Process and apparatus for the preparation of polycarbonate
The invention relates to a process for the pretreatment of material surfaces in order to minimize the interaction between polycarbonate and metal and, in the processing and synthesis of polycarbonate, to obtain a high-quality polymer which in particular does not become discolored and is free of insoluble constituents.
1. A process for passivating the metal surface of an apparatus used for preparing or processing polycarbonates comprising the step of contacting said metal surface with a polycarbonate melt comprising one or more phosphorus compounds at least partly in the regions of said metal surface which are in contact with reagents.
2. The process of claim 1 , wherein said contacting is effected with said polycarbonate melt comprising one or more phosphorus compounds at a temperature in the range of from 280 to 480° C. with a residence time of from 1 to 24 hours.
3. The process of claim 1 , wherein the concentration of said one or more phosphorus compounds in said polycarbonate melt is in the range of from 0.1 g to 5000 g of phosphate per m 2 of metal surface.
4. The process of claim 1 , wherein said one or more phosphorus compounds are phosphoric acid or phosphoric acid derivatives or organic phosphate compounds.
5. The process of claim 1 , wherein said one or more phosphorus compounds is a phosphite or a phosphate.
6. The process of claim 1 , wherein said contacting is effected in the presence of an oxygen-containing gas or under inert gas.
7. The process of claim 1 , wherein said metal surface is thermally pretreated in an oxidizing atmosphere before the contacting with said polycarbonate melt comprising one or more phosphorus compounds.
8. An apparatus for preparing or processing of polycarbonates, wherein the metal surfaces used in the preparation or processing of said polycarbonates have been passivated according to the process of claim 1 .
9. A process for preparing polycarbonate comprising the step of obtaining polycarbonate via melt polycondensation of a bisphenol with a carbonate diester in the apparatus of claim 8 .
10. The process of claim 9 , wherein said bisphenol is bisphenol A.