Transparent plastic due to high light transmittance, it must require strict surface quality requirements of plastic products, can not have any markings, pores, white. Fog halo, black spots, discoloration, poor luster and other defects, so in the whole injection molding process to raw materials, equipment.

Mold, and even product design, should pay great attention to and put forward strict and even special requirements. Secondly, because transparent plastics are mostly high melting point and poor fluidity, in order to ensure the surface quality of the product, it is often necessary to make subtle adjustments in the process parameters such as high temperature, injection pressure, injection speed, so that the injection of plastic can be filled with mold, and will not produce internal stress and cause product deformation and cracking.

Below on its raw material preparation, equipment and mold requirements, injection molding process and raw material treatment of products, talk about matters that should be paid attention to.

Raw material preparation and drying

Due to any impurities contained in the plastic, it may affect the transparency of the product, so and storage, transportation. During the feeding process, attention must be paid to sealing to ensure that the raw materials are clean.

Especially the raw materials contain water, after heating will cause the deterioration of raw materials, so be sure to dry, and in the injection molding, feeding must use a drying hopper. It should also be noted that during the drying process, the input air should best be filtered and dehumidified, so as to ensure that it will not pollute the raw materials.

barrel, screw and its accessories cleaning

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

When the temporary shutdown, in order to prevent the raw material from staying at high temperature for a long time, causing degradation, the temperature of the dryer and barrel should be reduced, such as PC, PMMA and other barrel temperatures should be reduced to below 160¡æ. (Hopper temperature for PC should be reduced to below 100¡æ)

Mold design (including product design)

In order to prevent the back flow is not smooth, or uneven cooling caused by poor plastic molding, surface defects and deterioration, generally in mold design, should pay attention to the following points:

The wall thickness should be as uniform as possible, and the demoulding inclination should be large enough;

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

gate. The runner should be 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;

Mold surface should be smooth, roughness is low (preferably less than 0.8);

vent hole. The slots must be sufficient to discharge air and gases in the melt in a timely manner;

In addition to PET, the wall thickness should not be too thin, generally not less than 1 mm.

Injection molding process and injection molding machine

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:

should choose a special screw, with a separate temperature control nozzle injection molding machine;

Injection temperature in the plastic resin does not decompose under the premise, it is appropriate to use higher injection humidity;

injection pressure: generally higher to overcome the defect of large viscosity of the molten material, but the pressure is too high will produce internal stress resulting in difficult demording and deformation;

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

pressure holding time and molding cycle: in the case of meeting the product filling mold, without depression and bubbles; It should be as short as possible to minimize the residence time of molten material in the barrel;

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;

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.

Other aspects of the problem

Because in order to prevent the deterioration of the quality of the upper surface, generally try to use less release agent when injection molding; When using recycled materials shall 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 in clean air, glycerin. Liquid paraffin and other heating 110-135¡æ, the time depends on the product, the highest need for more than 10 hours. And PET must go through the bidirectional drawing process in order to get good mechanical properties.

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