Color-changeable ink composition, electrophoretic display using same, and manufacturing method therefor

Abstract

The present invention relates to a color-changeable ink composition with a color changing by the application of an electric field, which is used in an electrophoretic display. The color-changeable ink composition comprises: first particles containing a pigment of a first color; a fluid having a solution in which a dye of a second color is saturated and dissolved; and second particles in a colloidal form of the second color where the dye, being supersaturated, remains in an undissolved state within the solution, wherein the first particle and the second particle may move in opposite directions by the application of the electric field.

Description

Color-variable ink composition, electrophoretic display using the same, and manufacturing method thereof

[0001] The present invention relates to a color-variable ink composition, an electrophoretic display using the same, and a method for manufacturing the same, and more particularly, to an ink composition whose color changes by application of an electric field, an electrophoretic display using the same, and a method for manufacturing the same.

[0002] This invention is the result of research conducted under the "Small and Medium Enterprise Technology Innovation Development Project" supported by the Ministry of SMEs and Startups. [Project Title: Development and Mass Production of Large-Area Smart Energy-Saving Electrical Color-Variable Film / Module, Project Number: S3383819]

[0003] With the recent surge in research and development into next-generation displays, a variety of display technologies are being introduced. A prime example of this type of display is electronic ink. Electronic ink is a display that expresses a specific color (e.g., black and white) by applying an electric field to capsules containing particles of a specific color, each with a negative or positive charge. This reduces power consumption and enables flexible displays.

[0004] However, conventional electronic ink has the limitation that it can only be driven by an electric field because it only contains particles with an electric charge, and it cannot go beyond a simple display pattern that turns on / off depending on the direction of the applied electric field.

[0005] Furthermore, these displays are mostly implemented using a multi-particle method utilizing two or more types of particles. Typically, the multi-particle method involves two or more pigment particles with opposite charges, each capable of producing two or more contrasting color variations. Pigment particles with opposite charges that move under an electric field offer excellent color clarity and shielding capabilities, but because they must be expressed using pigments, their ability to produce a wide range of colors is limited.

[0006] Alternatively, displays can be manufactured using a single particle method. This method offers the advantage of being able to produce a variety of colors by dissolving various colored dyes in a fluid. However, to clearly control the color displayed by the fluid, a larger amount of dye must be dissolved. Furthermore, when a specific electrophoretic particle moves to the upper electrode, the color of the colored particle and the dye in the fluid are mixed, resulting in a lower contrast ratio than the multi-particle method.

[0007] The present invention aims to solve various problems, including the above-mentioned problems, and provides a color-variable ink composition that enables the implementation of various colors while maintaining superior color clarity compared to conventional electrophoretic displays even when manufactured using a single particle method, an electrophoretic display using the same, and a manufacturing method thereof. However, these tasks are exemplary and the scope of the present invention is not limited thereby.

[0008] A color-variable ink composition according to the invention for solving the above problem comprises: first particles including a pigment of a first color; a fluid in which a dye of a second color is saturated and dissolved in a solution; and second particles in the form of a colloid of a second color in which the dye is supersaturated and not dissolved in the solution; wherein the first particles and the second particles can move in opposite directions by application of the electric field.

[0009] Additionally, according to the present invention, the solution may be a mixture of two or more solvents.

[0010] In addition, according to the present invention, at least one solvent among the solvents mixed in the solution may have a solubility in water of 2 wt% to 4 wt% at 20°C.

[0011] Additionally, according to the present invention, the dielectric constant of the solution may be 4 to 6.

[0012] Additionally, according to the present invention, the solvent may be a mixture of Isopar M and nitroethane in a volume ratio of 7:3 to 8:2.

[0013] Additionally, according to the present invention, 1 wt% to 4 wt% of the dye can be dissolved in the fluid.

[0014] Additionally, according to the present invention, the second particle may be formed of 1 wt% to 5 wt% of the dye in the form of a fluid colloid.

[0015] Additionally, according to the present invention, the second particle may have a diameter of 100 nm or less (greater than 0).

[0016] In addition, according to the present invention, one specific solvent included in the solution may be included in a volume ratio of less than 12% (more than 0) of the total solvent.

[0017] Additionally, according to the present invention, the first particle can be charged.

[0018] Additionally, according to the present invention, the first color may be white, and the second color may be at least one of cyan, magenta, yellow, and black, or at least one of red, green, blue, and white.

[0019] An electrophoretic display according to the invention for solving the above problem comprises: a first electrode layer; a second electrode layer formed to face the first electrode layer; and an electrophoretic driving layer formed between the first electrode layer and the second electrode layer; wherein the electrophoretic driving layer comprises: a binder; and at least one capsule disposed within the binder; wherein the capsule comprises: a color-variable ink whose color changes by application of an electric field; and a capsule wall surrounding the color-variable ink; wherein the color-variable ink comprises: first particles comprising a pigment of a first color; a fluid in which a dye of a second color is saturatedly dissolved in a solution; and second particles in a colloidal form of a second color in which the dye is supersaturated and not dissolved in the solution; wherein the first particles and the second particles can move in opposite directions by application of the electric field.

[0020] In addition, according to the present invention, the solution is a mixture of two or more solvents, and at least one solvent among the solvents mixed in the solution may have a solubility in water of 2 wt% to 8 wt% at 20°C.

[0021] Additionally, according to the present invention, the dielectric constant of the solution may be 4 to 6.

[0022] Additionally, according to the present invention, the solution may be a mixture of Isopar M and nitroethane in a volume ratio of 7:3 to 8:2.

[0023] Additionally, according to the present invention, 1 wt% to 4 wt% of the dye can be dissolved in the fluid.

[0024] Additionally, according to the present invention, the second particle may be formed of 1 wt% to 5 wt% of the dye in the form of a fluid colloid.

[0025] Additionally, according to the present invention, the second particle may have a diameter of 100 nm or less (greater than 0).

[0026] In addition, according to the present invention, one specific solvent included in the solution may be included in a volume ratio of less than 12% (more than 0) of the total solvent.

[0027] According to the spirit of the present invention for solving the above problem, a method for manufacturing an electrophoretic display includes the steps of forming an electrophoretic driving layer using a color-variable ink composition whose color changes by application of an electric field; and forming a first electrode layer and a second electrode layer on top and bottom of the driving layer; wherein the step of forming the electrophoretic driving layer may include the steps of: forming a dispersion by mixing a pigment of a first color coated with a charge into a solvent; supersaturating a solution containing two or more solvents mixed in a volume ratio of 7:3 to 8:2 with a dye of a second color to form a fluid including second particles in a colloidal form of a second color that exist in an undissolved state in the solution; forming a color-variable ink by mixing the dispersion and the fluid including the second particles; and forming the electrophoretic driving layer by encapsulating using the color-variable ink.

[0028] According to various embodiments of the present invention as described above, by utilizing a color-variable ink composition that can be manufactured using a single particle method, an electrophoretic display capable of implementing a variety of colors while exhibiting excellent color clarity can be provided. Of course, the scope of the present invention is not limited by these effects.

[0029] FIG. 1 is an exemplary drawing showing the structure of an electrophoretic display according to one embodiment of the present invention.

[0030] Figure 2 is a drawing schematically showing the movement of particles within the display when an electric field is applied to the electrophoretic display of Figure 1.

[0031] Figure 3 is a process flow diagram sequentially illustrating a method for manufacturing an electrophoretic display according to one embodiment of the present invention.

[0032] Figure 4 is a process flow chart sequentially illustrating a method for manufacturing the electrophoretic driving layer illustrated in Figure 3.

[0033] Hereinafter, various preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0034] The embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. The following embodiments may be modified in various ways, and the scope of the present invention is not limited to the following embodiments. Rather, these embodiments are provided to more faithfully and completely explain the present disclosure and to fully convey the spirit of the present invention to those skilled in the art. In addition, the thickness and size of each layer in the drawings are exaggerated for convenience and clarity of explanation.

[0035] The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Furthermore, when used herein, the words "comprise" and / or "comprising" specify the presence of stated features, numbers, steps, operations, parts, elements, and / or groups thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, parts, elements, and / or groups thereof.

[0036] Hereinafter, embodiments of the present invention will be described with reference to drawings schematically illustrating ideal embodiments of the present invention. In the drawings, variations in the shapes depicted may be expected, for example, depending on manufacturing techniques and / or tolerances. Therefore, embodiments of the present invention should not be construed as limited to the specific shapes of the regions depicted herein, but should include, for example, variations in shapes resulting from manufacturing processes.

[0037] FIG. 1 is an exemplary drawing showing the structure of an electrophoretic display according to one embodiment of the present invention, and FIG. 2 is a drawing schematically showing the driving of particles within the display when an electric field is applied to the electrophoretic display of FIG. 1.

[0038] Referring to FIG. 1, an electrophoretic display (100) according to one embodiment of the present invention includes a first electrode layer (10), a second electrode layer (20), and an electrophoretic driving layer (30). The second electrode layer (20) is formed to face the first electrode layer (10), and the electrophoretic driving layer (30) is formed between the first electrode layer (10) and the second electrode layer (20).

[0039] The first electrode layer (10) and the second electrode layer (20) are implemented as front electrodes in a planar shape, and examples of the conductive material forming the first electrode layer (10) and the second electrode layer (20) include metals or transparent conductive oxides such as ITO. The first electrode layer (10) and the second electrode layer (20) are not limited to the term and may be implemented as a transparent conductive material as well as a translucent conductive material.

[0040] The electrophoretic driving layer (30) is composed of a binder (40) and at least one capsule (31) disposed within the binder (40). The capsule (31) includes a color-variable ink (33) whose color changes by application of an electric field and a capsule wall (32) surrounding the color-variable ink (33). At least one capsule (31) can be fixed between the first electrode layer (10) and the second electrode layer (20) by the binder (40).

[0041] The material forming the capsule wall (32) may include, for example, polyvinyl alcohol, polyvinyl acetate, cellulose derivatives, gelatin, acacia, carrageenan, arginate, urea, urethane, melanin, and mixtures thereof. The material forming the binder (40) may include, for example, polyacrylate, polyurethane, polyester, polyolefin, and mixtures thereof.

[0042] The particles included in the color-variable ink (33) are particles that can move by an electric field, and may be, for example, particles having a positive (+) or negative (-) charge, or particles having a zeta charge. Alternatively, they may be magnetic particles having magnetism. These particles exist in a uniformly dispersed form within the capsule (31). At this time, as illustrated in FIG. 2, when an electric field is applied to the first electrode layer (10) and the second electrode layer (20), various colors can be realized due to the movement of the particles by the electric field.

[0043] In the present invention, the color-variable ink (33) can be manufactured using a color-variable ink composition using a single particle method. Typically, using the single particle method, dyes of various colors can be dissolved in a solvent to produce a fluid of various colors. However, to vividly display the colors of the fluid, a large amount of dye must be dissolved. Nevertheless, when a specific electrophoretic particle moves to the upper electrode, the color of the colored particles and the dye color of the fluid are mixed, resulting in a lower contrast ratio than with the multi-particle method.

[0044] To solve this problem, in the present invention, two types of solvents are mixed at a certain volume ratio to increase the solubility of the dye while controlling the dielectric constant of the entire fluid not to increase significantly, thereby improving the clarity of color compared to the prior art.

[0045] Specifically, a color-variable ink composition for producing a color-variable ink (33) includes first particles (36) containing a pigment of a first color, a fluid (34) in which a dye of a second color is saturated and dissolved in a solution, and second particles (38) in the form of a colloid of a second color in which the dye is supersaturated and exists in an undissolved state in the solution.

[0046] Hereinafter, in the present invention, the fluid (34) means a mixture of a second color dye and the entire solution (i.e., the entire solvent contained within the fluid). The solution means a mixture of two or more solvents. The solvent means a single substance for dissolving the dye.

[0047] The fluid (34) includes a solution that dissolves a dye, and in order to improve the dye solubility, the solution includes a mixture of two or more solvents. At least one solvent among the solvents mixed in the solution must have a solubility in water of 2 wt% to 8 wt% at 20°C. Here, a substance having high solubility in water usually has some hydrophilicity even if it is a fat-soluble solvent. This property allows the solubility of the dye to be controlled. If the solvent has hydrophilic properties, it means that it has solubility in water. The higher the solubility of the solvent in water, the higher the solubility of the dye. If the solubility of the solvent in water is very high, the polarity increases, the dielectric constant of the medium increases, and the electrophoretic properties of the particles may be hindered. For this reason, the solubility of the solvent in water must be appropriately controlled.

[0048] If the solubility in water is less than 2 wt%, the polarity is low and there is no effect of improving the solubility of the ink dye. On the other hand, if it exceeds 8 wt%, the solubility of the ink dye is good, but the dielectric constant of the solvent is high, which affects particle migration during electric driving.

[0049] The dielectric constant of the above solution should be 4 to 6. If the dielectric constant is less than 4, the dielectric constant of the fluid (34) becomes too low, thereby lowering the characteristics of the electrophoretic driving layer (30). On the other hand, if the dielectric constant exceeds 6, the dielectric constant of the fluid (34) becomes too high, making it difficult to use it as the electrophoretic driving layer (30).

[0050] For example, the solvent may be used by mixing Isopar M and nitroethane in an appropriate volume ratio. At this time, Isopar M and nitroethane may be mixed in a volume ratio of 7:3 to 8:2. Here, the volume ratio may be controlled so that the volume of Isopar M is greater than the volume of nitroethane in the order described.

[0051] If the volume ratio of Isopar M and Nitroethane deviates from 7:3 to 8:2, the above-mentioned solubility and dielectric constants are not satisfied, and thus the solvent in which they are mixed cannot be used as an electrophoretic driving layer (30). Therefore, the volume ratio of Isopar M and Nitroethane must be controlled to satisfy 7:3 to 8:2.

[0052] A dye having a second color is dissolved in the solution in the fluid (34). At this time, the dye may be dissolved in the aforementioned solution in an amount of 1 wt% to 4 wt%. This means that the dye is dissolved in the fluid (34) in an amount of 1 wt% to 4 wt%. The content of the dye present in the fluid (34) may vary depending on the solubility of the solution. The content of the dye having a second color that is saturated in the solvent is determined depending on the solubility of the solution.

[0053] When a dye having a second color is added to a fluid (34) in which the dye is saturated and dissolved in the solution in an amount greater than the above content, the dyes that are supersaturated and not dissolved in the solution form second particles (38) having the second color. The second particles (38) are formed in the form of a fluid-phase colloid of the dye that is supersaturated and not dissolved in the solution, and the second particles have a diameter of 100 nm or less (greater than 0).

[0054] The fluid (34) may contain second particles (38) having a content of 1 wt% to 5 wt%. If the content of the second particles (38) is less than 1 wt%, the color contrast effect due to improved solubility cannot be obtained. On the other hand, if the content of the second particles (38) exceeds 5 wt%, the number of second particles (38) present in the fluid (34) becomes relatively larger than that of the first particles (36). At this time, the second particles (38) may interfere with the first particles (36), making it difficult to clearly implement the first color.

[0055] One type of solvent (meaning one type of fluid specified above) included in the solution contained in the fluid (34) may be included in a volume ratio of less than 12% (more than 0) of the entire solvent. In the present invention, the entire solution means the solvent constituting the fluid (34). It means that the volume ratio of one type of solvent having high solubility among the solvents is included in less than 12%. In summary, the entire fluid (34) includes not only a dye saturated with a second color, but also a solvent mixed with pigment particles having a first color. At this time, one type of specified specific solvent among the solvents mixed in the solution may be included in a volume ratio of less than 12% (more than 0) of the entire solution, and if the volume ratio exceeds 12%, there is a problem that the dielectric constant of the fluid (34) increases, which interferes with electrophoresis and deteriorates color characteristics.

[0056] For example, the first particle (36) is charged with a positive (+) or negative (-) charge, and the second particle (38) can move in the opposite direction to the first particle (36) by application of an electric field. The second particle (38) is a particle generated by precipitation of a dye in a solvent, and a charge coating is not separately performed on the surface of the particle, but the second particle (38) has a relative charge by a dispersant mixed in the fluid (34). Here, the dispersant may be selected and used from among, for example, glycol ether, acetylene glycol, alkanolamide, sorbitol derivative, alkyl amine, quaternary amine, imidazoline, dialkyl oxide, and sulfosuccinate.

[0057] For example, the first color may be white, and the second color may be at least one of cyan, magenta, yellow, and black, or at least one of red, green, blue, and white. Particles that emit these colors may be implemented using, for example, the following materials.

[0058] For example, it can be implemented as white particles including metal inorganic particles including TiO2, MgO, ZnO, CaO or ZrO2 or organic compounds thereof. And it can be implemented as colored particles including inorganic pigments such as iron oxide, CrCu, carbon black, etc. The dye can include colors other than black such as phthalocyanine blue, phthalocyanine green, diarylide yellow, diarylide AAOT yellow, and quinacridone, azo, rhodamine, etc.

[0059] Hereinafter, a method for manufacturing an electrophoretic display (100) using the aforementioned color-variable ink (33) will be described with reference to drawings.

[0060] FIG. 3 is a process flow chart sequentially illustrating a method for manufacturing an electrophoretic display according to one embodiment of the present invention, and FIG. 4 is a process flow chart sequentially illustrating a method for manufacturing an electrophoretic driving layer illustrated in FIG. 3.

[0061] First, referring to FIG. 3, a method (S100) for manufacturing an electrophoretic display (100) according to one embodiment of the present invention includes a step (S110) of forming an electrophoretic driving layer (30) and a step (S120) of forming a transparent electrode layer.

[0062] The step (S110) of forming an electrophoretic driving layer (30) means forming an electrophoretic driving layer (30) using a color-variable ink composition whose color changes by application of an electric field. The step (S110) of forming an electrophoretic driving layer (30) can be formed, for example, by a method as illustrated in FIG. 4.

[0063] The step (S110) of forming an electrophoretic driving layer (30) includes a step of forming a dispersion (S111), a step of forming a fluid (S112), a step of forming a color-variable ink (S113), and a step of forming an electrophoretic driving layer (30) (S114).

[0064] Specifically, the step of forming a dispersion (S111) includes a step of preparing a dispersion by mixing a pigment of a first color coated with a charge into a solvent. Here, the mixing refers to a process of mixing and dispersing a pigment in a solvent.

[0065] The step of forming a fluid (S112) includes a step of supersaturating a solution containing two or more solvents mixed in a volume ratio of 7:3 to 8:2 with a dye of a second color, thereby producing a fluid (34) including second particles in a colloidal form of a second color that exist in an undissolved state in the solution.

[0066] The step of forming a color-variable ink (S113) includes a step of mixing a prepared dispersion and a fluid containing supersaturated second particles in a solution at a weight ratio of 1:1, and stirring the mixture for 5 to 7 hours or more to prepare a color-variable ink.

[0067] Finally, the step (S114) of forming an electrophoretic driving layer (30) includes a step of manufacturing the electrophoretic driving layer (30) by encapsulating using the manufactured color-variable ink. Hereinafter, the method for the encapsulation is a known technology, so a detailed description thereof will be omitted.

[0068] By forming a first electrode layer (10) and a second electrode layer (20) on the upper and lower portions of the electrophoretic driving layer (30) formed by this method, an electrophoretic display (100) according to one embodiment of the present invention can be provided.

[0069] Below, in order to confirm the dielectric constant and color characteristics of the electrophoretic driving layer by the color-variable ink composition of the present invention, various types of ink compositions were prepared and their characteristics are summarized in Table 1 below.

[0070] Experimental Example 1

[0071] A dispersion containing the white pigment was prepared by mixing / dispersing a white pigment (200 g) coated with a charge, Span85 (10 g), poly(isobutylene) (10% w / w 20 g), and Isopar M (500 mL). In addition, a black dye (6 g) was dissolved in Isopar M (100 g) to prepare a fluid.

[0072] The prepared white pigment dispersion and black dye fluid were mixed in a weight ratio of 1:1 and stirred for more than 6 hours to prepare an electrophoretic ink composition.

[0073] Experimental Example 2

[0074] A dispersion containing the white pigment was prepared by mixing / dispersing a white pigment (200 g) coated with a charge, Span85 (10 g), poly(isobutylene) (10% w / w 20 g), and Isopar M (500 mL). In addition, a succinic anhydride polyisobutenyl derivative dispersant (0.1 g) and a black dye (6 g) were dissolved in Isopar M (100 g) to prepare a fluid.

[0075] The prepared white pigment dispersion and black dye fluid were mixed in a weight ratio of 1:1 and stirred for more than 6 hours to prepare an electrophoretic ink composition.

[0076] Experimental Example 3

[0077] A dispersion of white pigment (200 g) with a charge-coated white pigment was prepared by mixing / dispersing Span85 (10 g), poly(isobutylene) (10% w / w 20 g), and Isopar M (500 mL). In addition, a black dye (6 g) was dissolved in a mixed solvent (100 g) composed of Isopar M: Nitroethane = 8:2 by volume ratio by ultrasonic treatment at 40°C, and then the temperature was lowered to 15°C to prepare colloidal particles and a dye solution.

[0078] The prepared white pigment dispersion and black dye fluid were mixed in a weight ratio of 1:1 and stirred for more than 6 hours to prepare an electrophoretic ink composition.

[0079] Experimental Example 4

[0080] A dispersion containing a white pigment (200 g) was prepared by mixing / dispersing a white pigment coated with Span85 (10 g), poly(isobutylene) (10% w / w 20 g), and Isopar M (500 mL). In addition, a black dye (6 g) and a succinic anhydride polyisobutenyl derivative dispersant (0.1 g) were dissolved in a mixed solvent (100 g) consisting of Isopar M: Nitroethane = 8:2 by volume ratio by ultrasonic treatment at 40°C, and then the temperature was lowered to 15°C to prepare colloidal particles and a dye solution.

[0081] The prepared white pigment dispersion and black dye fluid were mixed in a weight ratio of 1:1 and stirred for more than 6 hours to prepare an electrophoretic ink composition.

[0082] Experimental Example 5

[0083] A dispersion containing a white pigment (200 g) coated with a charge was prepared by mixing / dispersing Span85 (10 g), poly(isobutylene) (10% w / w 20 g), and Isopar M (500 mL). In addition, a black dye (6 g) and a succinic anhydride polyisobutenyl derivative dispersant (0.1 g) were dissolved in a mixed solvent (100 g) consisting of Isopar M: Nitroethane = 7:3 by volume ratio by ultrasonic treatment at 40°C, and then the temperature was lowered to 15°C to prepare colloidal particles and a dye solution.

[0084] The prepared white pigment dispersion and black dye fluid were mixed in a weight ratio of 1:1 and stirred for more than 6 hours to prepare an electrophoretic ink composition.

[0085] In order to evaluate the dielectric constant and color characteristics of the electrophoretic ink compositions according to the comparative examples and examples described above, cells were manufactured so that the distance between the electrodes of double-sided ITO glass was maintained at 25 μm. The electrophoretic ink compositions manufactured between the electrodes were each filled, and the color characteristics were evaluated by driving the voltage on both electrode surfaces. The dielectric constant of the electrophoretic ink compositions was measured using a Liquid Dielectric constant Meter (Model 871, Sanyo Trading Co., Ltd), and the measurement was performed at 25 degrees at 50 Hz. Positive and negative voltages of 7 V were repeatedly applied for 10 seconds (sec). The color contrast summarized in the table below is an index representing the difference in color reflectance when implementing white reflectance and black.

[0086] Dielectric constant White Black Color Contrast Experimental example 12.53 23.50 4.25 5.53:1 Experimental example 22.7 1 26.75 2.80 9.55:1 Experimental example 34.75 26.20 0.98 26.73:1 Experimental example 44.9 2 30.83 1.0 23 0.26:1 Experimental example 56.20 25.24 2.05 12.30

[0087] Referring to Table 1 above, it was confirmed that the samples of Experimental Examples 1 and 2 of the present invention had a dielectric constant lower than 4, and thus the color contrast was low at 10:1 or less. On the other hand, the samples of Experimental Examples 3 and 4 of the present invention had a dielectric constant satisfying 4 to 6, and the color contrast was also confirmed to be significantly higher than the samples of Experimental Examples 1 and 2, at approximately 25:1 to 35:1.

[0088] In particular, in the case of Experimental Example 4, where a black dye was added to a solvent mixed with a volume ratio of Isopar M: Nitroethane of 8:2 and a small amount of a succinic anhydride polyisobutenyl derivative dispersant was added, it was confirmed that the color contrast effect was much better. However, in the case of the 7:3 solvent of Experimental Example 5, although the color contrast effect was higher than that of the samples of Experimental Examples 1 and 2, it was confirmed that the dielectric constant was high at 6 or higher, which deteriorated the characteristics of the electrophoretic medium.

[0089] As described above, a color-variable ink composition according to one embodiment of the present invention is prepared in the form of a solution by adding a dye expressing a second color in an amount greater than saturation to a solvent, and the dye not dissolved in the solvent exists as second particles in a colloidal form. These second particles exist as small dispersed particles that are larger than molecules but do not settle due to gravity.

[0090] The second particle dye precipitated in this way exists in a colloidal form, and moves in the opposite direction to the first particle when an electric field is applied due to the interaction between its own functional group and the charge control agent added in the fluid.

[0091] In typical electrophoretic display materials, solvents are typically non-polar and possess low dielectric constants. However, most of these solvents have the disadvantage of not being able to dissolve dyes well. Therefore, the present invention limits the composition of the solvent to two or more types, and one of them is a fluid that is partially soluble in water and exhibits good dye solubility. However, colloidal dye particles that are not dissolved in the solvent must be present. If the amount of solvent used is high, the overall solvent dielectric constant increases, which causes various disadvantages. Therefore, restrictions are placed on the mixing ratio of the solvents and the overall solvent dielectric constant when mixed.

[0092] In this patent, the concentration of a saturated dye that exhibits a second color is reduced as much as possible, so that the first color and the second color are not mixed, thereby enabling the electrophoretic pigment particles that reflect the first color to have a high reflectivity, and by causing the precipitated colloidal dye that exhibits the second color to move in the opposite direction to the first particles that reflect the first color, the vividness of the second color is maintained, thereby enabling the implementation of various colors with excellent contrast.

[0093] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will appreciate that various modifications and equivalent alternative embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. A color-variable ink composition applicable to an electrophoretic display whose color changes by application of an electric field, The above color-variable ink composition, A first particle comprising a pigment of a first color; A fluid in which a second color dye is saturated and dissolved in a solution; and A second particle in the form of a colloid of a second color, wherein the dye is supersaturated and exists in an undissolved state in the solution; The first particle and the second particle move in opposite directions due to the application of the electric field. Color-variable ink composition.

2. In paragraph 1, The above solution is a mixture of two or more solvents. Color-variable ink composition.

3. In paragraph 2, At least one solvent mixed in the above solution has a solubility in water of 2 wt% to 8 wt% at 20°C. Color-variable ink composition.

4. In paragraph 1, The dielectric constant of the above solution is 4 to 6, Color-variable ink composition.

5. In paragraph 1, The above solution is a mixture of Isopar M and nitroethane in a volume ratio of 7:3 to 8:

2. Color-variable ink composition.

6. In paragraph 1, The above fluid contains 1 wt% to 4 wt% of the dye dissolved therein. Color-variable ink composition.

7. In paragraph 1, The second particle is composed of 1 wt% to 5 wt% of the dye in the form of a fluid colloid. Color-variable ink composition.

8. In paragraph 1, The second particle has a diameter of 100 nm or less (greater than 0), Color-variable ink composition.

9. In paragraph 2, One type of solvent included in the above solution is included in a volume ratio of less than 12% (greater than 0) of the total solvent. Color-variable ink composition.

10. In paragraph 1, The above first particle is charged, Color-variable ink composition.

11. In paragraph 1, The above first color is white, The second color is at least one of cyan, magenta, yellow and black, or at least one of red, green, blue and white. Color-variable ink composition.

12. First electrode layer; A second electrode layer formed to face the first electrode layer; and An electrophoretic driving layer formed between the first electrode layer and the second electrode layer; The above electrophoretic driving layer is composed of a binder; and at least one capsule disposed within the binder; The capsule includes a color-variable ink whose color changes by application of an electric field; and a capsule wall surrounding the color-variable ink; The above color-variable ink is, A first particle comprising a pigment of a first color; A fluid in which a second color dye is saturated and dissolved in a solution; and A second particle in the form of a colloid of a second color, wherein the dye is supersaturated and exists in an undissolved state in the solution; The first particle and the second particle move in opposite directions due to the application of the electric field. Electrophoretic display.

13. In paragraph 12, The above solution is a mixture of two or more solvents, and at least one solvent among the solvents mixed in the solution has a solubility in water of 2 wt% to 8 wt% at 20°C. Electrophoretic display.

14. In paragraph 12, The dielectric constant of the above solution is 4 to 6, Electrophoretic display.

15. In paragraph 12, The above solution is a mixture of Isopar M and nitroethane in a volume ratio of 7:3 to 8:

2. Electrophoretic display.

16. In paragraph 12, The above fluid contains 1 wt% to 4 wt% of the dye dissolved therein. Electrophoretic display.

17. In paragraph 12, The second particle is composed of 1 wt% to 5 wt% of the dye in the form of a fluid colloid. Electrophoretic display.

18. In paragraph 12, The second particle has a diameter of 100 nm or less (greater than 0), Electrophoretic display.

19. In paragraph 12, One type of solvent included in the above solution is included in a volume ratio of less than 12% (greater than 0) of the total solvent. Electrophoretic display.

20. A step of forming an electrophoretic driving layer using a color-variable ink composition whose color changes by application of an electric field; and A step of forming a first electrode layer and a second electrode layer on the upper and lower portions of the driving layer; The step of forming the above electrophoretic driving layer is: A step of forming a dispersion by mixing a first color pigment coated with a charge into a solvent; A step of forming a fluid including second particles in a colloidal form of a second color that exist in an undissolved state in the solution by supersaturating a dye of a second color in a solution containing two or more solvents mixed in a predetermined ratio; A step of forming a color-variable ink by mixing a fluid containing the above dispersion and the second particles; and A step of forming the electrophoretic driving layer by encapsulating using the color-variable ink; comprising; Method for manufacturing an electrophoretic display.

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