Glass Sheet Warpage Control via Differential Fluorination
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Solution Overview
Problem
Chemical strengthening of glass sheets for flat panel displays often results in warpage due to differences in the degree of chemical strengthening between the top and bottom surfaces, leading to issues like luminance irregularity and Newton rings, and existing methods to mitigate this, such as grinding or polishing, are inefficient and affect productivity.
Innovation Solution
Fluorination of the glass surfaces to adjust the fluorine concentration and ion diffusion rates, ensuring a higher fluorine concentration on one surface compared to the other, thereby reducing warpage without the need for pre-treatment processes like grinding or polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If chemical strengthening is performed to increase surface compressive stress and depth of compressive stress layer for high scratch resistance, then scratch resistance is improved, but warpage occurs due to difference in chemical strengthening behavior between top and bottom surfaces
Solution Approach 1:
The patent applies different fluorine concentrations to different surfaces of the glass sheet. The first surface has a higher fluorine concentration (0.03-0.15 at%) than the second surface (0.00-0.08 at%), creating local compositional differences that control ion diffusion rates during chemical strengthening. This local quality variation balances the chemical strengthening behavior between the two surfaces, suppressing warpage while maintaining high scratch resistance through adequate compressive stress levels.
Solution Approach 2:
The patent modifies the chemical composition parameters of the glass sheet by controlling fluorine concentration at different surfaces. By adjusting the fluorine concentration ratio between the first and second surfaces, the patent changes the ion diffusion characteristics during chemical strengthening. This parameter change approach allows optimization of both scratch resistance (through sufficient compressive stress) and flatness (through balanced diffusion behavior), resolving the technical contradiction.
2Shape
If grinding treatment or polishing treatment is performed before chemical strengthening to reduce warpage, then flatness is improved, but productivity decreases due to additional process steps
Solution Approach 1:
The patent performs preliminary fluorination treatment during the glass manufacturing process itself, before the glass sheet is removed from the production line. By incorporating fluorine into the glass surface composition at the manufacturing stage, the patent creates a built-in mechanism that prevents warpage during subsequent chemical strengthening, eliminating the need for separate grinding or polishing steps and maintaining high productivity.
Solution Approach 2:
The patent enables the glass sheet to self-regulate its chemical strengthening behavior through its inherent compositional structure. The differential fluorine concentration embedded in the glass during manufacturing creates self-balancing ion diffusion rates at the two surfaces, allowing the glass to maintain flatness without requiring external mechanical intervention like grinding or polishing, thus preserving production efficiency.
3Weight of moving object
If the thickness of the cover glass is reduced to decrease weight and meet thinness requirements, then weight and thickness are reduced, but strength is lowered and the glass may break during use or drop
Solution Approach 1:
The patent changes the chemical composition parameters of the glass by incorporating fluorine at controlled concentrations in the surface layers. This compositional modification enhances the glass's mechanical properties and enables effective chemical strengthening, allowing thin glass sheets to achieve sufficient strength and scratch resistance without increasing thickness, thus maintaining weight reduction while improving durability.
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 fluorination method effectively suppresses warpage after chemical strengthening, maintaining compressive stress and improving flatness without lowering the strengthening stress, thus enhancing the glass sheet's performance and productivity.
Implementation Method 1
a fluorine concentration in the one surface is higher than the fluorine concentration in the other surface... by subtracting an average fluorine concentration (mol %) by SIMS at a depth of 1 to 24 μm
Implementation Method 2
in order to improve scratch resistance, a float glass produced by a float method is chemically strengthened to form a compressive stress layer in the surface thereof
Data Source
AI summary
A glass sheet has one surface and the other surface facing the one surface in a thickness direction, wherein a fluorine concentration (average fluorine concentration by SIMS at a depth of 1 to 24 μm) in the one surface is higher than that in the other surface. The following expression is satisfied: 0.07≦ΔF/ΔH2O. ΔF (mol %) is a value obtained by subtracting an average fluorine concentration in the surface having the lower fluorine concentration from that in the surface having the higher fluorine concentration, and ΔH2O (mol %) is an absolute value of a value obtained by subtracting an average H2O concentration in the surface having the higher fluorine concentration from that in the surface having the lower fluorine concentration.