Aqueous Colloidal Titanium Dioxide Coatings for Neutral White Color
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Solution Overview
Problem
Conventional titanium dioxide pigments used in automotive coatings exhibit a yellow-gold color at near off-specular angles, limiting the achievement of a pure white look and restricting the creation of pastel colors, due to factors like impurities, particle size distribution, and agglomeration.
Innovation Solution
Aqueous colloidal titanium dioxide dispersions with controlled particle sizes between 30 nm to 220 nm and a narrow particle size distribution span of 0.7 to 1.5 are produced through mechanical grinding and pH adjustment, using dispersing agents to stabilize the particles, resulting in a more neutral white color.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional titanium dioxide pigments are used, then the coating provides white color and hiding power, but the coating exhibits yellow-gold color at near off-specular angles and bluish tint at far off-specular angles, preventing pure white look
Solution Approach 1:
The patent changes the particle size parameter of titanium dioxide from conventional ranges to a specific range of 30-220 nm with a narrow distribution span of 0.7-1.5. This parameter change fundamentally alters the light scattering properties, eliminating the yellow-gold and bluish tints while achieving neutral white appearance at various viewing angles.
Solution Approach 2:
The patent segments the broad particle size distribution of conventional titanium dioxide into a narrow, controlled distribution with span 0.7-1.5. This segmentation ensures uniform light scattering behavior across all particles, preventing the angular color variations caused by heterogeneous particle sizes.
2Illumination intensity
If coarser particle size distribution is used, then the scattering power for red and green light is improved, but blue light is absorbed to a greater extent resulting in yellowish appearance
Solution Approach 1:
The patent optimizes the particle size parameter to the narrow range of 30-220 nm, which is fine enough to scatter all visible wavelengths uniformly including blue light, yet coarse enough to maintain adequate scattering power. This eliminates the yellowish tint caused by preferential blue light absorption in coarser particles.
3Object-generated harmful factors
If fine particle size is used, then the yellowish tint is reduced, but the scattering power for longer wavelengths is lost resulting in reduced hiding power
Solution Approach 1:
The patent identifies and implements the optimal particle size range of 30-220 nm that balances two opposing requirements: fine enough to minimize yellowish tint by scattering blue light effectively, yet coarse enough to maintain strong scattering power for red and green wavelengths, thereby preserving hiding power.
4Ease of manufacture
If titanium dioxide particles are dispersed in aqueous medium, then the coating composition becomes environmentally friendly and easier to apply, but the particles tend to agglomerate reducing dispersion stability
Solution Approach 1:
The patent introduces dispersing agents as intermediary substances that mediate between the hydrophobic titanium dioxide particles and the aqueous medium. These dispersing agents adsorb onto particle surfaces, providing steric or electrostatic repulsion that prevents agglomeration and maintains stable dispersion in water-based formulations.
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 coating compositions with a neutral white color, suitable for automotive coatings, enhancing the range of achievable colors and improving hiding power while maintaining scattering efficiency.
Implementation Method 1
B. grinding the pre-mix obtained in step A by use of a bead mill or shaker mill until titanium dioxide particles are obtained
Implementation Method 2
one or more dispersing agents comprising groups which bind to the titanium dioxide particles
Implementation Method 3
one or more pH value adjusting compounds
Implementation Method 4
the particle size distribution span [(D90-D10)/(D50)] in the range from 0.7 to 1.5... providing the coating compositions with a white color
Data Source
Figure 1
AI summary
The invention relates to an aqueous colloidal titanium dioxide dispersion preferably having a pH value in the range of 6.2 to 7.8 at 25 °C and comprising titanium dioxide particles, the titanium particles having a Z-average particle size in the range from 30 nm to 220 nm as determined by dynamic light scattering and a particle size distribution span [(D90-D10)/(D50)] in the range from 0.7 to 1.5; one or more dispersing agents comprising groups which bind to the titanium dioxide particles; one or more organic solvents; and if necessary, one or more pH value adjusting compounds. The invention further relates to a method of preparing such dispersions, a coating composition containing the components of such dispersions, coated substrates and methods of coating the substrates with such dispersions and the use of the dispersions in the manufacture of coating compositions.