Norbornene Copolymer Alignment Layer for LCD Thermal Stability
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Solution Overview
Problem
Existing photo-alignment polymers for liquid crystal display (LCD) devices suffer from low thermal stability, insufficient liquid crystal alignment, poor miscibility with organic solvents and additives, and compromised coating properties due to their chemical structure, leading to suboptimal performance in alignment layers.
Innovation Solution
A photo-reactive norbornene-based copolymer with halogen-substituted and methoxy-functional groups is developed, which exhibits superior thermal stability, photo-reactivity, and miscibility with organic solvents, enabling improved liquid crystal alignment and adhesive strength, and enhanced coating properties through polymerization with specific catalysts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photo-alignment polymers with cinnamate groups are used, then liquid crystal alignment is achieved through photo-reaction, but thermal stability of the polymer main chain deteriorates
Solution Approach 1:
The polymer structure is segmented into two functional parts: a thermally stable main chain (polyester or polycarbonate backbone) and photo-reactive side chains (cinnamate groups). This segmentation allows the main chain to provide thermal stability while the side chains enable photo-alignment functionality, resolving the contradiction between thermal stability and photo-reactivity.
Solution Approach 2:
The invention creates a composite polymer structure combining the thermally stable polyester/polycarbonate backbone with photo-reactive cinnamate side groups. This composite approach integrates the advantages of both components: the robust main chain ensures thermal stability while the attached photo-sensitive groups maintain liquid crystal alignment capability through UV irradiation.
2Reliability
If photo-alignment polymers are used, then liquid crystal alignment is achieved, but miscibility with organic solvents and additives deteriorates
Solution Approach 1:
The polymer design applies local quality by concentrating the photo-reactive cinnamate groups in the side chains while maintaining a polar main chain structure. This localized arrangement ensures that the photo-alignment function is preserved in the side chains while the main chain's polarity provides good miscibility with organic solvents and additives used in alignment layer formulations.
Solution Approach 2:
The invention changes the chemical parameters of the polymer by introducing polar groups (ester or carbonate linkages) in the main chain and adjustable cinnamate substituents in the side chains. These parameter changes enhance solubility and miscibility with organic solvents while maintaining the photo-reactive properties necessary for liquid crystal alignment.
3Reliability
If rubbing process is used for alignment, then liquid crystal alignment is achieved, but mechanical scratches and high static are generated
Solution Approach 1:
The invention replaces the mechanical rubbing process with a photochemical alignment mechanism. Instead of using physical contact with rubbing cloths that cause scratches and static, the alignment is achieved through UV irradiation that induces photo-reaction of cinnamate groups, creating molecular orientation without mechanical contact. This substitution eliminates the harmful effects of the rubbing process while maintaining alignment functionality.
4Reliability
If photo-alignment polymers are used, then liquid crystal alignment is achieved, but coating property deteriorates due to poor solubility
Solution Approach 1:
The polymer structure is modified by changing chemical parameters: introducing polar ester or carbonate groups in the main chain and adjusting cinnamate side chain substituents. These changes enhance the polymer's solubility in organic solvents, enabling proper coating formulation and application while maintaining the photo-alignment functionality through the preserved cinnamate groups.
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 norbornene-based copolymer demonstrates superior liquid crystal alignment, thermal stability, and solubility, resulting in improved adhesive strength and coating properties, effectively addressing the limitations of previous polymers and enhancing the performance of alignment layers in LCD devices.
Implementation Method 1
photo-sensitive groups bonded to a certain photo-reactive polymer are photo-reacted by a linear polarized UV, the main chain of the polymer is aligned in a certain direction during the process, and the liquid crystal is aligned finally
Implementation Method 2
the double bonds of the cinnamate form a cyclobutane through a [2+2] cycloaddition reaction by a UV radiation, anisotropy appears and the liquid crystal molecules are arranged in one direction according to this
Data Source
Figure 1
AI summary
The present invention relates to a photo-reactive norbornene-based copolymer which has superior miscibility to various organic solvents or additives while exhibiting superior liquid crystal alignment property and can be preferably used to an alignment layer of liquid crystal display device, a method of preparing the same, and an alignment layer including the same.