ELECTROPHORETIC INK PROVIDING BISTABILITY

Abstract

The present invention refers to an electrophoretic ink, a method for preparing an electrophoretic ink, an electrophoretic display comprising the electrophoretic ink, a smart window comprising the electrophoretic ink as well as the use of the electrophoretic ink in electrophoretic displays or smart windows and the use of at least one surface-treated silica for improving the bistability of an electrophoretic ink.

Claims

1. An electrophoretic ink, comprising a) at least one carrier fluid, b) pigment particles dispersed in the at least one carrier fluid, c) a mixture of charge control agents comprising i) at least one polydimethylsiloxane substituted primary amine and/or polydimethylsiloxane substituted secondary amine and/or polydimethylsiloxane substituted tertiary amine, and ii) at least one polydimethylsiloxane substituted quaternary ammonium with counterion, and d) at least one surface-treated silica.

2. The electrophoretic ink according to claim 1, wherein the at least one carrier fluid is selected from the group consisting of an aliphatic hydrocarbon, a halogenated alkane, a silicon oil and a mixture thereof.

3. The electrophoretic ink according to claim 1, wherein the pigment particles are selected from the group consisting of color pigments, effect pigments, electrically conductive pigments, magnetically shielding pigments, fluorescent pigments, extender pigments, anticorrosion pigments, organic pigments, inorganic pigments, and a mixture thereof.

4. The electrophoretic ink according to claim 1, further comprising at least one dispersing agent.

5. The electrophoretic ink according to claim 1, wherein component i) and component ii) in the mixture of charge control agents are present in a weight ratio [i)/ii)] ranging from 1:10 to 1:1.5.

6. The electrophoretic ink according to 5 claim 1, wherein component i) is a polydimethylsiloxane substituted tertiary amine.

7. The electrophoretic ink according to claim 1, wherein component i) is a compound of Formula (IIa) ##STR00045## where x is an integer ranging from 5 to 20, and/or a compound of the following Formula (IIb) ##STR00046## where x is an integer ranging from 5 to 20 and y is an integer ranging from 0 to 12, and/or a compound of the following Formula (IIc) ##STR00047## where x is an integer ranging from 5 to 20 and y and z are independently an integer ranging from 0 to 12.

8. The electrophoretic ink according to claim 1, wherein component ii) in the mixture of charge control agents is a compound of Formula (III) ##STR00048## where x is an integer ranging from 5 to 20; y and z are independently an integer ranging from 0 to 12 and X.sup. is selected from the group consisting of iodide, bromide, chloride, methyl sulfate anion, and ethylsulfate anion.

9. The electrophoretic ink according to claim 1, wherein component ii) in the mixture of charge control agents is a compound of Formula (IV) ##STR00049## where x is an integer ranging from 5 to 20; y and z are independently an integer ranging from 0 to 12 and X.sup. is selected from the group consisting of iodide, bromide, chloride, methyl sulfate anion, and ethylsulfate anion.

10. The electrophoretic ink according to claim 1, wherein the at least one surface-treated silica i) is at least one surface-treated fumed silica, and/or ii) comprises aluminum oxide in an amount ranging from 0.5 to 22 wt.-%, based on a total weight of the at least one surface-treated silica, and/or iii) comprises a treatment layer on a surface of the at least one surface-treated silica comprising a silicon-containing compound selected from the group consisting of a silane, a reaction product of a silane, a siloxane, a reaction product of a siloxane, a silazane, a reaction product of a silozane, a silicon oil, a reaction product of a silicon oil, and a mixture thereof.

11. The electrophoretic ink according to claim 1, wherein the at least one surface-treated silica has i) a weight median particle size d.sub.50 from 4 to 200 nm, and/or ii) a specific surface area (BET) of from 10 to 400 m.sup.2/g as measured using nitrogen and in accordance with ISO 9277.

12. A method of preparing the electrophoretic ink according to claim 1, the method comprising combining the at least one carrier fluid, the pigment particles, the mixture of charge control agents, the at least one surface-treated silica, and optionally at least one dispensing agent.

13. An electrophoretic display, comprising a) a top layer and a bottom layer, wherein at least one of the top layer and the bottom layer is transparent, and b) an array of cells sandwiched between the top layer and the bottom layer and the cells are at least partially filled with the electrophoretic ink according to claim 1.

14. A smart window, comprising a) a top layer and a bottom layer, wherein the top layer and the bottom layer are transparent, and b) an array of cells sandwiched between the top layer and the bottom layer and the cells are at least partially filled with the electrophoretic ink according to claim 1.

15. (canceled)

16. A method for improving bistability of an electrophoretic ink, the method comprising: introducing at least one surface-treated silica into the electrophoretic ink.

17. The method according to claim 16, further comprising introducing a mixture of charge control agents with the at least one surface-treated silica into the electrophoretic ink, wherein the mixture of charge control agents comprises i) at least one polydimethylsiloxane substituted primary amine and/or polydimethylsiloxane substituted secondary amine and/or polydimethylsiloxane substituted tertiary amine, and ii) at least one polydimethylsiloxane substituted quaternary ammonium with counterion.

18. The electrophoretic ink according to claim 4, wherein the at least one dispersing agent is represented by Formula (I) ##STR00050## where p+q is an integer ranging from 30 to 200, n+m is an integer ranging from 5 to 50, X.sup. is an anion of a monovalent organic or inorganic acid, R.sub.1 is a C.sub.4-C.sub.22-linear or branched alkyl group, and R.sub.2 is a C.sub.1-C.sub.12-comprising group.

Description

BRIEF DESCRIPTION OF FIGURES

[0266] FIG. 1 refers to a schematic illustration of a display cell containing a black or coloured electrophoretic ink.

[0267] FIG. 2 refers to a schematic illustration of a smart window cell containing a black or coloured electrophoretic ink.

[0268] FIG. 3 refers to a schematic illustration of a display or smart window cell viewed from above.

[0269] FIG. 4 refers to a schematic illustration of stacked display cells containing coloured electrophoretic inks.

[0270] FIG. 5 refers to a schematic illustration of stacked smart window cells containing coloured electrophoretic inks.

EXAMPLES

[0271] The following materials were used:

1. Silica Materials

[0272] In this application, silica materials are defined as an oxide of silicon with the chemical formula of SiO.sub.2 in the bulk. Both commercially available silica materials and surface-treated silica materials were used in this invention.

1.1 Commercially Available Silica Materials

[0273] Fumed silica powders (surface area 200-400 m.sup.2 g.sup.1) were obtained from Sigma-Aldrich, as well as from Evonik: AEROSIL 200, AEROSIL 255, AEROSIL 300, and AEROSIL 380.

[0274] The following surface-treated fumed silica were obtained from Evonik: AEROSIL R 104, AEROSIL R 106, AEROSIL R 208, AEROSIL R 709, AEROSIL R 711, AEROSIL R 805, AEROSIL R 816, AEROSIL R 972, AEROSIL R 974, AEROSIL R 8200, AEROSIL R 812 S, AEROSIL R 976 S, AEROSIL RX 50, AEROSIL RX200, AEROSIL RY50, AEROSIL RY 51, AEROSIL RY 200, AEROSIL NX 90 S, and AEROSIL NX 130.

1.2 Methods

[0275] The weight median particle size d.sub.50 of the surface-treated silica was determined using TEM. The method and the instrument are known to the skilled person and are commonly used to determine the size of silica or other pigment materials.

[0276] The specific surface area (in m.sup.2/g) of the surface-treated silica was determined by using the BET method in accordance with ISO 9277:2010 and nitrogen as adsorbing gas. The method is known to the skilled person and is commonly used to determine the specific surface area.

[0277] The bistability was determined by measuring the Lightness (L*) over time by using a commercially available device for measuring the Lightness. The method and the instrument are known to the skilled person and are commonly used to determine the Lightness. In particular, the display filled with the electrophoretic ink is first driven from the black state to the white state (about 71 L*) by applying a voltage of +15 V or 15 V (depending on the charge of the pigment particle surface) during 4 to 30 seconds. Then, the display is switched from the white state to the black state again by switching off the voltage and the time required to reach a drop in Lightness of 7 L* is determined. The time required to reach a drop in Lightness of 7 L*corresponds to the determined bistability.

[0278] The contrast is determined by measuring the reflection in the black state as well as the white state by using a commercially available device for measuring the reflection. The method and the instrument are known to the skilled person and are commonly used to determine the reflection. In particular, the reflection of the display filled with the electrophoretic ink is measured in the black state and the white state which is obtained by applying a voltage of +15 V or 15 V (depending on the charge of the pigment particle surface). The reflection ratio between the white state and the black state corresponds to the determined contrast.

1.3 Surface-Treated Silica

[0279] Surface-treated silica materials were prepared by anchoring molecules (so-called surface groups) to the surface of fumed silica. The surface treatment process is given in the following examples.

Example 1

[0280] 2.0 g of fumed silica (obtained from Sigma-Aldrich, surface area 200 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 1.0 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the silica dispersion. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 2

[0281] 2.0 g of fumed silica (obtained from Sigma-Aldrich, surface area 400 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 2.0 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the silica dispersion. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 3

[0282] 1.0 g of fumed silica 1 (obtained from Sigma-Aldrich, surface area 200 m.sup.2 g.sup.1) and 1.0 g of fumed silica 2 (surface area 400 m.sup.2 g.sup.1) were mixed and dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 1.5 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the silica dispersion. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 4

[0283] 2.0 g of fumed silica (obtained from Sigma-Aldrich, surface area 200 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 1.0 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 5

[0284] 2.0 g of fumed silica (obtained from Sigma-Aldrich, surface area 400 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 2.0 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 6

[0285] 1.0 g of fumed silica 1 (Sigma Aldrich, surface area 200 m.sup.2 g.sup.1) and 1.0 g of fumed silica 2 (surface area 400 m.sup.2 g.sup.1) were mixed and dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 1.5 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 7

[0286] 2.0 g of fumed silica (Sigma Aldrich, surface area 200 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 0.5 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane was added to the silica dispersion. 0.5 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 8

[0287] 2.0 g of fumed silica (obtained from Sigma-Aldrich, surface area 400 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 1.0 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. 1.0 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 9

[0288] 1.0 g of fumed silica 1 (obtained from Sigma-Aldrich, surface area 200 m.sup.2 g.sup.1) and 1.0 g of fumed silica 2 (surface area 400 m.sup.2 g.sup.1) were mixed and dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 0.75 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. 0.75 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 10

[0289] 2.0 g of fumed silica (obtained from Sigma-Aldrich, surface area 200 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 0.75 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. 0.25 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 11

[0290] 2.0 g of fumed silica (obtained from Sigma-Aldrich, surface area 400 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 1.5 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. 0.5 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 12

[0291] 1.0 g of fumed silica 1 (obtained from Sigma-Aldrich, surface area 200 m.sup.2 g.sup.1) and 1.0 g of fumed silica 2 (surface area 400 m.sup.2 g.sup.1) were mixed and dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 1.125 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. 0.375 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 13

[0292] 2.0 g of fumed silica (obtained from Sigma-Aldrich, surface area 200 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 0.25 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. 0.75 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 14

[0293] 2.0 g of fumed silica (obtained from Sigma-Aldrich, area 400 m.sup.2 g.sup.1) were dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 0.5 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. 1.5 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

Example 15

[0294] 1.0 g of fumed silica 1 (obtained from Sigma-Aldrich, surface area 200 m.sup.2 g.sup.1) and 1.0 g of fumed silica 2 (obtained from Sigma-Aldrich, surface area 400 m.sup.2 g.sup.1) were mixed and dispersed in 100 mL ethanol (95%) at 25 C. for 2 h, 0.375 g of dimethoxydimethylsilane, or ethyl(trimethoxy)silane, or trimethoxy(propyl)silane, or isobutyl(trimethoxy)silane, or [3-(methacryloyloxy)propyl]trimethoxysilane were added to the silica dispersion. 1.125 g of docosanylsilane, or octadecylsilane, or hexadecylsilane, or dodecylsilane, or decylsilane, or octylsilane, or hexylsilane were added to the mixture afterwards. The reaction mixture was aged for 15-72 h under stirring at 25 C. After removing the solvent in a rotary evaporator, the obtained powder material was dried in an oven at 120 C. for 2 h.

2. Application of Silica Materials in Electrophoretic Ink

[0295] Electrophoretic ink black, yellow, magenta, and cyan were prepared as described in unpublished European patent application 16 179 079.5

[0296] A typical formulation of electrophoretic ink black contained 2.0-3.0% pigment, 0.2-0.3% dispersant, 15.0-20.0% charge control agent, and dodecane.

[0297] A typical formulation of electrophoretic ink yellow contained 0.5-2.0% pigment, 0.1-1.0% dispersant, 15.0-20.0% charge control agent (mixed PDMS-amine and PDMS-ammonium), and dodecane.

[0298] A typical formulation of electrophoretic ink magenta contained 1.0-2.5% pigment, 0.5-1.5% dispersant, 15.0-20.0% charge control agent, and dodecane.

[0299] A typical formulation of electrophoretic ink cyan contained 0.5-2.5% pigment, 0.1-2.0% dispersant, 5.0-20.0% charge control agent, and dodecane.

[0300] The (surface-treated) silica materials were added to the electrophoretic ink and homogenized in a Skandex. Afterwards the ink-(surface-treated) silica mixture was applied in a test cell and the performance of the ink was recorded and evaluated. A typical test cell included two glass planes with indium tin dioxide (ITO) coating as electrodes. The two glass planes were assembled with a cell gap of 15 m.

Example 0 (Comparative)

[0301] 0.5 g black pigment (such as Irgaphor Black, Paliogen Black, Paliotol Black, or their mix), 0.05 g dispersant, 0.5 g PDMS-amine, 1.0 g PDMS-ammonium, and 7.95 g dodecane were mixed with micro pearls in a vial and dispersed in Skandex for at least 45 h. The obtained preliminary ink was diluted with 0.4 g PDMS-amine, 1.5 g PDMS-ammonium, and 8.1 g dodecane to a final formulation of 2.5% pigment, 0.25% dispersant, 5.0% PDMS-amine, 11.3% PDMS-ammonium, and 80.95% dodecane. Bistability was 0.6 seconds and contrast was 14.

Example 1 (Comparative)

[0302] 0.5 g black pigment (such as Irgaphor Black, Paliogen Black, Paliotol Black, or their mix), 0.05 g dispersant, 0.5 g PDMS-amine, 1.0 g PDMS-ammonium, and 7.95 g dodecane were mixed with micro pearls in a vial and dispersed in Skandex for at least 45 h. The obtained preliminary ink was diluted with 0.4 g PDMS-amine, 1.5 g PDMS-ammonium, and 8.1 g dodecane to a final formulation of 2.5% pigment, 0.25% dispersant, 5.0% PDMS-amine, 11.3% PDMS-ammonium, and 80.95% dodecane. 3.5 g fumed silica (surface area 200-400 m.sup.2 g.sup.1) were added to the obtained ink and the mixture was dispersed in Skandex for 2.5 h. Bistability was from 6-10 seconds and contrast was between 7 and 10.

Example 2 (Inventive)

[0303] 0.5 g black pigment (such as Irgaphor Black, Paliogen Black, Paliotol Black, or their mix), 0.05 g dispersant, 0.5 g PDMS-amine, 1.0 g PDMS-ammonium, and 7.95 g dodecane were mixed with micro pearls in a vial and dispersed in Skandex for at least 45 h. The obtained preliminary ink was diluted with 0.4 g PDMS-amine, 1.5 g PDMS-ammonium, and 8.1 g dodecane to a final formulation of 2.5% pigment, 0.25% dispersant, 5.0% PDMS-amine, 11.3% PDMS-ammonium, and 80.95% dodecane. 4.4 g surface-treated silica (from Example 10 in 1.3) were added to the obtained ink and the mixture was dispersed in Skandex for 2.5 h. Bistability for all Examples was from 10-20 seconds and contrast was between 10 and 14.

Example 3 (Inventive)

[0304] 0.5 g yellow pigment (such as Irgalite Yellow, Irgaphor Yellow, Irgazin Yellow, Cromophtal Yellow, Paliotol Yellow, or their mix), 0.1 g dispersant, 0.7 g PDMS-amine, 1.4 g PDMS-ammonium, and 7.3 g dodecane are mixed with micro pearls in a vial and dispersed in Skandex for 45 h. The obtained preliminary ink was diluted with 1.8 g PDMS-amine, 5.5 g PDMS-ammonium, and 32.8 g dodecane to a final formulation of 1.0% pigment, 0.2% dispersant, 5.0% PDMS-amine, 12.5% PDMS-ammonium, and 81.3% dodecane. 12.0 g surface-treated silica (from Example 1-15 in 1.3) is added to the obtained ink and the mixture is dispersed in Skandex for 2.5 h. Bistability for all Examples was from 10-20 seconds and contrast was between 10 and 14.

Example 4 (Inventive)

[0305] 0.5 g magenta pigment (Cinquasia Magenta, Cinquasia Violet, Cromophtal Violet, Irgazin Red, or their mix), 0.2 g dispersant, 0.6 g PDMS-amine, 1.4 g PDMS-ammonium, and 7.3 g dodecane were mixed with micro pearls in a vial and dispersed in Skandex for 45 h. The obtained preliminary ink was diluted with 1.4 g PDMS-amine, 6.2 g PDMS-ammonium, and 32.4 g dodecane to a final formulation of 1.0% pigment, 0.4% dispersant, 4.0% PDMS-amine, 14.0% PDMS-ammonium, and 80.6% dodecane. 12.0 g surface-treated silica (from Example 1-15 in 1.3) were added to the obtained ink and the mixture was dispersed in a Skandex for 2.5 h. Bistability for all Examples was from 10-20 seconds and contrast was between 10 and 14.

Example 5 (Inventive)

[0306] 0.5 g cyan pigment (Cromophtal Cyan, Heliogen Blue, Paliogen Blue, or their mix), 0.25 g dispersant, 0.5 g PDMS-amine, 1.2 g PDMS-ammonium, and 7.55 g dodecane were mixed with micro pearls in a vial and dispersed in Skandex for 45 h. The obtained preliminary ink was diluted with 1.1 g PDMS-amine, 3.5 g PDMS-ammonium, and 85.4 g dodecane to a final formulation of 0.5% pigment, 0.25% dispersant, 1.2% PDMS-amine, 4.3% PDMS-ammonium, and 93.35% dodecane. 24.0 g surface-treated silica (from Example 1-15 in 1.3) were added to the obtained ink and the mixture was dispersed in a Skandex for 2.5 h. Bistability for all Examples was from 10-20 seconds and contrast was between 10 and 14.

Example 6 (Inventive)

[0307] 0.5 g black pigment (such as Irgaphor Black, Paliogen Black, Paliotol Black, or their mix), 0.05 g dispersant, 0.5 g PDMS-amine, 1.0 g PDMS-ammonium, and 7.95 g dodecane were mixed with micro pearls in a vial and dispersed in Skandex for at least 45 h. The obtained preliminary ink was diluted with 0.4 g PDMS-amine, 1.5 g PDMS-ammonium, and 8.1 g dodecane to a final formulation of 2.5% pigment, 0.25% dispersant, 5.0% PDMS-amine, 11.3% PDMS-ammonium, and 80.95% dodecane. 5.0 g of surface-treated silica AEROSIL R 709 or AEROSIL R 711 or AEROSIL R 805 or AEROSIL R 816 or the mixture of them were added to the obtained ink and the mixture was dispersed in Skandex for 2.5 h. Bistability for all Examples was from 10-20 seconds and contrast was between 10 and 14.

Example 7 (Inventive)

[0308] 0.5 g black pigment (such as Irgaphor Black, Paliogen Black, Paliotol Black, or their mix), 0.05 g dispersant, 0.5 g PDMS-amine, 1.0 g PDMS-ammonium, and 7.95 g dodecane were mixed with micro pearls in a vial and dispersed in Skandex for at least 45 h. The obtained preliminary ink was diluted with 0.4 g PDMS-amine, 1.5 g PDMS-ammonium, and 8.1 g dodecane to a final formulation of 2.5% pigment, 0.25% dispersant, 5.0% PDMS-amine, 11.3% PDMS-ammonium, and 80.95% dodecane. 3.75 g of surface-treated silica AEROSIL R 709 or AEROSIL R 711 or fumed silica (200-400 m.sup.2 g.sup.1) or the mixture of them were added to the obtained ink and the mixture was dispersed in Skandex for 2.5 h. Bistability for all Examples was from 10-20 seconds and contrast was between 10 and 14.