Defining the optimum ink deposit for UV starts before the ink is applied

When analyzing the thousands of technical and customer service calls Sericol receives during the year, a vast number of these calls deal with problems relating to the proper deposit of UV inks.
UV ink technology provides many advantages over solvent-based ink systems, including: lower cost in use, faster production, more efficient use of space, better print definition and being more environmentally safe. These advantages lead to higher quality products in less time, which ultimately results in higher profits for the printer. However, due to the uniqueness of the technology, greater control in the process of application is necessary to fully achieve these advantages.
It does not take very long for a printer with years of experience and expertise in printing solvent-based inks to realize that the majority of techniques they have learned are not entirely applicable to UV technology. Sericol has identified six main areas that, with a little more careful attention and fine-tuning, can assist you in maximizing your UV investment return. In this issue we will address the first two areas, which are mesh and stencil selection.

Mesh-Finer Is Better
One of the biggest differences between solvent-based and UV inks is that UV ink is 100% solids. A solvent-based ink is generally 60%-75% solvent, so when it dries and the solvent evaporates, you are left with only solids, which are 25%-40% of the actual ink. Since UV ink is 100% solids, when it is cured you are left with what you printed. Therefore, UV inks require less wet ink deposit which leads us to the logical conclusion of a much finer mesh. In fact, even with a 390 mesh screen, the cured film deposit of UV ink will exceed that of a typical solvent-based ink printed through a 230 mesh screen. Because UV inks do not dry in the screen, screen preparation becomes a critical part of your process, even the finest pinholes will show up on your substrate.
To achieve quality lines and dot definition, we recommend that printers use UV ink through a 355 to 390 monofilament mesh, attempting to achieve a 0.5 mil deposit of ink. You can also use plain weave mesh instead of twill, which will result in even thinner deposits of wet ink film. All Sericol UV inks are manufactured to perform within these particular parameters.

Stencil Selection-Thin Is In
Whatever stencil type you are most comfortable using, always think less instead of more. A stencil that is too thick will result in poor curing and print quality, especially on those projects where small type and halftones are involved. When using conventional direct emulsions or a diazo-photopolymer emulsion, such as Dirasol 914, 911, or 905 Rapid, we recommend a thin film coating that would consist of 2-8 microns thicker than the mesh. You may also use a thin capillary film of about 18 microns. When using a direct emulsion, it is critical that the print surface is uniform and level. An uneven coating with low and high spots will produce changes in color density and will also affect proper curing. The ability to achieve stencil consistency using direct emulsions is affected by several key variables, including the type of emulsion, its chemical properties, number of coatings, coating technique, and the position of the screen during drying.