Thin Aluminum Flakes with Oxidized Inner Layer for Shear Stability
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Solution Overview
Problem
Conventional aluminum flakes, especially those thinner than 100 nm, suffer from poor mechanical and shear stability, leading to degradation under stress, which affects their metallic appearance and usability in applications like paints and coatings.
Innovation Solution
Incorporating an inner layer of oxidized aluminum within the aluminum flakes, surrounded by additional outer layers of oxidized aluminum, enhances their mechanical and shear stability while maintaining a pure silver color and metallic effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the thickness of aluminum flakes is reduced to below 100 nm to improve metallic appearance, then the coloristical appearance is improved, but the shear stability deteriorates causing color degradation under mechanical stress
Solution Approach 1:
The patent creates a composite structure by combining aluminum with an oxidized aluminum layer. The aluminum flake core (10-200 nm) provides metallic appearance while the oxidized aluminum layer (5-50 nm) provides mechanical strength and shear stability, resolving the contradiction between thinness for metallic effect and thickness for stability
Solution Approach 2:
The patent applies different properties to different parts of the flake structure: the aluminum core maintains thinness for optical properties while the oxidized aluminum coating provides enhanced mechanical properties. This local differentiation allows the flake to simultaneously achieve both metallic appearance and shear stability
2Productivity
If conventional mechanical stamping is used to produce aluminum flakes, then production efficiency is high, but the flakes exhibit poor mechanical stability and degradation under shear stress
Solution Approach 1:
The patent replaces the conventional mechanical stamping process with a chemical oxidation process. Instead of mechanically flattening aluminum granules which creates weak points, the aluminum is chemically oxidized to form a strengthened composite structure that maintains integrity under shear stress while still enabling efficient production
3Strength
If thick aluminum flakes above 500 nm are used to improve mechanical stability, then the mechanical stability is improved, but the metallic appearance is reduced due to light scattering
Solution Approach 1:
The patent creates a composite where a thin aluminum core (10-200 nm) provides metallic appearance and a thinner oxidized aluminum layer (5-50 nm) provides mechanical stability. This composite structure achieves both goals without needing the thickness of conventional non-degrading flakes (>500 nm)
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 inner layer of oxidized aluminum significantly improves the shear stability of the flakes, preventing color degradation and maintaining a mirror-like appearance even under mechanical stress, as demonstrated by comparison with commercially available flakes.
Implementation Method 1
oxidizing the aluminium surface by contact with air
Implementation Method 2
metallizing the precoated polyester film with an aluminum layer in a vacuum via physical vapor deposition
Data Source
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AI summary
Described are thin plane-parallel aluminum flakes illustrated in Fig. 1 having a thickness of up to 200 nm and comprising an inner layer of oxidized aluminium having a thickness of 0.5 - 30 nm, a process for the manufacture thereof and the use thereof, e.g. in formulations, like paints, electrostatic coatings, printing inks, plastics materials, and cosmetics. Surprisingly, due to the inner layer of oxidized aluminum the aluminum flakes have an improved shear stability as evidenced e.g. by the difference in lightness before and after shear stress.