The whole idea sounds like something out of a Michael Crichton
novel. At first thought, the notion of using silver to fend-off
bacteria seems as alien a concept as bringing back the dinosaurs,
traveling through time or, well… aliens.
But the truth about silver is that its protective qualities are
very real and have been prized for thousands of years, dating back
as far as the Ancient Egyptians, who used it to keep their food
stores free of mold and fungus, and the Phoenicians, who used silver
containers to keep water from being invaded by germs. Since the
1300’s, the Catholic Church has specifically chosen silver
for chalices and Eucharist trays to prevent the spread of disease
between priests and parishioners. In North America, pioneers moving
west put silver and copper coins in their water barrels to keep
the water safe to drink. Some scholars have even argued that silver’s
antimicrobial qualities may have earned the metal its role in werewolf
mythology.
Today’s applications of silver may not be as exciting as
the prospect of disposing of your friendly neighborhood lycanthrope,
but the element has come to play a critical role in the medical
world. Silver has been used in heart valve suture rings, catheters,
external fixation pins, burn treatment bandages and salves and even
in eye drops for newborns. Now, four years into the 21st Century,
silver is playing a defining role in the powder coating industry.
How Does It Work?
A safe material for human contact, silver is a natural antimicrobial
that has been shown to be effective in killing over 650 strains
of bacteria, yeast, fungi and molds.
Because it is an inorganic antimicrobial, silver has been able
to address many of the issues associated with its organic counterparts
that have been developed over the years. These include: thermal
stability, environmental compatibility, effective life expectancy
and last but not least bacterial resistance.
That means that - unlike antibiotic drugs, which face a growing
threat of antimicrobial resistance – silver’s antimicrobial
properties stand up over the course of time.
Even if the exact mechanism for killing bacteria is not well documented,
the results are “Silver kills microbes by interacting with
multiple binding sites that are unlike those used by organic antibiotics,”
explained Michele Potenza of Boston-based AgION Technologies Inc,
“the use of silver as antimicrobial is therefore unlikely to
promote antibiotic resistance.”
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Applications
of antimicrobial powder coatings include outdoor furniture to
dinnerware to appliances
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DuPont
Powder Coatings USA works with AgION
Technologes in the incorporation of AgION’s antimicrobial
compound directly into its Alesta® AM line of powder coatings.
The antimicrobial is a compound of elemental silver, ionically bonded
to an inert and bio-compatible ceramic material, known as zeolite.
The end user applies the powder just as he or she would any conventional
powder coating.
Once applied, Alesta® AM’s antimicrobial properties are
stable to 800° celsius and through a pH range of 3–10.
Moisture in the air triggers a propriety ion exchange process by
which silver is released at a controlled rate, maintaining an antimicrobial
surface (see Figure 1). If humidity increases, creating a more bacteria-friendly
environment, more silver is released. The compound does have a maximum
release rate, so even under very wet conditions, the silver still
releases slowly, insuring long term protection.
Though antimicrobial powder coatings have demonstrated an ability
to stand up to the evolving nature of bacteria, one potential drawback
of the coatings is that frequent washing can lower the antimicrobial
life of the coating.
Antibacterial Age
In today’s “Antibacterial Age,” in which everything
from hand soap to window cleaner touts antibacterial qualities,
neither the popularity nor the applications of antimicrobial powder
coatings is surprising. Applications for the technology include
food processing equipment, building materials, storage containers
and tanks, utensils and kitchen equipment, outdoor furniture, bathroom
fixtures, appliances, water coolers, ice making equipment, medical
equipment and fitness and playground equipment.
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The silver ions in the
zeolite carrier exchange with the sodium ions in the environment/moisture,
causing a controlled release of silver on demand.
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But if the technology–or at least the principles behind it–has
been around for thousands of years, how do experts explain the recent
explosion in popularity of antimicrobial powder coatings? For the
answer, one need not look further than recent headlines. A year
ago, the world was captivated by the SARS outbreak. In December
2003, scientists warned of a possible flu pandemic. It's natural
that headlines like these would migrate into the consumer conscious.
“During our investigation of the market for an antimicrobial
powder coating, we discovered a tremendous interest for these specialized
products. Consumers are becoming more concerned about surfaces that
may exhibit microbial growth, and prefer products that can assist
in reducing this,” said Doug Bach, senior vice president of
marketing and business development–Americas of DuPont Powder
Coatings USA. “There may also be a cosmetic benefit resulting
from this technology, since the growth of unsightly mildew and mold
may be reduced on such things as patio furniture used in warm, humid
climates.”
Future Applications
Though it would be unwise to “coat our entire world with antimicrobial
substances,” warns Marjorie Kelly Cowan, Ph.D., professor of
microbiology at Miami University in Middletown, OH, the technology
does hold tremendous promise, especially in hospitals and medical
facilities.
Antimicrobial powder coatings are currently in use at the new
City of Hope’s Helford Clinical Research Hospital in Duarte,
CA, on ductwork, door handles and hardware and push plates. Other
hospitals and clinics are looking into using antimicrobial powder
coated materials in emergency rooms, surgery areas and patient rooms,
on cabinets, counters and other surfaces.
At Montgomery, Illinois-based Lyon Workspace Products—a supplier
of steel shelving, lockers, storage cabinets, ergonomic workspace
products and pallet racks—antimicrobial powder coatings are
being used to coat lockers for schools and public facilities. The
company has become so enamored with antimicrobial coatings, it prominently
features the technology on its web
site.
“It has definitely been a selling point [for Lyon],”
said Matt Washington, vice president of manufacturing for Lyon.
“The last couple of jobs we’ve gotten have been because
of [antimicrobial powder coatings]. We first started using it on
lockers. But since then we’ve had a couple of people come forward
and say, ‘this is something we’ve been wanting for a while,
can you make it for us?’”
In addition to consumer-demand, another aspect of the appeal of
antimicrobial powder coating technology is that it did not require
the company to purchase new capital equipment. “We had to make
no changes [in order to implement the antimicrobial powder coatings],
which is why we like this all the more,” said Mr. Washington.
“It sprays the same as any other powder.”
According to Greg Bocchi, executive director of The
Powder Coating Institute, the emergence of antimicrobial powder
coatings represents a juncture of powder coatings with several key
industries. “With germ resistance even more critical these
days, this could become quite a breakthrough for not only the powder
coating industry, but also for the medical industry, food service
industry and others.”
