Chemically Strengthened Glass With Deep Compression Layer
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Solution Overview
Problem
Conventional chemically strengthened glasses lack sufficient survivability when subjected to tensile stresses and deep flaws, particularly upon contact with hard or sharp surfaces, leading to inadequate performance in drop tests and bending scenarios.
Innovation Solution
Chemically strengthened glass articles with deep compressive layers extending up to 45 μm, achieved through a two-step ion exchange process, featuring compressive stress profiles with specific slope ranges to enhance survivability and resistance to fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional chemical strengthening is used, then manufacturing simplicity is maintained, but survivability under tensile stress and deep flaws is insufficient
Solution Approach 1:
The strengthening process is divided into multiple sequential ion exchange steps, each creating a distinct compressive stress layer at different depths. This segmentation allows the glass to achieve enhanced survivability by distributing compressive stresses throughout the thickness, with shallower layers (0-20 μm) and deeper layers (20-45 μm) working together to resist both surface flaws and subsurface damage
Solution Approach 2:
The patent systematically varies ion exchange parameters including temperature (300-450°C), duration (1-24 hours), and bath composition (KNO3, NaNO3, RbNO3, CsNO3) across different processing steps. These parameter changes enable precise control over compressive stress magnitude (100-1200 MPa) and depth of compression (0.05t-0.2t), optimizing survivability while managing process complexity
2Strength
If compressive stress layer depth is increased, then resistance to deep flaws improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements preliminary ion exchange steps that create compressive stress layers at shallower depths before performing deeper ion exchange. This preliminary action establishes a foundation of compression that prevents flaw initiation at the surface, while subsequent steps extend compression to deeper regions (DOC≥0.1t), reducing the need for extreme precision in each individual step's depth control
Solution Approach 2:
The multi-step ion exchange process applies partial strengthening at each stage, with each step contributing a portion of the total compressive stress. The cumulative effect of multiple partial actions achieves the desired deep compression (DOC≥0.1t) with relaxed precision requirements compared to attempting single-step deep strengthening
3Strength
If compressive stress magnitude is increased, then fracture resistance improves, but risk of surface damage during processing increases
Solution Approach 1:
The patent performs preliminary ion exchange at lower temperatures (300-400°C) and shorter durations to establish initial compressive stress (100-400 MPa) before conducting high-temperature exchanges. This preliminary compression protects the glass surface during subsequent aggressive processing steps, preventing surface damage while enabling the final high-strength state (500-1200 MPa)
Solution Approach 2:
The multi-step process creates a cushioning effect where intermediate compressive stress layers protect the glass structure during processing. Each completed ion exchange step establishes a protective compressed zone that buffers against thermal stress and mechanical damage during subsequent processing, enabling safe achievement of high fracture resistance
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 articles demonstrate a 60% survival rate in inverted ball drop tests and peak loads exceeding 10 kgf in abraded ring-on-ring testing, indicating improved resistance to impact and bending stresses.
Implementation Method 1
a compressive region under a compressive stress CS of from about 100 MPa up to about 1200 MPa at a surface of the glass article. The compressive region extends from the surface to a depth of compression DOC
Data Source
AI summary
Chemically strengthened glass articles having at least one deep compressive layer extending from a surface of the article to a depth of at least about 45 μm within the article are provided. In one embodiment, the compressive stress profile includes a single linear segment extending from the surface to the depth of compression DOC. Alternatively, the compressive stress profile includes two linear portions: the first portion extending from the surface to a relatively shallow depth and having a steep slope; and a second portion extending from the shallow depth to the depth of compression. The strengthened glass has a 60% survival rate when dropped from a height of 80 cm in an inverted ball drop test and a peak load at failure of at least 10 kgf as determined by abraded ring-on-ring testing. Methods of achieving such stress profiles are also described.