Alpha-hydroxyketone photoinitiators for UV-A curing
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Solution Overview
Problem
Alpha-hydroxyketone photoinitiators used in clear coatings with UV light of wavelengths less than 320 nm provide insufficient through-cure and surface cure when combined with light stabilizers or pigments, requiring additional photoinitiators like mono- or bisacylphosphine oxides for effective curing.
Innovation Solution
Development of new alpha-hydroxyketone compounds with a blue-shifted absorption spectrum, capable of efficient through and surface cure under UV-A light irradiation, offering improved performance without the need for additional photoinitiators like acylphosphine oxides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional alpha-hydroxyketone photoinitiators are used with UV light of wavelengths less than 320 nm, then surface cure is achieved, but through-cure is insufficient
Solution Approach 1:
The patent modifies the molecular structure of alpha-hydroxyketone photoinitiators by introducing specific substituents (Ar groups at positions 1 and 3, and R1 groups that can be OR7, O-X+, NR8R9, or C1-C20alkyl) to change the absorption spectrum from UV-B to UV-A range, enabling efficient through-cure while maintaining surface cure quality
Solution Approach 2:
The patent creates composite photoinitiator systems by combining the new alpha-hydroxyketone compounds with light stabilizers and pigments, achieving synergistic effects that improve both through-cure and surface cure while maintaining color stability during weathering
2Reliability
If additional photoinitiators like mono- or bisacylphosphine oxides are added to achieve through-cure, then curing performance improves, but yellowing increases
Solution Approach 1:
The patent changes the absorption spectrum parameter of photoinitiators by designing new alpha-hydroxyketone compounds with blue-shifted absorption in the UV-A range, eliminating the need for red-shifted acylphosphine oxide photoinitiators that cause yellowing, thus achieving through-cure without increased yellowing
Solution Approach 2:
The patent replaces expensive and problematic acylphosphine oxide photoinitiators with the newly developed alpha-hydroxyketone compounds that provide equivalent or superior performance without the harmful yellowing side effect
3Reliability
If photoinitiators with red-shifted absorption are used to improve through-cure, then curing depth increases, but color stability during weathering deteriorates
Solution Approach 1:
The patent changes the absorption spectrum from red-shifted to blue-shifted in the UV-A range by modifying the photoinitiator molecular structure, achieving both improved through-cure efficiency and enhanced color stability during long-term weathering
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 new alpha-hydroxyketone photoinitiators provide both excellent surface and through-cure under UV-A irradiation, reducing yellowing and maintaining color stability during long-term weathering, outperforming previous combinations by achieving better cure results with less red-shifted absorption.
Implementation Method 1
The compounds of the formula I are photoinitiators for the photopolymerization of radically poymerizable components
Implementation Method 2
a new type of α-hydroxyketones, although possessing an absorption that is blue-shifted compared to acylphosphine oxides or other UV-A photoinitiators, is very reactive upon irradiation with UV-A light
Data Source
AI summary
Compounds of the Formula (I) wherein x is an integer from 1-4; p is an integer from 1-3; q is an integer from 0-3; Ar is phenyl, naphthyl, anthryl or phenanthryl each of which optionally is substituted by one or more Cl, CN, OR5, C3-C5alkenyl or C1-C6alkyl which optionally is substituted by one or more OR6, COOR or halogen; R1 if x is 1, is OR7, O—X+, NR8R9, C1-C20alkyl optionally substituted by one or more COOR10, or is C2-C20alkyl interrupted by one ore more O, or is C2-C5alkenyl or phenyl-C1-C4alkyl; R1 if x is 2, is for example C1-C20alkylene; R1 if x is 3, is for example a tri-valent radical; R1 if x is 4, is for example a tetravalent radical; R2 and R3 are hydrogen or C1-C8alkyl, or R2 and R3 together are O, C1-C3alkylene or CH═CH; R4 is C1-C4alkyl; R5, R6, R7, R8, R9 and R10 are for example hydrogen or C1-C4alkyl; and X is a x-valent cationic counter ion; are in particular suitable as photoinitiators for the curing with UV-A light (320-450 nm).