Paper Tips: Printing on Uncoated Stock

CreativePro Staff

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It is essential to keep in mind the physical characteristics of uncoated papers when planning your printing job. Uncoated papers are absorbent, so inks, varnishes and coatings perform differently than on coated papers. New technology in the pressroom and pre-press area has enabled designers to use premium uncoated papers in exciting new ways. With current prepress technology, the natural surface of these papers becomes a perfect background for four-color process printing.

Separations
Good, well-planned separations are crucial for successful printing on uncoated paper. Because inks soak into the paper, precise halftone dots spread and deform – a feature called dot gain. By opening the separation, the actual dot size is decreased and the space surrounding the dot is increased. Opening the separation allows the press operator to print to normal ink densities. This results in truer color fidelity, image brightness and detail. Opening the separation also allows the use of finer line screens — 175, 200, even 300 lpi.

Depending on the color densities in a transparency and where you want to hold detail, the critical areas to be opened will vary from the highlights to the shadow areas. A separation made for coated paper holding a 1-3% dot in the highlight areas would appear dull on uncoated paper. Completely eliminating the highlight dots up to 4% for uncoated paper, and reducing the dot in the 6% highlight areas to 2-3% will produce brighter highlights on an uncoated sheet. A 50% middletone dot on a separation for coated paper should be reduced by at least 5% for uncoated paper. This will give you more clarity and definition on press. A 90-95% shadow dot for coated paper should be reduced to 85% for the deepest tones.

Adjustments should also be made to compensate for paper color. For warm white stock, reduce the densities overall with particular attention to skin tones and warmer areas. For cool white stock, densities should be increased.

Printing
Printing on uncoated paper can be as straightforward as printing on coated papers if the separations are properly prepared. The adjustments will allow the press to carry more ink, thus increasing color saturation, clarity and contrast.

After a wet press sheet has been approved, all ink colors should be increased by approximately five points based on densitometer readings. This increase will compensate for any dryback. Density readings for both wet and dry press sheets should be taken and recorded for reference later in the run, or for anticipated re-runs.

Inks
Process inks for uncoated paper or quick setting inks, if back-up time is limited, are suggested. Most ink manufacturers offer these. Uncoated paper normally needs more drying time than coated paper so stacks should be kept small — 500 to 700 sheets — to prevent offsetting.

Depending on the image, you may achieve better results with the addition of fluorescent ink to the magenta and yellow process colors. The fluorescents will increase the perceived reflective light of the paper surface thus increasing brightness and clarity. Adding 10-20% fluorescent magenta to process magenta will enhance red, violet purple, magenta and orange. The addition of fluorescent yellow to process yellow brightens yellows, oranges, reds and greens. Contact your ink supplier for assistance.

Paper
Good quality uncoated papers are formulated to strike the delicate balance between ink holdout and ink receptivity. There is an extensive range of uncoated papers on the market, all manufactured to varying quality standards. It is vitally important to specify not only that you are choosing an uncoated paper, but also the manufacturer and the grade.

For printed samples on uncoated papers, please call your local merchant or mill representative.

This information provided by Mohawk Paper.