MFDigital CD DVD Information Library
Wednesday, June 23, 2004
CD Manufacturing > Replication > Injection Moulding
Optical grade polycarbonate is 'baked' to remove any moisture and is injection moulded in a high pressure moulding machine (press) using the stamper mounted in the mould fixed to the press. This mould is in two parts and provides a cavity which ensures that perfectly moulded discs are produced with the correct dimensions every time. One half of the mould contains the stamper while the other half contains the mirror block to ensure a smooth surface.
The hydraulic press applies a force to the two halves of the mould which are closed. Molten polycarbonate is then injected into the cavity and held in place by the applied pressure while the disc cools and solidifies. Pressed discs, after cooling, are transferred by robot arms for the next stage in the process.
Successful moulding of CDs which meet the CD specification, require stable processes with the machines setup correctly. Moulding parameters which can affect the resultant CD include stamper geometry, mould temperature, polycarbonate temperature, compression force and cycle time.
Cycle times for injection moulding have decreased substantially from over 10 seconds some 10 years ago to under 4 seconds for the latest presses and moulds. Cycle times of under 3 seconds are also becoming possible.