JP2006292878A - Electrophoretic display element and electrophoretic display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophoretic display element with which excellent display characteristics are obtained, and an electrophoretic display device. <P>SOLUTION: A particle dispersion liquid, composed of a dispersion medium 2 and a plurality of charged coloring particles 1, is filled in a space surrounded by a first substrate 3a and a second substrate 3b, which are disposed in a state of being separated with a prescribed distance, and a partition wall member 5 disposed in a gap between the first substrate 3a and the second substrate 3b. At the same time, by making the zeta potential range of the inner wall surface of the space be a range in which no flow of the particle dispersion liquid along the inner wall surface of the space is produced, unstable migration behavior of the charged coloring particles 1 is stabilized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophoretic display element and an electrophoretic display device that perform display by moving charged particles, and more particularly to a configuration for stabilizing the migration operation of charged particles.

  In recent years, with the development of information equipment, the need for low power consumption and thin display devices is increasing, and research and development of display devices that meet these needs are actively conducted. In particular, reflective display devices are expected from the viewpoints of low power consumption and reduction of visual burden. An electrophoretic display device is known as an example of such a reflective display device.

  Here, the electrophoretic display device includes an electrophoretic display element configured to perform display by causing charged particles to migrate between electrodes by an electric field (electrostatic force). Here, as such an electrophoretic display element, an electric field in a direction perpendicular to the substrate is generated by switching between the pixel electrode and the common electrode arranged to face each other, and the charged particles are placed on the upper and lower substrates. There is an up-and-down type electrophoretic display element that is moved between them (for example, see Patent Document 1).

  In addition, switching is performed between the pixel electrode and the common electrode formed on one of the opposed substrates, and an electric field in the horizontal direction is generated with respect to the substrate, so that the charged particles are directed to the substrate. There is an in-plane electrophoretic display element that is moved in the horizontal direction (see, for example, Patent Document 2).

  In addition, in such an in-plane type electrophoretic display element, when used in a reflective electrophoretic display device, either one of a pair of opposing substrates superposed while maintaining a constant gap A reflective electrophoretic display element configured to display light and dark by forming a reflective layer on the opposite surface of the substrate and moving, for example, black charged particles dispersed in a transmissive dispersion medium on the reflective layer. Yes (for example, see Patent Document 3). Further, as such a reflection type electrophoretic display element, there is a structure in which a pixel electrode or a common electrode is formed on the lower side of the reflection layer, that is, between the base material of the reflection substrate (for example, see Patent Document 4). ).

  FIG. 3 shows a schematic configuration of a conventional in-plane electrophoretic display element. A particle dispersion liquid composed of colored charged particles 11 and dispersion medium 12 which are fine particles is separated by a partition wall 15 into a predetermined shape. When a voltage is applied between the pair of electrodes 14a and 14b formed on one substrate 13b by the switching means 18 between the pair of substrates 13a and 13b held at an interval, the colored charged particles 11 themselves show. It is attracted to an electrode that exhibits a potential opposite to the electric charge. FIG. 3 shows a case where the colored charged particles 11 are positively charged. Here, by coloring the colored charged particles 11 and using a reflective material for the insulating layer 16 or the first electrode 14a, display can be performed as a reflective electrophoretic display element.

JP-A-9-185087 JP 49-24695 A JP-A-11-202804 JP 2003-161966 A

  By the way, many of the solid interfaces in contact with the liquid are electrically positively or negatively charged by dissociation of polar groups existing on the surface or adsorption of ions existing in the liquid. Therefore, an ion cloud called a diffusion electric double layer exists near the solid interface. In this ion cloud, there are overwhelmingly more electrolyte ions having a charge opposite in polarity to the surface charge of the solid interface than ions having the same polarity as the surface charge of the solid interface.

  Here, when the solid in contact with the liquid is a microparticle floating in the solution, when an electric field is applied to the system from the outside, the microparticle will be electrically charged in the liquid toward the electrode having the opposite polarity to the surface charge. Run.

  Therefore, in the conventional electrophoretic display element using charged particles that are fine particles, the basis of the particle movement (migration) phenomenon is the formation of a diffusion electric double layer near the interface between the charged particles and the liquid dispersion medium. Be deeply involved.

  By utilizing the phenomenon as described above, microparticles are electrophoresed in a liquid placed between equivalent electrodes facing each other, the migration speed of the microparticles, the strength of the voltage (electric field) applied between the electrodes, The surface potential of the microparticles calculated taking into account the hydrodynamic effects (liquid viscosity, dielectric constant, etc.) is called the zeta (ζ) potential.

  Therefore, the value of the zeta potential is an important parameter related to the display characteristics of the electrophoretic display element using charged particles, as can be understood from the calculation method. That is, when designing an electrophoretic display element, a dispersion medium that is a liquid for dispersing charged particles and charged particles is designed based on the zeta potential of the charged particles in the particle dispersion.

  Therefore, when an in-plane type electrophoretic display element is prepared, the zeta potential of the particle dispersion prepared with the charged particles and the dispersion medium used in the electrophoretic display element is originally displayed on the electrophoretic display element. It is thought to be directly reflected in the characteristics.

  However, the zeta potential of the particle dispersion may not be directly reflected in the display characteristics of the electrophoretic display element and may exhibit unstable behavior. Furthermore, there is an electrophoretic display device in which the particle dispersion behaves as if it has a surface charge having a polarity opposite to the polarity of the particle surface charge obtained by zeta potential measurement. If the unstable behavior in the particle dispersion medium becomes remarkable in this way, problems are likely to occur in the reproducibility of gradation of the electrophoretic display element and in-plane display uniformity, and good display characteristics are obtained. It was hard to get.

  Accordingly, the present invention has been made to solve such problems, and an object thereof is to provide an electrophoretic display element and an electrophoretic display device capable of obtaining good display characteristics. .

  The present invention includes a first substrate and a second substrate disposed in a state where a predetermined gap is provided, a partition member disposed in a gap between the first substrate and the second substrate, the first substrate and the second substrate, A dispersion medium filled in a space surrounded by the partition wall member and a particle dispersion composed of a plurality of charged particles, and a first electrode and a second electrode disposed facing the space, and the space between the electrodes In an electrophoretic display element that performs display by changing the distribution of the charged particles by an electric field generated by a voltage applied to the zeta potential range of the inner wall surface of the space along the inner wall surface of the space when a voltage is applied. The particle dispersion is in a range in which no flow occurs.

  As in the present invention, a dispersion medium and a space in a space surrounded by a first substrate and a second substrate arranged with a predetermined gap and a partition member arranged in a gap between the first substrate and the second substrate By charging a particle dispersion composed of a plurality of charged particles and setting the range of the zeta potential of the inner wall surface of the space to a range in which the flow of the particle dispersion liquid along the inner wall surface of the space does not occur, Unstable electrophoretic behavior can be stabilized and good display characteristics can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an electrophoretic display element according to an embodiment of the present invention. As shown in FIG. 1, the electrophoretic display element is a pair arranged with a predetermined gap therebetween. This is a partition member for keeping the gap between these substrates 3a and 3b constant, and the transparent counter substrate 3a that is the first substrate on the observer side that is the substrate and the electrode substrate 3b that is the second substrate on the opposite side. Colored charged particles as an example of the partition wall 5, the transparent dispersion medium 2 filled in the space surrounded by the substrates 3a and 3b and the partition wall 5, and a plurality of fine particles dispersed in the dispersion medium 2 1 is provided.

  This electrophoretic display element has pixels arranged in a matrix on a substrate, and the partition wall 7 also has a function of preventing the colored charged particles 1 from moving between adjacent pixels.

  Further, a first electrode 4a and a second electrode 4b to which a voltage different from that of the first electrode 4a is applied are formed on the electrode substrate 3b, and the colored charged particles 2 are formed by the first and second electrodes 4a and 4b. By forming an electric field that controls the spatial distribution of the colored charged particles 2, the colored charged particles 2 can be moved in the horizontal direction between the first electrode 4a and the second electrode 4b.

  In FIG. 1, reference numeral 6 denotes an insulating layer which is formed on the electrode substrate 3b and insulates the first and second electrodes 4a and 4b. Reference numeral 7 denotes the surfaces of the substrates 3a and 3b and the partition 7, that is, the partition 5 and the substrate 3a. 3 is a coating layer that is provided on the inner wall surface of the space surrounded by 3b and is in contact with a particle dispersion liquid composed of colored charged particles 1 and a dispersion medium 2 in which the colored charged particles 1 are dispersed. Reference numeral 8 denotes switching means for applying voltages having different polarities to the first and second electrodes 4a and 4b formed on one substrate 3b.

  In FIG. 1, the first electrode 4a and the second electrode 4b are provided on the electrode substrate 3a with the insulating layer 6 therebetween, but the structure is not particularly limited. A second electrode 4b may be provided.

  Here, in this electrophoretic display element, by applying a voltage between the first electrode 4a and the second electrode 4b, the colored charged particles 1 are moved along the substrates 3a and 3b to the first electrode side or the second electrode side. The display is performed by moving to the electrode side and changing the distribution of the colored charged particles 1. That is, the electrophoretic display element in the present embodiment is of a horizontal movement type in which the colored charged particles 1 move along the substrates 3a and 3b.

  For example, when black charged particles 1 that are colored white and have a positive charge are used, and a positive voltage is applied to the first electrode 4a and a negative voltage is applied to the second electrode 4b, FIG. As shown in (a), the colored charged particles 1 are distributed so as to cover the second electrode 4b. In this case, when viewed from the normal direction of the upper second substrate surface, the entire pixel appears white.

  When a negative voltage is applied to the first electrode 4a and a positive voltage is applied to the second electrode 4b, the colored charged particles 1 are distributed along the first electrode 4a as shown in FIG. Therefore, when viewed from the normal direction of the second substrate surface, the entire pixel appears black. In addition, switching the voltage can change the state of black and white.

  By the way, the present inventor has found that the cause of the unstable migration behavior of the colored charged particles 1 as described above is due to the electroosmotic flow accompanying the generation of the surface potential in the electrophoretic display element structure. .

  That is, in the electrophoretic display element, as described above, surface charges derived from the formation of the diffusion electric double layer are generated between the colored charged particles 1 and the dispersion medium 2, but the particle dispersion is retained. Also on the surface of the structure for the purpose of contact, the surface charge is generated by contacting the dispersion medium 2 and generating a diffusion electric double layer.

  When the solid surface in contact with the liquid dispersion medium 2 is fixed as a structure in this way, when an electric field is applied to the system from the outside, electrolyte ions having a polarity opposite to the solid surface charge existing on the solid surface are generated. , It migrates in the liquid toward the electrode of the opposite polarity.

  Here, when the value of the solid surface charge is large, the flow due to such electrolyte ions also increases, and as a result, as shown by the arrow B in FIG. Then, when such electroosmotic flow is generated, the colored charged particles 1 which are about to move in the direction of the arrow A due to the electric field generated between the electrodes 14A and 14B are unstable. Electrophoretic behavior occurs. In addition, the flow of the liquid generated along with the migration of the electrolyte ions is called an electroosmotic flow.

  Accordingly, the present inventors have come to the idea that stable electrophoretic behavior of the colored charged particles 1 can be obtained by reducing the generation of electroosmotic flow, and the dispersion medium 2 used for the in-plane electrophoretic display element. The relationship between the zeta potential generated when contacting with the coating layer 7 on the inner wall surface and the electroosmotic flow generation was analyzed using particles having a zeta potential of 0 with respect to the dispersion medium 2 as monitor particles.

  As a result, when the dispersion 2 capable of developing an electrophoretic phenomenon is used for charged particles in a range usable in the working system, the zeta potential of the inner wall surface coating material is −10 mV or less, or 10 mV or more. It was found that osmotic flow actively moves the monitor particles. It was also found that when the zeta potential of the inner wall surface coating material is in the range of −5 mV to 5 mV, the electroosmotic flow is suppressed and the monitor particles do not move.

  Therefore, the inventor of the present invention stabilizes the unstable migration behavior of the colored charged particles 1 and obtains good display characteristics, so that the zeta on the inner wall surface of the space surrounded by the partition walls 5 and the substrates 3a and 3b can be obtained. The potential range was set to a range in which the flow of the particle dispersion along the inner wall surface of the space did not occur.

  Specifically, the range of the zeta potential on the inner wall surface of the space was set to a range of −10 mV to 10 mV. In addition, it is preferable that the range of the zeta potential on the inner wall surface of this space is in the range of −5 mV to 5 mV.

  By setting the zeta potential range of the inner wall surface of the space to such a range, the generation of electroosmotic flow can be suppressed, and the unstable electrophoretic behavior of the colored charged particles 1 is eliminated. As a result, the zeta potential of the particle dispersion can be directly reflected in the display characteristics of the electrophoretic display element, and an in-plane type electric device having good display characteristics realizing more stable gradation. The electrophoretic display element can be designed and created.

  In the present embodiment, it is preferable that the absolute value of the zeta potential at the interface between the colored charged particles 1 and the dispersion medium 2 is 15 mV or more. Can be made less susceptible to zeta potential.

  Since the zeta potential at such an inner wall interface is determined by the combination of the coating layer 7 and the dispersion medium 2, the material used for the coating layer 7 constituting the inner wall surface of the space has high transparency. In addition to the thin film, it must be selected by a combination of the dispersion medium 2 and an additive to the dispersion medium 2 so that the zeta potential is in the range of −10 mV to 10 mV, preferably in the range of −5 mV to 5 mV.

  For this reason, specific examples of the material used for the coating layer 7 include polyimide resin, polyurethane resin, polyester resin, polyacrylate resin, polymethacrylate resin, polycarbonate resin, polyarylate resin, novolac resin, epoxy resin, and the like. Although selected, it is not particularly limited as long as it is within the scope of the present invention.

  The colored charged particles 1 are insoluble in the solvent in combination with the solvent used as the dispersion medium 2 and can exist in a dispersed state in the solvent, and the zeta potential is within the above range. It must be selected by a combination of the dispersion medium 2 and the additive to the dispersion medium 2 so that

  For this reason, the components of the colored charged particles 1 may be any of inorganic coloring materials, organic pigments, polymer materials, and mixtures thereof, and are not particularly limited as long as they are within the scope of the present invention. The colored charged particles 1 can be colored according to the display method of the electrophoretic display element to be used.

  Furthermore, as the colored charged particles 1, commercially available particles can be used. Examples of such commercially available particles include Micropearl (manufactured by Sekisui Chemical Co., Ltd.), Natoko Spacer Particles (manufactured by Natco Corporation). , Epocolor particles (produced by Nippon Shokubai Chemical Co., Ltd.), Chemisnow (produced by Soken Chemical Co., Ltd.), Tospearl (produced by GE Toshiba Silicone Co., Ltd.), Techpolymer (Sekisui Chemicals Co., Ltd.), etc. It is not limited to these.

  In addition, the surface of the commercially available particles can be used by coating a resin layer. Here, as the resin used for such particle coating, specifically, polyamide resin, polyimide resin, polyurethane resin, polyester resin, polyacrylate resin, polymethacrylate resin, polycarbonate resin, polyarylate resin, novolac resin, polystyrene Resins, epoxy resins, polyvinyl chloride, polyfluorinated ethylene resins and the like can be mentioned, but are not particularly limited as long as they are within the scope of the present invention.

  Furthermore, the average particle diameter of the colored charged particles 1 is preferably in the range of 0.1 μm to 5 μm. In the present embodiment, if necessary, particles can be classified by a known method such as dry classification or wet classification.

  The dispersion medium 2 and the additive added to the dispersion medium 2 affect the zeta potential on the surface of the coating agent 7 and the colored charged particles 1 in combination with the coating agent 7 and the colored charged particles 1. Therefore, it must be selected by a combination of the coating agent 7 and the colored charged particles 1.

  For this reason, as the solvent of the dispersion medium 2, a highly insulating organic solvent having low electrical conductivity, specifically, aromatic hydrocarbon solvents such as benzene, ethylbenzene, dodecylbenzene, toluene, xylene, naphthenic hydrocarbons, trichloro, etc. Halogenated hydrocarbon solvents such as trifluoroethylene and ethyl bromide, silicon oil, high-purity petroleum, and the like can be mentioned. Among them, aliphatic hydrocarbon solvents are preferably used. Specifically, Isopar G, H, M , L (all manufactured by Exxon Chemical Co., Ltd.), Shellsol (Showa Shell Japan), IP Solvents 1016, 1620, 2028, 2835 (Idemitsu Petrochemical). These can be used alone or in admixture of two or more.

  Further, the dispersion medium 2 can be colored in a different color from the colored charged particles 1 in accordance with the display method of the electrophoretic display element to be used. The colorant is not particularly limited as long as it is an oil-soluble dye that can be dissolved in the solvent of the dispersion medium 2.

  Furthermore, as the particle dispersion, a rosin ester or a rosin derivative can be used for the purpose of increasing the charge amount of the colored charged particles 1 or imparting charging stability. Here, the rosin ester or rosin derivative is not particularly limited as long as it is soluble in the solvent of the dispersion medium. For example, gum rosin, wood rosin, tall oil rosin, rosin modified maleic acid, rosin modified pentaerythritol, rosin glycerin ester, partial Hydrogenated rosin methyl ester, partially hydrogenated rosin glycerin ester, partially hydrogenated rosin triethylene glycol ester, fully hydrogenated rosin pentaerythritol ester, maleic acid modified rosin ester, fumaric acid modified rosin ester, acrylic acid modified rosin ester, maleic acid Modified rosin pentaerythritol ester, fumaric acid modified rosin pentaerythritol ester, acrylic acid modified rosin glycerin ester, maleic acid modified rosin glycerin ester, fuma Acid-modified rosin glycerin esters, acrylic acid-modified rosin glycerin ester.

  In the present embodiment, these charge control agents and charge stabilizers can be used alone or in combination of two or more.

  Further, in the dispersion liquid, additives other than the dispersion stabilizer according to the present embodiment, such as a charge control agent and a dissociation stabilizer, are provided for the purpose of increasing the charge amount of the colored charged particles 1 or imparting charge stability. It may be contained. Specifically, for example, cobalt naphthenate, zirconium naphthenate, copper naphthenate, iron naphthenate, lead naphthenate, manganese naphthenate, zinc naphthenate, cobalt octenoate, zirconium octenoate, iron octenoate, lead octenoate, Although metal soaps, such as nickel octenoate, manganese octenoate, and zinc octenoate, are mentioned, if it is in the range of the present invention, it will not be limited to these.

  On the other hand, the material of the transparent counter substrate 3a constituting the electrophoretic display element is not particularly limited as long as it has high transparency, and examples thereof include inorganic materials such as glass and quartz, and organic materials such as polymer films. be able to. In addition, the material of the electrode substrate 3b does not need to have particularly high transparency, and a stainless steel substrate having an insulating layer on the surface can also be used.

  The material of the first electrode 4a and the second electrode 4b is not particularly limited as long as it is a conductive material that can be patterned, and examples thereof include indium tin oxide (ITO), aluminum, and titanium.

  In the case where the first electrode 4a and the second electrode 4b are formed on the same plane of the electrode substrate 3b as shown in FIG. 1, the first electrode 4a is formed on the entire pixel partitioned by the partition wall 7, and the second The electrode 4b is formed in a state of being insulated from the first electrode 4a via a material (insulating layer 6) that is insulative below the partition wall, but of course not limited thereto. Further, the electrodes 4a and 4b may be formed at different heights via the partition wall 5. In this case, if an insulating material is used for the partition 5 or the like, the electrodes 4a and 4b are insulated.

  Here, the shape of the partition wall 5 may be, for example, a trapezoidal shape, a curved side wall surface, or a bowl-like shape as a whole in addition to the rectangle shown in FIG. 1, and the partition wall 5 is made of polymer resin or the like. Can do. Specific examples include polyimide resins, polyester resins, polyacrylate resins, polymethacrylate resins, polycarbonate resins, polyarylate resins, novolac resins, and epoxy resins. Furthermore, the place where the second electrode 4b is disposed need not be limited to the structure where the partition 5 is disposed on the transparent substrate 3a side or the electrode substrate 3b side. For example, it may be a structure arranged on the pixel side surface of the partition wall 5 or at the center position of the partition wall 5.

  The material used for the insulating layer 6 is preferably a thin film in which pinholes are difficult to be formed. Specific examples include a highly transparent polyimide resin, polyester resin, polyacrylate resin, polymethacrylate resin, polycarbonate resin, polyarylate resin, novolac resin, and epoxy resin.

  When the electrophoretic display element of the present embodiment is a reflective electrophoretic display element, the insulating layer 6 may be provided with a function of a reflective layer. In this case, as a material for forming the insulating layer 6 Specific examples include a white scattering layer in which an acrylic resin or a urethane resin contains titanium oxide having a submicron particle size. Furthermore, it is possible to form a reflective electrophoretic display element by forming the first electrode 4a from a reflective material such as aluminum and using a highly transparent resin material for the insulating layer 6.

  Next, examples of the present embodiment and comparative examples will be described.

  In Examples and Comparative Examples, the zeta potential of the charged particles in the dispersion is determined by a laser zeta potential measuring device (ELS-6000 manufactured by Otsuka Electronics, ZetaPALS manufactured by Brookhaven, etc.) or a zeta potential measuring device using a microscopic electrophoresis method. (Zeecom, etc. manufactured by Microtech Co., Ltd.) can be used, but in this example and comparative examples, the zeta potential is measured by ZetaPALS manufactured by Brookhaven.

  Moreover, the zeta potential measurement of the material surface of the coat layer 7 can be measured using a cell for flat plate samples of a laser zeta potential measuring device (ELS-6000, manufactured by Otsuka Electronics Co., Ltd.). If the surface material of the coating layer 7 is applied to the surface of the sample cell and particles having a zeta potential of about 0 with respect to the dispersion medium are used as monitor particles, the movement of the particles due to the generated electroosmotic flow can be analyzed. Although the zeta potential on the surface of the coat layer can be measured, in the examples and comparative examples, the measurement is performed using a plate sample cell of a laser zeta potential measuring device (ELS-6000, manufactured by Otsuka Electronics Co., Ltd.).

  Furthermore, as the electrophoretic display element used for evaluating the electrophoretic characteristics in the examples and comparative examples, a reflective electrophoretic display element having the configuration shown in FIG. 1 is used. In this electrophoretic display element, white glass is used for the electrode substrate 3b, and the first electrode 4a is provided on the electrode substrate. Further, the region of the first electrode 4a corresponds to the plane defined by the partition walls 5, and is formed by vapor deposition of aluminum so as to be partitioned into square regions with a pitch of 90 μm.

  The second electrode 4b is provided around each first electrode 4a via an insulating layer 6. The width of the second electrode 4b is made of aluminum having a width of 5 μm so as to be covered with the partition wall 5. Yes. Further, the first electrode 4 a and the second electrode 4 b formed on the electrode substrate 3 b are insulated so as to be covered with the insulating layer 6. The insulating layer 6 is a polymethyl methacrylate resin having a thickness of 1 μm.

  Further, the partition wall 5 is provided on the second electrode 4b provided on the electrode substrate 3b, and this partition wall 5 is a gap between the insulating layer 6 provided on the electrode substrate 4b and the facing surface of the transparent counter substrate 3a. Is made of photosensitive epoxy resin so as to have a height of 15 μm and a width of 10 μm.

  Then, after forming a coat layer 7 on the surface of the electrode substrate 3b partitioned by the partition walls 5 and on one surface of the counter substrate 3a, the particle dispersion is filled into the space on the electrode substrate 3b. Then, the counter substrate 3a was fixed in contact with the partition walls 5 so that the coat layer 7 side of the transparent counter substrate 3a and the coat layer 7 side on the electrode substrate 3b face each other. Although not shown in FIG. 1, the partition walls 5 and the transparent counter substrate 3a were fixed with a UV curable adhesive.

  Further, a power source and switching means 8 are connected to the first electrode 4a and the second electrode 4b so that an electric field can be applied between the first electrode 4a and the second electrode 4a. By switching the switching means 8, for example, When the colored charged particles 1 are positively charged, the colored charged particles 1 move as shown in FIG.

Example 1
As the colored charged particles 1 used in Example 1, black particles in which the surface of polystyrene particles in which carbon black is dispersed are coated with a polyacrylate resin are used. Further, Isopar H as a main solvent as the dispersion medium 2 used in Example 1, 0.4 parts by weight of styrene-butadiene rubber, 1.5 parts by weight of rosin ester, polyisobutylene rubber as additives with respect to 100 parts by weight of Isopar H 0.1 part by weight is added to prepare a dispersion medium. In Example 1, polyacrylic resin is used as the coating layer 7.

  Then, a dispersion prepared by dispersing 1 part by weight of the colored charged particles in 100 parts by weight of the dispersion medium is sealed in a bowl-shaped space on the electrode substrate 3b to obtain an electrophoretic display element of Example 1.

  Here, the zeta potential of a dispersion prepared by dispersing 0.1 part by weight of charged particles in 100 parts by weight of the dispersion medium is +60 mV. Further, the polyacrylic resin used in Example 1 is applied as a coating layer 7 on quartz, and the zeta potential measured with a dispersion medium is +2 mV.

  When a voltage is applied between the two electrodes with the first electrode 4a as the cathode and the second electrode 4b as the anode of the electrophoretic display element produced as described above, the colored charged particles 1 are shown in FIG. As shown in the figure, it is uniformly developed on the first electrode 4a and displays black (dark state).

  On the other hand, when a voltage is applied between both electrodes using the first electrode 4a as an anode and the second electrode 4b as a cathode, the colored charged particles 1 gather near the second electrode 4b as shown in FIG. The first electrode 4a is exposed to display white (bright state).

  In the reflective display element of the present embodiment, if the voltage waveform applied between the first electrode 4a and the second electrode 4b is varied and gradation display is performed, the reproducibility of the reflected luminance level by the voltage waveform is high, It becomes an element with high gradation controllability.

(Example 2)
As the colored charged particles 1 used in Example 2, black particles in which the surface of polystyrene particles in which carbon black is dispersed are coated with a polyacrylate resin are used. Further, as a dispersion medium 2 used in Example 2, Isopar H is a main solvent, 0.4 parts by weight of styrene-butadiene rubber, 1.5 parts by weight of rosin ester, polyethylene wax 0 as an additive with respect to 100 parts by weight of Isopar H. Add 2 parts by weight to make a dispersion medium. In Example 2, a polyurethane resin is used as the coating layer 7.

  Then, a dispersion prepared by dispersing 1 part by weight of the colored charged particles in 100 parts by weight of the dispersion medium is sealed in a bowl-shaped space on the electrode substrate 3b to obtain an electrophoretic display element of Example 2.

  Here, the zeta potential of a dispersion prepared by dispersing 0.1 part by weight of charged particles in 100 parts by weight of the dispersion medium is +73 mV. Moreover, the polyurethane resin used for Example 2 as a coating layer 7 was apply | coated on quartz, and the zeta potential measured with the said dispersion medium is -3mV.

  When a voltage is applied between the two electrodes with the first electrode 4a as the cathode and the second electrode 4b as the anode of the electrophoretic display element produced as described above, the colored charged particles 1 are shown in FIG. As shown in the figure, it is uniformly developed on the first electrode 4a and displays black (dark state).

  On the other hand, when a voltage is applied between both electrodes using the first electrode 4a as an anode and the second electrode 4b as a cathode, the colored charged particles 1 gather near the second electrode 4b as shown in FIG. The first electrode 4a is exposed to display white (bright state).

  In the reflective display element of the present embodiment, if the voltage waveform applied between the first electrode 4a and the second electrode 4b is varied and gradation display is performed, the reproducibility of the reflected luminance level by the voltage waveform is high, It becomes an element with high gradation controllability.

(Example 3)
As the colored charged particles 1 used in Example 3, black particles obtained by coating polystyrene resin on the surface of polystyrene particles in which carbon black is dispersed are used. Further, as a dispersion medium 2 used in Example 3, Isopar H is a main solvent, and 100 parts by weight of Isopar H is 0.4 parts by weight of styrene-butadiene rubber, 1.5 parts by weight of rosin ester, and polyisobutylene rubber as additives. 0.1 parts by weight and 0.2 parts by weight of polyacrylate resin are added to prepare a dispersion medium. In Example 3, a polyacrylate resin is used as the coating layer 7.

  Then, a dispersion prepared by dispersing 1 part by weight of the colored charged particles in 100 parts by weight of the dispersion medium is enclosed in a bowl-shaped space on the electrode substrate 3b to obtain an electrophoretic display element of Example 3.

  Here, the zeta potential of a dispersion prepared by dispersing 0.1 part by weight of charged particles in 100 parts by weight of the dispersion medium is −33 mV. Moreover, the polyacrylate resin used for Example 3 as a coating layer 7 was apply | coated on quartz, and the zeta potential measured with the said dispersion medium is +5 mV.

  When a voltage is applied between the two electrodes with the first electrode 4a as the anode and the second electrode 4b as the cathode of the electrophoretic display element produced as described above, the colored charged particles 1 are shown in FIG. As shown in the figure, it is uniformly developed on the first electrode 4a and displays black (dark state).

  On the other hand, when a voltage is applied between both electrodes using the first electrode 4a as an anode and the second electrode 4b as a cathode, the colored charged particles 1 gather near the second electrode 4b as shown in FIG. The first electrode 4a is exposed to display white (bright state).

  In the reflective display element of this example, if the voltage waveform applied between the first electrode 4a and the second electrode 4b is varied and gradation display is performed, the reproducibility of the reflected luminance level by the voltage waveform is good, An element capable of gradation control is obtained.

(Comparative Example 1)
As the colored charged particles 1 used in Comparative Example 1, black particles in which the surface of polystyrene particles in which carbon black is dispersed are coated with a polyacrylate resin are used. Further, Isopar H as a main solvent as the dispersion medium 2 used in Comparative Example 1, 0.4 parts by weight of styrene-butadiene rubber, 1.5 parts by weight of rosin ester, polyisobutylene rubber as additives with respect to 100 parts by weight of Isopar H 0.1 part by weight is added to prepare a dispersion medium. In Comparative Example 1, a polyurethane resin is used as the coating layer 7.

  Then, a dispersion prepared by dispersing 1 part by weight of the colored charged particles in 100 parts by weight of the dispersion medium is sealed in a bowl-shaped space on the electrode substrate 3b to obtain an electrophoretic display element of Comparative Example 1.

  Here, the zeta potential of a dispersion prepared by dispersing 0.1 part by weight of charged particles in 100 parts by weight of the dispersion medium is +60 mV. Moreover, the polyurethane resin used for the comparative example 1 as a coating layer 7 was apply | coated on quartz, and the zeta potential measured with the said dispersion medium is -15mV.

  When a voltage is applied between the two electrodes with the first electrode 4a as the cathode and the second electrode 4b as the anode of the electrophoretic display element produced as described above, the colored charged particles 1 are shown in FIG. As shown in the figure, it is uniformly developed on the first electrode 4a and displays black (dark state).

  On the other hand, when a voltage is applied between both electrodes using the first electrode 4a as a cathode and the second electrode 4b as an anode, the colored charged particles 1 gather near the second electrode 4b as shown in FIG. The first electrode 4a is exposed to display white (bright state).

  However, the black (dark state) display in this comparative example displays a brighter black than the black (dark state) display in the first embodiment. For this reason, the reflective display element of Comparative Example 1 has a lower contrast ratio than the reflective display element of Example 1. Further, in the reflective display element of Comparative Example 1, when the voltage waveform applied between the first electrode 4a and the second electrode 4b is varied and gradation display is performed, the reproducibility of the reflected luminance level by the voltage waveform is low. The tone controllability is lowered.

(Comparative Example 2)
As the colored charged particles 1 used in Comparative Example 2, black particles in which the surface of polystyrene particles in which carbon black is dispersed are coated with a polyacrylate resin are used. Further, Isopar H as a main solvent as the dispersion medium 2 used in Comparative Example 2, 0.4 parts by weight of styrene-butadiene rubber, 1.5 parts by weight of rosin ester, polyisobutylene rubber as additives with respect to 100 parts by weight of Isopar H 0.1 parts by weight and 0.2 parts by weight of polyacrylate resin are added to prepare a dispersion medium. In Comparative Example 2, a polyacrylic resin is used as the coating layer 7.

  Then, a dispersion prepared by dispersing 1 part by weight of the colored charged particles in 100 parts by weight of the dispersion medium is sealed in a bowl-shaped space on the electrode substrate 3b to obtain an electrophoretic display element of Comparative Example 1.

  Here, the zeta potential of a dispersion prepared by dispersing 0.1 part by weight of charged particles in 100 parts by weight of the dispersion medium is +20 mV. Moreover, the polyacryl resin used for the comparative example 2 as a coating layer 7 was apply | coated on quartz, and the zeta potential measured with the said dispersion medium is -15mV.

  When a voltage is applied between the two electrodes with the first electrode 4a as the cathode and the second electrode 4b as the anode of the electrophoretic display element produced as described above, the colored charged particles 1 are shown in FIG. As shown in the figure, it is uniformly developed on the first electrode 4a and displays black (dark state). However, this black (dark state) display displays a brighter black than the black (dark state) display in the first embodiment.

  On the other hand, when a voltage is applied between both electrodes using the first electrode 4a as a cathode and the second electrode 4b as an anode, the colored charged particles 1 gather near the second electrode 4b as shown in FIG. The first electrode 4a is exposed to display white (bright state). However, this white (bright state) display is darker than the white (bright state) display in the first embodiment. For this reason, the reflective display element of Comparative Example 2 has a lower contrast ratio than the reflective display element of Example 1.

  Further, in the reflective display element of Comparative Example 2, when gradation display is performed by changing the voltage waveform applied between the first electrode 4a and the second electrode 4b, the reproducibility of the reflected luminance level by the voltage waveform is low. The tone controllability is remarkably lowered.

(Comparative Example 3)
As the colored charged particles 1 used in Comparative Example 3, black particles in which the surface of polystyrene particles in which carbon black is dispersed are coated with a polystyrene resin are used. Further, Isopar H as a main solvent as the dispersion medium 2 used in Comparative Example 3, 0.4 parts by weight of styrene-butadiene rubber, 1.5 parts by weight of rosin ester, polyethylene wax 0 as an additive to 100 parts by weight of Isopar H Add 2 parts by weight to make a dispersion medium. In Comparative Example 3, a polyurethane resin is used as the coating layer 7.

  Then, a dispersion prepared by dispersing 1 part by weight of the colored charged particles in 100 parts by weight of the dispersion medium is sealed in a bowl-shaped space on the electrode substrate 3b to obtain an electrophoretic display element of Comparative Example 1.

  Here, the zeta potential of a dispersion prepared by dispersing 0.1 part by weight of charged particles in 100 parts by weight of the dispersion medium is -10 mV. Moreover, the polyurethane resin used for the comparative example 3 as a coating layer 7 was apply | coated on quartz, and the zeta potential measured with the said dispersion medium is -3mV.

  When a voltage is applied between the first electrode 4a and the second electrode 4b as the cathode of the electrophoretic display element produced as described above, most of the colored charged particles 1 are on the first electrode 4a. However, since there are also colored charged particles 1 straying in the vicinity of the second electrode 4b, the reflective layer of the first electrode 4a cannot be concealed and grayish black (dark state) is displayed.

  On the other hand, when a voltage is applied between both electrodes using the first electrode 4a as a cathode and the second electrode 4b as an anode, most of the colored charged particles 1 gather near the second electrode 4b, but remain on the first electrode 4a. Since some of the particles are present, a light grayish white color (bright state) is displayed.

  For this reason, the reflective display element of Comparative Example 3 has a much lower contrast ratio than the reflective display element of Example 1. Further, in the reflective display element of Comparative Example 3, if the voltage waveform applied between the first electrode 4a and the second electrode 4b is varied and gradation display is performed, the reproducibility of the reflected luminance level by the voltage waveform is low, and the level is reduced. The controllability is extremely low.

1 is a diagram showing a schematic configuration of an electrophoretic display element according to an embodiment of the present invention. The figure which shows an electroosmotic flow. The figure which shows schematic structure of the conventional electrophoretic display element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Colored charged particle 2 Dispersion medium 3a Transparent counter substrate 3b Electrode substrate 4a 1st electrode 4b 2nd electrode 5 Partition wall 6 Insulating layer 7 Coat layer 8 Switching means 11 Colored charged particle 12 Dispersion medium 13a Transparent counter substrate 13b Electrode substrate 14a 1st Electrode 14b Second electrode 15 Partition 16 Insulating layer 18 Switching means

Claims (7)

A first substrate and a second substrate disposed in a state where a predetermined gap is provided; a partition member disposed in a gap between the first substrate and the second substrate; the first substrate, the second substrate and the partition member; A voltage applied between the electrodes, comprising a dispersion medium filled in a space surrounded by a particle and a particle dispersion composed of a plurality of charged particles, and a first electrode and a second electrode disposed facing the space. In an electrophoretic display element that performs display by changing the distribution of the charged particles by an electric field generated by
An electrophoretic display element, wherein a range of zeta potential on the inner wall surface of the space is set to a range in which no flow occurs in the particle dispersion along the inner wall surface of the space when a voltage is applied.   The coating layer according to claim 1, wherein a coating layer is provided on an inner wall surface of the space, and the coating layer and the dispersion medium are each formed of a material such that a zeta potential of the inner wall surface of the space is in the range. Electrophoretic display element.   The electrophoretic display element according to claim 1, wherein a range of zeta potential of the inner wall surface of the space is set to a range of −10 mV to 10 mV.   4. The electrophoretic display element according to claim 3, wherein a range of zeta potential of the inner wall surface of the space is in a range of −5 mV to 5 mV.   5. The electrophoretic display element according to claim 1, wherein an absolute value of a zeta potential at an interface composed of the charged particles and the dispersion medium is 15 mV or more.   The electrophoretic display element according to claim 1, wherein a reflective layer is provided on one of the first substrate and the second substrate. An electrophoretic display device comprising the electrophoretic display element according to claim 1.

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