Polyurethane Acrylate Vinyl Ether Adhesive for Foldable Displays

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Solution Overview

Problem

Current optically clear adhesives (OCAs) for flexible and foldable displays do not meet the requirements for high bendability and durability, particularly failing to maintain low modulus and high creep recovery rates necessary for 100,000 cycles of 180-degree bending across a wide temperature range without residual strain.

Innovation Solution

A co-cured polyacrylate/vinyl ether adhesive polymer composition is developed, which exhibits a very low modulus at -20°C (less than 10.0 mPa) and excellent creep recovery (greater than 50%), achieved by co-curing polyurethane acrylate and vinyl ether, resulting in a combination of low modulus and high creep recovery, specifically a creep recovery from >70% to >90% and a modulus of <1.0 mPa to <0.3 mPa at -20°C.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a highly crosslinked network with high elasticity is used to achieve high creep recovery, then the polymer exhibits high creep recovery, but the modulus becomes relatively high, especially at low temperatures

Engineering Contradiction:

Improvecreep recoveryVSAvoidmodulus

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent employs a composite polymer system combining polyacrylate chains with vinyl ether crosslinks. This composite structure integrates the flexibility and low modulus characteristics of polyacrylate with the elastic recovery properties of vinyl ether crosslinked networks, achieving both high creep recovery (>90%) and low modulus (<1.0 mPa at -20°C) simultaneously

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent optimizes specific parameters including the ratio of polyacrylate to vinyl ether (70:30 to 90:10), molecular weight of polyacrylate (20,000 to 500,000), and crosslink density to achieve the desired balance between creep recovery and modulus. By controlling these parameters, the adhesive maintains low modulus at low temperatures while achieving high creep recovery

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If a polymer is designed to be highly bendable with low modulus at low temperatures, then the adhesive can accommodate folding stress, but the creep recovery rate decreases

Engineering Contradiction:

ImprovebendabilityVSAvoidcreep recovery rate

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent creates a flexible adhesive layer with thin film characteristics that can bend repeatedly without cracking. The polyacrylate-based adhesive forms a flexible matrix that accommodates the bending stresses of foldable displays while maintaining structural integrity through controlled crosslinking

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The vinyl ether crosslinks act as intermediary elements between the polyacrylate chains, providing reversible bonding that allows the adhesive to flex during bending while maintaining connectivity. These crosslinks break and reform during deformation, enabling both flexibility and recovery

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of operation

If typical visco-elastic OCAs are used to provide adhesion and damping properties, then the adhesive maintains good pressure-sensitive behavior, but the properties are insufficient to enable foldable or durable displays

Engineering Contradiction:

Improvepressure-sensitive behaviorVSAvoidfoldability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent designs an adhesive with dynamic mechanical properties that adapt to different operational conditions. The adhesive exhibits pressure-sensitive behavior during application for proper bonding, then transitions to high creep recovery mode during folding cycles to accommodate repeated bending without permanent deformation or failure

Inventive Principle:

Principle #15Dynamics

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 adhesive polymer composition provides enhanced foldability and durability by maintaining low modulus and high creep recovery, enabling the adhesive to effectively absorb folding-induced stress and protect fragile components in flexible displays, meeting the stringent requirements for foldable OLED devices.

Implementation Method 1

Flexible electronic displays, where the display can be bent freely without cracking or breaking

Methodology Applied

Scientific EffectViscoelasticity: Viscoelasticity

Implementation Method 2

the OCA will also serve as the assembly layer, which in addition to the typical OCA functions, may also absorb most of the folding induced stress to prevent damage to the fragile components of the display panel

Methodology Applied

Scientific EffectStress absorption: Damping

Implementation Method 3

A foldable adhesive should have a high recovery speed and a low residual strain for good foldability

Methodology Applied

Scientific EffectCreep recovery: Elastic Recovery

Data Source

PatentUS20220380645A1High creep recovery, low modulus polymer systems and methods of making them

Publication Date: 2022.12.01 HENKEL KGAA

AI summary

Disclosed herein are methods of making an adhesive composition, the methods comprising providing a polyurethane acrylate and combining with a vinyl ether and co-curing the combination to form an adhesive composition, wherein after curing the adhesive composition has a modulus at −20° C. of less than about 10.0 mPa and a creep recovery of greater than about 50%. Also disclosed are the resulting adhesive compositions.