JP4035550B2 - Display device - Google Patents

Description

  The present invention relates to a display device that displays an image, and more particularly to a thin and flexible display device that displays an image by moving fine particles between electrodes.

  In recent years, there has been proposed an electrophoretic display device that displays an image by moving electrophoretic particles between electrodes in a liquid phase filled between a pair of opposing substrates (see, for example, Patent Document 1). . Since such an electrophoretic display device performs display using fine particles, the electrophoretic display device can have a thin and flexible structure.

  However, in the case of the electrophoretic display device as described above, there is a problem that the response is slow because the resistance of the liquid when the electrophoretic particles move in the liquid phase is large. Therefore, in order to improve the response speed, a display device that displays an image by moving particles in a gas phase provided between a pair of opposing substrates has been proposed. In such a display device, since the particles move in the gas phase, the response can be made faster than in the case of the electrophoretic display device. At present, the response speed of particles in an electrophoretic display device is about 100 msec, whereas the response speed of particles in a display device in which particles move in a gas phase is 1 msec or less.

  As described above, examples of display devices that perform image display by moving particles in the gas phase include those disclosed in Patent Document 2 and Patent Document 3. FIG. 1A is a schematic diagram illustrating a configuration of a conventional display device disclosed in Patent Document 2 and a display operation during black display. FIG. 1B is also a schematic diagram showing the configuration of the conventional display device and the display operation during white display. As shown in FIGS. 1A and 1B, the image display medium includes a first substrate 20 that is disposed on the observation side and transmits light, and a first substrate that is disposed to face the first substrate 20. 2 substrates 21. On the inner surfaces of the first and second substrates 20 and 21, electrodes 22 and 23 and charge transport layers 24 and 25 are sequentially arranged, respectively. In the space between the first substrate 20 and the second substrate 21, positively charged black particles 26 and negatively charged white particles 27 are enclosed.

In the conventional display device configured as described above, a voltage corresponding to an image is applied between the electrode 22 and the electrode 23. Here, the applied voltage has a reverse polarity between black display and white display. First, the operation of the display device during black display will be described with reference to FIG. First, a voltage is applied between the electrodes 22 and 23 from the power source, whereby the electrode 22 becomes a negative electrode and the electrode 23 becomes a positive electrode. Then, due to the electric field generated between the electrodes 22 and 23, the black particles 26 and the white particles 27 existing between the substrates 20 and 21 move by Coulomb force, respectively. In this case, the positively charged black particles 26 move to the negative electrode 22 side, while the negatively charged white particles 27 move to the positive electrode 23 side. When the black particles 26 are collected on the first substrate 20 side and the white particles 27 are collected on the second substrate 21 side in this manner, the observer observes the display device from the first substrate 20 side. The display is observed. On the other hand, as shown in FIG. 1B, during white display, a voltage having a polarity opposite to that during black display is applied from the power source to the electrodes 22 and 23. Thereby, the electrode 22 becomes a positive electrode and the electrode 23 becomes a negative electrode. Therefore, in this case, the positively charged black particles 26 move to the electrode 23 side, while the negatively charged white particles 27 move to the electrode 22 side. When the observer observes the image display medium from the first substrate 20 side with the black particles 26 gathering on the second substrate 21 side and the white particles 27 gathering on the first substrate 20 side in this way, A white display is observed. A desired image can be displayed based on the principle as described above.
JP-A-11-202804 JP 2001-31225 A JP 2002-72256 A

  However, in the case of the conventional display device as described above, it is necessary to apply a voltage of about 50 V between the electrode 22 and the electrode 23 in order for the two kinds of colored particles 26 and 27 to start moving, and most of them. In order to move the colored particles 26 and 27 to display white or black, a voltage of about 200 V to 300 V had to be applied. In contrast, in the case of the electrophoretic display device described above, a driving voltage of 100 V or less is sufficient to display white or black. Thus, in the case of a display device that moves particles in the gas phase, the drive voltage is high, and thus there is a problem that it is difficult to save power.

  This invention is made | formed in view of such a situation, The objective is to provide the display apparatus which can aim at reduction of a drive voltage by moving a particle | grains smoothly.

In order to achieve this object, a display device according to the present invention is arranged in a matrix with a pair of opposing substrates, at least one of which is transparent, a plurality of charged particles contained between the pair of substrates. A first electrode and a second electrode that are provided for each pixel and that drive the charged particles; and a voltage application unit that applies a voltage corresponding to an image signal to the first electrode and the second electrode. On the surface of at least one of the electrode and the second electrode, a concavo-convex layer having a plurality of concavo-convex layers formed of a coating material in which titanium oxide fine particles having an anatase-type crystal structure are dispersed using water as a medium is formed. In addition, the charged particles move between the first electrode and the second electrode in accordance with the voltage applied by the voltage application unit, thereby displaying an image corresponding to the image signal. It is configured so that.

  In the display device according to the invention, it is preferable that the plurality of irregularities have a substantially uniform shape.

  In the display device according to the invention, it is preferable that a particle diameter of the fine particles is smaller than an average particle diameter of the charged particles.

  The above object, other objects, features, and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments with reference to the accompanying drawings.

  The display device of the present invention can reduce the driving voltage by smoothly moving the particles.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 3 is a block diagram showing a configuration of the display device according to Embodiment 1 of the present invention. FIG. 2A is a perspective plan view showing the main configuration of the display unit included in the display device according to Embodiment 1 of the present invention when white display is performed, and FIG. ) Is a cross-sectional view taken along line AA in FIG. 4A is a perspective plan view showing the main structure of the display unit included in the display device according to Embodiment 1 of the present invention when black display is performed, and FIG. ) Is a cross-sectional view taken along line AA in FIG. For convenience of explanation, the X direction and Y direction in the figure are the horizontal direction and vertical direction of the display unit, respectively, and the Z direction is the upward direction of the display unit.

  As shown in FIG. 3, in the display device 100, the display unit includes an image display medium 34. As shown in FIGS. 2A and 2B, the image display medium 34 includes an active matrix substrate (hereinafter referred to as a TFT array substrate) 102 which is a substrate disposed on the lower side, and the TFT array substrate. 2, the black substrate 11 and the positive particles negatively charged in the air layer 10 formed between the TFT array substrate 102 and the counter substrate 101. The white particles 12 are charged and sealed.

  The TFT array substrate 102 and the counter substrate 101 are made of a transparent resin film of about 0.1 mm to 0.5 mm. In order to realize a foldable display device called a so-called electronic paper, it is preferable that the thickness of the TFT array substrate 102 and the counter substrate 101 is about 0.1 mm to 0.2 mm.

  The black particles 11 are spherical particles synthesized from acrylic particles, black carbon, or the like, and the particle size is about 1 μm to 10 μm. The white particles 12 are spherical particles synthesized from acrylic particles, TiO 2 or the like, and the particle size is about 1 μm to 10 μm. In order to prevent the particles from aggregating, the black particles 11 and the white particles 12 preferably have a uniform particle size.

  The black particles 11 and the white particles 12 are preferably those having a small specific gravity and excellent fluidity. In order to produce a specific structure for this purpose, the spherical silica fine particles with a diameter of 30 nm are fixed on the entire surface of the spherical acrylic particles with a diameter of 5 μm by a method such as mechanochemical. Here, the silica fine particles were subjected to charging treatment, and the particles as a whole had charging properties. In order to further reduce the specific gravity, the acrylic particles are more preferably hollow or porous. With such a structure, the fluidity of the particles is improved, so that the frictional resistance when the particles move is reduced, and the kinetic energy required for the movement of the particles is reduced. Therefore, the response speed is increased and driving with a low voltage is possible.

  As shown in FIG. 3, the TFT array substrate 102 is provided with a plurality of scanning signal lines 5 and video signal lines 7 that are orthogonal to each other in plan view, and is divided by the scanning signal lines 5 and the video signal lines 7. The region formed constitutes one pixel 35. A plurality of such pixels 35 are formed in a matrix to form an image display medium 34. Although not shown, the TFT array substrate 102 is provided with a well-known thin film transistor (TFT) as a switching element for each pixel 35. A first electrode 4 provided on the TFT array substrate 102 side is connected to the drain region of the TFT. Thus, the display device of this embodiment is an active drive type in which a TFT is formed for each pixel 35.

  A source driver 33 for driving the video signal line 7 and a gate driver 32 for driving the scanning signal line 5 are disposed around the image display medium 34. Further, a control unit 31 that controls the source driver 33 and the gate driver 32 according to an image signal input from the outside is provided.

  The TFT includes a gate electrode formed on the TFT array substrate 102, a gate insulating film formed on the gate electrode, a gate insulating film, and a source electrode and a drain electrode formed on the TFT array substrate 102. And an organic semiconductor layer for forming a channel region. Since the TFT is formed by printing or the like using an organic material, the flexibility of the TFT array substrate 2 is not impaired. The scanning signal line 5 is connected to the gate electrode of the TFT, and the video signal line 7 is connected to the source electrode of the TFT.

  2A, FIG. 2B, FIG. 4A, and FIG. 4B, the counter substrate 101 has a rectangular first electrode 3 on the lower surface of the support 1 and a pixel. Each is formed and configured. Here, the first electrode 3 is a transparent conductor made of ITO (Indium Tin Oxide) or the like. A surface treatment layer 9 for covering the first electrode 3 to suppress the adsorption force acting between the first electrode 3 and the particles and preventing the adsorption between the first electrode 3 and the particles is provided. Is formed. Further, the TFT array substrate 102 is constructed by laminating the scanning signal line 5 and the insulating layer 6 on the upper surface of the support 2, and further laminating the second electrode 4, the video signal line 7 and the TFT 8 thereon. Yes. Then, the second electrode 4 and the particles are adsorbed by covering the second electrode 4, the video signal line 7 and the TFT 8 and suppressing the adsorption force acting between the second electrode 4 and the particles. A surface treatment layer 9 for preventing this is formed.

  The details of the surface treatment layer 9 will be described later.

  The gap G of the air layer 10 maintained by the spacer described above is about 25 μm. The filling rate of the black particles 11 and the white particles 12 is about 10% to 30% in terms of volume with respect to the air layer 10. After the black particles 11 and the white particles 12 are filled in the air layer 10, the peripheral portions of the upper substrate 1 and the lower substrate 2 are hermetically sealed with an epoxy adhesive or the like.

  In the display device 100 configured as described above, the control unit 31 outputs control signals to the gate driver 32 and the source driver 33 in accordance with an image signal input to the signal input unit 30 from the outside. As a result, the gate driver 32 outputs a gate signal to the scanning signal line 5 to sequentially turn on the switching elements (TFTs) of the respective pixels 35, while the source driver 33 matches the timing with the video signal line 7 for video. A signal is sequentially input to each pixel 35. As a result, as will be described later, in each pixel 35, the black particles 11 and the white particles 12 move in the air layer 10 between the TFT array substrate 2 and the counter substrate 1. As a result, an image corresponding to the video signal appears in the eyes of a person observing the display device 100.

  White display in the pixel 35 is realized as follows. In accordance with a control signal output from the control unit 31, a voltage corresponding to an image is applied between the first electrode 3 and the second electrode 4 so that the first electrode 3 becomes a negative electrode and the second electrode 4 becomes a positive electrode. The As described above, since the white particles 12 are positively charged, as shown in FIGS. 2A and 2B, the white particles 12 are attracted to the first electrode 3 and moved to move to the first electrode. 3 adheres to the surface treatment layer 9 in the vicinity. Here, since the first electrode 3 is made of the transparent conductor as described above, the white particles 12 are observed by the observer, and white display is realized.

  On the other hand, black display in the pixel 35 is realized as follows. In accordance with a control signal output from the control unit 31, a voltage corresponding to an image is applied between the first electrode 3 and the second electrode 4 so that the first electrode 3 becomes a positive electrode and the second electrode 4 becomes a negative electrode. The As described above, since the black particles 11 are negatively charged, as shown in FIGS. 4A and 4B, the black particles 11 are attracted to the first electrode 3 and moved to move to the first electrode. 3 adheres to the surface treatment layer 9 in the vicinity. As a result, black particles 11 are observed from the observer, and black display is realized.

  In order to change from white display to black display or from black display to white display, particles attached to the surface treatment layer 9 in the vicinity of the electrode by an electric field generated between the first electrode 3 and the second electrode 4 are changed. It must be peeled off. In the present embodiment, the presence of the surface treatment layer 9 reduces the adhesion force generated between the electrode and the particles. As a result, as will be described later, the voltage required for image display can be reduced.

The voltage characteristics described below are a threshold voltage Vc at which particles start to peel from the electrode, a saturation voltage Vs at which all particles have completely peeled off, and a voltage difference from the threshold voltage Vc to the saturation voltage Vs. . This voltage characteristic depends on the balance of the Coulomb force acting on the particles when a voltage is applied between the electrodes, gravity, image force, van der Waals force, and the adhesion force between the particles and the electrode. In the case of the display device 100 of the present embodiment, it has been confirmed that the threshold voltage Vc is dominant over the image power and the saturation voltage Vs is dominant over the van der Waals force. TiO ₂ particles have a semiconductor-like electrical characteristic that has a lower electrical resistance than resin materials such as polycarbonate and acrylic, and a higher electrical resistance than conductors such as ITO and Al. By using a conductive material having a low electric resistance or an insulating material having a high electric resistance in addition to TiO ₂ , the charging characteristics between the particles and the electrode surface can be improved, and the threshold voltage Vc can be lowered. Further, as described below, by using the surface treatment layer 9, the van der Waals force can be reduced and the saturation voltage Vs can be lowered.

FIG. 5 is a cross-sectional view schematically showing an example of the configuration in the vicinity of the surface of the TFT array substrate 102 provided in the display device 100 according to Embodiment 1 of the present invention. As shown in FIG. 5, the surface treatment layer 9 has a structure in which minute irregularities are formed. In the present embodiment, the surface treatment layer 9 is composed of TiO ₂ fine particles having an anatase crystal structure having a particle diameter of 30 nm smaller than that of the black particles 11 and the white particles 12. Here, the particle diameter of the TiO ₂ fine particles was set to 30 nm because when the unevenness of the surface treatment layer 9 is larger than the particle diameter of the black particles 11 and the white particles 12, for example, 5 μm, these colored particles themselves Since it adheres along the unevenness and the effect of reducing van der Waals force is lost, it is desirable that the particle diameter of the TiO ₂ fine particles forming the unevenness is smaller than the particle diameter of the black particles 11 and the white particles 12. is there.

As shown in FIG. 5, the interval between the protrusions formed by the TiO ₂ fine particles constituting the surface treatment layer 9, that is, the pitch p of the unevenness of the surface treatment layer 9 is black which is a charged particle for display. It is smaller than the average particle diameter of the particles 11 (white particles 12). This is because when the unevenness pitch p of the surface treatment layer 9 is equal to or larger than the average particle diameter of the black particles 11 (white particles 12), the black particles 11 (white particles 12) are unevenness of the surface treatment layer 9. This is because the effect of reducing the van der Waals force cannot be expected.

  In the present embodiment, the surface treatment layer 9 formed on the counter substrate 101 side has the same configuration as described above.

Surface treatment layer 9 made of the TiO ₂ fine particles and the medium of water, after coating a slurry prepared by dispersing TiO ₂ particulates, by drying, can be at a high film hardness and obtain a layer of high permeability. The surface treatment layer 9 obtained by this manufacturing method is a uniform layer having a thickness of about 100 nm in which particles having a relatively small aggregation of TiO ₂ fine particles and a uniform particle size distribution are laminated, and the unevenness of the surface treatment layer 9 is substantially uniform. It has a nice shape. Accordingly, conditions such as electrical resistance, chargeability, and shape on the substrate side are almost uniform, and the colored particles attached to the electrodes have almost the same voltage characteristics, and as a whole, good voltage characteristics can be obtained. it can.

In this embodiment, TiO ₂ fine particles are used to form the unevenness of the surface treatment layer 9, but the present invention is not limited to this. For example, fine particles such as SiO ₂ (silica) and ZnO (zinc oxide) are used. May be used. Even when these are used, a highly transparent uneven layer can be formed on the electrode surface. More specifically, SiO ₂ fine particles (or ZnO fine particles) having an average particle diameter of about 15 nm to 30 nm are dispersed in a solvent such as isopropyl alcohol to form a slurry. Then, by applying this slurry to the substrate in the same manner as in the present embodiment and then drying it, it is possible to form an uneven layer with high film hardness and high transmittance. In the case of the concavo-convex layer formed using the SiO ₂ fine particles (or ZnO fine particles) in this way, the conductivity is lower than that of the concavo-convex layer formed using the TiO ₂ fine particles, and the electrode surface has a larger chargeability. There is an advantage that it can be granted.

As a result of experiments and evaluations by various combinations of display particles and materials to which the particles are attached by the present inventors, acrylic resin (PMMA) is used as a constituent material of the particles as in this embodiment. ) And TiO ₂ was used for the surface treatment layer 9, and the voltage characteristics were dramatically improved. Specifically, the saturation voltage necessary for displaying from black to white in the configuration in which the surface treatment layer 9 is not formed is 150 V, whereas in the configuration in this embodiment, the saturation voltage is reduced to 80 V. I was able to. This is because the relationship between the charging characteristics is improved due to the microconductive characteristics of the TiO ₂ fine particles, and the van der Waals force is dominant for the adsorption force between the surface treatment layer 9 and the particles. This is because the van der Waals force acting is reduced by minimizing the contact surface between the surface treatment layer 9 and the surface treatment layer 9.

  FIG. 8 is a graph showing the relationship between the van der Waals force and the uneven pitch of the surface treatment layer 9 in the display device 100 according to the first embodiment of the present invention. This graph shows the van der Waals force generated between the black particles 11 and the surface treatment layer 9 and the surface when the black particles 11 are composed of mother particles 11a having a diameter of 5 μm and child particles 11b having a diameter of 16 nm. The relationship with the magnitude | size of the unevenness | corrugation of the process layer 9 is shown. This relationship is based on the calculation result obtained based on the theoretical formula when the closest distance is assumed to be 0.4 mm.

  As shown in FIG. 8, when the unevenness pitch of the surface treatment layer 9 is up to about 7 nm, the effect of reducing the van der Waals force is larger as the unevenness pitch is smaller. In addition, when the uneven pitch of the surface treatment layer 9 is larger than about 7 nm, the van der Waals force gradually increases. Considering this result, it can be said that the uneven pitch of the surface treatment layer 9 is preferably about 5 nm to 50 nm, and more preferably about 7 nm.

As another good combination, acrylic resin (PMMA) was used as the constituent material of the particles, and polycarbonate was used as the surface treatment layer 9. Specifically, the surface treatment layer 9 is formed by a coating agent in which TiO ₂ fine particles are dispersed in a medium obtained by melting polycarbonate powder which is an insulating resin powder in a cyclic ether solvent THF. The voltage characteristics can be improved by such a combination because polycarbonate is an insulating material having charging characteristics relatively close to acrylic.

  By the way, as a method for forming the unevenness in the surface treatment layer 9, in addition to the case described above, for example, a transparent resin layer such as PMMA is formed on the substrate, and then press working is performed with a mold provided with the uneven structure. There is a method of forming a transparent resin layer such as PMMA, and then forming irregularities on the surface by chemical etching or the like. Further, after applying a photosensitive resin on the substrate, a predetermined pattern is formed by exposure, and the pattern is subjected to heat treatment at a temperature of about 100 ° C., thereby forming irregularities having a predetermined spherical shape. May be.

[Modification 1]
FIG. 6 is a cross-sectional view schematically showing another example of the configuration in the vicinity of the surface of the TFT array substrate 102 included in the display device 100 according to Embodiment 1 of the present invention. The surface treatment layer 9 includes a TiO ₂ fine particle layer 9a for forming unevenness and an insulating layer 9b made of polycarbonate exposed on the outermost surface. In this case, the TiO ₂ fine particles do not necessarily have an anatase type crystal structure, and when an organic substance is used as a medium, a rutile type or amorphous type may be used. In such a configuration, even better voltage characteristics could be obtained, and the saturation voltage could be reduced to 60V.

[Modification 2]
FIG. 7 is a cross-sectional view schematically showing another example of the configuration in the vicinity of the surface of the TFT array substrate 102 provided in the display device 100 according to Embodiment 1 of the present invention. In the example shown in FIG. 7, the surface treatment layer 9 is configured similarly to the case shown in FIG. In addition, you may be comprised similarly to the case shown in FIG.

  In the example shown in FIG. 7, the black particles 11 are composed of mother particles 11a and child particles 11b. In order to improve the voltage characteristics, it is preferable that the black particles 11 have a small specific gravity and excellent fluidity. Therefore, by making the black particles 11 into a composite structure composed of the mother particles 11a and the child particles 11b in this way, the fluidity depends on the particle size of the child particles 11b, not the particle size of the mother particles 11a. As a result, the van der Waals force acting between the black particles 11 or between the black particles 11 and the surface treatment layer 9 is reduced, so that the fluidity is improved and the voltage characteristics are further improved.

In this example, spherical acrylic particles having a diameter of 5 μm are used as the mother particles 11a, and spherical silica particles having a diameter of 16 nm that have been subjected to charging treatment are used as the child particles 11b. It was supposed to have. As the material used for the mother particles 11a, other resin materials such as styrene and melamine may be used. Moreover, the reason why silica is used for the child particles 11b is that it is possible to perform a charging process which is stable and can obtain a large charge amount by a silane coupling agent or the like. Since the mother particles 11a are made of acrylic, the true specific gravity is as small as 1.2 g / cm ³ and the softening point is low.

On the other hand, the child particle 11b has a large true specific gravity of 2.1 g / cm ^{3 as} compared with the mother particle 11a, but its blending ratio is small, so that the influence of the whole particle is small. Further, since the softening point is higher than that of the mother particle 11a, it is easily fixed to the mother particle 11a by a method such as mechanochemical.

  The child particles 11b are fixed by a high-speed air current impact method, which is a kind of mechanochemical, so as to cover substantially the entire surface of the mother particles 11a. The blending ratio for coating the child particles 11b on almost the entire surface of the mother particles 11a is 100: 3 to 100: 5 in terms of the weight ratio of the mother particles 11a: child particles 11b, and is slightly larger than the theoretical blending ratio. . Here, the theoretical blending ratio is a calculated value when it is assumed that the entire surface of the mother particle 11a is covered with one layer of the child particles 11b. In this example, the reason why the compounding ratio is made larger than the theoretical value is that there is a limit in making the layer of the child particles 11b uniform in the high-speed airflow impact method, and the entire surface of the mother particle 11a is covered with the child particles 11b. This is because it is difficult to cover with one layer.

  As described above, when the child particles 11b are coated on almost the entire surface of the mother particles 11a, the humidity resistance is dramatically improved as compared with the conventional acrylic polymerized toner without the child particles. That is, when the humidity is increased from 50% to 90% at an atmospheric temperature of 45 ° C., the charge amount of the conventional polymerized toner is reduced by 55% compared to the initial value, but in the case of the composite particles of the present embodiment, 15%. Only a decrease of about%.

  Therefore, the resin film used for the counter substrate 101 and the TFT array substrate 102 does not require a special moisture-proof treatment, and an inexpensive commercial product such as a PET film can also be used.

  As a method of producing such composite particles, there is a method of producing by a single process such as a suspension polymerization method in addition to a method such as mechanochemical in which child particles are fixed after producing mother particles. However, in this case, a film made of an additive used in the manufacturing process, such as a surfactant, is formed on the child particle surface of the produced composite particle. The fluidity of the composite particles is not improved.

  Here, the behavior of particles near the surface of the TFT array substrate 102 has been described as an example, but it goes without saying that the same behavior can be obtained near the surface of the counter substrate 101. Of course, it is desirable that the white particles 12 have a composite structure as in the case of the black particles 11.

  Further, in the present embodiment, the configuration in the case where the vertical electric field acts has been described, but the configuration using the horizontal electric field generated by providing both the first electrode 3 and the second electrode 4 on the same substrate side is also applicable. Can be applied. In this case, instead of using two types of charged particles as in the present embodiment, display can be made with only one type of charged particles, and a lower voltage can be achieved. The configuration using such a lateral electric field will be described in detail in a fifth embodiment to be described later.

  Further, although an example of active matrix driving has been described in this embodiment mode, simple matrix driving can be applied to a small display device having a threshold voltage of about 20 V to 30 V and a size of about 5 inches. it can. In this case, it is possible to provide an inexpensive display device as compared with the active matrix driving type.

(Embodiment 2)
The display device according to Embodiment 2 of the present invention is configured such that a repulsive force acts between the display particles and the electrode to which the particles adhere by changing the charge train of the pair of electrodes. It is a thing.

  FIG. 9 is a cross-sectional view schematically showing the configuration of the display device according to Embodiment 2 of the present invention. As shown in FIG. 9, the first substrate 41 and the second substrate 42 are disposed to face each other with a spacer 43 interposed therebetween, and between the first substrate 41 and the second substrate 42. The formed air layer 44 is filled with a plurality of negatively charged black particles 45 and a plurality of positively charged white particles 46. Here, the particle group may be preliminarily charged by stirring or the like, or may be charged by applying an electric field as a charging process after being filled in the air layer 44. It may be charged by friction and stirring.

  In addition, the display speed and contrast at the time of image display change with the rates with which the air layer 44 is filled with particles. In the case of a packing rate of 80% or more in terms of volume, the display characteristics are good, but the presence of particles becomes a barrier and the movement of the particles is hindered, so the voltage required to move the particles is high. Problem arises. Therefore, the filling rate is preferably about 50 to 60% in terms of volume.

  The spacer 43 is made of an insulating material. In the present embodiment, a PET (polyethylene terephthalate) sheet is used as a material for the spacer 43. A cell is formed by disposing a PET sheet serving as the spacer 43 in a hole formed at an appropriate position of the image display unit. In addition to the PET sheet, the spacer 43 may be made of, for example, a resin material having a low melting point that is pattern-printed at a predetermined interval by screen printing and heat-cured, or a light-sensitive resin material that is spin-coated. It is also possible to use a material that has been subjected to a photo process through a mask and patterned and then cured. In addition, it is also possible to use a rubber or plastic sheet instead of the PET sheet. Further, when there is a variation in the height of the spacer 43, display unevenness occurs due to the variation, and therefore it is desirable that the height can be uniformed.

  Further, the black particles 45 and the white particles 46 are made of a thermoplastic resin such as styrene, methyl acrylate, or vinyl ethyl ether, or a thermosetting resin such as a melamine resin or a phenol resin. Carbon black, titanium oxide, magnesium oxide, or an azo dye is mixed as a colorant in the resin.

  In this embodiment, monochrome display is realized using black particles and white particles, but color display can also be realized by configuring particles using colorants of other colors. is there. In general, polyester having a large amount of oxygen in the main chain exhibits good negative chargeability. When a polar group is added to control chargeability, an amino group is used for imparting positive charge. A charge control agent can also be used. In the case of imparting a positive charge, a nigrosine dye, a quaternary ammonium salt, or the like is used. In the case of imparting a negative charge, an azo metal-containing dye, a salicylic acid metal-containing dye, a fluoride, or the like is used. In addition, the fluidity of the particles may be improved by adding silica or alumina in advance to the outside of the particles, and the particles may be treated with an organic substance with a silane coupling agent.

  The first substrate 41 described above is configured by forming the first electrode 49 on the upper surface of the support 47. The second substrate 42 is configured by laminating the second electrode 50 and the coat layer 52 in this order on the lower surface of the support 48. In the case of the present embodiment, the observer observes from the second substrate 42 side. Details of the coat layer 52 will be described later.

  The supports 47 and 48 are made of glass, acrylic resin, polycarbonate resin, or the like. In particular, the support 48 on the side to be observed is preferably made of a material that transmits light.

  The first electrode 49 and the second electrode 50 are made of ITO, aluminum, gold, polythiophene, or the like. As in the case of the support 48, the second electrode 50 is preferably made of a material that transmits light.

  In the display device of the present embodiment configured as described above, a voltage is applied to the first electrode 49 and the second electrode 50 so that the first electrode 49 is negative and the second electrode 50 is positive. In this case, the negatively charged black particles 45 adhere to the second electrode 50 on the plus side. Thereby, when an observer observes from the 2nd board | substrate 42 side, the several black particle 45 adhering to the surface of the 2nd electrode 50 is observed, and a black image display is implement | achieved. On the other hand, when a voltage is applied to the first electrode 49 and the second electrode 50 so that the first electrode 49 is positive and the second electrode 50 is negative, the negative second electrode 50 is positive. Charged white particles 46 adhere. Thereby, when an observer observes from the 2nd board | substrate 42 side, the several white particle 46 adhering to the surface of the 2nd electrode 50 is observed, and a white image display is implement | achieved.

  The inventors of the present invention have a configuration in which the coat layer 52 is removed from the configuration of the display device of the present embodiment, that is, a display device in which no coat layer is formed on any of the pair of electrodes (hereinafter, the display of the configuration A). And a display device of the present embodiment in which a polycarbonate coat layer 52 is formed on the surface of the second electrode 50 by spin coating (hereinafter referred to as a display device of configuration B). . In both display devices, the distance (cell gap) between the upper and lower substrates 41 and 42 was set to 100 μm. At this time, a voltage of +300 V was applied between the first electrode 49 and the second electrode 50 so that the second electrode 50 was positive, and the black particles 45 were attached to the second electrode 50. When the reflection density at this time was measured with a reflection densitometer, it was 1.5.

  FIG. 11 is a graph showing the relationship between the reflection density and the applied voltage in the display unit of the display device. In this graph, the relationship in the display device of configuration A is indicated by A, and the relationship in the display device of configuration B is indicated by B.

  In both display devices, a voltage is applied between the first electrode 49 and the second electrode 50 so that the second electrode 50 is negative. As a result, as shown in FIG. 11, in the case of the display device of configuration A, the black particles 45 start to be peeled off from the second electrode 50 around −100 V applied between the electrodes, and are replaced with the white particles 46. Saturated in degree. The reflection density at this time was 0.4. On the other hand, in the case of the display device of configuration B, the black particles 45 began to be replaced with the white particles 46 in the vicinity of −50V and became saturated in the vicinity of −100V. The reflection density at this time was 0.3, and a good contrast was obtained as compared with the case of the display device of configuration A.

  As described above, by changing the material of the electrode surface, the saturation voltage (applied voltage required for complete removal of all particles) can be halved, and the white reflection density can be improved. it can. This is presumably because the negative side of the charge train moved from ITO to polycarbonate and attracted positively charged white particles 46, and the white particles 46 moved at a low voltage. On the other hand, in the case of the negatively charged black particles 45, both of them are on the negative side from the polycarbonate coating layer 52, so that they are repelled and easily separated, and the adhesion of the black particles 45 is the second electrode 50 made of ITO. Therefore, it is considered that the black particles 45 moved at a low voltage.

  The case where the display is changed from black display to white display has been described above. When changing from white display to black display by the same driving method, the white particles 46 start to move because the adsorption force acting between the polycarbonate coat layer 12 on the surface of the second electrode 50 and the white particles 46 is large. For this purpose, a voltage of 100 V or more had to be applied between the electrodes. Also, in the case of the black particles 45, the charged column is difficult to adhere to the minus-side polycarbonate coat layer 12, and the white particles 46 are also unlikely to be detached from the coat layer 12 in terms of conversion. The reflection density was 1.3. For this reason, the contrast in the display apparatus of this Embodiment fell compared with the case of a comparative example.

  Therefore, in order to facilitate the change from black display to white display, a driving method of always performing white display after resetting to black display is conceivable.

  FIG. 12 is a graph for explaining a driving method of the display device according to the second embodiment of the present invention. In this graph, the vertical axis represents the voltage applied between the electrodes, and the horizontal axis represents time.

  As shown in FIG. 12, first, a voltage of +300 V is applied between the electrodes for 0.5 ms so that the second electrode 50 becomes positive (see symbol E). Hereinafter, such an operation is referred to as a reset operation. After this reset operation, as indicated by symbols F and G in FIG. 12, a pulse waveform of 0.5 ms is applied between the electrodes as a drive voltage so that the second electrode 50 becomes negative. As a result, the white particles 46 move to the second substrate 42 side. Here, since the white particles 46 are easily attracted to the polycarbonate coat layer 12, the reflection density from black display to white display can be changed by changing the applied voltage in the range of about -50V to -100V.

  In the case of such a driving method, since the black particles 45 and the white particles 4 are always moved on the surface of the coat layer 52, the adsorption of each particle to the surface of the coat layer 52 can be prevented and reproduced. Therefore, a high-contrast display can be realized at a low voltage. Note that the pulse width, reset voltage, drive waveform, and the like in this driving method are not limited to those described above, and can be selected to be optimal for each cell.

  In the present embodiment, the coat layer is formed only on the second substrate 42 side, but may be formed on the first substrate 41 side in the same manner. Thus, even in the case of a display device in which the surface of the first electrode 49 is provided with a coat layer made of polycarbonate, a comparative example in which such a coat layer is not formed on the surfaces of both electrodes. Compared with such a conventional display device, the display particles move easily, and the drive voltage can be reduced.

  Further, unlike the case of the present embodiment, even when the coat layer is formed only on the first substrate 41 side, the display particles are easily moved in the same manner as described above, and the drive voltage Needless to say, this can be reduced.

(Embodiment 3)
In the case of Embodiment 2, by providing a polycarbonate coat layer on one substrate side, a configuration in which the charged columns on the pair of electrode surfaces are different is realized. On the other hand, in the display device according to Embodiment 3 of the present invention, a coat layer is provided on both the surfaces of the pair of electrodes, and a positive charge control agent is used on one side and a negative charge control agent is used on the other side.

  FIG. 10 is a cross-sectional view schematically showing the configuration of the display device according to Embodiment 3 of the present invention. As shown in FIG. 10, a coat layer 61 is formed on the surface of the first electrode 49 on the first substrate 41 side, and a coat layer 62 is formed on the surface of the second electrode 50 on the second substrate 42 side. Has been. Note that other configurations of the display device of the present embodiment are the same as those of the second embodiment, and thus the same reference numerals are given and description thereof is omitted.

  The coat layer 62 is configured using a positive charge control agent. Specifically, a positive charge control agent mainly composed of styrene acrylic resin and added with an ammonium salt is dissolved and applied to the surface of the second electrode 50 with toluene, and then heated to evaporate the solvent. 62 is formed.

  On the other hand, the coat layer 61 is configured using a negative charge control agent. Specifically, it is formed in the same manner as in the case of the coat layer 62 using a styrene acrylic resin with a carboxylic acid group added as a negative charge control agent.

  The present inventors have confirmed that both the display device of the present embodiment configured as described above (hereinafter referred to as the display device of configuration C) and the coat layer are formed using a negative charge control agent. Except for the display device having the same configuration as the configuration C (hereinafter referred to as the display device of the configuration D) and the display device having a configuration in which the coat layer is not provided on any substrate side (hereinafter referred to as the display device of the configuration E). ) And a comparative experiment. In the display devices of these configurations C to E, the distance (cell gap) between the upper and lower substrates 41 and 42 was set to 100 μm. At this time, a voltage of −150 V was applied between the first electrode 49 and the second electrode 50 so that the second electrode 50 was positive, and the white particles 46 were adhered to the second electrode 50. When the reflection density at this time was measured with a reflection densitometer, it was 0.35.

  FIG. 13 is a graph showing the relationship between the reflection density and the applied voltage in the display unit of the display device. In this graph, the relationships in the display devices of configurations C, D, and E are indicated by C, D, and E, respectively.

  In the display devices of these configurations C to E, a voltage is applied between the first electrode 49 and the second electrode 50 so that the second electrode 50 becomes positive. As a result, as shown in FIG. 13, in the case of the display device of configuration C, the white particles 46 start to be peeled off from the second electrode 50 around the time when + 50V is applied between the electrodes and are replaced with the black particles 45, and are saturated at about + 100V. did. The reflection density at this time was 1.5.

  Further, in the case of the display device of configuration D, even if the second electrode 50 has a positive voltage, the adsorption acting between the white particles 46 and the coat layer 62 formed using the negative charge control agent. Since the force becomes larger than that of the display device of the configuration C, the white particles 46 need a voltage of +100 V or more to start to be replaced with the black particles 45, and are saturated at about + 200V. Further, since the replacement of the particles was insufficient, the black reflection density when saturated was 1.4, and the contrast was lower than in the case of the display device of configuration C.

  Further, in the case of the display device of configuration E, even if the second electrode 50 has a positive voltage, the adsorptive force acting between the white particles 46 and the surface of the second electrode 50 is the configuration C and D. Therefore, a voltage of +150 V or more is required to replace the white particles 46 with the black particles 45, and the voltage is saturated at about + 300V. Further, since the replacement of particles is impure, the reflection density of black when saturated is about 1.2, and the contrast is lowered as compared with the display devices of configurations C and D.

  In this way, by changing the charge train using positive and negative charge control agents on the electrode surface material, the saturation voltage can be halved, and the black reflection density is increased, thereby improving the contrast. Can do. In addition, the charge control agent is excellent in heat resistance and moisture resistance, and since the charging characteristics hardly change even after long-term storage, it is possible to maintain stable characteristics. In other words, the display device in this embodiment has a function of holding the display after voltage application. This is mainly due to the adsorption force between the display particles and the electrode surface. Furthermore, in order to ensure the same display function as before storage after storage, it is necessary to maintain the charge amount of the particle group. Therefore, as in this embodiment, by applying a charge control agent to the electrode surface in contact with the particle group, a display device excellent in insulation effect and moisture resistance can be realized, and the charge amount of the particle group is sufficient. To be able to maintain.

  Even when both coat layers are formed using a negative charge control agent as in the display device of configuration D, no such coat layer is formed as in configuration E. Compared to the case, a good display device with low voltage and high contrast can be realized.

  In addition, even when the charge control agent is provided only on one electrode surface and the other electrode surface is not provided with a coat layer, the charge trains on the electrode surfaces are different. The adsorption force with the electrode surface can be changed. Incidentally, since the first electrode 49 is not on the observation side, it does not have to be a transparent electrode. Therefore, the electrode on which aluminum is deposited can be used as the first electrode 49. Aluminum, like ITO, has a positive charge column, so that the opposing second electrode 50 is made of ITO and a negative charge control agent is used for the coat layer 62. As a result, the adhesion between the coat layer 62 and the positively charged white particles 46 is increased, and the voltage can be lowered when the display is shifted from black display to white display. Further, if the coating layer 61 is formed by applying a negative charge control agent to the surface of the first electrode 49 made of aluminum, the adhesion between the white particles 46 and the coating layer 61 is increased, and the ITO Since the white particles 46 are easily peeled off from the second electrode 50 made of the material, the transition from white display to black display can be realized with a low voltage.

  In the case of transition from white display to black display, a black image is displayed on a white background, so that the observer can easily confirm the image. Therefore, it is preferable to drive the display device so that the pixels are first displayed in white and only the display region is shifted to black display. In view of this, it is possible to display images with good reproducibility by applying the voltage of the drive waveform after resetting all pixels to white display before display each time in the same manner as in the second embodiment. .

  Although color display can be realized by using particles colored with colors other than white and black, even in the case of such color display, the color is similarly displayed after white display. By doing so, a high-contrast image display can be realized.

(Embodiment 4)
In the case of Embodiments 2 and 3, a cell is manufactured by using a PET (polyethylene terephthalate) sheet as a material of the spacer and arranging it using holes formed in the image display unit. However, in this case, the inventors have confirmed that a phenomenon in which white particles adhere to the edge of the PET when the cell is produced is observed. This is considered to be caused by attracting positively charged white particles because the PET charge train is extremely negative.

  Therefore, in the display device according to Embodiment 3 of the present invention, the spacer is formed using styrene resin instead of PET. As a result, adhesion of white particles to the spacer was not observed, and the display characteristics were further improved as compared with the cases of the second and third embodiments. This is considered to be because it was possible to prevent the white particles coming into contact with the spacer from being reversely charged or stuck and stuck.

  Note that the configuration of the display device of the present embodiment is the same as that of the second embodiment, and a description thereof will be omitted. Hereinafter, a description will be given with reference to FIG.

  In the present embodiment, the charged row on the surface of the spacer 43 is set to the middle of the charged row of the two types of display particles 45 and 46, so that these particles 45 and 46 are attracted to the spacer 43 and hardly move. Can be prevented. In addition, since the part of the spacer 43 is a place where the particles 45 and 46 tend to aggregate, it is necessary to avoid the particles 45 and 46 from adhering to the spacer 43 as much as possible, and this embodiment realizes this. be able to.

  As a material for the spacer 43, for example, a resin material having a low melting point is printed by pattern printing at a predetermined interval by screen printing and heat-cured, or a photo-sensitive resin material subjected to spin coating is subjected to a photo process through a mask. It is also possible to use a material cured after patterning. In addition, rubber or plastic sheets can be used. Further, when there is a variation in the height of the spacer 43, display unevenness occurs due to the variation, and therefore it is desirable that the height can be uniformed. When the charged column of the material of the spacer 43 is outside the charged column of the particles 45 and 46 as in PET, a coat layer such as styrene resin may be formed on the surface.

(Embodiment 5)
In Embodiments 1 to 4, a display device using two types of display particles has been described, but it is possible to perform image display even with one type of particle. The display device according to Embodiment 5 of the present invention is configured to move particles using a lateral electric field generated by providing both the first electrode and the second electrode on the same substrate side.

  FIG. 14 is a cross-sectional view schematically showing the configuration of the display device according to Embodiment 5 of the present invention. As shown in FIG. 14, the first substrate 41 and the second substrate 42 are disposed to face each other with a spacer 43 interposed therebetween, and between the first substrate 41 and the second substrate 42. The formed air layer 44 is filled with a plurality of negatively charged black particles 45. As in the case of the second embodiment, the second substrate 42 is made of a transparent material.

  A rectangular first electrode 49 and a second electrode 50 made of aluminum are formed on the upper surface of the first substrate 41 with a predetermined distance therebetween. A coat layer similar to that of the second embodiment may be formed on the surfaces of the first electrode 49 and the second electrode 50. In the present embodiment, the coat layer 52 is formed so as to cover the surface of the second electrode 50.

  In addition, a shielding layer 53 wider than the first electrode 49 is formed on the lower surface of the second substrate 42 at a position overlapping the first electrode 49 in plan view. The shielding layer 53 is made of a black material that does not transmit light. Therefore, when the observer observes the display device from the second substrate 42 side, the first electrode 49 is blocked by the shielding layer 53, and therefore the observer observes the first electrode 49. Only the coat layer 52 covering the second electrode 50 is observed. Here, white display can be realized by making the coat layer 52 white. In the case where the coat layer 52 is not formed, white display may be realized by roughening the surface of the second electrode 10 made of aluminum.

  In the display device of the present embodiment configured as described above, a voltage is applied to the first electrode 49 and the second electrode 50 so that the first electrode 49 is negative and the second electrode 50 is positive. In this case, the negatively charged black particles 45 adhere to the second electrode 50 on the plus side. Thereby, when an observer observes from the 2nd board | substrate 42 side, the several black particle 45 adhering to the surface (coat layer 52) of the 2nd electrode 50 is observed, and a black image display is implement | achieved. On the other hand, when a voltage is applied to the first electrode 49 and the second electrode 50 so that the first electrode 49 is positive and the second electrode 50 is negative, the positive first electrode 49 is negative. Charged black particles 45 adhere. Thereby, when an observer observes from the 2nd board | substrate 42 side, the surface (coat layer 52) of the 2nd electrode 50 is observed, and a white image display is implement | achieved.

  When the first electrode 49 and the second electrode 50 are produced by vapor-depositing aluminum, and the coat layer 52 is formed only on the surface of the second electrode 50 using, for example, an acrylic resin with a positive charge column If so, the adsorption force between the black particles 45 and the surface of the second electrode 50 can be increased. As a result, the black particles 45 can be moved from the first electrode 49 to the second electrode 50 with a low voltage. On the contrary, when the coating layer is formed on the first electrode 49 using polycarbonate, which is a negative-side charged column, the adsorption force between the black particles 45 and the surface of the first electrode 49 can be reduced. Therefore, similarly, the black particles 45 can be moved from the first electrode 49 to the second electrode 50 at a low voltage.

  In addition, when the surface of the second substrate 42 is coated with polycarbonate, it is possible to prevent the black particles 45 from being attracted or adhered to the second substrate 42 and to perform uniform display. Become. Further, as in the case of the fourth embodiment, the material of the surface of the spacer 43 is made of PET whose charged column is close to the charged column of the black particles 45, thereby preventing the black particles 45 from adhering to the spacer 43. be able to.

  In this embodiment, the black particles 45, which are one kind of display particles, are used. However, instead of the black particles 45, white particles may be used, and other color particles are used. Needless to say, a configuration capable of color display is also possible.

(Other embodiments)
The display device according to each of the above embodiments performs display of images by enclosing display particles in an air layer formed between a pair of opposing substrates and moving the particles in the air layer. is there. However, the display device of the present invention is not limited to the one in which particles move in such a gas phase. Therefore, a so-called electrophoretic display device in which particles are enclosed in a liquid phase filled between a pair of opposing substrates and the particles move in the liquid phase to perform image display may be used.

  Note that various display devices can be realized by appropriately combining some of the above-described embodiments in accordance with the use of the display device. Therefore, for example, as described with reference to FIG. 7, display particles having a composite configuration in which display particles include mother particles and child particles may be used in the second to fifth embodiments.

  From the foregoing description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

  The display device according to the present invention is useful as a thin and flexible display device.

It is a schematic diagram which shows the structure of the conventional display apparatus, and the display operation at the time of black display. It is a schematic diagram which shows the structure of the conventional display apparatus, and the display operation at the time of white display. It is a perspective top view which shows the main structures of the display part with which the display apparatus which concerns on Embodiment 1 of this invention in case of performing white display is provided. It is sectional drawing in the AA of FIG. It is a block diagram which shows the structure of the display apparatus which concerns on Embodiment 1 of this invention. It is a perspective top view which shows the main structures of the display part with which the display apparatus which concerns on Embodiment 1 of this invention in the case of performing black display is provided. It is sectional drawing in the AA of FIG. 4 (A). It is sectional drawing which shows typically the example of a structure of the surface vicinity of the TFT array substrate with which the display apparatus which concerns on Embodiment 1 of this invention is provided. It is sectional drawing which shows typically the other example of the structure of the surface vicinity of the TFT array substrate with which the display apparatus which concerns on Embodiment 1 of this invention is provided. It is sectional drawing which shows typically the other example of the structure of the surface vicinity of the TFT array substrate with which the display apparatus which concerns on Embodiment 1 of this invention is provided. It is a graph which shows the relationship between the van der Waals force and the pitch of the unevenness | corrugation of a surface treatment layer in the display apparatus which concerns on Embodiment 1 of this invention. It is sectional drawing which shows typically the structure of the display apparatus which concerns on Embodiment 2 of this invention. It is sectional drawing which shows typically the structure of the display apparatus which concerns on Embodiment 3 of this invention. It is a graph which shows the relationship between the reflection density in the display part of a display apparatus, and an applied voltage. It is a graph for demonstrating the drive method of the display apparatus which concerns on Embodiment 2 of this invention. It is a graph which shows the relationship between the reflection density in the display part of a display apparatus, and an applied voltage. It is sectional drawing which shows typically the structure of the display apparatus which concerns on Embodiment 5 of this invention.

Explanation of symbols

3 First electrode 4 Second electrode 5 Scanning signal line 6 Insulating layer 7 Video signal line 8 TFT
9 surface treatment layer 9a TiO ₂ particulate layer 10 air layer 11 black particles 11a mother particles 11b subparticles 12 white particles 31 control unit 32 gate driver 33 source driver 34 image display medium 35 pixels 100 display device 101 counter substrate 102 TFT array substrate

Claims (3)

A pair of opposing substrates, at least one of which is transparent;
A plurality of charged particles contained between the pair of substrates;
A first electrode and a second electrode which are provided for each pixel arranged in a matrix and drive the charged particles;
A voltage application unit that applies a voltage according to an image signal to the first electrode and the second electrode;
On the surface of at least one of the first electrode and the second electrode, there is a concavo-convex layer having a plurality of concavities and convexities formed of a coating material in which titanium oxide fine particles having an anatase crystal structure are dispersed using water as a medium. Formed,
A display configured to display an image according to the image signal by moving the charged particles between the first electrode and the second electrode in accordance with a voltage applied by the voltage application unit. apparatus.   The display device according to claim 1, wherein the plurality of irregularities have a substantially uniform shape.   The display device according to claim 1, wherein a particle diameter of the fine particles is smaller than an average particle diameter of the charged particles.

Images