JPH02196227A - Thermal writing type electrophoresis display element - Google Patents

Abstract

PURPOSE:To form the electrophoresis display element to a larger area and to obtain sharp images which are fine, are high in quality and are wide in angle of field by locally forming a dispersion medium into the sol and locally migrating the electrophoresis particles. CONSTITUTION:The voltage of the same polarity as the polarity at which electrophoresis particles 8 are electrified is applied to an electrode 3 stuck with the particles 8 over the entire surface. The voltage of the reverse polarity is applied to the other electrode 4. Since the dispersion medium 7 is gelatinized, the particles 8 cannot move at this time. The position where writing is required is then irradiated with laser light 90 from the rear surface of the substrate 2 opposite to the substrate 1 on a visual observation side. The dispersion medium 7 in the position subjected to the irradiation is heated and is increased in temp., by which the medium is locally formed into the sol. The particles 8 are migrated in the part where the dispersion medium 7 is locally formed into the sol in addition, the particles adhere to the electrode surface having the polarity reverse from the polarity to be electrified. The writing is thus executed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a thermal writing type electrophoretic display element.

[Prior Art] A writing type image display device is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 1986-5.
As disclosed in Japanese Patent Application No. 6621, it is composed of an electrophoretic display element that displays a written image, and a charge applying means that applies electric charge to the electrophoretic display element to write an image.

[Problems to be Solved by the Invention] The stability of the display performance of the electrophoretic display element used in the above writing type image display device is greatly influenced by the state of dispersion of the electrophoretic particles in the dispersion medium. Therefore, adjustment operations such as adjusting the specific gravity of the dispersion medium and adding an appropriate amount of surfactant to the dispersion medium taking into account aggregation and sedimentation of electrophoretic particles are troublesome. In addition, in electrophoretic display elements, when the area of the display section that displays a self-contained image is expanded, the amount of dispersion medium used increases, and it is difficult to maintain uniformity of the specific gravity. In addition, blurring occurred in the pixels, making it difficult to display fine details.

An object of the present invention is to provide a thermal writing type electrophoretic display element that solves the above problems.

[Means for Solving the Problems] The thermal writing type electrophoretic display element of the present invention includes a pair of substrates, at least one of which is transparent, and a device formed on opposing surfaces of the pair of substrates and formed on at least the transparent substrates. The electrodes include a pair of transparent electrodes, a dispersion medium that is disposed between the pair of substrates and that reversibly gels and becomes a sol due to temperature, and electrophoretic particles dispersed in the dispersion medium, It is characterized in that the electrophoretic particles can be locally migrated by locally solizing the dispersion medium.

The thermal writing type electrophoretic display element of the present invention is characterized by the dispersion medium used. The dispersion medium used is a substance that reversibly gels and becomes a sol depending on the temperature. The substance is a non-conductive insulating substance, and is usually a halogen-based solvent such as bromine having a relatively large specific gravity to which a gelling agent or a thickening agent is added. As the gelling agent and the thickening agent, it is preferable to use a polymeric substance whose solvent is a poor solvent. A poor solvent refers to a solvent that dissolves the polymeric substance when the temperature of the solvent is high, but that makes the polymeric substance insoluble and gelatinizes when the temperature is low. Usually, a poor solvent is obtained by mixing a good solvent that dissolves the polymeric substance and a liquid that does not dissolve the polymeric substance. The gelling temperature can be adjusted by adjusting the mixing ratio of the good solvent and the liquid and the molecular weight of the polymer substance. It is adjusted so that when added, it gels at room temperature and becomes solid, and when heated, it gels and becomes liquid.

Electrophoretic particles dispersed in this dispersion medium are prevented from migrating when the dispersion medium is in a gelled state, and are allowed to migrate when the dispersion medium is in a solized state.

In addition, heating for converting the dispersion medium in the gelation state 1) into a sol can be performed using, for example, laser beam irradiation, ultrasonic irradiation, or other heating means. In short, any material that can locally heat the dispersion medium may be used.

Note that the dispersion medium can be colored in advance with a coloring agent having a color depending on the purpose of use. As this colorant, a dye that can be dissolved in a dispersion medium is used.

The electrophoretic particles used have a color different from that of the dispersion medium, and are dispersed in the dispersion medium.

These electrophoretic particles are either positively or negatively charged.

[Function] In the thermal writing type electrophoretic display element of the present invention, the dispersion medium is entirely heated to become a sol prior to the thermal writing operation. Then, a voltage with the opposite polarity to the polarity with which the electrophoretic particles are charged is applied to one of the electrodes, and a voltage with the same polarity is applied to the other electrode.

Then, the electrophoretic particles dispersed in the dispersion medium adhere to the entire surface of one of the pair of electrodes. This state is
When the heating of the dispersion medium is stopped, the dispersion medium naturally cools and gels, thereby being retained.

When performing thermal writing, a voltage of the same polarity as that of the charged electrophoretic particles is applied to the electrode to which the electrophoretic particles are fully attached, and a voltage of the opposite polarity is applied to the other electrode. Apply. At this time, the electrophoretic particles cannot move because the dispersion medium is gelled. Here, for example, a laser beam is irradiated from the back side of the substrate facing the viewing side substrate M to the position where the thickening is required. Then, the dispersion medium at the position irradiated with this laser light is heated and its temperature increases,
Locally becomes a sol. As a result, the electrophoretic particles migrate in the portion where the dispersion medium is locally solized, and write is performed by adhering to the electrode surface having the opposite polarity to the charged polarity.

Note that during this thermal writing, two types of writing display can be used. That is, when electrophoretic particles are attached in advance to one side of the electrode facing the viewing side electrode, during thermal writing (the image is displayed in the color of the electrophoretic particles attached to the viewing side electrode as a written image). In addition, if electrophoretic particles are attached to one surface of the electrode on the viewing side in advance, the electrophoretic particles will move to the opposite electrode side during thermal writing, and the blank part of the electrode on the viewing side will become blank. The image is displayed in the color of the dispersion medium.

[Example] (Example 1) The thermal writing type electrophoretic display element of Example 1 is comprised of first transparent elements arranged at a predetermined distance from each other, as shown in FIGS. 1 to 4 as cross sections. It consists of a substrate 1 and a second transparent substrate 2, a first transparent electrode 3 and a second transparent electrode 4, a spacer 6 and a seal member 60, a dispersion medium 7 and electrophoretic particles 8. A drive control section 5 is connected to the first transparent electrode 3 and the second transparent electrode 4 of this display element.

The first substrate 1 and the second substrate 2 are both made of transparent soda lime glass plates. Further, each of the opposing inner surfaces 10 and 20 of both substrates 1.2 is provided with a first transparent electrode 3.
and a second transparent electrode 4 are formed. Both transparent electrodes 3 and 4 are connected to the inner surface 10 of the first substrate 1 and the second substrate 2.
and 20 were formed by vacuum deposition. In addition, when forming the second transparent electrode 4 on the inner surface 20 by vacuum deposition, the second substrate 2 is coated with anti-reflection multilayer films 20a and 21a at the interface between the two and on the outer surface 21. .

The spacer 6 is provided with a dispersion medium 7 at the periphery of the mutually opposing inner surfaces 10 and 20 of the first transparent substrate 1 and the second transparent substrate 2.
The substrates 1.2 and 1.2 are arranged in a sandwich shape except for a portion that will serve as an injection port (not shown), and form a gap in which the dispersion medium 7 can be sealed in the first and second substrates 1.2. This spacer 6 is
A polyester film having a thickness of 100 μm is cut to form a frame shape that is surrounded by a band between the first substrate 1 and the second substrate 2 with a circumference of about 5 mm and a portion cut out as an injection port. An epoxy adhesive is applied to the outer peripheral portion of the spacer 6 except for the injection port portion, thereby forming a sealing member 60. In this way, a cell portion is formed.

As the dispersion medium 7, tetrafluorodibromoethane and 0.5Q/100ml of a gelling agent (Ajinoki GP-1, amino acid type) dissolved therein are used. Furthermore, Sudan Black B (black) is mixed in this dispersion medium 7 as a coloring dye 70.

As the electrophoretic particles 8, a white pigment (titanium oxide) having a specific gravity almost the same as that of the dispersion medium 7 was used. This is a negatively charged particle. Note that the average particle diameter of the electrophoretic particles 8 is about 0.5 μm. A dispersion liquid is prepared so that the concentration of the electrophoretic particles 8 is about 1% by weight. Since this dispersion medium is in a gel state at room temperature, it is first heated to form a highly fluid sol and then injected from the injection port of the cell section to fill the interior space of the cell section. A seal member (not shown) made of the same material as the seal member 60
Filled and sealed.

The drive control section 5 has a write drive circuit 50 and an erase drive circuit 51. In the writing drive circuit 50, one end of each of the lead wires 30 and 40 for transmitting the applied voltage for writing is connected to each peripheral edge of the first transparent electrode 3 and the second transparent electrode 4.

This mixing drive circuit 50 is capable of applying a voltage of 50 V, which is a necessary magnitude when moving the electrophoretic particles 8, through the first transparent electrode 3, the second transparent electrode 4, and the lead wires 30 and 40. . The erasing drive circuit 51 is capable of applying a large voltage to the second transparent electrode 4 to create a heat generating state capable of turning the dispersion medium 7 into a sol.
The lead wires 40 and 4 connected to one end and the other end of
Connected to 1. Both drive circuits 50 and 51 can be driven either alone or simultaneously.

A writing laser beam irradiation device 9 capable of irradiating a laser beam to the outer surface 21 of the second substrate 2 at a constant interval is disposed in the thermal writing type electrophoretic display element formed in this manner. The writing laser beam irradiation device 9 irradiates the second transparent electrode 4 or the dispersion medium 7 from the direction of the outer surface 21 of the second substrate 2 so as to locally heat the dispersion medium 7 sealed therein. Light irradiation standards are set. This writing laser beam irradiation device 9 includes an argon laser, 1
．． A material having a performance of 0.09 μm and 5 mW is used.

In the thermal writing type electrophoretic display element of the first embodiment, in order to cause the electrophoretic particles 8 in the dispersion medium 7 to adhere to the entire surface of the first transparent electrode 3 prior to the thermal writing action, the erasing drive circuit 51
is driven, and a heat generating current is applied to the second transparent electrode 4 from the lead wires 40 and 41. Then, the second transparent electrode 4 generates heat over its entire surface and disperses a! '7 is completely heated and feels sore. In this state, the write drive circuit 50
is driven, and a voltage of 50 V DC with a positive polarity is applied to the first transparent electrode 3 from the lead wire 30 and a voltage of 50 V DC with a negative polarity is applied to the second transparent electrode 4 from the lead wire 40. Then, the negatively charged electrophoretic particles 8 in the dispersion medium 7 adhere to the entire surface of the first transparent electrode 3, as shown in FIG. Therefore, a white display due to the electrophoretic particles 8 attached to the entire surface of the first transparent electrode 3 is visible from the first transparent substrate 1 side. This state is maintained by the dispersion medium 7 being gelled by natural cooling as the drive of the drive circuit 51 is stopped. Next, the write drive circuit 50 is driven while the white electrophoretic particles 8 are completely attached to the first transparent electrode 3 side. At this time, the first transparent electrode 3 is connected to the lead wire 30 with a negative polarity, and the second transparent electrode 4 is connected to the lead wire 40 with a positive polarity of DC.
A voltage of 50V is applied. Then, the negatively charged electrophoretic particles 8 try to move away from the first transparent electrode 3,
And it tries to be attracted to the second transparent electrode 4 side. However, since the dispersion medium 7 is in a gelled state, the electrophoretic particles 8 cannot move toward the second transparent electrode 4 due to its high viscosity. Here, the laser light irradiation device 9 is driven to emit laser light 90 to the second transparent electrode 4 via the second substrate 2.
Alternatively, when the dispersion medium 7 is irradiated, only that part is heated and the temperature rises, and the dispersion medium 7 is locally turned into a sol rather than a gelatinous state, and its viscosity is reduced. Therefore, as shown in FIG. 3, the electrophoretic particles 8 move away from the first transparent electrode 3 and adhere to the second transparent electrode 4 at a position where the dispersion medium 7 is locally solified. Then, some of the electrophoretic particles 8 that formed the white surface of the first transparent electrode 3 are separated and the blank area, that is, the written image, is displayed in the black color of the colored dye 70 in the dispersion medium 7. It is visible from the board 1 side. Therefore, by controlling the irradiation position of the laser beam 90 onto the thermal writing type electrophoretic display element, it is possible to display a black and white display in which the background is white and the necessary characters and patterns are black.

Note that it is possible to display the above black and white display in a reverse pattern. That is, contrary to the above case, as shown in FIG. 4, white electrophoretic particles 8 are placed on the second transparent electrode 4 side in advance.
The dispersion medium 7 is then irradiated with a laser beam 90 to heat the dispersion medium 7 and locally become a sol, thereby removing the white electrophoretic particles 8 that had adhered to the second electrode 4 side. It is moved to the side of the first transparent electrode 3. White characters or patterns can be written on the first transparent electrode 3 using J- as a background against the black color of the colored dye 70 in the dispersion medium 7, thereby making it possible to display black and white.

In the above embodiment, the colors of the electrophoretic particles 8 and the dispersion medium 7 are displayed in black and white or black and white, but it is also possible to use a combination of other chromatic colors.

(Example 2) The thermal writing type electrophoretic display element of Example 2 shown in FIG. The irradiation light is irradiated and the reflected light is enlarged and projected onto a screen 97. This electrophoretic display element is made of electrophoretic particles and silver powder coated with phenol resin, AB-800-40 made by Mitsubishi Metals, with a particle size of 1 to 5 μm.
The surface was coated with an insulating coating.

In addition, as the dispersion medium 7 (), 1.5 i of a thickener (manufactured by Shiraishi Kogyo, New-B-ORBDN) was added to tetrafluoroethylene.
n1%, and 0.2% by weight of an infrared absorber (manufactured by Mitsui Toatsu Chemical Co., Ltd., PA-1005, maximum absorption wavelength 850 nm) was added in order to increase the heat absorption rate of laser light. No dye was added to the medium so as not to inhibit the reflection efficiency of the electrophoretic particles.The settings other than the above were the same as in Example 1.

The thermal writing type electrophoretic display element 1A of Example 2 is arranged at an angle of about 45 degrees, and various devices are arranged around it. That is, as shown in FIG. 5, on the second substrate 2 side, a laser beam irradiation device 9 and a writing lens 92 for writing by focusing the laser beam are arranged at a certain distance. Ru. Also, the first substrate 1
Halogen lamp 93 and parabolic mirror 94 placed on the side
and a condenser lens 9 which focuses the light emitted from the halogen lamp 93 and reflected by the parabolic mirror 94 parallel to the optical axis P and irradiates it parallel to the first substrate 1 side of the electrophoretic display element 1A; a central optical axis S perpendicular to the central optical axis P;
A projection lens 96 is disposed above and collects and projects the reflected light reflected by the electrophoretic particles of the electrophoretic display element 1A and travels parallel to the central optical axis S, and the reflected light collected by the projection lens 96 It consists of a screen 97 on which light is projected.

In the thermal writing type electrophoretic display element of the second embodiment disposed between such various devices, writing irradiation is performed from the second substrate 2 side of the laser element 1A. The diameter of the irradiation beam is focused to 20 to 50 μmψ by the writing lens 92, and as in Example 1, the dispersion medium in the enclosure is locally solified by the heating of the laser beam 90, allowing the electrophoretic particles to move.
The locally moved electrophoretic particles adhere to the second transparent electrode 4 side, and thermal writing is performed. The irradiated light emitted from the halogen lamp 93, reflected by the parabolic mirror 94, and focused in one direction is further focused in parallel by the condenser lens 95, and then directed to the first transparent electrode 3 side of the display element 1A. irradiated. This irradiation light a is reflected by electrophoretic particles having a silvery white reflective surface attached to the first transparent electrode 3 as a written image. This reflected light a1 is condensed by the projection lens 96 and then projected and displayed on the entire surface of the screen 97. In this case, the written image on the thermal writing type electrophoretic display element 1A is displayed in an enlarged manner,
It becomes possible to enlarge the display field of view.

[Effects] According to the thermal writing type electrophoretic display element of the present invention, the dispersion medium enclosed in the cell can be reversibly gelled and solified by temperature. Therefore, when writing, a dispersion medium that is gelatinous at room temperature can be locally solified by controlling heating. This dispersion medium can locally migrate electrophoretic particles at the sol-formed position. Furthermore, a written image can be formed by attaching electrophoretic particles to the electrodes of either one of the substrates. Therefore, the written image can be displayed on the viewing side electrode to which electrophoretic particles have adhered, depending on the color. When the migrated electrophoretic particles adhere to the electrode opposite to the electrode on the viewing side, a written image can be displayed by the color of the dispersion medium in the portion of the electrode on the viewing side that is not attached.

In addition, even when the local heating for locally solizing the dispersion medium is stopped and the voltage application to the pair of electrodes is stopped, electrophoretic display elements may still be partially damaged due to temperature drop. As the sol-formed dispersion medium turns into a gel, the electrophoretic particles adhering to the viewing side electrode and the other electrode are prevented from moving by the gelled dispersion medium, thereby stabilizing the writing/displaying state. , can be held.

In this way, according to the present thermal writing type electrophoretic display element, even when the specific gravity of the electrophoretic particles and the dispersion medium is different,
Since the dispersion medium is in a gelatinous state at room temperature, the electrophoretic particles do not settle or aggregate in the dispersion medium, making it possible to increase the area of the electrophoretic display element.

Further, it is possible to eliminate crosstalk (a phenomenon in which non-selected pixels are displayed) and blur caused by using matrix electrodes. As a result, a high-definition, high-quality image can be obtained.

In addition, it is possible to create a large projection type display, and since it is not visually dependent like a liquid crystal element, clear images with a wide viewing angle can be obtained.

[Brief explanation of the drawing]

1 to 4 show a thermal writing type electrophoretic display element according to Example 1 of the present invention, and FIG. 1 shows a first transparent electrode and a second transparent electrode.
FIG. 3 is a cross-sectional view showing a state in which no voltage is applied to the transparent electrode. FIG. 2 is a cross-sectional view showing a state before thermal writing in which electrophoretic particles are attached to the entire surface of the first transparent electrode. FIG. 3 is a cross-sectional view showing a state in which voltage is applied to both electrodes and thermal writing is performed by irradiation with laser light. FIG. 4 is a sectional view showing a state before thermal writing in which electrophoretic particles are attached to the entire surface of the second transparent electrode. FIG. 5 shows Example 2 of the present invention.
FIG. 2 is an explanatory diagram combining a cross-sectional view and a side view showing a state in which a voltage is applied to both electrodes and a written pattern and a written image are projected onto a screen, showing a thermal writing type electrophoretic display element. 1... First transparent substrate 2... Second transparent substrate 3...
- First transparent electrode 4... Second transparent electrode 5... Drive control unit 50... Write drive circuit 51... Erase drive circuit 6... Spacer 7... Dispersion medium 8... Electricity Migrating particles 90...Laser light 60...Seal member 70...Colored dye 9...Laser light irradiation device Fig. 5 Patent applicant Toyota Motor Corporation

Claims (1)

[Claims] (1) A pair of substrates, at least one of which is transparent, a pair of electrodes formed on opposing surfaces of the pair of substrates, the electrodes of which are formed on at least the transparent substrates, and a gap between the pair of substrates. It consists of a dispersion medium that reversibly gels and becomes a sol depending on the temperature and electrophoretic particles dispersed in the dispersion medium. A thermal writing type electrophoretic display element characterized by being able to migrate particles.