Why does color fade or change after injection molding and how to improve it?
Color changing or fading might happen sometimes during process. There are several causes.
If the color fades after injection molding, it is usually due to the temperature resistance problem of pigment. Make sure that you set up the process temperature at right range to avoid degradation of pigment. Consult your supplier about the temperature resistance of pigment.
If your material color turns more yellow tone than usual, please check the barrel temperature to avoid material degradation.
If you encounter color change, it might be contamination from residual material or pigment in the barrel or screw grooves. Make sure you purge the barrel completely clean before converting into different color batch. We suggest using Polypropylene to purge the barrel before using TPEs.
If you face problem of lighter color, the pigment might coat the feed section of screw.
Suggest using higher viscosity TPEs or higher concentrate of pigment. If problem continues, consider using masterbatch.
For more guidelines, please refer to our technical bulletins for more information or contact our representatives.
What is air trap and how to eliminate this problem?
Air trap is air that is caught inside the mold cavity. It becomes trapped by converging polymer melt fronts or because it failed to escape from the mold vents. Entrapped air will result in voids and bubbles inside the molded part, short shot (incomplete fill), or surface defects, such as blemishes or burn marks. Air trap locations are usually in areas that fill last.

Air trap can be eliminated by modifying the filling pattern by enlarging venting, by placing proper venting in the cavity or reducing injection speed so the air will have sufficient time to escape for the vents. Increasing the back pressure setting will make the melt denser and help remove gases and minimize trapped air volume.
What is delamination and how to eliminate it?
Delamination is a separation of the layers within a molded part. It can also appear as fish-scaling. There are several reasons that cause the problem. Normally it happens that the molten doesn't fuse properly before solidification. The material enters the cavity in layers. If the injection speed is too slow or the temperature is too low, the layers will solidify before they are packed and fused. Sometimes it is because the material is contaminated or with too much moisture.

To eliminate delamination, increase the injection speed, barrel temperature and maintain enough injection hold time. Dry the material according to the specification and select material from reliable suppliers.
How does jetting happen and how to improve this problem?
Jetting occurs when polymer melt is pushed at a high velocity through restrictive areas, such as nozzle, runner, or gate, into open, thicken area, without forming contact with the mold wall.

Remedies used to eliminate jetting are: reducing the melt velocity by adjusting the injection speed, enlarging the gate, and promoting the melt-mold contact by locating the gate in such a way that the flow is directed against a cavity wall.
Why does sink mark often occur in the molding with thicker section and how to improve it?
Sink marks and voids are caused by localized shrinkage of the material at thick sections without sufficient compensation when the part is cooling. After the material on the outside has cooled and solidified, the core material starts to cool. Its shrinkage pulls the surface of the main wall inward, causing a sink mark. If the skin is rigid enough, as in engineering resins, deformation of the skin may be replaced by formation of a void in the core.

Sink marks can be eliminated by decreasing the barrel temperature. Increase the amount of pressure or the time applied. Upon initial startup the mold should be filled incrementally starting with intentional short shots (if the mold design allows) and progressively increasing pressure shot-by-shot until the mold is filled and packed properly. If injection pressure and time are adequate the shrinkage should be uniform and consistent resulting in parts without sink marks.
Why short shot occurs and how to eliminate this problem?
A short shot is a molded part that is incomplete because insufficient material was injected into the mold. The reasons are entrapped air, insufficient machine injection pressure, insufficient injection speed, presence of oils or mold preservatives in the mold cavities, pre-mature solidification of the polymer melt, and machine defects.

Remedies to eliminate short shot problem is increasing the injection pressure, injection speed, injection volume and the mold wall temperature.
How does weld line occur and how to eliminate this problem?
A weld line is formed when separate melt fronts traveling in opposite directions meet. A meld line occurs if two emerging melt fronts flow parallel to each other and create a bond between them. The formation of weld and meld line can be caused by holes or inserts in the part, multi-gate cavity system, or variable wall thickness where hesitation or race tracking occurs.

Remedies can be increasing the size of gate and runners. Place a vent in the area of the weld/meld line to eliminate entrapped air which would further weaken the weld/meld-line strength. Increase the melt temperature, injection speed, or injection pressure.