JPS62299824A - Electrophoresis display element - Google Patents

Abstract

PURPOSE:To improve the sharpness and contrast of display greatly without a decrease in response speed nor a rise in driving voltage and to improve weather resistance by using a noncolored dispersion medium where special fluorescent particles are dispersed instead of a colored dispersion medium where dye is solved. CONSTITUTION:An electrophoresis display element is formed by charging liquid formed by dispersing at least one kind of fluorescent particles of dispersible resin dyed with fluorescent dye having a color tone in the noncolored dispersion medium with high insulation and low viscosity and at least one kind of pigment particles having a color tone different to above-mentioned one in a cell formed of two opposite electrodes and a spacer arranged on the peripheral edge parts of both electrodes so that at least one of the electrodes is transparent. This electrophoresis display element is supplied with an external electric field from a driving power source 5 (output voltage: normally <=200V), and then the fluorescent particles (or pigment particle) 3 and pigment particles (or fluorescent particle) 3' cause electrophoresis to stick on the electrodes 1 and 1', thereby displaying the color tones of the particles 3 and 3'.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Technical Field The present invention relates to computer displays, destination display boards,
Useful as a reversible display element for characters, numbers, figures, and images such as large display screens, image information conversion elements for optical image storage, X-ray image formation, etc., or soft copies for electronic blackboards, reusable electronic sheets, etc. The present invention relates to an electrophoretic display element.

PRIOR ART In general, when solid fine particles such as pigments are dispersed in an insulating liquid, the particles become positively or negatively charged. Furthermore, when a DC voltage is applied to this dispersion system, the charged particles become an anode or an anode depending on their polarity. Migrate to the cathode. A liquid obtained by dispersing such electrophoretic fine particles having a certain color tone in a highly insulating dispersion medium dyed in a color different from the color tone is connected to two opposing electrodes, at least one of which is transparent. A device sealed in a cell formed by spacers placed on the periphery of both electrodes can be used as a display element for various devices due to changes in reflected light due to the movement of particles within the cell when a voltage is applied and memory properties. This type of display element is called an electrophoretic display element, and is actually used as a reversible display element for characters, numbers, figures, and images such as computer displays, destination display boards, large display panels, optical image storage, and Xll1I image formation. Proposals have been made for use as image information converting elements such as, electronic whiteboards, reusable electronic sheets, and other soft copies.

Although this electrophoretic display element has advantages that other display elements do not have, such as low manufacturing costs, the ability to display multiple colors, and a wide viewing angle, it has many disadvantages from a practical standpoint. have. Among the most serious drawbacks are poor display clarity and contrast. This is due to the dispersion liquid used in conventional electrophoretic display elements. In other words, in conventional dispersions, the dye dissolved in the dispersion medium for the purpose of dyeing only the dispersion medium also dyes the pigment particles.
Moreover, even if these dyed pigment particles adhere to the electrode surface due to an external electric field, dyed droplets are present between these particles, so that during display, the pigment particles cannot adhere to the first electrode surface. This is because the original color tone does not appear. This tendency is particularly strong when white pigments are used. One possible solution to the decrease in sharpness is to reduce the amount of dye used, but this would be unwise as it would result in a decrease in contrast. On the other hand, in order to reduce the contrast, it may be possible to widen the spacing between the electrodes, but in this case, the response speed is reduced and the drive voltage is increased, which is also unwise.

There is also the problem that the dye itself has poor weather resistance.

Purpose The purpose of the present invention is to improve display clarity and contrast without reducing response speed or increasing drive voltage by using an uncolored dispersion medium in which special fluorescent particles are dispersed instead of a colored dispersion medium in which dyes are dissolved. It is an object of the present invention to provide a practical electrophoretic display element which has greatly improved the weather resistance and also solved the problem of weather resistance.

Structure The electrophoretic display element of the present invention has a highly insulating, low-viscosity inorganic material in a cell formed by two opposing electrodes, at least one of which is transparent, and a spacer arranged on the inner surface of the periphery of both electrodes. At least one type of fluorescent particles made of a dispersing resin dyed with a fluorescent dye having a certain color yA and at least one type of pigment particles having a color tone different from the color tone are dispersed in a colored dispersion medium. It is characterized by being filled with liquid.

In order to solve the above-mentioned problem of color tone in conventional electrophoretic display elements, the present inventors first prepared a dispersion solution in a non-colored dispersion medium with the color tone and band 1! It was proposed to use a liquid in which at least 2w1 pigment particles of different polarities are dispersed, and to utilize the mutual imaging and masking properties of these particles. In order to determine whether satisfactorily satisfactory color reproducibility can be obtained with the display element of this proposal, the present invention aims to determine whether at least one of the pigment particles of at least one of the two types of pigment particles in the dispersion liquid in the display water droplet of this proposal is used as described above. By replacing the fluorescent particles with fluorescent particles such as the above, the clarity was further improved than in the case of the display element proposed by Azuma, and a precise color reproduction that could hardly be expected with the display element proposed above was realized. .

To explain the present invention with reference to the drawings, FIG. 1 and FIG. 2 are both cross-sectional views of the electrophoretic display element of the present invention when a voltage is applied. Note that in these figures, one type of each of fluorescent particles and pigment particles is used for the sake of simplification. FIG. 1 shows an example in which fluorescent particles (or pigment particles) 3 and pigment particles (or fluorescent particles) 3' are charged to different polarities in an uncolored dispersion medium 4, and FIG. An example will be shown in which these two types of particles 3 and 3' are charged to the same polarity in the same dispersion medium 4. In these figures, the fluorescent particles (or pigment particles) 3 and the pigment particles (or fluorescent particles) 3' are originally uniformly distributed in the uncolored dispersion medium 4 in a positively or negatively charged state as described above. Distributed. The structure of the cell itself is exactly the same as the conventional one, with at least one transparent electrode. r and a spacer 2. 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), the fluorescent particles (or pigment particles) 3 and the pigment particles (or fluorescent particles) 3' undergo electrophoresis. Raise the electrode 1. as shown in FIGS. 1 and 2. The color tone of each particle 3.3' is displayed. As shown in FIG. 2, when a dispersion g in which fluorescent particles (or pigment particles) 3 and pigment particles (or fluorescent particles) are charged to the same polarity is used, these two types of particles 3.
3' is selected from those having different electrophoretic speeds.

Next, the dispersion liquid used in the electrophoretic display element of the present invention will be explained. The fluorescent particles used in this dispersion are composed of a dispersing resin dyed with a fluorescent dye. Such fluorescent particles are called daylight fluorescent pigments and are stimulated by light in the short wavelength range from the ultraviolet to the visible (violet, blue, and blue edges), which make up a large portion of daylight. It emits photovolatile fluorescence, which makes it possible to further emphasize the clarity of the display and achieve precise color reproduction than the previously proposed electrophoretic display element using two or more types of cost particles. . Fluorescent dyes constituting such fluorescent particles include diaminostilbene dyes such as chrysophenine G; fluorescein; thioflapine; brilliant sulfoflavine FP (Hoechst Co., Ltd.);
Liter: Leather Yellow HG (manufactured by Hoechst); Eosin; Eosin PA (manufactured by BAaF); Rhodamine B (I
(manufactured by OI); rhodamine BN (manufactured by BASF), and the like. Examples of the dispersible resin include acrylic resin, vinyl chloride resin, alkyd resin, aromatic sulfonamide resin, urea resin, melamine resin, benzoguanamine resin, and cocondensation polymers thereof. Examples of methods for producing fluorescent particles made of the above-mentioned materials include a method of impregnating resin powder in a solution of a fluorescent dye and drying it, and a method of producing resin Fe in the presence of a fluorescent dye and pulverizing it. can. Next, an example of producing fluorescent particles will be shown.

Production Example 1 Uncured butylated urea resin (Kneepan 10 manufactured by Mitsui Toatsu Co., Ltd.)
8) 60 parts (by weight, the same applies hereinafter), butanol 24
16 parts xylene and red fluorescent dye (Nio 272 people)
Three parts were mixed and dispersed in a Henschel mixer for 1 hour, dried on a polyethylene sheet at 120°C for 30 minutes, and then heated at 150°C for 2 hours to cure. Next, after coarsely pulverizing this cured product with a homogenizer, 2
The mixture was ground for 4 hours to produce red fluorescent particles with a particle size of 3 to 4 μm.

Production Example 2 An uncured butylated melamine resin (Kneepan x28 manufactured by Mitsui Toatsu Co., Ltd.) 'F was used instead of the uncured butylated urea resin, and a yellow fluorescent dye (Leather Yellow H was used instead of the red fluorescent dye).
Yellow fluorescent particles with a particle size of 3 to 4P were produced in the same manner as in Production Example 1, except that G) was used.

Production Example 3 Beckamine G-1850 (manufactured by Dainippon Ink Chemical Co., Ltd.) 8 was used instead of Kneepan 1080 as an uncured butylated urea resin.
In addition, pink fluorescent particles having a particle size of 3 to 4 P were prepared in the same manner as in Production Example 1, except that 4 parts of a red fluorescent dye (Rhodamine B) was used instead of 3 parts of a red fluorescent dye.

In the fluorescent particles obtained in this way, the fluorescent dye is coated or adsorbed on the resin, so if the fluorescent dye is used alone, it has poor solvent resistance and weather resistance (the fluorescent dye itself has a certain polarity). They are soluble in solvents and have significantly improved weather resistance (generally poor) compared to organic or inorganic fluorescent pigments that are insoluble in solvents. Therefore, even if such fluorescent particles are used in a dispersion medium for a long period of time, the fluorescent dye will not fall off or dissolve from the particles, nor will any discoloration or decomposition occur. In the present invention, as mentioned above, organic or inorganic fluorescent pigments that have no problems in solvent resistance and weather resistance are not used, or this is because these pigments have poor dispersion stability. In any case, the ratio of fluorescent dye and dispersing resin in the fluorescent particles is 1:5 to 2 in terms of heavy leaf ratio.
Approximately 0 or so.

Specific examples of pigment particles that can be combined with the above-mentioned fluorescent particles include inorganic pigments such as titanium oxide (rutile type or anatase type) and zinc white for white types, and yellow iron oxide, yellow iron oxide, etc. for yellow types. Inorganic pigments such as cadmium yellow, titanium yellow, and yellow lead; organic pigments such as Hansa Yellow and Pigment Yellow, and red pigments such as red pigments such as iron pigments and cadmium red, and quinacridones such as Shi/Kasha Red Y1 Hostapalm Red. Pigments, organic pigments such as azo orchid pigments such as No9-Manent Red and Fast Slow Red, and blue pigments such as ultramarine, deep blue, Conoluto blue, and Cerulia 7F7.
Inorganic pigments such as L/-, phthalocyanine pigments such as phthalocyanine sol, fast sky blue, and organic pigments such as indanthrene pigments such as indanthrene blue,
Examples of green pigments include inorganic pigments such as chrome green, chromium oxide, and viridian, nitroso pigments such as pigment green and naphthol green, and organic pigments such as phthalocyanine pigments such as phthalocyanine green.

On the other hand, as the non-colored dispersion medium constituting the dispersion liquid, a highly insulating and low viscosity organic solvent is used. Specific examples of such organic solvents include o-1rn- or p-xylene, toluene, benzene, cyclohexane, n-hexane, chlorobutane, trichloroethane, carbon tetrachloride, kerosene, cyclohexyl chloride, chlorobenzene, 1. 2
．． 2-tetrachloroethylene, trichlorofluoroethane, tetrafluorodibromoethane, tetrafluorodifluoroethane, methylene iodide,
Examples include triiodosilane, methyl iodide, carbon disulfide, olive oil, etc., or a mixture thereof.

The above dispersion may further contain polyethylene glycol fatty acid ester, sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyoxyethylene sorbitan fatty acid ester, or Surfactants such as oxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, alkyl ether carbonate, alkyl 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, ball mill, 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 transparent electrodes, fix one electrode, and apply a desired thickness to the periphery of the electrode. A spacer, that is, a thermosetting adhesive in which particles such as hard resin particles are dispersed, is attached so as to obtain an inter-electrode spacing (usually 10 to 1010O4), and the other electrode is placed on top of this.
After the adhesive is cured to form a spacer and thereby a cell is formed, 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 Anatase type titanium oxide (A-100 manufactured by Ishihara Sangyo Co., Ltd.)
15 f1 Red fluorescent particles 151F prepared in Production Example 1,
Xylene 502, olive oil 50F and polyoxyethylene alkylphenyl ether (@-
A mixture consisting of EIA-73) α1t manufactured by Kogyo II was dispersed in a paint shaker for about 1 hour to obtain display dispersion liquid 8.
It was made by m11. Next, this dispersion liquid is injected using a syringe through the injection port of a cell formed by two opposing transparent glass electrodes and a spacer, a cyclone bulb is embedded in the injection port, and the top is sealed with adhesive. An electrophoretic display element was created using this method.

Next, when a DC voltage of IOV was applied between both electrodes of this display element, a clear white-red display was quickly produced due to electrophoresis of particles within the cell.

At this time, the microphotometer (Union Optical Co., Ltd. [MP
The contrast (color difference) between white and red measured in M-2) was as high as 15.

Example 2 When preparing a dispersion, rutile type titanium oxide (KR310 manufactured by Titan Kogyo Co., Ltd.) was used instead of anatase type titanium oxide, yellow fluorescent particles prepared in Production Example 2 were used instead of red fluorescent particles, and xylene was used instead of the red fluorescent particles. An electrophoretic display element was produced in the same manner as in Example 1 except that cyclohexane was used instead.

Next, the performance of this display element was evaluated in the same manner as in Example 1. As a result, a clear white-yellow display was quickly produced by applying a voltage of 10 V.

The contrast between white and yellow at this time was as high as 10.

Example 3 When preparing a dispersion liquid, rutile type titanium oxide (R-820 manufactured by Ishihara Sangyo Co., Ltd.) was used instead of anatase type titanium oxide, and pink fluorescent particles prepared in Production Example 3 were used instead of red fluorescent particles. An electrophoretic display element was produced in the same manner as in Example 1 except for using the same method as in Example 1.

Next, the performance of this display element) was evaluated in the same manner as in Example 1. As a result, a clear white-pink color display was quickly performed by applying the IOV voltage. The contrast between white and pink at this time was 10.

Comparative example: Red dye (Lionogen Red C-1068 manufactured by Toyo Ink Co., Ltd.) was used in place of the red fluorescent particles for the 14# dispersion (in this case, the dispersion medium was dyed red).Others were Example 1
An electrophoretic display element was made using the same method.

In this case, the white-red color was fortunately displayed by applying the IOV voltage, or because a red dye was used, the white part was slightly pinkish. Further, the contrast between white and red at this time was 5, which was considerably lower than in each example.

Effects As described above, the electrophoretic display element of the present invention replaces the conventional dyed dispersion medium with the above-mentioned uncolored dispersion medium in which fluorescent particles are dispersed, thereby solving all the various problems caused by dyes at once. As a result, the clarity and contrast of the display were greatly improved, and the weather resistance was also improved, making it even more practical.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of an example of the electrophoretic display element of the present invention when a voltage is applied. 1, f... Electrode 2... Spacer 3.3
'...Pigment particles or fluorescent particles 4...Uncolored dispersion medium

Claims (1)

[Claims] 1. A color tone in a highly insulating, low viscosity, uncolored dispersion medium is applied to 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. An electrophoretic display comprising a liquid containing a dispersion of at least one type of fluorescent particles made of a dispersible resin dyed with a fluorescent dye and at least one type of pigment particles having a color tone different from the above color tone. element.