Precise Mould Temperature Control
A new mould temperature control system permits production of optical discs with exceptional replication accuracy at very short cycle times. The wider process window simplifies production of HD-DVDs and Blu-ray Discs.
A new generation of optical storage media is just being introduced to the market: the new HD-DVD and Blu-ray Disc formats exceed the data capacity of previously employed DVDs by several fold. The higher data density also presents production systems with new challenges: the specifications can be met only through exact replication and minimal tolerances.
In this regard, mould temperature control during injection moulding is a decisive criterion. During injection, the mould temperature must be relatively high in order that the polycarbonate flows freely and precisely replicates the cavity. A few seconds later, the mould temperature should be cool in order that the just-moulded DVD can be ejected sooner.
Under the designation Dynamic Temperature Control (DTC), Krauss-Maffei offers a special mould temperature control system for disc production. Each mould half contains a set of cooling channels close to the cavity and another farther away from the cavity. The cooling channels close to the cavity permit a very rapid temperature change. The cooling channels farther away from the cavity keep the temperature level constant and serve as a reservoir for the rapid temperature change.
By changing between hot and cold in the cooling channels close to the cavity, a high surface temperature is achieved rapidly for injection and a low surface temperature for the cooling/ejection. The four sets of cooling channels are paired in mirror images. The decisive benefit here is that the temperature levels in the two mould halves equalise without any additional control means.
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