FR2966832A1 - USE OF A HIGH-SPECIFIC SURFACE PRECIPITED SILICA AND 3-ACRYLOXY-PROPYLTRYHOXYSILANE IN AN ISOPRENE (S) ELASTOMER COMPOSITION - Google Patents

Abstract

The invention relates to the joint use, in an elastomer composition (s) comprising an isoprene elastomer, of a precipitated silica, as a reinforcing inorganic filler, having a BET specific surface area between 180 and 260 m 2 / g, a CTAB surface area between 175 and 250 m / g, a porous distribution such that the pore volume constituted by the pores whose diameter is between 175 and 275 Å represents less than 55% of the pore volume constituted by the pores of smaller or equal diameters at 400 Å, a pore volume (V) consisting of pores with a diameter of less than 1 μm of at least 1.50 cm / g, and 3-acryloxypropyltriethoxysilane, as an inorganic filler-elastomer coupling agent. It also relates to the elastomer compositions (s) obtained and the articles made from said compositions.

Description

USE OF A HIGH SPECIFIC SURFACE-PRECIPITATED SILICA AND 3-ACRYLOXY-PROPYLTRIETHOXYSILANE IN AN ISOPRENE (S) ELASTOMER (S) COMPOSITION The invention relates to the joint use in elastomer compositions (s) comprising a 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 stresses, for example such as a temperature variation, a significant frequency stress variation in dynamic regime, a significant static stress and / or fatigue. in non-negligible flexion in dynamic mode. Such articles are, for example, tires, shoe soles, floor coverings, conveyor belts, power transmission belts, hoses, seals, especially appliance seals, playing supports. the 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 furthermore offer these compositions a generally lower hysteresis, synonymous with a decrease in the internal heating of 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 "elastomeric inorganic filler 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 "NVM", in which: - N represents a functional group ("N" function) capable of binding physically and / or chemically to the inorganic filler, such a bond can be established, for example, between a silicon atom of the coupling agent and the hydroxyl groups (OH) of 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 (divalent / hydrocarbon) group which makes it possible to connect "N" and M ". The coupling agents must not be confused with simple inorganic charge-covering agents which, in known manner, may comprise the function "N" active vis-à-vis the inorganic filler but are devoid of the function "M" active vis-à-vis 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) sulfurized silanes, mention may especially be made of bisistroxysilylpropyl tetrasulfide (abbreviated to 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 terms of safety roasting, 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 made it possible to achieve a wear resistance performance comparable to that of carbon black-reinforced elastomer blends, while significantly improving rolling resistance (hence a decrease in 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 truck tires, tires which are obtained from compositions based on isoprene elastomer (s), mainly natural rubber. However, the same polysulfide silica / silane combination applied to an isoprene elastomer, such as natural rubber, did not provide a sufficient level of reinforcement compared to what is obtained when carbon black is used as a filler. recessed reinforcement leading especially to 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 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, particularly with respect to their rheological properties and / or dynamic, especially hysteretic. Advantageously, it allows an improvement of the wear resistance. In addition, the elastomer compositions obtained preferably have good adhesion to both the reinforcing inorganic filler employed 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: precipitated silica, as reinforcing inorganic filler, said precipitated silica having: a BET specific surface area (SBET) of between 180 and 260 m 2 / g, a CTAB specific surface area (ScTAB) of between 175 and 250 m 2 / g, a porous distribution such that the pore volume constituted by the pores whose diameter is between 175 and 275 A represents less than 55% of the pore volume constituted by pores with diameters less than or equal to 400 A, a pore volume (V d 1) consisting of pores with a diameter of less than 1 μm of at least 1.50 cm 3 / g, with 3-acryloxypropyltriethoxysilane (or γ-acryloxypropyltriethoxysilane), as charge coupling agent inorganic - elastomer

Preferably, the precipitated silica used according to the invention has a BET specific surface area of between 185 and 250 m 2 / g. Very preferably, its BET surface area is between 185 and 215 m 2 / g, in particular between 190 and 210 m 2 / g. Likewise, preferably, the precipitated silica used according to the invention has a CTAB specific surface area of between 180 and 240 m 2 / g. Very preferably, its CTAB surface area is between 185 and 210 m 2 / g, in particular between 190 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).

One of the characteristics of the precipitated silica used in the invention lies in the distribution, or distribution, of its pore volume, and in particular in the distribution of the pore volume which is generated by pores with diameters less than or equal to 400 A. This latter volume corresponds to the useful pore volume of the charges used in the reinforcement of the elastomers. Thus, it is used according to the invention a precipitated silica having (and this can be illustrated by the analysis of porograms) a porous distribution such as the pore volume generated by the pores whose diameter is between 175 and 275 A (V2) represents less than 55%, in particular less than 50%, for example 25 and 45%, of the pore volume generated by 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 relationship with a theta contact angle equal to 130 ° and a voltage superficial gamma equal to 484 Dynes / cm (DIN 66133 standard). In addition, another characteristic of the precipitated silica used in the invention lies in the fact that it has a pore volume (Vdl), constituted by pores with a diameter of less than 1 μm, greater than 1.50 cm 3 / g, preferably greater than 1.65 cm3 / g; this pore volume may be greater than 1.70 cm3 / g, for example between 1.75 and 1.80 cm3 / g.

In general, the precipitated silica employed according to the invention 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. 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. The dispersibility (and deagglomeration) ability of the precipitated silica implemented according to the invention can be assessed by means of the following test, by a particle size measurement (by laser diffraction) carried out on a silica suspension previously deagglomerated. by ultra-sonification (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 particle size measurement is then carried out by introducing into the vial of the granulometer a volume V (expressed in ml) of the homogenized suspension necessary to obtain an optical density of about 20. The value of the median diameter 050 that is obtained according to this test is even lower than the silica has a high deagglomeration ability. A deagglomeration factor Fo is given by the equation: Fp = 10 x V / optical density of the suspension measured by the particle size analyzer (this optical density is about 20). This disagglomeration factor Fp is indicative of the level of particles smaller than 0.1 μm which are not detected by the particle size analyzer. This factor is all the higher as the silica has a high deagglomeration ability. In general, the precipitated silica implemented according to the invention has a median diameter of 050, after deagglomeration with ultrasound, less than 8.5 μm, for example between 5 and 8 μm. It usually has an ultrafast deagglomeration factor 30 Fp greater than 5.5 ml, in particular greater than 9 ml, for example greater than 10 ml.

Preferably, the precipitated silica employed according to the invention has a level of fines (if), after deagglomeration with ultrasound, of at least 50%, for example at least 55%. The measurement of the content of fines (if), that is to say the proportion (by weight) of particles smaller than 0.3 μm, after deagglomeration with ultrasound, is carried out according to the test described below. after, and also illustrates the dispersibility of the precipitated silica used in the invention. In this test, the dispersibility of the silica is measured by a granulometric measurement (by sedimentation) carried out on a suspension of silica previously deagglomerated by ultra-sonification. Deagglomeration (or dispersion) under ultrasound is carried out using a VIBRACELL BIOBLOCK (600 W) sonifier, equipped with a 19 mm diameter probe. The granulometric measurement is carried out using a SEDIGRAPH granulometer (gravity field sedimentation + X-ray scanning).

Four grams of silica are weighed into a pillbox (with a volume equal to 75 ml) and the mixture is made up to 50 grams by addition of deionized water: an 8% aqueous suspension of silica is thus prepared which is homogenized for 2 minutes by magnetic stirring. Ultrasound deagglomeration (dispersion) is then carried out as follows: the probe being immersed over a length of 4 cm, the output power is adjusted so as to obtain a deviation of the power needle indicating 20%. Deagglomeration is performed for 210 seconds. The granulometric measurement is then carried out using a SEDIGRAPH granulometer. For this purpose, the vertical scan rate of the cell is first adjusted by the X-ray beam at 918, which corresponds to a maximum analyzed size of 85 mA. Permuted water is circulated through the cell and then the electrical zero and the mechanical zero of the paper recorder are adjusted (this adjustment is made with the "100%" potentiometer of the recorder at the maximum sensitivity). The pen of the paper recorder is placed at the point representing the starting size of 85 μm. The deagglomerated silica slurry, optionally previously cooled, is then circulated in the SEDIGRAPH granulometer cell (granulometric analysis is carried out at 30 ° C.) and the analysis then starts. The analysis stops automatically as soon as the 0.3 μm size is reached (approximately 45 minutes). The rate of fines (tif), that is to say the proportion (by weight) of particles smaller than 0.3 μm, is then calculated. This level of fines (if), or particle size less than 0.3 {Gm, is even higher than the silica has a high dispersibility.

The precipitated silica used according to the invention may have a fineness index (IF) of between 70 and 100 Å, in particular between 80 and 100 Å. The fineness index (IF) represents the median radius of the intra-aggregated pores. that is, the pore radius to which the S0 / 2 pore surface area measured by mercury porosimetry (So is the area contributed by all pores with a diameter greater than or equal to 100 A).

The pH of the precipitated silica used according to the invention is generally between 6.0 and 7.5.

The pH is measured according to the following method deriving from the ISO 787/9 standard (pH of a 5% suspension in water): Apparatus: - calibrated pH meter (reading accuracy to 1 / 100th) - combined glass electrode - 200 mL beaker - 100 mL test specimen - 0.01 gram precision balance. Procedure: 5 grams of silica are weighed to the nearest 0.01 gram in the 200 mL beaker. 95 mL of water measured from the graduated cylinder is 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 the precipitated silica to be used according to the invention may be any, that is to say, it may be for example in the form of powder, granules or microbeads (substantially spherical beads ).

It can thus 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). It may preferably 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 300 μm, for example 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%.

The precipitated silica used in the context of the invention may be prepared for example by a process as described in patent application EP-A-0917519. Preferably, the precipitated silica employed in the invention can be obtained by a preparation process comprising the precipitation reaction between a silicate and an acidifying agent whereby a suspension of precipitated silica is obtained, followed by separation and drying. of this suspension, in which inter alia: the precipitation is carried out in the following manner: (i) an initial stock having at least a part of the total amount of the silicate involved in the reaction and at least one electrolyte is formed ( whose concentration in said bottom of tank is for example cimporise between 12 and 20 g / L), the concentration of silicate (expressed in SiO2) in said initial base stock being between 50 and 60 g / L, (ii) the acidifying agent is added to said heelstock until a pH value of the reaction medium of between 7 and 8.5 is reached; (iii) acidifying agent is added to the reaction medium and, if appropriate, applicable at the same time, the remaining amount of the silicate, the separation comprises a filtration and a washing with the aid of a filter equipped with a compaction means (in particular a filter press), it is spray dried, for example by means of a nozzle atomizer, a suspension, preferably having a solids content of less than 17% by weight.

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

The precipitated silica used according to the present invention as the reinforcing inorganic filler and the 3-acryloxypropyltriethoxysilane used according to the present invention as the reinforcing inorganic filler-elastomer coupling agent may be mixed together prior to their use. A first variant is that the 3-acryloxypropyltriethoxysilane is not grafted onto said precipitated silica; a second variant is that the 3-acryloxypropyltriethoxysilane is grafted onto said precipitated silica which will thus be "pre-coupled" 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 on support being carried out prior to its use) on a solid 25 compatible with its structure. chemical, this solid support may be for example carbon black or, preferably, precipitated silica used according to the present invention.

The elastomer compositions in which 3-acryloxypropyltriethoxysilane is used according to the invention may contain at least one precipitated silica coating agent used as a reinforcing filler. This covering agent is capable, in a known manner, of improving the processing power 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 trialkanolamine), a α, β-dihydroxylated polydimethylsiloxane or an α, β-diamine polydimethylsiloxane. This coating agent may optionally be mixed with said precipitated silica and 3-acryloxypropyltriethoxysilane prior to their use.

The elastomer compositions in which the 3-acryloxypropyltriethoxysilane and the precipitated silica described above are used according to the invention may optionally comprise at least one other inorganic filler-elastomer coupling agent, in particular a sulphurised silane. or polysulfide.

Examples of such a coupling agent are: bis-triethoxysilylpropyl disulfide (abbreviated TESPD) of formula: (C2H5O) 3Si - (CH2) 3 -S2- (CH2) 3 -Si (OC2H5) 3 bis-triethoxysilylpropyl tetrasulfide (abbreviated TESPT) of formula: (C2H5O) 3Si - (C H2) 3-54- (C H2) 3 -Si (OC2H5) 3 - bis-monohydroxydimethylsilylpropyl tetrasulfide of formula: (HO) (CH3) 2Si- (CH2) 3 -S4- (CH2) 3-Si (CH3) 2 (OH) - bis-monoethoxydimethylsilylpropyl disulfide (abbreviated to MESPD) of formula: (C2H5O) (CH3) Si - (C H 2) 3 -S 2 - (CH 2) 3 -Si (C H 3) 2 (OC 2 H 5) - bis-monoethoxydimethylsilylpropyl tetrasulfide (abbreviated as MESPT) of formula: (C2H5O) (CH3) 2Si - (CH2) 3 -S4- (CH2) 3-Si (CH3) 2 (OC2H5) - bis-monoethoxydimethylsilylisopropyl tetrasulfide (abbreviated to MESiPrT) of formula: (C2H5O) (CH3) 2Si-CH2-CH- (CH3) -S4- ( However, preferably, said elastomer compositions (s) do not contain any other inorganic filler coupling agent - ela (CH3) 2 (OC2H5). stomere 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 energetic activation, to generate free radicals in situ, in its surrounding environment, in this case in 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 (t-butyl) -3,3,5-trimethylcyclohexane, peroxide optionally being placed on a solid support, such as calcium carbonate. However, preferably, the invention is carried out 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) 30 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-methylbutadiene 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 from 4 to 22 carbon atoms, such as by 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlorobutadiene-1,3 (or chloroprene), 1-phenyl-1,3-butadiene, 1,3-pentadiene and the like. 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 having from 6 to 12 carbon atoms, for example elastomers obtained from ethylene propylene with a non-conjugated diene monomer of the aforementioned type such as in particular 1,4-hexadiene, héthylidénenorbornène, dicyclopentadiène (EPDM elastomer). Preferably, the elastomer composition (s) comprises at least one isoprene elastomer selected 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 aforementioned 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 further 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 selected from vulcanizing agents (e.g., sulfur or a sulfur donor compound (such as a thiuram derivative)), vulcanization accelerators (e.g., a guanidine derivative or a thiazole derivative), vulcanization activators (e.g., stearic acid, zinc stearate and zinc oxide, which may optionally be introduced in a fractional manner during the preparation of the composition), the carbon black, protective agents (especially antioxidants and / or antiozonants, such as, for example, N-phenyl-N '- (1,3-dimethyl-butyl) -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 silica described in the previous discussion and 3-acryloxypropyltriethoxysilane can be done more particularly in shoe soles, floor coverings, gas barriers, flame retardant materials, ropeway rollers, appliance joints, liquid or gas line joints, braking system joints, hoses, ducts (including cable ducts), cables, supports motor, 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 precipitated silica as described above and 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, chosen especially in 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 amount used of the precipitated silica as described above. 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 second subject of the present invention is the elastomer compositions (s) described above, and therefore 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 precipitated silica such as described in the above disclosure 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 said precipitated silica 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 phase of mechanical work (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 joints, liquid or gas pipe joints, brake system seals, hoses (flexible ), sheaths (in particular cable sheaths), cables, motor supports, conveyor belts, transmission belts, or, preferably, tires (in particular 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 S, as recommended by the invention, and 3-acryloxypropyltriethoxysilane in an elastomeric composition. The precipitated silica S, which is in the form of substantially spherical beads, has the following characteristics: aluminum content by weight <0.5% It is subjected to the deagglomeration test as defined previously in the description. - CTAB surface area 191 m2 / g - BET specific surface area 195 m2 / g - V2 / V1 ratio <50% - Vd1 pore volume> 1.65 cm3 / g generated by the pores of d <1 pm After ultrasonic deagglomeration it has a median diameter (050) of less than 8.5 micrograms and an ultrasonic deagglomeration factor (Fp) of greater than 10.0 ml. 2- In an internal mixer of the Haake type, elastomeric compositions are prepared whose constitution, expressed in parts by weight per 100 parts of elastomers (phr), is shown in Table 1 below.

Table 1: Formulations used for mixtures Compositions Control Composition 1 NR (1) 100 100 Silica (2) 50 50 Coupling Agent 1 (3) 5.0 - Coupling Agent 2 (4) - 5.6 ZnO 3.0 3.0 Stearic acid 2.5 2.5 Antioxidant 1 (5) 1.5 1.5 Antioxidant 2 (6) 1.0 1.0 Carbon black (N330) 3.0 3.0 CBS (7) 1 1.5 DPG (8) 0.5 0.5 Sulfur 1.5 2.0 (1) Natural rubber SMR 5 - CV60 (supplied by Safic-Alcan) (2) Silica S (3) TESPT ( Z-6940 from Dow Corning) (4) 3-acryloxypropyltriethoxysilane (5) N-1,3-dimethylbutyl-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from Flexsys) (6) 2, 2,4-trimethyl-1H-quinoline (Permanax TQ from Flexsys) (7) N-cyclohexyl-2-benzothiazyl-sulfenamide (Rhenogran CBS-80 from RheinChemie) (8) 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 110 ° 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 allows to incorporate, in a first pass, the elastomer (natural rubber), then the reinforcing inorganic filler consisting of silica (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. using a MV 2000 rheometer according to standard NF ISO 289. 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.

10 - 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. by means of a Monsanto ODR rheometer according to the standard NF ISO 3417, are shown in Table III. According to this test, the test composition is placed in the chamber. controlled test at a temperature of 150 ° C for 30 minutes, and measuring the resistive torque, opposed by the composition, a low amplitude oscillation (3 °) of a biconical rotor included in the test chamber, the composition completely filling the chamber considered. 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 maximum torque (Cmax); Delta-torque (AC = C max - C min); 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 Compositions Control Composition 1 ML (1 + 4) - 100 ° C 59 61 Cmin (dN.m) 12.1 11.7 Cmax (dNm) 79.5 77.7 Delta couple (dN.m) 67.4 66.0 TS2 (min) 5.57 5.63 It is found that the composition resulting from the invention (composition 1) has a satisfactory set of rheological properties.

In particular, while having an acceptable viscosity, it has lower minimum and maximum torque values than those of the control composition, which reflects a greater ease of use of the mixture prepared. And the composition resulting from the invention (composition 1) has a satisfactory vulcanization kinetics (TS2), and this without penalizing the viscosity of the raw mixture (illustrated in particular by the minimum torque).

Mechanical properties of vulcanizates

The measurements are made on the optimum vulcanized compositions (i.e., at a state of vulcanization corresponding to 98% of complete vulcanization) at a temperature of 150 ° C. The uniaxial tensile tests are carried out in accordance with the NF ISO 37 standard with specimens of type H2 at a speed of 500 mm / min on an INSTRON 5564. The x% modules correspond to the stress measured at x% of tensile deformation and are expressed, such as tensile 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. 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 mm3) after wear by abrasion; the lower it is, the better the resistance to abrasion.

The measured properties are collated in Table III.

Table III Compositions Control Composition 1 Module 10% (Mpa) 0.6 0.5 Module 100% (Mpa) 2.5 2.4 Module 300% (Mpa) 11.7 15.2 Resistance rupture (Mpa) 28.2 29.1 IR 4.7 6.3 Loss by abrasion (mm3) 125 99 It is found that the composition resulting from the invention (composition 1) has a good compromise of mechanical properties with respect to that obtained with the composition witness. The composition 1 thus has relatively low 10% and 100% modules and a relatively high 300% modulus, hence a higher reinforcement index. In addition, the composition 1 has, in addition to a fairly good breaking strength, a lower abrasion loss, that is to say a better resistance to abrasion, hence 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 (E1 are recorded on vulcanized samples (cylindrical specimen of section 95 mm 2 and height 14 mm). is initially subjected to a predeformation of 10%, then to a sinusoidal deformation in alternating compression of +/- 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 compressive modulus (E * - 60 ° C 10 Hz) and the loss factor (tan b - 60 ° C - 10 Hz) In a second set of measurements, the values of the loss factor (tan b) and elastic modulus in dynamic shear (G ') are recorded on vulcanized samples (parallelepipedal specimen of section 8 mm2 and height 7 mm) The sample is subjected to a sinusoidal deformation in alternating double shear at a temperature of40 ° C and at a frequency of 10 Hz. The scanning processes in amplitude of deformations are carried out according to a round-trip cycle, ranging from 0.1 to 50% and then back from 50 to 0.1%. The results, presented in Table IV, are derived from the amplitude scan of the return strains and concern 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 Compositions Control Composition 1 E * - 60 ° C - 10 Hz (MPa) 7.4 5.6 Tang b - 60 ° C - 10 Hz 0.098 0.080 AG '- 60 ° C - 10 Hz (MPa) 2.4 1.1 Tang b max back - 0.138 0.100 60 ° C-10 Hz The composition resulting from the invention (composition 1) has good dynamic properties (hysteretic properties at 60 ° C), especially with respect to the control composition.

It can be seen from the results of Tables II to IV that the composition resulting from the invention (Composition 1) has a good compromise of properties.

Claims (37)

CLAIMS1- Use in an elastomer composition (s), comprising at least one isoprene elastomer: precipitated silica, as reinforcing inorganic filler, said precipitated silica having: a BET specific surface area (SBET) of between 180 and 260 m 2 / g, a CTAB specific surface area (ScTAB) of between 175 and 250 m 2 / g, 10. a porous distribution such that the pore volume constituted by the pores whose diameter is between 175 and 275 A represents less than 55% of the pore volume constituted by pores with diameters less than or equal to 400 A, a pore volume (Vd1) consisting of pores with a diameter of less than 1 μm of at least 1.50 cm3 / g, with 3-acryloxypropyltriethoxysilane, as an inorganic filler-elastomer coupling agent. 20 2- Use according to claim 1, characterized in that said precipitated silica has:. a BET specific surface area (SBET) of between 185 and 250 m 2 / g, a CTAB specific surface area (ScTAB) of between 180 and 240 m2 / g. 25 3- Use according to one of claims 1 and 2, characterized in that said precipitated silica has:. a BET specific surface area (SBET) of between 185 and 215 m 2 / g, a CTAB specific surface area (ScTAB) of between 185 and 210 m 2 / g. 30 4- Use according to one of claims 1 to 3, characterized in that said precipitated silica has an aluminum content of less than 0.5% by weight, preferably less than 0.35% by weight, for example less than 0.2% by weight. 5- Use according to one of claims 1 to 4, characterized in that said precipitated silica has a pore volume (Vdl) consisting of pores with a diameter less than 1 pm greater than 1.65 cm3 / g. 6. Use according to one of claims 1 to 5, characterized in that said precipitated silica has a porous distribution such that the pore volume constituted by pores whose diameter is between 175 and 275 Å represents less than 50% of the volume. porous constituted by pores with diameters less than or equal to 400 Å. 7- Use according to one of claims 1 to 6, characterized in that said precipitated silica has a median diameter (050), after deagglomeration with ultrasound, less than 8.5 .mu.m. 8- Use according to one of claims 1 to 7, characterized in that said precipitated silica has an ultrasonic deagglomeration factor (Fp) greater than 5.5 ml, in particular greater than 9 ml. 9- Use according to one of claims 1 to 8, characterized in that said precipitated silica has a level of fines (tif), after deagglomeration with ultrasound, at least 50%. 10- Use according to one of claims 1 to 9, characterized in that said precipitated silica is in the form of substantially spherical beads, preferably of average size of at least 80 pm, for example between 150 and 300 pm. 11- Use according to one of claims 1 to 10, characterized in that the amount of 3-acryloxypropyltriethoxysilane used represents from 1 to 20%, in particular from 2 to 15%, relative to the amount of said silica used rushed. 12- Use according to one of claims 1 to 11, characterized in that said precipitated silica and 3-acryloxypropyltriethoxysilane are premixed together. 13- Use according to one of claims 1 to 12, characterized in that said elastomer composition (s) further comprises at least one covering agent of said precipitated silica, optionally premixed with said precipitated silica and 3- acryloyloxy-propyltriethoxysilane. 14- Use according to one of claims 1 to 13, characterized in that said elastomer composition (s) does not include another inorganic filler - elastomer coupling agent. 15- Use according to one of claims 1 to 14, in the absence of free radical initiator. 16- Use according to one of claims 1 to 15, characterized in that said elastomer composition (s) does not include other elastomers that said (s) elastomer (s) isoprene (s). 17- Use according to one of claims 1 to 15, characterized in that said elastomer composition (s) comprises at least one isoprene elastomer and at least one diene elastomer other than isoprene, the amount of elastomer (s) isoprene (s) relative to the total amount of elastomer (s) being preferably greater than 50% by weight. 18- Use according to one of claims 1 to 17, characterized in that said elastomer composition (s) comprises at least one isoprene elastomer selected from: (1) synthetic polyisoprenes obtained by homopolymerization of isoprene or methyl -2 butadiene-1,3; (2) synthetic polyisoprenes obtained by copolymerizing isoprene with one or more ethylenically unsaturated monomers selected from: (2.1) conjugated diene monomers, other than isoprene, having from 4 to 22 carbon atoms; (2.2) vinyl aromatic monomers having 8 to 20 carbon atoms; (2.3) vinyl nitrile monomers having from 3 to 12 carbon atoms; (2.4) acrylic ester monomers derived from acrylic acid or methacrylic acid with alkanols having from 1 to 12 carbon atoms; (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; (3) natural rubber; (4) copolymers obtained by copolymerization of isobutene and isoprene, as well as the 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 isoprenic. 20 19. Use according to claim 18, characterized in that said elastomer composition (s) comprises at least one isoprene elastomer chosen from: (1) homopolymeric synthetic polyisoprenes; (2) copolymeric synthetic polyisoprenes 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 non-isoprene diene elastomer consisting of polybutadiene, polychloroprene, poly ( butadiene-styrene), poly (butadiene-acrylonitrile) or a terpolymer (ethylene-propylene-diene monomer non-conjugated). 20- Use according to one of claims 1 to 19, characterized in that said elastomer composition (s) comprises as isoprene elastomer at least natural rubber, preferably said elastomer composition (s) comprising as elastomer (s) only natural rubber. 21. Use according to one of claims 1 to 20, characterized in that said elastomer composition (s) further comprises at least one compound chosen from vulcanizing agents, vulcanization accelerators, vulcanization activators, carbon black, protective agents, plasticizers. 15 22- Use according to one of claims 1 to 21 in the soles of shoes, floor coverings, gas barriers, flame retardant materials, rollers of cable cars, appliance joints, liquid pipe joints or gas, braking system seals, hoses, ducts, cables, motor mounts, conveyor belts, transmission belts or, preferably, tires. 23. Use according to one of claims 1 to 22 in a tire for heavy goods vehicles, in particular for trucks. 25 24- 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 30 is 3-acryloxypropyltriethoxysilane, said reinforcing inorganic filler and said inorganic filler-elastomer coupling agent being as defined in one of claims 1 to 10. 25. Composition according to claim 24, characterized in that the amount of 3-acryloxypropyltriethoxysilane represents from 1 to 20%, in particular from 2 to 15%, relative to the amount of said precipitated silica. 26- Composition according to one of claims 24 and 25, characterized in that said precipitated silica and 3-acryloxypropyltriethoxysilane are premixed together. 27- Composition according to one of claims 24 to 26, characterized in that said composition further comprises at least one covering agent of said precipitated silica, optionally premixed with said precipitated silica and 3-acryloxy-propyltriethoxysilane. 28. Composition according to one of claims 24 to 27, characterized in that said composition does not comprise another inorganic filler-elastomer coupling agent. 29. Composition according to one of Claims 24 to 28, characterized in that the said composition does not comprise a free radical initiator. 30- Composition according to one of claims 24 to 29, characterized in that said composition does not comprise other elastomers that said (s) elastomer (s) isoprene (s). 25 31- The composition according to one of claims 24 to 29, characterized in that said composition comprises at least one isoprene elastomer and at least one diene elastomer other than isoprene, the amount of isoprene elastomer (s) relative to the total amount of elastomer (s) being preferably greater than 50% by weight. 30 32- Composition according to one of claims 24 to 31, characterized in that said composition comprises at least one isoprene elastomer chosen from: (1) synthetic polyisoprenes obtained by homopolymerization of isoprene or 2-methylbutadiene-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 from 4 to 22 carbon atoms; (2.2) vinyl aromatic monomers having 8 to 20 carbon atoms; (2.3) vinyl nitrile monomers having from 3 to 12 carbon atoms; (2.4) acrylic ester monomers derived from acrylic acid or methacrylic acid with alkanols having from 1 to 12 carbon atoms; (2.5) a mixture of at least two of the aforementioned monomers (2.1) to (2.4); 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; (3) natural rubber; (4) copolymers obtained by copolymerization of isobutene and isoprene, as well as the 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 isoprenic. 33. Composition according to claim 32, characterized in that said composition 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% by weight of the aforementioned elastomer (1) or (3) and less than 50% by weight of non-isoprene diene elastomer consisting of polybutadiene, polychloroprene, poly (butadiene-styrene), poly (butadiene-acrylonitrile) or a terpolymer (ethylene-propylene-diene 5 non-conjugated monomer). 34. Composition according to one of claims 24 to 33, characterized in that said composition comprises, as isoprene elastomer, at least natural rubber, preferably said elastomer composition (s) comprising as elastomer ( s) only natural rubber. 35- The composition according to one of claims 24 to 34, characterized in that said composition further comprises at least one compound selected from vulcanizing agents, vulcanization accelerators, vulcanization activators, carbon black, protective agents, antireversions agents, plasticizers. 36. Article comprising at least one composition according to one of claims 24 to 35, this article consisting of a shoe sole, a floor covering, a gas barrier, a flame-retardant material, a cable-car wheel, a gasket appliances, a gas or liquid line joint, a brake system gasket, a pipe, a jacket, a cable, an engine support, a conveyor belt, a transmission belt or, preferably, a tire. 37- A tire according to claim 36 for heavy goods vehicles, in particular for trucks.