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Process-Color Pad Printing

(January 2002) posted on Wed Jan 30, 2002

The authors explain machine tolerances, color-separation quality, ink characteristics, and pad specifications.

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By Carol Swift, Peter Kiddell

Advances in inline screen-printing equipment now enable screen printers to produce large-format, process-color work with UV inks at rapid speeds. The new generation of presses generally meets very rigorous standards of accuracy and control, and printers who use them are profiting from the high image quality they provide on high-volume orders.

However, if you're thinking about adding a multicolor inline printing system to your operation, you'll need to consider more than just printing characteristics as you compare models. The UV-curing devices built into these systems can influence the machine's overall productivity, and should be carefully compared before you make a decision.

An inline press for process-color printing with UV inks has curing stations between each of the first three colors and a final curing station after the last color. The final curing station always consists of a conventional UV-curing unit. This curing system is used to saturate the completed print with UV energy, which helps ensure that all colors are properly cured and the ink film is firmly adhered to the surface. However, after each of the first three print stations, you have two types of UV-curing systems to choose from: flash (or pulse) or scanning systems.

Flash curing devices function similar to a flash bulb on a camera, using pulses of UV energy to cure the print. The UV energy that cures the print can be delivered in either a single, high-intensity pulse or a series of lower intensity pulses.

These systems generate minimal heat and consume less power than conventional UV-curing units. Printers generally can use flash-curing systems with their existing transparent process-color UV inks.

However, flash curing may not provide sufficient UV output to quickly cure spot colors, which have greater pigment density and require a higher level of photoinitiator, or colors printed on dark substrates. Using the flash-curing unit in such situations can slow production and lead to greater electrical costs.

Scanning involves a conventional UV lamp that is moved across the substrate and back again. The power consumption of such units is greater than with flash curing, but they can cure a broader range of inks. This means that with a scanning system, you aren't limited to using only transparent process-color inks.

We have clients who use both systems, and they are all very pleased with the results. And surely, the manufacturers of both systems will be able to bombard you with all the advantages of their product and the many disadvantages of their competitors' products. Just recognize that your choice could affect the overall performance and productivity of your inline printing system.

Before you accept a job for your four-color inline press, make sure that the ink color required for the job can be cured by the system you've chosen--you'll lose the benefit of having a high-speed, large-format press if you use inks that aren't appropriate.



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