Transparent plastics because of high transmittance, the relative requirements of plastic products surface quality requirements are severe, can not have any markings, stomata, whitening. Fog halo, black spot, discoloration, poor gloss and other shortcomings, so in the entire injection process of information, equipment.

Mold, even product planning, must be very careful and put forward severe or even special requirements. Secondly, because transparent plastics have high melting point and poor activity, in order to ensure the surface quality of products, it is necessary to fine adjust the technological parameters such as machine temperature, injection pressure and injection speed, so that when plastics are injected, they can be filled with moulds, and internal stress will not occur, which will cause deformation and cracking of products.

The following is the preparation of the information. In terms of equipment and mould requirements, injection moulding process and product data processing, matters needing attention are discussed.

Preparation and monotony of data

Because any impurity in the plastic may affect the transparency of the product, and consequently storage and transportation. In the process of feeding, there is a need to pay attention to sealing to ensure that the information is clean.

In particular, the data contains moisture, which will cause data transformation after heating, so it is relatively monotonous. In injection moulding, monotonous hopper is needed for feeding. It is also important to note that in the monotonous process, the input air should be filtered and dehumidified to ensure that the data are not polluted.

Cleaning of barrel, screw and accessories

In order to avoid data contamination and the presence of old materials or impurities in the holes of screw and accessories, especially resin with poor thermal stability, screw cleaners are used to clean the parts before and after shutdown, so that impurities can not be adhered to them. When there is no screw cleaner, the screw can be cleaned with PE, PS and other resins.

When the machine is temporarily shut down, in order to avoid the data staying at high temperature for a long time and causing degradation, the temperature of monotone machine and barrel should be reduced, such as pc, PMMA and other barrel temperatures should be reduced to below 160 C. (hopper temperature for PC should be below 100 C)

Mold Planning (including Product Planning)

In order to avoid the appearance of inadequate return movement, or poor plastic forming caused by uneven cooling, surface defects and metamorphosis, the following points should be paid attention to in die planning:

The wall thickness should be as uniform as possible, and the demoulding slope should be satisfied.

The transition should be gradual. Oil slippery transition, avoid sharp corners. Sharp edges occur, especially PC products do not have gaps.

Gate. The runner may be as wide and short as possible, and the gate orientation should be set according to the shortening of condensation process, and the cooling well should be used when needed.

The surface of the die should be bright with low roughness (less than 0.8);

Vent hole. The groove has the requirement to satisfy, and the gas in the air and melt can be discharged in time.

Except for pet, the wall thickness should not be too thin, generally not less than 1 mm.

Injection Molding Technology and Injection Molding Machine

In order to reduce internal stress and surface quality shortcomings, attention should be paid to the following aspects in injection molding process:

Special screw and injection moulding machine with independent temperature control nozzle should be selected.

Under the premise that the plastic resin does not decompose, the injection temperature should be higher than the injection humidity.

Injection pressure: generally higher, to overcome the shortcomings of high melt viscosity, but too high pressure will occur internal stress to make demoulding difficult and deformation;

Injection speed: In the case of satisfactory filling, it is generally appropriate to lower, can choose slow one fast one slow multi-stage injection;

Pressure holding time and forming period: in the case of satisfying product filling without depression and bubbles, it should be as short as possible to minimize the residence time of melt in the barrel;

Screw speed and back pressure: On the premise of satisfactory plasticizing quality, it should be as low as possible to avoid the possibility of descent.

Mold temperature: The cooling quality of products has a great impact on the quality, so the mould temperature should be able to accurately control its process. If possible, the mould temperature should be higher.

Other aspects

Because in order to prevent the deterioration of the surface quality, the release agent should be used as little as possible in general injection moulding, and not more than 20% of the reusable material should be used.

With regard to all products except pet, post-treatment should be carried out to eliminate internal stress. PMMA should be circulated in 70-80t hot air for 4 hours, and PC should be in clean air and glycerol. Liquid paraffin and other heating 110-135 C, according to the product at any time, high demand more than 10 hours. Pet has to be biaxially stretched to obtain excellent mechanical properties.