Demand for VOC-free coatings is increasing, and that demand will accelerate as more global regulatory attention is paid to products containing solvents and producing carbon emissions.
Many countries have or will enact regulations limiting the manufacture and use of solvents and evaluating various carbon tax schemes. This regulatory pressure is motivating coating consumers and users alike to seek out coatings that are at least are classified as “low VOC” and can be used as substitutes or replacement for solvent-containing coatings.
This shift is challenging resin and coating suppliers to develop new products and modify existing lines, an increasingly difficult proposition, given the new materials and solutions are required.
The fastest growing segment of the coatings industry is waterborne liquid coatings, which use water as a major solvent constituent material, but may contain other types of solvents such as alcohols, amines, and ethers. These other solvents assist with leveling and performance properties.
Liquid coating products dominate the $100 billion global coatings industry and are the product leaders in three broad industry segments: architectural, manufacturing and marine/specialty coatings.
But UV-cured powder coatings are becoming a viable substitute for solvent-borne and solvent-containing liquid coatings. The ability to finish heat-sensitive substrates and various other products with UV-cured powder coatings extends their market reach beyond that of both thermal powder and liquid coatings.
Powder coatings, which currently represent approximately 10 percent of the global coatings market, are 100 percent VOC-free and meet all air quality regulatory requirements with respect to manufacturing and application.
There are two types of powder coatings: thermal cured and ultra violet (UV) light cured. Thermal powder coatings require time and thermal energy to melt and cure the applied powder coatings. UV-cured power coatings melt rapidly and are instantaneously cured with UV light energy.
As the “Process Temperature/Dwell Time Analysis” in Figure 2 shows, UV-cured powder coatings are significantly faster and use much less energy. The area below each slope represents total energy consumed over time. This chart represents time and temperature to finish medium density fiberboard (MDF) substrate.
Figure 3 illustrates the fundamental difference between UV and thermal curing—separation of melting and the curing. In standard liquid or powder curing, the melt/flow or evaporation phase is continuous with the crosslinking of the coating to produce a cured product. In UV-curing the melt/flow or evaporation and curing is separated into two discrete processes, enabling proper timing and conditions for melt/flow followed by virtually instantaneous UV-curing.
A UV-cured powder coating system production cycle is faster than a thermal powder system. The speed has many benefits: smaller plant size, lower operating costs, less energy, higher sales per production cycle and faster return on investment.
There is also proportional size advantage of a UV-cured powder coating application system. Based upon an example of a typical UV-cured coating plant at 2,050 sq ft and a typical solvent-borne finishing plant at 16,000 sq ft—and assuming a $5/sq ft building cost—annual savings produced by the UV-cured powder system is $65,750.
Constraints of UV-Cured Powder Coatings
UV-cured powder coating is not without its constraints or limitations. UV curing is “line of sight,” meaning the UV light has to “see” the object or surface being cured. Certain geometries or parts with shadows can be difficult if not impossible to cure with UV light. And it’s not practical to retrofit an existing system to apply and cure UV-cured powder coatings.
A firm that wants to use UV-cured powder will have to build an application system or find a toll coater to do the finishing. Unfortunately, very few companies are applying UV-cured powder coatings, so until the installed base of application systems expands, the growth of UV-cured powder coatings will be limited.
One clear advantage of both UV-cured and thermal powder coatings is that the materials are not classified as hazardous, and manufacturing, application and waste disposal are not subject to onerous regulatory reporting or requirements. Ordinarily, they are classified on an MSDS as nuisance material and material handling; hand application requires an N95 dust mask; booth cleaning requires only a dust mask and Tyvek-style suit, and material spills can be cleaned with a standard shop vacuum.
Limitations aside, UV-cured powder coating is an exceptionally viable replacement for solvent liquid coatings and can be successfully applied on a variety substrates; ferrous and non-ferrous metals and heat sensitive substrates such as wood, plastics and composites. These are substrates that cannot be coated with thermal powder coatings or some types of solvent coatings. As the breadth of UV-cured powder chemistry expands, the use of these coatings on various types of substrates and for exterior and other rigorous demands will increase.
Any coating application has discrete process steps measured by time: application, melt and flow, solvent flash, cure (UV or thermal) and cool. Figure 5 illustrates the time values of each of those process steps according to the type of coating. UV-cured powder coating application has the shortest total process time, reinforcing the speed advantage of UV-cured powder coating application.
To demonstrate efficiency advantages, a model was developed to finish an 11.5 sq ft ¾-inch-thick MDF panel; one face and all edges. The model evaluates five finishing systems—three liquid and two UV-cured powder coating. Using pricing and technical data supplied by the coatings manufacturers, a material cost was calculated for each system.
Figure 6 shows the cost per square foot of material for each system. The three liquid systems are two-coat systems—primer and top coat. The costs shown represent the cost of paint material for both coats. The UV-cured powder cost is based on the typical one-coat to finish a product. System No. 5 UV-cured powder spray-to-reclaim has the lowest cost per square foot and a transfer efficiency of 95 percent. System No. 2 alkyd air dry enamel low VOC has the next lowest cost per square foot, followed by No. 4 UV-cured powder coating, a spray-to-waste process with a 65 percent transfer efficiency.
Assuming the work is done, the analyst often will stop once the cost per square foot he has been determined. In reality, it is only just beginning. Throughput and revenue generation must be calculated and evaluated to fully develop an ROI for each finishing system. Again using technical data sheets and production process assumptions, Table 1 shows the volume of parts that can be finished during a standard eight-hour shift.
The UV-cured powder coating models produce an equal number of parts and significantly more parts than any of the liquid systems. The typical time to produce a finished part on a UV-cured powder coating system is 20 minutes, start to finish. The advantage of the UV-cured powder-reclaim model is higher transfer efficiency, thereby reducing the material costs. In this model, the spray-to-reclaim saves $1,071 per eight-hour production cycle.
Gross Revenue Analysis
The model uses a selling price of $2/sq ft or $23/part. The production rate for both the UV-cured powder systems is the same, producing $26,772 gross revenue per shift. This is 2.8 times the gross revenue production of the No. 1 the best-performing liquid system.
UV-cured powder coatings are well worth considering when seeking coatings that are have low environmental impact and minimal or no regulatory restrictions on production, use or disposal. UV-cured powder coatings are highly productive, safe and VOC-free.
Michael Knoblauch is president of DVUV Powder Coatings. He can be reached at 216-741-5511.