PROCESS FOR THE PREPARATION OF PRECIPITATED SILICAS, PRECIPITATED SILICAS AND THEIR USES, IN PARTICULAR FOR THE REINFORCEMENT OF POLYMERS

Abstract

Precipitated silica having a BET specific surface area in the range of from 35-700 m.sup.2/g, a CTAB specific surface area in the range of from 30 to 400 m.sup.2/g, and a content of polycarboxylic acid and/or carboxylate groups, expressed as total carbon content, of at least 0.15 wt %

Claims

1. Precipitated silica having: a BET specific surface in the range of from 35-700 m.sup.2/g, a CTAB specific surface in the range of from 30 to 400 m.sup.2/g, a pore volume distribution V.sub.2/V.sub.1 between the pore volume generated by the pores having a diameter of between 175 and 275 (V.sub.2) and the pore volume generated by the pores with diameters of less than or equal to 400 (V.sub.1) of at most 0.50, and a content of carboxylic acid and/or carboxylate groups, expressed as total carbon content, of at least 0.15 wt %.

2. Precipitated silica in accordance with claim 1 having a ratio V.sub.2/V.sub.1 in the range of from 0.20 to 0.49.

3. Precipitated silica in accordance with claim 1, with a DPB oil uptake in the range of from 140 to 350 ml/100 g.

4. Precipitated silica in accordance with claim 1, wherein the carboxylic acid groups are derived from at least one polycarboxylic acid.

5. Precipitated silica in accordance with claim 1, having: a BET specific surface in the range of from 120 to 300 m.sup.2/g, a CTAB specific surface of from 100 to 300 m.sup.2/g, and a ratio BET surface/CTAB surface of from 0.8 to 1.3.

6. Precipitated silica in accordance with claim 1, having: a BET specific surface of from 35 to 350 m.sup.2/g, a CTAB specific surface of from 30 to 350 m.sup.2/g, a DBP oil uptake in the range of from 150 to 300 ml/100 g, a ratio BET specific surface/CTAB specific surface of from 0.8 to 1.1, a ratio V.sub.2/V.sub.1 in the range of from 0.19 to 0.46, and a ratio DPB oil uptake/CTAB specific surface ratio of from 1.2 to 2.4.

7. Precipitated silica in accordance with claim 1, having: a ratio BET specific surface/CTAB specific surface of at least 1.7 with the BET specific surface area being at least 135 m.sup.2/g and the CTAB surface area being at least 75 m.sup.2/g.

8. Precipitated silica in accordance with claim 1, having an aluminium content, measured as Al.sub.2O.sub.3, in the range of from 0.1 to 5.0 wt %.

9. A process for the manufacture of a precipitated silica in accordance with claim 1, or of a precipitated silica suspension, the method comprising: a) reacting at least at least one silicate with at least one acidifying agent to provide a silica suspension, b) submitting said silica suspension to filtration to provide a filter cake, c) submitting said filter cake to a liquefaction step, said liquefaction step being carried out with or without the addition of an aluminium compound to obtain a suspension of precipitated silica, and, optionally d) drying the precipitated silica obtained after the liquefaction step wherein at least one polycarboxylic acid is added to the filter cake during or after the liquefaction step.

10. Process in accordance with claim wherein a silicate is precipitated with a mineral acid at a temperature of from 55 to 95 C. at a pH in the range of from 7 to 14 under continuous stirring until a solids content in the suspension of from 40 to 110 g/l is achieved, thereafter the pH is reduced to a value below 5 by the addition of an acid, filtering the precipitated silica, and submitting the filter cake to a liquefaction step, optionally with the use of shearing forces.

11. Process in accordance with claim 9, wherein the at least one polycarboxylic acid is selected from the group consisting of adipic acid, succinic acid, ethylsuccinic acid, glutaric acid, methylglutaric acid, oxalic acid, citric acid and mixtures thereof.

12. Process in accordance claim 9, wherein the at least one polycarboxylic acid is a mixture comprising 15 to 35 wt % adipic acid, 40 to 60 wt % glutaric acid and 15 to 25 wt % succinic acid.

13. Process in accordance with claim 9, wherein the at least one polycarboxylic acid is a mixture comprising 60 to 96 wt % methylglutaric acid, 3.9 to 20 wt % ethyl succinic acid and 0.05 to 20 wt % adipic acid.

14. A process for the manufacture of a precipitated silica in accordance with claim 1, or of a precipitated silica suspension, the method comprising reacting at least at least one silicate with at least one acidifying agent to produce a precipitated silica suspension; filtering said precipitated suspension to obtain a filter cake; optionally subsequently disintegrating said filter cake and subsequently drying the product, said process comprising contacting at least one polycarboxylic acid and, optionally, an aluminium compound with the product during or after drying of the disintegrated filter cake.

15. A composition of matter comprising a precipitated silica of claim 1 and an elastomer or a vulcanizable rubber.

16. An article of manufacture comprising a composition in accordance with claim 15.

17. A method for manufacturing a pneumatic tire or a tire thread, the method comprising fabricating the pneumatic tire or tire thread from a rubber composition comprising the precipitated silica of claim 1.

18. The article of claim 16, wherein the article is selected from a pneumatic tire or a tire thread.

Description

EXAMPLES

Example 1

Preparation of Precipitated Silica in Accordance with the Invention

[0181] 700 grams of Ultrasil 7000GR (commercially available from Evonik) was introduced into a vessel with a diameter of 350 mm and a height of 280 mm. A solution of 2-methylglutaric acid with an acid content of approximately 34 wt % was injected into the vessel via a jet stream die at a pressure of 101,325 kPa and at ambient temperature. The methylglutaric acid solution had a content of at least 90 wt % of 2-methylglutaric acid, the remander acid components being ethylsuccinic acid and adipic acid.

[0182] The impregnation operation was carried out for 18 min at a stream rate of 2.07 ml/min, corresponding to 1.2 wt % of acid, based on the amount of silica introduced.

Example 2

Elastomeric Composition Comprising the Product of Example 1

[0183] In an internal Brabender mixer (380 ml volume) the compositions set forth in Table 1 were prepared. The amounts given are in parts by weight

TABLE-US-00001 TABLE 1 Comparative Composition Example 1 Example 2 SBR (1) 103 103 BR (2) 25 25 Silica (3) 80 Silica (4) 80 Coupling agent (5) 6.4 6.4 Nytex 4700 (6) 7 7 Carbon black N330 3 3 ZnO 2.5 2.5 Stearic acid 2 2 Antioxydant (7) 1.9 1.9 DPG (8) 1.5 1.5 CBS (9) 2 2 Sulfur 1.1 1.1 (1) Styrene butadiene rubber solution (Buna VSL 5025-2, obtained from Lanxess) with 50 +/ 4% vinyl groups, 25 +/ 2% styrene groups and a glass transition temperature of 20 C. 100 parts of SBR comprised 37.5 +/ 2.8% of oil (2) Butadiene rubber (Buna CB 25, obtained from Lanxess) (3) Ultrasil 7000GR, obtained from Evonik (4) Product obtained in Example 1 (5) TESPT (LUVOMAXX TESPT), a sulphur silane coupling agent obtained from Lehman & Voss France Sarl) (6) Naphthenic plasticiser oil Nytex 4700, obtained from NynasAB (7) N-1,3-dimethylbutyl-N-phenyl-p-phenylene diamine (Santoflex 6-PPD from Flexsys) (8) Diphenyl guanidine (Rheonogran DPG 80 from Rhein Chemie) (9) N-cyclohexyl-2-benzothiazyl-sulfonamide (Rhenogran CBS-80 from Rhein Chemie)

[0184] Preparation of the Rubber Compositions

[0185] The process for the manufacture of the rubber compositions was carried out in two subsequent preparation steps. The first step was a thermomechanic treatment at elevated temperatures. This step was followed by a second mechanical treatment at temperatures beolw 110 C. This step was used for the addition of the vulcanization system. The first step was realized in an internal mixer of the Brabender type with a capacity of 380 ml and a degree of filling of 0.6. The initial temperature and the rotor speed were in each case adjusted to achieve a starting temperature in the range of from 140 to 160 C. In the first step the elastomers and the reinforcing filler together with the coupling agent and the stearic acid were introduced. This step took 4-10 minutes. After cooling the mixture to a temperature below 100 C., zinc oxyde and the protective agents (e.g. 6-PPD) were introduced within 2 to 5 minutes. In the second step, after cooling to a temperature of less than 100 C. the vulcanization system (sulphur plus accelerators) was added through a cylindric mixer preheated to a temperature of 50 C. during 2 to 6 minutes.

[0186] The final composition was calendered to sheets with a thickness of 2-3 mm.

[0187] An evaluation of the rheologic properties of the crude mixtures allows optimizing time and temperature of the vulcanization. Thereafter, the mechanical and dynamical properties of the mixtures vulcanized under optimum conditions were determined.

[0188] Viscosity of the Crude Mixtures

[0189] The Mooney viscosity of the crude compositions and the degree of relaxation Mooney were determined at a temperature of 100 C. with a MV 2000 rheometer in accordance with NF ISO289. The ML(1+4)-100 C. values (preheat time 1 minute and taking of the reading 4 minutes after the rotor had been started is given in Table 2. The measurements were made immediately after mixing and after an aging time of 8 days at a temperature of 23+/3 C.

TABLE-US-00002 TABLE 2 Comp. Parameter Example 1 Example 2 ML (1 + 4) - Initial 79 76 100 C. Relaxation Initial 0.303 0.318 Mooney ML (1 + 4) - After 8 days 86 79 100 C. (23 +/ 3 C.) Relaxation After 8 days 0.290 0.315 Mooney (23 +/ 3 C.)

[0190] The evaluation of the measurements yielded the following observations: the precipitated silica in accordance with the present invention led to a reduction of the initial viscosity of the crude mixture compared to the composition with a standard grade silica without acid group content. Furthermore, the viscosity increase over time of the compositions comprising a silica in accordance with the present invention was lower than with the composition of the comparative examples.

[0191] A lower initial viscosity and a reduced viscosity increase over time are valuable improvements for the skilled person.

[0192] The compositions in accordance with the present invention showed also improved rheometric properties while maintaining the mechanical properties at the same level as the comparative composition. Scorch time TS2 (an indicator of the time required for the beginning of the crosslinking process) was increased which improves the available handling time of the compositions.

Example 3

[0193] A silica suspension is prepared according to the process described in EP647591A. The suspension of precipitated silica thus obtained is filtered providing a filter cake. The filter cake is subjected to a liquefaction operation in a continuous vigorously stirred reactor in the presence of a solution of 2-methylglutaric acid with an acid content of approximately 34 wt % having a content of at least 90 wt % of 2-methylglutaric acid, the remainder acid components being ethylsuccinic acid and adipic acid. The total amount of the acid mixture added during the liquefaction operation corresponds to 1.2 wt % of acid based on the amount of silica (SiO.sub.2) in the cake. The disintegrated cake is subsequently dried using a nozzle atomizer.

[0194] The precipitated silica of Example 3 has a BET surface area of 165-175 m.sup.2/g, a CTAB surface area of 155-170 m.sup.2/g, a V.sub.2/V.sub.1 ratio of about 0.47 and a content of carboxylic acid and/or carboxylate groups, expressed as total carbon content, of 0.20 wt %-0.70 wt %.