Radiation Curable Intaglio Ink Stability and Wipeability
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Solution Overview
Problem
Radiation curable intaglio inks for security documents face challenges with stability upon storage and use, optimized rheology, good wipeability, and detergeability in standard alkaline aqueous wiping solutions, as existing inks suffer from poor pot life, surface skin formation, and instability on printing presses.
Innovation Solution
A radiation curable intaglio ink composition comprising 10-60 wt% radiation curable compounds, 2-20 wt% photoinitiators, 5-12 wt% high molecular weight acid modified alkyd or alkylarene sulfonic acid surfactants, and 10-55 wt% fillers, with specific viscosity and surfactant properties, optimized for UV-Vis curing and alkaline aqueous cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If radiation curable compounds are used in intaglio ink, then rapid curing and high production rates are achieved, but stability upon storage and surface skin formation occur
Solution Approach 1:
The patent modifies the chemical parameters of the radiation curable compounds by selecting specific types (epoxy acrylates, polyester acrylates, urethane acrylates) and controlling their molecular weight and functionality. It also adjusts the photoinitiator system composition and concentration to optimize both storage stability and curing performance, resolving the contradiction between rapid curing and storage stability
Solution Approach 2:
The patent creates a composite ink formulation combining multiple radiation curable compounds with different chemical structures, photoinitiators, resins, and additives. This composite approach allows the ink to maintain stability during storage while enabling complete and uniform curing during printing, thus resolving the contradiction between storage stability and production rate
2Manufacturing precision
If intaglio printing process is used, then high quality fine line printing and relief features are achieved, but massive quantities of ink-impregnated waste are generated
Solution Approach 1:
The patent employs oxidative polymerization mechanism where oxygen from air acts as a crosslinking agent during drying. This oxidation process allows the ink to cure completely without requiring excessive ink removal, reducing waste while maintaining the characteristic intaglio relief and fine line quality
Solution Approach 2:
The patent replaces the traditional mechanical wiping system with a chemical curing system. Instead of relying on physical removal of excess ink through wiping cylinders, the ink chemically cures in place, eliminating the need for massive waste removal while preserving the intaglio printing quality
3Productivity
If polymeric wiping cylinder is used to remove ink excess, then printing speed is maintained, but cleaning of the wiping cylinder becomes problematic
Solution Approach 1:
The radiation curable ink formulation is designed to cure rapidly upon exposure to UV or visible light, allowing the wiping cylinder to self-clean as the cured ink adheres to the substrate rather than sticking to the wiping surface. This eliminates the need for complex cleaning systems while maintaining high printing speeds
4Stability of the object's composition
If conventional oxidative drying is used, then ink stability is maintained, but drying time is extended and set-off occurs
Solution Approach 1:
The patent incorporates photoinitiators and oxidation catalysts in the ink formulation that are activated by UV or visible light exposure during printing. This preliminary activation triggers rapid polymerization and crosslinking, eliminating the need for extended oxidative drying time while preventing set-off, thus resolving the contradiction between ink stability and drying time
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 exhibits improved stability, rapid curing, enhanced wipeability, and effective detergeability, ensuring high production rates and reduced set-off issues, while maintaining security features as patterns or images on substrates.
Implementation Method 1
radiation curable compounds, wherein at least one of said one or more radiation curable compounds is a fatty acid polyester (meth)acrylate oligomer
Implementation Method 2
from about 2 wt-% to about 20 wt-% of one or more photoinitiators
Implementation Method 3
from about 5 wt-% to about 12 wt-% of a high molecular weight acid modified alkyd surfactant and/or an alkylarene sulfonic acid surfactant
Implementation Method 4
enhanced wipeability
Implementation Method 5
Wiping off using an aqueous solution as an emulsifying medium for the wiped-off excess ink
Implementation Method 6
effective detergeability
Data Source
Figure 1A~1B
AI summary
The present invention relates to the field of security documents and their protection against counterfeit and illegal reproduction and relates to the field of intaglio printing processes for the printing of said security documents. In particular, the present invention relates to radiation curable intaglio inks suitable for intaglio printing a pattern or image, wherein said intaglio printing comprises wiping off ink excess with a polymeric wiping cylinder and cleaning said cylinder with an alkaline aqueous wiping solution. The disclosed radiation curable intaglio inks comprise one or more radiation curable compounds, wherein at least one of said one or more radiation curable compounds is a fatty acid polyester (meth)acrylate oligomer; one or more photoinitiators; and a high molecular weight acid modified alkyd surfactant and/or an alkylarene sulfonic acid surfactant; one or more fillers or extenders.