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Solving Color Stability Issues for TPU Outdoor Parts During Prototype Testing
How we helped a German design studio overcome color stability challenges in TPU outdoor safety products through innovative material solutions and rigorous testing protocols.
Project Overview
A product designer from a professional German design studio approached us to assist in producing an outdoor safety product for their client in the European market. This project required a custom injection molding solution that ensured flexibility, waterproofing, and impact resistance, while maintaining high visibility through vibrant colors.
The designer had already completed the 3D modeling and appearance design. After receiving the design drawings, our engineering team immediately conducted a structural and process feasibility analysis. Structurally, the product was fully suitable for injection molding production.
Project Details
The Challenge
Color Challenge
To meet the functional and usage requirements, the designer decided—after consulting with us—to use TPU/TPE soft rubber material and requested a fluorescent orange color to enhance outdoor visibility.
Engineering Alert: Based on our extensive experience, fluorescent orange in TPU/TPE materials is highly susceptible to UV degradation and discoloration, making it unsuitable for long-term outdoor use.
Our Solution Process
Hypothesis Verification(Trial Production and Outdoor Testing):
To verify this risk, we decided to conduct a practical trial. Using one of our existing TPU soft rubber molds, we produced a small batch of fluorescent orange TPU samples and carried out outdoor exposure testing.
Test Results
During testing, the results confirmed our engineers' prediction — the color changed noticeably within a short time, showing fading and slight shade variation.
Solutions and Implementation Steps:
① Pause Formal Tooling — Solve the Problem First
We advised the client to postpone formal mold development and production while conducting a detailed analysis of the pigment system and dispersion process. This step reflects our standard practice as a custom mold maker that values process stability before scaling up.
② Technical Solution: TPU Masterbatch Analysis
Advantages:
- Pre-dispersed pigments prevent clumping
- Improved dispersion uniformity
- Enhanced weather resistance
Limitations:
- High MOQ requirements
- Expensive for small batches
- Not economical for initial orders
③ Optimization Direction: Color System Adjustment
After engineering evaluation, adjusting the color system was more practical and economical than using masterbatch for cost-conscious clients who still needed weather resistance.
Final Solution
Since fluorescent orange belongs to a bright but unstable color system that easily degrades under UV exposure, we suggested switching to a light orange-red color as a compromise — it maintained good visibility while offering much better weather resistance.
Verification and Results:
Testing Success
We used our in-house TPU soft rubber mold for a second round of trial production and outdoor testing. The improved samples underwent 14 days of continuous outdoor exposure.
Fast Delivery:
After confirming the feasibility of the new solution, we immediately proceeded with tooling and production, quickly completing the small-batch samples in the new color. The samples were delivered on schedule, allowing the client to successfully exhibit the product at their European trade show — where it received highly positive feedback.
Root Cause Analysis
① Different Coloring Systems:
TPU soft rubber behaves very differently from hard plastics such as ABS or PC. TPU requires the use of special organic pigments for coloring, while hard plastics often use dyes that are more stable and less prone to fading.
② Fluorescent Pigments Are Difficult to Disperse
To achieve the original bright fluorescent orange effect, a significantly higher pigment loading (10–20× that of regular colors) is required. Such high concentrations are extremely difficult to disperse evenly in TPU.
③ Incompatibility of Pigments and TPU
Even fluorescent pigments developed for hard plastics are poorly compatible with TPU. During outdoor use, fading, surface discoloration, and gloss loss can be clearly observed after just 10–15 days of exposure.
Key Outcomes & Benefits
Risk Prevention
Through in-depth analysis during the prototype phase, we helped identify potential risks early on — effectively avoiding large-scale scrap and production loss in later stages.
Cost & Time Optimization
This proactive process streamlined the overall project schedule and significantly reduced costs by minimizing mold revisions and preventing material waste.
Client Insight
"Throughout the collaboration, the designer realized a key insight — involving an experienced injection mold manufacturer at the early stage of product development is often the key to ensuring a smooth transition from design to reality. Early collaboration not only makes the design more practical for production but also prevents many potential process issues."
About ZetarMold
ZetarMold is a professional China injection mold and plastic injection manufacturers group with strong capabilities in custom molded plastic parts, plastic part production, and injection molding mold making.
Our Expertise
- Over 20 years cross-industry experience
- Consumer electronics to industrial components
- Flexible materials to high-performance plastics
Our Approach
- Material consultation & process analysis
- Structural optimization support
- Early problem identification
We are not just a plastic product supplier, but a partner in design realization. Our goal is to enable ideas to land faster and help products reach the market more efficiently.
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