JP2733677B2 - Electrophoretic display device, display dispersion system, and method for producing the dispersion system - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a display device using electrophoretic particles, a dispersion for display, and a method for producing the dispersion, and in particular, uses titanium oxide as the electrophoretic particles. An electrophoretic display device in which titanium oxide is subjected to a baking treatment in order to prevent discoloration of the coloring dye, which is a problem of the display dispersion system, thereby preventing discoloration of the dye and improving light resistance. And a dispersion for display and a method for producing the dispersion.

`` Prior art and its problems '' This type of electrophoretic display device encloses a dispersion system in which electrophoretic particles are dispersed in a liquid dispersion medium between a pair of electrode plates, at least one of which is transparent and opposed to each other. A structure in which desired characters, symbols or figures can be displayed while controlling the polarity so that the electrophoretic particles in the dispersion medium can be adsorbed or separated from the transparent electrode plate according to the polarity of the electrode plate. It is.

Examples of the dispersion medium used in the dispersion system of the electrophoretic display device include aromatic hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, various esters, alcohol solvents, halogenated hydrocarbons, and other various kinds. The oils and the like are used alone or in a suitable mixture as general ones.

Further, in the electrophoretic particles, titanium oxide or barium sulfate as a white substance, and as the yellow substance, in addition to the inorganic pigments described above, some organic pigments and the like are considered to be excellent in terms of hiding power. I have. In addition, oil-soluble dyes, disperse dyes, and the like are used to dye the liquid dispersion medium into various colors in order to ensure contrast with the color of the electrophoretic particles. In addition, when the liquid dispersion medium is not colored, there is a method using electrophoretic particles having two kinds of opposite charges.

As a means for improving the dispersibility of the electrophoretic particles, improving the electrophoretic properties of the electrophoretic particles, that is, improving the display property, or securing a long life as a display device, various surfactants and various additives are added to the dispersion system. You.

As shown in FIG. 4, this type of electrophoretic display device using such a dispersion system uses a suitable transparent conductive material such as indium tin oxide or the like on the opposing surface to form a required display electrode pattern 2, 4 , Two transparent glass plates 1 formed separately,
3 is provided, and a sealing member 5 also serving as a spacer is provided on an outer peripheral portion so as to enclose a dispersion system 7 in which electrophoretic particles 6 are dispersed in a liquid dispersion medium between the opposed gaps. In such a display device, a display driving voltage is applied to the electrode patterns 2 and 4 to attract the electrophoretic particles 6 to the electrode patterns 2 and 4.
By applying an electric field to the dispersion system 7 so as to be able to separate them, the distribution state of the electrophoretic particles 6 is changed, thereby changing the optical characteristics of the dispersion system 7 and performing a desired display operation.

Since the electrophoretic display device as described above utilizes a change in the optical characteristics of the dispersion system, sunlight can be used outdoors.
In a room, the reflection of illumination light such as a fluorescent lamp is used, but when titanium oxide is used for the electrophoretic particles, the discoloration of the coloring dye of the liquid dispersion medium, which is considered to be caused by the catalytic action of titanium oxide, is performed. The big problem that arises has turned out.
This problem of dye discoloration occurs in both visible light and ultraviolet light, and the degree of discoloration due to ultraviolet light is particularly high.

"Object and Configuration of the Invention" The present invention is to solve the problem of discoloration of the dye in the liquid dispersion medium as described above by using titanium oxide which has been calcined at a required temperature not higher than the melting point as the electrophoretic particles. The present invention provides an electrophoretic display device, a dispersion for display, and a method for producing the dispersion.

Therefore, the electrophoretic display device according to the present invention is characterized in that the dispersion medium for display is configured so that the liquid dispersion medium preferably includes titanium oxide subjected to alumina surface treatment and calcined, and the coloring dye. The display dispersion is preferably prepared by mixing a titanium oxide and a coloring dye, which are preferably subjected to an alumina surface treatment of 3% by weight or more and calcined at a temperature of 700 ° C. or more and a melting point or less. .

By such a calcination treatment on titanium oxide, the water of crystallization of titanium oxide is removed to suppress the catalytic action of titanium oxide itself, thereby preventing the discoloration of the dye or reducing the degree of discoloration.

"Examples" First, as a first comparative example, a dispersion for electrophoretic display having the following composition was obtained by using unfired titanium oxide having no alumina surface treatment as electrophoretic particles. Was dispersed in a ball mill for 12 hours, and the degree of discoloration caused by ultraviolet irradiation in an electrophoretic display device constituted by sealing a dispersion system between conventional ITO glass electrode plates was examined.

FIG. 1 is a graph showing the results of the discoloration test, in which the horizontal axis represents the ultraviolet irradiation energy (mJ / cm ² ) from a high-pressure mercury lamp.
Is shown as a logarithmic value, and the vertical axis represents luminance (Cd / m ² ).
Is shown.

In order to express the discoloration, X, Y, and Z when the electrophoretic particles are moved to the electrode opposite to the display side electrode are displayed in an off-display state.
Luminance was used.

In the above, untreated titanium oxide is 600B manufactured by Teikoku Chemicals Co., Ltd., and oil-soluble blue dye is OB manufactured by Chuo Gosei Co., Ltd.
BA was used for each.

As shown in FIG. 1, in the above-mentioned composition using untreated titanium oxide having no alumina surface treatment, the Z luminance was remarkably reduced, and the color was changed to black at an irradiation energy of 2.5 × 10 ³ mJ / cm ² , and further 7.2 × 10 3 Green at ³ mJ / cm ² and finally
The color changed to yellow at 3.5 × 10 ⁴ mJ / cm ² . Therefore, it is sufficient to follow the change in the Z luminance to see the degree of the color change from the change accompanying the color change in the X, Y, and Z luminances in FIG.
Only the change in luminance is shown.

Next, as a first example, 10 g of titanium oxide used for electrophoretic particles which was calcined at 900 ° C. for 2 hours was prepared (calcined by 600B manufactured by Teikoku Chemical Co., Ltd.), and another dispersion medium was prepared. A dispersion system was prepared by using the same coloring dye and dispersing agent as those of the comparative example in the same weight.

When a discoloration test was performed on the above-mentioned dispersion system, the results shown in FIG. 2 were obtained. As can be seen from the figure, the decrease in Z luminance is extremely small up to an ultraviolet irradiation energy of 3.8 × 10 ³ mJ / cm ^2, and when compared with a dispersion containing unfired titanium oxide, the discoloration luminance due to firing is reduced. Prevention of the drop and thus a marked improvement in lightfastness were observed.

In the following second comparative example, 3
And 5% by weight of alumina surface-treated titanium oxide (manufactured by Teikoku Chemical Co., Ltd.), and before preparing a dispersion, heat treatment these alumina-treated titanium oxide at 150 ° C. for 2 hours. The water content was removed. Dispersions were prepared in the same manner as in Comparative Example 1 using 10 g of the alumina surface-treated titanium oxide subjected to these heat treatments.

As a result of performing a discoloration test on the dispersion of the second comparative example, as shown in FIG. 3, the initial value of the luminance was somewhat higher than that of the unsintered one shown in Comparative Example 1, but the initial value of the luminance was compared with the progress of ultraviolet irradiation. As in Example 1, a significant decrease in luminance occurred.

Therefore, as a second example, before mixing the 3 and 5% by weight alumina surface treated titanium oxide of Comparative Example 2, the mixture was calcined at 900 ° C. for 2 hours, and the alumina surface coated and calcined titanium oxide was prepared. Was used to prepare a dispersion having the same composition as in Comparative Example 1, and an electrophoretic display device in which the dispersion was sealed was constructed.

As is clear from the graph of FIG. 3, the discoloration test result of the electrophoretic display device enclosing the dispersion system constituted in this example is even when compared with the dispersion system in which the baking treatment of Example 1 is merely performed. It can be seen that the superiority of the discoloration resistance is improved as a whole.

Here, in order to examine the difference in the calcination conditions of the titanium oxide having been subjected to the alumina surface treatment, as an example, the same composition as described above was used by using 5 wt% alumina surface-treated titanium oxide which had been calcined at 700 ° C. for 2 hours. As a result of conducting a color change test of the electrophoretic display device having a dispersion system as shown in FIG.
The improvement of the initial value of the luminance was recognized, and the improvement of the light resistance was obtained as in the case of the calcination treatment at 900 ° C. for 2 hours. Therefore, as a firing condition, it is preferable to apply a firing process at 700 ° C. or more for 2 hours to at least 3% by weight or more of titanium oxide having been subjected to surface treatment with alumina.

As the means for preventing discoloration of the dye in the dispersion system, titanium oxide was subjected to alumina surface treatment and calcined in the above. However, in addition to alumina surface treatment alone to suppress the catalytic action of titanium oxide, silica or silica was used. A plurality of types of surface treatments can also be performed using titania or the like.

As described above, according to the electrophoretic display device of the present invention,
The titanium oxide used as the electrophoretic particles constituting the display dispersion system is fired to remove as much as possible the water of crystallization. Preferably, an alumina surface coating layer is provided, so that the titanium oxide is used. The discoloration of the colored dye in the dispersion system can be prevented or the degree of the discoloration can be sufficiently reduced to the extent that it can be practically used by suppressing the catalytic action of the disperse system. Therefore, the use environment under severe ultraviolet light including natural light and artificial light can be used. A stable electrophoretic display operation with high display performance can be achieved over a long period of time even under the low temperature.

Since the structure for preventing discoloration of the coloring dye can be constituted by the display dispersion system itself, the durability of the display operation can be remarkably increased while reducing the cost of the display device without requiring any additional structure.

Such a display dispersing system having high discoloration durability is easily manufactured by suitably preparing a titanium oxide which is preferably subjected to an alumina surface treatment and subjected to a calcination treatment under the required conditions, optionally with other components. it can.

[Brief description of the drawings]

FIG. 1 shows the degree of discoloration of the display dispersion when the titanium oxide as the electrophoretic particles in the electrophoretic display dispersion was not fired without any alumina surface treatment in order to explain the comparison with the present invention. FIG. 2 shows X, Y, and Z luminance variation characteristics with respect to ultraviolet irradiation energy. FIG. 2 shows a titanium oxide not subjected to alumina surface treatment of FIG. FIG. 3 is a graph showing a change in Z luminance when a system is prepared. FIG. 3 is a diagram showing a display dispersion system having titanium oxide subjected to alumina surface treatment and baking treatment used in the electrophoretic display device of the present invention. Processing weight% is 3 and 5,
And the heat treatment condition is 150 ° C for 2 hours, the firing condition is 700 ° C and
FIG. 4 is a view showing similar Z-luminance change characteristics of the display dispersion system at 900 ° C. for 2 hours, and FIG. 4 is a conceptual cross-sectional configuration diagram of this type of electrophoretic display device. 1: Transparent glass plate 2: Electrode pattern 3: Transparent glass plate 4: Electrode pattern 5: Spacer and sealing member 6: Electrophoretic particles 7: Dispersion system for display

Continuing on the front page (72) Inventor Takashi Mori 757 Tenhoki Kusazaki-cho, Inashiki-gun, Ibaraki Japan Nippon Mektron Co., Ltd. Minami-Ibaraki Plant (72) Inventor Tatsuhiko Ogi 757 Tenhoki Kisazaki-cho, Inashiki-gun, Ibaraki Nippon Mektron, Ltd. Inside the Minami-Ibaraki Plant

Claims (6)

(57) [Claims] 1. A dispersion system in which electrophoretic particles are dispersed between a pair of opposed electrode plates, at least one of which is transparent, is encapsulated, and the dispersion system is controlled by a display control voltage applied between the electrode plates. In the electrophoretic display device for changing the distribution state of the electrophoretic particles in the inside to change the optical reflection characteristics and perform the required display operation, the baked titanium oxide as the electrophoretic particles and coloring An electrophoretic display device, wherein the dispersion system is configured to include a dye. 2. The electrophoretic display device according to claim 1, wherein said titanium oxide has an alumina surface coating layer. 3. A dispersion system in which electrophoretic particles are dispersed between a pair of opposed electrode plates, at least one of which is transparent, is encapsulated, and the dispersion system is acted upon by a display control voltage applied between the electrode plates. Titanium oxide baked as electrophoretic particles in an electrophoretic display dispersion system to change the distribution of the electrophoretic particles in the interior to change the optical reflection characteristics and perform the required display operation And a coloring dye. 4. The electrophoretic display dispersion according to claim 3, wherein said titanium oxide has an alumina surface coating layer. 5. A dispersion system in which electrophoretic particles are dispersed between a pair of electrode plates, at least one of which is transparent, is disposed under an action of a display control voltage applied between the electrode plates. In the method of manufacturing a dispersion system for electrophoretic display for performing a required display operation by changing the optical reflection characteristics by changing the distribution state of the electrophoretic particles in the
A method for producing a dispersion system for electrophoretic display, comprising a step of baking the titanium oxide at a temperature of 700 ° C. or more and a melting point or less before preparing titanium oxide as an electrophoretic particle and a coloring dye. 6. The method according to claim 3, wherein the titanium oxide is subjected to an alumina surface treatment of 3% by weight or more before the calcination treatment.