UV-Vis Curable Security Inks for Dichroic Features
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Solution Overview
Problem
Current security inks for producing dichroic security features on value documents suffer from limited mechanical resistance and high production costs, making them unsuitable for industrial-scale production, as they require high concentrations of silver platelets and use solvents that are environmentally unfriendly and provide coatings with low mechanical resistance.
Innovation Solution
Development of UV-Vis radiation cationically curable and hybrid curable security inks containing silver nanoplatelets with specific surface stabilizing agents and perfluoropolyether surfactants, which provide improved mechanical resistance and attractive visual appearance, allowing for high-speed printing of dichroic security features with a blue color in transmission and metallic yellow color in reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high concentrations of silver platelets are used to achieve attractive dichroic visual appearance, then the visual contrast and color effect are improved, but the mechanical resistance of the security feature deteriorates and production costs increase
Solution Approach 1:
The patent changes the concentration parameter of silver platelets from high (3:1.1 weight ratio in prior art) to optimized ranges (0.1-5 wt% in ink composition), finding the optimal balance point that provides sufficient visual contrast while maintaining mechanical resistance. This parameter optimization resolves the contradiction by identifying that excessive silver concentration harms mechanical properties without providing proportional visual benefit.
Solution Approach 2:
The patent employs composite binder systems combining polyvinyl chloride copolymers with acrylic or vinylester copolymers, creating a composite material that provides both adhesion for silver platelets and mechanical resistance. The composite binder system allows the security feature to maintain structural integrity even at reduced silver concentrations, resolving the contradiction between visual appearance and mechanical strength.
2Ease of manufacture
If UV radically curable inks or solvent-based inks are used to produce dichroic security features, then the production process is simplified, but the mechanical resistance of the cured coating deteriorates
Solution Approach 1:
The patent uses composite binder formulations combining polyvinyl chloride copolymers (providing adhesion and flexibility) with acrylic or vinylester copolymers (providing mechanical strength and UV curability). This composite material approach maintains production simplicity while achieving superior mechanical resistance compared to single-component systems.
Solution Approach 2:
The patent optimizes the composition parameters of the binder system, including specific ratios of polyvinyl chloride to acrylic/vinylester copolymers, and adjusts molecular weight distributions and functional group concentrations to achieve the optimal balance between ease of manufacture and mechanical resistance.
3Ease of manufacture
If increased amounts of organic solvent are added to UV curable ink to reduce silver platelet concentration, then the ink becomes easier to process, but the environmental impact worsens and additional drying steps are required
Solution Approach 1:
The patent modifies the ink composition parameters by reducing organic solvent content to environmentally friendly levels while compensating for viscosity and processability through optimized binder system selection and formulation. The acrylic and vinylester copolymers provide appropriate rheological properties without requiring high solvent levels, thus maintaining ease of manufacture while eliminating environmental harm.
4Illumination intensity
If high concentrations of silver platelets are used to ensure adequate coverage and color intensity, then the visual appearance is improved, but the production cost increases
Solution Approach 1:
The patent optimizes the silver platelet concentration parameter to the minimal effective level (0.1-5 wt%), discovering that high concentrations (3:1.1 ratio) provide diminishing returns on color intensity while linearly increasing cost. The optimized parameter range achieves adequate visual appearance at significantly reduced material cost.
Solution Approach 2:
The patent uses composite binders with enhanced adhesion properties that improve silver platelet distribution and light interaction efficiency, allowing adequate color intensity to be achieved with lower silver concentrations, thus reducing production cost while maintaining visual appearance.
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 new inks enable the production of dichroic security features with enhanced mechanical resistance and attractive visual contrast, suitable for high-speed industrial printing, while reducing production costs and environmental impact by using lower silver nanoplatelet concentrations and environmentally friendly components.
Implementation Method 1
d1) from 25 wt-% to 55 wt-% of a cycloaliphatic epoxide, and from 1 wt-% to 10 wt-% of a cationic photoinitiator
Implementation Method 2
from 1 wt-% to 6 wt-% of a free radical photoinitiator
Implementation Method 3
dichroic security features exhibiting a first color upon viewing in transmitted light and a second color different from the first color upon viewing in incident light
Implementation Method 4
silver nanoplatelets containing inks for producing dichroic security, or decorative elements showing a gold/copper color in reflection and a blue color in transmission
Data Source
AI summary
The present invention provides a UV-Vis radiation curable security ink for producing a security feature for securing value documents, wherein said security feature exhibits a blue color upon viewing in transmitted light and a metallic yellow color upon viewing in incident light. The UV-Vis radiation curable security ink comprises a cationically curable or a hybrid curable ink vehicle, and silver nanoplatelets bearing a surface stabilizing agent of general formula (I) wherein the residue RA is a C2-C4alkyl group substituted with a hydroxy group; the residue RB is selected from a C1-C4 alkyl group, and a C2-C4alkyl group substituted with a hydroxy group; and Cat+ is a cation selected from the group consisting of Na+, K+, Cs+ and Rb+.