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How to Avoid Color Changes in Screen Printing

(November 2002) posted on Mon Dec 09, 2002

It's true: Colors do change with screen printing. Find out why and what you can do about it.

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By Carol Swift, Peter Kiddell

It's true: Colors do change with screen printing. Find out why and what you can do about it.

Our definition of printing is "replicating original artwork by laying down a controlled thickness of ink." Maintaining edge definition is also a key part of replicating original artwork, but controlling the thickness of the ink deposit is even more critical--and more difficult.

In graphics screen printing, ink-deposit thickness has a major effect on the color that will be visible to the viewer. In industrial printing, the ink-film thickness can affect the functionality of the print. This month, we'll focus on ink-deposit thickness in graphics applications by considering some of the variables you can control in your plant to reproduce color as consistently as possible. Our discussion won't address color separations or other artwork considerations, although these aspects of production obviously influence color, too.

Ink Condition

The ink is the most influential component in determining whether or not you can correctly match a color. The ink has to be correct at the start of the job, and it must stay that way throughout the run. If the ink contains any fluids that are likely to evaporate, the color can change as this evaporation occurs. The most obvious occurrences of this phenomenon happen with solvent-based ink systems. As the solvents evaporate from the ink on screen, the concentration of pigments in the ink increases, resulting in a color change. Inks containing water (conventional water-based inks and water-miscible UV formulations) are similarly affected, as are any inks that are dried and cured by heat/evaporation.

Because they are nonevaporative, pure UV inks and plastisols are the only ink systems that don't introduce this variable. However, the temperature during curing can affect the color of these inks, as we'll discuss later.

You can deal with ink-induced color shifts in a number of ways, but the two things that you don't want to do are add solvents to the ink on the screen, or remove ink from the screen and put it back in with freshly mixed ink. Both of these approaches are guaranteed to change the color of your prints. Treat any ink you remove from the screen as waste ink. This includes UV inks and plastisols, which may experience color shifting from dust and other contaminants they collect on the screen.

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