Author Mike Thibault (Vice President of Technical Services for leading Canadian pressroom chemical manufacturer Unigraph International), has been at the forefront of solving printing quality issues and reducing downtime in pressrooms across North America for over 33 years. Here, he examines closely the common problem of roller glazing encountered by today’s press operators. If you’re a commercial printer, quick-print shop, digital printer, offset specialist, packaging printer, or any type of shop looking to save money and improve quality, you should read this.
Why do we continue to live with roller glazing problems? Are you using the right deglazer for today’s press problems? A good brand-name deglazer should do the job, right? Not necessary! With all the changes to paper in the last 15 to 20 years, it’s crucial to understand exactly what’s happening on press and what a deglazer should be doing for you.
Let’s examine glaze
It can form and accumulate from three primary sources:
- By-products from the fountain solution and/or an alcohol substitute
- Ink
- High-filler-content papers
…..or a combination of all three
A good deglazer should be able to clean what is water soluble (#1 and #3 above) and what is solvent soluble (#2 above). One of the biggest changes in our industry has been the introduction of alkaline-based paper to replace acid-based paper. There are many reasons for the change – from environmental concerns in paper making to an ongoing trend to increase sheet brightness. With these changes, commercial printers have also had to address many other issues.
Calcium carbonate
Here are some of the most common problems caused by high-filler-content papers (i.e. calcium carbonate):
- Plate blinding or ink walking off the plate (dot blowout)
- Premature plate wear
- Poor ink transfer down the ink train
- Inconsistent ink/water balance causing colour variations throughout the run
- Reduced drying time
- Hardening of rollers
- Premature roller wear
- Picture framing on the blanket, especially when running a short sheet
- Build-up on the impression cylinder
There’s really no way of stopping calcium from coming off the paper. Let’s review what happens as paper passes through your press:
- Calcium (whiteners, chalks and fillers) leaves the surface of the sheet and is released onto a humid blanket.
- From the blanket, it transfers to the plate and dissolves from a powder to a liquid because of the fountain solution on the plate.
- The liquefied calcium touches the dampener form and ink form rollers.
On the dampening side, it transfers from the dampener form back onto the pan roller and into the tray, and then back into the re-circulation unit. For those without a re-circulation unit, it sits in the tray and accumulates. On the ink side, it touches the ink form rollers and starts to contaminate the rollers all the way up the ink train. When the press is not running, the calcium in the rollers dries and then crystallizes.
What’s the result of all this? You now have a glaze that is locked into the pores of your rubber rollers due to the crystallization of the calcium. This hardens the rollers, causing not only a poor ink transfer (resulting in a low-quality print), but substantially decreases the life expectancy of your rollers. It also means that you’ll be spending hundreds or even thousands more dollars to replace your rollers, rather than “de-glaze” them or “rejuvenate” them for re-use.
The solution
Using a deglazer that has proven itself on press as part of a regular preventive maintenance program is the best possible solution. It’s really as simple as that.