Black-to-Color Shifting Security Element via Angle-Dependent Spectral Absorption
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Solution Overview
Problem
Existing color-shifting security elements that change from a first color to black at grazing view are difficult to see due to their appearance being limited to a narrow range of observation angles, and colors like claret, olive, or violet already appear almost black, making it hard to distinguish the shift effectively.
Innovation Solution
A security element combining optically variable pigments with selective spectral absorbing materials that block visible spectral components at orthogonal incidence, resulting in a black appearance at orthogonal view and a colored appearance at grazing view, using a combination of optically variable pigments and absorbing materials to achieve a more evident color shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If optically variable pigment is mixed with conventional dye or pigment to achieve black at grazing view, then black appearance is obtained, but the black is difficult to see and only appears in a very narrow range of observation angles
Solution Approach 1:
The patent inverts the conventional approach by making the security element appear black at orthogonal view (instead of at grazing view) and colored at grazing view. This is achieved by using an optically variable pigment that reflects blue light at orthogonal incidence combined with a yellow absorbing material that absorbs the reflected blue light, creating black appearance at orthogonal view. At grazing view, the optically variable pigment reflects green light which is not absorbed by the yellow material, producing a visible green color.
Solution Approach 2:
The patent employs color change phenomena through the combination of optically variable pigment and absorbing material. The optically variable pigment changes its reflected color from blue at orthogonal incidence to green at grazing incidence. The absorbing material selectively absorbs the blue reflected light at orthogonal view, creating black appearance, while allowing the green reflected light to pass through at grazing view, creating a evident color shift from black to green.
2Adaptability or versatility
If optically variable pigment with low refractive index is used, then substantial angle-dependent color variation is achieved, but the color shift is not evident enough for security purposes
Solution Approach 1:
The patent enhances the evidence of color shift by combining the inherent angle-dependent color variation of optically variable pigment with selective absorption. The yellow absorbing material absorbs the blue reflected light at orthogonal view, making the appearance black, while at grazing view the green reflected light is not absorbed, creating a stark contrast between black and green appearances that is easily detectable.
Solution Approach 2:
The patent uses a composite material system consisting of optically variable pigment particles combined with yellow absorbing material particles in a coating composition. This composite structure allows the optically variable pigment to provide angle-dependent color variation while the absorbing material enhances the contrast by selectively absorbing certain wavelengths, creating a more evident black-to-green color shift.
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 security element provides a more defined and easily identifiable color shift from black to color when changing the viewing angle, enhancing visibility even under difficult illumination conditions and allowing for easier integration into existing security document designs without altering the orthogonal view image.
Implementation Method 1
Optically variable pigments are interference pigments which exhibit a substantial angle-dependent color variation
Implementation Method 2
which exhibit clearly observable different colors under e.g. an orthogonal and a grazing view
Implementation Method 3
a light-absorbing material which substantially blocks out the visible spectral components which are reflected by said optically variable pigment at orthogonal incidence
Data Source
AI summary
The invention discloses a security element for a banknote, a document of value, right or identity, a ticket, a label, a branded good identifier, or a tax banderole. The element comprises a combination of a coating containing at least one optically variable pigment having a substantial viewing-angle dependent color variation, with at least one selective spectral absorbing material, which blocks out visible spectral components reflected by the optically variable pigment at orthogonal incidence. The security element appears black when viewed at orthogonal angle, and colored when viewed at grazing angle.