Sealing layer comprising electrically conductive filler for sealing microcells of electrophoretic displays

Abstract

The present invention relates to a sealing layer comprising a poly(vinyl alcohol) homopolymer or a poly(vinyl alcohol-co-ethylene) copolymer, a polyurethane and an electrically conductive filler. The sealing layer shows good barrier properties against non-polar fluids. The sealing layer can be used to seal micro-cells of electro-optical devices, contributing to improved good electro-optical performance of the devices, especially at low temperatures.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 145,582, filed February 4, 2021. The entire contents of any patent, published application, or other published work referenced herein are incorporated herein by reference. Invention Field

[0003] This invention relates to an aqueous polymer composition comprising conductive fillers and a sealing layer. The aqueous polymer composition can be used to form a sealing layer for sealing micro-units of electro-optic devices, such as electrophoretic displays. Background of the Invention

[0005] When applied to materials or displays, the term "electro-optic" is used herein in its conventional sense in the field of imaging to refer to a material having a first display state and a second display state that differ in at least one optical property, which changes from the first display state to the second display state by applying an electric field to the material. While this optical property is generally color perceptible to the human eye, it can be another optical property, such as optical transmission, reflection, emission, or, in the case of a display intended for machine reading, pseudo-color in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible range.

[0006] The terms “bistable” and “bistable” are used herein in their conventional sense in the art to refer to a display comprising display elements having a first display state and a second display state that differ in at least one optical property, such that after any given element has been driven to present its first or second display state by means of an addressing pulse of finite duration, the state will persist for at least several times, for example, at least four times, the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse terminates. U.S. Patent No. 7,170,670 shows some particle-based electrophoretic displays with grayscale capability that are stable not only in their extreme black and white states but also in their intermediate gray states, and similarly, some other types of electro-optical devices. This type of display is appropriately referred to as “multistable” rather than bistable; however, for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0007] One type of electro-optic device that has been the subject of intensive research and development for several years is the particle-based electrophoretic display, in which multiple charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays, electrophoretic displays can offer advantages such as good brightness and contrast, wide viewing angle, bistable state, and low power consumption.

[0008] Numerous patents and applications assigned to, or registered in the name of, MIT, E Ink Corporation, E Ink California, LLC and related companies, describe various techniques for encapsulating and micro-unit electrophoretic media and other electro-optic media. Encapsulated electrophoretic media comprise numerous microcapsules, each microcapsule itself comprising an inner phase and a capsule wall surrounding the inner phase, the inner phase containing particles that electrophoretically move in a fluid medium. Typically, the capsules themselves are held within a polymer binder to form a coherent layer located between two electrodes. In micro-unit electrophoretic displays, charged particles and fluid are not encapsulated within microcapsules, but rather retained within multiple cavities formed within a carrier medium, typically a polymer film.

[0009] The technologies described in these patents and applications include:

[0010] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patents 7,002,728 and 7,679,814;

[0011] (b) Encapsulation, adhesives, and encapsulation methods; see, for example, U.S. Patents 6,922,276 and 7,411,719;

[0012] (c) Microunit structures, wall materials, and methods of forming microunits; see, for example, U.S. Patents 7,072,095 and 9,279,906;

[0013] (d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942; 7,005,468; and 7,715,088; and U.S. Patent Application Publications Nos. 2004-0120024 and 2004-0219306;

[0014] (e) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patents 6,982,178 and 7,839,564;

[0015] (f) Backplane, adhesive layer and other auxiliary layers and methods for display; see, for example, U.S. Patents 7,116,318 and 7,535,624;

[0016] (g) Color formation and color adjustment; see, for example, U.S. Patents 7,075,502 and 7,839,564;

[0017] (h) A method for driving a display; see, for example, U.S. Patents 7,012,600 and 7,453,445;

[0018] (i) Applications of displays; see, for example, U.S. Patents 7,312,784 and 8,009,348; and

[0019] (j) Non-electrophoretic displays; as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160; and applications of packaging and microcell technologies other than displays; see, for example, U.S. Patent No. 7,615,325; and U.S. Patent Application Publications Nos. 2015 / 0005720 and 2016 / 0012710.

[0020] The contents of all the above references are incorporated herein by reference in their entirety.

[0021] Structures with multiple sealed microcells are commercially used in electrophoretic displays, where the sealed microcells comprise a dispersion of charged pigment particles in a nonpolar fluid. Microcells are also referred to in the literature as microcavities or microcups. A general process for fabricating a sealed microcell structure for an electrophoretic display includes (a) fabricating a polymer sheet with multiple microcavities via microimprinting, each microcavity having an opening, (b) filling the microcavities with an electrophoretic medium, which is a dispersion of charged pigment particles contained in a nonpolar fluid, and (c) sealing the microcavities with an aqueous polymer composition to form a sealing layer. The sealed microcavities containing the electrophoretic medium form an electro-optic material layer for the device. The electro-optic material layer is disposed between a front electrode and a rear electrode. An electric field is applied across the electrophoretic medium via these electrodes, causing pigment particles to migrate through the electrophoretic medium, producing an image. The sealing layer plays a crucial role in the function and performance of the device.

[0022] First, since the sealing layer contacts the electrophoretic medium and seals it within the microcavity, (1) it must be a non-polar fluid that is almost insoluble in the electrophoretic medium, and (2) it must be a good barrier to the non-polar fluid so that the non-polar fluid does not diffuse out of the microcell during the lifetime of the device.

[0023] Secondly, the sealing layer must not absorb large amounts of moisture from the environment. That is, it must prevent ambient moisture from entering the electrophoretic medium of the device; such moisture would negatively affect the electro-optic performance of the device.

[0024] Finally, it is crucial that the sealing layer of the electrophoretic display possesses good electrical properties. The electric field applied across the electrophoretic medium for the operation of the display permeates through the sealing layer.

[0025] Therefore, the barrier properties, moisture absorption, and electrical properties of the sealing layer have a significant impact on the electro-optic performance of the display. Poor properties lead to performance degradation. Providing a sealing layer with properties that achieve good electro-optic performance is technically challenging because different objectives may require different formulation strategies. For example, the barrier properties of non-polar fluids generally require more hydrophilic components, which absorb more moisture from the environment. Furthermore, sealing layers with high resistivity require higher power consumption for display operation, while sealing layers with low resistivity result in poor image resolution. Therefore, there is a need for polymer compositions that form optimized sealing layers for improved barrier properties against non-polar fluids, reduced moisture absorption, and optimal resistivity. The inventors of this invention have discovered that aqueous polymer compositions comprising poly(vinyl alcohol) homopolymers or poly(vinyl alcohol-co-ethylene) copolymers, polyurethane, and conductive fillers form sealing layers with a specific range of surface energies, achieving excellent electro-optic performance. Invention Overview

[0027] On one hand, the present invention relates to a sealing layer comprising: (i) 30 to 70% by weight, of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, excluding solvent, wherein the poly(vinyl alcohol) has a degree of hydrolysis of 90 to 99.9%, and the poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90 to 99.9% and an ethylene content of less than 10%; (ii) 7 to 29% by weight, of a polyurethane, excluding solvent; and (iii) 1 to 45% by weight, of a conductive filler, excluding solvent, selected from carbon black, graphene, graphite, and carbon nanotubes, wherein the conductive filler has a total surface energy greater than 40 mN / m as determined by the Washburn method using hexane as the test liquid. The conductive filler also has a dispersive component of its surface energy. The dispersive component of the surface energy of the conductive filler, determined by the Washburn method using hexane as the test liquid, can be greater than 15 mN / m.

[0028] The sealing layer has a total surface energy greater than 55 mN / m. The total surface energy of the sealing layer is determined using the contact angle method by the following steps: (a) forming the sealing layer by coating an aqueous polymer composition on a substrate to a dry thickness of 30 mm, heating it at 100°C for 15 minutes, and conditioning it at 25°C and 55% relative humidity for 24 hours; (b) measuring the contact angles of water droplets and diiodomethane droplets on the formed sealing layer; and (c) calculating the total surface energy using the OWRK model.

[0029] The sealing layer may have a dispersive component of surface energy, which may be higher than 40 mN / m. The dispersive component of the surface energy of the sealing layer is determined using the contact angle method by the following steps: (a) forming the sealing layer by coating an aqueous polymer composition on a substrate with a dry thickness of 30 mm, heating it at 100°C for 15 minutes, and conditioning it at 25°C and 55% relative humidity for 24 hours; (b) measuring the contact angles of water droplets and diiodomethane droplets on the formed sealing layer; and (c) calculating the dispersive component of the surface energy using the OWRK model.

[0030] The sealing layer is formed of an aqueous polymer composition. The aqueous polymer composition comprises: (i) 30 to 70% by weight, based on the weight of the sealing layer excluding solvent, a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, wherein the poly(vinyl alcohol) has a degree of hydrolysis of 90 to 99.9%, and the poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90 to 99.9% and an ethylene content of less than 10%; (ii) 7 to 29% by weight, based on the weight of the sealing layer excluding solvent, a polyurethane; and (iii) 1 to 45% by weight, based on the weight of the sealing layer excluding solvent, a conductive filler selected from carbon black, graphene, graphite, and carbon nanotubes, wherein the conductive filler has a total surface energy greater than 40 mN / m as determined by the Washburn method using hexane as the test liquid. The conductive filler has a dispersive component of surface energy. The dispersive component of the surface energy of the conductive filler, determined by the Washburn method using hexane as the test liquid, can be greater than 15 mN / m. The sealing layer has a total surface energy greater than 55 mN / m. The total surface energy of the sealing layer is determined using a contact angle method through the following steps: (a) forming the sealing layer by coating an aqueous polymer composition to a substrate at a dry thickness of 30 mm, heating at 100°C for 15 minutes, and conditioning the sealing layer at 25°C and 55% relative humidity for 24 hours; (b) measuring the contact angles of water droplets and diiodomethane droplets on the formed sealing layer; and (c) calculating the total surface energy using an OWRK model. The sealing layer has a dispersive component of surface energy, which can be greater than 40 mN / m. The dispersive component of the surface energy of the sealing layer is determined using a contact angle method.

[0031] The polyurethane in the sealing layer can be crosslinked using a crosslinking agent. The crosslinking agent can be a polyisocyanate, a polyfunctional polycarbodiimide, a polyfunctional aziridine, a silane coupling agent, a boron / titanium / zirconium-based crosslinking agent, or melamine-formaldehyde. The polyurethane in the sealing layer can have a number average molecular weight of 1,000 to 2,000,000 Daltons.

[0032] The polyurethane of the sealing layer has a polar component of surface energy. The polar component of the surface energy of the polyurethane can be from 10 mN / m to 20 mN / m. The polar component of the surface energy of the polyurethane is determined on the polyurethane film using a contact angle method. The contact angle method includes the following steps: (a) forming a polyurethane film by coating an aqueous polyurethane composition onto a substrate with a dry thickness of 30 mm, heating at 100°C for 15 minutes, and conditioning the polyurethane film at 25°C and 55% relative humidity for 24 hours; (b) measuring the contact angles of water droplets and diiodomethane droplets on the formed polyurethane film; and (c) calculating the polar component of the surface energy of the polyurethane using an OWRK model.

[0033] The sealing layer may include a wetting agent. The wetting agent may be an organosilicon surface tension reducer.

[0034] The conductive filler for the sealing layer can be carbon black. The carbon black can have an oil absorption value of less than 100 mL per 100 mg carbon black, measured according to the oil absorption value method of ASTM 2414. The carbon black can have an average particle size greater than 20 nm, measured according to the electron microscopy method of ASTM D3849. The carbon black can have an average particle size of less than 90 nm, measured according to the nitrogen adsorption method of ASTM D6556. 2 The specific surface area is [value missing] / g. Measured by the nitrogen adsorption method according to ASTM D6556, carbon black can have a specific surface area of ​​less than 200 m² / g. 2 The specific surface area per g, and the volatile matter content of carbon black, as measured according to DIN 53552, can be higher than 5%.

[0035] The poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer of the sealing layer may have a number average molecular weight of 1,000 to 1,000,000 Daltons. The poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer of the sealing layer may have a degree of hydrolysis of 92% to 99%. The poly(vinyl alcohol-co-ethylene) copolymer of the sealing layer may have an ethylene content of less than 9%.

[0036] A sealing layer can be used to seal microcells of an electrophoretic display. The electrophoretic display may include: a first transparent electrode layer; an electro-optic material layer comprising a plurality of microcells and the sealing layer, wherein each of the plurality of microcells includes a bottom, a wall, and an opening, and contains an electrophoretic medium comprising at least one type of charged pigment particles dispersed in a nonpolar fluid, and wherein the sealing layer spans the openings of the plurality of microcells; a second electrode layer; wherein the electro-optic material layer is disposed between the first transparent electrode layer and the second electrode layer. The sealing layer may be formed from an aqueous polymer composition.

[0037] On the other hand, the present invention provides a sealing layer comprising: (i) 30 to 70 wt% of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, excluding solvent, wherein the poly(vinyl alcohol) has a degree of hydrolysis of 90 to 99.9% and the poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 90 to 99.9% and an ethylene content of less than 10%; (ii) 7 to 29 wt% of a polyurethane, excluding solvent, having a total surface energy greater than 50 mN / m, the total surface energy of which is determined on a polyurethane film using a contact angle method; and (iii) 1 to 45 wt% of a conductive filler, selected from carbon black, graphene, graphite, and carbon nanotubes, having a total surface energy greater than 40 mN / m, the total surface energy being determined by the Washburn method using hexane as the test liquid. The sealing layer has a total surface energy. The total surface energy of the sealing layer can be higher than 55 mN / m. The total surface energy of the sealing layer is determined using a contact angle method. This contact angle method includes the following steps: (a) forming a polyurethane film by coating an aqueous polyurethane composition onto a substrate with a dry thickness of 30 mm, heating at 100°C for 15 minutes, and conditioning the sealing layer at 25°C and 55% relative humidity for 24 hours; (b) measuring the contact angles of water droplets and diiodomethane droplets on the formed polyurethane film; and (c) calculating the total surface energy of the polyurethane using an OWRK model. The sealing layer can have a dispersive component of its surface energy, which is higher than 40 mN / m. The dispersive component of the surface energy of the sealing layer is determined using a contact angle method.

[0038] A sealing layer can also be used to seal the microcells of a front-plane laminate. The front-plane laminate may include a first transparent electrode layer, an electro-optic material layer, an adhesive layer, and a release sheet. An electrophoretic display may include a first transparent electrode layer, an electro-optic material layer, and a second electrode layer. The electro-optic material layer is disposed between the first transparent electrode layer and the second electrode layer. The electro-optic material layer includes a plurality of microcells and a sealing layer. The sealing layer may be formed from an aqueous polymer composition. Each of the plurality of microcells includes a bottom, a wall, and an opening, and contains an electrophoretic medium, wherein the electrophoretic medium contains at least one type of charged pigment particles dispersed in a nonpolar fluid. The sealing layer spans the openings of the plurality of microcells.

[0039] A sealing layer can also be used to seal microcells of a dual-release sheet. The dual-release sheet may include a first release sheet, a first adhesive layer, an electro-optic material layer, a second adhesive layer, and a second release sheet. The electro-optic material layer may include multiple microcells and the sealing layer. The sealing layer may be formed from an aqueous polymer composition. Each of the multiple microcells includes a bottom, walls, and an opening, and contains an electrophoretic medium comprising at least one type of charged pigment particles dispersed in a nonpolar fluid. The sealing layer spans the openings of the multiple microcells. Brief description of the attached diagram

[0041] Figure 1 The illustration shows the structure of multiple micro-units before they are filled and sealed.

[0042] Figure 2 The illustrations show examples of electro-optic devices with micro-unit structures.

[0043] Figure 3 The illustration shows an example of a front-plane laminate assembly that can be used to form an electro-optic device including a micro-unit structure.

[0044] Figure 4 The illustration shows an example of a dual-release sheet that can be used to form an electro-optic device including a micro-unit structure.

[0045] Figure 5 This demonstrates a method for manufacturing micro-units using a roll-to-roll method.

[0046] Figure 6A and 6B The paper details the fabrication of microcells using photolithography through a photomask coated with a conductive film of a thermosetting precursor.

[0047] Figure 6C and 6D This section details alternative implementation schemes that utilize photolithography for manufacturing. Figure 6C and 6D In this process, a combination of top and bottom exposures is used, which allows one wall in the lateral direction to be cured by exposure through the top photomask and another wall in the lateral direction to be cured by exposure through the bottom of the opaque substrate conductor film.

[0048] Figures 7A-7D The illustration shows the steps involved in filling and sealing the microcell array.

[0049] Figure 8A and 8B The diagram illustrates the structure of an electro-optic device used to evaluate the barrier properties and electro-optic performance of the sealing layer embodiments.

[0050] Figures 9A-9F The diagram illustrates waveforms used to evaluate the electro-optic performance of the device in the embodiment.

[0051] Figure 10A-10D Microscopic images showing the micro-units whose barrier properties are being evaluated.

[0052] Figure 11 The viscosity distribution of the aqueous polymer composition is shown at various shear rates.

[0053] Figure 12 Microscopic images showing polymer films comprising a combination of poly(vinyl alcohol-co-ethylene) copolymers and polyurethanes with different interfacial tensions. Invention Details

[0055] When referring to the weight of the sealing layer or the weight of the aqueous polymer composition of the present invention, the term "excluding solvents" means that the weight of the sealing layer or the weight of the aqueous polymer composition does not include water and other solvents that may be present in the sealing layer or the aqueous polymer composition.

[0056] Unless otherwise stated, the terms “molecular weight” or “MW” used herein refer to exponential molecular weight. Number-average molecular weight can be measured by gel permeation chromatography.

[0057] A. Structure of micro-units

[0058] Figure 1 The illustration shows the structure of multiple micro-units 100 before they are filled and sealed. Each micro-unit includes a bottom 101, a wall 102, and an opening 103.

[0059] B. Structure of electro-optic devices containing micro-unit structures

[0060] Figure 2 The illustration shows an example of an electro-optic device 200 including a micro-unit structure 220. This example of the electro-optic device 200 includes a first transparent electrode layer 210, a micro-unit layer 220, a sealing layer 230, an adhesive layer 240, and a second electrode layer 250. The micro-unit layer includes a plurality of micro-units defined by a bottom 221 and walls 222. Each of the plurality of micro-units contains an electrophoretic medium 225 containing charged particles in a nonpolar fluid. The micro-units are sealed with the sealing layer 230, which spans the openings of the plurality of micro-units. The second electrode layer 250 is connected to the sealing layer 230 with the adhesive layer 240. The plurality of micro-units and the sealing layer constitute an electro-optic material layer of the electro-optic device 200. An electric field source (not shown) may be connected to the first transparent electrode layer 210 and the second electrode layer 250. An electric field is applied across the electro-optic material layer, causing charged particles to migrate through the electrophoretic medium, producing an image that can be observed by an observer from the viewing side 210 of the electro-optic device 200. Optional grassroots ( Figure 2 (Not shown in the image) can be disposed between the first light-transmitting electrode layer 210 and multiple micro-units 230.

[0061] Figure 2 Examples of electro-optical devices illustrated in the diagram can be derived from... Figure 3 The front panel laminate 300 shown in the image is constructed. The front panel laminate 300 includes a first light-transmitting electrode layer 310, a plurality of microcells 320, a sealing layer 330, an adhesive layer 340, and a release sheet 360. Each of the plurality of microcells contains an electrophoretic medium 325, which contains charged particles in a non-polar fluid. The microcells are sealed by the sealing layer 330, which spans the openings of the plurality of microcells. The release sheet 360 is connected to the sealing layer 330 via the adhesive layer 340. Removing the release sheet 360 exposes the surface of the adhesive layer 340, which can then be attached to a second electrode layer to form an electro-optic device. Optional base layer ( Figure 3 (Not shown in the image) can be disposed between the first light-transmitting electrode layer 310 and multiple micro-units 330.

[0062] Figure 2 The example of the electro-optical device illustrated can also be derived from... Figure 4 The dual-release sheet 400 shown in the image is constructed. The dual-release sheet 400 includes a first release sheet 480, a first adhesive layer 470, a plurality of microcells 420, a sealing layer 430, a second adhesive layer 440, and a second release sheet 460. Each of the plurality of microcells contains an electrophoretic medium 425, which contains charged particles in a nonpolar fluid. The microcells are sealed with the sealing layer 430, which spans the openings of the plurality of microcells. The first release sheet 480 is attached to the plurality of microcells 420 with the first adhesive layer 470. The second release sheet is attached to the sealing layer 430 with the second adhesive layer 440. Removing the first release sheet 460 exposes the surface of the first adhesive layer 470, which can be attached to a first transparent electrode layer. Removing the second release sheet 460 exposes the surface of the second adhesive layer 440, which can be attached to a second electrode layer to form an electro-optic device. Optional base layer ( Figure 4 (Not shown in the image) can be disposed between the first adhesive layer 470 and the plurality of micro-units 430.

[0063] C. Formation of micro-unit structures

[0064] Techniques for constructing microcells. Microcells can be formed using batch methods or continuous roll-to-roll methods, as disclosed in U.S. Patent No. 6,933,098. The latter provides a continuous, low-cost, high-volume manufacturing technique for producing compartments used in a variety of applications, including beneficial drug delivery and electrophoretic displays. Figure 5As illustrated, the microcell array suitable for use in this invention can be produced using microimprinting. A male die 500 can be placed above or below a screen 504 (not shown); however, alternative arrangements are possible. See, for example, U.S. Patent No. 7,715,088, which is incorporated herein by reference in its entirety. A conductive substrate can be constructed by forming a conductive film 501 on a polymer substrate, which becomes a backing layer of the device. A composition 502 comprising a thermoplastic, thermosetting, or precursor thereof is then coated onto the conductive film. The thermoplastic or thermosetting precursor layer is imprinted by a male die in the form of a roller, plate, or strip at a temperature above the glass transition temperature of the thermoplastic or thermosetting precursor layer.

[0065] Thermoplastic or thermosetting precursors used to prepare microunits can be multifunctional acrylates or methacrylates, vinyl ethers, epoxides and their oligomers or polymers, etc. Combinations of multifunctional epoxides and multifunctional acrylates are also very useful for achieving the desired physicomechanical properties. Crosslinkable oligomers that impart flexibility, such as urethane acrylates or polyester acrylates, can be added to improve the flexural strength of the imprinted microunits. The composition may contain polymers, oligomers, monomers, and additives, or only oligomers, monomers, and additives. The glass transition temperature (or Tg) of such materials... g Typically, the temperature range is from approximately -70°C to approximately 150°C, or from approximately -20°C to approximately 50°C. Microimprinting methods generally operate at temperatures above T... g The process is carried out at a specific temperature. The heated male mold or die pressed against the heated outer substrate can be used to control the temperature and pressure of the microimprinting.

[0066] like Figure 5As shown, the mold is removed during or after the precursor layer curing to expose the array of microcells 503. Curing of the precursor layer can be accomplished by cooling, solvent evaporation, radiation crosslinking, heat, or moisture. If curing of the thermosetting precursor is accomplished by ultraviolet (UV) radiation, UV light can radiate from the bottom or top of the mesh onto the transparent conductor film, as shown in the two figures. Alternatively, a UV lamp can be placed inside the mold. In this case, the mold must be transparent to allow UV light to radiate onto the thermosetting precursor layer through a pre-patterned male mold. The male mold can be prepared by any suitable method, such as diamond turning or photoresist methods, followed by etching or electroplating. The master template for the male mold can be manufactured by any suitable method, such as electroplating. Using electroplating, a thin layer (typically 3000 Å) of a seed metal, such as chrome inconel, is sputtered onto a glass substrate. The mold is then coated with a photoresist layer and exposed to UV light. A mask is placed between the UV light and the photoresist layer. The exposed areas of the photoresist harden. The unexposed areas are then removed by washing with a suitable solvent. The remaining hardened photoresist is dried and sputtered again with a thin layer of seed metal. The master is then ready for electroforming. A typical material for electroforming is nickel-cobalt. Alternatively, the master can be made of nickel by electroforming or electroless nickel deposition. The mold base is typically about 50 to 400 micrometers. The master can also be manufactured using other microengineering techniques, including electron 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 manufactured using plastics, ceramics, or metals via optomechanical processing.

[0067] Before applying the UV-curable resin composition, the mold can be treated with a release agent to aid the demolding process. The UV-curable resin can be degassed before dispensing and may optionally contain a solvent. The solvent (if present) is readily evaporable. The UV-curable resin is dispensed onto the male mold by any suitable method, such as coating, impregnation, casting, etc. The dispenser can be mobile or stationary. The conductor film is covered with the UV-curable resin. If necessary, pressure can be applied to ensure proper bonding between the resin and plastic and to control the thickness of the micro-unit substrate. Pressure can be applied using laminating rollers, vacuum molding, pressure devices, or any other similar means. If the male mold is metallic and opaque, the plastic substrate is generally transparent to the photochemical radiation used to cure the resin. Conversely, the male mold can be transparent, while the plastic substrate can be opaque to photochemical radiation. For good transfer of the molded features onto the transfer sheet, the conductor film needs to have good adhesion to the UV-curable resin, which should have good release properties against the mold surface.

[0068] The microcell arrays used in this invention generally comprise a pre-formed conductive film, such as indium tin oxide (ITO) conductor lines; however, other conductive materials, such as silver or aluminum, can be used. The conductive layer can be supported by or integrated into a substrate such as polyethylene terephthalate, polyethylene naphthalate, polyaramid, polyimide, polycyclic olefin, polysulfone, epoxy resin, and composites thereof. The conductive film can be coated with a radiation-curable polymer precursor layer. The film and precursor layer are then image-exposed to radiation to form a microcell wall structure. After exposure, the precursor material is removed from the unexposed areas, leaving cured microcell walls bonded to the conductive film / support mesh. Image-exposing can be performed by passing ultraviolet light or other forms of radiation through a photomask to produce an image or predetermined pattern of the exposed radiation-curable material coated on the conductive film. Although typically not required, the mask can be positioned and aligned relative to the conductive film, i.e., the ITO lines, such that the transparent mask portion is spatially aligned with the ITO lines, and the opaque mask portion is aligned with the ITO material (intended for use in the microcell base plate region).

[0069] Photolithography. Micro-units can also be fabricated using photolithography. Photolithography methods used to fabricate micro-unit arrays include... Figure 6A The illustration is shown in the diagram. (For example...) Figure 6A and 6B As shown, the micro-unit array 600 can be fabricated by exposing a radiation-curable material 601a, coated onto a conductor electrode film 602 using known methods, to ultraviolet light (or alternatively, other forms of radiation, electron beams, etc.) through a mask 606 to form walls 601b corresponding to an image projected through the mask 606. The substrate conductor film 602 is preferably mounted on a supporting substrate substrate mesh 603, which may include a plastic material.

[0070] exist Figure 6A In the photomask 606, dark squares 604 represent opaque areas of the mask 606, and the spaces between the dark squares represent transparent areas 605 of the mask 606. Ultraviolet light is radiated onto the radiation-curable material 601a through the transparent areas 605. Exposure is preferably performed directly onto the radiation-curable material 601a, i.e., the ultraviolet light does not penetrate the substrate 603 or the substrate conductor 602 (top exposure). Therefore, neither the substrate 603 nor the conductor 602 needs to be transparent to the ultraviolet light or other radiation wavelengths used.

[0071] like Figure 6BAs shown, the exposed area 601b hardens. The unexposed area (protected by the opaque area 604 of the mask 606) is then removed by a suitable solvent or developer to form microunits 607. The solvent or developer is selected from those commonly used to dissolve or reduce the viscosity of radiation-curable materials, such as methyl ethyl ketone (MEK), toluene, acetone, isopropanol, etc. The fabrication of the microunits can be similarly accomplished by placing a photomask under a conductor film / substrate support mesh, in which case ultraviolet light radiates from the bottom through the photomask, and the substrate needs to be radiation-transparent.

[0072] Imaging exposure. Another alternative method for preparing the microcell array of the present invention by imaging exposure is... Figure 6C and 6D The diagram illustrates this. When using opaque conductor lines, the conductor lines can be used as a photomask for bottom-level exposure. Durable microcell walls are formed through additional top-level exposure using a second photomask with opaque lines perpendicular to the conductor lines. Figure 6C The illustration shows the use of top and bottom exposure principles to fabricate the microcell array 610 of the present invention. The substrate conductor film 612 is opaque and line-patterned. A radiation-curable material 611a coated on the substrate conductor 612 and substrate 613 is exposed from the bottom through the conductor line pattern 612, which serves as a first photomask. A second exposure is performed from the "top" side through a second photomask 616 having a line pattern perpendicular to the conductor lines 612. The spaces 615 between the lines 614 are substantially transparent to ultraviolet light. During this process, wall materials 611b are cured from bottom to top in a lateral orientation and from top to bottom in a vertical direction, connecting to form an integral microcell 617. Figure 6D As shown, the unexposed areas are then removed by solvents or developers as described above to expose microunits 617.

[0073] The microunits can be composed of thermoplastic elastomers that are well compatible with the microunits and do 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; and B is butadiene, isoprene, ethylene, propylene, butene, dimethylsiloxane, or propylene sulfide; A and B cannot be the same. The number n ≥ 1, preferably 1-10. Particularly useful are diblock or triblock copolymers of styrene or oxymethylstyrene, 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 / butene-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-propenesulfide-b-α-methylstyrene), and poly(α-methylstyrene-b-dimethylsiloxane-b-α-methylstyrene). Commercially available styrene block copolymers, such as the Kraton D and G series (from 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 (from Exxon Mobil, Houston, Tex.) and its graft copolymers, have also been found to be very useful.

[0074] Thermoplastic elastomers can be dissolved in solvents or solvent mixtures that are immiscible with the carrier in the microunits and exhibit a lower specific gravity than the carrier. Low surface tension solvents are preferred for external coating compositions due to their better wetting properties than the microunit walls and fluids. Solvents or solvent mixtures with a surface tension below 35 dynes / cm are preferred. More preferably, a surface tension below 30 dynes / cm is preferred. Suitable solvents include alkanes (preferably C44). 6-12 Alkanes, such as heptane, octane or Isopar solvent from Exxon Chemical Company, nonane, decane and their isomers), cycloalkanes (preferably C44-2 ... 6-12 Cycloalkanes, such as cyclohexane and naphthane, and alkylbenzenes (preferably mono- or di-C) 1-6 Alkylbenzenes, such as toluene, xylene, etc.), alkyl esters (preferably C450) 2-5 Alkyl esters (such as ethyl acetate, isobutyl acetate, etc.) and C 3-5 Alkyl alcohols (such as isopropanol and their isomers). Mixtures of alkylbenzenes and alkanes are particularly useful.

[0075] In addition to polymer additives, polymer mixtures may also contain wetting agents (surfactants). Wetting agents (such as FC surfactants from 3M Company, Zonyl fluorosurfactants from DuPont, fluoroacrylates, fluoromethacrylates, fluorinated long-chain alcohols, perfluorinated long-chain carboxylic acids and their derivatives, and Silwet silicone surfactants from OSi, Greenwich, and Conn) may also be included in the composition to improve the adhesion of the sealant to the micro-units and provide more flexible coating methods. Other components, including crosslinking agents (e.g., diazidides such as 4,4'-diazidodiphenylmethane and 2,6-di-(4'-azidobenzylmethyl)-4-methylcyclohexanone), vulcanizing agents (e.g., 2-benzothiazolyl disulfide and tetramethylthiuram disulfide), multifunctional monomers or oligomers (e.g., hexanediol, diacrylate, trimethylolpropane, triacrylate, divinylbenzene, diallylphthalene), thermal initiators (e.g., dilauroyl peroxide, benzoyl peroxide), and photoinitiators (e.g., isopropylthioxanthone (ITX), Irgacure 651 and Irgacure 369 from Ciba-Geigy), are also very useful for enhancing the physical-mechanical properties of the sealant through crosslinking or polymerization reactions during or after the external coating process.

[0076] The microcell array 700 can be fabricated using any of the methods described above. For example... Figures 7A-7D As shown in the cross-section, microcell walls 702 extend upward from the backing layer 701 and the conductive layer 710 to form open microcells. In one embodiment, the conductive layer 710 is formed on or at the backing layer 701. Although Figures 7A-7D The conductive layer 710 is shown to be continuous and extends above the backing layer 701, but the conductive layer 710 may also be continuous and extend below or inside the backing layer 701, or be interrupted by the microcell wall 702. Before filling, the microcell array 700 can be cleaned and sterilized to ensure that the beneficial agents are not damaged before use.

[0077] Next, microcells are filled with an electrophoretic medium 725, which contains charged particles in a nonpolar fluid, to form a plurality of filled microcells 770. Various techniques can be used to fill the microcells. In some embodiments, a doctor blade can be used to coat the microcells to a depth of the microcell wall 702. In other embodiments, inkjet microinjection can be used to fill the microcells. In still other embodiments, a microneedle array can be used to fill an array of microcells with the electrophoretic medium 725.

[0078] like Figure 7C As shown, after filling, the microcells are sealed by applying an aqueous polymer composition to form a sealed microcell 780 including a sealing layer 730. In some embodiments, the sealing process may include exposure to heat, dry hot air, or ultraviolet radiation. The sealing layer must have good barrier properties against non-polar fluids of the electrophoretic medium 725.

[0079] In alternative implementations, individual microcells can be filled with a desired mixture using repeated photolithography. This method generally involves coating an empty microcell array with a positive working photoresist layer, selectively opening a number of microcells by imaging the positive photoresist, subsequently developing the photoresist, filling the opened microcells with the desired mixture, and sealing the filled microcells through a sealing process. These steps can be repeated to produce sealed microcells filled with other mixtures. This process enables the formation of large sheets of microcells with a desired mixture ratio or concentration.

[0080] Sealing of the filled microcells can be accomplished in several ways. One method involves mixing an aqueous polymer composition with an electrophoretic medium composition. The aqueous polymer composition may be immiscible with the electrophoretic medium composition, preferably having a lower specific gravity than the electrophoretic medium composition. The two compositions, the aqueous polymer composition and the electrophoretic medium composition, are thoroughly mixed and immediately applied to multiple microcells using precision coating machinery, such as a Meyer bar, gravure printing, a doctor blade, slot coating, or slit coating. Excess fluid is scraped off by a doctor blade or similar device. Residual fluid on the top surface of the microcell partition walls can be cleaned using a small amount of a weak solvent or solvent mixture, such as isopropanol, methanol, or an aqueous solution thereof. The aqueous polymer composition then separates from the electrophoretic medium composition and floats on top of the electrophoretic medium composition. Alternatively, after filling the microcells with the mixture of the electrophoretic medium composition and the aqueous polymer composition, a substrate can be laminated on top to control the mixing of the compositions and promote phase separation of the aqueous polymer composition and the electrophoretic medium composition to form a uniform sealing layer. The substrate used can be a functional substrate in the final structure, or it can be a sacrificial substrate, such as a release substrate, which can be removed later. The sealing layer is then formed by in-situ curing of the aqueous polymer composition (i.e., when in contact with the electrophoretic medium composition). Curing of the aqueous polymer composition can be accomplished by ultraviolet light or other forms of radiation, such as visible light, IR, or electron beams. Alternatively, if a thermosetting or moisture-curable composition is used, heat or moisture can also be used to cure the aqueous polymer composition in place.

[0081] In the second method, the electrophoretic dielectric composition can first be filled into microcells, and then the aqueous polymer composition is externally coated onto the filled microcells. The external coating can be accomplished using conventional coating and printing methods, such as blanket coating, inkjet printing, or other printing methods. In this method, the sealing layer is formed in situ by curing the aqueous polymer composition through solvent evaporation, radiation, heat, moisture, or interfacial reaction. UV curing after interfacial polymerization is beneficial to the sealing process. The formation of a thin barrier layer at the interface through interfacial polymerization significantly suppresses mixing between the electrophoretic dielectric composition and the sealing external coating. Sealing is then completed through a post-curing step, such as UV radiation. The degree of mixing can be further reduced when the specific gravity of the aqueous polymer composition is lower than that of the electrophoretic dielectric composition. Volatile organic solvents can be used to adjust the viscosity and thickness of the sealing external coating. The rheological properties of the aqueous polymer composition can be adjusted to obtain optimal sealing and coatability. When using a volatile solvent in the external coating, it is preferable that it is immiscible with the solvent in the electrophoretic dielectric composition.

[0082] After filling and sealing the microcells, the sealed array can be laminated together with a second electrode layer 750 comprising multiple electrodes. The second electrode layer 750 is attached to the sealing layer 730 to form an electro-optic device 790, such as... Figure 7D As shown. An adhesive can be used to attach the second electrode layer 750 to the sealing layer 730 (the adhesive layer is not on...). Figure 7D (As shown in the image). The adhesive can be conductive. The adhesive layer can be a pressure-sensitive adhesive, a hot-melt adhesive, or an adhesive that can be cured by heat, moisture, or radiation. If the top conductive layer is transparent to radiation, the laminated adhesive can be cured by radiation through the top conductive layer, such as ultraviolet light. In other embodiments, multiple electrodes can be directly bonded to an array of hermetically sealed microcells.

[0083] Typically, micro-units can be of any shape, and their size and shape can vary. Within a system, micro-units can have substantially uniform size and shape. However, micro-units with mixed shapes and sizes are possible. The openings of micro-units can be circular, square, rectangular, hexagonal, or any other shape. The dimensions of the dividing regions between the openings can also vary. The size of each individual micro-unit can be approximately 1 × 10⁻⁶. 1 To approximately 1×10 6 μm 2 or about 1×10 2 To approximately 1×10 6 μm 2 or about 1×10 3 To approximately 1×10 5 μm 2 Within the range.

[0084] The depth of the micro-units can range from about 5 to about 200 μm or from about 10 to about 100 μm. The ratio of openings to total area ranges from about 0.05 to about 0.95 or from about 0.4 to about 0.9.

[0085] Electrophoretic displays typically comprise an electro-optic material layer and at least two other layers disposed on the opposite side of the electro-optic material layer, one of which is an electrode layer. In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define pixels of the display. For example, one electrode layer may be patterned as elongated row electrodes and the other electrode layer may be patterned as elongated column electrodes extending at right angles to the row electrodes, with the intersection of the row and column electrodes defining a pixel. Alternatively and more commonly, one electrode layer has the form of a single continuous electrode and the other electrode layer is patterned as a matrix of pixel electrodes, where each pixel electrode defines a pixel of the display. In another type of electrophoretic display intended for use with styluses, printheads, or similar movable electrodes separate from the display, only one layer of the layers adjacent to the electro-optic material layer includes electrodes, and the layer on the opposite side of the electro-optic material layer is generally a protective layer designed to prevent damage to the electro-optic material layer by the movable electrodes.

[0086] The fabrication of a three-layer electro-optic display typically involves at least one lamination operation. For example, several of the aforementioned MIT and EInk patents and applications describe methods for manufacturing encapsulated electrophoretic displays, wherein an encapsulated electrophoretic medium, contained in an adhesive capsule, is coated onto a flexible substrate comprising an indium tin oxide (ITO) or similar conductive coating on a plastic film. A backplane is prepared separately, comprising a pixel electrode array and suitable conductor arrangements for connecting the pixel electrodes to driving circuitry. To form the final display, a substrate having an electro-optic material layer is laminated to the backplane using a lamination adhesive.

[0087] U.S. Patent No. 6,982,178 describes a method for assembling a solid electrophoretic display, which is well-suited for mass production. Essentially, the patent describes a so-called “front-plane laminate” (“FPL”) comprising, in sequence, a light-transmitting electrode layer; an electro-optic material layer in electrical contact with the light-transmitting electrode layer; an adhesive layer; and a release sheet. Generally, the light-transmitting electrode layer is carried on a light-transmitting substrate, which is preferably flexible, in the sense that the substrate can be manually wrapped around a roller with a diameter of (reportedly) 10 inches (254 mm) without permanent deformation. The term “light-transmitting” in this patent and herein refers to a layer that transmits sufficient light to allow an observer viewing through the layer to observe changes in the display state of the electrophoretic medium, typically through the light-transmitting electrode layer and an adjacent substrate (if present); where the electrophoretic medium exhibits changes in reflectivity at non-visible wavelengths, the term “light-transmitting” should, of course, be interpreted as referring to the transmission at the relevant non-visible wavelengths. The substrate will generally be a polymer film and will typically have 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-transmitting electrode layer is conveniently a thin metal or metal oxide layer, such as an aluminum or ITO layer, or it may be a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, from EI duPont de Nemours & Company, Wilmington DE under the name "aluminized Mylar" ("Mylar" is a registered trademark), and such commercial materials can be used in front-plane laminates with good results. Assembling an electrophoretic display using such a front-plane laminate can be achieved by removing the release sheet from the front-plane laminate and contacting the adhesive layer with the backplate under conditions that effectively adhere the adhesive layer to the backplate, thereby fixing the adhesive layer, electro-optic material layer, and light-transmitting electrode layer to the backplate. This method is well-suited for mass production because front-plane laminates can be mass-produced, typically using a roll-to-roll coating technique, and then cut into sheets of any size required for use with a specific backing.

[0088] U.S. Patent No. 7,561,324 describes a so-called "dual-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 dual-release sheet includes an electro-optic material layer sandwiched between two adhesive layers, wherein one or both adhesive layers are covered by the release sheet. Another form of the dual-release sheet includes a solid electro-optic material layer sandwiched between two release sheets. Both forms of the dual-release film are intended for processes generally similar to those used for assembling electrophoretic displays from the previously described front-plane laminates, but involving two separate lamination processes; generally, in the first lamination, the dual-release sheet is laminated to the front electrode to form the front sub-assembly, and then in the second lamination, the front sub-assembly is laminated to the backplate to form the final display, but the order of these two laminations can be reversed if desired.

[0089] U.S. Patent No. 7,839,564 describes a so-called "inverted front-plane laminate," a variation of the front-plane laminate described in U.S. Patent No. 6,982,178. This inverted front-plane laminate may sequentially include at least one of a light-transmitting protective layer and a light-transmitting electrode layer; an adhesive layer; an electro-optic material layer; and a release sheet. This inverted front-plane laminate is used to form an electrophoretic display having a laminated adhesive layer between the electro-optic material layer and the light-transmitting electrode layer; a second, generally thin adhesive layer may or may not be present between the electro-optic material layer and the backsheet. Such an electrophoretic display can combine good resolution with good low-temperature performance.

[0090] Electrophoretic media

[0091] In the context of this invention, an electrophoretic medium refers to a composition within a microcell. For display applications, the microcell can be filled with at least one type of charged pigment particles in a nonpolar fluid. The electrophoretic medium can contain one type of charged particles or more than one type of particles with different colors, charges, and charge polarities. Under the influence of an electric field applied across the electro-optic material layer, the charged particles move through the electrophoretic medium. The charged particles can be inorganic or organic pigments with polymer surface treatments to improve their stability. The electrophoretic medium can contain pigments having white, black, cyan, magenta, yellow, blue, green, red, and other colors. The electrophoretic medium may also contain charge control agents, charge aids, rheology modifiers, and other additives. Examples of nonpolar fluids include hydrocarbons such as Isopar, decalin, 5-ethylidene-2-norbornene, fatty oils, paraffin oils, silicone fluids, aromatic hydrocarbons such as toluene, xylene, phenylxylene ethane, dodecylbenzene, or alkylnaphthalene, halogenated solvents such as perfluoronaphthene, perfluorotoluene, perfluoroxylene, dichlorotrifluorotoluene, 3,4,5-trichlorotrifluorotoluene, chloropentafluorobenzene, dichlorononane, or pentachlorobenzene, and perfluorinated solvents such as FC-43, FC-70, or FC-5060 from 3M Company, St. Paul MN, low molecular weight halogenated polymers such as poly(perfluoropropylene oxide) from TCI America, Portland, Oregon, poly(trifluorochloroethylene) such as Halocarbon Oils from Halocarbon Product Corp., River Edge, NJ, and perfluoropolyalkyl ethers such as Galden from Ausimont or Krytox Oils and Greases from DuPont, Delaware. K-Fluid Series, from Dow-corning, polydimethylsiloxane silicone oil (DC-200).

[0092] sealing layer

[0093] The sealing layer must provide a barrier to the electrophoretic medium, preventing the removal of non-polar fluids from multiple microcells. Furthermore, the sealing layer must not negatively impact the electro-optical performance of the device.

[0094] An important property of the seal layer is its volume resistivity. If the seal layer's resistivity is too high, a significant voltage drop will occur within the seal layer, requiring an increase in the cross-electrode voltage to operate the device. Increasing the cross-electrode voltage in this way is undesirable because it increases the display's power consumption and may require more complex and expensive control circuitry to handle the increased voltage. On the other hand, if the seal is too low, undesirable crosstalk between adjacent pixel electrodes is observed, degrading image quality. Furthermore, because volume resistivity generally increases rapidly with decreasing temperature, excessively high volume resistivity of the seal layer negatively impacts the display's low-temperature electro-optical performance. The seal layer can have a resistivity of 4 × 10⁻⁶. 7 Volume resistivity of ohm·cm or higher. The sealing layer can have a resistivity of 5 × 10⁻⁶. 7 Volume resistivity of ohms·cm or higher. The sealing layer can have a resistivity of 10 ohms·cm or higher. 8 Volume resistivity of ohm·cm or higher. The sealing layer can have a resistivity of 5 × 10⁻⁶. 7 Up to 10 12 Ohm-cm or 10 8 Up to 10 10 Volume resistivity in ohms per centimeter. The sealing layer can have a resistivity of 10 ohms per centimeter. 10 Or even lower volume resistivity.

[0095] Besides barrier properties and volume resistivity, another important property of the sealing layer is its hygroscopicity. If the sealing layer absorbs a large amount of moisture from the environment over time, the electro-optical performance of the device will deteriorate.

[0096] The inventors of this invention have discovered that a sealing layer with a total surface energy of over 55 mN / m, formed from an aqueous polymer composition comprising a combination of water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer and polyurethane, a conductive filler having a total surface energy of over 40 mN / m, and an aqueous carrier, provides excellent barrier properties.

[0097] The inventors of this invention have also discovered that a sealing layer comprising a combination of water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, polyurethane and conductive filler forms a sealing layer for an electro-optic display that exhibits excellent electro-optic performance, especially at low temperatures.

[0098] The sealing layer may comprise (i) 30 to 70% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, excluding solvents; (ii) 7 to 29% by weight of a polyurethane, excluding solvents; and (iii) 1 to 45% by weight of a conductive filler, excluding solvents. The poly(vinyl alcohol) homopolymer may have a degree of hydrolysis of 90 to 99.5%, and the poly(vinyl alcohol-co-ethylene) copolymer may have 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 may be 92 to 99%, or 93 to 99%, or 92 to 98%, or 92 to 96%, or 95 to 99%, or 92% to 95%. The ethylene content of the poly(vinyl alcohol-co-ethylene) copolymer may be less than 9%, or less than 8.5%, or less than 8%. The ethylene content of poly(vinyl alcohol-co-ethylene) copolymers can be 7 to 11%, or 8 to 10%, or 8 to 9%, or 9 to 11%, or 10 to 11%. The degree of hydrolysis of polyvinyl alcohol homopolymers and copolymers is typically reported by the manufacturer of such polymers, showing the ratio of ethylene alcohol units (moles) to total ethylene units in the polymer. Other units are generally vinyl acetate (ester). Manufacturers also report the ethylene content of poly(vinyl alcohol-co-ethylene) copolymers, which represents the ratio of ethylene units (moles) to other units in the polymer. In this case, the other units are ethylene alcohol.

[0099] The sealing layer may be formed from an aqueous polymer composition. The aqueous polymer composition may comprise (i) 30 to 70% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, excluding the solvent; (ii) 7 to 29% by weight of a polyurethane, excluding the solvent; and (iii) 1 to 45% by weight of a conductive filler, excluding the solvent; and (iv) an aqueous carrier. The poly(vinyl alcohol) homopolymer may have a degree of hydrolysis of 90 to 99.5%, and the poly(vinyl alcohol-co-ethylene) copolymer may have 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 may be 92 to 99%, or 92% to 95%. The ethylene content of the poly(vinyl alcohol-co-ethylene) copolymer may be less than 9%, or less than 8.5%, or less than 8%. The degree of hydrolysis of polyvinyl alcohol homopolymers and copolymers is typically reported by the manufacturers of such polymers, showing the ratio of ethylene alcohol units (moles) to total ethylene units in the polymer. Other units are generally vinyl acetate (ester). Manufacturers also report the ethylene content of poly(vinyl alcohol-co-ethylene) copolymers, which represents the ratio of ethylene units (moles) to other units in the polymer. In this case, the other unit is ethylene alcohol. The application, drying, or curing of an aqueous polymer composition forms a sealing layer having (i) 30 to 70% by weight of water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, excluding solvents, and (ii) 7 to 29% by weight of polyurethane, excluding solvents. The sealing layer may have some residual water and other solvents remaining in the layer after drying or curing.

[0100] The sealing layer may comprise 30 to 70 wt%, or 30 to 65 wt%, or 30 to 60 wt%, or 30 to 55 wt%, or 30 to 50 wt%, or 35 to 70 wt%, or 35 to 65 wt%, or 35 to 60 wt%, or 35 to 55 wt%, or 35 to 50 wt%, or 40 to 70 wt%, or 40 to 65 wt%, or 40 to 60 wt%, or 40 to 55 wt% of water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer.

[0101] The sealing layer may comprise 7 to 29% by weight, or 10 to 29% by weight, or 15 to 29% by weight, or 17 to 29% by weight, or 18 to 29% by weight, or 20 to 29% by weight, or 10 to 25% by weight, or 15 to 25% by weight, or 17 to 25% by weight, or 18 to 25% by weight, or 20 to 25% by weight, or 10 to 21% by weight, or 15 to 21% by weight, or 17 to 21% by weight, of polyurethane based on the weight of the aqueous polymer composition excluding solvents.

[0102] The sealing layer may comprise 4.0 to 1.2, or 3.5 to 1.2, or 3.3 to 1.2, or 3.0 to 1.2, or 2.5 to 1.2, or 4.0 to 1.5, or 3.5 to 1.5, or 3.3 to 1.5, or 3.0 to 1.5, or 2.5 to 1.5, or 4.0 to 1.8, or 3.5 to 1.8, or 3.3 to 1.8, or 3.0 to 1.8, or 2.5 to 1.8, or 4.0 to 2.2, or 3.5 to 2.2, or 3.3 to 2.2, or 3.0 to 2.2 or 2.5 to 2.2 of water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer to polyurethane by weight ratio.

[0103] The weight-average molecular weight (MW) of the poly(vinyl alcohol) homopolymer and poly(vinyl alcohol-co-ethylene) copolymer of the sealing layer can be from 1,000 to 1,000,000 Daltons, or from 10,000 to 500,000 Daltons, or from 20,000 to 400,000 Daltons.

[0104] Polyurethanes are generally prepared via addition polymerization involving diisocyanates. Non-limiting examples of polyurethanes include polyether polyurethanes, polyester polyurethanes, polycarbonate polyurethanes, polyether polyurea, polyurea, polyester polyurea, polyester polyurea, polyisocyanates (e.g., polyurethanes containing isocyanate bonds), and polycarbodiimides (e.g., polyurethanes containing carbodiimide bonds). Typically, polyurethanes contain urethane groups. The polyurethanes used in the aqueous polymer compositions and sealing layers described herein can be prepared using methods known in the art. Preferably, the polyurethane in the aqueous polymer compositions of the present invention is a polyester polyurethane, a polycarbonate polyurethane, or a mixture thereof.

[0105] The polyurethane of the sealing layer may have a weight-average molecular weight (MW) of 1,000 to 2,000,000 Daltons, or 10,000 to 300,000 Daltons, or 15,000 to 200,000 Daltons.

[0106] Good barrier properties were observed in sealing layers containing polyurethane with a polar component of surface energy of 10 to 20 mN / m. The polar component of the surface energy of the polyurethane can be 10 to 25 mN / m, or 10 to 20 mN / m, or 11 to 20 mN / m, or 12 to 20 mN / m, or 13 to 20 mN / m, or 14 to 20 mN / m, or 15 to 20 mN / m, or 10 to 18 mN / m, or 11 to 18 mN / m, or 12 to 18 mN / m, or 13 to 18 mN / m, or 14 to 18 mN / m, or 15 to 18 mN / m, or 10 to 16 mN / m, or 11 to 16 mN / m, or 12 to 16 mN / m, or 13 to 16 mN / m, or 14 to 16 mN / m.

[0107] The polyurethane sealing layer can be added to the aqueous polymer composition as an aqueous solution, aqueous dispersion, aqueous emulsion, or latex, and the sealing layer is formed from the aqueous polymer composition.

[0108] The interfacial tension between water-soluble poly(vinyl alcohol) polymers or poly(vinyl alcohol-co-ethylene) copolymers and polyurethane can be less than 2 mN / m. The interfacial tension between water-soluble poly(vinyl alcohol) polymers or poly(vinyl alcohol-co-ethylene) copolymers and polyurethane can be less than 1.9 mN / m, or less than 1.8 mN / m, or less than 1 mN / m, or less than 0.8 mN / m, or less than 0.6 mN / m, or less than 0.7 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 0 to 2.0 mN / m, or 0.1 to 2.0 mN / m, or 0.2 to 2.0 mN / m, or 0.3 to 2.0 mN / m, or 0.4 to 2.0 mN / m, or 0.5 to 2.0 mN / m, or 0.6 to 2.0 mN / m, or 0.7 to 2.0 mN / m, or 0.8 to 2.0 mN / m, or 1.0 to 2.0 mN / m, or 1.5 to 2.0 mN / m, or 0 to 1.8 mN / m, or 0.1 to 1.8 mN / m, or 0.2 to 1.8 mN / m, or 0.3 to 1.8 mN / m, or 0.4 to 1.8 mN / m, or 0.5 to 1.8 mN / m. mN / m, or 0.6 to 1.8 mN / m, or 0.7 to 1.8 mN / m, or 0.8 to 1.8 mN / m, or 1.0 to 1.8 mN / m, or 0 to 1.5 mN / m, or 0.2 to 1.5 mN / m, or 0.3 to 1.5 mN / m, or 0.4 to 1.5 mN / m, or 0.5 to 1.5 mN / m, or 0.6 to 1.5 mN / m, or 0.7 to 1.5 mN / m, or 0.8 to 1.5 mN / m, or 1.0 to 1.5 mN / m, or 0 to 1.0 mN / m, or 0.1 to 1.0 mN / m, or 0.2 to 1.0 mN / m, or 0.3 to 1.0 mN / m, or 0.4 to 1.0 mN / m, or 0.5 to 1.0 mN / m. mN / m, or 0.6 to 1.0 mN / m, or 0.7 to 1.0 mN / m, or 0.8 to 1.0 mN / m, or 0 to 0.8 mN / m, or 0.1 to 0.8 mN / m, or 0.2 to 0.8 mN / m, or 0.3 to 0.8 mN / m, or 0.4 to 0.8 mN / m, or 0.5 to 0.8 mN / m, or 0 to 0.7 mN / m, or 0.1 to 0.7 mN / m, or 0.2 to 0.7 mN / m, or 0.3 to 0.7 mN / m, or 0.4 to 0.7 mN / m, or 0 to 0.6 mN / m, or 0.1 to 0.6 mN / m, or 0.2 to 0.7 mN / m, or 0.3 to 0.7 mN / m, or 0 to 0.6 mN / m. mN / m, or 0.1 to 0.6 mN / m, or 0.2 to 0.6 mN / m, or 0.3 to 0.6 mN / m, or 0.4 to 0.6 mN / m, or 0 to 0.5 mN / m, or 0.1 to 0.5 mN / m, or 0.2 to 0.5 mN / m.

[0109] The aqueous polymer composition may contain 40 to 96% by weight, or 60 to 95% by weight, or 70 to 92% by weight, or 80 to 90% by weight of an aqueous carrier based on the weight of the aqueous polymer composition.

[0110] The sealing layer may contain cross-linked polyurethane.

[0111] Polyurethane can be crosslinked using a crosslinking agent, which can be a polyisocyanate, a polyfunctional polycarbodiimide, a polyfunctional aziridine, a silane coupling agent, a boron / titanium / zirconium-based crosslinking agent, or melamine-formaldehyde. Because the sealing layer is formed from an aqueous polymer composition, the aqueous polymer composition can contain 0.5 to 10% by weight of the crosslinking agent, excluding the solvent. The crosslinking agent forms chemical bonds between polyurethane molecules. Crosslinking of the polyurethane in the sealing layer can increase adhesion between the sealing layer and the micro-units. The crosslinking agent is preferably soluble or dispersed in an aqueous carrier of the aqueous polymer composition. The crosslinking agent can be a monomer, oligomer, or polymer. Examples of crosslinking agents include polyisocyanates, polyfunctional polycarbodiimides, polyfunctional aziridine, silane coupling agents, boron / titanium / zirconium-based crosslinking agents, or melamine-formaldehyde. Polycarbodiimide crosslinking agents are reactive under acidic pH conditions. Preferably, the crosslinking agent is free of sulfosuccinate surfactants.

[0112] The aqueous polymer composition forming the sealing layer may also contain a pH adjuster. The pH adjuster is added to the aqueous polymer composition to adjust its pH value to a value between 6.5 and 8.5. One example of a pH adjuster is ammonium hydroxide, but various acids and bases can be used. The pH adjuster increases the pH of the aqueous polymer composition, which can reduce the crosslinking rate of the aqueous polymer composition before its use and provide optimal pH conditions for the interaction of the rheology modifier with the particles of the aqueous polymer composition, thus improving its efficacy. The pH adjuster can be used at a content of 0.2% to 1% by weight of the aqueous polymer composition excluding the solvent.

[0113] The sealing layer may also contain 0.05 to 10% by weight, or 0.1 to 5% by weight, or 0.5 to 2% by weight of a rheology modifier based on the weight of the sealing layer excluding solvent. The rheology modifier increases the storage stability of the aqueous polymer composition used to form the sealing layer. It also promotes film formation, improves sealing stability, and provides other functions. Non-limiting examples of rheology modifiers include associative thickeners, alkali-swellable acrylic emulsions, and other polymer thickeners. The aqueous polymer composition may be shear-thinned, meaning its viscosity decreases at higher shear rates. For example, the rheological distribution of the aqueous polymer composition may exhibit a viscosity at 10... -4 Viscosity at a shear rate of l / s and at 10 2 Viscosity decreases by 5 to 10,000 times at shear rates of l / s.

[0114] The sealing layer may also contain a wetting agent, also known as a surfactant. Examples of wetting agents include FC surfactants from 3M Company, Zonyl fluorinated surfactants from DuPont, fluorinated acrylates, fluorinated methacrylates, fluorinated long-chain alcohols, perfluorinated long-chain carboxylic acids and their derivatives, and Silwet silicone surfactants from OSi, Greenwich, and Conn. Wetting agents can increase the affinity between the sealing layer and the microunits, increase the interfacial area between them, improve the adhesion of the sealing layer to the microunits, and provide a more flexible coating process.

[0115] The sealing layer may also contain 1 to 45% by weight of filler, excluding the solvent. The filler may be a conductive filler. The filler for the sealing layer may be selected from carbon black, graphene, graphite, and carbon nanotubes. The filler reduces the volume resistivity of the sealing layer, but it may also affect other properties of the layer, such as its surface energy. For effective use as a filler, carbon black must have excellent dispersibility in the aqueous polymer composition. The aqueous polymer composition and the corresponding sealing layer may contain 1 to 45% by weight, or 5 to 45% by weight, or 10 to 45% by weight, or 15 to 40% by weight, or 17 to 38% by weight, or 18 to 36% by weight, or 15 to 36% by weight, or 20 to 36% by weight of filler, excluding the solvent.

[0116] The inventors of this invention observed that an important aspect enabling excellent electro-optic performance is the surface energy of the sealing layer, especially at low temperatures. The total surface energy of the sealing layer must be higher than 55 mN / m. The total surface energy of the sealing layer can be 55 to 80 mN / m, or 55 to 70 mN / m. The dispersive component of the surface energy can be higher than 40 mN / m. The dispersive component of the surface energy of the sealing layer can be higher than 41 mN / m, or higher than 43 mN / m. The dispersive component of the surface energy of the sealing layer can be 40 to 60 mN / m, or 40 to 50 mN / m, or 40 to 45 mN / m.

[0117] The high surface energy of the sealing layer can be achieved by selecting the components of the aqueous polymer composition forming the sealing layer. For example, the conductive filler may have a total surface energy greater than 40 mN / m, or greater than 45 mN / m, or greater than 50 mN / m. The dispersion component of the conductive filler may be greater than 15 mN / m, or greater than 20 mN / m. The conductive filler may have a total surface energy of 40 to 80 mN / m, or 40 to 70 mN / m, or 40 to 65 mN / m, or 40 to 60 mN / m. The dispersion component of the conductive filler may be 15 to 40 mN / m, or 15 to 30 mN / m, or 15 to 25 mN / m. The high surface energy of the sealing layer can also be achieved by selecting a polyurethane with high surface energy. For example, the polyurethane in the sealing layer may have a total surface energy greater than 50 mN / m. The dispersion component of the polyurethane may be greater than 40 mN / m. Polyurethane can have a total surface energy greater than 45 mN / m, or greater than 50 mN / m, or greater than 55 mN / m. Polyurethane can also have a total surface energy of 45 to 75 mN / m, or 45 to 70 mN / m, or 45 to 65 mN / m, or 50 to 75 mN / m, or 50 to 70 mN / m, or 50 to 65 mN / m. The dispersion component of polyurethane can be 40 to 70 mN / m, or 40 to 50 mN / m.

[0118] The inventors of this invention have discovered that the oil absorption value of the carbon black used in the sealing layer is preferably 100 mL or less per 100 mg carbon black. As shown in Table 10 below, an electro-optical display having a sealing layer containing carbon black filler exhibits improved resolution, wherein the OAN of the carbon black filler is less than 100 mL per 100 mg carbon black. The oil absorption value of the carbon black in the sealing layer can be less than 95 mL per 100 mg carbon black, or less than 90 mL per 100 mg carbon black, or less than 85 mL per 100 mg carbon black, or less than 80 mL per 100 mg carbon black, or less than 70 mL per 100 mg carbon black, or less than 60 mL per 100 mg carbon black, or less than 50 mL per 100 mg carbon black.

[0119] The oil absorption value of the carbon black in the sealing layer can be 30 mL to 100 mL per 100 mg carbon black, or 40 mL to 100 mL per 100 mg carbon black, or 45 mL to 100 mL per 100 mg carbon black, or 50 mL to 100 mL per 100 mg carbon black, or 40 mL to 95 mL per 100 mg carbon black, or 45 mL to 95 mL per 100 mg carbon black, or 50 mL to 95 mL per 100 mg carbon black. Or 55 to 95 mL per 100 mg carbon black, or 40 to 90 mL per 100 mg carbon black, or 45 to 90 mL per 100 mg carbon black, or 50 to 90 mL per 100 mg carbon black, or 40 to 80 mL per 100 mg carbon black, or 45 to 80 mL per 100 mg carbon black, or 50 to 80 mL per 100 mg carbon black, or 55 to 80 mL per 100 mg carbon black.

[0120] Oil absorption value is typically reported by carbon black manufacturers as OAN, measured using a method according to ASTM 2414. It represents the structure and degree of aggregation of the carbon black particles. That is, the higher the OAN, the higher the structure (interconnected and branched structure) of the carbon black particles and / or the higher the degree of aggregation of the particles. More structured / aggregated carbon black can generally provide higher conductivity for the sealing layer.

[0121] Another conclusion of the experimental work disclosed in this paper is that the carbon black filler in the sealing layer preferably has an average particle size greater than 20 nm. Therefore, carbon black with a very small average particle size is difficult to disperse and will result in poor properties of the sealing layer. The average particle size of the carbon black filler in the sealing layer can be greater than 30 nm, or greater than 40 nm, or greater than 50 nm, or greater than 60 nm, or greater than 80 nm, or greater than 100 nm. The average particle size of the carbon black filler in the sealing layer can be 31 to 150 nm, or 40 to 150 nm, or 50 to 150 nm, or 60 to 150 nm, or 80 to 150 nm, or 100 to 150 nm, or 31 to 100 nm, or 40 to 100 nm, or 50 to 100 nm. Average particle size is another physical property of the carbon black grade reported by carbon black manufacturers. Average particle size corresponds to the average particle diameter, which is generally determined by transmission electron microscopy (TEM) using ASTM method D3849.

[0122] As can be seen in Table 7 of the Examples section, by using a material with a diameter of less than 90 m 2 Carbon black fillers with a specific surface area of ​​ / g yielded improved results in terms of carbon black dispersion quality. The carbon black in the sealing layer can have a specific surface area of ​​less than 85 m². 2 / g, or less than 80m 2 / g, or less than 75 m 2 / g, or less than 70 m 2 / g, or less than 60 m 2 / g, or less than 50 m 2 / g or less than 40 m 2 The specific surface area of ​​the sealing layer can be 20 to 89 m² / g. 2 / g, or 30 to 89 m 2 / g, or 35 to 89 m 2 / g, or 40 to 89 m 2 / g, or 50 to 89 m 2 / g, or 20 to 88 m 2 / g, or 30 to 88 m 2 / g, or 35 to 88 m 2 / g, or 40 to 88 m 2 / g, or 50 to 88 m 2 / g, or 20 to 85 m 2 / g, or 30 to 85 m 2 / g, or 35 to 85 m 2 / g, or 40 to 85 m 2 / g, or 50 to 85 m 2 / g, or 20 to 80 m 2 / g, or 30 to 80 m 2 / g, or 35 to 80 m 2 / g, or 40 to 80 m 2 / g, or 50 to 80 m 2 / g, or 20 to 70m 2 / g, or 30 to 70 m 2 / g, or 35 to 70 m 2 / g, or 40 to 70 m 2 / g, or 50 to 70 m 2 / g, or 20 to 65 m 2 / g, or 30 to 65 m 2 / g, or 35 to 65 m 2 / g, or 40 to 65 m 2 / g, or 50 to 65 m 2 Specific surface area per g. It has a specific surface area of ​​90 m². 2 Carbon black with a specific surface area of ​​ / g or greater exhibits poor dispersion quality, which leads to poor aqueous polymer compositions and sealing layers with poor properties. However, the inventors of this invention have also found that carbon black products with higher volatile content are easier to disperse than carbon black products with lower volatile content, even though they exhibit high specific surface areas. The relevant results are shown in Table 7. That is, the carbon black in the sealing compositions of this invention can have a specific surface area of ​​less than 200 m². 2The specific surface area per g and the volatile matter content above 4.5% are considered. The carbon black in the sealing composition of the present invention can have a specific surface area of ​​less than 200 μm. 2 The specific surface area per g and the volatile matter content above 5%. The carbon black in the sealing composition of the present invention can have a specific surface area of ​​less than 190 μm. 2 / g, or less than 180 m 2 / g, or less than 170 m 2 The specific surface area per g, and the volatile matter content exceeding 5%, or exceeding 7%, or exceeding 8%, or exceeding 9%, or exceeding 10%, or exceeding 12%. The carbon black in the sealing composition of the present invention can have a specific surface area of ​​30 to 195 μm. 2 / g, or 40 to 195 m 2 / g, or 50 to 195 m 2 / g, or 60 to 195 m 2 / g, or 30 to 190 m 2 / g, or 40 to 190 m 2 / g, or 50 to 190 m 2 / g, or 60 to 190 m 2 / g, or 30 to 180 m 2 / g, or 40 to 180 m 2 / g, or 50 to 180 m 2 / g, or 60 to 180 m 2 / g, or 100 to 195 m 2 / g, or 100 to 190 m 2 / g, or 150 to 195 m 2The specific surface area is 5.1 to 25%, or 5.1 to 20%, or 5.1 to 15%, or 7 to 25%, or 7 to 10%, or 7 to 15%, or 10 to 25%, or 10 to 20%, or 10 to 15%. Specific surface area is a physical property routinely reported by carbon black manufacturers. It is measured using the nitrogen adsorption method according to ASTM D6556. It represents the surface area per unit weight (per gram) of carbon black particles. The volatile matter content of carbon black is a property typically reported by carbon black manufacturers. It corresponds to the content of oxygen-containing substances in the product, such as substances containing carbonyl groups, carboxylic acids, pyranones, phenols, quinones, lactols, ethers, lactones, etc. These substances are bound to the surface of carbon black particles and generally cannot be removed by ordinary extraction techniques. They are formed by certain conditions during the formation of the carbon black material or by post-oxidative treatments, such as, for example, ozonation. The volatile matter content of carbon black is measured as the percentage by weight of material removed from the product after heating at 950°C. The method, entitled "Testing of Carbon Black; Determination of the Amount of Components of Carbon Black that are Volatile on Heating," is described in DIN 53552. The volatile content does not include the moisture or solvent content that may be present in the particles.

[0123] Generally, the sealing layer of an electrophoretic display plays a crucial role in its performance. Poor barrier properties of the sealing layer allow non-polar fluids of the electrophoretic medium to escape from the electro-optic material layer over time, leading to severe degradation of the display's electro-optic performance. Increasing the content of poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer in the sealing layer has been observed to improve its barrier properties. However, sealing layers with high contents of poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer increase their hygroscopicity, which is also undesirable. The interfacial tension between the poly(vinyl alcohol) polymer or poly(vinyl alcohol-co-ethylene) copolymer and the polyurethane can be less than 2 mN / m.

[0124] These and other aspects of the invention will be further understood by considering the following embodiments, which are intended to illustrate certain specific implementations of the invention and are not intended to limit its scope as defined in the claims. Example

[0125] Evaluation method of sealing layer

[0126] A. Examples of preparation of aqueous polymer compositions forming a sealing layer.

[0127] A1. Example of carbon black dispersion preparation. Carbon black powder was mixed with 1.6 liters of aqueous solution of poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer. In one embodiment, 162 g of carbon black and 105.6 g of polymer were used. The dispersion was mixed in a top-mounted mixer (Hei - torque value 200) at 300 rpm for 30 minutes. The dispersion was then recirculated in a Generation 1 Q1375 Flocell sonicator, wherein the jacket of the sonicator was cooled with cold water at 10°C and at 100% amplitude for 3 hours and 23 minutes. The dispersion was continuously stirred until it was suitable for preparing an aqueous polymer composition.

[0128] A2. Preparation Example of Aqueous Polymer Composition. In a container, an aqueous polyurethane dispersion is mixed with a wetting agent and an aqueous solution of a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer comprising about 20% by weight of the homopolymer or copolymer. In one embodiment, 194 g of 35% by weight of the aqueous polyurethane dispersion and 372 g of 20% by weight of the poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer are used. The dispersion is mixed at 90 rpm for 10 minutes using a Hei-torque value 200 overhead mixer. Then, an appropriate amount of crosslinking agent is added, and the dispersion is further mixed at 90 rpm for 60 minutes. An appropriate amount of the carbon black dispersion prepared in A1 (1.39 L in one embodiment) is added, and the mixture is mixed at 500 rpm for 60 minutes. The pH is then adjusted to 6.5-8.5 with ammonium hydroxide, and the dispersion is further mixed for 30 minutes. An appropriate amount of rheology modifier is added dropwise to the dispersion, and mixing is continued for an additional 60 minutes. The dispersion was then degassed under reduced pressure (25 mmHg) for 5 days. Within 7 days of preparing the aqueous polymer composition, the resulting aqueous polymer composition was used to prepare the sealing layer of the corresponding device.

[0129] B. An example of preparing a sealing layer using the drawdown method.

[0130] The aqueous polymer composition prepared in A2 above was coated onto the indium tin oxide (ITO) side of the ITO-PET film using a Gradco drop coater. A 15-mil gap and an eight-way square coater were used. The drop speed was set to 2 m / min, with a target dry film thickness of 30 ± 2 μm. The coating was dried in an oven at 100°C for 15 minutes. The dried film was then conditioned at 25°C and 55% relative humidity for 24 hours.

[0131] C. Evaluate the barrier properties of the sealing layer against non-polar fluids.

[0132] An aqueous dispersion was prepared by mixing 10 g of poly(vinyl alcohol) homopolymer or 10 g of poly(vinyl alcohol-co-ethylene) copolymer and 10 g of polyurethane in 100 mL of water. This dispersion was used as an aqueous polymer composition to form... Figure 8A The sealing layer of the device 800 is illustrated. The sealing layer is formed by the method described in section B above. The device 800 sequentially includes: a substrate 803, a light-transmitting conductive layer 804, a base layer 805, a micro-unit layer 806, and a sealing layer 807. The micro-units comprise an electrophoretic medium containing white, black, and red pigment particles in Isopar E. The device 800 is stored at 70°C for at least 24 hours. After this period, the sealing layer sag caused by non-polar fluid loss of the electrophoretic medium is examined using an optical microscope. If the distance between the bottom of the examined microcavity and the lowest point of the bottom surface of the sealing layer is less than 85% of the distance between the bottom of the microcavity and the highest point of the bottom surface of the sealing layer at the same micro-unit, the sealing layer is marked as FAIL due to its barrier properties. Otherwise, that is, if the distance between the bottom of the examined micro-unit and the lowest point of the sealing layer is 85% or more of the distance between the bottom of the micro-unit and the highest point of the bottom surface of the sealing layer at the same micro-unit, the sealing layer is marked as PASS due to its barrier properties. For example, used to prepare Figure 10C The sealing layer of the electro-optic device illustrated is marked as qualified because the h2:h1 ratio is 1 (no sagging), and it is used for the preparation of... Figure 10D The sealing layer of the illustrated electro-optic device was marked as substandard because the h2:h1 ratio was 35% (exceeding the 85% sag level). Barrier properties were also qualitatively evaluated by observing the fabricated electro-optic device under an optical microscope from its viewing surface. Devices with severely sag sealing layers have a significantly different appearance (non-uniform surface vs. uniform surface) compared to devices with sealing layers exhibiting good barrier properties against non-polar fluids. For example, as... Figure 10A As shown, Figure 10C The micro-units with sealing layers (qualified) appear uniform, and... Figure 10D In contrast to micro-units with sealing layers (non-conforming), such as... Figure 10B As shown, Figure 10D The micro-units with sealing layers appear non-uniform. An evaluation of various combinations of (1) poly(vinyl alcohol) homopolymers or poly(vinyl alcohol-co-ethylene) copolymers and (2) polyurethanes is shown in Table 1. Polymer 1 is a poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, and polymer 2 is a polyurethane. Details regarding the commercial materials of polymers 1 and 2 can be found in Table 2.

[0133] D. Use the contact angle method to determine the surface energy of the sealing layer.

[0134] The surface energy of the prepared sealing layer was measured using a Drop Shape Analyzer provided by Kruss GmbH (as described in section B above). Using a syringe with a needle, a 2.6 μL droplet of deionized water was placed on the top surface of the sealing layer, and the contact angle between the liquid (water) and the sealing layer was measured. Measurements were repeated using a diiodomethane droplet instead of a water droplet. The surface energy of the membrane was calculated using contact measurements with these two liquids of known surface energies. Contact angle measurements were repeated three times for each liquid (water and diiodomethane). The contact angle between the liquid and the top surface of the sealing layer was measured using a high-resolution camera at 5, 30, and 55 seconds after the droplet was placed on the sample membrane. The total surface energy, along with its polarity and dispersion components, was then calculated for each data point using the Owens, Wendt, Rabel, and Kaelble (OWRK) method. The reported surface energy is the average of nine data points (three droplets × three time measurements).

[0135] E. The surface energy of the polyurethane film was determined using the contact angle method.

[0136] The surface energy of polyurethane was determined by first preparing a polymer film on a substrate. The polymer film was prepared by coating an aqueous polyurethane dispersion onto the substrate using a Gradco drop coater. A 15-mil gap and an eight-way square coater were used. The drop speed was set to 2 m / min, with a target dry film thickness of 30 ± 2 μm. The coating was dried in an oven at 100°C for 15 minutes. The dried film was then conditioned at 25°C and 55% relative humidity for 24 hours. The contact angles with two different liquids (water and diiodomethane) were then determined using the method described in section D above, and the total surface energy of the polymer film, along with its polar and dispersive components, was calculated using the OWRK model.

[0137] F. Fabrication of electro-optic devices.

[0138] An electro-optic device was fabricated by filling multiple microunits with a mixture of charged pigment particles (white, black, and red) in Isopar E, followed by coating with an aqueous polymer composition as described in section B above. A [further details on the fabrication process are needed for accurate translation]. Figure 8BThe illustrated device 850 comprises, in sequence, a protective film 851, an optically transparent first adhesive layer 852, a substrate 853, a light-transmitting conductive layer 854, a base layer 855, a micro-unit layer 856, a sealing layer 857, a second adhesive layer 858, an ITO electrode layer 859, and a glass layer 860. An electric field source 861 electrically connects the light-transmitting conductive layer 854 to the ITO electrode layer 859. A waveform is applied through this electric field source to drive a desired optical state. The first light-transmitting layer 852 has a thickness of approximately 25 μm. The substrate 853 has a thickness of approximately 100 μm. The base layer 855 has a thickness of approximately 0.4 μm. The micro-unit layer 856 comprises a plurality of micro-units. Each micro-unit has a bottom thickness of approximately 0.4 μm and a height of approximately 14 μm. The sealing layer 857 has a thickness of approximately 10 μm, and the second adhesive layer has a thickness of approximately 6 μm.

[0139] G. Red Ra* measurement.

[0140] The electro-optic performance of the sample device prepared in E above was evaluated by collecting color data. Color data was collected by applying two different waveforms, a short waveform PD and a long waveform PP, to drive the desired red state at two different temperatures. Additionally, waveforms were applied to drive the white state at two different temperatures. The applied waveforms were... Figures 9A to 9F It is displayed in the middle. Figure 9A This corresponds to the PD waveform driven in the red state at 25℃. Figure 9B This corresponds to the PD waveform driven in the red state at 0℃. Figure 9C This corresponds to the PP waveform driven in the red state at 25℃. Figure 9D This corresponds to the PP waveform driven in the red state at 0℃. Figure 9E The waveform corresponds to the white state driven at 25°C. Figure 9F The waveform corresponds to the white state driven at 0°C. A waveform is applied over a wide voltage range to measure the red a* as a function of the applied waveform. A spectrophotometer i1 provided by x-rite is used to measure the color state of the image obtained on the device sample and report it as red a*. Color performance is evaluated as the red a* value. A higher a* value means a better red (a more saturated red).

[0141] H. Determination of the voltage required for the maximum a* in the red state.

[0142] In addition to the color values ​​for each display, a series of experiments were conducted to determine the voltage required to generate the maximum a*. Specifically, the applied voltage for each waveform was varied, and the a* value for each voltage value was determined using the method F described above. The voltage at which each waveform generated the highest a* value was reported. Generally, a lower voltage is desirable because a higher applied voltage increases power consumption.

[0143] I. Measurement of interfacial tension.

[0144] For a specific combination of polymers, the interfacial tension between polymer 1 and polymer 2 is calculated using the surface energy value (determined via the method described in D above). The calculation of the interfacial tension between the two components is performed using the surface energy value of each component and the following geometric equation:

[0145]

[0146] in It is the interfacial tension between polymers A and B; It is the total surface energy of polymer A; It is the total surface energy of polymer B; and These are the dispersive components of the surface energies of polymers A and B, respectively. and These are the polar components of the surface energy of polymers A and B, respectively.

[0147] J. Evaluation method for carbon black dispersibility

[0148] Carbon black dispersions for various carbon black samples were prepared using the method described in A1 above. The polymer used in the dispersions was a poly(vinyl alcohol-co-ethylene) copolymer (Exceval TM RS-1717 (provided by Kuraray). After preparing the carbon black dispersion, place a droplet of the dispersion between a microscope slide and a cover plate. Examine the sample under a 20x magnified optical microscope. For the number of aggregates with a diameter of 7 μm or larger, visually analyze the corresponding image for an area of ​​140 μm × 140 μm. If the sample shows 10 or more aggregate particles with a diameter of 7 μm or larger, the sample is marked as undispersible. Otherwise, it is marked as dispersible.

[0149] L. Evaluation method for the volume resistivity of the sealing layer.

[0150] The volume resistivity of the sealing layer prepared using the method described in section B above was determined using a Keithley Model 8009 resistivity jig and a Model 6571 electrometer. This equipment allows the user to determine the volume resistivity of the self-supporting film by applying an AC voltage to the substrate and measuring the output current. The resistance of the sample is calculated based on the voltage and current. The method involves cutting a 4-inch × 4-inch square portion of the sealing layer and peeling this portion from the ITO-PET substrate to obtain the self-supporting sealing film. The thickness is measured using a thickness gauge, and the film is then conditioned for 4 days in an ambient chamber at 25°C and 55% relative humidity. The film is then placed in the Model 8009 resistivity jig and tested for 15 seconds at a setting of 15 volts. The electrometer provides the volume resistivity value.

[0151] M. Methods for evaluating the resolution of displayed images.

[0152] The resolution of an electrophoretic display prepared by the method described in section E above is evaluated by measuring the actual line thickness of the color on the display, where the line is the result of forming a line with a width of 1 pixel (at 50°C) under the command of a pixel controller. The measured thickness is then compared to the thickness of a standard 1-pixel line without blurring. 100% resolution corresponds to the highest resolution without blurring, and 0% resolution corresponds to an actual line that is twice as thick as the standard line.

[0153] K. Evaluation method for viscosity distribution of aqueous polymer compositions.

[0154] The viscosity distribution of the aqueous polymer composition prepared as described in A2 above was determined using a rotating TA Instruments rheometer equipped with parallel plates having a diameter of 40 mm and a gap of 50 μm. The aqueous polymer composition sample was placed between the parallel plates and the viscosity was measured at 10 μm within a 30-minute time period. -3 l / s and 10 2 Viscosity was measured at a series of shear rates between l / s. The viscosity distribution of the aqueous polymer compositions of the present invention is shown in the following figures. Figure 11 The illustration in the diagram is as follows. Figure 11 The evaluated aqueous polymer compositions showed shear-thinning properties, exhibiting a decrease in viscosity at higher shear rates compared to lower shear rates. Specifically, Figure 11 The waterborne polymer compositions evaluated in 10 -3 Viscosity ratio at a shear rate of l / s at 10 2 The viscosity at a shear rate of l / s is more than 10 times greater.

[0155] O. Evaluation method for the total surface energy and the dispersive component of surface energy of conductive fillers.

[0156] A glass tube with a porous substrate is filled with powdered conductive filler. The glass tube is placed on top of a container containing hexane as the test liquid. The hexane is drawn upwards along the glass tube by capillary action. The glass tube is connected to a force sensor, which measures the change in mass over time as the liquid moves upwards along the glass tube and wets the filler surface. By taking the slope of this measurement and the known properties of the hexane test liquid, the following equation can ultimately be used to calculate the contact angle of the conductive filler.

[0157]

[0158] In the equation, m is the mass of the packing material, t is time, and c is a constant. It tests the density of the liquid. Here, θ is the surface tension of the test liquid, η is the contact angle, and η is the viscosity of the test liquid. Due to the high wettability of hexane, using hexane as the test liquid makes θ zero, allowing the instrument's software to calculate the constant c. Then, another known liquid is used to measure the contact angle, which the software can use to calculate the surface energy of the filler. Surface energy calculations are performed using the Owens, Wendt, Rabel, and Kaelble (OWRK) model to determine the total surface energy, as well as the polarity and dispersion components of the filler.

[0159] Evaluation results

[0160] Unless otherwise stated, the amounts of the components in the disclosed compositions are on a dry basis (excluding solvents). The term QS (sufficient quantity) is used in some compositions to indicate the amount of the carrier. This means that the amount of the component in the composition is the amount required to achieve 100% of the entire composition, and not more.

[0161] Many aqueous polymer compositions were prepared using the general methods described in A1 and A2 above. The weight ratio of poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer to polyurethane was 2.3, and the amount of aqueous carrier in the aqueous polymer composition was 80 to 83% by weight. The crosslinking agent content was 0.90% by weight, while the wetting agent (Silwet L-7607) content was 0.19% by weight based on the weight of the aqueous polymer composition excluding solvent. Furthermore, the aqueous polymer composition also contained 0.22% by weight of rheology modifier (modified alkali-swellable acrylic emulsion (Solthix A100 provided by Lubrizol) based on the weight of the aqueous polymer composition excluding solvent. The carbon black content in the aqueous polymer was adjusted to obtain a value with a 10 8 Up to 10 10 A sealing layer with a volume resistivity in the ohm-cm range typically has a weight percentage of 3.6 to 6% based on the weight of the aqueous polymer composition excluding the solvent. The type of aqueous polymer prepared...

[0162] The sealing layer compositions are summarized in Table 1. Sealing layers were prepared from these aqueous polymer compositions using the method described in section B above. The total surface energy and the dispersive component of the surface energy of the sealing layers were then evaluated using the method described in section D above. Specifically, the total surface energy and dispersive component of the corresponding control films prepared from each polyurethane used in the aqueous polymer compositions were measured using the method described in section E above. These polyurethane control films were free of poly(vinyl alcohol) homopolymers or poly(vinyl alcohol-co-ethylene) copolymers or carbon black. Finally, the total surface energy and the dispersive component of the surface energy for two carbon black grades were measured using the method described in section O above.

[0163] Electrophoretic displays were constructed from various compositions using the method described in F above. As described in G above, the electrophoretic displays were driven to the red state at 0°C using two different waveforms. Finally, the voltage required to produce the highest a* value for the red state of each waveform was determined using the method described in H above.

[0164] Table 1: Surface energy properties of sealing layers of various compositions, and electro-optic properties of corresponding devices.

[0165]

[0166]

[0167]

[0168]

[0169] Information on materials in Table 1: [1] Poly(vinyl alcohol-co-ethylene) copolymer; Exceval TM RS-1717, supplied by Kuraray; [2] Aqueous polyurethane dispersion; L3838 aqueous dispersion, supplied by Hauthaway, 35% in water; [3] Aqueous polyurethane dispersion; HD2125 aqueous dispersion, supplied by Hauthaway, 35% in water; [4] Aqueous polyurethane dispersion (polyester); Witcobond® 386-03, supplied by Chemtura Corp.; [5] Carbon black; Raven® 1060 UP, supplied by Colombia; [6] Carbon black; Nerox® 3500, supplied by Orion Engineered Carbons; [7] Carbon black; Nerox® 2500, supplied by Orion Engineered Carbons; [8] Carbon black; TPK1227R, supplied by Cabot Corporation; [9] Carbon black; Raven® 14, supplied by Colombia.

[0170] The evaluation results in Table 1 show that improved electro-optic performance was observed in Examples 1 to 5 of the present invention compared to Comparative Example 6. Driven by the PP waveform, the electro-optic device formed by the composition examples of the present invention exhibited a better (more saturated) color in the red state at low temperature (0°C) than the comparative example, as indicated by the higher a* value measured by a spectrophotometer. The same phenomenon was observed in the red state driven by the PD waveform. Not only is the color of the display of the present invention more saturated, but it is also achieved with a lower voltage, as can be seen from the lower voltage value at maximum a*. This means that the display of the present invention consumes less power than the display using the comparative composition examples. This is achieved because the total surface energy of the sealing layer of the embodiments of the present invention is approximately 66 mN / m, which is higher than 55 mN / m, compared to the total surface energy of 53 mN / m of the sealing layer formed by the comparative example. Similarly, the improved performance of the display of the present invention is achieved due to the higher dispersive surface energy of the sealing layer (above 40 mN / m) compared to the 38 mN / m of the sealing layer of the display of the present invention. The total surface energy of the composition components positively influences the surface energy of the sealing layer. Specifically, polyurethanes that form films with a total surface energy greater than 50 mN / m (such as polyurethane dispersions L3838 and HD2125) perform better than polyurethanes that form films with a lower total surface energy (Witcobond® 386-03).

[0171] The surface energy of conductive fillers also plays a role in the improved performance. Carbon blacks with a total surface energy above 40 mN / m, such as Raven® 1060 UP, outperform carbon blacks with a total surface energy below 40 mN / m, such as Raven® 14. Additionally, carbon blacks with a dispersion component above 15 mN / m exhibit good performance. Without being theoretically limited, the improved electro-optic properties of seals with high surface energy (especially at low temperatures) allow them to transfer charge through the interlayer with lower interfacial resistance and capacitance. Lower resistance and capacitance at the seal / electrophoretic medium interface result in significantly lower electro-optic deviation (recoil), especially at low temperatures. The higher surface energy of the seal also leads to lower contact resistance and capacitance at the seal interface, which has an adhesive layer that may be adjacent to it. The high surface energy of the seal can increase the adhesive work between the seal and adhesive layers, resulting in lower contact resistance between the layers. Furthermore, lower contact resistance at the seal / adhesive interface leads to lower voltage drop and lower power dissipation, as well as improved electro-optic performance across the temperature range. The influence of the surface energy of the sealing layer on the electro-optic performance of the electrophoretic display is not disclosed in the literature.

[0172] Table 2 provides surface energy data for various polymer 1 and polymer 2 materials. It also includes the interfaces of various polymer combinations for the evaluation and calculation of the barrier properties of each layer. The preparation methods of the corresponding polymer layers used for barrier property evaluation are described in section C above. Surface energy determination (according to the method described in section D above) is performed by first preparing and adjusting the sealing layer from the corresponding aqueous polymer composition containing only one polymer. The interfacial tension of each polymer combination is calculated based on the surface energy data and the calculation method described in section I above.

[0173] Table 2 : Barrier properties of the sealing layer.

[0174]

[0175]

[0176]

[0177]

[0178] Table 3 : Commercial materials used in Examples 7-32 of Table 2.

[0179]

[0180]

[0181]

[0182] The data in Table 2 show that the sealing layer formed by the combination of polymer 1 and polymer 2, which has low interfacial tension, exhibits good barrier properties against non-polar fluids. The sealing layer comprises (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) polyurethane.

[0183] The data in Table 2 also show that the sealing layer comprises (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) polyurethane. The sealing layer comprising polyurethane with a polar component of surface energy of 10 to 20 mN / m exhibits good barrier properties against nonpolar fluids.

[0184] Microscopic evaluation of polymer films prepared from four aqueous polymer compositions using the method described in section B above showed a correlation between film uniformity and interfacial tension between the two polymers. In the prepared films, the weight ratio of polymer 1 to polymer 2 was 1:1. Table 4 and Figure 12Microscopic images show that lower interfacial tension provides a more uniform polymer film. The improved compatibility obtained through polymer combinations with lower interfacial tension can explain the improved barrier properties of the corresponding layers.

[0185] Table 4 : A polymer film comprising a combination of poly(vinyl alcohol-co-ethylene) copolymers and polyurethane with different interfacial tensions.

[0186]

[0187] Additional sealing layers are prepared from aqueous polymer compositions comprising different amounts of polymer 1 and polymer 2. In addition to the polymer combination, these aqueous polymer compositions also contain carbon black filler, crosslinking agent, wetting agent, rheology modifier, and aqueous carrier. Aqueous polymer compositions showing the aqueous carrier content are provided in Table 5. Table 6 corresponds to the same compositions as in Table 5, but the compositions in Table 6 have been adjusted to show the weight percentage of each component based on the weight of the aqueous polymer composition excluding the solvent. Aqueous polymer compositions are prepared using the methods described in A1 and A2 above. The corresponding sealing layers are prepared using the methods described in B above.

[0188] Table 5 Aqueous polymer compositions containing various polymer contents. Content is the weight percentage of the components based on the total composition (including the aqueous carrier).

[0189]

[0190]

[0191] Table 6 : Aqueous polymer compositions corresponding to the aqueous polymer compositions in Table 5. Content is the weight percentage of the component excluding the water carrier.

[0192]

[0193]

[0194] Information on the components in Tables 5 and 6 [1] Exceval TMRS-1717, supplied by Kuraray; [2] Dispercoll® U XP2815, supplied by Covestro; 35% dispersion in water; [3] Hauthane HD-2125, supplied by Hauthaway; 35% dispersion in water; [4] Hauthane L3838, supplied by Hauthaway; 35% dispersion in water; [5] CARBODILITE® V-02-L2, supplied by Nisshimbo Chemical; 40% solution in water; [6] Picassian® XL-701, supplied by Stahl; [7] Silwet® L-7607 copolymer, supplied by Momentive; [8] Solthix TM A-100, supplied by Lubrizol.

[0195] A series of carbon black products were evaluated for their dispersibility in polymer compositions. Carbon blacks exhibiting good dispersibility resulted in aqueous polymer compositions with good dispersion quality. The dispersion quality of the aqueous polymer composition is an important parameter affecting the properties of the resulting sealing layer. Poor dispersion quality of the aqueous polymer composition leads to a sealing layer with very low volumetric conductivity, resulting in poor electro-optical performance and low electrical efficiency of the device. Table 7 presents the results of the investigation. The dispersion quality of the carbon black dispersion was determined by the method described in section H above.

[0196] Table 7 Evaluation of the dispersibility of carbon black samples with various specific surface areas.

[0197]

[0198]

[0199]

[0200] Table 7 shows the evaluation results of carbon black dispersibility, indicating that it has a dispersion of less than 85 μm. 2 Carbon black grades with a specific surface area of ​​85 to 200 m² / g exhibit good dispersibility in aqueous polymer dispersions. 2 Carbon black with a specific surface area of ​​85 g / g and a volatile content higher than 5% also exhibits good dispersibility in aqueous polymer dispersions. Carbon black with a specific surface area higher than 85 g / g and a volatile content lower than 5% does not exhibit good dispersibility in aqueous polymer dispersions. Finally, carbon black with a specific surface area higher than 200 g / g and a volatile content lower than 5% also exhibits good dispersibility in aqueous polymer dispersions. 2Carbon black with a specific surface area of ​​ / g did not exhibit good dispersibility in aqueous polymer dispersions. The volatile content of carbon black is measured as a percentage by weight of material removed from the product after heating at 950°C. The method, entitled "Testing of Carbon Black; Determination of the Amount of Components of Carbon Black that are Volatile on Heating," is described in DIN 53552. The volatile content does not include moisture or solvent content that may be present in the particles.

[0201] A series of carbon black products were also evaluated for their dispersibility in polymer compositions. The supplier has reported the average particle size of the series of carbon black products using transmission electron microscopy (TEM). Table 8 provides the findings. The dispersion quality of the carbon black dispersions was determined using the method described in section H above.

[0202] Table 8 Evaluation of the dispersibility of carbon black samples with different average particle sizes.

[0203]

[0204]

[0205] The evaluation results of the carbon black dispersibility in Table 8 show that carbon black products with an average particle size greater than 20 nm exhibit good dispersibility in aqueous polymer dispersions. The carbon black supplier (Orion Engineered Carbon) determined the average particle size of the product using ASTM D3849 (Standard Method for Carbon Black – Morphological Characterization of Carbon Black Using Electron Microscopy).

[0206] The volume resistivity of a series of sealing layers formed from aqueous polymer compositions containing various carbon black commodities was evaluated using the method described above (I. Method for evaluating the volume resistivity of sealing layers). An electro-optic display was prepared using the method described above (E. Preparation of electro-optic devices). The resolution of the prepared electro-optic display was evaluated using the method described above (J. Method for evaluating the resolution of displayed images). Tables 9 and 10 provide the aqueous polymer compositions prepared for this study. Table 9 provides the aqueous polymer compositions showing the content of all components of the aqueous polymer compositions, including the content of the aqueous carrier. Table 10 provides sealing layer compositions (excluding potential water content), the sealing layers being prepared from the aqueous polymer compositions in Table 9. The compositions in Table 9 provide the weight percentage of each component based on the weight of the aqueous polymer composition containing water. Various aqueous polymer compositions were prepared using the methods described in A1 and A2 above. The corresponding sealing layers were prepared using the method described in B above.

[0207] Table 9 This is an aqueous polymer composition used to evaluate the volume resistivity and electro-optic properties (image resolution) of sealing layers containing various carbon black fillers. The content of the components is reported as a percentage by weight (%) of the components based on the weight of the composition.

[0208]

[0209]

[0210] Table 10 This refers to aqueous polymer compositions used to evaluate the volume resistivity and electro-optic properties (image resolution) of sealing layers containing various carbon black fillers. The content of the components is reported as a percentage by weight (%) of the composition excluding the water carrier. These compositions approximate the content of a dry sealing layer.

[0211]

[0212]

[0213] The data in Table 10 show that the optimal volume resistivity and device resolution of the sealing layer are achieved using carbon black with an oil absorption value of less than 100 mL / 100 g.

[0214] Furthermore, during the study, it was observed that aqueous polymer compositions containing more than 70% by weight of poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, based on the weight of the aqueous polymer composition excluding solvents, form a sealing layer that absorbs a large amount of moisture from the environment. Such high hygroscopicity has a negative impact on the electro-optical performance of the display.

Claims

1. A sealing layer comprising: (i) 30 to 70% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, the poly(vinyl alcohol) homopolymer having a degree of hydrolysis of 90 to 99.9%, and the poly(vinyl alcohol-co-ethylene) copolymer having a degree of hydrolysis of 90 to 99.9% and an ethylene content of less than 10%; (ii) 7 to 29% by weight of polyurethane, excluding solvents; (iii) 1 to 45% by weight of the sealing layer excluding solvent, the conductive filler being selected from carbon black, graphene, graphite and carbon nanotubes, the conductive filler having a total surface energy greater than 40 mN / m, the total surface energy of the conductive filler being determined by the Washburn method using hexane as the test liquid. The sealing layer has a total surface energy greater than 55 mN / m, which is determined using the contact angle method by the following steps: (a) forming the sealing layer by coating an aqueous polymer composition on a substrate with a dry thickness of 30 mm, heating it at 100°C for 15 minutes and conditioning it at 25°C and 55% relative humidity for 24 hours; (b) measuring the contact angles of water droplets and diiodomethane droplets on the formed sealing layer; and (c) calculating the total surface energy using the OWRK model.

2. The sealing layer of claim 1, wherein the sealing layer has a dispersion component of surface energy, the dispersion component of surface energy being higher than 40 mN / m, and the dispersion component of surface energy of the sealing layer is determined using the contact angle method.

3. The sealing layer of claim 1, wherein the conductive filler has a dispersive component of surface energy, and the dispersive component of surface energy of the conductive filler is determined by the Washburn method using hexane as the test liquid to be higher than 15 mN / m.

4. The sealing layer of claim 1, wherein the polyurethane is crosslinked by a crosslinking agent, the crosslinking agent being a polyisocyanate, a polyfunctional polycarbodiimide, a polyfunctional aziridine, a silane coupling agent, a boron / titanium / zirconium-based crosslinking agent, or melamine-formaldehyde.

5. The sealing layer of claim 1, further comprising a wetting agent, said wetting agent being an organosilicon surface tension reducer.

6. The sealing layer of claim 1, wherein the conductive filler is carbon black.

7. The sealing layer of claim 6, wherein the carbon black has an oil absorption value of less than 100 mL per 100 mg carbon black, as measured by the oil absorption value method according to ASTM 2414.

8. The sealing layer of claim 6, wherein the carbon black has an average particle size greater than 20 nm as measured by electron microscopy according to ASTM D3849.

9. The sealing layer of claim 6, wherein the carbon black has a nitrogen adsorption content of less than 90 μm as measured by nitrogen adsorption method according to ASTM D6556. 2 Specific surface area per g.

10. The sealing layer of claim 6, wherein the carbon black has a nitrogen adsorption density of less than 200 μm as measured by nitrogen adsorption method according to ASTM D6556. 2 The specific surface area per g, and the volatile content of more than 5% as measured by the method according to DIN 53552.

11. The sealing layer of claim 1, wherein the polyurethane has a number-average molecular weight of 1,000 to 2,000,000 Daltons.

12. The sealing layer of claim 1, wherein the polyurethane has a polar component of surface energy, the polar component of the surface energy of the polyurethane being 10 mN / m to 20 mN / m, the polar component of the surface energy of the polyurethane being determined using a contact angle method.

13. The sealing layer of claim 1, wherein the poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer has a number average molecular weight of 1,000 to 1,000,000 Daltons.

14. The sealing layer of claim 1, wherein the poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer has a degree of hydrolysis of 92% to 99%.

15. The sealing layer of claim 1, wherein the poly(vinyl alcohol-co-ethylene) copolymer has an ethylene content of less than 9%.

16. A sealing layer comprising: (i) 30 to 70% by weight of a water-soluble poly(vinyl alcohol) homopolymer or poly(vinyl alcohol-co-ethylene) copolymer, the poly(vinyl alcohol) homopolymer having a degree of hydrolysis of 90 to 99.9%, and the poly(vinyl alcohol-co-ethylene) copolymer having a degree of hydrolysis of 90 to 99.9% and an ethylene content of less than 10%; (ii) 7 to 29% by weight of the sealant excluding solvent, the polyurethane having a total surface energy greater than 50 mN / m, the total surface energy of the polyurethane being determined using a contact angle method by the following steps: (a) forming a polyurethane film by coating an aqueous polyurethane composition on a substrate to a dry thickness of 30 mm, heating at 100°C for 15 minutes and conditioning at 25°C and 55% relative humidity for 24 hours; (b) measuring the contact angles of water droplets and diiodomethane droplets on the formed polyurethane film; and (c) calculating the total surface energy using an OWRK model. (iii) 1 to 45% by weight of the sealing layer excluding solvent, the conductive filler being selected from carbon black, graphene, graphite and carbon nanotubes, the conductive filler having a total surface energy greater than 40 mN / m, the total surface energy being determined by the Washburn method using hexane as the test liquid. The sealing layer has a total surface energy, which is higher than 55 mN / m, and the total surface energy of the sealing layer is determined using the contact angle method.

17. The sealing layer of claim 16, wherein the sealing layer has a dispersion component of surface energy, the dispersion component of surface energy being greater than 40 mN / m, and the dispersion component of surface energy of the sealing layer is determined using a contact angle method.

18. The sealing layer of claim 16, wherein the polyurethane has a dispersive component of surface energy, the dispersive component of surface energy of the polyurethane being greater than 40 mN / m, and the dispersive component of surface energy of the polyurethane being determined using a contact angle method.

19. An electrophoretic display comprising: First transparent electrode layer; An electro-optic material layer comprising a sealing layer according to claim 1 and a plurality of micro-units, each of the plurality of micro-units comprising a bottom, a wall and an opening, and comprising an electrophoretic medium comprising at least one type of charged pigment particles dispersed in a nonpolar fluid, the sealing layer spanning the opening of the plurality of micro-units; Second electrode layer; The electro-optic material layer is disposed between the first transparent electrode layer and the second electrode layer.

20. The electrophoretic display of claim 19, wherein the electrophoretic medium comprises four types of charged pigment particles, wherein the color of the charged pigment particles is selected from white, magenta, yellow, cyan, blue, red, green, and black.

Images