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Match the right ink to the paper.

Dec 1, 1996 12:00 AM

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Have you taken a good look at your ink room lately? "Look at all these different sets of inks," you might think. "Why won't one set of inks suffice for all my printing jobs?"

Every set of inks holds its own particular story. Maybe you got a bad lot of paper and your regular inks picked like crazy. It was a rush job - you had no time to get paper, so you made a quick call to your ink supplier for a lower tack set.

Or maybe it was a high gloss job where the inks seemed to dive right into the stock. Or it could have been a dull coat stock that acted like sandpaper and would mark at the slightest touch when it came in contact with a printed area.

When it comes to paper problems, you've got to have the right weapons in your ink arsenal. Now, if you are a magazine printer that never uses anything but the same grade of publication coated stock, settling on one standard ink is easy. If, however, you are like the majority of commercial printers, you print on a variety of papers. Therefore, you'll need to build up an inventory of specialty grade inks for difficult situations.

I once knew a printer who had a variety of presses. Over a period of time, his inkmaker had developed a series of inks that would work well on all the presses. One day, the printer was running a high-class job that required a much better grade of paper than he typically used. Putting it on press, the printer was dismayed to realize the output came nowhere near matching the proof. He played around with the job, sharpening plates, repacking blankets and so on. Finally, he concluded that the ink was the problem - he figured his current ink supplier had let him down.

The printer called in another ink company, gave their rep the paper and asked for an ink that would give him the sharpest print. Sure enough, when the new ink was put into the fountain and the job pulled up, the print was much sharper. The printer then called his regular ink supplier and raised Cain.

"Wait a minute," cautioned the service technician for the first supplier. "The tack and body of these inks are much higher than you normally run. If we gave you these inks all the time, you would have more picking and linting than you could shake a stick at. Next time, show us the paper first and let us know you need the least amount of dot gain. We'll get you the best ink for the job."

This cautionary tale illustrates that an ink set designed to work across a variety of papers is not necessarily the best for any given stock. Alert your inkmaker when a special stock comes along that might need a specifically formulated ink.

Some typical ink adjustments to suit a particular type of paper might include the following:

Newsprint. Typically, newsprint requires a particularly low-tack ink to avoid picking and linting. Because tack is the single most influential characteristic of an ink that will influence dot gain, high dot gain can be a problem. To compensate for the low tack, ink companies formulate ink for newsprint with as high a body as possible. Another trick is to put a small amount of a resin varnish in the ink - these "resin-set" inks can minimize dot spread.

Cast-coated papers. These are coated papers or boards that have been dried in contact with a chrome drum. The result is a very high gloss on the surface. You might expect that cast-coated papers would therefore produce a very high gloss with just about any ink. Not so. Because the paper hasn't been calendered, it actually remains very absorbent. Consequently, the varnish portion of a regular ink will quickly sink into it, frequently leaving the pigment with no binder on the surface. "Chalking" is the term used to describe the result - you literally can brush the pigment off the sheet.

Matte or dull-coated stock. These stocks are very difficult for an ink to resist rubbing off when the unprinted area comes in contact with the printed portion, as frequently happens in the bindery. Although some printers may blame the ink, this usually is not the problem.

Rather, what happens is that the process that makes the paper matte or dull leaves little peaks and valleys. The ink on the peaks then breaks off on contact. There's not much you can do when this happens. You could try to improve the rub resistance by adding more wax, but this often creates another problem: carbonizing. The extra wax can make the ink so soft that it acts like carbon paper. Using the hardest drying ink you can formulate as well as a judicial amount of Teflon wax is one way to address this problem. Prevention, however, is the best course. Before you start, check the coefficient of friction of the paper and select the grade with the lowest reading.

These are just some of the reasons to keep specialty ink sets on hand. Most ink companies will supply you with the most versatile inks possible. However, there's always that special case that requires something different. So keep your supplier in the loop - clearly communicate any special requirements.

TERRY SCARLETT Contributing editor and president of Burntwood Industrie, a consulting company specializing in inks and coatings