Hybrid UV-LED Protective Varnish With Low Fluorescence Curing
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Solution Overview
Problem
Existing hybrid UV-LED radiation curable protective varnishes for security documents suffer from reduced curing efficiency and high fluorescence levels when exposed to UV light, impairing the detection and recognition of luminescent security features.
Innovation Solution
A hybrid UV-LED radiation curable protective varnish comprising specific compositions and concentrations of cycloaliphatic epoxide, radically curable monomers, diaryl iodonium salt, free radical photoinitiator, non-ionic surfactant, and a photosensitizer of defined formula, optimized for curing with UV-LED light sources, minimizing fluorescence and ensuring effective adhesion and mechanical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photoinitiators are used in hybrid UV-LED radiation curable protective varnishes, then curing can occur, but fluorescence levels become high impairing detection of luminescent security features
Solution Approach 1:
The patent changes the chemical parameters of the photoinitiator system by selecting specific compounds (alpha-hydroxyketones, alpha-alkoxyketones, benzyl diketals, benzoin ethers, phosphine oxides, phenylglyoxylates) and controlling their concentrations (0.1-5 wt%), thereby modifying the curing characteristics and fluorescence emission properties to achieve low fluorescence while maintaining effective curing
Solution Approach 2:
The patent creates a composite photoinitiation system combining multiple photoinitiators (cationic, free radical, and photosensitizer components) working together to achieve synergistic effects that reduce fluorescence while ensuring rapid and complete curing of the protective varnish
2Use of energy by moving object
If UV-LED light sources are used for curing, then energy efficiency improves, but curing speed and efficiency are reduced compared to conventional UV sources
Solution Approach 1:
The patent modifies the photopolymerization parameters by adjusting the photoinitiator concentration (1-10 wt%), the ratio of cationic to free radical curable monomers, and the molecular weight distribution of monomers to optimize curing kinetics for UV-LED wavelengths, achieving rapid curing despite the lower intensity of UV-LED light
Solution Approach 2:
The patent introduces photosensitizer compounds as intermediaries that absorb UV-LED light and transfer energy to the photoinitiators, enhancing the curing efficiency and enabling rapid curing at lower light intensities provided by UV-LED sources
3Productivity
If high concentrations of photoinitiators are used to improve curing efficiency, then curing speed increases, but fluorescence levels increase impairing security feature detection
Solution Approach 1:
The patent optimizes the concentration parameters of photoinitiators within specific ranges (0.1-5 wt% for free radical photoinitiators, 1-10 wt% for cationic curable compounds) to achieve the optimal balance between curing speed and fluorescence emission, preventing excessive fluorescence while maintaining rapid curing
Solution Approach 2:
The patent develops a composite formulation combining multiple photoinitiator types and photosensitizers that work synergistically to achieve high curing efficiency at lower individual concentrations, reducing overall fluorescence while maintaining fast curing speed through the combined action of different initiation mechanisms
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 varnish provides rapid curing with minimal fluorescence, maintaining the visibility of luminescent security features and enhancing the durability of security documents.
Implementation Method 1
a photosensitizer of general formula (I)... which transfers the energy to the photoinitiators
Implementation Method 2
a photosensitizer of general formula (I)... which transfers the energy to the photoinitiators
Implementation Method 3
Free-radically UV radiation curable coatings, which are cured by free radical mechanisms consisting of the activation of one or more free radical photoinitiators able to liberate free radicals upon the action of radiation
Implementation Method 4
Cationic UV radiation curable coatings, which are cured by cationic mechanisms consisting of the activation by UV-Vis light of one or more cationic photoinitiators, which liberate cationic species
Implementation Method 5
cured by exposure to UV light emitted by a UV-LED source
Data Source
AI summary
The present invention relates to the technical field of varnishes for protecting security documents, such as banknotes, against premature detrimental influence of soil and/or moisture upon use and time. In particular, the present invention provides a hybrid UV-LED radiation curable protective varnish comprising: a) from about 60 wt-% to about 85 wt-% of either a cycloaliphatic epoxide, or a mixture of a cycloaliphatic epoxide and one or more cationically curable monomers other than the cycloaliphatic epoxide; b) from about 3 wt-% to about 15 wt-% of one or more radically curable monomers and/or oligomers; c) from about 1 wt-% to about 6 wt-% of a diaryl iodonium salt; d) from about 0.5 wt-% to about 3 wt-% of a free radical photoinitiator selected from the group consisting of alpha-hydroxyketones, alpha-alkoxyketones, benzyl diketals, benzoin ethers, phosphine oxides, phenylglyoxylates, and mixtures thereof; e) from about 0.01 wt-% to about 5 wt-% of a non-ionic surfactant; and f) a photosensitizer of general formula (I) wherein the weight percents are based on the total weight of the hybrid UV-LED radiation curable protective varnish.