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

Abstract

The invention relates to a novel process for preparing 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 filter cake, said filter cake is subjected to a liquefaction operation comprising the addition of an aluminum compound, after the liquefaction operation, a drying step is performed, characterized in that at least one polycarboxylic acid is added to the filter cake, during or after the liquefaction operation. The invention also relates to novel precipitated silicas and to uses thereof.

Claims

1. A precipitated silica having: a BET specific surface area of between 45 and 550 m.sup.2/g, a CTAB specific surface area of between 40 and 525 m.sup.2/g, a content (C) of polycarboxylic acids, expressed as total carbon, of at least 0.15% by weight, an aluminum (Al) content of at least 0.20% by weight, an object size distribution width Ld ((d84-d16)/d50), measured by XDC particle size analysis after ultrasound deagglomeration, of at least 0.91, and a pore volume distribution such that the ratio V.sub.(a5−d50)/V.sub.(d5−d100) is at least 0.65; wherein the polycarboxylic acids comprise a mixture of adipic acid, ethylsuccinic acid, and methylglutaric acid.

2. The precipitated silica as claimed in claim 1, wherein the content (C) of polycarboxylic acids, expressed as total carbon, of the precipitated silica is at least 0.24% by weight.

3. The precipitated silica as claimed in claim 1, wherein the aluminum (Al) content of the precipitated silica is at least 0.30% by weight.

4. The precipitated silica as claimed in claim 1, wherein the precipitated silica has a dispersive component of the surface energy γ.sub.s.sup.d of less than 52 mJ/m.sup.2.

5. A precipitated silica having: a BET specific surface area of between 45 and 550 m.sup.2/g, a CTAB specific surface area of between 40 and 525 m.sup.2/g, a content (C) of polycarboxylic acids, expressed as total carbon, of at least 0.15% by weight, an aluminum (Al) content of at least 0.20% by weight, a pore distribution width ldp of greater than 0.65; wherein the polycarboxylic acids comprise a mixture of adipic acid, ethylsuccinic acid, and methylglutaric acid.

6. A process for preparing the precipitated silica of claim 1, the process comprising: precipitating a silicate and an acidifying agent by: (i) forming an aqueous feedstock with a pH of between 2 and 5, (ii) simultaneously adding silicate and acidifying agent to said feedstock, such that the pH of the reaction medium obtained is maintained between 2 and 5, (iii) discontinuing the addition of the acidifying agent while continuing the addition of the silicate to the reaction medium until a pH value of the reaction medium of between 7 and 10 is obtained, (iv) simultaneously adding silicate and acidifying agent to the reaction medium, such that the pH of the reaction medium is maintained between 7 and 10, (v) discontinuing the addition of the silicate while continuing the addition of the acidifying agent to the reaction medium until a pH value of the reaction medium of less than 6 is obtained, thus providing a silica suspension, filtering the silica suspension to form a filter cake, subjecting the filter cake to a liquefaction operation comprising the addition of at least one aluminum compound, wherein polycarboxylic acids are added to the filter cake, either during the liquefaction operation, or after the liquefaction operation and before a drying step, wherein the polycarboxylic acids comprise a mixture of adipic acid, ethylsuccinic acid, and methylglutaric acid.

7. The process as claimed in claim 6, wherein, during the liquefaction operation, the polycarboxylic acids and at least one aluminum compound are simultaneously added to the filter cake.

8. The process as claimed in claim 6, wherein, during the liquefaction operation, at least one aluminum compound is added to the filter cake prior to the addition of the polycarboxylic acids.

9. The process as claimed in claim 6, wherein the polycarboxylic acids are added to the filter cake after the liquefaction operation.

10. The process as claimed in claim 6, wherein the aluminum compound is an alkali metal aluminate.

11. A method for reinforcing a polymer, the method comprising adding a precipitated silica as claimed in claim 1 to the polymer as a reinforcing filler.

12. A method for reducing the viscosity of a polymer composition, the method comprising adding the precipitated silica as claimed in claim 1 to the polymer composition.

13. A polymer composition comprising a precipitated silica as claimed in claim 1.

14. An article comprising the polymer composition as claimed in claim 13, wherein the article is selected from the group consisting of a footwear sole, a floor covering, a gas barrier, a flame-retardant material, a roller for cableways, a seal for domestic electrical appliances, a seal for liquid or gas pipes, a braking system seal, a pipe, a sheathing, a cable, an engine support, a battery separator, a conveyor belt, a transmission belt and a tire.

15. The article as claimed in claim 14, wherein the article is a tire.

Description

EXAMPLES

Example 1

(1) 700 liters of industrial water are introduced into a 2000 liter reactor. This solution is brought to 80° C. by heating by direct injection of steam. With stirring (95 rpm), sulfuric acid, with a concentration equal to 80 g/l, is introduced until the pH reaches a value of 4.

(2) A sodium silicate solution (with an SiO.sub.2/Na.sub.2O weight ratio equal to 3.52) having a concentration of 230 g/l is introduced into the reactor over 35 minutes, at a flow rate of 190 l/h, simultaneously with sulfuric acid, with a concentration equal to 80 g/l, at a flow rate regulated so as to maintain the pH of the reaction medium at a value of 4.

(3) After the 35 minutes of simultaneous addition, the introduction of acid is stopped as long as the pH has not reached a value equal to 8. A further simultaneous addition is then performed over 40 minutes with a sodium silicate flow rate of 190 l/h (same sodium silicate as for the first simultaneous addition) and a flow rate of sulfuric acid, with a concentration equal to 80 g/l, regulated so as to maintain the pH of the reaction medium at a value of 8.

(4) After this simultaneous addition, the reaction medium is brought to a pH of 5.2 with sulfuric acid with a concentration equal to 80 g/l. The medium is matured for 5 minutes at pH 5.2.

(5) The slurry is filtered and washed on a filter press, to give a precipitated silica cake with a solids content of 22%.

Example 2

(6) Part of the silica cake obtained in Example 1 is then subjected to a liquefaction operation.

(7) During the liquefaction operation, a solution of an MGA mixture at 34% by mass (mixture of polycarboxylic acids: 94.8% by weight of methylglutaric acid, 4.9% by weight of ethylsuccinic anhydride, 0.2% by weight of adipic acid, 0.1% others) is used.

(8) The cake obtained in the filtration step is subjected to a liquefaction operation in a continuous vigorously stirred reactor with simultaneous addition to the cake of 33.62 grams of a sodium aluminate solution (Al/SiO.sub.2 weight ratio of 0.3%) and 45 grams of the MGA solution (MGA mixture/SiO.sub.2 weight ratio of 1.0%).

(9) This disintegrated cake (with a solids content of 22% by weight) is subsequently dried using a two-fluid nozzle atomizer by spraying the disintegrated cake through a 2.54 mm SU5 nozzle (Spraying System) with a pressure of 1 bar under the following mean conditions of flow rate and of temperatures:

(10) Mean inlet temperature: 250° C.

(11) Mean outlet temperature: 135° C.

(12) Mean flow rate: 15 l/h.

(13) The characteristics of silica 51 obtained (in the form of substantially spherical beads) are then the following:

(14) TABLE-US-00002 BET (m.sup.2/g) 210 Content of polycarboxylic acid + carboxylate (C) (%) 0.40 Aluminum (Al) content (%) 0.39 Ratio (R) 0.77 CTAB (m.sup.2/g) 206 γ.sub.s.sup.d (mJ/m.sup.2) 44.9 Width Ld (XDC) 0.97 V.sub.(d5-d50)/V.sub.(d5-d100) 0.69 Pore distribution width ldp 0.91 Width L'd (XDC) 1.00 Water uptake (%) 8.7 Ø.sub.50M (μm) after ultrasound deagglomeration 6.4 F.sub.DM after ultrasound deagglomeration 15.7 pH 5.36

Example 3 (Comparative)

(15) Part of the silica cake obtained in Example 1 is then subjected to a liquefaction operation.

(16) The cake obtained in the filtration step is subjected to a liquefaction operation in a continuous vigorously stirred reactor with simultaneous addition to the cake of 27.8 grams of a sodium aluminate solution (Al/SiO.sub.2 weight ratio of 0.3%) and 29.8 grams of a sulfuric acid solution at 7.7% by mass.

(17) This disintegrated cake (with a solids content of 22% by weight) is subsequently dried using a two-fluid nozzle atomizer by spraying the disintegrated cake through a 2.54 mm SU5 nozzle (Spraying System) with a pressure of 1 bar under the following mean conditions of flow rate and of temperatures:

(18) Mean inlet temperature: 250° C.

(19) Mean outlet temperature: 135° C.

(20) Mean flow rate: 15 l/h.

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

(22) TABLE-US-00003 BET (m.sup.2/g) 221 Content of polycarboxylic acid + carboxylate (C) (%) — Aluminum (Al) content (%) 0.4 Ratio (R) 0.0 CTAB (m.sup.2/g) 206 γ.sub.s.sup.d (mJ/m.sup.2) 59.6 Width Ld (XDC) 1.08 V.sub.(d5-d50)/V.sub.(d5-d100) 0.69 Pore distribution width ldp 1.06 Width L'd (XDC) 0.97 Water uptake (%) 8.9 Ø.sub.50M (μm) after ultrasound deagglomeration 6.2 F.sub.DM after ultrasound deagglomeration 15.3 pH 6.47

Example 4

(23) 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):

(24) TABLE-US-00004 TABLE I Composition Control 1 Composition 1 SBR (1) 70 70 BR (1) 30 30 Silica C1 (2) 75 Silica S1 (3) 75 Coupling agent (4) 6.6 6.6 Plasticizer (5) 20 20 Carbon black (N330) 5.0 5.0 ZnO 2.5 2.5 Stearic acid 2.0 2.0 Antioxidant (6) 1.9 1.9 DPG (7) 2.0 2.0 CBS (8) 1.7 1.7 Sulfur 1.5 1.5 (1) S-SBR (HPR355 from the company JSR) functionalized with 57% of vinyl units; 27% of styrene units; Tg in the region of −27° C./BR (Buna CB 25 from the company Lanxess) (2) Silica C1 (liquefaction with simultaneous addition of sodium aluminate and sulfuric acid (Example 3 - comparative)) (3) Silica S1 according to the present invention (liquefaction with simultaneous addition of sodium aluminate and of a mixture of MGA acids (Example 2 above)) (4) Bis-triethoxysilylpropyldisulfidosilane (JH-S75 TESPD from the company Castle Chemicals) (5) Plasticizing oil of TDAE type (Vivatec 500 from the company Hansen & Rosenthal KG) (6) N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from the company Flexsys) (7) Diphenylguanidine (Rhenogran DPG-80 from RheinChemie) (8) N-cyclohexyl-2-benzothiazolylsulfenamide (Rhenogran CBS-80 from the company RheinChemie)

(25) Process for preparing the elastomeric compositions:

(26) The process for preparing the rubber compositions is performed 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 below 110° C. This phase allows 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 speed of the rotors are set on each occasion so as to achieve mixture dropping temperatures of approximately 115-170° 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 (portionwise introduction) 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 allows the introduction of the vulcanization system (sulfur and accelerators, such as CBS). It is performed 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 calendered in the form of plates with a thickness of 2-3 mm.

(32) An evaluation of the rheological properties of these “crude” mixtures obtained makes it possible to optimize the vulcanization time and the vulcanization temperature.

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

(34) Rheological Properties

(35) Viscosity of the Crude Mixtures:

(36) The Mooney consistency is measured on the compositions in the crude state at 100° C. using an MV 2000 rheometer and also the determination of the Mooney stress-relaxation rate according to 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 performed after preparing the crude mixtures and then after aging for 3 weeks at a temperature of 23±3° C.

(38) TABLE-US-00005 TABLE II References Control 1 Composition 1 ML (1 + 4) - 100° C. Initial 166 128 Mooney relaxation Initial 0.204 0.249 ML (1 + 4) - 100° C. After 17 days (23 ± 182 140 3° C.) Mooney relaxation After 17 days (23 ± 0.175 0.236 3° C.) ML (1 + 4) - 100° C. After 21 days (23 ± 183 141 3° C.) Mooney relaxation After 21 days (23 ± 0.183 0.234 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 mixture with the reference (Control 1).

(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 mixture with the reference (Control 1), 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 using rubber mixtures containing silica.

(42) Rheometry of the Compositions:

(43) The measurements are performed on the compositions in crude form. The results relating to the rheology test, which is performed at 160° C. using a Monsanto ODR rheometer according to the standard NF ISO 3417, are 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: the minimum torque (Tmin), which reflects the viscosity of the composition at the temperature under consideration; the maximum torque (Tmax), the delta torque (ΔT=Tmax−Tmin), which reflects the degree of crosslinking brought about by the action of the crosslinking system and, if the need arises, of the coupling agents; the time T98 necessary to obtain a vulcanization state corresponding to 98% of complete vulcanization (this time is taken as the vulcanization optimum); 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 implement the raw mixtures at this temperature without having initiation of vulcanization (the mixture cures at and above TS2).

(46) The results obtained are shown in Table III.

(47) TABLE-US-00006 TABLE III Compositions Control 1 Composition 1 Tmin (dN .Math. m) 32.6 25.6 Tmax (dN .Math. m) 73.9 69.3 Delta torque (dN .Math. m) 41.3 43.7 TS2 (min) 3.1 4.7 T98 (min) 27.1 26.2

(48) The use of silica S1 of the present invention (Composition 1) makes it possible to reduce the minimum viscosity (sign of an improvement in the crude viscosity) relative to the control mixture (Control 1) without impairing the vulcanization behavior.

(49) It is also found that the use of silica S1 of the present invention (Composition 1) makes it possible to improve the scorch time TS2 relative to the control mixture (Control 1) without impairing the time T98.

(50) Mechanical Properties of the Vulcanizates:

(51) The measurements are performed on the optimally vulcanized compositions (T98) for a temperature of 160° C.

(52) Uniaxial tensile tests are performed in accordance with the instructions of standard NF ISO 37 with test specimens of H2 type at a rate of 500 mm/min on an Instron 5564 machine. 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 %. 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.

(53) The Shore A hardness measurement of the vulcanizates is performed according to the instructions of standard ASTM D 2240. The given value is measured at 15 seconds.

(54) The properties measured are collated in Table IV.

(55) TABLE-US-00007 TABLE IV Compositions Control 1 Composition 1 10% Modulus (MPa) 0.91 0.90 100% Modulus (MPa) 3.1 3.0 300% Modulus (MPa) 12.2 12.1 Ultimate strength (MPa) 16.1 16.0 Elongation at break (%) 373 369 RI 3.9 4.0 Shore A hardness - 15 s (pts) 73 68

(56) The use of a silica S1 of the present invention (Composition 1) makes it possible to obtain a satisfactory level of reinforcement, relative to the control mixture (Control 1) and in particular to conserve a high level of the 300% strain modulus.

(57) Dynamic Properties of the Vulcanizates:

(58) The dynamic properties are measured on a viscosity analyzer (Metravib VA3000) according to standard ASTM D5992.

(59) The values for loss factor (tan δ) 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 ±2%. The measurements are performed at 60° C. and at a frequency of 10 Hz.

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

(61) TABLE-US-00008 TABLE V Compositions Control 1 Composition 1 E*, 60° C., 10 Hz (MPa) 13.6 12.0 Tan δ, 60° C., 10 Hz 0.164 0.155

(62) The use of a silica S1 of the present invention (Composition 1) makes it possible to maintain the dynamic properties at the level of that of the control mixture (Control 1).

(63) 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 composition (Control 1), and in particular a sizeable gain in raw viscosity, which remains stable on storage over time.

Example 5

(64) 955 liters of industrial water are introduced into a 2500 liter reactor. This solution is brought to 90° C. by heating by direct injection of steam. With stirring (95 rpm), 15 kg of solid sodium sulfate are introduced into the reactor. Sulfuric acid, with a mass concentration of 7.7% and a density of 1050 g/l, is then added until the pH reaches a value of 3.6.

(65) A sodium silicate solution (with an SiO.sub.2/Na.sub.2O weight ratio equal to 3.52 and a density equal to 1.237 kg/l) is introduced into the reactor over 35 minutes, at a flow rate of 190 l/h, simultaneously with sulfuric acid (with a mass concentration equal to 7.7% and a density of 1050 g/l), at a flow rate regulated so as to maintain the pH of the reaction medium at a value of 3.6.

(66) After the 35 minutes of simultaneous addition, the introduction of acid is stopped as long as the pH has not reached a value equal to 8. A further simultaneous addition is then performed over 40 minutes with a sodium silicate flow rate of 190 l/h (same sodium silicate as for the first simultaneous addition) and a flow rate of sulfuric acid (with a mass concentration of 7.7% and a density of 1050 g/l) regulated so as to maintain the pH of the reaction medium at a value of 8.

(67) After this simultaneous addition, the reaction medium is brought to a pH of 5.6 by introduction of sulfuric acid (with a mass concentration of 7.7% and a density of 1050 g/l). 2090 liters of slurry are obtained after this operation. The slurry is filtered and washed on a filter press, to give a precipitated silica cake with a solids content of 20%.

Examples 6 and 7

(68) A first portion of the silica cake obtained in Example 5 is then subjected to a liquefaction step to obtain a silica S2.

(69) During this liquefaction operation, a solution of an MGA mixture at 34% by mass (mixture of polycarboxylic acids: 94.8% by weight of methylglutaric acid, 4.9% by weight of ethylsuccinic anhydride, 0.2% by weight of adipic acid, 0.1% others) is used.

(70) The cake obtained in the filtration step is subjected to a liquefaction operation in a continuous vigorously stirred reactor with simultaneous addition to the cake of 15.32 grams of a sodium aluminate solution (Al/SiO.sub.2 weight ratio of 0.3%) and 16.00 grams of the MGA solution (MGA mixture/SiO.sub.2 weight ratio of 1.0%).

(71) This disintegrated cake (with a solids content of 20% by weight) is subsequently dried using a two-fluid nozzle atomizer by spraying the disintegrated cake through a 2.54 mm SU5 nozzle (Spraying System) with a pressure of 1 bar under the following mean conditions of flow rate and of temperatures:

(72) Mean inlet temperature: 250° C.

(73) Mean outlet temperature: 140° C.

(74) Mean flow rate: 11.5 l/h.

(75) A second portion of the silica cake obtained in Example 5 is then subjected to a liquefaction step to obtain a silica S3, using a solution of an MGA mixture at 34% by mass (mixture of polycarboxylic acids: 94.8% by weight of methylglutaric acid, 4.9% by weight of ethylsuccinic anhydride, 0.2% by weight of adipic acid, 0.1% others).

(76) The cake obtained in the filtration step is subjected to a liquefaction operation in a continuous vigorously stirred reactor with addition to the cake of 15.32 grams of a sodium aluminate solution (Al/SiO.sub.2 weight ratio of 0.3%). Once the liquefaction has been performed, 16.00 g of the MGA solution (MGA

(77) This disintegrated cake (with a solids content of 20% by weight) is then dried as described above for the first portion of the cake, with an average flow rate of 11.1 l/h.

(78) The characteristics of these two silicas S2 and S3 obtained (in the form of substantially spherical beads) are then the following:

(79) TABLE-US-00009 Characteristics S2 S3 BET (m.sup.2/g) 244 247 Content of polycarboxylic acid + carboxylate (C) (%) 0.49 0.45 Aluminum (Al) content (%) 0.39 0.40 Ratio (R) 0.94 0.84 CTAB (m.sup.2/g) 245 245 γ.sub.s.sup.d (mJ/m.sup.2) 36.1 37.7 Width Ld (XDC) 1.34 1.58 V.sub.(d5-d50)/V.sub.(d5-d100) 0.69 0.68 Pore distribution width ldp 0.69 0.69 Width L'd (XDC) 1.22 1.21 Water uptake (%) 8.4 8.7 Ø.sub.50M (μm) after ultrasound deagglomeration 7.7 7.9 F.sub.DM after ultrasound deagglomeration 11.9 11.6 pH 5.9 5.9

Example 8 (Comparative)

(80) Part of the silica cake obtained in Example 5 is then subjected to a liquefaction step.

(81) The cake obtained in the filtration step is subjected to a liquefaction operation in a continuous vigorously stirred reactor with simultaneous addition to the cake of 15.32 grams of a sodium aluminate solution (Al/SiO.sub.2 weight ratio of 0.3%) and 37.9 grams of a sulfuric acid solution at 7.7% by mass.

(82) This disintegrated cake (with a solids content of 20% by weight) is subsequently dried using a two-fluid nozzle atomizer by spraying the disintegrated cake through a 2.54 mm SU5 nozzle (Spraying System) with a pressure of 1 bar under the following mean conditions of flow rate and of temperatures:

(83) Mean inlet temperature: 250° C.

(84) Mean outlet temperature: 140° C.

(85) Mean flow rate: 9.8 l/h.

(86) The characteristics of silica C2 obtained (in the form of substantially spherical beads) are then the following:

(87) TABLE-US-00010 BET (m.sup.2/g) 254 Content of polycarboxylic acid + carboxylate (C) (%) — Aluminum (Al) content (%) 0.42 Ratio (R) 0.0 CTAB (m.sup.2/g) 250 γ.sub.s.sup.d (mJ/m.sup.2) 65.9 Width Ld (XDC) 1.23 V.sub.(d5-d50)/V.sub.(d5-d100) 0.68 Pore distribution width ldp 0.70 Width L'd (XDC) 1.08 Water uptake (%) 9.3 Ø.sub.50M (μm) after ultrasound deagglomeration 6.7 F.sub.DM after ultrasound deagglomeration 14.4 pH 6.2

Example 9

(88) 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):

(89) TABLE-US-00011 TABLE VI Composition Control 2 Composition 2 Composition 3 SBR (1) 103 103 103 BR (1) 25 25 25 Silica C2 (2) 80 Silica S2 (3) 80 Silica S3 (4) 80 Coupling agent (5) 10 10 10 Plasticizer (6) 12 12 12 Carbon black (N234) 3 3 3 ZnO 2.5 2.5 2.5 Stearic acid 2 2 2 Antioxidant (7) 1.2 1.2 1.2 DPG (8) 2.5 2.5 2.5 CBS (9) 2.3 2.3 2.3 Sulfur 1.6 1.6 1.6 (1) Solution SBR (Buna VSL4526-2 from the company Lanxess) with 44.5 ± 4% of vinyl units; 26 ± 2% of styrene units; Tg in the region of −30° C.; 100 phr of SBR extended with 37.5 ± 2.8% by weight of oil/Buna CB 25 from the company Lanxess) (2) Silica C2 (liquefaction with simultaneous addition of sodium aluminate and sulfuric acid (Example 8 - comparative) (3) Silica S2 according to the present invention (liquefaction with simultaneous addition of sodium aluminate and of a mixture of MGA acids (Example 6 above)) (4) Silica S3 according to the present invention (liquefaction with addition of a mixture of MGA acids (Example 7 above)) (5) Bis-triethoxysilylpropyldisulfidosilane (HP 1589 TESPD from the company HungPai) (6) Plasticizing oil of TDAE type (Vivatec 500 from the company Hansen & Rosenthal KG) (7) N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from the company Flexsys) (8) Diphenylguanidine (Rhenogran DPG-80 from RheinChemie) (9) N-cyclohexyl-2-benzothiazolesulfenamide (Rhenogran CBS-80 from the company RheinChemie) (1) Solution SBR (Buna VSL4526-2 from the company Lanxess) with 44.5±4% of vinyl units; 26±2% of styrene units; Tg in the region of −30° C., 100 phr of SBR extended with 37.5±2.8% by weight of oil/BR (Buna CB 25 from the company Lanxess) (2) Silica C2 (liquefaction with simultaneous addition of sodium aluminate and sulfuric acid (Example 8—comparative)) (3) Silica S2 according to the present invention (liquefaction with simultaneous addition of sodium aluminate and of a mixture of MGA acids (Example 6 above)) (4) Silica S3 according to the present invention (liquefaction with addition of a mixture of MGA acids (Example 7 above)) (5) Bis-triethoxysilylpropyldisulfidosilane (HP 1589 TESPD from the company HungPai) (6) Plasticizing oil of TDAE type (Vivatec 500 from the company Hansen & Rosenthal KG) (7) N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from the company Flexsys) (8) Diphenylguanidine (Rhenogran DPG-80 from RheinChemie) (9) N-cyclohexyl-2-benzothiazolesulfenamide (Rhenogran CBS-80 from the company RheinChemie)

(90) Process for Preparing the Elastomeric Compositions:

(91) The process for preparing the rubber compositions is performed in two successive preparation phases according to the same procedure as that for Example 4.

(92) An evaluation of the rheological properties of these “crude” mixtures obtained makes it possible to optimize the vulcanization time and the vulcanization temperature.

(93) The mechanical and dynamic properties of the mixtures vulcanized at the curing optimum (T98) are then measured.

(94) Rheological Properties

(95) Viscosity of the Crude Mixtures:

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

(97) 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 performed after preparing the crude mixtures and then after aging for 2 weeks, and then 28 days, at a temperature of 23±3° C.

(98) TABLE-US-00012 TABLE VII Compo- Compo- References Control 2 sition 2 sition 3 ML (1 + 4) - Initial 129 107 117 100° C. Mooney relaxation Initial 0.176 0.218 0.208 ML (1 + 4) - After 14 days 144 122 129 100° C. (23 ± 3° C.) Mooney relaxation After 14 days 0.155 0.201 0.190 (23 ± 3° C.) ML (1 + 4) - After 28 days 151 129 136 100° C. (23 ± 3° C.) Mooney relaxation After 28 days 0.145 0.188 0.179 (23 ± 3° C.)

(99) It is found that the silicas S2 and S3 of the present invention (Compositions 2 and 3) allow a substantial reduction in the initial crude viscosity, relative to the value of the mixture with the reference (Control 2).

(100) It is also found that the silicas S2 and S3 of the present invention (Compositions 2 and 3) make it possible to retain the advantage in reduced crude viscosity, relative to the value of the mixture with the reference (Control 2), after 28 days of storage.

(101) This type of behavior over time is of great use to a person skilled in the art in the case of using rubber mixtures containing silica.

(102) Rheometry of the Compositions:

(103) The measurements are performed on the compositions in crude form. The results relating to the rheology test, which is performed at 160° C. using a Monsanto ODR rheometer according to standard NF ISO 3417 and as described in Example 4, are given in Table VIII.

(104) The results obtained are shown in Table VIII.

(105) TABLE-US-00013 TABLE VIII Compositions Control 2 Composition 2 Composition 3 Tmin (dN .Math. m) 36.3 28.8 29.2 Tmax (dN .Math. m) 76.5 73.4 74.3 Delta torque (dN .Math. m) 40.1 44.7 45.1 TS2 (min) 3.2 4.8 4.4 T98 (min) 27.0 26.1 25.0

(106) The use of silicas S2 and S3 of the present invention (Compositions 2 and 3) makes it possible to reduce the minimum viscosity (sign of an improvement in the crude viscosity) relative to the control mixture (Control 2) without impairing the vulcanization behavior.

(107) It is also found that the use of silicas S2 and S3 of the present invention (Compositions 2 and 3) makes it possible to improve the scorch time TS2 relative to the control mixture (Control 2) without impairing the time T98.

(108) The measurements are performed on the optimally vulcanized compositions (T98) for a temperature of 160° C.

(109) Uniaxial tensile tests are performed in accordance with the instructions of standard NF ISO 37 with test specimens of H2 type at a rate of 500 mm/min on an Instron 5564 machine. 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 %. 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.

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

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

(112) TABLE-US-00014 TABLE IX Compositions Control 2 Composition 2 Composition 3 10% Modulus (MPa) 0.9 0.8 0.8 100% Modulus (MPa) 2.6 2.6 2.7 300% Modulus (MPa) 9.9 10.6 10.6 Ultimate strength (MPa) 16.9 16.8 17.9 Elongation at break (%) 450 415 440 RI 3.8 4.1 3.9 Shore A hardness - 15 s 72 70 72 (pts)

(113) The use of silicas S2 and S3 of the present invention (Compositions 2 and 3) makes it possible to obtain a satisfactory level of reinforcement, relative to the control mixture (Control 2) and in particular to conserve a high level of the 300% strain modulus.

(114) Compositions 2 and 3 thus have relatively low 10% and 100% moduli and a relatively high 300% modulus, hence a good reinforcing index.

(115) Dynamic Properties of the Vulcanizates:

(116) The dynamic properties are measured on a viscosity analyzer (Metravib VA3000) according to standard ASTM D5992.

(117) The values for the loss factor (tan δ) and the dynamic shear elastic modulus (G*.sub.12%) are recorded on vulcanized samples (parallelopipedal 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 performed according to an outward-return cycle, proceeding outward from 0.1% to 50% and then returning from 50% to 0.1%.

(118) The results, presented in Table X, result from the return strain amplitude sweep and relate to the maximum value of the loss factor (tan δ max return, 40° C., 10 Hz) and also the elastic modulus G.sup.*.sub.12%.

(119) TABLE-US-00015 TABLE X Compositions Control 2 Composition 2 Composition 3 G*.sub.12%, 40° C., 10 Hz 2.0 1.8 1.8 (MPa) Tan δmax return, 40° 0.282 0.279 0.281 C., 10 Hz

(120) The use of silicas S2 and S3 of the present invention (Compositions 2 and 3) makes it possible to maintain the dynamic properties at the level of that of the control mixture (Control 2).

(121) Examination of the various Tables VII to X shows that the compositions in accordance with the invention (Compositions 2 and 3) makes it possible to improve the processing/reinforcement/hysteresis properties at 40° C. compromise, relative to the control composition (Control 2), and in particular to achieve a substantial gain in crude viscosity, which remains stable on storage over time.