Durability and weather-resistance are non-negotiable requirements when specifying powder coatings for applications such as heavy equipment, agricultural vehicles, outdoor lighting and architectural products, playground equipment, and recreational goods.
For years, triglicydyl isocyanurate crosslinkers (TGICs) have been employed in exterior, polyester-based powder coating applications to provide those required characteristics. TGIC cross-links the film within a powder coating. At a certain temperature in the coating process, it reacts with the polyester resin to create a durable, weather-resistant film that adheres to a wide range of substrates.
A commercial alternative to TGIC powder coatings was developed in the early ’90s using beta hydroxyalkylamide (HAA), an alternative crosslinker that reacts with the same or improved versions of polyester resin used with TGIC. HAA (TGIC-free) delivered a durable, UV-resistant finish similar to TGIC powder coatings, but until the late ’90s, it remained more of a technical curiosity than a regularly specified product.
TGIC was classified as a Category 2 mutagen by all European Economic Union member states in 1998, resulting in restricted sales of TGIC-based products in Europe. Australia has also acted to regulate and restrict the use of TGIC powder coatings. While not an outright ban on TGIC, various EEU-member state regulations require finishers who use TGIC powder coatings to store them separately from other finishes, isolate workers who work with them and establish separate finishing lines. It is largely the extra handling required and the associated costs of establishing those practices that has led the majority of European finishers to opt for TGIC-free powder coatings.
As both products are priced similarly, purchase price is not an issue, and it is regulation that largely dictates where each technology is used today.
In the United States, TGIC powder coatings remain popular, but TGIC-free coatings have developed loyal followers as well. Several years ago, TGIC was placed on the state of California’s Proposition 65 watch list, but no regulations regarding its use exist in California or any other state at this time. TGIC coatings are also popular in Eastern Europe and the Middle East, where no regulations against the chemical exist, although the TGIC product is less popular in countries that are considering membership in the EEU. TGIC-free coatings have been widely used in China since 2005 as Chinese producers of HAA compete against each other for market share within the country.
TGIC-free coating options are available and are being used by manufacturers worldwide to achieve the same durable finish benefits as TGIC powder coatings. In fact, there are several advantages to the newer technology. It offers not just exterior durability, but enhanced mechanical performance, as well as flow and leveling properties.
TGIC-free powder coatings provide cost-saving benefits to finishers by offering superior first-pass transfer efficiencies. Companies that have converted to TGIC-free based coatings have documented first-pass transfer efficiency improvements of as much as 20 percent, with 10 percent being the minimum improvement usually documented. This means more powder transferring to the part and less going into the recovery system. If powder is sprayed to waste, these are real dollar savings to the finisher. If powder is reclaimed, the reduced amount of powder that is sent through the reclaim system means a reduced amount of fine particles (less than 10 microns) produced during the sieving operation. Smaller reclaimed particles may reduce transfer efficiency as they inhibit proper fluidization and are less likely to hold a proper charge.
Any complex part with interior edges and corners may be coated more efficiently with TGIC-free powder coatings. These products will penetrate into Faraday cage areas much more efficiently than TGIC powder coatings. Feed air pressures also can be substantially reduced, as not as much time and effort is required for those hard-to-coat interior corners.
TGIC-free technology is capable of holding an electrostatic charge better than TGIC powder coating technology; this provides a more consistent batch-to-batch finish with more even film across the part and less work required to coat more intricate parts. This also reduces the amount of powder drifting around (and potentially out of) the powder booth, as the particles will hold their charge long enough to transfer to the part.
TGIC-free technology is FDA-approved and is listed in the Code of Federal Regulations Title 21, Section 175.300, allowing for certification of an exterior durable coating to NSF Standard 51 for food contact and NSF Standard 61 for potable water.
One drawback of TGIC-free powder coating is the technology’s inability to meet the lower cure temperatures that can be achieved via TGIC technology. The lowest cure temperature that can be obtained with TGIC-free products is in the 315°F range, while TGIC products can be formulated to cure as low as 280°F. For the vast majority of finishers, this is not an issue. The bottom line is that finishers who use TGIC-free powder coatings instead of TGIC powder coatings will find that the cost savings from a transfer efficiency and application perspective will more than offset the savings in gas that could be obtained with a lower-cure product.
Both TGIC-free and TGIC powder coatings are available with newer, super-durable polyester resins. These coatings provide vastly improved gloss retention for products exposed to constant ultraviolet exposure. Application examples include construction and farm equipment, light poles, metal building components, and window and door frames. TGIC-free super-durable polyesters can be designed to meet the requirements of AAMA 2604-10 for commercial building applications as well as of GSB Master and Qualicoat Class 2 specifications.
TGIC-free powder coatings perform particularly well when a high-gloss, wet-look finish is desired, where miniscule batch-to-batch resin variations often cause gloss loss or hazing issues with TGIC powder coating. Here are a few examples:
A manufacturer of high-end commercial lawn mowers that desired the high-gloss, wet look switched to TGIC-free powder coatings several years ago, but also made improvements to its finishing line at the same time, adding new spray guns and equipment. The finish consistency dramatically improved and transfer efficiency increased by 15 percent. However, the manufacturer’s engineering staff suspected that the improvement may have been the result of the finishing line upgrades alone and chose to return to TGIC powder coatings. Transfer efficiency dropped and gloss rating variations returned. The company has since used TGIC-free powder coatings exclusively for this application.
A producer of structural steel components moved to TGIC-free powder coatings after an OSHA inspection of the company’s existing powder coatings line required line employees to be fitted with expensive protective-air-supplied suits. After the switch, employees needed to wear only dust masks, saving thousands of dollars. As an added benefit, the manufacturer found that the new coatings were easier to apply and provided better transfer efficiency than those used in the past.
A North American manufacturer of outdoor garden equipment was purchased by a European company that already used TGIC-free powder coatings based on European regulations. The new owner required that the North American facility convert all its coatings to TGIC-free for a consistent global product. When the conversion was made, the North American facility immediately recognized a significant improvement in first-pass transfer efficiency. This mandate provided added savings: fewer touch-ups were required, less powder was used, and a smaller amount of powder entered the facility’s reclaim system, reducing both the potential for powder breaking down and other reclaim system issues.
Is it Right for You?
TGIC powder coatings remain a major player in exterior powder coatings in North America, but TGIC-free coating technologies offer an attractive alternative with enhanced performance properties. And as the potential for regulation affecting the use of TGIC powder coatings continue to be discussed, finishers owe it to themselves to learn about the alternatives well before any new directives are in place.
Is TGIC-free technology right for your application today? Often, the choice comes down to whether a finisher is multi-national. TGIC-free powder coatings provide a true global platform. For finishers that operate facilities in countries where TGIC is already regulated, the choice to use TGIC-free powder coatings may be made globally for the sake of product consistency and to simplify purchasing, storage and handling.
And certainly, coatings manufacturers that offer technical support to customers should be consulted to help finishers understand the options available and to assist in making the choice between technologies. It goes beyond recognizing the complexities of the parts that need to be coated and where those parts will be used. The choice also involves reviewing a finisher’s current coating line capabilities and equipment, production schedule requirements and—if important—its customer’s specification process.
Bob Cregg is senior marketing director for building products at Sherwin-Williams. For more information, please visit oem.sherwin-williams.com. Photos courtesy of Sherwin-Williams.