Transparent IR Reflecting Films Suppressing Visible Reflections
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Solution Overview
Problem
Multilayer infrared (IR) reflecting films often exhibit unwanted higher order reflections in the visible region, which are undesirable in applications like window films, necessitating the suppression of these reflections while maintaining IR reflectivity.
Innovation Solution
A multilayer IR reflecting film design featuring an optical repeating unit with alternating high refractive index polymeric layers (A) and low refractive index isotropic fluoropolymer layers (B), arranged in a specific thickness ratio (7:1:1:7:1:1) to achieve constructive and destructive interference, suppressing higher order reflections in the visible range while reflecting IR light effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If multilayer polymeric films are designed to reflect infrared light, then infrared reflectance is improved, but higher order reflections in the visible region occur causing unwanted visible light reflection
Solution Approach 1:
The patent applies local quality by creating layers with different refractive indices (high refractive index layers and low refractive index fluoropolymer layers) at specific positions within the multilayer structure. This spatial variation in optical properties enables selective reflection of infrared light while suppressing visible light reflection through controlled constructive and destructive interference patterns at different wavelengths.
Solution Approach 2:
The patent changes physical parameters by optimizing the thickness ratio of alternating layers to approximately 7:1:1:7:1:1 and selecting materials with specific refractive indices. These parameter changes tune the optical interference conditions to reflect infrared wavelengths while minimizing visible wavelength reflections, thereby resolving the contradiction between infrared reflectance and visible light transmission.
2Loss of energy
If layer thickness and material composition are optimized for infrared reflection, then infrared reflectance is improved, but visible light transmission may be compromised
Solution Approach 1:
The patent uses composite materials by combining polymeric layers with high refractive indices and fluoropolymer layers with low refractive indices in an alternating multilayer structure. This composite approach creates optimized optical interference conditions that simultaneously achieve high infrared reflectance and high visible light transmission, as the different materials contribute different optical properties that work together to resolve the contradiction.
3Illumination intensity
If fluoropolymer layers are used to reduce visible reflection, then visible light transmission is improved, but maintaining interlayer adhesion becomes challenging
Solution Approach 1:
The patent addresses the adhesion challenge by carefully selecting fluoropolymer materials and combining them with compatible polymeric layers in a composite multilayer structure. The selection of materials with appropriate surface properties and chemical compatibility ensures sufficient interlayer adhesion while maintaining the low refractive index properties of fluoropolymers that enable high visible light transmission.
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 film achieves high IR light reflectance (50-100%) and high visible light transmission (70-90%) with minimal UV absorption, maintaining transparency and effective solar heat rejection while preventing delamination and color non-uniformity.
Implementation Method 1
The plurality of optical polymeric layers are arranged to reflect light by constructive and destructive interference
Data Source
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AI summary
Multilayer infrared (IR) reflecting films are provided. An optical repeating unit of the film include a plurality of optical polymeric layers arranged to reflect light by constructive and destructive interference. Optical layer A is a high refractive index polymeric layer, and optical layer B is a low refractive index isotropic polymeric layer containing fluoropolymers. The film has an average reflectance of about 50% to about 100% in a near infrared wavelength range of about 850 nm to about 1850 nm, and an average transmission of about 70% to about 90% in a visible light range.