Common Problems in Transparent Plastic Injection Molding Process

Transparent plastics, because of their high transmittance, are bound to require strict surface quality of plastic products, and can not have any defects such as markings, pores, whitening, fog halo, black spots, discoloration, poor gloss, etc. Therefore, in the entire injection molding process, the design of raw materials, equipment, molds, and even products should be paid great attention to and put forward strict. To special requirements. Secondly, transparent plastics are mostly of high melting point and poor fluidity, so in order to ensure the surface quality of products, it is often necessary to have higher temperature, injection pressure, injection speed and other technological parameters should be fine-tuned, so that the injection molding can be full of 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 product raw material processing must be strictly operated.

1. The preparation and drying of raw materials may affect the transparency of the products because of any impurities in the plastics. Therefore, we must pay attention to sealing in the process of storage, transportation and feeding to ensure that the raw materials are clean. In particular, water is contained in raw materials, which causes deterioration of raw materials after heating, so it must be dried. For injection, the dry hopper must be used. It is also important to note that in the drying process, the input air should be filtered and dehumidified to ensure that the raw materials will not be polluted. The drying process is as follows: drying process of transparent plastics:

2.Cleaning of cylinder, screw and accessories

In order to prevent pollution of raw materials and the existence of used materials or impurities in the hollows of screw and accessories, especially the existence of resin with poor thermal stability, so before use and after shutdown, screw cleaners are used to clean the parts so that no impurities can be adhered to them. When there is no screw cleaner, the screw can be cleaned with PE, PS and other resins. When the temporary shutdown, in order to prevent the raw material staying at high temperature for a long time, causing a drop in dryer and barrel temperature should be reduced, such as PC, PMMA barrel temperature should be reduced to below 160 degrees Celsius (hopper temperature for PC should be reduced to below 100 degrees Celsius).

3. In mold design, attention should be paid (including product design) In order to prevent backflow obstruction, or uneven cooling resulting in poor plastic molding, surface defects and deformation, in general mold design, should pay attention to the following points:

1) the thickness of the wall should be as uniform as possible and the release angle should be large enough.

2) The transition part should be smooth, and gradually transition, to prevent sharp corners, sharp edges, especially PC products must not have a gap;

3) The gate and runner should be as wide and thick 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.

4) the surface of the mold should be smooth and low in roughness (well below 0.8).

5)vent hole. The tank must be sufficient to discharge the air and the gas in the melt in time.
6) except for PET, the wall thickness should not be too thin, generally not less than LMM.

4. The problems that should be paid attention to in injection molding process (including the requirements of injection molding machine) In order to reduce internal stress and surface quality defects, the following problems should be paid attention to in injection molding process:

1) special screw and injection molding machine with single temperature control nozzle should be selected.

2) the injection temperature should be relatively high when the plastic resin is not decomposed.

3) Injection pressure: generally higher to overcome the defect of high melt viscosity, but too high pressure will produce internal stress and cause difficult demoulding and deformation;

4) Injection speed: under the condition of satisfying filling mold, generally low, good can use slow one fast one slow multi-stage injection;

5)Pressure holding time and molding cycle: in order to meet the
requirements of product filling, no hollows, bubbles, should be as short as possible, in order to minimize the residence time of melt in the barrel;

6) Screw speed and back pressure: under the premise of meeting the plasticizing quality, should be as low as possible to prevent the possibility of release;

7) Mold temperature: the cooling quality of the products has a great impact on the quality, so the mold temperature must be able to accurately control its process, if possible, the mold temperature should be higher.

5. In order to prevent the deterioration of the upper surface quality, the mold release agent should be used as little as possible in general injection molding, and not more than 20% when the recycled material is used.

In addition to PET, the products should be post-processed to eliminate internal stress, PMMA should be 70-80t hot air cycle drying for 4 hours; PC should be in clean air, glycerin, liquid paraffin and other heating 110-135 degrees Celsius, time according to the product, high need more than 10 hours. PET must be subjected to biaxial stretching to obtain good mechanical properties.


JasonMould Industrial Company Limited, established in 2010, is a leading injection moulding manufacturer in China. JasonMould specializes in plastic mould production for household appliances, medical equipments, electronic equipments, safety equipments as well as monitoring system.
The company has over 15000 square metres factory. With plastic injection tooling divisions possessing different machinery and expertise, JasonMould offers tools from small and precise mobile phone parts to as big as automotive parts. Our tools are mainly exported to U.S.A., Europe, Japan and UK. JasonMould’s diversification strategy and full service has won compliment from customers all over the world.
Our mission is to provide our customers high quality moulding products and services. We aim to exceed our customers’ expectations of pricing, quality and on-time delivery. To achieve our mission, JasonMould:
Commits to continually improve employee skills and efficiency,
Provides our employees a clean and safe working environment,
Upgrades machine technology and support equipment through a strict maintenance program, and
Maintains customers’ tooling to its highest peak of performance
For more about custom manufacturer of plastic molding products,please visit
Inquiry Contact:
Contact person: James Yuan
Company name: JasonMould Industrial Company Limited
Address: LongGang Village,LongXi Town,BoLuo County,HuiZhou City,GuangDong Province, China
Telephone: 86-752-6682869
Email: [email protected]

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