Retardation Film with Intermediate Layer for Thin LC Displays
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Solution Overview
Problem
Existing retardation films for liquid crystal displays are thick, leading to lower front contrast and difficulties in forming uniform, thin coatings due to hydrophilicity and hydrophobicity differences between layers, and are prone to separation under heat, hindering the fabrication of thinner optical films.
Innovation Solution
A retardation film configuration with a first optically anisotropic layer containing a leveling agent and a second optically anisotropic layer, both with specific order parameters and thicknesses, and an intermediate layer with a solubility parameter of 21.5 to 24.7, ensuring high adhesion and stability, particularly using a (meth)acrylic resin with a polymerizable group.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a retardation film with both an optically anisotropic layer and a retardation layer is used, then the film provides necessary optical compensation, but the film becomes thick and reduces front contrast
Solution Approach 1:
The patent combines the optically anisotropic layer and the retardation layer into a single integrated layer that simultaneously provides both optical alignment and retardation functions. This merging eliminates the need for separate layers, thereby reducing overall film thickness while maintaining both optical compensation performance and front contrast.
2Ease of operation
If an aqueous PVA composition is applied to form an alignment film, then the film provides alignment function, but coating defects occur due to hydrophilicity differences between layers
Solution Approach 1:
The patent changes the solvent parameter from aqueous to nonaqueous, creating a PVA composition that is soluble in nonaqueous solvents. This parameter change eliminates the hydrophilicity mismatch between the PVA alignment film and the underlying optically anisotropic layer, preventing coating defects and ensuring uniform coating formation while maintaining the alignment function.
3Ease of operation
If a thick PVA alignment film is used, then the film provides sufficient alignment, but the film separates under heat and is unsuitable for thin optical films
Solution Approach 1:
The patent changes the solvent parameter to nonaqueous, which fundamentally alters the film formation and adhesion characteristics. This enables the formation of thin, uniform PVA alignment films that do not separate under heat, as the nonaqueous solvent provides better compatibility and bonding with the adjacent layers, achieving both thin film requirements and heat stability.
4Length of stationary object
If thinner retardation films are fabricated, then the profile of mobile devices can be reduced, but adhesion between layers becomes insufficient
Solution Approach 1:
The patent changes the solvent parameter from aqueous to nonaqueous in the PVA composition, which fundamentally improves adhesion between the PVA alignment film and the optically anisotropic layer. This parameter change enables the formation of strong interfacial bonding, allowing thin film fabrication while maintaining sufficient layer adhesion and preventing separation.
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 configuration achieves high front contrast and stability in hot and humid environments, enabling the production of thinner, high-performance retardation films for liquid crystal displays.
Implementation Method 1
an intermediate layer containing a resin having an SP value of 21.5 to 24.7, where the SP value is a solubility parameter calculated by Hoy's method
Implementation Method 2
a first optically anisotropic layer containing liquid crystal compounds fixed in a homogeneously aligned state and a leveling agent, the first optically anisotropic layer having an order parameter of 0.75 to 0.95
Implementation Method 3
an optically anisotropic layer that exploits the orientation of a liquid crystal compound
Data Source
AI summary
A retardation film includes a first optically anisotropic layer having liquid crystal compounds fixed in a homogeneously aligned state and a leveling agent, and having an order parameter of 0.75 to 0.95 and a thickness of 0.3 to 3.0 μm; an intermediate layer including a resin having a solubility parameter SP value of 21.5 to 24.7, calculated by Hoy's method, the intermediate layer having a thickness of 3.0 μm or less; and a second optically anisotropic layer having liquid crystal compounds fixed in a homeotropically aligned state, and having an order parameter OP of 0.6 to 0.95 and a thickness of 0.3 to 3.0 μm, wherein OP is represented by the following equation; OP=(A∥−A⊥)/(2A⊥+A∥) where A∥ is absorbance of the liquid crystal compounds for light polarized parallel to an alignment direction, and A⊥ is absorbance of the liquid crystal compounds for light polarized perpendicular to the alignment direction.