Seal film and seal composition for sealing microcells of electro-optical devices

Abstract

The present invention is directed to an aqueous seal composition comprising a combination of a polymer, a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, a polyurethane, and a rheology modifier in an aqueous carrier. The aqueous seal composition can be used to form a seal film with few defects in an electro-optical device having an electro-optical material layer comprising (a) a plurality of microcells filled with charged particles and a nonpolar fluid and (b) a seal film (the electro-optical material layer being disposed between two electrode layers). The corresponding electro-optical device exhibits good electro-optical performance.

Description

Technical Field

[0001] Cross - reference to related applications This application claims priority based on U.S. Provisional Patent Application No. 63 / 357,745, filed on July 1, 2022. Any patents, published applications, or other published documents referenced herein are hereby incorporated by reference in their entirety.

[0002] Field of the Invention The present invention relates to a seal film that can be used in electro - optical devices, such as electrophoretic displays. The seal film includes a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol - co - ethylene) copolymer, a polyurethane, and a rheology modifier, and the rheology modifier is selected from the group consisting of a hydrophobic modified ethoxylated urethane and an alkali - swellable emulsion polymer.

Background Art

[0003] Background of the Invention As used herein, the term "electro - optical" when applied to a material, device, or display refers to a material having first and second display states with at least one different optical property, and which changes from the first display state to the second display state upon application of an electric field to the material, in its conventional meaning in the imaging field. The optical property is typically a color perceptible to the human eye, but may also be another optical property, such as light transmission, reflectivity, luminescence, or in the case of a display intended for machine reading, a pseudo - color in the sense of a change in reflectivity of electromagnetic wavelengths outside the visible range.

[0004] The terms "bistable" and "bistability" are used herein in their conventional meaning in the art and refer to a display including a display element having first and second display states with at least one different optical characteristic, wherein after any given element is driven, it assumes either its first or second display state using an addressing pulse of finite duration, and after the addressing pulse has ended, the state persists for at least several times, such as at least four times, the minimum duration of the addressing pulse necessary to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays capable of grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and the same applies to some other types of electro-optic devices. This type of display is properly referred to as "multi-stable" rather than bistable, but for convenience, the term "bistable" can be used herein to encompass both bistable and multi-stable displays.

[0005] One type of electro-optic device that has been the subject of extensive research and development over the years is the particle-based electrophoretic display, in which a plurality of charged particles move in a fluid under the influence of an electric field. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, bistability of state, and low power consumption when compared to liquid crystal displays.

[0006] Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT), E Ink Corporation, E Ink California, LLC, and related companies describe various technologies used in encapsulated electrophoretic media and microcell electrophoretic media, as well as other electro-optic media. Encapsulated electrophoretic media include a number of small capsules, each of which itself includes an internal phase containing particles movable by electrophoresis in a fluid medium and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymer binder to form a coherent layer located between two electrodes. In a microcell electrophoretic display, charged particles and fluid are not encapsulated within microcapsules, but instead are held within a plurality of cavities formed within a carrier medium, typically a polymer film.

[0007] The technologies described in these patents and applications include the following: (a) Electrophoretic particles, fluids, and fluid additives, see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814; (b) Capsules, binders, and encapsulation processes, see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719; (c) Microcell structures, wall materials, and methods of forming microcells, see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906; (d) Methods for filling and sealing microcells, see, for example, U.S. Patent Nos. 7,144,942, 7,005,468, and 7,715,088, as well as U.S. Patent Application Publication Nos. 2004-0120024 and 2004-0219306; (e) Films and subassemblies containing electro-optic materials, see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564; (f) Backplane, adhesive layer and other auxiliary layers, and methods used in displays, see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624; (g) Color formation and color adjustment, see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564; (h) Methods for driving a display, see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445; (i) Applications of displays, see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; and (j) Non-electrophoretic displays described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160, and applications of encapsulation and microcell technologies other than displays, see, for example, U.S. Patent No. 7,615,325, and U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710.

[0008] The entire contents of the foregoing references are hereby incorporated by reference into this specification.

[0009] A structure having a plurality of sealed microcells containing a dispersion of charged dye particles in a nonpolar fluid is commercially used in electro-optical devices. Microcells are also known in the literature as microcavities or microcups. A typical method of fabricating a sealed microcell structure for an electro-optical device includes: (a) fabricating a polymer sheet having a plurality of microcavities each having an opening by microembossing; (b) filling the microcavities with an electrophoretic medium which is a dispersion containing charged dye particles in a nonpolar fluid; and (c) sealing the microcavities with an aqueous seal composition to form a seal film. The sealed microcavities containing the electrophoretic medium form the electro-optical material layer of the device. The electro-optical material layer is disposed between a front electrode and a back electrode. Application of an electric field across the electrophoretic medium by these electrodes causes the dye particles to migrate in the electrophoretic medium to produce an image. The seal film plays an important role for the function and performance of the device. First, the seal film contacts the electrophoretic medium and seals the electrophoretic medium inside the microcavity, so the seal layer should be (1) actually insoluble in the nonpolar fluid of the electrophoretic medium and (2) a good barrier to the nonpolar fluid so that the nonpolar fluid does not diffuse out of the microcell during the device lifetime. Poor barrier properties of the seal film to the nonpolar fluid result in reduction of the fluid of the electrophoretic medium and sagging of the seal film. Second, the seal film should not absorb a significant amount of moisture from the environment. That is, the seal film should prevent environmental moisture from entering the electrophoretic medium of the device. Such moisture may have an adverse effect on the electro-optical performance of the device. Third, since significant coating defects have an adverse effect on the electro-optical performance of the corresponding device, the seal composition should be coated on the microcell layer to form a seal film without such defects. Fourth, the seal film should be mechanically resilient during the useful lifetime of the device.Finally, the seal film should have an optimal volume resistivity that is actually maintained constant over time. Since the potential is applied across the device and conducted through, among other components, the seal film, the conductive properties of the seal film are important. The technical problem in providing an aqueous seal composition that forms a seal film having these characteristics is difficult because various formulation strategies may be required for various purposes. For example, barrier properties against nonpolar fluids typically require more hydrophilic components, while such components absorb more moisture from the environment. Furthermore, if the seal film has a low electrical conductivity, an increase in power consumption is required for device operation, while if the conductivity is too high, image quality degradation can be caused by blooming. Therefore, there is a need for an aqueous seal composition that forms an optimized seal film with fewer defects for improved barrier against nonpolar fluids, reduced moisture absorption, and improved electro-optical performance. The inventors have found that a seal film composition comprising a combination of a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, a polyurethane, and a rheology modifier, wherein the rheology modifier is a hydrophobically modified ethoxylated urethane or an alkali-swellable emulsion polymer, provides a seal film with fewer defects and good electro-optical performance.

Prior Art Documents

Patent Documents

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Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0011] Summary of the Invention In one aspect, the present invention is directed to a seal film comprising 15 to 60 wt% of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer based on the weight of the seal film, 7 to 29 wt% of polyurethane based on the weight of the seal film, and 0.05 to 10 wt% of a rheology modifier based on the weight of the seal film. The poly(vinyl alcohol) homopolymer has a degree of hydrolysis of 90% to 99.5%. The poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90% to 99.5% and an ethylene content of less than 10%. The rheology modifier is selected from the group consisting of a hydrophobically modified ethoxylated urethane and an alkali-swellable emulsion polymer. The seal film may further comprise 0.001 to 5 wt% of a surfactant based on the weight of the seal film. The seal film may comprise 0.01 to 5 wt% of a surfactant, or 0.01 to 2 wt% of a surfactant based on the weight of the seal film. The surfactant of the seal film may be a fluorosurfactant. The seal film may further comprise 5 to 70 wt% of carbon black based on the weight of the seal film. The carbon black can have an oil absorption amount of less than 100 mL per 100 mg of carbon black when measured using the OAN method in accordance with ASTM 2414. The carbon black can have a total surface area of less than 70 m 2 / g when measured using the nitrogen adsorption method in accordance with ASTM D6556.

[0012] The sealing film can further contain 4.5 to 25% by weight of a water-soluble ether based on the weight of the sealing film. The water-soluble ether has a molecular weight of 75 to 5,000 Daltons and contains a hydroxyl group as needed.

[0013] The total surface energy of the sealing film may be lower than 60 mN / m. The interfacial tension between the water-soluble poly(vinyl alcohol) polymer or poly(vinyl alcohol-co-ethylene) copolymer and the polyurethane can be less than 2 mN / m. The sealing film can have a volume resistivity of 10 7 ~10 11 ohm·cm.

[0014] The polyurethane of the sealing film can be an ester polyurethane, a polycarbonate polyurethane, or a combination thereof. The polyurethane of the sealing film can have a number average molecular weight of 1,000 to 2,000,000 Daltons.

[0015] The poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer of the sealing film can have a number average molecular weight of 1,000 to 1,000,000 Daltons. The poly(vinyl alcohol) polymer or poly(vinyl alcohol-co-ethylene) copolymer of the sealing film can have a degree of hydrolysis of 92% to 99%. The poly(vinyl alcohol-co-ethylene) copolymer of the sealing film can have an ethylene content of less than 9%.

[0016] In another aspect, the present invention is directed to an electro-optical device including a conductive layer, a microcell layer, a seal film, an adhesive layer, and an electrode layer. The microcell layer includes a plurality of microcells, each microcell having an opening, and each microcell containing an electrophoretic medium. The electrophoretic medium contains charged particles in a nonpolar carrier. The seal film of the electro-optical device contains 15 to 60% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer based on the weight of the seal film, 7 to 29% by weight of polyurethane based on the weight of the seal film, and 0.05 to 10% by weight of a rheology modifier based on the weight of the seal film. The poly(vinyl alcohol) homopolymer has a degree of hydrolysis of 90% to 99.5%. The poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90% to 99.5% and an ethylene content of less than 10%. The rheology modifier is selected from the group consisting of a hydrophobically modified ethoxylated urethane and an alkali-swellable emulsion polymer. The electrophoretic medium of the electro-optical device can contain at least three types of charged dye particles, and at least one type of charged particle has a color selected from the group consisting of blue, green, red, cyan, magenta, and yellow.

[0017] In yet another aspect, the present invention is directed to an aqueous seal composition comprising 15 to 60% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer based on the weight of the aqueous seal composition excluding water, 7 to 29% by weight of polyurethane based on the weight of the aqueous seal composition excluding water, 0.05 to 5% by weight of a rheology modifier based on the weight of the aqueous seal composition excluding water, 0.01 to 5% by weight of a surfactant based on the weight of the aqueous seal composition, and 20 to 95% by weight of water based on the weight of the aqueous seal composition. The poly(vinyl alcohol) homopolymer has a degree of hydrolysis of 90% to 99.5%. The poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90% to 99.5% and an ethylene content of less than 10%. The rheology modifier is selected from the group consisting of a hydrophobically modified ethoxylated urethane and an alkali-swellable emulsion polymer. The surfactant of the aqueous seal composition can be a fluorine-based surfactant.

[0018] The aqueous seal composition can further comprise 5 to 70% by weight of carbon black based on the weight of the aqueous seal composition excluding water. The carbon black can have an oil absorption amount of less than 100 mL per 100 mg of carbon black as measured using the OAN method in accordance with ASTM 2414. The carbon black can have a total surface area of less than 70 m 2 / g as measured using the nitrogen adsorption method in accordance with ASTM D6556.

[0019] The aqueous seal composition can further comprise 1.0 to 40% by weight of a water-soluble ether based on the weight of the aqueous seal composition excluding water. The water-soluble ether has a molecular weight of 75 to 5,000 daltons (grams per mole) and optionally contains a hydroxyl group.

[0020] The aqueous sealant composition can also contain 0.1 to 8% by weight of a polyurethane crosslinking agent based on the weight of the aqueous sealant composition excluding water. The polyurethane crosslinking agent is a polyisocyanate, a polyfunctional polycarbodiimide, a polyfunctional aziridine, a silane coupling agent, a boron / titanium / zirconium-based crosslinking agent, or a melamine formaldehyde.

[0021] 10 -4 The ratio obtained by dividing the viscosity of the aqueous sealant composition at a shear rate of 1 / second by 10 2 can be 7 or less. 10 -4 The ratio obtained by dividing the viscosity of the aqueous sealant composition at a shear rate of 1 / second by 10 2 can be 1 to 7. The aqueous sealant composition can have an H-B speed index of 0.7 or higher. The aqueous sealant composition can have an H-B speed index of 0.7 to 1, 0.7 to 0.9, or 0.7 to 2. The aqueous sealant composition can have a thixotropy index of 1.5 or higher. The aqueous sealant composition can have a thixotropy index of 1.5 to 3.

Brief Description of the Drawings

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BEST MODE FOR CARRYING OUT THE INVENTION

[0038] DETAILED DESCRIPTION OF THE INVENTION As used herein, "molecular weight" or "MW" refers to the weight average molecular weight, unless otherwise specified. The molecular weight is measured using gel permeation chromatography ("GPC").

[0039] The degree of hydrolysis of a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer is the ratio of the number of moles of vinyl alcohol groups to the total number of moles of vinyl alcohol groups and vinyl acetate groups in the polymer. Thus, in the example of the simplified polyvinyl alcohol formula provided below (Formula I), the degree of hydrolysis is calculated by Equation 1. Degree of hydrolysis = 100 × p / (p + q) Equation 1 Since this parameter affects important physical properties of the polymer, such as the water solubility of the polymer and the water resistance of the corresponding dry film, manufacturers of polyvinyl alcohol typically report the degree of hydrolysis of their products. A titration method is used to determine the degree of hydrolysis of polyvinyl alcohol (homopolymers and copolymers). Details of the method are described in Method JIS K6726 (Japanese Standards Association, 94th Edition, October 20, 2017).

Chemical formula

[0040] The terms "sealing film" and "sealing layer" are synonymous and are used interchangeably with respect to electro-optical devices.

[0041] The terms "adhesive film" and "adhesive layer" are synonymous and are used interchangeably with respect to electro-optical devices.

[0042] The terms "surfactant", "surface active agent", and "wetting agent" are synonymous in this specification. A "surfactant" or "surface active agent" or "wetting agent" is a substance capable of reducing the surface tension of a liquid, the interfacial tension between two liquids, the interfacial tension between a gas and a liquid, and the interfacial tension between a liquid and a solid. Surfactants are usually amphiphilic organic compounds, which means they contain both one or more hydrophobic functional groups (tails) and one or more hydrophilic groups (heads). A "fluorinated surfactant" is a surfactant having at least one fluorine atom in its molecular structure, more specifically, a surfactant having a fluorine atom in the alkyl chain of the tail of the surfactant. A fluorinated surfactant can have more than one fluorine atom in the alkyl chain of the tail of the surfactant.

[0043] Unless otherwise stated, the disclosed content of the components of the seal film is calculated as the weight percentage of the components relative to the weight of the seal film. Unless otherwise stated, the disclosed content of the components of the aqueous seal composition is calculated as the weight percentage of the aqueous seal composition excluding water (naturally, excluding the disclosed content of water in the aqueous composition).

[0044] A. Structure of Microcells

[0045] Figure 1 shows the structure of a plurality of microcells 100 shown in a side view. This figure represents a plurality of microcells 100 before being filled and sealed. Each microcell includes a bottom 101, a wall 102, and an opening 103.

[0046] B. Structure of Electro-Optical Device Containing Microcell Structure

[0047] Figure 2 shows an example of an electro-optical device 200 shown in a side view. This example of an electro-optical device includes a first light-transmissive electrode layer 210, a microcell layer 220, a seal film 230, an adhesive layer 240, and a second electrode layer 250. The microcell layer includes a plurality of microcells defined by a bottom portion 101 and a wall portion 102 of the microcells. Each microcell of the plurality of microcells has an opening 103. Each microcell of the plurality of microcells houses an electrophoretic medium 225, and this electrophoretic medium contains charged particles in a non-polar fluid. The microcells are sealed with a seal film 230, and this seal film extends across the openings 102 of the plurality of microcells. The second electrode layer 250 is connected to the seal film 230 using the adhesive layer 240. Each microcell of the plurality of microcells sealed with the seal film forms an electro-optical material layer of the electro-optical device 200. A source of an electric field can connect the first light-transmissive electrode layer 210 to the second electrode layer 250. By applying an electric field across the electrophoretic material layer, charged particles move in the electrophoretic medium to create an image, and this image can be observed by an observer viewing from the observation side 215 of the electro-optical device 200. A primer layer (not shown in Figure 2) may be disposed between the first light-transmissive electrode layer 210 and the microcell layer 220 as required.

[0048] The example of the electro-optical device shown in FIG. 2 can be constructed by the front plane laminate 300, the side view depiction of which is shown in FIG. 3. The front plane laminate 300 includes a first light transmissive electrode layer 210, a microcell phase 220, a seal film 230, an adhesive layer 240, and a release sheet 360. Each of the plurality of microcells houses an electrophoretic medium 225, which contains charged particles in a nonpolar fluid. The microcells are sealed with the seal film 230, which extends across the openings of the plurality of microcells. The release sheet 360 is connected to the seal film 230 using the adhesive layer 240. Removal of the release sheet 360 exposes the surface of the adhesive layer 240, which can be connected onto the second electrode layer to form the electro-optical device. A primer layer (not shown in FIG. 3), if required, can be disposed between the first light transmissive electrode layer 210 and the microcell layer 220.

[0049] The example of the electro-optical device shown in FIG. 2 can also be constructed by a double release sheet 400, a side view depiction of which is shown in FIG. 4. The double release sheet 400 includes a first release sheet 480, a first adhesive layer 470, a microcell layer 220, a seal film 230, a second adhesive layer 340, and a second release sheet 360. Each of the plurality of microcells houses an electrophoretic medium 225, which contains charged particles in a nonpolar fluid. The microcells are sealed with a seal film 230. The seal film 230 extends across the openings of the plurality of microcells. The first release sheet 480 is connected to the microcell layer 220 using the first adhesive layer 470. The second release sheet 360 is connected to the seal film 230 using the second adhesive layer 240. Removal of the first release sheet 460 exposes the surface of the first adhesive layer 470, which can be connected onto the first light-transmissive electrode layer. Removal of the second release sheet 360 exposes the surface of the second adhesive layer 240, which can be connected onto the second electrode layer to form an electro-optical device. A primer layer (not shown in FIG. 4) as required can be disposed between the first adhesive layer 470 and the microcell layer 220.

[0050] C. Formation of the Microcell Structure

[0051] Techniques for constructing microcells. The microcells can be formed by either a batch process or the continuous roll-to-roll process disclosed in U.S. Patent No. 6,933,098. The latter provides a continuous low-cost high-throughput manufacturing technique for generating compartments for the delivery of beneficial agents and for use in various applications including electrophoretic displays. A microcell array suitable for use in combination with the present invention can be created using microembossing as shown in FIG. 5. The male mold (500) can be placed either on or under the web 504 (not shown). However, alternative arrangements are possible. See, for example, U.S. Patent No. 7,715,088, which is hereby incorporated by reference in its entirety. The conductive substrate can be constructed by forming a conductor film 501 on a polymer substrate that serves as a backing layer for the device. Next, a composition containing a thermoplastic material, a thermosetting material, or a precursor thereof is coated on the conductor film 501. The precursor layer 502 of the thermoplastic or thermosetting material is embossed by a male mold in the form of a roller, plate, or belt at a temperature higher than the glass transition temperature of the material of the precursor layer 502 of the thermoplastic or thermosetting material.

[0052] The precursor layer 502 of the thermoplastic or thermosetting material for the preparation of the microcells can be, for example, a polyfunctional acrylate or methacrylate, a vinyl ether, an epoxide, and their oligomers or polymers. A combination of a polyfunctional epoxide and a polyfunctional acrylate is also very useful for achieving desirable physical and mechanical properties. Crosslinkable oligomers that impart flexibility, such as urethane acrylate or polyester acrylate, can be added to improve the bend resistance of the embossed microcells. The composition of the precursor layer 502 of the thermoplastic or thermosetting material can contain polymers, oligomers, monomers, and additives, or it can contain only oligomers, only monomers, and only additives. The glass transition temperature of this class of materials (i.e., T g) is typically in the range of about -70°C to about 150°C, or about -20°C to about 50°C. The micro-embossing process is typically carried out at a temperature higher than T g . The heated male mold, or the heated housing substrate against which the mold applies pressure, can be used to control the temperature and pressure of the micro-embossing process.

[0053] As shown in FIG. 5, the mold is released while or after the precursor layer 502 of the thermoplastic or thermosetting material is cured, revealing an array of microcells 503. Curing of the precursor layer 502 of the thermoplastic or thermosetting material can be achieved by cooling, solvent evaporation, radiation, heat or crosslinking by moisture. In the case of a precursor layer of a thermosetting material, curing can be achieved by UV radiation. In such a case, the UV can be radiated onto the transparent conductor film from the bottom or top of the web as shown in the two figures. Alternatively, the UV lamp can be placed inside the mold. In this case, the mold must be transparent in order to radiate UV light onto the precursor layer of the thermosetting material through a pre-patterned male mold. The male mold can be prepared by any suitable method, such as by either etching or electroplating following a diamond turning process or a photoresist process. The master template for the male mold can be manufactured by any suitable method, such as by electroplating. In electroplating, a thin layer of a seed metal such as chromium inconel is sputtered onto a glass base (typically 3000 Å). Next, the mold is coated with a layer of photoresist and exposed to UV. A mask is placed between the source of UV light and the layer of photoresist. The exposed area of the photoresist is cured. Next, the unexposed area is removed by washing with a suitable solvent. The remaining cured photoresist is dried and the thin layer of the seed metal is sputtered again. Thereby, the master is ready for electroforming. A typical material used for electroforming is nickel cobalt. Alternatively, the master can be made of nickel by electroforming or electroless nickel deposition. The floor surface of the mold is typically between about 50 and about 400 micrometers. The master can also be fabricated using other micro-engineering techniques including e-beam writing, dry etching, chemical etching, laser writing or laser interference as described in “Replication techniques for micro-optics”, SPIE Proc. Vol. 3099, pp. 76-82 (1997).Alternatively, the mold can be made by photomachining using plastic, ceramic, or metal.

[0054] Prior to applying the UV curable resin composition, the mold can be treated with a release agent to assist in the demolding process. The UV curable resin can be degassed prior to dispensing and may contain a solvent, if desired. The solvent, if present, evaporates readily. The UV curable resin is dispensed by any suitable method such as coating, dipping, injection, etc. so as to cover the male mold. The dispensing apparatus may be moving or stationary. The conductor film is overlaid on the UV curable resin. If necessary, pressure can be applied to ensure a proper bond between the resin and the plastic and to control the thickness of the bottom (floor) of the microcell. The pressure can be applied using a lamination roller, vacuum forming, a compression device, or any other similar means. If the male mold is made of metal and is opaque, the plastic substrate typically transmits the actinic radiation used to cure the resin. Conversely, the male mold may be transparent and the plastic substrate may not need to transmit actinic radiation. The conductor film needs to have good adhesion to the UV curable resin and this resin should have good release characteristics with respect to the mold surface in order to transfer the molded features well onto the transfer sheet.

[0055] The microcell array for the present invention typically includes a conductive layer formed by a preformed conductor film, such as indium tin oxide (ITO) conductor lines, although other conductive materials, such as silver or aluminum, may be used. The conductive layer can be backed or integrated with a substrate such as polyethylene terephthalate, polyethylene naphthalate, polyaramide, polyimide, polycycloolefin, polysulfone, epoxy, and composites thereof. The conductor film can be coated with a radiation curable polymer precursor layer. Next, the film and the precursor layer are imagewise exposed to radiation to form the microcell wall structure. After exposure, the precursor material is removed from the unexposed regions, leaving behind the cured microcell walls bonded to the conductor film / support web. Imagewise exposure can be achieved by passing UV or other forms of radiation through a photomask for generating an exposed image or a predetermined exposure pattern of the radiation curable material coated on the conductor film. Although not generally necessary, the mask can be positioned and aligned with respect to the conductor film, i.e., the ITO lines, such that the transparent mask portions are aligned with the spaces between the ITO lines and the opaque mask portions are aligned with the ITO material (intended to be the cell floor regions of the microcells).

[0056] Photolithography. The microcells can also be generated using photolithography. The photolithography process for fabricating the microcell array is shown in FIGS. 6A and 5B. As shown in FIGS. 6A and 6B, the microcell array 600 can be prepared by exposing a radiation curable material 601a coated on a conductor electrode film 602 by a known method through a mask 606 to UV light (or alternatively other forms of radiation, such as electron beam) to form wall portions 601b corresponding to the image projected through the mask 606. The base conductor film 602 is preferably mounted on a support substrate base web 603, which can include a plastic material.

[0057] In the photomask 606 of FIG. 6A, the dark squares 604 represent opaque regions, and the spaces between the dark squares represent the transparent regions 605 of the mask 606. UV is radiated onto the radiation-curable material 601a through the transparent regions 605. The exposure is preferably carried out directly on the radiation-curable material 601a, i.e., the UV does not pass through to the support substrate base web 603 nor to the base conductor film 602 (top exposure). For this reason, neither the support substrate base web 603 nor the conductor 602 needs to transmit the UV or radiation of other wavelengths used.

[0058] As shown in FIG. 6B, the exposed regions are cured, and then the unexposed regions (protected by the opaque regions 604 of the mask 606) are removed by an appropriate solvent or developer to form the microcells 607. The solvent or developer is selected from those commonly used to dissolve the radiation-curable material or reduce its viscosity, such as methyl ethyl ketone (MEK), toluene, acetone, isopropanol, etc. The preparation of the microcells can be achieved in the same way by placing the photomask under the conductor film / support substrate base, in which case the UV light is radiated from the bottom through the photomask, and this support substrate base web 603 needs to transmit the radiation.

[0059] Proper exposure. Yet another alternative method for the preparation of the microcell array of the present invention by proper exposure is shown in FIGS. 6C and 6D. When an opaque conductor line is used, the conductor line can be used as a photomask for exposure from the bottom. The durable microcell wall portion is formed by further exposure from above through a second photomask having an opaque line perpendicular to the conductor line. FIG. 6C shows the use of the exposure principle from both the top and the bottom to generate the microcell array 610 of the present invention. The base conductor film 612 is opaque and has a patterned line. The radiation-curable material 611a coated on the base conductor film 612 and the substrate 613 is exposed from the bottom through the base conductor film 612, and this base conductor film 612 serves as the first photomask. The second exposure is performed from the "top" side through a second photomask 616 having a line pattern perpendicular to the base conductor film 612. The space 615 between the lines 614 substantially transmits UV light. In this process, the wall material 611b cures in one side direction from the bottom upward and cures in the vertical direction from the top downward to together form a complete microcell 617. Next, as shown in FIG. 6D, the unexposed regions are removed by a solvent or a developer as described above to reveal the microcells 617.

[0060] The microcell can be constructed from a thermoplastic elastomer that has good compatibility with the microcell and does not interact with the medium. Examples of useful thermoplastic elastomers include ABA, and (AB)n type diblock, triblock, and multiblock copolymers, where A is styrene, α-methylstyrene, ethylene, propylene or norbornene, B is butadiene, isoprene, ethylene, propylene, butylene, dimethylsiloxane or propylene sulfide, and A and B must not be the same in the formula. The number n is ≧1, preferably 1 to 10. Particularly useful are diblock or triblock copolymers of styrene or ox-methylstyrene, such as SB (poly(styrene-b-butadiene)), SBS (poly(styrene-b-butadiene-b-styrene)), SIS (poly(styrene-b-isoprene-b-styrene)), SEBS (poly(styrene-b-ethylene / butylene-b-styrene)) poly(styrene-b-dimethylsiloxane-b-styrene), poly((α-methylstyrene-b-isoprene), poly(α-methylstyrene-b-isoprene-b-α-methylstyrene), poly(α-methylstyrene-b-propylene sulfide-b-α-methylstyrene), poly(α-methylstyrene-b-dimethylsiloxane-b-α-methylstyrene). Commercially available styrene block copolymers, such as Kraton D and G series (manufactured by Kraton Polymer, Houston, Tex.), are particularly useful. Crystalline rubbers, such as poly(ethylene-co-propylene-co-5-methylene-2-norbornene) or EPDM (ethylene-propylene-diene terpolymer) rubbers, such as Vistalon 6505 (manufactured by Exxon Mobil, Houston, Tex.) and their grafted copolymers have also been found to be very useful.

[0061] The thermoplastic elastomer can be dissolved in a solvent or a solvent mixture, which is immiscible with the carrier in the microcell and has a specific gravity lower than that of the carrier. A solvent with a low surface tension is preferred for the overcoating composition because it has better wetting properties than the microcell wall and its fluid. A solvent or a solvent mixture having a surface tension lower than 35 dynes / cm is preferred. A surface tension lower than 30 dynes / cm is more preferred. Suitable solvents include alkanes (preferably C 6~12 alkanes such as heptane, octane or Isopar solvents manufactured by Exxon Chemical Company, nonane, decane and their isomers), cycloalkanes (preferably C 6~12 cycloalkanes such as cyclohexane and decalin), alkylbenzenes (preferably mono- or di-C 1~6 alkylbenzenes such as toluene, xylene, etc.), alkyl esters (preferably C 2~5 alkyl esters such as ethyl acetate, isobutyl acetate, etc.) and C 3~5 alkyl alcohols (such as isopropanol, etc. and their isomers). A mixture of alkylbenzene and alkane is particularly useful.

[0062] The polymer mixture may contain a wetting agent (surfactant) in addition to the polymer additive. Also, to improve the adhesion of the sealant to the microcells and provide a more flexible coating process, wetting agents (e.g., FC surfactants from 3M Company, Zonyl fluorosurfactants from DuPont, fluoroacrylates, fluoromethacrylates, long-chain alcohols substituted with fluorine, perfluorinated long-chain carboxylic acids and their derivatives, and Silwet silicone surfactants from OSi, Greenwich, Conn.) may be included in the composition. During or after the overcoating process, crosslinking agents (e.g., bisazides such as 4,4'-diazidodiphenylmethane and 2,6-di-(4'-azidobenzal)-4-methylcyclohexanone), vulcanizing agents (e.g., 2-benzothiazolyldisulfide and tetramethylthiuram disulfide), polyfunctional monomers or oligomers (e.g., hexanediol, diacrylate, trimethylolpropane, triacrylate, divinylbenzene, diallylphthalene), thermal initiators (e.g., dilauroryl peroxide, benzoyl peroxide) and photoinitiators (e.g., isopropylthioxanthone (ITX), Irgacure 651 and Irgacure 369 from Ciba-Geigy) and other components may also be very useful to enhance the physical and mechanical properties of the seal film by crosslinking or polymerization reactions.

[0063] The microcell array 700 can be prepared by any of the methods described above. As shown in the cross-sectional views of FIGS. 7A-7D, the microcell wall portion 102 extends upward from the backing layer 101 and the conductive layer 210 (the first light-transmissive electrode layer 210) to form an open microcell. In one embodiment, the first light-transmissive electrode layer 210 is formed on or in the backing layer 101. FIGS. 7A-7D show that the first light-transmissive electrode layer 210 extends continuously over the backing layer 101, but the first light-transmissive electrode layer 210 can also extend continuously under or within the backing layer 101 or be interrupted by the microcell wall portion 102. The microcell array 700 can be cleaned and sterilized prior to filling to prevent the active agent that provides the benefit from being damaged before use.

[0064] Next, the microcells are filled with an electrophoretic medium 225 containing charged particles in a non-polar fluid to form a plurality of filled microcells 770. The microcells can be filled using various techniques. In some embodiments, blade coating can be used to fill the microcells to the depth of the microcell wall portion 102. In other embodiments, an inkjet type of micro-injection can be used to fill the microcells. In yet other embodiments, a micro-needle array can be used to fill the array of microcells with the electrophoretic medium 225.

[0065] As shown in FIG. 7C, after filling, the microcells are sealed by applying an aqueous seal composition to form a sealed microcell 780 including a seal film 230. In some embodiments, the sealing process can include exposure to heat, hot dry air, or UV radiation. The seal film must have good barrier properties against the non-polar fluid of the electrophoretic medium 225.

[0066] In an alternative embodiment, various individual microcells can be filled with a desired mixture by using iterative photolithography. This process typically involves coating an array of empty microcells with a layer of photoresist that acts as a positive type, selectively opening a certain number of microcells by imagewise exposing the positive type photoresist, subsequently developing the photoresist, filling the opened microcells with the desired mixture, and sealing the filled microcells by a sealing process. These steps can be repeated to create sealed microcells filled with other mixtures. This procedure enables the formation of large sheets of microcells having the desired ratio of mixtures or concentrations.

[0067] The seal of the filled microcells can be achieved in several ways. One approach involves mixing an aqueous seal composition with the electrophoretic medium composition. The aqueous seal composition can be immiscible with the electrophoretic composition and preferably can have a lower specific gravity than the electrophoretic medium composition. The two compositions, the aqueous seal composition and the electrophoretic medium composition, are thoroughly mixed and immediately coated onto a plurality of microcells using an accurate coating mechanism, such as a Mayer bar, gravure, doctor blade, slot coating or slit coating. The excess fluid is wiped off by a wiper blade or a similar device. A small amount of a weak solvent or solvent mixture, such as isopropanol, methanol or an aqueous solution thereof, can be used to clean the fluid remaining on the upper surface of the partition wall of the microcells. Thereafter, the aqueous seal composition is separated from the electrophoretic medium composition and floats on top of the liquid composition of the electrophoretic medium. Alternatively, after the mixture of the electrophoretic medium composition and the seal composition is filled into the microcells, a substrate can be laminated on top to control the metering of the mixture of the compositions and to promote phase separation of the aqueous seal composition from the electrophoretic medium composition to form a uniform seal film. The substrate used can be a functional substrate in the final structure or can be a sacrifice substrate, such as a release substrate, that can be removed later. Next, a seal film is formed by curing the aqueous seal composition in situ (i.e., while in contact with the electrophoretic medium composition). The curing of the aqueous seal composition can be achieved by UV or other forms of radiation, such as visible light, IR or electron beam. Alternatively, heat or moisture can also be used to cure the aqueous seal composition if a heat- or moisture-curable aqueous seal composition is used.

[0068] In the second method, first, the electrophoretic medium composition can be filled into the microcells, and then, an aqueous seal composition is overcoated on the filled microcells. The overcoating can be achieved by conventional coating and printing processes, such as blanket coating, inkjet printing, or other printing processes. In this method, a seal film is formed in situ by curing the aqueous seal composition by solvent evaporation, radiation, heat, moisture, or interfacial reaction. Subsequent UV curing after interfacial polymerization is beneficial for the sealing process. The mixing of the electrophoretic medium composition and the overcoat for sealing is significantly suppressed by the formation of a thin barrier layer at the interface by interfacial polymerization. Next, the sealing is completed, for example, by a post-curing step using UV radiation. The degree of mixing can be further reduced by using an aqueous seal composition having a specific gravity lower than that of the electrophoretic medium composition. A volatile organic solvent can be used to adjust the viscosity and thickness of the overcoat for sealing. The rheology of the aqueous seal composition can be adjusted according to the optimal sealability and coatability. When a volatile solvent is used in the overcoat, the volatile solvent is preferably immiscible with the solvent in the electrophoretic medium composition.

[0069] After the microcells are filled and sealed, a second electrode layer 250 including a plurality of electrodes can be laminated on the sealed array. As shown in FIG. 7D, the second electrode layer 250 is bonded on the seal film 230 to form an electro-optical device 790. An adhesive can be used to bond the second electrode layer 250 on the seal film 230 (the adhesive layer is not shown in FIG. 7D). The adhesive can be conductive. The adhesive of the adhesive layer can be a pressure-sensitive adhesive, a hot-melt adhesive, or a heat-, moisture- or radiation-curable adhesive. The adhesive for lamination can be post-cured by radiation passing through the upper conductive layer, such as UV, when the upper conductive layer transmits radiation. In other embodiments, a plurality of electrodes can be directly bonded to the sealed array of microcells.

[0070] Generally, the microcells can be of any shape, and their sizes and shapes can vary. The microcells can be of uniform size and shape in a given system. However, it is possible to have microcells with a mixture of multiple shapes and sizes. The openings of the microcells can be circular, square, rectangular, hexagonal, or any other shape. The size of the partition region between the openings can also vary. The dimensions of each individual microcell can range from about 1×10 1 to about 1×10 6 μm 2 or from about 1×10 2 to about 1×10 6 μm 2 or from about 1×10 3 to about 1×10 5 μm 2 and can be in this range.

[0071] The depth of the microcells can be from about 5 to about 200 μm, or from about 10 to about 100 μm. The ratio of the area of the openings of the microcells to the total area of the microcell layer is from about 0.05 to about 0.95, preferably from about 0.4 to about 0.9. The total area of the microcell layer is the total area of the side of the microcell layer on the same side as the microcell openings.

[0072] An electrophoretic display typically includes a layer of electrophoretic material and at least two other layers disposed on either side of the electrophoretic material, one of these two layers being an electrode layer. In most such displays, both layers are electrode layers, and one or both of these electrode layers are patterned to define the pixels of the display. For example, one electrode layer may be patterned into elongated row electrodes, and the other may be patterned into elongated column electrodes extending perpendicular to the row electrodes, and the pixels are defined by the intersections of the row and column electrodes. Alternatively, and more generally, one electrode layer has the form of a single continuous electrode, and the other electrode layer is patterned into a matrix of pixel electrodes, each of which defines one pixel of the display. In another type of electrophoretic display intended to be used in combination with a stylus, print head or similar movable electrode separated from the display, only one of the layers adjacent to the electro-optic material layer includes an electrode, and the layer on the opposite side of the electro-optic material layer is typically a protective layer intended to prevent the movable electrode from damaging the electro-optic material layer.

[0073] The manufacture of a three-layer electrophoretic display typically involves at least one lamination operation. For example, some of the aforementioned MIT and E Ink patents and applications describe methods for manufacturing encapsulated electrophoretic displays, in which the encapsulated electrophoretic medium, which contains capsules in a binder, is coated onto a flexible substrate containing indium tin oxide (ITO) or onto a similar conductive coating coated onto a plastic film. Separately, a backplane is prepared that includes an array of pixel electrodes and conductors arranged to connect the pixel electrodes and drive the circuit. To form the final display, the substrate having the electro-optic material layer is laminated to the backplane using a lamination adhesive.

[0074] U.S. Patent No. 6,982,178, supra, describes a method of assembling a solid electro-optic device well-suited for mass production. In essence, this patent describes a so-called "front plane laminate" ("FPL"), which in turn includes a light-transmissive electrode layer, an electro-optic material layer in electrical contact with the light-transmissive electrode layer, an adhesive layer, and a release sheet. An example of this structure is provided in FIG. 3. In FIG. 3, the electrophoretic material layer includes a microcell layer and a seal film. Typically, the light-transmissive electrode layer is carried on a light-transmissive substrate, which is preferably flexible in the sense that it can be manually wrapped around a drum, for example, 10 inches (254 mm) in diameter without undergoing permanent deformation. The term "light-transmissive" as used in this patent and in this specification is used to mean that the layer so designated transmits sufficient light for an observer looking through the layer so designated to be able to observe changes in the display state of the electrophoretic medium, which changes are ordinarily viewed through the light-transmissive electrode layer and an adjacent substrate, if present. If the electrophoretic medium exhibits a change in reflectivity at non-visible wavelengths, the term "light-transmissive" should of course be interpreted to refer to transmission of the relevant non-visible wavelengths. The substrate is typically a polymer film and usually has a thickness in the range of about 1 to about 25 mils (25 to 634 μm), preferably about 2 to about 10 mils (51 to 254 μm). The light-transmissive electrode layer may conveniently be, for example, a thin metal or metal oxide layer of aluminum or ITO, or a conductive polymer. A poly(ethylene terephthalate) (PET) film coated with aluminum or ITO is commercially available, for example, as "aluminum-coated Mylar" from E.I. du Pont de Nemours & Company, Wilmington, DE, and such commercially available materials can be used to good effect in front plane laminates.The assembly of an electrophoretic display using such a front plane laminate can be carried out by removing the release sheet from the front plane laminate and bringing the adhesive layer into contact with the back plane under conditions effective to adhere the adhesive layer to the back plane, thereby fixing the adhesive layer, the electro-optical material layer, and the light-transmissive electrode layer to the back plane. This process is well-suited for mass production since the front plane laminate is typically mass-produced using roll-to-roll coating techniques and can then be cut into pieces of any size required for use in combination with a particular back plane.

[0075] U.S. Patent No. 7,561,324 describes a so-called "double release sheet", which is essentially a simplified version of the front plane laminate of the aforementioned U.S. Patent No. 6,982,178. One form of the double release sheet includes an electro-optical material layer sandwiched between two adhesive layers, with one or both of the adhesive layers being covered by a release sheet. FIG. 4 shows an example of this form of the double release sheet. In FIG. 4, the electrophoretic material layer includes a microcell layer and a seal film. Another form of the double release sheet includes a layer of solid electro-optical material sandwiched between two release sheets. Both forms of the double release film are substantially similar to the process for assembling an electrophoretic display from the front plane laminate already described, but are intended for use in a process that includes two separate laminates. Typically, in the first laminate, the double release sheet is laminated to the front electrode layer (the first light-transmissive electrode layer) to form the front subassembly, and then in the second laminate, the front subassembly is laminated to the back plane to form the final display, although these two lamination orders can be reversed if desired. The back plane includes a second electrode layer.

[0076] U.S. Patent No. 7,839,564 describes a so-called "reverse front plane laminate", which is a modification of the front plane laminate described in the aforementioned U.S. Patent No. 6,982,178. This reverse front plane laminate may include, in order, at least one of a light-transmissive protective layer and a light-transmissive electrode layer, an adhesive layer, an electro-optic material layer, and a release sheet. Using this reverse front plane laminate, an electro-optic device having a layer of lamination adhesive between the electro-optic material layer and the light-transmissive electrode layer is formed, although a typical thin second adhesive layer may or may not be present between the electro-optic material layer and the backplane. Such electro-optic devices can combine good resolution and good low-temperature performance.

[0077] Electrophoretic medium.

[0078] An electrophoretic medium, in the context of the present invention, refers to a composition in a microcell. The microcell can be filled with at least one type of charged dye particles in a nonpolar fluid for display applications. The electrophoretic medium can include one type of charged particles, or one or more types of particles having different colors, charges, and charge polarities. The charged particles move within the electrophoretic medium under the influence of an electric field applied across the electro-optical material layer. The charged particles can be inorganic or organic dyes having a polymer surface treatment to improve their stability. The electrophoretic medium can include dyes having colors such as white, black, cyan, magenta, yellow, blue, green, red, and other colors. The electrophoretic medium can also include a charge control agent, a charge adjuvant, a rheology modifier, and other additives. Examples of nonpolar fluids include hydrocarbons such as Isopar, decahydronaphthalene (decalin), 5-ethylidene-2-norbornene, fatty oils, paraffin oils, silicon fluids, aromatic hydrocarbons such as toluene, xylene, phenylxylylethane, dodecylbenzene or alkylnaphthalenes, halogenated solvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene, dichlorobenzotrifluoride, 3,4,5-trichlorobenzotrifluoride, chloropentafluoro-benzene, dichlorononane or pentachlorobenzene, and perfluorinated solvents such as FC-43, FC-70 or FC-5060 manufactured by 3M Company, St. Paul MN, low molecular weight halogen-containing polymers such as poly(perfluoropropylene oxide) manufactured by TCI America, Portland, Oregon, poly(chlorotrifluoro-ethylene), such as Halocarbon oil manufactured by Halocarbon Product Corp., River Edge, NJ, perfluoropolyalkyl ethers such as Galden manufactured by Ausimont, or Krytox oils and Greases K-Fluid series manufactured by DuPont, Delaware, and polydimethylsiloxane-based silicone oils (DC-200) manufactured by Dow-corning.

[0079] The electrophoretic medium can contain two types of charged particles having different colors, a first type of charged particles having a first charge polarity, and a second type of charged particles having a second charged polarity opposite to the first charged polarity. The first type of charged particles may be black, and the second type of charged particles may be white.

[0080] The electrophoretic medium can contain three types of charged particles all having different colors, a first type of charged particles having a first charge polarity, a second type of charged particles having a second charge polarity opposite to the first charge polarity, and a third type of charged particles having a third charge polarity the same as the first or second charge polarity. The first type of charged particles may be black, the second type of charged particles may be white, and the third type of charged particles may be selected from the group consisting of red, yellow, blue, cyan, magenta, green, and orange.

[0081] The electrophoretic medium can contain four types of charged particles all having different colors, a first type of charged particles having a first charge polarity, a second type of charged particles having a first charge polarity, a third type of charged particles having a second charge polarity opposite to the first charge polarity, and a fourth type of charged particles having a second charge polarity. The magnitude of the charge of the first type of particles may be greater than the magnitude of the charge of the second type of particles, and the magnitude of the charge of the third type of particles may be greater than the charge of the fourth type of particles. In one example, the first type of charged particles is cyan, the second type of charged particles is magenta, the third type of particles is yellow, and the fourth type of charged particles is white.

[0082] The electrophoretic medium can contain four types of charged particles, all having different colors, namely, the first type of charged particles having a first charge polarity, the second type of charged particles having a first charge polarity, the third type of charged particles having a first charge polarity, and the fourth type of charged particles having a second charge polarity opposite to the first charge polarity. The magnitudes of the charges of the first, second, and third particles may be different from each other. The magnitude of the charge of the third type of particles may be greater than the magnitude of the charge of the first type of particles, and the magnitude of the charge of the first type of particles may be greater than the magnitude of the charge of the second type of particles. In one example, the first type of particles is cyan, the second type of particles is magenta, the third type of particles is yellow, and the fourth type of particles is white.

[0083] The electrophoretic medium can contain five types of charged particles, all having different colors, namely, the first type of charged particles having a first charge polarity, the second type of charged particles having a first charge polarity, the third type of particles having a first charge polarity, the fourth type of particles having a second charge polarity opposite to the first charge polarity, and the fifth type of particles having a second charge polarity. The magnitudes of the charges of the first, second, and third may be different from each other. The magnitude of the charge of the third type of particles may be greater than the magnitude of the charge of the first type of particles, and the magnitude of the charge of the first type of particles may be greater than the magnitude of the charge of the second type of particles. The charge of the fourth type of particles can have a higher charge than the fifth type of charged particles. In one example, the first type of particles is cyan, the second type of particles is magenta, the third type of particles is black, the fourth type of particles is yellow, and the fifth type of particles is white.

[0084] Sealing film derived from an aqueous sealant composition

[0085] The seal film plays an important role for the performance of the microcell electro-optical device. The seal film can be formed by coating a seal composition on the microcell layer of the electro-optical device. Since the seal film contacts the electrophoretic medium and seals the electrophoretic medium inside the microcell, the seal film must actually be insoluble in the non-polar fluid of the electrophoretic medium and must be a good barrier to the non-polar fluid so that the non-polar fluid does not scatter out of the microcell during the life of the device. If the barrier property of the seal film against the non-polar fluid of the electrophoretic medium is poor, reduction of the fluid of the electrophoretic medium and sagging of the seal film occur. Furthermore, the seal film must not absorb a significant amount of moisture from the environment. That is, the moisture in the environment must be prevented from entering the electrophoretic medium of the device. Such moisture may affect the conductivity of the seal film and the electrophoretic medium, and may have an adverse effect on the electro-optical performance of the device. The seal film for sealing the microcell layer must not have significant coating defects. Such defects have an adverse effect on the electro-optical performance of the device. The seal film must have mechanical elasticity during the useful life of the device. Also, it should practically have an optimal volume resistivity over time.

[0086] Another important property of the seal film is its electrical volume resistivity. If the resistivity of the seal film is too high, a significant voltage drop occurs within the seal film, and a voltage increase across the electrodes is required to operate the device. Increasing the voltage across the electrodes in this manner is undesirable because it increases the power consumption of the display and may require the use of a more complex and expensive control circuit to handle the increased voltage. On the other hand, if the volume resistivity of the seal film is too low, unwanted crosstalk is observed between adjacent pixel electrodes, and the image quality deteriorates. In addition, since the volume resistivity typically rises rapidly with decreasing temperature, too high a volume resistivity of the seal film has an adverse effect on the electro-optical performance of the display at low temperatures. The seal film is 10 8It can have a volume resistivity of ohm·cm or higher. The seal film is 1.0×10 7 ~1.0×10 12 ohm·cm, 1.0×10 7 ~1.0×10 11 ohm·cm, 1.0×10 8 ~1.0×10 11 ohm·cm, 3.5×10 7 ~×10 12 ohm·cm, or can have a volume resistivity of 1.0×10 8 ~1.0×10 10 ohm·cm. The seal film can have a volume resistivity of 10 11 ohm·cm or less, or 10 10 ohm·cm or less.

[0087] The seal film can be prepared from an aqueous seal composition. The aqueous seal composition contains 15 - 60 wt% of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, 7 - 29 wt% of a polyurethane, and 0.05 - 10 wt% of a rheology modifier, based on the weight of the aqueous seal composition excluding water. The rheology modifier can be a hydrophobic modified ethoxylated urethane or an alkali-swellable emulsion polymer, or a combination thereof.

[0088] The content of the rheology modifier in the aqueous sealant composition can be 0.05 to 10 wt%, 0.05 to 3 wt%, 0.05 to 2 wt%, 0.07 to 1 wt%, or 0.08 to 1 wt% based on the weight of the aqueous sealant composition excluding water. The rheology modifier increases the stability during storage of the aqueous sealant composition. The rheology modifier also promotes film formation, improves seal stability, and reduces defects in the seal film. Examples include associative thickeners, alkali-swellable acrylic emulsion polymers, and other polymeric thickeners. The aqueous sealant composition can be shear-thinning, i.e., its viscosity is reduced at higher shear rates. For example, the rheology profile of the aqueous sealant composition can show a viscosity reduction from 1 / 5 to 1 / 10,000 between the viscosity at a shear rate of 10 -4 1 / sec and the viscosity at a shear rate of 10 2 1 / sec.

[0089] Hydrophobically modified ethoxylated urethane (or HEUR) is a rheology modifier that can contain polyethylene glycol blocks covalently linked by urethane. These belong to the family of "associative thickeners". Associative thickeners have both hydrophilic and hydrophobic regions. An example of a HEUR rheology modifier is a block of polyethylene oxide linked by urethane and modified with a nonylphenol hydrophobic group. The polyethylene oxide block of the HEUR rheology modifier has a relatively low molecular weight, for example, less than 12,000 daltons (grams per mole), typically 50 - 700 daltons. HEUR rheology modifiers are typically nonionic polymers that are soluble in water at any pH. The water solubility of HEUR rheology modifiers is a result of the presence of ethylene oxide groups in their molecular structure. HEUR can be a branched or unbranched polymer. HEUR can have a terminal long-chain alkyl or alkylene group having 8 - 30 carbon atoms. Typical alkyl groups are, for example, dodecyl or stearyl groups, typical alkenyl groups are, for example, oleyl groups, typical aryl groups are phenyl groups, and typical alkylated aryl groups are, for example, nonylphenyl groups. Some HEUR moles also contain one or more internal hydrophobic blocks or groups.

[0090] Non-limiting examples of HEUR rheology modifiers include ACULYN™ 44, ACULYN™ 46, ACUSOL™ 880, ACUSOL™ 882, ACRYSOL™ RM-3000, ACRYSOL™ RM-895, ACRYSOL™ RM-8W, ACRYSOL™ RM-12W, ACRYSOL™ RM-995, ACRYSOL™ SCT-275, ACRYSOL™ RM-845, ACRYSOL™ RM-825, ACRYSOL™ RM-6000, ACRYSOL™ RM-5000, ACRYSOL™ RM 2020E, ACRYSOL™ RM-8W, ACRYSOL™ RM-725, supplied by Dow Chemical; RHEOVIS® PU 1190, RHEOVIS® PU 1191, RHEOVIS® PU 1291, RHEOVIS® PU 1241 and RHEOVIS® PU 1331, supplied by BASF; RHEOLATE® 212, RHEOLATE® 255, RHEOLATE® 655, RHEOLATE® 278, RHEOLATE® 678, RHEOLATE® 288, RHEOLATE® 299 and RHEOLATE® 475, supplied by Elementis Specialties; OPTIFLO® T 1000, OPTIFLO® L 1400, OPTIFLO® M 2600 VF, OPTIFLO® H 7500 VF, OPTIFLO® 3300, supplied by BYK; the TEGO ViscoPlus® range, supplied by TEGO; and TAFIGEL® PUR 61, TAFIGEL® PUR 50, and TAFIGEL® PUR 85, supplied by Munzing. Alkali-swellable emulsion (ASE) rheology modifiers are polymers produced using emulsion polymerization. ASE rheology modifiers are not associative thickeners, in contrast to HEUR rheology modifiers. ASE rheology modifiers can be formed from hydrophilic monomers such as (meth)acrylic acid monomers and less hydrophilic monomers such as (meth)acrylate ester monomers of lower alcohols (C1-C4 aliphatic alcohols such as ethyl acrylate, propyl acrylate, butyl acrylate, and methyl methacrylate, etc.). ASE rheology modifiers can thicken aqueous compositions at high pH. At high pH values, the (meth)acrylic acid groups are water-soluble in water, while the (meth)acrylate esters are water-insoluble. At low pH values, the polymer is water-insoluble and does not thicken the aqueous composition. At high pH, the acid is neutralized to its salt, and the polymer swells, resulting in a more viscous composition. Typically, ASE rheology modifiers have a relatively high weight average molecular weight, i.e., higher than 300,000 daltons (grams per mole), higher than 400,000 daltons, or higher than 500,000 daltons. Examples of hydrophilic groups include acrylic acid, methacrylic acid, and maleic acid. Examples of hydrophobic groups include esters of acrylic acid esters and methacrylic acid esters of aliphatic alcohols. Non-limiting examples of ASE rheology modifiers include RHEOVIS® 1125, RHEOVIS® 1130, ACULYN™ 33, ACULYN™ 38, ACUSOL™ 810A, ACUSOL™ 830, ACUSOL™ 835, ACUSOL™ 842, and ACRYSOL™ RM-38 (supplied by Dow Chemical), as well as Carbopol® Aqua 30 (supplied by Lubrizol Corporation).

[0091] Hydrophobically modified alkali swellable emulsion polymers (HASE) rheology modifiers are undesirable rheology modifiers for the aqueous sealant compositions of the present invention. These rheology modifiers swell at high pH values and thicken the aqueous composition. These rheology modifiers include monomers having highly hydrophobic properties. For example, ASE polymers can be formed by monomers such as (meth)acrylic acid monomers and (meth)acrylates of C1-C4 alcohols, and HASE polymers can be formed by monomers such as (meth)acrylic acid monomers and (meth)acrylates of C8-C 22 alcohols.

[0092] Non-limiting examples of HASE rheology modifiers include RHEOVIS® PU 1212, 1125, RHEOVIS® 1130 supplied by BASF, ACULYN® Excel, ACRYSOL® TT615, ACULYN® 22, ACULYN® 88, ACUSOL® 801S, ACUSOL® 805S, ACUSOL® 820 and ACUSOL® 823 supplied by Dow Chemical.

[0093] The aqueous sealant composition may further include a conductive filler. The content of the conductive filler in the aqueous sealant composition can be 5 to 70% by weight based on the weight of the aqueous sealant composition excluding water. The filler of the aqueous sealant composition can be selected from the group consisting of carbon black, graphene, graphite, and carbon nanotubes. The filler reduces the volume resistivity of the seal film but can also affect other properties of the layer, such as its surface energy. Carbon black must have good dispersibility in the aqueous sealant composition to be useful as a filler. The content of the conductive carbon black in the aqueous sealant composition can be 10 to 60%, 15 to 50%, 20 to 45%, or 30 to 40% by weight of the aqueous sealant composition.

[0094] The oil absorption value of the carbon black used in the aqueous seal composition is 100 cm per 100 mg of carbon black 3 or less. The oil absorption value is typically reported as the OAN (oil absorption amount) measured by the method according to ASTM 2414 by the carbon black manufacturer. The oil absorption value represents the structure and degree of aggregation of carbon black particles. That is, the larger the OAN, the higher the degree of structure of carbon black particles (bonded to each other and having a branched structure), and / or the higher the degree of aggregation of particles. Carbon black with a higher degree of structure / aggregation can generally bring a higher conductivity to the seal film, but the conductivity may vary depending on the dispersibility of the filler, indicating that the higher the OAN, the more difficult it may be to disperse the carbon black. The carbon black filler of the aqueous seal composition can preferably have an average primary particle diameter larger than 30 nm. This is another physical property of the carbon black grade that can be reported by the carbon black manufacturer. The primary particles can be determined by an electron microscope. Typically, carbon black with a very small average primary particle diameter is difficult to disperse. The carbon black can have a total surface area of less than 80 m 2 / g, less than 75 m 2 / g, or less than 70 m 2 / g. This is another general physical property routinely reported by the carbon black manufacturer. The total surface area is measured using the nitrogen adsorption method according to ASTM D6556. The carbon black can have a volume resistivity higher than 0.1 ohm·cm when measured in powder form at a pressure of 40 MPa using the method ASTM D2663.

[0095] The total surface energy of the conductive carbon black in the aqueous seal composition may be determined using the Washburn method with hexane as the test liquid and be higher than 40 mN / m, or may also be higher than 55 mN / m. The total surface energy of the conductive carbon black in the aqueous seal composition can be 40 mN / m to 80 mN / m, 40 mN / m to 70 mN / m, or 40 mN / m to 65 mN / m. The dispersive component of the surface energy of the conductive carbon black may be determined using the Washburn method with hexane as the test liquid and be higher than 15 mN / m. The dispersive component of the conductive filler can be 15 mN / m to 40 mN / m, or 15 mN / m to 30 mN / m.

[0096] The content of the water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer in the aqueous seal composition can be 15 to 60 wt%, 18 to 55 wt%, 20 to 50 wt%, or 22 to 40 wt% based on the weight of the aqueous seal composition excluding water.

[0097] The poly(vinyl alcohol) homopolymer has a degree of hydrolysis of 90% to 99.5%, and the poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90% to 99.5% and an ethylene content of less than 10%. The degree of hydrolysis of the poly(vinyl alcohol) homopolymer and the poly(vinyl alcohol-co-ethylene) copolymer can be 92% to 99%, or 92% to 95%. The ethylene content of the poly(vinyl alcohol-co-ethylene) copolymer can be less than 9%, less than 8.5%, or less than 8%. The degree of hydrolysis of the homopolymer and copolymer of polyvinyl alcohol is customarily reported by the manufacturers of such polymers and indicates the proportion by units (moles) of vinyl alcohol in the polymer relative to all vinyl units. The other units are typically vinyl acetate (ester). The ethylene content of the poly(vinyl alcohol-co-ethylene) copolymer is also reported by the manufacturer and represents the proportion of units (moles) of ethylene in the polymer relative to the other units. In this case, the other units are vinyl alcohol and vinyl acetate. The poly(vinyl alcohol) homopolymer and the poly(vinyl alcohol-co-ethylene) copolymer of the aqueous seal composition can have a weight average molecular weight (MW) of 1,000 to 1,000,000 daltons (grams per mole), 10,000 to 500,000 daltons, or 20,000 to 400,000 daltons.

[0098] Polyurethanes are typically prepared by a polyaddition process involving diisocyanates. Non-limiting examples of polyurethanes include polyether polyurethanes, polyester polyurethanes, polycarbonate polyurethanes, polyether polyureas, polyureas, polyester polyureas, polyester polyureas, polyisocyanates (e.g., polyurethanes containing isocyanate linkages), and polycarbodiimides (e.g., polyurethanes containing carbodiimide linkages). Generally, polyurethanes contain urethane groups. The polyurethanes utilized in the aqueous sealant compositions and sealant films described herein can be prepared using methods known in the art. The polyurethanes of the aqueous sealant compositions of the present invention are polyester polyurethanes, polycarbonate polyurethanes, and mixtures thereof. The polyurethanes of the aqueous sealant compositions can have a weight average molecular weight (MW) of 1,000 to 2,000,000 daltons (grams per mole), 10,000 to 300,000 daltons, or 15,000 to 200,000 daltons. The polyurethanes can be added to the aqueous sealant compositions as aqueous solutions, aqueous dispersions or emulsions, or latexes.

[0099] The content of the polyurethane in the aqueous sealant composition can be 7 to 29 wt%, 8 to 25 wt%, 12 to 22 wt%, or 14 to 20 wt% based on the weight of the aqueous sealant composition excluding water.

[0100] The aqueous seal composition may include a polyurethane crosslinker (or otherwise referred to as a polyurethane crosslinking agent). The content of the polyurethane crosslinker in the aqueous seal composition may be 0.1 to 8% by weight of the polyurethane crosslinker based on the weight of the aqueous seal composition excluding water. During the curing of the aqueous seal composition for preparing the seal film, the polyurethane crosslinker forms chemical bonds between the polyurethanes of the aqueous seal composition and potentially the polymer molecules of the microcells, increasing the adhesion between the seal film and the microcells. The polyurethane crosslinker is preferably soluble or dispersible in the aqueous carrier of the aqueous seal composition. The crosslinker can be a monomer, oligomer or polymer. Examples of the polyurethane crosslinker include polyisocyanate, polyfunctional polycarbodiimide, polyfunctional aziridine, silane coupling agent, boron / titanium / zirconium-based crosslinker, or melamine formaldehyde. The polycarbodiimide crosslinker is reactive under acidic pH conditions. Preferably, the polyurethane crosslinker does not contain a sulfosuccinate surfactant. The content of the polyurethane crosslinker in the aqueous seal composition may be 0.2 to 6% by weight, 0.4 to 4% by weight, 0.5 to 3% by weight, 0.6 to 2% by weight, or 0.7 to 1.8% by weight based on the weight of the aqueous seal composition excluding water.

[0101] The inventors have found that an aqueous seal composition comprising a combination of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer and a polyurethane, wherein the interfacial tension between the water-soluble poly(vinyl alcohol) polymer or poly(vinyl alcohol-co-ethylene) copolymer and the polyurethane is less than 2 mN / m, can form a seal film having excellent performance.

[0102] It has also been clarified that excellent performance was observed even in an aqueous seal composition containing a combination of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer and a polyurethane, wherein the polar component of the surface energy of the polyurethane is 10 to 20 mN / m, through extensive experimental work.

[0103] The aqueous seal composition may further contain 1 to 40% by weight of a water-soluble ether based on the weight of the aqueous seal composition excluding water. The aqueous seal composition may contain 1 to 30% by weight, 1 to 25% by weight, 1 to 22% by weight, 1 to 20% by weight, 1 to 15% by weight, 1 to 10% by weight, 1 to 5% by weight, or 1 to 3% by weight of a water-soluble ether based on the weight of the aqueous seal composition excluding water. The content of the water-soluble ether in the aqueous seal composition may be higher than 0.2% by weight, higher than 0.5% by weight, higher than 1% by weight, higher than 2% by weight, higher than 5% by weight, higher than 6% by weight, higher than 7% by weight, higher than 8% by weight, or higher than 10% by weight based on the weight of the aqueous seal composition excluding water. The content of the water-soluble ether in the aqueous seal composition may be lower than 40% by weight, lower than 30% by weight, lower than 20% by weight, lower than 15% by weight, lower than 10% by weight, lower than 5% by weight, or lower than 2% by weight based on the weight of the aqueous seal composition excluding water.

[0104] The water-soluble ether has a weight average molecular weight of 75 to 5,000 Daltons (grams per mole). The water-soluble ether can have a weight average molecular weight of 85 to 3,000 Daltons, 90 to 1,000 Daltons, 90 to 500 Daltons, or 90 to 300 Daltons. The water-soluble ether can have a weight average molecular weight higher than 75, higher than 90, higher than 100, or higher than 200. The water-soluble ether can have a weight average molecular weight lower than 5,000, lower than 3,000, lower than 1,000, lower than 500, lower than 300, lower than 200, or lower than 150.

[0105] The water-soluble ether is a polar compound soluble in water and polar organic solvents. The water-soluble ether can be represented by Formula II, Formula III, or Formula IV. [Chemical formula] The value of n is from 1 to 145. The value of n can be from 1 to 100, from 1 to 50, from 1 to 20, from 1 to 10, from 1 to 5, from 1 to 4, from 1 to 3, or from 1 to 2. R1 is hydrogen, methyl or ethyl group, and R2, R3, R4, R5, R6, and R7 are independently selected from the group consisting of hydrogen, a linear or branched alkyl group containing 1 to 6 carbon atoms, phenyl, and benzyl group. Formula II contains at least one ether functional group. Formula III contains at least one ether functional group. Formula IV contains at least one ether functional group.

[0106] Water-soluble ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol monoisopropyl ether, ethylene glycol n-monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol mono-t-butyl ether, ethylene glycol monobenzyl ether, ethylene glycol monophenyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di-n-propyl ether, ethylene glycol diisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol monoisopropyl ether, diethylene glycol n-monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol mono-t-butyl ether, diethylene glycol monobenzyl ether, diethylene glycol monophenyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol di-n-propyl ether, diethylene glycol diisopropyl ether, diethylene glycol di-n-butyl, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol mono-n-propyl ether, triethylene glycol monoisopropyl ether, triethylene glycol n-monobutyl ether, triethylene glycol monoisobutyl ether, triethylene glycol mono-t-butyl ether, triethylene glycol monobenzyl ether, triethylene glycol monophenyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol di-n-propyl ether, triethylene glycol diisopropyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, triethylene glycol monophenyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol monomethyl ether,It may be selected from the group consisting of polyethylene glycol monoethyl ether, polyethylene glycol monophenyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, propylene glycol mono-n-butyl ether, propylene glycol monoisobutyl ether, propylene glycol monophenyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol monoisobutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol di-n-propyl ether, dipropylene glycol diisopropyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol mono-n-propyl ether, tripropylene glycol monoisopropyl ether, tripropylene glycol mono-n-butyl ether, tripropylene glycol monoisobutyl ether, or a mixture thereof.

[0107] The aqueous sealant composition may also include a wetting agent, also known as a surfactant. Non-limiting examples of wetting agents include FC surfactants manufactured by 3M Company, Zonyl fluorosurfactants manufactured by DuPont, fluoroacrylates, fluoromethacrylates, fluorine-substituted long-chain alcohols, perfluorine-substituted long-chain carboxylic acids and their derivatives, and Silwet silicone surfactants manufactured by OSi (Greenwich, Conn.). The wetting agent can increase the affinity between the seal film and the microcells, enhance the interfacial region between them, improve the adhesion of the seal film to the microcells, and provide a more flexible coating process. The content of the surfactant in the aqueous sealant composition can be 0.001 to 5 wt%, 0.01 to 5 wt%, or 0.01 to 2 wt% based on the weight of the aqueous sealant composition excluding water.

[0108] The aqueous sealant composition may contain water in an amount of 20 to 95 wt%, 50 to 94 wt%, 70 to 92 wt%, 75 to 90 wt%, or 80 to 88 wt% based on the weight of the aqueous sealant composition.

[0109] The aqueous sealant composition may also include a pH adjuster. The pH adjuster is added to the aqueous sealant composition to adjust its pH to a value of 6.5 to 8.5. An example of a pH adjuster is ammonium hydroxide, although various acids and bases can be used. The pH adjuster can increase the pH of the aqueous sealant composition, thereby reducing the crosslinking rate of the aqueous sealant composition before use and providing optimal pH conditions for the rheology modifier to interact with the particles of the aqueous sealant composition, improving its effectiveness. The pH adjuster can be used in a content of 0.2 wt% to 1 wt% based on the weight of the aqueous sealant composition excluding water.

[0110] The aqueous sealant composition can be used to form a seal film by application of the aqueous sealant composition and drying or curing of the aqueous sealant composition. The seal film can constitute most of the components of the aqueous sealant composition. When the aqueous composition contains a polyurethane crosslinking agent, the polyurethane crosslinking agent is incorporated into the polyurethane polymer of the seal film during curing. In addition, the water in the sealant composition evaporates during drying or curing of the aqueous sealant composition towards the preparation of the seal film. When the aqueous sealant composition contains a water-soluble ether, the formed seal film also contains the water-soluble ether of the aqueous sealant composition, but a part of the water-soluble ether evaporates during the formation of the seal film. If any water or moisture or water-soluble ether remaining or absorbed in the seal film is present, the disclosed content of the components of the seal film is calculated as the weight % of the components with respect to the weight excluding residual water, residual water-soluble ether and absorbed water, unless otherwise stated.

[0111] The seal film contains 15 to 60% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, 7 to 29% by weight of polyurethane, and 0.05 to 10% by weight of a rheology modifier, based on the weight of the seal film. The poly(vinyl alcohol) homopolymer has a degree of hydrolysis of 90% to 99.5%. The poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90% to 99.5% and an ethylene content of less than 10%. The rheology modifier is a hydrophobically modified ethoxylated urethane (HEUR) or an alkali-swellable emulsion polymer (ASE). The seal film may further contain a conductive filler. The conductive filler can be carbon black. The seal film may contain 11 to 60% by weight, 24 to 55% by weight, 29 to 50% by weight, or 30 to 45% by weight of conductive carbon black, based on the weight of the seal film.

[0112] The seal film may contain a surfactant (wetting agent). The content of the surfactant in the seal film may be 0.001 to 5 wt%, 0.01 to 5 wt%, or 0.01 to 2 wt% based on the weight of the aqueous seal composition. The surfactant may be an anionic, cationic, zwitterionic, or nonionic surfactant. The surfactant may be a fluorosurfactant. The surfactant may be a silicone surfactant containing a polydimethylsiloxane group in its molecular structure.

[0113] The seal film may contain 4.5 to 25 wt% of a water-soluble ether based on the weight of the seal film. The seal film may contain 4.5 to 10 wt%, or 5 to 9 wt%, 5 to 8 wt%, or 5 to 7 wt% of a water-soluble ether based on the weight of the seal film. The content of the water-soluble ether in the seal film may be higher than 4.5 wt%, higher than 5 wt%, higher than 6 wt%, higher than 7 wt%, higher than 8 wt%, higher than 9 wt%, or higher than 10 wt% based on the weight of the seal film. The content of the water-soluble ether in the seal film may be lower than 25 wt%, lower than 20 wt%, lower than 15 wt%, lower than 10 wt%, or lower than 5 wt% based on the weight of the seal film.

[0114] The addition of a water-soluble ether to the aqueous seal composition and the seal film is thought to reduce the electrical resistance at the interface between the seal film and one or both of the adjacent layers, for example, the interface between the seal film and the adhesive layer and the interface between the seal film and the electrophoretic medium. This reduction in the electrical resistance at the interface was experimentally demonstrated using volume resistivity measurements and electrical impedance spectroscopy experiments as shown in the Examples section. Importantly, this electrical resistance at the interface did not affect the electrical conductivity of the seal film itself. In fact, as shown by the data, the seal film of the present invention has a higher volume resistivity than that of a control film that does not contain a water-soluble ether. As described above, the higher the volume resistivity of the seal film, the more it contributes to lower blooming, which is a phenomenon well-known in the electro-optical field.

[0115] A seal film prepared from an aqueous seal composition can be used to seal the microcells of an electro-optical device. The electro-optical device includes a conductive layer and a microcell layer including a plurality of microcells, each microcell having an opening, each microcell including an electrophoretic medium, the electrophoretic medium including charged particles in a nonpolar carrier, the microcell layer, a seal film extending across the opening of each microcell, an adhesive layer, and an electrode layer.

[0116] Generally, the seal film of an electro-optical device plays an important role in display performance. Poor barrier properties of the seal film result in the time-dependent outflow of the nonpolar fluid of the electrophoretic medium from the electro-optical material layer, thereby causing a serious deterioration of the electro-optical performance of the display. An increase in the content of poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer in the seal film was observed to improve its barrier properties. However, a seal film having a high content of poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer increases the moisture absorption of the layer, which is also undesirable.

[0117] The inventors have surprisingly found that an aqueous composition containing a rheology modifier selected from the group consisting of HEUR and ASE improves the quality of the coating of the seal film. That is, the seal film reduces coating defects. If there are defects, the electro-optical performance of the corresponding device will be inferior. Coating defects may be related to poor wetting, delamination, chattering, or clouding spot unevenness (CSM). These effects are described in detail below. Specifically, the reduction of seal film defects (higher coating quality) is observed when (a) the viscosity ratio is lower than 7, the viscosity ratio is 1 to 7, 2 to 7, or 0.5 to 7, (b) the H-B velocity index is 0.7 or higher, 0.7 to 1, 0.7 to 0.9, or 0.7 to 2, and (c) the thixotropy index is 1.5 or higher, or 1.5 to 3.

[0118] The viscosity ratio of the aqueous seal composition is determined as the ratio of the viscosity at low shear rate divided by the viscosity at high shear rate, as described in the Examples section. The H-B velocity index of the aqueous seal composition is determined by measuring the viscosity of the composition with a shear rate ramp, constructing a graph of stress versus shear rate, and analyzing the graph based on the Herschel-Bulkley model. The thixotropy index is the ratio of viscosities measured by a thixotropy loop experiment in which a low shear rate to a high shear rate is applied to the aqueous composition, followed by a high shear rate to a low shear rate. The thixotropy index indicates the thixotropic behavior of the aqueous seal composition. The inventors have conducted a detailed study of the rheological characteristics of various aqueous seal compositions and then used the aqueous compositions to form devices having corresponding films and determined the coating quality and performance of such seal films. Surprisingly, it has been found that aqueous compositions containing HEUR and ASE rheology modifiers provide seal films with better performance and significantly fewer defects. It has also been observed that the use of fluorinated surfactants in the aqueous composition shows less interaction between the surfactant and the rheology modifier. That is, the content of the fluorinated surfactant has less influence on the rheological characteristics of the aqueous composition compared to other surfactants, thereby allowing for better flexibility in adjusting the surface energy of the resulting seal film, and it has been shown that this has a significant effect on the performance of the seal film. Specifically, as described above, when a combination of a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer and polyurethane is used and the interfacial tension between the poly(vinyl alcohol) polymer or poly(vinyl alcohol-co-ethylene) copolymer and polyurethane is less than 2 mN / m, improved performance is observed. Furthermore, the inventors have surprisingly found that optimal performance is also observed when a combination of a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer and polyurethane is used and the polar component of the surface energy of the polyurethane is 10 to 20 mN / m.

[0119] These and other aspects of the present invention will be further understood in view of the following examples, which are intended to illustrate certain embodiments of the present invention but are not intended to limit its scope as defined by the claims.

Example

[0120] Evaluation Method of Aqueous Seal Composition and Seal Film

[0121] A. Example of Preparation of Aqueous Seal Composition

[0122] A1. Example of Preparation of Carbon Black Dispersion. An aqueous solution of a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol - co - ethylene) copolymer containing 20% by weight of the polymer with respect to the volume of the solution was prepared. In one example, the polymer is a poly(vinyl alcohol - co - ethylene) copolymer (Exceval™ RS - 1717 supplied by Kuraray), i.e., the solution contains 200 g of the polymer per liter of the solution. Carbon black powder is mixed with the aqueous solution of the poly(vinyl alcohol) homopolymer or poly(vinyl alcohol - co - ethylene) copolymer. In one example, an aqueous solution containing 106 g of the poly(vinyl alcohol - co - ethylene) copolymer was mixed with 162 g of carbon black (Nerox® 3500 supplied by Orion Engineered Carbon). The dispersion was mixed with an overhead mixer (Hei - Torque Value 200) at 300 rpm for 30 minutes. Next, the dispersion was recirculated through a Generation 1 Q1375 Flocell sonicator, and the jacket of the sonicator was cooled with cold water at 10°C at 100% amplitude for 3 hours and 23 minutes. The dispersion was continuously stirred until used to prepare the seal composition.

[0123] Example of Preparation of an Aqueous Sealant Composition. An aqueous polyurethane dispersion was combined in a container with a wetting agent and an aqueous solution of a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer. In one example, 227.17 g of a 35 wt% aqueous polyurethane dispersion (L3838 aqueous dispersion supplied by Hauthaway) was mixed with 683.2 g of an aqueous solution of a poly(vinyl alcohol-co-ethylene) copolymer (containing 20 wt% copolymer based on the volume of the solution). In this example, the poly(vinyl alcohol-co-ethylene) copolymer was Exceval™ RS-1717 supplied by Kuraray. The mixture was mixed for 10 minutes at 90 rpm using a Hei-torque Value 200 overhead mixer. Next, an appropriate amount of a crosslinking agent was added and the dispersion was mixed for an additional 60 minutes at 90 rpm. An appropriate amount of the carbon black dispersion prepared in A1 was added (0.530 L in one example) and the resulting dispersion was mixed for 60 minutes at 500 rpm. Next, ammonium hydroxide was used to adjust the pH to 6.5 - 8.5 and the dispersion was mixed for an additional 30 minutes. An appropriate amount of a rheology modifier was added dropwise to the dispersion and mixing was continued for an additional 60 minutes. Next, the dispersion was degassed under reduced pressure (25 mmHg) for 5 days. The resulting aqueous sealant composition was used for the preparation of the seal film of the corresponding device within 7 days after the sealant composition was prepared.

[0124] B1. Example of Preparation of a Seal Film Using the Drawdown Method.

[0125] The sealant composition prepared in A2 above was coated on the indium tin oxide (ITO) side of an ITO-PET film using a Gardco drawdown coater. A 15 mil gap and an 8-pass square applicator were used. The drawdown speed was set at 2 m / min targeting a dry film thickness of 30 + / - 2 μm. The coating was dried in an oven at 100°C for 15 minutes. The dried film was conditioned at 25°C and 55% RH for 24 hours.

[0126] Example of Preparation of Seal Film Using a Roll-to-Roll Coating Line.

[0127] The seal composition prepared in A2 above was coated at a dry thickness of 30 μm on the indium tin oxide (ITO) side of an ITO-PET thin film using a slot die of a roll-to-roll coating line at a speed of 9 feet per minute. The film was moved through a convection oven consisting of four heating zones at a speed of 9 feet per minute. Each heating zone was 5 feet in length. The first zone was set at a temperature of 80 °C and the remaining heating zones were set at a temperature of 100 °C. Once the dried seal film on the ITO-PET passed through the drying oven, the film was cut into three parts, each approximately 24 - 30 inches in length, and placed in a controlled clean room environment at a temperature of 25 °C and 55% relative humidity (RH).

[0128] C. Determination of the Surface Energy of the Film.

[0129] The surface energy of the prepared seal film (as described in B1 above) was measured using a drop shape analyzer supplied by Kruss GmbH. A syringe equipped with a needle was used to place a 2.6 μL sized deionized water droplet on the upper surface of the seal film, and the contact angle between the liquid (water) and the seal film was measured. The measurement was repeated by replacing the water droplet with an iodine methane droplet. The surface energy of the film was calculated by performing contact measurements using these two liquids with known surface energies. The contact angle measurement was repeated three times for each liquid (water and iodine methane). The contact angle between the liquid and the upper surface of the seal film was measured using a high-resolution camera 5 seconds, 30 seconds, and 55 seconds after placing the droplet on the sample film. Next, the Owens, Wendt, Rabel, and Kaelble (OWRK) method was used to calculate the total surface energy, as well as its polar and dispersive components, for each data point. The reported surface energy was the average of nine data points (3 droplets × 3 time scales).

[0130] D. Preparation of the electro-optical device.

[0131] The electro-optical device was prepared by filling a plurality of microcells with a mixture of electrically charged dye particles (white, cyan, magenta, and yellow) in Isopar E. The white and yellow particles were negatively charged, and the cyan and magenta particles were positively charged. Next, an aqueous seal composition was coated onto the openings of the microcells as described in B above. The device shown in FIG. 8 was constructed. The electro-optical device 800 included, in order, a protective film 801, an optically transparent first adhesive layer 802, a substrate 803, a light-transmissive conductive layer 804, a primer layer 805, a microcell layer 806, a seal film 807, a second adhesive layer 808, an ITO electrode layer 809, and a glass layer 810. The light-transmissive conductive layer 804 was electrically connected to the ITO electrode layer 809 by an electric field source 811. A waveform was applied by this source to drive the desired optical state. The first light-transmissive layer 802 had a thickness of approximately 25 μm. The substrate 803 had a thickness of approximately 100 μm. The primer layer 1005 had a thickness of approximately 0.4 μm. The microcell layer 806 included a plurality of microcells. Each microcell had a bottom thickness of approximately 0.4 μm and a height of approximately 10 μm. The seal film 807 had a thickness of approximately 10 μm, and the second adhesive layer had a thickness of approximately 4.5 μm.

[0132] E. Determination of the interfacial tension of the polymer.

[0133] For a specific combination of polymers, the interfacial tension between polymer 1 and polymer 2 was calculated from the surface tension values (determined by the method described in C above). The calculation of the interfacial tension between the two components was carried out by using the values of the surface energy of each component and the following geometric equation.

Equation

[0134] Similarly, the interfacial tension between the seal film and the adhesive layer can also be measured. The adhesive layer standard containing polyurethane was formed by an aqueous dispersion of water-dispersible polyurethane.

[0135] F. Evaluation of the barrier properties of the seal film against non-polar fluids.

[0136] An aqueous dispersion was prepared by mixing 10 grams of a poly(vinyl alcohol) homopolymer or 10 grams of a poly(vinyl alcohol-co-ethylene) copolymer and 10 grams of polyurethane in 100 mL of water. The dispersion was used as an aqueous polymer composition to form a seal film for device 900 shown in FIG. 9. The seal film was formed by the method described in B1 above. Device 900 included, in order, a substrate 903, a light-transmissive conductive layer 904, a primer layer 905, a microcell layer 906, and a seal film 907. The microcells contained an electrophoretic medium containing white, black, and red pigment particles in Isopar E. Device 900 was stored at 70 °C for at least 24 hours. After this period, the electro-optical device was examined using an optical microscope for sagging of the seal film caused by loss of the non-polar fluid of the electrophoretic medium. If the distance between the bottom of the examined microcavity and the lowest point of the bottom surface of the seal film is less than 85% of the distance between the bottom of the microcavity in the same microcell and the uppermost point of the lower surface of the seal film, the aqueous polymer composition is classified as "failed" with respect to its barrier properties. Otherwise, i.e., if the distance between the bottom of the examined microcell and the lowest point of the seal film is 85% or greater of the distance between the bottom of the microcell and the uppermost point of the bottom surface of the seal film in the examined microcell, the aqueous seal polymer composition is classified as "passed" with respect to its barrier properties. For example, the aqueous polymer composition used to prepare the electro-optical device shown in FIG. 10C was classified as "passed" because the ratio of h2:h1 is 1 (no sag), while the aqueous polymer composition used to prepare the electro-optical device shown in FIG. 10D was classified as "failed" because the ratio of h2:h1 is 35% (a sag level greater than 85%). Evaluation of the barrier properties can also be carried out qualitatively by observing the prepared electro-optical device as seen from the observation surface of the device using an optical microscope.Devices containing severely sagging seal films have a significantly different appearance (non-uniform surface vs. uniform surface) from devices containing seal films with good barrier properties against non-polar fluids. For example, in contrast to the microcells ("failed") having an aqueous polymer composition corresponding to the seal film of FIG. 10D, which appears non-uniform as shown in FIG. 10B, the microcells ("passed") having an aqueous polymer composition corresponding to the seal film of FIG. 10C appear uniform as shown in FIG. 10A. Evaluations of various combinations of (1) poly(vinyl alcohol) homopolymers or poly(vinyl alcohol-co-ethylene) copolymers and (2) polyurethanes are shown in Table 3. Polymer 1 is a poly(vinyl alcohol) homopolymer or a poly(vinyl alcohol-co-ethylene) copolymer, and Polymer 2 is a polyurethane. Details regarding commercially available materials for Polymer 1 and Polymer 2 can be found in Table 4.

[0137] G. Method for determining the thixotropy index of an aqueous seal composition.

[0138] To explain one aspect of the rheological behavior of an aqueous seal composition, the thixotropy index (T.I.) was used. The thixotropy index is the ratio of viscosities measured by a rheometer during a thixotropy loop test. The thixotropy loop test measures viscosities at different shear rates from low shear (10 -4 1 / s) to high shear (10 3 1 / s) in a first flow ramp (Flow Ramp 1) using a shear rate ramp, and then measures from high shear to low shear in a second flow ramp (Flow Ramp 2) to create a shear loop. The thixotropy index is calculated using the following equation for the viscosity value at a shear rate of 10 0 1 / s, where η(A) is the viscosity at 10 0 1 / s in Flow Ramp 1, and η(B) is the viscosity at 10 0 1 / s in Flow Ramp 2.

Equation

[0139] H. Method for determining the H-B velocity index of the aqueous seal composition.

[0140] To explain the rheological behavior of the aqueous seal composition, the H-B velocity index (or Herschel-Bulkley velocity index) was also used. The shear stress of the aqueous seal composition was determined for shear rates from 0 to 600 1 / s. The Herschel-Bulkley parameters were fitted to the data and calculated using the Herschel-Bulkley equation σ = σ y +Kγ n (where σ is the shear stress, K is the consistency coefficient (viscosity), γ is the shear rate, n is the H-B velocity index, and σ y is the yield stress). The H-B velocity index n quantifies the fluid behavior of the seal fluid. When n < 1, the fluid has a shearing behavior. When n > 1, the fluid has a shearing thinning behavior. When n = 1 and the yield stress (σ y) If it is equal to 0, the fluid is a Newtonian fluid. HASE rheology modifiers (Solthix™ A100 and Rheovis® HS1212) have an H-B velocity index lower than that of ASE rheology modifiers (Rheovis® AS1130) and HEUR rheology modifiers (Rheovis® PU 1191, ACRYSOL™ RM-8W, OPTIFLO® 3300). It has been observed that aqueous sealant compositions containing ASE and HEUR rheology modifiers have improved coating quality (fewer defects).

[0141] I. Method for the viscosity ratio of an aqueous sealant composition.

[0142] The viscosity ratio of the aqueous sealant composition was determined by using a rheometer of the HR30 Discovery series manufactured by TA Instruments and a parallel plate sensor having a diameter of 40.0 mm and a geometry gap of 1000.0 μm, and maintaining the Peltier plate at a temperature of 25 °C to obtain the rheology profile of each aqueous sealant composition. The viscosity of the aqueous sealant composition was measured by using a flow ramp in the shear rate range of 10 -4 Hz to 1000 Hz, and obtaining 2 points every 10. -3 The viscosity ratio is calculated as the ratio of the low shear viscosity (at 10 3 1 / s) to the high shear viscosity (at 10 -3 1 / s). That is, the equation viscosity ratio = η(L) / η(H) is used, where η(L) is the viscosity at a shear rate of 10 3 1 / s, and η(H) was the viscosity at a shear rate of 10

[0143] J. Method for determining the coating quality of a seal film.

[0144] A front plane laminate containing a microcell layer filled with an electrophoresis medium was coated with an aqueous seal composition. The resulting panel was cut into panels having a length of approximately 32 inches, and the quality of the coating was inspected. The panel was placed on the surface under a fluorescent lamp (a 5000K fluorescent bulb), and the seal film was visually inspected. The quality of the coating was determined based on four different quality defects such as poor wetting, peeling, chattering, and clouding spot mura (CSM). Each of the seal films was graded based on a ranking system for each quality defect. Specifically, the defects were graded on a scale of 0 to 3, where 0 indicates no defect and 3 indicates the one containing the highest level of defect. That is, the larger the number, the worse the quality. FIG. 11 shows an example of a seal film corresponding to the poor wetting ranking system. FIG. 12 shows an example of a seal film corresponding to the peeling ranking system. FIG. 13 shows an example of a seal film corresponding to the chattering ranking system. FIG. 14 shows an example of a seal film corresponding to the clouding spot mura ranking system.

[0145] Poor wetting occurs when the seal fluid evaporates from the filled microcell layer before drying is complete, leaving one or more spots where the seal fluid has been lost. Seal films with more spots of poor wetting were given a higher poor wetting grade. A seal film with 1 to 2 spots was given a grade of 1, a seal film with 3 to 5 spots was given a grade of 2, and a seal film with 6 or more spots was given a grade of 3.

[0146] Peeling occurs when the dried seal film separates / peels off from the filled microcell. A panel with 2 to 5 small-sized spots (less than 0.25 cm) was given a grade of 1, a panel with 5 to 10 small or medium-sized spots (less than 1.25 cm) was given a grade of 2, and a seal film with large spots (more than 1.25 cm) or spots over the entire surface thereof was given a grade of 3.

[0147] Chattering draws vertical lines across the entire panel. If there are faint lines that are only visible with light reflection at a specific angle, a Grade 1 was assigned. If the lines are easily visible at all angles, a Grade 2 was assigned. If the lines are thick and prominent, a Grade 3 was assigned.

[0148] Cloudy spot mottling (CSM) is used to describe circular spots that often exist on the surface of the seal film. The size, shape, and thickness of CSM vary depending on many factors including, but not limited to, seal formulation, electrophoretic medium, and coating parameters. CSMs without a nucleation spot (small dark center point) in the center and that are bright and / or small in size (less than 0.25 cm) were assigned a Grade 1. If nucleation is visible in the CSM, a Grade 2 was assigned. If the CSM is extremely thick and / or large in size (greater than 1 cm) in addition to having nucleation, a Grade 3 was assigned.

[0149] Evaluation Results

[0150] Unless otherwise stated, the amounts of components in the disclosed compositions in the following table are provided as weight percentages of the components relative to the weight of the composition excluding water. In some compositions, the term Q.S. (quantity sufficient) is used to represent the content of the water carrier. This term means that the content of water in the composition is the amount necessary to achieve and not exceed 100% of the total composition.

[0151] If any water or moisture remains in or is absorbed by the seal film, the disclosed contents of the components of the seal film are calculated as weight % of the components relative to the weight excluding the remaining or absorbed water, unless otherwise stated.

[0152] The compositions of the examples having numbers ending with the letter F correspond to the seal film compositions, while the rest of the compositions of the examples correspond to the aqueous seal compositions. The examples of the seal film compositions correspond to the same example numbers (having the suffix F) as the aqueous seal compositions used to prepare the seal film compositions. Thus, Example 1F (seal film composition) is prepared from Example 1 (aqueous seal composition).

[0153]

Table 1A

[0154]

Table 1B

[10] Optiflo (registered trademark) 3300 supplied by Byk

[11] Silwet (registered trademark) L-7607 copolymer supplied by Momentive

[0155]

Table 2A

[0156]

Table 2B

[10] Optiflo® 3300 supplied by Byk

[11] Silwet® L-7607 copolymer supplied by Momentive

[0157] Table 2B shows that an aqueous seal composition containing a HEUR rheology modifier, such as Optiflo® 3300, improves the coating quality of the corresponding seal film compared to an aqueous seal composition containing a HASE rheology modifier, such as Solthix™ A-1000. This can be demonstrated by the higher grades of the corresponding clouding spot mottle (CSM), wetting failure, and chattering observed (comparison of Example 4, Example 7, and Example 8 with Comparative Example 5 and Comparative Example 9). The rheological characteristics of the aqueous seal composition containing the HEUR rheology modifier are clearly different from those of the aqueous seal composition containing the HASE rheology modifier. Specifically, the improved seal film is formed from an aqueous seal composition in which (a) the H-B speed index is 0.7 or higher, or 0.7 - 1 or 0.7 - 0.9 or 0.7 - 2, (b) the viscosity ratio is 7 or less, or 1 - 7 or 2 - 7 or 0.5 - 7, and (c) the thixotropy index is 1.5 and higher, or between 1.5 - 3. Similarly, an aqueous seal composition containing an ASE rheology modifier (Example 1) exhibits similar rheological characteristics and provides a seal film with good coating quality. Further, when the image resolution is measured at 50 °C, it is observed that the image resolution of a display device having a seal film formed by an aqueous seal composition containing a HEUR rheology modifier is better than that of a display device having a seal film formed by an aqueous seal composition containing a HASE rheology modifier.

[0158]

Table 2C-1

Table 2C-2

[0159]

Table 2D-1

Table 2D-2

[10] Optiflo (registered trademark) 3300 supplied by Byk

[11] Silwet (registered trademark) L-7607 copolymer supplied by Momentive

[12] Capstone (trademark) FS-31 supplied by The Chemours Company

[13] Capstone (trademark) FS-3100 supplied by The Chemours Company

[0160] Tables 2C and 2D disclose compositions containing a rheology modifier (Solthix™ A-100) and various different surfactants such as siloxane and fluorosurfactants. In the case of siloxane-based surfactants, it was observed that changes in the surfactant content of the formulation resulted in significant changes in the viscosity of the aqueous seal composition (see Examples 12 and 13). In contrast, the viscosity of the aqueous composition containing fluorosurfactants changes relatively little with changes in the surfactant content (see Examples 10 and 12). This phenomenon is not trivial as the surfactant enables adjustment of the surface energy of the aqueous seal composition on the microcell layer, which in turn affects the quality of the resulting seal film coating. Therefore, the aqueous seal composition can be adjusted using different surfactant contents to achieve good coating quality, improve wettability, and minimize coating defects for various microcell layers. Different surfactants interact differently from the rheology modifier of the aqueous composition. As observed when using siloxane surfactants, when there is a strong interaction between the surfactant and the rheology modifier, small changes in the surfactant content significantly change the coatability and rheology profile, increasing the sensitivity to the operable formulation window. That is, when the surfactant interacts strongly with the rheology modifier, it becomes impossible to select a high content of surfactant to effectively control the surface energy and wettability of the aqueous seal composition. The inventors have surprisingly found that aqueous seal compositions containing fluorosurfactants show little change in their viscosity with changes in the surfactant content. Therefore, the use of fluorosurfactants enables easier optimization of the rheology profile and optimal coating quality.

[0161] Table 3 contains surface energy data for various types of Polymer 1, which is a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, and various types of Polymer 2, which is a polyurethane. This also includes the calculated interface evaluations of the barrier properties of various layers and combinations of various polymers. The method for preparing the corresponding polymer layers used to evaluate the barrier properties is described in I above. The determination of surface energy (according to the method described in E above) was carried out by first preparing and conditioning a seal film from the corresponding aqueous composition containing only one polymer. The interfacial tension for each combination of polymers was calculated from the surface energy data and the calculation method described in H above.

[0162]

Table 3-1

Table 3-2

[0163]

Table 4

[0164] The interfacial tension data of Polymer 1 and Polymer 2 in Table 3 show that a seal film containing (a) a poly(vinyl alcohol) polymer or poly(vinyl alcohol-co-ethylene) copolymer having a degree of hydrolysis of 90% to 99.5% and an ethylene content of less than 10%, and (b) a polyurethane in an aqueous carrier, with an interfacial tension between the two polymers (a) and (b) of less than 2 mN / m, forms a seal film having good barrier properties against non-polar fluids.

[0165] Also, the data in Table 3 show that a seal film made from an aqueous polymer composition containing (a) a poly(vinyl alcohol) polymer or poly(vinyl alcohol-co-ethylene) copolymer having a degree of hydrolysis of 90 to 99.5% and an ethylene content of less than 10%, and (b) a polyurethane in an aqueous carrier, wherein the polar component of the surface energy of the polyurethane is between 10 and 25 mN / m, forms a seal film having good barrier properties against non-polar fluids.

[0166] Microscopic evaluation of polymer films prepared from four aqueous seal compositions prepared by the method described in B1 above showed a correlation between film uniformity and the interfacial tension between the two polymers. The microscopic images in Table 5 and Figure 15 show that the lower the interfacial tension, the more uniform the polymer film provided. The improved compatibility achieved by combinations of polymers having lower interfacial tensions may explain the improved barrier properties of the corresponding layers.

[0167]

Table 5

[0168] Furthermore, during the study, it was observed that an aqueous seal composition containing more than 70% by weight of a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer relative to the weight of the aqueous seal composition excluding water forms a seal film that absorbs a significant amount of moisture from the environment. This high moisture absorption has a negative impact on the electro-optical performance of the display.

Claims

1. A seal film comprising: 15 to 60% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer based on the weight of the seal film, wherein the poly(vinyl alcohol) homopolymer has a degree of hydrolysis of 90% to 99.5%, and the poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90% to 99.5% and an ethylene content of less than 10%, a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer; 7 to 29% by weight of polyurethane based on the weight of the seal film; 0.05 to 10% by weight of a rheology modifier based on the weight of the seal film, wherein the rheology modifier is selected from the group consisting of a hydrophobic modified ethoxylated urethane and an alkali-swellable emulsion polymer, a rheology modifier; A seal film containing the above components.

2. The seal film according to claim 1, further comprising 0.01 to 5% by weight of a surfactant based on the weight of the seal film.

3. The seal film according to claim 2, wherein the surfactant is a fluorine-based surfactant.

4. The seal film according to claim 1, further comprising 5 to 70% by weight of carbon black based on the weight of the seal film.

5. The seal film according to claim 1, further comprising 4.5 to 25 wt% of a water-soluble ether based on the weight of the seal film, wherein the water-soluble ether has a molecular weight of 75 to 5,000 daltons and optionally contains a hydroxyl group.

6. The seal film according to claim 1, wherein the total surface energy of the seal film is lower than 60 mN / m.

7. The seal film according to claim 1, wherein the interfacial tension between the water-soluble poly(vinyl alcohol) polymer or poly(vinyl alcohol-co-ethylene) copolymer and the polyurethane is less than 2 mN / m.

8. An electro-optical device comprising: A conductive layer; A microcell layer containing a plurality of microcells, each microcell having an opening and each microcell containing an electrophoretic medium, the electrophoretic medium containing charged particles in a non-polar carrier, a microcell layer; The seal film according to claim 1, which extends across the opening of each microcell, an adhesive layer, an electrode layer An electro-optical device comprising.

9. An aqueous seal composition, 15 to 60% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer based on the weight of the aqueous seal composition excluding water, wherein the poly(vinyl alcohol) homopolymer has a degree of hydrolysis of 90% to 99.5%, and the poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90% to 99.5% and an ethylene content of less than 10%, a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, 7 to 29% by weight of polyurethane based on the weight of the aqueous seal composition excluding water, 0.05 to 10% by weight of a rheology modifier based on the weight of the aqueous seal composition excluding water, wherein the rheology modifier is selected from the group consisting of a hydrophobically modified ethoxylated urethane and a hydrophobically modified alkali-swellable emulsion polymer, a rheology modifier, 0.01 to 5% by weight of a surfactant based on the weight of the aqueous seal composition excluding water, 20 to 95% by weight of water based on the weight of the aqueous seal composition An aqueous seal composition comprising.

10. The aqueous seal composition according to claim 9, wherein the surfactant is a fluorine-based surfactant.

11. The aqueous seal composition according to claim 9, further comprising 5 to 70% by weight of carbon black based on the weight of the aqueous seal composition excluding water.

12. The aqueous seal composition according to claim 9, further comprising 1.0 to 40% by weight of a water-soluble ether based on the weight of the aqueous seal composition excluding water, wherein the water-soluble ether has a molecular weight of 75 to 5,000 daltons and optionally contains a hydroxyl group, an aqueous seal composition.

13. The aqueous seal composition according to claim 9, further comprising 0.1 to 8% by weight of a polyurethane crosslinking agent based on the weight of the aqueous seal composition excluding water.

14. The aqueous seal composition according to claim 13, wherein the polyurethane crosslinking agent is a polyisocyanate, a polyfunctional polycarbodiimide, a polyfunctional aziridine, a silane coupling agent, a boron / titanium / zirconium-based crosslinking agent, or a melamine formaldehyde.

15. 10 －４ The 10 of the aqueous seal composition at a shear rate of 1 / second ２ The aqueous seal composition according to claim 9, wherein the viscosity ratio obtained by dividing the viscosity of the aqueous seal composition at a shear rate of 1 / second is 7 or less.

16. 10 －４ 10 of the aqueous seal composition at a shear rate of 1 / second ２ The aqueous seal composition according to claim 9, wherein the viscosity ratio obtained by dividing the viscosity of the aqueous seal composition at a shear rate of 1 / second by the viscosity is 1 to 7.

17. The aqueous seal composition according to claim 9, having an H-B speed index of 0.7 or higher.

18. The aqueous seal composition according to claim 9, having an H-B speed index of 0.7 to 1.

19. The aqueous seal composition according to claim 9, having a thixotropy index of 1.5 or higher.

20. The aqueous seal composition according to claim 9, having a thixotropy index of 1.5 to 3.

Images