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The Working Principle and Performance of LCD Polarizer

Blaze Display Technology Co., Ltd. | Updated: Nov 27, 2018

As one of the main raw materials of liquid crystal displays (LCDs), polarizer accounts for approximately 20% to 30% of its manufacturing costs.


1.      How polarizer works

When natural light passes through a polarizer, the light whose vibration direction is perpendicular to the transmission axis of the polarizer will be absorbed, leaving only the polarized light whose vibration direction is parallel to the transmission axis of the polarizer.

The lower polarizer of the LCD screen is used to convert the light beam generated by the backlight into polarized light, and the upper polarizer is used to analyze the polarized light after being electrically modulated by the liquid crystal to produce a contrast between light and dark, thereby producing a display image. The imaging of the LCD module must rely on polarized light. Without any polarizer, the LCD module cannot display images.


2.      The structure of polarizer

Polarizers are mainly made of PVA film, TAC film, protective film, release film and pressure-sensitive adhesive.

The core film material that plays a polarizing role in polarizers is PVA film. After dyeing, the PVA film adsorbs iodine molecules with bidirectional absorption function. By stretching, the iodine molecules are arranged in an orderly manner on the PVA film to form a polarizing film with uniform bidirectional absorption performance. Its transmission axis is perpendicular to the direction of stretching.


3.      Materials, characteristics and functions of polarizer film

Polarizing layer: PVA film (PolyvinylAlcohol), the full name of polyvinyl alcohol film, is mainly composed of light atoms such as carbon, hydrogen and oxygen, so it has the characteristics of high light transmittance and high ductility. PVA molecules are originally distributed randomly at any angle. Under certain temperature and humidity conditions, after being stretched by force, they gradually deflect in the direction of the force and tend to be distributed in a straight line.

The stretched PVA molecules are arranged linearly along the stretching direction, and the dye molecules adsorbed on the PVA layer also deflect in a directional manner to form long chains of dye molecules. Because iodide ions (or dye molecules) have good polarization properties, they can absorb polarized light parallel to their arrangement direction and only allow vertically polarized light to pass through. This principle can be used to create polarizing films.


AC layer: The polarizing layer made of PVA film is easy to absorb water, fade and lose polarizing properties. Therefore, a layer of TAC (tricellulose acetate) film with good optical uniformity and transparency needs to be used on both sides to isolate moisture and air. ,to protect the polarizing layer. Anti-UV polarizers and anti-glare polarizers can be made using TAC film with UV isolation (UV CUT) and anti-glare (Anti-Glare) functions.


Adhesive: It can be divided into reflective film side adhesive and peeling film side adhesive. The function of the adhesive on the side of the reflective film is to firmly bond the reflective film to the TAC film, and its process requirements do not allow for re-peelability. The adhesive on the side of the release film is a layer of pressure-sensitive adhesive, which determines the adhesive performance and patch processing performance of the polarizer. Its performance is one of the most concerning issues for LCD polarizer users.


Separate film: It is a PET (ethylene terephthalate) film coated with silicone coating on one side. It mainly plays the role of protecting the pressure-sensitive adhesive layer. At the same time, its peeling force is very important when LCD patching. It has a certain impact on the workability.


Protective film: a PE (polyethylene) film coated with an EVA layer (ethylene vinyl acetate copolymer) on one side. It has low viscosity and plays a role in protecting the surface of the TAC film.


Reflective film: It is a PET film that is evaporated aluminum on one side. Currently, most of the non-directional reflective evaporated aluminum films are used. If the reflective film is replaced with a transflective film, a transflective polarizer can be made. In addition, various gold plating, silver plating, and laser films can also be used as reflective films to obtain various background colors and mirror surfaces. Reflection and other effects.

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