Name: Photoinitiator TPO (Acylphosphine Oxide)
Brand: Coatingsink
SKU: photoinitiator-tpo
Availability: InStock

Question 1

Why is TPO preferred over benzophenone for white or pigmented UV coatings?

Accepted Answer

White pigments (especially TiO₂) strongly scatter and absorb UV light below 360 nm, drastically reducing the effective photon flux available to Type II initiators like benzophenone. TPO absorbs efficiently in the 370–420 nm range where TiO₂ is more transparent, allowing photons to penetrate deeper into the film. Its Type I α-cleavage mechanism also means TPO generates radicals autonomously without requiring a co-initiator, giving reliable through-cure in opaque, white, or high-build coatings.

Question 2

What is the bleaching behaviour of TPO and why does it matter for coatings formulation?

Accepted Answer

Upon UV exposure TPO undergoes α-cleavage and the resulting phosphinoyl and benzoyl radicals are colorless. This photoinitiated bleaching means that the characteristic pale yellow color of TPO in the uncured film disappears after cure, making it suitable for clear lacquers and near-white coatings where residual yellowness is unacceptable. The bleaching is substantially complete within the first few seconds of exposure under a medium-pressure mercury or LED (395 nm) lamp.

Question 3

Can TPO be used with LED UV lamps, and what lamp wavelength is recommended?

Accepted Answer

Yes. TPO is one of the few conventional photoinitiators with meaningful absorption at 385 nm and 395 nm, making it directly compatible with high-power UV LED arrays operating in the 385–405 nm range. For optimal efficiency, 395 nm LEDs are preferred over 365 nm units because the molar absorptivity of TPO is higher in the 375–400 nm window. In LED-UV formulations, TPO is often combined with TPO-L (the liquid ethyl ester analogue) to improve solubility and reduce surface bloom risk.

Purity	≥97.0%
Melting Point	88–92°C
Molecular Weight	348.4 g/mol
UV Absorption Max	~380 nm (extended to 420 nm)
Recommended Dosage	1–4%

Photoinitiator TPO (Acylphosphine Oxide)

Specifications

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