Dear Gordo:
Thank you for your reply, can you explain to me in what way this calcium carbonate be giving us this problem and to overcome it.
The link I gave you lists the symptoms of calcium problems. If it sounds like this might be related to the problems you're having then here is some more detailed information:
You need to track down the source of the problem. There are three main sources of calcium in the pressroom; water, red and blue inks, and alkaline papers and coatings. Today, it's typically the paper that is the number one cause of the problem.
In small amounts the calcium has very little effect on the press, however if the sources combine then the effect starts the process of calcium accumulation. It will collect in the fountain solution, travel to the plate and into the ink, where it will collect on the roller train.
If calcium collects in the fountain solution it will be distributed everywhere else so you'll see calcium buildup and its effects on all units. It will also cause a drift in the pH of your fountain solution from acid to alkaline which won't be seen as a change in conductivity because calcium does not impact conductivity.
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. The result is toning and increased 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.
The press operator will likely increase the water to clean up the plate but this will break down the paper coating more quickly and increase the calcium leaching effect. Eventually he'll check the fountain solution and see that the pH is out of range and then adjust it to get the pH back to normal. Unfortunately this will further leach calcium from the paper which will collect through the roller train and deposit on the plates and blankets.
When calcium collects on the plate the gum is no longer active - it is no longer able to desensitize the plate, and so the plate oxidizes. Short press shutdowns will 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'll see toning, and as the calcium deposits in the grain of the plate, the plates may start to pick up and print the image from previous units. Eventually you'll be forced to replace the plates.
As the calcium builds up in the roller train, it will start to collect on the outside distributors first and move from there. 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 the rollers are cleaned very regularly and your print runs are short, the problem can be manageable. But if the runs lengths are long and you're not doing constant and daily roller maintenance, the problem can becomes severe as the calcium precipitates and hardens.
Calcium will also accumulate on the blanket (a.k.a. "milking"). The calcium builds 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 probably pick up a backtrap image from the previous unit, which in extreme cases will start to print and appear on the plate.
Solving the problem:
If water is the problem -
Use treated/RO water and a fountain solution that can handle calcium since preventing the calcium from accumulating in the fountain solution eliminates a great part of the problem. Use conductivity as a measure to check freshly mixed uncontaminated solution only. However, once the solution is put into your recirculator, the conductivity is irrelevant since your fount solution could be loaded with calcium and show no change in conductivity. Instead, 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 or include a calcium-fighting additive in the fountain solution
Use the mildest wash possible - check with your roller manufacturer for their suggestions. Wash up your presses regularly and then use a calcium deglazer to remove calcium. After the cleanup with the calcium deglazer do a thorough hot water wash and then a final rinse with the roller wash. If you don't the rollers will strip and will not carry ink since the same components in the deglazer that remove calcium will cause the rollers to become desensitized to ink unless they are completely removed.
If ink is the problem-
You'll only see it on the one specific unit. Switch to a calcium-free ink and use a calcium fighting fountain concentrate.
If alkaline paper is the problem -
You'll see buildup of calcium across whole roller (not just on the edge), roller stripping, plate blinding, fountain solution contamination or pH & conductivity drift, picture framing, and blanket contamination. Again, use a calcium fighting fountain concentrate or use additives. Use a strong calcium dissolver to clean rollers regularly and a water miscible press wash to remove contaminates.
As always do preventive maintenance and clean up regularly.
Hope this helps - gordo
