JPS62269124A - Electrophoretic display element - Google Patents

Abstract

PURPOSE:To obtain an electrophoretic display element having a large color difference, high response speed and shelf life of a dispersion by sealing a liquid prepd. by dispersing two kinds of pulverized electrophoretic particles having the color tones and electrophoretic polarities different from each other into colorless dispersion medium having a high insulating property and low viscosity into a cell. CONSTITUTION:Two kinds of the pulverized electrophoretic particles 4a, 4b having the color tones and electrophoretic polarities different from each other are intrinsically uniformly dispersed into the colorless dispersion medium 3' having the high insulating property and low viscosity to form electrical double layers. An example in which the particles 4a are electrified negative and the particles 4b are electrified positive is shown here. The pulverized electrophoretic particles 4a electrified negative are electrically migrated by an external electric field to stick to a transparent electrode 1 side on a display side when said electric field is applied by a driving power source 5 to such electrophoretic display element. On the other hand, the pulverized electrophoretic particles 4b electrified positive are electrically migrated to stick to a counter electrode 1' side. The color tone of the pulverized electrophoretic particles 1a is displayed on the display electrode 1 side in this stage.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an electrophoretic display element used for display and memory in various devices such as computers, destination display boards, and electronic blackboards.

[Prior art] Electrophoretic display elements used in various devices such as computers, destination displays, boards, electronic whiteboards, etc. generally have two opposing electrodes 1.1, at least one of which is transparent, as shown in FIG.
' and a spacer 2 arranged on the inner surface of the peripheral edge of both electrodes, electrophoretic fine particles 4 are formed in a highly insulating and low viscosity colored dispersion medium 3 with a color tone different from that of the colored dispersion medium. It is constructed by enclosing a liquid in which pigment fine particles are dispersed. Note that this figure is a cross-sectional view when a voltage is applied (5 in the figure is a small moving power source), and the pigment particles 4 are simply dispersed in the dispersion medium as described above when no voltage is applied, that is, when no external electric field is applied. However, when subjected to an external electric field, it undergoes aerophoresis and adheres to one electrode depending on its electrophoretic polarity (charged polarity). When it adheres to the transparent quadrupole on the display side, the color tone of the pigment particles is displayed, and when it adheres to the counter electrode on the opposite side, the color tone of the colored dispersion medium is displayed. If the polarity of the external electric field is reversed, each display will be reversed. Therefore, the actual display depends on the difference between the color tone of the pigment particles and the color tone of the colored dispersion medium, that is, the color difference. . Once the pigment particles adhere to the electrode surface, even if the external driving power source is removed, the pigment particles will remain on the electrode surface due to the electrical coercive force between the particles and the electrode surface and the physical adhesion force represented by van der Waalska. It has a so-called memory effect.

Conventionally, titanium oxide, titanium oxide,
A white material such as zinc oxide is used, and as a colored dispersion medium, a highly insulating and low viscosity organic solvent such as xylene, benzene, or di-chloroethylene is used, and the solubility in these solvents and the color difference with respect to white pigments are high. Dissolved oil-soluble dyes such as large anthraquinone dyes (e.g., Macrolex Blue), metal-containing dyes, and azo dyes (e.g., Sudan Black) are used (e.g., JP-A-48-71).
No. 990, No. 48-71991, No. 4B-71992
issue).

However, in conventional electrophoretic display elements, the dispersion liquid is composed of pigment particles dispersed in a colored dispersion medium, and the pigment particles are also dyed by the dye in the colored dispersion medium, causing the original color of the pigment particles to be lost. As a result, a large color difference cannot be obtained.

One possible way to reduce these drawbacks is to reduce the amount of dye in the colored dispersion medium. Since the coloring power is weak, light is transmitted through the display-side transparent electrode and the color of the pigment particles and the color of the colored dispersion medium are mixed, so that a display with a large color difference cannot be obtained. It is also possible to widen the distance between the display-side transparent electrode and the counter electrode, but in this case, the electrophoretic distance of the pigment particles increases, which reduces the response speed of the electrophoretic display element and requires high voltage. Problems arise in terms of practicality.

Furthermore, in conventional electrophoretic display elements, the dyes have poor weather resistance and the dyes contain components and impurities that are insoluble in the dispersion medium.Due to long-term use or storage, the dyes in the colored dispersion medium may decompose. There are also disadvantages in that the color fades and the color difference decreases, and that the insoluble components and the like act as nuclei and cause aggregation of pigment particles.

Purpose The purpose of the present invention is to provide an electrophoretic display that avoids the use of dyes, provides a display with a large color difference, has a high response speed, does not require high voltage, and has excellent storage stability of the dispersion. The purpose is to provide an element.

Structure The electrophoretic display element of the present invention has two parts, at least one of which is transparent.
In a cell formed by a pair of opposing electrodes and a spacer arranged on the inner surface of the periphery of both electrodes, at least two species having different color tones and electrophoretic polarities are placed in a highly insulating, low viscosity, uncolored dispersion medium. It is made by enclosing a liquid in which electrophoretic fine particles are dispersed.

□To explain the present invention with reference to the drawings, Fig. 2 is a cross-sectional view of the electrophoretic display element of the present invention when a voltage is applied. , are uniformly dispersed in a highly insulating, low-viscosity, uncolored dispersion medium y, forming an electric double layer.

Here, an example is shown in which the particles 4a are negatively charged and the particles 4b are positively charged. The structure of the cell itself is exactly the same as the conventional one. When an external electric field is applied to such an electrophoretic display element by a drive power source 5 (output voltage is usually 200 V or less), negatively charged electrophoretic fine particles 4a are electrophoresed toward the transparent electrode 1 on the display side by this field. On the other hand, positively charged electrophoretic fine particles 4b electrophoretically adhere to the counter electrode 1' side. At this time, the color tone of the electrophoretic fine particles 1a is displayed on the display electrode 1 side.

If the polarity of the a-driving power source 5 is reversed, electrophoretic fine particles 6 4m
, 4b are the counter electrode 1' and the display electrode 1, respectively, contrary to the above.
As a result, the color tone of the electrophoretic fine particles 4b is displayed on the display electrode 1 side. Therefore, the actual display is based on the color difference between the electrophoretic fine particles 4a and the electrophoretic fine particles 4b. In addition, electrophoretic fine particles 4m.

4b, as in the conventional case, even if the external driving power source 5 is removed, each particle is held on each electrode surface by the electrical mirror force between each particle and each electrode surface and the physical adhesion force such as van der Waalska. Ru. That is, the electrophoretic fine particles of the present invention have a memory effect like conventional electrophoretic fine particles.

As can be seen from the above description, the principle of display operation in the electrophoretic display element of the present invention is that the at least two electrophoretic fine particles electrophores in opposite directions due to the action of an external electric field in a non-colored dispersion medium. This is due to

Next, the dispersion liquid used in the invention will be explained in more detail. First, as the electrophoretic fine particles constituting the dispersion liquid, pigment fine particles exhibiting electrophoretic polarity in a dispersion medium are used. Specific examples of such pigments include inorganic pigments such as titanium oxide (rutile type or anatase type) and zinc white for white pigments, and yellow iron oxide, cadmium yellow, titanium yellow, yellow lead, etc. for yellow pigments. Inorganic pigments and organic pigments such as Hansa Yellow and Pigment Yellow, red pigments include inorganic pigments such as Red Garla and Cadmium Red, quinacridone pigments such as Shinkasha Red Y and Hostapalm Red, permanent red, fast slow red, etc. Organic pigments such as azo pigments, blue pigments include inorganic pigments such as ultramarine blue, navy blue, cobalt blue, cerulean blue, phthalocyanine pigments such as phthalocyanine blue and fast sky blue, and indanthrene pigments such as indanthrene blue. Examples of green organic pigments include inorganic pigments such as chrome green, chromium oxide, and viridian, nitroso pigments such as bagment green and naphthol green, and phthalocyanine pigments such as phthalocyanine green.

Two or more kinds of the above pigment fine particles are selected and used so that the color tone and electrophoretic polarity are different from each other. Note that the electrophoretic polarity of pigments can change depending on the type of dispersion medium (
For example, phthalocyanine blue exhibits negative polarity in an aliphatic hydrocarbon dispersion medium, but exhibits positive polarity in a halogenated aliphatic hydrocarbon dispersion medium. ), based on the same dispersion medium.

On the other hand, a highly insulating and low viscosity organic solvent is used as the uncolored dispersion medium constituting the dispersion. Specific examples of such organic solvents include 0-lm- or p-xylene, toluene, benzene, cyclohexane, n-hexane, chlorobutane, trichloroethane, carbon tetrachloride, kerosene, cyclohexyl chloride, chlorobenzene, 1°1.2.
2-tetrachloroethylene, trichlorofluoroethane, tetrafluorodibromoethane, tetrafluorodifluoroethane, methylene iodide, triiodosilane, methyl iodide, carbon disulfide, olive oil, etc. alone, or Mixtures may be mentioned.

The above-mentioned dispersion liquid may contain polyethylene glycol fatty acid ester, sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyoxyethylene sorbitan fatty acid ester, etc. to improve display color difference, clarity, etc., as necessary. Surfactants such as polyoxyethylene alkyl ether, preoxyethylene alkylphenyl ether, alkyl ether carbon m salt, furkyl sulfonate, alkyl ether sulfate, and alkyl ether phosphate can be added.

To prepare the dispersion of the present invention, the above-mentioned components may be dispersed and mixed using a conventional dispersing machine such as a paint shaker, a Zeel mill, a sand grind mill, etc.

Next, in order to make the electrophoretic display element of the present invention using the dispersion obtained in this way, first prepare two electrodes, one of which is transparent, fix one of the electrodes, and apply a desired thickness to the periphery of the electrode. Extra spacer, i.e. the distance between electrodes (usually 10-100μm)
A thermosetting adhesive in which particles such as hard resin particles are dispersed is attached so as to obtain a 1f! After stacking A and curing the adhesive to form a spacer and thereby forming a cell, the dispersion liquid may be injected using a syringe through an injection port previously provided in the cell, and the injection port may be sealed. .

The present invention will be explained below by way of examples.

Example 1 m-xylene (Kanto Kagaku Co., Ltd.) Titanium oxide as a 10I white pigment (Titan Kogyo Co., Ltd. Yacronos KR-38ON)
2JF Cadmium red as red pigment (No Palette 6R manufactured by Toyo Pigment Industry Co., Ltd.) 1
．． Mix and disperse the #5 material in a paint shaker for about 1 hour to prepare a dispersion liquid. Next, ITOli on one side
A particle size of 30 μs is applied to the periphery of the film of the glass electrode with i.
An epoxy resin adhesive (Structopond, manufactured by Mitsui Tsukaa Chemical Co., Ltd.) in which divinylbenzene particles (Micropearl 5P-229, manufactured by Block Fine Chemical Co., Ltd.) were dispersed was applied, and the ITO film surface of the same glass electrode as above was placed on it. Create a display cell by stacking the cells and heating and hardening the adhesive.Preliminarily form this cell using a syringe, inject the dispersion liquid through the injection port, and then fill the injection port with adhesive. An electrophoretic display element was created by sealing.

When a DC voltage of 20V is applied to this display element, the white pigment particles and the red pigment particles each cause electrophoresis in opposite directions, and the white pigment particles adhere to the positive electrode side, producing a clear white display. Red pigment adhered to the negative electrode side, resulting in a clear red display. Next, when the polarity of this applied voltage was reversed, each display color was reversed. In either case, the displayed color difference between white and red is chromatic.

The color difference meter (Minolta Corporation! jAcR-too) showed a large value of 45. Furthermore, when a test was conducted in which the polarity of the voltage at both electrodes was alternately reversed at a frequency of 10 Hz and the display was repeated, it was possible to display the same color difference about 10 times or more. It should be noted that the electrophoretic polarity of each of the nine pigment particles was measured in advance and was found to be negative for white pigment particles and positive for red pigment particles.

Comparative example: Cadmium Red 1.577, Sudan Red 4
A dispersion liquid (in this case, a liquid in which a white pigment was dispersed in a red dispersion medium) was prepared in the same manner as in Example 1, except that 60 (red oil-soluble dye manufactured by Bayer AG) 0.29 was used, and the following procedure was repeated in the same manner. An electrophoretic display element was prepared using 90. When this display element was tested in the same manner as in Example 1, the white pigment particles were successfully electrophoresed to the positive electrode side, but because they were dyed with red dye, The displayed color could hardly be called white, and was closer to pink. This ninth color difference was as small as about 20.

Example 2 m-xylene (Kanto Kagakusha #) 5Ji' as a material for dispersion
An electrophoretic display element was prepared in the same manner as in Example 1, except that olive oil (same as above) 59 was used, and the same tests as in Example 1 were conducted. the result,
The yellow pigment particles were electrophoresed toward the negative electrode, and the blue pigment particles were electrophoresed toward the positive electrode, resulting in clear yellow and blue displays, respectively. The color difference between these displays is 40. In addition, the number of times of repeated display is approximately 105 times or more t0 Example 3 Tetrachlorethylene (manufactured by Kanto Kagaku Co., Ltd.) as a dispersion liquid material Titanium oxide (Tiebake R830, manufactured by Bancho Sangyo Co., Ltd.) as a 1ag white pigment 5
g Using cobalt chromium green (Novagreen, manufactured by Toyo Pigment Co., Ltd.) 3JF as a green pigment, Tomo et al. prepared an electrophoretic display element in the same manner as in Example 1, and conducted the same tests as in Example 19. As a result, the white pigment particles were electrophoresed toward the negative electrode side, and the green pigment particles were electrophoresed toward the white polarization side, resulting in clear white and green displays, respectively. The color difference of these displays is 35, and the number of repeated displays is about 106 times or more. EA102) Q,
19 Titanium oxide (Tieeek A-100 manufactured by Bancho Sangyo Co., Ltd.) as a white pigment 3.
92 Cerulean Blue (manufactured by Toyo Pigment Industries Co., Ltd.) as a pigment 3! An electrophoretic display element was prepared in the same manner as in Example 1 except that i was used, and the same tests as in Example 1 were conducted. the result,
The white pigment particles are electrophoresed to the negative electrode side, and the back pigment particles are electrophoresed to the positive electrode side, and a clear display of white and back is obtained, respectively. The color difference in these displays was 35, and the number of repeated displays was about 106 or more.

Effects As described above, since the electrophoretic display element of the present invention does not use dye in the dispersion liquid, the pigment particles are not dyed and color mixing does not occur.
There is no need to widen the distance between the electrodes, weather resistance is improved, the dispersion medium does not contain insoluble components or impurities, and displays with a large color difference can be obtained, the response speed is high, and high voltage is not required. Moreover, it has advantages such as excellent storage stability of the dispersion.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views of electrophoretic display elements according to the prior art and the present invention, respectively, when a voltage is applied.

Claims (1)

[Claims] 1. In a cell formed by two opposing electrodes, at least one of which is transparent, and a spacer placed on the inner surface of the periphery of both electrodes, color tone and electrophoresis are carried out in a highly insulating, low viscosity, uncolored dispersion medium. An electrophoretic display element comprising a liquid in which at least two types of electrophoretic fine particles having different polarities are dispersed is sealed.