JP2006317509A - Display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display element with which full-color image reproducibility, in particular with color reproducibility and contrast improved in the display element having memory properties. <P>SOLUTION: The display element has a plurality of liquid crystal dispersed layers being laminated together, each of which has a chiral nematic liquid crystal for selectively reflecting the desired wavelength region component of the visible ray and being dispersed in a binder, where the respective liquid crystal dispersed layers reflect light having peaks of wavelengths that are different from each other and further, the display element has a black image forming layer and a white image forming layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display device including a chiral nematic liquid crystal composition dispersed in a binder.

  In recent years, with the increase in computer operating speed, the spread of network infrastructure, the increase in capacity and price of data storage, information such as documents and images provided on printed paper has been processed as digital information. It has come to be distributed as simple electronic information. In addition to electronic books that are viewed personally, there is a movement to directly output electronic information of printed materials such as advertisements to electronic posters and the like. Currently, liquid crystal displays, LED displays, and the like are used, but it has also been proposed to use display elements called electronic paper.

  As electronic paper technology used for such display, electrophoresis, powder transfer, chiral nematic liquid crystal, electrochromic, etc. have been proposed, but chiral nematic liquid crystal is particularly suitable for color display. It is.

  The chiral nematic liquid crystal is a method in which a chiral agent is added to the nematic liquid crystal and the liquid crystal molecules have a twisted structure to selectively reflect light (Bragg reflection) to express different colors. The desired color can be reflected by selecting the type and amount of the chiral agent.

  It has been disclosed that full-color display using chiral nematic liquid crystals can be obtained by laminating chiral nematic liquid crystal layers having different reflection colors (see, for example, Patent Documents 1 and 2).

  However, full-color display using chiral nematic liquid crystals has a basic drawback. A chiral nematic liquid crystal is basically a substance that repeats a selective reflection state (planar state) and a transparent state (focal conic state) by applying an electric field, and therefore cannot express black. For this reason, a black layer is usually provided in the lowest layer, and this layer is shown in a transparent state in all layers.

  For this reason, the black density becomes relatively low, the overall contrast is lowered, and there is no reproduction of “black tightening” that is well evaluated for printed matter. In addition, there is a drawback that fine reproduction such as characters is difficult to obtain.

Further, since the black layer is always present at the lowermost layer, there is a drawback that the color reproduction range becomes narrow as when black paper is colored. In addition, when expressing white, it is necessary to express each layer in a reflective state and mix it to express white, so if the balance of the reflection intensity of each color is poor, the white appears cloudy (covering state) As a result, there is a problem that the contrast is lowered and the overall color reproduction is also lowered.
Japanese Patent No. 3209254 JP 2003-22843 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a display element with improved full color image reproducibility, particularly color reproduction and contrast, in a display element having a memory property.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
A display element having a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder, wherein a black image formation layer and a white image formation layer are laminated separately from the liquid crystal dispersion layer.

(Claim 2)
In the binder, a plurality of liquid crystal dispersion layers in which chiral nematic liquid crystals that selectively reflect a desired wavelength range of visible light are dispersed are laminated, and each of the liquid crystal dispersion layers has a different wavelength peak and a black image. A display element comprising a forming layer and a white image forming layer.

(Claim 3)
The display element according to claim 1, wherein the black image forming layer is an uppermost layer.

(Claim 4)
The display element according to claim 1, wherein an image forming layer located immediately below the black image forming layer is the white image forming layer.

(Claim 5)
The display element according to claim 1, wherein the black image forming layer is a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder.

(Claim 6)
The display element according to claim 1, wherein the black image forming layer is a layer in which a black dichroic dye is dispersed in a chiral nematic liquid crystal.

(Claim 7)
The display element according to claim 1, wherein the black image forming layer is a field deposition type image forming layer.

(Claim 8)
The display element according to claim 1, wherein the black image forming layer is an electrophoretic type or a powder transfer type image forming layer.

(Claim 9)
The display element according to claim 1, wherein the white image forming layer is a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder.

  ADVANTAGE OF THE INVENTION According to this invention, the display element which improved the color reproduction and contrast in the display element with a memory property can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above problems, the present inventor has found that in a display element having a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder, a black image forming layer and a white color are separated from the liquid crystal dispersion layer. It has been found that a display element having a memory property with improved color reproduction and contrast can be realized by a display element characterized in that an image forming layer is laminated.

  Details of the display element of the present invention will be described below.

  The display element of the present invention has a liquid crystal dispersion layer in which chiral nematic liquid crystal that selectively reflects a desired wavelength range of visible light is dispersed in a binder, and has a substantially black color different from the liquid crystal dispersion layer. A black image forming layer that forms an image to be displayed and a white image forming layer that forms an image that displays white are included as constituent layers. As a component layer, in addition to a liquid crystal dispersion layer, a black image forming layer, and a white image forming layer, an intermediate layer containing only a binder that does not contain a liquid crystal composition, a filter layer containing a dye, and a light shielding layer are required. It may be arranged appropriately according to

  Hereinafter, each component of the display element of this invention is demonstrated in detail.

〔binder〕
In the display device of the present invention, a hydrophilic binder is preferable as the binder used in the liquid crystal dispersion layer and the like according to the present invention. Examples of binders applicable to the present invention are described in, for example, Research Disclosure (hereinafter abbreviated as RD), Volume 176 Item / 17643 (December 1978), Volume 308, Item / 308119 (December 1989). And those described in pages (71) to (75) of JP-A No. 64-13546.

  The binder suitable for the present invention is transparent or translucent, generally colorless, and may be any medium that forms a film, such as natural polymers and synthetic polymers. For example: gelatin, gum arabic, poly (vinyl alcohol) , Hydroxyethyl cellulose, cellulose acetate, cellulose acetate butyrate, poly (vinyl pyrrolidone), casein, starch, poly (acrylic acid), poly (methyl methacrylic acid), poly (vinyl chloride), poly (methacrylic acid), copoly (styrene -Maleic anhydride), copoly (styrene-acrylonitrile), copoly (styrene-butadiene), poly (vinyl acetal) s (eg, poly (vinyl formal) and poly (vinyl butyral)), poly (esters), poly (esters) Urethane), phenoxy resin, Li (vinylidene chloride), poly (epoxides), poly (carbonates), poly (vinyl acetate), cellulose esters, poly (amides), and the like.

  In the present invention, a hydrophobic transparent binder can be used as the binder as long as it is incompatible with the liquid crystal composition. Examples of the hydrophobic transparent binder include polyvinyl butyral, cellulose acetate, cellulose acetate butyrate, polyester, polycarbonate, polyacrylic acid, and polyurethane. Among the hydrophobic binders, polyvinyl butyral, cellulose acetate, cellulose acetate butyrate, and polyester are particularly preferably used.

Two or more of these binders may be used in combination, and the coating amount of the binder is preferably 100 g or less per m ² , and particularly preferably 20 g or less.

  The binder according to the present invention is important for securing the film strength of the liquid crystal dispersion layer, particularly when the counter electrode is used. In order to make the film thickness constant together with the binder, a resin pillar structure or spacer particles may be used. Although possible, it is preferable not to use them because of simplification of the process. Gelatin is a preferred binder that can provide a constituent layer having a uniform film thickness in each step of heat dissolution, coating, cooling set, and drying. Examples of other than gelatin include, for example, carrageenan in polyvinyl alcohols. It is possible to take steps similar to those of gelatin by using a thickening polysaccharide such as gel or gellan gum in combination, and in this case, a constituent layer having a uniform film thickness can be obtained.

  In addition, examples of the binder used in the present invention include aqueous solvent dispersions such as polyurethane resins, polyacrylic resins, and silicone resins, photo-curing resins, thermosetting resins, and thermoplastic resins.

  In the display element of the present invention, it is preferable that at least one of the binders is gelatin or a gelatin derivative.

  Examples of gelatin that can be used in the present invention include acid-treated gelatin and alkali-treated gelatin, as well as enzyme-treated gelatin and gelatin derivatives that undergo enzyme treatment in the gelatin production process, that is, amino groups and imino as functional groups in the molecule. It may be modified by treatment with a reagent having a group, a hydroxyl group, or a carboxyl group, and a group obtained by reaction with the group. The general method for producing gelatin is well known and is described, for example, in T.W. H. James: The Theory of Photographic Process 4th. ed. Reference can be made to descriptions such as 1977 (Maccillan), p. 55, Science Photo Handbook (above), p. 72-75 (Maruzen), Photographic Engineering Basics-Silver Salt Photo Hen, pages 119-124 (Corona).

  In the present invention, when gelatin is used as a binder, it can be hardened with a hardener. Examples of hardeners preferably used in the present invention include US Pat. No. 4,678,739, column 41, US Pat. No. 4,791,042, JP-A-59-116655, JP-A-62-245261, Examples thereof include hardeners described in JP-A-61-18942, JP-A-61-249054, JP-A-61-245153, and JP-A-4-218044. More specifically, aldehyde hardeners (eg, formaldehyde), aziridine hardeners, epoxy hardeners, vinyl sulfone hardeners (eg, N, N′-ethylene-bis (vinylsulfonyl) Acetamide) ethane), N-methylol hardeners (for example, dimethylolurea, etc.), boric acid, metaboric acid, or polymer hardeners (for example, compounds described in JP-A-62-2234157). Can be mentioned. Among these hardeners, it is preferable to use a vinyl sulfone type hardener or a chlorotriazine type hardener alone or in combination.

  Examples of the vinyl sulfone hardener used in the present invention include aromatic compounds such as those described in German Patent No. 1,100,942 and US Pat. No. 3,490,911. Alkyl compounds bonded with hetero atoms as described in 44-29622, 47-25373 and 47-24259, sulfonamides and ester compounds as described in JP-B 47-8736, etc. 1,3,5-tris [β- (vinylsulfonyl) -propionyl] -hexahydro-s-triazine or JP-B-50-35807, JP-A-51-51, as described in JP-A-49-24435, etc. And alkyl compounds such as those described in JP-A No. 44164 and compounds described in JP-A No. 59-18944.

  These vinyl sulfone-based hardeners are dissolved in water or an organic solvent and have a mass ratio of 0.001 to 0.200, particularly preferably 0.001 to 0.050, with respect to the binder that can react with the hardener. Used.

  Among the vinyl sulfone hardeners according to the present invention, use of a vinyl sulfone hardener having a hydroxyl group in the molecule is preferred. In the present invention, aldehyde hardeners (formaldehyde, etc.), aziridine hardeners, epoxy hardeners, N-methylol hardeners (dimethylol urea, etc.) hardeners are vinylsulfone hardeners. It can be used in combination with a film agent.

  These hardeners are used in an amount of 0.001 to 1 g, preferably 0.005 to 0.5 g, per 1 g of binder.

[Chiral Nematic Liquid Crystal]
The liquid crystal dispersion forming the chiral nematic liquid crystal dispersion layer according to the present invention is a chiral nematic liquid crystal dispersion having a cholesteric phase.

  The chiral nematic liquid crystal is a typical liquid crystal exhibiting a cholesteric phase, and can be obtained by adding a predetermined amount of a chiral agent (also referred to as a chiral dopant) to the nematic liquid crystal. This chiral nematic liquid crystal generally has a twisted arrangement of rod-like liquid crystal molecules and exhibits a cholesteric phase. When light is incident on this liquid crystal, when light is incident from a direction parallel to the helical axis, light having a wavelength represented by λ = np is selectively reflected (planar state). Here, λ is the wavelength, n is the average refractive index of the liquid crystal molecules, and p is the distance at which the liquid crystal molecules are twisted 360 °. On the other hand, when light is incident from a direction perpendicular to the helical axis, the light is transmitted without being reflected (focal conic state). Display is performed using this selective reflection and transmission.

  The operation mode of the reflective liquid crystal display element having memory characteristics is disclosed in Technical Paper SID International Symposium Technical Paper Vol. 29, page 897. This operation mode is a method of performing display by switching the alignment state of the chiral nematic liquid crystal to either a planar state (light selective reflection state) or a focal conic state (light transmission state). Since the planar state and the focal conic state are stable states, once the liquid crystal is set to any state, the state is maintained semipermanently unless an external force is applied. That is, it is useful as a reflective liquid crystal display element having a memory property that once an image is displayed, the displayed image is maintained as it is even when the power is turned off.

  The reflective liquid crystal display element described in the above document has a structure in which a chiral nematic liquid crystal is sandwiched between a pair of substrates each provided with an electrode. The liquid crystal is changed to a predetermined state (planar state and focal conic state) by controlling the intensity of the electric field and / or the application time.

  When a voltage equal to or higher than a threshold voltage for untwisting the liquid crystal is applied to the liquid crystal for a sufficient time, the liquid crystal is all in a homeotropic state (the long axis direction of the liquid crystal molecules is perpendicular to the substrate). In this state, since there is no memory property, when the electric field is erased, the liquid crystal is twisted. From the homeotropic state, when the electric field is suddenly erased, it becomes a planar state, and when the electric field is gradually erased, it becomes a focal conic state.

  In addition, when a pulse voltage higher than the threshold voltage for solving the twist is applied to the liquid crystal in the focal conic state (a voltage having a pulse width at which some liquid crystals are in a homeotropic state), the liquid crystal in the homeotropic state is The planar state is established after the application of the pulse voltage. By controlling the width of the pulse voltage and / or the height of the voltage, it is possible to adjust the ratio of the liquid crystal in the planar state (display halftone).

  In the liquid crystal-polymer composite film using chiral nematic liquid crystal, the amount of chiral dopant added to the nematic liquid crystal is adjusted, and the helical pitch of the chiral nematic liquid crystal is selected, and the selective reflection wavelengths are, for example, blue light, green light, red, respectively. By adjusting to light and yellow light, the liquid crystal is in a selective reflection state colored in red, green, blue and yellow in the case of the planar arrangement, and a colorless and transparent light transmission state in the case of the focal conic arrangement. -A polymer composite membrane is obtained. A color liquid crystal display device is obtained by sandwiching the liquid crystal-polymer composite film thus obtained between transparent electrodes. In the display element of the present invention, the chiral nematic liquid crystal composition is preferably composed of a liquid crystal composition that selectively reflects at least one light selected from blue light, green light, red light, and yellow light.

  Also, by adjusting the amount of chiral dopant added and adjusting the helical pitch of the chiral nematic liquid crystal so that the selective reflection wavelength is infrared light, the planar arrangement is colorless and transparent, the focal conic arrangement is the same, etc. A liquid crystal-binder composite film showing a light scattering state that appears white due to side scattering is obtained. A white display device is obtained by sandwiching the liquid crystal-binder composite film thus obtained between the transparent electrodes.

  The relationship between the helical pitch p (nm) and the selective reflection wavelength λ (nm) is expressed by the following formula (1).

Formula (1)
λ = n × p
In the formula, n represents an average refractive index, and n = (n1 ² + n2 ² ) ^1/2 . n1 represents a refractive index when light is incident in the major axis direction of the liquid crystal molecule, and n2 represents a refractive index when light is incident in a direction perpendicular to the major axis direction of the liquid crystal molecule.

  In order to produce a white display device or a color display device of each color, for example, a method in which a mixture of liquid crystal and a binder is sandwiched between substrates and then cured with a hardener or the like to phase separate the liquid crystal and the binder. can do. At this time, if the spacer is sandwiched between the substrates together with the mixture, the thickness of the liquid crystal-binder composite film can be easily controlled.

  As a chiral dopant to be added to the nematic liquid crystal, a plurality of kinds of chiral dopants may be mixed and used. The use of multiple types of chiral dopants increases the phase transition temperature of liquid crystals, improves the transparency of the composite film in the transparent state, and particularly speeds up the display switching between the transparent state and the selective reflection state of the color display device. It is effective to do.

  A first display device having a composite film using a left-handed chiral nematic liquid crystal as a color display device of a specific color, and a right-handed chiral hand that selectively reflects light having the same wavelength as that of the left-handed chiral nematic liquid crystal It is also one of preferred embodiments of the present invention to use a laminate of a second display device having a composite film using a nematic liquid crystal. By doing so, the reflectance can be increased and a better color display can be performed. In particular, when blue and red, whose relative visibility is lower than that of green, are strongly displayed, the overall color balance is improved. Therefore, such a multilayer structure is effective in a blue display device or a red display device.

  A smectic liquid crystal may be added to the liquid crystal-binder composite film used in the white display device. By adding the smectic liquid crystal, the transparency of the liquid crystal-binder composite film is improved, and the contrast between the colorless and transparent state and the white state can be increased.

  The film thickness of the liquid crystal-binder composite film used for each color display device is not particularly limited, but the film thickness of the liquid crystal-binder composite film used for the white display device is the film of the liquid crystal-binder composite film used for the color display device. It is desirable to make it larger than the thickness.

  Specific examples of the liquid crystal composition exhibiting a cholesteric phase include compounds described in US Pat. No. 5,695,682.

  Other scattering-type liquid crystal compositions used in the present invention include 4-substituted benzoic acid 4'-substituted phenyl esters, 2- (4-substituted phenyl) -5-substituted pyrimidines, 4-substituted cyclohexanecarboxylic acid 4'-substituted. Biphenyl ester, 4- (4-substituted cyclohexyl) benzoic acid 4'-substituted phenyl ester, 4-substituted cyclohexanecarboxylic acid 4'-substituted phenyl ester, 4-substituted biphenyl 4'-substituted cyclohexane, 4- (4-substituted cyclohexane) Carbonyloxy) benzoic acid 4'-substituted phenyl ester, 4- (4-substituted cyclohexyl) benzoic acid 4'-substituted cyclohexyl ester, 4-substituted 4 "-substituted terphenyl, 4-substituted 4'-substituted biphenyl, 4- Substituted phenyl-4'-substituted cyclohexane and the like, and further JP-A-2001-51260 JP-A-8-43846, JP-A-7-4950, JP-A-2000-147476, JP-A-8-160470, JP-A-10-54996, JP-A-2002-221709, JP-A-2001-92383, JP-A-2003-131234, JP-A-2004-77754, JP-A-2004-2771, etc., polymer network liquid crystal (PNLC), polymer-dispersed liquid crystal A liquid crystal composition called (PDLC) can be given.

  In the display element of the present invention, the liquid crystal composition according to the present invention is present in a state dispersed in a binder. For example, after mixing the liquid crystal and the chiral agent according to the present invention, the mixture can be prepared by adding the mixture to a gelatin solution containing a surfactant and dispersing the mixture using a known disperser.

[Surfactant]
Examples of surfactants that can be used for the dispersion include ionic surfactants such as aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, and imidazolinium salts. , Etc.

  Examples of the anionic surfactant include fatty acid soap, N-acyl-N-methylglycine salt, N-acyl-N-methyl-β-alanine salt, N-acyl glutamate, acylated peptide, alkyl sulfonic acid Salt, alkylbenzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl sulfoacetate, α-olefin sulfonate, N-acylmethyl taurine, sulfated oil, higher alcohol sulfate, secondary Higher alcohol sulfate, alkyl ether sulfate, secondary higher alcohol ethoxy sulfate, polyoxyethylene alkylphenyl ether sulfate, monoglyculate, fatty acid alkylolamide sulfate, alkyl ether phosphate, alkyl phosphate D Stealth salt, lignin sulfonate, formalin condensate of naphthalene sulfonate, formalin condensate of alkyl naphthalene sulfonate, formalin condensate of special aromatic sulfonate (eg Mohr C) creosote oil sulfonate Formalin condensate and the like can be mentioned.

  Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate, imidazolinium betaine and the like.

  Nonionic activators include, for example, polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester , Polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, poly Oxyethylene fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide Acetylene glycol, block copolymers with acetylene alcohol, ethylene oxide and propylene oxide, and ethylene oxide adduct of alkylphenol.

  Examples of the dispersing device that can be used include a shearing stirrer, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker.

[Microcapsule]
The liquid crystal composition of the present invention can be used in a state of being encapsulated in microcapsules.

  As a method for producing a microcapsule that can be used in the present invention, a known method such as a coacervation method, an interfacial polymerization method, or an in-situ method can be used. Among these, the production method by the coacervation method can be preferably used with little chemical influence on the liquid crystal composition which is an oil phase.

  When gelatin is used as one of the binders, coacervates can be produced by hydrophobic interaction with gum arabic, sodium alginate, carrageenan, carboxymethylcellulose, agar, polyvinylbenzenesulfonic acid, maleic anhydride copolymer, and other surfactants. Thereafter, by performing a gelatin hardening reaction using formaldehyde or the above-described gelatin hardener, the coacervated gelatin composite film can be hardened, and the strength of the microcapsule wall can be improved.

  The interfacial polymerization method can form a microcapsule wall by polymerizing polyamine, polyhydric phenol and the like with a polybasic acid halide, polyisocyanate and the like at the interface between the aqueous phase and the oil phase.

  As an in-situ polymerization method, microcapsules can be formed by crosslinking amide resin, phenol resin alone or a copolymer thereof used for urea-melamine or the like with formaldehyde or glutaraldehyde.

  For the microcapsule wall, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, polyvinyl alcohol, polyethylene oxide, polypropylene oxide, ethylene-vinyl alcohol copolymer, polyacetal , Acrylic resin, methylcellulose, ethylcellulose, phenolic resin, fluororesin, silicone resin, diene resin, polystyrene-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyphenylene ether, polyphenylene sulfide, Polyethersulfone, polyetherketone, polyarylate, aramid, polyimide, poly- -Microcapsule wall strength is improved by coexisting -phenylene, poly-p-xylene, poly-p-phenylene vinylene, polyhydantoin, polyparabanic acid, polybenzimidazole, polybenzothiazole, polybenzoxadiazole, polyquinoxaline, etc. Can be improved.

  The microcapsules according to the present invention can be dried and classified after being prepared in a solution system. Examples of the classification method include a spray dryer, a rotary dryer, and a band dryer.

〔Antioxidant〕
An antioxidant can be used in the liquid crystal dispersion layer of the present invention as necessary. Antioxidants include phenolic antioxidants, monophenolic antioxidants, polyphenolic and polymeric phenolic compounds, hindered phenolic antioxidants, phosphoric acid antioxidants, sulfur antioxidants, amines System antioxidants, hydroquinone derivatives and the like.

  Of these antioxidants, preferred compounds are phenolic antioxidants and amine antioxidants.

  The usage-amount of a preferable antioxidant is 0.1-100 g with respect to 1 kg of binders, More preferably, it is 1-10 g.

[Natural polymer polysaccharides derived from red algae]
The display element of this invention can contain the natural high molecular polysaccharide derived from red algae in a structural layer.

  The natural high molecular polysaccharides derived from red algae used in the present invention are all polysaccharides extracted and purified from red algae. For details, see “Food Industry” Vol. 31 (1988) p. 21. Are listed. Specific examples of natural polymeric polysaccharides derived from red algae include gellan gum, agar, κ-carrageenan, λ-carrageenan, ι-carrageenan, and far selelaen. κ-carrageenan, λ-carrageenan, and ι-carrageenan are preferred. Of these, ι-carrageenan and κ-carrageenan are particularly preferable, and ι-carrageenan is most preferable.

  The natural polymer polysaccharide derived from the red algae may be used alone in a single coating solution, or two or more kinds may be used in combination. In particular, when κ-carrageenan is used, it is preferable to use λ-carrageenan from the viewpoint of film physical properties of the display element. In this case, the ratio of κ-carrageenan to λ-carrageenan is in the range of 2: 8 to 9: 1 by mass ratio, preferably 4: 6 to 8: 2, particularly preferably 5: 5 to 7: 3. It is.

  Gellan gum is a polysaccharide composed of glucose, glucuronic acid and rhamnose sugar. Available types include gellan gum K9A50, a food and industrial product kelcogel, microbial medium, plant tissue culture and confectionery. Gellan gum GELLITE is known.

  The concentration of these natural polymer polysaccharides in the coating solution is generally 0.02 to 5%, preferably 0.05 to 2%, particularly preferably 0.1 to 1%. This preferred range varies depending on the type and concentration of gelatin and other water-soluble polymers in the coating solution to be used and is not unambiguous, but the coating solution is a natural polymer substantially derived from gelatin and red algae. In the case where only the polysaccharide is used as a binder, the range is preferably used when the gelatin concentration is usually 1 to 6%.

  The binder according to the present invention includes xanthan gum, konjac mannan, locust bean gum, guar gum, pectin, gum arabic, tamarind gum, sodium alginate, karaya gum, tragacanth gum, farcel, in addition to natural high molecular polysaccharides derived from red algae. Thickening polysaccharides such as orchid and pullulan can be used together.

[High-boiling organic solvent]
The display element of the present invention can contain a high-boiling organic solvent in the constituent layers.

  The high-boiling organic solvent used in the display element of the present invention can be any organic solvent as long as the boiling point is an organic solvent having a boiling point of 80 ° C. or higher, but is preferably a hydrophobic high-boiling organic solvent. Examples of high boiling point organic solvents include chlorinated paraffin, liquid paraffin, tricresyl phosphate, dibutyl phthalate, dioctyl phthalate, tri (2-ethyl-hexyloxy) phosphate, diethyl-lauroylamide, dinonylphenol, etc. For example, there can be mentioned exemplified compounds described in JP-A Nos. 1-196048, 1-209446 and JP-A-62-253943. Of these, the compounds preferably used are paraffinic compounds.

  In the present invention, the high-boiling organic solvent is preferably contained in the binder of the display element by forming a dispersion using a known oil-in-water dispersion method together with the binder and the surfactant.

[Antidepressant]
In the display element of the present invention, an antifungal agent can be used in the constituent layer for the purpose of preventing deterioration of the binder contained in the constituent layer due to flaws at high temperature and high humidity and improving the durability of the display element.

  Specific examples of antifungal agents include thiazolylbenzimidazole compounds, isothiazolone compounds, chlorophenol compounds, bromophenol compounds, thiocyanic acid and isothiocyanic acid compounds, acid azide compounds, diazines and triazines. Active halogen compounds such as compounds, thiourea compounds, alkylguanidine compounds, quaternary ammonium salts, organic tin and organic zinc compounds, cyclohexylphenol compounds, imidazole and benzimidazole compounds, sulfamide compounds, and chlorinated isocyanurate sodium There are various antibacterial agents and antifungal agents such as chelating agents, sulfite compounds, and antibiotics represented by penicillin. In addition, other L. E. West, “Water Quality Criteria”, Photo. Sci. and Eng. , Vol. 9, no. 6 (1965); various antifungal agents described in JP-A-57-8542, 58-105145, 59-126533, 55-111942, and 57-157244; Use of compounds such as those described in “History of antibacterial and antifungal” by Hiroshi Horiguchi, Sankyo Publishing (Sho 57), “Handbook of Antibacterial and Antifungal Technology”, Japanese Society of Antibacterial and Antifungal Society, Gihodo (Akira 61) Can do.

  The addition amount of the antifungal agent is about 0.1 to 50 mg, preferably 1 to 20 mg per 1 g of binder.

[Black image forming layer]
The display element of the present invention is characterized in that a black image forming layer is provided separately from the liquid crystal dispersion layer according to the present invention described above.

  The position of the black image forming layer suitable for the present invention is preferably positioned on the uppermost layer, that is, the most image viewing side. By disposing the black image forming layer as the uppermost layer, it is possible to perform display with the least deterioration in character quality.

  The black image referred to in the present invention is an image having absorption in substantially the entire wavelength range of visible light, and the visual color tone can include a color tone such as dark blue, dark green, and dark brown.

  A preferred form of the black image forming layer of the present invention is an electrolytic deposition type black image forming layer, and examples thereof include those described in JP-A No. 2004-177756. In the invention, since the color image located at the bottom needs to be seen through, titanium oxide or the like is not necessary as a filler.

  Another preferable form of the black image forming layer is an electrophoretic type or a powder transfer type image forming layer. For example, electrochromic described in JP-A-2002-328401 Although an example by the method can be given, in this case as well, since the color image located at the bottom needs to be seen through, titanium oxide or the like as a filler is unnecessary.

  The black image forming layer according to the present invention is preferably a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder. Examples of the chiral nematic liquid crystal and the binder that can be applied to the black image forming layer according to the present invention include the same compounds as the above-described chiral nematic liquid crystal and the binder, and, if necessary, the aforementioned additives ( Antioxidants and the like) can be appropriately selected and used.

  Another preferred embodiment of the black image forming layer according to the present invention is a liquid crystal dispersion layer in which a cholesteric liquid crystal in which a black dichroic dye is dispersed or dissolved is dispersed in a binder. As the black dichroic dye dispersed or dissolved in the cholesteric liquid crystal, an anthraquinone type or azo type which is a dichroic dye well mixed with the liquid crystal can be mixed and more preferably used alone. What shows sex is good. Examples of such a dye include Black-1, Black-2, Black-3, Black-4, Black-5, and Black-6 manufactured by Mitsubishi Chemical Corporation.

(White image forming layer)
The display element of the present invention is characterized in that a white image-forming layer is provided together with the liquid crystal dispersion layer and the black image forming layer according to the present invention described above.

  The preferred position of the white image forming layer in the present invention is to place it adjacent to the lower part of the black image forming layer described above when viewed from the image viewing side, so that the display with the least deterioration in character quality can be performed. From the viewpoint of being able to.

  The white image-forming layer according to the present invention is preferably a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder. Examples of the chiral nematic liquid crystal and binder that can be applied to the white image forming layer according to the present invention include the same compounds as the above-described chiral nematic liquid crystal and binder, but particularly from the viewpoint of suitably forming a white image. By setting the selective reflection wavelength of the chiral nematic liquid crystal in the infrared region, it is preferable from the viewpoint of showing a white state in the focal conic state and being transparent in the planar state. Moreover, each above-mentioned additive (antioxidant etc.) can be suitably selected and used as needed.

  Next, other components of the display element of the present invention will be described.

[Support]
Examples of the support that can be used in the present invention include polyolefins such as polyethylene and polypropylene, polycarbonates, cellulose acetate, polyethylene terephthalate, polyethylene dinaphthalene dicarboxylate, polyethylene naphthalates, polyvinyl chloride, polyimide, and polyvinyl. Synthetic plastic films such as acetals and polystyrene can also be preferably used. Syndiotactic polystyrenes are also preferred. These can be obtained, for example, by the methods described in JP-A Nos. 62-117708, 1-46912 and 1-178505. Further, as a support in JP-A-62-253195 (pages 29 to 31), which is provided with a metal base such as stainless steel, a paper support such as baryta paper and resin coated paper, and a reflection layer on the plastic film. What has been described. RDNo. 17643, page 28, ibid. No. 18716, page 647, right column to page 648, left column, and No. 307105, page 879 can also be preferably used. As these supports, those having resistance to curling due to heat treatment of Tg or less as in US Pat. No. 4,141,735 can be used. Further, the surface of these supports may be subjected to surface treatment for the purpose of improving the adhesion between the support and other constituent layers. In the present invention, glow discharge treatment, ultraviolet irradiation treatment, corona treatment, and flame treatment can be used as the surface treatment. Furthermore, the support body described in pages 44 to 149 of publicly known technology No. 5 (issued by Aztec Co., Ltd. on March 22, 1991) can also be used. Furthermore, RDNo. 308119, page 1009, Product Licensing Index, Volume 92, P108, “Supports”, and the like. In addition, a glass substrate or an epoxy resin kneaded with glass can be used.

(Light absorption layer)
The light absorption layer essential for the chiral nematic liquid crystal display element may be used together with the black image forming layer of the present invention or may not be provided.

  The light absorbing layer may be any method, for example, applying a metallic reflector, a scattering plate, a colored paint on the substrate, or providing a binder constituent layer containing a colored material such as a pigment or dye. In the present invention, by providing, for example, a layer in which carbon black or the like is dispersed in an adjacent layer close to the liquid crystal layer, good black display with higher light absorption efficiency can be performed. Moreover, when using the resin substrate with a transparent electrode for a counter electrode, a light absorption layer can be provided in the surface on the opposite side to the liquid crystal layer of a board | substrate. The color of light to be absorbed may be black for black display, or may be a filter color that compensates for the reflected color of the liquid crystal.

[Transparent electrode]
In the present invention, it is preferable to use a transparent electrode for at least one of the pair of electrodes. The transparent electrode is not particularly limited as long as it is transparent and can conduct electricity. For example, Indium Tin Oxide (ITO: Indium Tin Oxide), Indium Zinc Oxide (IZO: Indium Zinc Oxide), Tin Oxide (FTO) ), Indium oxide, zinc oxide, platinum, gold, silver, rhodium, copper, chromium, carbon, aluminum, silicon, amorphous silicon, magnesium, BSO (Bismuth Silicon Oxide), or a mixture thereof. In the mixture, for example, an ITO layer having a thickness of about 50 nm and a silver layer having a thickness of about 50 nm may have a laminated structure.

  Further, a conductive polymer such as a polythiophene-based, polypyrrole-based, polyaniline-based, polyacetylene-based, polyparaphenylene-based, polyselenophenylene-based polymer, or a mixture thereof can be used as the transparent electrode.

  Further, a transparent electrode is produced by applying a liquid in which ITO fine powder fired at 350 ° C. to 800 ° C. is dispersed in a solution containing a solvent or a polymer material to a substrate and volatilizing the solvent or curing the polymer. It is also possible. In this case, the solidification temperature after coating is preferably 40 ° C. or higher and 200 ° C. or lower. ITO fine powder, for example, by mixing tin chloride aqueous solution and indium chloride aqueous solution, adding ammonia etc. to cause coprecipitation reaction while keeping pH at 9, fractionate and wash the resulting hydroxide precipitate Thus, it can be produced by baking at 500 ° C. for 2 hours. By changing the mixing ratio of tin chloride and indium chloride, a fine powder having an arbitrary mixing ratio can be formed. The shape of the fine powder may be any of a granular shape, a needle shape, a plate shape, and a flake shape, and a mixture of a needle shape and a granular shape may be used.

  In addition, a coating liquid in which about 10% of organic indium and organic tin are mixed in a xylol at a mass ratio of 97: 3 is applied on the substrate, and the solvent is volatilized and baked at 100 ° C. or higher and 150 ° C. or lower. A solidifying method can also be preferably used.

  For the purpose of improving the mechanical strength of the electrode, a polymer compound such as a compound species capable of forming a polyurethane resin containing blocked isocyanate or a compound species capable of forming an epoxy resin may be mixed in the coating solution.

  The surface resistance value of the transparent electrode is preferably 500Ω / □ or less, particularly preferably 300Ω / □ or less. The film thickness is preferably 0.2 μm or more and 50 μm or less.

[Production method of electrode]
In order to form a transparent electrode and a metal electrode, a known method can be used. For example, mask deposition may be performed on the substrate by sputtering or the like, or patterning may be performed by photolithography after the entire surface is formed. Electrodes can also be formed by electrolytic plating, electroless plating, printing methods, and ink jet methods.

  After forming an electrode pattern including a catalyst layer having a monomer polymerization ability on a substrate using an inkjet method, a monomer component that is polymerized by the catalyst and becomes a conductive polymer layer after polymerization is added, It is also possible to form a metal electrode pattern by polymerizing and further performing metal plating such as silver on the conductive polymer layer, and the process is greatly reduced because no photoresist or mask pattern is used. It can be simplified.

  When the electrode material is formed by coating, known methods such as a dipping method, a spinner method, a spray method, a roll coater method, a flexographic printing method, and a screen printing method can be used.

[Electrostatic inkjet method]
In the display element of the present invention, at least one of the pair of electrodes has a liquid discharge head having a nozzle with an internal diameter of 30 μm or less for discharging a charged liquid, and a supply means for supplying a solution into the nozzle And a liquid discharge apparatus including discharge voltage applying means for applying a discharge voltage to the solution in the nozzle.

  Furthermore, it is preferable that the solution in the nozzle is formed using a discharge device provided with a convex meniscus forming means for forming a state where the solution rises in a convex shape from the nozzle tip.

  In addition, an operation control unit that controls application of a drive voltage for driving the convex meniscus forming unit and application of a discharge voltage by the discharge voltage application unit is provided, and the operation control unit applies the discharge voltage by the discharge voltage application unit. It is also preferable to use a liquid ejection apparatus having a first ejection control unit that applies a driving voltage to the convex meniscus forming means when ejecting liquid droplets while performing the above.

  In addition, an operation control unit that controls driving of the convex meniscus forming unit and voltage application by the discharge voltage applying unit is provided, and the operation control unit is configured to swell the solution by the convex meniscus forming unit and apply the discharge voltage. And a second discharge control unit that performs the operation in synchronization with the liquid discharge device. It is also a preferred form to use a liquid ejection apparatus having a liquid level stabilization control unit that performs operation control for drawing the liquid level inward.

  By producing an electrode pattern using such an electrostatic inkjet, it is advantageous that an electrode having excellent on-demand characteristics, little waste material, and excellent dimensional accuracy can be obtained.

[Display element drive method]
In the display element of the present invention, it is preferable that the driving operation of the counter electrode described above is simple matrix driving.

  The simple matrix driving in the present invention is a driving method in which a current is sequentially applied to a circuit in which a positive line including a plurality of positive electrodes and a negative electrode line including a plurality of negative electrodes are opposed to each other in a vertical direction. Say that. By using simple matrix driving, there is an advantage that the circuit configuration and driving IC can be simplified and manufactured at low cost.

  The display element of the present invention may use active matrix driving. The active matrix drive is a system in which scanning lines, data lines, and current supply lines are formed in a grid pattern, and are driven by TFT circuits provided in each grid pattern. Since switching can be performed for each pixel, there are advantages such as gradation and memory function.

  In order to drive the display element of the present invention, for example, the driving circuit and driving described in JP-A Nos. 2003-5222, 2003-228045, 2002-14323, 2003-29301, and 2002-287175 Waveforms can be used.

  The display element of the present invention preferably has a configuration in which a liquid crystal layer containing a binder and a liquid crystal composition dispersed in the binder is disposed between a pair of counter electrodes.

[Black image data]
In the present invention, since there is a black image forming layer, it is necessary to put black image data in the output data, but this can be done by a known method.

[White image data]
In the present invention, since there is a white image forming layer, it is necessary to put white image data into the output data, but this can be done by a known method.

[Application field of the display element of the present invention]
The display element of the present invention can be used in ID card related fields, public related fields, transportation related fields, broadcasting related fields, payment related fields, distribution logistics related fields, and the like. Specifically, keys for doors, student ID cards, employee ID cards, various membership cards, convenience store cards, department store cards, vending machine cards, gas station cards, subway and railway cards, bus cards, Examples include cash cards, credit cards, highway cards, driver's licenses, hospital examination cards, health insurance cards, Basic Resident Registers, passports, electronic book terminals, document viewers, signboards and bulletin boards.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of Display Element 1: Present Invention >>
[Preparation of Black Image Forming Layer Unit 1]
(Preparation of transparent electrode 1)
An indium tin oxide (hereinafter abbreviated as ITO) film having a pitch of 145 μm and an electrode width of 130 μm was formed on a glass substrate having a thickness of 1.5 mm according to a known method, whereby a transparent electrode 1 was obtained.

(Formation of black image forming layer 1)
To the following electrolyte solution, polyacrylic spherical beads having an average particle diameter of 20 μm are added and stirred so that the volume fraction becomes 10%, and this solution is applied onto the transparent electrode 1 produced above, The other transparent electrode 1 is stacked so that the electrode side is in contact with the electrolyte solution, pressed with a pressure of 9.8 kPa, and the periphery is sealed with an olefin-based sealant to form a black image forming layer 1. A black image forming layer unit 1 was prepared.

<Preparation of electrolyte solution>
In 2.5 g of dimethyl sulfoxide, 90 mg of sodium iodide and 75 mg of silver iodide were added and completely dissolved, and then 150 mg of polyethylene glycol (average molecular weight 500,000) was added and stirred for 1 hour while heating to 120 ° C. An electrolyte solution was obtained.

[Preparation of Liquid Crystal Dispersion Layer and White Image Forming Layer Unit 1]
(Preparation of chiral nematic liquid crystal composition)
<Preparation of liquid crystal composition 1>
Nematic liquid crystal BL012 (manufactured by Merck & Co.) exhibiting positive dielectric anisotropy 60.0% by mass, right-handed chiral agent CB15 (manufactured by Merck & Co.) 20.0% by weight, right-handed chiral agent CE2 (Merck) 20.0% by mass was sufficiently mixed to prepare a dextrorotatory green light reflective liquid crystal composition 1.

<Preparation of liquid crystal composition 2>
Nematic liquid crystal BL011 (manufactured by Merck) showing positive dielectric anisotropy as well as 35.4% by mass of nematic liquid crystal E44 (manufactured by Merck) showing positive dielectric anisotropy of 35.4% by mass, dextrorotatory property 49.5% by mass of the chiral agent CB15 (manufactured by Merck & Co., Inc.) was sufficiently mixed to obtain a dextrorotatory blue light reflective liquid crystal composition 2.

<Preparation of liquid crystal composition 3>
Nematic liquid crystal BL012 (manufactured by Merck) having a positive dielectric anisotropy 69.0% by mass, right-handed chiral agent CB15 (manufactured by Merck) 15.5% by weight, right-handed chiral agent CE2 (Merck) 15.5% by mass was sufficiently mixed to obtain a dextrorotatory red light reflective liquid crystal composition 3.

<Liquid crystal composition 4: Preparation of liquid crystal composition for white image forming layer>
Nematic liquid crystal E44 (manufactured by Merck & Co., Inc.) 87% by mass and dextrorotatory chiral agent S-811 (manufactured by Merck & Co., Ltd.) 13% by mass are mixed, and an infrared reflective liquid crystal having a selective reflection wavelength of 1.5 μm. Composition 4 was prepared.

(Preparation of liquid crystal layer coating solution)
<Preparation of liquid crystal layer coating solution 1>
8% by weight of photographic gelatin was added to ion-exchanged water, stirred at room temperature, allowed to stand for 30 minutes to sufficiently swell the gelatin, and then the temperature was raised to 42 ° C. to completely dissolve the gelatin. Next, an isopropyl alcohol solution containing 10% by mass of alkanol XC (alkylnaphthalenesulfonic acid) as a surfactant is added to this gelatin solution in an amount corresponding to 12% by mass with respect to the water component of the gelatin solution, and then the liquid crystal composition prepared above. Product 1 was added at 12% by weight with respect to the water of the gelatin solution. While this mixed solution was kept at 42 ° C., it was stirred with a comb-type disperser to obtain a liquid crystal layer coating solution 1 containing a liquid crystal dispersion having an average liquid crystal dispersion particle diameter of 5 μm.

<Preparation of liquid crystal layer coating liquids 2 to 4>
In the preparation of the liquid crystal layer coating liquid 1, liquid crystal layer coating liquids 2 to 4 were prepared in the same manner except that the liquid crystal compositions 2 to 4 prepared above were used in place of the liquid crystal composition 1.

(Formation of liquid crystal layer)
<Preparation of transparent electrode 2>
An ITO film was formed on the entire surface of polyethylene terephthalate having a thickness of 100 μm by a known sputtering method, and then a transparent electrode 2 having an electrode pattern with a pitch of 145 μm and an electrode width of 130 μm was produced using a photolithographic method.

<Preparation of transparent electrode 3>
A transparent electrode 3 having an electrode pattern with a pitch of 145 μm and an electrode width of 130 μm was obtained on both sides of 100 μm thick polyethylene terephthalate in the same manner as the transparent electrode 2.

<Formation of liquid crystal layer>
The liquid crystal layer coating solution 1 was applied on the transparent electrode 2 produced above, and then the transparent electrode 3 was overlaid on the liquid crystal layer, cooled and dried. Next, the liquid crystal layer coating liquid 2 was applied on the other electrode of the transparent electrode 3, and the transparent electrode 3 was similarly stacked, cooled and dried. Next, a liquid crystal layer coating solution 3 was further applied thereon, and the transparent electrode 3 was stacked, cooled and dried. Next, after the liquid crystal coating liquid 4 which is a white display liquid crystal layer is applied thereon and cooled, the electrode surface of the transparent electrode 2 is overlaid and cooled so as to be in contact with the liquid crystal layer coating liquid, and dried to obtain a liquid crystal dispersion layer. And the white image formation layer unit 1 was produced.

[Production of display element]
After the black image forming layer 1 surface of the black image forming layer unit 1 produced above and the electrode surface of the transparent electrode 2 of the liquid crystal dispersion layer and the white image forming layer unit are overlapped, polyethylene composed of glass and the transparent electrode 2 A display element 1 was prepared by bonding a terephthalate film.

<< Preparation of Display Element 2: Present Invention >>
[Preparation of black image forming layer unit 2]
(Production of substrate 1)
Antimony-doped tin oxide fine particles (average particle size 0.5 μm) were dispersed in a 0.5% isopropanol solution of indium (III) isopropoxide, and the surface resistance was 10 Ω / cm ² by spin coating. It apply | coated on the glass substrate with an ITO thin film. Subsequently, the porous electrode with a film thickness of 3 micrometers was formed on the ITO film | membrane by heat-processing at 100 degreeC for 1 hour. A coating film of tungsten oxide was formed on the porous electrode by a sputtering method, and a tungsten oxide layer having a thickness of 100 nm was provided on the electrode surface.

(Production of substrate 2)
Similarly to the substrate 1, an iridium oxide layer having a thickness of 100 nm was formed by sputtering on a glass substrate with an ITO thin film on which a porous electrode was formed.

(Formation of black image display layer 2)
To a 20% by mass ethanol solution of Neocepta SA-2 (ion conductive polymer) manufactured by Tokutama Co., Ltd., 0.1% by mass polymethyl methacrylate particles (particle size 5 μm, spherical) were mixed and dispersed. This solution is applied to the surfaces of the substrate 1 and the substrate 2 so as to have a dry film thickness of 5 μm, heated at 90 ° C. for 3 minutes, and then the substrate 1 and the substrate 2 are bonded and sealed to form the black image forming layer 2. A black image forming layer unit 2 was prepared.

[Production of display element]
A liquid crystal dispersion layer and a white image forming layer unit 1 similar to those of the display element 1 were used, and the produced black image forming layer unit 2 was bonded thereto to produce a display element 2.

<< Preparation of Display Element 3: Present Invention >>
[Preparation of Black Image Forming Layer Unit 3]
A black dichroic dye Black-4 (manufactured by Mitsubishi Chemical Corporation) is added to and mixed with 86.0% by mass of the liquid crystal composition 2 used for the production of the display element 1, and is described in the display element 1. In the same manner as in the preparation of the liquid crystal layer coating liquid, a liquid crystal layer coating liquid 5 for a black image forming layer was obtained.

[Production of display element]
Similarly to the production of the display element 1, the liquid crystal layer 1, the transparent electrode 3, the liquid crystal layer 2, the transparent electrode 3, and the liquid crystal layer 3 are stacked on the transparent electrode 2, and the transparent electrode 3 is stacked before the liquid crystal layer 3 is dried. Then, the liquid crystal layer 3 is cooled and dried. Further, after the liquid crystal layer 4 which is a white image forming layer is applied and cooled, the transparent electrode 3 is overlaid and dried, the liquid crystal layer coating liquid 5 for the black image forming layer is applied on the transparent electrode, and the transparent electrode 2 is applied. The electrodes were stacked so that the electrode surface was in close contact with the black image forming layer, dried after cooling, and the display element 3 was obtained.

<< Preparation of Display Element 4: Present Invention >>
(Preparation of liquid crystal composition)
(Preparation of liquid crystal composition 5)
Nematic liquid crystal E48 (manufactured by Merck & Co., Inc.) 53 mass% and dextrorotatory chiral material CB15 (manufactured by Merck & Co., Inc.) 47 mass% were sufficiently mixed to prepare liquid crystal composition 5 having a selective reflection color of cyan.

(Preparation of liquid crystal composition 6)
Nematic liquid crystal E48 (manufactured by Merck & Co., Inc.) 50 mass% and dextrorotatory chiral material CB15 (manufactured by Merck & Co., Inc.) 50 mass% were sufficiently mixed to prepare liquid crystal composition 6 having a selective reflection color of reddish purple.

(Preparation of liquid crystal composition 7)
70% by mass of nematic liquid crystal E48 (manufactured by Merck) and 30% by mass of dextrorotatory chiral material CB15 (manufactured by Merck) were sufficiently mixed to prepare a liquid crystal composition 7 having a selective reflection color of red.

(Preparation of liquid crystal composition 8)
Nematic liquid crystal E44 (manufactured by Merck) having positive dielectric anisotropy and BL011 (manufactured by Merck) were 44.05% by mass and 19.05% by mass, respectively, and a right-rotating chiral agent CB15 (manufactured by Merck) 36.5% by mass was sufficiently mixed to obtain a liquid crystal composition 8 having yellow selective reflection.

[Preparation of liquid crystal dispersion]
In the same manner as the preparation of the liquid crystal layer coating liquid used in the production of the display element 1, liquid crystal layer coating liquids 6 to 9 were prepared using the liquid crystal compositions 5 to 8 prepared above.

[Production of display element]
The liquid crystal layer coating solution 5 for the black image forming layer used in the production of the display element 3 is applied on the transparent electrode 2 using a wire bar, cooled and dried, and then the transparent electrode 3 is overlaid thereon. Furthermore, the liquid crystal layer coating liquid 4 for the white image forming layer used in the production of the display element 1 was applied on the electrode on the opposite surface of the transparent electrode 3, cooled, and the transparent electrode 3 was stacked and dried. Next, a liquid crystal layer coating liquid 9 (liquid crystal composition 8) was applied thereon, cooled, and the transparent electrode 3 was stacked and dried. Next, a liquid crystal layer coating liquid 8 (liquid crystal composition 7) was applied thereon, cooled, and the transparent electrode 3 was stacked thereon and dried. Next, a liquid crystal layer coating solution 7 (liquid crystal composition 6) is applied and cooled thereon, and then a liquid crystal layer coating solution 8 (liquid crystal composition 7) is laminated thereon, and the transparent electrode 3 is stacked thereon, cooled and dried. It was. Next, a liquid crystal layer coating liquid 6 (liquid crystal composition 5) is applied thereon and cooled to form the liquid crystal layer 6. Then, the transparent electrode 2 is overlaid so that the electrode surface is in contact with the liquid crystal layer 6, and the display element 4 Got.

<< Preparation of Display Element 5: Comparative Example >>
(Preparation of light absorbing layer coating solution)
20% by mass of carbon black was added to a 5% by mass aqueous solution of gelatin and mixed well to obtain a light absorbing layer coating solution.

[Production of display element]
In the same manner as in the production of the display element 1, the liquid crystal layer coating liquid 1 was applied on the transparent electrode 2, and then the transparent electrode 3 was overlaid on the liquid crystal layer, cooled and dried. Next, the liquid crystal layer coating liquid 2 was applied on the other electrode of the transparent electrode 3, and the transparent electrode 3 was similarly stacked, cooled and dried. Next, a liquid crystal layer coating solution 3 was further applied thereon, and the transparent electrode 3 was stacked, cooled and dried. Next, the light absorption layer coating solution was applied and dried thereon to form a light absorption layer. Next, an electrode pattern perpendicular to the electrode pattern of the transparent electrode 3 with a pitch of 145 μm and an electrode width of 130 μm is formed on the light absorbing layer by screen printing using silver paste ink (DW-250H-5 manufactured by Toyobo Co., Ltd.). Thus, a comparative display medium 5 was obtained.

<< Evaluation of display element >>
Each of the manufactured display elements was connected to a drive circuit according to a known method, and each display performance was evaluated according to the following method.

[Evaluation of color reproducibility]
A voltage at which each layer of each display element is in a 100% reflective state is applied, RGBK colors composed of RGBK and their mixed colors are output, and color reproducibility is measured with a CM3700d colorimeter manufactured by Konica Minolta Sensing. . Chromaticity diagram (a ^* , b ^* ) based on CIE1976L ^* a ^* b ^* color space is created by calculation from measurement data, and results obtained for display elements 1 to 4 of the present invention and comparative display element 5 Are shown in FIG. 1 (display element 1) and FIG. 2 (display element 4). However, since the display elements 1 to 3 have almost the same result, the result of the display element 1 is shown in FIG. 1 as a representative.

[Evaluation of fine line reproducibility]
A black thin line and a character pattern with a different number of points were displayed on each display element, and the visibility of the thin line was visually evaluated. The obtained results are shown below.

Display element 1 (present invention): fine line reproducibility was good and 4-point characters could be distinguished Display element 2 (present invention): fine line reproducibility was good and 5-point characters could be distinguished Display element 3 (present invention): fine line reproducibility was good and 5 point characters could be distinguished Display element 4 (present invention): fine line reproducibility was good and 5 point characters could be distinguished Display element 5 (comparative example): Slight blur was observed on the black thin line, and characters of 8 points or less were difficult to distinguish [Black image reproducibility]
A black image is displayed on each display element, and a visual evaluation by a person skilled in printed matter evaluation is performed. The results obtained are shown below.

Display element 1 (present invention): black image is tight and has a very good image Display element 2 (present invention): black image has a slight bluish tone but is tight and has a good black image Display element 3 (invention): Black image is tight and has a good image Display element 4 (invention): Black image has a tightness and is a good image Display element 5 (comparative example) ): The black image is not tightened and the color tone is shifted [Evaluation of contrast ratio]
About each display element, the ratio (white reflectance / black reflectance) of the reflectance in 550 nm of a white state and a black state was measured, and this was made into contrast ratio. The reflectance was measured using a CM3700d colorimeter manufactured by Konica Minolta Sensing. The obtained results are shown below. A higher contrast ratio indicates that a clearer image can be displayed.

<Display element><Contrastratio><Remarks>
Display Element 1 8.5 Present Invention Display Element 2 8.2 Present Invention Display Element 3 7.2 Present Invention Display Element 4 7.0 Present Invention Display Element 5 4.8 Comparative Example As is clear from the above results, chiral The display element of the present invention, which is composed of a liquid crystal dispersion layer in which nematic liquid crystal is dispersed, a black image forming layer, and a white image forming layer, has a wide color reproduction range, excellent black image reproducibility, and a comparative example. It can be seen that it has a high contrast ratio.

It is a figure which shows the chromaticity diagram (a ^* , b ^* ) of the display element 1 of this invention, and the display element 5 of a comparison. It is a figure which shows the chromaticity diagram (a ^* , b ^* ) of the display element 4 of this invention, and the display element 5 of a comparison.

Claims (9)

A display element having a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder, wherein a black image formation layer and a white image formation layer are laminated separately from the liquid crystal dispersion layer. A plurality of liquid crystal dispersion layers in which chiral nematic liquid crystals that selectively reflect a desired wavelength range of visible light are dispersed are laminated in a binder, and each of the liquid crystal dispersion layers has a different wavelength peak and a black image. A display element comprising a forming layer and a white image forming layer. The display element according to claim 1, wherein the black image forming layer is an uppermost layer. The display element according to claim 1, wherein an image forming layer located immediately below the black image forming layer is the white image forming layer. The display element according to claim 1, wherein the black image forming layer is a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder. The display device according to claim 1, wherein the black image forming layer is a layer in which a black dichroic dye is dispersed in a chiral nematic liquid crystal. The display element according to claim 1, wherein the black image forming layer is a field deposition type image forming layer. The display element according to claim 1, wherein the black image forming layer is an electrophoretic type or a powder transfer type image forming layer. The display element according to claim 1, wherein the white image forming layer is a liquid crystal dispersion layer in which chiral nematic liquid crystal is dispersed in a binder.

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