Tilted Cholesteric Optical Film for Oblique Shade Reduction
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Solution Overview
Problem
Liquid crystal display devices with immobilized cholesteric liquid crystalline phases experience shade unevenness when viewed from oblique directions due to non-zero oblique retardation, which existing solutions fail to fundamentally address by using additional compensation layers rather than modifying the cholesteric layer itself.
Innovation Solution
An optical film with a light reflection layer where liquid crystal molecules are immobilized, forming a helical structure with a tilt angle of 15° to 55°, specifically 25° to 45°, is developed, using a polymerizable liquid crystal composition that includes a chiral agent, and is manufactured by curing between supports with alignment films, reducing oblique retardation and enhancing front surface brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cholesteric liquid crystalline phase is used as a light reflection layer, then circular polarization reflecting properties are achieved, but shade unevenness occurs when viewed from oblique directions due to non-zero oblique retardation
Solution Approach 1:
The invention changes the fundamental optical parameter of the light reflection layer by using a tilted liquid crystal phase (SmC* or tilted cholesteric phase) instead of a conventional cholesteric phase. This parameter change in the molecular orientation (tilt angle of 15° to 55° relative to the substrate normal) fundamentally reduces the oblique retardation, thereby suppressing shade unevenness while maintaining circular polarization reflecting properties
Solution Approach 2:
The invention employs a composite light reflection layer comprising liquid crystal molecules with specific chiral dopants and tilt-inducing agents. This composite material structure achieves both the desired tilt angle and the circular polarization reflection properties, resolving the contradiction between maintaining reflection functionality and eliminating shade unevenness
2Loss of energy
If a conventional cholesteric liquid crystalline phase with zero in-plane retardation is used, then polarized light recycling is achieved, but oblique retardation causes shade change when seen from oblique direction
Solution Approach 1:
The invention fundamentally changes the retardation parameter by transitioning from a conventional cholesteric phase (with zero in-plane but non-zero oblique retardation) to a tilted liquid crystal phase. This parameter transformation achieves both low oblique retardation and effective polarized light recycling, as the tilted molecular structure allows simultaneous optimization of both optical properties
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 optical film achieves a significant reduction in oblique retardation, thereby suppressing shade changes when viewed from oblique directions, resulting in improved front surface brightness and reduced oblique shade variations in liquid crystal display devices.
Implementation Method 1
a liquid crystal molecule forms a helical structure in a film thickness direction of the light reflection layer
Implementation Method 2
alignment of liquid crystal molecules is immobilized
Implementation Method 3
using a polymerizable liquid crystal composition that includes a chiral agent, and is manufactured by curing between supports with alignment films
Data Source
AI summary
The present invention provides an optical film including a light reflection layer, in which the light reflection layer is a layer in which alignment of liquid crystal molecules is immobilized, the liquid crystal molecule forms a helical structure in a film thickness direction of the light reflection layer, and a tilt angle of the liquid crystal molecule is 15° to 55°. The present invention also provides a manufacturing method of the optical film including curing a polymerizable liquid crystal composition including a liquid crystal compound and a chiral agent interposed between a support and another support. In the optical film according to the present invention, an absolute value of oblique retardation is smaller. In the liquid crystal display device including the optical film, front surface brightness is high and an oblique change in the shade is suppressed.