Title of Invention

A TIRE HAVING A TREAD COMPRISING PARTICLES OF SILICONE

RUBBER

1. FIELD OF THE INVENTION

[ 0 0 0 1 ]

The present invention relates to tire treads and to rubber compositions forming said treads. It relates more particularly to tires having treads that comprise rubber compositions capable to reduce noise from the tires when the vehicle is moving.

2. BACKGROUND

[ 0 0 0 2 ]

A regulation of tire rolling noise emission (Directive 2001/43 EC) was introduced in Europe in 2001, and limits of the tire rolling sound emission level was described in the regulation. The limits were adopted into UN/ECE (United Nations Economic Commission for Europe) Regulation No.117 revision 1 concerning the Approval of Tire with regard to rolling sound emission (called Rl 17-01 below) in 2005.

[ 0 0 0 3 ]

The World Forum for Harmonization of Vehicle Regulations in UN/ECE (WP.29) adopted the revision 2 (called Rl 17-02 below) in 2010. Limits in Rl 17-02 are more severe than that in Rl 17-01 by about 4 dB(A). Rl 17-02 has been implemented in Europe since 2012 and several countries and zones are going to ratify Rl 17-02.

l Therefore, there is a compelling need for any technology to reduce the tire rolling noise emission (called coast-by noise below) is needed in the worldwide.

[ 0 0 0 4 ]

In order to reduce coast-by noise, tire manufactures have provided different solutions which consist of modifying the formulation of rubber compositions themselves.

[ 0 0 0 5 ]

A proposal has been made to incorporate foam rubber in a rubber composition forming a tread composing a tire. The rubber composition including the foam rubber makes specific gravity of the tread decreased, which makes it possible to reduce coast-by noise of the tire (JP 2002-241528 A).

[ 0 0 0 6 ]

Other solution has been proposed to incorporate an organic bentonite in a rubber composition forming a tread composing a tire. The rubber composition comprising the organic bentonite is capable of absorbing vibration/noise generated by the tire contacting the ground, which makes it possible to reduce sound pressure level at frequency values (1000 and 1250 Hz). It is well known that the reduction of sound pressure level at the above frequency values is effective in order to reduce coast-by noise of the tire (JP 2003-034736 A).

[ 0 0 0 7 ]

However, said known approaches may have a negative impact on the rolling resistance and/or stability performances of the tires. Moreover, limits of tire rolling resistance coefficient have been also introduced in Rl 17-02, so that it is needed today to reduce coast-by noise without degrading the rolling resistance and without deterioration of stability of the tires. 3. BRIF DESCRIPTION OF THE INVENTION

[ 0 0 0 8 ]

Now, the applicants have discovered a novel and specific rubber composition of a tread of a tire which makes it possible to achieve the above objective, that is to say to reduce the coast-by noise without degrading the rolling resistance, in addition while maintaining the stability performance.

[ 0 0 0 9 ]

Thus, a first subject matter of the present invention is a tire having a tread that comprises a rubber composition comprising at least:

a diene elastomer;

- more than 25 phr of a plasticizer chosen from the group consisting of liquid plasticizers, hydrocarbon resins and the mixtures thereof;

- 40 to 150 phr of a reinforcing filler;

- more than 30 phr of particles of silicone rubber, said particles having a median size by weight of between 4 μιη and 2000 μπι.

[ 0 0 1 0 ]

Moreover, aspects of the present invention can be as follows. [1] A tire having a tread that comprises a rubber composition comprising at least: - a diene elastomer; more than 25 phr of a plasticizer chosen from the group consisting of liquid plasticizers, hydrocarbon resins and the mixtures thereof;

40 to 150 phr of a reinforcing filler; more than 30 phr of particles of silicone rubber, said particles having a median size by weight of between 4 μπι and 2000 μιη.

[2] The tire according to [1], wherein the content of the particles is more than 35 phr.

[3] The tire according to [1] or [2], wherein the particles have the median size by weight of between 10 μηι and 1500 μη .

[4] The tire according to any one of [1] to [3], wherein the particles have Shore A hardness of less than 60.

[5] The tire according to any one of [1] to [4], wherein the particles are isometric or anisometric particles.

[6] The tire according to [5], wherein the particles are isometric particles.

[7] The tire according to any one of [1] to [6], wherein the particles are in the form of powder, granules, beads, spheres or mixtures thereof.

[8] The tire according to any one of [1] to [7], wherein the particles are coated with a resin. [9] The tire according to [8], wherein the resin for coating the particles is a silicone resin.

[10] The tire according to any one of [1] to [9], wherein the diene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and the mixtures thereof.

[11] The tire according to any one of [1] to [10], wherein the rubber composition comprises 50 to 100 phr of a copolymer based on styrene and butadiene, and 0 to 50 phr of another optional diene elastomer.

[12] The tire according to [11], wherein the copolymer based on styrene and butadiene is chosen in the group consisting of styrene-butadiene copolymers, styrene-butadiene-isoprene copolymers and the mixtures thereof.

[13] The tire according to [11], wherein the copolymer based on styrene and butadiene is a styrene-butadiene copolymer (SBR).

[14] The tire according to any one of [11] to [13], wherein the copolymer based on styrene and butadiene has a glass transition temperature at greater than -40 °C.

[15] The tire according to [14], wherein the copolymer based on styrene and butadiene has a glass transition temperature within a range from -30 °C to +30°C. [16] The tire according to any one of [11] to [15], wherein the other optional diene elastomer is chosen in the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes having a content of cis-1,4 bonds of greater than 90%, and mixtures thereof. [17] The tire according to any one of [1] to [16], wherein the reinforcing filler comprises an inorganic filler, a carbon black or a mixture thereof.

[18] The tire according to any one of [1] to [17], wherein the content of the reinforcing filler is within a range from 60 to 120 phr.

[19] The tire according to any one of [1] to [18], wherein the plasticizer contains liquid plasticizers, and wherein the liquid plasticizers are chosen from the group consisting of polyolefinic oils, naphthenic oils, paraffinic oils, DAE oils, MES oils, TDAE oils, RAE oils, TRAE oils, SRAE oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and the mixtures thereof.

[20] The tire according to any one of [1] to [19], wherein the plasticizer contains hydrocarbon resins, and wherein the hydrocarbon resins are chosen from the group consisting of cyclopentadiene homopolymer or copolymer resins, dicyclopentadiene homopolymer or copolymer resins, terpene homopolymer or copolymer resins, C ₅ fraction homopolymer or copolymer resins, C ₉ fraction homopolymer or copolymer resins, alpha-methyl styrene homopolymer or copolymer resins, and the mixtures of these resins.

[21] The tire according to any one of [1] to [20], wherein the content of the plasticizer is more than 30 phr.

[ 0 0 1 l ] The tires of the present invention are particularly intended to equip passenger motor vehicles, including 4x4 (four-wheel drive or all-wheel drive) vehicles and SUV (Sport Utility Vehicles) vehicles, two-wheel vehicles (in particular motorcycles), and also industrial vehicles in particular chosen from vans and heavy-duty vehicles (i.e., underground vehicles, bus vehicles or heavy road transport vehicles (lorries, tractors, trailers)), or off-road vehicles, such as agricultural vehicles or earthmoving equipment.

[ 0 0 1 2 ]

The invention and its advantages will be easily understood in the light of the description and implementation examples which follow.

3. MEASUREMENTS AND TESTS USED

[ 0 0 1 3 ]

The rubber compositions and the tires according to the present invention including Examples are characterized and tested as indicated below.

3-1. Tensile tests

[ 0 0 1 4 ]

These tensile tests make it possible to determine the elasticity stresses and the properties at break. Unless otherwise indicated, they are carried out in accordance with French Standard NF T 46-002 of September 1988. The nominal secant moduli (or apparent stresses, in MPa) are measured in second elongation (i.e., after a cycle of accommodation to the degree of extension expected for the measurement itself) at 10% elongation (denoted M10), 100% elongation (denoted Ml 00) and 300% elongation (denoted M300). All these tensile measurements are carried out under the standard conditions of temperature (23 ± 2°C) and hygrometry (50 ± 5% relative humidity), according to French Standard NF T 40-101 (December 1979). 3-2. Shore A Hardness

[ 0 0 1 5 ]

The Shore A hardness of the compositions after curing is assessed in accordance with Standard ASTM D 2240-86. 3-3. Test on tires with regard to rolling sound emission (Coast-by noise)

[ 0 0 1 6 ]

The rolling sound emission of test tires is assessed in accordance with JASO C606- 86. The sound pressure levels at 1000, 1250, 2000 and 2500Hz were recorded by two remote-field microphones located on each either side at distance of 7.5m from a track's central reference line and 1.2m above the ground when wind speed at the microphones was less than 5m s and a l,400cc passenger car as the test vehicle provided on all the four wheels with the same kinds of test tires under 180kPa of tire inflation pressure mounted onto 6.5Jxl6 rim was coasting at 80km/h with the test vehicle's gear selector put on neutral on a specified road surface in accordance with ISO 10844.

3-4. Test on tires with regard to rolling resistance

[ 0 0 1 7 ] The rolling resistance (RR) of a tire is measured on a test drum according to ISO 28580. The tire mounted onto 6.5Jxl6 rim under 210kPa of tire inflation pressure is tested on the test drum at 80km/h and 80% of the maximum rated load. A value greater than that of the control, arbitrarily set at 100, indicates an improved result, i.e., a lower rolling resistance.

4. DETAILED DESCRIPTION OF THE INVENTION

[ 0 0 1 8 ]

The abbreviation "phr" means parts by weight per 100 parts of elastomer. In the present description, unless expressly indicated otherwise, all the percentages (%) shown are % by weight. Moreover, any interval of values denoted by the expression "between a and b" represents the range of values extending from greater than a to less than b (that is to say, limits a and b excluded) whereas any interval of values denoted by the expression "from a to b" means the range of values extending from a up to b (that is to say, including the strict limits a and b).

r

4-1. Diene elastomer

[ 0 0 1 9 ]

The tread of the tire according to the present invention comprises a rubber composition which has an essential feature of comprising a diene elastomer.

[ 0 0 2 0 ]

It should be remembered that "diene" elastomer or rubber should be understood as meaning an elastomer resulting at least in part (i.e., a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds which may or may not be conjugated).

[ 0 0 2 1 ]

Diene elastomers can be classified in a known way into two categories: those "essentially unsaturated" and those "essentially saturated". Butyl rubbers, such as, for example copolymers of dienes and of a-olefins of EPDM type, come within the category of essentially saturated diene elastomers, having a content of units of diene origin which is low or very low, always less than 15% (mol%). In contrast, essentially unsaturated diene elastomer is understood to mean a diene elastomer resulting at least in part from conjugated diene monomers, having a content of units of diene origin (conjugated dienes) which is greater than 15% (mol%). In the category of "essentially unsaturated" diene elastomers, "highly unsaturated" diene elastomer is understood to mean in particular a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

[ 0 0 2 2 ]

It is preferable to use at least one diene elastomer of the highly unsaturated type, in particular a diene elastomer chosen from the group consisting of polybutadienes (BR), synthetic polyisoprenes (IR), natural rubber (NR), butadiene copolymers, isoprene copolymers (other than IIR) and mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene/styrene copolymers (SBR), isoprene butadiene copolymers (BIR), isoprene/styrene copolymers (SIR), isoprene/butadiene/styrene copolymers (SBIR) and mixtures of such copolymers.

[ 0 0 2 3 ] More preferably, the rubber composition composing the tread of the tire of the present invention comprises, as the diene elastomer, from 50 to 100 phr of a copolymer based on styrene and on butadiene, that is to say a copolymer of at least one styrene monomer and of at least one butadiene monomer; in other words, said copolymer based on styrene and on butadiene comprises, by definition, at least units derived from styrene and units derived from butadiene.

[ 0 0 2 4 ]

Still more preferably, the content of said copolymer in the rubber composition is within a range from 50 to 90 phr, particularly within a range from 60 to 85 phr.

[ 0 0 2 5 ]

Suitable butadiene monomers are in particular 1,3 -butadiene, 2 -methyl- 1,3 -butadiene, 2,3-di(Cl-C5 alkyl)- 1,3 -butadienes such as for example 2,3-dimethyl-l,3-butadiene, 2,3-diethyl-l,3-butadiene, 2-methyl-3-ethyl-l,3-butadiene or 2-methyl-3-isopropyl- 1,3-butadiene and an aryl-l,3-butadiene. Suitable styrene monomers are in particular styrene, methylstyrenes, para-(tert-butyl)styrene, methoxystyrenes and chlorostyrenes.

[ 0 0 2 6 ]

Said copolymer based on styrene and on butadiene may have any microstructure, which is a function of the polymerization conditions used, in particular of the presence or absence of a modifying and/or randomizing agent and of the amounts of modifying and/or randomizing agents used. It may be, for example, a block, statistical, sequential or microsequential copolymer, and may be prepared in dispersion or in solution; it may be coupled and/or star-branched or else functionalized with a coupling and/or star-branching or functionalizing agent. [ 0 0 2 7 ]

Preferably, the copolymer based on styrene and on butadiene is chosen from the group consisting of styrene-butadiene (abbreviated to SBR) copolymers, styrene- butadiene-isoprene (abbreviated to SBIR) copolymers and blends of such copolymers.

[ 0 0 2 8 ]

Among the SBIR copolymers, mention may especially be made of those having a styrene content between 5% and 50% by weight and more particularly between 10% and 40%, an isoprene content between 15% and 60% by weight and more particularly between 20% and 50%, a butadiene content between 5% and 50% by weight and more particularly between 20% and 40%, a content (mol%) of 1,2- units of the butadiene part of between 4% and 85%, a content (mol%) of trans- 1,4- units of the butadiene part of between 6% and 80%, a content (mol%) of 1,2- units plus 3,4- units of the isoprene part of between 5% and 70% and a content (mol%) of trans- 1,4- units of the isoprene part of between 10% and 50%.

[ 0 0 2 9 ]

More preferably, an SBR copolymer is used. Among the SBR copolymers, mention may especially be made of those having a styrene content of between 5% and 60% by weight and more particularly of between 20% and 50%, a content (mol%) of 1,2- bonds of the butadiene part of between 4% and 75% and a content (mol%) of trans- 1 ,4- bonds of between 10% and 80%.

[ 0 0 3 0 ]

The Tg (glass transition temperature) of copolymer based on styrene and on butadiene is preferably greater than -40°C, more preferably greater than -35°C, particularly within a range from -30°C to +30°C, more particularly within a range from -25°C to +25°C.

[ 0 0 3 1 ]

The Tg of the elastomers described here is measured in a conventional manner, well known to a person skilled in the art, on an elastomer in the dry state (i.e. without extender oil) and by DSC {Differential Scanning Calorimetry) (for example according to ASTM D3418 (1999)).

[ 0 0 3 2 ]

A person skilled in the art knows how to modify the microstructure of a copolymer based on styrene and on butadiene, in particular of an SBR, in order to increase and adjust its Tg, especially by playing with the contents of styrene, of 1,2- bonds or else of trans- 1,4- bonds of the butadiene part. Use is more preferably made of an SBR (solution or emulsion) having a styrene content (mol%) which is greater than 35%, more particularly between 35% and 60%, in particular within a range from 38% to 50%. SBRs having a relatively high Tg are well known to a person skilled in the art; they have been used in particular in tire treads for improving some of their standard properties.

[ 0 0 3 3 ]

With the preferable copolymer based on styrene and on butadiene described above, at least another optional (or second) diene elastomer, optional and different from said copolymer (i.e. not comprising units derived from styrene and butadiene) may be combined, said second diene elastomer being present in a weight content which is consequently at most equal to 50 phr in case of that content of copolymer based on styrene and on butadiene is at least equal to 50 phr. That means content of the other diene elastomer(s) is 100 phr minus that of copolymer based on styrene and on butadiene.

[ 0 0 3 4 ]

This optional second diene elastomer is preferably chosen from the group consisting of natural rubbers (NR.), synthetic polyisoprenes (IR), polybutadienes (BR), isoprene copolymers and blends of these elastomers. Such copolymers are more preferably chosen from the group consisting of isoprene-butadiene copolymers (BIR) and isoprene-styrene copolymers (SIR).

[ 0 0 3 5 ]

Especially suitable, among the latter, are polybutadiene (BR) homopolymers and in particular those having a content (mol%) of 1,2- units of between 4% and 80% or those having a content (mol%) of cis-1,4- units of greater than 80%; polyisoprene (IR) homopolymers; butadiene-isoprene copolymers (BIR) and especially those having an isoprene content of between 5% and 90% by weight and a Tg from -40°C to -80°C; and isoprene-styrene copolymers (SIR) and especially those having a styrene content of between 5% and 50% by weight and a Tg of between -25°C and - 50°C.

[ 0 0 3 6 ]

According to one preferred embodiment, the second diene elastomer is an isoprene elastomer, more preferably natural rubber or a synthetic polyisoprene of cis-1,4- type; among these synthetic polyisoprenes, use is preferably made of polyisoprenes having a content (mol%) of cis-1,4- bonds of greater than 90%, more preferably still of greater than 98%.

[ 0 0 3 7 ] According to another more preferred embodiment, the second diene elastomer is a polybutadiene, preferably a polybutadiene having a content (mol%) of cis-1,4 bonds of greater than 90%.

[ 0 0.3 8 ]

According to another more preferred embodiment, the second diene elastomer is a mixture of polybutadiene with the following isoprene elastomer (natural rubber or synthetic polyisoprene).

4-2. Plasticizing system

[ 0 0 3 9 ]

The tread of the tire according to the present -invention comprises the rubber composition which has another essential feature of comprising more than 25 phr (notably between 25 and 100 phr) of a plasticizer chosen from the group consisting of liquid plasticizers, (solid) hydrocarbon resins and the mixtures thereof.

[ 0 0 4 0 ]

Liquid plasticizers are liquid at 20°C by definition , their role is to soften the matrix by diluting the elastomer and the reinforcing filler; their Tg is by definition less than -20°C, preferably less than -40°C.

[ 0 0 4 1 ]

Any extending oil, whether of aromatic or non-aromatic nature, any liquid plasticizing agent known for its plasticizing properties with regard to diene elastomers, can be used. At ambient temperature (20°C), these plasticizers or these oils, which are more or less viscous, are liquids (that is to say, as a reminder, substances that have the ability to eventually take on the shape of their container), as opposed, in particular, to plasticizing hydrocarbon resins which are by nature solid at ambient temperature.

[ 0 0 4 2 ]

Liquid plasticizers chosen from the group consisting of polyolefinic oils, naphthenic oils (low or high viscosity, in particular hydrogenated or otherwise), paraffinic oils, DAE (Distillate Aromatic Extracts) oils, MES (Medium Extracted Solvates) oils, TDAE oils (Treated Distillate Aromatic Extracts), RAE oils (Residual Aromatic Extracts), TRAE oils (Treated Residual Aromatic Extracts), SRAE oils (Safety Residual Aromatic Extracts), mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and the mixtures thereof are particularly suitable.

[ 0 0 4 3 ]

According to a preferred embodiment, the liquid plasticizer is chosen from the group consisting of MES oils, TDAE oils, naphthenic oils, vegetable oils and the mixtures thereof.

[ 0 0 4 4 ]

Mention may be made, as phosphate plasticizers for example, of those that contain between 12 and 30 carbon atoms, for example trioctyl phosphate. As examples of ester plasticizers, mention may especially be made of the compounds chosen from the group consisting of trimellitates, pyromellitates, phthalates, 1 ,2-cyclohexane dicarboxylates, adipates, azelates, sebacates, triesters of glycerol, and mixtures thereof. Among the above triesters, mention may be made of glycerol triesters, preferably composed predominantly (for more than 50% by weight, more preferably for more than 80% by weight) of an unsaturated C ₁₈ fatty acid, that is to say an unsaturated fatty acid chosen from the group consisting of oleic acid, linoleic acid, linolenic acid and the mixtures thereof. More preferably, whether of synthetic origin or natural origin (in the case, for example, of sunflower or rapeseed vegetable oils), the fatty acid used is composed for more than 50% by weight, more preferably still from 80% by weight, of oleic acid. Such triesters (trioleates) comprising a high content of oleic acid are well known; for example they have been described in Application WO 02/088238, as plasticizing agents in treads for tires.

[ 0 0 4 5 ]

Hydrocarbon resins, which are solid plasticizers (at 20°C), exhibit a Tg of greater than +20°C, preferably greater than +30°C, such as is described, for example in Applications WO 2005/087859, WO 2006/061064 and WO 2007/017060.

[ 0 0 4 6 ]

Hydrocarbon resins are polymers well known to a person skilled in the art which are essentially based on carbon and hydrogen and thus miscible by nature in diene elastomer composition(s), when they are additionally described as being "plasticizing". They have been described, for example, in the work entitled "Hydrocarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), chapter 5 of which is devoted to their applications, in particular in the tire rubber field (5.5. "Rubber Tires and Mechanical Goods"). They can be aliphatic or aromatic or also of the aliphatic/aromatic type, that is to say based on aliphatic and/or aromatic monomers. They can be natural or synthetic and may or may not be petroleum-based (if such is the case, also known under the name of petroleum resins). They are preferably exclusively hydrocarbon, that is to say that they comprise only carbon and hydrogen atoms. [ 0 0 4 7 ]

Preferably, the plasticizing hydrocarbon resin exhibits at least one, more preferably all, of the following characteristics:

a Tg of greater than 20°C (more preferably between 40 and 100°C;

- a number-average molecular weight (Mn) of between 400 and 2000 g/mol (more preferably between 500 and 1500g/mol);

a polydispersity index (PI) of less than 3, more preferably less than 2 (reminder: PI = Mw/Mn with Mw the weight-average molecular weight).

[ 0 0 4 8 ]

The Tg is measured in a known way by DSC (Differential Scanning Calorimetry) according to Standard ASTM D3418 (1999). The macrostructure (Mw, Mn and PI) of the hydrocarbon resin is determined by steric exclusion chromatography (SEC): solvent tetrahydrofuran; temperature 35°C; concentration 1 g/1; flow rate 1 ml/min; solution filtered through a filter with a porosity of 0.45 μηι before injection; Moore calibration with polystyrene standards; set of 3 "Waters" columns in series ("Styragel" HR4E, HR1 and HR0.5); detection by differential refractometer ("Waters 2410") and its associated operating software ("Waters Empower").

[ 0 0 4 9 ]

According to a particularly preferred embodiment, the plasticizing hydrocarbon resin is chosen from the group consisting of cyclopentadiene (abbreviated to CPD) homopolymer or copolymer resins, dicyclopentadiene (abbreviated to DCPD) homopolymer or copolymer resins, terpene homopolymer or copolymer resins, C ₅ fraction homopolymer or copolymer resins, C ₉ fraction homopolymer or copolymer resins, alpha-methyl styrene homopolymer or copolymer resins and the mixtures thereof. Use is more preferably made, among the above copolymer resins, of those chosen from the group consisting of (D)CPD/ vinylaromatic copolymer resins, (D)CPD/terpene copolymer resins, (D)CPD/C ₅ fraction copolymer resins, (D)CED/C9 fraction copolymer resins, terpene/vinylaromatic copolymer resins, terpene/phenol copolymer resins, C ₅ fraction/vinyl-aromatic copolymer resins, C ₉ fraction/vinylaromatic copolymer resins, and the mixtures thereof.

[ 0 0 5 0 ]

The term "terpene" combines here, in a known way, the a-pinene, β-pinene and limonene monomers; use is preferably made of a limonene monomer, which compound exists, in a known way, in the form of three possible isomers: L-limonene (laevorotatory enantiomer), D-limonene (dextrorotatory enantiomer) or else dipentene, the racemate of the dextrorotatory and laevorotatory enantiomers. Styrene, a-methylstyrene, ortho-, meta- or para-methylstyrene, vinyltoluene, para-(tert- butyl)styrene, methoxystyrenes, chlorostyrenes, hydroxystyrenes vinylmesitylene, divinyibenzene, vinylnaphthalene, or any vinylaromatic monomer resulting from a C ₉ fraction (or more generally from a C ₈ to C ₁₀ fraction) are suitable, for example, as vinylaromatic monomer. Preferably, the vinylaromatic compound is styrene or a vinylaromatic monomer resulting from a C ₉ fraction (or more generally from a C ₈ to Cio fraction). Preferably, the vinylaromatic compound is the minor monomer, expressed as molar fraction, in the copolymer under consideration.

[ 0 0 5 1 ]

The content of liquid plasticizer in the composition of the present invention is preferably more than 10 phr, more preferably within a range from more than 10 phr to 35 phr. [ 0 0 5 2 ]

The content of hydrocarbon resin is preferably more than 15 phr, more preferably within a range from more than 15 phr to 50 phr.

[ 0 0 5 3 ]

The content of total plasticizing agent is, for example, more than 25 phr, preferably more than 30 phr (notably between 30 and 90 phr), more preferably within a range from 35 to 80 phr.

4-3. Reinforcing filler

[ 0 0 5 4 ]

Use may be made of any type of reinforcing filler -known for its capabilities of reinforcing a rubber composition which can be used for the manufacture of tires, for example an organic reinforcing filler, such as carbon black, or a reinforcing inorganic filler, such as silica, with which a coupling agent is combined in a known way.

[ 0 0 5 5 ]

Such a reinforcing filler typically consists of nanoparticles, the mean size (by weight) (see, for example, ISO- 13320 - Particle size analysis-Laser diffraction methods), of which is less than 500 nm, generally between 20 nm and 200 nm, in particular and preferably between 20 nm and 150 nm.

[ 0 0 5 6 ]

All carbon blacks, in particular blacks of the HAF, ISAF or SAF type, conventionally used in treads for tires ("tire-grade" blacks) are suitable as carbon blacks. Mention will more particularly be made, among the latter, of the reinforcing carbon blacks of the 100, 200, 300, 600 or 700 series (ASTM grades), such as, for example, the N115, N134, N234, N326, N330, N339, N347, N375 blacks. The carbon blacks might, for example, be already incorporated in the isoprene elastomer in the form of a masterbatch (see, for example, Applications WO 97/36724 or WO 99/16600).

[ 0 0 5 7 ]

Mention may be made, as examples of organic fillers other than carbon blacks, of the functionalized polyvinyl organic fillers as described in Applications WO 2006/069792, WO 2006/069793, WO2008/003434 and WO2008/003435.

[ 0 0 5 8 ]

The term "reinforcing inorganic filler" should be understood here as meaning any inorganic or mineral filler, whatever its colour and its origin (natural or synthetic), also known as "white filler" or sometimes "clear filler" in contrast to carbon black, capable of reinforcing by itself, without means other than an intermediate coupling agent, a rubber composition intended for the manufacture of tires, in other words capable of replacing, in its reinforcing role, a conventional tire-grade carbon black; such a filler is generally characterized, in a known way, by the presence of hydroxyl (-OH) groups at its surface.

[ 0 0 5 9 ]

Mineral fillers of the siliceous type, in particular silica (Si0 ₂ ), or of the aluminous type, in particular alumina (AI2O3), are suitable in particular as reinforcing inorganic fillers. The silica used can be any reinforcing silica known to a person skilled in the art, in particular any precipitated or pyrogenic silica exhibiting a BET surface and a CTAB specific surface both of less than 450 m ² /g, preferably from 30 to 400 m ² /g, in particular between 60 and 300 m ² /g. Mention will be made, as highly dispersible ("HD precipitated silicas"), for example, of the Ultrasil 7000 and Ultrasil 7005 silicas from Evonik, the "Zeosil" 1165MP, 1.135MP and 1115MP silicas from Rhodia, the "Hi-Sil" EZ150G silica from PPG, the "Zeopol" 8715, 8745 and 8755 silicas from Huber. Mention may be made, as examples of reinforcing aluminas, of the "Baikalox A125" or "Baikalox CR125" aluminas from Ba ^' ikowski, the "APA- 100R X" alumina from Condea, the "Aluminoxid C" alumina from Degussa or the "AKP-G015" alumina from Sumitomo Chemicals.

[ 0 0 6 0 ]

The tread of the tire according to the present invention comprises the rubber composition which has another essential feature of comprising within a range from 40 to 150 phr of a reinforcing filler (in particular of silica or carbon black or a mixture of silica and carbon black). Beyond 150 phr, there is a risk of increasing the hysteresis and thus the rolling resistance of the tires. For this reason, the total content of reinforcing filler is preferably within a range from 60 to 120 phr, more preferably within a range from 70 to 100 phr.

[ 0 0 6 1 ]

According to a specific embodiment, the reinforcing filler comprises predominantly an inorganic filler, in particular silica; in such a case, the inorganic filler, in particular silica, is present at a content preferably of between 70 and 120 phr, in combination or not with carbon black in a minor amount; the carbon black, when it is present, is preferably used at a content of less than 15 phr, more preferably less than 10 phr (for example between 0.1 and 10 phr).

[ 0 0 6 2 ] In order to couple the reinforcing inorganic filler to the diene elastomer, use is made, in a well-known way, of an at least bifunctional coupling agent (or bonding agent) intended to provide a satisfactory connection, of chemical and/or physical nature, between the inorganic filler (surface of its particles) and the diene elastomer. Use is made, in particular, of bifunctional organosilanes or polyorganosiloxanes.

[ 0 0 6 3 ]

Use is made in particular of silane polysulphides, referred to as "symmetrical" or "asymmetrical" depending on their specific structure, as described, for example, in Applications WO 03/002648 (or US 2005/016651) and WO 03/002649 (or US 2005/016650).

[ 0 0 6 4 ]

"Symmetrical" silane polysulphides corresponding to the following general formula (I): (I) Z - A - S _x - A - Z , in which:

- x is an integer from 2 to 8 (preferably from 2 to 5);

- A is a divalent hydrocarbon radical (preferably, Q-Qs alkylene groups or C ₆ - C ₁₂ arylene groups, more particularly C do, in particular CrC ₄ , alkylenes, especially propylene);

- Z corresponds to one of the formulae below: R1 R1 R2

I I I

Si— — Si— -Si- R2 R2

in which:

- the R1 radicals, which are unsubstituted or substituted and identical to or different from one another, represent a Ci-Ci alkyl, Cs-Qg cycloalkyl or C ₆ -

C ₁₈ aryl group (preferably, CrC ₆ alkyl, cyclohexyl or phenyl groups, in particular C1-C4 alkyl groups, more particularly methyl and/or ethyl),

- the R2 radicals, which are unsubstituted or substituted and identical to or different from one another, represent a C1-C18 alkoxyl or C ₅ -C ₁₈ cycloalkoxyl group (preferably a group chosen from Q-Cs alkoxyls and C ₅ -C ₈ cycloalkoxyls, more preferably still a group chosen from C1-C4 alkoxyls, in particular methoxyl and ethoxyl),

are suitable in particular, without the above definition being limiting.

[ 0 0 6 5 ] In the case of a mixture of alkoxysilane polysulphides corresponding to the above formula (I), in particular the usual mixtures available commercially, the mean value of the "x" index is a fractional number preferably of between 2 and 5, more preferably in the vicinity of 4. However, the present invention can also advantageously be carried out, for example, with alkoxysilane disulphides (x=2).

[ 0 0 6 6 ]

Mention will more particularly be made, as examples of silane polysulphides, of bis((C 1 -C ₄ )alkoxyl(C 1 -C ₄ )alkylsilyl(C j -C ₄ )alkyl)polysulphides (in particular disulphides, trisulphides or tetrasulphides), such as, for example, bis(3- trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl)poly sulphides. Use is in particular made, among these compounds, of bis(3-triethoxysilylpropyl)tetrasulphide, abbreviated to TESPT, of formula [(C ₂ H ₅ 0) ₃ Si(CH ₂ ) ₃ S ₂ ] ₂ , or bis(3- triethoxysilylpropyl)disulphide, abbreviated to TESPD, of formula [(C ₂ HsO) ₃ Si(CH ₂ ) ₃ S] ₂ . Mention will also be made, as preferred examples, of bis(mono(C _\ -C ₄ )alkoxyldi(C i -C ₄ )alkylsilylpropyl)polysulphides (in particular disulphides, trisulphides or tetrasulphides), more particularly bis(monoethoxydimethylsilylpropyl)tetrasulphide, as described in Patent Application WO 02/083782 (or US 7 217 751).

[ 0 0 6 7 ]

Mention will in particular be made, as coupling agent other than alkoxysilane polysulphide, of bifunctional POSs (polyorganosiloxanes) or of hydroxysilane polysulphides (R ² = OH in the above formula (I)), such as described in Patent Applications WO 02/30939 (or US 6 774 255) and WO 02/3-1041 (or US 2004/051210), or of silanes or POSs carrying azodicarbonyl functional groups, such as described, for example, in Patent Applications WO 2006/125532, WO 2006/125533 and WO 2006/125534.

[ 0 0 6 8 ]

As examples of other silane sulphides, mention will be made, for example, of the silanes bearing at least one thiol (-SH) function (referred to as mercaptosilanes) and/or at least one blocked thiol function, such as described, for example, in patents or patent applications US 6 849 754, WO 99/09036, WO 2006/023815 or WO 2007/098080. [ 0 0 6 9 ]

Of course, use could also be made of mixtures of the coupling agents described previously, as described in particular in the aforementioned application WO

2006/125534.

[ 0 0 7 0 ]

In the rubber compositions in accordance with the present invention, the content of coupling agent is preferably between 2 and 15 phr, more preferably between 3 and 12 phr.

[ 0 0 7 1 ]

A person skilled in the art will understand that a reinforcing filler of another nature, in particular organic nature, might be used as filler equivalent to the reinforcing inorganic filler described in the present section, provided that this reinforcing filler is covered with an inorganic layer, such as silica, or else comprises, at its surface, functional sites, in particular hydroxyls, requiring the use of a coupling agent in order to form the connection between the filler and the elastomer.

4-4. Particles of silicone rubber

[ 0 0 7 2 ]

The rubber composition of the tread of the tire according to the present invention has another essential feature of comprising more than 30 phr of particles of silicone (that may be polyorganosiloxane, which is synonymous) rubber, said particles, that are silicone rubber particles, having a median size by weight of between 4 μπι and 2000 μιη.

[ 0 0 7 3 ] The content of the particles of the silicone rubber is preferably between 30 and 150 phr. Below the indicated minimum, the targeted technical effect is insufficient, where above the recommended maximum, there is a risk of worsening wear resistance of the tire. For the reason, this content is more preferably more than 35 phr (in particular between 35 and 135 phr), still more preferably more than 40 phr (in particular between 40 and 120 phr) and particularly more than 45 phr (in particular between 45 phr and 100 phr).

[ 0 0 7 4 ]

The median size by weight of the particles of the silicone rubber is between 4 μιη and 2000 μπι. Below the indicated minimum, the targeted technical effect is insufficient, where above the recommended maximum, there is a risk too of worsening wear resistance of the tire. For the reason, the median size by weight is preferably between 10 μηι and 1500 μιη, more preferably between 15 μιη and 1000 μηι, still more preferably, particularly between 25 μιη and 500 μπι, especially between 25 μπι and 50 μτη .

[ 0 0 7 5 ]

Shore A hardness of the particles of the silicone rubber is preferably less than 60, more preferably less than 50 (in particular between 10 and 50), and still more preferably less than 40 (in particular between 20 and 40).

[ 0 0 7 6 ]

Moreover, the particles of the silicone rubber may be isometric particles or anisometric particles. Preferably, the particles are isometric particles. According to a specific and preferred embodiment, the particles are in the form of powder, granules, beads, spheres or mixtures thereof. More preferably, the particles are in the form of powder, beads or spheres.

According to another specific embodiment, the anisometric particles are needle- shaped, rod-shaped, ellipsoidal or amorphous particles. Preferably, the anisometric particles are amorphous particles.

[ 0 0 7 7 ]

The particles of the silicone rubber may comprise organic radicals including alkyl radicals, aryl radicals and the derivative radicals on a polymer backbone made of siloxane repeating unit (-Si-O-Si-) such silicone rubber being or not crosslinked.

[ 0 0 7 8 ]

According to a specific embodiment, the particles of the silicone rubber comprise linear dimethylpolysiloxane and/or methylphenylpolysiloxane which are crosslinked with methyl hydrogen polysiloxane.

[ 0 0 7 9 ]

According to a preferred embodiment, the particles of the silicone rubber are coated with a resin. In particular, the resin is a silicone resin.

This silicone resin for coating the particles may be any thermosetting silicone resin which is heat-treated liquid material of linear polysiloxane, such as instance, linear dimethylpolysiloxane, and has a three-dimensionally crosslinked structure. Such thermosetting silicone resin may be a resin hardener or a resin modification of polyorganosilsesquioxane which is three-dimensionally cured and siloxane bonds of which are expressed by a formula (RSi0 ₃ / ₂ ) _n . R in the formula is for instance CH ₃ , C ₆ H ₅ or a long-chain alkyl radical. The particles of the silicone rubber, being coated with the silicone resin, may have outstanding dispersion and excellent impact resistance.

[ 0 0 8 0 ]

These particles of the silicone rubber are well known and are available commercially, for example known as X-52-875, KMP-594, KMP-597, KMP-598, KMP-600, KMP- 601 and KMP-602 as provided by ShinEtsu Co., Ltd.

[ 0 0 8 1 ]

For the particle size analysis and the calculation of the median diameter of the particles, various known methods can be applied, for example via laser scattering (for example according to ISO-8130-13 standard or JIS K5600-9-3 standard); it is also possible to simply use a particle size analysis via a mechanical screening through screens of different diameters. The median diameter (or median size) is ultimately calculated in a known manner from the histogram of the particle size distribution.

4-5. Various additives

[ 0 0 8 2 ]

The tread of the tire according to the present invention comprises the rubber composition which can comprise all or a portion of the usual additives generally used in the elastomer compositions intended for the manufacture of treads for tires, such as, for example, pigments, protection agents, such as antiozone waxes, chemical antiozonants, antioxidants, antifatigue agents, reinforcing resins, such as methylene acceptors (for example phenolic novolac resin) or methylene donors (for example HMT or H3M), a crosslinking system based either on sulphur or on donors of sulphur and or peroxide and/or bismaleimides, vulcanization accelerators, or vulcanization activators.

[ 0 0 8 3 ]

The rubber composition can also comprise coupling activators when a coupling agent is used, agents for covering the inorganic filler or more generally processing aids capable, in a known way, by virtue of an improvement in the dispersion of the filler in the rubber matrix and of a lowering of the viscosity of the compositions, of improving their property of processing in the raw state; these agents are, for example, hydrolysable silanes, such as alkylalkoxysilanes, polyols, polyethers, amines, or hydroxylated or hydrolysable polyorganosiloxanes.

4-6. Manufacture of the rubber compositions and of the treads

[ 0 0 8 4 ]

The rubber compositions composing the tread of the present invention are manufactured in appropriate mixers using two successive preparation phases according to a general procedure well known to a person skilled in the art: a first phase of thermomechanical working or kneading (sometimes described as "nonproductive" phase) at high temperature, up to a maximum temperature of between 130°C and 200°C, preferably between 145°C and 185°C, followed by a second phase of mechanical working (sometimes described as "productive" phase) at a lower temperature, typically of less than 120°C, for example between 60°C and 100°C, finishing phase during which the crosslinking or vulcanization system is incorporated.

[ 0 0 8 5 ] A process which can be used for the manufacture of such compositions forming the tread of the tire according to the present invention comprises, for example and preferably, the following steps:

incorporating in the diene elastomer, in a mixer, more than 25 phr of a -plasticizer chosen from the group consisting of liquid plasticizers, hydrocarbon resins and the mixtures thereof, within a range from 40 to 150 phr of a reinforcing filler, more than 30 phr of particles of silicone rubber and the particles having a median size by weight of between 4 μπι and 2000 μιη, everything being kneaded thermomechanically, in one or more goes, until a maximum temperature of between 130°C and 200°C is reached;

cooling the combined mixture to a temperature of less than 100°C;

subsequently incorporating a crosslinking system;

kneading everything up to a maximum temperature of less than 120°C; extruding or calendering the rubber composition thus obtained, in particular in the form of a tire tread.

[ 0 0 8 6 ]

By way of example, the first (non-productive) phase is carried out in a single thermomechanical stage during which all the necessary constituents, the optional additional covering agents or processing aids, and various other additives, with the exception of the crosslinking system, are introduced into an appropriate mixer, such as a normal internal mixer. After cooling the mixture thus obtained during the first non-productive phase, the crosslinking system is then incorporated at low temperature, generally in an external mixer, such as an open mill; everything is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

[ 0 0 8 7 ]

The crosslinking system proper is preferably based on sulphur and on a primary vulcanization accelerator, in particular on an accelerator of sulphenamide type. Added to this vulcanization system are various known secondary accelerators or vulcanization activators, such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), and the like, incorporated during the first nonproductive phase and/or during the productive phase. The content of sulphur is preferably between 0.5 and 5.0 phr, and that of the primary accelerator is preferably between 0.5 and 8.0 phr.

[ 0 0 8 8 ]

Use may be made, as accelerator (primary or secondary) of any compound capable of acting as accelerator of the vulcanization of diene elastomers in the presence of sulphur, in particular accelerators of the thiazoles type and their derivatives, accelerators of thiurams types, or zinc dithiocarbamates. These accelerators are more preferably chosen from the group consisting of 2-mercaptobenzothiazyl disulphide (abbreviated to "MBTS"), N-cyclohexyl-2-benzothiazole-sulphenamide (abbreviated to "CBS"), N,N-dicyclohexyl-2-benzothiazolesulphenamide ("DCBS"), N-tert-butyl- 2-benzothiazolesulphenamide ("TBBS"), N-tert-butyl-2- benzothiazolesulphenimide ("TBSI"), zinc dibenzyldithiocarbamate ("ZBEC"), tetrabenzylthiuram disulfide ("TBZTD") and the mixtures thereof.

[ 0 0 8 9 ] The final composition thus obtained is subsequently calendered, for example in the form of a sheet or of a plaque, in particular for laboratory characterization, or else extruded in the form of a rubber profiled element which can be used directly as a part of a tire tread.

[ 0 0 9 0 ]

The present invention relates to the tires described above, both in the raw state (i.e., before curing) and in the cured state (i.e., after crosslinking or vulcanization).

5. EXAMPLES OF THE IMPLEMENTATION OF THE INVENTION

Results shown in Table 2, 3 and 4 are obtained by methods of measurements and tests mentioned in "3. MEASUREMENTS AND TESTS USED" unless otherwise instructed.

5-1. Preparation of the rubber compositions and of the treads

[ 0 0 9 1 ]

The tests which follow are carried out in the following way: the reinforcing fillers (for example a reinforcing inorganic filler, such as silica, and its associated coupling agent), the plasticizers, the particles of the silicone rubber, the diene elastomer (or blend of diene elastomers) and the various other ingredients, with the exception of the vulcanization system, are successively introduced into an internal mixer having an initial vessel temperature of approximately 60°C; the mixer is thus approximately 70% full (% by volume). Thermomechanical working (non-productive phase) is then carried out in one stage, which lasts in total approximately 3 to 4 minutes, until a maximum "dropping" temperature of 165°C is reached. The mixture thus obtained is recovered and cooled and then sulphur and an accelerator of sulphenamide type are incorporated on an external mixer (homo finisher) at 30°C, everything being mixed (productive phase) for an appropriate time (for example between 5 and 12 min).

[ 0 0 9 2 ]

The compositions thus obtained are subsequently calendered, either in the form of plaques (thickness of 2 to 3 mm) or of fine sheets of rubber, for the measurement of their physical or mechanical properties, or extruded in the form of treads for tires for passenger vehicles.

6-2. Rubber tests

[ 0 0 9 3 ]

In this test, two compositions (indentified as C-1, C-2) based on diene elastomers (BR and SRB blend) are compared, which compositions are reinforced with a blend of silica and carbon black with which is or is not combined a fraction (47 phr) of particles of silicone rubber.

[ 0 0 9 4 ]

Formulations of the two compositions (Table 1- contents of the various products expressed in phr) and their properties after curing (30 min at 150°C) are given in Table 1 and 2; the vulcanization system is composed of sulphur and sulphenamide.

[ 0 0 9 5 ]

In composition C-2, the total amount of plasticizer (that is, oil and resin) has been reduced in order to keep the two compositions C-1 and C-2 at the same level of Shore A hardness.

[ 0 0 9 6 ] First of all, the examinations of the various results in Table 2 do not reveal any significant modification in the rubber properties for the composition of the present invention (C-2) in comparison with the control (C-l), despite the presence of a high content of the particles, which already constitutes an unexpected result for a person skilled in the art: Shore A hardness and moduli (M10, Ml 00 and M300) in extension remain constant, which is favourable to the mechanical behaviour of the tread and thus to the stability performance of the tire.

[ 0 0 9 7 ]

It is in fact only during actual running tests carried out on tires that the unexpected results introduced by the present invention are revealed, as clearly shown by the following tire tests.

6-3. Tests on tires

[ 0 0 9 8 ]

The compositions C-l and C-2 tested above are subsequently used as treads for radial carcass passenger vehicle tires, respectively denoted T-1 (control tires) and T-2 (tires in accordance with the present invention), with a size of 205/55R16 conventionally manufactured and in all respects identical apart from the rubber compositions forming their treads.

[ 0 0 9 9 ]

The results from Table 3 express the differences in the recorded sound level between T-2 in accordance with the present invention and the control T-1, at four frequency values (1000, 1250, 2000 and 2500 Hz),

[ o i o o ] These differences are expressed as sound energy (dB(A)) which corresponds to the integration of the sound pressure as a function of the frequency at the frequency values in question, a negative value indicating a reduction in the noise relative to the control tires (T-1).

[ 0 1 0 1 ]

Two of the former frequencies (1000 and 1250 Hz) are well known that the reduction of sound pressure level at the frequency values is effective in order to reduce coast- by noise as JP 2003 034736 A mentions. Each of others (2000 and 2500 Hz) has double frequency value of each of the formers.

1 0 1 0 2 ]

On reading Table 3, it is unexpectedly observed that, at the effective frequency values in coast-by noise, the tires of the present invention always emit less noise than the control tires, a reduction of from 1.2 to 1.7 dB(A) for example being considered as quite significant for a person skilled in the art.

[ 0 1 0 3 ]

Furthermore, the result of rolling resistance are reported in Table 4, in relative unit, the base 100 being chosen for the control tires T-1 (it should be remembered that a vehicle of greater than 100 indicates an improved performance).

[ 0 1 0 4 ]

It is noted in this Table 4 that rolling resistance performance of the present invention tire (T-2) substantially improves in comparison to that of the control tire (T-1).

[ 0 1 0 5 ] Such a result can of course only be attributed to the specific formulation of the tread of the tire of the present invention, particularly to the presence of the particles of the silicone rubber at the content that is recommended.

[ 0 1 0 6 ]

In conclusion, the tread of the tire in accordance with the present invention comprising particles of silicone rubber, which gives the tires a noise performance, especially coast by noise, significantly improved and also a rolling resistance substantially improved, without deterioration of stability performance of the tire.

[ 0 1 0 7 ]

Table 1

(1) BR with 0.3% of 1,2 vinyl; 2.7% of trans; 97% of cis-1,4 (Tg = - 105°C);

(2) SBR with 26% of styrene, 74% of butadiene (21% of -1,4 trans, 21% of -1,4 cis and 58% of -1,2) (Tg = -25°C);

(3) Silica "Zeosil 165MP" from Rhodia

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

(5) KMP-602 silicone powder from Shin-Etsu Chemical CO., LTD, (median size of the particles: around 30 μηι, Shore A: 30, Silicone rubber spherical powder coasted with silicone resin);

(6) Grade ASTM N234 (Cabot);

(7) MES oil ("Catenex SNR" from Shell)

(8) Escorez 2173 Resin (Exxon)

(9) Diphenylguanidine (Perkacit DPG from Flexsys);

(10) N-( 1 ,3 -dimethylbutyl)-N-phenyl-para-phenylenediamine

(Santoflex 6-PPD from Flexsys);

(11) N-dicyclohexyl-2-benzothiazolesulphenamide

("Santocure CBS" from Flexsys).

Table 2 Table 3

(*)Difference between the invention (T-2) and the control (T-1) tires

Table 4