Covering UV-coatings - part 1

For many years, the UV-technology is applied in the field of furniture coating and today it is absolutely state of the art.

Up to now, most UV-coatings are made in the field of clear or translucent surfaces.

Due to further developments of the photo initiators, the lacquer formulations and of the application- and UV-curing technologies, there is now the possibility to process covering-coloured UV-lacquers, as well!

For the "flat", 2-dimensional sector, which we want to deal with today, the application by roller coating and the use of 100% UV-Lacquers is especially well applicable.

In the field of 3-dimensional coatings, the use of Hydro-UV-Lacquers is preferred. We will report about these products in the next edition of lacktuell!

One of the most important components in the UV-technology is the UV-radiation

The UV-radiation is a part of the spectrum of electromagnetic rays and follows the short-wave sector of the visible light (violet).

According to DIN 5031, part 7, the UV-light is divided into three ranges:

• UV-C-range 100-280 nm
• UV-B-range 280-315 nm
• UV-A-range 315-380 nm

Depending on the applied UV-lacquer-qualities (clear or pigmented), in practice a radiation between 200-420 nm is used for the cross-linking process. The part of radiation below 200 nm is strongly absorbed by the air and therefore no more available for the real curing process.

The most commonly used UV-lamps are high-pressure mercury-vapour lamps with a power of 80 to 120 W/cm. Those are suitable for the curing of clear lacquer systems.

By doping, i.e. by charging the mercury with halogenides, the lamps-manufacturer can change the spectrum in certain ranges and adjust it according to the spectral arc of action of the particular UV-curing formulation.

Mostly used is the gallium-doping. These lamps are mainly required for pigmented, coloured UV-systems.

The energy distribution of a UV-lamp:

This listing shows, that only 25% of the total electric energy is used for the UV-curing.

Even with an optimum selection of UV-lamps, adjusted to the particular formulation, the following statement is still valid:

"Covering coloured UV-coatings require special technologies"

The principle item is the application of the top coat with a grooved roll.

The line is equipped as follows:

The required high application quantity, offering the following advantages, can only be achieved by the grooves.

• Production of high-quality furniture surfaces (Fulfills the IKEA-demand according to IOS-MATT-0066 class R2)
• The lacquer surface is very smooth and without the typical roller structure
• The surface finish is almost the same as of a curtain coated or sprayed surface

Leider sind der Farbenvielfalt und Deckfähigkeit aufgrund der physikalischen Eigenschaften der Pigmente Grenzen gesetzt.

Unfortunately, colour variety and covering capacity are limited because of the physical features of the pigments. Even if not every colour wish can be realized by now, we have made a good progress in using the UV-technology for covering coloured coatings.

In our report "Covering UV-coatings - Part 2", we will present you a pigmented UV-Hydro application.