5 TPE Molding Surface Defects and Fixes

When manufacturing Thermoplastic Elastomer (TPE) products with strict surface requirements, proper material preparation is non-negotiable. Before molding, TPE must be thoroughly dried to prevent moisture-related defects. You can check our full TPE molding processing guide for complete material pre-processing steps: TPR/TPE 사출 성형에 대한 종합 가이드: 공정, 파라미터 및 문제 해결

TPE Injection Molding

Recommended Drying Parameters:

Hopper Dryer: 70–80°C for 2 hours
Tray Dryer: 80–100°C for 1 hour (Note: Keep material layer thickness under 50mm. Tray drying is highly recommended).

? 전문가 팁: If you notice bubbles on the surface of the extruded strands, internal voids when cut, or radial silver streaks on the molded part, your TPE/TPR raw material contains too much moisture.

Even with proper drying, surface defects can occur. Below are the top 5 common TPE injection molding surface issues and expert solutions to resolve them.

Flow Marks

Flow marks appear as streaks with varying gloss levels on the molded surface. In resin injection molding, they typically manifest in three ways:

Narrow, closely spaced streaks.
Wider streaks with the same phase appearing vertically on the part.
Narrow streaks with different phases appearing vertically.

For more universal flow mark troubleshooting across all plastic resins, refer to our defect reference article: 16 Common Injection Molding Defects: Root Causes & Solutions

✅ Solutions: The most effective fixes include increasing the injection speed and raising the mold temperature. Other adjustments include adding pure monomer resin, enlarging the gate, increasing resin/molding temperatures, or in some cases, reducing the injection speed.

Poor Ejection (Demolding Issues)

Poor ejection occurs when the molded part is difficult to remove from the mold or deforms during extraction. This is especially common with tacky TPE materials. It can also be caused by insufficient cooling (incomplete solidification).

✅ Solutions:

Material & Mold: Add an internal mold release agent or apply an external release agent to the mold.
Cooling: Ensure adequate cooling time for complete solidification.
Mold Design: Increase the draft angle at the gate and widen the runner channel to prevent sticking. If you frequently struggle with stuck parts and ejection deformation, our dedicated ejection failure guide offers mold design and maintenance fixes: Injection Molding Ejection Problems, Solutions

Material Aging

Symptoms: Noticeable reduction in mechanical properties and degraded appearance. Cause: Compared to inorganic and metallic materials, polymers have lower heat and UV resistance, making them prone to aging over time.

✅ Solutions: Incorporate heat and weather-resistant stabilizers during compounding. Adding UV absorbers and light stabilizers can significantly inhibit the aging process.

Uneven Color Distribution

When using TPE pellets mixed with dry color masterbatch, color inconsistency is a frequent issue.

✅ Solutions: Increase the screw back pressure and enhance the mixing/kneading action during the plastication phase to ensure uniform pigment dispersion.

Blooming (Whitening)

Blooming occurs when additives (like stabilizers) migrate to the surface, creating a powdery white film. This is usually caused by excessive additive loading or poor compatibility with the polymer matrix.

✅ Solutions:

Select stabilizers with high compatibility with the base polymer.
Keep additive concentrations within the optimal range.
Upgrade to high-molecular-weight stabilizers, which are less prone to migration.
참고: For anti-static agents or lubricants designed to migrate, choose formulations that resist visible whitening. In harsh environments (high heat, humidity, outdoor exposure), adding specialized heat/weather stabilizers is crucial to prevent accelerated migration.

Quick Reference: TPE Surface Defects Cheat Sheet

Surface Defect	Primary Cause	Recommended Solution
Flow Marks	Improper flow dynamics or temperature	Increase injection speed & mold temp
Poor Ejection	Tacky material, poor cooling, or bad draft	Add release agent, increase draft angle
Aging	UV/Heat exposure degrading polymer	Add UV absorbers & heat stabilizers
Uneven Color	Poor pigment dispersion	Increase screw back pressure & mixing
Blooming	Additive migration / incompatibility	Use high-MW stabilizers, optimize dosage

저자 소개

Alex Yu

아이디얼 프로 매뉴팩처링

알렉스는 Ideal Pro의 공동 창립자이지만, 주요 프로젝트를 총괄하거나 기술 팀을 이끌지 않을 때는 장거리 자전거 타기를 즐기거나, 동네에서 가장 맛있는 커피를 찾아다니거나, 다음 여행 계획을 세우는 모습을 볼 수 있습니다. 국제 무역 영업과 프로젝트 관리 분야에서 20년 이상의 경력을 쌓아온 그는 촉박한 마감 기한부터 까다로운 엔지니어링 문제까지, 그 사이의 모든 상황을 다 겪어보았습니다. 그는 훌륭한 성과는 충분한 휴식을 취한 마음과 맛있는 커피에서 나온다고 믿으며, 맡은 모든 프로젝트에 그와 같은 호기심과 세심한 주의를 기울입니다. 사무실에 있지 않을 때는 대개 야외 어딘가에서 새로운 장소를 탐험하며, 나중에 나눌 이야기를 수집하곤 합니다.