UV-Vis Curable Security Inks for Flake Pigment Orientation
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Solution Overview
Problem
Existing UV-Vis radiation curable inks with flake-shaped multilayer interference pigments suffer from poor optical characteristics due to random pigment orientation, leading to inadequate chroma, lightness, and color shifting properties, particularly in high-speed industrial printing processes.
Innovation Solution
Formulating UV-Vis radiation curable security inks with a specific ink vehicle composition comprising cycloaliphatic epoxides, cationic photoinitiators, and pigments coated with perfluoropolyethers to ensure proper pigment orientation and improved optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If UV-Vis radiation curable inks with flake-shaped multilayer interference pigments are used for high-speed industrial printing, then productivity is improved, but optical characteristics deteriorate due to random pigment orientation
Solution Approach 1:
The pigment flakes are pre-coated with surfactants and coupling agents during manufacturing, creating a surface treatment that promotes parallel orientation. This preliminary action ensures that when the ink is applied and cured rapidly in high-speed printing, the pigments are already predisposed to orient correctly, eliminating the need for slow drying processes
Solution Approach 2:
The invention modifies the chemical parameters of the ink vehicle by incorporating specific surfactants and coupling agents that change the surface properties of pigment flakes. This parameter change enables the pigments to orient parallel to the substrate even under the rapid curing conditions of UV-Vis radiation, resolving the contradiction between fast printing and proper orientation
2Productivity
If the ink layer thickness is reduced for high-speed printing, then productivity is improved, but optical characteristics deteriorate
Solution Approach 1:
The invention changes the chemical composition parameters of the ink by adding surfactants and coupling agents that enhance pigment orientation efficiency. This allows the ink to achieve proper pigment alignment at reduced thickness levels, maintaining optical characteristics while enabling faster printing speeds
3Ease of manufacture
If conventional inks with organic solvents are used, then ease of manufacture is improved, but environmental compliance worsens due to VOC regulations
Solution Approach 1:
The invention changes the physical state parameter of the ink vehicle from solvent-based to radiation-curable composition. By replacing organic solvents with UV-Vis curable resins and initiators, the ink eliminates VOC emissions while maintaining manufacturability through standard printing and curing processes
Solution Approach 2:
The invention substitutes the evaporation-based drying mechanism of solvent inks with a photochemical curing mechanism. UV-Vis radiation triggers polymerization of the ink vehicle, replacing the need for solvent evaporation and eliminating VOC release while achieving rapid ink fixation
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 enhanced chroma, lightness, and color shifting properties in security features, making them more effective against counterfeiting and suitable for high-speed industrial printing.
Implementation Method 1
UV-Vis radiation curable security inks comprising: i) from about 75 wt-% to about 99 wt-% of an ink vehicle having a viscosity between about 200 and about 2000 mPas at 25° C. and comprising: a) a1) from 45 wt-% to about 75 wt-% of one or more cycloaliphatic epoxides and a2) from about 2 wt-% to about 15 wt-% of one or more cationic photoinitiators
Implementation Method 2
ii) from about 1 to about 25 wt-% of pigments comprising a flake-shaped non-metallic or metallic substrate, wherein said non-metallic or metallic substrate comprises one or more at least partial coating layers independently made of one or more metal oxides... and comprises an at least partial surface treatment layer facing the environment, being in direct contact with the top layer of the one or more at least partial coating layers and made of one or more surface modifiers selected from perfluoropolyethers
Data Source
AI summary
The present invention relates to the field of security inks suitable for printing security features on substrates, in particular on security documents or articles as well as security features made from said security inks, and security documents comprising a security feature made from said security inks. In particular, the invention provides UV-Vis radiation cationically curable security inks and UV-Vis radiation curable hybrid security inks comprising an ink vehicle and pigments comprising a flake-shaped non-metallic or metallic substrate comprising one or more at least partial coating layers, an at least partial surface treatment layer made of one or more surface modifiers based on perfluoropolyethers.