For the purpose of processing technology, lacquering is a coating of a liquid, pasty or powdery coating material on previously mostly printed materials. Lacquer gives the material surface a more or less glossy and protective film or gives specific technical properties. Paintings in the sense of refinement attract attention and stand for high quality. In addition to influencing the optical properties, in particular the gloss, haptically perceptible effects are achieved. A classification can be made with regard to the varnish types, where overprint varnish (oil printing varnish), dispersion varnish and UV varnish are the typical representatives. Furthermore, a distinction is made with regard to the design effects resulting from varnishing. Relief varnish, texture varnish and soft-touch varnish produce very different haptic sensations, while drip-off varnishes produce gloss contrasts.
The lacquering takes place inline in printing machines with lacquer towers or lacquer printers, but also offline with special lacquering machines. Printing is often used in offset printing, especially UV lacquers but also in screen printing, with which high layer thicknesses and thus tangible structures are created. Digital printing machines also allow varnishing by generating visible and tangible lacquer effects with transparent toners or special inks.
The print image can be provided with high-gloss or pronounced matte effects, special painting methods allow a targeted matt-gloss contrast. Special visual effects are achieved with special lacquers containing, for example, metal pigments. When applying high lacquer thicknesses (up to a tenth of a millimeter), motifs can be felt in a relief-like manner, or structures can be created that imitate certain materials (for example, sand, wood). The lacquer is applied both over the entire surface and partially to remove motif parts. In addition, lacquers also have an influence on technical properties such as lubricity and protective function for the printing ink film.
As a creative means, coatings can be used for all printed products, from visiting and postcards to high-end books, for packaging and products for paper processing.
Printing ink should be matched to the following lacquer (solvent and alkalinity), powder should be dispensed with, so that powdered grains are not embedded in the lacquer. Due to the displacement of the reflection plane in the lacquer layer and due to light absorption, a shift of chromaticities and reduction of the brightness occurs, which requires consideration in the prepress stage. Apart from relief and structural lacquers, the lacquer layers (5 ... 8 μm) are thinner than a laminating film (12 ... 20 μm), which results in less protection of the printed images. Thick lacquer layers can crack on creasing, folding and cutting lines and embossed areas. UV varnish should be removed at these processing lines and at bonding sites.
Compared to laminating with similar effects, the coating is often in-line in the printing machine, now also digital, can be executed and thus simpler and less expensive.