Touch Panel Moisture Sealing for Reliable Capacitive Detection
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Solution Overview
Problem
Projected capacitive touch screen devices face issues with misdetection due to changes in relative permittivity of transparent adhesive materials under varying temperature and humidity conditions, especially when exposed to moisture, which affects electrostatic capacitance and leads to unreliable touch coordinate detection, especially when gloves are worn or water droplets adhere to the protective glass.
Innovation Solution
Incorporating a moisture-proof sealing member with lower water vapor permeability than the transparent adhesive material to cover regions of the adhesive not in contact with the protective plate or touch sensor panel, thereby reducing the influence of humidity on the adhesive's relative permittivity and stabilizing touch coordinate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If transparent adhesive material is used to attach touch sensor panel and protective plate, then ease of manufacture is improved, but reliability deteriorates due to moisture absorption causing relative permittivity changes and misdetection
Solution Approach 1:
The patent applies local quality by making the water vapor permeability of the transparent adhesive material non-uniform: the peripheral portion has lower water vapor permeability than the central portion. This local differentiation prevents moisture absorption at edges where it would cause relative permittivity changes and misdetection, while maintaining ease of manufacture with a single material type.
Solution Approach 2:
The patent changes the water vapor permeability parameter of the transparent adhesive material from uniform to non-uniform distribution. By controlling the peripheral portion to have lower water vapor permeability, the material's resistance to moisture absorption is enhanced at critical areas, preventing reliability issues while maintaining manufacturing simplicity.
2Reliability
If peripheral portion of transparent adhesive material is sealed to prevent moisture absorption, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent uses local quality by varying the water vapor permeability within the transparent adhesive material itself, creating a gradient where the peripheral portion has lower permeability. This internal differentiation eliminates the need for external sealing structures, maintaining device simplicity while improving reliability.
Solution Approach 2:
The transparent adhesive material provides its own moisture protection function through its non-uniform water vapor permeability distribution. The material self-regulates moisture absorption by having lower permeability at the periphery, eliminating the need for separate sealing components and reducing device complexity.
3Ease of manufacture
If uniform water vapor permeability is used in transparent adhesive material, then ease of manufacture is improved, but measurement precision deteriorates due to relative permittivity distribution changes
Solution Approach 1:
The patent applies local quality by creating a non-uniform water vapor permeability distribution in the transparent adhesive material, with the peripheral portion having lower permeability than the central portion. This prevents moisture-induced relative permittivity changes at edges that would affect capacitance measurement precision, while maintaining ease of manufacture.
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
This configuration effectively suppresses misdetection under high humidity and temperature conditions, maintaining high sensitivity and robustness by minimizing changes in electrostatic capacitance, even when water droplets adhere, and reducing the need for costly conductive components.
Implementation Method 1
a moisture-proof sealing member having water vapor permeability that is lower than water vapor permeability of the transparent adhesive material
Implementation Method 2
Relative permittivity of the transparent adhesive material is changed depending on a temperature, and may be reduced by up to 40% with respect to a room temperature state under an environment of a low temperature (−30° C.) or a high temperature (70° C.). Further, relative permittivity of the transparent adhesive material may be changed through moisture absorption.
Implementation Method 3
a detection circuit detects slight change in touch sensors provided in a touch panel, which is caused by electrostatic capacitance of a human finger
Data Source
AI summary
A touch sensor panel includes a plurality of sensors. A protective plate protects the touch sensor panel. A transparent adhesive material attaches the touch sensor panel and the protective plate. A moisture-proof sealing member has water vapor permeability that is lower than water vapor permeability of the transparent adhesive material. A flexible wiring board connects the plurality of sensors to an external circuit. The transparent adhesive material has a region that is out of contact with the protective plate or the touch sensor panel, and at least a part of the region is covered by the moisture-proof sealing member.