Classification and working principle of polarizers in LCD panels

1 The principle and classification of polarizers

1.1 Principle

Because iodine molecules are arranged in the same direction, asymmetric electron density will be generated, so the absorption coefficient of polarized light in different directions is different. Light can pass through. On the contrary, the intensity of the transmitted light will continue to decrease, or even completely obstructed. Therefore, it can be concluded that the polarizing property of the long chain of iodine molecules is good. At this stage, the most common polarizer is the H film invented by Rand in 1938.

1.2 Classification

Divided according to functions, polarizers include transmissive polarizers, reflective polarizers, transflective polarizers, and compensation polarizers.

Divided according to the polarizing material, polarizers include the following: Metal polarizers directly adsorb gold, silver, iron and other metal salts on the polymer film, and then reduce the rod-shaped metal to have a certain polarizing ability; iodine Based on the combination of PVA and iodine molecules, the system polarizer has the advantages of high transmittance and high degree of polarization, but its resistance to high temperature and humidity is poor. The cost of this kind of polarizer is relatively low, so the market share is relatively high, and it has a wide range of applications; dye-based polarizers directly adsorb organic dyes with dichroism on PVA, and then extend and orientate them to make them have certain properties. However, the disadvantage is that the transmittance and polarization degree are low, and the advantage is high temperature and high humidity resistance, so it is mostly used in industries such as automobiles and ships.

2 Polarizer performance index and its influencing factors

2.1 Appearance index of polarizer and its influencing factors

The appearance indicators of polarizers include surface flatness, the number of defects in appearance, etc., which have a direct impact on the utilization rate of polarizer products in the patching process. Strict control, including material selection, production process, transportation and storage, storage environment, etc.

2.2 Optical properties of polarizers and their influencing factors

The optical properties of polarizers include the following indicators, namely the degree of polarization, transmittance, and UV protection. For ordinary LCD products, when applying polarizers to polarizers, products with relatively high degrees of polarization and transmittance are generally used. This promotes the improvement of the display quality and efficiency of LCD display devices, and fully reduces energy consumption; however, for ordinary iodine dyed polarizers, the degree of polarization and transmittance are two contradictory factors. Generally, if the degree of polarization is high, the transmittance The decrease is inevitably affected by the hue, so the polarization degree of the conventional polarizer is in the range of 90% to 99%, and the light transmittance index is in the range of 41% to 44%. The basic function of the hue index is to satisfy the visual habits, and the polarizer requires as little hue deviation as possible to ensure the consistency of the LCD product hue.

2.3 Durability index of polarizer and its influencing factors

The durability of the polarizer refers to the durability of the polarizing film and the durability of the pressure-sensitive adhesive. The former refers to the high temperature, damp heat, low temperature and thermal shock resistance of the polarizing film. The specific influencing factors include its basic material, Dyeing materials, dyeing processes, etc. Specifically, the molecular weight of the PVA film selected by the polarizer, the stretching ratio and its durability are proportional. In addition, the degree of coloration of the polarizing film and the hydrolysis resistance of dyes during production also have a positive impact on the durability of the polarizing film. Because iodine and iodide are both very easily hydrolyzed materials, the durability of dye-based polarizers is comparable to that of iodine. There is a great advantage in comparing the durability of dyed polarizer products.

In order to ensure that the polarizer can be closely attached to the glass panel of the liquid crystal display, pressure-sensitive adhesive should be applied on the outer layer of the polarizer, and a release film should be combined to protect the pressure-sensitive adhesive. For bonding, the release film is directly torn off, no solvent, heat, etc. are required. Only a light finger pressure is applied. The pressure-sensitive adhesive can be firmly bonded to the adherend. Therefore, pressure-sensitive adhesives must be Adhesive has certain re-peelability, peeling strength, and certain holding force and initial tack force. In the production process, the pressure-sensitive adhesive technology has a certain impact on the production of polarizers, including the production, storage, and process of the adhesive. Therefore, conventional polarizer manufacturers will use it for a long time after determining the adhesive process conditions. time, and its process quality requirements are very strict, so as to ensure the production quality.

3 Additional functions of polarizers

At this stage, with the use of large-scale, vehicle-mounted, and small and medium-sized liquid crystal displays, especially to meet the effect of personalized display, in the production of polarizers, special materials and processes are selected, and additional polarizers are added. Lots of new features.

In the early days, the functions of many LCD monitors were limited to office, text, simple image display, etc., and the requirements for picture quality were very low. Quality requirements have been greatly improved. Among them, I have to mention the wide viewing angle function, which means that the liquid crystal display can observe the picture quality within a very large viewing angle range, provided that the image remains unchanged, so as to satisfy a larger number of viewers with a wider viewing angle. At present, wide viewing angle technology includes WV/SWV wide viewing angle film, compensation film technology and IPS technology.

IPS wide viewing angle technology is also called plane control mode wide viewing angle technology. As the name suggests, this technology mainly improves the viewing angle by switching the plane of liquid crystal molecules. It makes full use of the changes of space thickness, friction strength and transverse electric field drive to make the liquid crystal molecules make a large plane rotation angle. This technology allows users to only see the short axis of the liquid crystal molecules under any circumstances, so that viewing the screen from all angles has less impact on the visual range of the screen. IPS wide viewing angle technology is more perfect than the previous two technologies. The viewing angle of the LCD monitor using IPS technology can reach 170 degrees, which can be said to achieve a real ultra-wide viewing angle.

The full name of IPS is In-PlaneSwitching. The liquid crystal molecules are arranged horizontally, and the two poles are in the same plane. These two points are important features of IPS technology that distinguish it from other panel technologies, and also ensure that the IPS panel is blocked. The screen is more stable. . Due to the distinctive internal structure, the IPS panel has a very recognizable product feature. The IPS panel is not easily deformed by the water pattern when it is lightly scratched by hand, so it is called a hard screen. When you look at the screen carefully, if you see fish-scale pixels facing left, plus a hard screen, then you can be sure that it is an IPS panel. IPS panel technology enhances the dynamic display effect of the monitor, and can obtain better picture quality when watching sports events, action movies and other fast-moving programs. Compared with other types of panels, IPS has the advantages of high color reproduction accuracy, fast response time, rich color rendering, large viewing angle and high contrast. The advantages of these five aspects also make the IPS wide viewing angle surface launched by LG Display quickly become popular.