WO2012059230A1 - Use of precipitated silica containing aluminum, of precipitated silica, and of 3-acryloxy-propyltriethoxysilane in an isoprene elastomer composition - Google Patents

Abstract

The invention relates to the joint use, in an elastomer composition including an isoprene elastomer, of a combination of precipitated silica containing aluminum, the aluminum content of said precipitated silica being higher than 0.5 wt %, and precipitated silica as an inorganic reinforcing filler, and of 3-acryloxy-propyltriethoxysilane as an agent for binding the inorganic filler and the elastomer together. The invention also relates to the resulting elastomer compositions and to articles manufactured from said compositions.

Description

 USE OF PRECIPITATED SILICA CONTAINING ALUMINUM.

 PRECIPITATED SILICA

 AND 3-ACRYLOXY-PROPYLTRIETHOXYSILANE IN AN ISOPRENE (S) ELASTOMER COMPOSITION

The invention relates to the joint use, in elastomer compositions (s) comprising an isoprene elastomer, such as natural rubber, of a particular reinforcing inorganic filler and a particular inorganic filler - elastomer coupling agent.

 It also relates to the corresponding elastomer compositions and articles, in particular tires, comprising such compositions.

It is known that the elastomeric articles are generally subjected to various constraints, for example such as a temperature variation, a variation of high frequency stress in dynamic regime, a significant static stress and / or fatigue in significant bending in dynamic mode. Such articles are, for example, tires, shoe soles, floor coverings, conveyor belts, power transmission belts, hoses, seals, especially appliance seals, role of engine vibration extractors either with metal reinforcements or with a hydraulic fluid inside the elastomer, cable sheaths, cables, ropeway rollers.

It was then proposed to use in particular elastomer compositions (s) reinforced with specific inorganic fillers described as "reinforcing", preferably having a high dispersibility. These fillers, in particular white fillers such as precipitated silicas, are capable of competing with or even exceeding at least from the point of view reinforcing the conventionally used carbon black, and also offer these compositions a generally lower hysteresis, which is synonymous especially a decrease in internal heating of the elastomeric articles (s) during their use.

 It is known to those skilled in the art that it is generally necessary to employ in the elastomer compositions containing such reinforcing fillers a coupling agent, also called a binding agent, whose function is, in particular, to providing the connection between the surface of the inorganic filler particles (for example a precipitated silica) and the elastomer (s), while facilitating the dispersion of this inorganic filler within the elastomeric matrix.

 The term "inorganic filler-elastomer coupling agent" is understood to mean an agent capable of establishing a sufficient chemical and / or physical connection between the inorganic filler and the elastomer.

 Such a coupling agent, at least bifunctional, has for example as simplified general formula "N-V-M", in which:

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

 M represents a functional group ("M" function) capable of binding physically and / or chemically to the elastomer, in particular via a suitable atom or group of atoms (for example an atom of sulfur);

 - V represents a group (divalent / hydrocarbon) for connecting "N" and "M".

 The coupling agents should not be confused with simple inorganic filler agents which, in a known manner, may have the "N" function active with respect to the inorganic filler but lack the "M" function. active with respect to the elastomer.

Coupling agents, in particular (silica-elastomer), have been described in numerous documents of the state of the art, the best known being (poly) sulphide silanes, in particular (poly) sulphidized alkoxysilanes. Among these (poly) sulphurized silanes, mention may be made especially of tetrasulphide of tethoxysilylpropyl (abbreviated TESPT), which is generally still considered today as a product providing, for vulcanizates comprising an inorganic filler as a reinforcing filler, such as silica, a very good, or even the best, compromised in term safety to the grid, ease of implementation and strengthening power.

 The combined use of precipitated silica, in particular highly dispersible silica and a silane (or organosilic compound functionalized) polysulfide in a modified elastomer composition (s) allowed the development of the "green tire" for passenger vehicles (Light vehicles). This combination achieved a wear resistance performance comparable to that of carbon black-reinforced elastomer blends, while significantly improving rolling resistance (resulting in lower fuel consumption). fuel), and grip on wet ground.

 It would therefore be interesting to also be able to use an inorganic filler such as silica in tires for trucks, tires which are obtained from compositions based on isoprene elastomer (s), mainly natural rubber.

However, the same combination of polysulfurized silica and silane applied to an isoprene elastomer such as natural rubber did not make it possible to obtain a level of reinforcement (which can be illustrated by a stress-strain curve uniaxial) sufficient compared to what is obtained when carbon black is used as a filler, this backing resulting in poor wear resistance. The object of the present invention is to propose in particular the combination for elastomer compositions comprising a diene elastomer, such as natural rubber, with a particular coupling agent with a particular reinforcing inorganic filler, this combination consisting of as an alternative to the use of known coupling agents with known reinforcing inorganic fillers, this combination further providing said elastomer compositions with a satisfactory compromise of properties, in particular with respect to their mechanical, rheological properties. and / or dynamic, especially hysteretic. Advantageously, it allows an improvement of the wear resistance and the compromise hysteresis / reinforcement. In addition, the elastomer compositions obtained preferably have very good adhesion to both the reinforcing inorganic filler used and the substrates to which they are subsequently applied.

The invention relates in its first object to the use in an elastomer composition (s), comprising at least one isoprene elastomer:

a precipitated silica containing aluminum (S1), the aluminum content of said precipitated silica (S1) being greater than 0.5% by weight, and a precipitated silica (S2), the whole ( S1) + (S2) being used as a reinforcing inorganic filler, with

 3-acryloxypropyltriethoxysilane (or γ-acryloxypropyltriethoxysilane), as an inorganic filler-elastomer coupling agent.

 In the invention, each of the precipitated silicas (S1) and (S2) is in itself a reinforcing inorganic filler. Thus according to the invention, it can be said that the reinforcing inorganic filler used is formed of two reinforcing inorganic fillers ((S1) and (S2)), or in other words, it can be said that two inorganic fillers are used. reinforcing agents ((S1) and (S2)).

The precipitated silica containing aluminum (S1) used generally has an aluminum content of at most 7.0% by weight, preferably at most 5.0% by weight, in particular at most 3, 5% by weight, for example not more than 3.0% by weight.

 Preferably, its aluminum content is between 0.75 and 4.0% by weight, even more preferably between 0.8 and 3.5% by weight, in particular between 0.9 and 3.2% by weight. weight, especially between 0.9 and 2.5% by weight or between 1.0 and 3.1% by weight. It is for example between 1.0 and 3.0% by weight, or even between 1.0 and 2.0% by weight.

The amount of aluminum can be measured by any suitable method, for example by ICP-AES ("Inductively Coupled Plasma - Atomic Emission Spectroscopy") after dissolution in water in the presence of hydrofluoric acid. Aluminum is, in general, essentially on the surface of the precipitated silica (S1).

 Even though, aluminum can be present both in tetrahedral, octahedral and pentahedral form, particularly in tetrahedral and octahedral form, in the precipitated silica (S1) used in the invention, it is found preferably substantially in tetrahedral form (more than 50%, in particular at least 90%, especially at least 95% by number, of the aluminum species are then in tetrahedral form); the links are then rather essentially of the SiOAI type.

 The precipitated silica containing aluminum (S1) used in the invention is advantageously highly dispersible, that is to say that in particular it has an ability to deagglomerate and to disperse in a very polymeric matrix. important, particularly observable by electron or optical microscopy, on thin sections.

The precipitated silica (S2) used according to the invention preferably has an aluminum content of less than 0.5% by weight, in particular less than 0.35% by weight, for example less than 0.2% by weight.

Preferably, the precipitated silica (S2) used in the invention is highly dispersible, that is to say that, in particular, it has an ability to deagglomerate and to disperse in a very important polymeric matrix, in particular that can be observed by electron or optical microscopy, on thin sections. Preferably, the precipitated silica containing aluminum (S1) used according to the invention has a CTAB specific surface area of between 70 and 240 m ² / g.

This may be between 70 and 100 m ² / g, for example between 75 and 95 m ² / g.

However, very preferably, its CTAB surface area is between 100 and 240 m ² / g, in particular between 140 and 200 m ² / g.

Likewise, preferably, the precipitated silica (S1) used according to the invention has a BET specific surface area of between 70 and 240 m ² / g. This may be between 70 and 100 m ² / g, for example between 75 and 95 m ² / g.

However, very preferably, its BET surface area is between 100 and 240 m ² / g, in particular between 140 and 200 m ² / g.

Preferably, the precipitated silica (S2) used according to the invention has a CTAB specific surface area of between 70 and 300 m ² / g.

This may be between 70 and 100 m ² / g, for example between 75 and 95 m ² / g.

However, preferably, its CTAB surface area is between 0O and 300 m ² / g, in particular between 100 and 240 m ² / g, for example between 140 and 200 m ² / g.

Likewise, preferably, the precipitated silica (S2) used according to the invention has a BET specific surface area of between 70 and 300 m ² / g.

 This can be between 70 and 100 m / g, for example between 75 and

95 m ² / g.

However, preferably, its BET specific surface area is between 100 and 300 m ² / g, in particular between 100 and 240 m ² / g, for example between 140 and 200 m ² / g.

The CTAB specific surface area is the external surface, which can be determined according to the NF T 45007 method (November 1987). The BET surface area can be measured according to the method of BRUNAUER - EMMETT - TELLER described in "The Journal of the American Chemical Society", vol. 60, page 309 (1938) and corresponding to standard NF T 45007 (November 1987).

According to one variant of the invention, the precipitated silica (S2) has a BET specific surface area (respectively CTAB) close to or similar to the BET specific surface area (respectively CTAB) of the precipitated silica (S1).

According to another variant of the invention, the precipitated silica (S2) has a BET specific surface area (respectively CTAB) which is quite different or remote from the BET specific surface area (CTAB respectively) of the precipitated silica (S1). Thus, in a particular embodiment of the invention in which the precipitated silica containing aluminum (S1) has a CTAB specific surface area of between 140 and 170 m ² / g and a BET specific surface area of between 140 and 180 m. ² / g, the precipitated silica (S2) may, for example, also have a CTAB specific surface area of between 140 and 170 m ² / g and a BET specific surface area of between 140 and 180 m ² / g, or, for example, own :

a CTAB specific surface area of between 70 and 140 m ² / g, in particular between 70 and 100 m ² / g, and a BET specific surface area of between 70 and 140 m ² / g, in particular between 70 and 100 m ² / g; boy Wut,

 or

a CTAB specific surface area of between 170 and 300 m ² / g, in particular between 180 and 220 m ² / g, and a BET specific surface area of between 180 and 300 m ² / g, in particular between 185 and 230 m ² / g. boy Wut.

The dispersibility (and deagglomeration) ability of each of the precipitated silicas (S1) and (S2) used according to the invention can be assessed by means of the following test, by a granulometric measurement (by laser diffraction) carried out on a suspension of silica previously deagglomerated by ultrasonic sonication (breaking objects from 0.1 to a few tens of microns). Ultrasonic deagglomeration is carried out using a VIBRACELL BIOBLOCK (750 W) sonicator equipped with a 19 mm diameter probe. The particle size measurement is carried out by laser diffraction on a SYMPATEC granulomer, using the Fraunhofer theory.

In a pillbox (height: 6 cm and diameter: 4 cm), 2 grams of silica are weighed and the mixture is made up to 50 grams by addition of deionized water: a 4% aqueous suspension of silica is thus obtained which is homogenized during 2 minutes by magnetic stirring. The deagglomeration is then carried out under ultrasound as follows: the probe being immersed over a length of 4 cm, it is put into action for 5 minutes and 30 seconds at 80% of its nominal power (amplitude). The granulometric measurement is then carried out by introducing into the vat of the granulometer a volume V (expressed in ml) of the homogenized suspension required to obtain an optical density of about 20.

The value of the median diameter 0 ₅ o obtained according to this test is even lower than the silica has a high ability to deagglomerate.

A disaggregation factor F _D is given by the equation:

 FD = 10 x V / optical density of the suspension measured by the granulometer (this optical density is about 20).

 This deagglomeration factor FD is indicative of the level of particles smaller than 0.1 μm which are not detected by the granulometer. This factor is all the higher as the silica has a high deagglomeration ability.

In general, the aluminum-containing precipitated silica (S1) used according to the invention has a median diameter δ ₅₀ , after deagglomeration with ultrasound, less than 5 μm, in particular less than 4 μm, in particular less than 3.5 μm, for example less than 3 μm.

 It usually has an ultrasonic deagglomeration factor FD greater than 4.5 ml, in particular greater than 5.5 ml, especially greater than 9 ml, for example greater than 10 ml.

The precipitated silica (S2) implementation according to the invention may have a median diameter 0 ₅ o, after disintegration with ultrasound, smaller than 5 .mu.m, in particular at most 4.5 pm, especially less than 4 pm for example less than 3.5 μm, or even less than 3 μm.

It may have a deagglomeration factor with ultrasound F _D greater than 4.5 ml, in particular greater than 5.5 ml, especially greater than 9 ml, for example greater than 10 ml, or even greater than 12.5 ml.

The DOP oil uptake of the precipitated silica containing aluminum (S1) used according to the invention may be less than 300 ml / 100 g, for example between 200 and 295 ml / 100 g. DOP oil uptake can be determined according to ISO 787/5 by using dioctylphthalate. One of the parameters of the precipitated silica containing aluminum (S1) used in the invention may reside in the distribution, or distribution, of its pore volume, and in particular in the distribution of the pore volume that is generated by the pores diameters less than or equal to 400 A. This last volume corresponds to the useful pore volume of the charges used in the reinforcement of elastomers.

 If this precipitated silica (S1) can have a porous distribution such that the pore volume generated by the pores whose diameter is between 175 and 275 A (V2) represents less than 50% of the pore volume generated by the pores of smaller diameters or equal to 400 A (V1), it may be advantageous to employ a precipitated silica (S1) having a porous distribution such that the pore volume generated by the pores whose diameter is between 175 and 275 A (V2) represents at least 50% (for example between 50 and 60%) of the pore volume generated by the pores with diameters less than or equal to 400 A (V1).

 The porous volumes and pore diameters are measured by mercury porosimetry (Hg), using a MICROMERITICS Autopore 9520 porosimeter, and are calculated by the WASHBURN relation with a theta contact angle of 130 ° and a voltage. superficial gamma equal to 484 Dynes / cm (DIN 66133 standard).

The pH of the precipitated silicas (S1) and (S2) used according to the invention is generally between 6.3 and 8.0, for example between 6.3 and 7.6.

 The pH is measured according to the following method deriving from the ISO 787/9 standard (pH of a suspension at 5% in water):

 Apparatus:

 - calibrated pH meter (reading accuracy at 1 / 100th)

 - combined glass electrode

 - 200 mL beaker

 - 100 mL test tube

 - precision balance to 0.01 gram.

 Operating mode:

5 grams of silica are weighed to the nearest 0.01 gram in the beaker of 200 ml. 95 mL of water measured from the graduated cylinder are then added to the silica powder. The suspension thus obtained is stirred vigorously (magnetic stirring) for 10 minutes. The pH measurement is then performed. The physical state in which each of the precipitated silicas (S1) and (S2) to be used according to the invention is present may be arbitrary, that is to say that they may each be present, for example, independently of one another. on the other, in the form of microbeads (substantially spherical beads), powder or granules.

 Each precipitated silica (S1) and / or (S2) can thus be in the form of substantially spherical beads of average size of at least 80 μm, preferably at least 150 μm, in particular between 150 and 270 μm; this average size is determined according to standard NF X 11507 (December 1970) by dry sieving and determination of the diameter corresponding to a cumulative refusal of 50%.

 It may be in the form of a powder of average size of at least 3 μm, in particular at least 10 μm, preferably at least 15 μm. This is for example between 15 and 60 pm.

 It may be in the form of granules (generally of substantially parallelepipedal shape) of size of at least 1 mm, for example between 1 and 10 mm, especially along the axis of their largest dimension (length).

According to one particular nonlimiting variant, the precipitated silica (S1), having an aluminum content greater than 0.5% by weight, used according to the invention may have:

a CTAB specific surface area of between 140 and 200 m ² / g,

a BET specific surface area of between 140 and 200 m ² / g,

 - optionally, a DOP oil intake of less than 300 ml / 100g,

a median diameter 5 ₅ o, after deagglomeration with ultrasound, less than 3 μm, and

a deagglomeration factor with ultrasound F _D greater than 10 ml. According to another particular nonlimiting variant, the precipitated silica (S1), having an aluminum content greater than 0.5% by weight, used according to the invention may have:

a CTAB specific surface area of between 140 and 200 m ² / g,

 - optionally, a DOP oil intake of less than 300 ml / 100g,

 a porous distribution such that the pore volume constituted by the pores whose diameter is between 175 and 275 A (V2) represents less than 60%, for example less than 50%, of the pore volume constituted by the pores of smaller diameters or equal to 400 A (V1), and

 a median diameter Oso, after deagglomeration with ultrasound, less than 5 μm.

The precipitated silica (S1) used in the context of the invention may be prepared for example by a process as described in patent applications EP-A-0762992, EP-A-0762993, EP-A-0983966, EP-A-1355856.

 Preferably, this aluminum-containing precipitated silica (S1) used in the invention can be obtained by a preparation process comprising the precipitation reaction between a silicate and an acidifying agent whereby a silica suspension is obtained. precipitated, and then the separation and drying of this suspension, wherein:

 the precipitation reaction is carried out as follows:

(i) forming an initial stock having a silicate and an electrolyte, the silicate concentration (expressed as SiO ₂ ) in said initial stock being less than 100 g / L and the electrolyte concentration in said stock initial value being less than 17 g / L,

 (ii) the acidifying agent is added to said heelstock until a pH value of the reaction medium of at least 7 is obtained,

 (iii) acidifying agent and a silicate are added to the reaction medium simultaneously,

a suspension having a solids content of not more than 24% by weight is dried,

said method comprising one of the following three operations (a), (b) or (c): (a) after step (iii), at least one aluminum compound A is added to the reaction medium and, subsequently or simultaneously, a basic agent,

 (b) after step (iii) or in place of step (iii), the reaction medium is simultaneously added a silicate and at least one aluminum compound A, (c) step (iii) ) is carried out by simultaneously adding to the reaction medium acidifying agent, a silicate and at least one compound B of aluminum.

 It should be noted, in general, that this preparation process is a precipitation silica synthesis process, that is to say that it is made to act, under particular conditions, an acidifying agent with a silicate.

 The choice of acidifying agent and silicate is in a manner well known per se.

 The acidifying agent used is a strong mineral acid such as sulfuric acid, nitric acid or hydrochloric acid, or an organic acid such as acetic acid, formic acid or carbonic acid.

 The acidifying agent may be diluted or concentrated; its normality can be between 0.4 and 36 N, for example between 0.6 and 1.5 N.

 In particular, in the case where the acidifying agent is sulfuric acid, its concentration may be between 40 and 180 g / l, for example between 60 and 130 g / l.

 It is also possible to use, as silicate, any current form of silicates such as metasilicates, disilicates and advantageously an alkali metal silicate, in particular sodium or potassium silicate.

The silicate may have a concentration (expressed as SiO ₂ ) of between 40 and 330 g / l, for example between 60 and 300 g / l.

 In general, sulfuric acid is used as acidifying agent and sodium silicate as silicate.

In the case where sodium silicate is used, it generally has a weight ratio SiO ₂ / Na ₂ O of between 2.5 and 4, for example between 3.1 and 3.8.

 The reaction of the silicate with the acidifying agent is in a specific manner according to the following steps.

Firstly, a stock is formed which comprises silicate and an electrolyte (step (i)). The amount of silicate present in the initial stock advantageously represents only a part of the total amount of silicate involved in the reaction.

 The term electrolyte is understood here in its normal acceptation, that is to say that it signifies any ionic or molecular substance which, when in solution, decomposes or dissociates to form ions or charged particles . As electrolyte, mention may be made of a salt of the group of alkali and alkaline earth metal salts, in particular the salt of the starting silicate metal and of the acidifying agent, for example sodium chloride in the case of the reaction of a sodium silicate with hydrochloric acid or, preferably, sodium sulfate in the case of the reaction of a sodium silicate with sulfuric acid.

 The concentration of electrolyte in the initial stock is (greater than 0 g / L and) less than 17 g / l, for example less than 14 g / l.

The silicate concentration (expressed in Si0 ₂ ) in the initial stock is (greater than 0 g / L and) less than 100 g / L; preferably, this concentration is less than 90 g / l, especially less than 85 g / l.

 The second step consists in adding the acidifying agent to the stock base composition described above (step (ii)).

 This addition, which causes a correlative drop in the pH of the reaction medium, is carried out until a pH value of at least 7, generally between 7 and 8, is reached.

 Once the desired pH value is reached, then simultaneous addition (step (iii)) of acidifying agent and silicate is carried out.

 This simultaneous addition is generally carried out in such a way that the pH value of the reaction medium is constantly equal (within +/- 0.1) to that reached at the end of step (ii).

 This preparation method comprises one of the three operations (a), (b) or (c) mentioned above, that is to say:

(a) after step (iii), at least one aluminum compound A is added to the reaction medium and, subsequently or simultaneously, a basic agent, the separation, which is carried out in the process, preferably comprising filtration and disintegration of the cake resulting from this filtration, said disintegration then preferably being carried out in the presence of at least one compound B of aluminum, (b) after step (iii) or in place of step (Ni), a silicate and at least one aluminum compound A are added to the reaction medium simultaneously, the separation, which is carried out in the process, preferably comprising a filtration and a disintegration of the cake resulting from this filtration, the disintegration then being preferably carried out in the presence of at least one compound B of aluminum, or

(c) during step (iii), acidifying agent, a silicate and at least one aluminum compound B are added to the reaction medium simultaneously, the separation, used in the process, preferably comprising filtration and disintegration of the cake resulting from this filtration, the disintegration then being optionally carried out in the presence of at least one compound B of aluminum.

 In a first variant of this preparation process (that is to say when it comprises the operation (a)), it is advantageous, after carrying out the precipitation according to steps (i), (ii) and (iii) previously described, the following steps:

 (iv) adding to the reaction medium (that is to say to the suspension or reaction mixture obtained) at least one aluminum compound A,

 (v) a basic agent is added to the reaction medium, preferably until a pH value of the reaction medium of between 6.5 and 10 is obtained, in particular between 7.2 and 8.6, and then

 (vi) acidifying agent is added to the reaction medium, preferably until a pH value of the reaction medium of between 3 and 5, in particular between 3.4 and 4.5, is obtained.

 Step (v) may be performed simultaneously or, preferably, after step (iv).

 After the simultaneous addition of step (iii), the reaction medium may be cured, this curing may for example last from 1 to 60 minutes, in particular from 3 to 30 minutes.

In this first variant, it may be desirable, between step (iii) and step (iv), and in particular before said optional maturing, to add to the reaction medium an additional amount of acidifying agent. This addition is generally carried out until a pH value of the reaction medium of between 3 and 6.5, in particular between 4 and 6, is obtained. The acidifying agent used during this addition is generally identical to that used in steps (ii), (iii) and (vi) of the first variant of the process.

 Ripening of the reaction medium is usually carried out between step (v) and step (vi), for example for 2 to 60 minutes, in particular for 5 to 45 minutes.

 Similarly, a ripening of the reaction medium is most often carried out after step (vi), for example for 2 to 60 minutes, in particular for 5 to 30 minutes.

 The basic agent used in step (v) may be an ammonia solution or, preferably, a solution of sodium hydroxide (or sodium hydroxide).

 In a second variant of said method (that is to say when it comprises operation (b)), after steps (i), (ii) and (iii) described above, or in place of of step (iii) described above, a step (iv) which consists in adding to the reaction medium simultaneously a silicate and at least one compound A of aluminum.

 Only in the case where the compound A of aluminum is sufficiently acidic (for example this may be the case when this compound A is an aluminum sulphate), it is indeed possible (but not obligatory) to substitute the step (iii) by step (iv), which in fact means that step (iii) and step (iv) then form only one step, the compound A of aluminum then playing the role of acidifying agent.

 The simultaneous addition of step (iv) is generally carried out in such a way that the pH value of the reaction medium is constantly equal (within +/- 0.1) to that reached at the end of the step ( iii) or step (ii).

 It is possible, after the simultaneous addition of step (iv), to ripen the reaction medium, which curing may for example last from 2 to 60 minutes, in particular from 5 to 30 minutes.

In this second variant, it may be desirable, after step (iv), and in particular after this optional ripening, to add to the reaction medium an additional quantity of acidifying agent. This addition is generally carried out until a pH value of the reaction medium of between 3 and 6.5, in particular between 4 and 6, is obtained. The acidifying agent used during this addition is generally identical to that used in step (ii) of the second variant of the process.

 Ripening of the reaction medium is usually carried out after this addition of acidifying agent, for example for 1 to 60 minutes, in particular for 3 to 30 minutes.

 The aluminum compound A used in the preparation process (especially in the first two variants mentioned) is generally an organic or inorganic salt of aluminum.

 As examples of organic salt, mention may be made in particular of carboxylic or polycarboxylic acid salts, such as the salts of acetic, citric, tartaric or oxalic acid.

 As examples of inorganic salt, mention may in particular be made of halides and oxyhalides (such as chlorides, oxychlorides), nitrates, phosphates, sulphates and oxysulphates.

 In practice, compound A of aluminum may be used in the form of a solution, generally aqueous.

 Aluminum compound A is preferably used as aluminum compound A.

 In a third variant of this preparation method (that is to say when it comprises the operation (c)), it is advantageous to carry out, after carrying out the steps (i) and (ii) described above, a step (iii) which consists in adding to the reaction medium simultaneously with the acidifying agent, a silicate and at least one compound B of aluminum.

 This simultaneous addition is generally carried out in such a way that the pH value of the reaction medium is constantly equal (within +/- 0.1) to that reached at the end of step (ii).

 In this third variant, it may be desirable, after step (iii), to add to the reaction medium an additional amount of acidifying agent. This addition is generally done until a pH value of the reaction medium of between 3 and 6.9, in particular between 4 and 6.6, is obtained.

The acidifying agent used during this addition is generally identical to that used in steps (ii) and (iii). Ripening of the reaction medium is usually carried out after this addition of acidifying agent, for example for 1 to 60 minutes, in particular for 3 to 30 minutes.

 The compound B of the aluminum employed in the third variant is, in general, an alkali metal aluminate, in particular potassium or, preferably, sodium.

 The temperature of the reaction medium is generally between 70 and 98 ° C.

 According to one variant, the reaction is carried out at a constant temperature of between 75 and 96 ° C.

 According to another (preferred) variant, the end-of-reaction temperature is higher than the reaction start temperature: thus, the temperature at the start of the reaction is preferably maintained between 70 and 96 ° C., and then the temperature is raised. in a few minutes, preferably to a value between 80 and 98 ° C, the value at which it is maintained until the end of the reaction; the operations (a) or (b) are thus usually performed at this constant temperature value.

 At the end of the steps which have just been described, a silica slurry is obtained which is then separated (liquid-solid separation).

 In general, this separation comprises a filtration (followed by a washing if necessary) and a disintegration, said disintegration can be then (preferably in the case of the first two variants mentioned, possibly in the case of the third variant) carried out in the presence at least one aluminum compound B and, optionally, in the presence of an acidifying agent as described above (in the latter case, the compound B of the aluminum and the acidifying agent are advantageously added simultaneously ).

 The disintegration operation, which can be carried out mechanically, for example by passing the filter cake in a colloidal or ball mill, notably makes it possible to lower the viscosity of the suspension to be dried (in particular to be atomized) subsequently.

The aluminum compound B is usually different from the aluminum compound A mentioned above and generally consists of an alkali metal aluminate, especially potassium or, preferably, sodium aluminate. The amounts of aluminum compounds A and B used in this preparation process are such that the precipitated silica (S1) obtained has more than 0.5% by weight of aluminum, and in particular a preferred amount of aluminum such as as mentioned above.

 The separation carried out in this process usually comprises filtration (with washing if necessary) carried out using any suitable method, for example by means of a belt filter, a vacuum filter or, preferably, a filter. a filter press.

 The precipitated silica suspension thus recovered (filter cake) is then dried.

 In this preparation process, this suspension must present immediately before drying a dry matter content of at most 24% by weight, preferably at most 22% by weight.

 This drying can be done by any means known per se.

 Preferably, the drying is done by atomization. For this purpose, any suitable type of atomizer may be used, such as a turbine, nozzle, liquid pressure or two-fluid atomizer. In general, when the filtration is carried out using a filter press, a nozzle atomizer is used, and when the filtration is carried out using a vacuum filter, a turbine atomizer is used. .

 When the drying is carried out using a nozzle atomizer, the precipitated silica that can then be obtained is usually in the form of substantially spherical beads.

 At the end of this drying, it may optionally proceed to a grinding step on the recovered product; the precipitated silica that can then be obtained is generally in the form of a powder.

 When the drying is carried out using a turbine atomizer, the precipitated silica that may then be obtained may be in the form of a powder.

Finally, the dried product (in particular by a turbine atomizer) or milled as indicated above may optionally be subjected to an agglomeration step, which consists, for example, of a direct compression, a wet-path granulation (that is, with the use of a binder such as water, silica suspension ...), extrusion or, preferably, dry compaction. When the latter technique is used, it may be advisable, before compacting, to deaerate (operation also called pre-densification or degassing) the pulverulent products so as to eliminate the air included in these products. ci and ensure a more regular compaction.

 The precipitated silica that can then be obtained by this agglomeration step is generally in the form of granules.

As precipitated silica (S2) used in the context of the invention, it is possible to use a commercially available precipitated silica, in particular a commercial highly dispersible silica such as, inter alia, Z1165MP, Z1115 P.

 The precipitated silica (S2) used in the invention can be prepared for example by a process as described in EP0520862, EP0670813, EP0670814.

The 3-acryloxypropyltriethoxysilane (or γ-acryloxypropyltriethoxysilane) used in the invention as an inorganic filler-elastomer coupling agent can be prepared by a process as described in US-A-3179612, starting from US Pat. allyl acrylate and triethoxysilane.

The precipitated silicas (S1) and (S2) employed according to the present invention may optionally be, and therefore without being obligatory, mixed together prior to their use.

One of the two precipitated silicas (S1) and (S2), in particular the precipitated silica (S1), or the two precipitated silicas (S1) and (S2), used according to the present invention as reinforcing inorganic filler, and the 3-acryloxypropyltriethoxysilane used according to the present invention as reinforcing inorganic filler - elastomer coupling agent may be mixed together prior to their use. An alternative is that the 3-acryloxypropyltriethoxysilane is grafted onto any of said precipitated silicas (S1) and (S2); another variant is that the 3-acryloxypropyltriethoxysilane is grafted onto one of the two precipitated silicas (S1) or (S2), in particular on the precipitated silica (S1), or on each of the two precipitated silicas (S1) and (S2), which will thus be "precoupled" before mixing with the elastomer composition (s). It is possible to use all or part of the 3-acryloxypropyltriethoxysilane used according to the invention as a coupling agent in supported form (the setting is carried out prior to its use) on a solid compatible with its chemical structure this solid support may for example be carbon black or, preferably, one of the precipitated silicas (S1) and / or (S2) used according to the present invention.

In general, the used amount of precipitated silica (S1) is from 10 to 90%, in particular from 20 to 80%, of the total amount used of the precipitated silica (S1) + precipitated silica (S2).

 If the used amount of precipitated silica (S1) can thus for example represent 20 to 40% of the total amount used of the precipitated silica (S1) + precipitated silica (S2), preferably it can represent from 60 to 80 % of the total amount used of the precipitated silica (S1) + precipitated silica (S2).

The elastomer compositions (s) in which 3-acryloxypropyltriethoxysilane is used according to the invention may contain at least one covering agent of said silicas (S1) and (S2) used as reinforcing filler. This covering agent is capable, in a known manner, of improving the processability of the elastomer compositions in the green state.

Such a coating agent may consist, for example, of an alkylalkoxysilane (in particular an alkyltriethoxysilane), a polyol, a polyether (in particular a polyethylene glycol), a polyetheramine, a primary, secondary or tertiary amine (in particular a trialkanol amine), a α, ω-dihydroxylated polydimethylsiloxane or an α, ω-diamine polydimethylsiloxane. The coating agent may optionally be mixed with precipitated silicas (S1) and (S2) and 3-acryloxypropyltriethoxysilane prior to their use. The elastomer compositions in which the 3-acryloxypropyltriethoxysilane and the precipitated silicas (S1) and (S2) described above are optionally used may optionally comprise at least one other inorganic filler coupling agent. elastomer, in particular a sulphurized or polysulphurized silane.

 Examples of such a coupling agent are:

 bis-triethoxysilylpropyl disulphide (abbreviated TESPD) of formula:

(C 2 H ₅ O) ₃ Si- (CH2) 3-S2- (CH2) 3-Si (OC ₂ H ₅₎ 3

 bis-triethoxysilylpropyl tetrasulfide (abbreviated TESPT) of formula:

(C2H ₅ O) 3Si- (CH 2) 3 -S 4 - (CH 2) 3 -Si (OC ₂ H ₅ ) 3

bis-monohydroxydimethylsilylpropyl tetrasulfide of formula:

(HO) (CH ₃ ) ₂ Si- (CH 2) 3 -S 4 - (CH 2) 3 -Si (CH ₃ ) ₂ (OH)

 bis-monoethoxydimethylsilylpropyl disulfide (abbreviated as MESPD) of formula:

(C 2 H ₅ O) (CH3) 2Si- (CH2) 3-S2- _(CH2) 3-Si (CH3) 2 (OC2H ₅₎

bis-monoethoxydimethylsilylpropyl tetrasulfide (abbreviated as MESPT) of formula:

(C2H5O) (CH3) 2Si- (CH2) 3-S4- (CH2) 3-Si (CH3) 2 (OC2H ₅₎

 bis-monoethoxydimethylsilylisopropyl tetrasulfide (abbreviated to MESiPrT) of formula:

(C 2 H ₅ O) (CH 3) 2 Si-CH2-CH- (CH3) -S4- (CH ₃₎ -CH-CH2-Si (CH3) 2 (OC2H5)

However, preferably, said elastomer compositions (s) do not contain any other inorganic filler-elastomer coupling agent other than 3-acryloxypropyltriethoxysilane. The use according to the invention may optionally be carried out in the presence of a free radical initiator (for example from 0.02 to 5%, in particular from 0.05 to 0.5%, by weight relative to the amount in question. weight of elastomer (s)), that is to say of a compound (especially organic compound) susceptible, in particular following a energy activation, to generate free radicals in situ, in its surrounding environment, in this case in the (the) elastomer (s). The initiator of free radicals is here an initiator of the type with thermal initiation, that is to say that the energy supply, for the creation of free radicals, is in thermal form. Its decomposition temperature should generally be below 180 ° C, in particular below 160 ° C.

 It is for example chosen from the group consisting of organic peroxides, organic hydroperoxides, azido compounds, bis (azo) compounds, peracids, peresters or a mixture of at least two of these compounds. It is in particular an organic peroxide, for example benzoyl peroxide, acetyl peroxide, lauryl peroxide, peroxide of 1, 1 bis-buty-SS-trimethylcyclohexane, the peroxide being optionally placed on a solid support , such as calcium carbonate.

 However, preferably, the invention is implemented in the absence of any free radical initiator.

The elastomer composition (s) employed in the invention may advantageously not comprise other elastomers than the isoprene elastomer (s) it contains.

 It may optionally (non-preferred variant) comprise at least one elastomer other than isoprene. In particular, it may optionally comprise at least one isoprene elastomer (for example natural rubber) and at least one diene elastomer other than isoprene, the amount of isoprene elastomer (s) relative to the total amount of elastomer (s) then being preferably greater than 50% (generally less than 99.5%, and for example between 70 and 99%) by weight.

The elastomer composition (s) used according to the invention generally comprises at least one isoprene elastomer (natural or synthetic) chosen from:

(1) synthetic polyisoprenes obtained by homopolymerization of isoprene or 2-methyl-1,3-butadiene; (2) synthetic polyisoprenes obtained by copolymerization of isoprene with one or more ethylenically unsaturated monomers chosen from:

 (2.1) conjugated diene monomers, other than isoprene, having from 4 to 22 carbon atoms, such as, for example, butadiene-1,3, 2,3-dimethyl-1,3-butadiene, 2-chloro butadiene-1,3 (or chloroprene), 1-phenyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene;

 (2.2) aromatic vinyl monomers having 8 to 20 carbon atoms, such as, for example, styrene, ortho-, meta- or paramethylstyrene, the commercial "vinyl-toluene" mixture, paratertiobutylstyrene, methoxystyrenes, chlorostyrenes vinylmesitylene, divinylbenzene, vinylnaphthalene;

 (2.3) vinyl nitrile monomers having 3 to 12 carbon atoms, such as, for example, acrylonitrile, methacrylonitrile;

 (2.4) acrylic ester monomers derived from acrylic acid or methacrylic acid with alkanols having from 1 to 12 carbon atoms, such as, for example, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, methacrylate, isobutyl;

 (2.5) a mixture of at least two of the aforementioned monomers (2.1) to (2.4); the copolymeric polyisoprenes containing between 20 and 99% by weight of isoprenic units and between 80 and 1% by weight of diene units, aromatic vinyls, vinyl nitriles and / or acrylic esters, and consisting, for example, in poly (isoprene-butadiene) ), poly (isoprene-styrene) and poly (isoprene-butadiene-styrene);

 (3) natural rubber;

 (4) copolymers obtained by copolymerization of isobutene and isoprene, as well as the halogenated versions, in particular chlorinated or brominated, of these copolymers;

(5) a mixture of at least two of the aforementioned elastomers (1) to (4);

(6) a mixture containing more than 50% (preferably less than 99.5%, and for example 70-99%) by weight of the aforementioned elastomer (1) or (3) and less than 50% (preferably more than 0.5%, and for example between 1 and 30%) by weight of one or more diene elastomers other than isoprenic.

By diene elastomer other than isoprene, is meant in a manner known per se including: homopolymers obtained by polymerization of one of the conjugated diene monomers defined above in (2.1), such as polybutadiene and polychloroprene; copolymers obtained by copolymerization of at least two of the abovementioned conjugated dienes (2.1) with one another or by copolymerization of one or more of the abovementioned conjugated dienes (2.1) with one or more unsaturated monomers mentioned above (2.2), (2.3) and / or or (2.4), such as poly (butadiene-styrene) and poly (butadiene-acrylonitrile); ternary copolymers obtained by copolymerization of ethylene, of an α-olefin having from 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 hexadiene-1,4, ethylidene norbornene, dicyclopentadiene (elastomer EPDM).

 Preferably, the elastomer composition (s) comprises at least one isoprene elastomer chosen from:

(1) homopolymeric synthetic polyisoprenes;

 (2) the synthetic polyisoprenes copolymers consisting of poly (isoprene-butadiene), poly (isoprene-styrene) and poly (isoprene-butadiene-styrene);

 (3) natural rubber;

(4) butyl rubber;

 (5) a mixture of at least two of the aforementioned elastomers (1) to (4);

(6) a mixture containing more than 50% (preferably less than 99.5%, and for example 70-99%) by weight of the aforementioned elastomer (1) or (3) and less than 50% (preferably more than 0.5%, and for example from 1 to 30% by weight of non-isoprene diene elastomer consisting of polybutadiene, polychloroprene, polybutadiene-styrene, polybutadiene-acrylonitrile or a terpolymer (ethylene - propylene - nonconjugated monomeric diene). More preferentially, the elastomer composition (s) comprises at least one isoprene elastomer chosen from: (1) homopolymeric synthetic polyisoprenes; (3) natural rubber; (5) a mixture of the aforementioned elastomers (1) and (3); (6) a mixture containing more than 50% (preferably less than 99.5%, and for example 70-99%) by weight of the above-mentioned elastomer (1) or (3) and less than 50% (preferably more than 0.5%, for example from 1 to 30% by weight of diene elastomer other than isoprene, consisting of polybutadiene or polybutadiene-styrene.

 According to a very preferred variant of the invention, the elastomer composition (s) comprises as isoprene elastomer at least natural rubber, or even only natural rubber.

 According to an even more preferred variant, the elastomer composition (s) comprises as elastomer (s) only natural rubber. In general, the elastomer composition (s) used according to the invention also comprises all or part of the other constituents and auxiliary additives usually employed in the field of elastomeric compositions.

Thus, generally, it comprises at least one compound chosen from vulcanizing agents (for example sulfur or a sulfur-donor compound (such as a thiuram derivative)), vulcanization accelerators (for example a guanidine derivative or a thiazole derivative), vulcanization activators (for example, stearic acid, zinc stearate and zinc oxide, which may optionally be introduced in a fractional manner during the preparation of the composition), carbon, protective agents (especially antioxidants and / or antiozonants, such as, for example, N-phenyl-N '- (1,3-dimethylbutyl) -p-phenylenediamine), antireversions (such as for example, hexamethylene-1,6-bis (thiosulfate), 1,3-bis (citraconimidomethyl) benzene), plasticizers. The combined use according to the invention of the precipitated silicas (S1) and (S2) described in the preceding discussion and 3-acryloxypropyltriethoxysilane can be done more particularly in shoe soles, floor coverings, barriers to gas, flame retardant materials, pebbles cable cars, appliance joints, liquid or gas line joints, braking system joints, hoses, ducts (including cable ducts), cables, motor mounts, conveyor belts, transmission belts or, preferably, tires (especially tire treads), advantageously in tires for heavy goods vehicles, in particular for trucks.

The elastomer composition (s) obtained according to the use according to the invention contains an effective amount of 3-acryloxypropyltriethoxysilane.

 More particularly, the elastomer compositions resulting from the invention may comprise (parts by weight), per 100 parts of isoprene elastomer (s):

 10 to 200 parts, in particular 20 to 150 parts, especially 30 to 110 parts, for example 30 to 75 parts, of the precipitated silica (S1) + precipitated silica (S2) used as reinforcing inorganic filler;

 1 to 20 parts, in particular 2 to 20 parts, especially 2 to 12 parts, for example 2 to 10 parts, of 3-acryloxypropyltriethoxysilane used as reinforcing inorganic filler-elastomer coupling agent.

 Preferably, the amount of 3-acryloxypropyltriethoxysilane used, especially chosen from the abovementioned ranges, is determined so that it generally represents 1 to 20%, in particular 2 to 15%, for example 4 to 12%, by weight relative to the total amount used of the precipitated silica (S1) + precipitated silica (S2).

 In general, the total amounts of coupling agents + optional coating agent are identical to those mentioned above when using, in addition to the coupling agent (3-acryloxypropyltriethoxysilane) used according to the invention. another coupling agent (especially sulphide or polysulfide) and / or a covering agent.

The present invention has the second object the elastomer compositions (s) described above, and thus comprising:

at least one isoprene elastomer, at least one reinforcing inorganic filler,

 at least one inorganic filler - elastomer coupling agent,

characterized in that said reinforcing inorganic filler and said inorganic filler - elastomer coupling agent are as defined above according to the first subject of the invention, that is to say that said reinforcing inorganic filler is formed by the silica group precipitated (S1) + precipitated silica (S2) and said inorganic filler-elastomer coupling agent is 3-acryloxypropyltriethoxysilane.

 All that has been previously described in the context of the use according to the first subject of the invention applies to these elastomer compositions (s).

 In particular, these compositions may further comprise at least one covering agent for precipitated silicas used as a reinforcing filler. The elastomer compositions according to the invention may be prepared according to any conventional two-phase procedure. A first phase (called non-productive) is a thermomechanical work phase at high temperature. It is followed by a second mechanical working phase (so-called productive) at temperatures generally below 110 ° C. in which the vulcanization system is introduced.

The invention, taken in its second object, relates to elastomer compositions (s) both in the raw state (that is to say before cooking) and in the cooked state (that is to say, before cooking). say after crosslinking or vulcanization).

The elastomer compositions according to the invention can be used to manufacture finished or semi-finished articles comprising said compositions.

The present invention thus has for third object articles comprising at least one elastomer composition (s) as defined above, in particular a composition comprising (for example as sole elastomer) natural rubber, these articles consisting of soles footwear, floor coverings, gas barriers, fire-retardant materials, ropeway rollers, appliance seals, liquid or gas lines, braking system joints, hoses, ducts (especially cable ducts), cables, motor mounts, conveyor belts, transmission belts, or, preferably, tires (especially tire treads), advantageously tires for heavy goods vehicles, in particular for trucks.

The following example illustrates the invention without limiting its scope. EXAMPLE

This example illustrates the use and behavior of a precipitated silica S1, containing more than 0.5% by weight of aluminum and having the following characteristics, in combination with another precipitated silica S2 (containing less than 0, 5% by weight of aluminum), and 3-acryloxypropyltriethoxysilane in an elastomeric composition.

1- The precipitated silica S1 has the following characteristics:

- CTAB specific surface 160 m ² / g

- BET specific surface 164 m ² / g

 - weight content of aluminum 1, 6%

 - V2A / 1 ratio 56%

 It is subjected to the disagglomeration test as defined above in the description.

 After deagglomeration with ultrasound, it has a median diameter

(0 ₅₀ ) of 3.1 μm and 9.4 ml ultrasonic deagglomeration factor (F _D ).

2- In an internal mixer of the Haake type, elastomeric compositions are prepared whose constitution, expressed in part by weight per 100 parts of elastomers (phr), is shown in Table I below. Table I: Formulations used for blends

(1) Natural rubber SMR 5 - CV60 (supplied by Safic-Alcan)

(2) Silica S1

 (3) Silica S2: Z1 165MP (Rhodia company)

 (4) TESPT (Z-6940 from Dow Corning Company)

 (5) 3-acryloxypropyltriethoxysilane

 (6) N-1,3-dimethylbutyl-N-phenyl-para-phenylenediamine (Santoflex

 6-PPD from Flexsys)

 (7) 2,2,4-trimethyl-1H-quinoline (Permanax TQ from Flexsys)

 (8) N-cyclohexyl-2-benzothiazyl sulfenamide (Rhenogran CBS-80 from

 RheinChemie company)

 (9) Diphenylguanidine (Rhenogran DPG-80 from RheinChemie) Process for the preparation of elastomeric compositions

The process for preparing the compositions is conducted in two successive preparation phases. A first phase consists in a thermomechanical work phase at high temperature. It is followed by a second phase of mechanical work at temperatures below 1 10 ° C; this phase allows the introduction of the vulcanization system.

 The first phase is carried out in a Haake type internal mixer (capacity of 300 mL). The fill factor is 0.75. The initial temperature and the speed of the rotors are fixed each time so as to reach mixing temperatures of the vicinity of 150-170 ° C.

 The first phase is decomposed here in two passes.

 It makes it possible to incorporate, in a first pass, the elastomer (natural rubber), then the reinforcing inorganic filler consisting of all the silicas (fractional introduction) with the coupling agent and stearic acid; the duration of this pass is between 4 and 10 minutes.

 After cooling the mixture (temperature below 100 ° C.), a second pass makes it possible to incorporate the zinc oxide and the protective / antioxidant agents (6-PPD in particular); the duration of this pass is between 2 and 5 minutes.

 After cooling the mixture (temperature below 100 ° C), the second phase allows the introduction of the vulcanization system (sulfur and accelerators, such as CBS). It is carried out on a roll mill, preheated to 50 ° C. The duration of this phase is between 2 and 6 minutes.

 Each final mixture is then calendered in the form of plates 2-3 mm thick.

 On these so-called raw mixtures obtained, an evaluation of their rheological properties makes it possible to optimize the duration and the vulcanization temperature.

 Then, the mechanical and dynamic properties of the optimum vulcanized mixtures are measured.

Rheological properties

- Viscosity of raw mixtures

The Mooney consistency is measured on the compositions in the uncured state at 100 ° C. by means of a MV 2000 rheometer according to the NF ISO 289 standard. The value of the torque read after 4 minutes after preheating for one minute (Mooney Large (1 +4) at 100 ° C) is shown in Table II.

- Rheometry of the compositions

The measurements are performed on the compositions in the green state. The results relating to the rheology test, which is conducted at 150 ° C. using a Monsanto ODR rheometer according to the NF ISO 3417 standard, are shown in Table III.

 According to this test, the composition to be tested is placed in the controlled test chamber at a temperature of 150 ° C. for 30 minutes, and the resistive torque opposed by the composition is measured at a low amplitude oscillation (3 °). a biconical rotor included in the test chamber, the composition completely filling the chamber in question.

 From the curve of variation of the torque as a function of time, we determine:

 the minimum torque (Cmin), which reflects the viscosity of the composition at the temperature considered;

 the roasting time TS2 corresponding to the time required to have a rise of 2 points above the minimum torque at the temperature in question (150 ° C.) and reflecting the time during which it is possible to use the raw mixtures with this temperature without initiation of vulcanization (the mixture cures from TS2).

 The results obtained are shown in Table II.

Table II

The compositions resulting from the invention (compositions 1 and 2) lead to low values of Mooney consistency and minimum torque. Thus, it is found that the compositions of the invention have a satisfactory viscosity at raw (Mooney consistency), at least equivalent to, or better (composition 2) than that of the control composition.

 It is also noted that these compositions in accordance with the invention have very satisfactory rheological properties. In particular, they have low minimum torque values. And especially the compositions resulting from the invention have a good kinetics of vulcanization (TS2), especially with respect to the control composition, and without penalizing the viscosity of the raw mixture (illustrated by the minimum torque).

Mechanical properties of vulcanizates

The measurements are carried out on the compositions vulcanized at the optimum (that is to say at a state of vulcanization corresponding to 98% of the complete vulcanization) for a temperature of 150 ° C.

 The uniaxial tensile tests are carried out in accordance with the NF ISO 37 standard with type H2 specimens at a speed of 500 mm / min on an INSTRON 5564 device. The x% modules correspond to the stress measured at x% deformation. in tension and are expressed, as the breaking strength, in MPa. It is possible to determine a reinforcement index (I.R.) which is equal to the ratio between the 300% deformation modulus and the 100% deformation modulus.

The measurement of loss of mass by abrasion is carried out according to the indications of standard NF ISO 4649, using a Zwick abraser where the cylindrical specimen is subjected to the action of an abrasive cloth of grains P60 and fixed on the surface of a drum rotating under a contact pressure of 10 N and a stroke of 40 m. The measured value is a volume of loss of substance (in mm ³ ) after wear by abrasion; the lower it is, the better the resistance to abrasion.

The measured properties are collated in Table III. Table III

It is found that the compositions of the invention (compositions 1 and 2) have a very good compromise of mechanical properties, especially compared to what is obtained with the control composition.

 The compositions resulting from the invention thus have relatively low 10% and 100% moduli and a 300% high modulus, hence a higher reinforcement index.

 In addition, these compositions 1 and 2 have, in addition to good breaking strength, a lower abrasion loss, that is to say a better resistance to abrasion, resulting in a gain in resistance to abrasion. wear, which is important in pneumatic applications, especially for heavy goods vehicles. Dynamic properties of vulcanizates

Dynamic properties are measured on a viscoanalyzer (Metravib VA3000) according to ASTM D5992.

In a first series of measurements, the values of loss factor (tan δ) and complex modulus in dynamic compression (E *) are recorded on vulcanized samples (cylindrical specimen of section 95 mm ² and height 14 mm). The sample is initially subjected to a predeformation of 10%, then to a sinusoidal deformation in alternating compression of + 1-2%. The measurements are carried out at 60 ° C. and at a frequency of 10 Hz.

The results, presented in Table IV, are the complex modulus in compression (E * - 60 ° C - 10 Hz) and the loss factor (tan δ - 60 ° C - 10 Hz). In a second series of measurements, the values of the loss factor (tan δ) and elastic modulus in dynamic shear (G ¹ ) are recorded on vulcanized samples (parallelepipedal specimen of section 8 mm ² and height 7 mm). The sample is subjected to an alternating double shear sinusoidal deformation at a temperature of 40 ° C. and at a frequency of 10 Hz. The amplitude-deformation sweep processes are carried out in a round-trip cycle, ranging from 0.degree. 1 to 50% then return 50 to 0.1%.

 The results, presented in Table IV, are derived from the amplitude sweep of the return strains and relate to the maximum value of the loss factor (tan δ max return - 40 ° C - 10 Hz) as well as the amplitude of the elastic modulus ( AG '- 40 ° C - 10 Hz) between the values at 0.1% and 50% deformation (Payne effect).

Table IV

The compositions resulting from the invention (compositions 1 and 2) have very good dynamic properties (hysteretic properties at 60 ° C.), particularly with respect to the control composition.

It can be seen from the results of Tables II to IV that the compositions resulting from the invention (compositions 1 and 2) have a very good compromise of properties.

Claims

CLAIMS 1- Use in a composition of elastomer(s), comprising at least one isoprene elastomer: - of a precipitated silica containing aluminum (A), the aluminum content of said precipitated silica (S1) being greater than 0.5% by weight, and a precipitated silica (S2), the whole (S1) + (S2) being used as reinforcing inorganic filler, with - 3-acryloxy-propyltriethoxysilane, as inorganic filler coupling agent - elastomer. 2- Use according to claim 1, characterized in that said precipitated silica (S2) has an aluminum content less than 0.5% by weight, preferably less than 0.35% by weight, for example less than 0.2 % in weight. 3- Use according to one of claims 1 and 2, characterized in that said precipitated silica (S2) is highly dispersible. 4- Use according to one of claims 1 to 3, characterized in that said precipitated silica (S2) has: - a CTAB specific surface area of between 70 and 300 m2/g, and - a BET specific surface area of between 70 and 300 m2/g. 5- Use according to one of claims 1 to 4, characterized in that said precipitated silica (S2) has a median diameter (0so), after deagglomeration with ultrasound, less than 5 pm, in particular less than 4 μιπ. 6- Use according to one of claims 1 to 5, characterized in that said precipitated silica (S2) has an ultrasonic deagglomeration factor (FD) greater than 4.5 ml, in particular greater than 5.5 ml . 7- Use according to one of claims 1 to 6, characterized in that said precipitated silica (S1) has an aluminum content of at most 7.0% by weight, preferably at most 5.0% by weight. weight, in particular not more than 3.5% by weight. 8- Use according to one of claims 1 to 7, characterized in that said precipitated silica (S1) has an aluminum content of between 0.75 and 4.0% by weight, preferably between 0.8 and 3, 5%, in particular between 0.9 and 3.2% by weight. 9- Use according to one of claims 1 to 8, characterized in that said precipitated silica (S1) is highly dispersible. 10- Use according to one of claims 1 to 9, characterized in that said precipitated silica (S1) has: - a CTAB specific surface area of between 70 and 240 m /g, and - a BET specific surface area of between 70 and 240 m2/g. 1 1- Use according to one of claims 1 to 10, characterized in that said precipitated silica (S1) has a median diameter (05o), after deagglomeration with ultrasound, less than 5 μιτι, in particular less than 4 pm . 12- Use according to one of claims 1 to 11, characterized in that said precipitated silica (S1) has an ultrasonic deagglomeration factor (FD) greater than 4.5 ml, in particular greater than 5.5 ml . 13- Use according to one of claims 1 to 12, characterized in that said precipitated silica (S1) is obtained by a process comprising the precipitation reaction between a silicate and an acidifying agent, whereby a suspension of precipitated silica, then the separation and drying of this suspension, in which: - the precipitation reaction is carried out in the following manner: (i) an initial stock comprising a silicate and an electrolyte is formed, the silicate concentration ( expressed in Si02) in said initial stock base being less than 100 g/L and the electrolyte concentration in said initial stock stock being less than 17 g/L, (H) the acidifying agent is added to said stock stock until 'to obtain a pH value of the reaction medium of at least 7, (iii) the acidifying agent and a silicate are added to the reaction medium simultaneously, - a suspension having a dry matter content of d at most 24% by weight, said process comprising one of the following three operations (a), (b) or (c): (a) at least one compound of aluminum and, then or simultaneously, a basic agent, (b) we add, after step (iii) or instead of step (iii), to the reaction medium simultaneously a silicate and at least one compound of aluminum, (c) step (iii) is carried out by simultaneously adding to the reaction medium the acidifying agent, a silicate and at least one aluminum compound. 14- Use according to one of claims 1 to 13, characterized in that the quantity used of precipitated silica (S1) represents 10 to 90%, in particular 20 to 80%, relative to the total quantity used of the the precipitated silica (S1) + precipitated silica (S2) assembly. 15- Use according to one of claims 1 to 14, characterized in that the quantity used of 3-acryloxy-propyltriethoxysilane represents from 1 to 20%, in particular from 2 to 15%, relative to the total quantity used of the the precipitated silica (S1) + precipitated silica (S2) assembly. 16- Use according to one of claims 1 to 15, characterized in that said precipitated silicas (S1) and (S2) and the 3-acryloxy-propyltriethoxysilane are mixed beforehand with each other. 17- Use according to one of claims 1 to 16, characterized in that said composition of elastomer(s) further comprises at least one covering agent for said precipitated silicas (S1) and (S2), optionally previously mixed with said precipitated silicas (S1) and (S2) and 3-acryloxy-propyltriethoxysilane. 18- Use according to one of claims 1 to 17, characterized in that said elastomer(s) composition does not comprise another inorganic filler - elastomer coupling agent. 19- Use according to one of claims 1 to 18, in the absence of free radical initiator. 20- Use according to one of claims 1 to 19, characterized in that said composition of elastomer(s) does not comprise other elastomers than said isoprene elastomer(s). 21- Use according to one of claims 1 to 19, characterized in that said composition of elastomer(s) comprises at least one isoprene elastomer and at least one diene elastomer other than isoprene, the quantity of elastomer(s) isoprene(s) relative to the total quantity of elastomer(s) being preferably greater than 50% by weight. 22- Use according to one of claims 1 to 21, characterized in that said composition of elastomer(s) comprises at least one isoprene elastomer chosen from: (1) synthetic polyisoprenes obtained by homopolymerization of isoprene or methyl -2 butadiene-1,3; (2) synthetic polyisoprenes obtained by copolymerization of isoprene with one or more ethylenically unsaturated monomers chosen from: (2.1) conjugated diene monomers, other than isoprene, having 4 to 22 carbon atoms; (2.2) vinyl aromatic monomers having 8 to 20 carbon atoms; (2.3) vinyl nitrile monomers having 3 to 12 carbon atoms; (2.4) acrylic ester monomers derived from acrylic acid or methacrylic acid with alkanols having 1 to 12 carbon atoms; (2.5) a mixture of at least two of the aforementioned monomers (2.1) to (2.4); copolymer polyisoprenes containing between 20 and 99% by weight of isoprene units and between 80 and 1% by weight of diene units, aromatic vinyls, vinyl nitriles and/or acrylic esters; (3) natural rubber; (4) copolymers obtained by copolymerization of isobutene and isoprene, as well as halogenated versions of these copolymers; (5) a mixture of at least two of the aforementioned elastomers (1) to (4); (6) a mixture containing more than 50% by weight of the aforementioned elastomer (1) or (3) and less than 50% by weight of one or more diene elastomers other than isoprene. 23- Use according to claim 22, characterized in that said composition of elastomer(s) comprises at least one isoprene elastomer chosen from: (1) homopolymeric synthetic polyisoprenes; (2) synthetic polyisoprene copolymers consisting of poly(isoprene-butadiene), poly(isoprene-styrene) and poly(isoprene-butadiene-styrene); (3) natural rubber; (4) butyl rubber; (5) a mixture of at least two of the aforementioned elastomers (1) to (4); (6) a mixture containing more than 50% by weight of the aforementioned elastomer (1) or (3) and less than 50% by weight of diene elastomer other than isoprene consisting of polybutadiene, polychloroprene, poly(butadiene -styrene), poly(butadiene-acrylonitrile) or a terpolymer. 24- Use according to one of claims 1 to 23, characterized in that said composition of elastomer(s) comprises as isoprene elastomer at least natural rubber, preferably said composition of elastomer(s) comprising title of elastomer(s) only natural rubber. 25- Use according to one of claims 1 to 24, characterized in that said composition of elastomer(s) further comprises at least one compound chosen from vulcanization agents, vulcanization accelerators, vulcanization activators, carbon black, protective agents, plasticizing agents. 26- Use according to one of claims 1 to 25 in shoe soles, floor coverings, gas barriers, flame retardant materials, cable car rollers, household appliance joints, liquid pipe joints or gas, brake system seals, pipes, ducts, cables, engine mounts, conveyor belts, transmission belts or, preferably, tires. 27- Use according to one of claims 1 to 26 in a tire for heavy goods vehicles, in particular for trucks. 28- Composition of elastomer(s) comprising: - at least one isoprene elastomer, - at least one reinforcing inorganic filler, - at least one inorganic filler - elastomer coupling agent, characterized in that said inorganic filler - elastomer coupling agent is 3-acryloxy-propyltriethoxysilane, said reinforcing inorganic filler and said inorganic filler - elastomer coupling agent being as defined in one of claims 1 to 13. 29- Composition according to claim 28, characterized in that the quantity of precipitated silica (S1) represents from 10 to 90%, in particular from 20 to 80%, relative to the total quantity of the precipitated silica (S1) + precipitated silica (S2) assembly. 30- Composition according to one of claims 28 and 29, characterized in that the quantity of 3-acryloxy-propyltriethoxysilane represents from 1 to 20%, in particular from 2 to 15%, relative to the total quantity of the whole precipitated silica (S1) + precipitated silica (S2). 31- Composition according to one of claims 28 to 30, characterized in that said precipitated silicas (S1) and (S2) and the 3-acryloxy-propyltriethoxysilane are mixed beforehand with each other. 32- Composition according to one of claims 28 to 31, characterized in that said composition further comprises at least one covering agent for said precipitated silicas (S1) and (S2), optionally previously mixed with said precipitated silicas (S1) and (S2) and 3-acryloxy-propyltriethoxysilane. 33- Composition according to one of claims 28 to 32, characterized in that said composition does not comprise another inorganic filler - elastomer coupling agent. 34- Composition according to one of claims 28 to 33, characterized in that said composition does not comprise a free radical initiator. 35- Composition according to one of claims 28 to 34, characterized in that said composition does not comprise any elastomers other than said isoprene elastomer(s). 36- Composition according to one of claims 28 to 34, characterized in that said composition comprises at least one isoprene elastomer and at least one diene elastomer other than isoprene, the quantity of isoprene elastomer(s) relative to to the total quantity of elastomer(s) being preferably greater than 50% by weight. 37- Composition according to one of claims 28 to 36, characterized in that said composition comprises at least one isoprene elastomer chosen from: (1) synthetic polyisoprenes obtained by homopolymerization of isoprene or 2-methyl-1-butadiene, 3; (2) synthetic polyisoprenes obtained by copolymerization of isoprene with one or more ethylenically unsaturated monomers chosen from: (2.1) conjugated diene monomers, other than isoprene, having 4 to 22 carbon atoms; (2.2) vinyl aromatic monomers having 8 to 20 carbon atoms; (2.3) vinyl nitrile monomers having 3 to 12 carbon atoms; (2.4) acrylic ester monomers derived from acrylic acid or methacrylic acid with alkanols having 1 to 12 carbon atoms; (2.5) a mixture of at least two of the aforementioned monomers (2.1) to (2.4); copolymer polyisoprenes containing between 20 and 99% by weight of isoprene units and between 80 and 1% by weight of diene units, aromatic vinyls, vinyl nitriles and/or acrylic esters; (3) natural rubber; (4) copolymers obtained by copolymerization of isobutene and isoprene, as well as halogenated versions of these copolymers; (5) a mixture of at least two of the aforementioned elastomers (1) to (4); (6) a mixture containing more than 50% by weight of the aforementioned elastomer (1) or (3) and less than 50% by weight of one or more diene elastomers other than isoprene. 38- Composition according to claim 37, characterized in that said composition comprises at least one isoprene elastomer chosen from:

(1) homopolymer synthetic polyisoprenes;

(2) synthetic polyisoprene copolymers consisting of poly(isoprene-butadiene), poly(isoprene-styrene) and poly(isoprene-butadiene-styrene);

(3) natural rubber;

(4) butyl rubber;

(5) a mixture of at least two of the aforementioned elastomers (1) to (4);

(6) a mixture containing more than 50% by weight of the aforementioned elastomer (1) or (3) and less than 50% by weight of diene elastomer other than isoprene consisting in polybutadiene, polychloroprene, poly(butadiene-styrene), poly(butadiene-acrylonitrile) or a terpolymer.

39- Composition according to one of claims 28 to 38, characterized in that said composition comprises, as isoprene elastomer, at least natural rubber, preferably said composition of elastomer(s) comprising, as elastomer(s), ) only natural rubber.

40- Composition according to one of claims 28 to 39, characterized in that said composition further comprises at least one compound chosen from vulcanization agents, vulcanization accelerators, vulcanization activators, carbon black, agents protectors, anti-reversion agents, plasticizing agents. 41- Article comprising at least one composition according to one of claims 28 to 40, this article consisting of a shoe sole, a floor covering, a gas barrier, a flame retardant material, a cable car roller, a gasket household appliances, a liquid or gas pipe joint, a braking system joint, a pipe, a sheath, a cable, a motor support, a conveyor belt, a transmission belt or, preferably, a tire .

42- Tire according to claim 41 for heavy goods vehicles, in particular for trucks.