Mastering
This is when the nickel matrix is created, which is removed from the glass and creates the basis for further production stages. In addition, the final matrix is subjected to a wide range of tests. It is checked for mechanical faults and other defects.
Mastering itself may be divided into two processes – preparation of the glass and galvanisation treatment. We can also differentiate between the stages of glass preparation – glassmastering, optical verification and testing of the glass. However the galvanisation treatment consists of a galvanisation process itself i.e. matrix creation and the process of cleaning matrix surface as well as mechanical processing of matrix.
One of the most important stages not just of mastering but of the entire process of pressing and of the final result is the creation of a matrix on the so-called glass master (glass disc), popularly referred to as glassmastering. Its creation consists of glue, which has previously been placed and dried onto the glass being covered with a fluidic photosensitive emulsion. After re-drying, this time of the emulsion, the information which is to be contained on the future disc is exposed onto it with the aid of a laser beam. The exposed emulsion is developed. After washing of the photosensitive substance on the glass master there remain only the exposed layers of emulsion with data in the form of spirals. In order to harden the remaining layers of emulsion against metallisation, the glass is dried at a specialised workstation. A thin layer of silver is deposited on the glassmaster prepared in this method, aimed at preparing it for the electrolysis process (creation of layers which conduct electric current). In the future this metal will be replaced with a nickel-vanadium alloy which, thanks to its properties, will allow a more accurate reflection of the data.
The next phase in the mastering process is testing. The glass master for CDs is verified on the basis of its value and parameters, in the case of glass for DVD this is checked on thin glass specially designated for this purpose. Already at the mastering stage GM Records is concerned with the high quality of its services. We care about whether the customer will be satisfied with the finished product, and in this case with the precisely reflected data.
If there have been no defects discovered during the phases of the mastering process up to this point, and the result of tests is positive, then the glass master is subjected to galvanisation treatment which takes approximately 1 hour. During the electrolyte process a 0.3mm thick layer of nickel is deposited on the glass, on which the track of laser recording is reproduced. In further stages of media pressing, discs are replicated from the created nickel matrix from which the glass master is revealed. In the “family” process we can produce up to 10 matrixes from this matrix.
However, before we reach the process of pressing optical media itself, the nickel matrix is subjected to further cleaning. In the first instance it is soaked in sodium hydroxide through which an electric current is passed. This phase leads to the passivation of the silver, i.e. its blackening. Next the matrix is poured with a solution of ammonia, sodium hydroxide, 30% perhydrol (hydrogen peroxide solution) and deionised water (nuclear – applied in nuclear power stations to cool the rods). As an effect of this treatment, the matrix is cleaned of the base materials – silver, remnants of the glue and photosensitive emulsion. However, the final stage of cleaning is anodic passivation, during which all other remains are removed.
The matrix created is optically verified, the surface containing the data is varnished and subsequently mechanically processed. In order to obtain a perfect surface to fit closely to the forms of the injection moulding machine for replication, the matrix is polished. It is also centred and cut out in the required shape, more often than not a circle. The matrix ready for replication is pure nickel, which is hard and demonstrates high heat resistance.
The life-span of one matrix for CDs is approx. 80 thousand items and more, whereas for DVD one matrix may serve the pressing of upwards of 40 thousand discs.