Transparent plastic PC+gf products due to high light transmission, so of course PC+gf plastic products surface quality requirements are too strict, can not have any markings, pores, white, fog halo, black spots, discoloration, poor luster and other defects, so in the whole injection process of raw materials, equipment, mold, and even product design, We should pay great attention to and put forward strict and even special requirements.

In addition, because the transparent PC+gf plastic is mostly high melting point and poor fluidity, so in order to ensure the surface quality of the product, often need a higher temperature, injection pressure, injection speed and other process parameters should also be slightly adjusted, so that the injection of 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, injection molding process and raw material treatment of the product must be strictly operated.

First, the preparation and drying of raw materials

Because of any impurities contained in PC+gf plastic, it may affect the transparency of the product, so in the storage, transportation, feeding process must pay attention to sealing, to ensure the clean raw materials. Especially the raw materials contain water, heating will cause the deterioration of raw materials, so be sure to do drying treatment. When injection molding, adding material must use a dry hopper. It should also be noted that during the drying process, the input air should preferably be filtered and dehumidified, so as to ensure that it will not pollute the raw materials.

Two, barrel, screw and accessories cleaning

In order to prevent PC+gf raw material pollution and there are old materials or impurities in the screw and accessories depression, especially in the presence of resin with poor thermal stability, so before use, after the shutdown are used screw cleaning agent to clean each piece, so that it is not sticky impurities, when there is no screw cleaning agent, PE, PS and other resins can be used to clean screw.

When the temporary shutdown, in order to prevent the raw material from staying at high temperature for too long, causing the drop, the temperature of the dryer and barrel should be reduced, such as PC+gf, PMMA and other barrel temperatures should be reduced to below 160 бу C (hopper temperature for PC should be reduced to below 100 бу C).

Three, in the mold design should pay attention to the problem

a) wall thickness should be as uniform as possible, the demoulding slope should be large enough;

b) the transition part should be smooth, and gradually transition, to prevent sharp corners, sharp edges, especially PC+gf products must not have gaps;

c) gate and runner as wide and short as possible, and the gate position should be set according to the shrinkage condensation process, and the cooling well should be added if necessary;

d) the surface of the mold should be smooth and clean, with low roughness (preferably lower than 0.8);

e) exhaust hole. The slots must be sufficient to discharge air and gases from the melt in a timely manner;

f) In addition to PET, the wall thickness should not be too thin, generally not less than lmm.

Four, the injection molding process should pay attention to the problems

In order to reduce the internal stress and surface quality defects, in the injection molding process should pay attention to the following aspects of the problem.

a) Special screw, injection molding machine with a separate temperature control nozzle should be selected;

b) the injection temperature in the plastic resin does not decompose the premise, it is recommended to use relatively high injection humidity;

c) injection pressure: generally high, to overcome the large viscosity of the molten material defects, but the pressure is too high will produce internal stress resulting in difficult to release the meme and deformation;

d) Injection speed: in the case of meeting the mold filling, it is generally appropriate to be low, it is best to use slow one fast one slow multi-stage injection;

e) pressure holding time and molding cycle: in the case of meeting the filling of the product, without dents and bubbles; It should be as short as possible to minimize the time that the molten material stays in the barrel;

f) screw speed and back pressure: under the premise of meeting the plasticizing quality, it should be as low as possible to prevent the possibility of degradation;

g) mold temperature: the cooling of the product is good or bad, which has a great impact on the quality, so the mold temperature must be able to accurately control the process, if possible, the mold temperature should be higher.

Five, other aspects of the problem

Because in order to prevent the deterioration of the quality of the upper surface, the general injection molding should be used as little as possible release agent; When using recycled materials should not be greater than 20%.

For the exception of PET, products should be post-treated to eliminate internal stress, PMMA should be in 70-80t hot air circulation drying for 4 hours; PC should be heated at 110-135бц in clean air, glycerin, liquid paraffin, etc., the time depends on the product, the highest need for more than 10 hours. And PET must go through the bidirectional stretching process in order to get good mechanical properties.

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