Cobalt 12% at 1.50 percent
Cobalt 12 percent at 1.50 percent
Cobalt 12% at 1.50%
Are these three totally different pieces of information? Just what is the Cobalt content of such an ink from anyone of those statements? Are we to multiply .12 by .015?
You need to ask your ink manufacturer to provide information in plain language.
Al as you surmised the paper curl was a big clue. If the sheet had curled up and not down we would have known instantly that it was the paper picking up water.
Interesting discussion which I am trying to follow.
Question and clarification. How do you define the curl direction up or down?
From what I have seen, if one wets paper with water on one side, the paper will curl away from that surface. Water tending to elongate the paper fibers. When it dries, it tends to recover some what. Is this curl defined as up or down?
Also if one runs paper over a small roller or a sharp edge, it will give it a curl away from the surface where there is a mechanical stretch of the fibers. Is this up or down curl?
The old printing adage is "eliminate the variables". You altered something and now are having problems.
If everything but the fount is the same, and you now have a problem when you didn't before, you already know what the immediate cause is. Finding a workable solution shouldn't be very hard at all. I would personally try adjusting the mix so I could temporarily, at least, run less water overall...which is what you should be doing anyway in most cases. As you most likely already know, the least amount of ink and water necessary to run the job at proper density is always the best condition, for curl, drying, prevention of set-off, everything. It's even cheaper by a miniscule amount.
You could also try a different ink if you've got something available, or adjust the tack of your usual ink with body gum or reducer, to make your your ink a bit more compatible with your current solution mix. In a generic, hypothetical case, and depending on what you suspect is the mostly likely cause of the curl, ink or water, you could probably increase tack and run with a lower water setting, or decrease tack and run the water a little faster, depending on conditions and the kind of image you're trying to print.
All larger-format sheetfed printing presses print much better when the grain is running across the press. Anyone who's been running a press for a decade or more should have seen that for themselves many, many times by now. It generally produces less curl and much better fit. Parent sizes and bindery concerns can often take priority over what the press/operator might prefer, unfortunately, and on single color black, fit certainly isn't a factor. But even then, running the grain across the width of the press ("long-grain" on the actual press sheet) is still ideal. Judging from the sheet size used in this case, the grain would appear to be correct, so that probably isn't it.
I think we sometimes try to be TOO technical about this stuff. What works this time may not work at all next time, and the reason could be something as simple as humidity in the pressroom. I think the better plan is to have an arsenal of practical experience and knowledge from which to draw on, such that you've always got something else to try that could realistically cure an unusual problem.
In the good ol' days, we'd have just cranked the IPA up to about 30% and then run less solution overall, and it would usually come out looking, running and drying great...and flat. Also, if you've got curl at the tail, you could always try feathering the packing to make the sheet release more gradually. That's usually not worth the effort on shorter runs, but on a 26K run it could be. I haven't had to do that myself in years though, since I started running presses with decurlers.
Understanding technology is great and important, yes. But in this case, all you're really trying to do is get through a job so you can move on to the next. You probably don't need to spend two extra hours investigating what exactly is going wrong, when all you need to do is try one or two quick-fixes that might take ten minutes total and may not even be necessary next time you run the job.
If a seasoned engineer can't tell up from down, we are in serious trouble. ;-)
But taking you seriously: the curl direction terms are used here in connection with a real press event. Particularly the arrival of the sheets at the press delivery pile printed side up. Curl "down" describes the shape of the sheet, in the delivery, with the corners or edges being lower than the center of the sheet. Curl "up" would be the opposite.
Note that this use of the terms does not involve the cause of this effect. That's what the discussion is trying to determine.
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Originally Posted by Sustainable
