Segmented Adhesive Bonding for Touch Panel Light Guide Strength
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Solution Overview
Problem
Conventional touch pad input devices face issues with mechanical strength and light guide efficiency due to insufficient fixing between the reflection plate and light guide plate, leading to non-uniform luminance and operational challenges, especially with temperature changes and the presence of air layers.
Innovation Solution
The input device employs a multilayer structure with a light guide member, bonded sheet, and sensor, using double-sided adhesive tapes to ensure mechanical strength and prevent air layer formation, along with optical regions on the light guide member for enhanced light guidance and clear mark display, eliminating the need for a reflection plate and improving operability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the reflection plate and light guide plate are entirely joined with adhesive, then mechanical strength is improved, but the prism surface is buried in adhesive causing light guide efficiency to decrease
Solution Approach 1:
The bonding area is segmented into multiple discrete bonding portions rather than a continuous adhesive layer. This allows the prism surface to remain exposed in non-bonding areas, maintaining light guide efficiency while providing sufficient mechanical strength through distributed bonding points.
Solution Approach 2:
Different areas of the light guide plate serve different functions: bonding portions have adhesive for mechanical strength, while non-bonding portions have exposed prism surfaces for light guide efficiency. This local differentiation resolves the contradiction between strength and optical performance.
2Ease of manufacture
If the reflection plate and light guide plate are simply fixed with adhesive, then ease of manufacture is improved, but air layer formation causes temperature stress deterioration
Solution Approach 1:
The adhesive is applied in segmented portions rather than as a continuous layer, which simplifies the manufacturing process while preventing air layer entrapment. The segmented application method is easier to control and less prone to creating voids.
Solution Approach 2:
The prism surface irregularities, which could trap air and cause reliability issues, are strategically positioned in non-bonding areas. This converts a potential harm (air layer formation) into a benefit (maintained light guide efficiency) while the bonding portions provide reliable mechanical attachment.
3Adaptability or versatility
If multiple electrodes are provided on the sensor substrate, then functionality is improved, but surface irregularities cause insufficient joint strength
Solution Approach 1:
The bonding structure is segmented into multiple discrete bonding portions distributed across the sensor surface. This segmentation allows the adhesive to bond to flat areas between electrodes while maintaining overall joint strength, accommodating the electrode-induced surface irregularities.
Solution Approach 2:
The bonding portions are strategically located in areas with favorable surface characteristics (flat regions between electrodes), while electrode areas with irregularities are excluded from bonding. This local quality differentiation maintains both sensor functionality and joint strength.
4Device complexity
If an LED is disposed adjacent to the light guide plate end face, then simplicity of structure is improved, but light guiding efficiency into the light guide plate is low
Solution Approach 1:
Instead of attempting to improve coupling in the lateral dimension (adjacent placement), the solution uses optical dimensionality by creating a virtual image of the LED through the prism surface. This allows light to enter the light guide plate more efficiently by utilizing total internal reflection and optical path manipulation.
Solution Approach 2:
The prism surface acts as an optical intermediary between the LED and the light guide plate. By forming a virtual image of the LED through the prism, it mediates the light transfer process to improve coupling efficiency without requiring direct contact or complex alignment mechanisms.
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 enhances mechanical strength, maintains light guide efficiency, and ensures clear visual recognition of operation modes and marks on the operation surface, improving overall operability and durability.
Implementation Method 1
a light guide plate having a prism surface is provided on the reflection plate
Implementation Method 2
entirely joining an upper surface of the reflection plate and a bottom surface of the light guide plate with an adhesive such as a double-sided adhesive tape
Data Source
AI summary
A light guide member and a sensor that constitute a front light mechanism are bonded with a bonded sheet. A double-sided adhesive tape is provided on each surface of the bonded sheet. A repairing material is printed on a surface of the sensor so as to fill concave portions provided between the adjacent X-electrodes. This substantially increases the contact area with the double-sided adhesive tape, and increases the bonding strength between the light guide member and the sensor.