Recently, as information technology continues to evolve, mobile phones, computers, and even the common household appliances are gradually developed to have advantages of intelligent, lightweight and mobility. Therefore, efficiency of information exchange between man and machine becomes critical. In order to efficiently and clearly transmit the information treated by the machine to humans, the display with high-efficiency, high-quality, high-capacity, lightweight, low-cost and low-power plays an important role and leads the traditional CRT monitor to be replaced by LCD monitors in few years.
The liquid crystal display in early year generally uses twisted nematic(TN) or super-twisted nematic(STN) mode liquid crystal materials which are the positive type nematic liquid crystal, and a certain amount of chiral agent is added. When not being energized, a longitudinal axis of the liquid crystal molecules arrange parallel to the substrate surface, arrangement direction of liquid crystal molecules on the substrate surface is determined by the rubbing direction of the alignment layer. The alignment layer is typically made of polyimide and forms a certain angle, which is generally 90 degrees, with the upper and lower surface of the substrate. Therefore, the liquid crystal molecules are arranged in a continuous state of torsion from a substrate surface to the other surface of the substrate. It is called the TN type if the twist angle is 90 degrees, or the twist angle is 270 degrees for the STN type. In addition to the upper substrate, the lower substrate and the liquid crystal layer, LCD also has a polarizer attached to the outer surface of the substrates in a direction perpendicular to the absorption axis and a backlight, etc. The light of the backlight becomes linearly polarized light through the polarizer, and then passes through the liquid crystal layer which is twistedly arranged. Therefore, the polarization direction is changed to smoothly pass another polarizer, and the display is in a transparent state. When a voltage is applied to the liquid crystal layer, the longer axis of the liquid crystal molecules tends to arrange in a direction along the electric field. At this time, the ability for changing polarization state of the liquid crystal layer is disappeared or decreased, and the display is in the opaque state or lower transparency. Therefore, the display can be controlled by changing the voltage.
TN/STN-type liquid crystal display is one of the earliest commercial displays. However, because of its small viewing angle, the difference in brightness and serious color aberration in big viewing angle, the application is greatly limited. Later, viewing angle and color issues of TN/STN display can be improved through the way of compensation film, but its manufacturing cost is raised at the same time. Further, the improvement is still not fully satisfying people's requirements for high-quality display.
Multi-domain vertical alignment (MVA) type liquid crystal display is a well solution to the restrictions of the viewing angle in TN/STN type liquid crystal display. It uses a negative liquid crystals and vertical alignment film material. When no voltage is applied, the long axis of liquid crystal molecular is perpendicular to the substrate surface. When a negative voltage is applied, the liquid crystal molecules will dump and long axis thereof tend to arrange in the direction vertical to the electric field. In order to solve the problem of viewing angle, a sub-pixel is divided into a plurality of regions, so that the liquid crystal molecules in different regions will dump in different directions. Thus, the effect will converge when the display being seen from different directions. There are many ways to make the liquid crystal molecules in different regions orient in different directions in a sub-pixel. The first way is to form the indium tin oxide electrode (Full ITO) on the whole area of the upper and lower substrate of the LCD by exposure and development, and the misalignment bumps were produced on the entire surface of the ITO electrodes of the upper and lower substrates. The liquid crystal molecules near the bumps will form a certain angle, so as to guide other liquid crystal molecules towards the predetermined direction. The second way is formed patterned indium tin oxide electrode (ITO electrode) on the upper and lower substrates, and the patterned ITO electrodes on the upper and lower substrates are arranged in misalignment position, so that the direction of the electric field generated thereby has a certain angle. Therefore, the orientation of the liquid crystal molecules in different regions can be controlled. This technique is called patterned vertical alignment (PVA). The third way is to form an ITO electrode on the side of a thin film transistor of the LCD substrate with a predetermined pattern (usually fishbone), and the entire surface of another substrate is the ITO electrode (Full ITO). The reactive monomer (RM) is added in a polymerizable liquid crystal material. First, an electric field is applied so that the liquid crystal molecules in different regions will dump towards the predetermined direction, and then UV light irradiation is applied to make the reactive monomers in the liquid crystal material proceed ultraviolet polymerization. The polymer protrusions are formed and disposed on the surface of the substrate to play the role of alignment for guiding the liquid crystal molecules. This technique is called a polymer stabilized vertical alignment (PSVA). Comparing to other MVA technology, PSVA technologies has advantages of high transmittance, high contrast and fast response, thus becoming the mainstream technology of large-size LCD panel.
A key step of PSVA technology is to control the reaction of the reactive monomer, including the reaction rate, the reaction uniformity, the residue after the reaction, and so on. Only good control of the abovementioned situation can get high-quality PSVA LCD panel. Currently, it is known that too high concentration of the residue of the reactive monomer will cause the panel image retention problems. However, it is still an important issue to well control the reactive monomers concentration after UV irradiation.
It is therefore tried by the inventor to develop a liquid crystal composition to solve the problems existing in the conventional technology as described above.