Pressure-Sensitive Adhesive Touch Sensors for High-Contrast Displays
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Solution Overview
Problem
The use of a touch sensor with a pressure sensitive adhesive layer in image display devices results in increased brightness of black display areas adjacent to white display areas, leading to a decrease in contrast.
Innovation Solution
Incorporating a visible light absorber into the pressure sensitive adhesive layer with specific absorbance and parameter values to minimize light transmission and scattering, maintaining white display brightness while enhancing contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a touch sensor with a pressure sensitive adhesive layer is applied to an image display device, then the touch sensor provides touch sensing functionality, but the brightness of black display portions increases and contrast decreases
Solution Approach 1:
The pressure sensitive adhesive layer is designed with spatially varying optical properties: the first pressure sensitive adhesive layer (between touch sensor and image display element) has different optical characteristics compared to the second pressure sensitive adhesive layer (between touch sensor and protective layer). This local differentiation allows optimization of light transmission in different regions to prevent brightness increase in black display areas while maintaining touch functionality.
Solution Approach 2:
The invention changes the optical parameters (transmittance, reflectance, absorption) of the pressure sensitive adhesive layer by controlling the content of visible light absorbers and adjusting layer thickness. By precisely controlling these parameters, the brightness of black display portions is suppressed while maintaining adequate light transmission for white display areas and touch sensing performance.
2Illumination intensity
If a pressure sensitive adhesive layer with visible light absorber is used, then contrast between black and white display is improved, but the layer thickness and material composition become more complex
Solution Approach 1:
The pressure sensitive adhesive layer is segmented into multiple functional layers: a first pressure sensitive adhesive layer positioned between the touch sensor and the image display element, and a second pressure sensitive adhesive layer positioned between the touch sensor and the protective layer. Each layer can be independently optimized for specific functions, with the first layer focusing on light transmission and the second layer on light absorption to suppress black area brightness.
Solution Approach 2:
The pressure sensitive adhesive layers are formulated as composite materials containing pressure sensitive adhesive polymers combined with visible light absorbers (such as carbon black, iron oxide, copper oxide, or organic dyes). This composite structure integrates multiple functions (adhesion, light absorption, brightness control) into a single material system, managing complexity through material science rather than structural complexity.
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 brightness increase in black display areas and improves contrast between black and white displays, achieving display characteristics comparable to devices without a touch sensor.
Implementation Method 1
the pressure sensitive adhesive layer includes a visible light absorber, and the pressure sensitive adhesive layer has an internal absorbance Aa of 0.03 or less
Data Source
AI summary
A touch sensor with a pressure sensitive adhesive layer that is excellent in contrast between black display and white display and is excellent in performance of suppressing a decrease in brightness of white display when the touch sensor with a pressure sensitive adhesive layer is applied to an image display device and black and white display is made, as well as an image display device including the touch sensor with a pressure sensitive adhesive layer. The touch sensor with a pressure sensitive adhesive layer includes a touch sensor and a pressure sensitive adhesive layer disposed on one surface side of the touch sensor. The pressure sensitive adhesive layer includes a visible light absorber and has an internal absorbance Aa of 0.03 or less and a parameter X of 20 m−1 or more, the internal absorbance Aa being calculated with Test X.