Crosslinked LCD Alignment Film for Stepped Substrate Contrast Control
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Solution Overview
Problem
Liquid crystal display devices with stepped substrates experience light leakage and decreased contrast ratio due to alignment film thickness variations on and around steps, particularly in high-definition displays like head-mounted displays (HMDs).
Innovation Solution
Employ a two-layer alignment film comprising a base layer and a liquid crystal alignment layer, both derived from polymers with crosslinkable functional groups, to maintain uniform thickness and alignment despite substrate steps, using crosslinking to prevent the film from flowing down.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer alignment film is used on a stepped substrate, then the manufacturing process is simple, but the alignment film thickness becomes non-uniform causing light leakage and decreased contrast ratio
Solution Approach 1:
The alignment film is divided into two separate layers: a base layer formed first on the stepped substrate, and a liquid crystal alignment layer formed subsequently on the base layer. This segmentation allows each layer to serve specific functions - the base layer fills and covers the steps to provide a flat surface, while the alignment layer provides uniform thickness for proper liquid crystal alignment, thereby preventing light leakage and maintaining contrast ratio.
Solution Approach 2:
The alignment film structure uses composite materials with different properties - the base layer is made from a polymer solution with specific viscosity to fill steps effectively, while the alignment layer uses a different polymer solution optimized for liquid crystal alignment. This composite structure combines the advantages of both materials to achieve both step coverage and uniform thickness, resolving the contradiction between manufacturing simplicity and thickness precision.
2Area of stationary object
If the alignment film flows down during formation on stepped substrates, then the film can cover the steps, but the thickness becomes non-uniform causing display defects
Solution Approach 1:
The base layer is formed first as a preliminary step before forming the alignment layer. This base layer is specifically designed to flow down and fill the steps on the substrate, creating a flat underlying surface. By performing this flow action in advance with the base layer, the subsequent alignment layer can be formed with uniform thickness without being affected by the substrate steps, thus achieving both complete coverage and thickness uniformity.
Solution Approach 2:
The base layer acts as an intermediary between the stepped substrate and the liquid crystal alignment layer. It mediates the interaction by absorbing the thickness variations of the substrate through its own flow and leveling, providing a flat intermediate surface that allows the alignment layer to maintain uniform thickness while still covering the entire substrate area including the steps.
3Area of stationary object
If a thicker alignment film is used to cover steps, then step coverage is improved, but light leakage increases due to excessive thickness variations
Solution Approach 1:
By segmenting the alignment film into base layer and alignment layer, the function of step coverage is separated from the function of light control. The base layer handles step coverage by flowing into and filling the steps, while the alignment layer maintains controlled, uniform thickness to prevent light leakage. This segmentation allows the system to achieve both complete step coverage and prevention of light leakage that would occur with a single thick layer.
Solution Approach 2:
Different regions of the alignment film structure have different qualities - the base layer has higher flowability and forms in the step regions to provide coverage, while the alignment layer has controlled viscosity and uniform thickness to prevent light leakage. This local differentiation of material properties and functions allows the system to simultaneously achieve good step coverage and prevent light leakage.
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
Reduces or prevents light leakage and maintains high contrast ratio by ensuring uniform alignment film thickness even on stepped substrates, enhancing display quality in high-definition displays.
Implementation Method 1
the base layer and the liquid crystal alignment layer each having a structure derived from a crosslinking material represented by the following structural formula (1)
Data Source
AI summary
A liquid crystal display device includes: a pair of substrates; a liquid crystal layer held between the pair of substrates; and an alignment film arranged between one substrate of the pair of substrates and the liquid crystal layer. The one substrate includes a step on a surface that is in contact with the alignment film. The alignment film includes a base layer arranged adjacent to the one substrate and a liquid crystal alignment layer arranged adjacent to the liquid crystal layer. The base layer and the liquid crystal alignment layer each have a structure derived from a crosslinking material represented by the following structural formula (1):wherein E1, E2, and E3 each independently represent an amino, methyl amino, or hydroxy group, and w1, w2, and w3 each independently represent an integer of 1 or greater and 18 or less.