Color fluorescent particles for electrophoretic display and methods of making the same

Abstract

The application discloses a kind of color fluorescent particles for electrophoretic display, it is related to the field of photoelectric display, color fluorescent particle is core-shell structure, color fluorescent particle includes successively from inside to outside: core, intermediate layer and shell layer;Core is pigment unit, intermediate layer is quantum dot layer coated on the surface of pigment particle, shell layer includes high molecular polymer selected from one or more of polymethyl methacrylate lauryl, polymethyl methacrylate, and is constituted, shell layer is coated on the surface of intermediate layer;Color fluorescent particle contains intrinsic base color presented by pigment unit and compensation fluorescence excited by quantum dot layer receiving light;Compensation fluorescence is compatible with the color of intrinsic base color.In addition, the application also provides the preparation process of color fluorescent particle.The color fluorescent electrophoretic particle provided by the application is pure and full of color, and the color is more brilliant under ultraviolet excitation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photoelectric display, in particular to a kind of color fluorescent particles for electrophoretic display and preparation method thereof. BACKGROUND

[0002] Electrophoretic display is a new type of display technology, compared with traditional liquid crystal display, light emitting diode display etc., electrophoretic display has wide viewing angle, bistable, low energy consumption, flexible display and other advantages.Electrophoretic display is driven by external electric field to realize the display of letter, image, video by moving electrophoretic particles.Electrophoretic display technology is widely used in many fields, such as advertising board in shopping mall, bus stop, luggage label, vacuum cup temperature screen, etc., which is deeply loved by consumers.Currently, the commercial electrophoretic display products are mainly black and white display, which has been difficult to meet the huge market prospect.In order to expand the application field of electrophoretic display and improve the use experience of consumers, color electrophoretic particles have become a research hotspot.

[0003] In recent years, color electrophoretic display usually adopts filter scheme or color double particle scheme.Filter scheme covers a layer of filter on traditional black and white electrophoretic display to realize colorization;while color double particle scheme uses two kinds of color electrophoretic particles to realize color display, and controls the electric field intensity of each pixel point to realize color display.However, using filter will reduce the saturation and brightness of electrophoretic display, and double particle electrophoretic display needs complex technology to accurately control color conversion and charge value, which is not convenient to operate and has complex process, thereby leading to reduced brightness. SUMMARY

[0004] In view of the shortcomings of the prior art, the primary object of the present application is to make up for the deficiencies of the prior art, and provide a kind of color fluorescent particles for electrophoretic display, which breaks the shortcomings of using filter or double color particle scheme to cause insufficient display brightness, and provides a kind of quantum dot coated pigment particle color fluorescent electrophoretic particle on the basis of original pigment particle total internal reflection display, which improves the display brightness.The present application also provides a preparation method of color fluorescent electrophoretic particle for electrophoretic display, which has simple preparation process, can improve the content of active group-OH on the surface of nanocomposite particles, effectively improve the zeta potential, and accelerate the response speed of composite particles.

[0005] To achieve the above object, in a first aspect of the present application, a color fluorescent particle for electrophoretic display is provided, which is of core-shell structure and comprises, from inside to outside, a core, an intermediate layer and a shell layer; the core is a pigment unit, the intermediate layer is a quantum dot layer coated on the surface of the pigment particle, and the shell layer comprises a high polymer and is coated on the surface of the intermediate layer; the color fluorescent particle comprises an intrinsic base color presented by the pigment unit and a compensatory fluorescence excited by the quantum dot layer under light; the compensatory fluorescence is adapted to the color of the intrinsic base color.

[0006] In a second aspect of the present application, a preparation method of the color fluorescent particle is provided, which comprises the following steps:

[0007] In step S1, a color paste is prepared by dispersing pigment particles in a first dispersion solvent to have a pigment particle content of 5-20 wt%;

[0008] In step S2, quantum dots are coated on the surface of the pigment particles in step S1 by chemical precipitation or sol-gel method to prepare first composite pigment particles coated with the quantum dots on the surface;

[0009] In step S3, a high polymer is coupled, the first composite pigment particles obtained in step S2 are dispersed in water or an aqueous solution of ethanol to form a first mixture, the content of the first composite pigment particles in the first mixture is 10-60 wt%, the pH value of the mixture is adjusted to 6-8, 1-15 wt% of a silane coupling agent is added to the first mixture, and the mixture is reacted at 30-60°C for 1-20 h, followed by centrifugation and washing to obtain second composite pigment particles grafted with the silane coupling agent;

[0010] In step S4, the second composite pigment particles obtained in step S3 are dispersed in an organic solvent to have a content of 10-60 wt%, and then an initiator is added in an amount of 0.01-0.06 wt% after the temperature is raised to 50-60°C, and the mixture is continuously reacted for 10-20 h to obtain the electrophoretic display particles.

[0011] In a specific embodiment, when the first dispersion solvent is water, the quantum dots are coated by the chemical precipitation method in step S2; the chemical precipitation method comprises the following steps: 0.1-5 mol / L of a quantum dot solution is simultaneously added dropwise to the color paste in step S1 at 20-50°C, the dropping speed is controlled to keep the pH value of the reaction system constant at 5-7, and the dropwise addition is continued for 30-120 min; then the mixture is aged for 120-300 min, cooled to room temperature, and centrifuged and washed to obtain the first composite pigment particles coated with the quantum dots on the surface.

[0012] In one specific embodiment, when the first dispersing solvent is one or a combination of several of organic alcohols, organic benzenes, and water, step S2 employs the sol-gel method to coat the quantum dots. The sol-gel method includes: adding 0.1–5 mol / L quantum dot solution to the pigment paste from step S1, wherein the volume ratio of the added quantum dots to the first dispersing solution is 1:100–20:100, stirring until homogeneous, adding dropwise a mixed solution of water and isopropanol in a volume ratio of 1–5:5–10, adjusting the pH of the reaction system to 6–7, and sonicating for 5–30 min, then heating to 40–60°C, stirring and aging, and cooling the reaction system to room temperature; centrifuging and washing to obtain the first composite pigment particles coated with quantum dots.

[0013] In one specific embodiment, the pigment particles are one or a combination of two or more of the following: carbon black, copper chromium black, copper iron manganese black, iron black, titanium dioxide, zinc white, barium sulfate, iron oxide red, iron oxide yellow, ultramarine, chrome yellow, cadmium red, manganese violet, chrome green, iron blue, and cobalt blue.

[0014] In one specific embodiment, the average particle size of the electrophoretic display particles is 300 nm to 600 nm, the content of quantum dots coated on the surface of the pigment particles is 1 wt% to 5 wt%, and the content of the polymer coated on the surface of the display particles is 5 wt% to 10 wt%.

[0015] In one specific embodiment, the shell layer is one or a combination of two or more of γ-mercaptopropyltrimethoxysilane (KH580), N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (KH792), vinylbenzylaminoethylaminopropyltrimethoxysilane (VAPMS), and isopropyltrioleoyloxytitanate.

[0016] In one specific embodiment, the silane coupling agent is selected from one or more of 3-aminopropyltriethoxysilane (KH550), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), and γ-(methacryloyloxy)propyltrimethoxysilane (KH570).

[0017] In one specific embodiment, the initiator is one or a combination of two or more of lauroyl peroxide, tert-butyl peroxide, or cyclohexanone peroxide.

[0018] A third aspect of the present invention provides a display device based on the first aspect, characterized in that the device includes an upper substrate, a lower substrate, and a receiving space pixel array disposed between the upper substrate and the lower substrate, wherein the colored fluorescent particles are disposed within the receiving space pixel array.

[0019] The beneficial effects of this invention are as follows: 1) The electrophoretic display particles provided by this invention have a structure with pigment as the core, quantum dots as the intermediate layer, and a polymer as the shell. These electrophoretic display particles have a high charge and a high ζ-potential, reaching ±60–80 mV. When applied to electrophoretic display devices, these particles not only exhibit good dispersion stability but also demonstrate excellent electrophoretic rate and short response time, enabling the fabrication of electrophoretic display devices with superior display performance. 2) In the preparation of electrophoretic display particles, this invention first coats the pigment particles with a layer of quantum dots. This allows the quantum dots to be excited by light (including ultraviolet light), emitting colored light and enhancing the brightness of the electrophoretic particles. Silane coupling agents contain a large number of charged groups, such as amino, carboxyl, and siloxy groups, providing more activating groups for the organic modification of electrophoretic particles. Using the preparation process of this invention, the surface luminescence intensity and bonding of the electrophoretic particles can be increased, greatly enhancing the charge and resulting in a high ζ-potential, reaching ±60–80 mV. The preparation process of this invention can further improve the reflectivity of electrophoretic particles and reduce their response time. 3) The method for preparing electrophoretic display particles according to this invention is simple, environmentally friendly, and easy to operate. The resulting electrophoretic particles have a core tightly bonded to a polymer shell via a quantum dot intermediate layer, and the intermediate and shell layers are uniformly coated on the pigment particle surface. The resulting electrophoretic display particles exhibit good stability and strong charge. The electrophoretic display particles prepared by this invention can be grafted with 1–15 wt% coupling agent, and the surface of the display particles can be coated with 5–10 wt% polymer. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the preparation process of the color fluorescent electrophoretic particles provided in Example 1;

[0021] Figure 2 This is a cross-sectional schematic diagram of the electrophoresis display device;

[0022] Figure 3 This is a schematic cross-sectional view of an electrophoretic display device excited by ultraviolet light.

[0023] Explanation of reference numerals in the attached figures: 1. Upper substrate; 2. Negatively charged electrophoretic particles; 3. Transparent microcup; 4. Positively charged electrophoretic particles; 5. Lower substrate. Detailed Implementation

[0024] The embodiments of this patent are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this patent, and should not be construed as limiting this patent.

[0025] likeFigures 1-3 As shown, the embodiment of the present application provides a color fluorescent particle for electrophoretic display, characterized in that the color fluorescent particle is a core-shell structure, and the color fluorescent particle comprises, from inside to outside, a core, an intermediate layer and a shell layer; the core is a pigment unit, the intermediate layer is a quantum dot layer coated on the surface of the pigment particle, and the shell layer comprises a high polymer, and the shell layer is coated on the surface of the intermediate layer; the color fluorescent particle comprises an intrinsic base color presented by the pigment unit and a compensation fluorescence excited by the quantum dot layer under light; the compensation fluorescence is adapted to the color of the intrinsic base color.

[0026] In other embodiments, a preparation method of a color fluorescent particle for electrophoretic display is provided.

[0027] Embodiment 1

[0028] In the first embodiment of the present application, a preparation method of a color fluorescent particle for electrophoretic display is provided, and the preparation steps are as follows:

[0029] 1) Color paste preparation: an appropriate amount of iron oxide red is weighed and added into 500 mL of water, and stirred and dispersed at 500 rpm for 20 min to prepare an original color paste with a pigment particle content of 8 wt%;

[0030] 2) Quantum dot coating: the temperature of the reaction system is kept constant at 40°C, and 0.5 mol / L cesium lead iodide is added dropwise into the color paste of step 1); the dropwise adding speed of the cesium lead iodide solution is adjusted to maintain the pH value of the reaction system at 6-8; after continuous dropwise adding for 40 min, aging for 180 min, cooling to room temperature, centrifugation and washing, the composite pigment particles A coated with cesium lead iodide quantum dots are obtained.

[0031] 3) Coupling of ethylaminopropyltrimethoxysilane: an appropriate amount of composite pigment particles A prepared in step 2) is mixed with 500 mL of ethanol and 500 mL of water to form a mixture with a composite pigment particle A content of 10 wt%, and stirred and dispersed at 400 rpm for 20 min; the temperature of the reaction system is kept constant at 30°C, the pH value of the mixture is adjusted to 7-9, and 1 wt% of ethylaminopropyltrimethoxysilane based on the total mass of the mixture is added into the mixture, and reacted at 30°C for 15 h; then centrifugation and washing are performed to obtain composite pigment particles B grafted with silane coupling agent;

[0032] 4) Take the appropriate amount of composite pigment particles B prepared in step (3) and mix with 500 mL of toluene and 500 mL of ethanol to form a mixture with a mass concentration of 10 wt% of composite pigment particles B, stir and disperse at 400 rpm for 20 min, add 0.02 wt% of initiator azobisisobutyronitrile, continue to react for 8 h, and then red electrophoretic display particles coated with high molecular polymers are obtained. The grafting amount of the coupling agent is 1 wt%, the content of the quantum dot solution coated on the surface of the particles is 1 wt%, and the content of the high molecular polymer coated on the surface of the particles is 8 wt%. The preparation mechanism of this embodiment can be seen in the accompanying Figure 1 .

[0033] 5) Test the zeta potential of the electrophoretic particles: mix the electrophoretic particles prepared in step (4) with 50 g of tetrachloroethylene and 5 g of Span-80, ultrasonically disperse for 60 min; stir at a speed of 400 rpm for 24 h to prepare a test sample, take 10 g of the test sample, and test the potential. Test five times with a Zeta potential tester, and the average value is 56 mV.

[0034] Example 2

[0035] In the second embodiment of the present application, a color fluorescent particle for electrophoretic display is provided, and the preparation steps are as follows:

[0036] 1) Prepare a color paste: take an appropriate amount of cobalt blue, add 1000 mL of water, stir and disperse at 400 rpm for 20 min, and prepare a color paste with a pigment particle content of 15 wt%;

[0037] 2) Coat quantum dots: keep the temperature of the reaction system at 50°C, simultaneously add 0.5 mol / L of cesium lead bromide solution to the color paste of step 1); adjust the dropping speed of the cesium lead bromide solution so that the pH value of the reaction system is maintained at 5-6; continue to drop for 180 min, then age for 240 min, cool to room temperature, centrifuge and wash, and then composite pigment particles A coated with cesium lead bromide are obtained.

[0038] 3) Coupling: take an appropriate amount of composite pigment particles A prepared in step 2) and mix with 500 mL of ethanol and 500 mL of water to form a mixture with a content of 10 wt% of composite pigment particles A, stir and disperse at 400 rpm for 20 min, keep the temperature of the reaction system at 30°C, adjust the pH value of the mixture to 7-9, add 10 wt% of γ-(methacryloyloxy)propyltrimethoxysilane based on the total mass of the mixture, and react at 50°C for 2 h; then centrifuge and wash, and then composite pigment particles B grafted with silane coupling agent are obtained;

[0039] 4) The composite pigment particles B prepared in step 3) were mixed with 500 mL of toluene to form a mixture with a composite pigment particle B content of 50 wt%, and dispersed at 400 rpm for 20 min. 0.05 wt% of azobisisobutyronitrile was added, and the reaction was continued for 20 h to obtain blue electrophoretic display particles coated with high molecular polymers. The prepared electrophoretic display particles had a particle size of about 500 nm, a silane coupling agent grafting amount of 2 wt%, a particle surface coated cesium lead bromide content of 3 wt%, and a particle surface coated high molecular polymer content of 8 wt%.

[0040] 5) Zeta potential test: The electrophoretic particles prepared in step (4) were mixed with 50 g of tetrachloroethylene and 2 g of Span-80, ultrasonically dispersed for 60 min, and stirred at 400 rpm for 24 h to obtain a test sample. 10 g of the test sample was taken to test the zeta potential. The zeta potential was tested five times with a Zeta potential tester, and the average value was -69 mV.

[0041] Example 3

[0042] In the third embodiment of the present application, a preparation step of color fluorescent particles for electrophoretic display is provided as follows:

[0043] 1) Color paste preparation: An appropriate amount of yellow iron oxide was weighed and added to 1000 mL of water, and dispersed at 400 rpm for 20 min to prepare a color paste with a pigment particle content of 15 wt%;

[0044] 2) Quantum dot coating: The temperature of the reaction system was kept constant at 50°C, and a 0.5 mol / L cesium lead chloride solution was simultaneously added to the color paste of step 1). The dropwise addition rate of the cesium lead chloride solution was adjusted to maintain the pH value of the reaction system at 6-8. After continuous dropwise addition for 120 min, aging for 240 min, and cooling to room temperature, centrifugation and washing were performed to obtain composite pigment particles A coated with cesium lead chloride quantum dots.

[0045] 3) Coupling of ethylaminopropyltrimethoxysilane: The composite pigment particles A prepared in step (2) were mixed with 500 mL of ethanol and 500 mL of water to form a mixture with a composite pigment particle A content of 50 wt%, and dispersed at 400 rpm for 20 min. The temperature of the reaction system was kept constant at 30°C, the pH value of the mixture was adjusted to 8-10, and 6 wt% of ethylaminopropyltrimethoxysilane based on the total mass of the mixture was added to the mixture, and the reaction was continued at 50°C for 10 h. After centrifugation and washing, composite pigment particles B grafted with silane coupling agents were obtained;

[0046] 4) The composite pigment particles B prepared in step 3) were mixed with 500 mL of toluene to form a mixture with a content of 50 wt% of the composite pigment particles B, and 0.03 wt% of azobisisobutyronitrile was added, and the reaction was continued for 15 h, to obtain electrophoretic display particles coated with high molecular polymers. The electrophoretic display particles prepared had a particle size of about 600 nm, the grafting amount of the coupling agent was 3 wt%, the content of the quantum dots coated on the surface of the particles was 2.11 wt%, and the content of the high molecular polymers coated on the surface of the particles was 6 wt%.

[0047] 5) The zeta potential was tested as follows: the electrophoretic particles prepared in step 4) were mixed with 50 g of tetrachloroethylene and 5 g of Span-80, and were ultrasonically dispersed for 60 min; a test sample was prepared by stirring at a rotation speed of 400 rpm for 24 h, and 10 g of the test sample was taken for testing the zeta potential. The zeta potential was tested five times with a Zeta potential tester, and the average value was 62 mV.

[0048] The pigment particles, the silane coupling agent, and the initiator in the above Examples 1-3 are not limited to the listed substances. The pigment particles can be selected from one or a combination of two or more of carbon black, copper-chromium black, copper-iron-manganese black, iron black, titanium dioxide, zinc white, barium sulfate, red iron oxide, yellow iron oxide, ultramarine blue, chromium yellow, cadmium red, manganese violet, chromium green, iron blue, and cobalt blue; the silane coupling agent can be selected from one or a combination of two or more of γ-mercaptopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, vinylbenzylaminoethylaminopropyltrimethoxysilane, and isopropyl trioleate titanate; and the initiator can be selected from one or a combination of two or more of azobisisobutyronitrile, azobisisoheptyl nitrile, benzoyl peroxide, lauryl peroxide, t-butyl perbenzoate, and cyclohexanone peroxide. The quantum dots in Examples 1-3 are not limited to the listed quantum dots.

[0049] Finally, in other embodiments, a display device is provided, the device comprising an upper substrate, a lower substrate, and an array of containment space pixels disposed between the upper and lower substrates, the array of containment space pixels having the colored fluorescent particles disposed therein.

[0050] The preferred embodiments of the present application have been described in detail. It should be understood that modifications and variations can be resorted to without departing from the spirit of this application, as those skilled in the art will readily understand. Accordingly, the scope of the present application should be determined with reference to the appended claims.

Claims

1. A type of colored fluorescent particle for electrophoretic display, characterized in that, The colored fluorescent particles have a core-shell structure, comprising, from the inside out, a core, an intermediate layer, and a shell. The core is a pigment particle, the intermediate layer is a quantum dot layer covering the surface of the pigment particle, and the shell layer comprises a polymer and covers the surface of the intermediate layer. The colored fluorescent particles contain an intrinsic primary color exhibited by the pigment particles and a compensating fluorescence excited by the quantum dot layer upon light exposure. The compensating fluorescence is compatible with the color of the intrinsic primary color.

2. The method for preparing colored fluorescent particles according to claim 1, characterized in that, The method includes: Step S1, Color paste preparation: Disperse the pigment particles in the first dispersion solvent to prepare a color paste with a pigment particle content of 5~20wt%; Step S2, Coating with quantum dots: Coating the surface of the pigment particles in step S1 with quantum dots by chemical precipitation or sol-gel method to prepare a first composite pigment particle with the quantum dots coated on the surface. Step S3: Disperse the first composite pigment particles obtained in step S2 in an aqueous solution of water or ethanol to form a first mixture. The content of the first composite pigment particles in the first mixture is 10~60wt%. Adjust the pH value of the mixture to 6~8. Add 1~15wt% of the total mass of silane coupling agent to the first mixture. React at 30~60℃ for 1~20h. Then centrifuge and wash to obtain the second composite pigment particles grafted with silane coupling agent. Step S4: Disperse the second composite pigment particles obtained in step S3 in an organic solvent, so that the content of the second composite pigment particles is 10~60wt%. After heating to 50~60℃, add 0.01~0.06wt% initiator and continue the reaction for 10~20h to obtain colored fluorescent particles.

3. The preparation method according to claim 2, characterized in that, When the first dispersing solvent is water, step S2 uses the chemical precipitation method to coat the quantum dots. The chemical precipitation method includes: simultaneously adding a prepared 0.1-5 mol / L quantum dot solution to the pigment paste from step S1 at 20-50°C, controlling the dropping rate to keep the pH of the reaction system constant at 5-7, and continuing to add for 30-120 min; then aging for 120-300 min, cooling to room temperature, and after centrifugation and washing, the first composite pigment particles with quantum dots coated on the surface are obtained.

4. The preparation method according to claim 2, characterized in that, When the first dispersing solvent is one or a combination of organic alcohols and organic benzenes, step S2 employs the sol-gel method to coat the quantum dots. The sol-gel method includes: adding 0.1~5 mol / L quantum dot solution to the pigment paste from step S1, wherein the volume ratio of the added quantum dots to the first dispersing solvent is 1:100~20:100, stirring evenly, adding dropwise a mixed solution composed of water and isopropanol with a volume ratio of 1~5:5~10, adjusting the pH of the reaction system to 6~7, and ultrasonically reacting for 5~30 min, then heating to 40~60℃, stirring and aging, and cooling the reaction system to room temperature; centrifuging and washing to obtain the first composite pigment particles coated with quantum dots.

5. The preparation method according to claim 2, characterized in that, The pigment particles are one or a combination of two or more of the following: carbon black, copper chromium black, copper iron manganese black, iron black, titanium dioxide, zinc white, barium sulfate, iron oxide red, iron oxide yellow, ultramarine, chrome yellow, cadmium red, manganese violet, chrome green, iron blue, and cobalt blue.

6. The preparation method according to claim 2, characterized in that, The average particle size of the colored fluorescent particles is 300 nm to 600 nm, the content of quantum dots coated on the surface of the pigment particles is 1 wt% to 5 wt%, and the content of polymer coated on the surface of the colored fluorescent particles is 5 wt% to 10 wt%.

7. The preparation method according to claim 2, characterized in that, The silane coupling agent is selected from one or more of 3-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane.

8. The preparation method according to claim 2, characterized in that, The initiator is one or a combination of two or more of lauroyl peroxide, tert-butyl peroxide, or cyclohexanone peroxide.

9. A display device based on the colored fluorescent particles according to claim 1, characterized in that, The device includes an upper substrate, a lower substrate, and a pixel array in a receiving space disposed between the upper substrate and the lower substrate, wherein the colored fluorescent particles are disposed in the pixel array in the receiving space.

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