"In general, modern water-based paints are much more user-friendly than they are said to be," says Reinhard Huber, a trained carpenter and application technician at Adler-Werk Lackfabrik Johann Berghofer GmbH & Co KG in Schwaz, Austria. With many water-based paints, drying is somewhat slower than with solvent-based paints. "The right ambient conditions are important here. An air-conditioned drying room with regulated humidity in which the air is in motion is ideal," says Huber. In the industry, an oven has often replaced this drying room in the past, whereby air circulation was also important here.
Paint drying requires a lot of energy
However, strong fluctuations in energy prices and occasional fears of a gas shortage make other drying options appear interesting. This is because a lot of energy is needed to dry water-based paints: around 2350 to 2500 kilojoules are required to evaporate one liter of water. Reason enough to take a close look at the drying process and search for efficiency potential. Harter GmbH in Stiefenhofen has done just that and offers heat pump-based condensation drying systems. One advantage of this process is its speed: according to Harter, up to 50 percent of the time can be saved with condensation drying compared to conventional processes such as hot air drying or simple blower technology.
Hellmann-Hygrex GmbH in Kaltenkirchen also offers its own drying process, which consumes significantly less energy than conventional dryers - up to 80 percent. The company's dry air generator uses one kilowatt of drive power to generate around three to five kilowatts of cooling power (condensation of water) and four to five kilowatts of heat power (heating of the dry air), similar to a heat pump.
Gentle drying is well suited to wood substrates
The process is well suited to the sensitive substrate wood: The water-based paints are dried without thermal stress. The risk of skin formation is significantly lower than with thermal drying or infrared radiation.
Harter projects show what can be achieved in practice. In one case, a manufacturer of window frames wanted to use low-temperature drying for gentle dehumidification, the safe process and to save energy. Harter converted an existing drying chamber with a chain conveyor to its process.
In a second case, a manufacturer of beer bench sets wanted to improve the quality of the coating and achieve block resistance, ensure the downstream process in production, shorten the cycle time, increase production capacity, save energy and also integrate a new system into extremely tight spaces. To achieve this, Harter installed a drying cabinet in a niche and installed the heat pump module on the second floor. Both parts of the system are connected via insulated piping.
Infrared drying is also evolving
However, other drying processes are also continuing to develop. Excelitas Noblelight GmbH in Hanau, for example, has launched carbon infrared emitters onto the market. While conventional medium-wave emitters are equipped with a heating coil made of alloyed resistance wire made of iron, chrome and aluminum, the new emitters use a carbon strip. They also emit very effective medium-wave infrared radiation, but also offer high area outputs and short reaction times.
When drying with infrared radiation, some of the radiation is absorbed by the material, some is reflected and the rest penetrates the materials. Each material has its own absorption spectrum, i.e. the range in which the electromagnetic rays are best absorbed. If this area is optimally targeted, the material heats up faster and more effectively.
The wavelength of the infrared radiation has a significant influence on the process, as Excelitas Noblelight reports. Short-wave radiation penetrates deep into solid parts and heats them quickly and evenly. Medium-wave radiation is more effective on surfaces and is also well absorbed by water, glass and many plastics and converted into heat.
Fast drying has priority depending on the application
Noblelight uses an example to explain how infrared emitters can be used effectively in practice: in the manufacture of furniture, panels made of untreated wood are stained in color and then coated with a UV varnish. The stain must be completely dry before the UV coating can be applied. Water-based color stains can cause problems here, as water dries relatively slowly.
A Scottish company compared various methods in the search for an efficient drying process. They initially considered gas convection ovens, but rejected this option: they would have required a footprint of around 20 meters and a dwell time of around 30 minutes for complete drying. In the end, the decision was made to use two medium-wave infrared modules from Noblelight.
Curing the paints is even faster with UV radiation. However, this only works with special UV coatings. Strictly speaking, these paints do not dry either: the transition from liquid paint to solid paint layer takes place via a chemical reaction, the paint molecules cross-link with each other. For this reason, "UV drying" is only comparable with other processes to a very limited extent. SI
Read more in the upcoming print issue mo 7-8/2024 of mo and soon on oberflaeche.de!