Wavelength-Selective Reflective Layer for Window Glass Color Stability
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Solution Overview
Problem
Existing window glass technologies that incorporate reflective layers for near-infrared light shielding often lead to changes in color tone due to variations in incident angle, causing undesirable heat island effects and aesthetic issues.
Innovation Solution
An optical element with a wavelength-selective reflective layer comprising alternately laminated high refractive-index and metal layers, where the geometric film thickness is optimized to maintain specific ratios of optical film thicknesses, thereby minimizing changes in color tone across different incident angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a multilayer film is designed by conventional methods on a flat plate, then the heat shielding function is provided, but the color tone changes to have blueness or redness due to changes in refractive index and incident angle
Solution Approach 1:
The patent applies parameter changes by precisely controlling the film thickness of each layer in the multilayer structure. By adjusting the thickness parameters of the high refractive index layer and metal layer to specific ranges, the optical properties are optimized to maintain stable color tone while achieving effective heat shielding. This resolves the contradiction by changing the dimensional parameters to simultaneously satisfy both heat rejection and color stability requirements.
Solution Approach 2:
The patent uses composite materials by combining a high refractive index material layer with a metal layer in a multilayer configuration. This composite structure leverages the complementary properties of each material: the high refractive index material provides optical control and the metal layer provides thermal reflection, achieving both heat shielding and color stability that neither material could provide alone.
2Temperature
If a reflective layer is provided on flat film or window glass, then near-infrared light shielding is achieved, but specular reflection increases ambient temperature and promotes heat island phenomenon
Solution Approach 1:
The patent applies spheroidality by forming the reflective layer on a convex curved surface rather than a flat plate. This curvature causes incident sunlight to be reflected in multiple directions (diffuse reflection) rather than as a concentrated specular beam. The curved surface scatters the reflected light, preventing the formation of high-temperature zones and reducing the heat island effect while maintaining effective near-infrared shielding.
3Manufacturing precision
If the refractive index or incident angle changes, then the designed spectrum deviates from optimal value, but this causes color tone change with blueness or redness
Solution Approach 1:
The patent addresses this contradiction by optimizing the film thickness parameters of each layer in the multilayer structure. By carefully selecting the thickness of the high refractive index layer and metal layer within specific ranges, the design compensates for variations in refractive index and incident angle, maintaining both spectral performance and color stability across different viewing conditions.
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 effectively suppresses changes in color tone, enhancing transparency and heat shielding properties while reducing heat absorption, thus mitigating urban heat island effects and maintaining aesthetic neutrality.
Implementation Method 1
an optical element having a high reflectance in the near-infrared region
Implementation Method 2
the refractive index at at least one interface of the multilayer film and the incident angle of light incident on the interface are changed
Implementation Method 3
building glass for high-rise buildings and houses and window glass for vehicles have been increasingly provided with layers for absorbing or reflecting some of sunlight
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3C
AI summary
An optical element comprising a first optical layer having a light emission surface, a wavelength-selective reflective layer provided on the first optical layer, a second optical layer provided on the wavelength-selective reflective layer and having a light incidence surface. Therein the wavelength-selective reflective layer has a structure including at least five layers in which high refractive-index layers and metal layers are alternately laminated to each other. When a geometric film thickness L of the entire wavelength-selective reflective layer is 120 nm, a ratio α of an optical film thickness of the entire metal layers to an optical film thickness of the entire high refractive-index layers and a ratio β of an optical film thickness of a third high refractive-index layer from one of a first optical layer side and a second optical layer side to an optical film thickness of a first high refractive-index layer therefrom are included in a first region surrounded by the following formulas (21) to (24). When the geometric film thickness L of the entire wavelength-selective reflective layer is 140 nm, the ratio α and the ratio β are included in a second region surrounded by the following formulas (29) to (32), and when the geometric film thickness L of the entire wavelength-selective reflective layer is in a range of 120 to 140 nm, the ratio α and the ratio β are included in a space enclosed by the first region, the second region, and lines derived from these regions.