Invisibly Printed Security Images Using Fluorescent Inkjet Inks
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Solution Overview
Problem
Current security printing methods using fluorescent materials for currency and identification documents often rely on visible fluorescent colors, which can be easily counterfeited and lack the desired level of security, as they are detectable under ordinary white-light illumination and do not provide multiple authentication features.
Innovation Solution
The development of inkjet printing methods and ink compositions that create invisibly printed, full-color, high-resolution images only visible under specific excitation energy, utilizing fluorescent inks that emit colors such as purple, blue, green, yellow, orange, red, brown, and white, and incorporating optical brighteners and quenchers to mask or enhance emissions, allowing for multiple layers of security and authentication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If visible fluorescent colors are used for security printing, then authentication can be easily performed by visual inspection, but the security level decreases because the markings can be easily detected and counterfeited under ordinary white-light illumination
Solution Approach 1:
The patent applies color changes by using fluorescent materials that are invisible under ordinary white light but emit visible fluorescence under UV or NIR illumination. This allows the security markings to remain hidden during normal handling while becoming visible for authentication when illuminated with the appropriate wavelength, thus simultaneously maintaining security and ease of verification
Solution Approach 2:
The patent changes the illumination parameter from visible white light to UV or NIR light. By using fluorescent materials that respond to these different wavelength parameters, the security markings transition from invisible to visible states, enabling authentication without compromising security under ordinary lighting conditions
2Reliability
If UV-fluorescent materials are used for security markings, then the markings remain invisible under ordinary white light providing higher security, but the markings cannot be easily detected by simple visual observation requiring specialized equipment
Solution Approach 1:
The patent applies dynamics by making the visibility of security markings conditional rather than static. The markings dynamically transition between invisible and visible states based on the illumination wavelength applied, allowing them to remain hidden under ordinary light and reveal themselves under UV or NIR illumination for authentication
3Reliability
If multiple fluorescent colors are combined for security markings, then the authentication features are enhanced, but the complexity of the printing system and ink composition increases
Solution Approach 1:
The patent applies universality by using a single inkjet printing system to deliver multiple fluorescent ink compositions. The printing system maintains its standard functionality while the inks provide multiple authentication features through different fluorescent responses to UV and NIR illumination, avoiding the need for separate printing systems for different security features
4Ease of operation
If conventional subtractive-color inks are used in inkjet printing, then the inks are visible under ordinary white light providing clear images, but the inks are generally not fluorescent and cannot provide security authentication features
Solution Approach 1:
The patent applies composite materials by formulating ink compositions that combine fluorescent compounds with inkjet-compatible carriers and additives. These composite inks maintain the printability and visibility characteristics of conventional inks while adding fluorescent authentication features that respond to UV and NIR illumination
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
These methods enable the creation of secure images that are undetectable under ordinary light but visible with specific illumination or optical filters, providing enhanced security and authentication capabilities, including machine-readable features, thereby improving the detection of counterfeits and ensuring the integrity of documents.
Implementation Method 1
The use of fluorescent materials such as ultraviolet (UV)-fluorescent, infrared (IR)-fluorescent, or near-infrared (NIR)-fluorescent materials for security markings is well known. The use of fluorescent materials allows the user to easily detect the security markings by irradiation of the marks with a suitable UV or NIR/IR light source.
Implementation Method 2
The fluorescent compounds may include optical brighteners and/or quenchers
Implementation Method 3
The fluorescent compounds may include optical brighteners and/or quenchers
Data Source
AI summary
An article is marked with image indicia for authentication, information, or decoration by providing a plurality of inks having a plurality of fluorescence colors when exposed to excitation energy, separating colors of the image indicia into a plurality of image levels in accordance with the fluorescence colors of the inks, and printing each image level in mutual registration on the article using the corresponding ink. The image printed with each ink may be substantially invisible under illumination within the visible spectrum. The invisibly printed images have multiple authentication features, including the use of covert UV-fluorescent materials, IR-fluorophores, microparticles, and other chemical taggants. Ink compositions, methods for making the inks, and methods and apparatus for using the inks are also disclosed.