Touch Panel Protective Layer Refractive Index Gradient
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Solution Overview
Problem
Conventional touch panels experience issues with visibility and total reflection of visible light due to differences in refractive indices between the transparent electrode and substrate, leading to framework and taper visibility, and high reflectance.
Innovation Solution
A touch panel member with a protective layer that has a refractive index decreasing continuously from the transparent substrate side to the opposite side, with specific refractive index ranges and a thickness of 0.04 to 10 μm, covering the transparent electrode to reduce visibility and reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional protective layer with uniform refractive index is used, then the structure is simple and easy to manufacture, but framework visibility and taper visibility occur due to refractive index differences, and total reflection increases
Solution Approach 1:
The protective layer is designed with a refractive index gradient, where the refractive index varies continuously from the transparent substrate side to the opposite side. Specifically, the refractive index at the transparent electrode interface is controlled to be within ±0.05 of the electrode's refractive index, while the refractive index at the outer surface is lower. This local variation in refractive index eliminates the abrupt interface that causes framework and taper visibility, allowing the electrode structure to blend smoothly with surrounding materials.
Solution Approach 2:
The patent applies parameter changes by controlling the refractive index distribution within the protective layer. The refractive index is not uniform but changes continuously through the layer thickness. The gradient is designed such that n(protect-electrode) - n(transparent substrate) ≤ 0.05 and n(protect-surface) - n(transparent substrate) ≤ 0.03, where n(protect-electrode) is the refractive index at the electrode interface and n(protect-surface) is the refractive index at the outer surface. This parameter optimization suppresses both framework and taper visibility while reducing total reflection.
2Object-affected harmful factors
If a protective layer with refractive index gradient is used, then framework and taper visibility are suppressed, but the layer structure becomes more complex
Solution Approach 1:
The protective layer is designed with a refractive index gradient, where the refractive index varies continuously from the transparent substrate side to the opposite side. Specifically, the refractive index at the transparent electrode interface is controlled to be within ±0.05 of the electrode's refractive index, while the refractive index at the outer surface is lower. This local variation in refractive index eliminates the abrupt interface that causes framework and taper visibility, allowing the electrode structure to blend smoothly with surrounding materials.
Solution Approach 2:
The protective layer is constructed as a composite material combining inorganic particles (such as silicon oxide, titanium oxide, zirconium oxide, or their combinations) dispersed in an organic resin matrix. The inorganic particles have higher refractive indices than the organic resin, creating the desired refractive index gradient when the composite is formed. This composite structure achieves the complex refractive index profile needed to suppress visibility issues while maintaining a single-layer configuration.
3Reliability
If the protective layer thickness is increased, then coverage and protection improve, but total reflection increases and visibility problems worsen
Solution Approach 1:
The patent applies parameter changes by controlling the refractive index distribution within the protective layer. The refractive index is not uniform but changes continuously through the layer thickness. The gradient is designed such that n(protect-electrode) - n(transparent substrate) ≤ 0.05 and n(protect-surface) - n(transparent substrate) ≤ 0.03, where n(protect-electrode) is the refractive index at the electrode interface and n(protect-surface) is the refractive index at the outer surface. This parameter optimization suppresses both framework and taper visibility while reducing total reflection.
Solution Approach 2:
The patent converts the potential harm of a thick protective layer (which would normally increase total reflection and visibility issues) into a benefit by introducing a refractive index gradient. The continuous variation of refractive index through the layer thickness allows light to transition gradually between different media, preventing abrupt reflections. This gradient structure enables the use of thicker protective layers for better coverage and protection while actually reducing total reflection compared to uniform-thickness layers with constant refractive index.
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 framework and taper visibility and total reflection, enhancing the visibility of the touch panel display by maintaining low reflectance, especially in outdoor conditions.
Implementation Method 1
at least part of the protective layer having a refractive index that decreases continuously from the transparent substrate side toward the side opposite to the transparent substrate
Implementation Method 2
the protective layer satisfying Expression 1 and Expression 2 below: |n(electrode)−n(protect-electrode)|≦0.2 and 0.2≦n(protect-electrode)−n(protect-surface)
Data Source
AI summary
The object of the present invention is to provide a touch panel member that is excellent in terms of suppression of visibility of a transparent electrode and has low total reflection for visible light, and a touch panel and a touch panel display device having the touch panel member.The touch panel member of the present invention comprises, in order, at least a transparent substrate, a transparent electrode, and a protective layer provided so as to cover the transparent electrode and having a thickness of 0.04 to 10 μm, at least part of the protective layer having a refractive index that decreases continuously from the transparent substrate side toward the side opposite to the transparent substrate, and the protective layer satisfying specific expressions.