Low-E Coating Absorbing Layers for Low Film Side Reflectance
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Solution Overview
Problem
Existing low-emissivity 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 maintain predictable optical characteristics during high-temperature heat treatments.
Innovation Solution
A double-silver stack low-E coating design with absorbing layers in both the middle and upper stacks, utilizing metallic or substantially metallic NiCr layers between nitride layers and IR reflecting layers to prevent oxidation and maintain desirable optical characteristics during heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If visible transmission is reduced to achieve low visible transmission (≤45%), then film side reflectance typically increases
Solution Approach 1:
The coating is divided into multiple functional stacks: a first stack containing an absorbing layer positioned to reduce visible transmission, and a second stack containing an IR reflecting layer positioned to reduce film side reflectance. This segmentation allows each stack to independently optimize its function, resolving the contradiction between low visible transmission and low film side reflectance.
Solution Approach 2:
Different regions of the coating are assigned different optical properties: the first absorbing layer is designed with specific optical characteristics to control visible transmission, while the second IR reflecting layer is designed with different characteristics to control film side reflectance. This local differentiation of properties enables simultaneous optimization of both parameters.
2Strength
If high temperature heat treatment is applied to achieve tempering, bending, or strengthening, then coating breakdown and deterioration occur
Solution Approach 1:
A buffer layer is introduced between the glass substrate and the low-E coating, and another buffer layer is introduced between the coating and the outer environment. These intermediary buffer layers act as protective mediators that allow the glass to undergo high-temperature heat treatment for tempering while protecting the sensitive low-E coating from thermal damage and oxidation, maintaining coating stability during the process.
Solution Approach 2:
The coating design incorporates protective measures in advance, such as the buffer layers and the specific arrangement of absorbing and reflecting layers, to prevent oxidation and thermal damage before they can occur during heat treatment. This preliminary protective action allows the coating to withstand high-temperature processing without breakdown or deterioration.
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 achieves low visible transmission, reduced film side reflectance, and stable optical properties, even after heat treatment, by strategically placing absorbing layers to prevent oxidation and maintain performance.
Implementation Method 1
absorbing layers of the low-E coating are positioned/designed to cause the coating to have both (i) a low visible transmission... and (ii) a reduced visible film side reflectance
Implementation Method 2
a metallic or substantially metallic infrared (IR) reflecting layer
Implementation Method 3
the absorbing layer in the middle stack may be provided between first and second nitride layers... in order to reduce or prevent oxidation of the absorbing layers during optional heat treatment
Data Source
Figure 1
Figure 2
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 positioned in order to reduce or prevent oxidation of the absorbing layers during optional heat treatment (e.g., 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.