Phase Difference Plate Copolymer Light Resistance
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Solution Overview
Problem
Existing phase difference plates for organic EL display devices suffer from deteriorated light resistance due to the type of rod-like liquid crystalline compounds or functional groups used, particularly photo-alignment groups, which affect their optical characteristics and viewing angle performance.
Innovation Solution
A phase difference plate is developed using a copolymer with a repeating unit A containing a photo-alignment group with a double bond structure and a repeating unit B capable of expressing birefringence having reciprocal wavelength dispersion, specifically incorporating a cinnamate or chalcone group, and an aromatic ring, applied as a monolayer with controlled refractive indices and retardation values to enhance light resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phase difference plate uses conventional photo-alignment groups or rod-like liquid crystalline compounds, then the device can be manufactured with existing materials, but the light resistance deteriorates under high light emission intensity
Solution Approach 1:
The patent changes the chemical structure parameters of the photo-alignment group by specifying a double bond structure (C═C or C═N) instead of conventional groups. This structural parameter change enhances light resistance while maintaining the necessary photo-alignment function. The copolymer composition parameters are also optimized with specific repeating unit ratios to achieve both durability and optical performance.
Solution Approach 2:
The patent employs a copolymer composition combining repeating unit A (with photo-alignment group) and repeating unit B (with birefringent moiety) in specific ratios. This composite material approach allows the phase difference plate to simultaneously achieve excellent light resistance from the photo-alignment group and desired optical characteristics from the birefringent moiety, resolving the contradiction between durability and optical performance.
2Manufacturing precision
If the phase difference plate uses materials with high birefringence, then the optical characteristics improve, but the viewing angle characteristics deteriorate
Solution Approach 1:
The patent applies local quality by creating specific spatial distribution of refractive indices through the copolymer structure. The phase difference layer is designed with controlled refractive index anisotropy (nx, ny, nz) that varies locally to simultaneously achieve high birefringence for optical performance and appropriate viewing angle characteristics. The reciprocal wavelength dispersion property is specifically engineered to balance these competing requirements.
Solution Approach 2:
The patent optimizes multiple parameters including the in-plane retardation values Re(450), Re(550), Re(650) satisfying Re(450)≤Re(550)≤Re(650), and the refractive index relationship nx>nz>ny. These parameter changes enable the phase difference plate to achieve both excellent optical characteristics and wide viewing angle performance by precisely controlling the birefringence distribution.
3Ease of manufacture
If conventional polymers are used in the phase difference layer, then the manufacturing process is simple, but the alignment stability deteriorates under prolonged light exposure
Solution Approach 1:
The patent modifies the polymer chemical structure by incorporating specific photo-alignment groups with double bond structures and controlling the copolymer composition ratios. These parameter changes enhance alignment stability under prolonged light exposure while maintaining manufacturability through standard coating and irradiation processes. The double bond structure specifically improves resistance to photodegradation.
Solution Approach 2:
The copolymer system combines photo-alignment functional groups with stable backbone structures in specific ratios, creating a composite material that achieves both alignment stability and manufacturing feasibility. The repeating unit composition is optimized to balance durability requirements with processability, allowing conventional manufacturing methods to produce highly stable devices.
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 significantly improves the light resistance and viewing angle characteristics of the phase difference plate, maintaining alignment and durability even under high light emission intensity, while maintaining desired optical properties.
Implementation Method 1
a phase difference layer formed from a composition containing a copolymer having both of a repeating unit A including a photo-alignment group and a repeating unit B including a moiety capable of expressing birefringence having reciprocal wavelength dispersion, in which the photo-alignment group includes a double bond structure of C═C or C═N
Implementation Method 2
a repeating unit B including a moiety capable of expressing birefringence having reciprocal wavelength dispersion
Data Source
AI summary
An object of the present invention is to provide a phase difference plate for an organic EL display device having excellent light resistance, an organic EL display device, and a method for producing a phase difference plate. The phase difference plate for an organic EL display device of an embodiment of the present invention is a phase difference plate for an organic EL display device having a phase difference layer formed from a composition containing a copolymer having both of a repeating unit A including a photo-alignment group and a repeating unit B including a moiety capable of expressing birefringence having reciprocal wavelength dispersion, in which the photo-alignment group includes a double bond structure of C═C or C═N.