An electronic ink and electrophoretic display device that combines fast response and bistable operation

Abstract

This application belongs to the field of electrophoretic display technology, and particularly relates to an electronic ink and electrophoretic display device that combine fast response and bistable properties. The electronic ink is characterized by comprising: electrophoretic particles, an electrophoretic medium, a charge control agent, and a self-healing material. The self-healing material includes one or more of epoxy resin, ultrafine kaolin, polyamide, hydrogel polymer, asphalt, and hydrophobic nano-SiO2. The self-healing system material of this application can achieve viscosity regulation of the electronic ink through thixotropy, thereby ensuring that the electrophoretic display device maintains good bistableness when driving is stopped, and maintains fast response during driving. This allows for switching between two operating modes under different usage scenarios, achieving a driving effect that combines fast response and bistable properties.

Description

Technical Field

[0001] This application belongs to the field of electrophoretic display technology, and in particular relates to an electronic ink and electrophoretic display device that combines fast response and bistable state. Background Technology

[0002] Electronic ink is the optical element of electrophoretic display devices, containing billions of microcapsules containing negatively charged black particles and positively charged white particles suspended in a clear liquid. The bound particles are affected by electrical pulses. When a positive / negative pulse occurs, the matched particles move to the top of the display, allowing the user to see specific patterns and text.

[0003] Traditional electronic inks typically use thickeners to increase the system viscosity and maintain bistableness, as seen in patents CN201880010867 and CN201980048552. These patents use polyisobutylene or other materials as thickeners to increase the viscosity of the electronic ink, ensuring that the electrophoretic particles remain in their original positions without movement when no external voltage is applied, thus achieving image stability. This stable image state without power is called bistableness. However, these materials keep the viscosity of the electronic ink consistently high. Under an applied electric field, high viscosity generates high viscous resistance, hindering the movement of electrophoretic particles and slowing their response speed, which is detrimental to display performance.

[0004] It is evident that existing electrophoretic displays require thickeners to achieve bistable properties in their electronic inks. However, the presence of thickeners reduces the response speed of electrophoretic display devices, making it difficult to achieve both bistable properties and fast response. Summary of the Invention

[0005] In view of this, this application provides an electronic ink and electrophoretic display device that combines fast response and bistableness. The electronic ink can achieve viscosity control through thixotropy, thereby ensuring that the electrophoretic display device maintains good bistableness when driving is stopped and maintains fast response during driving.

[0006] The first aspect of this application provides an electronic ink that combines fast response and bistableness, comprising: electrophoretic particles, electrophoretic medium, charge control agent and self-healing material;

[0007] The self-healing material comprises one or more of epoxy resin, ultrafine kaolin, polyamide, hydrogel polymer, asphalt, and hydrophobic nano-SiO2. When subjected to electric field shear stress, the electrophoretic particles and other microparticles in the self-healing material can slide on the water layer connecting them, causing a decrease in the macroscopic viscosity coefficient of the electrophoretic liquid system and an increase in particle migration rate. When the electric field shear stress disappears, this cross-linked structure formed by hydrogen bonding, van der Waals forces, and covalent bonds recovers in the Brownian motion of the particles. Macroscopically, the electronic ink recovers its high viscosity coefficient and achieves bistable characteristics even without an external electric field. By changing the driving voltage, the self-healing material spontaneously changes within the electronic ink system, achieving reversible viscosity adjustment.

[0008] This application uses a self-healing material to replace the traditional thickener. When the electronic ink of this application is driven by an electric field, its viscosity coefficient decreases significantly when subjected to electric field shear force, and the electrophoretic particles can migrate rapidly in the electrophoretic medium. When the driving is stopped and the static image is maintained, the thixotropic property of the self-healing material causes its viscosity coefficient to recover when it is at rest and not under force. The viscosity of the electronic ink increases significantly, making it difficult for the electrophoretic particles to migrate in the electrophoretic medium. Thus, the bistable characteristics of the electrophoretic display device are greatly improved without affecting the migration rate of ink particles during control.

[0009] In another embodiment, the electronic ink comprises, by weight percentage:

[0010] Electrophoretic particles: 25%–40%;

[0011] Electrophoresis medium content: 58.7%–74.6%;

[0012] Charge control agent 0.2%–1%;

[0013] Self-healing material 0.2%–0.3%.

[0014] In another embodiment, the epoxy resin is selected from one or more of bisphenol A type epoxy resin, bisphenol S type epoxy resin, and bisphenol F type epoxy resin.

[0015] Specifically, the epoxy resin is selected from bisphenol A type epoxy resin.

[0016] Specifically, the preparation method of the electronic ink includes: mixing electrophoretic particles, electrophoretic medium, charge control agent and self-healing material to obtain electronic ink; preferably, the above components are mixed by stirring in a stirrer at 3000 rpm for 1 minute.

[0017] It should be noted that the electrophoretic particles, the electrophoretic medium, and the charge control agent are conventional electrophoretic particles, electrophoretic medium, and charge control agents.

[0018] In another embodiment, the electrophoretic particles include one or more of black particles, white particles, and colored electrophoretic particles. The electrophoretic particles are dispersed in the electrophoretic medium and are capable of carrying charge and moving under the influence of an electric field.

[0019] In another embodiment, the black particles include carbon black and / or iron oxide black; the white particles include titanium dioxide and silicon nanoparticles; and the colored electrophoretic particles include one or more of diaryl yellow, toluidine red, phthalocyanine blue, and phthalocyanine green.

[0020] In another embodiment, the electrophoresis medium is a nonpolar solvent.

[0021] In another embodiment, the nonpolar solvent is selected from one or more of n-dodecane, isoalkanes Isopar G and Isopar L.

[0022] In another embodiment, the charge control agent is selected from one or more of organic sulfonates, organic sulfates, organic phosphates, organic phosphate esters, polyester compounds, polyolefin compounds, polyacrylate compounds, and polyether compounds. The charge control agent can form reverse micelles that attach to electrophoretic particles or disperse in the electrophoretic medium, thereby increasing the charge carried by the electrophoretic particles.

[0023] A second aspect of this application provides an electrophoretic display solution, comprising the aforementioned electronic ink and microcavities; the electronic ink is segmented and encapsulated within individual microcavities. The microcavities prevent electrophoretic particles from moving laterally over a large area, reducing the probability of aggregation and improving the lifespan of the electronic ink.

[0024] In another embodiment, the microcavity is selected from microcapsules and / or microcup cavities.

[0025] A third aspect of this application provides an electrophoretic display device, comprising the aforementioned electrophoretic display solution. The electrophoretic display device of this application, when matched with a driving method suitable for the aforementioned electrophoretic display solution, is capable of rapidly driving different gray levels and maintaining a static image for an extended period when driving stops.

[0026] The fourth aspect of this application provides an electronic ink driving method that adds a preset weak oscillation signal before the driving waveform. The weak oscillation signal added in this application uses the mentioned threshold voltage to drive charged reverse micelles formed by the charge control agent without driving ink particles, preventing the formation of a built-in electric field between the charged reverse micelles and ink particles, thereby improving the response speed of the electronic ink. The designed weak oscillation signal does not affect the response of the ink particles; by adding the designed weak oscillation signal, the response time of both black and white particles is significantly reduced compared to traditional driving methods.

[0027] Specifically, the preset weak oscillation signal has a duration of 0.14s, a voltage amplitude of 5V, and a signal frequency of 50Hz.

[0028] Compared with existing technologies, this application discovers that self-healing materials can replace thickeners in traditional electronic inks, preventing electrophoretic particles from moving randomly due to thermal motion or electrostatic effects in the absence of an external electric field, thereby maintaining the stability of the image in the electrophoretic display device. Under shear force, the viscosity coefficient of the self-healing material decreases over time, reducing the obstruction of particle movement caused by excessive viscosity of the electronic ink due to thickeners when voltage is applied, thus achieving a rapid response to the desired grayscale. By controlling whether it is driven or not, reversible switching between bistable and fast response operating modes is achieved, replacing the mutually exclusive and difficult-to-coexist effects of these two modes in traditional electronic inks. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0030] Figure 1 This is a schematic diagram of the structure of an electrophoretic display device that combines fast response and bistable state, provided in an embodiment of this application. In the diagram, the white and black particles are ink particles, and the blue curve represents self-healing material.

[0031] Figure 2 The relationship between the shear rate and viscosity coefficient of the electronic ink provided in Embodiment 1 of this application;

[0032] Figure 3 The light response intensity curves of the electrophoretic display device prepared with electronic ink provided in the embodiments of this application under the addition of different thickeners and self-healing materials;

[0033] Figure 4 The photoresponse intensity of carbon black particles in different electronic inks provided for embodiments and comparative examples of this application with the addition of thickeners / self-healing materials;

[0034] Figure 5 The photoresponse intensity of titanium dioxide particles in different electronic inks provided in the embodiments and comparative examples of this application with the addition of thickeners / self-healing materials;

[0035] Figure 6 A comparison of the waveforms of carbon black particles in the electronic ink provided in this application embodiment with the addition of a preset weak oscillation signal and a conventional driving signal;

[0036] Figure 7 A comparison of the waveforms of titanium dioxide particles in the electronic ink provided in this application embodiment with the addition of a preset weak oscillation signal and a conventional driving signal. Detailed Implementation

[0037] This application provides an electronic ink and electrophoretic display device that combines fast response and bistableness, thereby addressing the technical deficiency of existing electronic inks in achieving both bistableness and fast response.

[0038] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0039] In the following examples, all raw materials or reagents used are commercially available or self-made.

[0040] The epoxy resin used in this application was purchased from RON Reagents on the Ruijing platform; the ultrafine kaolin and polyamide used in the following comparative examples were both purchased from Maclean Reagents on the Ruijing platform.

[0041] This application provides an electronic ink that combines fast response and bistableness. It is an electrophoretic display liquid whose viscosity can be adjusted according to the electric field driving force using thixotropy. The ink is composed of electrophoretic particles, electrophoretic medium, charge control agent and self-healing material. The self-healing material can replace the thickener in traditional electronic inks. It can be epoxy resin or asphalt, or some hydrogels or nanopolymers. It achieves the effect of viscosity decreasing over time after application of flow and recovering high viscosity when at rest. It can maintain a static image for a long time when not driven and achieve a fast response when driven.

[0042] like Figure 1 As shown in the left figure, when at rest and without shear stress, the self-healing material forms a cross-linked structure through intermolecular forces and hydrogen bonds with water molecules, maintaining the high viscosity of the entire electronic ink system and fixing the electrophoretic particles in their positions, making them difficult to move. Figure 1 As shown in the middle figure, when an external electric field is applied, the cross-linked structure of the self-healing material is broken due to its thixotropic properties under shear stress from the electric field; as... Figure 1 As shown in the right figure, the viscosity coefficient of the electronic ink system decreases over time, allowing electrophoretic particles to be rapidly driven to the corresponding grayscale. After the driving process ends, the cross-linked structure recovers during the Brownian motion of the self-healing material particles, keeping the ink particles stationary at their positions, achieving good bistable characteristics and enabling low-power, long-term display.

[0043] Specifically, the electronic ink in this embodiment includes 40% by mass of electrophoretic particles, 1% by mass of charge control agent, 0.3% by mass of self-healing material, and 58.7% by mass of electrophoretic medium.

[0044] Specifically, the electronic ink in this embodiment includes 25% by mass of electrophoretic particles, 0.2% by mass of charge control agent, 0.2% by mass of self-healing material, and 74.6% by mass of electrophoretic medium.

[0045] Specifically, the epoxy resin used in the following examples and comparative examples is bisphenol A type epoxy resin WSR618.

[0046] Example 1

[0047] This application provides an electronic ink that combines fast response and bistable state, and the specific method includes:

[0048] 1. Mix 10% carbon black particles, 30% titanium dioxide particles, 1% sodium diisooctyl succinate sulfonate (AOT), 0.3% epoxy resin, and 58.7% Isopar L in a stirrer at 3000 rpm for 1 minute to obtain electronic ink.

[0049] 2. The relationship between the shear rate and viscosity coefficient of the above-mentioned electronic ink was determined, and the results are as follows: Figure 2 As shown. Figure 2 It can be seen that in epoxy resin-doped electronic inks, when the shear rate is very small, i.e., when carbon black particles and titanium dioxide particles are driven to the corresponding gray level and remain stationary, the viscosity coefficient of the electronic ink system is very large. This indicates that epoxy resin can replace the thickener in traditional electronic inks to improve the bistable characteristics of electronic inks. At the same time, in epoxy resin-doped electronic inks, as the shear rate increases, the viscosity coefficient of the system decreases significantly, indicating that the thixotropic properties of epoxy resin greatly improve the migration rate of electrophoretic particles and increase the device response speed.

[0050] Example 2

[0051] This application provides an electrophoretic display device that combines fast response and bistable operation. The specific method includes:

[0052] 1. Following conventional methods, the electronic ink prepared above was divided and encapsulated in independent microcavities to fabricate an electrophoretic display device. Its photoresponse intensity was tested, and the results are as follows: Figure 3 The 0.3% SiO2 curve is shown.

[0053] Figure 3 The results show that the electrophoretic display device of this application can be used as an adjustable viscosity electronic paper in the display of consumer electronics products. The electrophoretic display device described in this embodiment can switch between bistable and fast response modes to realize the display of animated images, and can maintain static image display for a long time without the application of driving voltage, thus achieving low power consumption and high refresh rate electrophoretic display.

[0054] 2. This application employs a driving method suitable for the electronic ink prepared above, specifically including:

[0055] A weak oscillation signal with a voltage amplitude of 5V and a frequency of 50Hz was added before the driving waveform for 0.14 seconds. This weak oscillation signal, using the mentioned threshold voltage, drives the charged reverse micelles formed by the charge control agent without driving the ink particles, preventing the formation of a built-in electric field between the charged reverse micelles and the ink particles, thus improving the response speed of the electronic ink. The results are as follows: Figure 6 and Figure 7 As shown.

[0056] The results show that the weak oscillation signal does not affect the response of the ink particles. By adding the designed weak oscillation signal, the response time of both carbon black particles and titanium dioxide particles is significantly reduced compared to the traditional driving method. This indicates that the electronic ink driving method of this embodiment can improve the response speed without affecting grayscale driving. Therefore, this electronic ink driving method is suitable for self-healing doped electronic inks and can effectively improve the response speed of electronic inks.

[0057] Comparative Example 1

[0058] This application provides a comparative example of an electrophoretic display device without the addition of a thickener, the specific method of which includes:

[0059] 1. Following the preparation method of electronic ink in Example 1, an electronic ink without thickener and epoxy resin was prepared by mixing 10% carbon black particles, 30% titanium dioxide particles, 1% sodium diisooctyl succinate sulfonate (AOT) and 59% Isopar L in a stirrer at 3000 rpm for 1 minute to obtain the electronic ink.

[0060] 2. The electronic ink prepared above is divided and packaged into independent microcavities according to conventional methods to obtain an electrophoretic display device.

[0061] 3. The photoresponse intensity of the electrophoretic display device in this comparative example was tested at 15V. The results are as follows: Figure 3 The curve without thickener is shown in red.

[0062] 4. The photoresponse intensity of the carbon black particles in the electronic ink of this comparative example was tested at 15V. The results are as follows: Figure 4 The curve without thickener is shown in red.

[0063] 5. The photoresponse intensity of the titanium dioxide particles in the electronic ink of this comparative example was tested at 15V. The results are as follows: Figure 5 The curve without thickener is shown in red.

[0064] The results show that when the electrophoretic particles are driven to the corresponding gray level and the external voltage driving is stopped, the black and white particles in the electronic ink without thickener will migrate significantly due to the small viscosity coefficient, resulting in a deterioration of the device's bistable characteristics.

[0065] Comparative Example 2

[0066] This application provides a conventional electrophoretic display device as a comparative example, the specific method of which includes:

[0067] 1. Following the preparation method of electronic ink in Example 1, an electronic ink with added polyisobutylene as a conventional thickener was prepared. Carbon black particles (10% by mass), titanium dioxide particles (30% by mass), sodium diisooctyl succinate sulfonate (AOT) (1% by mass), polyisobutylene (0.6% by mass), and Isopar L (58.4% by mass) were mixed in a stirrer at 3000 rpm for 1 minute to obtain the electronic ink.

[0068] 2. The electronic ink prepared above is divided and packaged into independent microcavities according to conventional methods to obtain an electrophoretic display device.

[0069] 4. The photoresponse intensity of the carbon black particles in the electronic ink of this comparative example was tested at 15V. The results are as follows: Figure 4 The curve showing the addition of thickener is shown in blue.

[0070] 5. The photoresponse intensity of the titanium dioxide particles in the electronic ink of this comparative example was tested at 15V. The results are as follows: Figure 5 The curve showing the addition of thickener is shown in blue.

[0071] like Figure 4 and Figure 5 The results show that in electronic inks with added conventional thickeners, the response times of black and white particles are significantly increased compared to inks without thickeners. The thickeners significantly increase the viscosity coefficient of the electronic ink, severely impacting its response speed while improving its bistable properties. In contrast, in the self-healing electronic ink doped with thickeners, the response times of both black and white particles are considerably reduced compared to traditional electronic inks containing thickeners. This indicates that 0.3% epoxy resin, due to its thixotropic properties, significantly reduces the viscosity coefficient of the electronic ink during the driving process, ensuring a high response speed. Furthermore, by analyzing the photoresponse of the 0.3% epoxy resin-doped electronic ink under different voltage amplitudes, the driving threshold voltage of the electronic ink can be determined. When the driving voltage is below this threshold voltage, the ink particles will not be driven.

[0072] Example 3

[0073] This application provides an electrophoretic display device with added ultrafine kaolin, the specific method of which includes:

[0074] 1. Following the preparation method of electronic ink in Example 1, an electronic ink with added ultrafine kaolin was prepared by mixing 10% carbon black particles, 30% titanium dioxide particles, 1% sodium diisooctyl succinate sulfonate (AOT), 0.3% ultrafine kaolin, and 58.7% Isopar L in a stirrer at 3000 rpm for 1 minute to obtain the electronic ink.

[0075] 2. The electronic ink prepared above is divided and packaged into independent microcavities according to conventional methods to obtain an electrophoretic display device.

[0076] The photoresponse intensity of the electrophoretic display device in this comparative example was tested at 15V, and the results are as follows: Figure 3 The curve for 0.3% ultrafine kaolin is shown.

[0077] It is evident that, compared to thickeners, ultrafine kaolin can effectively reduce the system viscosity coefficient and improve the particle response speed during particle-driven processes.

[0078] Example 4

[0079] This application provides an electrophoretic display device with added polyamide, the specific method of which includes:

[0080] 1. Following the preparation method of electronic ink in Example 1, an electronic ink with added polyamide was prepared by mixing 10% carbon black particles, 30% titanium dioxide particles, 1% sodium diisooctyl succinate sulfonate (AOT), 0.3% polyamide, and 58.7% IsoparL in a stirrer at 3000 rpm for 1 minute to obtain the electronic ink.

[0081] 2. The electronic ink prepared above is divided and packaged into independent microcavities according to conventional methods to obtain an electrophoretic display device.

[0082] The photoresponse intensity of the electrophoretic display device in this comparative example was tested at 15V, and the results are as follows: Figure 3 The curve for 0.3% polyamide is shown.

[0083] It is evident that, compared to thickeners, polyamides can effectively reduce the system viscosity coefficient and improve the particle response speed during particle-driven processes.

[0084] In summary, this application utilizes a self-healing material system to regulate the viscosity of electronic ink. By altering the viscosity coefficient of the thixotropic self-healing material under different shear stresses, the electrophoretic display device achieves a bistable effect while maintaining a static image and maintains a fast response when driving different gray levels. This satisfies the requirement that the electrophoretic display device simultaneously possesses bistable properties and a high response speed.

[0085] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. An electrophoretic display device, characterized by The display device comprises an electrophoretic display liquid; the electrophoretic display liquid comprises electronic ink and microcavities, and the electronic ink is separately encapsulated in the independent microcavities; The electronic ink comprises electrophoretic particles, an electrophoretic medium, a charge control agent and a self-repairing material; the self-repairing material comprises one or more of epoxy resin, ultra-fine kaolin, polyamide, hydrogel polymer, asphalt and hydrophobic nano-SiO2; The electronic ink is driven by applying a driving waveform to the electronic ink, and a preset oscillation signal is added before the driving waveform; the oscillation signal is used to drive the charged reverse micelles formed by the charge control agent, and the voltage of the oscillation signal is lower than the driving threshold voltage of the electrophoretic particles.

2. An electrophoretic display device according to claim 1, characterised in that, The electronic ink comprises, in terms of mass percentage: electrophoretic particles 25%-40%; electrophoretic medium 58.7%-74.6%; charge control agent 0.2%-1%; self-repairing material 0.2%-0.3%.

3. An electrophoretic display device as claimed in claim 1, characterized in that The epoxy resin is selected from one or more of bisphenol A type epoxy resin, bisphenol S type epoxy resin and bisphenol F type epoxy resin.

4. An electrophoretic display device as claimed in claim 1, characterized in that The electrophoretic particles comprise one or more of black particles, white particles and color electrophoretic particles.

5. An electrophoretic display device as claimed in claim 4, characterized in that The black particles comprise carbon black or / and iron oxide black; the white particles comprise titanium dioxide nanoparticles or silicon dioxide nanoparticles; and the color electrophoretic particles comprise one or more of diaryl yellow, toluidine red, phthalocyanine blue and phthalocyanine green.

6. An electrophoretic display device as claimed in claim 1, characterized in that The electrophoretic medium is a non-polar solvent; and the charge control agent is selected from one or more of organic sulfonate, organic sulfate, organic phosphate, organic phosphoric ester, polyester compound, polyolefin compound, polyacrylate compound and polyether compound.

7. An electrophoretic display device as claimed in claim 6, characterized in that The non-polar solvent is selected from one or more of n-dodecane, isoparaffin Isopar G and isoparaffin Isopar L.

8. An electrophoretic display device as claimed in claim 1, characterized in that The microcavities are selected from microcapsules or / and microcup cavities.

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