JP2007206145A - Electrophoresis display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microcapsule type electrophoresis display device contributing to improvement of contrast in particular, by making electro-optical characteristics excellent. <P>SOLUTION: The electrophoresis display device comprises an electrode layer, a microcapsule display layer, a transparent electrode layer, and a surface layer on a base material in this order. The microcapsule display layer comprises micro capsules in which black particles, white particles, and a dispersion medium dispersing them are stored in a capsule shell. The electrophoresis display device has a double structure in which the microcapsule 110 has a plurality of inner microcapsules where black particles 114 and a first dispersion medium 112 are stored in a first capsule cell 111 and white particles 113 and a second dispersion agent 116 are stored in a second capsule cell 115. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophoretic display device, and more particularly to a microcapsule type electrophoretic display device that exhibits excellent electro-optical characteristics and further improves contrast.

  Conventionally, as a flat panel display device, a liquid crystal display device (LCD) is widely used in various applications because it is thin and can be miniaturized. As another display method aiming at further thinner and lower power consumption than such an LCD, a display device using an electrophoretic phenomenon has been developed.

  As one of display devices using the electrophoresis phenomenon, a microcapsule electrophoresis system has been put into practical use. For example, in the case of monochrome display, a microcapsule type electrophoretic display device is a microcapsule in which white liquid with insulation and black charged particles are dispersed, or white and black particles that are positively and negatively charged are dispersed. There has been proposed a method of forming an image by using microcapsules dispersed in a medium and pulling up particles to a display surface by applying an external voltage.

  Since the size of the microcapsules is as small as several tens to several hundreds of μm, when the microcapsules are dispersed in a transparent binder, they can be coated like ink. This ink is called electronic ink because an image can be drawn by applying a voltage from the outside.

  An active matrix display panel can be obtained by coating this electronic ink on a transparent resin film on which a transparent electrode is formed, and bonding it to a substrate on which an electrode circuit for driving an active matrix is formed. In general, a component in which a transparent resin film on which a transparent electrode is formed is coated with electronic ink is called a “front plate”, and a substrate on which an electrode circuit for driving an active matrix is formed is called a “back plate”.

  In such a microcapsule type electrophoretic display device, it has been proposed to improve contrast. That is, in an electrophoretic display device in which a plurality of microcapsules (41) containing charged particles (32) and a colored liquid (33) are sandwiched between a pair of substrates (15), a pair of transparent electrodes (14) is provided. A spacer (13) is arranged between the provided substrates (41), the pair of substrates (41) are bonded together, and fixed while being pressed, thereby eliminating the gap between adjacent microcapsules (41). (For example, see Patent Document 1).

  However, the conventional internal structure of the microcapsule has a single-layer structure in which positively and negatively charged white particles and black particles are placed in a microcapsule filled with a transparent solvent. There was a problem that it could not be done.

The above prior art documents are shown below.
JP 2002-202534 A

  The present invention solves the problems of the prior art, and an object of the present invention is to provide an electrophoretic display device having good electro-optical characteristics related to contrast and the like.

  In order to achieve the above object in the present invention, in the invention of claim 1, an electrode layer, an image display layer, a transparent electrode layer, and a surface layer are provided in this order on a substrate, and the image display layer is black. In an electrophoretic display device comprising particles, white particles, and a microcapsule in which a dispersion medium for dispersing these particles is contained in a capsule shell, the microcapsule includes either black particles or white particles and a dispersion medium thereof. A plurality of internal microcapsules accommodated in the first capsule shell, another particle and its dispersion medium are accommodated in the second capsule shell and have a double structure. This is an electrophoretic display device.

  As a result of repeated studies to improve the electro-optical characteristics of the microcapsule type electrophoretic display device, particularly the contrast, the present inventors have found that the interaction between the black pigment and the white pigment has a great influence on the contrast. I found it.

  That is, according to the first aspect of the invention, in the microcapsule type electrophoretic display device, the microcapsule has a double structure in which a plurality of internal microcapsules and a dispersion medium are accommodated therein, and the black particles By separating the (pigment) and the white particles (pigment), it is possible to provide a microcapsule type electrophoretic display device capable of obtaining an excellent electro-optical characteristic, particularly a contrast, for example, a contrast of 7 or more. .

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a microcapsule type electrophoretic display device according to an embodiment of the present invention. That is, an electrode layer 2, an adhesive layer 3, a microcapsule display layer 4, a transparent electrode layer 5, a transparent resin layer 6, and a surface layer 8 are sequentially laminated on the base material 1 to form a microcapsule type electrophoretic display panel. Is configured.

  In the electrophoretic display device including the microcapsule-type electrophoretic display panel shown in FIG. 1, the microcapsule display layer 4 is transparent made of polyethylene terephthalate or the like having a transparent electrode layer (ITO film) 5 formed on the surface. It is formed by coating the surface of the transparent electrode layer 5 of the resin layer 6 with electronic ink using a known coating method. Next, the transparent resin layer 6 having the transparent electrode layer (ITO film) 5 and the microcapsule display layer 4 is attached to the substrate 1 having the electrode layer 2 on the surface via the adhesive layer 3.

  As the pressure-sensitive adhesive layer 3, a known pressure-sensitive adhesive or heat-sensitive adhesive can be used. These can be used in the form of a single-sided adhesive tape or a double-sided adhesive tape having release paper on the adhesive surface. That is, the pressure-sensitive adhesive layer 3 is formed by sticking the non-stick surface of a single-sided pressure-sensitive adhesive tape to the microcapsule display layer 4 with an adhesive, or peeling off one of the double-sided pressure-sensitive adhesive tapes and sticking it to the microcapsule display layer 4. I can do it.

  The affixing can be performed, for example, by peeling off the release paper, adhering the adhesive surface of the first adhesive layer 3 to the substrate 1, and pressing or heating. Glass, film, or the like can be used as the substrate 1, and a surface electrode layer 2 is independently patterned for each pixel as a pixel electrode, and a thin film transistor, a signal electrode, and a scanning electrode (not shown) are provided. I can do it. At this time, the transparent electrode layer 5 can be a common electrode whose entire surface has the same potential.

The surface layer 8 may include at least one functional layer selected from the group consisting of an antiglare hard coat layer, an ultraviolet absorption layer, and a gas barrier layer. These functional layers can be formed by a known method using a known material.

  According to the present invention, in the microcapsule type electrophoretic display device described above, the microcapsules included in the microcapsule display layer 4 have a two-layer structure.

  FIG. 2 schematically shows an example of the microcapsule 110 included in the microcapsule display layer 4 of the present invention. In FIG. 2, black particles 114 made of carbon black are enclosed in a first capsule shell 111 together with a first dispersion medium 112 such as silicone oil or tetrachloroethylene. Further, the first microcapsule shell 111 in which the black particles 114 are sealed and the white particles 113 made of titanium oxide are sealed in the second capsule shell 115 together with the second dispersion medium 116 such as silicone oil or tetrachloroethylene. ing. At this time, the titanium oxide that is the white particles 113 has a positive charge, while the carbon black that is the black particles 114 has a negative charge.

  As the material for forming the first and second microcapsule shells 111 and 115, acrylic resin such as polymethyl methacrylate and polyethyl methacrylate, urea resin, gelatin, gum arabic and the like can be used.

  The capsule wall formation method includes phase separation method, submerged drying method, melt dispersion cooling method, spray line method, pan coating method, interfacial polymerization method, in situ polymerization method, submerged cured coating method, interfacial reaction method, etc. Any suitable method can be used.

  By performing the partition formation twice, a microcapsule having a two-layer structure according to the present invention can be obtained. That is, a microcapsule in which a capsule made of the first capsule shell 111 is formed and microencapsulated with respect to the electrophoretic dispersion liquid comprising the black particles 114 and the first dispersion medium 112, and then the microcapsules in which the black particles 114 are enclosed. Then, with respect to the electrophoretic dispersion liquid composed of the white particles 113 and the second dispersion medium 116, a capsule composed of the first capsule shell 111 is formed and microencapsulated to obtain a microcapsule 110 having a two-layer structure. be able to.

  If necessary, the diameter of the microcapsules can be controlled by an arbitrary method such as sieving or specific gravity separation. The diameter of the first capsule shell 111 enclosing the black particles 114 and the first dispersion medium 112 is preferably about 5 to 25 μm, and the first capsule medium 111 in which the black particles 114 and the first dispersion medium 112 are enclosed. The diameter of the second capsule shell 115 in which the one capsule shell 111, the white particles 113, and the second dispersion medium 116 are enclosed is preferably about 20 to 100 μm.

  In the present invention, the material forming the first capsule shell 111 and the material forming the second capsule shell 115 may be the same or different. Similarly, the first dispersion medium 112 and the second dispersion medium 116 may be different or the same. In FIG. 2, microcapsules in which black particles and a dispersion medium are encapsulated and white particles and the dispersion medium are microencapsulated to form a microcapsule having a two-layer structure. By reversing the white particles and the black particles, the first capsule shell 111, the black particles 111, and the second dispersion medium 116 in which the white particles 113 and the first dispersion medium 112 are encapsulated are microencapsulated. A microcapsule 110 having a layer structure may be used.

The display body using the microcapsule type electrophoresis system including the microcapsule 110 shown in FIG. 2 operates as follows. That is, as the operation, for example, as shown in FIG. 3, an electric field is applied to the transparent electrode layer 5 on the transparent resin film side and the electrode layer 2 on the base material side, and the transparent electrode layer 5 has five electrodes, When 2 is a positive electrode, positively charged white particles 113 are drawn to the transparent electrode layer 5 side, and negatively charged black particles 114 are drawn to the electrode layer 2 side, so that observation is performed from above the transparent electrode layer 5 side. Then that part looks white.

  Conversely, when the transparent electrode layer 5 is a positive electrode and the electrode layer 2 is a negative electrode, the positively charged white particles 113 are attracted to the electrode layer 2 side, and the negatively charged black particles 114 are transferred to the transparent electrode layer. Since it is drawn to 5 side, when observed from the upper side of the transparent electrode layer 5 side, the part looks black.

  In the case of a display using a microcapsule type electrophoresis system including the microcapsules 110 shown in FIG. 4, for example, as shown in FIG. 5, the transparent electrode layer 5 on the transparent resin film side and the substrate When an electric field is applied to the side electrode layer 2 so that the transparent electrode layer 5 is a positive electrode and the electrode layer 2 is a negative electrode, positively charged black particles 114 are drawn to the transparent electrode layer 5 side and negatively charged white particles Since 113 is drawn to the electrode layer 2 side, the portion looks black when observed from above the transparent electrode layer 5 side.

  Conversely, when the transparent electrode layer 5 is a negative electrode and the electrode layer 2 is a positive electrode, the positively charged black particles 114 are drawn to the electrode layer 2 side, and the positively charged white particles 113 are transferred to the transparent electrode layer. Since it is drawn to 5 side, when observed from the upper side of the transparent electrode layer 5 side, the portion looks white.

  The microcapsule display layer 4 includes, for example, a large number of microcapsules 110 as shown in the side sectional view of FIG. 1, the transparent electrode layer 5 is a common electrode having the same potential, and each address electrode of the electrode layer 2 is By controlling the electric field, a desired character or figure can be displayed as white and black pixels by moving particles in the microcapsule based on the above-described principle.

  Similarly, by using the electrode layer 2 as a common electrode (with a potential of zero) and controlling the electric field of each address electrode on the transparent electrode 5 side (giving positive or negative potential), You may make it display a desired image by moving particle | grains.

  Various diameters of the microcapsule 110 can be adopted. However, when 85% is about 30 μm to about 60 μm, sufficient resolution and responsiveness can be obtained. The resolution of the display image mainly depends on the arrangement of the electrodes in the electrode layer. However, if the diameter of the microcapsules is small, the movement speed of the microcapsules in the dispersion medium increases, and as a result, the response at the time of display is excellent. There are benefits.

  A paper-like electronic display using a microcapsule type electrophoretic display panel as shown in FIG. 1 is made of a flexible material, and patterning of electrodes and the like is also formed on a plastic film by printing or vapor deposition. This can be realized. The display screen size can be created in any size according to the application and demand.

  In the microcapsule display layer 4, there is no problem in display even if the position of the microcapsules 110 varies slightly. Therefore, it can be used by being bent or used by being attached to a curved surface.

  In the microcapsule-type electrophoretic display panel as shown in FIG. 1, since each particle is dispersed in a highly viscous dispersion medium, the position of the particle changes even after the power is turned off once the electric field is applied. do not do. In this way, the display image does not disappear even when the display is turned off. It has non-volatility (memory property), so it is only necessary to apply an electric field at the time of initial display or rewriting, and it is necessary for display compared to a normal display device. The amount of electric power required is also small, and a significant power saving can be achieved.

  Further, in the display panel, there is no problem in display even if the position of the microcapsules 110 is slightly changed. Therefore, by using a material that makes the entire display including the transparent electrode layer 5 and the electrode layer 2 thin and portable, flexibility such as paper can be provided.

  Specific examples of the present invention will be described below.

<Example 1>
The present invention is not limited to these examples, and in the examples, “parts” indicates parts by weight unless otherwise specified.

  First, a dispersion was prepared in which 40 parts of carbon black powder (black particles) having an average particle diameter of 4 μm, which had been surface-treated with alkyltrimethylammonium chloride, were dispersed in 100 parts of a tetrachloroethylene solvent.

  Next, 40 parts of this dispersion was mixed with an aqueous solution in which 10 parts of gelatin and 0.1 part of sodium polystyrene sulfonate were mixed in 80 parts of water, and after adjusting the liquid temperature to 40 ° C., while maintaining the liquid temperature, The mixture was stirred with a homogenizer to obtain an O / W emulsion.

  Next, the obtained O / W emulsion and an aqueous solution prepared by mixing 10 parts of gum arabic with 80 parts of water prepared at 40 ° C. are mixed using a dispenser, and the liquid temperature of the solution is maintained at 40 ° C. While adjusting the pH of the solution to 4 using acetic acid, microcapsule walls were formed by coacervation.

  Further, after the liquid temperature of both samples was lowered to 5 ° C., 1.9 parts of a 37 wt% formalin solution was added to harden the microcapsule wall, and a dispersion liquid in which black particles (carbon black particles) were dispersed was enclosed. Microcapsules were obtained. The microcapsules in which the black particles thus obtained were encapsulated were sieved, and the particle diameters were adjusted so that the average particle diameter was 15 μm, and the ratio of particle diameters of 10-20 μm was 80% or more.

  Next, a dispersion liquid was prepared in which 60 parts of the obtained microcapsules and 60 parts of titanium oxide powder (white particles) having an average particle diameter of 3 μm whose surface was coated with a polyethylene resin were dispersed in 100 parts of a tetrachloroethylene solvent.

  First, a dispersion was prepared in which 40 parts of carbon black powder (black particles) having an average particle diameter of 4 μm and surface-treated with alkyltrimethylammonium chloride were dispersed. Next, 40 parts of this dispersion was mixed with an aqueous solution in which 10 parts of gelatin and 0.1 part of sodium polystyrene sulfonate were mixed in 80 parts of water, and after adjusting the liquid temperature to 40 ° C., while maintaining the liquid temperature, The mixture was stirred with a homogenizer to obtain an O / W emulsion.

  Next, the obtained O / W emulsion and an aqueous solution prepared by mixing 10 parts of gum arabic with 80 parts of water prepared at 40 ° C. are mixed using a dispenser, and the liquid temperature of the solution is maintained at 40 ° C. While adjusting the pH of the solution to 4 using acetic acid, microcapsule walls were formed by coacervation.

  Further, after the liquid temperature of both samples was lowered to 5 ° C., 1.9 parts of a 37 wt% formalin solution was added to harden the microcapsule wall, and the microcapsules in which black particles (carbon black particles) and a dispersion medium were enclosed A microcapsule having a two-layer structure enclosing white particles and a dispersion medium was obtained.

  Next, 2000 parts of water-dispersed microcapsules having a solid content of 40% by weight, 250 parts of urethane binder having a solids content of 40% by weight, 2 parts of a surfactant, 9 parts of a thickener, and 300 parts of pure water are mixed together to form a slurry. It was created.

  This slurry was applied on an ITO / PET substrate to obtain a sheet composed of an ITO / PET / microcapsule display layer. The obtained sheet was bonded to the TFT substrate with a polyester-urethane adhesive to obtain an image display device.

Below, the comparative example of this invention is demonstrated.
<Comparative Example 1>
First, 100 parts of a tetrachloroethylene solvent, 60 parts of titanium oxide powder (white particles) with an average particle diameter of 3 μm coated with a polyethylene resin, and carbon black powder (black particles with an average particle diameter of 4 μm surface-treated with alkyltrimethylammonium chloride) ) A dispersion was prepared in which 40 parts were dispersed.

  Next, 40 parts of this dispersion was mixed with an aqueous solution in which 10 parts of gelatin and 0.1 part of sodium polystyrene sulfonate were mixed in 80 parts of water, and after adjusting the liquid temperature to 40 ° C., while maintaining the liquid temperature, The mixture was stirred with a homogenizer to obtain an O / W emulsion.

  Next, the obtained O / W emulsion and an aqueous solution prepared by mixing 10 parts of gum arabic with 80 parts of water prepared at 40 ° C. are mixed using a dispenser, and the liquid temperature of the solution is maintained at 40 ° C. While adjusting the pH of the solution to 4 using acetic acid, microcapsule walls were formed by coacervation. The sample which performed this operation once and the sample which performed twice are created.

  Furthermore, after lowering the liquid temperature of both samples to 5 ° C., 1.9 parts of a 37 wt% formalin solution was added to harden the microcapsule wall to obtain white particles (titanium oxide particles) and black particles (carbon black particles). A microcapsule having an inner structure of one layer, in which a dispersion in which is dispersed was encapsulated, was obtained.

  The microcapsules thus obtained were sieved, and the particle diameters were adjusted so that the average particle diameter was 40 μm and the ratio of the particle diameters of 20-60 μm was 80% or more.

  Using the microcapsules obtained above, an image display device was obtained in the same manner as in the example.

The electro-optical characteristics of the image display devices obtained in Example 1 and Comparative Example 1 were evaluated. That is, a positive waveform h having a pulse length of 400 ms, followed by i having a rest length of 2000 ms, a negative waveform j having a pulse length of 400 ms, and then a rectangular wave having a rest length of 2000 ms are applied at a voltage of 15 V, and the white reflectance WS is applied. (White State) and black reflectance DS (Dark State) were measured. This measurement was performed using an international standard white diffused reflector and black diffused reflector manufactured by Labsphere, Inc., USA as standards of 99% and 5%, respectively. Also, a contrast ratio of WS / DS was obtained. Furthermore, in order to consider the visibility of human eyes, L ^* values WL * and DL * of WS and DS were obtained based on CIE L ^* a ^* b ^* . And the comprehensive evaluation of those results was performed on the following reference | standard.

  As said comprehensive evaluation, it showed with (circle) when satisfying the preferable target value target value, and x shown when not satisfying the preferable target value. The above results are shown in Table 1 below.

上記表１から、マイクロカプセルが２層の場合（実施例１）に、そのコントラストは７
以上で、総合評価は○であった。

From Table 1 above, when the microcapsule has two layers (Example 1), the contrast is 7
The overall evaluation was “Good”.

  On the other hand, when the microcapsule has one layer (Comparative Example 1), the contrast was less than 7, and the overall evaluation was x.

  From the above results, it was found that the two-layered internal structure of the microcapsule contributes to excellent electro-optical characteristics, particularly improvement in contrast.

  Since the electrophoretic display device of the present invention has excellent electro-optical characteristics, it can be widely used as a display device in various applications other than the above-described paver-like electronic display.

It is explanatory drawing which represented a part of example of the electrophoretic display device of this invention with the side cross section. It is a schematic diagram showing the cross section of the microcapsule contained in the microcapsule display layer which comprises an example of the electrophoretic display device of this invention. It is the schematic diagram which represented the example of the display form of the microcapsule display layer which comprises an example of the electrophoretic display device of this invention in the cross section. It is a schematic diagram showing the cross section of the microcapsule contained in the microcapsule display layer which comprises another example of the electrophoretic display device of this invention. It is the schematic diagram which represented the example of the display form of the microcapsule display layer which comprises another example of the electrophoretic display device of this invention in the cross section. It is a conceptual diagram which shows the principle of the display body of the conventional electrophoresis system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Electrode layer 3 ... Adhesive layer 4 ... Microcapsule display layer 5 ... Transparent electrode layer 6 ... Transparent resin layer 8 ... Surface layer 110 ... Microcapsule 111 ... First Capsule shell 112 first dispersion medium 113 white particles 114 black particles 115 first capsule shell 116 second dispersion medium

Claims (1)

  On the substrate, an electrode layer, an image display layer, a transparent electrode layer, and a surface layer are provided in this order. The image display layer is a micro particle in which black particles, white particles, and a dispersion medium for dispersing these particles are contained in a capsule shell. In the electrophoretic display device comprising a capsule, the microcapsule includes a plurality of internal microcapsules in which one of black particles or white particles and a dispersion medium thereof are accommodated in a first capsule shell, and the other An electrophoretic display device, wherein the particles and the dispersion medium thereof are accommodated in a second capsule shell and have a double structure.

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