Flexible Display Neutral Axis Shift via Bent Bonding

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Solution Overview

Problem

The existing methods for manufacturing flexible organic EL display devices result in increased overall thickness, which compromises the flexibility of the devices and can lead to damage when bent due to stress on the sealing film.

Innovation Solution

A display device is manufactured by stacking and bonding a flexible display panel with an optical member in a bent state and then stretching it into a flat shape, ensuring that the moisture-proof layer and sealing film are positioned outside the neutral axis to prevent stress accumulation at the bent portion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the thicknesses and materials of substrates are set so that the neutral axis coincides with the sealing film when bending stress is applied, then cracks in the sealing film are prevented, but the overall thickness of the display device increases, degrading flexibility

Engineering Contradiction:

Improvecrack prevention in sealing filmVSAvoidflexibility of display device

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

Instead of positioning the neutral axis at the sealing film interface during normal operation, the patent inverts the approach by positioning the neutral axis at the center of the display panel during bending. This is achieved by making the display panel thicker than the combined thickness of the optical member and second substrate, ensuring the neutral axis falls within the display panel thickness rather than at the interface between sealing film and second substrate.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the thickness parameters of the components to achieve the desired neutral axis positioning. Specifically, the display panel thickness is set to be greater than the combined thickness of the optical member and second substrate, which shifts the neutral axis position from the sealing film interface to the center of the display panel, thereby protecting the sealing film from stress while maintaining flexibility.

Inventive Principle:

Principle #35Parameter changes

2Strength

If the neutral axis is positioned at the interface between inorganic insulating film and second substrate, then stress on sealing film is reduced, but the display device loses flexibility due to increased thickness

Engineering Contradiction:

Improvestress resistance of sealing filmVSAvoidflexibility of display device

Core Design Contradiction:

StrengthVSAdaptability or versatility

Solution Approach 1:

The patent inverts the conventional approach by not positioning the neutral axis at the sealing film interface, but rather at the center of the display panel. This is accomplished by making the display panel the thickest component, ensuring the neutral axis during bending falls within the display panel rather than at the critical interface between the sealing film and second substrate.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent applies different thickness characteristics to different parts of the display device structure. The display panel is made thicker than the combined thickness of the optical member and second substrate, creating a local thickness variation that positions the neutral axis within the display panel where it can accommodate bending stress without compromising the sealing film.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If multiple layers are stacked in a flat state, then manufacturing is simpler, but stress accumulates at bent portions causing damage to the display panel

Engineering Contradiction:

Improvesimplicity of stacking processVSAvoiddamage resistance of display panel

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies preliminary action by pre-bending the display device to a predetermined curvature before bonding the display panel and optical member. This preliminary bending ensures that when the device is subsequently bent during use, the stress distribution is optimized and accumulated stress at bent portions is prevented, thereby protecting the display panel from damage.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces curvature into the stacking process by bonding the display panel and optical member in a bent state rather than a flat state. The display device is configured with a predetermined bending radius, and the bonding is performed while maintaining this curvature, which prevents stress accumulation when the device is subsequently bent during operation.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentUS10388909B2Display device, bonding jig, bonding device, and stretching jig used for manufacturing the display device, and method for manufacturing display device

Publication Date: 2019.08.20 SHARP KK

AI summary

Provided is a display device 100 that includes a display panel having flexibility (an organic EL panel 1 as an example), and an optical member 2 having flexibility, arranged so as to be stacked on the display panel, wherein the display panel and the optical member 2 are stacked and bonded in a bent state, and thereafter stretched into a flat shape.