Sophisticated electronic displays are increasingly being situated outdoors, both to offer information to the public, for example in train stations or at ATMs, and as an eye catching method of presenting advertising messages. In each case it is vital that the information being displayed can be viewed clearly at all times of the day, and in any light condition. This is facing the manufacturers of these displays with a considerable challenge; in addition to offering consistent optical clarity in any environment, the screens they develop must be able to avoid problems such as reflection and glare, which can often impair the viewer’s ability to read a display, particularly in strong sunlight. Furthermore, being situated outside, the displays must also be resistant to scratches, abrasions and discolouration, without the protective elements affecting the light transmission levels.

Previously, manufacturers have had to make compromises in this area, primarily due to the limitations of the materials available for use as the surface layers of displays. For example, the materials typically 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 light transmission levels and screen uniformity, limiting viewing angles, and leaving displays prone to reflection and glare.

However, a new generation of specially designed diffuser and optical film substrates are now available that have been developed to offer excellent optical clarity in all light conditions, eliminating the problems previously encountered.

These films include a range of superior light diffusion films, which are able to provide uniform backlit illumination for LCD displays, with as much light as possible reaching the viewer. The construction of a backlight unit typically consists of 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. A high quality light diffusion film is necessary to provide optimum levels of light transmission, effectively diffusing the light uniformly across the LCD. This has the added benefit of helping minimise the power required to drive the backlight.

Conventionally, light diffusion films have incorporated a PET base material with an acrylic or fixative surface coating; however, this requires 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.

By contrast, the latest MacDermid Autotype films feature transparent hard coatings that eliminate the need for filler materials and significantly improve the brightness, diffusion and homogeneity of the emitted light. As a result, light absorption losses are reduced to less than 1percent. Bottom diffusers incorporate a mechanically stable, high clarity PET base, with a micro-roughened anti-Newton back coating, to eliminate Moiré interference, and a front layer coating that is resistant to chemicals and physical damage, yet produces outstanding optical characteristics. The new films are capable of allowing over 92percent of the light to be directly transmitted, with no adverse effect on the colour balance or uniformity of the light emitted.

In addition to offering considerably improved results, the new light diffusion films are simpler to handle in production than conventional solutions, due to their robust mechanical properties. With no particles or fillers to become dislodged and therefore contaminate the backlight production process, greater production yields are achievable, with less waste, and higher quality.

Improving the performance of electronic displays further, in addition to these diffuser films, this latest generation of substrates from MacDermid Autotype also includes optical films that are able to form the outer layer of display screens, countering the effects of ambient sunlight and therefore minimising reflection and glare. Typically, instrument manufacturers use either complex multi-layer coatings or dip coating processes for this purpose; however, both of these can prove expensive and difficult to control in their production.

For instance, multi-layer coatings often require vacuum chamber environments, which can be expensive to build, maintain and operate. Each coating is applied using a sputtering process that makes achieving a uniform finish difficult due to inconsistencies in the application and, furthermore, three layers are typically required, lowering light transmission levels, and adversely affecting the readability of a display. Likewise the dipped coating process also requires multiple applications; again, this makes it difficult to control and can also increase production costs.

By comparison, the new generation of MacDermid Autotype films offers a far more cost effective and controllable alternative. By incorporating a specially developed single layer solution, the films are able to offer considerably increased brightness and contrast, in addition to intrinsic resistance to scratches, scuffs and abrasions thanks to an innovative hard coated layer. This feature also makes the films resistant to chemicals, such as cleaning fluids, and also to graffiti in some cases, as paint can easily be cleaned off with conventional isopropanol solvents or aqueous detergents without leaving any cleaning stain residues or marks.

These optical films incorporate sophisticated anti-reflection and glare technology, effectively improving light transmission and optical clarity by limiting the effect that ambient light has on a display. The substrates offer extremely low levels of reflectivity over the entire visible spectrum, enabling each display to be viewed clearly from any angle, even in bright sunlight, as well as combining low-haze and uniform texture to reduce glare, or specular reflection, and provide high levels of clarity greater than 91percent typically.

One film combines these properties, effectively countering both reflection and glare and enabling noticeably more readable displays to be produced cost effectively. Autoflex MARAG (MothEye AntiReflection AntiGlare) offers an exceptional level of optical clarity, with a hard coat finish that is resistant to scratches, chemicals and fingerprints.

Developed jointly by MacDermid Autotype and the Fraunhofer Institute for Solar Energy in Germany, this unique film replicates the nano-structures found in the eyes of moths. These compound eye structures have evolved to collect as much light as possible without reflection, in order to prevent moths being detected by night time predators. The result of this technology is a tough, dimensionally stable and formable film that reflects less than 1percent of light throughout the visible wavelength range and eliminates the problems of iridescence and light glare that are often associated with conventional display materials.

Conclusion

With electronic displays being located outdoors more and more, manufacturers are increasingly requiring materials that enable them to produce clear displays that can be viewed clearly in the most demanding light conditions. The latest generation of MacDermid Autotype films specially designed for this purpose are enabling screens to be designed that avoid problems such as reflection and glare and that can withstand scratches, abrasions and accidental damage. By enabling outdoor displays to be viewed clearly at all times, the potential for more sophisticated public information and advertising screens can now be realised. n

Dr Keith Parsons is Technology Manager Light Management Films at MacDermid Autotype, Wantage, Oxon, UK. www.macdermidautotype.com