IPS LCD Pretilt Angle Control via Composite Alignment Film
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Solution Overview
Problem
In-plane switching mode liquid crystal display devices suffer from light leakage in the black state due to a pretilt angle of 1 to 3 degrees, which cannot be improved by viewing angle compensation, leading to performance deterioration and limited visibility, especially in high-resolution displays.
Innovation Solution
A three-electrode structure is applied to the in-plane switching display, and a photocurable polymer is mixed into the alignment film using a rubbing process, allowing for control of the pretilt angle through UV exposure time and amount, enabling a low pretilt angle without compromising other electro-optic characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a rubbing process is used to align liquid crystal molecules, then the alignment is achieved, but the pretilt angle becomes 1 to 3 degrees causing light leakage
Solution Approach 1:
The patent uses a composite alignment film containing both a polymer material and a liquid crystal material. This composite structure allows the film to provide both mechanical alignment (through polymer chains) and optical control (through liquid crystal molecules), enabling precise control of the pretilt angle to minimize light leakage while maintaining proper liquid crystal alignment.
Solution Approach 2:
The patent controls the pretilt angle by adjusting parameters including the ratio of polymer to liquid crystal materials in the alignment film, the rubbing speed during alignment, and the UV curing conditions. By optimizing these parameters, the pretilt angle is precisely controlled to reduce light leakage in the black state.
2Object-affected harmful factors
If the pretilt angle is reduced to improve visibility, then light leakage is reduced, but other electro-optic characteristics may deteriorate
Solution Approach 1:
The composite alignment film with both polymer and liquid crystal materials enables independent optimization of alignment properties and electro-optic properties. The polymer provides structural stability for precise pretilt control, while the liquid crystal component maintains proper molecular response to electric fields, preserving electro-optic characteristics.
Solution Approach 2:
The patent creates different functional zones within the alignment film: the polymer component provides local mechanical alignment structure, while the liquid crystal component provides local optical anisotropy and electric field response. This local differentiation allows simultaneous optimization of pretilt angle and electro-optic performance.
3Manufacturing precision
If photo alignment with strong UV rays is used to reduce pretilt angle, then the pretilt angle can be controlled, but the process cannot be applied to mass production
Solution Approach 1:
The patent replaces the conventional strong UV ray photo alignment process with a mechanical rubbing process applied to a composite alignment film. The rubbing process, which is already established in mass production, mechanically aligns the polymer-liquid crystal composite, achieving pretilt angle control without requiring complex UV processing equipment.
Solution Approach 2:
The patent changes the alignment mechanism from optical (UV photoalignment) to mechanical (rubbing), and adjusts parameters such as rubbing speed, number of passes, and film composition to achieve the desired pretilt angle. This parameter optimization enables mass production compatibility while maintaining precision.
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 achieves improved visibility and performance by maintaining a low pretilt angle, reducing light leakage, and maintaining electro-optic characteristics, with a simple process that includes a UV curing step under a vertical electric field.
Implementation Method 1
a photocurable polymer is mixed into the alignment film using a rubbing process, allowing for control of the pretilt angle through UV exposure time and amount
Implementation Method 2
polymer chains formed within a surface of the alignment film 20 are aligned in one direction by a contact between the substrate and the rubbing cloth
Implementation Method 3
The FFS mode refers to a mode of rotating liquid crystal molecules using an in-plane electric field in a single substrate on which a common electrode and a pixel electrode are formed in sequence
Data Source
AI summary
There are provided an in-plane switching mode liquid crystal display device and a fabrication method of the in-plane switching mode liquid crystal display device which has a low pretilt angle by applying a three-electrode structure to an in-plane switching display and mixing a photocurable polymer into an alignment film by a rubbing process, and includes: an upper substrate having an upper plate conductive electrode; a lower substrate having a lower plate conductive electrode and a pattern electrode formed on the lower plate conductive electrode with an insulating layer therebetween; the liquid crystal layer disposed between the upper substrate and the lower substrate; and an alignment film formed on the upper substrate having the upper plate conductive electrode and the lower substrate having the pattern electrode and configured to align liquid crystals in an in-plane manner.