Use of a precipitated silica containing titanium and a specific coupling agent in an elastomer composition

Abstract

The invention concerns the combined use, in an elastomer composition preferably comprising an isoprene elastomer, a precipitated silica containing titanium and a specific conjugated diene compound, such as a conjugated diene phosphonate or phosphinate compound. It also concerns the elastomer compositions obtained and the items produced from said compositions.

Claims

1. An elastomer composition comprising: at least one elastomer, a precipitated silica containing titanium, as mineral filler, wherein the titanium content of said precipitated silica is not more than 10% by weight, and a compound of formula (I), said compound of formula (I) being optionally, totally or partly, in a polymerized form: ##STR00018## wherein: R represents R.sub.6 or OR.sub.8, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are each independently selected from hydrogen, alkyl, aryl, alkaryl, aralkyl, cycloalkyl, heterocycloalkyl and alkenyl groups, and R.sub.7 and R.sub.8 are each independently selected from hydrogen, alkyl, aryl, alkaryl, aralkyl, cycloalkyl and alkenyl groups, and metals selected from the group consisting of Na, Li and Ca.

2. The elastomer composition as claimed in claim 1, wherein the compound of formula (I), which is optionally, totally or partly, in a polymerized form, couples said precipitated silica and said elastomer(s).

3. The elastomer composition as claimed in claim 2, wherein said elastomer composition does not comprise any other mineral filler/elastomer coupling agent.

4. The elastomer composition as claimed in claim 1, wherein all or part of the compound of formula (I) is in the form of a polymer with a polymerization index of less than 20.

5. The elastomer composition as claimed in claim 1, wherein R represents R.sub.6.

6. The elastomer composition as claimed in claim 1, wherein R represents OR.sub.8.

7. The elastomer composition as claimed in claim 1, wherein R.sub.1, R.sub.2 and R.sub.4 each represent H.

8. The elastomer composition as claimed in claim 1, wherein R.sub.3 and R.sub.5 each represent a methyl group.

9. The elastomer composition as claimed in claim 1, wherein the compound of formula (I) is 4-methyl-2,4-pentadiene-2-phosphinic acid.

10. The elastomer composition as claimed in claim 1, wherein the titanium content of said precipitated silica is at least 0.5% by weight.

11. The elastomer composition as claimed in claim 1, wherein the titanium content of said precipitated silica is between 0.5% and 10% by weight.

12. The elastomer composition as claimed in claim 1, wherein the amount of compound of formula (I) in the composition is from 1% to 20% by weight relative to the amount of said precipitated silica.

13. The elastomer composition as claimed in claim 1, wherein said compound of formula (I) and said precipitated silica are premixed with each other.

14. The elastomer composition as claimed in claim 1, wherein the elastomer comprises at least one isoprene elastomer.

15. The elastomer composition as claimed in claim 14, wherein said elastomer composition does not comprise any elastomer(s) other than said isoprene elastomer(s).

16. The elastomer composition as claimed in claim 1, wherein the elastomer comprises at least one isoprene elastomer and at least one diene elastomer other than an isoprene elastomer, and wherein the amount of isoprene elastomer(s) relative to the total amount of elastomer(s) is greater than 50% by weight.

17. An article comprising at least one elastomer composition as claimed in claim 1, wherein the article is selected from a footwear sole, a floor covering, a gas barrier, a flame-retardant material, a roller for a cableway, a seal for a domestic electrical appliance, a seal for a liquid or gas pipe, 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.

18. A tire for heavy-goods vehicles, the tire comprising at least one elastomer composition as claimed in claim 1.

19. The elastomer composition as claimed in claim 13, wherein said compound of formula (I) is pregrafted onto said precipitated silica.

20. A method for reinforcing an elastomer composition, the method comprising contacting the elastomer with: a precipitated silica containing titanium, as mineral filler, wherein the titanium content of said precipitated silica is not more than 10% by weight, and a compound of formula (I), said compound of formula (I) being optionally, totally or partly, in a polymerized form: ##STR00019## wherein: R represents R.sub.6 or OR.sub.8, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are each independently selected from hydrogen, alkyl, aryl, alkaryl, aralkyl, cycloalkyl, heterocycloalkyl and alkenyl groups, and R.sub.7 and R.sub.8 are each independently selected from hydrogen, alkyl, aryl, alkaryl, aralkyl, cycloalkyl and alkenyl groups, and metals selected from the group consisting of Na, Li and Ca.

Description

EXAMPLES

Example 1

(1) 66 g of H.sub.3PO.sub.2 (50% in water), 49 g of mesityl oxide and 100 ml of toluene are placed in a 500 ml flask. The mixture is refluxed for 24 hours under nitrogen. .sup.31P NMR shows that 82.6% of the H.sub.3PO.sub.2 has reacted and that 4-methyl-2,4-pentadiene-2-phosphinic acid (PiDM) is obtained with a selectivity of 68.5%, accompanied by other minor impurities, after 6 hours of azeotropic distillation of the water. The reaction is continued for 24 hours to obtain a 97.3% conversion of the H.sub.3PO.sub.2 and a selectivity of 44.4% for 4-methyl-2,4-pentadiene-2-phosphinic acid (PiDM). The reaction mixture is cooled to room temperature and the residual solvent is removed on a rotary evaporator. The residue is dissolved in 200 ml of dichloromethane and the solution is washed three times with 100 ml of water. The combined dichloromethane phase is dried with anhydrous Na.sub.2SO.sub.4 and the solvent is evaporated off to obtain 46.5 g of a viscous yellow oil in a crude yield of 63.7% and a 71% purity of PiDM.

Example 2

(2) 107.8 g of mesityl oxide, 132 g of H.sub.3PO.sub.2 (50%) and 400 ml of toluene are placed in a 1 L three-necked round-bottomed flask protected under nitrogen. The system is rinsed with nitrogen and brought to reflux. Water is distilled off in the form of an azeotropic mixture with toluene. The reaction is continued for 20 hours until .sup.31P NMR shows that all the H.sub.3PO.sub.2 has been consumed. The reaction mixture is cooled to room temperature and washed with 400 ml of water, and then extracted with dilute NaOH solution. The aqueous phase is then acidified with 4 N HCl at pH 1, and then re-extracted with 50 ml of dichloromethane. The organic phase is collected, dried over anhydrous Na.sub.2SO.sub.4 and evaporated to give 68.5 g of a bright yellow oil. .sup.31P NMR shows that 89.7 mol % corresponds to PiDM in a crude yield of 46.9%.

Example 3

(3) A polymer is obtained by polymerization of purified PiDM of Example 2 at room temperature. The polymer is isolated by precipitation from toluene. 40 g of PiDM are dissolved in 100 ml of toluene. 0.1 g of AIBN (azobisisobutyronitrile) is added in three portions under a nitrogen atmosphere at 80° C. over 3 hours. After stirring for a further 1 hour at the same temperature, the precipitate is then filtered off and dried to obtain 30 g of a pale yellow solid polymer. The polymer may be hardened in 10% NaOH solution for 2 days, and then converted into a gel swollen with water.

Example 4

(4) 10 g of phosphorous acid, dried for 4 hours at 50° C. under vacuum, and 14.2 g of mixed isomers of mesityl oxide are mixed together in a flask at 28° C. The mixture turns black and .sup.31P NMR shows that 90% of the phosphorous acid has reacted. 24.7 g of acetic anhydride are then added slowly with stirring over 45 minutes, the temperature being maintained at about 28° C. The mixture is maintained at 48° C. for 4 hours. 98% conversion of the H.sub.3PO.sub.3 is observed with an 86% selectivity for PoDM and anhydride derivatives thereof.

Example 5

(5) H.sub.3PO.sub.3 is dried for about 4 hours at 50° C. under vacuum. 10 g of dry H.sub.3PO.sub.3 and 12.43 g of mesityl oxide are mixed together in a flask at 28-30° C. 24.7 g of acetic anhydride are then added slowly with mixing over 50 minutes, the reaction temperature being kept below 30° C. The mixture is kept stirring at this temperature for 4 hours. .sup.31P NMR shows 81.2% conversion of the H.sub.3PO.sub.3 and an 86% selectivity for PoDM and anhydride derivatives thereof.

Example 6

(6) 10 g of the PoDM monomer of Example 5 are placed in a 100 ml one-necked round-bottomed flask. The monomer is brought to 100° C. and matured for 5 hours. Once the maturation step is complete, the flask is cooled to room temperature. Analysis by .sup.1H NMR reveals that 87% of the PoDM has been converted into an oligomeric form.

Example 7

(7) A filter cake of Z1165MP silica, obtained from a filtration step and having a solids content of 24% by weight, is used. This cake is subjected to a liquefaction operation with water to form a silica slurry having a solids content of 10% by weight.

(8) 10 kg of this slurry are placed in a reactor, which is then heated at 60° C. for 40 minutes.

(9) 143 g of a sodium hydroxide solution (having a concentration of 1 mol NaOH/kg) is then added at a flow rate of 25 g/minute, allowing a pH of 8 to be reached.

(10) Still at 60° C., 1074 g of a titanium oxysulfate solution (having a concentration of 0.7 mol Ti/kg and prepared from a 15% titanium oxysulfate solution (sold by the company Simon Aldrich)) are then added over 45 minutes, at a pH of 8 regulated by addition of NaOH solution.

(11) The silica slurry thus obtained is then filtered and washed with four times 5 liters of water on a flat filter.

(12) The cake obtained from this filtration is subjected to a liquefaction operation with water to form a silica slurry having a solids content of 10% by weight.

(13) The liquefied cake is then dried using a nozzle atomizer by spraying the liquefied cake through a nozzle with an air pressure of 1 bar (mean inlet temperature: 350° C.; mean outlet temperature: 100° C.).

(14) The characteristics of the precipitated silica obtained are then as follows:

(15) TABLE-US-00001 CTAB surface area (m.sup.2/g) 157 BET surface area (m.sup.2/g) 196 Titanium (Ti) content (%) 3.7

(16) No crystalline TiO.sub.2 is observed by XRD.

Example 8

(17) A filter cake of Z1165MP silica, obtained from a filtration step and having a solids content of 24% by weight, is used. This cake is subjected to a liquefaction operation with water to form a silica slurry having a solids content of 10% by weight.

(18) 10 kg of this slurry are placed in a reactor, which is then heated at 60° C. for 40 minutes.

(19) 143 g of a sodium hydroxide solution (having a concentration of 1 mol NaOH/kg) is then added at a flow rate of 25 g/minute, allowing a pH of 8 to be reached.

(20) Still at 60° C., 358 g of a titanium oxysulfate solution (having a concentration of 0.7 mol Ti/kg and prepared from a 15% titanium oxysulfate solution (sold by the company Simon Aldrich)) are then added over 15 minutes, at a pH of 8 regulated by addition of NaOH solution.

(21) The silica slurry thus obtained is then filtered and washed with four times 5 liters of water on a flat filter.

(22) The cake obtained from this filtration is subjected to a liquefaction operation with water to form a silica slurry having a solids content of 10% by weight.

(23) The liquefied cake is then dried using a nozzle atomizer by spraying the liquefied cake through a nozzle with an air pressure of 1 bar (mean inlet temperature: 350° C.; mean outlet temperature: 100° C.).

(24) The characteristics of the precipitated silica obtained are then as follows:

(25) TABLE-US-00002 CTAB surface area (m.sup.2/g) 155 BET surface area (m.sup.2/g) 196 Titanium (Ti) content (%) 1.1

(26) No crystalline TiO.sub.2 is observed by XRD.

(27) The compounds as prepared in the preceding Examples 1 to 6 may be used as coupling agent between a precipitated silica containing titanium as prepared in the preceding Examples 7 and 8, and an elastomer, such as a natural rubber, for example.

Example 9

(28) 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 (70 ml):

(29) TABLE-US-00003 TABLE I Compositions Control Composition 1 Composition 2 NR (1) 100 100 100 Silica 1 (2) 50 Silica S1 (3) 50 Silica S2 (4) 50 Coupling agent (5) 4.0 4.0 4.0 ZnO 2 2 2 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) 1.5 1.5 1.5 PVI (9) 0.2 0.2 0.2 Sulfur 2.0 2.5 2.5 (1) Natural rubber SMR 5 - CV60 (supplied by the company Safic-Alcan) (2) Silica Z1165MP from the company Rhodia (3) Silica S1 according to the present invention (1.1% Ti - Example 7 above) (4) Silica S2 according to the present invention (3.7% Ti - Example 8 above) (5) 4-Methyl-2,4-pentadiene-2-phosphinic acid (PiDM) (6) N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from the company Flexsys) (7) 2,2,4-Trimethyl-1H-quinoline (Permanax TQ from the company Flexsys) (8) N-Cyclohexyl-2-benzothiazolylsulfenamide (Rhenogran CBS-80 from the company RheinChemie) (9) N-(Cyclohexylthio)phthalimide (Santograd PVI from the company Flexsys)

(30) Process for Preparing the Rubber Compositions:

(31) 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.

(32) The first phase is carried out using a mixing device, of internal mixer type, of Brabender brand (capacity of 70 ml). The filling coefficient is 0.75. The initial temperature and speed of the rotors are set on each occasion so as to achieve mixture dropping temperatures of approximately 150-170° C.

(33) 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.

(34) 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.

(35) 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.

(36) Each final mixture is subsequently calendered in the form of plates with a thickness of 2-3 mm.

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

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

(39) Rheological Properties

(40) Rheometry of the Compositions:

(41) The measurements are performed on the compositions in crude form. The results relating to the rheology test, which is performed at 150° C. using a Monsanto ODR rheometer according to standard NF ISO 3417, are given in table ii.

(42) 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.

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

(44) The results obtained are shown in table ii.

(45) TABLE-US-00004 TABLE II Compositions Control Composition 1 Composition 2 Tmin (dN .Math. m) 10.4 10.7 10.9 Tmax (dN .Math. m) 45.6 62.3 69.2 T98 (min) 22.3 19.8 17.9

(46) It is found that the compositions resulting from the invention (Compositions 1 and 2) have a satisfactory combination of rheological properties.

(47) The use of silicas S1 and S2 in the present invention (Compositions 1 and 2) makes it possible to achieve a higher maximum torque value without penalizing the vulcanization behavior and with a shorter optimum time (T98) relative to the control mixture.

(48) Mechanical Properties of the Vulcanizates:

(49) The measurements are performed on the optimally vulcanized compositions (T98) for a temperature of 150° C.

(50) Uniaxial tensile tests are carried out 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 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 %. It is possible to determine a reinforcing index (R.I.) which is equal to the ratio of the modulus at 300% strain to the modulus at 100% strain.

(51) 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.

(52) The properties measured are collated in table III.

(53) TABLE-US-00005 TABLE III Compositions Control Composition 1 Composition 2  10% Modulus (MPa) 0.7 0.68 0.63 100% Modulus (MPa) 1.3 1.8 1.7 300% Modulus (MPa) 4.2 6.2 6.3 Ultimate strength (MPa) 16.9 22.0 26.1 Elongation at break (%) 608 606 642 R.I. 3.10 3.53 3.69 Shore A hardness - 15 s 46 51 52 (pts)

(54) It is found that the compositions resulting from the invention (Composition 1 and Composition 2) have a good compromise of mechanical properties, relative to what is obtained with the control mixture.

(55) Compositions 1 and 2 thus have relatively low 10% and 100% moduli and a high 300% modulus, hence a greater reinforcing index.

(56) The use of silicas S1 and S2 of the present invention (Compositions 1 and 2) make it possible to improve the level of reinforcement by achieving a 300% modulus, a tensile strength and an elongation at break that are higher relative to those of the control mixture.

(57) It is also found that the increase in the titanium content in the silica (Composition 2 relative to Composition 1) makes it possible to increase the tensile strength and the elongation at break.

(58) Dynamic Properties of the Vulcanizates:

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

(60) 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 plus or minus 4%. The measurements are performed at 60° C. and at a frequency of 10 Hz.

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

(62) TABLE-US-00006 TABLE IV Compositions Control Composition 1 Composition 2 E*, 60° C., 10 Hz (MPa) 5.28 5.08 5.66 Tan δ, 60° C., 10 Hz 0.185 0.127 0.152

(63) The use of silicas S1 and S2 of the present invention (Compositions 1 and 2) allows a consequent reduction in the hysteresis behavior with much lower values of the loss factor (tan δ, 60° C.) relative to the control mixture, while at the same time having satisfactory dynamic rigidity.

(64) Examination of the various tables II to IV shows that the compositions in accordance with the invention (Compositions 1 and 2), i.e. the combined use of a particular silica and of a specific coupling agent, make it possible to increase the mechanical reinforcement and the hysteresis properties at 60° C. relative to the control mixture.

(65) One consequence of the combined use of a precipitated silica containing titanium and of a particular coupling agent as claimed is that it achieves an improvement in the compromise between wear resistance and rolling resistance when the elastomer composition is used for tire applications (for example: for cars, vans, trucks, heavy-goods lorries, etc.) and for various parts of the tire (such as: tread, sub-tread, belt, side wall, bead, carcass, envelope, liner, etc.).