1. Injection Molding Machine

(1) Model selection standard

According to the product capacity to choose the appropriate size of the molding machine. If the molding machine is too large, the residence time of the molten resin becomes long, and resin carbonization and yellowing tend to occur.

(2) Screw design

The compression ratio is preferably about 2, which is relatively low, and molding is possible even if it is set to 2.5.

When plasticizing, if the shear stress is large, the resin is prone to discoloration or mixing with black spots.

(3) Material of screw and barrel

Coatings with poor adhesion to molten resin are recommended.

In addition to chromium plating, TiN, TiCN, TiC, W2C and other coatings also have good results.

(4) Nozzle

Both open and closed nozzles can be used.

2. Mold design

(1) Basic structure

The mold design is based on 0.6% of the mold shrinkage, please fine-tune it later. In addition, in consideration of the mold shrinkage, the mold release angle should be set to 2 ° or more.

The COC material is a resin having high rigidity and low tensile strength, and is not suitable for the groove shape because it causes cracks in the molded part.

(2) the material of the mold

Full mirror grinding is possible.

(3) Gate, runner, runner

The same shape as the conventional resin design can be used.

The advantage of the point gate is that the gate part of the molded part is not easy to remain internal stress, and the gate part of the molded part does not need finishing treatment.

The resin retained in the hot runner is easy to cause black spots or scorch and discoloration, so it is recommended to use the cold runner.

The circular runner is the best choice.

(4) Exhaust

You can also exhaust from the position of the parting surface. If you find gas lines caused by gas, you need to open an exhaust groove with a depth of about 0.02mm.

(5) Preventing wire drawing

If the nozzle temperature is high, wire drawing may occur. The runner design with the function of preventing wire drawing can effectively prevent wire drawing.

3. Injection molding process

(1) Pre-drying

It is recommended to pre-dry the granular material.

The COC material is a low hygroscopic resin and can be molded even without pre-drying. However, when a trace amount of moisture is attached to the surface of the granular material, it may affect the appearance of the molded part. In addition, due to the particle material dissolved in the air, sometimes cause yellowing, or dissolved air gasification and lead to poor transfer. Therefore, when the appearance requirements are high, pre-drying is an effective method.

Pellet preheating is also effective for the successful completion of molding and plasticization.

Drying conditions: 100-120 degrees 6 hours

(2) Material clearing

When changing materials, please use 3~5kg of commercially available cleaning granules or polypropylene (homopolymer type) matching the molding temperature for cleaning, and then change to COC. After replacement, use 2 ~ 3kg COC for material cleaning. Please make sure that the molded parts after material cleaning are free from turbidity or air lines.

Even if it still cannot be cleaned, glass fiber reinforced PP can be used as the material or the screw can be drawn out for cleaning.

(3) Forming conditions

Barrel temperature:The heat resistance of the material varies depending on the variety. Please set it according to the variety used and according to the following formula.

Barrel temperature = softening temperature of COC (TMA value) +100~130 ℃

Except for the lower part of the hopper, the temperature setting of each barrel should be basically the same.

If the set temperature is too low, abnormal sound sometimes occurs in the barrel. Please increase the temperature of the barrel at this time. In particular, the occurrence of abnormal sound can be effectively prevented by increasing the temperature on the hopper side (in front of the screw compression portion).

　　Mold temperature: COC materials are susceptible to mold temperature. The closer the mold temperature (measured value) is to the glass transition temperature (Tg) of the resin, the recommended temperature is Tg-15 to Tg-3 ℃ (measured value).

Back pressure: If the back pressure is too high, scorching or discoloration or gel may occur.

Injection pressure:

Set as low as possible in the range of 50 ~ 150MPa.

The material solidifies faster in the mold, and if the holding pressure is too high, it will cause problems such as cracking or stress deformation at the gate.

　　Ejection speed:Improve the shooting speed, can improve the product appearance effect.

　　Loosening: Loosening has the effect of preventing wire drawing, but loosening may cause bubbles or scorching due to air entering from the nozzle. When loosening and returning are necessary, please try to ensure the minimum loosening and returning amount.

Screw speed: If the speed is too high, there may be air bubbles and other phenomena involved.

(4) Shutdown for disposal

When the interruption time reaches more than 1 hour, please reduce the temperature of the cylinder to 170°C to prevent the resin in the cylinder from burning.

At the end of the run, switch off the heater after replacing the barrel with PP.