PIGMENT AND INK FOR ELECTROPHORETIC DISPLAY USING BLACK TITANIUM DIOXIDE

Abstract

The present invention relates to a pigment for a black electrophoretic display having high electrical insulation and excellent dispersibility in the visible region. An objective of the present invention is to provide black titanium dioxide as a pigment for an electrophoretic display. In addition, another objective of the present invention is to provide an ink composition for an electrophoretic display comprising a black titanium dioxide pigment, and an electrophoretic display.

Claims

1. A pigment for electrophoretic display, the pigment containing inorganic oxide.

2. The pigment of claim 1, wherein the inorganic oxide is black titanium dioxide (TiO.sub.2-x).

3. The pigment of claim 2, wherein the black titanium dioxide has a crystal phase selected from the group consisting of anatase phase, rutile phase, and mixtures thereof.

4. The pigment of claim 1, wherein the pigment includes a core part made of the inorganic oxide and a shell part surrounding the surface of the core part.

5. The pigment of claim 4, wherein the shell part is hydrophobic.

6. The pigment of claim 4, wherein the shell part comprises any one among one or more hydrocarbons, phosphoric acid, and a combination thereof.

7. The pigment of claim 6, wherein the hydrocarbon is a methyl group.

8. The pigment of claim 1, wherein the pigment has a particle diameter of 5 nm to 200 nm.

9. The pigment of claim 1, wherein the pigment exhibits a reflectance of 14% or less for visible light.

10. An ink composition for an electrophoretic display, the ink composition comprising the pigment of claim 1, a dielectric medium in which the pigment particles are dispersed, and an additive for enhancing the dispersion properties of the pigment.

11. The composition of claim 10, wherein the dielectric medium has a dielectric constant of 2 to 10 F/m.

12. An electrophoretic display comprising the ink composition of claim 10.

13. An electrophoretic display comprising the ink composition of claim 11.

Description

DESCRIPTION OF DRAWINGS

[0023] FIG. 1 is a photograph of gray and black titanium dioxide (TiO.sub.2-x) powder;

[0024] FIG. 2 is a view showing a result of X-ray diffraction analysis of a synthesized TiO.sub.2-x powder;

[0025] FIG. 3 is a view showing a result of Raman analysis of a synthesized TiO.sub.2-x powder and the commercial TiO.sub.2-x powder;

[0026] FIG. 4 is a view showing an FT-IR analysis result of the black titanium dioxide powder prepared in Example 1;

[0027] FIG. 5 is a view showing a reflectance analysis result of gray and black TiO.sub.2-x nanoparticles;

[0028] FIG. 6 is a transmission electron microscope photograph of TiO.sub.2-x powder according to an embodiment of the present disclosure;

[0029] FIG. 7 is a photograph of ink including a synthesized TiO.sub.2-x powder and a solvent according to an embodiment of the present disclosure;

[0030] FIGS. 8(a), 8(b), and 8(c) are graphs showing the results of particle size analysis of the ink including the synthesized TiO.sub.2-x powder and the solvent, respectively, according to an embodiment of the present disclosure;

[0031] FIGS. 9(a) and 9(b) are graphs showing dispersion evaluation results according to an Example and a Comparative Example of the present disclosure, respectively; and

[0032] FIGS. 10(a), 10(b), and 10(c) are evaluations of the driving speed of the electrophoretic display according to the average particle size of the ink according to an embodiment of the present disclosure, respectively.

BEST MODE

[0033] Advantages and features of the present disclosure, and methods for achieving them, will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below but may be implemented in various different forms. The present embodiment is provided to complete the disclosure of the present disclosure and to completely inform the scope of the present disclosure to those skilled in the art, and the present disclosure is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

[0034] The terminology used herein is for the purpose of describing the embodiments and is not intended to limit the present disclosure. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, ‘comprises’ and/or ‘comprising’ does not preclude the presence or addition of one or more other elements, steps, operations, and/or devices mentioned.

[0035] The present disclosure provides pigment for an electrophoretic display, the pigment including inorganic oxide.

[0036] The inorganic oxide may include any one of silicon (Si), titanium (Ti), barium (Ba), strontium (Sr), iron (Fe), nickel (Ni), cobalt (Co), lead (Pb), aluminum (Al), copper (Cu), silver (Ag), gold (Au), tungsten (W), molybdenum (Mo), zinc (Zn), and zirconium (Zr), or a combination of one or more thereof. Preferably, the inorganic oxide may be black titanium dioxide.

[0037] The black titanium dioxide may have a crystal phase selected from the group consisting of anatase phase, rutile phase, and mixtures thereof.

[0038] The pigment may have inorganic oxide as a core part and a shell part surrounding a surface of the core part. The shell part may be hydrophobic.

[0039] The shell part may include any one among one or more hydrocarbon, phosphoric acid, and a combination thereof.

[0040] The pigment may have a particle diameter of 5 nm to 200 nm. The smaller the pigment particle size, the faster the driving speed in the electrophoretic display.

[0041] The visible light reflectance of the pigment may be 14% or less.

[0042] Provided is an ink composition for an electrophoretic display, including any one selected from the above-mentioned pigments, a dielectric medium in which the pigment particles are dispersed, and an additive for enhancing the dispersion characteristics of the pigment.

[0043] The dielectric medium may have a dielectric constant of 2 to 10 F/m.

[0044] Hereinafter, the present disclosure will be described in more detail through examples. These examples are only for illustrating the present disclosure, and it will be apparent to those of ordinary skilled in the art that the scope of the present disclosure is not to be construed as being limited by these examples.

Example 1—Method for Preparing Black Titanium Dioxide (TiO.SUB.2-x.) Powder

[0045] 0.1M titanium isopropoxide ethylene glycol solution 100 ml and 0.2M citric acid 200 ml were mixed and heated and stirred at 100° C. for 1 hour. Black titanium dioxide (TiO.sub.2-x) nanoparticles with a shell part including a hydrocarbon group were synthesized. After cooling the reaction mixture to room temperature, the reaction mixture was washed with ethanol three times using a centrifuge and dried at 60° C. to prepare black titanium dioxide (TiO.sub.2-x) nanoparticle powder. FIG. 1 (left) shows a photograph of the prepared powder.

Comparative Example 1—Method for Preparing Gray Titanium Dioxide (TiO.SUB.2-x.) Powder

[0046] Gray titanium dioxide powder was prepared in the same manner as in Example 1, except that the reaction temperature was set to 90° C. in Example 1. FIG. 1 (right) shows a photograph of the prepared powder.

Example 2—Preparation of Ink Containing Black Titanium Dioxide (TiO.SUB.2-x.) Powder and Solvent

[0047] Each of the black titanium dioxide nanoparticles prepared in Example 1 15 g, Isopar L 20 g, HaloCarbon oil 0.8 10 g, DISPERBYL-116 10 g, methyl isobutyl ketone (MIBK) 80 g, and 50 g of zirconia balls (500 μm) were added and dispersed for 14 days using a ball-mill disperser. Thereafter, zirconia balls and foreign substances were removed using a PP filter (300 mesh) to prepare a nanoparticle dispersion.

Examples 3 and 4—Particle Size Control of Black Titanium Dioxide (TiO.SUB.2-x.) Powder

[0048] Black titanium dioxide powder was prepared in the same manner as in Example 1, except that citric acid was set to 50 ml and 100 ml, respectively, in Example 1. Examples 3 and 4 dispersions were prepared in the same manner as in Example 2 using each of the powders prepared by the above method.

Comparative Example 2—Preparation of Ink Containing Carbon-Black Powder and Solvent

[0049] In order to prepare ink using carbon-black, several surface treatment processes are basically required. To shorten the surface treatment process experimentally, Monarch 1400 product produced by CABOT Co., whose surface was treated with nitric acid, was used. The carbon-black above 5 g, 1 L of hexane, and 100 g of oleic acid were stirred at 500 rpm for 24 hours in an atmosphere of 60° C. for 24 hours. After recovering the carbon-black particles using a centrifuge, the process of redispersing the carbon-black particles again in the same ratio of hexane and oleic acid solutions as above and recovering the particles using a centrifuge again was repeated 4 more times. 3 g of the carbon-black particles which the surface treatment has been completed, 65 g of Isopar L, 22 g of HaloCarbon oil 0.8, 10 g of TEGO-Dispers 760W, and 50 g of zirconia balls (500 μm) were added thereto and dispersed at 1500 rpm for 15 hours using a horizontal disk-mill disperser. Thereafter, zirconia balls and foreign substances were removed using a PP filter (300 mesh) to prepare a carbon-black particle dispersion.

Example 5—Black Titanium Dioxide (TiO.SUB.2-x.) Based Electrophoretic Display Fabrication

[0050] A display for confirming the electrophoretic properties of the ink containing black titanium dioxide (TiO.sub.2-x) powder and a solvent in Example 2 was manufactured. As the lower electrode, ITO Glass was patterned to form a plurality of line-shaped patterns with an ITO line width of 30 um and an interval between ITO patterns of 70 um. In addition, as the upper electrode, general ITO glass was used without a pattern. Parts of the edge were attached to maintain the gap with a double-sided tape having a thickness of 20 μm, and the ink prepared in Example 2 was injected into a gap between ITO glass plates for upper and lower electrodes using a dropper and then sealed.

Experimental Example 1—XRD Analysis

[0051] The black titanium dioxide (TiO.sub.2-x) nanoparticles prepared by the preparation method of Example 1 were analyzed by X-ray diffraction (XRD). As a result of the analysis, it was confirmed that only the TiO.sub.2 crystal peak appeared.

[0052] As a result of X-ray diffraction (XRD) analysis of the gray titanium dioxide (TiO.sub.2-x) nanoparticles prepared by the manufacturing method of Comparative Example 1, it was confirmed that only the TiO.sub.2 crystal peak appeared (FIG. 2).

Experimental Example 2—Raman Analysis

[0053] Through Raman comparison analysis with the commercial white titanium dioxide powder and the powder prepared in Example 1, it was confirmed that the prepared powder through the fact that the peak at about 200 cm.sup.−1 was observed and the peak at 300 cm.sup.−1 or less became gentle was TiO.sub.2-x with oxygen pores.

[0054] Through Raman comparative analysis with commercial white titanium dioxide powder and the powder prepared in the preparation method of Comparative Example 1, it was confirmed that the prepared powder through the fact that the peak at about 200 cm.sup.−1 was observed and a peak of 300 cm.sup.−1 or less became gentle was TiO.sub.2-x with oxygen pores (FIG. 3).

Experimental Example 3—FT-IR Analysis

[0055] As a result of FT-IR analysis of the black titanium dioxide powder prepared in Example 1, the peak observed between 1200 cm.sup.−1 and 1500 cm.sup.−1 is shown by the CO bond and the CH bond of the methyl group, showing that methyl group was formed on the surface of the nanoparticles (FIG. 4).

Experimental Example 4—Reflectance

[0056] The reflectance of the black titanium dioxide (TiO.sub.2-x) nanoparticle powder prepared by the preparing method of Example 1 was confirmed to be 13.98% as a result of measurement using an ultraviolet-visible light spectrometer. The reflectance of the gray titanium dioxide (TiO.sub.2-x) nanoparticle powder prepared by the preparing method of Comparative Example 1 was confirmed to be 16.68% as a result of measurement using an ultraviolet-visible light spectrometer. Through these results, it was found that the black titanium dioxide prepared in Example 1 had excellent blackness (FIG. 5).

Experimental Example 5—Particle Size

[0057] As a result of measuring the particle size of the black titanium dioxide (TiO.sub.2-x) nanoparticle powder prepared by the preparing method of Example 1 through a transmission electron microscope, the primary particle size was in the range of 5 nm to 200 nm (FIG. 5).

Experimental Example 6—Particle Size Analysis

[0058] As a result of analyzing the average particle size of black titanium dioxide nanoparticles distributed in ink containing the black titanium dioxide (TiO.sub.2-x) powder and the solvent prepared by the method of Example 2 using a nanoparticle size analyzer. It was confirmed to have an average particle size of 63.8 nm (FIG. 7(a)). In addition, the average particle size of black titanium dioxide nanoparticles distributed in each ink of the ink containing the black titanium dioxide (TiO.sub.2-x) powder and solvent prepared by the methods of Examples 3 and 4 was analyzed using a nanoparticle size analyzer. It was confirmed to have an average particle size of 137 nm and 203.5 nm (FIGS. 8(b) and 8(c)).

Experimental Example 7—Dispersibility of Black Titanium Dioxide (TiO.SUB.2-x.) Powder

[0059] The dispersibility of the ink prepared in Example 2 and Comparative Example 3 was compared and analyzed using LUMiSizer equipment manufactured by LUM-Gmbh, Germany (measure the sedimentation and non-uniformity of the material using an optical sensor while accelerating the sedimentation/rise rate of the particles by applying centrifugal force to the ink). FIG. 9 is a graph obtained using LUMiSizer under the same test conditions for ink containing black titanium dioxide (TiO.sub.2-x) and ink containing carbon-black, respectively. The dispersion stability index converted using the analysis result was 0.110 for ink containing black titanium dioxide (TiO.sub.2-x) and 0.243 for ink containing carbon-black, indicating better dispersion stability when containing black titanium dioxide (TiO.sub.2-x).

Example 4—Black Titanium Dioxide (TiO.SUB.2-x.) Based Electrophoretic Display Fabrication

[0060] A display for confirming the electrophoretic properties of the ink containing black titanium dioxide (TiO.sub.2-x) powder and a solvent in Example 2 was manufactured. As the lower electrode, ITO Glass was patterned to form a plurality of line-shaped patterns with an ITO line width of 30 um and an interval between ITO patterns of 70 um. In addition, as the upper electrode, general ITO glass was used without a pattern. Parts of the edge were attached to maintain the gap with a double-sided tape having a thickness of 20 μm, and the ink prepared in Example 2 was injected into a gap between ITO glass plates for upper and lower electrodes using a dropper and then sealed.

Experimental Example 8—Evaluation of Characteristics of Black Titanium Dioxide (TiO.SUB.2-x.)-Based Electrophoretic Display

[0061] In order to evaluate the driving characteristics of the ink in the black titanium dioxide (TiO.sub.2-x)-based electrophoretic display prepared in Example 4, a voltage of DC V is applied to the upper and lower electrodes of the display using a power supply. After application, the change in transmittance with time was measured in real-time with a time interval of 2 seconds through a UV-Spectrometer. As a result, shown in FIG. 10, it can be confirmed that the smaller the size of the nanoparticles of black titanium dioxide (TiO.sub.2-x), the faster the reaction rate.

[0062] As described above, it will be apparent to those skilled in the art that such a specific technique is merely a preferred embodiment, and thus the scope of the present disclosure is not limited thereto. Accordingly, it is intended that the substantial scope of the present disclosure be defined by the appended claims and their equivalents.