Adhesive Sheet for Flexible Displays Resolving Delamination at Low Temperatures
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Solution Overview
Problem
Existing adhesive films for flexible image display devices face issues with delamination and folding trace retention, especially at low temperatures, due to high elastic modulus and low adhesiveness, which are not adequately addressed by current solutions.
Innovation Solution
An adhesive sheet with a storage shearing elastic modulus of ≤700 kPa at -20°C, formed from an acrylic polymer and a radically polymerizable compound, including a di(meth)acrylate with a short alkylene group, which improves flexibility and adhesiveness while preventing delamination and rapid stress relaxation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If an adhesive film containing carbitol acrylate is used to reduce storage elastic modulus at low temperature, then flexibility is improved, but adhesiveness decreases causing delamination
Solution Approach 1:
The patent changes the chemical composition parameters of the adhesive by incorporating specific rubber particles (polybutadiene or styrene-butadiene rubber with 10-90 parts by mass relative to 100 parts by mass of carbitol acrylate) and controlling the glass transition temperature within -100°C to -50°C, thereby achieving both low elastic modulus for flexibility and maintained adhesiveness for preventing delamination
Solution Approach 2:
The patent creates a composite adhesive system by combining carbitol acrylate with rubber particles (polybutadiene or styrene-butadiene rubber) to form a multi-component adhesive composition that exhibits both flexibility and high adhesiveness, resolving the contradiction between these two properties
2Strength
If an adhesive film with high elastic modulus is used to maintain structural integrity, then strength is improved, but folding trace remains and recovery is slow
Solution Approach 1:
The patent optimizes the glass transition temperature parameter to -100°C to -50°C and controls the elastic modulus to 100-1000 MPa, creating an adhesive that maintains structural integrity while enabling rapid folding recovery and minimizing folding traces through its viscoelastic properties at low temperatures
3Shape
If an adhesive composition is designed for low elastic modulus to reduce folding stress, then flexibility is improved, but adhesiveness becomes too low causing delamination at low temperature
Solution Approach 1:
The patent precisely controls the glass transition temperature parameter within -100°C to -50°C and adjusts the rubber particle content to 10-90 parts by mass relative to 100 parts by mass of carbitol acrylate, achieving the optimal balance where the adhesive maintains both flexibility and sufficient adhesiveness even at low temperatures
Solution Approach 2:
The patent uses rubber particles (polybutadiene or styrene-butadiene rubber) as sacrificial soft segments that provide flexibility and stress relief during folding, while the carbitol acrylate matrix maintains adhesiveness, creating a composite system where each component performs its specific function
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 sheet effectively recovers to a flat state upon folding and maintains high adhesiveness, preventing delamination and cracking, even under repeated folding operations at low temperatures, making it suitable for durable flexible image display devices.
Implementation Method 1
an adhesive sheet having a storage shearing elastic modulus at -20° C. of not greater than 700 kPa, wherein the adhesive sheet is formed from an adhesive composition containing an acrylic polymer and a radically polymerizable compound
Data Source
AI summary
Provided is an adhesive sheet having good flexibility and recovering ability, and excellent adhesiveness. An adhesive sheet having a storage shearing elastic modulus at −20° C. [G′(−20° C.)] of not greater than 700 kPa, wherein the adhesive sheet is formed from an adhesive composition [I] including an acrylic polymer (A) and a radically polymerizable compound (B), the acrylic polymer (A) includes: a structural portion derived from an alkyl (meth)acrylate (a1) with an alkyl group having 5 to 20 carbon atoms; and a structural portion derived from a hydroxy-group-containing (meth)acrylate (a2), and the radically polymerizable compound (B) includes a di(meth)acrylate (B1) having an alkylene group having 2 to 4 carbon atoms.