Titanium Dioxide Pigment Coating with Segmented SiO2 and Al2O3 Layers
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Solution Overview
Problem
Existing methods for surface treating titanium dioxide pigment particles with a dense silicon dioxide shell and aluminum oxide layer fail to produce clearly separated layers, leading to impaired brightening power, gloss, and dispersibility due to the incorporation of Al2O3 into the SiO2 layer.
Innovation Solution
A process involving an aqueous suspension of inorganic particles, where a separate, dense silicon dioxide layer is applied, followed by washing, drying, and heat treatment, then re-suspension for additional coating with aluminum oxide, with drying at temperatures over 100°C and heat treatment between 200°C and 850°C to form a pure, closed Al2O3 layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dense silicon dioxide shell is applied to titanium dioxide particles, then photochemical stability is improved, but brightening power and dispersibility deteriorate
Solution Approach 1:
The coating is divided into multiple separate layers: an inner dense silicon dioxide layer for photochemical stability, and an outer aluminum oxide layer for brightening power and dispersibility. This segmentation allows each layer to perform its specific function without compromising the other properties.
Solution Approach 2:
Different regions of the coating have different compositions and properties. The inner layer has high silicon dioxide content for stability, while the outer layer has high aluminum oxide content for optical properties. This local differentiation resolves the contradiction by assigning specific functions to specific regions.
2Reliability
If sequential precipitation of SiO2 and Al2O3 layers is performed, then photochemical stability is improved, but layer separation deteriorates due to Al2O3 incorporation into SiO2 layer
Solution Approach 1:
The silicon dioxide layer is formed first and allowed to dry and heat-treat before aluminum oxide precipitation begins. This preliminary action creates a stable, pre-densified barrier that prevents aluminum oxide from incorporating into the silicon dioxide layer during subsequent coating, achieving both stability and clear layer separation.
Solution Approach 2:
The process maintains continuous control over layer formation by keeping the suspension acidic during aluminum oxide precipitation and ensuring the silicon dioxide layer is already densified. This continuous useful action prevents unwanted incorporation and ensures distinct layer boundaries throughout the coating process.
3Manufacturing precision
If drying temperature is increased above 100°C, then SiO2 layer densification is improved, but particle aggregation may increase
Solution Approach 1:
The drying temperature is optimized to a specific range above 100°C that achieves sufficient SiO2 layer densification without causing excessive particle aggregation. This parameter change balances the competing requirements of layer quality and particle stability.
Solution Approach 2:
The system utilizes the composite nature of the coating suspension, where the acidic environment and specific drying conditions work together to densify the SiO2 layer while the aluminum oxide present in the suspension helps prevent particle aggregation during drying.
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
This method enhances the brightening power, dispersibility, and acid solubility of titanium dioxide pigment particles by forming a dense, separate Al2O3 layer, improving the isoelectric point and maintaining particle size, while reducing acid solubility and preventing mixed layer formation.
Implementation Method 1
a separate, dense silicon dioxide layer is applied
Implementation Method 2
the drying takes place at a temperature of more than 100 °C
Implementation Method 3
the heat treatment takes place at a temperature of 200 °C to 850 °C
Implementation Method 4
coated with at least one further inorganic compound... forming a dense, separate Al2O3 layer
Data Source
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AI summary
The invention relates to a method for surface coating of inorganic particles in aqueous phase, in particular of titanium oxide pigment particles with a dense silicon dioxide shell and at least one additional inorganic compound, in particular with aluminum oxide, wherein the coating extensively consists of separate layers. The method is characterized in that, following application of the silicon dioxide layer, the particles are separated from the suspension, washed, and heat-treated and then pasted into an aqueous suspension again and coated with at least one additional inorganic compound. The heat treatment preferably occurs at temperatures from 400°C to 800°C. Titanium dioxide pigment particles treated with SiO2 and Al2O3 according to the invention are characterized by improved tint reducing power, reduced acid solubility, and an isoelectric point shifted to higher pH values.