Optical Laminate AR Layer for Stable Reflection Color
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Solution Overview
Problem
Conventional optical laminates installed on image display devices exhibit color irregularities and coloration of reflected light when the viewing angle is altered, which is undesirable.
Innovation Solution
An optical laminate comprising a transparent substrate, a hard coat layer, and an anti-reflective layer with alternating low and high refractive index material layers, designed to satisfy specific conditions in the CIE-Lab color system to minimize a* and b* values of reflected light, ensuring low saturation and hue stability across varying viewing angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional optical laminates are used on image display devices, then the device can be manufactured with standard materials and processes, but color irregularities and coloration of reflected light occur when viewing angle is altered
Solution Approach 1:
The anti-reflective layer is divided into multiple sub-layers with different refractive indices (first anti-reflective sub-layer with lower refractive index, second anti-reflective sub-layer with higher refractive index). This segmentation allows each sub-layer to contribute differently to the overall optical performance, enabling control over reflected light coloration while maintaining manufacturability through standard multi-layer deposition processes.
Solution Approach 2:
The patent specifies precise refractive index ranges for the different sub-layers (first sub-layer: 1.20-1.40, second sub-layer: 1.40-1.60) and thickness relationships (second sub-layer thickness is 0.5-2.0 times the first sub-layer thickness). By optimizing these parameters, the patent achieves color consistency across viewing angles while using materials and processes that remain manufacturable.
2Device complexity
If the anti-reflective layer uses a simple single-layer structure, then the manufacturing process is simpler, but it cannot effectively suppress coloration and color irregularities across different viewing angles
Solution Approach 1:
The anti-reflective layer is segmented into multiple sub-layers with different refractive indices. The first anti-reflective sub-layer has a lower refractive index (1.20-1.40) while the second anti-reflective sub-layer has a higher refractive index (1.40-1.60). This segmentation enables the structure to suppress coloration and color irregularities across different viewing angles while maintaining reasonable manufacturing complexity through standard multi-layer deposition processes.
Solution Approach 2:
The patent employs a composite anti-reflective layer structure combining materials with different refractive indices. The first sub-layer uses materials with lower refractive index (such as silicon oxide) while the second sub-layer uses materials with higher refractive index (such as titanium oxide or tantalum oxide). This composite structure achieves superior color suppression performance compared to single-layer designs.
3Illumination intensity
If the anti-reflective layer is designed to minimize reflected light at normal incidence, then reflectance at 5° incident angle is reduced, but color irregularities become more pronounced at higher viewing angles
Solution Approach 1:
The patent optimizes the thickness parameters of the anti-reflective sub-layers to achieve a balance between normal incidence reflectance and viewing angle performance. The second anti-reflective sub-layer thickness is specifically designed to be 0.5-2.0 times the first sub-layer thickness, which optimizes the optical path differences to maintain hue consistency across viewing angles while controlling overall reflectance.
Solution Approach 2:
Different regions of the anti-reflective layer (first and second sub-layers) have different optical properties tailored to specific functions. The first sub-layer with lower refractive index primarily addresses normal incidence reflectance, while the second sub-layer with higher refractive index specifically targets color consistency at oblique viewing angles. This local differentiation of optical properties resolves the contradiction between normal incidence and viewing angle performance.
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 optical laminate effectively suppresses coloration and color irregularities of reflected light, maintaining consistent hue and low saturation even with changes in viewing angle, thereby enhancing the visual appearance of image display devices.
Implementation Method 1
an anti-reflective layer 4 which is a laminate of a low refractive index material layer 4a, 4c and a high refractive index material layer 4b formed from a material having a higher refractive index than the low refractive index material layer 4a, 4c laminated in an alternating arrangement
Implementation Method 2
when a light with a wavelength of 380 nm to 780 nm from a standard light source D65 is incident upon the optical laminate, the a* value and the b* value in the CIE-Lab color system of the reflected light satisfy (condition A) to (condition C) and (condition E) described below
Data Source
Figure 1~2
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Figure 4
AI summary
In this optical laminate (1), a transparent substrate (2), a hard coat layer (3) and an anti-reflective layer (4) are laminated in that order, the anti-reflective layer (4) is a laminate having low refractive index material layers (4a, 4c) and high refractive index material layers (4b) laminated in an alternating arrangement, the a* value and the b* value of reflected light, when light with a wavelength of 380 nm to 780 nm is incident upon the optical laminate, satisfy (condition A) to (condition C) and (condition E), and the anti-reflective layer is a sputtered layer. (Condition A) when the light is incident at an incident angle of 30° to 40° relative to the surface of the optical laminate, the a* value and the b* value of the reflected light each have an absolute value of not more than 3. (Condition B) when the light is incident at incident angles of 5°, 10°, 20° and 30° relative to the surface of the optical laminate, the a* values and the b* values of the reflected light satisfy a prescribed inequality formula. (Condition C) when the light is incident at an incident angle of 5° relative to the surface of the optical laminate, one or both of the a∗ value and the b* value of the reflected light have an absolute value of 5 or greater, and the a* value and the b* value have absolute values of not more than 15. (Condition E) when the light is incident at an incident angle of 5° to 25°, the a* value and the b* value in the CIE-Lab color system of the reflected light are within the same quadrant in the a*b* plane.