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Pinning Inks with UV LEDs

(April 2012) posted on Tue Apr 17, 2012

How UV-LED is used to gel ink droplets

click an image below to view slideshow

By Paul Mills and Jennifer Heathcote

Drop gain
Just as it’s easier to shoot water from a squirt gun than it is cream cheese; thinner, less viscous inks jet more easily. UV jettable inks are typically in the 10-15 cP viscosity range and tend to spread more easily than thicker inks. Any number of formulating tweaks for color, gloss, or rheological properties can have unintended consequences when it comes to drop gain, and so there’s not likely to be a one-size-fits-all setting.
The substrate plays an equally important though often less predictable role in determining drop gain. While some materials absorb ink and have varying degrees of porosity, other materials present a slick surface making it easier for inks to spread around more easily. For example, coated papers designed to promote wetting also promote drop gain. With an ever expanding choice of paper and plastic films and the advent of variable data printing systems designed for small production runs on a range of parts, it is unrealistic to expect a “set it and forget it” solution.
Other nuts and bolts of the process also affect drop gain—such as the web or press speed, the distance from the print head to the substrate, and the local airflow, heat and humidity. In the end, a daunting combination of variables from ink to substrate to process requires a pinning system that can be quickly, but precisely fine tuned—sometimes color-by-color, to achieve the needed resolution. UV LEDs provide that level of simple, but effective control over the pinning process.


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