Photopolymerizable Composition for Bonding and Sealing
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Solution Overview
Problem
Traditional redox-initiated and light-cured photopolymerization systems face challenges in controlling reactivity, especially in rapid curing processes, which can lead to difficulties in manufacturing, particularly when dealing with opaque substrates and requiring high monomer conversion or rapid assembly.
Innovation Solution
The development of photopolymerizable compositions that include a free-radically polymerizable compound, an organic photoactivatable reducing agent precursor, a reducible transition metal compound, and an organic peroxide, with a photoinitiator that does not contain an organic peroxide, allowing for controlled curing through an external stimulus, reducing oxygen inhibition, and improving cohesive and static shear strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If redox free-radical polymerization is used for rapid curing, then polymerization speed is improved, but reactivity control becomes difficult
Solution Approach 1:
The system is divided into separate components: a photopolymerizable composition containing photoinitiator and monomer, and a separate redox initiator system. This segmentation allows independent control of each component, enabling rapid curing when needed while maintaining stability during storage and transport.
Solution Approach 2:
The photoinitiator is prepared in advance within the photopolymerizable composition, ready to initiate polymerization upon light exposure. This preliminary preparation enables rapid response when curing is required, while the actual polymerization reaction is delayed until light activation occurs.
2Ease of operation
If light curing is used for precise control, then reactivity control is improved, but polymerization cannot occur in areas inaccessible to actinic radiation
Solution Approach 1:
The system merges photopolymerization (light-initiated) and redox polymerization (chemical-initiated) mechanisms into a single composition. The photoinitiator provides controlled initiation where light reaches, while the redox initiator system provides alternative initiation pathways in areas where light penetration is limited, combining the advantages of both methods.
Solution Approach 2:
The redox initiator system acts as an intermediary mechanism that can initiate polymerization through chemical reaction rather than direct light absorption. This intermediary pathway enables polymerization in regions where actinic radiation cannot directly reach, expanding the effective application scope.
3Ease of operation
If low viscosity adhesive fluids are used for dispensing, then dispensing performance is improved, but oxygen inhibition increases due to rapid oxygen diffusion
Solution Approach 1:
The photoinitiator initiates polymerization immediately upon light exposure, creating a preliminary cured layer at the surface. This preliminary action occurs before oxygen diffusion can significantly inhibit the reaction, as the initial polymerization increases viscosity and reduces oxygen permeability, thereby mitigating oxygen inhibition effects.
Solution Approach 2:
The rapid photopolymerization reaction rushes through the initial stages of curing before oxygen diffusion can fully inhibit the process. By completing the critical initial polymerization step quickly, the system skips through the vulnerable period where oxygen inhibition would be most problematic.
4Productivity
If rapid curing is used for manufacturing efficiency, then productivity is improved, but cohesive strength and static shear strength may be compromised
Solution Approach 1:
The system provides continuous polymerization action through multiple mechanisms: photoinitiator continues to generate radicals under sustained light exposure, and the redox initiator system provides ongoing chemical initiation. This continuity ensures that polymerization proceeds thoroughly over time, achieving both rapid initial curing for productivity and complete conversion for maximum strength.
Solution Approach 2:
The composition uses a composite initiator system combining photoinitiator and redox initiator components, each contributing different polymerization pathways. This composite approach ensures that both rapid curing (from photoinitiator) and complete polymerization (from redox system) occur, achieving both productivity and strength 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 enhances manufacturing flexibility, particularly for low viscosity adhesive fluids, by allowing for tunable curing times and improved adhesive properties, such as cohesive strength and reduced oxygen sensitivity, making it suitable for applications like piezo inkjet dispensing and valve jet dispensing.
Implementation Method 1
Free-radically photopolymerizable systems can provide precise control of polymerization by the application of actinic radiation (e.g., ultraviolet light)
Implementation Method 2
at least one photoinitiator, wherein the at least one photoinitiator does not comprise an organic peroxide
Implementation Method 3
redox free-radical polymerization is a prominent and industrially relevant chemical technique for rapidly generating polymers at ambient conditions. Redox radical polymerization systems generally include a free-radically polymerizable compound, an oxidizing agent, and a reducing agent. The oxidizing and reducing agents are selected to react with one another to generate free-radical species
Data Source
AI summary
A photopolymerizable composition comprises at least one free-radically polymerizable compound; at least one organic photoactivatable reducing agent precursor; at least one reducible transition metal compound comprising at least one of cobalt, copper, iron, manganese, nickel, or vanadium; at least one organic peroxide; and at least one photoinitiator. The at least one photoinitiator does not comprise an organic peroxide. Methods of bonding and sealing, and an at least partially polymerized composition are also disclosed.