I. Customer Needs and Background

The customer is a manufacturer of medical shoe insoles, and their core requirements are as follows:

• Low hardness (35A Shore A) Ensure foot comfort and reduce fatigue from prolonged wear.
• High resilience After prolonged stress (＞8 hours/day), the deformation is less than 5%, and the recovery rate exceeds 90%.
• Processing adaptability Suitable for 200℃ injection molding process, with short molding cycle and high yield rate.
• Weather resistance Tolerant to changes in temperature and humidity, with stable material performance.
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II. Development Process and Sample Validation

1. First-generation test material: ES35A-XND (baseline material)

• Formula Design ：
  • TPE matrix + silicone modifier, optimizing molecular chain flexibility.
  • Add a lightweight filler to achieve a specific gravity of 0.88 g/cm³.
• Performance performance ：
  • Hardness: 35A, tensile strength: 3 MPa, elongation at break: 580%; overall performance meets the standards.
  • The injection molding exhibits excellent flowability (melt index of 1.2 g/10 min), and the molded parts have a smooth, flawless surface.
• Test results ：
  • Simulated tread test (10,000 cycles): Deformation rate: 2.8%; Rebound rate: 96%.
  • Conclusion Initially meets the requirements, but the customer requests further optimization of costs and process stability.

2. First optimization trial sample: ES35A-01 (Result: NG)

• Adjust direction ：
  • Replace some of the high-cost silicone modifiers with low-cost plasticizers, aiming to reduce costs by 10%.
  • Adjust the filler ratio to reduce the target specific gravity to 0.85 g/cm³.
• Reason for failure ：
  • Flowability has decreased (melt index 0.8 g/10 min), resulting in insufficient injection molding fill and a yield rate dropping to 70%.
  • The hardness has increased to 38A, and the customer feedback indicates reduced foot fit.
  • The elongation at break has dropped to 520%, and the resilience fails to meet the standard.
• Conclusion Cost optimization comes at the expense of critical performance. NG 。

3. Second optimization test sample: ES35A-SL (Result: NG)

• Adjust direction ：
  • Add an anti-aging additive (UV-531) to enhance weather resistance.
  • Adjust the vulcanization system with the goal of enhancing long-term stability.
• Reason for failure ：
  • The uneven dispersion of the additive resulted in a tensile strength dropping to 2.4 MPa and a tear strength of 8.5 kN/m.
  • After the high-temperature and high-humidity test (60℃/95% RH, 500 h), microcracks appeared on the surface.
  • The injection molding process window has narrowed, requiring the temperature to be raised to 210℃, which in turn increases energy consumption.
• Conclusion : Weather resistance is improved, but mechanical properties and processability are deteriorated. NG 。

4. Baseline return plan: ES35A-XND (final OK)

• Improvement measures ：
  • Retain the original formulation and optimize the injection molding parameters (hold pressure time +10%, mold temperature +5℃).
  • Strengthen control over the stability of raw material batches and narrow the range of performance fluctuations.
• Verification results ：
  • Mass production yield has been increased to 98%, and the cost per unit has been reduced by 5% (through process optimization).
  • Customer’s actual test over 12 weeks: average daily usage of 8 hours, deformation rate of 4.7%, and recovery rate of 94%.
• Conclusion ： OK , passing final acceptance and entering mass production.

III. Key Issues and Solutions

 

IV. Case Summary and Value

1. Technical Insights ：
2. The development of TPE materials requires striking a balance among the “performance-cost-process” triad; optimizing along any single dimension alone can easily lead to systemic imbalance.
3. In the medical field, long-term reliability is given greater priority; material stability takes precedence over short-term cost advantages.
4. Commercial value ：
5. After the successful introduction of ES35A-XND, the customer’s order volume increased by 30%, and the product has expanded into the rehabilitation insole market.
6. Establish a “rapid trial-and-error—data feedback” model to shorten the development cycle of similar projects by 40%.
7. Follow-up plan ：
8. Develop the ES35A-XND Pro series, supporting customized hardness levels (30A-50A) and antibacterial functionality.
9. Explore supercritical foaming technology to further reduce material density (target: 0.80 g/cm³).