UV Absorber Application Analysis in Polycarbonate

1. Application background

Polycarbonate (PC) is a high-performance engineering plastic featuring high transparency, impact resistance and heat resistance, and is 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, which manifests as:

• Yellowing: ultraviolet light triggers the scission of molecular chains and generates chromophores.

• Decline in mechanical properties: impact strength and tensile strength decrease.

• Surface powdering or cracking: structural damage caused by the scission of molecular chains.

Adding ultraviolet absorbers (UVAs) is the core method for solving this problem.

2. Mechanism of action of ultraviolet absorbers

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

• Benzotriazoles (such as Tinuvin 234 and UV-327): highly efficient absorption of UV-A and UV-B, high temperature resistance, and suitable for the PC processing temperature (280-320°C).

• Benzophenones (such as UV-531): relatively low cost, but may slightly affect the transparency of PC.

• Triazines (such as Tinuvin 1577): broad-spectrum absorption and good migration resistance, suitable for scenarios requiring high weathering resistance.

3. Key application points

(1) Selection of additives

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

• Thermal stability: the PC processing temperature is high, so the absorber must be heat-resistant (for example, Tinuvin 234 is stable at 300°C).

• Synergistic effect: when used in combination with hindered amine light stabilizers (HALS), long-term weathering resistance can be enhanced (HALS capture free radicals, while UVAs block ultraviolet light).

(2) Method of addition

• Internal addition: directly blended in during the polymerization or processing of PC, with uniform dispersion.

• Surface coating: a coating containing UVAs (such as a UV-curing coating) is applied to the PC surface, which is suitable for already formed products.

(3) Concentration control

• Typical addition level: 0.1%-1% (excessive amounts may affect transparency or mechanical properties).

• The concentration needs to be optimized through aging tests (such as QUV accelerated aging).

4. Practical application cases

• Automotive field: PC containing benzotriazole UVAs is used in lamp covers, sunroofs and the like, with weathering resistance improved by 5-10 years.

• Electronic devices: UVAs are added to the housings of mobile phones and laptop computers to prevent yellowing and embrittlement.

• Optical lenses: high-transparency PC lenses adopt a combined solution of surface coating plus internal addition, achieving both scratch resistance and UV resistance.