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Letting through only light that moves in specific directions |
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Not so long ago, cathode-ray tubes (CRTs) accounted for nearly all display screens. The CRT was the obvious choice for many applications from televisions and security monitors to computer screens. Today, however, LCDs are spreading rapidly and may supplant the CRT in the role where it was previously dominant. LCDs are much more compact than CRTs, and recent years have seen substantial improvements in LCD features like viewing angles.
In simple terms, LCDs create text and images on screen by allowing or not allowing light to pass through a given pixel when an electric field to it is turned on or off. What is displayed on-screen results from this control of light, and in this polarizing films play a key role.
“In nature, there are various kinds of light in random electric fields,” explains Nobuyuki Kurata, group manager at Sumitomo Chemical’s IT-related Chemicals Research Laboratory. “LCDs operate by allowing only light which has an electric field in certain directions, what we call linearly polarized light, to pass through. LCDs use two polarizing films. One allows only linearly polarized light through, then the liquid crystal elements bend the light 90ΕΎ, and finally the other polarizing film either blocks the light or allows it to pass.”
Polarizing films are thus one of the key technologies in LCDs. Sumitomo Chemical Co., Ltd. began making polarizing films in the early 1990s. It now manufactures and sells them under the brand name SUMIKALAN, which has an overwhelming share of the market for polarizing films for smaller LCD displays such as those used in mobile phones and digital cameras. Almost all color displays for mobile phones use SUMIKALAN, while the brand also continues to grow in the large-LCD segment, for applications such as televisions and notebook computers. |
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| LCDs have become an indispensable component in the IT age, and are found in products such as office machines, mobile phones, automotive instrument panels, flat-panel televisions, PDAs, and LCD projectors. Polarizing films are an indispensable component of LCDs, and demand is rising steadily for more advanced and more diverse film capabilities. |
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Strength as a chemicals maker |
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Sumitomo Chemical’s products have numerous outstanding properties. For example, the company’s distinctive rolling technology enables it to produce polarizing films up to 1,250 mm wide, which gives Sumitomo Chemical a particular advantage of being able to supply low-cost polarizing films for use in big-screen LCD displays, since few manufacturers can produce such wide films of uniform quality. Moreover, the company’s films are color neutral and have sharp contrast and good clarity.
“Polarizing films use materials that absorb light moving in a certain direction within an electrical field,” Kurata said. “The two chief types of materials are iodines and dyes. Most manufacturers use essentially the same type of iodine. But in dyes, we use materials with a unique structure that we developed. As a diversified integrated chemicals manufacturer, we build on long years of experience developing and manufacturing dyes, which allows us to differentiate our products from those of competitors with our dual technologies in dye manufacturing and coloration.
Besides polarizing film, Sumitomo Chemical manufactures a variety of other optical films for LCDs. SUMIKALIGHT, a retardation film, is one example. This film’s structure controls vertical refraction to correct for viewing angles and phase-shift mismatches that can arise as linearly polarized light passes through liquid crystal elements. Although polarizing films generally sufficed in the past, quality and performance demands have increased rapidly so that retardation film has become an essential element in the array of technologies that go into thin-film transistor (TFT) displays, today’s primary LCD technology. Sumitomo Chemical was the first to begin making retardation film.
Kurata is unreserved in his confidence in the company’s strengths.
“Large LCDs all use TFT technology,” he said, “and the primary role of retardation film is to improve viewing angles. As with polarizing films, our position as a diversified chemicals maker gives us a competitive advantage in materials development, and this starts right at the top of the value chain and extends all the way to marketing. Since polarizing film is attached to the LCD’s glass substrate with an adhesive, for example, the material properties of the adhesive itself are critical. Since adjusting such properties falls squarely within the realm of chemistry, our foundation in chemicals gives us tremendous strength in this area.”
In 2001, Sumitomo Chemical consolidated its IT business, which was formerly spread across several Sectors, into a new, integrated IT-related Chemicals Sector. Within that, the Optical Materials Division is involved in development and manufacturing of products that combine chemistry, electronics, and optics. Kurata said this division will focus on raising its development and manufacturing capabilities in large LCDs. Before long, we will undoubtedly see new key technologies and devices for LCDs on the order of SUMIKALAN.
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The extremely thin polarizing film has six layers. They allow LCDs to work by allowing only linearly polarized light to pass through from the natural random electrical field. |
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