Cholesteric Reflection Film for Bright Head-Up Display Windshields
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Solution Overview
Problem
Existing head-up display systems face challenges in achieving high visible light transmittance and maintaining image brightness while ensuring a transparent external tint, as reducing reflectivity to meet legal transmittance requirements often compromises display image visibility.
Innovation Solution
A reflection film comprising a selective reflection layer formed of cholesteric liquid crystal layers with specific reflectivity and bandwidth characteristics, combined with a polarization conversion and retardation layer, to enhance transmittance and image brightness while maintaining tint transparency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the reflectivity is lowered to achieve high transmittance, then the external tint transparency is improved, but the display image visibility is compromised
Solution Approach 1:
The patent uses a composite structure consisting of multiple selective reflection layers with different optical properties. Each layer is designed with specific reflectivity and transmittance characteristics for different wavelengths. The composite structure achieves overall high transmittance while maintaining display visibility through the coordinated reflection properties of individual layers, effectively combining transparency and image visibility requirements
2Illumination intensity
If multiple light reflection layers with different central reflection wavelengths are used, then the color rendering is improved, but the device complexity increases
Solution Approach 1:
The patent segments the spectral reflection function into discrete wavelength bands, with each layer responsible for a specific range (e.g., blue 400-500nm, green 500-600nm, red 600-700nm). This segmentation approach improves color rendering by ensuring adequate reflection in each spectral region while keeping the number of layers manageable through targeted wavelength division rather than using numerous narrow-band layers
Solution Approach 2:
Each selective reflection layer is designed to serve multiple functions: it provides wavelength-specific reflection for color rendering, contributes to overall transmittance control, and maintains display image visibility. This multi-functionality reduces the need for additional specialized layers, thereby limiting the increase in device complexity while achieving good color rendering
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 reflection film achieves a transmittance of 70% or more with improved display image brightness and tint transparency, even when viewed from various angles, by optimizing reflectivity and bandwidths across different wavelength ranges.
Implementation Method 1
a selective reflection layer formed of a cholesteric liquid crystal layer with a cholesteric liquid crystalline phase immobilized
Implementation Method 2
the selective reflection layer satisfies all of requirements (i) to (iii), (i) in a wavelength range of 400 nm or more and less than 500 nm, a maximum value of a natural light reflectivity is 10% to 25%
Data Source
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AI summary
Provided are a reflection film, which enables high visible light transmittance, an increase in the brightness of a display image, and favorable transparency of an external tint, a windshield glass, and a head-up display system. The reflection film includes a selective reflection layer formed of a cholesteric liquid crystal layer with a cholesteric liquid crystalline phase immobilized. In each of a wavelength range of 400 nm or more and less than 500 nm and a wavelength range of 500 nm or more and less than 600 nm, a maximum value of a natural light reflectivity is 10% to 25%, the greatest difference between the greatest maximum value and the smallest minimum value of the natural light reflectivity is 3% or more, and a total value of wavelength bandwidths in a region where a reflectivity is higher than an average value of the maximum value and the minimum value of the natural light reflectivity is 20 nm to 80 nm. In a wavelength range of 600 nm or more and 800 nm or less, a maximum value of a natural light reflectivity is 10% to 25%, and a total value of wavelength bandwidths in a region where a reflectivity is higher than an average value of the maximum value and the minimum value of the natural light reflectivity is 120 nm or more.