Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
  • G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
  • G02F1/094—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect based on magnetophoretic effect
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1347—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2202/00—Materials and properties
  • G02F2202/28—Adhesive materials or arrangements

Definitions

• This application relates to an electrophoretic display with improved contrast ratio, switching performance, reflectivity at the Dmin state and structural integrity, and methods for its manufacture.
• the electrophoretic display is a non-emissive device based on the electrophoresis phenomenon of charged pigment particles suspended in a solvent. It was first proposed in 1969.
• the display usually comprises two plates with electrodes placed opposing each other, separated by spacers. One of the electrodes is usually transparent. A suspension composed of a colored solvent and charged pigment particles is enclosed between the two plates. When a voltage difference is imposed . between the two electrodes, the pigment particles migrate to one side and then either the color of the pigment or the color of the solvent can be seen according to the polarity of the voltage difference.
• US Patent Nos. 5,961 ,804, 5,930,026 and 6,017,584 describe microencapsulated electrophoretic displays.
• the reference display has a substantially two dimensional arrangement of microcapsules each having therein an electrophoretic composition of a dielectric solvent and a suspension of charged pigment particles that visually contrast with the dielectric solvent.
• the microcapsules can be formed by interfacial polymerization, in-situ polymerization or other known methods such as physical processes, in-liquid curing or simple/complex coacervation.
• the microcapsules, after their formation, may be injected into a cell housing two spaced-apart electrodes, or "printed" onto or coated on a transparent conductor film.
• the microcapsules may also be immobilized within a transparent matrix or binder that is itself sandwiched between the two electrodes.
• the electrophoretic displays prepared by these processes have many shortcomings.
• the electrophoretic display manufactured by the microencapsulation process suffers from sensitivity to environmental changes (in particular, sensitivity to moisture and temperature) due to the wall chemistry of the microcapsules.
• the electrophoretic display based on the microcapsules has poor scratch resistance due to the thin wall and large particle size of the microcapsules.
• microcapsules are embedded in a large quantity of polymer matrix which results in a slow response time due to the large distance between the two electrodes and a low contrast ratio due to the low payload of pigment particles. It is also difficult to increase the surface charge density on the pigment particles because charge-controlling agents tend to diffuse to the water/oil interface during the microencapsulation process. The low charge density or zeta potential of the pigment particles in the microcapsules also results in a slow response rate. Furthermore, because of the large particle size and broad size distribution of the microcapsules, the electrophoretic display of this type has poor resolution and addressability for color applications.
• the improved EPD comprises isolated cells formed from microcups of well-defined shape, size and aspect ratio and filled with charged pigment particles or pigment-containing microparticles dispersed in a dielectric solvent or solvent mixture, preferably a fluorinated solvent or solvent mixture.
• the filled cells are individually sealed with a polymeric sealing layer, preferably formed from a composition comprising a material selected from the group consisting of thermoplastics, thermoplastic elastomers, thermosets and precursors thereof.
• a polymeric sealing layer preferably formed from a composition comprising a material selected from the group consisting of thermoplastics, thermoplastic elastomers, thermosets and precursors thereof.
• the displays can be prepared on a continuous web of a conductor film such as ITO/PET by, for example, (1) coating a radiation curable composition onto the ITO/PET film, (2) forming the microcup structure by a microembossing or photolithographic method, (3) filling an electrophoretic fluid into the microcups and sealing the filled microcups, (4) laminating the sealed microcups with the other conductor film and (5) slicing and cutting the display to a desirable size or format for assembling.
• a conductor film such as ITO/PET by, for example, (1) coating a radiation curable composition onto the ITO/PET film, (2) forming the microcup structure by a microembossing or photolithographic method, (3) filling an electrophoretic fluid into the microcups and sealing the filled microcups, (4) laminating the sealed microcups with the other conductor film and (5) slicing and cutting the display to a desirable size or format for assembling.
• microcup wall is in fact a built-in spacer to keep the top and bottom substrates apart at a fixed distance.
• the mechanical properties and structural integrity of microcup displays are significantly better than any displays previously known including those manufactured by using spacer particles.
• displays involving microcups have desirable mechanical properties including reliable display performance when the display is bent, rolled or under compression pressure from, for example, a touch screen application.
• the use of the microcup technology also eliminates the need of an edge seal adhesive which would limit and predefine the size of the display panel and confine the display fluid inside a predefined area. The display fluid within a conventional display prepared by the edge sealing adhesive method will leak out completely if the display is cut in any way, or if a hole is drilled through the display.
• the damaged display will be no longer functional.
• the display fluid within the display prepared by the microcup technology is enclosed and isolated in each cell.
• the microcup display may be cut to almost any dimensions without the risk of damaging the display performance due to the loss of the display fluid in the active areas.
• the microcup structure enables a format flexible display manufacturing process, wherein the process produces a continuous output of display panel in a large sheet format which can be cut into any desired format.
• the isolated microcup or cell structure is particularly important when cells are filled with fluids of different specific properties such as colors and switching rates. Without the microcup structure, it will be very difficult to prevent the fluids in adjacent areas from intermixing or being subject to cross-talk during operation.
• one of two approaches may be taken: (1) using a darkened background to reduce the light leaking through the inactive partition wall or (2) using microcups of wider opening and narrower partition to increase the payload.
• the darkened background typically results in a lower reflectivity at the Dmin state.
• display cells formed from wider microcups and narrower partition walls tend to have a poor resistance against compression and/or shear forces imposed by, for example, a sharp stylus for a touch screen panel.
• the present application is directed to a novel multilayer EPD structure which has shown improved contrast ratio, switching performance, reflectivity at the Dmin state and structural integrity.
• this type of multiplayer EPD structure shallower microcups may be employed to achieve an acceptable contrast ratio with improved reflectivity at the Dmin state.
• the manufacturing cost is significantly reduced and the release properties during microembossing are also considerably improved.
• the first aspect of the invention is directed to an electrophoretic display having two or more layers of display cells stacked together. The display cells are filled with electrophoretic display fluids and individually sealed.
• the second aspect of the invention is directed to an electrophoretic display having two or more layers of display cells stacked together and the cells are filled with electrophoretic fluids of different colors, optical densities or switching speeds.
• the third aspect of the invention is directed to an electrophoretic display having two or more layers of display cells stacked together and the cells are of different shapes, dimensions or ratios of opening to total area.
• the fourth aspect of the invention is directed to an electrophoretic display having two or more layers of display cells stacked together and in the stack the inactive partition areas of one layer are at least partially overlapped with the active cell areas of the layer above or underneath, preferably completely overlapped.
• staggered will be used throughout the application to describe this arrangement. The staggered arrangement is necessary to allow the colors from the cells (generated by reflection or absorption of the light) in a lower layer to be seen through the partition areas of an upper layer.
• the fifth aspect of the invention is directed to an electrophoretic display having two or more layers of display cells stacked together and in the stack the bottom layer comprises cells which are filled with an electrophoretic fluid comprising white pigment particles or pigment-containing microparticles dispersed in a black solvent or solvent mixture.
• the sixth aspect of the invention is directed to a full color or multi-color electrophoretic display having two layers of display cells stacked together and the upper layer comprises red, green or blue cells which are filled with electrophoretic display fluids comprising white pigment particles or pigment-containing microparticles dispersed in red, green or blue solvents or solvent mixture, respectively.
• the seventh aspect of the invention is directed to a full color or multi-color electrophoretic display having two layers of display cells stacked together and the bottom layer comprises black cells which are filled with an electrophoretic fluid comprising white pigment particles or pigment-containing microparticles dispersed in a black solvent or solvent mixture and the black cells are positioned with inactive partition areas of the upper layer in a staggered fashion.
• the eighth aspect of the invention is directed to a full color or multi-color electrophoretic display having two layers of display cells stacked together.
• the bottom layer comprises red, green, blue and black cells which are filled with electrophoretic display fluids comprising white pigment particles or pigment-containing microparticles dispersed in red, green, blue and black solvent or solvent mixture, respectively.
• the top layer comprises red, green and blue cells which are filled with electrophoretic display fluids comprising white pigment particles or pigment-containing microparticles dispersed in red, green and blue solvent or solvent mixture, respectively.
• the colored cells and the inactive partition areas of the two layers are arranged in a staggered fashion with the black cells of the bottom layer registered to the inactive partition areas of the top layer.
• the pigment particles or pigment-containing microparticles may also be magnetic.
• the ninth aspect of the invention is directed to an electromagnetophoretic display having two or more layers of display cells stacked together.
• the bottom layer comprises display cells which are filled with an electromagnetophoretic fluid comprising a mixture of black magnetic particles and white non-magnetic particles dispersed in a colorless clear solvent or solvent mixture.
• the top layer may comprise red, green and blue cells which are filled with electrophoretic fluids comprising white particles dispersed in red, green and blue solvents or solvent mixtures, respectively.
• the top layer may comprise display cells which are filled with an electrophoretic fluid comprising a mixture of white and colored particles dispersed in a colorless clear solvent or solvent mixture.
• the tenth aspect of the invention is directed to methods for the manufacture of an electrophoretic display having two or more layers of display cells stacked together, as described in the first through ninth aspect of the invention.
• display cell is used in this application, it is understood that the term broadly covers the partition type display cells, the microgroove or microchannel type display cells (US Patent No. 3,612,758), the microcapsule type display cells (US Patent Nos. 5,961 ,804, 5,930,026 and 6,017,584) and the display cells prepared according to the microcup technology as described in WO01/67170.
• microcup When the term "microcup” is used in the application, it is understood that the multilayer display of the present invention is also applicable to other display cells such as the partition type display cells, the microgroove or microchannel type display cells and the microcapsule type display cells.
• the top (or upper) layer referred to above is usually the viewing side whereas the bottom (or lower) layer is the non-viewing side.
• Figure 1 shows a typical electrophoretic display cell prepared by the microcup technology with a darkened background to improve the contrast ratio.
• the viewer will see the background color through the inactive partition areas.
• a display having a low reflectivity in the Dmin state is obtained.
• Figures 2a and 2b show the "on” (Dmin) and “off (Dmax) states, respectively, of a two-layer electrophoretic display.
• Dmin white particles of both layers will be attracted to the top of the microcups.
• the inactive partition areas of the upper layer will appear white since light is reflected back by the white particles in the bottom microcup layer.
• the inactive partition areas of the upper layer will appear colored since light is absorbed by the colored solvent in the bottom microcup layer.
• Figures 3a and 3b show the methods for the manufacture of an electrophoretic display having two or more layers of display cells.
• Figure 3a shows a process of preparing a two layer electrophoretic display by laminating two microcup layers with the sealing sides of the microcups facing each other.
• Figure 3b shows another process of preparing a two layer electrophoretic display by (i) transferring a microcup layer from a release substrate onto a second microcup layer on a conductor film and (ii) laminating the resultant composite film onto a conductor film, optionally with an adhesive. The process (i) may be repeated to prepare an electrophoretic display having more than two layers of display cells.
• Figures 4a and 4b show a two-layer color electrophoretic display wherein the top layer comprises microcups filled with red, green and blue electrophoretic fluids and the bottom layer comprises microcups filled with a black electrophoretic fluid.
• Figures 5a and 5b show a two-layer full color electrophoretic display wherein the top layer comprises microcups filled with red, green and blue electrophoretic fluids and the bottom layer comprises microcups filled with red, green, blue and black electrophoretic fluids.
• the red, green, blue and inactive partition areas of the upper layer are overlapped with registration to the red, green, blue and black microcups of the lower layer, respectively.
• microcup refers to the cup-like indentations created by microembossing or imagewise exposure.
• microcups or cells when describing the microcups or cells, is intended to indicate that the microcup or cell has a definite shape, size and aspect ratio which are pre-determined according to the specific parameters of the manufacturing process.
• spect ratio is a commonly known term in the art of electrophoretic displays. In this application, it refers to the depth to width or depth to length ratio of the cells.
• Dmax refers to the maximum achievable optical density of the display.
• Dmin refers to the minimum optical density of the display background.
• contrast ratio is defined as the ratio of the % reflectance of an electrophoretic display at the Dmin state to the % reflectance of the display at the Dmax state.
• Electrophoretic display cells prepared by the microcup technology comprise two conductor films (10, 11 ), at least one of which is transparent (10), and a layer of cells (12) enclosed between the two conductor films.
• the cells are filled with charged pigment particles or pigment-containing microparticles dispersed in a colored dielectric solvent and sealed with a sealing layer (13).
• the sealing layer preferably extends over the partition walls (16) and forms a contiguous layer thereon.
• the sealed cells are laminated onto the second conductor film (10) optionally with an adhesive layer (14). When a voltage difference is imposed between the two conductor films, the charged particles migrate to one side, such that either the color of the pigment or the color of the solvent is seen through the transparent conductor film (10).
• At least one of the two conductor films is patterned.
• one of two approaches are typically taken: (a) using microcups of a higher payload (a higher aspect ratio and/or a higher ratio of opening area to total area) or (b) using a blackened conductor film (11) on the non- viewing side. Since no light scattering particles are present in the inactive partition areas (16), the viewer will see the background color through the partition areas in both the "on" and "off” states. The blackened background of such a single layer EPD results in a higher Dmax and contrast ratio, but a lower reflectivity in the Dmin state. Moreover, the use of high payload cells, on the other hand, increases not only the degree of difficulty but also the cost of manufacturing.
• the display has an upper cell layer (21) and a lower cell layer (22).
• the cells of the two layers are individually sealed with a sealing layer (23).
• the two layers are arranged in a staggered fashion and the sealing sides of the two layers face each other.
• the two layer structure is sandwiched between a top transparent conductor film (24) and a bottom conductor film (25).
• the two-layer or multilayer EPD also allows the use of cells with a lower payload (a lower aspect ratio and a lower ratio of opening area to total area) to achieve a high contrast ratio with a higher reflectivity at the Dmin state. This also significantly improves the release properties of the microembossing process and reduces the cost and degree of difficulty in the manufacture of a mold for microembossing. Preparation of the Microcups
• the microcup-based display cells may be prepared by either microembossing, photolithography or pre-punched holes as disclosed in copending patent applications, US Serial Number 09/518,488 filed on March 3, 2000 (corresponding to WO01/67170), US Serial Number 09/942,532 filed on August 29, 2002 (US Publication No. 2002- 75556 published on June 20, 2002), US Serial Number 09/606,654 filed on June 28, 2000 (corresponding to WO02/01280) and US Serial Number 09/784,972 filed on February 15, 2001 (corresponding to WO02/65215), all of which are incorporated herein by reference in their entirety.
• the microcup-based cells can be of any shape, and their sizes and shapes may vary.
• the cells may be of substantially uniform size and shape in one system.
• cells having a mixture of different shapes and sizes may be produced.
• cells filled with a dispersion of a red color may have a different shape or size from the green cells or the blue cells.
• a pixel may consist of different numbers of cells of different colors.
• a pixel may consist of a number of small green cells, a number of large red cells and a number of small blue cells. It is not necessary to have the same shape and number for the three colors.
• the openings of the microcups may be circular, square, rectangular, hexagonal or any other shape.
• the partition areas between the openings are preferably kept small in order to achieve a high color saturation and contrast ratio while maintaining desirable mechanical properties. Consequently, the honeycomb-shaped opening is preferred over, for example, the circular opening.
• each individual microcup may be in the range of about 10 2 to about 10 6 ⁇ m 2 , preferably from about 10 3 to about 10 5 ⁇ m 2 .
• the depth of the microcups is in the range of about 3 to about 100 microns, preferably from about 10 to about 50 microns.
• the ratio of opening area to total area is in the range of from about 0.1 to about 0.95, preferably from about 0.4 to about 0.90.
• the width of the partition between microcups is in the range of from about 2 to about 50 microns, preferably from about 5 to about 20 microns.
• the electrophoretic display fluid may also be prepared by methods known in the art, such as US Patent Nos. 6,017,584, 5,914,806, 5,573,711 , 5,403,518, 5,380,362, 4,680,103, 4,285,801 , 4,093,534, 4,071,430, 3,668,106 and IEEE Trans. Electron Devices, ED-24, 827 (1977), and J. Appl. Phys. 49(9), 4820 (1978).
• the charged pigment particles visually contrast with the medium in which the particles are suspended.
• the medium is a dielectric solvent which preferably has a low viscosity and a dielectric constant in the range of about 2 to about 30, preferably about 2 to about 15, for high particle mobility.
• suitable dielectric solvents include hydrocarbons such as decahydronaphthalene (DECALIN), 5-ethylidene-2-norbomene, fatty oils, paraffin oil, aromatic hydrocarbons such as toluene, xylene, phenylxylylethane, dodecylbenzene and alkylnaphthalene, halogenated solvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene, dichlorobenzotrifluoride, 3,4,5- trichlorobenzotrifluoride, chloropentafluoro-benzene, dichlorononane, pentachlorobenzene, and perfluoro solvents such as FC-43, FC-70 and FC-5060 from 3M Company, St.
• hydrocarbons such as decahydronaphthalene (DECALIN), 5-ethylidene-2-norbomene, fatty oils, paraffin oil, aromatic hydrocarbons
• halogen containing polymers such as poly(perfluoropropylene oxide) from TCI America, Portland, Oregon, poly(chlorotrifluoroethylene) such as Halocarbon Oils from Halocarbon Product Corp., River Edge, NJ, perfluoropolyalkylether such as Galden from Solvay Solexis or Krytox Oils and Greases K-Fluid Series from DuPont, Delaware.
• poly(chlorotrifluoroethylene) is used as the dielectric solvent.
• poly(perfluoropropylene oxide) is used as the dielectric solvent.
• the suspending medium may be colored by dyes or pigments.
• Nonionic azo and anthraquinone dyes are particularly useful. Examples of useful dyes include, but are not limited to: Oil Red EGN, Sudan Red, Sudan Blue, Oil Blue, Macrolex Blue, Solvent Blue 35, Pylam Spirit Black and Fast Spirit Black from Pylam Products Co., Arizona, Sudan Black B from Aldrich, Thermoplastic Black X-70 from BASF, anthraquinone blue, anthraquinone yellow 114, anthraquinone red 111 , 135, anthraquinone green 28 from Aldrich.
• the pigment particles for generating the color of the medium may also be dispersed in the dielectric medium.
• color particles are preferably uncharged. If the pigment particles for generating color in the medium are charged, they preferably carry a charge which is opposite from that of the charged pigment particles. If both types of pigment particles carry the same charge, then they should have different charge density or different electrophoretic mobility. In any case, the dye or pigment for generating color of the medium must be chemically stable and compatible with other components in the suspension.
• the charged pigment particles may be organic or inorganic pigments, such as Ti0 2 , phthalocyanine blue, phthalocyanine green, diarylide yellow, diarylide AAOT yellow, and quinacridone, azo, rhodamine, perylene pigment series from Sun Chemical, Hansa yellow G particles from Kanto Chemical, and Carbon Lampblack from Fisher. Submicron particle size is preferred.
• the particles should have acceptable optical characteristics, should not swollen or softened by the dielectric solvent, and should be chemically stable. The resulting suspension must also be stable against sedimentation, creaming or flocculation under normal operating conditions.
• the pigment particles may exhibit a native charge, or may be charged explicitly using a charge controlling agent, or may acquire a charge when suspended in the dielectric solvent.
• Suitable charge controlling agents are well known in the art; they may be polymeric or non-polymeric in nature, and may also be ionic or non-ionic, including ionic surfactants such as Aerosol OT, sodium dodecylbenzenesulfonate, metal soap, polybutene succinimide, maleic anhydride copolymers, vinylpyridine copolymers, vinylpyrrolidone copolymer (such as Ganex from International Specialty Products), (meth)acrylic acid copolymers or N,N-dimethylaminoethyl (meth)acrylate copolymers.
• Fluorosurfactants are particularly useful as charge controlling agents in perfluorocarbon solvents. These include FC fluorosurfactants such as FC-170C, FC-171 , FC-176, FC430, FC431 and FC-740 from 3M Company and Zonyl fluorosurfactants such as Zonyl FSA, FSE, FSN, FSN-100, FSO, FSO-100, FSD and UR from Dupont.
• FC fluorosurfactants such as FC-170C, FC-171 , FC-176, FC430, FC431 and FC-740 from 3M Company
• Zonyl fluorosurfactants such as Zonyl FSA, FSE, FSN, FSN-100, FSO, FSO-100, FSD and UR from Dupont.
• Suitable charged pigment dispersions may be manufactured by any of the well- known methods including grinding, milling, attriting, microfluidizing and ultrasonic techniques. For example, pigment particles in the form of a fine powder are added to the suspending solvent and the resulting mixture is ball milled or attrited for several hours to break up the highly agglomerated dry pigment powder into primary particles. Although less preferred, a dye or pigment for generating color of the suspending medium may be added to the suspension during the ball milling process. Sedimentation or creaming of the pigment particles may be eliminated by microencapsulating the particles with suitable polymers to match the specific gravity to that of the dielectric solvent. Microencapsulation of the pigment particles may be accomplished chemically or physically. Typical microencapsulation processes include interfacial polymerization, in-situ polymerization, phase separation, coacervation, electrostatic coating, spray drying, fluidized bed coating and solvent evaporation.
• Density matched pigment-containing microparticles may be prepared according to methods disclosed in copending US patent applications, US Serial Number 10/335,210 filed on December 31 , 2002 (corresponding to WO03/58335), US Serial Number 10/335,051 (corresponding to WO03/57360) also filed on December 31 , 2002, US Serial Number 10/632,171 filed July 30, 2003 and US Serial Number 10/364,270 (corresponding to WO03/69403) filed on February 10, 2003, the contents of all of which are incorporated herein by reference in their entirety.
• the suspension comprises charged white particles of titanium oxide (TiO 2 ) dispersed in a blackened dielectric solvent containing a black dye or dye mixture, or charged black particles.
• a black dye or dye mixture such as Pylam Spirit Black and Fast Spirit Black from Pylam Products Co. Arizona, Sudan Black B from Aldrich, Thermoplastic Black X-70 from BASF, or an insoluble black pigment such as carbon black may be used to generate the black color of the solvent.
• a black dye or dye mixture such as Pylam Spirit Black and Fast Spirit Black from Pylam Products Co. Arizona, Sudan Black B from Aldrich, Thermoplastic Black X-70 from BASF, or an insoluble black pigment such as carbon black may be used to generate the black color of the solvent.
• the charged TiO 2 particles or Ti0 2 -containing particles may be suspended in a dielectric solvent of cyan, yellow or magenta color.
• the cyan, yellow or magenta color may be generated via the use of a dye or a pigment.
• the charged Ti0 2 particles or TiO 2 -containing particles may be suspended in a dielectric solvent of red, green or blue color generated also via the use of a dye or a pigment.
• the red, green and blue color system is preferred for most applications.
• microcup-based cells may be filled with an electrophoretic fluid and sealed as disclosed in WO 01/67170 and copending patent applications, US Serial Number 09/874,391 (corresponding to WO02/98977) filed June 4, 2001 , US Serial Number 10/618,257 filed on July 10, 2003, US Serial Number 10/665,898 filed on September 18, 2003 and US Serial Number 10/651 ,540 filed on August 29, 2003, the contents of all of which are incorporated herein by reference in their entirety.
• the sealing of the microcups may be accomplished in a number of ways.
• a sealing composition comprising a solvent and a sealing material selected from the group consisting of thermoplastic elastomers, polyurethanes, polyvalent acrylates or methacrylates, cyanoacryiates, polyvalent vinyls including vinylbenzenes, vinylsilanes, vinylethers, polyvalent epoxides, polyvalent isocyanates, polyvalent allyls, oligomers or polymers containing crosslinkable functional groups and the like.
• Additives such as polymeric binder or thickener, photoinitiator, catalyst, filler, colorant or surfactant may be added to the sealing composition to improve the physicomechanical and optical properties of the display.
• the sealing composition is essentially incompatible with the electrophoretic fluid and has a specific gravity lower than that of the electrophoretic fluid. Upon solvent evaporation, the sealing composition forms a conforming seamless seal on top of the filled microcups.
• the sealing layer may be further hardened by heat, radiation, e-beam, moisture, interfacial crosslinking or other curing methods. Interfacial polymerization followed by UV curing is very beneficial to the sealing process. Intermixing between the electrophoretic layer and the overcoat is significantly suppressed by the formation of a thin barrier layer at the interface by interfacial polymerization.
• the sealing is then completed by a post curing step, preferably by UV radiation.
• the specific gravity of the overcoating is significantly lower than that of the electrophoretic fluid.
• Volatile organic solvents may be used to adjust the viscosity and the thickness of the coatings. When a volatile solvent is used in the overcoat, it is preferred that it is immiscible with the dielectric solvent. This two-pass overcoating process is particularly useful when the dye used is at least partially soluble in the sealing composition.
• thermoplastic elastomers include tri-block or di-block copolymers of styrene and isoprene, butadiene or ethylene/butylene, such as the KratonTM D and G series from Kraton Polymer Company. Crystalline rubbers such as poly(ethylene-co-propylene-co-5-methylene-2-norbornene) and other EPDM (Ethylene Propylene Diene Rubber terpolymer) from Exxon Mobil have also been found very useful.
• EPDM Ethylene Propylene Diene Rubber terpolymer
• the sealing composition may be dispersed into an electrophoretic fluid by, for example, an in-line mixer and immediately coated onto the microcups with a precision coating mechanism such as Myrad bar, gravure, doctor blade, slot coating or slit coating. Volatile organic solvents may be used to control the viscosity and coverage of the electrophoretic fluid. Excess fluid may be scraped away by a wiper blade or a similar device. A small amount of a weak solvent or solvent mixture such as isopropanol, methanol or aqueous solutions thereof may be used to clean the residual electrophoretic fluid on the top surface of the partition walls of the microcups.
• the sealing composition is essentially incompatible with the electrophoretic fluid and is lighter than the electrophoretic fluid. Upon phase separation and solvent evaporation, the sealing composition floats to the top of the filled microcups and forms a seamless sealing layer thereon. The sealing layer may be further hardened by heat, radiation or other curing methods. This is the one-pass sealing process.
• the polymeric sealing layer is in contact with the top surface of the electrolytic fluid.
• the sealing layer encloses the electrolytic fluid within each cell and sealingly adheres to the surface of the partition walls.
• the sealed microcups finally are laminated with the second conductor film (10) optionally pre-coated with an adhesive layer (14).
• a preferred group of dielectric solvents exhibiting desirable density and solubility discrimination against most commonly used polymers and precursors thereof are halogenated, particularly fluorinated, hydrocarbons and derivatives thereof.
• Surfactants may be used to improve the adhesion and wetting at the interface between the electrophoretic fluid and the sealing composition.
• Useful surfactants include the FC surfactants from 3M Company, Zonyl fluorosurfactants from DuPont, fluoroacrylates, fluoromethacrylates, fluoro-substituted long chain alcohols, perfluoro-substituted long chain carboxylic acids and derivatives thereof.
• the process can be a continuous roll-to-roll process as disclosed in WO01/67170. It may comprise the following steps:
• thermoplastic or thermoset precursor optionally with a solvent on a conductor film.
• the solvent if present, readily evaporates.
• thermoplastic or thermoset precursor layer at a temperature higher than the glass transition temperature of the thermoplastic or thermoset precursor layer by a pre-patterned male mold.
• the laminate adhesive may be post cured by radiation such as UV through the top conductor film if the latter is transparent to the radiation.
• the finished product may be cut to various sizes and shapes after the lamination step.
• microcups described above can be conveniently replaced by the alternative procedure of photolithography as disclosed in WO01/67170.
• a full color EPDs may be prepared by sequentially filling red, green and blue electrophoretic fluids into the microcups and subsequently sealing the filled microcups as described above.
• Figures 3a and 3b show the methods for the manufacture of an electrophoretic display having two or more layers of display cells.
• Figure 3a shows the process of preparing a two layer electrophoretic display by laminating a top layer (31 ) and a bottom layer (32) of display cells prepared by, for example, the procedure described in the steps 1-4 in Section IV.
• the filled display cells are individually sealed with a sealing layer (33).
• the conductor film (34) on the viewing side is transparent and the conductor film (35) on the non-viewing side may be blackened.
• An adhesive layer may be used to facilitate the lamination process.
• the two layers (31 and 32) are arranged with the inactive partition areas (36) of one layer and the active cell areas of another layer in a staggered fashion.
• Figure 3b shows another process of preparing a two layer electrophoretic display by (i) preparing a layer of display cells (32) on a conductor film (35) by, for example, the procedure described in the steps 1-4 in Section IV; (ii) preparing another layer of display cells (31) on a release substrate (37) by the same procedure in (i); (iii) laminating the layer of display cells (31) on the release substrate (37) onto the layer (32), optionally with an adhesive (not shown); (iv) removing the release substrate and (v) laminating the resultant composite film onto a conductor film (34), optionally with an adhesive (not shown).
• the steps (ii), (iii), and (iv) may be repeated to prepare an electrophoretic display having more than two layers of display cells.
• the inactive partition areas of a microcup layer are arranged with the active microcup areas of another layer in a staggered manner.
• At least one of the two conductor films (34 and 35) is pre-patterned. Also at least the conductor film (34) on the viewing side is transparent.
• Figures 4a and 4b show a two-layer color electrophoretic display wherein the top layer (41) comprises display cells filled with red, green and blue electrophoretic fluids and the bottom layer (42) comprises display cells filled with a black electrophoretic fluid.
• the inactive partition areas (46) of the upper layer (41) are staggered with the active cell areas of the lower layer (42).
• the two layer structure is sandwiched between two conductor films (44) and (45). At least one of the two conductor films is transparent.
• Figures 5a and 5b show a two layer full color electrophoretic display wherein the top layer (51) comprises display cells filled with red, green and blue electrophoretic fluids and the bottom layer (52) comprises display cells filled with red, green, blue and black electrophoretic fluids.
• the colored cells and the inactive partition areas (56) of the two layers are arranged in a staggered manner so that the red, green, blue and inactive partition areas of the top layer (51) are overlapped with registration to the red, green, blue and black microcups of the bottom layer (52), respectively.
• the two layer structure is sandwiched between two conductor films (54) and (55). At least one of the two conductor films is transparent.
• the top microcup layer may be laminated onto the bottom layer at an appropriate angle to avoid formation of the undesirable Moire pattern.
• a less symmetrical microcup array may be used for similar purposes.
• a two-layer electromagnetophoretic display may have a bottom layer comprises display cells which are filled with an electromagnetophoretic fluid comprising a mixture of black magnetic particles and white non-magnetic particles dispersed in a colorless clear solvent or solvent mixture.
• the top layer may comprise red, green and blue cells which are filled with electrophoretic fluids comprising white particles dispersed in red, green and blue solvents, respectively.
• the top layer may comprise display cells which are filled with an electrophoretic fluid comprising a mixture of white and black particles dispersed in a colorless clear solvent or solvent mixture.
• the cell gap or the shortest distance between the two conductor films in a multilayer display is preferably in the range of 15 to 200 ⁇ m, more preferably in the range of 20 to 50 ⁇ m.
• the thickness of each display cell layer may be varied preferably in the range of 10 to 100 ⁇ m, more preferably in the range of 12 to 30 ⁇ m.
• concentration of particles and dyes or colorants in each display cell layer may also be varied for different applications.
• a solution containing 1.67 gm of 1 ,5-pentanediol (BASF), 1.35 gm of polypropylene oxide (molecular weight 725, from Aldrich), 2.47 gm of MEK and 0.32 gm of a 2% dibutyltin dilaurate (Aldrich) solution in MEK was added and further homogenized for 2 minutes.
• BASF 1 ,5-pentanediol
• MEK 2% dibutyltin dilaurate
• R r amine 4900 prepared from Preparation 1 in 40.0 gm of HT-200 (Solvay Solexis) was added and homogenized for 2 minutes, followed by addition of additional 0.9 gm of R r amine 4900 in 33.0 gm of HT-200 and homogenization for 2 minutes. A low viscosity microcapsule dispersion was obtained.
• microcapsule dispersion obtained was heated at 80°C overnight and stirred under low shear to post-cure the particles.
• the resultant microcapsule dispersion was filtered through a 400-mesh (38 micrometer) screen.
• the particle and the solid content of the filtered dispersion was measured to be 29 wt% by weight with an IR-200 Moisture Analyzer (Denver Instrument Company).
• the average particle size of the filtered dispersion was measured with a Beckman Coulter LS230 Particle Analyzer to be about 2 ⁇ m.
• EPD fluid containing 1.0 wt% by weight of CuPc-C 8 F 17 (structure given below and prepared according to US Patent No. 3,281 ,426) and various amount of the resultant TiO 2 -containing microcapsule dispersion in HT-200 was filled into the microcups which were then sealed and sandwiched between two ITO/PET films according to the procedure described in Preparation 3.
• IrgacureTM 369 [(2-benzyl-2-(dimethylamino)-1- [4-(4-morpholinyl)phenyl]-1-butanone), Ciba, Tarrytown, NY], 0.04 gm of ITX (Isopropyl- 9H-thioxanthen-9-one, Aldrich, Milwaukee, Wl), 0.1 gm of IrganoxTM 1035
• the microcup composition was slowly coated onto a 4"x4" electroformed Ni male mold for an array of 100 ⁇ m (length) x 100 ⁇ m (width) x 25 ⁇ m (depth) x 15 ⁇ m (width of top surface of the partition wall between cups) microcups.
• a plastic blade was used to remove excess of fluid and gently squeeze it into “valleys" of the Ni mold.
• the coated Ni mold was heated in an oven at 65°C for 5 minutes and laminated with the primer coated ITO/PET film prepared in Preparation 3A, with the primer layer facing the Ni mold using a GBC Eagle 35 laminator (GBC, Northbrook, IL) preset at a roller temperature of 100°C, lamination speed of 1 ft/min and the roll gap at "heavy gauge".
• GBC Eagle 35 laminator GBC, Northbrook, IL
• a UV curing station with a UV intensity of 2.5 mJ/cm 2 was used to cure the panel for 5 seconds.
• the ITO/PET film was then peeled away from the Ni mold at a peeling angle of about 30 degree to give a 4"x4" microcup array on ITO/PET. An acceptable release of the microcup array from the mold was observed.
• the thus obtained microcup array was further post-cured with a UV conveyor curing system (DDU, Los Angles, CA) with a UV dosage of 1.7 J/cm 2 .
• An electrophoretic fluid containing 9.7% by weight (dry weight) of the TiO 2 - containing microcapsules prepared according to the Preparation 2, 1.0% by weight of CuPc-C 8 F 17 and 0.5% by weight of R r amine2000 (based on the total dry weight of the TiO 2 -containing microcapsule) prepared according to Preparation 1 in HT-200 was filled into the 4"x4" microcup array prepared from Preparation 3B using a #0 drawdown bar. The excess of fluid was scraped away by a rubber blade.
• the lamination of the conductor film over the sealed microcups was accomplished by pressing the ITO side of an ITO/PET film (5 mil) onto the sealing layer by a laminator at 120°C and at the speed of 20cm/min.
• the resultant single layer microcup EPD prepared according to the Preparation 3C was then coated with a thin layer of black coating on the outer surface of a conductor film on the sealing side of the display (the non-viewing side).
• a conductor film on the side opposite to the sealing layer is the viewing side from which all the electro- optic performances were measured.
• the test results including contrast ratio and Dmin at various normalized field strengths were listed in Table 2.
• An electrophoretic fluid containing 6.0% by weight (dry weight) of the TiO 2 - containing microcapsules prepared according to Preparation 2, 1.0 wt% by weight of CuPc-C 8 F 17 and 0.5 % by weight (based on the total dry weight of the TiO 2 -containg microparticles) of R r amine2000 (from Preparation 1) in HT200 was filled and sealed into a microcup array prepared in Preparation 3C (the lower layer).
• the sealed microcup layer was laminated to a second sealed microcup layer (the upper layer) prepared in the Comparative Example 1 to form a staggered two-layer EPD film in which the inactive partition areas of the upper microcup layer were arranged in a staggered manner with registration to the active microcup areas of the lower layer.
• the resultant two-layer EPD film was evaluated as in the Comparative Example 1.
• the contrast ratio and Dmin at various normalized field strengths measured from the upper layer side are also summarized in Table 2.
• Example 2 The same procedure of Example 2 was followed except that the upper microcup layer was filled with an electrophoretic fluid containing 9.7% by weight (dry weight) of TiO 2 -containing microparticles from Preparation 2, 1.0% by weight of CuPc-C 8 F 17 and 0.5% by weight (based upon the total dry weight of the TiO 2 -containing microparticles) of R r amine2000 in HT200; and the lower microcup layer was filled with 9.7% by weight of the Ti0 2 -containing microparticles, 1.5% by weight of CuPc-C 8 F 1 and 0.5% by weight (based upon the total dry weight of the Ti0 2 -containg microparticles) of R r amine 2000 in HT200.
• the contrast ratio and Dmin at various normalized field strengths are summarized in Table 2. The contrast ratio and Dmin are shown to have been further improved by the increases in dye and particle concentrations in the lower layer.
• Example 2 The same procedure of Example 2 was followed, except that the electrophoretic fluid of the upper microcup layer contained 9.7% by weight of the TiO 2 -containing microparticles from Preparation 2, 0.7% by weight of CuPc-C 8 F 17 and 0.5% by weight (based upon the total dry weight of the TiO 2 -containing microparticles) of R r amine2000 in HT200; and the lower microcup layer contained 9.7% by weight of the TiO 2 - containing microparticles, 1.5% by weight of CuPc-C 8 F 17 and 0.5% by weight (based upon the total dry weight of the TiO 2 -containing microparticles) of R r amine2000 in HT200.
• the contrast ratio and Dmin at various normalized field strengths are summarized in Table 2. Table 2: Contrast Ratios and Dmin of Examples 1-4

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