Multilayer Adhesive Sheet for Foldable Displays
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Solution Overview
Problem
Adhesive films used in foldable display apparatuses face challenges in maintaining adhesion, flexural reliability, impact resistance, and optical clarity while being susceptible to external impacts and punching processes, which can lead to damage such as dents and scratches.
Innovation Solution
A multilayer adhesive sheet comprising a polyurethane-based film as the base layer, combined with first and second adhesive layers made from hydroxyl group-containing (meth)acrylic copolymer compositions, organic and inorganic particles, and initiators, providing a storage modulus range that enhances flexural reliability, impact resistance, and optical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adhesive film is designed to have both adhesion and flexural reliability, then bonding performance is improved, but the adhesive film becomes vulnerable to external impact
Solution Approach 1:
The adhesive film is constructed as a multilayer composite structure comprising a first adhesive layer, a base layer, and a second adhesive layer. Each layer has specifically controlled storage modulus values, creating a composite material system that combines the high adhesion of adhesive layers with the impact resistance and flexibility of the polyurethane base layer, thereby achieving both bonding performance and impact resistance simultaneously
Solution Approach 2:
The patent specifies precise parameter ranges for storage modulus at different temperatures (−20°C and 85°C) for each layer. By controlling the storage modulus parameters within these ranges, the adhesive film achieves optimal balance between adhesion strength and impact resistance, resolving the contradiction between bonding performance and vulnerability to external impact
2Ease of manufacture
If adhesive film is subjected to punching process, then shaping and mounting is enabled, but dents and scratches are generated on the adhesive film
Solution Approach 1:
The multilayer structure provides local quality differentiation where the base layer with specific storage modulus (700-1500 MPa at −20°C, 10-100 MPa at 85°C) is positioned to absorb punching stresses, while the adhesive layers maintain their bonding function. This local differentiation allows the base layer to protect the adhesive layers from punching-induced surface damage
Solution Approach 2:
The base layer acts as a cushioning layer positioned between the adhesive layers,预先 absorbing and distributing the stress from punching operations. This beforehand cushioning prevents the adhesive layers from directly承受 punching forces, thereby preventing dents and scratches while maintaining good punchability
3Adaptability or versatility
If layer with completely different characteristics is interposed between adhesive films, then functional differentiation is achieved, but punchability of the adhesive film worsens
Solution Approach 1:
The base layer's storage modulus is specifically controlled within defined ranges at different temperatures to balance functional differentiation and punchability. By adjusting the modulus parameters, the base layer provides sufficient functional differentiation while maintaining compatibility with punching processes, preventing excessive hardness that would worsen punchability
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 multilayer adhesive sheet achieves good flexural reliability across temperatures, effective absorption and distribution of external impacts, improved punchability, and low haze, ensuring the integrity and visibility of foldable display apparatuses.
Implementation Method 1
the base layer includes a polyurethane-based film manufactured by solution casting and has a storage modulus of 700 MPa to 1,500 MPa at −20° C. and a storage modulus of 10 MPa to 100 MPa at 85° C.
Implementation Method 2
a first adhesive layer stacked on a surface of the base layer; and a second adhesive layer stacked on another surface of the base layer
Data Source
AI summary
A multilayer adhesive sheet, an optical member including the same, and a display apparatus including the same are provided. A multilayer adhesive sheet includes: a base layer; a first adhesive layer stacked on a surface of the base layer; and a second adhesive layer stacked on another surface of the base layer, and the base layer includes a polyurethane-based film manufactured by solution casting and has a storage modulus of 700 MPa to 1,500 MPa at −20° C. and a storage modulus of 10 MPa to 100 MPa at 85° C.