Chemically Strengthened Glass with Segmented Stress Profile for Drop Resistance
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Solution Overview
Problem
Glasses strengthened by ion exchange do not provide sufficient protection when dropped onto an abrasive surface due to stress profiles that are inadequate for such impacts.
Innovation Solution
A chemically strengthened glass article with a specific stress profile varying by thickness, featuring a first region with a maximum compressive stress of at least 280 MPa at the surface, a second region with a local compressive stress maximum, and a third region extending to a depth of compression, achieved through a three-step ion exchange process involving different alkali cation concentrations and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ion exchange strengthening is used, then the glass provides adequate protection against sharp impact, but it does not provide sufficient protection when dropped onto an abrasive surface
Solution Approach 1:
The stress profile is segmented into three distinct regions: a first region with maximum compressive stress at the surface, a second region with a local compressive stress maximum at intermediate depth, and a third region extending to the depth of compression. This segmentation creates a multi-layered stress distribution that better resists abrasive surface impacts compared to conventional single-region stress profiles.
Solution Approach 2:
Different regions of the glass are given different stress characteristics tailored to their specific functional needs. The surface region has high compressive stress for abrasion resistance, the intermediate region has a local stress maximum for crack initiation resistance, and the deeper region provides gradual stress transition. This local optimization of stress properties enhances overall drop performance.
2Reliability
If a single ion exchange bath is used, then the manufacturing process is simple, but the resulting stress profile does not achieve optimal drop performance
Solution Approach 1:
The ion exchange process is divided into three sequential steps, each using a bath with different alkali cation concentrations and compositions. The first bath creates the surface compressive stress layer, the second bath creates the intermediate stress maximum, and the third bath completes the deep compression layer. This stepwise approach enables precise control of the stress profile.
Solution Approach 2:
The manufacturing process utilizes systematic changes in bath composition parameters across the three steps. Each subsequent bath has different alkali cation concentrations and types compared to the previous bath, allowing progressive building of the complex stress profile. The parameters are optimized to achieve the desired stress distribution while maintaining process feasibility.
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 glass exhibits superior resistance to damage when dropped onto abrasive surfaces, with a 90% survival rate in drop tests from heights of up to 220 cm on 180 grit silicon carbide sandpaper, significantly outperforming reference samples.
Implementation Method 1
immersing the glass article in a first ion exchange bath comprising first alkali cations and second alkali cations, wherein the second alkali cations from the ion exchange bath replace the first alkali cations in the glass article
Implementation Method 2
the second alkali cations from the ion exchange bath replace the first alkali cations in the glass article
Data Source
AI summary
Chemically strengthened glass articles exhibiting superior resistance to damage when dropped onto an abrasive surface. The strengthened glass article has a stress profile in which the compressive and tensile stresses within the article vary as a function of the thickness t of the glass article. The stress profile has a first region extending from the surface of the glass article to a depth d1 into the glass, wherein d1≤0.025t or ≤20 μm and has a maximum compressive stress of at least about 280 MPa at the surface, a second region extending from a depth of at least d1 to a second depth d2 and having a local compressive stress maximum, and a third region extending from a third depth d3 in the glass to a depth of compression DOC, wherein d2≤d3 and DOC≤0.15t. A method of strengthening a glass article to provide resistance to damage when dropped is also provided.