HK1093782B - Electrophoretic device, method of driving electrophoretic device, and electronic apparatus - Google Patents

Description

Electrophoretic device, method of driving electrophoretic device, and electronic apparatus

Technical Field

The present invention relates to an electrophoretic device, a method of driving an electrophoretic device, and an electronic apparatus. In particular, the present invention relates to an electrophoretic device having an electrophoretic dispersion liquid including a liquid dispersion medium and electrophoretic particles, to a method of driving the electrophoretic device, and to an electronic apparatus including the electrophoretic device using the driving method.

The present invention claims priority from Japanese patent application No.2005-60532, filed on 3/4/2005, the contents of which are incorporated herein by reference.

Background

As for an electrophoretic device having an electrophoretic dispersion liquid including a liquid dispersion medium and electrophoretic particles, there has heretofore been known an electrophoretic display device using the fact that: when an electric field is applied to the electrophoretic dispersion liquid, the distribution of the electrophoretic particles changes and the optical characteristics of the electrophoretic dispersion liquid change (for example, refer to japanese examined patent application, second publication No. s 50-15115). Since such an electrophoretic device does not require a backlight, it can contribute to cost reduction and make the display device thinner. Moreover, the electrophoretic display device has a storage property of display in addition to a wide viewing angle and a high contrast ratio. Therefore, it is attracting attention as a next generation display device.

Further, a method has been proposed in which an electrophoretic dispersion liquid is encapsulated in microcapsules in an electrophoretic display device (for example, refer to japanese unexamined patent application, first publication No. h 01-86116). The advantage of encapsulating the electrophoretic dispersion liquid in microcapsules is that leakage of the electrophoretic dispersion liquid during the manufacturing process of the electrophoretic display device can be avoided and precipitation and aggregation of the electrophoretic particles can be reduced.

Further, there is known an electrophoretic display device which is a combination of an electrophoretic display device and an active matrix device in which an electric field is applied to an electrophoretic dispersion liquid by operating the active matrix device so that the distribution of electrophoretic particles is changed (for example, refer to japanese unexamined patent application, first publication No. 2000-35775).

Fig. 12 shows a structure of a conventional electrophoretic display device. Fig. 12A is a plan view of an electrophoretic display device, and fig. 12B is a cross-sectional view of a pixel portion in the electrophoretic display device.

As shown in fig. 12A, the electrophoretic display device 1 has a plurality of data signal lines 9, a plurality of scanning signal lines 3 intersecting the data signal lines, a switching element 6 such as a transistor arranged at the intersection of the data signal lines 9 and the scanning signal lines 3, a data signal operating circuit 4, a scanning signal operating circuit 5, and a pixel electrode 7.

Here, the pixel electrode 7 can be subjected to electrical noise by appropriately supplying a data signal to the data signal line 9 and a scan signal to the scan signal line 3, and then controlling ON/OFF switching of the switching element 6. For example, when a scanning signal that selects only one of the plurality of scanning signal lines is supplied while some of the data signals are supplied to the data signal lines, the switching element 6 connected to the selected scanning signal line is closed, and then the data signal line 9 and the pixel electrode 7 are substantially turned on. That is, at this time, a signal (voltage) supplied to the data signal line 9 is supplied to the pixel electrode 7 through the closed switching element 6. In contrast, the switching elements connected to the non-selected scanning signal lines remain off, and the data signal lines and the pixel electrodes 7 are not substantially conducted.

In this manner, since the electrophoretic display device can selectively turn ON/OFF (ON/OFF) only the transistor connected to a desired scanning signal line, a crosstalk problem hardly occurs and the circuit operation can be speeded up.

As shown in the sectional view of fig. 12B, in a general example of a conventional electrophoretic display device, the pixel electrode 7 and the common electrode 8 are disposed opposite to each other with a predetermined space (typically from several micrometers to several tens of micrometers) therebetween. In the space formed between the electrodes, the electrophoretic dispersion liquid 10 including the liquid dispersion medium 11 and the electrophoretic particles 12 is enclosed. Here, the data signal lines and the scanning signal lines are omitted in fig. 12B for the sake of simplicity.

With this structure, when the above-described operation is performed and a desired data signal (voltage) is supplied to the pixel electrode 7 while the common electrode 8 is maintained at a predetermined voltage, the electrophoretic particles 12 migrate according to a voltage potential difference (electric field) generated between the common electrode 8 and the pixel electrode 7, and the spatial distribution changes. For example, when the electrophoretic particles 12 are positively charged, if a ground potential (0V) is supplied to the common electrode 8 and a negative voltage is supplied to the pixel electrode 7, the electrophoretic particles 12 are attracted to the pixel electrode. In contrast, if a positive voltage is supplied to the pixel electrode 7, the electrophoretic particles 12 are attracted to the surface of the common electrode opposite to the pixel electrode. When the electrophoretic particles 12 are negatively charged, the above-mentioned movement proceeds in the opposite way. Based on this principle, by appropriately controlling the data signal (voltage) supplied to each pixel, a desired image can be obtained.

Further, as a method for realizing gray scale expression in a conventional electrophoretic display device, there is known a so-called area gradation (area gradation) method in which a plurality of minute pixel pieces are grouped to constitute one pixel and gray scale display of the entire pixel is obtained by ON/OFF combination of the respective minute pixel pieces (for example, refer to japanese unexamined patent application, first publication No. s 50-51695). In the area gray scale, each pixel displays any one of a first optical characteristic state (for example, a state in which all electrophoretic particles are deposited on the pixel electrode shown in fig. 12B) and a second optical characteristic state (similarly, a state in which all electrophoretic particles are deposited on the surface of the common electrode opposite to the pixel electrode shown in fig. 12B). Also, with respect to a plurality of pixels included in a certain area, by adjusting a ratio of the number of pixels displaying the first optical characteristic state to the number of pixels displaying the second optical characteristic state, the average optical characteristic in the area can display a value between the first optical characteristic and the second optical characteristic. Here, in order for the pixel to display the first optical characteristic state, a first voltage is applied to the pixel. On the other hand, in order to cause the pixel to display the second optical characteristic state, a second voltage is applied to the pixel. In the above example, the negative voltage becomes the first voltage and the positive voltage becomes the second voltage.

The area gray scale will be described in further detail below. As shown in fig. 13, a display area 2 including four pixel electrodes 7 is considered. Here, the first optical characteristic state is black, and the second optical characteristic state is white. In fig. 13A, a first voltage is applied to all pixels, thus displaying a first optical characteristic state (i.e., a ratio of 4: 0). In fig. 13B, a first voltage is applied to three pixels and a second voltage is applied to the remaining one pixel. As a result, three pixels display the first optical characteristic state and the remaining one pixel displays the second optical characteristic state (i.e., the ratio is 3: 1). As shown in FIGS. 13C, 13D, 13E, the ratios were varied in the order of 2: 2, 1: 3, and 0: 4. In this case, the average optical characteristic for the entire region is apparent as the first optical characteristic in fig. 13A and as the second optical characteristic in fig. 13E. However, in the state therebetween, the average optical characteristic becomes an optical characteristic that is proportionally distributed between the first optical characteristic and the second optical characteristic corresponding to a ratio of the number of pixels in the first optical characteristic state and the number of pixels in the second optical characteristic state.

For example, the reflectance is considered as an optical characteristic, and it is assumed that the reflectance of a black pixel is Rb and the reflectance of a white pixel is Rw. At this time, the average reflectance in the entire region in fig. 13A to 13E becomes the following reflectances, respectively:

FIG. 13A: (4Rb +0Rw)/4 ═ Rb

FIG. 13B: (3Rb + Rw)/4

FIG. 13C: (2Rb +2Rw)/4 ═ 2Rb + Rw/2

FIG. 13D: (Rb +3Rw)/4

FIG. 13E: (0Rb +4Rw)/4 ═ Rw

That is, the reflectance proportionally distributed between Rb and Rw can be expressed corresponding to the ratio of the number of white pixels to the number of black pixels.

In such an area gray scale, since the gray scale is determined as a proportion of the number of pixels by a digital value, it is hardly affected by a difference in characteristics of each pixel. Further, since it can be controlled by a digital circuit and does not require an analog circuit such as a digital/analog converter, it can effectively simplify a control circuit and improve reliability. However, in contrast, since the displayed gray level becomes an average value in a certain area as described above, there is a problem in that: if the pixel size is too large, averaging cannot be done with the naked eye and the image appearance deteriorates. However, in this connection, since the minimization of the pixel size is well advanced due to a high-quality thin film circuit represented by, for example, a low-temperature polysilicon thin film transistor, it is considered that this will not become a large problem in the future.

However, the following problems exist in the conventional art.

In an electrophoretic display device, electrophoretic particles are desirably deposited on a pixel electrode or on a surface of a common electrode opposite to the pixel electrode. In practice, however, in some cases, the electrophoretic particles overflow the ideal deposition area due to leakage of the electric field through the electrophoretic dispersion liquid.

This will be described below with reference to the drawings. For example, in the electrophoretic display device having the structure shown in fig. 12B, as described above, when the electrophoretic particles 12 are positively charged, if the ground potential (0V) is supplied to the common electrode 8 and the positive voltage is supplied to the pixel electrode 7, the electrophoretic particles 12 will be attracted to the surface of the common electrode opposite to the pixel electrode. At this time, the electrophoretic particles 12 are desirably deposited only in the region on the common electrode opposite to the pixel electrode, as shown in fig. 14A. In reality, however, in some cases, since the electric field from the pixel electrode to the common electrode leaks horizontally to some extent, the particles overflow from the ideal region and are deposited as shown in fig. 14B, or they are deposited inside the ideal region as shown in fig. 14C. In this case, the pixel size in the appearance viewed from the common electrode side becomes larger than the actual pixel electrode size in fig. 14B, and becomes smaller than the actual pixel electrode size in fig. 14C. Further, if the structure is such that a plurality of pixel electrodes are arranged in a matrix form, the manner of leakage differs depending on the state of the voltage applied to the adjacent pixel electrodes. As a result, in the actual area gray scale, even if the first voltage or the second voltage is appropriately applied to the respective pixels so as to obtain a desired ratio of the number of pixels of the first optical characteristic state and the number of pixels of the second optical characteristic state, the pixel area ratio of the appearance becomes different, thereby causing a problem that the desired optical characteristics cannot be obtained.

Disclosure of Invention

It is, therefore, an object of the present invention to provide an electrophoretic device, a method of driving the electrophoretic device, and an electronic apparatus, by which desired optical characteristics can be obtained using an area gray scale method.

In order to solve the above-described problems in the conventional art, in the electrophoresis device of the present invention, the optical characteristics when the ratio of the number of pixel electrodes to which the first voltage is supplied to the number of pixel electrodes to which the second voltage is supplied is changed are measured in advance, so that when an image is displayed, the ratio corresponding to the desired optical characteristics is calculated based on the measured values.

That is, the electrophoresis apparatus of the present invention includes: an electrophoretic dispersion liquid including a liquid dispersion medium and electrophoretic particles; a plurality of pixel electrodes; and a voltage supply device that supplies the first voltage or the second voltage to the plurality of pixel electrodes individually, and is configured to obtain a plurality of different optical characteristics by changing a ratio of the number of pixel electrodes to which the first voltage is supplied and the number of pixel electrodes to which the second voltage is supplied, and to measure the optical characteristics when the ratio is changed in advance, so that when an image is displayed, a ratio corresponding to a desired optical characteristic is calculated based on the measured value.

Due to the above structure, the following effects are achieved: an electrophoretic device capable of reliably realizing desired optical characteristics can be provided.

Further, in the electrophoresis apparatus of the present invention, a function R ═ f (x) representing a relationship between the scale x and an actually measured value R of the optical characteristic is obtained by measuring the optical characteristic when the scale is changed in advance, and when the image is displayed, the scale corresponding to the desired optical characteristic is obtained by substituting the desired optical characteristic into an inverse function x ═ f (x) of the function^-1(R) is calculated.

Due to the above structure, the following effects are achieved: the proportion of the number of pixels for obtaining the desired optical characteristics can be calculated more accurately.

Also, in the electrophoretic device of the present invention, the electrophoretic particles include a plurality of types of particles having different optical characteristics. Due to the above structure, the following effects are achieved: complex changes in optical characteristics such as luminance and chrominance can be expressed.

Further, the structure may be such that the electrophoretic dispersion liquid is encapsulated in microcapsules. By filling the electrophoretic dispersion liquid into the microcapsule, leakage of the dispersion liquid during the manufacturing process of the electrophoretic device can be avoided, and precipitation and aggregation of the electrophoretic particles can be reduced.

Further, in the electrophoretic device of the present invention, the pixel electrodes are arranged in a matrix form. Due to the above structure, there is an effect that an image of a complicated shape can be displayed.

In addition, the electrophoretic device of the present invention has a common electrode, and the pixel electrode and the common electrode are formed on the same substrate.

In the method of driving an electrophoretic device of the present invention, the electrophoretic device has: an electrophoretic dispersion liquid including a liquid dispersion medium and electrophoretic particles; a plurality of pixel electrodes; and a voltage supply device that supplies the first voltage or the second voltage to the plurality of pixel electrodes individually, and is configured to obtain a plurality of different optical characteristics by changing a ratio of the number of pixel electrodes to which the first voltage is supplied and the number of pixel electrodes to which the second voltage is supplied, measure the optical characteristics when the ratio is changed in advance, so that when an image is displayed, a ratio corresponding to a desired optical characteristic is calculated based on the measured value, and the first voltage or the second voltage is supplied from the voltage supply device to the plurality of pixel electrodes corresponding to the calculated ratio.

Due to the above structure, the following effects are achieved: a method of driving an electrophoretic device that can reliably achieve desired optical characteristics can be provided.

Further, in the method of driving an electrophoretic device of the present invention, a function R ═ f (x) representing a relationship between the ratio x and an actually measured value R of the optical characteristic is calculated by measuring the optical characteristic when the ratio is changed in advance, and when an image is displayed, a ratio corresponding to a desired optical characteristic is calculated by substituting the desired optical characteristic into an inverse function x ═ f (x) of the function^-1(R) and a first voltage or a second voltage is supplied from the voltage supply device to the plurality of pixel electrodes corresponding to the calculated ratio.

Further, an electronic apparatus of the present invention includes any one of the above electrophoretic devices. Due to the above structure, the following effects are achieved: an electronic apparatus having a display device which can reliably realize desired optical characteristics can be provided.

Drawings

FIG. 1A is a cross-sectional view of a pixel showing a first embodiment of an electrophoretic device, according to the present invention;

fig. 1B and 1C are schematic diagrams showing a pixel structure;

fig. 2A is a schematic view of the structure of a pixel portion, showing a second embodiment of an electrophoretic device according to the present invention;

fig. 2B is a graph and a graph showing an example of a function of a relationship between the reflectance and an example of the number of pixels;

FIG. 2C is a diagram showing an inverse function of the function shown in FIG. 2B;

fig. 2D is a diagram showing a measurement example when the present embodiment is applied;

fig. 3 is a sectional view showing the structure of a pixel portion in a third embodiment of an electrophoretic device according to the present invention;

fig. 4 is a sectional view showing the structure of a pixel portion in a fourth embodiment of an electrophoretic device according to the present invention;

fig. 5A is a cross-sectional view showing an example of a pixel portion in a fifth embodiment of an electrophoretic device according to the present invention;

fig. 5B is a cross-sectional view showing another example of a pixel portion of a fifth embodiment of an electrophoretic device according to the present invention;

fig. 6 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to a portable telephone;

fig. 7 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to a digital camera;

fig. 8 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to an electronic book;

fig. 9 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to an electronic paper;

fig. 10 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to an electronic notebook;

fig. 11A and 11B are schematic views showing an embodiment in which the electronic apparatus of the present invention is applied to a display;

fig. 12A is a plan view of an electrophoretic display device showing the structure of a conventional electrophoretic device;

fig. 12B is a sectional view showing a structure of a pixel portion of a conventional electrophoretic device;

fig. 13A to 13E are sectional views showing a case in which a conventional electrophoretic device has four pixel electrodes;

fig. 14A to 14C are sectional views showing electrophoretic particles in a conventional electrophoretic device.

Detailed Description

The following is a description of embodiments of the present invention with reference to the accompanying drawings.

(example 1)

Fig. 1 shows a first embodiment of an electrophoretic device according to the invention, in which fig. 1A is a cross-sectional view of a pixel, and fig. 1B and 1C show the pixel structure.

As shown in fig. 1A, the present electrophoretic device includes a first substrate 30, a common electrode 8 formed on the first substrate 30, a second substrate 31, an insulating layer 32, a pixel electrode 7 disposed on the common electrode side of the second substrate, and a voltage supply circuit 13, the voltage supply circuit 13 supplying a first voltage or a second voltage to the pixel electrode. The pixel electrode 7 and the common electrode 8 are arranged to be opposed to each other with a predetermined interval formed by a member (not shown) such as a spacer, a partition, or the like. Further, an electrophoretic dispersion liquid 10 including a liquid dispersion medium 11 and electrophoretic particles 12 is filled in the space between the pixel electrode 7 and the common electrode 8

The following is a description of the operation of the present electrophoretic apparatus. In the following description, it is assumed that the liquid dispersion medium 11 is dyed black and the electrophoretic particles 12 are white and positively charged. However, the above assumption is purely for convenience, and the liquid dispersion medium and the electrophoretic particles may be of any color. Furthermore, even if the electrophoretic particles are negatively charged, only the direction of the applied voltage needs to be changed, and the same principle can be applied for explanation.

In fig. 1A, when a negative first voltage (e.g., -10V) is applied to the pixel electrode while the common electrode 8 is held at the ground potential (i.e., 0V), an electric field is generated from the common electrode toward the pixel electrode, and the positively charged electrophoretic particles migrate along the electric field toward the pixel electrode. As a result, the color of the liquid dispersion medium, which is black, is observed from the common electrode side. On the other hand, when a positive second voltage (e.g., +10V) is applied to the pixel electrode while the common electrode 8 is held at the ground potential (i.e., 0V), an electric field is generated from the pixel electrode to the common electrode. Thus, the positively charged electrophoretic particles migrate towards the common electrode. As a result, the color of the electrophoretic particles, which are white, is observed from the common electrode side.

Here, the following items may be used as the liquid dispersion medium 11, but the liquid dispersion medium 11 is not particularly limited thereto. For example, either alone or in admixture with surfactants and the like: water, methanol, ethanol, isopropanol, butanol, octanol, methylcellosolve (methylcellosolve), and other alcohol-based solvents, ethyl acetate, butyl acetate, and other various esters, acetone, methylethyl ketone, methylisobutyl ketone, and other ketones, pentane, hexane, octane, and other aliphatic hydrocarbons, cyclohexane, methylcyclohexane, and other alicyclic hydrocarbons, benzene, toluene, xylene, hexylbenzene, heptylbenzene (hebutyllbenzene), octylbenzene, nonylbenzene, decylbenzene, undecylbenzene, dodecylbenzene, tridecylbenzene, tetradecylbenzene, and other aromatic hydrocarbons, such as benzenes containing long chain alkyl groups, methylene chloride, chloroform, carbon tetrachloride, 1, 2-dichloroethane, and other halogenated hydrocarbons, carboxylic esters, and other various oils, and the like.

Further, the liquid dispersion medium 11 may be substantially transparent or may be opaque. Also, if necessary, it may be appropriately colored with a desired color. The following substances may be used as a colorant for coloring the liquid dispersion medium 11, but are not particularly limited thereto. For example the following, alone or in mixture: anthraquinone series, azo series, diazo series, amine series, diamine series, and other chemical compound dyes, cochineal dye, carminic acid dye, and other natural dyes, azo series, polyazo series, anthraquinone series, quinacridone series, isoindoline (isoindolene) series, isoindolinone (isoindololone) series, phthalocyanine series, perylene series, and other organic pigments, carbon black, silica, chromium oxide, iron oxide, titanium oxide, zinc sulfide, and other inorganic pigments.

Further, the electrophoretic particles 12 may be inorganic or organic particles, or composite particles that electrophoretically migrate in a dispersion medium due to a potential difference. The following substances may be used as the electrophoretic particles 12, but are not particularly limited thereto. For example, singly or in combination of two or more of: nigrosine, carbon black, or other black pigments, titanium dioxide, zinc oxide, antimony trioxide, and other white pigments, monoazo, disazo, polyazo, and other azo-based pigments, isoindolinone, chrome yellow, yellow iron oxide, cadmium yellow, titanium yellow, antimony, and other yellow pigments, monoazo, disazo, polyazo, and other azo-based pigments, quinacridone (quinacrilidone) red, chrome vermilion, and other red pigments, phthalocyanine blue, indanthrene blue, anthraquinone-based dyes, prussian blue, ultramarine blue, cobalt blue, and other blue pigments, phthalocyanine green, and other green pigments.

Also, if necessary, the following substances may be added to the above pigment: electrolytes, anionic, cationic, nonionic and other various surfactants, charge control agents composed of particles of metal soaps, resins, rubbers, oils, varnishes, compounds and the like, titanium-based coupling agents, aluminum-based coupling agents, silane-based coupling agents, and other coupling agents, various polymer dispersants composed of one or more block copolymers such as polyethylene oxide, polystyrene, acrylic, and other macromolecules, lubricants, stabilizers and the like.

As the voltage supply circuit 13, for example, a semiconductor element such as a transistor and a diode, a mechanical switch, or the like can be used. By appropriately controlling the voltage supply circuit 13, a desired voltage, i.e., a first voltage or a second voltage, is supplied to the pixel electrode 7.

As shown in fig. 1B and 1C, in the present electrophoretic apparatus, the display region 2 is constituted by N pixel electrodes 7. The pixel electrodes may be arranged relatively randomly as shown in fig. 1B, or arranged in a matrix form as shown in fig. 1C. However, since an image of a complicated shape can be displayed more accurately, the regular arrangement of pixels in a matrix form is more preferable.

Here, the value of N within the actual display device is determined in consideration of the pixel size, the image to be displayed, the desired gray level to be expressed, and the like. As N becomes larger, the possible gray levels to be expressed increase, but the size of the display area 2 increases, resulting in a decrease in image quality. The smaller the pixel size becomes, the more minute an image can be displayed.

In the following description, for the sake of simplicity, as an example, reflectance is used as an optical characteristic, black (which is a low reflectance state) is used as a first optical characteristic, and white (which is a high reflectance state) is used as a second optical characteristic state. However, these examples are purely for convenience, and substantially similar methods may be used in other cases, for example, where the optical characteristic is hue, chroma, etc.

First, in the pixel structure shown in fig. 1C, the reflectance in the case where the proportions of the pixel in the black state and the pixel in the white state are changed as follows is measured.

Black pixel number to white pixel number reflectance

(0) N∶0 R1

(1) N-1∶1 R2

(2) N-2∶2 R3

(i) N-i∶i Ri

(i+1) N-i-1∶i+1 Ri+1

(N) 0∶N RN

Next, when a desired image is displayed, a ratio corresponding to the desired reflectance is obtained based on the measured value. The first voltage or the second voltage is supplied from the voltage supply circuit 13 to each pixel electrode 7 in correspondence with the calculated ratio. For example, if the reflectivity Ri is desired to be expressed, the ratio of black pixels to white pixels may be N-i: i. More specifically, a first voltage is applied to (N-i) pixels and a second voltage is applied to the remaining i pixels.

Here, if the desired reflectance is between Ri and Ri +1, for example, a ratio closer to either one of them may be adopted. Alternatively, if there are a plurality of display areas, by arranging the area of the reflectivity Ri and the area of the reflectivity Ri +1 side by side, the total average reflectivity of the two areas may be in the middle of Ri and Ri + 1.

In the conventional electrophoretic display device, when a desired reflectance is obtained, a proportion of the number of pixels obtained by a proportional distribution calculation has been used. That is, for example, when the reflectance Ri is obtained, control has been performed assuming that the number of white pixels is (((Ri-R1)/(RN-R1)) × N) and the number of black pixels is (N-number of white pixels). However, the apparent pixel size is different from the size of the pixel electrode due to the leakage of the electric field as described above, and thus a desired reflectance cannot be obtained in such a conventional method. On the other hand, in the method of the present invention, since the ratio of the number of pixels is obtained using the actual measured value, the desired reflectance can be expressed more accurately.

(example 2)

Fig. 2 shows a second embodiment of an electrophoretic device according to the invention.

Fig. 2A shows a pixel structure. In the present electrophoretic device, the display area 2 includes four pixel electrodes 7, two of which are arranged horizontally and two of which are arranged vertically. In the following description, as an example, reflectance is used as the optical characteristic, black (which is a low reflectance state) is used as the first optical characteristic, and white (which is a high reflectance state) is used as the second optical characteristic state. However, these examples are purely for convenience, as described above.

Fig. 2B is an example of reflectance measurement data in the case where the ratio of the number of black pixels to the number of white pixels is changed in an electrophoretic display device having such a pixel structure. A spectrophotometer, SpectroEye manufactured by Gretag Macbeth AG, was used for reflectance measurements. Although the number of measurement data is limited, an approximate curve can be obtained from the data shown in the graph. The approximation curve shows a function R ═ f (x) representing the relationship between x and R assuming that the ratio of the number of black pixels to the number of white pixels is x and the reflectance is R.

Next, when a desired image is displayed, the inverse function x to f of the above function is substituted by the desired reflectance^-1In (R), a ratio corresponding to a desired reflectance is calculated. Then, the first voltage or the second voltage is applied to each pixel electrode corresponding to the calculated ratio. Here, as for obtaining the inverse function x ═ f^-1The method of (R) can be obtained by calculation, for example, if the function R ═ f (x) is given in a numerical formula such as a higher-order polynomial. Alternatively, if the function R ═ f (x) is given as a curve as shown in fig. 2B, it can be obtained by replacing the x-axis and the y-axis (i.e., the horizontal axis and the vertical axis) of the curve. Fig. 2C shows the inverse function x-f obtained by the latter method, i.e. replacing the x-axis and the y-axis of the curve shown in fig. 2B representing the function^-1Curve of (R). The pixel number ratio corresponding to the desired reflectance can be obtained using the curve shown in fig. 2C.

Fig. 2D shows the relationship between the desired reflectance and the actually displayed reflectance when the above-described method is used, and it can be found that excellent linearity can be obtained. In this way, in the method of the present invention, a desired reflectance can be expressed more accurately.

(example 3)

Fig. 3 is a sectional view showing a structure of a pixel part in a third embodiment of an electrophoretic device according to the present invention.

In the present embodiment, the electrophoretic particles include two different types of particles 12a and 12b, as shown in fig. 3. The other elements are similar to those in embodiment 1 described above.

The following is a description of the operation of the electrophoretic device according to this embodiment. In the following description, it is assumed that the electrophoretic particles 12a are white and positively charged, and the electrophoretic particles 12b are black and negatively charged. However, the color and charging polarity of the particles are not particularly limited. For example, even if the charging polarity is reversed, only the direction of the applied voltage needs to be reversed, and the same principle can be used for explanation.

In fig. 3, when a negative first voltage (e.g., -10V) is applied to the pixel electrode while the common electrode 8 is held at ground potential (i.e., 0V), an electric field is generated from the common electrode toward the pixel electrode, and the positively charged electrophoretic particles 12a migrate toward the pixel electrode along the electric field and the negatively charged electrophoretic particles 12b migrate toward the common electrode. At this time, if viewed from the common electrode side, the color of the electrophoretic particles 12b, which are black, is observed over the entire display area. On the other hand, when a positive second voltage (for example, +10V) is applied to the pixel electrode while the common electrode 8 is held at the ground potential (i.e., 0V), an electric field is generated from the pixel electrode to the common electrode. Thus, the positively charged electrophoretic particles 12a migrate towards the common electrode, while the negatively charged electrophoretic particles 12b migrate towards the pixel electrode. As a result, the color of the electrophoretic particles 12a, which are white, is observed from the common electrode side.

For the liquid dispersion medium 11 and the electrophoretic particles 12 in this embodiment, the same materials as those described in embodiment 1 can be used.

Further, the liquid dispersion medium 11 in this embodiment may be substantially transparent or opaque. Further, if necessary, it may be appropriately colored with a desired color.

In the above description, although the electrophoretic particles are composed of two different types of particles, the structure may be such that the electrophoretic particles are composed of three or more different types of particles. In this case, multicolor display can be realized by adjusting signals (voltages) applied to the pixel electrodes and controlling the mutual distribution of three or more different types of particles.

Further, during the above-described image writing operation, by appropriately adjusting the magnitude of the signal (voltage) applied to the pixel electrode and the length of time for applying the signal (voltage) thereto so as to control the distribution of the particles, it is also possible to display a mixed color of the electrophoretic particles 12a and the electrophoretic particles 12b, in other words, an intermediate color.

(example 4)

Fig. 4 is a cross-sectional view of a pixel portion in a fourth embodiment of an electrophoretic device according to the invention.

In the present embodiment, as shown in fig. 4, the electrophoretic dispersion liquid 10 is enclosed in a microcapsule 21 and is disposed between the pixel electrode 7 and the common electrode 8. The other elements are the same as those in embodiment 2.

The structure is such that the electrophoretic particles 12 contained in the electrophoretic dispersion liquid 10 are composed of one type of particles as in example 1 or two or more types of particles as in example 2.

By encapsulating the electrophoretic dispersion liquid in microcapsules in this manner, leakage of the dispersion liquid during the electrophoretic device manufacturing process can be avoided and precipitation and aggregation of the electrophoretic particles can be reduced. Further, a member such as a spacer, a partition or the like for arranging the pixel electrode and the common electrode opposite to each other with a predetermined interval therebetween becomes unnecessary. This brings about an effect of reducing cost and enabling an electrophoretic dispersion liquid to be disposed between flexible substrates. Also, application to electronic paper can be expected.

Examples of the wall film material of the microcapsules 21 include, for example, gelatin, polyurethane resin, polyurea resin, urea resin, melamine resin, acrylic resin, polyester resin, polyamide resin, and other various resin materials. The above materials may also be used singly or in combination of two or more of the above materials.

Also, as a method of forming the microcapsules 21, for example, an interfacial polymerization method, an in-situ polymerization method, a phase separation method, an interfacial precipitation method, a spray drying method, and other various microencapsulation methods can be used.

The size of the microcapsules used in the electrophoretic device according to the present invention is preferably uniform. As a result, a better display function can be exhibited by the electrophoretic device 20. The size of the microcapsules 21 can be made uniform by, for example, percolation (percolation), sieving (screening), segregation (segregation) using a difference in specific gravity, and the like.

The size (average particle diameter) of the microcapsules 21 is not particularly limited, however, about 10 to 150 μm is preferable, and about 30 to 100 μm is more preferable.

Further, it is desirable that: the microcapsules in the present embodiment are arranged between the pixel electrode and the common electrode so as to be in contact with the opposing electrode, and are formed into a flat shape along at least either one of the pixel electrode or the common electrode. As a result, a better display function can be exhibited by the electrophoretic device 20.

Also, in the electrophoretic device according to the present embodiment, the structure may be such that the binder material is disposed between the pixel electrode 7 and the common electrode 8 and around the microcapsule 21. That is, in the present embodiment, the adhesive material may be an element of the electrophoretic device. By providing the adhesive material in this manner, each microcapsule is firmly fixed, and the microcapsule can be protected from mechanical vibration. In addition, the adhesive strength of the microcapsule and the pixel electrode or the common electrode can be enhanced.

The binder material is not particularly limited as long as it has good affinity and adhesiveness with the wall film material of the microcapsules 21 and has insulation properties. Examples of the binder material include, for example: polyethylene, chlorinated polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polypropylene, ABS resin (acrylonitrile-butadiene-styrene copolymer), methyl methacrylate resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylic ester copolymer, vinyl chloride-methacrylic acid copolymer, vinyl chloride-acrylonitrile copolymer, ethylene-vinyl alcohol-vinyl chloride copolymer, propylene-vinyl chloride copolymer, vinylidene chloride resin, vinyl acetate resin, polyvinyl alcohol, polyvinyl formal, cellulose-based resin, or other thermoplastic resin, polyamide-based resin, polyacetal, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene ether, polysulfone, polyamideimide, polyaminobismaleimide, polyethersulfone, polyphenylenesulfone, polyarylate, grafted polyphenylene ether, polyetheretherketone, polyetherimide, and other polymers, polytetrafluoroethylene, polyethylene propylene fluoride, tetrafluoroethylene-perfluoroalkoxyethylene copolymers, ethylene-tetrafluoroethylene copolymers, polyvinylidene fluoride, polychlorotrifluoroethylene, fluororubbers, or other fluororesins, silicones, silicone rubbers, and other silicones. Examples thereof also include methacrylic acid-styrene copolymers, polybutene, methyl methacrylate-butadiene-styrene copolymers as other binder materials, and other various resin materials. These materials may be used alone or in combination of two or more.

Further, the permittivity of the binder material and the permittivity of the liquid dispersion medium 6 are preferably approximately the same. Thus, dielectric constant modifiers such as 1, 2-butanediol, 1, 4-butanediol, and other alcohols, ketones, and carboxylates are preferably added to the binder material.

A composite film of microcapsules and binder material can be obtained in the following manner. For example, the microcapsules and the dielectric constant improver are mixed, if necessary, into the binder material, and then the obtained resin composite (emulsion or organic solvent solution) is disposed on the pixel electrode or the transparent electrode by, for example, a roll coating method, a roll lamination method, a screen printing method, a spraying method, an ink-jet method or other application methods.

(example 5)

Fig. 5A is a sectional view showing a structure of a pixel portion in a fifth embodiment of an electrophoretic device according to the present invention.

The present electrophoretic device includes a first substrate 30, a second substrate 31 disposed opposite to the first substrate, a common electrode 8 and a pixel electrode 7 formed ON the second substrate 31, and a switching element 6 that turns ON/OFF (ON/OFF) a signal supplied to the pixel electrode. Further, the electrophoretic dispersion liquid 10 including the liquid dispersion medium 11 and the electrophoretic particles 12 is enclosed in a space between the first substrate 30 and the second substrate 31.

For the liquid dispersion medium 11 and the electrophoretic particles 12 in this embodiment, the same materials as those described in embodiment 1 can be used.

In the electrophoretic device of the present embodiment, the electrophoretic particles 12 move horizontally with respect to the substrate according to the electric field applied between the common electrode 8 and the pixel electrode 7. Therefore, the difference in-plane distribution of the particles between when the particles are deposited on the common electrode and when the particles are deposited on the pixel electrode is used to display a picture.

The following is a description of the operation of the present electrophoretic apparatus. In the following description it is assumed that the electrophoretic particles 12 are positively charged. However, even if they are negatively charged, it is only necessary to reverse the direction of the applied voltage, and the same principle can be applied for illustration.

In fig. 5A, when a negative first voltage (e.g., -10V) is applied to the pixel electrode while holding the common electrode 8 at the ground potential (i.e., 0V), an electric field is generated from the common electrode to the pixel electrode, and the positively charged electrophoretic particles migrate along the electric field toward the pixel electrode. On the other hand, when a positive second voltage (for example, +10V) is applied to the pixel electrode while the common electrode 8 is held at the ground potential (i.e., 0V), an electric field is generated from the pixel electrode to the common electrode. Thus, the positively charged electrophoretic particles migrate toward the common electrode.

In fig. 5A, the common electrode 8 is shown larger than the pixel electrode 7. However, this is purely for convenience purposes, and the size may be appropriately determined according to desired image characteristics. Therefore, there is no problem if the pixel electrode 7 is larger than the common electrode 8 or if they are the same size.

Further, it is not necessary to arrange the common electrode 8 and the pixel electrode 7 in the same plane. For example, as shown in fig. 5B, the structure may be such that the pixel electrode 7 is superimposed on the common electrode 8.

(example 6)

The following is a description of embodiments of the electronic device according to the invention.

Portable telephone

First is a description of an embodiment in which the electronic apparatus of the present invention is applied to a portable telephone.

Fig. 6 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to a portable telephone. The portable telephone 300 shown in fig. 6 has a plurality of operation buttons 301, an ear piece (ear piece)302, a mouthpiece (mouth piece)303, and a display panel 304.

In such a cellular phone 300, the display panel 304 is constituted by the above-described electrophoretic device 20.

Digital camera

The following is a description of an embodiment in which the electronic apparatus of the present invention is applied to a digital camera.

Fig. 7 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to a digital camera. In fig. 7, the rear side of the sheet is referred to as "the front of the camera", and the front side of the sheet is referred to as "the back of the camera". The connection state with the external device is also schematically shown in fig. 7.

The digital camera 400 shown in fig. 7 has a housing 401, a display panel 402 formed on the back surface of the housing 401, a light receiving unit 403 formed on the observation side (front surface in fig. 7) of the housing 401, a flash button 404, and a circuit board 405. The light receiving unit 403 has, for example, an optical lens, a Charge Coupled Device (CCD), or the like.

Further, the display panel 402 displays based on an image signal from the CCD.

An image signal of the CCD is transferred and stored in the circuit board 405 when the shutter button 404 is pressed.

Also, in the digital camera 400 of the present embodiment, a video signal output terminal 406 and an input-output terminal 407 for data communication are provided on the side surface of the housing 401.

Of these elements, if necessary, for example, a television monitor 406A is connected to the video signal output terminal 406, and a personal computer 407A is connected to the input-output terminal 407.

The digital camera 400 is configured to output an image signal stored in a memory of the circuit board 405 to the television monitor 406A, or the personal computer 407A by a predetermined operation.

In such a digital camera 400, the display panel 402 is constituted by the electrophoresis device 20 described above.

Electronic book

The following is a description of an embodiment in which the electronic apparatus of the present invention is applied to an electronic book.

Fig. 8 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to an electronic book.

The electronic book 500 shown in fig. 8 has a book-shaped frame 501, and a rotatable (openable and closable) cover 502 for the frame 501.

Inside the frame 501, a display panel 503 having an exposed display surface and an operation member 504 are mounted.

In this electronic book, the display panel 503 is constituted by the electrophoresis device 20 described above.

Electronic paper

The following is a description of an embodiment in which the electronic apparatus of the present invention is applied to electronic paper.

Fig. 9 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to electronic paper.

The electronic paper 600 shown in fig. 9 has a main body 601 and a display unit 602 that are constituted by a writable sheet having the same texture and flexibility as paper.

In this electronic paper 600, the display unit 602 is constituted by the above-described electrophoretic device 20.

Electronic notebook

The following is a description of an embodiment in which the electronic apparatus of the present invention is applied to an electronic notebook.

Fig. 10 is a perspective view showing an embodiment in which the electronic apparatus of the present invention is applied to an electronic notebook.

The electronic notebook 700 shown in fig. 10 has a cover 701 and electronic paper 600.

The electronic paper 600 has the above-described structure, i.e., the same structure as that shown in fig. 9. A plurality of electronic papers are bound together so as to be inserted into the cover 701.

Also, an input device for inputting data is provided in the cover 701. As a result, the display content of the electronic paper 600 can be changed under the condition of stapling.

In this electronic notebook 700, the electronic paper 600 is constituted by the electrophoresis device 20 described above.

Display (display)

The following is a description of an embodiment in which the electronic device of the present invention is applied to a display.

Fig. 11A and 11B show an embodiment in which the electronic apparatus of the present invention is applied to a display. Fig. 11A is a sectional view, and fig. 11B is a plan view.

The display (electrophoretic device) 800 shown in fig. 11 has a main body 801, and an electronic paper 600 detachably provided with respect to the main body 801. The electronic paper 600 has the above-described structure, i.e., the same structure as that shown in fig. 9.

An insertion groove 805 into which the electronic paper 600 can be inserted is formed in a side surface (right side in fig. 11) of the main body 801. Also, two pairs of bearing rollers 802a and 802b are provided within the main body 801. When the electronic paper 600 is inserted into the main body 801 through the insertion slot 805, the electronic paper 600 is set into the main body 801 while being inserted between the bearing rollers 802a and 802 b.

A rectangular opening 803 is formed on the display side (front side of the paper in fig. 11B) of the main body 801, and a transparent glass plate 804 is fitted into the opening 803. As a result, the electronic paper 600 set into the main body 801 is visible from the outside of the main body 801. That is, the display 800 constitutes a screen that displays a picture by viewing the electronic paper 600 set in the main body 801 through the transparent glass plate 804.

Further, a terminal member 806 is provided on the front end of the electronic paper 600 in the insertion direction (left side in fig. 11). A socket 807 to which a terminal member 806 is connected is provided in the main body 801 in a state where the electronic paper 600 is set in the main body 801. The controller 808 and the operation section 809 are electrically connected to the socket 807.

In such a display 800, the electronic paper 600 is detachably provided in the main body 801, and it can be used portably in a condition of being detached from the main body 801.

In the display 800, the electronic paper 600 is formed of the electrophoretic device 20.

The electronic device of the present invention is not limited to the applications of the above items. Examples of suitable applications include televisions, viewfinder or monitor-direct-view video tape recorders, car navigation devices, paper, electronic data books, calculators, electronic newspapers, word processors, personal computers, workstations, video telephones, point-of-sale terminals, devices with touch screens, and the like. The electrophoretic device 20 of the present invention can be applied to display sections of these various electronic apparatuses.

While preferred embodiments of the invention have been described and illustrated above, it is to be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions and other modifications can be made to the embodiments without departing from the spirit or scope of the invention. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

According to the electrophoretic device of the present invention, desired optical characteristics can be accurately obtained for gray scale representation, particularly in terms of area gray scale.

Claims (9)

1. An electrophoretic device comprising:

an electrophoretic dispersion liquid including a liquid dispersion medium and electrophoretic particles;

a combined pixel including a plurality of pixels;

a plurality of pixel electrodes provided at each of the plurality of pixels; and

a voltage supply device that individually supplies a first voltage or a second voltage to the plurality of pixel electrodes,

and the electrophoretic device is configured to obtain a plurality of different optical characteristics of the combined pixel by changing a ratio "x" of the number of pixel electrodes supplied with the first voltage to the number of pixel electrodes supplied with the second voltage,

wherein when displaying the image, a preferred proportion "x" displaying the desired optical characteristic of the combined pixel is calculated based on an actual measurement value R determined based on an actual measurement of the optical characteristic of the combined pixel when the proportion "x" is varied.

2. An electrophoretic device according to claim 1 wherein

A function R ═ f (x) representing the relationship of the ratio "x" and the actually measured value R of the optical characteristic is obtained in advance, and when an image is displayed, a preferred ratio at which a desired optical characteristic is displayed is obtained by substituting the desired optical characteristic as a value R into an inverse function x ═ f (x) of the function^-1(R) is calculated.

3. An electrophoretic device according to claim 1 wherein the electrophoretic particles comprise a plurality of types of particles having different optical properties.

4. An electrophoretic device according to claim 1 wherein the electrophoretic dispersion liquid is encapsulated within microcapsules.

5. An electrophoretic device according to claim 1 wherein the pixel electrodes are arranged in a matrix.

6. An electrophoretic device according to claim 1 having a common electrode, and the pixel electrode and the common electrode are formed on the same substrate.

7. An electronic device comprising an electrophoretic apparatus according to claim 1.

8. A method of driving an electrophoretic device, the electrophoretic device comprising:

an electrophoretic dispersion liquid including a liquid dispersion medium and electrophoretic particles;

a combined pixel including a plurality of pixels;

a plurality of pixel electrodes disposed at each of the plurality of pixels; and

a voltage supply device that individually supplies a first voltage or a second voltage to the plurality of pixel electrodes,

and the method comprises:

a plurality of different optical characteristics of the combined pixel are obtained by changing the ratio "x" of the number of pixel electrodes in the combined pixel to which the first voltage is supplied to the number of pixel electrodes to which the second voltage is supplied,

measuring the optical characteristic as an actual measurement value R in advance when changing the ratio "x"; and

when an image is displayed, a preferred proportion "x" at which a desired optical characteristic is obtained is calculated based on the measured value R, and the first voltage or the second voltage is supplied from the voltage supply device to the plurality of pixel electrodes corresponding to the calculated preferred proportion "x".

9. The method of driving an electrophoretic device according to claim 8, wherein:

obtaining in advance a function R ═ f (x) representing a relationship between the ratio "x" and the actually measured value R of the optical characteristic, and

when displaying an image, by substituting the desired optical characteristic as the value R into the inverse of the function x-f^-1(R) calculating a preferred proportion "x" at which the desired optical characteristic R is obtained, and supplying the first voltage or the second voltage from the voltage supply device to the plurality of pixel electrodes corresponding to the calculated preferred proportion "x".