Research demonstrates benefits of carbon medium wave infrared emitters for drying printing varnishes

Citation

(2000), "Research demonstrates benefits of carbon medium wave infrared emitters for drying printing varnishes", Pigment & Resin Technology, Vol. 29 No. 4. https://doi.org/10.1108/prt.2000.12929daf.001

Research demonstrates benefits of carbon medium wave infrared emitters for drying printing varnishes

Keywords Varnish, Drying, Printing, Infrared, Heraeus Noblelight

New research from Germany is reported to have demonstrated that high energy cost savings of up to 50 per cent can be achieved by using carbon medium wave infrared emitters in the drying of water-based varnishes in the printing industry. The research has been carried out at the Department of Polygraphic Technology of HTKW (Hochschule fur Technik, Werkstoffe und Kultur) in Leipzig and at the Applications Centre of Heraeus Noblelight GmbH in Kleinostheim (Plate 1).

Plate 1 Heraeus medium wave infrared emitters being used to dry inks and varnishes

Varnishes are used in printing, mainly for in-line surface finishing to achieve a higher gloss, to reduce post-process times or simply for surface protection. Because of environmental considerations, there is an increasing trend towards solvent-free, water-based varnishes.

However, these take longer to dry than solvent-based varnishes and to increase drying and finishing speeds, convection (hot air) dryers are often combined with infrared.

The purpose of the German research was to establish which wavelength of infrared was best suited to this specific drying process. Theoretically, because the spectral absorption range of around three (urn) is best suited for heating water, medium wave infrared would appear to be the preferred technique for drying water-based varnishes. Comparing different radiation sources shows that the efficiency of water removal of an emitter with a filament temperature of 2,600°K (short wave) is only half of that of an emitter with a filament temperature of 1,500°K (medium wave).

This theoretical conclusion was investigated in two controlled experiments, one under laboratory conditions and one on an actual printing machine. In the laboratory experiment, at the HTWK, a paper web was offset printed with ink and then finished in-line with a water-based varnish, using laboratory-coating equipment. The degree of drying was monitored in-line after the web had passed through the drying section and the web speed was increased until the surface started to become tacky. Three types of dryer were used: a short wave infrared emitter, with a filament temperature of around 2,600°K; a carbon medium wave infrared emitter with a filament temperature of around 1,500°K; and a medium wave emitter with a filament temperature of around 1,150°K.

In the practical test, the same emitters were fitted to a dryer on a sheet offset printing machine. Energy input and print quality were recorded and compared at different speeds.

We are informed that the results from both experiments demonstrated that, at the same speed and for the same degree of drying, the energy consumption was 30 to 50 per cent lower with carbon medium wave infrared emitters.

Apart from the significant energy savings, this is thought to bring further benefits as the lower heat irradiation ensures that paper temperatures are lower and there is less heating of the printing machine and the immediate environment.

The carbon infrared emitter is the product of a joint collaborative venture between EA Technology and Heraeus Noblelight. It is believed to represent a new class of quartz linear infrared lamps with low thermal mass, carbon fibre elements, operating at a temperature of around 1,500°K. As a result, the energy-efficiency of medium wave infrared can reportedly now be combined with very rapid response and precise controllability. Apart from providing further energy savings, as the emitters need to be switched on only when required, making them ideal for cyclical operations, carbon emitters also eliminate the possibility of burning heat sensitive substrates.

Heraeus carbon infrared emitters are supplied in lengths of 300mm up to 1,500mm and can be tailor-made to suit particular web widths. Power densities of up to 100kW/m² are available and operational life is said to be of the order of 8,000 hours. Emitter modules can be easily retrofitted into existing dryer installations.

Details available from: Heraeus Noblelight Ltd, Tel: +44 (0)151343 0545; Fax: +44 (0)151343 9883.