[0169] The substantial process parameters, such as ratio of diary 1 carbonate to dihydroxyary 1 compound at the beginning of the process, pressure, temperature and residence time should be chosen in the total plant before the final or finish reactor so that a molecular weight sufficient for the intended use of the product to be prepared and certain terminal OH group contents are reached before entry of the reaction melt into the final or finish reactor. The final molecular weight is dependent substantially on the chosen exit temperature of the reactor, the pressure and the terminal OH group concentra› tion. These conditions should therefore be chosen in the pen› ultimate reactor in order to be able to prepare the desired end product. The content of terminal OH groups in the polycar› bonates is preferably above 150 ppm, particularly preferably above 250 ppm, very particularly preferably above 350 ppm. A terminal OH group content between 150 and 750 ppm is particularly preferred, preferably between 250 and 650 ppm, particularly preferably between 350 and 600 ppm. 

[0170] In order to obtain a low content of residual mono› mers, the melt should be thoroughly mixed with at least one of the abovementioned suitable inhibitors before the finish reac› tor, preferably between penultimate and final reactor or before a devolatilization apparatus, in order to stop the reac› tion. The monomers can then be evaporated in the finish reactor ( or devolatilization apparatus). 

[0171] The polycarbonate prepared by the process accord› ing to the invention is suitable in particular for optionally rewritable optical data media having good coatability and wettability and little tendency to soiling. In addition, a low level of deposits on moulds or on the corresponding shaped articles or extrudates occurs during the processing of the polycarbonate to give shaped articles or extrudates. 

[0172] The polycarbonate prepared by the process accord› ing to the invention is also suitable for the production of injection moulded articles, which have surprisingly low val› ues for the electric field strength and high charge homogene› ity. For injection moulded articles which were produced by means of known injection processes without the use of ion› izers, for example, values in an acceptable range from -20 kV/m to +20 kV/m can be achieved for the average electric field strength and an average variation of the electric field strength ofless than 15 kV/m. 

[0173] Such polycarbonates prepared by means of melt transesterification methods have not been available to date and are not described in the literature. 

[0174] The invention therefore also relates to the polycar› bonates prepared from the process according to the invention. 

[0175] These polycarbonates preferably have a content of phenolic terminal OH groups of more than 150 ppm, prefer› ably more than 200 ppm, particularly preferably more than 250ppm. 

[0176] The amount of terminal OH groups can be deter› mined by NMR measurement, IR measurement or on-line IR measurement of the terminal OH groups. Furthermore, the OH groups can be determined photometrically. The IR method and the photometric method are described in Har› bach, A.; Veiel, U.; Wunderlich, H., Makromolekulare Che› mie [Macromolecular Chemistry] 1965, volume 88, pages 215-231. The values stated in connection with the invention for the content of phenolic OH groups were determined by means of IR measurement. 

[0177] Injection moulded bodies comprising conventional polycarbonate prepared by the melt transesterification pro› cess have the property of building up high and locally inho- 

mogeneous electric fields at the surface of the injection moul› ded article. Thus, for example, discs for optical data media comprising this polycarbonate build up a high electric field during their production in the injection moulding process. This high field strength on the substrate leads, for example, to the attraction of dust from the environment or to sticking of the injection moulded articles, for example discs, to one another, during the production of the optical data stores, which reduces the quality of the finished injection moulded articles and also makes the injection moulding process more complicated. 

[0178] Furthermore, the buildup of electrostatic charge, in particular on discs (for optical data media) leads to poor wettability especially with nonpolar media, such as, for example, a nonpolar dye or a dye coat comprising solvents, such as, for example, dibutyl ether, ethylcyclohexane, tet› rafluoropropanol, cyclohexane, methylcyclohexane or octafluoropropanol. Thus, a high buildup of electric charge on the surface of the substrate causes, for example, irregular and incomplete coating with dye during the dye application in the case of writable data stores and thus leads to defects in the information layer. 

[0179] It has been found that the polycarbonates according to the invention are particularly suitable for giving injection› moulded articles which, after a certain production period, do not exceed a certain electric field strength, measured at a defined distance from the substrate surface and at a defined temperature and atmospheric humidity. In order to achieve acceptable coating behaviour, it is desirable that an electric field strength of –20 kV/mis not exceeded after 2 hours of a continuous injection moulding process and the electrostatic field on the disc surface is very homogeneous, i.e. has little field strength variation. The values achieved for the polycar› bonates according to the invention for the average electric field strength are preferably from -20 to +20 kV/m and have a small field strength variation of less than 15 kV/m after 2 hours of a continuous injection moulding process. The values for the electric field strength are established in general within an hour and change only slightly or not at all thereafter per unit time. The abovementioned values of the electric field strength for the substrate materials according to the invention can also be achieved without the use of ionizers, so that the use of ionizers can be substantially reduced in the further processing of the polycarbonates. 

[0180] An injection moulded body comprising polycarbon› ate, such as, for example, an optical disc, having the above› mentioned properties with regard to the electric field strength is distinguished by good coatability with dyes. This is impor› tant for ensuring defect-free application of the writable layer and hence a trouble-free production process. This leads to a substantially reduced spoilage rate compared with conven› tional substrate materials. 

[0181] Owing to surface charges on the corresponding sub› strate, the electric field strength is dependent on the geometry and the dimensions of the injection moulded body and the type of injection moulding process. The measurement of the electric field strength should therefore be carried out on a finished injection moulded body, such as, for example, a disc for an optical data medium. 

[0182] The low values for the electric field strength are particularly surprising in view of the relatively high content of phenolic OH groups in the polycarbonates according to the invention. 

