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  • Acrylic Windows Improve Scanning

Photonics Spectra
May 2001
Daniel C. McCarthy

The material quality of a barcode scanner's window may seem to be a trivial detail to scanner users, but careless material selection by the manufacturer contributes to misreads, failures and the need for frequent maintenance.

Polycarbonate's impact resistance makes it the material of choice for the windows in handheld scanners, but window supplier Dawar Technologies instead selected Clarex acrylic from Astra Products Inc.

"[Polycarbonate] would never work better, but it is always cheaper," said Tom Fabek, vice president of sales and marketing at Dawar. "If the end users are not having problems with 'bad reads' due to scratching, reflection, poor light transmission and so on, then [it] is used to lower costs."

Selection criteria for handheld scanner applications prioritize a window material's hardness and the degree to which it accepts custom-engineered optical properties. Dawar manufactures windows using a casting process that, unlike injection molding and extrusion methods, produces sheets that are equally strong on both sides to reduce warping. The processed material carries a pencil hardness of 2H, comparable to a Lexan window, but it can be coated to 7H, Fabek said.

Dawar also modifies the optical properties, producing, for example, red windows that match the wavelength of the scanner's laser. The company makes three red windows, one for 630-nm, one for 650-nm and one for 670-nm applications.

It also processes acrylic sheets with five different antiglare surface finishes that, unlike coatings, cannot be rubbed off. "Clarex is an excellent nonglare display window," he said. "We sell a large volume of Clarex for this application, in addition to the special, custom-red exit windows for bar-code scanners."

The material also can be coated. All of Dawar's acrylic windows are available with coatings to resist reflection, fogging and other problems. "In some cases, if the laser inside the scanner is set at a difficult angle relative to the exit window, antireflectivity becomes critical," Fabek said. "Our cast acrylic material with a vapor-deposited antireflective coating can solve the bad reads that will otherwise occur."

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