Security Element with Transition Metal and Organic Layers
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Solution Overview
Problem
Existing security elements fail to effectively control color appearance in reflection and transmission, lacking a method to achieve significant chroma and angle-dependent color flip-flop effects with minimal change in transmission color when additional layers are added.
Innovation Solution
A security element comprising a transparent substrate with a first layer of transition metal particles (silver, copper, or gold) and a second organic layer of refractive index 1.2 to 2.3 and thickness 20 to 1000 nm, where the weight ratio of metal particles to binder is optimized, allowing for controlled color appearance in reflection and minimal change in transmission color.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single layer of transition metal particles is used, then the structure is simple, but the color control in reflection and transmission is insufficient
Solution Approach 1:
The single layer of transition metal particles is segmented into two distinct layers: a first layer containing transition metal particles (silver, copper, or gold) and a second layer comprising an organic material with specific refractive index and thickness. This segmentation enables independent optimization of each layer's function - the first layer provides metallic color and reflection properties, while the second layer controls transmission color and angle-dependent effects, thereby resolving the contradiction between structural simplicity and color control precision.
Solution Approach 2:
The patent employs a composite structure combining inorganic transition metal particles with organic binder material in the first layer, and organic material with specific optical properties in the second layer. This composite material approach allows the security element to exhibit both metallic reflection characteristics and controlled transmission color, achieving superior color control that cannot be obtained with a single homogeneous layer.
2Device complexity
If additional layers are added to enhance color effects, then chroma and angle-dependent effects improve, but transmission color changes significantly
Solution Approach 1:
The second layer's organic material is specifically selected with a refractive index between 1.2 and 2.3 and a thickness between 20 and 1000 nm. By precisely controlling these parameters, the patent achieves angle-dependent color effects and enhanced chroma in reflection while maintaining consistent transmission color. The specific refractive index range ensures that the layer provides the necessary optical interference and scattering effects without significantly altering the transmission characteristics, thus resolving the contradiction between enhancing color effects and maintaining transmission color stability.
3Quantity of substance
If transition metal particles with high weight ratio to binder are used, then color intensity increases, but manufacturing difficulty increases
Solution Approach 1:
The patent applies different metal particle concentration ranges to different layers: the first layer has a weight ratio of transition metal particles to binder from 20:1 to 1:2 for polymeric binders or 5:1 to 1:15 for UV curable binders, while the second layer has optimized composition for optical properties. This local quality differentiation allows the first layer to provide strong metallic color intensity through high metal content, while the second layer's optimized composition ensures ease of manufacturing and application, thereby resolving the contradiction between color intensity and manufacturing ease.
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 enhances chroma and angle-dependent color effects in reflection while maintaining consistent transmission color, offering improved security features through controlled refractive index and thickness adjustments.
Implementation Method 1
a first layer showing high gloss (metallic aspect) and comprising transition metal particles showing color due to localized surface plasmon resonance (LSPR)
Implementation Method 2
a second layer, comprising an organic material and having a refractive index of from 1.2 to 2.3 and having a thickness of from 20 to 1000 nm
Data Source
AI summary
The present invention relates to security, or decorative elements, comprising a transparent, or translucent substrate, which may contain indicia or other visible features in or on its surface, and on at least part of the substrate surface, a first layer, comprising transition metal particles having an average diameter of from 5 nm to 500 nm and a binder, on at least part of the first layer a second layer, comprising an organic material and having a refractive index of from 1.2 to 2.3 and having a thickness of from 20 to 1000 nm, wherein the transition metal is silver, copper, gold and palladium, wherein the weight ratio of transition metal particles to binder in the first layer is in the range from 20:1 to 1:2 in case the binder is a polymeric binder, or wherein the weight ratio of transition metal particles to binder in the first layer is in the range from 5:1 to 1:15 in case the binder is an UV curable binder. The security or decorative element show a certain color in transmission and a different color in reflection and a color flop on the coating side. The color in reflection and the color flop of the security or decorative elements are controlled by adjusting the refractive index and thickness of the second layer.