The Alkaline Paper Advocate

Volume 10, Number 4
1997


Calcium Control in the Pressroom

By Rick Hundal

Rick Hundal was a color pressman for 25 years, working for a number of North America's largest printing organizations, the most recent being Southam. He founded his own company, Graphics Associated, which provides capital equipment and printing rollers to printers as well as consulting services in the area of quality and process control.

© Rick Hundal, 1940 Limerick Place, North Vancouver, BC, V70 3A1, Canada (604/922-0414). Please acknowledge the source when quoting from this article. Permission is required to reprint in whole or in part.


Anybody who has run a printing press has noticed that every few years the nature of their printing problems would change. We used to joke that whenever we thought we had all the answers, something would change and this would impact everything else you were doing on the press. We would turn from confident know-it-alls into blithering idiots pacing around trying to figure out what happened.

The printing process is an extremely complex one with a large number of variables which need to be taken into account with each job you run. The pressman's job is to bring all these variables under control and produce a consistent printed product day after day. To do that we learn the proper way to operate and maintain our presses. We try to find the right mix of chemistry, blankets, inks, and plates. After many months, sometimes years, we arrive at that happy balance which is repeatable and consistent, the pressman's heaven. We can now confidently predict how long the job will take to run as well as how it will print.

This may last a week, a month, a year, and then something happens. Your colors don't show the same strength, your trap has changed, you can't keep your plates clean. Now comes the blithering idiot phase. You try to find out what has changed by checking all the variables, but nothing stands out. This can be very frustrating, but we need to understand that change is constant. We need to be constantly alert to subtle revisions being made to our printing process by the suppliers of paper, ink and chemistry.

Suppliers are constantly improving and changing their products with the hope of building a better mouse trap. What is often not understood by the suppliers is the impact of their revisions on the rest of the printing process.

In this article, I discuss one such change and its impact on the printing process. The paper on which we print is not what we are used to. Fifteen years ago, almost all the mills in North America produced paper using an acid process. Now, how-ever, most of the small and medium-sized mills that make printing paper use an alkaline process, and all but one or two of the major mills in the U.S. and Canada are 100% alkaline. Alkaline papermaking in North America is expected to grow until 90% or more of all mills produce nothing but alkaline paper.

The move from acid paper to alkaline paper is not an arbitrary one. Alkaline paper offers several advantages over acid paper: the process is less polluting to our environment, and the paper lasts longer. Calcium carbonate as a filler for alkaline paper is attractive to papermakers because paper made with it is brighter and more opaque than paper made with clay. Since brightness and opacity are signs of quality, the papermakers have no problem selling the paper. And calcium carbonate is much cheaper than titanium dioxide--another attractive feature.

For all its benefits, alkaline paper also creates a whole new set of printing parameters that you must learn to troubleshoot in order to produce top quality results. The primary problems you encounter are:

There are two fundamental reasons why these problems occur, the first being calcium carbonate in either its precipitated or its ground form. Calcium carbonate is used as a filler in alkaline paper as a replacement for the clay and titanium dioxide that are used in acid paper. It is the mildly alkaline papermaking in addition to calcium carbonate that gives alkaline paper its long life. Alkaline paper lasts about 300 years without becoming brittle, compared to about 25 years for normal acid paper. Unfortunately, calcium carbonate is also one of the causes of alkaline paper's printing problems.

Some calcium carbonate particles may be drawn out of the paper during the printing process. When this happens, the transparent particles, which have sizing particles attached to them, transfer to the upper form roller. Once there, they work into the ink and disperse throughout the moisture system and the ink train.

The second reason for the occurrence of problems is sizing. The discovery of special alkaline-compatible sizing systems made the production of alkaline paper a reality. But when the calcium carbonate/sizing particles come into contact with the ink, the sizing compounds sometimes activate the ink dryers prematurely, resulting in both ink feedback on metal-surfaced dampening rollers and a calcium glaze buildup on the blanket. Conventional blankets and roller washes will not remove this buildup.

In the attempt to come up with solutions, many people have gone to the grocery store for the magic solution. Some use vinegar and water, and others try Lime-Away. This is a dangerous practice, since these products have not been tested for safety with the rest of the chemicals used in the pressroom. They could have an adverse impact on rollers/plates/blankets or anything else that comes in contact with them. Don't forget, we are taking strong chemicals and throwing them on an open roller train where they will spray on plates, blankets and people. In addition, they are a blunt instrument compared to washes and etches now designed to control and remove calcium. (These washes and etches are, in some cases, ten times more effective than vinegar or Lime-Away.)

Pressroom chemicals have been tested for compatibility and safety of use. While calcium is a relatively new problem, many of the leading chemical suppliers have come up with calcium washes and a few have even developed fountain solutions which will trap the calcium, break it down and render it harmless. Talk to your chemistry supplier and ask him to provide a calcium wash. If they don't have one or don't know what you are talking about, maybe it's time to look for a new supplier.

What Uncontrolled Calcium Can Do to Presses

Let's look at what happens on press to create the problem. There are at least three sources of calcium on the press. In moderate amounts the calcium has very little effect on the press. We have always had calcium in certain process colors, red and blue being the worst. Artificial gums also contain significant amounts of calcium. This, combined with the calcium from alkaline paper, is enough to throw the calcium equation over the top and start the process of calcium accumulation. The calcium will collect in the fountain solution. It will travel to the plate and into the ink, where it will collect on the roller train. In sufficiently high amounts, here is what happens wherever it accumulates:

In the fountain solution: Calcium collected here will be distributed everywhere else. More importantly, the calcium will cause a shift in the pH of your fountain solution. This pH drift from acid to alkaline cannot be seen as a change in conductivity because calcium does not impact conductivity. Therefore, today's most common measure for fountain solution strength is totally useless in monitoring the problem.

As the pH shifts past 4.5 to 5.0 or higher, the gum in an acid etch becomes ineffective and unable to protect and desensitize the printing plate. This causes toning and extreme sensitivity of the plates during shutdowns. The gum arabic also cannot remain in solution as the pH shifts to neutral and precipitates in the roller train, causing roller glazing.

It happens this way: Initially, the pressman will turn up the water which, instead of cleaning up the plate, will break down the coating more quickly and increase the leaching effect. The pressman will eventually check his fountain solution, note that the pH is out of range, and will adjust his fountain solution to get the pH back to normal. This is the worst thing he can do. What happens is that the other active ingredients in fountain solution become more concentrated and the solution becomes very aggressive. Also, bringing the pH back to normal starts another round of calcium removal until the pH again shifts back to neutral, at which point the pressman adjusts the pH and so on. What he has started is a self-reinforcing process of removing calcium from the paper. This calcium coming from the paper in ever-increasing amounts starts to collect everywhere. It collects and distributes itself through the roller train and deposits on the plates and blankets.

On the plate: Since the gum is no longer active, it is not able to desensitize the plate, and the plate oxidizes. Even short press shutdowns create large amounts of waste because the plates won't clean up. The calcium will also deposit and collect in the grain of the plate, causing further pH drift right on the plate. The deeper the grain of the plate, the more likely it is that this will happen. You will have toning, and, as the calcium deposits in the grain of the plate, the plates will even start to pick up the image from the previous units and start to print that. Eventually you will be forced to replace the plates. In some cases on long runs, I have encountered plants which were having to replace their plates every four hours or less.

In the roller train: As the calcium builds up in the roller train, it will start to deposit on the rollers. It tends to collect on the outside distributors first and moves from there. The last rollers are usually the ink forms because the ink only stays on those rollers for a brief second before it is deposited on the plate. As the calcium builds up, the rollers lose their ability to carry ink and you will see the rollers start to strip. This will be more pronounced in the nonimage areas because very little ink is being removed from the rollers in those areas. If you clean the rollers very regularly and print short runs, the problem can be manageable, but if the runs are longer and you are not doing constant and daily roller maintenance, the problem becomes severe, as when running heatset webs. The calcium precipitates and hardens.

Web offset presses tend to run for longer periods without stopping. A press run of 100,000 copies is generally considered small for a web press. In many cases the press can run for many hours before being stopped for blanket cleaning, and roller cleaning is only done on long shutdowns or when changing colors.

While the precipitate is relatively easy to remove when fresh, after it has had time to harden, it becomes extremely difficult to remove. The only way I have managed to remove calcium at that point is by putting the roller on the bench and cleaning it with a calcium deglazer. This can take 30 minutes. Because the calcium penetrates right into the rubber and because it cannot be removed except on the surface, the calcium builds up quickly again, rendering the roller useless. At this point you might as well replace the roller. In one extreme case, the rollers were actually pitted, and every roller on the press had to be replaced. Subsequent tests showed the calcium had penetrated right to the core of the roller.

On the blanket: The calcium will also accumulate on the blanket in what is sometimes called milking. The calcium will build up in the nonimage area, creating a framing effect. This area will not transfer ink properly and will render a poor quality broken dot when printed. The image area will also have the buildup but less so. As the plates desensitize, you will pick up a backtrap image from the previous unit, which in extreme cases will start to print and appear on the plate.

The Solution to the Problem

It is important to attack the problem at its source and then to implement a procedure for press maintenance which removes whatever calcium does manage to get through.

Use a fountain solution that can handle calcium. Keeping the calcium from accumulating in the fountain solution eliminates a great part of the problem. Use conductivity as a measure to check fresh uncontaminated solution only. It is a highly accurate way to mix solutions once you have decided where you would like your pH to run, i.e., if 3 ounces per gallon gives you your desired pH of 4.5 and a conductivity reading for that mix of 1500, then you can accurately mix more fresh solution by looking for a conductivity of 1500 (assuming the water hasn't changed). Conductivity will give a more accurate mix because it will show the concentration of mix more readily than pH.

However, once the solution is put into your recirculator, the conductivity is irrelevant. Your solution could be loaded with calcium and show no change in conductivity. At this point, you should occasionally check pH using an instrument (not pH strips), looking for pH drift. If you start to notice pH drift along with print problems, you should seriously consider changing fountain solutions. There are many fine solutions out there, formulated not only to remove the calcium but to quench it and render it harmless.

A strong wash will not help. The tendency in the pressroom is to equate the effectiveness of washes with how strong they smell. The smell is an indication of the amount of aromatic solvents in a wash. These washes will have ZERO effect on calcium and will cause severe damage to your rollers.

Use the mildest washes possible. There are excellent ones out there. Your roller manufacturer can either supply one or recommend a safe roller wash to purchase. Wash up your presses regularly and then use a calcium deglazer to remove calcium. If the calcium has not been allowed to stay on press for many days, the calcium wash will suffice. For more severe buildup you will need to clean up by hand. After the cleanup with the calcium deglazer, it is very important to do a thorough water wash and then a final rinse with the roller wash. If you do not wash the rollers with water, the rollers will strip and will not carry ink. The same components in the deglazer that remove calcium will cause the rollers to become desensitized to ink unless they are completely removed.

Printers are Meeting the Challenge

While initially confused by the effects of the calcium carbonate in alkaline paper, the majority of printers are gradually emerging from the "What the heck happened?" phase, and adopting solid solutions to this problem.

Acknowledgments

This article is a compilation of my own research into the problem, but it also includes excellent information and research provided by Joe Williams of Rotadyne Rollers, GATF, Unigraph Chemistry and many, many pressmen who shared their problems with me. If it is inaccurate in a strictly scientific sense, I apologize for my lack of formal training in chemistry, but I can assure the reader it accurately reflects the problems faced by printers every day.

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Timestamp: Sunday, 03-Mar-2013 21:42:56 PST
Retrieved: Friday, 24-Nov-2017 14:40:25 GMT


[Search all CoOL documents]


URL: http://cool.conservation-us.org/byorg/abbey/ap/ap10/ap10-4/ap10-402.html
Timestamp: Sunday, 03-Mar-2013 21:42:56 PST
Retrieved: Friday, 24-Nov-2017 14:40:25 GMT