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Optical Polarizing Film: Structure, Working Principles, and Its Core Role in Modern Display

Image quality is one of the most critical performance indicators in TVs, smartphones, automotive dashboards, industrial terminals, and other IT equipment. To achieve clear, high-contrast, and stable image output, the polarizer is an essential optical material.

Natural light vibrates randomly in multiple directions. When it passes through a polarizer, only light waves vibrating in one specific direction can pass. This directional filtering effect eliminates stray light and sharpens the image—hence polarizers are often referred to as “optical shutters.”

Unlike LCD, which rely on backlight and polarization to control brightness, OLED are self-emissive. However, OLED display may still use polarizing films to improve contrast and reduce reflection.

1. Structure of a Polarizer

Modern polarizers are multi-layer optical laminates. Each functional layer works together to achieve high polarization efficiency, optical stability, and environmental durability.

1.1 PVA Polarizing Film (Core Polarizing Layer)

Made from polyvinyl alcohol (PVA).
Absorbs iodine or organic dichroic dyes to create polarization capability.
After stretching, iodine molecules align directionally, forming the absorption axis and transmission axis.
Transmission axis is perpendicular to the stretching direction.

1.2 TAC Protective Film

Triacetyl cellulose film protects the PVA layer from moisture, heat, and oxidation.
Provides scratch resistance and dimensional stability.
Essential for long-term reliability.

1.3 PSA Pressure-Sensitive Adhesive

Optically clear adhesive for bonding the polarizer to the LCD module.
Features high transparency, low haze, and excellent weather resistance.

1.4 Release Film

Protects the adhesive layer prior to assembly.

Typical Polarizer Structure

TAC (Protective Layer)
＋ PVA (Polarizing Layer)
＋ TAC (Protective Layer)
＋ PSA (Adhesive)
＋ Release Film

2. Working Principles of Polarizers

LCD operation is based on the optical rotation properties of liquid crystals in combination with the directional filtering effect of polarizers.

Optical Operation Process

Backlight → Bottom Polarizer
Natural light is converted into linear polarized light.
Polarized Light → Liquid Crystal Layer
- No voltage: LC molecules twist the polarization direction by 90° or 270°.
- Voltage applied: LC molecules stand vertically, no rotation occurs.
Liquid Crystal Layer → Top Polarizer (Analyzer)
- If the polarization direction matches the transmission axis → light passes → pixel ON.
- If it does not match → light is absorbed → pixel OFF.

Thus, LCD image formation relies on:
Polarizers determine the “direction” of the light, while liquid crystals determine the “amount” of light passing.

Without Polarizers

Light loses directional control.
No contrast is formed.
The entire display appears blank or emits scattered white light.

3. Types of Polarizers

3.1 By Function

Transmissive Polarizer – The most common type for LCD.
Reflective Polarizer – Used in reflective displays, e-paper.
Transflective Polarizer – For sunlight-readable display.
Compensation Polarizer – Reduces color shift and improves viewing angles.

3.2 By Coloring Method

(1) Iodine-based Polarizers

High polarization efficiency and high transmittance.
Slightly weaker resistance to heat and humidity.
Most widely used today.

(2) Dye-based Polarizers

Use dichroic organic dyes.
Strong environmental resistance, but lower polarization efficiency.

3.3 By Polarizing Material Type

Metal Polarizers (obsolete)
Iodine Polarizers
Dye Polarizers
Ethylene Polarizers (structure formed via dehydration reaction)

4. Surface Treatment Technologies

To meet different application requirements, polarizers often incorporate optical coatings:

AG (Anti-Glare) – Reduces surface reflection.
AG + LR (Low Reflection) – Improves outdoor readability.
CHC (Clear Hard Coating) – Enhances scratch resistance, ideal for touch devices.
CHC + LR – Widely used on mobile and smart devices.
AR (Anti-Reflection) – Boosts contrast and visibility in bright environments.

These coatings are typically applied using wet coating processes, ensuring uniform optical performance.

5. Key Design Considerations for Polarizers

Selecting the right polarizer requires evaluating optical, mechanical, and reliability parameters.

5.1 Optical Performance

Transmittance
Polarization efficiency
Color tone
Haze

Critical alignment rules:

The absorption axis of the bottom polarizer must be perpendicular to the DBEF film’s transmission axis.
For displays using privacy film (light-control film), the orientation must be carefully matched to avoid Moiré patterns.

5.2 Mechanical Performance

Warpage
Adhesive bonding strength
Total thickness and process compatibility

5.3 Reliability

Polarizers must withstand:

High-temperature tests
Low-temperature tests
Damp-heat tests
UV exposure
Adhesive aging tests

6. Future Trends in Polarizer Technology

The rapid evolution of mobile and wearable devices is driving major advancements in polarizer materials and structures.

6.1 Ultra-thin, High-Transmittance Polarizers

Next-generation devices require:

Higher brightness
Lower power consumption
Thinner optical stacks

6.2 In-Cell Polarizer Technology

Integrating the polarizer directly inside the display module offers:

Ultra-thin design
Higher transmittance
Better environmental durability
Lower cost

This trend is particularly important for:

Flexible OLED
Foldable displays
Flexible LCD

6.3 Integration with Compensation Films

Combining polarizers and phase-retardation films improves:

Viewing angle
Color consistency
Light-use efficiency
Supporting high-performance displays such as IPS, FFS, Mini-LED LCD.

Conclusion

Polarizers are a fundamental component of modern display technology. Their multilayer structure, precise optical function, and essential role in image formation make them indispensable for achieving high-quality visual performance.

As the industry moves toward ultra-thin, flexible, and energy-efficient displays, polarizer technology will continue evolving—serving as a key driver for next-generation display innovation.