Low-E Coating Absorbing Layers for Low Film Side Reflectance
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Solution Overview
Problem
Existing low-E coatings struggle to achieve a combination of low visible transmission and low film side reflectance, with most designs either increasing film side reflectance when reducing visible transmission or failing to simultaneously meet both criteria.
Innovation Solution
Incorporating metallic or substantially metallic absorbing layers in the upper and lower stacks of the low-E coating, sandwiched between silicon nitride layers, while omitting an absorbing layer in the middle dielectric stack, to prevent oxidation and maintain predictable optical characteristics during heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If visible transmission is reduced via low-E coating design, then IR radiation blocking is improved, but film side reflectance increases
Solution Approach 1:
The patent applies local quality by placing absorbing layers at specific locations within the coating stack (in the first and second dielectric stacks, but not in the middle dielectric stack between silver layers). This localized placement allows different regions of the coating to have different functions: the absorbing layers in the outer stacks control visible transmission and reduce film side reflectance, while the middle stack maintains IR reflection without adding absorbance. This spatial differentiation resolves the contradiction by optimizing each region's contribution to the overall optical performance.
Solution Approach 2:
The patent uses composite materials by combining metallic or substantially metallic absorbing layers with dielectric layers (including silicon nitride) and silver infrared reflecting layers. This composite structure creates a multi-functional coating system where each material contributes specific properties: the metallic absorbing layers provide visible light absorption, the dielectric layers provide structural support and optical control, and the silver layers provide IR reflection. The composite nature allows simultaneous achievement of low visible transmission and low film side reflectance.
2Loss of energy
If absorbing layers are added to reduce visible transmission, then IR blocking is improved, but coating oxidation during heat treatment worsens
Solution Approach 1:
The patent introduces dielectric layers (particularly silicon nitride layers) as intermediaries that sandwich the metallic absorbing layers. These dielectric intermediary layers serve as protective barriers that prevent direct exposure of the metallic absorbing layers to the high-temperature oxidizing environment during heat treatment. The intermediaries allow the metallic layers to maintain their absorbance properties while being protected from oxidation, thus resolving the contradiction between achieving low visible transmission and maintaining coating stability.
Solution Approach 2:
The patent applies preliminary action by providing the dielectric protective layers around the metallic absorbing layers before the heat treatment process occurs. This pre-established protective structure ensures that when heat treatment is later applied, the metallic layers are already shielded from oxidation. The preliminary placement of protective dielectric layers prevents the harmful oxidation effect before it can occur, allowing the metallic layers to maintain their optical properties through the heat treatment process.
3Illumination intensity
If absorbing layers are placed in all dielectric stacks, then visible transmission is reduced, but manufacturing complexity and oxidation risk increase
Solution Approach 1:
The patent applies the taking out principle by selectively removing the absorbing layer from the middle dielectric stack (the stack between the two silver infrared reflecting layers). This extraction decision is based on the understanding that the middle stack primarily needs to maintain IR reflection, and adding absorbing layers there would not significantly improve visible transmission control while would increase complexity and oxidation risk. By taking out the absorbing layer from the middle stack and keeping it only in the first and second dielectric stacks, the patent simplifies the overall structure while maintaining the desired optical performance.
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
This configuration allows for a simultaneous achievement of low visible transmission and low film side reflectance, with the coated article's visible film side reflectance potentially being less than its visible glass side reflectance, suitable for applications in insulating glass window units and vehicle windows.
Implementation Method 1
the absorbing layers are metallic or substantially metallic and are each provided between first and second nitride layers (e.g., silicon nitride based layers) in order to reduce or prevent oxidation of the absorbing layers during optional heat treatment
Implementation Method 2
Low-emissivity (low-E) and low sheet resistance characteristics permit such coated articles to block significant amounts of IR radiation so as to reduce for example undesirable heating of vehicle or building interiors
Data Source
AI summary
Absorbing layers of a low-emissivity (low-E) coating are designed to cause the coating to have a reduced film side reflectance which is advantageous for aesthetic purposes. In certain embodiments, the absorbing layers are metallic or substantially metallic (e.g., NiCr or NiCrNx) and are each provided between first and second nitride layers (e.g., silicon nitride based layers) in order to reduce or prevent oxidation of the absorbing layers during optional heat treatment thermal tempering, heat bending, and/or heat strengthening). Coated articles according to certain example embodiments of this invention may be used in the context of insulating glass (IG) window units, other types of windows, etc.