Joined: 16 Mar 2004
|Posted: Fri Jun 15, 2007 12:10 pm Post subject: Nanotechnology enhances electronic displays
|Nanotechnology enhances film substrates for electronic displays
Devices with high resolution displays are now a part of everyday life; mobile phones, PDAs, in-car entertainment, satellite navigation equipment, industrial instrumentation and control systems provide unmatched levels of performance and reliability, while being smaller, slimmer and more lightweight than ever.
Less visible though is the complex, multi-layer arrangement of materials and components behind each application, responsible for ensuring optimum light transmission, mechanical properties or protection.
Manufacturers of electronic displays have traditionally had to find a compromise between functionality and the characteristics of the materials used, often limiting the quality of the display. In particular, the optical film materials used to produce light diffusion layers in LCDs, and the exterior or upper layers in touch screens and OLED panels, have had a considerable impact on performance, affecting factors such as light transmission and uniformity, panel flexibility, viewing angles, reflection and glare, and resistance to chemicals and abrasions.
Superior light diffusion
Light diffusion films like, for example, the MacDermid Autotype BLD range, are designed to provide uniform backlit illumination for LCD displays, with as much light as possible reaching the viewer. Typically, the construction of a backlight unit comprises a source of illumination, such as LEDs or a cold cathode fluorescent lamp (CCFL), plus a reflector and light guide, above which a prismatic layer, sandwiched between two light diffusion layers, is mounted. The diffuser films are required to provide optimum levels of light transmission, helping to minimise the power required to drive the backlight, while effectively diffusing the light so that it is uniform across the LCD.
Traditional light diffusion films that use a PET base material with an acrylic or fixative surface coating, require diffusing particles and filler materials to provide acceptable properties. Some of these fillers can adversely affect the optical characteristics of the film, scattering or absorbing light and reducing levels of light transmission and uniformity.
As a solution to this problem, a new generation of films has been developed by MacDermid Autotype, which eliminates the need for filler materials and features optically clear hard coatings that significantly improve the brightness, diffusion and homogeneity of emitted light, while reducing light absorption losses through the diffuser to less than 1percent.
The new films use a mechanically stable, high clarity PET base, with a micro-roughened anti-Newton back coating, to eliminate Moiré interference, and a uniquely formulated front layer coating, that is resistant to chemical and physical damage, yet produces outstanding optical characteristics. In particular, the new films allow over 92percent of the light to be directly transmitted, without affecting the colour balance or uniformity of the light emitted.
The robust mechanical properties of the new BLD Diffuser films make them easy to handle in production. There are no particles or fillers to become dislodged and therefore to contaminate the backlight production process, leading to greater production yields, with significantly less scrap, and higher overall product quality. In addition, the new films are manufactured in the latest cleanroom production facilities, ensuring that the quality of the diffusion hardcoat layers are consistent and uniform across every sheet of film produced, eliminating the problems of pin holes and scratches that were often associated with earlier generations of materials.
Developments in coating technology
In many electronics applications, the mechanical and chemical properties of the film substrates are also of importance. Touch screens, flat panel displays, and lenses for mobile phones and PDAs require a durable, perfectly clear and often flexible layer, which is free from light reflections and glare. A number of new developments in coatings technology look set to improve the overall performance of these outer optical layers.
For instance, an innovative film developed jointly by MacDermid Autotype and the Fraunhofer Institute for Solar Energy in Germany, replicates the nano-structures found in the eyes of moths, which have evolved to collect as much light as possible without reflection, in order to prevent moths being detected by night time predators.
The new film, called Autoflex MothEye, is now being manufactured in the UK using nano-replication techniques and is the first of its kind to combine both anti-reflective and anti-glare properties, with a hardcoat finish that is resistant to scratches, chemicals and fingerprints and which has an exceptional level of optical clarity. The result is a tough, dimensionally stable and formable film, using PMMA, PC, PET and TAC substrates, which reflects less than 1percent of visible light, regardless of viewing angle, and eliminates the problems of iridescence and light glare that are often associated with conventional display materials.
The new film will be of particular benefit in small high resolution portable devices, where the combination of colour with mobility has traditionally had an adverse affect on battery life, as it allows enhanced perceived brightness or reduced power consumption for any type of LCD panel without sacrificing reproduction characteristics or view angle.
Electro-magnetic interference (EMI) shielding is needed to protect electronics equipment, by either filtering out conducted electromagnetic interference or shielding radiated electromagnetic waves, and must be incorporated into the design of the new film substrates as well as optical and mechanical demands.
The addition of display windows to equipment effectively creates a break in the shielding, requiring a screen or mesh to be incorporated to attenuate the electromagnetic waves. Conventionally, manufacturers have used a screen with a regular square pattern. This severely restricts light transmission and can create moiré effects when placed over a computer display screen.
A company called Optical Filters Ltd has recently designed a solution to this problem, using a mesh pattern with rectangular openings formed in an extremely fine copper wire screen, which is coated by means of a proprietary chemical blackening process and then integrated into a multi-layer construction between outer layers of a hardcoated polycarbonate optical film. This new design provides a superior level of light transmission of over 80 per cent and virtually eliminates the common problem of moiré fringing.
The specially coated optical film is crucial to the success of this design, creating a protective outer layer that is resistant to scratches, abrasions and a wide range of solvents, while exhibiting excellent optical clarity and mechanical characteristics.
These advanced optical film substrates are enabling manufacturers of a wide range of electronic products to improve the functionality and performance of LCD and other graphics displays, and giving product designers considerable potential to develop the capabilities of display screens even further.
Dr Keith Parsons is Technology Manager Light Management Films, MacDermid Autotype, Wantage, Oxon, UK. www.macdermidautotype.com
Story first posted: 22nd January 2007.