Colour-neutral wear-resistant coating, substrate with such a neutral wear-resistant coating and process for producing the same
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Solution Overview
Problem
Conventional wear protection layers for glass and glass ceramic substrates face challenges in maintaining scratch resistance, thermal stability, and color neutrality, particularly under varying lighting conditions, due to differences in thermal expansion coefficients and optical properties.
Innovation Solution
A temperature-stable, hard wear protection layer with a low chroma in the CIELAB color system and controlled light transmittance is applied over the substrate, comprising multiple sub-layers with specific refractive index gradients and materials like titanium aluminum carbonitride, ensuring high hardness, elasticity, and chemical inertness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard coating based on aluminum nitride or boron nitride is applied to glass ceramic substrates, then scratch resistance is improved, but the coating becomes unsuitable due to excessively high coefficients of thermal expansion
Solution Approach 1:
The patent employs composite coating systems combining multiple materials (e.g., aluminum oxide and silicon oxide layers, or titanium aluminum carbonitride with specific compositions) to achieve both high hardness for scratch resistance and low thermal expansion coefficient matching the glass ceramic substrate. The composite structure allows optimization of both mechanical and thermal properties that single materials cannot provide.
Solution Approach 2:
The patent modifies the chemical composition and stoichiometry of the coating materials (e.g., varying Al2O3-SiO2 ratios, controlling oxygen content in TiAlON layers) to adjust the coefficient of thermal expansion to match the substrate while maintaining hardness. By changing material parameters, the coating achieves compatibility with the substrate's thermal properties.
2Strength
If a wear-resistant coating is applied to glass or glass-ceramic substrates, then scratch resistance is improved, but the color appearance varies under different lighting conditions
Solution Approach 1:
The patent creates coatings with homogeneous optical properties by controlling material composition and structure uniformly throughout the layer. The wear-resistant layers are designed to have consistent refractive indices and minimal absorption variations across the visible spectrum, ensuring uniform color appearance under different lighting conditions while maintaining scratch resistance.
3Strength
If a hard coating is applied to increase scratch resistance, then mechanical protection is improved, but the coating exhibits high layer stresses due to differing coefficients of thermal expansion
Solution Approach 1:
The patent adjusts the chemical composition and physical parameters of the coating materials to match the thermal expansion characteristics of the glass ceramic substrate. By changing the material parameters (composition, density, crystalline structure), the coating's thermal expansion coefficient is optimized to minimize differential expansion and resulting layer stresses during temperature cycles.
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 wear protection layer that maintains a homogeneous color appearance and high mechanical resistance across different lighting conditions and temperatures, while being chemically inert and free from hazardous substances, ensuring long-term durability and aesthetic consistency.
Implementation Method 1
The wear-resistant layer exhibits a chromaticity in the CIELAB color system of C* less than 14, preferably less than 7, and particularly preferably less than 4 when illuminated by light
Implementation Method 2
measured in reflectance with light of standard illuminant type A or standard illuminant type C
Implementation Method 3
a temperature-stable, hard wear protection layer... is applied over the substrate
Data Source
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AI summary
The present invention relates to a color-neutral wear-resistant coating for substrates. The invention further relates to a substrate with such a color-neutral wear-resistant coating and a method for its production. The substrate comprises glass or glass-ceramic, wherein the wear-resistant coating is formed over the entire surface or largely over the entire surface of at least one surface of the substrate and has a chromaticity in the CIELAB color system of C* less than 14, preferably less than 7, and particularly preferably less than 4 when illuminated, measured in reflectance under standard illuminant A or standard illuminant C or under blackbody radiation with a temperature between 2,500 K and 10,000 K, and wherein the wear-resistant coating has a light transmittance in the visible wavelength spectrum of less than 60%, preferably less than 50%, and particularly preferably less than 40%.