Thin Glass Stress Profile via Metal Oxide Gradient
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Solution Overview
Problem
Thermally tempered glass is limited to thick applications due to the need for a thermal gradient, while chemically strengthened glass lacks the stress profile of thermally tempered glass, making it difficult to achieve superior fracture resistance in thin, lightweight glass articles commonly used in consumer electronics and other applications.
Innovation Solution
A glass-based article with a non-zero metal oxide concentration gradient along its thickness, generating a stress profile with a steep surface compressive stress region and a less steep central tension region, achieved through ion exchange processes that create a specific distribution of metal oxides like Li2O, Na2O, K2O, and Cs2O, resulting in enhanced fracture resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermal tempering is used to achieve large compressive stress layers for improved fracture resistance, then fracture resistance is improved, but the glass article thickness must be 3 millimeters or greater
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the glass (specific metal oxide concentrations within defined ranges) and the thermal processing parameters (heating to specific temperature ranges, cooling rates) to achieve the desired stress profile in thinner glass articles. This allows fracture resistance improvement without being constrained by the minimum thickness requirement of thermal tempering.
Solution Approach 2:
The patent creates a composite stress profile within the glass article by establishing two distinct regions: a first region with a first stress profile characteristics and a second region with a second stress profile characteristics. This composite approach allows the thin glass article to exhibit both surface compressive stress for flaw prevention and controlled central tension for overall structural integrity.
2Length of moving object
If chemically strengthened glass is used to reduce thickness, then thickness is reduced, but the stress profile lacks the characteristics of thermally tempered glass with insufficient central tension
Solution Approach 1:
The patent merges the advantages of both chemical strengthening (ability to treat thin glass) and thermal tempering (superior stress profile with adequate central tension). By combining specific metal oxide concentrations with thermal processing, the invention achieves a composite stress profile that incorporates both surface compressive stress from chemical strengthening and adequate central tension characteristic of thermal tempering.
Solution Approach 2:
The patent modifies the chemical and thermal parameters to transform the stress profile characteristics. By adjusting metal oxide concentrations and thermal processing conditions, the invention changes the stress distribution to ensure adequate central tension (at least 75 MPa) while maintaining thin dimensions, thereby correcting the insufficient central tension problem of conventional chemically strengthened glass.
3Ease of manufacture
If a single stress profile region is used in chemically strengthened glass, then manufacturing is simplified, but fracture resistance is insufficient due to flat or constant tensile stress in the central region
Solution Approach 1:
The patent applies local quality by creating spatially varying stress profile characteristics within different regions of the glass article. The first region has distinct stress profile characteristics compared to the second region, with each region optimized for its specific function. This local differentiation ensures that the central region provides adequate tension support while surface regions provide compressive protection, thereby improving fracture resistance without excessive manufacturing complexity.
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-based article exhibits improved fracture resistance, fracturing into multiple fragments and maintaining structural integrity under impact, with a surface compressive stress of 200 MPa or greater and a maximum central tension of less than 80 MPa, suitable for thin applications.
Implementation Method 1
achieved through ion exchange processes that create a specific distribution of metal oxides like Li2O, Na2O, K2O, and Cs2O
Data Source
AI summary
Glass-based article including a first surface and a second surface opposing the first surface defining a thickness (t), and a stress profile are disclosed having a thickness (t) of about 3 millimeters or less, and wherein all points of the stress profile between a thickness range from about 0·t up to 0.3·t and from greater than 0.7·t, comprise a tangent with a slope that is less than about −0.1 MPa/micrometers or greater than about 0.1 MPa/micrometers. Also disclosed are glass-based articles having a thickness (t) in a range of 0.1 mm and 2 mm; and wherein at least one point of the stress profile in a first thickness range from about 0·t up to 0.020·t and greater than 0.98·t comprises a tangent with a slope of from about −200 MPa/micrometer to about −25 MPa/micrometer or about 25 MPa/micrometer to about 200 MPa/micrometer, and wherein all points of the stress profile in a second thickness range from about 0.035·t and less than 0.965·t comprise a tangent with a slope of from about −15 MPa/micrometer to about 15 MPa/micrometer.