Ultra-thin Non-frangible Glass via Controlled Ion Exchange
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Solution Overview
Problem
Existing ion exchangeable glasses with thicknesses less than 0.4 mm are prone to frangibility when subjected to impact due to limitations in stress profiles and center tension values, which are not adequately addressed by current ion exchange processes.
Innovation Solution
The development of a glass article with a thickness range of 0.1 mm to less than 0.4 mm, featuring a compressive stress layer and a tensile region with specific stress profiles and physical center tension values that exceed the frangibility limit, achieved through a method involving ion exchange in a bath with controlled KNO3 and NaNO3 concentrations at elevated temperatures, creating a non-frangible glass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the glass thickness is reduced to less than 0.4 mm, then the glass becomes thinner and more suitable for modern applications, but the glass becomes more prone to frangibility under impact
Solution Approach 1:
The patent applies parameter changes by modifying the stress profile parameters through controlled ion exchange processes. Specifically, it creates a compressive stress layer with optimized depth (0.05t ≤ DOC ≤ 0.22t) and magnitude (200-950 MPa), and controls the physical center tension to exceed the frangibility limit. These parameter adjustments enable thin glass (0.1-0.4 mm) to achieve non-frangible behavior despite reduced thickness.
Solution Approach 2:
The patent implements local quality by creating a non-uniform stress distribution within the glass cross-section. A compressive stress layer is formed at the surface region (extending to depth DOC), while the center region maintains a controlled tensile stress. This localized stress differentiation provides surface protection against impact while maintaining overall structural integrity, enabling thin glass to resist frangibility.
2Reliability
If the physical center tension is increased to exceed the frangibility limit, then the glass becomes non-frangible, but the stress profile becomes more complex and difficult to control
Solution Approach 1:
The patent applies segmentation by dividing the stress profile into distinct regions: a compressive stress layer region (from surface to depth DOC) and a tensile region (from depth DOC to center). This segmentation is achieved through controlled ion exchange processes that create different stress characteristics in different depth zones. The compressive layer depth is specifically controlled to be 0.05t ≤ DOC ≤ 0.22t, creating a manageable two-region stress distribution that simplifies control while achieving non-frangibility.
Solution Approach 2:
The patent implements preliminary action by pre-forming a compressive stress layer at the glass surface through ion exchange before the glass is subjected to impact loads. The compressive stress layer (depth DOC, stress 200-950 MPa) is created in advance to counteract future impact forces. This preliminary stress configuration ensures that when impact occurs, the pre-existing compressive stresses help prevent crack initiation and propagation, achieving non-frangibility without complex real-time control.
3Ease of manufacture
If ion exchange is performed with traditional KNO3 bath, then the process is simple, but the resulting stress profile does not provide adequate protection against frangibility in thin glass
Solution Approach 1:
The patent introduces an intermediary substance (NaNO3) into the ion exchange bath, creating a mixed salt bath containing both KNO3 and NaNO3. This intermediary addition modifies the ion exchange kinetics and resulting stress profile. The NaNO3 component facilitates deeper ion penetration and creates the desired compressive stress layer depth (0.05t ≤ DOC ≤ 0.22t) and magnitude (200-950 MPa), while maintaining process simplicity. This intermediary approach enables adequate frangibility protection in thin glass without significantly complicating the manufacturing process.
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 resulting glass is non-frangible, with a compressive stress profile that extends from the surface to a depth of compression and a tensile region in the center, effectively preventing fracture under impact, and can be used in consumer electronic products for enhanced durability.
Implementation Method 1
In an ion exchange process diffusion of the larger cations (e.g., K+) into a glass is guided by a classical complementary error function
Implementation Method 2
diffusion of the larger cations (e.g., K+) into a glass
Implementation Method 3
The shape and value of the stress profile resulting from ion exchange was previously determined by the physical center tension limit
Data Source
AI summary
Glasses having a thickness t in a range from about 0.1 mm to less than 0.4 mm which, when chemically strengthened, is non-frangible and has a physical center tension CT (also referred to herein as “physical CT”), wherein CT>|−1.956×10−16×t6+1.24274×10−12×t5−3.09196×10−9×t4+3.80391×10−6×t3−2.35207×10−3×t2+5.96241×10−1×t+36.5994|, where t is expressed in microns.