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 mixture of polycarboxylic acids is added to the filtration cake, during or after the liquefaction operation. It also relates to novel precipitated silicas and to their uses.

Claims

1. 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, and an aluminum (Al) content of at least 0.20% by weight; wherein the polycarboxylic acid comprises a mixture of polycarboxylic acids comprising at least one of ethylsuccinic acid, glutaric acid and methylglutaric acid.

2. The precipitated silica as claimed in claim 1, wherein the mixture of polycarboxylic acids further comprises adipic acid, succinic acid, oxalic acid, citric acid or a mixture thereof.

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

4. The precipitated silica as claimed in claim 1, wherein the mixture of polycarboxylic acids comprises the following acids: adipic acid, glutaric acid and succinic acid.

5. The precipitated silica as claimed in claim 4, wherein the mixture of polycarboxylic acids comprises from 15% to 35% by weight of adipic acid, from 40% to 60% by weight of glutaric acid and from 15% to 25% by weight of succinic acid.

6. The precipitated silica as claimed in claim 1, wherein the mixture of polycarboxylic acids comprises the following acids: methylglutaric acid, ethylsuccinic acid and adipic acid.

7. The precipitated silica as claimed in claim 6, wherein the mixture of polycarboxylic acids comprises from 60% to 96% by weight of methylglutaric acid, from 3.9% to 20% by weight of ethylsuccinic acid and from 0.05% to 20% by weight of adipic acid.

8. An article comprising at least one polymer composition as claimed in claim 3, this article 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 or a tire.

9. A process for the preparation of a precipitated silica as claimed in claim 1, the process comprising: reacting at least one silicate with at least one acidifying agent, so as to obtain a suspension of precipitated silica, filtering said suspension of precipitated silica, so as to obtain a filtration cake, subjecting said filtration cake to a liquefaction operation comprising the addition of an aluminum compound, and optionally drying the filtration cake after the liquefaction operation, wherein a mixture of polycarboxylic acids comprising at least one of ethylsuccinic acid, glutaric acid and methylglutaric acid is added to the filtration cake, during or after the liquefaction operation.

10. The process as claimed in claim 9, wherein the mixture of polycarboxylic acids and the aluminum compound are simultaneously added to the filtration cake during the liquefaction operation.

11. The process as claimed in claim 9, wherein the aluminum compound is added to the filtration cake during the liquefaction operation prior to the addition of the mixture of polycarboxylic acids.

12. The process as claimed in claim 9, wherein the mixture of polycarboxylic acids is added to the filtration cake after the liquefaction operation.

13. The process as claimed in claim 9, wherein the mixture of polycarboxylic acids comprises the following acids: adipic acid, glutaric acid and succinic acid.

14. The process as claimed in claim 13, wherein the mixture of polycarboxylic acids comprises from 15% to 35% by weight of adipic acid, from 40% to 60% by weight of glutaric acid and from 15% to 25% by weight of succinic acid.

15. The process as claimed in claim 9, wherein the mixture of polycarboxylic acids comprises the following acids: methylglutaric acid, ethylsuccinic acid and adipic acid.

16. The process as claimed in claim 15, wherein the mixture of polycarboxylic acids comprises from 60% to 96% by weight of methylglutaric acid, from 3.9% to 20% by weight of ethylsuccinic acid and from 0.05% to 20% by weight of adipic acid.

17. The process as claimed in claim 9, wherein a portion or all of the polycarboxylic acids are in the anhydride, ester, alkali metal salt (carboxylate) or ammonium salt (carboxylate) form.

18. The process as claimed in claim 17, wherein the mixture of polycarboxylic acids is a mixture comprising: methylglutaric acid in a proportion of 60% to 96% by weight, ethylsuccinic anhydride in a proportion of 3.9% to 20% by weight, and adipic acid in a proportion of 0.05% to 20% by weight.

19. The process as claimed in claim 17, wherein the mixture of polycarboxylic acids is a mixture comprising: methylglutaric acid in a proportion of 10% to 50% by weight, methylglutaric anhydride in a proportion of 40% to 80% by weight, ethylsuccinic anhydride in a proportion of 3.9% to 20% by weight, and adipic acid in a proportion of 0.05% to 20% by weight.

20. The process as claimed in claim 9, wherein the aluminum compound is an alkali metal aluminate.

21. The process as claimed in claim 9, wherein the step of reacting at least one silicate with at least one acidifying agent comprises: (i) forming an initial vessel heel comprising at least a portion of the total amount of the silicate involved in the reaction and an electrolyte, the concentration of silicate (expressed as SiO.sub.2) in said initial vessel heel being less than 100 g/l, (ii) adding the acidifying agent to said vessel heel until a value for the pH of the reaction medium of at least 7.0 is obtained, and (iii) adding additional acidifying agent and, if appropriate, simultaneously adding the remaining amount of silicate to the reaction medium, wherein the mixture of polycarboxylic acids is added to the filtration cake, either during the liquefaction operation, or after the liquefaction operation and before the drying stage.

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 AGS (mixture of adipic acid, glutaric acid and succinic acid) is prepared by dissolving AGS flakes (26% by weight of adipic acid, 52% by weight of glutaric acid, 21% by weight of succinic acid and 1% of others) in water (at 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 simultaneous addition to the cake of 2270 grams of a sodium aluminate solution (Al/SiO.sub.2 ratio by weight of 0.33%) and of 10 557 grams of the 100 g/l AGS solution (AGS/SiO.sub.2 ratio by weight of 1.1%).

(5) 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:

(6) Mean inlet temperature: 558 C.

(7) Mean outlet temperature: 157 C.

(8) Mean flow rate: 214 l/h.

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

(10) TABLE-US-00002 BET (m.sup.2/g) 147 Content of polycarboxylic acid + carboxylate (C) (%) 0.35 Aluminum (Al) content (%) 0.33 Ratio (R) 1.0 CTAB (m.sup.2/g) 155 .sub.s.sup.d (mJ/m.sup.2) 32.9 .sub.50 (m) after deagglomeration with ultrasound 2.8 Fd after deagglomeration with ultrasound 14.0 V2/V1 (%) 62 pH 5.8

Example 2

(11) 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):

(12) TABLE-US-00003 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 simultaneous addition of sodium aluminate and of a mixture of AGS (Adipic-Glutaric-Succinic) acids (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)

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

(14) TABLE-US-00004 BET (m.sup.2/g) 161 Content of polycarboxylic acid + 0.00 carboxylate (C) (%) Aluminum (Al) content (%) 0.30 Ratio (R) 0 CTAB (m.sup.2/g) 155 .sub.s.sup.d (mJ/m.sup.2) 48.7 Water uptake (%) 9.4

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

(16) 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.

(17) 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.

(18) 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.

(19) 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.

(20) 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.

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

(22) 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.

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

(24) Rheological Properties Viscosity of the Raw Mixtures:

(25) 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.

(26) 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.

(27) TABLE-US-00005 TABLE II References Control 1 Composition 1 ML (1 + 4) - 100 C. Initial 79 71 Mooney relaxation Initial 0.312 0.339 ML (1 + 4) - 100 C. After 3 weeks 93 77 (23 +/ 3 C.) Mooney relaxation After 3 weeks 0.258 0.309 (23 +/ 3 C.)

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

(29) 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.

(30) 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. Rheometry of the Compositions:

(31) 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.

(32) 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.

(33) 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 (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; the time T98 necessary to obtain a vulcanization state corresponding to 98% of complete vulcanization (this time is taken as 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 process the raw mixtures at this temperature without having initiation of vulcanization (the mixture cures from TS2).

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

(35) TABLE-US-00006 TABLE III Compositions Control 1 Composition 1 Tmin (dN .Math. m) 17.0 15.5 Tmax (dN .Math. m) 56.0 61.7 Delta torque (dN .Math. m) 39.0 46.2 TS2 (min) 5.8 6.9 T98 (min) 26.2 26.6

(36) The use of the silica S1 of the present invention (Composition 1) makes it possible to reduce the minimum viscosity (sign of an improvement in the raw viscosity) with respect to the reference (Control 1) without damaging the vulcanization behavior.

(37) Mechanical Properties of the Vulcanisates:

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

(39) 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.

(40) 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.

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

(42) TABLE-US-00007 TABLE IV Compositions Control 1 Composition 1 10% Modulus (MPa) 0.6 0.6 100% Modulus (MPa) 2.1 2.3 300% Modulus (MPa) 11.6 13.4 RI 5.6 5.8 Shore A hardness - 15 s (pts) 55 55

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

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

(45) 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 reference (Control 1).

(46) Dynamic Properties of the Vulcanisates:

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

(48) 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 +/2%. The measurements are carried out at 60 C. and at a frequency of 10 Hz.

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

(50) 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%.

(51) 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).

(52) TABLE-US-00008 TABLE V Compositions Control 1 Composition 1 E*, 60 C., 10 Hz (MPa) 5.8 5.4 Tan , 60 C., 10 Hz 0.125 0.111 G, 40 C., 10 Hz (MPa) 1.4 1.0 Tan max return, 40 C., 10 Hz 0.190 0.172

(53) 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 reference (Control 1).

(54) 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 sizable gain in raw viscosity, which remains stable on storage over time.

Example 3

(55) 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.

(56) The silica suspension (698 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.

(57) Prior to the liquefaction operation, a 100 g/l solution of an MGA mixture is prepared by dissolving the 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 and 0.1% of others) in water (35 C.) with stirring.

(58) The cake obtained in the filtration stage is subjected to a liquefaction operation in a continuous vigorously stirred reactor (for 80 minutes) with simultaneous addition to the cake of 1135 grams of a sodium aluminate solution (Al/SiO.sub.2 ratio by weight of 0.33%) and of 6044 grams of the MGA solution (MGA mixture/SiO.sub.2 ratio by weight of 1.26%).

(59) 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:

(60) Mean inlet temperature: 540 C.

(61) Mean outlet temperature: 153 C.

(62) Mean flow rate: 207 l/h.

(63) The characteristics of the silica S2 obtained (in the form of substantially spherical beads) are then the following:

(64) TABLE-US-00009 BET (m.sup.2/g) 144 Content of polycarboxylic acid + carboxylate (C) (%) 0.53 Aluminum (Al) content (%) 0.29 Ratio (R) 1.4 CTAB (m.sup.2/g) 156 .sub.s.sup.d (mJ/m.sup.2) 33.5 Water uptake (%) 8.5 .sub.50 (m) after deagglomeration with ultrasound 2.8 Fd after deagglomeration with ultrasound 16.2 V2/V1 (%) 58 pH 5.4

Example 4 (Comparative)

(65) 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.

(66) 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.

(67) 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%).

(68) 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:

(69) Mean inlet temperature: 577 C.

(70) Mean outlet temperature: 157 C.

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

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

(73) TABLE-US-00010 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 .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 5

(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-00011 TABLE VI Composition Control 2 Composition 2 SBR (1) 103 103 BR (1) 25 25 Silica 1 (2) 80 Silica S2 (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 S2 according to the present invention (liquefaction with simultaneous addition of a mixture of MGA acids and of sodium aluminate (example 3 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)

(76) Process for the Preparation of the Rubber 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). The duration of this pass 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) Each final mixture is subsequently calandered in the form of plaques with a thickness of 2-3 mm.

(83) 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.

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

(85) Rheological Properties Viscosity of the Raw Mixtures:

(86) 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.

(87) 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 3 weeks at a temperature of 23+/3 C.

(88) TABLE-US-00012 TABLE VII Compositions Control 2 Composition 2 ML (1 + 4) - 100 C. Initial 79 71 Mooney relaxation Initial 0.312 0.324 ML (1 + 4) - 100 C. After 3 weeks 93 76 (23 +/ 3 C.) Mooney relaxation After 3 weeks 0.258 0.324 (23 +/ 3 C.)

(89) It is found that the silica S2 of the present invention (Composition 2) makes possible a sizable reduction in the initial raw viscosity, with respect to the control mixture.

(90) It is also found that the silica S2 of the present invention (Composition 2) makes it possible to retain the advantage in reduced raw viscosity after 3 weeks of storage, with respect to the control mixture, and to obtain a satisfactory Mooney relaxation, mainly over time.

(91) This type of behavior is of great use to a person skilled in the art in the case of the processing of a silica-comprising rubber mixture. Rheometry of the Compositions:

(92) 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 VIII.

(93) 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.

(94) 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 (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; the time T98 necessary to obtain a vulcanization state corresponding to 98% of complete vulcanization (this time is taken as 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 process the raw mixtures at this temperature without having initiation of vulcanization (the mixture cures from TS2).
The results obtained are shown in table VIII.

(95) TABLE-US-00013 TABLE VIII Compositions Control 2 Composition 2 Tmin (dN .Math. m) 17.0 14.9 Tmax (dN .Math. m) 56.0 65.6 Delta torque (dN .Math. m) 39.0 50.7 TS2 (min) 5.8 9.0 T98 (min) 26.2 26.6

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

(97) 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.

(98) The use of the silica S2 of the present invention (Composition 2) thus makes it possible to reduce the minimum viscosity (lower minimum torque Tmin, which is a sign of an improvement in the raw viscosity) with respect to the control mixture without damaging the vulcanization behavior.

(99) Mechanical Properties of the Vulcanisates:

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

(101) 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.

(102) 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.

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

(104) TABLE-US-00014 TABLE IX Compositions Control 2 Composition 2 10% Modulus (MPa) 0.6 0.6 100% Modulus (MPa) 2.1 2.3 300% Modulus (MPa) 11.6 13.6 RI 5.6 5.9 Shore A hardness - 15 s (pts) 55 55

(105) It is found that the composition resulting from the invention (Composition 2) exhibits a good compromise in mechanical properties, with respect to what is obtained with the control mixture.

(106) Composition 2 thus exhibits relatively low 10% and 100% moduli and a high 300% modulus, hence a greater reinforcing index.

(107) The use of a silica S2 of the present invention (Composition 2) makes it possible to obtain a satisfactory level of reinforcement, with respect to the control mixture.

(108) Dynamic Properties of the Vulcanisates:

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

(110) 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.

(111) 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).

(112) 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%.

(113) 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, 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).

(114) TABLE-US-00015 TABLE X Compositions Control 2 Composition 2 E*, 60 C., 10 Hz (MPa) 5.8 5.7 Tan , 60 C., 10 Hz 0.125 0.108 G, 40 C., 10 Hz (MPa) 1.4 1.5 Tan max return, 40 C., 10 Hz 0.190 0.187

(115) The use of a silica S2 of the present invention (Composition 3) makes it possible to improve the maximum value of the loss factor at 60 C. while keeping the amplitude of the elastic modulus constant (or Payne effect) at the level of that of the control mixture.

(116) 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, with respect to the control mixture, in particular with a gain in raw viscosity which remains substantially stable on storage over time.

Example 6

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

(118) TABLE-US-00016 TABLE XI Composition Control 3 Control 4 Composition 3 NR (1) 100 100 100 Silica 1 (2) 55 Silica C1 (3) 55 Silica S2 (4) 55 Coupling agent (5) 4.4 4.4 4.4 ZnO 3 3 3 Stearic acid 4 4 4 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 Z1165MP from Rhodia (3) Silica C1 (liquefaction with addition of maleic acid (example 4, comparative)) (4) Silica S2 according to the present invention (liquefaction with simultaneous addition of a mixture of MGA acids and of sodium aluminate (example 3 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)

(119) Process for the Preparation of the Rubber Compositions:

(120) 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.

(121) 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 (90 C.) and the speed of the rotors (80 rev/min) are set on each occasion so as to achieve mixture dropping temperatures of approximately 140-160 C.

(122) 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 (speed of the rotors of 90 rev/min and temperature of 100 C.), the duration is between 4 and 10 minutes

(123) 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.

(124) 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.

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

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

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

(128) Rheological Properties Viscosity of the Raw Mixtures:

(129) 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.

(130) 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 XII. The test is carried out after preparing the raw mixtures and then after aging for 10 days at a temperature of 23+/3 C.

(131) TABLE-US-00017 TABLE XII Compositions Control 3 Control 4 Composition 3 ML (1 + 4) - Initial 59 56 53 100 C. Mooney Initial 0.392 0.385 0.418 relaxation ML (1 + 4) - After 11 days 65 59 56 100 C. (23 +/ 3 C.) Mooney After 11 days 0.380 0.399 0.445 relaxation (23 +/ 3 C.)

(132) It is found that the silica S2 of the present invention (Composition 3) makes possible a reduction in the initial raw viscosity, with respect to the control mixture 3 and the control mixture 4.

(133) It is also found that the silica S2 of the present invention (Composition 3) shows an enhanced performance in terms of reduction in the raw viscosity, with respect to the control mixture 3 and the control mixture 4.

(134) It is also observed that the use of the silica S2 of the present invention (Composition 3) makes it possible to retain the advantage in reduced raw viscosity, with respect to the control mixture, after 11 days of storage.

(135) This type of behavior is of great use to a person skilled in the art in the case of the processing of a silica-comprising rubber mixture. Rheometry of the Compositions:

(136) 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 XIII.

(137) 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.

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

(139) The results obtained are shown in table XIII.

(140) TABLE-US-00018 TABLE XIII Compositions Control 3 Control 4 Composition 3 Tmin (dN .Math. m) 13.6 13.5 11.1 Tmax (dN .Math. m) 71.6 69.4 82.9 Delta torque (dN .Math. m) 58 56 72 T98 (min) 25.2 26.9 23.6

(141) It is found that the composition resulting from the invention (Composition 3) exhibits a satisfactory combination of rheological properties.

(142) 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 3 and the control mixture 4, which reflects a greater processability of the prepared mixture.

(143) The use of the silica S2 of the present invention (Composition 3) 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 3 and the control mixture 4 without damaging the vulcanization behavior.

(144) Mechanical Properties of the Vulcanisates:

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

(146) 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 %.

(147) 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.

(148) The properties measured are collated in table XIV.

(149) TABLE-US-00019 TABLE XIV Compositions Control 3 Control 4 Composition 3 10% Modulus (MPa) 0.6 0.5 0.7 300% Modulus (MPa) 12.3 12.6 15.0 Ultimate strength (MPa) 26.0 26.8 30.5 Elongation at break (%) 532 521 548 Shore A hardness - 15 s (pts) 59 55 64

(150) It is found that the composition resulting from the invention (Composition 3) exhibits a satisfactory compromise in mechanical properties, with respect to what is obtained with the control mixture 3 and with the control mixture 4.

(151) Composition 3 thus exhibits a relatively low 10% modulus and a relatively high 300% modulus.

(152) The use of a silica S2 of the present invention (Composition 3) makes it possible to retain substantially the same level of reinforcement while achieving a 300% modulus, a higher ultimate strength, a higher elongation at break and a higher Shore A hardness, with respect to the control mixture 3 and the control mixture 4.

(153) Dynamic Properties of the Vulcanisates:

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

(155) 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.

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

(157) 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%.

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

(159) TABLE-US-00020 TABLE XV Compositions Control 3 Control 4 Composition 3 E*, 60 C., 10 Hz (MPa) 6.5 5.6 7.9 Tan , 60 C., 10 Hz 0.125 0.118 0.098 Tan max return, 60 C., 10 Hz 0.138 0.135 0.134

(160) The use of a silica S2 of the present invention (Composition 3) makes it possible to improve the maximum value of the loss factor, with respect to the control mixture 3 and the control mixture 4.

(161) The examination of the various tables XII to XV shows that the composition in accordance with the invention (Composition 3) makes it possible to obtain a good processing/reinforcement/hysteresis properties compromise at 60 C., with respect to the control mixture 3 and the control mixture 4, in particular with a gain in raw viscosity which remains substantially stable on storage over time.