A process for producing a as a delustering agent in paints suitable silica filler

摘要

1,229,125. Spray drying silica. FARBENFABRIKEN BAYER A.G. 16 May, 1969 [2 July, 1968], No. 24984/69. Heading C1A A silica filler is obtained by spray drying an aqueous suspension of precipitated silica with a specific surface of from 50-200 m.SP2/SP/g. (according to BET) and a salt content of less than 1 % by weight, based on SiO 2 , the solids concentration being less than 12% by weight and the outlet temperature of the heating gases being between 250‹ and 700‹ C. The preferred conditions are a turbulent gas stream so that at least 100 kg. of water are evaporated per m.SP3/SP of drier volume per hour; a residence time of 1 second or less and an outlet temperature of 450-700‹ C. The silica suspension may be obtained by removing metal cations by hydrogen ion exchange from a suspension of filter cake after washing the latter. In an example sulphuric acid is added to a waterglass solution over a period of 3 hrs. at 70‹ C., the mixture boiled for 1 hr., adjusted to pH 7 and finally filtered. The filter cake was washed, suspended in salt free water and delivered to the spray drier.