On a Sprue System Forming the Central Hole at Injection Moulding of Optical Disks Substrates
Dimiter Trifonov, Nikolai Tzonev, Ognian Tzarnoretchki
Institute of Information Technologies, 1113 Sofia
A constructive design is proposed of the sprue system at injection moulding of optical disks substrates with the possibility to obtain the substrate central hole avoiding gate punching. The design is based on the alteration of the gate location with respect to the central hole and the mold spreading perpendicularly to the substrate surface. This enables the complete formation of the central hole during the time of melt filling, which removes the need of a punching system. The construction enables the use of a maximally open gate depending on the engineer preferences, which is a prerequisite for optimization of the process of sprue system melt filling and for products with lower internal tensions, and hence, lower level of the basic criterion for substrates quality - birefringence.
Keywords: optical disks substrates, sprue system, central hole formation.