UV Absorber Application Analysis in Polycarbonate

1. Application background

Polycarbonate (PC) is a high-performance engineering plastic with high transparency, impact resistance and heat resistance, widely used in automotive parts (such as lamp covers and windows), electronic device housings, optical lenses, medical devices and other fields. However, PC is prone to photo-degradation when exposed to ultraviolet light for a long time, manifesting as: yellowing—UV triggers molecular-chain scission, generating chromophores; decline in mechanical properties—reduced impact and tensile strength; surface powdering or cracking—structural damage caused by molecular-chain scission.

Adding ultraviolet absorbers (UVAs) is the core method to solve this problem.

2. Mechanism of ultraviolet absorbers

Ultraviolet absorbers selectively absorb ultraviolet light (usually 290-400 nm) and convert it into low-energy heat or harmless fluorescence, thereby blocking the photo-oxidation reaction. Common types include:

Benzotriazoles (such as Tinuvin 234, UV-327): efficiently absorb UV-A and UV-B, are heat-resistant, and suit PC processing temperatures (280-320°C).

Benzophenones (such as UV-531): lower cost, but may slightly affect PC transparency.

Triazines (such as Tinuvin 1577): broad-spectrum absorption, good migration resistance, suitable for high-weatherability requirements.

3. Key application points

(1) Additive selection

Compatibility: must be well compatible with the PC matrix to avoid blooming (benzotriazoles are more suitable for PC).

Heat stability: PC processing temperatures are high, so the absorber must be heat-resistant (e.g., Tinuvin 234 is stable at 300°C).

Synergistic effect: used in combination with hindered amine light stabilizers (HALS) to enhance long-term weatherability (HALS capture free radicals, UVAs block UV).

(2) Addition method

Internal addition: directly blended in during PC polymerization or processing, for uniform dispersion.

Surface coating: coat the PC surface with a UVA-containing coating (such as a UV-curable coating), suitable for already-molded products.

(3) Concentration control

Typical addition level: 0.1%-1% (too high may affect transparency or mechanical properties).

The concentration should be optimized through aging tests (such as QUV accelerated aging).

4. Practical application cases

Automotive: lamp covers, sunroofs, etc. using PC containing benzotriazole UVAs show 5-10 years improved weatherability.

Electronic devices: mobile-phone/laptop housings with added UVAs prevent yellowing and embrittlement.

Optical lenses: high-transparency PC lenses use a surface-coating + internal-addition combined solution, balancing scratch resistance and UV protection.