Anodic Oxide Coating Structure for Low-Angle White Aluminum
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Solution Overview
Problem
Conventional aluminum members with anodic oxide coatings do not maintain a white appearance when viewed obliquely, lacking sufficient whiteness and angular dependence.
Innovation Solution
An aluminum member is produced with a substrate of aluminum or aluminum alloy, featuring a barrier layer, a first porous layer with branching or larger pores, and a second porous layer with aligned pores, formed through specific anodization processes to enhance diffused reflection and reduce angular dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional anodic oxide coating is formed on aluminum substrate, then the surface obtains a white appearance, but the whiteness shows high angular dependence and does not maintain white color when viewed obliquely
Solution Approach 1:
The anodic oxide coating is segmented into three distinct layers: a barrier layer (5-50 nm thick) providing a smooth base, a first porous layer (50-500 nm thick) with small pores (5-50 nm diameter) for light scattering, and a second porous layer (500 nm-5 μm thick) with large aligned pores (50-500 nm diameter) for directional light transmission. This segmentation allows each layer to contribute differently to the overall optical properties, achieving white appearance with low angular dependence.
Solution Approach 2:
Different regions of the coating have different pore structures optimized for specific functions: the barrier layer provides a dense smooth surface, the first porous layer provides fine light scattering with small pores, and the second porous layer provides coarse light scattering with large aligned pores. This local quality variation enables the coating to maintain white appearance from multiple viewing angles.
2Ease of manufacture
If the anodic oxide coating has a simple single-layer structure, then the manufacturing process is simple, but the appearance quality and whiteness are insufficient
Solution Approach 1:
The coating is formed through periodic anodization cycles: a first anodization process creates the barrier layer and first porous layer with small pores, followed by a second anodization process that forms the second porous layer with large aligned pores while preserving the underlying structure. This periodic action with controlled parameters produces the complex three-layer structure through sequential processing steps.
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 resulting aluminum member achieves a white color with low angular dependence, resembling paper, suitable for applications such as smartphone and personal computer housings.
Implementation Method 1
performing a first anodization on a substrate formed by aluminum or an aluminum alloy using an electrolytic solution that is capable of forming multiple pores aligned and extending linearly
Implementation Method 2
performing a second anodization on the substrate that has been subjected to the first anodization using an electrolytic solution. The electrolytic solution for the second anodization is capable of forming at least one of multiple branching pores, or multiple pores having an average pore diameter larger than that of the multiple pores linearly extending
Implementation Method 3
The first porous layer includes at least one of multiple branching pores, or multiple pores having an average pore diameter larger than that of the second porous layer
Data Source
AI summary
Provided is an aluminum member including: a substrate formed of aluminum or an aluminum alloy. The aluminum member includes an anodic oxide coating that includes a barrier layer in contact with a surface of the substrate, a first porous layer in contact with a surface of the barrier layer on an opposite side to the substrate, and a second porous layer in contact with a surface of the first porous layer on an opposite side to the barrier layer and including multiple pores aligned and linearly extending from a surface in contact with the first porous layer toward an exposed surface. The first porous layer includes at least one of: multiple branching pores; or multiple pores having an average pore diameter larger than that of the second porous layer.