Manufacturers and those that specify metal products are confronted with a range of choices concerning so-called sustainable paints and coatings. Multiple formulas, application types and sourcing models make sifting through green claims a real challenge. Understanding how paints and coatings are applied, including different business models for fabrication, can help you make an informed choice for your next project.
Types and Application Methods
Paints and coatings are intended to beautify and protect their substrate, whether it be metal or another material. The three primary reasons for application include modifying color, altering appearance and offering protection. Paints are designed to mask a surface while remaining separate from that surface. Coatings are designed to bond to a surface and become united. There generally are four processes for applying a finish to metal products.
Electrocoating is an application method that uses an electrical current to deposit the material. The fundamental physical principle of electrocoating is that materials with opposite electrical charges attract. For example, the base material is positively charged and then dipped in a solution with a negative charge. The opposite charges attract, thereby depositing a well-adhered coating to the base material.
Powder coating is different from electrocoating in that there are no liquids or solvents. The process uses heat to convert a sprayed fine powder into a continuous film. The dry powder overspray can be reclaimed for an efficient application process. The absence of a liquid binder helps reduce or eliminate VOCs.
Traditional liquid painting—applied during manufacturing or after installation—offers features that are not necessarily available from powder or electrocoat coating technologies, including greater flexibility regarding color choice. With liquid painting, multiple colors can be applied using manual or automatic paint changeovers within spray booths. Changing colors with other systems can be more labor intensive. In addition, liquid painting offers greater color matching..
A fourth choice is galvanization, which involves the application of a thin layer of zinc to the surface of a metal part. The zinc bonds with the metal substrate to create a coating.
In addition to multiple application methods, different chemistries help meet a variety of durability, appearance, formability and cost considerations. These chemistries include acrylics, epoxies, fluorocarbons, polyesters, siliconized polyesters, plastisols, urethanes and acrylic waterborne.
Manufacturers select individual chemistries based upon a physical property the coating exhibits. These properties include hard surface; dirt and stain resistance; adhesion; recoatability; cost effectiveness; weathering and chemical resistance; flexible resistance to post-bend fracture; or color/gloss retention. Painted metal products are used in a variety of applications, including residential and commercial building products, HVAC equipment, signage, appliances and decorative trim.
Perhaps more so than other products, paints and coatings receive a lot of attention for their potential to adversely affect occupants and the environment. These products have the potential for offgassing and release of VOCs during drying or curing. Paint manufacturers have responded to concerns by altering chemistries and substituting ingredients where available. These formula modifications may be due in part to the rise of green-building programs like the Washington, D.C.-based U.S. Green Building Council’s LEED certification.
Green-building programs like LEED specify different emissions thresholds for interior and exterior paints, as well as other substances like adhesives, sealants, etc., to avoid air quality impacts. This usually is expressed in grams of VOCs per liter of paint (g/L). These thresholds usually are created by accredited standards-setting bodies like Washington-based Green Seal. Green Seal’s GS-11 (Paints and Coatings) standard specifies that paints and coatings should not exceed a specified g/L of VOCs depending on the specific formulation. For example, flat top coats should not exceed 50 g/L while anti-corrosive coatings should not exceed 250 g/L. Other programs like the Green Guide for Health Care—created and administered by a diverse coalition of health care stakeholders—rely on the VOC content limits established in the Diamond Bar, Calif.-based South Coast Air Quality Management District Rule 1113, Architectural Coatings. The SCAQMD is the governmental body charged with regulating air quality in smog-prone southern California.
Despite the potential for air quality impacts from paints and coatings, one important factor specifiers must consider is the durability and useful life of the coating. Metals can oxidize or corrode when exposed to rain, wind or chemicals. Properly applied coatings can extend the life of metal substrates, thus reducing raw material consumption and associated impacts during the life of a product.
In addition to choosing the right finish for the metal product, manufacturers increasingly are examining the best sourcing model for paints and coatings. Options include in-house paint shops, outsourced painting, or purchase of pre-painted or coil-coated metals.
In-house or Outsourced Coatings
Traditionally, manufacturers have applied paints and coatings as an intermediate or final step during production. In-house paint shops require knowledgeable staff, special equipment and sufficient working space. Tougher environmental regulations and advancements in technology have forced many manufacturers to move away from in-house applications to third-party vendors. Coating contractors operate regional coating centers for multiple manufacturers, design/build/operate coating centers for manfuactuers or provide staffing for a manufacturer’s existing paint shop.
Some metal fabricators are taking the outsourcing further by purchasing pre-painted or coil-coated metal. Coil coating refers to metal in a coil form that is cleaned, pre-treated and applied with various coatings using a continuous process.
According to the Cleveland-based National Coil Coatings Association, there are several reasons to eliminate a manufacturer’s paint operation and move toward purchase of pre-painted metals. They are to reduce costs, reduce capital outlay, reduce environmental compliance expenses, improve quality and minimize hassles.
Some manufacturers switch to coil coatings as a cost-effective alternative to in-house paint shops when costs grow due to compliance with tougher environmental regulations. Other times, coating quality needs improvement and coil-coated metals are uniformly cleaned, pretreated, painted and cured as a flat surface, so edge-to-edge and side-to-side variability is nearly eliminated.
By purchasing coil-coated metals, manufacturers may be better able to control the life-cycle costs associated with the end product by allowing a coating specialist to address the environmental consequences associated with vapor degreasers, paint booths and washers. A well-run coil-coating operation can be more efficient and better able to control waste than a general manufacturer. Furthermore, outsourcing paint operations using coil-coated metal can reduce a manufacturer’s total energy consumption by shifting the energy costs to the coil coater. In most cases, the coil coater uses less total energy due to the highly efficient nature of the process.
Some coating manufacturers also seek higher level process or product certifications, such as the Cradle-to-Cradle certification from Charlottesville, Va.-based MBDC, which considers environmentally safe materials, design for material reutilization, use of renewable energy and other attributes. Other coating manufacturers focus on total carbon emissions and work to reduce their carbon footprint or phase out specific ingredients of concern, such as fluorosurfactants.
Whether modifying an in-house painting operation or deciding to outsource coating operations to a vendor, sustainability can be an important criterion for manufacturers and purchasers. Gathering facts, evaluating options and having clear sustainability goals will help lead to long-term success.
Scott Florida writes about architecture and sustainability from Oakland, Calif.