Guide to UV Measurement
Reactive Chemistry
The choice of reactive chemistry for a UV-curable formulation is the most important factor in determining the final properties of a product after cure. The chemistry chosen largely determines whether the final article is flexible or stiff, tacky or non-tacky, scratch- or solvent-resistant, etc. In addition, the chemistry determines the viscosity and other physical properties of the uncured formulation, which affects the ease with which the formulation can be run on printing or coating equipment. A UV-curable lithographic ink formulation requires a significantly different chemical composition than a UV-curable silicone release coat.
The simplest UV-curable formulation is a blend of reactive materials, called monomers and oligomers that are chosen to meet specific performance requirements when blended with one or more photoinitiators and exposed to an appropriate source of UV energy.
Reactive chemistries can be classified into two main categories that differ in the mechanism by which they polymerize: i) free radical and ii) cationic. Examples of chemistries that polymerize by a free radical mechanism include acrylates and methacrylates while epoxies and vinyl ethers undergo polymerization via a cationic mechanism. Hybrid systems in which both types of reactive chemistries are present in a single formulation also exist.
An in-depth review of the types of reactive chemistries and additives that can be used and the properties that can be achieved is beyond the scope of this CD. The interested reader can go to a number of excellent monographs and articles for more detailed information on the various chemistries available to the formulator.