JP6035885B2 - Electrophoretic material, electrophoretic display device, and electronic apparatus - Google Patents

Description

  The present invention relates to an electrophoretic material, an electrophoretic display device, and an electronic device technical field.

  In an electrophoretic display device, a voltage is applied between a pixel electrode and a common electrode facing each other with an electrophoretic material interposed therebetween, and the electrophoretic particles such as charged black particles and white particles are moved spatially to display a display area. An image is formed. Once the electrophoretic particles move spatially, even if the voltage is removed, diffusion is suppressed by the cohesive force between the particles. For this reason, the electrophoretic display device has a property of maintaining an image even when power is not supplied, and thus is adapted to an electronic book or the like with low power consumption. In the conventional electrophoretic display device, as described in Patent Document 1, white particles such as titanium oxide and black particles such as carbon black are used as the electrophoretic particles. At that time, in order to increase the reflectance of white display or to increase the contrast ratio, titanium oxide was contained much more than the black particles.

JP 2009-145873 A

However, when a large amount of titanium oxide is contained in the electrophoretic material, there is a problem that electrophoresis becomes difficult to perform. Since titanium oxide has a large density of 4.2 g / cm ³ , the titanium oxide surface must be coated with a large amount of dispersant or surfactant in order to disperse it in a light solvent having a density of about 1 or less. . As a result, the viscosity of the electrophoretic material increased and electrophoresis was inhibited. That is, the conventional electrophoretic display device using the electrophoretic material has a problem that high-quality display (white display with high contrast and high reflectance) and electrophoretic properties (low voltage driving and high-speed response) are not compatible. It was.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

(Application Example 1) The electrophoretic material according to this application example is characterized in that first pigment particles charged to a first polarity, second pigment particles, and transparent fine particles are dispersed in a solvent.
If the electrophoretic material having this configuration is applied to an electrophoretic display device, the transparent fine particles dispersed in the solvent scatter light, so that the color of the second pigment particles can be made to stand out in the electrophoretic display device. That is, it is possible to display the color of the second pigment particles vividly while reducing the amount of the second pigment particles. Since the amount of the second pigment particles can be reduced, the addition amount of a dispersant or the like is also reduced, the viscosity of the electrophoretic material is not increased, and high electrophoretic properties can be maintained. Therefore, an electrophoretic display device using the electrophoretic material having this configuration can achieve both high-quality display (high contrast and high reflectance white display) and excellent electrophoretic properties (low voltage drive and high-speed response). Can do.

Application Example 2 In the electrophoretic material according to the application example described above, the ratio (area ratio) of the total surface area of the second pigment particles to the sum of the total surface area of the second pigment particles and the total surface area of the transparent fine particles is 4% or more. % Or less is preferable.
If the electrophoretic material having this configuration is applied to an electrophoretic display device, the display color of the second pigment particles can be made brighter than before. For example, when the color of the second pigment particles is white and the electrophoretic display device performs white display, the reflectance of white can be increased more than before, and the white color can be made brighter.

Application Example 3 In the electrophoretic material according to the application example described above, the area ratio is preferably 10% or more and 56% or less.
If the electrophoretic material having this configuration is applied to an electrophoretic display device, the display color of the second pigment particles can be made particularly brighter than before. For example, when the color of the second pigment particles is white and the electrophoretic display device displays white, the reflectance of white can be greatly increased as compared with the conventional case, and an extremely bright white can be obtained.

Application Example 4 In the electrophoretic material according to the application example described above, the second pigment particles are preferably white.
The light scattering of the transparent fine particles is milky white. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, the second pigment particles are white, so that a white display with high brightness can be achieved with a small amount of the second pigment particles together with light scattering of the transparent fine particles. Can be realized.

Application Example 5 In the electrophoretic material according to the application example described above, the first pigment particles are preferably black.
Since the black pigment particles absorb light, the effect of the transparent fine particles to highlight the color of the pigment particles by light scattering cannot be applied to black display. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, the transparent fine particles can highlight the color of the second pigment particles that exhibit a color different from that of the first pigment particles.

Application Example 6 In the electrophoretic material according to the application example described above, it is preferable that the transparent fine particles have a particle size in the range of 50 nm to 1 μm.
The center wavelength of visible light is about 550 nm, and if the size of the fine particles is about one-tenth or less, the visible light is Rayleigh scattered by the fine particles. On the other hand, when the particle size of the fine particles is about 1/10 or more and cannot be ignored compared with the wavelength, the visible light is scattered by the fine particles. Further, the transparent fine particles absorb very little light. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, the transparent fine particles cause Mie scattering of the color of the second pigment particles as they are, so that the color of the second pigment particles can be made to stand out. In addition, since the thickness of the electrophoretic display device is usually several tens of μm, when the particle size of the transparent fine particles is 1 μm or less, a sufficient amount of transparent fine particles for display can be added to the electrophoretic material.

Application Example 7 In the electrophoretic material according to the application example described above, the density of the transparent fine particles is preferably 2.5 g / cm ³ or less.
The density of silica beads that are chemically stable, non-toxic, inexpensive, and easy to handle is about 2.45 g / cm ³ . The density of most resin materials is 2.5 g / cm ³ or less. Therefore, if the electrophoretic material having this configuration is applied to the electrophoretic display device, the resin material and silica beads having a large density and difficult to disperse are reduced, and the resin material and silica beads having a small density and easy handling and a wide variety are available. Can be used as transparent fine particles. On the other hand, if the density is as small as 2.5 g / cm ³ or less, the sedimentation rate will be as low as about 0.8 μm / s according to Stokes' law, even if the transparent fine particles have a large particle size of 1 μm. For this reason, even when the thickness of the electrophoretic display device is as thin as about 50 μm, the sedimentation time is about 1 minute, and sufficient image retention is exhibited. That is, high-definition display (high contrast and high reflectance white display) and excellent electrophoretic properties (low voltage drive and high-speed response) are compatible with each other, and an electrophoretic display device excellent in image retention is used. The electrophoretic material can be realized safely and easily.

Application Example 8 In the electrophoretic material according to the application example, the transparent fine particles are preferably a resin.
There are many materials for resin, and there are a wide range of material options. Moreover, the adjustment of the particle size is relatively easy. In addition, the dispersion in an organic solvent is easy and the dispersion stability is high. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, high-quality display (high contrast and high reflectance white display) and excellent electrophoretic properties (low voltage drive and high-speed response) can be easily achieved. Can be compatible. Further, since the density of the resin is about the same as the density of the solvent, precipitation due to gravity hardly occurs. Therefore, the sedimentation time becomes extremely long, and the electrophoretic display device to which the electrophoretic material having this configuration is applied exhibits sufficiently long image retention.

Application Example 9 In the electrophoretic material according to the application example described above, the electrophoretic mobility of the first pigment particles is preferably larger than the electrophoretic mobility of the second pigment particles and the electrophoretic mobility of the transparent fine particles. .
Since the second pigment particles and the transparent fine particles use Mie scattering to make the color of the second pigment particles stand out, it is not necessary to be localized in a spatially narrow region. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, the display can be switched mainly by electrophoresing the first pigment particles.

Application Example 10 In the electrophoretic material according to the application example, it is preferable that the second pigment particles are charged to the second polarity.
If the electrophoretic material having this configuration is applied to an electrophoretic display device, the distribution position of both the first pigment particles and the second pigment particles can be controlled by an electric field applied to the electrophoretic material. That is, the image quality can be stabilized between different images. For example, when trying to display the color of the first pigment particles, the same brightness and reflectance can be displayed at any time.

Application Example 11 In the electrophoretic material according to the application example described above, the electrophoretic mobility of the second pigment particles is preferably larger than the electrophoretic mobility of the transparent fine particles.
Since the transparent fine particles scatter visible light by Mie, it is not necessary to be localized in a spatially narrow region. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, the display can be switched by mainly electrophoresing the first pigment particles and the second pigment particles.

Application Example 12 In the electrophoretic material according to the application example, it is preferable that the second pigment particles are electrically neutral.
Since the display using the second pigment particles utilizes the Mie scattering of the transparent fine particles, the necessity for the second pigment particles to be localized in a spatially narrow region is small, and the necessity for electrophoresis is also small. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, the display can be switched by electrophoresing the first pigment particles. Furthermore, since the second pigment particles are not charged, the leakage current through the electrophoretic material is reduced, and an electrophoretic material having good electrophoretic properties can be obtained. Further, since the second pigment particles are not charged, the first pigment particles and the second pigment particles do not undergo Coulomb coupling, and both can be easily separated. That is, if the electrophoretic material having this configuration is applied to an electrophoretic display device, high-quality display (high contrast and high reflectance white display) and excellent electrophoretic properties (low voltage drive and high-speed response) can be easily achieved. Can be compatible.

Application Example 13 In the electrophoretic material according to the application example described above, the transparent fine particles are preferably electrically neutral.
Since the transparent fine particles cause Mie scattering of visible light, the necessity for being localized in a spatially narrow region is small, and the necessity for electrophoresis is also small. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, the display can be switched by electrophoresing the first pigment particles and the second pigment particles. Furthermore, since the transparent fine particles are not charged, the leakage current through the electrophoretic material is reduced, and the electrophoretic material having good electrophoretic properties can be obtained.

Application Example 14 In the electrophoretic material according to the application example, it is preferable that the transparent fine particles are charged to the second polarity.
The transparent fine particles serve to make the display color of the second pigment particles stand out. Therefore, if the electrophoretic material having this configuration is applied to an electrophoretic display device, the transparent fine particles and the second pigment particles have the same polarity, and both can be electrophoresed in the same manner.

Application Example 15 An electrophoretic display device according to this application example includes the electrophoretic material according to any one of the above application examples.
According to this configuration, high-quality display (white display with high contrast and high reflectance) and excellent electrophoretic properties (low voltage drive and high-speed response) can be easily achieved, and electrophoresis with excellent image retention is also achieved. A display device can be realized.

Application Example 16 An electronic apparatus according to this application example includes the electrophoretic display device described in the application example.
According to this configuration, high-quality display (white display with high contrast and high reflectance) and excellent electrophoretic properties (low voltage drive and high-speed response) can be easily achieved, and electronic devices with excellent image retention Can be realized.

FIG. 3 is a perspective view of the electronic device according to the first embodiment. FIG. 3 is a cross-sectional view illustrating the electrophoretic display device according to the first embodiment. The figure explaining the effect which the weight ratio of a 2nd pigment particle has on a 2nd display. The figure explaining the effect which the particle number ratio of the 2nd pigment particle exerts on the 2nd display. 1 is a circuit diagram of an electrophoretic display device according to Embodiment 1. FIG. The perspective view which shows the structure of electronic paper. The perspective view which shows the structure of an electronic notebook. 9 is a cross-sectional view illustrating an electrophoretic display device according to Embodiment 2. FIG. FIG. 6 is a cross-sectional view illustrating an electrophoretic display device according to Embodiment 3. FIG. 6 is a cross-sectional view illustrating an electrophoretic display device according to a fourth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the scale of each layer and each member is made different from the actual scale so that each layer and each member can be recognized.

(Embodiment 1)
"Outline of electronic equipment"
FIG. 1 is a perspective view of an electronic apparatus according to the first embodiment. First, an outline of the electronic apparatus and the electrophoretic display device according to the first embodiment will be described with reference to FIG.

  As shown in FIG. 1, an electronic device 100 according to the present invention includes an electrophoretic display device 150 and an interface for operating the electronic device 100. Specifically, the interface is the operation unit 120 and includes a switch and the like. The electrophoretic display device 150 is a display module having a display area 10. The display area 10 includes a plurality of pixels 20 (see FIG. 5A), and an image is displayed on the display area 10 by electrically controlling these pixels 20.

"Structure of electrophoretic display device"
2A and 2B are cross-sectional views illustrating the electrophoretic display device according to the first embodiment. FIG. 2A illustrates a second display, and FIG. 2B illustrates a first display. In addition, the case where the color of the 1st pigment particle 241 is made into the 1st color and the 1st color is displayed is made into the 1st display. Similarly, the case where the color of the second pigment particle 242 is the second color and the second color is displayed is the second display. The first color and the second color are different, and in the present embodiment, as an example, the first color is black and the second color is white. Next, the structure of the electrophoretic display device 150 according to this embodiment will be described with reference to FIG.

  The electrophoretic display device 150 includes a first substrate 80 and a second substrate 90. A plurality of pixels 20 are arranged in a matrix in the display area 10. A pixel electrode 22 and a pixel circuit (see FIG. 5B) are formed for each pixel 20 in a region to be the display region 10 on the first substrate 80, and the common electrode 23 is formed on the second substrate 90 almost on the entire surface. Is formed. The pixel circuit includes a pixel switching transistor 21 and a storage capacitor 25, and one pixel 20 is formed at the intersection of the scanning line 30 and the data line 40. Furthermore, a common potential line 50 is also wired to the pixel 20. The electrophoretic material 24 is sandwiched between the first substrate 80 and the second substrate 90. The electrophoretic material 24 includes first pigment particles 241 charged to the first polarity, second pigment particles 242, and transparent fine particles 243, which are added to an unillustrated solvent together with an additive such as an unillustrated dispersant. The electrophoretic material 24 is dispersed.

  In the present embodiment, the second pigment particles 242 are charged to the second polarity, and the transparent fine particles are electrically neutral. The second polarity is electrically opposite to the first polarity. In this embodiment, as an example, the first polarity is positive (plus) and the second polarity is negative (minus). As a result, the electrophoretic material 24 exhibits electrophoretic properties between the pixel electrode 22 and the common electrode 23. Since the first pigment particles 241 and the second pigment particles 242 are charged with opposite polarities, the distribution positions of the first pigment particles 241 and the second pigment particles 242 are controlled by the electric field applied to the electrophoretic material 24. I can do it. That is, the image quality can be stabilized between different images. For example, when the first color is to be displayed by the first pixel and the second image, the distribution position of the second pigment particles 242 can be controlled by either image. The same brightness and reflectivity can be displayed at any time.

  The first color of the first pigment particles 241 and the second color of the second pigment particles 242 are preferably complementary to each other. That is, when the first pigment particles 241 are irradiated with white light, it is preferable that the reflected color obtained by the first pigment particles 241 absorbing the second color is the first color. In the present embodiment, as an example, the second color is white, and the second pigment particles 242 are white. Accordingly, the first color exhibited by the first pigment particles 241 is black. The transparent fine particles 243 are transparent. The term “transparent” as used herein means that when a film or thin plate having a thickness of about 25 μm is made of the material forming the transparent fine particles 243, the film or thin plate has a light transmittance of about 80% or more in the visible light region. , And the meaning.

  The second substrate 90 is transparent, and the user views the electrophoretic display device 150 from the second substrate 90 side. Accordingly, as shown in FIG. 2A, for example, in order to display white, the white second pigment particles 242 are brought closer to the common electrode 23 side, and the black first pigment particles 241 are brought closer to the pixel electrode 22 side. . The light 60 incident on the electrophoretic display device 150 is scattered by the second pigment particles 242 and the transparent fine particles 243 to be displayed second. On the other hand, in order to display black, as shown in FIG. 2B, the black first pigment particles 241 are brought closer to the common electrode 23 side, and the white second pigment particles 242 are brought closer to the pixel electrode 22 side. The light 60 incident on the electrophoretic display device 150 is absorbed by the first pigment particles 241 and is first displayed.

  In general, an object is white in two types: when it appears white due to a white pigment such as titanium oxide or alumina, and when it appears white when light is scattered (mainly Mie scattering) by fine particles dispersed in a fluid. In contrast to conventional electrophoretic materials and electrophoretic display devices that display white using white pigment, in this embodiment, white pigment (second pigment particle 242) and transparent fine particles 243 are used to display white. We use Mie scattering together. By doing so, the color of the second pigment particles 242 can be displayed vividly while reducing the amount of the second pigment particles 242 such as titanium oxide. Since the amount of the second pigment particles 242 can be reduced, the addition amount of a dispersant or the like can be reduced, the viscosity of the electrophoretic material 24 can be kept low, and high electrophoretic properties can be maintained. Furthermore, since the second pigment particles 242 are added in small amounts, and the transparent fine particles 243 that are superior in dispersibility and dispersion stability to the second pigment particles 242 are added, sedimentation of the second pigment particles 242 is suppressed, Also from this point, the image retention of the electrophoretic display device 150 is improved. As described above, since the second color is displayed using Mie scattering, the first color is preferably a complementary color to the second color. Further, since the electrophoretic display device 150 is often used in the electronic device 100 such as electronic paper, it is preferable that the first color is black and the second color is white.

  In the present embodiment, since the second pigment particles 242 are charged to the second polarity and the transparent fine particles 243 are electrically neutral, the electrophoretic mobility of the transparent fine particles 243 is almost zero, The electrophoretic mobility of the pigment particles 242 is larger than the electrophoretic mobility of the transparent fine particles 243. Further, the first pigment particles 241 are subjected to a strong charging process so that the electrophoretic mobility of the first pigment particles 241 is larger than the electrophoretic mobility of the second pigment particles 242. As can be seen from a comparison between FIGS. 2A and 2B, it is the first pigment particles 241 that always undergo electrophoresis in this embodiment. Therefore, the first pigment particles 241 need to be strongly charged, and the electrophoretic mobility must be large. On the other hand, since the second pigment particles 242 and the transparent fine particles 243 cause visible light to be Mie scattered, it is not necessary to be localized in a spatially narrow region. That is, the second pigment particles 242 and the transparent fine particles 243 need only be relatively uniformly distributed between the first substrate 80 and the second substrate 90, and it is not always necessary to be strongly electrophoresed. Therefore, in the present embodiment, the first pigment particles 241 mainly perform electrophoresis in the electrophoretic display device 150, and the display is switched by causing the second pigment particles 242 to perform weak electrophoresis. Generally, when particles are charged, ions having opposite polarities are released into the solvent, and the insulating properties of the solvent are lowered. In the electrophoretic material 24 of the present embodiment, the transparent fine particles 243 are not charged, and the second pigment particles 242 are weakly charged. Therefore, the amount of ions released into the solvent is reduced, and the insulating properties of the solvent are increased. When the electric insulation of the solvent increases, an electric field is efficiently applied to the charged particles, so that the electrophoretic properties are improved. That is, since the effective electric field intensity that the charged particles are subjected to increases, the electrophoretic properties are improved. Thus, the electrophoretic display device 150 exhibits excellent electrophoretic properties.

"Electrophoretic materials"
Next, the electrophoretic material 24 will be described. The electrophoretic material 24 is mainly composed of pigment particles such as first pigment particles 241 and second pigment particles 242, transparent fine particles, a solvent, and other additives. In addition, when it is not necessary to distinguish the 1st pigment particle 241 and the 2nd pigment particle 242 in particular, both are named generically and are only called a pigment particle.

  The pigment particles include a pigment itself and a product obtained by mixing a color material such as a pigment or a dye with a resin-based particle (resin-based color particle). The pigment particles are preferably small from the viewpoint of dispersion stability. Specifically, those having an average particle size in the range of about 10 nm to about 3 μm are preferable, and those having an average particle size in the range of about 100 nm to about 1 μm are more preferable.

  When the pigment itself is used as the pigment particles, the pigment itself may be used as it is, or the surface of the pigment itself may be coated with a material such as a resin material or another pigment. Examples of pigment particles in which the surface of the pigment itself is coated with another material include those in which the surface of titanium oxide particles is coated with silicon oxide or aluminum oxide. These particles are suitable as white particles.

  When using resin-based color particles as pigment particles, examples of the resin-based particles include acrylic resins, urethane resins, urea resins, epoxy resins, polystyrene, polyester, polyethylene, and polypropylene. One or two or more of these are combined to form resin-based particles. Resin-based colored particles, in which color materials are mixed with resin-based particles, cover the surface of resin-based particles with pigments or dyes, in addition to those obtained by mixing pigments and dyes with the above-mentioned basic materials in an appropriate composition ratio. Including goods. The surface of the resin-based color particles thus obtained may be further modified with an organic material such as a polymer, or may be modified with an inorganic material such as silicon oxide.

The first pigment particle 241 is a pigment exhibiting a first color, and in this embodiment, the first color is black. Therefore, titanium black (density 4.3 g / cm ³ ) is preferably used as the first pigment particle 241. Is used. The average particle size of titanium black is 250 nm. In addition to this, the first pigment particles 241 may use aniline black or carbon black.

The second pigment particle 242 is a pigment exhibiting a second color, and in this embodiment, the second color is white. Therefore, as a preferred example, titanium oxide (density 4.25 g / cm ³ ) is added to the second pigment particle 242. Is used. The average particle diameter of titanium oxide is 250 nm. In addition to this, the second pigment particles 242 include antimony trioxide (density 5.2 g / cm ³ ), aluminum oxide (density 4.0 g / cm ³ ), calcium carbonate (density 2.8 g / cm ³ ), barium oxide (density). 5.7 g / cm ³ ), barium carbonate (density 4.3 g / cm ³ ), barium sulfate (density 4.5 g / cm ³ ), magnesium oxide (density 3.65 g / cm ³ ), etc. good.

  The transparent fine particles 243 preferably have a particle size (diameter) in the range of 50 nm to 1 μm. Since the center wavelength of visible light is about 550 nm, when the size of the transparent fine particles 243 is about one-tenth or more and cannot be ignored as compared with the visible light wavelength, the visible light is Mie scattered by the transparent fine particles 243. Further, since the transparent fine particles 243 absorb very little light, the transparent fine particles 243 can cause the color of the second pigment particles 242 to be scattered as they are, and the color of the second pigment particles 242 can be made to stand out. Further, since the thickness of the electrophoretic display device 150 (the distance between the first substrate 80 and the second substrate 90 in FIG. 2) is usually several tens of μm, the transparent fine particles having a particle diameter of 1 μm or less are sufficient for display. A sufficient amount of transparent fine particles 243 can be added to the electrophoretic material 24 to cause a sufficient number of light reflections suitable for Mie scattering between the pixel electrode 22 and the common electrode 23. In the present embodiment, as a suitable example, the transparent fine particles 243 use silica beads having a particle diameter of 500 nm.

The density of the transparent fine particles 243 is preferably 2.5 g / cm ³ or less. Silica beads vary in density depending on the material, but are generally less than 2.45 g / cm ³ , are chemically stable, have no toxicity, are easy to adjust the particle size distribution, are inexpensive, and are easy to manufacture. It can be handled and is suitable for the transparent fine particles 243. The density of most resin materials is 1.5 g / cm ³ or less. Therefore, when silica beads or a resin material is used as the transparent fine particles 243, the amount of the second pigment particles 242 having a high density and difficult to disperse can be reduced. On the other hand, if the density is as small as 2.5 g / cm ³ or less, the sedimentation rate is slowed down to about 0.8 μm / s according to Stokes' law shown in Equation 1, even if the transparent fine particles 243 have a large particle size of about 1 μm.

Here, v is the sedimentation velocity, ρ _P is the density of the transparent fine particles 243, ρ _S is the density of the solvent, g is the acceleration of gravity, r _P is the radius of the transparent fine particles 243 (therefore, the particle size of the transparent fine particles 243 is 2r _P ). , Η is the viscosity of the solvent. The density of the silica beads used in this embodiment is 2.20 g / cm ³ . The density of the solvent is about 1 g / cm ³ and the viscosity is about 1 mPas. Therefore, in this embodiment, the sedimentation speed of the transparent fine particles 243 is about 0.65 μm / s. Thus, since the density of the transparent fine particles 243 is small and the sedimentation speed is slow, even when the thickness of the electrophoretic display device 150 is as thin as about 50 μm, the sedimentation time is about 1 minute or more, and sufficient image retention is exhibited. Become.

The material of the transparent fine particles 243 may be a resin. This is because there are various materials for the resin, and options for the transparent fine particles 243 are widened. Even if the transparent fine particles 243 made of resin are small in particle size, the particle size can be adjusted relatively easily, and the standard deviation can be reduced with respect to the average particle size, and the particle size distribution can be adjusted. Furthermore, the transparent fine particles 243 made of a resin can be easily dispersed in a solvent and have high dispersion stability. In addition, a 1.5 g / cm ³ degree density from 1.0 / cm ³ in a number of resins, since close to the density of the solvent (1.2 g / cm ³ order of 0.8 / cm ^3), after dispersion Almost no sedimentation occurs in the solvent. Specifically, as the resin of the transparent fine particles 243, linear polyethylene or cyclic polyethylene such as a cycloolefin polymer (density 0.92 / cm ³ to 0.97 g / cm ³ ) or polypropylene (density 0.90 / cm ³ 0.92 g / cm ³ ), polystyrene (density 1.04 / cm ³ to 1.07 g / cm ³ ), acrylic resin such as polymethyl methacrylate (density 1.18 / cm ³ to 1.22 g / cm) ³ )). These resin simple substances, composites of these resins, or those obtained by reacting these resin simple substances or composites with a cross-linking agent are used for the transparent fine particles 243. In addition, the transparent fine particles 243 can be used by coating the surface of fine particles made of the above-described resin with an inorganic material such as silica coat. In this case, resistance to the solvent is improved, and the temporal stability of the electrophoretic material is increased. Furthermore, since wettability is also improved, dispersibility and dispersion stability are also improved, which is preferable. Alternatively, the transparent fine particles 243 may be formed by coating silica beads with a resin layer to adjust the refractive index or reduce the specific gravity.

  As the solvent, a highly insulating organic solvent is preferable, and a poor solvent for the transparent fine particles 243 is used. The poor solvent here is a solvent that does not dissolve the transparent fine particles 243. That is, the poor solvent either does not dissolve the transparent fine particles 243 at all, or dissolves slightly to keep the shape of the transparent fine particles 243, or dissolves to such an extent that the low molecular components of the transparent fine particles 243 are slightly eluted. It is a solvent that exhibits properties. This is because the use of the poor solvent improves the resistance of the transparent fine particles 243 to the solvent and increases the temporal stability of the electrophoretic material 24.

  When the transparent fine particles 243 are formed of polyethylene, as a suitable poor solvent, water, alcohol solvents such as methanol, ethanol, butanol, isopropanol, octanol, and methyl cellosolve, silicone oil such as polydimethylsiloxane, or large Examples include vegetable oils such as bean oil, sunflower oil, and olive oil. In order to exhibit high electrophoretic properties, the solvent is required to have high insulating properties, and the optimum poor solvent is silicone oil.

  When the transparent fine particles 243 are formed of polypropylene, as a suitable poor solvent, water, alcohol solvents such as methanol, ethanol, butanol, isopropanol, octanol, and methyl cellosolve, silicone oil such as polydimethylsiloxane, or large Examples thereof include vegetable oils such as bean oil, sunflower oil, olive oil, and petroleum solvents such as isoparaffinic solvents. In order to exhibit high electrophoretic properties, the solvent is required to have high insulation properties, and the optimum poor solvent is silicone oil or petroleum solvent.

  In the case where the transparent fine particles 243 are formed of polystyrene, water or silicone oil such as polydimethylsiloxane can be used as a suitable poor solvent. In order to exhibit high electrophoretic properties, the solvent is required to have high insulating properties, and the optimum poor solvent is silicone oil.

  When the transparent fine particles 243 are formed of an acrylic resin, water, or o-xylene, m-xylene, p-xylene, toluene, benzene, dodecylbenzene, hexylbenzene, phenylxylylethane, naphthene series are preferable as a poor solvent. Examples thereof include aromatic hydrocarbon solvents such as hydrocarbons, silicone oils such as polydimethylsiloxane, vegetable oils such as soybean oil, sunflower oil, olive oil, and petroleum solvents such as isoparaffin solvents. In order to exhibit high electrophoretic properties, the solvent is required to have high insulation properties, and the optimum poor solvent is silicone oil or petroleum solvent.

  In the case where transparent fine particles 243 are formed from a resin-coated fine particle surface coated with an inorganic material such as silica coat or silicon beads, water, methanol, ethanol, butanol, isopropanol, octanol, methyl are used as suitable poor solvents. Alcohol solvents such as cellsolve, or aromatic hydrocarbon solvents such as o-xylene, m-xylene, p-xylene, toluene, benzene, dodecylbenzene, hexylbenzene, phenylxylylethane, naphthene hydrocarbons, Or aliphatic hydrocarbon solvents such as cyclohexane, n-hexane, kerosene, paraffin hydrocarbons, various ester solvents such as ethyl acetate and butyl acetate, or ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone Or Silicone oil such as polydimethylsiloxane, vegetable oil such as soybean oil, sunflower oil, olive oil, or chlorobutane, chloroform, dichlorobenzene, trichloroethylene, trichlorofluoroethylene, trichloroethane, carbon tetrachloride, cyclohexyl chloride, chlorobenzene, 1,1,2 Halogenated hydrocarbon solvents such as, 2-tetrachloroethylene, trifluorochloroethane, ethyl tetrafluoride dibromide, ethane bromide, ethane tetrafluoride difluoride, methylene iodide, triiodosilane, methyl iodide Or water and most organic solvents such as carbon disulfide or petroleum solvents such as isoparaffinic solvents. In order to exhibit high electrophoretic properties, the solvent is required to have high insulation properties, and the optimum poor solvent is silicone oil or petroleum solvent.

  As the solvent, a good solvent for the transparent fine particles 243 may be employed. The good solvent here is a solvent that dissolves the transparent fine particles 243 originally, but is a substance that is substantially a poor solvent by means such as resin cross-linking reaction. By using a good solvent, the transparent fine particles 243 include the solvent and swell. However, since the density is closer to that of the solvent, it contributes to dispersion stability and Mie scattering also occurs between the first substrate 80 and the second substrate 90. And the second color of the second pigment particles 242 is clearly displayed.

  When the transparent fine particles 243 are formed of polyethylene, as a suitable good solvent, a petroleum solvent such as an isoparaffin solvent, o-xylene, m-xylene, p-xylene, toluene, benzene, dodecylbenzene, hexylbenzene, Aromatic hydrocarbon solvents such as phenylxylylethane, naphthenic hydrocarbons, or chlorobutane, chloroform, dichlorobenzene, trichloroethylene, trichlorofluoroethylene, trichloroethane, carbon tetrachloride, cyclohexyl chloride, chlorobenzene, 1,1,2, Halogenated hydrocarbon solvents such as 2-tetrachloroethylene, trifluorochloroethane, ethyl tetrafluoride dibromide, ethane bromide, ethane tetrafluoride difluoride, methylene iodide, triiodosilane, methyl iodide, Etc.

  When the transparent fine particles 243 are formed of polypropylene, examples of suitable good solvents include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, or o-xylene, m-xylene, p-xylene, toluene, benzene, dodecylbenzene, Examples thereof include aromatic hydrocarbon solvents such as hexylbenzene, phenylxylylethane, and naphthene hydrocarbons, and various ester solvents such as ethyl acetate and butyl acetate.

  When the transparent fine particles 243 are formed of polystyrene, examples of suitable good solvents include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, or o-xylene, m-xylene, p-xylene, toluene, benzene, dodecylbenzene, Aromatic hydrocarbon solvents such as hexylbenzene, phenylxylylethane, naphthenic hydrocarbons, or various ester solvents such as ethyl acetate and butyl acetate, or chlorobutane, chloroform, dichlorobenzene, trichloroethylene, trichlorofluoroethylene, trichloroethane , Carbon tetrachloride, cyclohexyl chloride, chlorobenzene, 1,1,2,2-tetrachloroethylene, trifluorochloroethane, ethyl tetrafluoride dibromide, ethane bromide, ethane tetrafluoride difluoride, methyl iodide Emissions, triiodo silane, halogenated hydrocarbon solvents, such as methyl iodide, and the like.

  When the transparent fine particles 243 are formed of an acrylic resin, as a suitable good solvent, alcohol solvents such as methanol, ethanol, butanol, isopropanol, octanol, and methyl cellosolve, or ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone Or o-xylene, m-xylene, p-xylene, toluene, benzene, dodecylbenzene, hexylbenzene, phenylxylylethane, aromatic hydrocarbon solvents such as naphthene hydrocarbons, or ethyl acetate or butyl acetate Various ester solvents, or chlorobutane, chloroform, dichlorobenzene, trichloroethylene, trichlorofluoroethylene, trichloroethane, carbon tetrachloride, cyclohexyl chloride, chlorobenzene, 1,1,2, -Halogenated hydrocarbon solvents such as tetrachloroethylene, trifluorochloroethane, ethyl tetrafluoride dibromide, ethane bromide, ethane tetrafluoride difluoride, methylene iodide, triiodosilane, methyl iodide, etc. Is mentioned.

"Electrophoretic material composition"
FIG. 3 is a diagram for explaining the effect of the weight ratio of the second pigment particles on the second display. Next, the weight ratio of the second pigment particles 242 and the transparent fine particles 243 is described with reference to FIG. 3 in order to display the second display clearly.

  In FIG. 3, the result in the simple experiment system regarding how the second display (white display) of the electrophoretic display device 150 changes in accordance with the ratio of the second pigment particles 242 is shown. In examining this change, the second display shown in FIG. 2A is reproduced and evaluated in a simple experimental system. In a simple experimental system, a flat cell in which a dispersion was sealed between transparent substrates was formed, this flat cell was placed on a black background with a reflectance of 1.18%, and the reflectance of the surface was measured. The dispersion uses silicone oil as the solvent, and the second pigment particles 242 (titanium oxide) and the transparent fine particles 243 (silica beads) are added to the solvent and dispersed by adding a dispersant (acrylic / silicone copolymer). Yes. The total weight of the second pigment particles 242 and the transparent fine particles 243 is 30 wt% of the dispersion, and the weight ratio of the second pigment particles 242 to the total weight is the horizontal axis in FIG. Therefore, 0% on the horizontal axis of FIG. 3 indicates a dispersion liquid containing only the transparent fine particles 243 without containing the second pigment particles 242. Similarly, 100% on the horizontal axis of FIG. 3 indicates a dispersion liquid that does not include the transparent fine particles 243 but includes only the second pigment particles 242, and corresponds to a conventional electrophoretic material. The vertical axis in FIG. 3 is the reflectance of the surface. In addition, the distance (cell gap) between transparent substrates is 60 micrometers, and 10 wt% of dispersing agents are added with respect to the solvent.

  Since 0% on the horizontal axis in FIG. 3 does not include the second pigment particles 242, it represents the whiteness of Mie scattering by the transparent fine particles 243. In a state where the cell gap is as narrow as 60 μm, it is difficult to express whiteness only by Mie scattering, and the reflectance is about 7%. In short, at a cell gap of 60 μm, Mie scattering is insufficient, the back surface can be seen through, and the reflectance is close to that of a black background.

  On the other hand, 5% on the horizontal axis in FIG. 3 means 5% for the second pigment particles 242 and 95% for the transparent fine particles 243. In this case, the reflectance is rapidly improved from 7% to nearly 50% of the transparent fine particles alone. This is because the transparent fine particles 243 cause Mie scattering of the color of the second pigment particles 242. That is, when the second pigment particles 242 are added to the transparent fine particles 243 even slightly, the second color of the second pigment particles 242 is vividly displayed due to the Mie scattering of the transparent fine particles 243.

  Since 100% of the horizontal axis in FIG. 3 does not include the transparent fine particles 243, it corresponds to a conventional electrophoretic material. In the simple experimental system, the first pigment particles 241 are not included in the dispersion, so the white display has a reflectivity of about 75%. If the electrophoretic material contains, the reflectance of white display is almost halved due to Coulomb coupling between black particles and white particles. That is, in the conventional electrophoretic material, 75% in FIG. 3 is actually reduced to a white reflectance of slightly less than 40%. On the other hand, in the electrophoretic material of the present embodiment including the weakly charged second pigment particles 242 and the transparent fine particles 243, the white reflectance is slightly lowered from the reflectance shown in FIG. For example, even if the electrophoretic material 24 is manufactured with the second pigment particles 242 being 5% and the transparent fine particles 243 being 95%, the white reflectance is hardly lowered. This is because, in the electrophoretic material 24 according to the present invention, the second pigment particles 242 are weakly treated as in the present embodiment, or are neutral as shown in the third and fourth embodiments. However, since the amount thereof is smaller than in the conventional case (in this example, 1/20 of the conventional amount), the Coulomb coupling between the first pigment particle 241 and the second pigment particle 242 is extremely small. In short, if the weight ratio of the second pigment particles 242 to the second pigment particles 242 and the transparent fine particles 243 is 5% or more, a second display that is brighter than before is performed. When the second color is white, the white reflectance is higher than before and the contrast ratio is improved. In addition, since the viscosity of the electrophoretic material 24 is also reduced, the electrophoretic properties are improved, and display switching at high speed and low voltage driving are realized. Furthermore, since the dispersion stability is increased, the image retention is also improved.

  The upper limit of the weight ratio of the second pigment particles 242 to the second pigment particles 242 and the transparent fine particles 243 is 99%. From FIG. 3, if the weight ratio is 75% or less, the white reflectance is definitely higher than the conventional one. I understand that. This is because the larger the ratio of the second pigment particles 242, the greater the Coulomb coupling between the first pigment particles 241 and the second pigment particles, and the white display reflectance of the electrophoretic material 24 deviates from FIG. Further, as the weight ratio of the second pigment particles 242 is increased, the improvement in electrophoretic properties is reduced, and at the same time, the improvement in image retention is also reduced. Therefore, the optimal weight ratio of the second pigment particles 242 to the second pigment particles 242 and the transparent fine particles 243 is in the range of 10% to 50%.

Next, the optimal amount of the first pigment particles 241, the second pigment particles 242, and the transparent fine particles 243 will be described. First, the first pigment particles 241, the second pigment particles 242, and the transparent fine particles 243 are considered as spheres, and the composition of the electrophoretic material 24 necessary for realizing the electrophoretic display device 150 having a high contrast ratio is considered. The density of the second pigment particles 242 (white particles) is ρ _W , the radius of the white particles is r _W , the density of the first pigment particles 241 (black particles) is ρ _B , the radius of the black particles is r _B , and the transparent fine particles 243 ( The density of the transparent particles is ρ _P , and the radius of the transparent particles is r _P. At this time, the cross-sectional area of the black particles is expressed by Equation 2.

  When the circle is closely packed in the plane, the area ratio of the circle is Equation 3.

  Therefore, the area occupied by the black particles when densely packed is obtained by dividing Formula 2 by Formula 3 and Formula 4.

Next, it is assumed that a cell having a cell gap d is a square whose side is L in plan view. Since the area of the square is L ² , the number of particles necessary to completely cover the square in a plane is expressed by Equation 5.

Denoting the number of layers of the required black particles N _B, the total number of black particles necessary is the formula 6.

  The weight of one black particle is Equation 7.

  Therefore, the total weight of the black particles in the cell is the product of Equation 6 and Equation 7, and is given by Equation 8.

The depth of the cell is d, white particles, black particles and transparent particles are put in the cell, and the density of the solvent is ρ _S. The weight of the solvent filling the cell is from the volume of the square to the volume of the white particles. Then, the volume obtained by subtracting the volume of the black particles and the volume of the transparent particles is multiplied by the density of the solvent to obtain Equation 9.

N _W is the number of layers when white particles are arranged in layers, and N _P is the number of layers when transparent particles are arranged in layers. From Equation 8 and Equation 9, the weight of the particles of the electrophoretic material 24 and the solvent (solvent + black particles + white particles + transparent particles) is expressed by Equation 10.

Since usually additives are added to the other particles and a solvent, the ratio W _B of the black particle weight to the total weight of the electrophoretic material 24 is divided by equation 10 in consideration of the effect k additives Equation 8 Thus, Equation 11 is obtained. In addition, although k changes with cases, it is 1 or more and is generally about 1.1 in many cases.

Similarly, the ratio W _W of the white particle weight to the total weight of the electrophoretic material is expressed by Equation 12.

Similarly, the ratio W _P of the transparent particle weight to the total weight of the electrophoretic material is expressed by Equation 13.

Incidentally, the ratio R _W (weight ratio) of the weight of the white particles (second pigment particles 242) to the sum of the weight of the white particles (second pigment particles 242) and the weight of the transparent particles (transparent fine particles 243) is expressed by Equation 14.

As described with reference to FIG. 3, a preferred range of weight proportions R _W is 99% or more than 5%, the optimum range is 50% or less than 10%. If the lower limit of the preferred range of the weight ratio R _W is R _Wmin and the upper limit of the preferred range is R _Wmax , Equation 14 can be rewritten as Equation 15.

When R _Wmin = 5% and R _Wmax = 99%, Equation 15 becomes Equation 16.

Further, when R _Wmin = 10% and R _Wmax = 50%, Expression 15 becomes Expression 17.

When N _B = 1, there is a gap of 9.31% according to Equation 3. Therefore, even in an ideal system where the reflectance of white particles is 80% and the reflectance of black particles is 0%, black display The reflectance of is 7.4%. That is, if there is only one layer of black particles, the contrast ratio is lowered by the gap. If the two layers of particles are densely packed, theoretically, the surface is completely covered. Therefore, in the ideal system, the reflectance of black display is 0%. Therefore, it is preferable that at least two layers of black particles and white particles are included in the electrophoretic material 24. As for black particles, it is only necessary to absorb incident light, so in principle, the black particles can be displayed in two layers, but for the second display, incident light is repeatedly reflected and scattered multiple times as reflected light. Must be emitted. Therefore, the sum of the number of layers of the second pigment particles 242 and the transparent fine particles 243 (N _W + N _P ) is larger than N _B , and is preferably 10 or more and 40 or less according to experiments, and a preferred example is N _W + N _P. = About 25. That is, the layer number N _B of the electrophoretic display device 150 of minimum one pigment particles 241, the layer number of the sum of the minimum required secondary pigment particles 242 and the transparent fine particles 243 (N _W + N _P) Is expressed by Equation 18.

  Both Equations 15 through 17 and Equation 18 need to be satisfied. When Formula 14 is rewritten, Formula 19 is obtained.

  Using Expression 19, Expression 18 is expressed as Expression 20.

After all, in order to make an excellent electrophoretic material 24, 5% ≦ R _W ≦ 99%, more preferably 5% ≦ R _W ≦ 75%, ideally 10% ≦ R _W ≦ 50%. And N _B , N _W, and N _P are determined so as to satisfy Equations 18 and 19. Next, N _B , N _W, and N _P obtained in this way are substituted into Formulas 11 to 13 to determine W _B , W _W , and W _P. As an example, when considering the minimum amount W _Bmin of black particles for setting the reflectance of black display to 0% in an ideal system, this is expressed by Equation 21 with N _B = 2 and is based on the total weight of the electrophoretic material 24. The black particle weight ratio W _B must be greater than or equal to W _Bmin .

In this embodiment, r _B = r _W = 0.125 μm, r _P = 0.25 μm, d = 60 μm, ρ _B = 4.3 g / cm ³ , ρ _W = 4.25 g / cm ³ , ρ _P = 2 20 g / cm ³ and ρ _S = 0.78 g / cm ³ . When R _W = 0.2, N _P = 3.86 N _{W according} to Equation 19. In order to satisfy this relationship and to satisfy Equation 18 with N _B = 2, N _W ≧ 2.06. Therefore, as a preferred example for W _Bmin , N _W = 2.06 and N _P = 7.96. (N _W + N _P = 10.02). When these are k = 1.1 (with few additives) and adapted to Equations 11 to 13, W _B = 2.3 wt%, W _W = 2.3 wt%, W _P = 9.4 wt% Become.

In an ideal system, as described above, in reality, both white particles and black particles are aggregated in the electrophoretic material 24 or are adsorbed by a partition wall or a microcapsule that encloses the electrophoretic material 24. , N _B and N _W are preferably larger than the above-mentioned minimum values. According to an experiment, the reflectance of a black display is decreased in accordance with increasing N _B with 4,5, 5 or more did not change almost. Therefore, a preferable range of N _B and N _W is 4 or more and 6 or less, and N _B = N _W = 5.5 as a preferable example. At this time, N _P = 21.25 according to Equation 19 (thus N _W + N _P = 26.75), W _B = 5.3 wt%, W _W = 5.2 wt%, W _P = 25.0 wt%. It becomes. Therefore, W _W + W _P = 30.2 wt%, which is the basis for the experimental conditions in the simple experimental system shown in FIG.

  FIG. 4 is a diagram for explaining the effect of the ratio of the number of second pigment particles on the second display when the electrophoretic display device performs the second display. Next, with reference to FIG. 4, the ratio between the number of layers of the second pigment particles 242 and the number of layers of the transparent fine particles 243 will be described in order to clearly display the second display.

So far, the silica beads used as the transparent fine particles 243, but the relationship between the second pigment particles 242 and the transparent fine particles 243 have been described with reference to the weight ratio R _W, actually strongly influence the second display reflectance The effect is the ratio of the total surface area of the second pigment particles 242 and the transparent fine particles 243 contained in the electrophoretic material 24. Therefore, with reference to FIG. 4, the results shown in FIG. 3 will be described using the ratio of the total surface area by generalizing the transparent fine particles 243 from silica beads to other materials. In FIG. 4, the effect of coupling with black particles generated when the electrophoretic material 24 is used is also taken into consideration. First, from Equation 6, the number of white particles per unit volume is Equation 22.

From Equation 22, the ratio R _S (area ratio) of the total surface area of the second pigment particles 242 (white particles) to the sum of the total surface area of the second pigment particles 242 (white particles) and the total surface area of the transparent fine particles 243 (transparent particles). ) Is expressed by Equation 23.

As shown in Equation 23, the area ratio R _S is equal to the ratio of the number of layers. Substituting Equation 19 into Equation 23 yields Equation 24.

Formula 24 is a conversion formula from the weight ratio R _W to the area ratio R _S. The horizontal axis in FIG. 4 is obtained by converting the horizontal axis in FIG. 3 using Equation 24. Since the deviation between the white reflectance of the simple experimental system and the second display of the electrophoretic display device 150 is proportional to the number of particles of the second pigment particles 242, the vertical axis in FIG. 3 is converted in accordance with this. It is a vertical axis. Thus, FIG. 4 shows the area ratio R _S dependency of the reflectance in the second display of the electrophoretic display device 150. As can be seen from FIG. 4, when the area ratio R _S is 4% or more and 96% or less, the reflectance of white display is 40% or more, and the reflectance is higher than that of the conventional electrophoretic display device. If the area ratio R _S is 10% or more and 56% or less, the reflectance of white display is 60% or more, and an extremely bright white display is realized. The optimum value is around R _S = 21%.

  When Formula 23 is rewritten, Formula 25 is obtained.

When the composition of the preferable electrophoretic material 24 is summarized, first, appropriate N _B and N _W are determined. A preferable range of N _B and N _W is 4 or more and 6 or less as described above. Next, N _P is determined according to Equation 25. A preferable range of the ratio R _S is 4% or more and 96% or less, and more preferably 10% or more and 56% or less. N _B , N _W and N _P determined in this way are applied to Equations 11 to 13 to determine the weight ratio of each particle. As a preferred example, cross-linked polymethyl methacrylate (density 1.2 g / cm ³ ) having a particle size of 0.3 μm (radius 150 nm) is used as transparent particles, and titanium black (particle size 125 nm) having a particle size of 0.25 μm (radius 125 nm). using density 4.3 g / cm ^3), using a titanium oxide having a particle size of 0.25 [mu] m (radius 125 nm) (density of 4.25 g / cm ³⁾ to white particles, and _{N B = N W = 5.5,} Rs = 0.21 (R _W = 0.44), N _P = 20.7 (hence N _W + N _P = 26.2) according to Equation 25, and k = 1.1 (additives slightly As a result, from Equation 11 to Equation 13, W _B = 6.0 wt%, W _W = 5.9 wt%, and W _P = 7.9 wt%. At this time, it can be seen from FIG. 4 that the reflectance when the electrophoretic display device 150 displays white is about 70.7%. In the above structure, when transparent polymethyl methacrylate (density 1.2 g / cm ³ ) having a particle size of 0.1 μm (radius 50 nm) is used for the transparent particles, N _B = N _W = 5.5, If the _{rs = 0.21 (R W = 0.70} ), N P = 20.9 ( _{thus, N W + N P = 26.4} ) by equation 25 becomes as k = 1.1 (the additive According to Equations 11 to 13, the white display reflectance of the electrophoretic display device 150 is 70 when W _B = 6.1 wt%, W _W = 6.0 wt%, and W _P = 2.7 wt%. About 7%. Thus, it is preferable to reduce the particle diameter of the transparent fine particles 243 because high display quality and excellent electrophoretic properties can be secured even if the weight of the transparent fine particles 243 is reduced. As described above, the particle diameter of the transparent fine particles 243 is preferably in the range of 50 nm or more and 1 μm or less. However, from the viewpoint that the transparent fine particles 243 are easy to handle and the amount of addition can be reduced, as described herein, The particle diameter of the transparent fine particles 243 is more preferably in the range of 0.1 μm to 0.3 μm.

"Circuit configuration"
5A and 5B are circuit diagrams of the electrophoretic display device according to the first embodiment. FIG. 5A is a diagram for explaining the overall configuration, and FIG. 5B is a diagram for explaining a pixel circuit. Next, the drive circuit of the electrophoretic display device according to this embodiment will be described with reference to FIG.

  As shown in FIG. 5A, in the display area 10, m rows × n columns of pixels 20 are arranged in a matrix (two-dimensional plane). In the display area 10, there are m scanning lines 30 (that is, scanning lines Y1, Y2,..., Ym) and n data lines 40 (that is, data lines X1, X2,..., Xn). It is provided so as to cross each other. Specifically, m scanning lines 30 extend in the row direction (that is, the X direction), and n data lines 40 extend in the column direction (that is, the Y direction). Pixels 20 are arranged corresponding to the intersections of m scanning lines 30 and n data lines 40.

  A drive circuit 70 is provided outside the display area 10. The drive circuit 70 includes a controller 71, a scanning line drive circuit 72, a data line drive circuit 73, a common potential supply circuit 74, and the like. The controller 71 controls operations of the scanning line driving circuit 72, the data line driving circuit 73, the common potential supply circuit 74, and the like, and supplies various signals such as a clock signal and a timing signal to each circuit.

Based on the timing signal supplied from the controller 71, the scanning line driving circuit 72 sequentially supplies a scanning signal in a pulse manner to each of the scanning lines Y1, Y2,. The data line driving circuit 73 supplies image signals to the data lines X1, X2,..., Xn based on the timing signal supplied from the controller 71. The image signal takes a multilevel potential between a high potential V _H (for example, 15 V) and a low potential V _L (for example, −15 V). In the present embodiment, the image signal is binary, and the image signal of the high potential V _H is supplied to the pixel electrode 22 rewritten to the first display (black display), and the second display (white display). image signal of low potential V _L is supplied to the pixel electrode 22 are rewritten).

The common potential supply circuit 74 supplies the common potential V _com to the common potential line 50. Note that the common potential V _com may be a constant potential, or may be changed according to, for example, a gradation to be written or a frame. In the present embodiment, the common potential V _com is a reference potential for all potentials, and the common potential is 0V. Therefore, the previous high potential V _H (for example, 15 V) and low potential V _L (for example, −15 V) are directly used as a potential difference with respect to the common potential V _com . Various signals are input / output to / from the controller 71, the scanning line driving circuit 72, the data line driving circuit 73, and the common potential supply circuit 74, but the description of those not particularly related to the present embodiment is omitted. ing.

  As shown in the circuit diagram of FIG. 5B, the pixel 20 includes a pixel switching transistor 21, a pixel electrode 22, a common electrode 23, an electrophoretic material 24, and a storage capacitor 25.

  The pixel switching transistor 21 is composed of, for example, an N-type transistor. Here, an upper gate type thin film transistor is employed as shown in FIG. 2, but a lower gate type thin film transistor may be used. The pixel switching transistor 21 has a gate electrically connected to the scanning line 30, a source electrically connected to the data line 40, and a drain connected to one end of the pixel electrode 22 and the storage capacitor 25. Electrically connected. The storage capacitor 25 is composed of a pair of electrodes that are arranged to face each other with a dielectric film therebetween, and one electrode (one end) is electrically connected to the pixel electrode 22 and the pixel switching transistor 21 and the other electrode (others). End) is electrically connected to the common potential line 50. The holding capacitor 25 can maintain the image signal for a certain period. The pixel switching transistor 21 receives the image signal supplied from the data line driving circuit 73 via the data line 40 and the timing according to the scanning signal supplied in a pulse form from the scanning line driving circuit 72 via the scanning line 30. Thus, the data is output to the pixel electrode 22 and the storage capacitor 25.

An image signal is supplied to the pixel electrode 22 from the data line driving circuit 73 through the data line 40 and the pixel switching transistor 21. The pixel electrode 22 is disposed so as to face the common electrode 23 with the electrophoretic material 24 interposed therebetween. The common electrode 23 is electrically connected to a common potential line 50 to which a common potential V _com is supplied. The common electrode 23 is provided on the second substrate 90 facing the first substrate 80 on which the pixel electrode 22 is formed. The first pigment particles 241 and the second pigment particles 242 are in the vertical direction of the cross-sectional view shown in FIG. Electrophoresis with Note that the common electrode 23 may be provided on the first substrate 80 on which the pixel electrode 22 is formed, and the electrophoretic particles may be electrophoresed in the horizontal direction (left-right direction in FIG. 2) of the cross-sectional view of FIG.

"Electronics"
Next, electronic devices to which the above-described electrophoretic display device is applied will be described with reference to FIGS. Hereinafter, the case where the above-described electrophoretic display device 150 is applied to the electronic paper 400 and the electronic notebook 500 is taken as an example.

  FIG. 6 is a perspective view illustrating a configuration of electronic paper. As shown in FIG. 6, the electronic paper 400 includes an electrophoretic display device 150 according to the present embodiment. The electronic paper 400 has flexibility, and is composed of a rewritable sheet that exhibits the same texture and flexibility as conventional paper.

  FIG. 7 is a perspective view showing the configuration of the electronic notebook. As shown in FIG. 7, an electronic notebook 500 is obtained by bundling a plurality of electronic papers 400 shown in FIG. 6 and sandwiching them between covers 501. The cover 501 includes a display data input unit for inputting display data sent from an external device, for example. Thereby, according to the display data, the display content can be changed or updated while the electronic paper 400 is bundled.

  Since the electronic paper 400 and the electronic notebook 500 described above include the electrophoretic display device 150 according to the present embodiment, high-quality image display can be performed. In addition to these, the electrophoretic display device 150 according to the present embodiment may be applied to electronic devices such as watches, mobile phones, portable audio devices, electronic tablet terminals, personal computers, electronic signboards, and electronic blackboards. it can.

As described above, according to the electrophoretic material 24 according to the present embodiment, the electrophoretic display device 150 to which the electrophoretic material 24 is applied, and the electronic apparatus to which the electrophoretic display device 150 is applied, the following effects can be obtained. .
Since the transparent fine particles 243 dispersed in the solvent scatter the light of the color of the second pigment particles 242, the color of the second pigment particles 242 can be made to stand out by the electrophoretic display device 150. As a result, it is possible to display the color of the second pigment particle 242 vividly while reducing the amount of the second pigment particle 242 as compared with the conventional case. Since the amount of the second pigment particles 242 can be reduced, the Coulomb coupling between the first pigment particles 241 and the second pigment particles 242 is also reduced, the second color is displayed vividly, and the contrast ratio is improved. Furthermore, since the amount of the second pigment particles 242 can be reduced, the addition amount of a dispersant or the like is also reduced, the viscosity of the electrophoretic material 24 is not increased, and high electrophoretic properties can be maintained. Therefore, the electrophoretic display device 150 using the electrophoretic material 24 having this configuration achieves both high-quality display (high contrast and high reflectance white display) and excellent electrophoretic properties (low voltage drive and high-speed response). You can make it.
Furthermore, high-quality display (white display with high contrast and high reflectance) and excellent electrophoretic properties (low voltage drive and high-speed response) can be easily achieved, and the electronic device 100 with excellent image retention can be realized. I can do things.

  Regarding the color of the pigment particles, the combination of the first color and the second color is not limited to black and white, and various combinations are possible. For example, it is good also as a combination of the color (complementary color) of the relationship located in the opposite direction in a color coordinate. Specifically, the additive primary color of red, green, and blue is the second color, the subtractive primary color of cyan, magenta, and yellow is the primary color, and the complementary colors are the primary colors. And a second color combination. In other words, the pigment particles exhibiting the three primary colors of additive color mixture may be used as the second pigment particles 242, and the pigment particles exhibiting the three primary colors of subtractive color mixing that absorb these three primary colors of additive color may be used as the first pigment particles 241. Specifically, the second color is red and cyan that absorbs red is the first color, or the second color is green and magenta that absorbs green is the first color, or Alternatively, the second color may be blue, and yellow that absorbs blue may be the first color.

(Embodiment 2)
"Transparent particles are charged to the second polarity"
FIG. 8 is a cross-sectional view illustrating the electrophoretic display device according to the second embodiment, where (a) illustrates the second display and (b) illustrates the first display. Hereinafter, the electrophoretic material 24 and the electrophoretic display device 150 according to this embodiment will be described. In addition, about the component same as Embodiment 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

  The present embodiment (FIG. 8) differs from the first embodiment (FIG. 2) in that the transparent fine particles 243 are charged to the second polarity. Other configurations are almost the same as those of the first embodiment. In Embodiment 1 (FIG. 2), the transparent fine particles 243 were electrically neutral. On the other hand, in this embodiment (FIG. 8), the transparent fine particles 243 are negatively (negatively) weakly charged. When the transparent fine particles 243 are neutral, the transparent fine particles 243 are always uniformly distributed between the first substrate 80 and the second substrate 90 regardless of the electric field applied to the electrophoretic material 24. Therefore, as shown in FIG. 2B, when the first display is performed, the transparent fine particles 243 may be slightly mixed with the first pigment particles 241 on the common electrode 23 side. As a result, the saturation of the first display may be reduced. In contrast, in the present embodiment, as shown in FIGS. 8A and 8B, the spatial distribution of the transparent fine particles 243 is controlled by an electric field, so that the above-described fear can be eliminated. . Thus, the transparent fine particles 243 may be electrically charged with the same polarity as the second pigment particles 242.

  As described above, according to the electrophoretic material 24 and the electrophoretic display device 150 according to the present embodiment, the following effects can be obtained in addition to the effects of the first embodiment. Since the spatial distribution of the transparent fine particles 243 is controlled, a vivid first display can be realized.

(Embodiment 3)
"Form in which the second pigment particles are neutral"
FIG. 9 is a cross-sectional view illustrating the electrophoretic display device according to the third embodiment, where (a) illustrates the second display and (b) illustrates the first display. Hereinafter, the electrophoretic material 24 and the electrophoretic display device 150 according to this embodiment will be described. In addition, about the component same as Embodiment 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

  This embodiment (FIG. 9) differs from the first embodiment (FIG. 2) in that the second pigment particles 242 are electrically neutral. Other configurations are almost the same as those of the first embodiment. In Embodiment 1 (FIG. 2), the second pigment particles 242 were weakly charged to the second polarity. On the other hand, in this embodiment (FIG. 9), the second pigment particles 242 are electrically neutral. If the second pigment particles 242 and the transparent fine particles 243 are neutral, they are always uniformly distributed between the first substrate 80 and the second substrate 90 regardless of the electric field applied to the electrophoretic material 24. doing. Accordingly, as shown in FIGS. 9A and 9B, it is the first pigment particles 241 that change the display by electrophoresis. Since both the second pigment particles 242 and the transparent fine particles 243 are neutral, the first pigment particles 241 and these particles do not undergo Coulomb coupling, and therefore the second display becomes extremely vivid. For example, when white is adopted as the second color, the reflectivity is extremely high, and a reflectivity substantially equal to the reflectivity shown in FIG. 3 is obtained.

  As described above, according to the electrophoretic material 24 and the electrophoretic display device 150 according to the present embodiment, the following effects can be obtained in addition to the effects of the first embodiment. Since the second pigment particles 242 are not charged, vivid second display can be realized.

(Embodiment 4)
"Form in which the second pigment particles are neutral and the transparent fine particles are charged to the second polarity"
FIG. 10 is a cross-sectional view illustrating the electrophoretic display device according to the fourth embodiment, where (a) illustrates the second display and (b) illustrates the first display. Hereinafter, the electrophoretic material 24 and the electrophoretic display device 150 according to this embodiment will be described. In addition, about the component same as Embodiment 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

  This embodiment (FIG. 10) differs from the first embodiment (FIG. 2) in that the second pigment particles 242 are electrically neutral and the transparent fine particles 243 are weakly charged to the second polarity. Yes. Other configurations are almost the same as those of the first embodiment. In Embodiment 1 (FIG. 2), the second pigment particles 242 are weakly charged to the second polarity, and the transparent fine particles 243 are electrically neutral. On the other hand, in the present embodiment (FIG. 10), the second pigment particles 242 are electrically neutral, and the transparent fine particles 243 are weakly charged to the second polarity. Even in such a case, since the first pigment particles 241 charged to the first polarity are electrophoresed, it is possible to display correctly.

  The present invention is not limited to the above-described embodiment, and various changes and improvements can be added to the above-described embodiment.

  DESCRIPTION OF SYMBOLS 10 ... Display area, 20 ... Pixel, 22 ... Pixel electrode, 23 ... Common electrode, 24 ... Electrophoretic material, 60 ... Light, 70 ... Drive circuit, 80 ... First substrate, 90 ... Second substrate, 100 ... Electronic equipment 150 electrophoretic display, 241 first pigment particles, 242 second pigment particles, 243 transparent particles.

Claims (12)

An electrophoretic material in which black particles charged to the first polarity, white particles, and transparent particles are dispersed in a solvent ,
An electrophoretic material, wherein the ratio of the total surface area of the white particles to the sum of the total surface area of the white particles and the total surface area of the transparent particles is 10% to 56% .   The electrophoretic material according to claim 1, wherein the transparent particles have a particle size in a range of 50 nm to 1 μm. The electrophoretic material according to claim 1, wherein the density of the transparent particles is 2.5 g / cm 3 or less. The electrophoretic material according to claim 1 , wherein the transparent particles are a resin. Electrophoretic mobility of the black particles, the greater than the electrophoretic mobility of the white particles, according to any one of claims 1 to 4, characterized in that greater than electrophoretic mobility of the transparent particles Electrophoretic material. The electrophoretic material according to claim 1, wherein the white particles are charged to a polarity different from the first polarity. The electrophoretic material according to claim 6 , wherein the electrophoretic mobility of the white particles is larger than the electrophoretic mobility of the transparent particles. The electrophoretic material according to claim 1, wherein the white particles are electrically neutral. The electrophoretic material according to claim 1, wherein the transparent particles are electrically neutral. The electrophoretic material according to claim 1, wherein the transparent particles are charged to a polarity different from the first polarity. An electrophoretic display device comprising the electrophoretic material according to claim 1 . An electronic apparatus comprising the electrophoretic display device according to claim 11 .

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