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The Heidelberg website glossary explains, in alphabetical order, a multitude of terms relevant to printing, as well as some terms used in Heidelberg's product catalogue.

Simply click on the letter of your choice to access the information you need.

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ULWC

See "HWC".

Umbra

See "deep shadow".

Uncoated paper (untreated paper)

Paper with no additional protective layer.

Under color addition (UCA)

A method of darkening areas of a printed image by adding colored inks, used when making color separations from RGB to CMYK data. The process works as follows: cyan, magenta and yellow portions are added in shadows and black is accordingly removed. Not all achromatic portions, however, are replaced with black, rather a portion of black is generated according to the principle of chromatic composition from the primary colors cyan, magenta and yellow. The aim is to enhance neutral image depths (gray tones) where the density of black is insufficient.

Under color removal (under color reduction, UCR)

A technique for reducing the amount of magenta, cyan, and yellow in dark and neutral areas and replacing the amounts of CMY with black. The technique works in the following way: colored ink is used up to a certain value, after which black is added in order to improve the dark areas of an image, so that total ink coverage (TIC) is not exceeded. Cyan, magenta and yellow are removed as far as they are identical and replaced with the equivalent amount of black. The depth of colors is thus improved and the total amount of printing ink reduced.

Unicode

A standard method of coding characters for electronic processing using 16-digit binary (16-bit) numbers. Unlike ASCII and other codes, which work with eight-bit numbers, Unicode is capable of representing 65,536 different characters. This covers all characters and commonly used scripts in the world.

Upstream

A kind of transmission in which information or data is fed from an end user to a server. See “downstream”.

UV (ultra-violet) coating

Coating systems based on unsaturated polyesters or polyacrylates, or a combination of the two, in which ultra-violet light triggers the drying process. This high-energy light breaks chemical bonds in the coating material’s molecules, which then link up to form long, highly-branched chains, causing the material to solidify. The drying process takes only seconds, which means that UV coatings can be worked quickly. These coatings contain no volatile substances, making the layer thickness of the liquid and dry coating similar. UV coatings can be applied inline in very high layer thicknesses (up to 8 µm), have excellent gloss and can be barely distinguished from laminated products (film-lamination), though they do emit a odor.

UV (ultra-violet) inks

Printing inks cured with ultraviolet light. These inks contain no volatile substances, but instead, in addition to color pigments, individual molecules and short molecular chains that can link to form polymers and so-called photo-initiators. The latter decompose when exposed to UV light and form highly reactive fragments. These radicals trigger a polymerization process in which stable, three-dimensional network structures are formed. UV inks are primarily used to print non-absorbent materials, such as metal (sheet metal) and plastic, but also high-quality paper boards and labels.

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