Coatings Innovation

A new resin combines benefits of thermoplastics and thermosets for powder coating applications.

Innovation. Whether it’s the high-tech industry or any other industry, innovation is the driving force behind success and growth. For example, five years ago, very few people used e-mail, or even knew what the Internet was. But, thanks to a variety of innovations, this industry has achieved unprecedented success and growth in recent years, and has changed the way people live and conduct business.

Innovation is just as important to the success and growth of the coatings industry. This month, as people from throughout the world gather at the International Coatings Expo (ICE) in Chicago, a variety of new innovations are sure to take center stage. In fact, show organizers have captured this thought in the theme of this year’s show — Driving Innovation.

Recent Coatings Innovations

Among the innovations showcased at ICE will be a variety of new products for powder-coating applications. Although the powder-coating process was introduced approximately 40 years ago, this segment of the coatings industry continues to experience phenomenal growth that far outpaces that of other coating methods.

Using the principle of “opposites attract,” the powder coating application method uses electrostatically charged particles that are sprayed onto electrically grounded parts. The charged powder particles adhere to the parts and are held in place until they enter a baking oven, where they are melted and fused to form the paint film. Because these dry powders do not run or drip, they produce a smooth, superior-quality finish.

In addition, the powder coating application method provides a number of environmental and economical benefits. Because the process does not use solvents, little or no volatile organic compounds (VOCs) are emitted into the atmosphere. And, because it is a powder process, uncon-taminated coating overspray can be collected and reused.

In addition to the need to meet increasingly stringent environmental regulations, growth in the powder-coating segment is being driven by the continual development of innovations that help manufacturers overcome the challenges of the past.

Among these innovations are a variety of new raw materials available for use in formulations. These materials allow powder coatings to be used in applications previously dominated by liquid coatings.

The durability of BLOX adhesive resins allows for the formulations of coatings with outstanding aesthetics, as well as abrasion and scratch resistance, for applications such as display racks.

Continuing Innovation in Powder Coating Materials

One innovative new material for powder coating applications is BLOX* thermoplastic resins from The Dow Chemical Co. This polymer breaks the rules of traditional powder coating resins, offering a combination of features that make it ideal for use in a variety of coating applications.

Traditionally, powder coating formulators have had to choose between two types of polymers for powder coating applications — thermoplastics and thermosets. Thermoplastics melt and flow when heat is applied, and continue to have the same chemical composition once they cool and solidify. Thus, these polymers can be melted and re-molded.

In powder coatings, thermoplastics offer superior performance in applications that require a thick, flexible coating — items such as metal fences and dishwasher baskets. In these applications, the coating must be flexible so that it does not crack or chip when the coated part undergoes stress or strain, such as vibration. Thermoplastics also provide a soft, rubbery feel for applications such as playground equipment.

The disadvantage of most thermoplastics available for powder-coating applications, such as polyethylene and polypropylene, is that they exhibit poor adhesion to metal. This results in coatings that tend to peel or blister. To formulate a thermoplastic powder coating with outstanding flexibility as well as adhesion, formulators use a high-performance, high-cost polymer such as Nylon 11 or 12.

Thermoset resins also melt when exposed to heat. When cured, however, they have a different chemical structure than the base resin. Unlike thermoplastics, they are crosslinked and will not soften back into the liquid phase when reheated.

In powder coatings, thermosets offer superior performance in decorative and protective applications that require a thin, durable coating — items such as automotive parts and electrical components. In these applications, aesthetics and durability, such as abrasion and scratch resistance, are a priority.

The disadvantage of these materials, however, is their lack of flexibility, which can cause the coating to chip or crack when the coated part vibrates, bends or expands/retracts.

Today, approximately 90% of all powder coating formulations are based on thermosets — epoxies, polyesters or acrylics. Because of their superior adhesion, epoxies or epoxy/polyester blends are used in a majority of these applications.

Figures 1-3 / Comparative Properties Charts

The Best of Both Worlds

With BLOX adhesive resins, formulators no longer have to choose between the flexibility of a thermoplastic and the toughness of a thermoset — these “epoxy thermoplastic” resins offer both. The combination of features provided by these polymers make them ideal for powder coating applications.

BLOX adhesive resins provide a number of benefits that can help powder-coating formulators take advantage of the benefits associated with thermoplastics and thermosets, without any of the disadvantages of either. These features include the following.

Superior Adhesion — As shown in Table 2, the adhesive resins offer exceptional adhesion to a variety of substrates, including steel, aluminum, glass and paper. In fact, the adhesion of these resins is equal to, or better than, two-part epoxies and Nylon 11 (see Figure 1). This outstanding adhesion provides for an extremely tough coating that will not peel or blister, which is especially beneficial for coating irregular shapes or other hard-to-adhere surfaces.

Figure 2
Durability — The adhesive resins also offer outstanding durability. In fact, they have a modulus better than ABS resins, and nearing that of Nylon 6,6. This durability allows for coatings that maintain gloss and have outstanding abrasion and scratch resistance (see Figure 2).

Figure 3
Flexibility — Because the adhesive resins are thermoplastic, they offer outstanding flexibility. This flexibility allows coatings formulated with the resins to resist cracking and chipping when the coated part undergoes stress or strain. It also means that they can be heated and re-molded over and over again.
Clarity — The adhesive resins also offer exceptional clarity. In fact, the clarity of these resins rivals that of PET and acrylics (see Figure 3), which is especially beneficial for decorative coatings in which it is advantageous to have the surface of the coated part show through — items such as automotive accessories and brass parts.
Improved Economics — In powder coating applications, the adhesive resins provide performance comparable to high-performance polymers such as Nylon 11 or 12, but with considerable cost advantages. In fact, formulators using the resins can save more than a dollar per pound versus Nylon 11 or 12. In addition, the use of the resins could cut system costs by eliminating the need to use primer coating or adhesive tie layers.

Conclusion

The combination of properties provided by BLOX adhesive resins will allow formulators to develop tougher, more durable coatings; replace current high-performance, high-cost polymers; or even improve their product offering.

Several leading powder coating formulators are already benefiting from the outstanding performance of powder coating formulations based on the adhesive resins. These companies use the resins to coat display racks, automotive accessories and sporting equipment.

In addition to powder coatings, Dow is also targeting the adhesive resins for a variety of other coating applications. The company has recently developed the technology that will allow formulators to use the adhesive resins in dispersions and solutions.

For more information on adhesive resins, call 800/441.4369 in North America or 517/832.1426 internationally (refer to element #1-63S08); or visit www.dowepoxy.com or www.bloxadhesiveresins.com.