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

Abstract

A precipitated silica having a CTAB specific surface in the range of from 50 to 300 m.sup.2/g; a BET/CTAB specific surface ratio equal to or greater than 1.3 and comprising at least one polycarboxylic acid.

Claims

1. Precipitated silica having: a CTAB specific surface in the range of from 50 to 300 m.sup.2/g; a BET/CTAB specific surface ratio equal to or greater than 1.3; and a content of polycarboxylic acid and/or carboxylate, expressed as total carbon content, of at least 0.15 wt %.

2. The precipitated silica according to claim 1 comprising at least one polycarboxylic acid.

3. The precipitated silica according to claim 1 having a relative breadth Y of pore size distribution of less than or equal to 3.5.

4. The precipitated silica according to claim 1 having a BET specific surface from 200 to 300 m.sup.2/g; a CTAB specific surface from 150 to 250 m.sup.2/g; and a BET/CTAB specific surface ratio from 1.3 to 1.5.

5. The precipitated silica according to claim 1 having a content of aluminium (Al) of at least 0.30% by weight.

6. The precipitated silica according to claim 1, wherein the at least one polycarboxylic acid is selected from the group consisting of linear or branched, saturated or unsaturated, aliphatic polycarboxylic acids having from 2 to 20 carbon atoms and aromatic polycarboxylic acids.

7. The precipitated silica according to claim 1, 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 or mixtures thereof.

8. The precipitated silica according to claim 1, 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.

9. The precipitated silica according to claim 1, 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.

10. A process for the manufacture of a precipitated silica in accordance with claim 1 or of a suspension thereof, comprising the steps of: heating an initial solution of aqueous alkali metal silicate having a desired alkaline pH to a desired reaction temperature; simultaneously adding an acidifying agent and additional alkali metal silicate solution with agitation to the initial solution while maintaining the alkaline pH and temperature at the desired values; discontinuing the addition of alkali metal silicate while continuing the addition of acidifying agent to adjust the pH of a resulting silica suspension to a desired acid value; submitting said silica suspension to filtration to provide a filter cake; submitting said filter cake to a liquefaction step, optionally in the presence of an aluminum compound, to obtain a suspension of precipitated silica; and optionally, 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.

11. The process of claim 10 wherein the at least one polycarboxylic acid is selected from the group consisting of linear or branched, saturated or unsaturated, aliphatic polycarboxylic acids having from 2 to 20 carbon atoms and aromatic polycarboxylic acids.

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

13. An article of manufacture comprising a composition in accordance with claim 12.

14. The article of claim 13, wherein the article is a pneumatic tire or a tire thread.

15. The precipitated silica according to claim 4 having a BET specific surface from 220 to 280 m.sup.2/g and a CTAB specific surface from 180 to 240 m.sup.2/g.

Description

EXAMPLES

Example 1 and Comparative Example 1

[0140] A silica suspension is prepared according to the process described in WO2010129518A1, Example 1. The suspension of precipitated silica thus obtained is filtered providing a filter cake.

[0141] One part of the filter cake is dried (Comp. Example 1).

[0142] A second part of 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 % 2-methylglutaric acid, the remainder acid components being ethylsuccinic acid and adipic acid corresponding to 1.2 wt % of acid, based on the amount of silica introduced.

[0143] The disintegrated cake (having a solids content of 22% by weight) is subsequently dried using a nozzle atomizer by spraying through a 1.5 mm nozzle with a pressure of 25 bar for 35 minutes. The final content (C) of polycarboxylic acid and/or carboxylate groups, expressed as total carbon content, in the dried silica is 0.20-0.70 wt %.

Example 2 and Comparative Example 1

[0144] In an internal Brabender mixer (380 ml volume) the compositions set forth in Table 1 are prepared. In a first step a thermomechanic treatment at elevated temperatures is performed. This step is followed by a second mechanical treatment at temperatures below 110 C. to add the vulcanization system. The first step is 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 are 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 are introduced. After cooling the mixture to a temperature below 100 C., zinc oxyde and the protective agents (e.g. 6-PPD) are 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) is added through a cylindric mixer preheated to a temperature of 50 C. during 2 to 6 minutes.

[0145] The final composition is calendered to sheets with a thickness of 2-3 mm. The amounts given in Table 1 are in parts by weight.

TABLE-US-00001 TABLE 1 Comparative Composition Example 2 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) Product of Comparative Exmple 1 (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 guanide (Rheonogran DPG 80 from Rhein Chemie) (9) N-cyclohexyl-2-benzothiazyl-sulfonamide (Rhenogran CBS-80 from Rhein Chemie)

[0146] The precipitated silica in accordance with the present invention leads 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 is lower than with the composition of the comparative examples.

[0147] A lower initial viscosity and a reduced viscosity increase over time are valuable improvements for the skilled person.