Two-Layer Alignment Film for LCD Seal Reliability
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Solution Overview
Problem
The reliability of liquid crystal display panels is compromised due to weak bonding strength at the seal portion, caused by the weak mechanical strength of the alignment film in the IPS mode, which is exacerbated by the photo alignment process that breaks the main chain of the polyamide acid ester upper layer, leading to reduced adhesiveness with the sealing material.
Innovation Solution
A two-layer alignment film structure is implemented, where the lower layer of polyamide acid is not subjected to alignment treatment and forms a raised portion or 'hollow' to act as a dam for the upper layer, ensuring controlled profile and increased bonding strength by allowing the lower alignment film to contact the sealing material, thereby enhancing the reliability of the seal portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If photo alignment treatment is applied to the upper alignment film to achieve uniaxial anisotropy and alignment stability, then the alignment stability is improved, but the main chain of the polyimide is broken reducing the film strength and bonding strength with sealing material
Solution Approach 1:
The alignment film is divided into two separate layers: a lower alignment film made of polyamide acid that is not subjected to photo alignment treatment, and an upper alignment film made of polyimide that receives photo alignment treatment. This segmentation allows the lower layer to maintain mechanical strength and bonding capability while the upper layer provides the necessary alignment stability through photo alignment.
2Stability of the object's composition
If the upper alignment film is made of polyimide with excellent alignment stability, then the alignment stability is improved, but the bonding strength with sealing material is reduced due to weak film strength
Solution Approach 1:
The alignment film is divided into two separate layers: a lower alignment film made of polyamide acid that is not subjected to photo alignment treatment, and an upper alignment film made of polyimide that receives photo alignment treatment. This segmentation allows the lower layer to maintain mechanical strength and bonding capability while the upper layer provides the necessary alignment stability through photo alignment.
Solution Approach 2:
The lower alignment film acts as an intermediary layer between the substrate and the upper alignment film. It provides a strong bonding interface with the sealing material and substrate, while the upper alignment film provides the photo alignment function. The lower layer mediates between the mechanical strength requirements and the alignment stability requirements.
3Stability of the object's composition
If a two-layer structure with polyamide acid ester upper layer and polyamide acid lower layer is used to increase uniaxial anisotropy, then the alignment stability is improved, but the resistivity is large causing charge accumulation and residual images
Solution Approach 1:
The material composition and electrical properties of the alignment film are modified by using polyamide acid instead of polyamide acid ester in the lower layer. This parameter change reduces the resistivity of the alignment film, preventing charge accumulation and residual images while maintaining alignment stability through the two-layer structure and photo alignment treatment of the upper layer.
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 effectively increases the reliability of the seal portion by ensuring a minimum bonding strength and controlled profile of the upper alignment film, even when the lower alignment film reaches the substrate end, thus addressing the issue of weak mechanical strength and adhesiveness in the IPS mode.
Implementation Method 1
a raised portion or 'hollow' with an increased film thickness is formed in an end portion of the lower alignment film
Implementation Method 2
Photo alignment is a technique to form a uniaxial anisotropy by breaking the main chain of polyimide of an alignment film in a specific direction by polarized ultraviolet light
Implementation Method 3
A two-layer alignment film structure is implemented, where the lower layer of polyamide acid is not subjected to alignment treatment and forms a raised portion or 'hollow' to act as a dam for the upper layer
Data Source
AI summary
In a liquid crystal display device, a TFT substrate and a counter substrate are bonded by a sealing material, with a liquid crystal interposed between the two substrates. An alignment film has a two-layer structure of a lower alignment film not subjected to photo alignment treatment and an upper alignment film subjected to photo alignment treatment and contacting the liquid crystal. A hollow with an increased film thickness is formed in an end portion of the lower alignment film. An end portion of the upper alignment film is determined by the hollow of the lower alignment film. The material, process conditions, or other conditions of the lower alignment film for easy control of outer end dimensions can be selected to easily control the profile of the alignment film as a whole. Thus, it is possible to avoid the reduction of reliability due to the reduction of the bonding strength between the sealing material and the alignment film.