WO2008023498A1

WO2008023498A1 - Electrophoretic display medium

Info

Publication number: WO2008023498A1
Application number: PCT/JP2007/063077
Authority: WO
Inventors: Yumiko Oshika
Original assignee: Brother Kogyo Kabushiki Kaisha
Priority date: 2006-08-25
Filing date: 2007-06-29
Publication date: 2008-02-28
Also published as: JP2008052084A

Abstract

In display panel (2), the surface configurations of black charged particles (50) and white charged particles (60) are different from each other. The black charged particles (50) are dimple particles having a multiplicity of dimples on the particle surface, thereby exhibiting high straight marching capability. On the other hand, the white charged particles (60) are protrudent particles having a multiplicity of offspring particles on the particle surface, thereby exhibiting low straight marching capability. Consequently, while the black charged particles (50) make shortest-distance migration between display substrate (10) and backside substrate (20), the white charged particles (60) migrate in a manner keeping away from the black charged particles (50). Therefore, as collision of the black charged particles (50) with the white charged particles (60) can be avoided, there can be attained an enhancement of response performance of display switching.

Description

Specification

Electrophoretic display medium

Technical field

The present invention relates to an electrophoretic display medium, and more particularly, to an electrophoretic display medium that displays an image using an electrophoretic phenomenon.

Background art

Conventionally, an electrophoretic display device that can display an image on a display panel (electrophoretic display medium) using an electrophoretic phenomenon is known. This display panel includes a transparent display substrate and a rear substrate disposed to face the display substrate. Electrodes are formed on the surfaces of the display substrate and the back substrate. A display liquid is sealed between the display substrate and the back substrate via a spacer, and two kinds of charged particles are dispersed in the display liquid. These charged particles are generally composed of black charged particles and white charged particles that are charged to a polarity different from that of the black charged particles. As such a display panel, for example, a liquid in which two types of electrophoretic fine particles (charged particles) having different color tones and charging characteristics are dispersed in a highly insulating, low-viscosity, non-colored dispersion medium is used. An encapsulating electrophoretic display element (electrophoretic display medium) is known (for example, see Patent Document 1).

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In this electrophoretic display element, when a voltage is applied between a pair of electrodes and an electric field is generated in the dispersion medium, each electrophoretic fine particle undergoes electrophoresis. Specifically, one electrophoretic fine particle moves to and adheres to one electrode according to its charging polarity. The other electrophoretic fine particles move to and adhere to the other electrode. At this time, the color tone of the electrophoretic fine particles adhering to the electrode is displayed on the transparent electrode.

Patent Document 1: JP-A 62-269124

Disclosure of the invention

[0004] However, in the electrophoretic display element described in Patent Document 1, when the direction of the electric field applied to the dispersion medium is switched, the two types of electrophoretic fine particles move to the electrodes opposite to each other. To do. At this time, the electrophoretic fine particles having different polarities are There is a problem that the time required for switching the display becomes long because of collision during movement.

[0005] An object of the present disclosure is to provide an electrophoretic display medium capable of improving display switching responsiveness by avoiding collision between charged particles having different polarities.

[0006] According to the present disclosure, a pair of substrates spaced apart from each other, a display liquid sealed with a spacer interposed between the pair of substrates, and dispersed in the display liquid, by the action of an electric field A pair of charged particles moving in the display liquid, wherein the pair of charged particles is a first charged particle and a second charged particle having a different color and polarity from the first charged particle. The amount of movement in the direction of the shortest distance with respect to the amount of movement of the first charged particles in a direction orthogonal to the direction of the shortest distance between the pair of substrates when the first charged particles move between the pair of substrates. And the direction of the shortest distance with respect to the amount of movement of the second charged particles in a direction perpendicular to the direction of the shortest distance between the pair of substrates when the second charged particles move between the pair of substrates. Electrophoretic display media with different rates of movement It is.

Brief Description of Drawings

FIG. 1 is a cross-sectional view of a display panel 2.

FIG. 2 is a front view of black charged particles 50.

FIG. 3 is a front view of white charged particles 60.

FIG. 4 is an explanatory diagram showing the movement of black charged particles 50 and white charged particles 60.

FIG. 5 is an explanatory diagram showing the movement of black charged particles 50 and white charged particles 60.

FIG. 6 is an explanatory diagram showing the movement of black charged particles 50 and white charged particles 60.

FIG. 7 is an explanatory diagram showing the movement of black charged particles 50 and white charged particles 60.

FIG. 8 is an explanatory diagram showing the movement of black charged particles 50 and white charged particles 60.

FIG. 9 is an explanatory diagram showing a test method for a straightness evaluation test.

FIG. 10 is a table showing the results of a straightness evaluation test.

FIG. 11 is an explanatory diagram showing movement amounts of convex particles 82, spherical particles 81, and dimple particles 83.

FIG. 12 is a table showing the results of a display switching time evaluation test. FIG. 13 is an explanatory view showing the movement of black charged particles 50 and white charged particles 60 in display panel 600.

FIG. 14 is an explanatory diagram showing the movement of black charged particles 50 and white charged particles 60 in display panel 600.

FIG. 15 is an explanatory diagram showing the movement of black charged particles 50 and white charged particles 60 in display panel 600.

FIG. 16 is an explanatory diagram showing the movement of black charged particles 50 and white charged particles 60 in the display panel 600.

BEST MODE FOR CARRYING OUT THE INVENTION

[0008] Hereinafter, the display panel 2 according to an embodiment of the present disclosure will be described with reference to the drawings.

1, 4 to 8, the upper surface of the display panel 2 is the upper surface of the display panel 2, and the lower surface is the lower surface of the display panel 2.

[0009] The display panel 2 of the present embodiment is mounted on, for example, a portable electronic device. Various images can be displayed by being driven and controlled by a control device (not shown).

First, the configuration of the display panel 2 will be described. As shown in FIG. 1, the display panel 2 includes a display substrate 10 provided horizontally, and a rear substrate 20 disposed horizontally opposite to the display substrate 10 with a spacer 31 interposed therebetween. ing. In the present embodiment, the separation width between the display substrate 10 and the rear substrate 20 is adjusted to 25 m. In the gap between the display substrate 10 and the back substrate 20, a plurality of display portions 30 divided by the partition walls 32 are formed in a lattice shape. The partition wall 32 is provided so as to surround each pixel.

Next, the structure of the display substrate 10 will be described. As shown in FIG. 1, the display substrate 10 is formed of a transparent member. The display substrate 10 includes a display layer 11 as a display surface. A transparent display electrode layer 12 for generating an electric field in the display section 30 is provided on the lower surface side of the display layer 11. The display layer 11 is formed of a material having high transparency and high insulation. For example, polyethylene naphthalate, polyether sulfone, polyimide, polyethylene terephthalate, glass and the like are used. Meanwhile, display The electrode layer 12 is made of a material that has high transparency and can be used as an electrode.For example, indium tin oxide, which is a metal oxide, tin oxide doped with fluorine, aluminum oxalate aluminum Doped acid zinc oxide or the like is used. In the present embodiment, the display layer 11 is a transparent glass substrate. On the other hand, the display electrode layer 12 is a transparent electrode formed of indium tin oxide. By providing such a structure, the user can visually recognize the display unit 30 through the transparent display substrate 10.

[0012] Next, the structure of the back substrate 20 will be described. As shown in FIG. 1, the back substrate 20 includes a housing support layer 21 that supports the display panel 2. Further, a back electrode layer 22 corresponding to each display unit 30 is provided on the upper surface of the housing support layer 21. The back electrode layer 22 generates an electric field in each display unit 30. On the other hand, the casing support layer 21 is made of a highly insulating material. For example, glass, an inorganic material such as an insulated metal film, or an organic material such as polyethylene terephthalate is used. Note that each layer forming the back substrate 20 may be transparent or colored, unlike the display substrate 10. In the present embodiment, the housing support layer 21 is a glass substrate, and the back electrode layer 22 is an electrode formed of indium tin oxide.

[0013] Channel CH1 is connected to each back electrode layer 22, and channel CH2 is connected to display electrode layer 12. These channels CH1 and CH2 are controlled by a control device (not shown), and a voltage is applied to the back electrode layer 22 and the display electrode layer 12. As a result, an electric field is generated in the display unit 30. In the present embodiment, when the display electrode layer 12 is set to the reference potential (zero volts) and a positive voltage is applied to the back electrode layer 22, the back electrode layer 22 is positive and the display electrode layer 12 is negative. When a negative voltage is applied to the back electrode layer 22, the back electrode layer 22 is negative and the display electrode layer 12 is positive. On the other hand, the display electrode layer 12 may be set at a reference potential (zero volts). Further, the method for generating the electric field may be other methods.

Next, the structure of the display unit 30 will be described. As shown in FIG. 1, a spacer 31 is provided between the display substrate 10 and the back substrate 20. The spacer 31 is provided along the outer periphery of the display panel 2. Further, a sealed space is formed between the display substrate 10, the back substrate 20, and the spacer 31. This sealed space is evenly divided by the partition wall 32. A plurality of display portions 30 are formed by being divided. Each of the display units 30 corresponds to a pixel. That is, the display panel 2 is a panel in which a plurality of display units 30 are arranged in a lattice pattern. The spacer 31 and the partition wall 32 are made of polyethylene terephthalate resin film. The display liquid 40 is sealed in the sealed space of the display unit 30 of the display panel 2 having such a structure.

[0015] Next, the display liquid 40 will be described. The display liquid 40 is a dispersion medium in which a plurality of white charged particles 60 and a plurality of black charged particles 50 are dispersed. The dispersion medium refers to a liquid substance in which particles (dispersoid) are dispersed. The display liquid 40 of the present embodiment uses black liquid particles 50 and white charged particles 60 as a dispersoid, and a liquid substance obtained by adding a predetermined amount of a polar solvent to a nonpolar solvent as a dispersion medium. As the nonpolar solvent, a hydrocarbon solvent is mainly used. In the present embodiment, no << raffin solvent (73 wt%) (trade name "Isopar Gj: manufactured by ExxonMobil Co., Ltd.) is used. On the other hand, an alcohol that is soluble in a nonpolar solvent is used as a polar solvent. In this embodiment, hexanol is used, and a part of the polar solvent in the display liquid 40 stays around the white charged particles 60 and the black charged particles 50 so that these charged particles are used. The charging property is improved.

Next, the black charged particles 50 and the white charged particles 60 will be described. As shown in FIG. 1, black charged particles 50 and white charged particles 60 are suspended in the display liquid 40. In this embodiment, the black charged particles 50 are positively charged (+), and the white charged particles 60 are negatively charged (−). Therefore, when an electric field is generated in the display unit 30 with the display substrate 10 side minus and the back substrate 20 side plus, the black charged particles 50 move to the display substrate 10 side, and the white charged particles 60 are the back substrate 20 side. Move to. At this time, black is displayed on the display substrate 10. In addition, when a reverse electric field is generated in the display unit 30 with the display substrate 10 side being positive and the back substrate 20 side being negative, the black charged particles 50 move to the back substrate 20 side, and the white charged particles 60 are Move to display board 10 side. At this time, the black color displayed on the display substrate 10 is switched to white. As will be described later, the black and white display switching time is greatly affected by the movement time of the black charged particles 50 and the white charged particles 60 in the display liquid.

Here, “straightness” of the charged particles will be described. The straightness of charged particles refers to the display base. It shows the ratio of the amount of movement in the direction of the shortest distance to the amount of movement in the direction orthogonal to the direction of the shortest distance between the plate 10 and the back substrate 20. In other words, the amount of movement in the direction of the shortest distance force The greater the amount of movement in the direction perpendicular to the direction of the shortest distance, the higher the straightness of the charged particles. Conversely, the greater the amount of movement in the direction perpendicular to the direction of the shortest distance than the amount of movement in the direction of the shortest distance, the lower the straightness. In general, particles having a surface shape that is not easily resisted by the surrounding liquid have high rectilinearity and are susceptible to ambient resistance, and particles having a surface shape have low rectilinearity.

In the present embodiment, since the black charged particles 50 and the white charged particles 60 having different surface shapes are used, the straightness of the black charged particles 50 and the straightness of the white charged particles 60 are different from each other. Yes. Thereby, since the collision frequency between the black charged particles 50 and the white charged particles 60 can be reduced, the display switching time can be shortened. The effect of shortening the display switching time will be described later.

Next, the structure of the black charged particles 50 will be described. As shown in FIG. 2, the black charged particles 50 are so-called “polymerized dimple particles”, and have a large number of dimples 51 on a spherical surface. The large number of dimples 51 can improve the straightness when the display liquid 40 is moved. The effect of improving the straightness of the black charged particles 50 by the dimple structure and the evaluation thereof will be described later.

[0020] Next, a method for producing the black charged particles 50 having the dimple structure will be described. The black dimple particles as the basis of the black charged particles 50 are cross-linked polymer particles obtained by adding a cross-linking agent while polymerizing monomers. The method for producing the crosslinked polymer particles includes a polymer particle production step of producing a polymerized dimple particle by adding a crosslinking agent while polymerizing a monomer, and a dyeing process in which the produced polymer particle is dyed via a dye or the like. Process.

First, the process for producing polymer particles will be described. First, in a reactor equipped with a stirrer, a cooling pipe, a thermometer, a gas introduction pipe, etc., 582 g of methanol (manufactured by Kanto Yigaku Co., Ltd.) and 145 g of isopropyl alcohol (manufactured by Kanto Yigaku Co., Ltd.) as solvents Fill. Furthermore, as a dispersant, 30 g of polybulurpyrrolidone (K-30, manufactured by Nacalai Testa Co., Ltd.) and 7 g of 1-hexanedeol (Nakora Tester Co., Ltd.) are charged into the reactor. Subsequently, as a monomer that becomes a resin material, Charge 207 g of styrene monomer (manufactured by Kanto Chemical Co., Ltd.) and 43 g of n-butyl acrylate (manufactured by Kanto Chemical Co., Ltd.) to the reactor. Next, nitrogen gas replacement is performed by filling the reactor with nitrogen gas from the gas introduction pipe.

[0022] Thereafter, 15 g of α, α'-azobisisobutyl-tolyl (manufactured by Kanto Chemical Co., Ltd.) as a polymerization initiator is charged into the reactor. Then, while stirring the solution prepared as described above with a stirrer, the solution is heated to about 60 ° C. and polymerized for 8 hours. By this polymerization reaction, spherical polymer particles (styrene Zn-butyl acrylate copolymer) can be obtained. Here, the polymer particles have a substantially spherical shape. The average particle size and dispersity of the polymer particles were measured with a dispersity meter (using a Coulter Coulter Multisizer), and it was confirmed that the average particle size was about 4111 and the dispersity was 1.03. It was done.

[0023] After the spherical polymer particles as described above are obtained, 5 g of dibutenebenzene (manufactured by Nacalai Testa Co., Ltd.) is added as a cross-linking agent to the polymerization reaction system, and the polymerization is continued for about 2 hours. Perform the reaction. At this time, in the process in which the polymerization reaction of the polymer particles proceeds, the crosslinking agent added to the polymerization reaction system causes a crosslinking reaction randomly between the monomer molecules. As a result, it is considered that a plurality of dimples are formed on the surface portion of the polymer particles. Then, when the polymer particles produced by this polymerization reaction are separated from the dispersion medium and dried, polymer particles having a plurality of dimples on the surface as shown in FIG. 2 are obtained. The polymer particles had an average particle size of 4.9 / ζ πι and a dispersity of 1.05.

[0024] Further, there is a mutual relationship between the particle size of the polymer particles at the time when the cross-linking agent is added and the amount of the cross-linking agent added. For example, when the particle size of the polymer particles at the time of adding the cross-linking agent is small, it is difficult to form dimples on the polymer particles unless the addition amount of the cross-linking agent to be added is increased. On the other hand, when the particle size of the polymer particles at the time when the cross-linking agent is added is large, dimples are easily formed on the polymer particles even if the amount of the cross-linking agent added is small. For example, when the particle size of the polymer particles at the time of adding the cross-linking agent is in the range of 3 to 6 μm, the polymer particles can be added by adding 1% or more of the cross-linking agent with respect to the charged amount of monomer. Dimples can be formed on the substrate. The cross-linking material is desirably added at 2% or more, more desirably 3% or more.

[0025] Further, it is desirable to adjust the addition amount of the crosslinking agent according to the average particle diameter of the polymer particles. . For example, when the particle diameter of the polymer particles is in the range of 2 to 8 / ζ πι, the crosslinking agent is preferably added in an amount of 8% to 1% with respect to the charged amount of the monomer. Further, when the particle size of the polymer particles is in the range of 1 to: LO / zm, it is preferable to add 10% to 0.1% of a crosslinking agent. The crosslinking agent that can be used in this example is not limited to divinylbenzene, and various compounds shown below can be used as the crosslinking agent. For example, aromatic divinyl compounds and carboxylic acid esters having two or more vinyl groups can be used.

Aromatic dibule compounds include dibulalnaphthalene, N, N dibularin and their derivatives. As the carboxylic acid ester having two or more vinyl groups, polyethylene glycol dimethacrylate Tatari, polyethylene glycol di Atari rate, Toryechi glycol dimethacrylate, triethylene glycol di Atari rate, 1, ₃ Buchiren glycol dimethacrylate Tatari rate, 1 , 3 Butylene glycol diatalylate, 1,6 hexylene glycol dimetatalate, 1, 6 hexylene glycol diatalate, neopentyl glycol dimetatalylate, neoventil glycol ditalariate, dipropylene glycol dimetatalate , Dipropylene glycol diatalylate, polypropylene glycol dimethacrylate, polypropylene glycol diathalate, 2, 2 bis (4-methacryloxydiethoxyphenol) Bread, 2, 2 bis (4-atarioxydiethoxyphenol) propane, trimethylolpropane trimetatalylate, trimethylolpropane tritalatolate, tetramethylolmethane tetrametatalylate, tetramethylolmethane tetraatalylate, Dibromoneopentylglycol dimetatalylate, dibu-mouth neopentylglycol diacrylate, diacrylic phthalate, ethylene glycol dimethacrylate, ethylene glycol diatalate, diethylene glycol dimethacrylate, diethylene glycol dimethylate, trimethylolpropane trimetatali Rate, trimethylolpropane tritalylate, aryl methacrylate, aryl arylate, t-butylaminoethyl dimetatalylate, t-butylamino Chill di Atari rate, tetraethylene glycol dimethacrylate Tatari rate, tetraethylene glycol di Atari rate, 1, 3-butanediol dimethacrylate Tatari rate, there is a 1, 3 pigs down di Atari rates. In addition, dibilyl compounds such as dibule ether, divinylsulfide and divinylsulfone, and compounds having three or more bur groups can be used alone or as a mixture. [0027] Next, the dyeing process will be described. First, black dye (Oil Black 860 manufactured by Orienti Chemical Co., Ltd.) 15. Og and charge control agent (E-84 manufactured by Orient Chemical Co., Ltd.) 6. Og in ethanol 750cc as the dispersion solvent To prepare a dyeing solution. In such a dye solution, add 150 g of polymer particles with dimples and stir for about 1 hour while heating to 30 ° C. Thereby, the polymer particles with dimples are dyed with the black dye. Then, dried black particles can be obtained by filtering and separating the dyed polymer particles with dimples and the dispersion solvent. The black charged particles 50 can be obtained by positively charging the black particles in the display liquid 40.

[0028] Next, the white charged particles 60 will be described. As shown in FIG. 3, the white charged particle 60 is a particle in which a large number of child particles 62 having a diameter smaller than that of the mother particle 61 are combined with a spherical mother particle 61. And the surface is convex. The mother particle 61 is formed of a chargeable material, and for example, acrylic resin is used. Examples of this acrylic resin include polyacrylic acid and esters thereof. In addition to acrylic resin, PC (polycarbonate), HDPE (high density polyethylene), PP (polypropylene), ABS (acrylonitrile butadiene styrene), PET (polyethylene terephthalate), POM (polyacetal), etc. are available. is there. On the other hand, the child particle 62 is mechanically coupled in a state where a part of the child particle 62 is buried in the surface of the mother particle 61. The child particles 62 increase the resistance received from the display liquid 40 when the white charged particles 60 move the display liquid 40. Therefore, it is possible to reduce the straightness in the movement of the white charged particles 60 contrary to the black charged particles 50.

[0029] Next, a method for binding the child particles 62 to the mother particles 61 will be described. As shown in FIG. 3, the child particle 62 is mechanically bonded to the surface of the mother particle 61 by a hybridization method. Specifically, the child particle 62 is bonded to the surface of the mother particle 61 in a state where a part of the child particle 62 is buried. The treatment method of this hybridization method is as follows. The processing equipment used was the Nobbridation System (NHS) manufactured by Nara Machinery Co., Ltd. This NHS is a mixer that forms a mixture of powders, a hybridizer that combines fine powders in a dry manner, a collector, a control panel that controls each device, and an operation for operating the device. And a board. [0030] First, powder lOg serving as mother particles and 0.4g serving as child particles are mixed with a mixer. Next, these powders are put into a hybridizer. In the hybridizer, the treatment is performed at 25 ° C. and 9700 rpm for 3 minutes. Then, in the hybridizer 1, while the particles are dispersed in the gas phase, the mechanical and thermal energy mainly composed of an impact force is given to the particles, and thus the fixed metal treatment is performed. The generated processed powder is quickly collected by a collector. In this way, white charged particles 60 in which the child particles 62 are bonded to the surface of the mother particles 61 can be generated.

In the present embodiment, the child particles 62 may be mechanically bonded to the surface of the mother particle 61 by a hybridization method. Further, a plurality of convex shapes may be formed by covering the surface of the mother particle 61. Furthermore, a plurality of convex shapes may be formed by processing the surface shape of the mother particle 61.

Next, the movements of the black charged particles 50 and the white charged particles 60 when the display panel 2 is driven will be described with reference to FIGS. 4 to 8. 4 to 8, the particle diameter, the number of particles, etc. are changed and shown in order to clearly explain the movement of the black charged particles 50 and the white charged particles 60.

First, as shown in FIG. 4, an electric field is generated in the display unit 30 with the display electrode layer 12 minus and the back electrode layer 22 plus. Then, the positively charged black charged particles 50 move to the display substrate 10 side and adhere to the display electrode layer 12. On the other hand, the white charged particles 60 move to the back substrate 20 side and adhere to the back electrode layer 22. At this time, black is displayed on the display substrate 10. Next, all of the black charged particles 50 are gathered together in the center of the display electrode layer 12 to form a black charged particle layer consisting of one layer in a close-packed state. The close-packed means that the adjacent black charged particles 50 are in contact with each other. A gap is formed on both sides of the black charged particle layer so that at least one white charged particle 60 can be disposed. The distance between the gaps may be adjusted according to the particle diameter and the number of particles of the black charged particles 50 and the white charged particles 60, the distance between the spacer 31 and the partition wall 32, the distance between the partition wall 32 and the partition wall 32, and the like.

Next, when the direction of the electric field applied to the display unit 30 is switched with the display electrode layer 12 being positive and the back electrode layer 22 being negative, the black charged particles 50 are displayed as shown in FIG. The white charged particles 60 are separated from the back electrode layer 22 away from the electrode layer 12. In addition, it is shown in Figure 6. In this way, the black charged particles 50 having high straightness move toward the back electrode layer 22 without substantially destroying the arrangement. On the other hand, the white charged particles 60 that are easily subjected to the resistance of the display liquid 40 are pushed toward the back substrate 20 by the flow of the display liquid 40 accompanying the movement of the black charged particles 50. For this reason, the white charged particles 60 are divided into two groups at the center and move so as to wrap around the gaps on both sides of the black charged particles 50 aligned in a row. In other words, the closer the black charged particles 50 are to the white charged particles 60, the more the white charged particles 60 are pushed away by the display liquid 40 and move away from the black charged particles 50. Thereby, the collision between the black charged particles 50 and the white charged particles 60 can be avoided. Even when display switching is repeated a plurality of times, the black charged particle layer moves straight in the display liquid 40. From this, since the gaps on both sides of the black charged particle layer are maintained, collision between different particles can be avoided.

Further, the black charged particles 50 move toward the back electrode layer 22. On the other hand, the white charged particles 60 move toward the display electrode layer 12 while wrapping around the black charged particles 50. Then, as shown in FIG. 7, the arrangement of the black charged particles 50 and the arrangement of the white charged particles 60 are reversed and switched. As shown in FIG. 8, the black charged particles 50 adhere to the back electrode layer 22 as they are in a line. On the other hand, the white charged particles 60 also adhere to the display electrode layer 12 in a state of being arranged in a line. At this time, white is displayed on the display substrate 10. In this way, collisions between particles can be avoided by using two types of particles that are different from each other. Further, since the time required for switching between the black charged particles 50 and the white charged particles 60 can be shortened, the display switching response of the display panel 2 can be improved.

Next, a straightness evaluation test for dimple particles will be described. This test evaluates the straightness of dimple particles. First, the test method will be described. In this test, as shown in FIG. 9, an experimental cell 500 having the same configuration as that of the display panel 2 was used. The cell 500 includes a first substrate 100 and a second substrate 200. In the meantime, a display unit 300 formed with a spacer 310 interposed is provided. In the display unit 300, the display liquid 400 is sealed. The first substrate 100 includes a display layer 110 and a first electrode layer 120 provided on the inner surface of the display layer 11 (the surface facing the display unit 300). It is. The second substrate 200 includes a housing support layer 210 and a second electrode layer 220 provided on the inner surface of the housing support layer 210 (the surface facing the display unit 300). The distance between the first substrate 100 and the second substrate 200 was lcm. Furthermore, 0.1 wt. / c ^ Test particle 80 was charged and test particle 80 was negatively charged.

[0037] Further, the first electrode layer 120 of the cell 500 is connected to the ground 71 via a wiring. The second electrode layer 220 is connected to the switch 72 via a wiring. Further, the switch 72 is connected to the positive side of the 200V DC power source 73. The negative side of the DC power supply 73 is connected to the ground 74 through wiring. When the switch 72 is turned on, the first electrode layer 120 becomes the reference potential (zero volts), and a positive voltage is applied to the second electrode layer 220. Accordingly, since the second electrode layer 220 is positive and the first electrode layer 120 is negative, an electric field can be applied to the display liquid 40.

[0038] Then, in the cell 500 having the structural force, the amount of movement of the test particles 80 after 5 seconds from applying an electric field to the display liquid 400 was observed with a microscope. The amount of movement of the test particles 80 was selected from a number of test particles 80 dispersed in the display liquid, and the amount of movement of the test particles 80 was measured by image analysis using a PC (personal computer). . In the image analysis, based on the amount of movement of the test particle 80, the amount of movement in the X direction and the amount of movement in the y direction, which will be described later, were obtained, and xZy indicating straightness (T) was calculated. Then, the straightness of the three types of test particles 80 was compared. Three types of test particles 80 were prepared: 1. spherical particles 81 (standard), 2. convex particles 82, and 3. dimple particles 83. Here, the convex particles 82 correspond to the white charged particles 60 (see FIG. 3) of the present embodiment. The dimple particles 83 correspond to the black charged particles 50 (see FIG. 2) in the present embodiment. These three kinds of test particles 80 all have the same diameter. Furthermore, the diameter of the convex particles was based on the diameter of the mother particles.

Note that “straightness” in this test is the shortest distance between the first substrate 100 and the second substrate 200 when the test particles 80 move between the first substrate 100 and the second substrate 200. The ratio of the amount of movement in the direction of the shortest distance to the amount of movement in the direction perpendicular to the direction of distance shall be indicated. Then, as shown in FIG. 9, the thickness direction of the cell 500 (direction of force from the first substrate 100 to the second substrate 200) was taken as the X direction. Furthermore, the direction perpendicular to the thickness direction was taken as the y direction. And test opening The amount of movement of the test particle 80 in the x direction and the amount of movement in the y direction after 5 seconds from the beginning was obtained, and straightness (T) = xZy was calculated to evaluate the straightness of the test particle 80.

[0040] Next, the results of the straightness evaluation test will be described. As shown in Fig. 10 and Fig. 11, the amount of movement of convex particles 82 in the X direction was 3.0 (X 10 ^_2 mm), and the amount of movement in the y direction was 22.0 (X 10 " ² mm). The amount of movement of the conventional spherical particles 81 in the X direction was 6.3 (X 10 " ² mm), and the amount of movement in the y direction was ^5.3 (X 10 ^_2 mm). Furthermore, the amount of movement of the dimple particle 83 in the x direction was 20.3 (X 10 ^_2 mm), and the amount of movement in the y direction was 2.8 (X 10 ^_2 mm).

[0041] Next, the above test results will be considered. As shown in FIG. 11, the spherical particles 81 having the conventional shape move to the second substrate 200 side while receiving the resistance of the display liquid 400. Therefore, not only the amount of movement in the X direction but also the amount of movement in the y direction occurs. On the other hand, the movement amount in the _y direction of the convex particle 82 is higher than the movement amount in the X direction. This is presumed that the straightness was greatly reduced because the large number of child particles 62 bonded to the surface of the mother particle 61 was strongly subjected to the resistance of the display liquid 400. On the other hand, the dimple particle 83 has a much higher amount of movement in the X direction than that in the y direction. This is presumably because the display liquid 400 smoothly circulates behind the particles due to a large number of dimples provided on the particle surface, so that the resistance of the display liquid 400 is reduced and the straightness is improved.

Next, a display switching evaluation test for the display panel 2 will be described. In this test, the relationship between the combination of particle shapes and the time required for switching display was investigated. First, the test method will be described. In this test, the same experimental display panel (not shown) as the display panel 2 shown in FIG. 1 was used. In this display panel, two types of test particles 1 and 2 were combined, and each was added so as to have a predetermined concentration in the display liquid.

Here, the test particles 1 and 2 will be described. The test particles 1 and 2 are particles corresponding to the black charged particles 50 and the white charged particles 60 of the present embodiment. The test particles 1 were adjusted to white and the test particles 2 were adjusted to black so that the charging polarities were different from each other. For test particles 1 and 2, three types were prepared: 1. spherical particles (standard), 2. convex particles, and 3. dimple particles. These three kinds of particles are combined as test particles 1 and 2, respectively. 1. Spherical particles Spherical particles 2. Spherical particles Dimple particles 3. Spherical particles-Convex particles 4. Convex particles Dimple particles 5. Convex particles -6 types of combinations were set: convex particles and 6. dimple particles and dimple particles. Then, according to these combinations, a plurality of test particles 1 and 2 were put into the display liquid 40, and the time required for display switching in the display panel 2 was measured. In this test, the time required to switch the white display power to black display was also measured.

Next, the result of the switching display evaluation test will be described. As shown in FIG. 12, it was 70 (msec) in the case of a combination of spherical particles and spherical particles. In the case of a combination of spherical particles and dimple particles, it was 40 (msec). In the case of a combination of spherical particles and convex particles, the value was 50 (msec). In the case of a combination of convex particles and dimple particles, the value was 30 (msec). In the case of the combination of convex particles and convex particles, the value was 100 (msec). In the case of a combination of dimple particles and dimple particles, it was 50 (msec).

Next, the test result will be considered. The conventional spherical particle combination of spherical particles had a display switching time of 70 (msec), while the combination of spherical particles and dimple particles shortened the display switching time to 40 (msec). This is presumably because test particle 2 which is a dimple particle has improved straightness compared to spherical test particle 1, and a difference has occurred between the straightness of test particle 1 and test particle 1. In other words, it is considered that the rectilinearity of the test particles 1 and the rectilinearity of the test particles 2 are different from each other, thereby reducing the collision frequency and shortening the display switching time. Similarly, in the combination of spherical particles and convex particles, the shape of test particle 1 and the shape of test particle 2 are different from each other, so that the straightness of test particle 1 and the straightness of test particle 2 are different from each other. Therefore, it is considered that collision between particles was avoided and display switching time was shortened. However, since the moving speed of each particle is slower than the dimple particle which is not the dimple particle, the display switching time is estimated to be longer than the combination of the spherical particle and the dimple particle.

[0046] The combination of convex particles and dimple particles was the shortest of 30 (msec), and the display switching time was further shortened compared to the combination of spherical particles and dimple particles. This is because the convex particles receive the resistance of the display liquid more strongly than the spherical particles, so they move quickly with respect to the dimple particles moving straight, and more reliably avoid collision with the dimple particles. It is guessed. On the other hand, in the combination of convex particles and convex particles, the surface shape is easy to receive the resistance of the display liquid, so the time required for movement between the substrates becomes longer. Spherical particles It is estimated that the display switching time is longer than the combination of spherical particles. In addition, in the combination of dimple particles and dimple particles, both the surface shapes of the dimple particles with high straightness and force straightness are the same, so the collision frequency is higher and the display switching time is longer. Presumed to be Natsuta. From the above, the display switching time of the display panel 2 can be shortened the most by making the combination of the particle shapes a combination of convex particles and dimple particles.

[0047] As described above, the display panel 2 of the present embodiment uses the black charged particles 50 and the white charged particles 60 having different surface shapes. As a result, the straightness of the black charged particles 50 and the straightness of the white charged particles 60 can be made different from each other, so that collision between these particles can be avoided. For example, the black charged particles 50 are dimple particles having a large number of dimples 51 on the surface, and the white charged particles 60 are convex particles having a large number of child particles 62 on the surface. Accordingly, the straightness of the black charged particles 50 is improved, and the white charged particles 60 are strongly subjected to the resistance of the display liquid 40, so that the straightness is lowered. That is, the black charged particles 50 move between the display substrate 10 and the back substrate 20 with the shortest distance, and the white charged particles 60 move so as to avoid the black charged particles 50. Therefore, collision between the black charged particles 50 and the white charged particles 60 can be effectively avoided. And since the display switching time of the display panel 2 is shortened, the responsiveness of display switching can be improved.

[0048] Needless to say, the electrophoretic display medium according to the present disclosure is not limited to the above-described embodiment, and various modifications are possible. For example, in the above embodiment, the surface area of the display electrode layer 12 and the surface area of the back electrode layer 22 are the same as each other. By making the surface areas different from each other, collisions between charged particles can be avoided more reliably. . Therefore, as a modification of the above embodiment, a display panel 600 in which the surface area of the display electrode layer and the surface area of the back electrode layer are different from each other will be described with reference to FIGS. Note that the same components as those of the display panel 2 of the above embodiment are denoted by the same reference numerals and description thereof is omitted.

As shown in FIG. 13, the display panel 600 has a configuration similar to that of the display panel 2.

A back substrate 90 different from the back substrate 20 of the above embodiment is provided. The back substrate 90 includes a housing support layer 91, and a back electrode layer 92 is provided at the center of the top surface of the housing support layer 91. The back electrode layer 92 has a smaller surface area than the display electrode layer 12. When the cross section of the panel 600 is viewed, the panel 600 is provided on the upper surface of the housing support layer 91 with a gap between both sides. The display liquid 40, the black charged particles 50, and the white charged particles 60 are the same as those in the above embodiment. The black charged particles 50 are “dimple particles”, and the white charged particles 60 are “convex particles”.

Next, the movements of the black charged particles 50 and the white charged particles 60 when the display panel 600 is driven will be described with reference to FIGS. 13 to 16. In FIGS. 13 to 16, the particle diameter, the number of particles, and the like are changed in order to clearly explain the movement of the black charged particles 50 and the white charged particles 60.

First, as shown in FIG. 13, when an electric field is generated in the display unit 30 with the display electrode layer 12 minus and the back electrode layer 92 plus, the positively charged black charged particles 50 are added to the display substrate 10. And adheres to the display electrode layer 12 in a line. On the other hand, the white charged particles 60 move to the back substrate 20 side and adhere to the back electrode layer 92. However, since the back electrode layer 92 is disposed at the center of the back substrate 90, the plurality of white charged particles 60 are folded in a dump shape and attached to the back electrode layer 92. At this time, black is displayed on the display substrate 10.

Next, when the direction of the electric field applied to the display unit 30 is switched with the display electrode layer 12 being positive and the back electrode layer 92 being negative, as shown in FIG. 14, the black charged particles 50 are converted into the display electrode layer. The white charged particles 60 are separated from the back electrode layer 92. Further, as shown in FIG. 15, the black charged particles 50 having high straightness move straightly by directing the back electrode layer 92. Therefore, the black charged particles 50 move so that the arrangement thereof collapses and gathers in the center of the display unit 30. On the other hand, the white charged particles 60 that are easily subjected to the resistance of the display liquid 40 are pushed by the flow of the display liquid 40 as the black charged particles 50 move. Therefore, the plurality of white charged particles 60 are divided into two aggregates at the center, and move while wrapping around both sides of the black charged particles 50 assembled at the center.

[0053] Next, the arrangement of the black charged particles 50 and the white charged particles 60 is reversed and reversed. As shown in FIG. 16, the black charged particles 50 adhere to the back electrode layer 92 in a bunched state, and the white charged particles 60 adhere to the display electrode layer 12 in a row. At this time, white is displayed on the display substrate 10. Thus, by making the surface area of the back electrode layer 92 smaller than the surface area of the display electrode layer 12, the black charged particles 50 gather from the display electrode layer 12 while gathering at the center of the display liquid 40. It moves toward the back electrode layer 92. A large gap is formed between the black charged particles 50 adhering to the back electrode layer 92 and the spacers 31 or the partition walls 32. Since the white charged particles 60 can pass through the gap with a margin, it is possible to more reliably avoid the black charged particles 50 and the white charged particles 60 from colliding with each other. Further, since the surface area of the back electrode layer 92 is made smaller than the surface area of the display electrode layer 12, the display area of the color displayed on the display substrate 10 cannot be reduced.

[0055] It should be noted that various modifications are possible in addition to such modifications. For example, the white charged particles 60 may be dimple particles and the black charged particles 50 may be convex particles.

[0056] In the above embodiment, the display electrode layer 12 and the back electrode layer 22 are provided on the display substrate 10 and the back substrate 20, respectively. However, in the present disclosure, these electrodes (the display electrode layer 12 and the back electrode) With the layer 22), it can also be applied to display panels.

[0057] As described above, according to the present disclosure, when an electric field is applied to the display liquid sealed between a pair of substrates, the first charged particles are arranged on one substrate side according to their own charge polarity. The second charged particles move to the other substrate side according to their charge polarity. The ratio of the amount of movement in the direction of the shortest distance to the amount of movement of the first charged particles in the direction perpendicular to the direction of the shortest distance between the pair of substrates when the first charged particles move between the pair of substrates is shown. The straightness of the first charged particles and the shortest distance relative to the amount of movement of the second charged particles in the direction perpendicular to the direction of the shortest distance between the pair of substrates when the second charged particles move between the pair of substrates. The second charged particles, which indicate the ratio of the amount of movement in the direction, are different from the straightness of the second charged particles, so the charged particles with lower straightness and the higher charged particles should move so as to avoid movement of the charged particles with higher straightness. To do. This is because the charged particle force with the lower straightness is more resistant to the peripheral force than the charged particle with the higher straightness. In other words, the charged particles with the lower straightness receive the flow of the charged particles with the higher straightness as resistance, and move so as to avoid the resistance. Therefore, the first charged particles and the second charged particles can be effectively prevented from colliding with each other. And since the movement time of the 1st charged particle and the 2nd charged particle can be shortened, the time required for display switching can be shortened. [0058] Furthermore, according to the present disclosure, since the shape of the first charged particles and the shape of the second charged particles are different from each other, the resistance to the flow of the display liquid can be made different from each other. As a result, the straightness of the first charged particles and the straightness of the second charged particles can be made different from each other.

[0059] Furthermore, according to the present disclosure, the surface shape of the first charged particles has a dimple structure. Therefore, straightness can be improved like a golf ball with dimples. That is, the display liquid smoothly flows behind the first charged particles by the dimples, so that the resistance due to the display liquid is reduced and the straightness can be improved. Accordingly, the straight traveling property of the first charged particles can be made higher than the straight traveling property of the second charged particles, so that the first charged particles and the second charged particles can be effectively prevented from colliding with each other.

Furthermore, according to the present disclosure, the first charged particles are cross-linked polymer particles obtained chemically by polymerizing a monomer. Therefore, since a plurality of concave portions can be formed on the surface of the particle, a dimple structure can be easily formed.

Furthermore, according to the present disclosure, the surface shape of the second charged particles is a convex shape. Accordingly, since the resistance to the flow of the display liquid can be increased, the straightness of the second charged particles can be made lower than the straightness of the first charged particles. In addition, since the straightness of the second charged particles decreases, the second charged particles move so as to avoid the movement of the first charged particles. As a result, the probability that the first charged particles and the second charged particles collide with each other can be lowered, so that the moving time of the first charged particles and the second charged particles can be shortened.

[0062] Furthermore, according to the present disclosure, the resistance of the display liquid to the second charged particles can be easily increased by the child particles bonded to the mother particles of the second charged particles. This makes it possible to form second charged particles having straightness lower than that of the first charged particles.

[0063] Furthermore, according to the present disclosure, since the child particles are physically and firmly bonded to the surface of the mother particle by the hybridization method, the child particles are separated from the surface of the mother particle in the display liquid. It will not peel off.

Furthermore, according to the present disclosure, one charged particle attached to the first electrode moves so as to converge toward the second electrode having a surface area smaller than the surface area of the first electrode. In addition, the other charged particles adhering to the second electrode move so as to diffuse toward the first electrode. Move. In other words, for one charged particle that moves to the second electrode so as to converge, the other charged particle moves to the first electrode while diffusing outward to escape one charged particle force. Thereby, for example, even when a large number of first charged particles adhere to the surface of the first electrode without a gap, the large number of first charged particles move so as to converge toward the second electrode. That is, a space through which the second charged particles can pass is formed outside the first charged particles that converge and move. Therefore, collision between the first charged particles and the second charged particles can be effectively avoided. Furthermore, by providing the first electrode on the display substrate side and the second electrode on the rear substrate side, the color region displayed on the display substrate is not reduced.

[0065] Further, according to the present disclosure, for example, when the first charged particles are most densely arranged in one layer and moved from one substrate cover to the other substrate side, the second charged particles are It can pass through the gap between the first charged particle and the spacer located at the end. Thereby, the probability that the first charged particles and the second charged particles collide with each other can be effectively reduced.

Industrial applicability

[0066] The electrophoretic display medium of the present disclosure can be applied to various electronic devices including a display unit.

Claims

The scope of the claims

[1] a pair of substrates spaced apart from each other;

A display liquid sealed with a spacer between the pair of substrates;

A pair of charged particles dispersed in the display liquid and moving in the display liquid by the action of an electric field;

With

The pair of charged particles is a first charged particle and a second charged particle having a color and polarity different from the first charged particle,

When the first charged particles move between the pair of substrates, the amount of movement in the direction of the shortest distance with respect to the amount of movement of the first charged particles in a direction orthogonal to the direction of the shortest distance between the pair of substrates. And the direction of the shortest distance with respect to the amount of movement of the second charged particles in a direction orthogonal to the direction of the shortest distance between the pair of substrates when the second charged particles move between the pair of substrates. An electrophoretic display medium characterized in that the ratio of the amount of movement differs from each other.

2. The electrophoretic display medium according to claim 1, wherein the shape of the first charged particles and the shape of the second charged particles are different from each other.

[3] The electrophoretic display medium according to [1] or [2], wherein the surface shape of the first charged particles has a dimple structure.

4. The electrophoretic display medium according to claim 3, wherein the first charged particles are cross-linked polymer particles.

5. The electrophoretic display medium according to any one of claims 1 to 3, wherein the surface shape of the second charged particles is a convex shape.

[6] The second charged particles are mother particles,

6. The electrophoretic display medium according to claim 5, wherein the electrophoretic display medium is composed of child particles bonded to a surface of the mother particle and having a smaller diameter than the mother particle.

7. The electrophoretic display medium according to claim 6, wherein the child particles are physically bonded to the surface of the mother particle by a hybridization method.

[8] The pair of substrates includes a transparent display substrate and a back substrate, A first electrode provided on the display substrate and a second electrode provided on the back substrate;

8. The electrophoretic display medium according to claim 1, wherein a surface area of the second electrode is smaller than a surface area of the first electrode.

When a plurality of the first charged particles form a first charged particle layer that is closest to one another along the surface of the first substrate or the second substrate,

The gap between the first charged particle and the spacer located at an end of the first charged particle layer is a space in which at least one second charged particle can be arranged. The electrophoretic display medium according to any one of 1 to 7.