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Recommendations for processinguncoated woordfree papers

General

Uncoated papers are commonly used when the finished printed product is intended to convey a genuinesense of natural authenticity. But just as coated papers have their own, distinguishing characteristics whichtranslate into distinct requirements for the printing process, uncoated paper grades also demand specialattention to specific aspects in order to achieve optimal results.

First and foremost, it is essential for all parties involved in the job at hand end customer, advertisingagency, prepress, printer and converter to communicate efficiently in the preliminary stages of the project.

Glossy coated paper Matt coated paper Uncoated paper

Advertising agencyIt is important for people who, by the nature of their jobs, concentrate on the creative elements of a project,to clearly understand some of the practical implications of material choices. For instance, the range ofcolours that can be reproduced on uncoated paper is approx. 25% less than it is with coated papers.In other words, to match print results that can realistically be expected from coated paper, this intrinsiclimitation in colour scope has to be compensated for in the pre-press stages of any print job when, foraesthetic reasons, the decision has been made to use uncoated paper.

Prepress

Print data need to be perfectly aligned to the press characteristics, with special attention to the reproductioncurve. Dot gain of up to 25% is not unusual and must be taken into account.

Some "cleaning up" of the print Image is also highly recommendable, by means of reducing K (black) infavour of primary colour dominance (cyan, magenta, yellow), which will generally produce a fresher, morevivid looking end result.

Furthermore, it is sound practice to apply a degree of under colour reduction (UCR) and to print 4 colourimages with a maximum ink coverage of 280 to 300%. Higher ink coverage will only result in darker imaging,due to the inevitable loss of colour and contrast in the printed image.

For dark print areas, screen coverage should not exceed 85%. This leaves the screen agreeably open andhas the additional advantage that, optionally, the ink density can be increased for maximum expression and

a more colourful effect.

With due regard to these considerations, screen rulings of 0 l/cm are definitely possible on most uncoated

papers, as are 20 micron resolutions.

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Proof printing

Proofs, obviously, should always be printed on the paper to be used for the actual print job.

Actual printing

For the actual print run, relatively hard blankets generally work very well, although in solids, a medium hardblanket usually produces the best results.

Blanket-to-impression cylinder pressure should be at 0.2 to 0.25 mm, depending on roughness of the papersurface.

For optimal print results it is recommendable to use inks with strong oxidative drying and normal ink settingbehaviour. Most standard four colour inks dry very quickly. Oxidative drying can be further assisted byadding ink drying accelerators (consult your ink supplier). Where possible, the use of fresh inks should be

avoided.

If protective varnishes are used, matt varnishes usually work better than gloss types, if only to avoidcompromising the naturally matt character of uncoated papers.

The risk of ink transfer is relatively small with uncoated papers. However, in heavy solids it can still be agood idea to use anti-setoff powder.

Postprocessing

Once printed, uncoated papers can be moved to postprocessing rather quickly, although, as always, thereare exceptions to the general rule.

To avoid mechanical rub problems, covers should always be varnished, especially in the case of high inkcoverage.

In the guillotine, hardened steel blades are essential to produce clean edges. Blade angles should be at 22,or 24in pre-cutting.

Additional precautions

To avoid "curling" after uncoated papers have been cut, it is very important always to remove the bottomsheet from the stack. In stacking, always put new sheets on top in alignment with the sheets below. Never

stack sideways, as this will inevitably damage the paper edges and can easily lead to curling.

All types of binding, including dispersion, hotmelt and PUR binding, can be used for uncoated paper print

jobs. Stitching can also be freely applied.

Folding, embossing and die-cutting present no special problems with uncoated papers. With grammages of150 g/m and higher, however, scoring is essential for good folding results.