Low-E Coating Thermal Stability via NiCr and Silicon Nitride
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Solution Overview
Problem
Existing low-emissivity coatings for windows degrade or become unstable during high-temperature heat treatments, such as thermal tempering, leading to unpredictable changes in visible transmission and color, and fail to maintain desirable durability and low sheet resistance.
Innovation Solution
A coated article with a low-emissivity coating comprising silver-based infrared reflecting layers separated by NiCr contact layers and a silicon nitride dielectric layer, which is thermally stable and maintains low visible transmission, durability, and low sheet resistance even after heat treatment, achieved through a specific layer structure and materials like amorphous silicon nitride and NiCr contact layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional low-E coatings are used to achieve low emissivity and good visible transmission, then IR blocking performance is improved, but the coating deteriorates or becomes unstable during high-temperature heat treatments
Solution Approach 1:
The coating is divided into multiple functional layers including bottom contact layer, first IR-reflecting layer, first dielectric layer, second IR-reflecting layer, and top contact layer. Each layer serves a specific function and is designed to withstand heat treatment temperatures, with the dielectric layer acting as a thermal barrier to protect the sensitive IR-reflecting layers during tempering
Solution Approach 2:
The first dielectric layer acts as an intermediary between the two IR-reflecting layers, providing thermal protection and preventing direct interaction between the silver layers during heat treatment. This intermediate layer stabilizes the coating structure when exposed to high temperatures
2Illumination intensity
If high visible transmission is achieved in low-E coatings, then natural light transmission is improved, but the coating cannot maintain desirable color and low sheet resistance after heat treatment
Solution Approach 1:
The coating parameters are specifically optimized to achieve visible transmission of 63% or more while maintaining color stability (ΔE* ≤ 5.0) and sheet resistance below 5.0 ohms/sq after heat treatment. The dielectric layer thickness and material composition are tuned to balance optical performance with thermal stability
3Strength
If zinc oxide contact layers are used below silver IR-reflecting layers to provide good structural properties, then silver layer adhesion is improved, but the coating durability and environmental resistance degrade
Solution Approach 1:
The contact layer material composition is changed from zinc oxide to alternative materials such as indium tin oxide (ITO), indium zinc oxide (IZO), or nickel chromium (NiCr) alloys. These materials provide both good adhesion to the silver IR-reflecting layer and superior chemical durability and environmental resistance
Solution Approach 2:
The contact layers are designed as composite structures, potentially combining multiple materials or using graded compositions to achieve both strong adhesion to the silver layer and resistance to environmental degradation. The composite structure allows optimization of both bonding and durability properties
4Reliability
If thick SnO2 dielectric layers are used in low-E coatings, then IR reflection performance is improved, but micro crystallization and stress occur upon heat treatment causing interface roughness and durability degradation
Solution Approach 1:
The dielectric layer material is changed from tin oxide (SnO2) to silicon nitride (Si3N4) or other materials with higher thermal stability. Silicon nitride maintains its amorphous structure during heat treatment, preventing micro crystallization and interface roughness while still providing effective IR reflection
Solution Approach 2:
Instead of using thick dielectric layers that require complex stress management, the design uses multiple thinner IR-reflecting layers separated by stable dielectric spacers, distributing the optical function across multiple stable, heat-resistant components
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 coating maintains consistent transmission and color characteristics before and after heat treatment, offering improved durability and thermal stability with reduced sheet resistance, making it suitable for insulating glass units and other window applications.
Implementation Method 1
at least first and second infrared (IR) reflecting layers (e.g., silver based layers) that are spaced apart by contact layers (e.g., NiCr based layers) and a dielectric layer of or including a material such as silicon nitride
Implementation Method 2
the low-E coating is provided on a substrate (e.g., glass substrate) and includes at least first and second infrared (IR) reflecting layers (e.g., silver based layers) that are spaced apart by contact layers (e.g., NiCr based layers)
Implementation Method 3
the coated article has a low visible transmission (e.g., no greater than 50%, more preferably no greater than about 42%, and most preferably no greater than about 39%). In certain example embodiments, the coated article may be heat treated (e.g., thermally tempered and/or heat bent), and is designed to be substantially thermally stable upon heat treatment (HT) in that its ΔE* value (glass side reflective) due to HT is no greater than 4.6
Data Source
AI summary
This invention relates to a coated article including a low-emissivity (low-E) coating. In certain example embodiments, the low-E coating is provided on a substrate (e.g., glass substrate) and includes at least first and second infrared (IR) reflecting layers (e.g., silver based layers) that are spaced apart by contact layers (e.g., NiCr based layers) and a dielectric layer of or including a material such as silicon nitride. In certain example embodiments, the coated article has a low visible transmission (e.g., no greater than 50%, more preferably no greater than about 40%, and most preferably no greater than about 39%).