UV-LED Coating Composition for Surface Cure Without Yellowing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
UV-LED curing technologies face issues with oxygen inhibition and yellowing due to the use of thioxanthones and amines in photoinitiator systems, which are problematic for clear or white coating formulations.
Innovation Solution
Incorporating a UV-LED curable coating composition with a thioxanthone and amine type II photoinitiator system, along with a colorant and optical brightener, to minimize yellowing and ensure thorough surface cure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thioxanthone and amine type II photoinitiator system is used for UV-LED curing, then surface cure is improved, but yellowing occurs in clear or white coating formulations
Solution Approach 1:
The patent removes the harmful thioxanthone and amine photoinitiators from the coating formulation, extracting the yellowing-causing components while maintaining curing functionality through alternative photoinitiator systems that do not produce yellowing effects
Solution Approach 2:
The patent changes the photoinitiator system parameters by selecting alternative photoinitiators with different chemical structures and absorption characteristics that are compatible with UV-LED wavelengths but do not cause yellowing, thereby resolving the contradiction between cure effectiveness and color stability
2Reliability
If oxygen scavengers or reducing agents are used to counteract oxygen inhibition, then surface drying is improved, but storage stability of the coating composition deteriorates
Solution Approach 1:
The patent employs oxygen scavengers that are consumed during the curing process to counteract oxygen inhibition at the surface, accepting their degradation as a necessary temporary measure that provides surface drying functionality without long-term stability issues since they are depleted during curing
Solution Approach 2:
The patent optimizes the concentration and type of oxygen scavengers to achieve sufficient surface drying while minimizing their impact on storage stability, using carefully controlled amounts that are effective during curing but do not excessively compromise shelf life
3Object-affected harmful factors
If UV-LED dryers emit at 365-405 nm to reduce oxygen inhibition, then surface cure is improved, but lower wavelengths that are favorable for surface cure are missing
Solution Approach 1:
The patent selects photoinitiators with broad absorption spectra that can utilize the 365-405 nm UV-LED emission range effectively, allowing a single photoinitiator system to provide both surface cure and bulk cure functionality without requiring multiple wavelength sources
Solution Approach 2:
The patent changes the photoinitiator selection to compounds with absorption maxima and broad absorption bands that overlap with the UV-LED emission spectrum, optimizing the utilization of available wavelengths to achieve effective curing despite the absence of lower wavelengths
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 composition achieves minimal to no yellowing and complete cure, suitable for overprint varnishes and protective coatings, while being cost-effective and using less expensive type I phosphine oxide photoinitiators.
Implementation Method 1
UV-LED light curable coating compositions... that are curable by exposure to ultraviolet light emitted by light emitting diode (LED) sources
Implementation Method 2
along with a colorant and optical brightener, to minimize yellowing
Data Source
Figure 1
AI summary
The present invention relates to UV-LED light curable coating compositions comprising a compound having at least one alpha, beta-ethylenically unsaturated polymerizable double bond, a type II photoinitiator system based on a thioxanthone and an amine, and a colorant. Optional inclusions are a type I photoinitiator and an optical brightener. The UV-LED curable composition provides good surface cure and low yellowing.