JP2005221520A - Electrophoretic display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophoretic display device having excellent contrast characteristics and display characteristics. <P>SOLUTION: The electrophoretic display device includes a first substrate, a second substrate arranged to face the first substrate, partitions disposed between the first and the second substrate so as to surround respective pixels, an insulative liquid disposed between the first and the second substrate, a plurality of electrostatic charge particles dispersed in the insulative liquid, a first electrode disposed in correspondence to the respective pixels on the first substrate, a second electrode disposed in correspondence to the respective pixels with the area smaller than the area of the first electrode on the first substrate or the second substrate, and a driving means for applying a voltage to the first electrode and the second electrode. The partitions are so disposed that the first width thereof at the end on the side nearer the first substrate is smaller than the second width of the partitions at the end on the side nearer the second substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophoretic display device.

  In recent years, portable information terminals have been rapidly developed, and the need for low power consumption, light weight, and thin display devices is increasing. At present, reflective liquid crystal display devices are widely used as display devices for portable information terminals. However, since the reflective liquid crystal display device uses a polarizing plate, the light use efficiency is low, and sufficient brightness may not be obtained depending on the use environment, and the display visibility may be poor.

  An electrophoretic display device is known as a method for obtaining a bright reflective display without using a polarizing plate. The electrophoretic display device has a structure in which a dispersion liquid is sandwiched between a pair of substrates on which transparent electrodes are formed. The dispersion liquid is composed of charged particles (charged particles) and an insulating liquid colored by dissolving a dye. When a voltage is applied to the dispersion through the transparent electrode, charged particles having a charge move to an electrode having a polarity opposite to that of the charge. When charged particles gather on the observer side electrode, the color of the charged particles is observed. On the other hand, when charged particles gather on the electrode opposite to the observer side, the observer visually recognizes the color of the insulating liquid. That is, the display is performed by the difference in color between the charged particles and the insulating liquid.

  In order to enable multicolor display in an electrophoretic display device, it has been proposed that a partition wall (bank portion) is provided around each pixel and dispersion liquids of various colors are placed in each pixel (for example, patents). Reference 1).

  In addition, in order to prevent poor display retention due to the movement of charged particles, it has been proposed to provide a partition around each pixel and further form a barrier in the pixel (see, for example, Patent Document 2).

However, if a partition wall is formed around the pixel, light cannot be controlled in the partition wall portion, so that sufficient contrast cannot be obtained. For example, when a light-transmitting or light-scattering partition wall is used, light leaks from the partition wall during black (dark) display (light leakage occurs). Therefore, a sufficient dark state cannot be obtained. On the other hand, when a black (light-absorbing) partition is used, the amount of reflected light (brightness) is reduced as compared with a case where there is no partition because the partition is in a black (dark) state during white display. Such a decrease in contrast due to the partition walls has a problem of reducing the visibility of the display device and increasing the burden on the eyes of the observer.
Japanese Patent Laid-Open No. 2001-235771 (page 3-4, FIG. 1) JP 2001-356373 A (page 6-15, FIG. 10)

  As described above, conventionally, there is a problem that the contrast and display characteristics are deteriorated by using the partition walls.

  In view of the above problems, an object of the present invention is to provide an electrophoretic display device having excellent contrast characteristics and display characteristics.

  Therefore, the present invention provides a first substrate, a second substrate disposed opposite to the first substrate, a partition provided so as to surround each pixel between the first substrate and the second substrate, and the first substrate An insulating liquid provided between the first substrate and the second substrate, a plurality of charged particles dispersed in the insulating liquid, a first electrode provided on the first substrate corresponding to each pixel, and the first substrate Alternatively, the second substrate includes a second electrode that is provided corresponding to each pixel and has a smaller area than the first electrode, and a driving unit that applies a voltage to the first electrode and the second electrode. An electrophoretic display device is provided, wherein a first width of a partition wall at a near end is smaller than a second width of a partition at a near end of the second substrate. In the present invention, when the length of the first width is W1, the length of the second width is W2, and the average particle diameter of the charged particles is a, the following equation (1) may be satisfied.

0.3 μm <W1 <W2-5a (1)
The present invention also provides a first substrate, a second substrate disposed opposite to the first substrate, a partition wall provided between the first substrate and the second substrate so as to surround each pixel, and the first substrate An insulating liquid provided between the first substrate and the second substrate, a plurality of charged particles dispersed in the insulating liquid, a first electrode provided on the first substrate corresponding to each pixel, and the first substrate Alternatively, the second substrate includes a second electrode provided corresponding to each pixel and having a smaller area than the first electrode, and driving means for applying a voltage to the first electrode and the second electrode. Provided is an electrophoretic display device characterized in that a gap is provided between the partition walls. In the present invention, when the length of the partition in the direction perpendicular to the first substrate surface is L, the average particle diameter of the charged particles is a, and the distance between the first substrate and the second substrate is d, the following ( 2) The equation may be satisfied.

0.75d <L <d-2a (2)
In the present invention, at least the surface of the charged particles may be made of a light absorbing material.

  In the present invention, the partition may be made of a light transmissive material.

  In the present invention, the insulating liquid may be light transmissive.

  In the present invention, at least the surface of the charged particles may be made of a light scattering material.

  In the present invention, the specific gravity of the insulating liquid and the charged particles may be approximately equal.

  In the present invention, the second electrode may be provided on the second substrate so as to surround each pixel, and a partition may be provided on the second electrode.

  According to the present invention, an electrophoretic display device having excellent contrast characteristics and display characteristics can be provided.

Hereinafter, an electrophoretic display device according to an embodiment of the present invention will be described in detail with reference to the drawings.
(First embodiment)
First, an electrophoretic display device according to a first embodiment of the present invention will be described with reference to FIGS.

  As shown in the cross-sectional view of FIG. 1, in the electrophoretic display device of the present embodiment, the first substrate 1 and the second substrate 2 are arranged to face each other, and the first substrate 1 and the second substrate 2 are interposed between them. The partition 4 is provided so as to surround each pixel. In FIG. 1, two pixels are extracted and shown for convenience, and a one-dot chain line in the center of the figure indicates a boundary portion between the two pixels. That is, one pixel extends from the dotted line at the end of the figure to this alternate long and short dash line. Further, a pixel electrode (first electrode) 3 provided in an inner region surrounded by the partition 4, that is, a region corresponding to the pixel is formed on the first substrate 1, and the partition 4 is formed on the second substrate 2. A counter electrode (second electrode) 5 provided in a corresponding region is provided. The pixel electrode 3 is connected to a TFT element 11 formed on the first substrate 1. A dispersion 8 made of an insulating liquid 6 in which charged particles 7 are dispersed is disposed between the first substrate 1, the second substrate 2, and the partition 4 on which these electrodes are formed. Moreover, the 1st board | substrate 1 and the partition 4 are arrange | positioned at intervals. In the present embodiment, by providing a gap between the first substrate 1 and the partition 4 in this way, the contrast and display characteristics in the partition 4 are prevented from being deteriorated.

  FIG. 2 is a plan view of a part of the electrophoretic display device of the present embodiment. FIG. 2A is a plan view seen from the first substrate 1 side, and a plan view seen from the second substrate 2 side. It is FIG.2 (b). As shown in FIG. 2A, the first substrate 1 is provided with signal lines 9 and gate lines 10 intersecting each other. On the first substrate 1, a TFT element 11 is provided at the intersection of the signal line 9 and the gate line 10, and a pixel electrode 3 is provided in a region corresponding to the pixel surrounded by the signal line 9 and the gate line 10. Yes. Although not shown in detail, the gate electrode of the TFT element 11 is connected to the gate line 10, the source electrode is connected to the signal line 9, and the drain electrode is connected to the pixel electrode 3. Further, as shown in FIG. 2B, the second substrate 2 has a counter electrode 5 on the second substrate 2 in a grid pattern in the area overlapping the signal line 9, the gate line 10, and the partition 4, that is, around the pixel area including the pixel electrode 3. Is provided.

  In the present embodiment, the display principle will be described in the case where a member having the following characteristics is used. The charged particles 7 are black and are positively charged. As the insulating liquid 6 in which the charged particles 7 are dispersed, a liquid having optical transparency in the visible light region is used. Transparent substrates such as glass are used for the first substrate 1 and the second substrate 2, and transparent electrodes such as ITO (Indium tin oxide) are used for the pixel electrode 3 and the counter electrode 5. A white plate (not shown) is placed outside the second substrate 2. The partition wall 4 is made of light transmissive material. In FIG. 1, with the first substrate 1 side as the observation plane, the left pixel performs white display and the right pixel performs black display.

  When the counter electrode 5 is set to a reference potential (zero volts) and a positive voltage is applied to the pixel electrode 3, the charged particles 7 move to the vicinity of the counter electrode 5 as shown in the pixel on the left side of FIG. When this electrophoretic display device is viewed from the first substrate 1 side, the counter electrode 5 has a small area ratio, and the pixel electrode 3, the first substrate 1, and the second substrate 2 are all light transmissive. The color of the white plate placed on the outside of 2 is visually recognized, and white display is obtained. At this time, the charged particles 7 hardly exist in the gap between the partition wall 4 and the first substrate 1. Therefore, in the partition 4 portion, the partition 4, the counter electrode 5, the first substrate 1, and the second substrate 2 are all light transmissive, so that the color of the white plate placed outside the second substrate 2 is changed. As a result, the partition wall 4 is also white.

  On the other hand, when the counter electrode 5 is set to the reference potential (zero volts) and a negative voltage is applied to the pixel electrode 3, the charged particles 7 move to the vicinity of the pixel electrode 3 as shown in the right pixel of FIG. When this electrophoretic display device is viewed from the first substrate 1 side, the pixel electrode 3 has a large area ratio, the pixel electrode 3 and the first substrate 1 are light transmissive, and the black color of the charged particles 7 is visible. Is black. At this time, due to the influence of the electric field between the pixel electrode 3 and the counter electrode 5 generated around the pixel electrode 3, the charged particles 7 are not only between the pixel electrode 3 and its periphery but also between the partition wall 4 and the first substrate 1. Enters. As a result, the black color of the charged particles 7 is visually recognized also in the partition wall 4 portion, and the partition wall 5 portion also exhibits black color.

  Conventionally, when all of the first substrate, the second substrate, and the counter electrode are light transmissive, the partition wall portion exhibits the color of the partition wall if the partition wall is in contact with both substrates. In this case, the color of the partition wall portion is always the same regardless of the display color of the electrophoretic display device. For example, if the partition wall is light transmissive, light is transmitted through the partition wall portion during black display, and light leakage occurs, so that it looks white. As a result, the luminance (brightness) of black increases and the contrast decreases. If the partition wall is black, light is absorbed in the partition wall portion when white is displayed, and the partition wall appears black. As a result, the brightness (brightness) of white decreases and the contrast decreases.

  On the other hand, in the present embodiment, when the black display is performed, the partition 4 portion is also black, and when the white display is performed, the partition 4 portion is also white, so that the black is more than when the partition 4 is in contact with both substrates. Black and white become whiter and display visibility and contrast are improved. In the present embodiment, the case where the charged particles are black has been described. However, even if the charged particles are light-absorbing particles having colors such as red, green, blue, purple, and gray, display can be performed similarly. Similar effects can be obtained. Note that black particles can be easily prepared with carbon black as a main component, and white particles described later with titanium oxide as a main component, and can be obtained at a relatively low cost compared to other colors. Further, by placing a white plate, a diffuse reflection plate or the like on the outside of the first substrate 1, the second substrate side can be used as an observation surface. The polarity of the charged particles and the polarity of the voltage applied to each electrode are not limited to those described above.

  In the present embodiment, a material is used in which the partition walls 4 are light transmissive, the insulating liquid 6 is light transmissive, and the charged particles 7 are light absorptive.

  When the partition 4 is light transmissive, that is, transparent or nearly transparent, there are the following advantages. When a photosensitive resin is used for the partition wall 4 material and the partition wall 4 is formed by photolithography, if the partition wall 4 material is light transmissive, the light to be exposed reaches the inside of the photosensitive resin. 4 can be formed. Therefore, the aperture ratio of each pixel is increased and the contrast of the display is improved.

  Moreover, there are the following advantages about making the insulating liquid 6 light-transmissive. Many organic solvents are colorless and transparent, and in order to color the insulating liquid 6, a solution obtained by dissolving a dye in an organic solvent is used. This dye contains a lot of ionic impurities. Therefore, the light-transmitting insulating liquid 6 containing no pigment has a higher resistivity than the colored insulating liquid 6 mixed with the pigment. Therefore, the electrophoretic display device using the light-transmissive insulating liquid 6 can be driven at a lower voltage and can operate with higher reliability. In order to obtain high reflectivity and high contrast using the light-transmitting insulating liquid 6, the charged particles 7 are made light-absorbing and a reflecting plate is attached to the outside of the substrate, or the electrode or the reflection on the electrode is reflected. Just make a board.

  In the present embodiment, the case where the charged particles are light-absorbing and a white plate is placed outside the substrate has been described. On the contrary, the charged particles are light-scattering particles such as white and the outside of the substrate. If the black plate is followed, the effect of improving the contrast and improving the display characteristics can be obtained. In addition, color display such as red, green, and blue may be formed on the substrate to perform color display.

  Further, instead of placing a white or black plate on the outside of the substrate, the insulating liquid 6 may be white or black, and the first substrate 1 side may be the observation surface. In this case, in order to perform color display, it is necessary to form a color filter not on the second substrate 2 but on the first substrate 1.

  Also, red charged particles 7 are applied to the cyan insulating liquid 6, blue charged particles 7 are applied to the yellow insulating liquid 6, and green charged particles 7 are applied to the magenta insulating liquid 6. If these dispersion liquids 8 are dispersed and arranged in order on each pixel and the observation surface is on the first substrate side, color display is possible without using a color filter. In this case, since color mixing may occur in the present embodiment in which a gap is provided, it is preferably performed in the second embodiment described later. In addition, the color of the partition 4 is preferably black, white, or transparent.

  In this embodiment, the grid-like counter electrode 5 is provided on the second substrate 2 and the grid-like partition 4 is provided thereon. However, the present invention is not limited to this, and the counter electrode is provided at the center of the pixel. For example, the pattern of the partition wall 4 and the counter electrode 5 may not be the same. When the pattern of the partition wall 4 and the counter electrode 5 is not the same, the ratio of the area of the pixel electrode 3 and the counter electrode 5 is preferably about 5: 1 to 50: 1. It is preferable to have the counter electrode 5 on the partition wall 4 as in the present embodiment, because the charged particles 7 in the gap can be moved at a lower voltage than when the counter electrode 5 is provided at the center of the pixel.

Further, as shown in FIG. 3, the length L of the partition 4 in the direction perpendicular to the substrate surface is such that the average particle diameter of the charged particles 7 is a and the distance between the first substrate 1 and the second substrate 2 is d. When
0.75d <L <d-2a (2)
It is preferable that the relationship is satisfied. FIG. 3 shows a case where the partition wall 4 is formed on the counter electrode 5 as in the present embodiment. In this case, the thickness of the counter electrode 5 is set as L (the length in the direction perpendicular to the substrate surface). Including. By making L larger than 75% of d, the charged particles 7 can move from the gap between the partition 4 and the first substrate 1 to the adjacent pixel when the electrophoretic display device is driven for a long time. It is possible to prevent display unevenness due to different concentrations of the charged particles 7 in each pixel. The distance between the partition walls 4 and the first substrate 1, that is, dL is preferably larger than the average particle diameter of the charged particles 7. At this time, two charged particles 7 having an average size can enter the gap between the partition wall 4 and the first substrate 1, and when the black charged particle 7 is used, the partition wall 4 has a sufficient portion. Black can be obtained.

  As in the present embodiment, a method of providing a gap by arranging the first substrate 1 and the partition wall 4 at a distance is to form a columnar spacer having a height of d in a non-display area such as on a TFT. When the display area is relatively small, spherical spacer particles having a diameter d or a cylindrical substance are mixed in the sealant applied to the outer peripheral portion of the substrate, and spherical spacer particles having a diameter dL are dispersed. There is.

  Moreover, it is preferable that the specific gravity of the insulating liquid 6 and the charged particles 7 is substantially equal. Thereby, an effect of preventing the charged particles 7 from moving from the gap between the partition wall 4 and the first substrate 1 to the adjacent pixel can be obtained.

  Moreover, if a photosensitive material is used for the material which comprises the partition 4, a partition can be formed easily. In particular, since the chemically amplified photosensitive epoxy resin has a high aspect ratio, a narrow partition wall 4 can be formed even when the distance between the first substrate 1 and the second substrate 2 is large.

  The average particle diameter of the charged particles 7 is preferably 0.05 μm or more and 5 μm or less because a stable dispersion state can be obtained.

Further, it is preferable that the width (maximum width) of the central portion of the partition wall 4 is 1 μm or more because it can be easily formed using a photosensitive resin, and the adhesion to the substrate is improved.
(First embodiment (first modification))
Next, a first modification according to the first embodiment will be described. In this modification, description of the same parts as those in the first embodiment will be omitted.

  As shown in the cross-sectional view of FIG. 4, the electrophoretic display device of this modification is formed uniformly on one surface without forming the shape of the counter electrode 21 made of a transparent electrode into a lattice shape matching the shape of the partition wall 4. However, the first embodiment differs from the first embodiment in that the insulating liquid 6 is not transparent but white opaque and the first substrate 1 side is the observation surface. In this modification, a white opaque liquid is used as the insulating liquid 6, so that the observation surface is on the first substrate 1 side having a region not in contact with the partition wall 4.

  Further, when the driving is performed in the same manner as in the first embodiment, the left pixel is displayed in white and the right pixel is displayed in black as in the first embodiment, but the left pixel is white opaque. It is different in that white display is made when the insulating liquid is visually recognized.

Also in this modified example, since the partition 4 and the first substrate 1 are arranged with a gap and a gap is provided, the partition can be displayed in the same color as the display color.
(First Embodiment (Second Modification))
Next, a second modification according to the first embodiment will be described. In this modification, description of the same parts as those in the first embodiment will be omitted.

  As shown in the cross-sectional view of FIG. 5, the electrophoretic display device according to the present modification has a region corresponding to the pixel forming the pixel electrode 22 as well as the inner region surrounded by the partition wall 4, It differs from the first embodiment in that it extends to the gap with one substrate 1. Adjacent pixel electrodes 22 are electrically separated from each other, and a distance of about 2 μm or more is sufficient. The width of the partition wall 4 may be about 5 μm to 10 μm.

Also in this modified example, since the partition 4 and the first substrate 1 are arranged with a gap and a gap is provided, the partition can be displayed in the same color as the display color. Further, in the present modification, the pixel electrode 22 is formed even in the gap between the partition wall 4 and the first substrate 1, so that the charged particles 7 can easily enter the gap, and the contrast characteristics and display characteristics are improved.
(First Embodiment (Third Modification))
Next, a third modification according to the first embodiment will be described. In this modification, description of the same parts as those in the first embodiment will be omitted.

  As shown in the cross-sectional view of FIG. 6, the display device according to the present modification has a pixel on the first substrate 1 without the configuration in which the pixel electrode is formed on the first substrate and the counter electrode is formed on the second substrate. The difference from the first embodiment is that the first electrode 23 used as the electrode and the second electrode 24 having a smaller area than the first electrode 23 are formed. The second electrode 24 may have a stripe shape that is common to pixels in one row or column across the center of the pixel. The first electrode 23 has a shape in which two electrodes divided into the second electrode 24 are spread over the entire pixel, and the two electrodes are connected to one TFT 11. The second electrode 24 may be connected to the TFT 11 and the first electrode 23 may be a common electrode.

  In this modification, when the transparent insulating liquid 6 and the black charged particles 7 are used, when the charged particles 7 spread on the first electrode 23 that is almost the entire pixel, the black display and the area When the charged particles 7 are collected on the small second electrode 24, white display is performed. The size ratio between the first electrode 23 and the second electrode 24 is preferably about 5: 1 to 50: 1.

  Also in this modified example, the partition wall 4 and the first substrate 1 are arranged with a space therebetween and a gap is provided, so that the charged particles 7 also enter the partition wall portion and the color of the charged particles 7 can be displayed. It becomes. However, in the present modification, since the second electrode 24 is arranged at the center of the pixel, there is a possibility that the spread (area) of the charged particles 7 during white display may be increased. Less effective than the example.

  As described above, in the present embodiment and the modification thereof, the partition 4 and the first substrate 1 are arranged at intervals without contacting each other, and the charged particles are also disposed in the gap between the partition 4 and the first substrate 1. By allowing 7 to enter, the amount of charged particles in the gap changes according to the display state of each pixel, so that it is possible to provide an electrophoretic display device having better contrast characteristics and display characteristics.

Moreover, it is preferable that the electrophoretic display device according to the present embodiment and the modification thereof is mainly observed from the first substrate 1 side. Since the electrophoretic display device is used as a reflective display device, there is a high possibility that the observation surface faces upward, and when observed from the arrow direction in FIG. 7, the gap between the partition wall 4 and the first substrate 1 faces upward. It can suppress that the charged particle 7 moves to the adjacent pixel. In either case, it is preferable that the charged particles 7 hardly move by making the specific gravity of the insulating liquid 6 and the charged particles 7 substantially equal regardless of the observation surface. The specific gravity of the insulating liquid 6 and the charged particles 7 is preferably substantially equal, and the ratio of these specific gravity is preferably 0.95 or more and 1.05 or less. If the ratio is smaller than 0.95 or larger than 1.05, the migrating particles may move from the gap between the partition 4 and the first substrate 1 to the adjacent pixel during driving.
(Second Embodiment)
Next, an electrophoretic display device according to a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, only differences from the first embodiment will be described, and description of similar parts will be omitted.

  As shown in the cross-sectional view of FIG. 8, in the electrophoretic display device of this embodiment, the partition wall 31 may be in contact with the first substrate 1, and the cross-sectional area cut along a plane parallel to the first substrate 1 surface of the partition wall 31. However, it becomes smaller as it gets closer to the first substrate 1 and becomes the smallest on the first substrate 1 surface. That is, in the cross-sectional view of FIG. 8 cut in a direction perpendicular to the substrate surface, the width W1 of the partition wall 31 at the end on the first substrate 1 surface side is smaller than the partition wall width at other positions. As shown in FIG. 8, W2 is the width of the widest part of the partition wall 31. The partition wall 31 has the same width (W2) from the second substrate 2 side toward the first substrate 1 side and has a shape that decreases thereafter.

  Also in the present embodiment, since the width of the partition wall 31 is reduced on the first substrate 1 side, charging is performed in the gap between the portions where the width of the partition wall 31 on the first substrate 1 side is reduced as in the first embodiment. When the particles 7 enter, it is possible to display a color desired to be displayed even in the partition wall 31 portion.

  Further, in this embodiment, since each pixel is independent by the partition wall 31, there is an effect that the charged particles 7 do not move between the pixels and unevenness does not occur.

  Furthermore, in the present embodiment, the partition wall 31 is in contact with the first substrate 1 although the width is narrow. Therefore, there is an advantage that the distance between the first substrate 1 and the second substrate 2 can be uniformly controlled by the partition wall 31. However, since the charged particles 7 cannot enter the portion where the partition wall 31 is in contact with the first substrate 1, light leakage occurs. In order to prevent this light leakage, a light shielding layer (not shown) may be provided on the inner surface of the substrate on the observer side. The light shielding layer may be formed using a chromium thin film or the like, and if a switching element such as a TFT (thin film transistor) or a wiring electrically connected to the switching element is used, the process of forming the light shielding layer is shortened. be able to.

Further, as shown in FIG. 8, the width W1 of the partition wall 31 at the end on the first substrate 1 side and the largest partition wall width W2 at other positions are the average particle size of the charged particles 7 as a. When
0.3 μm <W1 <W2-5a (1)
It is preferable to have the following relationship.

  By making the width (W1) between the partition wall 31 and the end on the first substrate 1 side larger than 0.3 μm, it can function as a spacer for controlling the distance between the first substrate 1 and the second substrate 2. it can. More preferably, by making W1 larger than 1 μm, the distance between the first substrate 1 and the second substrate 2 can be maintained accurately and uniformly. However, if the contact part width (W1) is too large, light leakage at this part increases, so that W1 is from the maximum width to the average grain so that the charged particles can enter the part where the partition wall width is narrowed from both sides. 5 times the diameter a is preferably small.

As in the present embodiment, as a method of reducing the width of the partition wall 31 on the first substrate 1 side and providing a gap, the partition wall 31 is formed by forming a resist mask having a width of about W1 after the partition wall 31 is formed. Etching is performed and finally the resist is removed. Alternatively, by using a positive photosensitive resin, the portion corresponding to W1 is not exposed to light during exposure, the portion other than W2 is strong, and the portion other than W2 is irradiated with light. It may be exposed lightly and then developed.
(Second Embodiment (Modification))
Next, a modification according to the second embodiment will be described. In this modification, description of the same parts as those of the second embodiment will be omitted.

  As shown in the cross-sectional view of FIG. 9, the electrophoretic display device of the present modification includes a partition second region 32 in which the partition is formed with a uniform width (W2) on the second substrate 2 side, and the first substrate 1 side. And a partition first region 33 formed with a width smaller than W2. The width W1 in the partition first region at the position in contact with the surface of the first substrate 1 preferably satisfies the relationship of the above formula (1).

  Also in this modification, the width of the partition wall 31 is reduced on the first substrate 1 side, and the same effect as in the second embodiment can be obtained.

  As in the present modification, the partition second region 32 formed with a uniform width (W2) on the second substrate 2 side, and the partition first region 33 formed with a width smaller than W2 on the first substrate 1 side, As a method of forming a partition wall having a gap and providing a gap, the partition wall first region 33 may be formed thereon after the partition wall second region 32 is formed by a photolithography process.

  As described above, in the present embodiment and the modification thereof, although the partition wall and the first substrate 1 are arranged in contact with each other, the width of the partition wall is reduced on the first substrate 1 side. Accordingly, since the charged particles 7 enter the gap between the first substrate 1 and the partition wall, the amount of charged particles in the gap changes according to the display state of each pixel, so that more excellent contrast characteristics and display characteristics can be obtained. An electrophoretic display device having the above can be provided.

Examples relating to each embodiment will be described below.
(Example 1)
An electrophoretic display device of Example 1 relating to the first embodiment as shown in FIGS. 1 and 2 will be described.

  First, a TFT element 11, a signal line 9, and a gate line 10 were formed on a first substrate 1 made of an alkali-free glass substrate having a thickness of about 0.7 mm by a conventional method. Next, the pixel electrode 3 made of ITO was formed by patterning for each pixel so that the pixel electrode 3 and the drain electrode of the TFT element 11 were electrically connected.

  The counter electrode 5 made of ITO was formed by patterning on the second substrate 2 made of an alkali-free glass substrate having a thickness of about 0.7 mm by a conventional method. A partition wall 4 was formed on the second substrate 2 by the following process. A chemically amplified photosensitive epoxy resin (negative type) was applied over the entire surface to a thickness of 30 μm using a spinner. After pre-baking with a hot plate at 95 ° C., a region corresponding to the partition wall was irradiated with 365 nm ultraviolet light for 1 minute through a photomask. This was baked on a hot plate at 95 ° C. and then developed to form partition walls 4 having a height of 30 μm. Thereafter, the substrate was post-baked with a hot plate at 180 ° C. to sufficiently cure the chemically amplified photosensitive epoxy resin.

  A room temperature curing type two-component epoxy adhesive in which a cylindrical glass rod having a diameter of 35 μm is mixed is applied to the periphery of the second substrate 2 using a dispenser, and the partition wall 4 is filled with the dispersion 8, One substrate 1 was bonded and fixed while aligning, and a room temperature curing type two-component epoxy adhesive was cured. A voltage application circuit (driving means, not shown) was connected to this to form an electrophoretic display device. As the dispersion liquid 8, a silicone oil was used as the insulating liquid 6, and carbon particles having an average particle diameter of 0.5 μm whose surface was coated with polystyrene as the charged particles 7 were used. At this time, the insulating liquid 6 was transparent and the charged particles 7 were black. Further, glossy paper (not shown) is pasted on the surface of the second substrate 2 opposite to the surface on which the counter electrode 5 is formed, thereby forming a white reflecting plate.

The distance between the partition wall 4 and the first substrate 1 of this electrophoretic display device was 5 μm, and it was confirmed by microscopic observation that the dispersion liquid 8 had entered between the partition wall 4 and the first substrate 1. When the electrophoretic display device was driven to perform black display, the charged particles 7 entered between the partition walls 4 and the first substrate 1, and the partition wall 4 portion was also black. When white display was performed, almost all of the charged particles 7 moved to the vicinity of the counter electrode 5, and the partition 4 portion also showed white. This electrophoretic display device had a contrast of 10: 1 and an excellent display characteristic of 50% reflectivity during white display.
(Comparative Example 1)
As shown in the cross-sectional view of FIG. 10, there is no gap between the first substrate 1 and the same as in the first embodiment except that a partition wall 100 that contacts both the first substrate 1 and the second substrate 2 is provided. An electrophoretic display device was produced. As a result, light leakage from the partition wall 100 occurred, and the contrast was 7: 1.
(Comparative Example 2)
As shown in the cross-sectional view of FIG. 11, electrophoresis is performed in the same manner as in Example 1 except that a partition wall 200 is provided which is in contact with the first substrate 1 and is not in contact with the second substrate 2 and is provided with a gap. A display device was produced. When the electrophoretic display device was driven to perform black display, almost all charged particles moved to the vicinity of the pixel electrode 3 and the partition wall 200 portion was white. Further, when white display was performed, the charged particles 7 entered the gap between the partition wall 200 and the first substrate 1, and the partition wall 200 portion was black. As a result, the contrast opposite to the color desired to be displayed in the partition wall 200 was displayed, and the contrast was 5: 1.
(Example 2)
An electrophoretic display device of Example 2 related to the first modification of the first embodiment as shown in FIG. 4 will be described.

  In the electrophoretic display device of this embodiment, the shape of the counter electrode 21 formed on the second substrate 2 is made uniform over the entire surface, and white titanium oxide particles (average particle size is 0.3 μm) as the charged electrophoretic particles 7. This was prepared in the same manner as in Example 1 except that the insulating liquid 6 was a dimethyl silicon-dissolved black pigment (Sudan Black).

When the electrophoretic display device is driven to display white by using the first substrate 1 side as an observation surface, the charged particles 7 enter between the partition walls 4 and the first substrate 1, and the partition wall 4 also exhibits white. . When black display was performed, almost all of the charged particles 7 moved to the vicinity of the counter electrode 5, and the partition 4 portion was also black. The electrophoretic display device had a contrast of 9: 1 and an excellent display characteristic of 30% reflectance during white display.
(Example 3)
An electrophoretic display device according to Example 3 relating to the second modification example according to the first embodiment as illustrated in FIG. 5 will be described.

  In the electrophoretic display device of this example, an electrophoretic display device was fabricated in the same manner as in Example 1 except that the pixel electrode 22 was enlarged and extended between the partition wall 4 and the first substrate 1.

When the electrophoretic display device was driven to perform black display, the charged particles 7 entered between the partition walls 4 and the first substrate 1, and the partition wall 4 portion was also black. When white display was performed, almost all of the charged particles 7 moved to the vicinity of the counter electrode 5, and the partition 4 portion also showed white. The electrophoretic display device had a contrast of 11: 1 and an excellent display characteristic of a reflectance of 50% during white display.
Example 4
The electrophoretic display device of Example 4 relating to the second embodiment as shown in FIG. 8 will be described.

  In the electrophoretic display device of this example, an electrophoretic display device was manufactured in the same manner as in Example 1 except that the partition wall 31 was provided so that the width of the partition wall decreased on the first substrate 1 side. A method for forming the partition wall 31 will be described below.

  A counter electrode 5 made of ITO was formed by a conventional method on the second substrate 2 made of an alkali-free glass substrate having a thickness of about 0.7 mm. A partition wall 31 was formed on the second substrate 2 by the following process. An acrylic positive resist was applied over the entire surface to a thickness of 30 μm using a spinner. After pre-baking with a hot plate at 80 ° C., exposure was performed through a photomask. The photomask has a chromium (light-shielding layer) pattern in the region corresponding to W1, and the resist does not receive light during exposure. Therefore, the resist remains in this area even after development. In the region corresponding to other than W2, there is no chrome pattern on the photomask, and the resist is irradiated with light during exposure. Therefore, the resist is removed by development in areas other than W2. The region corresponding to the portion other than W1 in W2 is a chromium pattern in which the exposure amount gradually increases from the W1 side toward the outside of the partition wall. This can be produced by providing a plurality of minute openings of about 0.2 square microns in chromium and gradually increasing the number of openings from the W1 side toward the outside of the partition wall. After the exposure, development was performed using an organic alkaline aqueous solution, whereby the partition wall 31 having a shape shown in FIG. 8 and a height of 30 μm could be formed. Then, it post-baked with a 150 degreeC hotplate.

  When the electrophoretic display device was driven to perform black display, the charged particles 7 entered the region where the width of the partition wall 31 on the first substrate side was reduced, and the partition wall 31 portion was also black. When white display was performed, almost all of the charged particles 7 moved to the vicinity of the counter electrode 5 and the partition wall 31 also showed white. The electrophoretic display device had a contrast of 9: 1 and an excellent display characteristic of a reflectance of 40% during white display.

In addition, since the partition wall 31 is in contact with the first substrate 1 on the first substrate 1 side having a reduced width, the distance between the first substrate 1 and the second substrate 2 even if the electrophoretic display device is pressed with a finger or the like. Was kept uniform and display unevenness did not occur.
(Example 5)
An electrophoretic display device according to Example 5 relating to the modified example according to the second embodiment as illustrated in FIG. 12 will be described.

  In the electrophoretic display device of this embodiment, by performing the photolithography process twice, the partition wall second region 32 formed with a uniform width (W2) on the second substrate 2 side and the first substrate 1 side. A partition having a partition first region 33 formed with a width smaller than W2 is formed, and the partition is in contact with both the first substrate 1 and the second substrate 2. Further, before forming the counter electrode 5 and the partition walls 32 and 33 on the second substrate 2, a red color filter 301, a green color filter 302, and a blue color filter 303 are periodically arranged for each pixel. . Carbon black is used as the charged particles 7, and dimethyl silicon is used as the insulating liquid 6. A manufacturing method will be described only for parts different from the first embodiment.

  First, red, green, and blue color filters were provided inside the second substrate 2 by a conventional method. On this, in the same manner as in Example 1, a counter electrode 5 and a partition second region 32 made of a cured product of a chemically amplified photosensitive epoxy resin were formed. Next, a chemically amplified photosensitive epoxy resin (negative type) was applied on the entire surface of the substrate using a printing machine. After pre-baking with a hot plate at 95 ° C., a region corresponding to the partition first region 33 was irradiated with 365 nm ultraviolet light for 1 minute through a photomask. This was baked on a hot plate at 95 ° C. and developed to form a partition first region 33 having a height of 5 μm on the partition second region 32 having a height of 30 μm. Thereafter, it was post-baked on a hot plate at 180 ° C. and sufficiently cured. The width (= W2) of the second region was 7 μm, and the width (= W1) of the first region was 2 μm.

  When the electrophoretic display device was driven and black display was performed using the first substrate 1 surface as an observation surface, the charged particles 7 entered between the partition walls and the first substrate 1, and the partition wall portions were also black. Further, when a positive voltage was applied to the pixel electrode 3, almost all the charged particles 7 moved to the vicinity of the counter electrode 5 and exhibited the same color as the color filters 301, 302, and 303. At this time, the partition wall also exhibited the same color as the color filter. The electrophoretic display device had a contrast of 8: 1 and an excellent display characteristic of 15% reflectance during white display.

1 is a cross-sectional view showing two pixels of an electrophoretic display device according to a first embodiment of the present invention. It is a top view which shows the electrophoretic display device which concerns on the 1st Embodiment of this invention, (a) is the figure seen from the 1st board | substrate side, (b) is the figure seen from the 2nd board | substrate side. 3 is a cross-sectional view illustrating a gap between a first substrate and a partition wall of the electrophoretic display device according to the first embodiment of the invention. FIG. It is sectional drawing which shows two pixels of the electrophoretic display device of the 1st modification concerning the 1st Embodiment of this invention. It is sectional drawing which shows three pixels of the electrophoretic display device of the 2nd modification concerning the 1st Embodiment of this invention. It is sectional drawing which shows two pixels of the electrophoretic display device of the 3rd modification concerning the 1st Embodiment of this invention. It is sectional drawing which shows the observation direction of the electrophoretic display device which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows two pixels of the electrophoretic display device which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows two pixels of the electrophoretic display device of the modification based on the 2nd Embodiment of this invention. 6 is a cross-sectional view showing two pixels of an electrophoretic display device of Comparative Example 1. FIG. 6 is a cross-sectional view showing two pixels of an electrophoretic display device of Comparative Example 2. FIG. It is sectional drawing which shows three pixels of the electrophoretic display device of the modification concerning the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st board | substrate 2 ... 2nd board | substrate 3, 22 ... Pixel electrode 4, 31, 100, 200 ... Partition 5, 21 ... Counter electrode 6 ... Insulating liquid 7 ... Charged particle 8 ... Dispersion liquid 9 ... Signal line 10 ... Gate line 11 TFT element 23 First electrode 24 Second electrode 32 Partition second region 33 Partition first region 301 Red color filter 302 Green color filter 303 Blue color filter

Claims (10)

A first substrate;
A second substrate disposed opposite the first substrate;
A partition provided between the first substrate and the second substrate so as to surround each pixel;
An insulating liquid provided between the first substrate and the second substrate;
A plurality of charged particles dispersed in the insulating liquid;
A first electrode provided on the first substrate corresponding to each pixel;
A second electrode provided on the first substrate or the second substrate corresponding to each pixel and having a smaller area than the first electrode;
Driving means for applying a voltage to the first electrode and the second electrode;
The first width of the partition wall at the end close to the first substrate is smaller than the second width of the partition wall at the end close to the second substrate. Electrophoretic display device. A first substrate;
A second substrate disposed opposite the first substrate;
A partition provided between the first substrate and the second substrate so as to surround each pixel;
An insulating liquid provided between the first substrate and the second substrate;
A plurality of charged particles dispersed in the insulating liquid;
A first electrode provided on the first substrate corresponding to each pixel;
A second electrode provided on the first substrate or the second substrate corresponding to each pixel and having a smaller area than the first electrode;
Driving means for applying a voltage to the first electrode and the second electrode;
An electrophoretic display device, wherein a gap is provided between the first substrate and the partition wall. The electrophoretic display device according to claim 1, wherein at least a surface of the charged particle is made of a light absorbing material. The electrophoretic display device according to claim 1, wherein the partition wall is made of a light transmissive material. The electrophoretic display device according to claim 1, wherein the insulating liquid is light transmissive. The electrophoretic display device according to claim 1, wherein at least a surface of the charged particles is made of a light scattering material. The electrophoretic display device according to claim 1, wherein specific gravity of the insulating liquid and the charged particles is substantially equal. The electrophoretic display device according to claim 1, wherein the second electrode is provided on the second substrate so as to surround each pixel, and the partition is provided on the second electrode. The following formula (1) is satisfied, where the length of the first width is W1, the length of the second width is W2, and the average particle size of the charged particles is a. Electrophoretic display device.
0.3 μm <W1 <W2-5a (1) When the length of the partition in the direction perpendicular to the first substrate surface is L, the average particle diameter of the charged particles is a, and the distance between the first substrate and the second substrate is d, the following ( The electrophoretic display device according to claim 2, wherein the expression (2) is satisfied.
0.75d <L <d-2a (2)

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