Foldable Substrate Adhesive Neutral Plane Design
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Solution Overview
Problem
Existing foldable displays and protective covers face challenges in achieving both small minimum bend radii and good impact and puncture resistance, while also avoiding fatigue-related failures and ensuring mechanical reliability.
Innovation Solution
The development of foldable apparatus comprising a foldable substrate with compressive stress regions, an adhesive layer with a low elastic modulus, and a polymer-based portion, which together provide improved impact and puncture resistance while maintaining small bend radii and reducing mechanical instabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thicker glass-based sheets are used to improve impact and puncture resistance, then impact and puncture resistance is improved, but minimum bend radius increases and mechanical reliability deteriorates
Solution Approach 1:
The patent uses a composite structure combining glass-based substrate with polymer-based portions and adhesive layers. The glass-based substrate provides impact and puncture resistance, while the polymer-based portions with low elastic modulus provide flexibility and small bend radius. The adhesive layers with neutral planes further enhance flexibility. This composite approach allows achieving both strength and reliability without using thicker glass sheets alone.
Solution Approach 2:
The patent changes the elastic modulus parameter of the adhesive layer to be very low (0.4 MPa or less), which is much lower than the glass-based substrate. This parameter change allows the adhesive layer to accommodate bending stresses without creating mechanical instabilities, enabling small bend radii while maintaining the strength benefits of the glass-based material.
2Shape
If ultra-thin glass-based sheets are used to achieve small minimum bend radii, then minimum bend radius is reduced, but impact and puncture resistance deteriorates
Solution Approach 1:
The patent combines glass-based substrate with polymer-based portions having low elastic modulus. The glass-based substrate maintains small bend radius capability, while the polymer-based portions compensate for reduced impact resistance by providing flexibility and stress distribution. The adhesive layers with neutral planes further enable small bend radii without compromising the strength benefits of the glass-based material.
Solution Approach 2:
The patent applies different material properties to different regions: the glass-based substrate provides strength where needed, while the polymer-based portions provide flexibility. The adhesive layers with neutral planes are strategically positioned to enable bending without creating mechanical instabilities, allowing local optimization of both bend radius and strength.
3Reliability
If adhesive layer with low elastic modulus is used to reduce bend-induced stresses, then mechanical instabilities are reduced, but device complexity increases
Solution Approach 1:
The patent specifies precise parameter ranges for the adhesive layer: elastic modulus of 0.4 MPa or less, thickness of 5 μm or more, and flexural rigidity of 10−7 Pa m3 or less. These parameter changes create a neutral plane within the adhesive layer that reduces bend-induced stresses. While this increases manufacturing precision requirements, it significantly improves reliability by preventing mechanical instabilities during folding.
Solution Approach 2:
The adhesive layer acts as an intermediary between the glass-based substrate and polymer-based portions. With its low elastic modulus and neutral plane, it mediates the stress distribution during bending, preventing mechanical instabilities. This intermediary layer, while adding structural complexity, enables the combination of stiff and flexible materials to work together reliably.
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 proposed solution enhances the impact and puncture resistance of foldable apparatus with small minimum bend radii, reduces fatigue, and improves mechanical reliability, thereby addressing the limitations of existing technologies.
Implementation Method 1
Providing an adhesive layer between a polymer-based portion and a central surface area of the foldable substrate can provide a neutral plane within the first adhesive portion
Implementation Method 2
Providing a low elastic modulus (e.g., about 0.4 MPa or less), a thickness of about 5 μm or more, and/or a low flexural rigidity (e.g., about 10−7 Pa m3 or less) can enable a neutral plane within the adhesive layer and/or reduce bend-induced stresses in adjacent first portions
Implementation Method 3
The foldable apparatus can comprise glass-based and/or ceramic-based materials comprising one or more compressive stress regions, which can further provide increased impact resistance and/or puncture resistance while simultaneously facilitating good bending performance
Implementation Method 4
Providing an adhesive layer comprising a much lower (e.g., from about 500 times to about 500,000 times, from about 10,000 times to about 100,000 times) elastic modulus and/or flexural rigidity than a polymer-based portion can reduce bend-induced stresses on the polymer-based portion or the foldable substrate
Implementation Method 5
Providing an adhesive layer and/or a polymer-based portion with a glass transition temperature outside of an operating range (e.g., from about 0° C. to about 40° C., from about −20° C. to about 60° C.) of a foldable apparatus can enable the foldable apparatus to have consistent properties across the operating range
Data Source
AI summary
Foldable apparatus comprise a foldable substrate comprising a first portion, a second portion, and a central portion positioned therebetween. The first portion and the second portion comprise a substrate thickness. The central portion comprises a central thickness that is less than the substrate thickness. A first central surface area of the central portion is recessed from the first major surface by a first difference and defines a first recess. The foldable apparatus comprises a first adhesive layer disposed in the first recess. The first adhesive layer comprises a first adhesive thickness of about 5 micrometers or more. The first adhesive layer comprises an elastic modulus of about 0.4 MegaPascals of less. The foldable apparatus comprises a first polymer-based portion disposed on the first adhesive layer such that the first adhesive layer is positioned between the first central surface area and the first polymer-based portion.