Cycloolefin Resin Touch Sensor Buffer Layer Stress Relief
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Solution Overview
Problem
Touch sensors with cycloolefin-based resin films are prone to cracking due to differences in linear expansion coefficients with the adhesive layer, leading to operational failures under temperature changes.
Innovation Solution
Incorporating a buffer layer with viscoelastic properties between the cycloolefin-based resin film and the adhesive layer to relieve stress and prevent cracking, while maintaining transparency and visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a transparent adhesive layer (LOCA) is used to bond the sensor body to the LCD, then adhesion and optical clarity are improved, but stress concentration and crack generation occur in the cycloolefin-based resin film due to different linear expansion coefficients
Solution Approach 1:
A buffer layer made of silicone resin is introduced as an intermediary between the cycloolefin-based sensor body and the transparent adhesive layer. This buffer layer has a coefficient of thermal expansion between those of the sensor body and the adhesive layer, allowing it to absorb and distribute thermal expansion stresses. The buffer layer acts as a stress-relief medium that prevents stress concentration at the interface, thereby preventing crack generation while maintaining strong adhesion.
2Illumination intensity
If the sensor body is made with a cycloolefin-based resin film for transparency, then optical clarity is improved, but the film becomes susceptible to cracks under temperature changes due to its low linear expansion coefficient
Solution Approach 1:
The invention changes the physical parameters of the system by introducing a buffer layer with specific material properties (silicone resin) that has a coefficient of thermal expansion intermediate between the cycloolefin-based sensor body and the transparent adhesive layer. This parameter change allows the system to accommodate thermal expansion differences without concentrating stress on the transparent film, thereby maintaining both transparency and resistance to temperature-induced cracking.
3Ease of manufacture
If a gap structure is used between the touch sensor and LCD, then manufacturing is simplified, but reflection increases and visibility with bright light deteriorates
Solution Approach 1:
The invention merges the sensor body and LCD into a gapless contact structure, eliminating the air gap between them. The sensor body is directly bonded to the LCD via the transparent adhesive layer, creating an integrated assembly. This merging eliminates reflection at the air-gap interface and improves visibility with bright light, while the buffer layer ensures that the increased manufacturing precision required is justified by the performance gains.
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 buffer layer effectively suppresses cracks in the cycloolefin-based resin film, ensuring the touch sensor's functionality and optical excellence even under thermal stress.
Implementation Method 1
The buffer layer has viscoelasticity at 25° C.
Data Source
AI summary
To suppress cracks generated by a change in environmental temperature in a sensor body of a touch sensor that includes a light-transmissive resin film substantially made of a cycloolefin-based resin. A liquid optically clear adhesive layer is an adhesive layer including a cured body of an adhesive adhering to a glass plate that is a solid member. A sensor body having a film shape firmly adheres to the glass plate by the liquid optically clear adhesive layer, and detects a position of a contact point on a display area. A light-transmissive resin film of the sensor body is substantially made of a cycloolefin-based resin. A buffer layer having viscoelasticity at 25° C. is provided between the light-transmissive resin film and the liquid optically clear adhesive layer to relieve stress transferred from the liquid optically clear adhesive layer to the light-transmissive resin film.