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Do you know the injection moulding process of transparent plastic products?
- Dec 29, 2018 -

Transparent plastics, because of their high transmittance, are bound to require strict surface quality of plastic products, without any markings, blowhole and whitening. Fog halo, black spot, discoloration, poor gloss and other defects, so in the whole injection process for raw materials and equipment. The design of moulds and even products should pay great attention to and put forward strict and even special requirements.

Secondly, because transparent plastics have high melting point and poor fluidity, in order to ensure the surface quality of products, the process parameters such as machine temperature, injection pressure and injection speed should be adjusted slightly, so that the plastics can be filled with moulds, and internal stress will not occur, which will lead to product deformation and cracking. Therefore, strict operation should be carried out in terms of raw material preparation, equipment and mould requirements, injection molding process and raw material treatment of products.

1. The preparation and drying of materials may affect the transparency of products due to any impurities in plastics, so they can be stored and transported. In the process of feeding, attention must be paid to sealing to ensure that raw materials are clean. Especially when the raw material contains water, it will deteriorate after heating, so it must be dry, and when injection molding, the feeding must use the dry hopper.

Also note that in the drying process, the air input should be filtered and dehumidified to ensure that the raw materials are not polluted. For example, the drying process of transparent plastics: drying temperature (?) drying time (h) material layer thickness (mm) pmma70 ~ 802 ~ 430 ~ 40pc120 ~ 130 > 6 < 30 using hot air circulation drying pet140 ~ 1803 ~ 4 using continuous drying feeding device is preferred.

2. The cleaning of barrel, screw and its accessories is to prevent the pollution of raw materials and the existence of old materials or impurities in the holes of screw and accessories, especially the resin with poor thermal stability. Therefore, screw cleaning agents are used to clean all parts before and after use, so that impurities can not be adhered to them. When there is no screw cleaning agent, the screw can be cleaned with PE, PS and other resins.

When temporary shutdown occurs, in order to prevent material from staying at high temperature for a long time and causing degradation, the dryer and barrel temperature should be reduced, such as pc, PMMA and other barrel temperatures should be reduced to below 160 degrees. (hopper temperature for PC should be below 100 C)

3. The problems that should be paid attention to in die design (including product design) in order to prevent backflow impediment or poor plastic forming caused by uneven cooling, resulting in surface defects and deterioration, the following points should be paid attention to in die design.

A = The wall thickness should be uniform and uniform as far as possible, and the demoulding slope should be large enough.

B = The transition part should be gradual. Smooth transition to prevent sharp corners. Sharp edges, especially PC products, must not have gaps;

C= gate. The runner should be as wide and short as possible, and the gate position should be set according to the shrinkage and condensation process, and the material well should be cooled if necessary.

D = die surface should be smooth and low roughness (preferably less than 0.8);

E = vent. The tank must be sufficient to discharge air and gas from the melt in time.

F = Except pet, the wall thickness should not be too thin, generally not less than lmm.