Helically Aligned Liquid Crystal Phase Difference Plate for Display Color Mixing
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Solution Overview
Problem
Organic EL display apparatuses using circularly polarizing plates face issues with mixing of black with another color when viewed from the front direction, leading to suboptimal image quality due to reflection effects from layer interfaces.
Innovation Solution
A phase difference plate comprising two optically anisotropic layers with helically aligned liquid crystal compounds, where the helix angles and refractive index anisotropy products are specifically controlled to minimize color mixing, eliminating the need for additional alignment films and enhancing the conversion of linearly-polarized light to circularly-polarized light across a broader wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional phase difference plate (λ/2 plate and λ/4 plate) is used for a circularly polarizing plate, then the structure is simple and easy to manufacture, but the mixing of black with another color is not sufficiently suppressed when viewed from the front direction
Solution Approach 1:
The phase difference plate is divided into multiple specific layers (first phase difference layer, second phase difference layer, third phase difference layer) with distinct optical characteristics. Each layer has specific retardation values and axial relationships that work together to suppress black mixing while maintaining manufacturability through standardized layer construction
Solution Approach 2:
The invention specifies precise parameter ranges for each layer including retardation values (S1, S2, S3), helix angles (26.5±10.0° and 78.6±10.0°), and refractive index anisotropy products (Δn1·d1, Δn2·d2, Δn3·d3). These controlled parameter changes enable effective suppression of black mixing while maintaining practical manufacturability
2Ease of manufacture
If the helix angle and refractive index anisotropy are not precisely controlled, then the manufacturing process is simpler, but the suppression of black mixing and improvement of image quality is insufficient
Solution Approach 1:
The invention establishes specific parameter ranges for helix angles (26.5±10.0° and 78.6±10.0°) and refractive index anisotropy products (Δn1·d1, Δn2·d2, Δn3·d3) that optimize the suppression of black mixing. These controlled parameter specifications ensure reliable image quality while maintaining practical manufacturability through clear manufacturing targets
Solution Approach 2:
Different layers are assigned different local optical properties including specific helix angles and retardation values. The first phase difference layer has different characteristics from the second and third layers, with each layer optimized for its specific position and function in the overall circularly polarizing plate structure
3Manufacturing precision
If additional alignment films are used to improve layer alignment, then the alignment precision is improved, but the device complexity and manufacturing steps increase
Solution Approach 1:
The liquid crystal layers themselves provide the alignment function through their inherent helical structure and optical anisotropy characteristics. The layers self-align based on their specified helix angles and axial relationships without requiring additional alignment films, thereby maintaining alignment precision while reducing device complexity and manufacturing steps
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 effectively suppresses the mixing of black with other colors when the phase difference plate is used as a circularly polarizing plate, improving image quality by reducing unwanted reflections and enhancing the display's contrast ratio.
Implementation Method 1
an optically anisotropic layer containing a helically aligned liquid crystal compound
Implementation Method 2
external light is reflected from the interfaces between the respective layers, and this leads to problems such as a decrease in contrast
Data Source
AI summary
The phase difference plate for a circularly polarizing plate includes a first optically anisotropic layer; and a second optically anisotropic layer, in which the first and second optically anisotropic layers contain a liquid crystal compound that is helically aligned around a helical axis which is in a thickness direction of each of the layers, the liquid crystal compound has a same helix direction in the first optically anisotropic layer and in the second optically anisotropic layer, and a helix angle of the liquid crystal compound each in the first optically anisotropic layer and in the second optically anisotropic layer is in a predetermined range. The phase difference plate can sufficiently suppress the mixing of black with another color observed in the front direction when being stuck as a circularly polarizing plate on a display apparatus.