Homeotropic Liquid Crystal Alignment Without Polyimide Layers
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Solution Overview
Problem
Conventional liquid crystal displays (LCDs) face challenges in achieving homeotropic alignment without polyimide layers, which complicates manufacturing and can reduce electrical resistance and contrast, especially in VA and VA-IPS displays, where the production of polyimide layers is labor-intensive and can interact negatively with the liquid crystal medium.
Innovation Solution
Incorporating polymerizable self-orientation additives with specific functional group positions into the liquid crystalline medium, allowing for homeotropic alignment of the liquid crystal relative to the substrate surfaces without the need for polyimide layers, by mixing these additives with low-molecular-weight liquid-crystalline components and optionally other polymerizable compounds, and then polymerizing them to stabilize the alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyimide layers are used for homeotropic alignment, then alignment is achieved, but manufacturing complexity increases and electrical resistance decreases
Solution Approach 1:
The patent extracts and eliminates the polyimide alignment layer from the display structure, replacing it with a small-molecule compound (compound 1) that provides homeotropic alignment functionality directly within the liquid crystal layer, thereby simplifying manufacturing while maintaining alignment stability
Solution Approach 2:
The patent merges the alignment function previously performed by the separate polyimide layer into the liquid crystal composition itself by incorporating compound 1, which has specific molecular structure features (rigid rod-like structure with terminal groups) that enable homeotropic alignment when polymerized in situ
2Reliability
If polyimide layers are used for homeotropic alignment, then alignment is achieved, but contrast ratio deteriorates
Solution Approach 1:
By removing the polyimide layer entirely and using compound 1 for alignment, the patent eliminates the interface between polyimide and liquid crystal that causes light scattering and reduces contrast, thereby improving the contrast ratio while maintaining homeotropic alignment
3Ease of manufacture
If polymerizable self-orientation additives are used, then manufacturing is simplified, but alignment stability may be compromised
Solution Approach 1:
The patent incorporates compound 1 (a polymerizable self-orientation additive) into the liquid crystal composition before cell assembly, allowing the alignment function to be established during the liquid crystal filling process itself, without requiring subsequent polyimide layer deposition and rubbing steps
Solution Approach 2:
The patent uses the polymerization transition of compound 1 (from monomeric to polymeric state) to lock in the homeotropic alignment configuration, where the polymerization process transforms the liquid crystal mixture into a gel structure that permanently maintains the alignment established during the isotropic-to-nematic phase transition
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
This approach simplifies the manufacturing process, enhances the stability of the liquid crystal alignment, and maintains the advantages of VA technology such as fast switching times and good viewing angles, while eliminating the need for polyimide layers, thus improving the overall efficiency and quality of the display.
Implementation Method 1
homeotropic alignment of the liquid crystal relative to the substrate surfaces
Implementation Method 2
The principle of electrically controlled birefringence, the ECB effect (electrically controlled birefringence) or DAP effect (deformation of erected phases)
Implementation Method 3
The principle of electrically controlled birefringence, the ECB effect (electrically controlled birefringence) or DAP effect (deformation of erected phases)
Data Source
AI summary
The present invention relates to liquid crystalline media (LC media) having negative or positive dielectric anisotropy, containing a low-molecular-weight component and a polymerizable component. The polymerizable component comprises self-aligning, polymerizable mesogens (polymerizable self-orientation additives), which effect a homeotropic (vertical) alignment of the LC media on a surface or the cell walls of a liquid crystal display (LC display). Therefore, the invention also comprises FC displays having homeotropic alignment of the LC medium without orientation layers. The invention discloses novel structures for polymerizable self-orientation additives that have a certain position of the functional groups.