Plastic ND Filter with NiOx Moisture Barrier
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Solution Overview
Problem
Plastic substrates in neutral density filters for eyeglasses are prone to moisture absorption, which affects the adhesion of light and dielectric films, leading to reduced weather resistance and durability.
Innovation Solution
A neutral density filter with a plastic base, featuring an optical multilayer film structure that includes light absorbing and antireflection layers formed from unsaturated metal oxides like NiOx and CoOx, with specific layer thicknesses and adjacent layers made from different materials to manage moisture permeation and stress, enhancing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a plastic substrate is used for the ND filter, then weight is reduced and break resistance is improved, but moisture absorption increases leading to reduced adhesion of films and deteriorated weather resistance
Solution Approach 1:
An unsaturated metal oxide film (NiOx or CoOx) is introduced as an intermediary layer between the plastic substrate and the light absorbing film. This intermediate layer acts as a barrier to moisture permeation from the substrate while maintaining adhesion of the overlying films, thereby preventing deterioration of weather resistance despite using a moisture-absorbing plastic substrate
Solution Approach 2:
The patent employs a composite multilayer structure combining plastic substrate, unsaturated metal oxide film, light absorbing film, and dielectric films. This composite construction leverages the moisture-blocking properties of the metal oxide layer to protect the entire film stack from moisture-induced adhesion failure, resolving the contradiction between using plastic for durability and preventing moisture-related degradation
2Reliability
If the NiOx layer and CoOx' layer are made with specific thin thickness (not greater than 6 nanometers), then adhesion is improved and stress is managed, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise thickness parameters for the unsaturated metal oxide film (not greater than 6 nanometers) to optimize its moisture-blocking function while maintaining adhesion. This parameter control ensures the film is thin enough to manage stress and prevent cracking, yet sufficiently continuous to block moisture permeation from the substrate
3Reliability
If adjacent layers are made from different materials, then moisture permeation is managed and stress is distributed, but device complexity increases
Solution Approach 1:
The patent segments the film structure into distinct functional layers with different materials: unsaturated metal oxide film for moisture blocking, light absorbing film for neutral density filtering, and dielectric films for optical performance. This segmentation allows each layer to be optimized for its specific function while collectively achieving improved durability through differentiated material properties
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 provides a neutral density filter with improved durability and weather resistance for eyeglasses, ensuring uniform light absorption and antireflection while maintaining visibility equivalent to naked eyes, with enhanced resistance to moisture and environmental factors.
Implementation Method 1
the plastic easily absorbs moisture, and the absorbed moisture is easily released
Implementation Method 2
a filter that uniformly absorbs at least light (visible light) having a wavelength in a visible region
Implementation Method 3
a plurality of light absorbing films and a plurality of dielectric films are layered and formed on one or both surfaces of a transparent substrate
Data Source
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AI summary
[Object] Provided is a ND filter and a ND filter, for spectacles, each of which has a base formed from plastic and excellent durability. [Solution] In a ND filter, a base is formed from plastic, and a light absorbing film having a plurality of layers is disposed on at least one surface of the base. The layer (initial layer) that is a first layer from the base side in the light absorbing film_is a SiO2 layer or an Al2O3 layer. The light absorbing film includes one or more NiOx layers formed from NiOx (x is not less than 0 and not greater than 1). At least one of the NiOx layers is disposed between a base-side adjacent layer which is the layer adjacent to the at least one of the NiOx layers on the base side, and an opposite-side adjacent layer which is formed from a material different from the base-side adjacent layer and which is the layer adjacent to the at least one of the NiOx layers on the opposite side.