Precipitated silicic acid, method and compositions containing same

A process for the production of hydrophobic silicic acid comprising treating precipitated silicic acid having the following properties:

• ______________________________________ BET surface acc. to DIN 66 131 m.sup.2 /g 150 .+-. 30 Average size of the primary particles from EM pictures nm 15-22 Loss after drying acc. to DIN 55 921 after 2 hours at 105.degree. C. % 2.5-3.5 Loss at red heat (related to the substance dried for 2 hours at 105.degree. C.) acc. to DIN 55 921 % 3 .+-. 0.5 pH value (in 5% aqueous dis- persion) acc. to DIN 53 200 3.5-5.5 Conductivity (in 4% aqueous dispersion) us <500 Tamped density of the unaerated substance acc. to g/l 60 .+-. 20 DIN 53 194 SO.sub.3 content (related to the substance dried for 2 hours at 105.degree. C.) % <0.3 Na.sub.2 O content (related to the substance dried for 2 hours at 105.degree. C.) % <0.3 ______________________________________
• with a hydrophobic agent in a ratio of 10:0.5 to 10:3 and agitating the precipitated silicic acid with hydrophobic agent, and tempering the product obtained for 60 to 180 minutes at a temperature of 200.degree. C. to 400.degree. C. and thereafter grinding to form a finely divided product.