LCD Reactive Mesogen Alignment Layer Uniformity
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Solution Overview
Problem
In liquid crystal display (LCD) devices, the non-uniform curing of reactive mesogens (RMs) between substrates leads to uneven pretilt angles of liquid crystal molecules, causing afterimages on the display screen due to incomplete curing and varying RM concentrations.
Innovation Solution
A method involving the use of alignment layers with reactive mesogens (RMs) and initiators on both substrates, where UV light is applied to cure the RMs, ensuring uniform pretilt angles of liquid crystal molecules by controlling the RM content and initiator amounts, and optimizing UV light exposure conditions to prevent RM elution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reactive mesogens are injected between substrates to pretilt liquid crystal molecules, then liquid crystal alignment is achieved, but non-uniform curing occurs leading to uneven pretilt angles and afterimages
Solution Approach 1:
The alignment layer is formed on the substrate before the liquid crystal layer is injected. This preliminary formation allows the reactive mesogens to be positioned and cured in advance, ensuring uniform pretilt angles are established before the liquid crystal molecules are introduced, thereby preventing afterimages and ensuring manufacturing precision.
Solution Approach 2:
An alignment layer comprising reactive mesogens and initiators is introduced as an intermediary component between the substrate and the liquid crystal layer. This intermediary layer mediates the alignment process by providing a controlled surface that ensures uniform curing and pretilt angle formation, preventing direct contact between uncured RM and liquid crystal that would cause non-uniform alignment.
2Ease of manufacture
If reactive mesogens remain in the liquid crystal layer to be cured by backlight light, then curing can occur, but cured amounts vary by location causing non-uniform pretilt angles
Solution Approach 1:
The alignment layer with reactive mesogens is formed and cured in advance before liquid crystal injection. This preliminary curing action ensures that the pretilt structure is established beforehand, eliminating the need for post-injection curing by backlight and ensuring uniform pretilt angles across the entire display area.
Solution Approach 2:
The reactive mesogens are extracted from the liquid crystal layer and concentrated in a separate alignment layer. This extraction prevents the mesogens from being dispersed throughout the liquid crystal where they would cause non-uniform curing, while still allowing them to perform their alignment function through the alignment layer's controlled curing process.
3Manufacturing precision
If UV light is irradiated to cure reactive mesogens in alignment layer, then pretilt angles are formed, but excessive irradiation may cause RM elution
Solution Approach 1:
The UV light irradiation parameters are precisely controlled, including irradiation intensity, duration, and wavelength selection. By optimizing these parameters, the curing process achieves complete pretilt angle formation while stopping short of the threshold that would cause reactive mesogen elution, thus maintaining reliability.
Solution Approach 2:
The curing process incorporates feedback mechanisms to monitor and adjust UV irradiation in real-time. This ensures that sufficient irradiation is applied to achieve proper pretilt angle formation while preventing excessive irradiation that would lead to RM elution, thereby maintaining both precision and reliability.
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 enhances the reliability and display quality of LCDs by ensuring uniform pretilt angles and reducing afterimages, thereby improving the alignment and response time of liquid crystal molecules.
Implementation Method 1
Polarized ultraviolet light is irradiated to photocrosslinkable copolymer including a mesogenic group having liquid crystal properties, the mesogenic group being referred as a reactive mesogen ('RM'), to induce anisotropy to the photocrosslinkable copolymer
Implementation Method 2
heat is applied to the photocrosslinkable copolymer to enhance the anisotropy of an alignment layer, to thereby align liquid crystal molecules
Implementation Method 3
Polarized ultraviolet light is irradiated to photocrosslinkable copolymer including a mesogenic group having liquid crystal properties, the mesogenic group being referred as a reactive mesogen ('RM'), to induce anisotropy to the photocrosslinkable copolymer
Data Source
AI summary
In a method of forming a liquid crystal display device, a black matrix is disposed on a substrate including a switching element formed thereon, a color filter is disposed on the switching element, a pixel electrode is electrically connected to the switching element, and a first alignment layer is disposed on the pixel electrode, to form a first substrate. A second substrate including a second alignment layer is formed. At least one of the first alignment layer and the second alignment layer includes a reactive mesogen. A liquid crystal layer is interposed between the first substrate and the second substrate. A light is irradiated onto the second substrate to provide pretilt angles of liquid crystal molecules of the liquid crystal layer.