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Since time immemorial, powder coatings have been extolled as the finishing industry’s ultimate “environmentally friendly” technology. In the 1960s through 1980s, this revolutionary coating material and technique promised the complete elimination of volatile organic compounds (VOCs) in commercial finishing operations and boldly predicted its eventual dominance in factory-applied coating processes.
Fast-forward to the first quartile of this century, and — depending on who you’re talking to —powder’s market share of factory-applied coatings accounts for somewhere around 17-22%. Nevertheless, it’s undeniable that powder’s eco-friendly attributes have significantly influenced its growth over the past few decades.
The concept of environmentally friendly coating technology is multi-faceted and surpasses the simple elimination of VOCs. The “reduce, recycle, reuse” adage is a good place to embark upon an analysis of the many ways powder coatings are good for the environment, illuminating how switching to powder coatings can make a huge impact on sustainability and the environment.
Virtual Elimination of VOCs
The most obvious effect of switching from solventborne paint to powder coatings is a nearly complete elimination of VOCs. These compounds include most solvents and co-solvents found in liquid coatings. When released into the atmosphere, VOCs combine with nitrogen oxides and create photochemical smog in the presence of sunlight. This reaction produces ground-level ozone and fine particulates (< 2.5 microns) that can accumulate with high ambient temperatures, stagnant air, and temperature inversions.
Smog irritates the respiratory system, producing coughing, wheezing, and shortness of breath. Long-term effects include chronic respiratory disease, such as COPD and chronic bronchitis; inflammation of the cardiovascular system, causing hypertension, heart attacks, and strokes; neurological diseases such as Parkinsons and Alzheimer’s Disease; and an increased risk of lung, breast, prostate, and colorectal cancer.
VOCs emanating from solventborne paint can be captured by energy-intensive processes such as regenerative thermal oxidizers (RTOs) that use ceramic heat recovery beds to convert VOCs into carbon dioxide (CO₂) and water vapor through high-temperature combustion. This merely trades one form of environmental distress (VOCs) to another (high energy consumption). In addition, RTO produces CO₂, a greenhouse gas that is known to contribute to global temperature rise.
Reduction in Hazardous Waste
The powder coating process relies upon the deposition of electrostatically charged particles to a grounded conductive part. This process is highly efficient and achieves first-pass transfer efficiency of 70-90%, depending upon part complexity. Conversely, liquid paint processes exhibit a transfer efficiency ranging from 25-65%, depending upon the technique used.
The overspray of liquid paint is difficult to handle and nearly impossible to reclaim into a useable form. What’s more, liquid paint waste can be labeled hazardous for ignitability (flash point < 140°F), corrosivity (high or low pH), reactivity (especially isocyanates), or toxicity (mainly heavy metal compounds). Collecting liquid paint overspray is cumbersome, and disposal costs can be very high due to the special handling required.
High volume usage powder coatings are typically applied in booths that can capture and reuse overspray. This can result in an overall system efficiency of 95% or more percent (adhesion to racks and hooks accounts for most losses). In addition, most powder coatings are considered non-hazardous and can be easily disposed of in local landfills. It is highly recommended to confer with your local waste regulator for details on how to handle powder coating waste.
Worker Exposure and Workplace Safety
One immediate environmental advantage of powder coatings is reduction or elimination of worker exposure to hazardous materials. The solvents and chemicals used in many liquid paints are toxic and pose health risks. Commonly used solvents like acetone, toluene, and xylene cause acute neurological effects such as headaches, dizziness, and confusion, as well as long-term damage to the nervous system, liver and kidneys.
Isocyanates, often found in polyurethane paints, are highly toxic and can cause respiratory sensitization even at low exposure. Some liquid paints contain heavy metal-containing compounds (e.g. lead, chromium, cobalt, etc.) that are carcinogenic. Exposure routes include respiratory, skin contact, and accidental ingestion (e.g. coughing and swallowing phlegm) and therefore operators are instructed to use specialized personal protective equipment including respirators, googles, gloves and chemical resistant coveralls.
Powder coatings, on the other hand, are relatively non-toxic and require significantly less and simpler protection equipment for operators. Safety glasses, a NIOSH-approved dust mask, and optional dust-resistant coveralls are recommended for the handling of most powder coatings. (Please consult product safety data sheets for recommended PPE.)
Energy Costs
Compared to industrial liquid coatings, powder coatings typically require a relatively high-temperature curing process, ranging from 325-400°F. Nevertheless, in many cases, a switch to powder coatings can achieve lower overall energy costs.
Powders can be applied quickly and evenly in one coat, whereas many liquid paints require multiple coats with time-consuming solvent flash-off required between coats. Indeed, solvent/water flash-off with some liquid paints includes energy-consuming convection heat to accelerate the process. In addition, with the advent of newer powder technologies offering lower temperatures and less curing time, system energy costs continue to plummet and make powders more energy efficient.
Lower Carbon Footprint
DSM Resins and, more recently, Covestro (which bought DSM in 2021) published a thorough Life Cycle Analysis of several industrial coating technologies, such as solventborne, high solids, waterborne, and powder coatings. These technologies were compared in a cradle-to-grave fashion that included raw materials, coating manufacture, transport, metal pretreatment, coating application, and the final curing process.
They concluded that powder coatings, applied on a flat metal surface, can reduce carbon emissions by 10-55% compared to conventional solventborne coating systems. Specifically, they found that:
- Powder coatings applied in thinner layers generate approximately 0.3 kg CO₂ eq per m²
- Powder coatings at thicker layers and waterborne paints generate 0.3-0.4 kg CO₂ eq per m²
- Solventborne and high-solids (@30μ) coatings generate 0.44-0.6 kg CO₂ eq per m²
Production Efficiency and Yields
Powder coatings intrinsically produce films with excellent adhesion and chip resistance. After switching to powder, fabricators report higher production yields due to a lower incidence of chipping and damage to powder coated parts.
In addition, powder’s lack of defects from paint sagging, popping, and blistering further improve production yields vs. traditional solventborne paint processes. Higher production yields translate to less wasted resources, fewer reworked parts, lower disposal costs, and less energy expended.
Durability and End of Life
One of the most overlooked advantages is the durability — and hence, longevity — that powder coating provides. From metal office furniture and automotive components to household appliances and agricultural implements, powder-coated surfaces are known for their durability.
Powders are typically more corrosion resistant, UV durable, and chip resistant compared to most liquid paints, which means products stay in service longer. This reduces the demand for raw materials, energy, waste, and manpower associated with frequent repainting and replacement. In a way, powder coating supports a “buy once, use longer” mentality, which is at the heart of sustainability.
Furthermore, when fabricated goods eventually wear out and can no longer be refurbished, powder-coated films are non-toxic and pose minimal danger to the environment. Disposal of coated goods is straightforward and economical.
Case Studies
Powder coatings have replaced solventborne paints across various industries primarily to eliminate VOC emissions, reduce hazardous waste, and comply with evolving environmental regulations. Below are a few specific cases and industry examples where this transition has occurred.
Agricultural and Construction Equipment
- The Case: A manufacturer of agricultural equipment replaced a traditional liquid paint line with a powder coating system to reduce their VOC footprint and meet environmental regulations.
- Application: Small parts, such as gussets and brackets, were moved to the powder line, eliminating the need for hazardous waste disposal associated with solvent-based, high-temperature cure wet paint.
- Environmental Result: The shift allowed the company to reduce its VOC output by 7.8% within a year, with xylene emissions dropping by over 56%.
Contract Manufacturer
- The Case: A company specializing in custom metal fabrication and coating was experiencing high operational costs and high environmental impact from a traditional liquid coating system. They faced limitations on expansion due to air pollution regulations.
- Environmental Impact: The move to powder coating allowed the company to eliminate the VOCs inherent in solvent-based paint, directly improving indoor air quality for workers and reducing environmental pollutants. In addition, the transition eliminated the need for handling and disposing of hazardous solvents, paints, and sludge.
- Operational Benefits: The company reported a 50-75% reduction in utility costs (gas, electric, water) because the operation no longer needed the same level of exhaust and air make-up required for solvent fumes. The company also increased production capacity, allowing them to finish more parts in-house.
Office Furniture Manufacturer
- The Case: An American manufacturer of office furniture was using high-VOC solventborne coatings on metal components. The process involved significant hazardous air pollutants (HAPs) and required extensive hazardous waste disposal for excess paint and cleaning solvents.
- Environmental Impact: The shift to powder coating, along with other clean technologies, resulted in a dramatic drop in total VOC emissions at the facility, from 200 to 25 tons per year. By eliminating solvent-based coatings, the facility removed the need for hazardous waste disposal associated with liquid paint waste. The change eliminated hazardous emissions (like methyl chloroform, which dropped from 54 tons to 0 tons per year). To support the switch, the company adopted a high-temperature fluidized bed system (using sand at ~1,000°F) to clean coating hooks. This replaced chemical strippers that previously created hazardous liquid waste, replacing it with inert, disposable sand.
- Operational Benefits: The project was a financial success, with a return on investment of less than one year for the cleaning system; total project payback was achieved through improved efficiency and material savings.
Automotive Industry Components
- The Case: Through the years, the automotive sector has transitioned from solvent-based coatings to powder coatings for various parts (e.g., wheels, under-hood parts, EV components, and as a body primer) to meet durability and sustainability standards.
- Environmental Impact: Powder coatings provide superior corrosion resistance with negligible VOC emissions associated with traditional solvent-based primers and topcoats.
- Electric Vehicle Specifics: Electric vehicle (EV) manufacturers have embraced powder coatings for battery enclosures and power infrastructure parts due to its low-VOC nature and durability.
Architectural and High-Rise Construction
- The Case: High-performance (AAMA 2605 compliant) powder coatings have replaced liquid fluoropolymer paints on aluminum extrusions, curtain walls, and window frames in major construction projects.
- Environmental Impact: Powder coatings often allow for 95-98% transfer efficiency, meaning overspray is reclaimed and reused, reducing material waste compared to the 30-50% efficiency of many liquid systems.
- Examples: Projects like 55 Hudson Yards and 10 & 30 Hudson Yards in Manhattan specified powder coatings to achieve durable, UV-resistant finishes without the volatile solvents used in traditional liquid coatings.
Environmental and Economic Benefits
In summary, switching from traditional solventborne paint to powder coatings offers a wealth of environmental and coincidental economic advantages. VOCs are virtually eliminated, providing cleaner air and safer work conditions. No energy-intensive VOC mitigation techniques are required, and the environmental and economic impact of handling hazardous waste is avoided. Intensive studies have determined that powders have a smaller carbon footprint compared to solvent- and waterborne industrial coating technologies.
Powder’s utilization efficiency is high, often eclipsing 90%, which reduces material costs and minimizes waste streams. Single-coat, direct-to-metal application of powder coatings streamlines finishing processes, eliminates the need for cumbersome solvent flash-off, and produces no blisters or sags.
Powder’s renowned durability provides attractive economics by lowering in-plant rework caused by chipping and handling damage. And finally, the product longevity powder imparts reduces the frequency needed for refurbishment and replacement of manufactured goods. Without a doubt, powder coatings are the ideal industrial finishing option for sustainability and environmental friendliness.
To learn more, reach out to the author at kbiller@chemquest.com.
Read in Products Finishing.