Energy-Curable Ink Wet Trapping via Storage Modulus Control
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Solution Overview
Problem
Flexographic printing faces challenges in achieving high-quality multicolor printing due to limited ink viscosity range, leading to issues with wet trapping and back-trapping, especially with energy-curable inks that require inter-station curing or the use of fugitive solvents, which increase production costs and reduce printing speed.
Innovation Solution
Formulating energy-curable inks with controlled storage modulus (G') to enable wet trapping without back-trapping, by ensuring the highest G' ink is printed first and subsequent colors are trapped in order of declining G' values, without the need for volatile components or inter-station curing, using rheological measurements to maintain sufficient G' separation across relevant strain values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If energy-curable inks with low viscosity are used for flexographic printing, then printing quality and uniformity are improved, but wet trapping becomes problematic due to insufficient tack characteristics
Solution Approach 1:
The patent changes the physical-chemical parameters of the ink by introducing a rheology modifier that exhibits shear-thinning behavior. This modifies the ink's viscosity characteristics so that it maintains low viscosity during printing operations (ensuring uniform ink transfer) but exhibits increased apparent viscosity under the high shear conditions of wet trapping (preventing back transfer and mixing).
Solution Approach 2:
The patent employs a dynamic viscosity control mechanism where the ink's rheological properties change in response to shear rate variations. The rheology modifier causes the ink to be non-Newtonian, with viscosity that dynamically adjusts based on the mechanical stress applied during different stages of the printing process, enabling both quality printing and effective wet trapping.
2Object-generated harmful factors
If inter-station curing is implemented to prevent back transfer, then wet trapping problems are resolved, but equipment complexity and production costs increase
Solution Approach 1:
The patent replaces the mechanical/physical curing system (inter-station curing equipment) with a chemical/rheological solution (rheology modifier). Instead of using external energy input to cure the ink between stations, the invention uses the ink's modified rheological properties to naturally prevent back transfer, thereby eliminating the need for complex curing equipment modifications.
3Manufacturing precision
If inter-station curing is used to prevent ink mixing, then layer separation is achieved, but printing speed decreases due to extended curing time
Solution Approach 1:
The patent eliminates the time-consuming inter-station curing process by using rheology modifiers that provide immediate tack control through shear-thinning behavior. The ink's natural rheological properties achieve layer separation without requiring additional curing time, thereby maintaining high printing speeds.
4Object-generated harmful factors
If fugitive solvents are added to enable wet trapping, then tack characteristics are improved, but production costs and environmental compliance costs increase
Solution Approach 1:
The patent changes the fundamental approach to tack control by using a rheology modifier instead of fugitive solvents. This modifies the ink's rheological parameters to achieve the desired tack characteristics without adding volatile components, thereby reducing solvent content and associated environmental compliance costs.
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
This method allows for clean wet trapping of energy-curable inks in flexographic printing, maintaining image integrity and reducing production costs by eliminating the need for inter-station curing and fugitive solvents, while maintaining printing speed and quality over extended print runs.
Implementation Method 1
They are fixed to the substrate not by drying but by curing via actinic radiation, such as ultraviolet light or electron beam
Data Source
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AI summary
Methods and apparatus for flexographic color printing, and more particularly for implementing "wet trapping" in flexographic printing using energy curable flexographic liquid inks are presented. Radiation curable inks can be formulated that wet trap over each other without back-trapping onto the plates and anilox units of down-line printing units by controlling the storage modulus of the inklcoating. The storage modulus G' in the inks can be controlled to ensure that the highest G' ink is printed ISt down with successive colors being trapped in the order of their (declining) G' values. An image in wet ink can thus be trapped over a different image in wet ink of a different color without picking the ISt ink back up and redepositing it onto the subsequent plates and rollers in the printing press (back-trapping).