Common Problems Associated with Clear Injection Molded Plastics

Proper care and precision should be taken during the process of clear plastic moulding. This makes the process more complex compared with other colored parts. Some clear plastic moulding parts include PC, POM, ABS, PMMC, and PET. These clear plastic kits are used widely in medical devices, cosmetic packaging, food packs, water tank, car parts, and auto lights.

clear injection molded plastics

The mold design and injection molding are two factors that determine the outcome of your injection molding process. However, there are solutions to the common problems that occur during the clear plastic molding process.

Silver streak

This is common during the filling and cooling process due to expansion that may weaken the plastic parts. Annealing is one of the solutions since plastics in PC materials can be heated above 160 degrees for about 5mins and allowed to cool naturally. This procedure can eliminate the silver streak which occurs due to wet resin. However, it is crucial to ensure the resin is dry before processing.

Air bubble

clear plastic moulding

During the clear plastic molding process, the water and air in the resin can get trapped inside the cavity due to insufficient filling and excessive cooling, leading to a vacuum bubble. This problem can be solved by:
●Drying up the transparent plastic raw material before pouring them into the barrel. This can significantly reduce the air and water contained.
●Slow down the filling process and give some time to allow air escape.

Surface gloss defects

This is another common problem with clear plastic molding. It occurs when the mold surface is not well polished or cooled down too fast. This prevents the resin from getting into a molded state. To resolve this, the molding temperature and ejection pressure should be increased. The cooling time should also last longer.

Flow marks

Flow marks occur when the melt viscosity is too large, and the melt flow has been condensed in the cavity leaving the surface with flow marks. The best solution, in this case, is to optimize the melt flow, increase the mold temperature, and ejection pressure. Adding vents and using lubrication less frequently can also help.
To avoid a huge loss, manufacturers need to avoid the common problems in clear plastic molding. Any contamination of raw materials can also cause problems for the whole batch.
Here are some tips to ensure a quality batch of clear plastic molding products.

Choose the right mold steel for clear plastic molding

To get clear plastic parts, you need to reach mirror polishing on the cavity by choosing high-quality stainless steel for the cavity and core. Work with the right injection mold factory to make the mold for clear plastic molding.
It’s always best to work with a manufacture who has knowledge about clear plastic products. Your mold factory should also have vast experience sourcing the right goods and a good customer base to prove their best practices in purchasing materials.

Get the right draft angle for a clear plastic product.

You need sufficient draft for your clear plastic molding process to prevent scratches. If scratches occur, the injection-molded will need to be polished again and change the product design with a big draft. Only an experienced injection molder will have the foresight to know which draft is sufficient.

Reduce ribs on the design for easy mirror polishing

It may be challenging to polish the plastic ribs due to small gaps for polishing operators. Optimizing your plastic product design can reduce the ribs. When the ribs are thin, it is also easier for the resin to fill the gap to form the ribs.

Choose a suitable plastic injection machine

This goes without saying; the right plastic injection machine is crucial to a successful molding process. The injection screw can also affect the injection outcome. The smaller the injection screw, the more likely you are to have better results.
For thin wall clear plastic molding, it’s more beneficial to go with a high-speed injection machine. On the other hand, for a thick wall, it is preferable to use a hydraulic injection machine with a high servo motor and a small injection screw.
To get high-quality clear plastic molding parts, you also have to carry out your injection molding process in a cleanroom. To get the best results from your clear plastic molding process, it’s important to familiarize yourself with the best transparent plastic for your needs.


It is a popular plastic for outdoor equipment due to its UV resistance, clarity, scratch-proof and non-toxic features. During the injection molding process, acrylic can distribute addictive applications like colorants uniformly. Hence, it is widely chosen for items like colored lenses, reflectors, and light fixtures.
One major downside to this plastic material is that it cannot withstand high pressure due to its brittle and inflexible nature. It also absorbs moisture which is necessary for plastic drying.

High-density polyethylene (HDPE)

This popular thermoplastic is created by applying high heat and pressure to petroleum. Its UV-resistant nature and susceptibility to high-pressure damage make it similar to acrylic. It is inexpensive and can be molded into various parts. Hence, it is used in the mass production of bottles, containers, and pipes.


This is a much stronger and more expensive material with high impact resistance. However, it has similar features to acrylic in terms of UV resistance and transparency.
It is used in manufacturing items that undergo a lot of stress shields, helmets, safety windows, and heavy-duty containers. The downside of this material is that it can absorb moisture. So it’s important to dry the resin before the injection molding process.

Polyetherimide (PEI)

This plastic is widely used in industrial, mechanical, and chemical parts. It is strong, durable, UV resistant, and capable of withstanding extreme preside and heat. Many electrical, automobile, and medical items are made from this material.


It is one of the most flexible plastics ideal for non-loading bearing parts. It is highly sourced in the textile industry to produce waterproof bags, gear, totes, etc. it is also used for electronics due to its high electrical resistance.
Finally, knowing the features of each material helps you make an informed choice. Remember, it is essential to work with the best plastic injection molding company. We can help you determine the right material for your clear plastic molding. For questions or inquires on clear plastic molding, contact us today.


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