Multilayer AR Glass Coating for Heat-Treated Color Stability
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Solution Overview
Problem
Existing antireflective coatings on glass substrates experience significant color shift and reflectance changes upon heat treatment, such as thermal tempering, leading to undesirable appearance differences and stability issues.
Innovation Solution
A multilayer dielectric coating structure comprising high and low index layers, including silicon and niobium oxides, is applied to the glass substrate, which maintains low reflective ΔE* values and neutral coloration before and after heat treatment, without using IR reflecting layers of silver or gold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional AR coatings are applied on glass substrate, then antireflective properties are achieved, but significant color shift occurs upon heat treatment
Solution Approach 1:
The AR coating is divided into multiple distinct layers with different refractive indices (high index layers and low index layers) and different thicknesses. This segmentation allows each layer to contribute differently to the overall optical properties, enabling the coating to maintain low reflective ΔE* values (≤3.0) and neutral coloration before and after heat treatment without significant color shift.
Solution Approach 2:
The coating uses composite dielectric materials including silicon oxide, niobium oxide, and other metal oxides with varying refractive indices. This composite structure enables precise control over optical characteristics, achieving both antireflective properties and thermal stability with neutral coloration maintained through heat treatment.
2Stability of the object's composition
If AR coating is designed to reduce color shift, then reflective ΔE* value is reduced, but coating complexity increases
Solution Approach 1:
The coating is segmented into a specific number of layers (at least 5 layers including high and low index layers) with optimized thicknesses. This segmentation provides enough degrees of freedom to control optical properties while maintaining a practical manufacturing complexity level.
Solution Approach 2:
The invention optimizes specific parameters including layer thicknesses (e.g., first low index layer thickness, second low index layer thickness), refractive indices of materials, and the sequence of layers. By carefully controlling these parameters, the coating achieves low reflective ΔE* values while maintaining a manageable structural complexity.
3Temperature
If heat treatment is applied to glass substrate, then thermal tempering is achieved, but haze increases significantly
Solution Approach 1:
The AR coating is designed and applied before heat treatment, with its optical properties pre-optimized to compensate for expected changes during thermal tempering. The coating structure is configured in advance to maintain low haze and neutral coloration even after exposure to high temperatures during heat treatment.
Solution Approach 2:
The coating parameters (layer thicknesses, materials, refractive indices) are specifically selected and optimized to remain stable during heat treatment. This parameter optimization ensures that the coating maintains its optical properties (low haze, neutral color) through the thermal tempering process.
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 reflective ΔE* values of no greater than 3.0, improved thermal stability, reduced haze, and stable reflectance over time, ensuring consistent appearance before and after heat treatment.
Implementation Method 1
A multilayer dielectric coating structure comprising high and low index layers... maintains low reflective ΔE* values... providing substantially neutral coloration
Data Source
Figure 1~2
AI summary
A coated article including a first antireflective (AR) coating supported by a glass substrate, wherein the first coating can include, moving away from the glass substrate: a dielectric first high index layer; a dielectric first low index layer; a dielectric second high index layer; a dielectric second low index layer; a dielectric third high index layer; a dielectric first medium index layer; a dielectric third low index layer; and an overcoat layer; wherein the first coating contains no IR reflecting layer based on silver and/or gold; wherein, from the perspective of a viewer of the coated article, the first coating can be configured so that the coated article has a film side reflective ΔE* value of no greater than 3.0 upon heat treatment of at least about 580 degrees C. The ΔE* value(s) can be measured either with a substantially symmetrical/similar AR coating on the other side of the same glass substrate, or absent any AR coating on the other side of the glass substrate.