Photo-addressable display medium and photo-addressable display device

A photo-addressable display medium is provided, the photo-addressable display medium including: a pair of electrodes having transparency; a photoconductive layer disposed between the pair of electrodes and having a laminated structure of a first charge generation layer, a charge transport layer and a second charge generation layer in this order from an exposing light irradiation side; and a liquid crystal layer disposed between an electrode of the inverse side to the exposing light irradiation side and the second charge generation layer and having memory performance, wherein the first charge generation layer and the second charge generation layer contain a phthalocyanine compound, and the charge transport layer contains a stilbene compound represented by the following formula (1):wherein, R1 to R4 each independently represents a hydrogen atom, a methyl group or an ethyl group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2009-195960 filed Aug. 26, 2009.

BACKGROUND

1. Technical Field

The present invention relates to a photo-addressable display medium and a photo-addressable display device.

2. Related Art

As conventional photo-addressable display media and photo-addressable display devices, for example, there are photo-addressable display media formed by combining a photoconductive element that switches a functional element driven by an alternating electric field or alternating current, which results from stacking sequentially at least an electrode layer, a lower part charge generation layer, a charge transport layer and an upper part charge generation layer, with a functional element (a display element) on a substrate and photo-addressable display devices and the like.

SUMMARY

According to an aspect of the present invention, there is provided a photo-addressable display medium, including:

a pair of electrodes having transparency;

a photoconductive layer disposed between the pair of electrodes, the photoconductive layer having a laminated structure of a first charge generation layer, a charge transport layer and a second charge generation layer in this order from an exposing light irradiation side; and

a liquid crystal layer disposed between an electrode of an inverse side to the exposing light irradiation side out of the pair of electrodes and the second charge generation layer, the liquid crystal layer having memory performance,

wherein the first charge generation layer and the second charge generation layer contain a phthalocyanine compound, and

the charge transport layer contains a stilbene compound represented by following formula (1):

wherein, R1to R4each independently represents a hydrogen atom, a methyl group or an ethyl group.

DETAILED DESCRIPTION

Constitution of Photo-Addressable Display Medium:

FIG. 1is an outline view showing a constitutional example of a photo-addressable display medium according to an exemplary embodiment of the present invention.

A photo-addressable display medium100according to an exemplary embodiment of the invention is constituted by having, for example in order from a light irradiation side, a light irradiation side substrate1, an electrode2, a photoconductive layer3(a lower part charge generation layer3C/a charge transport layer3B/an upper part charge generation layer3A), an internal light absorption layer5, an adhesion layer6, a liquid crystal layer7, an electrode8, and a display side substrate9. The lower part charge generation layer3C corresponds to a first charge generation layer, and the upper part charge generation layer3A corresponds to a second charge generation layer. An isolation layer having translucency (not shown) may be set for purpose of increasing adhesiveness, quality of layer or electric property, in some case. The isolation layer may be arranged, for example, between an upper part charge generation layer and a light absorption layer. Depending on a material or a formation method to be used, the isolation layer may be arranged between the photoconductive layer3and the internal light absorption layer5, in order to prevent the photoconductive layer3from being damaged. In addition, an external light absorption layer10may be arranged on the light irradiation side of the light irradiation side substrate1, in order to absorb external light that is unnecessary and gives damage to the medium.

Hereinafter, the constitution of respective sections of the photo-addressable display medium100will be described. Meanwhile, “light irradiation” means “irradiation of light for writing” unless otherwise noted.

Light Irradiation Side Substrate1, Display Side Substrate9:

The light irradiation side substrate1and the display side substrate9hold respective layers between the substrates, to maintain the structure of the display medium100. The substrates1and9are not necessarily to be provided, but are desirably provided for maintaining the form or protecting the surface of the display medium100.

The light irradiation side substrate1is constituted of an optically transparent material through which exposing light may transmit. Specifically, a substrate constituted of glass, ceramic, triacetylcellulose, polyethylene terephthalate (PET), polycarbonate (PC), polyethylene, polystyrene, polyimide, polyether sulfone (PES), or the like is used. From the standpoint of flexible properties, forming simplicity, cost and the like, the use of a sheet or a film constituted of PET or the like is desirable.

The display side substrate9is constituted of the same material as that of the light irradiation side substrate1, but the use of glass, PET or the like having transparency that allows light in a visible region to transmit substantially (transmittance of 80% or more) so as not to hinder the display.

As the thickness of the substrates1and9, the range from 50 μm to 500 μm is favorable.

Electrodes2and8are members for applying voltage to be applied via feeding terminals (not shown) to respective layers provided between electrodes2and8, and are constituted from a material having an electroconductive property.

The electrode2is constituted from an optically transparent material that allows exposing light to transmit. For example, metallic thin films of gold (Au), Aluminum (Al), copper (Cu) or the like; electroconductive metal oxides such as indium tin oxide (ITO), tin oxide (SnO2) or zinc oxide (ZnO); or thin films of translucent electric conductor such as electroconductive polymer (e.g. polypyrrole) is used, and the use of an ITO film is desirable.

The electrode8is constituted from the same material as that for the transparent electrode3, and the use of an ITO film is desirable, which has transparency that allows light invisible region to transmit so as not to hinder the display.

No particular limitation is imposed on the thickness of these electrodes2and8, but thickness in the range from 10 nm to 10 μm is favorable. These electrodes2and8may be formed on the substrates1and9by evaporation, sputtering, or the like.

The photoconductive layer3is arranged between the electrode2and the electrode8, and has a structure obtained by laminating the lower part charge generation layer3C, the charge transport layer3B, and the upper part charge generation layer3A in order from the exposing light irradiation side. As the photoconductive layer3, it is sufficient only when the charge transport layer is placed between charge generation layers, and a photoconductive structure having such laminated structure as a charge generation layer/a charge transport layer/a charge generation layer/a charge transport layer/a charge generation layer is also possible.

The photoconductive layer3changes impedance properties in accordance with the irradiation intensity of the exposing light, and shows the distribution of electric properties in accordance with the distribution of the irradiation intensity of the exposing light. That is, the photoconductive layer3has sensitivity for light in the wavelength region of the exposing light and absorbs light in the wavelength region to show the distribution of electric properties in accordance with the distribution of the irradiation intensity of the exposing light.

The upper part charge generation layer3A and the lower part charge generation layer3C have function of absorbing the exposing light to generate charges, and contain phthalocyanine compound as a charge generation material.

In the charge generation layers3A and3C, the phthalocyanine compound may be used alone or in mixture.

For the upper part charge generation layer3A and the lower part charge generation layer3C, the same degree of carriers and free electrons are necessary to be generated. Therefore, they needs to have the same degree of sensitivity for wavelength, light amount and voltage, and the same material is desirably used for the upper and lower layers, but different materials may be used when they have comparable sensitivities.

As a method for forming the charge generation layers3A and3C, in addition to dry film-forming methods such as a vacuum evaporation method, a sputtering method, an ion plating method or a CVD method, wet film-forming methods, such as a spin coat method, a dip method, a bar coat method, a roll coat method, a casting method, a blade coating method or a spray coating method using a solution or a dispersion liquid containing a charge generation material and binder resin, are applicable. When using the solution or the dispersion liquid, the concentration of the charge generation material in the liquid is desirably from 1% by mass to 20% by mass, more desirably from 1.5% by mass to 5% by mass.

As the binder resin for use in the charge generation layer, for example, polycarbonate resin, polyvinyl butyral resin, polyallylate resin, polyethylene resin, polyester resin, phenoxy resin, vinyl chloride-vinyl acetate resin, carboxyl-modified vinyl chloride-vinyl acetate copolymer, polyamide resin (including nylon resin), acrylic resin, polyacrylamide resin, polyvinylpyridine resin, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol resin, polyvinyl pyrrolidone resin, or the like may be used. Here, since carboxyl-modified vinyl chloride-vinyl acetate copolymer is soluble in keto-alcohol, and favorably disperses hydroxygallium phthalocyanine or the like being a charge generation material, it is a desirable binder resin. These may be used alone, or in two or more kinds in combination.

Examples of solvents usable for the solution or the dispersion liquid include alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol or benzyl alcohol, ketones such as acetone, methyl ethyl ketone or cyclohexanone, cyclopentanone, amides such as dimethylformamide or dimethylacetamide, sulfoxides such as dimethylsulfoxide, cyclic or chain ethers such as tetrahydrofuran, dioxane, diethyl ether, methyl cellosolve or ethyl cellosolve, esters such as methyl acetate, ethyl acetate or n-butyl acetate, aliphatic halogenated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride, chloroethylene or trichloroethylene, mineral oil such as ligroin, aromatic hydrocarbons such as benzene, toluene or xylene, and aromatic halogenated hydrocarbons such as chlorobenzene or dichlorobenzene.

The mixing ratio of the charge generation material and the binder resin (charge generation material/binder resin) in the charge generation layers3A and3C is desirably in the range from 1/10 to 20/1, more desirably in the range from 1/1 to 10/1.

The thickness of the charge generation layers3A and3C is desirably from 10 nm to 1 μm, more desirably from 20 nm to 500 nm. When the thickness is smaller than 10 nm, photosensitivity is insufficient and production of a uniform film becomes difficult, and when it is larger than 1 μm, the photosensitivity is saturated and peeling tends to occur due to intra-film stress.

The charge transport layer3B has such function that charges generated in the upper part charge generation layer3A or the lower part charge generation layer3C are injected and drift in the direction of an applied electric field, and contains a stilbene compound shown by the following Formula (1) as a charge transport material.

Desirably it contains a stilbene compound shown by the following Formula (2), and more desirably it contains at least one kind of stilbene compound selected from stilbene compounds shown by the following structural formula (III-1), (III-2) or (III-3), from the standpoint that the effect of the invention is more remarkably exerted.

structural formula (III-1)

structural formula (III-2)

structural formula (III-3)

For the charge transport layer3B, the above-described stilbene compound may be used alone or in mixture.

As a method for forming the charge transport layer3B, the same method as that for forming the charge generation layers3A and3C described above may be applied. When using a solution or a dispersion liquid containing the charge transport material and the binder resin, the concentration of the charge transport material in the liquid is desirably from 5% by mass to 50% by mass, more preferably from 10% by mass to 20% by mass.

As a binder resin for use in the charge transport layer, the same one as the binder resin that is used for the charge transport layer as described above may be used, but polycarbonate resin is desirable from the standpoint of charge transport properties, strength, flexibility and transparency.

Examples of the solvent usable for the solution or the dispersion liquid include aforementioned ketones, cyclic or chain ethers, aliphatic halogenated hydrocarbons, aromatic hydrocarbons, aromatic halogenated hydrocarbons and the like.

The mixing ratio of the charge transport material and the binder resin in the charge transport layer3B (the charge transport material/binder resin) is desirably in the range from 1/10 to 10/1, more desirably from 3/7 to 7/3.

The thickness of the charge transport layer3B is desirably from 1 μm to 100 μm, more desirably from 1 μm to 50 μm, furthermore preferably from 3 μm to 20 μm. When it is less than 1 μm, voltage endurance lowers and the securement of the reliability becomes difficult, and when it is more than 100 μm, the impedance matching with a functional element becomes difficult and occasionally the design becomes difficult.

Between the photoconductive layer3and the liquid crystal layer7, any functional layer may be provided. For example, an isolation layer, an internal light absorption layer5, and an adhesion layer6described below may be provided respectively. Alternatively, a functional layer having these plural functions at the same time may be provided. Such functional layer may be applied in a range that does not considerably hinder the flow of electric current. The order of the isolation layer, the internal light absorption layer5, and the adhesion layer6may be changed, but the isolation layer desirably lies adjacent to the photoconductive layer3.

Depending on the material or formation method of the internal light absorption layer5or the adhesion layer6, the photoconductive layer3is occasionally damaged, and the isolation layer is provided to prevent this phenomenon.

As the material for the isolation layer, a water-soluble resin, a water/organic solvent soluble resin, an aqueous emulsion, dispersion or latex, or the like is utilized. The isolation layer has such a purpose, for example, as preventing the diffusion of a low molecular nonaqueous component or an organic solvent contained in an adhesive of the adhesion layer6, and, therefore, a water-soluble resin that is hardly swollen by an organic solvent is most desirable.

As the water-soluble resin, in addition to polyvinyl alcohol, alkyl celluloses such as methyl cellulose or ethyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, polyethylene imine, polyacrylic acid, polyacrylic acid, polyacrylic acid esters such as polyacrylic acid salt or polyacrylamide, polyethylene oxide, polyvinyl pyrrolidone, starch, casein, glue, gelatin, gum arabic, guar gum, alginate, locust bean gum, carrageenan, tamarind and pectin, urethane resin, epoxy resin and acrylic resin having such a hydrophilic group as a hydroxyl group, a carboxyl group, a sulfonic group or an amino group, and the like may be utilized.

The internal light absorption layer5is provided for such purposes as optically separating the exposing light from reading write to inhibit a false operation caused by mutual interference, and optically separating light entering from the non-display surface side (the substrate1side) of the display medium100from the displayed images displayed on the liquid crystal layer7upon the display to inhibit the degradation of the image quality. The reading light is light that enters the internal light absorption layer5from the display surface side (the substrate9side) of the display medium100while transmitting the liquid crystal layer7, which includes sunlight, room light and the like.

Specifically, the internal light absorption layer5shows desirably light absorption properties of the absorbance1or more in the range of wavelength to be absorbed, more desirably light absorption properties of the absorbance2or more.

The material for use in the internal light absorption layer5is determined based on the range of wavelength to be absorbed, and ordinary pigment or dye may be employed, utilizing resin with dispersed pigment, resin with dissolved dye, resin colored with dye, or the like. As the pigment, inorganic compounds such as carbon black, aniline black or chromium oxide, and organic compounds such as azo compound or phthalocyanine compound are utilized. As the dye, nitroso dye, nitro dye, stilbene azo dye, diphenylmethane dye, triphenylmethane dye, xanthene dye, quinoline dye, polymethine dye, thiazole dye, indophenol dye, azine dye, oxazine dye, thiazine dye, sulfureted dye, aminoketone dye, anthraquinone dye, indigoid dye, and the like are utilized.

As the resin for dispersing the pigment or dissolving the dye, in order to make a coated film upon coating have film-forming properties, a water-soluble resin is utilized. The polymerization degree of the water-soluble resin is not limited as far as the water-soluble resin forms a film. Examples of water-soluble resins include fully or partially saponified polyvinyl alcohol, water-soluble polyvinyl acetal, water-soluble polyvinyl formal, polyacrylamide, polyvinyl pyrrolidone, poly(meth)acrylic acid, water-soluble poly(meth)acrylic acid copolymer, polyalkylene oxide, water-soluble polyester, polyethylene glycol, and water-soluble maleic acid resin, and the like. Among these, polyvinyl alcohol, and polyvinyl alcohol derivatives such as water-soluble polyvinyl acetal or water-soluble polyvinyl formal are particularly desirable.

As the method for forming the internal light absorption layer5, there are mentioned printing methods such as screen printing, relief printing, intaglio printing, lithographic printing or flexographic printing, and coating methods such as a spin coat method, a bar coat method, a dip coat method, a roll coat method, a knife coat method or a die coat method.

The internal light absorption layer5desirably has a thickness from 1 μm to 10 μm. Further, the internal light absorption layer5is desirably constituted as an insulating layer.

The adhesion layer6is provided for the purpose of absorbing irregularity and playing a roll of adhesion upon laminating respective layers formed for the substrates1and9.

The adhesion layer6is constituted of a high-molecular weight material having low glass transition temperature, wherein a material that sticks or adheres layers being objects to be laminated (in the exemplary embodiment, the internal light absorption layer5and the liquid crystal layer7) by heat or pressure is selected. Further, in the exemplary embodiment, the adhesion layer6is desirably constituted as an insulating layer.

As the material for the adhesion layer6, publicly known adhesives are utilized, including acrylic-based, urethane-based, cyano acrylate-based and silicone-based ones, rubber-based ones including isoprene, ethylene-vinyl acetate copolymer, and the like. No particular limitation is imposed on the type of the adhesive, including a two-component-curing type, a heat-curing type, a moisture-curing type, a ultraviolet-curing type, a hot-melt type, a pressure-sensitive type (an agglutinant), and the like.

Liquid Crystal Layer7:

The liquid crystal layer7is desirably the liquid crystal layer7with a memory performance, and is provided between the electrode8on the reverse side relative to the exposing light irradiation side out of the pair of electrodes2and8, and the upper part charge generation layer3A.

As the liquid crystal layer7having a memory performance, for example, a liquid crystal layer having a memory performance may be mentioned. A liquid crystal having a memory performance is a liquid crystal having such characteristic that keeps the alignment of the liquid crystal for a certain period of time by controlling the alignment by the application of voltage and even after releasing the applied voltage. For example, there are polymer-dispersed liquid crystal (PDLC), ferroelectric liquid crystal such as chiral smectic C-phase, cholesteric liquid crystal, and the like. Further, a liquid crystal layer formed after encapsulating these is also applicable. The liquid crystal with a memory performance does not require electric power for maintaining the image display because of the memory performance, and makes it possible to use the display medium100in a state separated from a photo-writing device. Meanwhile, as the liquid crystal layer7with a memory performance, there may be mentioned an electrochromic element, an electrophoretic element and an electric field rotation element, in addition to the liquid crystal display layer.

In the exemplary embodiment, when connecting the photoconductive layer3and the liquid crystal layer7, it is preferable to unite these with the adhesion layer6to form the photo-addressable display medium100. By the unification, it is possible to stabilize the connection between the photoconductive layer3and the liquid crystal layer7. Since the united photo-addressable display medium100may be separated from a photo-writing device, the display medium100may be, for example, distributed.

External Light Absorption Layer10:

The external light absorption layer10is provided as the outermost layer on the writing side, that is, outside the light irradiation side substrate1. The external light absorption layer10is provided for the purpose of absorbing light having wavelengths other than the wavelength used for writing, which is irradiated from the light irradiation side of the display medium100(inFIG. 1, the substrate1side) to the display medium100. Consequently, for the external light absorption layer10, a material, which transmits exposing light (desirably with a transmittance of 80% or more) and absorbs light that is not used for the writing, is used. When the charge generation material is phthalocyanine compound and the exposing light is in the wavelength range from 600 nm to 700 nm, for example, light absorption performance of absorbance1or more (desirable 2 or more) is desirable for all the wavelength region from 300 nm to 550 nm being shorter wavelength light. This suppresses the irradiation of light, which has wavelengths other than the wavelength used for the writing, to the photoconductive layer3.

For the external light absorption layer10, resin dispersed with pigment is utilized, which is formed, for example, by coating and drying a coating liquid prepared by dispersing pigment in a water-insoluble resin liquid. As the pigment, one that satisfies only the light absorption performance that is required as the external light absorption layer10is sufficient, and generally used red pigment (such as pyrrolo pyrrole based compounds and quinacridone based compounds) or yellow pigment (such as indoline based compounds and ferric hydroxide based compounds) may be used. These may be used alone, or in two or more kinds in mixture.

As the resin for use in the external light absorption layer10, water-insoluble resin is preferable because of good manufacturability and good adhesiveness with the substrate1, and resin such as alkyd (phthalic acid) resin, vinyl chloride resin, vinylidene chloride resin, unsaturated polyester resin, melamine resin, urea resin, phenol resin, acrylic resin, polyurethane resin, vinyl acetate resin, epoxy resin, cellulose, silicone resin or butyral resin may be utilized. A hardening agent such as polyisocyanate or a thickener may be contained as an additive.

As a method for forming the external light absorption layer10, a printing method such as screen printing, relief printing, intaglio printing, lithographic printing or flexographic printing, or a coating method such as a spin coat method, a bar coat method, a dip coat method, a roll coat method, a knife coat method or a die coat method is employed. In the coating method, a coating liquid prepared by dispersing or dissolving the pigment with the resin in an appropriate solvent may be used.

The thickness of the external light absorption layer10is not particularly limited, but is preferably in the range that does not damage the portability or flexibility of the display medium100. For example, it is desirably from 1 μm to 50 μm.

Meanwhile, the external light absorption layer10is not necessarily laminated in the photo-addressable display medium100, but is desirably arranged in a unified manner to the photo-addressable display medium100. This makes it possible to exert light resistance more significantly for allowing it to be used in environments that are exposed to sunlight such as places near a window or out of doors, as compared with an instance in which no external light absorption layer10is provided.

Production of Photo-Addressable Display Medium:

The photo-addressable display medium100according to the exemplary embodiment is prepared according to a procedure below.

On the electrode2formed on the substrate1, the lower part charge generation layer3C, the charge transport layer3B and the upper part charge generation layer3A are laminated successively to form the photoconductive layer3. Then, on the photoconductive layer3, the internal light absorption layer5and the adhesion layer6are laminated successively to form a laminated body A.

On the other hand, on the electrode8formed on the substrate9, the liquid crystal layer7is formed to form a laminated body B.

Next, the laminated body A and the laminated body B are bonded so that the adhesion layer6of the laminated body A contacts to the liquid crystal layer7of the laminated body B to form a laminated body C.

Further, when arranging the external light absorption layer, separately, the external light absorption layer10and the adhesion layer are laminated on a substrate to form a laminated body D, and the adhesion layer of the laminated body D is bonded to the substrate1of the laminated body C to prepare the display medium100.

Constitution of Photo-Addressable Display Device:

FIG. 2is an outline view showing a constitution example of a photo-addressable display device according to an exemplary embodiment of the invention.

A photo-addressable display device200is provided with the aforementioned photo-addressable display medium100, and a writing device (having at least a light irradiation section201, a voltage application section202and a control section203) for performing photo-writing to the display medium100.

The writing device is a device for writing an image to the display medium100, which is constituted by including, for example, an exposure device for scanning and irradiating exposing light to the display medium100(the light irradiation section201), the voltage application section202for applying voltage between the electrode2and the electrode8of the display medium100, and the control section203that is electrically connected to the light irradiation section201and the voltage application section202and controls these.

The exposure device (the light irradiation section201) has a light source that irradiates exposing light from the non-display surface side of the display medium100toward the photoconductive layer3via the light irradiation side substrate1or the external light absorption layer10.

On the light source, no particular limitation is imposed, only when it is one that irradiates intended exposing light (spectrum, intensity, spatial frequency) to the photoconductive layer3of the display medium100on the basis of input signal from the control section203. Meanwhile, as the exposing light irradiated from the light source is desirably light having a lot of energy of the absorption wavelength region of the photoconductive layer3.

The voltage application section202is sufficient when it applies voltage, on the basis of the input signal from the control section203, that has polarity and voltage value corresponding to the input signal between the electrode2and the electrode8of the display medium100for a time period corresponding to the input signal. As the voltage application section202, for example, a bipolar high voltage amplifier or the like is employed.

The voltage application to the display medium100by the voltage application section is performed, specifically, between the electrode2and the electrode8via a contact terminal (a feeding terminal). Here, the contact terminal is a member that contacts to the voltage application section202and the electrodes2and8to make the both be in a conduction state, and one having a high electroconductivity and a small contact resistance with the voltage application section202and the electrodes2and8is selected. Meanwhile, the contact terminal desirably has such structure that enables it to be separated form either the electrodes2and8or the voltage application section202, or from both, so that the display medium100may be separated from the writing device.

The control section203is constituted of CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory) and the like, the diagrammatic representation thereof being omitted, which controls respective sections of the writing device according to a program stored in the ROM, and controls the exposure device (the light irradiation section201) and the voltage application section202so as to display an image, which corresponds to image data obtained from an exterior device or the like via a wireless line or a wire line, on the display medium100.

The display medium100may have a constitution unified with the writing device, or have a constitution separable from the writing device. When constituting so that the display medium100is separable from the writing device, for example, the display medium100may be constituted so that, by being mounted on a slot or the like whose diagrammatic representation is omitted, the electrodes2and8of the display medium100are so connected that voltage is applicable from the voltage application section202, and that the display medium100is in such state that the exposing light may be irradiated from the non-display surface side of the display medium100toward the charge generation layer3A of the photoconductive layer3from the exposure device.

When the display medium100is constituted separable from the writing device as described above, it becomes easy to distribute only the display medium100as a single item, and to provide it to browse, circulation, distribution and the like. Further, by mounting the display medium100again on a slot of the writing device, it becomes possible to write a new image or to delete a written image.

Operation of Photo-Addressable Display Device:

In the display device200so constituted as described above, the exposure device (the light irradiation section201) and the voltage application section202are controlled by the control section203in accordance with the image data of an image to be written, and the image is written into the display medium100. Specifically, by the control of the control section203, voltage is applied between the electrode2and the electrode8from the voltage application section202, and the exposing light from the light source of the exposure device (the light irradiation section201) is irradiated from the non-display surface side of the display medium100. As the result, an image is written to the display medium100.

Here, when the external light absorption layer10is provided for the display medium100, the exposing light is irradiated toward the photoconductive layer3via the external light absorption layer10. Further, light from the sun or a fluorescent lamp that enters the display medium100is absorbed corresponding to the absorption region of the external light absorption layer10to be suppressed from arriving at the photoconductive layer3. Consequently, the display medium100more excellent in light resistance is provided, and the optical degradation of the photoconductive layer3by external light is suppressed.

Next, the invention will be explained on the basis of Examples, but the invention is not limited by these Examples.

Firstly, on an ITO film (the electrode2) (thickness 800 angstroms) formed on polyethylene terephthalate (PET) (the light irradiation side substrate1) (thickness 125 μm), the lower part charge generation layer3C is formed. As the charge generation material, chlorogallium phthalocyanine (one that has diffraction peaks at the Bragg angle (2θ±0.2°) of 7.4°, 16.6°, 25.5°, and 28.3° in an X-ray diffraction spectrum) is employed, and polyvinyl butyral (S-LEC BX-5, manufactured by Sekisui Chemical Co., Ltd.) is employed as a binder. While setting a mass ratio thereof to 1:1, they are dispersed with a DYNO MILL using butanol to prepare a 4% by mass butanol dispersion liquid (a coating liquid A). On the ITO film, the coating liquid A is coated by a spin coat method, which is then dried to form the lower part charge generation layer3C having thickness of 0.2 μm.

Next, on the lower part charge generation layer3C, the charge transport layer3B is formed. Specifically, firstly, a stilbene compound shown by the structural formula (III-1) is employed as the charge transport material, and polycarbonate {PCZ 300, manufactured by Mitsubishi gas Chemical Company, inc.} is employed as the binder resin. They are mixed at a mass ratio 3:2, which are then dissolved in monochlorobenzene to prepare a 20% by mass solution (a coating liquid B). The coating liquid B is coated on the lower part charge generation layer3C using a spin coat method and dried to form the charge transport layer3B having thickness of 6.5 μm.

Next, on the charge transport layer3B, the upper part charge generation layer3A is formed. Specifically, the coating liquid A is coated using a spin coat method and dried to form the upper part charge generation layer3A having thickness of 0.2 μm.

Next, on the photoconductive layer3having been formed, the internal light absorption layer5is formed.

Specifically, Pigment Blue 15:6 being blue pigment is dispersed in water so as to give a mass ratio of 1:1 relative to polyvinyl alcohol (POVAL 217EE, manufactured by Kuraray Co., Ltd.) being a binder resin to prepare a 10% by mass aqueous dispersion liquid (a coating liquid D). Then, the coating liquid D is coated on the photoconductive layer3by a spin coat method and dried to form the internal light absorption layer5having thickness of 1 μm.

Next, on the internal light absorption layer5, a butyl acetate solution of a two-component type polyurethane-based adhesive, TAKENATE (A50)/TAKELAC (A315) (trade names, manufactured by Mitsui Chemicals inc.), is coated to form the adhesion layer6having thickness of 1.2 μm.

As above, a laminated body A is formed.

Specifically, in 74.8 parts by mass of nematic liquid crystal E8 (manufactured by Merck & Co., Inc.) having positive permittivity anisotropy, 21 parts by mass of a chiral agent CB15 (manufactured by BDH Industries Ltd.) and 4.2 parts by mass of a chiral agent R1011 (manufactured by Merck & Co., Inc.) are dissolved with heating, and, after that, the temperature of the product is lowered to room temperature to give chiral nematic liquid crystal that selectively reflects light of blue-green color.

To 10 parts by mass of the blue-green chiral nematic liquid crystal, 3 parts by mass of an adduct of xylene isocyanate 3 moles and trimethylolpropane 1 mole (D-110N, manufactured by Takeda Chemical Industries, Ltd.), and 100 parts by mass of ethyl acetate are added to form a homogeneous solution and to form liquid to be an oil phase. On the other hand, 10 parts by mass of polyvinyl alcohol (POVAL 217EE, manufactured by Kuraray Co., Ltd.) is added to 1000 parts by mass of heated ion-exchanged water, which is stirred and left to be cooled to prepare liquid for a water phase.

Next, 10 parts by mass of the oil phase is emulsified and dispersed in 100 parts by mass of the water phase for one minute by a mixer for home use to which 30 V alternating current is applied with a slidac to prepare oil-in-water emulsion in which oil phase droplets are dispersed in the water phase. The oil-in-water emulsion is stirred for 2 hours while heating with a water bath at 60° C. to complete interfacial polymerization, thereby forming a liquid crystal microcapsule. An average particle diameter of obtained liquid crystal microcapsules is measured with a laser particle size distribution meter and is estimated as about 12 μm.

After filtering the obtained liquid crystal microcapsule dispersion liquid through a stainless-steel mesh having a mesh size of 38 μm, the filtrate is left for a whole day and night, and milk white supernatant is removed to give slurry constituted of a liquid crystal microcapsule having a solid component of about 40% by mass. To the obtained slurry, a 10% by mass polyvinyl alcohol solution is added so as to give polyvinyl alcohol in an amount of ⅔ relative to the mass of the solid component, to prepare a coating liquid C.

On the ITO film (the electrode8), the coating liquid C is coated with a #44 wire bar to form the display layer (liquid crystal layer)7(thickness 50 μm)

As above, the laminated body B is formed.

Next, the laminated body A and the laminated body B are closely contacted so that the adhesion layer6contacts to the liquid crystal layer7, which is subjected to lamination at 70° C. to prepare the photo-addressable display medium100.

A photo-writing medium is prepared in the substantially similar processes as that in Example 1, except for using a stilbene compound shown by the structural formula (III-2) as the charge transport material in the display medium100prepared in Example 1.

A photo-writing medium is prepared in the substantially similar processes as that in Example 1, except for using a stilbene compound shown by the structural formula (III-3) as the charge transport material in the display medium100prepared in Example 1.

Appropriate quantities of nematic liquid crystal E7 (manufactured by Merck & Co., Inc.), a first chiral agent (CB15, manufactured by Merck & Co., Inc.) and a second chiral agent (R1011, manufactured by Merck & Co., Inc.) are mixed to prepare a cholesteric liquid crystal that selectively reflects light of red color.

The red cholesteric liquid crystal is emulsified in 0.25% aqueous solution of sodium dodecylbenzene acid using a membrane emulsification devise (Micro kit, manufactured by SPG Technology Co., Ltd.) equipped with a ceramic porous membrane with 4.2 μm diameter. The average particle diameter of cholesteric liquid crystal drops in the obtained emulsion is measured with a laser particle size distribution meter and is estimated as about 15 μm. Thus obtained emulsion is left for a whole day and night. After the liquid crystal drops are precipitated, supernatant is removed to give concentrated emulsion in which the volume ratio of the liquid crystal drops is about 60% by mass. To the concentrated emulsion, 10% gelatin solution prepared in advance is added so that the weight ratio between liquid crystal and gelatin satisfies 7:3, to prepare a coating liquid for liquid crystal display layer (coating liquid E). Coating liquid E is coated by using an applicator and then dried to form a crystal liquid layer7having a film thickness of 20 μm.

Comparative Example 1

A photo-addressable display medium (Comparative Example 1) is prepared in the substantially similar processes, material and condition as those in Example 1, except for using a benzidine compound shown by a structural formula below in place of the stilbene compound shown by the structural formula (III-1) as the charge transport material in the display medium100prepared in Example 1.

Comparative Example 2

A photo-addressable medium (Comparative Example 2) is prepared in the substantially similar processes as that in Example 1, except for using a benzidine compound shown by a structural formula below as the charge transport material in the display medium100prepared in Example 1.

Evaluation of Light Resistance

For each of display media prepared in Examples 1 to 3 and Comparative Examples 1 to 2, the light resistance is evaluated in a process described below.

That is, for each of display media prepared in Examples 1 to 3 and Comparative Examples 1 to 2, writing is performed by applying a drive voltage of 300 V between electrodes (between ITOs corresponding to the first electrode and the second electrode) and irradiating exposure light of 1500 μW/cm2, 660 nm for 0.1 second and then releasing the voltage application in a circumstance of 25° C. and 50% RH, and, after that, the reflectance is measured when white is displayed using a spectrometer CM-2022 (manufactured by Konica-Minolta).

As the result, for each of media obtained in Examples 1 to 3 and Comparative Examples 1 to 2, about 35% change in the reflectance is found. Consequently, no difference is confirmed between Examples and Comparative Examples in the initial state (the state before the light exposure described below).

Next, for each of display media prepared in Examples 1 to 3 and Comparative Examples 1 to 2, the reflectance is measured in the same measurement condition as that for the initial state after light-exposing the lower part charge generation layer3C side of the photoconductive layer3just under a pseudo-Sunlight (a xenon lamp, about 100,000 lux), in a circumstance of 25° C. and 50% RH. And, a ratio of the reflectance after the light exposure by the pseudo-Sun relative to the reflectance before the light exposure, which is defined as “1,” is obtained as a relative reflectance to evaluate the light resistance. Results are shown inFIG. 3.

FromFIG. 3, it is understood that media in Examples 1 to 3 have remarkably improved light resistance under the pseudo-Sun as compared with those in Comparative Examples 1 to 2.