WO2014018007A1

WO2014018007A1 - Pigment-based inks

Info

Publication number: WO2014018007A1
Application number: PCT/US2012/047924
Authority: WO
Inventors: Qin Liu; Zhang-Lin Zhou; Tim R. Koch
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2012-07-24
Filing date: 2012-07-24
Publication date: 2014-01-30
Also published as: TW201407250A

Abstract

An ink is disclosed. The ink includes a non-polar carrier fluid, a pigment particle, and a liquid crystal additive.

Description

PIGMENT-BASED INKS

BACKGROUND

[001] Ultrathin, flexible, reflective electronic displays that look like print on paper are of great interest as they have potential applications in wearable computer screens, electronic paper, smart identity cards, and electronic signage. Electro-optical display technology, such as electrophoretic or electrokinetic display technology, is an important approach to this type of display medium. In electrophoretic or electrokinetic displays, pixel or segment electrodes, electrodes within the viewing area of a display that are electrically isolated, may control the local position of charged colorant particles in the ink by application of electric fields. The local position of the particles may influence the reflectance of such pixel or segment electrodes. Without subscribing to any particular theory, in electronic inks, particles that exhibit good dispersibility and charge properties in non-polar dispersing media may increase the stability of the ink and may improve the switching behavior of the ink, as further discussed below, which may increase the useful lifetime of the ink. Additionally, use of non-polar dispersing media in the electrophoretic or electrokinetic devices may minimize current leakage.

BRIEF DESCRIPTION OF THE DRAWINGS

[002] The detailed description will make reference to the following drawings, in which like reference numerals may correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals having a previously described function may or may not be described in connection with other drawings in which they appear.

[003] FIG. 1 depicts a cross-sectional view of one example of a stacked electro-optical display including an ink with a liquid crystal additive as disclosed herein.

[004] FIG. 2 depicts a method from improving an electronic display by adding an ink including a liquid crystal additive.

DETAILED DESCRIPTION

[005] Reference is now made in detail to specific examples of inks including liquid crystal additives. When applicable, alternative examples are also briefly described.

[006] It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[007] As used in this specification and the appended claims, "about" means a ± 10% variance caused by, for example, variations in manufacturing processes.

[008] As used herein, the "carrier fluid" is a fluid or medium that fills up a viewing area defined in an electronic ink display and is generally configured as a vehicle to carry pigment particles therein.

[009] In the past, research has been conducted on displays utilizing electrokinetic/electrophoretic architecture that rely on pigment compaction, which permits both a colored state when the pigment/colorant particles are spread out and a clear state when the particles are tightly compacted within a cell or pixel, and wherein the repeated motion of spreading out and compacting is known as "switching". (See e.g., Yeo, J. et al., "Electro-optical Display", US Patent 8,018,642).

[0010] A bi-state display cell having a dark state and a clear state may be achieved using an electronic ink with charged pigment particles in an optically transparent fluid. A clear state may be achieved when the pigment particles are compacted, and a colored state may be achieved when the pigment particles are spread. For example, an electronic ink with charged white particles in a colored fluid may enable white and spot-color states, with the color of the colored state depending on the color of the fluid. The ink fluid may be colored by a dye, nanoparticle colorants, pigments or other suitable colorants. A white state may be achieved when the white particles are spread, and a colored state may be achieved when the white particles are compacted. By combining the white particles in the colored fluid with a colored resin on the back of the display cell, a tri-state display cell may be achieved.

[0011] An electrokinetic/electrophoretic display cell may use a three- dimensional architecture to provide a clear optical state. In this architecture, the geometrical shape of the display cell has narrowing portions in which electrophoretically/electrokinetically translated pigment particles may compact in response to appropriate bias conditions applied to driving electrodes on opposite sides of the display cell. The three-dimensional structure of the display cell may introduce additional control of electrokinetically/electrophoretically moving pigment particles. As a result, desired functionalities may be achieved with a developed and more stable electrokinetic/electrophoretic ink. In some examples, the driving electrodes may be passivated with a dielectric layer, thus eliminating the possibility of electrochemical interactions through the driving electrodes from direct contact with the electrokinetic/electrophoretic ink. In other examples, the driving electrodes may not be passivated, thus allowing electrochemical interactions with the electrokinetic/electrophoretic ink.

[0012] However, inks currently used in prior art displays may not work in stacked versions of an electrophoretic/electrokinetic architecture as such inks may be unable to achieve the level of compaction necessary to provide the clear states used in displays with stacked color architectures, as further described below.

[0013] For example, current commercial displays, such as displays manufactured by prior art display technology companies, utilize front to rear particle motion, which may only be able to provide opaque color and white states or black and white states. Additionally, such displays may not be capable of producing the clear states that allow displays to be used in stacked architectures, as further described below, and may rely on color filters to achieve full color. However, color filters, such as red, green, or blue filters, may often be arranged side-by-side in a pixel, which may result in a decreased surface area within the pixel for modulating light and a decreased surface area within the pixel for reflecting incident light when not all of the color filters are required to produce a color. Accordingly, the resulting displayed image using color filters may have dull colors.

[0014] The ability to achieve a clear state, on the other hand, may allow displays to sit in a stacked architecture and may allow the entire viewable area in the display to be used (i.e. the entire pixel of every pixel) when modulating light and reflecting incident light. The result may be a display able to achieve brighter colors and a better clear or light state. Additionally, because the entire viewable area in the display may be used to modulate light, such displays may also have a larger color gamut volume.

[0015] While significant progress toward developing working electronic inks for this stacked architecture has been made in the last few years, researchers continue to seek ways for improving the quality and versatility of these inks. (See e.g., Zhou, Z. L. et al., "Electronic Inks" published on April 21 , 201 1 as WO201 1/046562; Zhou, Z. L. et al., "Dual Color Electronically Addressable Ink" published on April 21 , 201 1 as WO201 1/046564; and Zhou, Z. L. et al., "Electronic Inks" published on April 21 , 201 1 as WO201 1/046563.)

[0016] In accordance with the teachings herein, an additive for inks is provided, wherein the additive is any liquid crystal additive. As used herein, a "liquid crystal additive" is any material having an intermediate state wherein the material, in its intermediate state, behaves as a solid crystal in one or two dimension(s) and liquid in the other dimension(s). In electronic inks, the addition of liquid crystal additives may result in improved lightness in the electrophoretic/electrokinetic reflective displays including such inks. For example, the white point or clear state of a stacked full color display (as further described below) may be improved by the increased ability to pass light through the display, resulting in a display with an image quality that may be close to or may exceed SNAP standards (i.e. Specifications for Newsprint Advertising Production). This increased ability to pass light through the display may lead to better contrast between the clear and dark states in the devices, leading to more vibrant colors and an improved color gamut.

[0017] FIG. 1 illustrates a cross-sectional view of one example of a stacked electro-optical display 100 including an ink with liquid crystal additives as described herein. The electro-optical display 100 includes a first display element 102a, a second display element 102b, and a third display element 102c. The third display element 102c is stacked on the second display element 102b, and the second display element 102b is stacked on the first display element 102a.

[0018] In some examples, each display unit includes a first substrate 104, a first electrode 106, a dielectric layer 108 including reservoir or recess regions 1 10, thin layers 1 12, a display cell 1 14, a second electrode 1 16, and a second substrate 1 18. In other examples, the display unit does not include thin layers 1 12. The display cell 1 14 may be filled with the electronic ink 120, 122 disclosed herein including a carrier fluid 120, pigment/colorant particles 122, and liquid crystal additives as described herein. In some examples, wherein thin layers 1 12 are included, the thin layers 1 12 may be opaque. In other examples, the thin layers 1 12 may be transparent. In examples wherein thin layers 1 12 are included, the thin layers 1 12 may include dielectric materials or conductive materials. In one specific example, a metallic material, such as nickel, may be used.

[0019] In examples wherein thin layers 1 12 are included, the first display element 102a includes thin layers 1 12a self-aligned within the recess regions 1 10. The first display element 102a also includes pigment particles 122a having a first color (e.g., cyan) for a full color electro-optical display. The second display element 102b includes thin layers 1 12b self-aligned within the recess regions 1 10. The second display element 102b also includes pigment particles 122b having a second color (e.g., magenta) for a full color electro-optical display. The third display element 102c includes thin layers 1 12c self-aligned within the recess regions 1 10. The third display element 102c also includes pigment particles 122c having a third color (e.g., yellow) for a full color electro-optical display. In other examples, pigment particles 122a, 122b, and 122c may include other suitable colors for providing an additive or subtractive full color electro- optical display.

[0020] In the example illustrated in FIG. 1 , in the electro-optical display 100 including the ink disclosed herein 120, 122, the first display element 102a, the second display element 102b, and the third display element 102c are aligned with each other. As such, the thin layers 1 12a, 1 12b, and 1 12c are also aligned with each other. In this example, since the recess regions 1 10 and the self-aligned thin layers 1 12a, 1 12b, and 1 12c of each display element 102a, 102b, and 102c, respectively, are aligned, the clear aperture for the stacked electro-optical display 100 may be improved as compared to a stacked electro- optical display without such alignment.

[0021] In an alternate example (not shown), the first display element 102a, the second display element 102b, and the third display element 102c may be offset from each other. As such, the thin layers 1 12a, 1 12b, and 1 12c are also offset from each other. In this example, since the recess regions 1 10 and the self-aligned thin layers 1 12a, 1 12b, and 1 12c are just a fraction of the total area of each display element 102a, 102b, and 102c, respectively, the clear aperture for the stacked electro-optical display 100 may remain high regardless of the alignment between the display elements 102a, 102b, and 102c. As such, the process for fabricating the stacked electro-optical display 100 may be simplified. The self-aligned thin layers 1 12a, 1 12b, and 1 12c may prevent tinting of each display element due to the pigment particles 122a, 122b, and 122c, respectively, in the clear optical state. Therefore, a stacked full color electro- optical display having a bright, neutral clear state and precise color control may be provided.

[0022] Turning now to inks that include the liquid crystal additive described herein and may be used in the electro-optical displays described above in FIG. 1 , such as electrophoretic/electrokinetic displays, examples of such electronic inks may generally include a non-polar carrier fluid, a pigment/colorant particle, and a liquid crystal additive. Additionally, in some examples, such electronic inks may further include other additives, such as surfactants, dispersants or charge directors.

[0023] Table 1 shows examples of formulations for electronic inks including liquid crystal additives and cyan pigment particles and one example of a formulation for an electronic ink not including any liquid crystal additives, which may serve as a control sample (i.e. ink 1 1 ). In Table 1 , Additive I is polyisobutylene succinimide, Additive II is polyhydroxystearic amide salt, and each different Additive III is either a commercially available or non-commercially available proprietary liquid crystal additive from a third party chemical manufacturer such as Sigma Aldrich (St. Louis, Missouri), EMD Chemicals (Billerica, Massachusetts) or Dainippon Ink and Chemical (Tokyo, Japan). More specifically, the Additive III indicated by E is 4-cyano-4^,-pentylbiphenyl, a nematic-phase liquid crystal sold by Sigma Aldrich, and the Additive IN indicated by F is n-(4-methoxybenzylidene)-4-butylaniline_! another nematic-phase liquid crystal sold by Sigma Aldrich. In Table 1 , the remaining Additive 111 materials are proprietary, non-commercially available liquid crystals from the third party chemical suppliers listed above.

Table 1. Examples of Cyan Electronic Ink Formulations with Liquid Crystal

Additives

[0024] After formulation, the inks from Table 1 were added to a test cell including electrodes and tested under an electric field. Table 2 shows the measured values for nominal contrast for each ink, defined as the difference between the measured light intensity of the light state and the measured light intensity of the dark state. The experiments were conducted by measuring light passed through the test cells including the electronic inks with liquid crystal additives in arbitrary units (au). In its initial state, the pigment particles in the electronic ink were spread out in the test cell, i.e. in the dark state. Next, an electric field was applied to the test cell resulting in the compacting of pigment particles in the electronic ink into the clear state. In both states, light intensity was measured in arbitrary units. Finally, the nominal contrast was determined by calculating the difference between the measured light and dark states. Table 2. Switching Behavior of Cyan Electronic Inks with Liquid Crystal

Additives

[0025] As seen in Table 2, the electronic inks including liquid crystal additives had higher values for nominal contrast than the control electronic ink without liquid crystal additives. It should be noted that although the nominal contrast of inks 6 and 9 appear to be below that of similar inks using both higher and lower concentrations of the same liquid crystal additives, this data does not change the conclusion summarized below. The data from ink 6 may be due to experimental error, while the data for ink 9 is not statistically different from ink 8 such that a conclusion of improvement or non-improvement from ink 8 may be determined. However, in any event, both inks 6 and 9 show improvement over the control ink. Accordingly, the data in Table 2 suggest that inks including liquid crystal additives may result in inks capable of producing better contrast, more vibrant colors, and may have a better color gamut.

[0026] Table 3 shows examples of formulations for electronic inks including liquid crystal additives and black pigment particles, one example formulation for an electronic ink including a non-liquid crystal additive (i.e. ink 28), and one example formulation for an electronic ink not including any liquid crystal additives, which may serve as a control sample (i.e. ink 29). In Table 3, Additives I and II are the same as Additives I and II in Table 2, and each different Additive III is either a commercially available or non-commercially available proprietary liquid crystal additive from a third party chemical manufacturer, as in Table 2. Additive III materials E and F comprise the same materials as the E and F materials described in Table 1 and Additive III material G is a nematic-phase, substituted biphenyl liquid crystal. Finally, in Table 3, "non-LC" refers to a non-liquid crystal additive that has good nominal contrast properties but due to its instability, is inappropriate for use in commercial inks.

Table 3. Examples of Black Electronic Ink Formulations with Liquid Crystal

Additives

[0027] The inks were used in a test cell including electrodes and tested under an electric field in a substantially similar fashion as described in Table 2 above. Table 4 shows the measured values for nominal contrast, defined as the difference between light intensity of the light state and the dark state, for each of the formulations of ink described in Table 3.

Table 4. Switching Behavior of Black Electronic Inks with Liquid Crystal

Additives

[0028] As seen in Table 4, the addition of liquid crystal additives results in improvement in nominal contrast for many of the inks (e.g. inks 12, 14, 18, etc.). Additionally, as seen in Table 4, the values for nominal contrast for inks 12-21 are similar to the value for nominal contrast for ink 28, the electronic ink with a non-liquid crystal additive that has good nominal contrast properties but due to its instability, is not suitable for commercial inks. This comparison suggests that inks 12-21 perform similar or better than an ink with good nominal contrast properties. [0029] With respect to all of the trials in Table 4, without subscribing to any particular theory, liquid crystal additives may influence the movement of pigment particles in ink. For example, the crystal portion of a liquid crystal may twist and move when an electric field is applied to it, and such movement may influence the movement of the pigment particles. In some examples, the addition of other additives, such as surfactants, dispersants, among other additives, may also influence the movement of pigment particles in ink, which may affect contrast. In other examples, without subscribing to any particular theory, there may be further behavioral differences between inks of different colors, such as between cyan inks and black inks including liquid crystal additives, as a result of differences in surface chemistry. Therefore, and as further seen in Table 4, the impact of liquid crystal additives on performance of electronic inks can be optimized as performance varies with different pigment types, different liquid crystals, different additives, and different concentrations of the included ink components.

[0030] As discussed above, liquid crystal additives may be added to an electronic ink, which may generally include a carrier fluid and a pigment particle, in addition to the liquid crystal additive. The ink may also further include other additives such as surfactants, dispersants or charge directors.

[0031] In some examples, the carrier fluid may act as a vehicle for dispersing the pigment particle, as described herein, and may act as an electrokinetic/electrophoretic medium. In one example, non-polar fluids are used, as such fluids may reduce leakages of electric current when driving the display and may increase the electric field present in the ink. In some examples, the non-polar carrier fluid may be a fluid having a low dielectric constant k such as, e.g., less than 20 or, in some examples, less than 2. In other examples, carrier fluids may also vary with respect to viscosity, resistivity, specific gravity, chemical stability or toxicity, wherein such differences may be considered when formulating an electronic ink. For example, a carrier fluid that is too viscous may slow down the spread or compaction of the pigment particles, which may affect switching speed and may result in a less effective electronic ink. [0032] Specifically, in some examples, the non-polar carrier fluid may include one or more fluids selected from the group consisting of hydrocarbons, halogenated hydrocarbons, partially halogenated hydrocarbons, oxygenated fluids, siloxanes, and combinations thereof. Some specific examples of non- polar carrier fluids may include, but are not limited to, perchloroethylene, cyclohexane, dodecane, mineral oil, isoparaffinic fluids, cyclopentasiloxane, cyclohexasiloxane, cyclooctamethylsiloxane or combinations thereof.

[0033] In some examples, the pigment particle, if added to an ink such as an electronic ink, may provide color and charge to the ink. Also, in response to a sufficient electric potential or field applied to the pigment particles while driving electrodes in the display, as described above, the pigment particles may move or rotate in the carrier fluid to different spots in the area of the display viewable by a user to produce different images. Different pigment particles may have different characteristics, such as different sizes, dispersibility properties, hues, colors or lightness. Additionally, different pigment particles may be further functionalized to contain different functional groups, which may further vary properties of the particle, including, but not limited to, hydrophilicity and hydrophobicity, acidity and basicity, or density of the particles.

[0034] The pigment particle may be a colored pigment or colored polymeric particle in any possible color, such as RGB or CYMK, with a size ranging from 10 nm to 10 μιτι. In some examples, smaller particles, with a particle size from 1 to 10 nm, such as quantum dots, may be employed. In other examples, the particle size may range to a few micrometers. Additionally, organic or inorganic pigments may be used.

[0035] Organic and inorganic pigment particles may be selected from black pigment particles, yellow pigment particles, magenta pigment particles, red pigment particles, violet pigment particles, cyan pigment particles, blue pigment particles, green pigment particles, orange pigment particles, brown pigment particles, white pigment particles or combinations thereof. In some instances, the organic or inorganic pigment particles may include spot-color pigment particles, which may be formed from a combination of a predefined ratio of two or more primary color pigment particles. [0036] In some examples, non-limiting specific examples of inorganic black pigments may include carbon blacks such as No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100 or No. 2200B manufactured by Mitsubishi Chemical Corporation; Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255 or Raven 700 manufactured by Columbian Chemicals Company; Regal 400R, Regal 330R, Regal 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1 100, Monarch 1300 or Monarch 1400 manufactured by Cabot Corporation; or Color Black FW1 , Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A or Special Black 4 manufactured by Degussa Corporation. In other examples, specific examples of organic black pigments may include aniline black (C.I. Pigment Black 1 ).

[0037] In other examples, non-limiting examples of suitable yellow organic pigments may include C.I. Pigment Yellow 1 , C.I. Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. Pigment Yellow 4, C.I. Pigment Yellow 5, C.I. Pigment Yellow 6, C.I. Pigment Yellow 7, C.I. Pigment Yellow 10, C.I. Pigment Yellow 1 1 , C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 16, C.I. Pigment Yellow 17, C.I. Pigment Yellow 24, C.I. Pigment Yellow 34, C.I. Pigment Yellow 35, C.I. Pigment Yellow 37, C.I. Pigment Yellow 53, C.I. Pigment Yellow 55, C.I. Pigment Yellow 65, C.I. Pigment Yellow 73, C.I. Pigment Yellow 74, C.I. Pigment Yellow 75, C.I. Pigment Yellow 81 , C.I. Pigment Yellow 83, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 95, C.I. Pigment Yellow 97, C.I. Pigment Yellow 98, C.I. Pigment Yellow 99, C.I. Pigment Yellow 108, C.I. Pigment Yellow 109, C.I. Pigment Yellow 1 10, C.I. Pigment Yellow 1 13, C.I. Pigment Yellow 1 14, C.I. Pigment Yellow 1 17, C.I. Pigment Yellow 120, C.I. Pigment Yellow 124, C.I. Pigment Yellow 128, C.I. Pigment Yellow 129, C.I. Pigment Yellow 133, 138, C.I. Pigment Yellow 139, C.I. Pigment Yellow 147, C.I. Pigment Yellow 151 , C.I. Pigment Yellow 153, C.I. Pigment Yellow 154, C.I. Pigment Yellow 167, C.I. Pigment Yellow 172 or C.I. Pigment Yellow 180. [0038] Non-limiting examples of suitable magenta, red or violet organic pigments may include C.I. Pigment Red 1 , C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 4, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 8, C.I. Pigment Red 9, C.I. Pigment Red 10, C.I. Pigment Red 1 1 , C.I. Pigment Red 12, C.I. Pigment Red 14, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 17, C.I. Pigment Red 18, C.I. Pigment Red 19, C.I. Pigment Red 21 , C.I. Pigment Red 22, C.I. Pigment Red 23, C.I. Pigment Red 30, C.I. Pigment Red 31 , C.I. Pigment Red 32, C.I. Pigment Red 37, C.I. Pigment Red 38, C.I. Pigment Red 40, C.I. Pigment Red 41 , C.I. Pigment Red 42, C.I. Pigment Red 48(Ca), C.I. Pigment Red 48(Mn), C.I. Pigment Red 57(Ca), C.I. Pigment Red 57:1 , C.I. Pigment Red 88, C.I. Pigment Red 1 12, C.I. Pigment Red 1 14, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 144, C.I. Pigment Red 146, C.I. Pigment Red 149, C.I. Pigment Red 150, C.I. Pigment Red 166, C.I. Pigment Red 168, C.I. Pigment Red 170, C.I. Pigment Red 171 , C.I. Pigment Red 175, C.I. Pigment Red 176, C.I. Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 179, C.I. Pigment Red 184, C.I. Pigment Red 185, C.I. Pigment Red 187, C.I. Pigment Red 202, C.I. Pigment Red 209, C.I. Pigment Red 219, C.I. Pigment Red 224, C.I. Pigment Red 245, C.I. Pigment Violet 19, C.I. Pigment Violet 23, C.I. Pigment Violet 32, C.I. Pigment Violet 33, C.I. Pigment Violet 36, C.I. Pigment Violet 38, C.I. Pigment Violet 43 or C.I. Pigment Violet 50.

[0039] Non-limiting examples of blue or cyan organic pigments may include C.I. Pigment Blue 1 , C.I. Pigment Blue 2, C.I. Pigment Blue 3, C.I. Pigment Blue 15, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:34, C.I. Pigment Blue 15:4, C.I. Pigment Blue 16, C.I. Pigment Blue 18, C.I. Pigment Blue 22, C.I. Pigment Blue 25, C.I. Pigment Blue 60, C.I. Pigment Blue 65, C.I. Pigment Blue 66, C.I. Vat Blue 4 or C.I. Vat Blue 60.

[0040] Other non-limiting examples of green, brown, or orange organic pigments may include C.I. Pigment Green 7, C.I. Pigment Green 10, C.I. Pigment Brown 3, C.I. Pigment Brown 5, C.I. Pigment Brown 25, C.I. Pigment Brown 26, C.I. Pigment Orange 1 , C.I. Pigment Orange 2, C.I. Pigment Orange 5, C.I. Pigment Orange 7, C.I. Pigment Orange 13, C.I. Pigment Orange 14, C.I. Pigment Orange 15, C.I. Pigment Orange 16, C.I. Pigment Orange 24, C.I. Pigment Orange 34, C.I. Pigment Orange 36, C.I. Pigment Orange 38, C.I. Pigment Orange 40, C.I. Pigment Orange 43 or C.I. Pigment Orange 63.

[0041] In some examples, the ink may further include other additives. In one example, the other additive may be a charge director. The charge director may be selected from small molecules or polymers that may be capable of forming reverse micelles in the non-polar carrier fluid. Such charge directors may be colorless and may be dispersible or soluble in the carrier fluid. Examples of charge directors include, but are not limited to, neutral and non- dissociable charge directors such as polyisobutylene succinimide amines; Chevron Corporation's Oronite dispersant; ionizable charge directors that may disassociate to form charges such as sodium di-2-ethylhexylsulfosuccinate dioctyl sulfosuccinate (AOT); zwitterionic charge directors such as Lecithin; and non-chargeable and neutral charge directors, which may not disassociate or react with acids or bases to form charges, such as fluorosurfactants.

[0042] In one example, the charge director may be basic and may react with the functionalized pigment particle to negatively charge the particle. In other words, the charging of the particle may be accomplished via an acid-base reaction (or interaction) between the charge director and the acid-modified particle surface. In examples wherein, such pigments are used in electronic inks, the charge director may also be used in such inks to prevent undesirable aggregation of the pigment particles in the inks. In other examples, the charge director may be acidic and may react (or interact) with the base-modified pigment particle to positively charge the particle. Again, the charging of the particle may be accomplished via an acid-base reaction (or interaction) between the charge director and the base-modified particle surface.

[0043] Additionally, in some examples, the electronic ink including and not including a charge director may further include one or more other additives such as dispersants, optical brighteners, polymers, rheology modifiers, surfactants, viscosity modifiers or combinations thereof. Such additives may serve to modify properties of an ink including, but not limited to, viscosity or brightness. [0044] In some examples, the concentration of liquid crystal additives in the ink may range from 0.5 to 30% by weight (wt-%), the concentration of pigment particles may range from 0.5% to 20% by weight, and the concentration of other additives, such as dispersants, charge directors, or surfactants (all as described above) may range from about 0.5 to 20% by weight in an electronic ink. In such examples, the carrier fluid makes up the balance of the ink.

[0045] FIG. 2 depicts a method from improving an electronic display by adding an ink including a liquid crystal additive. As seen in FIG. 2, in some examples, an ink including a non-polar carrier fluid and a pigment particle, as described herein, may be provided 200, and a liquid crystal additive, also as described herein, may be added to such ink 205. Such liquid crystal additive may be added to the ink using any suitable method.

[0046] It should be understood that while the electronic inks including liquid crystal additives as described herein have been described with specific reference to electrokinetic/electrophoretic applications, such additives may find use in other applications as well, such as liquid electrophotographic printing applications.

Claims

CLAIMS What is claimed is:

1 . An ink including:

a non-polar carrier fluid;

a pigment particle; and

a liquid crystal additive.

2. The ink of claim 1 wherein the non-polar carrier fluid is a non-polar solvent selected from the group consisting of hydrocarbons, halogenated hydrocarbons, partially halogenated hydrocarbons, siloxanes, and combinations thereof.

3. The ink of claim 2 wherein the non-polar solvent is selected from the group consisting of perchloroethylene, cyclohexane, dodecane, cyclopentasiloxane, cyclohexasiloxane, cyclooctamethylsiloxane, isoparaffinic fluids, mineral oil, and combinations thereof.

4. The ink of claim 1 wherein the pigment particle is selected from the group consisting of black pigment particles, yellow pigment particles, magenta pigment particles, red pigment particles, violet pigment particles, cyan pigment particles, blue pigment particles, green pigment particles, orange pigment particles, brown pigment particles, white pigment particles, and combinations thereof.

5. The ink of claim 1 wherein the pigment particle is a colored polymeric particle having a size ranging from 10 nm to 10 μιτι.

6. The ink of claim 1 further including a charge director, wherein the charge director is a small molecule or polymer that is capable of forming reverse micelles in the non-polar carrier fluid.

7. The ink of claim 1 further including an additional additive selected from the group consisting of dispersants, optical brighteners, polymers, rheology modifiers, surfactants, viscosity modifiers, and combinations thereof.

8. In combination, an electronic display and an ink, wherein the electronic display includes:

a first electrode

a second electrode; and

a display cell having a reservoir region defined by a dieletric material, the first electrode, and the second electrode; wherein the display cell contains the ink; and wherein the ink includes:

a non-polar carrier fluid;

a pigment particle; and

a liquid crystal additive.

9. The combination of claim 8 wherein the electronic display includes a plurality of display cells in a stacked configuration, associated first electrodes and second electrodes, and a plurality of the inks in different colors, each display cell containing an ink of a different color.

10. The combination of claim 8 wherein the non-polar carrier fluid is a non-polar solvent selected from the group consisting of hydrocarbons, halogenated hydrocarbons, partially halogenated hydrocarbons, siloxanes, and combinations thereof.

1 1 . The combination of claim 8 wherein the pigment particle is selected from the group consisting of black pigment particles, yellow pigment particles, magenta pigment particles, red pigment particles, violet pigment particles, cyan pigment particles, blue pigment particles, green pigment particles, orange pigment particles, brown pigment particles, white pigment particles, and combinations thereof.

12. The combination of claim 8 wherein the ink further includes an additional additive selected from the group consisting of oligomers, polymers, surfactants, dispersants, charge directors, optical brighteners, rheology modifiers, viscosity modifiers, or combinations thereof and wherein if the additional additive is a charge director, the charge director is a small molecule or polymer that is capable of forming reverse micelles in the non-polar carrier fluid.

13. A method for improving an electronic display including:

providing an ink including a non-polar carrier fluid and a pigment particle; and

adding a liquid crystal additive to the ink.

14. The method of claim 13 further including adding a charge director to the ink, wherein the charge director is a small molecule or polymer that is capable of forming reverse micelles in the non-polar carrier fluid.

15. The method of claim 13 further including adding an additional additive to the ink, wherein the additional additive is selected from the group consisting of optical brighteners, polymers, rheology modifiers, surfactants, dispersants, viscosity modifiers, and combinations thereof.