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An Overview of UV Curing

(December 2011) posted on Wed Jan 25, 2012


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By Screen Printing's Solution Sourcebook

UV technology gives screen printers the capability to print faster, more efficiently, and more accurately on a wide range of materials. But to realize the full benefits of UV, users must understand the nature of UV inks and the equipment required to cure them.

Resins give UV ink its major characteristics, such as adhesion and flexibility. Monomers are selected to dissolve the resins and pigments in the formula to a workable viscosity. They’re also selected to complement the resin in achieving the desired performance characteristics of cured or dry ink film. Additives contained in UV inks inlcude pigments (for color), flow agents, catalysts, and others. In UV inks, these catalysts are called photoinitiators. They absorb UV energy at certain wavelengths, creating free radicals that connect with the molecules of the resins and monomers and, in turn, cross-link with each other, forming chains of molecules we recognize as the cured ink film. Chemists call this cross-linking reaction polymerization. UV inks are considered 100% solids because almost everything in them is used up in the polymerization process.

One of the major advantages of UV over conventional inks is that no volatile organic compounds (VOCs) are released into the air during the curing process. In addition, UV curing relies on polymerization rather than evaporation, which means UV inks can be cured much more quickly and in less space than solvent-based inks. Finally, the lack of solvent in UV inks allows them to be used with higher mesh counts and support finer detail and higher print resolutions.

UV curing
The function of the curing unit is to deliver the UV energy that sets off the photoiniators and starts the polymerization process. However, before we ex-plore just how this energy is delivered, it might be beneficial to review the nature of electromagnetic energy. The UV range of the electromagnetic spectrum occurs at approximately 10-400 nm. The photoiniators used in UV inks typically react to specific wavelengths within the 200- to 400-nm range. However, the wavelengths that drive the curing reaction vary for different ink systems, which is why curing systems support different lamp types that deliver specific frequencies of UV energy.

