in more recent patents US-A-5 580 919, US-A-5,583,245, US-A-5,663,396, US-A-5,684,171, US-A-5,684,172, US-A-5,696,197, which describe such known compounds in detail.

Any coupling agent known to effectively can be used in diene rubber compositions which can be used for the manufacture of tires, the bond or coupling between silica and diene elastomer, such as organosilanes, in particular polysulphurized alkoxysilanes such as polysulphides , in particular tetrasulfides, of bis (trialkoxyl (C ₁ -C) -silylpropyl), in particular of bis (3-trimethoxysilylpropyl) or of bis (3-triethoxysilylpropyl). Use is made in particular of bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, of formula [(C2H5θ) 3Si (CH2) 3S2] 2; marketed for example by Degussa under the name Si69.

Those skilled in the art will be able to adjust the content of coupling agent in the compositions of the invention, depending on the intended application, the nature of the polymer used, and the amount of modified black used, supplemented if necessary. any white reinforcing filler used as an additional filler.

In order to take into account the differences in specific surface and density of the reinforcing fillers that may be used, as well as the molar masses of the coupling agents, it is preferable to determine the optimal level of coupling agent, for the modified black. , in moles per square meter of modified black, calculated from the weight ratio [coupling agent / modified black], of the BET surface area of the modified black and of the molar mass of the coupling agent (noted below), according to the following relation:

(moles / m ² modified black) = [coupling agent / modified black] (1 / BET) (MM)

Of course, an equivalent relationship will be applied for example to silica if it is used as additional reinforcing white filler, to also determine the optimal rate of additional coupling agent for this silica, in moles per square meter of this filler white.

Preferably, the (total) amount of coupling agent used in the compositions in accordance with the invention is between 10 ^-7 and 10 " ⁵ moles per square meter of [modified carbon black plus, if appropriate, associated reinforcing white filler More preferably still, the amount of coupling agent is between 5.10 ' ⁷ and 5.10 " ⁶ moles per square meter of [modified carbon black plus, if necessary, associated reinforcing white filler].

II-4. Miscellaneous additives

Of course, the compositions in accordance with the invention contain, in addition to the compounds already described, all or part of the constituents usually used in diene rubber compositions intended for the manufacture of tires, such as for example plasticizers, pigments, antioxidants, antiozonants, a cross-linking system based either on sulfur or on donors of sulfur and / or peroxide and / or bismaleimides, vulcanization accelerators, extension oils, etc.

The compositions in accordance with the invention could also contain, in addition to the coupling agents described above, covering agents for white filler, such as for example alkylalkoxysilanes, polyols, amines. These compositions in accordance with the invention can be used alone or in combination with any other rubber composition which can be used for the manufacture of tires.

II-5. Preparation of the compositions

The rubber compositions are prepared using the diene polymers according to quite known techniques, for example by thermomechanical work in one or two stages in an internal paddle mixer, followed by mixing on an external mixer.

According to a conventional one-step process, all the necessary constituents, with the exception of the vulcanization system, are introduced into a conventional internal mixer, for example. The result of this first mixing step is then taken up on an external mixer, generally a roller mixer, and the vulcanization system is then added to it. A second step can be added to the internal mixer, essentially for the purpose of subjecting the mixture to an additional heat treatment.

III. EXAMPLES OF EMBODIMENT OF THE INVENTION

III- 1. Synthesis of the modified black

The synthesis is carried out in accordance with the indications given in paragraph II-2 of the preceding chapter II, according to the specific conditions which follow.

a) preparation of the impregnation solution;

Initially, 8.0 g of aluminum isopropoxide (Al (OCH (CH3) 2) 3 at 98% sold by the company Sigma) are dissolved in 200 ml of anhydrous ethanol by magnetic stirring at 500 revolutions / min at a temperature of 60 ° C; after one hour, 42.4 g of demineralized water are added and stirring is continued at 60 ° C; two hours later, 10 ml of concentrated nitric acid (53%) are added and the temperature is gradually lowered to ambient temperature, thus leaving the stirring for 12 h. A colloidal suspension is thus obtained by hydrolysis of the alcoholic solution of aluminum isopropoxide. b) carbon black impregnation:

40 g of carbon black N234 are placed in the flask of a rotary evaporator (Rotavapor R-124 from Bϋchi sold by the company Bioblock). The temperature of the bath is fixed at 50 ° C. and the speed of rotation at 80 revolutions / min (time "t" = 0). After 55 min of stirring (ie t = 55 min), one third of the impregnation solution is added, another third at t = 85 min, and finally the last third at t = l 15 min. Agitation is thus maintained for approximately three hours, then a vacuum is made (t = 5 h) to remove the excess of alcoholic solvent; after 30 minutes, the bath temperature is fixed at 60 ° C. and stirring is thus continued under vacuum until t = 7 h, for complete evacuation of the solvent. The carbon black thus impregnated is then removed from the flask, placed in a vacuum oven (200 mm Hg) and dried at 100 ° C overnight. The black thus treated is then extracted with water for 48 hours in a Soxhlet, then dried again under the same conditions.

c) heat treatment:

The carbon black is then placed in a tabular oven (Carbolite CTF 15/75 610 type sold by the company Osi), under a flow of argon (200 ml / min), then subjected to the following thermal cycle: 30 min at 200 ° C, then 1 hour at 800 ° C; the temperature ramps are set at 10 ° C / min.

The characteristics of the carbon black thus obtained are summarized in table 1. It is noted that the size of the particles d _w is not significantly modified compared to the starting black, but that its BET surface is on the other hand greatly increased, moreover 50%. The aluminum content is high, around 1.5%, a result well correlated with the measured ash content.

On the other hand, the disagglomeration speed α is much higher than the fixed lower limit of 1.10 ^-3 μπOs (i.e. 2/3 of α ₀ ). A speed α of 3.1.10- ³ μnr ¹ / s should be considered here as particularly high, since it is approximately 100% higher than the speed α ₀ recorded on a highly dispersible control silica (Zeosil 1165MP).

Figures 2 and 3 reproduce the evolution curves [1 / d _v (t) = f (l)] of the size of the agglomerates, recorded in the ultrasonic deagglomeration test, respectively for the modified black and for this highly controlled silica dispersible (Zeosil 1165MP), the determined speed α being the slope of the line [l / d _v (t) = / (t)].

We can clearly see on these figures 2 and 3 that the first recorded points ("t" varying from 0 to 30 s approximately) correspond to the measurement of the initial diameter d _v [0], followed (after activation of the ultrasonic probe) from a gradual transition (here, "t" from 30 s to approximately 3 min) to a stable deagglomeration regime during which the inverse of "d _v " varies linearly with time "t"; data recording is stopped here after about 8 minutes. One deduces from it by an elementary calculation of linear regression, supported by the calculator of the granulometer, the speed of disagglomeration α in the zone of steady regime of disagglomeration.

N234 carbon black at the start presents. at the same ultrasonic deagglomeration test, a particularly high speed α (17.10- ³ μπr s - not shown on the figures), which was of course expected given the very high known dispersibility of carbon blacks for tires, in general.

III-2. Preparation of the compositions

The compositions tested below are prepared in a known manner in laboratory mixers, as follows: the diene elastomer is introduced into an internal mixer filled to 75% and whose temperature is about 70 ° C, then after an appropriate mixing time, for example of the order of 1 minute, all the other ingredients are added, including the filler and, if appropriate, the associated coupling agent, with the exception of the vulcanization system. Thermomechanical work is then carried out for a duration of approximately 5.5 minutes, with an average speed of the pallets of 70 revolutions / min, until a drop temperature of approximately 140 ° C. is obtained. The mixture thus obtained is recovered and then the vulcanization system is added on an external mixer (homo-finisher) at 30 ° C. Vulcanization is carried out at 150 ° C (40 min).

III-3. Essays

Two diene rubber compositions intended for the manufacture of tires or tire treads are compared below. The SBR elastomer (styrene-butadiene copolymer) is prepared in solution and comprises 25% of styrene, 58% of 1-2 polybutadiene units and 23% of 1-4 trans polybutadiene units.

These 2 compositions are identical except for the following differences:

- Nol composition (control): conventional reinforcing filler constituted by a carbon black type N234; - composition No2 (in accordance with the invention): reinforcing filler constituted exclusively by carbon black N234 modified, with which the coupling agent Si69 (TESPT) is associated.

The Si69 coupling agent was introduced at a rate corresponding to a surface coverage of approximately 9.6 × 10 ^-7 mole / m ² of modified carbon black.

Tables 2 and 3 successively give the formulation of the different compositions (Table 2 - rate of the different products expressed in phr), their properties before and after cooking at 150 ° C for 40 minutes (Table 3).

The study of these different results leads to the following observations:

the Mooney plasticity value appears lower on the composition in accordance with the invention than on the control composition, a result which in any case reveals a very good ability to process the composition of the invention raw; the composition according to the invention has values of modules, in particular of modules M 100 and M300 indicators in a known manner of the quality of reinforcement, which are at least equal if not greater than those obtained on the control composition;

the composition in accordance with the invention also has very advantageous hysteretic properties, compared to those offered by conventional carbon black, with a very significant reduction in rebound losses (PH), non-linearity ΔG ^* and tan (δ) _max .

In summary, the compositions of the invention unexpectedly exhibit significantly improved hysteresis properties, without their properties of processing in the raw state and of reinforcement after cooking being affected.

These results suggest both good wear resistance and particularly low rolling resistance for tire treads, while ensuring that these treads have satisfactory electrical conductivity, sufficient to dissipate, for example, electrostatic charges which can be formed by friction, in particular when rolling tires.

It is believed that the specific process for preparing the modified black (cold impregnation followed by heat treatment) makes it possible to deposit, on the surface of the carbon black particles or aggregates, a fine, stable, highly adherent and distributed aluminous layer of relatively homogeneously (average particle size little modified but strong increase in the BET surface).

Such a coating quality of its reinforcing filler could explain the unexpected performance of the rubber composition according to the invention, improved both compared to compositions reinforced with conventional carbon black (reduction in hysteresis) and compared to compositions reinforced with precipitated silica even highly dispersible (increased dispersibility; high electrical conductivity).

The compositions of the invention thus offer an interesting alternative to the use of conventional compositions loaded with carbon blacks or highly dispersible silicas, or even carbon blacks coated with a siliceous layer. Table 1

Table 2

(1) Butadiene styrene copolymer

(2) N-1,3 dimethylbutyl N-phenylparaphenylenediamine

(3) Diphenylguanidine

(4) N-cyclohexyl-2-benzothiazylsulfenamide

Table 3

Claims

1. Sulfur-vulcanizable rubber composition, usable for the manufacture of tires, comprising at least one diene elastomer, a reinforcing filler and a coupling agent ensuring the connection between the reinforcing filler and the elastomer, characterized in that said reinforcing filler is made up entirely or in part of a so-called “modified” carbon black having the following characteristics:

- (i) it is coated at least in part with a layer of aluminum oxide and/or hydroxide;

- (ii) its BET specific surface area is between 30 and 400 m ² /g;

- (iii) its average particle size (by mass), denoted d _w , is between 20 and 400 nm;

- (iv) its deagglomeration speed, denoted α, measured in the so-called ultrasonic deagglomeration test, at 10% power of a 600 watt ultrasonic probe, is greater than ^1.10-3 μm-Vs.

2. Composition according to claim 1, characterized in that the deagglomeration speed α is greater than 1.5.10-3 μm-Vs.

3. Composition according to claims 1 or 2, characterized in that the surface aluminum content of the modified carbon black is greater than 0.25% (% by mass).

4. Composition according to claim 3, characterized in that the surface aluminum content of the modified carbon black is between 0.5% and 5%.

5. Composition according to any one of claims 1 to 4, characterized in that the modified carbon black represents more than 50% by weight of the total reinforcing filler.

6. Composition according to claim 5, characterized in that the modified carbon black represents all of the reinforcing filler.

7. Composition according to any one of claims 1 to 6, characterized in that it comprises, in addition to modified carbon black, silica as reinforcing white filler.

8. Composition according to any one of claims 1 to 7, characterized in that the total reinforcing filler is present at a rate of 20 to 300 phr (parts by weight per hundred parts of elastomer).

9. Composition according to any one of claims 1 to 8, characterized in that the quantity of coupling agent is between 10" ⁷ and 10' ⁵ mole per square meter of modified carbon black and, where appropriate, filler associated reinforcing white.

10. Composition according to claim 9, characterized in that the quantity of coupling agent is between 5.10 ^-7 and 5.10" ⁶ moles per square meter of modified carbon black and, where appropriate, associated reinforcing white filler.

11. Composition according to any one of claims 1 to 10, characterized in that the diene elastomer is chosen from the group consisting of polybutadienes, polyisoprenes or natural rubber, butadiene-styrene copolymers, butadiene copolymers -isoprene, isoprene-styrene copolymers, butadiene-styrene-isoprene copolymers, or a mixture of two or more of these compounds.

12. Composition according to claim 11, characterized in that the diene elastomer is a butadiene-styrene copolymer prepared in solution having a styrene content of between 20% and 30% by weight, a content of vinyl bonds in the butadiene part between 15% and 65%, a trans-1,4 bond content of between 20% and 75% and a glass transition temperature of between -20°C and -55°C, this butadiene-styrene copolymer optionally being used in mixture with a polybutadiene preferably having more than 90% cis-1,4 bonds.

13. Use of a rubber composition according to any one of claims 1 to 12 for the manufacture of rubber articles.

14. Use of a rubber composition according to any one of claims 1 to 12, for the manufacture of tires or semi-finished rubber products intended for such tires, these semi-finished products being chosen from the group consisting of treads, tread underlays, top layers, sidewalls, carcass layers, beads, protectors, inner tubes or waterproof inner rubbers for tubeless tires.

15. Rubber article comprising a composition according to any one of claims 1 to 12.

16. Tire comprising a composition according to any one of claims 1 to

12.

17. Tire tread based on a composition according to any one of claims 1 to 12.