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Over the past 15 years North American Paper Manufacturers have changed from an acid to an alkaline process for making printing papers.
First with copier papers where paper’s PH mattered little, but when exposed to fountain chemistry of the printing process, calcium carbonate, styrenated starches leaches away from the paper and into the process from blanket, to plate, to dampener and inking system causing much grief.
Larger press and graphic supply manufacturers addressed this issue with calcium cleaners, PH neutralizers, and fountain re-circulators, but there are still improtant steps that need to be taken by offset pressman.
The primary problems/symptoms of alkaline poisoning are;
* Dry toning on the plate.
* Calcium build-up on blanket that produces ink framing around sheet contact area.
* Blanket looses affinity to pick-up complete image/ink from plate.
* Ink tinting on printed sheet.
* Fountain PH shifts from acid 4.5 – 5.0 to a more alkaline 5.5 – 6.0 and even a 7.0 PH.
* Ink rollers strip, and will not carry ink properly causing an increase in ink feed, resulting in an over-inked condition and eventually emulsification and plugging.
The solution is not to use a stronger roller wash, it simply is to use a good water misible roller wash (Like Varn V-120) followed periodically by a good calcium deglazer (Like Varn Revitol) to remove calcium glaze, followed by a rinse of 15% white kitchen vinegar and water to neutralize and condition roller to accept ink properly.
In addition to using a good graphic supplied calcium remover (not CLR!), you should use an approved fountain solution designed to handle calcium.
Keeping calcium from accumulating in the fountain eliminates a major portion of this problem.
Purge old solution and replentish fountain solution frequently.
This simple step can keep plates, blanket, dampener, and rollers from developing a calcium build-up.
If you use the Kompac dampener, the problem of calcium build-up in the dampener is more noticable and can develope within only a few thousand sheets when printing on high alkaline stocks.
If you experience a calcium build-up with your Kompac, using a ‘Slim’ or ‘Spot’ Blanket with a Kompac KwikVac and TimeSaver Seals will make a dramatic difference in reducing calcium build-up in Kompac, as well as your ink system, and blanket.