Frankly Speaking: Paper is Part of the Process
If you've been following the printing world—and if you're reading this column we've got a hunch that you have—you know that advances in digital printing have transformed the technology from the world of the small-run to a viable print-on-demand option for publishers of all sizes and stripes.
But don't be fooled: Digital and offset lithography remain quite different beasts. As such, the process choices you make for one won't necessarily translate to the other. And while offset processes present a fairly consistent set of choices, digital printing is schizophrenic by comparison: It can use dry or liquid toner, or inkjet using water, solvent or UV. It all depends on the printing system that will be employed and there are now about 40 systems you can select from. And that all depends on what system your printer of choice is using.
Here's a handy guide to help you navigate the new set of choices this miracle technology will throw at you.
● In digital printing, paper is part of the system. Offset uses more or less plain paper but digital papers must be treated or specially formulated. There is no such thing as "plain paper" when it comes to digital printing. Choose a paper that has been tested and approved for the digital printing system that will be using it, or you may encounter poor results such as flaking and streaking. Your print provider can show you the approved paper stocks and substrates for its system. A test run or proof may be the best way to determine if the paper that is to be used is the best choice for the application.
● Once you know the printing system that will be used, get a list of approved papers, usually posted on supplier or service websites.
● For dry toner printers, the temperature and moisture content of the paper are critical for the paper to receive the correct electrostatic charge during the digital printing process, which will ensure proper image transfer and toner adhesion. Like all forms of printing, paper used in digital presses, printers and copiers must be properly acclimated for best results.
● Digital papers for dry toner must be able to withstand the high heat created during the image fusion process. Liquid toners do not have this issue but may require special coatings to assist in ink adhesion. Newly announced liquid toner printers may not require coated or treated paper but always check first.
● Paper manufacturers are constantly developing paper stocks that are stronger and cleaner to help eliminate the picking problem that can occur with waterless inkjet technology. Fibers can be transferred to the printed areas, producing poor quality. Water-based inkjet printers usually deposit a spot of pre-coating as a base for the colored inks.
The direction of the paper grain is critical for smooth operation. It also affects some finishing processes (folding especially). If the ink or toner image crosses the covers and spine, there could be cracking, which means the toner flakes off at the fold; this, however, is less of a problem than ever before. Printing using the proper grain direction will help, but a test is recommended. In digital printing, a proof is a run length of one so you will be able to see the actual effect of the design and the printing. You would not do a makeready for an offset press and then run one impression.
Make sure the printing system is calibrated and the correct ICC [International Color Consortium] color profile is used. Up-to-date color profiles usually can be downloaded from an ICC archive maintained by the printing service. Proper calibration and use of the ICC color profile appropriate for the RIP [raster image processor] in use avoids excessive ink deposit and ensures accurate color reproduction. Bleeding, mottling, banding and warping all can be linked to poor calibration and profiling. In inkjet printers, banding may also be caused by misdirected or clogged nozzles. Running a cleaning cycle on the printer usually resolves the problem.
Well over 80 percent of all Pantone colors can be printed from the CMYK toners/inks that most printers use. HP Indigo printers are capable of up to seven colors and Pantone and other special colors can be mixed. The Kodak NexPress has a fifth toner station and can handle many special colors and effects. Canon Océ also provides special inks. Some Xerox printers can print special clear toners for dramatic effects.
Most newer digital printers have excellent software that makes some decisions for you. Designers who use RGB color models are saved by automatic RGB-to-CMYK conversions, although this is never recommended. It ideal to work in CMYK, but some workflows let you work in RGB. Many workflows can also accept files profiled for offset litho for conversion, and this is also ungood. Do not rely on automatic conversion. You should ultimately create for the system you'll be using. Proper file preparation is still mandatory no matter how you print. BB
Frank Romano is RIT Professor Emeritus with over 50 years in book technology and publishing.