Not all inks are created equal. Inks perform differently on various papers, depending on how the ink is applied, what the finish and color of the paper is, and what other post-press operations the ink will be subjected to. Some Advance Planning should be considered.
Offset presses operate on the principle that oil and water don’t mix well so, until the last few years, offset inks were made from petroleum. The two downsides were that petroleum is an expensive and non-renewable resource and that petroleum inks have a melting point low enough that products pre-printed with petroleum-based inks couldn’t be later imprinted using heat-laser devices that would re-melt and smudge the pre-printed ink.
Today’s offset presses nearly all use vegetable-based inks made usually from soybean oil. Soybeans are an abundant agricultural crop, and inks made from soya can have very high melting temperatures that make them laser compatible. The most common example of a benefit of that change has been the laser addressing of envelopes and letterhead that have been pre-printed on offset presses.
The best quality of reproduction on an offset press happens when paper is used that has had one of several coatings applied by the manufacturer to seal the surface of the paper. On a sealed surface, the ink does not soak and create a fuzzy image by spreading into the paper (the ink blotter effect). The use of white paper has the least effect of changing the colors of the inks by adding the reflected pigments of the paper to those of the inks.
Offset inks nonetheless do soak into the paper to some extent (varying by the type and amount of coatings), yielding a benefit: when folds cross printed areas, the resulting breaks in the paper tend not to reveal white fibers underneath. And, that is one of the greatest liabilities of using laser inks.
Laser printers and presses use a heat transfer process to apply powdered ink to the surface of paper. Laser inks do not penetrate the surface of the paper, which tends to yield consistently crisp images, but which also can prove problematic when folding or subjecting to other wear and tear.
Compared to offset inks, laser inks remain brittle on the surface and, when the paper is folded, the ink breaks and reveals the white paper beneath – a condition called laser cracking. When it can be cost-justified to do so, products that need to be folded across areas where toner has been applied can be creased manually to avoid damaging the ink and revealing the paper beneath. Of course, that process involves extra time and expense.
Advance Planning is recommended.