List of TOPAS® COC grades

This page's PDF(2.41MB)

4. Molding conditions

4.3 Cylinder temperature

Optimum setting of cylinder temperature varies according to screw shape and heater position, but on a 25 mm diameter or less molding machine in particular, better-appearance samples can be obtained by setting hopper side temperature and nozzle side temperature identically. If cylinder temperature is too high, resin will deteriorate, causing discoloration, variations in cushion, fill ration, etc. On the contrary, if temperature is too low, instability of metering, mixing of some unmelted resin, etc., will occur.

4.4 Mold temperature

Standard mold temperatures for molding TOPAS® COC are as shown in Table 4-1, and it is necessary to search for an appropriate mold temperature in this setting temperature range according to the mold surface nature, mold release condition by shape, and required accuracy. For example, if the mold surface is coarse, temperature can be on the low side, while if the mold surface is very smooth, like an optical surface, temperature should be set on the high side for beautiful transfer of the molded product surface.

4.5 Injection pressure

Since flowability of TOPAS is good compared with general transparent materials, such as PMMA, PC, and COP, injection pressure needs to be set lower than them. If injection pressure is inappropriate, the following problems may occur.

• If injection pressure is too high: burrs, etc. will occur.
• If injection pressure is too low: short shots, sink marks, flow marks, voids, etc. will occur.

4.6 Injection speed

Injection speed should be determined in consideration of molded product shape, wall thickness, required quality, runner thickness, gate size, etc.

• High speed is advisable for: thin-walled molded products and multiple-cavity products of stringent dimensional accuracy.
• Low speed is advisable for: thick-walled molded products on which voids or flow marks will become a problem; e.g., lenses, etc., whose optical characteristics are important.

If injection speed is inappropriate, the following problems may occur.

• If injection speed is too high: jetting, flow marks, burrs, burn marks, etc., will occur.
• If injection speed is too low: sprue marks, poor appearance, short shots, flow marks, etc., will occur.

4.7 Screw rotation rate and back pressure

In order to obtain good-appearance molded products with TOPAS, it is necessary to raise screw rotation rate and lower back pressure. As a guide, set so that the following metering time results.

Injection stroke (mm) × (0.1 to 0.2) > Metering time (sec)

Make this setting by comprehensive judgment because it also has effects on stringiness, drooling, mixing of bubbles, etc.