Polymerizable Norrish Type II Photoinitiators for Low Extraction
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Solution Overview
Problem
Norrish Type II photoinitiators used in radiation curable compositions for food packaging and other applications face challenges with high extractable residues, reduced curing speed, and increased viscosity due to their molecular weight and limited solubility, leading to health risks and inefficiencies in curing processes.
Innovation Solution
Development of polymerizable Norrish Type II photoinitiators with specific structural modifications, such as incorporating ethylenically unsaturated polymerizable groups, and the use of diffusion hindered co-initiators to minimize extractable residues and maintain low viscosity while enhancing curing speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Norrish Type II photoinitiators with higher molecular weight are used to minimize extraction, then extractable residues are reduced, but viscosity increases to an undesirable level
Solution Approach 1:
The patent modifies the molecular weight parameter of the Norrish Type II photoinitiator by using lower molecular weight compounds (e.g., benzophenone, thioxanthone derivatives) while compensating for extraction through optimized co-initiator selection and formulation chemistry, thereby maintaining acceptable viscosity levels for inkjet printing applications
Solution Approach 2:
The patent creates a composite photoinitiator system combining Norrish Type II initiators with specific co-initiators (amines, thiols) and polymerizable monomers, where the synergistic interaction between components achieves effective curing while controlling extractable residues and viscosity through the collective properties of the formulation rather than relying solely on high molecular weight initiators
2Object-affected harmful factors
If polymerizable Norrish Type II photoinitiators are used to reduce extractable residues, then mobility is reduced and curing speed decreases
Solution Approach 1:
The patent optimizes the polymerizable group parameters (e.g., using acrylate or vinyl groups with appropriate reactivity) and controls the degree of polymerization of the photoinitiator to maintain sufficient mobility and curing speed while still achieving reduced extractable residues through copolymerization
Solution Approach 2:
The patent applies different strategies to different components: the photoinitiator is partially polymerized to reduce extraction, while the co-initiator and monomer system are designed to maintain high reactivity and curing speed, creating local optimization throughout the formulation
3Productivity
If conventional Norrish Type II initiators are used, then curing can proceed, but extractable residues remain mobile and may be extracted into food causing health risks
Solution Approach 1:
The patent converts the potential harm of extractable residues by designing the photoinitiator system to copolymerize with the monomer mixture, transforming mobile, extractable low molecular weight compounds into part of the crosslinked polymer network, thereby eliminating the health risk while maintaining curing capability
Solution Approach 2:
The patent uses polymerizable monomers and co-initiators as intermediaries that facilitate the incorporation of the Norrish Type II photoinitiator into the polymer network, mediating between the need for effective curing and the requirement to minimize extractable residues
4Speed
If a mixture of polymerizable and non-polymerizable Type II-initiators is used to achieve sufficient curing speed, then extractable photoinitiator and residues increase
Solution Approach 1:
The patent changes the formulation parameters by using higher concentrations of polymerizable photoinitiators combined with optimized co-initiator ratios and monomer selection to achieve sufficient curing speed without relying on non-polymerizable initiators, thereby eliminating extractable photoinitiator residues
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 solution achieves low levels of extractable residues, improved curing speed, and suitable viscosity in radiation curable compositions, ensuring safety and efficiency in applications like food packaging and inkjet printing.
Implementation Method 1
A free radical photoinitiator initiates the polymerization of monomers when exposed to actinic radiation by the formation of a free radical
Implementation Method 2
A Norrish Type II-initiator is a photoinitiator which is activated by actinic radiation and forms free radicals by hydrogen abstraction from a second compound
Data Source
AI summary
A new type of polymerizable Norrish Type II photoinitiators having an optionally substituted benzophenone group or an optionally substituted thioxanthone group is disclosed exhibiting improved compatibility with and solubility in radiation curable compositions. Radiation curable compositions and inkjet inks containing these polymerizable Norrish Type II photoinitiators, exhibiting low extractable amounts of the photoinitiators and their residues after curing, are also disclosed.