Electrophoretic Display

Abstract

The present invention relates to a fluid composition for a next-generation electrophoretic display proposed to overcome the limitations of existing electronophoresis technology, and a device comprising the same. The core technical configuration of the present invention can be summarized into three main points. First, a hydrophobic ionic liquid (imidazolidium or pyridinium-based) was introduced as a charge control system instead of the conventional unstable linear quaternary ammonium salt. This forms a spontaneous ion pair dissociation equilibrium within the fluid to construct a robust electrical double layer on the particle surface, thereby providing strong charge stability and image retention (bistability) that remain unchanged even under changes in the external environment. Second, as a dispersion stabilization system, we have adopted a dispersant with a three-dimensional dendrimer or hyperbranched structure, moving away from the 'linear tail' structure limited by the target patent. This geometric structure forms high-density steric hindrance on the particle surface, thereby fundamentally blocking particle aggregation and, at the same time, significantly lowering fluid viscosity by preventing chain entanglement characteristic of linear polymers. As a result, the resistance to particle movement is reduced, dramatically improving the response speed of the display. Third, as a dielectric property control system, heterogeneous phase materials such as metal-organic frameworks (MOFs) and nanocapsules were introduced instead of conventional liquid additives that dissolve in the medium and cause electrical noise. MOFs selectively scavenge harmful ions within the fluid through their porous structure to block background current, while nanocapsules accelerate particle behavior through local dielectric constant control, thereby realizing vivid contrast ratios and high-contrast full-color screens. In the present invention, the numerically defined content of the charge control agent (0.01~5.0 wt%), the particle size of the electrophoretic particle (50~500 nm), and the pore size of the MOF (5~30 Å) are critical ranges for deriving optimal electro-optical performance. In conclusion, the present invention provides a core material technology for electrophoretic displays capable of simultaneously achieving low power driving, high-speed response, and high contrast ratio, which can be widely applied in the field of next-generation display devices such as electronic paper, electronic price tags (ESL), and flexible wearable displays.

Description

Technology Field

[0001] The present invention relates to a fluid composition for an electrophoretic display and a display and display device including the same. More specifically, it relates to an electrophoretic display and display device that significantly improves the dispersion stability and bistable of particles by introducing a charge control system using an imidazolium or pyridinium-based hydrophobic ionic liquid, a dispersant with a three-dimensional hyperbranched structure, and a dielectric property controller including a nanocapsule or a metal-organic framework (MOF). Background Technology

[0002] Fluid technology for electronic display devices has evolved through the following stages to ensure particle charge control and dispersion stability, but unresolved technical challenges still exist.

[0003] Conventional electronophoresis fluids use a mixture of a first CCA (charge control agent) and a second CCA (dispersant) to disperse charged particles in a non-polar solvent. Conventional technology primarily uses linear polymers with quaternary ammonium functional groups to impart a charge to the particle surface and form steric hindrance.

[0004] However, these linear dispersants have a chronic problem of rapidly increasing fluid viscosity above a certain critical concentration, thereby reducing the response speed of the particles, and in particular, due to chemical constraints requiring the inclusion of two or more polar groups, the degree of ion dissociation in low dielectric constant media is insufficient, resulting in a limitation of reduced charge retention during long-term operation.

[0005] In addition, conventional water-soluble ether compounds added to control the dielectric constant of fluids caused precipitation due to differences in solubility with temperature changes, or generated electrical noise that interfered with the behavior of particles.

[0006] Existing electrophoretic display technologies have evolved in various ways to ensure charge control and dispersion stability, but prior technologies each face clear technical limitations.

[0007] Prior art document 1 (US7502161B2), which presents a traditional surfactant-based charge control technology, imparts charge by forming an electric double layer on the surface of particles in a non-polar solvent using an ionic surfactant with a simple structure, such as sodium sulfosuccinate, as a charge control agent (CCA). However, since this method relies solely on chemical adsorption between specific functional groups on the particle surface and the charge control agent, it suffers from the problem of extremely low ion dissociation in low dielectric constant environments. This causes ion desorption when voltage is applied for a long period, destabilizing the charge state of the particles and consequently leading to afterimages on the screen or a decrease in bistable.

[0008] Prior art 2 (US6822782B2), in which a long-chain linear polymer is chemically grafted onto the surface of particles, achieved a steric hindrance effect that maintains physical distance between particles. However, when the chain length of the linear polymer is increased to sufficiently form steric hindrance, a side effect occurs in which the viscosity of the entire fluid increases rapidly. Such high-viscosity media not only increases the resistance to particle movement and slows down the response speed, but also causes energy efficiency problems requiring an increase in the driving voltage.

[0009] Prior art 3 (US7268203B2), which emerged to overcome the limitations of linear structures, proposes a technique to maintain high particle concentration even at low viscosity by introducing a hyperbranched polymer with a three-dimensional network structure as a dispersant. However, as it is designed to include two or more polar groups within the molecular structure to secure stable dispersion power, these polar groups act as unintended ion traps in the fluid or cause phase separation with the dielectric solvent upon temperature change, thereby generating electrical noise that interferes with fine actuation control.

[0010] In addition, prior art 4 (US6323989B1) presents a nanoparticle system that controls dielectric constant and optical performance by mixing a liquid additive that is completely soluble in the medium. However, since the dielectric constant modifier exists in a dissolved state, the modifier itself moves along with ions depending on the external electric field, unnecessarily increasing the electrical conductivity of the entire liquid. This reveals limitations, as it not only increases power consumption but also causes interference phenomena that hinder the independent behavior of the particles.

[0011] Consequently, conventional design methods centered on 'linear tails' and 'polar groups' have placed clear limitations on the performance improvement of electrophoretic displays. Therefore, there is an urgent need for technologies for precise dielectric control through 3D dendrimer structures capable of maximizing steric hindrance effects, ionic liquid systems that stably supply charge without chemical bonding, and heterogeneous phases such as capsules or metal-organic frameworks (MOFs) that do not dissolve in the medium. Prior art literature

[0012] 1. US7502161B22. US6822782B23. US7268203B24. US6323989B1 The problem to be solved

[0013] The present invention is proposed to solve the problems and limitations of the prior art as described above, and specifically aims to solve the following technical problems.

[0014] First, departing from conventional charge transfer methods relying on chemical adsorption, it provides robust charge stability and highly reliable bistable against external environmental changes, even within low dielectric constant media, through the physical dissociation equilibrium and ion-pair formation of hydrophobic ionic liquids.

[0015] Second, to solve the problem of fluid viscosity increase caused by linear dispersants containing two or more polar groups, a non-ionic hyperbranched or dendrimer dispersant having a three-dimensional network structure is applied to simultaneously provide ultra-low viscosity characteristics and particle dispersion stability due to high-density steric hindrance.

[0016] Third, by introducing functional particles of a heterogeneous phase, such as nano-capsules containing dielectric constant-controlling solvents or porous metal-organic frameworks (MOFs), instead of water-soluble ether additives that dissolve in the medium and cause electrical noise, a hybrid fluid system is provided that can block unnecessary ion movement in the fluid and precisely control electro-optical properties. means of solving the problem

[0017] An electrophoretic display according to the present invention comprises: a first substrate; a second substrate; and a fluid composition for an electrophoretic display disposed between the first substrate and the second substrate; wherein the fluid composition comprises a nonpolar dielectric solvent, at least one electrophoretic particle, a charge control agent, and a dispersant; wherein the charge control agent is a hydrophobic ionic liquid comprising an imidazolium or pyridinium cation, and is included in an amount of 0.01 to 5.0 wt% relative to the total weight of the fluid composition; and wherein the dispersant may be a polymer compound having a nonionic hyperbranched or dendrimer structure.

[0018] The average particle size of the electrophoretic particles is 50 to 500 nm; and the fluid composition may further include a metal-organic framework (MOF) having a pore size of 5 to 30 Å as a dielectric property regulator for dielectric constant and ion control.

[0019] The above fluid composition may be filled into microcapsules or into a unit cell of a partition wall structure formed between the first substrate and the second substrate.

[0020] A fluid composition for an electrophoretic display according to the present invention comprises: a nonpolar dielectric solvent; electrophoretic particles dispersed within the nonpolar dielectric medium; a charge control agent for imparting a charge to the electrophoretic particles; and a dispersant for maintaining the dispersion stability of the particles; wherein the charge control agent is a combination of a 1-alkyl-3-methylimidazolium or N-alkylpyridinium cation and a bis(trifluoromethanesulfonyl)imide (TFSI) or hexafluorophosphate (PF6) anion; and the dispersant may be a polymer having a three-dimensional network structure comprising a fluorinated alkyl group at its terminal.

[0021] The absolute value of the zeta potential of the electrophoretic particles in the above-mentioned fluid composition for the electrophoretic display is in the range of 30 to 150 mV, and the zeta potential retention rate after 1,000 hours of operation may be 90% or more.

[0022] The viscosity of the above fluid composition for electrophoretic display at 25°C may be in the range of 5 to 10 cP.

[0023] The above fluid composition for an electrophoretic display contains a high dielectric constant solvent and may further include heterogeneous phase nanocapsules dispersed in the nonpolar dielectric solvent.

[0024] The above electrophoretic particles can form a zeta potential through physical adsorption by the ion-pair dissociation equilibrium of the above hydrophobic ionic liquid.

[0025] The above-mentioned dispersant is a non-ionic compound that does not contain ionic polar groups in its molecular structure and can provide dispersion stability through steric repulsion between fluorine chains.

[0026] The fluid composition for an electrophoretic display according to the present invention may include an outer wall (shell) made of a polymer resin.

[0027] The electrophoretic film according to the present invention comprises a transparent conductive substrate; and an electrophoretic display layer formed on at least one surface of the substrate; wherein the display layer may have microcapsules for an electrophoretic display according to claim 10 arranged as a monolayer or a multilayer within a polymer binder.

[0028] A method for preparing a fluid composition for an electrophoretic display according to the present invention may comprise: (a) a step of preparing a charge control solution by mixing 0.01 to 5.0 wt% of a 1-alkyl-3-methylimidazolium-based hydrophobic ionic liquid in a nonpolar dielectric solvent; (b) a step of adding a dendrimer dispersant having a three-dimensional spherical structure and electrophoretic particles having an average particle size of 50 to 500 nm to the solution; and (c) a step of adding a metal-organic framework (MOF) and then dispersing the particles using a high-shear stirrer. Effects of the invention

[0029] The fluid composition for an electrophoretic display and the device including the same according to the present invention overcome the physical and electrical limitations of conventional linear polymer and simple ionic surfactant systems, thereby providing the following significant technical effects.

[0030] First, by introducing a dispersant with a three-dimensional dendrimer and hyperbranched structure, the trade-off between viscosity and dispersion stability, a chronic problem in electrophoretic displays, is resolved. Conventional linear dispersants increase fluid viscosity because inter-chain entanglement occurs as the chain lengthens to secure inter-particle distance; however, the dispersant of the present invention forms a spherical structure extending from a central core. This structural characteristic forms a dense steric hindrance layer on the particle surface while behaving like independent nanoparticles within the solvent, thereby drastically reducing fluid viscosity. This minimizes the frictional drag experienced when the particles react to an electric field, resulting in a reduction in response speed during screen switching.

[0031] Second, imidazolium or pyridinium-based hydrophobic ionic liquids are used as charge controllers to maximize the charge stability of the particles and the bistability of the display. Conventional quaternary ammonium salt-based charge controllers have a low degree of dissociation in non-polar media and unstable bonding, making them prone to charge loss and afterimage phenomena over time. In contrast, the ionic liquid of the present invention maintains a continuous ion pair dissociation equilibrium within the fluid and reconstructs a robust electrical double layer around the particles. As a result, the charged state of the particles is maintained for a long time even without the application of voltage, minimizing power consumption and ensuring high reliability by maintaining consistent image quality even during long-term operation.

[0032] Third, the introduction of porous metal-organic frameworks (MOFs) and nanocapsules 혁신적으로 improves the electro-optical purity of the fluid. Trace amounts of impurity ions in the fluid hinder particle movement and generate background currents, which are a major cause of reduced contrast ratio. This invention fundamentally blocks electrical noise by selectively capturing these harmful ions through MOFs having a specific range of pore sizes. Furthermore, nanocapsules containing high-dielectric constant solvents efficiently transmit the electric field without increasing the conductivity of the entire medium, enabling the realization of high-contrast full-color displays with distinct contrast differences between black and white.

[0033] Fourth, the adoption of a nonionic and fluorinated system provides high resistance to environmental changes. Conventional systems relying on polar functional groups had a vulnerability where particles aggregated due to changes in solubility with temperature variations; however, the present invention utilizes structural steric repulsion and nonpolar interactions as the primary mechanisms. Consequently, the physical and electrical properties of the fluid remain unchanged even in sub-zero temperatures or high-temperature, high-humidity environments, maintaining uniform driving performance. This provides the effect of extending the lifespan of electronic price tags (ESLs) and wearable devices that are frequently exposed to the outside.

[0034] Finally, the numerical limitations of each component presented in this invention have critical significance for the optimal operation of electrophoretic displays, such as buoyancy balance to prevent particle sedimentation, particle size control for optimal light scattering, and ion concentration control to prevent excessive leakage current. Through this, the yield of the entire manufacturing process is increased, and core material technology for next-generation electrophoretic displays capable of realizing high resolution and full color is provided. Brief explanation of the drawing

[0035] FIG. 1 is a schematic diagram comparing the particle surface adsorption type and fluid behavior of a linear dispersant according to the prior art and a three-dimensional dendrimer structure dispersant according to the present invention. (a) Conventional linear dispersant: formation of high viscosity due to chain entanglement. (b) Dendrimer dispersant of the present invention: low viscosity and high density steric hindrance formation due to a spherical structure. FIG. 2 is a conceptual diagram showing the electrical double layer (EDL) and ion pair dissociation equilibrium formed around an electrophoretic particle by an imidazolium-based ionic liquid according to one embodiment of the present invention. Specific details for implementing the invention

[0036] The present invention is capable of various modifications and may have various embodiments; specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, and the methods for achieving them, will become clear by referring to the embodiments described below in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various forms.

[0037] FIG. 1 is a schematic diagram comparing the particle surface adsorption type and fluid behavior of a linear dispersant according to the prior art and a three-dimensional dendrimer structure dispersant according to the present invention.

[0038] FIG. 1(a) shows a conventional linear dispersant forming high viscosity due to chain entanglement. FIG. 1(b) shows the dendrimer dispersant of the present invention forming low viscosity and high density steric hindrance due to a spherical structure.

[0039] Referring to Figures 1(a) and 1(b), the physical properties according to the difference in geometric structure of the dispersant that helps the stable dispersion of particles in the electrophoretic medium are as follows.

[0040] 1. Characteristics of Linear Dispersants

[0041] Linear dispersants have a structure in which long molecular chains are connected in a one-dimensional manner and arranged in a disordered manner. This long-chain structure causes entanglement, a phenomenon in which neighboring molecules become intricately entangled within the fluid. Such entanglement between chains causes a rapid increase in the internal frictional resistance of the fluid, resulting in high viscosity. Consequently, the movement speed of electrophoretic particles is inevitably limited within a fluid with high viscosity.

[0042] 2. Characteristics of Dendrimer Dispersants

[0043] Dendrimer (or hyperbranched) dispersants form a three-dimensional spherical structure in which branch structures extend uniformly from a central nucleus. This structure maintains a very compact and aligned geometric shape, and unlike linear structures, physical entanglement between chains does not occur. Therefore, it can maintain low viscosity in fluids and significantly reduce frictional resistance when particles move.

[0044] 3. Technological Advantage and Effects

[0045] When the dendrimer structure is adsorbed onto the particle surface, it forms a high-density protective layer, providing effective steric hindrance that blocks mutual access between particles. This fundamentally prevents particle aggregation while simultaneously accelerating particle movement by utilizing low viscosity characteristics. Consequently, by introducing a dendrimer dispersant, it is possible to simultaneously achieve high-speed response and excellent dispersion stability, which are key performance characteristics of electrophoretic displays.

[0046] FIG. 2 is a conceptual diagram showing the electrical double layer (EDL) and ion pair dissociation equilibrium formed around an electrophoretic particle by an imidazolium-based ionic liquid according to one embodiment of the present invention.

[0047] Referring to Figure 2, the charge formation mechanism on the surface of electrophoretic particles and the behavior of charge control agents in the fluid are explained by the following two key physical mechanisms.

[0048] 1. Electric Double Layer (EDL): Electrical stabilization of particles

[0049] An electrical double layer (EDL) is formed on the particle surface to ensure charge stability. The Stern layer, formed by the strong adsorption of cations directly onto the particle surface, plays a key role in charge imparting. On the outer edge, a diffuse layer exists where ions are loosely distributed as they move away from the particle, and these layers exhibit fluid behavior depending on the movement of the particle. This double-layer structure neutralizes the charge surrounding the particle while generating a potential difference (zeta potential), allowing the particles to maintain a stable electrical state within the fluid without clumping together.

[0050] 2. Ion-Pair Dissociation Equilibrium: Dynamic Generation of Charge

[0051] Ionic liquid-based charge control agents introduced into a nonpolar fluid maintain an ion pair dissociation equilibrium. In the low dielectric constant environment of a nonpolar solvent, cations and anions essentially exist as ion pairs bound to each other. However, through externally applied thermal energy, a spontaneous dissociation process occurs, and the bound ion pairs separate into individual ions that can move freely. Through this dissociation equilibrium process, continuously supplied free ions participate in the formation of an electrical double layer, imparting robust charge characteristics to the particles.

[0052] 3. Technical Significance

[0053] The formation of an electrical double layer and the dissociation equilibrium of ion pairs are the fundamental principles for realizing the strong charge stability and bistable pursued by the present invention. In particular, this system utilizing an imidazolium-based ionic liquid enables the construction of a more robust double layer on the particle surface than the conventional quaternary ammonium salt method, which consequently leads to the realization of a highly reliable display in which image retention remains unchanged even with changes in the external environment.

[0054] 1. Components of a fluid composition for an electrophoretic display

[0055] The fluid composition for an electrophoretic display according to the present invention is driven by the interaction of four major key components.

[0056] Nonpolar dielectric solvent: Forms a continuous phase that serves as the transport medium for particles.

[0057] Electrophoretic particles: These are dispersed phases that move in response to an external electric field and form a visible image.

[0058] Hybrid Charge Control Agent (CCA): Contains an ionic liquid and imparts a stable charge to particles.

[0059] 3D structured dispersant: Prevents particle aggregation through dendrimer or hyperbranch structures.

[0060] Heterogeneous dielectric property regulators: Precisely control the electrical properties of fluids by including nanocapsules or MOFs.

[0061] 2. Detailed description and physicochemical properties of each component

[0062] a. Charge control system: Hydrophobic ionic liquid

[0063] The fluid composition for electrophoretic display of the present invention excludes traditional quaternary ammonium functional group-based CCA and uses an imidazolium or pyridinium-based hydrophobic ionic liquid as the main component.

[0064] Physicochemical Advantage: Conventional CCAs rely on chemical bonding forces with particle surfaces to form charges, making them vulnerable to environmental changes. In contrast, ionic liquids form a spontaneous ion-pair dissociation equilibrium within the fluid. This enables the formation of a very robust and thick electric double layer around the particles, providing excellent bistability in which charge density is not lost even with repeated voltage application.

[0065] While conventional ionic CCAs have difficulty completely canceling out the electrical attraction between particles, hydrophobic imidazolium salts form a thicker and more robust electrical double layer (EDL) around the particles with large volumes of cations and anions, effectively suppressing the electrostatic cohesive force that causes particles to stick together.

[0066] To control the charge on the particle surface, one or more of the following ionic liquids and salts are mixed and used.

[0067] 이미다졸리움계: 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imi de, 1-Ethyl-3-methylimidazolium hexafluorophosphate, 1-Hexyl-3-methyl imidazolium tetrafluoroborate, 1-Octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-Decyl-3-methylimidazolium bromide, 1-Dodecyl-3-methylimidazolium chloride, 1-Tetradecyl-3-methylimidazolium iodide 등.

[0068] 피리디늄계: N-Butylpyridinium bis(trifluoromethylsulfonyl)imide, N-Hexylpyridinium hexafluorophosphate, N-Octylpyridinium tetrafluoroborate, 1-Butyl-4-methylpyridinium chloride, 1-Ethyl-3-hydroxymethylpyridinium ethylsulfate 등.

[0069] 기타 소수성 이온성 액체: 1-Methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide, 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, Tetrabutylphosphonium p-toluenesulfonate 등.

[0070] It includes dozens of types of hydrophobic ionic molecules as compounds, such as 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-Ethyl-3-methylimidazolium hexafluorophosphate, N-Octylpyridinium tetrafluoroborate, and 1-Decyl-3-methylimidazolium bromide.

[0071] B. Dispersion Stabilization System: 3D Structured Dispersant

[0072] The present invention deviates from the 'linear tail' structure of the target patent and adopts a geometrically differentiated dendrimer or hyperbranched structure.

[0073] Physicochemical Advantage: Linear polymers are disordered and unraveled on the particle surface, failing to completely prevent inter-particle penetration and increasing fluid viscosity due to chain entanglement. The three-dimensional structure of the present invention is a spherical structure with branches extending from the center, forming high-density steric hindrance that completely covers the particle surface. This eliminates chain entanglement, thereby maintaining low viscosity characteristics while maximizing dispersion power, dramatically increasing the response speed of electrophoretic displays.

[0074] The following compounds are used to maximize steric hindrance and nonpolar repulsion.

[0075] Dendrimer / hyperbranched systems: PAMAM (Polyamidoamine) Dendrimers (G1-G5), PPI (Poly(propylene imine)) Dendrimers, Boltorn™ series (H20, H30, H40), Hyperbranched Polyglycidol, Hyperbranched Polyesteramides, Hyperbranched Polyurethanes, Hyperbranched Polycarbonates, etc.

[0076] Fluorinated: Perfluorooctyl acrylate, Perfluorodecyl acrylate, 1H,1H,2H,2H-Perfluorooctyltriethoxysilane, Perfluoropolyether (PFPE)-based nonionic surfactants, Perfluorinated Dendritic Polymers, Poly(perfluoroalkylethyl methacrylate), etc. Examples of compounds: PAMAM Dendrimers (G1-G5), Boltorn™ H2O / H3O / H4O, Hyperbranched Polyesteramides, nonionic fluorinated surfactants (Perfluoropolyether-based), etc.

[0077] C. Dielectric Property Controllers: Nanocapsules and Metal-Organic Frameworks (MOFs)

[0078] Instead of conventional soluble additives such as water-soluble ethers, the present invention introduces a heterogeneous phase that does not mix with the medium.

[0079] Metal-organic frameworks (MOFs) are porous crystalline compounds formed through coordination bonding between metal ions (or metal clusters) and organic crosslinking agents (ligands). In fluid compositions for electrophoretic displays, MOFs are utilized as key materials that control the electrical purity and dielectric properties of the fluid, going beyond the role of simple additives.

[0080] (1) Structural features and mechanism

[0081] MOFs possess a very high specific surface area due to the regular arrangement of nanoscale pores within a lattice structure. In this invention, this structure is utilized to implement the following mechanism.

[0082] Selective Ion Scavenging: Blocks electrical noise by trapping residual impurity ions present in the fluid inside the pores.

[0083] Precise control of dielectric properties: Uniformly controls the dielectric constant distribution throughout the fluid by encapsulating specific molecules within the pores or utilizing the properties of the framework itself.

[0084] Physicochemical advantages: Nanocapsules contain high dielectric constant solvents to locally accelerate particle mobility, and MOFs selectively scavenge excess ions in the fluid through their porous structure. This blocks electrical noise in the entire fluid and ensures temperature stability, thereby realizing high contrast.

[0085] It includes various MOF structures such as polymer nanocapsules filled with propylene carbonate as a compound, ZIF-8 (Zinc (Zn), 2-Methylimidazole), UiO-66 (Zirconium (Zr), Terephthalic acid), MIL-101 (Chromium (Cr) Terephthalic acid), and HKUST-1 (Copper (Cu) Trimesic acid).

[0086] Nanocapsule core materials: Propylene Carbonate, Ethylene Carbonate, Gamma-Butyrolactone, Dimethyl Sulfoxide (DMSO), N-Methyl-2-pyrrolidone (NMP), Acetonitrile, etc.

[0087] Metal-organic frameworks (MOFs): porous crystalline structures such as ZIF-8 (Zinc-imidazolate), UiO-66 (Zirconium-based), MIL-101 (Cr) (Chromium (Cr), Terephthalic acid), MOF-5 (Zn), HKUST-1 (Cu) (Copper (Cu), Trimesic acid), PCN-222, NU-1000, etc.

[0088] 3. Critical Significance of Numerical Limitations

[0089] The numerical range specified in the present invention defines a critical limit point for optimal driving of an electrophoretic display.

[0090] Composition content (0.01 ~ 5.0 wt%): Less than 0.01 wt%, particle charging and dispersion stabilization are impossible, and when exceeding 5.0 wt%, fluid viscosity increases excessively, causing particle behavior to stop or power consumption to increase rapidly.

[0091] Particle size (50 nm ~ 500 nm): Less than 50 nm, uncontrollable Brownian motion is dominant, and if it exceeds 500 nm, precipitation by gravity occurs, shortening the lifespan of the display.

[0092] MOF pore size (5 Å ~ 30 Å): Less than 5 Å results in a significantly reduced capture rate of impurity ions, and exceeding 30 Å results in the capture of charge control agents, which are essential components in the fluid, causing adverse effects that interfere with charge formation. The optimal range (5 ~ 30 Å) is a critical range that minimizes the background current of the electrophoretic display and maintains the highest contrast ratio.

[0093] 4. Preparation Example of Hybrid Charge Control Agent (CCA)

[0094] Preparation Example 1-1 : Imidazolidium-based hydrophobic ionic liquids CCA1-methylimidazole and 1-bromodecane are mixed in a 1:1.1 molar ratio and a quaternization reaction is carried out at 80°C for 24 hours with stirring. The resulting 1-decyl-3-methylimidazolidium bromide is washed with distilled water, and then an ion exchange reaction is performed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Finally, liquid 1-decyl-3-methylimidazolidium TFSI, which has excellent miscibility with hydrophobic media, is obtained.

[0095] Preparation Example 1-2: Pyridinium-based ion pairs CCA pyridine and 1-chlorooctane are refluxed in acetonitrile solvent for 12 hours. After the reaction is complete, the solvent is removed, and sodium hexafluorophosphate (NaPF6) is added to replace the anions. Through this, N-octylpyridinium hexafluorophosphate (N-octylpyridinium PF6) salt, which has excellent dissociation equilibrium in a non-polar dielectric solvent, is prepared, which is physically adsorbed onto the particle surface to form a stable electrical double layer.

[0096] Preparation Examples 1-3 : Heterionic liquid blending CCA imidazolium TFSI (Preparation Example 1-1) and a pyrrolidinium-based ionic liquid are mixed in a weight ratio of 7:3. By mixing cations of different sizes, the mobility of ions within the fluid is diversified, and the degree of ion dissociation is induced not to drop sharply even in low-temperature regions, thereby completing a hybrid CCA with enhanced temperature stability.

[0097] 5. Example of preparation of a three-dimensional structured dispersant

[0098] Preparation Example 2-1 : Fluorinated hyperbranched polyester dispersant Boltorn™ H30 (hyperbranched polyester) is dissolved in tetrahydrofuran (THF), and then 50% of the terminal hydroxyl groups are reacted with perfluorooctanoyl chloride. Through this process, a three-dimensional spherical fluorinated hyperbranched polymer is prepared in which the inner core of the molecule maintains multi-point adsorption function and the outer shell is covered with nonpolar fluorine chains.

[0099] Preparation Example 2-2: PAMAM-based dendrimer nonionic dispersant G3 (3rd generation) polyamidoamine (PAMAM) dendrimer is used as a starting material, and an ethylene oxide (EO) unit is added to the terminal amine group. Subsequently, a hydrophobic alkyl chain is additionally grafted onto the terminal to produce a spherical nonionic dendrimer dispersant in which the polar group is minimized while the steric hindrance effect on the particle surface is maximized.

[0100] Preparation Example 2-3 : A hyperbranched polyurethane precursor is synthesized using isophorone diisocyanate (IPDI) and trimethylolpropane (TMP). By introducing a non-polar silicone chain (polydimethylsiloxane) at the ends, a supramolecular dispersant with a network structure is obtained that can maintain low fluid viscosity without chain entanglement.

[0101] 6. Preparation Example of a Heterogeneous Genetic Characteristic Regulator

[0102] Preparation Example 3-1 : A high dielectric constant solvent-encapsulated nanocapsule emulsion polymerization method is used. Interfacial polymerization is carried out using propylene carbonate (PC) as the core material and methyl methacrylate (MMA) as the shell material. PC-PMMA nanocapsules with an average particle size of 150 nm are prepared, which exist in a dispersed state without dissolving in the solvent, thereby locally improving the dielectric constant.

[0103] Preparation Example 3-2 ZIF-8 (MOF) nanoparticles for ion capture: Zinc nitrate and 2-methylimidazole are mixed in a methanol solvent and reacted at room temperature for 24 hours. Through centrifugation and washing processes, ZIF-8 (metal-organic framework) nanocrystals (approx. 100 nm) with a pore size of approximately 11 Å are obtained. These selectively trap residual impurity ions in the fluid to eliminate electrical noise.

[0104] Preparation Example 3-3Surface-modified UiO-66 MOF modifier: After synthesizing UiO-66, a zirconium-based MOF, the surface is hydrophobically treated with octyltriethoxysilane. This ensures dispersibility in non-polar dielectric solvents and completes a functional nanofiller that uniformly controls the dielectric constant distribution of the fluid through its porous structure.

[0105] 7. Example of preparing a fluid composition for an electrophoretic display

[0106] Preparation Example 4-1: 4-component color fluid composition (white / black / red / yellow)

[0107] To minimize electrical interference between particles and increase color reproduction power relative to 100 parts by weight of Isopar-G solvent, particles are formulated as follows.

[0108] Particle input: 20 parts by weight of surface-modified TiO₂ particles (white), 1.5 parts by weight of iron oxide (Fe₂O₃) particles (black), 3.5 parts by weight of pigment red 254 (red), and 3.5 parts by weight of pigment yellow 155 (yellow) are added.

[0109] Additive mixing: Here, 0.8 parts by weight of imidazolium CCA of Preparation Example 1-1, which has a high charge contribution, 2.5 parts by weight of fluorinated hyperbranch dispersant of Preparation Example 2-1, which prevents aggregation between particles, and 0.3 parts by weight of ZIF-8 MOF of Preparation Example 3-2, which captures ionic impurities to enhance bistables, are mixed.

[0110] Dispersion process: After vigorously stirring at 3,000 rpm for 3 hours using a high-shear stirrer, additionally disperse for 30 minutes using an ultrasonic disperser (Vibra-Cell) to prepare a color fluid composition in which the charge distribution of the four types of particles is uniformly controlled.

[0111] Preparation Example 4-2: Low-viscosity fluid composition for high-speed response

[0112] 0.3 parts by weight of Pyridinium CCA of Preparation Example 1-2 and 1.0 parts by weight of Dendrimer Dispersant of Preparation Example 2-2 are added to a hydrocarbon-based solvent. Additionally, 0.5 parts by weight of Nano Capsules of Preparation Example 3-1 are added to control the viscosity to 8.5 cP or less. This composition exhibits a response speed that is 35% improved compared to the conventional one.

[0113] Preparation Example 4-3: Fluid composition with enhanced environmental stability

[0114] The blended CCA of Preparation Example 1-3 and the silicon-based hyperbranch dispersant of Preparation Example 2-3 are used. By adding 0.3 parts by weight of the hydrophobic UiO-66 of Preparation Example 3-3, a high-reliability fluid composition for an electrophoretic display is prepared in which the change in charge density is less than 5% even in a wide temperature range of -20℃ to 70℃.

[0115] Preparation Example 5: Preparation of a fluid composition for an electrophoretic display containing MOF

[0116] In this embodiment, a final formulation ratio and process are presented to optimize charge transfer efficiency in the fluid by introducing ZIF-8 (Zinc Imidazolate Framework-8) MOF and to realize independent behavior of four types of particles.

[0117] A. Formulation Table

[0118] Table 1: Composition Formula Table

[0119]

[0120] B. Manufacturing Process

[0121] Particle Wetting and Primary Dispersion: The entire amount of hyperbranch dispersant is dissolved in 60% of dodecane solvent. White, black, red, and yellow particles are sequentially added to this, and the mixture is wetted using a homogenizer at 2,000 rpm for 1 hour.

[0122] High-precision bead milling: To homogenize the particle size to the level of 200~300 nm, high-shear milling is performed at 3,500 rpm for 3 hours using a bead mill (Bead Mill, using 0.1 mm zirconia beads).

[0123] MOF and ionic liquid complexation: ZIF-8 powder and imidazolium CCA are added to the remaining solvent. Ultrasonication is performed for 1 hour so that the ionic liquid is partially impregnated into the pores of ZIF-8 and gradually releases the charge, after which this is added to the particle dispersion above.

[0124] Final stabilization and filtering: The entire mixture is stabilized for 2 hours with low-speed stirring (500 rpm) to allow the dispersant and CCA to reach chemical equilibrium on the surface of the four types of particles. Finally, large aggregates are removed through a 1 µm mesh filter to complete the four-component color electrophoretic fluid.

[0125] 8. Experimental Example of Microcapsule Preparation for Electrophoretic Displays

[0126] Example 1-1: Polyurea shell microcapsules using interfacial polymerization

[0127] An oil phase is prepared by dissolving 5g of polyfunctional isocyanate (TDI) in 100g of the fluid composition of Preparation Example 4-1. This is added to 400ml of a 5% aqueous gum arabic solution and emulsified at 3,000rpm using a high-shear stirrer. An aqueous ethylenediamine (EDA) solution is slowly added dropwise to induce interfacial polymerization at 60°C for 4 hours. Uniform polyurea microcapsules with an average particle size of 50–100μm are obtained, which possess mechanical properties resistant to external impact.

[0128] Examples 1-2 : Complex Coacervation-based Gelatin Shell Microcapsules

[0129] The low-viscosity fluid composition of Preparation Example 4-2 is dispersed in a mixed solution of gelatin and gum arabic. The pH is adjusted to 4.5 to allow the coacervate to immerse around the oil droplets, and then the temperature is rapidly cooled to 10°C or lower. Glutaraldehyde is added to harden the shell to produce an eco-friendly gelatin microcapsule. This method is advantageous for improving contrast ratios because the shell has high transparency.

[0130] Examples 1-3 : Melamine-formaldehyde capsules produced by in-situ polymerization

[0131] A melamine and formaldehyde prepolymer is prepared in an aqueous solution. The prepolymer is introduced into an emulsion system in which the fluid composition of Preparation Example 4-3 is dispersed, and polymerization is carried out by heating to 70°C under acidic conditions (pH 3-4). Melamine resin microcapsules with a very dense structure are formed, preventing long-term leakage of the internal ionic liquid or fluid composition.

[0132] 9. Experimental example of preparing an electrophoretic film containing microcapsules

[0133] Example 2-1: Slot die coated film using a water-based binder

[0134] A coating slurry is prepared by mixing 50g of the microcapsules from Example 1-1, 20g of a water-soluble polyurethane binder, and 0.1g of a surfactant. This is applied to a thickness of 100μm on a PET film coated with ITO (Indium Tin Oxide) using a slot die coater. A flexible electrophoretic film is prepared by drying in an 80°C oven for 10 minutes.

[0135] Example 2-2: UV-curable binder-based roll-to-roll (R2R) coating film

[0136] The capsules of Examples 1-3 are dispersed in a UV-curable acrylate resin. After continuous coating on a transparent electrode substrate using a roll-to-roll system, the film is cured in seconds by passing it through a UV irradiation device (365 nm). This process has a very fast production speed and can obtain a film with improved transmittance by matching the refractive index of the binder with the fluid.

[0137] Example 2-3: High-density monolayer film using the electrostatic spray method

[0138] By applying voltage to a microcapsule slurry and electrostatically spraying it through a nozzle, the capsules are densely arranged in a monolayer on an electrode substrate. By minimizing the binder content and reducing the gaps between capsules, a film with a maximized aperture ratio is manufactured.

[0139] 10. Experimental Example of Manufacturing a Display Layer with a Unit Cell Structure

[0140] Example 3-1 : Partition Wall structure cell using photolithography

[0141] After applying a photosensitive resin onto a transparent substrate, a partition structure (Honeycomb or Square) with a height of 40 μm and a width of 10 μm is formed through exposure and development processes. After precisely injecting the fluid composition of Preparation Example 4-1 into each unit cell using an inkjet printing method, the upper substrate is laminated to complete the partition-type unit cell display layer. This structure prevents afterimages by blocking the lateral movement of particles.

[0142] 11. Experimental example of manufacturing an electrophoretic display containing microcapsules

[0143] Example 4-1 : TFT Substrate-Combined Active Matrix (AM) Display

[0144] A conductive adhesive (OCA) is applied to the back surface of the electrophoretic film prepared in Example 2-1. This is laminated by precisely aligning it with a thin-film transistor (TFT) array substrate. A high-resolution electrophoretic display capable of individual control for each pixel is manufactured by connecting a driver IC. Thanks to the low-viscosity fluid of the present invention, high-speed driving of 50 Hz or higher is possible. A reflective full-color electrophoretic display that maintains vivid colors is completed thanks to the high contrast ratio of the fluid composition containing MOF.

[0145] Example 4-2: Segment-type driven flexible display

[0146] Patterned electrodes are formed on a flexible plastic substrate, and the high-density film of Examples 2-3 is laminated. A low-power wearable display is manufactured that displays only specific information through segment electrodes patterned with numbers or characters. Thanks to the stability of the dendrimer dispersant, no image distortion occurs even with repeated bending with a bending radius of 5 mm or less.

[0147] 12. Test Example

[0148] Test Example 1: Performance Evaluation According to Charge Control Agent (CCA) Content

[0149] Exam Objectives

[0150] The correlation between charge retention performance and power consumption (leakage current) according to changes in the content of Preparation Example 1-1 (1-decyl-3-methylimidazolium TFSI) is demonstrated, and the technical superiority over the conventional quaternary ammonium salt (OTAB) is confirmed.

[0151] Experimental design

[0152] The concentration of the charge control agent (CCA) in the fluid composition for the electrophoretic display is varied from 0.005 wt% to 10.0 wt% and injected. After 1,000 hours of continuous operation, the zeta-potential retention rate is measured and the leakage current generated during operation is monitored.

[0153] Measurement results

[0154] Table 2: Performance evaluation results according to charge control agent (CCA) content

[0155]

[0156] The 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (Preparation Example 1-1, TFSI) used in Test Example 1 increases the miscibility of the alkyl chain of the imidazolium cation with a hydrophobic medium and allows the TFSI anion to maintain a stable dissociated state in the fluid.

[0157] Physical adsorption mechanism:This compound is physically adsorbed onto the particle surface without separate chemical bonding and achieves ion-pair dissociation equilibrium. As confirmed by the results in the table, this serves as the key technical basis for recording a charge retention rate of 95%, which is significantly higher than that of conventional OTAB (Comparative Example 1).

[0158] Charge stability: The ionic liquid of Preparation Example 1-1 exhibited superior charge retention performance compared to conventional OTAB even at a minute amount of 0.01 wt%. This is because the ionic liquid achieves dynamic dissociation equilibrium within the medium and rebuilds a strong electric double layer on the particle surface.

[0159] Reason for numerical limitation: In order to realize the effects of the present invention through Test Examples 1-1 to 1-5, the CCA concentration must 0.01 ~ 5.0 wt% It was proven that it must be controlled within a range. In particular, when it exceeds 5.0 wt% (Test Example 1-5), the leakage current increases by nearly 10 times without an additional increase in charge retention rate, thus confirming the criticality of setting an upper limit for low power consumption driving.

[0160] Test Example 2: Dispersant Structure and Viscosity-Response Rate Correlation Test

[0161] Exam Objectives

[0162] This demonstrates the effect of the three-dimensional structure of Preparation Example 2-1 (fluorinated hyperbranched polyester) on achieving low viscosity and improving response speed compared to conventional linear dispersants.

[0163] Experimental design

[0164] The dispersant content is fixed at 1.5 wt%, and the fluid viscosity (25 ℃) and white-black transition response time (Rise Time) are measured according to structural differences.

[0165] 3. Result Analysis

[0166] Table 3: Dispersant Structure and Viscosity-Response Rate Correlation Test Results

[0167]

[0168] 1. Achievement of low viscosity through 3D structure

[0169] Conventional linear dispersants (Comparative Example 2) exhibit a high viscosity of 13.5 cP due to the entanglement of molecular chains, but the hyperbranch and dendrimer structures of the present invention (Test Examples 2-1, 2-2) fundamentally solve this problem and maintain the viscosity at a level of 7.9 to 8.2 cP, which is reduced by about 40%.

[0170] 2. Dramatic reduction in response time (achieved less than 200 ms)

[0171] As fluid viscosity decreases, the drag force exerted by particles within the solvent is significantly reduced. As a result, the white-black transition response time is shortened from the conventional 390 ms to 185–195 ms, securing a high-speed response speed that is more than twice as fast as that of conventional technology.

[0172] 3. Enhancement of steric hindrance and dispersion stability

[0173] In particular, the dendrimer structure (Test Example 2-2) forms strong steric hindrance on the particle surface through a dense three-dimensional spherical structure. This plays a role in maximizing dispersion stability by effectively blocking aggregation between particles while maintaining low viscosity characteristics.

[0174] Through this test, it was proven that changing the geometric structure of the dispersant from linear to a three-dimensional network or spherical structure is a key technical critical factor for realizing viscosity reduction of the electrophoretic fluid and high-speed driving of the display.

[0175] Test Example 3: Performance test according to pore size of heterogeneous phase modifier (MOF)

[0176] Exam Objectives

[0177] Confirm the critical significance of the pore size of Preparation Example 3-2 (ZIF-8) on the improvement of impurity ion capture efficiency and contrast ratio (CR).

[0178] Experimental design

[0179] Three types of MOFs with different pore sizes are added at 0.2 wt%, and the noise (background current) and contrast ratio during operation are measured.

[0180] Table 4: Performance test results table according to pore size of heterogeneous phase control agents (MOFs)

[0181]

[0182] 1. Electrical noise blocking effect through background current reduction

[0183] Comparative Example 3 (Prior Art): When a soluble regulator such as water-soluble PEG is used, the background current is very high at 480 nA. This is because ions dissolved in the fluid move freely according to the electric field and generate electrical noise.

[0184] Test Examples 3-1 and 3-2 (The present invention): As a result of introducing a heterogeneous MOF material, the background current decreases sharply to a level of 92 to 115 nA. This demonstrates that the porous structure of the MOF effectively captures impurity ions in the fluid, thereby fundamentally blocking noise caused by charge transfer.

[0185] 2. Selective Capture Performance and Critical Significance According to Pore Size

[0186] Test Example 3-1 (ZIF-8, pores 11A˚): Recorded the best noise blocking performance with a background current of 92 nA. It was proven that the micropores of 11A˚ are a critical size optimized for selectively scavenging only fine impurity ions in the fluid.

[0187] Test Example 3-2 (UiO-66, pore size 25A˚): As the pore size increases, the background current rises slightly to 115 nA, but still maintains superior performance compared to conventional technology. This suggests that controlling the pore size has the effect of inducing a uniform distribution of the dielectric constant.

[0188] 3. Achievement of High Image Quality through Contrast Ratio (CR) Enhancement

[0189] Contrast ratio analysis: Comparative Example 3 shows a low contrast ratio of 8:1 due to noise, whereas Test Example 3-1, which uses ZIF-8, shows a contrast ratio of 16:1, which is exactly twice as high. As electrical noise is eliminated, the behavior of black and white particles is accelerated and arranged more precisely on the electrode surface, thereby realizing a clear screen.

[0190] This test demonstrated that, unlike conventional methods where MOFs dissolve in fluids and cause noise, the introduction of MOFs with specific pore sizes plays a decisive role in controlling impurity ions and improving image quality. In particular, ZIF-8, with a pore size of approximately 11 Å, provides a key numerical range capable of maximizing the contrast ratio of electrophoretic displays.

[0191] Test Example 4: Test of dispersion stability and optical properties according to particle size

[0192] Exam Objectives

[0193] Demonstrates the critical significance of the size of electrophoretic particles (50 to 500 nm) on gravity sedimentation and reflectance (saturation).

[0194] Experimental design

[0195] In the composition of Preparation Example 4-1, the average particle diameter is varied, and the sedimentation rate and color saturation after stacking color filters are measured after leaving it for 90 days.

[0196] Table 5: Table of test results for dispersion stability and optical properties according to particle size

[0197]

[0198] 1 . Derivation of optimal particle size range (100~300 nm)

[0199] When the particle size is in the range of 100 to 300 nm (Test Examples 4-2, 4-3), the sedimentation rate is extremely low at 1.1% or less, and the saturation reaches a maximum of 35. This proves that the steric hindrance effect of the dendrimer dispersant and the buoyancy of the particles are in optimal equilibrium, thereby maintaining a state of high dispersion and high saturation.

[0200] 2. Problems when lower threshold is not met (less than 100 nm)

[0201] When the particle size is 30 nm (Test Example 4-1), dispersion stability is good, but the saturation drops sharply to level 11 due to a lack of light scattering power. This suggests that a particle size of a certain level or larger is essential for realizing vivid colors.

[0202] 3. Problems when the upper threshold is exceeded (exceeding 500 nm)

[0203] When the particle size exceeds 500 nm (Test Example 4-5), the sedimentation rate increases rapidly to 24.1% because Brownian motion alone cannot overcome gravity due to the weight of the particles. As the particles become heavier, dispersion stability and optical properties show a tendency to deteriorate simultaneously.

[0204] MOF (ZIF-8), which is a key component of the present invention, removes electrical noise ions to increase background purity, and the dendrimer dispersant forms strong steric hindrance between 100-300 nm particles, thereby being superior to the prior art (Comparative Example 4) in terms of preventing precipitation and color clarity.

[0205] Experimental results confirmed that the critical range of particle size for long-term storage stability and high-contrast color realization of electrophoretic displays is 100–500 nm, and that optimal performance is observed particularly at 100–300 nm.

[0206] Test Example 5: Full-color reflectance and temperature stability test following the introduction of nanocapsules

[0207] Exam Objectives

[0208] We verify the effect of dielectric constant control nanocapsules on maintaining reflectance in a temperature change environment (-20 to 60 ℃).

[0209] Table 6: Full-color reflectance and temperature stability test results following the introduction of nanocapsules

[0210]

[0211] Comparative Example 5 (Dissolved type): It exhibits a reflectance of 25% at low temperature (-10℃) and 38% at high temperature (60℃). This is a level where the screen is generally dark and opaque.

[0212] Test Example 5 (Capsule type): It recorded a reflectance of 42% at low temperature and 44% at high temperature, showing a value more than 1.5 times higher than the comparative example. This means that the nano capsules optimize the movement of particles to realize brighter and clearer white and color screens.

[0213] In the comparative example, the reflectance fluctuates by as much as 13% with temperature changes, whereas the test example of the present invention exhibits a deviation of only 2%*. Conventional dissolved type (comparative example): In a form where the modifier is directly dissolved in the fluid, as the temperature decreases, solubility drops, causing components to precipitate or the viscosity and dielectric constant of the fluid to change rapidly, thereby hindering the movement of particles. As a result, a phenomenon occurs where the screen darkens rapidly as the temperature decreases.

[0214] Capsule type of the present invention (Test Example): The control component is protected within a nano-capsule, minimizing chemical and physical effects caused by external temperature changes. This enables 'temperature-independent driving,' allowing for the maintenance of nearly identical screen quality even in extreme environments such as winter (-10℃) or summer (60℃).

[0215] Electrophoretic displays (electronic paper) are primarily used outdoors or in various environments. While existing technologies suffered from critical drawbacks, such as slow screen transitions or blurring in cold weather, the introduction of nano-capsule technology suggests that these environmental limitations have been completely overcome.

[0216] Test Example 6: Evaluation of Ion Capture and Contrast Ratio Performance with and without MOF

[0217] Test conditions

[0218] Panel structure: ITO / Fluid layer (40μm) / ITO (Test unit cell)

[0219] Driving voltage: ±15 V Square wave

[0220] Measuring equipment: Spectrophotometer (Minolta CM-2600d) and precision ammeter (Keithley 6487)

[0221] Table 7: Performance evaluation results of ion capture and contrast ratio according to the presence or absence of MOF

[0222]

[0223] Result Analysis and Critical Significance

[0224] Background current blocking effect: In the comparative example that did not include MOF (ZIF-8), fine impurity ions in the fluid moved according to the electric field and generated a background current of about 420 nA. On the other hand, Example 5 drastically reduced the background current to 85 nA by physically scavenging these impurity ions through the porous structure of ZIF-8.

[0225] Black State Depth Enhancement: As the background current was blocked, the black particles could adhere more closely to the electrode surface. This was because disordered movement (noise) between particles was suppressed, and as a result, the black reflectance was reduced from 4.2% to 2.8%, achieving a deeper and richer black color.

[0226] Dramatic Improvement in Contrast Ratio (CR): With the simultaneous increase in white reflectance and decrease in black reflectance, the overall contrast ratio improved by more than 1.7 times. This suggests that the addition of MOF is indispensable for securing visibility similar to paper.

[0227] Table 8: Characteristics Summary

[0228]

[0229] The numerical range of each component claimed in the present invention is of an electrophoretic display Low power - Fast response - High contrast It has been proven to be an organic and critical figure for achieving.

[0230] 1. Fluid Viscosity and Response Speed: "Realization of High-Speed ​​Driving"

[0231] Fluid viscosity (12.5 → 8.2 cP, 34% reduction): Conventional linear polymer dispersants had high viscosity because their molecular chains were prone to entanglement, but the three-dimensional hyperbranched (dendrimer) structure of the present invention maintained a shape close to a sphere, thereby drastically reducing frictional resistance in dielectric solvents.

[0232] Response time (350 → 210 ms, 40% reduction): This is the result of the combination of reduced viscosity and the rapid ionic dissociation characteristics of the imidazolium-based ionic liquid (IL). As particles move faster through the solvent, screen switching speed has been dramatically improved.

[0233] 2. Contrast Ratio (CR) and Color Purity: "Vivid Picture Quality"

[0234] Contrast Ratio (10:1 → 13.5:1, 35% improvement): As dispersion stability increases, particles do not clump together but are densely arranged on the electrode surface. As a result, white is expressed brighter and black / colored is expressed more intensely, achieving much sharper image quality.

[0235] 3. Charge Retention Time and Bistability: "Achieved Ultra-Low Power"

[0236] Charge retention time (600 → 1,000 seconds or more, 66% improvement): The MOF (ZIF-8), which is the core of the present invention, prevents the loss of charge of particles by trapping impurity ions in the fluid. Bistability, which maintains the screen even when the voltage is cut off, is greatly enhanced, allowing for extremely low power consumption when maintaining the screen.

[0237] 4. Temperature Stability (ΔE): "Ensuring Environmental Reliability"

[0238] Temperature stability (3.5 → 1.2, reliability significantly enhanced): A smaller color difference (ΔE) value indicates less color change due to temperature variations. Nano-encapsulation technology and the ion control capabilities of the MOF suppress dielectric fluctuations of the fluid due to temperature, thereby maintaining a constant color even in extreme environments (-20 to 60℃).

[0239] The figures presented in the evaluation results were proven to be critical values ​​generated by the interaction of each component, going beyond simple improvement.

Claims

Claim 1 An electrophoretic display comprising: a first substrate; a second substrate; and a fluid composition for an electrophoretic display disposed between the first substrate and the second substrate; wherein the fluid composition comprises a nonpolar dielectric solvent, at least one type of electrophoretic particle, a charge control agent, and a dispersant; wherein the charge control agent is a hydrophobic ionic liquid comprising an imidazolium or pyridinium cation, and is included in an amount of 0.01 to 5.0 wt% relative to the total weight of the fluid composition; and wherein the dispersant is a polymer compound having a nonionic hyperbranched or dendrimer structure. Claim 2 The electrophoretic display according to claim 1, wherein the average particle size of the electrophoretic particles is 50 to 500 nm; and the fluid composition further comprises a metal-organic framework (MOF) having a pore size of 5 to 30 Å as a dielectric property regulator for dielectric constant and ion control. Claim 3 The electrophoretic display according to claim 1, characterized in that the fluid composition is filled into a microcapsule or filled into a unit cell having a partition wall structure formed between the first substrate and the second substrate. Claim 4 A fluid composition for an electrophoretic display comprising: a nonpolar dielectric solvent; electrophoretic particles dispersed in the nonpolar dielectric solvent; a charge control agent for imparting a charge to the electrophoretic particles; and a dispersant for maintaining the dispersion stability of the particles; wherein the charge control agent is a combination of a 1-alkyl-3-methylimidazolium or N-alkylpyridinium cation and a bis(trifluoromethanesulfonyl)imide (TFSI) or hexafluorophosphate (PF6) anion; and the dispersant is a polymer having a three-dimensional network structure containing a fluorinated alkyl group at its terminal. Claim 5 A fluid composition for an electrophoretic display according to claim 4, characterized in that the absolute value of the zeta potential of the electrophoretic particles in the fluid composition for an electrophoretic display is in the range of 30 to 150 mV, and the zeta potential retention rate after 1,000 hours of operation is 90% or more. Claim 6 A fluid composition for an electrophoretic display according to claim 4, characterized in that the viscosity of the fluid composition for an electrophoretic display at 25°C is in the range of 5 to 10 cP. Claim 7 A fluid composition for an electrophoretic display according to claim 4, characterized in that the fluid composition for the electrophoretic display contains a high dielectric constant solvent and further comprises a heterogeneous phase nanocapsule dispersed in the nonpolar dielectric solvent. Claim 8 A fluid composition for an electrophoretic display according to claim 5, characterized in that the electrophoretic particles form a zeta potential through physical adsorption by the ion-pair dissociation equilibrium of the charge control agent. Claim 9 A fluid composition for an electrophoretic display according to claim 4, wherein the dispersant is a non-ionic compound that does not contain ionic polar groups in its molecular structure and provides dispersion stability through steric repulsion between fluorine chains. Claim 10 A microcapsule for an electrophoretic display characterized by containing a fluid composition for an electrophoretic display according to any one of claims 4 to 6, and including an outer wall (shell) made of a polymer resin. Claim 11 An electrophoretic film comprising: a transparent conductive substrate; and an electrophoretic display layer formed on at least one surface of the substrate; wherein the display layer is characterized in that microcapsules for an electrophoretic display according to claim 10 are arranged in a monolayer or multilayer within a polymer binder. Claim 12 A method for preparing a fluid composition for an electrophoretic display according to any one of claims 4 to 6, comprising: (a) preparing a charge control solution by mixing 0.01 to 5.0 wt% of a 1-alkyl-3-methylimidazolium-based hydrophobic ionic liquid in a nonpolar dielectric solvent; (b) adding a dendrimer dispersant having a three-dimensional spherical structure and electrophoretic particles having an average particle size of 50 to 500 nm to the solution; and (c) adding a metal-organic framework (MOF) and then dispersing the particles using a high-shear stirrer; characterized by comprising the above steps.

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