Performance and indicators of polarizing film for LCD display

Performance and indicators of LCD polarizer

The optical performance of polarizing film includes three main performance indicators: polarization degree, transmittance, and color tone.

Other performance indicators include UV resistance, transmittance, total reflectance, and diffuse reflectance of semi transparent polarizing film semi permeable membranes. In the use of general LCD products, it is required that the higher the polarization and transmittance performance indicators, the better. The higher the polarization and transmittance, the higher the display efficiency of LCD display devices and the lower the relative energy consumption. But for conventional iodine dyed polarizing film products, polarization degree and transmittance are contradictory. The higher the polarization degree, the lower the transmittance, and it is also constrained by color tone. Therefore, the polarization degree of ordinary polarizing film products is generally between 90% and 99%, and the transmittance is between 41% and 44%. The "Fudi" brand polarizer universal PLN product produced by Guangdong Fudi Rihe Polarizing Device Co., Ltd. has a polarization degree of over 97% and a transmittance of 43%, while the medium durability and high contrast PMN product has a polarization degree of over 99.9% and a transmittance of over 42%. The color tone index is mainly to meet people's visual habits, while requiring the color tone deviation of polarizer products to be small to ensure the consistency of the appearance color tone of LCD final products. This is mainly identified by the chromaticity coordinate parameters L, a, b values of polarizer products and their control tolerance range. Generally, the smaller the control tolerance range, the better.

The durability technical indicators of polarizing film include four technical indicators: high temperature resistance, moisture and heat resistance, low temperature resistance, and thermal shock resistance, among which the most important is the level of moisture and heat resistance performance indicators. High temperature resistance refers to the temperature resistant working conditions of polarizing film at a constant baking temperature. Currently, according to the technical level of polarizing film, it is usually divided into three levels: universal type: working temperature of 70 ℃× 500HR; medium durability type: working temperature of 80 ℃× 500HR; high durability type: working temperature above 90 ℃× 500H. The moisture and heat resistance technical indicators refer to the moisture and heat resistance performance of polarizing films under constant temperature and humidity conditions. It is usually divided into three technical levels: universal type: moisture and heat working conditions of 40 ℃ × 90% RH × 500HR; medium durability type: moisture and heat working conditions of 60 ℃ × 90% RH × 500HR; high durability type: moisture and heat working conditions of 70 ℃ × 95% RH × 500HR or above. Due to the fact that PVA film, iodine, and iodide, which are the basic materials that make up polarizing films, are easily hydrolyzed, and the pressure-sensitive adhesive used in polarizing films is also prone to degradation under high temperature and high humidity conditions, the most important durability technical indicators for polarizing films are high temperature resistance and moisture resistance. If the high temperature resistance and moisture resistance indicators are passed, other durability indicators usually do not have problems.

The technical indicators of the adhesive properties of polarizing film mainly refer to the various characteristics of the pressure-sensitive adhesive of polarizing film, 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 polarizing film protective film and the polarizing film, and the adhesive durability of the pressure-sensitive adhesive. The peeling force between pressure-sensitive adhesive and glass substrate, also known as the adhesive strength of the adhesive, is the most important adhesive characteristic index 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 units of g/25mm. Typically, the peeling force of LCD polarizer pressure-sensitive adhesive on glass substrates is specified at 500g/25mm or above, while in actual use, the upper limit is generally below 1000g/25mm. There are practical examples showing that when the peeling force of the adhesive on the glass substrate is below 500g/25mm, the phenomenon of automatic peeling and warping of the polarizer after bonding on the surface of the glass screen will occur.

The appearance performance technical indicators of polarizing film mainly refer to the surface flatness and the number of appearance defects of polarizing film products. These technical indicators mainly affect the utilization rate of polarizing film products during surface mounting. These technical indicators usually have relatively consistent technical regulations in the polarizer industry, generally with less than 15 defects of no more than 150 μ m per polarizer product (500 × 1000mm). Due to the fact that the final appearance inspection of polarizing film products is carried out through manual visual inspection, there will be a certain degree of dispersion in the distribution of appearance defects during the mass production process of polarizing film products. Therefore, various polarizing film production enterprises adopt a certain difference between internal control specifications and delivery specifications to ensure delivery quality standards. However, it should be noted that due to the fact that 150 μ m is already close to the minimum limit of human visual resolution, especially in industrial mass production processes, inspectors may still experience visual fatigue during long-term operations. Therefore, the under point inspection standard of 150 μ m is relatively reasonable and reliable.

The main factors affecting the performance indicators of LCD polarizing film
The main factors affecting the performance of polarizers are related to their basic performance indicators.
The main influencing factors on the optical performance technical indicators of polarizing films include: the selection of polarizing film materials, the selection of dyeing materials, the dyeing of polarizing films, the selection of stretching process conditions, and the limitations of equipment capabilities. These all involve the core technology of polarizer production, so polarizer manufacturers are very cautious in choosing these materials and process conditions, and generally do not easily change them. Once the products of polarizer manufacturers are recognized by customers, they will take strict production quality management measures to ensure the stability of the optical performance of polarizer products.

The durability technical indicators of polarizing film products actually include two aspects of durability indicators: the durability of polarizing film and the durability of pressure-sensitive adhesive. The main influencing factors on the durability of polarizing film include: the selection of basic materials for polarizing film, the selection of dyeing materials, and the process conditions for polarizing film dyeing, stretching, and composite. Generally speaking, the higher the molecular weight and stretching ratio of PVA film used for polarizing film, the better the durability of the polarizing film, and vice versa. The better the coloring degree of the polarizing film during the production process, the stronger the resistance of the dye used to hydrolysis, and the better the durability of the polarizing film. Therefore, the durability of dye based polarizing films is much better than that of iodine based polarizing film products. The main factors affecting the durability of pressure-sensitive adhesives include the selection of adhesive formula, adhesive solvent, adhesive blending process conditions, adhesive drying process conditions, and adhesive storage conditions. It should be noted that the durability index of adhesives is a comprehensive index, and its impact is multifaceted. This is another core technology in the production of polarizing films. Generally, polarizing film production enterprises will not easily change the process conditions of adhesives after determining them, and have strict process quality management requirements. Otherwise, it is easy to cause batch product defects.

The main factors affecting the appearance and performance of polarizing films are also multifaceted. Mainly includes: environmental purification conditions for polarizer production, material selection for polarizer production, equipment conditions for polarizer production, process flow and formula for polarizer production, packaging, storage, and transportation conditions for polarizer, as well as storage environment and processing methods for polarizer during customer use. In short, polarizing film is a very delicate product that must be carefully stored and used, otherwise it is easy to cause surface defects such as pits, black spots, and warping.