Machine Design

Materials Engineering: Why You Shouldn’t Sit on Your Keyboard

Microbial counts on computer keyboards can be more than 60 times higher than on toilet seats, averaging 3,300 bacteria/in.2 Public surfaces, such as those of ATM machines, present even greater possibilities for the product damaging microorganisms.

Edited by Jean M. Hoffman

The good news is that a new HM 4100 antimicrobial additive from Biosafe Inc., Pittsburgh, has a structure engineered to puncture and rupture cell walls, killing 99.99% of the microbes on plastic surfaces in about 4 hr. “This contrasts with conventional antimicrobials that take up to 24 hr to reach the same kill rate. Conventional silver-ion-based additives leach into the cell, where they are metabolized and interfere with critical life processes,” explains Donald J. Wagner II, Biosafe vice president business development. “This mode of action, however, has been shown to cause microorganisms to mutate and adapt, becoming resistant to the antimicrobial.”

HM 4100 previously protected textiles from microbial growth. But until now it was available only as a liquid that had no application in polymer processing, says Wagner. “Drawing on organofunctional silane technology, we converted this material to a dry crystalline powder that is thermally stable for use in extrusion and injection molding. It permanently protects polymers from staining and degradation caused by bacteria, mold, mildew, and fungi and is more economical.” The material costs $0.25 to $0.50/lb compared to the $0.75 to $1.50/lb for silver-ion chemistry. HM 4100 also eliminates common problems including discoloration and opacity seen with silver-based additives, Wagner adds.

Biosafe sends the HM 4100 antimicrobial in crystalline powder or masterbatch form to RTP Co., Winona, Minn., for compounding. RTP can also render fillers — including hollow or solid-glass microspheres, ground silica, or diatomaceous earth — antimicrobial through a surface treatment. The Biosafe chemistry is FDA listed as a modifier to medical devices and has received its EPA label approval.

Make contact
Biosafe Inc.,
(412) 770-1302,
RTP Co.,
(800) 433-4787,

Keyboards made from Biosafe anitmicrobial plastics won’t stain or degrade from contact with bacteria, mold, mildew, and fungi. The antimicrobial plastics contain no volatile organic compounds, heavy metals, arsenic, or polychlorinated phenols.

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.