Sharp's Optical Film Improves Viewing Angle of TN LCD

Apr 20, 2014
Naoki Tanaka, Nikkei Electronics
A TN LCD (left) and TN LCD to which the new optical film is attached (right). Even when viewed at an angle, the right display causes much less gradation inversion, color deviation, etc.
A TN LCD (left) and TN LCD to which the new optical film is attached (right). Even when viewed at an angle, the right display causes much less gradation inversion, color deviation, etc.
[ If it clicks, the expanded picture will open ]
The new film was placed on part of the image displayed on the left display.
The new film was placed on part of the image displayed on the left display.
[ If it clicks, the expanded picture will open ]

Sharp Corp exhibited an optical film that can improve viewing angle characteristics of a TN (twisted nematic) LCD just by attaching it to the surface of the display.

The optical film, which has a newly-developed structure, was exhibited at the 24th Finetech Japan, a trade show that runs from April 16 to 18, 2014.

Compared with IPS (in-plane switching) LCDs, which are often seen in large-size TVs and smartphones, TN LCDs have lower manufacturing costs. However, when a TN LCD is viewed at an angle, it causes gradation inversion, color deviation and contrast ratio degradation. The new optical film can lessen such dependence on viewing angle.

There have already been some optical films that can improve viewing angle characteristics of a TN LCD. One example is phase difference film, which is placed between liquid crystal cells and a polarizing plate to improve viewing angle characteristics.

However, though it can drastically improve viewing angle characteristics in the horizontal direction, it is difficult to improve viewing angle characteristics in the vertical direction. Therefore, Sharp decided to try a method of attaching an optical film capable of scattering light on the surface of an LCD.

Even with a TN LCD, light coming perpendicularly from the display is free from gradation inversion, color deviation, etc. To improve viewing angle characteristics, some of such light is scattered in oblique directions in the aim of preventing degradation of the quality of an image viewed at an angle. Therefore, Sharp developed the new optical film that enables to control the direction and amount of scattered light.

The new optical film consists of a PET (polyethylene terephthalate) film (base material), transparent resin (negative resist), multiple black dots and multiple voids formed for the black dots. Inside the film, there are multiple voids having shapes such as cone and elliptic cone.

Most of the perpendicular light emitted from an LCD display comes into the transparent resin of the optical film. Then, part of the light is totally reflected from the boundaries with the voids. In other words, light free from gradation inversion, color deviation, etc comes out in oblique directions.

As a result, it becomes possible to prevent degradation of the quality of an image viewed at an angle. The other part of the light passes straight through the transparent resin and comes out on the side of the viewer.