JP2004500583A - Electrophoretic displays and materials - Google Patents

Abstract

Disclosed are novel electrophoretic displays and materials useful for making such displays. Specifically, a novel encapsulated display is disclosed. The particles encapsulated in the display are dispersed in a suspension or electrophoretic fluid. The fluid may be a mixture of two or more fluids or a single fluid. The display further includes particles dispersed in the suspending fluid, the particles including a liquid. In any case, the suspending fluid may have a density or refractive index that substantially matches the density or refractive index of the particles dispersed in the suspending fluid. Finally, an electro-osmotic display is also disclosed. These displays include at least one capsule that includes either a cellulosic or gelled internal phase and a liquid phase, or that includes two or more immiscible fluids. The application of an electric field to any of the electrophoretic displays described herein affects the optical properties of the display.
[Selection] Fig. 6A

Description

[0001]
The present invention relates to electrophoretic displays, and in particular, to encapsulated electrophoretic displays and materials useful for making such displays.
[0002]
(Background of the Invention)
Electrophoretic displays have been the subject of intense research and development for many years. Electrophoretic displays have the attributes of superior brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared to liquid crystal displays. Nevertheless, the long-term image quality issues of these displays have, to date, hindered their widespread use.
[0003]
Recent inventions of encapsulated electrophoretic displays have solved many of these problems and provide additional advantages over liquid crystal displays. Some additional advantages are the ability to print or coat the display material on a variety of flexible or rigid substrates. The problems of clustering and sedimentation that plague prior art electrophoretic displays and consequently result in poor display life are now resolved.
[0004]
The purpose of this disclosure is to describe electrophoretic displays, particularly encapsulated electrophoretic displays, a classification of materials that would be useful in constructing these displays, and some specific materials. It is.
[0005]
(Summary of the Invention)
The successful construction of an encapsulated electrophoretic display requires proper interaction of several different types of materials and processes. Materials such as polymer binders, capsule membranes, and electrophoretic particles and fluids must all be chemically compatible. The capsule membrane may engage the electrophoretic particles with useful surface interactions and may serve as an inert physical interface between the fluid and the binder. The polymeric binder may cure as an adhesive between the capsule membrane and the electrode surface.
[0006]
In some cases, a separate encapsulation step of the process is not required. The electrophoretic fluid may be directly dispersed or emulsified in a binder (or precursor of the binder material) to form what may be referred to as a "polymer dispersed electrophoretic display". In such displays, the individual electrophoretic phases can be referred to as capsules or microcapsules, even without the presence of a capsule membrane. Such a polymer dispersed electrophoretic display is considered to be a subset of the encapsulated electrophoretic display.
[0007]
In an encapsulated electrophoretic display, a binder material surrounds the capsule and separates the two bordering electrodes. The binder material must be compatible with the capsule and the bordering electrodes and have properties that allow easy printing or coating. Binder materials may also have barrier properties to water, oxygen, ultraviolet light, electrophoretic fluids, and other materials. Further, the binder material may include surfactants and crosslinkers, which may aid in coating or durability. Polymer dispersed electrophoretic displays may be emulsion or phase separated.
[0008]
The present invention provides an electrophoretic display, specifically an encapsulated electrophoretic display, and the materials used in such a display. Capsules may be spherical or non-spherical. In an electrophoretic display, the application of an electric field causes at least some of the particles to move or rotate. The electric field may be an AC electric field or a DC electric field. The electric field may be created by at least one electrode pair located adjacent to the binder material containing the particles. The particles may be, for example, absorbing pigments, scattering pigments, or luminescent particles. The particles may be composed of any combination of dyes, pigments, polymers.
[0009]
Such displays may also include, for example, one type of particle that reflects or substantially reflects light back and another type that absorbs light. By the application of an electric field, the particles of the encapsulated display may be oriented such that the capsule reflects or substantially reflects light. By applying another electric field, the particles may be oriented such that the capsule does not absorb or retroreflect light. The display may also include a retroreflective substrate, in which case when one type of particles is oriented in a particular pattern, light will pass through the capsule to the substrate and the substrate will reflect the light. When the second type of particles are oriented in a particular pattern, the capsule absorbs light or otherwise does not retroreflect. Types of retroreflective or reflective materials that can be used in constructing the retroreflective or reflective substrate, respectively, include glass spheres and diffractive reflective layers.
[0010]
Another type of display has particles of different colors. Such a display has at least two, preferably at least three, different particle types, each type of particle having a different electrophoretic mobility. The different electrophoretic mobilities provide particles with substantially non-overlapping electrophoretic mobilities, so that upon application of different electric fields, different subsets of the colored particles are visible on the surface of the capsule.
[0011]
Another type of display includes luminescent particles and a visible light blocking medium that can include light absorbing particles or dyes. When a different electric field is applied, the particles may selectively or uniformly luminesce on the front surface (the eye sees bright pixels) or the back surface (the fluid absorbs radiation). When a different electric field is applied, either the luminescent particles or the light-blocking particles can rise to the capsule surface, thus giving the capsule a bright or dark appearance, respectively.
[0012]
In another type of electrophoretic display, the particles themselves may be encapsulated pigments, dyes, pigment dispersions, dye solutions, and any combination thereof. These particles are dispersed in a suspending fluid and then encapsulated in capsules in a binder. The particles may be dispersed in a suspending fluid, and each particle may include a plurality of solid particles, or a dye, or both. The suspending fluid may be a single fluid or a mixture of two or more fluids. In one embodiment, the particles may have a diameter between about 10 nm and about 5 μm, and the capsule may have a diameter between about 5 μm and about 200 μm. In another embodiment, the particles may have a flexible outer surface and may be a polymer layer surrounding a dye or dye solution.
[0013]
The advantages of this system include the well-known methods for making improved particles with better control of absorbance, optical properties, charge, mobility, shape, size, density, surface chemistry, stability, and processability. The ability to use emulsification or encapsulation techniques. The number of dyes and / or particles and liquids of all polarities that can be used to obtain a high level of control of the optical properties of this system is enormous. To obtain properties that are difficult to achieve with pigments, it is possible to create particles which are capsules containing dyes and / or particles. The present invention relates to these encapsulated electrophoretic displays and materials, such as dyes, pigments, binders, etc., that may be useful in constructing these displays.
[0014]
An encapsulated electrophoretic display may include two or more different types of particles. Such a display may include, for example, a display including a plurality of anisotropic particles and a plurality of second particles in a suspending fluid. Application of the first electric field may cause the anisotropic particles to be in a particular orientation and may provide optical properties. Then, application of the second electric field can cause the plurality of second particles to move in parallel, thereby disturbing the orientation of the anisotropic particles and disturbing the optical characteristics. Alternatively, the orientation of the anisotropic particles may allow for easier translation of the plurality of second particles. The particles may have a refractive index that substantially matches the refractive index of the suspending fluid.
[0015]
Finally, the encapsulated display can include an electro-osmotic display. Such a display may include a capsule containing a fluid with a matched refractive index, the fluid moving within the capsule upon application of an electric field to create a homogeneous capsule. The capsule may also include a porous inner material, such as an alkyl cellulose, that swells upon movement of a refractive index matched fluid within the capsule. An electro-osmotic display may also include two or more immiscible fluids that move within the capsule to create different optical properties when an electric field is applied. Optical effects can result from a planar index mismatch or a non-planar index mismatch.
[0016]
Materials used in making electrophoretic displays relate to, but are not limited to, the type of material used in making the display, such as particles, dyes, suspending fluids and binders. In one embodiment, types of particles that can be used in the manufacture of a suspended particle display include scattering pigments, absorbing pigments, and luminescent particles. Such particles may be transparent. Suitable particles include titania, which can be coated in one or two layers with a metal oxide such as, for example, aluminum oxide or silicon oxide. Such particles may also be retroreflective and have a reflective coating. Such particles may be configured as corner cubes. The luminescent particles can include, for example, zinc sulfide particles. The zinc sulfide particles may also be encapsulated with an insulating coating to reduce conductivity. The light blocking or absorbing particles may include, for example, a dye or pigment.
[0017]
The suspending (ie, electrophoretic) fluid may be a highly resistive fluid. The suspending fluid may be a single fluid or a mixture of two or more fluids. The suspending fluid, whether a single fluid or a mixture of fluids, can have a density that substantially matches the density of the particles within the capsule. The suspending fluid may be, for example, a halogenated hydrocarbon such as tetrachloroethylene. The halogenated hydrocarbon may also be a low molecular weight polymer. One such low molecular weight polymer is poly (chlorotrifluoroethylene). The degree of polymerization of the polymer may be from about 2 to about 10.
[0018]
The types of dyes used in electrophoretic displays are well known in the art. These dyes may be soluble in the suspending fluid. These dyes may also be part of a polymer chain. Dyes can be polymerized by thermal, photochemical and chemical diffusion processes. A single dye or a mixture of dyes may be used.
[0019]
Further, the capsules may be formed in a binder or later dispersed in the binder. Materials used as binders include water-soluble polymers, water-dispersible polymers, oil-soluble polymers, thermosetting polymers, thermoplastic polymers, and uv or radiation-cured polymers.
[0020]
The invention will be better understood in view of the following drawings, description and claims.
[0021]
(Detailed description of the invention)
In the figures, the same reference numerals indicate corresponding parts.
[0022]
The present invention relates to improved encapsulated electrophoretic displays and materials useful for constructing these displays. Generally, an encapsulated electrophoretic display includes one or more particle species that absorb or scatter light. One example is a system in which the capsule includes one or more species of electrophoretically migrating particles dispersed in a stained suspension fluid. Another example is where the capsule contains two separate particle types suspended in a clear suspending fluid, one particle type absorbing light (black) and the other particle type scattering light. (White) system. There are other extensions (more than two particle types, with or without dyes, etc.). The particles are usually solid pigments, dyed particles, or pigment / polymer composites.
[0023]
The electrophoretic display of the present invention is described below. These displays are preferably microencapsulated electrophoretic displays. Materials that may be useful for such displays are also described below.
[0024]
I. Electrophoretic display
It is an object of the present invention to provide a very flexible reflector which can be easily manufactured and consumes little power (or, in the case of a bistable display, no power consumption) and thus can be integrated into various applications. It is to provide a type display. The invention features a printable display that includes an encapsulated electrophoretic display medium. The resulting display is flexible. Since the display medium can be printed, the display itself can be manufactured at low cost.
[0025]
An encapsulated electrophoretic display can be configured such that the optical state of the display is stable for some time. If the display has two states that are stable in this manner, the display is said to be bistable. If more than two states of the display are stable, the display is said to be multi-stable. For the purposes of the present invention, the term bistable is used to indicate a display in which any optical state remains fixed once the addressing voltage is removed. The definition of the bistable state depends on the display application. A slowly decaying optical state can be effectively bistable if the optical state does not change substantially over the required viewing time. For example, on a display that is updated every few minutes, a displayed image that is stable for hours or days is effectively bistable for that application. In the present invention, the term bistable also refers to a display having an optical state that lasts long enough to be effectively bistable for the application of interest. Alternatively, it is possible to construct an encapsulated electrophoretic display in which the image is immediately attenuated once the addressing voltage to the display is removed (ie, the display is not bistable or polystable). As described below, in some applications it is advantageous to use an encapsulated electrophoretic display that is not bistable. Whether the encapsulated electrophoretic display is bistable and the bistability of the encapsulated electrophoretic display should be controlled by appropriate chemical modification of the electrophoretic particles, suspending fluid, capsule, and binder material. Can be.
[0026]
Encapsulated electrophoretic displays can take many forms. The display may include a capsule dispersed in a binder. Capsules can be of any size or shape. Capsules can be, for example, spherical and have a diameter in the millimeter or micron range, but are preferably from 10 microns to several hundred microns. As described below, the capsule may be formed by an encapsulation technique. The particles may be encapsulated in a capsule. The particles may be of two or more different particle types. The particles may be, for example, colored, luminescent, light absorbing, or transparent. The particles may include, for example, neat pigments, dyed (lake) pigments, or pigment / polymer composites. The display may further include a suspending fluid in which the particles are dispersed.
[0027]
In electrophoretic displays, particles can be oriented or translated by applying an electric field to the capsule. The electric field may include an alternating electric field or a direct electric field. The electric field may be provided by at least one pair of electrodes located adjacent to the display containing the capsule.
[0028]
Throughout the specification, reference will be made to the term printed or printed. As used throughout the specification, the term print refers to pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, and curtain coating; knife over roll coating, forward or reverse roll coating Roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing process; electrostatic printing process; thermal printing process; It is intended to include all forms of printing and coating. "Print element" refers to an element formed using any of the above techniques.
[0029]
FIG. 1 shows an electrophoretic display of the present invention. The binder 11 comprises at least one capsule 13, which is filled with a plurality of particles 15 and a dyed suspension fluid 17. In one embodiment, particles 15 are titania particles. When a DC field of the appropriate polarity is applied to the capsule 13, the particles 15 move to the viewing surface of the display and scatter light. When the applied electric field is reversed, the particles 15 move to the rear surface of the display. At this time, the view surface of the display looks dark.
[0030]
FIG. 2 shows an electrophoretic display of the present invention. The display includes an anisotropic particle 10 and a second set of particles 12 in a capsule 14. The capsule has electrodes 16 and 16 'located adjacent to the capsule. The electrodes are connected to a voltage source 18. Voltage source 18 may provide an alternating (AC) or direct current (DC) electric field to capsule 14. In this display, an anisotropic particle 10 is oriented by an AC electric field to allow light to pass through the capsule. Brownian motion usually slowly restores particles to an isotropic state. However, this display uses a second set of transparent, index-matched particles 12 to provide internal turbulence and disrupt the orientation of the anisotropic particles. By applying a DC electric field that is switched at a much lower frequency, the second set of particles translates and disturbs any oriented anisotropic particles. This causes the display to reset to its scattered state much more quickly. If the orientation of the anisotropic particles is disturbed, the display cell will appear dark. This mechanism works in encapsulated liquid cells, polymer dispersed liquid cells, or regular liquid cells.
[0031]
In another embodiment of the present invention, an electrophoretic display using a retro-reflective surface is described. This realization need not be encapsulated and can be implemented in the form of a standard electrophoretic display. Figures 3 and 4 show such a display.
[0032]
In FIG. 3, the capsule 20 is filled with a suspending fluid and particles 22. The suspending fluid may be a highly resistive fluid. When the particles are attracted toward the electrodes 24 by the application of an electric field, the particles occupy a small portion of the viewable area of the display. This exposes the transparent electrode 26 and allows light to be reflected from the surface 28. This surface may consist of a glass sphere, a diffractive reflective layer such as a holographically formed reflector, any other known retroreflective surface, or any other surface that contrasts with particles. . At this time, the capsule looks like the substrate 28 at first glance.
[0033]
FIG. 4 shows a second state of the capsule. The particles 22 contained in the capsule 20 move toward the electrode 26 by applying an electric field. Thus, these particles obscure the surface 28, and when the capsule is viewed from above, the capsule appears to have the properties of a particle.
[0034]
FIG. 5 shows another embodiment of the present invention. In this embodiment, the reflective display can be made selectively retroreflective by manipulating the charged particles to block the retroreflected light path or create a retroreflective surface. In the present embodiment, the capsule 30 includes retroreflective particles 32 and black particles 34. The retroreflective particles may include, for example, retroreflective corner cubes or hemispherically reflective coated particles. When a suitable voltage is applied between the electrodes 36 and 36 ', the black particles 34 can move to the viewing surface of the display and create a dark state. If the application of different electric fields allows the retroreflective particles to move to the top surface of the display, these retroreflective particles create a retroreflective surface, resulting in a bright state.
[0035]
In another embodiment, a display is described that can be made selectively retroreflective. In general, the display works by manipulating the charged particles to block the retroreflected light path or create a retroreflective surface. The particles move within the capsule (eg, electrophoretically). 6A-6C show contemplated configurations.
[0036]
The capsules are arranged in a two-dimensional or three-dimensional corner cube type structure that can be created by embossing or other means. In two states, as shown in FIGS. 6A and 6B, particles 38 allow light 40 to pass through and be reflected by corner cube 42. However, in the third state, as shown in FIG. 6C, the particles 38 block most of the incident light 40 from being retroreflected by the corner cube 42.
[0037]
In another embodiment, shown in FIG. 7, a single capsule acts as a retroreflector, much like glass beads. Only light that enters the incident side 44 with a vertical displacement away from the center by a distance greater than the critical distance y strikes the total internal reflection (TIR) side 46 at an angle large enough to be totally internally reflected. This light hits near the center on the TIR side. Therefore, on the incident side 44, the retroreflection effect occurs in a direction away from the central axis. However, on the TIR side 46, most retroreflection occurs at the vertical center.
[0038]
Therefore, an electronically addressable retro-reflective display in which the retro-reflective state and the non-retro-reflective state are as shown in FIGS. 8A and 8B can be configured. In FIG. 8A, particles 43 are shown towards the front of capsule 45. This configuration allows light to enter and exit the TIR side of the capsule. In FIG. 8B, particles 43 are shown towards the bottom of capsule 45. In this configuration, the particles block the light path and thereby prevent light from being reflected from the TIR side of the capsule.
[0039]
That is, any configuration capable of rearranging particles within a capsule or capsule cavity in a binder, with or without an external physical reflector, to switch from a retroreflective state to a non-retroreflective state. Is contemplated.
[0040]
In another embodiment of the present invention, a multi-color encapsulated electrophoretic display is contemplated. In this embodiment, the display, which may include a capsule, is filled with at least one suspending fluid and at least two, preferably three, particle species. These particles are of different colors and have substantially non-overlapping electrophoretic mobilities. As used herein, the expression "substantially non-overlapping electrophoretic mobility" refers to that less than 25%, preferably less than 5%, of particles of different colors have the same or similar electrophoretic mobility. means. As an example, in a system having two particle species, less than 25% of the particles of one species have the same or similar electrophoretic mobility as the particles of the other species. Finally, in another embodiment, one of the colors may be represented by a dye dispersed in the suspending fluid.
[0041]
Examples of multicolor encapsulated electrophoretic displays may include magenta particles having an average zeta potential of 100 mV, cyan particles having an average zeta potential of 60 mV, and yellow particles having an average zeta potential of 20 mV. When addressing the display in a magenta state, applying an electric field in one direction draws all particles to the back of the cell. The electric field is then reversed for just enough time for the magenta particles to move to the top surface of the display cell. Cyan and yellow particles also move in this inversion field, but they do not move as fast as magenta particles and are therefore obscured by magenta particles.
[0042]
When addressing the display to the cyan state, applying an electric field in one direction draws all particles to the back of the cell. The electric field is then reversed just enough for the magenta and cyan particles to move to the top surface of the display cell. Then, when the electric field is reversed again, the magenta particles, which move faster than the cyan particles, expose the cyan particles at the top of the display.
[0043]
Finally, if a yellow display is to be achieved, all particles are drawn to the front of the display. Then, when the electric field is reversed, yellow particles that lag behind the magenta and cyan particles are exposed at the front of the display.
[0044]
A display using field effect luminescence is also an embodiment of the present invention. Examples of the field effect luminescent embodiments of the present invention require an AC voltage of about 300-400 Hz. However, this high frequency does not cause any net displacement of the luminescent particles. Luminescent particles are generally conductive. Thus, encapsulation in a polymer or other dielectric material is useful for reducing conductivity.
[0045]
9 and 10 show a white state and a dark state of the display cell 48 of this embodiment, respectively. The luminescent particles 50 may be, for example, zinc sulfide particles that emit light when excited by an AC electric field. The AC electric field may be superimposed on the DC electric field used to address the particles or dye, or may be superimposed after the DC electric field. The second particle species 52 in the fluid blocks light emitted from the particles when the display is addressed to a dark state.
[0046]
When a DC electric field is applied by the two electrodes 53, the luminescent particles 50 move to the viewing surface of the display 48 and are excited to emit light, resulting in a bright state. When an electric field of the opposite polarity is applied, the luminescent particles 50 move to the back of the display 48 and the light blocking particles 52 cause the light emitted from the luminescent particles 50 to exit the viewing surface of the display. , Resulting in a dark state. The luminescent particles may be photoluminescent or electroluminescent. The photoluminescent particles may be excited by continuous ultraviolet light, otherwise they may be excited by radiation from the front of the display, or the illumination source may be behind the display. In the latter case, the dye or second particle species allows ultraviolet radiation to pass through the display.
[0047]
In another embodiment of the present invention, the electrophoretic display comprises a capsule in a binder, wherein the capsule comprises a plurality of particles, which themselves are encapsulated pigments, dyes, dispersions, or dyes. Solution. In this embodiment, for example, the pigment is encapsulated to form particles ranging from tens of nanometers to several micrometers, and these particles are then dispersed and encapsulated. Examples are scattering pigments, absorbing pigments, or luminescent particles. These particles are then used as electrophoretic particles. Further, in this embodiment of the invention, it is possible to encapsulate the dye solution and use it as electrophoretic particles.
[0048]
Further, in this embodiment, it is possible not only to encapsulate the fluid dye or particles, but also to encapsulate the fluid dye and the solid particles. These particles have their own optical or electrical properties, which can complement the properties of the dye.
[0049]
These encapsulated particles can be useful for both encapsulated and non-encapsulated electrophoretic displays. The average diameter of the particles ranges from about 10 nm to about 5 μm. These capsules must be small enough to move in larger capsules, and typically have a size in diameter ranging from about 5 μm to about 400 μm.
[0050]
In another embodiment of the present invention, an encapsulated electro-osmotic display is described. In this embodiment, the porous or gel-like internal phase of the capsule is of a refractive index matched fluid (ie, the difference between the refractive index of the fluid and that of the internal phase is preferably within 0.5). Swell (i.e., fill) and drain due to movement caused by electroosmosis. When the pores of the material are filled with the fluid, the capsule acts as a homogeneous optical material, thereby transmitting or reflecting light primarily according to the bulk properties of the medium. However, as the holes are emptied by the moving fluid, there is a large amount of optical index mismatch and light scattering is greatly increased.
[0051]
The porous internal phase of the capsule may include a cellulosic material such as an alkyl cellulose. Examples of alkyl cellulose include, but are not limited to, methylcellulose, methylhydroxyethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, and sodium carboxymethylcellulose.
[0052]
In another embodiment of the present invention, the capsule of the electrophoretic display preferably has a non-spherical shape. There is some light loss associated with encapsulated electrophoretic displays as compared to non-encapsulated displays due to absorption or scattering by the encapsulant and absorption or scattering of the binder. Many of these losses result from spherical cavities. Accordingly, it would be advantageous to provide a non-spherical microcapsule, specifically a tightly packed array of non-spherical cavities. Desirably, the top of the microcapsule has a flat surface that is coplanar with the view electrode and a vertical or near vertical wall. The capsule may be, for example, a slightly flattened sphere, an essentially cylindrical, very flattened sphere, or a polyhedral polyhedron.
[0053]
A display having a non-spherical capsule may include a binder having a non-spherical cavity containing oil. The cavities containing these oils may be elastomeric capsules. In a preferred embodiment, the aspect ratio of these cavities (ie, the ratio of width to height) is preferably greater than about 1.2. The aspect ratio is more preferably greater than about 1.5, and in a particularly preferred embodiment, the aspect ratio is greater than about 1.75. In a preferred embodiment, displays with non-spherical capsules have a binder volume fraction (ie, a fraction of the total volume) of between about 0 and about 0.9. More preferably, the volume fraction is between about 0.05 and about 0.2.
[0054]
This type of display has both a rear surface and a viewing surface. In a preferred embodiment, the view plane is substantially planar. As used herein, the expression “substantially planar” means a curvature of less than about 2.0 m (ie, the reciprocal of the radius of curvature). In a particularly preferred embodiment, both the rear surface and the view surface are substantially planar. Further, such display embodiments preferably have an optically active portion (ie, a percentage of the total surface area that can alter optical properties) of greater than about 80%, and more preferably about 90%. % Of optically active moieties.
[0055]
Non-spherical microcapsules may be formed during the encapsulation phase, for example, by using a non-uniform shear field or compression pressure. Such non-spherical capsules may also be formed during processing of the display when the binder is drying or curing. In such a system, as the binder shrinks, the binder brings the capsules closer together and pulls the capsules down toward the substrate on which the capsules are coated. For example, aqueous evaporative binders such as aqueous acrylics, urethanes, or poly (vinyl alcohol) tend to exhibit such shrink properties. Any other evaporative binder, emulsion, or solution is also suitable. The solvent need not be water, and may be an organic liquid or a combination of liquids.
[0056]
Such non-spherical capsules can be formed by applying force to the membrane as it dries or cures, causing the capsule to permanently deform. Such a force may be applied by a roller pair, a vacuum lamination press, a mechanical press, or any other suitable means. Such non-spherical capsules may also be formed by stretching the cured film in one or both of the plane axes of the film. After completion of the curing process, the capsule can protrude above the surface of the cured film, resulting in a lens effect that enhances the optical properties of the capsule. Finally, the capsule may also consist of a material that softens in the binder, which allows a flattened capsule when the capsule and the binder are placed and the binder is cured.
[0057]
In another embodiment, a polymer dispersed electrophoretic display is configured in a manner similar to a polymer dispersed liquid crystal display. As the binder dries or hardens, the encapsulated phase is drawn into the non-spherical cavity.
[0058]
Electrophoretic displays are configured as either encapsulated electrophoretic displays or polymer dispersed electrophoretic displays (similar configurations to polymer dispersed liquid crystal displays), and the capsules or droplets are flattened, binder shrinkage Or a non-spherical shape due to mechanical force. In each case, the capsule must be able to deform, otherwise the capsule may burst. In the case of polymer dispersed electrophoretic displays, the encapsulated phase changes shape as the polymer shrinks. Further, the encapsulated phase may be deformed asymmetrically by stretching the substrate. Another technique that can be used is to first dry the binder so that a firm skin is formed on it. The remainder of the binder can then be dried slowly without fear of tearing or excessively uneven top surface.
[0059]
The electrodes adjacent to the electrophoretic display can include a conductive polymer, such as, for example, polyaniline. These materials may be soluble, allowing them to be coated, for example, by web coating.
[0060]
Means for addressing the encapsulated electrophoretic display (or other display) are also described. Referring to FIG. 11, electrodes 66 and 66 'are on one side of the display. These electrodes may be part of the head ("stylus") that is scanned over the display. The number of capsules may be more than one, less than one, or just one per electrode pair. Applying a DC electric field to the pixel moves the particles to one side and exposes the underlying substrate 68 (eg, mirror, retroreflective coating, diffuse reflective coating, etc.). Under the influence of an AC electric field, the particles 70 can be distributed throughout space and can cause the appearance of predominantly dark pixels. The electrodes themselves may be transparent or opaque.
[0061]
A similar structure is described with reference to FIGS. 12A and 12B. However, the electrodes 72 and 72 'are different in size (e.g., a factor greater than 2). By changing the polarity of the electric field, the particles move and mask either electrode. In one case (FIG. 12A), the particles cover a small area and the pixels are primarily reflective. In the other case (FIG. 12B), the particles 74 'cover a large area and the pixels are primarily absorbent. The materials may be reversed. For example, the particles may be reflective and the backing material may be absorbent. There may be a mask covering one of the electrode locations on the material.
[0062]
This display addressing method involves writing using an electrostatic head that is permanently attached to a fixture or held by hand. This method may also be applied to encapsulated magnetophoretic materials. This method may also be applied to polymer stabilized liquid crystal technology, and may be applied to any type of bistable liquid crystal material, for example, nematic on a photo-alignment layer. This method may also be applied to suspended particle displays.
[0063]
Referring again to both FIGS. 11 and 12, in either embodiment, the back electrode is not reflective and may be provided as a transmissive, translucent, or otherwise transparent backing material. Good. In these embodiments, as described above, due to the DC electric field, dark (absorbing) particles can cover one electrode, and the pixels are primarily transparent. These embodiments allow the display to be used to be a "shutter" of light. For example, a display including the described capsule may be addressed such that all pixels present in the display are primarily transparent. In this case, the display acts as a window or transparent device. Alternatively, if portions of the capsule are addressed, the display is partially transparent. If all capsules are addressed using an AC electric field, the display is either opaque or reflective.
[0064]
II. Materials used for electrophoretic displays
Useful materials for constructing the above-described encapsulated electrophoretic display are described below. Many of these materials are known to those skilled in the art of constructing conventional electrophoretic displays or to those skilled in microencapsulation. The combination of these materials and processes, together with other necessary components found in an encapsulated electrophoretic display, make up the invention described below.
[0065]
A.particle
As mentioned above, the choice of particles used in an electrophoretic display is very flexible. For the purposes of the present invention, a particle is any component that is charged or capable of acquiring a charge (ie, has or can acquire electrophoretic mobility), and in some cases, This mobility may be zero or near zero (ie, the particles do not move). The particles may be neat pigments, dyed (lake) pigments, or pigment / polymer composites, and may be any other component that can be charged or acquire a charge. Typical considerations for electrophoretic particles are the optical, electrical, and surface chemistry of the particles. The particles may be organic or inorganic compounds, and the particles may absorb light or scatter light. The particles used in the present invention can further include scattering pigments, absorbing pigments, and luminescent particles. The particles may be retroreflective, such as corner cubes, and may be electroluminescent or photoluminescent, such as zinc sulfide particles that emit light when excited by an AC electric field. Finally, the particles may be surface-treated to enhance their interaction with the charging agent or charging, or to improve their dispersibility.
[0066]
A preferred particle used in the electrophoretic display of the present invention is titania. The titania particles may be coated with a metal oxide, for example, aluminum oxide or silicon oxide. The titania particles may have one, two or more layers of a metal oxide coating. For example, the titania particles used in the electrophoretic display of the present invention may have a coating of aluminum oxide and a coating of silicon oxide. These coatings may be applied to the particles in any order.
[0067]
The electrophoretic particles are typically pigments, polymers, lake pigments, or some combination of the above. The neat pigment may be any pigment, and in the case of light-colored particles, pigments such as rutile (titania), anatase (titania), barium sulfate, kaolin, or zinc oxide are usually useful. Some typical particles have a high refractive index, a high scattering coefficient, and a low absorption coefficient. Some particles are absorbent, such as colored pigments or carbon black used in paints and inks. The pigment must also be insoluble in the suspending fluid. Yellow pigments, such as diarylide yellow, hansa yellow, and benzidine yellow, also find use in similar displays. For the light colored particles, any other reflective material may be used, including non-pigmented materials such as metal particles.
[0068]
Useful neat pigments include, but are not limited to: PbCr₄, Cyan Blue GT 55-3295 (American Cyanamid Company, Wayne, NJ), Cibacron Black BG (Ciba Company, Inc., Newport, DE), Cibacron Turquoise Blue G (Ciba), Civalon Black BGL (Cib). Orasol Black BRG (Ciba), Orasol Black RBL (Ciba), Acetamine Black, CBS (EI du Pont de Nemours and Company, Inc., Wilmington, DE), Closet Scarlet N Ex (du Pont) (27290), Fiber Black VF (duPont) (30235), Luxor Fast Black L (duPont) (Solv. Black 17) , Nyrosine base No. 424 (duPont) (50415 B), Oil Black BG (duPont) (Solv. Black 16), Rotalin Black RM (duPont), Sebron Brilliant Red 3B (duPont); Basic Black DSC (Dye Specialties, Inc.) Hectoren Black (Dye Specialties, Inc.), Azosol Brilliant Blue B (GAF, Diestuff and Chemical Division, Wayne, NJ) (Solv. Blue 9), Azosol Brilliant Green BA (GAF) (Solv. Green 2). , Azosol Fast Brilliant Red B (GAF), Azosol Fast Orange RA Conc. (GAF) (Solv. Orange 20), Azosol Fast Yellow GRA Conc. (GAF) (13900 A), Basic Black KMPA (GAF), Benzofix Black CW-CF (GAF) (35435), Seritazol BNFV Ex Soluble CF (GAF) (Disp. Black 9), Seriton Fast Blue AF Ex Conc (GAF) (Disp. Blue 9), Cyper Black IA (GAF) (Basic Black 3), Diamine Black CAP Ex Conc (GAF) (30235), Diamond Black EAN Hi Conc. CF (GAF) (15710), diamond black PBBA Ex (GAF) (16505); direct deep black EA Ex CF (GAF) (30235), Hansa Yellow G (GAF) (11680); indanthrene black BBK powder (GAF) ) (59850), India Carbon CLGS Conc. CF (GAF) (53295), Kachigen Deep Black NND Hi Conc. CF (GAF) (15711), Rapidogen Black 3 G (GAF) (Azoic Black 4); Sulfocyanine Black BA-CF (GAF) (26370), Zambezi Black VD Ex Conc. (GAF) (30015); Lubanox Red CP-1495 (The Sherwin-Williams Company, Cleveland, OH) (15630); Jet Black 11 (Columbian Carbon Company, Atlanta, GA), (carbon black having a particle size of about 25 μm) Aggregates), Statex B-12 (Columbian Carbon Co.) (furnace black with an average particle size of 33 μm), and chrome green.
[0069]
The particles may also include lake pigments or dye pigments. Lake pigments are particles on which a dye has been deposited or which are to be dyed. Lakes are readily soluble metal salts of anionic dyes. These are dyes of azo, triphenylmethane or anthraquinone structure containing one or more sulfonic or carboxylic acid groups. These are usually deposited on a substrate by means of calcium, barium or aluminum salts. Typical examples are Peacock Blue Lake (CI Pigment Blue 24) and Persian Orange (lake of CI Acid Orange 7), Black M Toner (GAF) (mixture of black dye and carbon black deposited on the lake).
[0070]
The dyed type dark particles may be composed of any light absorbing material, such as carbon black or inorganic black material. Dark materials may also be selectively absorbent. For example, a dark green pigment can be used. Black particles may also be formed by dyeing the latex with metal oxides, such latex copolymers include butadiene, styrene, isoprene, methacrylic acid, methyl methacrylate, acrylonitrile, vinyl chloride, acrylic acid, sodium styrene Consists of any of sulfonate, vinyl acetate, chlorostyrene, dimethylaminopropyl methacrylamide, isocyanoethyl methacrylate, and N- (isobutoxymethacrylamide), optionally, diacrylate, triacrylate, dimethyl acrylate, and trimethacrylate, etc. Conjugated diene compounds. Black particles may also be formed by dispersion polymerization techniques.
[0071]
In systems including pigments and polymers, the pigments and polymers may form multiple domains within the electrophoretic particles and may be aggregates of smaller pigment / polymer combination particles. Alternatively, the central pigment core may be surrounded by a polymer shell. The pigment, the polymer, or both, may include a dye. The optical purpose of the particles can be light scattering, light absorption, or both. Useful sizes can range from 1 nm to about 100 μm, as long as the particles are smaller than the bounding capsule. The density of the electrophoretic particles can substantially match the density of the suspension (ie, electrophoresis) fluid. As used herein, if the density difference between the suspending fluid and the particles is between about 0 g / ml and about 2 g / ml, the suspending fluid has a density that “substantially matches” the density of the particles. It is prescribed. This difference is preferably between about 0 g / ml and about 0.5 g / ml.
[0072]
Useful polymers for the particles include, but are not limited to: Polystyrene, polyethylene, polypropylene, phenolic resin, DuPont Elvax resin (ethylene-vinyl acetate copolymer), polyester, polyacrylate, polymethacrylate, ethylene acrylic acid or methacrylic acid copolymer (Nucrel resin-DuPont, Primacor resin-Dow Chemical), acrylic Copolymers and terpolymers (Elvacite resin, DuPont), and PMMA. Useful materials for homopolymer / pigment phase separation in high shear melting include, but are not limited to: Polyethylene, polypropylene, polymethyl methacrylate, polyisobutyl methacrylate, polystyrene, polybutadiene, polyisoprene, polyisobutylene, polylauryl methacrylate, polystearyl methacrylate, polyisobornyl methacrylate, poly-t-butyl methacrylate, polyethyl methacrylate, polymethyl acrylate , Polyethyl acrylate, polyacrylonitrile, and copolymers of two or more of the above materials. Some useful pigment / polymer composites available commercially include, but are not limited to: Process Magenta PM 1776 (Magruder Color Company, Inc., Elizabeth, NJ), Methyl Violet PMA VM6223 (Magruder Color Company, Inc., Elizabeth, NJ), and naphthol FGR RFerg, Eger, Niger, Eger, Norg. .
[0073]
The pigment-polymer complex is formed by a physical process (eg, attrition or ball milling), a chemical process (eg, microencapsulation or dispersion polymerization), or any other process known in the particle manufacturing art. obtain. From the following examples, it can be seen that processes and materials for both particle production and particle charging generally come from the field of liquid toner or immersion phenomena. These examples do not limit the invention. Thus, any of the known processes from liquid phenomena are particularly relevant, but not only.
[0074]
New useful electrophoretic particles may still be found, but many particles already known to those skilled in the art of electrophoretic displays and liquid toners may also prove useful. Generally, polymer requirements for liquid toners and encapsulated electrophoretic inks are such that pigments or dyes must be easily incorporated into them by either physical, chemical or physico-chemical processes, and colloidal stability As well, in that it may include a charging site or may incorporate a material that includes a charging site. One common requirement from the liquid toner industry, which is not shared by encapsulated electrophoretic inks, is that the toner must be able to "fix" the image, i.e., after the deposition of toner particles. It must be able to produce a uniform film by heat melting.
[0075]
Typical particle manufacturing techniques are obtained from liquid toners and other fields and include ball milling, attrition, jet milling, and the like. The process is described for the case of colored polymer particles. In such cases, the pigment is incorporated into the polymer, usually in some type of high shear mechanism such as a screw extruder. The composite is then ground (wet or dry) to a starting size of about 10 μm. This is then converted to, for example, ISOPAR^?(Exxon, Houston, TX) in a carrier liquid, optionally with any charge control agent (s), and under high shear until the final particle size and / or size distribution is achieved. Crush for several hours.
[0076]
Another particle manufacturing technique available from the liquid toner field is to add polymers, pigments and suspending fluids to a media mill. The mill is heated upon start-up to a temperature at which the polymer substantially swells with the solvent. This temperature is typically around 100 ° C. In this state, the pigment is easily encapsulated in the swollen polymer. After a suitable time, typically a few hours, the mill is slowly cooled down to ambient temperature with stirring. Particle size small enough, typically a number? ? ? Milling may be continued for some time to achieve a diameter of from a few microns. At this time, a charging agent may be added. Optionally, additional suspending fluid may be added.
[0077]
Any chemical process such as dispersion polymerization, mini or microemulsion polymerization, suspension polymerization precipitation, phase separation, solvent evaporation, in situ polymerization, seed emulsion polymerization, or any in the general category of microencapsulation Can be used. A typical process of this type is a phase separation process in which dissolved polymer material is deposited from a solution onto a dispersed pigment surface by solvent dilution, evaporation, or thermal change. Other processes include chemical means for dyeing the polymer latex, for example, using metal oxides or dyes.
[0078]
B.Suspended fluid
The suspending fluid containing the particles can be selected based on properties such as density, refractive index, and solubility. Suitable suspending fluids have low dielectric constant (about 2), high volume resistivity (about 10-15 ohm-cm), low viscosity (less than 5 cst), low toxicity and environmental impact, low water solubility (less than 10 ppm), It has high specific gravity (above 1.5), high boiling point (above 90 ° C.), and low refractive index (below 1.2).
[0079]
The choice of the suspending fluid may be based on considerations of chemical inertness, density matching with the electrophoretic particles, or chemical compatibility with the electrophoretic particles and the bounding capsule. When moving the fluid, the viscosity of the fluid must be low. The refractive index of the suspending fluid may also substantially match the refractive index of the particles. As used herein, if the refractive index difference between the suspending fluid and the particles is between about zero and about 0.3, and preferably between about 0.05 and about 0.2, the suspending fluid Is said to "substantially match" the refractive index of the particles.
[0080]
Further, the fluid may be selected to be a poor solvent for some polymers. This is advantageous when used for the production of microparticles. This is because poor solvents increase the range of polymeric materials useful for producing polymer and pigment particles. Organic solvents such as halogenated organic solvents, saturated linear or branched hydrocarbons, silicone oils, and low molecular weight halogen-containing polymers are some useful suspending fluids. The suspending fluid may include a single fluid. However, the fluid is often a blend of more than one fluid to adjust its chemical and physical properties. In addition, the fluid may include a surface modifier to modify the surface energy or charge of the electrophoretic particles or the bounding capsule. Reactants or solvents (eg, oil-soluble monomers) for the microencapsulation process may also be included in the suspending fluid. Charge control agents may also be added to the suspending fluid.
[0081]
Useful organic solvents include, for example, epoxides such as decane epoxide and dodecane epoxide, for example, cyclohexyl vinyl ether and vinyl ethers such as Decave ™ (International Flavors & Fragrances, Inc., New York, NY), and toluene and naphthalene, for example. , Aromatic hydrocarbons, but is not limited thereto. Useful halogenated organic solvents include, but are not limited to, tetrafluorodibromoethylene, tetrachloroethylene, trifluorochloroethylene, 1,2,4-trichlorobenzene, carbon tetrachloride. These materials have a high density. Useful hydrocarbons include dodecane, tetradecane, Isopar ™ series (Exxon, Houston, TX), Norpar ™ (series of ordinary paraffin liquids), Shell-Sol ™ (Shell, Houston, TX) , And Sol-Trol ™ (Shell) aliphatic hydrocarbons, naphtha, and other petroleum-based solvents. These materials usually have a low density. Useful examples of silicone oils include, but are not limited to, octamethylcyclosiloxane and higher molecular weight cyclic siloxanes, poly (methylphenylsiloxane), hexamethyldisiloxane, and polydimethylsiloxane. These materials usually have a low density. Useful low molecular weight halogen-containing polymers include poly (chlorotrifluoroethylene) polymers (Halogenated hydroxycarbon Inc., River Edge, NJ), Galden ™ (perfluoroether of Ausimont (Morristown, NJ)) or Dupont ( Wilmington, DE) Krytox ™, but is not limited thereto. In a preferred embodiment, the suspending fluid is a poly (chlorotrifluoroethylene) polymer. In a particularly preferred embodiment, the polymer has a degree of polymerization from about 2 to about 10. Many of the above materials are available in a range of viscosities, densities, and boiling points.
[0082]
The fluid must be able to be broken into small droplets before the capsule is formed. Processes for forming small droplets include flow-through jets, membranes, nozzles, or orifices, and shear-based emulsification mechanisms. The formation of small droplets may be assisted by an electric or sound field. In the case of emulsion type encapsulation, surfactants and polymers may be used to help stabilize and emulsify the droplets. A preferred surfactant used in the displays of the present invention is sodium dodecyl sulfate.
[0083]
In some displays, it may be advantageous for the suspending fluid to include a light absorbing dye. The dye must be soluble in the fluid, but is generally insoluble in the other components of the capsule. The choice of dye material is very flexible. Dyes can be pure compounds or blends of dyes to achieve a particular color, such as black. These dyes may be fluorescent. In this case, a display is created whose fluorescence properties depend on the location of the particles. Dyes may be photoactive, in which case they either turn to another color or become colorless when irradiated with either visible or ultraviolet light, providing another means for obtaining an optical response . The dye may also be polymerizable, in which case it forms a solid absorbent polymer inside the bordering shell.
[0084]
There are many dyes that can be selected for use in an encapsulated electrophoretic display. Important properties here include light fastness, solubility in suspension, color, and cost. These dyes are generally from the class of the azo, anthraquinone, and triphenylmethane dyes and can be chemically modified to increase solubility in the oil phase and reduce adsorption by fluid surfaces. .
[0085]
Many dyes already known to those skilled in the electrophoretic display art find useful. Useful azo dyes include, but are not limited to, oil red dyes and the Sudan Red and Sudan Black dye series. Useful anthraquinone dyes include, but are not limited to, oil blue dyes and macrolex blue dye series. Useful triphenylmethane dyes include, but are not limited to, Michler's hydrol, malachite green, crystal violet, and auramine O.
[0086]
C.Charge control agents and particle stabilizers
Charge control agents are used to provide electrophoretic particles with excellent electrophoretic mobility. The stabilizer prevents aggregation of the electrophoretic particles and prevents the electrophoretic particles from irreversibly depositing on the capsule wall. Either component can be composed of materials that span a wide range of molecular weights (low molecular weight, oligomers or polymers) and can be pure or mixtures. Specifically, suitable charge control agents are generally adapted from the liquid toner field. The charge control agents used to modify and / or stabilize the particle surface charge are applied as generally known in the fields of liquid toners, electrophoretic displays, non-aqueous paint dispersions, and engine oil additives. You. In all of these fields, charged species may be added to non-aqueous media to increase electrophoretic mobility or increase electrostatic stabilization. These materials can also improve steric stabilization. Different charging theories are assumed, such as selective ion adsorption, proton transfer, and contact charging.
[0087]
Any charge control or charge directing agent may be used. These components typically consist of low molecular weight surfactants, polymeric agents, or blends of one or more components to stabilize the sign and / or magnitude of the charge on the electrophoretic particles or Serves to denature in other ways. The charging properties of the pigment itself may be described by taking into account the acidic or basic surface properties of the pigment, or the charging site may occur at the carrier resin surface, if any; Or, a combination of these two. Additional pigment properties that may be relevant are particle size distribution, chemical composition, and light fastness. The charge control agents used to modify and / or stabilize the particle surface charge are applied as generally known in the fields of liquid toners, electrophoretic displays, non-aqueous paint dispersions, and engine oil additives. You. In all of these fields, charged species may be added to non-aqueous media to increase electrophoretic mobility or increase electrostatic stabilization. These materials can also improve steric stabilization. Different charging theories are assumed, such as selective ion adsorption, proton transfer, and contact charging.
[0088]
Charge adjuvants may also be added. These materials increase the efficacy of the charge control or charge directing agent. The charge adjuvant may be a polyhydroxy compound or an amino alcohol compound. These compounds are preferably soluble in the suspending fluid in an amount of at least 2% by weight. Examples of polyhydroxy compounds containing at least two hydroxyl groups include ethylene glycol, 2,4,7,9-tetramethyl-decyn-4,7-diol, poly (propylene glycol), pentaethylene glycol, Examples include, but are not limited to, propylene glycol, triethylene glycol, glycerol, pentaerythritol, glycerol-tri-12 hydroxystearate, propylene glycerol monohydroxystearate, and ethylene glycol monohydroxystearate. Examples of amino alcohol compounds containing at least one alcohol function and one amine function in the same molecule include triisopropanolamine, triethanolamine, ethanolamine, 3-amino-1 propanol, o-aminophenol, 5- But not limited to amino-1-pentanol and tetra (2-hydroxyethyl) ethylene-diamine. The charge adjuvant is preferably present in the suspension fluid in an amount from about 1 mg / g to about 100 mg / g, more preferably from about 50 mg / g to about 200 mg / g of the particle mass.
[0089]
The surface of the particles may also be chemically modified, for example, to aid dispersion, to increase surface charge, and to increase dispersion stability. Surface modifiers include organosiloxanes, organohalogensilanes, and other functional silane coupling agents (Dow @ Corning ™ Z-6070, Z-6124, and three additives, Midland, MI); organic titanates And zirconates (Tyzor ™ TOT, TBT, and TE series, Dupont, Wilmington, DE); long chain (C12-C50) alkyl and alkyl benzene sulfonic acids, fatty amines or diamines, and their salts or quaternary derivatives And amphiphilic polymers that can be covalently attached to the particle surface.
[0090]
In general, it is believed that charging results in an acid-base reaction between some of the parts present in the continuous phase and the particle surface. Thus, useful materials are those that can participate in such reactions or any other charging reactions known in the art.
[0091]
Different classes of useful charge control agents include organic sulfates or sulfonates, metal soaps, block or comb copolymers, organic amides, organic zwitterions, and organic phosphates and phosphonates. These classifications do not limit the invention. Useful organic sulfates and sulfonates include bis (2-ethylhexyl) sodium sulfosuccinate, calcium dodecylbenzene sulfonate, calcium petroleum sulfonate, neutral or basic barium dinonyl naphthalene sulfonate, neutral or basic calcium disulfide. Non-limiting examples include, but are not limited to, nonylnaphthalenesulfonate, sodium dodecylbenzenesulfonate, and ammonium lauryl sulfate. Useful metal soaps include basic or neutral barium petronate; calcium petronate; Co, Ca, Cu, Mn, Ni, Zn and Fe salts of naphthenic acid; Ba, Al, Zn, Cu, Pb of stearic acid And Fe salts; aluminum tristearate, aluminum octylate, lithium heptanoate, iron stearate, iron distearate, barium stearate, chromium stearate, magnesium octylate, calcium stearate, iron naphthenate, zinc naphthenate, etc. And carboxylates of divalent and trivalent metals; Mn and Zn heptanoate; and Ba, Al, Co, Mn and Zn octylate. Useful block or comb polymers include (A) a polymer of 2- (N, N) dimethylaminoethyl methacrylate quaternized with methyl-p-toluenesulfonate and (B) poly-2-ethylhexyl methacrylate. An AB diblock copolymer and a comb graft copolymer having an oil-soluble tail of poly (12-hydroxystearic acid), having a molecular weight of about 1800, and depending on the oil-soluble anchor group of poly (methyl methacrylate-methacrylic acid). , But is not limited to these. Useful organic amides include, but are not limited to, polyisobutylene succinimide, such as OLOA 1200, and N-vinyl pyrrolidone polymer. Useful organic zwitterions include, but are not limited to, lecithin. Useful organophosphates and phosphonates include, but are not limited to, the phosphorylated mono and diglyceride sodium salts having a saturated or unsaturated acid substituent.
[0092]
A particle dispersion stabilizer may be added to prevent flocculation or adhesion of the particles to the capsule wall. Non-aqueous surfactants may be used for typical high resistance liquids used as suspending fluids in electrophoretic displays. These surfactants include, but are not limited to, glycol ethers, acetylene glycols, alkanoamides, sorbitol derivatives, alkylamines, quaternary amines, imidazolines, dialkyl oxides, and sulfosuccinates.
[0093]
D.Encapsulation
Encapsulation has a long and rich history, and many processes and polymers have been found to be useful in creating capsules. Encapsulation of the internal phase can be achieved in a number of different ways. A number of suitable procedures for microencapsulation are described in Microencapsulation, Processes and Applications (edited by IE Vandegaer), Plenum Press, New York, NY (1974), and Gutcho, Micronescaps. Park Ridge, N .; J. (1976). In this specification, both of the above documents are incorporated by reference. Processes fall into several general categories: physical processes such as interfacial polymerization, in situ polymerization, coextrusion and other phase separation processes, in-liquid curing, and simple / complex coacervation. All of these categories can be applied to the present invention.
[0094]
Many materials and processes must be found to be useful for making the displays of the present invention. Useful materials for the simple coacervation process include, but are not limited to, gelatin, polyvinyl alcohol, polyvinyl acetate, and cellulose derivatives such as, for example, carboxymethylcellulose. Useful materials for the complex coacervation process include gelatin, acacia, carrageenan, carboxymethylcellulose, hydrolyzed styrene anhydride copolymer, agar, alginate, casein, albumin, methyl vinyl ether comalein anhydride, and phthalate. Acid cellulose, but is not limited thereto. Useful materials for the phase separation process include, but are not limited to, polystyrene, PMMA, polyethyl methacrylate, polybutyl methacrylate, ethyl cellulose, polyvinyl pyridine, and polyacrylonitrile. Useful materials for the in situ polymerization process include polyhydroxyamides with aldehydes, melamine, or urea and formaldehyde; water-soluble oligomers of melamine or condensates of urea and formaldehyde; and, for example, styrene, MMA, and acrylonitrile; Such as, but not limited to, vinyl monomers. Finally, useful materials for the interfacial polymerization process include, but are not limited to, diacyl chlorides, such as, for example, sebacoyl, adipoyl, and di- or polyamines or alcohols, and isocyanates. Useful emulsion polymerization materials can include, but are not limited to, styrene, vinyl acetate, acrylic acid, butyl acrylate, t-butyl acrylate, methyl methacrylate, and butyl methacrylate.
[0095]
The resulting capsules can be dispersed in a curable carrier, resulting in an ink that can be printed or coated on large surfaces of any shape or curvature using conventional printing and coating techniques.
[0096]
In the context of the present invention, one skilled in the art will select the encapsulation procedure and the wall material based on the desired capsule properties. These properties include the distribution of the capsule radius; the electrical, mechanical, diffusive and optical properties of the capsule wall; and the chemical compatibility with the internal phase of the capsule.
[0097]
The capsule wall generally has a high electrical resistivity. It is possible to use walls with relatively low resistivity, but this can limit performance when relatively high addressing voltages are required. A complete description of the relevant electrical properties of the capsule wall can be found in U.S. Pat. No. 4,605,284, which is hereby incorporated by reference in its entirety. The capsule wall must also be mechanically strong (although mechanical strength is not critical if the finished capsule powder is dispersed and coated in a curable polymer binder) ). The capsule wall should generally not be porous. However, if it is desired to use an encapsulation procedure that produces porous capsules, these capsules may be overcoated in a post-processing step (ie, a second encapsulation). Furthermore, when the capsules are dispersed in a curable binder, the binder serves to close the pores. The capsule wall must be optically transparent. However, the wall material may be selected to match the refractive index of the internal phase of the capsule (ie, the suspending fluid) or the binder in which the capsule is dispersed. For some applications (eg, insertion between two fixed electrodes), a monodisperse capsule radius is desirable.
[0098]
Encapsulation techniques that are very suitable for the present invention are described in U.S. Pat. No. 4,087,376, the entire disclosure of which is incorporated herein by reference. This procedure involves the polymerization of urea and formaldehyde in the aqueous phase of an oil / water emulsion in the presence of a negatively charged carboxyl-substituted linear hydrocarbon polyelectrolyte material. The resulting capsule wall is a urea / formaldehyde copolymer that separates and encloses the internal phase. The capsule is transparent, mechanically strong and has excellent resistance properties.
[0099]
A related technique of in situ polymerization uses an oil / water emulsion formed by dispersing an electrophoretic composition (ie, a dielectric liquid including a suspension of pigment particles) in an aqueous environment. The monomers polymerize to form a polymer having a higher affinity for the inner phase than for the aqueous phase, thereby condensing around the emulsified oily droplets. In one particularly useful in situ polymerization process, urea and formaldehyde are condensed in the presence of poly (acrylic acid) (see, for example, US Pat. No. 4,001,140). In another useful process described in U.S. Pat. No. 4,273,672, any of a variety of crosslinkers carried in an aqueous solution is deposited around very small oil droplets. Such crosslinking agents include aldehydes, especially formaldehyde, glyoxal, or glutaraldehyde; alum; zirconium salts; and polyisocyanates. In this specification, the entire disclosures of the aforementioned U.S. Patent Nos. 4,001,140 and 4,273,672 are incorporated by reference.
[0100]
The coacervation approach also uses an oil / water emulsion. One or more colloids are dropletized (i.e., agglomerated) from the aqueous phase and are deposited as a shell around the oily droplets by controlling temperature, pH and / or relative concentration, thereby providing microcapsules. To produce Suitable materials for coacervation include gelatin and acacia. See, for example, U.S. Patent No. 2,800,457. In this specification, the entire disclosure of the above patent is incorporated by reference.
[0101]
Interfacial polymerization approaches rely on the presence of oil-soluble monomers in the electrophoretic composition. This oil-soluble monomer is present again as an emulsion in the aqueous phase. The monomers in the small hydrophobic droplets react with the monomers introduced into the aqueous phase, polymerize at the interface between the droplets and the surrounding aqueous medium, and form a shell around the droplets. Although the resulting wall may be relatively thin and permeable, this process does not require the high temperature properties of some other processes, thus providing greater flexibility with regard to the choice of dielectric liquid. give.
[0102]
FIG. 13A illustrates an exemplary apparatus and environment for performing emulsion-based encapsulation. The oil / water emulsion is prepared in a container 76 comprising a device 78 for monitoring temperature and a device 80 for controlling temperature. A pH monitor 82 may also be included. The impeller 84 may be used to maintain agitation throughout the encapsulation process and, in combination with an emulsifier, to control the size of the emulsion droplets 86 that result in a finished capsule. The aqueous continuous phase 88 may include, for example, a prepolymer or various system modifiers.
[0103]
FIG. 13B shows an oil droplet 90 including a substantially transparent suspending fluid 92 in which white microparticles 94 and black particles 96 are dispersed. Preferably, particles 94 and 96 have a density that substantially matches the density of suspending fluid 92. The liquid phase may also include some threshold / bistable modifiers, charge control agents, and / or hydrophobic monomers to effect interfacial polymerization.
[0104]
FIG. 13C shows a similar oil droplet 98 containing a suspension fluid 100 that has been stained dark with a dispersion of white particles 94 and a suitable charge control agent.
[0105]
Coating aids may be used to improve the uniformity and quality of the coated or printed electrophoretic ink material. Wetting agents are typically added to adjust the interfacial tension at the coating / substrate interface and to adjust the liquid / air surface tension. Wetting agents include, but are not limited to, anionic and cationic surfactants and non-ionic species such as silicone or fluoropolymer based materials. Dispersants may be used to modify the interfacial tension between the capsule and the binder to provide control of flocculation and particle settling.
[0106]
A surface tension modifier may be added to adjust the air / ink interfacial tension. In such applications, polysiloxanes are typically used to improve surface leveling and minimize other defects in the coating. Surface tension modifiers include, for example, the Zonyl ™ series of DuPont (Wilmington, DE), the Fluorod ™ series of 3M (St. Paul, MN), and the fluoroalkyl series of Autochem (Glen @ Rock, NJ), Siloxanes, such as, but not limited to, fluorinated surfactants such as; Silwet ™ from Union Carbide (Danbury, Conn.); And polyethoxy and polypropoxy alcohols. Defoamers such as silicone and silicone-free polymeric materials may be added to enhance air movement from within the ink to the surface and to facilitate the rupture of air bubbles on the coated surface. Other useful defoamers include glyceryl esters; polyhydric alcohols; compounded defoamers such as alkylbenzenes, natural fats, fatty acids, and oils of metal soaps; and silicones made from combinations of dimethylsiloxane polymers and silica. Defoamers, and the like, but are not limited to these. Stabilizers such as uv absorbers and antioxidants may also be added to increase the life of the ink.
[0107]
Other additives for controlling properties such as coating viscosity and foaming may also be used in the coating fluid. Stabilizers (uv absorbers, antioxidants) and other additives may prove useful in practical materials.
[0108]
E. FIG.Binder material
Binders are used as a non-conductive adhesive medium to support and protect the capsule and bind the electrode material to the capsule dispersion. Many forms and chemical types of binders are available. Among these binders are water-soluble polymers, aqueous polymers, oil-soluble polymers, thermosetting and thermoplastic polymers, and radiation-curable polymers.
[0109]
Among the water soluble polymers are various polysaccharides, polyvinyl alcohol, N-methylpyrrolidone, N-vinylpyrrolidone, various Carbowax ™ species (Union @ Carbide, Danbury, CT), and poly-2-hydroxyethyl acrylate , There is.
[0110]
Water-dispersed or aqueous systems are generally latex compositions, typical of which are Neorez ™ and Neocryl ™ resins (Zeneca Resins, Wilmington, Mass.), Acrysol ™ (Rohm and Haas, Philadelphia, PA), Bayhydrol ™ (Bayer, Pittsburg, PA), and Cytec Industries (West Paterson, NJ) HP lines. These latex compositions are generally polyurethane latexes, which may be formulated with one or more of acrylic, polyester, polycarbonate, or silicone, where each latex has a glass transition temperature, "tack" degree, softness, It gives the cured resin in a specific set of properties defined by clarity, flexibility, water penetration and solvent resistance, elongation and tensile strength, thermoplastic flow, and solids level. Some aqueous systems can be mixed with reactive monomers and catalyzed to form more complex resins. Some can be further cross-linked by the use of a cross-linking agent, such as aziridine, which reacts with the carboxyl group.
[0111]
Typical applications of aqueous resins and aqueous capsules are shown below. Centrifuge large amounts of particles at low speed to separate excess water. After a given centrifugation process, eg, 10 minutes at 60 × G, capsules are found at the bottom of the centrifuge tube and the water portion is found at the top. Carefully remove the water portion (by decantation or pipette). The weight of the remaining capsules is measured and the resin is added in a weight such that it is between 1/8 and 1/10 of the weight of the capsule. The mixture is mixed gently with a vibrating mixer for about 30 minutes. After about 30 minutes, the mixture is ready for coating on a suitable substrate.
[0112]
An example of a thermosetting system is epoxy. The viscosities of these two-component systems can vary widely, and the reactivity of the pair determines the "pot life" of the mixture. If the pot life is long enough to allow the coating operation, the capsules can be coated in a regular sequence in the coating process before curing and curing of the resin occurs.
[0113]
Thermoplastic polymers are melted at high temperatures. The thermoplastic polymer is often a polyester. A typical application of this type of product is hot melt glue. The dispersion of the heat-resistant capsule may be coated with such a medium. The solidification process begins during cooling and the final hardness, clarity and flexibility are affected by the branching and molecular weight of the polymer.
[0114]
Oil-soluble or solvent-soluble polymers are often similar in composition to aqueous systems. However, the water itself is clearly the exception. The tolerances in making the solvent system are very large and are limited only by the choice of solvent and the solubility of the polymer. Of considerable importance in solvent-based systems is the viability of the capsule itself, and no matter what, the integrity of the capsule can be reduced by the solution.
[0115]
Radiation curable resins are generally found in solvent-based systems. The capsules may be dispersed and coated in such a medium, and the resin may then be cured by timed exposure to a threshold level of long or short wavelength ultraviolet radiation. As in all cases of curing a polymer resin, the final properties depend on the branching and molecular weight of the monomers, oligomers, crosslinkers.
[0116]
However, a number of "water reducing" monomers and oligomers are on the market. In a strict sense, these monomers and oligomers are not water-soluble, but water can be relatively easily dispersed in the mixture because at low concentrations, it is an acceptable diluent. Under these circumstances, water is used to reduce the viscosity (from the first thousands to hundreds of thousands of centipoise). Water-based capsules, for example capsules made from protein or polysaccharide materials, can be dispersed in such media and coated, provided the viscosity can be reduced sufficiently. Curing of such systems is generally due to ultraviolet radiation.
[0117]
III. Example
Example 1
The following procedure describes the gelatin / acacia microencapsulation used in the electrophoretic display of the present invention.
[0118]
APreparation of oil (inner) phase
In a 1 L flask, 0.5 g of Oil Blue N (Aldrich, Milwaukee, Wis.), 0.5 g of Sudan Red 7B (Aldrich), 417.25 g of halogenated hydrocarbon oil 0.8 (Halogenated Hydrocarbon, Products Corp., River) Edge, NJ), and 73.67 g of Isopar-G ™ (Exxon, Houston, TX). The mixture is stirred at 60 ° C. for 6 hours and then cooled to room temperature. 50.13 g of the resulting solution was placed in a 50 mL polypropylene centrifuge tube, into which 1.8 g of titanium dioxide (TiO 2) was added.₂) (DuPont, Wilminfront, DE), 0.78 g of a 10% solution of OLOA 1200 (Chevron, Somerset, NJ) in 0.8 halogenated hydrocarbon oil, and 0.15 g of Span85 (Aldrich). The mixture is then sonicated in an Aquasonic Model 75D sonicator (VWR, Westchester, PA) at 30 ° C. with power 9 for 5 minutes.
[0119]
B.Preparation of the aqueous phase
10.0 g of acacia (Aldrich) are dissolved in 100.0 g of water with stirring at room temperature for 30 minutes. The resulting mixture is decanted into two 50 mL polypropylene centrifuge tubes and centrifuged at about 2000 rpm for 10 minutes to remove insoluble material. Then 66 g of the purified solution are decanted into a 500 mL unbaffled jacketed reactor, and the solution is then heated to 40 ° C. A 6 blade (vertical geometry) paddle stirrer is then placed just below the surface of the liquid. While stirring the solution at 200 rpm, 6 g of gelatin (300 bloom, type A, Aldrich) is carefully added over about 20 seconds to avoid clumping. The agitation is then reduced to 50 rpm to reduce foaming. The resulting solution is then stirred for 30 minutes.
[0120]
C.Encapsulation
While stirring at 200 rpm, slowly pour the oil phase prepared above into the aqueous phase also prepared as described above for about 15 seconds. The resulting oil / water emulsion is emulsified for 20 minutes. To this emulsion is slowly added 200 g of water preheated to 40 ° C. over a period of about 20 seconds. The pH is then lowered to 4.4 over 5 minutes using a 10% acetic acid solution (acetic acid from Aldrich). Monitor the pH using a pH meter previously calibrated with pH 7.0 and pH 4.0 buffers. Stir for 40 minutes. Then 150 g of water, which has been preheated to 40 ° C., are added, then the reactor contents are cooled to 10 ° C. When the solution temperature reaches 10 ° C., 3.0 mL of a 37% formalin solution (Aldrich) is added and the solution is further stirred for another 60 minutes. The pH is raised to 10.0 by adding 20 g of sodium carboxymethylcellulose (NaCMC) and then adding a 20 wt% sodium hydroxide (NaOH) solution. The thermostat bath is then set at 40 ° C. and allowed to stir for another 70 minutes. The slurry is allowed to cool to room temperature with stirring overnight. At this time, the resulting capsule slurry is ready for sieving.
[0121]
D.Display formation
Two procedures for preparing an electrophoretic display from the capsule slurry are described below.
[0122]
1. Procedure using urethane binder
The resulting capsule slurry from above is mixed with an aqueous urethane binder NeoRez @ R-9320 (Zeneca @ Resins, Wilmington, Mass.) In a ratio of 1 part binder to 10 parts capsule. The resulting mixture is then coated on a 0.7 mm thick sheet of indium-tin-oxide sputtered polyester film using a doctor blade. The blade gap of the doctor blade is controlled to 0.18 mm so as to place a single capsule layer. The coated film is then dried in hot air (60 ° C.) for 30 minutes. After drying, in a hot roll lamination of Cheminstruments (Fairfield, OH), the dried film was applied to a backplane containing a 3 mm thick polyester sheet screen printed with thick film silver and dielectric ink at 15 psi and 60 ° C. Laminate at high temperature. The backplane is bonded to the membrane using anisotropic tape. The conductive areas form the addressable areas of the resulting display.
[0123]
2. Procedure using urethane / polyvinyl alcohol binder
The resulting capsule slurry from the above was combined with an aqueous binder comprising a mixture of NeoRez @ R-966 (Zeneca @ Resins) and a 20% solution of Airvol 203 (polyvinyl alcohol, Airvol Industries, Allentown, PA), and 1 part of Airvol 203 solution. Mix NeoRez @ R-966 at a ratio of 1 part to 5 parts capsule. The resulting mixture is then coated on a 0.7 mm thick sheet of indium-tin-oxide sputtered polyester film using a doctor blade. The blade gap of the doctor blade is controlled to 0.18 mm so as to place a single capsule layer. The coated film is then dried in hot air (60 ° C.) for 30 minutes. After drying, the thick silver ink is printed directly on the back of the dried film and cured at 60 ° C. The conductive areas form the addressable areas of the display.
[0124]
Example 2
The following is an example of the preparation of microcapsules by in situ polymerization.
[0125]
In a 500 mL jacketed reactor without baffles, mix 50 mL of a 10 wt% aqueous solution of ethylene comain anhydride (Aldrich), 100 mL of water, 0.5 g resorcinol (Aldrich), and 5.0 g urea (Aldrich). The mixture is stirred at 200 rpm and the pH is adjusted to 3.5 over 1 minute using a 25 wt% NaOH solution. Monitor the pH using a pH meter previously calibrated with pH 7.0 and pH 4.0 buffers. To this, slowly add the oil phase prepared as described in Example 1 above, and accelerate the stirring to 450 rpm to reduce the average particle size to less than 200 μm. Then 12.5 g of a 37 wt% aqueous formaldehyde solution are added and the temperature is raised to 55 ° C. The solution is heated at 55 ° C. for 2 hours.
[0126]
Example 3
The following is an example of the preparation of microcapsules by interfacial polymerization.
[0127]
To 44 g of the oil phase prepared as described in Example 1 above, 1.0 g of sebacoyl chloride (Aldrich) is added. 3 ml of this mixture are then dispersed in 200 ml of water at room temperature with stirring at 300 rpm. Next, 2.5 mL of a 10 wt% aqueous solution of 1,6-diaminohexane is added to the dispersion. After about 1 hour, a capsule is formed.
[0128]
Thus, an encapsulated electrophoretic display and materials useful for constructing the encapsulated electrophoretic display have been described. Other aspects and advantages of the invention will be apparent in light of the above description. Accordingly, the scope of the present invention is limited solely by the appended claims.
[Brief description of the drawings]
FIG.
FIG. 2 is a schematic view of encapsulated light scattering particles.
FIG. 2
1 shows a capsule containing particles in a suspension fluid, wherein the electrode pair is arranged adjacent to the capsule.
FIG. 3
FIG. 2 is a diagram of a capsule containing light absorbing particles in a suspending fluid, wherein a reflective or retroreflective substrate is disposed on the bottom surface of the capsule. The situation is shown where the particles move towards one of the electrode pairs so that light can pass through the capsule and be reflected by the substrate.
FIG. 4
FIG. 4 shows the capsule of FIG. 3 in which particles move to prevent light from reaching the substrate, thereby preventing light from being reflected by the substrate.
FIG. 5
3 shows a capsule containing light absorbing particles and retroreflective particles.
FIG. 6A
Figure 2 shows a capsule containing particles with a reflective corner cube on the bottom. In this figure, the particles are arranged so that light can pass through the capsule and be reflected by the corner cube.
FIG. 6B
Figure 2 shows a capsule containing particles with a reflective corner cube on the bottom. In this figure, the particles are arranged so that light can pass through the capsule and be reflected by the corner cube.
FIG. 6C
Fig. 2 shows a microcapsule containing a reflective corner cube on the bottom and particles. In this figure, the particles are arranged such that light cannot pass through the capsule and cannot be reflected by the corner cube.
FIG. 7
It shows how a capsule can reflect light.
FIG. 8A
FIG. 8 shows the capsule of FIG. 7, wherein the particles contained within the capsule are arranged to allow light to enter and be reflected by the capsule.
FIG. 8B
FIG. 8 shows the capsule of FIG. 7 in which particles contained within the capsule are arranged to prevent light incident on the capsule from being reflected.
FIG. 9
3 shows a capsule containing luminescent particles and light absorbing particles. In this figure, the luminescent particles are positioned towards the top of the capsule, thereby providing light.
FIG. 10
FIG. 10 shows the capsule of FIG. 9 in which light absorbing particles are placed towards the top of the capsule, thereby preventing light from exiting the capsule.
FIG. 11
Fig. 7 shows a capsule disposed adjacent to a reflective substrate and two electrodes, wherein particles within the capsule are aligned to allow light to pass through the capsule and be reflected by the substrate.
FIG. 12A
Fig. 2 shows two capsules in a binder, positioned adjacent to a reflective substrate and two electrodes, wherein particles within the capsule allow light to pass through the capsule and be reflected by the substrate Are aligned as follows.
FIG. 12B
Fig. 7 illustrates a capsule disposed adjacent to a reflective substrate and two electrodes, wherein particles within the capsule are aligned to prevent light from passing through the capsule and being reflected by the substrate.
FIG. 13A
FIG. 2 is a diagram of an apparatus for performing emulsion-based encapsulation.
FIG. 13B
FIG. 3 is a diagram of oil droplets of a suspension fluid in which white and black particles are dispersed.
FIG. 13C
FIG. 2 is a diagram of oil droplets of a suspended fluid stained with a dark color in which white microparticles and a charge control agent are dispersed.

Claims (28)

An encapsulated electrophoretic display comprising a polymer matrix having a viewing surface and a rear surface and having a cavity containing a fluid, the cavity being non-spherical. The display of claim 1, wherein the fluid in the cavity is oil. The display according to claim 1 or 2, wherein the aspect ratio of the width to the height of the cavity is greater than 1.2. The display of claim 3, wherein the aspect ratio is greater than 1.5. The display of claim 4, wherein the aspect ratio is greater than 1.75. The display according to any of the preceding claims, characterized in that the volume fraction of the polymer matrix is between 0.0 and 0.9. The display according to claim 6, wherein the volume fraction is between 0.05 and 0.2. A display according to any of the preceding claims, wherein the view surface is substantially planar. The display of claim 8, wherein both the view surface and the rear surface are substantially planar. 10. A display according to any of the preceding claims, characterized in that the optically active part of the view surface is greater than 80%. 11. The display of claim 10, wherein the optically active portion is greater than 90%. The display according to any of the preceding claims, characterized in that the cavity containing the fluid is arranged in an elastomeric capsule. A process for making an encapsulated electrophoretic display,
(A) curing the binder,
(B) applying a mechanical force to the binder, thereby causing the binder to form at least one capsule having a non-spherical shape. 14. The process of claim 13, wherein steps (a) and (b) occur simultaneously. The process according to claim 13, wherein the mechanical force is applied by one or more of a roller, a vacuum lamination press, and a mechanical press. 16. The process according to any of claims 13 to 15, wherein the mechanical force causes the binder to stretch. A process for making an encapsulated electrophoretic display, comprising the step of curing a binder, wherein the binder is an evaporative binder that deforms upon curing to form at least one non-spherical capsule. Characterized by a process. 18. The process according to claim 17, wherein the evaporative binder is an acrylic, urethane or poly (vinyl alcohol) binder. A plurality of anisotropic particles (10) dispersed in a suspension fluid, wherein the anisotropic particles (10) are arranged in an optically transparent state when a first electric field is applied;
Encapsulated electrophoretic display characterized by a plurality of second particles (12) that translate in parallel upon application of a second electric field and disturb the anisotropic particles (10) into a light scattering or absorbing state. . Encapsulation, characterized in that it comprises one or more particle species (32, 34) each having a distinct electrophoretic mobility, at least one of the particle species (32) being a retroreflective corner cube. Electrophoretic display. Including at least three species of particles having substantially non-overlapping electrophoretic mobilities and predominantly representing one of the species in response to a sequence of electrical pulses of which both time and amplitude are controlled. An encapsulated electrophoretic display featuring a multicolor display. An encapsulated electrophoretic display comprising particles dispersed in a suspending fluid, said particles comprising a liquid. A capsule having optical properties, the capsule comprising a plurality of particles, each having a density, and a suspending fluid, wherein application of an electric field affects the dispersion of the particles, whereby the optical properties of the capsule are reduced. An encapsulated electrophoretic display characterized by modulating properties, characterized in that the suspending fluid consists essentially of a single fluid having a density substantially matching the density of the particles. A process for making an encapsulated electrophoretic display,
(A) encapsulating the dye in the suspension fluid in a plurality of first capsules;
(B) encapsulating the plurality of first capsules in a second capsule in a binder. A suspension fluid and at least one species of electrophoretically migrating particles (50), wherein said particle species (50) is associated with a second portion capable of emitting visible light; An encapsulated electrophoretic display comprising a first portion capable of reflecting visible light. A capsule comprising a refractive index matching fluid, wherein the fluid moves within the capsule upon application of a first electric field to create an optically homogeneous capsule. , Encapsulated electrophoretic display. A capsule, wherein the capsule includes at least two immiscible fluids, each having a different optical property value, wherein the fluid moves within the capsule in response to a first electric field to produce a new optical property value. An encapsulated electrophoretic display that creates a capsule with An encapsulated electrical device characterized by at least two particle species (32, 34) each having distinct electrophoretic mobilities, wherein at least one of the particle species (32) is a retroreflective particle species. Electrophoretic display.