Electrophoretic display

Abstract

The present invention provides an electrophoretic display device comprising: an upper substrate; a lower substrate; an upper electrode disposed on one surface of the upper substrate; a lower electrode disposed on one surface of the lower substrate; and a display layer disposed between the upper electrode and the lower electrode, wherein the display layer comprises an electrophoretic fluid, the electrophoretic fluid comprises a nonpolar solvent; and a composite pigment particle comprising a core pigment particle and a ternary block copolymer attached to the surface of the core pigment particle, which is dispersed in the nonpolar solvent.

Description

Technology Field

[0001] The present invention relates to an electrophoretic display (EPD), and more specifically, to an electrophoretic display having ultra-low voltage driving, high image quality, improved response speed, and uniform response characteristics, and a method for manufacturing the same. Background Technology

[0002] Electrophoretic displays (EPDs) are non-emissive display technologies that create images by driving charged particles dispersed in a dielectric solvent using an externally applied electric field. Due to paper-like visibility and low power consumption characteristics, their applications are increasing in various fields such as e-books, electronic price tags (ESLs), smart cards, and outdoor billboards. Key performance characteristics of EPDs, such as contrast ratio, color gamut, response speed, and long-term reliability, are entirely determined by the physical and chemical properties of the particles constituting the electrophoretic fluid.

[0003] From early technologies to the present, various techniques have been proposed to ensure the stability of these charged particles.

[0004] First, there is a density matching technique to address the problem of particle sedimentation. A widely known technique involves coating a low-density polymer shell around a pigment core to prevent high-density inorganic pigments (e.g., TiO₂) from settling by gravity in low-density non-polar solvents (e.g., U.S. Patent No. 6,822,782). While this technique has partially improved operational stability by suppressing gravity-induced particle sedimentation, it has limitations in that it does not provide a detailed solution regarding specifically which polymer to coat and how to achieve optimal dispersion stability and electrical properties simultaneously.

[0005] Second, surface stabilization techniques have been proposed to prevent particle aggregation. To address the aforementioned problem, U.S. Patent No. 9,864,253 discloses a technique for chemically bonding a solvent-friendly steric stabilizer to the surface of a polymer shell. This [core-shell-stabilizer] three-stage structure significantly improved dispersion stability through steric repulsion. However, this method requires a complex multi-stage process involving a shell formation process and a stabilizer bonding process, and the interface between the shell and the stabilizer becomes a vulnerable point susceptible to physical and chemical stress, thus containing potential instability that may lead to delamination or degradation during long-term operation.

[0006] Third, there is the traditional charge control method using external additives. To impart charge to particles, which is the core of EPD driving, the most commonly used method involves adding an external Charge Control Agent (CCA) to the electrophoretic fluid. This technology is disclosed in numerous patent documents (e.g., U.S. Patent No. 5,961,804), and small molecule surfactants such as oleic acid or polymeric dispersants such as polyisobutylene succinimide (PIBSA) are used as CCAs. While this method is easy to implement, it has a critical drawback. Over time, CCA molecules detach from the particle surface or decompose under an electric field, generating unwanted ionic impurities within the system. These ionic impurities cause leakage current, increasing the driving voltage, disrupt the charge state of the particles to induce ghosting, and ultimately become the primary cause of shortened display lifespan.

[0007] Fourth, there have been attempts to introduce charge functional groups into the particles themselves. To address the problems of the aforementioned CCA, a technique has been proposed to bond a polymer containing a charged functional group to the surface of pigment particles. For example, a technique is disclosed in which a copolymer containing a charge-carrying functional group, such as an amine, is bonded to pigment particles. While this method was an advanced attempt to reduce dependence on external CCA, it focuses solely on introducing charge functional groups. This technique also failed to consider the function of 'actively removing ionic impurities' that are already present in the system or introduced from the external environment (such as moisture). Therefore, the charge-carrying function alone cannot fundamentally solve the leakage current problem and is still not free from issues of increased driving voltage and shortened lifespan.

[0008] In conclusion, conventional technologies have attempted to solve the individual problems of density matching, dispersion stability, and charge imparting in different ways, but in the process, they have faced chronic issues such as process complexity, structural instability, and, above all, failure to control ionic impurities. This ionic impurity problem acts as the biggest obstacle to achieving the ultimate goals of EPD technology, such as low-voltage operation, improved image quality, and long lifespan.

[0009] Therefore, there is an urgent need to develop a new concept of composite pigment particle technology that has a simple manufacturing process and high structural completeness, while simultaneously generating a stable charge of the particle itself and actively capturing and removing ionic impurities within the system, allowing it to operate at low voltage without an external charge controller and significantly improving long-term reliability. Prior art literature

[0010] 1. US 6,822,782 B22. US 9,864,253 B23. US 5,961,804 B24. WO 2015 / 013279 A1 The problem to be solved

[0011] The problem that the present invention aims to solve is to achieve the highest level of performance and reliability required by next-generation electrophoretic displays (EPDs). To this end, the invention aims to improve the fundamental characteristics of composite pigment particles, which are key materials that determine the image quality, driving efficiency, and durability of the display.

[0012] The problem that the present invention aims to solve is to provide a composite particle with an integrated structure in which a shell function protecting the pigment core and a stabilizer function preventing aggregation between particles are perfectly integrated at the molecular level. Through this structural integrity, the invention aims to realize an inherently robust and highly reliable particle that does not peel off or damage the functional layer even after long-term use.

[0013] The problem that the present invention aims to solve is to endow the composite pigment particles themselves with the function of actively purifying and controlling the ionic environment within the system. Through this, the invention seeks to realize a self-regulating system that minimizes the influence of external factors and maintains a clean and stable operating environment at all times.

[0014] The problem that the present invention aims to solve is to implement an ultra-low power display that is perfectly driven even at a low voltage of 10V or less, in order to maximize battery life and simplify the design of the driving circuit as an ultra-low power drive.

[0015] The problem that the present invention aims to solve is to ensure perfect visibility, like paper, by providing a clean and sharp image that leaves absolutely no trace of the previous screen. To this end, the goal is to fundamentally eliminate image afterimage phenomena.

[0016] The problem that the present invention aims to solve is to realize a display with significantly improved durability and long-term reliability that can be used for a long time without performance degradation even in harsh actual usage environments such as high temperature and high humidity.

[0017] The problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0018] An electrophoretic display device according to one embodiment of the present invention comprises: an upper substrate; a lower substrate; an upper electrode disposed on one surface of the upper substrate; a lower electrode disposed on one surface of the lower substrate; and a display layer disposed between the upper electrode and the lower electrode, wherein the display layer comprises an electrophoretic fluid, the electrophoretic fluid comprises a nonpolar solvent; and a composite pigment particle comprising a core pigment particle and a ternary block copolymer attached to the surface of the core pigment particle, which is dispersed in the nonpolar solvent.

[0019] The above ternary block copolymer may include: (a) an anchor block attached to the surface of the core pigment particle; (b) a stabilization block connected to the anchor block by a covalent bond and providing stereostabilization in the nonpolar solvent; and (c) a reactive charge-regulating block comprising a Lewis acid or Lewis base functional group that performs the function of chemically capturing ionic impurities in the nonpolar solvent.

[0020] The above reactive charge-regulating block may be included in an amount of 2% to 10% by weight based on the total weight of the ternary block copolymer.

[0021] The above reactive charge-regulating block may include a Lewis base functional group comprising a tertiary amine group or a nitrogen-containing heterocyclic compound.

[0022] The Lewis base functional group can be formed from one or more monomers selected from the group consisting of dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and N-vinylpyridine.

[0023] The above reactive charge-regulating block may include a boron compound, a Lewis acid functional group including a sulfonic acid group or a phosphate group.

[0024] The Lewis acid functional group can be formed from diethylboranyloxyethyl methacrylate or 2-acrylamido-2-methylpropanesulfonic acid monomer.

[0025] The above anchor block may be formed from one or more monomers selected from the group consisting of methyl methacrylate, styrene, and 2-hydroxyethyl methacrylate.

[0026] The above stabilization block may be formed from an alkyl (meth)acrylate or polydimethylsiloxane macromonomer having 8 to 22 carbon atoms.

[0027] The above electrophoretic fluid may substantially not contain an externally added charge control agent.

[0028] The electrophoretic fluid according to one embodiment of the present invention further comprises a second type of composite pigment particle having a color and opposite polarity charge that is contrasting with the composite pigment particle, and the second type of composite pigment particle may comprise a ternary block copolymer as described in claim 1.

[0029] A method for manufacturing composite pigment particles according to one embodiment of the present invention may include: (a) forming a polymerization initiation site on the surface of a core pigment particle; and (b) sequentially growing an anchor block, a reactive charge-regulating block, and a stabilizing block from the polymerization initiation site through controlled radical polymerization, which is a reversible addition-fractional-chain-transfer (RAFT) polymerization, to form a ternary block copolymer comprising a Lewis acid or Lewis base functional group on the surface of the core pigment particle.

[0030] The composite pigment particles produced by the method for producing composite pigment particles according to one embodiment of the present invention may have the core pigment particles as titanium dioxide (TiO₂) or carbon black.

[0031] A method for manufacturing an electronic paper film according to one embodiment of the present invention may include: (a) a step of dispersing the electrophoretic fluid of claim 12 in an aqueous solution to form an emulsion, and a step of manufacturing microcapsules by aggregating a wall material including gelatin and acacia at the interface of the emulsion; (b) a step of mixing the microcapsules with a water-soluble binder to prepare a slurry; (c) a step of applying the slurry onto a conductive transparent film and drying it to form a film; and (d) a step of laminating the film with a substrate having electrodes formed thereon using a conductive adhesive layer.

[0032] An electronic paper film according to one embodiment of the present invention can be driven at a voltage of 10 V or less.

[0033] The above electronic paper film may have a voltage retention rate (VHR) of 95% or more after 16.7 ms has elapsed since the application of a voltage of 1 V. Effects of the invention

[0034] The present invention provides novel composite pigment particles in which a ternary block copolymer containing a ‘reactive charge-regulating block’ is bonded to a core pigment particle, thereby achieving multifaceted and remarkable effects as follows.

[0035] Realization of ultra-low voltage driving and innovation in power consumption: 'Ion capture,' a core function of the present invention, chemically removed ionic impurities, which are the source of leakage current within the system. The overwhelming voltage retention rate (VHR) of 99.2% confirmed in [Test Example 2] demonstrated that there was almost no applied voltage loss. As a result, the net energy required for particle driving is reduced, enabling ultra-low voltage driving of 10V or less, which is about 45% lower than conventional technology. This reduces the burden on the display driving circuit and extends battery life.

[0036] Ultimate High-Definition Realization (Elimination of Image Afterimage Source): Image afterimage is primarily caused by charge disturbances caused by impurity ions. The particles of the present invention immediately capture surrounding ions to stabilize the local electric field. In [Test Example 4], the value of 0.8, which represents an 87% reduction in the afterimage index (ΔL) compared to conventional technology, signifies that the present invention has almost perfectly solved the afterimage problem. This level of performance is unattainable by simple physical filtering (ion exchange resin) methods and guarantees clean and sharp image quality.

[0037] Improved reaction speed and securing uniform response characteristics: As shown in [Test Example 3], the particles of the present invention demonstrated that not only was the electrophoretic mobility improved by 67%, but the standard deviation was extremely low, proving that all particles possess a very uniform charge. This is due to ① a clean electric field environment in which interfering factors are eliminated by 'ion trapping', and ② structural stability in which the charge control function is perfectly fixed to the polymer chain. As a result, the display responds faster and more precisely, possessing the potential to expand the range of applications, such as video implementation.

[0038] Long-term reliability and extended lifespan: Since the present invention does not use external CCA, there is no secondary contamination caused by CCA decomposition, and it actively captures even moisture (strong ionic impurities) introduced from the outside in high temperature and high humidity environments. The result showing that performance degradation was only 7% in the harsh accelerated life evaluation of [Test Example 8] demonstrated that the present invention possesses overwhelming durability that is hardly affected by changes in the actual usage environment. This is a key effect that satisfies both user convenience and economic efficiency by dramatically extending the replacement cycle of the display.

[0039] In conclusion, this invention does not merely improve upon existing technology but fundamentally resolves the chronic problems of EPDs through a new paradigm of 'ion impurity control.' By ensuring processability and stability through an integrated structure and simultaneously achieving four key objectives—low-voltage operation, high image quality, high-speed response, and long-term reliability—through its inherent ion trapping function, it has paved the way for a groundbreaking advancement in accelerating the commercialization of next-generation electronic paper technology. Brief explanation of the drawing

[0040] Figure 1 is a graph showing the ion capture performance and conductivity of composite pigment particles. Figure 2 is a graph showing the minimum driving voltage of an electrophoretic film containing composite pigment particles. Figure 3 is a graph showing the long-term driving stability (lifetime) of an electrophoretic film containing composite pigment particles. Figure 4 shows the dynamic electrophoretic mobility and standard deviation including composite pigment particles It is a graph representing. Figure 5 is a graph showing the change in driving voltage after an accelerated test containing composite pigment particles. Figure 6 is a graph showing the change in minimum driving voltage according to the content of the reactive charge control block (DMAEMA). Figure 7 is a graph showing the change in image afterimage according to the content of the reactive charge control block (DMAEMA). Figure 8 is a graph showing the change in accelerated lifetime according to the content of the reactive charge control block (DMAEMA). Specific details for implementing the invention

[0041] 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.

[0042] The present invention relates to novel composite pigment particles used in electrophoretic displays (EPDs) and electrophoretic fluids containing the same. Various embodiments of the present invention are described in detail below, but these are illustrative and the scope of the present invention is not limited thereto.

[0043] 1. Composition of composite pigment particles

[0044] The composite pigment particle according to the present invention comprises a core pigment particle located in the center and a ternary block copolymer of a specific structure that surrounds the surface of the core pigment particle.

[0045] (1) Core pigment particles

[0046] Core pigment particles serve to impart a desired color to the display. The types of core pigment particles are not particularly limited and may be inorganic or organic pigments commonly used in the industry. Non-limiting examples of inorganic pigments include titanium dioxide (TiO₂, anatase or rutile type), zinc oxide (ZnO), barium sulfate (BaSO₄), etc. for achieving white; carbon black, manganese ferrite black spinel, copper chromite black spinel, iron oxides, etc. for achieving black; and other colored pigments such as chromium oxide and cobalt blue.

[0047] Non-limiting examples of organic pigments include CI Pigment Red series (e.g., PR 254, PR 122, PR 149), CI Pigment Green series (e.g., PG 7, PG 36), CI Pigment Blue series (e.g., PB 15:3, PB 15:6), CI Pigment Yellow series (e.g., PY 138, PY 150), CI Pigment Violet series, etc.

[0048] The average particle size of the core pigment particles may be in the range of 50 nm to 1000 nm, preferably 100 nm to 500 nm, but is not limited thereto.

[0049] In some embodiments, the core pigment particles may be surface-treated to increase the bonding strength with the block copolymer described later. As a surface-treating agent, a silane coupling agent containing vinyl groups, acrylate groups, amine groups, epoxy groups, etc., such as 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) and 3-aminopropyltriethoxysilane (APTES) may be used.

[0050] (2) ternary block copolymer

[0051] The ternary block copolymer, which is the core component of the present invention, is attached to the surface of a core pigment particle and simultaneously performs three functions within a single molecule: shell formation, stereostabilization, and ionic impurity capture. It comprises (a) an anchor block, (b) a stabilization block, and (c) a reactive charge-regulating block.

[0052] (a) Anchor Block

[0053] The anchor block is insoluble or has low solubility in the non-polar hydrocarbon solvent, which is the main solvent of the electrophoretic fluid, and serves to form a shell layer by strongly attaching to the surface of the core pigment particles (110).

[0054] The monomers forming the anchor block are not particularly limited as long as the polymer is insoluble in non-polar hydrocarbon solvents. For example, methyl methacrylate (MMA), ethyl methacrylate, styrene and its derivatives, 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate (HEA), acrylic acid, methacrylic acid, acrylonitrile, etc. may be used alone or in a mixture of two or more.

[0055] (b) Stabilizer Block

[0056] The stabilization block is connected to the anchor block by covalent bonds and has a high affinity for non-polar hydrocarbon solvents, forming long polymer chains that extend within the solvent. These chains form a steric barrier around the particles, acting as a steric stabilizer that prevents aggregation between particles.

[0057] It is preferable that the monomer forming the stabilization block includes a long alkyl chain or a siloxane chain and has high solubility in non-polar solvents. Non-limiting examples include long-chain alkyl (meth)acrylates such as lauryl (meth)acrylate, stearyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, and behenyl (meth)acrylate; or polydimethylsiloxane (PDMS) macromonomers, polyisobutylene macromonomers, hydrogenated polybutadiene macromonomers, etc., having polymerizable functional groups at their ends, which may be used alone or in a mixture of two or more. Here, '(meth)acrylate' means including both acrylates and methacrylates.

[0058] (c) Reactive Charge-Regulating Block

[0059] The reactive charge-regulating block is the most characteristic component of the present invention and includes a Lewis acid or Lewis base functional group. This block imparts an intrinsic charge to the particle and simultaneously acts as an 'ion scavenger' that chemically captures and deactivates ionic impurities of opposite nature present in the solvent.

[0060] This block can be located between the anchor block and the stabilization block (ACB structure) or at the ends of the block copolymer (ABC structure).

[0061] Examples of monomers containing Lewis basic functional groups (for capturing cationic impurities) may include monomers containing tertiary amine groups such as dimethylaminoethyl (meth)acrylate (DMAEMA), diethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate; nitrogen-containing heterocyclic compounds such as N-vinylpyridine and N-vinylimidazole; and N-[3-(dimethylamino)propyl]methacrylamide.

[0062] Examples of monomers containing Lewis acidic functional groups (for capturing anionic impurities) may include monomers containing boron compounds such as dialkylboranyloxyethyl (meth)acrylate and diarylboranyloxyethyl (meth)acrylate; vinylphenylboronic acid and its ester derivatives; 2-acrylamido-2-methylpropanesulfonic acid (AMPS) containing a sulfonic acid group; vinyl phosphoric acid containing a phosphate group, etc.

[0063] Preferably, the content of the monomer forming the reactive charge control block may be in the range of about 2% by weight to about 10% by weight based on the total weight of the entire ternary block copolymer. If the content is less than 2% by weight, the ion capture effect is negligible, making it difficult to achieve low-voltage driving and lifespan improvement effects, and if it exceeds 10% by weight, side effects such as unnecessary interactions between particles due to excessive polarity or reduced insulation of the shell may occur.

[0064] 2. Method for manufacturing composite pigment particles

[0065] The composite pigment particles of the present invention can be manufactured using various Controlled Radical Polymerization (CRP) technologies. Representative methods include Atomic Transfer Radical Polymerization (ATRP), Reversible Addition-Segmental Transfer (RAFT) Polymerization, and Stable Free Radical Polymerization (SFRP).

[0066] One embodiment of the 'Grafting-from' method may include the following steps.

[0067] (a) A step of forming a polymerization initiation site on the surface of a core pigment particle: A functional group capable of initiating polymerization is chemically fixed to the surface of the core pigment particle using the silane coupling agent described above.

[0068] (b) ternary block copolymer growth step: After dispersing the surface-treated core pigment particles in a reaction solvent, monomers forming an anchor block, a reactive charge-regulating block, and a stabilizing block are sequentially added to grow a block copolymer directly from the particle surface through 'living' polymerization.

[0069] (c) Purification step: After the completion of polymerization, unreacted monomers or physically adsorbed polymers are removed through centrifugation and solvent washing to obtain the final composite pigment particles.

[0070] Another embodiment of the ‘Grafting-to’ method may include a method in which the ternary block copolymer described above is first synthesized separately, and then added to a solution in which core pigment particles are dispersed, so that the anchor blocks of the block copolymer are attached to the surface of the core pigment in a self-assembly manner.

[0071] 3. Electrophoretic Fluids and Their Performance

[0072] The electrophoretic fluid of the present invention is in the form in which the aforementioned composite pigment particles are dispersed in a nonpolar solvent. The nonpolar solvent preferably has a low dielectric constant (preferably about 3 or less) and a high volume resistivity (preferably about 10¹² Ω·cm or more). Examples of suitable solvents may include aliphatic hydrocarbon solvents such as the Isopar™ series, Norpar™, and Soltrol™; straight-chain or branched-chain hydrocarbons such as dodecane, tetradecane, and hexadecane; or mixtures thereof with halogenated solvents or silicone oil.

[0073] One of the greatest advantages of this invention is that, since the composite pigment particles themselves exhibit a stable charge and remove ionic impurities, it is possible to eliminate the use of a separate externally added Charge Control Agent (CCA) or minimize its usage. This fundamentally prevents the problem of display performance degradation caused by the decomposition or side effects of CCA.

[0074] The electrophoretic fluid of the present invention may be composed of a one-particle system comprising only one type of composite pigment particle, or a multi-particle system comprising two or more types of composite pigment particles having different colors and opposite polarity charges. For example, a black / white electrophoretic fluid may be composed by combining white particles and black particles prepared according to the present invention.

[0075] An electrophoretic display fabricated using an electrophoretic fluid configured in this way can be driven at a low voltage of 10V or less, preferably 9V or less, as leakage current caused by ionic impurities is extremely suppressed. This simplifies the design of the display driving circuit and brings about the effect of drastically reducing power consumption, especially in portable devices. In addition, since there is no charge disturbance caused by ions, image afterimage phenomena are significantly improved, and electrode contamination or particle degradation caused by CCA and ionic impurities is prevented, exhibiting an excellent effect of dramatically improving the long-term operating life of the display.

[0076] The present invention will be explained in more detail below through examples, but the scope of the present invention is not limited by these examples.

[0077] [Preparation Example 1] Synthesis of a reactive ternary block copolymer (ACB structure)

[0078] Formation of anchor block (A) and reactive block (C): 10 g of 2-hydroxyethyl methacrylate (HEMA) and 2 g of dimethylaminoethyl methacrylate (DMAEMA, reactive block monomer) are dissolved in 100 mL of tetrahydrofuran (THF) solvent. To this, 0.5 g of S-1-dodecyl-S'-(α,α'-dimethyl-α''-acetic acid)trithiocarbonate, a RAFT (Reversible Addition-Fragmentation Chain Transfer) control agent, and 0.05 g of AIBN, an initiator, are added. The P(HEMA-co-DMAEMA) block is synthesized by polymerizing at 70°C for 6 hours under a nitrogen atmosphere.

[0079] Formation of stabilization block (B): 30 g of lauryl methacrylate (LMA, stabilization block monomer) and 0.05 g of AIBN are additionally added to the above reaction solution, and additional polymerization is carried out at 70°C for 12 hours.

[0080] Purification: After the reaction is complete, the product is precipitated in excess methanol to remove unreacted monomers and byproducts, and this process is repeated three times. By vacuum drying, a ternary block copolymer (P1) composed of an anchor / reactive block (P(HEMA-co-DMAEMA)) and a stabilizing block (PLMA) is finally obtained. GPC analysis confirmed that the molecular weight (Mn) was approximately 25,000 g / mol and the molecular weight distribution (PDI) was 1.25, indicating that the molecular weight was well controlled.

[0081] [Example 1] Preparation of composite white pigment particles according to the present invention

[0082] Surface modification: 10 g of TiO₂ pigment (average particle size 200 nm) was dispersed in 100 mL of toluene, then 1 g of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) was added and stirred under reflux at 80°C for 5 hours to introduce polymerizable methacrylate functional groups onto the TiO₂ surface. After washing and drying, TiO₂-TMSPMA with a polymerization initiation function was obtained.

[0083] Grafting-from polymerization: 10 g of the above TiO₂-TMSPMA was dispersed in 200 mL of toluene. Polymerization was carried out using a 'grafting-from' method in which the same monomers as in [Preparation Example 1] were sequentially added.

[0084] Step 1 (Anchor / Reactive Block Formation): Add 10g of HEMA, 2g of DMAEMA, and 0.1g of AIBN, and polymerize at 70°C for 6 hours.

[0085] Step 2 (Stabilization Block Formation): Add 30g of LMA and 0.1g of AIBN, and polymerize for an additional 12 hours at 70°C.

[0086] Purification and Completion: After the reaction, the composite particles were recovered by centrifugation, and physically adsorbed unreacted materials and polymers were removed by washing several times with toluene and methanol. Finally, composite white particles (W-1) were prepared by vacuum drying. As a result of TGA (thermogravimetric analysis), the organic content of the final particles was approximately 45 wt%.

[0087] [Comparative Example 1] Preparation of composite particles according to the prior art (US '253) (shell + stabilizer structure)

[0088] Shell formation: 10g of TiO₂ pigment was coated with a polymethyl methacrylate (PMMA) shell by dispersion polymerization.

[0089] Stabilizer bonding: A comparative composite particle (CW-1) was prepared by chemically bonding a polysiloxane stabilizer having a reactive isocyanate group at the terminal end to the surface of the particle coated with the PMMA shell. The organic content was controlled to about 45 wt%, similar to Example 1.

[0090] [Comparative Example 2] Preparation of composite particles using a simple block copolymer

[0091] Synthesis of binary block copolymer: A binary block copolymer (P2) composed only of an anchor block (PHEMA) and a stabilizing block (PLMA) was synthesized, excluding the reactive block monomer DMAEMA from [Preparation Example 1].

[0092] Composite particle preparation: Comparative composite particles (CW-2) without reactive blocks were prepared by sequentially polymerizing only HEMA and LMA without adding DMAEMA, in the same manner as in [Example 1]. The organic content was adjusted to about 45 wt%.

[0093] [Method for manufacturing an electrophoretic display device using the electrophoretic fluid of the present invention]

[0094] (A) Fabrication process of a Microcup®-based electrophoretic display device

[0095] The micro-cup method is a technology that implements pixels by creating a fine cup-shaped structure on a TFT substrate and directly injecting an electrophoretic fluid into it.

[0096] [Step 1: Formation of lower substrate and microcup structure]

[0097] Preparation of Backplane: A glass or plastic substrate was prepared in which a Thin Film Transistor (TFT) is formed for each pixel. The TFT acts as a switch to drive each pixel individually and is connected to each pixel electrode.

[0098] Barrier Rib Formation: An insulating polymer material, such as photosensitive acrylic resin or polyimide, was uniformly coated on the TFT substrate. Subsequently, ultraviolet (UV) light was exposed using a mask with a desired microcup pattern through a photolithography process.

[0099] Development: The exposed substrate is immersed in a developer solution to remove the resin from areas that did not receive light (or received light, depending on the type of resin), thereby forming barriers surrounding each pixel electrode. The arrangement of these barriers forms numerous microcup structures. Generally, the height of the cups ranges from 15 to 30 μm, and the diameter ranges from 30 to 60 μm.

[0100] [Step 2: Filling and Sealing Electrophoretic Fluid]

[0101] 4. Fluid Filling (Ink Filling): The electrophoretic fluid prepared according to the present invention was precisely applied onto a substrate on which a microcup was formed. For this purpose, a precision application technique such as inkjet printing or slot-die coating was used. The applied fluid was filled into each microcup.

[0102] 5. Formation of Sealing Layer: A transparent polymer sealant (e.g., polyurethane, acrylic resin) was coated over the top of the fluid-filled microcup to seal the fluid and flatten the surface. This sealant must not react with the solvent and can also serve as an adhesive layer with the upper substrate in subsequent processes.

[0103] 6. Curing: The applied sealant was completely cured through heat or UV irradiation to perfectly seal the fluid inside each cup.

[0104] [Step 3: Top Substrate Bonding and Final Panel Completion]

[0105] 7. Preparation of Top Plane: A substrate was prepared on which Indium Tin Oxide (ITO), a transparent electrode, was deposited on the front surface of a glass or plastic film. This ITO served as a common electrode.

[0106] 8. Lamination: The sealed lower substrate and the upper ITO substrate were aligned and bonded using a lamination adhesive.

[0107] 9. Final process: The driver IC and flexible printed circuit board (FPCB) were connected, and if necessary, an anti-glare film or a protective film was attached to the surface to complete the final electrophoretic display panel.

[0108] (B) Fabrication process of a microcapsule-based electrophoresis display device

[0109] The microcapsule method is a technology that implements pixels by encapsulating an electrophoretic fluid inside numerous tiny capsules and coating these capsules between electrodes.

[0110] [Step 1: Microcapsule Manufacturing]

[0111] Fluid Emulsification: An electrophoretic fluid (oil phase, a) prepared according to the present invention is added to an aqueous solution (aqueous phase, b) in which a polymer precursor (e.g., gelatin, gum arabic, polyurethane precursor, etc.) to form a capsule shell is dissolved, and stirred at high speed to create an emulsion (o / w emulsion) in which fine fluid droplets are dispersed. The size of the fluid droplets determines the size of the final microcapsules, and is generally in the range of 20-100 μm.

[0112] Capsule Shell Formation: The capsule shell formation reaction was induced by methods such as controlling the temperature or pH of the emulsion or adding a curing agent. For example, Complex Coacervation: When using gelatin and gum arabic, the pH was controlled so that the two polymers condensed on the surface of the fluid droplet due to electrostatic attraction to form a shell.

[0113] Interfacial Polymerization: When a diisocyanate was dissolved inside a fluid droplet and a diamine was dissolved in an aqueous solution and then emulsified, a reaction occurred at the interface of the fluid droplet to form a polyurea shell.

[0114] Curing and Separation: After increasing the mechanical strength of the formed capsule shells by treating them with a crosslinking agent (e.g., glutaraldehyde), the microcapsules were separated from the aqueous solution by centrifugation or filtration, and then washed and dried to obtain microcapsule powder.

[0115] [Step 2: Electronic Ink Manufacturing and Coating]

[0116] 4. Manufacturing of electronic ink: The microcapsule powder manufactured above was mixed with a transparent polymer binder (e.g., acrylic resin), a solvent, and other additives to manufacture an 'electronic ink' having a printable viscosity.

[0117] 5. Coating and drying: Electronic ink is uniformly coated on a substrate on which a thin-film transistor (TFT) is formed using methods such as screen printing or slot die coating. Then, by applying heat to evaporate the solvent, a display layer is formed in which microcapsules are fixed to the substrate by a polymer binder.

[0118] [Step 3: Top Substrate Bonding and Final Panel Completion]

[0119] 6. Preparation of upper substrate: In the same way as the microcup method, an upper substrate with a transparent electrode (ITO) formed thereon was prepared.

[0120] 7. Lamination: The lower substrate with the display layer formed thereon and the upper ITO substrate were aligned and pressed together using a transparent adhesive.

[0121] 8. Final process: The driving circuit and other components were connected in the same way as the microcup method, and the necessary film was attached to complete the final electrophoretic display panel.

[0122] (C) Microcapsule-based electrophoretic film fabrication process

[0123] A test panel in the form of an electrophoretic film can be produced by mixing the above-manufactured microcapsules with a binder to prepare a slurry, applying it to and drying it on an upper substrate of a film substrate having a transparent electrode formed thereon to form a display layer, and laminating it with a lower substrate of a film substrate having a lower electrode formed thereon using a conductive adhesive layer.

[0124] A display panel or display device comprises an upper substrate; a lower substrate; an upper electrode disposed on one surface of the upper substrate; a lower electrode disposed on one surface of the lower substrate; and a display layer comprising a plurality of microcapsules formed between the upper electrode and the lower electrode.

[0125] (D) Fabrication process of an electrophoretic display device based on a unit pixel structure

[0126] This method is a technology that implements a display by forming partition walls that define each pixel to create independent spaces, or 'unit pixels,' and injecting electrophoretic fluid into them.

[0127] [Step 1: Formation of lower substrate and unit pixel partition structure]

[0128] Preparation of Backplane: A glass or flexible plastic substrate was prepared in which Thin Film Transistors (TFTs), which are switching elements for individually controlling each pixel, were arranged in a matrix form. Each TFT is electrically connected to a pixel electrode responsible for driving the corresponding pixel.

[0129] Formation of Pixel-Defining Partition Walls: A photosensitive insulator was uniformly coated over the entire TFT substrate. Typically, photosensitive acrylic resin, polyimide, or other organic insulators were used as this material. A photolithography process was applied. First, a photomask designed with a partition pattern was aligned on the substrate. Then, ultraviolet (UV) light was irradiated through the mask to expose specific areas of the resin. The exposed substrate was treated with a developer to selectively remove unexposed (negative type) or exposed (positive type) resin areas. Through this process, a grid-shaped partition wall was formed surrounding each pixel electrode. This partition wall physically defines the boundary of each pixel, serving to prevent electrical / optical crosstalk and fluid mixing between neighboring pixels. Each independent space enclosed by these partition walls constitutes a 'unit pixel'. The height of the partition wall is typically 15-30 μm, and the width is 5-15 μm.

[0130] [Step 2: Filling and Sealing Electrophoretic Fluid]

[0131] Ink Filling: An electrophoretic fluid (including particles of the present invention, contrast color particles, a non-polar solvent, a charge control agent, etc.) prepared according to the embodiments of the present invention was precisely injected onto a substrate having a partition structure. An inkjet printing method was primarily used. An inkjet head moved to the location of each unit pixel and accurately sprayed and filled a calculated amount of fluid. This method is particularly useful when fluids of different colors need to be injected into adjacent pixels, such as in the RGB color filter method. Alternatively, the fluid may be applied to the entire surface of the substrate using a slot-die coating method, and then the excess fluid may be scraped off using a squeegee or blade so that the fluid remains only inside each unit pixel.

[0132] Formation and Curing of Sealing Layer: A transparent polymer sealant was applied over the fluid-filled unit pixels to seal the fluid and flatten the surface. This sealant may be a solvent-reactive polyurethane, epoxy, or acrylic resin. The applied sealant was fully cured through heat or UV irradiation to physically and completely trap the electrophoretic fluid within each unit pixel.

[0133] [Step 3: Top Substrate Bonding and Final Panel Completion]

[0134] Preparation of Top Plane: Prepare the top plane by depositing Indium Tin Oxide (ITO), a transparent conductive thin film that acts as a common electrode, onto the front surface of a transparent glass or plastic film substrate.

[0135] Lamination: The sealed lower substrate and the upper ITO substrate are precisely aligned. Subsequently, an Optical Clear Adhesive (OCA) is applied between the two substrates, and pressure is applied to perform lamination. After lamination, the adhesive is fully cured using heat or UV light to firmly secure the two substrates.

[0136] Final process: A flexible printed circuit board (FPCB) was attached to the edge of the panel to connect a driver IC and an external controller. Finally, to improve user visibility, a protective film with anti-glare and anti-reflection coatings was attached to the surface of the panel to complete the final electrophoretic display.

[0137] [Driving method for electrophoretic film (panel) and electrophoretic display device]

[0138] The upper common electrode of the above-manufactured display panel is set to ground (0V), and the following voltage pulse is applied to the lower TFT pixel electrode through a driving driver IC. The amplitude of the driving voltage was maintained constant at ±15V.

[0139] 4. Performance Evaluation and Verification of Effectiveness

[0140] [Test Example 1] Evaluation of Ion Scavenging Performance

[0141] After intentionally adding ionic impurities (benzoic acid, 100 ppm) to the electrophoretic fluid (Isopar G), each prepared particle (W-1, CW-1, CW-2) was dispersed at a concentration of 10 wt% and stirred for 24 hours. Afterward, the fluid was filtered to remove the particles, and the conductivity of the remaining solution was measured.

[0142] [Table 1]

[0143]

[0144] Figure 1 is a graph showing the ion capture performance and conductivity of composite pigment particles.

[0145] Referring to Figure 1 and Table 1, it is clearly shown that only the particles of Example 1 (W-1) according to the present invention chemically captured ionic impurities in the fluid and drastically lowered the conductivity. It can be seen that the comparative examples have almost no ion removal ability other than simple physical adsorption. This is key data demonstrating the unpredictable and remarkable effects of the present invention.

[0146] [Test Example 2] Electrophoretic Film Fabrication and Driving Voltage Evaluation

[0147] Each white particle (W-1, CW-1, CW-2) and a black particle with an opposite charge were dispersed in Isopar G solvent to prepare a 2-particle electrophoretic fluid. At this time, no CCA was added to the fluid of Example 1, while a small amount of CCA was added to the fluids of Comparative Examples 1 and 2 for optimal operation. Test electrophoretic films with a gap of 50 μm were fabricated using these fluids, and the minimum driving voltage required for a complete transition between the white and black states was measured.

[0148] [Table 2]

[0149]

[0150] Figure 2 is a graph showing the minimum driving voltage of an electrophoretic film containing composite pigment particles.

[0151] Referring to Figure 2 and Table 2, Example 1 was able to operate stably using only the charge of the particle itself without CCA, and in particular, the driving voltage was reduced by about 45% compared to the comparative examples. This is because the unnecessary voltage drop caused by the removal of ionic impurities was eliminated, clearly demonstrating the practical excellence of the present invention.

[0152] [Test Example 3] Evaluation of Long-term Driving Stability (Lifespan)

[0153] A driving voltage of ±15V was continuously applied to each fabricated test electrophoretic film at a frequency of 1Hz, and the number of driving cycles until the reflectance decreased by 10% compared to the initial reflectance was measured.

[0154] [Table 3]

[0155]

[0156] Figure 3 is a graph showing the long-term driving stability (lifetime) of an electrophoretic film containing composite pigment particles.

[0157] Referring to Figure 3 and Table 3, almost no performance degradation was observed in the electrophoretic film of Example 1 even after more than 1 million repeated drives. On the other hand, the comparative examples containing CCA showed relatively rapid performance degradation due to CCA decomposition and electrode contamination as the drives were repeated. This demonstrates that the present invention has a significant effect of improving the lifespan of the display by more than 2.5 times.

[0158] Through the above examples and comparative examples, it has been clearly demonstrated that the reactive ternary block copolymer-based composite pigment particles and electrophoretic films containing the same according to the present invention go beyond simply integrating a shell and a stabilizer, and through the unique function of 'active ion capture', they exhibit complex and unpredictable effects that could never be achieved in conventional technologies, such as (1) a dramatic reduction in driving voltage, (2) the realization of a CCA-free system, and (3) a dramatic improvement in long-term lifespan.

[0159] [Test Example 4] Evaluation of Image Ghosting Characteristics

[0160] Objective: To evaluate the effect of ion impurity removal on the image quality of actual displays.

[0161] A DC 15V voltage was applied to only half of the test cell made of each fluid for 30 seconds to maintain it in a black state (stress application), and then the entire cell was operated in a white state. Immediately afterward, the difference in luminance (ΔL) between the stressed area and the unstressed area was measured. The larger the ΔL value, the more severe the afterimage phenomenon is, where the previous image remains faint.

[0162] [Table 4]

[0163]

[0164] Referring to Table 4, the particles of Example 1 immediately capture ionic impurities near the particle surface to stabilize the charge distribution, so almost no afterimage phenomenon was observed. On the other hand, significant afterimages were observed in the comparative examples due to the influence of residual ions. In particular, it demonstrated superior performance compared to a simple mixture (Comparative Example 3) or a separate ion exchange resin (Comparative Example 4), proving the excellence of the 'inherent ion capture structure' of the present invention.

[0165] [Test Example 5] Measurement of Voltage Holding Ratio (VHR) of Electrophoretic Film

[0166] Objective: Quantitatively evaluate the insulation properties and ion leakage current levels of a fluid.

[0167] Each fluid was injected into a cell with a structure similar to a liquid crystal cell, and after briefly applying a voltage of 1V and then cutting off the voltage supply, the percentage of the voltage maintained after 16.7ms relative to the initial voltage was measured. A higher VHR indicates lower ion leakage current and superior insulation characteristics.

[0168] [Table 5]

[0169]

[0170] Referring to Table 5, the fluid of Example 1 exhibited a very high VHR value because it had almost no ionic impurities, which minimized leakage current. This means that the applied voltage is used for particle driving without loss, and this data directly explains the fundamental cause of low-voltage driving.

[0171] [Test Example 6] Measurement of Dynamic Electrophoretic Mobility of Electrophoretic Film

[0172] Objective: Evaluate the charge stability and response speed of particles.

[0173] Electrophoretic mobility was measured when an alternating current (AC) electric field was applied to each particle using Laser Doppler Velocimetry. Higher and more stable mobility values ​​indicate that the particles move quickly and uniformly.

[0174] [Table 6]

[0175]

[0176] Figure 4 shows the dynamic electrophoretic mobility and standard deviation including composite pigment particles It is a graph representing.

[0177] Referring to Figure 4 and Table 6, the particles of Example 1 exhibited very uniform and high mobility (low standard deviation) as the charge control function was fixed to the polymer chains. On the other hand, Comparative Examples 1 and 3 showed degraded response characteristics due to large charge deviations between particles (high standard deviation) caused by the non-uniform distribution or desorption of the charge-giving material.

[0178] [Test Example 7] Lewis Acid / Base Function Verification (FT-IR Spectroscopic Analysis)

[0179] Objective: Spectroscopically prove that ion capture is actually due to chemical interactions.

[0180] The FT-IR spectra of the W-1 particles (DMAEMA, Lewis base) of Example 1 before and after treatment with a solution containing benzoic acid (Lewis acid) were compared.

[0181] * Before treatment: DMAEMA's CN stretching vibration peak is 1150 cm -1 Observed in.

[0182] * After treatment: As acid-base interactions occur between the carboxyl group (-COOH) of benzoic acid and the amine group (-N(CH₃)₂) of DMAEMA, the corresponding peak is at 1165 cm⁻¹. -1 Shift to and a new N + Confirmed that the -H peak appeared.

[0183] The clear change in the spectrum is direct evidence proving that chemical interactions between Lewis acids and bases (coordination bonding or proton transfer) actually occurred, rather than simple physical adsorption.

[0184] [Test Example 8] Evaluation of Accelerated Life in Harsh Environments

[0185] Objective: To evaluate the stability of the present invention in a high temperature / high humidity environment.

[0186] After storing the cells made of each fluid in a chamber at 60°C and 90% RH (relative humidity) for 500 hours, the change in driving voltage was measured in the same way as in [Test Example 2].

[0187] [Table 7]

[0188]

[0189] Figure 5 is a graph showing the change in driving voltage after an accelerated test containing composite pigment particles.

[0190] Referring to FIG. 5 and Table 7, the system of Example 1 showed almost no performance degradation even in harsh environments because the reactive block immediately captured moisture (strong ionic impurities) introduced from the outside. On the other hand, the driving voltage of the comparative example system increased significantly as the ion concentration increased rapidly due to the influx of moisture. This suggests that the present invention can dramatically improve reliability in actual usage environments.

[0191] 5. Comparative experiment to prove critical significance

[0192] 5-1. Numerical Limitation Invention (1): Content of Reactive Charge Control Block (DMAEMA)

[0193] Objective: It was demonstrated that when the content of the reactive charge control block (DMAEMA) is outside a specific range or is absent, the driving voltage exceeds 10V, which causes unpredictable and rapid performance degradation (cliff-like effect) in the core performance (power consumption, panel lifespan) of the display.

[0194] Experimental design: In the method for manufacturing composite particles of [Example 1], the total amount of the anchor block (HEMA) and the stabilization block (LMA) was fixed, but the content of the reactive charge-regulating block monomer (DMAEMA) polymerized together with the anchor block was varied from 0 wt% to 10 wt% relative to the total polymer to produce six types of comparative particles (CE-1 to CE-6).

[0195] Electrophoretic films were fabricated using each of the six types of particles mentioned above, and the following four key performance indicators were measured.

[0196] - Minimum driving voltage (V): Voltage required for complete black / white switching.

[0197] - Power consumption per unit area (mW / cm²): A practical energy efficiency indicator that considers both driving voltage and leakage current.

[0198] - Image Afterimage Index (ΔL)*: A measure of image quality degradation.

[0199] - Accelerated life (cycles): The number of cycles until the initial reflectance drops by 10% during repeated ±15V operation.

[0200] [Table 8]

[0201]

[0202] Figure 6 is a graph showing the change in minimum driving voltage according to the content of the reactive charge control block (DMAEMA).

[0203] Figure 7 is a graph showing the change in image afterimage according to the content of the reactive charge control block (DMAEMA).

[0204] Figure 8 is a graph showing the change in accelerated lifetime according to the content of the reactive charge control block (DMAEMA).

[0205] Referring to FIGS. 6-8 and Table 8, the objective of the invention was achieved and unpredictable significant effects were exhibited only when the technical configuration of the present invention was within a specific numerical range.

[0206] 1. Critical Significance of the Lower Limit (DMAEMA Content 2% and Driving Voltage 10V)

[0207] Cliff-like Effect of Driving Voltage: When the DMAEMA content increased from 0% to 1%, the driving voltage decreased gradually from 14.8V to 12.1V. This is a predictable result of simply a slight increase in charge. However, in the range where the content increased from 1% to 2%, the driving voltage dropped sharply from 12.1V to 9.8V. This suggests that beyond the effect of a simple increase in charge, this marks a critical point where the 'ion trapping' mechanism—which increases system resistance by capturing ionic impurities—begins to operate effectively. In other words, below 2%, the ion trapping ability is negligible, causing the driving voltage to exceed 10V.

[0208] Non-linear improvement in power consumption and lifespan: Starting with CE-3 (2% content), where the driving voltage drops below 10V, power consumption plummeted to less than 1.0 mW / cm², and accelerated lifespan nearly doubled from 550,000 cycles to 950,000 cycles. This signifies that driving below 10V represents a turning point that goes beyond mere numerical significance, dramatically enhancing the practical value of the display in terms of energy efficiency and durability. Such dramatic performance improvements were not observed when driving at 11V or 12V.

[0209] Therefore, the composition of "DMAEMA content of about 2% or more" and the result of "driving voltage of 10V or less" achieved thereby have clear technical significance as a critical boundary at which the unique 'ion capture' effect of the present invention begins to manifest and unpredictable and significant effects in power consumption and lifespan begin to be obtained.

[0210] 2. Critical Significance of the Upper Limit (Near 10% DMAEMA Content)

[0211] Performance saturation and side effects: When the DMAEMA content increased from 4% to 7%, the driving voltage, power consumption, afterimage, etc. showed little improvement and the performance tended to saturate.

[0212] Furthermore, in CE-6, where the content reached 10%, adverse effects were observed, such as increased power consumption and reduced accelerated life. This is analyzed to be because an excessive amount of polar groups (amine groups) induces minute electrostatic attraction between particles or partially impairs the insulation of the polymer shell, thereby slightly increasing leakage current. In other words, an excessive content is actually detrimental to system stability.

[0213] Therefore, the upper limit of "DMAEMA content of about 10% or less" is also important. Since exceeding this range results in no further improvement in performance and instead causes side effects, it has critical significance as a necessary and reasonable range for optimally achieving the effects of the present invention.

[0214] 5-2. Numerical Limitation Invention (2): Voltage Retention Rate (VHR) 95% or Higher

[0215] Objective: It was demonstrated that a VHR of 95% is a threshold directly associated with image retention and long-term lifespan, which are key performance aspects of EPD, and that these performance aspects deteriorate rapidly below 95%.

[0216] Experimental Design: Five types of fluid samples (SF-1 to SF-5) were prepared with VHR values ​​distributed across the 80% to 99% range by intentionally controlling the amount of trace ionic impurities (e.g., unreacted initiator residue) during the manufacturing process. For each sample, VHR, image afterimage, and accelerated lifetime were measured.

[0217] [Table 9]

[0218]

[0219] Referring to Table 9, it is as follows.

[0220] (A) Critical significance of the lower limit (95%): "Minimum condition for implementing high definition and long lifespan"

[0221] Existence of a Performance Cliff: As the VHR improved from 85% to 91.5%, afterimage and lifetime improved progressively. However, the moment the VHR exceeded the critical point from 91.5% to 95.2%, the afterimage index (ΔL*) dropped from 3.1 to 1.4 and the accelerated lifetime improved from 0.5 to 0.9 million cycles, resulting in a steep, cliff-like performance improvement. This implies that a VHR of 95% is the critical point where leakage current within the system is sufficiently suppressed to prevent image afterimages and accelerated electrode degradation. A VHR below 95% is direct evidence that a significant number of impurity ions are still floating in the fluid, disturbing the electric field.

[0222] Therefore, the minimum electrical insulation condition required for EPDs to simultaneously achieve the commercially demanded high image quality (low afterimage) and long-term reliability (long lifespan) is precisely 'VHR 95%'. This figure is not merely a target value, but holds clear critical significance as a qualitative boundary that determines the practicality of the display.

[0223] Example 1 (Fluid containing W-1) Performance Effect

[0224] The electrophoretic fluid containing W-1 particles developed in the present invention (Example 1) achieved excellent improvements in all key performance indicators compared to existing electrophoretic display technology. In particular, by fundamentally solving the problem of performance degradation caused by ionic impurities through an inherent ion trapping structure, it was proven that it is possible to simultaneously realize image quality improvement and long-term stability required in actual display applications.

[0225] <Analysis by Key Performance Indicators>

[0226] 1. Improvement of image afterimage characteristics

[0227] In Example 1, the afterimage index (ΔL*) was measured at 0.8 in the image afterimage evaluation, showing a significant reduction of approximately 87% compared to 4.5 of the conventional Comparative Example 1 (fluid containing CW-1). This means that the ion trapping structure inherent on the surface of the W-1 particles immediately stabilized the charge distribution, thereby almost completely eliminating the residual effect of the previous image. These results demonstrate performance that is significantly superior to simple physical mixing (Comparative Example 3: 3.8) or the application of a separate ion exchange resin (Comparative Example 4: 2.5), clearly proving the effectiveness of the inherent ion trapping mechanism, which is the core technology of the present invention.

[0228] 2. Verification of insulation characteristics through voltage maintenance rate

[0229] As a result of measuring the voltage retention rate (VHR), Example 1 recorded an excellent figure of 99.2%. This indicates a significant improvement in performance compared to 85.4% of Comparative Example 1 and 82.1% of Comparative Example 2. The high voltage retention rate directly demonstrates that ionic impurities in the fluid are effectively removed, thereby minimizing leakage current. This provides the fundamental reason why low-voltage driving is possible, as the applied voltage can be utilized for particle driving without loss.

[0230] 3. Improvement of uniformity and responsiveness of electrophoretic mobility

[0231] In dynamic electrophoretic mobility measurements, Example 1 had an average of 3.5 × 10 -10m²V -1 s -1 By recording a high mobility of Comparative Example 1 (2.1 × 10⁻⁶ -10 m²V -1 s -1 It showed an improvement of approximately 67% compared to ). More importantly, the standard deviation was very low at 0.2, confirming that the charge distribution between particles was uniform. On the other hand, the comparative examples showed high standard deviations of 0.8 to 1.1, indicating significant performance variation due to the non-uniform distribution or desorption of the charge-carrying material. These results demonstrate that the charge control function of the W-1 particles is chemically fixed to the polymer chain, enabling stable and uniform electrophoretic characteristics.

[0232] 4. Verification of long-term stability through accelerated life assessment

[0233] In an accelerated life evaluation conducted for 500 hours in a high temperature and high humidity environment (60°C, 90% RH), Example 1 showed only a 7% increase in the initial operating voltage from 8.5V to 9.1V. This implies approximately 10 times better stability compared to Comparative Example 1, which increased by 70% from 15.2V to 25.8V. These results demonstrate that the reactive block of W-1 particles can immediately capture strong ionic impurities, such as moisture introduced from the outside, thereby minimizing the degradation of the system's performance.

[0234] The results above comprehensively demonstrate that electrophoretic fluids containing W-1 particles can overcome the limitations of existing technologies and satisfy all the requirements for high image quality, low power consumption, and long lifespan in actual display applications. In particular, the fundamental problem-solving approach utilizing an inherent ion trapping structure presents a new paradigm for electrophoretic display technology, and accelerated life evaluations confirmed that it can be reliably implemented in real-world usage environments.

[0235] The materials and manufacturing process required for the manufacturing of color particles, unit pixels, and microcapsules of the present invention, as well as for the manufacturing of a display device including the same, were referenced in a patent of the same applicant registered prior to this application.

[0236] KR 10-1984763 B1 (2019.05.27.)

[0237] KR 10-1913709 B1 (2018.10.25.)

[0238] KR 10-2102294 B1 (2020.04.13.)

[0239] KR 10-2255328 B1 (2021.05.17.)

[0240] KR 10-2156044 B1 (2020.09.09.)

[0241] KR 10-2156063 B1 (2020.09.09.)

[0242] KR 10-2340892 B1 (2021.12.14.)

Claims

Claim 1 An electrophoretic display device comprising: an upper substrate; a lower substrate; an upper electrode disposed on one surface of the upper substrate; a lower electrode disposed on one surface of the lower substrate; and a display layer disposed between the upper electrode and the lower electrode, wherein the display layer comprises an electrophoretic fluid, the electrophoretic fluid comprises a nonpolar solvent; and a composite pigment particle dispersed in the nonpolar solvent, comprising a core pigment particle and a ternary block copolymer attached to the surface of the core pigment particle, wherein the ternary block copolymer comprises: (a) an anchor block attached to the surface of the core pigment particle; (b) a stabilization block connected to the anchor block by a covalent bond and providing stereostabilization in the nonpolar solvent; and (c) a reactive charge control block comprising a Lewis acid or Lewis base functional group that performs the function of chemically capturing ionic impurities in the nonpolar solvent, wherein the Lewis acid functional group comprises a boron compound, a sulfonic acid group, or a phosphate group, and the Lewis base functional group comprises a tertiary amine group or a nitrogen-containing heterocyclic compound. Claim 2 delete Claim 3 An electrophoretic display device according to claim 1, characterized in that the reactive charge control block is included in an amount of 2% to 10% by weight based on the total weight of the ternary block copolymer. Claim 4 delete Claim 5 An electrophoretic display device according to claim 1, characterized in that the Lewis base functional group is formed from one or more monomers selected from the group consisting of dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and N-vinylpyridine. Claim 6 delete Claim 7 An electrophoretic display device according to claim 1, characterized in that the Lewis acid functional group is formed from diethylboranyloxyethyl methacrylate or 2-acrylamido-2-methylpropanesulfonic acid monomer. Claim 8 An electrophoretic display device according to claim 1, characterized in that the anchor block is formed from one or more monomers selected from the group consisting of methyl methacrylate, styrene, and 2-hydroxyethyl methacrylate. Claim 9 An electrophoretic display device according to claim 1, characterized in that the stabilization block is formed from an alkyl (meth)acrylate or polydimethylsiloxane macromonomer having 8 to 22 carbon atoms. Claim 10 An electrophoretic display device according to claim 1, characterized in that the electrophoretic fluid substantially does not contain an externally added charge control agent. Claim 11 An electrophoretic fluid comprising: a nonpolar solvent; a composite pigment particle dispersed in the nonpolar solvent and comprising a core pigment particle and a ternary block copolymer attached to the surface of the core pigment particle; and a second type of composite pigment particle having a color contrasting with that of the composite pigment particle and a charge of opposite polarity, and comprising a core pigment particle and a ternary block copolymer attached to the surface of the core pigment particle, wherein the ternary block copolymer comprises: (a) an anchor block attached to the surface of the core pigment particle; (b) a stabilizing block connected to the anchor block by a covalent bond and providing stereostabilization in the nonpolar solvent; and (c) a reactive charge-regulating block comprising a Lewis acid or Lewis base functional group that performs the function of chemically capturing ionic impurities in the nonpolar solvent; wherein the Lewis acid functional group comprises a boron compound, a sulfonic acid group, or a phosphate group, and the Lewis base functional group comprises a tertiary amine group or a nitrogen-containing heterocyclic compound. Claim 12 A method for manufacturing composite pigment particles according to claim 1, comprising: (a) a step of forming a polymerization initiation site on the surface of a core pigment particle; and (b) a step of sequentially growing an anchor block, a reactive charge-regulating block, and a stabilizing block through Controlled Radical Polymerization, which is a reversible addition-fractional-chain-transfer (RAFT) polymerization, from the polymerization initiation site to form a ternary block copolymer containing a Lewis acid or Lewis base functional group on the surface of the core pigment particle. Claim 13 The composite pigment particles produced by the method for producing composite pigment particles of claim 12 are composite pigment particles characterized in that the core pigment particles are titanium dioxide (TiO₂) or carbon black. Claim 14 (a) a step of dispersing the electrophoretic fluid of claim 11 in an aqueous solution to form an emulsion, and aggregating a wall material including gelatin and acacia at the interface of the emulsion to produce microcapsules; (b) a step of mixing the microcapsules with a water-soluble binder to produce a slurry; (c) a step of applying the slurry onto a conductive transparent film and drying it to form a film; and (d) a step of laminating the film with a substrate having electrodes formed thereon using a conductive adhesive layer; characterized by comprising the above steps. Claim 15 An electronic paper film manufactured by the method of manufacturing an electronic paper film of claim 14 and characterized by being driven at a voltage of 10 V or less. Claim 16 An electronic paper film according to claim 15, characterized in that the voltage retention rate (VHR) after 16.7 ms has elapsed after the application of a voltage of 1 V is 95% or higher.

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