Photo-alignment Liquid Crystal Display Substrate
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Solution Overview
Problem
FFS mode liquid crystal display devices face challenges in achieving uniform liquid crystal alignment due to differences in substrate properties, with the electrode-side substrate requiring high alignment and reliability, and the non-electrode side substrate needing a lower temperature alignment process to prevent peripheral member deterioration.
Innovation Solution
A liquid crystal display device is constructed with a first substrate having a pixel electrode and counter electrode overlaid with a polyimide-based alignment film, and a second substrate with a photosensitive side chain type polymer alignment film, both treated with polarized ultraviolet rays for alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a rubbing method is used to align the liquid crystal, then alignment control performance is improved, but dust generation and static electricity occur
Solution Approach 1:
The patent replaces the mechanical rubbing method with a photo-alignment method using polarized ultraviolet light. The alignment film contains photoreactive groups that undergo photo-isomerization or photo-crosslinking when irradiated with polarized UV light, creating anisotropic alignment without mechanical contact, thereby eliminating dust generation and static electricity while maintaining alignment control performance.
Solution Approach 2:
The patent changes the alignment mechanism from mechanical force (rubbing) to optical field interaction (polarized UV light). By introducing photoreactive groups into the alignment film and using polarized light irradiation, the alignment is achieved through photochemical parameter changes rather than mechanical parameters, resolving the contradiction between alignment quality and harmful factor generation.
2Manufacturing precision
If high temperature alignment treatment is applied to achieve uniform liquid crystal alignment, then alignment quality is improved, but peripheral members deteriorate due to heat
Solution Approach 1:
The patent replaces thermal alignment treatment with photo-alignment using polarized ultraviolet light. The photoreactive groups in the alignment film undergo photochemical reactions at room temperature or low temperature, creating the necessary anisotropic alignment without subjecting peripheral members to high temperature stress, thereby maintaining both alignment quality and peripheral member reliability.
Solution Approach 2:
The patent changes the alignment treatment parameter from temperature (thermal energy) to light wavelength and polarization (optical energy). By using photo-isomerization or photo-crosslinking reactions initiated by polarized UV light, the alignment is achieved through optical parameter changes rather than thermal parameters, eliminating heat-induced peripheral member deterioration while achieving uniform liquid crystal alignment.
3Object-generated harmful factors
If photo-alignment method is used to avoid rubbing, then dust and static electricity are eliminated, but alignment uniformity may be insufficient due to substrate irregularities
Solution Approach 1:
The patent applies local quality by incorporating photoreactive groups specifically into the alignment film structure. These groups are distributed uniformly at the molecular level within the film, ensuring that each local region responds consistently to polarized UV light irradiation. This molecular-level uniformity compensates for macroscopic substrate irregularities, achieving both harmful factor elimination and alignment uniformity.
Solution Approach 2:
The patent uses photo-alignment with polarized ultraviolet light to achieve alignment without mechanical rubbing. The photoreactive groups in the alignment film undergo photochemical changes when irradiated with polarized UV light, creating uniform molecular orientation that is not affected by substrate surface irregularities, thereby eliminating dust and static electricity while maintaining alignment uniformity.
4Reliability
If different alignment treatments are applied to electrode-side and non-electrode side substrates, then specific requirements are met, but process complexity increases
Solution Approach 1:
The patent applies a universal photo-alignment process using polarized ultraviolet light that can be used on both electrode-side and non-electrode side substrates. The alignment film containing photoreactive groups responds uniformly to polarized UV irradiation regardless of the substrate type, allowing the same alignment treatment to meet different substrate requirements and thereby reducing process complexity while maintaining substrate-specific performance.
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 configuration ensures high-efficiency alignment control, maintaining display performance even during long-term operation by addressing the substrate property differences and temperature sensitivity issues.
Implementation Method 1
a polyimide film is irradiated with polarized ultraviolet rays to cause anisotropic decomposition utilizing dependency of the molecular structure on the polarization direction of ultraviolet absorption, and the liquid crystal is aligned by the polyimide remained undecomposed
Implementation Method 2
using polyvinyl cinnamate, the film is irradiated with polarized ultraviolet rays to cause a dimerization reaction (crosslinking reaction) at a double bond portion of two side chains in parallel with the polarized light to align the liquid crystal in a direction perpendicular to the polarization direction
Implementation Method 3
in the case of using a side chain type polymer having azobenzene in its side chains, the film is irradiated with polarized ultraviolet rays to cause isomerization at the azobenzene portion of side chains in parallel with the polarized light to align the liquid crystal in a direction perpendicular to the polarization direction
Data Source
AI summary
A liquid crystal display device, which includes a first substrate and a second substrate disposed to face each other with a liquid crystal sandwiched therebetween. The first substrate is an electrode-provided substrate having a first electrode and a plurality of second electrodes overlaid on the first electrode via an insulating film, formed on a pixel region on a surface on the liquid crystal side, where one of the first electrode and the second electrodes is a pixel electrode and the other is a counter electrode, having a first liquid crystal alignment film formed on the surface on the liquid crystal side of the first substrate covered with the second electrodes. The second substrate is a substrate having a second liquid crystal alignment film formed on a surface on the liquid crystal side, the second liquid crystal alignment film containing a photosensitive side chain type polymer which develops liquid crystallinity.