UV-Curable Ink Multi-Exposure Curing Oxygen Inhibition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing UV-curable flexo and inkjet inks face challenges with oxygen inhibition during curing, leading to poor surface cure, especially with UV-LED light sources emitting in the 365-405 nm wavelength range, and current solutions like nitrogen inertion, multiple UV-LED lamps, and oxygen scavengers are inefficient or costly.
Innovation Solution
A UV-curable ink composition with ≤5% (w/w) photoinitiators and aminoacrylates, cured using a multi-exposure approach with total UV doses as low as 100 mJ/cm2, effectively overcoming oxygen inhibition and achieving superior surface cure without the need for nitrogen inertion or multiple UV-LED lamps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional UV-curable inks are cured with UV-LED light sources in air, then the curing process is simple and cost-effective, but oxygen inhibition occurs leading to poor surface cure
Solution Approach 1:
The patent applies parameter changes by modifying the photoinitiator concentration to ≤5% (w/w) and using specific photoinitiator types (Type II photoinitiators like amino ketones and thioxanthones) that work effectively at lower concentrations and are less susceptible to oxygen inhibition. This chemical parameter change enables effective curing in air without compromising surface quality
Solution Approach 2:
The patent uses composite material strategies by formulating ink compositions with specific monomer blends (acrylates, methacrylates, vinyl ethers) combined with low-concentration Type II photoinitiators. This composite formulation creates a synergistic system where the monomers provide reactivity and the specialized photoinitiators provide oxygen-resistant initiation, achieving both simplicity and reliability
2Reliability
If photoinitiator concentration is increased to overcome oxygen inhibition, then surface cure improves, but migration risk and cost increase
Solution Approach 1:
The patent fundamentally changes the photoinitiator concentration parameter to ≤5% (w/w), which is significantly lower than conventional formulations. This parameter change reduces migration risk while maintaining effective curing through the use of Type II photoinitiators that have higher quantum efficiency and are less affected by oxygen inhibition
Solution Approach 2:
The patent employs Type II photoinitiators (amino ketones, thioxanthones) that are generally less expensive than Type I photoinitiators and function effectively at lower concentrations. These photoinitiators generate free radicals through hydrogen abstraction and are consumed during the curing process, reducing residual migration risk
3Reliability
If nitrogen inertion is used to prevent oxygen inhibition, then surface cure quality improves, but equipment complexity and operating costs increase
Solution Approach 1:
The patent extracts and eliminates the need for nitrogen inertion systems by using photoinitiator formulations and curing conditions that are inherently resistant to oxygen inhibition. This removes the complex gas handling equipment, nitrogen storage systems, and associated safety infrastructure while maintaining surface cure quality
Solution Approach 2:
The patent enables the curing system to be self-sufficient by using Type II photoinitiators and optimized monomer formulations that naturally resist oxygen inhibition without requiring external inert gas protection. The ink composition itself provides the resistance to oxygen, making the system self-protecting
4Reliability
If UV-LED lamps with mixed wavelength arrays are used to overcome oxygen inhibition, then curing effectiveness improves, but energy consumption and equipment cost increase
Solution Approach 1:
The patent changes the wavelength parameter by using UV-LEDs with peak emission at 365-405 nm that match the absorption maxima of Type II photoinitiators. This targeted wavelength selection provides efficient curing with lower energy consumption compared to broad-spectrum mixed arrays, as the light energy is optimally matched to the photoinitiator activation requirements
Solution Approach 2:
The patent uses Type II photoinitiators that can be activated by a range of UV wavelengths (365-405 nm), providing universal compatibility with standard UV-LED technology. This multi-functional approach allows a single wavelength range to effectively initiate curing across different formulations without requiring complex multi-wavelength systems
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 multi-exposure process enables efficient curing at lower UV doses, reducing energy consumption, allowing for higher press speeds, and using lower power UV-LED lamps, while minimizing photoinitiator content for reduced migration risks in food packaging applications.
Implementation Method 1
A UV-curable ink composition comprising ≤20% (w/w) of any blend of monofunctional acrylate monomers, an acrylated amine and ≤5% (w/w) of any blend of photoinitiators
Data Source
AI summary
The invention describes the unique finding that UV-curable flexo (and single pass inkjet) ink compositions can be more effectively cured by curing the pigmented ink compositions through two or more exposures to UV rather than a single exposure, where the total UV dose supplied by the multi-exposure approach is the same or less than the dose supplied by the single exposure.