JP2007114800A - Display panel for electrophoresis display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display liquid for electrophoresis display in which a display color obtained by pigment component particles and a display color obtained by a dispersion medium colored with a dye are not mixed. <P>SOLUTION: As pigment particles (dispersed particles) included in the display liquid, (1) a pigment whose particle shape is not spherical, (2) a pigment which is partially in a plane shape, and (3) a pigment in a compound body shape are used. Using such dispersed particles makes it possible to prevent the dispersion medium from entering gaps formed between dispersed particles, and between dispersed particles and a display surface (transparent plate) as much as possible. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display liquid for an electrophoretic display medium capable of reversibly changing a visual state by the action of an electric field.

  In an electrophoretic display device, at least one of two transparent substrates is placed opposite to each other with a desired interval through a spacer to form a sealed space, and dispersed particles (pigment components) are mixed with this in a color tone. A display panel is filled with display liquids dispersed in different dispersion media to obtain a display by applying an electric field to the display panel, and the transparent substrate surface becomes the display surface.

  The display liquid for electrophoretic display filled in the sealed space is a dispersion medium such as xylene or isoparaffin, fine particles (dispersion particles) such as titanium dioxide, a dye for giving a color contrast to the color of the dispersion particles, It is comprised from additives, such as dispersing agents, such as surfactant, and a charge provision agent. By applying an electric field to the display liquid, the dispersed particles in the display liquid move to the transparent plate side, and the color of the dispersed particles appears on the surface. By applying an electric field in the opposite direction, the dispersed particles move to the back side, and the color of the dispersion medium or the color of the dye appears on the surface.

  An electrophoretic display device is a display device that obtains a desired display by controlling the direction of an electric field, and is a low-cost material in which a display liquid is relatively easily available. The viewing angle is as wide as that of a normal printed product. However, it has attracted attention as an inexpensive display device because of its advantages such as small size and memory property.

  The display liquid of such an electrophoretic display device generally contains high refractive index dispersion particles (pigment component) such as titanium oxide and a dispersion medium colored by dissolving a dye. In contrast, a decrease in contrast is likely to occur due to color mixing between the two during image formation. In particular, in the state in which the dispersed particles move to the display surface side and the color of the dispersed particles appears on the surface, voids that exist between the dispersed particles or voids that are formed between the dispersed particles and the transparent plate, When the dispersion medium colored with the dye is present, the color of the dispersion medium is mixed with the color of the dispersed particles. In particular, when the dispersed particles are white pigments, the whiteness of the background portion (non-recording portion) is reduced, which may lead to a fatal defect for the display material.

  In order to solve such problems, in the past, a dye that is non-adsorptive to the pigment particle surface is used as a dye for coloring the dispersion medium (Phlips Lab: Conference Record of 1980 Biennial Disp. Res .Conf.) Has been proposed. However, although this method may reduce the adsorption of a small amount of dye on the surface of the pigment particles, it cannot fundamentally prevent the dispersion medium from entering the gaps between the pigment particles and does not lead to a significant improvement.

  In addition, lowering the dye concentration in the dispersion medium (Xerox Paio Alto: Proc. SID, Vol. 18, 3/4, 1977) and improvements by optimizing the dye concentration, pigment concentration, and surfactant (Matsushita: Proc. SID, Vol. 18, No. 3/4, 4977) has also been proposed. However, these methods also reduce the density of the display color due to the dispersion medium by lowering the dye concentration in the dispersion medium in order to reduce color mixing. In order to prevent a decrease in density, the cell thickness as a display medium is also increased at the same time. However, in this case, another problem of a decrease in response speed is caused, resulting in a fundamental solution. There is no current situation.

  The object of the present invention is to prevent the dispersion medium from entering the voids formed between the dispersed particles and the voids formed between the dispersed particles and the display surface (transparent plate). It is intended to provide a display liquid for an electrophoretic display device having good contrast so that display colors are not mixed by a dispersion medium colored with a dye.

  The present invention relates to a display liquid for an electrophoretic display device mainly composed of pigment particles (dispersed particles) and a dispersion medium having a different color tone, and formed between the pigment particles and between the pigment particles and the transparent plate on the display surface side. By preventing the dispersion medium from entering the gaps, display with good contrast is made possible.

  First, in an electrophoretic display display liquid mainly comprising a pigment component and a dispersion medium having a different color tone, an electrophoretic display display liquid is provided, wherein the pigment component is non-spherical particles. The

  Second, the first display liquid for electrophoretic display is provided, wherein the non-spherical pigment component particles partially have a planar shape.

  Third, the first display liquid for electrophoretic display is provided, wherein the non-spherical pigment component particles have a composite shape of particles having different particle diameters.

  In the present invention, pigment particles whose particle shape is not spherical are used as pigment components (dispersed particles) contained in the display liquid for electrophoretic display devices. This prevents the infiltration of the dispersion medium colored with the dye by filling the voids formed between the pigment particles and between the pigment particles and the transparent plate on the display surface side with pigment particles whose particle shape is not spherical. This is because it is possible to display with good contrast without mixing the color of the pigment particles and the color of the dye.

  In this case, it is desirable to use non-spherical pigment particles having a partially planar shape. The non-spherical pigment particles partially have a planar shape, thereby inhibiting the formation of voids formed between the pigment particles and between the pigment particles and the transparent plate on the display surface side. Display without color mixing between the dye and the color of the dye becomes more possible. There are various shapes of these pigment particles, for example, leaf-like shape, needle-like shape, columnar particle, disc-like particle, flat-like particle, etc. Among them, disc-like particle and flat-like particle are particularly preferable. These fine particles such as leaf-like, needle-like, columnar particles, disk-like particles or flat particles can be obtained as commercial products, and are deformed on page 39 of "New Development of Fine Particle Polymer (Toray Research Center, Inc.)". It is described as the specific shape of the particles. Furthermore, the shape of the flat particles is also described on page 441 of “Functions and Application Technologies of Emulsification / Dispersion Process (Science Forum)”.

  In addition, non-spherical pigment particles are formed between the pigment particles and between the pigment particles and the transparent plate on the display surface side, as described above, by being a composite of particles having different particle sizes. By inhibiting the formation of voids, it becomes possible to display without mixing the color of the pigment particles and the color of the dye. In this case, the composite particles include particles (barb type or confetti type) that are combined so that a smaller particle is entirely taken in around a certain size particle, or around a certain size particle. In addition, there are particles (dharma type) in which only one smaller particle is combined. These fine particle shapes are described in "Polymer Processing 34, 109 (1985)".

  According to the present invention, when the color of the dispersed pigment (white when a white pigment is used) is displayed, mixing with the dispersion medium colored by the dye is difficult to occur, and mixing of both colors is difficult to occur. A display liquid for electrophoretic display and an electrophoretic display medium are provided.

  The present invention is described in further detail below. As described above, the present invention is a display liquid for electrophoretic display, characterized in that the pigment component and the dispersion medium having a different color tone are the main components, and the pigment component is a mixture of pigment particles having different particle sizes. It is related to. The effect is obtained by using a pigment whose particle shape is not spherical as the pigment particles (dispersed particles) contained in the display liquid for an electrophoretic display device. In particular, this non-spherical pigment particle has a partial shape. In particular, an excellent effect is obtained when it has a planar shape or is a composite of particles having different particle sizes.

  As the pigment used as the dispersed particles in the present invention, a colored or white inorganic pigment can be used. Examples of the colored pigment include chrome yellow, cadmium yellow, molybdate orange, bengara, cadmium red, manganese violet, bitumen, ultramarine blue, emerald green, carbon black, and iron black. Examples of white pigments include zinc oxide, basic lead carbonate, basic lead sulfate, lead sulfate, lithopone, zinc sulfide, titanium oxide, antimony oxide, etc. When these white pigments are used, white and colored contrast Among these, titanium oxide is a particularly preferable pigment when obtaining a white color.

  These pigment components can be used in any form of fine particles / hollow particles of pigment alone, composite particles in which the surface of pigment particles is covered with resin, and composite particles in which the surface of polymer particles / hollow polymer particles are covered with pigment. These fine particles may be used as dispersed fine particles.

  When the pigment component is used as particles of pigment alone, fine particles or hollow particles of pigment may be used directly as dispersed particles. In the case of using pigment hollow particles, it is necessary to prepare pigment fine particles having a pigment component on the surface and having internal voids of fine particles having voids inside, and as a means for that, the pigment component is porous or hollow. As a method in the case of using a method of forming in a state, an interfacial polymerization method described in “Coloring Materials, 59 (9), 543, (1986)”, “Coloring Materials, 70 (6), 378, (1997) It can be prepared using the interfacial gelation reaction method described in the above.

  Further, when using the pigment component as various composite particles, it is possible to use a technique performed by surface modification of various particles, and in the case of composite particles in which the pigment particle surface is covered with a resin, Examples thereof include a method of coating the pigment particle surface with a silicone resin, a surface treatment with a coupling agent having a long-chain alkyl group, a coating using a coupling agent and silicone in combination, and a surface modification by grafting.

  On the other hand, in the case of composite particles in which the surface of polymer particles or hollow polymer particles is covered with a pigment, it can be prepared by an existing method, and is described in, for example, “Coloring Materials, 59 (9), 543, (1986)”. And vacuum deposition method, powder bed method, topochemical method, mechanochemical method, surface deposition method, impregnation method, suspension method, and composite emulsion method. In addition, as other methods, the inorganic wall encapsulation method, coatmizer method, “coloring material, 71 (2), 103, ( 1998) ”, and the reverse micelle method described in“ Coloring Materials, 71 (7), 449, (1998) ”.

  In this case, various polymer particles including polyethylene, polystyrene, silicone polymer, polymethyl methacrylate, and urea-formalin resin can be used as the polymer particles serving as the nucleus. The hollow polymer particles include polyester-based porous particles obtained by suspension polymerization of W / O / W emulsion, acrylic-based porous particles, styrene-acrylic hollow latex produced by seed polymerization, vinylidene chloride-acrylonitrile-based, acrylonitrile. It is possible to use thermal expansion microcapsules of the system. Specifically, ROHMAKE of Rohm and Haas Co., Ltd., JSR hollow particles manufactured by Nippon Synthetic Chemical Co., Ltd., thermal expansion microcapsules manufactured by Matsumoto Yushi Co., Ltd.

  In the present invention, as the dispersion medium having a color tone different from that of the pigment particles, a highly insulating organic solvent having a low conductivity in which a dye having a color different from that of the pigment particles is dissolved is used.

  As the dye, an oil-soluble dye that is soluble in an organic solvent is used. Oil Yellow 3G, First Orange G, Oil Red 5B, Oil Violet # 730, Macrolet Sprue RR, Sumiplast Green G, Oil Brown GR, Sudan Black X60 and the like can be cited as representative items.

  Highly insulating organic solvents with low electrical conductivity include aromatic hydrocarbons such as benzene, toluene, xylene, naphthenic hydrocarbons, aliphatic hydrocarbons such as hexane, cyclohexane, kerosene, paraffinic hydrocarbons, chloroform , Halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene, trifluoroethylene, tetrafluoroethylene, and ethyl bromide. These organic solvents can be used alone or in admixture of two or more.

  In the present invention, in order to supplement the dispersibility of the pigment particles in the dispersion medium as required, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant that can be dissolved in the dispersion medium. Dispersing agents such as a surfactant, a fluorosurfactant, a block polymer, and a graft polymer can be used alone or in admixture of two or more.

As an example of the electrophoretic display device using such a display liquid, the following forms may be mentioned.
(1) Create a space by placing transparent electrodes 21 and 22 formed in a desired pattern on one of a pair of transparent members such as a pair of glass substrates 11 and 12 through a spacer 3 to create a space. The display liquid of the present invention is filled (FIG. 1).
(2) A discontinuous space is formed on the substrate on which the entire surface electrode has been provided by facing the insulating film 5 through a number of spacers 3, and the display liquid 4 of the present invention is filled in the space (FIG. 2).
(3) One having a transparent electrode formed in a desired pattern on one of a pair of transparent members such as a glass substrate is disposed oppositely with a spacer 3 therebetween to create a space, and the display liquid of the present invention is placed in the space. The encapsulated microcapsule 6 is filled (FIG. 3). In this example, a binder may be present instead of the space.
(4) A discontinuous space is formed by facing an insulating film through a large number of spacers on a substrate provided with a full-surface electrode, and the space is filled with microcapsules containing the display liquid of the present invention (FIG. 4). In this example, a binder may be present instead of the space.
(5) A microcapsule 6 in which the display liquid of the present invention is encapsulated is applied together with a binder 7 on a substrate having a full-surface electrode (FIG. 5).

  Here, as a method of encapsulating the display liquid of the present invention in a microcapsule, it can be prepared by an in-situ method, an interfacial polymerization method, a coacervation method, or the like. Polyurethane, polyurea, polyurea-polyurethane, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide, polyester, polysulfonamide, polycarbonate, polysulfinate, epoxy resin, acrylic ester, methacrylic ester, polyvinyl acetate, gelatin, etc. Is mentioned.

  Next, an Example is given and this invention is demonstrated concretely.

Example 1
A dispersion medium containing 0.5 wt% blue dye (Macrolex Blue RR: Bayer) dissolved in tetrachloroethylene is used as a dispersion medium, and as a migration particle (dispersion particle), a polymerization reaction between polystyrene seed particles and a crosslinkable monomer is performed. 10 g of flat polymer particles having an average particle diameter (flat surface diameter) of 2.0 μm and 5 g of titanium dioxide (TAF-510AS, manufactured by Fuji Titanium Industry Co., Ltd.) having an average particle diameter of 0.05 μm obtained by performing in isooctane. After mixing, flat particles having titanium oxide on the surface obtained by treatment at 8000 rpm using an impact mill (vibrizer) in a high-speed air stream were used. The particles and sodium dioctylsulfosuccinate were mixed in a dispersion medium at 5 vol% and 0.01 wt%, respectively, to prepare a display solution for electrophoretic display.

  Subsequently, a glass plate having a thickness of 3 mm is used as the transparent substrate, and a transparent conductive film (ITO film) formed on one side thereof is disposed oppositely through a nylon bead of a spacer to form a space of about 80 μm. After the display liquid was injected into the space using a syringe, both glass plates were sealed with an epoxy resin adhesive to prepare an electrophoretic display panel. Wiring was applied to the electrophoretic display panel with a conductive paste, and this was connected to a DC power supply, and a voltage was applied to migrate the dispersed particles to obtain a white display.

Example 2
A dispersion medium containing 0.5 wt% blue dye (Macrolex Blue RR: Bayer) dissolved in tetrachloroethylene was used as the electrophoretic particles (dispersed particles) on the surface prepared in Example 1 with an average particle diameter. Flat particles having 0.05 μm titanium oxide (TAF-510AS, manufactured by Fuji Titanium Industry Co., Ltd.) were used. These particles and oleic acid were mixed in a dispersion medium at 10 wt% and 0.5 wt%, respectively, to obtain a dispersion. Subsequently, a microcapsule enclosing the dispersion was produced as follows. An aqueous gelatin solution and an aqueous gum arabic solution are mixed, heated to 50 ° C., and an aqueous sodium hydroxide solution is added to adjust the pH to 9. The above dispersion is added to this and stirred to emulsify. Further, the pH was gradually lowered to 4 to deposit a concentrated gelatin / gum arabic solution at the dispersion interface, and then the temperature was lowered to gel the film, followed by addition of a glutaraldehyde aqueous solution to cure. Thus, a microcapsule slurry using gelatin as a wall material was obtained. The emulsification conditions were controlled so that the capsule diameter averaged 60 μm. The microcapsule slurry and a 10% aqueous solution of polyvinyl alcohol were mixed at an equal weight to prepare a display liquid for electrophoretic display.

  The microcapsules are shared by applying the display liquid for electrophoretic display prepared above on a common electrode in which an ITO thin film is formed by sputtering on a substrate (100 μm thick PET film) and drying. An electrophoretic display medium fixed as a coating layer on the electrode was produced. A counter electrode was installed on the display surface side of the electrophoretic display medium, a DC power source was connected to the cell between the counter electrode and the common electrode, a voltage was applied, and dispersed particles were migrated to obtain a white display.

Example 3
4. The average particle diameter obtained by conducting a polymerization reaction of polystyrene using a water-soluble initiator (potassium persulfate) on the outer part of polyethyl acrylate as seed particles as electrophoretic particles (dispersed particles). After mixing 10 g of 0 μm wild silk (combined sugar) type composite particles and 5 g of titanium oxide having an average particle diameter of 0.05 μm (manufactured by Fuji Titanium Industry Co., Ltd., TAF-510AS) at 8000 rpm using a high-speed impact mill (hybridizer). A display liquid for electrophoretic display and an electrophoretic display medium were produced in the same manner as in Example 1 except that the surface obtained by the treatment was used in the form of wild-type composite particles having titanium oxide on the surface. Further, a white display was obtained in the same manner as in Example 1.

Example 4
Example 2 except that flat particles having titanium oxide (TAF-510AS, manufactured by Fuji Titanium Industry Co., Ltd.) having an average particle diameter of 0.05 μm on the surface produced in Example 3 are used as the migrating particles (dispersed particles). In the same manner, a display liquid for electrophoretic display and an electrophoretic display medium were produced. Further, a white display was obtained in the same manner as in Example 2.

Example 5
The same procedure as in Example 1 was performed except that needle-like titanium dioxide (FTL-102, manufactured by Ishihara Sangyo Co., Ltd.) having a fiber diameter of 0.05 to 0.10 μm and a fiber length of 3 to 6 μm was used as the electrophoretic particles (dispersed particles). A display liquid for electrophoretic display and an electrophoretic display medium were prepared. Further, a white display was obtained in the same manner as in Example 1.

Example 6
Except using needle-like titanium dioxide (FTL-102, manufactured by Ishihara Sangyo Co., Ltd.) having a fiber diameter of 0.05 to 0.10 μm and a fiber length of 3 to 6 μm as electrophoretic particles (dispersed particles), the same as in Example 2 A display liquid for electrophoretic display and an electrophoretic display medium were prepared. Further, a white display was obtained in the same manner as in Example 2.

Comparative Example 1
A display liquid for electrophoretic display and electrophoretic display in the same manner as in Example 1 except that titanium dioxide (CR-50-2, manufactured by Ishihara Sangyo Co., Ltd.) having an average particle diameter of 0.25 μm was used as the electrophoretic particles (dispersed particles). A medium was made. Further, a white display was obtained in the same manner as in Example 1.

Comparative Example 2
A display liquid for electrophoretic display and electrophoretic display in the same manner as in Example 2 except that titanium dioxide having an average particle diameter of 0.25 μm (CR-50-2, manufactured by Ishihara Sangyo) was used as the electrophoretic particles (dispersed particles). A medium was made. Further, a white display was obtained in the same manner as in Example 2.

Reference example 1
As a dispersion medium, a solution in which 0.5 wt% of a blue dye (Macrolex Blue RR: Bayer) is dissolved in tetrachloroethylene is used, and as electrophoretic particles (dispersion particles), titanium dioxide having an average particle size of 0.25 μm (manufactured by Ishihara Sangyo, A mixture of CR-50-2) and titanium dioxide having an average particle size of 0.2 μm (manufactured by Ishihara Sangyo Co., Ltd., CR-63) (1: 1 by weight) was used. The particles and sodium dioctylsulfosuccinate were mixed in a dispersion medium at 5 vol% and 0.01 wt%, respectively, to prepare a display solution for electrophoretic display.

  Subsequently, a glass plate having a thickness of 3 mm is used as the transparent substrate, and a transparent conductive film (ITO film) formed on one side thereof is disposed oppositely through a nylon bead of a spacer to form a space of about 80 μm. After the display liquid was injected into the space using a syringe, both glass plates were sealed with an epoxy resin adhesive to prepare an electrophoretic display panel. Wiring was applied to the electrophoretic display panel with a conductive paste, and this was connected to a DC power supply, and a voltage was applied to migrate the dispersed particles to obtain a white display.

Reference example 2
A dispersion medium containing 0.5% by weight of a blue dye (Macrolex Blue RR: Bayer) dissolved in tetrachloroethylene is used as the migrating particles. 50-2) and a mixture of titanium dioxide (CR-63, manufactured by Ishihara Sangyo Co., Ltd.) having an average particle diameter of 0.2 μm (1: 1 by weight) was used. These particles and oleic acid were mixed in a dispersion medium at 10 wt% and 0.5 wt%, respectively, to obtain a dispersion. Subsequently, a microcapsule enclosing the dispersion was produced as follows. An aqueous gelatin solution and an aqueous gum arabic solution are mixed, heated to 50 ° C., and an aqueous sodium hydroxide solution is added to adjust the pH to 9. The above dispersion is added to this and stirred to emulsify. Further, the pH was gradually lowered to 4 to deposit a concentrated gelatin / gum arabic solution at the dispersion interface, and then the temperature was lowered to gel the film, followed by addition of a glutaraldehyde aqueous solution to cure. Thus, a microcapsule slurry using gelatin as a wall material was obtained. The emulsification conditions were controlled so that the capsule diameter averaged 60 μm. The microcapsule slurry and a 10% aqueous solution of polyvinyl alcohol were mixed at an equal weight to prepare a display liquid for electrophoretic display.

  The microcapsules are shared by applying the display liquid for electrophoretic display prepared above on a common electrode in which an ITO thin film is formed by sputtering on a substrate (100 μm thick PET film) and drying. An electrophoretic display medium fixed as a coating layer on the electrode was produced. A counter electrode was installed on the display surface side of the electrophoretic display medium, a DC power source was connected to the cell between the counter electrode and the common electrode, a voltage was applied, and dispersed particles were migrated to obtain a white display.

Reference example 3
As the migrating particles (dispersed particles), titanium dioxide having an average particle diameter of 0.25 μm (manufactured by Ishihara Sangyo, CR-50-2) and titanium dioxide having an average particle diameter of 0.02 to 0.05 μm (manufactured by Ishihara Sangyo, TTO-55) A display liquid for electrophoretic display and an electrophoretic display medium were prepared in the same manner as in Reference Example 1 except that the mixture (S) was used (1: 1 by weight). Further, a white display was obtained in the same manner as in Reference Example 1.

Reference example 4
As the migrating particles (dispersed particles), titanium dioxide having an average particle diameter of 0.25 μm (manufactured by Ishihara Sangyo, CR-50-2) and titanium dioxide having an average particle diameter of 0.02 to 0.05 μm (manufactured by Ishihara Sangyo, TTO-55) A display liquid for electrophoretic display and an electrophoretic display medium were prepared in the same manner as in Reference Example 2 except that the mixture (S)) (1: 1 by weight) was used. Further, a white display was obtained in the same manner as in Reference Example 2.

<Evaluation results>
The white display portion of the electrophoretic display medium formed as described above was visually observed, and the decrease in whiteness due to color mixture with the dispersion medium colored with the dye was evaluated. The results are shown in Table 1. In Table 1, it indicates that the whiteness is not decreased due to the color mixture, and the color decreases in accordance with ◯, Δ ○, Δ, and × Δ in order from × where the decrease is remarkable.

  The present invention is suitable for a display liquid for an electrophoretic display medium that can reversibly change its visual state by the action of an electric field, and is less likely to cause color mixing between the color of the dispersed pigment and the dispersion medium colored with the dye. Can be used.

Schematic of an example of the display medium produced using the display liquid for electrophoretic display of this invention. Schematic of an example of the display medium produced using the display liquid for electrophoretic display of this invention. Schematic of an example of the display medium produced using the display liquid for electrophoretic display of this invention. Schematic of an example of the display medium produced using the display liquid for electrophoretic display of this invention. Schematic of an example of the display medium produced using the display liquid for electrophoretic display of this invention.

Explanation of symbols

3 Spacer 4 Display Liquid 5 Insulating Film 6 Microcapsule 7 Encapsulating Display Liquid Binder 11 Base 12 Transparent Substrate 21, 22 Transparent Electrode

Claims (3)

A display liquid for electrophoretic display comprising a pigment component and a dispersion medium having a different color tone as a main component, wherein the pigment component is non-spherical particles. The display liquid for electrophoretic display according to claim 1, wherein the non-spherical pigment component particles partially have a planar shape. The display liquid for electrophoretic display according to claim 1, wherein the non-spherical pigment component particles have a composite shape of particles having different particle diameters.