Density-Matched Composite Pigment Particles for Electrophoretic Fluids
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Solution Overview
Problem
Current electrophoretic display fluids face performance issues due to pigment particles having a density higher than the solvent, leading to poor grey level bistability, vertical driving, and settling phenomena.
Innovation Solution
The development of composite pigment particles with a core pigment coated by a shell and steric stabilizers, where the density of the composite particles matches that of the solvent, typically less than 2 g/cm3, and the shell is formed from inorganic or organic materials, ensuring compatibility and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pigment particles with high density are used in electrophoretic fluid, then the pigment particles can provide strong color contrast and visibility, but they cause poor grey level bistability, vertical driving, and settling phenomena
Solution Approach 1:
The patent applies composite materials by creating composite pigment particles consisting of a dense inorganic pigment core surrounded by a low-density polymer shell. This composite structure allows the particle to maintain strong color contrast from the pigment core while achieving density matching with the solvent through the low-density shell, thereby eliminating settling phenomena and improving bistability.
Solution Approach 2:
The patent changes the density parameter of the pigment particles by coating them with polymer shells of controlled thickness and composition. By adjusting the shell thickness and polymer type, the overall particle density is tuned to match the solvent density, transforming the particles from high-density settling particles to density-matched stable particles while preserving color contrast.
2Illumination intensity
If pigment particles with high density are used in electrophoretic fluid, then the pigment particles can provide strong color contrast, but they cause vertical driving and settling phenomena
Solution Approach 1:
The composite pigment particle structure with low-density polymer shell compensates for the high density of the pigment core, achieving overall density matching with the solvent. This eliminates the gravitational settling while the pigment core maintains its color contrast function.
Solution Approach 2:
The low-density polymer shell acts as a counterweight to the high-density pigment core, reducing the overall particle density to match the solvent density. This counterbalancing effect prevents settling phenomena while preserving the optical properties of the pigment.
3Stability of the object's composition
If a shell is coated over the core pigment particle to match density, then the composite pigment particles achieve density matching with the solvent, but the shell material must be chemically stable and compatible with other materials
Solution Approach 1:
The patent applies different materials with specific local functions: the inorganic pigment core provides color contrast, the polymer shell provides density matching and chemical stability, and the surfactant layer provides interfacial compatibility. Each layer is optimized for its specific function while maintaining compatibility with adjacent layers.
Solution Approach 2:
The multi-layer composite structure combines materials with complementary properties: the pigment core for optical properties, the polymer shell for density control and chemical stability, and the surfactant for interfacial compatibility. This composite approach allows simultaneous optimization of multiple 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 density-matched composite pigment particles improve the performance of electrophoretic displays by enhancing bistability, reducing settling, and maintaining chemical stability, thus improving the overall display characteristics.
Implementation Method 1
An electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon influencing charged pigment particles dispersed in a dielectric solvent
Implementation Method 2
each of said composite pigment particles comprises at least a core pigment particle, a shell coated over the core pigment particle and steric stabilizer molecules on the surface of the composite pigment particles
Data Source
AI summary
The present invention is directed to a display fluid comprising charged composite pigment particles dispersed in a solvent. The composite pigment particles have a density which matches to the density of the solvent in which they are dispersed. A display fluid comprising the composite pigment particles provides improved display performance.