Interference from Moisture Can Wash Out Your Image Quality

A printing defect will occur which is commonly referred to as Water Interference without balance

A printing defect will occur which is commonly referred to as Water Interference without balance

If you’ve been thinking about trying figure out why your printing doesn’t look as vibrant as you imagined, but don’t know much about it, relax for a moment . It’s easy to learn about what can go wrong, especially if you want to get to the bottom of it right away right away. Searching for the right answer is easy; if you don’t want to spend much time, but want an answer now, read on.

1. Ink and fountain solution mixing.

In both sheet fed and web printing, the interaction of ink, fountain solution and paper must be kept in proper balance or a printing defect will occur which is commonly referred to as Water Interference. Water Interference manifests itself as white specks in printing, and can originate from three different sources: Ink-Water Emulsification* Rates Paper- Receptivity to Water Fountain Solution– Wettability

* There are some arguments as to whether true H2O and ink emulsion is attained in offset printing. For the purpose of this discussion, we will be using the term Emulsification ‘to describe inks and fountain solution mixing. The three characteristic H2O pick-up curves of inks, according to Surland. (Sun Chemical Corp.)

2. Ink and Water Emulsification

See how Emulsified Ink & Water Affect Print

See how Emulsified Ink & Water Affect Print

Offset inks are formulated to pick up and emulsify an amount of “water” that will:

1) Allow the inks and plate to print a sharp dot with minimal dot gain.

2) Allow a quantity of fountain solution to be run on press which will keep the non-image areas of the plate running clean and free of scumming and tinting.

3) Allow the ink to remain “lubricated” to run through the multiple units on a printing press.

4) Allow the ink to release the H2O for proper drying in the sheet fed lifts, or in the web ovens.

According to Surland (Sun Chemical Corp.), inks have three (3) characteristic water emulsification curves. (Figure 2) Ink #1 continually picks up H2O. Ink #2 has what has been described as an “ideal” curve in that it picks up a volume of H2O initially, reaches equilibrium, and can print a sharp dot. Ink #3 lacks the ability to pick up H2O. This ink will carry excess water on its surface and can result in Water Interference.

Ink’s Effect in Water Interference

Since the ink and H2O hit the paper simultaneously in the image area, the paper must have the capacity to accept both ink and water.

Diagram 3 depicts Ink #2

Which picks up the ideal amount of H2O. This inks will carry water to the paper on its surface as well as H2O emulsified in it. It should produce a dot which is sharp and clear.

If the paper cannot accept water, or if the inks are carrying an excess of water, then the result will be white specks where the water hits the paper first, and the inks will not transfer.

Diagram 4 depicts Ink #3

which lacks the ability to pick up water. Instead, it carries too much ‘free’ water on its surface and, when printed, results in broken dots and the appearance of white specks in the printed image.
How Ink is Effected by Water Interference

How Ink is Effected by Water Interference

3. Ink #2 which picks up the ‘idea!” amount of water. How ink #2 prints.

4. Ink #3 which lacks the ability to pick up water. How Ink #3 prints.
5. Diagram showing how the fountain solution on the non-image area from the 1st printing unit can interfere with the transfer of the ink in the 2nd printing unit.

When ink and water are balanced - Press is Normal

When ink and water are balanced - Press is Normal

Paper’s Effect in Water Interference

When the ink and water balance on press is normal, water interference can still occur if the paper is too watertight. That is, the water in the non-image area from a previous printing unit can remain in excess on the papers surface, and then interfere with the transfer of the subsequent colors. Figure 5 above demonstrates how the non-image area from the 1st printing unit (black) can remain on the surface of a water tight sheet and cause specks in the 2nd unit (cyan) print. Running minimum fountain solution or increased isopropyl alcohol can minimize this problem, and running a different, more ‘water receptive” stock can often eliminate it.

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