New Breakthrough in Eyeglass Manufacturing: Application Example of TPE Material RN35A-YJK in Low-Hardness Overmolding
Time of issue:2026-03-06
I. Project Background
We recently received a customer request: their product’s temple arms need to be coated with a low-hardness elastomeric material that must bond firmly to the PC substrate while also providing a soft and comfortable tactile feel. The customer’s original solution suffered from poor adhesion of the coating and an unsatisfactory hand feel, resulting in a low yield rate. They urgently require a TPE/TPR material that strikes a balance among moldability, coating performance, and tactile comfort.
II. Analysis of Technical Challenges
- Balancing Low Hardness with Encapsulating Performance
Low-hardness TPEs (typically with a Shore A rating of ≤ 50) exhibit high flowability, but they are prone to issues such as flash formation or weak weld lines during overmolding. It is essential to ensure that the material maintains an appropriate viscosity at an injection molding temperature of 200℃—enabling it to fill precision molds without inducing stress cracking in the PC substrate. - Reliability of rubber-coated PC
PC is a polar material, and TPE must incorporate specific polar functional groups or be formulated accordingly to achieve interfacial adhesion and prevent delamination. - Weather resistance and tactile requirements
Glasses need to be in long-term contact with sweat and ultraviolet rays; the materials must resist yellowing and aging, and the surface should feel smooth and silky to the touch, avoiding any sticky sensation.
III. Material Recommendations and Validation
Based on the above requirements, we recommend the self-developed... RN35A-YJK Modified TPE Material , its characteristics are as follows:
- Hardness and Fluidity Shore A 44 combines low hardness with high flowability, making it ideal for thin-wall overmolding.
- Coating performance Through polarity-modified design, the peel strength with the PC substrate reaches... 2.8 N/mm (ASTM D903) No delamination was observed after undergoing cold and thermal shock testing (-20℃ to 60℃ cyclically).
- Molding process Suitable for injection molding at 200℃, with mold temperature controlled between 30 and 40℃, reducing the molding cycle by 15%.
- Weather resistance After 1000 hours of QUV aging test (ASTM G154), the color difference ΔE ≤ 1.5, and the surface shows no cracking.
- Haptic optimization Add a smoothness-enhancing additive system with a dynamic coefficient of friction ≤ 0.25 to prevent fingerprint residue.
IV. Customer Onboarding Process
- Internal testing
Conduct a PC substrate overmolding test using simulated customer molds, with a focus on verifying: - Flash issue: Optimize injection pressure and holding pressure time, and keep the flash width within 0.05 mm.
- Bond strength: The material penetration depth was confirmed to reach 5–8 μm through peel tests and microscopic examination of the interface.
- Customer pilot production
Provide RN35A-YJK samples for customers to conduct pilot production on their machines. Results: - Injection Molding Stability: Continuous production of 200 molds with dimensional tolerances of ±0.02 mm, no sticking to the mold or insufficient filling.
- Finished product testing: Lens leg bending test (±90°, 1,000 cycles) – no cracking; sweat resistance test (artificial sweat, 48 hours) – no discoloration.
V. Conclusion
Thanks to its low hardness, high fluidity, excellent PC encapsulation performance, and weather resistance, the RN35A-YJK successfully replaced the customer’s previous solution, enabling comfortable encapsulation of eyeglass temples and boosting product yield to over 98%. This case demonstrates the feasibility of TPE in precision encapsulation applications and provides a valuable reference for similar requirements.
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ADD: Huangxi Industrial Park, Shiwan Town, Boluo County, Huizhou City, Guangdong Province，China