February 18, 2021
by Tammy Schroeder
Building owners, facility managers, architects, specifiers, product manufacturers, and tenants are expressing an increased interest in paints and coatings offering microbial control.
Hospitals and clinics, schools and universities, government centers and office towers, hotels and hospitality venues, retail stores, residential high-rises, and senior living facilities include a myriad of painted or coated surfaces on which microorganisms may survive. The coated surfaces within these high-traffic buildings may include:
Most surfaces within commercial and institutional buildings should be cleaned on a regular basis to help prevent the growth of bacteria, mold, and mildew that can cause stains and odors on the surface of a product. However, cleaning alone may not remove the microbes.
Microbes usually are not seen until they have multiplied and are concentrated on a surface. They can break down these surfaces and finishes, and can cause a loss of coating or paint integrity. This microbial growth is perceived as a stain. The stain will continue to expand, using the surface itself as a food source and releasing unpleasant odors, until the microbial population is removed.
To augment regular cleaning programs, coating technologies containing antimicrobial compounds have been developed to provide an additional level of protection. Antimicrobial compounds can help prevent growth of stain- and odor-causing bacteria to help maintain the integrity of the paint or coating. These coatings may be employed on a wide range of products in high-traffic commercial and institutional buildings, including architectural aluminum products. This article focuses on antimicrobial coatings for architectural aluminum products.
The need for microbial control stems from the fact that there are an estimated 4.5 million bacterial and fungal species throughout the planet, many of which travel and migrate via the ebb and flow of people visiting commercial and institutional buildings. Microbes or microorganisms are living cells that can be detected by the naked eye once they have multiplied to the millions. Under the right conditions, some microbes can double in number every 30 minutes or faster.
Types of microorganisms include bacteria, algae, fungi, and mold.
Billions of years ago, bacteria were among the earliest forms of life on Earth. Bacteria are microscopic, single-cell organisms that are divided into two main groups by virtue of cell wall constitution: Gram-positive, such as Staphylococcus and Methicillin-resistant Staphylococcus aureus (MRSA), and Gram-negative, such as E. coli, Pseudomonas, and Salmonella.
There is no escaping the presence of bacteria. The majority of the bacteria that are encountered benefit the environment by helping return nutrients to the soil through decomposition of organic waste, or helpful to the human body (probiotics) through the digestion of food. In contrast, some bacteria cause stains, odors, and product and coating surface deterioration as their metabolisms produce acidic materials and sulfur-based compounds. These bacteria can adversely affect every day surfaces.
Most bacterial test protocols require the testing of two organisms, one Gram-positive and the other Gram-negative, due to the differences in the cell wall structure. Some antimicrobials are more effective against one or the other of these groups. Other types are broad-spectrum with good efficacy measured against both.
Early fossil records suggest fungi have been on Earth for more than 550 million years. Some experts estimate more than 1.5 million fungus species exist today. Common fungi include mushrooms, puffballs, truffles, yeasts, and most mildews.
Unlike bacteria, fungi are multi-cellular organisms containing membrane-bound organelles, and a ‘true nucleus.’ Fungal cells are encompassed by a strong, but flexible, nitrogen-containing polysaccharide called “chitin.” The chitin protects the fungus and, depending on the mode of action, can reduce or eliminate the effectiveness of many antimicrobials.
The most common means of fungal reproduction is the formation of spores. The spore formation occurs in fungi, such as Aspergillus niger (black shower mold), Penicillium pinophilum (bread mold), and Trichophyton mentagrophytes (Athlete’s Foot).
Mold spores are present everywhere in both indoor and outdoor environments, and many of the products found in buildings provide rich nutrient sources. The most common defense is prevention. This can include controlling the moisture in a building in order to avoid high humidity levels, and specifying products with antimicrobial protection to resist mold growth.
An antimicrobial agent in a coating is designed to inhibit the growth of stain- and odor-causing bacteria and to help prevent product deterioration of the coating from mold and mildew. The agent neither replaces normal cleaning practices nor is intended to protect users from disease-causing microorganisms. Microbes landing on surfaces treated with silver-ion antimicrobial coatings are not killed; rather, the silver-based particles emit ions that interfere with the microorganism’s metabolism, reducing its ability to reproduce.
Coupled with regularly scheduled cleanings, the antimicrobial coatings create an inhospitable environment for microbial growth by damaging the microbes’ cell walls. Additionally, this interferes with the conversion of nutrients into energy, inhibiting reproduction. The microbes die and are not replaced within the population.
Antimicrobial treatments in solid products are largely surface treatment effects. For most, efficacy is related to controlled diffusion at the surface. Limited or no migration out of the surface provides durability as the incorporated active ingredient is not used up.
The benefits of antimicrobial coatings on surfaces include odor control, and reduced staining and surface discoloration from bacteria, mold, and mildew. Again, please note products and surfaces treated with antimicrobial coatings do not disinfect their surroundings or contents. For example, neither is the water in a treated cup sterilized nor is growth in the water inhibited.
An antimicrobial coating technology can provide an added level of protection for the coated surface. Through research and testing, a high-performance architectural coating system containing silver-ion antimicrobial protection has been developed for use on both interior and exterior aluminum surfaces of architectural products to inhibit the growth of stain- and odor-causing bacteria. This architectural liquid coating uses a 70-percent polyvinylidene fluoride (PVDF) resin-based system.
When moisture is present, the antimicrobial technology in the PVDF coating activates the ion exchange mechanism and small amounts of silver cations (positively charged ions) are released into aqueous environments. The release rate is regulated by the unique amorphous glass structure, giving extraordinary longevity. The released silver acts on stain- and odor-causing bacteria by disrupting their metabolism and reproduction.
This architectural coating with antimicrobial technology consists of a three-coat finishing process designed to meet the requirements of American Architectural Manufacturers Association (AAMA) 2605-20, Voluntary Specification, Performance Requirements and Test Procedures for Superior Performing Organic Coatings on Aluminum Extrusions and Panels. This is the most stringent, high-performance specification standard used for architectural coatings published by the Fenestration and Glazing Industry Alliance (FGIA).
For building teams seeking these high-performance architectural coatings with antimicrobial protection to inhibit the effects of non-pathogenic bacteria including stain- and odor-causing mold and mildew, specifiers can include such language as:
PVDF-based, AAMA 2605-20, fluoropolymer finish containing minimum 70% PVDF resin, three-coat system with antimicrobial protection, [paint code].
The architectural coating’s antimicrobial protection safeguards the finished aluminum product’s surface throughout its useful lifetime. Incorporated during the coating’s manufacturing process, the antimicrobial additives operate on the cellular level in order to continuously disrupt and prevent uncontrolled growth of the microorganism.
The antimicrobial technology with the 70-percent PVDF resin-based architectural coating helps prevent the growth of stain- and odor-causing bacteria on the coating itself, while the painted finish protects the aluminum substrate. As microbes come into contact with the coating, the antimicrobial agent in the paint penetrates the microorganism’s cell wall, disrupting its ability to grow and reproduce. The enhanced coating does not replace traditional cleaning methods, but works to keep the surface cleaner longer by inhibiting microbial growth.
The proprietary antimicrobial technologies used in these architectural coating products are registered and approved by the U.S. Environmental Protection Agency (EPA) for their specific use in the product in which they are incorporated. They have a history of safe use in consumer, industrial, and medical product applications around the world.
All applications must follow guidelines set by EPA, including the language that is used to market products with antimicrobial protection. EPA regulates built-in antimicrobial claims under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), which limits claims to protection of the treated product and prohibits public health claims.
Surfaces labeled to be antimicrobial, resisting odors and stains that can adversely affect the coating, must be effective against multiple bacterial species, as confirmed by approved test methodologies. International standard-setting bodies are responsible for producing and validating antimicrobial test methodologies that are unbiased and provide an accurate representation of the efficacy against bacterial species.
These standard-setting companies include the International Standards Organization (ISO), ASTM, and the Japanese Industrial Society (JIS). The most common methodologies are ISO 22196, Measurement of antibacterial activity on plastics and other non-porous surfaces, JIS Z2801, Test for Antimicrobial Activity of Plastics, and ASTM E2180, Standard Test Method for Determining the Activity of Incorporated Antimicrobial Agent(s) In Polymeric or Hydrophobic Materials—a comparison of these methods can be found in Figure 1.
Testing of antimicrobial-treated hard surfaces is similar, regardless of the standard-setting body. Testing is conducted by placing the organisms onto the protected surface and in parallel on an unprotected surface. The samples are incubated for a specified amount of time at an optimal temperature for bacterial growth. After incubation, microbiologists remove the organisms and count them. The amount of bacteria remaining on the unprotected surface is compared with that on the protected surface resulting in a percent or log reduction. Since the bacteria are counted, this quantitative test is the ‘gold standard’ of antimicrobial testing to determine if the product is effective at resisting the growth on the coating of mold, stains, and odor-causing bacteria.
In addition to quantitative testing, samples also can be evaluated using qualitative test methods. These methods are visually assessed for bacterial inhibition. If bacteria grow to the edge of a sample, the underlying substrate becomes opaque. If it is well protected, there will be a clear zone around the sample where bacteria cannot grow; this is referred to as a zone of inhibition. The type of test utilized for a specific antimicrobial compound will depend on the antimicrobial being utilized and the matrix being treated.
These are all relatively complicated and involved test procedures. For this reason, it is suggested a well-accredited microbiology laboratory be employed for testing coatings and maintaining alignment with developmental bodies, such as ISO, ASTM, or the American Association of Textile Chemists and Colorists (AATCC). Additionally, laboratories can be accredited by ISO to ensure that there is no variation from accepted methodologies.
Even with the addition of the antimicrobial agent, 70-percent PVDF resin-based architectural coatings that meet AAMA 2605 will maintain their exceptional durability. This performance standard includes a 10-year South Florida exposure test in which the coating must lose no more than 5ΔEs of color. As per the specification, these finishes would exhibit outstanding resistance to humidity, color change, chalk, chemicals, and must retain a minimum of 50 percent of the original gloss value.
The antimicrobial product protection offered by these painted coatings is available in nearly any color option, including mica and metallic coatings. Some coatings manufacturers may limit certain bright colors that could fall short of AAMA 2605’s requirements. Finishing applicators can provide guidelines regarding color selection and material sizes, as well as samples, estimates, and warranties.
Choosing a factory finishing applicator that has experience working with PVDF resin-based coatings and antimicrobial technology will ensure the coating is applied in a quality-controlled setting in order to achieve the intended appearance and performance. For projects with additional sustainability goals, specifiers can indicate the 70-percent PVDF resin-based coating be applied by a factory finishing applicator utilizing a chrome-based, five-stage pretreatment system used in accordance with AAMA and ASTM standards and a 100 percent air capture system and regenerative thermal oxidizer to destroy the volatile organic compounds (VOCs) contained with the liquid coatings’ solvents. This means the VOCs are safely off-gassed and cured at the factory before the finished products arrive on the building site, so there is no adverse environmental impact.
Note architectural coatings with antimicrobial technology are not designed to replace normal cleaning practices. In high-traffic and public areas, where people may lean, sit, and touch exposed surfaces, more frequent cleaning may
be recommended. The simplest cleaning method of painted aluminum is to flush the finished surface with water using moderate pressure to remove dirt and soil. If the dirt is still adhering after the finished surface is dry, then a mild cleaning solution may be used. Choose a gentle soap solution that is safe for bare hands and apply with a soft cloth, sponge, or brush.
To avoid damaging the finished aluminum products, do not use strong acid or alkali cleaners including bleach. Also, do not apply abrasive materials and methods. Gently clean the finished surface, thoroughly rinse with clean water, and dry with a soft cloth. Always test cleaning agents in an inconspicuous area before using on a large scale. If in doubt, check with the product manufacturer or finishing applicator to ensure the product and finish warranties are maintained.
The warranty length depends on the paint type, color, and manufacturer, and project location and material. Some factory finishing applicators provide a 10-year warranty for 70-percent PVDF resin-based coatings including those with antimicrobial technology. The antimicrobial protection that is built into these high-performance architectural coatings during their manufacturing process works continuously for the useful lifetime of the coating.
Tammy Schroeder, LEED GA, is a marketing manager at Linetec, an independent architectural metals finishing company. With 20 years of experience in the finishing industry, she serves as an industry educator on high-quality, high-performance architectural coatings and services. She enjoys sharing her knowledge with architects, specifiers, and architectural product manufacturers working in commercial and residential building markets. Schroeder can be reached via e-mail at firstname.lastname@example.org.
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