This discussion centers on cost comparisons, challenges with UV inks, and how photoinitiators work.
By Gail Flower
Johnny Shell, Ray Greenwood, and Jeff Burton Moderately. LED is a new technology that has been recently incorporated into the industry. The cure parameters of the ink are more tuned to the light energy emitted with LED, so there is a smaller curing window. With traditional mercury-vapor systems, the cure window is wider that accommodates a wider range of UV raw materials in the formulation. The slow adoption rate for digital LED UV is due to issues with insufficient power output and problems achieving surface cure at production speeds. LED units are also expensive for integrating in wide-array applications.
Peter Saunders At Sun Chemical we have UV inks designed specifically for LED curing units in a variety of market industries, but the majority of LED lamps used today are in inkjet applications. SunJet, the inkjet ink division, is a leader in the development of UV curing inks and has supported the industry developments for several years. It was one of the first ink companies to recognize the potential benefits to customers of inks that have the ability to part cure or pin with UV LED lamp exposure in scanning head systems. SunJet has discovered a route in formulation that allows the increased response to LED UV output to be applied to a full range of SunJet ink families. This means that popular inksets can be used with the new LED lamp technology if correctly integrated. While inkjet is currently leading the way in LED usage right now, we expect increased usage of LED UV lamps as they are developed in screen printing.
What are photoinitiators and how do they work?
Bruce Ridge Photoinitiators are chemicals that are added to the inks that are sensitive to specific wavelengths in the electromagnetic spectrum. When these chemicals are exposed to that particular wavelength of energy, they will facilitate the cross linking of the molecules in the oligomers and monomers (the resin of the system) in the ink, which results in a polymer or cured ink film.
Larry Hettinger Photoinitiators are compounds that absorb light to generate free radicals. These free radicals then react with monomers and oligomers to initiate the polymerization chain reaction. The photoinitiator package of an ink can be specifically designed to optimize the cure of the ink vehicle and UV curing equipment.
Curt Baskin Photoinitiators are compounds that absorb the UV energy from the light source on a lamp head, causing a chemical reaction that converts the liquid ink in to a solid film.
Scott Schinlever Photoinitiators have the unique capability of initiating a chain polymerization reaction. This reaction is initiated by the absorption of UV radiation and has the result of linking/cross linking all of the polymer chains within the ink, transforming the ink from a liquid to a solid.
Steve Mitchell Once UV light hits an energy curable ink or coating film, photoinitiators are the items in the ink that get the reaction started to turn a wet ink film in to a dry, cured ink film.
Johnny Shell, Ray Greenwood, and Jeff Burton Photoinitiators are the magic components of UV ink. After absorbing UV energy from the curing lamps, the photo initiators fragment in to reactive materials that start the chemical reaction known as polymerization. The process converts the liquid ink into a solid film. The types of photoinitiators most commonly used in inkjet inks free-radical in nature. Ink formulators work with photoinitiator suppliers to develop inks that are compatible with the UV output of medium-pressure mercury-vapor bulbs found in most curing systems. Unfortunately, light sources often emit excessive IR energy, have high power consumption, and need routine lamp replacement.
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