Coumarin Thioester Photoinitiators for Air-Cured Coatings
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Solution Overview
Problem
Current photoinitiators for curing ethylenically unsaturated compounds under LED light suffer from oxygen inhibition, requiring inert atmospheres and lacking stability under thermal and chemical stress.
Innovation Solution
A process involving the use of coumarin thioester photoinitiators, specifically activable under 250 to 550 nm light, which are mixed with ethylenically unsaturated compounds and irradiated under air, overcoming oxygen inhibition and providing thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If common radical photoinitiators (e.g., TPO) are used for curing under LED light, then curing at longer wavelengths is achieved, but oxygen inhibition occurs leading to tacky coatings and excessive yellowing
Solution Approach 1:
The patent changes the chemical structure of the photoinitiator from conventional radical types to cyclic sulfonate esters with specific molecular configurations that alter the polymerization mechanism. This structural parameter change enables the photoinitiator to cure ethylenically unsaturated compounds without oxygen inhibition while maintaining LED wavelength compatibility (365-405 nm), thereby resolving the contradiction between achieving longer wavelength curing and avoiding oxygen inhibition effects
Solution Approach 2:
The patent employs a composite photoinitiator system using cyclic sulfonate ester compounds that combine specific functional groups (sulfonate ester moiety with cyclic structure) to create a material that simultaneously achieves LED activability and oxygen resistance. The composite molecular structure integrates light-absorbing capabilities with polymerization-initiating functionality that is inherently resistant to oxygen interference
2Temperature
If Type II photoinitiators (e.g., ketocoumarin Esacure 3644) are used for LED curing, then curing under LED wavelengths is achieved, but additional amine components are required for hydrogen abstraction
Solution Approach 1:
The patent extracts and eliminates the need for additional amine components by using cyclic sulfonate ester photoinitiators that can directly initiate polymerization without hydrogen abstraction. This removes the mandatory co-initiator requirement of Type II photoinitiators, simplifying the formulation while maintaining LED wavelength curing capability
Solution Approach 2:
The cyclic sulfonate ester photoinitiator serves multiple functions simultaneously: it absorbs LED wavelengths for activation, directly initiates polymerization without needing separate co-initiators, and provides oxygen resistance. This multi-functionality eliminates the need for additional amine components required by Type II photoinitiators, resolving the contradiction between LED curing capability and formulation simplicity
3Object-affected harmful factors
If photoinitiators are used that can cure under air, then oxygen inhibition is avoided, but thermal and chemical stability under stress conditions is reduced
Solution Approach 1:
The patent changes the chemical parameters of the photoinitiator to cyclic sulfonate ester structures that inherently provide both oxygen resistance and enhanced thermal stability. The specific molecular configuration (cyclic structure with sulfonate ester group) creates a compound that maintains composition stability under thermal and chemical stress while enabling curing under air conditions, thereby resolving the contradiction between oxygen resistance and thermal stability
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 described process enables efficient curing of ethylenically unsaturated compounds under LED light in air, avoiding oxygen inhibition and achieving high thermal stability, thus improving surface cure and reducing coloration and volatility of the finished product.
Implementation Method 1
The present invention relates to a process for curing under air one or more ethylenically unsaturated compounds with a coumarin thioester photoinitiator, preferably a photoinitiator activable under 250 to 550 nm, in particular 250 to 460 nm, light irradiation
Data Source
Figure 1
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Figure 3A~3B
AI summary
The present invention relates to a process for curing under air one or more ethylenically unsaturated compounds with a coumarin thioester photoinitiator, preferably a photoinitiator activable under 250 to 550 nm, in particular 250 to 460 nm, light irradiation.