Method for preparing precipitated silicas, novel precipitated silicas and their uses, in particular for strengthening polymers

Abstract

The invention relates to a novel process for the preparation of a precipitated silica, in which: a silicate is reacted with an acidifying agent, so as to obtain a suspension of precipitated silica, said suspension of precipitated silica is filtered, so as to obtain a filtration cake, said filtration cake is subjected to a liquefaction operation comprising the addition of an aluminum compound, after the liquefaction operation, a drying stage is carried out, characterized in that a polycarboxylic acid chosen from dicarboxylic acids and tricarboxylic acids is added to the filtration cake after the addition of the aluminum compound. It also relates to novel precipitated silicas and to their uses.

Claims

1. A tire comprising a precipitated silica having: a BET specific surface of between 45 and 550 m.sup.2/g, a content (C) of polycarboxylic acid and corresponding carboxylate, expressed as total carbon, of at least 0.15% by weight, wherein the polycarboxylic acid comprises succinic acid, and an aluminum (Al) content of at least 0.20% by weight, wherein the precipitated silica exhibits a dispersive component of the surface energy .sub.s.sup.d of at least 40 mJ/m.sup.2 and of less than 43 mJ/m.sup.2.

2. The tire as claimed in claim 1, wherein the BET specific surface is between 100 and 240 m.sup.2/g.

3. The tire as claimed in claim 1, wherein the content (C) of polycarboxylic acid and corresponding carboxylate, expressed as total carbon, is at least 0.25% by weight.

4. The tire as claimed in claim 1, wherein the aluminum (Al) content is at least 0.30% by weight.

5. The tire as claimed in claim 1, wherein the precipitated silica exhibits a dispersive component of the surface energy .sub.s.sup.d of less than 42 mJ/m.sup.2.

6. The tire as claimed in claim 1, wherein the precipitated silica exhibits a water uptake of greater than 6%.

7. The tire as claimed in claim 1, wherein the precipitated silica exhibits a ratio (R), defined by the following formula: $\left(R\right)=N\frac{\left[\left(100C/C_{\mathrm{Theo}}\right)M_{\mathrm{Al}}\right]}{\left(\mathrm{Al}{M}_{\mathrm{Ac}}\right)},$ in which: N is the number of carboxylic functional groups of the polycarboxylic acid, C.sub.T is the carbon content of the polycarboxylic acid, M.sub.Al is the molecular weight of aluminum, M.sub.Ac is the molecular weight of the polycarboxylic acid, of between 0.4 and 3.5.

8. The tire as claimed in claim 7, wherein the ratio (R) exhibited by the precipitated silica is between 0.5 and 2.5.

Description

EXAMPLES

Example 1

(1) The suspension of precipitated silica used is a silica slurry obtained on conclusion of the precipitation reaction during the process for the preparation of the Z1165MP silica.

(2) The silica suspension (1396 liters) is filtered and washed on a filter press and is then subjected to compacting at a pressure of 5.5 bar on the same filter. The silica cake which results therefrom exhibits a solids content of 23% by weight.

(3) Prior to the liquefaction operation, a 100 g/l solution of succinic acid is prepared by dissolving the succinic acid in water (35 C.) with stirring.

(4) The cake obtained in the filtration stage is subjected to a liquefaction operation in a continuous vigorously stirred reactor (for approximately 3 hours) with 2270 grams of the sodium aluminate solution (Al/SiO.sub.2 ratio by weight of 0.33%).

(5) Once the liquefaction has been carried out, 9670 grams of the succinic acid solution prepared beforehand are added to a portion (303 liters) of the disintegrated cake (succinic acid/SiO.sub.2 ratio by weight of 1.15%).

(6) This treated portion (having a solids content of 22% by weight) of the disintegrated cake is subsequently dried using a nozzle atomizer by spraying the disintegrated cake through a 1.5 mm nozzle with a pressure of 25 bar for 50 minutes under the following mean conditions of flow rate and of temperatures:

(7) Mean inlet temperature: 535 C.

(8) Mean outlet temperature: 155 C.

(9) Mean flow rate: 202 l/h.

(10) The characteristics of the silica S1 obtained (in the form of substantially spherical beads) are then the following:

(11) TABLE-US-00002 BET (m.sup.2/g) 147 Content of polycarboxylic acid + carboxylate (C) (%) 0.35 Aluminum (Al) content (%) 0.30 Ratio (R) 1.3 CTAB (m.sup.2/g) 151 Y.sub.s.sup.d (mJ/m.sup.2) 33.2 Water uptake (%) 8.5 .sub.50 (m) after deagglomeration with ultrasound 2.7 Fd after deagglomeration with ultrasound 18.9 V2/V1 (%) 56 pH 5.2

Example 2 (Comparative)

(12) The suspension of precipitated silica used is a silica cake (having a solid content of 23% by weight) obtained on conclusion of the filtration stage during the process for the preparation of the Z1165MP silica.

(13) Prior to the liquefaction operation, a 100 g/l maleic acid solution is prepared by dissolving maleic acid in water (at 35 C.) with stirring.

(14) The cake obtained in the filtration stage is subjected to a liquefaction operation in a continuous vigorously stirred reactor (for approximately 90 minutes) with addition to the cake of 4400 grams of the 100 g/l maleic acid solution (maleic acid/SiO.sub.2 ratio by weight of 1.0%).

(15) This disintegrated cake (having a solids content of 22% by weight) is subsequently dried using a nozzle atomizer by spraying the disintegrated cake through a 1.5 mm nozzle with a pressure of 25 bar under the following mean conditions of flow rate and of temperatures:

(16) Mean inlet temperature: 577 C.

(17) Mean outlet temperature: 157 C.

(18) Mean flow rate: 220 l/h.

(19) The characteristics of the silica C1 obtained (in the form of substantially spherical beads) are then the following:

(20) TABLE-US-00003 BET (m.sup.2/g) 169 Content of polycarboxylic acid + carboxylate (C) (%) 0.19 Aluminum (Al) content (%) <0.05 Ratio (R) >4.3 CTAB (m.sup.2/g) 178 Y.sub.s.sup.d (mJ/m.sup.2) 51 .sub.50 (m) after deagglomeration with ultrasound 3.6 Fd after deagglomeration with ultrasound 19.3 V2/V1 (%) 58 pH 3.8

Example 3

(21) The elastomeric compositions, the make up of which, expressed as parts by weight per 100 parts of elastomers (phr), is shown in table I below, are prepared in an internal mixer of Brabender type (380 ml):

(22) TABLE-US-00004 TABLE I Composition Control 1 Composition 1 SBR (1) 103 103 BR (1) 25 25 Silica 1 (2) 80 Silica S1 (3) 80 Coupling agent (4) 6.4 6.4 Carbon black (N330) 3.0 3.0 Plasticizer (5) 7 7 ZnO 2.5 2.5 Stearic acid 2 2 Antioxidant (6) 1.9 1.9 DPG (7) 1.5 1.5 CBS (8) 2 2 Sulfur 1.1 1.1 (1) Solution SBR (Buna VSL5025-2 from Lanxess) with 50 +/ 4% of vinyl units; 25 +/ 2% of styrene units; Tg in the vicinity of 20 C.; 100 phr of SBR extended with 37.5 +/ 2.8% by weight of oil/BR (Buna CB 25 from Lanxess) (2) Silica Z1165 MP from Rhodia (3) Silica S1 according to the present invention (liquefaction with addition of sodium aluminate, then addition of succinic acid after liquefaction (example 1 above)) (4) TESPT (Luvomaxx TESPT from Lehvoss France sarl) (5) Nytex 4700 from Nynas (6) N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from Flexsys) (7) Diphenylguanidine (Rhenogran DPG-80 from RheinChemie) (8) N-Cyclohexyl-2-benzothiazolesulfenamide (Rhenogran CBS-80 from RheinChemie)

(23) The silica Z1165 MP exhibits the following characteristics:

(24) TABLE-US-00005 BET (m.sup.2/g) 161 Content of polycarboxylic acid + carboxylate (C) (%) 0.00 Aluminum (Al) content (%) 0.30 Ratio (R) 0 CTAB (m.sup.2/g) 155 Y.sub.s.sup.d (mJ/m.sup.2) 48.7 Water uptake (%) 9.4

(25) Process for the Preparation of the Elastomeric Compositions:

(26) The process for the preparation of the rubber compositions is carried out in two successive preparation phases. A first phase consists of a phase of high-temperature thermomechanical working. It is followed by a second phase of mechanical working at temperatures of less than 110 C. This phase makes possible the introduction of the vulcanization system.

(27) The first phase is carried out using a mixing device, of internal mixer type, of Brabender brand (capacity of 380 ml). The filling coefficient is 0.6. The initial temperature and the speed of the rotors are set on each occasion so as to achieve mixture dropping temperatures of approximately 140-160 C.

(28) Broken down here into two passes, the first phase makes it possible to incorporate, in a first pass, the elastomers and then the reinforcing filler (introduction in installments) with the coupling agent and the stearic acid. For this pass, the duration is between 4 and 10 minutes.

(29) After cooling the mixture (temperature of less than 100 C.), a second pass makes it possible to incorporate the zinc oxide and the protecting agents/antioxidants (in particular 6-PPD). The duration of this pass is between 2 and 5 minutes.

(30) After cooling the mixture (temperature of less than 100 C.), the second phase makes possible the introduction of the vulcanization system (sulfur and accelerators, such as CBS). It is carried out on an open mill, preheated to 50 C. The duration of this phase is between 2 and 6 minutes.

(31) Each final mixture is subsequently calandered in the form of plaques with a thickness of 2-3 mm.

(32) With regard to these raw mixtures obtained, an evaluation of their rheological properties makes it possible to optimize the vulcanization time and the vulcanization temperature.

(33) Subsequently, the mechanical and dynamic properties of the mixtures vulcanized at the curing optimum (T98) are measured.

(34) Rheological Properties

(35) Viscosity of the Raw Mixtures:

(36) The Mooney consistency is measured on the compositions in the raw state at 100 C. using an MV 2000 rheometer and also the determination of the Mooney stress-relaxation rate according to the standard NF ISO 289.

(37) The value of the torque, read at the end of 4 minutes after preheating for one minute (Mooney Large (1+4)at 100 C.), is shown in table II. The test is carried out after preparing the raw mixtures and then after aging for 3 weeks at a temperature of 23+/3 C.

(38) TABLE-US-00006 TABLE II Compositions Control 1 Composition 1 ML (1 + 4) 100 C. Initial 79 74 Mooney relaxation Initial 0.312 0.343 ML (1 + 4) 100 C. After 3 weeks 93 83 (23 +/ 3 C.) Mooney relaxation After 3 weeks 0.258 0.307 (23 +/ 3 C.)

(39) It is found that the silica S1 of the present invention (Composition 1) makes possible a sizeable reduction in the initial raw viscosity, with respect to the value of the control mixture.

(40) It is also found that the silica S1 of the present invention (Composition 1) makes it possible to retain the advantage in reduced raw viscosity, with respect to the value of the control mixture, after 3 weeks of storage.

(41) This type of behavior over time is of great use to a person skilled in the art in the case of the processing of silica-comprising rubber mixtures.

(42) Rheometry of the Compositions:

(43) The measurements are carried out on the compositions in the raw state. The results relating to the rheology test, which is carried out at 160 C. using a Monsanto ODR rheometer according to the standard NF ISO 3417, have been given in table III.

(44) According to this test, the test composition is placed in the test chamber regulated at the temperature of 160 C. for 30 minutes, and the resistive torque opposed by the composition to a low-amplitude (3) oscillation of a biconical rotor included in the test chamber is measured, the composition completely filling the chamber under consideration.

(45) The following are determined from the curve of variation in the torque as a function of time:

(46) the minimum torque (Tmin), which reflects the viscosity of the composition at the temperature under consideration;

(47) the maximum torque (Tmax);

(48) the delta torque (T=TmaxTmin), which reflects the degree of crosslinking brought about by the action of the crosslinking system and, if the need arises, of the coupling agents;

(49) the time T98 necessary to obtain a vulcanization state corresponding to 98% of complete vulcanization (this time is taken as vulcanization optimum);

(50) and the scorch time TS2, corresponding to the time necessary in order to have a rise of 2 points above the minimum torque at the temperature under consideration (160 C.) and which reflects the time during which it is possible to process the raw mixtures at this temperature without having initiation of vulcanization (the mixture cures from TS2).

(51) The results obtained are shown in table III.

(52) TABLE-US-00007 TABLE III Compositions Control 1 Composition 1 Tmin (dN .Math. m) 17.0 15.7 Tmax (dN .Math. m) 56.0 61.9 Delta torque (dN .Math. m) 39.0 46.2 TS2 (min) 5.8 6.2 T98 (min) 26.2 26.4

(53) It is found that the composition resulting from the invention (Composition 1) exhibits a satisfactory combination of rheological properties.

(54) In particular, while having a reduced raw viscosity, it exhibits a lower minimum torque value and a higher maximum torque value than those of the control mixture, which reflects a greater processability of the prepared mixture.

(55) The use of the silica S1 of the present invention (Composition 1) makes it possible to reduce the minimum viscosity (which is a sign of an improvement in the raw viscosity) with respect to the control mixture without damaging the vulcanization behavior.

(56) Mechanical Properties of the Vulcanisates:

(57) The measurements are carried out on the optimally vulcanized compositions (T98) for a temperature of 160 C.

(58) Uniaxial tensile tests are carried out in accordance with the instructions of the standard NF ISO 37 with test specimens of H2 type at a rate of 500 mm/min on an Instron 5564 device. The x % moduli, corresponding to the stress measured at x % of tensile strain, are expressed in MPa. It is possible to determine a reinforcing index (RI) which is equal to the ratio of the modulus at 300% strain to the modulus at 100% strain.

(59) The Shore A hardness measurement on the vulcanisates is carried out according to the instructions of the standard ASTM D 2240. The given value is measured at 15 seconds.

(60) The properties measured are collated in table IV.

(61) TABLE-US-00008 TABLE IV Compositions Control 1 Composition 1 10% Modulus (MPa) 0.6 0.7 100% Modulus (MPa) 2.1 2.4 300% Modulus (MPa) 11.6 13.4 RI 5.6 5.7 Shore A hardness - 15 s (pts) 55 55

(62) It is found that the composition resulting from the invention (Composition 1) exhibits a satisfactory compromise in mechanical properties, with respect to what is obtained with the control composition 1.

(63) Composition 1 thus exhibits relatively low 10% and 100% moduli and a relatively high 300% modulus, hence a good reinforcing index.

(64) The use of a silica S1 of the present invention (Composition 1) makes it possible to obtain a satisfactory level of reinforcement, with respect to the control mixture.

(65) Dynamic Properties of the Vulcanisates:

(66) The dynamic properties are measured on a viscosity analyser (Metravib VA3000) according to the standard ASTM D5992.

(67) The values for loss factor (tan ) and compressive dynamic complex modulus (E*) are recorded on vulcanized samples (cylindrical test specimen with a cross section of 95 mm.sup.2 and a height of 14 mm). The sample is subjected at the start to a 10% prestrain and then to a sinusoidal strain in alternating compression of plus or minus 2%. The measurements are carried out at 60 C. and at a frequency of 10 Hz.

(68) The results, presented in table V, are the compressive complex modulus (E*, 60 C., 10 Hz) and the loss factor (tan , 60 C., 10 Hz).

(69) The values for the loss factor (tan ) and for amplitude of dynamic shear elastic modulus (G) are recorded on vulcanized samples (parallelepipedal test specimen with a cross section of 8 mm.sup.2 and a height of 7 mm). The sample is subjected to a double alternating sinusoidal shear strain at a temperature of 40 C. and at a frequency of 10 Hz. The strain amplitude sweeping processes are carried out according to an outward-return cycle, proceeding outward from 0.1% to 50% and then returning from 50% to 0.1%.

(70) The results, presented in table V, result from the return strain amplitude sweep and relate to the maximum value of the loss factor (tan max return, 40 C., 10 Hz) and to the amplitude of the elastic modulus (G, 40 C., 10 Hz) between the values at 0.1% and 50% strain (Payne effect).

(71) TABLE-US-00009 TABLE V References Control 1 Composition 1 E*, 60 C., 10 Hz (MPa) 5.8 5.5 Tan , 60 C., 10 Hz 0.125 0.117 G , 40 C., 10 Hz (MPa) 1.4 1.2 Tan max return, 40 C., 10 Hz 0.190 0.179

(72) The use of a silica S1 of the present invention (Composition 1) makes it possible to improve the maximum value of the loss factor and the amplitude of the elastic modulus or Payne effect, with respect to the control mixture.

(73) The examination of the various tables II to V shows that the composition in accordance with the invention (Composition 1) makes it possible to obtain a good processing/reinforcement/hysteresis properties compromise, with respect to the control mixture, and in particular a sizeable gain in raw viscosity which remains stable on storage over time.

Example 4

(74) The elastomeric compositions, the make up of which, expressed as parts by weight per 100 parts of elastomers (phr), is shown in table VI below, are prepared in an internal mixer of Brabender type (380 ml):

(75) TABLE-US-00010 TABLE VI Composition Control 2 Control 3 Composition 2 NR (1) 100 100 100 Silica 1 (2) 55 Silica C1 (3) 55 Silica S1 (4) 55 Coupling agent (5) 4.4 4.4 4.4 ZnO 3 3 3 Stearic acid 2.5 2.5 2.5 Antioxidant 1 (6) 1.5 1.5 1.5 Antioxidant 2 (7) 1.0 1.0 1.0 Carbon black (N330) 3.0 3.0 3.0 CBS (8) 1.7 1.7 1.7 Sulfur 1.5 1.5 1.5 (1) Natural rubber CVR CV60 (supplied by Safic-Alcan) (2) Silica Z1165 MP from Rhodia (3) Silica C1 (liquefaction with addition of maleic acid (example 4, comparative)) (4) Silica S1 according to the present invention (liquefaction with addition of sodium aluminate, then addition of succinic acid after liquefaction (example 1 above)) (5) TESPT (Luvomaxx TESPT from Lehvoss France sarl) (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-benzothiazolesulfenamide (Rhenogran CBS-80 from RheinChemie)

(76) Process for the Preparation of the Elastomeric Compositions:

(77) The process for the preparation of the rubber compositions is carried out in two successive preparation phases. A first phase consists of a phase of high-temperature thermomechanical working. It is followed by a second phase of mechanical working at temperatures of less than 110 C. This phase makes possible the introduction of the vulcanization system.

(78) The first phase is carried out using a mixing device, of internal mixer type, of Brabender brand (capacity of 380 ml). The filling coefficient is 0.6. The initial temperature and the speed of the rotors are set on each occasion so as to achieve mixture dropping temperatures of approximately 140-160 C.

(79) Broken down here into two passes, the first phase makes it possible to incorporate, in a first pass, the elastomers and then the reinforcing filler (introduction in installments) with the coupling agent and the stearic acid. For this pass, the duration is between 4 and 10 minutes.

(80) After cooling the mixture (temperature of less than 100 C.), a second pass makes it possible to incorporate the zinc oxide and the protecting agents/antioxidants (in particular 6-PPD). For this pass, the duration is between 2 and 5 minutes.

(81) After cooling the mixture (temperature of less than 100 C.), the second phase makes possible the introduction of the vulcanization system (sulfur and accelerators, such as CBS). It is carried out on an open mill, preheated to 50 C. The duration of this phase is between 2 and 6 minutes.

(82) The final composition is subsequently calandered in the form of plaques with a thickness of 2-3 mm.

(83) With regard to these raw mixtures, an evaluation of their rheological properties makes it possible to optimize the vulcanization time and the vulcanization temperature.

(84) Subsequently, the mechanical and dynamic properties of the mixtures vulcanized at the curing optimum (T98) are measured.

(85) Rheological Properties

(86) Viscosity of the Raw Mixtures:

(87) The Mooney consistency is measured on the compositions in the raw state at 100 C. using an MV 2000 rheometer and also the determination of the Mooney stress-relaxation rate according to the standard NF ISO 289.

(88) The value of the torque, read at the end of 4 minutes after preheating for one minute (Mooney Large (1+4)at 100 C.), is shown in table VII. The test is carried out after preparing the raw mixtures and then after aging for 10 days at a temperature of 23+/3 C.

(89) TABLE-US-00011 TABLE VII Control Control Composition Compositions 2 3 2 ML (1 + 4) - 100 C. Initial 59 56 53 Mooney relaxation Initial 0.392 0.385 0.395 ML (1+ 4) - 100 C. After 11 days 65 59 57 (23 +/ 3 C.) Mooney relaxation After 11 days 0.380 0.399 0.384 (23 +/3 C.)

(90) It is found that the silica S1 of the present invention (Composition 2) makes possible a reduction in the initial raw viscosity, with respect to the control mixture 2 and the control mixture 3.

(91) It is also found that the silica S1 of the present invention (Composition 2) comprising succinic acid shows an enhanced performance in terms of reduction in the raw viscosity, with respect to the control mixture 2 and the control mixture 3.

(92) It is also observed that the use of the silica S1 of the present invention (Composition 2) makes it possible to retain the advantage in reduced raw viscosity, with respect to the control mixture 2 and the control mixture 3, after 11 days of storage.

(93) This type of behaviour over time is of great use to a person skilled in the art in the case of the processing of a silica-comprising rubber mixture.

(94) Rheometry of the Compositions:

(95) The measurements are carried out on the compositions in the raw state. The results relating to the rheology test, which is carried out at 150 C. using a Monsanto ODR rheometer according to the standard NF ISO 3417, have been given in table VIII.

(96) According to this test, the test composition is placed in the test chamber regulated at the temperature of 150 C. for 30 minutes, and the resistive torque opposed by the composition to a low-amplitude (3) oscillation of a biconical rotor included in the test chamber is measured, the composition completely filling the chamber under consideration.

(97) The following are determined from the curve of variation in the torque as a function of time:

(98) the minimum torque (Tmin), which reflects the viscosity of the composition at the temperature under consideration;

(99) the maximum torque (Tmax);

(100) the delta torque (T=TmaxTmin), which reflects the degree of crosslinking brought about by the action of the crosslinking system and, if the need arises, of the coupling agents;

(101) the time T98 necessary to obtain a vulcanization state corresponding to 98% of complete vulcanization (this time is taken as vulcanization optimum).

(102) The results obtained are shown in table VIII.

(103) TABLE-US-00012 TABLE VIII Compositions Control 2 Control 3 Composition 2 Tmin (dN .Math. m) 13.6 13.5 11.8 Tmax (dN .Math. m) 71.6 69.4 77.3 Delta torque (dN .Math. m) 58 56 66 T98 (min) 25.2 26.9 25.0

(104) It is found that the composition resulting from the invention (Composition 2) exhibits a satisfactory combination of rheological properties.

(105) In particular, while having a reduced raw viscosity, it exhibits a lower minimum torque value and a higher maximum torque value than those of the control mixture 2 and the control mixture 3, which reflects a greater processability of the prepared mixture.

(106) The use of the silica S1 of the present invention (Composition 2) makes it possible to reduce the minimum viscosity (low minimum torque Tmin, which is a sign of an improvement in the raw viscosity) with respect to the control mixture 2 and the control mixture 3 without damaging the vulcanization behavior.

(107) Mechanical Properties of the Vulcanisates:

(108) The measurements are carried out on the optimally vulcanized compositions (T98) for a temperature of 150 C.

(109) Uniaxial tensile tests are carried out in accordance with the instructions of the standard NF ISO 37 with test specimens of H2 type at a rate of 500 mm/min on an Instron 5564 device. The x % moduli, corresponding to the stress measured at x % of tensile strain, and the ultimate strength are expressed in MPa; the elongation at break is expressed in %.

(110) The Shore A hardness measurement on the vulcanisates is carried out according to the instructions of the standard ASTM D 2240. The given value is measured at 15 seconds.

(111) The properties measured are collated in table IX.

(112) TABLE-US-00013 TABLE IX Compositions Control 2 Control 3 Composition 2 10% Modulus (MPa) 0.6 0.5 0.6 300% Modulus (MPa) 12.3 12.6 14.0 Ultimate strength (MPa) 26.0 26.8 28.8 Elongation at break (%) 532 521 541 RI 4.9 5.2 4.7 Shore A hardness - 15 s (pts) 59 55 60

(113) It is found that the composition resulting from the invention (Composition 2) exhibits a satisfactory compromise in mechanical properties, with respect to what is obtained with the control mixture 2 and with the control mixture 3. In particular, it exhibits a better ultimate strength and a higher elongation at break, with respect to the control mixture 2 and the control mixture 3.

(114) Composition 2 thus exhibits a relatively low 10% modulus and a relatively high 300% modulus.

(115) The use of a silica S1 of the present invention (Composition 2) makes it possible to obtain a good level of reinforcement.

(116) Dynamic Properties of the Vulcanisates:

(117) The dynamic properties are measured on a viscosity analyser (Metravib VA3000) according to the standard ASTM D5992.

(118) The values for loss factor (tan ) and compressive dynamic complex modulus (E*) are recorded on vulcanized samples (cylindrical test specimen with a cross section of 95 mm.sup.2 and a height of 14 mm). The sample is subjected at the start to a 10% prestrain and then to a sinusoidal strain in alternating compression of plus or minus 2%. The measurements are carried out at 60 C. and at a frequency of 10 Hz.

(119) The results, presented in table X, are the compressive complex modulus (E*, 60 C., 10 Hz) and the loss factor (tan , 60 C., 10 Hz).

(120) The values for the loss factor (tan ) are recorded on vulcanized samples (parallelepipedal test specimen with a cross section of 8 mm.sup.2 and a height of 7 mm). The sample is subjected to a double alternating sinusoidal shear strain at a temperature of 60 C. and at a frequency of 10 Hz. The strain amplitude sweeping processes are carried out according to an outward-return cycle, proceeding outward from 0.1% to 50% and then returning from 50% to 0.1%.

(121) The results, presented in table X, result from the return strain amplitude sweep and relate to the maximum value of the loss factor (tan max return, 60 C., 10 Hz).

(122) TABLE-US-00014 TABLE X Compositions Control 2 Control 3 Composition 2 E*, 60 C., 10 Hz (MPa) 6.5 5.6 6.7 Tan , 60 C., 10 Hz 0.125 0.118 0.104 Tan max return, 60 C., 10 Hz 0.138 0.135 0.128

(123) The use of a silica S1 of the present invention (Composition 2) makes it possible to improve the maximum value of the loss factor in dynamic compression, just like the Tan max return loss factor, with respect to the control mixture 2 and the control mixture 3.

(124) The examination of the various tables VII to X shows that the composition in accordance with the invention (Composition 2) makes it possible to obtain a good processing/reinforcement/hysteresis properties compromise at 60 C., with respect to the control mixture 2 and the control mixture 3. The raw viscosity of the mixture comprising the silica of the present invention changes very little on storage over time.