1. Field of the Invention
This invention relates to a display device and a manufacturing method thereof; more particularly, this invention relates to a display device that can reduce the visibility of scratches thereon and a manufacturing method thereof.
2. Description of the Prior Art
Liquid crystal displays (LCDs) have been widely used in all kinds of electronic products, such as LCD televisions, computers, mobile phones, and personal digital assistants (PDA). LCDs have the advantages of light weight, low power consumption, and low radiation. Moreover, because the sizes of LCDs can be relatively larger and the product specifications are largely improved, the variety of applications in the market continuously increases. However, because the liquid crystal material in the LCDs does not emit light, backlight modules are required to provide light source to achieve the display effect. Therefore, backlight modules are indeed one of the most important parts of LCDs. As the difference in panel size increases and the application field diverges, it is predictable that the backlight module industry is going to be further developed. Especially, because the demand on LCDs has largely increased recently, the design of backlight module for LCD devices has become diverse to meet the function and exterior appearance requirements of the LCD devices.
As illustrated by FIG. 1A, a conventional LCD device include a light guide 13, a light source 15, a brightness enhancement film (BEF) 31, a dual brightness enhancement film (DBEF) 33, and a display panel 20. The light source 15 is disposed corresponding to the edge of the light guide 13 to emit light into the light guide 13. After the light is transmitted by the light guide 13, the light goes upwards into the BEF 31. Prisms 37 are disposed on the BEF 31 which can recycle the light with large incident angles to concentrate the light and enhance brightness. The light then enters the DBEF 33. The DBEF 33 having a transmission axis 35 allows the polarization light in the direction of the transmission axis 35 to pass through and recycles the polarization light that is not in the direction of the transmission axis 35. In the conventional design, the transmission axes 35 are generally designed to be perpendicular to the disposing direction of the prisms 37. On the other hand, the transmission axis 35 is parallel to the transmission axis of lower polarizer (not shown) of the display panel 20. In NB or desktop products the transmission axis 35 is often designed a bias degree β1 to be 135° as shown in FIG. 1A. The prism 37 is often put in a bias degree β2 from 0° to 45° for the design has higher brightness than the case that prism is put in a bias from 135° to 180°. Therefore, in the cases where the prism 37 is put in a bias degree 45° as shown in FIG. 1A, the transmission axes 35 are perpendicular to the disposing direction of the prisms 37. The light that passes through finally reaches the display panel 20 to facilitate image display of the display panel 20.
The brightness performance of the conventional LCD device varies with the viewing direction (i.e. azimuth angle) and the viewing angle. The viewing angle refers to the angle of the observer deviates from the central axis of the panel. As illustrated by FIG. 1B, from the observation direction of the azimuth angle 30°-210°, the brightness of LCD decreases from the central viewing angle 0° to viewing angles of 20°, 40°, 60°, etc. However, from the observation direction of the azimuth angle 120°-300°, as shown in FIG. 1C, the brightness (vertical axis) of LCD gradually decreases from 200 to about 50 as the viewing angle (horizontal axis) shifts from the center (0°) to the viewing angles of 20°, 40°, 60°, 90°, etc. Furthermore, as shown in FIG. 1C, as the viewing angle exceeds 60°, the brightness significantly increases and then decreases to form another brightness peak value 90 at the viewing angle of about 70°.
Because the DBEF 33 has a lower hardness, the DBEF is readily scratched during the manufacture process. As illustrated by the dotted line in FIG. 1C, the brightness of light that passes through the scratched part gradually decreases as the viewing angle increases. Because the overall brightness distribution curve illustrated by the solid line shows that a significant increase of brightness occurs at larger viewing angle when no scratch occurs, the increased brightness exceeds the brightness distribution when scratches occur which is illustrated by the dotted line. Therefore, the overall optical performance of the scratched part is different from that of the unscratched part, such that users can notice the existence of scratches when viewing the LCD device.