The principle and function of polarizer
Polaroid was invented in 1938 by EdwinH.Land, an American Polaroid company, and is an optical element that generally does not have polarized natural light into polarized light. All liquid crystal panels have two polarizing plates, one of which is polarizer, and the other is polarizer.Polarizer plays the role of optical switch, liquid crystal display must rely on polarized light can be imaged. The backlight module is responsible for providing the most basic source for LCD screen imaging, but send out the light direction is not consistent, radial, if this light by reversing the liquid crystal molecules, we see on the screen is a piece of white, or the brightly coloured color block.The lower polarizer is responsible for the direction of the light into a uniform specification and then sent to the liquid crystal layer. The liquid crystal molecules reversed under the control of TFT to control the direction of light will be uniformly illuminated and thus changed to behind the pixel unit light intensity. The LCD itself has no color, so color to produce a variety of colors.The light direction after originally consistent torsion of the liquid crystal layer and then becomes not the direction, so if you don't like a diffuse light is again regular, see in front of the screen is still white, is a light liquid crystal torsion is not reflected, so this must be in the diffuse light are neat, the use of a piece and the lower polarizer polarizing direction orthogonal polarizer by liquid crystal light re torsion deflection, different angles of light through the brightness on the polarizing plate is different, so we can see on the screen can be alternated with pictures, because the light is deflected by the color light color filter, so we can see we need the image in front of the screen.
The structure and type of polarizer
Polaroid is a composite film composed of polarizing film, protective film, pressure-sensitive adhesive layer and outer protective film. The basic structure of the utility model is that a polyvinyl alcohol film (PVA) which can produce polarized light is sandwiched between three cellulose acetate membranes (TAC). There are mainly the following several types of polarizer on the market: the transmission type polarizer, reflective polarizer (a brightening film), semi transparent and semi reflective polarizer, compensation type polarizer, the surface after the general anti glare (AG) or anti reflection (AR) treatment. In the use of pressure sensitive adhesive to prevent ultraviolet light through the composition of components, can be made into anti ultraviolet polaroid. The use of pressure sensitive adhesive, PVA film or TAC film coloring, that is, the color polarizer.
Process for countries around the world have not much difference between the polarizer, only in terms of the use of raw materials and technical details have different characteristics. The main technology is the extension of iodine system.
The polarizing plate is provided with an extension method and a coating method. Polarizing film production technology is divided into two categories: dry process and wet process, with the extension of PVA film. Dry film is refers to the PVA extension in the steam environment has certain conditions of temperature and humidity, in the early stage to improve the production efficiency of the production process, and not often broken film using PVA film width larger. But the limitations of this process lies in the uniformity of PVA films in the extension process is limited, so the original Polaroid film formed by the composite tension, color uniformity and durability is stable, and the actual application. Wet process refers to the PVA film is a certain proportion of liquid in the dyeing, stretching process. The limitations of this process lies in the early PVA membrane extension in the liquid in the stability control is difficult, therefore the processing time of PVA membrane and PVA membrane membrane easily broken, the width is limited. However, with the improvement, the limitation of the wet process has been greatly improved. From the end of 1990s, Japanese enterprises have been widely using polaroid TAC film width 1330mm by wet process. In particular, due to the large-scale popularization of large size TFT-LCD products, in order to improve the utilization rate of polarizer products, the basic width of 1330mm has become the basic method for the production of polarizer for lcd.
The PVA film is divided into two processes: iodine staining and dye staining. Iodine staining refers to staining, the polarizer tensile process, using potassium iodide as the two medium to make the PVA membrane polarity polarization characteristic. The advantage is that it is easy to get more than 99.9% of the high polarization and more than 42% high transmittance of the polarization characteristics. Therefore, in the early polarized material products or the need for high polarization, high transmittance characteristics of the polarizing material products are mostly used iodine dyeing process. But the shortcomings of this process is due to the molecular structure of iodine is easy to damage in the condition of high temperature and high humidity, polarizer poor durability so using iodine dyeing process, the general can only meet the dry temperature of 80 DEG C: * 500HR: Damp heat working conditions 60 C * 90%RH * 500HR using the following. However, with the expansion of the scope of the LCD products, the requirements of the hot and humid working conditions of the polarizer products become more and more severe, and the demand of the polarizer has appeared under the conditions of 100 DEG C and 90%RH.
For this requirement, iodine dyeing process can do nothing. In order to meet the technical requirements, first by the Japanese pharmaceutical company has developed the Polaroid production of dyes, high durability of Polaroid products by Nippon Kayaku subsidiary of Japan Paula produced dye system. The use of two directional dyes for polarizing film produced by the process of polarizing film products, the highest can meet the dry temperature: 105 degrees C * 500HR, hot and humid: 500HR * 95%RH * below the working conditions of use requirements. However, the polarizing film produced by this process is of low degree of polarization and transmittance, and its polarization is generally not more than 90%, the transmittance is not more than 40%, and the price is expensive.
Iodine polarizer: easy to obtain high transmittance, high degree of polarization of optical properties, but the ability to withstand high temperature and humidity is poor. The price is relatively cheap, so the market share of up to 80%~90%, a wide range of applications, such as: watches, computers, PC, OA machines, etc., are required to use a large number of iodine LCD polarizer.
Dye polarizer: it is not easy to obtain high transmittance, high degree of polarization of optical properties, but the ability to withstand high temperature and humidity. Therefore, in the automobile, ship, aircraft, outdoor measurement instruments have to use this kind of durability polarizer.
Process flow diagram of polarizer
The polarizing film production technology is divided into two categories: dry process and wet process, which is based on the stretching process of PVA film. Dry drawing process is the first in a certain temperature and humidity conditions in an inert gas environment, PVA membrane tensile to a certain ratio, and then the preparation process of dyeing and fixation, composite and drying; wet drawing process is the first dyeing refers to the PVA film, and then stretched in solution, solid color, composite and dry production method. At present, the main production enterprises in the world mainly in wet tensile technology.
The three is the mainstream technology of Lipu iodine production technology and wet drawing technology of current polarizing film production. The production process of the polarizer is divided into three parts: front, middle and back. The main process diagram as follows:
1.the former process (TAC membrane cleaning and PVA film extension and composite)
The former process includes the pretreatment of TAC membrane and the extension and recombination of PVA film. Department of pretreatment process of TAC film TAC film after alkali treatment, water washing tank cleaning residue lye, drying and winding process, the main purpose is to reduce the contact angle of the TAC films, PVA film and fit for. Specifically as follows:
PVA film and composite process is the first through the PVA membrane immersed in pure water swelling after dyeing tank, adsorption to two iodine absorption, and then extends through the slot orientation on molecular iodine, after drying the TAC membrane after PVA membrane with two layer pretreatment composite together, get a polarizing film. Specifically as follows:
2.The middle Process (coating and composite production line)
The process is the process of coating pressure sensitive adhesive and composite membrane. The Department will process pressure sensitive adhesive coating on the film, after the oven evaporation pressure sensitive adhesive in and out, together with the rolling laminating process before polarizing film production, then placed into constant temperature curing room curing, sometimes because of different types of products, need other related optical thin film composite. Specifically as follows:
3.The after process (cutting production line)
The cured polarizer will be cut, cut, cleaned, tested and packaged according to the required size. Specifically as follows: