Transparent plastic injection molding process, do you know?

Transparent plastic as a result of high transmittance, the inevitable requirements for quality plastic products strict, can not have any markings, stomata, white. Fog halo, black spots, discoloration, poor gloss and other defects, so in the entire injection molding process on raw materials, equipment. Mold, and even product design, must pay great attention to and put forward strict or even special requirements.

Secondly, because transparent plastics are mostly high melting point and poor fluidity, in order to ensure the surface quality of products, It is often necessary to make subtle adjustments in the process parameters such as high machine temperature, injection pressure, injection speed, etc., so that the injection plastic can be filled with mold, and will not produce internal stress and cause product deformation and cracking. Therefore, from the raw material preparation, the equipment and mold requirements, the injection molding process and the raw material treatment of the product must be strictly operated.

1. Preparation and drying of the material Due to the inclusion of any impurities in the plastic, it may affect the transparency of the product, so it is easy to store and transport. During the feeding process, attention must be paid to sealing to ensure that the raw materials are clean. In particular, the raw material contains water, which will cause the raw material to deteriorate after heating, so it must be dried, and when injection molding, the feeding must use a dry hopper.

It should also be noted that during the drying process, the input air should preferably be filtered and dehumidified to ensure that the raw materials will not be contaminated. Its drying process such as, Drying process of transparent plastics: material processDrying temperature (°C) Drying time (h) Material layer thickness (mm) Remarks pmma70 ~ 802 ~ 430 ~ 40pc120 ~ 130 > 6 < 30 Adopt hot air circulation drying pet140 ~ 1803 ~ 4 Adopt continuous drying feeding device
2. The cleaning of cylinder, screw and its accessories to prevent raw material pollution and the existence of old materials or impurities in the sunken screw and accessories, especially the existence of resin with poor thermal stability, so that screw cleaning agent is used to clean each piece before and after use, so that it should not be stuck with impurities. When there is no screw cleaning agent, pe, ps and other resins can be used to clean the screw.

When temporary shutdown, in order to prevent the raw materials from staying at high temperature for a long time and cause the drop, the dryer and cylinder temperature should be reduced, such as pc, pmma and other cylinder temperature should be reduced to below 160 ℃. (hopper temperature should be reduced to below 100 ℃ for pc)

Third, the problems that should be paid attention to in die design (including product design) in order to prevent poor return flow, or uneven cooling caused by poor plastic molding, resulting in surface defects and deterioration, generally in die design, we should pay attention to the following points.

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

B = the transition component should be gradual. Smooth transition to prevent sharp corners. Sharp edge generation, especially pc products must not have a gap

C = gate. The flow channel is as wide and thick as possible, and the gate position should be set according to the shrinkage condensation process, and if necessary, the cold material well should be added.

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

E = exhaust holes. The tank must be sufficient to drain the gas from the air and melt in time

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