Taken from the June 2000 issue of FDM.

New surface finishing systems from Europe

Learn the latest improvements in surface finishing, including application, filtering and recycling of lacquers .

by Urs Buehlmann and Joerg Schleusener

The reduction or elimination of Volatile Organic Compound (VOC) emissions is at the core of new environmental regulations coming into effect over the next few years in Europe. Starting this year, Switzerland, for example, will levy a fee of $1.50 per liter of VOC used. This is a powerful incentive for companies to switch from their traditional VOC-based finishing systems to systems containing no or very few VOCs.
Ultraviolet (UV) or water-based systems are clearly the most widely pursued alternative to VOC-based systems.

Even though these new UV or water-based systems cost slightly more than conventional VOC-based systems, they offer the opportunity to use less material and enable users to recycle as much as 90 percent of their overspray. New equipment needed for non-VOC systems has advanced computer controls, allowing for fast, frequent change of stain and lacquer and further decreasing production costs.

Surface finishing materials Companies like Votteler, Bergolin, 3H-Lacke, Akzo Nobel or Zweihorn emphasized the trend towards no or low VOC systems, such as UV or water-based systems. The goals of these new systems are to create cleaner and healthier working conditions and to more efficiently protect the environment.

Oils and waxes (often called “natural materials” in Europe) were well represented at last year’s Ligna show, too. Companies like Livos, Naturhaus Farben, Hesse and Osmo presented these materials, in addition to the first companies mentioned. Osmo and Hesse presented a new oil, which when applied twice with 5 to 7 g/cubic meter (0.016 - 0.023 oz./cubic foot) and a speed of 10 m/min (33 feet/min.), is cured in a few seconds under special UV-light (2x80 watts). The resulting surface is of high quality and very appealing.

Gori Industry in Kolding, Germany, presented a new paint called Gori 875, which can be diluted with water. This paint was specifically developed for wood-aluminum windows. The paint has excellent properties with respect to mechanical abrasion and chemical resistance, for example against window cleaning agents. However, the paint is not intended to be used for outside applications.

Powder lacquering was another process of high interest at the Ligna show. However, except for a few special cases, there are few actual applications of this technique in the industry so far. High melting temperatures and long drying times are major obstacles for more widespread use of powder systems. A true breakthrough for such systems will most likely require additional research.

3H-Lacke showed its new website (www.3h-lacke.com), which features an interactive planning tool for new finishing lines. The site offers information concerning the redesign and planning of finishing lines, in addition to information about the company’s finishing products.

Application techniques

In the area of application techniques, only incremental improvements were observed. These are nonetheless noteworthy.

Since flat panel processing is predominant in Europe, systems for this type of application make up a significant portion of the equipment offered, However, there were also some interesting application techniques for assembled products displayed.

Flow coating technique

Wagner showed a newly developed flow coating installation in stainless steel that uses a double diaphram pump. This piece of equipment, named Flutura, is of special interest for small- and medium-size enterprises (10 to 100 employees) because use and maintenance is very simple. Using numerous jets and a pressure of between 0.5 to 1.0 bar (0.73 to 1.45 psi), an even flow curtain is created that covers pieces evenly and in all places. Changing lacquer or color can be done within five minutes. This system is thought to reduce finishing time by about 25 percent compared to dipping.

Spraying

The major issue for spraying techniques was, as always, the challenge to reduce overspray. High volume, low pressure (HVLP) and electrostatic systems received a lot of attention. Also, improved high-solid material systems that use warm spraying could be seen.

Bollhoff-Verfahrenstechnik showed a newly developed system for piston pumps, which uses a piston pump with less pulsation. This system is particularly useful for applying more demanding materials, such as water or UV lacquers.

The same company also showed an improved installation for mixing two component materials, which has very accurate electronic controls with twist and static mixing devices. Furthermore, Bollhoff’s mixing installation allows fast lacquer and color changes, since only the material requested is mixed.

Another novelty shown by Bollhoff was an electrostatic hand spray gun for water lacquers that minimizes overspray and allows the operator to finish difficult-to-reach spots on parts, such as chairs, stairs and similar items.

Wagner showed a cold spray gun system for waxes that does not require heating the wax prior to its application. Using a leverage pump (scoop-piston pump), high pressure pushes the paste-like wax to the spray gun and beyond. Advantages of this system include:

1. No preheating is necessary (i.e. the equipment can be used anytime immediately), saving time and

2. Several guns can be employed and fed with wax simultaneously.

Wagner’s GM 2800 EA electrostatic spray gun was refurbished with an exchangeable jet system, which can be exchanged easily without flushing the entire system when changing lacquer. This system works with air atomization and achieves even material layer thickness.

Hot spray devices were shown by Bollhoff (hose lacquer heating systems), MK-Lackiertechnik (Air-Thermsystem), Aichach (Air Therm System), Kremlin, Dietzenbach and Wagner. All these systems are for high-solids lacquers, meaning low-solvent content lacquer materials with 60 to 80 percent solids. For such systems, it is crucial to heat not only the lacquer (or the wax), but also to heat the air used for atomization. Doing so allows the use of less air pressure for atomization, resulting in reduced overspray and lower material requirements. Heating the finishing material and the air results in a softer spray pattern, better running lacquers and faster drying.

Automatic spray equipment

Although there were no revolutionary developments in this type of equipment, several incremental improve ments were presented concerning vision systems and computer controls used for the recognition of part sizes, part positions and the control of the guns. These new systems help reduce overspray and increase equipment capacity. Other improvements were shown for changing lacquer or color and for faster cleaning.

Cattinair continues to improve its reliable circulation drive, which now has nine conveyor strips. This is an improved air circulation system that achieves an overspray recapture and recycling rate of approximately 80 percent due to a newly developed scrape device. Cattinair believes that the circulation drive, because of the closer spray cycles compared to linear drives, allows for a very evenly distributed application of the material and thus saves finishing material. The distance between the spray cycles is less than 50 percent for a circulation drive compared to a linear drive with four guns and a feed speed of 4 m/min. (13 ft./min.).

Cefla-Group introduced a new vision system to its automatic spray equipment for part recognition. Using this new system, all the spray guns are automatically put in positions that allow the most efficient and best application of the material (Figure 1).

Giardina presented its “Dual-Tech” automatic spray equipment. This system features a wash tower for cleaning the outgoing air and a lacquer recycling system for the conveyor.

Giardina also presented the new “robotic spray system” in its Robotech GS25 equipment. A six-axis robot adjusts the guns to the very best position for the most efficient application of the material according to the vision system’s recognition of part location, size and shape at the entrance of the conveyor. This way, a high-quality surface can be applied to the flat panels, as well as to edges that may be of complicated form. Furthermore, the system reproduces the exact material application sequence on every surface, as entered by the equipment operator. Thanks to advanced controls, the tasks can easily be programmed and thus used for small batch sizes.

Venjakob improved its automatic spray booth “HGS-Duo” (Figure 2).

Both gun supports are located at the infeed and outfeed opening of the equipment. The gun positioning motor is located outside the overspray area. The guns were equipped with a fast-lacquer/color changer system that allows changing from one lacquer/color to another within minutes (Figure 3).

Valtorta showed an improved version of its spray robot for spraying assembled cases (Figure 4).

This new concept allows finishing of three-dimensional parts, such as cases, finished furniture and tables. Furthermore, this robot is useful in lacquering part edges of flat parts stacked upon each other. By means of an automatic vision system that reads the three-dimensional geometrical sizes of the objects, the movements of the robot are optimized and adjusted to the shape of the case.

Vacuum applications

Vacuum application techniques are environmental friendly systems that work only with 100 percent UV or with water lacquers. Since no overspray is created, there is no lacquer loss. These systems have gained considerably in sophistication and versatility over the past years. For example, layers of UV lacquers up to 8g/cubic meter (0.03 oz./cubic foot) can be applied on parts with widths of up to 600mm (24 inches) featuring very high feed speeds of up to 40 m/min. (130 feet/min.).

Schiele showed a completely redesigned Vacumat-Future program, with increased efficiency for a wide range of profiles that need to be finished (Figure 5).

The Future-Coat-Vario system adjusts automatically to differences in part size and can be used for mouldings of different widths and for doorframe panels. The Vacumat-Kante- Vario (Vacumat-Edge-Vario) allows finishing of solid wood edges exactly to the glue line where the laminate starts. No covering of the laminate surface is necessary since the system works without overspray.

Giardina showed vacuum moulding spray equipment that features additional spray guns that assist the vacuum in covering the entire moulding surface. This principle is especially valuable for the treatment of mouldings featuring complex profiles that are difficult to cover evenly using a vacuum alone.

Roller and curtain coating applications

Burkle presented new combi-roller-coating equipment called SAS (Sealer Applying Equipment), a special spackling machine with reverse turning and a partially heated smoothing roll for viscous UV-based materials (Figure 6).

This combi-roller coater is used to fill veneer joints or cracks, as they often occur with veneer made from species that split easily. A UV lamp cures the filler after its application.

Hymmen presented a Siegel-Coater, which is suited to smooth and fill porous surfaces. Using a heated smoothing roll, a “Thermo-Siegel” can be achieved. Pores and cracks are evened out optimally and, due to the better run of the lacquer, an even, homogenous surface can be produced. Besides resulting in a higher quality surface, the Thermo-smoothing effect also reduces the amount of lacquer that needs to be applied.

Hymmen and Burkle also offer equivalent equipment for the application of “natural” materials (i.e. oils and waxes). For this equipment, heating of the application and smoothing rollers increases the quality of the resulting surface significantly.

Though not a new development, the Hymmen ProfiCoater (Figure 7) is nonetheless an important piece of equipment, especially for small and medium shops.

Being small, versatile and cost efficient, this is a one-person surface finishing line that uses UV lacquers to achieve high quality surfaces. The entire line consists of a roller coater and a UV lamp. The treated and cured parts come back to the operator. The cycle, depending on the finishing schedule, is computer guided and repeated as many times as necessary. Although this finishing line’s capacity cannot be compared to a larger finishing line, it allows smaller shops to use UV lacquers.

No revolutionary new developments could be observed for the curtain coating machines. Due to the increasing importance of low VOC systems, such as UV or water lacquers and colors that require only thin layers of material, curtain coaters are being replaced by roller coaters and spray guns. However, Burkle refurbished its curtain coater with a new generation of curtain heads that allow more accurate control of the amount of lacquer applied, and also minimizes the amount of lacquer needed to run the equipment. Both improvements allow an increase in material efficiency.

Edge coating

Interesting edge coating developments were observed. Particleboard producers are trying to recapture some market share from MDF panels by encouraging equipment producers to create equipment that allows preparing the particleboard edge for application of lacquer or of very thin foils. For this purpose, the edges are compressed with a special spackle.

Elmac-Superfici, Giardina and Cefla showed equipment in which modified 100 percent UV-acrylic spackle can be applied and cured with UV lamps. After sanding, a smooth edge is available whose structure no longer shows through the surface finishing or the thin edge foil.

Drying and curing

The topic of drying and curing has become very important due to changes in the finishing materials, but also due to changes in plant organization and logistics. In particular, the water-based surface finishing systems are a problem because their drying and curing time is significantly longer than for comparable VOC-solvent based systems. As a result, existing drying equipment, calculated to dry VOC-based lacquers and paints, does not have sufficient capacity for the new water-based systems.

The change from the often-used finger rack charts or jet dryers to systems that allow longer curing times, such as vertical dryers, is often impossible due to space limitations and the high investments required. For this reason, change from VOC-based systems to water-based systems is often delayed indefinitely.

These problems, however, do not apply to UV-based systems. The change from VOC-based systems to UV-based requires new drying technology, but typically requires less space and investment.

Convection drying

As in the past, such dryers are offered by Cefla, Hackemack, Rippert, Elmac-Superfici and others. Rippert presented the new Dry-Air system (Figure 8) at Ligna. This drying system, which is of greatest use when drying water-based lacquers and paints, is based on the artificial drying of the air used in the process to low levels of humidity. To adsorb the humidity, two systems can be employed: either condensation of the water vapor in the air (i.e. the humidity) on a very cold surface as used by Venjakob or the adsorption of humidity using an adsorption material, as used by Rippert. Feeding very dry air into the dryers increases the ability of the air circulating over the part surfaces to adsorb moisture for the finish. Also, because the temperature of the circulating air can be lower compared to systems that do not dry the air before injection into the dryer, the danger of having a rough and low quality surface is low. This is because the forming of the skin on the lacquer surface is delayed, i.e. the moisture from deeper levels of the lacquer layer can evaporate longer during the drying process. Since such systems control air humidity and air temperature closely, better surface finishing quality can be achieved. Often, existing air-drying systems can be updated to include air pre-drying units.

Venjakob showed its Hydrex-Trockenverfahren (Hydrex drying system), which is a closed system with dried air (Figure 9).

As previously noted, this system is based on the principle of condensing air moisture on a cold surface. The circulating air travels through a cold temperature exchanger, where the moisture condenses at temperatures of approximately -10 to -15 degrees Celsius (14 to 5 F). After this process, the air moisture content at 1 to 4 g/cubic meter (0.001 to 0.004 oz./cubic foot) is very low. After reheating the air in the heat exchanger to about 30 to 40 degrees Celsius (86 to 104F), very dry air is produced, which is very efficient in drying wet surfaces. Using this air, water lacquers are said to dry within 4 to 10 minutes, depending on the layer thickness of the material. Of course, flash off time before drying is absolutely necessary.

Infrared drying

A new infrared dryer shown by Rippert, the “Thermoreaktor-Sunkiss,” uses a wave emitter (lamp) to emit infrared energy and circulate gas heated air. Organic solvents (i.e. VOC solvents) are converted to non-polluting gases through this process. By means of air ventilation, hot air convection that supports the infrared waves is created. Cefla produces a gas-infrared-dryer based on the same principle.

However, for both systems, only limited experience is available. Therefore, the implementation of these systems has to be started carefully by testing different lacquer systems and optimizing process data, such as feed speeds and energy requirements.

At Schiele’s booth, the company Industrie Servis showed the “NIR (Near InfraRed)” technology. The NIR technology uses close proximity infrared waves, waves that have lengths close to the ones of visible light. These waves dry materials fast and carefully. Water lacquer layers up to 80 micrometers (0.003 in) thick can be dried within a few seconds. Also, the substrate is heated only slightly by this technique.

As with the infrared drying technique, the NIR technology is brand new, and very limited experience and knowledge about its use for wooden materials is available. Also, the energy requirements (energy prices in Europe are much higher than in North America and therefore of much more concern to manufacturers) of these systems have to be carefully evaluated.

UV drying

In the area of UV drying, IST Strahlentechnik, Elmag-Superfici, Hackemack, Burkle and other companies are offering equipment. Cefla equipped its UV drying equipment with a UV lamp with 160 W/cm (406 W/in).

Surface finishing materials recycling

Even though water lacquer systems are more expensive compared to VOC-based systems, water-based systems offer the opportunity of capturing and recycling overspray and reusing this material. Therefore, many companies presented new developments in the area of water lacquer recycling.

Cefla showed a redesigned scrape-system combined with a device that cleans the conveyors at their automatic spray booths. A reverse-turning application drum is used as a scrape, and it “rubs” the material on the conveyors away very carefully. Venjakob still offers its widely tested and used circulating scrape system for automatic spray booths. The company also has a low-priced transverse belt scrape combined with a conveyor cleaning unit, which removes overspray from conveyors very efficiently and carefully (Figure 10).

For small- and medium-size companies, Range und Heine Systemtechnik developed the low-cost Coolac system. This system allows water lacquer overspray to be recycled, and the system can easily be installed into traditional air exhaust spray booths. The overspray condenses on cooled surface plates and can be collected on the bottom of the plates and returned to the spray guns. This way, up to 40 percent of the lacquer can be saved. Change of color or lacquer can be executed quickly and there is no lacquer mud that needs to be thrown out.

Uvilac, a continuation of the idea behind the Coolac system, is a process that recycles UV-based lacquers with 100 percent solid particle content. At room temperature, such UV lacquers have high viscosity and are sticky. By heating the overspray collection plates, however, the lacquer becomes liquefied and can be collected on the bottom of the plates and reused.

Dust extraction systems for spray booths

Poorly functioning overspray exhaust systems for spray booths are a reality in many plants. Several companies offer help in saving as much as 60 percent energy by installing more energy efficient ventilators. Furthermore, significantly improved filter systems enable exhaust air to be cleaned and returned into the room, saving significant heating costs.

Rippert is a specialist when it comes to spray walls with dry separation and paper or metal-sheet filters. Rippert also offers the RTS-Rotation system with continuing cleanup of the filter for physically drying lacquers, such as VOC-based or water-based lacquers (Figure 11).

One advantage of this system is the automatically functioning prefilter, where most overspray is collected as dry waste.

Bergmann showed the newest generation of filter cleaners. An automatic filter cleaner either cleans the filter mats during breaks or the cleaning function is activated by computer controls at certain times. Thus, the mats are always clean and can take up the maximum amount of overspray, but do not hinder air penetration, which helps reduce energy requirements.

Another innovation was shown at GEW-Lackiertechnik, with its AB-Wibolack-spray booths with dry separation. The overspray is sucked into the Wibojekt-separation, where an air curtain collects incoming overspray. This system is designed to reduce exhaust requirements by up to 60 percent, and also decreases energy consumption.

Conclusions

Last year’s Ligna show presented many incremental improvements in the area of surface finishing. The trend toward VOC-free lacquers was dominant and will lead to fewer solvent-based applications being used in the future. Other innovative technologies were shown in the areas of application, filtering and recycling of lacquers. With more stringent environmental regulations to cope with, and high quality surface finishings, the Europeans are definitely a viable source of new ideas for North American producers. s

The authors:

Urs Buehlmann is assistant professor and extension specialist, North Carolina State University, Department of Wood and Paper Science, Biltmore Hall 3036B, Raleigh, NC 27695-8003. Telephone 919/515-5580, fax 919/515-8739,e-mail: urs_buehlmann@ncsu.edu, URL: www.ces.ncsu.edu/nreos/wood/.

Joerg Schleusener is professor emeritus, Swiss School of Engineering for the Wood Industry, Eschenweg 8c, CH-2554 Meinisberg, Switzerland. Telephone 011-41-32-377-2494 (from North America).

©2000 Chartwell Communications, Inc.