Inkjet Ink with Polymeric Thioxanthone for UV LED Cure
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Solution Overview
Problem
Existing inkjet inks for food packaging face challenges with high UV LED cure speed and good surface cure while maintaining low viscosity, particularly when using LED UV light sources, due to issues like poor surface cure from oxygen presence and narrow spectral output.
Innovation Solution
Incorporation of a specific blend of polymeric thioxanthone photoinitiators and TPO-L in the ink, with amounts of 4% by weight or more and 10% by weight or more, respectively, to enhance UV LED cure speed and surface cure while keeping viscosity low.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If UV LED light sources are used to cure inkjet inks, then energy efficiency and cost are improved, but surface cure quality deteriorates due to narrow spectral output and oxygen presence
Solution Approach 1:
The patent modifies the chemical composition parameters of the ink by incorporating specific photoinitiators (polymeric thioxanthone and TPO-L) in optimized concentrations. This changes the ink's responsiveness to UV LED radiation, enabling effective curing at the narrow wavelength range emitted by LEDs while maintaining surface cure quality despite oxygen presence.
Solution Approach 2:
The patent uses a composite photoinitiator system combining two different types (polymeric thioxanthone and TPO-L) with complementary absorption characteristics. This composite approach allows the ink to absorb the narrow spectral output of UV LEDs more effectively across the required wavelength range, resolving the surface cure issue while maintaining LED energy efficiency advantages.
2Reliability
If photoinitiator concentration is increased to improve surface cure, then surface cure quality is improved, but viscosity increases
Solution Approach 1:
The patent optimizes the concentration parameters of photoinitiators to achieve effective surface cure with minimal impact on viscosity. By carefully selecting the amounts of polymeric thioxanthone and TPO-L, the formulation achieves high surface cure quality while maintaining low viscosity suitable for inkjet printing applications.
Solution Approach 2:
The patent uses low molecular weight photoinitiator molecules that provide high curing efficiency at low concentrations. These small molecules contribute minimally to the overall viscosity of the ink while delivering effective surface cure, essentially providing maximum benefit with minimum compositional impact.
3Productivity
If cure speed is increased for single pass printing, then productivity is improved, but the dose per unit area required decreases which may compromise cure quality
Solution Approach 1:
The patent modifies the photoinitiator system parameters to enhance the ink's curing efficiency. The specific combination and concentration of polymeric thioxanthone and TPO-L photoinitiators enable rapid polymerization response to UV LED irradiation, achieving high cure speeds for single pass printing while maintaining complete cure quality through optimized photoinitiator effectiveness.
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 ink achieves high UV LED cure speed and good surface cure with low viscosity, suitable for food packaging applications, reducing migration and odour issues, and maintaining ink stability.
Implementation Method 1
Another type of inkjet ink contains unsaturated organic compounds, termed monomers and/or oligomers, which polymerise when cured. This type of ink has the advantage that it is not necessary to evaporate the liquid phase to dry the print; instead the print is cured
Implementation Method 2
LEDs offer significant cost reduction, longer maintenance intervals, higher energy efficiency and are an environmentally friendlier solution
Data Source
AI summary
The present invention provides an inkjet ink comprising: a radiation-curable material; 4% by weight or more in total of one or more polymeric thioxanthone photoinitiators; and 10% by weight or more of wherein the amounts are based on the total weight of the ink. The present invention also provides a method of inkjet printing comprising inkjet printing the inkjet ink of the present invention onto a substrate and curing the inkjet ink by exposing the inkjet ink to a curing source.