Two-Layer Polyimide Alignment Film for LCD Stability
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Solution Overview
Problem
Existing photo-alignment techniques for liquid crystal display devices suffer from long-term structural instability and mechanical weakness due to ultraviolet degradation, affecting display stability under external vibrations, impacts, and thermal strain.
Innovation Solution
A liquid crystal display device with a two-layer alignment film structure, where the first alignment film layer is a photodecomposition type photo-alignment film containing polyimide and the second layer is a low resistive underlayer with decreased specific resistivity to eliminate electric charges, and a common polyimide structure is used to enhance mechanical strength and stability, combined with a manufacturing method involving ozone water processing and polarized ultraviolet irradiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer photo-alignment film is used, then the alignment function is provided, but the mechanical strength and long-term structural stability are insufficient due to ultraviolet degradation
Solution Approach 1:
The alignment film is divided into two distinct layers: a first alignment film layer (50-200 nm thick) that contacts the liquid crystal layer and provides photo-alignment function, and a second alignment film layer (50-200 nm thick) formed below it that provides mechanical strength. This segmentation allows each layer to specialize in its primary function while working together as a unified structure.
Solution Approach 2:
The patent uses composite material structure where the first alignment film layer contains photodecomposition type photo-alignment materials (such as polyimide with specific molecular structures) and the second alignment film layer contains materials with high mechanical strength and low specific resistivity. This composite structure combines the photo-alignment properties of the first layer with the mechanical reinforcement of the second layer.
2Reliability
If the second alignment film layer has high resistivity, then it provides good insulation, but electric charges accumulate causing afterglow and reduced display stability
Solution Approach 1:
The patent specifically controls the specific resistivity of the second alignment film layer to be in the range of 10^3 to 10^8 Ω·cm, which is significantly lower than conventional alignment films. This parameter change allows the layer to conduct away accumulated electric charges while still providing sufficient insulation function, thereby preventing afterglow and improving display stability.
3Ease of operation
If ultraviolet light is applied for photo-alignment, then liquid crystal alignment is achieved, but the alignment film undergoes degradation reducing long-term stability
Solution Approach 1:
The patent performs photo-alignment treatment by applying polarized ultraviolet light to the first alignment film layer before the liquid crystal display device is assembled and before long-term storage begins. This preliminary alignment action establishes the liquid crystal molecule orientation in advance, and the device is then stored in a dark environment to prevent further ultraviolet-induced degradation during storage.
Solution Approach 2:
The patent designs the first alignment film layer with specific photodecomposition type photo-alignment materials that are optimized to provide sufficient alignment function when exposed to polarized ultraviolet light during manufacturing, while the second alignment film layer serves as a protective layer that cushions against further ultraviolet degradation during long-term storage and operation.
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 provides a liquid crystal display device with improved mechanical strength, long-term storage stability, wide viewing angles, high display contrast, and reduced afterglow, effectively addressing the limitations of previous photo-alignment techniques.
Implementation Method 1
the first alignment film layer is a material that is enabled to provide liquid crystal alignment regulating force by applying polarized light
Implementation Method 2
applying polarized ultraviolet irradiation
Implementation Method 3
the second layer is a low resistive underlayer with decreased specific resistivity to eliminate electric charges
Implementation Method 4
combined with a manufacturing method involving ozone water processing
Data Source
AI summary
A liquid crystal display device includes: a TFT substrate formed with an alignment film on a pixel; a counter substrate disposed opposite to the TFT substrate and formed with an alignment film on a top surface on the TFT substrate side; and a liquid crystal sandwiched between the TFT substrate and the counter substrate. In the liquid crystal display device, the alignment film is configured of a first alignment film layer contacting the liquid crystal layer and having at least one kind of polyimide and a second alignment film layer formed below the first alignment film layer and having at least one kind of polyimide, the first alignment film layer is a material that is enabled to provide liquid crystal alignment regulating force by applying polarized light, and the first alignment film layer and the second alignment film layer contain a common polyimide structure.