Preparation method of black electrophoretic particles with low reflectivity and high charge quantity

Abstract

The invention relates to the technical field of electrophoretic display, in particular to a preparation method of black electrophoretic particles with low reflectivity and high charge quantity. The method comprises the following steps: S1, mixing pre-dried black electrophoretic particles with ethanol, water and zirconium beads, adjusting the pH value by using ammonia water, and carrying out ball milling; transferring to a four-neck flask, adding a silane coupling agent, adjusting the pH value again, reacting at 80 DEG C, washing, centrifuging and drying to obtain modified particles; s2, carrying out ball milling on the modified particles, a monomer 1, a monomer 2 and a solvent, transferring into a four-neck flask, heating to 50 DEG C under the protection of nitrogen, adding an initiator, and reacting at 70-85 DEG C; after cooling, adding 3-5 parts of monomers and a solvent, repeatedly heating, adding an initiator, and reacting at 70-85 DEG C; and cooling again, supplementing the monomer 2 or 3, reacting under the same condition, and finally centrifuging, washing and drying to obtain the modified electrophoretic particle with the controllable shell structure. According to the invention, controllable regulation and control of low reflectivity and high charge quantity of the black electrophoretic particles are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrophoretic display, and in particular to a preparation method of black electrophoretic particles with low reflectivity and high charge. BACKGROUND

[0002] In recent years, paper electronic books have attracted widespread attention due to their high brightness, high contrast, low power consumption, low cost and large-area production. Electrophoretic display is the only commercialized electronic paper technology, and its display device has the advantages of both printing media and electronic media, and has significant environmental benefits. It can be widely used in newspapers, magazines, books, large outdoor advertisements, printed advertisements and wearable devices.

[0003] An electrophoretic display controls the movement of electrophoretic particles in a non-polar medium by applying a voltage between two parallel electrodes, thereby realizing the display and switching of images. The main factors affecting electrophoretic display are: dispersion medium, electrophoretic particles, charge control agent and external electric field. Although the current electrophoretic display technology has entered the stage of commercialization and practicality, there are still many problems, such as the easy deposition of electrophoretic particles, the increase of response time caused by the weakening of electric potential, and the low gray scale of the display.

[0004] Most of the electrophoretic display devices on the market are black and white, and a small part of the color devices are mostly displayed in color by adding a filter film to the black and white devices. Therefore, the optimization of electrophoretic display should start from black and white display devices, and the main factor restricting the performance of black and white electrophoretic display is black and white electrophoretic particles. Black and white electrophoretic particles are mostly prepared by using inorganic particles, such as titanium oxide, aluminum oxide, iron manganese black and copper chromium black. Since the surface of the commercially available particles cannot be unified, and the density of the particles is greatly different from that of the electrophoretic medium, the compatibility is poor, and the particles are difficult to stably disperse, surface modification is needed to unify the surface and improve the properties of the particles in the dispersion medium. SUMMARY

[0005] The present application provides a preparation method of black electrophoretic particles with low reflectivity and high charge to solve the above problems.

[0006] The present application provides a preparation method of black electrophoretic particles with low reflectivity and high charge, which comprises: S1, surface grafting of silane coupling agent on electrophoretic particle raw material: pre-dried black electrophoretic particle raw material, ethanol, water and zirconium beads are added into a ball mill bottle and mixed uniformly, and then the pH value is adjusted once using ammonia water, followed by ball milling. Then the ball milling liquid is transferred to a four-necked flask and stirred, and then silane coupling agent is added, and the pH value is adjusted twice using ammonia water, and then heated to 80℃ for reaction. After the reaction is completed, washing and centrifugation are performed, and then drying is performed to obtain modified electrophoretic particles treated by silane coupling agent grafting.

[0007] S2, constructing surface shell layer of electrophoretic particles in stages: monomer 1, monomer 2, solvent and modified electrophoretic particles are added into a ball mill bottle, after ball milling, the ball mill liquid is transferred to a four-necked flask, and the temperature is raised to 50 DEG C under nitrogen protection, an initiator is added, and the temperature is raised to 70-85 DEG C for reaction, after the reaction system is cooled to room temperature, monomer 3, monomer 4, monomer 5 and solvent are added, then the system is heated to 50 DEG C, an initiator is added again, and then reacted at 70-85 DEG C, after being cooled to room temperature again, monomer 2 or monomer 3 is added, heated to 50 DEG C, an initiator is added, and reacted at 70-85 DEG C. The reaction is centrifuged to collect the precipitate, which is washed and dried to obtain the controllably constructed modified electrophoretic particles.

[0008] Through the above technical solutions, the present application realizes the controllable regulation of low reflectivity and high charge of black electrophoretic particles through the silane coupling agent grafting of S1 and the segmented shell layer construction of S2, which has significant advantages compared with the prior art. First, the S1 step ensures uniform grafting of the silane coupling agent on the particle surface through ball milling and pH adjustment, unifies the particle surface properties, and enhances the bonding force with the subsequent polymer shell layer. Second, the S2 segmented polymerization constructs a multi-layer shell structure, and through accurate control of the addition time and proportion of different monomers, the thickness and chemical composition of the shell layer are accurately regulated. This structure optimization makes the particles have higher dispersion stability and less deposition tendency in non-polar media. In particular, by introducing specific monomers and adjusting the monomer proportion, the charge of the electrophoretic particles can be increased in a targeted manner, and the Zeta potential can be as high as-101.625 mV, which is significantly higher than the prior art, effectively solving the problem of response time growth caused by weak electric potential, and improving the response speed and stability of the electrophoretic display. In addition, the optimized particle surface shell layer has good optical performance, so that the prepared prototype device has low black state reflectivity, thereby realizing higher display contrast. At the same time, the preparation method has high stability, and the obtained particles have uniform particle size distribution, which is beneficial to improve the overall performance and reliability of the electrophoretic display.

[0009] Optionally, in step S1, the black electrophoretic display particles are 1 part, the ethanol solvent is 10-20 parts, the silane coupling agent is 0.1-0.5 parts, and the zirconium beads are 5-20 parts by mass fraction.

[0010] By the technical scheme, the following beneficial effects are realized by precisely controlling the mass fraction of the reactants in step S1: firstly, the range of 10-20 parts of the ethanol solvent ensures the stable dispersion of the black electrophoretic particles in the reaction system, effectively prevents the particle agglomeration before the grafting reaction, and ensures the uniformity of the subsequent grafting layer. Secondly, the use amount of the silane coupling agent in the range of 0.1-0.5 parts makes the coupling agent fully grafted on the particle surface to form a uniform and moderate modified layer, provides high-density active sites for the stepwise polymerization of S2, and avoids the incomplete grafting layer caused by insufficient coupling agent or the waste caused by excessive coupling agent. Finally, the use amount of the zirconium beads in the range of 5-20 parts provides appropriate mechanical dispersion force in the ball milling process, further improves the uniformity of the particle surface and the reaction efficiency. The precise ratio control jointly acts to make the finally obtained modified electrophoretic particles have highly uniform surface properties, lays a solid foundation for S2 to construct a surface shell layer with low reflectivity and high charge quantity, and significantly improves the stability and electrophoretic performance of the electrophoretic particles.

[0011] Optionally, in step S1, the pH value adjustment target in the primary adjustment process is 7-10. In the secondary adjustment process, the pH value adjustment target is 7-10. The duration of the ball milling is 5-12 hours, the reaction condition is mechanical stirring reaction at a speed of 200-400 rpm for 5-10 hours, and the drying condition is drying at 60-100 DEG C.

[0012] By the technical scheme, the following beneficial effects are realized by precisely controlling the key process parameters of step S1: the control of the pH value in the range of 7-10 ensures the efficiency of the hydrolysis and grafting reaction of the silane coupling agent, avoids the self-polymerization of the coupling agent caused by too high pH value, and improves the grafting rate and the quality of the grafting layer. The ball milling duration of 5-12 hours ensures the complete dissociation of the particle agglomerates, so that the grafting reaction is carried out on the uniformly dispersed particle surface, and the uniformity and dispersion stability of the modified electrophoretic particles are improved. The mechanical stirring speed of 200-400 rpm and the reaction time of 5-10 hours ensure the uniformity of the reaction system and the sufficiency of the grafting reaction, so that the modified particles have uniform surface properties and high-density active sites. The drying condition of 60-100 DEG C effectively removes the solvent and moisture, and ensures the purity of the modified particles, providing high-quality raw materials for the stepwise polymerization of S2. The optimization of these process parameters collectively improves the quality of the modified electrophoretic particles, and enhances the stability and electrophoretic performance of the particles in the electrophoretic medium.

[0013] Optionally, in step S2, the modified electrophoretic particles are 1 part, the solvent is 10-20 parts, monomer 1 is 0.1-1 part, monomer 2 is 0.1-1 part, monomer 3 is 0.1-1 part, monomer 4 is 0.01-0.1 part, monomer 5 is 0.1-1 part, and zirconium beads are 5-20 parts, all by mass fraction.

[0014] By precisely controlling the proportion of reactants in step S2, the present application achieves the following beneficial effects: first, the use of 10-20 parts of solvent ensures the uniform dispersion of the modified electrophoretic particles before polymerization, providing an ideal reaction environment for subsequent stepwise polymerization, allowing the shell to grow uniformly on the particle surface. Second, the use of 0.1-1 parts of monomer 1, monomer 2, monomer 3, and monomer 5 ensures that the shell has sufficient thickness and optimal chemical composition, thereby improving the dispersion stability of the particles and their compatibility with the electrophoretic medium. Most importantly, the precise amount of monomer 4 is limited to 0.01-0.1 parts, which is used to precisely control the charge and crosslinking degree, allowing the final electrophoretic particles to have a high charge, effectively solving the problem of weak potential in the prior art. At the same time, precise monomer proportioning helps control the polymerization rate, reduces side reactions, and improves product yield and quality. The reuse of zirconium beads ensures the uniformity of the polymerization reaction, further ensuring the concentration of the particle size distribution.

[0015] Optionally, in step S2, the duration of the ball milling is 5-12 hours, the reaction conditions are mechanical stirring at a speed of 200-500 rpm, and the drying conditions are vacuum drying at 80-120°C for 5-12 hours. The mass of the initiator is 0.5-5% of the total mass of the monomers.

[0016] By precisely limiting the key process parameters of step S2, the above technical solutions bring significant benefits. Ball milling for 5-12 hours ensures that the particles are fully dispersed before polymerization, which is the basis for obtaining a uniform core-shell structure. Mechanical stirring at a speed of 200-500 rpm ensures the uniformity of the polymerization reaction, allowing the polymer shell to grow uniformly on the particle surface and improving the coverage and stability of the shell. Vacuum drying at 80-120°C for 5-12 hours ensures the purity of the final product, completely removing residual solvents and unreacted monomers, and improving the electrical properties and long-term stability of the electrophoretic particles. Precise control of the amount of initiator to 0.5-5% allows for a moderate polymerization rate, which is conducive to the formation of a high-molecular-weight, high-coverage polymer shell, thereby effectively improving the charge and dispersion stability of the electrophoretic particles, as shown in the accompanying Figure 4 Zeta potential is significantly improved.

[0017] Optionally, in step S1, the raw material of the black electrophoretic particle is one or a combination of iron manganese black, copper chromium black, and carbon black.

[0018] By the above technical solution, by selecting iron manganese black, copper chromium black, and carbon black as the raw material of the black electrophoretic particle, the present application has obtained significant beneficial effects. These raw materials themselves have excellent blackness, which lays the foundation for realizing low reflectance electrophoretic display. For example, in the embodiment, iron manganese black raw material A is used, and the final prototype device has a black state reflectance of 1.4-1.9%. Through subsequent silane coupling agent grafting and segmented shell construction, the problem of non-uniform surface properties of these inorganic particles and poor compatibility with the electrophoretic medium is successfully solved, and the dispersion stability and charge amount of the particles are significantly improved. In particular, carbon black, with its high electrical conductivity, is effectively controlled by the coating of the surface polymer shell, avoiding charge leakage while maintaining high blackness. This combination strategy enables the final electrophoretic particle to have the characteristics of high blackness, high stability, and high charge amount.

[0019] Optionally, in step S1, the silane coupling agent is one of γ-(methacryloyloxy)propyltrimethoxysilane, trimethoxy(7-octen-1-yl)silane, 10-undecenyltrichlorosilane, and [3-(triethoxysilyl)propyl]carbamic acid 2-propynyl ester.

[0020] By the above technical solution, the selection of specific silane coupling agents brings the following beneficial effects: first, these coupling agents can form a high-density active site on the particle surface, significantly improving the efficiency and shell coverage of the S2 polymerization reaction. Second, the shell structure connected by chemical bonds (core-shell) has higher stability and durability than the physically adsorbed shell, effectively preventing the electrophoretic particles from de-shelling and agglomerating in the electrophoretic medium. For example, the use of γ-(methacryloyloxy)propyltrimethoxysilane enables the subsequent polymerization reaction to proceed in a "grafting to" manner, ensuring the firm combination of the shell and the core. This reinforced core-shell structure helps to improve the mechanical strength and chemical stability of the electrophoretic particle, thereby prolonging the service life of the electrophoretic display.

[0021] Optionally, in step S2, the solvent is one of ethanol, isopropanol, toluene, cyclohexane, Isopar L, and Isopar G.

[0022] By the above technical solution, the selection of the specific solvent system brings the following beneficial effects: first, the diversity of solvents enables the method to adapt to different monomer combinations with different polarity and solubility characteristics, improving the flexibility of the segmented polymerization. Second, the use of IsoparL or IsoparG as a solvent can enable the polymer shell to grow in an environment similar to the actual electrophoretic medium, thereby optimizing the compatibility of the shell with the electrophoretic medium and improving the dispersion stability and electrophoretic mobility of the electrophoretic particles. For example, in the examples, ethanol is used as a solvent to ensure good solubility of the monomers and uniformity of the reaction. Suitable solvent selection is a key factor in ensuring uniform core-shell structure and concentrated particle size distribution.

[0023] Optionally, in step S2, the initiator is one of benzoyl peroxide, potassium persulfate, azobisisobutyronitrile, and dimethyl azobisisobutyrate.

[0024] By the above technical solution, the selection of the specific initiator brings the following beneficial effects: first, these initiators have moderate decomposition rates and high initiation efficiency, ensuring the stability and controllability of the polymerization reaction. Second, by precisely controlling the amount of initiator, the molecular weight and grafting density of the polymer can be adjusted, thereby optimizing the physical and chemical properties of the shell. For example, the use of azobisisobutyronitrile ensures uniform initiation in organic solvents, which is beneficial to the formation of a uniform polymer shell. Precise control of the initiator is key to achieving segmented polymerization and helps to obtain electrophoretic particles with controllable surface properties and high charge.

[0025] Optionally, in step S2, monomer 1, monomer 2, monomer 3, monomer 4, and monomer 5 are any one of styrene, divinylbenzene, 1,3-butadiene, methyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, acrylic acid, acrylamide, oleic acid, oleylamine, isocyanate, N,N'-methylene bisacrylamide, and fatty acid polyoxyethylene ester.

[0026] By the above technical solution, first, by combining the use of hydrophobic monomers and polar monomers, the surface properties of the shell can be precisely controlled to have excellent compatibility with non-polar electrophoretic media, significantly improving the dispersion stability of the particles. Second, the introduction of a crosslinking agent (such as divinylbenzene) enhances the structural stability of the polymer shell, effectively preventing swelling and shedding of the shell. Most importantly, by precisely controlling the amount and introduction position of the charge monomer (such as acrylic acid and diallyldimethylammonium chloride), controllable regulation of the charge amount and polarity of the electrophoretic particles is achieved, with a high Zeta potential, effectively enhancing the response speed to the electric field. The combined use of such multifunctional monomers is a key technology for achieving black electrophoretic particles with low reflectivity, high charge, and high stability. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0028] Figure 1 The flow chart of the preparation method of the low reflectivity and high charge black electrophoretic particles provided by an embodiment of the present application; Figure 2 The TGA curve of the C-H particles prepared by the present application; Figure 3 The particle size distribution curve of the C-H particles prepared by the present application; Figure 4 The prototype device diagram of the C-H particles prepared by the present application; Figure 5 The Zeta potential broken line diagram of the C-H particles prepared by the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be described clearly and completely in combination with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without any creative effort fall within the scope of protection of the present application.

[0030] In addition, the term "and / or" in this paper is only to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents an "or" relationship between the associated objects before and after it, unless otherwise specified.

[0031] The embodiments of the present application will be further described in detail below in combination with the accompanying drawings of the specification.

[0032] Currently, most of the electrophoretic display devices on the market are black and white, and a small number of color devices are mostly displayed in color by adding a filter film to the black and white device. Therefore, the optimization of the electrophoretic display device should start from the black and white display device, and the main factor restricting the performance of the black and white electrophoretic display is the black and white electrophoretic particle. The black and white electrophoretic particle is mostly prepared by using inorganic particles, such as titanium oxide, aluminum oxide, iron manganese black, copper chromium black, etc. Since the surface of the commercially available particles cannot be unified, and the density of the particles is greatly different from that of the electrophoretic medium, the compatibility is poor, and the particles are difficult to stably disperse, surface modification is needed to unify the surface and improve the properties of the particles in the dispersion medium.

[0033] Based on this, the application provides a preparation method of a black electrophoretic particle with low reflectivity and high charge quantity. The method realizes the controllable regulation of the low reflectivity and high charge quantity of the black electrophoretic particle through the grafting of the silane coupling agent in S1 and the construction of the segmented shell layer in S2, and has a significant advantage compared to the prior art. First, the S1 step ensures uniform grafting of the silane coupling agent on the surface of the particles through ball milling and pH adjustment, unifies the surface properties of the particles, and enhances the bonding force with the subsequent polymer shell layer. Second, the S2 segmented polymerization constructs a multi-layer shell structure, and through accurate control of the addition time and proportion of different monomers, the thickness and chemical composition of the shell layer are accurately regulated. This structure optimization makes the particles have higher dispersion stability and less sedimentation tendency in non-polar media. In particular, by introducing specific monomers and adjusting the monomer ratio, the charge quantity of the electrophoretic particle can be increased in a targeted manner, and the Zeta potential can be as high as -101.625 mV, which is significantly higher than the prior art, effectively solving the problem of response time growth caused by weak electric potential, and improving the response speed and stability of the electrophoretic display. In addition, the optimized particle surface shell layer has good optical performance, so that the prepared prototype device has low black state reflectivity, thereby realizing higher display contrast. At the same time, the preparation method has high stability, and the obtained particles have uniform particle size distribution, which is conducive to improving the overall performance and reliability of the electrophoretic display. The specific implementation can refer to the following embodiments.

[0034] Figure 1 A flow chart of a preparation method of a black electrophoretic particle with low reflectivity and high charge quantity provided by an embodiment of the application is shown in Figure 1 The method comprises: S1, surface grafting of silane coupling agent on electrophoretic particle raw material: pre-dried black electrophoretic particle raw material, ethanol, water and zirconium beads are added to a ball mill bottle and mixed uniformly, and then ball milling is performed after adjusting the pH value once with ammonia water. Then the ball milling liquid is transferred to a four-necked flask and stirred, and then the pH value is adjusted again with ammonia water after adding the silane coupling agent. Then the temperature is raised to 80℃ for reaction. After the reaction is completed, washing, centrifugation and drying are performed to obtain modified electrophoretic particles after silane coupling agent grafting treatment.

[0035] S2, segmental construction of the surface shell of electrophoretic particles: monomer 1, monomer 2, solvent and modified electrophoretic particles are added to a ball mill bottle, after ball milling, the ball mill liquid is transferred to a four-necked flask, and heated to 50°C under nitrogen protection, initiator is added, and then heated to 70-85°C for reaction, after the reaction system is cooled to room temperature, monomer 3, monomer 4, monomer 5 and solvent are added, then the system is heated to 50°C, initiator is added again, then reacted at 70-85°C, after cooling to room temperature again, monomer 2 or monomer 3 is added, heated to 50°C, and initiator is added, and reacted at 70-85°C. The precipitate is collected by centrifugation, washed and dried to obtain the controllably constructed modified electrophoretic particles.

[0036] Technical background and working principle: Although the current electrophoretic display technology has been commercialized, it still faces problems such as easy deposition of electrophoretic particles, increase of response time due to weakening of electric potential, and low gray scale of display. The existing black and white electrophoretic particles are mostly inorganic particles, such as titanium oxide, iron manganese black, copper chromium black, etc., and their surface properties are not uniform, and they have large density difference and poor compatibility with non-polar electrophoretic medium, which is difficult to disperse stably. The present application aims to solve these problems, and prepare black electrophoretic particles with low reflectivity and high charge by surface grafting and segmental shell construction. The working principle of the present application is based on chemical modification and controllable polymerization: in S1, through silane coupling agent grafting reaction, using ammonia to adjust pH value, under the action of ball milling, the silane coupling agent is uniformly grafted on the surface of the black electrophoretic particle raw material, which unifies the surface properties of the particles and provides active sites for subsequent polymerization reaction. In S2, segmental polymerization is adopted, first, under nitrogen protection, through the first stage of polymerization reaction, monomer 1 and monomer 2 form a first layer of shell on the surface of the modified particles, which is mainly used to improve the compatibility of the particles with the solvent. Then, in the second stage of polymerization, monomer 3, monomer 4 and monomer 5 are added to construct the second layer of shell, which is mainly responsible for introducing charge groups and controlling particle size. Finally, in the third stage of polymerization, monomer 2 or monomer 3 is added to further optimize the surface charge density and shell structure. This segmental construction method realizes accurate control of the surface properties, charge quantity and particle size distribution of the electrophoretic particles, thereby significantly improving the dispersion stability and electrophoretic performance of the particles.

[0037] Technical solutions and component functions: The method provided by the present application mainly includes two core steps of S1 electrophoretic particle raw material surface grafting silane coupling agent and S2 segmented construction of electrophoretic particle surface shell. In S1, black electrophoretic particle raw material as core colorant, ethanol and water as dispersion medium, zirconium beads as grinding and dispersion aid, ensure that the particles are fully dispersed and exposed to the surface active site during ball milling. Ammonia is used to adjust the pH value to the alkaline range (preferably 7-10) to catalyze the hydrolysis and condensation reaction of silane coupling agent, and enhance its grafting efficiency on the surface of the particle. The silane coupling agent is used to introduce organic functional groups on the surface of inorganic particles, realizing the construction of inorganic to organic transition layer. In S2, the modified electrophoretic particles are used as the core of the polymerization reaction, monomer 1, monomer 2, monomer 3, monomer 4 and monomer 5 are the key components of the surface shell, which form a multi-layer structure on the surface of the modified particles through polymerization reaction, wherein monomer 1, monomer 2, monomer 3 and monomer 5 mainly provide the shell skeleton and compatibility, and monomer 4 is mainly used to introduce charge groups or crosslinking structure. Solvent is used to disperse particles and monomers, and initiator (such as azobisisobutyronitrile) is used to start free radical polymerization reaction. The segmented polymerization reaction realizes the accurate control of the shell thickness, components and charge quantity by controlling the addition time of different monomers and initiators and the reaction temperature. For example, the first stage polymerization is carried out at 70-85℃ to form the first layer of shell, then the temperature is lowered to room temperature, new monomer components are added, and the temperature is raised to 50℃ to add initiator, and the second stage polymerization is carried out at 70-85℃ to ensure the diversity and functionality of the shell structure. The third stage polymerization further optimizes the surface charge. Ball milling steps are used in S1 and S2 to ensure uniform dispersion of particles before reaction, avoid agglomeration, and thus ensure uniformity of subsequent grafting and polymerization reactions.

[0038] Beneficial effects: The present application realizes the controllable regulation of low reflectivity and high charge quantity of black electrophoretic particles through silane coupling agent grafting in S1 and segmented shell construction in S2, which has significant advantages compared with the prior art. First, the S1 step ensures uniform grafting of silane coupling agent on the surface of the particles through ball milling and pH adjustment, unifies the particle surface properties, and enhances the bonding force with the subsequent polymer shell. Second, the S2 segmented polymerization constructs a multi-layer shell structure, which realizes the accurate control of the shell thickness and chemical components by accurately controlling the addition time and proportion of different monomers. This structure optimization makes the particles have higher dispersion stability and less sedimentation tendency in non-polar medium. The prepared black modified electrophoretic particles have a weight loss rate of 10-15% and a thermal weight loss temperature of 300-500℃ (as shown in Figure 2 ). At the same time, by increasing the amount of specific monomers, the coating amount of black electrophoretic particles can be increased. In particular, by introducing specific monomers (such as monomer 4) and adjusting the monomer ratio, the charge quantity of electrophoretic particles can be increased, such as Figure 5As shown, the Zeta potential can be up to 101.625 mV, which is significantly higher than the prior art, effectively solving the problem of response time growth caused by potential weakening, and improving the response speed and stability of the electrophoretic display. In addition, the optimized particle surface shell has good optical performance, so that the prepared prototype device has low black-state reflectivity (e.g. Figure 4 As shown, between 1.4 and 1.9%), thereby achieving higher display contrast. At the same time, the preparation method has high stability, and the obtained particles have uniform particle size distribution (e.g. Figure 3 As shown, the particle size is between 160 and 180 nm), which is beneficial to improve the overall performance and reliability of the electrophoretic display.

[0039] In some embodiments, in step S1, the black electrophoretic display particles are 1 part, the ethanol solvent is 10-20 parts, the silane coupling agent is 0.1-0.5 parts, and the zirconium beads are 5-20 parts by mass fraction.

[0040] Technical background and working principle: Based on the method of claim 1, the present claim further limits the mass fraction range of the key components in step S1 to optimize the efficiency and uniformity of the silane coupling agent grafting reaction. In the prior art, improper proportioning of reactants during inorganic particle surface modification can result in low grafting rate, particle agglomeration, or incomplete reaction. The proportioning limitation of the present application aims to provide a scientifically reasonable reaction system, ensuring that when the black electrophoretic particles are 1 part, the amount of ethanol solvent is 10-20 parts, which ensures good dispersion of the particles in the solvent and avoids the problem of too low reaction concentration caused by excessive solvent. The amount of silane coupling agent is limited to 0.1-0.5 parts, which ensures that there is enough silane coupling agent on the surface of the particles for grafting, while avoiding the self-polymerization reaction of excessive coupling agent. The amount of zirconium beads is limited to 5-20 parts, which provides moderate mechanical dispersion force through ball milling to ensure uniform exposure of the particle surface and full reaction. This precise proportioning control is the technical basis for achieving high uniformity of surface-modified electrophoretic particles.

[0041] Technical solutions and component functions: The present embodiment precisely limits the proportion of reactants in step S1. Black electrophoretic display particles serve as the reaction core, with 1 part by mass. The ethanol solvent is 10-20 parts, which provides a uniform dispersion environment and ensures that the particles do not hard-agglomerate during ball milling and subsequent reactions. If the amount of ethanol is less than 10 parts, the particle dispersion may not be sufficient; if it is more than 20 parts, the reaction system concentration is too low, and the reaction efficiency may decrease. The silane coupling agent is 0.1-0.5 parts, which functions to graft on the particle surface to form an active intermediate layer. An appropriate amount of coupling agent ensures sufficient surface coverage while controlling the thickness of the grafted layer, avoiding the formation of non-grafted polymers due to excessive coupling agent, thereby improving grafting efficiency and uniformity. Zirconium beads are 5-20 parts, which are used to provide high-intensity shear force during ball milling to break up particle agglomeration, allowing the silane coupling agent to contact every active site on the particle surface, thereby improving grafting uniformity and coverage. This proportioning range ensures efficient and controllable silane coupling agent grafting reactions, which is a key technical feature of preparing high-quality modified electrophoretic particles.

[0042] Beneficial effects: By precisely controlling the mass fraction of reactants in step S1, the present application achieves the following beneficial effects: First, the range of 10-20 parts of ethanol solvent ensures the stable dispersion of black electrophoretic particles in the reaction system, effectively preventing particle agglomeration before the grafting reaction, and ensuring the uniformity of the subsequent grafted layer. Second, the use of 0.1-0.5 parts of silane coupling agent allows the coupling agent to graft sufficiently on the particle surface, forming a uniform and moderate modification layer that provides a high density of active sites for the segmented polymerization of S2, avoiding incomplete grafting due to insufficient coupling agent or waste due to excessive coupling agent. Finally, the use of 5-20 parts of zirconium beads provides appropriate mechanical dispersion force during ball milling, further improving the uniformity of the particle surface and reaction efficiency. These precise proportioning controls work together to produce modified electrophoretic particles with highly uniform surface properties, laying a solid foundation for S2 to construct a low-reflectivity, high-charge surface shell, and significantly improving the stability and electrophoretic performance of the electrophoretic particles.

[0043] In some embodiments, in step S1, the pH value adjustment target in the first adjustment process is 7-10; In the second adjustment process, the pH value adjustment target is 7-10; The duration of the ball milling is 5-12 hours, the reaction conditions are mechanical stirring for 5-10 hours at a rotation speed of 200-400 rpm, and the drying conditions are drying at 60-100°C.

[0044] Technical background and working principle: The present claim specifically limits the pH adjustment in step S1, the ball milling time and the reaction conditions, which are crucial for the grafting efficiency of silane coupling agent on the particle surface and the quality of the product. The hydrolysis and condensation reaction of silane coupling agent usually needs to be carried out under specific pH conditions. A weak alkaline environment with a pH value of 7-10 can effectively catalyze the formation of silanol and promote its condensation grafting with the particle surface hydroxyl group, but also avoids the excessive self-polymerization of silane coupling agent caused by strong alkalinity. Both the first adjustment and the second adjustment are set at 7-10, ensuring that the entire process from dispersion to grafting reaction is in the best catalytic environment. The ball milling duration is 5-12 hours, ensuring the complete dissociation and uniform dispersion of particle agglomerates. The mechanical stirring speed is 200-400 rpm and the reaction time is 5-10 hours, ensuring uniform mixing of the reaction system and sufficient grafting of the silane coupling agent. The drying condition is 60-100°C, which is used to completely remove residual solvents and water, avoiding interference with the subsequent S2 polymerization reaction. These precise process parameter controls are the key technical foundation for achieving high-efficiency and high-uniformity surface modification.

[0045] Technical solution and component function: In the above embodiment, the pH adjustment target of step S1 is precisely set at 7-10. Ammonia is commonly used as an alkaline adjusting agent, and its dosage needs to be strictly controlled to maintain the system pH value in the weak alkaline range of 7-10. This range is the best condition for the hydrolysis of silane coupling agent and the condensation with the inorganic particle surface hydroxyl group. The first adjustment is carried out before ball milling, which helps to stabilize the dispersion of particles in the water / ethanol mixed solvent; the second adjustment is carried out after the addition of silane coupling agent, ensuring efficient grafting reaction. The ball milling duration is 5-12 hours, ensuring the complete dispersion of black electrophoretic particle raw materials and the uniformization of particle size, providing the maximum surface area for the grafting reaction. If the ball milling time is less than 5 hours, the particles may be agglomerated; if it exceeds 12 hours, it may cause excessive grinding. The reaction condition is mechanical stirring at a speed of 200-400 rpm for 5-10 hours, ensuring the uniformity of the reaction system, allowing the silane coupling agent to fully contact and react with the particle surface. The drying condition is 60-100°C, which is used to remove physically adsorbed moisture and solvents, avoiding the decomposition of the grafting layer caused by high temperature, and ensuring the chemical stability of the modified electrophoretic particle surface.

[0046] Beneficial effects: The present application has obtained significant beneficial effects by precisely limiting the key process parameters of S1 step. The control of pH value 7-10 ensures the high efficiency of silane coupling agent hydrolysis and grafting reaction, avoids the self-polymerization of coupling agent caused by too high pH value, and improves the grafting rate and grafting layer quality. The ball milling duration of 5-12 hours ensures the sufficient dissociation of particle agglomerates, so that the grafting reaction is carried out on the surface of uniformly dispersed particles, improving the uniformity and dispersion stability of modified electrophoretic particles. The mechanical stirring speed of 200-400 rpm and the reaction time of 5-10 hours ensure the uniformity of the reaction system and the sufficiency of the grafting reaction, so that the modified particles have uniform surface properties and high-density active sites. The drying condition of 60-100℃ effectively removes the solvent and moisture, ensuring the purity of the modified particles, and providing high-quality raw materials for S2 segmented polymerization. The optimization of these process parameters collectively improves the quality of the modified electrophoretic particles, enhancing their stability and electrophoretic performance in the electrophoretic medium.

[0047] In some embodiments, in step S2, the modified electrophoretic particles are 1 part, the solvent is 10-20 parts, monomer 1 is 0.1-1 part, monomer 2 is 0.1-1 part, monomer 3 is 0.1-1 part, monomer 4 is 0.01-0.1 part, monomer 5 is 0.1-1 part, and zirconium beads are 5-20 parts by mass fraction.

[0048] Technical background and working principle: The present application precisely limits the mass fraction of key components for constructing the surface shell layer in step S2. These ratio controls are the key to achieving controlled polymerization, precise control of shell structure and charge quantity. In the prior art, the preparation of core-shell structure electrophoretic particles often results in uneven shell, insufficient charge quantity or wide particle size distribution due to improper monomer ratio. The present application limits the modified electrophoretic particles to 1 part, the solvent to 10-20 parts, ensuring that the polymerization reaction is carried out in a diluted and uniformly dispersed system, which is conducive to the formation of a uniform shell. The use amount of monomer 1, monomer 2, monomer 3 and monomer 5 is in the range of 0.1-1 part, which ensures that there is enough polymerized monomer to construct a stable shell with a certain thickness. The use amount of monomer 4 is in the range of 0.01-0.1 part, as monomer 4 is mainly used to introduce charge groups or crosslinking structures, its lower use amount range ensures the precise control of charge density and crosslinking degree, avoiding excessive repulsion of particles or unnecessary crosslinking caused by too high charge quantity. Zirconium beads 5-20 parts are used for ball milling dispersion of modified particles to ensure that the subsequent polymerization reaction is carried out on the surface of uniformly dispersed particles. Precise ratio is the core technical guarantee for realizing low reflectivity and high charge quantity electrophoretic particles.

[0049] Technical solutions and component functions: In the above embodiments, the reactant ratio of step S2 is precisely defined. The modified electrophoretic particles are used as the core, with 1 part by mass. The solvent is used in an amount of 10-20 parts to provide a uniform dispersion medium, ensuring the uniformity and controllability of the polymerization reaction. If the amount of solvent is too low, the particles may agglomerate, resulting in uneven shell layers; if it is too high, the reaction rate may be too slow. Monomer 1, monomer 2, monomer 3, and monomer 5 are used as the main constituent units of the shell layer, with a usage range of 0.1-1 parts, ensuring the thickness and stability of the shell layer. For example, monomer 1 and monomer 2 are used for the first-stage polymerization, and monomer 3, monomer 4, and monomer 5 are used for the second-stage polymerization. The precise control of their proportions directly determines the chemical composition and physical properties of the shell layer. Monomer 4 is used in an amount of 0.01-0.1 parts, and its role is to introduce functional groups such as carboxyl, amine, or crosslinking groups, which play a key role in the charge quantity and structural stability of the particles. A lower usage range ensures the precise introduction of functional groups and avoids affecting the main shell structure. Zirconium beads are used in an amount of 5-20 parts for re-milling and dispersing the modified electrophoretic particles before polymerization, eliminating possible slight agglomeration and ensuring the uniformity of the start of the polymerization reaction.

[0050] Advantages: By precisely controlling the reactant ratio in step S2, the present application achieves the following advantages: First, the use of 10-20 parts of solvent ensures the uniform dispersion of the modified electrophoretic particles before polymerization, providing an ideal reaction environment for subsequent stepwise polymerization, allowing the shell layer to grow uniformly on the particle surface. Second, the usage range of monomer 1, monomer 2, monomer 3, and monomer 5 is 0.1-1 parts, ensuring that the shell layer has sufficient thickness and optimal chemical composition, thereby improving the dispersion stability of the particles and their compatibility with the electrophoretic medium. Most importantly, the usage of monomer 4 is precisely limited to 0.01-0.1 parts, which is used to precisely control the charge quantity and crosslinking degree, allowing the finally prepared electrophoretic particles to have a high charge quantity (e.g. Figure 5 ), effectively solving the problem of weak potential weakening in the prior art. At the same time, precise monomer ratio helps to control the polymerization rate, reduce side reactions, and improve product yield and quality. The re-use of zirconium beads ensures the uniformity of the polymerization reaction, further ensuring the concentration of the particle size distribution (e.g. Figure 3 ).

[0051] In some embodiments, in step S2, the duration of the ball milling is 5-12 hours, the reaction conditions are mechanical stirring at a speed of 200-500 rpm, and the drying conditions are vacuum drying at 80-120°C for 5-12 hours; the mass of the initiator is 0.5-5% of the total mass of the monomers.

[0052] Technical background and working principle: The present claim limits the ball milling time, reaction stirring condition, drying condition and initiator dosage in step S2. The precise control of these process parameters is the key to ensure the success of the segmented polymerization reaction, uniform growth of the shell layer and the quality of the final product. The ball milling duration is 5-12 hours, which is used to ensure the sufficient dispersion of the modified electrophoretic particles before polymerization, eliminating agglomeration. The mechanical stirring speed is 200-500 rpm, which ensures uniform mixing of the polymerization reaction system and avoids local high concentration leading to homogeneous polymerization or uneven shell. The drying condition is vacuum drying at 80-120°C for 5-12h, which is used to completely remove residual solvents and unreacted monomers, ensuring the purity of the particles, while avoiding particle agglomeration or decomposition at high temperature. The mass of the initiator is limited to 0.5-5% of the total mass of the monomers, which is the commonly used optimization range for free radical polymerization, ensuring a moderate reaction rate and avoiding reaction runaway due to excessive initiator or incomplete reaction due to insufficient initiator.

[0053] Technical solution and component function: In the above embodiment, the ball milling duration of step S2 is 5-12 hours, which further disperses the modified electrophoretic particles prepared in step S1, ensuring their existence in a monodisperse state in the polymerization reaction, which is a prerequisite for obtaining core-shell structure particles with concentrated particle size distribution (as shown in Figure 3 The reaction condition is mechanical stirring at a speed of 200-500 rpm, which ensures the mixing of the reactants in the four-necked flask, allowing the monomers to polymerize uniformly on the particle surface. If the speed is lower than 200 rpm, the mixing may not be uniform; if it is higher than 500 rpm, it may cause excessive shearing of the system. The drying condition is vacuum drying at 80-120°C for 5-12h, which helps to reduce the boiling point of the solvent and accelerate the removal of the solvent. The temperature range of 80-120°C ensures the complete removal of the solvent and residual monomers, while avoiding thermal damage to the polymer shell. The mass of the initiator is 0.5-5% of the total mass of the monomers. The initiator is used to start the free radical polymerization reaction, and its dosage directly affects the polymerization rate and the molecular weight of the polymer. The dosage range of 0.5-5% ensures a moderate polymerization rate, which is beneficial to the formation of a uniform and stable polymer shell.

[0054] Beneficial effects: Precise limitation of key process parameters in S2 step brings significant beneficial effects. Ball milling time 5-12 hours ensures sufficient dispersion of particles before polymerization, which is the basis for obtaining uniform core-shell structure. Mechanical stirring speed 200-500 rpm ensures the uniformity of polymerization reaction, making the polymer shell grow uniformly on the particle surface, improving the coverage and stability of the shell. Drying conditions 80-120 °C under vacuum drying for 5-12 h ensure the purity of the final product, completely removing residual solvents and unreacted monomers, improving the electrical properties and long-term stability of electrophoretic particles. Precise control of initiator dosage 0.5-5% makes the polymerization rate moderate, which is conducive to the formation of high molecular weight and high coverage polymer shell, thereby effectively improving the charge quantity and dispersion stability of electrophoretic particles, as shown in Figure 5 Zeta potential is significantly improved.

[0055] In some embodiments, in step S1, the raw material of the black electrophoretic particle is one or a combination of iron manganese black, copper chromium black, and carbon black.

[0056] Technical background and working principle: The present claim limits the specific type of black electrophoretic particle raw material in step S1. In the prior art, black electrophoretic particles are mostly selected from inorganic particles such as iron manganese black, copper chromium black, and carbon black. These particles have the characteristics of high blackness and low reflectivity, but their surface properties are complex and have poor compatibility with non-polar electrophoretic medium. The present application selects these high blackness inorganic particles as the core raw material, and through subsequent silane coupling agent grafting and segmented shell construction, it can fully utilize their high blackness characteristics, while solving the problem of inconsistent surface properties and poor dispersion stability. Iron manganese black, copper chromium black, and carbon black, as black pigments, have low reflectivity, which is an ideal basic material for achieving high-contrast electrophoretic display (as shown in Figure 4 ).

[0057] Technical solution and component function: In the above embodiments, the black electrophoretic particle raw material used in step S1 is limited to one or a combination of iron manganese black, copper chromium black, and carbon black. Iron manganese black and copper chromium black are commonly used inorganic black pigments with excellent weather resistance and chemical stability, and carbon black is known for its extremely low reflectivity and high electrical conductivity. Selecting these materials as raw materials can ensure that the final electrophoretic particles have good coloring ability and low reflectivity. These raw materials all belong to inorganic particles, and their surfaces contain a large number of hydroxyl or oxide groups, which are active sites for silane coupling agent grafting reactions. In step S1, through ball milling and pH adjustment, the surface of these raw materials is fully activated, and the silane coupling agent can be uniformly grafted on the surface to form modified electrophoretic particles. If a combination of multiple materials is used, for example, a combination of iron manganese black and carbon black, the blackness and electrical properties of the final particles can be optimized by adjusting the ratio.

[0058] Beneficial effects: By selecting iron manganese black, copper chromium black, carbon black as the black electrophoretic particle raw material, the application has obtained significant beneficial effects. These raw materials themselves have excellent blackness, which lays the foundation for realizing low reflectivity electrophoretic display. For example, in the examples, iron manganese black raw material A is used, and the final prototype device has a black state reflectivity of 1.4-1.9% (as shown in Figure 4 The subsequent silane coupling agent grafting and segmented shell construction successfully solve the problem of inconsistent surface properties of these inorganic particles and poor compatibility with the electrophoretic medium, significantly improving the dispersion stability and charge amount of the particles. In particular, the high conductivity of carbon black is effectively controlled by the coating of the surface polymer shell, avoiding charge leakage while maintaining high blackness. This combination strategy enables the final electrophoretic particles to have the characteristics of high blackness, high stability and high charge amount.

[0059] In some embodiments, in step S1, the silane coupling agent is one of γ-(methacryloyloxy)propyl trimethoxysilane, trimethoxy(7-octen-1-yl)silane, 10-undecenyltrichlorosilane, and [3-(triethoxysilyl)propyl] carbamic acid 2-propynyl ester.

[0060] Technical background and working principle: The present claim defines the specific type of silane coupling agent in step S1. The selection of silane coupling agent directly determines its grafting efficiency on the surface of black electrophoretic particle raw material and the type of organic functional groups introduced, which further affects the success rate of subsequent S2 polymerization reaction and shell structure. In the prior art, silane coupling agent is a bridge connecting inorganic particles and organic polymers. The four silane coupling agents selected in the present application all contain hydrolyzable alkoxy groups (such as trimethoxy, triethoxy) or chlorine groups (trichlorosilane), and active functional groups (such as methacryloyloxy, alkenyl, alkynyl or carbamate) that can participate in polymerization reaction. These active functional groups can copolymerize with the monomers in S2 to form a polymer shell connected by chemical bonds, thereby significantly improving the bonding strength and stability between the shell and the particle core.

[0061] Technical solutions and component functions: In the above embodiments, the silane coupling agent used in step S1 is limited to one of γ-(methacryloyloxy)propyltrimethoxysilane, trimethoxy(7-octen-1-yl)silane, 10-undecenyltrichlorosilane, and [3-(triethoxysilyl)propyl] carbamic acid 2-propynyl ester. These silane coupling agents have the common feature of having a bifunctional structure: one end is a silane group that can react with the hydroxyl groups on the surface of inorganic particles, and the other end is an active functional group that can undergo polymerization reaction with the monomers in S2. For example, γ-(methacryloyloxy)propyltrimethoxysilane contains a methacryloyloxy group that can directly participate in free radical polymerization. Trimethoxy(7-octen-1-yl)silane and 10-undecenyltrichlorosilane contain carbon-carbon double bonds that can also participate in polymerization. The presence of these active functional groups ensures that the S2 segmented polymerization reaction can start from the modified particle surface, achieving "surface growth" of the polymer shell, thereby forming a firm core-shell structure. In S1, the hydrolysis of the silane coupling agent is promoted by adjusting the pH value with ammonia, which allows it to undergo condensation reaction with the hydroxyl groups on the surface of the particles, completing the graft modification.

[0062] Benefits: The use of specific silane coupling agents brings the following benefits: First, these coupling agents can form a high density of active sites on the particle surface, significantly improving the efficiency and shell coverage of the S2 polymerization reaction. Second, the shell structure connected by chemical bonds (core-shell) has higher stability and durability than the physically adsorbed shell, effectively preventing the dehulling and agglomeration of electrophoretic particles in the electrophoretic medium. For example, the use of γ-(methacryloyloxy)propyltrimethoxysilane allows the subsequent polymerization reaction to proceed in a "grafting to" manner, ensuring a firm bond between the shell and the core. This strengthened core-shell structure helps to improve the mechanical strength and chemical stability of the electrophoretic particles, thereby prolonging the service life of the electrophoretic display.

[0063] In some embodiments, in step S2, the solvent is one of ethanol, isopropanol, toluene, cyclohexane, Isopar L, and Isopar G.

[0064] Technical background and working principle: The present claim defines the type of solvent used in step S2 of the segmented polymerization. Solvents play a crucial role in the polymerization process by dispersing particles, dissolving monomers, and initiating agents, and their selection directly affects the uniformity of the polymerization and the dispersion stability of the final particles. In existing electrophoretic display technologies, the electrophoretic medium is often a non-polar solvent (such as the Isopar series). The solvent selected in this invention includes polar solvents (ethanol, isopropanol) and non-polar solvents (toluene, cyclohexane, Isopar L, Isopar G). This diversity of choices is to meet the needs of different monomers and polymerization stages. For example, in the first stage of polymerization, polar solvents may be needed to dissolve certain monomers; while in subsequent polymerization, non-polar solvents may be needed to simulate the environment of the electrophoretic medium, ensuring that the final shell layer has good compatibility with the electrophoretic medium.

[0065] Technical solution and component function: In the above embodiment, the solvent used in step S2 is limited to one of ethanol, isopropanol, toluene, cyclohexane, Isopar L, and Isopar G. Ethanol and isopropanol are commonly used polar organic solvents with good monomer solubility and can form azeotropes with water, which helps to control the water content of the system during the reaction process. Toluene and cyclohexane are commonly used non-polar or weakly polar solvents suitable for dissolving non-polar monomers. Isopar L and Isopar G are commonly used electrophoretic fluid media, with low dielectric constant and high resistivity characteristics, making them ideal solvents for preparing electrophoretic particles, which can directly simulate the final application environment. In the S2 segmented polymerization, a single solvent can be used throughout, or the solvent can be changed in different polymerization stages, for example, ethanol is used in the first stage of polymerization to improve the solubility of the monomer, and Isopar L is used in the second and third stages of polymerization to optimize the hydrophobicity of the shell layer. The role of the solvent is to ensure that the modified electrophoretic particles and monomers remain uniformly dispersed throughout the reaction process, avoiding agglomeration, and thus ensuring the uniformity of the shell growth.

[0066] Beneficial effects: The selection of a specific solvent system brings the following beneficial effects: First, the diversity of solvents enables the method to adapt to different polarities and solubility characteristics of monomer combinations, improving the flexibility of the segmented polymerization. Second, the use of Isopar L or Isopar G as a solvent enables the polymer shell to grow in an environment similar to the actual electrophoretic medium, thereby optimizing the compatibility of the shell layer with the electrophoretic medium and improving the dispersion stability and electrophoretic mobility of the electrophoretic particles. For example, in the embodiment, ethanol is used as a solvent to ensure good solubility of the monomers and uniformity of the reaction. The selection of appropriate solvents is a key factor in ensuring uniform core-shell structure, concentrated particle size distribution (as shown in Figure 3 ), and improved electrophoretic performance.

[0067] In some embodiments, in step S2, the initiator is one of benzoyl peroxide, potassium persulfate, azobisisobutyronitrile, and dimethyl azobisisobutyrate.

[0068] Background and working principle: The present application defines the type of initiator used in the step S2 of the segmented polymerization. The selection of initiator is the key to the success of free radical polymerization, which determines the initiation temperature, rate and molecular weight of the polymer. In the prior art, the initiator needs to be selected according to the type of monomer and reaction conditions. The four initiators selected in the present application are common free radical polymerization initiators: benzoyl peroxide (BPO) and potassium persulfate (KPS) are peroxide initiators, and azobisisobutyronitrile (AIBN) and dimethyl azobisisobutyrate (AIBMe) are azo initiators. The thermal decomposition temperature of these initiators is moderate, suitable for the polymerization temperature range of 70-85℃, and can provide stable free radical source to ensure the controllable and efficient polymerization.

[0069] Technical solution and component function: In the above embodiments, the initiator used in step S2 is limited to one of benzoyl peroxide, potassium persulfate, azobisisobutyronitrile, and dimethyl azobisisobutyrate. Azobisisobutyronitrile (AIBN) is a commonly used oil-soluble initiator, suitable for polymerization in organic solvents, for example, in the embodiments. Potassium persulfate (KPS) is a water-soluble initiator, suitable for aqueous systems or emulsion polymerization. Benzoyl peroxide (BPO) and dimethyl azobisisobutyrate (AIBMe) are also commonly used thermal decomposition initiators. In the segmented polymerization, the role of the initiator is to provide free radicals to initiate the polymerization of the monomer on the surface of the modified electrophoretic particles. The amount of initiator (0.5-5% of the total mass of the monomer) and the decomposition temperature need to match the reaction temperature of 70-85℃ to ensure a moderate polymerization rate and avoid explosive polymerization leading to particle agglomeration or uneven shell. In each segmented polymerization of S2, an initiator needs to be added to ensure that the growth of each shell layer is effectively initiated and controlled.

[0070] Beneficial effects: The selection of specific initiators brings the following beneficial effects: First, these initiators have moderate decomposition rate and high initiation efficiency, ensuring the stability and controllability of the polymerization. Second, by precisely controlling the amount of initiator, the molecular weight and grafting density of the polymer can be adjusted, thereby optimizing the physical and chemical properties of the shell. For example, the use of azobisisobutyronitrile ensures uniform initiation in organic solvents, which is beneficial to the formation of a uniform polymer shell. Precise control of the initiator is the key to achieving segmented polymerization, which helps to obtain electrophoretic particles with controllable surface properties and high charge.

[0071] In some embodiments, in step S2, monomer 1, monomer 2, monomer 3, monomer 4, monomer 5 are any one of styrene, divinyl benzene, 1,3-butadiene, methyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, acrylic acid, acrylamide, oleic acid, oleylamine, isocyanate, N,N'-methylene bisacrylamide, fatty acid polyoxyethylene ester, diallyl dimethyl ammonium chloride.

[0072] Technical background and working principle: The present claim defines the specific types of monomer 1, monomer 2, monomer 3, monomer 4, monomer 5 used in the step S2 segmented polymerization reaction. The selection of monomers is the core of building a functional surface shell, which determines the chemical composition, hydrophobicity, crosslinking degree and charge density of the shell. In the prior art, the surface modification of electrophoretic particles requires the introduction of monomers that can improve dispersion stability, adjust charge amount and enhance compatibility with electrophoretic medium. The selected monomers in the present application include: styrene (styrene, divinyl benzene), acrylate (methyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl methacrylate, octadecyl methacrylate), functional monomers (acrylic acid, oleic acid, oleylamine, isocyanate, diallyl dimethyl ammonium chloride) and crosslinking agents (divinyl benzene, N,N'-methylene bisacrylamide). This diversity ensures precise regulation of shell structure and function through combination.

[0073] Technical solution and component function: In the above embodiments, monomer 1, monomer 2, monomer 3, monomer 4, monomer 5 are any one of styrene, divinyl benzene, 1,3-butadiene, methyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, acrylic acid, acrylamide, oleic acid, oleylamine, isocyanate, N,N'-methylene bisacrylamide, fatty acid polyoxyethylene ester, diallyl dimethyl ammonium chloride. These monomers play different roles in the segmented polymerization: Skeleton monomers: styrene, methyl acrylate, methyl methacrylate, etc., used to build the main structure of the shell, providing mechanical strength and stability.

[0074] Hydrophobic monomers: dodecyl methacrylate, octadecyl methacrylate, etc., used to increase the hydrophobicity of the shell and improve compatibility with non-polar electrophoretic medium.

[0075] Crosslinking agent: divinyl benzene, N,N'-methylene bisacrylamide, used to form a crosslinked network in the shell, enhancing the structural stability and solvent resistance of the shell.

[0076] Charge or functional monomers: Acrylic acid (introducing negative charge groups), oleic acid (introducing negative charge groups), oleylamine (introducing positive charge groups), diallyl dimethyl ammonium chloride (introducing positive charge groups) are used to precisely control the charge amount and polarity of electrophoretic particles. In segmented polymerization, by controlling the timing and ratio of different monomers, a gradient distribution of shell components can be achieved. For example, the first segment polymerization can mainly use hydrophobic monomers to enhance compatibility, and the second segment polymerization can introduce charge monomers to increase the charge amount.

[0077] Beneficial effects: The use of specific monomer combinations brings the following beneficial effects: First, by combining the use of hydrophobic monomers and polar monomers, the surface properties of the shell can be precisely controlled, making it have excellent compatibility with non-polar electrophoretic medium, significantly improving the dispersion stability of the particles. Second, the introduction of cross-linking agents (such as divinylbenzene) enhances the structural stability of the polymer shell, effectively preventing the swelling and shedding of the shell. Most importantly, by precisely controlling the amount and introduction position of charge monomers (such as acrylic acid, diallyl dimethyl ammonium chloride), the charge amount and charge polarity of electrophoretic particles can be controlled, and the Zeta potential can reach a high value, effectively enhancing the electric field response speed. The combination application of such multifunctional monomers is the key technology to realize low reflectivity, high charge amount, and high stability of black electrophoretic particles.

Claims

1. A method for preparing black electrophoretic particles with low reflectivity and high charge, characterized in that, include: S1. Grafting silane coupling agent onto the surface of electrophoretic particle raw material: Pre-dried black electrophoretic particle raw material, ethanol, water and zirconium beads are added to a ball mill flask and mixed evenly. The pH value is adjusted once with ammonia water and then ball milled. The ball milling liquid is then transferred to a four-necked flask and stirred. After adding silane coupling agent, the pH value is adjusted again with ammonia water. The mixture is heated to 80°C for reaction. After the reaction is complete, the particles are washed, centrifuged and dried to obtain modified electrophoretic particles grafted with silane coupling agent. S2. Segmented Construction of the Surface Shell of Electrophoretic Particles: Monomer 1, Monomer 2, solvent, and modified electrophoretic particles were added to a ball mill flask. After ball milling, the milling solution was transferred to a four-necked flask. Under nitrogen protection, the temperature was raised to 50°C, an initiator was added, and the reaction was repeated at 70–85°C. After cooling the reaction system to room temperature, Monomer 3, Monomer 4, Monomer 5, and solvent were added. The system was then heated to 50°C, and the initiator was added again. The reaction was then repeated at 70–85°C. After cooling to room temperature again, Monomer 2 or Monomer 3 was added, and the temperature was raised to 50°C. The initiator was added, and the reaction was repeated at 70–85°C. The precipitate was collected by centrifugation, washed, and dried to obtain the controllably constructed modified electrophoretic particles.

2. The method according to claim 1, characterized in that, In step S1, by mass fraction, the black electrophoretic display particles are 1 part, the ethanol solvent is 10-20 parts, the silane coupling agent is 0.1-0.5 parts, and the zirconium beads are 5-20 parts.

3. The method according to claim 1, characterized in that, In step S1, during the first adjustment process, the target pH value is 7-10; During the secondary adjustment process, the target pH value is 7-10; The ball milling duration is 5–12 hours, the reaction conditions are mechanical stirring at 200–400 rpm for 5–10 hours, and the drying conditions are drying at 60–100°C.

4. The method according to claim 1, characterized in that, In step S2, by mass fraction, the modified electrophoretic particles are 1 part, the solvent is 10-20 parts, monomer 1 is 0.1-1 part, monomer 2 is 0.1-1 part, monomer 3 is 0.1-1 part, monomer 4 is 0.01-0.1 part, monomer 5 is 0.1-1 part, and zirconium beads are 5-20 parts.

5. The method according to claim 1, characterized in that, In step S2, the ball milling lasts for 5 to 12 hours, the reaction conditions are mechanical stirring at 200 to 500 rpm, and the drying conditions are vacuum drying at 80 to 120°C for 5 to 12 hours. The initiator has a mass of 0.5% to 5% of the total mass of the monomers.

6. The method according to claim 1, characterized in that, In step S1, the raw material for the black electrophoretic particles is one or more combinations of iron manganese black, copper chromium black, and carbon black.

7. The method according to claim 1, characterized in that, In step S1, the silane coupling agent is one of γ-(methacryloyloxy)propyltrimethoxysilane, trimethoxy(7-octen-1-yl)silane, 10-undecenyltrichlorosilane, and [3-(triethoxysilyl)propyl]carbamate-2-propynyl ester.

8. The method according to claim 1, characterized in that, In step S2, the solvent is one of ethanol, isopropanol, toluene, cyclohexane, Isopar L, and Isopar G.

9. The method according to claim 1, characterized in that, In step S2, the initiator is one of benzoyl peroxide, potassium persulfate, azobisisobutyronitrile, and dimethyl azobisisobutyrate.

10. The method according to claim 1, characterized in that, In step S2, monomer 1, monomer 2, monomer 3, monomer 4, and monomer 5 are all any one of styrene, divinylbenzene, methyl 1,3-butadiene acrylate, methyl methacrylate, butyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, acrylic acid, acrylamide, oleic acid, oleylamine, isocyanate, N,N'-methylenebisacrylamide, fatty acid polyoxyethylene ester, and diallyl dimethylammonium chloride.

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