UV LED Inkjet Inks with Controlled Double Bond Density
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Solution Overview
Problem
UV LED free radical curable inkjet inks face challenges in achieving good scratch resistance and adhesion while minimizing polymerization shrinkage and odor, and ensuring high printing reliability, particularly due to issues with polyfunctional monomers and cationic curable inks causing nozzle clogging in industrial printing systems.
Innovation Solution
A UV LED free radical curable inkjet ink formulation containing organic color pigments, acylphosphine oxide photoinitiators, monofunctional polymerizable compounds, and specific polyfunctional compounds, with a double bond density between 5.28 and 5.78 mmol/g, and a high content of vinyl methyl oxazolidinone, which balances scratch resistance, adhesion, and odor reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a large amount of polyfunctional monomers is used to achieve good scratch resistance, then scratch resistance is improved, but adhesion deteriorates due to high polymerization shrinkage
Solution Approach 1:
The patent applies parameter changes by carefully controlling the double bond density within a specific range (5.28-5.78 mmol/g) and adjusting the ratio of monofunctional to polyfunctional monomers. This optimization allows achieving good scratch resistance with reduced polymerization shrinkage, thereby maintaining adhesion. The specific parameter control resolves the contradiction by finding an optimal balance point rather than using extreme values.
Solution Approach 2:
The patent uses a composite monomer system combining monofunctional monomers (84-98 wt%) with specific polyfunctional monomers (2-16 wt%). This composite approach leverages the low shrinkage advantage of monofunctional monomers while incorporating enough polyfunctional monomers to provide crosslinking for scratch resistance, thus resolving the adhesion-strength contradiction through material composition design.
2Loss of substance
If cationic curable ink is used to achieve low shrinkage, then polymerization shrinkage is reduced, but printing reliability deteriorates due to nozzle clogging from UV stray light curing
Solution Approach 1:
The patent extracts the harmful effect of premature curing by using free radical polymerization instead of cationic polymerization. Free radical species have much shorter lifetimes and are less sensitive to UV stray light, preventing nozzle clogging. This extraction of the problematic curing mechanism resolves the contradiction between low shrinkage and printing reliability.
Solution Approach 2:
The patent employs short-living free radical species that quickly complete polymerization without lingering activity. These short-living radicals cure the ink efficiently upon UV exposure but do not continue to react from stray light, unlike long-living cationic species. This use of short-living polymerizing agents resolves the nozzle clogging issue while maintaining low shrinkage.
3Strength
If polyfunctional monomers are used to achieve good scratch resistance, then scratch resistance is improved, but odor increases
Solution Approach 1:
The patent reduces odor by controlling the double bond density within 5.28-5.78 mmol/g and limiting polyfunctional monomer content to 2-16 wt%. This parameter optimization minimizes the formation of odorous byproducts during polymerization while still achieving adequate crosslinking for scratch resistance, thus resolving the strength-odor contradiction.
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 formulation provides excellent scratch resistance, adhesion, and low odor, while minimizing stickiness and polymerization shrinkage, ensuring high printing reliability and efficient surface curing, even in industrial settings.
Implementation Method 1
UV LED free radical curable inkjet inks that combine good scratch resistance and good adhesion, while exhibiting good surface curing
Data Source
AI summary
A UV LED free radical curable inkjet ink containing an organic colour pigment; an acylphosphine oxide photoinitiator; monofunctional polymerizable compounds including vinyl methyl oxazolidinone; and one or more polyfunctional polymerizable compounds; wherein: the double bond density DD is between 5.28 and 5.78 mmol double bonds/g; the content of monofunctional polymerizable compounds is between 84 and 98 wt % based on the total weight of the polymerizable composition; and the content of vinyl methyl oxazolidinone is at least 13.3 wt % based on the total weight of the polymerizable composition.