Backlight Unit Warpage Control via Friction-Expansion Relation
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Solution Overview
Problem
Conventional backlight units experience deformation due to warpage of the light diffusion sheet caused by the differing expansion/contraction amounts between the light diffusion sheet and the light guide sheet, leading to friction and wrinkles.
Innovation Solution
The backlight unit is designed with an optical element and a light diffusion sheet where the coefficient of static friction between them is controlled to satisfy specific relational expressions, reducing the impact of the light guide sheet's expansion/contraction on the light diffusion sheet, thereby minimizing deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light diffusion sheet is placed on the light guide sheet, then light diffusion function is achieved, but deformation due to warpage occurs because of different expansion/contraction amounts between the two sheets
Solution Approach 1:
An intermediate layer is introduced between the light diffusion sheet and the light guide sheet. This intermediate layer acts as a mediator that absorbs the differential expansion/contraction forces between the two sheets, preventing direct friction and warpage of the light diffusion sheet while maintaining the light diffusion function.
Solution Approach 2:
The invention changes the physical parameters of the intermediate layer (such as its material composition, thickness, and mechanical properties) to optimize its ability to accommodate differential expansion/contraction. By adjusting these parameters, the intermediate layer can effectively reduce friction and prevent warpage while maintaining system functionality.
2Adaptability or versatility
If the light guide sheet expands/contracts due to temperature changes, then thermal adaptation is achieved, but friction occurs between the light guide sheet and light diffusion sheet causing warpage
Solution Approach 1:
The intermediate layer serves as a protective mediator that decouples the thermal expansion of the light guide sheet from the light diffusion sheet. It allows the light guide sheet to expand and contract freely while preventing these movements from causing friction and warpage to the light diffusion sheet.
Solution Approach 2:
The intermediate layer provides beforehand cushioning by being positioned in advance between the two sheets. It is designed to anticipate and absorb the friction forces that would otherwise occur during thermal expansion/contraction cycles, preventing warpage before it happens.
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 approach effectively reduces deformation of the light diffusion sheet due to the expansion/contraction of the light guide sheet, ensuring stable performance under various temperature and humidity conditions.
Implementation Method 1
a light diffusion sheet disposed on the front surface of the light guide sheet and having a light diffusion function
Implementation Method 2
a rectangular plate-like light guide sheet disposed with its edge being along the light source
Data Source
AI summary
A backlight unit (5) includes a light guide sheet (21) and a light diffusion sheet (23) provided on the surface of the light guide sheet (21). Assuming that the coefficient of static friction between the light guide sheet (21) and the light diffusion sheet (23) measured at a temperature of 23° C. and a humidity of 50% in accordance with JIS K 7125 is Y1, and the difference in coefficient of linear expansion between the light guide sheet (21) and the light diffusion sheet (23) measured in accordance with JIS K 7197 is X, the following relational expression (1) is satisfied.[Math. 1]Y1≤1.00×10−4X2−3.43×10−2X+2.35 (1).