Preparation method of electrophoretic blue particles with high charge retention capability

Abstract

The invention belongs to the technical field of electrophoretic display, and particularly relates to an electrophoretic blue particle and a preparation method and application thereof. The charge control agent and the cross-linking agent are added in the preparation process of the particles, so that the charge quantity and the charge retention capability of the spherical particles obtained by emulsion polymerization are improved, and the display effect of the device is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrophoretic display, and in particular relates to electrophoretic blue particles and a preparation method and application thereof. Background Art

[0002] Electronic paper (E-paper) is a display made by coating an electrophoretic dispersion onto a thin film, which can be applied to a thin-film transistor circuit and then controlled by a backplane driver IC to display pixel graphics. There are many E-paper display technologies, but electrophoretic display is widely used in the E-paper display field due to its wide viewing angle and environmental friendliness. Electrophoretic display (EPD) is essentially a reflective display technology. The size and nature of the charge carried by electrophoretic particles vary. By applying voltages of different magnitudes and directions to the electrophoretic display liquid, the two electrodes cause the relative positions of the electrophoretic particles encapsulated in the microcups or microcapsules to change. Positively charged particles move along the direction of the electric field lines, while negatively charged particles move in the opposite direction of the electric field lines. Ultimately, particles or electrophoretic liquids of different colors reach the display unit corresponding to the electric field, presenting different colors, thus achieving electrophoretic display.

[0003] Electrophoretic dispersions are generally composed of electrophoretic particles, dispersion stabilizers, charge control agents, and dispersion media. Among them, electrophoretic particles largely affect the response time and display effect of electrophoretic display devices. In particular, whether the charge of the electrophoretic particles themselves can be stably maintained in the dispersion system is very important for the display device. Color electrophoretic particles generally use organic pigment particles with low toxicity, solvent resistance, and better solubility in organic solvents. Common organic pigments used for blue electrophoretic particles include pigment blue 15:0, pigment blue 15:3, pigment blue 60, etc., which all have the characteristics of high surface polarity, easy flocculation, small and unstable charge, which makes the charge and charge retention ability of electrophoretic particles based on this type of pigment insufficient. Summary of the Invention

[0004] To solve the above problems, the present application provides a method for preparing electrophoretic blue particles, comprising the following steps:

[0005] Pre-dispersion of S1 raw material particles: take 1 part of raw material particles, take 5-20 parts of polymer monomer solution, take 0.1-0.3 parts of charge control agent, take 0.25-2 parts of cross-linking agent monomer, prepare mixed solvent I, add 5-20 parts of zirconium beads and ball mill for 6-12 hours, remove the zirconium beads after ball milling to obtain solution I; take 10-15 parts of deionized water, add 0.75-1.5 parts of emulsifier, and completely dissolve in deionized water to obtain solution II;

[0006] Preparation of S2 prepolymer emulsion: slowly dropwise add the obtained solution I to solution II under stirring in a homogenizer, and continue stirring for 10 to 60 minutes after the dropwise addition to obtain a prepolymer emulsion;

[0007] S3 Emulsion Polymerization: Add the obtained prepolymer emulsion to a flask, raise the temperature to 50°C, mechanically stir at 200-400 rpm, and dropwise add the initiator under inert gas to initiate polymerization. After the addition, raise the temperature to 70-90°C, mechanically stir at 200-400 rpm, and react under inert gas for 8-12 hours. The resulting reaction solution is centrifuged, washed until the conductivity stabilizes, freeze-dried for 12 hours, and vacuum-dried at 80-100°C to obtain electrophoretic blue particles.

[0008] Furthermore, the polymer monomer in step S1 includes at least one of methacrylates and styrene.

[0009] Furthermore, the charge control agent in step S1 includes one or more of fatty acid polyoxyethylene ester (SE-10), diallyldimethylammonium chloride (DMDAAC) and allyloxynonyl-phenoxypropanol polyoxyethylene ether sulfonate (ANPS).

[0010] Furthermore, the crosslinking agent monomer in step S1 includes one or more of divinylbenzene, N-hydroxymethyl acrylamide and diacetone acrylamide.

[0011] Furthermore, the emulsifier in step S1 includes one or more of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate or sodium dodecyl sulfate.

[0012] Furthermore, the stirring speed of the homogenizer in step S2 is 5000-7000 rpm; and the time for slowly adding the obtained solution I to the solution II under stirring by the homogenizer in step S2 should be maintained at 10-20 minutes.

[0013] Furthermore, the initiator in step S3 includes one or more of potassium persulfate, sodium persulfate and ammonium persulfate.

[0014] Furthermore, the initiator in step S3 is added dropwise within 30 minutes.

[0015] The present invention also provides electrophoretic blue particles with high charge retention capability, which are prepared by any one of the preparation methods described above.

[0016] The present invention also provides the use of the electrophoretic blue particles with high charge retention ability in the preparation of displays.

[0017] The present invention has the following beneficial effects:

[0018] (1) By introducing a charge control agent during the emulsion polymerization process, the charge is encapsulated inside the polymer particles. Compared with charge adsorption or chemical grafting on the particle surface, the charge amount and charge stability of the electrophoretic blue particles in the dispersion medium are improved.

[0019] (2) By introducing a cross-linking agent during the emulsion polymerization process, a rigid cross-linking layer is provided on the particle surface, which further improves the charge stability of the electrophoretic blue particles in the dispersion medium.

[0020] (3) By preparing electrophoretic particles through emulsion polymerization, spherical polymer electrophoretic blue particles can be obtained. This shape is conducive to the displacement of particles under electric field drive and is beneficial to the display of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a scanning electron microscope image of the raw material pigment blue 15:3 particles and blue particles D in an embodiment of a method for preparing electrophoretic blue particles with high charge retention capacity of the present invention:

[0023] Figure 2 Transmission electron microscope images of raw material pigment blue 15:3 particles and blue particles D according to an embodiment of a method for preparing electrophoretic blue particles with high charge retention capacity of the present invention:

[0024] Figure 3 This is a time-dependent curve of the zeta potential of blue particles A to D in an embodiment of a method for preparing electrophoretic blue particles with high charge retention capacity according to the present invention.

[0025] Figure 4 This is a response time diagram of blue particles D after being placed for 1 minute and 6 hours in an embodiment of a method for preparing electrophoretic blue particles with high charge retention ability of the present invention. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention are now described in detail. Unless otherwise specified, the methods in the examples are conventional methods. Unless otherwise specified, the reagents used are conventional commercially available reagents or reagents prepared using conventional methods. This detailed description should not be considered a limitation of the present invention, but rather should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] Example 1

[0032] Take 1g of raw material pigment blue 15:3 particles, take 20g of styrene monomer solution, prepare mixed solvent I, add 20g of zirconium beads and ball mill for 12h. After ball milling, remove the zirconium beads to obtain solution I; take 300mL of deionized water, add 0.75g of sodium dodecyl sulfate, and completely dissolve it in deionized water to obtain solution II.

[0033] The obtained solution I was added dropwise to the solution II which was stirred at high speed. The adding time was controlled within 20 min. After the adding was completed, the stirring was continued for 30 min. The stirring speed was 5000 rpm to obtain a prepolymer emulsion.

[0034] The resulting prepolymer emulsion was added to a flask, heated to 50°C, mechanically stirred at 300 rpm, and the initiator was added dropwise under an inert gas atmosphere to initiate polymerization. Within 30 minutes, the temperature was raised to 70°C, mechanically stirred at 300 rpm, and reacted under an inert gas atmosphere for 12 hours. The resulting reaction solution was centrifuged, washed until the conductivity stabilized, freeze-dried for 12 hours, and then dried under vacuum at 80°C to obtain electrophoretic blue particles A.

[0035] Example 2

[0036] Take 1g of raw material pigment blue 15:3 particles, take 20g of styrene monomer solution, take 0.2g of SE-10, prepare mixed solvent I, add 20g of zirconium beads and ball mill for 12h. After ball milling, remove the zirconium beads to obtain solution I; take 300mL of deionized water, add 0.75g of sodium dodecyl sulfate, and dissolve it completely in deionized water to obtain solution II.

[0037] The obtained solution I was added dropwise to the solution II which was stirred at high speed. The adding time was controlled within 20 min. After the adding was completed, the stirring was continued for 30 min. The stirring speed was 5000 rpm to obtain a prepolymer emulsion.

[0038] The resulting prepolymer emulsion was added to a flask, heated to 50°C, mechanically stirred at 300 rpm, and the initiator was added dropwise under an inert gas atmosphere to initiate polymerization. Within 30 minutes, the temperature was raised to 70°C, mechanically stirred at 300 rpm, and reacted under an inert gas atmosphere for 12 hours. The resulting reaction solution was centrifuged, washed until the conductivity stabilized, freeze-dried for 12 hours, and then dried under vacuum at 80°C to obtain electrophoretic blue particles B.

[0039] Example 3

[0040] Take 1g of raw material pigment blue 15:3 particles, take 20g of styrene monomer solution, take 1.5g of divinylbenzene monomer, prepare mixed solvent I, add 20g of zirconium beads and ball mill for 12h. After ball milling, remove the zirconium beads to obtain solution I; take 300mL of deionized water, add 0.75g of sodium dodecyl sulfate, and completely dissolve it in deionized water to obtain solution II.

[0041] The obtained solution I was added dropwise to the solution II which was stirred at high speed. The adding time was controlled within 20 min. After the adding was completed, the stirring was continued for 30 min. The stirring speed was 5000 rpm to obtain a prepolymer emulsion.

[0042] The resulting prepolymer emulsion was added to a flask, heated to 50°C, mechanically stirred at 300 rpm, and the initiator was added dropwise under an inert gas atmosphere to initiate polymerization. Within 30 minutes, the temperature was raised to 70°C, mechanically stirred at 300 rpm, and reacted under an inert gas atmosphere for 12 hours. The resulting reaction solution was centrifuged, washed until the conductivity stabilized, freeze-dried for 12 hours, and then dried under vacuum at 80°C to obtain electrophoretic blue particles C.

[0043] Example 4

[0044] Take 1g of raw material pigment blue 15:3 particles, take 20g of styrene monomer solution, take 0.2g of SE-10, take 1.5g of divinylbenzene monomer, prepare mixed solvent I, add 20g of zirconium beads and ball mill for 12h. After ball milling, remove the zirconium beads to obtain solution I; take 300mL of deionized water, add 0.75g of sodium dodecyl sulfate, and dissolve it completely in deionized water to obtain solution II.

[0045] The obtained solution I was added dropwise to the solution II which was stirred at high speed. The adding time was controlled within 20 min. After the adding was completed, the stirring was continued for 30 min. The stirring speed was 5000 rpm to obtain a prepolymer emulsion.

[0046] The resulting prepolymer emulsion was added to a flask, heated to 50°C, mechanically stirred at 300 rpm, and the initiator was added dropwise under an inert gas atmosphere to initiate polymerization. Within 30 minutes, the temperature was raised to 70°C, mechanically stirred at 300 rpm, and reacted under an inert gas atmosphere for 12 hours. The resulting reaction solution was centrifuged, washed until the conductivity stabilized, freeze-dried for 12 hours, and then dried under vacuum at 80°C to obtain electrophoretic blue particles D.

[0047] Experimental testing

[0048] (1) Take 0.1g of blue particles D and pigment blue 15:3 and put them into a 5mL centrifuge tube. Add 4mL of anhydrous ethanol to each to obtain a particle dispersion. Place the dispersion under a 40kHz ultrasonic machine for 30 minutes. Drop an appropriate amount of ultrasonic dispersion onto the SEM scanning electron microscope sample stage. After the anhydrous ethanol evaporates, perform scanning electron microscope testing. The instrument model used is Regulus8100. The results are as follows. Figure 1 As shown, Pigment Blue 15:3 is a rod-shaped particle with a particle size of 200 to 300 nm. After emulsion polymerization, polymer spherical particles with an average particle size of 600 nm are obtained. The particle morphology changes to a spherical shape, which is conducive to the movement of the particles in the electric field.

[0049] (2) Take 0.05g of blue particles D and pigment blue 15:3 and put them into a 5mL centrifuge tube. Add 4mL of anhydrous ethanol to each to obtain a particle dispersion. Place the dispersion under a 40kHz ultrasonic machine for 30 minutes. Drop an appropriate amount of the ultrasonic dispersion onto the ultrathin carbon film. After the anhydrous ethanol evaporates, perform transmission electron microscopy (TEM) testing using a JEM-2100F instrument. The results are as follows. Figure 2 As shown, pigment blue 15:3 exhibits a sticky rod-like structure, while the spherical particles of blue particles D have less adhesion between them, which is beneficial to the electric field response of the electrophoretic particles.

[0050] (3) Take 0.01g of each of blue particles A to D and place them in a 5mL centrifuge tube. Add 4mL of isoparaffin to each to obtain a dispersion of particles. Place this dispersion in a 40kHz ultrasonic machine for ultrasonic dispersion for 30 minutes. Take an appropriate amount of dispersion and place it in a test dish to test the change of particle charge over time. The instrument model used is a JS94J microelectrophoresis instrument. The particles are first tested once with a voltage of 150V, and then the charge change after being placed for 6 hours is tested, and the test is conducted every 1 hour. The curve of the change of particle charge over time is shown as follows: Figure 3 As shown, comparing blue particles A and B, particles with the charge control agent SE-10 all have higher initial potentials, with blue particle B reaching 268.8 mV. However, after 4 hours, the potential drops significantly, likely due to the slow swelling of the particles in the isoparaffin solvent, which reduces the charge. Comparing blue particles A and C, particles with the crosslinker divinylbenzene show a slight decrease in initial potential, but the potential remains relatively stable, likely due to the formation of a rigid crosslinked layer. Comparing blue particles A and D, particles with both the charge control agent SE-10 and the crosslinker divinylbenzene maintain both a high charge and extended charge stability. After the charge stabilizes, the particles still retain 90% of their initial charge.

[0051] (4) Take 0.2g of blue particle D, 2.3g of isoparaffin, and 10g of zirconium beads, and ball mill them in a ball mill for 12h to obtain a blue dispersion. Take 0.75g of titanium dioxide particles, 3.81g of isoparaffin, 0.1g of hyperdispersant, and 10g of zirconium beads, and ball mill them in a ball mill for 12h to obtain a white dispersion. Take 0.8g of blue dispersion and 1.6g of white dispersion, mix them evenly, and ultrasonically disperse them for 30min to obtain a mixed electrophoretic dispersion. The mixed electrophoretic dispersion was filled into a prototype device composed of two pieces of 3mm◇2mm◇0.7mm high-transmittance conductive glass with a plate spacing of 25μm. The response curves of the blue and white devices were tested just after filling (placed for 1min) and after placing for 6h. The instrument model used was TST06401C-3NT3-A electronic ink coating platform. The results are as follows Figure 4 As shown, the response time of the blue-white device made of blue particles D after 6 hours is 3.5ms slower than the response time just after filling (1 minute), and still maintains a good response state.

[0052] Therefore, the present invention adopts the above-mentioned method for preparing electrophoretic blue particles with high charge retention ability. By adopting the emulsion polymerization route in the modification process of the pigment blue particles and adding a charge control agent and a cross-linking agent during the preparation process, the prepared spherical electrophoretic blue particles have a high charge and strong charge retention ability in the isoparaffin system, thereby improving the display effect of the blue particles in the device and having better display performance.

[0053] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing electrophoretic blue particles, characterized in that: The following steps are involved: Pre-dispersion of S1 raw material particles: take 1 part of raw material particles, take 5-20 parts of polymer monomer solution, take 0.1-0.3 parts of charge control agent, take 0.25-2 parts of cross-linking agent monomer, prepare mixed solvent I, add 5-20 parts of zirconium beads and ball mill for 6-12 hours, remove the zirconium beads after ball milling to obtain solution I; take 10-15 parts of deionized water, add 0.75-1.5 parts of emulsifier, and completely dissolve in deionized water to obtain solution II; Preparation of S2 prepolymer emulsion: slowly dropwise add the obtained solution I to solution II under stirring in a homogenizer, and continue stirring for 10 to 60 minutes after the dropwise addition to obtain a prepolymer emulsion; S3 Emulsion Polymerization: Add the obtained prepolymer emulsion to a flask, raise the temperature to 50°C, mechanically stir at 200-400 rpm, and dropwise add the initiator under inert gas to initiate polymerization. After the addition, raise the temperature to 70-90°C, mechanically stir at 200-400 rpm, and react under inert gas for 8-12 hours. The resulting reaction solution is centrifuged, washed until the conductivity stabilizes, freeze-dried for 12 hours, and vacuum-dried at 80-100°C to obtain electrophoretic blue particles.

2. The method for preparing electrophoretic blue particles according to claim 1, wherein: In step S1, the polymer monomer includes at least one of methacrylate and styrene.

3. The method for preparing electrophoretic blue particles according to claim 1, wherein: The charge control agent in step S1 includes one or more of fatty acid polyoxyethylene ester (SE-10), diallyldimethylammonium chloride (DMDAAC) and allyloxynonyl-phenoxypropanol polyoxyethylene ether sulfonate (ANPS).

4. The method for preparing electrophoretic blue particles according to claim 1, wherein: The crosslinking agent monomer in step S1 includes one or more of divinylbenzene, N-hydroxymethyl acrylamide and diacetone acrylamide.

5. The method for preparing electrophoretic blue particles according to claim 1, wherein: The emulsifier in step S1 includes one or more of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate and sodium dodecyl sulfate.

6. The method for preparing electrophoretic blue particles according to claim 1, wherein: The stirring speed of the homogenizer in step S2 is 5000-7000 rpm; the time for slowly adding the obtained solution I to the solution II under stirring by the homogenizer in step S2 should be maintained at 10-20 minutes.

7. The method for preparing electrophoretic blue particles according to claim 1, wherein: The initiator in step S3 includes one or more of potassium persulfate, sodium persulfate and ammonium persulfate.

8. The method for preparing electrophoretic blue particles according to claim 1, wherein: The initiator in step S3 is added dropwise within 30 minutes.

9. An electrophoretic blue particle with high charge retention capacity, characterized in that: The method is as described in claims 1 to 8.

10. Use of the electrophoretic blue particles with high charge retention ability as claimed in claim 9 in the preparation of displays.

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