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Adhesives Hold the Big Picture

Photonics Spectra
Jun 2002
Brent D. Johnson

Although demand for large-screen televisions hasn't exactly exploded in North America, it is picking up momentum in a much larger market: China. In a country where there is one car for every 1000 people, large-screen TVs have become the ultimate status symbol, making China the biggest market in the world for these devices. This growing demand has made the market more competitive, increasing the pressure to make large-screen liquid crystal displays (LCDs) more viewable.

Looking at the big picture in large-screen display manufacture: Not all dispersed particle diffusers adhere the same. An optically clear silicone transfer adhesive helped eliminate optical layers in the display and reduced loss by 3 to 4 percent. Courtesy of Adhesives Research Inc.

To provide higher contrast in screen sizes as large as 60 inches and to improve the angle of view, newer displays laminate graded-index diffusers beneath the front polarizer in the LCD stack. However, a variety of film materials are available and many have different surface characteristics and bonding regions that make reliable adhesion problematic.

Such was the problem confronted by Microsharp Corp., which manufactures a large-area dispersed particle diffuser called Projexis that can be used in both front- and rear-projection systems. The diffuser, placed above or below the brightness enhancement films, improves contrast over lenticular projection screens and an angle of view from 20° to 100°.

Despite these benefits, the company found that off-the-shelf bonding adhesives were incompatible with its technology. It had difficulty finding an adhesive that met the appropriate optical requirements, defect levels, wavelengths and nonbirefringence. After extensive trials, the company found that ARClear 8932 optically clear adhesive from Adhesives Research Inc. was superior with respect to delamination; this was attributed to adhesive promoters in the silicones.

Dave Williams, market development manager at Adhesives Research, said that his company developed its transfer adhesive because new optical materials with higher bond levels have different rates of expansion and low surface energy that are resistant to contact. The adhesive can help eliminate optical layers or components, reducing loss by 3 to 4 percent. This a significant increase in performance if the total transmission from a backlight is only 15 percent.

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