Two-Stage UV Curing for Flexible Display Adhesive
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Solution Overview
Problem
Existing methods for manufacturing adhesive members for flexible display devices face challenges in achieving the right balance of curing rate, loss tangent, and peel strength, which affects the reliability and folding capabilities of the display devices.
Innovation Solution
A method involving the application of a resin composition with a viscosity of 5 cP to 50 cP, exposed to a first light to form a preliminary adhesive member with a curing rate of 80% to 98%, and then exposed to a second light with a higher light integral to form an adhesive member with specific properties, including a glass transition temperature of -70°C to -30°C and a 180-degree peel strength of 800 gf/25 mm or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the resin composition is exposed to a first light to form a preliminary adhesive member with a curing rate of 80% to 98%, then the adhesive member achieves good initial adhesion and flexibility, but the curing is incomplete and requires additional light exposure to achieve full adhesive strength
Solution Approach 1:
The patent applies preliminary action by exposing the resin composition to a first light to form a preliminary adhesive member with 80-98% curing rate before final assembly. This preliminary curing provides sufficient adhesion for handling and assembly operations, while leaving the adhesive in a state that can be fully cured later to achieve maximum strength.
Solution Approach 2:
The curing process is segmented into two distinct stages: first light exposure (200-1000 mJ/cm²) to achieve preliminary curing for assembly, and second light exposure (3500-4500 mJ/cm²) through the protective member to complete the curing for final strength. This segmentation allows the adhesive to serve different functional requirements at different times.
2Ease of manufacture
If the resin composition has low viscosity (5 cP to 50 cP) for easy application, then the resin can be easily applied and forms uniform thin layers, but the resin may spread too much and lose positioning precision
Solution Approach 1:
The patent carefully controls the viscosity parameter of the resin composition within the range of 5-50 cP at 25°C. This parameter optimization ensures the resin is fluid enough for easy application and uniform coating formation, yet viscous enough to maintain pattern positioning accuracy and prevent excessive spreading during the application process.
3Reliability
If the adhesive member has high peel strength (800 gf/25 mm or more) for strong bonding, then the display device achieves excellent adhesive reliability, but the adhesive becomes too rigid and reduces folding capability
Solution Approach 1:
The patent optimizes the glass transition temperature parameter of the adhesive member to be between -70°C and -30°C. This parameter change ensures the adhesive maintains a rubbery, flexible state at operating temperatures, providing both high peel strength (800 gf/25 mm or more) for reliable bonding and sufficient flexibility to accommodate folding and bending of the display device.
Solution Approach 2:
The resin composition uses a composite formulation including (meth)acrylate monomers with specific molecular weights (100-500), urethane (meth)acrylate oligomers (10,000-40,000), and photoinitiators. This composite material design achieves the dual requirement of high adhesive strength and flexibility by combining different molecular components with complementary properties.
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 method achieves an adhesive member with excellent adhesive reliability and folding reliability, ensuring the display device maintains its structural integrity and functionality even when folded or bent.
Implementation Method 1
The resin composition may include at least one (meth)acrylate monomer containing a (meth)acryloyl group, at least one urethane (meth)acrylate oligomer, and at least one photoinitiator. The resin composition is exposed to a first light to form a preliminary adhesive member
Data Source
AI summary
A method of manufacturing an adhesive member includes providing, for a substrate, a resin composition having a viscosity of about 5 cP to about 50 cP, as measured according to JISK2283 method, at about 25° C. The resin composition is exposed to a first light to form a preliminary adhesive member having a curing rate of about 80% to about 98%. The preliminary adhesive member is exposed to a second light having a light integral/dose that is more than that of the first light to form an adhesive member. The preliminary adhesive member may have a loss tangent (tan δ) of about 0.2 to about 0.6 and may have a glass transition temperature of about −70° C. to −30° C. Accordingly, the preliminary adhesive member and adhesive member formed by the method of manufacturing an adhesive member may exhibit increased reliability.