Genuine vs. False Overmolding in TPE Applications
Time of issue:2024-10-23
Genuine vs. False Overmolding in TPE Applications:
Based on the principles of overmolding, only materials with similar polarity can form a robust bond. True overmolding refers to the strong adhesion between TPE and hard plastics when their polarities are close. Currently, TPE can form true overmolding bonds with many types of plastics. False overmolding occurs when there is a significant difference in polarity between TPE and hard plastics, preventing the formation of a burn-off and mutual melting layer, thus offering no adhesion. However, special structural designs of the hard plastic parts, such as embedding features, can leverage physical and mechanical structures to improve the encapsulation strength of TPE over the hard plastic.
A Brief Analysis of Common Overmolding Defects:
1. Deformation of Hard Plastic Parts:
This can occur if the hard plastic part is thin, making it susceptible to deformation from the high temperatures during the secondary injection molding process. Additionally, if the soft overmold layer is thick and wraps around a narrow section, the contraction of the soft layer can cause the hard part to warp. Recommendations include optimizing gate placement and adding ribs to the hard plastic part in the mold design.
2. Insecure Local Overmolding:
This typically happens where the flow path of the molten material is long and far from the gate. Suggestions include raising the injection temperature appropriately, improving material flowability, and optimizing the gate design.
3. Bloom and Exudation in Overmolded Products:
This is usually due to issues with the compounding quality of the TPE material. It is recommended to optimize the compounding system.
4. Peeling and Delamination at the Gate:
This often occurs in parts with small gates and long flow paths. Typically, it results from inadequate compatibility of the materials, and the structure of the product tends to create strong shear forces at the gate, leading to delamination and peeling.
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