A Fresh Coat
U.S. Manufacturers' use of low-volatile organic compound paint is improving air quality
- By Hank Godshalk
- Sep 01, 2005
Virtually all metal product manufacturers insist that their products perform well and look good. Often, a key factor in determining if these goals are met is the coating they receive before leaving the factory.
These same companies also want their factories to meet all U.S. Environmental Protection Agency (EPA) air quality standards and to be healthy environments for their employees. In many cases, this is also a function of the coatings applied to the products.
From a marketing perspective, appearance is critical. How a product looks conveys an important message about its value, quality, and performance expectations. Companies manufacturing items as diverse as furniture, tool boxes, lockers, generators, and construction equipment all insist that their products arrive with a consistent color, texture, and sheen. The color of some products is actually a legally protected identification feature. Today, a growing number of companies are producing painted glass products with the same appearance mandates.
Many metal products must perform in a surface-hostile environment. Portable metal chairs, for example, are constantly being kicked, spilled upon, and knocked over. Construction equipment often sits outside exposed to hot sun, cold snow, and abrasive dust and sand. Many products, such as automotive or industrial components, are primarily coated for protection rather than long-term appearance since they are hidden from view when installed, and because their appearance is relatively unimportant.
The manufacturers of all of these products want a coating that is as resistant as possible to chipping, scratching, and environmental forces.
Achieving all this used to be fairly simple. An air-dry or bake-enamel, solvent-based coating was applied to these products. These kinds of coatings hold their surface appearance and are resistant to chemicals, moisture, and abrasion. Unfortunately, solvent-based coatings also give off odors and air contaminants while being applied and while drying, resulting in environmental and workplace air contamination. But for many years, manufacturers using these coatings had few options. Other coatings failed to deliver the same production, quality, appearance, field performance, and economic requirements that were achieved by solvent-based paint.
Along Came the Act
The Clean Air Act passed in 1970, and things began to change. The statute was not targeted only at the coating industry but the Clean Air Act did mandate that coatings could only contain VOC (volatile organic compounds) levels of 3.5 pounds (lbs.) per gallon sans (without) water. Then, the most commonly used solvent-based paints ranged up to 6.0 lbs/gallon sans water. Actually, different federal and state VOC requirements were permitted, creating additional challenges for many manufacturers and their paint suppliers.
At its core, the difference between solvent-based paints and waterborne paints is the difference in their water levels. For example, the VOC content of solvent-based paint can range from 2.5 lbs./gallon sans water up to 6.0 lbs./gallon sans water, depending on the formulation of the paint. By excluding water from the calculation, the results reflect only the volume of VOCs and non-volatile solids. During the production of waterborne paint, however, the organic solvents are, in part, replaced by water, resulting in VOC levels between 1.5 and 3.5 lbs./gallon sans water.
Industrial manufacturers realized that reducing the coating-related VOCs in their factories would also help lead to plant-wide compliance with the Clean Air Act and improve factory conditions. If this could be achieved using waterborne coatings, they could comply with VOC requirements without sacrificing their significant investment in liquid paint lines, which often include integrated wash lines, spray paint booths, and drying ovens.
They saw other advantages, too. Paint booths are equipped with filters that absorb any over-spray. When they are replaced and discarded, solvent paint-laden filters must be treated as hazardous waste. When waterborne paint is used, the filters are less hazardous as long as spontaneous combustion of the oxidizing vehicle is guarded against. In addition, the risk of fire with solvent-based coatings disappears with waterborne coatings, providing both a practical advantage and a financial incentive in the form of reduced insurance premiums.
Waterborne coating manufacturers reached the same conclusions and began making significant research and production investments to create high-performance, low-VOC, waterborne liquid coatings that would empower manufacturers to meet market requirements and improve working conditions.
Underlying this trend in low-VOC coatings was a mutual understanding by industrial and coating manufacturers that any new coating also had to meet all the necessary economic and field performance requirements. No company could afford to adopt a coating that made a poor impression on the market, failed during use, or was too expensive to apply. For example, colors had to match that of the solvent paint being replaced, and color consistency had to be exact from batch to patch. Some companies market products that feature a metallic appearance as a key focal point. This product category had to be filled by waterborne companies as well.
Trial and Error
This was not an overnight effort. Paint companies first tried to emulsify resins in water, but this proved unsuccessful. Next came the use of water soluble-resins, which in the mid 1970s, allowed production of coatings with VOC levels of 3.5 lbs/gallon sans water but this also was not sufficient. By replacing organic solvents with water, VOC levels in a few coatings were reduced to as low as 1.5 lbs./gallon sans water.
In the mid-1980s came the adoption of latex polymerization with resins produced in water. This was suitable for creating flat- and semi-gloss coatings with VOCs as low as 2.5 lbs./gallon sans water, but this technology could not create high-gloss coatings.
Continued research led to VOC levels from 1.8 to 2.20 lbs./gallon sans water, but only in certain colors. New color dispersions, introduced in 2000, solved these color limitations. The adoption of still newer resin technology resulted in coatings with VOC levels as low as 0.3 lbs/gallon sans water.
Recent research has led to waterborne coatings with VOC levels near zero lbs/gallon sans water. These coatings are still under development to broaden their application, but the potential is significant. A factory using waterborne coatings and consuming 24,000 gallons per year can further reduce VOCs by 4,000 gallons if near-zero can be perfected. This represents $15,000 in raw-material savings.
While paint company labs were perfecting low-VOC formulas, the industrial market was still insistent that production efficiencies had to be achieved. For example, "Just In Time" manufacturers must switch production runs, and thus product colors, on short notice. Changing colors quickly to keep up with a rapidly changing manufacturing schedule is easily achieved with waterborne paint because the lines can be cleaned quickly between colors by flushing them with water.
In the factory, wasted paint means wasted production costs. The measurement of how much paint actually ends up on the surface of a product is called transfer efficiency and is also a determination of how thick the coating is. High transfer efficiency occurs when most of the paint is on the surface but at the minimum film-thickness required for tested field performance. When modern paint line equipment is used, waterborne paint can be applied with a very high transfer-efficiency rate that prevents overspending due to paint waste.
Many products have very small crevices and protected areas that can't be coated in a paint booth and must be touched up later. Solvent-based paint operations usually accomplish this touch-up process using small aerosol cans. This adds to air contamination and also requires a can disposal cost. Using waterborne paint, this touch up can be achieved with small, secondary spray booths.
Companies using bake-enamel coatings on their products must factor in the cost of fuel for the drying ovens. Waterborne bake-enamel coatings cure at a much lower temperature than the solvent-based coatings, resulting in lower fuel costs to achieve the required coating hardness.
The growing importance of ISO certification among industrial manufacturers has, of course, increased the demand for vendors who are also ISO certified. Recognizing that an ISO rating will impact their ability to market paint, many waterborne-coating manufacturers are seeking, or have already received, their own ISO certification.
Waterborne-coating companies are also attacking the Hazardous Air Pollutants (HAPs) issue. It is now possible for companies that operate high-volume production lines, and want to ship products as quickly as possible, to purchase a HAPs-free, quick-drying, air-dry coating. It is also highly moisture resistant, which is a requirement for many products that operate in both indoor and outdoor environments where there is a great deal of moisture and humidity.
This article originally appeared in the 09/01/2005 issue of Environmental Protection.