Chemically Tempered Glass Plate for Mobile Displays
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Solution Overview
Problem
Thin cover glasses for mobile devices face a trade-off between thickness and strength, where reducing thickness for weight and thickness reduction compromises protection against breakage, and existing chemical tempering methods struggle to balance compressive and tensile stresses effectively.
Innovation Solution
A glass composition with specific oxide content ratios, including SiO2, Al2O3, Na2O, K2O, MgO, and ZrO2, is chemically tempered using a KNO3 molten salt to enhance the thickness of the surface compressive stress layer without increasing internal tensile stress, allowing for improved strength without post-treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the thickness of the cover glass is reduced for weight and thickness reduction, then the weight and thickness decrease, but the strength is lowered and the glass becomes more prone to breakage
Solution Approach 1:
The patent applies chemical tempering by immersing the glass plate in a molten salt bath, which changes the chemical composition and physical properties of the glass surface. This process creates a compressive stress layer that significantly enhances the strength of thin glass plates, allowing them to maintain high strength despite reduced thickness.
2Strength
If chemical tempering is applied to thinner glass plates to increase surface compressive stress, then the surface compressive stress increases, but the internal tensile stress also increases causing spontaneous breakage
Solution Approach 1:
The patent precisely controls the chemical tempering parameters including molten salt composition (KNO3 with LiNO3), temperature (400-450°C), and time (2-10 hours) to achieve the optimal balance between surface compressive stress and internal tensile stress. This parameter optimization ensures high surface compressive stress while keeping internal tensile stress at acceptable levels.
Solution Approach 2:
The patent references and builds upon previously established chemical tempering methods and glass compositions, adapting them for thin glass plates by modifying the tempering conditions and glass formulation to achieve the desired stress distribution.
3Reliability
If the depth of the surface compressive stress layer is reduced to decrease internal tensile stress, then the internal tensile stress decreases, but the glass becomes extremely weak against breakage or crack
Solution Approach 1:
The patent optimizes the chemical tempering parameters to achieve the precise depth and magnitude of compressive stress required. By controlling temperature, time, and salt composition, the process creates an optimal stress distribution profile that provides both sufficient surface compression and acceptable internal stress levels.
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 solution achieves a surface compressive stress layer thickness exceeding 40 μm and maintains stress below 1,050 MPa, providing enhanced protection for display devices without additional processing steps, while being produced through a float process for stability and low environmental impact.
Implementation Method 1
a chemical tempering method wherein alkali metal ions having a small ion radius (typically Li ions or Na ions) on a glass plate surface are exchanged with alkali ions having a larger ion radius (typically K ions) by ion exchange at a temperature lower than the glass transition point
Implementation Method 2
an air quenching tempering method (physical tempering method) wherein a surface of a glass plate heated to near the softening point is quenched by air cooling
Data Source
AI summary
To provide a glass plate for display devices wherein without carrying out a post treatment, the depth of a compression stress layer is increased, while the surface compression stress is prevented from being excess only by chemical tempering. A glass plate for display devices, which is obtained by chemically tempering a glass plate comprising, as represented by mol % based on the following oxides, from 50 to 74% of SiO2, from 1 to 10% of Al2O3, from 6 to 14% of Na2O, from 3 to 15% of K2O, from 2 to 15% of MgO, from 0 to 10% of CaO and from 0 to 5% of ZrO2, wherein the total content of SiO2 and Al2O3 is at most 75%, the total content of Na2O and K2O, i.e. Na2O+K2O, is from 12 to 25%, and the total content of MgO and CaO, i.e. MgO+CaO, is from 7 to 15%.