Low Migration Inkjet Inks via Segmented Photoinitiators
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Solution Overview
Problem
Current inkjet inks for digital food packaging printing face challenges in achieving low viscosity, high curing speed, and low migrating properties, with polymeric photoinitiators increasing viscosity and residual monomers causing issues in polyolefin substrates.
Innovation Solution
A free radical radiation curable inkjet ink formulation using a combination of polymeric or polymerizable photoinitiators, thiol compounds with limited thiol groups, and vitrification control monomers with (meth)acrylate and ethylenically unsaturated functional groups, maintaining low viscosity and reducing extractables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polymeric photoinitiators are used to improve low migrating properties, then migration resistance is improved, but viscosity increases
Solution Approach 1:
The photoinitiator system is segmented into two distinct components: a polymeric photoinitiator (for low migration) and a small molecule photoinitiator (for low viscosity). This segmentation allows each component to fulfill its specific function without compromising the other, resolving the contradiction between migration resistance and viscosity.
Solution Approach 2:
The patent uses a composite photoinitiator system combining polymeric and small molecule photoinitiators. This composite approach leverages the advantages of both types: the polymeric component provides low migration properties while the small molecule component maintains low viscosity, achieving a balance that neither component could achieve alone.
2Productivity
If polyfunctional monomers are used to improve polymerization completeness, then curing speed is improved, but viscosity increases and extractables increase
Solution Approach 1:
The patent optimizes the functionality parameter of monomers by primarily using monofunctional and difunctional monomers instead of higher functionality monomers. This parameter change reduces crosslinking density and viscosity while maintaining adequate curing speed through optimized photoinitiator selection and concentration.
Solution Approach 2:
The patent applies different monomer functionalities at different locations in the polymerization network. Monofunctional monomers provide low viscosity and flexibility, while difunctional monomers provide crosslinking points for structural integrity. This local differentiation of monomer roles achieves both low viscosity and adequate curing performance.
3Shape
If monofunctional monomers are used to reduce viscosity, then viscosity is reduced, but polymerization completeness decreases due to longer reaction time
Solution Approach 1:
The patent uses a photoinitiator system that enables continuous and efficient polymerization. The combination of polymeric and small molecule photoinitiators ensures sustained radical generation throughout the curing process, allowing monofunctional monomers to react completely without requiring extended reaction times, thus maintaining both low viscosity and high polymerization completeness.
Solution Approach 2:
The small molecule photoinitiator acts as an intermediary that accelerates the polymerization of monofunctional monomers. By providing a high concentration of initiating radicals, it compensates for the lower reactivity of monofunctional monomers, enabling complete polymerization without increasing viscosity.
4Productivity
If high concentration of photoinitiators is used to improve curing speed, then curing speed is improved, but extractables increase
Solution Approach 1:
The photoinitiator system is segmented into polymeric and small molecule components with different concentrations. The polymeric photoinitiator is used at higher concentrations to provide sustained radical generation and fast curing, while the small molecule photoinitiator is used at lower concentrations to minimize extractables. This segmentation allows optimization of curing speed without excessive extractable formation.
Solution Approach 2:
The composite photoinitiator system combines the advantages of both polymeric and small molecule photoinitiators. The polymeric component provides fast curing at higher concentrations with low extractables, while the small molecule component supplements the initiation at lower concentrations. This composite approach achieves high curing speed while controlling extractable levels better than either component alone.
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 viscosity and minimal odor in cured layers, with reduced extractables and improved monomer conversion, enhancing printing reliability and image quality on various substrates.
Implementation Method 1
free radical radiation curable inkjet ink
Implementation Method 2
polymerizable photoinitiators
Data Source
AI summary
A free radical radiation curable inkjet ink having a viscosity smaller than 30 mPa.s at 40°C and at a shear rate of 1,000 s-1 including a polymeric or polymerizable photoinitiator; a thiol compound; and a vitrification control monomer, wherein the vitrification control monomer includes a (meth)acrylate group and an ethylenically unsaturated functional group selected from the group consisting of a vinyl ether group, an allyl ether group and an allyl ester group; and wherein the thiol compound includes no more than six thiol groups.