CN1490657A - Color electrophoretic display display method and display based on photonic crystal concept - Google Patents

Abstract

The present invention relates to a color electrophoretic display method and display based on the concept of photonic crystals, and belongs to the technical field of electrophoretic displays. It is characterized in that an external electric field is applied to microspheres encapsulated in microcapsules between two parallel electrode panels. Under the action of the external electric field, the microspheres move in a directional manner and are arranged in an orderly manner due to their own charge, thereby completely reflecting light with a wavelength matching therewith to obtain a color display. Since the present invention adjusts the arrangement state of the microspheres, that is, the ordered structural period of the photonic crystal, by changing the external electric field, that is, the voltage, different reflected light can be generated to achieve the purpose of color display. The color electrophoretic display provided by the present invention has the characteristics of low energy consumption, high reflection, wide viewing angle, etc., and is particularly suitable for making displays used under daylight conditions, and has important application value.

Description

Color electrophoretic display display method and display based on photonic crystal concept

technical field

The invention relates to a display method and a display for a color electrophoretic display based on the concept of photonic crystals, belonging to the technical field of electrophoretic displays.

Background technique

Since the electrophoretic display has performance advantages such as low energy consumption, high reflection, and wide viewing angle, extensive research has been done on this technology. However, in the initial research work, the electrophoretic display could not work stably due to particle agglomeration and migration, so it has not been commercially applied. In 1997, B.Comiskey et al. of E-INK Corporation of the United States proposed the method of constructing electrophoretic display (also known as electronic paper) with microcapsules. This method successfully solved the problem of particle agglomeration and migration, thus making electrophoretic display effective possibility of commercial application. Most of the currently researched microcapsule electrophoretic displays can only display two colors (usually black and white), so it is of great application value to study high-efficiency and low-cost color electrophoretic displays.

A generalized photonic crystal is an ordered structure arranged periodically. When the period of the ordered structure is comparable to the wavelength of the incident electromagnetic wave, the intensity of electromagnetic waves in certain frequency bands decays exponentially due to destructive interference, and cannot propagate in the medium, forming a photonic band-gap. Light in the frequency range of the bandgap is completely reflected. The wavelength of reflected light is related to the refractive index of the material, the periodicity of the ordered structure, and the filling rate. By changing external conditions, such as electric field strength, magnetic field strength, temperature, etc., the ordered structure period or the refractive index of the filling material can be changed, thereby changing the wavelength of reflected light. The invention changes the arrangement state of the microspheres in the microcapsules by changing the applied electric field (voltage), that is, the ordered structural period of the photonic crystal, thereby achieving the purpose of changing the wavelength of reflected light (obtaining color display).

Contents of the invention

The object of the present invention is to provide a color electrophoretic display method and display device based on the concept of photonic crystals capable of color electrophoretic display.

The color electrophoretic display method based on the photonic crystal concept proposed by the present invention is characterized in that the method is to apply an external electric field on the microspheres coated in the microcapsules between two parallel electrode panels, and the applied electric field Under the action, the microspheres move directionally and arrange in an orderly manner under the action of the electric field due to their self-charging, so that they completely reflect the light with a matching wavelength and obtain a color display.

In the display method of the above-mentioned color electrophoretic display, the size of the microcapsules is 20-100 μm, and the median size is 30-50 μm.

In the display method of the above-mentioned color electrophoretic display, the particle size of the microspheres coated in the microcapsules is 200-600 nm.

In the display method of the above-mentioned color electrophoretic display, the material of the microsphere is a polymer material, and its refractive index is 1.5-2.1.

In the display method of the above-mentioned color electrophoretic display, the material of the microspheres can also be a silicon dioxide material, and its refractive index is 1.48.

In the display method of the above-mentioned color electrophoretic display, the voltage of the applied electric field is 1-10V.

The color electrophoretic display based on the photonic crystal concept proposed by the present invention is characterized in that the electrophoretic display contains two parallel electrode panels and a layer of microcapsules sandwiched between the two parallel electrode panels, and the microcapsules contain There are microspheres with uniform particle size.

In the above color electrophoretic display, at least one of the two parallel electrode panels is a transparent patterned electrode panel.

The invention adjusts the arrangement state of the microspheres by changing the applied electric field (voltage), that is, the orderly structure period of the photonic crystal, so as to generate different reflected light and achieve the purpose of color display. The color electrophoretic display provided by the invention has the characteristics of low energy consumption, high reflection, wide viewing angle, etc., and is especially suitable for making a display used under sunlight conditions, so it has important application value.

Description of drawings

Fig. 1 is a schematic diagram of the distance between the microspheres of the present invention being 1.2 times the diameter of the microspheres (when the applied voltage is low).

Fig. 2 is a schematic diagram showing that the distance between the microspheres of the present invention is 1.1 times the diameter of the microspheres (when the applied voltage is higher).

FIG. 3 is a schematic structural diagram of a color electrophoretic display based on the concept of photonic crystals according to the present invention.

Detailed ways

The present invention is realized according to the following technical scheme:

The invention is a color electrophoretic display based on the concept of photonic crystals, the core part of which is a microcapsule wrapped with a large number of uniform submicron microspheres.

Electrophoretic display has the characteristics of low energy consumption, high reflection, wide viewing angle, etc., so it is especially suitable for display used under sunlight conditions, such as: mobile phones, electronic books, billboards, etc. Microcapsule electrophoretic displays generally consist of two parallel electrode panels (at least one of which is transparent) and a layer of microcapsules sandwiched between the two panels. Each microcapsule contains an insulating liquid and a charged pigment particle. When a certain voltage is applied between two electrodes, the pigment particle will migrate to one side, so that a graphic display can be obtained. The microcapsule (capsule diameter between 20-100 μm) based on the concept of photonic crystals involved in the present invention is also located between the two electrode panels. Unlike traditional microcapsule electrophoretic displays, it contains submicron particles with uniform particle sizes. Microspheres, under the action of an external electric field, due to their own charge, the microspheres move directionally and arrange in an orderly manner under the action of the electric field, so that they completely reflect the light with a matching wavelength and obtain a color display. The color obtained by reflection is related to the particle size, refractive index of the submicron spheres, the refractive index of the filling medium and the arrangement state of the microspheres. The specific calculation formulas involved are: (1) ${\mathrm{no}}_{\mathrm{eff}}=\sqrt{{{\mathrm{no}}_1}^{2}f+{{\mathrm{no}}_2}^2(1-f)}$ , where n ₁ , n ₂ are the relative refractive indices of the sphere and the solvent, f is the filling factor of the sphere, and n _eff is the effective refractive index; for the spheres arranged in face-centered cubic, (2) $d=\sqrt{\frac{2}{3}}\mathrm{D.}$ , where d is the distance between (111) planes, and D is the diameter of the ball; (3) $\mathrm{\λ}=2d\sqrt{{{\mathrm{no}}^2}_{\mathrm{eff}}-{\sin }^2\mathrm{\θ}}$ , where λ is the wavelength of the reflected light, and θ is the reflection angle of the light.

In the present invention, we are given a number of system microspheres, the particle size, refractive index and filling medium of the submicron microspheres are fixed, and the arrangement state of the microspheres is changed by changing the applied electric field (voltage), That is, the ordered structural period of the photonic crystal changes the wavelength of the reflected light. The microspheres used for orderly arrangement in microcapsules can be made of inorganic materials or organic materials, commonly used are: SiO ₂ microspheres, polystyrene microspheres and other polymer microspheres.

The production of microcapsules can use some existing mature methods, such as interfacial polymerization, in-situ polymerization, complex coacervation and so on. The capsule wall should be transparent, and suitable wall materials include urea-formaldehyde condensate, gum arabic, gel, etc. Taking the urea-formaldehyde microcapsules synthesized by in-situ polymerization as an example, the spheres need to be dispersed in a solvent first. The solvent used is a transparent liquid with good insulating properties. In addition, the solvent effect between the solvent and the pellets should be small. For example, organic pellets can be dispersed in water, while inorganic pellets can be dispersed in water or solvents such as hexane, octane, Dodecane, toluene, xylene, etc. Some dispersants and charging additives can be optionally added when dispersing the pellets. After the above dispersion step is completed, the solution containing the microspheres is emulsified and then dispersed in the water in which the urea-formaldehyde prepolymer is dissolved, and a catalyst is added to cause a polymerization reaction to form microcapsules coated with a large number of microspheres. In the process of emulsification, appropriate surfactants can be selectively added according to the type of emulsion, such as: sodium dodecylbenzene sulfonate, Siben 85, Siben 60, Tween 60, Tween 20, sodium petroleum sulfonate wait. The particle size of the microcapsules coated with submicron microspheres involved in the present invention is between 20-100 μm, and the median size is close to 30-50 μm.

A solution containing the microcapsules, which may also be immobilized in an adhesive between the two electrodes, is then injected between the two electrode panels, or "printed" or coated onto a transparent conductive film. The external voltage is applied to the surface electrodes through the leads to form a controllable electric field between the two electrode panels. Under the action of an external electric field, the microspheres move directionally and arrange in an orderly manner under the action of the electric field due to their self-charging, so that they completely reflect the light with a matching wavelength to obtain a color display.

Microcapsule electrophoretic displays generally consist of two parallel electrode panels (at least one of which is transparent) and a layer of microcapsules sandwiched between the two panels. Each microcapsule contains an insulating liquid and a charged pigment particle. When a certain voltage is applied between two electrodes, the pigment particle will migrate to one side, so that a graphic display can be obtained. Affair (1) ${\mathrm{no}}_{\mathrm{eff}}=\sqrt{{{\mathrm{no}}_1}^{2}f+{{\mathrm{no}}_2}^2(1-f)}$ , where n ₁ , n ₂ are the relative refractive indices of the sphere and the solvent, f is the filling factor of the sphere, and n _eff is the effective refractive index; for the spheres arranged in face-centered cubic, (2) $d=\sqrt{\frac{2}{3}}\mathrm{D.}$ , where d is the distance between (111) planes, and D is the diameter of the ball; (3) $\mathrm{\λ}=2d\sqrt{{{\mathrm{no}}^2}_{\mathrm{eff}}-{\sin }^2\mathrm{\θ}}$ , where λ is the wavelength of the reflected light, and θ is the reflection angle of the light.

In the present invention, given a number of system microspheres, the particle size, refractive index, and filling medium of the submicron microspheres are all constant, and the arrangement state of the microspheres is changed by changing the applied electric field (voltage), Thereby changing the wavelength of the reflected light. The spheres used for orderly arrangement in microcapsules can be made of either inorganic materials or organic materials. The commonly used ones are: SiO ₂ microspheres, polystyrene microspheres and other polymer microspheres.

The production of microcapsules can use some existing mature methods, such as interfacial polymerization, in-situ polymerization, complex coacervation and so on. The capsule wall should be transparent, and suitable wall materials include urea-formaldehyde condensate, gum arabic, gel, etc. Taking the urea-formaldehyde microcapsules synthesized by in-situ polymerization as an example, the microspheres need to be dispersed in a solvent first. The solvent used is a transparent liquid with good insulating properties. In addition, the solvent effect between the solvent and the microspheres should be small. For example, organic microspheres can be dispersed in water, while inorganic microspheres can be dispersed in water or solvents such as hexane, octane, Dodecane, toluene, xylene, etc. Some dispersants and charging additives can be optionally added when dispersing the pellets. After the above dispersion step is completed, the solution containing the microspheres is emulsified and then dispersed in the water in which the urea-formaldehyde prepolymer is dissolved, and a catalyst is added to cause a polymerization reaction to form microcapsules coated with a large number of microspheres. In the process of emulsification, appropriate surfactants can be selectively added according to the type of emulsion, such as: sodium dodecylbenzene sulfonate, Siben 85, Siben 60, Tween 60, Tween 20, sodium petroleum sulfonate wait. The particle size of the microcapsules coated with submicron microspheres involved in the present invention is between 20-100m, and the median size is close to 30-50m.

A solution containing the microcapsules, which may also be immobilized in an adhesive between the two electrodes, is then injected between the two electrode panels, or "printed" or coated onto a transparent conductive film. The external voltage is applied to the surface electrodes through the leads to form a controllable electric field between the two electrode panels. (The red letter above seems to be unnecessary?) Under the action of an external electric field, the specific implementation method for obtaining a color display is: the microspheres move directionally and arrange in an orderly manner under the action of a given electric field due to their own charge. When the value is low, the arrangement of microspheres in the capsule is relatively loose, and the distance between the centers of adjacent microspheres is relatively large, so that the longer light with a matching wavelength is completely reflected. At this time, it appears as a reflection of long-wavelength light, such as red light. When the electric field intensity is further increased, the distance between the centers of the microspheres in the capsule decreases (as shown in Figures 1 and 2), so that the light with a matching wavelength is completely reflected to obtain a color display. In a specific case, the applied voltage required to obtain reflected light of the same wavelength in the same direction is related to the size of the microcapsules. Generally, the larger the particle size of the capsule, the greater the applied voltage.

The following examples further illustrate the present invention:

Example 1

Firstly, microcapsules whose walls are urea-formaldehyde polymers were synthesized by in-situ polymerization, and microcapsules with a median size of 20-60 μm were screened out. These microcapsules contained a large number of particles with a particle size of 370 μm. ±10nm polystyrene microspheres and water. Then these microcapsules with a particle size of 20-60 μm are coated between two electrode panels. One of the two electrodes is glass containing a patterned transparent indium tin oxide (ITO) conductive film, and the distance between the two electrode panels is microspheres. 1.5-2 times the diameter. The lead wire is used to apply voltage between the two electrode panels, and the microspheres are arranged in different ways by applying different voltages to different pixel units, thereby obtaining different reflected light. For example, in this embodiment, when the voltage applied to the pixel unit is 2V, the reflected light obtained in the direction perpendicular to the electrode panel is red; and when the applied voltage is 5V, the reflected light obtained in the direction perpendicular to the electrode panel is red. Reflected light is blue. In this way, a continuously changing light ranging from red to blue can be obtained by applying a voltage in the range of 2-5V.

Claims (8)

1, based on the color electrophoretic display display packing of photonic crystal notion, it is characterized in that, described method is to apply extra electric field being positioned on the microballoon that is coated on microcapsules between two parallel electrode panels, under the effect of extra electric field, microballoon is because self is charged, directed movement and arranging in order under electric field action, thus the light that wavelength matches is reflected fully and obtains colored the demonstration.

2, color electrophoretic display display packing according to claim 1 is characterized in that, described microcapsules are of a size of 20～100 μ m, and its intermediate value is of a size of 30～50 μ m.

3, color electrophoretic display display packing according to claim 1 is characterized in that, its particle diameter of microballoon that is coated in the microcapsules is 200～600nm.

4, color electrophoretic display display packing according to claim 1 is characterized in that, the material of described microballoon is a macromolecular material, and its refractive index is 1.5～2.1.

5, color electrophoretic display display packing according to claim 1 is characterized in that, the material of described microballoon also can be earth silicon material, and its refractive index is 1.48.

6, color electrophoretic display display packing according to claim 1 is characterized in that, described extra electric field voltage is 1～10V.

7, the color electrophoretic display based on the photonic crystal notion according to claim 1, it is characterized in that, described electrophoretic display device (EPD) contains two parallel electrode panels and a microcapsule that is clipped between described two parallel electrode panels, is surrounded by the uniform microballoon of particle diameter in its microcapsules.

8, color electrophoretic display according to claim 7 is characterized in that, has at least one to be transparent patterned electrodes panel in described two parallel electrode panels.