# US 8,570,639 B2 · Electrophoretic liquid, image display medium, and image display device

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- Number: US 8,570,639 B2
- Document ID: US8570639B2
- Status: Granted
- Kind: B2
- Application number: 13/139,603
- Filed: 2009-11-26
- Published: 2011-10-20
- Granted: 2013-10-29
- Earliest claimed: 2009-01-13
- Assignees: Ricoh Company, Ltd.; Chiba University
- Applicants: Masahiro Masuzawa; Takashi Kitamura; Yoshitaku Yoshimatsu
- Inventors: Masahiro Masuzawa; Takashi Kitamura; Yoshitaku Yoshimatsu
- Web page: https://patentgrep.com/patent/US8570639B2

## CPC

- G02F 1/167: by electrophoresis
- G02F 1/1675: Constructional details
- G02F 1/16757: Microcapsules
- G02F 1/16762: having three or more electrodes per pixel
- G02F 2001/1678: {characterised by the composition or particle type}
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS

## Abstract

An electrophoretic liquid includes a first electrophoretic particle, a second electrophoretic particle having a polarity opposite to that of the first electrophoretic particle, a non-electrophoretic particle, and a transparent dispersion medium. In the electrophoretic liquid, the first, second, and non-electrophoretic particles are dispersed in the transparent dispersion medium.

## Claims

### Claim 1

An image display medium comprising:
a plurality of display elements, each display element amongst the plurality of display elements comprising an electrophoretic liquid comprising:
a first electrophoretic particle,
a second electrophoretic particle having a polarity opposite to that of the first electrophoretic particle,
a non-electrophoretic particle, and
a transparent dispersion medium;
a first transparent electrode;
a second electrode; and
a third electrode,
wherein the first, second, and non-electrophoretic particles are dispersed in the transparent dispersion medium,
wherein in said each display element, the first electrode is arranged so as to face the second electrode and the third electrode, and
wherein absorbance of the electrophoretic liquid is one or more in an entire wavelength range of 400 to 700 nm in a case where an optical length is determined as a distance between the first electrode and the second and third electrodes, and
wherein a ratio of an absolute value of a zeta potential of the first electrophoretic particle to that of a zeta potential of the non-electrophoretic particle is in a range of 2 to 100,
wherein the first particle is made of surface-modified titanium dioxide, a surface of the titanium dioxide having been modified with a silane coupling agent having a methoxy group and additionally having been polymerized with a monomer having a lauryl group,
wherein the second particle is made of at least one of (a) surface-modified carbon black, a surface of the carbon black having been modified with a diazo coupling agent having a vinyl group and additionally having been polymerized with a monomer having a 2-ethylhexyl group, and (b) surface-modified titanium black, a surface of the titanium black having been modified with a silane coupling agent having a methoxy group and additionally having been polymerized with monomers having a lauryl group,
wherein the non-electrophoretic particle is made of at least one of polyvinylnaphthalene, polyvinylcarbazole and surface-modified titanium dioxide, the titanium dioxide having been coated with polyvinylnaphthalene, and
wherein the dispersion medium includes a nonpolar solvent and a dye.

### Claim 2 (depends on 1)

The image display medium as claimed in claim 1,
wherein a first one of the plurality of display elements contains the electrophoretic liquid having the dispersion medium colored with yellow;
a second one of the plurality of display elements contains the electrophoretic liquid having the dispersion medium colored with cyan; and
a third one of the plurality of display elements contains the electrophoretic liquid having the dispersion medium colored with magenta.

### Claim 3 (depends on 1)

The image display medium as claimed in claim 1,
wherein a first one of the plurality of display elements contains the electrophoretic liquid having the dispersion medium colored with red;
a second one of the plurality of display elements contains the electrophoretic liquid having the dispersion medium colored with green; and
a third one of the plurality of display elements contains the electrophoretic liquid having the dispersion medium colored with blue.

### Claim 4 (depends on 1)

An image display device comprising the image display medium as claimed in claim 1.