Thin Strengthened Glass with Deep Compression and Flat Surfaces
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional thermal strengthening methods struggle to achieve high surface compressive stresses and deep depths of compression in thin glass articles, making it challenging to produce fully tempered glass with thicknesses less than 2 mm, while also facing issues with energy efficiency and surface quality.
Innovation Solution
A combination of thermal and chemical strengthening processes is employed, where high heat transfer rates are used for thermal strengthening, followed by ion exchange in a molten salt bath to achieve deep compressive stress profiles and high surface compressive stresses in thin glass articles, without contact-related defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermal strengthening is used on thin glass articles, then surface compressive stress is generated, but the depth of compression is insufficient and surface compressive stress levels are low
Solution Approach 1:
The patent combines thermal strengthening and chemical strengthening processes into a sequential treatment. The thermal strengthening first establishes a baseline compressive stress profile, then chemical strengthening is applied to enhance both the magnitude of surface compressive stress and the depth of the compressed layer, achieving synergistic effects that neither process could achieve alone.
Solution Approach 2:
The patent modifies key process parameters including heating temperature (400-700°C), quenching conditions, and chemical strengthening parameters (molten salt composition, temperature, and duration) to optimize the compressive stress profile. By carefully controlling these parameters, the process achieves both high surface compressive stress and deep compression depth in thin glass articles.
2Strength
If higher cooling rates are used to strengthen thinner glass, then surface compressive stress increases, but energy consumption increases and surface quality deteriorates
Solution Approach 1:
The patent optimizes the heating temperature range (400-700°C) and quenching parameters to achieve effective strengthening at moderate energy input. The chemical strengthening step further enhances stress levels, allowing lower cooling rates to be used than would be required for thermal strengthening alone, thereby reducing energy consumption.
Solution Approach 2:
The patent introduces molten salt as an intermediary medium for chemical strengthening. This mediator enables ion exchange that generates compressive stress without requiring extreme cooling rates, thus avoiding the energy penalties and surface quality issues associated with rapid quenching of thin glass.
3Ease of manufacture
If thermal strengthening alone is used on thin glass, then processing is simpler, but desirable dicing behavior and high surface compressive stress cannot be achieved
Solution Approach 1:
The patent merges thermal and chemical strengthening processes to achieve performance targets that neither process can achieve alone. The thermal step provides initial stress distribution, while the chemical step enhances surface stress and depth, delivering both high surface compressive stress and deep compression necessary for dicing behavior in thin glass.
Solution Approach 2:
The chemical strengthening process creates a non-uniform distribution of compressive stress concentrated at the surface and near-surface regions, with the depth of layer (DOL) being less than the depth of compression (DOC). This localized enhancement of compressive stress quality achieves the desired dicing behavior without requiring uniform stress throughout the entire glass thickness.
4Length of stationary object
If chemical strengthening is used to achieve deep compression, then depth of layer increases, but surface compressive stress may be reduced
Solution Approach 1:
The patent applies thermal strengthening before chemical strengthening. This preliminary action establishes a foundation of compressive stress that works synergistically with the subsequent chemical strengthening. The thermal pre-treatment ensures that when chemical strengthening increases the depth of layer, the surface compressive stress is maintained at high levels due to the combined effect of both processes.
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 process effectively enhances the strength and durability of thin glass articles by achieving deep compressive stress profiles and high surface compressive stresses, preventing flaw penetration and fatigue, while maintaining surface quality and reducing energy consumption.
Implementation Method 1
Thermally strengthened glass articles are strengthened by heating a glass substrate to an elevated temperature above the glass transition temperature of the glass, and cooling the surfaces of the substrate rapidly ('quenching'), while the inner regions of the substrate, insulated by the thickness and fairly low thermal conductivity of the glass, are cooled at a slower rate.
Implementation Method 2
In some ion diffusion based processes, exterior portions of the resulting glass article may be strengthened by exchanging larger ions for smaller ions near the surface to impart a CS (also called negative tensile stress) on or near the surface.
Implementation Method 3
layers of glass compositions that have differing coefficients of thermal expansion are combined or laminated together while hot. For example, by sandwiching molten glass with a higher coefficient of thermal expansion (CTE) between layers of molten glass with a lower CTE, positive tension in the interior glass compresses the outer layers when the glasses cool, again forming CS on the surface
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Embodiments of thermally and chemically strengthened glass-based articles are disclosed. In one or more embodiments, the glass-based articles may include a first surface and a second surface opposing the first surface defining a thickness (t), a first CS region comprising a concentration of a metal oxide that is both non-zero and varies along a portion of the thickness, and a second CS region being substantially free of the metal oxide of the first CS region, the second CS region extending from the first surface to a depth of compression of about 0.17•t or greater. In one or more embodiments, the first surface is flat to 100 µm total indicator run-out (TIR) along any 50 mm or less profile of the first surface. Methods of strengthening glass sheets are also disclosed, along with consumer electronic products, laminates and vehicles including the same are also disclosed.