Photoinitiators for UV LED Curing

What are Photoinitiators?

A photoinitiator is a chemical compound used to activate a drying process (typically referred to as ‘curing’) for inks, coatings, and adhesives.  Photoinitiators are designed to react to specific wavelengths of light, primarily in the UV range. When the photoinitiator is exposed to the right wavelength of light, it releases free radicals which initiate cross-linking with binders (monomers and oligomers) in a photopolymerization reaction. This reaction results in a hardened (or cured) material. UV material formulations also incorporate various additives such as stabilizers, wetting agents, adhesion promoters, defoamers and pigments to provide desirable characteristics or color of the cured material.

Photoinitiator Types

Selecting a suitable photoinitiator, or a combination of photoinitiators, is essential to achieve the expected speed and result of the cure. Photoinitiators are generally divided into two types:

  • Type 1 — Free-radical photoinitiators: Photoinitiators that generate unimolecular free-radicals. No other compound is need for these photoinitiators to work, once the UV light has been absorbed.
  • Type 2 — Cationic photoinitiators: Photoinitiators that undergo a bimolecular reaction and require a co-initiator. After absorption of light, the photoinitiator with another molecule (a co-initiator) to create a reaction.

Numerous factors affect the photoinitiator selection process, including the properties of the ink, coating or adhesive, the substrate type, the wavelength of the UV LED light source, the required cure speed, other additives, and more.

Photoinitiator Uses

No matter what the UV LED curing application is, the photoinitiator is fundamental to obtaining the ideal cure. The best photoinitiator for UV LED curing depends on the application, whether curing for industrial and medical bonding and sealing, coatings, or printing for digital, screen and flexographic processes.