Crosslinkable Adhesive Composition for UV-Blocking OCA Films
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Solution Overview
Problem
Optically clear adhesives (OCAs) in electronic devices face challenges in balancing mechanical robustness with UV-blocking functionality, as UV-absorbing additives can interfere with photopolymerization and post-curing processes, limiting the adhesive's ability to adjust to complex geometries and ensure long-term mechanical performance.
Innovation Solution
A crosslinkable composition comprising a (meth)acrylate polymer with alkyl (meth)acrylate monomers, acylphosphine oxide photoinitiators, and crosslinking monomers with allyl or methallyl terminal groups, allowing for a two-step curing process that separates polymerization and crosslinking functions, enabling efficient UV-absorbing and post-lamination curing without requiring multiple wavelength emission equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If UV-absorbing additives are incorporated into OCA to block UV light, then UV-blocking functionality is improved, but photopolymerization and post-curing processes are interfered with
Solution Approach 1:
The patent segments the curing process into two distinct stages: initial photopolymerization using a first wavelength (e.g., 385nm) that penetrates the UV-absorbing additives, and subsequent post-curing using a second wavelength (e.g., 254nm) that is absorbed by the photoinitiator. This segmentation allows UV-blocking functionality to be maintained while ensuring both curing stages can proceed effectively despite the presence of UV-absorbing additives.
Solution Approach 2:
The patent changes the wavelength parameter of the curing light source between two different stages. The first curing stage uses a first wavelength range that allows penetration through UV-absorbing additives, while the second curing stage uses a second wavelength range that is effectively absorbed by the photoinitiator. This parameter change enables the system to overcome the interference caused by UV-absorbing additives during different phases of the curing process.
2Device complexity
If a single-wavelength UV source is used for curing, then device complexity is reduced, but the ability to achieve both polymerization and crosslinking is limited
Solution Approach 1:
The patent segments the curing process into two distinct stages with different wavelength requirements. The first stage uses a first wavelength (e.g., 385nm) for polymerization, and the second stage uses a second wavelength (e.g., 254nm) for crosslinking. This segmentation allows each stage to be optimized for its specific chemical process while using relatively simple, commercially available UV LED sources for each wavelength.
Solution Approach 2:
The patent performs preliminary polymerization first using the first wavelength to form the base polymer network, then subsequently performs crosslinking using the second wavelength. This preliminary action sequence ensures that the adhesive achieves adequate initial strength and flow characteristics before the crosslinking stage enhances mechanical properties, allowing each curing stage to build upon the previous one.
3Strength
If the OCA is made highly crosslinked for mechanical robustness, then adhesive strength is improved, but compliance and ability to adjust to complex geometries deteriorates
Solution Approach 1:
The patent performs preliminary polymerization first using the first wavelength to form the base polymer network while the adhesive is still in its uncrosslinked, more compliant state. This allows the adhesive to flow and conform to complex geometries during initial bonding. Subsequently, crosslinking is performed using the second wavelength to enhance mechanical strength and provide long-term durability, achieving both compliance during application and strength during service.
Solution Approach 2:
The patent creates a dynamic curing process where the crosslinking density of the adhesive evolves over time. Initially, the adhesive has low crosslinking density, providing high compliance and ability to conform to substrates. As the two-stage curing process progresses, crosslinking density increases, transitioning the material from a compliant state during application to a rigid, high-strength state during service, thus adapting the material properties to different operational requirements.
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
This approach allows for the development of UV-absorbing and post-lamination curable OCA films that maintain compliance and mechanical stability, ensuring high performance and reliability throughout the device's lifespan while incorporating UV-blocking functionality.
Implementation Method 1
an acylphosphine oxide photoinitiator
Implementation Method 2
a crosslinking monomer, the crosslinking monomer comprising at least two terminal groups selected from the group consisting of allyl, methallyl, or combinations thereof
Data Source
AI summary
Crosslinkable compositions including a (meth)acrylate polymer comprising an alkyl (meth)acrylate monomer; an acylphosphine oxide photoinitiator; and a crosslinking monomer, the crosslinking monomer comprising at least two terminal groups selected from the group consisting of allyl, methallyl, or combinations thereof. Methods of preparing such crosslinkable compositions and articles including such crosslinkable compositions are disclosed.