Reflective microcell for electrophoretic display and method of making the same

Abstract

A polymer film includes a plurality of conical microcells, the conical microcells including a dispersion of a first group of charged particles and a second group of charged particles. The first group of charged particles and the second group of charged particles have opposite charge polarities. The conical microcells include walls and at least a portion of the walls are configured to repel the first group of charged particles. A method for manufacturing a laminate for an electrophoretic display is also provided, comprising embossing a plurality of conical microcells through a polymer film layer and into a release sheet to form an embossed film; laminating the embossed film to a conductive material layer on a protective sheet to form a laminated film; removing the release sheet from the polymer film to form an opening to the interior of each microcell of the laminated film; filling the microcells with a dispersion fluid; and sealing the microcells.

Description

Field of the Invention

[0001] The present invention relates to electrophoretic displays. More specifically, in one aspect, the present invention relates to improved microcells containing electrophoretic fluids for electrophoretic displays. In another aspect, the present invention relates to methods of making improved microcells for electrophoretic displays. Background of the Invention

[0003] The term "electro-optical" as applied to a material or display is used herein in its conventional sense in the field of imaging to refer to a material having a first display state and a second display state that differ in at least one optical property, the material being changed from its first display state to its second display state by application of an electric field to the material. While the optical property is typically a color perceptible to the human eye, it may also be another optical property such as optical transmission, reflection, luminescence, or, in the case of a display intended for machine reading, a pseudo-color in the sense of a change in reflectivity of electromagnetic wavelengths outside the visible range.

[0004] The term "gray state" is used herein in its conventional meaning in the field of imaging to refer to a state that is intermediate between the two extreme optical states of a pixel, and does not necessarily imply a black-to-white transition between the two extreme states. For example, many of the E Ink patents and published applications referred to below describe electrophoretic displays in which the extreme states are white and dark blue, so that the intermediate "gray state" is actually light blue. In fact, as mentioned, the change in optical state may not be a color change at all. The terms "black" and "white" that may be used below refer to the two extreme optical states of a display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above. The term "monochrome" may be used below to refer to a drive scheme in which pixels are driven only to their two extreme optical states without an intermediate gray state.

[0005] The terms "bistable" and "bistability" are used herein in their conventional sense in the art to refer to a display that includes display elements having first and second display states that differ in at least one optical property, and such that after any given element has been driven to assume its first or second display state by means of an addressing pulse of finite duration, that state will persist after termination of the addressing pulse for at least several times, e.g., at least 4 times, the minimum duration of the addressing pulse required to change the state of the display element. Some particle-based electrophoretic displays with grayscale capability are shown in U.S. Pat. No. 7,170,670 to be stable not only in their extreme black and white states, but also in their intermediate gray states, and some other types of electro-optical displays are likewise. This type of display is properly referred to as "multistable" rather than bistable, but for convenience, the term "bistable" may be used herein to cover both bistable and multistable displays.

[0006] One type of electro-optical display that has been the subject of intensive research and development for several years is a particle-based electrophoretic display, in which a plurality of charged particles move through a fluid under the influence of an electric field. When compared to liquid crystal displays, electrophoretic displays can have the properties of good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, issues regarding the long-term image quality of these displays have hindered their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in insufficient useful life for these displays.

[0007] As described above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but electrophoretic media can be prepared using gaseous fluids; for example, see Kitamura, T. et al., "Electrical toner movement for electronic paper-like display," IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y. et al., "Toner display using insulative particles charged triboelectrically," IDW Japan, 2001, Paper AMD4-4). See also U.S. Pat. Nos. 7,321,459 and 7,236,291. When the medium is used in a direction that allows particle sedimentation, such as when used in a label in which the medium is set in a vertical plane, such gas-based electrophoretic media appear to be susceptible to the same type of problems caused by particle sedimentation as liquid-based electrophoretic media. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media, because the lower viscosity of the gaseous suspending fluid allows for faster electrophoretic particle sedimentation compared to liquid electrophoretic media.

[0008] Many patents and applications assigned to or under the names of the Massachusetts Institute of Technology (MIT), E Ink Corporation, E Ink California, LLC. and related companies describe various techniques for encapsulating electrophoretic media and microcell electrophoretic media and other electro-optical media. The encapsulated electrophoretic media comprises a plurality of small capsules, each capsule itself comprising an inner phase containing electrophoretically mobile particles in a fluid medium and a capsule wall surrounding the inner phase. In a microcell electrophoretic display, the charged particles and fluid are not encapsulated in microcapsules, but are retained in a plurality of cavities formed in a carrier medium, which is usually a polymer film. See, for example, International Application No. WO 02 / 01281 and Published U.S. Application No. 2002 / 0075556. The above techniques can be found, for example, in the following patents and applications:

[0009] (a) electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Pat. Nos. 7,002,728 and 7,679,814;

[0010] (b) capsules, adhesives and packaging methods; see, e.g., U.S. Pat. Nos. 6,922,276 and 7,411,719;

[0011] (c) microcell structures, wall materials, and methods of forming microcells; see, e.g., 6,672,921; 6,751,007; 6,753,067; 6,781,745; 6,788,452; 6,795,229; 6,806,995; 6,829,078; 6,833,177; 6,850,355; 6,865,012; 6,870,662; 6,885,495; 6 ,906,779;6,930,818;6,933,098;6,947,202;6,987,605;7,046,228;7,072,095;7,079,303;7,141,279;7,156,945;7,205,355;7,233,429;7,261,920;7,271,947;7,304,780;7,307,778; 7,327,346; 7,347,957; 7,470,386; 7,504,050; 7,580,180; 7,715,087; 7,767,126; 7,880,958; 8,002,948; 8,154,790; 8,169,690; 8,441,432; 8,582,197; 8,891,156; 9,279,906; 9,291,872 ; and U.S. Patent No. 9,388,307, and U.S. Patent Application Publication Nos. 2003 / 0175480; 2003 / 0175481; 2003 / 0179437; 2003 / 0203101; 2013 / 0321744; 2014 / 0050814; 2015 / 0085345; 2016 / 0059442; 2016 / 0004136; and 2016 / 0059617;

[0012] (d) Methods for filling and sealing microlocations; see, e.g., U.S. Pat. Nos. 7,144,942 and 7,715,088;

[0013] (e) Films and subassemblies comprising electro-optical materials; see, e.g., U.S. Pat. Nos. 6,982,178 and 7,839,564;

[0014] (f) Backplanes, adhesive layers and other auxiliary layers and methods for displays; see, e.g., U.S. Pat. Nos. 7,116,318 and 7,535,624;

[0015] (g) color formation and color adjustment; see, e.g., U.S. Pat. Nos. 7,075,502 and 7,839,564;

[0016] (h) Methods for driving displays; see, e.g., U.S. Pat. Nos. 7,012,600 and 7,453,445;

[0017] (i) Display applications; see, for example, U.S. Pat. Nos. 7,312,784 and 8,009,348;

[0018] (j) Non-electrophoretic displays; such as U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160; and applications of packaging and micro-unit technology other than displays; see, for example, U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710.

[0019] Microcell electrophoretic displays generally do not suffer from the aggregation and sedimentation failure modes of conventional electrophoretic devices, and offer further advantages such as the ability to print or coat the display on a variety of flexible and rigid substrates.

[0020] Electrophoretic displays typically include a layer of electrophoretic material and at least two other layers disposed on opposite sides of the electrophoretic material, one of the two layers being an electrode layer. In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define display pixels. For example, one electrode layer may be patterned as an elongated column electrode and the other electrode layer may be patterned as an elongated row electrode extending at right angles to the column electrode, with the intersection of the column electrode and the row electrode defining the pixel. Alternatively, more commonly, one electrode layer has a single continuous electrode shape and the other electrode layer is patterned as a matrix of pixel electrodes, each of which defines a pixel of the display. In another type of electrophoretic display intended for use with a stylus, print head, or similar movable electrode that is separate from the display, only one of the layers adjacent to the electrophoretic layer includes an electrode, and the layer on the opposite side of the electrophoretic layer is generally a protective layer intended to prevent the movable electrode from damaging the electrophoretic layer.

[0021] Electro-optical displays, including electrophoretic displays, are expensive, with the price of color LCDs such as those found in portable computers typically accounting for a large portion of the overall computer price. As the use of such displays expands to devices such as cell phones and personal digital assistants (PDAs), which cost much less than portable computers, there is great pressure to reduce the cost of such displays. The ability to form electrophoretic media layers by printing techniques on flexible substrates, as discussed above, opens the possibility of reducing the cost of display electrophoretic components using commercially available equipment for producing coated papers, polymer films, and similar media using mass production techniques such as roll-to-roll coating.

[0022] Current electrophoretic displays may also suffer from insufficient reflectivity of the white optical state. For example, referring to FIG. 1 , a plurality of cubic microcells 10 imprinted in a polymer film are filled with an electrophoretic fluid comprising a black pigment 12 and a white pigment 14. The microcells 10 may be incorporated as a layer in a black and white electrophoretic display. When one or more pixels of the display are displaying a white optical state (viewed from above in FIG. 1 ), a significant amount of light may be transmitted through the white pigment layer 14 without being reflected back to the viewer. Light entering the microcells 10 may be lost and may be absorbed by the black pigment layer 12. The light loss may cause the color state to be flat.

[0023] Therefore, there is a need for microcell designs for electrophoretic displays with improved reflectivity during specific optical states, such as the white optical state. Summary of the invention

[0024] One aspect of the present invention is to provide a polymer film comprising a plurality of conical microunits, the conical microunits comprising a dispersion of a first group of charged particles and a second group of charged particles. The first group of charged particles may have a charge polarity opposite to the charge polarity of the second group of charged particles. The conical microunits include a wall and at least a portion of the wall is configured to repel the first group of charged particles.

[0025] Another aspect of the present invention is to provide a method for manufacturing a laminate for an electrophoretic display, which includes imprinting a plurality of microcells having a conical geometry through a polymer film layer and into a release sheet to form an imprinted film; laminating the imprinted film to a conductive material layer on a protective sheet to form a laminated film; removing the release sheet from the polymer film to form an opening to the interior of each microcell of the laminated film; filling the microcells with a dispersion fluid; and sealing the microcells.

[0026] These and other aspects of the invention will be apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings depict one or more embodiments of the inventive concept by way of example only and not by way of limitation. The same reference numerals in the drawings refer to the same or similar elements.

[0029] 1 is a side cross-sectional view of a series of microcells containing black pigment and white pigment in a dispersion fluid.

[0030] Figure 2a is a side cross-sectional view of a microcell in a white optical state according to a first embodiment of the present invention.

[0031] Figure 2b In black optical state Figure 2a A side cross-sectional view of a microunit.

[0032] Figure 3a is a plan view of four micro units according to another embodiment of the present invention.

[0033] Figure 3b is a plan view of six micro units according to yet another embodiment of the present invention.

[0034] Figure 3c is a plan view of three micro units according to still another embodiment of the present invention.

[0035] Figure 4 is incorporated Figure 2a Schematic side cross-sectional view of an electrophoretic display of a microcell.

[0036] Figure 5 is a side cross-sectional view of an embossed polymer film and a release sheet used in a method according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] In the following detailed description, many specific details are set forth by way of example to provide a thorough understanding of the relevant teachings. However, it is obvious to one skilled in the art that the present teachings can be implemented without these details.

[0039] The present invention is directed to a microcell design that improves light reflectivity and minimizes light loss. Microcell designs according to embodiments of the present invention may include pyramidal geometries to provide angled reflective walls that repel black or dark pigments. Embodiments of the present invention may substantially improve reflectivity when the microcell is displaying an extreme optical state, such as a white state. When a film including microcells according to the present invention is combined with a color filter array (CFA), the addition of a white state may improve display visibility in low light conditions and may improve the color gamut of an electrophoretic display.

[0040] according to Figure 2a and 2b In one embodiment of the present invention illustrated in FIG. 1 , a microcell 10 may include a white pigment 14 and a black pigment 12 in a light-transmitting fluid, wherein the microcell 10 has a conical shape such as an inverted pyramid, with the base of the pyramid facing the viewer and the peak of the pyramid being farthest from the viewer. By providing a conical geometry, when a pixel including the microcell 10 has switched to a white state, the black pigment 12 will be located at the tip of the microcell 10 ( Figure 2b ). Therefore, unlike the micro-unit design with cubic geometry as shown in Figure 1, Figure 2b The area of ​​the black pigment 12 in the pyramidal microunit on the viewing side is smaller than the viewing area of ​​the white pigment 14, thereby reducing the possibility of light loss due to absorption by the black pigment 12.

[0041] The geometry of the microcells according to various embodiments of the present invention also promotes reflection. Figure 2b 14, light 16 that at least partially passes through the white pigment 14 can be reflected back by the walls 11 of the microcell 10 and back through the white pigment layer 14 to the viewer. As known to those skilled in the art, light 16 represents only a single possible path for a portion of the light that enters the microcell 10 and is not intended to represent the path taken by all light that passes through the white pigment 14 to enter the microcell 10. By forming the walls 11 of the microcell 10 with a polymer material having a highly reflective property, light scattered by the microcell 10 will have several points from which the light can be reflected back to the viewer. The angled walls 11 of the microcell 10 are preferably mirrored / mirrored so that the walls of the microcell form a retroreflector. In another embodiment, the walls 11 of the microcell 10 can be configured to be a diffuse reflector rather than a mirrored / mirrored surface. This can be achieved by embossing the microcell 10 in a polymer film filled with a reflective filler such as titanium dioxide.

[0042] The geometric shape of the micro-unit can be provided in various shapes. Figure 3a , 3b 3c, the micro-unit geometry may be a quadrangular, triangular or hexagonal pyramid. The geometry is not limited to a pyramid structure. For example, the geometry may be a cone or a triangular prism, but an equilateral polygonal pyramid is preferred because its geometry allows for close coverage of micro-units with similar beveled walls in the display area. In addition, the tip of the conical geometry of the micro-unit may be optionally truncated or hemispherical. However, a hemispherical geometry is less preferred because such a geometry cannot cover black or other color pigments as small as the area away from the viewer.

[0043] Providing a steep wall angle (i.e., a more acute angle at the tip) of the microcell geometry can prevent black pigment from adhering to the wall and minimize the exposed area of ​​the pigment coated on the tip. In addition, steeper walls may result in a more uniform coating of the viewing surface with pigment. For example, when switching from a black optical state to a white optical state, the white pigment is initially coated in the tip of the microcell and must then migrate from the tip to the viewing surface of the microcell. If the microcell is too shallow, the vertical distance traveled by the white pigment is short relative to the lateral dimension of the viewing area. For relatively steeper walls, the ratio of the lateral distance traveled by the pigment to the vertical distance is low. A high ratio may result in a thicker pigment coating in the center of the viewing area when switching optical states, and a thinner, more light-transmissive coating around the viewing area. The ratio of the lateral movement of the pigment to the vertical movement should be selected to promote substantially uniform coverage of the pigment over the entire viewing area of ​​each microcell. Other factors may also be considered when selecting the geometry of the microcell. For example, a shallow geometry will promote reflectivity by providing a shorter light reflection path. The dimensions of the microcell geometry may also be selected based on the desired display resolution, contrast, and switching speed of the electrophoretic display. In a preferred embodiment, the depth of the microcell is 20 to 50 microns.

[0044] Providing microcells with a conical geometry may also result in an increase in the optically active surface area of ​​the electrophoretic display. Referring again to FIG. 1 , increasing the active surface of the electrophoretic display requires either reducing the thickness of the vertical walls of the cubic microcell 10 or incorporating microlenses into the microcells. However, manufacturing the vertical walls for the microcells becomes increasingly difficult as the wall thickness decreases due to the risk of parts of the microcell falling off the film and remaining on the imprinting tool during the imprinting process. In addition, the use of microlenses may result in a reduction in viewing angle. Therefore, using a conical geometry for the microcells provides a simpler manufacturing method that increases the potential optically active surface area without sacrificing the viewing angle range of the electrophoretic display.

[0045] Reference Figure 4 , for example, a polymer film embossed with microcells 10 having a pyramidal geometry can be incorporated into an electrophoretic display 30. As will be appreciated by those skilled in the art, Figure 4A schematic cross-sectional view of a laminated electrophoretic display is not drawn to scale. A polymer film 18 embossed with a plurality of sealed microcells 10 may be laminated between a series of pixel electrodes 22 and a continuous front electrode 20, which is a thin layer of a light-transmitting conductive material such as indium tin oxide (ITO). The pixel electrodes 22 may be disposed on a backplane 28 in the form of a thin film transistor (TFT) array. The top layer of the laminated display 30 further includes a protective light-transmitting layer 24 such as PET and an optical CFA 26, which includes red (R), green (G) and blue (B) regions that are also light-transmitting. Each of the microcells 10 is filled with a dispersion fluid containing a charged white pigment 14 and a charged black pigment 12. Thus, excluding the optical CFA 26 will provide a black and white display. An adhesive layer may be incorporated between one or more pairs of the above adjacent layers so that the layers can be laminated together.

[0046] In an alternative embodiment of an electrophoretic display, the positions of the single continuous electrode layer and the pixel electrodes can be reversed so that the single continuous electrode layer is located on the backplane and the pixel electrodes are located on the viewing side of the microcell. In this embodiment, the single continuous electrode layer does not need to be light transmissive, but the pixel electrodes must be light transmissive. In this arrangement, a color pixel electrode can be provided so that the pixel electrode can also serve as a CFA.

[0047] In another embodiment of the present invention, a method for making a conical microcell is provided. As is known to those skilled in the art of microcell formation, an embossing technique is generally used, wherein a tool such as an embossing cylinder having a pattern of microcell appearance on its surface is rolled onto a polymer film. After embossing, the microcell is filled with a dispersion containing a charged pigment. To seal the microcell, a crosslinkable oligomer or monomer fluid may be applied to the filled microcell. An optional sealing step may include laminating a sealant layer onto the cup.

[0048] Reference Figure 5 , the most preferred method for manufacturing and sealing microcells according to the present invention includes imprinting microcells in a polymer film, wherein a plurality of microcells have a pyramidal geometry; laminating the imprinted polymer film to a continuous front electrode layer; forming openings in the microcells; filling the interior of the microcells with a dispersion fluid through the small openings; and sealing the microcells.

[0049] The embossing step of the preferred method may include embossing an array of microcells 10 having a pyramidal geometry into a polymer film 32, such as polyester, laminated to a release sheet 34. The film should be made highly reflective, for example, by metallization or incorporation of reflective additives into the polymer film. If the polymer film is metallized before embossing, the metal layer is likely to be discontinuous at all edges of the microcells, thereby avoiding electrical shorts between the front and rear electrodes of the display. Non-conductive reflective coatings designed for constructive interference may also be applied to the film, such as commercially available films, to improve the efficiency of emissive display backlights, such as those known to those skilled in the art. Non-conductive reflective coatings are preferably applied after embossing because these coatings are generally composed of oxides that may not be resistant to embossing.

[0050] In a preferred embodiment of the present invention, the reflective coating on the imprinted polymer film can be a dielectric mirror. As known to those skilled in the art, a dielectric mirror comprises a plurality of thin layers of dielectric material deposited on a substrate. The reflective properties of the dielectric mirror depend on the type of dielectric material and the thickness of the coating. Dielectric mirrors can be manufactured using various thin film deposition methods such as physical vapor deposition (e.g., vapor deposition and ion beam assisted deposition), chemical vapor deposition, ion beam deposition, molecular beam epitaxy, and sputtering deposition. Dielectric materials used to form dielectric mirrors include, but are not limited to, aluminum, magnesium fluoride, silicon dioxide, tantalum pentoxide, zinc sulfide (n=2.32), and titanium dioxide (n=2.4).

[0051] To further enhance the reflectivity of the microcell walls, embodiments of the present invention may include features to prevent black pigment from adhering to the microcell walls. To limit the presence of black pigment dispersed on the front viewing surface or coated in the tip of the microcell, the wall may be surface treated to repel black pigment. For example, a fluorinated polymer or other low surface energy material may be coated on the microcell wall. Alternatively, after the surface of the microcell is metallized, the microcell wall may be treated with the same chargeable groups used to form the electrophoretic black pigment. If the microcell wall has a charge polarity similar to that of the black pigment, the microcell wall will repel the black pigment.

[0052] In one embodiment, the metallized surface of the imprinted polymer film may contain reactive sites that can react with a reagent having a silane moiety bonded to one or more polar groups and / or one or more polymerizing / polymerizable groups. The reactive sites can be hydroxyl groups, amine groups, carboxylic acid groups or derivatives thereof (e.g., amides or esters), alcohol or phenolic groups, or halogens, depending on the chemical functionality of the material used to provide the reflective surface for the microcell walls. The reactive sites can also be implanted on the surface of the microcell walls by conventional means or by special treatments, such as the hydration treatments described in U.S. Patent No. 13 / 149,599, filed May 31, 2011, the entire contents of which are incorporated herein by reference in their entirety.

[0053] The polar groups of the reagents can contribute charge to the microunit wall surface. For example, polar groups such as --NH-- can contribute positive charge, while polar groups such as --OH or --COOH can contribute negative charge. Polymerization / polymerizable groups include, but are not limited to, vinyl, acrylate, methacrylate, etc.

[0054] The reactants may include, but are not limited to, N-(3-acryloxy-2-hydroxypropyl)-3-aminopropyltriethoxysilane (Gelest), 3-(N-allylamino)propyltrimethoxysilane (Gelest), 3-(N-phenylvinylmethyl-2-aminoethylamino)-propyltrimethoxysilane (Gelest), or vinylbenzylaminoethylaminopropyl-trimethoxysilane (Z-6032 from Dow Corning).

[0055] The silane coupling reaction of the reagent with the microlocation surface can be initiated by first hydrolyzing the silane moiety to form reactive silanol groups (Si-OH) which can subsequently bond with hydroxyl groups on the imprint film surface via a condensation reaction.

[0056] To prevent the white pigment with opposite charge polarity from strongly adhering to the microcell wall, a steric stabilizing layer may be added to the wall as used for the black pigment. For example, after the silane coupling reaction, if desired, the polymeric / polymerizable group may be polymerized with one or more types of monomers, oligomers or polymers and combinations thereof to form a polymer stabilizer. It is desirable that the polymer stabilizer creates a steric barrier of about 1 nm to about 50 nm, preferably about 5 nm to about 30 nm, and more preferably about 10 nm to about 20 nm on the surface of the microcell wall.

[0057] In the context of the present invention, suitable polymers may include, but are not limited to, polyethylene, polypropylene, polyacrylates, polyurethanes, polyesters or polysiloxanes. Suitable monomers include, but are not limited to, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, n-octadecyl acrylate and n-octadecyl methacrylate. The choice of material for the polymer stabilizer will depend on the compatibility of the material with the solvent used in the electrophoretic fluid.

[0058] The combined thickness of the polymer film 32 and the release sheet 34 should be greater than the final dimensions of the desired microcell geometry. The polymer film 32 should have a depth less than the height of the corresponding pattern on the imprint tool to ensure that the imprint tool penetrates the polymer film 32 and enters the release sheet 34 during imprinting. The release sheet 34 should have approximately the same elastic modulus as the polymer film 32 and sufficient thickness so that the imprint cylinder will not be damaged by the opposing cylindrical tool surface. In a preferred embodiment, the release sheet can comprise silicone-coated polyethylene terephthalate.

[0059] The lamination step of the preferred method may include laminating a protective PET layer, an optical CFA, and a front plate electrode film (ITO), such as Figure 4 The layers 24, 26 and 20 in the microunit are formed on the open ends of the microunits, for example Figure 5 The PET-ITO layer is preferably laminated to the polymer film before filling and sealing the microcells so that the pattern of microcells contains tightly packed cells to maximize the active area ratio of the display.

[0060] The formation of the opening in each of the microcells may include separating the release sheet 34 from the polymer film 32 to remove the bottom of the imprinted microcell 10, thereby forming a small hole at the bottom of each of the microcells 10. The width of the hole should be large enough to allow the dispersion fluid to easily enter and exit the interior of the microcell, but the size should be minimized to facilitate sealing after filling.

[0061] The filling step of the preferred method can be accomplished by a variety of techniques.

[0062] In one method, the microcells can be filled by first evacuating the interior of the microcells, for example, by placing the laminated polymer film 32 and PET-ITO layer with the release sheet 34 removed in a vacuum chamber. After applying a vacuum to evacuate the microcells, the dispersion fluid can be applied to the surface of the polymer film 32 containing the small holes, and then the vacuum is immediately released to draw the dispersion fluid into the microcells. To minimize the possibility of evaporation of the solvent in the dispersion fluid, it is preferred to place the combined polymer film 32 and PET-ITO layer in a vacuum chamber with as small a volume as possible, i.e., slightly larger than the volume of the combined polymer film 32 and PET-ITO layer, and release the vacuum once a sufficient amount of the dispersion fluid for filling the microcells has been applied to the polymer film 32.

[0063] Another method of filling the microcells may include immersing the laminated polyester film 32 and PET-ITO layer with the release sheet 34 removed in an ultrasonic bath filled with a dispersion fluid. Ultrasonic agitation will drive out the gas in the microcells, causing it to be replaced by the dispersion fluid. The bath may be kept under a slight vacuum if necessary to speed up the process. Ultrasonic agitation is the preferred filling method because it has the potential to be scaled up to a continuous process.

[0064] Yet another filling method may include filling the microcell with, for example, a solvent vapor having a boiling point below ambient temperature but above the pour point or solidification temperature of the dispersion fluid. The laminated polymer film 32 and PET-ITO layer with the release sheet 34 removed may then be immersed in the dispersion fluid and then cooled to a temperature below the boiling point of the solvent vapor in the microcell. This will cause the solvent vapor to condense and draw the dispersion fluid into the microcell. The solvent vapor is preferably miscible in the dispersion fluid.

[0065] When filling the microcells with a dispersion fluid, it is preferred to use a sealant that is miscible in the dispersion fluid to seal the microcells. A laminating adhesive that simultaneously meets the electrical, optical and mechanical requirements of the electrophoretic display and has low solvent permeability can be used to seal the microcells and form a front plate laminate (FPL) including the microcell design of the present invention. Alternatively, a separate sealant can be used to seal the microcells before applying a laminating adhesive layer and an optional releasable sheet to form the FPL. Because the openings in the polymer film 32 are relatively small relative to the total area of ​​the polymer film, the surface of the polymer film 32 will provide sufficient area for wetting and bonding with the sealant. Since the sealant is applied to the rear non-viewing surface of the electrophoretic display of the preferred method, the sealant is unlikely to interfere with the optical properties of the display.

[0066] Although preferred embodiments of the present invention have been shown and described herein, it will be understood that these embodiments are provided by way of example only. Various changes, modifications and substitutions may be made by those skilled in the art without departing from the spirit of the present invention. Therefore, it is intended that the appended claims cover all such changes within the spirit and scope of the present invention.

Claims

1. A polymer film comprising a plurality of conical microunits, wherein the conical microunits comprise a dispersion of a first set of charged particles and a second set of charged particles, wherein the first set of charged particles are light absorbing and have a charge polarity opposite to that of the second set of charged particles, and the second set of charged particles are light scattering, wherein the pyramidal microunits include walls and at least a portion of the walls have a charge polarity similar to that of the first group of charged particles, thereby repelling the first group of charged particles, wherein the portion of the wall comprises a mirrored surface.

2. The polymer film of claim 1, wherein the first set of charged particles are black. The polymer film of claim 1 , wherein the second set of charged particles are white. The polymer film of claim 1 , wherein the pyramidal microunits are conical in shape. The polymer film of claim 1 , wherein the pyramidal microunits are pyramidal in shape. The polymer film of claim 1 , wherein the pyramidal microunits have an inverted pyramid shape. The polymer film of claim 1 , wherein the pyramidal microunits have an inverted pyramidal shape. The polymer film of claim 1 , wherein the pyramidal microunits have an inverted triangular prism shape.

9. The polymer film of claim 1 wherein the portion of the wall comprises a diffusely reflective surface.

10. The polymer film of claim 1, wherein the portion of the wall comprises a low energy surface material.

11. The polymer film of claim 10, wherein the low energy surface material comprises a fluorinated polymer.

12. A method for manufacturing a laminate for an electrophoretic display, comprising the following steps of preparing the polymer film according to any one of claims 1 to 11: embossing a plurality of pyramidal micro-elements through the polymer film layer and into the release sheet to form an embossed film; laminating the stamped film to the conductive material layer on the protective sheet to form a laminated film; removing the release sheet from the polymer film to form an opening to the interior of each microcell of the laminated film; filling the microlocations with a dispersion fluid; and The microcell is sealed.

13. The method of claim 12, wherein the polymer film comprises a metallized surface.

14. The method of claim 12, further comprising applying a non-conductive reflective coating to a surface of the polymer film prior to the laminating step.

15. The method of claim 12, wherein the polymer film comprises a reflective additive.

16. The method of claim 12, wherein a color filter array is located between the protection sheet and the conductive material layer.

17. The method of claim 12, wherein the filling step comprises: placing a laminated film having an opening to the interior of each microcell in a vacuum chamber; evacuating the interior of each microcell to create a vacuum within the vacuum chamber; applying the dispersion fluid to the opening of each microcell; and The vacuum in the vacuum chamber is released.

18. The method of claim 12, wherein the filling step comprises immersing the laminate film having the opening to the interior of each microlocation in an ultrasonic bath filled with the dispersion fluid.

19. The method of claim 12, wherein the filling step comprises: filling the interior of each microcell with a solvent having a boiling point higher than the pour point or freezing point of the dispersion fluid; immersing a laminate film having an opening to the interior of each microcell in the dispersion fluid; and The temperature of the solvent is lowered to below the boiling point of the solvent to introduce the dispersion fluid into the interior of each microlocation.

20. The method of claim 12, wherein the sealing step comprises covering the opening of each microlocation with a sealant.

Images