1. Field of the Invention
The present invention relates to a liquid crystal for use in a liquid crystal display (LCD); and more particularly, relates to a liquid crystal material combination for use in a polymer sustained alignment (PSA) LCD.
2. Descriptions of the Related Art
In the display apparatus market, LCDs are the most established and popular displays. The LCDs have many advantages over the conventional cathode ray tube (CRT) display, such as a light weight, low power consumption, good portability and radiation-free. Therefore, the LCD has been widely used in 3C products such as mobile phones, digital cameras, notebook computers and desktop displays.
The property of the liquid crystal material has a critical impact on the performance of the LCD. Generally, in terms of dielectric anisotropy (Δ∈), the liquid crystal material may be classified into a positive type liquid crystal material (i.e., Δ∈>0) and a negative type liquid crystal material (Δ∈<0). The positive type liquid crystal material is typically used in a parallel alignment (PA) LCD, while the negative type liquid crystal material is typically used in a vertical alignment (VA) LCD.
To improve the performance of the LCD, technologies of assisted liquid crystal alignment have been proposed to provide liquid crystal molecules with a pretilt angle, in an attempt to obtain an LCD featuring a fast response and a high contrast ratio. One of the assisted alignment technologies is to add a polymerizable monomer into the liquid crystal material. Once polymerized, the polymerized monomer gives the liquid crystal molecules a pretilt angle, thus achieving an assisted alignment effect and an improved optical behavior. An LCD using such a liquid crystal material doped with a polymerizable monomer is commonly known as a polymer sustained alignment (PSA) LCD.
However, since the pixel structures of LCDs have become increasingly complicated, and particularly with the development of the multi-domain pixel structure, the LCD industry is facing a challenge of coping with the decreasing liquid crystal transmittance. Briefly speaking, the effective electrical field has become increasingly smaller given the same driving voltage. Consequently, with other conditions kept the same, transmittance of the liquid crystal material will tend to decrease, thus imposing an adverse impact on the optical behavior of the LCDs.
In view of the above problem, the inventors of the present application have found in a research that, by selecting a liquid crystal material having particular characteristics, the optical performance, e.g., the transmittance, of the LCD can be improved.