Polymerizable Thioxanthone Photoinitiators for Low Odor UV Curing
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Solution Overview
Problem
Current UV curable systems for coatings and adhesives face issues with toxic by-products and odor, particularly with α-cleavage type photoinitiators, and polymerizable Type II systems suffer from photoefficiency drawbacks, necessitating improved H-abstraction photoinitiators for low odor and reduced extractable by-products.
Innovation Solution
Development of novel polymerizable thioxanthone photoinitiators that are curable by UV radiation from LED light sources, offering good photochemical activity, low oxygen sensitivity, and are halogen-free, with advantages including low yellowing, good solubility, and reduced by-product formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If α-cleavage type photoinitiators are used for UV curing, then rapid and effective curing is achieved, but toxic by-products and odor are generated
Solution Approach 1:
The patent extracts the harmful α-cleavage photoinitiator system and replaces it with a Type II H-abstraction photoinitiator system that does not produce toxic by-products. The novel polymerizable thioxanthone photoinitiator is designed to work with a co-initiator to generate radicals through H-abstraction rather than α-cleavage, eliminating benzaldehyde and other odorous extractables while maintaining curing effectiveness.
Solution Approach 2:
The patent changes the photoinitiation mechanism parameter from α-cleavage to H-abstraction. By developing polymerizable thioxanthone derivatives that function as Type II photoinitiators, the system transitions from a mechanism producing toxic fragments to one that generates radicals through hydrogen abstraction, fundamentally altering the chemical pathway to eliminate harmful by-products.
2Object-generated harmful factors
If polymerizable Type II photoinitiators are used to reduce by-products, then extractable components are reduced, but photoefficiency is compromised
Solution Approach 1:
The patent optimizes the molecular structure of thioxanthone derivatives by introducing specific substituents and polymerizable groups. This structural modification changes the photophysical parameters to enhance photoefficiency while maintaining the Type II H-abstraction mechanism. The novel structures achieve both low extractable by-products and high curing efficiency.
Solution Approach 2:
The patent creates a composite photoinitiation system combining polymerizable thioxanthone photoinitiator with a co-initiator. This composite approach allows the photoinitiator to be incorporated into the polymer matrix while maintaining effective radical generation through H-abstraction, achieving both reduced extractables and high photoefficiency.
3Productivity
If conventional photoinitiators are used, then curing is achieved, but yellowing occurs and mechanical properties are reduced
Solution Approach 1:
The patent modifies the chemical structure of thioxanthone derivatives by introducing specific substituents that alter the photostability and optical properties. These structural changes reduce yellowing while maintaining the H-abstraction mechanism for effective curing. The novel polymerizable structures provide both curing effectiveness and color 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 polymerizable thioxanthone photoinitiators provide effective curing with low odor and reduced extractable by-products, suitable for sensitive applications like food packaging and medical devices, with improved mechanical properties and reduced yellowing.
Implementation Method 1
The photoinitiator forms radical species upon irradiation with photons and initiates free-radical polymerisation of unsaturated groups
Implementation Method 2
curable by UV radiation from light emitting diode (LED) light sources due to their absorption band in the range of 365-420 nm
Implementation Method 3
The use of polymerizable or polymeric H-abstraction type photoinitiators, in principle, presents the possibility of creating a system with zero extractable components related to the photoinitiation system
Data Source
AI summary
The invention relates to a polymerizable photoinitiator, to a process for preparing a polymerizable photoinitiator, to a polymerizable composition comprising a polymerizable photoinitiator and an ethylenically unsaturated compound. The invention also relates to different uses of the polymerizable photoinitiator or polymerizable composition.