NiCr Absorbing Layer for Neutralizing Off-Axis Color in Low-E Coatings
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Solution Overview
Problem
Coated articles used in window applications face issues with undesirable reddish off-axis coloration and degradation of desirable characteristics during high-temperature heat treatment, which affects visible transmission, emissivity, and sheet resistance.
Innovation Solution
Incorporating a metallic absorbing layer of NiCr with a thickness of 2.0-3.0 nm between silicon nitride layers to prevent oxidation and an interlayer of tin oxide between silicon nitride and zinc oxide layers to enhance thermal stability and mechanical durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heat treatment is performed at high temperatures (≥600°C) to temper or strengthen the coated article, then the glass substrate gains improved strength and tempering, but the coating layers undergo oxidation and breakdown causing undesirable off-axis coloration and deterioration of optical properties
Solution Approach 1:
A metallic absorbing layer (Ni, Pd, Pt, or their alloys) is deposited beforehand as a protective barrier layer between the glass substrate and the subsequent coating layers. This preliminary layer prevents oxidation of the coating during high-temperature heat treatment (≥600°C) and maintains the structural integrity and optical properties of the coating stack during tempering processes
Solution Approach 2:
The metallic absorbing layer serves as an intermediary protective element that absorbs oxygen and prevents it from reaching and oxidizing the underlying coating layers during heat treatment. This mediator layer sacrifices itself to protect the critical optical coating structure from thermal degradation and oxidation
2Device complexity
If the metallic absorbing layer is made thinner to reduce material cost and simplify structure, then manufacturing complexity decreases, but oxidation protection during heat treatment becomes insufficient leading to unpredictable coloration
Solution Approach 1:
The thickness of the metallic absorbing layer is precisely controlled within the range of 0.5-5 nm (with preferred range of 1-3 nm). This specific thickness parameter provides optimal balance between oxidation protection capability and material consumption, ensuring sufficient barrier function while maintaining cost-effectiveness and structural simplicity
3Ease of manufacture
If conventional coating structures are used without optimized absorbing layer thickness, then manufacturing process remains simple, but off-axis viewing angles exhibit undesirable reddish coloration
Solution Approach 1:
The metallic absorbing layer is strategically positioned at a specific location within the coating stack (between the glass substrate and the first dielectric layer), and its thickness is locally optimized to 0.5-5 nm. This localized optimization at the critical interface region effectively neutralizes off-axis coloration without requiring changes to the entire coating structure, maintaining manufacturing simplicity
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 achieves predictable coloration, improved thermal stability, mechanical durability, and reduced emissivity, maintaining desirable characteristics post-heat treatment, with less red and more green off-axis coloration.
Implementation Method 1
an absorbing layer of the low-E coating is designed to cause the coating to have a more neutral and/or green color at normal and/or certain off-axis viewing angles
Implementation Method 2
the absorbing layer is metallic, or substantially metallic, and is provided between first and second nitride layers (e:g., silicon nitride based layers) in order to reduce or prevent oxidation thereof during heat treatment
Data Source
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AI summary
An absorbing layer of a low-E coating is designed to cause the coating to have a more neutral and/or green color at normal and/or certain off-axis viewing angles. In certain example embodiments, the metallic or substantially metallic absorbing layer (e.g., NiCr) is from about 20-30 angstroms (Å) thick; this thickness has been found to unexpectedly provide less red and more neutral coloration for the coated article at certain off-axis viewing angles (e.g., at a 45 degree off-axis viewing angle). In certain example embodiments, the absorbing layer is provided between first and second nitride layers in order to reduce or prevent oxidation thereof during heat treatment thereby permitting predictable coloration to be achieved following the heat treatment. Coated articles according to certain example embodiments of this invention may be used in the context of insulating glass (IG) window units; vehicle windows, other types of windows, or in any other suitable application.