What problems can rollers cause?
What problems can rollers cause?x_white
A worn out roller, a roller with damaged bearings, rollers set with too much pressure or, a roller that has not been properly cleaned, can cause:
- color inconsistency
- poor solids, or mottling
- streaks
- dirty print
- excessive dot gain
Besides the obvious costs of poor print quality, including wasted paper and ink, bad or poorly maintained rollers can cause excessive press downtime, increased running costs, and shorter roller life.
Many times the problems caused by bad rollers are blamed on other factors. Or worse, pressmen accept them as inevitable and “learn to live with it” by making frequent adjustments, using extra ink or fountain solution, or throwing out a lot of spoiled paper. The good news is that using the proper rollers, and using them correctly, can eliminate many of these problems. When a press is fitted with high-quality rollers, and the rollers are properly set, cleaned and maintained, they can give months, even years of trouble-free printing and superior print results. You will notice, too, that you use less ink and fountain solution, less energy to run the presses, and waste less paper. And, the rollers may last two or three times longer.
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Anatomy of a Roller
What does the surface of a roller look like?x_white
If you look under a microscope at a new roller surface it looks very uneven, full of fingers and ridges and gorges, almost like saw tooth mountain ranges. This roughness is created when the roller is made and the rubber stretches and breaks around the grinding wheel. The “mountains” add enormous surface area to a roller—and they move. When looking at them under a microscope you can see the ridges. This rough surface carries ink and water, and the constant agitating motion of the fingers keeps the ink and water in a uniform emulsion.
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Contrary to what some people think, rollers do not have pores. Pores are holes surrounded by a rigid surface. The surface of a roller is continuous ridges and valleys and entirely flexible.

Nap
From our normal perspective this rough surface of a good roller is called the nap. A good nap is essential for good printing. You can test for sufficient nap by pushing your index finger away from you down the axis of the roller. If the roller catches your finger, it has nap and will print well.
Some rubber compounds have very little nap. If a roller is smooth out of the box, it’s a defective roller for offset.

Glaze

With use, rollers tend to get glazed, which means the mountains become filled and sealed with particles from the many inks and solutions that the roller is subject to.
Rollers that have no nap or are glazed will not be able to keep the ink and water uniformly emulsified. This can cause ink and water inbalance, color variation, and other problems. Think of it as trying to paint with a new brush as compared to an old dried paintbrush. The old paintbrush cannot possibly lay down a smooth layer of paint. Remember this the next time you are struggling with a glazed roller that is causing printing problems.
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What is roller glaze?
What is roller glaze?x_white
If the rollers look shiny and have a glassy feel to them, they are glazed. When rollers are glazed, the “fingers” in the rubber surface do not transfer ink effectively, which means you will need to run more ink and more water on the press to achieve the required ink densities. Higher levels of ink and water will result in dot gain, mottled solids, hickies, ink drying problems, reduced quality, and most likely, increases in your spoilage or unplanned waste.
Glaze is caused by the buildup of particles in the nap of the roller surface. See the Anatomy of a Roller for a detailed explanation and some great microscopic close-ups of roller nap.
One step in fighting glaze is proper cleaning. See Roller Cleaning for advice on the best technique.
But the first step is to use Böttcher’s glaze-free rollers. These rollers run much longer than conventional rollers without developing glaze, and they’re easier to clean.
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