KR20040030815A - In-plane switching electrophoretic display - Google Patents

Abstract

The present invention is directed to an improved EPD comprising an in-plane switching mode. More specifically, the EPD of the present invention includes discrete cells formed from microcups of definite size, shape and aspect ratio, and the movement of particles in the cells is controlled by an in-plane switching mode. The EPD of the present invention can be produced in a continuous manufacturing process, and the display device provides improved color saturation.

Description

In-Plane Switching Electrophoresis Display {IN-PLANE SWITCHING ELECTROPHORETIC DISPLAY}

background

Electrophoretic displays (EPDs) are non-emissive devices based on the phenomenon of electrophoresis that affects charged pigment particles suspended in colored dielectric solvents. to be. This general type of display device was first proposed in 1969. EPDs typically have a pair of opposed and spaced plate-shaped electrodes with spacers that determine a particular distance between the electrodes. At least one electrode, typically on the viewing side, is transparent. Even in the passive type EPD, row and column electrodes on the upper (observation) and lower plates, respectively, to drive the display are required. In contrast, in active type EPDs, a thin film transistor (TFT) arrangement on the bottom plate and a common, unpatterned transparent conductor plate on the top viewing substrate are required. An electrophoretic fluid consisting of a colored dielectric solvent and dispersed charged pigment particles is enclosed between the two electrodes.

When a potential difference is applied between the two electrodes, the attraction force moves the pigment particles to the plate having opposite poles of the pigment particles. Thus, the color seen in the transmissive plate, determined by selectively charging the plate, may be either the color of the solvent or the color of the pigment particles. By reversing the polarity of the plate, the particles move to the opposite plate, whereby the color is reversed. The intermediate color density (or gradation) by the intermediate pigment density in the transmissive plate can be obtained by controlling the plate charge through a range of voltages. In this reflective EPD display, no backlight is required.

Transmissive EPDs are disclosed in US Pat. No. 6,184,856 using a substrate having a backlight, a color filter, and two transmissive electrodes. The electrophoretic cell operates as a light valve. In the collected state, particles are positioned to minimize the horizontal area coverage of the cell to allow the backlight to pass through the cell. In the dispersed state, the particles cover the horizontal area of the pixel and are positioned to scatter or absorb the backlight. However, the backlight and color filters used in the device consume enormous power and are therefore undesirable for portable devices such as personal digital assistants (PDAs) and e-books.

In addition to the normal top / bottom electrode switching mode EPD, the reflective "in-plane" switching EPD can be found in 2000 by E. Kishi of Canon Research Center in "5.1: development of In-Plane EPD", SID 00 Digest. Page 24-27 and Sally A. Swanson of the IBM almaden Research Center, et al., Published in 2000, "5.2: High Performance Electrophoretic Displays", pages 29-31 of SID 00 Digest. However, this reference discloses only monochrome in-plane switching EPDs. In order to produce a multicolor display, a color filter or a separate color pixel or cell structure for color separation and rendition is required. Color filters are typically expensive and inefficient in terms of power. On the other hand, the manufacture of discrete pixels or cells for color separation and rendition in in-plane switching mode has not been previously known.

EPDs of various pixel or cell structures have been reported in the prior art, for example, partition type EPD (Ma Hopper and V. Novotny, IEEE Trans.Electr. Sev., Vol ED 26, No. 8 pp 1148-1152 (1979). ) And microencapsulated EPDs (US Pat. Nos. 5,961,804 and 5,930,026), each of which has the following problems.

In the case of the partition type EPD, there is a partition between the two electrodes to prevent undesirable behavior of the particles, such as sedimentation, by dividing the space into smaller cells. However, difficulties are encountered in the formation of partitions, filling the display with fluid, enclosing the fluid in the display, and keeping the suspensions of different colors separate. do.

Microencapsulated EPDs generally have two-dimensional arrays of microcapsules, each microcapsule array having an electrophoretic composition of the dielectric fluid therein and visually contrasting with the dielectric solvents. It has a dispersion of pigment particles. Microcapsules are usually made in aqueous solvents and their average size is relatively large (50 to 150 microns) to obtain a useful contrast ratio. Since large gaps are required between two opposing electrodes for large capsules, large microcapsule sizes result in poor scratch resistance and slow response time at a given voltage. In addition, hydrophilic shells of microcapsules made in aqueous solvents are typically sensitive to high humidity and temperature conditions. To avoid this drawback, if microcapsules are embedded in a large polymer matrix, the use of such a matrix will result in a slower response time and / or a lower contrast ratio. In this type of EPD, a charge-controlling agent is often needed to improve the switching rate. However, microencapsulation processes in aqueous solvents limit the type of charge control agent that can be used. Another disadvantage associated with microcapsule systems is low resolution and low addressability for color applications.

Recently, US Application No. 09 / 518,488 filed March 3, 2000 (corresponding to WO01 / 67170), filed Jan. 11, 2001, filed on March 3, 2000, with improved EPD technology co-pending. / 759,212, US Application No. 09 / 606,654 filed June 28, 2000 (corresponding to WO02 / 01281) and US Application No. 09 / 784,972, filed February 15, 2001, All of these are referenced herein. The improved EPD is formed into microcups having a well-defined shape, size, and aspect ratio, and into closed separation cells filled by discharging charged pigment particles in a dielectric solvent. Is done. The electrophoretic fluid is separated into each microcup and sealed.

In fact, the microcup structure enables a format flexible and efficient roll-to-roll continuous manufacturing method for producing EPDs. The display device comprises (1) coating a radiation curable composition on ITO / PET, (2) fabricating a microcup structure by microembossing or photolithographic methods, and (3) Slicing and cutting the electrophoretic fluid and sealing the microcups, (4) laminating the sealed microcups to another conductor film, and (5) the size or form desired for assembling the display. cutting), for example, on a continuous web of a conductor film, such as ITO / PET.

One advantage of this EPD design is that the microcup wall is in fact a built-in spacer that keeps the upper and lower substrates a certain distance apart. The mechanical properties and structural integrity of the microcup display device are remarkably superior to any conventional display device including a display device fabricated using spacer particles. In addition, displays comprising microcups exhibit desirable mechanical properties, including reliable display characteristics when the display is bent, rolled or, for example, under the pressure of a touch screen application. Have The use of microcup technology also eliminates the need for an edge seal adhesive, which limits and predetermines the size of the display panel to confine the display fluid within a defined area. If the display device is cut in any way or a hole is formed in the display device, the display fluid in the conventional display device manufactured by the edge sealing method is completely leaked out. The damaged display no longer functions. In contrast, display fluids in displays fabricated by microcup technology are enclosed in separate cells and separated. The microcup display can be cut to any dimension without the risk of compromising display performance due to loss of display fluid in the active area. In other words, the microcup structure allows for a process of fabricating a format flexible display, in which case the process is a large sheet (diced) in the shape of a cube or sliced into any desired format. In sheet form, displays are produced continuously. Separate microcups or cell structures are particularly important when the cell fills a variety of fluids with inherent properties such as color or switching rate. Without the microcup structure, it is very difficult to prevent fluids in adjacent regions from intermixing or cross-talk during operation.

Thus, multi-color displays can be fabricated using spatially adjacent arrays of small pixels formed of microcups filled with dyes of different colors (e.g. red, green, or blue). However, this type of system with conventional top / bottom electrode switching modes has significant disadvantages. White light reflected from the "turned-off" colored pixels severely reduces the color saturation of the "turned-on" color. Details in this regard are described in the "Detailed Description" section below.

Although this drawback can be solved by an overlapping shutter device, such as a polymer dispersed crystal display that converts each pixel to black, the disadvantage of this method is that of an overlapping device. And high cost due to complex drive circuit design.

Thus, there is still a need for an improved quality EPD that can be manufactured in an efficient manner.

Summary of the Invention

The present invention relates to an improved EPD comprising an in-plane switching mode for image formation. More specifically, the EPD of the present invention includes a separation cell formed of a microcup having a definite size, shape and aspect ratio, wherein the movement of particles within the cell is controlled in in-plane switching mode. The EPD of the present invention can be manufactured by a continuous roll-to-roll manufacturing process, and the resulting display device has improved color saturation and contrast ratio.

All figures are shown schematically and are not to scale.

1 shows a common disadvantage of conventional EPDs having only the top / bottom switching mode.

2 shows the general location of conventional electrophoretic cells and in-plane switching electrodes of the present invention.

3A and 3B show a monochrome display device of the present invention.

4A-4D illustrate various multi-color scenarios of the present invention.

5A and 5B show the fabrication of microcups associated with imagewise photolithographic exposure through a photomask.

Unless defined otherwise herein, all technical terms used herein are in accordance with conventional definitions commonly used and understood by those skilled in the art. The terms "cell", "microcup", "well-defined", aspect ratio ", and" imagewise exposure "are referred to in the co-pending application described above. As defined.

The term "isolated" refers to an individually sealed electrophoretic cell, wherein the fluid in the cell does not move from one cell to another.

I. Disadvantages of conventional electrophoretic display with top / bottom switching

The EPD of FIG. 1 has a normal top / bottom electrode switching mode. The cells are filled with a suspension in which white charged particles are dispersed in (red, green, and blue) colored dielectric solvent. The three cells of FIG. 1 are shown charged with a potential difference between the upper and lower electrodes (not shown). In green and blue cells white particles migrate to the transparent, upper viewing electrode, and as a result the color of the particles (eg white) is reflected back to the viewer through the transparent conductor film in both cells. do. In red cells, white particles migrate to the bottom of the cell, and the color of the solvent (eg red) is visible through the top of the transparent conductor film. In FIG. 1, the white light reflected from the green and blue cells dramatically reduces the saturation and contrast ratio of the red color.

In addition to the problems mentioned above, low solubility and slowness of the dyes in very low polarity dielectric solvents, such as, for example, perfluoro and hydrocarbon solvents, It is a challenge to achieve a high contrast ratio in the type of EPD.

II. Electrophoretic display device of the present invention

2 shows a typical electrophoretic cell of the present invention. Cell 20 includes an upper layer 21 and a lower layer 22. The lower layer has in-plane switching electrodes 23, 24, and background layer 25. There is a common electrode 29 between two in-plane electrodes separated by 30. Alternatively, the bottom layer may have only one in-plane switching electrode and one common electrode with a gap therebetween. Another method is that the background layer 25 is on top of the lower layer electrode (not shown). The in-plane electrode layer can function as a background layer, in which case the in-plane electrode (s) can be white or colored.

Typically, the cell of FIG. 2 is filled with a dispersion of colored particles 31 in a clear dielectric solvent. The particles can be white, black or (red, green or blue) in color. Background layer 25 may be colorless, white, black or colored. After that, the filled cell is sealed with a sealing layer 26. Thereafter, an upper layer 21 and preferably an adhesive layer 28 having a transparent insulator layer 27 are laminated on the sealed cell.

Preferably, the microcup arrangement is made in an up-side-down manner. In this scenario, the microcup array is co-pending US patent application Ser. No. 09 / 518,488 filed March 3, 2000 (corresponding to WO01 / 67170), US patent application filed on January 11, 2001. No. 09 / 759,212, US patent application Ser. No. 09 / 606,654 filed June 28, 2000 (corresponding to WO02 / 01281) and US patent application Ser. No. 09 / 784,972, filed February 15, 2001. As disclosed in the present invention, fabrication is made on top of the transparent insulator substrate by microembossing or photolithography, the above materials being referred to herein. The microcups are filled with an electrophoretic fluid and then sealed with a sealing layer. Thereafter, on the sealing microcup, a bottom layer comprising a patterned electrode and preferably an adhesive layer is laminated. The color background can be added by painting, printing, coating or laminating the color layer on the lower electrode substrate.

One of the advantages of the in-plane switching mode is that the microcups can be fabricated on a clean plastic insulator substrate. This eliminates the risk of damaging brittle conductor electrodes, such as ITO / PET, during microembossing and other web handling steps. The patterned in-plane conductor film is used only in the final step of completing the fabrication of the display device after laminating onto a filled and sealed microcup.

(1) Reflective monochrome display

In the cell shown in FIG. 3A, white particles are dispersed in a clean, colorless dielectric solvent. The background of all cells is the same color (black, blue, cyan, red, magenta, etc.). When there is a potential difference between the common electrode (not shown) and the two in-plane switching electrodes (not shown), the white particles move to the side of the cell and show the background color through the upper transparent opening. do. When there is no potential difference between the common electrode and the two in-plane electrodes, the white particles are dispersed in the dielectric solvent, as a result of which the color (eg white) of the particles is visible through the upper transparent insulator layer.

As shown in FIG. 3B, in another method, particles of the same color are dispersed in a clear, colorless dielectric solvent in every cell, and the background of the cell is white. When there is a potential difference between the common electrode (not shown) and the two in-plane switching electrodes (not shown), the colored particles move to the side of the cell and through the upper transparent openings the color of the background ( White, for example. When there is no potential difference between the two in-plane electrodes, the colored particles are dispersed in the dielectric solvent, with the result that the color of the particles is visible through the upper transparent layer.

(2) reflective multi-color display

4A to 4D show a multi-color display device of the present invention.

In FIG. 4A, the cell is filled with a colorless dielectric solvent in which white charged particles are dispersed therein, and have different background colors (eg, red, green, or blue). When there is a potential difference between the in-plane electrodes (not shown), the white particles move to the side of the cell, and the background color (eg red, green, or blue) is visible through the upper transparent opening. When there is no potential difference between the two in-plane electrodes, the particles are distributed into the dielectric solvent, resulting in white (e.g., the color of the particles) being seen through the upper transparent openings.

In FIG. 4B, the cell is filled with a colorless dielectric solvent, in which black particles are dispersed therein, and have various background colors (eg red, green, or blue). When there is a potential difference between the in-plane electrodes (not shown), the particles move to the side of the cell and the background color (e.g. red, green, or blue) is visible through the upper transparent opening. When there is no potential difference between the in-plane electrodes, the particles dispensed in the dielectric solvent result in black (e.g., the index of the particles) showing black through the upper permeable opening.

4C shows a cell filled with a colorless dielectric solvent in which particles of various colors (eg red, green or blue) are dispersed therein. The background of the cell is black. When there is a potential difference between the in-plane electrodes (not shown), the colored charged particles move to the side of the cell, and the background color (eg black) is visible through the upper transparent opening. When there is no potential difference between the in-plane electrodes, the colored particles are distributed in the dielectric solvent, resulting in the color of the particles being seen through the upper transparent openings. In this design, the black state is high quality.

In FIG. 4D, the cell is filled with a colorless dielectric solvent in which particles of various colors (eg red, green or blue) are dispersed therein. The background of the cell is white. When there is a potential difference between the in-plane electrodes (not shown), the particles move to the side of the cell and the background color (e.g. white) is visible through the upper transparent opening, resulting in a high quality white state. . When there is no potential difference between the in-plane electrodes, the particles are distributed in the dielectric solvent, resulting in the color of the particles being seen through the upper transparent openings.

As shown in Figures 4A-4D, the in-plane switching mode allows the particles to move in the in-plane (left / right) direction, and to produce different multi-color EPDs, different color combinations of particles, background, and fluids. Can be used, in which case the color combinations are white, black, red, green or blue, respectively.

In addition, the particles in the dielectric solvent may have a mixed color, and the cells have the same background color.

In another reflective display device of the present invention, the upper transparent viewing layer of the display device may be colored or a color filter may be added. In this case, the cell is filled with an electrophoretic composition, which contains white charged particles in a clean colorless or colored dielectric solvent, and the background of the cell may be black. The transparent observation layer is the same color (such as black, red, green, blue, sulfur, cyan, magenta, etc.). In multi-color displays, the transparent viewing layer may be of various colors.

III. Fabrication of Microcup Arrays of the Invention

In general, as disclosed in US Patent Application No. 09 / 518,488 filed March 3, 2000 (corresponding to WO01 / 67170) and 09 / 784,972 filed February 15, 2001, microcups Can be produced by microembossing or photolithography.

III (a) Fabrication of Microcup Arrays by Microembossing

Fabrication of the male mold

The male mold may be manufactured by any suitable method, such as etching or electroplating after a diamond turn process or a photoresist process. The master template for the male mold can be produced by any suitable method, such as electroplating. In electroplating, the glass base is sputtered with a thin layer of seed metal, typically 3000 mm 3, such as chrome inconel. It is then coated with a layer of photoresist and exposed by radiation, such as ultraviolet (UV) light. The mask is located between the UV and photoresist layer. The exposed area of the photoresist is hardened. Thereafter, the unexposed areas are removed by washing with a suitable solvent. The remaining cured photoresist is dried and sputtered back into a thin layer of seed metal. Thereafter, a master for electroforming is prepared. A common material used for electroforming is nickel cobalt. Alternatively, SPICE Proc. Vol. As described in " Continuous manufacturing of thin cover sheet optical media ", page 324 of 1663 (1992), the disc can be made of nickel or electroless nickel precipitates by electroforming. The floor of the mold is typically about 50 to 400 microns thick. In addition, the original is SPICE Proc. As described in "Replication technuques for micro-optics", Vol. 3099 (1997), pages 76-82, e-beam writing, dry etching, chemical etching, laser writing or laser interference. and other microengineering techniques, including interference). Alternatively, it can be produced by photomatching using plastics, ceramics or metals.

Thus, typically produced mail molds have protrusions between 1 and 500 microns, preferably between 2 and 100 microns, and most preferably between 4 and 50 microns. The mail mold may be in the form of a belt, roller, or sheet. Belt type molds are preferred for continuous fabrication. Before applying the UV curable resin composition, the mold may be treated with a mold release to assist in the demolding process.

As described in 09 / 784,972, filed February 15, 2001, the microcups can be formed by a batch process or a continuous roll-to-rollprocess.

In the first step of the microembossing process, the UV curable resin is first applied onto the substrate, preferably on the transparent insulator, by any suitable means such as roller coating, die coating, slot coating, slit coating, doctor blade coating, or the like. Coating. Suitable permeable insulator substrates include polyethylene terephthalate, polyethylene naphthalate, polyaramid, polyimide, polycycloolefin, polysulfone, epoxy and their compositions It includes. The radiation cured materials used are thermoplastic or thermoset, such as multifunctional acrylates or methacrylates, vinylethers, epoxides and their oligomers, polymers and the like. Is a precursor of. Most preferred are multifunctional acrylates and oligomers thereof. In addition, the combination of multifunctional epoxides and multifunctional acrylates is very useful for achieving desirable physico-mechanical properties. The UV curable resin may be degassed prior to preparation and may optionally include a solvent. The solvent, if present, evaporates easily.

The spin cured material coated on the substrate is embossed by a mail mold under pressure. If the mail mold is metallic and opaque, the plastic insulator is typically transparent to the actinic radiation used to cure the resin. Conversely, for radiation of actinic radiation, the male mold may be transparent and the plastic insulator may be impermeable. Since plastic insulators are typically viewing planes, it is desirable to be transparent to plastic insulators. In this case, the electrode may be opaque. Alternatively, microembossing may be performed on the substrate including the electrode.

After exposure by radiation, the radiation cured material is cured. Thereafter, the male mold is removed and the formed microcups are exposed.

III (b) Fabrication of Microcup Arrays by Photolithography

Photolithographic processes for the fabrication of microcup arrays are shown in FIGS. 5A and 5B.

As shown in FIGS. 5A and 5B, the microcup array 50 is formed by ultraviolet radiation (or other methods) through a mask 56 with a radiation cured material 51a coated on an insulating substrate base 53 in a known manner. And other forms of radiation, electron beams, etc.) to form walls 51b corresponding to the image projected through the mask 56.

In the photomask 56 of FIG. 5A, the dark rectangular portions 54 represent regions that are opaque to the adopted radiation, and the space 55 between the dark rectangular portions represents a radiation transmissive region. UV emits through the opening region 55 onto the radiation curable material 51a.

As shown in FIG. 5B, after curing the exposed area 51b, the unexposed area (blocked by the opaque area 54 of the mask 56) is formed to form the microcups 57. Remove with a suitable solvent or developer. The solvent or developer is selected from those generally used for dissolving or dispersing spinning hardening materials, such as methyl ethyl ketone, toluene, acetone, isopropanol and the like.

Alternatively, the photomask may be disposed under the insulator substrate to perform exposure. In this case, the substrate should be transparent to the radiation wavelength used for exposure.

Openings of the microcups manufactured according to the method described above may be circular, square, rectangular, hexagonal, or any other shape. The partition area between the openings is preferably kept small to achieve high color saturation and contrast while maintaining desirable mechanical properties. Thus, for example, honeycomb-shaped openings are preferable to circular openings.

In reflective electrophoretic displays, the dimensions of each individual microcup range from about 10 ² to about 1 × 10 ⁶ μm ² , preferably from 10 ³ to 1 × 10 ⁵ μm ² . The depth of the microcups ranges from about 5 to about 200 microns, preferably from about 20 to about 100 microns. The ratio of the opening to the entire area of the cup including the wall measured at the wall center ranges from about 0.2 to about 0.95, preferably from about 0.5 to about 0.9. The distance of the opening is usually about 15 to about 450 microns, preferably about 25 to about 300 microns from edge to edge of the opening.

III (c) Sealing of Microcups

After filling with electrophoretic fluid, the microcups are sealed. The critical step of microcup sealing can be done in a number of ways. A preferred method is to disperse the UV curable composition in an electrophoretic fluid comprising charged pigment particles dispersed in a colored dielectric solvent. Suitable UV curable materials are acrylates, methacrylates, styrenes, alpha-methylstyrenes, butadiene, isoprene, aliacrylates, polyvalent acrylates, or methacrylates, cyanoacrylates, polyvelant vinyls. Polyvinylvinyl, in this case, vinylbenzene, vinylsilane, vinylether, polyvalent epoxide, polyvalent isocyanate, polyvalent aryl, and oligomers or crosslinkable functions. Polymers comprising groups. The UV curable composition is not mixed with the dielectric solvent and has a specific gravity lower than the specific gravity of the electrophoretic fluid, such as for example a combination of dielectric solvent and pigment particles. The two components, the UV curable composition and the electrophoretic fluid, are thoroughly mixed in an in-line mixer and then Myrad bar, gravure, doctor blade, slot coating or slit Coating onto the microcups using a precision coating mechanism such as coating. The excess fluid is removed using a wiper blade or similar device. A small amount of dilute solvent or a mixture of solvents, such as isopropanol or methanol, can be used to remove residual electrophoretic fluid on the top surface of the partition wall of the microcups. Volatile organic solvents may be used to control the viscosity and coverage of the electrophoretic fluid. The so-filled microcups are then dried and the UV curable composition floats to the top of the electrophoretic fluid. The microcups may be sealed by curing the supernatant UV cured layer during or after flotation. UV or other forms of radiation, such as visible, infrared (IR) and electron beams, can be used to cure the sealing layer and seal the microcups. Alternatively, when heat or moisture cure compositions are used, heat or moisture may be employed to cure the sealing layer and seal the microcups.

Preferred groups of dielectric solvents that exhibit the desired density and solubility differences for acrylate units and oligomers are halogenated hydrocarbons and derivatives. Surfactants may also be used to improve adhesion and wetting at the interface between the electrophoretic fluid and the sealing material. Surfactants include 3M FC surfactants, DuPont Zonyl fluorosurfactants, fluoroacrylates, fluoromethacrylates, fluoro-substituted long chain alcohols, Perfluoro-substutited long chain carboxylic acids and derivatives thereof.

Alternatively, if the sealing precursor is at least partially coexistable with the dielectric solvent, the electrophoretic fluid and the sealing precursor are sequentially microcups to prevent intermixing with each other. Can be coated on. Thus, the microcups are sealed by coating a thin layer of the encapsulating material cured by radiation, heat, moisture or interface reaction on the surface of the filled microcups. To adjust the viscosity and thickness of the coating, volatile organic solvents can be used. When using volatile solvents for overcoating, in order to reduce the degree of intermixing between the sealing layer and the electrophoretic fluid, it is preferred to be immiscible with the dielectric solvent. In order to further reduce the degree of mixing, it is highly desirable that the specific gravity of the overcoat is much lower than that of the electrophoretic fluid. In co-pending patent application, filed June 4, 2001, US Patent Application No. 09 / 874,391 discloses thermoplastic elastomers as preferred sealing materials.

Examples of useful thermoplastic elastomers include two block, three block, and multiblock copolymers of type ABA and (AB) n, where A is styrene, alpha-methylstyrene, ethylene, propylene, or nord Norbonene, B is butadiene, isoprene, ethylene, propylene, butylene, dimethylsiloxane or propylene sulfide, and A and B in this formulation may not be identical. The number n is 1 or more, Preferably it is 1-10. SB (poly (styrene-b-butadiene)), SBS (poly (styrene-b-butadiene-b-styrene)), SIS (poly (styrene-b-isoprene-b-styrene)), SEBS (poly (styrene- b-ethylene / butylenes-b-styrene) poly (styrene-b-dimethylsiloxane-b-styrene), poly ((α-methylstyrene-b-isoprene), poly (α-methylstyrene-b-isoprene-b-α-methylstyrene 2 blocks or 3 of styrene or alpha-methylstyrene, such as poly (α-methylstyrene-b-propylene sulfide-b-α-methylstyrene), poly (α-methylstyrene-b-dimethylsiloxane-b-α-methylstyrene) Block interpolymers are particularly useful.

Alternatively, UV curing after the polymerization of the interface It is known to be very beneficial to the sealing process. By the formation of a thin barrier at the interface where the interface polymerization reaction occurs, mixing between the electrophoretic layer and the overcoat is severely inhibited. The sealing is then completed by a post curing step, preferably by UV radiation. If the dye is at least partially soluble, a two step overcoating process is particularly useful.

III (d) Lamination of Microcups

The sealed microcups are then laminated to a top layer comprising a patterned in-plane conductor film and preferably an adhesive layer. Suitable adhesive materials include acrylic and rubber type, pressure sensitive adhesives, such as UV curable adhesives including multifunctional acrylates, epoxides, or vinyl ethers, and epoxy, polyurethane, and cyanoacrylates, for example. Moisture or heat curable adhesives.

The cells fabricated in the methods of sections III (a) to III (d) may be fabricated upside down, with the permeable viewing layer on top and the layer with in-plane electrodes going down.

III (e) other methods

Alternatively, in the microembossing process, the UV curable resin is sprayed onto the mail mold using any suitable means, such as coating, dipping, pouring and similar methods. The injector may be moving or stationary. Then, on the UV cured resin, an in-plane conductor patterned on a plastic substrate, such as polyethylene terephthalate, polyethylene naphthalate, polyaramid, polyimide, polycycloolefin, polysulfone, epoxy and its composition Nest the acts. Pressure may be applied to ensure proper bonding between the resin and plastic substrate and to control the thickness of the microcup floor. If the mail mold is metallic and impermeable, the plastic substrate is typically transparent to the radiation of actinic rays used to cure the resin. Conversely, the mail mold may be transparent and the plastic substrate may be impermeable to radiation of actinic radiation.

After exposure to UV radiation, the UV curable resin can be cured and the male mold can be removed. The formed microcup array is filled and sealed as described above. The sealed microcups are then laminated to a transparent insulator layer, preferably with an adhesive.

Although less preferred, photolithographic exposure may also be performed on a substrate having in-plane electrodes. The radiation cured material is coated onto the patterned conductor film. As shown in FIG. 5 and described above in section III (b), the microcups are formed by radiation exposing the radiation cured material through a photomask.

The microcups thus produced are filled and sealed as described above and laminated with a transparent insulator layer, preferably an adhesive.

In any method of fabricating the microcups disclosed herein, a substrate comprising an array of thin film transistors (TFTs) can be used as the bottom in-plane electrode layer, and in this case the TFT layer is also an active drive mechanism. driving mechanism).

IV. Preparation of the suspension

The suspension in which the charged pigment particles, filled in the microcups, are dispersed contains a dielectric solvent, and the particles move under the influence of an electric field. The suspension may optionally include additional colorants that do not migrate in the electric field. Dispersions are as in U.S. Pat.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, and 3,668,106 And IEEE Trans. Electron devices, ed-24, 827 (1977) and J. Akppl. Phys. 49 (9), 4820 (1978)., According to methods well known in the art.

Suspending fluid medium is preferably a dielectric solvent having a low viscosity and a dielectric constant in the range of about 2 to about 30, preferably a high particle mobility of about 2 to about 15. Examples of suitable dielectric solvents are hydrocarbons such as decahydronaphthalene (DECALIN), 5-ethylidene-2-norbornene, toluene, xylene ( aromatic hydrocarbons such as xylene, phenylxylylethane, dodecylbenzene and alkylnaphthalene, fatty oils, paraffin oils, dichlorobenzotrifluoro Dichlorobenzotrifluoride, 3,4,5-trichlorobenzotrifluoride, chloropentfluoro-benzene, dichlorononane, pentachlorobenzene Halogenated solvents, such as perfluorodecalin, perfluorotoluene, perfluoroxylene, Minn. Perfluoro solvents such as FC-43, FC-70 and FC-5060 from 3M company in Paul, poly (perfluoropropylene oxide), TCI America, Portland, Oregon, NJ Halocarbon Product Corp., River Edge Poly (chlorotrifluoroethylne) such as Halocarbon Oils, Galden, HT-200 of Ausimont, and perfluoropolyalkyl such as Kryptox Oils and Greases K-Fluid series of DuPont from Fluolink or Delaware Low molecular weight fluorine including polymers such as ether (perfluoropolyalkylether). In one preferred embodiment, poly (chlorotrifluoroethylene) is used as the dielectric solvent. In another preferred embodiment, poly (perfluoroprophylene oxide) is used as the dielectric solvent.

Fluid colorants that do not migrate can be formed from dyes or pigments. In particular, nonionic nitrogen (azo) and anthraquinone dyes are useful. Examples of useful dyes include, but are not limited to, the following examples: Oil Red EGN, Sudan Red, Sudan Blue, Oil Blue, Mcrolex blue, Solvent Blue 35, Pylam Spirit Black and Fast Spirit black (Pylam Products Co., Arizona) Thermoplastic Black X-70 (BASF), anthraquinon blue, anthraquinone yellow 14, anthraquinonereds 111 and 135, anthraquinonr green 28 and Sudan Black B (Aldrich). When using perfluorinated solvents, fluorinated dyes are particularly useful. In the case of the dye, it is possible to disperse the pigment particles for producing the non-moving fluid colorant in the dielectric solvent, and the colored particles are preferably not charged. When the pigment particles for the production of the non-moving fluid colorant are charged, the particles preferably carry a charge opposite to that of the charge-moving dye particles. If both types of pigment particles carry the same charge, they should have different charge densities or different electrophoretic mobility. The dyes or pigments for producing non-moving fluid colorants must be chemically stable and compatible with the other components in the suspension.

The charge transfer pigment particles are preferably white, and may be organic or inorganic pigments such as TiO ² .

When using colored migrating particles, the particles are phthalocyanine blue, phthalocyanine green, diarylide yellow, diarylide AAOT yellow, and quinacrydone, azo. ), Rhodamine, perylene pigment series (Sun Chemical), Hansa yellow G particles (Kanto Chemical), and Carbon Lampblack (Fisher). Submicron particle sizes are preferred. These particles must have suitable optical properties, must not be swollen or softened by a dielectric solvent, and must be chemically stable. In addition, the resulting suspension under normal operating conditions must be stable to sedimentation, creaming or focculation.

The moving pigment particles may be originally charged, or may be directly charged using a charge control agent, or may be charged when suspended in a dielectric solvent. Suitable charge control agents are well known in the art. These may or may not be polymers in nature, may or may not be ions, such as aerosol OT, sodium dodecylbenzenesulfonate, metal soaps, polybutene succinimide, Maleic anhydride copolymers, vinylpyridine copolymers, vinylpyrrolidone copolymers (Ganex, International Specialty Products), (meth) acrylic acid copolymers (meth) acrylic acid copolymers) and ionic surfactants such as N, N-dimethlaminoethl (meth) acrylate copolymers. Fluorinated surfactants are useful as charge control agents in perfluorocarbon solvents. FC fluorides such as FC-170C, FC-171, FC-176, FC430, FC431 from 3M Company and FC-740 and Zonyl FSA, FSN, FSN-100, FSO, FSO-100, FSD and UR from Dupont Surfactants.

Suitable charged pigment dispersions can be made by any known method including grinding, milling, attriting, microfludizing, and ultrasonic techniques. For example, fine powdery pigment particles are added to a suspending solvent, and the resulting mixture is milled or abraded for several hours into agglomerated dry pigment powder as the primary particle. crushed into primary particles. Although less preferred, dyes or pigments that produce non-moving fluid colorants may be added to the suspension during the ball milling process.

By microencapsulating the particles with suitable polymers that match the specific gravity with that of the dielectric solvent, precipitation or creaming of the pigment particles can be eliminated. Microencapsulation of the pigment particles is done by chemical or physical methods. Conventional microencapsulation processes include interface polymerization, in-situ polymerization, phase separation, coacervation, electrostatic coating, spray drying, fluidized bed coating and solvent evaporation ( solvent evaporation).

There are many means for pigment suspensions. In a subtractive color system, charged TiO ² particles may be suspended in a dielectric fluid of cyan yellow or magenta color. Cyan, yellow or magenta colors can be produced through the use of dyes or pigments. In additive color systems, charged TiO ² particles may also be suspended in red, green, or blue dielectric solvents, produced through the use of dyes or pigments. For most applications, red, green and blue color systems are preferred.

Although the present invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to the objects, spirit, and scope of the present invention in order to adapt to particular circumstances, materials, compositions, processes, steps or steps of the process. Such modifications are included within the scope of the appended claims.

Accordingly, the invention is defined as broadly and in terms of the specification as the prior art allows by the scope of the appended claims.

Claims (58)

An electrophoretic display having an in-plane switching mode and comprising isolated electrophoretic cells formed of microcups having a well-defined size, shape and aspect ratio. The electrophoretic display of claim 1, having two in-plane electrodes. An electrophoretic display device according to claim 1, having one in-plane electrode. The electrophoretic display of claim 1, wherein the microcups have an upper opening of about 10 ² μm to about 1 × 10 ⁶ μm 2. The electrophoretic display of claim 4, wherein the microcups have an upper opening of about 10 ³ μm 2 to about 1 × 10 ⁵ μm 2. The method of claim 1, wherein the microcups have a depth of about 5 Electrophoretic displays ranging from μ to about 200 μ. 7. The method of claim 6, wherein the microcups have a depth of about 20 Electrophoretic displays ranging from μ to about 100 μ. The electrophoretic display of claim 1, wherein the ratio of the opening to the total area is in the range of about 0.2 to about 0.95. In an electrophoretic display having discrete cells formed of microcups having a definite size, shape and aspect ratio, the cells A transparent viewing layer on one side of the display device; And A layer having an in-plane electrode on an opposite side of the display device, And the cells are filled with a dielectric solvent or a solvent mixture in which charged particles are dispersed. 10. The electrophoretic display of claim 9, further comprising a separate background layer. 10. The electrophoretic display of claim 9, wherein the transparent viewing layer is colorless. 12. The electrophoretic display of claim 11, wherein the separate background layer is over a top of the layer having in-plane electrodes. 12. The electrophoretic display of claim 11, wherein the separate background layer is below a layer having in-plane electrodes. 12. The electrophoretic display of claim 11, wherein the layer with in-plane electrodes serves as a background layer and the in-plane electrodes can be white or colored. 10. The electrophoretic display of claim 9, wherein the display device is a monochrome display device. 16. The electrophoretic display of claim 15, wherein the dielectric solvent is clear and colorless. 17. The electrophoretic display of claim 16, wherein all of the cells have particles of white and the same background color. 18. The electrophoretic display of claim 17, wherein the background color is black, red, green, blue, yellow, cyan or magenta. 17. The electrophoretic display of claim 16, wherein all of the cells have particles of the same color and a white background color. 20. The electrophoretic display of claim 19, wherein the particles are black, red, green, blue, sulfur, cyan or magenta. 17. The electrophoretic display of claim 16, wherein each of said cells has particles of mixed color and the same background color. 22. The electrophoretic display of claim 21, wherein the mixed color is at least two colors selected from the group consisting of black, white, red, green, blue, yellow, cyan and magenta. The electrophoretic display of claim 22, wherein the background color is a color selected from the group consisting of black, white, red, green, blue, yellow, cyan, and magenta. The electrophoretic display of claim 9, wherein the display is a multiple color display. 25. The electrophoretic display of claim 24, wherein the cells have particles of white and other background colors. 25. The electrophoretic display of claim 24, wherein the cells have particles in black and other background colors. 25. The electrophoretic display of claim 24, wherein the cells have particles of different color and white background. 25. The electrophoretic display of claim 24, wherein the cells have particles of different color and black background. 10. The electrophoretic display of claim 9, wherein the transparent viewing layer is colored or a color filter is added. 30. The electrophoretic display of claim 29, wherein the separate background layer is over a top of the layer having in-plane electrodes. 30. The electrophoretic display of claim 29, wherein said separate background layer is below a layer having in-plane electrodes. 30. The electrophoretic display of claim 29, wherein the layer with in-plane electrodes serves as a background layer and the in-plane electrodes can be white or colored. 30. The electrophoretic display of claim 29, wherein all of the cells have white particles and a black background. 34. The electrophoretic display of claim 33, wherein all of said cells have a transparent viewing layer of the same color. 34. The electrophoretic display of claim 33, wherein the cells have transmissive viewing layers of different colors. A method of manufacturing an electrophoretic display device having separate cells formed of microcups having a definite size, shape and aspect ratio, a) coating a radiation cured material on a transparent insulator substrate to form a layer; b) forming microcups on the radiation cured material by imagewise exposure by microembossing or radiation; c) filling the microcups with an electrophoretic composition; d) sealing the microcups; And e) stacking the sealed microcups into a substrate comprising an in-plane electrode. 37. The method of claim 36, wherein the substrate comprises a substrate comprising an in-plane electrode and an adhesive. A method of manufacturing an electrophoretic display device having separate cells formed of microcups having a definite size, shape and aspect ratio, a) coating a radiation cured material on a substrate comprising an in-plane electrode to form a layer; b) forming microcups on the radiation cured material by microembossing and exposing the imagewise by radiation; c) filling the microcups with an electrophoretic composition; d) sealing the microcups; And e) stacking the sealed microcups into a transparent insulator substrate. 39. The method of claim 38, wherein the electrophoretic display device has a transparent insulator substrate and an adhesive. The method of claim 36, wherein the microcups have an upper opening of about 10 ² μm to about 1 × 10 ⁶ μm 2. The method of claim 38, wherein the microcups have an upper opening of about 10 ² μm to about 1 × 10 ⁶ μm 2. 37. The method of claim 36, wherein the transmissive insulator substrate is colorless. 43. The method of claim 42, wherein all of the cells have the same background color and are filled with an electrophoretic composition comprising charged particles of the same color dispersed in a clean, colorless dielectric solvent. 43. The method of claim 42, wherein the cells have a different background color and are filled with an electrophoretic composition comprising charged particles of the same color dispersed in a clean, colorless dielectric solvent. 43. The method of claim 42, wherein the cells have the same background color and are filled with an electrophoretic composition comprising charged particles of different colors dispersed in a clean, colorless dielectric solvent. 39. The method of claim 38, wherein the transmissive insulator substrate is colorless. 47. The method of claim 46, wherein all of the cells have the same background color and are filled with an electrophoretic composition comprising charged particles of the same color dispersed in a clean, colorless dielectric solvent. 47. The method of claim 46, wherein the cells have a different background color and are filled with an electrophoretic composition comprising charged particles of the same color dispersed in a clean, colorless dielectric solvent. 47. The method of claim 46, wherein the cells have the same background color and are filled with an electrophoretic composition comprising charged particles of different colors dispersed in a clean, colorless dielectric solvent. 37. The method of claim 36, wherein the transmissive insulator substrate is colored. 51. The method of claim 50, wherein the cells have a black background and are filled with an electrophoretic composition comprising white charged particles dispersed in a clean, colorless dielectric solvent. 52. The method of claim 51, wherein all cells have a transparent insulator substrate of the same color. 52. The method of claim 51, wherein said cells have transmissive insulator substrates of different colors. 39. The method of claim 38, wherein the transmissive insulator substrate is colored. 55. The method of claim 54, wherein the cells have a black background and are filled with an electrophoretic composition comprising white charged particles dispersed in a clean, colorless dielectric solvent. 56. The method of claim 55, wherein all cells have a transparent insulator substrate of the same color. 56. The method of claim 55, wherein all cells have transmissive insulator substrates of different colors. 10. An electrophoretic display according to claim 9, wherein a substrate comprising an array of thin film transistors is used as the layer of in-plane electrodes.