JPH075466Y2 - Electrophoretic display element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a transmissive electrophoretic display device. INDUSTRIAL APPLICABILITY The electrophoretic display device of the present invention can be used for a vehicle sunroof, a sun visor, a variable color tone lamp and the like.

[Prior Art] A transmissive electrophoretic display device can display various color tones by using color pigments composed of organic pigments or inorganic pigments as dispersed particles. However, it is difficult to display a delicate color tone by mixing a plurality of types of pigments for the following reasons. That is, when a plurality of color pigments are mixed, particles that tend to settle and particles that tend to float occur due to the difference in specific gravity. Therefore, the color tone may be partially different. Further, if the type of the pigment is different, the ζ potential is different, so that the polarities of the particles are reversed and the migration speed is different, which makes it difficult to display uniformly.

It was also difficult to display black. Although aniline black and carbon black are known as black pigments, aniline black cannot be used as an electrophoretic display element because of poor electrophoretic properties and durability. Further, since carbon black has conductivity, it cannot be used due to a short circuit in the cell. It has also been proposed to coat the carbon black with a resin or the like to provide insulating properties, but it is difficult to make the ratio of carbon black and resin uniform for each particle, and the specific gravity varies and is uniform. Display becomes difficult. Further, if the color pigments of the three primary colors are mixed and an attempt is made to display black, the same problem as described above occurs.

Japanese Patent Publication No. 52-28556 discloses a method of displaying an intermediate color by applying an asymmetrical alternating voltage to an electrophoretic display element. However, even in this method, when a plurality of color pigments are mixed and used, the same problems as described above occur.

[Problems to be Solved by the Invention] The present invention has been made in view of such circumstances.
The purpose of the invention is to provide an electrophoretic display device capable of displaying a delicate color tone in which the color tones of a plurality of types of pigments are mixed and capable of displaying uniformly without the above-mentioned problems, and transmitting light to be transparent when not displaying. And

[Means for Solving the Problems] An electrophoretic display device according to the present invention includes a plurality of transparent substrates arranged at a predetermined interval from each other to form a plurality of cell spaces,
A pair of transparent electrodes respectively provided on the facing surfaces of a plurality of pairs of transparent substrates facing each other, a dispersion medium enclosed in each of the plurality of cell spaces, and a color tone mutually dispersed in each of the dispersion mediums of the plurality of cell spaces. Of different electrophoretic particles,
At least one of the pair of transparent electrodes has a mesh shape or a stripe shape, and the transparent electrodes in each cell space are provided at a position where they overlap and a position where they do not overlap when viewed from the viewing side. It is characterized in that the electrophoretic particles are selectively attached to the transparent electrode in the overlapping position and the transparent electrode in the non-overlapping position by reversing the polarity.

As the transparent substrate, a glass substrate, a resin substrate or the like can be used as in the conventional case. The transparent substrates are arranged at predetermined intervals to form a plurality of cell spaces. The number of cell spaces is not particularly limited and can be variously selected according to the desired color tone. For example, in the case of black display, three cell spaces are usually formed from four transparent substrates.

These transparent substrates are generally laminated with a spacer having a predetermined thickness interposed between them, and the cell space is formed by sealing the edges with an epoxy resin or the like. A dispersion medium is enclosed in each of the plurality of cell spaces in the same manner as in the conventional case, and electrophoretic particles such as organic pigments are dispersed therein.

Here, as the dispersion medium, a halogen compound such as tetrachloroethylene is used as in the conventional case. Various organic pigments or inorganic pigments are used as the electrophoretic particles. In the electrophoretic display device of the present invention, generally one kind of electrophoretic particle is enclosed in each cell space.
Therefore, the specific gravity of the electrophoretic particles in each cell space is uniform and the polarities are the same, so that uniform display can be performed.

The transparent electrode is provided in a mesh shape or a stripe shape on the surface of the transparent substrate forming the cell space. The cross-sectional shape can be selected from various shapes such as a rectangle, a triangle, and a sawtooth shape. This transparent electrode can be formed from a material such as ITO or tin dioxide by a known method such as a PVD method or a photoetching method.

The greatest feature of the present invention lies in the structure of the transparent electrode. That is, the transparent electrodes in each cell space are provided at positions where they overlap and when they do not overlap when viewed from the viewing side, and when the polarity of the applied voltage is reversed, the transparent electrodes overlap at the positions where the respective electrophoretic particles overlap. It is configured to selectively adhere to a transparent electrode at a position that does not match. Therefore, when each electrophoretic particle adheres to the transparent electrode at the overlapping position, the portion where the transparent electrode is not formed becomes transparent and transmits light.
On the other hand, when the respective electrophoretic particles adhere to the transparent electrodes in the positions where they do not overlap, the color tone of the electrophoretic particles attached to each transparent electrode appears from the viewing side and is displayed in a mixed color tone. .

[Operation] In the electrophoretic display device of the present invention, when no voltage is applied, each electrophoretic particle is in a dispersed state in the cell space and is in an opaque state. From the viewer side, the color tone of the electrophoretic particles dispersed in the cell space existing at the end portion on the viewer side can be seen.

Next, a DC voltage is applied to attach the electrophoretic particles to the transparent electrodes at the overlapping positions. Then, all the electrophoretic particles are in an overlapping state, and the portions other than the transparent electrodes at the overlapping positions are in a transparent state in which no electrophoretic particles are present. Therefore, the electrophoretic display element is used as a transparent body that transmits light.

Next, when a DC voltage with reversed polarity is applied, each electrophoretic particle adheres to the transparent electrode in a non-overlapping position. Therefore, since all the electrophoretic particles can be seen from the viewing side, the pattern of the transparent electrode is visually displayed in a mixed color tone.

[Advantage of the Invention] According to the electrophoretic display device of the present invention, since there can be only one type of electrophoretic particle in each cell space, it is possible to perform a stable display with a uniform specific gravity. Therefore, the color tones of mixed colors can be uniformly displayed in the state where a plurality of cell spaces are overlapped, and the color tones that have been difficult in the past such as black can be uniformly displayed. That is, the transparent state and the mixed color display state can be alternately switched and displayed, which is extremely useful for a variable color tone lamp or the like. In addition, by increasing the number of cell spaces, it is possible to improve the contrast and display various gradations.

Further, in the electrophoretic display device of the present invention, the striped electrodes can face each other in each cell space. In the past, the striped electrode and the planar electrode were opposed to each other, but in the electrophoretic display device of the present invention, the electric field in the cell is more uniform and the migration of particles is better than in the past. Further, since the particle densities on the electrodes are the same for the respective electrodes, the responsiveness when changing from the colored state to the transparent state is improved.

[Examples] Hereinafter, specific examples will be described.

(Example 1) Fig. 1 shows a cross-sectional view of an electrophoretic display device of this example.
This electrophoretic display element has a three-layer structure including a first cell space 1, a second cell space 2 and a third cell space 3. That is, four glass substrates 4a to 4d made of soda-lime glass and having a thickness of 1.1 mm are arranged at predetermined intervals by PET film spacers 5a to 5c having a thickness of 100 μm, and an epoxy resin adhesive 6 is provided around the periphery. Each cell space is formed by being bonded and fixed by and sealed.

The first cell space 1 is formed between the glass substrate 4a and the glass substrate 4b, and the red organic pigment as electrophoretic particles is provided inside.
10 (“Magenta B” manufactured by Ciba Geigy Co., Ltd.) is dispersed and enclosed in a dispersion medium.

The second cell space 2 is formed between the glass substrate 4b and the glass substrate 4c, and the inside thereof is a blue organic pigment as electrophoretic particles.
20 (“Fastgen Blue” manufactured by Dainippon Ink and Chemicals, Inc.) is dispersed and enclosed in a dispersion medium.

The third cell space 3 is formed between the glass substrate 4c and the glass substrate 4d, and has a yellow organic pigment as electrophoretic particles therein.
30 (“Pigment Yellow 14” manufactured by Dainippon Ink and Chemicals, Inc.) is dispersed and enclosed in a dispersion medium.

The dispersion medium enclosed in each cell space is composed of a mixed solvent of xylene and tetrachloroethylene, and is mixed and enclosed in a ratio having the same specific gravity as each electrophoretic particle. Therefore, in each cell space, the electrophoretic particles have the same specific gravity as the dispersion medium and are uniformly dispersed.

The glass substrate 4a and the glass substrate 4b that compose the first cell space 1
Striped transparent electrodes on each of the opposite surfaces
11 and 12 are formed. Stripe-shaped transparent electrodes 21 and 22 are formed on the surfaces of the glass substrate 4b and the glass substrate 4c forming the second cell space 2 which face each other. Further, the glass substrate 4c and the glass substrate which form the third cell space 3
A striped transparent electrode 31 is formed on the surface of the glass substrate 4c of the 4d, and a planar transparent electrode 32 is formed on the entire surface of the glass substrate 4d.

Here, the transparent electrodes 11, 21, and 31 are formed in the same pattern with a line width of 50 μm and a line interval of 100 μm, respectively.
Or it is formed in a position where they completely overlap each other when viewed from the 4d side. On the other hand, the transparent electrodes 12 and 22 are formed in the same pattern as the transparent electrode 11 and the like, but are out of phase with each other, and formed at positions where they do not overlap with other transparent electrodes when viewed from the glass substrate 4a or 4d side. Has been done. Each stripe-shaped transparent electrode is formed to a thickness of 500 Å from ITO using a known photolithography method.
The planar transparent electrode 32 is also formed of ITO to a thickness of 500Å.

The operation of the electrophoretic display device of this embodiment having the above structure will be described below.

First, the transparent electrode 11 is a negative electrode in the cell space 1.
Apply a DC voltage of 30V so that 12 is positive.
As a result, the red organic pigment 10 adheres to the transparent electrode 11. A DC voltage of 30 V is applied to the cell space 2 so that the transparent electrode 21 is negative and the transparent electrode 22 is positive. As a result, the blue organic pigment 20 adheres to the transparent electrode 21. In addition, a DC voltage of 30 V is applied to the cell space 3 so that the transparent electrode 31 is positive and the planar transparent electrode 32 is negative. As a result, the yellow organic pigment 30 adheres to the transparent electrode 31. When this electrophoretic display element is viewed from the glass substrate 4a or 4d side, all the pigments are striped transparent electrodes as shown in FIG.
Since most of the light is attached to 11, 21, and 31 and appears to overlap, most of light is transmitted except for the transparent electrodes 11, 21, and 31. In this case, the light transmittance is about 60%, and the electrophoretic display device of this embodiment functions as a transparent body.

Next, when a voltage having opposite polarities is applied to the cell space 1 and the cell space 2, the red organic pigment 10 adheres to the transparent electrode 12 and the blue organic pigment 20 transmits the transparent electrode as shown in FIG. The yellow organic pigment 30 adheres to the transparent electrode 31 while maintaining the state of being adhered to the transparent electrode 31. When this electrophoretic display element is viewed from the glass substrate 4a or 4d side, as shown in FIG. 3, all the pigments do not overlap each other, so that three colors are visible and the electrode patterns are displayed in black due to the color mixture. The light transmittance in this case is about 1%.

If a voltage of opposite polarity is applied in the cell space 3 as well, the yellow organic pigment 30 will become a planar transparent electrode as shown in FIG.
Adhere to 32. In this case, all three colors are visible when viewed from the glass substrate 4a side, so that black display is performed, but only yellow is visible when viewed from the glass substrate 4d side. Therefore, different colors can be displayed depending on the viewing direction.

That is, according to the electrophoretic display element of the present embodiment, it becomes a transmissive electrophoretic display element for black display, which has been difficult in the past.
It can be widely applied to automobile lamp covers, roofs, etc.

(Embodiment 2) FIG. 5 shows an electrophoretic display device according to a second embodiment of the present invention. This electrophoretic display element is the same as that of Example 1 except that the transparent electrode of the glass substrate 4d is changed from the planar electrode 32 to the stripe transparent electrode 33. The transparent electrode 33 is provided at a position overlapping the transparent electrode 11 and the like.

According to the electrophoretic display device of this embodiment, it is difficult to display yellow, but the areas of the electrodes facing each other in each cell space are the same, and the electric field is uniform, so that the display response is excellent and the display performance is improved. Are better. By the way, in the conventional electrophoretic display element in which the striped electrode and the planar electrode are opposed to each other, the response at the time of coloring is 500 msec and the response at the time of transmission is 2000 msec. Responsiveness when coloring is 200msec, Responsiveness when transmitting is 2
It was remarkably shortened from 00msec to the conventional one. Further, although the conventional electrophoretic display element may have a display disorder, the electrophoretic display element of the present example can always display uniformly.

[Brief description of drawings]

1 to 4 relate to an electrophoretic display device according to an embodiment of the present invention, in which FIG. 1 is a schematic sectional view thereof, and FIGS. 2, 3, and 4 are schematic sectional views thereof in a display state, respectively. Is.
FIG. 5 is a schematic sectional view of an electrophoretic display device of another embodiment. 1, 2, 3 ... Cell space 4a, 4b, 4c, 4d ... Glass substrate 10 ... Red organic pigment, 20 ... Blue organic pigment 30 ... Yellow organic pigment, 32 ... Planar transparent electrode 11, 12, 21, 22, 31, 33 ... Striped transparent electrodes 5a, 5b, 5c ... Spacer 6 ... Epoxy adhesive

Claims (1)

[Scope of utility model registration request] 1. A plurality of transparent substrates which are arranged at a predetermined interval from each other to form a plurality of cell spaces, and a pair of transparent electrodes which are respectively provided on the facing surfaces of a plurality of pairs of the transparent substrates facing each other. Of the dispersion medium enclosed in each of the cell spaces and electrophoretic particles having different color tones dispersed in each of the dispersion mediums of the plurality of cell spaces, and at least one of the pair of transparent electrodes has a mesh. -Shaped or stripe-shaped, the transparent electrodes in the respective cell spaces are provided at positions overlapping and not overlapping when viewed from the viewer side, and the respective electrophoretic particles are formed by reversing the polarity of the applied voltage. An electrophoretic display device, wherein the transparent electrode at the overlapping position and the transparent electrode at the non-overlapping position selectively adhere to each other.