JPH01105990A - Dispersion liquid for electrophoretic display - Google Patents

Abstract

PURPOSE: To prevent unequal display and operation defect by preparing a dispersion for electrophoresis display by using particulates of a diameter within a specific range. CONSTITUTION: The particulates having the diameter in a range of 0.001 to 0.1μm are used as the electrophoretic particulates constituting the dispersion. Then, the particulates make so-called Brownian movement in the liquid and, therefore, the stable dispersion state is maintained against the gravity by the difference in the sp. gr. between the particulates and the liquid. Further, the distances between the particulates decrease and the good display with the equivalently large light scattering power is obtd. when the particulates are gathered on the electrode surfaces by effecting electrophoresis. The occurrence of the unequal display and operation defect by the sepn. of the particulates and the liquid is thereby prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a dispersion liquid for electrophoretic display that performs display by applying an electric field to cause particles to migrate.

[Prior Art] The drawing shows a container sandwiched between a pair of substrates, at least one of which is transparent, and a dispersion liquid in which electrophoretic fine particles are dispersed. This figure shows an example of an electrophoretic display device for displaying figures and the like.

In this figure, an electrochromic medium 1 has a transparent conductive layer 2 . Liquid layer 4 in which charged colored particles 3 are dispersed in an insulating liquid. Consists of insulation 5. Note that 6 is a substrate and 7 is an electrostatic image.

The liquid layer 4 is created by using high-purity petroleum (Esso Corporation, trade name Isopar) as the insulating liquid, and mixing it with an organic substance containing an ionic surfactant and a dye. As a result, the ionic surfactant adsorbs to the organic substance containing the pigment, and the organic substance is electrochemically stably charged and dispersed.
It begins to show the properties of electrophoresis.

The operation of this is that when no electric field is applied or when a reverse electric field is applied, the color of the dye dispersed in the insulating liquid layer 4 is visible, but when the electrostatic image 7 is written, the charged colored particles 3 This is done by moving to the transparent conductive layer 2 side and making the color of the pigment visible.

The insulating dispersion liquid used for the liquid layer 4 is usually made of a liquid in which electrophoretic fine particles such as inorganic pigments are uniformly dispersed, but it is difficult to sufficiently match the specific gravity of the fine particles and the liquid. As time passes, the particles and liquid separate, causing problems such as uneven display and malfunction. As a method to match the specific gravity of fine particles and liquid, the following (A
) and (B) are known.

(A) Mix several types of liquids with different specific gravities to adjust the specific gravity of the liquid.

(B) New fine particles having a desired specific gravity are prepared by mixing a polymer substance or the like with a small specific gravity with particles having a large specific gravity.

[Problems to be Solved by the Invention] However, in the above method, the specific gravity of the liquid is a constant value, whereas the aggregate of fine particles, which are the charged colored particles 3, has a specific gravity distribution. There was a problem that only fine particles matched the specific gravity of the liquid, and because of the difference in specific gravity with most fine particle force analysis night bodies, they would separate over time.

This can be avoided by using monodisperse particles with as little distribution of specific gravity as possible, but producing monodisperse particles with the desired specific gravity requires advanced technology, resulting in high costs. was there. Furthermore, even if a dispersion liquid is prepared using monodisperse fine particles, the state in which the specific gravity of the fine particles and the liquid are the same is extremely unstable, and the liquid may change due to changes in temperature or evaporation of the liquid. There was a problem in that due to changes in the specific gravity of the fine particles, the specific gravity of the particles and the liquid did not match, and they eventually separated (see Japanese Patent Publication No. 46396/1989 for these conventional specific gravity matching techniques).

On the other hand, even though the specific gravity of the particles and liquid is different, is it considered that the particles are stably dispersed in the liquid?
The night is known.

This is because the fine particles have a small size of 0.1 μm or less, so the Brownian motion of the fine particles stabilizes the dispersion state.

However, fine particles (ultrafine particles) of 0.1 μm or less
Because of their low light scattering ability, it was thought that they could not be used for display purposes (see Organic Synthetic Chemistry Association, ``Dye Handbook'', Maruzensha, 1971, p. 161).

This invention is based on the fact that when fine particles of 0.1 μm or less, which have a small light scattering ability and cannot be used for display, are electrophoresed and collected on an electrode surface, the distance between the particles decreases, and the light scattering ability equivalently increases. This study was based on this finding. Therefore, an object of the present invention is to provide a dispersion liquid for electrophoretic display that improves display unevenness and malfunction caused by separation of fine particles and liquid, which are observed in conventional dispersion liquids for electrophoretic display.

[Means for solving problems]

The dispersion liquid for electrophoretic display of the present invention has a diameter of 0.001 to 01 μm as electrophoretic fine particles constituting the dispersion liquid.
This method uses fine particles within the range of .

(Function) Since this invention uses ultrafine particles with a diameter in the range of 0.001 to 0.1 μm, the particles undergo so-called Brownian motion in the liquid, so they are stable against the force of gravity due to the difference in specific gravity between the particles and the liquid. If a dispersed state can be maintained and the particles are further electrophoresed and collected on the electrode surface, the distance between the particles is reduced, and the light scattering ability is equivalently increased, resulting in a good display.

(Example) Electrophoretic fine particles = titanium dioxide (manufactured by Sumitomo Cement, diameter 0.01 μm)...800 m
g Meta-xylene...3mfl Liquid: Tetrachlorodifluoroethane (Daikin Industries, Ltd., Daiflon 52)...7mnDye: Macrolex Blue RR (Bayer)...
- 1g Surfactant Sodium Nidioctyl Sulfosuccinate (manufactured by Tokyo Kasei Kogyo) 100mg The above composition was stirred with an ultrasonic homogenizer to prepare a display dispersion for electrophoresis.

Next, two glass plates with transparent ITO electrodes were pasted together with a 50 μm spacer interposed therebetween, and the periphery was sealed with epoxy adhesive except for two places to produce a cell. The above dispersion liquid was injected into the cell and the remaining two places were closed to prepare an electrophoretic display cell.

With this electrophoretic display cell upright, ±30V (I
As a result of applying a square wave voltage (Hz), the cell turned white or blue depending on the polarity of the voltage. Further, even after this electrophoretic display cell was left for one day, the electrophoretic fine particles remained uniformly dispersed, and the same operation as described above could be repeated. The reason why such a clear color change occurred using so-called ultrafine particles with low light scattering ability is because the ultrafine particles are gathered on the cell surface, the distance between the ultrafine particles becomes smaller, and the light scattering ability of the particle system increases. It is interpreted that this is because

[Comparative example]

An electrophoretic display dispersion liquid was prepared with the same composition as in the example except that titanium dioxide (Tipure PR-900 manufactured by DuPont) with a diameter of 0.2 μm was used as the electrophoretic fine particles. Next, the same electrophoretic display cell as in Example was prepared, and a square wave voltage of ±30 V (IHz) was applied to the cell in an upright state. As a result, the cell changed to white or blue depending on the polarity of the voltage. However, after this electrophoretic display cell was left for one hour, the particles began to settle, and since there were no particles at the top of the cell, the upper part of the cell remained blue even when a voltage was applied, and the color changed. did not show.

Furthermore, as a result of emitting sound to the above cell for one day, the fine particles settled at the bottom of the cell, and the part that showed a white or blue color change depending on the polarity when voltage was applied was only a small part of the entire cell. There was obvious malfunction.

As is clear from these results, in the case of using the dispersion liquid for electrophoretic display according to the present invention, the separation of fine particles and liquid that was observed in conventional dispersion liquids did not occur, and the display quality was significantly improved.

In the examples, the case where titanium dioxide fine particles are used as the electrophoretic fine particles is explained, but the present invention is not limited to this, and the present invention can also be applied to the case of fine particles of inorganic pigments such as zinc oxide or organic pigments. It is clear that similar effects can be obtained.

(Effects of the Invention) As explained above, according to the present invention, a dispersion liquid for electrophoretic display is prepared using fine particles having a diameter of 0.001 to 031 μm as electrophoretic fine particles. There is an advantage that separation of liquid does not occur and excellent electrophoretic display without display unevenness or malfunction can be realized.

[Brief explanation of the drawing]

The drawing is a schematic cross-sectional view showing the main parts of an apparatus for explaining a conventional electrophoretic display method. In the figure, 1 is an electrochromic medium, 2 is a transparent conductive layer, 3 is charged colored particles, 4 is a liquid layer, 5 is an insulating layer, 6 is a substrate, and 7 is an electrostatic image.

Claims (1)

[Claims] A dispersion liquid for electrophoretic display characterized by dispersing electrophoretic fine particles having a diameter of 0.001 to 0.1 μm in a liquid.