People often ask us about how coated and uncoated material each affect the look and feel of a finished document. I thought I’d try and explain some of the differences.
In the initial stages, most paper is made in a similar way, through drying, compressing and separating a dilute mixture of wood pulp, textile fibre, or recycled paper products. In industrial paper manufacture, the dried and separated material is treated and wound onto large rolls. The type and quality of the materials used in the manufacture, plus the manner of treatment during processing will determine the quality and feel of the finished paper.
Coated papers are made by applying a fine layer of calcium carbonate, or china clay (or other material) to the surface of an uncoated sheet during manufacture. This coating process may be done once, twice, or three times, depending on how smooth a finished surface is required. The material will usually also be ‘calendared’, or milled smooth between hard rollers at the end of the process, to increase the sheet’s smoothness. Also, the material can be treated to provide different finishes – typically gloss, matt, or silk.
The same ink will look different printed on coated or uncoated paper
Adding coating to a sheet changes the nature of the paper in a number of ways. Because the coating is relatively more dense than the substrate, the more coating there is on a sheet, the thinner it will be. So, for example, an uncoated 135gsm will be quite a stiff sheet of paper – thicker than the average corporate letterhead paper, but a 135gsm triple coated silk paper will thin by comparison, although both are the same weight. This is because more of the weight of the silk paper will be taken up by coating, which adds surface weight (but not thickness) to the sheet. For similar reasons, an uncoated sheet will often appear more opaque than a coated sheet of the same weight, since a disproportionately large part of the bulk of a coated sheet can be taken up by the coating materials themselves.
However, more coating added to a sheet generally means more smoothness, which generally means it will hold the detail and colour of fine screen litho printing much better. It will also enable a better colour range (shadow areas will usually appear darker in photos on coated materials) whereas on some uncoated papers imagery can look comparatively flat and lifeless. Unfortunately, for a printer, it is difficult to predict the results of four colour printing on uncoated papers without advance testing, as differences in how each brand is made can affect how each sheet will print. (This is far less the case with coated materials where the coating forms a fairly stable and predictable surface for the ink, no matter what is going on with the substrate.)
It is of course possible to make uncoated papers which give high quality results for four colour printing – this material will generally be quite smooth and white itself, and the best ones can be quite expensive – often much more expensive than high quality coated material. The results of colour print on uncoated materials are often very pleasing – but it is a good idea to explore these issues with your printer before embarking on a major project.
So, in summary, coated papers will often give better colour reproduction than uncoated papers, but can feel much smoother and thinner. Uncoated papers will give a softer and more tactile quality, but may raise questions about colour reproduction.
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Tom Clark is Production Director at PrintHouse Corporation. If you’d like to work with PrintHouse Corporation click here or call us on Tel: 020 8963 0123.
