Pigment Core Polymer Particles for Electrophoretic Displays
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Solution Overview
Problem
There is a need for improved electrophoretic fluids and coloured polymer particles that can be easily prepared and dispersed in non-polar media, with enhanced reflectivity and stability for use in electrophoretic displays, particularly for electronic paper applications.
Innovation Solution
The development of particles comprising a pigment core encapsulated by a polymer, which includes monomer units of polymerisable dye, steric stabiliser, co-monomer, and optionally charged co-monomer, allowing for controlled size, reflectivity, and density, and featuring a surfactant for improved dispersibility and stability, eliminating the need for drying processes and enabling easy dispersion in non-polar solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional polymer particles are used in electrophoretic displays, then the particles can be dispersed in dielectric media, but the reflectivity is insufficient and multiple drying processes are required
Solution Approach 1:
The patent employs composite particles combining inorganic pigment cores (titanium dioxide) with organic polymer shells containing dye molecules. This composite structure provides both the high reflectivity needed for bright displays and the coloration required for visual output, while the polymer matrix eliminates the need for separate drying processes by providing inherent stability in non-polar media
Solution Approach 2:
The patent modifies particle parameters by controlling the polymer shell composition (including steric stabilizers and crosslinking co-monomers) to achieve optimal dispersibility in non-polar media without requiring drying. The polymerizable dye and steric stabilizer are incorporated during synthesis to create particles with controlled size, reflectivity, and stability
2Illumination intensity
If particles are designed for high reflectivity with pigment cores, then brightness is improved, but particle stability in non-polar media may be compromised
Solution Approach 1:
The patent introduces steric stabilizer molecules as intermediaries between the inorganic pigment core and the non-polar media. These stabilizers prevent aggregation and ensure stable dispersion while allowing the pigment core to maintain its high reflectivity. The steric stabilizer acts as a protective layer that mediates interactions between the particle and surrounding medium
Solution Approach 2:
The composite structure combines inorganic pigment cores with organic polymer shells containing steric stabilizers and crosslinking agents. This composite design provides both high reflectivity from the pigment and stability from the polymer matrix, creating particles that maintain their properties in non-polar media without aggregation or degradation
3Manufacturing precision
If multiple drying processes are used to prepare particles, then particle purity is improved, but manufacturing time and cost increase
Solution Approach 1:
The patent extracts and eliminates the drying process from the particle preparation methodology. By designing particles that are inherently stable in non-polar media through polymer shell formation with steric stabilizers, the patent removes the need for time-consuming drying steps while maintaining particle purity and preventing aggregation
Solution Approach 2:
The patent achieves continuous useful action by forming the polymer shell during a single synthesis step that also completes particle formation. The polymerizable components are incorporated in one operation, eliminating the need for sequential drying and processing steps, thereby reducing manufacturing time while maintaining precision
4Speed
If polymer particles are synthesized with specific composition for EPD, then electrophoretic mobility is improved, but dispersibility in non-polar media becomes difficult
Solution Approach 1:
The patent applies local quality by incorporating steric stabilizer molecules specifically at the particle surface and interface with non-polar media. This localized modification enhances dispersibility and stability in the surrounding medium without affecting the core particle's electrophoretic properties or mobility
Solution Approach 2:
The composite particle structure combines electrophoretically active components with steric stabilizers and crosslinking agents in the polymer shell. This composite design provides both good electrophoretic mobility for display operation and enhanced dispersibility in non-polar media through the steric stabilization provided by the polymer matrix
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 resulting particles exhibit increased reflectivity, improved bistability, and enhanced mobility, resulting in brighter and more appealing displays with controlled optical properties, while simplifying the manufacturing process by eliminating the need for multiple steps and expensive drying processes.
Implementation Method 1
polymer comprising monomer units of at least one polymerisable dye, at least one polymerisable steric stabiliser
Implementation Method 2
particles comprising at least one surfactant
Implementation Method 3
charged particles move to the electrode of opposite polarity
Data Source
AI summary
This invention relates to particles comprising a pigment core particle encapsulated by a polymer, a process for their preparation, electrophoretic fluids comprising such particles, and electrophoretic display devices comprising such fluids.