Performance indicators of LCD polarizers and their influencing factors

The basic performance indicators of LCD polarizers mainly include: basic technical indicators of optical performance, durability, bonding characteristics, appearance performance and other special performances.

The optical performance of polarizers includes three main performance indicators: polarization, transmittance and hue. Others include UV protection and transmittance, total reflectance and diffuse reflectance indicators of semi-transparent polarizer semi-transparent membrane. In the use of general LCD products, the higher the polarization and transmittance performance indicators, the better. The higher the polarization and transmittance, the higher the display efficiency of the LCD display device and the lower the relative energy consumption. However, for conventional iodine-dyed polarizer products, polarization and transmittance are a contradiction. The higher the polarization, the lower the transmittance, and it is also subject to the constraints of hue. Therefore, the polarization of ordinary polarizer products is between 90% and 99%, and the transmittance is between 41% and 44%. The polarization degree of the general-purpose PLN products of the "Fudi" brand polarizer produced by Guangdong Fudi Rihe Polarizer Device Co., Ltd. is above 97% and the transmittance is 43%, while the polarization degree of the medium-durability, high-contrast PMN products is above 99.9% and the transmittance is above 42%. The color tone index is mainly to meet people's visual habits. At the same time, it is required that the color tone deviation of the polarizer products should be small to ensure the consistency of the appearance color tone of the final LCD product. This is mainly indicated by the chromaticity coordinate parameters L, a, b values ​​of the polarizer products and their control tolerance range. Generally, the smaller the control tolerance range, the better. 

The durability technical indicators of polarizers include four technical indicators: high temperature resistance, humidity and heat resistance, low temperature resistance and resistance to cold and heat shock. The most important of these is the humidity and heat resistance performance indicator. High temperature resistance refers to the temperature resistance working conditions of polarizers at a constant baking temperature. At present, according to the technical level of polarizers, they are usually divided into three levels: general type: working temperature is 70℃×500HR; medium durability type: working temperature is 80℃×500HR; high durability type: working temperature is above 90℃×500H. The humidity and heat resistance technical indicators refer to the humidity and heat resistance working performance of polarizers under constant temperature and humidity conditions. It is also usually divided into three technical levels, namely general type: humidity and heat working conditions are 40℃×90%RH×500HR; medium durability type: humidity and heat working conditions are 60℃×90%RH×500HR; high durability type: humidity and heat working conditions are: 70℃×95%RH×500HR or above. Since the basic materials of polarizing film, PVA film, iodine and iodide are all very easy to hydrolyze, and the pressure-sensitive adhesive used in polarizing film is also easy to deteriorate under high temperature and high humidity conditions, the most important durability technical indicators of polarizing film are high temperature resistance and humidity resistance. If the high temperature resistance and humidity resistance indicators are passed, other durability indicators will usually not have problems. "Fudi" brand general PLN products and medium durability PMN products can well meet the requirements of durability technical indicators specified by their respective technical levels (see Figure 2).

The technical indicators of the bonding characteristics of polarizers mainly refer to the various characteristics of polarizer pressure-sensitive adhesives, generally including: the peeling force between the pressure-sensitive adhesive and the glass substrate, the peeling force between the pressure-sensitive adhesive and the peeling film, the peeling force between the polarizer protective film and the polarizer, and the bonding durability of the pressure-sensitive adhesive. The peeling force between the pressure-sensitive adhesive and the glass substrate is also called the bonding strength of the adhesive, which is the most important bonding characteristic indicator of LCD polarizer products. This technical indicator is usually measured using the EIAJ-ED-2521A standard of the Japan Electronic Machinery Industry Association, expressed in g/25mm. Usually, the peeling force of LCD polarizer pressure-sensitive adhesives on glass substrates is specified to be above 500g/25mm, and the upper limit in actual use is generally below 1000g/25mm. There are actual examples showing that when the peeling force of the adhesive on the glass substrate is below 500g/25mm, the polarizer will automatically peel off and warp after being bonded to the surface of the glass screen. 

The technical indicators of the appearance performance of polarizers mainly refer to the surface flatness of polarizer products and the number of appearance defects. These technical indicators mainly affect the utilization rate of polarizer products during patching. These technical indicators usually have relatively consistent technical regulations in the polarizer industry, generally 15 or less defects not larger than 150μm for each polarizer product (500×1000㎜). Since the final appearance inspection of polarizer products is carried out by manual visual inspection, the distribution of appearance defects will have a certain discrete distribution during the mass production of polarizer products. In this regard, each polarizer manufacturer uses a certain difference between the internal control specifications and the delivery specifications to ensure the delivery quality standard. However, it should be noted that since 150μm is close to the minimum limit of human visual resolution, especially in the process of industrial mass production, inspectors will also experience visual fatigue during long-term work, so the 150μm defect inspection standard is more reasonable and reliable.

The main factors affecting the performance indicators of LCD polarizers.

The main factors affecting the performance of polarizers are related to the basic performance indicators of polarizers.

The main factors affecting the technical indicators of polarizer optical performance include: the selection of polarizing film materials, the selection of dyeing materials, polarizing film dyeing, the selection of stretching process conditions and the limitation of equipment capacity. These all involve the core technology of polarizer production, so polarizer manufacturers are very cautious in the selection of these materials and process conditions, and generally will not change them easily. Once the products of polarizer manufacturers are recognized and approved by customers, polarizer manufacturers will take strict production quality management measures to ensure the stability of the optical performance of polarizer products. The technical indicators of
polarizer
product durability actually include two aspects of durability indicators: the durability of polarizing film and the durability of pressure-sensitive adhesive. The main factors affecting the durability of polarizing film include: the selection of basic materials of polarizing film, the selection of dyeing materials, polarizing film dyeing, stretching, and composite process conditions. Generally speaking, the larger the molecular weight of the PVA film used in the polarizer and the higher the stretch ratio, the better the durability of the polarizer, and vice versa. At the same time, the better the coloring degree of the polarizer during the production process and the stronger the anti-dissolution ability of the dye used, the better the durability of the polarizer. Therefore, the durability of the dye-based polarizer is much better than that of the iodine-dyed polarizer. The main factors affecting the durability of pressure-sensitive adhesives include: the selection of adhesive formula, the selection of adhesive solvents, the selection of adhesive blending process conditions, the selection of adhesive drying process conditions, and the selection of adhesive storage conditions. It should be noted that the durability index of the adhesive is a comprehensive index, and its influence is multifaceted. Moreover, this is another core technology of polarizer production. Generally, polarizer manufacturers will not easily change the process conditions of the adhesive after determining them and have strict process quality management requirements, otherwise it is very easy to cause batch product defects. 

  The main factors affecting the appearance performance of polarizers are also multifaceted. The main issues include: environmental purification conditions for polarizer production, material selection for polarizer production, equipment conditions for polarizer production, process flow and process formula for polarizer production, polarizer packaging, storage, and transportation conditions, as well as the storage environment and processing methods for polarizers when used by customers. In short, polarizers are very "delicate" products and must be carefully stored and used, otherwise it is easy to cause surface defects such as surface pits, black spots, and warping.