Flexographic Ink Gel Formation for Wet-on-Wet Printing
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Solution Overview
Problem
Flexographic printing faces challenges with high Volatile Organic Compounds (VOC) emissions and low color strength due to high solvent content in inks, which limits the ability to achieve high pigment load and color density, and requires intermediate drying that is not always effective, leading to incomplete ink drying and tack issues.
Innovation Solution
A flexographic printing process utilizing controlled gel formation based on the precipitation of polymers or their segments in ink formulations, achieved by adjusting the Hansen Solubility Parameter, allowing for wet-on-wet printing with reduced VOC emissions and energy use, and a single final curing step using UV or EB radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional solvent-based inks are used to achieve adequate color strength, then pigment load can be increased, but VOC emissions increase and intermediate drying is required which complicates the process
Solution Approach 1:
The invention changes the chemical parameters of the ink system by using UV-curable monomers and oligomers instead of traditional volatile solvents. The ink formulation includes specific ratios of monomers (30-70 wt%), oligomers (20-50 wt%), and photoinitiators (1-5 wt%), creating a non-VOC based system that cures through photopolymerization rather than evaporation, thereby eliminating VOC emissions while maintaining color strength through high pigment loading
Solution Approach 2:
The invention utilizes the phase transition from liquid monomer/oligomer mixture to solid polymer network through photopolymerization. The ink starts as a fluid suitable for printing, then undergoes phase change upon UV exposure where monomers and oligomers polymerize to form a cured film, replacing the traditional evaporation-based drying process and enabling wet-on-wet printing without intermediate drying
2Manufacturing precision
If high anilox screening (1200-1600 lines per inch) is used to achieve 200 lines per inch printing quality, then screening resolution improves, but the volume of ink transported decreases making it difficult to achieve required color densities
Solution Approach 1:
The invention creates a composite ink system combining low-viscosity monomers, higher-viscosity oligomers, and pigments in specific proportions. This composite formulation provides both the fluidity needed for high anilox screening transfer and the pigment concentration required for color density, with oligomers serving as thickening agents that maintain color strength while monomers ensure adequate flow and transfer to the substrate
Solution Approach 2:
The invention changes the viscosity parameter of the ink system by selecting monomers with low viscosity and oligomers with controlled higher viscosity. This parameter adjustment allows the ink to be transferred effectively to high-line anilox rolls while maintaining sufficient pigment load, as the low-viscosity monomers facilitate flow and transfer even when oligomers provide the necessary color strength and thickness
3Ease of operation
If intermediate drying is used in traditional flexographic printing, then ink layers can be overprinted, but the process time increases and complete drying is not always achieved leading to tack issues
Solution Approach 1:
The invention replaces the thermal/mechanical drying system with a photochemical curing system. Instead of using heat or air circulation to evaporate solvents, the ink is cured through photopolymerization when exposed to UV radiation. This substitution eliminates the need for intermediate drying time, allows immediate wet-on-wet overprinting, and completely cures the ink in a single final step, removing tack issues entirely
Solution Approach 2:
The ink formulation is designed with monomers and oligomers that are pre-configured to polymerize rapidly upon UV exposure. The photoinitiators are selected to activate quickly, and the monomer/oligomer composition ensures fast curing kinetics, allowing the ink to be printed in wet state and then immediately cured without intermediate drying time, enabling continuous wet-on-wet printing processes
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 process results in inks with high color strength, reduced VOC content, and improved adhesion to substrates, enabling efficient wet-on-wet printing with enhanced color trapping capabilities and compliance with environmental regulations.
Implementation Method 1
controlled gel formation based on precipitation of a polymer or segments thereof in ink formulations
Implementation Method 2
this causing formation of a gel with suitable mechanical strength
Implementation Method 3
single final curing step by UV or EB radiation
Implementation Method 4
single final curing step by UV or EB radiation
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention refers to a flexographic printing process with wet on wet capability based on controlled polymer or polymer segment precipitation that leads to gel formation of ink compounds by controlling the solubility parameter of the ink system. The mechanism to obtain a desirable wet on wet color trapping is the formation and/or presence of a gel in the applied ink film due to a controlled physicochemical mechanism of resin precipitation. This is accomplished either by controlling a change in the Hansen Solubility Parameter of the liquid in the ink through evaporation of some or all of a non-reactive and volatile solvent, or alternatively by use of a polymer comprised of two distinct and separate segments one of which is soluble in the monomer/oligomer mix and the other of which is not. The insoluble segments form a reversible gel that is broken to a liquid by shear in the application process, allowing application of a liquid ink, and is reestablished in the applied ink film in such a manner and with such strength as to allow overprinting in the wet on wet flexographic printing process.