Coloured Polymer Particles for Electrophoretic Displays

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Solution Overview

Problem

There is a need for improved electrophoretic fluids and coloured polymer particles with enhanced photostability for use in electrophoretic displays, particularly in non-polar media, as existing particles tend to degrade over time, especially when exposed to ambient light and sunlight.

Innovation Solution

The development of coloured polymer particles incorporating polymerisable hindered amine light stabilisers (HALS) with polymerisable groups, which are chemically entangled into the particles during dispersion polymerisation, providing improved light stability and preventing leaching, thus enhancing the photostability of the particles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional coloured polymer particles are used in electrophoretic displays, then the device can display colours, but the particles degrade over time when exposed to ambient light and sunlight, reducing photostability

Engineering Contradiction:

ImprovephotostabilityVSAvoidparticle lifetime

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent applies preliminary action by incorporating light stabilisers (HALS) into the polymer particles during the polymerisation process itself, before the particles are deployed in the electrophoretic display. This ensures the stabilisers are already present and active when the particles are exposed to light, preventing degradation from the outset rather than applying protection afterward.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses light stabilisers (specifically hindered amine light stabilisers with polymerisable groups) as intermediary substances that mediate between the harmful light exposure and the polymer particle matrix. These stabilisers act as chemical intermediaries that absorb and dissipate light energy, protecting the dye molecules embedded in the particle from photodegradation.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If light stabilisers are incorporated into polymer particles, then photostability improves, but the complexity of particle preparation increases

Engineering Contradiction:

Improvelight stabilityVSAvoidparticle preparation process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges multiple functions into a single integrated process by combining the light stabiliser incorporation, dye embedding, and polymerisation steps into one simultaneous reaction process. The HALS monomer is added to the polymerisation mixture along with the dye and other monomers, allowing all components to be incorporated into the particle structure in a single step rather than requiring separate processing steps.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent applies parameter changes by modifying the chemical structure of the light stabiliser to include polymerisable groups (such as vinyl or epoxy groups), which changes the physical-chemical parameters of the stabiliser from a simple additive to a reactive monomer that can be co-polymerised with the particle matrix, thereby simplifying the overall process.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If conventional dyes are used in polymer particles, then the particles can be coloured, but the dyes degrade and lose colour fastness when exposed to light

Engineering Contradiction:

Improvecolour fastnessVSAvoidlight-induced degradation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The light stabiliser acts as a chemical intermediary between the light source and the dye molecules. It absorbs the harmful light energy and dissipates it harmlessly through its own molecular structure, preventing the light from reaching and degrading the dye chromophores, thereby maintaining colour fastness.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the potentially harmful light exposure into a beneficial effect by using the light energy to drive the polymerisation of the HALS monomer, creating a crosslinked network that further protects the dye. The light that would normally cause degradation is instead utilized to enhance the protective structure.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 incorporation of HALS into the polymer particles significantly improves their photostability, including light-fastness and prevention of degradation, particularly for cyan and black dyes, ensuring stable performance in bright sunlight conditions without hindering the free-radical polymerisation process.

Implementation Method 1

the free-radical polymerisation process

Methodology Applied

Scientific EffectFree-radical polymerisation: Photopolymerisation

Implementation Method 2

If a voltage is applied between the electrodes, charged particles move to the electrode of opposite polarity

Methodology Applied

Scientific EffectElectrophoresis: Electrophoresis

Data Source

PatentUS10428220B2Particles for electrophoretic displays

Publication Date: 2019.10.01 E INK CORP

AI summary

This invention relates to polymer particles, a process for their preparation, the use of these particles for the preparation of an electrophoretic device, and electrophoretic displays comprising such particles.