Circular Polarizing Plate for Bendable Displays
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Solution Overview
Problem
Bendable organic electroluminescence (EL) panels face issues with reflection and color change due to bending, especially when using circularly polarizing plates with retardation films that exhibit reverse wavelength dispersion characteristics, as they are subjected to significant forces, leading to a reduction in antireflection function and color changes at bent portions.
Innovation Solution
A circularly polarizing plate is designed with a retardation film that has a slow axis direction adjusted between 20° to 70° relative to the bending direction of the display apparatus, and includes a second retardation film on the viewer side to maintain excellent reflection hue and prevent color change, even when bent with a small radius of curvature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a circularly polarizing plate with a retardation film is used to prevent reflection of ambient light, then the antireflection function is improved, but color change occurs at bent portions due to force-induced retardation change
Solution Approach 1:
The patent changes the dispersion characteristic parameter of the retardation film from conventional positive dispersion to reverse dispersion type. This parameter change makes the retardation less sensitive to force-induced variations, thereby suppressing color change at bent portions while maintaining the antireflection function.
Solution Approach 2:
The patent applies different dispersion characteristics to different wavelength ranges by selecting a reverse dispersion type retardation film. This local quality approach optimizes the retardation behavior specifically for the visible light spectrum under bending conditions, reducing color change in the displayed image.
2Adaptability or versatility
If the organic EL panel is bent with an extremely small radius of curvature to achieve flexibility, then the bendability is improved, but the retardation film is subjected to large force resulting in color change
Solution Approach 1:
The patent changes the dispersion characteristic parameter of the retardation film from conventional positive dispersion to reverse dispersion type. This parameter change makes the retardation less sensitive to force-induced variations, thereby suppressing color change at bent portions while maintaining the antireflection function.
3Stability of the object's composition
If a retardation film with reverse wavelength dispersion characteristic is used to suppress color change, then the color stability is improved, but the reflection hue may be affected
Solution Approach 1:
The patent applies different dispersion characteristics to different wavelength ranges by selecting a reverse dispersion type retardation film. This local quality approach optimizes the retardation behavior specifically for the visible light spectrum under bending conditions, reducing color change in the displayed image.
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 effectively suppresses color change and maintains excellent reflection properties in bendable display apparatus, particularly organic EL displays, by optimizing the orientation of the retardation film and using a second retardation film to enhance viewability and durability.
Implementation Method 1
the retardation film showing reverse dispersion-type wavelength dependence
Implementation Method 2
an absolute value of an photoelastic coefficient of the retardation film is 2×10−12 (m2/N) or more
Implementation Method 3
a circularly polarizing plate including a retardation film (typically a λ/4 plate) on a viewer side
Data Source
AI summary
There is provided a circularly polarizing plate capable of realizing a bendable display apparatus in which an excellent reflection hue is obtained and a color change due to bending is suppressed. A circularly polarizing plate according to the present invention is used in a bendable display apparatus. The circularly polarizing plate includes: a polarizer; and a retardation film arranged on one side of the polarizer. In-plane retardations of the retardation film satisfy a relationship of Re(450)<Re(550)<Re(650), and a slow axis direction of the retardation film is adjusted so as to form an angle of from 20° to 70° with respect to a bending direction of the display apparatus.