ES365680A1 - Highly textured amorphous silica - Google Patents

Abstract

Finely divided, highly textured amorphous silica, for use as a lacquer matting agent, is produced by reacting an alkali metal silicate solution in an alkaline medium with an acid, wherein the reaction mixture is subjected to high shear forces during precipitation in the alkaline medium by means of a continuously operating dispenser and/or rotary pump, through which the reaction medium passes with an hourly throughput frequency of at least 10 h-1. The mixture is advantageously subjected to shear forces during the flocculation phase over a period of 10 minutes. The precipitation process is carried out at 70-100 C., using concentrated acetic acid or acetic acid for the flocculation phase and sulphuric acid for the rest of the precipitation, the alkali number being kept constant at between 10 and 4. The precipitation suspension is adjusted to an end silica concentration of more than 65 g./l. The product is used as a matting agent for lacquers, in which it is dispersed by means of a high-speed stirrer. In an example, 10À8 g. of matting agent are added to 100 g. of a lacquer mixture comprising 700 parts polyester, 2 parts silicone oil, 60 parts polyvinyl acetate, 6 parts of cellulose acetobutyrate, 200 parts butyl acetate, 140 parts methyl glycol acetate, 200 parts of ethyl glycol acetate and 592 parts of "Shellsol" (Shellsol is a Registered Trade Mark) and 100 parts/200 parts of methoxy butylacetate. The mixture is stirred for 8 minutes with a high-speed mixer rotating at 2000 r.p.m. 50 g. of polyisocyanate are added to the mixture which is then diluted to a viscosity of 18 seconds with D.D. diluent. The lacquer is applied in layer thicknesses of 30- 40 Á.