EP2104710A1

EP2104710A1 - Tyre tread having a composition containing a xanthan gum powder

Info

Publication number: EP2104710A1
Application number: EP07847884A
Authority: EP
Inventors: Jean-Denis Hidrot; Salvatore Pagano
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2006-12-27
Filing date: 2007-12-06
Publication date: 2009-09-30
Also published as: US20100069530A1; FR2910904A1; JP5450091B2; US8372901B2; WO2008080751A1; JP2010514868A; FR2910904B1

Abstract

The invention relates to a tyre tread having a composition based on at least one diene elastomer, a reinforcing filler and a curing system, characterised in that the composition contains between 10 and 40 pce of a xanthan gum powder. The invention also relates to a method for obtaining a rubber tread composition based on at least one diene elastomer, a reinforcing filler and a curing system, said method including a first phase involving the thermomechanical milling of the constituents of the composition except the curing system. The invention is characterised in that the composition contains between 10 and 40 pce of a xanthan gum powder and in that the xanthan gum powder is incorporated during the first milling phase.

Description

ROLLER BAND COMPRISING A XANTHAN GUM POWDER

The invention relates to rubber compositions for tire tread and more particularly to rubber compositions used in tire treads called "winter" that is to say tires particularly effective on wet floors or coated with snow or melting ice, that is to say for temperatures between -10 ⁰ C and 0 ⁰ C, preferably between -5 ° C and 0 ⁰ C.

Various solutions exist to obtain good adhesion of tires even on floors covered with snow or ice. Thus studded tires meet these criteria and can effectively withstand sliding on ice, however their very strong abrasive action on the floor itself itself gradually leads to their prohibition.

The manufacturers have therefore sought other types of solutions consisting in modifying the rubber composition itself of the treads of the tires.

Some solutions consist for example of incorporating into the constitutive rubber mixture of the tread, water-soluble powders. Such powders solubilize on contact with snow or melted ice, which allows on the one hand the creation on the surface of the tire tread of porosities likely to improve the "hooking" of the tire strip. bearing on the ground and on the other hand the creation of grooves acting as evacuation channels of the liquid film created between the tire and the ground. [0005] Thus, publication JP-3 159803 describes tire treads whose rubber composition comprises from 3 to 25 phr (pce meaning parts by weight per 100 parts of elastomers), of polysaccharide powder such as carboxymethylcellulose. of sodium or of vinyl alcohol powder with a particle size of between 20 and 600 μm and having a solubility at 0 ^° C. of at least 5 g per 100 ml of water, solubility obtained in a few tens of seconds of mixing .

Similarly, EP 0 940 435 discloses a rubber composition for tread comprising from 1 to 25 phr of modified polyvinyl alcohol with a particle size of between 10 and 100 μm and a solubility at ^0.degree. C Ig for 200 ml of water for a very short mixing time, that is to say of the order of one minute.

Finally publication JP200211203 describes a rubber composition for tread comprising 3 to 40 phr of starch powder whose particles have a size greater than or equal to 20 microns and a solubility of 1 g in 100 ml of water at 10 ⁰ C reached after 3 minutes of mixing.

In all these examples it is clear that the solubility at very low temperature and in a very short time of the powder used in the rubber composition is an essential factor for the proper functioning of the tread made. In fact, it is stated in the aforementioned documents that if the powder is not soluble in the conditions of use of the tire, no more adherent layer is formed on the surface of the tread and that, for example, therefore, slip resistance is penalized. Unfortunately this good adhesion performance is accompanied by very poor results in terms of wear resistance, controllable by the degradation of rubber properties such as stiffness, elongation properties and tensile stress and hysteretic losses. which render these solutions unusable industrially. The Applicant has surprisingly discovered that the introduction into the constitutive rubber composition of the tread of a particular polysaccharide powder not faded into the water in a very short time (of the order of one minute ) and at very low temperatures (of the order of 0 °) nevertheless allowed to improve the behavior of the tires in terms of resistance to sliding and adhesion on snow-covered or frozen ground without the slight drop in resistance to wear accompanying this amendment is unacceptable for the industrial use of such tires.

In what follows will be designated tread tire, the entire tread or part of the latter, especially when it is composed of several layers in contact with the ground.

The invention thus relates to a tire tread having a rubber composition based on at least one diene elastomer, a reinforcing filler, a vulcanization system characterized in that the composition comprises a powder of xanthan gum in a proportion of 10 to 40 phr, and preferably 15 to 30 phr.

More particularly, the size of the particles of xanthan gum powder is between 10 and 500 microns, preferably between 50 and 300 microns.

According to one characteristic of the invention, the xanthan gum powder is used in a blend with one or more other polysaccharide powders and in particular with a guar gum powder.

[0014] Advantageously, the diene elastomer is predominantly, for more than 50 phr, an isoprene elastomer. - AT -

According to one embodiment of the invention, the reinforcing filler mainly comprises carbon black.

According to another embodiment, the reinforcing filler mainly comprises silica or comprises a blend of carbon black and silica.

The invention also relates to a process for obtaining a rubber composition for a tread based on at least one diene elastomer, a reinforcing filler, a vulcanization system, which comprises a first kneading phase. thermomechanical composition of the constituents of the composition with the exception of the vulcanization system characterized in that the composition comprises a powder of xanthan gum in a proportion of 10 to 40 phr, preferably 10 to 30 phr, and that the Xanthan gum powder is incorporated during the first mixing phase.

Preferably, the first phase of the process is carried out in two steps: a first kneading step of all the constituents of the composition with the exception of xanthan gum powder and a second step in which the powder of xanthan gum is incorporated.

According to one embodiment of the invention, the first step of the first mixing step is carried out at a temperature between 110 ⁰ C and 190 ⁰ C and, preferably, between 130 ⁰ C and 180 ⁰ C; the second step of the first kneading phase is carried out at a temperature of less than or equal to 130 ^° C., after cooling after the first step, preferably at a temperature of less than or equal to 100 ^° C.

Advantageously, the second phase of the process is carried out at a temperature between 60 ⁰ C and 100 ⁰ C. The invention also relates to a tire comprising a tread whose rubber composition is based on at least one diene elastomer, a reinforcing filler, a vulcanization system characterized in that the composition comprises a powder of xanthan gum in a proportion of 10 to 40 phr, and particularly a winter tire comprising such a tread.

The invention also relates to a tire intended to equip a vehicle called "heavyweight" (that is to say, subway, bus, road transport equipment (trucks, tractors, trailers), off-road vehicles. -route), aircraft, civil engineering, agrarian, or handling equipment, comprising a tread according to the invention.

The invention finally relates to a tire for equipping a passenger vehicle, comprising a tread according to the invention.

The skilled person usually refers to "polysaccharide gums" all polysaccharides or their derivatives which are dispersed in water produce gels, highly viscous or solutions.

Xanthan gum is part of the polysaccharide gums, it is food fibers "considered" as thickeners and gelling that are not soluble in water, indeed they form a gel on contact.

The rubber compositions according to the invention are based on the following constituents: at least one diene elastomer, a reinforcing filler and a crosslinking system. By the term "composition based on" is meant a composition comprising the mixture and / or the reaction product in situ of the various basic constituents used, some of these constituents being able to react and / or being intended to react. between them, at least partially, during the various phases of manufacture of the composition, or during subsequent cooking.

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

In general, the term "diene elastomer" is used herein to mean 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. % (mole%).

Thus, for example, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins EPDM type (ethylene-propylene-diene terpolymer) do not fall within the previous definition and can be particularly 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%.

These definitions being given, is meant in particular by essentially unsaturated diene elastomer capable of being used in the compositions according to the invention: any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

any copolymer obtained by co-polymerization of one or more conjugated dienes with one another or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms.

By way of conjugated dienes 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C 1 -C 5) alkyl-1,3-butadienes, such as 2,3dimethyl-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.

As vinyl aromatic compounds are suitable for example styrene, ortho-, meta-, para-methylstyrene, the commercial mixture "vinyl-toluene", para-tertiarybutylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene , divinylbenzene, vinylnaphthalene.

The copolymers may contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinyl aromatic units. The elastomers may 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 amounts of modifying and / or randomizing agent used. The elastomers can be for example block, statistical, sequence, microsequential, and be prepared in dispersion or in solution; they can be coupled and / or star or functionalized with a coupling agent and / or starring or functionalization.

[0036] Polybutadienes and, in particular, those having a content of -1.2 units of between 4% and 80% or those having a cis-1,4 content of greater than 80%, polyisoprenes or copolymers, are preferably suitable. of butadiene-styrene and in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, a 1,2-butadiene content of the butadiene part between 4% and 65%, a content of trans-1,4 bonds of between 20% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90% by weight and a glass transition temperature (Tg) of -40 ^° C. to -80 ^° C., the 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 are especially suitable 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% 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 part butadiene content of between 4% and 85%, a trans-1,4 content of the butadiene part of between 6% and 80%, a content of -1,2 units plus -3,4 of the isoprenic part of between 5% and 80%; % and 70% and a trans-1,4 content of the isoprene portion of between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg of between -20 ^° C. and -70 ^° C. .

In a particularly preferred manner, the diene elastomer of the composition according to the invention is chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (BR), polyisoprenes (IR) or natural rubber (NR). , butadiene-styrene copolymers (SBR), butadiene-isoprene copolymers (BIR), isoprene-styrene copolymers (SIR), butadiene-acrylonitrile copolymers (NBR), isoprene-styrene copolymers ( SIR), butadiene-styrene-isoprene copolymers (SBIR), butadiene-styrene-acrylonitrile copolymers (NSBR) or a mixture of two or more of these compounds.

According to another preferred embodiment, the diene elastomer is predominantly (for more than 50 phr) an isoprene elastomer. This is particularly the case when the compositions of the invention are intended to constitute, in the tires, the rubber dies of certain treads (for example for industrial vehicles).

By "isoprene elastomer" is meant in known manner a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR ), the various isoprene copolymers and the mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene copolymers (butyl rubber-HR), isoprene-styrene copolymers (SIR), isoprene-butadiene copolymers (BIR) or isoprene-butadiene-styrene copolymers. (SBIR). This isoprene elastomer is preferably natural rubber or synthetic cis-1,4 polyisoprene; of these synthetic polyisoprenes, polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used.

However, such diene polymers can be used alone or in combination with other elastomers conventionally used in tires such as essentially saturated diene elastomers such as:

a ternary copolymer obtained by copolymerization of ethylene, of an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer containing from 6 to 12 carbon atoms, for example 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;

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

or a copolymer of isobutene and paramethylstyrene, as well as the halogenated, in particular chlorinated or brominated (BIMS) versions, of this type of copolymer. As a reinforcing filler, it may in particular use carbon black or silica or other reinforcing fillers alone or in a cut with each other.

More particularly, carbon blacks are suitable for all carbon blacks, especially blacks of the type HAF, ISAF, SAF, conventionally used in tires and particularly in the treads of tires. By way of non-limiting examples of such blacks, mention may be made of blacks

N115, N134, N234, N330, N339, N347, N375.

In the case of a silica, a highly dispersible precipitated silica is preferably used, in particular when the invention is used for the manufacture of tires having a low rolling resistance; as non-limiting examples of such preferential highly dispersible silicas, mention may be made of the Ultrasil 7000 and Ultrasil 7005 silicas from Degussa, the Zeosil 1165MP, 1135MP and II 15MP silicas from Rhodia, the Hi-SiI silica EZ150G from PPG. Zeopol silicas 8715, 8745 and 8755 from the Huber Company, treated precipitated silicas such as, for example, the "aluminum doped" silicas described in the above-mentioned application EP-A-0735088.

The vulcanization system itself is preferably based on sulfur and a primary vulcanization accelerator, in particular a sulfenamide type accelerator. To this basic vulcanization system are added, various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), etc. Sulfur is used at a preferential rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr, for example between 0.5 and 3.0 phr, when the invention is applied to a strip. of tire rolling. The primary vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr, in particular when the invention is applied to a tire tread. It goes without saying that the invention relates to the previously described rubber compositions both in the so-called "raw" state (ie, before firing) and in the so-called "cooked" or vulcanized state (ie, after crosslinking). or vulcanization).

Of course, the compositions according to the invention can be used alone or in cutting (i.e., mixed) with any other rubber composition used for the manufacture of tires. 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 plasticizers or extension oils, which these are of aromatic or non-aromatic nature, pigments, protective agents such as anti-ozone waxes, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing 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 (or US2003-0212185).

The examples which follow illustrate the invention without however limiting it.

In the examples, the rubber compositions are characterized after baking as indicated below.

- Hysteretic losses:

These losses, denoted P60 °, are measured at 60 ^° C. in percentage. The strain for the measured losses is 35%.

- Stresses and elongations at break:

The stresses at break (in MPa) and the elongations at break (in%) are measured at 60 ^° C. - Dynamic properties:

The dynamic properties G * and tan (δ) max are measured on a viscoanalyzer (Metravib V A4000), according to the ASTM D 5992 - 96 standard. The response of a sample of vulcanized composition (cylindrical test specimen 2 mm in diameter) is recorded. thickness and 78.5 mm2 section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under normal temperature conditions according to ASTM D 1349 - 99. A strain amplitude sweep is carried out peak to peak of 0.1 to 50% (forward cycle), then 50% to 1% (return cycle). The results exploited are the complex dynamic shear modulus (G *) and the loss factor, tan (δ). For the return cycle, the maximum value of tan (δ) observed (tan (δ) max) is indicated.

In the examples which follow, the rubber compositions were produced as follows.

The compositions are manufactured in appropriate mixers, using two successive preparation phases well known to those skilled in the art: a first phase of work or thermo-mechanical mixing (sometimes called "non-productive" phase) to high temperature, up to a maximum temperature (denoted Tmax) of between 110 ^° C. and 190 ^° C., preferably between 130 ^° C. and 180 ^° C., followed by a second phase of mechanical work (sometimes referred to as a "productive" phase ") at a lower temperature, typically less than 110 ⁰ C, for example between 60 ⁰ C and 100 ⁰ C, finishing phase during which is incorporated the crosslinking system or vulcanization; such phases have been described for example in the aforementioned EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

In the process according to the invention, the first phase (non-productive) is conducted in two thermomechanical steps. During the first step, all the necessary basic constituents, any coating agents or application agents are introduced into a suitable mixer such as a conventional internal mixer. and other miscellaneous additives, with the exception of the vulcanization system. This first step is carried out at a temperature of between 110 ^° C. and 190 ^° C. and, preferably, between 130 ^° C. and 180 ^° C. The second thermomechanical working step is carried out in this internal mixer, after intermediate cooling (cooling temperature). cooling preferably less than 100 ⁰ C), to introduce the polysaccharide powders and also for the purpose of subjecting the compositions a complementary heat treatment, and in particular to further improve the dispersion in the elastomeric matrix of the reinforcing filler. The total mixing time, in this non-productive phase, is preferably between 2 and 10 minutes at a temperature of less than or equal to 130 ^° C. in order to avoid any degradation of the polymer.

After cooling the mixture thus obtained, the low temperature vulcanization system is then incorporated, generally in an external mixer such as a roller mixer; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 minutes.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or extruded, to form for example a rubber profile used for the manufacture semi-finished products such as treads.

The vulcanization (or cooking) is conducted in a known manner at a temperature generally between 130 ⁰ C and 200 ⁰ C, under pressure, for a sufficient time which may vary for example between 5 and 90 minutes depending in particular on the cooking temperature, the vulcanization system adopted, the kinetics of vulcanization of the composition in question or the size of the tire.

This example is intended to show the superiority of a tread according to the invention with respect to a control tread in an ice-start situation of a tire, with a temperature of between -5 ^° C. and 0 ^° C.

The control tread is made from a control composition Al and the tread according to the invention from a composition A2 according to the invention, that is to say comprising a Xanthan gum powder in proportions and for a particle size corresponding to the invention

The compositions A1 and A2 have the same basic formula A. This basic formulation A is as follows:

NR (I) 80

BR (2) 20

Carbon black N234 53

Paraffin 1

Antioxidant (3) 3

Stearic acid 2

ZnO 3

Sulfur 1,1

Accelerators (4) 1,1

(1) NR: natural rubber (peptized)

(2) BR: polybutadiene with 4.3% del-2; 2.7% trans; 93% of cis 1-4 (Tg = -106 ⁰ C) (3) N-1,3-dimethylbutyl N-phenylparaphenylenediamine (6-PPD)

(4) N-cyclohexyl-2-benzothiazylsulfenamide (CBS) The particular characteristics of the compositions A1 and A2 are shown in Table 1 which follows.

Table 1

(5) Xanthan gum: RHODOPOL 23, RHODIA (particle size: 106 μm)

Preparation of the compositions

The composition A1 is manufactured with an introduction of all the constituents on an internal mixer, with the exception of the vulcanizing agents (sulfur and accelerator) introduced on an external mixer at low temperature (the constituent cylinders of the mixer being about 30.degree. ⁰ C).

The composition A2 is manufactured according to the process of the invention, with the introduction, during the first step of the non-productive phase, of the constituents on an internal mixer with the exception of xanthan gum, said xanthan gum being introduced in the second step on the internal mixer with a temperature not exceeding 130 ⁰ C so as not to degrade the polysaccharide powder. The vulcanization system is then introduced, during the second "productive" phase, onto an external mixer.

The treads corresponding to the compositions A1 and A2 are then manufactured in accordance with the method described above in the description.

[0062] Tests

The tests were carried out for a tire of dimensions 11R22.5XDW «ICE GRIP "mounted on a 7.5 * 22.5 wheel of a" SCANIA SV81 "truck for start-up tests and a" SV79 TDH "truck for braking tests.

The measurements were carried out as follows:

- For start: we measure the distance traveled during the first two seconds after starting, starting with a constant engine speed imposed distance and the brutal application of a torque and maintaining torque.

The measurements are performed for the empty vehicle and for the laden vehicle, that is to say, with a nominal load.

- for braking: stopping distance of the truck from a steady speed of 30 km / h with ABS braking.

The results obtained are shown in Table 2 which follows.

Table 2

It is clear that the tire corresponding to the tread composition A2, according to the invention, significantly improves the grip of the tire on frozen ground.

Example 2

The purpose of this example is to compare the properties of stiffness, stress and elongation properties, and so on. of several rubber compositions according to the invention with those of a tread composition conforming to the state of the aforementioned technique that is to say comprising a water-soluble powder such as carboxymethylcellulose or polyvinyl alcohol, PV A.

The compositions were prepared according to the procedure described in Example 1 for A2, A2 being identical to the composition of the same name of Example 1.

All the compositions noted A2, E (PVA) and F (CARBO) have the basic formulation A specified in Example 1, they are distinguished from each other by their content of xanthan gum or powder hydrolso lubie as follows: - A2 contains 20 phr of xanthan gum, RHODOPOL 23, RHODIA (particle size: 106 μm)

- E (PVA): 20 phr of PVA sold under the name Mowiol 4-88 by the company Alrich, PVA 86.7-88.7 mol% hydrolysis, degree of polymerization 630, viscosity at 4% in H20 at 20 ^° C 3-5mPa. s, (particle size: 500 μm) - F (CARBO): 20 phr of carboxymethylcellulose, sodium salt, originating from FLUKA (N ° 21903), characterized by a solution viscosity of 700-1500 mPa.s ( at 1% in H 2 O at 25 ° C) and a degree of substitution of 0.7- 0.85 (particle size: 89 μm).

Table 3 gives the properties measured after cooking at 150 ⁰ C for 25 minutes.

Table 3

It is found that the compositions A2 according to the invention have a much better compromise of mechanical reinforcement without a significant penalty for the hysteresis of the material, that the mixtures comprising polyvinyl alcohol, E (PVA), or carboxymethylcellulose, F (CARBO).

This example therefore allows us to illustrate the improvement of rubber properties of the compositions according to the invention with respect to the compositions described in the prior art, and consequently the improvement of the wear resistance of the compositions. compositions according to the invention with respect to these compositions of the prior art. However, it is precisely this degradation of the wear resistance for the compositions of the prior art that made them, as was said at the beginning of the description, unusable industrially.

EXAMPLE 3 The purpose of this example is, in the same way as in Example 1, to compare the different rubber properties of a diene control tread composition which does not include polysaccharide or water-soluble powder with compositions for tread according to the invention, that is to say comprising a powder of xanthan gum. The two base formulation compositions B have a blend of natural rubber and synthetic rubber different from that of Example 1.

This basic formulation B is the following:

NR (I) 40

BR (2) 60

Silica (3) 80

Carbon black N234 5

Aromatic oil 65

Anti-ozone wax 1,5

Coupling Agent (4) 5 Antioxidant (5) 2

Stearic acid 1

ZnO 1.5

DPG (6) 1.5

Sulfur 2

Accelerators (7) 1,5

(1) NR: natural rubber (peptized)

(2) BR: polybutadiene with 4.3% del-2; 2.7% trans; 93% cis 1-4 (Tg = -106 ⁰ C) (3) "Zeosil 1165Mp" silica from Rhodia, type "HDS"

(4) Coupling agent TESPT ("Si69" from Degussa)

(5) Antioxidant: N-1,3 dimethylbutyl N-phenylparaphenylenediamine (6-PPD)

(6) DPG: diphenylguanidine (Perkacit DPG from Flexys)

(7) Accelerator: N-cyclohexyl-2-benzothiazylsulfenamide (CBS)

The particular characteristics of the compositions B1 and B2 are given in Table 4 which follows:

Table 4

(8) Xanthan gum: RHODOPOL 23, RHODIA

The first mixing stage of the process (so-called non-productive phase) is carried out in a mixing tank. The main ingredients (elastomer, silica, oil and chemical additives) are introduced. In a finishing phase of the process (so-called productive phase) performed on a cylinder tool, the vulcanization system is introduced. Table 5 gives the properties measured after cooking at 150 ⁰ C for 40 minutes.

Table 5

It is found that the composition B2 according to the invention, comprising a xanthan gum, has rubber properties in terms of elongation and breaking stress degraded compared to the control composition, however this degradation is not not prohibitive for the skilled person.

In addition, it is very surprisingly noted a decrease in hysteresis losses for B2 compared to the control composition B1, which means an improvement in rolling resistance in a tire tread application.

Thus, on the one hand, the foreseeable degradation of the rubber properties in terms of elongation and stress at break, due to the introduction of xanthan gum into the composition according to the invention, remains acceptable by the skilled in the art and, on the other hand, he notes an improvement on the hysteretic properties.

Example 4

This example is intended to show the superiority of a tread according to the invention with respect to a control tread in an ice-up situation of a tire with a temperature of between -5 ° C. and 0 ° C. ⁰ C for treads manufactured according to the method detailed in the description with rubber compositions Bl, control, and B2, according to the invention, identical to those of Example 3 above. These compositions B1 and B2 were used for the manufacture of tire treads 205 / 55R16 brand "MICHELIN X Ice", mounted on a vehicle "TOYOTA PRONAR" with a braking system with anti Wheel Lock (ABS) and Start Control (TCS).

Ice driving tests were conducted, during which different types of icy slopes and temperature conditions were tested.

Braking test:

The results obtained after longitudinal braking (distance traveled to decelerate from 20 to 5 km / h) are indexed with respect to the braking distance of the control tire. The braking tests are carried out on ice track under shelter.

The braking performance index of tires "tests" is obtained by the following formula:

IPFreinage = (Braking distance of the indicator / tire braking distance test) * 100.

Start-up test: The results obtained after the start-up test (active anti-skid system) correspond to the time required to accelerate from 5 to 20 km / h at full engine speed under the control of the TCE system.

The ice acceleration tests are performed on a covered track.

The performance index for the start of tires "tests" is obtained by the following formula:

IPStart = (Light start time / Test tire acceleration time) * 100. The results obtained are shown in Table 6 which follows.

Table 6

It is clear that the tire corresponding to the tread composition B2, according to the invention, significantly improves the grip of the tire on frozen ground.

Claims

1) Tread of a tire having a composition based on at least one diene elastomer, a reinforcing filler, a vulcanization system characterized in that the composition comprises a powder of xanthan gum in a proportion of 10 to 40 parts by weight. weight per hundred parts of elastomer, p.

2) A tread according to claim 1, wherein the proportion of xanthan gum powder included in the composition is 15 to 30 phr.

3) A tread according to any one of claims 1 or 2, wherein the size of the particles constituting the xanthan gum powder is between 10 and 500 microns.

4) A tread according to any one of claims 1 or 2, wherein the size of the particles constituting the xanthan gum powder is between 50 and 300 microns.

5) Tread according to any one of the preceding claims, wherein the xanthan gum powder is used in a blend with one or more other polysaccharide powders.

The tread of claim 5, wherein the xanthan gum powder is used in a blend with a guar gum powder.

7) Tread according to any one of the preceding claims, wherein the diene elastomer is predominantly, for more than 50 phr, an isoprene elastomer.

8) A tread according to any one of the preceding claims, wherein the reinforcing filler comprises predominantly carbon black.

9) tread according to any one of the preceding claims, in which reinforcing filler mainly comprises silica.

A tread according to any one of the preceding claims, wherein the reinforcing filler comprises a blend of carbon black and silica.

11) Process for obtaining a tread rubber composition based on at least one diene elastomer, a reinforcing filler, a vulcanization system, which comprises a first thermomechanical kneading phase of the constituents of the composition at Except for the vulcanization system, characterized in that the composition comprises a xanthan gum powder in a proportion of 10 to 40 phr and in that the xanthan gum powder is incorporated during the first mixing phase.

12) The method of claim 11, wherein the proportion of incorporated xanthan gum is between 15 and 30 phr.

13) Process according to any one of claims 11 or 12, wherein the first phase of the process is conducted in two steps: - a first step of kneading of all the constituents of the composition with the exception of xanthan gum and a second step in which the xanthan gum powder is incorporated.

14) The method of claim 13, wherein the first step of the first mixing phase is carried out at a temperature between 110 ⁰ C and 190 ⁰ C.

15) The method of claim 13, wherein the first step of the first kneading phase is carried out at a temperature between 130 ⁰ C and 180 ⁰ C.

16) The method of claim 13, wherein the second step of the first mixing step is carried out at a temperature less than or equal to 130 ⁰ C, after cooling at the end of the first step.

The method of claim 16, wherein the cooling between the first and second steps of the first kneading phase is carried out at a temperature below or equal to 10O ⁰ C.

18) Process according to any one of claims 11 to 17, wherein the second phase of the process is carried out at a temperature between 60 ⁰ C and 100 ⁰ C.

19) tire comprising a tread according to any one of claims 1 to 10.

20) winter tire comprising a tread according to any one of claims 1 to 10.

Pneumatic tire intended for equipping heavy goods vehicles, comprising a tread according to any one of claims 1 to 10.

22) Tire intended for equipping passenger vehicles, comprising a tread according to any one of claims 1 to 10.