Degussa Aktiengesellschaft

Degussa - Huls Ag

Ralf Rausch

Robert Kuhlmann

Heinz Esch

Udo Gorl

Karin Otto

Udo Görl

Karl Meier

Mattias Neumueller

Walter Meon

Guenter Tuerk

Matthias Neum&uuml;ller

Klaus-Peter Thomas

Rubber compositions comprising a precipitated silica with the following physico-chemical properties: 

Precipitated silicas

A precipitated silica with the following physicochemical properties: is produced by reacting alkali silicate with mineral acids at temperatures of 60&#xb0; C. to 95&#xb0; C. while maintaining a pH of 7.5 to 10.5 and continuously stirring, continuing the reaction to a solids concentration in the precipitation suspension of 90 g/l to 120 g/l, adjusting the pH value to a value of less than or equal to 5, filtering out, washing, drying and optionally grinding or granulating the precipitated silica. The precipitated silica is used as a filler in vulcanizable rubber compounds and vulcanizates.

A precipitated silica which contains an active substance with a characteristic, delayed release of active substance is prepared by adding the active substance during preparation of the precipitated silica. The precipitated silica containing the active substance may be added to oral hygiene agents such as toothpastes, topical fluoride preparations, dental materials or medicinal chewing gums.

Precipitated silicas which contain an active substance

A precipitated silica with the following physicochemical properties:

Precipitated silica with a sodium sulphate content of 4 to 18 wt. %, particularly with the physical-chemical data:

Precipitated silica

Precipitated silica which has a BET surface area of 10-130 m.sup.2 /g, a CTAB surface area of 10-70 m.sup.2 /g , an average particle diameter of 5-20 .mu.m, a Cu abrasion value in a 10% glycerol dispersion of 4-50 mg and thickening behavior in a CMC solution (20% dispersion) of 300-3500 mPa.multidot.s, is produced by simultaneously adding alkali silicate (weight modulus SiO.sub.2 :alkali oxide=2.5-3.9:1) and a mineral acid to an initial amount of water which has been adjusted to a pH value of 7.0 to 9.9 or 10.0 to 10.7 by the addition of water glass, holding the pH value constant between 7.0 and 9.9 or 10.0 to 10.7 during addition, wherein the initial precipitation temperature is 50.degree.-90.degree. C. and an increase in viscosity occurs after at most 25% of the duration of precipitation, adjusting the pH value to .ltoreq.6, preferably 3.5, once a silica content of greater than 120 g/l or greater than 150 g/l, preferably .gtoreq.160 g/l to 240 g/l, has been reached, separating the solid by filtration, washing, drying and grinding it. The precipitated silica may be used as an abrasive and/or thickening component in toothpastes.

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Kreuzau, Germany

Ralf Rausch