DISPLAY DEVICE
TECHNICAL FIELD The invention relates to a display device, and more particularly, to a display device that can be used as electronic paper.
BACKGROUND ART International Patent application Number PCT/US1999/29922 discloses an electronic display device using microcapsules. The electronic display device is an electronic-optical device using magnetically migrating particles or electrophoretic particles. The electronic display device may use a flexible substrate as a substrate. The electronic display deice uses an electric field to induce an optical change, thereby realizing image displays. Such an electronic display device may be used as electronic paper which is currently being developed. Such application as electronic paper has technological limitations in that a thin and flexible substrate material is required, the thickness of the entire device should be small, etc. The development of electronic paper is focused on the manufacturing of a display device that can display color images close to natural colors and be flexible enough to change the shape as freely as real paper and a method of manufacturing the display device. DETAILED DESCRIPTION OF THE INVENTION
Technical Goal of the Invention 1 , The present invention provides a display device with a new structure that can display color images. The present invention also provides a display device that can be used as electronic paper and can display high quality images.
Disclosure of the Invention According to an aspect of the present invention, there is provided a display
device comprising: a front panel and a rear panel; an image display layer, which is placed between the front panel and the rear panel and includes a plurality of magnetooptical elements and a plurality of electrooptical elements; at least one electric field generating unit, which generates an electric field to be applied to the electrooptical elements; and at least one magnetic field generating unit, which generates a magnetic field to be applied to the magnetooptical elements. According to another aspect of the present invention, there is provided a display device comprising: a front panel and a rear panel; an image display layer, which is placed between the front panel and the rear panel and includes a plurality of magnetooptical elements and a plurality of electrooptical elements; a plurality of first electrodes, which are arranged on the front panel; a plurality of second electrodes, which are arranged on the rear panel to be orthogonal to the first electrodes; and a plurality of magnetic field generating units, which are arranged at intersections of the first and second electrodes to generate a magnetic field to be applied to magnetooptical elements. In a display device according to the present invention, the electrooptical elements may be electrically charged particles, and the magnetooptical elements may be magnetic particles. The electrooptical elements and the magnetooptical elements may be in particle form and dispersed in liquid. The image display layer may comprise a plurality of capsules containing the electrooptical elements and the magnetooptical elements. The electric field generating units may comprise a plurality of electrodes arranged on both sides of the image display layer. The magnetic field generating units may comprise a plurality of magnetic field generating coils arranged on one side of the image display layer. Alternatively, the magnetic field generating units may comprise a plurality of magnetic field generating coils arranged in pair on both sides of the image display layer. The electrooptical elements may include a plurality of negatively charged particles and a plurality of positively charged particles, and the color of the negatively charged particles differs from the color of the positively charged particles. In a display device according to the present invention, the first and second electrodes may be arranged in an X-Y matrix. The magnetic field generating units may comprise: a plurality of first bus lines parallel to the first electrodes and a plurality of second bus lines parallel to the second electrodes; and a plurality of magnetic field
generating coils, which are placed at intersections of the first bus electrodes and the second bus electrodes and apply a magnetic field to the intersections of the first electrodes and the second electrodes.
Effect of the Invention As described above, the present invention provides a display device including in an image display unit particles that are moved by a magnetic field and an electric field. The display device is suitable for use as electronic paper. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the concept of image display in a display device according to the present invention; FIG. 2 illustrates particles used in the display device according to the present invention; FIGS. 3 and 4 are illustrations for explaining an image display mechanism depending on the movement of charged elements in the display device according to the present invention; FIGS. 5 and 6 are illustrations for explaining an image display mechanism depending on the movement of magnetic elements in the display device according to the present invention; FIG. 7 is a schematic perspective view of a pixel of a display device according to an embodiment of the present invention; FIG. 8 is a plan view of a magnetic field generating unit of the display device shown in FIG. 7; FIG. 9 is a schematic perspective view of a pixel region of a display device according to another embodiment of the present invention; FIG. 10 is a plan view of a magnetic field generating unit of the display device shown in FIG. 9; FIGS. 1 1 and 12 are cross-sectional views illustrating modified exemplary structures of an image display unit in the display devices shown in FIGS. 7 and 9; and FIG. 13 illustrates an example of a magnetic particle used in the display device according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a displace device according to the present invention are described in detail with reference to the appended drawings. In a display device according to the present invention, charged particles that are moved by an electric field are used as electrooptical elements, and magnetic particles that are moved by a magnetic field are used as magnetooptical elements. For the convenience of understanding of the mechanism of the invention, the concept of the invention will be described with reference to FIG. 1. As shown in FIG. 1 , a plurality of magnetic particles, negatively charged particles and positively charged particles are dispersed in emulsion. A feature element of the present invention is an activation layer in which image display takes place. The negatively charged particles and the positively charged particles have different surface colors according to the direction of an electric field. In FIG. 2, the negatively charged particles have orange color, and the positively charged particles have white color. Each magnetic particle has two colors; for example, N pole and S pole of each magnetic particle respectively have red and blue colors. FIGS. 3 and 4 are diagrams illustrating the movement of charged particles in an activation layer 10 under the influence of an electric field. As shown in FIG. 3, when a side of the actuation layer 10 which is being viewed is charged with positive charges, and an opposite side is charged with negative charges, the electric field moves the negatively charged particles toward the side being viewed and the positively charged particles toward the opposite side. At this time, the magnetic particles are in a free floating state, not influenced by external forces, and thus are isolated in the middle of the actuation layer 10 due to the pressure of the charged particles. In this case, the color, for example, orange, of the negatively charged particles is perceived at the view site. On the contrary, as shown in FIG. 4, when the side of the actuation layer 10 which is being viewed is charged with negative charges and the opposite side thereof is charged with positive charges, the positively charged particles move to the side being viewed while the negatively charged particles move to the opposite side. At this time, the magnetic particles are in a free floating state, not influenced by external forces, and thus are isolated in the middle of the actuation layer 10 due to the pressure of the charged particles. In this case, the color, for example, white, of the positively charged
particles is perceived at the view site. FIGS. 5 and 6 are diagrams illustrating the movement of charged particles in the actuation layer 10a when a magnetic field instead of an electric field is applied to the actuation layer 10. Referring to FIG. 5, when the S pole of an external magnetic field is placed on a side of the actuation layer 10 at the view site and the N pole thereof is placed on the opposite side, the magnetic particles are oriented in the direction of magnetic fluxes of the external magnetic field. In particular, the magnetic particles migrate toward both sides of the actuation layer 10, namely, toward the N and S poles of the external magnetic field. At this time, the positively and negatively charged particles are isolated in the middle of the actuation layer 10 due to the pressure generated by the migration of the magnetic particles. Therefore, the color, for example, red, of the N poles of the magnetic particles is perceived at the view site. On the contrary, when the external magnetic field is reversed such that the N pole of the magnetic field is placed on the side of the actuation layer 10 at the view site and the S pole of the magnetic field is placed on the opposite side of the actuation layer 10, the magnetic particles are oriented close to the two poles. In particular, the magnetic particles migrate toward the both sides of the actuation layer 10, namely, toward the N and S poles of the external magnetic field. At this time, the positively and negatively charged particles are isolated in the middle of the actuation layer 10 due to the pressure generated by the migration of the magnetic particles. Therefore, the color, for example, blue, of the S poles of the magnetic particles is perceived at the view site. The positively and negatively charged particles which have migrated to both sides of the actuation layer 10 by the electric field are stuck to the both sides of the actuation layer 10 due to residual charges, thereby leading to a memory effect. To offset this memory effect, charges with opposite polarities must be instantaneously applied. By doing this, the charged particles concentrated near the both sides of the actuation layer 10 due to the remaining electric charges can move freely. Then, the particles adhering to the both sides of the actuation layer 10 are separated, and consequently all the particles of four different colors are freely mingled and thus are seen gray color. For the magnetic particles migrated by the magnetic field, the memory effect can be eliminated by instantaneously reversing the poles of the magnetic field.
As described above, in the present invention, a plurality of charged particles and magnetic particles of proper colors are placed in the actuation layer, and a properly adjusted magnetic field and electric field is applied across the actuation layer to achieve display in desired colors. In a flat display device, the actuation layer described above is placed at each intersection of electrodes arranged in an X-Y matrix. In an embodiment, the actuation layer may be disposed between two facing substrates as in common LCDs. In another embodiment, the actuation layer may be implemented in capsule form or fiber form using capsules and disposed between two substrates. Here, the substrates mean flat members supporting the actuation layer and electric elements, such as electrodes, etc., which drive the actuation layer. FIG. 7 is a schematic perspective view of a pixel region in a flat display device according to an embodiment of the present invention. Referring to FIG. 7, a first electrode 11 and a second electrode 12 are arranged on and under the actuation layer 10 to cross each other. The first and second electrodes 11 and 12 are respectively covered with protective layers 11a and 12a. The first and second electrodes 11 and 12 are electric field generating units for driving electrically charged particles. The electric field generating units generate an electric field across the entire area of unit pixels to move the charged particles in the direction of electric fluxes. The first and second electrodes 11 and 12 are formed of a transparent material, such as ITO, etc. The second electrode 12 is formed on the inner surface of a second substrate 17, namely, on the upper surface of the second substrate 17 as can be seen in FIG. 7. The second substrate 17 may be a flexible film, a solid plastic substrate, or a glass substrate. In other words, the second substrate 17 may be formed of various materials in other embodiments. The second substrate 17 may be formed of any material, without departing from the scope of the invention. Referring to FIG. 7, a first intermediate insulating layer 13a is placed on the first electrode 11. A first bus electrode 14 and a second bus electrode 15 with a second intermediate insulating layer 13b therebetween are placed on the first intermediate insulating layer 13a. A first substrate 16 is placed on the second bus electrode 15. Referring to FIG. 8, the first and second bus electrodes 14 and 15 are arranged to be orthogonal to each other. A coil layer 18 as a magnetic field generating source is placed between the first and second bus electrodes 14 and 15. In the present
embodiment, the coil layer 18 has a serpentine shape. One end of the coil layer 18 is connected to the first bus electrode 14 and the other end is connected to the second bus electrode 14. The coil layer 18 is formed on the same level as the first bus electrode 14 and is connected to the second bus electrode 15 via a contact hole 13c, which penetrates through the second intermediate insulating layer 13b. However, the coil layer 18 may be formed in a layer where the first and second bus electrodes 14 and 15 are not formed. The coil layer 18 may be formed in various shapes, without departing from the scope of the present invention. The flat display device with the above-described pixel structure illustrated in FIGS. 7 and 8 includes separate circuits connected to the first and second electrodes 1 1 and 12 to move the charged charges and separate circuits connected to the first and second bus electrodes 14 and 15 to move the magnetic particles. FIG. 9 is a schematic perspective view of a flat display device according to another embodiment of the present invention. The flat display device of FIG. 9 has a structure in which a coil layer acting as a magnetic field generating source and bus electrodes corresponding to the coil layer are symmetrically arranged on both sides of the actuation layer. Compared with the display panel of FIG. 7 having the magnetic field generating source on one side of the actuation layer, the structure of the display device illustrated in FIG. 9 can form a strong magnetic field with desired orientation. Referring to FIG. 9, a first electrode 11 and a second electrode 12 are placed on and under the actuation layer 10 to cross each another. The first and second electrodes 11 and 12 are respectively covered with protective layers 11a and 12a. The first and second electrodes 1 1 and 12 are electric field generating units for manipulating the charged particles as in the previous embodiment illustrated in FIGS. 7 and 8. The electric field generating units form an electric field across the entire area of unit pixels to move the charged particles in the direction of electric fluxes. The first and second electrodes 11 and 12 are formed of a transparent material, such as ITO, etc. Symmetric magnetic field generating units are respectively placed between the first electrode 11 and the first substrate 16 and between the second electrode 12 and the second substrate 17. First, in a structure formed on the first substrate 16, a first intermediate insulating layer 13a is placed on the first electrode 1 1 , a first bus electrode 14 and a second bus electrode 15 with a second intermediate insulating layer 13b therebetween are placed
on the first intermediate insulating layer 13a, and the first substrate 16 is placed on the second bus electrode 15. Next, in a structure formed on the second substrate 17, a third intermediate insulating layer 13d is placed below the second electrode 12, a third bus electrode 14' and a fourth bus electrode 15' with a fourth intermediate insulating layer 13e therebetween are placed below the third intermediate insulating layer 13d, and the second substrate 17 is placed on the fourth bus electrode 15'. Referring to FIG. 10, the first and second bus electrodes 14 and 15 are arranged to cross each other, and the third and fourth bus electrodes 14' and 15' are arranged to cross each other. A coil layer 18 serving as a magnetic field generating source is formed between the first and second bus electrodes 14 and 15, and a coil layer 18' serving as a magnetic field generating source is formed between the third and fourth bus electrodes 14' and 15'. The coil layers 18 and 18' have serpentine shapes as in the previous embodiment illustrated in FIGS. 7 and 8. Respective one ends of the coil layers 18 and 18' are connected to the first and third bus electrodes 14 and 14', and respective other ends thereof are connected to the second and fourth bus electrodes 15 and 15'. The coil layers 18 and 18' form magnetic fluxes in the same direction, for example, in a forward direction, so that the combined magnetic fluxes pass through the actuation layer 10. The coil layers 18 and 18' are formed on the same levels as the first and third bus electrodes 14 and 14', respectively, and are connected to the second and fourth bus electrodes 15 and 15' via contact holes 13c and 13c', respectively. The contact holes 13c and 13c' respectively penetrate through the second and fourth intermediate insulating layers 13b and 13e. However, the coil layers 18 and 18' may be formed in layers where no bus electrode is formed. The coil layers 18 and 18' may have other structures without departing from the scope of the present invention. Meanwhile, the charged particles and magnetic particles dispersed in the actuation layer 10 may drift in one direction due to gravity, thereby hindering image display. To prevent this, the actuation layer 10 can be divided into sub-pixel units to suppress the drifting of the charged particles and magnetic particles. FIG. 1 1 illustrates a structure suppressing the drifting of liquid between pixels to prevent conglomeration and coagulation of the charged and magnetic particles. Referring to FIG. 11 , a wall 10b with channels 10c having semi-spherical cross-sections is disposed between the first and second electrodes 1 1 and 12. The
channels 10c of the wall 10b is filled with a dispersion of the charged magnetic and electric particles in an actuation liquid 10a. Therefore, in this embodiment, the actuation layer 10 includes the wall 10b with the channels 10c and the actuation liquid 10a filling each of the channels 10c. In addition to the structure described above, the actuation liquid 10b may be encapsulated into spherical capsules 10d and placed between the first and second electrodes 1 1 and 12, as shown in FIG. 12. In other words, the activation liquid 10b is contained in the spherical capsules 10d. Meanwhile, to prevent the coagulation of the magnetic particles by the magnetic force, an insulating layer composed of a non-magnetic material and having an appropriate thickness may be formed on one side (i.e., the N pole in the present embodiment) of a magnetic element. The insulating layer is thick enough to sufficiently weaken the attraction between the magnetic particles and prevent the coagulation of the magnetic particles. FIG. 13 illustrates an exemplary magnetic particle with a rectangular cross-section for convenience of illustration. A flat display device according to the present invention may include a plurality of sub-units (pixels) described in the previous embodiment. The flat display device according to the present invention includes pixels arranged in an X-Y matrix as in general displays, and the actuation layer 10 described above is included in the pixels. In the flat display device according to the present invention, a plurality of charged particles and magnetic particles in micro-particle shapes are dispersed in the actuation liquid. Accordingly, one sub-unit or pixel may contain millions of such particles. A method of manufacturing the charged particles used in the flat display device according to the present invention will now be described. The charged particles can be manufactured based on the technology disclosed in Korea Patent Publication Nos. P2000-0076345 and P2003-0029597. The charged particles used in the present invention are surface-charged micro-particles. Such charged particles may be dispersed in a medium and encapsulated into microcapsules. Alternatively, such charged particles may be dispersed in a carrier liquid and directly injected directly into the space between glass or plastic plates. The microcapsules of charged particles may be dispersed in a binding agent and deposited on a glass or plastic plate using, for example, a printing process. A various kinds of pigments in micro-particles may be used. A proper pigment can be
selected based on a desired electric charge level, particle size, color and the conditions described below. The micro-particles may have different sizes according to the use of the display. However, it is preferable that the micro-particles have radii of about 1 μ m in various aspects. As described above, the flat display device according to the present invention uses positively and negatively charged particles. As a method, the positively and negatively charged particles in micro-particles may be separately charged with a charging agent or a charge-control agent (CCA) or by being dispersed in a dielectric liquid. The CCA may be added to pigment particles to provide a surface potential (zeta potential). The CCA may be either attached directly onto the surfaces of the pigment particles or mixed with pigment particles. In general, the CCA provides a zeta potential that is equal to a 50-100 elementary charge onto the surfaces of particles having radii of 1 μ m. The CCA provides a sufficient electrophoretic mobility on the order of 10"4-10"5 cm2Λ/sec. CCAs may be plastic or non-plastic and may also be ionic or non-ionic. Non-ionic plastic CCAs may be polyethylene, polybutene succinimide, and various polyvinyl pyridine block copolymers. The CCA, pigments in particles, a plastic mixture, and any underlying coating should be selected in consideration the zeta potential not to interfere with the optical properties of the pigment particles. The CCA may be put into a polymer when forming micro-particles. The CCA may be adsorbed onto the particles immediately before being put into a dispersion solvent or being milled. As the CCA mixed with the micro-particles is slowly dissolved in the actuation liquid over a long period of time and dispersed over the lifetime of the micro-particles, the micro-particles may be charged. As another method, the micro-particles may be charged through dielectric coating. For example, when magnesium fluoride and aluminum are vaporized in a vacuum, a black coating is formed. When indium is slowly vaporized, a white coating is formed. As another method of charging the micro-particles, a set of triboelectric series of plastics, which are separated from each other, may be used. For example, when a polyethylene of a first color and a nylon polymer of a second color are rubbed, nylon particles are positively charged, and polyethylene particles are negatively charged. As another method of charging the micro-particles, polyethylene may be
negatively charged while a fused polymer is flowed through a glass tube. This principle may be used to electrically charge micro-particles formed using spraying or other methods by friction. The charged particles used in the present invention should have allowable optical properties, should not swell or soften in a dielectric solvent, and should be chemically stable. The final suspension should be stable against sedimentation, coagulation, and cohesion under typical operating conditions. The charged particles can be made into micro-particles using one of conventional technologies, such as, grinding, milling, spraying through nozzles, rotational spraying, a ultrasonic technology, a polymer building block, and so on. The final particles are usually spherical and have different sizes. Accordingly, only particles in a certain range of sizes should be used. The final particles having desired sizes can be screened using well-known methods, for example, vibrating a screen with the final particles thereon, where the vibration can be obtained by subjecting the screen to ultrasonic vibration. A screening method may involve two stages: screening out particles which are too small; and obtaining particles having desired sizes. Too small or too large particles may be recycled for further uses. The above-described methods of obtaining micro-particles, charging the micro-particles, and screening micro-particles of proper sizes are well known in the field. Hereinafter, a method of manufacturing the magnetic particles will be described. The magnetic particles may be spherical. The surface of each spherical magnetic particle may be divided into two parts in different colors. Such two-color spherical magnetic particles may be prepared using the methods disclosed in U.S. Patent Nos. 4,810,431 and 4,143,103. In an embodiment, the magnetic particles may be formed by spraying a melted mixture of a magnetic substance, plastic, and a pigment of a first color. The particles are magnetized and disposed in one layer. When magnetizing the particles, an external magnetic field of greater than 10,000 gausses is applied to fully saturate the magnetic substance. The intensity of the external magnetic field is maintained when manufacturing magnetic particles using other methods. When the ground color is black, there is no need to add a pigment because the natural color of the magnetic substance is black. The magnetized particles are coated with a second pigment. When the particles are cured at a high temperature in a coating process, the particles
are magnetized once more to increase the magnetization of the particles. In another method, a melted mixture of a magnetic substance, plastic, and a pigment is fed into an upper part of a nozzle while another melted mixture in a color different from the melted mixture fed into the upper part of the nozzle is fed into the lower part of the nozzle, to induce laminar flows such that the upper and lower layers do not mix. The resulting product is passed through a magnetic field of 50 gausses or greater to obtain magnetized spherical particles. In another embodiment, two thin layers of different colors may be formed on a temporary carrier, such as, a polyethylene web or glass, using melted mixtures of magnetic substances, plastics, and pigments, magnetized, separated from the temporary carrier, and ground into micro-particles. In consideration of the width of a magnetizer, the widths of the two thin layers may be about 8mm. The temporary carrier can be removed from the two thin layers using general delaminating methods, such as twisting and air blowing, etc. The grinding can be accomplished using usual methods, such as, by vigorously agitating the two thin layers using an agitator.
Micro-particles of proper sizes can be screened using methods that are commonly used in the powder production field. Detailed operating conditions will be described below. To form a first thin layer, a mixture is prepared by mixing 17 parts by weight of styrene butadiene copolymer (about 40% - 60% by weight of a first pigment is included to express a desired color) with 25 parts by weight of toluol. This mixture is coated on a plastic web with rotogravure and dried in an oven at about 120°C. To form a second thin layer, a mixture is prepared by mixing 4.5 parts by weight of styrene butadiene copolymer (40-65% by weight of a second pigment is included) with 0.224 parts by weight of barium ferrite and 14.5 parts by weight of toluol. This mixture is coated on the first layer and dried at 120°C. Then, the dried films are magnetized with a magnetic field of 10,000 gausses or greater. The films are removed from the plastic web by, for example, twisting and air blasting, and ground into micro-particles. Micro-particles in desired sizes are selected. The diameter of each particle may be about 150% of the thickness thereof. In an example of the ratio of pigments, the amount of titanium oxide may be 168% of the copolymer, and the amount of carbon black may be 67% of the copolymer. A composition is prepared using a lacquer containing cellulose nitrate, ester gum, plasticizer, glycolic ester, alcohols, and aromatic and aliphatic hydrocarbons, a small
amount of a lacquer thinner and corn starch (controlling viscosity to improve spreadability), and pigment barium ferrite. The first layer contains 60 parts by weight of the lacquer and 50 parts by weight of titanium oxide by weight, and the second layer contains 25 parts by weight of a red pigment, 10 parts by weight of barium ferrite, and 75 parts by weight of the lacquer. The first and second layers are sequentially coated on a polyethylene carrier. The thickness of the first layer (white) is 0.013mm, and the thickness of the second layer (red) is 0.0065mm. The thickness of each of the two layers may be controlled by drawing the layer between bars that are spaced a distance corresponding to the thickness. Next, magnetization, grinding, and size screening processes are performed to obtain magnetic particles having desired particle diameters. Suspension liquids, namely, carrier liquids, used in the present invention are widely known. The carrier liquid may be either polar or non-polar. Examples of usual polar carrier liquids include water, lower grade alcohols, such as ethanol, synthetic esters, etc. In the present invention, water is preferably used as a carrier liquid. Examples of usual non-polar carrier liquids include organic solvents, such as heptane, xylene, or toluene, other hydrocarbons, polyglycol, polyphenyl ether, perfluoropolyether, silahydrocarbon, stylene, etc. To be compatible with the carrier for charged particles, heptane or toluene can be used as the carrier liquid. Various dyes and pigments, which are disclosed in U.S Patent No. 5,717,514 and other references, are available as coloring agents for the micro-particles.
Examples of various dyes and pigments include: Cresyl violet blue and Rhodamine 6G (available from Baker Chemical); Rhodamine B1 , Spirit Blue NS, Victoria B base and R900 titanium dioxide (available from Dupont); 6331 black pigment (available from Ferro); Isol Blue (available from Allied Chemicals); Acridine orange (available from Estman); Calco Oil blue N and Calco Oil black (available from Calco); Mogul L carbon black and Monarch 1000 carbon black (available from Cabot); Phthalocyanine blue, Phthalocyanine green; Diarylide yellow, Diarylide AAOT yellow; series of Quinacridone, Azo and Perylene (available from Sun Chemical); Hansa Yellow G powders and Carbon Lampblack. Examples of inorganic pigments, which are classified according to chemical compositions, include barium sulfate (white), cadmium red, cadmium sulfo-selenide (black), cadmium silicate (white), chromium oxide (green), iron oxide (black), iron oxide (red), lead chromate (yellow), manganese dioxide (brown), selenium (arsenic dope), silicon monoxide (reddish brown), sulfur (yellow), Wermilion red, zinc
oxide (white), zirconium oxide, etc. If a pigment is photosensitive, an appropriate filter should be used. A process of encapsulating the particles and other processes will now described. There are a process of directly sealing the prepared magnetic particles and charged particles into paper or fabric or after being encapsulated into microcapsules, a process of attaching an actuating electric device to the paper or fabrics, and a process of coating the final product with a non-abrasive plastic to protect the product. The final coating process is performed using a commonly known coating method. Embodiments of the sealing process and the electric device attaching process will now be described. When the particles are have been magnetized, a spontaneously volatile adhesive or a UV curable adhesive may be used in the electric device attaching process. In an embodiment, a mixture of microcapsules with a binder may be directly coated on a substrate. In this embodiment, to maintain the clearance between the substrate and an upper layer, micro cups or a mixture of spacers with micro cups may be used as spacers. The spacers may function as sensors when the display uses a touch screen. In an embodiment of using micro cups, a multi-functional acrylate, an acrylated oligomer, and a UV curable composition containing a photoinitiator are dispersed in a suspension or a mixture ("display liquid") of microcapsules and a binder. Since the density of the UV curable composition is smaller than the display liquid, it is not mixed with the display liquid. After the UV curable composition and the display liquid are completely mixed in a mixer, the mixture is immediately coated on coated on a lower substrate or micro cups using a precision coating mechanism, such as, Myrad bar printing, gravure printing, doctor-blade printing, slot coating, slit coating, etc. Excess liquid may be removed using a wiper blade or similar devices. The suspension remaining on the top of micro cup walls can be removed with a small amount of a chemical solvent, such as isopropanol, methanol, an aqueous solution of the suspension, or a solvent mixture. Once the UV curable composition is dried, the UV curable composition can float above an electrophoretic solution. After or while UV curable composition floats above the eletrophoretic solution, the floated UV curable composition is hardened to seal the micro cups. When hardening the UV curable composition to seal the display liquid, UV rays can be used.
A method of sealing a display device using the swelling property of elastomer to obtain a fabrics or paper-like structure is suitable when using mixed particles in the present invention. First, the particles are thoroughly mixed with a transparent liquid elastomer, for example, Dow Corning Sylgard 182, and then cured. When using sylgard, the mixture is cured through heating at 140°C for 10 minutes to obtain a flat plate (slab). Then, the solid flat slab is dipped in a dielectric plasticizer, such as silicon oil, for example, Dow Corning 200 fluid 100cst, for about 8 hours. The elastomer more easily absorbs the plasticizer and swells than the particles, thereby resulting in voids filled with the dielectric liquid (plastisizer) in the slab. The particles cannot laterally move on the plate but can rotate in the voids filled with the dielectric liquid. In this case, the particles may be formed of polyethylene or polystyrene. These materials absorb less of the plasticizer than the elastomer so that voids in which the particles can move can be formed in the slab. The slab may be formed of rigid plastics, such as polyethylene, polystyrene, and plexiglass, instead of elastomer. Encapsulation collectively refers to processes of forming cavities allowing particles to move therein and enclosing particles in the cavities, as described in the embodiment of using elastomer. In the case of using rigid plastics, encapsulation may be achieved using an encapsulant molten or dissolved in a volatile solvent. An uncured rigid material, such as transparent epoxy, may be used as the encapsulant. The important factor is that the slab material should absorb the plasticizer faster than the elements so that the space where the elements can move can be created. In this case, the elements should be made of glass that cannot absorb the plasticizer or other materials that absorb only a small amount of the plasticizer. In another embodiment, the particles are enclosed in oil droplets and then into plastic. First, the particles are mixed with oil and then with plastic and coated on a lower substrate of a display part or on a bottom surface of a substrate or a first electrode when no separate lower substrate is used. The coating is dried at an ambient temperature to form a thin plastic film on the surface of the substrate. The thin plastic film is further dried for about 8 hours to complete the formation of the display part. The particles enclosed in oil droplets float in the display unit and can be moved by external forces. In another encapsulating method, threads containing a suspension liquid are
spun through a double-walled, concentric tube. The suspension liquid flows through an inner tube of the double-walled, concentric tube while a transparent plastic flows through an outer tube thereof. A fabric is woven from the threads. It is necessary for each microcapsule to enclose a sufficient number of particles. If too many particles are enclosed in each microcapsule, the particles collide with each other and thus cannot move freely. Therefore, these two factors should be balanced. The amount of the particles in the suspension is preferably about 10% by volume, not exceed 20% by volume. If the diameter of each particle is smaller than the wavelength of visible rays, the particles reflect few of the visible rays. Therefore, it is necessary to eliminate particles having diameters of 1 μ m or less such that the average diameter of the particles becomes about 2 μ m. Since a display device is used in a vertical or almost vertical position, the particles may coagulate or sediment. Therefore, it is preferable to set the width of each sub-pixel to be no greater than 1.5 times the inner diameter of each microcapsule and to set the inner diameter of the microcapsule to 200 μ or less. The plate obtained through the processes described above is flat, like paper or fabric (hereinafter, referred to as "display part"). An electric device for activating the display elements is attached to one or both sides of the plate, thereby resulting in a complete display device. The external electric device may be used as a sealing material for the display part. When the particles should get electric charges from a dielectric liquid, a dielectric plasticizer has to be used. A circuit, microcapsules (or cups), and a solenoid may be formed simultaneously when manufacturing a printed circuit board (PCB). In this embodiment, holes formed in the PCB may function like microcapsules. The holes are coated with a conductive material, such as aluminum, and the coating is partially removed in a spiral shape using a screw tap. Then, the residual part of the coating in each hole forms a coil on the inner wall of the microcapsule. When manufacturing a display device according to the present invention, bus lines for activating the magnetic elements, transparent electrodes for generating an electric field, and coils for generating a magnetic field can be installed by attaching electrodes and magnetic poles to the upper and lower layers of an image display layer, i.e., an actuation layer, wherein the upper layer is a display panel, and the lower layer is an opposite panel facing the display panel.
The transparent electrodes are formed of a material, for example, ITO, tin oxide (NESA glass), tin oxide doped with antimony, a very thin stainless steel wire, an organic conductive material (a polymer conductive material or a molecular organic conductive material), conductive powder, aluminum, copper, copper oxide, silver, gold, platinum, brass, an alloy of iron, etc. Use of metallic materials for opaque electrodes is gradually decreasing. Examples of the polymer conductive material include: polyaniline and its derivatives; polythiophene and its derivatives; poly 3,4-ethylenedioxythipene (PEDOT) and its derivatives, etc. Examples of the organic molecular conductive material include naphthalene derivatives, phthalocyanine derivatives, pentacene derivatives, etc. In particular, since there is no need to apply a large current across the transparent electrodes for generating an electric field, the transparency of the transparent electrodes can be improved by forming the transparent elements to be thin through coating. Examples of the conductive powder include Welec ECP (available from Dupont chemical), etc. Examples of a material for the opaque electrode include graphite ink, metal-containing ink, solder paste, polyamide coated with copper, etc., in addition to the above-listed metallic materials. A method of connecting a transistor to each pixel or sub-pixel to control electric power in the present invention is similar to methods used in LCD panels. This method is referred to as an active matrix addressing method, which is well known in the industry. In this method, since pixels can be individually addressed using main electrodes and subordinate electrodes, diversified color tones can be expressed without using several sub-pixels as in a passive matrix addressing method, which will be described below. In the active matrix addressing method, each pixel consists of two sub-pixels. A main electrode is connected to one end of each sub-pixel, and a subordinate electrode is connected to the other end of the sub-pixel. The resistivities of the subordinate electrodes connected in parallel to the sub-pixels increase in a direction away from the main electrodes. The passive matrix addressing method costs low because no transistor is used. In the passive matrix addressing method, electricity is applied to both row and column electrodes to double the intensity of an electric or magnetic field in a pixel at which the row and column electrodes intersect, thereby activating the pixel. However, this method has a limitation in that the display elements can move only when a voltage greater than a threshold voltage is applied. In a method improved from the passive matrix addressing method, one transistor is placed at each row and column of
a controller. A magnetic field can be controlled more effectively. In another method suggested in the present invention, to express multiple color tones based on the passive matrix addressing method, the number of sub-pixels is increased. In particular, when one pixel consists of, for example, 16 sub-pixels, and each sub-pixel is divided into four for red (R), green (G), blue (B), and white (W), a maximum of 12 color tones can be expressed. For example, when expressing red color, 12 different tones of red can be expressed by varying the number of white sub-pixels that operate in a range of 0-11. In other words, by changing the number of sub-pixels, which have different light intensities, multiple color tones, which are obtained in active matrix displays, can be expressed at low production and investment costs, similar to those of passive matrix displays. In addition, it is easy to control the production and quality of the display, which is a benefit obtained when manufacturing passive matrix displays. There is no need to consider the expression of multiple color tones in, for example, signboards, which are monochromatic display devices.
Industrial Applicability The present invention provides a display that is flexible like paper. Although some exemplary embodiments have been described and illustrated in the attached drawings for the convenience of understanding of the flexible display, the embodiments are only for illustrative purposes and are not intended to limit the scope of the invention. It will be understood by those of ordinary skill in the art that the present invention is not limited to the described and illustrated structures and arrangements and various changes may be made without departing from the spirit and scope of the present invention as defined by the following examples.