Electrophoretic inks, which are suspensions of colorant particles that are controllably concentrated and dispersed by applied electric fields, are the leading commercial technology for high-quality reflective displays. Extending the state of the art for high-fidelity color in these displays requires improved understanding and control of the colloidal systems. In these inks, reverse micelles in nonpolar media play key roles in media and particle charging. Here we investigate the effect of surfactant structure on reverse micelle size and charging properties by synthesizing different surfactants with variations in polyamine polar head groups. Small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) were used to determine the micelle core plus shell size and micelle hydrodynamic radius, respectively. The results from SAXS agreed with DLS and showed that increasing polyamines in the surfactant head increased the micelle size. The hydrodynamic radius was also calculated on the basis of transient current measurements and agreed well with the DLS results. The transient current technique further determined that increasing polyamines increased the charge stabilization capability of the micelles and that an analogous commercial surfactant OLOA 11000 made for a lower concentration of charge-generating ions in solution. Formulating magenta inks with the various surfactants showed that the absence of amine in the surfactant head was detrimental to particle stabilization and device performance.
A four‐particle electrophoretic display (EPD), Spectra™ 3100, was released in 2021. It targets electronic shelf label applications and signage applications by providing four primary optical states of black, white, red, and yellow, as well as dithering capability to show graphic images. Specially engineered black, white, red, and yellow particles in the electrophoretic ink respond to different electric fields to show pigment intrinsic colors on the display. The imaging film produced from this technology can reach a typical contrast ratio of 30:1 while maintaining a maximum driving voltage of ±15 V. The vibrant red and yellow colors are ideal for highlighting. Consistent optical performances are achieved for all four optical states across the operating temperature range of 0°C to 40°C for a typical indoor environment. The electrophoretic ink is coated and sealed in a thin‐film Microcup® structure using an additive and high yield roll‐to‐roll manufacturing process to produce the imaging film. Active matrix (AM) module integration follows the conventional EPD module production process of lamination between the imaging film and thin‐film transistor (TFT) backplane.
Reflective display technologies aim to enable the delivery of dynamic digital content to devices that have the look and feel of ink on paper. We are presenting herein a novel device architecture design and proprietary electrically addressable inks, which enable low power, disruptive, print-like full color reflective display that can exceed the chromaticity represented by the Specifications for Newsprint Advertising Production (SNAP) standard. We are approaching the challenge of generating bright high-quality reflective color images from the perspective of printing by stacking electro-optic layers of subtractive colorants to address every available color at every location. Using in-plane optical effects, our novel media technology provides fast switching between clear and color states. Thin, flexible electronic media based on this technology has been fabricated by imprinting three-dimensional micro-scale structures with a continuous roll-to-roll (R2R) manufacturing platform. HP's combination of novel device architecture, proprietary inks, and R2R manufacturing platform enables the required attributes for electronic media such as flexibility, robustness, low power, transparency, print-quality color, and scalability at low cost. The structure property relationship of surfactants has been carried out; their impact on performance of display devices has been studied. These results have been applied to improve the performance of electronic inks. We have demonstrated 3-layer stacked segmented reflective display prototypes, as well as pixelated stacked color reflective display prototypes. The innovations described in this paper are applicable to electronic skins for customizable electronic surfaces and are currently being developed further for electronic paper and signage markets.
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