TPE Overmolding Keeps Peeling Off? 3 Key Factors 90% of Factories Ignore

Time of issue:2026-07-16 20:18

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TPE Overmolding Keeps Peeling Off? 3 Key Factors 90% of Factories Ignore！

Overmolding Peeling Off? Process Tweaks and Mold Mods Didn't Work? Batch Rejections from Customers?
It’s Not a Lack of Effort—You Might Be Heading in the Wrong Direction from the Start.
1. Wrong Material Selection: Process Tweaks Are Pointless
This is the #1 misconception for 90% of factories: assuming all TPEs are the same. Completely wrong. The core of TPE overmolding is adhesion, and adhesion requires compatibility.
• Overmolding PP? You need a PP-based TPE.
• Overmolding ABS/PC? You need an SEBS-based TPE.
• Overmolding Nylon (PA)? You need a modified Nylon-based TPE.
Mismatched substrates are like oil and water; no amount of pressure will make them stick.

In our product line, we’ve specifically developed series for bonding PP, PC/ABS, and Nylon PA to solve this exact issue. Choosing the right material boosts your success rate from 50% to 90%.
2. Poor Temperature Control: No True "Fusion" at the Bonding Interface
Many factories inject TPE directly after molding the rigid part, simply copying the rigid plastic's temperature parameters. But TPE and rigid plastics have different melting points and injection temperatures.
For example:
• PP melts at around 160-170℃.
• SEBS-based TPEs are typically processed at 170-220℃.
If the TPE injection temperature is too low, the rigid plastic's surface won't be "melt-activated." The two layers will only physically touch, not chemically bond. Peeling off is inevitable.
Best Practices:
• The TPE injection temperature must exceed the rigid plastic's softening point by at least 10-20℃.
• Ensure the rigid part's surface is clean and oil-free before overmolding.
• Apply plasma treatment to the rigid surface when necessary to boost adhesion.
3. Mold Design Ignoring TPE’s "Elastic Nature"
TPE is not a rigid plastic; its flow behavior, shrinkage rate, and ejection requirements are completely different. Many factories design overmolds using rigid plastic logic, resulting in:
• Gates that are too small, causing high flow resistance and short shots.
• Insufficient venting, leading to gas traps, burn marks, and incomplete filling.
• Improper ejection methods, causing ejector pins to pierce the soft part.
Solutions:
• Increase gate sizes by 15%-30% compared to rigid plastics.
• Add venting slots (0.02-0.04mm deep) at weld lines and flow ends.
• Replace small ejector pins with large-area stripper plates or air ejection.
Summary
99% of weak TPE overmolding adhesion comes down to these 3 reasons:
① Wrong material → Choose a TPE matched to the substrate.
② Poor temperature → TPE temp must exceed the rigid plastic's softening point.
③ Unoptimized mold → Larger gates, proper venting, and gentle ejection.
Struggling with overmolding issues?
Tell us your specific situation—the substrate, hardness requirements, and application. Our expert team will help you pinpoint the perfect material solution.