Phase Difference Film for Liquid Crystal Display Front Contrast

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Solution Overview

Problem

Commercially available phase difference films with a thickness of approximately 100 μm suffer from significant deterioration in front contrast and reduced polarization plate compensation, leading to light leakage at view angles in liquid crystal display devices.

Innovation Solution

A phase difference film comprising two adjacent optical anisotropic layers with specific alignment states, order parameters, and thickness ranges, where the first layer is formed with a homogeneous alignment and an order parameter of 0.75 to 0.95, and the second layer is formed with a homeotropic alignment and an order parameter of 0.60 to 0.95, optimized for in-plane retardation and refractive index properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the phase difference film thickness is reduced to thin the liquid crystal display device, then the device thickness is reduced, but front contrast deteriorates and light leakage occurs at view angles

Engineering Contradiction:

Improvedevice thicknessVSAvoidfront contrast

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The phase difference film is divided into multiple optical anisotropic layers with different alignment states (homogeneous and homeotropic). This segmentation allows each layer to contribute differently to the overall optical compensation, maintaining front contrast even when the total film thickness is reduced.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining different types of optical anisotropic layers (positive C plate, positive A plate, optically biaxial plate) with specific order parameters and alignment states. This composite approach enables effective optical compensation in a thinner configuration, preventing light leakage while reducing overall device thickness.

Inventive Principle:

Principle #40Composite materials

2Volume of moving object

If the phase difference film thickness is reduced, then the device is thinner, but polarization plate compensation is reduced leading to light leakage

Engineering Contradiction:

Improvefilm thicknessVSAvoidlight leakage at view angles

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

Different regions of the optical anisotropic layers are designed with specific local properties - homogeneous alignment in some layers and homeotropic alignment in others. This local quality differentiation ensures that each layer provides the appropriate optical compensation for its specific position in the stack, effectively preventing light leakage at various view angles while maintaining thin film thickness.

Inventive Principle:

Principle #3Local quality

3Reliability

If liquid crystal compounds with high order parameters are used, then front contrast is enhanced, but manufacturing precision requirements increase

Engineering Contradiction:

Improvefront contrastVSAvoidalignment state control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The invention specifies predetermined order parameter ranges (0.30≤S1<0.45 for homogeneous alignment layer, 0.10≤S2<0.30 for homeotropic alignment layer) that must be established before final assembly. This preliminary establishment of optical properties ensures that high front contrast is achieved without requiring excessive manufacturing precision during the assembly process, as the key optical characteristics are predetermined.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution enhances front contrast and improves display tint and vertical symmetry in liquid crystal display devices by aligning liquid crystal compounds with high order parameters, reducing light scattering and depolarization, thereby improving overall display performance.

Implementation Method 1

the first optical anisotropic layer is formed by fixing a liquid crystal compound in a homogeneous alignment state

Methodology Applied

Scientific EffectHomogeneous alignment:

Implementation Method 2

the second optical anisotropic layer is formed by fixing a liquid crystal compound in a homeotropic alignment state

Methodology Applied

Scientific EffectHomeotropic alignment:

Implementation Method 3

a phase difference film including a first optical anisotropic layer; and a second optical anisotropic layer on a surface of the first optical anisotropic layer

Methodology Applied

Scientific EffectBirefringence: Birefringence

Data Source

PatentUS10215899B2Phase difference film, polarization plate, and liquid crystal display device

Publication Date: 2019.02.26 FUJIFILM CORP

AI summary

A liquid crystal (LC) display device uses a phase difference film which increases front contrast of the device, and a polarization plate. The film includes a first optical anisotropic layer, and a second optical anisotropic layer thereon, the first layer formed by fixing an LC compound in a homogeneous alignment state, has an order parameter (OP) of 0.75 to 0.95, and layer thickness of 0.3 μm to 3.0 μm, the second layer formed by fixing an LC compound in a homeotropic alignment state, has an OP of 0.60 to 0.95, and layer thickness of 0.3 μm to 3.0 μm, the OP which is denoted by OP=(A∥−A⊥)/(2A⊥+A∥), “A∥” which represents absorbance of the LC compound regarding light polarized parallel to an alignment direction, and “A⊥” which represents absorbance of the LC compound regarding light polarized vertical to the alignment direction.