UV varnish

see also UV offset printing

Unlike oil and water-based coatings,UV coating is provided with non-volatile components. It contained neither water nor solvent. UV coatings thus consist of 100% solids.

Technical background

In addition to the reactive acrylates (unsaturated polymers of acrylic acid) and excipients they contain photoinitiators. It can also effect pigments in the UV coating may be incorporated. In specially equipped machines they are inline processed. By means of an anilox roller of the coating film is applied to the substrate and then irradiated with UV light. The photoinitiators decompose by the irradiation and activate the cross-linking process of the resin particles. After a few seconds, the coating layer is fully cured. In the production process, no additional drying time must be considered. However, the UV lamps must be properly screened, as it may cause respiratory irritation else. It can transmit high layer thicknesses. Inline varnishing reach thicknesses up to 8 microns and offline coatings, for example screen printing, up to 100 microns.

Effect

UV coatings call of all paints produced the strongest effect: they shine brighter and look duller than others. They are mostly used as a high-gloss clear lacquer, rare as matt or metallic effect pigment paint. Even partial painting is possible.

Application possibilities

It can be paper and cardboard with a smooth surface and/or low absorbency printing, plastics or metal surfaces are well suited to this. In a subsequent operation may be additionally foil bonding and embossing. The stacking and shear strength are very high. Least yellowing papers have their pulp and/or filler on a high base color.

Limitations

For cast-coated papers and cardboards can occur due to the extreme surface smoothness to a limited adhesion of the paint. For highly absorbent material a portion of the photoinitiators absorbed into the substrate whereby the gloss is impaired. Optical brighteners in the substrate are due to yellowing caused by UV radiation. In the further processing or precursor should make sure that they last no sprays within creasing, grooving or fold lines, because the UV coating can be very brittle.

Costs

The costs are in principle to those of dispersion coatings. On one hand can be used for transmitting high layer thicknesses much material, on the other hand, the machines have to have special equipment. Also the energy required for drying (UV light) is not to be underestimated.

Sources and additional literature

[1] Beckmann, Till; Morlok, Franziska: Extra: Enzyklopädie der experimentellen Druckveredelung; Birkhäuser Verlag, 2009

[2] Hille, Frauke Helene: Veredlungsmöglichkeiten und Spezialeffekte für Bücher und Broschuren; Diplomarbeit, Hochschule für Technik, Wirtschaft und Kultur Leipzig (FH), Fachbereich Medien, Studiengang Verlagsherstellung, 2008

[3] Kipphan, Helmut: Handbuch der Printmedien – Technologien und Produktionsverfahren; Springer-Verlag Berlin Heidelberg, 2000, Seite 149

[4] Kleeberg, Dieter: Inline-Druckveredelung mit Lack. KBA Process Nr. 4, Ausgabe 1/2007

[5] Murvai, Geza; Ober, Juliane: Inline-Veredelung im Bogen- und Endlosdruck. Bundesverband Druck und Medien, 2007  

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